GB2156476A

GB2156476A - A gas spring of variable spring force

Info

Publication number: GB2156476A
Application number: GB08505205A
Authority: GB
Inventors: Winfried Wirges; Leo Lauderbach; Willi Schafer
Original assignee: Stabilus GmbH
Current assignee: Stabilus GmbH
Priority date: 1984-03-21
Filing date: 1985-02-28
Publication date: 1985-10-09
Also published as: GB2156476B; GB8505205D0

Abstract

A gas spring particularly for jumping stilts comprises a working cylinder 1 and a plunger 4. In the working cylinder there is a working chamber 8 containing a mass of gas. A gas exchange chamber 10 is fixed with respect to the working cylinder and is connected to the working chamber by an exchange passage in which is provided a gas exchange valve 14. The valve 14 is opened to admit gas in response to pressure produced by a pumping piston 12 or can be opened by operating rod 15. In another embodiment (Fig. 3) a wall separating the working and exchange chambers is movable. <IMAGE>

Description

SPECIFICATION A gas spring of variable spring force BACKGROUND OF THE INVENTION This invention relates to a gas spring of variable force. Gas springs are e.g. used in socalled jumping stilts. In jumping stiits the spring force of the gas spring must be adapted to the weight and to the skilfulness of the user. This invention provides means for varying the spring force of such gas springs.

STATEMENT OF THE PRIOR ART For the adaptation of the outward thrust force of a gas spring it is known from German patent Specification 1,264,879 to connect the working chamber of a gas spring with atmosphere as from a predetermined outward travel against the force of a helical compression spring. In this way the outward thrust force of the gas spring can be reduced. This German Patent further shows that in view of increasing the outward thrust force of a gas spring a reservoir with gas filling under high pressure can be arranged in the cavity of the gas spring and can be connected through a gas exchange valve with the working chamber of the gas spring; this exchange valve is actuatable by a portion of the plunger, namely a working piston connected with a working piston rod.It is disadvantageous in these embodiments that the variation of the outward thrust force of the gas spring is possible only in specific positions of the working piston.

Furthermore, it is known from German Patent Specification 1,282,364 to provide a reservoir under higher pressure for adaptation of the gas spring to the desired outward thrust. This reservois is connectable with the working chamber on the one hand through a first exchange valve by the piston movement, so that when the valve is pushed open by the inwardly moving working piston pressure medium flows out of the reservoir into the working chamber and thus the outward thrust force is increased.A second exchange valve connects a pump chamber on the piston rod side of the working piston with the reservoir, so that when the piston rod is in the nearly fully extended position, on further outward movement of the piston rod pressure medium is pumped against the force of a spring out of the pump chamber into the reservoir and thus the outward thrust force of the gas spring is reduced. it is disadvantageous in this construction that unskilled operation of the gas spring, that is pushing in or pulling out of the working piston rod too far, can result in an unintended variation of outward thrust force.

The arrangement of a gas spring of variable force in a stilt or pogo stick is known from German 'Offenlegungsschrift' 2,704,170. An exchange valve is provided in the working cylinder of the gas spring which renders possible either letting off of the pressure in the working chamber or pumping up. It is disadvantageous in this construction that the letting off of pressure cannot be effected in a finely sensitive manner and a separate pump is necessary for increasing the pressure. Exact adjustment of the support force to the desired value can be carried out only with difficulty and requires great skill of the operator, in the case of this gas spring construction.

OBJECT OF THE INVENTION It is the object of the present invention to avoid the disadvantages of the known constructions and to provide a gas spring of variable force, the outward thrust force of which can be adapted exactly and without difficulty to the required loading. The gas spring should be simple in assembling and guaratee high reliability of operation even if the piston stroke is fully used.

SUMMARY OF THE INVENTION In view of the above mentioned object a gas spring comprises a working cylinder having an axis and defining a cavity therein. A plunger member extends inwardly and outwardly of the cavity and defines a first working chamber within the cavity. The plunger member is axially movable with respect to the working cylinder inwardly and outwardly of the cavity. A mass of gas is provided within the first working chamber. The pressure of the gas is responsive to the axial position of the plunger member with respect to the working cylinder. Gas exchange means are provided for selectively increasing and decreasing the mass of gas contained within the first working chamber. The gas exchange means comprise a gas exchange chamber fixed with respect to the working cylinder. Exchange passage means extend between the first working chamber and the gas exchange chamber.Exchange valve means are provided within the exchange passage means. Exchange operating means are provided which are separate from the plunger member.

This arrangement and actuation of the gas exchange valve guarantee high functional reliability of the gas spring with full exploitation of the piston stroke, since no undesired variation of the outward thrust force can occur as a result of excessive inward or outward movement of the working piston rod. The gas spring itself is very simple in assembly and can easily be adapted to the required loading.

The variation of force can here be effected without a separate air pump.

The plunger member may comprise a working piston rod sealingly guided by piston rod sealing and guiding means adjacent one end of the working cylinder and a working piston at the inner end of the working piston rod.

The working piston rod defines one end of the first working chamber. A second working chamber is defined around the working piston rod axially between the working piston and the piston rod guiding and sealing means.

Working piston valve means of the checkvalve type may be provided between the first working chamber and the second working chamber. These working piston valve means are closed in response to the pressure of gas within the first working chamber exceeding the pressure of gas within the second working chamber. By these constructional features the functional reliability of the gas spring is increased sinde the guiding and sealing means are provided such that slight leakages between the working piston and the working cylinder during operation of the gas spring do not lead to any loss of gas and thus the support force is maintained.This results essentially from the fact that any leakage losses between the working piston and the working cylinder occurring and through the working piston valve means are returned from the second working chamber into the first working chamber on outward movement of the working piston rod.

According to a first preferred embodiment of the invention the gas exchange chamber accommodates a pumping piston movable between an innermost position adjacent the first working chamber and an outermost position remote from the first working chamber. The pumping piston defines a pumping chamber within the gas exchange chamber. This pumping chamber is adjacent the exchange valve means. The pumping piston is provided with suction valve means permitting aspiration of air into the pumping chamber on outward movement of the pumping piston and closing said pumping chamber on inward movement of the pumping piston. The exchange valve means are of the check-valve type and are closed in response to the pressure within the first working chamber exceeding the pressure within the pumping chamber.On the other hand, the exchange valve means are opened in response to the pressure within the pumping chamber exceeding the pressure within the first working chamber. The pumping piston is provided with a pump operating member outside the gas exchange chamber and with an exchange valve actuating pin opening said exchange valve means when the pumping piston is in or adjacent its innermost position. The pumping piston comprises manually operable bleed valve means for connecting the pumping chamber with atmosphere.

This results in a very compact construction.

The pumping chamber may be defined within a pumping cylinder fixed to one end wall of the working cylinder. In this preferred construction the bleed valve means may comprise a bleed valve member which is connected for common movement with the exchange valve actuating pin with respect to the pumping piston. The bleed valve member is manually movable by a bleed valve operating member from a frist closing position to a second closing position through an open position and is biased towards the first closing position. The exchange valve actuating pin opens the exchange valve means when the bleed valve means is in the second closing position. This embodiment allows letting off of the gas out of the gas spring by small portions, on the one hand and a finely sensitive feed of pressure medium into the first working chamber, on the other hand.

According to another preferred embodiment of the invention the gas exchange chamber is a gas reservoir.

The gas spring of the invention can be easily accommodated within a stilt e.g. a pogo stick. The gas exchange is easily possible while the gas spring remains in its operative location within the stilt.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail below by reference to the forms of embodiment represented in the drawings. In detail: FIGURE 1 shows a gas spring of variable force in longitudinal section in which a pumping chamber is arranged outside the working cylinder; FIGURE la shows a detail of Figure 1; FIGURE 2 shows a gas spring of variable force with a gas exchange chamber arranged within the working cylinder; FIGURE 3 shows a form of embodiment of a gas spring of variable force in which a separator piston is arranged between the working chamber and the gas exchange chamber and this separating piston is axially adjustable; FIGURE 4 shows the arrangement of a gas spring of variable force in a pogo stick.

DETAIL DESCRIPTION OF THE DRAWING The gas spring of variable force according to Figure 1 consists of a working cylinder 1 which is closed at one end by an end wall 2 and at the other end comprises a piston rod guiding and sealing unit 6, 7. A working piston 4 sliding on the inner wall of the working cylinder 1 is connected with a working piston rod passing through the guiding and sealing unit 6, 7. The working piston 4 divides the cavity within the working cylinder 1 into a first working chamber 8 and a second working chamber 9, both working chambers 8, 9 being filled with gas. A gas exchange chamber 10 is arranged outside the working cylinder 1 within a pumping cylinder 11 connected with the end wall 2. A pumping piston 12 is provided within the gas exchange chamber 10 and defines a pumping chamber 10a therein.The pumping piston 1 2 is secured on a pumping piston rod 1 3 which is of tubular formation and carries a pump operating member 1 3a. The pumping piston 1 2 is provided with a suction valve 1 2a. In the interior of the pumping piston rod 1 3 there is an operating rod 1 5 with a bleed valve operating member 1 spa. The operating rod 1 5 is provided with an extension piece or valve actuating pin 1 6 at the lower end.Furthermore, the operating rod 15 has a section 1 7 of smaller diameter which cooperates with a sealing ring 18 clamped in between the end face of the pumping piston rod 1 3 and the pumping piston 1 2. The section 1 7 and the sealing ring 1 8 define a bleed valve 17, 1 8. The first working chamber 8 is connectable with the pumping chamber 1 0a through a non-return valve or check valve 14 arranged in the end wall 2.

On movement of the working piston rod 3 inwards of the working cylinder 1 the piston ring 5, arranged in a groove of the working piston 4 and axially movable therein, places itself against the piston disc 5a and thus sealingly separates the first working chamber 8 from the second working chamber 9. On pulling the working piston rod 3 out of the working cylinder 1 the piston ring 5 forming the working piston valve 5 places itself against the working piston member 5b and clears the passage of gas between the working chambers 8 and 9. Thus a gas pressure can build up in the second working chamber 9 which, the more the working piston rod 3 moves outwards, forms a compressed gas cushon and thus damps the outward movement of the piston rod 3.

If an increase of the support force of the gas spring according to Figure 1 becomes necessary, this is obtained by a pumping movement of the pumping piston 1 2. By pushing down of the pumping piston rod 1 3 the pumping piston 1 2 moves downwards; the pumping chamber 1 0a is sealed off to the atmosphere by the suction valve 1 2a. Due to the excess pressure occurring in the pumping chamber 1 0a compared with the pressure in the first working chamber 8 the check valve 14 is opened and the air can flow from the pumping chamber 1 0a into the first working chamber 8. This pumping movement is continued until the pressure in the first working chamber 8 has risen so far that the desired supporting force on the working piston rod 3 is achieved.

If the supporting force on the working piston rod 3 is to be reduced, the operating rod 1 5 is displaced downwards axially in the pumping piston rod 1 3 and the section 1 7 of smaller diameter travels from its first closing position as illustrated in Figure 1 through an opening position to a second closing position beyond the sealing ring 18. This may occur in a predetermined position of the pumping piston 1 2 which may be defined by an abutment member (not shown). The check valve 1 4 is pushed by the extension piece 1 6 of the operating rod 15, so that gas can flow out of the first working chamber 8 into the pumping chamber 10.Now the operating rod 1 5 is released, whereby it is returned into the first closing position as a result of the force of the return spring 15b and the gas force, the section 1 7 of smaller diameter passing over the sealing ring 1 8. The gas filling situated in the pumping chamber 10 therefore flows away to atmosphere through the bore in the pumping piston rod 1 3. This operation renders possible letting off of compressed gas by portions from the first working chamber 8. It is repeated until the desired outward thrust force of the piston rod is set.

In the form of embodiment of a gas spring of variable force as represented in Figure 2, an exchange chamber 11 9 is arranged in the interior of the working cylinder 101 and has no connection to the atmosphere. This exchange chamber 11 9 is separated from the first working chamber 108 by a separating piston 121 made fast in the working cylinder 101 by means of corrugations 122.A valve body 1 20 of an exchange valve with an operating pin 11 5 is provided in the separating piston 121 and can open and close an exchange passage 1 23. The operating pin 11 5 is in this case axially displaceable in the bore of a separating piston rod 1 24 penetrating the end wall 102 and connected with the separaing piston 1 21 and is sealed off to the atomosphere therein. The highest support force achievable with this form of embodiment is determined by the filling pressure in the first working chamber 108 which is obtained when the exchange valve 1 20 is opened with the working piston 104 being in its outermost position and when the exchange valve 1 20 is thereafter closed. If a lower supporting force on the working piston rod 103 is desired, the exchange valve 1 20 is opened by means of the operating pin 11 5, whereby the exchange chamber 11 9 is connected through the exchange passage 1 23 with the first working chamber 108 and the working piston rod 103 is pushed into the working cylinder 101 so that the filling medium is forced out of the first working chamber 108 into the exchange chamber 11 9 whereupon the exchange passage 1 23 is closed again. This forcing of gas out of the working chamber 108 into the exchange chamber 11 9 has the effect that the mean pressure in the working chambers 108 and 109 decreases and thus a lower support force is set on the piston rod.

The form of embodiment according to Figure 3 differs from that according to Figure 2 essentially in that the separating piston 221 is arranged in the working cylinder 201 axially displaceably by means of the separating piston rod 224 connected therewith. The separating piston rod 224 has at its upper end a securing device consisting essentially of a threading 225 which comes to engage in a corresponding counter-threading of the end wall 202. When the desired position of the separating piston 221 is reached, this position is fixed by means of a lock nut 226. The adjustable separating piston 221 provides the possibility of varying the volume of the first working chamber 208, the exchange chamber 219 diminishing correspondingly. This measure provides a further possibility of pressure regulation.

In Figure 4 there is shown an arrangement of a gas spring of variable force in a pogo stick 27. This pogo stick 27 has a tube part 28 in which the working cylinder 1 of the gas spring according to Figure 1 is secured. At one end of the tube part 28 of the pogo stick 27 there is provided a handle part 29, while a foot rest 30 is secured to the lower end. The piston rod 3 of the gas spring protrudes at the lower end from the tube part 29 of the pogo stick 27 and is provided at its free end with an elastic, slip-proof bugger 31.To protect the piston rod 3 a bellows-fold element 32 is situated between the buffer 31 and the lower end of the tube part 28. An actuating lever 34 connected with the separating member 1 3a and an actuating lever 35 connected with the operating member 15a are conducted to the exterior through an aperture 33 in the tube part 28. Specifically in such pogo sticks it is necessary that the support force of the gas spring should be easily adaptable to the weight of the user. This is effected through the actuating levers 34 and 35 in the manner as described in the form of embodiment according to Figure 1.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

It is to be understood that the reference numbers in the claims are only for better understanding and are by no means restrictive.

Claims

1. A gas spring comprising a working cylinder (1) having an axis and defining a cavity (8, 9) therein; a plunger member (3, 4) extending inwardly and outwardly of said cavity (8, 9) and defining a first working chamber (8) within said cavity (8, 9), said plunger member (3, 4) being axially movable with respect to said working cylinder (1) inwardly and outwardly of said cavity (8, 9); a mass of gas within said first working chamber (8), the pressure of said gas being responsive to the axial position of said plunger member (3, 4) with respect to said working cylinder (1); gas exchange means for selectively increasing and decreasing the mass of gas contained within said first working chamber (8), said gas exchange means comprising a gas exchange chamber (10) fixed with respect to said working cylinder (1); exchange passage means extending between said first working chamber (8) and said gas exchange chamber (10); exchange valve means (14) within said exchange passage means; and exchange operating means separated from said plunger member (3, 4).

2. A gas spring as set forth in claim 1, said plunger member (3, 4) comprising a working piston rod (3) sealingly guided by piston rod sealing and guiding means (6, 7) adjacent one end of said working cylinder (1) and a working piston (4) at the inner end of said working piston rod (3), said working piston (4) defining one end of said first working chamber (8), a second working chamber (9) being defined around said working piston rod (3) axially between said working piston (4) and said piston rod guiding and sealing means (6, 7).

3. A gas spring as set forth in claim 2, working piston valve means (5) of the check valve type being provided between said first working chamber (8) and said second working chamber (9), said working piston valve means (5) being closed in response to the pressure of gas within said first working chamber (8) exceeding the pressure of gas within said second working chamber (9).

4. A gas spring as set forth in claim 3, said working piston valve means (5) being responsive to axial movement of said working piston rod such as to be opened in response to outward movement of said working piston rod (3) with respect to said working cylinder (1).

5. A gas spring as set forth in one of claims 1 to 4, said gas exchange chamber (10) being axially adjacent said first working chamber (8) and being axially aligned therewith.

6. A gas spring as set forth in one of claims 1 to 5, said gas exchange chamber (10) accommodating a pumping piston (12) movable between an innermost position adjacent said first working chamber (8) and an outermost position remote from said first working chamber (8), said pumping piston (12) defining a pumping chamber (10a) within said exchange chamber (10), said pumping chamber (1 0a) being adjacent said exchange valve means (14), said pumping piston (12) being provided with suction valve means (12a) permitting aspiration of air into said pumping chamber (1 0a) on outward movement of said pumping piston (12) and closing said pumping chamber (10) on inward movement of said pumping piston (12), said exchange valve means (14) being of the check-valve type and being closed in response to the pressure within said first working chamber (8) exceeding the pressure within said pumping chamber (1 0a) and being opened in response to the pressure within said pumping chamber (1 0a) exceeding the pressure within said first working chamber (8), said pumping piston (12) being provided with a pump operating member (13a) outside said gas exchange chamber (10) and with an exchange valve actuating pin (16) opening said exchange valve means (14), when said pumping piston (12) is in or adjacent its innermost position, said pumping piston (12) comprising manually operable bleed valve means (17, 18) for connecting said pumping chamber (10a) with atmosphere.

7. A gas spring as set forth in claim 6, said pumping chamber (10a) being defined within a pumping cylinder (11) fixed to one end wall (2) of said working cylinder (1).

8. A gas spring as set forth in claim 6 or 7, said bleed valve means (14, 18) comprising a bleed valve member (17), said bleed valve member (17) being connected for common movement with said gas exchange valve actuating pin (1 6) with respect to said pumping piston (12), said bleed valve member (17) being manually movable by a bleed valve operating member (15a) from a first closing position (Figure 1) to a second closing position through an opening position and being biased towards said first closing position, said exchange valve actuating pin (16) opening said exchange valve means (14) when said pumping piston (12) is in a position adjacent said exchange valve means (14) and said bleed valve member (17) is in said second closing position.

9. A gas spring as set forth in one of claims 6 to 8, said pumping piston (12) being biased towards its outermost position.

10. A gas spring as set forth in one of claims 1 to 5, said gas exchange chamber (119) being a gas reservoir separated from atmosphere.

11. A gas spring as set forth in claim 10, said gas exchange chamber (11 9) being defined within said cavity and separated from said first working chamber (108) ba a separating piston (121), said exchange passage means (123) extending through said separating piston (121), said exchange valve means (120) being located adjacent said separating piston (121).

1 2. A gas spring as set forth in claim 11, said exchange valve means (120) being actuated by an operating pin (11 5) guided within a tubular guiding member (124) extending along said gas exchange chamber (119) between said separating piston (121) and an end wall (102) of said gas exchange chamber (119) remote from said separating piston (121).

13. A gas spring as set forth in claim 12, said tubular guiding member (224) being fastened to said separating piston (221) and being adjustable with respect to said end wall (202) such as to vary the volume ratio between said first working chamber (208) and said gas exchange chamber (219).

14. A gas spring as set forth in one of claims 1 to 13, said gas spring being accommodated within a stilt member (27).

1 5. A gas spring as set forth in claim 14, said gas spring comprising a piston rod member (3) extending beyond a tubular part (28) of said stilt member (27), said piston rod member (3) being surrounded by a bellows (32).

16. A gas spring as set forth in one of claims 14 and 15, said stilt member (27) being provided with at least one recess (33) granting passage to at least one operating member (34, 35) of said gas exchange means.

1 7. A gas spring substantially as described with reference to Figures 1 and 1 a, Figure 2, Figure 3, Figure 4 or Figure 5 of the accompanying drawings.