Slotted guide ring with circulating lubrication and piston-cylinder unit having such slotted guide ring

Abstract

The present invention relates to a slotted guide ring (24) for a piston-cylinder unit (10), which has a first free end section (34) and a second free end section (36), which are spaced apart from each other in the circumferential direction of the guide ring with an axial channel gap (38) being formed, and whose end sides (40, 42) are arranged parallel or substantially parallel to each other. The end sides (40, 42) enclose an acute angle α of 15° ≤ α ≤ 75° with the central axis Z in their projection onto the central axis Z. A lubricant channel (46) is constructed on the guiding side, which extends from the first free end section (34) to the second free end section (36), and the lubricant channel is open towards the axial channel gap (38) on both sides. The present invention also relates to a piston-cylinder unit having such a guide ring.

Description

Background Art

[0001] In a piston-cylinder unit, a piston (or piston rod) is usually guided via one or more guide rings on the cylinder. The guide rings prevent metal contact between the two components and withstand radial forces and balance said radial forces. The latter is also important for the reliable sealing performance and lifespan of the sealing elements used between the moving components. The guide rings are usually slotted to enable simplified assembly of the guide rings.

[0002] The slotted guide rings used in practice can be made of a variety of materials to ensure the best possible wear resistance for the specific application. By correspondingly selecting their base materials, the guide rings can be designed for different running times and different radial forces to be received during operation. Special modified thermoplastic materials such as polytetrafluoroethylene (PTFE), polyamide (PA) or polyoxymethylene (POM) are usually used here. Other aspects that the guide rings must meet are as low a coefficient of friction as possible (in the pairing with the material of the machine component that dynamically abuts against the guide ring), anti-seizure properties, a suitable operating temperature range, chemical resistance if necessary, and as great an aging resistance as possible.

[0003] In the case of the guide rings offered on the market, faults such as increased wear or a pronounced stick-slip effect may occur, or in extreme cases even guide ring failure, based on the manufacturing tolerances of the guide rings themselves and the manufacturing tolerances of the machine components moving relative to each other. In this regard, sufficient lubrication of the guide rings in the area of their contact zone with the machine components that dynamically abut against the guide rings is of decisive importance.

[0004] DE 20 2008 012 376 U1 discloses a profiled guide strip for a piston-cylinder unit, which is arranged in a ring shape during operation. The guide strip has a guide side with a plurality of lubricant channels extending parallel to each other, and the lubricant channels are arranged to extend diagonally with respect to the guide strip or the flank of the guide ring formed thereby. In this regard, the lubricant channels partially extend from one flank to the other flank in the axial direction and have a considerable length difference. In the case of the guide strip / ring, a significant temperature gradient of the material of the guide ring and the associated shape change can occur during operation, especially because the lengths of the lubricant channels are different. In addition, there is a risk that individual lubricant channels become blocked due to impurities contained in the lubricant, and the impurities can cause local lubrication problems and undesired stick-slip effects and increase the undesired shape change 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 guiding side. The lubricant channel extends in the circumferential direction of the guide ring from a first free end section of the guide ring to a second free end section of the guide ring, and opens towards an axial channel gap between two end sections of the guide ring on both sides. Summary of the Invention

[0006] The object of the present invention is to provide a guide ring for a piston-cylinder unit and a piston-cylinder unit having at least one such guide ring, wherein the above-mentioned manufacturing tolerances have a small influence and further improvement of the lubrication and cooling of the above-mentioned contact area of the guide ring can be achieved.

[0007] The object related to the guide ring is solved by a guide ring having the features given in claim 1. The piston-cylinder unit according to the present invention has the features given in claim 8. Preferred expansions of the present invention are given in the dependent claims and the description.

[0008] The guide ring according to the present invention is arranged for installation in a piston-cylinder unit and is partially or entirely composed of a viscoplastic deformable base material. The guide ring has a guiding side which points inwards or outwards in the radial direction relative to the central axis of the guide ring, and the guiding side is used for dynamically contacting and guiding on a machine part, especially on the cylinder of the piston-cylinder unit. The guide ring further includes a rear side which points away from the guiding side in the radial direction and the rear side is used for statically supporting the guide ring on another machine part, especially on the piston (or piston rod) of the piston-cylinder unit. It should be noted that the term "piston" should also be understood as a known piston rod. The first and second free end sections of the guide ring are arranged spaced apart from each other in the circumferential direction of the guide ring with an axial channel gap being formed. The end sides of the free end sections are arranged parallel to each other or substantially parallel to each other, wherein the two end sides enclose an acute angle α of 15° ≤ α ≤ 75°, especially 25° ≤ α ≤ 60° with the central axis in their projections onto the central axis.

[0009] Furthermore, a plurality of annular beads are formed on the guiding side, and the annular beads are arranged at intervals from each other in the axial direction with respect to the central axis Z of the guiding ring. Lubricant channels are respectively formed between two adjacent annular beads arranged in sequence. Therefore, each lubricant channel is bounded on both sides in the axial direction by a corresponding one of the annular beads. In particular, the guiding ring may have exactly one, two or exactly three lubricant channels. The guiding ring may also have more than three lubricant channels. According to the present invention, each lubricant channel extends from a first free end section to a second free end section in the circumferential direction of the guiding ring and opens towards the passage clearance of the guiding ring on both sides. In other words, each lubricant channel of the guiding ring leads to the above-mentioned axial channel clearance.

[0010] Due to its annular beads, the guiding ring provides a plurality of linear or annular load receiving surfaces or contact areas for the machine components of the piston cylinder unit guided thereon during installation. Due to the linearly spaced-apart contact areas of the guiding ring, a particularly low-friction guiding of two machine components relative to each other can be achieved. In addition, due to and through the viscoplastic material of the guiding ring, undesired stick-slip behavior can be offset.

[0011] Through the respective lubricant channels of the guiding ring, improved lubrication characteristics of the dynamic contact areas formed by the annular beads can be achieved over the entire or substantially the entire circumferential extent of the guiding ring during operation, for machine components that are guided in a form-locking manner with a sliding clearance against the guiding ring, and thereby an improved service life of the guiding ring can be achieved. At least one lubricant channel or each lubricant channel is implemented to be open only towards the end sides of the two free end sections at both ends, resulting in a particularly uniform cooling and lubrication of the guiding ring from a thermal perspective in the region of the contact areas on the sliding surfaces of the machine components that are dynamically in contact with the guiding ring during operation. In addition, the production of the guiding ring is simplified.

[0012] In the installed state of the guide ring, the viscoplastic deformability of the guide ring enables the size of the corresponding (annular) load-receiving surface / contact zone to be adjusted dynamically in accordance with the radial force acting on the guide ring. The size of the corresponding contact zone of the guide ring thus increases as the locally acting radial force on the guide ring increases, and vice versa. It follows that: compared with a conventional guide ring, when the radial load on the guide ring increases, there is a general flattening progression of the contact pressure (surface pressure, in N / mm2) between the sliding surface of the machine part sliding dynamically along the guide ring and the guide ring. In a conventional guide ring, the size of the contact zone is constant and is thus substantially independent of the correspondingly acting radially directed load on the guide ring. Therefore, the structural form of the guide ring according to the invention can compensate for the inevitable manufacturing tolerances of the guide ring itself and the machine parts supported by each other via the guide ring in the piston-cylinder unit. In addition, the guide ring can withstand a greater radial load than a conventional guide ring made of the same base material. According to the invention, each lubricant channel has a wavy course in the circumferential direction. In this structural form, particularly effective cooling of the guide ring and flushing of each lubricant channel can be achieved.

[0013] According to the invention, the free end sections preferably each have a flow funnel for the lubricant, and each of the lubricant channels of the guide ring leads into this flow funnel. Each of the flow funnels widens towards the axial channel gap. Thus, on the one hand, a particularly large inflow opening can be provided for the lubricant channels. On the other hand, a sufficiently large dynamic pressure head of the lubricant flowing into the flow funnel can be established in the region of the respective flow funnel. This ensures that in the start-up operation, the lubricant from the relative movement of the two machine parts (piston / cylinder) is pressed into the respective lubricant channels at a sufficiently high flow rate, which is used for the flushing, lubrication, and cooling of the dynamic contact zone formed by the annular beads. In this way, impurities contained in the lubricant channels can be reliably removed or flushed out of the lubricant channels during the start-up operation.

[0014] According to the invention, each lubricant channel can have a wavy course in the circumferential direction. With this structural form, particularly effective cooling of the guide ring and flushing of the individual lubricant channels can be achieved.

[0015] Each lubricant passage may 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 the guide ring has a flow cross-section that remains unchanged during operation of the guide ring. In contrast, in the region of the dynamic constriction, the lubricant passage has a variable flow cross-section depending on the lubricant pressure or the volume flow in the lubricant passage. This can be achieved, for example, by an inlet element that is itself flexibly deformable or flexibly articulated on the guide ring and that can be flowed through by the lubricant. The inlet element can be embodied, for example, in the form of an elastically deformable tongue that is embodied integrally with the rest of the guide ring and that projects into the lubricant passage. The tongue can preferably be deflected / deformed bidirectionally in the circumferential direction of the guide ring. Alternatively, the inlet element can also be a ball or the like that projects into the lubricant passage and that can be moved (at least partially) out of the lubricant passage in the axial or radial direction against the force of a spring element or the material of the guide ring.

[0016] Due to the circumferential beads of the guide ring arranged on the guide side, the guide ring provides, in the installed state, a plurality of linear or circumferential load-receiving surfaces or contact zones for machine components of a piston-cylinder unit guided thereon. Due to the linearly arranged load-receiving surfaces of the guide ring spaced apart from one another, a particularly low-friction guidance of two machine components relative to one another can be achieved. In addition, unwanted stick-slip characteristics can be compensated for thereby and by the viscoplastic material of the guide ring.

[0017] According to the invention, each of the circumferential beads preferably has a vertex that has flanks that drop on both sides of the vertex in the radial direction relative to the central axis of the guide ring.

[0018] According to a preferred embodiment of the invention, the circumferential beads of the guide ring are each embodied in the unloaded cross-section of the guide ring as curved convexly outward in the radial direction. Thereby, the guide ring can in particular receive large and maximum bearing forces. The radial projection can in particular (in the unloaded cross-section of the guide ring) have a curvature that is at least partially or substantially a circular line.

[0019] The rear side of the guide ring can be embodied cylindrically in the unloaded cross-section of the guide ring. Thereby, the guide ring can be fully supported on the cylindrically shaped groove base of the retaining groove of the machine component.

[0020] According to an alternative embodiment, the rear side can be embodied in a wavy or serrated shape in the cross-section of the unloaded or installed guide ring, i.e., it can have a plurality of radial projections. The radial projections preferably extend in the circumferential direction of the guide ring in a manner corresponding to the circumferential beads over the entire or substantially the entire circumferential extent of the guide ring.

[0021] It should be noted that the annular beads and the radial protrusions can be arranged to be aligned with each other in the radial direction in the cross-section of the guide ring. Therefore, the response characteristics of the guide ring to the changing radial load can be set in a simple manner by the geometric configuration of the radial protrusions. In addition, one and the same guide ring can be used as a so-called rod or piston rod guide ring, or also 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. Thereby, the scope of use of the guide ring is improved and the provision and storage costs are reduced. The annular beads and the radial protrusions are preferably implemented to have the same structure in terms of size and geometry respectively.

[0022] The guide ring is particularly preferably provided with spherically formed flank sections on both sides in the axial direction. Thereby, in the installed state of the guide ring in the retaining groove or the like, the deformation of the guide ring in the axial direction can be made easier. Thereby, the undesired inclination in the assembly of the guide ring can be offset in a simple manner.

[0023] According to the invention, the base material of the guide ring is in particular a thermosetting plastic, or also a thermoplastic plastic. In particular, special modified thermoplastic materials such as polytetrafluoroethylene (PTFE), polyamide (PA) or polyoxymethylene (POM) can be used.

[0024] According to the invention, the guide ring can have a multi-component structural form. In particular, the guide ring can have a support or reinforcement insert which is known per se and which is preferably made of metal or technical ceramic. This is advantageous for the scope of use of the guide ring.

[0025] According to the invention, the annular beads can comprise a material that is harder than the base material of the guide ring or the rest of the guide ring, and the harder material preferably has a smaller coefficient of friction.

[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 second machine part the first machine part is guided to move back and forth along a movement axis. At least one guide ring according to the above-described embodiment is arranged in a retaining groove of one of the two machine parts. By means of this retaining ring, the piston is supported and guided in a form-locking manner with a sliding clearance on the cylinder in the case where there is a bearing clearance between the piston and the cylinder. This is carried out in such a way that, during the forward stroke movement of the first machine part, the lubricant arranged in the bearing clearance flows through one of the two free end sections of the guide ring, and during the return stroke of the first machine part, the lubricant flows into at least one lubricant channel of the guide ring via the respective other of the two free end sections of the guide ring. Due to the axial relative movement of the two machine parts, the lubricant is thus introduced into at least one lubricant channel of the guide ring and is guided to flow through the lubricant channel.

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

[0028] If at least one lubricant channel has a dynamic constriction, when the defined dynamic pressure head of the lubricant in at least one flow channel is reached or exceeded, a medium-actuated deactivation of the dynamic constriction of the flow cross-section of at least one lubricant channel is achieved. Due to the constriction, turbulence can be achieved in the lubricant channel, and through the turbulence, a particularly effective mixing of the lubricant and an improved discharge of impurities introduced into the lubricant channel are achieved.

[0029] Relative to the movement axis, the guide ring is preferably arranged in the retaining groove with an axial clearance. Thereby, a simplified assembly and trouble-free operation of the piston-cylinder unit can be ensured. Description of the Drawings

[0030] Other advantages of the invention can be found in the description and the drawings. The illustrated and described embodiments should not be understood as an exhaustive listing, but rather have exemplary features for describing the invention.

[0031] Shown in the drawings are:

[0032] Figure 1 : the piston-cylinder unit according to the invention with a guide ring in a partial sectional view;

[0033] Figure 2: the guide ring according to Figure 2A () in an isolated perspective detailed view and in a cross-section Figure 2B (); Figure 1

[0034] Figure 3: Another guide ring in the detailed part, having a lubricant channel and a flow funnel constructed on the end side, the lubricant channel leading into the flow funnel at both ends;

[0035] Figure 4 : Another guide ring in the partial cross-section, having two lubricant channels arranged strictly in the circumferential direction of the guide ring;

[0036] Figure 5 : Another guide ring in the partial cross-section, having a rear side radially protruding;

[0037] Figure 6 : A guide ring having a lubricant channel with a constant flow cross-section, the lubricant channel having a wavy course in the circumferential direction;

[0038] Figure 7 : A guide ring having a flow cross-section course that is not constant in the circumferential direction; and

[0039] Figure 8 : A guide ring having an inflow element extending into the lubricant channel, through which an inflow element causes a variable constriction of the lubricant channel depending on the lubricant flow, wherein the inflow element can be deflected bidirectionally and flexibly from an intermediate position shown in the circumferential direction of the guide ring. Detailed Description

[0040] Figure 1 A partial cross-sectional view of the piston-cylinder unit 10 is shown. 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 guided to move back and forth along the movement axis L within the cylinder 14. It should be noted that the term "piston" can also be understood as a piston rod known per se.

[0041] Here, the sealing ring 18 is used for a fluid or pressure-sealed seal of the bearing clearance 16 formed between the piston and the cylinder. The sealing ring 18 seals against the sliding surface 20 of the cylinder formed by the inner wall of the cylinder. The sealing ring 18 can be provided with a prestressing element 22. Here, 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.

[0042] As Figure 1The two guide rings 24 shown are each arranged in the circumferential retaining groove 26 of the first machine part 12. Each guide ring 24 has a dynamically guided front side or guide side 28 and a rear side 30, which are connected to each other via the flank 32 of the guide ring 24. The guide side 28 serves for the respective guide ring 24 to come to rest in a dynamically contacting manner on the cylinder 14. Thus, the guide side 28 points outwards in the radial direction relative to the central axis Z of the guide ring 24. In the assembled state of the guide ring 24, the central axis Z of the guide ring 24 coincides or substantially coincides with the movement axis L of the piston-cylinder unit 10 (see for example Figure 1 ). The contact area of each guide ring 24 with the sliding surface 20 is denoted by C.

[0043] The rear side 30 of the respective guide ring 24 serves for the statically contacting support of the guide ring 28 on the groove base of the machine parts 12, 14 having the retaining groove 26, here, for example Figure 1 the piston 12 shown.

[0044] In FIG. 2, the guide ring 24 is shown in a partially cut-away perspective detail. The guide ring 24 is embodied as slotted. Thus, the guide ring 24 has a first and a second end section 34, 36 in the circumferential direction, which are arranged spaced apart from each other with an axial channel clearance 38 being formed therebetween. The slotted shape of the guide ring 24 simplifies its assembly. The two end sections 34, 36 have end sides 40, 42 facing each other, which are arranged extending parallel or substantially parallel to each other. The end sides 40, 42 enclose an acute angle α of 15° ≤ α ≤ 75° with the central axis Z in their projection onto the central axis Z (see Figure 1 ). According to Figure 1 , the angle α can in particular be 40°.

[0045] During the start-up of the piston-cylinder unit 10, each guide ring 24 sometimes has to receive high radial loads and is also inevitably subject to wear due to mechanical and thermal loads caused by friction. Due to the manufacturing tolerances of the usual guide rings themselves, but also due to the manufacturing tolerances of the machine parts moving relative to each other, malfunctions can occur, such as increased wear, undesired stick-slip effects, or in extreme cases even lead to premature failure of the usual guide rings. Therefore, each guide ring 24 has a plurality of annular beads 44 constructed on its guide side 28, which are arranged spaced apart from each other in the axial direction relative to the central axis Z of the guide ring 24. The lubricant channels 46 are bounded on both sides in the axial direction by the annular beads 44. The lubricant channels 46 extend in the circumferential direction of the guide ring 24 from the first free end section 34 to the second free end section 36 and are open towards the axial channel clearance 38 on both sides. Thus, the lubricant channels 46 are fluidly connected to the axial channel clearance 38 at both ends.

[0046] During the forward stroke movement V and the return stroke movement R of the first machine component 12, the lubricant S arranged in the bearing or seal gap 16 is alternately dragged or pressed into the lubricant channels 46 via the respective free end sections 34, 36 of the guide ring 24, and the end sides 40, 42 of the ends are opposite to the respective movement directions of the first machine component 12 in the axial direction.

[0047] During the start-up of the piston-cylinder unit 10, it is possible in this way to ensure that the lubricant channels 46 are specifically flowed through by the lubricant S, and thus the lubrication and cooling of the contact area C of the guide ring 24 on the sliding surface 20 of the second machine component 14 can be improved. Overall, premature wear of the guide ring 24 and undesired stick-slip can be reliably counteracted thereby.

[0048] According to Figure 3 , the individual lubricant channels 46 of the guide ring 24 can be widened towards the end sides 40, 42 of the respective ends 34, 36 and thus form flow funnels 48 or flow funnels 48 of the channel end sections 34, 36. Thereby, on the one hand, a particularly large inflow opening 46a can be provided for each of the lubricant channels 46. On the other hand, thereby during the forward stroke movement V and the return stroke movement R of the piston ( Figure 1 ), a dynamic pressure head of the lubricant flowing into the respective flow funnels 48 can be established. Thereby it is ensured that during start-up the lubricant S (resulting from the relative movement of the two machine components 12, 14) is pressed into the individual lubricant channels 46 at a flow rate high enough for flushing, lubricating and cooling purposes. Particle impurities (not shown in the drawing) contained in the lubricant S entering at least one lubricant channel 46 of the guide ring 24 can be reliably removed or flushed out of the lubricant channels 46 in this way during start-up.

[0049] According to Figure 4 , the guide ring can also have more than two, in particular three, annular beads 44 on its guiding side 28. The respective two of the annular beads 44 delimit the lubricant channels 46 pairwise between each other. Two lubricant channels 46 are preferably jointly constructed in each of the two end sections 34, 36 of the guide ring 24 to form one of the flow funnels Figure 3 explained or lead into it. It should be noted that the lubricant channels 46 can be fluidly connected to each other by one or more axial connecting channels 50.

[0050] According to as Figure 5In the sectional view shown, the guide ring 24 can also have a rear side 30 that is corrugated in the axial direction and has radial protrusions 52. In this structural form, the manufacturing tolerances of the two machine components and the guide ring 24 can be compensated particularly effectively. The radial protrusions 52 on the rear side of the guide ring 24 can be arranged in alignment with the annular bead 44 on the front side of the guide ring in the radial direction. They can also be consistent with the annular bead 44 in terms of their geometry and dimensions.

[0051] According to Figure 6 In the embodiment of the guide ring 24 shown in, the lubricant channels 46 can have a particularly uniform wavy course in the circumferential direction. In this structural form, particularly effective lubrication of the contact area C between the annular bead 44 and the corresponding sliding surface 20 of the cylinder 14 is shown.

[0052] According to Figure 7 , each lubricant channel 46 of the guide ring 24 can have one or more statically and / or dynamically variable constrictions 54 (of the free cross-section through which the lubricant can flow). Each constriction 54 can be provided in particular by an inflow element 56, for example in the form of one or more wall protrusions as shown in Figure 7 . In the case of a dynamically variable constriction 54, the inflow element 56 can be, for example, flexibly deformable or flexibly deflectable on the guide ring. Thus, the inflow element 56 can be actuated by the lubricant to deflect in the direction of the central axis Z of the guide ring 24. By means of such constrictions 54, a dynamic pressure head of the lubricant can be generated in the lubricant channels 46, and thus the lubrication can be set locally as required.

[0053] The annular bead 44 and / or the rear-side radial protrusions 52 of the guide ring 24 can be made of a material with a lower modulus of elasticity or a lower coefficient of friction than the material of the rest of the guide ring 24.

[0054] The guide ring 24 can consist at least partially or entirely of an elastomer, such as ethylene propylene diene monomer rubber (=EPDM) or fluoroelastomer (=FKM), as well as additives familiar to those skilled in the art. PA (polyamide) or high-temperature thermoplastics, such as PEEK (=polyetheretherketone), are also suitable. It should be understood that the guide ring 24 can have strengthening or support inserts known per se, for example in the form of support rings. The strengthening or support inserts can in particular be made of metal, technical ceramics or also of a composite material containing carbon fibers, for example. The guide ring can also be pre-assembled in a cartridge and can be installed together with the cartridge in a retaining groove of the piston or cylinder.

Claims

1. A slotted guide ring (24) for a piston-cylinder unit (10), which is partially or completely composed of a viscoplastic deformable base material, - having a guide side (28) which points inwards or outwards in the radial direction relative to the central axis Z of the guide ring (24), and which is used for dynamically contacting and abutting against machine components (12, 14), and - having a rear side (30) which points away from the guide side (28) in the radial direction, and which is used for statically contacting support of the guide ring (24), - having a first free end section (34) and a second free end section (36), the first free end section and the second free end section being arranged spaced apart from each other in the circumferential direction of the guide ring with an axial channel gap (38) formed therebetween, and their end sides (40, 42) being arranged to extend parallel to each other or substantially parallel to each other, wherein, the end sides (40, 42) enclose an acute angle α of 15° ≤ α ≤ 75° with the central axis Z in their projection onto the central axis Z; - having a plurality of annular beads (44) formed on the guide side (28), the annular beads being arranged spaced apart from each other in the axial direction relative to the central axis Z of the guide ring (24), - having at least one lubricant channel (46), the lubricant channel being bounded on both sides in the axial direction by two corresponding annular beads of the annular beads (44), wherein 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 towards the axial channel gap (38) on both sides, characterized in that, the at least one lubricant channel (46) has a wavy course in the circumferential direction, the rear side (30) is implemented to be wavy or serrated in the cross-section of the unloaded guide ring (24) and has a plurality of radial protrusions (52), the radial protrusions extending in the circumferential direction of the guide ring (24) respectively over the entire or substantially the entire circumferential extension of the guide ring (24).

2. The guide ring (24) according to claim 1, characterized in that, each of the two free end sections (34, 36) has a flow funnel (48), and each lubricant channel of the lubricant channels (46) leads into the flow funnel.

3. The guide ring (24) according to claim 1 or 2, characterized in that, the at least one lubricant channel (46) has a static or dynamic constriction (54) at at least one circumferential position of the guide ring (24).

4. The guide ring (24) according to claim 1, characterized in that, the annular beads (44) and the radial protrusions (52) are arranged radially aligned with each other.

5. The guide ring (24) according to claim 1 or 2, characterized in that, The annular bead (44) comprises a material that is harder than the base material of the guide ring (24), and the harder material has a lower coefficient of friction.

6. A piston-cylinder unit (10), which comprises: - a first machine component (12) in the form of a piston rod or a piston; - a second machine component (14) in the form of a cylinder, in which the first machine component (12) is guided so as to be movable back and forth along a movement axis (L); - at least one guide ring (24) according to any one of the preceding claims 1 to 5, the guide ring being arranged in a retaining groove (26) of one of the two machine components (12, 14), and the other of the two machine components being supported and guided in a form-fitting manner with a sliding clearance such that, in a forward stroke movement V of the first machine component (12), the lubricant S arranged in the bearing clearance (16) flows through one of the free end sections (34, 36) of the guide ring (24), and in a return stroke movement of the first machine component (12), the lubricant flows via the respective other of the two end sections (34, 36) of the guide ring (24) into at least one lubricant channel (46) of the guide ring (24).

7. The piston-cylinder unit (10) according to claim 6, characterized in that the at least one lubricant channel (46) has a static or dynamic constriction (54) at at least one circumferential position of the guide ring (24).

8. The piston-cylinder unit (10) according to claim 7, characterized in that the dynamic constriction (54) of the lubricant channel (46) can be reduced or deactivated during start-up due to the lubricant flowing through the lubricant channel (46).

9. The piston-cylinder unit (10) according to any one of claims 6 to 8, characterized in that the guide ring (24) is arranged in the retaining groove (26) with an axial clearance relative to the movement axis (L).

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