Suspension influences on a steer-by-wire torque vectoring vehicle

Abstract

Conventional steering systems with a mechanical connection between steering wheel and road wheels are limited in terms of adapting the steering ratio and the steering torque in dependence of the current operating condition. Steer-by-wire systems enable to decouple the mechanical connection of the steering wheel and the road wheels, thus enabling situation-dependent feedback to the driver’s steering inputs and also the possibility of autonomous steering interventions for automated driving. Because of the high safety requirements for steering systems, steer-by-wire systems require either a fail-safe system with a mechanical fallback solution e.g. actuated with a clutch, or a fail-tolerant system, [1]. These fail-tolerant systems can be achieved for example with full redundancy of all safety-critical components, but also by using torque vectoring (TV) as a redundant steering function, [2].

TV allows individual torque distribution on wheels to stabilize the vehicle in a critical driving situation like electronic stability control (ESC), or to influence the yaw motion of the vehicle in non-critical driving situations, e.g. to improve driving enjoyment, [1]. Since TV does not only influences the lateral dynamics significantly through the different longitudinal forces, but in addition different longitudinal forces can also generate a torque around the kingpin axis. This effect can also be used as a failtolerant system for a steer-by-wire system. However, the amount of torque that is required to steer the vehicle depends to a high amount on the suspension kinematics.

There are several requirements on suspension kinematics that have to be considered during the design process, with steering by TV not being the main optimization target. To still ensure an optimum performance of steering by TV under given constraints, an investigation is presented in this article to quantify influences of suspension kinematics and geometry on steering by torque vectoring. Based on a multi-body vehicle model which is described in Section 1.2, two different three-dimensional suspension models for the front axle were implemented, see Section 2, and validated using measurement data, see Section 3. Using these models, a parameter study was conducted to compare the influence of two selected suspension parameters on the steering behavior of a TV steered vehicle and a conventionally steered vehicle. The results of this parameter study are presented in Section 4. Finally, a discussion and outlook are given in Section 5.