Engine Mounting System Design Approach for Electric Vehicles 2019-26-0116
As we are moving towards complete electrification from combustion engine to electric motor, the system design approach also changes due to application. For a range of 100-150 kg EV powertrain weight, number of mounts as well as mount locations, orientations and stiffnesses plays a significant role during system design. The electric powertrains are usually lighter and their mounts are usually stiffer than the mounts for typical combustion engines, the static displacements at dead load are usually lower. However, currently it seems like there is no common direction of all OEM’s regarding the question of how stiff an e-motor mounting system should actually be. Due to the high torque of the EV’s one could even think about switching to a four point mounting instead of a pendulum mounting. That is actually something we observe in some benchmarks - that (modified) pendulum systems are used mainly for e-motors, which share a common vehicle platform with combustions engines, but if a vehicle is developed exclusively for electric drive, then the mounting system is a three or four point system with bush type mounts in most cases.
As E-motors provide vibration & noise excitation particularly in high frequency range (up to several kHz), a low dynamic hardening is beneficial. The methodology of decoupling and separating the powertrain rigid body modes is the same. However, the targets for modal alignment should be adjusted, as idle isolation is not required anymore, because there is no idle excitation with electric powertrains. That is also the reason why a mounting system for an electric powertrain can be much stiffer than the mounting system for a combustion engine, which has positive effects for engine shake and helps to control the high torque and quick torque changes of e-motors.
In addition, as there is no clutch anymore, the influence of the drive shafts on the powertrain eigen modes should be considered if possible. In the paper various configuration with generic system design approaches for EV engine mounting system have been presented along with a case study with three point mounting system.