Comfort and safety enhancement of passenger vehicles with in-wheel motors

Volatile oil prices and increased environmental sensitivity together with political concerns have moved the attention of governments, automobile manufacturers and customers to alternative power trains. From the actual point of view the most promising concepts for future passenger cars are based on the conversion of electrical into mechanical energy. In-wheel motors are an interesting concept towards vehicle electrification that provides also high potentials to improve vehicle dynamics and handling. Nevertheless in-wheel motors increase the unsprung mass worsening vehicle comfort and safety. The paper analyses potentials and limitations of innovative passive concepts as well as of new mechatronic suspension systems in order to assure appropriate levels of vehicle comfort and safety when using in-wheel motors with different torque requirements. To reach the mentioned objective, the weight of synchronous and asynchronous electric motors is computed for different torque requirements. The calculation is done by a computer program designed in the frame of an interdisciplinary research project concerning electrical drives for vehicle applications. Furthermore, an overview of the different magnitudes and parameters proposed in international standards to assess safety and comfort (e.g. ISO 2631-1997 and BS 6841-1987) is presented and possible excitation signals to be used are analyzed. The selection of reasonable evaluation parameters is based on measured data of a vehicle with increased unsprung masses and on simulation models. Afterwards, selected innovative passive systems as well as new mechatronic systems with different complexity levels are compared. The comfort and safety characteristics of a vehicle with conventional power train serve as reference. The comparison is made without considering changes on axle kinematics. The paper aims at getting a relation between the different analyzed systems and the torque requirements of in-wheel motors. This relation can be used to select the suitable suspension system necessary to assure the desired comfort and safety behavior of a certain passenger car while satisfying the required driving performance.