Lubrication Evaluation of EV Transmission

Advent of EV powertrain has considerable effect on transmission development activities as competed to regular ICE transmission. Conventional ICE transmission and the transmission for an e-powertrain differ on fundamental level. The conventional transmission has number of gear ratios, shift mechanism which enables the transmission to deliver a smooth power output as per demand from the driver. Whereas the e-powertrain transmission is mostly a single gear ratio transmission (reducer) which primarily depends on speed and torque variation from the motor to cater the driver requirement. Hence, the operating speeds of such e-transmissions can vary from 0 to 20000 rpm in both forward and reverse directions. Such a large speed variation as compared with conventional transmission calls for special attention towards the lubrication of internal components. High speeds and lower oil viscosities tend to disrupt the oil films in between contact surfaces causing metal to metal contact. This situation aggravates the wear and tear of the mechanical components such as gears, bearings etc. This paper describes the test methodology developed to ensure and evaluate the lubrication performance of the transmission. This paper takes into account the various operating conditions in terms of temperature, gradient, direction of rotation, loading conditions to derive test conditions. Paper also gives details of trials carried out on e-transmission to arrive at optimum lubricating oil quantity for performance and durability. The methodology described in this paper can be used for single and multispeed EV transmission.