Drive unit, fluid-operated working cylinder equipped therewith and related manufacturing process

Abstract

Drive unit for a fluid-operated working cylinder, comprising a drive piston (5) and a piston rod (8), wherein the drive piston (5) has a piston body (38) radially projecting beyond the piston rod (8), which is combined with the piston rod (8) to form a one-piece piston body-piston rod assembly (54) made of plastic, which, including the piston body (38) and the piston rod (8), consists of a fiber-reinforced plastic with fibers embedded in a plastic matrix, characterized in that the fiber-reinforced plastic is a carbon fiber-reinforced plastic, the fibers of which embedded in the plastic matrix are carbon fibers, which are short fibers with a fiber length in the range of 0.05 mm to 1 mm, wherein at least the piston body-piston rod assembly (54) is an injection-molded part.

Description

[0001] The invention relates to a drive unit for a fluid-operated working cylinder, which contains a drive piston and a piston rod, wherein the drive piston has a piston body which projects radially beyond the piston rod and which is combined with the piston rod to form a one-piece piston body-piston rod assembly made of plastic.

[0002] The invention further relates to a fluid-operated working cylinder, having a cylinder housing which defines a housing interior in which a drive piston of a drive unit which also has a piston rod is arranged to be linearly displaceable, wherein the drive piston has a piston body which projects radially beyond the piston rod and which is combined with the piston rod to form a one-piece piston body-piston rod assembly made of plastic.

[0003] The invention further relates to a manufacturing method for such a drive unit and for such a fluid-operated working cylinder.

[0004] A working cylinder designed in this way, which apart from sealing elements is made entirely of plastic, is known from US 3,703,125. It has a two-part cylinder housing with a first housing part containing a cylinder tube and an end wall, and a second housing part formed by an end cover screwed to the cylinder tube, through which a piston rod connected to a drive piston extends, forming a drive unit of the working cylinder that can be displaced by fluid. The piston rod is integrally combined with a piston body carrying a piston seal to form a piston body-piston rod assembly. Numerous plastic materials have been mentioned for the realization of the various cylinder components, including, for example, nylon, polyvinyl chloride and glass fiber reinforced polycarbonate. The use of plastic as a material enables cost-effective production.Furthermore, plastic, unless interspersed with glass fibers, has good sliding properties, which is advantageous for creating the sliding surfaces required between the piston, piston rod, and cylinder housing. However, unreinforced plastic material is subject to limitations in strength and stability, limiting practical applications. Large-sized components of working cylinders and / or components exposed to high pressures during operation are less suitable for unreinforced plastic. These shortcomings do not exist with glass fiber-reinforced plastic; however, the inorganic glass fibers can impair the contacting sliding surfaces and result in rapid and significant wear.

[0005] DE 101 41 560 C2 discloses a fluid-operated working cylinder comprising a cylinder housing consisting of a front housing section and a cover plate attached to it. The front housing section can be manufactured as a single piece from a plastic injection-molded part. The cover plate can also be a plastic part. Located inside the cylinder housing is a drive piston, which is combined with a piston rod, for example, by a welded connection to form a single unit. Aluminum is particularly preferred as the material for the piston rod and a piston body of the drive piston.

[0006] AT 298923 A discloses a working cylinder having a cylinder housing composed of a first housing part produced by deep drawing and a cover plate attached to the housing part. The housing part, produced by deep drawing, comprises an end wall and a cylinder tube in one piece.

[0007] DE 10 2010 008 349 A1 describes a process for producing pellets from fiber composite materials, wherein the pellets contain carbon fibers and a thermoplastic matrix material. These pellets are suitable for further processing in a plastics manufacturing process. Carbon fibers can generally be used as fiber reinforcement for thermoplastically or thermosetting bonded fiber composite materials.

[0008] The invention is based on the object of taking measures that promote the cost-effective production of a stable and low-wear fluid-operated working cylinder and a drive unit of such a working cylinder.

[0009] To achieve this objective, both in a drive unit of the type mentioned above and in a fluid-operated working cylinder of the type mentioned above, it is provided that the piston body-piston rod assembly, including the piston body and the piston rod, consists of a carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix

[0010] The object is further achieved by a manufacturing method in which at least the piston body-piston rod assembly consisting of a carbon fiber reinforced plastic with carbon fibers embedded in a plastic matrix is ​​produced by injection molding

[0011] Both the piston body and the integrally formed piston rod are made of carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix and are components of a one-piece piston body-piston rod assembly, which consists entirely of carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix. This design of the piston body-piston rod assembly enables cost-effective and efficient production of a lightweight, fluid-operated working cylinder. A low weight is advantageous, for example, when the working cylinder is moved as a whole during use, for example, due to its integration into a handling unit or a robot. The low weight of the piston body-piston rod assembly also allows for high accelerations of the drive unit with comparatively low energy consumption.Furthermore, the piston body-piston rod assembly can be manufactured using easily controllable plastics processing methods, particularly by injection molding or extrusion, if the plastic matrix consists of a thermoplastic. In the preferred injection molding of the piston body-piston rod assembly from carbon fiber-reinforced plastic, a predominantly parallel alignment of the carbon fibers can be observed, which obviously has a positive effect on the structural properties and wear behavior. In the area of ​​surfaces that slide against each other, the mechanically very stable carbon fibers provide a sliding-supporting effect. In comparison to glass fibers, a non-abrasive effect of the fiber ends of the carbon fibers can be observed. Fiber reinforcement using carbon fibers leads to very high strength, rigidity, and stability.Another advantage is that during the production of the piston body-piston rod assembly, precise coaxiality between the piston body and the piston rod can be achieved without special alignment measures. Furthermore, it has been shown that carbon fibers, unlike glass fibers, do not exhibit abrasive properties, so the carbon fiber-reinforced plastic offers very good tribological properties when used in conjunction with a fluid-actuated working cylinder. A working cylinder equipped with the piston body-piston rod assembly made of carbon fiber-reinforced plastic thus has a long service life with low maintenance requirements.

[0012] Advantageous further developments of the invention emerge from the subclaims.

[0013] Due to the aforementioned good sliding properties of the carbon fiber-reinforced plastic, it is advantageous if the radially outward-facing outer circumferential surface of the piston body is designed as a piston guide surface that, when the drive unit is in use, slides radially against the inner circumferential surface of a cylinder tube of a fluid-actuated working cylinder. Especially in combination with a cylinder tube also made of carbon fiber-reinforced plastic, this results in particularly smooth running of the drive piston relative to the cylinder tube.

[0014] If a particularly low-friction working cylinder is required, the drive piston can be dispensed with an elastomeric piston seal that slides against the inner circumferential surface of the cylinder barrel. The drive piston is then designed without a piston seal. In this case, the piston body alone can even form the drive piston.

[0015] In principle, it is also possible to equip the piston body with an additional guide ring on its outer circumference, which establishes contact between the drive piston and the cylinder barrel. Such a guide ring is inserted, for example, into a radially outwardly open annular groove in the drive piston.

[0016] Preferably, the piston body, made of carbon fiber-reinforced plastic, is provided with an annular groove open toward its radially outward-facing outer circumferential surface. This annular groove can be empty, resulting in weight savings. However, the annular groove can also be used as a receiving groove for an activation element used to detect the position of the drive piston, in particular for receiving an annular activation element. Such an activation element can, for example, interact with a position detection device consisting of one or more position sensors or a displacement measuring system. Depending on the design of the position detection device, the activation element can, for example, have permanent magnetic or ferromagnetic properties.

[0017] To ensure that the drive piston tightly seals at least one working chamber that can be pressurized with a fluid pressure medium to actuate the working cylinder during the intended use of the drive unit in the interior of the cylinder housing of a working cylinder, it is preferably provided with an elastomer structure that forms a piston seal designed to sealingly and slidably engage the inner circumferential surface of a cylinder tube of the cylinder housing. This elastomer structure is attached to the piston body, for example, by injection molding, and is preferably made of a thermoplastic elastomer. Alternatively, rubber, fluororubber (FKM), or other elastomers could also be used.

[0018] In a preferred embodiment, the elastomer structure additionally forms at least one impact damper with rubber-elastic properties, which is suitable for minimizing the intensity of the impact on an end wall of a cylinder housing in a stroke end position of the drive piston. Preferably, the at least one impact damper and the piston seal are formed integrally with one another.

[0019] In order to enable fluidic end-of-stroke cushioning of the drive unit during operation of a working cylinder equipped with the drive unit, it is advantageous if at least one buffering extension that protrudes axially relative to the drive piston is integrated as a single piece into the piston rod. If end-of-stroke cushioning is desired in both stroke directions of the drive unit, the piston rod has two buffering extensions that protrude from the drive piston on opposite sides. The buffering extension has a larger diameter than an adjoining length of the piston rod and is designed to dip into an end cover of a cylinder housing of the associated working cylinder to limit the flow cross-section available to the outflowing pressure medium when the drive unit moves to a stroke end position.

[0020] In the case of the presence of two buffering extensions, these two buffering extensions are expediently formed by integrally connected length sections of a piston rod length section having the desired outer diameter.

[0021] Preferably, the drive unit is partially hollow, which leads to material savings and consequently cost savings and which also reduces the moving mass, which benefits the agility of the lifting movement.

[0022] The drive unit preferably has a cavity divided into two axially adjacent cavity sections. The two cavity sections expediently extend coaxially into the piston rod from one of the two end faces of the drive unit and are separated from each other in a fluid-tight manner by a partition wall integral with the piston rod, thus preventing fluid passage.

[0023] If the cylinder barrel is also made of carbon fiber-reinforced plastic, the weight of the working cylinder is further reduced. Furthermore, due to the material's strength, even cylinder barrels with large diameters and lengths combined with thin walls can be easily realized. A working cylinder equipped with a cylinder barrel made of carbon fiber-reinforced plastic has a long service life and requires little maintenance.

[0024] At least on one end of the cylinder tube, the housing interior containing the drive piston is expediently delimited by an end wall of the cylinder housing. If the working cylinder is designed as a so-called plunger cylinder, in which the drive piston protrudes from the cylinder tube at one end with a length section acting as a piston rod, the cylinder housing can be equipped with only a single end wall.

[0025] Preferably, the cylinder housing is equipped with an end wall on each end of the cylinder tube that axially defines the interior of the housing. This allows, for example, a single-acting or double-acting fluid-operated working cylinder to be realized.

[0026] Preferably, at least one and expediently each end wall, such as the cylinder tube, consists of a carbon fiber reinforced plastic having carbon fibers embedded in a plastic matrix.

[0027] The same carbon fiber-reinforced plastic is expediently used for the cylinder barrel and the at least one end wall, which is also made of carbon fiber-reinforced plastic. The piston body-piston rod assembly is also expediently made of the same carbon fiber-reinforced plastic.

[0028] At least one end wall of the cylinder housing is slidably penetrated by the piston rod of the drive unit, whereby a force can be tapped off at an end section of the piston rod located outside the cylinder housing, for example to drive a machine component.

[0029] The end wall, through which the piston rod slides, expediently contains a guide bore through which the piston rod extends axially and whose inner circumference forms a piston rod guide surface that radially supports the piston rod. Preferably, the end wall equipped with the guide bore is made of the aforementioned carbon fiber-reinforced plastic, with the guide bore being formed directly in this carbon fiber-reinforced plastic of the end wall, so that the piston rod guide surface is an integral component of the respective end wall and is made of the carbon fiber-reinforced plastic of the end wall. In this way, the tribologically favorable effect mentioned above is utilized in addition to the sliding bearing of the piston rod in the end wall through which it passes.In this way, an additional separate guide bush can be avoided, which further contributes to cost minimization.

[0030] In principle, regardless of the material of the end wall, it would be possible to insert a separate guide bush defining the guide bore into the end wall, in particular by a press-in process.

[0031] The production and assembly of the working cylinder can be further optimized by forming at least one end wall of the cylinder housing integrally with the cylinder tube. This creates a one-piece cylinder tube-end wall assembly, which can be fitted with a separate end cover on the end face of the cylinder housing opposite the integral end wall to define a housing interior that is axially closed on both sides.

[0032] The end wall through which the piston rod slides is preferably formed integrally with the cylinder tube and thus forms part of the cylinder tube-end wall assembly mentioned above. However, the end wall in question can also be designed as a separate component from the cylinder tube.

[0033] At least one end wall of the cylinder housing is expediently designed as a separate end cover from the cylinder tube. With the end cover removed, the drive piston can be inserted into the housing interior through the then open cylinder tube during assembly of the working cylinder. The separate end cover is attached to the cylinder housing by suitable fastening means, which can be, for example, screw fasteners or adhesive fasteners to create an adhesive bond. It is considered particularly advantageous if the fastening means are designed as a welded connection, which is particularly advantageous when the cylinder tube and the separate end cover are made of the same carbon fiber reinforced plastic. Welding is carried out in particular by ultrasonic welding or friction welding.

[0034] At least one end cover, separate from the cylinder tube, may be made of a material different from the cylinder tube. For example, at least one separate end cover may be made of metal. However, each separate end cover, like the cylinder tube, is preferably made of a carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix.

[0035] A fluid channel is expediently integrated into at least one and preferably each end wall of the cylinder housing, which opens into the housing chamber and through which a pressure fluid used to actuate the working cylinder can be fed in and / or discharged.

[0036] The fluid-operated working cylinder is preferably a pneumatic working cylinder that can be operated with compressed air. However, the working cylinder can also be designed for operation with other fluidic pressure media, for example, for operation with a hydraulic fluid.

[0037] The fiber length of the carbon fibers embedded in the plastic matrix is, in principle, arbitrary. However, especially when the components made of carbon fiber-reinforced plastic are manufactured by injection molding or extrusion, it is advantageous for the carbon fibers to be so-called short fibers. The fiber length of these short fibers is preferably in the range between 0.05 mm and 1 mm, with a fiber length in the range between 0.1 mm and 0.4 mm considered optimal.

[0038] It is particularly advantageous if the proportion of carbon fibres in the carbon fibre reinforced plastic is between 5 and 60 percent by weight, preferably in the range of 40 percent by weight.

[0039] The plastic matrix, which could in principle also be made of a thermosetting plastic material, is preferably formed from a thermoplastic material. A polyamide-based plastic material, for example, polyamide 6 or polyamide 6.6, is preferably used. A construction made of semi-aromatic or fully aromatic polyamide is also considered advantageous.

[0040] In a preferred manufacturing process, all components of the working cylinder, which consist of a carbon fiber reinforced plastic with carbon fibers embedded in a plastic matrix, are manufactured by injection molding.

[0041] The invention is explained in more detail below with reference to the accompanying drawings, which show: Fig. 1 a preferred embodiment of the fluid-operated working cylinder according to the invention in an isometric view, Fig. 2 in an isometric view a longitudinal section of the working cylinder according to section line II-II of Fig. 1, wherein a preferred embodiment of a drive unit comprising a drive piston and a piston rod is also shown, Fig. 3 in a non-isometric planar sectional view of one of the Fig. 2 corresponding longitudinal section of the working cylinder Fig. 1, whereby alternative realisation possibilities are shown for some components framed by dash-dotted lines in separate detail illustrations IIIa, IIIb and IIIc, Fig. 4 a preferred alternative embodiment of a drive unit with buffer extensions integrated into the piston rod, and Fig. 5 a longitudinal section of the drive unit Fig. 4 according to the section line VV.

[0042] The drawing illustrates a fluid-operated working cylinder, designated overall by reference numeral 1, which can be actuated by means of a fluid pressure medium, in particular compressed air. The fluid-operated working cylinder 1 is therefore preferably a pneumatic cylinder. However, the working cylinder 1 is also generally suitable for actuation by means of other gaseous pressure media or even by means of liquid pressure media, such as hydraulic oil.

[0043] The working cylinder 1 has a cylinder housing 2 with a longitudinal axis 3. The cylinder housing 2 encloses a housing interior 4 in which a drive piston 5 is arranged so as to be linearly displaceable in the axial direction of the longitudinal axis 3.

[0044] Outside the cylinder housing 2 is a tapping section 6, which is motion-coupled to the drive piston 5 and follows the linear movement of the drive piston 5. The tapping section 6 is expediently formed by an outer end section 7 of a piston rod 8, which protrudes from the end face of the cylinder housing 2 and is firmly connected to the drive piston 5. The drive piston 5 and the piston rod 8 together form a drive unit 11, which is only uniformly displaceable in the axial direction of the longitudinal axis 3 relative to the cylinder housing 2, the resulting movement being referred to as the drive movement 12, which is indicated by a double arrow.

[0045] The cylinder housing 2 includes a cylinder tube 13 arranged, in particular, coaxially with respect to the longitudinal axis 3. The cylinder tube 13 delimits the housing interior 4 radially outwardly and has an inner circumferential surface 14 facing the housing interior 4.

[0046] The inner circumferential surface 14 is cylindrical and preferably has a circular-cylindrical contour. However, cross-sectional shapes of the housing interior 4 that deviate from the circular shape are also possible.

[0047] The cylinder tube 13 also has an outer peripheral surface 15 oriented radially outward relative to the longitudinal axis 3. The outer peripheral surface 15 is preferably cylindrical, and in particular circular-cylindrical. Apart from the greater distance from the longitudinal axis 3, the outer peripheral surface 15 preferably has the same cross-sectional contour as the inner peripheral surface 14. Especially with regard to easy production, it is advantageous if, according to the exemplary embodiment, the wall thickness of the cylinder tube 13 is constant throughout. Thus, the cylinder tube can be cost-effectively formed as a simple round tube.

[0048] The cylinder tube can be designed with a constant or varying wall thickness or as a tube with any desired profile.

[0049] The housing interior 4 is axially delimited on both sides by an end wall 16, 17, each of which also belongs to the cylinder housing 2. For better differentiation, the two end walls 16, 17 are also referred to below as the first end wall 16 and the second end wall 17. The drive piston 5 is located between the two end walls 16, 17, the clear distance between which is sufficiently large to enable the drive movement 12 of the drive piston 5.

[0050] The piston rod 8 has a smaller diameter than the drive piston 5 and extends axially to the tap section 6, sliding through the first end wall 16. The first end wall 16 has an axially continuous guide bore 18 through which the piston rod 8 extends in a linearly movable manner and whose inner circumference forms a piston rod guide surface 22 that radially supports the piston rod 8. The piston rod 8 bears with its outer circumferential surface 23 in sliding engagement with the piston rod guide surface 22 and is thus radially supported relative to the cylinder housing 2 in every axial position assumed relative to the cylinder housing 2.

[0051] In a non-illustrated embodiment, the drive piston 5 is designed as a plunger piston, in which the function of the piston rod 8 is integrated and which protrudes on one end face of the cylinder tube 13, so that an end wall is unnecessary there.

[0052] The drive piston 5 divides the housing interior axially into two sub-chambers, which are referred to below as first and second working chambers 24, 25 for better differentiation, wherein the first working chamber 24 extends between the drive piston 5 and the first end wall 16 and the second working chamber 25 extends between the drive piston 5 and the second end wall 17.

[0053] In the illustrated embodiment, the working cylinder 1 is designed as a double-acting working cylinder, which allows both working chambers 24, 25 to be pressurized with pressure medium in a controlled manner to actuate the drive unit 11. The required supply and discharge of the driving pressure medium can take place through two fluid channels 26, 27, of which a first fluid channel 26 opens into the first working chamber 24 and a second fluid channel 27 opens into the second working chamber 25. Each of these two fluid channels 26, 27 passes through the cylinder housing 2 and opens into the outer surface of the cylinder housing 2 via a connection opening 26a, 27a.These connection openings 26a, 27a are expediently assigned connecting means 28, which enable the fluid-tight connection of a fluid line, in particular a fluid hose, which is connected to a control valve device (not further illustrated) through which the supply and discharge of a fluid pressure medium can be controlled. For example, the connecting means 28 are formed by an internal thread formed integrally in the cylinder housing 2. Alternatively, separate plug-in connection units could also be fixed by pressing into the connection openings 26a, 27a.

[0054] The two fluid channels 26, 27 preferably have the same cross-section, but in special cases they can also be designed with different cross-sections.

[0055] Preferably, at least one, and preferably each, fluid channel 26, 27 is formed exclusively in one of the end walls 16, 17. This applies to the exemplary embodiment. Here, the first fluid channel 26 passes through the first end wall 16, while the second fluid channel 27 passes through the second end wall 17. Accordingly, the connection openings 26a, 27a are located on the end walls 16, 17. The inner channel openings 26b, 27b of the fluid channels 26, 27, opposite the connection openings 26a, 27a, are preferably located on the inner axial end face 16a, 17a of the respective first or second end wall 16, 17, facing the housing interior 4.

[0056] In a non-illustrated embodiment, at least one and preferably each fluid channel 26, 27 passes through the wall of the cylinder housing 2 at a location immediately adjacent to the associated end wall 16, 17.

[0057] In order to be able to fix the working cylinder 1 at the place of use, at least one and preferably each end wall 16, 17 is equipped with at least one mechanical fastening interface 32. For example, each fastening interface 32 consists of several fastening eyes 33, which are an integral part of the associated end wall 16, 17 and which project radially beyond the outer circumferential surface 15 of the cylinder tube 13. These several fastening eyes 33 are arranged distributed around the longitudinal axis 3, in particular in a uniform distribution. For example, a total of four fastening eyes 33 are provided per fastening interface 32, which are located in the corner regions of an imaginary square.

[0058] Each fastening eye 33 has a fastening hole 34, which is preferably axially continuous and into which, for example, a fastening screw can be inserted.

[0059] The mounting hole 34 can have an integrally formed internal thread. It is also possible to insert a separate internal thread element, such as a screw nut, into the mounting hole 34 in a rotationally fixed manner. The internal thread element can, for example, be pressed in or overmolded.

[0060] By a coordinated fluid application to the two working chambers 24, 25, a resultant actuating force can be generated which acts on the drive piston 5 in one direction or the other, causing the drive unit 11 to execute the drive movement 12 in one direction or the other. This can be an extension movement in which the drive piston 5 approaches the first end wall 16 and the piston rod 8 increasingly extends out of the front side of the cylinder housing 2. It can also be a retraction movement in which the drive piston 5 approaches the second end wall 17 and the piston rod 8 increasingly retracts into the cylinder housing 2. The drive movement 12 can take place between two stroke end positions which are defined by the drive piston 5 coming into axial contact either with the first end wall 16 or with the second end wall 17.

[0061] In an embodiment not shown, the working cylinder 1 is of a so-called single-acting design. Here, the movement of the drive unit 11 is caused in only one direction by controlled fluid pressure and in the other direction by, for example, a return spring.

[0062] During the drive movement 12, the drive piston 5 slides along the inner circumferential surface 14 of the cylinder tube 13. The inner circumferential surface 14 thus forms a so-called running surface for the drive piston 5.

[0063] Advantageously, the cylinder tube 13 is made entirely of a carbon fiber-reinforced plastic. This carbon fiber-reinforced plastic also forms the inner peripheral surface 14 of the cylinder tube 13, which serves as the running surface for the drive piston 5. The cylinder tube 13 is expediently manufactured by injection molding.

[0064] The carbon fiber reinforced plastic consists of a plastic matrix in which a large number of carbon fibers are embedded.

[0065] A synonym for "carbon" is "carbon." The material used for the cylinder barrel is a carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix.

[0066] Where this patent application refers to a carbon fiber reinforced plastic, it always refers to a composite material comprising a plastic matrix with embedded carbon fibers.

[0067] Preferably, each end wall 16, 17 is also made of carbon fiber-reinforced plastic. This allows for a cylinder housing 2 made of a single material. Manufacturing from carbon fiber-reinforced plastic results in low weight combined with high structural rigidity and strength.

[0068] In a preferred embodiment of the cylinder housing 2, which corresponds to the illustrated embodiment, the first end wall 16 through which the piston rod 8 passes is formed integrally with the cylinder tube 13, so that these two components form a cylinder tube-end wall assembly 35 that can be handled uniformly during assembly of the working cylinder 1. The second end wall 17, on the other hand, is designed as a separate end cover 170 with respect to the cylinder tube 13, which is fastened to the cylinder tube 13 by fastening means 36. This is preferably a permanent fastening, which applies to the illustrated embodiment. For example, the fastening means 36 consist of a welded connection, which is preferably an ultrasonic welded connection or a friction welded connection.

[0069] During the manufacture of the working cylinder 1, the cylinder end wall assembly 35 and the drive unit 11 are manufactured separately. Before the end cover 170 is subsequently mounted, the drive unit 11, with the piston rod 8 leading, is inserted into the housing interior 4 through the then still open end face of the housing interior 4, so that the piston rod 8 passes through the guide bore 18. The second end wall 17 is then attached and secured.

[0070] The separate end cover 170 preferably has an axial centering extension 37, which is particularly sleeve-shaped and whose outer cross-sectional profile corresponds to the cross-sectional profile of the housing interior 4, so that it extends into the cylinder tube 13 at the front end and fixes the cylinder tube 13 radially immovably while simultaneously centering the cylinder 5. The fastening means 36 are preferably located in the area of ​​the centering extension 37.

[0071] In a non-illustrated embodiment, the second end wall 17 is formed integrally with the cylinder tube 13, while the first end wall 16 is formed as a separately attached end cover.

[0072] In an embodiment also not shown, both end walls 16, 17 are designed as separate end covers with respect to the cylinder tube 13, which are fastened to the cylinder tube 13 by suitable fastening means 36, in particular independently of one another and in particular in the manner described above with reference to the end cover 170.

[0073] The drive piston 5 expediently contains a particularly rigid and preferably one-piece piston body 38, which projects radially all around the adjoining piston rod 8. Its outer diameter is larger than that of the coaxially adjoining piston rod 8. The piston body 38 is preferably disc-shaped. The piston body 38 is, in particular, the component of the drive piston 5 that is responsible for the stability of the drive piston 5 and that transmits the fluidic drive forces to the piston rod 8.

[0074] Preferably, the drive piston 5 is provided on its outer circumference with a radially outward-facing piston guide surface 42 extending around the longitudinal axis 3. With this piston guide surface 42, the drive piston 5 slideably engages the inner circumferential surface 14 or the running surface of the cylinder tube 13.

[0075] According to a preferred embodiment, which, apart from the embodiment shown in section IIIb of the Fig. 3 is implemented in all illustrated embodiments, it is directly the radially outward-facing outer circumferential surface 43 of the piston body 38 that forms the piston guide surface 42. The piston body 38 is therefore supported directly with its outer circumferential surface 43 in a sliding manner radially on the inner circumferential surface 14 of the cylinder tube 13. In this context, it is particularly advantageous if the piston body 38 is made of a carbon fiber reinforced plastic, so that the outer circumferential surface 43 is also made of this carbon fiber reinforced plastic. The effect is the same as explained above with reference to the cylinder tube 13, namely that a sliding surface pairing is created which ensures a particularly low-friction drive movement 12.

[0076] It is optimal if both the cylinder tube 13 and the piston body 38 are made of carbon fiber reinforced plastic, as this results in particularly good sliding behavior.

[0077] An annular groove 44 is expediently formed in the piston body 38, which is open radially outward toward the outer circumferential surface 43 and is arranged coaxially to the longitudinal axis 9 of the drive piston 5 and in particular of the entire drive unit 11. This annular groove 44 can remain empty and represent an unfilled cavity, for example to achieve weight savings. A further advantageous effect of the annular groove 44 is that the outer circumferential surface 43 is divided into two axially spaced-apart annular outer circumferential surface sections 43a, 43b, which is advantageous for supporting and guiding the drive piston 5 if these outer circumferential surface sections 43a, 43b directly form the piston guide surface 42.

[0078] According to the section IIIa of the Fig. In the modification illustrated in Figure 3, the annular groove 44 can also be designed as a receiving groove 44a, which accommodates at least one activation element 45 usable for detecting the position of the drive piston 5 or the entire drive unit 11. This activation element 45 is, for example, annular and arranged coaxially with the longitudinal axis 9.

[0079] The activation element 45 can cooperate with a position detection device, not further illustrated in the drawing, arranged particularly in the area of ​​the outer circumference of the cylinder tube 13, which, for example, comprises one or more position sensors or a displacement measuring system. Depending on the type and functionality of the position detection device, the activation element 45 has, for example, permanent magnetic or ferromagnetic properties.

[0080] The activation element 45 can, for example, be embedded into the piston body 38 during the injection molding process, so that the receiving groove 44a is also automatically formed. However, subsequent installation of the activation element 45 in the receiving groove 44a is also possible, for example, by using a slotted, spring-elastic activation element 45 that can be placed in the receiving groove 44a during a snap-in process.

[0081] In a non-illustrated embodiment, no annular groove 44 is formed in the piston body 38.

[0082] The piston body 38 may have ribbing, in particular to further increase its stability.

[0083] Under certain circumstances and depending on the application, a sufficient seal between the drive piston 5 and the cylinder tube 13 can be achieved even without additional soft-sealing structures. With appropriate manufacturing precision, the gap between the inner circumferential surface 14 of the cylinder tube 13 and the outer circumferential surface 43 of the piston body 38 can be kept so small that no leakage that could impair function occurs between the two working chambers 24, 25.

[0084] In most applications, however, it will be advantageous if the drive piston 5, in addition to the rigid piston body 38 made of a hard material, has an annular piston seal 46 made of a rubber-elastic material, which will be referred to below as an elastomer material for simplicity. Such a configuration is implemented in all illustrated embodiments. Here, the piston seal 46 is preferably formed by an elastomer structure 47, which is attached to the piston body 38, in particular by being applied to the piston body 38 by injection molding. Production takes place, in particular, using a two-component injection molding process.

[0085] The piston seal 46 has one or more annular sealing sections 46a, 46b, which are arranged coaxially to the longitudinal axis 9 and which slideably bear against the inner circumferential surface 14 of the cylinder tube 13.

[0086] Preferably, the piston seal 46 is divided into two annular sealing sections 46a, 46b, which are arranged at an axial distance from one another and which, in the case of the presence of an annular groove 44, are fixed axially on both sides of this annular groove 44 on the piston body 38.

[0087] To dampen impacts at the end positions of the stroke, the drive piston 5 is preferably equipped with at least one impact damper 48 made of a rubber-elastic material. This is the case in the illustrated embodiment. Here, an impact damper 48 is provided for each stroke direction of the drive unit 11, each of which is arranged on one of the two axially opposite end faces of the piston body 38. Each impact damper 48 preferably has a ring structure concentric with the longitudinal axis 9. Each impact damper 48 is preferably composed of several damper segments 52, which are arranged in a particularly regular distribution around the longitudinal axis 9.

[0088] Preferably, each impact damper 48 is an integral component of the aforementioned elastomer structure 47. The elastomer structure 47 preferably forms both the piston seal 46 and the at least one impact damper 48. A thermoplastic elastomer is recommended as the material. Alternatively, rubber, fluororubber (FKM), or other elastomers could also be used.

[0089] According to a statement in section IIIb of the Fig. In the modification illustrated in Figure 3, a guide ring 53, separate from the piston body 38, can also be present as a further component of the drive piston 5 to form the piston guide surface 42. This guide ring 53 has a wall thickness that is smaller than its length, so that it could also be referred to as a guide sleeve. It encloses the piston body 38 radially outward in a coaxial manner, preferably covering an annular groove 44 formed in the piston body 38 and any activation element 45 arranged therein radially outward. The guide ring 53 can, for example, be held axially between the two above-mentioned annular sealing sections 46a, 46b.

[0090] An embodiment that dispenses with a separate guide ring 53 has the great advantage that an activation element 45, which should be spaced apart from the inner peripheral surface 14, can be moved very close to this inner peripheral surface 14. This allows a small distance to the external position detection device to be achieved, which promotes functional accuracy and, in particular, also makes it possible to operate with low-strength magnetic fields.

[0091] Within the drive unit 11, the piston body 38 and the piston rod 8 are expediently combined into a one-piece piston body-piston rod assembly 54, with both the piston body 38 and the piston rod 8, and thus the entire piston body-piston rod assembly 54, being made of a carbon fiber-reinforced plastic. The piston body-piston rod assembly 54 can be manufactured using an injection molding process with high process reliability, extreme dimension accuracy, and yet cost-effectively.

[0092] With regard to the piston rod 8, the carbon fiber reinforced plastic not only has a weight-saving effect, but also has a positive influence on the sliding bearing of the piston rod 8 when passing through the first end wall 16.

[0093] The piston rod 8, with its outer peripheral surface 23, slides against the piston rod guide surface 22 defining the guide bore 18. This creates an extremely low-friction contact between the outer peripheral surface 23 of the piston rod 8 and the piston rod guide surface 22, which allows for a particularly smooth and low-wear drive movement 12.

[0094] This effect can be further optimized if the guide bore 18 according to the illustrated embodiments—apart from the modification shown in section IIIc—is directly defined by the first end wall 16 made of carbon fiber-reinforced plastic. In other words, the guide bore 18 is formed directly by a portion of the one-piece first end wall 16. According to the illustrated embodiment, the first end wall 16 can have an integrated sleeve-shaped portion 55 that encloses the guide bore 18.

[0095] The term "bore" in connection with the guide bore 18 is not necessarily to be understood as a mechanically created bore, but rather more generally as any bore-like opening, regardless of how it is manufactured. Furthermore, the guide bore 18 is expediently formed directly during the primary forming of the associated first end wall 16, in particular by injection molding.

[0096] The piston rod 8 can also be designed as a so-called continuous piston rod which extends simultaneously through both end walls 16, 17, wherein each of the end walls 16, 17 is then provided with a guide bore 18 forming a piston rod guide surface 22.

[0097] The first end wall 16, through which the piston rod 8 passes, expediently also carries a piston rod seal 56 arranged coaxially with the longitudinal axis 3, which slides against the outer circumferential surface 23 of the piston rod 8. The piston rod seal 56 is expediently fixed in a receiving groove 57 of the first end wall 16, which is coaxial with the guide bore 18. The piston rod seal 56 seals the first working chamber 24, which adjoins the first end wall 16, in the passage area of ​​the piston rod 8, from the environment. Preferably, a wiper function is also integrated into the piston rod seal 56, which is effective when the piston rod 8 retracts and prevents contaminants from penetrating the interior of the cylinder housing 2.

[0098] According to a non-illustrated embodiment, a piston rod seal 56 can also be omitted. The working cylinder is then designed without a piston rod seal.

[0099] According to the section IIIc of the Fig. 3, the guide bore 18 and the piston rod guide surface 22 can also be realized by a guide bushing 58 that is separate from the first end wall 16 and fastened in the first end wall 16. The guide bushing 58 is fixed in particular by being pressed into the first end wall 16 or by being encapsulated in the carbon fiber reinforced plastic during the injection molding of the first end wall 16. The guide bushing 58 can be made of any suitable material. The guide bushing 58 is made in particular of metal, so that a metal bearing of the piston rod 8 is achieved. The above-mentioned piston rod seal 56 can be formed separately as shown or combined with the guide bushing 58 to form a structural unit.

[0100] Preferably, the drive unit 11 is hollow along part of its length. A cavity 62 extends coaxially through the drive unit 11, but is not open throughout, so that no fluid connection occurs between the housing interior 4 and the atmospheric environment of the cylinder housing 2 through the drive unit 11.

[0101] The cavity 62 is divided by a partition wall 63, which is preferably integral with the piston rod 8, into two axially successive cavity sections 62a, 62b. These sections are an outer cavity section 62a, which opens out at the end face of the outer end section 7, and an inner cavity section 62b, which opens out at the opposite end face of the drive unit 11, located in the housing interior 4. The multi-part cavity 62 preferably extends exclusively within the piston body-piston rod assembly 54. While the outer cavity section 62a extends exclusively within the piston rod 8, the inner cavity section 62b extends both within the piston rod 8 and through the piston body 38. The partition wall 63 is expediently located in the transition area between the tapping section 6, which is provided with an external thread, and the adjoining longitudinal section of the piston rod 8.

[0102] The partition wall 63 could also be placed at a different longitudinal position of the drive unit 11. For example, it could also be provided directly on one of the two end faces of the piston body-piston rod assembly 54.

[0103] According to a non-illustrated embodiment, a further partition wall can be arranged in the cavity 62 at an axial distance from the partition wall 63, which partition wall is inserted into the cavity 62, in particular as a separate component, and is preferably pressed in. This allows dead spaces to be reduced.

[0104] All previous explanations also apply to the Fig. 4 and Fig. 5 illustrates a modified embodiment of a drive unit 11 of a fluid-operated working cylinder 1. This in the Fig. 4 and Fig.The embodiment illustrated in Fig. 5 furthermore makes it clear that at least one buffer extension 64, 65 which projects axially relative to the drive piston 5 can be integrated in one piece into the piston rod 8 and which serves to implement at least one fluidic end position damping device of the working cylinder 1.

[0105] By way of example, the piston rod 8 forms two such buffer extensions 64, 65, which are formed by two longitudinal sections of an inner piston rod longitudinal section 66, the outer diameter of which is larger than that of an outer piston rod longitudinal section 67 adjoining it in the direction of the outer end section 7. The drive piston 5 is seated at least substantially longitudinally centrally on the inner piston rod longitudinal section 66, which projects axially beyond it on both sides, forming one of the buffer extensions 64, 65. The optionally present inner hollow section 62b expediently extends uninterruptedly both along the inner piston rod longitudinal section 66 and along the outer piston rod longitudinal section 67.

[0106] Conveniently, the piston body 38 is formed integrally onto the inner piston rod length section 66.

[0107] Each buffer extension 64, 65 is provided to at least partially close an outflow cross-section for the outflowing pressure medium when a stroke end position is reached during operation of the working cylinder 1, so that a counterpressure is built up which results in a slowing down of the drive movement 12.

[0108] Depending on the damping principle, the buffer extensions 64, 65 can be designed with a smooth surface on their outer circumference or can be provided with longitudinal grooves 68.

[0109] It is particularly advantageous if all components of the working cylinder 1, which were described with regard to the possibility of being manufactured from carbon fiber-reinforced plastic, are made of this material, so that the working cylinder 1 is at least largely made of this carbon fiber-reinforced plastic. It is also advantageous to use the same carbon fiber-reinforced plastic for all these components.

[0110] The plastic matrix of the carbon fiber-reinforced plastic preferably consists of a thermoplastic material, in particular a polyamide plastic material, and expediently of polyamide 6 or polyamide 6.6. Compared to a thermosetting plastic material, which is also possible in principle, the thermoplastic material has the great advantage of being processable by injection molding or extrusion, thus making it suitable for use in manufacturing processes that are preferred for the working cylinder described. It is also advantageous to realize the plastic matrix from semi-aromatic or fully aromatic polyamide.

[0111] The carbon fibers embedded in the plastic matrix are preferably short fibers with an extremely short fiber length, making them ideal for processing using injection molding or extrusion techniques, for example, based on pellets. The fiber length is preferably in the range between 0.05 mm and 1 mm, and preferably in the range between 0.1 mm and 0.4 mm. An average fiber length of 0.3 mm is currently considered optimal.

[0112] The percentage by weight of carbon fibers within the carbon fiber-reinforced plastic is advantageously between 5 and 60 percent by weight. Preferably, the proportion of carbon fibers is in the range of 40 percent by weight.

[0113] Conveniently, all components of the working cylinder 1, which consist of a carbon fiber reinforced plastic with carbon fibers embedded in a plastic matrix, are manufactured by injection molding.

Claims

[1] Drive unit for a fluid-operated working cylinder, with a drive piston (5) and a piston rod (8), wherein the drive piston (5) has a piston body (38) projecting radially beyond the piston rod (8), which is combined with the piston rod (8) to form a one-piece piston body-piston rod assembly (54) made of plastic, which, including the piston body (38) and the piston rod (8), consists of a fiber-reinforced plastic with fibers embedded in a plastic matrix, characterized by in that the fiber-reinforced plastic is a carbon fiber-reinforced plastic, the fibers of which are embedded in the plastic matrix and are carbon fibers, which are short fibers whose fiber length is in the range from 0.05 mm to 1 mm, wherein at least the piston body-piston rod assembly (54) is an injection-molded part. [2] Drive unit according to claim 1, characterized bythat the radially outwardly facing outer peripheral surface (43) of the piston body (38) is designed as a piston guide surface (42) which is provided for direct sliding radial support on the inner peripheral surface (14) of a cylinder tube (13) of a fluid-operated working cylinder (1). [3] Drive unit according to claim 1 or 2, characterized by that an annular groove (44) is formed in the piston body (38) which is open towards its radially outwardly facing outer peripheral surface (43) and which expediently forms a receiving groove (44a) for an activation element (45) which can be used for position detection. [4] Drive unit according to one of claims 1 to 3, characterized bythat an elastomer structure (47) is fastened to the piston body (38), which elastomer structure forms a piston seal (46) provided for sealing and sliding engagement with the inner circumferential surface (14) of a cylinder tube (13) of the fluid-operated working cylinder (1) and which expediently also forms at least one impact damper (48) effective in a stroke end position of the drive piston (5). [5] Drive unit according to one of claims 1 to 4, characterized by that at least one buffer extension (64, 65) which projects axially with respect to the drive piston (5) and is provided for fluidic end-position damping is integrated in one piece into the piston rod (8) and / or that the drive unit (11) is hollow over only part of its length. [6] A fluid-operated working cylinder, comprising a cylinder housing (2) defining a housing interior (4) in which a drive piston (5) of a drive unit (11) also comprising a piston rod (8) is arranged to be linearly displaceable, wherein the drive piston (5) has a piston body (38) projecting radially beyond the piston rod (8) and is combined with the piston rod (8) to form a one-piece piston body-piston rod assembly (54) made of plastic, which, including the piston body (38) and the piston rod (8), consists of a fiber-reinforced plastic with fibers embedded in a plastic matrix, characterized byin that the fiber-reinforced plastic is a carbon fiber-reinforced plastic, the fibers of which are embedded in the plastic matrix and are carbon fibers, which are short fibers whose fiber length is in the range from 0.05 mm to 1 mm, wherein at least the piston body-piston rod assembly (54) is an injection-molded part. [7] Working cylinder according to claim 6, characterized by that the drive unit (11) is designed according to the characterizing features of one of claims 2 to 5. [8] Working cylinder according to claim 6 or 7, characterized by that the cylinder housing (2) has a cylinder tube (13) which circumferentially delimits the housing interior (4) and which, including its inner circumferential surface (14) which directly radially delimits the housing interior (4), consists of a carbon fiber-reinforced plastic with carbon fibers embedded in a plastic matrix. [9] Working cylinder according to claim 8, characterized bythat the cylinder housing (2) has an end wall (16, 17) axially delimiting the housing interior (4) on at least one end face of the cylinder tube (13). [10] Working cylinder according to claim 8 or 9, characterized by that the cylinder housing (2) has an end wall (16, 17) axially delimiting the housing interior (4) on each of the two end faces of the cylinder tube (13), wherein at least one of the end walls (16, 17) is slidably penetrated by the piston rod (8). [11] Working cylinder according to claim 10, characterized by that the end wall (16, 17) through which the piston rod (8) slides has a guide bore (18) through which the piston rod (8) extends and whose inner circumference forms a piston rod guide surface (22) radially supporting the piston rod (8). [12] Working cylinder according to claim 11, characterized bythat the guide bore (18) is defined directly by the associated end wall (16, 17), wherein the piston rod guide surface (22) is formed from a carbon fiber reinforced plastic of the end wall (16, 17). [13] Working cylinder according to one of claims 9 to 12, characterized by that at least one end wall (16, 17) of the cylinder housing (2) is formed integrally with the cylinder tube (13). [14] Working cylinder according to claim 13 in conjunction with one of claims 10 to 12, characterized by that the end wall (16, 17) through which the piston rod (8) slides is formed integrally with the cylinder tube (13). [15] Working cylinder according to one of claims 9 to 14, characterized by that at least one and expediently each end wall (16, 17) consists of a carbon fiber reinforced plastic with carbon fibers embedded in a plastic matrix. [16] Working cylinder according to one of claims 9 to 15, characterized by that at least one end wall (16, 17) of the cylinder housing (2) is designed as a separate end cover (170) with respect to the cylinder tube (13), which is fastened to the cylinder tube (13) by fastening means (36), wherein the fastening means (36) expediently consist of a welded connection. [17] Working cylinder according to claim 16, characterized by that the welded joint is an ultrasonic welded joint or a friction welded joint. [18] Working cylinder according to one of claims 9 to 17, characterized by that at least one end wall (16, 17) of the cylinder housing (2) is penetrated by a fluid channel (26, 27) opening into the housing interior (4). [19] Drive unit according to one of claims 1 to 5 and / or working cylinder according to one of claims 6 to 18, characterized bythat the carbon fibers of all components made of carbon fiber reinforced plastic are short fibers with a fiber length in the range of 0.05 mm to 1 mm. [20] Drive unit according to one of claims 1 to 5 or 19 and / or working cylinder according to one of claims 6 to 19, characterized by that the fiber length of the short fibers is in the range of 0.1 mm to 0.4 mm. [21] Drive unit according to one of claims 1 to 5 or 19 or 20 and / or working cylinder according to one of claims 6 to 20, characterized by that the proportion of carbon fibres in the carbon fibre reinforced plastic is between 5 and 60 percent by weight and preferably 40 percent by weight. [22] Drive unit according to one of claims 1 to 5 or 18 to 21 and / or working cylinder according to one of claims 6 to 21, characterized bythat the plastic matrix consists of a thermoplastic plastic material, expediently of a polyamide plastic material, or that the plastic matrix consists of semi-aromatic or fully aromatic polyamide. [23] Drive unit according to one of claims 1 to 5 or 18 to 22 and / or working cylinder according to one of claims 6 to 22, characterized by that any component consisting of a carbon fibre reinforced plastic with carbon fibres embedded in a plastic matrix is ​​an injection-moulded part. [24] Method for producing a drive unit according to one of claims 1 to 5 and 18 to 23 and / or a fluid-operated working cylinder according to one of claims 6 to 23, characterized by that at least the piston body-piston rod assembly (54) consisting of a carbon fiber reinforced plastic with carbon fibers embedded in a plastic matrix is ​​produced by injection molding. [25] Method according to claim 24 for producing a working unit according to claim 19 and / or a fluid-mounted working cylinder according to claim 19, characterized by that all components of the working cylinder (1) consisting of a carbon fibre reinforced plastic with carbon fibres embedded in a plastic matrix are manufactured by injection moulding.

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