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This article describes cavitation in a hydraulic disk valve to control an inlet pressure by changing a valve opening at a constant flow rate and an outlet pressure. In the hydraulic system, because the cavitation occurs often and causes an unpleasant noise as well as an instability in pressure-flow control, the cavitation avoidance is important. Hence, for cavitation avoidance under a high pressure condition, the influences of the specifications of the disk and nozzle as well as operating conditions on the cavitation and the inlet pressure change against the valve opening are experimentally investigated. Under a constant flow rate and an outlet pressure, the inlet pressure rises and the cavitation appears when the valve opening decreases. By decreasing the valve opening more, however, the cavitation disappears despite a rise in the inlet pressure. In addition, the round edge at the nozzle outlet is effective in avoiding the cavitation.

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.

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.