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Torque Steer Testing and Evaluation
Project BriefThe torque steer phenomenon is intrinsic to front-wheel drive (FWD) vehicles and is thought to be associated with asymmetrical vehicle geometry and out-of-phase power pulsing. In the past, this problem was manageable, as the magnitude of the torque steer was smaller because of the small engine sizes typically associated with front-wheel drive vehicles. With the increased use of larger size 200+hp engines into FWD vehicles, the magnitude of the torque steer effect has increased and requires significant testing to provide safe vehicles for public use.
Southwest Research Institute (SwRI) conducts testing and evaluation of the torque steer effects both in the laboratory and on a chassis dynamometer. The focus of the testing is to differentiate and quantify the effects of wheel position (s) and wheel speed (s).
To ascertain the effects of wheel position, an adjuster mechanism is connected to the spindle and frame in the area of the wheel. This mechanism allows the steering knuckle and spindles to be positioned and restrained in any desired location to simulate level vehicle and asymmetrical wheel positions. Typically, angles are varied from -5° to +15°.
Testing and evaluation is conducted at both wide-open throttle accelerations and steady-state conditions. To assure both wheels rotate at the same speed, the output from each spindle is connected with rigid shafting to the dynamometer and inertia wheels. This eliminates any differential effects within the transaxle.
To ascertain the effects of wheel speed differentials, testing is conducted at various wheel speeds and side-to-side wheel speed differentials ranging from -1 to 10 rpm. Mapping of the wheel speed differential values focuses on defining the differential speed region at which torque steer occurs, which, based upon test results, is a narrow band with an immediate transition from normal operation.
To realistically simulate the vehicle operation, road load and aerodynamic loading are applied from a programmable eddy current dynamometer. Inertia wheels are used to represent vehicle inertia. Output torques at each drive axle are measured with in-line torque transducers.
For more information about our drivetrain engineering capabilities and past performance briefs, or how you can contract with SwRI, please contact Douglas Fussner at dfussner@swri.org or (210) 522-3972.
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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions. | ||||||||||||
December 28, 2012 | ||||||||||||
