Piston-cylinder device

Abstract

Piston-cylinder device (10) with - a housing (12), - a piston rod (14) with an external thread (44) mounted within the housing (12) so as to be displaceable in the longitudinal direction (L), - a piston (16) with internal thread (46) which is detachably screwed onto the piston rod (14), - a pressure chamber (48) provided within the housing (12) and capable of being pressurized with a pressure medium to generate the longitudinal movement of the piston rod (14) with piston (16), characterized in that - in the connection area of ​​the piston (16) to the piston rod (14), the end face (32) of the piston rod (14) has a projection (40) in the longitudinal direction (L) relative to the end face (34) of the piston (16) when the piston (16) is connected, - a pre-tensioning device with a clamping flange disc (18) is mounted on the end face (32) of the piston rod (14), which has a projection area (26) projecting beyond the outer contour of the piston rod (14) in the radial direction (R), whereby a gap is present between the projection area (26) and the end face (34) of the piston (16), - the pre-tensioning device in the projection area of ​​the clamping flange disc (18) is clamped to the piston (16) via clamping screw units (24), whereby a pre-tensioning force is exerted on the external and internal threads (44, 46), - wherein the preload force is greater than the forces acting from the pressure medium acting on the pressure chamber (48) against the preload device / clamping flange disc (18).

Description

TECHNICAL FIELD

[0001] The present invention relates to a piston-cylinder device with a housing, a piston rod with an external thread which is mounted so as to be displaceable in the longitudinal direction within the housing, a piston with an internal thread which is detachably screwed onto the piston rod, and a pressure chamber which is present within the housing and can be pressurized with a pressure medium to generate the longitudinal movement of the piston rod with piston. STATE OF THE ART

[0002] Typically, in such piston-cylinder devices, the pistons are screwed onto the piston rod via large threads, requiring a very high tightening torque to clamp them together, which in practice is either very costly or impossible. Since such piston-cylinder devices operate at very high hydraulic pressures, the service life of the threaded connection is limited. For long-term reliable operation, the piston must be removable to replace the internal sealing and guide elements.

[0003] A piston must be removable to replace the seals and guide elements. Seals and guide elements age and wear. Such seals and guide elements can only be replaced if the piston is disassembled and then these elements are pulled down toward the end of the piston rod, as otherwise they are inaccessible. On the other hand, such elements cannot be pulled out to the side if the piston rod has a molded eyelet or flange or any other geometry that extends beyond the rod diameter.

[0004] To attach the piston to the piston rod, it is common practice to first screw the piston onto the piston rod using a thread and then drill a pin recess into which a pin is inserted. With increasing service life, there is a risk of cracks developing because the pin hole represents a kind of "predetermined breaking point". Furthermore, a high torque is required to securely clamp the piston to the piston rod, which is usually difficult or impossible to apply. This results in a short service life of the thread, so that the piston has to be replaced relatively frequently. Replacing the piston, however, is problematic because the relatively high torque cannot be applied due to the large thread and the lack of clamping devices on site.

[0005] A further problem is that the threaded connection can fail. If the threaded connection between the piston and piston rod is not sufficiently preloaded, the forces from the load cycle resulting from the extension and retraction of the piston rod with the piston and pressurized medium act on the thread with the full stress deflection once to the left and once to the right of the piston. The same relationship applies here as with a screw that is not preloaded. Above a certain size, this high stress deflection leads to thread failure. This damages the piston and piston rod to the point where the piston can be pulled completely off the rod.Depending on the application, this is associated with high risks because the piston rod can then move completely out of the cylinder, which can result in damage to the adjacent components and, moreover, can involve a high potential for injury to persons who may be in the working area of ​​such piston-cylinder devices.

[0006] Another well-known solution involves clamping the piston to the screw shaft using a central screw. This allows for good thread clamping, but this solution is only practical for very small piston-cylinder devices.

[0007] A well-known and frequently used variant of connecting the piston to the piston rod involves clamping the piston between a stop on the piston rod and a nut screwed onto the piston rod by rotating the nut. To ensure reliable clamping, very high torques are required to rotate the nut, making on-site replacement of the piston generally impossible.

[0008] Another known connection variant also uses a nut screwed onto the piston rod, through which threaded pins are guided, which press the piston against a stop via a heat-treated stop plate. The heat treatment of the stop plate is necessary to maintain defined friction values ​​and enable the high contact forces of the threaded pins. This design enables good clamping, but is very expensive and not economical due to the various components: nut with internal thread, threaded pins, and heat-treated stop plate.

[0009] Furthermore, the documents DE 1 400 536 B, DE 20 2005 006 469 U1 and US 46 69 364 A are known from the prior art. PRESENTATION OF THE INVENTION

[0010] Based on the cited prior art, the present invention is based on the object or technical problem of providing a piston-cylinder device that is simple and cost-effective to manufacture and assemble, that ensures permanently reliable function and that enables simple disassembly of the piston on site without great effort in order to replace sealing and guide elements that are subject to aging and wear.

[0011] The piston-cylinder device according to the invention is defined by the features of independent claim 1. Advantageous embodiments and further developments are the subject of the claims directly or indirectly dependent on independent claim 1.

[0012] The piston-cylinder device according to the invention is accordingly characterized in that in the connection area of ​​the piston to the piston rod, the front end surface of the piston rod, when the piston is connected, has a projection in the longitudinal direction relative to the front end surface of the piston, a pretensioning device with a clamping flange disk is mounted on the front end surface of the piston rod, which has a projection area projecting beyond the outer contour of the piston rod in the radial direction, whereby a gap is present between the projection area and the front end surface of the piston, the pretensioning device is clamped to the piston in the projection area of ​​the clamping flange disk via clamping screw units, whereby a pretensioning force is exerted on the external and internal threads, wherein the pretensioning force is greater than the forces acting against the pretensioning device / clamping flange disk from the pressure medium acting on the pressure chamber.

[0013] In the inventive design of the piston-cylinder device, the preload force is designed to be higher than the forces resulting from the hydraulic pressure acting against the preload device. This results in the same conditions as with a preloaded screw connection. The deflection stress on the thread between the piston and piston rod, which is responsible for the service life, is significantly lower than with a non-preloaded connection. This ensures a long service life and consistently reliable function. At the same time, the piston can be easily disassembled, allowing for on-site replacement of sealing and guide elements, which are subject to aging and wear.

[0014] Because there is a gap between the clamping flange disc and the piston end face, and the clamping is achieved by standard screw units, very high torques are not required. The thread diameters of the screw units are within a normal range, enabling permanently reliable clamping of the thread between the piston and piston rod, resulting in a long service life. At the same time, the piston can be easily replaced on-site by loosening the screw units. Standard torques are required to loosen the screw units, allowing the piston cylinder to be replaced in a relatively short time.

[0015] A particularly preferred embodiment of the piston-cylinder device according to the invention is characterized in that the clamping screw unit is arranged on the outer circumference in a predetermined grid angle dimension, wherein the grid angle dimension is preferably between 90° and 10°, in particular 90°, 45° or 30°.

[0016] The circumferentially distributed screw units allow for uniform and reliable clamping across the entire thread circumference, which has a positive effect on the long-term, reliable functionality of the connection.

[0017] The width of the gap between the clamping flange disc and the piston face is advantageously in the range between 1 mm and 5 mm, particularly between 1 mm and 3 mm. This size is sufficient to enable reliable clamping of the thread via the screw units.

[0018] A particularly simple design in terms of assembly technology, which enables quick and economical assembly or quick and economical replacement of the piston, is characterized in that the clamping flange disc has continuous stepped recesses in which the screw head of the clamping screw unit is located and the screw head has a recess with a polygon-like inner circumferential contour for the positive attachment of a turning tool.

[0019] A particularly advantageous embodiment is characterized in that a first connection unit for connecting further components is provided on the housing and further in that a second connection unit for connecting further components is provided in the end region of the piston rod located outside the housing.

[0020] The first and second connection units enable the piston-cylinder device to be connected to a wide variety of subsequent components, depending on its intended use.

[0021] A particularly advantageous embodiment with regard to simple production, high strength and simple assembly is characterized in that the piston has, in its end region facing the clamping flange disc, a circumferentially formed projection ring projecting in the longitudinal direction, the clear inner diameter of which is slightly larger than the outer diameter of the clamping flange disc.

[0022] A major advantage of the piston-cylinder device according to the invention is that commercially available screws can be used for the screws used to tighten the thread, which has an economically advantageous effect on the manufacture of the piston-cylinder unit, the assembly and the replacement of the piston on site.

[0023] Using simple structural means, the invention makes it possible to ensure reliable clamping of the thread and thus permanently reliable function, while at the same time enabling quick and easy replacement of the piston.

[0024] A particularly advantageous embodiment of the piston-cylinder device according to the invention is characterized in that the clamping flange disc has a central, continuous recess, i.e., it is designed as an annular disc. This makes it possible, for example, to pass a displacement sensor unit through it, which then extends into a blind recess in the piston rod. A displacement sensor unit makes it possible to define precise extension positions of the piston rod. It is also possible to connect an end-position damper unit or another component, if required, to the recess in the clamping flange disc.

[0025] Further embodiments and advantages of the invention will become apparent from the features further recited in the claims and from the exemplary embodiments given below. The features of the claims may be combined with one another in any way, provided they are not obviously mutually exclusive. SHORT DESCRIPTION OF THE DRAWING

[0026] The invention, as well as advantageous embodiments and further developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The features shown in the description and the drawings can be used individually or in any combination according to the invention. They show: Fig. 1 Perspective view of a piston-cylinder device with a housing to which a first connection unit is connected, a piston rod which is guided longitudinally displaceably inside the housing in conjunction with a piston, projects beyond the housing and has a second connection unit in the projecting area, Fig. 2 schematic longitudinal section through a first embodiment of a piston-cylinder device according to Fig. 1 with clamping of the thread between piston and piston rod via a clamping flange disc with screw units in the partially extended state of the piston rod, Fig. 3 schematic longitudinal section through a second embodiment of a piston-cylinder device according to Fig. 1 with clamping of the thread between piston and piston rod via a clamping flange disc and screw units, whereby the clamping flange disc is designed as a ring disc with a central continuous recess in the partially extended state of the piston rod, Fig. 4 schematic longitudinal section through the piston-cylinder device according to Fig. 3 with retracted piston rod with piston and Fig. 5 schematic cross-section through the piston-cylinder device according to section SS in Fig. 1. WAYS TO CARRY OUT THE INVENTION

[0027] The Fig. 1 shows an embodiment of a piston-cylinder device 10. The piston-cylinder device 10 has a housing 12 with a central hollow cylindrical housing area 13, on the Fig. 1, a front end termination unit 50 is connected to the left end region via a first weld seam 54, to which a first connection unit 20 is integrally formed, which is designed as a ring eyelet and serves for connection to further components. The front end termination unit 50 further comprises a pressure medium connection unit 56.1. A further pressure medium connection unit 56.2 is also present on the hollow cylindrical housing region 13.

[0028] In the Fig. 1 right end area, a connecting ring 64 is welded to the hollow cylindrical housing area 13 via a second weld seam 52, to which a front end guide and end unit 30 is screwed via screw units 31.

[0029] In the Fig. 1 On the right end region of a piston rod 14 projecting from the housing 12, a second connection unit 22 is formed, which is designed as a ring eyelet and serves to connect further components.

[0030] In Fig. 3 and Fig. 4 is a longitudinal section through the piston-cylinder device 10 of Fig. 1. The first and second connection units 20, 22 are shown in a highly schematic manner. Identical components bear the same reference numerals and will not be explained again.

[0031] Within the housing 12, a piston rod 14 with piston 16 is mounted so as to be displaceable in the longitudinal direction L. The piston 16 has a central through-hole with an internal thread 46, which is screwed onto an external thread 44 of the piston rod 14. The piston 16 itself is sealed by means of sealing means 60 against the inner wall of the housing 13 or the outer wall of the piston rod 14. In Fig. 2 In the right end area, the end guide and closure unit 30 is firmly connected to the housing 13 and sealed against the inner wall of the housing 13 and the outer peripheral contour of the piston rod 14 by means of a sealant 62. The piston rod 14 penetrates the end guide and closure unit 30 and projects outward with the second connection unit 22 connected.

[0032] A pressure medium connection unit 56.2 is provided on the housing 13, via which a first pressure chamber 48.1 within the housing 12 can be supplied with a pressure medium.

[0033] The Fig. 2 The front end closure unit 50, arranged on the left side, has a pressure medium connection unit 56.1, which communicates with a second pressure chamber 48.2 via a channel 58. Depending on the pressure applied to the pressure chambers 48.1, 48.2 via the pressure medium connection units 56.1, 56.2, the piston 16 with piston rod 14 is displaced in the longitudinal direction L (double-action principle).

[0034] When the piston 16 is screwed onto the piston rod 14, the end face 32 of the piston rod 14 has a projection 40 relative to the end face 34 of the piston 16. The projection 40 is in the range of 1 mm to 5 mm, in particular 1 mm to 3 mm.

[0035] A clamping flange disk 18 is mounted on the end face 32 of the piston rod 14, which has a projection area 26 projecting in the radial direction R. In this projection area 26, in the circumferential direction at a predetermined grid angle dimension 38 (see Fig. 5) arranged clamping screw units 24 are present, the screw heads 36 of which are each arranged in a stepped recess of the projection area 26 of the clamping flange disc 18 and which are each screwed into a recess with an internal thread of the piston 16. The clamping screw unit 24 clamps the clamping flange disc 18 to the piston rod 14 and the piston 16, so that a preload force is exerted on the external thread 44 of the piston rod 14 and the internal thread 46 of the piston 16, which ensures permanently reliable functionality of the connection even at high pressures.

[0036] In the outer edge area of ​​the front end surface 34 of the piston 16, a projection ring is formed, the clear inner diameter of which is slightly larger than the outer diameter of the clamping flange disk 18.1, which in the exemplary embodiment is designed as a circular disk.

[0037] In the illustrated embodiment according to the Fig. 3 and Fig. 4, the clamping flange disc 18.1 has a central recess 66, which is arranged congruently on a central blind hole recess 68 of the piston rod 14.1. A hollow profile tube 72 is provided through the central recess 66 and extending into the blind hole recess 68 of the piston rod 14.1, which is connected to the feed channel 59 by an external electrical connection unit 57 for a displacement sensor unit. Within the blind hole recess 68, a displacement sensor unit is provided, by means of which the current longitudinal position of the piston 16 relative to the housing 12 can be detected and which serves for the extension or retraction movement of the piston rod 14.1 via control units not shown. Alternatively, an end-position damper unit can also be connected, for example, in the central recess 66.

[0038] Fig. 2 shows a second embodiment of a piston-cylinder device which has essentially the same structure as the piston-cylinder device according to the Fig. 3 and Fig. 4, but with the difference that the clamping flange disc 18 has no central recess and the piston rod has no blind hole recess.

[0039] Identical components have the same reference symbol and are not explained again.

[0040] The inventive use of a clamping flange disk 18, 18.1, which is spaced from the end face 34 of the piston 16 and bears against the end face 32 of the piston rod 14, 14.1, enables the use of commercially available screws for clamping the external or internal thread 44, 46 of the piston rod 14 or the piston 16, respectively, without the need to apply excessively high torque due to the relatively small diameter of the threads. The clamping screw units 24, which are evenly distributed circumferentially on the clamping flange disk 18, 18.1, ensure uniform clamping with high effectiveness and reliability. At the same time, it is ensured that the piston 16 can be easily replaced on-site, since normal torques are applied to release the clamping and re-clamping, which do not require an additional clamping tool for the piston-cylinder device 10.

[0041] The Fig. 5 shows a plan view of a clamping flange disc 18 connected to the piston 16 via clamping screw units 24.

[0042] A total of twelve clamping screw units 24 with a grid angle of 20° are arranged in the circumferential direction.

Claims

[1] Piston-cylinder device (10) with - a housing (12), - a piston rod (14) with an external thread (44) mounted within the housing (12) so as to be displaceable in the longitudinal direction (L), - a piston (16) with internal thread (46) which is detachably screwed onto the piston rod (14), - a pressure chamber (48) provided within the housing (12) and pressurised with a pressure medium to generate the longitudinal movement of the piston rod (14) with piston (16), characterized by , that - in the connection area of ​​the piston (16) to the piston rod (14), the end face (32) of the piston rod (14) has a projection (40) in the longitudinal direction (L) relative to the end face (34) of the piston (16) when the piston (16) is connected, - a pre-tensioning device with a clamping flange disc (18) is mounted on the end face (32) of the piston rod (14), which has a projection area (26) projecting beyond the outer contour of the piston rod (14) in the radial direction (R), whereby a gap is present between the projection area (26) and the end face (34) of the piston (16), - the pre-tensioning device in the projection area of ​​the clamping flange disc (18) is clamped to the piston (16) via clamping screw units (24), whereby a pre-tensioning force is exerted on the external and internal threads (44, 46), - wherein the preload force is greater than the forces acting from the pressure medium acting on the pressure chamber (48) against the preload device / clamping flange disc (18). [2] Piston-cylinder device according to claim 1, characterized by , that - the clamping screw units (24) are arranged on the outer circumference in a predetermined grid angle dimension (38). [3] Piston-cylinder device according to claim 2, characterized by , that - the grid angle dimension (38) is between 90° and 10° (old degrees), in particular 90°, 45° or 30° (old degrees). [4] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - the width of the gap is in the range between 1 mm and 5 mm (millimeters), in particular between 1 mm and 3 mm (millimeters). [5] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - the clamping flange disc (18) has continuous stepped recesses in each of which the screw head (36) of the clamping screw unit (24) is present and the screw head (36) has a recess (42) with a polygonal inner circumferential contour for the positive attachment of a turning tool. [6] Piston-cylinder device according to one or more of the preceding claims, characterized by, that - a first connection unit (20) for connecting further components is provided on the housing (12). [7] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - in the end region of the piston rod (14) located outside the housing (12), there is a second connection unit (22) for connecting further components. [8] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - the clamping screw units are designed as commercially available screw units. [9] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - the piston (16) has, in its end region facing the clamping flange disc (18), a circumferentially formed projection ring projecting in the longitudinal direction (L), the clear inner diameter of which is slightly larger than the outer diameter of the clamping flange disc (18). [10] Piston-cylinder device according to one or more of the preceding claims, characterized by , that - the clamping flange disc (18.1) has a central continuous recess (66).

Images