AU651240B2 - Fluid spring and a method and apparatus for adjusting the internal pressure thereof - Google Patents

Description

651240

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventors: W.W. SHOCK ABSORBERS PTY. LTD.

MICHAEL ALBERT BARRAUD JUSTIN STUART BARRAUD Address for Service: Invention Title: oo e o CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

FLUID SPRING AND A METHOD AND APPARATUS FOR ADJUSTING THE INTERNAL PRESSURE THEREOF Details of Associated Provisional Applications: filed 3 September 1992 Nos. PK8101 o The following statement is a full description of this invention, including the best method of performing it known to us: 2 THE PRESENT INVENTION relates to a fluid spring. In particular, although not exclusively, the invention relates to a gas spring containing a mixture of gas and oil. The invention also relates to a method and apparatus for adjusting the internal pressure of a fluid spring.

Leakage is a problem common to all gas filled cylinders and as such gas springs have a shelf life of approximately only 5 years. Further, the design of many gas springs is such that they may not be pressurised subsequent to manufacture and this precludes regassing of the gas springs following leakage of the gas. Thus an expired gas spring must be replaced by a completely new gas spring even though mechanical wear of the expired gas spring is minimal if not non-existent. The inability to pressurise the gas springs after manufacture precludes storage of empty gas springs which might otherwise be pressurised as required to avoid the problem of limited shelf life. Furthermore, in prior art gas springs, it is not possible to selectively adjust the internal pressure of these gas springs by either adding more gas or 26 releasing gas. Thus in many cases articles employing gas springs must be designed according to the spring constant of a gas spring of predetermined characteristics rather than

*S.

S pressurising a spring to suit the application.

Many gas springs are of the type comprising a ~c4 -4e. vcfer cylinder closed at one end with a rod guide memberA through which a piston rod passes. -our- d- at- the- ther -nd. A of disadvantage4-a-i the rod guide member being fixed relative to the cylinder is that any slight misalignment between the bore the rod guide member and the piston rod will cause the 3 piston rod to jam in the rod guide member. Although this problem may be alleviated by increasing the clearance between the rod guide member and the piston rod, this merely results in a greater likelihood of leakage.

Some refillable gas springs are known but these possess disadvantages which will hereinafter become apparent.

Australian patent no. 533449 discloses a gas spring comprising a cylinder closed at one end and having a rod guide member disposed at the other end of the cylinder. A piston, reciprocable within the cylinder, is connected to one end of a piston rod which passes through the rod guide member. An annular closure member is provided which is located in an operating position in sealing engagement with the piston rod and the interior surface of the cylinder during operation of the fluid spring. For refilling, pressurised gas may enter through an annular gap provided between the rod guide member and the piston rod thereby dislodging the annular closure member from its operating position and the gas may flow through a gap now provided between the annular closure member 2 and the cylinder.

In practice, the annular closure member is an annular cup seal comprising an annulus of elastic material with an inner- circumferential lip and an outer circumferential lip, each of which extends into the cylinder, whereby in use the internal fluid pressure biases the inner circumferential lip and the outer circumferential lip against the piston rod and the cylinder bore respectively. Due to frictional effects such seals are difficult to dislodge from the operating position by gas pressure, requiring large pressures of 4 typically 20 MPa. Once the seal is dislodged, it will readily return to the operating position due to the excess pressure now inside the cylinder thereby making achievement of a predetermined internal cylinder pressure a most difficult, if not impossible, task.

Where an O-ring is used as the annular closure member, less difficulty is experienced in dislodging it from the operating position. However, O-rings are effective in this application for only a short period of time whereinafter they jam on the piston rod.

Further, prior art gas springs of this type are not able to be dismantled for service as the upper end of the cylinder is rolled inwardly to retain the rod guide member.

Australian patent application no. 82619/82 discloses l6 a pressurising arrangement for a gas filled shock absorber.

The shock absorber is closed at one end by an end cap. A rod guide member is located on the interior of the cylinder spaced from the end cap. An annular seal is located between the end cap and the rod guide member. A spring urges the seal into 2 I sealing engagement with the piston rod and the interior surface of the end cap. The application of gas pressure S between a gap provided between the piston rod and the end cap causes the seal to move away from the end cap allowing gas to flow through a passage between the seal and the end cap.

Such sealing arrangements while suitable for oil filled cylinders, are largely ineffective for preventing leakage from gas springs. Furthermore, this cylinder is unable to be serviced due to its welded construction.

US Patent no. 3595552 discloses a gas spring comprising a cylinder having a rod guide member and a pressure seal at one end. Inside the cylinder is a piston which is connected to one end of a piston rod. The piston rod extends slidably and sealingly through the pressure seal. The opposite end of the piston rod has a portion of reduced cross section which can, during pressurisation of the gas spring, be aligned with the pressure seal to create a passage between the rod and the seal without deflection of the seal, through which gas may pass into the cylinder.

It muat be seon that Filling a gas spring wherein the piston and the piston rod are fully retracted into the cylinder is a dangerous practice due to the fact that the internal pressure of the cylinder creates a strong force urging the piston rod out of the cylinder. Filling of these gas spring would need to be conducted under carefully controlled conditions in order to avoid accidents occurring.

.o .It is further known from German utility model 7422901 to fill the cylinder through a gap between the rod guide member and the piston rod across a lip shaped sealing member fixed at the piston rod passage, said lip shape sealing member acting as a check valve, which opens under the action of an outer filling pressure and sealingly engages the piston rod under the action the pressure of the fluid within the cavity. The main disadvantage of such a sealing arrangement is that the cylinder is not able to be depressurised at will.

Apparatus for pressurising refillable fluid springs are also known. General'- they comprise a body which is sealingly engageable with the cylinder at the end from which the piston rod extends.

6 Australian patent no. 533449 discloses a filling head comprising a body having an annular extension terminating in packing material which seals against the end of the cylinder. The difficulty with this design is that under typical gas filling pressures, the packing material extrudes out from between the annular extension and the cylinder, thereby breaking the seal. In order to overcome this problem, very high forces must be exerted by the filling head on the cylinder which may result in buckling of the cylinder.

US Patent no. 3595552 also discloses an apparatus for pressurising fluid springs. However, this apparatus is intended to be used with the fluid spring as disclosed in the same US patent wherein the piston rod is drawn completely into the cylinder. Therefore, this apparatus does not have a central bore through which the piston rod may extend.

It is an object of the present invention to provide an improved fluid spring, a method of filling a fluid spring and an apparatus for adjusting the internal pressure of a fluid spring which will substantially overcome or ameliorate the abovementioned disadvantages.

In accordance with a first aspect of the present invention there is disclosed a fluid spring comprising a cylinder having a guide member at one end and closed at the other end; a pressure seal located inwardly of the guide member; and an elongate displacement member having a region of s.e reduced cross-section adjacent one end, said one end being '"":i.nsertable axially into the cylinder through a bore in the ro.6 7 guide member and through the pressure seal, wherein when the seal is axially aligned with the region of reduced crosssection, pressurised gas may be introduced into, or released from, the cylinder through a passage between the seal and the region of reduced cross-section and when the elongate displacement member is inserted further into the cylinder, a fluid tight seal is effected between the elongate displacement member and the pressure seal.

In practice, the fluid spring may contain liquid and/or gas as the working medium. Preferably the working medium will be a mixture of oil and pressurised air.

Suitably, there is an annular gap between the elongate displacement member and the guide member for the passage of fluid. The guide member may be slidably movable along the length of the cylinder. Preferably the guide member is slidable between a guide operating position and a guide filling position which is spaced inwardly from the guide operating position. The guide member may also be removable from the cylinder for maintenance of the fluid spring.

The pressure seal may also be slidably movable along the cylinder. Preferably the pressure seal is slidable between an operating position and a pressurising position which is spaced inwardly from the operating position. The pressure seal may also be removable from the cylinder for maintenance of the fluid spring.

Suitably, the pressure seal comprises an annular ring of elastic material. In a preferred form of the invention, the pressure seal comprises an annular cup seal in the form of a ring of elastic material with an inner 8 circumferential lip and an outer circumferential lip each of which extend into the cylinder, whereby in use the internal fluid pressure of the cylinder biases the inner circumferential lip and the outer circumferential lip against the piston rod and the cylinder bore respectively.

The elongate displacement member may comprise a rod.

Preferably, the region of reduced cross-section comprises an annular groove in the rod.

The fluid spring may also be provided with a retaining means for retaining the pressure seal and the guide member within the cylinder. The retaining means may be removable to allow removal of the pressure seal and the guide member to enable servicing of the fluid spring.

The fluid spring may also be provided with a damper.

1E As in conventional gas springs, this may take the form of a piston connected to the said one end of the elongate displacement member. A valve may also be provided for through S flow of fluid from one side of the piston to the other.

Preferably, the valve comprises an aperture in the piston.

2b, Further, it is also preferred that the piston and the rod are removable from the cylinder to allow maintenance of the fluid spring.

A limit means may also be provided to prevent alignment of the pressure seal and the region of reduced cross section during normal operation of the fluid spring. The limit means may prevent outward movement of said region of reduced cross-section beyond the pressurising position.

Preferably, the limit means is removable to enable servicing of the fluid spring.

9 In accordance with a second aspect of the present invention there is disclosed a method of adjusting the internal pressure of a fluid spring of the type according to the first aspect of the invention, said method comprising the o steps of: aligning the pressure seal with the region of reduced cross-section whereby a passage is created between the seal and said region; introducing into the cylinder or releasing therefrom, pressurised fluid through said passage; and displacing the elongate displacement member further into the cylinder to cause the pressure seal to seal against said elongate displacement member.

In accordance with a third aspect of the present invention there is disclosed a pressurising means for a fluid 00, spring of the type according to the first aspect of the invention, said pressurising means comprising: a. i a body having a recess adapted to sealingly receive said one end of the cylinder, and a bore through which the

S..

displacement member may slidingly extend when said one end is received in the recess; the body further having a portion which abuts the guide member and displaces the guide member and pressure seal into the cylinder when said one end is cool received in the recess; a first sealing means to seal between the body and the outer surface of said one end of the cylinder; a second sealing means to seal between the body and 6460 was: the displacement member; a fluid inlet on the exterior of the body, the fluid inlet communicating with the bore in the guide member through a conduit in the body, whereby in use when the pressure seal is displaced into alignment with the region of reduced cross-section, fluid communication is established between the fluid inlet and the cylinder, and pressurised fluid may be selectively introduced into the cylinder or removed therefrom via the fluid inlet.

The pressurising means may also be used to release fluid from the fluid spring when the region of reduced crosssection is aligned with the pressure seal.

The pressurising means may also be provided with a\ plunger for retaining the rod guide member in the guide filling position during pressurisation/depressurisation.

One embodiment of the fluid spring will now be described by way of example with reference to the drawings in which: Figure 1 is a cross sectional view of a gas spring 0 :O in the operating mode in accordance with the first aspect of @0 the present invention; Figure 2 is a cross sectional view of the gas spring of figure 1 in the pressurisation or depressurisation mode; Figure 3 is a cross sectional view of the gas spring as shown in figure 2 with the apparatus for pressure adjustment in accordance with the third aspect of the present invention.

In practice, the gas spring of the preferred

S

embodiment contains a mixture of approximately 85% pressurised nitrogen and 15% oil.

As shown in figure 1, the gas spring 5 comprises a lOa cylinder 10 having a pressure seal 12 and a rod guide member 13 at one end, the rod guide member 13 being located externally of the pressure seal. In figure 1 the rod guide member 13 and the pressure seal are shown in their respective operating positions. The pressure seal 12 is of the annular *006 S* .1 0 6 0" *00S r .r* type comprising a ring 17 of elastic material with an inner circumferential lip 1 and an outer circumferential lip 19 each of which extends into the cylinder. A retaining member comprising a circlip located within an annular groove retains the rod guide member within the cylinder. The other end of the cylinder 10 is closed (not shown).

An elongate displacement member in the form of a piston rod 20 extends through the rod guide member 13 and the pressure seal 12, being sealingly and slidably engageable with the pressure seal 12. A pressurising gap 22 is provided between the rod guide member 13 and the piston rod 20, th purpose of which will be explained in connection with figure 3. The inner end 25 of the piston rod is connected to a piston 26 which is reciprocally slidable within the cylinder i rebate recess or 1 10. The piston rod 20 is provided with an annular groove 32 adjacent the piston 26. An aperture 33 is located in the piston for flow through of oil and/or air from one side of the S piston to the other.

During normal operation, the annular groove 32 of the piston rod 20 is prevented from entering into radial alignment with the pressure seal 12 by means of a stop spaced inwardly from the operating position of the pressure seal. 12. The reason for this will become apparent upon explanation of figures 2 and 3. The stop 35 comprises a circlip located within an annula:7 groove. Pressurised fluid within the cylinder biases the inner circumferential lip and the outer circumferential lip of the pressure seal against the piston rod and cylinder bore respectively maintaining an gairtight seal.

Figure 2 illustrates the respective pressurising positions of the pressure seal 12, rod guide member 13 and the piston 26. As shown, the piston 26 abuts against the stop and the annular groove 32 is in radidal alignment with the pressure seal 12 whereby a fluid passage is formed between the piston rod 20 and the pressure seal 12. In this orientation, the fluid spring 5 may be pressurised or depressurised at will to any desired pressure within a predetermined range.

Figure 3 illustrates an apparatus which may be used to adjust the internal pressure of the gas spring of the preferred embodiment. The apparatus comprises a body 40 which engages with the end of the cylinder 10 from which the piston rod 20 extends. The body 40 has a central elongate recess 42 through which the piston rod extends and an annular extension i 45 which surrounds the external cylindrical surface of the cylinder. The body 40 also has a plunging ring 47 to hold the rod guide member 13 and the pressure seal in their respective pressurising positions during pressurisation or depressurisation of the cylinder.

The body 40 is further provided with a gas port which connects with conduit 52 whic;, in turn connects to an annular gap 53 surrounding the piston rod 20. During the pressurisation or depressurisation process this annular gap 53 is in communication with the filling gap 12. The body 40 may be sealed against a fluid spring by means of a cylinder seal located on the internal cylindrical surface of the annular extension 45 and a rod seal 56 located in the rod bore 42.

Each of the seals comprises an O-ring located within an annular groove.

13 During the pressurisation, the piston rod 20 is firstly withdrawn from the cylinder 10 until the piston 26 abuts against the retaining means 35. Secondly, the block is then caused to engage with the end of the cylinder from which the piston rod extends. The cylinder seal 55 aid the rod seal 56 seal the block against the fluid spring. The plunging ring 47 abuts the external end of the rod guide member 13 to retain the rod guide member 13 and the pressure seal in their respective pressurisation positions. In this position, a passage is formed between the pressure seal 12 and the piston rod 20. The cylinder and the block is held between the platens of a press (not shown).

Thirdly, a source of pressurised gas is applied to the gas port 50. The gas passes through conduit 52, annular gap 53, pressurising gap 22 and the passage between pressure seal 12 and the piston rod 20 and into cylinder 10. Fourthly, S. when the desired internal pressure is reached, the rod is slid into the cylinder a short distance to allow the pressure seal 12 to engage and seal against the piston rod 20 ri.rthly, the A)0- source of pressurised fluid is removed. Sixthly, the platens of the press are slowly opened and the internal pressure of the cylinder 10 forces the pressure seal 12 and the rod guide member 13 to resume their respective operating positions. A similar procedure may also be employed in reducing the pressure inside the cylinder but with the absence of the source of pressurised fluid in the third step.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art can be made without departing from the scope of the 14 present invention. For example, the fluid spring may contain any mixture of liquid or gas such as 100% inert gas.

S S

S.

S. S S S

S.

*5S*

SS

!6 S S S S. S

S

SS b*

Claims (10)

1. A fluid spring comprising a cylinder having a guide member at one end and closed at the other end; a pressure seal located inwardly of the guide member; and an elongate displacement member having a region of reduced cross-section adjacent one end, said one end being insertable axially into the cylinder through a bore in the guide member and through the pressure seal, wherein when the seal is axially aligned with the region of reduced cross- section, pressurised gas may be introduced into, or released from, the cylinder through a passage between the seal and the region of reduced cross-section and when the elongate displacement member is inserted further into the cylinder, a fluid tight seal is effected between the elongate displacement member and the pressure seal. S" 2. A fluid spring as claimed in claim 1 wherein the :guide member is slidably moveable within the cylinder.

3. A fluid spring as claimed in claim 1 or claim 2 wherein the pressure seal is slidably moveable within the e. cylinder.

4. A fluid spring as claimed in any one of claims 1, 2 or 3 wherein the elongate displacement member comprises a rod.

5. A fluid spring as claimed in claim 4 wherein the region of reduced cross-section comprises an annular recess in the rod.

6. A fluid spring as claimed in any one of the preceding claims further comprising a retaining means for retaining the pressure seal and the guide member within the ft i cylinder.

7. A fluid spring as claimed in any one of the preceding claims further comprising a damper in the form of a piston connected to the said one end of the elongate displacement member, said piston having an aperture therein for through flow of fluid from one side of the piston to the other.

8. A fluid spring as claimed in any one of the preceding claims wherein the pressure seal is slidably moveable between an operating position and a pressurising position, said fluid spring further comprising a limit means to prevent outward movement of said region of redu,ed cross- section beyond the pressurising position.

9. A fluid spring as claimed in any one of the preceding claims wherein the guide member and the pressure seal are removable from the cylinder for maintenance of the fluid spring.

10. A method of adjusting the internal pressure of the fluid spring as claimed in any one of claims 1 to 9, said *SS o method comprising the steps of: ru aligning the pressure seal with the region of reduced cross-section whereby a passage is created between the seal and said region; r introducing into the cylinder or releasing therefrom, pressurised fluid through said passage; and displacing the elongate displacement member further into the cylinder to cause the pressure seal to seal against said elongate displacement member. 00 A pressurising means for use with the fluid spring 000 1i A pressurising means for use with the fluid spring 17 as claimed in any one claims 1 to 9, said pressurising means comprising: a body having a recess adapted to sealingly receive said one end of the cylinder, and a bore through which the displacement member may slidingly extend when said one end is received in the recess; the body further having a portion which abuts the guide member and displaces the guide member and pressure seal into the cylinder when said one end is received in the recess; a first sealing means to seal between the body and the outer surface of said one end of the cylinder; a second sealing means to seal between the body and the displacement member; a fluid inlet 6n the exterior of the body, the fluid inlet communicating with the bore in the guide member through a conduit in the body, whereby in use when the pressure seal is displaced into alignment with the region of reduced cross-section, fluid J, communication is established between the fluid inlet and the cylinder, and,pressurised fluid may be selectively introduced S into the cylinder or removed therefrom via the fluid inlet.

12. A fluid spring as hereinbefore described with reference to Figures 1 to 3. ~DATED this twenty-third day of March 1994 W.W. SHOCK ABSORBERS PTY..LTD. By their Patent Attorneys CULLEN CO. o*: 18 ABSTRACT The invention relates to a pressurised gas spring which in use contains a mixture of oil and air. The gas spring comprises a cylinder having a guide member (13) at one end and closed at the other end and with a pressure seal (12) located inwardly of the guide member An elongate displacement member (20) (piston rod) with a region of reduced cross- section (32) adjacent one end (25) is insertable through and slides with respect to the guide member Gas may be introduced or removed into the cylinder (10) by aligning the region of reduced cross-section (32) with the pressure seal (12) to create a passage therebetween. The invention also relates to a method and apparatus for adjusting the internal pressure of a fluid spring. *oo 6 0 0 o *o C C **oo ooo