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This article describes a design method for improving the mechanical efficiency in a small vane pump, which is driven by an electric motor with a battery for a conventional vehicle. An aim of designing is a decrease in friction torque without decreasing the volumetric efficiency. The influence of two important factors concerning the friction torque, i.e. the dimensions of pump parts such as a cam ring, a rotor and a vane, and the coefficient of friction between the cam contour and the vane tip on the mechanical efficiency is clarified in two stages. In the experimental analysis, the coefficient of friction between the vane and the cam contour in the actual pumps is estimated and the influence of the pump-operating conditions such as oil temperature is also investigated. Furthermore, the relationship between the coefficient of friction and the mechanical efficiency is demonstrated.

This paper deals with an advanced electro-hydraulic power steering (EHPS) system compactly integrating a hydraulic pump with an electric motor, a steering gearbox with a center-closed servo valve and an accumulator. In this EHPS system, the hydraulic pump with an electronically controlled motor works only during steering operation. Stopping the hydraulic pump during non-steering operation is extremely effective for reducing energy consumption in power steering because steering operations are infrequent. The EHPS system described in this paper is suitable for pollution free vehicles such as electric vehicle having no engine-driven accessories and has the advantages of reduced power consumption and ease of installation. This EHPS system may be also used for engine-driven vehicles and has been tested on a conventional gasoline engine vehicle with an 810 kg front weight. Test results demonstrate its effectiveness.