GB2073846A

GB2073846A - Shock Absorbers

Info

Publication number: GB2073846A
Application number: GB8111739A
Authority: GB
Original assignee: Alusuisse Holdings AG; Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1980-04-14
Filing date: 1981-04-13
Publication date: 1981-10-21
Also published as: BR8102208A; BE888414A; NL8101601A; DE3020840A1; FR2480382A1; IT8120858A0; IT1136877B

Abstract

The performance of shock absorbers with a sleeve (12) divided into two chambers by a floating piston (20) is markedly impaired by wear on the inner sleeve wall and on the piston due to tilting of the piston. Diminished performance is also caused by the passage of gas or liquid from one chamber to the other. In order to reduce this wear and to improve the operation of the shock absorber, tilt- resisting means (48, Fig. 4) are provided on the floating piston. The tilt-resisting ring (48) and the sealing ring (50) may be assembled on a blank the ends of which are turned outward to form annular grooves (52, 54). <IMAGE>

Description

SPECIFICATION Shock Absorbers The present invention relates to shock absorbers of the kind comprising a sleeve, a floating piston which can move freely backwards and forwards within the sleeve, and sealing means including at least one sealing ring carried by the piston for dividing the sleeve into two chambers.

Such shock absorbers are often fitted to vehicles so that one end is attached to the chassis and the other end is attached near the wheel axle.

The greater part of the mass in the shock absorber is in the part which is attached to the axle region.

It is very important to minimise such unsprung masses on vehicles, on lorries for example, not only to reduce fuel consumption but also because this results in a better suspension, and more comfort to the person travelling in the vehicle.

There is therefore great interest in the possibility of using relatively light shock absorbers which are fully effective over a long service life.

The methods for producing aluminium sleeves for such shock absorbers are, however, relatively expensive and this has hindered their use. The reason for the high expense is that the sleeves are normally provided with an anti-stick or lubricating layer to prevent scoring of the sleeve wall and, if metal floating pistons are used, to prevent friction welding between the sleeve wall and the piston.

Even so, the function of the shock absorber was still being imparied by wear on the inner wall of the sleeve, and after extensive investigations it was found that the floating piston, which moves freely backwards and forwards in the sleeve, tends to tilt and begins to make metallic contact with the sleeve wall.

When the sleeve is made of an aluminium alloy, the metallic contact between the floating piston and the sleeve wall resulting from this tilting causes damage mainly to the sleeve wall and consequently to any sealing ring or rings on the piston, all within a relatively short time.

The reason for the tilting of the piston which causes the wear can be found basically in the design of the piston.

It is therefore an object of the invention to develop a shock absorber which exhibits a long service life and by means of which the abovementioned disadvantages from which known shock absorbers suffer can be avoided.

In accordance with the present invention, a shock absorber comprises a sleeve, a floating piston which can move freely backwards and forwards within the sleeve, sealing means including at least one sealing ring carried by the piston for dividing the sleeve into two chambers, and tilt-resisting means carried by the piston for resisting such tilting as would bring an outer peripheral part of the piston into contact with an inner peripheral part of the sleeve.

It should be noted that, preferably, the tiltresisting means either fully or partially constitutes the sealing means.

The sealing ring can be of circular crosssection but could alternatively be a wiping blade.

Preferably, the tilt-resisting means includes at least one aligning ring, which can be square or rectangular in radial cross-section, and which can be in the form of a split ring.

In accordance with a further important aspect of the present invention, which relates to a method of assembly, the sealing means and the tilt-resisting means had been assembled onto a piston blank before the piston blank was shaped around the sealing means and the tilt-resisting means.

Further advantageous versions of the invention are revealed in the following description with the help of the accompanying drawings in Figures 1 to 4.

These drawings show, in a simplified schematic form, exemplified embodiments of the invention viz., Figure 1: A sectional side view of part of a compression sleeve of the shock absorber -- with the shock absorber shown in the compressed, load-bearing state.

Figure 2: A sectional side view of a compression sleeve of the shock absorber -- with the shock absorber shown in the non-loadbearing position.

Figure 3: An exemplified embodiment of a floating piston in a partly finished state.

Figure 4: A floating piston according to the first exemplified embodiment of the invention, but shown in its final, finished form.

The shock absorber 10 shown in Figures 1 and 2 features a sleeve 12 which is connected to the wheel axle of a vehicle, and a piston rod 14 which is connected to the chassis of the vehicle -- the means and manner of connection in both cases not shown here.

A working piston 1 6 is connected in a known manner to the piston rod 14. The piston 16 is provided with a closing or braking valve which operates from one or two sides and which is not shown here. Between the base 18 of the sleeve 12 and the piston 1 6 is a floating piston 20 which can move freely back and forwards in the sleeve 12, dividing the sleeve 12 into two chambers 22 and 24 viz., one chamber 22 for a gaseous medium and another chamber 24 for a liquid medium.

According to the exemplified embodiment of a floating piston 20 shown in Figures 3 and 4, a blank 26 is made first, as shown in Figure 3, in the form of an impact extrusion, diecasting or sintered part, in such a way that the machining otherwise normally required to make such a piston can be omitted.

The blank 26 features on its outer circumference a ring-shaped projection 28 with walls 32 and 34 running perpendicular to the longitudinal axis 30 of the blank, and on either side recesses 36 and 38 which are separated by a wall 40 and delimited circumferentially by walls 42 and 44. A further production step involves pushing plastic rings 48 and 50 over the ring shaped walls 42 and 44 until they lie next to the walls 32 and 34 of the projection 28. After the rings 48 and 50 which form the facility 46 to prevent wear have been stretched and pushed into place, these are secured there on the piston 20 by shaping the ring-shaped walls 42 and 44 by generally known methods e.g. expanding, pressing or upsetting -- as a result of which ringshaped grooves 52 and 54 are formed at the outer ends of the floating piston 20.

The outer diameter of the floating piston 20, the inner diameter of the sleeve 12, the depth of the ring-shaped grooves 52 and 54 and the height or thickness of the plastic rings 48 and 50 are - as viewed in cross section - of such dimensions that, when the floating piston 20 is in position in the sleeve 12, only the two plastic rings 48 and 50 make contact with the inner sleeve wall 56, and the circumferential wall 58 of the floating piston 20 is always at a predetermined distance from the inner sleeve wall 54 in all working positions.

The rings 48 and 50 can be such that one ring is designed for alignment and the other to provide a sealing action. It is, however, also possible to use the two sealing rings which at the same time serve to align the floating piston in the sleeve.

O-rings 50 are employed preferably for the sealing function; the ring 48 for aligning the floating piston on the other hand features a slit and is essentially rectangular or square in cross section. The preferred material for sealing or alignment rings is polytetrafluorethylene.

The invention is not limited to the exemplified embodiment shown in Figures 2 and 3. It is for example also possible, if desired, to manufacture a floating piston in the above, described manner with only one ring-shaped groove.

Claims

1. A shock absorber comprising a sleeve, a floating piston which can move freely backwards and forwards within the sleeve, sealing means including at least one sealing ring carried by the piston for dividing the sleeve into two chambers, and tilt-resisting means carried by the piston for resisting such tilting as would bring an outer peripheral part of the piston into contact with an inner peripheral part of the sleeve.

2. A shock absorber according to claim 1, in which the tilt-resisting means either fully or partially constitutes the sealing means.

3. A shock absorber according to claim 1 or claim 2, in which the tilt-resisting means includes at least one aligning ring.

4. A shock absorber according to claim 3, in which the or at least one of the aligning rings is square or rectangular in radial cross-section.

5. A shock absorber according to claim 3 or claim 4, in which the or at least one of the aligning rings is in the form of a split ring.

6. A shock absorber according to any one of claims 3 to 5, in which the tilt-resisting means consists of one said sealing ring and one said aligning ring which are located by means of respective annular grooves at opposite ends of the piston.

7. A shock absorber according to any preceding claim, in which the or at least one of the sealing rings is circular in radial cross-section.

8. A shock absorber according to any preceding claim, in which the sealing means and/or the tilt-resisting means are formed of polytetrafluorethylene.

9. A shock absorber according to any preceding claim, in which the sealing means and the tilt-resisting means had been assembled onto a piston blank before the piston blank was shaped around the sealing means and the tilt-resisting means.

1 0. A shock absorber according to claim 9, in which the piston blank was an impact extrusion.

11. A shock absorber according to claim 9, in which the piston blank was a diecasting.

12. A shock absorber according to claim 9, in which the piston blank was a sintered part.

13. A shock absorber according to any one of claims 9 to 12, in which the piston blank had presented a hollow cylinder, the outer circumference of the cylinder having an annular projection with side walls perpendicular to the longitudinal axis of the cylinder, and the inner circumference of the cylinder being bridged by a web-like wall.

14. A shock absorber according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.