Slotted guide ring with recirculating lubrication and piston-cylinder unit with such a

Description

[0001] In piston-cylinder units, the piston (or piston rod) is typically guided along the cylinder by one or more guide rings. The guide rings prevent metal-to-metal contact between the two components and absorb and compensate for radial forces. The latter is also essential for reliable sealing performance and the longevity of sealing elements used between the moving components. The guide rings are usually slotted to facilitate their installation.

[0002] The slotted guide rings used in practice are available in a wide variety of materials to ensure the best possible wear resistance for each application. By selecting the appropriate base material, the guide rings can be designed for different operating times and the different radial forces to be absorbed during operation. Specially modified thermoplastic materials such as polytetrafluoroethylene (PTFE), polyamide (PA), or polyoxymethylene (POM) are often used for this purpose. Other requirements that the guide rings must meet include the lowest possible coefficient of friction when paired with the material of the machine part that dynamically contacts the guide ring, anti-adhesive properties, a suitable operating temperature range, chemical resistance if necessary, and the greatest possible resistance to aging.

[0003] Due to manufacturing tolerances of the guide rings themselves, as well as of the machine parts moving relative to each other, the guide rings available on the market can lead to malfunctions such as increased wear or a pronounced slip-stick effect, or in extreme cases, even guide ring failure. In this respect, adequate lubrication of the guide ring in the area of ​​its contact zone(s) with the machine part dynamically resting against the guide ring is crucial.

[0004] DE 20 2008 012 376 U1 discloses a profiled guide band for piston-cylinder units, which is arranged in a ring shape during operation. The guide band has a guide side with several parallel lubricant channels, which are arranged diagonally with respect to the side flanks of the guide band or the guide ring formed from it. The lubricant channels extend partially in the axial direction from one side flank to the other and have a significant difference in length. With this guide band / ring, pronounced temperature gradients in the material of the guide ring and associated deformations can occur during operation, not least due to the different lengths of the lubricant channels.In addition, there is a risk of individual lubricant channels becoming blocked by contaminants contained in the lubricant, which can cause local lubrication problems and undesirable stick-slip effects and intensify undesirable deformations of the guide ring.

[0005] DE 37 31 158 A1 discloses a slotted guide ring for a piston-cylinder unit, which has at least one lubricant channel on its guide side, which extends in the circumferential direction of the guide ring from the first free end section to the second free end section of the guide ring and which is open on both sides towards the axial through gap between the two end sections of the guide ring.

[0006] It is the object of the invention to provide a guide ring for a piston-cylinder unit and a piston-cylinder unit with at least one such guide ring, in which the aforementioned manufacturing tolerances are less significant and in which a further improved lubrication and cooling of the aforementioned contact zones of the guide ring can be achieved.

[0007] The problem concerning the guide ring is solved by a guide ring having the features specified in claim 1. The piston-cylinder unit according to the invention has the features specified in claim 8. Preferred developments of the invention are specified in the subclaims and in the description.

[0008] The guide ring according to the invention is intended for use in a piston-cylinder unit and consists partially or completely of a viscoelastically deformable base material. The guide ring has a guide side that faces inwards or outwards in a radial direction to the central axis of the guide ring and which serves for dynamically contacting and guiding a machine part, in particular the cylinder of the piston-cylinder unit. The guide ring further comprises a rear side that faces away from the guide side in the radial direction and which serves for statically contacting support of the guide ring on another machine part, in particular the piston (or a piston rod) of the piston-cylinder unit. It should be noted that the term piston in this case also includes a piston rod known per se.A first and a second free end section of the guide ring are arranged spaced apart from one another in the circumferential direction of the guide ring, forming an axial through gap. The end faces of the free end sections are arranged parallel or substantially parallel to one another, with the two end faces, in their projection onto the central axis, enclosing an acute angle α with the central axis of 15° ≤ α ≤ 75°, in particular 25° ≤ α ≤ 60°.

[0009] Furthermore, a plurality of annular beads are formed on the guide side, each of which is arranged at a distance from one another in an axial direction relative to the central axis Z of the guide ring. A lubricant channel is formed between each two immediately adjacent annular beads. Each lubricant channel is thus bounded on both sides in the axial direction by one of the annular beads. The guide ring can in particular have exactly one, two, or exactly three lubricant channels. The guide ring can also have more than three lubricant channels. According to the invention, each lubricant channel extends in the circumferential direction of the guide ring from the first free end section to the second free end section and is open on both sides towards the through gap of the guide ring. In other words, each lubricant channel of the guide ring opens into the aforementioned axial through gap.

[0010] The guide ring, with its annular beads, provides several linear or ring-shaped load-bearing surfaces or contact zones for the machine part of the piston-cylinder unit guided by them. The spaced-apart linear contact zones of the guide ring enable particularly low-friction guidance of the two machine parts relative to each other. Furthermore, this, along with the viscoelastic material of the guide ring, counteracts undesirable stick-slip behavior.

[0011] During operation, each lubricant channel of the guide ring can be used to achieve improved lubrication of the dynamic contact zones formed by the annular beads for the machine part guided in contact with the guide ring in sliding clearance form fit over the entire or essentially entire circumferential extent of the guide ring, and thus to improve the service life of the guide ring. The fact that at least one lubricant channel or each lubricant channel is open at both ends only towards the front sides of the two free end sections results in particularly uniform cooling and lubrication of the guide ring in the area of ​​the contact zones of the annular beads on the sliding surface of the machine part dynamically contacting the guide ring during operation from a thermal point of view. Furthermore, the manufacture of the guide ring is also simplified.

[0012] The viscoelastic deformability of the guide ring enables dynamic adjustment of the size of the respective (annular) load-bearing surface / contact zone to a radial force acting on the guide ring when installed. The size of the respective contact zone of the guide ring thus increases with an increased radial force acting locally on the guide ring, and vice versa. Compared to conventional guide rings, in which the size of the contact zone is invariant and thus essentially independent of the respective radially directed load acting on the guide ring, this results in an overall flattened progression of the contact pressure (surface pressure in N / mm2) between the sliding surface of the machine part dynamically sliding along the guide ring and the guide ring as the radial load on the guide ring increases.The guide ring design according to the invention can thus compensate for unavoidable manufacturing tolerances of the guide ring itself as well as of the machine parts of the piston-cylinder unit that are supported by the guide ring. Furthermore, the guide ring can withstand greater radial loads than conventional guide rings made of the same base material. According to the invention, each lubricant channel has a wave-like shape in the circumferential direction. This design allows for particularly effective cooling of the guide ring and flushing of each lubricant channel.

[0013] According to the invention, the free end sections preferably each have a flow funnel for the lubricant, into which each of the lubricant channels of the guide ring opens. Each of these flow funnels widens towards the axial through gap. This, on the one hand, makes it possible to provide a particularly large inlet opening for the lubricant channels. On the other hand, a sufficiently high back pressure of the lubricant flowing into the flow funnel can be built up in the area of ​​the respective flow funnel. This ensures that the lubricant, during operation—derived from the relative movement of the two machine parts (piston / cylinder)—is pressed into each lubricant channel at a flow velocity sufficiently high for flushing, lubricating, and cooling purposes of the dynamic contact zones formed by the annular beads.In this way, contaminants contained in the lubricant channel can be reliably removed or flushed out of the lubricant channel during operation.

[0014] According to the invention, each lubricant channel can have a wave-like shape in the circumferential direction. This design allows for particularly effective cooling of the guide ring and flushing of each lubricant channel.

[0015] Each lubricant channel can have a static constriction or a dynamic constriction of its flow cross-section at at least one circumferential position of the guide ring. A static constriction exists when this has a flow-through cross-section that remains unchanged during operation of the guide ring. In contrast, in the region of a dynamic constriction, the lubricant channel has a variable flow-through cross-section depending on the lubricant pressure or volume flow within the lubricant channel. This can be achieved, for example, by an inflow element that is flexibly deformable or flexibly hinged to the guide ring (through which the lubricant can flow). The inflow element can, for example, be designed in the form of an elastically deformable tongue that is made in one piece with the rest of the guide ring and which projects into the lubricant channel.The tongue is preferably bidirectionally deflectable / deformable in the circumferential direction of the guide ring. Alternatively, the flow element can also be a ball or similar element that protrudes into the lubricant channel and can be moved (at least partially) out of the lubricant channel in an axial or radial direction against the force of a spring element or the material of the guide ring.

[0016] The guide ring, with its annular beads arranged on the guide side, provides several linear or ring-shaped load-bearing surfaces or contact zones for the machine part of the piston-cylinder unit guided by them when installed. The spaced-apart linear load-bearing surfaces of the guide ring enable particularly low-friction guidance of the two machine parts relative to each other. Furthermore, this, along with the viscoelastic material of the guide ring, counteracts undesirable stick-slip behavior.

[0017] According to the invention, each of the annular beads preferably has a vertex with side flanks which slope down on both sides of the vertex in a radial direction relative to the central axis of the guide ring.

[0018] According to a preferred embodiment of the invention, the annular beads of the guide ring are each designed to be convexly curved outward in the radial direction in the unloaded cross-section of the guide ring. This allows the guide ring to absorb even large and extremely high bearing forces. The radial projections can, in particular (in the unloaded cross-section of the guide ring), have a curvature that is at least partially or even essentially circular.

[0019] The back of the guide ring can be cylindrical in its unloaded cross-section. This allows the guide ring to fully support itself against a cylindrical groove base of a retaining groove in a machine part.

[0020] According to an alternative embodiment, the rear side of the unloaded or installed guide ring can be designed in a wave-like or zigzag-shaped cross-section, i.e., it can have a plurality of radial projections. These radial projections preferably extend in a manner corresponding to the annular beads in the circumferential direction of the guide ring, each over the entire or substantially entire circumferential extent of the guide ring.

[0021] It should be noted that the annular beads and the radial projections can be arranged radially aligned with one another in the cross-section of the guide ring. This allows the response of the guide ring to changing radial loads on the guide ring to be easily adjusted through the geometric design of the radial projections. Furthermore, one and the same guide ring can be used as a so-called rod or piston rod guide ring or even as a piston ring. In the former case, the guide ring is arranged in the retaining groove of the cylinder or housing of the (piston) rod, and in the latter case, the guide ring is arranged in the retaining groove of the piston. This increases the range of applications of the guide ring and reduces provisioning and storage costs. The annular beads and the radial projections are preferably identical in size and geometry.

[0022] Particularly preferably, the guide ring has a spherically shaped flank section on both sides in the axial direction. This facilitates axial deformation of the guide ring when installed in a retaining groove or the like. This also makes it easy to counteract unwanted tilting of the guide ring during assembly.

[0023] According to the invention, the base material of the guide ring can be a thermoset or a thermoplastic. Specially modified thermoplastic materials, such as polytetrafluoroethylene (PTFE), polyamide (PA), or polyoxymethylene (POM), can be used.

[0024] According to the invention, the guide ring can be designed in a multi-component construction. In particular, the guide ring can have a known support or reinforcement insert, preferably made of metal or a technical ceramic. This is advantageous for the guide ring's wide range of applications.

[0025] According to the invention, the annular beads can comprise a harder material with a preferably smaller coefficient of friction compared to the base material of the guide ring or to the rest of the guide ring.

[0026] The piston-cylinder unit according to the invention comprises a first machine part in the form of a piston or a piston rod and a second machine part in the form of a cylinder in which the first machine part is guided so as to be movable back and forth along a movement axis. At least one guide ring according to the above statements is arranged in a retaining groove of one of the two machine parts. The piston is supported and guided on the cylinder via this guide ring, forming a bearing gap between the piston and cylinder in a sliding fit. This is such that a lubricant arranged in the bearing gap flows into the at least one lubricant channel of the guide ring via one of the two free end sections of the guide ring during a forward stroke movement of the first machine part and via the other of the two free end sections of the guide ring during a return stroke movement of the first machine part.The lubricant is therefore - derived from the axial relative movement of the two machine parts - introduced into at least one lubricant channel of the guide ring and flowing through it.

[0027] The piston-cylinder unit can be used for pneumatic or hydraulic applications.

[0028] If the at least one lubricant channel has a dynamic constriction, a media-actuated deactivation of the dynamic constriction of the flow cross-section of the at least one lubricant channel is effected when a defined back pressure of the lubricant in the at least one flow channel is reached or exceeded. This constriction can create a turbulent flow within the lubricant channel, enabling particularly efficient mixing of the lubricant and improved removal of contaminants introduced into the lubricant channel.

[0029] The guide ring is preferably positioned with an axial clearance in the retaining groove relative to the movement axis. This ensures simplified assembly and less prone to failure of the piston-cylinder unit.

[0030] Further advantages of the invention will become apparent from the description and the drawings. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0031] The drawing shows: Fig. 1 shows a piston-cylinder unit according to the invention with a guide ring in a partial sectional view; Figs. 2A, 2b show a guide ring not according to the invention in a cut-out perspective detailed view ( Fig. 2A ) and in cross-section ( Fig. 2B ); Fig. 3 shows a detailed section of a further guide ring, not according to the invention, with a lubricant channel and with flow funnels formed on the end section, into which the lubricant channel opens at both ends; Fig. 4 shows a detailed section of a further guide ring, not according to the invention, with two lubricant channels arranged strictly in the circumferential direction of the guide ring; Fig. 5 shows a detailed section of a further guide ring with rear radial projections; Fig. 6 shows a guide ring, not according to the invention, with a lubricant channel running undulating in the circumferential direction with a constant flow cross-section; Fig. 7 shows a detailed section of a guide ring, not according to the invention, with a flow cross-section that is inconstant in the circumferential direction; and Fig.8a guide ring with an inflow element projecting into the lubricant channel, by means of which a variable narrowing of the lubricant channel is effected depending on the lubricant flow, wherein the inflow element is flexibly deflectable bidirectionally from a neutral position shown in the circumferential direction of the guide ring.

[0032] In Fig. 1 is a piston-cylinder unit 10 shown in a partial sectional view. The piston-cylinder unit 10 has a first machine part 12 in the form of a piston and a second machine part 14 in the form of a cylinder. The piston 12 is in the cylinder 14 along a movement axis L guided to move back and forth. It should be noted that the term "piston" in this case also includes a piston rod, which is known per se.

[0033] For fluid-tight or pressure-tight sealing of a bearing gap formed between the piston and the cylinder 16 A sealing ring is used here 18. The sealing ring 18 lies on a sliding surface formed by the inner wall of the cylinder 20 of the cylinder. The sealing ring 18 can be equipped with a preload element 22 The first machine part 12 is provided with two guide rings 24 via which the first machine part 12 is guided on the sliding surface 20 of the second machine part 14.

[0034] The two in Fig. 1 The guide rings 24 shown are each in a circumferential retaining groove 26 of the first machine part 12. Each guide ring 24 has a dynamically leading front or guide side 28 and a back 30 which have side flanks 32of the guide ring 24 are connected to each other. The guide side 28 serves for the dynamic contact of the respective guide ring 24 on the cylinder 14. Accordingly, the guide side 28 points outwards in a radial direction to the central axis Z of the guide ring 24. The central axis Z of the guide ring 24 coincides in the assembled state of the guide ring 24 with the movement axis L of the piston-cylinder unit 10 (cf. e.g. Fig. 1 ) together or substantially together. The contact zones of each guide ring 24 with the sliding surface 20 are C designated.

[0035] The rear side 30 of the respective guide ring 24 serves to statically support the guide ring 28 on the groove base of the machine part 12, 14 having the retaining groove 26, here for example the Fig. 1 shown piston 12.

[0036] In Fig. 2 The guide ring 24 is shown in a perspective detail. The guide ring 24 is designed with slots. Accordingly, the guide ring 24 has a first and a second end section in the circumferential direction. 34, 36 which are separated from each other by forming an axial through gap 38 are arranged at a distance from each other. The slotted shape of the guide ring 24 simplifies its assembly. The two end sections 34, 36 have mutually facing end faces 40, 42 which are arranged parallel to one another or essentially parallel to one another. The end faces 40, 42, in their projection onto the central axis Z, are aligned with the central axis Z (cf. Fig. 1 ) each have an acute angle α with 15° ≤ α ≤ 75°. The angle α can be calculated according to Fig. 1 in particular 40°.

[0037] During operation of the piston-cylinder unit 10, each guide ring 24 must occasionally absorb high radial loads and is inevitably subject to wear, not least due to friction-related mechanical and thermal loads. Due to manufacturing tolerances of conventional guide rings themselves, as well as of the machine parts moving relative to one another, malfunctions can occur, such as increased wear, an undesirable slip-stick effect, or in extreme cases, even premature failure of the conventional guide rings. Each guide ring 24 therefore has several annular beads formed on / on its guide side 28. 44 which are each arranged at a distance from one another in an axial direction relative to the central axis Z of the guide ring 24. A lubricant channel is formed through the annular beads 44 46bounded on both sides in the axial direction. The lubricant channel 46 extends in the circumferential direction of the guide ring 24 from the first free end section 34 to the second free end section 36 and is open on both sides toward the axial through gap 38. The lubricant channel 46 is thus fluidically connected to the axial through gap 38 at both ends.

[0038] A lubricant S arranged in the bearing or sealing gap 16 is thus V of the first machine part 12 and during a return stroke movement R of the first machine part 12 is alternately drawn or pressed into the lubricant channel 46 via the respective free end section 34, 36 of the guide ring 24, the end face 40, 42 of which is directed opposite to the respective direction of movement of the first machine part 12 in the axial direction.

[0039] In this way, during operation of the piston-cylinder unit 10, a targeted flow through the lubricant channel 46 with the lubricant S This ensures that the lubrication and cooling of the contact zone C of the guide ring 24 on the sliding surface 20 of the second machine part 14 are improved. Overall, this reliably counteracts premature wear of the guide ring 24 and undesirable stick-slip.

[0040] According to Fig. 3 Each lubricant channel 46 of the guide ring 24 can widen towards the end face 40, 42 of the respective end section 34, 36 and thus form a flow funnel 48 or flow into a flow funnel 48 of the end sections 34, 36. This allows a particularly large inlet opening 46afor each of the lubricant channels 46. On the other hand, this allows for a forward stroke movement V as well as a return stroke movement R of the piston ( Fig. 1 ) a back pressure of the lubricant flowing into the respective flow funnel 48 can be built up. This ensures that the lubricant S is pressed into each lubricant channel 46 during operation - derived from the relative movement of the two machine parts 12, 14 - at a flow rate sufficiently high for flushing, lubrication, and cooling purposes. Particulate contaminants contained in the lubricant S (not shown in the drawing) that enter the at least one lubricant channel 46 of the guide ring 24 can thus be reliably removed or flushed out of the lubricant channel 46 during operation.

[0041] The guide ring can be Fig. 4 on its guide side 28 also have more than two, in particular three, annular beads 44. Two of the annular beads 44 define a lubricant channel 46 between each other in pairs. The two lubricant channels 46 preferably together form one of the lubricant channels 46 in connection with Fig. 3 It should be noted that the lubricant channels 46 are connected to one another by one or more axial connecting channels 50 can be fluidly connected.

[0042] The guide ring 24 can be adjusted according to the Fig. 5 shown sectional view also a rear side 30 corrugated in the axial direction with radial projections 52This design allows for particularly effective compensation of manufacturing tolerances of both machine parts and the guide ring 24. The rear-side radial projections 52 of the guide ring 24 can be arranged radially aligned with the annular beads 44 on the front side of the guide ring. They can also match the annular beads 44 in terms of their geometry and size.

[0043] According to the Fig. 6 In the illustrated embodiment of the guide ring 24, the lubricant channel 46 can have a particularly uniform, undulating course in the circumferential direction. This design provides particularly efficient lubrication of the contact zone C of the annular beads 44 with the associated sliding surface 20 of the cylinder 12.

[0044] According to Fig. 7 Each lubricant channel 46 of the guide ring 24 may have one or more static and / or dynamically variable constrictions 54(its free cross-section through which the lubricant can flow). Each constriction 54 can in particular be formed by an inflow element 56, For example, it may be formed in the form of a wall projection or several wall projections, as in Fig. 7 is shown. In the case of a dynamically variable constriction 54, the inflow element 56 can, for example, be flexibly deformable or arranged on the guide ring so that it can be flexibly deflected. As a result, the inflow element 56 can be deflected—lubricant-actuated—in the direction of the central axis Z of the guide ring 24. Such constrictions 54 can generate a back pressure of the lubricant within the lubricant channel 46, thus allowing the lubrication to be locally adjusted as needed.

[0045] The annular beads 44 and / or the rear radial projections 52 of the guide ring 24 may comprise a material that has a smaller modulus of elasticity or a smaller coefficient of friction compared to the material of the remaining guide ring 24.

[0046] The guide ring 24 can be made at least partially or entirely of an elastomer, such as ethylene propylene diene rubber (EPDM) or fluororubber (FKM), as well as additives familiar to those skilled in the art. PA (polyamide) or high-temperature-resistant thermoplastics, such as PEEK (polyetheretherketone), are also suitable. It is understood that the guide ring 24 can have a conventional reinforcing or supporting insert, for example in the form of a supporting ring. The reinforcing or supporting insert can be made, in particular, of metal, a technical ceramic, or even of a composite material, e.g., one containing carbon fiber. The guide ring can also be preassembled in a cartridge and inserted together with the cartridge into a retaining groove of the piston or cylinder.

Claims

1. Slotted guide ring (24) for a piston-cylinder unit (10), which consists partially or completely of a viscoplastically deformable base material, - with a guide side (28) which points inward or outward in a direction radial to the central axis Z of the guide ring (24) and which is used for dynamically contacting abutment on a machine part (12, 14), and - with a rear side (30) which points away from the guide side (28) in the radial direction and which serves to support the guide ring (24) in a statically contacting manner, - with a first free end portion (34) and with a second free end portion (36), which are at a distance from one another in the circumferential direction of the guide ring, forming an axial passage gap (38), and the end faces (40, 42) of which extend parallel or substantially parallel to one another, the end faces (40, 42) enclosing an acute angle α of 15° ≤ α ≤ 75° with the central axis Z in their projection onto the central axis Z, - with a plurality of annular beads (44) formed on the guide side (28), which are each arranged at a distance from one another in an axial direction relative to the central axis Z of the guide ring (24), - with at least one lubricant channel (46) which is delimited on both sides in the axial direction by two of the annular beads (44), the lubricant channel (46) extending in the circumferential direction of the guide ring (24) from the first free end portion (34) to the second free end portion (36) and being open on both sides toward the axial passage gap (38), characterized in that the at least one lubricant channel (46) has a wavy course in the circumferential direction.

2. Guide ring (24) according to claim 1, characterized in that the two free end portions (34, 36) each have a flow funnel (48) into which each of the lubricant channels (46) opens.

3. Guide ring (24) according to one of the preceding claims, characterized in that the at least one lubricant channel (46) has a static or dynamic constriction (54) in at least one circumferential position of the guide ring (24).

4. Guide ring (24) according to one of the preceding claims, characterized in that the rear side (30) is designed to be wave-shaped or zigzag-shaped in cross section of the unloaded guide ring (24) and has a plurality of radial projections (52) which each extend in the circumferential direction of the guide ring (24) over the entire or substantially the entire circumferential extent of the guide ring (24).

5. Guide ring (24) according to claim 4, characterized in that the annular beads (44) and the radial projections (52) are arranged in alignment with one another in a radial direction.

6. Guide ring (24) according to one of the preceding claims, characterized in that the annular beads (44) comprise a harder material with a preferably lower coefficient of friction than the base material of the guide ring (24).

7. Piston-cylinder unit (10), comprising - a first machine part (12) in the form of a piston rod or piston; - a second machine part (14) in the form of a cylinder, in which the first machine part (12) is guided so that it can be moved back and forth along a movement axis (L); - at least one guide ring (24) according to one of the preceding claims 1 to 6, which is arranged in a retaining groove (26) of one of the two machine parts (12, 14), and via which the corresponding other machine part (12, 14) is supported and guided, in a form-fitting connection with sliding clearance, by the formation of a bearing gap (16) formed between the two machine parts (12, 14), in such a way that, during a forward stroke movement V of the first machine part (12), a lubricant S arranged in the bearing gap (16) flows via one of the free end portions (34, 36) of the guide ring (24) and, during a return stroke movement of the first machine part (12), via the corresponding other of the two end portions (34, 36) of the guide ring (24) into the at least one lubricant channel (46) of the guide ring (24).

8. Piston-cylinder unit (10) according to claim 7, if claim 7 is dependent on claim 3, characterized in that the dynamic constriction (56) of the lubricant channel (24) can be reduced or deactivated during operation by the lubricant flowing through the lubricant channel.

9. Piston-cylinder unit (10) according to claim 7 or 8, characterized in that the guide ring (24) is arranged with axial clearance in the retaining groove (26) with respect to the movement axis (L).