GB2336646A

GB2336646A - Monostrut having a "burp" valve

Info

Publication number: GB2336646A
Application number: GB9903245A
Authority: GB
Inventors: Dean Dodge; David Lee Steed; Michael Zebolsky
Original assignee: Tenneco Automotive Inc
Current assignee: Tenneco Automotive Inc
Priority date: 1998-02-13
Filing date: 1999-02-12
Publication date: 1999-10-27
Also published as: DE19906044A1; GB9903245D0; JPH11325149A

Abstract

A shock absorber has a one-way or "burp" valve 52 which is located in a fluid passageway 64 extending between the upper working chamber 20 and the reserve chamber 28 of the shock absorber (10, fig 1). Preferably, gas from the fluid in the upper working chamber 20 will accumulate within the fluid passageway 64 until sufficient pressure is created to open the one-way valve. The opening of the one-way valve "burps" the accumulated gas back into the reserve chamber 28.

Description

2336646 MONOSTRUT HAVING A BURP VALVE

Field of the Invention

The present invention relates to a hydraulic damper or shock absorber adapted for use in a suspension system such as the suspension systems used for automotive vehicles. More particularly, the present invention relates to a hydraulic damper or shock absorber having a pressure tube and a reservoir tube. The shock absorber uses a full displaced piston with no compression base valve and a high pressure gas disposed in a gas chamber located between the pressure tube and the reservoir. A burp valve allows gas mixed with the oil to purge itself back into the gas chamber.

Background and Summary of the Invention

A conventional prior art hydraulic damper or shock absorber comprises a working cylinder which is adapted at one end for attachment to the unsprung portion of a vehicle.

A piston is slidably disposed within the cylinder and the piston separates the interior of the cylinder into an upper and lower working chamber. A piston rod is attached to the piston and extends out of one end of the working cylinder where it is adapted for attachment to the sprung portion of the vehicle. A first valving system is incorporated within the piston for generating a damping force during an extension stroke of the piston with respect to the working cylinder:' A second valving system is incorporated Within the piston for generating a damping force during a compression stroke of the piston with respect to the working cylinder.

Some shock absorber designs incorporate a reserve cylinder disposed concentrically around the working cylinder to form a reservoir between the reserve cylinder and the working cylinder. The reservoir is partially filled with a hydraulic liquid with the remainder of the cylinder being filled with a pressurized gas. The amount of : 1 t, -. - '. i 1:1.. 4 liquid within the reservoir is dependent upon the position of the piston within the working cylinder. Because the piston rod is on only one side of the piston, the movement of the piston within the workiing chamber requires the reserve chamber to accept or replace the volume of liquid which is normally referred to as the rod volume.

During the stroking of the piston within the working chamber, gas from the reservoir can become mixed with the hydraulic fluid. For proper operation of the shock absorber it is advantageous to purge this mixed gas from the hydraulic fluid.

The present invention provides the art with a burp valve that is integrated into the rod guide located at one end of the shock absorber. The burp valve allows any gas mixed with the hydraulic fluid to purge itself back into the gas filled portion of the reservoir while maintaining a proper fluid seal during the operation of the shock absorber.

Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.

Brief Description of the Drawings

Ir the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

Figure 1 is a crosonal side view illustrating a shock absorber incorporating a rod guide with the unique burp valve in accordance with the present invention; Figure 2 is an enlarged cross-sectional side view of the rod guide. incorporating the unique burp valve shown in Figure 1; and Figure 3 is an enlarged cross-sectional side view of the piston assembly shown in Figure 1.

2 1 1 - -",. 1 -:, -J Detailed Description of the Preferred Embodimen

Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in Figure 1 a shock absorber incorporating the rod guide having the unique burp valve in accordance with the present invention which is designated generally by the reference numeral 10. Shock absorber 10 is a dual tube shock absorber which comprises a full displaced piston 12, a piston rod 14, a pressure tube 16 and a reserve tube 18. Piston 12 divides pressure tube 16 into an upper working chamber 20 and a lower working chamber 22. Piston rod 14 extends from piston 12 out of pressure tube 16 and reserve tube 18 for attachment to the sprung structure of a vehicle by methods known well in the art. Pressure tube 16 is filled with hydraulic fluid which moves between upper working chamber 20 and lower working chamber 22 during the movement of piston 12 and piston rod 14 with respect to pressure tube 16. The flow of fluid through piston 12 between chambers 20 and 22 of pressure tube 16 is controlled by a compression valve assembly 24 and an extension valve assembly 26. Valve assemblies 24 and 26 provide for the damping of the movement of piston 12 and piston rod 14.

Reserve tube 18 surrounds pressure tube 16 and with pressure tube 16 defines a reserve chamber 28. Reserve tube 18 is adapted for attachment to the unsprung structure'of the vehicle by methods known well in the art During the stroking of piston 12 and piston rod 14, a different volume of hydraulic fluid flows into or out of upper working chamber 20 than the fluid that flows out of or into lower working chamber 22.

This difference in volume is due to piston rod 14 being located only in upper working chamber 20 and not in lower working chamber 22. This difference in the volume of fluid is known a "rod volume'. The 'rod volume' of fluid is compensated for by the fluid located in reserve chamber 28 which moves into or out of reserve chamber 28 as required. Reserve chamber 28 is partially filled with hydraulic fluid and partially filled With a pressurized gas with the level of hydraulic fluid being determined by the position 3 :).-4 i of piston 12 within pressure tube 16. Full displaced piston 12 eliminates the need for a base valve between reserve chamber 28 and lower working chamber 22.

During the stroking of piston 12 within pressure tube 16, the pressurized gas within reserve chamber 28 can become mixed with the hydraulic fluid within reserve chamber 28. Some of this mixed gas will work itself back into the pressurized gas portion of reserve chamber 28 while some of this mixed gas will enter lower working chamber 22. From lower working chamber 22 this mixed gas can eventually flow through valve assemblies 24 and 26 and enter upper working chamber 20. Once in upper working chamber 20, the mixed gas can combine and create pockets of pressurized gas within upper working chamber 20. In prior art shock absorbers, these pockets of pressurized gas can accumulate near the top of the shock absorber and adversely affect the operation of the shock absorber by causing a lack of damping force during the extension stroke of piston 12 with respect to pressure tube 16.

The present invention is directed towards a unique rod guide 50 which ncorporates a burp valve assembly 52. Rod guide 50 is located at the end of pressure tube 16 and reserve tube 18 from which piston rod 14 extends. Rod guide 50 is attached to pressure tube 16 and reserve tube 18 and defines a rod bore 54 through which piston rod 14 extends. A piston rod bearing 56 guides the movement of piston rod 14 with repect to rod guide 50. A lubrication passage 58 extends through rod guide 50 to provide hydraulic fluid from upper working chamber 20 to a sealing system 60 which seals the internal chambers of shock absorber 10.

Burp valve assembly 52 comprises an annular chamber 62, a radial passage 64, an annular groove 66 and an elastomeric sealing ring 68. Annular chamber 62 is located above piston rod bearing 56 and is connected to annular groove 66 through radial passage 64. Elastomeric sealing ring 68 is located Within groove 66 and is sized such that K is stretched when located within groove 66 such that it sealingly closes radial 4 passage 64. Annular groove 66 is in communication with reserve chamber 28 through an annular gap 70 located between rod guide 50 and reserve tube 18.

Burp valve assembly 52 operates to remove gas build-up within upper working chamber 20 by "burping" the built-up gas to reserve chamber 28 when shock absorber 10 goes through an extension movement. During an extension movement of shock absorber 10, fluid pressure within upper working chamber 20 becomes greater than the fluid pressure within reserve chamber 28. This creates a pressure drop across rod guide 50. Any gas which may have accumulated above piston 12 within upper working chamber 20 is forced between piston rod 14 and piston rod bearing 56 into annular chamber 62. Annular chamber 62 is connected to reserve chamber 28 through radial passage 64, annular groove 66 and annular gap 70. Trapped gas Will accumulate Within radial passage 64 until it builds up sufficient pressure to offset the spring force generated by the hoop stress inherent in elastomeric sealing ring 68. When sufficient pressure has built up Within radial passage 64 to offset the spring force of elastomeric sealing ring 68, sealing ring 68 is moved off of radial passage 64 and the trapped gas is uburped' to reserve chamber 28.

During a compression stroke of shock absorber 10, piston 12 and piston rod 14 move downward thus creating a higher pressure within reserve chamber 28 than within upper working chamber 20. The higher pressure within reserve chamber 28 is additive to the spring force in elastomeric sealing ring 68 ensuring the sealing of radial passage 64. The sealing of radial passage 64 prevents any gas from within reserve chamber 28 from entering upper working chamber 20 through radial passage 64.

While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.

Claims

1. A shock absorber comprising:

a pressure tube defining a pressure chamber., a piston disposed within said pressure chamber, said piston dividing said pressure chamber into an upper working chamber and a lower working chamber, a valve assembly disposed within said piston for controlling fluid flow through said piston; a reserve tube surrounding said pressure tube, said reserve tube and said pressure tube defining a reserve chamber., a rod guide secured to said pressure tube and said reserve tube, said rod guide closing said upper working chamber and defining a piston rod bore; a piston rod attached to said piston, said piston rod extending through said piston rod bore of said rod guide. and is a one-way valve disposed in a fluid passageway extending between said upper working chamber and said reserve chamber.

2. The shock absorber according to claim 1, wherein said passageway includes an annular chamber disposed between said piston rod and said rod guide.

3. The shock absorber according to claim 2, wherein said passageway includes a flow path between said upper working chamber and said annular chamber.

4. The shock absorber according to any one of the preceding claims, wherein said passageway includes a radial passageway extending through said rod guide.

5. The shock absorber according to claim 4, wherein said one-way valve includes an elastomeric ring surrounding said rod guide and closing said radial passage.

6. The shock absorber according to claim 5, wherein said rod guide defines an annular groove, said elastomeric ring being disposed within said annular groove.

7. The shock absorber according to claim 1, wherein said passageway includes a flow path disposed between said piston rod and said rod guide.

6

8. The shock absorber according to claim 7, wherein said passageway includes a radial passageway extending between said flow path and said upper working chamber.

9. The shock absorber according to claim 8, wherein said one-way valve includes an elastomeric ring surrounding said rod guide closing said radial passage.

10. The shock absorber according to claim 9, wherein said rod guide defines an annular groove, said elastomeric ring being disposed within said annular groove.

11. A shock absorber substantially as described herein with reference to the accompanying drawings.

7