Experimental Validation of Full Toroidal Fatigue Life

Whilst infinitely variable traction drive transmissions (IVT) have demonstrated the potential to provide significant fuel economy benefits through the optimisation of the vehicle powertrain, greater emphasis is now being placed on reducing the overall package size. The inevitable increase in power density places increased demands on the variator elements to withstand the heavily loaded rolling contact conditions.

Described in this paper are the results of an experimental fatigue test program undertaken to establish the fatigue life of the variator rolling contacts when operating with the latest traction fluids. The experimental work utilised a number of full scale variator durability test rigs: all tests were conducted with real transmission contact operating conditions up to 220kW. Qualitative and quantitative analysis of the contact surfaces, including SEM, 3D area surface profile data and metallurgical analysis has been carried out. The fatigue results have enabled the interaction between the variator material and traction fluid to be optimised resulting in a ten fold increase in component life and consequently a significant reduction in variator size.