Transitioning from IC Engine to Electric Vehicle: An Optimized Wheel End Solution 2020-01-1632
This paper discusses the change in vehicle parameters when moving from a conventional internal combustion engine (ICE) to an electric motor. In particular, the paper discusses the impact on the wheel end bearings, which must handle higher GAWRs (gross axle weight ratings) at lower center of gravity heights on electric vehicles. These changes require bearings to handle higher loads. Typically, larger loads increase the bearing size and with it, the mounting interface dimensions for auxiliary components. In this paper, The Timken Company demonstrates an alternative bearing design that can handle higher electric vehicle GAWRs but allows for continuity in the surrounding brake corner components - potentially saving OEMs significant design costs and delays. This solution focuses on the mid- and large-size SUV market where bearing capacity could be a limiting factor for electric vehicle variants - driving significant wheel end brake corner design changes to accommodate the larger bearings.
The paper also looks at the effects of different vehicle parameters between internal combustion engines and electric vehicles, showing the major influencing factor is the GAWR. Further, the analysis evaluates the different bearing design load capacities and their performance under a USA duty cycle, including bearing life, torque and stiffness. This analysis shows that an existing design upgraded to meet the electric vehicle GAWR changes the envelope dimensions and increases the weight by 40%, an additional 1.8 kg per wheel end. However, with the new design, the bearing dimensions can be maintained, resulting in a similar weight and reaching the same bearing life under electric vehicle GAWRs with similar torques and higher expected stiffness. The analysis includes an FEA to evaluate the structural robustness of the wheel hub flange under elevated cornering loads and high stress areas identified in both the shaft inner bearing seat and rotor pilot radii.
In a secondary case study, a downsized optimized solution is also presented to address vehicle handling and performance under the current IC engine vehicle GAWR. The analysis shows that the design meets the USA duty cycle bearing life standards and exceeds the existing conventional design with a 20% weight reduction (equating to a 0.85 kg reduction per wheel end).