Mahmud, S., Pahlovy, S., Kubota, M., Ogawa, M. et al., "A Simulation Model for Predicting High Speed Torque Jump Up Phenomena of Disengaged Transmission Wet Clutch," SAE Technical Paper 2017-01-1139, 2017, doi:10.4271/2017-01-1139.
Reduction of drag torque is a crucial demand for improvement of transmission efficiency and fuel economy. In the low speed range, the drag torque at first increases with speed until it reaches a peak point, and then it starts decreasing sharply and finally stays at a minimum level until certain speed limit. Several analytical and simulation models have been presented by the researchers describing the drag torque characteristics at lower clutch speed. However, under certain conditions, the drag torque again starts to rise sharply in the high speed range (6000~10000+ rpm) and even exceeds the peak torque magnitude of low speed. The alarming jump of the drag torque at high rotational speed remains indeterminate to date. In this paper, we presented a simulation model that can predict the high speed torque jump up at different conditions. Simulation result shows that the static pressure decreases very sharply in the oil outlet region as the speed rises beyond 5000 rpm. We assumed that the sharp decrease of the static pressure gives rise to substantial vacuum force that draws the separator plates close to each other and as a result drag torque starts increasing. The separator plate will move to a new position such that the static pressure is increased sufficiently and vacuum force is no longer active. From the simulation we predicted the possible conditions at which torque jump up may occur and compared with test results. Simulation results show good agreement with the test results. Simulation is conducted for both no groove and grooved disks. It is found that torque jump up effect is more prominent in grooved disks compared to no grooved disks. As a whole, from our simulation model, we can predict the high speed torque jump up phenomena and also estimate possible solutions to control this problem.