Practical toroidal-type continuously variable transmissions (CVT) is subject to extremely severe operating conditions, namely, maximum contact pressure is very high at 3 GPa or higher, rolling speed exceeds over 30 m/s and lubricant temperature goes up over 120℃. The objective of this research is to grasp the traction characteristics of extremely severe EHL contact conditions The phase diagram of a synthetic traction oil to 2 GPa was first made up by high pressure density measurements and others. The bulk modulus and the shear modulus of a traction oil at quasi-static condition were evaluated using a phase diagram. The results indicated that the bulk modulus, shear modulus and limiting shear stress of oil are closely related to the oil molecular packing parameter T{sub}(VE)-T (T{sub}(VE): viscoelastic solid transition temperature, T: oil temperature). Next, the LHL traction of a traction oil was measured by the two disc machine and the four disc machine. The results indicated that the maximum traction coefficient is closely related to T{sub}(VE)-T, also. It was verified that the traction characteristics of extremely severe conditions were also based on the phase diagram of traction oil.
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