Development of Mount for Electric Powertrains - A Multi Degree of Freedom Optimization Approach 2020-01-0417
The recent vehicle development demands for electric powertrain as against conventional fuels engines. The electric powertrain offers advantages in terms of cleaner and quieter operations. In electric vehicle, the conventional engine is replaced by electric motor operated on batteries. Here, the conventional engine refers to those powered by diesel, petrol, CNG and some hybrid vehicles using fuel as primary source for power generation. Thus, the system design approach for mount also changes. At present, various approaches are being followed to mount electric powertrain like conventional pendulum type, with or without cradle, Common or different motor and electric box mountings etc. The electric powertrain differs from conventional powertrain in terms of weights, mass moment of inertia, torque, NVH requirements like Key in Key off, idling, low frequency vibrations etc. Thus conventional mount will not necessarily meet NVH requirements for Electric powertrains.
As electric motors are quieter compared to IC engines, the small vibration issue resulted in bigger engine presence in the passenger cabin. By proper modal placement of all major EV components, it is possible to isolate the system to avoid resonance. For the mounting of electric powertrains, the systems used are based on combustion engines and adapted exclusively for the new application. Consequently, it stands to reason that mounting systems optimized for use with combustion engines do not necessarily in line with the best solution for electric powertrains.
Depending on mounting scheme of powertrain, different degrees of freedom system modelling can be used. The 6 dof analysis provides powertrain modes decoupling which not necessarily correlate to vehicle environment. For better correlation, 16dof analysis is performed. In case of electric vehicles in addition to 16 dof, cradle dof i.e. 6 to be included to have better correlation.
In the paper various types for electric powertrain mounting has been discussed. The design approach for electric powertrain mounting presented. The case of vehicle with conventional powertrain mounting and its conversion to electric powertrain is presented. The mount stiffness optimization through multibody dynamics and HEEDS software used to predict the optimum stiffness which is correlating with actual measured NVH results.