Applicatin of a half-toroidal continuously variable transmission to an electric-vehicle drive-train and visualization of air-bubble behavior in the traction contact

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This research is a challenge of getting maximum acceleration of an electric vehicle with minimum electric power by applying a mechanically variable power-transmission. A half-toroidal continuously variable power transmission, CVT,has features of quick speed-ratio changing and quietness, which suits quick response for braking-energy recovery and high acceleration at starting. In this research, a new type of CVT is designed, manufactured and applied to an electric vehicle with 2.2 kw motor. (1) The performance test-result of the CVT is speed-transmission efficiency of 98%, torque-transmission of 78% at rotational speed of 1500 rpm and torque range of 10 to 40 N・m in the speed-ratio range of 0.4 to 2.5. The main loss of torque is caused by a pair of thrust ball bearings for supporting the transmitting torque, which is predicted by the theoretical analysis. (2) Next the vehicle performance tests clarify that the maximum electric power-duration of 200A,36V at starting is reduced by 20% and the maximum speed is increased to 40km/h from 20km/h by the equipment of the CVT.On the basic research of traction fluid, it is succeeded to visualize small bubble behavior running into thin film gap by using the high speed video-camera. Primary stream of small bubbles is avoiding the gap but 10% of them go through the gap by deforming their shape. It will be a reason of the flash temperature rise at high Hertzian pressure contact for which it is sometimes experienced at high temperature due to lack of bubble erasing capability of traction fluid.