Hydraulic tool

Abstract

A hydraulic tool (10, 100, 300), comprising: a hydraulic cylinder (11, 311); a piston (12, 112, 312) with a piston rod; a position-dependent pressure relief valve (13, 113) for adjusting a hydraulic pressure within the hydraulic cylinder (11, 311) depending on a position of the piston (12, 112, 312) within the hydraulic cylinder (11, 311); wherein the position-dependent pressure relief valve (13, 113) is configured to provide a continuously adjustable force depending on the position of the piston (12, 112, 312) within the hydraulic cylinder (11, 311).

Description

Field of invention

[0001] The present invention relates to a hydraulic tool according to the preamble of claim 1 and the use of a tool head in such a hydraulic tool.

[0002] Such a hydraulic tool is described in EP 2 107 169 A1. background

[0003] Hydraulic tools are generally known in the prior art. Hydraulic tools are used, for example, in pressing or cutting. In these processes, a pump generates hydraulic pressure, which moves a tool head (e.g., a pressing head or cutting head) against a workpiece, thus deforming or separating it. The force required for pressing or cutting depends, among other things, on the geometry of the workpiece. In this context, it has become apparent that there is a further need to provide a hydraulic tool. EP 2107169 A1 discloses a hydraulic cylinder. EP 3165333 A1 discloses a hydraulic unit for a mobile hydraulic tool.

[0004] It is therefore an object of the present invention to provide an improved hydraulic tool, in particular it is an object of the present invention to provide a hydraulic tool with force control during forming or separating.

[0005] These and other problems, which will be mentioned in the following description or which may be recognized by a person skilled in the art, are solved by the subject matter of the independent claims. The dependent claims further develop the central idea of ​​the present invention in a particularly advantageous way. Summary of the invention

[0006] According to a first aspect of the present invention, a hydraulic tool is provided comprising: a hydraulic cylinder; a piston with a piston rod; a position-dependent pressure relief valve for adjusting a hydraulic pressure within the hydraulic cylinder depending on the position of the piston within the hydraulic cylinder; wherein the pressure relief valve is configured to provide a continuously adjustable force depending on the position of the piston within the hydraulic cylinder.

[0007] The term "hydraulic tool" is to be understood broadly in this context and refers to a device with a hydraulic drive for applying hydraulic force to a tool head. The tool head can be, for example, a cutting tool, a forming tool, a punching tool, or a pressing tool. The hydraulic drive is preferably a hydraulic pump driven by an electric motor. The hydraulic tool can be a stationary tool or a hand tool. In this context, the term "hand tool" refers to a tool that a user holds in one or both hands. The pump is preferably also integrated into the hand tool. The term "stationary tool" refers to a tool that is stationary on the floor and is not held in the hands of a user.

[0008] The term "hydraulic cylinder" is to be understood broadly here and includes a cylinder tube. The hydraulic cylinder has, in particular, an inlet interface for hydraulic fluid. The hydraulic cylinder has, in particular, an outlet interface for hydraulic fluid. The inlet and / or outlet interface preferably includes a valve. The inlet interface preferably includes a pressure relief valve. The outlet interface preferably includes a shut-off valve. A piston is, in particular, arranged or guided inside the hydraulic cylinder. By applying hydraulic pressure to the piston, it is moved translationally.

[0009] The term "cylinder tube" is to be understood broadly here and refers to a hollow body. The cylinder tube is made, for example, of a material that contains at least some metal, such as aluminum.

[0010] The term "piston" is to be understood broadly here and refers to an insert geometrically corresponding to the hydraulic cylinder, which can be set in motion by pressurizing the hydraulic cylinder with fluid. The piston preferably also has a cylindrical outer contour. A piston rod is arranged on the piston. The piston rod preferably has an interface for attaching a tool head. The piston and the piston rod are preferably at least partially manufactured as a single piece.

[0011] In this context, the term pressure relief valve refers to a mechanical device designed to limit the pressure within a hydraulic cylinder. As soon as the pressure inside the hydraulic cylinder exceeds a threshold value set by the pressure relief valve, the valve opens and diverts at least some of the fluid to reduce the pressure to the desired level. The pressure relief valve can be, for example, a needle valve, a ball valve, or a poppet valve. It may also include a spring. The pressure relief valve may, for example, have a channel element for returning hydraulic fluid. The hydraulic fluid is preferably returned to a reservoir in the pump. In this context, the pressure relief valve is, for example, located in the piston or the piston rod.The pressure relief valve can, for example, be located in an outlet of the hydraulic cylinder. The pressure relief valve can be controlled, for example, by a mechatronic control system based on a detected piston position. The piston position can be detected, for example, using a displacement measuring system (e.g., a glass scale).

[0012] In this context, the term "stepless" refers specifically to the continuous adjustment of the pressure within the hydraulic cylinder. Furthermore, "stepless" can also refer to the adjustment of the pressure within the hydraulic cylinder between a minimum and a maximum pressure by continuously changing the pressure. In this way, a continuous force can also be provided by the tool head (for example, pressing force or cutting force).

[0013] The invention is based on the understanding that hydraulic tools are used for cutting or forming. Different forces are required for the cutting or forming processes, depending on the geometry of the workpiece being machined. In the prior art, different force levels are provided for this purpose, for example, by multi-stage piston systems, so-called telescopic pistons in the hydraulic cylinder. However, due to the discrete stages, only certain workpiece geometries can be subjected to an optimal pressing or cutting force. The invention solves this problem by enabling a stepless supply of the hydraulic force. This ensures that the optimal force is always available. For this purpose, a pressure relief valve is arranged in the hydraulic cylinder, which adjusts the pressure depending on the position of the piston in the hydraulic cylinder.For example, smaller diameter workpieces require less pressing force for forming, and vice versa. The position of the piston in the hydraulic cylinder indirectly reveals the position of the tool head, which is mounted on the piston rod. This information allows the dimensions (e.g., diameter) of a workpiece to be determined. This leads to improved results with the hydraulic tool. It enables the provision of varying forces, particularly continuously adjustable forces, with a single piston instead of a multi-stage telescopic piston. The hydraulic pressure causes a translational movement of the piston, piston rod, or tool head mounted on the piston rod. The product of the piston area and the hydraulic pressure yields a force acting on the piston. This force is approximately equal to the force acting on the piston tool.

[0014] Preferably, the position-dependent pressure relief valve comprises a spring whose travel changes depending on the position of the piston. The change in travel depending on the piston's position causes a change in the spring force acting on the position-dependent pressure relief valve. The spring is, for example, a coil spring. The spring is made, for example, of a material that at least partially comprises spring steel. The spring is preferably a compression spring. The spring is preferably in operative contact with the piston. For example, the spring is pre-tensioned and arranged inside the hydraulic cylinder below the piston. For example, the spring projects at least partially into the piston. The spring preferably exhibits linear behavior with respect to the ratio of travel to spring force. The spring preferably has a constant pitch.Depending on the spring deflection, i.e., the compression, a corresponding spring force is applied. This spring force acts on the pressure relief valve from one side. The fluid pressure acts on the pressure relief valve from the opposite side. The product of fluid pressure and the area under pressure (e.g., the area of ​​the sphere in the pressure relief valve) results in a force acting on the pressure relief valve. As soon as the fluid pressure exceeds a threshold value (e.g., 50 N) that results in a force greater than the applied spring force, the pressure relief valve opens, allowing the fluid to flow out and the fluid pressure to drop again until the pressure relief valve closes. This allows for a stepless force to be provided for the hydraulic tool in a simple design. By selecting a spring, separate measurement technology (e.g.,A glass scale is no longer needed to detect the piston's position. Furthermore, a mechatronic control logic that evaluates the detected piston position and adjusts the pressure relief valve accordingly is unnecessary. This results in a simple, compact solution.

[0015] Preferably, the spring is pre-tensioned. The pre-tension can be achieved, for example, by means of another spring that presses on the piston. For example, the other spring is arranged inside the hydraulic cylinder between the piston and an upper end of the hydraulic cylinder. For example, the other spring is a coil spring that at least partially surrounds the piston rod. Due to the pre-tension, a compression spring can be used for the position-dependent pressure relief valve.

[0016] Preferably, the piston has a hollow chamber which is fluidically connected to an interior of the hydraulic cylinder, so that hydraulic fluid can flow from the interior of the hydraulic cylinder into the hollow chamber.

[0017] The hollow chamber can have any geometric shape. For example, it can have an annular gap or a cylindrical shape. It should be noted that the hollow chamber is not limited to these geometries. The hollow chamber preferably has an opening that is fluidically connected to the interior of the hydraulic cylinder containing the hydraulic fluid. The hollow chamber is preferably fluidically connected to the pressure relief valve.

[0018] Preferably, the position-dependent pressure relief valve is arranged in the piston and / or the piston rod. This allows for a simple and compact design.

[0019] Preferably, the position-dependent pressure relief valve is arranged at an interface with an outlet opening of the hydraulic cylinder, and the spring is at least partially located inside the piston and / or piston rod. This represents an alternative arrangement of the pressure relief valve compared to the arrangement within the piston or piston rod. Only the spring needs to be located within the piston or piston rod. This simplifies the design.

[0020] Preferably, the position-dependent pressure relief valve comprises a channel element configured to fluidically connect the position-dependent pressure relief valve to an outlet interface. The channel element is, for example, designed as a hollow cylinder. When the pressure relief valve is open, the channel element allows hydraulic fluid to flow from the interior of the hydraulic cylinder through the opening of the pressure relief valve, via the channel element, to an outlet interface. The outlet interface is preferably connected to a hydraulic reservoir from which the pump pumps the hydraulic fluid into the hydraulic cylinder. The channel element is, for example, fixedly arranged within the interior of the hydraulic cylinder. The piston or piston rod is, for example, arranged concentrically around the channel element.The piston rod can move along the channel structure element. The channel structure element has, for example, a sealing ring to seal an outer surface of the channel structure element against the piston.

[0021] Preferably, the position-dependent pressure relief valve is a ball valve, a needle valve or a disc valve.

[0022] Preferably, the spring has a variable pitch. This allows for a non-linear displacement-force relationship of the spring and thus a non-linear, stepless force application during cutting, pressing, or forming. This can be advantageous in certain pressing and cutting applications. For example, the workpiece being processed may require such a non-linear force profile due to its material properties (e.g., composite material).

[0023] Preferably, the piston rod has an interface for the interchangeable attachment of a tool head. The interface can, for example, include a thread. The interface can, for example, include a plug connection. The tool head can, for example, be a single-mandrel tool. The interface allows the use of different tool heads. These can, for example, perform different tasks or be suitable for different workpiece geometries.

[0024] Preferably, the hydraulic tool comprises a tool head, wherein the tool head is one of the following: a single-mandrel tool head, a cutting tool head or a press head.

[0025] Preferably, the hydraulic tool includes an inlet interface for the hydraulic fluid with a fixed pressure relief valve. Preferably, the hydraulic tool also includes another fixed pressure relief valve in a pump of the hydraulic tool.

[0026] The term "inlet interface" refers to an opening to the interior of the hydraulic cylinder. The pressure relief valve in the inlet interface and / or the pump limits the maximum permissible pressure within the hydraulic cylinder. This pressure relief valve is preferably position-independent. This pressure relief valve prevents system-damaging pressures of the hydraulic fluid. This has a positive effect on the service life and load-bearing capacity of the hydraulic tool. Furthermore, this can have a positive effect on the machining of the workpiece, whereby the machining quality can be improved by ensuring that the workpiece is always machined with the required contact pressure of the tool head.By using a pressure relief valve in the inlet interface and / or the pump in combination with a position-dependent pressure relief valve (for example in the piston), a displacement force characteristic with a combination of constant displacement-independent force and displacement-dependent variable stepless force can be advantageously enabled.

[0027] Preferably, the piston and piston rod are at least partially integrally manufactured as a single piece. This at least partially one-piece design enables a compact construction.

[0028] Preferably, the hydraulic tool is a hand tool. In this context, the term "hand tool" refers to a tool that is held or operated by a user. It is therefore in contrast to a stationary system, such as a press.

[0029] Another aspect concerns the use of a tool head in a hydraulic tool described in more detail above.

[0030] The features described above, including those from different embodiments, can also be combined with each other, which can result in synergistic interactions that go beyond the sum of the individual effects. Description of preferred embodiments

[0031] The following is a description of the characters, in which they are shown Figure 1 a schematic view of a hydraulic tool; Figure 2 another schematic view of a hydraulic tool; Figure 3 a force path diagram; Figure 4 another schematic view of a hydraulic tool; and Figure 5 a force-displacement diagram.

[0032] The following section describes and explains exemplary embodiments based on the figures shown above. Identical reference numerals or analogous reference numeral structures refer to analogous or interacting components. Description of exemplary embodiments

[0033] Figure 1Figure 1 shows a schematic view of a hydraulic tool 10. The hydraulic tool 10 is a hand tool. It comprises a hydraulic cylinder 11, which is a hollow cylinder made of a metal, for example, aluminum. A piston 12 is arranged inside the cylinder. The piston 12 has a piston rod 29 integrally connected to it. At the upper end of the piston rod 29 is an interface 18 for a tool head 17. The interface 18 is an internal thread. The tool head 17 is a single-prong tool and has an external thread corresponding to the interface 18. The piston 12, together with the piston rod 29, moves translationally within the hydraulic cylinder 11. A coil spring 16 is also arranged inside the hydraulic cylinder 11, which pushes the piston 12 back into its initial position.The hollow cylinder 11 has an inlet interface 26 for hydraulic fluid. The maximum system pressure is regulated by a fixed pressure relief valve 27A in the pump housing. A pump (not shown) delivers the hydraulic fluid through the inlet interface 26 into an internal area of ​​the hydraulic cylinder 11. This creates pressure below the piston 12, causing a translational movement of the piston 11 forward. The hydraulic cylinder 28 also has an outlet interface 27 for the hydraulic fluid. Preferably, a valve (not shown) is located in the outlet interface 27 for blocking (during operation) or releasing (when switching off) a hydraulic flow. The hydraulic fluid flows through the outlet interface 27 back into a reservoir (not shown), from which the pump (not shown) delivers hydraulic fluid. This creates a closed loop.A position-dependent pressure relief valve 13 is arranged inside the piston rod 29. The piston rod 29 and the piston 12 are at least partially designed as hollow bodies for this purpose. The position-dependent pressure relief valve 13 is designed as a needle valve. The position-dependent pressure relief valve 13 serves to adjust the hydraulic pressure within the hydraulic cylinder 11 depending on the position of the piston 12 within the hydraulic cylinder 11. The hydraulic cylinder 11 has a shoulder 20. The shoulder limits the stroke of the piston 12 within the hydraulic cylinder 11. The pressure relief valve 13 has a spring 14. The spring 14 is designed as a compression spring. The spring 14 is pre-tensioned by the spring 16. The spring 14 is arranged at least partially within a channel structural element 19.Depending on its length, and in particular its compression, spring 14 exerts a spring force on the opening of pressure relief valve 13. As soon as the fluid pressure and a corresponding force on the pressure relief valve exceed the spring force, pressure relief valve 14 releases the opening, allowing the hydraulic fluid to flow through the opening of pressure relief valve 13 and from there into the interior of the channel structure element 19. In this case, the channel structure element 19 is fluidically connected to an outlet interface (not shown). This outlet interface is, in turn, connected to the pump reservoir (not shown). In this case, the piston 12 is fully retracted.

[0034] Figure 2 shows another schematic view of a hydraulic tool 100. In contrast to the one in Figure 1In the hydraulic tool 10 shown, the hydraulic tool 100 additionally features a pivotable counter-stop 130. A round workpiece 131 is arranged between the counter-stop 130 and the tool head 117. The piston 112 is fully extended. In the present illustration, an inlet interface 122 is shown on the piston 112, which is fluidically connected to a hollow chamber 123. The hollow chamber 123 is at least partially designed as an annular gap. The hollow chamber 123 is fluidically connected to the pressure relief valve 113. When the pressure relief valve 113 is open, the hydraulic fluid flows from the inlet interface 126 of the hydraulic cylinder 11, through the inner area 121 of the hydraulic cylinder 111, into the inlet interface 122 of the piston.From the inlet interface 122 of the piston 112, the hydraulic fluid flows further through the hollow chamber 123 of the piston 112 and from there, via an opening of the pressure relief valve 113 (when the pressure relief valve 113 is open), back through the inner area 128 of the piston 112. From the inner area 128 of the piston 112, the hydraulic fluid flows into the structural channel element 119 and from there back into the reservoir (not shown) via the outlet interface 125. The spring 114 is located in the present case, unlike the illustration in [reference missing]. Figure 1 elongated. Since this is a compression spring, the spring force is correspondingly lower than in Figure 1 Consequently, the pressure relief valve opens even at a lower hydraulic pressure. The length of the spring travel depends on the position of the piston 112. This position adjusts itself according to the geometry of the workpiece 130.

[0035] Figure 3A corresponding force-displacement diagram 201 is shown. The force is plotted on the vertical axis 203 and the maximum stroke length on the horizontal axis 202. It can be seen that the force is constant in the region 204. This is because the maximum pressure in this region is controlled by the fixed pressure relief valve in the pump housing. The pressure relief valve in the piston rod only triggers after this stroke length is exceeded, since below this stroke length, the spring force and the associated fluid pressure required to trigger the pressure relief valve are higher than the fluid pressure possible through the first pressure relief valve. When the stroke length exceeds 204, the pressure relief valve 113 in the piston rod then controls the hydraulic pressure within the hydraulic cylinder and thus the force supplied to the tool head. The maximum force is achieved up to a stroke length of 204.In the stroke length 202, the maximum force decreases by the amount 206 to the amount 207. The displacement-force point 208 represents the workpiece 131 with its geometric dimensions within the force-displacement diagram. It should also be mentioned here that the force decreases continuously and steplessly during, for example, a forming process, depending on the current diameter of the workpiece.

[0036] Figure 4 shows another schematic view of a hydraulic tool 300. Unlike the one in Figure 2 In the illustration shown, workpiece 331 is larger than workpiece 131. The piston 312 is located in a central position within the hydraulic cylinder 311.

[0037] Figure 5 shows a Figure 4 corresponding force-displacement diagram 401. In contrast to Figure 3In this case, the path-force point 408, which corresponds to the workpiece 331, is also located in the middle area of ​​the force-path diagram. Reference sign

[0038] 10, 100, 300 Hydraulic tool 11, 311 Hydraulic cylinder 12, 112, 312 Piston 13, 113 Pressure relief valve piston 14, 114 Spring 16 Spring 17, 117 Tool head 18 Interface 19, 119 Channel structure element 20 Shoulder 26 Inlet interface hydraulic cylinder 27 Outlet interface hydraulic cylinder 27A Fixed pressure relief valve in pump housing 29 Piston rod 30 Pump housing 121 Internal area hydraulic cylinder 122 Inlet interface piston 123 Hollow chamber 125 Outlet interface 128 Internal area piston 130 Counter stop 131, 331 Workpiece 201, 401 Force path diagram 202 Horizontal axis; Path axis 203 Vertical axis; Force axis 204, 205 Stroke 206, 207 Force range 208, 408 Path-Force-Point

Claims

1. Hydraulic tool (10, 100, 300), comprising: hydraulic cylinder (11, 311); piston (12, 112, 312) with a piston rod (29); position-dependent pressure relief valve (13, 113) for setting a hydraulic pressure within the hydraulic cylinder (11, 311) depending on a position of the piston (12, 112, 312) within the hydraulic cylinder (11, 311); wherein the position-dependent pressure relief valve (13, 113) is configured to provide a continuously adjustable force depending on the position of the piston (12, 112, 312) within the hydraulic cylinder (11, 311).

2. Hydraulic tool (10, 100, 300) according to claim 1, wherein the position-dependent pressure relief valve (13, 113) includes a spring (14) that changes its spring travel depending on the position of the piston (12, 112, 312), so that the spring force acting on the position-dependent pressure relief valve (13, 113) varies according to the position of the piston (12, 112, 312).

3. Hydraulic tool (10, 100, 300) according to claim 2, wherein the spring (14) is pretensioned.

4. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the position-dependent pressure relief valve (13, 113) is arranged in the piston (12, 112, 312) and / or in the piston rod (29).

5. Hydraulic tool (10, 100, 300) according to one of the preceding claims, wherein the position-dependent pressure relief valve (13, 113) is arranged at an interface to an outlet of the hydraulic cylinder (11, 311) and wherein the spring (14) is arranged at least partially inside the piston (12, 112, 312) and / or the piston rod (29).

6. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the piston (12, 112, 312) has a hollow chamber (123) that is in fluidic communication with an interior of the hydraulic cylinder (11, 311), so that hydraulic fluid can flow from the interior of the hydraulic cylinder (11, 311) into the hollow chamber (123).

7. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, further comprising a channel structure element (19, 119), which is configured to fluidically connect the position-dependent pressure relief valve (13, 113) with an outlet port (27), wherein the outlet port (27) being arranged on the hydraulic cylinder (11, 311).

8. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the position-dependent pressure relief valve (13, 113) is a ball valve or a needle valve.

9. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the spring (14) has a variable pitch.

10. Hydraulic tool (10, 100, 300) according to one of the preceding claims, wherein the piston rod (29) has an interface (18) for the detachable attachment of a tool head (17, 117).

11. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, further comprising a tool head (17, 117), wherein the tool head (17, 117) is one of the following: pin insertion tool head, cutting tool head, pressing head.

12. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, further comprising an inlet interface (122) for the hydraulic fluid with a pressure relief valve (13, 113), wherein the inlet interface (122) is arranged on the hydraulic cylinder (11, 311).

13. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the piston (12, 112, 312) and the piston rod (29) are formed as a single integral piece.

14. Hydraulic tool (10, 100, 300) according to any one of the preceding claims, wherein the hydraulic tool is a hand tool.

15. Use of a tool head in a hydraulic tool (10, 100, 300) according to any one of claims 1 to 14.

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