(19) TZZ ¥_T

(11) EP 2 749 437 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.: 02.07.2014 Bulletin 2014/27 B60C 23/04 (2006.01) B60C 23/06 (2006.01)

(21) Application number: 13198760.4

(22) Date of filing: 20.12.2013

(84) Designated Contracting States: (72) Inventors: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB • Kosugi, Masanori GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO Niwa-gun,, Aichi 480-0195 (JP) PL PT RO RS SE SI SK SM TR • Sakurai, Taketoshi Designated Extension States: Niwa-gun,, Aichi 480-0195 (JP) BA ME • Kumagai, Katsuhide Niwa-gun,, Aichi 480-0195 (JP) (30) Priority: 27.12.2012 JP 2012286286 03.06.2013 JP 2013116984 (74) Representative: TBK 13.09.2013 JP 2013190709 Bavariaring 4-6 80336 München (DE) (71) Applicant: KABUSHIKI KAISHA TOKAI RIKA DENKI SEISAKUSHO Niwa-gun, Aichi 480-0195 (JP)

(54) Tire position determination system

(57) Each tire pressure detector (4) detects a char- acteristic point in a detection signal of an acceleration sensor (10) indicating that the tire pressure detector (4) is located at a certain rotation position. When detecting the characteristic point, the tire pressure detector (4) transmits a notification signal (Spk) including the detector ID. Whenever a receiver (12) receives a notification sig- nal (Spk), the receiver (12) acquires an axle rotation amount (C) of a representative wheel (26) and stores the axle rotation amount (C) in a memory in association with the detector ID in the notification signal (Spk). After ac- quiring axle rotation amounts (C1-C4) associated with the detector IDs of all of the tire pressure detectors (4), the receiver (12) determines mounting positions of tires (2) from the angle each tire pressure detector rotated and the angle each axle (18) rotated between a first determi- nation timing (t1) and a second determination timing (t1). EP 2 749 437 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 749 437 A1 2

Description position determination processing unit acquires the de- tector ID whenever receiving the radio wave signal from [0001] This application is based upon and claims the each tire pressure detector and the axle rotation amount benefit of priority from prior Japanese Patent Application detected by each axle rotation amount sensor, associ- Nos. 2012-286236, filed on December 27, 2012,5 ates the detector IDs with the axle rotation amounts, and 2013-116984, filed on June 3, 2013, and 2013-190709, determines mounting positions of the tires based on the filed on September 13, 2013, the entire contents of which axle rotation amounts associated with the detector IDs are incorporated herein by reference. of the tire pressure detectors. [0002] The present invention relates to a tire position [0007] Anaspect of thepresent disclosure is a tire pres- determination system that determines the position of a 10 sure monitoring system including tire pressure detectors tire with a detection signal from a tire pressure detector. respectively attached to tires, a receiver coupled to a [0003] A vehicle may include a tire pressure monitoring vehicle body, and a display unit. Each tire pressure de- system. In a tire pressure monitoring system, a tire pres- tector transmits a tire pressure signal, which is in accord- sure detector that is attached to a tire directly detects the ance with the pressure of the corresponding tire, and a pressure of the tire and transmits, through wireless com- 15 radio wave signal, which differs from the tire pressure munication, a detection signal to a receiver that is ar- signal. The receiver is configured to receive a tire pres- ranged on a vehicle body. Preferably, the tire pressure sure signal from each tire pressure detector and monitor monitoring system notifies the driver of where a tire hav- the pressure of the corresponding tire based on the tire ing low pressure is located relative to the vehicle. Japa- pressure signal. Each tire pressure detector includes a nese Laid-Open Patent Publication Nos. 2006-062516 20 unique detector ID, an acceleration sensor that outputs and 2012-126341 each describe an example of a tire a detection signal indicative of a centripetal component pressure monitoring system implementing a function for of gravity, which varies as the corresponding tire rotates, automatically determining the position of each tire (auto- and a transmission control unit that transmits the radio matic tire location function) when the tire positions are wave signal including the detector ID based at a control- changed, such as when rotating the tires, or when ex- 25 led timing or a timing when the detection signal of the changing a tire with a new one. The tire pressure moni- acceleration sensor indicates that the tire pressure de- toring system includes an initiator attached to each wheel tectoris located at a certain rotation position. The receiver well. The initiator transmits a radio wave signal, through includes an interface that communicates with axle rota- wireless communication, to the corresponding tire pres- tion amount sensors, wherein each axle rotation amount sure detector so that a radio wave signal is returned in 30 sensor detects an axle rotation amount of a correspond- response. Based on the radio wave signal from each tire ing axle, and a tire mounting position determination pressure detector, the tire pressure monitoring system processing unit that acquires the detector ID whenever determines the position of each tire. receiving the radio wave signal from each tire pressure [0004] However, to implement the automatic tire loca- detector and the axle rotation amount detected by each tion function, an initiator needs to be arranged in each 35 axle rotation amount sensor, associates the detector IDs wheel well. Thus, the automatic tire location function in- with the axle rotation amounts, and determines mounting creases the number of components and raises costs. positions of the tires based on the axle rotation amounts [0005] It is an object of the present invention to provide associated with the detector IDs of the tire pressure de- a tire position determination system that does not use an tectors. The receiver is configured to show a warning on initiator arranged in a wheel well and is subtly affected 40 the display unit indicating a pressure decrease in at least by temperature changes or the centrifugal force pro- one tire in accordance with a determination result of the duced when a tire rotates. tire mounting position determination processing unit. [0006] One aspect of the present disclosure is a tire [0008] Other aspects and advantages of the present position determination system including tire pressure de- invention will become apparent from the following de- tectors respectively attached to tires. A receiver is cou- 45 scription, taken in conjunction with the accompanying pled to a vehicle body. The receiver is configured to re- drawings, illustrating by way of example the principles of ceive a tire pressure signal from each tire pressure de- the invention. tector and monitor the pressure of the corresponding tire [0009] The invention, together with objects and advan- based on the tire pressure signal. Each tire pressure de- tages thereof, may best be understood by reference to tector includes a unique detector ID. A gravity component 50 the following description of the presently preferred em- detection unit detects a certain directional component of bodiments together with the accompanying drawings in gravity and generates a detection signal. A transmission which: control unit transmits a radio wave signal including the detector ID based on the detection signal of the gravity Fig. 1 is a schematic diagram showing a first embod- component detection unit. The receiver includes an in- 55 iment of a tire position determination system; terfacethat communicates with axle rotationamount sen- Fig. 2 is a schematic diagram illustrating the centrip- sors. Each axle rotation amount sensor detects an axle etal component of gravity detected by a tire pressure rotation amount of a corresponding axle. A tire mounting detector;

2 3 EP 2 749 437 A1 4

Fig. 3 is a timing chart illustrating the count value of ponent of gravity; a pulse signal indicative of an axle rotation amount Fig. 25 is a waveform chart illustrating the gravity for a representative wheel and the detection signal and the rotation cycle in a sixth embodiment; of an acceleration sensor; Fig. 26 is a schematic diagram illustrating the end of Fig. 4 is a schematic diagram illustrating a detector 5 a transmission in the tire pressure detector; angle θk of a tire pressure detector arranged in each Fig. 27 is a schematic diagram illustrating determi- tire; nation timings in a seventh embodiment; Fig. 5 is a schematic diagram illustrating a detector Fig. 28 is a schematic diagram illustrating a tire de- rotation angle θa; termination system of the seventh embodiment; Fig. 6 is a schematic diagram illustrating an axle ro- 10 Fig. 29 is a schematic diagram illustrating determi- tation angle θb; nation timings in the seventh embodiment; Fig. 7 is a graph illustrating the vehicle velocity and Fig. 30 is a schematic diagram illustrating determi- an operation mode of the tire pressure detector; nation timings in an eighth embodiment; Fig. 8 is a flowchart illustrating the operation of a tire Fig. 31 is a schematic diagram illustrating a tire de- pressure detector; 15 termination system of the eighth embodiment; Fig. 9 is a schematic diagram illustrating the trans- Fig. 32 is a schematic diagram illustrating the detec- mission timing of a notification signal Spk from the tor ration angle and the axle rotation angle in a ninth tire pressure detector; embodiment; Fig. 10 is a flowchart illustrating a tire position deter- Fig. 33 is a schematic diagram illustrating a tire de- mination routine executed by a receiver; 20 termination system of the ninth embodiment; Fig. 11 is a flowchart illustrating another tire position Fig. 34 is a schematic diagram illustrating a tire po- determination routine executed by the receiver; sition determination method in a tenth embodiment; Fig. 12 is a schematic diagram illustrating a tire po- Fig. 35 is a schematic diagram illustrating the tire sition determination method in a second embodi- position determination method in the tenth embodi- ment; 25 ment; Fig. 13 is a waveform chart illustrating a pulse signal Fig. 36 is a timing chart illustrating a specific example Spl of an axle rotation amount sensor of which pulses of the determination of tire positions in the tenth em- are counted between timing t1 and timing t2 shown bodiment; in Fig. 12; Fig. 37 is a schematic diagram illustrating a total Fig. 14 is a schematic diagram illustrating a specific 30 pulse signal Dpl transmitted from an axle rotation example of the determination of tire positions in the amount sensor of a tire position determination sys- second embodiment; tem in an eleventh embodiment; Fig. 15 is a schematic diagram illustrating the count Fig. 38 is a waveform chart of the pulses output from value of a pulse signal from an axle rotation amount an axle rotation amount sensor of a tire position de- sensor corresponding to the specific example of Fig. 35 termination system in a twelfth embodiment; 14 and the transmission timing of a notification signal Fig. 39 is a schematic diagram illustrating an axle Spk from the tire pressure detector; rotation amount sensor in a modified example; and Figs. 16 and 17 are schematic diagrams illustrating Fig. 40 is a diagram showing the structure of a re- the problem resolved by a tire position determination ceiver in a further example. method of a third embodiment; 40 Fig. 18 is a schematic diagram illustrating the tire [0010] A first embodiment of a tire position determina- position determination method of the third embodi- tion system will now be described. ment; [0011] As shown in Fig. 1, the vehicle 1 includes a tire Fig. 19 is a schematic diagram illustrating a specific pressure monitoring system (TPMS) 3 that monitors the example of the determination of tire positions in the 45 pressure and the like of tires 2. The tire pressure moni- third embodiment; toring system 3 includes tire pressure detectors 4a to 4d Fig. 20 is a schematic diagram illustrating errors in (also referred to as the transmitters) respectively ar- the angle detected by the tire pressure detector at ranged on tires 2a to 2d. Each of the tire pressure detec- determination timings t1 and t2; tors 4a to 4d transmits, through wireless communication, Fig. 21 is a schematic diagram illustrating the prob- 50 a tire pressure signal Stp, which corresponds to the de- lem resolved by a tire position determination method tected tire pressure, to a vehicle body 5. of a fourth embodiment; [0012] Each of the tire pressure detectors 4a to 4d in- Fig. 22 is a schematic diagram illustrating a sampling cludes a pressure sensor 8, which detects the tire pres- cycle in the fourth embodiment; sure, an acceleration sensor 10, and a controller 6 (also Fig. 23 is a timing chart illustrating the relationship 55 referred to as the transmitter controller). Each transmitter of the centripetal component of gravity, the tire rota- controller 6 includes a memory 7 that stores a unique ID tion cycle, and the vehicle velocity; (also referred to as the tire ID code or the detector ID Fig. 24 is a waveform chart of the centripetal com- code). In the illustrated example, each of the tire pressure

3 5 EP 2 749 437 A1 6 detectors 4a to 4d includes a temperature sensor 9 that tational information generated by the acceleration sen- detects the tire temperature. A transmission antenna 11, sors 10 of the tire pressure detectors 4a to 4d. In one which allows for the transmission of a radio wave signal example, the automatic locator 20 repeats a routine for on the ultrahigh frequency (UHF) band, is connected to determining the position of the tires 2a to 2d in predeter- the transmitter controller 6. The acceleration sensor 10 5 mined fixed intervals. is one example of a gravity component detection unit. [0017] The receiver 12 includes an interface used for [0013] A receiver 12 (also referred to as the TPMS re- communication with the axle rotation amount sensors ceiver) receives tire pressure signals Stp from the tire 19a to 19d, which may be sensors for an antilock brake pressure detectors 4a to 4d. The receiver 12 includes a system (ABS). In the illustrated example, each of the axle tire pressure monitoring electronic control unit (ECU) 13 10 rotation amount sensors 19a to 19d provides the receiver and a reception antenna 14, which receives a UHF radio 12 with rectangular pulses Spl whenever detecting one wave signal. The tire pressure monitoring ECU 13 in- of the teeth arranged on the corresponding one of the cludes a memory 15 that stores tire ID codes of the tires axles 18a to 18d. For example, when there are 48 teeth, 2a to 2d in association with the tire positions (right front, a pulse Spl is output when each of the axle rotation left front, right rear, and left rear). A display unit 16, which 15 amount sensors 19a to 19d detects a tooth or a gap be- is arranged, for example, in the vehicle 1 on an instrument tween adjacent teeth. Thus, 96 pulses Spl are output for panel, is connected to the receiver 12. each tire rotation. [0014] Each transmitter controller 6 transmits a tire [0018] Each acceleration sensor 10 is configured to pressure signal Stp to the vehicle body in predetermined output a detection signal indicative of a certain directional fixed intervals or in variably controlled intervals when the 20 component of gravity varying with a rotation of the cor- corresponding tire 2 is rotating and/or stopped. The trans- responding tire 2, such as a centripetal component of mitter controller 6 may detect that the tire 2 has started gravity Gr as illustrated in Fig. 2. In one example, when to rotate based on, for example, a detection signal from the tire pressure detector 4 is located on a tire 2 at a the acceleration sensor 10. In the example of Fig. 3, when twelve o’clock position (i.e., uppermost position) or a six the tire 2 is rotating, the detection signal of the acceler- 25 o’clock position (i.e., lowermost position), as long as cen- ation sensor 10 indicates repetitive variations in the ac- trifugalforce isnot considered, the centripetal component celeration (gravity) acting on the tire pressure detector of gravity Gr is "-1 G" or "+1 G." When the tire pressure 4. In contrast, when the tire 2 is stopped, the detection detector 4 is located on a tire 2 at a three o’clock position signal of the acceleration sensor 10 substantially does or a nine o’clock position, the centripetal component of not change. Preferably, the transmission interval of the 30 gravity Gr is "0 G." tirepressure signal Stp when thetire 2 is stoppedis longer [0019] In the example illustrated in Fig. 1, each trans- than the transmission interval of the tire pressure signal mitter controller 6 includes a travel status determination Stp when the tire 2 is rotating. However, the intervals unit 21 and an operation mode switching unit 22. The may be the same. travel status determination unit 21 determines the travel [0015] The receiver 12 receives a tire pressure signal 35 status of the vehicle 1 based on the detection signal of Stp from each of the tire pressure detectors 4a to 4d with the acceleration sensor 10, in particular, the centripetal the reception antenna 14 and verifies the tire ID code component of gravity Gr. The operation mode switching that is included in the tire pressure signal Stp. When the unit 22 switches the operation mode of the corresponding tire ID code is verified, the receiver 12 checks the tire one of the tire pressure detectors 4a to 4d. The travel pressure that is included in the tire pressure signal Stp. 40 status determination unit 21 calculates the vehicle veloc- When the tire pressure is less than or equal to a lower ity V based on variations (varied amount and/or varied limit value, the receiver 12 indicates the position of the time) of the centripetal component of gravity Gr. When low-pressure tire on the display unit 16. In one example, the vehicle velocity V is greater than or equal to a first the receiver 12 determines the tire pressure whenever threshold V1, which corresponds to a relatively high ve- receiving the tire pressure signal Stp. 45 locity, the operation mode switching unit 22 switches the [0016] The tire pressure monitoring system 3 includes operation mode of the corresponding one of the tire pres- a tire position determination system 17 that determines sure detectors 4a to 4d to a pressure determination the mounting positions of the tires 2a to 2d on the vehicle mode. When the vehicle velocity V is between the first body 5 (right front, left front, right rear, left rear, and the threshold V1 and a second threshold V2, which corre- like). The tire pressure monitoring ECU 13 includes an 50 sponds to a relatively low velocity such as when the ve- automatic locator 20 that determines the mounting posi- hicle is about to stop, the operation mode switching unit tions of the tires 2a to 2d that are respectively mounted 22 switches the operation mode of the corresponding on axles 18 (18a to 18d). Axle rotation amount sensors one of the tire pressure detectors 4a to 4d to an automatic 19 (19a to 19d) are respectively attached to the axles 18 location preparation mode. When the vehicle velocity V (19a to 19d). The automatic locator 20 determines the 55 is less than the second threshold V2, the operation mode mounting positions of the tires 2a to 2d using axle rotation switching unit 22 switches the operation mode of the cor- amount information of the axles 18a to 18d generated by responding one of the tire pressure detectors 4a to 4d to the axle rotation amount sensors 19a to 19d and gravi- an automatic location mode. After a predetermined de-

4 7 EP 2 749 437 A1 8 termination time elapses from when the operation mode erence point) of each tire 2 and the corresponding one is switched to the automatic location mode, the operation of the tire pressure detectors 4a to 4d. As shown in Fig. mode switching unit 22 forcibly returns the operation 5, the angle θk is calculated at a first determination timing mode of the corresponding one of the tire pressure de- t1 and a second determination timing t2 with an interval tectors 4a to 4d to the pressure determination mode. The 5 Tu in between. predetermined determination time provides sufficient [0023] The automatic locator 20 includes a detector time for completing the automatic location. rotation angle calculation unit 28 that calculates the ro- [0020] Each transmitter controller 6 includes a charac- tation angle θa of each of the tire pressure detectors 4a teristic point detection unit 23 and a notification signal to 4d during a period from the first determination timing transmission unit 24. The characteristic point detection 10 t1 to the second determination timing t2 based on the unit 23 detects characteristics points in the detection sig- detector angle θk1 calculated at the first determination nal of the corresponding acceleration sensor 10, such as timing t1 and the detector angleθ k2 calculated at the an extreme point or a turning point. When the character- second determination timing. istic point detection unit 23 detects a characteristic point, [0024] The representative wheel 26 is preferably se- the notification signal transmission unit 24 transmits a 15 lected from a non-steered wheel (right rear wheel or left notification signal Spk to the receiver 12. In the illustrated rear wheel). This is because the rotation amount differ- example, the characteristic point detection unit 23 de- ence between the left and right non-steered wheels is tects the minimum point in the detection signal of the smaller than that between the left and right steered acceleration sensor 10 that corresponds to the twelve wheels. The detector angle calculation unit 27 and the o’clock position of the corresponding one of the tire pres- 20 detector rotation angle calculation unit 28 function as a sure detectors 4a to 4d. In one example, the notification position determination processing unit. signal Spk includes a tire ID code and a command that [0025] Fig. 3 illustrates variations in the detection sig- notifies that the centripetal component of gravity Gr is nals of the acceleration sensors 10 and variations in the indicative of a peak or valley. The characteristic point count value of the axle rotation amount acquisition unit detection unit 23 and the notification signal transmission 25 25 (counter 31). In the illustrated example, when the de- unit 24 form one example of a transmission control unit. tection signal of the acceleration sensor 10 in a tire 2 is The notification signal Spk is one example of a radio wave at a minimum point (valley), that is, when a transmitter 4 signal for notification of at least the tire ID code. The of the tire 2 is located at the twelve o’clock position, a characteristic point detection unit 23 is also referred to a notification signal Spk including the tire ID code of the specific rotation position detection unit that detects that 30 transmitter 4 is transmitted. The detector angle calcula- the tire pressure detector 4 is located at a specific rotation tion unit 27 acquires the axle rotation amount Cn (n = 1 position of the tire 2 such as the uppermost position or to 4) of the representative wheel 26 when the notification the lowermost position. signal Spk is received. For example, when the received [0021] The automatic locator 20 includes an axle rota- notification signal Spk includes tire ID code ID3, that is, tion amount acquisition unit 25 that acquires the number 35 when the right rear tire pressure detector 4c is located of pulses Spl output from the axle rotation amount sen- at the twelve o’clock position, the detector angle calcu- sors 19a to 19d, that is, the axle rotation amount C of lation unit 27 acquires, in association with tire ID code each of the axles 18a to 18d. The axle rotation amount ID3, 13 as the axle rotation amount C3 of the represent- acquisition unit 25 includes a counter 31 that counts the ative wheel 26. In the same manner, when the received rising and falling edges of the pulses Spl of the axle ro- 40 notification signal Spk includes tire ID code ID2, that is, tation amount sensors 19a to 19d. In the illustrated ex- when the left front tire pressure detector 4b is located at ample, the count value of the counter 31 is continuously the twelve o’clock position, the detector angle calculation varied between 0 and 95 during a single wheel rotation. unit 27 acquires, in association with tire ID code ID2, 27 [0022] The automatic locator 20 includes a detector as the axle rotation amount C2 of the representative angle calculation unit 27. Whenever a notification signal 45 wheel 26. When the received notification signal Spk in- Spk is received from each of the tire pressure detectors cludes tire ID code ID1, that is, when the right front tire 4a to 4d, the detector angle calculation unit 27 stores an pressure detector 4a is located at the twelve o’clock po- axle rotation amount Cn (e.g., n = 1 to 4) of a represent- sition, the detector angle calculation unit 27 acquires, in ative wheel 26 in association with the tire ID code in the association with tire ID code ID1, 40 as the axle rotation signal Spk. After acquiring the axle rotation amounts Cn 50 amount C1 of the representative wheel 26. When the (e.g., C1 to C4) of every one of the tires 2, the detector received notification signal Spk includes tire ID code ID4, angle calculation unit 27 calculates the detector angle θk that is, when the left rear tire pressure detector 4d is of each of the tire pressure detectors 4a to 4d based on located at the twelve o’clock position, the detector angle the axle rotation amount Cn corresponding to each tire calculation unit 27 acquires, in association with tire ID 2 and the present axle rotation amount Cref of the rep- 55 code ID4, 71 as the axle rotation amount C4 of the rep- resentative wheel 26. As shown in Fig. 4, for example, resentative wheel 26. In the description hereafter, the tire when viewing the vehicle body 5 from one side, the angle ID code refers to a notification signal Spk including the θk is the angle between the twelve o’clock position (ref- tire ID code or a detection signal of the acceleration sen-

5 9 EP 2 749 437 A1 10 sor 10 in a tire pressure detector 4 including a tire ID code. 1 is travelling along a curved road, the axles 18a to 18d [0026] After the axle rotation amounts C1 to C4 of the have different rotation amounts. Thus, the count values representative wheel 26 is acquired for every one of the of the pulses Spl differ between the axle rotation amount tire pressure detectors 4a to 4d, at an arbitrary determi- sensors 19a to 19b in accordance with the tire mounting nation timing, for example, when the axle rotation amount 5 position. Accordingly, the axle rotation angle θb is calcu- Cref of the representative wheel 26 becomes "83," the lated with high accuracy for each of the axles 18a to 18d. detector angle calculator 27 calculates the angle θk of The same applies to the rotation of the tires 2. each of the tire pressure detectors 4a to 4d. In one ex- [0031] As shown in Fig. 1, the automatic locator 20 ample, the arbitrary determination timing is when a pre- includes a tire mounting position determination unit 30 determined time elapses from when the axle rotation10 that determines tire mounting positions based on the de- amounts C1 to C4 corresponding to the tire pressure de- tector rotation angle θa and the axle rotation angle θb. tectors 4a to 4d are all acquired. In another example, the For example, the tire mounting position determination arbitrary timing is the moment the final axle rotation unit 30 checks which one of the detector rotation angle amount Cn is acquired. The notification signal Spk is θa conforms to which one of the axle rotation angles θb transmitted from each of the notification signals Spk in 15 to determine the mounting positions of the tires 2a to 2d. substantially fixed intervals. Thetire mountingposition determination unit 30 functions [0027] Referring to Fig. 4, the angle θk is the angle of as a position determination processing unit. each of the tire pressure detectors 4a to 4d from a refer- [0032] The operation of the tire pressure detectors 4a ence position (e.g., twelve o-clock position). In the ex- to 4d will now be described with reference to Figs. 3 and ample of Fig. 4, when the count value of the pulses Spl 20 7 to 11. is "83" for the representative wheel 26, tire ID code ID3 [0033] Referring to Fig. 7, each tire pressure detector indicates that the angle θk of the right rear tire pressure 4 switches modes in accordance with the vehicle velocity detector 4c is 262.5 degrees ((83-13)3360/96). In the V. When the vehicle velocity V is greater than or equal same manner, tire ID code ID2 indicates that the angle to the first threshold V1, the tire pressure detectors 4a to θk of the left front tire pressure detector 4b is 210 degrees 25 4d operates in a pressure determination mode. During ((83-27)3360/96). Tire ID code ID1 indicates that the an- the pressure determination mode, the transmission in- gle θk of the right front tire pressure detector 4a is 161.25 terval of a radio wave signal is set to, for example, one degrees ((83-40)3360/96). Tire ID code ID4 indicates minute. When the vehicle is stopped or parked, the trans- that the angle θk of the left rear tire pressure detector 4d mission interval of a radio wave signal is set to, for ex- is 45 degrees ((83-71)3360/96). 30 ample, five minutes. During the pressure determination [0028] Referring to Fig. 5, the detector rotation angle mode, pressure measurement and temperature meas- calculation unit 28 calculates the detector rotation angle urement are performed in fixed intervals whenever a ra- θa, which is the difference between angle θk1 at the first dio wave signal is transmitted. Further, in the pressure determination timing t1 and angle θk2 at the second de- determination mode, the measurement interval of the ac- termination timing t2 for each of the tire pressure detec- 35 celeration sensor 10 is set to, for example, ten seconds tors 4a to 4d. to determine whether the vehicle is travelling or stopped. [0029] Referring to Fig. 1, the automatic locator 20 in- [0034] When the vehicle velocity V is between the first cludes an axle rotation angle calculation unit 29 that cal- threshold V1 and the second threshold V2, the operation culates the axle rotation angle θb from the axle rotation mode switching unit 22 switches the corresponding one amount C counted during the intervals Tu. The axle ro- 40 of the tire pressure detectors 4a to 4d to the automatic tation angle calculation unit 29 calculates the axle rota- location preparation mode. When the tire pressure de- tion angle θb for each of the axles 18a to 18d. The axle tectors 4a to 4d are in the automatic location preparation rotation angle calculation unit 29 functions as a position mode, the measurement interval of the acceleration sen- determination processing unit and a tire position deter- sor 10 is shortened to, for example, twenty milliseconds mination unit. 45 to accurately determine whether the vehicle 1 is stopping. [0030] Referring to Fig. 6, the axle rotation angle θb is During the automatic location preparation mode, the the rotation angle of the axle 18 taken between the first monitoring of the tire pressure (i.e., pressure measure- determination timing t1 and the second determination ment, temperature measurement, and transmission of timing t2. However, under a situation in which a rotation measurements) is performed in the same manner as the amount difference is produced between an inner wheel 50 pressure determination mode. and an outer wheel such as when travelling along a [0035] When the vehicle velocity V is less than the sec- curved road, it is preferable that the tire mounting posi- ond threshold V2, the operation mode switching unit 22 tions be determined based on the rotation of the axles switches the corresponding one of the tire pressure de- 18 and the rotation positions of the tires 2. This is because tectors 4a to 4d to the automatic location mode. During under a situation in which a rotation difference is pro-55 the automatic location mode, the transmission interval of duced between the inner and outer wheels, the rotation radio wave signals is set to, for example, thirty seconds. of the axles 18 results in different rotation amounts or During the automatic location mode, the measurement different rotation angles. For example, when the vehicle interval of the acceleration sensor 10 is set to twenty

6 11 EP 2 749 437 A1 12 milliseconds, which is the same as the automatic location travel status determination unit 21 determines whether preparation mode. In the automatic location mode, pres- or not the vehicle velocity V is less than the first threshold sure measurement and temperature measurement are V1 based on variations in the detection signals of the not performed. When a predetermined duration time acceleration sensor 10 per unit time. When the vehicle (e.g., three minutes) elapses, the operation mode switch- 5 velocity V is less than the first threshold value V1, the ing unit 22 returns the automatic location mode to the tire pressure detectors 4a to 4d proceed to step 104. pressure determination mode. Otherwise, the tire pressure detectors 4a to 4d proceed [0036] In another example, when radio wave signals to step 103. are transmitted in fixed intervals for a predetermined [0042] In step 103, the tire pressure detectors 4a to 4d number of times (e.g., ten times) during the automatic 10 perform a normal tire pressure detection process. The location mode, the operation mode switching unit 22 for- tire pressure detectors 4a to 4d operate in the pressure cibly returns the operation mode to the pressure deter- determination mode, measure the pressure and temper- mination mode. In a further example, after the vehicle ature when radio wave signals are transmitted in fixed velocity V becomes greater than or equal to the first intervals, and transmit tire pressure signals Stp including threshold V1, if the vehicle velocity V falls again and be- 15 the measurement results to the receiver 12. comes less than the second value V2, the operation [0043] In step 104, the characteristic point detection mode switching unit 22 switches the operation mode to unit 23 determines whether or not the detection signal of the automatic location mode. the acceleration sensor 10 is indicative of a characteristic [0037] Referring to Fig. 3, when the vehicle velocity V point (e.g., minimum point). In the illustrated example, is relatively high at around 0 to 1 s, the waveform of the 20 thecharacteristic pointis theminimum point in a detection detection signal from each acceleration sensor 10 is plot- signal of the acceleration sensor 10 corresponding to the ted diagonally downward to the right. This is because the twelve o’clock position of the tire pressure detectors 4a detection signal of the acceleration sensor 10 reflects the to 4d. When the detection signal of the acceleration sen- centripetal component of gravity Gr and the centrifugal sor 10 is indicative of a characteristic point, the process- force, which is produced by the high-speed rotation of 25 ing proceeds to step 105. Otherwise, the processing pro- the corresponding tire 2 and relatively large. Thus, to ceeds to step 103. reduce the influence of the centrifugal force, it is prefer- [0044] In step 105, the notification signal transmission able that the operation mode be shifted to the automatic unit 24 records the time at which a characteristic point location mode after the vehicle velocity V becomes low. was detected in the detection signal of the acceleration [0038] The tire pressure detectors 4a to 4d are config- 30 sensor 10. ured to separately transmit radio wave signals (notifica- [0045] Fig. 9 shows the transmission timing of radio tion signals Spk). The length of time (frame time) used wave signals (notification signals Spk) when the vehicle to transmit a notification signal Spk is extremely short. velocity V is sufficiently low. As described above, if the However, when the tires 2a to 2d are rotating at a high radio wave signals (notification signals Spk) are trans- speed, notification signals Spk may interfere with one 35 mitted when the vehicle velocity V is high, interference another. For example, when a tire 2 completes a single occurs between the notification signals Spk. In this case, rotation in thirty milliseconds and each of the tire pressure the notification signals Spk are repetitively transmitted detectors 4a to 4d transmit a notification signal Spk within until correctly transferred to the receiver 12. This may a frame time of eight millisec onds, the notification signals result in excessive power consumption in the tire pres- Spk may interfere with one another. Thus, when the tires 40 sure detectors 4a to 4d. Thus, the tire pressure detectors 2ato 2d are rotated at a low speed, thenotification signals 4a to 4d transmit the notification signals Spk when the Spk are less likely to interfere with one another. Conse- vehicle speed V is sufficiently low and the time interval quently, the automatic location mode performed at a low between two consecutive characteristic points is greater speed is advantageous since interference may be re- than or equal to a predetermined time Tm. This obviates duced. 45 or reduces unnecessary transmissions of the notification [0039] Fig. 8 is a flowchart illustrating the operation of signals Spk and interference between the notification sig- each of the tire pressure detectors 4a to 4d. nals Spk. [0040] In step 101, each of the tire pressure detectors [0046] In step 106, which is illustrated in Fig. 8, the 4a to 4d samples the detection signals of the correspond- notification signal transmission unit 24 checks whether ing acceleration sensor 10 and temporarily stores the 50 the time between the detection of the present character- detection result in the memory 7. The travel status de- istic point and the detection of the previous characteristic termination unit 21 determines the travel status of the point is longer than or equal to a predetermined time Tm. vehicle 1, such as the vehicle velocity, based on the sam- When longer than or equal to the predetermined time, pled detection signals of the acceleration sensor 10. the processing proceeds to step 107. Otherwise, the [0041] In step 102, each of the tire pressure detectors 55 processing proceeds to step 103. In another example, a 4a to 4d determines whether or not the vehicle velocity predetermined time range Tm6ΔT is used in lieu of the V is less than the first threshold V1 based on the detection predetermined time Tm. signal of the acceleration sensor 10. In one example, the [0047] In step 107, the notification signal transmission

7 13 EP 2 749 437 A1 14 unit 24 transmits, through wireless communication, the [0056] The interval Tu between the first determination notification signal Spk to the receiver 12. timing t1 and the second determination timing t2 may be [0048] The operation of the receiver 12 will now be fixed or variable. A variable interval Tu, for example, may described. vary in accordance with the transmission timing of the [0049] In step 201, which is illustrated in Fig. 10, the 5 tire pressure detector 4. However, in this case, it is pref- receiver 12 receives notification signals Spk from the tire erable that the interval Tu not be a short time of merely pressure detectors 4a to 4d. The detector angle calcula- a few seconds. tion unit 27 stores the axle rotation amount Cn (n=1 to [0057] The interval Tu may be the time until the tire 4) of the representative wheel 26 when receiving the no- pressure detector 4 switches to the automatic location tification signals Spk in association with the tire ID codes. 10 mode. In this case, the switching to the automatic location The detector angle calculation unit 27 repeats step S201 mode is performed when the vehicle velocity V decreas- until receiving the notification signal Spk from every one es. This increases the possibility of a rotation amount of the tire pressure detectors 4a to 4d. difference being produced between the inner and outer [0050] In step 202, the detector angle calculation unit wheels after the mode is switched. 27 determines whether or not the notification signal Spk 15 [0058] Even when each tire pressure detector 4 is con- has been received from every one of the tire pressure figured to transmit radio wave signals in fixed intervals, detectors 4a to 4d. When the notification signal Spk has it is preferable that the tire pressure detectors 4 transmit been received from every one of the tire pressure detec- the radio waves within a relatively short period. For ex- tors 4a to 4d, the detector angle calculation unit 27 pro- ample, when a tire pressure detector 4 transmits a noti- ceeds to step 203. Otherwise, the detector angle calcu- 20 fication signal Spk, before that tire pressure detector 4 lation unit 27 returns to step 201. finishes a single rotation, it is preferable that the remain- [0051] Instep 203, afterreceiving the notification signal ing three tire pressure detectors 4 each complete the Spk from every one of the tire pressure detectors 4a to transmission of the notification signal Spk. 4d, the detector angle calculation unit 27 acquires the [0059] In step S301, which is illustrated in Fig. 11, the axle rotation amount Cref of the representative wheel 26 25 detector rotation angle calculation unit 28 calculates the and stores the axle rotation amount Cref in the memory detector rotation angle θa during the interval Tu based 15. on the detector angle θk1 at the first determination timing [0052] In step 204, the detector angle calculation unit t1 and the detector angle θk2at thesecond determination 27 calculates the angle θk1 of each of the tire pressure timing t2. detectors 4a to 4d at the first determination timing t1. In 30 [0060] In step 302, the axle rotation angle calculation the illustrated example, the detector angleθ k1 corre- unit 29 divides the count value of the counter 31, which sponding to tire ID code ID1 is calculated from (Cref- is the number of pulses Spl from each of the axle rotation C1)x360/96. The detector angle θk1 corresponding to amount sensors 19a to 19d, with the total number of puls- tire ID code ID2 is calculated from (Cref-C2)x360/96. The es for each tire rotation (in the illustrated example, 96) detector angle θk1 corresponding to tire ID code ID3 is 35 to obtain a quotient and a remainder. The axle rotation calculated from (Cref-C3)x360/96. The detector angle angle calculation unit 29 determines the axle rotation an- θk1 corresponding to tire ID code ID4 is calculated from gle θb from the remainder. (Cref-C4)x360/96. [0061] In step 303, the position determination unit 30 [0053] In step 205, the detector angle calculation unit uses the detector rotation angle θa obtained in step 301 27 stores in the memory 15 the detector angles θk1 cor- 40 and the axle rotation angle θb obtained in step 302 to responding to tire ID codes ID1 to ID4 at the first deter- determine the mounting position of each of the tires 2a mination timing. to 2d. For example, the position determination unit 30 [0054] In step 206, the axle rotation amount acquisition checks which one of the detector rotation angles θa con- unit 25 clears the counter 31. forms to which one of the axle rotation angles θb to de- Accordingly, the counter 31 of the axle rotation amount 45 termine the tire ID code (detector ID code) and the axle acquisition unit 25 counts the pulses Spl output from the (tire mounting position). When the detector rotation an- axle rotation amount sensors 19a to 19d as the vehicle gles θa all have conforming axle rotation angles θb, the travels after the detection angle θk1 is calculated for the mounting positions are determined for all of the tires 2. four wheels at the first determination timing t1. [0062] In step 304, the position determination unit 30 [0055] When the vehicle velocity V is relatively low after 50 determines whether or not the mounting positions of eve- the first determination timing t1, the receiver 12 receives ry one of the tires 2a to 2d have been determined within notification signals Spk from the tire pressure detectors a predetermined limited time. When the mounting posi- 4a to 4d. Through procedures similar to steps 201 to 205, tions of every one of the tires 2a to 2d cannot be deter- the receiver 12 calculates the detector angle θk2 of each mined within the limited time, the processing is forcibly of the tire pressure detectors 4a to 4d at the second de- 55 terminated and the routine of Fig. 11 is performed again termination timing t2 after receiving the notification sig- in another opportunity. nals Spk from every one of the tire pressure detectors [0063] When the mounting positions of every one of 4a to 4d. the tires 2a to 2d have been determined within the limited

8 15 EP 2 749 437 A1 16 time (YES in step 304), in step 305, the position deter- celeration sensor 10. Thus, the determination results mination unit 30 registers the tire mounting positions to of the tire mounting positions are subtly affected by the memory 15 of the tire pressure monitoring ECU 13. temperature changes and measurement errors in For example, the position determination unit 30 stores the detection signal of the acceleration sensor 10. whichone of the tireID codes (detectorID codes) belongs 5 This improves the determination accuracy of the tire to which one of the tires 2a to 2d. This completes the mounting positions. automatic location of the tires 2a to 2d. The automatic (2) Each of the tire pressure detectors 4a to 4d trans- location is repetitively performed in predetermined cy- mits, through wireless communication, the notifica- cles. tion signal Spk when the vehicle velocity V is low and [0064] The first embodiment has the advantages de- 10 less than the second threshold V2. The receiver 12 scribed below. transmits the notification signal Spk from which the influence of centrifugal force is reduced or eliminat- (1) Each of the tire pressure detectors 4a to 4d trans- ed. This improves the determination accuracy of the mits a notification signal Spk when detecting a char- tire mounting positions. acteristic point (twelve o’clock position) in the detec- 15 (3) Each of the tire pressure detectors 4a to 4d trans- tion signal of the acceleration sensor 10. Whenever mits, through wireless communication, the notifica- receiving a notification signal Spk from the tire pres- tion signal Spk when the vehicle velocity V is low and sure detectors 4a to 4d, the axle rotation amount Cn less than the second threshold V2. Thus, the timings of the present representative wheel 26 is stored in at which notification signals Spk are transmitted from the memory 15 in association with the tire ID code 20 different tire pressure detectors do not easily overlap in the notification signal Spk. When the axle rotation with one another. This reduces or obviates interfer- amount Cn is stored in association with every one ence between the notification signals Spk. Thus, the of the tire pressure detectors 4a to 4d, the receiver receiver 12 correctly transmits the notification sig- 12 reads the axle rotation amount Cref of the repre- nals Spk (establishes communication) more fre- sentative wheel 26 at the first determination timing 25 quently. t1 and uses the axle rotation amount Cn (n=1 to 4) (4) Each of the tire pressure detectors 4a to 4d in- and the axle rotation amount Cref to calculate the cludes the characteristic point detection unit 23 that angle θk1 of each of the tire pressure detectors 4a detects a characteristic point in the detection signal to 4d at the first determination timing t1. The receiver of the acceleration sensor 10 indicative of a certain 12 performs the same process at the second deter- 30 directional component of gravity varying with a rota- mination timing t2. The receiver 12 calculates the tion of the corresponding tire 2. This allows for the detector rotation angle θa of each of the tire pressure receiver 12 to accurately determine that the tire pres- detectors 4a to 4d in the interval Tu from the detector sure detectors 4a to 4d are located at a certain po- rotation angle θk1 at the first determination timing t1 sition in the tire rotation direction. and the detector angle θk2 at the second determi- 35 (5) When the time between two consecutive mini- nation timing t2. The receiver 12 calculates the axle mum points detected in the detection signal of an rotation angle θb of each of the axles 18a to 18d in acceleration sensor is longer than or equal to the the interval Tu from the number of pulses Spl (axle predetermined time Tm, the tire pressure detectors rotation amount C) of each of the axle rotation 4a to 4d are each allowed to transmit a notification amount sensors 19a to 19d in the interval Tu. The 40 signal Spk. Interference between different notifica- receiver 12 compares the calculated detector rota- tion signals Spk from the pressure detectors 4a to tion angle θa with the axle rotation angle θb to de- 4d is reduced or obviated. Thus, the receiver 12 cor- termine the tire mounting positions. rectly transmits the notification signals Spk (estab- The angle θk of each of the tire pressure detectors lishes communication) more frequently. 4a to 4d may be calculated from the difference of the 45 (6) Each of the tire pressure detectors 4a to 4d in- axle rotation number Cn of the representative wheel cludes the operation mode switching unit 22. The 26, when the acceleration sensor 10 of each of the operation mode switching unit 22 determines the tire pressure detectors 4a to 4d detects the charac- travel status of the vehicle from variations in the de- teristic point in the detection signal of the accelera- tection signal of the corresponding acceleration sen- tion sensor 10 indicating the twelve o’clock position, 50 sor 10 that is indicative of a certain directional com- and the axle rotation amount Cref of the represent- ponent of gravity varying with a rotation of the cor- ative wheel 26 at a determination timing after the responding tire 2. Then, the operation mode switch- axle rotation amount Cn of every one of the tires 2 ing unit 22 switches the operation mode of the cor- is acquired. In this manner, the detector angle θk is responding one of the tire pressure detectors 4a to obtained by detecting the characteristic point in the 55 4d in accordance with the travel status. Accordingly, detection signal of the acceleration sensor 10 and the tire mounting positions are determined in a travel not from the value of the centripetal component of status suitable for the tire mounting positions. gravity Gr included in the detection signal of the ac- (7) The operation mode switching unit 22 first switch-

9 17 EP 2 749 437 A1 18

es the corresponding one of the tire pressure detec- angle difference (phase difference) from the right rear tors 4a to 4d to the automatic location preparation tire pressure detector 4c. When the right front tire pres- mode when the vehicle velocity V becomes less than sure detector 4a is located at a reference position (twelve the first threshold. In the automatic location prepa- o’clock position), the right rear tire pressure detector 4c ration mode, the tire pressure detectors 4a to 4d fine- 5 is deviated from the reference position by -10 degrees. lysamples the detection signals of the corresponding At the first determination timing t1, the right front tire pres- acceleration sensors 10 to determine the travel sta- sure detector 4a, which is located at the twelve o’clock tus but does not transmit the notification signal Spk. position, transmits the notification signal Spk, which in- This reduces the power consumed by the tire pres- cludes an ID. Then, when the tires 2a and 2c are rotated sure detectors 4a to 4d and prolongs the battery life. 10 by 10 degrees, the right rear tire pressure detector 4c (8) The interval Tu from the first determination timing reaches the twelve o’clock position and transmits the no- t1 to the second determination timing t2 is set to a tification signal Spk. length during which a rotation amount difference is [0067] At the first determination timing t1, the receiver assumed to be produced between the inner and out- 12 acquires an axle rotation amount Cn of the axle rota- er wheels. When a rotation amount difference is pro- 15 tion amount sensor 19 associated with the representative duced between the inner and outer wheels, the re- wheel 26 at a first determination timing t1 when the re- lationship of the rotation positions of the tires 2 at ceiver 12 receives a notification signal Spk from the right the second determination timing t2 deviates from the front tire pressure detector 4a and when the receiver 12 relationship of the rotation positions of the tires 2 at receives a notification signal Spk from the right rear tire the first determination timing t1. The same applies 20 pressure detector 4c. The difference between the axle to the axles 18. This allows for the position determi- rotation amounts Cn corresponding to these different no- nation unit 30 to readily determine the tire mounting tification signals Spk is indicative of the angle difference positions with high accuracy. between the two tire pressure detectors 4a and 4c at the (9) Each of the tire pressure detectors 4a to 4d trans- first determination timing t1. In the illustrated example, mits a notification signal Spk when detecting a char- 25 the right rear tire pressure detector 4c has a -10 degree acteristic point in the detection signal of the corre- difference from the right front tire pressure detector 4a. sponding acceleration sensor 10 that is indicative of [0068] Then, the vehicle 1 may be turned as it travels a certain directional component of gravity varying and produce a rotation amount difference between the with a rotation of the corresponding tire 2. This allows right front tire 2a and the right rear tire 2c. For example, for the position determination processing unit (27, 30 the phase of the right rear tire pressure detector 4c may 28) to determine the rotation position of the tire from be advanced by 90 degrees from the right front tire pres- the transmission timing of the notification signal Spk. sure detector 4a. In this case, at determination timing t2, (10) The receiver 12 includes the position determi- the right rear tire pressure detector 4c, which is located nation unit 30 that determines the tire mounting po- at the twelve o’clock position, transmits the notification sitions by comparing the detector rotation angle θa, 35 signal Spk. Then, when the tires 2a and 2c are rotated which is indicative of rotation variations in the tire by 80 degrees, the right front tire pressure detector 4a pressure detectors 4 between the determination tim- reaches the twelve o’clock position and transmits a no- ings t1 and t2, and the axle rotation angle θb, which tification signal Spk. In one example, each tire pressure is indicative of rotation variations in the axles 18 be- detector 4 is configured to transmit a notification signal tween the determination timings t1 and t2. 40 Spk in fixed intervals at timings when a characteristic (11) The receiver 12 includes the position determi- point (e.g., minimum point) is detected in the detection nation processing unit (27, 28) that calculates the signal of the corresponding acceleration sensor 10 when detector angle θk of each of the tire pressure detec- the vehicle is travelling at the same velocity. In some tors 4a to 4d from the axle rotation amount C of the examples, each tire pressure detector 4 is configured to representative wheel 26 when receiving the notifica- 45 transmit a notification signal Spk in predetermined cycles tion signal Spk. This improves the calculation accu- (e.g., 60 seconds) regardless of the rotation speed of the racy of each detector angle θk and the calculation tires 2. accuracy of the detector rotation angle θa. [0069] At the second determination timing t2, the re- ceiver 12 acquires an axle rotation amount Cn of the axle [0065] A second embodiment will now be described 50 rotation amount sensor 19 corresponding to the repre- focusing on features that differ from the first embodiment. sentative wheel 26 when the receiver 12 receives a no- The second embodiment differs from the first embodi- tification signal Spk from the right rear tire pressure de- ment in how a characteristic point in the detection signal tector 4c and when the receiver 12 receives a notification of the acceleration sensor 10 is detected. signal Spk from the right front tire pressure detector 4a. [0066] Figs. 12 and 13 schematically show the tire po- 55 The difference between the axle rotation amounts Cn sition determination method of the second embodiment. corresponding to the different notification signals Spk is As shown in Fig. 12, at the first determination timing t1, indicative of the angle difference between the two tire the right front tire pressure detector 4a has a 10 degree pressure detectors 4a and 4c at the second determina-

10 19 EP 2 749 437 A1 20 tion timing t2. In the illustrated example, the right rear tire [0074] Referring to Fig. 14, based on the left front tire pressure detector 4c has a +80 degree angle difference pressure detector 4b having tire ID code ID4 at the first from the right front tire pressure detector 4a. By calcu- determination timing t1, the detector angle calculation lating the difference between the angle difference of +80 unit 27 uses the detector angle θα to θγ to calculate the degrees at the second determination timing t2 and the 5 angle θk1 of the other detectors having tire ID codes ID1 angle difference of -10 degrees at the first determination to ID3. In the illustrated example, the angleθ k1 of the timing t1, the detection rotation angle θa (90 degrees) of right front tire pressure detector 4a having tire ID code the right rear tire pressure detector 4c between the de- ID1 based on the left front tire pressure detector 4b hav- termination timings t1 and t2 may be calculated. ing tire ID code ID4 is the total value of the detector angles [0070] Referring to Fig. 13, by calculating the axle ro- 10 θα, θβ, and θγ. The angle θk1 of the left front tire pressure tation amount Cn acquired at the first determination tim- detector 4b having tire ID code ID2 based on tire ID code ing t1 and the axle rotation amount Cn acquired at the ID4 is the total value of the detector anglesθβ and θγ. second determination timing t2, the axle rotation amount The angle θk1 of the right rear tire pressure detector 4c Cn varied between the determination timings t1 and t2, having tire ID code ID3 based on tire ID code ID4 is the namely, the axle rotation angle θb, may be calculated. 15 detector angle θγ. For example, by checking which one of the axle rotation [0075] In the same manner as the first determination angles 6b conforms to the rotation angle θa of the right timing t1, whenever the tire pressure detectors 4a to 4c rear tire pressure detector 4c including tire ID code ID3, reach the twelve o’clock position at the second determi- the mounting position of the tire 2 corresponding to the nation timing t2, the tire pressure detectors 4a to 4c trans- right rear tire pressure detector 4c may be determined. 20 mit notification signals Spk including corresponding IDs. [0071] The determination of the tire mounting positions Whenever, the receiver 12 receives a tire ID code, the in the second embodiment will now be described with axle rotation amounts C1 to C2 are read from the axle reference to Fig. 14. rotation amount sensors 19a to 19d. The detector angle [0072] As shown in Figs. 14 and 15, at the first deter- calculation unit 27 calculates the angles θk2 of the other mination timing t1, when the right front tire pressure de- 25 tire pressure detectors having tire ID codes ID1 to ID3. tector 4a is located at the twelve o’clock position, the right [0076] By obtaining the difference of the detector angle front tire pressure detector 4a transmits a notification sig- θk1 at the first determination timing t1 and the detector nal Spk including ID1 to the receiver 12. When the re- angle θk2 at the second determination timing t2, the de- ceiver 12 receives the notification signal Spk including tector rotation angle calculation unit 28 calculates the tire ID code ID1, the axle rotation amount acquisition unit 30 rotation angle θa of the other tire pressure detectors hav- 25 acquires the axle rotation amount C of the represent- ing tireID codes ID1 to ID3. Morespecifically, the detector ative wheel 26 in association with the tire ID code. Sub- rotation angle θa corresponding to tire ID code ID1 is sequently, in the same manner, when receiving the no- calculated from the detector angles θk1 and θk2 corre- tification signals Spk including tire ID codes ID2 to ID4, sponding to tire ID code ID1, the detector rotation angle the axle rotation amount acquisition unit 25 acquires the 35 θa corresponding to tire ID code ID2 is calculated from axle rotation amount C of the representative wheel 26 in the detector angles θk1 and θk2 corresponding to tire ID association with each tire ID code. code ID2, and the detector rotation angle θa correspond- [0073] Referring to Fig. 15, the detector angle calcu- ing to tire ID code ID3 is calculated from the detector lation unit 27 uses the variation in the axle rotation angles θk1 and θk2 corresponding to tire ID code ID3. amount C of the representative wheel 26 during the pe- 40 The detector rotation angle θa corresponding to tire ID riod from when tire ID code ID1 is received to when tire code ID4 is based on the tire pressure detector having ID code ID2 is received to calculate the angle ea of the tire ID code ID4 and is thus zero. tire pressure detector 4a having tire ID code ID1 based [0077] The axle rotation angle calculation unit 29 cal- on the position of the tire pressure detector 4b having culates the axle rotation angleθ b of each of the axles tire ID code ID2. Further, the detector angle calculation 45 18a to 18d from the difference of the axle rotation amount unit 27 uses the variation in the axle rotation amount C Cn at the first determination timing t1 and the axle rotation of the representative wheel 26 during the period from amount Cn at the second determination timing t2. For when tire ID code ID2 is received to when tire ID code example, based on tire ID code ID4 finally receiving dur- ID3 is received to calculate the angle θβ of the tire pres- ing asingle tire rotation, when calculating theaxle rotation sure detector 4b having tire ID code ID2 based on the 50 angle θb of each of the axles 18a to 18d, the right front position of the tire pressure detector 4c having tire ID axle rotation angle θb is calculated from "C1-14" and code ID3. The detector angle calculation unit 27 uses the "C1-24," the left front axle rotation angle θb is calculated variation in the axle rotation amount C of the represent- from "C2-14" and "C2-24," the left rear axle rotation angle ative wheel 26 during the period from when tire ID code θb is calculated from "C3-14" and "C3-24," and the left ID3 is received to when tire ID code ID4 is received to 55 rear axle rotation angle θb is calculated from "C4-14" and calculate the angle θγ of the tire pressure detector 4c "C4-24." The calculation of the axle rotation angleθb having tire ID code ID3 based on the position of the tire does not have to be based on the tire pressure detector pressure detector 4b having tire ID code ID4. having tire ID code ID4 and may be any one of the tire

11 21 EP 2 749 437 A1 22 pressure detectors having ID1 to ID3. of the tire pressure detectors 4a to 4c transmit a notifi- [0078] The position determination unit 30 determines cation signal Spk when reaching the twelve o’clock po- the mounting positions of the tires 2a to 2d by comparing sition. the detector rotation angle θa and the axle rotation angle [0084] Each tire pressure detector 4 transmits a noti- θb. By checking which one of the detector rotation angles 5 fication signal Spk for a number of times at a first deter- θa conforms to which one of the axle rotation angles θb, mination timing t1 and a second determination timing t2, the position determination unit 30 determines the rela- which have an interval Tu in between. In the illustrated tionship of the tire ID code (detector ID code) and the example, during a first determination timing t1, a tire pres- axle (tire mounting position). Since the detector rotation sure detector 4 transmits a notification signal Spk at time angle θa of the tire ID code ID4 is zero, the remaining 10 t11, at time t12 after the tire 2 completes a single rotation single axle corresponding to the axle rotation angleθ b from time t11, at time t13 after the tire 2 completes a that does not conform to any one of the detector rotation single rotation from time t12, and at time t14 after the tire angles θa is determined as corresponding to tire ID code 2 completes a single rotation from time t13. ID4. [0085] The second determination timing t2 starts sub- [0079] In addition to advantages (1), (4), (5), and (8) 15 sequent to the first determination timing t1 after an inter- to (11) of the first embodiment, the second embodiment val Tu, which is when a rotation amount difference may has the following advantage. be produced between an inner wheel and an outer wheel. In the second determination timing t2, the tire pressure (12) The rotation difference between an inner wheel detectors 4a to 4d are likely to be located at different and an outer wheel does not cause an angle error 20 positions in the tire rotation direction in the first determi- in the calculation of the detector angle θk. This im- nation timing t1 and the second determination timing t2. proves the calculation accuracy of the detector angle Like the first determination timing t1, in the second de- θk. As a result, the calculation accuracy of the de- termination timing t2, a notification signal Spk is trans- tector rotation angle θa is improved, and the deter- mitted at times t21, t22, t23, and t24. mination accuracy of the tire mounting position is 25 [0086] The position determination unit 30 pairs times improved. t11 to t14 of the first determination timing t1 with times t21 to t24 of the second determination timing t2. Further, [0080] A third embodiment will now be described fo- the position determination unit 30 determines the tire cusing on features that differ from the embodiments de- mounting positions based on the combination of signals scribed above. 30 (axle rotation amount) at the paired times. For example, [0081] For example, when the vehicle 1 is continuously when assuming that the first determination timing t1 and travelling straight over a relatively long period of time, a the second determination timing t2 are both deviated by rotation amount difference between an inner wheel and thesame amount, the position determinationunit 30 pairs an outer wheel may not be produced during the period "t11 and t21", "t12 and t22", and so on. For example, between the first determination timing t1 and the second 35 when assuming that only the first determination timing t1 determination timing t2. In the second embodiment, as is deviated by a predetermined amount and that the sec- long as a rotation difference is not produced between ond determination timing t2 is not deviated, the position inner and outer wheels, the measurement result of the determination unit 30 pairs "t11 and t12", "t12 and t21", second determination timing t2 repetitively replaces the and so on. measurement result of the next first determination timing 40 [0087] Tire position determination will now be de- t1 (refer to Fig. 16). scribed with reference to Figs. 19 and 20. [0082] The accumulation of various tolerances in the [0088] As shown in Fig. 19, in the first determination actual tire pressure detector 4 may result in the tire pres- timing t1, the receiver 12 receives the notification signal sure detector 4 not transmitting a notification signal Spk Spk for a predetermined number of times (e.g., four when reaching the twelve o’clock position. As shown in 45 times). Whenever the axle rotation amount acquisition Fig. 17, the transmission timing of the notification signal unit 25 receives the notification signal Spk during the first Spk may include an error θe. The error θe is the deviated determination timing t1, the axle rotation amount acqui- angle from the ideal position shown by the broken lines sition unit 25 measures and holds consecutive axle ro- or the deviated time from the ideal timing corresponding tation amounts C during the first determination timing t1. to the ideal position. The error θe is one factor that in- 50 In the illustrated example, at time t11, the axle rotation creases the number of times the tire mounting positions amount C is 20 when the notification signal Spk including are determined. tire ID code ID1 is received, the axle rotation amount C [0083] Referring to Fig. 18, the determination of the is 40 when the notification signal Spk including tire ID tire mounting positions in the third embodiment will now code ID2 is received, the axle rotation amount C is 60 be described. The tire pressure detectors 4a to 4c (tire 55 when the notification signal Spk including tire ID code ID codes ID1 to ID3) are shown at positions taken when ID3 is received, and the axle rotation amount C is 70 the tire pressure detector 4d (tire ID code ID4) is located when the notification signal Spk including tire ID code at the reference position (twelve o’clock position). Each ID4 is received. In the same manner, at time t12, the axle

12 23 EP 2 749 437 A1 24 rotation amounts C corresponding to tire ID codes ID1 mination result is stored in the memory 15 as the updated to ID4 are 19, 42, 58, and 71, respectively. Each axle tire mounting position. rotation amount C at time t11 and each axle rotation [0093] Referring to Fig. 20, the error θe1 of a tire pres- amount C at time t12 are rotation amounts in the same sure detector 4 at the first determination timing t1 should determination timing t1 and thus may be a proximate val- 5 be the same value as the error θe2 of the same tire pres- ue deviated from the true value in correspondence with sure detector 4 at the second determination timing t2. anerror caused by the accumulation of tolerances in each Accordingly, in a configuration in which each transmitter detector 4. 4 transmits the notification signal Spk only once in each [0089] The interval between times t11 and t12 corre- of the first determination timing t1 and the second deter- sponds to a single tire rotation. Thus, the possibility is 10 mination timing t2, accurate determinations may be hin- low of a rotation amount difference being produced be- dered due to the errors θe1 and θe2. However, in the tween an inner wheel and an outer wheel during an in- third embodiment, each transmitter 4 transmits in each terval between times t11 and t12. Thus, the axle rotation of the first determination timing t1 and the second deter- amount C corresponding to tire ID code ID1 at time t11 mination timing t2 the notification signal Spk for a number takes substantially the same value as the axle rotation 15 of times and performs measurements at times t11 to t14 number C corresponding to tire ID code ID1 at time t12. and t21 to t24. Thus, coincidentally, the possibility in The same applies to the axle rotation amounts C respec- which the errors θe1 and θe2 may be handled in the same tively corresponding to the other tire ID codes ID2 to ID4. manner as true values increases in the first determination Accordingly, it is apparent that the determination of the timing t1 and the second determination timing t2. Accord- tire mounting positions from the combination of the infor- 20 ingly, the determination method of the third embodiment mation acquired at time t11 and the information acquired is advantageous in that the tire position determination is at time t12 is not realistic. accurate. [0090] At determination timing t2, the receiver 12 re- [0094] In addition to advantages (1) to (12) of the first ceives the notification signal Spk for a number of times and second embodiments, the third embodiment has the (e.g., four times). Whenever the axle rotation amount ac- 25 following advantage. quisition unit 25 receives a notification signal Spk during the second determination timing t2, the axle rotation (13) In each of the first and second determination amount acquisition unit 25 measures the axle rotation timings t1 and t2, the tire mounting position determi- amount C and holds the axle rotation amounts C con- nation routine is performed a number of times. This secutively measured during the second determination 30 completes the determination of the tire mounting po- timing t2. sitions at an early stage. [0091] The position determination unit 30 pairs signals (axle rotation amounts) at times t11 to t14 during the first [0095] A fourth embodiment will now be described fo- determination timing t1 with times t21 to t24 during the cusing on features that differ from the embodiments de- second determination timing t2, and compares the de- 35 scribed above. tector rotation angle θa and the axle rotation angle θb to [0096] As shown in Fig. 21, to accurately detect the determine the tire mounting positions. For example, the characteristic point of the centripetal component of grav- position determination unit 30 pairs times t11 to t14 of ity Gr, a sampling cycle Tb of the centripetal component the first determination timing t1 with times t21 to t24 of of gravity Gr is set to be sufficiently shorter than the cycle the second determination timing in temporal order from 40 Ta of a single tire rotation. However, as the sampling early ones. Referring to Fig. 19, even when a tire mount- cycle Tb of the centripetal component of gravity Gr be- ing position cannot be determined from the first pair (i.e., comes shorter, the acceleration sensor 10 is activated time t11 and time t21), the tire mounting position may be more frequently, and the power consumption of the tire determined from the second pair (i.e., time t12 and time pressure detector 4 is increased. t22) as long as the second pair (t12 and t22) allows for 45 [0097] Accordingly, referring to Fig. 22, in the fourth correct detection of a certain rotation position (e.g., up- embodiment, the sampling cycle Tc of the centripetal permost position) of the tire pressure detector 4. component of gravity Gr is a variable value that varies in [0092] When the tire mounting position cannot be de- accordance with the cycle Ta of a single tire rotation. termined from finally acquired signals of the first deter- Tc=Ta/n (where n is a natural number). The sampling mination timing t1 and the second determination timing 50 cycle Tc is set to be one-half or less of the cycle Ta of a t2, the tire position determination system 17 uses the single tire rotation but longer than the cycle Tb. The sam- finally acquired axle rotation amount of the second de- pling cycle Tc is set to be one-half or less of the cycle Ta termination timing t2 and the next axle rotation amount of a single tire rotation, and n is set to 4 in the example of the first determination timing t1 to perform a similar of Fig. 22. The cycle of a single tire rotation cycle Ta may tire mounting position determination routine. The above 55 be calculated from the axle rotation amount (pulse determination routine is repeated until the tire mounting number) output from the axle rotation amount sensor 19. position determination is completed. When the tire [0098] When extending the sampling cycle Tc of the mounting position determination is completed, the deter- centripetal component of gravity Gr, actual characteristic

13 25 EP 2 749 437 A1 26 point may be detected at point P that is deviated from a relatively large range G16Gth (Gthh1) is set in ad- the actual characteristic point Pk by time td. However, vance for the centripetal component of gravity Gr. Fur- the rotation cycle Ta of a single tire rotation may be cal- ther, to lower power consumption of the tire pressure culated from the axle rotation amount C and n is a con- detector, the sampling cycle of the centripetal component stant number. Thus, as long as the sampling cycle Tc 5 of gravity Gr is prolonged before the centripetal compo- satisfies "Tc=Ta/n," the interval between point P, which nent of gravity Gr reaches the determination range is detected last, and point P’, which is detected next, is G16Gth. The width Tt of the rotation cycle Ta and the the same as the cycle Ta, that is, the cycle between char- width Vth of the vehicle velocity V correspond to the width acteristic points of the true centripetal component of grav- Gth. ity Gr. Thus, even when prolonging the sampling cycle 10 [0104] When the detected centripetal component of Tc of the centripetal component of gravity Gr in accord- gravity Gr is in the range of G16Gth, the characteristic ance with "Tc=Ta/n," the same result is obtained as when point detection unit 23 samples the centripetal compo- determining the tire mounting position based on the cen- nent of gravity Gr in relatively short sampling cycles and tripetal component of gravity Gr. measures the peak-to-peak interval to calculate the cen- [0099] In addition to advantages (1) to (4), (6) to (8), 15 tripetal component of gravity Gr. The normal sampling and (10) to (13) of the first to third embodiments, the cycle of the centripetal component of gravity Gr is set to fourth embodiment has the advantages described below. be long. When the centripetal component of gravity Gr exceeds the determination range G1 6Gth, the sampling (14) The sampling cycle Tc of the centripetal com- cycle of the centripetal component of gravity Gr is ponent of gravity Gr is set to be shorter than the cycle 20 switched to a short value. Thus, the centripetal compo- Ta of a single rotation of the tire 2 in accordance with nent of gravity Gr is sampled many times only when truly "Tc=Ta/n." Thus, the tire mounting position may be necessary to determine the tire mounting positions. This determined, while reducing power consumption of reduces power consumption of the tire pressure detec- the tire pressure detector 4. tors 4a to 4d while improving the peak detection accura- (15) The characteristic point detection unit 23 and 25 cy. the notification signal transmission unit 24 may be [0105] In one example, the notification signal transmis- omitted from the tire pressure detector 4. sion unit 24 transmits a notification signal Spk when the calculated rotation cycle Ta is in a predetermined rotation [0100] A fifth embodiment will now be described focus- cycle range (e.g., Ta26ΔT). In this manner, each of the ing on features that differ from the embodiments de-30 tire pressure detectors 4a to 4d is set to transmit a noti- scribed above. fication signal Spk in accordance with the rotation cycle [0101] Referring to Fig. 23, the centripetal component Ta calculated from the peak-to-peak interval. Thus, the of gravity Gr may be converted to the rotation cycle Ta notification signal Spk is transmitted from each of the four of the tire 2 and the vehicle velocity V. For example, a wheels at substantially the same timing. This shortens peak-to-peak interval of the centripetal component of 35 the time used to determine the tire mounting positions. gravity Gr is indicative of the tire rotation cycle Ta. The [0106] In the example shown in Fig. 24, the centripetal vehicle velocity V may be calculated from the tire rotation component of gravity Gr is provided with a number of cycle Ta and the tire diameter. In the example of Fig. 23, determination ranges (G161, G261). When the charac- centripetal component of gravity Gr1 corresponds to ro- teristic point detection unit 23 is ready to calculate the 40 tation cycle Ta1 and vehicle velocity V1. rotation cycle Ta, the sampling cycle of the centripetal [0102] When determining the tire position in the component of gravity Gr is switched in accordance with present example, the tire pressure detectors 4a to 4d of the rotation cycle T. For example, when the rotation cycle all four wheels has to transmit radio wave signals (noti- Ta is Ta1 and relatively short, the characteristic point fication signals Spk) during the period the corresponding detection unit 23 sets a relatively short sampling cycle tire 2 rotates once. However, the present acceleration 45 (Ts1) for the centripetal component of gravity Gr. When sensor 10 cannot detect the absolute value of the cen- the rotation cycle Ta is Ta2 (>Ta1) and relatively long, tripetal component of gravity Gr with high accuracy. For the characteristic point detection unit 23 sets the sam- example, even if each of the tire pressure detectors 4a pling cycle of the centripetal component of gravity Gr to to 4d are programmed to transmit the notification signal Ts2 (>Ts1), which is relatively long. The sampling cycle Spk when the centripetal component of gravity Gr indi- 50 of the centripetal component of gravity Gr is optimized in cates a predetermined value, a certain number of tire accordance with the present tire rotation cycle Ta. This pressure detectors may not transmit the radio wave sig- reduces power consumption of the tire pressure detec- nal Spk. tors 4a to 4d. [0103] In contrast, the characteristic points of the cen- [0107] In addition to advantages (1) to (15) of the first tripetal component of gravity Gr may be accurately de- 55 to fourth embodiments, the fifth embodiment has the ad- tected. That is, the rotation cycle Ta may be accurately vantages described below. calculated. In the fifth embodiment, since the detection accuracy of the acceleration sensor 10 is relatively low, (16) The acceleration sensor 10 may not be able to

14 27 EP 2 749 437 A1 28

detect the absolute value of the centripetal compo- tection unit 23 resets an internal timer when the rotation nent of gravity Gr with high accuracy. Considering cycle T becomes greater than or equal to threshold Tth- that the acceleration sensor 10 has a rough detection a and starts measuring time. accuracy, the tire pressure detector 4 is provided [0110] The tire pressure detector 4 is allowed to trans- with the determination range G16Gth for the cen- 5 mit radio wave signals until a transmission permission tripetal component of gravity Gr. When the centrip- period T1 from the time origin point T0 expires. Prefera- etal component of gravity Gr is in the determination bly, the transmission permission period T1 is, for exam- range G16Gth, the tire pressure detector 4 starts ple, about one second and short. The sampling cycle of peak-to-peak measurement and calculates the rota- the centripetal component of gravity Gr during the trans- tion cycle Ta of the tire 2. When the rotation cycle 10 mission permission period T1 may be the same as the Ta is in a predetermined rotation cycle range (e.g., short cycle (e.g., about 10 ms) in which the centripetal Ta26ΔT), the tire pressure detector 4 transmits the component of gravity Gr exceeds the Gth1-a or may be notification signal Spk. In this manner, instead of the even shorter. During the transmission permission period absolute value of the detection signal of the accel- T1, the tire pressure detector 4 transmits a notification eration sensor 10, the tire pressure detector 4 uses 15 signal Spk to the receiver 12 whenever the tire pressure the rotation cycle Ta of the tire 2 that may be accu- detector 4 reaches the twelve o’clock position. The tire rately detected from variations in the detection signal pressure detectors 4a to 4d of the wheels are synchro- of the acceleration sensor to transmit notification sig- nized with respect to time by the rotation cycle Ta of the nals Spk at a determined timing. Thus, the tire pres- tire. This allows for the notification signal Spk to be trans- sure detector 4 may accurately transmit the notifica- 20 mitted at substantially the same timing. tion signal Spk. In this manner, repetitive transmis- [0111] When the transmission permission period T1 sion of unnecessary radio wave signals that cannot expires, the tire pressure detector 4 does not transmit be used for tire mounting position determination is any radio wave signals during the following transmission obviated or reduced. This prolongs the battery life of suspension period T2. Preferably, the transmission sus- the tire pressure detector 4. 25 pension period T2 is, for example, about 30 seconds and (17) The centripetal component of gravity Gr is pro- long. The sampling cycle of the centripetal component vided with plurality of determination ranges G161 of gravity Gr during the transmission suspension period and G261, and the rotation cycle Ta is provided with T2 may be extremely long such as about 3 to 20 seconds. a plurality of ranges. Further, the sampling cycle of This allowsfor thepower consumptionof the tirepressure the centripetal component of gravity Gr is switched 30 detector 4 to be reduced. in accordance with the present tire rotation cycle Ta. [0112] When the tire pressure detector 4 enters the Further, the sampling cycle of the centripetal com- transmission permission period T1 again, the tire pres- ponent of gravity Gr is switched in accordance with sure detector 4 shortens the sampling cycle of the cen- the rotation cycle Ta of the tire 2. The centripetal tripetal component of gravity Gr again (e.g., about 10 component of gravity Gr is sampled at an appropriate 35 ms). In this manner, when entering the transmission per- sampling cycle that is in accordance with the rotation mission period T1 again, the tire pressure detector 4 al- cycle Ta of the tire 2. This improves the transmission lows for a notification signal Spk to be accurately trans- timing accuracy of radio wave signals from the tire mitted to the receiver 12 when the tire pressure detector pressure detector 4. Further, the time used for tire 4 reaches the twelve o’clock position. Subsequently, the mounting position determination may be shortened, 40 transmission permission period T1 and the transmission and the battery life of the tire pressure detector 4 suspension period T2 are repeated. may be prolonged. [0113] In another example, when the centripetal com- ponent of gravity Gr becomes less than or equal to the [0108] A sixth embodiment will now be described fo- threshold Gth2 (≈0), the tire pressure detector 4 stops cusing on features that differ from the embodiments de- 45 the transmission performed every 30 seconds and enters scribed above. a standby state. The next time the centripetal component [0109] Referring to Fig. 25, when the detection value of gravity Gr becomes greater than or equal to the thresh- of the acceleration sensor 10, which has a rough detec- old Gth1, the tire pressure detector 4 starts synchroniza- tion accuracy, becomes greater than or equal to thresh- tion again. In this case, accumulative errors from the time old Gth1, the characteristic point detection unit 23 short- 50 origin point T0 are cancelled in the tire pressure detectors ens the sampling cycle (e.g., approximately 10 ms) for 4. This is advantageous for accurately measuring time. the centripetal component of gravity Gr of the accelera- Further, radio wave signals are transmitted from the tire tion sensor 10 and starts accurate measurement of the pressure detector 4 less frequently, and the power con- rotation cycle Ta of the tire 2. The characteristic point sumption of the tire pressure detector 4 is reduced. detection unit 23 sets the time when the measured rota- 55 [0114] Referring to Fig. 26, if the estimated time for tion cycle Ta first becomes greater than or equal to a completing automatic location (e.g., 20 minutes) elapses threshold Tth-a as a time origin point T0 for the tire pres- from when the time origin point T is set or if the number sure detector 4. For example, the characteristic point de- of radio wave signal transmissions from the tire pressure

15 29 EP 2 749 437 A1 30 detector 4 becomes greater than or equal to an upper 30 seconds to 60 seconds. This allows for radio wave limit value (e.g., 40 times), the tire pressure detector 4 signals to be transmitted less frequently from the tire may switch the transmission suspension period T2 to a pressure detector 4 and further prolongs the battery second transmission suspension period T3 that is longer life of the tire pressure detector 4. than the default transmission suspension period T2. In 5 (21) When the vehicle is travelling at a low velocity, the preferred example, the second transmission suspen- the tire pressure detector 4 may not be able to trans- sion period T3 is an additional time of 60 seconds plus mit radio wave signals for a specified amount (e.g., a random time length. Except for the point in that the four times) with the normal interval. In this case, transmission suspension period T2 is extended, the op- when the rotation cycle Ta is 240 ms or less, a non- eration of the tire pressure detector 4 is as described10 peak flag is set, and the remaining three radio wave above. signals are transmitted at 110 ms or less. Thus, even [0115] When the vehicle is travelling at a low speed, when the vehicle is travelling at a low velocity, the the tire 2 may not be rotated once during the transmission remaining three radio wave signals are transmitted permission period T1. Thus, the tire pressure detectors at 110 ms or less. This allows for the tire pressure 4 may include those that transmit a radio wave signal 15 detector 4 to transmit radio wave signals for the de- once during the transmission permission period T1 and termined number of times even when the vehicle ve- those that do not. Accordingly, in some examples, when locity is low. the measured rotation cycle Ta is less than or equal to a tolerable value (e.g., 240 ms), the tire pressure detector [0117] A seventh embodiment will now be described 4 that has not detected a peak may transmit a notification 20 focusing on differences from the above embodiments. signal Spk (frame) including non-peak information (no- [0118] Referring to Fig. 27, in a tire pressure detector peak flag or the like) at a certain bit in short time intervals 4, the axle rotation amount C (pulse number) generated (e.g., 10 ms), and the tire pressure detectors 4 may all from when a notification signal Spk is transmitted (first transmit a radio wave signal at least once during the determination timing t1) to when the next notification sig- transmission permission period T1. In this manner, upper 25 nal Spk is transmitted (second determination timing t2) and lower limits for the number of radio wave signal trans- would be the axle rotation amount Cn for a single rotation missions are unnecessary during the automatic location when there is a conforming axle 18 (tire 2). This is be- period. cause each of the tire pressure detectors 4a to 4d trans- [0116] The sixth embodiment has the advantages de- mits a notification signal Spk when the vehicle is about scribed below in addition to advantages (1) to (17) of the 30 to stop. However, when the steering angle is large, the first to fifth embodiments. axle rotation amount C of each wheel differs greatly due to the rotation amount difference between an inner wheel (18) When the centripetal component of gravity Gr and an outer wheel. is greater than or equal to the threshold Gth1, the [0119] Thus, the axles 18a to 18d may be associated sampling cycle of the centripetal component of grav- 35 with the tire codes ID1 to ID4 by performing counting ity Gr isshortened when calculating the rotationcycle operations with the axle rotation amount sensors 19a to Ta of the tire 2. The tire pressure detectors 4a to 4d 19d of the tires 2a to 2d and using the axle rotation are synchronized with the rotation cycle Ta. Thus, amount Cn from one peak to another peak of a received radio waves may be accurately transmitted from the ID to check whether the axle rotation amount conforms tire pressure detectors 4a to 4d. This allows for the 40 to the rotation amount of a single rotation (e.g., 96 counts) transmission of a radio wave signal from each of the of any one of the tires 2a to 2d. The axles 18a to 18d tire pressure detectors 4a to 4d at each peak during may also be associated with the tire codes ID1 to ID4. In a single rotation of the tire 2. Thus, a radio wave the present example, this principle is used to determine signal used for tire position determination may be the tire position. readily received. This further prolongs the battery life 45 [0120] The tire ID received between two peaks always of the tire pressure detector 4. has the same pulse number. In the example of Fig. 27, (19) When the centripetal component of gravity Gr the right rear axle 18c is "92." This is not limited to a single becomeslower than the thresholdGth2, the tirepres- tire rotation and also occurs for n rotations. Thus, the tire sure detector 4 suspends the radio wave signal rotation amount during determination is not necessarily transmission performed every 30 seconds. Then, the 50 limited to a single tire rotation. tire pressure detector 4 sets the time origin point T0 [0121] Referring to Fig. 28, the automatic locator 20 as a starting point. This allows for the cancellation includes a two-peak-interval axle rotation amount meas- of errors accumulated from the previous time origin urement unit 35 that measures the axle rotation amount point T0 to be cancelled. Cn from when a notification signal Spk is received to (20) When the estimated time for completing auto- 55 when the next notification signal Spk is received. The matic location from the time origin point T0 ends, the two-peak-interval axle rotation amount measurement time during which the radio wave signal transmission unit 35 measures the axle rotation amount Cn between is suspended may be extended from, for example, two consecutively received notification signals Spk

16 31 EP 2 749 437 A1 32

(peak-to-peak) for each of the tire codes ID1 to ID4. The (22) Tire positions may be determined just by com- position determination unit 30 determines the mounting paring the time used to receive the notification signal positions of the tires 2a to 2d by comparing an ID code Spk twice and the pulse numbers obtained in this received between two peaks with the axle rotation time. Thus, the tire positions may be determined amount Cn measured by the two-peak-interval axle ro- 5 within a short period. tation amount measurement unit 35. (23) A tire position may be determined just by con- [0122] The tire position determination operation will secutively transmitting the notification signal Spk two now be described with reference to Fig. 29. times. Thus, the tire positions may be determined [0123] As shown in Fig. 29, when the two-peak-interval within a short period. axle rotation amount measurement unit 35 receives the 10 notification signal Spk of a tire ID, the two-peak-interval [0127] An eight embodiment will now be described fo- axle rotation amount measurement unit 35 acquires the cusing on differences from the above embodiments. pulse number of each of the axle rotation amount sensors [0128] Referring to Fig. 30, if a rotation amount differ- 19a to 19d at the first determination timing t1, which is ence is produced between an inner wheel and an outer based on a peak reception. Further, when the two-peak- 15 wheel, a peak-to-peak time Tpk would take different val- interval axle rotation amount measurement unit 35 re- ues in the tire ID codes. In Fig. 30, the notification signal ceives the next consecutive notification signal Spk of a Spk with tire ID code ID1 has the shortest peak-to-peak tire ID, the two-peak-interval axle rotation amount meas- time Tpk1, the peak-to-peak time Tpk2 for tire ID code urement unit 35 acquires the pulse number of each of ID2 is the longest, the peak-to-peak time Tpk3 of the theaxle rotation amountsensors 19a to 19d atthe second 20 detection signal of the right rear tire pressure detector 4c determination timing t2, which is based on a peak recep- having tire ID code ID3 is the third shortest, and the peak- tion, in the same manner. The two-peak-interval axle ro- to-peak time Tpk4 for tire ID code ID4 is the second short- tation amount measurement unit 35 obtains a pulse est. number difference between the first determination timing [0129] Further, if a rotation amount difference is pro- t1 and the second determination timing t2. The position 25 duced between an inner wheel and an outer wheel, the determination unit 30 associates the tire ID received maximum value of the axle rotation amount C, that is, peak-to-peak to determine a tire position. the rotation amount cycle Tpl, which is the number of [0124] In the example of Fig. 29, the pulse number of pulses during a single rotation, takes different values in the right front axle 18a exceeds "95," the pulse number the axles 18a and 18d. In Fig. 30, the rotation amount of the right rear axle 18c is exactly "95," and the pulse 30 cycle Tpl1 of the right front axle 18a takes the shortest number of the left front axle 18b is less than "95," and time, the rotation amount cycle Tpl2 of the left front axle the pulse number of the left rear axle 18d exceeds "95." 18b takes the longest time, the rotation amount cycle Thus, when detecting two consecutive peaks in the re- Tpl3 of the right rear axle 18c takes the third shortest ceived ID code, the right rear axle 18c having pulse time, and the rotation amount cycle Tpl4 of the left rear number "96" that corresponds to a single tire rotation is 35 axle 18d takes the second shortest time. determined as corresponding to the received tire ID that [0130] In this manner, the order of the peak-to-peak is about to be determined, and the two are associated time Tpk and the order of the rotation amount cycle Tpl with each other. This process is performed for the other conform at the same tire position. The present example wheels to locate the four wheels. uses this principle and compares the order of the peak- [0125] In the present example, the sampling cycle of 40 to-peak time Tpk and the order of the rotation amount the centripetal component of gravity Gr may be set like cycle Tpl to associate the orders and determine the tire in the fourth embodiment. In this case, when setting the position. sampling cycle Tc of the centripetal component of gravity [0131] Referring to Fig. 31, the automatic locator 20 Gr to "Ta/n," n is a natural number. Thus, there would be includes a peak ordering unit 36, which orders the peak- an infinite number of sampling cycles Tc. For this reason, 45 to-peak times Tpk of the notification signals Spk having even when the sampling cycle Tc does not satisfy "Ta/n," the tire ID codes ID1 to ID4, and a rotation amount cycle the processing may be repeated a number of times so ordering unit 37, which orders the rotation amount cycles that a value satisfying "Ta/n" would be coincidentally tak- Tpl of the axles 18a to 18d. The position determination enthereby allowing for thedetermination of a tireposition. unit 30 determines the tire positions based on the peak The determination probability will become low but the tire 50 order obtained by the peak ordering unit 36 and the ro- positions may be satisfied when "Tc=Ta/n" is coinciden- tation amount cycle order obtained by the rotation tally satisfied. In this manner, in broad terms, the present amount cycle ordering unit 37. In the present example, example includes a case in which the sampling cycle Tc to determine the tire positions under a situation in which takes a value that does not satisfy "Ta/n." a rotation difference is produced between an inner wheel [0126] In addition to advantages (1) to (21) of the first 55 and an outer wheel, the determination process is started to sixth embodiments, the seventh embodiment has the when, for example, the steering angle is greater than or advantages described below. equal to a predetermined angle. [0132] The tire position determination will now be de-

17 33 EP 2 749 437 A1 34 scribed with reference to Fig. 30. degrees," "left rear: 10 degrees," and "right rear: 120 de- [0133] As shown in Fig. 30, when the steering angle is grees." Accordingly, the tire positions may be determined greater than or equal to the predetermined angle, the by comparing the orders of the detector rotation angle receiver 12 starts the tire position determination. When θa and the axle rotation angle θb. the peak ordering unit 36 receives a notification signal 5 [0139] Referring to Fig. 33, the automatic locator 20 Spk of a certain tire ID code, the peak ordering unit 36 includes a detector rotation angle ordering unit 38, which measures the time until the notification signal Spk of the orders the rotation angles θa of the tire pressure detec- next ID is received to measure the peak-to-peak time of tors having tire ID codes ID1 to ID4, and an axle rotation the tire ID. When completing the peak-to-peak time angle ordering unit 39, which orders the axle rotation an- measurement for every one of the tire IDs, the peak or- 10 gles θb of the axles 18a to 18d. The position determina- dering unit 36 compares and orders the time. When or- tion unit 30 compares the order of the detector rotation dered from a shorter time to a longer time, the first one angle θa and the order of the axle rotation angleθ b to is tire ID1, the second one is tire ID4, the third one is tire determine the tire positions. ID2, and the fourth one is tire ID3. [0140] In the example of Fig. 32, the order of the de- [0134] Under a situation in which the steering angle is 15 tection rotation angle θa from smaller ones is "ID1," "ID3," greater than or equal to the predetermined angle, the "ID2," and "ID4." The order of the axle rotation angles θb rotation amount cycle ordering unit 37 measures the ro- from smaller ones is "right front," "left rear," "left front," tation amount cycle Tpl for each rotation of the axles 18a and "right rear." The position determination unit 30 as- to 18d. When the measurement of the rotation amount sociates the orders to determine the tire positions. More cycle Tpl is completed for all of the axles 18a to 18d, the 20 specifically, "ID1" is determined as "right front," "ID3" is rotation amount cycle ordering unit 37 compares and or- determined as "left rear," "ID2" is determined as "left ders the cycles. When ordered from a shorter cycle, the front," and "ID4" is determined as "right rear." first one is the right front axle 18a, the second one is the [0141] In addition to advantages (1) to (24) of the first left rear axle 18d, the third one is the left front axle 18b, to eight embodiments, the ninth embodiment has the fol- and the fourth one is the right rear axle 18c. 25 lowing advantage. [0135] The position determination unit 30 associates the peak order obtained by the peak ordering unit 36 with (25) The tire positions may be determined just by the rotation cycle order obtained by the rotation amount comparing the order of the detector rotation angles cycle ordering unit 37 to determine the tire positions. θa and the axle rotation anglesθ b. Thus, the tire Here, tire ID code ID1 is associated with the right front 30 positions may be determined with a simple process. axle 18a, tire ID code ID4 is associated with the left rear Further, even when there is an error in the actual axle 18d, tire ID code ID2 is associated with the left front measurement of the axle rotation amount C, such axle 18b, and tire ID code ID3 is associated with the right an error may be cancelled by comparing the order. rear axle 18c. As a result, the position determination unit This is advantageous for accurately determining the 30 determines the mounting positions of the tires 2 having 35 tire positions. the tire ID codes ID1 to ID4. [0136] In addition to advantages (1) to (23) of the first [0142] A tenth embodiment will now be described fo- to seventh embodiments, the eighth embodiment has the cusing on differences from the above embodiment. advantages described below. [0143] Referring to Fig. 34, due to wireless communi- 40 cation, the tire position determination system 17 may not (24) The tire positions may be determined just by be able to receive all four tire IDs and a certain ID may comparing the order of the peak-to-peak times Tpk not be received. In the example shown in Fig. 34, at the with the order of the rotation amount cycles Tpl. first determination timing t1, only the notification signals Thus, the tire positions may be determined through Spk including the tire ID codes ID1 and ID2 are received. a simple process. Further, even when there is an 45 At the second determination timing t2, the notification error in the actual measurement of the axle rotation signals Spk including the tire ID codes ID1 to ID4 are all amount C, the above comparison cancels such an received. error. This is advantageous for accurately determin- [0144] When determining tire positions by calculating ing the tire positions. the detector rotation angle θa of a predetermined tire ID 50 based on a certain ID, even if a tire ID is not received, [0137] A ninth embodiment will now be described fo- as long as the same tire ID is obtained at the first deter- cusing on features that differ from the above embodi- mination timing t1 and the second determination timing ments. t2, the tire position for that tire ID may be determined. [0138] As shown in Fig. 32, the detector rotation angles That is, as long as at least one ID is received at the first θa corresponding to ID1 to ID4 may be "ID1: 0 degrees," 55 determination timing t1 and the second determination "ID2: 45 degrees," "ID3: 20 degrees," and "ID4: 90 de- timing t2, the tire position corresponding to that ID may grees." Further, the axle rotation angles θb of the axles be determined. The present example uses this principle 18a to 18d may be "right left: 0 degrees," "left front: 30 to determine tire positions.

18 35 EP 2 749 437 A1 36

[0145] The tire position determination will now be de- signal Spk that includes the tire ID codes ID3 and ID4 scribed with reference to Figs. 34 to 36. received at the determination timing t1’ to acquire all of [0146] Referring to Fig. 34, when only the notification the IDs that should be acquired at the first determination signals Spk including tire ID codes ID1 and ID2 are re- timing t1. ceived at the first determination timing t1, if the twelve 5 [0150] Based on all of the tire ID codes acquired at the o’clock position is "0 degrees" when receiving the notifi- first determination timings t1 and t1’ and the tire ID codes cation signal including the tire ID code ID2, the angle of received at the second determination timing t2, the po- the right front tire pressure detector 4a corresponding to sition determination unit 30 calculates the detector rota- the tire ID code ID1 is "150 degrees" based on the tire tion angle θa of each of the tire pressure detectors 4a to ID2. Further, when the notification signals Spk of the tire 10 4d. Further, the position determination unit 30 compares ID codes ID1 to ID4 are all received at the second deter- the detector rotation angle θa and the axle rotation angle mination timing t2, based on the angle of the right rear θb to determine the tire position of each of the four tire pressure detector having tire ID3, the angle of the wheels. Thus, when there are missing tire ID codes at right front tire pressure detector 4a having the tire ID code the first determination timing t1, the tire positions of all ID1 is "45 degrees," and the left front tire pressure de- 15 four wheels may consequently be determined. tector 4b having the tire ID code ID2 is "90 degrees." [0151] In the tenth embodiment, the advantages de- [0147] As shown in Fig. 35, the detector rotation angle scribed below may be obtained in addition to advantages calculation unit 28 calculates detector rotation angles θa (1) to (25) of the first to ninth embodiments. between the first determination timing t1 and the second determination timing t2 from the difference of the detector 20 (26) Even when the tire ID codes are not acquired angle θk1 during the first determination timing t1 and the in a single determination process, positions are se- detector angle θk2 during the second determination tim- quentially determined for the received tire ID codes. ing t2. Here, it may be determined that between the first This is repeated to determine all of the tire ID codes. determination timing t1 and the second determination Thus, the acquirement of all of the ID codes for a timing t2, the tire ID code ID1 is rotated by 255 degrees, 25 single determination process is not a condition for and the tire ID code ID2 is rotated by 90 degrees. The completing the tire position determination. This is ad- position determinationunit 30determines the tireposition vantageous for every one of the tire positions at an by comparing the detector rotation angle θa and the axle early stage. rotation angle θb. More specifically, the axle rotation an- (27) Even when the tire ID codes are not acquired gles θb of "255 degrees" and "90 degrees" are associated 30 in a single determination process, position determi- with the tire ID codes ID1 and ID2 of the axles 18 to nation is performed for only the received ID codes, determine the tire positions. and position determination is subsequently per- [0148] Position determination may not be performed formed for the tires of which positions could not be on tire ID codes ID3 and ID4 that are not the same at the determined. By repeating the determination, the de- first determination timing t1 and the second determina- 35 termination of the tire positions may be ultimately tion timing t2. However, under the assumption that the determined. vehicle 1 is travelling straight, as long as radio wave sig- nals may be received from the tire pressure detectors 4 [0152] An eleventh embodiment will now be described having the tire ID codes ID3 and ID4 at a determination focusing on features differing from the above embodi- timing that is one tire rotation after the first determination 40 ments. timing t1, notification signals Spk having the tire ID codes [0153] In some embodiments, each axle rotation ID1 and ID2 are received at the first determination timing amount sensor 19 is configured to output a pulse signal t1 and notification signals Spk having tire ID codes ID3 whenever detecting the passage of a tooth or a gap be- and ID4 are received one rotation after. This is equivalent tween adjacent teeth. For example, each axle rotation to the tire ID codes for all wheels being obtained. 45 amount sensor 19 may output a total count number signal [0149] Referring to Fig. 36, if the ID codes cannot be or a total pulse number signal Dpl corresponding to the all acquired at the single first determination timing, under sum of the number of count teeth passages and the the assumption that the vehicle 1 is travelling straight, number of gaps between adjacent teeth during a prede- the detector rotation angle calculation unit 28 waits for a termined count period. In the example of Fig. 37, when singlerotation of the tire2 and receives for anon-received 50 the count number is 12 from when the previous pulse ID code assumed to be transmitted one rotation after. number signal Dpk is transmitted to when the predeter- Here, notification signals Spk having tire ID codes ID1 mined count period Ts ends, each axle rotation amount and ID2 are received at the initial first determination tim- sensor 19 transmits the count number of 12 as the ing t1 and tire ID codes ID3 and ID4 are received at timing present total pulse number signal Dpl. The total pulse t1’ that is one tire rotation after. The detector rotation55 number signal Dpl is sent to the tire pressure monitoring angle calculation unit 28 combines the notification signal ECU 13 through, for example, a controller area network Spk that includes the tire ID codes ID1 and ID2 received (CAN). at the first determination timing t1 and the notification [0154] A tire ID that is peak-transmitted from the tire

19 37 EP 2 749 437 A1 38 pressure detector 4 may be received from when the total amount sensor 19b is 11 ms, the duration time length of pulse number signal Dpl is acquired to when the next a singlepulse ofthe rightrear axle rotation amount sensor total pulse signal Dpl is acquired. When the axle rotation 19c is 12 ms, and the duration time length of a single amount sensor 19 outputs the total pulse number signal pulse of the left rear axle rotation amount sensor 19d is Dpl in the predetermined output intervals Ts, the pulse 5 9 ms. In this case, an average duration time length of number cannot be known when a tire ID code is truly 10.5 ms may be measured as the duration time length received. For example, when the pulse number acquired of a single pulse. This increases the calculation accuracy at a certain timing is "50," even though a tire ID code is of the detector angle θk. received, for example, at pulse number "55," the next [0160] When the axle rotation amount sensor 19 out- total pulse number signal may be acquired at the timing 10 puts the total pulse number measured during a predeter- when the pulse number is "50+12=72," and the pulse mined time as the total pulse number signal Dpl, the cal- number cannot be accurately acquired during tire ID code culation illustrated in Fig. 39 may be applied. For exam- reception. ple, when right front is "12 pulses," left front is "12 pulses," [0155] Thus, the tire pressure monitoring ECU 13 in- right rear is "11 pulses," and left rear is "12 pulses," the cludes a pulse number calculation unit 40 that calculates 15 average value of "11.75 pulses" may be calculated as the true pulse number when receiving a tire ID code from the pulse number of the representative wheel 26. That the ratio of the timing at which the tire ID code is received is, even when the rotation speed slightly differs between during an output interval Ts when waiting for the next the four wheels, the representative wheel 26 may be as- total pulse number signal Dpl. When a tire ID code is sumed as having been rotated by the average value of received during the period of time of the output interval 20 11.75 pulses. The average value may be rounded off. Ts, the pulse number calculation unit 40 checks when For example, in this case, the average value may be the tire ID code was received during that period of time rounded off to "12 pulses." to obtain the ratio of the reception timing of the tire ID [0161] The tire ID codes are received as the pulses of code, and the ratio is used to calculate the true pulse the representative wheel 26 vary from 0 to 95. In one number of the received tire ID code. 25 example, the pulse number of the representative wheel [0156] In one example, after "12 pulses" is input from 26 when receiving the tire ID code ID4 is "83." In this the total pulse number signal Dpl, a notification signal case, if the pulse number of the representative wheel 26 Spk having tire ID1 is received before the next total pulse when the total pulse number signal Dpl that is received number signal Dpl is input. If the tire ID code ID1 is re- is, for example, "79,"when the next total pulse number ceived when 10 ms elapses after the preceding total30 signal Dpl is obtained, pulse number "12" is added and pulse number signal Dpl is input, the pulse number cal- recognized as "91," and the true pulse number of "83" culation unit 40 performs the calculation of 12 pulses 3 that is the true pulse number of the representative wheel 10 ms / 30 ms = 4 pulses. The pulse number calculation 26 when the tire code ID4 is received cannot be acquired. unit 40 adds "4" to "12" obtained from the preceding total [0162] Thus, like the eleventh embodiment, when the pulse number signal Dpl to calculate the pulse number 35 tire ID code ID4 is received during the period from when of "12+4=16" at the timing when the tire ID code ID1 is a total pulse number signal Dpl is acquired to when the received. The same calculation is performed for the other next total pulse signal Dpl is acquired, the true pulse tire ID codes ID2 to ID4. number of the representative wheel 26 when the tire ID [0157] The eleventh embodiment has the following ad- code ID4 is received may be calculated by obtaining the vantage in addition to advantages (1) to (27) of the first 40 ratio of the wait time when the tire ID is received. When, to tenth embodiments. for example, 10 ms has elapsed from when the preceding total pulse number signal Dpl has been received, 12 puls- (28) Even when the axle rotation amount sensor 19 es 3 10 ms / 30 ms = 4 pulses is calculated. Then, by outputsin fixed intervalsthe total ofthe pulse number adding "4" to "79," which is the preceding total pulse measured during the predetermined time as the total 45 number signal Dpl, the pulse number at the timing at pulse number signal Dpl, the tire position may be which tire ID code ID1 of the representative wheel is re- accurately determined. ceived is calculated as "12+4=16." [0163] In addition to advantages (1) to (28) of the first [0158] A twelfth embodiment will now be described fo- to eleventh embodiments, the twelfth embodiment has cusing on differences from the above embodiments. 50 the following advantage. [0159] Referring to Fig. 38, for example, the average time until when the pulse number for each of the four (29) The pulse number of the representative wheel wheels increases may be obtained, and the total of the 26 may be accurately calculated. This is advanta- pulse numbers of the four wheels may be used as pulses geous for improving the tire position determination for the representative wheel 26. For example, the dura- 55 accuracy. tion time length of a single pulse of the right front axle rotation amount sensor 19a is 10 ms, the duration time [0164] It should be apparent to those skilled in the art length of a single pulse of the left front axle rotation that the present invention may be embodied in many oth-

20 39 EP 2 749 437 A1 40 er specific forms without departing from the spirit or scope direction component. of the invention. Particularly, it should be understood that [0169] In each of the above embodiments, the detector the present invention may be embodied in the following rotation angle θa may be calculated from the sum or dif- forms. ference of θk1 and θk2. [0165] In the above embodiments, referring to Fig. 40, 5 [0170] In the above embodiments, the contents of each execution of the tire position determination of the present operation mode may be changed. example may be suspended when the steering wheel is [0171] In the above embodiments, the automatic loca- greater than or equal to a predetermined angle. In this tion preparation mode may be omitted. case, the tire pressure monitoring ECU 13 includes a [0172] In the above embodiments, the centripetal com- steering angle acquisition unit 41, which acquires steer- 10 ponent of gravity detection unit is not limited to the ac- ing angle information of the steering wheel, and a prohi- celeration sensor 10 and may be any sensor as long as bition unit 42, which prohibits execution of the tire position the centripetal component of gravity applied to the tire determination by the automatic locator 20. Thus, when pressure detector 4 may be detected. the steering wheel is rotated by a certain amount or great- [0173] In the above embodiments, the axle rotation er, that is, when the rotation amount difference between 15 amount sensor 19 is not limited to the ABS sensor as an inner wheel and an outer wheel is large, the tire po- long as the rotation amount of the axle 18 may be de- sition determination is not performed. Under a situation tected. when assumed that a large error will be produced in the [0174] In the above embodiments, the radio wave sig- calculated angle, the tire position determination is not nals transmitted in constant intervals from the tire pres- performed. The threshold for steering wheel determina- 20 sure detector 4 may have the same frame contents or tion is set so that, for example, the rotation amount dif- different frame contents in each mode. ference between an inner wheel and an outer wheel is a [0175] In the above embodiments, execution of the au- value that may be tolerated as an error by the entire tire tomatic location is not limited to when the vehicle 1 stops. position determination system 17 (e.g., several degrees The automatic location may be performed, for example, to several tens of degrees). 25 when the vehicle 1 starts to travel. In this case, reversed [0166] In the above embodiments, the transmission of rotation of the tire 2 that may occur when the vehicle the notification signal Skp includes a case when a noti- stops does not have to be taken into consideration. Thus, fication is issued after a certain delay time elapses from the tire position determination accuracy is high. when a characteristic point is detected in, for example, [0176] In the above embodiments, the automatic loca- the centripetal component of gravity. That is, the notifi- 30 tion (e.g., calculation of the detector angleθ k) may be cation signal Spk does not have to be issued the moment determined in any manner as long as the centripetal com- a characteristic point is generated and may be generated ponent of gravity is used. after the tire is rotated by a certain angle from when a [0177] In the above embodiments, the radio wave sig- peak is detected. nal transmitted from the tire pressure detector 4 when [0167] In each of the above embodiments, the execu- 35 determining a tire position may be, for example, a tire tion of the tire position determination is not limited to low pressure signal Stp as long as it includes at least the tire speeds and may be executed when the speed is high, ID code. for example, when the influence of centrifugal force is [0178] In the above embodiments, it is preferable that corrected to calculate the peak value and the moment a the certain directional component of gravity that varies peak is obtained may be transmitted through wireless 40 be the characteristic point of the centripetal component communication without any interference. For example, of gravity. Instead, the certain directional component of the rotation speed is obtained from the pulse signal Spl gravity may be variations in the physical amount related of the axle rotation amount sensor 19. This allows for with the certain directional component of gravity that var- calculation of the centrifugal force applied to the tire 2. ies in accordance with the tire rotation. Thus, the centrifugal force may be estimated through a 45 [0179] In the above embodiments, for example, when calculation and the corrected value may be reflected to the output of the acceleration sensor 10 (centripetal com- the peak. This allows for the centrifugal force component ponent of gravity Gr) takes a positive absolute value re- to be cancelled from the peak. To prevent interference gardless of the centrifugal force, the tire position may be of the radio wave signal, for example, the frequency of determined as described below. For example, when the each radio wave signal of the four wheels may 50 be tire pressure detector 4 transmits a notification signal Spk switched, and frames may be shortened as long as the and the vehicle 1 subsequently stops (or is slow enough ID codes may be determined (exclude pressure data and to be considered as having been stopped), the tire pres- temperature data). sure detector 4 transmits the centripetal component of [0168] In each of the above embodiments, the accel- gravity Gr to the receiver 12. In this case, as long as there eration sensor 10 may be a single axis sensor that detects 55 is a steering angle, there should be a difference in the only the centripetal component of gravity Gr in the direc- values of the pulse numbers of the axles 18 from when tion toward the axle or a dual axis sensor that detects a notification signal Spk is received to when the vehicle the centripetal component of gravity Gr and a rotation stops. Since the values may be associated with the

21 41 EP 2 749 437 A1 42 wheels, the axle rotation angle θb calculated from the the angle difference whenever a new radio wave signal axle rotation amount of each of the axle rotation amount is received and calculates the detector angle of each tire sensors 19a to 19d may be compared with the detector pressure detector based on the angle difference. The rotation angle θa calculated from the centripetal compo- angle calculation is performed at the first determination nent of gravity Gr to determine the tire position. 5 timing and the second determination timing. [0180] In the sixth embodiment, the time origin point [0187] In the tire position determination system of T0 is not limited to the time when the centripetal compo- some embodiments, the detector angle calculation unit nent of gravity Gr first becomes greater than or equal to calculates an average value of the axle rotation amounts threshold Gth1 and may be, for example, a time when indicated by the detection signals output from the axle the cycle is further shortened. In other words, the time 10 rotation amount sensors. Then, the detector angle cal- origin point T0 may be set anywhere. culation unit uses the average value to calculate the axle [0181] In the sixth embodiment, the sampling cycle of rotation amount. the centripetal component of gravity Gr may be set to a [0188] The present examples and embodiments are to length determined by the absolute value of the acceler- be considered as illustrative and not restrictive, and the ation sensor and a certain coefficient (e.g., inverse pro- 15 invention is not to be limited to the details given herein, portion coefficient). but may be modified within the scope and equivalence [0182] In the sixth embodiment, if the period from the of the appended claims. time origin point T0 to when the automatic location is [0189] Each tire pressure detector (4) detects a char- completed ends (after 20 minutes elapses from the time acteristic point in a detection signal of an acceleration origin point T0 or after 40 transmissions), each tire pres- 20 sensor (10) indicating that the tire pressure detector (4) sure detector 4 receives a radio wave signal at an accu- is located at a certain rotation position. When detecting rate timing when the characteristic point is detected once the characteristic point, the tire pressure detector (4) for the first time. Otherwise, each tire pressure detector transmits a notification signal (Spk) including the detector 4 may perform a transmission at a different timing. ID. Whenever a receiver (12) receives a notification sig- [0183] In the sixth embodiment, the measured rotation 25 nal (Spk), the receiver (12) acquires an axle rotation cycle is not limited to Ta that sets a single tire rotation as amount (C) of a representative wheel (26) and stores the a single cycle and may be, for example, Ta/2 of one half axle rotation amount (C) in a memory in association with of a rotation. the detector ID in the notification signal (Spk). After ac- [0184] In the tire position determination system of quiring axle rotation amounts (C1-C4) associated with some embodiments, the timing for calculating the detec- 30 the detector IDs of all of the tire pressure detectors (4), tor angle is the moment the receiver receives the radio the receiver (12) determines mounting positions of tires wave signal from every one of the tire pressure detectors. (2) from the angle each tire pressure detector rotated and [0185] In the tire position determination system of the angle each axle (18) rotated between a first determi- some embodiments, whenever receiving the radio wave nation timing (t1) and a second determination timing (t1). signal, the detector angle calculation unit stores the axle 35 rotation amount of the representative wheel associated with the detector ID included in the radio wave signal. Claims After storing the axle rotation amount associated with an detector ID included in the radio wave signal, the axle 1. A tire position determination system (17) comprising: rotation amount of the representative wheel at the first 40 determination timing and the stored axle rotation amount tire pressure detectors (4) respectively attached are used to obtain the detector angle of each tire pressure to tires (2); and detector, and the axle rotation amount of the represent- a receiver (12) coupled to a vehicle body (5), ative wheel at the second determination timing and the wherein thereceiver (12) is configured toreceive stored axle rotation amount are used to obtain the de- 45 a tire pressure signal (Stp) from each tire pres- tector angle of each tire pressure detector. sure detector (4) and monitor the pressure of [0186] In the tire position determination system of the corresponding tire based on the tire pressure some embodiments, after receiving a first radio wave sig- signal (Stp); nal from the first tire pressure detector, when the detector wherein each tire pressure detector (4) includes angle calculation unit receives a second radio wave sig- 50 nal from the second tire pressure detector, the detector a unique detector ID, angle calculation unit calculates the angle difference be- a gravity component detection unit (10) that tween the first tire pressure detector and the second tire detects a certain directional component of pressure detector based on variations in the axle rotation gravity and generates a detection signal, amount of the representative wheel measured during a 55 and period from when the first radio wave signal is received a transmission control unit (23, 24) that to when the second radio wave signal is received. The transmits a radio wave signal (Spk) includ- detector angle calculation unit repeats the calculation of ing the detector ID based on the detection

22 43 EP 2 749 437 A1 44

signal of the gravity component detection mination timing (t1), unit (10); and calculate a second detector angle θ(k2) using the axle rotation amount acquired at the second the receiver (12) includes determination timing (t2), 5 calculate a detector rotation angle ( θa) from the an interface that communicates with axle ro- first and second detector angles (θk1, θk2), tation amount sensors (19), wherein each calculate an axle rotation angle θ(b) from the axle rotation amount sensor (19) detects an axle rotation amount at the first determination axle rotation amount of a corresponding ax- timing and the axle rotation amount at the sec- le (18), 10 ond determination timing, and a tire mounting position determination compare the detector rotation angle ( θa) and the processing unit (27, 28, 29, 30) that ac- axle rotation angle ( θb) to determine the mount- quires the detector ID whenever receiving ing positions of the tires. the radio wave signal (Spk) from each tire pressure detector (4) and the axle rotation 15 6. The tire position determination system according to amount detected by each axle rotation claim 5, wherein the tire mounting position determi- amount sensor (19), associates the detec- nation processing unit is configured to tor IDs with the axle rotation amounts, and acquire an axle rotation amount (Cref) of a repre- determines mounting positions of the tires sentative wheel (26) from the rotation axle amount based on the axle rotation amounts associ- 20 sensor when receiving the radio wave signal (Spk) ated with the detector IDs of the tire pres- from the tire pressure detector (4), sure detectors (4). calculate the first and second detector angles (θk1, θk2) using the axle rotation amount (Cref) of the rep- 2. The tire position determination system according to resentative wheel (26), and claim 1, wherein the detection signal of the gravity 25 determine the mounting positions of the tires using component detection unit (10) is indicative of a char- the calculated detector angles (θk1, θk2). acteristic point when the tire pressure detector (4) is located at an uppermost position or lowermost posi- 7. The tire position determination system according to tion of the corresponding tire. claim 5 or 6, wherein 30 the tire mounting position determination processing 3. The tire position determination system according to unit is configured so that when receiving a first radio claim 1 or 2, wherein the transmission control unit is wave signal (Spk) having a first detector ID and then configured so that after a certain time (Tu) elapses a second radio wave signal (Spk) having a second from when the radio wave signal (Spk) is transmitted detector ID, the tire mounting position determination during which it may be assumed that a rotation35 processing unit calculates and stores an angle of a amount difference has been produced between an tire pressure detector (4) having one of the first and inner wheel and an outer wheel, the transmission second detector IDs relative to a tire pressure de- control unit transmits the next radio wave signal tector (4) having the other one of the first and second (Spk). detector IDs, and 40 the tire mounting position determination processing 4. The tire position determination system according to unit is configured to determine the mounting posi- claim 2, wherein the transmission control unit is con- tions of the tire using the stored detector angles re- figured to transmit the radio wave signal (Spk) when spectively corresponding to the tire pressure detec- detecting a characteristic point in the detection signal tors (4). of the gravity component detection unit (10). 45 8. The tire position determination system according to 5. The tire position determination system according to any one of claims 5 to 7, wherein claim 1, wherein the transmission control unit is configured to transmit the transmission control unit is configured to transmit the radio wave signal (Spk) at least once at each of the radio wave signal (Spk) at each of a first deter- 50 the first determination timing and the second deter- mination timing (t1) and a second determination tim- mination timing, and ing (t2), which is delayed from the first determination the tire mounting position determination processing timing by an interval (Tu); unit is configured to compare the detector rotation the tire mounting position determination processing angle (θa) and the axle rotation angle (θb) at least unit is configured to 55 once in a determination routine.

calculate a first detector angle (θk1) using the 9. The tire position determination system according to axle rotation amount acquired at the first deter- any one of the preceding claims, wherein

23 45 EP 2 749 437 A1 46

each tire pressure detector (4) includes a travel sta- located at a specific rotation position in a predeter- tus determination unit that determines a travel status mined cycle regardless of a rotation speed of the tire of a vehicle based on a detection signal of the gravity or when a vehicle is travelling at the same vehicle component detection unit (10), and velocity. the travel status determination unit is configured to 5 transmit the radio wave signal (Spk) when determin- 13. The tire position determination system according to ing that a vehicle velocity is within a predetermined any one of the preceding claims, wherein velocity range. the transmission control unit is configured to calcu- late a cycle during which a tire rotates once based 10. The tire position determination system according to 10 on variations in the detection signal of the gravity any one of the preceding claims, wherein the trans- component detection unit (10), and missioncontrol unit isconfigured to transmit theradio the certain directional component is sampled in a wave signal (Spk) if a length of time from when the cycle that is determined based on a proportional con- detection signal of the gravity component detection stant and the calculated cycle during which the tire unit (10) indicates that the tire pressure detector (4) 15 rotates once, and the sampling cycle is less than is located at a certain position to the next time when one-half of the cycle during which the tire rotates the detection signal of the gravity component detec- once. tion unit (10) indicates that the tire pressure detector (4) is located at the certain position is longer than or 14. The tire position determination system according to equal to a predetermined time. 20 any one of the preceding claims, wherein the certain directional component cyclically varies 11. The tire position determination system according to as the corresponding tire rotates; any one of the preceding claims, wherein the transmission control unit includes a determina- each tire pressure detector (4) includes tion range and a rotation cycle range, wherein the 25 determination range has a width that takes into con- a travel status determination unit that deter- sideration a detection accuracy of the gravity com- mines a travel status of a vehicle based on a ponent detection unit (10); detection signal of the gravity component detec- when the certain directional component exceeds the tion unit (10), and determination range, the transmission control unit an operation mode switching unit that switches 30 starts measuring time of a cycle of the certain direc- an operation mode of the tire pressure detector tional component to measure a cycle of a rotation of (4) based on a vehicle velocity, a first threshold, the tire; and and a second threshold that is smaller than the the transmission control unit is configured to transmit first threshold, wherein the vehicle velocity is in- the radio wave signal (Spk) when the measured cy- cluded in a determination result of the travel sta- 35 cle of a rotation of the tire is in the rotation cycle tus determination unit; range.

the operation mode switching unit 15. The tire position determination system according to claim 14, wherein switches the tire pressure detector (4) to a pres- 40 the determination range of the certain directional sure determination mode for monitoring tire component is one of a plurality of different determi- pressure when the vehicle velocity is higher than nation ranges, and or equal to the first threshold, the transmission control unit switches the sampling switches the tire pressure detector (4) to an au- cycle in accordance with the rotation cycle of the tire tomatic location preparation mode to increase 45 determined based on a selected one of the determi- the frequency for determining the vehicle veloc- nation ranges. ity when the vehicle velocity is between the first threshold and the second threshold, and 16. The tire position determination system according to switches the tire pressure detector (4) to an au- any one of the preceding claims, wherein tomatic location mode when the vehicle velocity 50 the certain directional component cyclically varies is less than the second threshold. as the corresponding tire rotates; the transmission control unit includes a threshold set 12. The tire position determination system according to taking into consideration that the gravity component any one of the preceding claims, wherein the trans- detection unit (10) has a rough detection accuracy; missioncontrol unit isconfigured to transmit theradio 55 when the certain directional component exceeds the wave signal (Spk) in fixed intervals when the detec- threshold, the transmission control unit shortens the tion signal of the gravity component detection unit sampling cycle and starts measuring a cycle of a (10) indicates that the tire pressure detector (4) is single rotation of the tire; and

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the transmission control unit is configured to set an to at least one detector ID cannot be determined and origin point of time measurement at a timing at which a vehicle is assumed to be travelling straight, the tire a cycle of a rotation of the tire becomes the threshold. mounting position determination processing unit waits until the tire corresponding to the at least one 17. The tire position determination system according to 5 detector ID rotates once; and any one of the preceding claims, wherein the tire the tire mounting position determination processing mounting position processing unit is configured to unit is configured to determine the mounting position determine the tire mounting positions by checking of the tire corresponding to the at least one detector whether an axle rotation amount of a single tire ro- ID with a radio wave signal (Spk) transmitted when tation conforms to an axle rotation amount measured 10 a time used by the tire to rotate once from the first from when the radio wave signal (Spk) is received determination timing elapses. at a first determination timing to when the radio wave signal (Spk) is received at a second determination 22. The tire position determination system according to timing. any one of the preceding claims, wherein 15 the axle rotation amount sensor (19) outputs a total 18. The tire position determination system according to pulse number signal (Dpl) that indicates a total pulse claim 9, wherein number counted during a predetermined interval; the tire mounting position determination processing when the tire mounting position determination unit stores a reception interval time used to receive processing unit receives a detector ID during a pe- two consecutive radio wave signals (Spk) including 20 riod from when a previous total pulse number signal the same detector ID in association with the detector (Dpl) is received to when a present total pulse ID; number signal (Dpl) is received, the tire mounting the tire mounting position determination processing position determination processing unit is configured unit stores, for each of a plurality of axles (18), an to calculate a true pulse number at a point of time axle time used until a count value of an axle rotation 25 when the detector ID is received from a ratio of a amount conforms to an axle rotation amount corre- length of time from when the previous total pulse sponding to a single tire rotation; and number signal (Dpl) is received to when the detector the tire mounting position determination processing ID is received and a length of time from when the unit is configured to determine the tire mounting po- detector ID is received to when the present total sitions by comparing a plurality of reception interval 30 pulse number signal (Dpl) is received. times respectively corresponding to a plurality of de- tector IDs with the axle times respectively corre- 23. The tire position determination system according to sponding to the axles (18). claim 22, wherein the tire mounting position deter- mination unit is configured to calculate an average 19. The tire position determination system according to 35 value from a total pulse number indicated by a plu- any one of claims 5 to 8, rality of total pulse number signals output from a plu- wherein the tire mounting position determination rality of axle rotation amount sensors (19) and use processing unit is configured to determine the tire the average value as an axle rotation amount of a mounting positions by comparing a plurality of de- representative wheel (26) to calculate a detector an- tector rotation angles (θa) respectively correspond- 40 gle. ing to the tires with a plurality of axle rotation angles (θb) respectively corresponding to a plurality of axles 24. The tire position determination system according to (18). any one of the preceding claims, further comprising:

20. The tire position determination system according to 45 a steering angle acquisition unit (41) that ac- any one of claims 5 to 8, quires a steering angle of a steering wheel of a wherein when a detector ID included in at least one vehicle; and radio wave signal (Spk) received at the first determi- a prohibition unit (42) that prohibits execution of nation timing is the same as a detector ID included the tire position determination when the steering in at least one radio wave signal (Spk) received at 50 angle is greater than or equal to a threshold. the second determination timing, the tire mounting position determination processing unit is able to de- termine the mounting position of the tire correspond- ing to the detector ID. 55 21. The tire position determination system according to claim 20, wherein when the mounting position of a tire corresponding

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• JP 2012286236 A [0001] • JP 2006062516 A [0003] • JP 2013116984 A [0001] • JP 2012126341 A [0003] • JP 2013190709 A [0001]

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