ASSEMBLY FOR A FLUID-FILLED PISTON-CYLINDER UNIT AND FLUID-FILLED PISTON-CYLINDER UNIT HAVING AN ASSEMBLY OF THIS TYPE

Abstract

An assembly for a fluid-filled piston-cylinder unit comprises a main body having an assembly longitudinal axis (24), a valve unit integrated in the main body and having an overflow channel, which valve unit seals the overflow channel when the assembly is moved along the assembly longitudinal axis in a first direction and releases the overflow channel, in dependence on the fluid pressure, when the assembly is moved along the assembly longitudinal axis in a second direction. Furthermore, the assembly comprises an outer seal element that is arranged on the main body so as to be moved along the assembly longitudinal axis, for abutting in a sealing manner against an inner surface of the housing, and at least one undercut element formed on the main body for engaging in an interlocking manner behind a mating element of the piston-cylinder unit.

Claims

1. An assembly for a fluid-filled piston-cylinder unit, the assembly comprising a. a main body having an assembly longitudinal axis, b. a valve unit integrated in the main body, wherein said valve unit i. has an overflow channel, ii. seals the overflow channel when the assembly is moved along the assembly longitudinal axis in a first direction, iii. releases the overflow channel, in dependence on the fluid pressure, when the assembly is moved along the assembly longitudinal axis in a second direction, c. an outer seal element that is arranged on the main body so as to be moved along the assembly longitudinal axis, for abutting in a sealing manner against an inner surface of the housing, d. at least one undercut element formed on the main body for engaging in an interlocking manner behind a mating element of the piston-cylinder unit.

2. An assembly according to claim 1, comprising a plurality of undercut elements.

3. An assembly according to claim 1, wherein the valve unit has a valve element which is movable along the assembly longitudinal axis and abuts in a sealing manner against a valve seat in order to seal the overflow channel.

4. An assembly according to claim 3, wherein the valve element is pressed against the valve seat by means of a spring element.

5. An assembly according to claim 1, wherein the main body is configured in two parts with a main body front part and a main body rear part which can be connected thereto.

6. An assembly according to claim 1, wherein the at least one undercut element is arranged on the end face of the main body.

7. An assembly according to claim 1, wherein the at least one undercut element is configured as a snap-on hook which is designed to snap axially onto the mating element.

8. An assembly according to claim 1, wherein the at least one undercut element defines a slot into which the mating element of the piston-cylinder unit is insertable.

9. An assembly according to claim 1, wherein the valve unit, when the assembly is moved along the assembly longitudinal axis in the first direction, is bringable into an overload position in which the overflow channel is released.

10. An assembly according to claim 1, wherein the overflow channel has at least one transverse channel which extends at least in sections transversely and in particular perpendicularly to the assembly longitudinal axis on an end face of the main body that faces the at least one undercut element.

11. An assembly according to claim 1, wherein the overflow channel has at least one axial recess extending along the assembly longitudinal axis on an end face of the main body that faces the at least one undercut element.

12. An assembly according to claim 1, wherein the overflow channel has a passage opening (39, 42) integrated in the main body.

13. A fluid-filled piston-cylinder unit comprising a. a cylindrical housing having a housing longitudinal axis and an interior space, b. a piston rod which is guided out of the housing in a sealed manner and is moveable along the housing longitudinal axis, c. a piston which is fastened to the piston rod and which divides the interior space into a first partial interior space and a second partial interior space, wherein the partial interior spaces can be connected to one another fluidically via the overflow channel, d. an assembly for a fluid-filled piston-cylinder unit, the assembly comprising a main body having an assembly longitudinal axis, a valve unit integrated in the main body, said valve unit i. having an overflow channel, ii. sealing the overflow channel when the assembly is moved along the assembly longitudinal axis in a first direction, iii. releasing the overflow channel, in dependence on the fluid pressure, when the assembly is moved along the assembly longitudinal axis in a second direction, an outer seal element that is arranged on the main body so as to be moved along the assembly longitudinal axis, for abutting in a sealing manner against an inner surface of the housing, at least one undercut element formed on the main body for engaging in an interlocking manner behind a mating element of the piston-cylinder unit, wherein the assembly is held in a form-fit manner on the piston rod along the housing longitudinal axis.

14. A piston-cylinder unit according to claim 13, wherein the assembly is mounted on the mating element one of by sliding on along the housing longitudinal axis and to the housing longitudinal axis.

15. A piston-cylinder unit according to claim 13, wherein the assembly is one of detachably and non-detachably connected to the piston rod.

16. An assembly according to claim 2, wherein the plurality of undercut elements are arranged distributed in the circumferential direction around the assembly longitudinal axis.

17. An assembly according to claim 5, wherein the main body rear part is detachably connected to the main body front part.

18. An assembly according to claim 5, wherein the main body rear part is to be screwable to the main body front part.

19. An assembly according to claim 6, wherein the at least one undercut element is arranged on the main body front part.

20. An assembly according to claim 7, wherein the snap-on hook has a press-on bevel.

21. An assembly according to claim 12, wherein the passage opening extends up to an end face of the main body that faces the at least one undercut element.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0040] FIG. 1 shows a perspective, partially sectioned illustration of a piston-cylinder unit according to a first embodiment example,

[0041] FIG. 2 shows an enlarged detailed illustration according to detail II in FIG. 1,

[0042] FIG. 3 shows a sectional representation according to section line III-III in FIG. 1,

[0043] FIG. 4 shows an enlarged detailed illustration of detail IV in FIG. 3 indicating a fluid flow when the piston-cylinder unit is actuated in a direction of extraction,

[0044] FIG. 5 shows an illustration corresponding to FIG. 4 indicating the fluid flow when the piston-cylinder unit is actuated in the direction of insertion,

[0045] FIG. 6 shows an enlarged perspective illustration of an assembly of the piston-cylinder unit according to FIG. 1,

[0046] FIG. 7 shows a sectional representation corresponding to FIG. 3 of a piston-cylinder unit according to a second embodiment example,

[0047] FIG. 8 shows an enlarged detailed illustration of detail VIII in FIG. 7,

[0048] FIG. 9 shows a perspective illustration of the assembly according to the second embodiment example corresponding to FIG. 6,

[0049] FIG. 10 shows an enlarged detailed illustration of the detail X in FIG. 8,

[0050] FIG. 11 shows an illustration of the assembly according to FIG. 9 corresponding to FIG. 4 when the piston-cylinder unit is actuated in the direction of extraction,

[0051] FIG. 12 shows an illustration corresponding to FIG. 11 when the piston-cylinder unit is actuated in the direction of insertion,

[0052] FIG. 13 shows a sectional representation corresponding to FIG. 8 of an assembly of a piston-cylinder unit according to a third embodiment example,

[0053] FIG. 14 shows an illustration corresponding to FIG. 1 of a piston-cylinder unit according to a fourth embodiment example,

[0054] FIG. 15 shows an enlarged detail view of detail XV in FIG. 14,

[0055] FIG. 16 shows an illustration of the assembly of the piston-cylinder unit according to FIG. 14 corresponding to FIG. 6,

[0056] FIG. 17 shows an enlarged longitudinal section of a piston-cylinder unit according to a fifth embodiment example,

[0057] FIG. 18 shows an enlarged sectional representation of the assembly according to FIG. 17,

[0058] FIG. 19 shows a side view of the assembly in FIG. 18,

[0059] FIG. 20 shows a view according to arrow XX in FIG. 19,

[0060] FIG. 21 shows a side view of the valve element of the assembly according to FIG. 18,

[0061] FIG. 22 shows a sectional view according to section line XXII-XXII in FIG. 21,

[0062] FIG. 23 shows a force-speed diagram for the piston-cylinder unit according to FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] A piston-cylinder unit marked as a whole with 1 in FIGS. 1 to 6 has a cylindrical housing 2 with a housing longitudinal axis 3, wherein the housing 2 encloses an interior space 4. A fluid is arranged in the interior space 4 of the housing 2. The piston-cylinder unit 1 is filled with fluid. The fluid can be a liquid, in particular a hydraulic liquid, in particular a hydraulic oil, or a gas. A piston rod 5 is led out of the housing 2 in a sealed manner. A guide/seal unit 6 that is arranged at the piston rod end of the housing 2 is used for this purpose. In addition to sealing the piston rod 5, the guide/seal unit 6 also ensures the guided displacement of the piston rod 5 along the housing longitudinal axis 3.

[0064] The guide/seal unit 6 is fixed in the housing 2 by means of indentations 7 axially with respect to the housing longitudinal axis 3.

[0065] The guide/seal unit 6 comprises a supporting disc 8 at the piston rod end of the housing 2, which ensures radial support of the piston rod 5. Along the housing longitudinal axis 3, a piston rod seal element 9 adjoins the supporting disc 8 and abuts in a sealing manner against the outside of the piston rod 5. In particular, this prevents impurities from entering the housing 2, in particular the interior space 4, and/or fluid from escaping from the housing 2. A limiting element 10 adjoins the piston rod seal element 9 along the housing longitudinal axis 3, which limiting element 10 faces the interior space 4 and limits the latter axially. The limiting element 10 serves in particular as an axial stop element for a piston 13 that is attached to the piston rod 5.

[0066] The piston rod 5 is arranged with a first, outer end 11 outside the housing 2. According to the embodiment example shown, the first end 11 is in the form of a threaded pin to which a fastening element not shown can be attached, in particular screwed on. Such a fastening element serves to fasten the piston-cylinder unit 1 to an object. The fastening element can also be firmly, in particular non-detachably, attached to the first end 11 of the piston rod 5.

[0067] At a second end 12 that is opposite the first end 11, the piston 13 and a mating element 14 are attached to the piston rod 5. The piston 13 and the mating element 14 are held axially on the piston rod 5 along the housing longitudinal axis 3 between an abutment shoulder 15 of the piston rod 5 and an end face collar 16 of the piston rod 5. The end face collar 16 of the piston rod 5 is produced in particular by forming and projects in the radial direction with respect to the housing longitudinal axis 3 with respect to the outer diameter of a region of the piston rod 5 in which the piston 13 and the mating element 14 are arranged. The piston 13 and the mating element 14 are held in an interlocking manner on the piston rod 5.

[0068] The piston 13 divides the interior space 4 into a first partial interior space 17 and a second partial interior space 18. The first partial interior space 17 faces the piston rod end of the housing 2. The first partial interior space 17 is formed between the piston 13 and the first limiting element 10. According to the illustrations in FIGS. 2 and 4, the piston rod 5 with the piston 13 is in a maximum extraction position. This means that the piston 13 is in contact with the limiting element 10. The first partial interior space 17 is not present in this arrangement.

[0069] The second partial interior space 18 is formed between the piston 13 and the end of the housing 2 on the housing side in the axial direction with respect to the housing longitudinal axis 3. In the arrangement of the piston rod 5 with the piston 13 according to FIGS. 2 and 4, the second partial interior space 18 corresponds to the interior space 4.

[0070] The piston 13 is designed in the shape of a disc. The piston 13 has at least one, and in particular multiple, through-flow openings 19 through which the fluid can flow from the first partial interior space 17 into the second partial interior space 18 and vice versa.

[0071] The through-flow openings 19 are arranged in a disc section 20 of the piston 13. The disc section 20 is characterized by the fact that its outer diameter d.sub.A essentially corresponds to the inner diameter d.sub.I of the housing 2. In particular, the following applies: d.sub.A<d.sub.I, in particular d.sub.A?0.9.Math.d.sub.I, in particular d.sub.A?0.95.Math.d.sub.I and in particular d.sub.A?0.98.Math.d.sub.I.

[0072] A spacer section 21 is integrally in one piece with the disc section 20 on the piston 13. The spacer section 21 has a reduced outer diameter d.sub.A,red compared to the disc section 20, which is at most 80%, in particular at most 70% and in particular at most 60% of the outer diameter d.sub.A of the disc section 20.

[0073] The piston 13 is configured in a stepped manner due to the design with disc section 20 and spacer section 21. The mating element 14 abuts against the distance section 21. The mating element 14 is designed as an annular disc with a disc diameter d.sub.S. The following applies: d.sub.A,red<d.sub.S<d.sub.A.

[0074] According to the embodiment example shown, the piston 13 and the mating element 14 are manufactured as two separate components. However, it is also conceivable that the disc-shaped mating element 14 is formed in one piece with the piston 13. In particular, it is conceivable that the piston 13 and/or the mating element 14 are configured in one piece with the piston rod 5.

[0075] An assembly designated as a whole with 22 is held in an interlocking manner on the mating element 14.

[0076] The assembly 22 has a main body 23 which has an assembly longitudinal axis 24. The assembly 22 is arranged in the housing 2 of the piston-cylinder unit 1 such that the assembly longitudinal axis 24 is oriented concentrically to the housing longitudinal axis 3. The main body 23 has a main body outer diameter d.sub.G which is substantially constant along the assembly longitudinal axis 24. The main body 23 is essentially configured to be sleeve-like. A maximum main body outer diameter d.sub.G is smaller than the inner diameter d.sub.I of the housing 2.

[0077] The main body 23 has an outer groove 25 in which an outer seal element 26 is arranged. The outer seal element 26 serves to abut in a sealing manner against the inner surface 27 of the housing 2 of the piston-cylinder unit 1. The outer groove 25 has a groove width b.sub.N oriented along the assembly longitudinal axis 24, which groove width b.sub.N is greater than the thickness d.sub.D of the outer seal element 26 oriented along the assembly longitudinal axis 24. The outer groove 25 is bounded by a first groove flank 28 which, according to the embodiment example shown, is oriented towards the piston rod 5. Due to the outer seal element 26 abutting against the first groove flank 28, a fluid flow on an outer side of the main body 23 is sealed by the outer seal element 26.

[0078] The outer groove 25 has a second groove flank 29, on whose end face facing the outer groove 25 at least one and in particular multiple, in particular four, groove transverse openings 30 are arranged along the outer circumference. This ensures a fluid flow through the at least one groove transverse opening 30 when the outer seal element 26 abuts against the second groove flank 29.

[0079] According to the embodiment example shown, the main body 23 is configured in two parts with a main body front part 31 and a main body rear part 32 detachably connected, in particular screwed, thereto. For this purpose, the main body front part 31 has an external thread onto which the main body rear part 32 is screwed with a corresponding internal thread. Due to the fact that the main body 23 is made in two parts, the design of the external groove 25 is simplified. In particular, the outer groove 25 is formed between the main body front part 31 and the main body rear part 32. In particular, the first groove flank 28 is formed on the main body front part 31. In particular, the second groove flank 29 is formed on the main body rear part 32.

[0080] The main body 23 has an undercut element 33 with which the assembly 22 is held on the mating element 14 and thus on the piston rod 5 in an axially interlocking manner. The undercut element 33 engages behind the mating element 14 in a direction along the assembly longitudinal axis 24. The undercut element 33 is arranged in one piece on the main body front part 31 and in particular on an end face 34 of the main body 23 facing the piston rod 5. In particular, the undercut element 33 is formed in one piece on the main body 23.

[0081] The undercut element 33 is designed as an axial web which extends along the assembly longitudinal axis 24 in the axial direction. The axial web is arranged in the region of the outer circumference of the main body 23, in particular of the main body front part 31. The axial web is essentially rigid. The axial web has a substantially hook-shaped contour. The axial web of the undercut element 33 has a hook projection 35 projecting radially inwards with respect to the assembly longitudinal axis 24. A slot 36 is defined in the axial direction by the hook projection 35 and the end face 34. The slot 36 has a slot width b.sub.Sch which essentially corresponds to the disc thickness of the mating element 14. In particular, the slot 36 has a slot inner diameter d.sub.IS which substantially corresponds to the disc diameter d.sub.S. The mating element 14 is arranged reliably and in an interlocking manner in the slot 36.

[0082] The undercut element 33, in particular the hook-shaped axial web, extends in the circumferential direction around the assembly longitudinal axis 24 with an opening angle of 180?. According to the embodiment example shown, the undercut element 33 extends along half the circumference of the main body 23. It is also conceivable that the opening angle is smaller than 180?.

[0083] The installation of the main body 23 on the piston rod 5, in particular on the mating element 14, is possible in a particularly uncomplicated manner by sliding the main body 23, as shown in FIG. 6, along a slide-on direction 37, which is oriented transversely and in particular perpendicularly to the assembly longitudinal axis 24, i.e. to the main body longitudinal axis 3. The slot 36 serves to receive the mating element 14. By sliding the assembly 22 onto the mating element 14, the assembly 22 is detachably connected to the piston rod 5. To release the connection, the assembly 22 can be pulled off the piston rod 5 or the mating element 14 in the opposite direction to the slide-on direction 37.

[0084] The main body 23 has a valve unit with an integrated overflow channel. The overflow channel has a first integrated passage opening 39, which is arranged on the end face of the main body 23 and faces the piston rod 5. In particular, the first passage opening 39 is arranged facing the undercut element 33 and the end face 34. The first passage opening 39 opens into a substantially U-shaped axial recess 40, which is arranged on the end face 34 of the main body 23. The axial recess 40 has a fluid connection with the first passage opening 39. As shown in FIG. 6, the axial recess 40 may extend in a radial direction with respect to the assembly longitudinal axis 24, to the outer contour of the main body 23. Alternatively, it is possible for the axial recess 40 to be configured cylindrically, for example, wherein a transverse channel ensures a fluid connection at the end face 34 of the main body 23 to the outer contour of the main body 23. Such a transverse channel is integrally formed by the axial recess 40 in the embodiment example shown.

[0085] The overflow opening has a spring receiving chamber 41 which has a fluid connection with the first passage opening 39. The spring receiving chamber 41 is essentially configured to be hollow-cylindrical and has a second passage opening 42 on an end side which is arranged opposite the first passage opening 39. The second passage opening 42 opens into the second partial interior space 18.

[0086] According to the embodiment example shown, the overflow channel is formed by the axial recess 40, the first passage opening 39, the spring receiving chamber 41 and the second passage opening 42, which are arranged one behind the other along the assembly longitudinal axis 24 in the order mentioned and each have a fluid connection with each other in pairs.

[0087] At the transition of the spring receiving chamber 41 into the second passage opening 42, an integral abutment shoulder is configured on the main body rear part. The integral abutment shoulder has a sealing surface which forms a valve seat 43 of the valve unit 38. The valve unit 38 further comprises a bolt-shaped valve element 44, which is arranged with a cylinder section 45 substantially within the second passage opening 42. A radial collar 46 that projects in a radial direction with respect to the assembly longitudinal axis 24 relative to the cylinder section 45 is arranged within the spring receiving chamber 41. On an underside of the radial collar 46, the valve element 44 has a sealing surface with which the valve element 44 can abut in a sealing manner against the valve seat 43. In this case, the overflow channel, in particular the second passage opening 42, is sealed. A fluid flow through the overflow channel is then prevented.

[0088] The valve unit 38 further comprises a spring element 47 in the form of a mechanical helical compression spring, which is supported in the axial direction on a transverse wall 48 surrounding the first passage opening 39 and on an end face 49 of the valve element 44. The spring element 47 is dimensioned such that it exerts a spring force on the valve element 44 in such a manner that the valve element 44 is pressed against the valve seat 43. According to the embodiment example shown, the effective direction of the spring force is oriented from left to right as shown in FIG. 4, i.e. in a direction along the assembly longitudinal axis 24 oriented from the first passage opening 39 towards the second passage opening 42.

[0089] In the following, the function of the piston-cylinder unit, in particular the valve unit 38 of the retrofittable assembly 22 is explained in more detail with reference to FIGS. 4 and 5. When the piston rod 5 is actuated along a direction of extraction 50, the fluid is displaced from the first partial interior space 17 into the second partial interior space 18. In the process, the fluid pressure acts on the valve element 44 on the one hand along the overflow channel, i.e. via the axial recess 40, the first passage opening 39 and the spring receiving chamber 41. The fluid pressure acting in this way acts in the same direction as the spring element 47. The valve element 44 abuts in a sealing manner against the valve seat 43. The overflow channel is sealed. According to this embodiment example, the direction of extraction 50 corresponds to a first direction.

[0090] However, the fluid pressure also acts on the outer seal element 26, which is moved away from the first groove flank 28 along the assembly longitudinal axis 24and towards the second groove flank 29. As a result of the transverse opening 33, the outer seal element 26 is arranged spaced apart from the second groove flank 29. Fluid can flow around the outer seal element 26 in the region of the outer groove 25 and thus pass from the first partial interior space 17 into the second partial interior space 18. The fluid flow is symbolized in FIG. 4 by means of the flow part 51.

[0091] When the piston-cylinder unit 1 is actuated in a second direction, i.e. along a direction of insertion 52, the fluid is displaced from the second partial interior space 18 into the first partial interior space 17. In doing so, the fluid causes a fluid pressure on the outer seal element 26, which is moved towards the first groove flank 28 and prevents a flow around the main body 23 along the outer circumference, in particular in the region of the main body front part 31. The outer seal element 26 seals the main body 23 against the inner surface 27 of the housing 2.

[0092] Due to the fact that the valve element 44 is spring-mounted, as soon as the fluid pressure exerts a force on the valve element 44 that is greater than the spring force of the spring element 47, the valve element 44 is lifted off the valve seat 43. In this case, the overflow channel 39 to 42 is released. A fluid flow 51 from the second partial interior space 18 into the first partial interior space 17 along the overflow channel is possible

[0093] In the following, a second embodiment example of the invention is described with reference to FIGS. 7 to 12. Constructively identical parts are given the same reference signs as in the first embodiment example, the description of which is hereby referred to. Constructively different but functionally similar parts are given the same reference signs with a trailing letter a.

[0094] The essential difference compared to the first embodiment example is that the valve unit 38a of the assembly 22a is designed such that the overflow channel is blocked when actuated in the direction of insertion 52 and released when actuated in the direction of extraction 50. If the overflow channel s blocked when actuated along the first direction, the main body 23 is overflowed by the fluid on its outer surface. Fluid damping, i.e. damping of the displacement movement of the piston-cylinder unit 1a, then does not take place. When the overflow channel is released due to the fluid pressure and the fluid flows through the overflow channel, fluid damping takes place because the overflow channel, at least in sections, has a reduced flow diameter. According to this embodiment example, the direction of insertion 52 corresponds to the first direction and the direction of extraction 50 corresponds to the second direction.

[0095] The valve element 44 is arranged at the first passage opening 39 in the assembly 22a. Correspondingly, the valve seat 43a is arranged at the transition region of the spring receiving chamber 41 and the first passage opening 39.

[0096] The spring force exerted by the spring element 47 has an effective direction which is oriented along the second direction, i.e. the direction of extraction 50.

[0097] As in the first embodiment, the spring element 47 is supported on the end face 49 of the valve element 44. A steel ring 53 inserted into an integrated inner groove on the main body 23a serves for the opposite support.

[0098] Due to the inversion of action of the valve unit 38a, the elements 30 are formed on the first groove flank 28 and not on the second groove flank 29.

[0099] The outer seal element 26 is designed as an O-ring according to the embodiment example shown.

[0100] A further difference compared to the first embodiment example is that the main body 23a is configured in one piece. The main body 23a is in particular made of a plastic material, in particular POM, PEEK and/or PA.

[0101] The design of the valve seat 43a is explained in more detail with reference to FIG. 10. In the region of an abutment shoulder 56, which surrounds the first passage opening 39, an annular flat seal 54 is inserted on the end face, against which the valve element 44 abuts with the underside of the annular collar 46 in a sealing manner. According to the second embodiment example, the valve seat 43a thus has an additional element with the flat seal 54. The flat seal 54 is made of a sealing material, in particular of an elastomer material, of polytetrafluoroethylene (PTFE) and/or of a plastic composite material having sealing properties.

[0102] In the following, a third embodiment example of the invention is described with reference to FIG. 13. Constructively identical parts are given the same reference signs as in the two previous embodiment examples, the description of which is hereby referred to. Constructively different but functionally similar parts are given the same reference signs with a trailing letter b.

[0103] The assembly 22b corresponds essentially to that according to the second embodiment example, wherein the outer seal element 26b is designed as a piston ring. The valve ring is configured to be more stable compared to the O-ring of the previous embodiment example. The outer seal element 26b is particularly robust.

[0104] In the following, a fourth embodiment of the invention is described with reference to FIGS. 14 to 16. Constructively identical parts are given the same reference signs as in the previous embodiment examples, the description of which is hereby referred to. Constructively different but functionally similar parts are given the same reference signs with a trailing letter c.

[0105] The piston-cylinder unit 1c corresponds essentially to that of the first embodiment, wherein multiple, in particular four, undercut elements are provided, which are arranged spaced apart from one another in the circumferential direction around the assembly longitudinal axis 24 and in particular evenly distributed relative to one another. In the direction around the assembly longitudinal axis 24, two adjacent undercut elements 33c are each arranged with an opening angle of 90? to one another. The individual undercut elements are configured to be hook-shaped. In a longitudinal sectional representation, the undercut elements 33c are essentially identical to the undercut element 33 according to the first embodiment example.

[0106] The undercut elements 33c are each configured as snap-on hooks and each have a press-on bevel 55. The press-on bevel 55 is arranged to be inclined with respect to the assembly longitudinal axis 24. Starting from a free end of the undercut elements 33c, which faces the piston rod 5, the press-on bevel 55 is oriented to be inclined inwards in the radial direction and extends up to the hook projection 35 that protrudes radially inwards.

[0107] The undercut elements 33c each have an elasticity that allows the snap-on hooks to be elastically deflected radially outwards.

[0108] The assembly 22c can be mounted in a particularly uncomplicated manner on the piston rod 5. The piston rod 5 is slid onto the assembly 22c with the piston 13 and the mating element 14 axially along the assembly longitudinal axis 24. When the mating element 14 comes into contact with the undercut elements 33c, in particular with their press-on bevels 55, the undercut elements 33c are deflected radially outwards due to their flexibility. The radial deflection increases the closer the mating element 14 is moved in the direction of the end face 34 of the main body 23c. When the mating element 14 has passed the respective hook projections 35 of the undercut elements 33c and is arranged in the slot 36 formed by the undercut elements 33c, the hook-shaped snap-on hooks snap back into their initial position as shown in FIG. 16 due to their elasticity. The snap-on hooks engage behind the mating element 14 with the hook projections 35. Since there is no press-on bevel provided on the underside of the hook projections 35 facing the mating element 14, it is impossible to pull the assembly 22c off the mating element 14. The assembly 22c is non-detachably connected to the piston rod 5. The assembly 22c is reliably and robustly held on the piston rod 5. The installation is uncomplicated and, in particular, can be carried out in a fully automated manner.

[0109] In the following, a fifth embodiment example of the invention is described with reference to FIGS. 17 to 23. Constructively identical parts are given the same reference signs as in the previous embodiment examples, the description of which is hereby referred to. Constructively different but functionally similar parts are given the same reference signs with a trailing letter d.

[0110] The main body 23 is manufactured in one piece as a plastic component, in particular from POM, in particular by injection moulding. At its front end facing the mating element 14, the main body 23 has a plurality of snap-on hooks 33d, eight according to the embodiment example shown. The snap-on hooks 33d are each axially formed on a circumferentially closed ring section 57. The individual snap-on hooks 33d extend in the axial direction from the ring section 57.

[0111] Adjacent snap-on hooks 33d are separated from each other by an axial gap 66. As a result, the individual snap-on hooks 33d have a structural flexibility that favours snapping the main body 23 onto the mating element 14.

[0112] In the region of the snap-on hooks 33d, the main body 23 has an outer diameter D.sub.a which essentially corresponds to an inner diameter D.sub.i of the housing 2 of the piston-cylinder unit 1d. In particular, the following applies: D.sub.i?D.sub.a, in particular 1.01?D.sub.a?D.sub.i?1.2?D.sub.a. Due to the diameter ratios, on the one hand, a collision-free axial displacement of the assembly 22d in the housing 2 is ensured. On the other hand, it is ensured that the main body 23 and thus the assembly 22d as a whole does not accidentally detach from the piston rod 5 or the mating element 14. A radial displacement of the snap-on hooks 33d to the outside which is necessary for this purpose is limited by the inner surface 27 of the housing 2. The main body 23 is held in an interlocking manner on the mating element 14.

[0113] The piston rod 5 has a turned shoulder 65 at its end facing the assembly 22d, onto which the mating element 14 is placed. The material projecting axially at the mating element 14 is flanged so that the radially projecting end face collar 16 is formed. The mating element 14 is riveted to the piston rod 5 and in particular to the shoulder 65. The mating element 14 is also referred to as a riveted washer.

[0114] At a front end opposite the snap-on hooks 33d, the main body 23 has the second passage opening 42 in which the valve element 44 is arranged. In contrast to the previous embodiment examples, in the embodiment example shown here the sealed arrangement of the valve element 44 is not achieved by means of an axial valve seat, but by means of an integrated sealing lip 58, which is integrally formed on the main body 23. The sealing lip 58 is arranged as a radial projection in the second passage opening 42. In the region of the sealing lip 58, the inner diameter of the passage opening 42 is minimal.

[0115] The valve element 44 protrudes from the second passage opening 42 on the main body 23. A cap 59 is fitted to the valve element 44 at its free end and is axially fixed thereto. The cap 59 is axially fixed by a plurality of circumferential beadings 60. The cap 59 is held in an interlocking manner on the valve element 44.

[0116] The cap 59 is designed in particular as a hollow rivet or tubular rivet. The cap 59 is in particular made of steel. The cap 59 has a radial collar 61 that faces the main body 23, which radial collar 61 projects in the form of an annular disc in the radial direction relative to the valve element 44.

[0117] The radial collar 61 serves as an axial stop for the spring element 47. The spring element 47 is configured as a helical compression spring. The helical compression spring 47 is designed such that it exerts a compressive force on the radial collar 61 of the cap 59, so that the cap 59 and thus the valve element 44 are pressed out of the main body 23. This arrangement is shown in FIG. 18. This arrangement is also referred to as the normal position.

[0118] The valve element 44 is configured to be bolt-like with a solid cross-section. The valve element 44 has an axial groove 62. The axial groove 62 extends along the assembly longitudinal axis 24 and is provided as an external groove on the valve element 44, in particular it is milled.

[0119] The valve element 44 is made in particular of a metallic material, in particular of an aluminium material, in particular of an aluminium alloy. The valve element 44 is manufactured in particular as a precision turned part. The axial groove is a control groove.

[0120] The axial groove 62 is arranged in the longitudinal direction in the region of the end face with which the valve element 44 is arranged within the main body 23. In particular, the axial groove 62 is arranged adjacent to the annular collar 46. In particular, the axial groove 62 is arranged in the region of the cylinder section 45 at the valve element 44. The cylinder section 45 has an outer diameter corresponding for the sake of sealing abutment against the sealing lip 58. In the region of the axial groove 62, the outer diameter of the cylinder section 45 is reduced. In this region, fluid flow is possible, in particular between the sealing lip 58 and the axial groove 62.

[0121] The cylinder section 45 has an axial length l.sub.1 which is greater than an axial length l.sub.0 of the second passage opening 42 in the main body 23. In particular, l.sub.1>1.05?l.sub.0, in particular l.sub.1>1.1?l.sub.0, in particular l.sub.1>1.2?l, in particular l.sub.01>1.5?l, in particular l.sub.01>2?l.sub.0 and in particular l.sub.1<10?l.sub.0.

[0122] The axial groove 62 has an axial length l.sub.2 which is smaller than or equal to the axial length l.sub.1 of the cylinder section 45. In particular, the following applies: l.sub.2?l.sub.1, in particular l.sub.2<0.9?l.sub.1, in particular l.sub.2<0.8?l.sub.1, in particular l.sub.2<0.75?l.sub.1, in particular l.sub.2<0.7?l.sub.1, in particular l.sub.2<0.6?l.sub.1, in particular l.sub.2<0.5?l.sub.1, and in particular l.sub.2>0.2?l.sub.1.

[0123] The axial length l.sub.2 of the axial groove 62 is substantially as great as the axial length l.sub.0 of the second passage opening 42. In particular, the following applies: 0.8?l.sub.2?l.sub.0?1.2?l.sub.2, in particular 0.9?l?l.sub.20?1.1?l.sub.2 and in particular 0.95?l?l.sub.20?1.05?l.sub.2. It has been found advantageous if the axial length l.sub.2 is slightly greater than the axial length l.sub.0, in particular l.sub.2>l.sub.0, in particular l.sub.2>1.01?l.sub.0 and in particular l.sub.2>1.05?l.sub.0.

[0124] When the valve element 44 is arranged with the cylinder section 45 but outside the axial groove 62 on the sealing lip 58, the second passage opening 42 is sealed. Fluid flow through the second passage opening 42 is then prevented. The valve element is then in a blockage position.

[0125] Along the assembly longitudinal axis 24, a waist section 63 adjoins the cylinder section 45 of the valve element 44. The waist section 63 has a reduced outer diameter d.sub.min which is smaller than the minimum inner diameter of the second passage opening 42 determined by the sealing lip 58.

[0126] When the valve element 44 is arranged with the waist section 63 in the region of the sealing lip 58, fluid flow through the second passage opening 42 is possible. The valve element 44 is then in an overload position.

[0127] The valve element 44 has the annular collar 46, with which the valve element 44 can be moved in an axially guided manner in an axial bore 64 in the main body 23 along the assembly longitudinal axis 24. For this purpose, the axial bore 64 has an inner diameter which essentially corresponds to the outer diameter of the annular collar 46. Multiple axial channels 65 are arranged in the axial direction, four according to the embodiment example shown.

[0128] The function of the piston-cylinder unit 1d, which is designed as a gas spring, is explained in more detail below.

[0129] If the gas spring 1d is arranged together with an electric drive for actuating a trunk lid on a motor vehicle, in normal operation when the trunk lid is closed, i.e. when the assembly 22d is moved along the first direction 50, the overflow channel will be open, in particular through the second passage opening 42, because the valve element 44 with the axial groove 62 is arranged in the region of the sealing lip 58. The fluid can flow past the valve element 44 through the assembly 22d.

[0130] It is conceivable to design the axial groove 62 with a variable groove depth along the longitudinal axis 24. For example, differently stepped groove depths can be designed to produce stepped switching behaviour. Accordingly, different groove widths are also conceivable. In particular, it is also conceivable to design a continuous, in particular linear, degressive or progressive course of the groove depth and/or groove width in order to achieve a correspondingly adapted switching behaviour.

[0131] The assembly 22d and in particular the valve element 44 are in the so-called normal position. In particular, the spring element 47 is dimensioned such that the fluid pressure caused during normal operation does not cause any axial displacement of the valve element 44 in the second passage opening 42.

[0132] In an unintended and in particular unforeseeable case, for example that the electric drive unit fails, an additional mechanical closing force, in particular as a result of the trunk lid's own weight, is exerted on the gas spring 1d along the first direction 50. Due to this increased insertion speed, the internal pressure on the valve element 44 is increased. The valve element 44 is moved to the left, i.e. towards the piston rod 5, as shown in FIG. 17, in particular until the valve element 44 is arranged with the cylinder section 45 outside the axial groove 62 on the sealing lip 58. In this case, the sealing lip 58 abuts in a sealing manner against the valve element 44 on the outer circumference of the cylinder section 45. The valve unit 38 is blocked. The valve element 44 is in a blockage position. The gas spring 1d as a whole is blocked. Unintentional slamming of the trunk lid is prevented. Material damage and destruction and, in particular, health hazards to persons are thus excluded.

[0133] If the axial length l.sub.2 of the axial groove 62 is the same as the axial length l.sub.1 of the cylinder section 45, the valve element 44 is designed without a blockage position. In this case, the valve element 44 is displaced from the normal position described above to the overload position described in the following.

[0134] To prevent the trunk lid from remaining in this blocked arrangement, the valve element 44 allows displacement to the overload position. By manual overpressure, i.e. by applying additional external force, and further excess pressure, the valve element 44 is moved further along the first direction 50 into the main body 23 towards the piston rod 5 until the valve element 44 is arranged with the waist section 63 in the second passage opening 42. Due to the fact that the minimum diameter d.sub.min is smaller than the minimum inner diameter of the second passage opening 42 determined by the sealing lip 58, fluid flow is possible again. The lid can be closed manually.

[0135] It is particularly advantageous with the piston-cylinder unit 1d and in particular the assembly 22d that the various positions of the valve element 44 at the main body 23 can be reversibly adjusted.

[0136] FIG. 23 shows the advantageous function of the gas spring 1d. Up to the first limit speed v.sub.1 the gas spring 1d behaves like a normal grooved gas spring. This means that an essentially linear increase in force results in dependence on the actuation speed.

[0137] In particular, the first speed v.sub.1 can be adjusted in a targeted manner. An adjustment is possible, for example, by adapting the depth of the axial groove 62. In addition or alternatively, the first speed v.sub.1 can also be adjusted by selecting the helical compression spring, i.e. the spring element 47, i.e. by the spring preload. When the first speed v.sub.1 is exceeded, the valve element 44 is moved into the blocking position. If the speed is increased further, the valve element 44 is moved into the overload region, i.e. with the waist section 63 arranged in the second passage opening 42.

[0138] This can be seen in the diagram in FIG. 23 by the fact that even with a further increase in speed, i.e. at speeds above the second speed v.sub.2, there is no further, in particular no further significant increase in force.

[0139] This function of the gas spring 1d ensures that the damping force is comparatively low in a predefinable application speed range. In the event of an unintentional failure case, the actuation speed can therefore increase significantly so that the gas spring 1d has a significantly increased actuation force and can thus dissipate or convert increased energy. The gas spring 1d is fail-safe and reliable. Incorrect operation is virtually excluded.