Land vehicles – Wheeled – Running gear
Patent
1989-02-14
1990-03-20
Bertsch, Richard A.
Land vehicles
Wheeled
Running gear
B60G 1708
Patent
active
049095358
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to the field of suspension systems for use between a terrain-following member (e.g., a wheel, a ski, a hydrofoil, etc.) and body of a vehicle, and, more particularly, to an improved "active" suspension system and method of operating same.
Background Art
Conventional vehicle suspension systems typically have a shock absorber and a spring arranged in parallel with one another, and operatively interposed between the body and wheel of a vehicle. The shock absorber is normally a piston-and-cylinder arrangement in which fluid is caused to flow from one chamber to another through a restricted orifice. These systems are referred to as being "passive" in that they respond reactively to variations in the applied load. It is well known that such systems are designed to be a practical compromise between vehicle handling, on the one hand, and ride comfort, on the other.
In recent years, there has been increasing interest in the development of "active" suspensions as alternatives to such "passive" systems. In some of these "active" systems, the conventional shock absorber is replaced by a servoactuator, usually in the form of an electrohydraulic servovalve operatively arranged to control the flows of fluid with respect to the opposed chambers of a double-acting fluid-powered actuator. The actuator is basically a piston-and-cylinder arrangement, and is structurally similar to the familiar shock absorber. However, rather than merely control the flow of fluid from one chamber to the other through a restricted orifice, the orifice is omitted altogether and the flows to and from the opposing chambers are controlled by the servovalve. Thus, by operating the servovalve in response to various sensed parameters, the suspension system may be controlled "actively" to correct for disturbances. Examples of prior art "active" suspension systems are shown and described in U.S. Pat. Nos. 2,992,837, 3,029,089, 3,035,853, 3,124,368, 4,215,403 and 4,625,993, and in British Patent No. GB 2 003 255 B.
The advent of such "active" systems, largely made possible by the development of on-board microprocessors, has heralded a new age of vehicle suspensions. However, such "active" systems as have been developed heretofore have been characterized by a feeling of "harshness", as compared with conventional "passive" systems. One reason for this is that a fluid-powered actuator constitutes, at any point in time, a rigid link between the vehicle's wheel and body. Thus, if the roughness of the road surface generates high-frequency, low-amplitude vibrations, or "noise", which is beyond the frequency response to the servoactuator or below its friction threshold, this can be transmitted through the actuator to the body.
To alleviate such "harshness", others have proposed that a rubber isolator be placed in series with the actuator. (See, e.g., British Patent No. GB 2 003 255 B, issued June 23, 1982). If, as described therein, such an isolator has hybrid properties akin to those of both a pure spring and a damper, then the isolator would emphasize the transmission of higher-frequency vibrations from the wheel to the actuator, and thence to the body.
DISCLOSURE OF THE INVENTION
The present invention provides an improved vehicle suspension system, and an improved method of operating same. The suspension system is operatively arranged between a portion of a sprung mass (e.g., a vehicle body) and an unsprung mass, such as a terrain-following member (e.g., a wheel, a ski, a hydrofoil, and the like).
The improved suspension system broadly includes: a servoactuator arranged to act between the body and the terrain-following member. The actuator may act directly on the member and body portion, or may act indirectly thereon, as through an isolation spring. A high-gain servoloop is closed immediately about the servoactuator. A force command signal is supplied to indicate a desired force to be transmitted from the member to the body. The actual force exerted on the body portion is determined, either by dir
REFERENCES:
patent: 4700972 (1987-10-01), Young
patent: 4702490 (1987-10-01), Yamaguchi et al.
patent: 4706787 (1987-11-01), Wossner
patent: 4711464 (1987-12-01), Bilas
Clark Daniel C.
Garnjost Kenneth D.
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