Computational Investigation of Friction Coefficient Effects on the Contact Mechanics Between Dynamic Seal and Motor Shaft in Electric Vehicles (EVs)

Abstract

As most countries tend to rely on green energy, electric vehicles (EVs) are increasing in usage. However, friction losses within them are major issues, reducing their energy efficiency. Main cause of these losses is the movement of the mechanical components. E-axle is one of such components, which is a drive unit consisting of an inverter, an electric motor, and a gearbox. A 4% of the total losses is exhibited by E-axle due to the mechanical interaction of its elements. Dynamic seals are one set of such elements, which exist between electric motor and gearbox, and their main roles are to prevent fluid leakage and to keep contaminants out. These sealing elements are attached to the motor shaft, thus generating a friction. Enhancing the tribological behaviour of dynamic seals is one effective method to reduce the friction loss. Considering materials that have low friction coefficients to make a dynamic seal contributes to improves the tribological and operational sealing performance. Such these materials are Polytetrafluoroethylene (PTFE), Polyimide (PI) and Polyetheretherketone (PEEK). Based on the research, PTFE exhibits the lowest friction coefficient, 0.038. A finite element (FE) simulation using Abaqus was done to investigate the three materials effects on the contact mechanics between the seal and the shaft. The most significant findings are the maximum contact pressures, which are 96.13, 244.8 and 269.7 MPa for PTFE, PI and PEEK, respectively. It can be noticed, PTFE is much lower than PI and PEEK regarding the contact pressure due to its minimal friction coefficient and low Young’s Modulus, which is 400 MPa. Furthermore, PTFE contains other key features that are desired inside E-axle. Such these features are the high and low service temperatures, 250 C and -268 C, and the high speed. With the merits stated, PTFE is suggested to be the most suitable material of a dynamic seal inside E-axle. Regarding the limitations of the project, the design of seal edges can be modified by obtaining specific dimensions to obtain accurate results. Also, the surfaces of both seal and shaft can be enhanced by considering the roughness/asperities to simulate the reality.