This invention relates to hydraulic dampers for wheeled or tracked vehicles. Vehicle wheel dampers are old in the art as represented by U.S. Pat. Nos. 2,060,590; 2,107,974; 2,546,051; 2,911,072 and 3,007,550. The present invention relates to a hydraulic damper designed to achieve an improved force-flow curve, hence an improved response to terrain disturbance.
Dampers are used in vehicles to control wheel travel and to maintain suspension force at a reasonably constant value. When a vehicle not equipped with dampers travels over rough terrain the road wheel is apt to experience an abnormally high upward acceleration as it impacts on a positive terrain disturbance (rock, log, back edge of a hole, etc.). Sometimes the wheel lifts off the terrain, leaving the hull in an unsupported condition. Resultant dropping movement of the hull can provide very high loads on the wheel-spring system, as well as disturbing the vehicle attitude. A single terrain disturbance (bump, hole, etc.) can produce multiple upward-downward excursions of the road wheel.
A vehicle equipped with dampers experiences lesser disturbances to the vehicle attitude, reduced shock loadings on the wheel-spring system, and improved wheel-terrain engagement (less lift-off and bounce). Dampers produce these desirable effects by limiting the upward acceleration that the wheel can experience when it impacts a bump or other terrain disturbance. The damper of the present invention achieves the desired acceleration-limiting action while at the same time permitting a relatively large total wheel travel (necessary when the vehicle is traversing large bumps or obstacles).
The hydraulic damper of this invention includes a special metering valve in a hydraulic flow passage system that controls movement of a piston-cylinder mechanism trained between the vehicle sprung mass and unsprung mass. Metering valve movement is controlled by a spring mechanism, such that the piston-cylinder unit exerts a substantial wheel deceleration effect when the wheel initially encounters a bump, a lessened deceleration effect as the wheel velocity increases (as when traversing a medium size disturbance), and a resilient snubber action as the wheel approaches the upper limits of its desirable velocities. The damper responds quickly to terrain disturbances without unduly restricting upward wheel travel. Wheel movement in the down (rebound) direction is substantially unrestricted so that the wheel is able to follow terrain undulations with a minimum of bounce or lift-off.
The invention makes it feasible to shape or structure the damper force-flow curve in a manner not previously thought possible.