End of travel damped working cylinder

Abstract

The invention relates to an end-position damped working cylinder which has a damping zone in at least one end region, wherein a pressure medium connection is assigned to the damping zone and is axially spaced from an axial boundary of the cylinder interior, wherein a piston unit comprises a piston body, a resiliently designed piston ring with a piston ring gap and a piston ring limiter, wherein the piston unit is configured to axially pass over the pressure medium connection with the piston ring during a retraction movement into the damping zone and to enclose a damping pressure medium volume in a damping zone space in the damping zone and wherein an overpressure of the damping pressure medium volume is present relative to the pressure medium connection and the piston ring gap is configured for a throttled outflow of the damping pressure medium volume, and wherein the piston ring limiter is configuredto limit the spring travel of the piston ring outside the damping zone in a relaxation direction and to fix the piston ring in a preload position.

Description

[0001] The invention relates to an end-position damped working cylinder with high-precision damping behavior.

[0002] The state of the art describes solutions for end-position damping in various versions.

[0003] Firstly, controlled hydraulic throttles are used in the inlets and outlets. This restricts the flow rate of the working cylinder. The throttling is controlled, for example, by electronic control systems as a function of the working cylinder's displacement. Disadvantages of this solution include high design complexity, low robustness, and a large hysteresis effect due to the inertia of the hydraulic system.

[0004] Furthermore, solutions are known in which the piston movement itself is used directly to reduce the volume flow of the hydraulic fluid inside the cylinder.

[0005] EP 0779 435 B1 discloses a solution, particularly for plunger cylinders, in which the piston has a cylindrical bottom-side chamber and the bottom-side cylinder closure part has a corresponding mandrel. In its end position, the piston moves towards the mandrel and engages it in the bottom-side chamber. An annular gap forms on the wall between the mandrel and the bottom-side chamber, through which the fluid volume enclosed in the bottom-side chamber and displaced by the mandrel flows out at a controlled rate, thus slowing the piston movement. This solution has proven effective but cannot be used if the available space does not permit the formation of a bottom-side chamber.

[0006] EP 0 949 422 B1 describes a solution as progressive throttling via a variable annular gap of a piston ring. This ring is located on the piston and, at one end of the cylinder, passes over the laterally arranged fluid port, enters a conical section, and encloses the fluid in a pressure chamber. This progressively restricts the fluid outflow through an increasingly narrow annular gap at the end of the piston's movement. It is a well-established solution, but technically demanding, requiring high precision in determining the piston ring preload to define the damping zone.

[0007] The object of the invention is to demonstrate an end-position damping system for a working cylinder which provides high precision and easy adjustability of the damping characteristics and the damping path, is suitable for different cylinder designs, exhibits high robustness and operational reliability, is particularly low in wear, and is easy and cost-effective to manufacture.

[0008] The problem is solved by the features listed in claim 1. Preferred embodiments are set forth in the dependent claims.

[0009] The end-position damped working cylinder comprises a cylinder and a piston unit as basic components, wherein, according to the invention, a piston ring limiter is assigned to the piston unit.

[0010] A cylinder of this type comprises a cylinder tube, a first closure element, and a second closure element, the cylinder tube having a first and a second end. The first closure element is located at the first end of the cylinder tube, and the second closure element is located at the second end. The cylinder tube and the closure elements form a cylinder interior. For this purpose, the closure elements are connected to the cylinder tube in a pressure-tight manner, for example, by welding or bolting. However, other joining methods are also possible. The closure elements also form an axial boundary, and their spacing defines the working stroke of the piston assembly of the working cylinder.

[0011] Furthermore, according to the invention, the cylinder has a damping zone in at least one end region. For hydraulic actuation, the cylinder has at least one laterally arranged pressure medium connection, which is assigned to the damping zone and is axially spaced from an axial boundary of the cylinder interior. The damping zone is defined by the distance between the pressure medium connection and the end stop in the closure part. Damping is understood as a force effect that develops over the travel path of the piston unit in the damping zone, counteracting the movement and thus delaying it.

[0012] The piston assembly slides through the first breechblock and forms at least one working chamber within the cylinder. This can be, for example, only one working chamber, particularly in a plunger cylinder, or two working chambers, particularly in a differential or synchronous cylinder. The piston assembly is guided in a sealing bore within the first breechblock. Depending on the design of the working cylinder, the piston assembly can be, for example, a plunger piston, as in a plunger cylinder, or a unit consisting of a piston and piston rod, as in a differential or synchronous cylinder.

[0013] The piston assembly comprises a piston body that is guided axially displaceably within the cylinder interior by means of a guide. The piston body can be, for example, the piston in a piston-piston rod assembly, a plunger piston, or the piston rod itself. According to the invention, the piston body has a circumferential inner ring groove on a radial outer surface.

[0014] Furthermore, the piston assembly also includes a piston ring. This is located in the inner ring groove. It is resilient and has an annular gap. The inner ring groove is sufficiently deep to allow the piston ring to move into the groove when its circumference decreases, thus reducing the annular gap opening.

[0015] According to the invention, the piston unit is designed to pass over the pressure medium connection during an inward movement towards the end position and to enclose a volume of damping pressure medium in a damping zone space.

[0016] During the retraction movement within the damping zone, the piston unit exhibits a first operating state. During an extension movement within the damping zone, the piston unit exhibits a second operating state. A third operating state exists during movement outside the damping zone.

[0017] In the first and second operating states, the piston ring rests with its outer surface against the inner cylinder wall, blocking the flow of pressurized fluid between the outer surface and the inner cylinder wall. The inner cylinder wall is defined as all sections of the cylinder wall opposite the outer surface of the piston ring. This can include sections of the cylinder tube as well as the sealing elements.

[0018] In the first operating state, the damping fluid volume is pressurized above the pressure at the pressure port, and the piston ring's annular gap is designed for a restricted outflow of the damping fluid. This annular gap forms a defined overflow channel for the pressure medium. The cross-section of the piston ring gap regulates the pressure loss and thus the flow rate of the pressure medium.

[0019] In the second operating state, the pressure medium connection is pressurized above the volume of the damping medium. The annular gap is also designed to allow a flow of pressure medium into the damping zone. This flow occurs when the pressure medium is pressurized, either through the annular gap or, preferably, via a bypass. An optional bypass allows the pressure medium to flow into the damping zone much faster than through the annular gap, thus avoiding the typically undesirable damping of the extension movement.

[0020] The end-position damped working cylinder according to the invention is characterized in particular by the fact that the piston unit has a piston ring limiter.

[0021] This is designed to limit the spring travel of the piston ring in a relaxation direction and to fix the piston ring in a preload position.

[0022] This is based on the fact that the piston ring is designed to be spring-loaded. This means that in the first and second operating states, it is designed to assume a working position and bear resiliently against the inner cylinder wall in the damping zone. In the working position, the piston ring is under tension and is compressed against its spring direction by the inner cylinder wall.

[0023] According to the invention, the piston ring is also designed to assume a preload position in the third operating state.

[0024] In the context of the present invention, the preload position is understood to mean that the piston ring's expansion is limited not by the inner wall of the cylinder, but by another means, wherein the spring tension of the piston ring in the preload position is lower than in the working position.

[0025] This surprisingly provided a solution that significantly improved the damping properties compared to the state of the art.

[0026] Since the piston ring is fixed to a precisely definable outer diameter by the preload position, undefined damping start-up ranges are avoided. Instead, the axial starting position of the damping is precisely defined by the limited expansion diameter of the piston ring in conjunction with the axial profile of the cylinder's inner diameter.

[0027] Upon reaching the axial position where the piston ring's outer diameter in its preload position corresponds to the cylinder's inner diameter in the taper region, the piston ring no longer engages with a spring force of zero, as in the prior art, but rather with a definable spring force. This ensures a spring-loaded, tight seal against the cylinder's inner wall from this axial point onward. The spring force is determined by the spring constant and the position of the preload relative to the piston ring's travel.

[0028] In this way, the damping zone can be designed to be advantageously shorter.

[0029] Furthermore, there is the advantage that the piston ring does not rub against the inner cylinder wall outside the damping zone, thus preventing wear in this respect.

[0030] Furthermore, tilting or initial uneven contact of the piston ring with the cylinder wall is prevented, as the piston ring limiter preferably centers the piston ring radially. Temporary parasitic flows of pressurized fluid through undefined ring gaps are thus eliminated.

[0031] The fundamental advantages of this solution according to the invention are therefore the precisely controllable damping and the better defined operating points. In particular, the operating point at the beginning of the damping and the operating point at the restart of the reversing movement of the piston unit can be set exactly.

[0032] According to a further development of the invention, the piston ring limiter is designed as a radial piston ring limiter.

[0033] A radial piston ring limiter is understood to mean that the expansion is limited by radially defining the preload position. This means that the maximum radial distance of the outer surface of the piston ring to the main longitudinal axis of the piston is determined.

[0034] According to a further development of the radial expansion limitation based on the invention, the piston ring has a base flange and a piston ring limiter.

[0035] The base flange provides a radial ring surface that is recessed relative to an outer surface. The piston ring thus has a stepped outer contour, with the radial ring surface of the base flange section having a smaller outer diameter than the outer ring surface of the main section.

[0036] The radial piston ring limiter is designed as a retaining ring.

[0037] For this purpose, it has a radial overlapping surface. This radial overlapping surface, by means of a radial positive fit with the radial ring surface of the piston, limits a radial expansion of the piston ring.

[0038] This further development according to the invention provides the piston ring not only with an expansion limiter, but also with additional centering relative to the piston assembly using the same, simple, and reliable design means. This ensures that the piston ring's starting position when entering the damping zone is precisely determined. Tilting or an undefined seal of the piston ring against the pressure medium is prevented. The volume flow through the piston ring gap is always precisely defined from the axially determined starting position of the damping.

[0039] According to a further advantageous development, the piston ring limiter is designed as a circumferential limiter.

[0040] This is an alternative advanced training method to radial expansion limitation.

[0041] This circumferential limiter can be designed as an additional molded element on the piston rod or as a separate component. The molded part or component can also be formed from a continuous or split mold. The circumferential limiter absorbs the tangential tensile forces in the annular gap caused by the spring action, thus limiting the widening of the annular gap.

[0042] The piston ring, with its limited expansion, offers the advantage of compensating for play when entering the damping zone. Any manufacturing tolerances in the synchronization between the piston assembly and cylinder tube can thus be compensated for. Furthermore, a defined damping engagement point is provided due to the circumferentially limited piston ring diameter, which remains constant in the preload position. The damping engagement zone is clearly defined in its characteristic curve by the predetermined piston ring gap. According to a further advantageous embodiment, the piston ring has a tensile connection at the piston ring gap designed to limit the opening width of the piston ring gap.

[0043] This is achieved by using a tension element to limit the tangential expansion of the piston ring to a specific dimension. The tension element can be in the form of a tie rod, but also in another form.

[0044] According to a further development, the circumferential limiter is formed by two shaped pins that engage in two axial elongated holes of the piston ring on both sides of the piston ring gap.

[0045] Here, the piston ring limiter is designed as a tangentially acting expansion limiter. The expansion limiter is configured as an arrangement of two forming pins. The piston ring has two elongated holes in the axial direction on both sides of the piston ring gap. The piston body has two axial bores and is designed to receive the forming pins in these two bores, with the bores of the piston body and the elongated holes of the piston ring having overlapping positions. This design of the expansion limiter is subsequently also referred to as a pin lock.

[0046] The pin lock has the advantage that a tangentially acting expansion limiter determines a maximum opening width of the annular gap particularly precisely, and at the same time a radial and rotational positional relationship between piston ring and piston can also be determined.

[0047] According to another advantageous embodiment, the piston ring has a tensile connection at the piston ring gap. This connection is designed to limit the opening width of the piston ring gap.

[0048] According to another advantageous embodiment, the piston body comprises a piston base body. This is guided axially displaceably within the cylinder interior by means of a guide. Furthermore, the piston body comprises at least one ring body. This ring body has a circumferential inner ring groove on a radial outer surface, wherein the piston ring is arranged in the inner ring groove and wherein the piston ring bears resiliently against the inner cylinder wall. The piston ring also has a piston ring gap.

[0049] The ring body receives a guide pin of the piston body in a ring opening, with an annular gap formed between a radial inner surface of the ring body and the guide pin. The ring body has axial and radial clearance relative to the piston body. Furthermore, the ring body has an axial annular surface on the piston body side. Correspondingly, the piston body has a corresponding axial counter-annular surface on the opposite side of the ring body.

[0050] Accordingly, the piston body is designed such that in the first operating state the axial ring surface on the piston base side and the axial counter-ring surface on the ring body side are in contact with each other and form a sealing plane.

[0051] This ensures a pressure-tight seal between the working chamber and the damping zone. Only flow across the piston ring gap is possible for pressure equalization. Damping is achieved by throttling the pressure medium through the cross-section of the piston ring gap, converting kinetic energy into dissipation energy.

[0052] In the second operating state, the axial ring surface on the piston base side and the axial counter-ring surface on the ring body side have an axial gap relative to each other. This axial gap and the annular gap form a pressure medium inlet channel. The pressure medium channel is designed to allow the pressure medium to flow into the damping zone. The piston ring gap can thus be bypassed. This enables an undamped extension movement of the piston assembly out of the damping zone. This ensures a rapid extension movement of the cylinder at the beginning of the stroke.

[0053] According to a further advantageous embodiment, the cylinder has a further damping zone in a further end region axially opposite the end region.

[0054] The further damping zone is designed in the same way as the damping zone, so that all descriptive content relating to the damping zone, in particular to the axially spaced lateral pressure medium connection, to the piston ring with piston ring limiter and to the operating conditions, also applies accordingly to the further damping zone.

[0055] According to this further training, the working cylinder is designed as a working cylinder that is dampened in both end positions.

[0056] The invention is described as an exemplary embodiment by reference to Fig. 1 Schematic sectional view of the working cylinder. Fig. 2 Schematic sectional view of the damping zone with piston ring and radial piston ring limiter. Fig. 3 Schematic oblique view of piston ring and radial piston ring limiter. Fig. 4 Schematic sectional view of the damping zone with piston ring and forming pin as circumferential limiter. Fig. 5 Schematic oblique view of the piston ring with forming pins as circumferential limiter. Fig. 6 Schematic oblique view of the piston ring with tension connection as circumferential limiter. Fig. 7 Force-displacement diagram for the piston ring explained in more detail.

[0057] The Figure 1Figure 1 shows an embodiment of the working cylinder 1, which here is designed as a differential cylinder with damping on both sides, in a sectional view. The cylinder tube 3 is shown with the two closure parts 6 and 7, where the first closure part 6 is the bottom closure part and the second closure part 7 is the guide closure part. The piston unit 2 is guided within these parts.

[0058] Within the cylinder interior 8 is the working chamber 10, which here comprises the piston crown chamber 10.1 and the piston rod chamber 10.2. The damping zone 9 is incorporated into the sealing elements 6, 7 at the cylinder tube ends 4, 5. The components required for end-position damping are located in the damping zone 9. These include the piston body 11, which is mounted on the piston unit 2. This unit receives the piston ring 14. To position the piston ring 14 and limit its radial rebound, a piston ring limiter 17 is installed in this variant.

[0059] The hydraulic fluid for the working movement of the piston unit 2 is supplied via hydraulic fluid connection 16 for the extension movement and via the additional hydraulic fluid connection 16.1 for the retraction movement. By actuating the hydraulic fluid connections 16 and 16.1 in series, the piston unit 2 moves linearly and alternately in the axial direction within the cylinder tube 3.

[0060] In the present embodiment, the piston unit 2 has a piston rod that passes through the second locking element 7, here a guide locking element. Furthermore, the piston unit 2 has a guide piston that guides the piston unit 2 radially within the cylinder tube 3. The seal of the guide piston separates the two working chambers 10.1, 10.2, i.e., the piston base chamber 10.1 and the piston rod chamber 10.2. In addition, the piston body 11 of the piston unit 2 has a ring body 25 that is axially displaceable relative to the piston rod. In this embodiment, the piston rod forms the piston base body. The inner ring groove 13, which receives the piston ring 14, is arranged in the ring body 25.

[0061] In another embodiment – ​​not shown here – the ring body is arranged on the piston. In this embodiment, the piston forms the piston body.

[0062] The Figure 2Figure 1 shows a detailed sectional view of the damping zone 9 of cylinder 1. In this embodiment, the damping zone 9 has an axial bore in the first sealing element 6. The piston ring 14 is accommodated by the ring body 25. The ring body 25 is coupled to the piston rod with slight axial and radial play. In its end position, the piston ring 14 rests with its outer surface against the inner wall of the damping zone 9, thus forming the operating position in the first and second operating states. The ring body 25 also accommodates the piston ring limiter 17, which in this embodiment is designed as a radial piston ring limiter.

[0063] Located in the damping zone, the piston ring 14's radial spring action is limited by the piston ring limiter 17, which also positions and centers it radially. In the present embodiment, the piston ring 14 is also fixed on one side in its axial position by the piston ring limiter 17.

[0064] In Fig. 2The figure also shows that, according to this embodiment, the ring body 25 is guided on a guide pin 28 with axial and radial play. In the present embodiment, the guide pin 28 is a section of the piston rod of the piston unit 2. Here, the axial annular surface 27 of the ring body 25 on the piston base side and the counter-annular surface 22 of the piston base, here the piston rod, are opposite each other and form the sealing plane 21. During a retraction movement, i.e., in the first operating state, the ring body 25 is pressed axially against the counter-annular surface 22 by the overpressure in the damping fluid volume opposite the pressure medium connection 16, so that the sealing plane seals and the pressure medium can only pass through the piston ring gap.During an extension movement, i.e., in the second operating state, the pressure conditions are reversed and an axial annular gap opens between the axial annular surface 27 and the counter-annular surface 22. The pressure medium can additionally flow into the damping chamber via the overflow channel (without reference numeral) as a bypass, thus avoiding unwanted extension damping.

[0065] The Figure 3Figure 1 shows a schematic oblique view of the piston ring 14 and the piston ring limiter 17. In this version, the piston ring limiter 17 is designed as a radial piston ring limiter. A base flange 14a is formed on the piston ring 14. This flange has a radial annular surface 18 extending outwards in the radial direction. Opposite this, the piston ring limiter 17 has a radial overlap ring surface 19. In the compressed state, the radial annular surface 18 of the piston ring 14 rests against this overlap ring surface. This limits the spring travel of the piston ring 14. The sealing plane 21, in conjunction with the ring body 25, seals the pressure medium from the damping zone chamber to the remaining piston crown chamber 10.1. This ensures that a defined flow of the pressure medium is only possible through the piston ring gap 15.

[0066] The Figure 4Figure 1 shows in detail a further variant of the expansion limitation of the piston ring 14 in the form of a pin lock. In this embodiment, the piston limiter 17 is designed as a circumferential limiter.

[0067] Here, the piston ring 14 is prevented from radially springing up by two axially arranged forming pins 23. The two forming pins 23 are positioned in the ring body 25 in two axial bores 24 in a ring shoulder. The locking of the axial movement of the piston ring 14 is ensured by the inner ring groove 13. A further retaining ring axially secures the forming pins 23 by positive locking.

[0068] The Figure 5 Figure 1 shows a detailed oblique view of the geometric design of the piston ring 14 in the embodiment as a pin lock. This is the one described in Figure 2. Figure 4The illustrated embodiment shows that the forming pins 23 engage in two elongated holes positioned opposite each other on the circumference of the piston ring 14 at the piston ring gap 15, thus defining the maximum circumferential deflection of the piston ring 14. This defines the maximum opening of the piston ring gap 15 and determines the maximum flow rate of the pressure medium.

[0069] In Figure 6A further embodiment of the piston ring 14 is shown as a schematic oblique view in detail. The piston ring limiter 17 is designed as a tension connector 20. In this embodiment, the circumference, and thus also the radial spring travel, of the piston ring 14 is limited by the tension connector 20. The tension connector 20 acts to limit the circumferential expansion of the piston ring 14. Two elongated holes are provided axially around the circumference of the piston ring 14. These elongated holes are opened circumferentially towards the piston ring gap 15. The tension connector 20, in the form of a tension anchor, is inserted here after assembly. This limits the maximum opening width of the annular gap 15. The piston ring gap 15 thus has a defined gap that allows for a specific volume flow of the pressure medium for damping.

[0070] Figure 7schematically shows the effect of the piston ring limiter 17 on the force-spring travel relationship.

[0071] The spring travel s is plotted on the abscissa axis, with the relaxed position (without the piston ring limiter 17) located at the origin. Here, the piston ring 14 is maximally compressed and the piston ring gap 15 is at its largest. At point s max, the piston ring gap 15 is closed and the piston ring 14 is maximally tensioned. The force F is plotted on the ordinate axis.

[0072] According to the invention, the spring travel s of the piston ring 14 is limited in the direction of the relaxed position by the piston ring limiter 17 at point sv. At this point, the preload position exists in the third operating state. Here, the piston ring 14 bears against the piston ring limiter with the force F v. When the piston ring 14 enters the damping zone during a retraction movement and comes into sliding contact with the inner cylinder wall, and deforms further along its spring travel from point sv towards s max, it bears against the inner cylinder wall with the force F v predefined by the piston ring limiter 17 from the very beginning of the damping process, in contrast to the prior art. In the case of a conical inner cylinder wall for progressive damping, the piston ring 14 is compressed further and further in the spring travel range between point sv and s max, so that the force F continues to increase from point F v to point F max.The area between point sv and s max or between point F v and F max corresponds to the first operating state for a progression in the direction of s max or F max and the second operating state for a progression in the opposite direction.

[0073] Extending the graph in the opposite direction to the origin of the coordinate system using the dash-dot line shows the hypothetical force-displacement curve, assuming the piston ring limiter was not present. However, due to the piston ring limiter 17, the piston ring 14 is held in position sv, so that the force F acting on the inner cylinder wall drops to virtually zero immediately. Reference symbols used

[0074] 1 Cylinder 2 Piston unit 3 Cylinder tube 4 First cylinder tube end 5 Second cylinder tube end 6 First sealing part 7 Second sealing part 8 Cylinder interior 9 Damping zone 10 Working chamber 10.1 Piston bottom chamber 10.2 Piston rod chamber 11 Piston body 12 Guide 13 Inner ring groove 14 Piston ring 14a Base flange 15 Piston ring gap 16 Pressure medium connection 16.1 Further pressure medium connection 17 Piston ring limiter 18 Radial ring surface 19 Radial overlap ring surface 20 Tension connection 21 Sealing plane 22 Counter ring surface 23 Form pin 24 Axial bore 25 Ring body 26 Ring gap 27 Axial ring surface 28 Guide pin

Claims

1. A cylinder with end position damping, comprising a cylinder (1) and a piston unit (2), wherein the cylinder (1) comprises a cylinder tube (3), a first closure part (6) and a second closure part (7), wherein the cylinder tube (3) has a first cylinder tube end (4) and a second cylinder tube end (5), wherein the first closure part (6) is arranged at the first cylinder tube end (4) and the second closure part (7) is arranged at the second cylinder tube end (5), wherein the cylinder tube (3) and the closure parts (6, 7) form a cylinder interior (8), wherein the cylinder (1) comprises a damping zone (9) in at least one end region, wherein the cylinder (1) has at least one opening which is connected to a pressure-medium connection (16), is assigned to the damping zone (9) and is axially spaced from an axial limitation of the cylinder interior (8), wherein the piston unit (2) slidably passes through the first closure part (6) and forms at least one working chamber (10) in the cylinder interior (8), wherein the piston unit (2) comprises a piston body (11) and a piston ring (14), wherein the piston unit (2) is guided in an axially displaceable manner in the cylinder interior (8) by means of a guide (12), and the piston body (11) has a circumferential inner ring groove (13) on a radial outer lateral surface, wherein the piston ring (14) is arranged in the inner ring groove (13), is a resiliently designed and comprises a piston ring gap (15), wherein the piston unit (2) is designed to pass axially with the piston ring (14) over the opening, which is connected to the pressure medium connection (16), during a retraction movement into the damping zone (9) and to enclose a damping pressure medium volume in a damping zone chamber in the damping zone (9), wherein the piston unit is designed to have a first operating state during a retraction movement within the damping zone (9), a second operating state during an extension movement within the damping zone (9) and a third operating state during a movement outside the damping zone (9), wherein in the first operating state, an overpressure of the damping pressure medium volume exists relative to the pressure medium connection (16) and the piston ring gap (15) is designed for a throttled outflow of the damping pressure medium volume, wherein in the second operating state, an overpressure of the pressure medium connection (16) exists relative to the damping pressure medium volume and the piston ring gap (15) is designed for an inflow of a pressure medium into the damping zone chamber, wherein the piston ring (14) is configured to assume a working position in the first and second operating states and to rest resiliently against the inner cylinder wall in the damping zone (9), and wherein the piston ring (14) is configured to assume a pre-tension position in the third operating state, characterized in that the piston unit (2) has a piston ring limiting member (17) which is designed to limit a spring deflection of the piston ring (14) in a relaxation direction and to fix the piston ring (14) in the pre-tension position.

2. The working cylinder with end position damping according to claim 1, characterized in that the piston ring limiting member is designed as a radial piston ring limiting member (17).

3. The working cylinder with end position damping according to claim 2, characterized in that the piston ring (14) has a base flange (14a) which forms a radial ring surface (18) that is set back with respect to an outer lateral surface, and in that the radial piston ring limiting member (17) is designed as a holdingdown ring which has a radially overlapping ring surface (19), wherein the radially overlapping ring surface (19) limits a radial expansion of the piston ring (14) by means of a positive fit with the radial ring surface (18) of the piston ring (14).

4. The working cylinder with end position damping according to claim 1, characterized in that the piston ring limiting member (17) is configured as a circumference limiting member.

5. The working cylinder with end position damping according to claim 4, characterized in that the piston ring (14) has a tensile connection (20) at the piston ring gap (15) which is designed to limit an opening width of the piston ring gap (15).

6. The working cylinder with end position damping according to claim 4, characterized in that the piston ring limiting member (17) has two form pins (23) which are arranged in a fixed position relative to the piston body (11) and each of them engages in one of two elongated holes of the piston ring (14), wherein the elongated holes are arranged opposite the piston ring gap (15) and are configured such that, in the third operating state, each of the form pins (23) rests against a wall of the ring gap side of the respective elongated hole and limits the radial expansion of the piston ring.

7. The working cylinder with end position damping according to one of the previous claims, characterized in that the piston body (11) of the piston unit (2) comprises a piston main body, which is guided in an axially displaceable manner in the cylinder interior (8) by means of the guide (12), and at least one ring body (25), wherein the ring body (25) comprises the circumferential inner ring groove (13) on a radial outer lateral surface, wherein the piston ring (14) is arranged in the inner annular groove (13), wherein the ring body (25) receives a guide pin (28) of the piston main body in a ring opening, and wherein a ring gap (26) is formed between a radial inner lateral surface of the ring body (25) and the guide pin (28), wherein the ring body (25) has an axial movement play and a radial movement play relative to the piston main body, wherein the ring body has an axial ring surface (27) on the piston main body side and the piston main body has an opposing axial mating ring surface (22) on the ring body side, wherein in the first operating state, the axial ring surface (27) on the piston main body side and the axial mating ring surface (22) on the ring body side abut against each another and form a sealing plane (21), wherein, in the second operating state, an axial gap is between the axial ring surface (27) on the piston main body side and the axial mating ring surface (22) on the ring body side, and wherein the axial gap and the ring gap (26) form a pressure medium inflow channel which is designed for an inflow of a pressure medium into the damping zone chamber.

8. The working cylinder with end position damping according to one of the previous claims, characterized in that the working cylinder has a further damping zone (9) in a further end region which is axially opposite the end region.

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