EP1295042A1

EP1295042A1 - Lifting device

Info

Publication number: EP1295042A1
Application number: EP01951615A
Authority: EP
Inventors: Klaus Brugger
Original assignee: Individual
Current assignee: Brugger Georg Maximilian En Brugger Christina
Priority date: 2000-06-21
Filing date: 2001-06-20
Publication date: 2003-03-26
Anticipated expiration: 2021-06-20
Also published as: ES2215917T3; EP1295042B1; AU2001272496A1; DE50101629D1; DK1295042T3; WO2001098671A1; DE10030545A1; ATE261068T1; EP1295042B8; PT1295042E; TR200401212T4

Abstract

The invention relates to a lifting device comprising a cylinder (102) with a cavity (104). A piston element (106) is arranged in the cavity (104) of the cylinder (102) and comprises a piston section (110) and a rod section (112). The piston section (110) subdivides the cavity of the cylinder into a piston-head space (114) and into a piston ring-space (116). A valve unit (118) is assigned to the piston element (106) and is closed until a predetermined pressure in the piston-head space (114) is reached in order to separate the piston-head space (114) from the piston-ring space (116). Otherwise, the valve unit (118) can be freely flown through. The valve unit (118) is arranged such that a pressure in the piston-ring space (116) does not act on the valve unit (118) in a direction along which the piston element (104) can be displaced.

Description

LIFTING DEVICE

description

The present invention relates to a lifting device, and in particular to a single-stage or multi-stage lifting or synchronous lifting device, which comprise a pull-out lock.

Hydraulic cylinders in the form of single- or double-acting single- or multi-stage cylinders or synchronous cylinders are known in the prior art. Such cylinders are described for example in DE-GM 1976924, in JP 10141323 A or in US-A-1, 812, 577.

These known cylinder arrangements pose a number of problems. A first problem arises in applications in which the cylinders serve to raise the loading area, for example of an LK. 'Here it happens again and again that the loading area is so overturned or that there is still load on the folded-down side wall, over which the load should slip, so that the cylinder is suddenly pulled out with the generation of a vacuum to the stop. Another disadvantage is that when using known telescopic cylinders, the entire hydraulic system is subjected to strong vibrations, which occur particularly when there is no load on the telescopic cylinders. Another problem associated with this is that due to the vibrations it is not possible to control the cylinder precisely, in particular it is extremely time-consuming, if not impossible, to reach a predetermined position between a maximally extended position and a retracted position of the cylinder. Based on this prior art, the present invention seeks to provide an improved lifting device which avoids an undesirable pulling out of the cylinder and vibrations thereof.

This object is achieved by a lifting device according to claim 1.

The present invention provides a lifting device with

a cylinder with a cavity;

a piston element arranged in the cavity of the cylinder, the piston element comprising a piston section and a rod section, the piston section dividing the cavity of the cylinder into a piston crown space and into a piston ring space; and

a valve unit which is assigned to the piston element and which is closed up to a predetermined pressure in the piston crown space in order to separate the piston crown space from the piston ring space and which can otherwise be flowed through;

wherein the valve unit is arranged such that a pressure in the piston annulus does not act on the valve unit in a direction along which the piston element is movable.

The valve unit is preferably connected to the piston crown space via a first connecting portion and to the piston ring space via a second connecting portion.

According to a preferred embodiment, the valve unit comprises a valve piston and a spring element, which prestresses the valve piston in a closed position, wherein an adjusting screw can preferably be provided in order to adjust a prestressing force of the spring.

According to a first preferred embodiment of the present invention, the valve unit is arranged in the piston element, and preferably the valve unit is arranged in a rod section of the piston element and the first connecting section extends substantially parallel to the direction along which the piston element is movable and that second connecting portion extends at an angle to the direction along which the piston member is movable.

According to a second, preferred embodiment, the valve unit is arranged outside the cylinder.

The present invention relates to simple cylinders or multi-stage cylinders (telescopic cylinders).

In the case of a multi-stage cylinder (telescopic cylinder), the lifting device preferably comprises, in addition to the cylinder, a cylinder / piston unit which is arranged in the cylinder, the piston element being arranged in a cavity of the cylinder / piston unit. Furthermore, a valve device is provided, which adjoins the cavity in the cylinder / piston unit, the valve device being in a rest position or in the event of a deviation from a fixed rest position such that the cylinder / piston unit is retracted further from the rest position, through which flow is free, and otherwise closed is.

Preferably, the valve device is formed by a check valve which is effective to keep the valve unit in the closed state. Furthermore, a pin member is provided, which engages with the check valve, so that the valve device is in the rest position or in the case of a deviation from the rest position of the cylinder / piston unit in the open state. Vorzugswei- se the pin member is formed by an adjustable pin, by means of which the degree of opening of the valve device is adjustable in the rest position. The lifting device further comprises a connection in order to introduce a fluid into the cylinder bottom space, the connection being fluidly usable with the cavity of the cylinder / piston unit via the valve device.

The present invention is based on the finding that the problems which occur in conventional cylinders can be avoided by simulating a predetermined load, which is achieved in that the device according to the invention comprises the valve unit which, when a predetermined pressure in the The piston crown space connects the same to the piston ring space.

The advantage of this arrangement is that it is not possible to pull out the cylinder when the hydraulic pump is at a standstill under a predetermined force. In particular in the case mentioned above when a loading area tilts over and the sudden load change, this means that the cylinder does not snap out, but simply stops due to the reduced tensile load.

Another advantage of the present invention is that in a situation where the cylinder is immobile due to traction and the pump is off, it is possible to further extend the cylinder by replenishing a predetermined amount of hydraulic fluid with the pump, in exactly proportional fashion according to the pumped quantity. It is therefore possible to start or stop the cylinder at any time even with a pulling load.

Preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it: Figure 1 is a schematic representation of a single cylinder according to a first embodiment of the present invention, in which the valve unit is arranged in the piston element.

2 shows a schematic illustration of a single cylinder according to a second exemplary embodiment of the present invention, in which the valve unit is arranged outside the cylinder;

3A shows an enlarged illustration of the valve unit from FIG. 1 according to a further exemplary embodiment;

3B shows a valve unit similar to that from FIG. 3A with a hydraulic accumulator; and

Fig. 4 is a schematic representation of a multiple cylinder with the pull-out lock according to the invention according to the first embodiment.

1 schematically shows a cylinder 100 (lifting device) which comprises a cylinder 102, in the cavity 104 of which a piston element 106 is movably arranged (see arrow 108). The piston element 106 comprises a piston section 110 and a rod section 112. The piston section 110 divides the cavity 104 of the cylinder 102 into a piston crown space 114 and a piston ring space 116.

In the exemplary embodiment shown in FIG. 1, a valve unit 118 is arranged in the rod section 112 of the piston element 106, which is connected to the piston crown space 114 via a first connecting channel 120 and to the piston ring space 116 via a second connecting channel 122. The valve unit 118 is also connected to the ambient atmosphere, for example via a channel 123. The valve unit 118 comprises a valve piston 124, which is arranged in a spring via a preferably adjustable spring 126 Is biased in the direction in which the piston element is retracted. Instead of the illustrated configuration of the second connecting channel 122, other configurations are also possible, as long as it is ensured that the pressure from the annular space does not act on the piston 124 of the valve unit 118 in the axial direction.

Furthermore, the piston section 110 of the piston element 106 comprises a valve device 128, for example in the form of a check valve that is biased into the closed position by a spring. The valve device 128 is connected between the piston crown space 114 and the piston ring space 116. The valve device 128 is provided in order to ensure a compensation of hydraulic fluid in the lifting device. When the piston element 106 is retracted, the pressure rising in the bottom space 114 finally causes the valve 128 to open, so that hydraulic fluid can flow into the annular space 116.

Furthermore, the lifting device 100 comprises a connection 130, via which the piston head space 114 can be connected to a hydraulic pump.

2, a second exemplary embodiment of the present invention is shown schematically, which differs from the first exemplary embodiment only in that the valve unit 118 is arranged outside the cylinder 102. In FIG. 2 the same or similarly acting elements that have already been described with reference to FIG. 1 are provided with the same reference numerals, and the same will not be described again.

As can be seen, the valve unit 118 is arranged, for example, in a block that can be flanged to an outside of the cylinder 102 and is connected to the piston crown space 114 and the piston ring space 116 via the connecting channels 120, 122. Unlike the exemplary embodiment in FIG. 1, the valve device 128 is in one Connection line between the second connection channel 122 or the annular space 116 and the connection 130 arranged, but functionally identical to the arrangement of FIG. 1st

In Fig. 2 the pump 132 is also shown, by means of the hydraulic fluid, e.g. Oil, is promoted from a hydraulic fluid reservoir 134. The pump 132 delivers in the direction shown and a return flow branch 136 is also shown, via which the hydraulic fluids of the reservoir 134 flow back when the cylinder is retracted. An orifice 138 is located in the return path before a check valve 140. Although several elements are arranged outside of the block in which the valve unit 118 is arranged in FIG. 2, these can also be arranged together with the valve in the block.

The operation of the lifting device according to the invention with pull-out lock is explained in more detail below with reference to FIGS. 1 and 2.

The examples shown in FIGS. 1 and 2 are normal non-telescopic cylinders, but the present invention is also used in the field of single-acting telescopic cylinders, as will be explained below with reference to FIG. 4. According to the present invention, the piston element 106 is formed by a double-acting step, namely by the piston section 110 and the rod section 112, as a result of which the annular space or piston annular space 116 is defined. The valve unit or valve arrangement 118 inside the piston rod 112 (FIG. 1) consists of the valve piston 124 with valve seat and a compression spring 126 which keeps the valve unit 118 closed, so that in the idle state there is no connection from the piston ring space 116 to the piston crown space 114. The check valve 128 in the piston section 110 only bypasses the valve unit 118 when the cylinder is retracted in order to fill the piston annulus 116 with oil when the cylinder is retracted. As long as the force generated by the pressure in the piston chamber 114, which acts on the piston 124, is smaller than the spring force, the valve piston 124 is kept closed by the spring 126, so that the piston ring chamber 116 is completely separated from the piston crown chamber 114. The valve piston is designed such that no force is exerted on the valve piston in the axial direction, that is to say in the direction in which the piston element 106 is moved. So it is pressure balanced in this direction. However, the pressure from the piston crown 114 is directly against the spring force of the spring 126 via the valve piston 120. If the pressure exceeds the spring force, the valve piston 124 opens and a connection is made to the piston annulus 116 until the pressure falls below the spring force again.

If the cylinder or the piston element 112 is now extended and there is no load on the cylinder or is pulled on the piston rod 112, a corresponding counterpressure builds up in the piston ring space 116. Since the oil quantities cannot escape, the piston element 106 remains stationary as long as the valve piston 124 is closed. The extension of the cylinder or the piston element 106 is thus completely prevented. In other words, this simulates a load. In order to enable this pressure in the piston ring space 116, a pressure in the piston crown space 114 is of course necessary, which acts on the end face of the valve piston 124. If this pressure exceeds the compression spring force of the spring 126, the valve piston 124 opens and the pressure in the piston ring space 116, which is considerably higher due to the area ratio, can decrease. The hydraulic fluid, the oil, is also used here as in a differential circuit for the piston crown space 114. According to a preferred embodiment, the spring force of the spring 126 is adjustable.

One advantage is that in the event that the cylinder is immobile due to a tensile force of the switched-off pump, this can be extended further by the pump supplying a quantity of hydraulic fluid in fact exactly proportional to the pumped quantity, since the pressure required to open the valve piston 124 is immediately reached. If the piston rod 112 races away, however, this pressure immediately collapses again and the valve piston 124 closes, so that it is possible to start and stop the piston rod at any time, even when the load is being pulled.

According to one embodiment, the piston 104 and the piston element 106 are dimensioned such that a pressure of 200 bar with a tensile force of approximately 1.1 t is created in the annular space 116. To achieve this, the diameter of the piston is approximately 40 mm and the diameter of the piston element is approximately 30 mm. A pressure of e.g. about 20 bar applied to the floor space 114, the valve unit being dimensioned in this case so that it opens at a pressure of 20 bar.

In the cylinders described in FIGS. 1 and 2, retraction is only possible with a load. The cylinder according to FIG. 1 or FIG. 2 does not develop a reaction pressure when a tensile force is applied and does not include a pressure limiting device. The cylinders must therefore be dimensioned such that they withstand a maximum pressure in the annular space 116. The pressure generated in this space depends on the tensile load, on the diameters of the piston and the piston element and on the pressure applied by the pump, which acts in addition to the pressure in the annular space 116 according to the transmission ratio. In order to prevent overpressure and thus possible damage to the cylinder, the following measures can be taken to avoid the build-up of overpressure.

In the embodiment shown in FIG. 1, the spring 126 can be selected so that it resists only a low pressure, for example less than 20 bar, and opens at a higher pressure. This means that the pump has to deliver at a low pressure in order to remove the cylinder. drive. Due to the low pressure, there is only a slight increase in pressure compared to the pressure in the annulus, which does not pose a danger to the cylinder.

Instead of the possibility just described, a pressure relief valve can also be provided, as shown at 142 in FIG. 2. There is a check valve which is connected between the annular space 116 and the tank 134. Check valve 142 opens when the pressure in the annulus exceeds a predetermined value.

A further exemplary embodiment for avoiding excess pressure is shown in FIG. 3A. In Fig. 3A are already based on the previous Figs. elements described with the same reference numerals and these will not be described again.

As can be seen, the exemplary embodiment shown in FIG. 3A differs from the previous exemplary embodiments in the design of the piston element 124.

The valve assembly 118 is disposed in a cavity 150 and the piston member 124 includes a first section 152 and a second section 154. The first section 152 extends from the first connecting section 120 to the second section 154, which in turn extends further to the spring 126 extends. The spring presses against the second section 154.

The first section 152 is designed in such a way that the first connecting section 120 is closed in the closed position of the valve unit 118. Furthermore, the first section 152 does not extend to the wall of the cavity 150, so that the inlet of the second connecting section 122 is spaced from the first section 152. The second section 154 adjoins the first section 152 and extends in such a way that the second section can be wall of the cavity is in contact. Seals 156 in the second section 154 provide a seal between the piston element 124 and the spring 126.

Due to the spaced arrangement of the first section 152 from the inlet of the connecting section 122, the pressure in the annular space 116 partially acts on the surface 158 of the second section. This surface is arranged in such a way that a pressure in the annular space which exceeds a maximum permissible pressure causes the valve unit 118 to open. However, the dimensioning is such that this only takes place when a predetermined maximum pressure in the annular space 116 is exceeded. In normal operation, in which the pressure in the annular space is below the maximum permissible pressure, the pressure present in the annular space does not open the valve 118.

A further exemplary embodiment is shown in FIG. 3B. In FIG. 3B, the elements already described with reference to FIG. 3A are provided with the same reference symbols and these will not be described again.

In contrast to the exemplary embodiment shown in FIG. 3A, channel 123 has been dispensed with in this valve unit. As shown in dashed lines, this exemplary embodiment instead comprises a bore 160 through the piston element 124, so that the bottom space 114 is connected to the spring space 162. A hydraulic accumulator 164 is also provided, which is connected to the annular space 116 via a line 166.

The exemplary embodiment shown in FIG. 3B is used in systems (for example single cylinders, telescopic cylinders) in which, for example, basically the force reverses into a pulling force after half the stroke and the cylinder can no longer be retracted. Starting from the fully retracted state, the following occurs when the vehicle is extended. First of all, there is no pulling force (only one load) and a load corresponding to the load is built up Pressure in the piston chamber 114. This pressure is reported to the hydraulic accumulator 164 via the check valve 128. The cylinder only moves when the hydraulic accumulator 166 is filled accordingly and the pressure for extending is established. The cylinder is extended when the required pressure is reached. The pressure in the hydraulic accumulator 164 increases in proportion to the path up to a maximum pressure. When the maximum pressure is reached, the piston element 124 opens, which is dimensioned accordingly. If the pump pressure is now released, the cylinder can retract again, since the hydraulic accumulator 164 exerts a corresponding force on the annular space 116 due to the stored pressure, as long as the tensile force does not exceed the force acting in the annular space. Although the retraction force decreases with the retracted path, the tractive force on the cylinder will also reverse or decrease at some point, so that the cylinder will actually retract.

As an example, consider the case where the cylinder is to be pressurized to the pump at a maximum pressure of 200 bar. In this example, the hydraulic accumulator 164 will be designed for a maximum pressure of 300 bar and will then be completely filled. If a pressure difference of 100 bar occurs on the piston element 124, this will open. The spring force of spring 126 was selected accordingly. If this pressure difference of 100 bar is not reached, the cylinder loses this pressure force because it simulates a load. If the pressure difference is greater than 100 bar, the piston element 124 opens, so that a force greater than that corresponding to the 100 bar can never be generated.

Otherwise, the exemplary embodiment described in FIG. 3B functions in exactly the same way as that shown in FIG. 3A. This exemplary embodiment can also be used with telescopic cylinders (see FIG. 4), for example with tippers. The exemplary embodiment shown in FIG. 3B is preferably used when the annular space is relatively small compared to the piston space and only a small restoring force is required.

A preferred exemplary embodiment of a synchronous telescopic cylinder is described below with reference to FIG. 4.

4 shows a synchronous cylinder 300 with a first stage I, a second stage II and a third stage III. The synchronous cylinder 300 includes a cylinder 302 that includes a jacket 302a and a bottom 302b. A first cylinder / piston unit 304 is arranged in the cylinder 302. A second cylinder / piston unit 308 is arranged in a cavity 306 of the first cylinder / piston unit 304. A first valve 310 is adjacent to the cavity 306 of the first cylinder / piston unit 304 and is operative to be in the open state in the rest position of the synchronous cylinder 300 shown in FIG. 4, the valve 310 being otherwise closed. The valve 310 comprises a first check valve 312, which is formed by a hemisphere. Bottom 302b includes a first pin 314. Check valve 312 is biased by a first spring 316. The pin 314 can be adjusted to ensure that the valve 310 is open in its rest position, which is particularly important when a force F acting on the cylinder 300 is not continuous, e.g. already touches a stop before reaching the lowest position.

The cylinder 300 is extended starting from a fixed rest position and this fixed rest position results, for example, from the position of the pistons after the retraction of the same, for example when a loading surface is already resting on a stop of a frame of a vehicle, so that no more force acts. In such a case, the lowest piston with its piston section does not reach the cylinder bottom. If the cylinder is in the rest position just described or in an arbitrarily extended position, the valve device is effective in order to device in the piston annulus to be freely flowable, whereas the valve unit is closed in one direction out of the cavity. In the event of a deviation from the rest position such that the pistons are retracted further than the rest position, the valve device is effective so that it can be freely flowed through both into and out of the cavity.

In another case, the rest position described above is reached when the cylinder acts as the lower stop and the lowest piston reaches this stop, in which case a force acts until this lower stop is reached. If the piston is in this fixed rest position, the valve device is effective so that it can flow freely in the direction into the cavity and in the direction out of the cavity. If the piston element is in any extended position, the valve device is effective so that the flow can flow freely into the cavity in one direction, whereas the valve unit is closed in one direction out of the cavity.

The cylinder 302 comprises a cylinder bottom space 320 and a cylinder annulus 322, which are separated from one another by the first cylinder / piston unit 304. More specifically, the cylinder / piston unit 304 is formed by a piston section 324 and a cylinder section 326, the piston section 324 separating the cylinder bottom space 320 and the cylinder annulus 322 from one another.

An opening 328, which extends through the cylinder 302, connects the cylinder base space 320 via a line 329 to a connection 330, via which a hydraulic fluid is introduced during operation and for starting up the synchronous cylinder 300, which hydraulic fluid is supplied by a pump from a hydraulic fluid tank , In order to ensure a seal between the cylinder bottom space 320 and the cylinder annulus 322, the piston Section 324 of the first cylinder / piston unit 304 provided with sealing elements (not shown).

The first stage I of the synchronous cylinder 300 moves during the operation of the cylinder through an opening 336 in the cylinder 302, wherein sealing elements are embedded in the area of the inner wall of the opening 336 in order to bring about the required sealing with respect to the first cylinder / piston unit 304. Likewise, the first cylinder / piston unit 304 includes an opening 340 through which the second stage II can move out during the operation of the cylinder. In order to ensure the required tightness in relation to stage II, 340 sealing elements are again arranged in the inner wall of the opening. The cylinder annulus 322 communicates with the cavity 306 of the first cylinder / piston unit 304 via at least one opening 346.

Furthermore, cylinder 302, like first cylinder / piston unit 304, includes stops against which first stage I and second stage II strike when they are in their fully extended position.

The second cylinder / piston unit 308 comprises a cylinder section 360 and a piston section 362, as well as a cavity 364, in which a piston 366 is arranged, which forms the stage III of the synchronous cylinder 300.

The piston section 362 of the second cylinder / piston unit 308 divides the cavity 306 of the first cylinder / piston unit 304 into an annular space 368 and into a floor space 370. In the exemplary embodiment shown in FIG. 4, the floor space 370 for the first valve 310 is with the floor space 320 of the cylinder 302 connectable. Similar to the piston section 324, the piston section 362 of the second cylinder / piston unit 308 also has sealing elements. Furthermore, the annular space 368 is connected to the cavity 364 of the second cylinder / piston unit 308 via a bore or opening 374. bound.

A second valve 380 is provided, which adjoins the cavity 364 of the second cylinder / piston unit 308, and which is open in the rest position of the second cylinder / piston unit shown in FIG. 4 and is otherwise closed. Similar to the first valve 310, the second valve 380 also includes a check valve which is designed in the shape of a hemisphere which is biased by a spring. Furthermore, a pin is provided which ensures that the valve is open in the rest position shown in FIG. 4. The pin is dimensioned such that, when the cylinder 300 is at rest, it ensures that the second valve 380 is open.

During the operation of the synchronous cylinder 300, the piston 366 moves through an opening in the second cylinder / piston unit 308, wherein sealing elements are embedded in the inner wall of the opening 390 for sealing.

In FIG. 4, similar to FIG. 1, a valve unit 418 is provided, which is arranged in the piston element 366, which comprises a piston section 410 and a rod section 412. In this way, the cavity 364 is divided into a piston crown space 441 and a piston ring space 416.

The valve unit 418 is connected to the piston crown space 414 via a first connection channel 420 and to the piston ring space 416 via a second connection channel 422. The valve unit 418 comprises a valve piston 424 with a valve seat 424a. Spring 426 presses against valve piston 424 to hold it in its closed position. The spring force of the spring 426 is adjustable via an adjusting screw 450. The valve unit 118 is e.g. connected to the ambient atmosphere via the thread of the adjusting screw of the spring.

The operation of the cylinder shown in Fig. 4 corresponds essentially to that of the arrangements of FIGS. 1 and 2. As already described, in the exemplary case of a load of less than 500 kp on the cylinder, without the pump delivering oil, a correspondingly high pressure arises in the piston ring space 416, so that the piston member 366 cannot move. This tensile force is transmitted to the piston annulus 368 with a correspondingly lower pressure of less than 80 bar. The oil in this annular space acts on the piston section 410 and on the valve piston 424, which does not open under a pressure of 80 bar. Thus, the second cylinder / piston unit 308 and the cylinder / piston unit 304 do not move either. If the tensile force exceeds 500 kp (4903.325 N), the pressure in the piston crown space 414 will also rise above 80 bar and the connection with the piston ring space 416 will be established, and the cylinder extends. This also leads to a pressure in the piston crown space 414 and accordingly in the other piston crown spaces, so that the remaining cylinders / piston units are pulled out.

As already stated above, in the piston ring area 416 creates a pressure of about 350 bar, and when ^• reaction pressure on it created in the piston head space 414 and thus the annular space 368, a pressure of about 80 bar. Again as a reaction pressure, this results in a pressure of about 50 bar in the piston crown space 370 and in the annular space 322. The cylinder can thus be extended with only approx. 20 bar when empty. If the load exceeds 500 kp, the opening pressure at the valve piston 424 is reached and the high pressure in the piston ring space 416 breaks down and the same pressure arises as in the piston crown space 414. No lifting force is lost.

The functional principle on which the synchronous cylinder 300 is based is explained in more detail below, since it is assumed that a force of more than 500 kp is applied, that is to say the valve unit 418 is open.

A hydraulic fluid is fed into the Cylinder 300 is inserted, and it is assumed that a force F (F> 500 kp [4903.325 N]) is applied to the piston rod 366. For the very first start-up, in which there is still no hydraulic fluid, e.g. B. hydraulic oil, is located within the synchronous cylinder 300, the cylinder bottom space 320 is initially filled with hydraulic fluid, and via the valve a connection to the bottom space 370 of the first cylinder / piston unit 304 is made, and this is filled with hydraulic fluid. The cylinder annulus 322 will also fill with hydraulic fluid via the one or more bores 346. When the floor space 370 and the cylinder interior 322 are completely filled with hydraulic fluid, a pressure will build up as a result of the further charging of the cylinder with hydraulic fluid, and the hydraulic fluid will penetrate into the cavity 364 of the second cylinder / piston unit 308 via the opened second valve 380. and simultaneously introduced into the annular space of the first cylinder / piston unit 304 via the one or more openings 374. As soon as there is hydraulic fluid everywhere, a stroke movement will result against the force F. As soon as the first cylinder / piston unit has left its rest position shown in FIG. 4, the check valves of the first and second valves 310, 380 close and all stages move in and out simultaneously. More specifically, the further charging of the cylinder 300 with hydraulic fluid causes the first cylinder / piston unit to be raised, the displacement of the hydraulic fluid from the cylinder annulus causing the second cylinder / piston unit to be raised at the same time, and again by its movement and the resulting displacement of Hydraulic fluid from the annular space 368 of the first cylinder / piston unit 304 results in a movement of the piston 366. Due to the smaller and smaller areas from level to level, a correspondingly higher pressure will build up in level II and a further higher pressure in level III, with the highest pressure prevailing in level III. When entering the individual stages, the first valve 310 is opened when the rest position is reached. The further valve will open if there is too much or too little hydraulic fluid in stages II and III.

The volume of the piston annulus is calculated to correspond to the volume of the rod section. According to one embodiment, the lifting device is designed such that the back pressure in the piston annulus must be 350 bar in order to simulate a force of 500 kp (4903.325 N). This pressure can only be generated without external forces if there is at least 80 bar pressure in the piston crown space. In this case, the spring force of the spring is set to 24 kp (235.3596 N), so that the valve piston opens proportionally at a pressure of 80 bar in the piston crown space. The pressure in the piston ring space does not act as a force on the valve piston, which is, as already mentioned, pressure balanced, while the pressure in the piston crown space opposes the external pressure (air pressure) and the pressure spring force.

If a load now acts on the piston rod that is greater than 500 kp (4903.325 N), the pressure in the piston crown space will rise to more than 80 bar and the valve piston will open fully because the pressure will no longer drop below 80 bar becomes. The pressure in the piston ring space will also adapt exactly to the pressure in the piston crown space. According to the present invention and the structure according to the invention, the force of 500 kp (4903.325 N) is not lost when a load of more than 500 kp (4903.325) has to be lifted.

If a load of less than 500 kp (4903.325 N) is now pulled on the cylinder or the piston rod without the pump delivering oil, a correspondingly high pressure is created in the piston ring space. The piston element cannot move. If hydraulic fluid is pumped by the pump in this situation, a pressure that exceeds 80 bar is created in the piston crown space and the cylinder or the piston rod moves as intended. It is possible to extend and stop the cylinder in a targeted manner, even if there is a tensile load. However, if the tractive force exceeds 500 kp (4903.325 N), the pressure in the piston crown space will also rise to over 80 bar and the connection between the piston crown space and the piston ring space will be established via the valve unit, and the cylinder will extend. This extension is required as an overpressure safety device, since an increase in pressure to 350 bar could lead to the cylinder bursting. In other words, the cylinder described in FIG. 4 comprises a pressure limiting device, so that the overpressure described in connection with FIGS. 1 and 2 does not arise.

Claims

claims

1. Lifting device with

a cylinder (102; 302) with a cavity (104; 306)

a piston member (106; 366) disposed in the cavity (104; 306) of the cylinder (102; 302), the piston member (104; 366) a piston section (110; 410) and a rod section (112; 412) The piston section (110; 410) divides the cavity (104; 306) of the cylinder (102; 302) into a piston crown space (114; 414) and into a closed piston ring space (116; 416); and

a valve unit (118; 418) associated with said piston member (106; 366) is associated with and up to a predetermined pressure in the piston base chamber (114; 414) is closed to the piston base chamber (114; 414) from the ^'piston annular chamber (116; 416 ) to separate, and which is otherwise flowable;

wherein the valve unit (118; 418) is arranged such that a pressure in the piston annulus (114; 414) does not exert pressure on the valve unit (118; 418) in a direction (108) along which the piston element (106; 366) can be moved. acts, and a fluid contained in the piston annulus (116; 416) flows from the piston annulus (116; 416) into the piston crown space (114; 414) when the valve unit (118; 418) is open.

2. Lifting device according to claim 1, wherein the valve unit (118; 418) via a first connecting section

(120; 420) with the piston crown space (114; 414) and via a second connecting section (122; 422) with the Piston annulus (116; 416) is connected.

3. Lifting device according to claim 1 or 2, wherein the valve unit (118; 418) comprises a valve piston (124; 424) and a spring element (126; 426) which biases the valve piston (124, 424) in a closed position.

4. Lifting device according to claim 3, wherein the valve unit (418) comprises an adjusting screw (450) to adjust a biasing force of the spring element (426).

5. Lifting device according to one of claims 1 to 4, wherein the valve unit (118; 418) in the piston element (106; 366) is arranged.

6. Lifting device according to claim 5, wherein the valve unit (118; 418) is arranged in the rod section (112; 412) of the piston element (106; 366), the first connecting section (120; 420) being substantially parallel to the direction along which the piston element

(106; 366) is movable, the second connecting portion (122; 422) extending at an angle to the direction along which the piston element (106; 366) is movable.

7. Lifting device according to one of claims 1 to 4, in which the valve unit is arranged outside the cylinder (102).

8. Lifting device according to one of claims 1 to 7, with

one _. Cylinder / piston unit (304) in the cylinder

(302) is arranged, wherein the piston element (366) is arranged in a cavity of the cylinder-piston unit (302); and

valve means (310) adjacent to the cavity (306) in the cylinder / piston unit (304), the Valve device (310) in a rest position or in the event of a deviation from the rest position such that the cylinder / piston unit (304) is retracted further with respect to the rest position, can be flowed through freely and is otherwise closed.

9. Lifting device according to claim 8, wherein the valve device (310) has the following features:

a check valve (312) operative to maintain the valve means (310) in the closed state; and

a pin member (314) which engages with the check valve (312) such that the valve unit is in the rest position or upon the deviation from the rest position of the cylinder / piston unit (304) in the open state.

10. Lifting device according to claim 9, wherein the pin member (314) has an adjustable pin to adjust the degree of opening of the valve device (310) 'in the rest position of the cylinder / piston unit (304).

11. Lifting device according to claim 10, with a connection

(330) in order to introduce a fluid into the cylinder bottom space (320), the connection (330) being fluidly connectable to the cavity (306) of the cylinder / piston unit (304) via the valve device (310).