Analysis of abnormal vibration phenomena by a lock-up clutch operating in an automatic transmission systems

A lock-up clutch system has been widely adapted to the modern automatic transmission vehicles for reducing fuel consumption and improving efficiency of powertrain system. However, abnormal vibrations such as slip shudder and surge might be happened by a lock-up clutch operating at low engine speed. In this paper, we designed a simulation program which includes an engine, a torque converter, a lock-up clutch and a transmission, based on the dynamic equations of vehicle system. In order to investigate the effect of a lock-up clutch operation, fuel economy of a vehicle with a slip controlled lock-up system was compared to that with an only lock-up control in a low gear shift. This paper focused on an abnormal vibration by a lock-up clutch operating in the unstable regions of the engine performance curve. To analyze the abnormal vibrations in the powertrain, we carried out simulations for several driving conditions according to unstable regions of engine performance curve. The results of simulation depicted that the abnormal vibrations in the powertrain occur more severely in the unstable regions of engine as compared to stable regions.