Dynamic characteristics analysis of lock-up clutch of automotive torque converter

Abstract

The torque converter is a kind of fluid coupling that is widely used as a start-up device for automobiles equipped with an automatic transmission. A lock-up clutch is often incorporated in the torque converter in order to improve vehicle fuel economy in the higher speed ratio range. This improvement is obtained because the lock-up clutch can reduce fluid losses by engaging the input and output shafts to rotate at relative speeds with only a small amount of slip. Operation of the lock-up clutch is controlled mainly by supply and discharge oil pressure of the torque converter. The purpose of this study was to better understand clutch behavior under the influence of oil flow. Flow through the lock-up clutch was computed by using a commercial CFD code at three speed ratios of 0.8, 1.0 and 1.2 under the prescribed supply and discharge oil pressure sequence. Unsteady computations were conducted under the assumption that the flow was weakly coupled with the solid mass motion. Quasi-steady computations were also conducted under the assumption that a dynamically equilibrium state was maintained when the clutch moved. The results showed that the response time of the lock-up clutch increased with a higher speed ratio and that flow through the clutch changed directions from outward to inward in the engagement process in all cases. The computed response time coincided reasonably well with the experimental data obtained with the actual machine. It was also found that the quasi-steady analysis results showed an unreasonable or meaningless tendency regarding the response time.