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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 article describes the friction torque caused by pushing vanes on a cam contour and its influence on a variation of pump driving torque in a balanced vane pump. In the vane pump, the friction torque of the vane is significant to discuss a variation in the driving torque as well as an improvement in the mechanical efficiency. In this work, the influence of the thickness of a vane and the number of vanes on the friction torque of the vane and their additional effect on the variation in the pump driving torque are theoretically and experimentally investigated. The friction torque of the vane occupies a large part of the total friction torque in the vane pump and strongly depends on the number of vanes existing in a suction area as well as the thickness of the vane. The variation in the pump driving torque is composed of the variation of the ideal torque and that of the friction torque of the vane.

To overcome the shortcomings of subjective evaluation, there have been several studies to examine the correlations between subjective and objective evaluations of on-center steering feel, and some useful results are obtained. However, it is still not clear how to design the steering characteristic based on the correlations. In this paper, we propose a methodology of identifying the optimal on-center steering force characteristic based on the correlations between subjective and objective evaluations. Firstly, significant correlations between subjective and objective evaluations regarding on-center steering feel are established and verified. These verified correlations are then used to design the steering force characteristic. With desired ratings of the subjective evaluation items set as optimization goals, the ideal values of objective evaluation indices are obtained by use of an optimal design method.