F2008-12-076
Stress Simulation on Elements of Metal Pushing V-Belt for Fatigue Strength Under Transient Operating Conditions
ABSTRACT - 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, while the use of cooperative control between the CVT and the engine to maintain engine speed in the range of highest fuel efficiency results in a level of fuel economy unmatched by AT. 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. However, almost none has looked at the dynamic strength of the belt itself. This is because it has generally proved difficult to measure the dynamic behaviour of the belt and stress on the elements. Previous research focused on the dynamic stress produced in the multi-layered rings when a metal pushing V-belt is in operation, and developed a technology that simulates the motion of the belt in steady state rotation. The effect of the deflection rigidity of the pulley on ring stress has also been studied. In addition, a method of calculating the detailed stress on individual elements using the element contact pressure obtained from simulations of the dynamic behaviour of the belt has been developed, and the distribution of element stress across the belt as a whole has been clarified. 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.
Session: Durability, Reliability, Materials