Working cylinder and method for its manufacture

Description

[0001] The invention relates to a working cylinder, in particular a hydraulic working cylinder. The invention further relates to a method for manufacturing such a working cylinder.

[0002] Working cylinders as such are known from the prior art. As a rule, such working cylinders comprise a cylinder tube, couplings to it, and a piston unit.

[0003] In the prior art, for example, the screwing of the sealing elements to the cylinder tube is known for the manufacture of such working cylinders. Such working cylinders are therefore also referred to as screw cylinders.

[0004] For example, the solution according to EP 3 559 480 A1 describes a screw cylinder with at least one screwed closure part, in which the cylinder tube has a tapered wall section at the contact ring surface to the closure part, so that improved sealing is made possible.

[0005] Another solution known according to the state of the art is the welding of the cylinder tube and closure parts.

[0006] Furthermore, a combined solution is known from the prior art in which the bottom closure part is connected to the cylinder tube by MAG welding and then only the guide closure part is screwed on.

[0007] The thread of the cylinder tube and closure parts is usually produced by a machining process.

[0008] Screw cylinders as well as cylinders with screw fastening of only one closure part and MAG welding of the other closure part are provided in high quality according to the state of the art and have proven themselves to be high-quality and reliable products.

[0009] A manufacturing disadvantage is that, particularly for the cylinder tube, an additional material thickness, i.e., the tube wall thickness, must be provided for the subtractively machined thread, because the thread inevitably weakens the cylinder tube. This results in a tube wall thickness that is considerably over-dimensioned to withstand the forces during operation, especially those caused by the operating pressure of the fluid. This adversely leads to increased material consumption and a higher final weight of the working cylinder. Furthermore, for screw-type working cylinders, a specific thread length is required to accommodate the high axial forces resulting from the operating pressure of the fluid and the additional preload during tightening.The minimum thread length also increases the overall dimensions, which, in addition to increased material usage, can be a disadvantage depending on the installation situation.

[0010] The object of the invention is to provide a working cylinder that exhibits high reliability and can be manufactured in a material-saving and cost-effective manner. Furthermore, the object of the invention is to provide a method for manufacturing such a working cylinder.

[0011] The problem is solved with respect to the working cylinder by the features listed in claim 1 and with respect to the method for manufacturing such a working cylinder by the features listed in claim 7. Preferred embodiments are described in the respective dependent claims.

[0012] The working cylinder according to the invention comprises a cylinder and a piston unit as basic elements and is connected to the cylinder tube in particular by a special coupling of at least one closure part.

[0013] According to the invention, the cylinder comprises a cylinder tube, a closure part and another closure part.

[0014] As is usual, the cylinder tube has one cylinder tube end and another cylinder tube end, and thus two opposing cylinder tube ends.

[0015] The closure elements are arranged at the cylinder tube ends, with one closure element at the end of the cylinder tube and another closure element at the other end. The cylinder tube end and the other end are hereinafter collectively referred to as the cylinder tube ends, and the closure element and the other closure element are hereinafter collectively referred to as the closure elements. The cylinder tube and the closure elements arranged thereon form a cylinder interior.

[0016] As a further basic element, the piston unit forms at least one working chamber within the cylinder interior. Preferably, the piston unit is designed as an assembly consisting of a piston and piston rod, with the piston rod sliding through one of the closure parts, which then serves as a guide closure part. However, the piston unit can also be, for example, a plunger piston of a plunger cylinder or a piston unit of a synchronous cylinder.

[0017] In particular, the working cylinder according to the invention is characterized by a specially designed coupling between the cylinder tube and the closure part. The cylinder tube and the closure part are also collectively referred to as the coupling partners.

[0018] For this purpose, the cylinder has a coupling section. The coupling section is formed by the closure part and the cylinder tube end section.

[0019] The cylinder tube end section has a cylinder tube thread section, a cylinder tube intermediate section and a cylinder tube end.

[0020] The closure element has an external thread, and the cylinder tube thread section has a corresponding internal thread, with the external and internal threads together forming a common threaded section. The external and internal threads are engaged within this common threaded section.

[0021] The threaded section is designed to couple the closure part and the cylinder tube in a form-fitting manner and thus, in particular, to absorb axial forces resulting from the operating pressure of the pressure medium during the intended use of the working cylinder according to the invention.

[0022] Furthermore, the cylinder tube end is materially connected to the closure element at an adapter end on the cylinder tube side by means of a circumferential ring weld. This ring weld is a laser-welded ring weld. The ring weld forms a pressure-tight sealing plane. This pressure-tight sealing plane separates the working chamber from the environment and prevents the escape of the pressure medium.

[0023] The working cylinder according to the invention is designed to assume a relief operating state or a load operating state.

[0024] The term "relief operating condition" refers to the operating condition in which there is no or only a low operating pressure of the pressure medium.

[0025] According to the invention, the coupling section is designed such that no axial tensile force is absorbed by the common threaded section in the unloaded operating state. An axial tensile force is understood to be a force directed from the locking element in a distal axial direction, i.e., away from the center of the cylinder.

[0026] This is based on the fact that the external and internal threads exhibit a slight axial relative movement, also known as "breathing" in working cylinders. This slight axial relative movement is subsequently referred to as axial play. Under tensile force, the external thread of the sealing element is in a distal end-of-play position, and under compressive force, i.e., a force acting towards the center of the cylinder, it is in a proximal end-of-play position. The intermediate play position lies between these two positions. Any axial tensile forces are absorbed exclusively by the ring weld in the unloaded operating state.In the relief operating state, by definition no axial tensile forces are absorbed by the common thread section, whereby either no axial forces are absorbed by the common thread section and the locking part is in a clearance intermediate position, or conversely, axial compressive forces can even be absorbed.

[0027] The term "load operating condition" refers to the operating condition in which the pressure medium is subjected to full or high operating pressure.

[0028] The coupling section is designed such that, under load, both the annular weld and the common threaded section each absorb an axial tensile force. This means that the high axial tensile forces acting on the closure element due to the operating pressure of the pressure medium are absorbed partly by the annular weld and partly by the common threaded section. According to the invention, this force distribution is achieved by the fact that, during the transition from the unloaded operating state to the loaded operating state and the associated increase in axial tensile force, the intermediate cylinder tube section located between the cylinder tube threaded section and the cylinder tube end is elastically stretched. This change in length within the elastic limit causes the common threaded section to be guided into the distal end position and to absorb an axial tensile force from this state onward.From this state onwards, the cylinder tube intermediate section is no longer elastically stretched, and the ring weld as a material-locking coupling and the common threaded section as a form-locking coupling jointly participate in absorbing the axial tensile forces.

[0029] The inventive distinction between the relief operating state and the load operating state is understood to be the state in which the operating pressure of the pressure medium is so large that the common thread section begins to absorb a part of the axial tensile forces.

[0030] The solution according to the invention has in particular the advantages described below.

[0031] A first particular advantage is that the axial tensile force which must be absorbed by the common thread section during intended use as a result of the operating pressure of the pressure medium is significantly reduced by two effects according to the invention.

[0032] Firstly, the axial preload caused by tightening the screw connection and pressing the annular contact surfaces of the cylinder tube and the sealing element, as is the case with screw-type working cylinders according to the prior art, is advantageously eliminated. This axial preload must be able to withstand the forces from the operating pressure in addition to the forces from the operating pressure and reduces the maximum forces that can be absorbed from the operating pressure in screw-type working cylinders according to the prior art. According to the invention, therefore, only the axial tensile forces resulting from the operating pressure need to be absorbed by the common thread section.

[0033] Secondly, the axial tensile forces resulting from the operating pressure are then further reduced by a force component absorbed by the ring weld.

[0034] The underlying principle is that, as a further special advantage, the force absorption of the axial tensile load at high operating pressures is made possible on the one hand by the ring weld and on the other hand by the common thread section.

[0035] Due to the force distribution, the common thread section is subjected to less stress than in conventional screw cylinders. This makes it advantageous to use a shorter common thread section or a thinner-walled cylinder tube. This saves on expensive cylinder tube material, reduces the time required for machining the thread, and also enables smaller working cylinder sizes for the same stroke.

[0036] At the same time, the force distribution also results in less stress on the ring weld seam compared to conventional welding cylinders. This also advantageously allows the use of thinner-walled cylinder tubes, thereby saving material and reducing the weight of the working cylinder.

[0037] A particular advantage here is that the geometry of the cylinder tube section allows the maximum axial force at the ring weld to be adjusted. In this respect, the ratio of length to wall thickness can be advantageously chosen to reliably maintain the elastic limit and thus limit the maximum axial force at the ring weld.

[0038] In contrast to screw-type working cylinders, the need for an anti-rotation device is also advantageously eliminated, as this is integrated into the function by the ring weld.

[0039] According to a first advantageous embodiment, the working cylinder according to the invention is characterized in that, in the unloaded operating state, the cylinder tube intermediate section has a tensile preload and the common threaded section absorbs an axial compressive force. According to this embodiment, the common threaded section is in a proximal end-of-play position in the unloaded operating state. This embodiment thus provides a solution in which the path of elastic elongation of the cylinder tube intermediate section is maximized. In this way, a high proportion of the axial tensile force can be dissipated via the ring weld.

[0040] In a further advantageous embodiment, the working cylinder is characterized in that, during a change from the unloaded operating state to the loaded operating state, the cylinder tube intermediate section is designed for axial elongation within its elastic limit.

[0041] The cylinder tube intermediate section may, for example, also have a wall reduction.

[0042] Furthermore, the intermediate cylinder tube section can be designed such that it is wholly or partially integrated into the threaded cylinder tube section. In this case, the internal thread of the cylinder tube section can preferably have a thread pitch in the distal direction such that it exhibits a slightly degressive pitch in a stress-free state and a linear pitch under elastic strain. According to this design, the flanks of all threads only fully engage under load. This advantageously results in a further reduction in the length of the cylinder tube end section. Alternatively or cumulatively, the external thread of the closure element can also be...

[0043] According to a further advantageous development, the working cylinder is characterized by the fact that the cylinder tube intermediate section has a wall reduction.

[0044] Wall tapering refers to a reduction in the wall thickness of the cylinder tube in the area of ​​the intermediate cylinder tube section. Advantageously, the wall thickness of the intermediate cylinder tube section is 60% or less, and particularly preferably 40% or less, of the wall thickness of the rest of the cylinder tube. Furthermore, the length of the intermediate cylinder tube section in the area of ​​wall tapering is preferably at least three times, and particularly preferably at least five times, the wall thickness of the cylinder tube in the area of ​​wall tapering. Wall tapering surprisingly provides a simple yet reliable solution for reducing the stress on the annular weld. This is based on the fact that, under load, the intermediate cylinder tube section is axially elastically stretched and thereby transmits a tensile force to the annular weld.The smaller the wall thickness is chosen, the smaller the force transmitted at the same elastic strain state.

[0045] According to a further advantageous embodiment, the working cylinder is characterized in that the ring weld has a ring weld depth which has a ratio of 1.1 to 2.5 to a cylinder tube wall thickness.

[0046] In this further development, the ring weld exhibits an inclination relative to the transverse plane perpendicular to the main longitudinal axis. This results in a ring weld depth exceeding the cylinder tube wall thickness, ranging from 1.1 to 2.5 times the cylinder tube wall thickness depending on the angle of inclination. This advantageously provides a larger contact area and thus a higher strength of the metallurgical bond between the closure element and the cylinder tube at its end.

[0047] According to a further advantageous embodiment, the working cylinder is characterized in that the ring weld has a ring weld center axis which has a ring weld inclination angle alpha of 20 to 70 degrees relative to a main longitudinal axis of the cylinder tube.

[0048] The central axis of the V-shaped ring weld is inclined relative to the transverse plane, forming a weld inclination angle alpha of 20 to 70 degrees. It was found that this inclination provides, on the one hand, an additional increase in strength by advantageously distributing the components of the multiaxial stress on the weld caused by tensile and buckling stresses, and on the other hand, results in a sufficiently low heat input to prevent undesirable excessive heating of the cylinder tube section during welding, depending on the intended force distribution.

[0049] According to a further embodiment, the working cylinder has an additional coupling section at its further cylinder tube end section, which is designed in a manner similar to the coupling section according to the invention. The description of the coupling section according to the invention and its advantages therefore also apply accordingly to the further coupling section.

[0050] According to another aspect, the invention relates to a method for manufacturing a working cylinder according to the invention.

[0051] The working cylinder produced by this process has the features described above. Accordingly, the descriptions of the working cylinder according to the invention also apply to the process according to the invention.

[0052] The method according to the invention comprises the following process steps: a) Screwing the cylinder tube with its cylinder tube end section onto the closure part and creating an engagement between the internal thread of the cylinder tube thread section and the external thread of the closure part, thus creating the common thread section; b) Creating a pressure contact at an axial annular contact surface between the cylinder tube end and the closure part; c) Applying a tightening torque, creating an axial compressive force and causing axial compression of the cylinder tube intermediate section; d) Performing laser welding of the cylinder tube end and the closure part at the axial annular contact surface with thermal softening and deformation of the cylinder tube end and the closure part in the immediate vicinity of the axial annular contact surface during thermal expansion and simultaneous relaxation of the axial compression of the cylinder tube intermediate section.e) Cooling with solidification of the cylinder tube end and the closure part in the vicinity of the axial ring contact surface and formation of the ring weld seam and axial thermal shrinkage of the cylinder tube intermediate section.

[0053] The process steps are described in more detail below. a) Screwing the cylinder tube with its cylinder tube end section onto the closure part and creating an engagement between the internal thread of the cylinder tube thread section and the external thread of the closure part and creating the common thread section.

[0054] In process step a), the external thread of the closure part and the internal thread of the cylinder tube thread section are brought into engagement with each other. A screw connection is then made, forming the common thread section. The screw connection is continued until the end of the cylinder tube section rests against the closure part.

[0055] b) Establishing a pressure contact on an axial ring contact surface between the cylinder tube end and the closure part,

[0056] The end of the cylinder tube has a distally directed axial cylinder tube ring surface, and the closure part has a proximally directed axial closure part ring surface, which are brought into pressure contact with each other in process step b). Both ring surfaces then form the common ring contact surface.

[0057] c) Applying a tightening torque, creating an axial compressive force and creating an axial compression of the cylinder tube intermediate section,

[0058] In process step c), a tightening torque is applied. This simultaneously creates an axial compressive force on the ring contact surface, resulting in high surface pressure. The thread is in its distal end position. Further tightening of the screw connection axially compresses the intermediate cylinder tube section, preferably exclusively within its elastic range. After this process step, the working cylinder is under axial preload. The degree of compression influences the subsequent distribution of axial tensile forces between the ring weld and the common threaded section. With increasing compression, the proportion of axial tensile force transmitted via the ring weld in the finished working cylinder increases.

[0059] d) Performing laser welding of the cylinder tube end and the closure part at the axial ring contact surface with thermal softening and deformation of the cylinder tube end and the closure part in a close area of ​​the axial ring contact surface with thermal expansion and simultaneous relaxation of the axial compression of the cylinder tube intermediate section.

[0060] In process step d), the welding laser is applied in the area of ​​the axial ring contact surface. The welding energy transferred by the laser beam causes heating and thus thermal softening of the material of the cylinder tube end and the closure element in the immediate vicinity of the axial ring contact surface. This softening causes the material to yield, and the elastic compression of the cylinder tube section is relieved. Furthermore, the cylinder tube section is also heated by thermal conduction from the immediate vicinity of the cylinder tube end, resulting in thermal expansion. Due to the softening of the material in the laser welding zone, i.e., in the immediate vicinity of the axial ring contact surface, this change in length due to thermal expansion is not impeded, thus achieving axial stress relief.The degree of heat applied to the cylinder tube section allows for targeted control over the subsequent distribution of axial tensile forces between the annular weld and the common threaded section. Greater heating increases the proportion of axial tensile force transmitted via the annular weld in the finished working cylinder. Optionally, the cylinder tube section can be additionally heated using the heat input generated by the laser welding process itself.

[0061] By compressing the materials at the ring contact surface in process step c), a particularly reliable material bond is advantageously achieved during welding in process step d), and detrimental air inclusions are avoided. This results in a highly resilient ring weld.

[0062] e) Cooling under solidification of the cylinder tube end and the closure part in a near area of ​​the axial ring contact surface and formation of the ring weld seam and under axial thermal contraction of the cylinder tube intermediate section.

[0063] In process step e), heat is dissipated, causing the softened material to solidify. This results in the formation of a ring weld as a laser weld in the area of ​​the axial ring contact surface, creating a metallurgical bond between the closure element and the cylinder tube. During the cooling process, which continues even after the ring weld has formed, the end section of the cylinder tube, and in particular its intermediate section, contracts. The axial component of this thermal contraction moves the common threaded section out of its distal end position and into the playing position, or—depending on the length of the thermal contraction—even into the proximal end position. The common threaded section is thus reliably free of any axial tensile preload.

[0064] According to an advantageous further development, the method is characterized in that process step e) is carried out as process step e1) and that in process step e1) the axial thermal contraction is carried out until an axial tensile prestress is formed in the cylinder tube intermediate section.

[0065] After this modification, the common thread section is in a proximal end-of-play position. This particular modification has the advantage that, under axial force due to operating pressure, the tensile force is initially absorbed entirely by the annular weld, and the common thread section remains relieved of the tensile force. As the elastic elongation of the cylinder tube section increases with increasing axial tensile force, the common thread section first reaches the end-of-play position and only subsequently the distal end-of-play position. Only with a further increase in force does force transmission via the common thread section begin. From this point on, the force transmission begins to be divided between the annular weld and the common thread section.While the force transmission via the ring weld essentially no longer increases from this point onwards, a further increase in the axial tensile force is transmitted via the common thread section.

[0066] The invention is described as an exemplary embodiment by reference to Fig. 1 Coupling section of the working cylinder after process steps a) to c) - schematic sectional view Fig. 2 Coupling section of the working cylinder after process step d) - schematic sectional view Fig. 3 Coupling section of the working cylinder after process step e) - schematic sectional view Fig. 4 Coupling section of the working cylinder in the transition from the unloaded operating state to the loaded operating state - schematic sectional view Fig. 5 Coupling section of the working cylinder in the loaded operating state - schematic sectional view Fig. 6 Further coupling section of the working cylinder in the loaded operating state - schematic sectional view explained in more detail.

[0067] In this context, identical reference symbols in different figures refer to the same features or components. These reference symbols are used in the description even if they are not shown in the figure in question.

[0068] The figures show an embodiment of the working cylinder and simultaneously illustrate an embodiment of the method in the various process steps.

[0069] Fig. 1 Figure 3 shows the working cylinder in the area of ​​the cylinder tube end section 5a and the closure part 4a, in the state after carrying out process steps a) to c). The cylinder tube end section 5a of the cylinder 3 is divided distally into the cylinder tube thread section 5.1a, the cylinder tube thread section 5.2a, and the cylinder tube end 5.3a. The internal thread 9a of the cylinder tube thread section 5.1a and the external thread 8a of the closure part 4a were engaged in process step a) and now form the common thread section. Furthermore, in process step b), pressure contact was established at an axial annular contact surface 11a between the cylinder tube end 5.3a and the closure part 4a by further tightening. In process step c), an axial compressive force was created by applying a tightening torque, as illustrated by the double arrow.The common threaded section was brought into the distal end-of-play position, and the cylinder tube intermediate section 5.2a was clamped between the cylinder tube threaded section 5.1a and the axial ring contact surface 11a, thereby creating an axial compression of the cylinder tube intermediate section 5.2a as its elastic deformation. The geometry of the pairing of internal thread 9a and external thread 8a is shown schematically and greatly exaggerated in all figures to better illustrate the play positions. In the present embodiment, the closure part 4a is designed as a bottom closure part, which, together with the cylinder tube 3, forms the working chamber 6.1, here as the piston chamber, of the cylinder channel space 6.

[0070] Fig. 2 Figure 1 shows the working cylinder after process step d) and at the beginning of process step e). By applying a laser to the axial ring contact surface 11a, the material of the closure part 4a and the cylinder tube 3 at the cylinder tube end 5.3a was softened. This material deformed under compressive stress, thus enabling axial stretching of the cylinder tube intermediate section 5.2a with subsequent axial elastic recovery. The ring weld 10a was then produced in the area of ​​the former axial ring contact surface 11a. The cylinder tube intermediate section 5.2a is now stress-free, and due to the onset of thermal axial shrinkage, the common threaded section is in a neutral position.

[0071] Fig. 3 Figure 1 shows the working cylinder after completion of all process steps a) to e) in the variant with tensile preload of the cylinder tube intermediate section 5.2a. After further axial thermal shrinkage of the cylinder tube intermediate section 5.2a following further cooling in process step e), the common thread section is in the proximal end position. The tensile force acting on the ring weld 10a is represented by the arrow at the ring weld 10a. The three opposing short arrows on the thread flanks represent the transmission of the axial compressive force via the common thread section.

[0072] In the unloaded operating state, the transmission of small axial forces therefore takes place exclusively via the ring weld 10a.

[0073] Fig. 4 and Fig. 5 show the working cylinder under load.

[0074] The representations in Fig. 4 and Fig. 5 The underlying principle is that, in the present embodiment, the working cylinder, as is typical, is equipped with fastening modules on both the piston rod and the bottom closure (not shown). A fastening module is a component for transmitting force from the working cylinder to components of an application device. In a common design, the fastening module has a bore – often also referred to as an eye – into which a locking element, such as a bolt, can be inserted. The locking element positively connects the piston-rod-side fastening module to a component of the application device and ensures force transmission during operation. In particular, such a fastening module can be designed as a spherical bearing. Fig. 4 and Fig. 5 This illustrates the case where the pressure medium in the piston rod chamber is pressurized and relaxed in the piston chamber. The working cylinder thus generates a tensile force between the mounting modules to perform a retraction movement. The pressure acting on the inner annular surface of the further closure part 4b – here acting as a guide closure part – causes a distal axial force, which is transmitted to the cylinder tube 3 and from there to the coupling section 7a. There, the tensile force transmitted to the application device via its mounting module acts on the closure part 4a as an opposing tensile force.

[0075] Fig. 4 Figure 1 shows the working cylinder in a transition state from the unloaded operating state to the loaded operating state. The tensile force transmitted via the cylinder tube 3 is represented by the arrow on the cylinder tube 3, and the tensile force acting on the closure part 4a via the fastening module is represented by the opposite arrow. The intermediate cylinder tube section 5.2a is axially stretched due to elastic deformation. However, the pressure of the hydraulic medium is not yet high enough to reach the maximum axial stretch of the intermediate cylinder tube section 5.2a and for the common threaded section to be in a neutral position. The force from the pressure of the hydraulic medium continues to be absorbed exclusively by the ring weld 10a.

[0076] Fig. 5 Figure 1 shows the working cylinder under load. Due to the high axial forces – represented by the double arrows – at high or full operating pressure of the hydraulic fluid in the piston rod chamber, the intermediate cylinder tube section is elastically stretched to such an extent that the common threaded section is brought into the distal end-of-play position. Additional forces are now transmitted between the external thread 8a and the internal thread 9a. The three short arrows on the thread flanks represent the transmission of the axial tensile force via the common threaded section. Because of the force transmission via the common threaded section, the intermediate cylinder tube section 5.2a cannot stretch further, thus preventing overloading of the annular weld 10a. The total transmitted tensile force is now divided between the force transmitted via the annular weld and the force transmitted via the common threaded section.

[0077] Fig. 6 Figure 1 shows an embodiment of a working cylinder which has a further coupling section 7b, where the load operating state is also shown.

[0078] In the example according to Fig. 6 The further closure part 4b is a guide closure part through which a piston rod of the piston unit 2 passes. The further working chamber 6.2 is therefore the piston rod chamber. The further cylinder end section 5b is designed like the cylinder end section 5a and has the further cylinder tube thread section 5.1b, the further cylinder tube thread section 5.2b, and the further cylinder tube end 5.3b. The further external thread 8b and the further internal thread 9b are engaged and form the further common thread section. At the same time, the cylinder tube 3 and the further closure part 4b are positively coupled via the further circumferential ring weld 10b. The pressure medium in the further working chamber 6.2. Due to the high operating pressure acting on the inner annular surface of the further closure part 4b under load – represented by the two parallel arrows – an axial distal force is exerted on the further closure part 4b. This force is firstly transmitted via the further annular weld 10b to the cylinder tube 3 – represented by the long arrow in the cylinder tube intermediate section 5.2b. This creates a tensile force in the area of ​​the further cylinder tube intermediate section 5.2b, which elastically stretches it. Secondly, due to the resulting axial displacement between the further internal thread 9b and the further external thread 8b, forces are also transmitted via the further common thread section to the cylinder tube 3 – represented by the three short arrows on the thread flanks. The descriptions of the structure and function of the coupling section 7a according to the [reference] also apply. Fig. 1 bis 5 similarly for the further coupling section 7b according to Fig. 6 . Reference symbols used

[0079] 1 Cylinder 2 Piston unit 3 Cylinder tube 4a Closing part 4b Further closing part 5a Cylinder tube end section 5.1a Cylinder tube thread section 5.2a Cylinder tube intermediate section 5.3a Cylinder tube end 5b Further cylinder tube end section 5.1b Further cylinder tube thread section 5.2b Further cylinder tube intermediate section 5.3b Further cylinder tube end 6 Cylinder interior 6.1 Working chamber 6.2 Further working chamber 7a Coupling section 7b Further coupling section 8a External thread 8b Further external thread 9a Internal thread 9b Further internal thread 10a Ring weld 10b Further ring weld 11a Axial ring contact surface 12 Ring weld center axis

Claims

1. A working cylinder, comprising a cylinder (1) and a piston unit (2), wherein the cylinder (1) comprises a cylinder tube (3), a closure part (4a) and a further closure part (4b), wherein the cylinder tube (3) comprises a cylinder tube end portion (5a) and a further cylinder tube end portion (5b), wherein the closure part (4a) is arranged at the cylinder tube end portion (5a) and the further closure part (4b) is arranged at the further cylinder tube end portion (5b), and wherein the cylinder tube (3) and the closure parts (4a, 4b) form a cylinder interior (6), wherein the piston unit (2) forms at least one working chamber (6.1) in the cylinder interior (6), wherein the cylinder (1) comprises a coupling portion (7a), which comprises the closure part (4a) and the cylinder tube end portion (5a), wherein the cylinder tube end portion (5a) comprises a threaded cylinder tube portion (5.1a), an intermediate cylinder tube portion (5.2a), and a cylinder tube end (5.3a), wherein the closure part (4a) has an external thread (8a) and the threaded cylinder tube portion (5.1a) has an internal thread (9a) corresponding to the external thread (8a), wherein the external thread (8a) and the internal thread (9a) form a common threaded portion which is designed to couple the closure part (4a) and the cylinder tube (3) in a form-fit manner, wherein the cylinder tube end portion (5a) is connected to the closure part (4a) in a positive substance manner by means of a circumferential ring weld seam (10a), wherein the ring weld seam (10a) is made as a laser ring weld seam and forms a pressure-medium-tight sealing plane, wherein the working cylinder is designed to assume a load-relieved operating state or a loaded operating state, wherein in the load-relieved operating state, no or only a low operating pressure of the pressure medium is applied, wherein in the loaded operating state the full or a high operating pressure of the pressure medium is applied, wherein in the load-relieved operating state the common threaded portion does not absorb any axial tensile force, wherein in the loaded operating state, the ring weld seam (10a) and the common threaded portion each absorb an axial tensile force.

2. The working cylinder according to claim 1, characterized in that in the load-relieved operating state the intermediate cylinder tube portion (5.2a) has a tensile prestress and the common threaded portion absorbs an axial compressive force.

3. The working cylinder according to one of the preceding claims, characterized in that the intermediate cylinder tube portion (5.2a) is designed for an axial expansion within its elastic limit when the load-relieved operating state changes to the loaded operating state.

4. The working cylinder according to one of the preceding claims, characterized in that the ring weld seam (10a) has a ring weld seam depth which has a ratio of 1.1 to 2.5 with respect to a cylinder tube wall thickness.

5. The working cylinder according to one of the preceding claims, characterized in that the ring weld seam (10a) has a ring weld seam centre axis which has a ring weld seam inclination angle alpha of 20 to 70 degrees with respect to a main longitudinal axis of the cylinder tube.

6. The working cylinder according to one of the preceding claims, characterized in that the piston unit (2) forms a further working chamber (6.2) in the cylinder interior (6), wherein the cylinder (1) comprises a further coupling portion (7b) which comprises the further closure part (4b) and the further cylinder tube end portion (5b), wherein the further cylinder tube end portion (5b) comprises a further threaded cylinder tube portion (5.1b), a further intermediate cylinder tube portion (5.2b) and a further cylinder tube end (5.3b), wherein the further closure part (4b) has a further external thread (8b) and the further threaded cylinder tube portion (5.1b) has a further internal thread (9b) corresponding to the further external thread (8b), wherein the further external thread (8b) and the further internal thread (9b) form a further common threaded portion which is designed to couple the further closure part (4b) and the cylinder tube (3) in a form-fit manner, wherein the further cylinder tube end (5b) is connected to the further closure part (4b) in a positive substance manner by means of a further circumferential ring weld seam (10b), wherein the further circumferential ring weld seam (10b) is made as a laser ring weld seam and forms a pressure-tight sealing plane, wherein in the load-relieved operating state the further common threaded portion does not absorb any axial tensile force, wherein in the loaded operating state the further circumferential ring weld seam (10b) and the further common threaded portion each absorb an axial tensile force.

7. A method for manufacturing a working cylinder, wherein the working cylinder is designed according to one of claims 1 to 5, comprising the following process steps: a) screwing the cylinder tube (3) with its cylinder tube end portion (5a) onto the closure part (4a), and producing an engagement of the internal thread (9a) of the cylinder tube threaded portion with the external thread (8a) of the closure part (4a), and producing the common threaded portion, b) establishing a pressure contact at an axial ring contact surface (11a) between the cylinder tube end (5.3a) and the closure part (4a), c) applying a tightening torque, exerting an axial compressive force and effecting an axial compression of the intermediate cylinder tube portion (5.2a), d) performing laser welding of the cylinder tube end (5.3a) and the closure part (4a) at the axial ring contact surface (11a) with thermal softening and deformation of the cylinder tube end (5.3a) and the closure part (4a) in a close range of the axial ring contact surface (11a) with thermal expansion and simultaneous relaxation of the axial compression of the intermediate cylinder tube portion (5.2a), e) cooling with solidification of the cylinder tube end (5.3a) and of the closure part (4a) in a close range of the axial ring contact surface (11a) and forming the ring weld seam (10a) and axial thermal contraction of the intermediate cylinder tube portion (5.2a).

8. The method for producing a working cylinder according to claim 7, characterized in that the process step e) is carried out as process step e1) and that in the process step e1) the axial thermal contraction is carried out until an axial tensile prestress is achieved in the intermediate cylinder tube portion (5.2a).