A model and simulation results are presented for the torsional dynamics of a rear wheel driveline while the vehicle is coasting in a turn. The model includes the effects of road load and powertrain drag, limited slip differential clutch friction, the inertias of the vehicle, wheels, axles, differential carrier, and driveshaft, the final drive ratio, torsional stiffnesses of the axles and driveshaft, vehicle track width, and radius of the turn. The dynamics of coasting in a turn differ from powered driving due to changes in the inertia loading the driveshaft, the damping effect of the disengaged transmission, and nonlinearities in the clutch friction.
Specific focus is given to vibration in the axles and driveshaft due to variations in the torque-speed slope of the clutches, which is determined by the slope of the friction coefficient ‘μ’ versus sliding speed ‘v’ in the limited slip clutches. The clutch μ-v slope is strongly influenced by the lubricant in the differential and understanding its effect on driveline vibration will help in the development of future lubricants.
Three cases are presented: (1) two clutches with the same static breakaway torque and positive torque-speed slopes, (2) one clutch with a lower breakaway torque and zero torque-speed slope, and (3) one clutch with a lower breakaway torque and negative torque-speed slope.
