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An infinitely variable traction drive transmission (IVT) has the potential to provide significant improvements in fuel economy, tailpipe emissions and driveability compared to conventional automotive transmissions. Recent developments in rolling contact materials and manufacturing methods have increased the ability of the variator elements to withstand the high Hertzian contact pressure, temperature and tangential shear force. Described in this paper are the results of an experimental study of the main factors influencing the spalling and surface distress fatigue life and surface texture modification of the variator elements. The experimental work utilised a number of full scale variator durability test rigs, all tests were conducted with realistic contact geometry and operating conditions.

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.

Full-toroidal traction drives (IVT, TCVT & TVAD) have demonstrated a significant fuel economy, emissions and cost benefits across a diverse range of applications. However, increasing emphasis is being placed on power density and endurance limits, hence additional demands are being placed on the ability of the variator elements and traction fluid to withstand the heavily loaded rolling contact fatigue conditions within the variator. This paper describes the experimental work done to demonstrate the high temperature durability of traction fluid and variator disc and roller material. In addition, the latest fatigue endurance limit testing results are presented which provide further evidence of traction fluid ‘fill for life’

A full-toroidal CVT has been expected as a new generation of transmission. However, high contact pressure is needed to generate traction force and temperature due to shear in contact areas becomes very high. Therefore, the fatigue life of variator is insufficient. This paper describes the application of developed bearing steel to improve the fatigue life of the varitator. Failure due to pitting depends on a film parameter Λ so that the limitation of Λ to prevent failure has been determined by a two roller test machine. Durability test of the variator made of developed bearing steel with the larger Λ than the limitation has been carried out to confirm the prevention of pitting by a dual-cavity full-toroidal CVT's variator test rig. The thickness of EHD (Elastohydrodynamic) fluid film has also been calculated by isothermal Newtonian EHD analysis with spin motion to confirm whether adequate film thickness is provided to avoid failure.