A differential unit of a vehicle is one of the important devices of a power transmission system that drives a vehicle by transmitting the output of an electric motor through an engine or a reducer through a transmission to wheels. When the vehicle turns left and right, the output is appropriately transmitted to both wheels. Generally, in the case of an EV system, The differential system consists of a ring gear to which the output torque of the motor is transmitted, a pinion gear inside, a set of side gears and a differential case supporting the same, and a differential pinion shaft serving as a guide for the pinion gear .In order to drive the wheels of the vehicle with motor torque, the torque is increased through the reducer gear train system of the EV system, resulting in a high torque overall in the differential gear system. Therefore, it is considered important to evaluate the durability of the differential gear system due to the high torque. Before the durability test evaluation, a preliminary review through structural analysis is important. It is difficult to apply the durability test mode of torque fluctuation over time and model configuration in assembly unit, which makes it difficult to analyze and evaluate. In order to cope with the recent failure of the differential gear system in the EV decelerator, the correlation of stress analysis was verified by measuring stress in the torsional rig test using a strain gauge. Through this, the influence of important design factors was identified, and a fatigue durability analysis technique reflecting the durability test mode was established. A fatigue durability analysis procedure was constructed in consideration of the torque-rotation number-cycle, and the breakage phenomenon was reproduced through a damage evaluation for each test mode. Based on the established procedure, the criteria for establishing and evaluating the fatigue safety factor DB for each model were selected, and the system specifications of the new platform under development were selected through prior analysis and reflected in the production design.

Mr. SANGWOO CHA, Research engineer, Hyundai motors company