Stress Simulation on Elements of Metal Pushing V-Belt for Fatigue on CVT at Start-Up

As the demand for improved automotive environmental performance increases, manufacturers are focusing on the CVT as a transmission type enabling the achievement of a balance between driving performance and fuel efficiency. In terms of driving performance, CVT offers quietness and smooth acceleration without shift shock. Given this, the requirement to extend the transmission capacity of CVT will increase in future. From the perspective of the maximum input torque that is transmitted to the drive train, the most severe demands are made on the CVT at start-up operation. The pulleys and metal pushing V-belt of a CVT with a torque converter are subjected to a sudden rapid increase in pulley thrust from a stationary state, and are required to transmit maximum torque with minimal time lag. The most important consideration at this time is the dynamic strength of the metal pushing V-belt. Dynamic strength cannot be determined simply from the maximum input torque, but must be determined in relation to the shift ratio, pulley piston pressure as well as the rated speed in time history. This paper reports on research that has succeeded, using a new simulation, in clarifying the stress history on the element neck under transient operating condition at CVT start-up. These results suggest that the compression stress generated by the load on the V surface is a fundamental component of element stress, and that bending stress generated by the pushing force between the elements is superimposed on this stress. A comparison of simulation results with test results for the load distribution on the element, conducted to confirm the accuracy of the simulation, demonstrated good qualitative correlation. This paper also discusses the method used to evaluate dynamic strength in response to transient stress and the application to a variety of vehicle start-up conditions to make it possible to determine operating conditions by considering the dynamic strength of the belt.