GB1599168A

GB1599168A - Shock absorbers

Info

Publication number: GB1599168A
Application number: GB5373877A
Authority: GB
Original assignee: Jonas Woodhead Ltd
Current assignee: Jonas Woodhead Ltd
Priority date: 1977-12-23
Filing date: 1977-12-23
Publication date: 1981-09-30

Description

(54) SHOCK ABSORBERS (71) We, JONAS WOODHEAD LIMITED, a Company registered under the laws of England, of 177 Kirkstall Road, Leeds, LS4 2AQ, Yorkshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- This invention relates to shock absorbers such as are used in vehicle suspension systems.

The invention is concerned with shock absorbers of the telescopic type comprising a working cylinder, a piston arranged to slide in the cylinder and connected to a piston rod extending through a fluid seal in the upper end, and passages in the piston arranged to permit but afford resistance to flow of fluid from one side thereof to the other. The present invention is concerned with shock absorbers of the two-tube type. In such shock absorbers, the working cylinder is surrounded by a rigid cylinder of larger diameter forming with it an annular chamber constituting a reservoir which is in communication through passages which may or may not contain valves with the lower part of the interior of the working cylinder. It is now customary in two-tube shock absorbers for the piston rod seal to be contained in a chamber separate from the working chamber within the working cylinder and defined by the piston rod guide and top closure. The piston rod guide, which closes the working chamber, also serves to protect the seal from the working pressure within the working chamber. Such an arrangement is described in our British Patent No. 1 077 587.

According to the present invention a shock absorber comprises a working cylinder, defining a working chamber, a piston arranged to slide in the working chamber and connected to a piston rod extending through a fluid seal adjacent the upper end preventing escape of fluid from the working chamber and a piston rod guide located on the side of the fluid seal remote from the piston, the fluid seal being exposed to the full pressure in the working chamber, a rigid cylinder surrounding the working chamber and forms ing with it an annular reservoir chamber, means providing communication between the reservoir chamber and the working chamber adjacent the lower end, and a restricted priming passage (as herinafter defined) connecting the upper end of the working chamber with the reservoir chamber.

The term "restricted priming passage" is used herein to refer to a narrow valveless passage which, because of its narrowness, presents a very considerable resistance to the passage of liquid so that its effect on the rebound resistance of the shock absorber will be negligible but which presents little resistance to the flow of gas. The restricted priming passage enables any gas which accumulates in the working chamber to be easily driven out of the working chamber through the priming passage without allowing a sufficient flow of liquid to affect the rebound resistance. Preferably, the priming passage has a cross-section which is less than 0-0005 square inch, for example about 0-0002 square inch.

The invention is particularly but not exclusively applicable to shock absorbers in which the cylinder is filled with liquid and gas in direct contact and under pressure. In operation the liquid and gas mix to form an emulsion having a degree of elasticity such, in relation to the resistance offered to flow through the appropriate passage or passages in the piston, that for movements ofthe piston relative to the cylinder in at least one direction there occurs additional compression of fluid on the appropriate side of the piston in company with decompression on the other side creating a pressure differential across the piston, and flow through the piston against the resistance offered by such passage or passages.

One advantage of eliminating the chamber in which the piston rod seal is located is that it reduces or avoids the alignment problems which are encountered when the piston rod is closely located at three axially spaced locations, namely at the piston, the piston rod guide and the external seal spaced from the piston rod guide by the chamber. Another advantage is that by transferring the piston rod guide from inside the piston rod seal to outside, it is possible to effect a reduction in dead length where other dimensions are unaltered. Where it is not advantageous to shorten the overall length of the shock absorber, the length released by the transfer of the piston rod guide and the elimination of the seal chamber can be used for a hydraulic rebound check and thus, in a preferred construction according to the invention, the end of the working chamber adjacent the piston rod seal is formed as a check cylinder open to the remainder of the working chamber and the piston rod carries a check piston positioned to enter the check cylinder towards the end of the rebound stroke.

Preferably valve means is provided arranged to permit flow into but not out of the check cylinder. Such valve means may be constituted by the check piston being axially movable on the piston rod and having a passage therethrough which is opened and closed by axial movement of the check piston on the piston rod. Preferably, there is a spring biasing the check piston away from the piston rod seal and to a position in which the passage is closed. The check cylinder may be formed by a sleeve which is axially interposed between the working cylinder and an end closure, the priming passage being formed by a groove in the sleeve. Alternatively, where such a sleeve is absent, the priming passage may be formed by a groove in the working cylinder itself.

The invention may be carried into practice in various ways but two shock absorbers embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1A and 1B are in combination a longitudinal section of the first shock absorber; and Figure 2 is a diagrammatic longitudinal section of the second shock absorber which is a modification of the first.

Figures 1A and 1B show a shock absorber comprising an inner or working cylinder 1 surrounded by an outer or reservoir cylinder 2, these providing a working chamber 3 which is within the working cylinder 1 and is divided into two parts 3a and 3b by a piston 4, and an annular reservoir chamber 5 between the inner and outer cylinders 1 and 2. The outer cylinder carries at the lower end an end closure 6 carrying an end mounting 7 and at the other end an end closure 8 having an opening 9 within which there is a guide 11 held rigidly in position by a disc 12 which is tack-welded to the end member 8. The guide 11 guides a piston rod 13 to which the piston 4 is attached. The outer end of the piston rod 13 carries an end mounting 14 and a dust cover 15.

The working cylinder 1 is held in position within the outer cylinder 2 by means of a bottom valve assembly 16 and an upper sleeve 17. The bottom valve assembly 16 includes a disc 18 supported on three spaced upstanding portions 19 on the closure 6 to provide communications 19a between the reservoir chamber 5 and a space 20 below the valve assembly 16. The valve assembly has a central passage 21 having at its upper end a mouth opening into a counterbore 22. Around the mouth there projects an annular rib 23 forming a valve seat against which a disc valve 24 is pressed by a spring 25. The rib 23 is interrupted by notches 26.

The piston rod 13 has a spigot 31 which carries a locating disc 32, a pack 33 of spring discs, the piston 4, a pack 34 of spring discs, a washer 35 and a piston retaining nut 36.

Each of the packs of spring discs is similar in construction to those described in our British Patent No. 1 482 813 to which reference may be made for further details.

The piston rod is formed with a groove 41 in which is retained a collar 42, and slidable on the piston rod on the portion between the groove 41 and the spigot 31 is a sleeve 43 which is biased into engagement with the aic 32 by a compression coil spring 44 acting between the collar 42 and the sleeve 43. The sleeve 43 is formed with ports 45 therethrough and its lower surface is formed with an annular rib 46 which cooperates with the disc 32 to form a valve. The sleeve 43 constitutes a rebound check piston and cooperates with the upper sleeve 17 which forms an open-ended rebound check cylinder with which the piston-forming sleeve 43 cooperates.

The upper sleeve 17 is formed with a lower outwardly directed rebate 51 which receives the upper edge of the inner cylinder 1 with which it makes a substantially fluid-tight seal. The upper part of the upper sleeve 17 seats within the upper end closure 8 and again makes a substantially fluid-tight seal, but a priming passage connecting the upper working chamber 3b and the annular reservoir chamber 5 is formed by a groove 52 which extends axially along the outer cylindrical surface of the upper sleeve 17 and radially inwards across the upper edge of the upper sleeve 17.

The upper sleeve is also formed with an upper and inwardly directed rebate 53 which receives one end of a compression coil spring 54 the other end of which bears against an annular washer 55 of inverted L-shaped cross-section. The washer 55 serves to position and compress an elastomeric sealing ring 56 which in its unstressed state is conical with a cylindrical bore but which is flattened by the force exerted by the spring 54 on the washer 55 so that the lower corner of the bore forms a downwardly directed sealing lip 57 bearing against the piston rod 13.

Operation of the shock absorber shown in Figure 1 is as follows. The interior of the shock absorber contains a mixture of a hydraulic fluid (such as oil) and gas under pressure.

During the first few strokes of the shock absorber when it is first put into use and after it has been standing idle for any length of time, gas present within the working cylinder 1, which will have risen to the top of the working chamber 3b, will be driven out through the priming passage 52. This passage is sufficiently large to allow this bleed of gas but is sufficiently fine to provide a very substantial resistance to the flow through it of liquid so that after any gas has been driven out of the working chamber the effect of the passage 52 is negligible. On compression, working fluid, primarily liquid, is driven from the chamber 3a to the chamber 3b through openings 34a in the larger discs of the pack 34 and past the upwardly deflected smaller disc of the pack 34, through bores 34b in the piston and past the upwardly deflected larger discs of the pack 33. In addition, liquid equal to the increased piston rod volume within the working cylinder will be displaced through the notches 26 in the rib 23 on the bottom disc 16 into the reservoir chamber 5. Both of the packs 34 and 33 and the notches 26 will provide resistance to the flow of fluid and in particular the resistance afforded by the notches 26 will cause the pressure in the lower part 3a of the working chamber to rise during the compression stroke. On rebound, flow through the packs 33, 34 will be reversed, the smaller disc of the pack 33 and the larger discs of the pack 34 being deflected to allow flow. The piston rod volume now has to be recuperated from the reservoir and to provide the desired characteristic the bottom valve opens by the disc 24 rising from the seat 23.

When the piston approaches the upper end of the working cylinder the sleeve 43 will enter the check valve cylinder afforded by the upper sleeve 17 and pressure between the piston afforded by the sleeve 43 and the cylinder afforded by the upper sleeve 17 will increase and will drive the valve seat 46 against the disc 32 so that the only means of escape will be through the passage 52 and between the sleeve 43 and the sleeve 17, thus providing a progressively increasing resistance to further extension of the shock absorber. As the piston 4 begins to move down again, pressure in the rebound check cylinder will fall so that the sleeve 43 will move upwardly relative to the piston rod against the bias afforded by the spring 44 to move the rib 46 away from the disc 32 so that fluid can flow through the passge 45 into the interior of therebound check cylinder; thus, the rebound check piston and cylinder afford little resistance to movement in the compression direction.

Figure 2 shows a second shock absorber represented in the conventional diagrammatic way in which the end fittings are omitted and the shock absorber is shown with zero stroke. In many respects, the shock absorber shown in Figure 2 is similar to that shown in Figure 1 and the same reference numerals are used to identify similar parts. The lower end of the shock absorber is of the same construction as that shown in Figure 1 and the piston is of similar construction but has a simpler compression valve on its upper side and is retained on the spigot by upsetting of the spigot instead of by means of a nut. No rebound check cylider is provided, and accordingly the upper sleeve 17 of Figure 1 has no equivalent. The piston rod guide and the working cylinder seal are of the same construction as those shown in Figure 1 but in this case the piston rod seal is located within the upper end of the working cylinder 1. The seal spring 34 is retained by means of a collar 61 which is held in place within the working cylinder 1 by means of dimples 62 which extend into a circumferential groove 63 in the collar. The collar also provides an abutment against which the rebound stop collar 42 on the piston rod engages.

In the construction shown in Figure 2 the priming passage is formed in the upper end of the working cylinder 1 and is constituted by a groove 64 which extends axially of the working cylinder and a groove 65 which extends radially across the end of the working cylinder and meets the axial groove 64.

In each of the embodiments the priming passage has an extremely small cross-section; the grooves have a width of approximately 0-1 inch and a depth of 0-002 inch.

The foregoing embodiments are also described in our co-pending patent application No. 53737/77 (Serial No. 1 599 167).

WHAT WE CLAIM IS:- 1. A shock absorber comprising a working cylinder defining a working chamber, a piston arranged to slide in the working chamber and connected to a piston rod extending through a fluid seal adjacent the upper end preventing escape of fluid from the working chamber and a piston rod guide located on the side of the fluid seal remote from the piston, the fluid seal being exposed to the full pressure in the working chamber, a rigid cylinder surrounding the working cylinder and forming with it an annular reservoir chamber, means providing communication between the reservoir chamber and the working chamber adjacent the lower end, and a restricted priming passage (as hereinbefore defined) connecting the upper end of the working chamber with the reservoir chamber.

2. A shock absorber as claimed in Claim 1 in which the working chamber and the reservoir chamber are filled with liquid and gas which are indirect contact and under pressure.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Operation of the shock absorber shown in Figure 1 is as follows. The interior of the shock absorber contains a mixture of a hydraulic fluid (such as oil) and gas under pressure. During the first few strokes of the shock absorber when it is first put into use and after it has been standing idle for any length of time, gas present within the working cylinder 1, which will have risen to the top of the working chamber 3b, will be driven out through the priming passage 52. This passage is sufficiently large to allow this bleed of gas but is sufficiently fine to provide a very substantial resistance to the flow through it of liquid so that after any gas has been driven out of the working chamber the effect of the passage 52 is negligible. On compression, working fluid, primarily liquid, is driven from the chamber 3a to the chamber 3b through openings 34a in the larger discs of the pack 34 and past the upwardly deflected smaller disc of the pack 34, through bores 34b in the piston and past the upwardly deflected larger discs of the pack 33. In addition, liquid equal to the increased piston rod volume within the working cylinder will be displaced through the notches 26 in the rib 23 on the bottom disc 16 into the reservoir chamber 5. Both of the packs 34 and 33 and the notches 26 will provide resistance to the flow of fluid and in particular the resistance afforded by the notches 26 will cause the pressure in the lower part 3a of the working chamber to rise during the compression stroke. On rebound, flow through the packs 33, 34 will be reversed, the smaller disc of the pack 33 and the larger discs of the pack 34 being deflected to allow flow. The piston rod volume now has to be recuperated from the reservoir and to provide the desired characteristic the bottom valve opens by the disc 24 rising from the seat 23. When the piston approaches the upper end of the working cylinder the sleeve 43 will enter the check valve cylinder afforded by the upper sleeve 17 and pressure between the piston afforded by the sleeve 43 and the cylinder afforded by the upper sleeve 17 will increase and will drive the valve seat 46 against the disc 32 so that the only means of escape will be through the passage 52 and between the sleeve 43 and the sleeve 17, thus providing a progressively increasing resistance to further extension of the shock absorber. As the piston 4 begins to move down again, pressure in the rebound check cylinder will fall so that the sleeve 43 will move upwardly relative to the piston rod against the bias afforded by the spring 44 to move the rib 46 away from the disc 32 so that fluid can flow through the passge 45 into the interior of therebound check cylinder; thus, the rebound check piston and cylinder afford little resistance to movement in the compression direction. Figure 2 shows a second shock absorber represented in the conventional diagrammatic way in which the end fittings are omitted and the shock absorber is shown with zero stroke. In many respects, the shock absorber shown in Figure 2 is similar to that shown in Figure 1 and the same reference numerals are used to identify similar parts. The lower end of the shock absorber is of the same construction as that shown in Figure 1 and the piston is of similar construction but has a simpler compression valve on its upper side and is retained on the spigot by upsetting of the spigot instead of by means of a nut. No rebound check cylider is provided, and accordingly the upper sleeve 17 of Figure 1 has no equivalent. The piston rod guide and the working cylinder seal are of the same construction as those shown in Figure 1 but in this case the piston rod seal is located within the upper end of the working cylinder 1. The seal spring 34 is retained by means of a collar 61 which is held in place within the working cylinder 1 by means of dimples 62 which extend into a circumferential groove 63 in the collar. The collar also provides an abutment against which the rebound stop collar 42 on the piston rod engages. In the construction shown in Figure 2 the priming passage is formed in the upper end of the working cylinder 1 and is constituted by a groove 64 which extends axially of the working cylinder and a groove 65 which extends radially across the end of the working cylinder and meets the axial groove 64. In each of the embodiments the priming passage has an extremely small cross-section; the grooves have a width of approximately 0-1 inch and a depth of 0-002 inch. The foregoing embodiments are also described in our co-pending patent application No. 53737/77 (Serial No. 1 599 167). WHAT WE CLAIM IS:-

1. A shock absorber comprising a working cylinder defining a working chamber, a piston arranged to slide in the working chamber and connected to a piston rod extending through a fluid seal adjacent the upper end preventing escape of fluid from the working chamber and a piston rod guide located on the side of the fluid seal remote from the piston, the fluid seal being exposed to the full pressure in the working chamber, a rigid cylinder surrounding the working cylinder and forming with it an annular reservoir chamber, means providing communication between the reservoir chamber and the working chamber adjacent the lower end, and a restricted priming passage (as hereinbefore defined) connecting the upper end of the working chamber with the reservoir chamber.

3. A shock absorber as claimed in Claim

1 or Claim 2 in which the end of the working chamber adjacent the piston rod seal is formed as a check cylinder open to the remainder of the working chamber and the piston rod carries a check piston positioned to enter the check cylinder towards the end of the rebound strike.

4. A shock absorber as claimed in Claim 3 in which valve means is provided arranged to permit flow into but not out of the check cylinder.

5. A shock absorber as claimed in Claim 41 in which the valve means is constituted by the check piston being axially movable on the piston rod and having a passage therethrough which is opened and closed by axial movement of the check piston on the piston rod.

6. A shock absorber as claimed in Claim 5 in which there is a spring biasing the check piston away from the piston rod seal and to a position in which the passage is closed.

7. A shock absober as claimed in any of Claims 3 to 6 in which the check cylinder is formed by a sleeve which is axially interposed between the working cylinder and an end closure, the priming passage being formed by a groove in the sleeve.

8. A shock absorber as claimed in any of Claims 1 to 6 in which the priming passage is formed by a groove in the working cylinder.

9. A shock absorber as claimed in Claim 1 or Claim 2 which includes a sleeve axially interposed between the working cylinder and an end closure, the priming passage being formed by a groove in the sleeve.

10. A shock absorber as claimed in any of the preceding claims in which the priming passage has a cross-section which is less than 0 0005 square inch.

11. A shock absorber as claimed in Claim 10 in which the priming passage has a cross-section which is 0-0002 square inch.

12. A shock absorber substantially as described herein with reference to Figures 1A and 1B or to Figure 2 of the accompanying drawings.