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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 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.

In recent years, higher performance of motorcycles has been attained through improvements in engine performance and rigidity of frames etc., and there is now increasing demand for a more efficient suspension which gives better ride and handling stability. In many of the conventional motorcycles, the rear suspension supported the rear body on both sides of the rear wheel by means of two suspension units. However, such two-unit-type suspension is presently being replaced by a single-unit-type suspension called a “mono shock” which is mounted on the central part of the body with a view to concentrating the body mass and also to lowering the gravity center of the motorcycle. Such change in the mounting location of the suspension unit greatly affects the operation of the suspension unit. For example, the ratio of displacement of the suspension unit to that of the axle is reduced to 0.3 - 0.5 from the previous ratio of about 1.