Shock absorber

Details Shock absorber Shock absorber

2001-05-30

2003-11-18

Butler, Douglas C. (Department: 3683)

Spring devices

Vehicle

Comprising compressible fluid

C188S315000, C188S286000, C188S269000, C267S064150

Reexamination Certificate

active

06648310

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a shock absorber.
In vehicles which, when being driven, are subjected to relatively high loading of the chassis, for example rally vehicles, shock absorbers on the single-tube damper principle are often used, it being possible for the piston rod to be attached to the wheel. A cylinder belonging to the shock absorber is covered by an outer tube which in turn is connected to the piston rod. In an annular space between the outer tube and the cylinder, annular bearings are arranged for guidance. In addition, the annular space is filled with a lubricant. One exemplary embodiment is illustrated in “Fahrwerktechnik”, Jörnsen Reimpell, Volume 3, p. 60, 1974 edition.
One general problem is that the grease in the annular space not only becomes thin at high temperatures but exerts an operating pressure on the annular bearings which can lead to leaks in the area of the annular bearings.
It is of course also possible to provide a partial filling for the annular space, but then the disadvantage arises that the air trapped in the annular space exerts a considerable insulating action on the cylinder and therefore restricts the maximum permissible development of heat, which is in turn dependent on the damping performance provided by the shock absorber.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a shock absorber which, firstly, has good guidance between the piston rod and the cylinder and, secondly, exhibits good heat dissipation.
According to the invention, the object is achieved by at least one of the seals of the annular space being arranged in a fixed location with respect to the cylinder and at least one of the seals being arranged in a fixed location with respect to the outer tube, so that the annular space has a volume which varies as a function of the reciprocating position of the shock absorber. The annular space is connected via at least one flow connection to at least one working chamber.
The advantage of the invention is that the volume of the annular space is in continuous interchange with the damping medium in the working chambers and is pumped around with the reciprocating movement. The possibility that insulating gas cushions will be formed is avoided. The interchange of the damping medium also tends to minimize the negative effect of a gas cushion between the cylinder and the outer tube.
Furthermore, a noticeable overlap between the outer tube and the cylinder can be maintained, which results in good guidance of the piston rod. It is therefore possible for transverse forces on the shock absorber to be absorbed by the outer tube.
In a further advantageous embodiment of the invention, provision is made for a volume displaced by the displacer in the working space to substantially correspond to the stroke-dependent volume of the annular space. If the cross section of the annular space is made equal to the cross section of the piston rod, and if the piston has at least one fluid connection, it is then ensured that the annular space is able to accommodate the volume displaced from the working chambers by the piston rod. The annular space therefore constitutes a compensation space with a variable volume.
If, for example, the overall space for the shock absorber does not permit a configuration of the annular space for the complete accommodation of the volume displaced by the piston rod, provision can be made for the shock absorber to have a compensation space.
Alternatively, provision is made for the volume of the compensation space to be designed to substantially match the thermal expansion of the damping medium. In the case of a shock absorber designed on the principle of a single-tube damper, a dividing piston is generally used. Consequently, the dividing piston has to execute only one stroke, which is carried out only as a result of the expansion of the damping medium which results from the thermal expansion in the shock absorber. The dividing piston is only very slightly dynamically loaded.
According to an advantageous embodiment, the compensation space has a pressurized gas filling. Alternatively, a mechanical spring can also be employed.
Furthermore, in each case a pressurized area of the outer tube, which acts in the axial direction of the shock absorber, and that of the displacer are substantially equal. This means that a shock absorber of single-tube damper design does not exert any load bearing force which acts on a vehicle. Precisely in the case of high-performance vehicles, which is used in the area of motor sport, the effect occurs that the development of heat causes the operating pressure in the shock absorber to rise considerably. Conventional single-tube shock absorbers have a load bearing force which is calculated from the cross-sectional area of the piston rod and the operating pressure. If the pressure rises because of the development of heat in the shock absorber, then the load bearing force increases to the same extent. This relationship leads to the vehicle superstructure being lifted, since the load bearing force of the single-tube damper and the spring force of the vehicle load bearing spring are oriented in the same direction. With the inventive configuration, the vehicle level remains constant.
It is also possible to provide for the pressurized area in the annular space to be greater than that of the displacer. This then provides a force which would compress the shock absorber and lower the vehicle superstructure. The design therefore depends on the vehicle and the intended use of the vehicle.
A valve device arranged outside the cylinder is connected via a duct starting from a first working chamber above the piston rod. An outlet from the valve device is connected to the second working chamber.
If the damping force is intended to be adjustable from both reciprocating directions of the displacer, then both working chambers are respectively connected to the valve device, the piston rod having separate ducts for the working chambers.
An advantageous development of the invention provides for an end stop to limit the reciprocating movement of the shock absorber. To this end, the end stop has a stop spring which is oriented counter to the further reciprocating movement. The stop spring opposes a mechanical force to the reciprocating movement.
According to a further advantageous embodiment, the stop spring is supported on a transfer ring which is driven by a component on the piston-rod side.
Furthermore, provision is made for the transfer ring to have at least one throttling cross section through which damping medium flows.
The throttling cross section in the transfer ring is formed by a central passage opening. As a result, the damping medium can be displaced, at least partially, from the reducing working space through a duct within the piston rod.
In order to switch off the end stop during the reverse reciprocating movement of the piston rod, provision is made for the at least one throttling cross section to be operatively connected to a nonreturn valve which opens in the direction of the force of the stop spring.
The nonreturn valve has a sealing disk which can move axially within a groove and controls at least one bypass to the at least one throttling cross section.
It is also possible to configure the end stop in such a way that the sealing disk contains the at least one throttling cross section.
The action of the end stop can be varied as a function of stroke in that during a reciprocating movement of the piston rod, a plunger dips into the throttling cross section and reduces the throttling cross section.
In addition, the plunger can be displaced in terms of its position in relation to the at least one throttling cross section, so that, based on a defined reciprocating position of the piston rod, the result is an adjustable effect of the end stop.
An end stop which acts in the opposed reciprocating direction of the piston rod is designed so that the outlet opening within the piston rod for the second working space is closed as a function of stroke by

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