EP2956678B1 - Working cylinder having pressure medium flow transfer - Google Patents

Description

The invention relates to a double-acting hydraulic working cylinder with a pressure medium overflow between the working spaces, preferably in the end positions of the piston.

In certain applications of working cylinders, such as master-slave systems, hydraulically actuated switches or in conjunction with hydraulic accumulators, it is necessary to allow in one end position or both end positions of the piston pressure equalization between the work spaces, or from one pressure chamber in the other Pressure chamber to transfer pressure medium. This should be compensated, for example, leakage.

In this way it is achieved that the piston of the working cylinder can always go to the end position and that its function and the function of the connected means, such as a hydraulic accumulator is ensured.

From the prior art valve systems are arranged for pressure equalization between the working spaces in the end positions in pistons or piston rods of working cylinders, which usually have biased with springs valve body with a plunger. In the respective end position of the piston, the corresponding valve is opened by the plunger in contact with the inside of a closure part of the cylinder tube opens the valve and the pressure medium flows from one to the other working space.

A generic working piston-cylinder unit is from the document DE 30 13 381 C2 out. In the working piston in this case two operable by plunger valves are arranged, which are opened in each case shortly before the respective end stop of the piston on a closure part of the cylinder tube to connect the working space with the return port to prevent damage to the components.

From the publication DE 83 24 442 U1 is the arrangement of a check valve in the piston and an inner connecting line in the piston and the piston rod of a double-acting piston-cylinder unit for pressure equalization with a hydraulic accumulator out. The hydraulic accumulator charge and the pressure medium loss compensation between the piston and piston rod chamber takes place in the retracted end position of the piston when subjected to a pressure medium via the main port of the working cylinder.

In the publication DE 12 79 908 A is a double-acting hydraulic lifting cylinder with both sides of the piston protruding valve spindles known. The valve spindles are unequal in length, whereby upon reaching the respective end position of the piston, a two-stage pressure equalization between the working spaces takes place.

Another arrangement of a controlled by plunger valve in the piston of a working cylinder is in the document DE 2 245 129 A disclosed. In the vicinity of the end positions of the piston of the respective plunger opens in contact with the inner wall of the closure member, the valve, both working chambers of the working cylinder are interconnected, whereby the overflow of the pressure medium, the pressure equalization takes place.

The publication DE 10 2005 008 070 A1 has a hydraulic cylinder for the object whose piston has a valve arrangement for pressure equalization between the working spaces. The valves are also opened in the vicinity of the end positions of the piston by means of plungers, so that pressure medium can flow over between the working spaces of the hydraulic cylinder.

Another working cylinder is from the document SE 441 117 B known.

All said valve assemblies in the piston of a working cylinder have symmetrically designed valve assemblies that lift with the help of plungers shortly before reaching the respective end position of the piston biased with springs valve body from the seat, a connection between the work spaces is prepared and for pressure equalization, an overflow of the pressure medium takes place.

The design-related effort and the relatively small cross-section to the overflow of the pressure medium as well as existing by the spatial conditions in the piston installation space of the valve components limit the potential application of the solutions described.

The object of the invention is to develop a structurally favorable solution for a definable pressure medium overflow between the working spaces of a double-acting hydraulic working cylinder in definable positions, in particular in the end positions of the piston.

The object is achieved by a cylinder with the features listed in claim 1 and, alternatively, by a cylinder with the features listed in claim 2. Preferred developments emerge from the subclaims.

An inventive cylinder according to claim 1 allows a pressure medium flow between the working spaces in both directions.

An inventive cylinder according to claim 2 with Druckmediumüberströmung between the working spaces has a cylinder tube with connections for supplying and discharging a pressure medium, a bottom closure part, a guide closure part, two working spaces, a piston rod which is guided in the guide closure part, a piston which is connected to the piston rod connected and guided in the cylinder tube and separates by means of seals two working spaces in the cylinder tube.

The working cylinder according to the invention is characterized in that the piston has a first side plate and a second side plate and a central portion between the first and second side plate and a first and a second annular elastic seal, wherein the first Seal on the first side plate is arranged axially in the direction of the second side plate and is supported on one side by the first side plate, while the second seal on the second side plate is arranged axially in the direction of the first side plate and is supported on one side by the second side plate. The annular space enclosed axially between the two seals and radially between the middle section of the piston and the cylinder tube wall is referred to below as the piston center space.

Each of the seals is deformed differently depending on the direction of the pressurization and thus has a different sealing behavior depending on the direction of the pressure gradient.

When pressure is applied from the middle section, that is, when there is a higher pressure of the pressure medium in the piston middle space than in the working space separated by the respective seal, the elastic deformability of the seal is limited by the respective side window. The side plate facing axial edge of the elastic annular seal is supported by the side window. The seal behaves sealingly even at high pressure drops in this direction.

When pressurizing in the direction of the central portion, ie at a higher pressure in the working space than in the piston center space, the seal deforms by the pressure-related force application to the axial edge of the elastic annular seal towards the central portion. In this case, a gap is formed between the cylinder surface facing the radial surface of the seal and the Zylinderrohrinnenwandung. About this gap a cross section is opened, which allows a pressure medium transfer on the working space in the piston central space and thus a pressure compensation. The height of the pressure gradient between the working space and the piston center space, from which a pressure fluid transfer occurs, can be adjusted by the geometry and the material properties of the relevant elastic seal application.

Each of the seals thus behaves like a valve, the opening direction and closing direction of both seals being opposite to each other. If, for example, a higher pressure prevails in the first working space than in the second working space, the seal facing the first working space allows pressure medium to pass into the piston center space, while the seal facing the second working space is supported by the second side disk and behaves in a sealing manner and no pressure medium passage between the piston central space and the second working space permits. As a result, there is no pressure medium transfer from the first working space into the second working space.

The cylinder tube has a first and a second recess, wherein the first recess is arranged axially so that the first seal is positioned in a first end position of the piston over the first recess and by means of the first recess between the first seal and cylinder tube, a first overflow cross section opens. Similarly, the second recess is axially arranged so that the second seal is positioned in a second end position of the piston over the second recess and opens a second overflow cross section by means of the second recess between the second seal and cylinder tube. Such an overflow cross section can preferably be provided by an annular groove-like depression of the cylinder tube inner wall or a conical expansion; However, other shapes are also possible in which the cylinder tube inner wall at least in sections springs back so far that the relevant sealing ring and, if appropriate, the side window assigned to this sealing ring no longer bears completely against the cylinder tube inner wall.

In an overflow position, shown on the example of a first end position, so that the sealing of the first seal between the piston central space and the first working space, so the working space with the lower pressure, repealed. The pressure medium can flow from the piston center space via the first overflow cross section into the first working space. In order to the pressure in the piston central space drops to the pressure of the first working chamber. As a result, elastic deformation of the second seal toward the center portion occurs; the second seal opens and there is a resulting overflow from the second working space via the gap between the second seal and cylinder tube inner wall in the piston central space and from there via the first overflow cross section in the first working space. The overcurrent can take place until, for example, leakage losses from the pressure medium system assigned to the first working space are compensated for and pressure equalization is again established. The operation in the second end position is corresponding. The end position in the sense of an overflow position can also be understood to be a different position than corresponds to the stroke end position predetermined by the cylinder. This may be the case, for example, when the means driven by the working cylinder do not permit movement of the piston all the way in the cylinder tube or require overflow at another position.

The simple design of the piston has a particularly advantageous effect, since it has no additional mechanically moving components which require special machining of the piston and assembly work. It is achieved an overflow in both directions between the working spaces, wherein the overflow direction is determined by the piston position.

With the elastic annular seals the function of pressure equalization between the work spaces is realized in a simple and reliable manner. In addition, a cylinder according to the invention operated as a particular advantage trouble-prone and easy to maintain. Furthermore, by choosing the geometry and the material properties of the seals, a desired pressure gradient, from which a pressure medium occurs, can also be adjusted without problems for each of the two overflow layers.

An alternative inventive working cylinder according to claim 2 allows a pressure medium flow between the work spaces in only one direction.

Such a cylinder initially has the same features and the same operation as a working cylinder according to claim 1, so that here is the description to claim 1, wherein the following differences exist. The cylinder tube only has to have a recess. This recess corresponds to the second recess according to claim 1. Furthermore, only one of the two seals must be formed as a first annular elastic seal, which is supported on one side by a first side window. The positioning of the recess defines an overflow position. In the overflow position, the second seal in height of the recess, so that over an overflow cross section corresponding to the second overflow cross section according to claim 1, pressure medium from the piston central space can pass into the separated by the second seal working space, which at the same time takes place a pressure compensation. This creates a pressure gradient between the working space, which is separated by the first elastic annular seal of the piston central space and the piston central space, whereby the elastic annular seal is deformed to form a gap, and pressure medium from this working space in the piston central space and from there via the overflow cross section into the other workspace.

The overflow layer is preferably positioned in an end position, but can also be positioned in other cases at a different axial location, if on the way of the piston stroke, for example, depending on a particular piston position, an overflow possible, but excluded in an end position.

Since an overflow in the alternative solution according to claim 2 should be possible only in one direction, the second seal can be formed without the special features of the elastic deformability in connection with the one-sided support and the valve effect achieved thereby.

In an advantageous development, the pressure medium overflow in an overflow position is limited by at least one additional throttle. In a particularly advantageous manner, the throttle is provided with very simple and interference-insensitive means in that an annular gap with a desired cross-section is provided by a suitable adaptation of the diameter of a side window to the inner diameter of the cylinder tube inner wall of the cylinder tube. The width of the annular gap is dimensioned according to the required overflow of the pressure medium between the work spaces for the particular application. If the piston is in an overflow position, an overflow limitation is brought about by the annular gap between the cylinder tube inner wall and the side window, which is not positioned above the recess, even at pressure drops caused by the elastic deformation of the elastic annular seal associated with this side disc with a larger cross-section and thus would lead to a larger Druckmediumübertritt per unit time. In addition to the regulation of the overflow volume, as a further advantage, the elastic annular seals are also protected against high loads.

Preferably, both side windows are formed so that each a throttle is provided. Thus, one throttle in each end position becomes active. Depending on the requirements, different throttle values in the two end positions can be defined as a particular advantage in this way.

In an advantageous development related to a working cylinder according to claim 2 with unidirectional overflow, the development described above according to claim 3, a throttle, which is formed by an annular gap between the first side window and the cylinder tube inner wall.

It has the central portion of the piston parallel to the vertical center axis of two spaced-apart annular grooves, between which in a advantageous development a circumferential collar is arranged with double-sided shoulder.

In this way, elastic annular seals are held securely and significantly reduces notch stresses during deformation of the seals for pressure equalization, whereby their long service life is guaranteed.

It is integrally formed on the side windows in the outer region of an annular collar. This collar allows reliable reception of the annular elastic seals without the need for additional fasteners.

The elastic annular seals have a T-shaped cross-section.

With the T-shaped cross-section of the elastic annular seals secure capture between the annular grooves in the central portion and the annular collar of the respective side window is guaranteed, so that their position in the deformation and the lifting of the inner shell of the working cylinder to overflow the pressure medium during pressure equalization between the workspaces can not change.

Relative to a working cylinder according to claim 2 with unidirectional overflow, the first annular seal on a T-shaped cross-section with the advantages described above.

Fig. 1

Schnitt eines Arbeitszylinders

Fig. 2

Schnitt eines Mittelabschnitts des Kolbens

Fig. 3

Schnitt einer elastischen kreisringförmigen Dichtung

näher erläutert.The invention will be described as an embodiment with reference to

Fig. 1

Cut a working cylinder

Fig. 2

Section of a middle section of the piston

Fig. 3

Section of an elastic annular seal

explained in more detail.

To Fig. 1 a double-acting cylinder has a cylinder tube 1 with a first port 2 and second port 3 for supplying and discharging a pressure medium, a bottom closure part 4, a guide closure part 5, a piston rod 6, guided in a bore 7 with seals 8 in the guide closure part 5 and a piston 9, taken from the piston rod 6, which is guided in the cylinder tube 1 and the working spaces in the cylinder tube 1 separates.

The piston 9 consists of a first side window 10 and a second side window 11 and a middle section 12.

Between the central portion 12 and the side windows 10; 11 is a respective first annular elastic seal 13 and a second annular elastic seal 14 is added.

The side windows 10; 11 have a diameter that is so far reduced compared to the inner diameter of the cylinder tube 1 that between a cylinder tube inner wall 15 of the cylinder tube 1 and the circumference of the side windows 10; 11, an annular gap 16 is formed whose width is dimensioned according to the required overflow of the pressure medium for pressure equalization between the working spaces, between the respective pressure-carrying piston chamber 17 or piston rod chamber 18 and the piston rod chamber 18 or the piston chamber 17, for the particular application.

The maximum outer diameter of the central portion 12 is at most equal to that of the side windows 10; 11th

On the side windows 10; 11 is an annular collar 19.1 in the outer region; 19.2 molded.

In the cylinder tube 1 are in the region of the end positions of the piston 9, a first recess 20 and second recess 21, in cooperation with the respective Side window 10; 11, the respective annular elastic seal 13; 14 and the central portion 12 form an overflow cross section for overflow of the pressure medium from the respective pressurized working space in the other working space in the end position of the piston 9.

The in Fig. 2 Sectionally sectioned central portion 12 of the piston 9 has parallel to the vertical center axis 22 a circumferential collar 23 with double-sided shoulder 24 and a first annular groove 25 and a second annular groove 26. The annular elastic seals 13; 14 are like in Fig. 3 shown enlarged in section, T-shaped.

Between the first side window 10 and the central portion 12, the first annular elastic seal 13 and between the central portion 12 and the second side window 11, the second annular elastic seal 14 by means of the respective annular collar 19.1; 19.2 on the side windows 10; 11 in cooperation with the respective annular groove 25; 26 held securely at the central portion 12 due to the T-shaped configuration.

When deforming the annular elastic seals 13; 14 notch stresses occurring in the region of the middle section 12 for pressure compensation are substantially reduced by means of the respective associated side of the shoulder 24 on both sides, so that their long service life is ensured.

When pressurizing the piston rod chamber 18 with the pressure medium of the piston 1 in the Fig. 1 shown end position, such as that of a master cylinder in a master-slave system reach.

The pressure medium previously located in the piston chamber 17 previously flowed via the second port 3 into the slave working cylinder. Due to leakage during operation of the system, the slave cylinder is not fully extended, so that pressure fluid must track and pressure equalization must be done.

The voltage applied in the piston rod space pressure of the pressure medium deforms the first annular elastic seal 13 in the direction of the facing side of the two-sided shoulder 24 at the central portion 12 so that the first annular elastic seal 13 lifts from the Zylinderrohrinnenwandung 15 of the cylinder tube 1 and forms a gap, and the pressure medium via the annular gap 16 between the first side window 10 and the cylinder tube inner wall 15 of the cylinder tube 1, said gap, the piston central space 27 in the region of the central portion 12 and the overflow cross section at the second recess 21 in the piston chamber 17 and further via the second port 3 flows to the slave cylinder and this extends completely.

The second annular elastic seal 14 and the second side plate 11 of the piston 9 are located in a position in the region of the second recess 21, so that a free space for overflow of the pressure medium is formed.

An analogous operation of the device for pressure equalization between the working chambers of the working cylinder is also in pressurization of the piston chamber 17 before.

In the end position of the piston 9 is each leading in the direction of movement elastic annular seal 13; 14 in the region of the recess 20; 21 in the cylinder tube 1, whereby there is a free passage in this area.

The pressure equalization between the working chambers of the working cylinder is then carried out by the located in the closed region of the cylinder tube inner wall 15 of the cylinder tube 1 elastic annular seal 13; 14 is deformed elastically on the circumference by the pressure of the pressure medium in the pressurized working space in the direction of the non-pressurized working space, whereby it is lifted from the inner shell 14 and the pressure medium, as described above, flows over.

In another embodiment, as it corresponds to claim 2, a working cylinder has a Überströmungsmöglichkeit only in one direction on. Such a working cylinder substantially corresponds initially to the embodiment shown in Figure 1, although only the second recess 21 is formed. If the piston is in the end position on the bottom closure part 4, the pressure medium from the piston rod space 18 can deform the first annular elastic seal 13 so that it forms a gap to the cylinder tube inner wall 15, with which the pressure medium can pass into the piston middle space 27. From the piston middle space 27, the pressure medium passes over the overflow cross section between the second seal, which in the FIG. 1 as the second annular elastic seal 14 is shown, but deviating from the illustration may also be formed as a normal seal without special deformation properties, and the cylinder tube 1 in the region of the second recess 21 in the piston chamber 17 via. In the opposite direction, ie from the piston chamber 17 into the piston rod chamber 18, no pressure medium can occur.

Used reference signs

1

cylinder tube

2

first connection

3

second connection

4

Bottom seal section

5

Guide closure part

6

piston rod

7

drilling

8th

seals

9

piston

10

first side window

11

second side window

12

midsection

13

first annular elastic seal

14

second annular elastic seal

15

Zylinderrohrinnenwandung

16

annular gap

17

piston chamber

18

Piston rod space

19

circular collar (19.1; 19.2)

20

first recess

21

second recess

22

vertical center axis

23

circumferential collar

24

double-sided shoulder

25

first ring groove

26

second annular groove

27

Piston means space

Claims (5)

1. A working cylinder, comprising a cylinder tube (1) with connections for leading in and out a pressurising medium, a bottom-closure element (4), a guide-closure element (5), two working chambers, a piston rod (6) being guided in the guide-closure element (5), a piston (9) with seals which is connected to the piston rod (6) and guided in the cylinder tube (1) and separates the working chambers in the cylinder tube (1), characterized in that the piston (9) comprises a first side plate (10) and a second side plate (11), each of them being provided with a circular ring-shaped collar (19.1; 19.2) integrally formed in their outer section,(12), as well as a centre section (12) arranged between the first and second side plates (10; 11), as well as a first and a second circular ring-shaped elastic seal (13, 14), wherein the centre section (12) of the piston (9) has a first annular groove (25) and a second annular groove (26) provided parallel to the vertical axis (22) of the piston (9), wherein the circular ring-shaped elastic seals (13; 14) have a T-shaped cross section, wherein the first circular ring-shaped elastic seal (13) at the first side plate (10) is arranged axially towards the second side plate (11) and is held by the circular ring-shaped collar (19.1) of the first side plate (10) and the first annular groove (25) of the centre section (12) due to the T-shaped design and is unilaterally supported by the second side plate (11), wherein each of the circular ring-shaped elastic seals (13; 14) can be elastically deformed with formation of a gap to the inner cylinder tube wall (15) if pressure is applied towards the centre section (12), and wherein the elastic deformability of the circular ring-shaped elastic seal (13; 14) is limited by the corresponding side plate (10; 11) if pressure is applied towards the opposite direction and the circular ring-shaped elastic seal (13; 14) is sealing,
   that the cylinder tube (1) comprises a first and a second recess (20; 21), wherein the first recess (20) is axially arranged such that exclusively the first circular ring-shaped elastic seal (13) is positioned above the first recess (20) in a first end position of the piston (9) and a first overflow cross section opens by the first recess (20) between the first circular ring-shaped elastic seal (13) and the cylinder tube (1), wherein the second recess (21) is axially arranged such that exclusively the second circular ring-shaped elastic seal (14) is positioned above the second recess (21) in a second end position of the piston (9) and a second overflow cross section opens by means of the second recess (21) between the second circular ring-shaped elastic seal (14) and the cylinder tube (1).
2. A working cylinder, comprising a cylinder tube (1) with connections for leading in and out a pressurising medium, a bottom-closure element (4), a guide-closure element (5), two working chambers, a piston rod (6) being guided in the guide-closure element (5), a piston (9) with seals which is connected to the piston rod (6) and guided in the cylinder tube (1) and separates the working chambers in the cylinder tube (1), characterized in that the piston (9) comprises a first side plate (10), which has a circular ring-shaped collar (19.1) in the outer section, and a first circular ring-shaped elastic seal (13; 14), a centre section (12) and a second seal, wherein the centre section (12) of the piston (9) has a first annular groove (25) parallel to the vertical centre axis (22) of the piston (9), wherein the first circular ring-shaped elastic seal (13) has a T-shaped cross section, wherein the first circular ring-shaped elastic seal (13) is arranged at the first side plate (10) axially towards the second seal and is supported by the circular ring-shaped collar (19.1) of the first side plate (10) and the annular groove (25) of the centre section (12) due to the T-shaped design and unilaterally by the first side plate (10), and wherein the centre section is arranged between the first side plate and the second seal, and wherein the first circular ring-shaped elastic seal (13; 14) can be elastically deformed with formation of a gap to the inner cylinder tube wall (15) if pressure is applied towards the centre section (12), and wherein the elastic deformability of the first circular ring-shaped elastic seal (13; 14) is limited by the first side plate (10; 11) if pressure is applied towards the opposite direction, and the first circular ring-shaped elastic seal (13; 14) is sealing,
   that the cylinder tube (1) has a recess (21), wherein the recess (21) is axially arranged such that exclusively the second seal is positioned above the recess (21) in an overflow position of the piston (9) and an overflow cross section opens by the recess (21) between the second seal and the cylinder tube (1).
3. The working cylinder according to claim 1, characterized in that the piston (9) comprises at least one pressurising medium restrictor, wherein the pressurising medium restrictor is formed by an annular gap (16) between the inner cylinder tube wall (15) of the cylinder tube (1) and the circumference of one of the side plates (10; 11).
4. The working cylinder according to claim 2, characterized in that the piston (9) comprises a pressurising medium restrictor, wherein the pressurising medium restrictor is formed by an annular gap (16) between the inner cylinder tube wall (15) of the cylinder tube (1) and the circumference of the first side plate (10).
5. The working cylinder according to claim 1 or 3, characterized in that a circumferential collar (23) with shoulder on both sides (24) is arranged at the centre section (12) of the piston (9) parallel to its vertical centre axis (22) between the two annular grooves (25; 26) spaced apart from each other.

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