GB2280487A

GB2280487A - Gas springs and seals therefor

Info

Publication number: GB2280487A
Application number: GB9315829A
Authority: GB
Inventors: Andrew Lee Bools; Peter James Boote; Merrill Karcher
Original assignee: Camloc UK Ltd
Current assignee: Camloc UK Ltd
Priority date: 1993-07-30
Filing date: 1993-07-30
Publication date: 1995-02-01
Also published as: WO1995004230A1; GB9315829D0

Abstract

A gas spring comprises a body (2) from which a piston rod (7) extends for connection to a member to be acted on by the spring. A seal/guide assembly comprising a bush (13) and seal (14) is provided to guide the piston rod and to form a seal between the piston rod and the body. The bush (13) includes a full diameter portion (16) which locates the bush and a reduced diameter portion (18) with which the seal (14) is frictionally engaged. The seal engages the piston rod by means of a sealing portion (20) and incorporates an extension (21) which extends axially beyond the sealing portion (20) to sealingly engage the body (2) and to act as a buffer for the piston. <IMAGE>

Description

GAS SPRINGS AND SEALS THEREFOR This invention relates to gas springs and to an improved seal arrangement for use between the body and the piston rod of such springs.

In a gas spring a piston is slidably mounted within a cylinder defined by the body of the spring and a piston rod, secured to the piston, extends outwardly of the body for connection to a member upon which the gas spring is to act. A seal and guide assembly is located between the body and the piston rod to guide movement of the piston rod and to form a seal between the piston rod and the body.

The seal/guide assembly in a commercially available gas spring consists of three separate members which are assembled together within the body and then secured in position by rolling a groove in the wall of the body. The use of three separate components complicates assembly of such gas springs and the formation of the groove necessitates an additional manufacturing operation.

The present invention provides an improved seal/guide assembly which can be pre-assembld whereby only a single item need be inserted into the body. Further, the improved seal/guide assembly does not require the retention groove of the prior art and accordingly eliminates one operation in manufacture of gas springs.

According to one aspect of the present invention there is provided a gas spring having a seal/guide assembly comprising a bush which slidably receives the piston rod and has a first portion with an outside diameter which is snugly received within the body and a second portion of reduced outside diameter to form an annular space between the second portion and the body; and a seal mounted on the bush and comprising a first portion which forms a sliding seal with the piston rod and a second portion which is received over the second portion of the bush and has an outside diameter which frictionally engages the adjacent interior of the body.

The bush and seal may be formed as separate components and pre-assembled by locating the second portion of the seal over the second portion of the bush prior to location of the assembly within the gas spring. In the alternative, the seal may moulded onto the bush to form an integral composite seal/guide assembly.

Preferably, the seal incorporates a portion which extends axially into the body beyond the portion of the seal which sealingly engages the piston rod. This extension portion sealingly engages the interior wall of the body and provides a buffer against which the piston will strike when the gas spring is extended to its full stroke. Since the material of the seal will, to an extent, be elastomeric, the buffer portion of the seal will resiliently deform if it is violently struck by the piston thereby reducing shock loading on the piston and the connection between the piston and the piston rod.

Preferably, a rigid ring is moulded within the seal in order to reduce excessive deformation of the seal.

By incorporating such a ring the material of the seal can be chosen from a wide range of materials in light of the particular service conditions under which the gas spring is to operate. Typically, the material from which the seal is moulded may be Viton, Nitrile, 90 Duro NBR or similar material.

The bush may be manufactured by any suitable process and may, for example, be turned from bar material or moulded from sintered metal, plastics or ceramic material.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings wherein: Figure 1 shows schematically and in transverse cross-section a prior art gas spring; Figure 2 shows schematically and in transverse cross-section a portion of a gas spring incorporating the seal/guide assembly of the present invention; Figure 3 illustrates, on a larger scale, details of the seal/guide assembly of the embodiment of Figure 2 prior to fitting within the body of the gas spring; and Figure 4 illustrates charging of the gas spring of Figure 2 with gas.

Referring firstly to Figure 1 the gas spring 1 illustrated is of a type in common commercial use and comprises a tubular body 2 sealed at one end by an end plug 3 having thereon a threaded portion 4 enabling the gas spring to be mounted on one of the two components between which it is to act. A piston 5 is slidably mounted within a cylinder 6 defined by the body 2 and is connected to a piston rod 7 which extends outwardly of the end of the body remote from the end plug 3. The piston does not form a complete seal with the cylinder 6 so that working fluid (either compressed gas or a mixture of gas and oil) can flow past the piston as the piston moves along the cylinder.

A seal/guide assembly 8 comprising a guide bush 9, a seal 10 and a spacer 11 is used to seal between the piston rod and the body and guide movement of the piston rod. The components are separately assembled into the body and, after assembly, are located in position by a groove 12 rolled in the body. The bush 9 guides movement of the piston rod 7; the seal 10 has an inner lip which seals against the piston rod and an outer lip which seals against the body; and the spacer 11 retains the seal 10 in position and acts as a buffer against which the piston 5 strikes if the gas spring is extended to its full stroke.

Referring to Figure 2 the improved seal/guide assembly comprises a bush 13 and a seal 14. The bush has a cylindrical surface 15 which slidingly receives the piston rod 7 and guides movement thereof. The outer diameter of the bush 13 includes a first portion 16 which is snugly received within the bore 17 of the body 2. The bush 13 is made of a rigid material (for example brass, sintered metal, plastics or ceramic material), and accordingly the outside diameter portion 16 ensures that the surface 15 of the bush is correctly located and rigidly held on the centre line of the spring.

The bush 13 also includes a reduced diameter portion 18 over which is mounted an annular portion 19 of the seal 14. The annular portion 19 fills the annular space defined between the bush portion 18 and the wall 17 of the body and the outside diameter of the seal is such that the seal, at this point, frictionally engages the interior surface 17.

In addition to the annular portion 19 the seal 14 incorporates an inner sealing portion 20 which slidingly and sealingly engages the piston rod 7, and an extension portion 21 which sealingly engages the wall 17 of the body and acts as a buffer against which the piston (not shown in Figure 2) will strike if the spring is extended to its full stroke.

Depending on the nature of the material from which the seal 14 is moulded a rigid reinforcing ring 22 of suitable material may be incorporated within the seal.

The portion 20 of the seal 14 which engages the piston rod 7 is formed with two sealing lips 20A and 20B.

In use, both lips engage the piston rod to form a double seal. A very small amount of oil from the interior of the body will tend to become trapped between the seals to lubricate the movement of the piston rod as the piston moves back and forth along the cylinder. The double lip seal increases the life expectancy of the product to ensure reliable sealing over a longer number of use cycles.

The seal 14 (optionally including the reinforcing ring 22) may be separately formed from the bush 13 in which case the two components will be pre-assembled by sliding the annular portion 19 of the seal onto the reduced diameter portion 18 of the bush prior to positioning of the assembly within the body of the gas spring. In this way, only a single item (albeit a composite assembly) need be located within the body of the gas spring. This considerably simplifies assembly as compared with the need to locate three separate components within the body in the case of the prior art. In the alternative, the bush 13 may be formed first and the seal 14 then moulded directly onto the bush to form a unitary assembly.

It will be noted that the seal 14 frictionally engages the surface 17 of the body over a substantial length. It has been found that the fictional resistance to movement thereby produced is such that the former practice of forming a groove 12 to hold the seal/guide assembly in position is no longer required. This eliminates one manufacturing stage in production of gas springs.

Referring to Figure 4, a preferred method of charging gas springs with pressurized gas is illustrated.

In this method, the pre-assembled gas spring is located in a jig 23 having a seal 24 engaging the exterior of the body and a seal 25 engaging the piston rod. Pressurized gas, for example dry nitrogen, is admitted through a port 26 and flows between the piston rod 7 and the bush 13 to lift the seal portion 20 away from the piston rod and enter the interior of the gas spring. It has been found that this charging technique can be operated satisfactorily with the seal/guide assembly of the present invention even though no groove is provided for positively retaining the seal/guide assembly in position.

Claims

1. A gas spring having a seal/guide assembly comprising a bush which slidably receives the piston rod and has a first portion with an outside diameter which is snugly received within the body and a second portion of reduced outside diameter to form an annular space between the second portion and the body; and a seal mounted on the bush and comprising a first portion which forms a sliding seal with the piston rod and a second portion which is received over the second portion of the bush and has an outside diameter which frictionally engages the adjacent interior of the body.

2. A gas spring according to claim 1 wherein the bush and seal are formed as separate components and preassembled by locating the second portion of the seal over the second portion of the bush prior to location of the assembly within the gas spring.

3. A gas spring according to claim 1 wherein the bush is preformed and the seal is moulded onto the bush to form an integral composite seal/guide assembly.

4. A gas spring according to any preceding claim wherein the seal incorporates a portion which extends axially into the body beyond the portion of the seal which sealingly engages the piston rod to form a buffer against which the piston will strike when the gas spring is extended to its full stroke.

5. A gas spring according to claim 4 wherein the extension portion sealingly engages the interior wall of the body.

6. A gas spring according to any preceding claim wherein a rigid ring is moulded within the seal in order to reduce excessive deformation of the seal.

7. A gas spring according to any preceding claim wherein the bush is turned from bar material or moulded from sintered metal, plastics or ceramic material.

8. A gas spring according to any preceding claim wherein the seal sealingly engages the piston rod by way of two adjacent sealing lips which are separated by a zone in which oil is trapped to lubricate the seal.

9. A gas spring according to any preceding claim wherein the spring may be charged by forcing gas and optionally oil between the seal and the piston rod.

10. A gas spring according to any preceding claim wherein the seal/guide assembly is retained in position within the body exclusively by frictional engagement of the seai/guide assembly with the interior surface of the body.