GB2072798A

GB2072798A - Seal for shock-absorber

Info

Publication number: GB2072798A
Application number: GB8106599A
Authority: GB
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1980-03-07
Filing date: 1981-03-03
Publication date: 1981-10-07
Also published as: GB2072798B; FR2477655A1; FR2477655B1; DE3008709A1

Abstract

In a cylinder piston device, the radial pressure exerted by the outer face of piston ring (11) is at a maximum in an axially intermediate zone. The axial length of the piston ring is at least twice its radial thickness. The piston (6) divides cylinder (2) into two working chambers (7a, 7b) interconnected by fluid throttles (8). <IMAGE>

Description

SPECIFICATION A cylinder piston device The present invention is directed to a cylinder piston device, particularly for use as part of a shock absorber of a vehicle or as part of a spring suspension unit of a vehicle.

It is known to have a cylinder piston device comprising a cylinder member having an axis and two ends defining a cavity therein, a piston rod unit with a piston rod member axially movable with respect to the cylinder member, a portion of the piston rod member being housed within the cavity, a piston unit being fixed to the portion of the piston rod member within the cavity, the piston unit defining two working chambers within the cavity, the working chambers being interconnected by throttled fluid connection means, the piston unit being provided with a piston ring support face which is directed substantially in a radially outward direction towards an inner circumferential surface of the cylinder member, a piston ring member with a radially inner circumferential face and a radially outer circumferential face being supported by its radially inner circumferential face on the piston ring supporting face and engaging by its radially outer circumferential face the inner circumferential surface of the cylinder member, the axial length of the piston ring member is at least twice the radial thickness of the piston ring member, the piston ring member being axially fixed with respect to the piston unit, and a fluid being contained within the working chambers.

Such a piston ring unit is known e.g. from German Gebrauchsmuster 77 25 888 or from German Offenlegungsschrift 27 16 927.

It has been found that in the known cylinder piston devices of this type (hereinafter referred to as "a cylinder piston device of the type defined") having piston ring members of considerable axial length there is the risk of the piston ring member to be blocked with respect to the inner circumferential surface of the cylinder member at elevated operational temperatures, whereas at low operational temperatures the sealing effect of the piston ring member becomes unsatisfactory; further at low temperatures the piston ring member becomes radially and/or axially movable with respect to the cylinder member and/or the piston unit so that in operation a noise occurs.

According to the present invention there is provided a cylinder piston device of the type defined in which the radial pressure exerted by the radially outer face of the piston ring member onto the inner circumferential surface of the cylinder member is at a maximum in an axially intermediate zone of the outer circumferential face and decreases towards the respective axial ends of the piston ring member.

The axial length of the piston ring member may be at least three times, and preferably at least four times the radial thickness of the piston ring member.

When increased operational temperatures occur or when radial forces are to be transmitted between the piston unit and the cylinder member the radial pressure between the piston ring member and the cylinder member is mainly increased outside said axially intermediate zone in which the pressure is a maximum under normal operational conditions so that the increase of pressure within said intermediate zone is moderate. This is of particular interest with shock absorbers and spring suspension units of motor vehicles which on the one hand are subject to considerable variations of the operational temperature and on the other hand may be used for transmitting transverse forces from an associated vehicle wheel to the body structure of the vehicle.

The distribution of radial pressure according to this invention may be achieved in that the radially outer circumferential face of the piston ring member is generated by a curve rotated around said axis, which curve is convex towards the inner circumferential surface of the cylinder member.

Alternatively or additionally the piston ring supporting face may be generated by a curve rotated about said axis, which curve is convex towards said inner circumferential surface of the cylinder member. According to a further alternative the supporting face may comprise a radially outwardly directed annular projection in an axially intermediate zone between the axial ends of said piston ring member.

In each case when the operational temperature is increased and/or when radial forces are to be transmitted between the piston unit and the cylinder member, the area in which radial pressure occurs is increased by radial deformation of the piston ring member and/or axial flow of the material of the piston ring member.

The various features of novelty which characterize the invention are pointed out with particularily in the claims annexed to and following part of this disclosure.

By way of example, eight embodiments of a cylinder piston device according to the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is an axially extending section through a spring device incorporating the present invention, Fig. 2 is a sectional view of the piston unit of the cylinder piston device as shown in Fig. 1, Fig. 3 is a sectional view of the piston unit according to a second embodiment, Fig. 4 is a detail of a piston ring member of the piston unit of Fig. 3, Fig. 5 is a sectional view of a third embodiment of a piston unit, Fig. 6 is a fourth embodiment of a piston unit of this invention, Fig. 7 is a fifth embodiment of a piston unit of this invention, Fig. 8 is a sixth embodiment of a piston unit of this invention, Fig. 9 is a seventh embodiment of a piston unit of this invention, and Fig. 10 is an eighth embodiment of a piston unit of this invention.

Fig. 1 shows a cylinder piston device of this invention forming a part of a spring suspension unit or a telescopic strut. The cylinder piston device of Fig. 1 is to be inserted into an outer container (not shown) of such a spring suspension unit or telescopic strut.

The cylinder piston device comprises a tubular container 1. Within this tubular container 1 there is provided a cylinder member 2. The cylinder member 2 is provided at its lower end in Fig. 1 with a bottom member 3. The bottom member 3 is in contact with a bottom wall I a of the tubular container 1. A piston rod sealing and guiding unit 4 is inserted into both the upper end of the cylinder member 2 and the upper end of the tubular container 1. The cylinder member 2 is centered with respect to the tubular container 1 by the bottom member 3 and the piston rod guiding and sealing unit 4. The cylinder member 2 is under axial compressive tension between the bottom wall 1 a and the piston rod guiding and sealing unit 4. A cavity 7 is defined within the cylinder member 2 between the bottom member 3 and the piston rod guiding and sealing unit 4.An annular chamber 9 is defined between the cylinder member 2 and the tubular container 1.

A piston rod member 5 extends inward and outward of the cavity 7 within the cylinder member 2 through the piston rod guiding and sealing unit 4. A piston unit 6 is provided at the inner end of the piston rod member 5. The cavity 7 is subdivided by the piston unit 6 into two working chambers 7a, 7b. The working chambers 7a and 7b are interconnected by throttled fluid connection means 8 passing through the piston unit 6 in substantially axial direction. The working chamber 7b is connected to the annular chamber 9 by throttled passage means 3a extending through the bottom member 3. The working chambers 7a and 7b are filled with a hydraulic liquid. The annular chamber 9 is partially filled with this hydraulic liquid while the remainder of the annular chamber 9 is filled with a gas. This gas may be under atmospheric or under superatmospheric pressure.

The piston unit 6 comprises a piston member 6a.

The piston unit is shown in more detail in Fig. 2.

The piston member 6a is provided as shown in Fig. 2 with an annular recess 10. This annular recess 10 is defined by a substantially radially directed piston ring supporting face 1 Oa and end walls lOb and 1 Oc. The end walls 1 Ob and 1 Oc are integral with the piston member 6a. In the recess 10 there is provided a piston ring member 11 having a radially inner circumferential face 11 a and a radially outer circumferential face 11 b. The radially inner circumferential face 11 a is supported in radial direction by the piston ring supporting face 1 Oa. The radially outer circumferential face 1 b is defined by a curve rotated around the axis of the piston unit, which curve is convex towards the inner circumferential face 2a of the cylinder member 2.It is to be noted that only the apex area 1 c of the outer circumferential face 11 b of the piston ring member 11 is in engagement with the inner circumferential surface 2a of the cylinder member 2. The piston ring member 11 is radially compressed between the piston ring supporting face 1 0a and the inner circumferential surface 2a when the piston unit 6 is inserted into the cylinder member 2. The radial compression occurring on assembling in the apex area 11 c is such that even under the lowest temperature conditions to be expected there is still a satisfactory sealing effect between the piston ring member 11 and the inner circumferential face 2a.On the other hand, when elevated temperature conditions occur the apex area 11 c in which radial pressure is transmitted from the piston ring member 11 to the inner circumferential surface 2a of the cylinder member 2 is broadened in axial direction due to the axial compressibility of the material of the piston ring member 11 which can be manufactured of plastic material such as polytetrafluorethylene. So, on occurring of elevated temperature conditions the radial pressure occurring between the piston ring member 11 and the inner circumferential surface 2a at the apex is increased only to a moderate extent, whereas the axial width of the apex area in which a radial pressure is transmitted is increased.

Therefore the frictional resistance against axial movement of the piston unit 6 with respect to the cylinder member 2 is increased only to a moderate extent.

Assuming that a lubricant is provided on the inner circumferential surface 2a of the cylinder member 2 it is to be noted that this lubricant is collected in the wedge-shaped gaps 111 d between the outer circumferential face 11 b and the inner circumferential surface 2a so that the lubrication is improved.

It is to be noted that the throttled fluid connection means 8 are defined by substantially axial bores and valve plates provided at the ends of these axial bores, which valve plates are biased in axial direction towards the ends of the bores.

In the embodiment of Fig. 3 analogous parts are designated by the same reference numerals as in Fig. 2 increased by 100.

It is to be noted that in the embodiments of Figs. 3 and 4 the piston ring member 111 comprises an annular carrier member 111 e and an anti-friction layer 111 f of e.g. plastic material. The outer circumferential face 111 b has the same convex configuration as shown in Fig. 2.

In the embodiment of Fig. 3 the recess 1-10 is defined by the piston ring supporting face 11 Oa and the lower end wall 11 Oc. The end wall 11 Oc is integral with the piston member 1 06a. At its upper axial end the recess 110 is confined by the axially extending wall 1 3a of a pot-shaped abutment unit 113. This pot-shaped abutment unit 113 is provided with a bottom portion 1 3b.

The bottom portion 1 3b is provided with a central aperture 1 3c which surrounds an axial extension 1 05a of the piston rod 105 and is axially fixed between the piston member 1 06a and a shoulder 1 05b of the piston rod 105, the piston member 1 06a being axially fixed by a nut 106b. A throttling valve member 108a and a valve member biasing member 1 08b are fastened between the upper terminal face of the piston member 1 06a and the bottom portion 113b. The bottom portion 11 3b is provided with axial bores 11 3d allowing flow of liquid between the working chambers 1 07a and 1 Q7b.

As shown in Fig. 4, the piston ring member 111 is provided with a slot 11 5 extending between the axial ends of the piston ring member 111. The slot 11 5 has a Z-shaped configuration comprising axially extending end portions 11 5a and 11 sub and a substantially peripherally extending middle portion 11 sic. The edges defining the middle portion 11 sic may be biased against each other due to an inner tension of the piston ring member 111 so that a good sealing action is defined also in the slot area.

It is to be noted that the slotted embodiment of the piston ring member as shown in Fig. 4 is particularly useful in an embodiment as shown in Fig. 2 in which the end walls 1 Ob and 10c are integral with the piston member 6a, because due to the slot the mounting of the piston ring member into the recess is facilitated. On the other hand it is to be noted that the closed piston ring member 11 of Fig. 2 could be used also in the embodiment of Fig. 3 where the mounting of the piston ring member is facilitated by the abutment unit 113 being detachably mounted onto the piston rod 105.

In the embodiment of Fig. 5 analogous parts are designated by the same reference numerals as in Figs. 2 and 3 increased by 200 and 100 respectively. In the embodiment of Fig. 5 the piston ring member 211 is defined by the axially extending portion of a pot-shaped piston ring unit 217. The recess 210 is defined by the piston ring supporting face 21 0a and the upper end wall 21 Ob. This upper end wall 21 Ob is integral with the piston member 206a. The piston ring unit 217 is provided with a bottom portion 217a. This bottom portion 21 7a is provided with a central aperture 21 7b surrounding the extension 205a of the piston rod 205.The lower end of the extension 205a is curled in radially outward direction so that the bottom portion 21 7a is fixed in axial direction with respect to the piston rod 205, the upper end of the axially extending piston ring member 211 being in engagement with the upper end wall 21 Ob. The lower end 219 of the extension 205a may be tubular before curling and may be curled only after the piston ring unit 21 7 has been mounted. The bottom portion 217a of the piston ring unit 217 is provided with holes 21 7c allowing liquid to pass between the working chambers 207a and 207b when the piston unit 206 moves in axial direction.

It is to be noted that within the pot-shaped piston unit 21 7 there is provided a helical compression spring 208c biasing a disc-shaped valve member 208d towards the lower exit of the fluid connection means 208. The lower end of the helical compression spring 208c is supported by a spring supporting nut 208e. A distance sleeve or a stack of distance discs may be provided between the spring support nut 208e and the piston fastening nut 206b. The embodiment of Fig. 6 is similar to the embodiment of Fig. 2. Analogous parts are designated by the same reference numerals as in Fig. 2 increased by 300.

In the embodiment of Fig. 6 the piston ring supporting face 31 0a on the piston member 306a is defined by a curve rotated about the axis of the piston unit, which curve is convex towards the inner circumferential surface 302a. The inner and outer circumferential faces 311 a and 311 b of the piston ring member 311 are both substantially cylindrical. Also in this embodiment the piston ring 311 is dimensioned such that when being mounted under normal operational temperature it is compressed between the inner circumferential face 302a and the piston ring supporting face 31 ova. The radial compression is such that even under low operational temperatures a sufficient sealing action is still achieved.When the operational temperature is increased the radial pressure in the apex area 311 c is increased only to a moderate extent, whereas the axial width of the apex area in which a radial pressure is transmitted is increased.

Moreover, when increase in operation temperature occurs the material of the piston ring member 311 can escape into the wedge-shaped gaps 320.

In the embodiment of Fig. 7 analogous parts are designated by the same reference numerals as in the preceding figures, increased by 400, 300, 200 and 100 respectively.

In Fig. 7 the piston unit 406 comprises two piston members 406a and 406d. The annular recess 410 is defined by piston ring supporting faces 41 Oaa and 41 Oab of the piston member 406a and the piston member 406d respectively.

In the piston ring supporting face 41 Oab there is provided an annular groove 41 owe. In the annular groove 41 0e there is housed an annular support member 410f which projects in radial direction beyond the piston ring supporting faces 41 Oaa and 41 Oab. The piston ring member 411 is supported with its radially inward circumferential face 411 a by the annular support member 410f and by the piston ring supporting faces 41 Oaa and 41 Oab. The piston ring member 411 is convex towards the inner circumferential surface 402a and concave towards the axis. This shape may be pre-fabricated when the piston ring member 411 is manufactured or may be due to the piston ring member 411 being mounted over the projecting annular support member 410f.

It is to be noted that the piston ring member 411 can easily be mounted before the piston members 406a and 406d are assembled.

It is to be noted that also in this embodiment the radial pressure is at a maximum in the apex area 411 c and decreases towards the ends of the piston ring member 411. On increase of temperature material of the piston ring member 411 can escape into the cavities defined on both axial sides of the annular support member 41 Of.

The embodiment as shown in Fig. 8 is similar to that of Fig. 7; analogous parts are designated by the same reference numerals increased by 100.

The piston unit of Fig. 8 comprises only one piston member 506. An annular groove 51 Oe is provided in the middle of the length of the piston ring supporting face 51 Oa. An annular support member 510f is housed in the groove SlOe. The annular support member 510f may be a metallic circlip having a slot. The piston ring member 511 is deformed in radially outward direction by said annular support member 510f so as to engage the inner circumferential face 502a. The piston ring member 511 is made of a plastic material and has a substantially cylindrical form before mounting.

The radial thickness of the piston ring member is relatively small so that the piston ring member 511 can be mounted in axial direction by extension in peripheral direction, and is brought into the configuration as shown in Fig. 8 when applied to the annular support member 510f.

The embodiments as shown in Figs. 9 and 10 are very similar to the embodiment as shown in Fig. 2, analogous parts being designated by the same reference numerals increased by 600 and 700 respectively.

In the embodiment of Fig. 9 the piston ring member 611 is fixed in axial direction by an annular wall 610b and by the lower end of the tubular piston member 606a being curled in outward direction, this deformation by curling being made only after the piston ring member 611 has been mounted onto the piston member 606a.

In the embodiment of Fig. 10 the piston ring member 711 is secured against downward movement by projections 710c which are made in the piston member 706a after the piston ring member 711 has been mounted on the piston member 706a.

In the embodiment of Figs. 9 and 10 the piston ring members 611 and 711 respectively, can be easily mounted even if they have a considerable radial thickness without having a slot dividing them in axial direction.

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.

In particular, it is to be noted that the features of the different embodiments of this invention can be combined.

With respect to the embodiment of Fig. 7 it is still to be noted that the piston unit consisting of two piston members can easily be manufactured because both piston members can be made according to conventional sintering technique without subsequent machining operation. Also the annular groove can be made during the sintering step.

It is to be noted that in all embodiments of the invention the radial pressure between the piston ring member and the inner circumferential surface of the cylinder member can be well defined to a predetermined value.

Further, in all embodiments on increase of temperature the material of the piston ring member can escape to a certain degree in axial direction so that the radial pressure is only increased to a moderate extent.

Some advantages of these embodiments of a cylinder piston device according to the present invention are that low frictional forces occur between the piston ring member and the inner circumferential surface of the cylinder member without the sealing action therebetween being adversely affected under low temperatures, and that radial forces can be transmitted between tulle piston unit and the cylinder member without a large increase in these frictional forces. Also, the elements of which the piston unit of these embodiments of a cylinder piston device according to the invention is comprised are both easily and economically manufactured and assembled.

Claims

1.A A cylinder piston device comprising: a cylinder member having an axis and two ends defining a cavity therein, a piston rod unit with a piston rod member axially movable with respect to said cylinder member, a portion of said piston rod member being housed within said cavity, a piston unit being fixed to said portion of said piston rod member within said cavity, said piston unit defining two working chambers within said cavity, said working chambers being interconnected by throttled fluid connection means, said piston unit being provided with a piston ring supporting face which is directed substantially in a radially outward direction towards an inner circumferential surface of said cylinder member, a piston ring member with a radially inner circumferential face and a radially outer circumferential face being supported by its radially inner circumferential face on said piston ring supporting face, and engaging by its radially outer circumferential face said inner circumferential surface of said cylinder member, the axial length of said piston ring member being at least twice the radial thickness of said piston ring member, said piston ring member being axially fixed with respect to said piston unit, and a fluid being contained within said working chambers, wherein the radial pressure exerted by the radially outer face of said piston ring member onto said inner circumferential surface of said cylinder member is at a maximum in an axially intermediate zone of said outer circumferential face and decreases towards the respective axial ends of said piston ring member.

2. A cylinder piston device as claimed in claim 1 ,wherein the axial length of said piston ring member is at least three times the radial thickness of said piston ring member.

3. A cylinder piston device as claimed in claim 1, wherein the axial length of said piston ring member is at least four times the radial thickness of said piston ring member.

4. A cylinder piston device as claimed in any preceding claim, wherein said piston ring member is made of plastic material.

5. A cylinder piston device as claimed in any one of claims 1,2 and 3 wherein said piston ring member consists of a carrier member which is coated at least on its radially outer face by an antifriction layer.

6. A cylinder piston device as claimed in claim 5, wherein said carrier member is a metallic carrier member and wherein said anti-friction layer comprises plastic material.

7. A cylinder piston device as claimed in any one of claims 1 to 4 wherein the radially outer circumferential face of said piston ring member is generated by a curve rotated around said axis, which curve is convex towards said inner circumferential surface of said cylinder member.

8. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said supporting face comprises a radially outwardly directed annular projection in an axially intermediate zone between the axial ends of said piston.ring member.

9. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said piston ring supporting face is generated by a curve rotated about said axis, which curve is convex towards said inner circumferential surface of said cylinder member.

10. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said piston unit comprises a piston member, a recess being provided in an outer circumferential face of said piston member, said recess having a bottom face defining said piston ring supporting face and end walls engaging the axially terminal faces of the piston ring member.

11. A cylinder piston device as claimed in claim 10, wherein said end walls are integral with said piston member.

12. A cylinder piston device as claimed in claim 10, wherein only one of said end walls is integral with said piston member and the other of said end walls is defined by an annular abutment member mounted onto said piston member.

13. A cylinder piston device as claimed in claim 12, wherein said annular abutment member is defined by an axially extending side wall of a pot-shaped abutment unit, said pot-shaped abutment unit having a bottom portion fixed to said piston rod unit.

14. A cylinder piston device as claimed in claim 13, wherein said throttled fluid connection means pass through said piston unit in a substantially axial direction and wherein said bottom portion of said pot-shaped abutment unit acts on at least one valve member of said throttled fluid connection means so as to fasten at least one valve member to said piston unit.

1 5. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said piston unit comprises two piston members axially adjacent each other, said piston ring supporting face extending over at least a part of the axial length of both said piston members.

1 6. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said supporting face is provided with an annular groove in an axially intermediate area between the axial ends of said piston ring member, said annular groove accommodating an annular support member, said annular support member extending in radially outward direction beyond said supporting face.

17. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said piston unit comprises a piston member said piston member comprising said piston ring supporting face and abutment faces for axially fixing said piston ring member with respect to said piston member, one of said abutment faces being defined by a deformation of said piston member, said deformation being made only after said piston ring member has been mounted onto said piston member

18.A cylinder piston device as claimed in any one of claims 1 to 3 wherein said piston unit is provided with a recess having a bottom face defining said piston ring supporting face and an axial abutment face only at one axial end thereof, and wherein said piston ring member is defined by an axially extending wall portion of a pot-shaped piston ring unit, said pot-shaped piston ring unit having a bottom portion axially fixed to said piston rod unit, the axial end of said wall portion remote from said bottom portion engaging said abutment face.

19. A cylinder piston device as claimed in claim 18, wherein said fluid connection means pass through said piston unit and throttling means associated to said throttled fluid connection means are at least partially housed within said pot-shaped piston ring unit.

20. A cylinder piston device as claimed in claim 18, wherein said bottom portion is fixed to said piston rod unit by a deformation of a portion of said piston rod unit, which deformation is made only after said pot-shaped piston ring unit has been mounted onto said piston member.

21. A cylinder piston device as claimed in any one of claims 1 to 3 wherein said piston ring member is provided with a slot extending between the axial ends of said piston ring member.

22. A cylinder piston device as claimed in claim 21, wherein said slot is substantially Z-shaped having substantially axially extending end portions adjacent the respective axial ends of said piston ring member and a middle portion extending in substantially peripheral direction.

23. A cylinder piston device as claimed in claim 22, wherein slot faces defining said middle portion are biased against each other in axial direction.

24. A cylinder piston device as claimed in any one of claims 1 to 4 wherein said cylinder member is provided with a piston rod guiding and sealing unit at one end thereof and with a bottom member at the other end thereof, a first working chamber being defined adjacent said guiding and sealing unit and a second working chamber being defined adjacent said bottom member, said second working chamber being connected by throttled passage means to a fluid reservoir.

25. A cylinder piston device as claimed in claim 24, wherein said cylinder member is surrounded by a tubular container member, said fluid reservoir being defined by an annular space positioned in radial direction between said cylinder member and said tubular container.

26. A cylinder piston device substantially as hereinbefore described with reference to and as shown in figures 1 and 2, or in figures 3 and 4, or figure 5 or figure 6, or figure 7 or figure 8, or figure 9 or figure 10 of the accompanying drawings.

27. A shock absorber for a vehicle having a cylinder piston device as claimed in any preceding claim.

28. A spring suspension unit for a vehicle comprising a cylinder piston device as claimed in any one of claims 1 to 26.