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This paper deals with a mathematical analysis of pump efficiencies in an internal gear and balanced vane pumps. They are commonly used in current automatic transmissions including a continuously variable transmission. For these pumps, the influence of oil temperature as well as pump-operating pressures and pump speeds is clarified by using mathematical models taking oil temperature into consideration, which are constructed on the basis of actual measured flow and torque data under various pump-operating conditions. For fuel economy in a vehicle, because the pump should be operated under conditions to obtain higher pump efficiencies, it is very important to understand the relationship between the pump efficiencies and the pump-operating conditions.

This paper deals with energy-saving and its thermal advantage in a hydraulic power steering system. Currently, hydraulic power steering systems are commonly used for passenger cars, and reduction of the driving energy of the pump under non-steering condition is important for energy-savings of the system to improve fuel economy. This paper describes a newly designed energy-saving pump and its experimental results. The energy-saving pump has lower driving torque with the advantage of lower heat generation in the power steering system. In addition, relationships between the pump driving energy and oil temperature in the system are analyzed for the basis of the mathematical model, which accurately predicts the pump driving torque.