Pushbelt CVT Efficiency Improvement Potential of Servo-electromechanical Actuation and Slip Control

By using the ability to shift to high overdrive ratios, a CVT equipped vehicle can outperform the fuel economy of its counterpart with conventional automatic transmission. A further signi cant reduction of fuel consumption can be obtained by reducing transmission power loss. The main sources of power loss are well known to be losses inside the V-belt variator and losses caused by driving the hydraulic pump. Signi - cant reduction of these losses will increase the attractiveness of the V-belt type CVT.

This paper rst analyses the most important loss contributions present in a reference transmission and how they depend on actuation and control properties, like pump driving power, over-clamping and variator slip. Based on this analysis, actuation and control improvements will be proposed. The effciency increase is presented, that can be expected when the hydraulic pump is replaced by a servo-electromechanical actuation system, and when variator slip control is introduced. The effciency benefit is shown to be substantial, especially at part load conditions. At 25 % of rated load the CVT losses are halved, whereas at full load, a reduction of 25 % can be expected.

The proposed servo-electromechanical actuation system is currently in the realization phase, as well as the slip control technique. Experimental results will be reported on when available.