F2008-12-026
Simulation and Analysis of Torque Vectoring Drives
Speed compensation between the wheels of an axle while the drive torque is distributed symmetrically at the same time is possible with conventional differentials. This solution, however, is only a compromise of agility and traction with regard to cornering. This is especially true in case of a sporty driving style. It is known from racing that the inside wheel tends to spin if powerful drive torques under high lateral acceleration are applied. The wheel thus loses its lateral grip potential. Therefore, systems are used in these vehicles which avoid speed compensation at least partly. Since such systems can also be controlled electronically, they become more and more interesting for production application. For reasons of economy, however, not only real torque vectoring systems (with at least 2 controllable clutches) are considered, but passive and active differential locks as well. The improvement potential in terms of driving dynamics, which can be achieved through different systems, depends heavily on the selected drive concept.
In this article, a modular, non-linear two-track model is introduced, representing the effects required for the simulative analysis of active drive systems (in this case especially tyre characteristics).
Subsequently, the potential of active and passive systems (e.g. Torsen differential, electro-mechanical clutches) for improving the lateral dynamic characteristics is presented systematically while taking the various drive train configurations front, rear and all-wheel drive into account. The constraints drive power, curve radius and lateral acceleration are pointed out in particular for those systems which only transfer energy to the lower turning wheel. The interaction with the steering system is also regarded for front-wheel-drive vehicles.
Due to the tyre characteristics, this results in to some extent serious differences in the driving behaviour, depending on the drive concept. These differences have to be taken into account in the constructive design or the application of the control strategy. This especially includes the driving behaviour on low-friction driving surfaces. The advantages and disadvantages as well as the physical limits of the individual systems in the various configurations are worked out and represented in representative driving manoeuvres.
Session: Chassis