Hydraulic cylinder

Abstract

A hydraulic cylinder comprising a cylinder, a piston element movably guided in the cylinder in a working direction and comprising an active surface, and a first opening for feeding a fluid into a cylinder chamber by the active surface. A working pressure of the fluid acting on the active surface drives the piston element in the working direction. The active surface includes a first partial surface and at least one second partial surface, the cylinder chamber being divided into a first sub chamber with the first opening by the first active surface and a second partial surface with a second opening by the second partial surface, and the partial surfaces are hydraulically separated from each other at least in a selectable operating mode.

Claims

1. A hydraulic cylinder, comprising: a cylinder, a piston element movably guided in the cylinder in a working direction W and having an active surface, and a first opening for feeding a fluid into a cylinder chamber by way of the active surface, wherein a working pressure of the fluid acting on the active surface drives the piston element in the working direction, in that the active surface has a first partial surface and at least one second partial surface, wherein the cylinder chamber is divided into a first partial chamber with the first opening by the first active surface as well as a second partial chamber with a second opening by the second partial surface, and wherein the partial chambers are hydraulically separated from each other at least in a selectable operating mode, wherein on one of the piston element or cylinder, a cylindrical step protrudes parallel to the working direction for separating the partial chambers.

2. The hydraulic cylinder as claimed in claim 1, wherein a ratio of the sizes of the partial surfaces is asymmetrical and lies between 45:55 and 20:80.

3. The hydraulic cylinder as claimed in claim 1, wherein the partial chambers extend concentrically about a center axis of the cylinder.

4. The hydraulic cylinder as claimed in claim 1, wherein the partial chambers are connected to a hydraulic pump unit and a valve assembly, wherein the valve assembly enables the partial chambers to admit fluid in at least two operating modes.

5. The hydraulic cylinder as claimed in claim 4, wherein, in a first of the operating modes a rapid advancement of the piston element is present under reduced piston force, while in a second of the operating modes, a slow advancement of the piston element is present under high piston force, and wherein the operating modes are realized by different admission of fluid under working pressure to the partial chambers.

6. The hydraulic cylinder as claimed in claim 4, wherein the valve assembly comprises a control valve with a pilot piston which is movable in the working direction.

7. The hydraulic cylinder as claimed in claim 4, wherein one of the partial chambers can be connected by the valve assembly to a hydraulic reservoir, especially one that is pressure-free.

8. The hydraulic cylinder as claimed in claim 4, wherein at least one of the partial chambers, especially both partial chambers, can be subjected to the fluid by means of a valve downstream from the partial chamber.

9. The hydraulic cylinder as claimed in claim 1, wherein the hydraulic cylinder comprises a resetting active surface, wherein the piston element can be reset opposite to the working direction by admitting the fluid to the resetting active surface.

10. The hydraulic cylinder as claimed in claim 1, wherein the entire active surface of the piston element amounts to at least 1000 cm.sup.2.

11. The hydraulic cylinder as claimed in claim 1, wherein three or more hydraulically separable partial chambers are provided with their associated partial surfaces of the piston element in each case.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the invention shall be described and explained with the aid of the accompanying drawings.

(2) FIG. 1 shows a sectional view of a hydraulic cylinder of a forming machine according to the invention in a first exemplary embodiment of the invention.

(3) FIG. 2 shows the hydraulic cylinder of FIG. 1 in another operating mode.

(4) FIG. 3 shows a sectional view of a hydraulic cylinder of a forming machine according to the invention in a second exemplary embodiment of the invention.

DETAILED DESCRIPTION

(5) The hydraulic cylinder 1 according to the invention as shown in FIG. 1 comprises a cylinder 2, in which a piston element is guided in linear displacement along a working direction W.

(6) The piston element 3 has a cylindrical step 3a, which protrudes into a corresponding shoulder of the cylinder 2. In this way, a first partial chamber 4 is hydraulically defined by means of a first partial surface 5 of an active surface of the piston element 3. The first partial chamber has substantially the shape of a solid cylinder.

(7) The first partial chamber 4 is hydraulically separated by the step 3a from a second partial chamber 6 by means of a second partial surface 7 of the active surface of the piston element 3. The second partial chamber 6 has substantially the shape of an annular cylinder.

(8) The partial chambers 4, 6 together form a cylinder chamber of the cylinder 2. The active surface of the piston element 3 is the sum of the partial surfaces 5, 7. The size of the partial chambers 4, 6 varies according to the instantaneous position of the piston element 3 in the cylinder 2.

(9) Each of the partial chambers 4, 6 has a respective opening 4a, 6a, through which a hydraulic fluid can flow into the partial chamber 4, 6. The openings 4a, 6a are connected by hydraulic lines 8 to a valve assembly 9 and a hydraulic pump unit (not shown). A flow direction of the fluid when subjected to working pressure by the pump unit is indicated as arrow P.

(10) The partial chambers 4, 6 are hydraulically separated from each other, according to the preceding remarks, but they can also be hydraulically joined together as needed, depending on the design of the valve assembly 9.

(11) In the present instance, the valve assembly 9 comprises, starting from the pump unit, a first branch 10, a first valve 11 located after this, and a second branch 12 located after this. The first branch 10 leads to the first partial chamber 4, so that, in the present example, this branch is permanently subjected to the fluid under working pressure by the pump unit.

(12) The second branch 12 leads, on the one hand, to the second partial chamber 6 and, on the other hand, to a reservoir 13, which can be blocked by a second valve 14 between the second branch 12 and the reservoir 13. The reservoir is filled with fluid substantially under atmospheric pressure.

(13) A drain 15 of the first partial chamber 4 leads to a sump and/or back to a suction side of the pump unit. The drain 15 can be closed in a controllable manner by a pilot piston 16 that can be driven to move in the working direction W, so that the pilot piston 16 with the drain 15 forms a control valve of the valve assembly 9. In the present case, the position of the piston element 3 in the working direction is adjusted by way of the pilot piston 16. In the present case, the pilot piston 16 is likewise hydraulically driven, but may also have an electric motor or some other drive, depending on the requirements in each case.

(14) Furthermore, for the dynamic changing of the position of the piston element 3 in both directions, a significantly smaller resetting force presses against the piston element 3 in a resetting chamber 18 via a resetting active surface 17.

(15) The resetting active surface 17 is likewise subjected to fluid under working pressure. The working pressure of the fluid here, by contrast with the two partial chambers, does not act in the working direction, but in the opposite direction.

(16) The functional principle of the pilot piston is also presented in detail in DE 198 46 348 A1.

(17) Now, embodiments of the invention functions as follows:

(18) In a first operating mode, the first valve 10 is closed and the second valve 14 is opened. In this way, only the first partial chamber 4 is supplied with fluid under working pressure by the pump unit. The second partial chamber is connected via the second valve to the reservoir 13. This ensures a continual filling with fluid under atmospheric pressure or slightly higher pressure to improve the flow velocity.

(19) Under these conditions, a maximum force of the piston element 3 is reduced, while at the same time a rapid piston movement is attained for a given volume flow through the pump unit.

(20) In a second operating mode, the first valve 10 is opened and the second valve 14 is closed. In this way, the reservoir 13 is no longer in communication with the cylinder 2, and the two partial chambers 4, 6 are hydraulically connected in parallel.

(21) This corresponds to the operation of a traditional hydraulic cylinder, whose working chamber amounts to the sum of the partial chambers 4, 6 and whose active surface amounts to the sum of the partial surfaces 5, 7. In this way, a greater maximum force of the piston element 3 is achieved as compared to the first operating mode, while the speed of the piston movement is slower for the same volume flow of the fluid.

(22) In a second embodiment of the invention according to FIG. 3, a simplified valve assembly 9 with no pilot piston 16 is chosen. Functionally identical components are given the same reference numbers as in the first example.

(23) The piston element 3 is shown hatched in the schematic drawing. A protruding cylindrical step 2a in this example is formed as part of the cylinder 2, so that the piston element substantially has a cup shape. This choice of configuration is independent of the design of the valve assembly 9.

(24) In the present case, the valve assembly 9 has a first branch 19, which leads to the first partial chamber 4. Downstream from the branch 19 is located a valve 20.

(25) The second partial chamber 6 and the resetting chamber 18 are directly supplied with fluid and have outlets 21, 22. Behind the outlets 21, 22, respective valves 23, 24 are situated.

(26) As can be recognized, one of the partial chambers 4, 6 or the resetting chamber 18 is subjected to fluid under working pressure precisely when its associated valve 20, 23, 24 is closed.

(27) In the case of the opening of the respective valve 20, 23, 24, the fluid flows in a circuit without building up pressure. Accordingly, the three feed lines P are each separately pressurized and not switched in parallel with each other. This can be achieved, for example, by separate hydraulic pumps.

(28) The operating modes of the hydraulic cylinder according to the second example are entirely analogous to those of the first example. In the second example, furthermore, it is easily possible to select which of the partial chambers 4, 6 will be subjected individually to working pressure. In this way, the operation can be chosen to be even more flexible, for example, when the partial surfaces are designed with different sizes.

(29) In the present instance, a hydraulic cylinder 1 according to one of the above described operating modes is designed as part of a forming machine in the form of a radial forging press (not shown). The sum of the active surfaces, corresponding to the total cross-sectional area of the cylinder chamber of the cylinder 2, amounts to around 25,000 cm. The working pressure of the fluid is around 400 bars. The size ratio of the two partial surfaces 5, 7 is approximately 50:50.

(30) The forming machine comprises four tools working in pairs against each other in a cross pattern, each of the tools being driven by a hydraulic cylinder 1, as described above.

(31) In keeping with the above-described operating modes of the hydraulic cylinder 1, the following operating modes of the forming machine or forging press are supported: Smoothing: This operation requires rapid tool strokes at high frequency, while the maximum force should be smaller in design, thanks to a smaller forming stroke. Accordingly, the hydraulic cylinders 1 are used in the first of the above-described operating modes. Forging: This operation requires slow tool strokes of low and medium frequency, while the maximum force must be large on the basis of a high forming stroke. Accordingly, the hydraulic cylinders 1 are used in the second of the above-described operating modes.

(32) Furthermore, it may be provided that, during the forging, a switching between the operating modes is carried out as needed, in order to move the tools rapidly over longer distances when no forming is being carried out. This may happen, for example, in the course of advancing a workpiece and it allows overall an acceleration of the forging process.