Spring devices – Vehicle – Mechanical spring and nonresilient retarder
Patent
1986-07-31
1987-12-08
Butler, Douglas C.
Spring devices
Vehicle
Mechanical spring and nonresilient retarder
137493, 1374937, 188280, 18832213, F16F 934, F16F 950
Patent
active
047114355
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for hydraulic damping for use, for example, in a vehicle suspension system.
Known hydraulic dampers are used to provide energy absorption of transient energy inputs and to reduce or to damp out resonant oscillations in a suspension system.
In known hydraulic dampers, an input force of a transient or of an oscillatory nature causes the translational movement of a piston in a chamber and incompressible fluid in the piston chamber is caused thereby to flow through a flow restrictor such as a narrow channel or a small orifice. The restriction of fluid flow through the flow restrictor causes the movement of the piston to be dependent upon the rate of fluid flow through the restrictor. Since the cross-sectional area of the flow restrictor is relatively small compared to that of the piston and the piston is required to move in the chamber such that the rate of volume displacement of the piston is equal to the rate of flow of incompressible fluid through the restrictor, the motion of the piston is restricted.
If the flow restrictor is a channel, the force applied by the fluid to the piston surface to restrict the motion of the piston is approximately proportional to the velocity of the piston, whereas if the flow restrictor is an orifice, the force is approximately proportional to the square of the velocity of the piston. In most known arrangements the relationship between force and velocity is between these two extremes.
Known hydraulic dampers of this type have a disadvantage in that, while at relatively low input velocities of the piston, the above-described level of restriction gives adequate damping characteristics, at high input velocities of the piston, such as, for example, when the damper is mounted in a suspension system of a vehicle which is driven over rough terrain, the high damping forces applied to the piston in the damper will cause the suspension in the vehicle to give an unacceptably hard and uncomfortable ride.
Known arrangements used to alleviate this phenomenon involve incorporation of a pressure relief valve in parallel with the flow restrictor. The relief valve allows relief of fluid pressure in the damper when the pressure attains a particular value.
Known valve arrangements are also employed in hydraulic dampers to give asymmetric damping characteristics, that is to provide a different level of damping during the impact mode to that provided during the rebound mode. These valve arrangements are complicated in design and expensive to manufacture using conventional valve manufacturing techniques.
The present invention relates to apparatus for hydraulic damping which has good high input velocity and asymmetric characteristics, is simple in operation, design and manufacture, and is insensitive to contamination of fluid in the apparatus.
The present invention provides apparatus for hydraulic damping comprising a housing having a chamber therein, the chamber dividing the housing into two enclosures, between which enclosures fluid may flow through the chamber, the chamber having a first port and a second port, each being in communication with a respective one of said enclosures, and a member arranged inside the chamber such that increase of fluid pressure difference between the ports in either direction causes the member to be deflected elastically so as to allow flow of fluid between the enclosures in the respective direction, the incremental deflection of the member for a particular incremental increase of fluid pressure difference increasing at increasing fluid pressure difference.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 shows an example of a known hydraulic damper system;
FIG. 2 shows diagrammatically a preferred relationship between the damping force (F) and the input velocity of the piston (V) for a hydraulic damping system;
FIG. 3 shows diagrammatically the relationship between the force (P) and the deflection (x) of a linear spring, and a non-linear spring
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Benyon John F.
Harris John L.
Butler Douglas C.
Farley Walter C.
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