Analysis of the Judder Stability of an Automatic Transmission Damper Clutch

In an automatic transmission vehicle, a torque converter is installed to reduce engine torque fluctuation and to improve the vehicle's drivability and durability of drive system. In most operating conditions except starting and shifting, the damper clutch is engaged to enhance fuel economy. However, in response to the increasing demand for fuel economy, damper clutch engagement is required at a low gear step or the engagement force margin is reduced. Frequent lock-up and abnormal vibrations increase the slip of the friction surface, generating excessive heat. The friction coefficient consequently becomes small, which further exacerbates the slip phenomenon. In this study, the effect of the reduced friction coefficient due to the deterioration of the damper clutch on the stability of the judder is analyzed in terms of vehicle dynamics and vibrations. A method for early detection of judder stability degradation due to damper clutch deterioration is also described.