EP2025951A2 - Piston/cylinder-unit - Google Patents

Abstract

Piston/cylinder unit (1) comprises a securing element (20) extending in the direction of an axis (9) and preventing loosening of the piston (7). The securing element is screwed with a thread (24, 27). The thread (15, 23) between the piston and the piston rod (18) and the thread between the securing element and the piston rod work in opposing directions. Preferred Features: The piston has an axially acting stop surface (12) and the securing element has an axially acting counter stop surface (29).

Description

The invention relates to a piston / cylinder unit with a cylinder housing, a piston having an opening and a piston rod having an axis, wherein the piston is connected via an internal thread arranged in the opening with an external thread provided on an extension of the piston rod without increased tightening torque.

The cylinder housing is usually supplemented by a guide bush, in which the piston rod of the piston / cylinder unit is guided and stored. The piston usually has a guide element and a static seal in addition to its dynamic piston seal. The piston rod can end in a bearing eye, with which it is arranged secured against rotation. The cylinder housing is also provided with a bearing, for example a bearing eye. The piston is connected to this in the cylinder housing movable end of the piston rod. If the seals and / or guide elements of the piston need to be replaced, it is only necessary to release the guide bushing relative to the cylinder housing and to pull the piston rod with the piston hanging therefrom out of the cylinder housing.

In contrast, when guide elements, seals and / or scrapers, which are associated with the piston rod and which are usually arranged in the guide bush, must be replaced, it is necessary to release the piston from the piston rod to access the inner opening of the guide bushing do. The releasable attachment of the piston to the piston rod is a fundamental problem for a piston / cylinder unit. The releasable attachment must be designed such that the piston passes through the fluid can absorb generated axial forces and transmitted to the piston rod. Furthermore, often a seal of the fluid between the piston and piston rod is required. In the case of a threaded connection between the piston and piston rod, a rotation of the piston relative to the piston rod is required to prevent an automatic release of the piston under operating loads.

This distinction between prestressed connections and non-prestressed connections. For preloaded connections, a tightening torque is applied via the threaded connection, so that the piston and piston rod are held biased in the mounted position against each pressed. In this case, the curing of end faces on the piston and piston rod is usually required to meet the permissible surface pressures when the required high tightening torques are applied. Such a high tightening torque has considerable advantages in the operation of the piston / cylinder unit in that the piston is subjected only to a swelling load and the axial force caused by the tightening torque always remains greater than the axial force brought about by the fluid. The tightening torque represents the first backup of the piston against loosening under operating conditions. In addition, often a second fuse is provided. In the case of replacement of the piston rod associated seal and / or the guide elements, however, the release of a high-torque-mounted piston on a piston rod is a significant problem, especially if one imagines that the repair of such piston / cylinder units, for example on construction machinery , Excavating u. Like. Usually must be done in the open field, without workshop devices can be used.

STATE OF THE ART

From the DE 101 56 504 C1 is a piston / cylinder unit of the type described above with a cylinder housing, an opening having a piston and a common axis having piston rod known. The piston has a piston seal and a guide element. The piston is connected via an internal thread arranged in the opening with an external thread provided on an extension of the piston rod without increased tightening torque. The internal thread of the piston and the external thread of the piston rod are provided with coincident eccentricity to the respective axes of the piston and the piston rod. The piston is on the piston rod screwed with such a Winkelendlage that the axes of piston and piston rod are aligned. The eccentricity is used to prevent rotation. This caused by the eccentricity rotation does not require additional security elements. The piston attachment thus advantageously has a few components and is therefore inexpensive to produce. There are not even attack surfaces for a turning tool on the piston required because the piston can be screwed and loosened by hand. Increased tightening torques are not used, so that advantageously accounts for the otherwise necessary hardening of the end faces on the piston and piston rod. The piston connection has a short design and contributes to the extent that the piston rod can be used in its full length.

In the prior art, a piston mounting for a piston / cylinder unit is further known, in which a piston is plugged with an axially continuous opening without thread on an extension of the piston rod. The extension of the piston rod has an external thread on which after attaching the piston, a lock nut is screwed. The lock nut has an opening and an associated internal thread. The lock nut is provided for example with a plastic insert, which acts as a securing element against loosening. Thus, a non-positive rotation is used.

It is also known in the prior art to combine the piston and the lock nut into a single part, so that the associated internal thread is provided in an opening of the piston. As a securing element, a stud provided radially in the piston is used, which presses in the mounted position on the extension of the piston rod. Here, the piston must have corresponding engagement surfaces for a turning tool to be able to apply the necessary high tightening torque during assembly and the corresponding release torque during disassembly. Special tools are usually indispensable.

Both known piston fasteners under the action of a high tightening torque have the following disadvantages. The high moments during assembly and disassembly can not be applied without special tools. The piston or an additional securing element must have corresponding engagement surfaces for the special tool. Additional components for the realization of an additional anti-rotation prove to be necessary and cause the overall length in the area of the piston increases. The mutually come to bear substantially radially extending end faces between the piston and piston rod must be cured in a complex manner. Such piston compounds are expensive to produce and comparatively less easy to repair.

In the event that the arrangement of a static seal between piston and piston rod is required, the piston and piston rod are designed so that they overlap in the axial direction by an amount necessary for the accommodation of the static seal. Thus, the already carefully machined surface of the piston rod can also be used as a counter surface for this static seal.

From the US 3,293,993 is a piston / cylinder unit known. It has a cylinder housing, an axis having a piston and an axis having a piston rod. The piston is connected via an internal thread arranged in an opening with an external thread provided on an extension of the piston rod. The piston is screwed onto the thread on the extension of the piston rod with high tightening torque, so that high tensile forces occur in this part of the piston rod. The axes of the threads and the axes of the piston rod and piston coincide. The well-known piston / cylinder unit shows no rotation of the piston against the piston rod and does not deal with a safe and repair-friendly training.

From the DE-OS 24 48 019 For example, a piston assembly for a fluid motor is known which comprises a piston / cylinder unit with a cylinder housing, an opening having a piston and a piston rod. The piston is screwed with a wrench on a arranged in the opening internal thread on a provided on an extension of the piston rod male thread with increased tightening torque and tightened that an edge of the piston bites into a tapered portion of the piston rod. On a further portion of the extension a lock nut is screwed so that it is firmly set against the piston. The threads of the locking nut and the further portion of the extension of the piston rod have a smaller inclination and greater number of threads than the threads of the piston and the engaging portion of the piston rod. All threads are formed and arranged in the same direction. Thus, the locking nut and the piston are only pulled against each other under the action of otherwise leading to loosening rotational forces during operation, the locking nut and the piston.

In order to make the piston attachment easier to repair, a piston / cylinder unit is already known in the prior art, in which the piston and the piston rod are loosely screwed onto one another via a threaded connection with internal thread and external thread. It is essential in this connection a rotation of the piston against the piston rod. The connection is made without applying a tightening torque. As a rotation, a bolt, a sleeve or the like is used, which protrudes into an axially guided bore, which is arranged so that it passes through the threaded portion between the piston rod and piston. During installation, chips are produced, which disadvantageously present a risk of contamination. The sleeve, the bolt or the like must be additionally secured against axial migration. This is usually done with a screw with lock washer, which passes through the piston in the axial direction and represents a stop for the wandering out of the socket, the bolt or the like. Such a piston attachment has a relatively large number of additional components that cause the rotation. The arrangement and design of the elements results in a relatively long construction in the region of the connection of the piston and the piston rod. The piston attachment is complex and causes in the production of the individual elements comparatively high costs. However, an advantage of this known piston fastening is the avoidance of a tightening torque, so that this piston connection is formed repair-friendly, because the piston can be solved by the removal of the securing means by relatively simple rotation of the piston rod.

OBJECT OF THE INVENTION

The invention has for its object to improve a piston / cylinder unit, which is mounted while avoiding an increased tightening torque, to the effect that the necessary rotation of a screwed onto a piston rod piston is achieved in a different manner than before. It is about a cost-effective and repair-friendly training piston / cylinder unit.

SOLUTION

According to the invention this is achieved in a piston / cylinder unit of the type described above, characterized in that extending substantially in the direction of the axis, axially acting and the loosening of the piston preventing securing element via a Thread pairing is connected to the piston rod. The thread pairing between the piston and the piston rod and the thread pairing between the securing element and the piston rod are formed in opposite directions.

DESCRIPTION OF THE INVENTION

The invention is based on the idea of accommodating on the piston rod or the extension of the piston rod, in addition to the piston, an axially acting securing element extending substantially in the direction of the axis of the piston / cylinder unit and preventing the piston from loosening. Also, this securing element has a thread and extends with its axis coaxial with the common axis of the piston / cylinder unit or the piston rod. The threads between piston and piston rod on the one hand (the first "thread pairing") and between the fuse element and piston rod on the other hand (the second "thread pairing") are designed in opposite directions, so one of the thread pairings as right-hand thread and the other as left-hand thread. The piston and the securing element abut each other via surfaces which transmit forces by friction. Thus, the Losdrehrichtung of a thread is assigned to the fixed direction of rotation of the other thread, so that a starting loosening of the one element, for example the piston, via a contact surface to the fuse element causes the fuse element is taken in the fixed direction.

The new way of securing the piston on the piston rod is in contrast to the known countering a screw connection in which z. B. two nuts are screwed onto a common thread of a screw. Here, both nuts are twisted in opposite directions on the common thread against each other. Thus, a tension is generated in the screw, which increases the preload forces in such a way that the frictional forces produced at the thread flanks counteract a loosening of the screw connection. Disadvantage of this screw lock is that the component to be secured, namely the first nut screwed on the thread of the screw is turned back and thus its locking system of the first nut on a collar of the screw is no longer given.

The new way of securing the piston on the piston rod is in contrast to the previously retracted development directions, in particular the development direction, which works with increased tightening torques of a screw-on piston. It follows a simplified assembly and disassembly. Both the piston and the securing element need only be screwed on with such tightening torques that are within a normal range. Thus, it is readily possible to unscrew the piston and / or the securing element by hand and to dispense with the use of tools. Just as easily, the piston can be easily removed in the field of the piston rod, for example, when it is necessary to replace the seals in a guide sleeve of the piston rod.

The new way of securing the piston also makes it possible to select and use comparatively larger diameters in the area of the thread compared with the prior art. Dispensing with increased tightening torques entails the omission of the high surface pressures required or occurring in the prior art, so that the diameter of the external thread on the extension, which is intended to receive the internal thread of the piston, is only slightly smaller than the outside diameter of the piston rod must be, and indeed suitably so that it does not hinder the insertion of the piston rod in a guide element and does not interfere with the housed seals there. The realization of larger diameter increases the areal proportion of the thread between the piston and piston rod, so that not only less high-quality materials for the piston rod and the piston can be used, but also the thread can get a comparatively shorter length. This has a positive effect on the overall length of the piston / cylinder unit. Furthermore, special measures, such as the hardening of corresponding surfaces on the piston rod and piston, as required for receiving high tightening torques, are eliminated.

The thread between the piston and the piston rod can also be applied with simple production methods, for example by cutting instead of rolling. This simplifies the production of small series for which the production and use of a rolling tool would be too time-consuming.

The thread can also be performed with relatively larger slopes. Since the piston can be screwed on by hand, the arrangement of special tightening surfaces on the piston is unnecessary for a torque tool, as is essential for the application of increased tightening torques.

A further significant advantage is to be seen in the comparatively smaller overall length of the cylinder, because the piston can be made structurally shorter and the arrangement of the axially acting securing element does not necessarily have to increase the overall length. Although then, when the fuse element is designed as a nut, the key engagement surface must be accessible to the mother, resulting in a slight increase in length. But if, conversely, the axially acting securing element is designed as a screw, there is the possibility of such a screw, for. B. as hexagon socket screw, without increasing the length of the piston / cylinder unit provided.

In addition, the axially acting securing element can have a safeguard against loosening. This fuse is thus assigned to the fuse element, but not the piston. The fuse extends effectively always on the fuse element. Here are all fuses conceivable as they are used in nuts and bolts against loosening, starting from a radially arranged threaded pin, a special design of the contact surfaces, the use of bendable lock washers or the addition of a corresponding securing means in the thread. The backup of the fuse element must be detachable in all cases, so that the simplified disassembly of the fuse element and subsequently the piston is possible.

The piston has an axially acting abutment surface and the securing element on an axially acting counter stop surface. The stop surface and the counter stop surface come to rest against each other, namely under frictional engagement. This ensures that the loosening direction of the one element is associated with the tightening direction of the other element.

Between the piston and the piston rod, a static seal may be provided. The arrangement of the seal in detail can be done in different places. The static seal increases the static friction of the piston on the piston rod.

The axially acting securing element thus extends substantially in the direction of the common axis of the piston / cylinder unit and can be moved or rotated by a screwing movement. The axially acting securing element is thus usually designed as a nut or screw, whose axes are arranged coaxially to the common axis of the piston / cylinder unit.

Also for securing the securing element, there are the various design options, in particular a radially mounted in the piston and acting on a rotating surface of the securing element stud. It is understood that this fuse, so the stud, must first be solved during disassembly in order to rotate the fuse element in the loosening direction can. If the securing element is turned off from the extension of the piston rod, then the piston can be rotated and turned off very easily and without significant application of force on its counter-rotating thread.

The internal thread of the piston and the associated external thread of the extension may have a pitch in the range between 1 mm and 5 mm. There are all common thread forms conceivable, especially those with large pitch and short overall length.

The piston is usually unscrewed or unscrewed by hand. The securing element is preferably screwed against the piston with a torque in the range between 20 Nm and 50 Nm. Such torques can be realized without the use of special tools.

The piston and the securing element may be arranged such that they at least partially overlap axially so as not to increase the overall length as required. This is especially true for the formation of the fuse element as a mother. When forming the securing element as a screw, this screw can even accommodate within the overall length of the piston, so that there is no increase in the overall length. The screw can be designed in particular as a hexagon socket screw.

The threads with which the piston on the one hand and the securing element are screwed on the other hand, are formed and arranged in opposite directions. Preferably, the piston and the piston rod are connected to each other via a left-hand thread and the securing element and the piston rod via a right-hand thread. This simplifies the availability of a fuse element and facilitates handling because a user, e.g. B. when loosening, a normal right-hand thread expected.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and combinations of several features mentioned in the introduction to the description are merely exemplary and can take effect alternatively or cumulatively, without the advantages of compelling embodiments of the invention must be achieved. Further features are the drawings - in particular the illustrated geometries and the relative dimensions of several components to each other and their relative arrangement and operative connection - refer. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be further clarified and described with reference to two embodiments.

Fig. 1

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer ersten Ausführungsform.

Fig. 2

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer zweiten Ausführungsform.

Fig. 3

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer dritten Ausführungsform.

Fig. 4

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer vierten Ausführungsform.

Fig. 5

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer fünften Ausführungsform.

Fig. 6

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer sechsten Ausführungsform.

Fig. 7

einen Schnitt durch eine Kolben/Zylinder-Einheit in einer siebten Ausführungsform.

Show it:

Fig. 1

a section through a piston / cylinder unit in a first embodiment.

Fig. 2

a section through a piston / cylinder unit in a second embodiment.

Fig. 3

a section through a piston / cylinder unit in a third embodiment.

Fig. 4

a section through a piston / cylinder unit in a fourth embodiment.

Fig. 5

a section through a piston / cylinder unit in a fifth embodiment.

Fig. 6

a section through a piston / cylinder unit in a sixth embodiment.

Fig. 7

a section through a piston / cylinder unit in a seventh embodiment.

DESCRIPTION OF THE FIGURES

In the Fig. 1 Piston / cylinder unit 1 shown has, as usual, a cylinder housing 2, which is tubular and merges at its one end into a bearing 3. At the other end of the piston / cylinder unit 1, a bearing 4 is provided. The bearing 4 facing the cylinder housing 2 carries z. B. the guide bush 5 engages via a thread 6 in the cylinder housing 2, but is of minor importance to the present invention.

In the cylinder housing 2, a piston 7 is slidingly and sealingly slidably mounted. The piston 7 has an outer peripheral surface 8, which, as usual, is cylindrical. Concentric with the peripheral surface 8, the piston 7 has an axis 9 which coincides with the axis of the piston / cylinder unit 1. On the outer peripheral surface 8 of the piston 7 guide and sealing elements are arranged, here a guide strip 10 and a dynamic seal 11. The piston 7 has a first stop surface 12 and a second stop surface 13. The piston 7 otherwise has an opening 14 which is stepped here. A portion of the stepped aperture 14 is provided with an internal thread 15, while another part of the stepped aperture 14 is formed as a cylindrical bore 16. In the region of this cylindrical bore 16, a static seal 17 is arranged. The opening 14 with its internal thread 15 and the bore 16 with its seal 17 are arranged centrally relative to the common axis 9 of the piston / cylinder unit 1.

The piston / cylinder unit 1 has a piston rod 18 which has an outer diameter 19 which forms the outer circumference of the piston rod 18. The piston rod 18 has at its end facing the piston 7 a projection 21. The extension 21 is also stepped in coordination with the opening 14 formed. A part of the extension 21 has a cylindrical peripheral surface 22. Another part of the extension 21 is provided with an external thread 23, which corresponds to the internal thread 15. The extension 21 has a collar 25, against which the piston 7 comes when screwed with its contact surface 13 to the plant. The coming into contact with the system parts of the contact surface 13 and the collar 25 can be made relatively small, as increased surface pressures not occur. Thus, the external thread 23 of the extension 21 can be advantageously realized on a large diameter.

The piston rod 18 is slidably guided in the guide bushing 5 and sealing. For this purpose, 5 different elements are housed in the guide bush, which are not important for the present invention. The piston rod further has at its end facing away from the piston 7, the bearing 4, via which the connection of a working device or the like can take place. At its end passing through the piston 7, the extension 21 has a stop 26, which is supported in the starting position on an end wall of the cylinder housing 2. An approximately acting on the piston rod 18 force is forwarded in this position, bypassing the piston 7 directly into the cylinder housing 2 and its bearing 3. The piston / cylinder unit 1 is here designed double-acting, ie, the pressure chambers formed on both sides of the piston 7 can each be acted upon by a fluid, in particular with hydraulic fluid. This is done in a known manner via a corresponding control valve. However, the invention can also be applied to single-acting cylinders ( Fig. 6 ) and use.

The piston 7 is associated with a securing element 20 which is formed here in the form of a nut. The securing element 20 has an opening 28 and in this a thread 24, here an internal thread 24, on. The projection 21 has matching the securing element 20 has a smaller diameter portion on which a thread 27, here an external thread 27, is provided, which corresponds to the internal thread 24 of the securing element 20. The securing element 20 has a counter-abutment surface 29, via which the securing element 20 abuts against the abutment surface 12 of the piston 7. The stop surface 12 and the counter stop surface 29 are formed so that they rub against each other, so can transmit friction.

The thread pairing 15, 23, ie between the piston 7 and extension 21, is in opposite directions to the thread pairing 24/27, that is to say the threads between the securing element 20 and the extension 21. So z. B. the threads 15, 23 as a left-hand thread and the threads 24, 27 may be formed as a normal right-hand thread.

To assemble the piston / cylinder unit 1, the elements are first mounted on the guide bush 5. Subsequently, the piston rod 18 through the guide bushing. 5 inserted through the piston 7 and screwed after insertion of the static seal 17. The piston 7 is pre-assembled before screwing with the guide band 10 and the seals 11 and 17. The screwing can be done by hand, since only appropriate frictional forces are overcome. In this Aufschraubvorgang the piston sets with its second contact surface 13 to the collar 25 of the piston rod 18, so that the surface pressure on the collar 25 is correspondingly low. The contact surface on the collar 25 can be structurally selected to be very small, so that advantageously results in a relatively large diameter at the threads 15/23. The threads 15/23 can be made comparatively shorter than in the prior art, which has an overall advantageous effect on a small overall length of the piston / cylinder unit 1. When forming the thread 15/23 as a left-hand thread, a corresponding screwing movement takes place.

Subsequently, the securing element 20 is screwed. Since the threads are formed in opposite directions, now the screwing takes place in the right direction. Also this Aufschraubvorgang can be done by hand. The screwing is terminated by the stop surface 12 of the securing element 20 rests against the counter stop surface 29 of the piston 7. At these surfaces 12, 29 creates frictional engagement and thus the securing effect. Should the piston 7 in the operation of the piston / cylinder unit 1 to move in the loosening direction or show a corresponding tendency, this leads to the securing element 20 is taken or acted upon by the frictional engagement in the fixed direction, so that the securing effect is not lost.

Subsequently, the preassembled unit with the piston rod 18, the screwed-on piston 7 and the screwed securing element 20 is inserted into the cylinder housing 2. Finally, the guide bush 5 is screwed and tightened by means of the thread 6 in the cylinder housing 2. The piston / cylinder unit 1 is thus mounted ready for use. In case of defects occurring after appropriate operation, such as leaks occur, the disassembly is done in reverse order, so that all the sealing elements that may need to be replaced, are easily and easily accessible. The piston / cylinder unit 1 is thus very repair and service-friendly.

In the embodiment of the piston / cylinder unit 1 according to Fig. 2 First, a basically similar attachment of the piston 7 is provided on the piston rod 18, as this based on the embodiment of the Fig. 1 has been described. Again, the parts have opposite threads 15/23 and 24/27. The further constructive training is quite comparable, so that it can be referenced. However, the piston 7 has at its end facing the bearing 3, a recess 30 whose axial length is dimensioned so that it forms a part of the securing element 20, here also designed as a nut. The securing element 20 can also be accommodated completely in the axial length of the piston 7. In this case, the recess 30 must be dimensioned so that the nut can be reached, for example, with a socket wrench. The axial lengths between piston 7 and securing element 20 cover each other completely or partially, which is advantageous to a total length of the piston / cylinder unit 1. It is understood that the stop surface 12 and the counter-abutment surface 29 are formed at a corresponding location in the piston 7. The location of the static seal 17 is changed. At the extension 21, a corresponding counter paragraph, which cooperates with the static seal 17, so that here the already precisely machined surface of the piston rod 18 is used as a counter surface for the seal 17. It can be seen that here the part of the extension 21, which faces the bearing 3 from the securing element 20, is designed to be short and advantageously extends the overall length only minimally. The purpose of such a design is to absorb forces in the piston rod 18 directly in the bearing 3 via a stop 31 formed at its free end. Also this piston / cylinder unit 1 according to Fig. 2 is designed as a double-acting unit. Corresponding supply lines to the corresponding Wirkräumen are readily apparent.

The embodiment of the piston / cylinder unit according to Fig. 3 complies with the training Fig. 2 at. In addition to the opposing formation of the thread, the fuse element 20 itself is assigned a fuse 33. The fuse 33 has a stud 34 which is arranged in the piston 7 radially to the common axis 9. After assembly of the piston 7 and the securing element 20 via the opposing threads 15/23 and 24/27 on the extension 21 of the piston rod 18, the stud 34 is tightened so that it radially against a surface on the securing element 20, so for example to a Key engagement surface of a conventional mother, rests. With this fuse 33, the fuse element 20 is additionally secured against loosening.

In itself, the fuse 33 can be realized for the securing element 20 in any conceivable embodiment, as is also known in screws and nuts against loosening, ie in particular in the form of split pins, locking screws, washers, etc.

The embodiment according to Fig. 4 agrees in a wide range with the previously described and described embodiments. However, the securing element 20 is designed here as a hexagonal screw 36 and extends with its screw shank into the interior of the piston rod 18, so that the length defined by the piston 7 is increased only by the head 32 of the hexagon screw 36. Also in this embodiment, the thread pairings 15/23 and 24/27 are formed in opposite directions and arranged. In this case, however, the thread 24 of the securing element 20 is here designed as an external thread 24 and the thread 27 of the piston rod 18 as an internal thread 27.

The embodiment according to Fig. 5 builds on that according to Fig. 4 on. In addition, the fuse element 20 is associated with a fuse 33 against loosening. Essential element of this fuse 33 is a lock washer 35. The fuse 33 can also be realized in other ways, for. B. as a blocking element, as a frictionally resilient element, as a form-fitting blocking element or in the form of a applied to the thread mass. Also in this embodiment, the thread pairings 15/23 and 24/27 are formed in opposite directions and arranged. In this case, however, the thread 24 of the securing element 20 is here designed as an external thread 24 and the thread 27 of the piston rod 18 as an internal thread 27.

The embodiment of the Fig. 6 used as a fuse element 20 also has a screw, here a hexagon socket screw 37. As a fuse 33, an adhesive can be found in the threads 24/27 application. This embodiment results in a particularly short length, since the hexagon socket screw 37 can be accommodated within the extension of the piston 7. The embodiment according to Fig. 6 clarifies at the same time that the invention is generally applicable to single-acting piston / cylinder units 1. The ventilation of the space around the piston rod 18 takes place through a bore 38. Also in this embodiment, the thread pairings 15/23 and 24/27 are formed in opposite directions and arranged. In this case, however, the thread 24 of the securing element 20 is here designed as an external thread 24 and the thread 27 of the piston rod 18 as an internal thread 27.

The embodiment of the Fig. 7 used as a securing element 20 has a groove nut 39 which is secured by a caulking 40.

LIST OF REFERENCE NUMBERS

1

Piston / cylinder unit

2

cylinder housing

3

camp

4

camp

5

guide bush

6

thread

7

piston

8th

peripheral surface

9

axis

10

guide band

11

poetry

12

stop surface

13

stop surface

14

perforation

15

inner thread

16

drilling

17

poetry

18

piston rod

19

diameter

20

fuse element

21

extension

22

peripheral surface

23

external thread

24

thread

25

Federation

26

attack

27

thread

28

perforation

29

Thrust face

30

recess

31

attack

32

head

33

fuse

34

Set screw

35

lock washer

36

Hex bolt

37

Allen screw

38

drilling

39

locknut

40

caulking

Claims (10)

Piston / cylinder unit (1), with
a cylinder housing (2),
an opening (13) having a piston (7), and
a piston rod (18) having an axis (9), wherein the piston (7) has an internal thread (15) arranged in the aperture (13) with an external thread (23) provided on an extension (21) of the piston rod (18) increased tightening torque is connected, characterized in that
an axially acting securing element (20), which extends substantially in the direction of the axis (9) and prevents the loosening of the piston (7) is provided, wherein the securing element (20) has a thread (24) and with this with a second thread (27) of the piston rod (18) is connected, and
the thread pairing (15/23) between the piston (7) and the piston rod (18) and the thread pairing (24/27) between the securing element (20) and the piston rod (18) are formed in opposite directions. Piston / cylinder unit according to claim 1, characterized in that the securing element (20) has a fuse (33) against loosening. Piston / cylinder unit according to claim 1 or 2, characterized in that the piston (7) has an axially acting abutment surface (12) and the securing element (20) has an axially acting counter-abutment surface (29). Piston / cylinder unit according to one or more of claims 1 to 3, characterized in that the securing element (20) is designed as a nut or screw. Piston / cylinder unit according to claim 2, characterized in that the lock (33) against loosening a in the piston (7) radially mounted and on a rotating surface of the securing element (20) engaging the stud (34). Piston / cylinder unit according to one or more of claims 1 to 5, characterized in that the internal thread (15) of the piston (7) and the associated external thread (23) of the extension (21) has a pitch in the range between 1 mm and 5 mm have. Piston / cylinder unit according to one or more of claims 1 to 6, characterized in that the securing element (20) is screwed with a torque in the range between 20 Nm and 50 Nm against the piston (7). Piston / cylinder unit according to one or more of claims 1 to 7, characterized in that the piston (7) and the securing element (20) are arranged under at least partial axial overlap. Piston / cylinder unit according to one or more of claims 1 to 8, characterized in that the piston (7) and the piston rod (18) via a left-hand thread and the securing element (20) and the piston rod (18) are connected via a right-hand thread , Piston / cylinder unit according to one or more of claims 1 to 9, characterized in that a static seal (17) is provided between the piston (7) and the piston rod (18).

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