Experimental analysis of the leakage characteristics of an oil cooled electric motor L-shaped lip seal in high-speed conditions

Over the past few years, electric vehicles have gained great popularity as a favored solution to cutdown greenhouse gas emissions. Moreover, the rise in the motor power density, as targeted in automotive roadmaps, would rely on improved machine designs, higher speeds and improved cooling solutions as direct oil cooling to extract the calories at the source improving as well the overall efficiency in operation. Nowadays, electric motors designed for vehicles exceed rotational speeds of 15 000 rpm aiming at 20 000 rpm and above. An effective solution to evacuate generated losses is direct oil cooling which requires an effective sealing solution limiting friction losses which impact the efficiency. Thus, PTFE L-shaped lip seals are commonly used to prevent oil leakage into the environment. Those seals are not only intended to retain oil in the electric motor, but they're also made to limit power losses over a wide range of rotation speed. In this work, leakage characteristics of PTFE L-shaped lip seals in different working conditions have been studied up to 15 000 rpm and compared to power losses measured directly on the motor. First, the effect of excitation time has been studied though friction torque and leakage flow rate. The results highlight a viscoelastic effect of the studied seal. In addition, oil cooling conditions, such as oil temperature or sprayed area, on seal's performance have been studied.