Adaptive Transfer Case Clutch Touchpoint Estimation With a Modified Friction Model

Abstract

The clutch touchpoint of an automotive transfer case is a key parameter for accurate clutch torque control, which varies over time due to clutch wear, clutch plate temperature change, and clutch actuation system part-to-part variation. Typically, the touchpoint displacement is unknown and needs to be estimated online. This article, based on the clutch actuation system model, proposes an adaptive scheme using normalized gradient method to estimate the clutch touchpoint in real time. The proposed algorithm uses only the motor control voltage of the clutch actuator and measured cam position while the clutch is engaged. Simulation studies reveal that clutch actuation system friction plays an important role, leading to the investigation of multiple friction models. Among the Coulomb friction, Stribeck friction and proposed modified general kinetic friction (MGKF) models, the MGKF is proved to be the best in describing the friction in the clutch actuation system. Multiple experimental datasets from proving ground and general driving cycle tests are used to validate the effectiveness of the proposed scheme with the MGKF model. In addition, the proposed adaptive estimation results are compared with that of existing direct-detection method (based on the sudden change in clutch torque or wheel speed), showing improved accuracy and robustness.