GB2156944A - Monotube shock absorber - Google Patents

Abstract

An unpressurised monotube shock absorber that can operate in a substantially horizontal mode, and which requires major damping in one direction only comprises a cylinder 5 divided into two chambers by a piston 2 and valve 3, one chamber 14 being filled with fluid and capable of being subjected to high pressure by the piston/valve, the other chamber 11 being filled with fluid and a gas filled flexible cell 12 and capable of being subjected to low pressure by the piston/valve. Flow from the chamber 14 into the gas cell containing chamber 11 on compression is throttled by passage 2a, whereas, on movement in the opposite direction, the valve 3 opens to give free flow. In Fig. 2 (not shown) the gas cell is in the other chamber, and the extension stroke is damped. <IMAGE>

Description

SPECIFICATION Improvements to Shock Absorbers The present invention is related to unpressurised monotube shock absorbers for use in a substantially horizontal mode, requiring major damping in one direction only.

Shock absorbers working at any angle have maximum efficiency when the fluid contained is not permitted to mix with gas; it is especially difficult to preventfluidlgas mixing when operating horizontally.

It is well known to solve the problem by replacing either of the end walls of the cylindrical body by a moving diaphragm, which may be lightly spring loaded so as to pressurise the fluid. The position of the moving diaphragm is always arranged such that the high pressures created by the damping do not act on the diaphragm. These methods require two dynamic seals, one on the piston rod, the other on the moving diaphragm, and this feature increases the chance of failure by fluid leakage.

According to the present invention, a monotube shock absorber contains fluid and a gas filled flexible cell. The gas is preferably a large molecule gas such as those used in refrigeration processes, and the flexible cell is made from nylon layflat tubing. Damping is produced by fluid flow through a small passage in a piston valve arrangement. The high pressure differences across the piston required to produce major damping do not act on the flexible gas cell due to the arrangement of the high pressure chamber in a position remote from the cell. If a vacuum is produced in the cylinder body due to fluid loss or low temperature or other reasons, the seal will tend to be drawn into the cylinder body. The seal is therefore attached to the rod guide to prevent such displacement, and subsequent fluid loss.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an axial section of a monotube shock absorber in accordance with the present invention, and having damping on compression.

Figure 2 is an axial section of a monotube shock absorber in accordance with the present invention, and having damping on extension.

Referring to figure 1 showing a piston rod 1 which carries a piston 2 and valve 3, secured by a nut 4.

The piston rod 1 moves along the axis of the cylinder 5, and passes through rod guide 6 and seal 7. End fittings 9 and 10 are provided to secure the unit to the equipment to be damped. Fluid is contained in the cylinder 5 which is divided into a first chamber 11 with a cell 12 containing gas 13 and a second chamber 14. The rod guide 6 and seal 7 are fitted together by means of an undercut 8 in the rod guide 6. The gas 13 is substantially at atmospheric pressure when the piston rod 1 is fully extended.

The piston 2 is prevented from crushing the cell 12 by indentation in the cylinder 5a. On compression of the unit, the fluid in chamber 14 is under high pressure and is forced through a small passage 2a in the piston 2 and valve 3 arrangement. On extension, the valve 3 flexes to allow fluid to pass from chamber 11 to chamber 14 under minimal pressure difference.

Referring to figure 2 showing a unit in which the damping is performed on the extension stroke. The piston 2 and valve 3 divide cylinder 5 into working chambers 11 containing cell 12 with gas 13, and chamber 14. It will be noted that in this variant the high pressure chamber 14 compresses the seal 7 onto the piston rod 1, and that the design of the seal 7 should take account of the intermittent pressures created. An extra indentation 5b is provided in cylinder 5 to protect seal 7 from piston 2. The operation of the unit is similar to the description for figure 1.

1. Amonotube shock absorber unit comprising a tubular cylinder having an axis and two end walls; a cavity being defined within said cylinder between said end walls; a piston rod passing through at least one of the two said end walls and being movable along said axis; a piston unit and valve unit mounted on said piston rod between said end walls and dividing said cavity into two chambers; the first of said two chambers containing fluid and the second of said two chambers containing fluid and also at least one gas filled flexible cell; said two chambers being interconnected by throttled fluid connection means; said means being arranged such that when fluid passes from said first to said second chamber there is substantial throttling of the fluid and when fluid passes from said second to said first chamber there is no substantial throttling of the fluid.

2. A monotube shock absorber unit as claimed in claim 1 wherein the said piston rod passes through a flexible seal which acts in conjunction with one of the said end walls.

3. A monotube shock absorber unit as claimed in either of the preceding claims wherein a stop is provided to prevent said piston unit from damaging the said cell.

4. A monotube shock absorber unit as claimed in any of the preceding claims wherein the said cell is made from layflat nylon tubing.

5. A monotube shock absorber unit as claimed in any of the preceding claims wherein the said cell is filled with a large molecule gas.

6. A monotube shock absorber unit substantially as hereinbefore described with reference to fig. 1 or fig. 2 of the accompanying drawings.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements to Shock Absorbers The present invention is related to unpressurised monotube shock absorbers for use in a substantially horizontal mode, requiring major damping in one direction only. Shock absorbers working at any angle have maximum efficiency when the fluid contained is not permitted to mix with gas; it is especially difficult to preventfluidlgas mixing when operating horizontally. It is well known to solve the problem by replacing either of the end walls of the cylindrical body by a moving diaphragm, which may be lightly spring loaded so as to pressurise the fluid. The position of the moving diaphragm is always arranged such that the high pressures created by the damping do not act on the diaphragm. These methods require two dynamic seals, one on the piston rod, the other on the moving diaphragm, and this feature increases the chance of failure by fluid leakage. According to the present invention, a monotube shock absorber contains fluid and a gas filled flexible cell. The gas is preferably a large molecule gas such as those used in refrigeration processes, and the flexible cell is made from nylon layflat tubing. Damping is produced by fluid flow through a small passage in a piston valve arrangement. The high pressure differences across the piston required to produce major damping do not act on the flexible gas cell due to the arrangement of the high pressure chamber in a position remote from the cell. If a vacuum is produced in the cylinder body due to fluid loss or low temperature or other reasons, the seal will tend to be drawn into the cylinder body. The seal is therefore attached to the rod guide to prevent such displacement, and subsequent fluid loss. The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an axial section of a monotube shock absorber in accordance with the present invention, and having damping on compression. Figure 2 is an axial section of a monotube shock absorber in accordance with the present invention, and having damping on extension. Referring to figure 1 showing a piston rod 1 which carries a piston 2 and valve 3, secured by a nut 4. The piston rod 1 moves along the axis of the cylinder 5, and passes through rod guide 6 and seal 7. End fittings 9 and 10 are provided to secure the unit to the equipment to be damped. Fluid is contained in the cylinder 5 which is divided into a first chamber 11 with a cell 12 containing gas 13 and a second chamber 14. The rod guide 6 and seal 7 are fitted together by means of an undercut 8 in the rod guide 6. The gas 13 is substantially at atmospheric pressure when the piston rod 1 is fully extended. The piston 2 is prevented from crushing the cell 12 by indentation in the cylinder 5a. On compression of the unit, the fluid in chamber 14 is under high pressure and is forced through a small passage 2a in the piston 2 and valve 3 arrangement. On extension, the valve 3 flexes to allow fluid to pass from chamber 11 to chamber 14 under minimal pressure difference. Referring to figure 2 showing a unit in which the damping is performed on the extension stroke. The piston 2 and valve 3 divide cylinder 5 into working chambers 11 containing cell 12 with gas 13, and chamber 14. It will be noted that in this variant the high pressure chamber 14 compresses the seal 7 onto the piston rod 1, and that the design of the seal 7 should take account of the intermittent pressures created. An extra indentation 5b is provided in cylinder 5 to protect seal 7 from piston 2. The operation of the unit is similar to the description for figure 1. CLAIMS

1. Amonotube shock absorber unit comprising a tubular cylinder having an axis and two end walls; a cavity being defined within said cylinder between said end walls; a piston rod passing through at least one of the two said end walls and being movable along said axis; a piston unit and valve unit mounted on said piston rod between said end walls and dividing said cavity into two chambers; the first of said two chambers containing fluid and the second of said two chambers containing fluid and also at least one gas filled flexible cell; said two chambers being interconnected by throttled fluid connection means; said means being arranged such that when fluid passes from said first to said second chamber there is substantial throttling of the fluid and when fluid passes from said second to said first chamber there is no substantial throttling of the fluid.

2. A monotube shock absorber unit as claimed in claim 1 wherein the said piston rod passes through a flexible seal which acts in conjunction with one of the said end walls.

3. A monotube shock absorber unit as claimed in either of the preceding claims wherein a stop is provided to prevent said piston unit from damaging the said cell.

4. A monotube shock absorber unit as claimed in any of the preceding claims wherein the said cell is made from layflat nylon tubing.

5. A monotube shock absorber unit as claimed in any of the preceding claims wherein the said cell is filled with a large molecule gas.

6. A monotube shock absorber unit substantially as hereinbefore described with reference to fig. 1 or fig. 2 of the accompanying drawings.