EP0151650A2 - Piston-cylinder assembly - Google Patents

Abstract

A double action piston/cylinder unit has a piston guided in a cylinder and attached to a piston rod, the piston to be charged with a pressure agent, particularly hydraulic fluid at a first end face, the hydraulic fluid to be conducted in a controlled manner into the cylinder via a first fitting disposed at an end section of the cylinder and is to be charged at its other, second end face with a pressure agent which is located in an annular chamber formed by a central section of the piston rod and the inner wall of the cylinder, the second end face of the piston and a cylinder end piece, the annular chamber is in communication with a pressure agent reservoir which is connected to the annular chamber via a second fitting disposed at the other end section of the cylinder. A connecting line by way of which a pressure compensation can occur when the piston is charged at its first end face is provided between the first fitting and the second fitting, the connection being interrupted when the piston is not charged by the pressure agent under pressure at its first end face.

Description

The invention relates to a double-acting piston-cylinder unit, the piston guided in the cylinder and fastened to a piston rod on its (first) end face to which a pressure medium, in particular hydraulic oil, is to be applied, which is controlled via a first connecting piece arranged on an end section of the cylinder is to be conducted into the cylinder and to be acted upon on its opposite other (second) end face with pressure medium which is located in one of a middle section of the piston rod and the inner wall of the cylinder, the second end face of the piston and a cylinder end piece formed annular chamber and is connected to a pressure medium reservoir which is connected to the annular chamber via a second connecting piece arranged at the other end section of the cylinder. - =

Such generic piston-cylinder units are usually operated hydraulically and accordingly - in accordance with the terminology customary in practice - also referred to below as a hydraulic cylinder.

_Do ppeltwirkende hydraulic cylinder had previously always two always appropriate at the end portions of the cylinder t _{e arrange} connecting piece for pressure medium, that is usually hydraulic oil, between which a connecting line with a corresponding reversing valve upstream was _hand en, with the desired depending on the _piston's t Depending _{on the} position, either the first or second piston face had to be applied. But now it is in the aforementioned control valve of the aforementioned connecting line to the second port, etc. to components that ydrozylindern terms of costs at such _{s H} are considerable already well and lead to a not inconsiderable cheaper if you can do without them. It must be added that often _ma n a second pressure medium connection for a second pressure medium line also for reasons of assembly, space constraints, etc.. not wanted, and especially not in devices to be equipped with such double-acting hydraulic cylinders, which must also be extremely inexpensive in order to be competitive.

For this reason, a piston-cylinder unit without a second connection piece (and of course without a corresponding connection line, without a correspondingly complicated control valve, etc.) was obtained and the piston rod was returned by means of an external spring. In the configuration discussed here, this spring is put under tension when the piston is pressurized. If the pressure medium is then switched off and the connecting line is released for backflow, then in such a hydraulic cylinder the spring in this extended position, under appropriate tension, ensures that the piston rod moves back into the starting position.

Now such external tension springs are highly undesirable in numerous applications. Not only are they considered dangerous by the professional associations (and therefore often require a certain encapsulation or the like, which increases the effort), but they are also not welcomed by the users, apart from the fact that such a design is quite provisional Makes an impression and is also exposed to a wide variety of interference.

For this reason, one has come to hydraulic cylinders with so-called hydraulic accumulators, that is to say the second connecting piece has been provided, as in the known design described at the outset, but is not connected to a pressure medium connecting line, but rather to a so-called hydraulic accumulator. This is a pressure described further below using the exemplary embodiment memory with a substantially closed housing, in which a membrane is arranged, on one side, which forms a closed chamber with the corresponding housing section, a pressurized gas (generally nitrogen) is arranged, while the opposite side of the membrane the remaining part of the housing having the connecting piece is connected to the connecting piece of the cylinder. If the hydraulic accumulator is pressurized with pressure medium from the hydraulic cylinder via its connecting piece, the pressure medium thus compresses the gas while deforming the membrane in its chamber and builds up a corresponding pressure which, depending on the pressure conditions prevailing at the connecting piece of the hydraulic accumulator, therefore again to the outside - ie here in the annular chambers of the hydraulic cylinder - can be released.

Such generic hydraulic cylinders with hydraulic accumulators have proven themselves in the best way, especially since the hydraulic accumulators are now manufactured in such large numbers that the unit price is relatively low. However, they still have considerable disadvantages, which lie in particular in the fact that the annular chamber and the hydraulic accumulator must first be filled with pressure medium when starting up, and above all in that due to the always present leakage losses (of hydraulic fluid) on the piston rod or / and on the piston side there is a pressure drop in the ring chamber / hydraulic accumulator system, which after a certain operating time ultimately leads to the failure of the piston-cylinder unit.

The present invention has for its object to improve the piston-cylinder unit of the type described above while avoiding the aforementioned and further disadvantages in that, despite the basically unavoidable leakage losses, there is still no pressure reduction and the piston-cylinder unit therefore despite the inevitably occurring leakage losses remain operational. It should also be possible to dispense with a separate filling process for the annular chamber and the hydraulic accumulator with pressure medium under appropriate pressure. It is also an aim that, in the event of operational malfunctions, a repair or an exchange of the piston-cylinder unit or the hydraulic accumulator can be carried out by laypersons without any risk to the person concerned. Finally, due to the embodiments according to the invention, further savings or reductions should be possible compared to the known generic design in that the piston-cylinder unit according to the invention permits the use of normal standard seals (in contrast to special seals in the known prior art of the generic type) and, moreover, not so As with the prior art, the Fal: ist places high demands on the surface qualities of the cylinder inner wall.

The solution to this problem is characterized in that between the first connecting piece and the second connecting piece the piston-cylinder unit: there is a connecting line via which pressure equalization can take place when the piston is at its first face from the pressure medium is pressurized _/ and that the connecting line is interrupted if the piston is not pressurized by the pressure medium on its first end face, that is to say the inflow and outflow line connected to the first connecting piece is "open", ie is without pressure and the pressure medium, So generally the hydraulic oil flows back in a known and customary manner, recognizable as a control or shut-off gear in the line leading to the first connecting piece of the piston-cylinder unit, only a simple ball valve or the like. needs to be present.

The connection line is preferably arranged within the cylinder, and that it _extends' in accordance with a preferred embodiment of the invention by the piston and a portion of the piston rod, it being arranged for the realization of the locking operation described above, in the connecting line a non-return valve.

In a particularly simple, robust and accordingly reliable and, moreover, also extremely inexpensive embodiment, the connecting line is designed as a (double) through-bore, which extends from the first end face of the piston to a peripheral section of the piston rod, which is always in contact with the annular chamber Connection is established.

The check valve preferably consists of a ball and a compression spring which is supported at one end on the piston rod and at its other end on the ball and this in the direction of the first end face the ball presses against a ball seat, the prestressing of the spring being able to be preferably changed, if necessary by replacing it, in order to be able to easily implement different back pressure conditions.

In order to ensure that a pressure equalization to the annular chamber and thus to the hydraulic accumulator can always result when pressure medium is applied to the first end face of the piston, as will be described in detail below, while this pressure equalization is interrupted in the other operating state, it is preferably provided that the ball, when pressurized by the pressure medium on the first end face of the piston, resiliently deforms the spring against a second ball seat, a flow path being present on the second ball seat, through which pressure medium can flow through the connecting line when the ball is in contact with the second ball seat, in the embodiment of the present invention, this flow path can be designed as at least one slot-shaped recess on the second ball seat, which always connects the sections of the connecting line which are adjacent to the second ball seat on both sides.

Preferred embodiments of the present invention are described in the subclaims.

The invention is explained below using an exemplary embodiment with reference to a drawing.

The drawing shows a double-acting piston-cylinder unit 1 according to the invention with a pressure medium accumulator 2 for hydraulic actuation, thus therefore a hydraulic cylinder with a hydraulic accumulator, the piston 6 of which is guided in the cylinder 3 and fastened to a piston rod 4 on its above and below with "first" Hydraulic oil is to be applied to the end face designated one end face 7, which is to be guided into the cylinder 3 in a controlled manner via a connecting piece 8 arranged on an end section of the cylinder 3.

It can be seen that the cylinder 3 essentially consists of a tube section 3 ', at the ends of which a cylinder end piece 9 or 10 is arranged. The cylinder end piece 9, which has a pivoting attachment 13 provided with a bore 12 and which is welded to the cylinder piece 9, is in turn welded to the pipe section 3 ′, the connecting piece 8 being located at the end of the piston-cylinder unit 1 described above .

At the opposite end, the pipe section 3 'is not permanently connected to the cylinder end piece 10 located there, in order to be able to carry out the assembly and, if necessary, disassembly of the piston rod 4 of the piston 6. Rather, the sleeve-shaped cylinder end piece 10 is provided with an external thread 14 and screwed into a corresponding internal thread, which is located at this end of the pipe section 3 '. A seal 16 is arranged between the cylinder end piece 9 and the inside of the tube section 3 'of the cylinder 3 in order to achieve the required tightness net, which is a normal standard gasket ..

Two further seals 17 are arranged at this end of the piston-cylinder unit 1 between the piston rod 4 and the inside of the cylinder end piece 10, which is circular in cross section.

At this end of the piston-cylinder unit 1 there is a second connection piece 18 for the hydraulic accumulator 2, which is screwed into the connection piece 18 with a connection 19 provided with a corresponding external thread.

The end of the piston rod 4 located at this end - like the articulation lug 13 - has a bore 21 and, as cannot be seen in the side view shown in the drawing, is provided in the center with a slot which extends from its free outer end via a Section extends in the direction of the other end of the piston rod 4, as is known per se.

The piston 6, which also has a seal 22 to the inner wall 23 of the piston 3, is also provided on its circumferential surface with a guide band 24 and has a configuration on its radial and external application side 7, which is referred to above and below as "first end face", which prevents that the first end face 7 can lay on the inside of the cylinder end piece 9 in full size without leaving a space 26. Rather, as can be seen from the drawing, it is always one Space 26 available so that a pressure can build up in this when pressure fluid under pressure is supplied via the connecting line (not shown in the drawing) to the first connecting piece 8 in the direction of arrow 27 in the room 26 (the pressure medium can pass through the connecting piece 8 through a bore 28 located in the cylinder 3 flows into the space 26).

If the piston rod 4 is to be moved from the one end position set in the drawing in the direction of arrow 29 to the left for the purpose of actuating any device, device or component (not shown in the drawing), the operator concerned opens one in the first Connection pipe 8 connecting line arranged ball valve and there is a flow of hydraulic oil in the direction of arrow 27 in the space 26, and then a force is exerted on the piston 6, which multiplies the product of the pressure built up (for example, 180 bar) corresponds to the projection surface of the first end face 7 on a plane running at right angles to the central axis 31, and this pressure causes the piston rod 4 to move in the direction of the arrow 29.

Without going into how pressure medium gets into the annular chamber 32 and how a pressure is built up in it at this point, it is assumed at this point - that is, according to the normal operating state - so that it can be determined accordingly the piston 6 with its annular second end face 33 one Pressure on the hydraulic fluid in the annular chamber 32 is exerted, so that it escapes in the direction of arrow 29 to the left via the second connecting piece 18 into the hydraulic accumulator when the piston rod 4 and the piston 6 'move, and there onto the membrane already described above presses so that the gas filling (nitrogen) on the other side of the membrane in a closed chamber is compressed accordingly.

It should also be pointed out that the area of the second end face 33 of the piston 6 is smaller than its first end face, so that in the annular chamber 32 in normal operating state when the space 26 is pressurized with pressure medium, there is a lower pressure than in the space 26.

Should or the like for the corresponding re-actuation of the device to be actuated with the piston-cylinder unit 1. a return movement against the arrow 29 take place, so the operator actuates the ball valve, not shown in the drawing, so that the connecting piece 8 and thus the space 26 no longer pressurized pressure medium is supplied. Rather, the line connecting to the first connecting piece 8 is then "open" and free of excess pressure for the backflow of hydraulic fluid. The pressure required for this is exerted by the hydraulic accumulator 2, which maintains the hydraulic fluid in the annular chamber 32 under the appropriate pressure and only has to cause it to be pushed out without considerable counterpressure during the return movement.

Now, as explained above, certain leaks at the seals 16, 17 inevitably occur in the course of operation, which would ultimately lead to failure of the piston-cylinder unit 1 in the course of operation if the leakage losses (below corresponding pressure) compensates.

In the embodiment of the invention described above and below, this takes place automatically, as does the initial filling of the annular chamber 32 or the pressure medium reservoir 2, in that a connection has been created between the first connecting piece 8 and the second connecting piece 18, via which a pressure equalization always takes place can, if the piston 6 is pressurized by the pressure medium on its first end face 7, while the connection is interrupted, if the piston 6 is not pressurized by pressure medium on its first end face 7, but the inflow line is open and that Hydraulic oil flows back. As can be seen from the drawing, this connecting line is arranged inside the cylinder 3, namely it extends through the piston 6 and a section of the piston rod 4. Both are provided with a bore 34 or 36 lying on the central axis 31, a radially extending bore 37 adjoining the axially extending bore 36, which leads to the annular chamber 32 and is connected to the latter in every piston position.

As can also be seen from the drawing, the bore 34 provided in the piston 6 widens at the end of the piston 6 facing the piston rod 4 and there forms a seat 38 for a ball 39 which can lie in the extension section 34 'of the bore 34, that is to say has a diameter which is smaller than the length of the extension section 34'. The bore 36 also has an expansion section 36 '. In this a prestressed compression spring 41 is arranged, which is therefore supported at one end on the shoulder 42, which is formed due to the expansion of the bore 36, and with its other end on the ball 39, so that it first of all holds in contact with ball seat 38.

If the space 26 is pressurized by supplying pressure medium according to the arrow 27 and the piston 6 is therefore moved to the left in the direction of the arrow 29, pressure medium can also flow into the bore 34 of the piston 6 and press the ball 39 against the action of the compression spring 41 , wherein the ball 39 comes to rest on the free end of the extension section 36 '. There, however, it does not seal the extension section 36 'and thus the bore 36, but slots 43 are provided on this "second" ball seat, at which pressurized pressure medium always passes from the bore 34 - past the ball 39 - into the bore 36 can flow.

This means that when operation starts, this process takes place first, ie in addition to the space 26 and the bores 34, 36, the annular chamber 32 is also filled with hydraulic fluid and thus also the corresponding part of the pressure medium reservoir 2 via the second connecting piece 18 until it is due to the geometric Relationships to a state of equilibrium comes when the piston rod 4 has moved completely to the left in the direction of arrow 29.

If in this position the pressure in the inflow line and thus at the first connection piece 8 is removed by actuating the ball valve (not shown), this has the consequence that the pressure prevailing in the hydraulic accumulator 2 and the annular chamber 32 does not only affect the second end face 33 of the Piston 6 affects, but via the holes 37, 36 and 36 'also on the ball 39, so that it is pressed into the position shown, in which it therefore lies close to the ball seat 38, so that the pressure medium liquid located beyond the ball 39 is therefore can flow against the arrow 27, but still (under appropriate pressure) pressure medium remains in the annular chamber 32 and in the hydraulic accumulator 2.

It can be seen that any leakage losses are automatically compensated for according to the same principle as the initial replenishment, and accordingly there is no pressure reduction in the course of the operation, which requires laborious refilling under appropriate pressure, etc.

For the same reasons, it is obvious that the piston-cylinder unit according to the invention manages with standard seals and not particularly high-quality surfaces, because the size of the leakage loss (of course within reasonable limits) in contrast to the prior art described above is completely uncritical. At the same time, however, this also results in a longer service life, since it is known that seals with low leakage losses require greater contact forces on the sealing surfaces, which in turn leads to correspondingly higher wear with a corresponding relative movement.

The piston-cylinder unit according to the invention therefore fulfills all of the tasks according to the requirements placed on it in an almost optimal manner, the measures taken for this purpose, namely the formation of the bores 34, 36 and the arrangement of the compression spring 41 and the ball 39 with extremely little effort are to be practiced, since the piston rod has already been clamped for machining purposes and therefore no additional alignment work is required to produce the bores. The assembly of the spring and the ball is obviously very simple, and there is also the fact that these additional costs are at least partly. can be compensated for by the fact that the inner wall 23 of the cylinder 3 does not have any particularly high smoothing requirements and, furthermore, because of their standard designs, the seals that are used are noticeably cheaper than the special seals that must be provided in the comparable prior art in order to prevent leakage and associated pressure drop as small as possible.

Claims (9)

1.Double-acting piston-cylinder unit, the piston of which is guided in the cylinder and fastened to a piston rod on its (first) end face with a pressure medium, in particular hydraulic oil, which is controlled by a first connection piece arranged on an end section of the cylinder Cylinder is to be guided and to be acted upon on its opposite other (second) end face with pressure medium, which is located in an annular chamber formed by a central portion of the piston rod and the inner wall of the cylinder, the second end face of the piston and a cylinder end piece and with is connected to a pressure medium accumulator which is connected to the annular chamber via a second connecting piece arranged at the other end section of the cylinder, characterized in that between the first connecting piece (8) and the second connecting piece (18) there is a connecting line - (34, 36 , 37) is available, via which e can take place in pressure compensation if the piston (6) is pressurized by the pressure medium on its first end face (7); and that the connection (34, 36, 37) is interrupted when the piston (6) on its first end face (7) is not pressurized by the pressure medium is applied. 2. Piston-cylinder unit according to claim 1, characterized in that the connecting line (34, 36,37) is arranged within the cylinder (3). 3. Piston-cylinder unit according to claim 2, characterized in that the connecting line (34, 36, 37) through the piston (6) extends from a portion of the piston rod (4). 4. Piston-cylinder unit according to claim 3, characterized in that the connecting line (34, 36, 37) is designed as a through hole which extends from the first end face (7) of the piston (6) to a peripheral portion of the piston rod ( 4), which is always connected to the annular chamber (32). 5. Piston-cylinder unit according to one or more of the preceding claims, characterized in that a check valve (38, 39, 41) is arranged in the connecting line (34, 36, 37). 6. Piston-cylinder unit according to claim 5 and one or more of claims 2 to 4, characterized in that the check valve (38, 39, 41) consists of a ball (39) and a compression spring (41) which is attached is supported at one end on the piston rod (4) and at the other end on the ball (39) and presses it in the direction of the first end face (7) of the piston (6) against a ball seat (38). 7. Piston-cylinder unit according to claim 6, characterized in that the bias of the spring (41) is variable. 8. Piston-cylinder unit according to claim 7, characterized in that the ball (39) when pressurized by the pressure medium on the first end face (7) of the piston (6) with elastic deformation of the spring (39) to a second ball seat creates a flow path (43) on the second ball seat, through which pressure medium can flow through the connecting line (34, 36, 37) when the ball (39) rests on the second ball seat. 9. Piston-cylinder unit according to claim 8, characterized in that the flow path is formed as at least one slot-shaped recess (43) on the second ball seat, which the mutually adjacent to the second ball seat portions (34 ', 36') of the connecting line (34, 36, 37) always connects.

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