SAE International Innovative Self-optimising Clamping Force Strategy for the Pushbelt CVT 2009-01-1537

The efficiency of continuously variable transmissions (CVT) based on the pushbelt principle is dominated by oil pump and variator losses that are directly related to the clamping force between the belt and pulleys. Currently applied safety strategies lead to relatively high forces that prevent destructive slip under all conditions. Recently, vehicle tests have shown that a large efficiency increase and significant fuel savings can be reached when the variator is operated close to the slip limit [ 1 ]. This paper describes the theory and realization of a self-optimizing control algorithm that is based on the transfer behavior of the variator in which slip and other effects play a role. The new algorithm does not need a given setpoint and so keeps the control simple and robust. It controls the clamping force to low values under both static and dynamic conditions without requiring additional or adapted hardware. The new algorithm enables an accelerated introduction of new CVT controller technology to the market and will help the CVT to maintain its forefront position on fuel consumption.