2018-01-0414 Published 0 3 Apr 2018 © 2018 SAE International. All Rights Reserved.A Study on Front End Auxiliary Drive(FEAD) System of 48V Mild Hybrid Engine Kibong Yoon Hyundai Motor Company Jisoo Hong and JaeYoung Shim National Instruments Citation: Yoon, K., Hong, J., and Shim, J.Y., “A Study on Front End Auxiliary Drive(FEAD) System of 48V Mild Hybrid Engine,” SAE Technical Paper 2018-01-0414, 2018, doi:10.4271/2018-01-0414. Abstract 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 configura - tion is relatively simple because it transfers power from crank - shaft 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 function - ality 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. Introduction According to the increasingly stringent global CO2 regulations, the electrification technology of the internal combustion engine is developing rapidly. The one of notable technology is the 48V mild hybrid system. The 48V mild hybrid system is less expensive than the high voltage full hybrid system with regard to system configuration and it enables to control high power compared to the 12V mild hybrid system. One of the most important components in 48V mild hybrid system is the MHSG which adds the motor function to the generator function to generate 48V power. This MHSG enables engine torque boost and engine recupera - tion besides the start/generation function. Therefore, the 48V mild hybrid engine has two power generating sources, crank - shaft and MHSG. And the power between the MHSG and crankshaft is transmitted by FEAD system. For stable power transmission, the conventional FEAD system has several alternator pulley devices i.e. OAP, OAD and researchers have developed its advantages [ 1, 2, 3]. However, they have an insufficient performance to apply to MHSG pulley which transfers bidirectionally big power.  So, they are not suitable in 48V mild hybrid FEAD application.The application regarding combination of hydraulic tensioner and mechanical tensioner has also devised for bidi - rectional power transmission [ 1]. However, it is not easy to apply two tensioners in the same time because of FEAD layout difficulties. Recently, pendulum type tensioner has devised for supporting bidirectional tension. And it is getting popular for 48V mild hybrid application. This paper shows the FEAD dynamic characteristics of 48V mild hybrid engine on applying pendulum type tensioner through functionality measurement. And