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Reduction of the drag torque and longevity of the clutch assembly are the most important factors for vehicle transmission improvement. The decreasing trend of the drag torque with speed after its peak is a common characteristic of the clutch assembly. Several theoretical models have been presented by the researchers describing the drag torque characteristics at lower clutch speed region. However, very little study has been made on the drag torque behavior at very high clutch speed region (6000~10000+ rpm). The unwanted occurrence of drag torque jump up at high speed operating condition remains unexplained till date. In this paper, we have investigated the possible reasons of torque jump up at high rotation speed and solution to overcome this problem. We have presented an analytical correlation of torque jump up with the excessive decrease of local static pressure and assumed that vacuum formation is one of the possible reasons of high speed torque rising and associated vibration.

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.