Observer-based identification of nonlinear clutch friction under operating conditions

This article presents a detailled description of the industrial application of a Proportional-Integral-(PI-)observer for identification of the dry friction in a torsion damper utilized in a vehicle clutch. The identification of the friction characteristics are performed on the basis of powertrain oscillation measurements that are recorded during vehicle operation. The available measurement instrumentation is limited to angular velocity sensors, providing measurements from the engine flywheel, the transmission inputshaft and the front wheels. The clutch friction torque is calculated from the measured angular motion of the transmission and the torque balance about the transmission inertia. These torques are not measured directly, but are estimated by an observer containing a model of the powertrain. The plant model and the observer are described in detail in this contribution. Furthermore, a method is explained which is used to extract the dry friction component from the identified effective torque, which acts on the transmission input shaft. The restrictions for the presented task are limited test time, a limited measurement setup and the lack of opportunity to dismount the test specimens for measurements on test rigs. Under these boundary conditions, the concept of PI-observer in conjunction with the mathematical treatment of the observed system states and external inputs has produced identification results of adequate accuracy.