Dry Clutch Micro-Slip Control and Temperature Considerations
(English)Manuscript (preprint) (Other academic)
With an automatic clutch in the powertrain it is possible to micro-slip the clutch. Micro-slip is a continuous small slip in the clutch used to isolate the driveline from the oscillations in the torque produced by a combustion engine. A control structure has been designed for a micro-slip controller. The basic components are a Linear Quadratic (LQ) controller based on a linearized driveline model and an Extended Kalman Filter (EKF) that can compensate the torque request from the LQ controller for the thermal dynamics of the clutch. To remove some stationary errors, integral action has been added to the LQ controller by adding an extra state. An anti-windup scheme is used, and the additional parameters depend on clutch conditions. The reference slip value is set according to a derived formula for the flywheel-speed-oscillation amplitude together with a dynamic safety margin that can increase during transients. Altogether the controller has a simple structure and there should be no technical problems to implement it in a production vehicle. In simulations with transient torque, unknown road grades, and a mass parameter that has been varied by a factor of 2, the controller is able to follow the slip reference without locking up. The simulations are performed on a non-linear driveline model, previously validated with data, that has been augmented with a model for the oscillative torque produced by the engine in order to more accurately describe micro-slip conditions. The torque model is a sinusoidal model and has been fitted to high resolution data. The oscillation amplitude and frequency agree well with the data. The thermal behavior of a clutch with micro slip is analyzed and the EKF should be used for temperature surveillance together with some suggested counter measures although there were no excessive temperatures during simulations of recorded driving missions. However, the simulations show that the fuel consumption increase might be too large for a heavy-duty-truck application if micro-slip control is to be used at all operating conditions. Further analysis of costs versus benefits are required on a vehicle level but the feasibility of a micro-slip control system for a dry clutch truck has been proven.
IdentifiersURN: urn:nbn:se:liu:diva-108837OAI: oai:DiVA.org:liu-108837DiVA: diva2:733163