Dynamic Torque Modeling of a Wet Lamella Clutch Pack

Abstract: Wet lamella clutches are used in the automotive industry to enable all-wheel drive and thereby increase acceleration, handling and safety of cars. The clutches work by transmitting torque from an incoming- to an outgoing shaft through a series of lamella - steel-disc friction surfaces (lamella pack), lubricated by an oil. Based on temperature- and wheel-speed measurements, a mathematical model of the clutch is used by the software to calculate the appropriate actuation of applied pressure to match a desired torque output. The primary goal of the thesis was to identify the dynamic behavior of the clutch in order to increase torque accuracy in the torque estimation model. This was done by first analysing previously collected data from tests in rigs and cars and thereby form two hypotheses. Hypothesis 1 was related to spline friction losses within the lamella pack and Hypothesis 2 was related to oil film reduction and an increase in friction coefficient. In an attempt to prove the hypotheses, rig tests were performed where dynamic torque responses were provoked. A novel measurement technique was introduced comprising of four thin force-measuring sensors being placed at the front and rear lamellas in the pack respectively in an attempt to measure variations of force. As some sensors were damaged during the tests it was not possible to get an absolute measurement of force, but by making relative comparisons as well as motivated assumptions, some indications related towards Hypothesis 1 could be observed. Two versions of a mathematical model assuming each lamella to be affected by a spring force, a damping force and a spline friction force acting on its body were suggested. Both of these versions were shown to increase torque accuracy on tested data.