Torque split between left and right drive shaft over a front wheel drive differential

Steering feel and vehicle steering motion is affected by wheel torques from propulsion, especially for front wheel drive cars. Often these problems are referred to as “torque steer”. Many systems interact to cause these problems: propulsion, steering and suspension. Torque steer contributors are not only the differential (friction, self locking effect, Torsen differential), but also the input from the ground and car geometry such as road conditions (friction and surface), the vehicle state (cornering, rolling, acceleration) and weight distribution (loading). In addition, the suspension design contributes as well, like the suspension geometry (kingpin offset, camber, caster, tolerances), the tire quality (conicity, wear, profile) and wheel geometry (size, uniformity, wheel offset). Finally, regarding the transmission contributors, the engine (torque, alignment) and drive shafts (alignment, length, symmetry) are contributors as well. Particularly, within the propulsion system, it is partly the asymmetry in differential and drive-shafts that could cause torque steer. In fact, the friction of the gear meshing and bearings, and mainly the contact with the housing (carrier) during slippery and static conditions or the housing stiffness itself might be causes of this torque steer problem. Hence, the losses over the differential can explain the torque steer effect due to the torque difference between left and right driveshaft. This fact affects the behaviour of the vehicle. This is the reason why Volvo Cars Corporation (VCC) is interested in studying the friction in a differential to use it in further simulations (vehicle dynamics purposes) or understand which parts of the design may be modified or changed in order to reduce or increase (depending on the goal, either getting as close as possible an open or a limited slip differential behaviour) the overall friction. The motivation of the thesis work comes from this problem. The thesis derives a model for an open differential in order to qualify and quantify the difference of torque between left and right side. In addition, to be able to test the differential, a rig is designed and machined outhouse. Moreover, during testing the model is updated and the parameters are changed according to the statistic experiment plan and the results from the FEM analysis carried out. Finally, not only all the conclusions and results are written down, but also some vehicle dynamics simulations to show the effect of the differential in the behaviour of the car