US0082390.97B2

(12) United States Patent (10) Patent No.: US 8,239,097 B2 Yasui et al. (45) Date of Patent: Aug. 7, 2012

(54) STEERING CONTROL APPARATUS FORA 6,349,789 B1* 2/2002 Nakano et al...... 180,446 VEHICLE 6,360,153 B1* 3/2002 Shinmura et al...... TO1/48 6,597,975 B1* 7/2003 Shinmura et al...... TO1/48 (75) Inventors: Yoshiyuki Yasui, Nagoya (JP); Hiroyuki 6,856,871 B2 * 2/2005 Mould et al...... TO1/41 Kodama, Kariya (JP); Kenji Asano, (Continued) Toyota (JP); Toshihisa Kato, Handa (JP) FOREIGN PATENT DOCUMENTS (73) Assignee: Advics Co., Ltd., Kariya, Aichi Pref. DE 10235039 A1 2, 2004 (JP) (Continued) (*) Notice: Subject to any disclaimer, the term of this OTHER PUBLICATIONS patent is extended or adjusted under 35 German Office Action dated Apr. 15, 2010 issued in the correspond U.S.C. 154(b) by 170 days. ing German Patent Application No. 10 2007 000 319.8-21 and (21) Appl. No.: 12/174,281 English-language translation. (Continued) (22) Filed: Jul. 16, 2008 Primary Examiner — John Nguyen (65) Prior Publication Data Assistant Examiner — Brian J Broadhead US 2008/O281.491 A1 Nov. 13, 2008 (74) Attorney, Agent, or Firm — Buchanan Ingersoll & Rooney PC Related U.S. Application Data (62) Division of application No. 1 1/760,106, filed on Jun. 8, (57) ABSTRACT 2007, now Pat. No. 7,970,513. A steering control apparatus for a vehicle having a power Source for generating power, and drive shafts for transferring (30) Foreign Application Priority Data the power to driving wheels of the vehicle, and a traction control device for controlling braking torque applied to the Jun. 15, 2006 (JP) ...... 2006-1656.65 wheels. The apparatus comprises a detection device for Jun. 15, 2006 (JP) ...... 2006-165666 detecting the braking torque applied to the wheels, a calcula tion device for calculating a driving force difference between (51) Int. Cl. the wheels, on the basis of the detected braking torque, a B62D 6/00 (2006.01) power source state detection device for detecting an actuating (52) U.S. Cl...... 701/41; 180/443 state of the power Source, and a control device for controlling (58) Field of Classification Search ...... 701/41–44, steering torque created by the steering wheel, and applying 701/69; 180/443,446 torque steer reducing torque to the steering wheel. A desired See application file for complete search history. value of the torque steer reducing torque is determined, based on the driving force difference and the actuating state of the (56) References Cited power source. And, the torque steer reducing torque is applied to the steering wheel, according to the desired value of the U.S. PATENT DOCUMENTS torque steer reducing torque, to reduce the torque steer. 6,032,755 A * 3/2000 Blandino et al...... 180,446 6,154,696 A 11/2000 Nishi et al. 4 Claims, 17 Drawing Sheets

M1 M2

DESIRED VALUE OF Tes POWER STEERING ASSIST TORQUE

DRIVING DESRED WALUE OF FORCE TORQUE STEER REDUCING TORQUE MOTOR CONTROL

DIFFERENCE FIRST CHARACTERSTC

SECOND CHARACTERISTC STATEPOWER SOURCE T FORCEDRIVING - Fd IRANSMISSION Rt. STATE US 8,239,097 B2 Page 2

U.S. PATENT DOCUMENTS JP 2005-67455 A 3, 2005 2003. O158642 A1 8, 2003 Mould et al. wo WO SS A. $39. 2003/022 1898 A1* 12/2003 Yasui et al...... 180,446 2004/0167694 A1* 8, 2004 Tamai ...... TO1/41 OTHER PUBLICATIONS 2006, OO15226 A1 1/2006 Bernzen et al. English-language translation of Chinese Office Action dated Sep. 18, FOREIGN PATENT DOCUMENTS 2009 issued in the corresponding Chinese Patent Application No. EP 1331, 158 A1 T 2003 2007101107699. JP 5-77653 A 3, 1993 JP 11-129927. A 5, 1999 * cited by examiner

U.S. Patent Aug. 7, 2012 Sheet 2 of 17 US 8,239,097 B2

U.S. Patent Aug. 7, 2012 Sheet 3 of 17 US 8,239,097 B2 FG. 3

START

1 O1 INTIALIZATIONS

O2 NPUT: SENSOR COMMUNICATION SIGNALS

O3 PROCESS: SIGNALS

CALCULATE: DESIRED WALUE (Tps) 1 O4 OF POWER STEERING ASSIST TORQUE

CALCULATE: DESIRED WALUE (Tts) 1 O 5 OF TORQUE STEER REDUCING TORQUE

1 O6 CALCULATE MOTOR CURRENT

O7 MOTOR CONTROL

RETURN U.S. Patent Aug. 7, 2012 Sheet 4 of 17 US 8,239,097 B2 FG. 4

TORQUE STEER REDUCING TORQUE

2O2

2O3

2O4

205 CALCULATE: DRIVING FORCE DIFFERENCE (AFd)

2O6

TORQUE STEER REDUCING CONTRO

CONTROL: TERMINATED

21 O

DESIRED WALUE (Tts) OF TORQUE STEER CALUCULATE: DESIRED WALUE (Tts) REDUCING TORQUE - O OF TORQUE STEER REDUCING TORQUE

numeroom

RETURN U.S. Patent Aug. 7, 2012 Sheet 5 of 17 US 8,239,097 B2 F.G. 5

THROTTLE OPENING: LARGE

ENGINE OUTPUT TORQUE (Te)

THROTTLE OPENING: SMALL ENGINE SPEED (Ne)

F.G. 6

FIRST CHARACTERSTC

DES RED WALUE OF TORQUE STEER REDUCING TORQUE (Tts)

NEGATIVE POSITIVE SIGN(-) SGN (+) 1. DRWING FORCE < DIFFERENCE (AFd) SECOND CHARACTERISTIC U.S. Patent Aug. 7, 2012 Sheet 6 of 17 US 8,239,097 B2

FG. 7

DRIVING FORCE (Fd): LARGE

DESRED WALUE OF TORQUE STEER REDUCING TORQUE (Tts)

NEGATIVE SIGN(-) POSITIVE DRIVING FORCE (Fd): LARGE- DRIVING FORCE SGN (+) N-2 DFFERENCE (AFd)

1. M N DRIVING FORCE (Fd): SMALL

FIRST CHARACTERISTIC Ttsm ------

DES RED WALUE OF TORQUE STEER REDUCING TORQUE (Tts)

NEGATIVE POSITIVE SGN (-) SIGN (+) DRWING FORCE DIFFERENCE (AFd)

------Y - - a -a ------Ttsm2 SECOND CHARACTERISTIC U.S. Patent Aug. 7, 2012 Sheet 7 of 17 US 8,239,097 B2

FG. 9

GRADENT CONSTANT

Kits 1 KtS2

DRIVING FORCE (Fd)

U.S. Patent Aug. 7, 2012 Sheet 9 of 17 US 8,239,097 B2 F.G. 11

11 O NITALIZATIONS

1 1 O2 INPUT: SENSOR COMMUNICATION SIGNALS

1 1 O3 PROCESS: SGNALS

CALCULATE: DES RED WALUE (Tps) 1 1 O4 OF POWER STEERING ASSIST TORQUE

CALCULATE: FIRST DES RED WALUE (Tts) 11 O5 OF TORQUE STEER REDUCING TORQUE

CALCULATE: SECOND DESIRED WALUE (Tts2) 1 1 O6 OF TORQUE STEER REDUCING TORQUE

CALCULATE: DESIRED WALUE (Tts) 1 O7 OF TORQUE STEER REDUCING TORQUE

11 O8 CALCULATE: MOTOR CURRENT

1 1 O9 MOTOR CONTROL

RETURN U.S. Patent Aug. 7, 2012 Sheet 10 of 17 US 8,239,097 B2

F.G. 12

CALUCULATE FIRST DESRED WALUE OF TORQUE STEER REDUCING TORQUE

12O1 READ: DRWING FORCE DISTRIBUTION STATE

12O2 CALCULATE: DRIVING FORCE DIFFERENCE (AFd)

12O3

FIRST TORQUE STEER NO REDUCING CONTROL

CONTROL: TERMINATED

YES 12O6 - 1207

FIRST DESIRED WALUE (Tts 1) OF CALUCULATE: FIRST DESIRED WALUE (Tts 1) TORQUE STEER REDUCING TORQUE - O OF TORQUE STEER REDUCING TORQUE

RETURN U.S. Patent Aug. 7, 2012 Sheet 11 of 17 US 8,239,097 B2

F.G. 13

FIRST DES RED WALUE (Tts 1) OF TORQUE STEER REDUCING TORQUE

wom-m-ambor DRIVING FORCE DIFFERENCE(AFd)

U.S. Patent Aug. 7, 2012 Sheet 12 of 17 US 8,239,097 B2

F.G. 14

CALUCULATE: SECOND DESRED WALUE OF TORQUE STEER REDUCING TORQUE

3O 1 CALCULATE: POWER SOURCE OUTPUT (Te)

13 O2 CALCULATE: GEAR RATIO (Rt)

13O3 CALCULATE: DRIVING FORCE (Fd)

13O4 CALCULATE: DRIVING FORCE WARIATION (dFol)

1305

SECOND TORQUE STEER NO REDUCING CONTROL

CONTROL: TERMINATED

/ 13O8 13 O9 SECOND DES RED WALUE (Tts2) OF CALUCULATE: SECOND DESIRED WALUE (Tts2) TORQUE STEER REDUCING TORQUE - O OF TORQUE STEER REDUCING TORQUE

RETURN U.S. Patent Aug. 7, 2012 Sheet 13 of 17 US 8,239,097 B2

F.G. 15

SECOND DES RED WALUE (Tts2) OF TORQUE STEER REDUCING TORQE

DRIVING FORCE (Fd)

F.G. 16

MODIFIED WALUE (Ttsh) OF TORQUE STEER REDUCING TORQUE

DRIVING FORCE WARIATION (dFd) U.S. Patent Aug. 7, 2012 Sheet 14 of 17 US 8,239,097 B2

F.G. 17 In MODIFIED WALUE (Ttsh) OF TORQUE STEER REDUCING TORQUE O

TIME

F.G. 18

MODIFIED WALUE (Ttsh) OF TORQUE STEER REDUCING TORQUE Ttsm

-- Thld TIME U.S. Patent Aug. 7, 2012 Sheet 15 of 17 US 8,239,097 B2

Torv U.S. Patent Aug. 7, 2012 Sheet 16 of 17 US 8,239,097 B2

F. G. 20

WH2

KP2 U.S. Patent Aug. 7, 2012 Sheet 17 Of 17 US 8,239,097 B2

was or im pow we

1-HWHSBAIH0QN00BS||4__

+

US 8,239,097 B2 1. 2 STEERING CONTROL APPARATUS FOR A On the other hand, in Japanese Patent Laid-open Publica VEHICLE tion No. 2005-067455, there is disclosed a method for reduc ing the torque steer when a traction control is being per This application is a divisional of application Ser. No. formed. Especially, referring to FIG. 3, it is described that if 11/760,106 filed on Jun. 8, 2007, the entire content of which it is determined that the traction control is being performed, a is incorporated herein by reference. This application claims driving force difference (AFdr) between right and left rear priority under 35 U.S.C. S 119 to Application No. 2006 wheels served as driving wheels is estimated according to a 165665 filed in Japan on Jun. 15, 2006 and Application No. known manner in a technical field in issue, and it is deter 2006-165666 filed in Japan on Jun. 15, 2006, the entire con mined whether the absolute value of the driving force differ 10 ence (AFdr) is larger than a reference value (AEFdr0 of posi tent of both of which is herein incorporated by reference. tive constant), i.e., it is determined whether the torque steer at the time of driving mode will be excessive, or not. If the result BACKGROUND OF THE INVENTION is negative, the torque steer reducing torque (Tdts) at the time The present invention relates to a steering control appara of driving mode is set to be zero. Whereas, if the result is 15 affirmative, the torque steer reducing torque (Tdts) will be tus for a vehicle, and particularly relates to a steering control calculated by the product of Kdts and AFdr, where Kdts is a apparatus for reducing torque steer created on a steering positive constant coefficient. wheel of the vehicle. However, it is still difficult to sufficiently reduce the torque In general, in a steering apparatus for a vehicle with steered steer, according to compensation based on the relationship of wheels thereof being served as its driving wheels, such a the difference in torque between the right and left driving phenomenon that steering effort or steer-holding force shall axles against the engine torque, as described in Japanese vary in response to variation of driving force, is called as Patent Laid-open Publication No. 2005-170116. torque steer, which is desired to be restrained. For example, Hereinafter, the cause for creating the torque steer will be Japanese Patent Laid-open Publication No. 11-129927, analyzed. The torque steer is meant by a phenomenon, which corresponds to U.S. Pat. No. 6,154,696, discloses a 25 wherein according to a front engine front drive vehicle (So vehicle equipped with an electric power steering device and a called FF vehicle) or four-wheel drive vehicle with the steered torque split arrangement for individually controlling (or, dis wheels thereof being served as its driving wheels, the steering tributing) traction and/or braking force between right and left wheel is steered by the steered wheels, when the vehicle is wheels), to improve its maneuverability and stability. In the accelerated, i.e., the phenomenon with the steered wheels U.S. Pat. No. 6,154,696, there is disclosed a steering control 30 provided for steering the steering wheel. As for the cause for system for controlling torque steerina vehicle equipped with creating the torque steer, mainly raised are “bent angle of a an electric power steering device and a torque split arrange constant speed universal joint for drive shafts” and "differ ment for individually controlling traction and/or braking ence in driving force between right and left wheels, when a force of right and left wheels, which comprises a torque kingpin offset is provided.” difference input unit for receiving a torque difference signal 35 At the outset, will be explained “torque steer caused by corresponding to a difference in traction and/or braking force bent angle of a constant speed universal joint for drive shafts'. between the right and left wheels, a torque steer canceling as (1). With respect to the relationship between the drive steering torque determining unit for producing a torque steer shafts and wheels, Supposing that the bent angle 0 of the canceling steering torque signal that is required to cancel a constant speed universal joint for the drive shafts is provided, steering torque arising from the difference in traction and/or 40 as shown in FIG. 19, if the driving torque transferred by the braking force between the right and left wheels, and a drive drive shafts is indicated by “Tarv', secondary couple moment circuit for Supplying a drive current to the electric power (MZ) is created for steering the wheels, according to the steering device according to the torque steer canceling steer following equation (1): ing torque signal. Mz=Tary-tan(0/2) (1) Furthermore, according to Japanese Patent Laid-open Pub 45 lication No. 2005-170116, an apparatus is proposed to solve In FIG.20, according to the vehicle with the steered wheels such a problem in the prior art as described above that the thereof being served as its driving wheels, a part of it includ torque steer cancelling control is performed only when the ing its steering apparatus is disclosed to clarify the corre difference in force was caused between the right and left sponding relationship between its front view and plan view. wheels, i.e., difference in rotation was caused between the 50 That is, in FIG.20, according to the vehicle with an engine EG right and left wheels. That is, there is proposed a steering and a transmission TR arranged in a transverse direction to control apparatus, wherein, instead of the difference in rota the vehicle moving direction, to obtain a space efficiency in an tion between the right and left wheels, by watching a differ engine compartment, length and arrangement of the drive ence in transferring torque between right and left driving shafts (maybe called as drive axles) DS1 and DS2 are not axles, which might cause the torque steer, detecting or esti 55 provided symmetrically in the transverse direction. There mating engine torque to cancel the torque steer, and obtaining fore, in the case where the joint bent angles for the drive shafts an estimated value of torque steer by a memory circuit which connected to the driving wheels are different between the memorizes a relationship of the difference in transferring right and left wheels WH1 and WH2, a moment (MZ) for torque between the right and left driving axles against the steering the wheels, or called as a steered torque, will be engine torque, to cancel the torque steer created by the dif 60 caused to provide its difference between the right and left ference in transferring torque between the right and left driv wheels WH1 and WH2, to create the torque steer for steering ing axles. With respect to the vehicle with steered wheels the steering wheel SW by the steered wheels when the vehicle thereof being served as its driving wheels, according to Japa is accelerated. Thus, the torque steer caused by the bent angle nese Patent Laid-open Publication No. 5-77653, a driving of the constant speed universal joint for the drive shafts is force distribution device is proposed for distributing the driv 65 called as the steady-state torque steer. ing force to right and left wheels of a vehicle of four-wheel Next will be explained “torque steer caused by the differ drive system, or the like. ence in driving force between the right and left wheels, when US 8,239,097 B2 3 4 the kingpin offset is provided', as (2). As shown in FIG. 20. Among them, with respect to (1) and (2-a), the torque steer the steered wheels WH1 and WH2 are provided with kingpins relates to the one resulted from the layout and characteristics KP1 and KP2 to be capable of being steered, and the position of the drive shafts, which will be called hereinafter as “torque of the steered center TC, i.e., intersection of the kingpin axis steer resulted from drive shafts'. Since this torque steer has and road Surface, does not correspond to the position of force been fixed as a characteristic of the vehicle, it will be created applied point DP of the driving force, so that there exists a only one direction limited with respect to a steering direction distance between those two points, i.e., kingpin offset (KPo), of the steering wheel. On the other hand, with respect to (2-b), whereas (KPc) in FIG. 20 designates a wheel center kingpin in order to reduce the torque steer created at the time when a offset. In the case where there exists the kingpin offset (KPo), traction control is performed, which will be called hereinafter when the vehicle is accelerated to apply the driving force to 10 the steered wheels WH1 and WH2, the torque for steering the as “torque steer resulted from traction control', in the case steered wheel, i.e., steered torque, is created, which can be where the torque steer reducing torque (Tdts) is calculated by obtained by driving force xkingpin offset. If the driving the product of the positive constant coefficient (Kdts) and the force is equal to each other between the right and left wheels driving force difference (AFdr), if the absolute values of the WH1 and WH2, the steered torque will be cancelled, so that 15 driving force differences are caused, the torque steer reducing no torque steer will be caused. If the driving force is different torque with the same absolute value will be determined to be from each other between the right and left wheels WH1 and applied, both in right and left steering directions. And, with WH2, however, “torque steer for steering the steering wheel respect to (2-c), the torque steer relates to the one resulted by means of the steered wheel (right and left wheels) will be from the driving force distribution device, which will be caused. called hereinafter as “torque steer resulted from driving force As for the case where the driving force is different from distribution'. each other between the right and left wheels as described in As described in the aforementioned (1) and (2-a), the (2), the following three cases may be considered: torque steer resulted from drive shafts will be created only (2-a) “Driving Force Difference Between Right and Left one direction limited with respect to the steering direction of Wheels Due to Characteristics of Drive Shafts’ 25 the steering wheel. However, when the traction control is In the case where there exists a difference in characteristic performed, the vehicle is being accelerated. Therefore, if the between the drive shafts DS1 and DS2, a transient (dynamic) steering direction for causing the torque steer resulted from difference will be caused in transferring the torque. Even in traction control and the steering direction for causing the the case where the drive shafts DS1 and DS2 are made of the torque steer resulted from drive shafts are the same, the torque same material, and formed with the same cross sectional area, 30 steer will be amplified with each other, thereby to be if their lengths are different from each other, torsional rigidity increased. On the contrary, if the steering direction for caus of them shall be different from each other. Therefore, when ing the torque steer resulted from traction control and the the vehicle is accelerated rapidly, the driving force applied to steering direction for causing the torque steer resulted from the wheel connected with the drive shaft, which is relatively drive shafts are opposite to each other, the torque steer will be short to provide relatively high torsional rigidity, will be 35 cancelled with each other, thereby to be decreased. As a increased rapidly with a slight delay. On the contrary, the result, if the torque steer reducing control is performed on the driving force applied to the wheel connected with the drive basis of the same characteristic both in the right and left shaft, which is relatively long to provide relatively low tor steering directions, a different feeling might be given to the sional rigidity, will be increased gradually. Therefore, the vehicle driver. difference in transient driving force will be caused between 40 In the case where the aforementioned torque steer resulted the right and left wheels, thereby to create the torque steer, from driving force distribution or torque steer resulted from which is called as the transient torque steer. traction control is being created, the vehicle is being acceler (2-b) “Driving Force Difference Between Right and Left ated, so that the torque steer resulted from drive shafts is Wheels Due to a Traction Control created at the same time. Therefore, if the steering direction If braking torque is applied to one wheel according to a 45 for causing the torque steer resulted from drive shafts is the traction control, the driving force applied to the other one same as the steering direction for causing the torque steer wheel corresponding to the braking torque will be increased. resulted from driving force distribution, or the steering direc Particularly, in the case where the traction control is per tion for causing the torque steer resulted from traction con formed on a so-called u-split road with different coefficients trol, the torquesteer will be amplified with each other, thereby of friction provided between the right and left wheels, the 50 to be increased. On the contrary, if the steering direction for driving force difference between the right and left wheels will causing the torque steer resulted from drive shafts is opposite be caused largely. to the steering direction for causing the torque steer resulted (2-c) “Driving Force Difference Between Right and Left from driving force distribution, or the steering direction for Wheels Due to a Driving Force Distribution Device' causing the torque steer resulted from traction control, the In the case where a driving force distribution device is 55 torque steer will be cancelled with each other, thereby to be provided between the right and left wheels, the difference in decreased. Therefore, in order to perform the torque steer driving force between the right and left wheels will be caused. reducing control without giving the different feeling to the As for the driving force distribution device, there are known vehicle driver, it is important to compensate the mutual influ the one controlled electronically, and the one for limiting their ence among the torque steers resulted from the causes as differential mechanically, e.g., viscous coupling or the like, as 60 described above. disclosed in the aforementioned Japanese Patent Laid-open Publication No. 5-77653, for example. SUMMARY OF THE INVENTION The aforementioned (1) and (2) relate to the causes of the torque steer created at the time when the vehicle is acceler Accordingly, it is an object of the present invention to ated, each part for creating the torque steer will be indicated 65 provide a steering control apparatus for reducing torque steer, in FIG. 21, wherein the torque steer will be caused at each part which will be caused when a traction control is performed, of a vehicle by the aforementioned (1), (2-a), (2-b) and (2-c). without giving a different feeling to a vehicle driver. US 8,239,097 B2 5 6 And, it is another object of the present invention to com second characteristic, when the sign of the driving force dif pensate an influence by the torque steer resulted from drive ference is negative, and the second characteristic may be shafts, in the case where the torque steer resulted from driving provided according to the driving force difference multiplied force distribution, or torque steer resulted from traction con by a second constant, which is provided to be decreased, with trol is caused, to provide the torque steer without giving the the driving force being increased. different feeling to the vehicle driver. Also, in accomplish the another object as described above, In accomplishing the above and other objects, the steering the steering control apparatus, which is provided for the control apparatus is provided for a vehicle having a steering vehicle having the steering wheel, power source, drive shafts, wheel for steering a pair of right and left steered wheels of the and traction control device as described above, comprises a vehicle, a power source for generating power, drive shafts for 10 transferring the power to the right and left steered wheels, to driving force distribution detection device for detecting a be served as right and left driving wheels of the vehicle, driving force distribution between the right and left steered respectively, and a traction control device for controlling wheels, a driving force difference calculation device for cal braking torque applied to the right and left steered wheels, culating a driving force difference between the right and left respectively. The apparatus comprises a braking torque detec 15 steered wheels, on the basis of the driving force distribution tion device for detecting the braking torque applied to the detected by the driving force distribution detection device, a right and left steered wheels, respectively, a driving force power source state detection device for detecting an actuating difference calculation device for calculating a driving force state of the power source, a driving force calculation device difference between the right and left steered wheels, on the for calculating the driving force, on the basis of the actuating basis of the braking torque applied to each of the right and left state of the power source detected by the power source state steered wheels detected by the braking torque detection detection device, a steering torque control device for control device, a power source state detection device for detecting an ling steering torque created by the steering wheel, and apply actuating state of the power source, a steering torque control ing torque steer reducing torque to the steering wheel, to device for controlling steering torque created by the steering reduce torque steer, first desired value determination device wheel, and applying torque steer reducing torque to the steer 25 for determining a first desired value of the torque steer reduc ing wheel, to reduce torque steer, and a desired value deter ing torque, on the basis of the driving force difference calcu mination device for determining a desired value of the torque lated by the driving force difference calculation device, a steer reducing torque, on the basis of the driving force differ second desired value determination device for determining a ence calculated by the driving force difference calculation second desired value of the torque steer reducing torque, on device, and the actuating state of the power source detected by 30 the power source state detection device. And, the steering the basis of the driving force calculated by the driving force torque control device is adapted to apply the torque steer calculation device, and a modifying device for modifying the reducing torque to the steering wheel, in accordance with the first desired value of the torque steer reducing torque deter desired value of the torque steer reducing torque determined mined by the first desired value determination device, in by the desired value determination device, to reduce the 35 accordance with the second desired value of the torque steer torque steer. reducing torque determined by the second desired value Preferably, the desired value determination device may determination device, to provide the desired value of the determine the desired value of the torque steer reducing torque steer reducing torque. torque in accordance with a first characteristic for determin Preferably, the steering torque control device determines to ing the desired value, when a sign of the driving force differ 40 start controlling the torque steer reducing torque, on the basis ence is positive, and determine the desired value of the torque of the driving force calculated by the driving force calculation steer reducing torque in accordance with a second character device. istic for determining the desired value, when the sign of the The steering control apparatus may further comprise a driving force difference is negative, which is different from modified value calculation device for calculating a modified the first characteristic. 45 value of the torque steer reducing torque, on the basis of the The steering control apparatus may further comprise a driving force calculated by the driving force calculation driving force calculation device for calculating the driving device. And, the modifying device is adapted to modify the force transferred to the driving wheels through the drive second desired value of the torque steer reducing torque shafts, and at least one of the first characteristic for determin determined by the second desired value determination device, ing the desired value and the second characteristic for deter 50 by adding the modified value of the torque steer reducing mining the desired value may be modified, on the basis of the torque to the second desired value of the torque steer reducing driving force calculated by the driving force calculation torque. device. The first characteristic for determining the desired value BRIEF DESCRIPTION OF THE DRAWINGS may be modified to be relatively large, when the driving force 55 calculated by the driving force calculation device is relatively The above stated object and following description will large, and the first characteristic for determining the desired become readily apparent with reference to the accompanying value may be modified to be relatively small, when the driving drawings, wherein like referenced numerals denote like ele force calculated by the driving force calculation device is ments, and in which: relatively small. The desired value of the torque steer reduc 60 FIG. 1 is a schematic block diagram of a steering control ing torque may be determined in accordance with the first apparatus according to an embodiment of the present inven characteristic, when the sign of the driving force difference is tion; positive, and the first characteristic may be provided accord FIG. 2 is a schematic block diagram of a vehicle having a ing to the driving force difference multiplied by a first con steering control apparatus according to an embodiment of the stant, which is provided to be increased, with the driving force 65 present invention; being increased. And, the desired value of the torque steer FIG. 3 is a flowchart of an example of steering control reducing torque may be determined in accordance with the according to an embodiment of the present invention; US 8,239,097 B2 7 8 FIG. 4 is a flowchart of an example for calculating a desired includes a steering torque control device, wherein steering value of torque steer reducing torque according to an embodi wheel torque (simply referred to as steering torque) (Ts) of ment of the present invention; the steering wheel SW is detected by a steering torque detec FIG. 5 is diagram showing an example of a map for pro tion device M1 as shown in FIG. 1, and on the basis of the viding torque steer reducing control starting conditions detected result, a desired value of torque served as an assist according to an embodiment of the present invention; torque for assisting the power steering control to reduce the FIG. 6 is a diagram showing an example of a map for steering force applied by the vehicle driver, is calculated by an providing a desired value of torque steer reducing torque, assist torque desired value determination device M2 for deter according to an embodiment of the present invention; mining the desired value of power steering assist torque, to FIG. 7 is a diagram showing another example of a map for 10 output a desired value (Tps) of the assist torque. providing a desired value of torque steer reducing torque, According to the present embodiment, the apparatus is according to an embodiment of the present invention; provided with a traction control device, which is adapted to FIG. 8 is a diagram showing a further example of a map for control braking torque applied to the right and left steered providing a desired value of torque steer reducing torque, wheels WHfr and WHfl, respectively, by means of a brake according to an embodiment of the present invention; 15 control device (BRK in FIG. 2). And, the braking torque FIG. 9 is a diagram showing an example of a map for applied to the wheels WHfrand WHfl is detected by a braking providing a gradient constant used in FIG. 8: torque detection device M3, respectively. As for the braking FIG. 10 is a schematic block diagram of a steering control torque detection device M3, may be employed hydraulic apparatus according to another embodiment of the present pressure sensors, as indicated by PSfr and PSfl in FIG. 2, invention; which are provided for detecting wheel cylinder pressure at FIG. 11 is a flowchart of an example of steering control each wheel. Or, even if the hydraulic pressure sensors are not according to another embodiment of the present invention; provided, the braking torque can be calculated by known FIG. 12 is a flowchart of an example of calculating a first methods on the basis of actuating State of the brake control desired value of torque steer reducing torque according to device. Furthermore, may be used a desired value of wheel another embodiment of the present invention; 25 cylinder pressure calculated for the traction control in an FIG. 13 is a diagram showing an example of a map for electronic brake control unit (indicated by ECU4 in FIG. 2), providing a first modified value of the torque steer reducing which will be described later. The brake control device is not torque according to another embodiment of the present inven limited to the one for applying the braking torque by the tion; hydraulic pressure as described above, but an electric brake FIG. 14 is a flowchart of an example of calculating a second 30 device (not shown) may be used. In the latter case, the object desired value of torque steer reducing torque according to to be detected by the braking torque detection device M3 will another embodiment of the present invention; be the output or input of an electric motor for actuating the FIG. 15 is a diagram showing an example of a map for electric brake device, so that a desired value for controlling providing a second desired value of the torque steer reducing the electric motor may be used. torque according to another embodiment of the present inven 35 In the case where the right and left driving wheels WHfr tion; and WHflare connected with each other through a differential FIG. 16 is a diagram showing an example of a map for gear, if the braking torque is applied to one wheel, driving providing a modified value of the torque steer reducing torque force corresponding to the braking torque will be applied to according to another embodiment of the present invention; the other one wheel. For example, if the braking torque (Btd) FIG. 17 is a diagram showing a pulse wave form indicative 40 is applied to the right driving wheel WHfr, the driving force of of a modified value of the torque steer reducing torque, the left driving wheel WHfr will be increased by the amount according to another embodiment of the present invention; of (Btc/r), where “r” is a radius of the wheel. On the basis of FIG. 18 is a diagram showing an example of a parameter this relationship, therefore, a driving force difference (AFd) for providing a pulse waveform indicative of a modified value can be calculated by a driving force difference calculation of the torque steer reducing torque, according to another 45 device M4. Then, on the basis of the driving force difference embodiment of the present invention; (AFd), a desired value (Tts) of the torque steer reducing FIG. 19 is a perspective view showing a relationship torque is determined by a desired value determination device between a drive shaft and a driving wheel, according to a MS. conventional vehicle: In the desired value determination device M5, there is FIG. 20 is a front and plan view of a part including a 50 provided a characteristic for determining the desired value of steering apparatus, according to a vehicle with steered wheels the torque steer reducing torque, which indicates the relation thereof being served as its driving wheels; and ship between the driving force difference (AFd) and the FIG. 21 is a block diagram showing parts which create desired value (Tts) of the torque steer reducing torque, so that torque steer, when a vehicle is accelerated. the desired value (Tts) is set, with reference to the character 55 istic. As for the characteristic for determining the desired DETAILED DESCRIPTION OF EMBODIMENTS value of the torque steer reducing torque, different character istics are set in accordance with the sign of the driving force Referring to FIG. 1, there is schematically illustrated a difference (AFd), in view of the aforementioned characteris steering control apparatus according to an embodiment of the tic resulted from the drive shafts, such as a first characteristic present invention, which is installed in a vehicle as shown in 60 for determining the desired value and a second characteristic FIG. 2, for example. That is, the apparatus is installed in the for determining the desired value, which will be described vehicle, which includes a steering wheel SW adapted to steer later in detail. For example, the sign of the driving force a pair of wheels WHfr and WHfl served as right and left difference (AFd) for creating the torque steer resulted from steered wheels, an engine EG served as a power source for the traction control in the same steered direction as the steered generating power, and drive shafts DSfr and DSfl adapted to 65 direction created by the torque steer resulted from the drive transfer the power to the wheels WHfr and WHfl, which are shafts is set to provide a characteristic with relatively large also served as right and left driving wheels. The apparatus value. On the contrary, the sign of the driving force difference US 8,239,097 B2 10 (AFd) for creating the torque steer resulted from the traction The steering control apparatus is installed in the vehicle as control in the opposite steered direction to the steered direc shown in FIG. 2, and the engine EG is installed transversely tion created by the torque steer resulted from the drive shafts in the engine compartment together with the transmission TR. is set to provide a characteristic with relatively small value. Within the transmission TR, a differential device DF is dis The desired value (Tts) of the torque steer reducing torque posed, to distribute the power generated by the engine EG to is added to the desired value (Tps) of the assist torque the wheels WHfr and WHfl, which are served as the steered obtained by the assist torque desired value determination wheels and driving wheels. In the vehicle, an electronic device M2, to output a new desired value, based on which the engine control unit ECU1 for controlling the engine EG, an electric motor MT is controlled by a motor control device M6. electronic steering control unit ECU2 for controlling the Consequently, the torque steer reducing control is performed 10 steering system, and an electronic transmission control unit ECU3 for controlling the transmission, and an electronic according to a map of torque steer characteristic, which is brake control unit ECU4 for controlling a brake system are different depending upon the right and left steering direc connected to one another through a communication bus, so tions, taking the torque steer resulted from the drive shafts that sensor signals and the information for each control unit into consideration, so that the torque steer resulted from the 15 can be provided commonly. The engine EG is provided with traction control will be reduced. Therefore, a reducing rate of a throttle valve TH for controlling an engine output. The the torque steer is made constant, with the braking torque opening of the throttle valve TH is adjusted by a throttle being given to the front and right wheels at the time of traction actuator TA, and its throttle opening (Tk) is detected by a control, so that the different feeling to the vehicle driver can throttle opening sensor TK. Also, an engine speed sensor EK be restrained. is provided for detecting an engine rotational speed (Ek). Furthermore, as indicated by broken lines in FIG. 1, it may And, the vehicle driver's requirement for acceleration is be so constituted that the driving force (Fd) is calculated on detected by an accelerator pedal sensor AP, as the amount of the basis of the results detected by a power source state operation (Ap) of an accelerator pedal (not shown). On the detection device M7 for detecting an actuating state of the basis of the detected results such as the amount of operation power source, and a transmission state detection device M8 25 (Ap) of the accelerator pedal, engine rotational speed (Ek) for detecting an actuating state of the transmission, to modify and throttle opening (Tk), therefore, the throttle actuator TA the map of the torque steer characteristic on the basis of the is controlled by the electronic engine control unit ECU1. driving force (Fd). In FIG. 1, an output (Te) indicative of the According to the present embodiment, the vehicle is provided actuating state of the power source is detected by the power with the gasoline engine EG as the power source, while source state detection device M7. As for the power source in 30 known power sources for generating the power may be the present invention, known devices for generating the driv employed, including an internal combustion engine Such as ing force for driving the wheels may be employed. For the diesel engine or the like, an electric motor used in an example, in addition to an internal combustion engine such as electric vehicle (abbreviated as “EV), and a combination of a gasoline engine (EG in FIG. 2), diesel engine or the like, them used in a hybrid vehicle (abbreviated as “HEV). may be employed an electric motor, and a combination of 35 As for the steering system, the steering torque applied to them used in a device (called as a hybrid system). Thus, the the steering wheel SW is controlled, on the basis of the result power source state detection device M7 is the device for detected by the steering torque sensor TS. In practice, the detecting information Such as a throttle opening, amount of electronic steering control unit ECU2 is so constituted that injected fuel, engine speed or the like according to the internal the electric motor MT is controlled in response to the steering combustion engine, and the device for detecting driving cur 40 torque (Ts) detected by the steering torque sensor TS. Also, it rent or Voltage according to the electric motor. Furthermore, may be so constituted that the electric motor MT is controlled, the detection device may be mounted directly on the output taking the vehicle speed (Vx) into consideration. This control axis of the power source. is a so-called power steering control, and may be called as an As for the transmission state detection device M8, a speed electric power steering control, because the electric motor reducing gear ratio (Rt) of the transmission TR as shown in 45 MT is used. Furthermore, when the vehicle is accelerated, for FIG. 2 is detected as the transmission state. And, in a driving example, created is the torque steer phenomenon, wherein the force calculation device M9, the driving force (Fd) transmit wheels WHfr and WHflare forced to steer the steering wheel ted by the drive shafts, also called as “driving torque', is SW. The torque steer reducing torque for reducing the torque calculated on the basis of the power source output (Te) or steer phenomenon is provided by the electric motor MT, as speed reducing gear ratio (Rt). Then, based on the driving 50 described later. The control for reducing the torque steer is force (Fd), the map of the torque steer characteristic is modi called as “torque steer reducing control”. In the transmission fied as follows. That is, if the driving force (Fd) is large, the TR, a gear position sensor GP is disposed for detecting the characteristic for determining the desired value is modified to gear ratio (Rt), which is output to the electronic transmission be relatively large in the steered direction for increasing the control unit ECU3. As for the transmission TR, known trans torque steer, whereas the characteristic is modified to be 55 missions such as a manual transmission, automatic transmis relatively small in the steered direction to be cancelled. On the sion, continuously variable transmission (CVT) or the like other hand, if the driving force (Fd) is small, the characteristic may be used. is modified to be relatively small in the steered direction for In the vehicle having a traction control function, the brake increasing the torque steer, whereas the characteristic is control device BRK is provided for controlling the brake modified to be relatively large in the steered direction to be 60 torque applied to each wheel, and the electronic brake control cancelled. Thus, since the torque steer resulted from the drive unit ECU4 for controlling the device is connected to the shafts is varied in accordance with the driving force transmit communication bus. To the electronic brake control unit ted by the drive shafts, as described above, if it is so consti ECU4, connected are wheel speed sensors WSXX, wherein tuted that the driving torque is calculated on the basis of the “XX' designates each wheel, i.e., “fr” designates the wheel at power source output or gear ratio, to modify the map of the 65 the front right side as viewed from the position of a driver's torque steer characteristic on the basis of the driving torque, seat, “fl” designates the wheel at the front left side, “rr more accurate torque steer reducing control can be achieved. designates the wheel at the rear right side, and “rl” designates US 8,239,097 B2 11 12 the wheel at the rear left side. On the basis of the detected indicates which wheel is larger in driving force between the wheel speeds, the vehicle speed (VX) is calculated. According right and left driving wheels. For example, provided that the to the electronic brake control unit ECU4, therefore, the sign of the driving force difference is set to be positive when wheel speed (VwXX) is being watched, and if the acceleration the driving force of the left driving wheel is larger than the slips of the wheels WHfr and WHfl served as the driving 5 driving force of the right driving wheel, the sign of the driving wheels have become large, the traction control will be per force difference is set to be negative when the driving force of formed. That is, the output of the engine EG will be reduced, the right driving wheel is larger than the driving force of the and the braking torque will be applied to the wheels WHfrand left driving wheel. Thus, since the sign of the driving force WHfl, thereby to restrain the acceleration slip. In each wheel difference (AFd) indicates which wheel is increased in driv cylinder, a hydraulic pressure sensor PSXX is disposed, to 10 ing force between the right and left wheels, according to the detect the wheel cylinder pressure for each wheel. traction control, the sign of the driving force difference (AFd) Next will be explained operation of the steering control also indicates the steered direction for creating the torque apparatus as constituted above, referring to the flowchart as steer resulted from the traction control. shown in FIG. 3. At the outset, the program provides for Then, it is determined at Step 206, whether the torque steer initialization of the system at Step 101, and the signals 15 reducing control is being performed, or not. If it is determined detected by various sensors and communication signals on that the control is not being performed, the program proceeds the communication bus are read at Step 102. Then, the pro to Step 207, where it is determined whether the torque steer gram proceeds to Step 103, where the signals are processed reducing control is to be started, or not. With respect to the by filtering or the like. Next, at Step 104, the desired value determination whether the torque steer reducing control is to (Tps) of the assist torque provided for the power steering be started, if the traction control is being performed, and the control is calculated on the basis of steering torque (Ts). driving force (Fd) is equal to or greater than a predetermined Then, the program proceeds to Step 105, where the desired value (Fd 1), it is determined that the torque steer reducing value (Tts) of the torque steer reducing torque is calculated, as control is to be started. If it is determined that the torque steer will be explained later with reference to FIG. 4. The program reducing control is to be started, the program proceeds to Step further proceeds to Step 106, where the desired value (Tts) of 25 210, where the desired value (Tts) of the torquesteer reducing the torque steer reducing torque is added to the desired value torque is calculated, and the torque steer reducing control is (Tps) of the assist torque, to provide a new desired value performed. Instead, if it is determined at Step 207 that the (Tps+Tts), so that a current command value to the electric torque steer reducing control is not required, the program motor MT is calculated on the basis of the new desired value. proceeds to Step 209, where the desired value (Tts) of the Then, on the basis of the current command value, the electric 30 torque steer reducing torque is set to be Zero (0). motor MT is controlled at Step 107. On the other hand, if it is determined at Step 206 that the The desired value (Tts) of the torque steer reducing torque torque steer reducing control is being performed, the program as described above is calculated according to the flowchart as proceeds to Step 208, where it is determined whether the shown in FIG. 4. At the outset, the output (Te) of the engine torque steer reducing control is to be terminated, or not. With EG served as the power source is calculated at Step 201, on 35 respect to the determination whether the torque steer reducing the basis of the sensor signals and communication signals control is to be terminated, if the traction control is not being read at Step 102 in FIG. 3. The output (Te) is calculated performed (prohibited state), and the driving force (Fd) is according to a relationship between the engine speed (Ne) smaller than a predetermined value (Fd2), it is determined and throttle opening (Tk) as shown in FIG. 5, for example. that the torque steer reducing control is to be terminated. Then, at Step 202, the gear ratio (Rt) is calculated on the basis 40 Accordingly, if it is determined at Step 208 that the torque of the result detected by the gear position sensor GP of the steer reducing control is not to be terminated, the program transmission TR. And, the driving force (Fd) transmitted proceeds to Step 210, where the desired value (Tts) of torque through the drive shafts is calculated at Step 203, on the basis steer reducing torque is continuously calculated. And, if the of the output (Te) of the power source and the gear ratio (Rt) conditions for terminating the torque steer reducing torque of the transmission. 45 are fulfilled, the program proceeds to Step 209, where the Next, calculated at Step 204 is the braking torque (Btd) desired value (Tts) of the torque steer reducing torque is set to applied to the driving wheels according to the traction con be zero. trol. In the case where the hydraulic pressure sensor PSXX is The calculation of the desired value (Tts) of the torque steer provided as shown in FIG. 2, the braking torque (Btc) can be reducing torque executed at Step 210, is made on the basis of calculated by use of the detected signal, i.e., wheel cylinder 50 the driving force difference (AFd) calculated at Step 205, pressure (PSXX). In the case where the hydraulic pressure according to a characteristic as shown in FIG. 6, for example. sensor PSXX has not been provided, the braking torque (Btd) FIG. 6 shows a case where the steered direction of the torque can be calculated according to an operating state of the brake steer resulted from the drive shafts provided in advance as the control device BRK, e.g., actuating states of Solenoid valves vehicle characteristic, is the same as the steered direction of or the like, by a known process. Furthermore, the braking 55 the torque steer resulted from the traction control provided torque (Btd) can be calculated by use of the desired value of when the driving force difference (AFd) is of the positive sign, wheel cylinder pressure for the traction control, which is and opposite to the steered direction of the torque steer calculated in the electronic brake control unit ECU4. In the resulted from the traction control provided when the driving case where an electric brake device (not shown) is installed, it force difference (AFd) is of the negative sign. Hereinafter, the can be calculated on the basis of the electric current for 60 relationship in magnitude of the characteristics will be actuating an electric motor provided in the device. Or, it can explained, with the relationship being based on the magnitude be calculated by use of a desired value for controlling the in absolute value, to simplify the explanation. electric motor. The desired value (Tts) of the torque steer reducing torque And, at Step 205, the driving force difference (AFd) is is determined in accordance with a first characteristic for calculated on the basis of the braking torque (Btd) as 65 determining the desired value of the torque steer reducing described above. This driving force difference (AFd) is pro torque, hereinafter called as first desired value characteristic, cessed as the one with a positive or negative sign, which as indicated by a solid line in the first quadrant in FIG. 6, and US 8,239,097 B2 13 14 a second characteristic for determining the desired value of (AFd) being negative, when the driving force (Fd) is relatively the torque steer reducing torque, hereinafter called as second large, the second desired value characteristic may be modi desired value characteristic, as indicated by a broke line in the fied to be relatively small, as indicated by the one-dot chain third quadrant in FIG. 6, which is different from the first line in FIG. 7, whereas it may be modified to be relatively desired value characteristic. Then, the first desired value char large, as indicated by the broken line in FIG. 7, when the acteristic provided when the driving force difference (AFd) is driving force (Fd) is relatively small, as will be explained in of the positive sign, is set to be the relatively large character detail hereinafter. At the outset, when the driving force (Fd) is istic, whereas the second desired value characteristic pro small, the torque steer resulted from the drive shafts will vided when the driving force difference (AFd) is of the nega become Small. And, according to the second desired value tive sign, is set to be the relatively Small characteristic. 10 characteristic, the steered direction for creating the torque In the case where the steered direction of the torque steer steer resulted from the drive shafts is opposite to the steered resulted from the drive shafts is the same as the steered direction for creating the torque steer resulted from the trac direction of the torque steer resulted from the traction control, tion control, whereby the torque steer resulted from the trac i.e., when the driving force difference (AFd) is of the positive tion control will be cancelled by the torque steer resulted from sign in FIG. 6, the torque steer resulted from the traction 15 the drive shafts. Therefore, when the driving force (Fd) is control will be increased by the torque steer resulted from the Small, the second desired value characteristic may be modi drive shafts. In this case, the characteristic for determining the fied to be relatively large, to output the desired value of the desired value is set to be relatively large, to provide the torque steer reducing torque to be of a relatively large value. desired value (Tts) of the torque steer reducing torque with Whereas, when the driving force (Fd) is large, the second relatively large absolute value against the driving force dif desired value characteristic may be modified to be relatively ference (AFd). In contrast, in the case where the steered Small, to output the desired value of the torque steer reducing direction of the torque steer resulted from the drive shafts is torque to be of a relatively small value. opposite to the steered direction of the torque steer resulted As described above, with the first desired value character from the traction control, i.e., when the driving force differ istic and the second desired value characteristic being modi ence (AFd) is of the negative sign in FIG. 6, the torque steer 25 fied or changed in accordance with the driving force (Fd), the resulted from the traction control will be cancelled by the torque steer resulted from the drive shafts, which is affected torque steer resulted from the drive shafts. In this case, there by the magnitude of the driving force transferred by the drive fore, the characteristic for determining the desired value is set shafts, can be compensated, to achieve the torque steer reduc to be relatively small, to provide the desired value (Tts) of the ing control accurately. Therefore, the torque steer, which is torque steer reducing torque with relatively small absolute 30 created when the vehicle is accelerated, and which is provided value against the driving force difference (AFd). Thus, with for the steered wheel forcing the steering wheel to be steered, the characteristic for determining the desired value for use in can be reduced appropriately without giving a different feel calculating the desired value (Tts) of the torque steer reducing ing to the vehicle driver. torque being provided to be different, i.e., between the first Furthermore, the first desired value characteristic and the desired value characteristic and the second desired value 35 second desired value characteristic may be provided by use of characteristic, depending on the sign of the driving force a function as shown in FIG. 8. Also, the first desired value difference (AFd), the influence by the torque steer resulted characteristic and the second desired value characteristic may from the drive shafts can be restrained effectively. be provided as a function with a dead Zone, in proportion to Furthermore, as shown in FIG. 7, the first desired value the driving force difference (AFd). For example, when the characteristic and the second desired value characteristic may 40 desired value of the torque steer reducing torque is deter be modified or changed in accordance with the driving force mined in accordance with the first desired value characteris (Fd) calculated at Step 203. In this case, the first desired value tic, i.e., the driving force difference (AFd)>0, the desired characteristic with the sign of the driving force difference value of the torque steer reducing torque is calculated accord (AFd) being positive may be modified to be relatively large, as ing to the equation of ITts=Kts1(Fd): AFd-a, wherein “Kts1 indicated by a one-dot chain line in FIG. 7, when the driving 45 (Fd) is a constant indicative of a gradient, to provide a force (Fd) is relatively large, whereas it may be modified to be characteristic in accordance with the driving force (Fd) as relatively small, as indicated by a broken line in FIG. 7, when shown in FIG.9, and 'a' is a constant indicative of the dead the driving force (Fd) is relatively small, as will be explained Zone. The gradient constant (KtS1) is set to indicate a charac in detail hereinafter. teristic to be increased, with the driving force (Fd) being At the outset, when the driving force (Fd) is large, the 50 increased, as indicated by a solid line in FIG. 9. And, in case torque steer resulted from the drive shafts will become large. of Tts.s0, it is set to be zero, i.e., Tts=0. Then, according to the first desired value characteristic, the On the other hand, when the desired value of the torque steered direction for creating the torque steer resulted from steer reducing torque is determined in accordance with the the drive shafts is the same as the steered direction for creating second desired value characteristic, i.e., the driving force the torque steer resulted from the traction control, whereby 55 difference (AFd)<0, the desired value of the torque steer the torque steer resulted from the traction control will be reducing torque is calculated according to the equation of increased by the torque steer resulted from the drive shafts. Tts=Kts2(Fd). AFd+b), wherein “Kts2(Fd) is a constant Therefore, when the driving force (Fd) is large, the first indicative of a gradient, to provide a characteristic in accor desired value characteristic may be modified to be relatively dance with the driving force (Fd) as shown in FIG.9, and “b' large, to output the desired value of the torque steer reducing 60 is a constant indicative of the dead Zone. The gradient con torque to be of a relatively large value. Whereas, when the stant (Kts2) is set to indicate a characteristic to be decreased, driving force (Fd) is small, the first desired value character with the driving force (Fd) being increased, as indicated by a istic may be modified to be relatively small, to output the broken line in FIG. 9. desired value of the torque steer reducing torque to be of a Particularly, the gradient constant (Kts 1) is set to be larger relatively small value. 65 the gradient constant (Kts2), so that the first desired value On the contrary, according to the second desired value characteristic will be relatively larger in value than the second characteristic with the sign of the driving force difference desired value characteristic. As a result, the influence affected US 8,239,097 B2 15 16 by the torque steer resulted from the drive shafts can be to reduce the torque steer resulted from the driving force compensated effectively. Furthermore, with the gradient con distribution, or the torque steer resulted from the traction stant (Kts1) and (Kts2) being modified in accordance with the control, as described before. driving force (Fd) as shown in FIG. 9, the influence affected In the driving force calculation device M9, the driving by variation of the torque steer resulted from the drive shafts 5 force (Fd) is calculated on the basis of the power source can be compensated effectively. When the desired value (Tts) output (Te) and gearratio (Rt). And, on the basis of the driving of the torque steer reducing torque is calculated, a linear force (Fd), a second desired value (Tts2) of the torque steer characteristic to the driving force difference (AFd) has been reducing torque is determined by a second desired value employed in FIG.8. Instead, a characteristicbentata point, or determination device M52, which is adapted to provide a 10 second desired value (Tts2) of the torque steer reducing curved characteristic may be employed. As shown in FIG. 8, torque. The second desired value (Tts2) relates to the one Ttsm1 and Ttsm2 may be provided as the limited values, resulted from the layout and characteristics of the drive shafts, wherein they are set to meet ITtsm1|>|Ttsm2. i.e., torque steer resulted from drive shafts. Since the layout In the above embodiment, there is assumed the case where and characteristics of the drive shafts are known, the torque the steered direction of the torquesteer resulted from the drive 15 steer resulted from the drive shafts is created always in a shafts is the same as the steered direction of the torque steer predetermined steered direction. Therefore, the second resulted from the traction control provided when the driving desired value (Tts2) of the torque steer reducing torque can be force difference (AFd) is of the positive sign, and opposite to obtained in the relationship with the driving force (Fd) deter the steered direction of the torque steer resulted from the mined in advance. Then, the first desired value (Tts1) of the traction control provided when the driving force difference torque steer reducing torque is modified by a modifying (AFd) is of the negative sign. And, the first desired value device M10, in accordance with the second desired value characteristic is set to be a relatively large characteristic, (Tts2) of the torque steer reducing torque, to provide the whereas the second desired value characteristic is set to be a desired value (Tts) of the torque steer reducing torque. This relatively small characteristic. On the contrary, in the case desired value (Tts) of the torque steer reducing torque is where the steered direction of the torque steer resulted from 25 added to the desired value (Tps) of the assist torque obtained the drive shafts is the same as the steered direction of the by the assist torque desired value determination device M2, to torque steer resulted from the traction control provided when output a new desired value, based on which the electric motor the driving force difference (AFd) is of the negative sign, and MT is controlled by the motor control device M6. opposite to the steered direction of the torque steer resulted As described above, the first desired value (Tts1) of the 30 torque steer reducing torque provided for reducing the torque from the traction control provided when the driving force steer resulted from the driving force distribution or the torque difference (AFd) is of the positive sign, the first desired value steer resulted from the traction control, which will be created characteristic and the second desired value characteristic as in any direction, is compensated by the second desired value described above may be replaced with each other. (Tts2) of the torque steer reducing torque provided for reduc Next will be explained another embodiment of the present 35 ing the torque steer resulted from the drive shafts, which will invention referring to FIGS. 10-18, wherein the same refer be created only in a fixed direction. Therefore, a sufficient ence numerals denote the same elements as those disclosed in torque steer reducing torque is created to achieve the torque FIGS. 1-9. In FIG. 10, there is schematically illustrated a steer reducing control certainly, and the different feeling to steering control apparatus according to another embodiment the vehicle driver can be restrained. The steering apparatus of of the present invention, which is installed in the vehicle as 40 the present embodiment is provided with devices having the shown in FIG. 2. According to the present embodiment, the same reference numerals as shown in FIG. 1, and installed in apparatus is provided with a driving force distribution detec the vehicle as shown in FIG. 2, in the same manner as the tion device M31, which detects a driving force distribution former embodiment. state (Dst) distributed to the right and left driving wheels, i.e., Next will be explained operation of the embodiment as steered wheels in the present embodiment. In the driving 45 shown in FIG. 10 (and FIG. 2), with reference to the flowchart force difference calculation device M4, therefore, the driving as shown in FIG. 11. At the outset, the program provides for force difference (AFd) is calculated on the basis of the distri initialization of the system at Step 1101, and the signals bution state (Dst) detected by the driving force distribution detected by various sensors and communication signals on detection device M31, which is adapted to detect the braking the communication bus are read at Step 1102. Then, the torque applied to the driving wheel, if the traction control is 50 program proceeds to Step 1103, where the signals are pro performed. Therefore, the driving force distribution detection cessed by filtering or the like. Next, at Step 1104, the desired device M31 may be provided for detecting or estimating the value (Tps) of the assist torque provided for the power steer hydraulic braking pressure, as described before. According to ing control is calculated on the basis of steering torque (Ts). a limited slip differential, a differential state may be detected, Then, the program proceeds to Step 1105, where the first to detect the driving force distribution state. Therefore, wheel 55 desired value (Tts 1) for reducing the torque steer resulted speed sensors (WSfr and WSfl in FIG. 2) for detecting the from the driving force distribution or the torque steer resulted wheel speeds of the driving wheels WHfr and WHfl, respec from the traction control is calculated, as will be explained tively, may be served as the driving force distribution detec later with reference to FIG. 12. Also, at Step 1106, the second tion device M31. In the case where an electronic driving force desired value (Tts2) for reducing the torque steer resulted distribution device (not shown) is installed in the vehicle, an 60 from the drive shafts is calculated, as will be explained later electronic control unit ECU5 (indicated by a broken line in with reference to FIG. 14. The program further proceeds to FIG. 2) for controlling the distribution device may be served Step 1107, where the first desired value (Tts1) is modified in as the driving force distribution detection device M31. Then, accordance with the second desired value (Tts2), to calculate on the basis of the driving force difference (AFd) calculated the desired value (Tts) of the torque steer reducing torque. by the driving force difference calculation device M4, a first 65 According to the present embodiment, the modification to the desired value (Tts1) of the torque steer reducing torque is first desired value (Tts1) is made by adding the second desired calculated by a first desired value determination device M51, value (Tts2). Then, at Step 1108, the desired value (Tts) of the US 8,239,097 B2 17 18 torque steer reducing torque is added to the desired value control unit ECU4. Therefore, a device for setting the desired (Tps) of the assist torque, to provide a new desired value value in the traction control may be served as the driving force (Tps+Tts), so that a current command value to the electric distribution detection device M31. motor MT is calculated on the basis of the new desired value. In the case where the traction control is performed, when On the basis of the current command value, the electric motor 5 the braking torque is applied to one driving wheel, the driving MT is controlled at Step 1109. force corresponding to the braking torque will be increased The first desired value (Tts1) for reducing the torque steer with respect to the other driving wheel. Therefore, the braking resulted from the driving force distribution or the torque steer torque applied in the traction control may be served as the resulted from the traction control is calculated according to driving force distribution state (Dst). Consequently, the driv the flowchart as shown in FIG. 12. At the outset, the driving 10 ing force difference (AFd) is calculated on the basis of the force distribution state (Dst) detected by the driving force driving force distribution state (Dst), i.e., braking torque, distribution detection device M31 is read at Step 1201, as the according to the driving force difference calculation device sensor signals and communication signals. Next, at Step M4. 1202, the driving force difference (AFd) between the right and Also, in the case where the limited slip differential is served left driving wheels is calculated on the basis of the distribu 15 as the driving force difference device, the detection device for tion state (Dst). The driving force distribution detection detecting the differential state of the limited slip differential device M31, distribution state (Dst), and driving force differ may be used as the driving force distribution detection device ence calculation device M4 will be described later in detail. M31. Since the limited slip differential torque used in the Then, the program proceeds to Step 1203, where it is deter limited slip differential has such a characteristic that the mined whether the first torque steer reducing control is being torque is shifted from a side rotated at a high speed to a side controlled, or not. If it is determined that the first torque steer rotated at a low speed, the wheel speed sensors VWXX for the reducing control is not being controlled, the program pro right and left driving wheels may be employed as the driving ceeds to Step 1204, where it is determined whether the first force distribution detection device M31, so that on the basis of torque steer reducing control is to be started. Or, if it is the results detected by the wheel speed sensors VWXX, the determined at Step 1204 that the first torque steer reducing 25 relative speed difference between the right and left driving control is not to be started, the program proceeds to Step wheels may be obtained to provide the driving force distribu 1206, where the first desired value (Tts1) of the torque steer tion state (Dst). Accordingly, the limited slip differential reducing torque is set to be Zero (0). Instead, if it is determined torque is calculated on the basis of the relative speed differ at Step 1203 that the first torque steer reducing control is ence between the right and left driving wheels, to provide the being performed, the program proceeds from Step 1205, 30 driving force difference (AFd). where it is determined whether the first torque steer reducing Furthermore, in the case where an electronically controlled control is to be terminated, or not. If it is determined that the driving force distribution device is provided, a device for torque steer reducing control is not to be terminated, the providing a desired value of driving force distribution may be program proceeds to Step 1207, where the first desired value served as the driving force distribution detection device M31. (Tts1) of the torque steer reducing torque is continuously 35 The electronically controlled driving force distribution calculated. And, if the conditions for terminating the first device is controlled in accordance with the traveling state of torque steer reducing torque are fulfilled, the program pro the vehicle, and the driving force between the right and left ceeds to Step 1206, where the first desired value (Tts 1) is set driving wheels is controlled in accordance with the desired to be zero. The calculation of the first desired value (Tts1) value of driving force distribution of the device. Therefore, executed at Step 1207 is performed on the basis of the driving 40 the device for providing the desired value of driving force force difference (AFd), as shown in FIG. 13. With respect to distribution may be served as the driving force distribution the driving force difference (AFd), i.e., the torque steer detection device M31, and the desired value of the driving resulted from the difference in driving force between the right force distribution may be used as the driving force distribu and left wheels, it cannot be determined which wheel of them tion state (Dst), and the driving force difference (AFd) can be will become larger in driving force, so that it can be created in 45 calculated on the basis of the desired value of driving force both directions in response to the steering direction of the distribution, by the driving force difference calculation steering wheel SW, as shown in FIG. 13. device M4. Hereinafter, will be explained the driving force distribution On the other hand, the second desired value (Tts2) of the detection device M31, distribution state (Dst), and driving torque steer reducing torque is calculated according to the force difference calculation device M4. In order to reduce the 50 flowchart as shown in FIG. 14. At the outset, the output (Te) torque steer resulted from the traction control, the hydraulic of the engine EG served as the power source is calculated at pressure sensor (indicated by PSXX in FIG. 2) disposed in Step 1301, on the basis of the sensor signals and communi each wheel cylinder can be used as the driving force distribu cation signals read at Step 1102 in FIG. 11. The output (Te) is tion detection device M31. In other words, the hydraulic calculated according to a relationship between the engine pressure sensor for obtaining the braking torque used in the 55 speed (Ne) and throttle opening (Tk) as shown in FIG. 5, for traction control, can be served as the driving force distribution example. Then, at Step 1302, the gear ratio (Rt) is calculated detection device M31. With respect to the hydraulic pressure on the basis of the result detected by the gear position sensor applied to the driving wheel in the traction control, it can be GP of the transmission TR. And, the driving force (Fd) trans estimated by means of the actuating state of hydraulic pres mitted through the drive shafts is calculated at Step 1303, on sure control valve or the like installed in the traction control 60 the basis of the output (Te) of the power source and the gear device, without using the hydraulic pressure sensor. There ratio (Rt) of the transmission. Further, at Step 1304, variation fore, a known device for estimating the braking torque in the (dFd) in time of the driving force (Fd) is calculated. traction control can be served as the driving force distribution Then, the program proceeds to Step 1305, where it is deter detection device M31. Furthermore, the braking torque in the mined whether the second torque steer reducing control is traction control is controlled by a desired value (desired 65 being controlled, or not. If it is determined that the second hydraulic pressure, desired wheel slip, or the like) for the torque steer reducing control is not being controlled, the traction control, which is calculated in the electronic brake program proceeds to Step 1306, where it is determined US 8,239,097 B2 19 20 whether the second torque steer reducing control is to be steering wheel, when the vehicle is accelerated, can be started, or not. If it is determined that the second torque steer reduced effectively, without giving a different feeling to the reducing control is to be started, the program proceeds to Step vehicle driver. 1309, where the second desired value (Tts2) of torque steer It should be apparent to one skilled in the art that the reducing torque is calculated, to perform the second torque 5 above-described embodiment are merely illustrative of but a steer reducing control. On the contrary, if it is determined that few of the many possible specific embodiments of the present the second torque steer reducing control is not to be started, invention. Numerous and various other arrangements can be the program proceeds to Step 1308, where the second desired readily devised by those skilled in the art without departing value (Tts2) is set to be zero (0). If it is determined at Step from the spirit and scope of the invention as defined in the 10 following claims. 1305 that the second torque steer reducing control is being What is claimed is: controlled, the program further proceeds to Step 1307, where 1. A steering control apparatus for a vehicle having a steer it is determined whether the second torque steer reducing ing wheel for steering a pair of right and left steered wheels of control is to be terminated, or not. If it is determined that the said vehicle, a power Source for generating power, drive second torque steer reducing control is not to be terminated, 15 shafts for transferring the power to said right and left steered the program proceeds to Step 1309, where the second desired wheels, to be served as right and left driving wheels of said value (Tts2) of torque steer reducing torque is calculated, vehicle, respectively, and traction control means for control whereas, if the conditions for terminating the second torque ling braking torque applied to said right and left steered steer reducing torque are fulfilled, the program proceeds to wheels, respectively, comprising: Step 1308, where the second desired value (Tts2) is set to be steering torque detection means for detecting a steering ZO. torque, The conditions for starting the torque steer reducing con driving force distribution detection means for detecting a trol used at Step 1306 are determined, depending whether the driving force distribution between said right and left driving force (Fd) is equal to or greater than a predetermined steered wheels; force (Fd 1), or not. In addition, variation (dFd) of the driving 25 driving force difference calculation means for calculating a force may be considered, so that the driving force (Fd)2pre driving force difference between said right and left determined force (Fd 1) and its variation (dFd)2predeter steered wheels, on the basis of the driving force distri mined variation (dfd1) may be used for the starting condi bution detected by said driving force distribution detec tions. Also, the starting conditions may be provided on the tion means; basis of a function of the driving force (Fd) and its variation 30 power Source state detection means for detecting an actu (dFd). And, the calculation of the second desired value (Tts2) ating state of said power source: executed at Step 1309 is performed on the basis of the driving driving force calculation means for calculating the driving force (Fd), as shown in FIG. 15. Furthermore, by use of the force, on the basis of the actuating state of said power relationship as shown in FIG. 16, a modified value (Ttsh) of Source detected by said power source State detection the torque steer reducing torque may be calculated to be 35 means, served as a modified value to the second desired value (Tts2), steering torque control means for controlling steering and added to the second desired value (Tts2) of the torque torque created by said steering wheel, and applying steer reducing torque, to modify the second desired value torque to said steering wheel on the basis of a Sum of a (Tts2). desired value of a power steering assist torque and a The modified value (Ttsh) of the torque steer reducing 40 desired value of a torque steer reducing torque, to reduce torque may be obtained in pulse wave forms for a predeter torque steer, mined time period, e.g., rectangular wave form, triangular desired value of power steering assist torque determination waveform or trapezoidal waveform as shown in FIG. 17. The means for determining the desired value of the power waveform shown at the lowest part in FIG. 17 can be provided steering assist torque on the basis of the steering torque as shown in FIG. 18. That is, at least more than one of 45 detected by the steering torque detection means; parameters including output time (Tpls) of the pulse wave first desired value determination means for determining a form, increasing gradient (KTup) of the modified value (Ttsh) first desired value of the torque steer reducing torque to of the torque steer reducing torque, maximum value (Ttsm) of reduce the torque steer created in any direction with the modified value (Ttsh) of the torque steer reducing torque, respect to the steering wheel direction, on the basis of the holding time (Thld) of the maximum value, and decreasing 50 driving force difference calculated by said driving force gradient (KTdwin) of the modified value (Ttsh) of the torque difference calculation means; steer reducing torque, may be set to be varied in accordance second desired value determination means for determining with the driving force (Fd) or its variation (dFd). a second desired value of the torque steer reducing According to the embodiment as described above, with torque to reduce the torque steer created only in a fixed respect to the torque steer resulted from the layout and char 55 direction with respect to the steering wheel direction, on acteristics of the drive shafts, i.e., the torque steer resulted the basis of the driving force calculated by said driving from the drive shafts, the steered direction and the magnitude force calculation means; of the driving force can be detected in advance. Therefore, modifying means for modifying the first desired value of Sufficient torque steer reducing torque can be calculated, with the torque steer reducing torque determined by said first the second desired value (Tts2) of the torque steer reducing 60 desired value determination means, in accordance with torque modifying the first desired value (Tts1) of the torque the second desired value of the torque steer reducing steer reducing torque provided for reducing the torque steer torque determined by said second desired value deter resulted from the driving force distribution or the torque steer mination means, to provide said desired value of the resulted from the traction control, which is determined by torque steer reducing torque; and road Surface conditions or vehicle traveling state, and which 65 modified value calculation means for calculating a modi will be caused in any steering direction. As a result, the torque fied value of the torque steer reducing torque, on the steer, which is created for the steered wheel to steer the basis of a variation of the driving force calculated by said US 8,239,097 B2 21 22 driving force calculation means, to increase the modified modified value calculation means for calculating a modi value of the torque steer reducing torque according to fied value of the torque steer reducing torque, on the increase of the variation of the driving force, wherein basis of a variation of the driving force calculated by said said modifying means modifies the second desired value driving force calculation means, to increase the modified of the torque steer reducing torque determined by said 5 value of the torque steer reducing torque according to second desired value determination means, by adding increase of the variation of the driving force, wherein the modified value of the torque steer reducing torque to said modifying means modifies the second desired value the second desired value of the torque steer reducing of the torque steer reducing torque determined by said torque. 10 second desired value determination means, by adding 2. A steering control apparatus as set forth in claim 1, the modified value of the torque steer reducing torque to wherein said steering torque control means determines to the second desired value of the torque steer reducing start controlling the steering torque by applying the second torque. desired value of the torque steer reducing torque, on the basis 4. A steering control apparatus for a vehicle having a steer of the driving force calculated by said driving force calcula 15 ing wheel for steering a pair of right and left steered wheels of tion means. said vehicle, a power Source for generating power, drive 3. A steering control apparatus for a vehicle having a steer shafts for transferring the power to said right and left steered ing wheel for steering a pair of right and left steered wheels of wheels, to be served as right and left driving wheels of said said vehicle, a power Source for generating power, drive vehicle, respectively, and traction control means for control shafts for transferring the power to said right and left steered ling braking torque applied to said right and left steered wheels, to be served as right and left driving wheels of said wheels, respectively, comprising: vehicle, respectively, and traction control means for control steering torque detection means for detecting a steering ling braking torque applied to said right and left steered torque, wheels, respectively, comprising: 25 driving force distribution detection means for detecting a driving force distribution detection means for detecting a driving force distribution between said right and left driving force distribution between said right and left steered wheels; steered wheels; driving force difference calculation means for calculating a driving force difference calculation means for calculating a 30 driving force difference between said right and left driving force difference between said right and left steered wheels, on the basis of the driving force distri steered wheels, on the basis of the driving force distri bution detected by said driving force distribution detec bution detected by said driving force distribution detec tion means; tion means; power Source state detection means for detecting an actu power source State detection means for detecting an actu 35 ating state of said power source: ating state of said power source: driving force calculation means for calculating the driving driving force calculation means for calculating the driving force, on the basis of the actuating state of said power force, on the basis of the actuating state of said power Source detected by said power source State detection Source detected by said power source State detection 40 means, means, steering torque control means for controlling steering steering torque control means for controlling steering torque created by said steering wheel, and applying torque created by said steering wheel, and applying torque to said steering wheel on the basis of a Sum of a torque steer reducing torque to said steering wheel, to desired value of a power steering assist torque and a reduce torque steer, 45 desired value of a torque steer reducing torque, to reduce first desired value determination means for determining a torque steer, first desired value of the torque steer reducing torque to desired value of power steering assist torque determination reduce the torque steer created in any direction with means for determining the desired value of the power respect to the steering wheel direction, on the basis of the steering assist torque on the basis of the steering torque driving force difference calculated by said driving force 50 detected by the steering torque detection means; difference calculation means; first desired value determination means for determining a second desired value determination means for determining first desired value of the torque steer reducing torque to a second desired value of the torque steer reducing reduce the torque steer created in any direction with torque to reduce the torque steer created only in a fixed 55 respect to the steering wheel direction, on the basis of the direction with respect to the steering wheel direction driving force difference calculated by said driving force resulting from a layout of the drive shafts, on the basis of difference calculation means; the driving force calculated by said driving force calcu second desired value determination means for determining lation means; a second desired value of the torque steer reducing modifying means for modifying the first desired value of 60 torque to reduce the torque steer created only in a fixed the torque steer reducing torque determined by said first direction with respect to the steering wheel direction desired value determination means, in accordance with resulting from a layout of the drive shafts, on the basis of the second desired value of the torque steer reducing the driving force calculated by said driving force calcu torque determined by said second desired value deter 65 lation means; mination means, to provide said desired value of the modifying means for modifying the first desired value of torque steer reducing torque; and the torque steer reducing torque determined by said first US 8,239,097 B2 23 24 desired value determination means, in accordance with increase of the variation of the driving force, wherein the second desired value of the torque steer reducing said modifying means modifies the second desired value torque determined by said second desired value deter of the torque steer reducing torque determined by said mination means, to provide said desired value of the second desired value determination means, by adding torque steer reducing torque; and the modified value of the torque steer reducing torque to modified value calculation means for calculating a modi the second desired value of the torque steer reducing fied value of the torque steer reducing torque, on the torque. basis of a variation of the driving force calculated by said driving force calculation means, to increase the modified value of the torque steer reducing torque according to