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We have developed a high capacity electromagnetic clutch by means of Si-containing diamond-like carbon (DLC-Si) coating. The durability of the new clutch is enhanced up to 8 times higher than that of the conventional one. Such a superior performance is due to several tribological properties of the DLC-Si film and micro morphology on the clutch surface. In particular, the DLC-Si plays a significant role in maintaining the groove shape of the clutch and giving sufficient friction in fluid, which is required for a drivetrain device. Besides, our deposition process (using direct current plasma-assisted chemical vapor deposition) has afforded homogeneous DLC-Si-coated clutches in large quantities. These techniques have enabled us to reduce the number of clutch discs per coupling and achieve a more compact and higher capacity AWD coupling at a lower cost.

A mathematical model for a hydraulic power steering system was constructed and numerical analysis was performed for self-excited vibration caused by rapid steering in the power steering system. From the examination, the guide of the prevention against the vibration was derived, such as positioning the rather long hose at near the power steering gear in the supply line, and the mechanism of the prevention was clarified. Moreover, the mathematical model and the guide of the prevention were verified by bench tests.

This paper deals with a case where H∞ control is applied to a basic control logic of a rack-assisted Electric Power Steering (EPS) system. In the body, the following three key features are described: Construction of the target controlled model including a vehicle Controller design for the model H∞ controller performance verification In this paper, it has been confirmed that H∞ control is valid as a basic control logic for the EPS system.

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.

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 a center-closed rotary servo valve in a hydraulic power steering (PS) system having an improved straight line stability during driving. Conventional rotary servo valves are of a center-open type and are poor in straight line stability because the assist pressure to steer occurs with even slight steering inputs. In the vicinity of neutral position the center-closed rotary servo valve does not produce assist pressure and leaves room for manual steering effort. The center-closed rotary servo valve is composed of a center-closed circuit and a center-open circuit in parallel. The center-closed circuit precisely controls the direction of oil flow to the cylinder chamber A or B in the vicinity of neutral position. The chamfers formed at center-closed metering edges control a lower level of assist pressure. Also the change of assist pressure from manual- to power-steering is smooth.

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 energy-savings in a hydraulic power steering systems by the reduction of the driving torque of a hydraulic pump in non-steering operation. In normal driving, steering operation is infrequent although the pump is continuously driven by the engine. Therefore, for energy-savings in power steering, it is effective to reduce the pump driving torque during non-steering operation. A reduction of the pump driving torque in non-steering operation is possible by decreasing the pump outlet flow rate regulated by a flow control valve. The authors have investigated a prototype pump with an additional device to minimize the regulated flow rate under a non-steering condition and to restore the flow rate during steering operation. The mechanism is a kind of pressure reducing valve that changes the operation of the flow control valve in response to the pump outlet port pressure which is an indication of steering operation.

This paper describes a system which, in order to give a more natural and pleasing steering feeling, has incorporated vehicle speed and steering angle sensors in a hydraulic reaction type power steering system for control in accordance with the frequency of steering angles, control in accordance with vehicle speed and steering angle and control in accordance with forward and reverse acceleration. This system enables the steering characteristics to be matched to the road conditions; light steering for driving in the city, or increased responsiveness for winding mountain roads or sporty driving. The aims in developing this system and details of the method of control are described.