Positional stop for a piston / cylinder assembly

Abstract

A positional stop (100) for a piston / cylinder assembly (200) is disclosed. The piston / cylinder assembly (200) comprises a housing (210) and a fluidic actuator (220) with at least one piston (221, 222). The housing (210) comprises a passage opening (215). The positional stop (100) comprises a position sensor (110); and a sensor holder (120) which holds the position sensor (110) and has a stop portion (125). The sensor holder (120) can be inserted into the passage opening (215) together with the position sensor (110) and the stop portion (125) of the sensor holder (120) forms, in the inserted state, a stop for the at least one piston (221, 222) of the fluidic actuator (220).

Description

[0001] DESCRIPTION

[0002] Position stop for a piston-cylinder assembly

[0003] The present invention relates to a position stop, a piston-cylinder assembly with the position stop and a method for manufacturing the piston-cylinder assembly.

[0004] Conventional transmissions, especially those for trucks, often require a large number of gears to be shifted. Accordingly, the shift rods are arranged so they can be moved axially over long distances, making precise positioning crucial. Conventional transmissions often result in inaccurate positioning of the shift rod, resulting in significant wear, not only on the gears but also on the fluid actuators (hydraulic or pneumatic), since the shifting events require high forces.

[0005] Therefore, there is a need for accurate position sensing in fluidic actuators that can be used in piston-cylinder assemblies, especially multi-position cylinders, and are easy and cost-effective to manufacture.

[0006] At least some of the above-mentioned problems are solved by a position stop according to claim 1 and a method for manufacturing a piston-cylinder assembly. The dependent claims relate to further advantageous developments of the subject matter of the independent claims.

[0007] The present invention relates to a position stop for a piston-cylinder assembly. The piston-cylinder assembly comprises a housing and a fluidic actuator with at least one piston. The housing comprises a through-opening. The position stop comprises a position sensor and a sensor holder that holds the position sensor and has a stop portion. The sensor holder, together with the position sensor, can be inserted into the through-opening, and the stop portion of the sensor holder, when inserted, forms a stop for the at least one piston of the fluidic actuator.

[0008] A fluidic actuator is understood, in particular, to be a pneumatic or hydraulic actuator that causes controlled linear movements when actuated. The sensor mount can, in particular, be monolithic (constant material) and formed in one piece. The position sensor can, for example, be integrated into the sensor mount.

[0009] Optionally, the actuator further comprises a positioning piston with a magnet. The piston-cylinder assembly can further comprise a shift rod coupled to the positioning piston so that, upon actuation of the actuator, it can be linearly displaced together with the positioning piston into a plurality of positions. Optionally, the position sensor is a magneto-resistive sensor (e.g., a Hall sensor) that triggers a sensor signal at at least one of the plurality of positions of the positioning piston.

[0010] Optionally, the at least one piston comprises a first sliding piston and a second sliding piston, both of which are arranged annularly and linearly displaceably between the housing and the positioning piston. Optionally, the sensor mount comprises a recess (or cutout) through which the positioning piston is linearly displaceable and to which the stop portion is adjacent (e.g., directly connected) to form the stop for the first sliding piston and / or the sliding piston on opposite sides.

[0011] Optionally, the sensor mount includes at least one fastening device for removably securing the sensor mount to the housing (e.g., via a screw connection). This allows the sensor mount to be installed or replaced at the end of the assembly process without having to disassemble the piston-cylinder assembly.

[0012] Embodiments also relate to a piston-cylinder assembly with a housing and a fluidic actuator. The housing comprises a through-opening, and the fluidic actuator comprises at least one piston. The piston-cylinder assembly further comprises a position stop as previously described, which forms a stop for the at least one piston at a predetermined position. The position stop can extend through the through-opening and can be detachably connected to the housing.

[0013] Optionally, the piston-cylinder assembly includes a shift rod that can be coupled to a shifting element (e.g., shift fork), for example, to shift transmission gears. Optionally, the fluidic actuator includes a position piston that is coupled to the shift rod so that, upon actuation of the actuator, it can be linearly displaced, together with the position piston, into a plurality of positions. The position piston can have a piston stop with a magnet at a predetermined axial position to trigger a sensor signal in the integrated position sensor of the position stop at at least one position (or at all positions).

[0014] Optionally, the inserted position stop with integrated position sensor can be pulled out or replaced even after the position piston has been inserted.

[0015] Optionally, the at least one position comprises three positions. The positioning piston can have a piston stop and can separate a first pressure chamber from a second pressure chamber in the piston housing in order to be linearly movable between the three positions under pressure control.

[0016] Optionally, the at least one piston comprises a first sliding piston and a second sliding piston, both of which are annular and linearly displaceable between the housing and the positioning piston. The position stop and the piston stop can be arranged between the first sliding piston and the second sliding piston such that, at a predetermined pressure ratio between the first pressure chamber and the second pressure chamber, the piston stop is in the same axial position as the position stop. This can define an intermediate position between the three positions. Optionally, the housing comprises a cylindrical cavity into which the at least one piston and / or the positioning piston can be inserted, e.g. from one side only. The cylindrical cavity can optionally be closed with a cover (or closing element).

[0017] Optionally, the cylindrical cavity includes a recess-free inner cylinder wall. Optionally, only the inserted position stop forms a projection on the inner cylinder wall, so only the monolithic position stop with integrated position sensor can be used as a stop.

[0018] Embodiments also relate to a transmission actuator with a piston-cylinder assembly as described above. Embodiments also relate to a commercial vehicle, in particular a truck, with the transmission actuator. The transmission actuator can be used in particular in an automatic transmission control unit.

[0019] Embodiments also relate to a method for manufacturing a piston-cylinder assembly. The method comprises:

[0020] - Providing a housing with a cylindrical cavity and a through opening;

[0021] - inserting at least one sliding piston and one positioning piston into the cylindrical cavity;

[0022] - Closing the cylindrical cavity with a lid;

[0023] - Inserting a position stop with an integrated position sensor into the through-opening, wherein the position stop forms a stop for the at least one sliding piston at a predetermined position; and

[0024] - Fixing the position stop to the housing with a detachable connecting device.

[0025] The integrated position sensor is designed to sense a linear position of the positioning piston. Optionally, the at least one sliding piston comprises a first sliding piston and a second sliding piston, and the step of inserting the position stop can optionally be performed after inserting the positioning piston, the first sliding piston, and the second sliding piston.

[0026] It is understood that all previously described functions or features of the piston-cylinder assembly can be implemented as additional optional method steps. Furthermore, it is understood that the order in which the steps are listed does not necessarily represent the order in which the method steps are executed. The steps can also be performed in a different order, or only some of the method steps are performed.

[0027] Embodiments of the present invention solve the above-mentioned technical problem by integrating the position sensor into a position stop, which serves as a stop wall. This improves the sensor functions. Furthermore, reliability is improved and manufacturing is simplified. Costs are also saved due to the simplified cylinder design.

[0028] The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the various embodiments, which, however, should not be construed to limit the disclosure to the specific embodiments, but are for explanation and understanding only.

[0029] Fig. 1 shows a spatial view of the position stop according to an embodiment of the present invention.

[0030] Fig. 2 shows a schematic representation of the piston-cylinder assembly with integrated position stop according to an embodiment.

[0031] Fig. 3 shows a sectional view through the housing with the inserted position stop according to an embodiment.

[0032] Fig. 4 shows a cross-sectional view through the piston-cylinder assembly along the same cross-sectional plane as in Fig. 3. Fig. 5 shows a schematic flow diagram for a process for manufacturing the piston-cylinder assembly.

[0033] Fig. 1 shows a perspective view of the position stop 100 according to one exemplary embodiment. The position stop 100 comprises a position sensor 110 and a sensor holder 120 that holds the position sensor 110 and has a stop section 125. The sensor holder 120, together with the integrated position sensor 110, can be inserted into a through-opening of a housing of a piston-cylinder assembly (not shown in Fig. 1). When inserted, the stop section 125 of the sensor holder 120 serves as a stop for at least one piston 221, 222 of a fluidic actuator of the piston-cylinder assembly.

[0034] By way of example, the at least one piston 221, 222 is a first sliding piston 221 and a second sliding piston 222, which are arranged on opposite sides of the position stop 100. The position stop 100 with the integrated position sensor 110 is designed, for example, as a cuboid that can be inserted into the through-opening of the housing (not shown in Fig. 2) and can be fastened to the housing with a first fastening device 121 and a second fastening device 122. The wall-shaped position stop 100 forms a stop for the two sliding pistons 221, 222 on both opposite sides. The first fastening device 121 and / or the second fastening device 122 can, for example, be tabs with openings through which a screw or bolt can be passed in order to screw the position stop 100 to the housing.

[0035] The cuboid-shaped position stop 100 comprises, for example, a round cutout 107 through which a positioning piston of the piston-cylinder assembly can pass. The sliding pistons 221, 222 are formed in a ring shape to allow sliding onto the positioning piston. The sliding pistons 221, 222 can each comprise a dedicated stop surface for abutting against the stop portion 125 to define an end position during sliding. For sealing, the sliding pistons comprise corresponding sealing elements 223, 224 (e.g., O-rings). The round cutout 107 in the position stop 100 has, for example, the same radius as the inner diameter of the ring-shaped sliding pistons 221, 222.

[0036] The integrated position sensor 110 serves to sense the position of the position piston and is arranged, for example, at a central position along the round-shaped cutout 107 in order to ensure a good coupling to the position piston.

[0037] Fig. 2 shows a piston-cylinder assembly 200 according to an embodiment of the present invention. The piston-cylinder assembly 200 includes a fluidic actuator 220 (e.g., a pneumatic or hydraulic actuator, not an electric motor actuator) having a position piston 225 to which a shift rod 230 is attached. A shift element 300, such as a shift fork, is attached to the shift rod 230, which can, for example, perform shifting operations in a transmission.

[0038] In addition, the piston-cylinder assembly 200 includes a housing 210 with a through-opening 215 into which the position stop 100 is inserted, as described in Fig. 1. The through-opening 215 thus not only represents a recess in the housing wall, but also connects an exterior space with an interior space of the housing 210. The housing 210 can be any unitary component that has one or more bearings 205 for the shift rod 230 and can be closed on one side by a cover 260.

[0039] In the housing 210, the fluidic actuator 220 with the positioning piston 225 can be formed in a cylindrical cavity, wherein the positioning piston 225 separates a first pressure chamber 201 from a second pressure chamber 202. Based on the pressure conditions present there, the positioning piston 225 is linearly movable within the cavity. Optionally, several interconnected positioning pistons can also be provided.

[0040] The actuation can occur as follows. If the first pressure chamber 201 is pressure-free or has little pressure and the second pressure chamber 202 has a minimum pressure (is filled), the positioning piston 225 moves towards the first pressure chamber 201 (right in Fig. 2). If, on the other hand, the second pressure chamber 202 is pressure-free (or has only a low pressure) and the first pressure chamber 201 has at least a further minimum pressure, the positioning piston 225 moves towards the second pressure chamber 202 (to the left in Fig. 2). Accordingly, the switching element 300 is in the first position P1 or the second position P2. The minimum pressure can be selected such that it ensures movement of the piston 150 in one direction or the other in any case. It is understood that it is not absolutely necessary for one of the two pressure chambers 201, 202 to be pressure-free for the movement of the positioning piston 225.In any case, however, the pressure difference between pressure chambers 201, 202 must be sufficiently large to trigger the movement.

[0041] A center position P3 (between the first position P1 and the second position P2) can be assumed at a predetermined pressure ratio between the first pressure chamber 201 and the second pressure chamber 202. To switch to this position, a piston stop 250 (e.g., firmly fixed to the piston) is provided on the piston 225 at a predetermined axial position, which in the center position P3 coincides with the position stop 100 in the housing 210. To move the positioning piston 225 into this center position P3, the sliding pistons 221, 222 (see also Fig. 1) are arranged to be axially displaceable such that the pressure on both sides moves the sliding pistons 221, 222 towards each other. Since the position stop 100 with the integrated position sensor 110 and the piston stop 250 are both located between the first sliding piston 201 and the second sliding piston 202, the position piston 225 is moved to the center position P3.

[0042] The piston stop 250 can further have a magnet 240 attached thereto. The magnet 240 can also be integrated into the piston stop 250. The magnet 240 serves to indicate the exemplary center position via the integrated position sensor 110. It is also possible for the integrated position sensor 110 to indicate all three positions, i.e., the first position P1, the second position P2, and the third position P3. This can be done, for example, by detecting the magnetic field direction (e.g., determining a magnetic north pole, a neutral position, or a magnetic south pole). The integrated position sensor 110 can, for example, be a magneto-resistive sensor (e.g., a Hall sensor), which outputs different sensor signals (e.g., to a control device) at the positions P1, P2, P3 of the positioning piston 225.

[0043] Thus, the position stop 100 (or the piston stop 250) defines the intermediate or middle position P3, and this can be freely selected between the end positions P1 and P2 (e.g., via appropriate positioning of the through-opening 215 or the piston stop 250). In particular, the intermediate position P3 can be fixed centrally between the two end positions P1 and P2. Furthermore, the active areas in the first pressure chamber 201 and the second pressure chamber 202 can be selected such that the intermediate position P3 is assumed when the pressure in the first pressure chamber 201 and the second pressure chamber 202 is the same (e.g., by fluidly connecting both chambers). However, the predetermined pressure ratio for assuming the intermediate position P3 can be adjusted by changing the active areas in the first pressure chamber 201 and / or in the second pressure chamber 202.The effective area is the area on which the linear force for linear movement of the actuator acts - triggered by pressure.

[0044] Fig. 3 shows a sectional view through the housing 210 with the inserted position stop 100, wherein the sectional view is taken along the axial axis of the positioning piston 225 (not shown in Fig. 3) and through the position sensor 110. The housing 210 comprises the cylindrical cavity 211, which is delimited on one side by a housing section 212 with a through-opening. On an opposite side, a cover 260 is formed, which can close the cavity 211 after the positioning piston 225 and the sliding pistons 221, 222 have been inserted into the latter (see also Fig. 2).

[0045] The housing section 212 can be an integral part (monolithically connected) of the housing 210. The position piston 225 is arranged to be axially displaceable, wherein the housing section 212 forms a first stop and the cover 260 forms a second stop to define the first position P1 and the second position P2. In the center position P3, the magnet 240 is at the piston stop 250, as shown in Fig. 3, at the same axial position as the position sensor 110. Therefore, the position sensor 110 is sensitive to the center position P3, but optionally the first

[0046] Position P1 and the second position P2 are detected.

[0047] Fig. 4 shows a cross-sectional view through the piston-cylinder assembly along the same cross-sectional plane as in Fig. 3. The positioning piston 225, the first sliding piston 221, and the second sliding piston 222 are inserted into the cylindrical cavity of the housing 210. In addition, the position stop 100 has been pushed between the two sliding pistons 221, 222 into the through-opening 215. The position stop 100 with the position sensor 110 is attached directly to the housing 210 via the fastening device 121 and could be pulled out of the housing 210 by loosening the fastening device 121.

[0048] In addition, the shift rod 230 is fixedly connected to the positioning piston 225 in order to transmit the linear movement of the positioning piston 225 to the shift rod 230, for example to move a shift fork 300 linearly. In comparison to the embodiment from Fig. 2, in this embodiment the shift rod 230 is arranged on the opposite side, i.e. the shift rod 230 extends through the second pressure chamber 202 (to the left) and not through the first pressure chamber 201, as shown in Fig. 2. It is understood that embodiments of the present invention are intended to cover both possibilities. The shift rod 230 can optionally also extend through the cover 260 (e.g. through the opening shown). If the shift rod 230 is only led out on one side, the opening in the cover 260 can be closed in order to maintain the pressure inside the housing 210 accordingly.The cover 260 can also be (removably) attached to the housing via fastening means.

[0049] The first sliding piston 221 comprises an outer sealing ring 223a and an inner sealing ring 223b, which seal the first sliding piston 221 to the cylindrical inner wall of the housing 210 and to the positioning piston 225. Similarly, the second sliding piston 222 can comprise an outer sealing ring 224a and an inner sealing ring 224b, which seal the second sliding piston 222 to the cylindrical inner wall of the housing 210 and to the positioning piston 225. In this way, the formation of an overpressure in the first pressure chamber 201 causes the sliding pistons 221, 222 to move linearly in the direction toward the second pressure chamber 202 until the first sliding piston 221 strikes the position stop 100. Subsequently, the position piston 225 can move further toward the second pressure chamber 202 because the position piston 225 extends into the first pressure chamber 201 and is exposed to pressure.The same applies conversely if an overpressure develops in the second pressure chamber 202, or the first pressure chamber 201 is vented, or if the pressure there is significantly lower. In this case, the positioning piston 225 will move toward the first pressure chamber 201.

[0050] The described fluidic actuator 220 can be controlled via a pressurized fluid (e.g., air or hydraulic oil), for which purpose fluid openings 171, 172 are provided to effect the inflow and outflow of the pressurized fluid. A first pressurized air opening 271 can supply compressed air to the first pressure chamber 201 or vent it. A second pressurized air opening 272 can supply compressed air to the second pressure chamber 202 or vent it.

[0051] It is understood that a movement of the sliding pistons 221, 222 together with the positioning piston 225 results in a larger effective cross-section than a movement of the positioning piston 225 alone. Therefore, to reach the center position P3, at which the sliding pistons 221, 222 are moved together with the positioning piston 225, a lower pressure can be present in the first pressure chamber 201 and the second pressure chamber 202. To reach the end positions P1, P2, a correspondingly higher pressure would be required in the first pressure chamber 201 or in the second pressure chamber 202 in order to move the positioning piston 225 up to the corresponding stop surface on the housing section 212 or the cover 260. This can ensure that at a maximum pressure in the first or second pressure chamber 201, 202, the positioning piston 225 moves to the second or first position P2, P1.

[0052] Fig. 5 shows a schematic flow diagram for a method for manufacturing the piston-cylinder assembly. The method comprises the steps: - Providing S210 a housing 210 with a cylindrical cavity 211 and a through-opening 215;

[0053] - Inserting S220 one or two sliding pistons 221, 222 and a positioning piston 225 into the cylindrical cavity 211;

[0054] - closing S230 the cylindrical cavity 211 with a cover 260;

[0055] - Inserting S240 a position stop 100 with an integrated position sensor 110 into the through-opening 215, wherein the position stop 100 forms a stop for the at least one piston 221, 222 at a predetermined position; and

[0056] - Fixing S250 of the position stop 100 to the housing 210 with a detachable connecting device 121, 122.

[0057] The integrated position sensor 110 is in turn designed to sense a linear position of the position piston 225.

[0058] It is understood that all of the previously described functions of the evaluation circuit can be implemented as additional optional process steps. Furthermore, it is understood that the order in which they are listed does not necessarily reflect the order in which the process steps are executed. The steps can also be performed in a different order, or only some of the process steps are executed.

[0059] The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention both individually and in any combination.

[0060] LIST OF REFERENCE SYMBOLS

[0061] 100 Position stop

[0062] 107 Recess or cutout

[0063] 110 Position sensor

[0064] 120 Sensor holder

[0065] 121 ,122 fastening device

[0066] 125 stop section

[0067] 200 piston cylinder assembly

[0068] 201 ,202 pressure chambers

[0069] 205 Storage

[0070] 210 housing

[0071] 211 cylindrical cavity in the housing

[0072] 212 Housing section

[0073] 215 passage opening

[0074] 220 fluidic actuator

[0075] 221 , 222 at least one piston (e.g. sliding piston)

[0076] 223,224 Sealing rings for pistons

[0077] 225 Position piston

[0078] 230 shift rod

[0079] 240 Magnet

[0080] 250 piston stop

[0081] 260 Cover for the housing

[0082] 271 ,272 openings (e.g. for compressed air)

[0083] 300 switching element (e.g. shift fork)

[0084] P1, P2, P3 (axial) positions

Claims

PATENT CLAIMS 1 . A position stop (100) for a piston-cylinder assembly (200), wherein the piston-cylinder assembly (200) comprises a housing (210) and a fluidic actuator (220) with at least one piston (221, 222), the housing (210) comprises a through-opening (215), characterized by - a position sensor (110); and - a sensor holder (120) which holds the position sensor (110) and has a stop section (125), wherein the sensor holder (120) can be inserted into the through-opening (215) together with the position sensor (110), and the stop section (125) of the sensor holder (120) forms a stop for the at least one piston (221, 222) of the fluidic actuator (220) in the inserted state.

2. The position stop (100) according to claim 1, wherein the actuator (220) further comprises a position piston (225) with a magnet (240) and the piston-cylinder assembly (200) further comprises a switching rod (230) which couples to the position piston (225) in order to be linearly displaced into a plurality of positions (P1, P2, P3) upon actuation of the actuator (220) together with the position piston (225), characterized in that the position sensor (110) is a magneto-resistive sensor which triggers a sensor signal at at least one of the plurality of positions (P1, P2, P3) of the position piston (225).

3. The position stop (100) according to claim 2, wherein the at least one piston (221, 222) comprises a first sliding piston (221) and a second sliding piston (222), both of which are arranged in a ring-shaped and linearly displaceable manner between the housing (210) and the position piston (225), characterized in that the sensor holder (120) has a recess (107) through which the position piston (225) is linearly displaceable and to which the stop portion (125) to form the stop for the first sliding piston (221) and the sliding piston (222) on opposite sides.

4. The position stop (100) according to one of the preceding claims, characterized in that the sensor holder (120) has at least one fastening device (121, 122) in order to releasably fix the sensor holder (120) to the housing (210).

5. A piston-cylinder assembly (200) with a housing (210) and a fluidic actuator (220), wherein the housing (210) comprises a through-opening (215) and the fluidic actuator (220) comprises at least one piston (221, 222), characterized by a position stop (100) according to one of the preceding claims, which forms a stop for the at least one piston (221, 222) at a predetermined position, wherein the position stop (100) extends through the through-opening (215) and is detachably connected to the housing (210).

6. The piston-cylinder assembly (200) according to claim 5, further comprising a shift rod (230) which can be coupled to a shift element (300) in order to shift transmission gears, characterized in that the fluidic actuator (220) comprises a position piston (225) which is coupled to the shift rod (230) in order to be linearly displaced into a plurality of positions (P1, P2, P3) together with the position piston (225) upon actuation of the actuator (220), wherein the position piston (225) has a piston stop (250) with a magnet (240) at a predetermined axial position in order to trigger a sensor signal in the integrated position sensor (110) of the position stop (100) at at least one position (P1, P2, P3).

7. The piston-cylinder assembly (200) according to claim 6, wherein the at least one position comprises three positions (P1, P2, P3), and wherein the position piston (225) in the piston housing (210) separates a first pressure chamber (201) from a second Pressure chamber (202) separates in order to be linearly movable between the three positions (P1, P2, P3) in a pressure-controlled manner, characterized in that the at least one piston (221, 222) comprises a first sliding piston (221) and a second sliding piston (222), both of which are formed in annular manner and can be moved linearly between the housing (210) and the position piston (225), wherein the position stop (100) and the piston stop (250) are arranged between the first sliding piston (221) and the second sliding piston (222), so that at a predetermined pressure ratio between the first pressure chamber (201) and the second pressure chamber (202), the piston stop (250) is located at the same axial position as the position stop (100), whereby an intermediate position (P3) of the three positions (P1, P2, P3) is defined.

8. The piston-cylinder assembly (200) according to one of claims 5 to 7, characterized in that the housing (210) has a cylindrical cavity (211) in which the at least one piston (221, 222) and / or the positioning piston (225) can be inserted from one side only and the cylindrical cavity (211) can be closed with a cover (260).

9. The piston-cylinder assembly (200) according to claim 8, characterized in that the cylindrical cavity (211) has a recess-free cylinder inner wall and only the inserted position stop (100) forms a projection on the cylinder inner wall.

10. A transmission actuator for an automatic transmission control unit, characterized by a piston-cylinder assembly (200) according to one of claims 5 to 9.

11. A commercial vehicle, in particular a truck, characterized by a transmission actuator according to claim 10.

12. A method for producing a piston-cylinder assembly (200), characterized by - Providing (S210) a housing (210) with a cylindrical cavity (211) and a through opening (215); - inserting (S220) at least one sliding piston (221, 222) and one positioning piston (225) into the cylindrical cavity (211); - closing (S230) the cylindrical cavity (211) with a cover (260); - Inserting (S240) a position stop (100) with an integrated position sensor (110) into the through-opening (215), wherein the position stop (100) forms a stop for the at least one piston (221, 222) at a predetermined position; and - fixing (S250) the position stop (100) to the housing (210) with a detachable connecting device (121, 122), wherein the integrated position sensor (110) is designed to sense a linear position of the position piston (225).

13. The method according to claim 12, wherein the at least one sliding piston (221, 222) comprises a first sliding piston (221) and a second sliding piston (222), characterized in that the step of inserting the position stop (100) can be carried out after inserting the position piston (225), the first sliding piston (221) and the second sliding piston (222).

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