GB2159235A

GB2159235A - A self-pumping hydropneumatic suspension strut with internal height control

Info

Publication number: GB2159235A
Application number: GB08512144A
Authority: GB
Inventors: Werner Kuchheuser
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1984-05-23
Filing date: 1985-05-14
Publication date: 1985-11-27
Also published as: JPS60261713A; GB2159235B; DE3419166C1; GB8512144D0; JPH0437301B2

Abstract

In a self-pumping hydropneumatic spring suspension strut with internal height control the pump rod is manufactured from two components 19a and 19b which are keyed together by a mechanical interengagement 26, 28, and a throttle 27 is disposed inside the pump rod in the region where the two parts 19a and 19b are joined together. Oscillations of the strut about a contracted position in which levelling port 25 is covered by the piston 2 cause liquid to be pumped from low pressure chamber 10 through the bore in the pump rod and suction valve 22 into the pump chamber 21 and then through exhaust valve 23 and passage 24 into the working chamber 16 which is in communication with the high pressure chamber 11,9. The throttle 27, formed as a notch in a valve seating engaged by a valve disc 31, does not influence the pumping up operation. When the strut extends sufficiently to cause the piston 2 to uncover the levelling port 25 in the pump rod, pumping stops and the working chamber is placed in communication with the low pressure chamber 10 via the port 25, the throttle 27 and the bore in the pump rod. <IMAGE>

Description

SPECIFICATION A self-pumping hydropneumatic suspension strut with internal height control This invention relates to a self-pumping hydropneumatic spring suspension strut with internal height control, in particular for a motor vehicle, comprising a working cylinder filled with hydraulic fluid and divided into first and second working chambers by a forcetransmitting piston which is slidable in the cylinder and is mounted on the end of a hollow piston rod, the interior of the piston rod constituting a pump cylinder within which works a pump rod secured to the working cylinder, the pump rod being provided with a bore which is connected to a low pressure chamber and which extends to an end of the pump rod provided with a suction valve, and the first working chamber being in connection with a high pressure chamber in which hydraulic fluid is subjected to pressure by a gas cushion and being connectable with the low pressure chamber through the bore of the pump rod, a throttle and a control opening which opens when the piston passes an appropriate position in the working cylinder.

Such a suspension strut will hereinafter be referred to as of the kind set forth.

German Patent application P 33 06 393.1-21, has previously proposed that the throttle be disposed in the end region of the pump rod. Such an arrangement has the drawback that manufacture of the pump rod with its bleed-off delay is expensive, in that additional correcting operations have to be performed when machining the surfaces of the pump rod and only limited machining lengths are available with a pump rod of small outside diameter. In addition a sealing groove has to be formed.

It is an aim of the present invention to provide, in a suspension strut of the kind set forth, a pump rod of a simple, reliable and robust construction which has a surface which can be readily machined as rapidly as possible, and with a throttle operating as a bleedoff discharge delay.

According to the present invention in a suspension strut of the kind set forth the pump rod comprises two parts which are keyed together mechanically and the throttle is disposed between said two parts of the pump rod.

The integration of the throttle into the pump rod results in a robust unit, the pump rod itself being made in two parts. Furthermore, by displacing the throttle from the suction valve into the region of the two-part piston rod a substantially shortened component length is achieved and the throttle is easy to machine and cheap to manufacture.

The assembled piston rod may comprise a part which is machined on its surface (the actual pump rod) and an unmachined part (the extension). This makes it possible to make pump rods of small outside diameter but of greater overall length.

Preferably, a first part of the pump rod extends into a recess in the end portion of the second part which in turn engages in a keying manner in an external groove in the first part.

The groove in the first part may also serve to receive a seal. In this way the groove may be formed simply in the final machining of the components of the pump rod which are to be assembled together.

In a preferred embodiment the throttle may be formed by a notch in a valve seating provided on one of the parts of the pump rod, and a valve disc engageable with the valve seating and which is cut away at its periphery.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a diagrammatic cross-section through a self-pumping hydropneumatic spring suspension strut with internal height control in accordance with the invention; and Figure 2 is an enlarged cross-sectional view of the two-part pump rod of the suspension strut of Fig. 1.

The vehicle height control device illustrated in Fig. 1 comprises substantially the working cylinder 1 of a suspension strut, in which a piston 2 on the end of a hollow piston rod 3 is slidable. The cylinder 1 is closed off at one end by a base component 4 and at its other end by a cap 5 through which the piston rod 3 extends outwards and in which it is sealed.

Although the suspension strut will normally be installed in a vehicle with the cap 5 uppermost, in this case it is illustrated with its base 4 uppermost. The base 4 may be secured by means of an attachment pin 6 to the framework of the vehicle and the piston rod 3 may be secured to the axle of the vehicle in a manner not shown by means of an attachment eye 7. The cylinder 1 is surrounded by an annular compensating chamber partially filled with oil and partially with gas, this chamber being divided by an intermediate wall 8 into a high pressure chamber 11, 9 and a low pressure chamber 10.

The high pressure chamber comprises a high pressure gas cushion 9 separated from an oil space 11 by a diaphragm 12. Oil and a low-pressure gas cushion 1 3 are present in the low pressure chamber 10 in which the oil level is indicated at 14. In the completely lowered condition, i.e. before being pumped up, there is in the low pressure chamber 10 the same pressure as is present in the high pressure chamber 11, 9.

The piston 3 divides the working cylinder 1 into first and second working chambers 1 6 and 1 8. The first working chamber 1 6 is between the working piston 2 and the base 4 and is in communication with the oil space 11 of the high pressure chamber through a passage 1 7. The second working chamber 18 between the working piston 2 and the cap 5 co-operates through valves in the working piston 2 with the first working chamber 1 6.

A pump rod 19 is secured by a resilient mounting 20 to the base 4, and the pump rod 1 9 is slidable in a control tube 32 provided in the interior of the piston rod 3 and which forms the pump cylinder 21 of an oil pump. Movements of the axle of the vehicle generated by uneven parts of the road surface and corresponding movements of the piston rod 3 connected to the axle actuate this oil pump which delivers oil from the low pressure chamber 10, through a bore in the pump rod 1 9 and a suction valve 22 at the end of the pump rod 19, through a pressure valve 23, and through a passage 24 into the working cylinder.In this way the piston 2, the piston rod 3 and the control tube 32 continue to be displaced outwards until the piston reaches a predetermined position in the cylinder when control openings 25 in the piston rod 1 9 are uncovered to connect the first working chamber 1 6 which is exposed to high pressure with the low pressure chamber 10 through a throttle (shown more clearly in Fig. 2) and the bore in the pump rod 1 9. This sets the height control in action.

In Fig. 2 the pump rod 1 9 is shown to a larger scale. The pump rod 1 9 comprises two parts 1 9a and 1 9b which are connected together by a mechanical deformation 26. The first part 1 9a extends into a recess 28 in the second part 1 9b and the end portion of the second part 1 9b is deformed in such a manner as to engage in a keying manner in a groove 29 in the first part 19a. The deformation operation may, for example, be performed in situ. The groove 29 also serves to receive a seal 30 by means of which the pump chamber between the control tube 32 and the pump rod 1 9 is sealed.

In the neighbourhood of the connection between the two parts 1 9a and 1 9b of the pump rod 1 9 the throttle 27 is provided in a cavity 33. The throttle comprises essentially a notch in a valve seating which is engaged by a valve disc 31. The disc 31 is flattened or cut away at its periphery so that the pumping of the oil is not throttle.

Claims

1. A self-pumping hydropneumatic spring suspension strut with internal height control, in particular for a motor vehicle, comprising a working cylinder filled with hydraulic fluid and divided into first and second working chambers by a force-transmitting piston which is slidable in the cylinder and is mounted on the end of a hollow piston rod, the interior of the piston rod constituting a pump cylinder within which works a pump rod secured to the working cylinder, the pump rod being provided with a bore which is connected to a low pressure chamber and which extends to one end of the pump rod provided with a suction valve, the first working chamber being in communication with a high pressure chamber in which hydraulic fluid is subjected to pressure by a gas cushion and being connectable with the low pressure chamber through the bore of the pump rod, a throttle and a control opening which opens when the piston passes an appropriate position in the working cylinder, the pump rod comprising two parts which are keyed together mechanically and the throttle being disposed between said two parts of the pump rod.

2. A suspension strut according to claim 1, in which a first part of the pump rod extends into a recess in an end portion of the second part of the pump rod which in turn engages in a keying manner in an external groove in the first part.

3. A suspension strut according to claim 2, in which a seal is received in the groove in the first part of the pump rod.

4. A suspension strut according to any of the preceding claims, in which the throttle is formed by a notch in a valve seating at the end of one of the parts of the pump rod and a valve disc engageable with the valve seating and which is cut away at its periphery.

5. A self-pumping hydropneumatic spring suspension strut with internal height control substantially as described herein with reference to the accompanying drawings.