Ralf Stroph

Vehicle Dynamics per Software – Potentials of an Electric Single Wheel Drive

This paper outlines the advantages of drive train architectures which allow free distribution of wheel torques on the rear wheel axle, so-called torque vectoring, with respect to driving dynamics. Electric cars open up new possibilities with regard to vehicle architectures. Utilization of the new degrees of freedom might lead to architectures with rear wheel drive and high rear axle loads. For conventional cars without counteractive measures, e.g. mixed tires, this would inevitably lead to inappropriate driving behavior. It is shown that such boundaries are no longer valid for electric cars with high rear axle load in com-bination with rear wheel drive and torque vectoring.

Single wheel drives for wheel slip control

Ever-increasing electrification of the drive train offers new possibilities for the power train layouts as well as for vehicle dynamics control. For a single-wheel driven electric vehicle, one should utilize the advantages of the electric engines compared to conventional components. Within this contribution, an optimized arrangement regarding installation space of the drive train with single rear wheel drive was investigated. The electric motors were used for acceleration and deceleration, hence regenerative braking. Often, for brake situations with excessive wheel slip, electric engines are switched off and conventional components as the hydraulic wheel brakes are used to control the wheel speed. A control scheme for a rear-wheel driven electric vehicle with single wheel drives is presented, where only the rear engines and no friction brakes are used for all driving and braking torques. The effectiveness of the proposed control scheme has been proven in real vehicle tests for acceleration as well as for braking situations on low friction coefficient surface (snow).

Potential of elastodynamic analysis for robust suspension design in the early development stage

In the chassis development process, requirements for each subsystem are deduced from complete vehicle targets regarding safety, ride comfort and driving dynamics. After the design of individual components, they are integrated into respective subsystems resulting in a complete vehicle. Late modifications in the development process after vehicle testing resulting from insufficient quality of simulations (e.g. because of disregarded effects or parameter uncertainties) and unnecessary target conflicts (e.g. regarding package) due to disregarded solution spaces lead to increasing development costs and time. Chassis development is focused on the design and optimization of the suspension system. Characteristic values calculated from kinematics and compliance are in the center of interest and play a decisive role in evaluating chassis performance. Interactions with the steering system are partially modeled with reduced complexity or not considered at all. This paper deals with a newly developed approach to evaluate suspension systems considering steering properties without a complete vehicle. For this purpose, analysis of a complete front suspension system including steering system is carried out using multi-body simulation. The suspension model comprehends kinematic and compliant properties. The steering system is modeled with relevant elasticities as well as speed-dependent steering assistance. Stiffness properties of the suspension system, including steering system, are studied using the compliance matrix of the suspension system. The focus is on the analysis of the compliant steering axis by means of the compliance matrix method in comparison to the kinematic steering axis. The proposed method is also used to calculate corresponding characteristic values for the suspension system. These are analyzed for relevant load cases. The objective is to gain further insights into suspension design to characterize and eventually optimize suspension performance in the early development stage. Therefore, respective interactions between the individual subsystems (suspension and steering system) and their components are analyzed. Their corresponding influences on the overall system are quantified. The advantage of considering compliant effects and the mentioned interactions for robust suspension design is shown.

The consequences of a closed rim design for the brakes of a high-efficiency vehicle

Highly efficient and especially electrified passenger vehicles labor to expand the CO2 reduction or driving range through many measures. One significant factor is the optimization of the aerodynamics. The wheel rim design of a vehicle has a noticeable impact on the drag coefficient (cd) of a passenger vehicle.