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. Qualitative and quantitative analysis of the contact surfaces, including optical micrographs, SEM, 3D areal surface profile data and metallurgical analysis before and after test has been carried out. The influence of the dominant parameters on the fatigue durability and wear rate of a real IVT variator, operating under unfavourable conditions in terms of fatigue, have been investigated and the failure modes observed and described. Solutions to the premature failure mode have been developed and tested such that the IVT variator durability life is optimised. The main conclusions are: 1. Providing suitable surface roughness (Ra) is chosen for the variator disc and rollers the premature surface distress failure mode can be avoided. Failure is then due to the classical sub-surface initiated spalling fatigue. In this case, typical gear and bearing life durability models are applicable to the IVT variator traction drive contacts. 2. The introduction of compressive residual stresses over that normally associated with grinding and lapping prevents the formation of surface cracks. These cracks are the only failure mode that is not similar in nature to that seen in bearing and gear contacts. 3. Suitably manufactured and heat treated through, hardened KUJ7 material shows excellent durability life with no microstructural changes or decrease in hardness after the tests. 4. The areal surface topography wear measurement results show that wear in the IVT variator is not a concern despite the relatively low Lambda values obtained from the composite component surface roughness and EHL calculated minimum film thickness.
Developing the durability of a dual-cavity full-toroidal IVT variator
Entwicklung zur Dauerhaltbarkeit eines toroidalen IVT-Variators mit Doppelhohlraum
2002
9 Seiten, 14 Bilder, 4 Tabellen, 17 Quellen
Conference paper
English
Developing the Durability of a Dual-Cavity Full-Toroidal IVT Variator
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