Improved understanding of axle oil rheology effects on torque transfer efficiency and axle oil operating temperature

Effective axle oils must efficiently transfer torque from the drive-train to the wheels, while maintaining low axle oil operating temperatures. The kinematic viscosity and viscosity index of oils can affect both torque transfer efficiencies and operating temperatures. However, the optimal oil rheological properties required to maximize torque efficiency and minimize operating temperature vary with operating conditions. For example, Bala et al found that to maximize torque transfer efficiencies and minimize operating temperatures under low torque and high axle speed conditions, low viscosity fluids are preferred. Under high torque and low axle speed conditions, higher viscosity fluids are preferred. Our current studies show that fluids, which form thicker EHD films and have lower EHD friction have higher torque transfer efficiencies and lower axle oil operating temperatures. In addition, the relative effect of these physical properties on torque transfer efficiencies and operating temperatures varies with operating conditions. These findings lead to an improved understanding of the lubrication regimes under which the axle operates as axle speeds and loads are varied. This, in turn, leads to an improved understanding of the effect of axle oil rheology on torque transfer efficiencies and axle oil operating temperatures. Copyright © 2003 Society of Automotive Engineers of Japan, Inc.