A Study on Front End Auxiliary Drive(FEAD) System of 48V Mild Hybrid Engine 2018-01-0414

48V mild hybrid engine is one of major eco-friendly technology for global CO₂ reduction policy. The 48V mild hybrid engine enables to operate torque boost, recuperation and ISG status by MHSG(Mild Hybrid Starter and Generator). The FEAD(Front End Auxiliary Drive) system is a very important role to transfer MHSG power to crankshaft at the mild hybrid engine. The conventional FEAD configuration is relatively simple because it transfers power from crankshaft to auxiliary drive components in one direction. But the FEAD configuration of 48V mild hybrid engine is not simple due to bidirectional power transmission between crankshaft and MHSG. For instance, in case of torque boost mode, the tight side of auxiliary belt is entry span of MHSG. On the contrary, the tight side of auxiliary belt is exit span of MHSG at recuperation mode. As a result, to continue auxiliary belt tension constantly is very difficult and important for 48V mild hybrid engine development because the change of belt tension is very frequently.

The purpose of this paper verifies the FEAD dynamic characteristics of 48V mild hybrid engine through functionality measurement. This paper shows 48V mild hybrid system configuration for dynamometer bench test with additional 48V power supply/MHSG controller and method for FEAD functionality test. As a result of measurement, MHSG start condition is critical for FEAD dynamics. The momentary slip at MHSG pulley reaches approximately maximum 80%. To reduce the momentary slip, several tests are conducted. The results show that the engine start torque reduction or the short start time can reduce momentary slip enough. This paper also shows the pendulum tensioner behavior, slip result and belt span vibration during MHSG torque boost and recuperation condition.