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 compen- sating 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 ap- plied 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 sen- sor 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).