The Institute for Automotive Engineering at RWTH Aachen University (ika), is currently developing, constructing, and implementing the research vehicle SpeedE as an open research and innovation platform for research and industry. The research focus of the SpeedE concept, amongst other things, is the innovative front suspension. Not only is the front axle's steer-by-wire system able to steer each wheel individually, but it is also able to achieve steering angles of up to 90°. These requirements lead to an unconventional setup of the axle replacing the tie rod and the rack and pinion steering gear of a double wishbone suspension by two steering actuators consisting of an electric motor and a harmonic drive reduction gear located at the outer kinematic hardpoint of the upper control arm and mounted to the wishbone through a cardan joint. This paper describes the development approach to design the kinematic and elasto-kinematic properties of this innovative axle concept by means of genetic algorithm based optimization. Requirements, challenges, and solutions are displayed. A special focus is laid on the effect of the cardan joint on the wheel alignment characteristics. The optimization is performed in three stages, as a simultaneous optimization of all criteria does not lead to satisfactory results. In the first step, the position of the steering axis is determined. To solve the conflict between the needed space due to the large wheel steering angles and the need to comply with maximum allowable wheel camber, a static camber angle of -1° is ultimately chosen in conjunction with a positive caster trail and a positive caster angle. Subsequently, the chassis attachment points and the orientation of the cardan joint are determined. For this purpose, the orientation of the cardan joint is primarily used to define the toe angle course during wheel travel. Thereby, the requirement is met that the during wheel travel almost no bump toe in occurs. In the third step the determination of the bushing stiffness takes place, such that a sufficient longitudinal elasticity with high transverse rigidity and low impact on the wheel position under the influence of force is achieved.
The wheel-individually steerable front axle of the research vehicle SpeedE
2013
17 Seiten, 18 Bilder, 5 Quellen
Aufsatz (Konferenz)
Englisch
The wheel-individually steerable front axle of the research vehicle SpeedE
Kraftfahrwesen | 2013
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