Oil temperature influence on friction torque characteristics in hydraulic pumps

Abstract

This article presents a practical approach to the investigation of the influence of oil temperature on the friction torque in various types of hydraulic pumps using a mathematical model. Currently, an external gear, an internal gear or a vane pump is commonly used for an automatic transmission. These pumps have their own friction torque characteristics, which depend not only on pump-operating conditions such as operating pressures, pump speeds and oil temperature but also on structures and dimensions of the pumps. For various pumps, however, the friction torque characteristics can be represented by an identical mathematical model. In the pump-operating conditions, the oil temperature significantly and complicatedly affects them. The pump should be operated under conditions to obtain a higher mechanical efficiency, and the mathematical model is helpful to analyse how the oil temperature influences the friction torque. It is found that with an increase in oil temperature, the friction torque at a high pump speed decreases in a low oil temperature region, but it would not decrease in a high oil temperature region for all the tested pumps. This fact suggests that the pump overall efficiency would not improve at a high oil temperature, even if the volumetric efficiency does not go down.