Method and Apparatus for Compensating Torque Steer

Europäisches Patentamt *EP000787642B1* (19) European Patent Office

Office européen des brevets (11) EP 0 787 642 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.7: B62D 6/00 of the grant of the patent: // B62D101:00, B62D119:00, 06.05.2004 Bulletin 2004/19 B62D121:00, B62D127:00, (21) Application number: 96120210.8 B62D137:00, B62D153:00

(22) Date of filing: 16.12.1996

(54) Method and apparatus for compensating torque steer Verfahren und Vorrichtung zum Ausgleich von Drehmoment-Lenkeffekten Procédé et appareil pour la compensation d’effet du couple entraînant sur la direction

(84) Designated Contracting States: • Mantjios, Chris DE FR GB IT Troy, MI 48098 (US)

(30) Priority: 30.01.1996 US 594253 (74) Representative: Geyer, Ulrich F., Dr. Dipl.-Phys. et al (43) Date of publication of application: WAGNER & GEYER, 06.08.1997 Bulletin 1997/32 Patentanwälte, Gewürzmühlstrasse 5 (73) Proprietor: TRW Automotive U.S. LLC 80538 München (DE) Livonia, Michigan 48150 (US) (56) References cited: (72) Inventors: DE-A- 19 536 989 • Blandino, Don Sterling Heights, MI 48313 (US) • "TORQUE STEER CONTROL SYSTEM" • Miller, Joseph D. RESEARCH DISCLOSURE, no. 327, 1 July 1991, Farmington, MI 48331 (US) EMSWORTH, GB, page 488 XP000258688

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 787 642 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 0 787 642 B1 2

Description present invention, an apparatus is provided for compensating torque steer in a vehicle having a power assist Technical Field steering system. The apparatus comprises means for sensing at least one operating characteristic of a vehicle [0001] The present invention is directed generally to 5 indicative of torque steer, said means for sensing at controlling a vehicle power steering system and specif- least one operating characteristic including means for ically directed to a method and apparatus for compen- sensing engine rotations-per-minute of the vehicle en- sating torque steer in front wheel drive vehicles. gine. Means are provided for sensing an operator applied steering torque. The apparatus further includes Background of the Invention 10 control means for controlling the power assist steering system in response to the sensed operator applied [0002] In most front wheel drive vehicles, a phenom- steering torque and in response to the at least one enon known as "torque steer" is experienced. Torque sensed operating characteristic so as to compensate for steer is a vehicle steering effect resulting from the torque torque steer, said at least one operating characteristic developed by a vehicle engine. There are two primary 15 being engine rotations. causes of torque steer. First, torque steer results when [0009] In accordance with a preferred embodiment of torque developed by the vehicle engine is transferred the present invention, the means for sensing an operat- unevenly to the vehicle front wheels. Second, uneven ing characteristic of a vehicle indicative of torque steer progress of the vehicle front wheels in response to the is engine speed. torque developed by the vehicle engine also results in 20 [0010] In accordance with another embodiment of the torque steer. present invention, a method is provided for compensat- [0003] The concept of torque steer is most easily un- ing torque steer in a vehicle power assist steering sys- derstood by way of example. Assume a driver is travel- tem. The method comprising the steps of sensing at ling in a front wheel drive vehicle on a straight path down least one vehicle operating characteristic indicative of a straight road. If this driver suddenly accelerates, i.e., 25 torque steer including sensing rotations-per-minute of rapidly increases engine revolutions-per-minute the vehicle engine, sensing applied steering torque by ("RPMs"), the vehicle will tend to steer either left or right a vehicle operator, and controlling the power assist as a result of the torque steer effect on the vehicle. This steering system to compensate for torque steer said situation thus requires the driver to compensate for the controlling being responsive to the sensed applied torque steer effect so as to maintain his correct path of 30 steering torque and the sensed operating characteristic travel down the road. indicative of torque steer, said at least one operating [0004] Attention is drawn to the article "Torque Steer characteristic being engine rotations. Control System", Research Disclosure, No. 327, July 1, [0011] In accordance with a preferred embodiment, 1991, Emsworth GB (page 488), which shows an appa- the step of sensing an operating characteristic indicative ratus and a method for compensating for torque steer 35 of torque steer includes either the step of sensing rota- in a steer-by-wire front steer vehicle, comprising the fea- tions-per-minute of the vehicle engine or the step of tures defined in the preamble of claim 1 or 5. The degree sensing road wheel drive torque. of torque steer is measured by an appropriate yaw sensor having a response time faster than the response Brief Description of the Drawings time of the driver. Further, a sensor for sensing whether 40 the vehicle driver is trying to steer the vehicle, is provid- [0012] The foregoing and other features and advan- ed. If the driver is not steering, but the yaw sensor indi- tages of the present invention will become apparent to cates that the vehicle is steering, a steering control mod- one skilled in the art to which the present invention re- ule is activated to compensate for the undesired torque lates upon consideration of the following detailed de- steer. 45 scription of the invention with reference to the accom- [0005] In accordance with the present invention, an panying drawing, wherein: apparatus and a method for compensating torque steer as set forth in claims 1 and 5, respectively, are provided. Fig. 1 is a block diagram of a torque steer compen- [0006] Preferred embodiments of the invention are sation system made in accordance with the present claimed in the dependent claims. 50 invention.

Summary of the Invention Description of Preferred Embodiments

[0007] The present invention is directed to a method [0013] Referring to Fig. 1, a vehicle torque steer com- and apparatus for compensating for torque steer in front 55 pensation system 10, in accordance with the present in- wheel drive vehicles and eliminate the need for driver vention, includes a vehicle steering wheel 12 connected interaction to correct for the effects of torque steer. to an input shaft 14. A pinion gear 16 is connected to an [0008] In accordance with one embodiment of the output shaft 18. The input shaft 14 is coupled to the out-

2 3 EP 0 787 642 B1 4 put shaft 18 through a torsion bar 20. The torsion bar 20 addition to the torque command output 40, the steering twists in response to torque applied to the vehicle steer- torque command circuit 36 provides a sign output 42 ing wheel 12 and permits relative rotation between the which has a sign value indicative of the direction the ap- input shaft 14 and the output shaft 18. Stops, not shown, plied steering torque (i.e., left turn or right turn) indicated limit the amount of relative rotation between the input 5 by the output on line 34 of the torque sensor 32. The shaft 14 and the output shaft 18 in a manner known in operation of a torque command circuit, such as circuit the art. 36, for control of an electric assist motor in response to [0014] The pinion gear 16 has helical gear teeth (not applied steering torque and vehicle speed is known in shown) which are meshingly engaged with straight cut the art and a detailed description of such operation is gear teeth (not shown) on a linear steering member or 10 not discussed herein in detail. An example of a torque rack 22. The rack 22 is coupled to vehicle steerable command circuit in accordance with the present inven- wheels 24 and 26 through steering linkage in a known tion is described in U.S. Patent No. 5,257,828 to Miller manner. The pinion gear 16 together with the rack 22 et al.. forms a rack and pinion gear set. [0020] The output 40 of the steering torque command [0015] The vehicle's engine 27 is drivably coupled to 15 circuit 36 is connected to one input of a summing circuit the wheels 24, 26 in a known manner. The wheels 24, 44. A multiplier circuit 46 provides a torque steer com- 26 are the front wheel drive vehicle. The present inven- pensation output 48 which is connected to another input tion is also applicable to an all wheel drive vehicle. of the summing circuit 44. The summing circuit 44 pro- [0016] When the steering wheel 12 is turned, the rack vides a compensated torque command output 50 which and pinion gear set converts the rotary motion of the 20 is equal to the sum of the torque command value on out- steering 22 moves linearly, the steerable wheels 24 and put 40 and the torque steer compensation value on out- 26 pivot about their associated steering axes and the put 48. The value of the compensated torque command vehicle is steered. An electric assist motor 28 is drivingly output 50 is the value of the assist torque needed to connected with the rack 22 through, preferably, a ball- cause the motor 28 to: 1) provide the desired steering nut drive arrangement (not shown). The motor 28, when 25 assist torque (output 40); and 2) compensate for the energized, provides power assist torque to aid a vehicle torque steer effect on the vehicle (output 48). driver in steering movement of the rack 22 and, in turn, [0021] The torque steer compensation output 48 is steering of the vehicle. the value of the sign output 42 times the value of a torque [0017] A shaft position sensor 30 is operatively con- steer output 56 provided by a torque steer control circuit nected across the input shaft 14 and the output shaft 18. 30 58. The torque steer control circuit 58 determines the The shaft position sensor 30, in combination with the value of the torque steer output 56 in response to: 1) torsion bar 20, form a torque sensor 32. The shaft posi- vehicle speed sensed by the vehicle speed sensor 38; tion sensor 30 provides an output signal on line 34 hav- and 2) vehicle engine r.p.m. sensed by an engine r.p.m. ing a value indicative of the relative rotational position sensor 60. In accordance with a preferred embodiment, between the input shaft 14 and the output shaft 18. This 35 the torque steer control circuit 58, along with the multi- relative rotational position between the input shaft 14 plier 46, summing circuit 44, and steering torque com- and the output shaft 18 is indicative of the steering mand circuit 36 are all programmed in a microcomputer torque applied by the vehicle operator to the vehicle controller 62. The engine speed is indicative of the steering wheel 12. Therefore, the value of the output sig- amount of torque steer. nal on line 34 from the shaft position sensor 30 is indic- 40 [0022] The functional relationship between the value ative of the value or amount of steering torque applied of the torque steer compensation output 56 and vehicle to the vehicle steering wheel 12 and is referred to as the speed from sensor 38 and engine r.p.m. from sensor 60 "applied steering torque." is dependent upon the particular vehicle platform of in- [0018] The applied steering torque signal on line 34 terest. It is anticipated that each vehicle platform will is connected to a steering torque command circuit 36. 45 have an associated functional relationship. For a partic- The steering torque command circuit 36 determines the ular vehicle platform of interest, the torque steer com- amount of desired assist torque to be provided by the pensation functional relationship may be determined motor 28 and provides a torque command output 40 empirically and stored in the form of an internal look-up having a value indicative of the determined amount of table (memory) in the microcomputer controller 62. Al- desired torque assist. The torque command output 40 50 ternatively, the torque steer compensation functional re- is a function of two parameters: (i) the value of the ap- lationship may be defined by an equation stored in the plied steering torque; and (ii) vehicle speed. controller 62. [0019] A vehicle speed sensor 38 provides a vehicle [0023] The torque compensating output 50 provided speed output signal to the torque command circuit 36 by the summing circuit 44 is connected to a drive control having a value indicative of the sensed vehicle speed. 55 circuit 52. The drive control circuit 52 uses the torque Typically, the amount of torque assist desired from the compensated output 50 in controlling the motor ener- motor 28 decreases as vehicle speed increases. This is gization current and the motor direction. A motor drive referred to in the art as "speed proportional steering." In output 54 is provided to the motor 28 to energize the

3 5 EP 0 787 642 B1 6 motor 28 which causes the motor to develop the com- power assist steering system, said method compensated torque assist, i.e., torque assist compensated prising the steps of: for any sensed torque steer effect. [0024] Although the present invention has been de- sensing at least one vehicle operating charac- scribed with regard to an electric power assist steering 5 teristic indicative of torque steer; system, the invention is not limited to such a system. sensing applied steering torque by a vehicle op- The present invention may be used with equal utility in erator; a front wheel drive or all wheel drive vehicle having a controlling the power assist steering system to hydraulic power steering system. In a hydraulic system, compensate for torque steer, said step of con- instead of an electrically controlled electric assist motor, 10 troling being responsive to said sensed applied hydraulic differential pressure is electrically controlled steering torque and said at least one sensed in response to measured engine r.p.m. or sensed road operating characteristic indicative of torque wheel drive torque to compensate for vehicle torque steer, characterised in that said step of sens- steer. Electric control of a hydraulic assist steering sys- ing at least one vehicle operating characteristic tem is accomplished through electrical control of a valve 15 indicative of torque steer includes sensing ro- between a pump and the hydraulic assist device. tations-per-minute of the vehicle engine. [0025] From the above description of the invention, those skilled in the art will perceive improvements, 6. The method and apparatus of claim 5 further includ- changes, and modifications. Such improvements, ing the step of sensing vehicle speed, said step of changes, and modifications within the skill of the art are 20 controlling is further responsive to said sensed ve- intended to be covered by the appended claims. hicle speed.

Claims Patentansprüche 25 1. An apparatus (10) for compensating for torque steer 1. Eine Vorrichtung (10) zum Ausgleichen bzw. Kom- in a vehicle having a power assist steering system, pensieren von Drehmoment-Lenkeffekten in einem said apparatus comprising: Fahrzeug, das ein Servolenksystem besitzt, wobei die Vorrichtung Folgendes aufweist: means (60, 61) for sensing at least one operat- 30 ing characteristic of a vehicle indicative of Mittel (60, 61) zum Abfühlen von mindestens torque steer; einem Betriebsmerkmal eines Fahrzeugs, das means (32) for sensing an operator applied eine Anzeige bildet für einen Drehmoment- steering torque; and Lenkeffekt; control means (62) for controlling in response 35 Mittel (32) zum Abfühlen eines vom Fahrer an- to the sensed operator applied steering torque gelegten Lenkdrehmoments; und and in response to the at least one sensed op- Steuermittel (62) zum Steuern des Servolenk- erating characteristic indicative of torque steer, systems, und zwar ansprechend auf das abge- the power assist steering system to compen- fühlte, vom Fahrer angelegte Lenkdrehmoment sate for torque steer, characterized in that the 40 und ansprechend auf das mindestens eine ab- sensed at least one operating characteristic of gefühlte Betriebsmerkmal, das eine Anzeige the vehicle indicative of torque steer is engine bildet für den Drehmoment-Lenkeffekt, um den rotations-per-minute of the vehicle engine (27). Drehmoment-Lenkeffekt zu kompensieren, dadurch gekennzeichnet, dass das mindestens 2. The apparatus (10) of claim 1 wherein said appara- 45 eine abgefühlte Betriebsmerkmal des Fahr- tus further includes means (38) for sensing vehicle zeugs, das eine Anzeige bildet für den Dreh- speed, said control means (62) being further re- moment-Lenkeffekt, die Motorumdrehungen- sponsive to sensed vehicle speed to compensate pro-Minute des Fahrzeugmotors (27) ist. for said torque steer. 50 2. Die Vorrichtung (10) nach Anspruch 1, wobei die 3. The apparatus recited in claim 1 wherein said power Vorrichtung ferner Mittel (38) aufweist zum Abfüh- assist steering system includes an electric motor len der Fahrzeuggeschwindigkeit, wobei die Steu- (28). ermittel (62) ferner auf die abgefühlte Fahrzeugge- schwindigkeit ansprechen, um den Drehmoment- 4. The apparatus recited in claim 1 wherein said power 55 Lenkeffekt zu kompensieren. assist steering system includes a hydraulic device. 3. Die Vorrichtung nach Anspruch 1, wobei das Ser- 5. A method for compensating torque steer in a vehicle volenksystem einen Elektromotor (28) aufweist.

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4. Die Vorrichtung nach Anspruch 1, wobei das Ser- 2. Appareil (10) selon la revendication 1, dans lequel volenksystem eine hydraulische Einrichtung auf- ledit appareil comprend en outre un moyen (38) weist. destiné à capter la vitesse du véhicule , ledit moyen de commande (62) réagissant en outre à la vitesse 5. Ein Verfahren zum Kompensieren von einem Dreh- 5 captée du véhicule pour compenser ledit braquage moment-Lenkeffekt in einem Fahrzeugservolenk- dû au couple. system, wobei das Verfahren folgende Schritte umfasst: 3. Appareil selon la revendication 1, dans lequel ledit système de direction assistée comprend un moteur Abfühlen von zumindest einem Fahrzeugbe- 10 électrique (28). triebsmerkmal, das eine Anzeige bildet für den Drehmoment-Lenkeffekt; 4. Appareil selon la revendication 1, dans lequel ledit Abfühlen des durch einen Fahrzeugfahrer an- système de direction assistée comprend un dispo- gelegten Lenkdrehmoments; sitif hydraulique. Steuern des Servolenksystems, um den Dreh- 15 moment-Lenkeffekt zu kompensieren, wobei 5. Procédé pour compenser un braquage dû au cou- der Schritt des Steuerns auf das abgefühlte an- ple dans un système de direction assistée de véhi- gelegte Lenkdrehmoment und das zumindest cule, ledit procédé comprenant les étapes qui eine, eine Anzeige für den Drehmoment-Lenk- consistent : effekt bildende abgefühlte Betriebsmerkmal 20 anspricht, dadurch gekennzeichnet, dass à capter au moins une caractéristique de fonc- der Schritt des Abfühlens des zumindest einen tionnement du véhicule représentative d'un Fahrzeugbetriebsmerkmals, das eine Anzeige braquage dû au couple ; bildet für den Drehmoments-Lenkeffekt, das à capter un couple de direction appliqué par un Abfühlen der Umdrehungen-pro-Minute des 25 conducteur du véhicule ; Fahrzeugmotors umfasst. à commander le système de direction assistée pour compenser un braquage dû au couple, la- 6. Das Verfahren und die Vorrichtung nach Anspruch dite étape de commande réagissant audit cou- 5, die ferner den Schritt des Abfühlens der Fahr- ple de direction appliqué, capté, et à ladite, au zeuggeschwindigkeit umfassen, wobei der Schritt 30 moins une, caractéristique de fonctionnement des Steuerns ferner auf die abgefühlte Fahrzeug- captée représentative d'un braquage dû au geschwindigkeit anspricht. couple, caractérisé en ce que l'étape consistant à capter au moins une caractéristique de fonctionnement du véhicule représentative Revendications 35 d'un braquage dû au couple comprend le fait de capter le régime auquel tourne le moteur du 1. Appareil (10) destiné à compenser le braquage dû véhicule. au couple dans un véhicule ayant un système de direction assistée, ledit appareil comportant : 6. Procédé et appareil selon la revendication 5, com- 40 prenant en outre l'étape consistant à capter la vi- un moyen (60,61) destiné à capter au moins tesse du véhicule, ladite étape de commande réa- une caractéristique de fonctionnement d'un vé- gissant en outre à ladite vitesse captée du véhicule. hicule représentatif d'un braquage dû au couple ; un moyen (32) destiné à capter un couple de 45 braquage appliqué par le conducteur ; un moyen de commande (62) destiné à commander, en réponse au couple capté de braquage appliqué par le conducteur et en répon- se à la, au moins une, caractéristique de fonc- 50 tionnement captée représentative d'un braquage dû au couple, le système de direction assis- tée afin de compenser le braquage dû au couple, caractérisé en ce que la, au moins une, caractéristique de fonctionnement captée du 55 véhicule représentative du braquage dû au couple est le régime auquel tourne le moteur (27) du véhicule.

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