Stroke dependent bypass

Details Stroke dependent bypass Stroke dependent bypass

1999-05-06

2001-04-24

Oberleitner, Robert J. (Department: 3613)

Brakes

Internal-resistance motion retarder

Valve structure or location

C188S282600, C188S282100, C188S283000, C188S322160

Reexamination Certificate

active

06220409

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a hydraulic damper or shock absorber adapted for use in a suspension system such as the systems used for automotive vehicles. More particularly, the present invention relates to a hydraulic damper having a two-stage damping characteristic where a relatively low level damping is provided for small amplitudes of movement and a relatively high level of damping is provided for large amplitudes of movement.
BACKGROUND OF THE INVENTION
A conventional prior art hydraulic damper or shock absorber comprises a cylinder defining a working chamber having a piston slidably disposed in the working chamber with the piston separating the interior of the cylinder into an upper and a lower working chamber. A piston rod is connected to the piston and extends out of one end of the cylinder. A first valving system is incorporated for generating damping force during the extension stroke of the hydraulic damper and a second valving system is incorporated for generating damping force during the compression stroke of the hydraulic damper.
Various types of damping force generating devices have been developed to generate desired damping forces in relation to the speed and/or the displacement of the piston within the cylinder. These multi-force damping force generating devices have been developed to provide a relatively small or low damping force during the normal running of the vehicle and a relatively large or high damping force during maneuvers requiring extended suspension movements. The normal running of the vehicle is accompanied by small or fine vibrations of the un-sprung mass of the vehicle and thus the need for a soft ride or low damping characteristic of the suspension system to isolate the sprung mass from these small or fine vibrations. During a turning or braking maneuver, as an example, the sprung mass of the vehicle will attempt to undergo a relatively slow and/or large vibration which then requires a firm ride or high damping characteristics of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. Thus, these multi-force damping force generating devices offer the advantage of a smooth steady state ride by eliminating the high frequency/small excitations from the sprung mass while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing larger excitations of the sprung mass.
The continued development of hydraulic dampers includes the development of multi-force damping force generating devices which are simpler to manufacture, can be manufactured at a lower cost and which improve the desired force generating characteristics.
SUMMARY OF THE INVENTION
The present invention provides the art with a multi-stage hydraulic damper or shock absorber that provides damping which varies according to the stroke amplitude. Soft damping is provided for small strokes and firm damping is provided for large strokes. The variable damping is provided by a fluid cylinder and piston assembly located on the end of the piston rod in the lower working chamber. The interior of the fluid cylinder is in communication with the hydraulic fluid in the upper working chamber. When the shock absorber undergoes a small stroke, the fluid flows through two separate flow paths to provide a soft damping. When the shock absorber undergoes a large stroke, fluid flow in one of two paths progressively reduces to provide a firm damping.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.


REFERENCES:
patent: 3180453 (1965-04-01), Murata
patent: 3232390 (1966-02-01), Chano
patent: 3379286 (1968-04-01), Takagi
patent: 3570635 (1971-03-01), Takagi
patent: 4765446 (1988-08-01), Murate et al.
patent: 4874066 (1989-10-01), Silberstein
patent: 4953671 (1990-09-01), Imaizumi
patent: 5058715 (1991-10-01), Silberstein
patent: 5248014 (1993-09-01), Ashiba
patent: 5505225 (1996-04-01), Niakan

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