GB2159604A - An adjustable hydraulic damper - Google Patents

Abstract

In an adjustable hydraulic two- tube damper an axially displaceable control tube 7 is provided in the interior of the piston rod 1 for varying the damping force. The control tube 7 is moved by an electromagnet 8 to close off a bore 20 in a path which bypasses the piston valves by connecting the upper working chamber 10 to the compensating chamber 6 through a central tube 3 that is fixed in a base valve 5, and through a hollow valve screw 4 of the base valve. The control tube 7 does not take up additional space in the damper and is effective not only in the extension phase but also in the contraction phase. <IMAGE>

Description

SPECIFICATIONAn adjustable hydraulic damperThis invention relates to an adjustable hydraulic damper comprising a working cylinder divided by a damping piston secured on a hollow piston rod into upper and lower chambers containing damping fluid, at least one throttling member, the upper chamber being connected to the interior of the piston rod through a transverse bore provided in the piston rod above the damping piston and the lower chamber being connected to a compensating chamber provided between the working cylinder and an outer tube surrounding the working cylinder through a base valve, and, for varying the damping force, an electromagnetically controlled axially displaceable adjusting device provided in the interior of the piston rod. Such a damper will hereinafter be referred to as "of the kind set forth".

Dampers of this kind are known (e.g. DE-PS 984 965), in which it has been proposed to vary the hydraulic pressure in order to adjust the damping forces. In such an arrangement, the pre-loading of the valve spring, as well as the cross-sectional area for flow, is altered by the hydraulic pressure. In such a system throttle-adjusting means and additional pipe systems are necessary.

Furthermore dampers are known (e.g. DEOS 32 41 984), which comprise an adjusting device above the piston rod for altering the cross-sectional area of a bypass passage in the region of the piston. This device substantially only effects an alteration in the damping forces in the extension phase. Moreover, there is scarcely enough space available to mount such an adjusting device, arranged axially, in a motor vehicle.

It is the aim of the invention to provide a damper of the kind set forth in which the adjusting device for a variable bypass passage can be integrated within the damper without taking up additional space and in which the characteristic of the damping forces can be adjusted effectively not only in the extension phase but also in the contraction phase.

According to the present invention there is provided a damper of the kind set forth in which the adjusting device comprises an axially displaceable control tube, the interior of the control tube being connected to the compensating chamber through a central tube which is secured to the base valve and which is arranged for telescopic movement within the control tube, and through a hollow valve screw of the base valve, the central tube being sealed off from the lower chamber, and the interior of the control tube also being in communication with the transverse bore in the piston rod through a bypass which can be closed upon axial displacement of the control tube.

With this arrangement the adjusting device for a variable bypass passage can be conveniently integrated inside a hollow piston rod and an effective bypass passage is in action not only in the extension phase but also in the contraction phase.

Preferably, the bypass comprises a bypass bore provided in a guide tube which is secured at one end to the inner surface of the piston rod above the transverse bore, so as to be fixed relative to the piston rod, the central tube is guided within the inner surface of the guide tube at its opposite end, and a valve member is guided on the outer surface of said opposite end for axial movement relative to the guide tube.

The interior of the control tube and, consequently, the compensating chamber may be sealed off from the lower chamber by means of a seal mounted in a collar on the guide tube in which the central tube is guided.

Preferably, the interior of the central tube communicates with the compensating chamber through a bore provided in the hollow valve screw of the base valve which locates the central tube in the base valve. This location can be readily achieved by clamping the base valve together with the central tube and the working cylinder tube against relative axial movement.

The central tube may be sealed off from the base valve by means of a rubber bush around the central tube which is mounted in a cap which is clamped to the working cylinder.

In a convenient construction the control tube is connected to the armature of an electromagnet through a securing ring mounted in a groove in the inner surface of the control tube.

An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawing, Fig. 1.

Figure 1 is a sectional view of an adjustable hydraulic damper in accordance with the invention which comprises a working cylinder 24 and hollow piston rod 1, to the end of which is secured a damping piston 9. The damping piston 9 divides the interior of the cylinder 24 into upper and lower chambers 10 and 11 and is provided with a contraction phase valve 1 2 mounted on the upper face of the piston 9, and an extension phase valve 13.

An electromagnet 8 is secured in the interior of the hollow piston rod 1 at its upper end and the armature of the electromagnet is connected to a control tube 7 by means of a securing ring mounted in a groove in the inner surface of the control tube. The interior 2 of the hollow piston rod 1 is in communication with a compensating chamber 6 through a telescoping central tube 3 and a bored-through valve screw 4 of a base valve 5. The compensating chamber 6 is formed between the working cylinder tube 24 and an outer tube 25. The guide tube 14 is pressed into the lower part of the piston rod 1 and the valve disc 1 5 of the extension phase valve 1 3 is guided on it. The inner surface of the guide tube 14 has a collar 1 6 which centres the central tube 3.A sealing ring 1 7 for sealing of the interior of the control tube 7 from the lower chamber 11 is mounted in the collar 16.

The upper chamber 10 is in communication with the lower chamber 11 through at least one transverse bore 18 above the damping piston 9 in the piston ring 1, through a cavity 19 formed between the guide tube 14 and the piston rod 1 and through the extension phase valve 1 3. A bypass bore 20 in the guide tube 14 also connects the two chambers 10 and 11 to the interior of the control tube 7 and thus to the compensating chamber 6 through the interior of the central tube 3 and the bore of the hollow valve screw 4 of the base valve 5. Adjustment of the bypass passage is effected by the control tube 7 which is connected to the armature of the electromagnetic 8 and is moved axially by that magnet. Displacement of the control tube 7 opens or closes the bypass bore 20.

In order to achieve high damping forces the bypass bore 20 of the guide tube 14 is closed off by axial displacement of the control tube 7 upon energisation of the electromagnet 8. A transfer bore 21 is provided in the upper part of the control tube and serves to allow the return flow of damping fluid which reaches the upper region of the interior of the piston rod 1 from the control tube 7 and the guide tube 14.

In the region of the base valve the central tube is sealed off from the base valve 5 by a vulcanised-on rubber bush 22 and a cap 23 clamped to the working cylinder tube 24 centres the central tube 3.

Claims (8)

1. An adjustable hydraulic damper comprising a working cylinder divided by a damping piston secured on a hollow piston rod into upper and lower chambers containing damping fluid, at least one throttle member, the upper chamber being connected to the interior of the piston rod through a transverse bore provided in the piston rod above the piston and the lower half of the chamber being connected to a compensating chamber provided between the working cylinder and an outer tube surrounding the working cylinder through a base valve, and an electromagnetically controlled adjusting device for varying the damping force which comprises an axially displaceable control tube provided in the interior of the piston rod, the interior of the control tube being connected to the compensating chamber through a central tube which is secured to the base valve and which is arranged for telescopic movement within the control tube and through a hollow valve screw of the base valve, the central tube being sealed off from the lower chamber, and the interior of the control tube also being in communication with the transverse bore in the piston rod through a bypass bore which can be closed upon axial displacement of the control tube.

2. A damper according to Claim 1, in which the bypass comprises a bypass bore provided in a guide tube, the guide tube being secured at one end to the inner surface of the piston rod above the transverse bore so as to be fixed relative to the piston rod, the central tube being guided within the inner surface of the guide tube at its opposite end, and a valve member being guided on the outer surface of said opposite end of the guide tube for axial movement relative to the guide tube.

3. A damper according to Claim 2, in which the interior of the control tube is sealed off from the lower chamber by means of a seal provided in a collar on the guide tube in which the central tube is guided.

4. A damper according to any of the preceding claims, in which the control tube is mounted in the interior of the piston rod and has a transfer bore connecting the interior of the piston rod to the interior of the control tube.

5. A damper according to any of the preceding claims, in which the interior of the central tube communicates with the compensating chamber through a bore provided in the hollow valve screw of the base valve which locates the central tube in the base valve.

6. A damper according to any of the preceding claims, in which a rubber bush around the central tube seals off the central tube from the base valve, the rubber bush being mounted in a cap which is clamped to the working cylinder.

7. A damper according to any of the preceding claims, in which the control tube is connected to the armature of an electromagnet by means of a securing ring mounted in a groove in the inner surface of the control tube.

8. An adjustable hydraulic damper substantially as described herein with reference to and as illustrated by the accompanying drawing.