Effect of Volume Viscosity on Traction Coefficient

The effect of volume viscosity or second vicosity on the traction coefficient has been investigated. The volume viscosity has been considered to cause the compression delay of the EHL film in the traction drive and as a result to decrease the shear force or the traction coefficient, because the oil film pressure changes from atmospheric pressure to several GPa in a shorter time interval than one millisecond. The volume viscosity and traction coefficient have been measured for five synthetic oils. The volume viscosity of oil has been estimated from the absorption coefficient of an ultrasonic wave which has been determined from the relation between a detected amplitude of ultrasonic pulse and the propagation distance.

It has been found that the traction coefficient has increased as the volume viscosity has decreased. For example, dicyclohexylester with lower volume viscosity has provided a higher traction coefficient than polybutene or 5P4E, though its shear viscosity under high pressure is lower than that of polybutene or 5P4E.