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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 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.

This paper deals with an energy-saving electro-hydraulic power steering (EHPS) system using a center-closed servo valve without an accumulator. During non-steering operation, the pump and motor in this EHPS system operate at an extremely low speed with a low voltage. At neutral position in non-steering condition, the pump delivery flow leaks through the clearances in the hydraulic components, raising the pump pressure because the center-closed servo valve does not pass oil-flow. With a lower delivery flow rate, the pump pressure rises slightly and the motor current is also low, resulting in low electric energy consumption. When the steering wheel is turned, the pump and motor operate at a high speed and supply as much oil as needed to produce sufficient assist force. This EHPS system was tested on a conventional engine-driven vehicle with a front weight of 720kg and its effectiveness was revealed.

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.