GB2179422A

GB2179422A - Gas spring

Info

Publication number: GB2179422A
Application number: GB08619088A
Authority: GB
Inventors: Werner Rohrmoser
Original assignee: Stabilus GmbH
Current assignee: Stabilus GmbH
Priority date: 1985-08-16
Filing date: 1986-08-05
Publication date: 1987-03-04
Also published as: IT8653765V0; JPS6298040A; DE3529462A1; GB2179422B; IT8667662A0; FR2586279A1; AU582669B2; FR2586279B1; IT1195137B; ES2001215A6; AU6153986A; BR8603915A; GB8619088D0

Abstract

A gas spring comprises a cylinder 2 and a piston rod 3, and defines an electrically conductive path included in an electrical circuit. A switch in unit the gas spring selectively opens and closes the conductive path according to the direction of relative movement of the piston rod and cylinder. The switch unit comprises a contact piece 9 which is in frictional and electrically conductive engagement with the internal sliding surface 2a of the cylinder 2. This contact piece 9 is axially movable with respect to the piston rod 3 between two terminal positions. In a first terminal position during outward movement of the rod 3 (as shown) the contact piece 9 closes the electrically conductive path by abutting the surface 11 of a conductive piston disc 7. In a second terminal position during inward movement of the rod 3, the contact piece 9 abuts the surface 12 of an insulating piston disc 8 and thus opens the electrically conductive path. The contact piece may be in frictional engagement with the rod as at 25 rather than the cylinder, the contact piece then engaging either insulating member 26 or projection 27. The unit is useful for switching an anti-theft device for a boot lid. <IMAGE>

Description

SPECIFICATION Gas spring This invention relates to a gas spring. Gas springs are frequently used for balancing the weight of trunk lids and engine hoods with motor vehicles and are intended to maintain these trunk lids and engine hoods in a predetermined opening position. Moreover, such gas springs can be used for completing electric circuits extending across the gap defined by the motor vehicle frame, on the one hand, and the trunk lid or engine hood, on the other hand. In such cases a switch unit may be allocated to the gas spring for opening and closing the circuit.

From Fed. German Utility Model 7,736,254 a gas spring with a switch is known, the latter being arranged to actuate internal lights. In this case a radially movable switch contact is brought out of engagement when the lid is closed, so that the interior lighting is actuated automatically in dependence upon the lid position. By reason of the tolerances of the gas spring and its articulation points on the vehicle, problems arise with such a formation as regards the switch function, for different angles of opening of the lid exist at which the switch function is to take place. For safety reasons relatively large angles of opening are exceeded before the switch function commences, which is unimportant for the switching of an internal lighting system, but is undesired for the switch of an anti-theft device.

It is the aim of the present invention to produce a gas spring having a switch which has a switch function responding at small angular movements of the boot lid. The aim further consists in obtaining the simplest possible construction with high operational reliability.

According to the present invention a gas spring comprises a cylinder member having an axis, an internal sliding surface and two ends and defining a cavity therein. A piston rod guiding and sealing unit is provided in at least one of said two ends. A piston rod member having an external sliding surface is axially guided by said piston rod guiding and sealing unit for axial movement with respect to the cylinder member. This piston rod member is electrically insulated from said cylinder member. Biasing means are provided within the cavity and act onto said piston rod member in axial direction thereof. The cylinder member provides a cylinder-side section of an electrically conductive path. The piston rod member provides a rod-side section of the electrically conductive path.A switch unit is provided for selectively connecting and separating these sections of electrically conductive path in response to relative movement of the members.

The switch unit comprises an electrically conductive contact element frictionally engageable with the sliding surface of one of the members. Two abutment faces are provided on the other member such as to permit a limited axial movement of the contact element with respect to the other member. These two abutment faces define respective terminal positions of the contact element with respect to the other member. The contact element is electrically connected with the section of electrically conductive path of the other member in one of the terminal positions and is insulated from the section of electrically conductive path of the other member in a further terminal position. The sliding surface of said one member is a part of said section of electrically conductive path of said one member.The switch unit is operable in response to the direction of movement of the piston rod member with respect to the cylinder member.

Due to the fact that the switch unit is provided in the interior of the cylinder of the gas spring, a very simple design is produced having high operational reliability, since the switch itself is exposed to no external damage. Even very small angles of opening of the lid suffice to actuate the switch, that is to say the switch responds to small piston rod movements and is accordingly optimally suitable in combination with an anti-theft installation. No adjustment of the switch is necessary when the gas spring is inserted in different constructions, because the switch unit is self-adjusting.

The sensibility of the switch operation to relative movement of the piston rod, the cylinder and the construction parts connected thereto can be adjusted by adjustment of the axial distance of the abutment faces. This axial distance can be made very small, such that the axial movement permitted to the contact element is in the order of size of 0.5 to 5, preferably 1 to 3 mm.

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. Far 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 and described preferred embodiments of the invention.

The invention will be explained in greater detail below by reference to the form of embodiments represented in the drawing, wherein: FIGURE 1 shows a gas spring in longitudinal section with a switch arranged in the interior of the cylinder and acting in dependence upon the direction of movement; FIGURE 2 shows a detail of the gas spring in the region of the piston in enlarged representation; FIGURE 3 shows a form of embodiment in which a separate contact carrier is clamped together with the piston on the piston rod.

The gas spring 1 as shown in Figure 1 is pivotably secured at one end to a lid (not shown) which is pivotable about a horizontal axis and at the other end to a component (not shown likewise) fast with the bodywork. For more details on the general arrangement it is referred to U.S. Patent 3,919,509 and-more particularly-to Figs. 2 and 3 of that U.S. Patent. As securing elements there serve for example the electrically insulating ball sockets (not designated further) secured to the bottom end of a cylinder 2 and on a piston rod 3. In the interior of the cylinder 2 there is a gas filling under pressure which exerts an outward thrust force upon the piston rod 3, the piston rod 3 being guided and sealed to the exterior at the cylinder exit end by means of an electrically insulating piston rod seal 4 and a piston rod guide 5.The end of the piston rod 3 protruding into the interior of the cylinder carries the piston unit 6 which is provided with a damping passage 20 diagrammatically indicated in Fig. 2. The piston unit 6 consists of an electrically conductive piston disc 7 and of an electrically insulating piston disc 8. The insulating piston disc 8 slides on an internal sliding surface 2a of the cylinder 2, and the conductive piston disc 7 is insulated from the sliding surface 2a by a gap 21 as indicated in Fig. 2. A metallic piston ring 9 is axially movably guided in an annular groove 10. The metallic piston ring 9, as a result of friction on the internal surface 2a of the metallic cylinder 2, places itself according to the direction of movement either on the contact surface 11 formed by the piston disc 7 or on the insulating surface 12 formed by the piston disc 8.

At the cylinder bottom end a cylinder plug connector 13 is secured electrically conductively with the cylinder 2, while the piston rod 3 at its upper end carries, likewise electrically conductively, the plug connector 14. Both plug connectors 14, 13 are electrically insulated from the motor vehicle frame and the lid by the electrically insulating ball sockets 22 and 23 such that the electrically conductive path defined by the gas spring can be electrically insulated from the mass of the motor vehicle frame and the lid. Such the electrically conductive path defined by the gas spring can be included in a circuit section having a potential different from the mass potential.

In Fig. 1 the metallic piston ring 9 is lying on the contact surface 11 of the electrically conductive piston disc 7. This piston ring 9 assumes this position during the entire outward thrust movement of the piston rod 3 out of the cylinder 2, so that the switch is closed and thus electrically conductively connects the cylinder 2 through the electrically conductive piston disc 7 with the metallic piston rod 3.

On an inward thrust movement of the piston rod 3 the piston ring 9, as shown in Fig. 2, places itself as a result of friction on the inner wall of the cylinder 2 against the insulating surface 12 of the electrically insulating piston disc 8. In this case the electric switch formed by the metallic piston ring 9 and the piston discs 7 and 8 is opened, that is to say the electrically conductive connection between the metallic cylinder 2 and the piston rod 3 is interrupted. It can be seen from Figs. 1 and 2 that the electric switch responds to very small relative movements between the cylinder 2 and the piston rod 3. The switch function is dependent upon the piston rod movement and acts over the entire stroke of the gas spring.

The sensitivity of the switch function is dependent on the difference of axial distance of the contact surface 11 and the insulating surface 12, on the one hand, and the axial dimension of the metallic piston ring 9, on the other hand. This difference can be very small as indicated above.

In Fig. 3 there is shown a form of embodiment in which for example the piston rod 3 is connected with an electrically conductive contact carrier or cage 15 which comprises an annular groove 16 in wich the metallic annular contact element 9 is axially movably arranged.

The damper piston 19, likewise secured on the piston rod 3, can be made for example as a synthetic plastics component, and this is also true for the piston ring 20. So that the contact carrier 15 does not impair the function of the passage 20, either it is provided with connection conduits 18 or the metallic piston ring 9 does not lie against the inner wall of the cylinder 2 over the entire circumference. In the position as illustrated the metallic piston ring 9 lies on the lower end face of the ring groove 16 of the contact carrier 15, so that the switch is closed, i. e. an electrically conductive connection is established from the metallic piston rod 3 through the metallic cage 15, the conductive annular element 9 and the internal sliding face 2a. This condition occurs in the outward movement of the piston rod 3 out of the cylinder 2.In the driving of the piston rod 3 into the cylinder 2 the annular contact element 9, arranged in frictional engagement on the internal surface 2a of the cylinder 2, places itself against the synthetic plastics ring 17 which forms an insulating surface, and thus interrupts the electric connection between the cylinder 2 and the piston rod 3.

In the forms of embodiment as described it is readily possible equally to reverse the switch function. By exchanging the electrically conductive piston disc 7 and the electrically insulating piston disc 8 according to Figs. 1 and 2 and by arranging the synthetic plastics ring on the lower end face of the ring groove 16 in fig. 3 the object is achieved that in the driving of the piston rod 3 inwards the current circuit between the cylinder 2 and the piston rod 3 is closed, while this circuit is interrupted in outward movement of the piston rod 3. It can be seen that the actuation of the electric switch of this gas spring is not determined by fixedly predetermined switch points, but is dependent only upon the direction of movement of the piston rod, while as already stated a small relative movement between piston rod and cylinder effects the switch function.Thus such a switch, combined with the gas spring, becomes independent of the tolerances of the attachment points and the overall length tolerances of the gas spring itself. For these reasons it is especially suitable for the switching of an electric or electronic switch circuit of an anti-theft device.

It is easily understandable that the switch unit can be provided also adjacent the upper end of the gas spring in Fig. 1. E. g. one can provide an annular contact element 25 in frictional engagement on the piston rod 3 as indicated in Fig. 1. This annular contact element engages on outward movement the insulating member 26 so that the circuit is open, and on inward movement of the piston rod 3 it engages the radially inner projection 27 of the cylinder 2, so that the circuit is closed. Needless to say, the annular contact element must again be electrically conductive and must be in electrical conductive frictional contact with the external surface 3a of the piston rod 3.

While specific embodiments of the invention have 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.

The reference numerals in the claims are only used for facilitating the understanding and are by no means restrictive.

Claims

1. A gas spring comprising a cylinder member (2) having an axis, an internal sliding surface (2a) and two ends and defining a cavity therein, a piston rod guiding and sealing unit (5, 4) provided in at least one of said two ends, a piston rod member (3) having an external sliding surface (3a), being axially guided by said piston rod guiding and sealing unit (5, 4) for axial movement with respect to said cylinder member (2) and being electrically insulated from said cylinder member (2), biasing means within said cavity acting onto said piston rod member (3) in axial direction thereof, said cylinder member (2) providing a cylinderside section of an electrically conductive path, said piston rod member (3) providing a rodside section of said electrically conductive path, a switch unit being provided for selectively connecting and separating said sections of electrically conductive path in response to relative movement of said members (2, 3), characterized in that said switch unit comprises an electrically conductive contact element (9) frictionally engageable with the sliding surface of one (2) of said members (2, 3), two abutment faces (11, 12) being provided on the other (3) of said members (2, 3) such as to permit a limited axial movement of said contact element (9) with respect to said other member (3), said two abutment faces (11, 12) defining respective terminal positions of said contact element (9) with respect to said other member (3), said contact element (9) being electrically connected with the section of electrically conductive path of said other member (3) in one of said terminal positions and being insulated from said section of electrically conductive path of said other member (3) in a further terminal position, said sliding surface of said one member (2) being a part of said section of electrically conductive path of said one member (2), said switch unit being operable in response to the direction of movement of said piston rod member with respect to said cylinder member.

2. A gas spring as claimed in claim 1, at least one of said sections of electrically conductive path comprising an electrical connector element (13, 14) on the respective member (2, 3) outside said cavity.

3. A gas spring as claimed in claim 1 or 2, said cylinder-side section of electrically conductive path comprising the construction material of said cylinder member (2).

4. A gas spring as claimed in any one of claims 1 to 3, said piston-side section of electrically conductive path comprising the construction material of said piston rod member (3).

5. A gas spring as claimed in any one of claims 1 to 4, said contact element (9) being in frictional engagement with said internal sliding surface (2a) of said cylinder member (2).

6. A gas spring as claimed in any one of claims 1 to 5, said piston rod member (3) being provided with a piston unit (6) inside said cavity.

7. A gas spring as claimed in claim 6. said contact element (9) being an electrically conductive piston ring of said piston unit (6) which is in frictional engagement with said internal sliding surface (2a) of said cylinder member (2), said abutment faces (11, 12) being defined by substantially axially directed end faces of an annular groove of said piston unit (6), which annular groove accommodates said piston ring (9).

8. A gas spring as claimed in any one of claims 1 to 7, one (11) of said abutment faces (11, 12) being an electrically conductive abutment face and being part of the section of electrically conductive path of said other member (3), and the other abutment face (12) being an insulating abutment face.

9. A gas spring as claimed in claim 7 or 8, said piston unit (6) being established by at least two axially adXacent piston discs (7, 8), said piston discs (7, 8) defining said annular groove, one (7) of said piston discs (7, 8) being electrically conductive, further being part of said piston rod-side section of conductive path and further being electrically insulated from said cylinder-side section of electrically conductive path, a further one (8) of said piston discs (7, 8) being made from insulating material and being slidingly engageable with said internal sliding surface (2a) of said cylinder (2).

10. A gas spring as claimed in claim 5 or 6, said piston rod (3) being provided with an annular cage member (15) inside said cavity, said annular cage member (15) defining a radially outwardly open annular groove about said axis, said groove accommodating an annular element (9) acting as said electrically conductive element, said annular groove having a first substantially axially directed end face being a part of said piston rod-side section of electrically conductive path and a further end face being electrically insulated from said piston rod-side section of electrically conductive path, said annular element (9) being engageable with the internal sliding surface (2a) of said cylinder member (2), said internal sliding surface (2a) of said cylinder member (2) being part of the cylinder-side section of electrically conductive path.

11. A gas spring as claimed in any one of claims 1 to 10, said electrically conductive path being included in an operating circuit of a burglary safety system.

12. A gas spring as claimed in any one of claims 1 to 11, said gas spring being provided with mechanical connectors (22, 23) on said cylinder member (2) and on said piston rcd member (3) for being mechanically connected to a frame-work and a door member like a trunk lid of a motor vehicle.

13. A gas spring as claimed in claim 12, said mechanical connectors 822, 23) insulating said gas spring from said frame-work and said door member.

14. A gas spring as claimed in any one of claims 1 to 13, said biasing means comprising a pressurized fluid within said cavity.

15. A gas spring as claimed in any one of claims 6 to 14, said piston unit (6) dividing said cavity into two working chambers, said working chambers being interconnected across said piston unit (6) by passage means (20).

16. A gas spring as claimed in claim 15, said passage means (20) being provided with damping means.

17. A gas spring substantially as described with reference to and as illustrated by any one of the embodiments shown in the accompanying drawings.