AT502339B1 - DRIVE DEVICE - Google Patents

Description

2 AT 502 339 B1

The invention relates to a drive device for a movable component, in particular for an upper tool of a press brake, according to the preamble of patent claim 1.

Drive devices for presses, punching machines and guillotine shears as well as closing units 5 for injection molds are often equipped with a hydraulic power transmission device to exert a high force even with a comparatively weakly dimensioned drive motor. However, a high gear ratio implies a slow displacement of the driven member and a long travel that an input member of the force translating device - e.g. a hydraulic piston - must travel for it. Therefore, force-io translation devices are often equipped with a so-called rapid traverse, which allows rapid execution of actuation movements in which only small forces are applied.

EP 1 307 330 B1 describes e.g. a closing unit for an injection molding machine. An electric motor drive unit comprises an electric motor and a screw drive. The screw drive is coupled with the interposition of a hydraulic power transmission to a displaceable molding of the injection mold. The power transmission consists essentially of a working hydraulic cylinder, on the hydraulic piston, the molding is mounted, and two - from the perspective of power transmission - drive side arranged hydraulic cylinders whose 20 pistons are coupled to the screw. A first piston with a small effective area is rigidly connected to the screw drive. The second piston with a larger effective area is in the pulling direction of the screw by a stop positively entrained by the first piston and in the thrust direction by a spring clutch or a releasable magnetic coupling only to a certain counter pressure mitnehmbar. The pressure chamber, from which the first 25 piston displaces pressure fluid in the thrust direction, is directly connected to a cylinder space of the working hydraulic cylinder. The corresponding pressure chamber of the second piston is connected to this cylinder space of the working hydraulic cylinder via a switching valve. A fast positioning movement in the closing direction of the injection mold, i. a rapid traverse, is achieved when the switching valve is open. In this case, pressure medium flows from the pressure chambers, which become smaller in the thrust direction of the screw drive 30, on the drive cylinders arranged on the drive side into the cylinder space of the working hydraulic cylinder. If the switching valve is closed, the pressure chamber of the second piston is locked against further reduction. The force acting on the drive side via the spring clutch or the magnetic coupling to the second piston is supported by the pressure built up in the locked pressure chamber, so that the second piston 35 remains. The first piston can be moved further in the thrust direction after release of the magnetic coupling or within the flexibility of the spring clutch and displace with its relatively small effective area pressure fluid from the pressure chamber adjacent to it. As a result, in the cylinder chamber of the working hydraulic cylinder, a high pressure and thus a high power transmission can be achieved. 40

In this conventional power transmission, in which a hydraulic cylinder is stopped by a drive side acting on it force is supported by a locked pressure chamber, inevitably results in a separation of the pressure chambers, which beauf by different pistons with the drive side applied force in the direction of a displacement of pressurized fluid -45 beats are. This is in the way of efforts to further simplify the power transmission device or the drive device.

Therefore, it is the object of the present invention to provide a drive device with an alternative design of a power transmission device, which allows in particular simpler and more efficiently constructed drive devices.

This object is achieved by a drive device having the features of patent claim 1. The drive device according to the invention is equipped with an electromotive drive device, which has a rectilinearly movable output element. A hydraulic power transmission device transmits the force applied by the output member to a movable member. The power transmission device comprises three hydraulic pistons. The first hydraulic piston defines a first pressure area with a first active area, the second hydraulic piston defines a second pressure area with a second active area, and the third hydraulic piston delimits a third pressure area with a third effective area and a fourth pressure space with a fourth effective area. The second effective area is substantially smaller than the first and as the third effective area. The second hydraulic piston is rigidly coupled to the output member. The first and second pressure chambers are permanently fluidically connected. By io a one-sided mechanical stop the third hydraulic piston from the second hydraulic piston in the direction of enlargement of the third pressure chamber is entrained. In this direction, therefore, the movement of the two pistons is positively coupled. In the other direction, the third hydraulic piston follows the second hydraulic piston up to a certain pressure in the third pressure chamber. With a switching valve one of the third hydraulic piston angren-15 zenden pressure chambers can be shut off.

The peculiarity of the present invention is that even the third pressure chamber is permanently connected to the first pressure chamber and that the fourth pressure chamber can be blocked by the switching valve. 20

In contrast to the conventional solution, a displacement of hydraulic fluid from the third pressure chamber into the first pressure chamber is not prevented by the switching valve. The third hydraulic piston is not supported against a drive side acting on it force. According to the invention, the third hydraulic piston is instead supported by the blocking of the fourth pressure chamber against a pressure acting on it from the third pressure chamber. Thus, a high pressure can be built up in the first, second and third pressure chambers when the second hydraulic piston which is small in comparison to the third and first hydraulic pistons is moved in the sense of a volume reduction of the second pressure chamber. 30 This amazingly simple solution allows not only the second and the third pressure chamber to be permanently fluidically connected, but also to connect the third pressure chamber, from which the first hydraulic piston receives pressurized fluid in rapid traverse, directly to the first pressure chamber. This opens up new possibilities for simplifying the drive device. Incidentally, the control of the switching valve can take place in the same way as in the conventional power transmission - open at rapid speed, closed to transmit high forces - so that a possibly already available control device can be used.

The terms "first pressure space", "second pressure space" and "third pressure space" are to be understood as meaning not only individual, clearly delimited pressure chambers. The count is intended to facilitate the understanding of the claim. In particular embodiments, as shown in Figures 1 and 2, in which two or three of these pressure chambers are combined to form a single pressure chamber, should be included in the wording of this claim. 45

Further advantageous embodiments are specified in the subclaims.

Thus, according to claim 2 at least two of the three permanently fluidly connected pressure chambers, these are the first, the second and the third pressure chamber, to summarize a single pressure-50 space. As a result, in particular, the third pressure chamber can also be integrated into a common housing with the first or second pressure chamber. Elaborate connection lines are saved. The number of sealing points can be kept low and the likelihood of leakage is reduced. 55 A particularly preferred embodiment provides that the second and the third hydraulic piston are arranged in a common cylinder housing. This allows a compact design of the two with the electric motor drive unit directly or via the mechanical stop coupled hydraulic piston reach. The often convenient division into a drive-side cylinder-piston unit with the second and third hydraulic piston 5 and a tool-side cylinder-piston unit with the first hydraulic piston is simplified.

Additional advantages are achieved when the second hydraulic piston is designed as a plunger and the third hydraulic piston annularly shaped, pushed onto the second hydraulic piston io and is guided axially movable on this. This results in a particularly simple and cost-effective construction of a cylinder-piston unit which contains the second and the third hydraulic pistons and in particular has only a small number of sealing points.

Preferably, the mechanical stop is formed by a shoulder on a housing in the Zylinderge-15 projecting end of the second hydraulic piston. Such a stop is simple and inexpensive to produce. The number of sealing points is further reduced because the third hydraulic piston does not require any passage to the outside of the cylinder housing. Thus, the structure of the drive device further simplified. A further advantageous embodiment provides that a hydraulic accumulator is present and that the switching valve controls a connection between the fourth pressure chamber and the hydraulic accumulator. The hydraulic accumulator can take over the function of a hydro-mechanical tensioning device which causes the third hydraulic piston to follow the second hydraulic piston while resting against the stop. The hydraulic accumulator can additionally compensate the pressure fluid balance in the hydraulic power transmission device so that it can be executed as a closed system.

Preferably, the first hydraulic piston bounded with a first active surface oppositely directed fifth effective area a fifth pressure chamber, so that a retraction 30 movement of the component is executable.

A very low cost power transmission apparatus having a rapid traverse mode, a closed hydraulic system, and a retracting movement function is obtained when a fluidic connection between the fifth pressure space and the fourth pressure space is controlled by the switching valve.

Preferably, the fifth pressure chamber is connected to a second memory. This can. a connecting line between the fifth and the fourth pressure chamber can be saved. 40 According to a particularly preferred embodiment, the switching valve is designed as a seat valve. As a result, the hydraulic power transmission device is substantially leak-free.

Hereinafter, the present invention and its advantages will be explained in detail with reference to the embodiment shown in the figures and its modifications. 45

Show it:

1 is a circuit diagram of a drive device with a hydraulic power transmission device, 50th

2 is a circuit diagram of the hydraulic power transmission device shown in Figure 1 in a slightly modified form, in which, inter alia, three pressure chambers are combined into a single cylinder housing,

Fig. 3 is a circuit diagram illustrating a further modification of a power transmission device with completely separate pressure chambers, and

Fig. 4 is a circuit diagram showing a modification of a power transmission device, in which a return line is replaced by a hydraulic accumulator 55 5 AT 502 339 B1.

To illustrate a concrete example, the following description refers to a drive device for a top tool of a press brake. However, the described drive-5 device is fully suitable for many other applications, be it punching machines, guillotine shears or closing devices for injection molding machines, etc.

Referring to Fig. 1, a drive unit 1 of a press brake is provided with an electric motor 10, a screw drive 12, e.g. a ball or a roller screw, and a hydraulic power transmission device 20 equipped. A tool holder 16 with the upper tool mounted thereon is shown simplified in the form of a mass block.

The hydraulic power transmission device 20 is formed by three different hydraulic pistons 24, 28 and 36. Into a cylinder housing 22 protrudes designed as a plunger 15 hydraulic piston 24 into it. The hydraulic piston 24 is mechanically rigidly connected to a threaded rod 14 of the screw 12. At the projecting into the cylinder housing 22 end of the hydraulic piston 24, a shoulder 26 is formed. On the hydraulic piston 24 designed as an annular piston hydraulic piston 28 is movably guided. This subdivides the cylinder housing 22 into a cylinder chamber 30 and an annular space 31. 20

In a further cylinder housing 34 of the hydraulic piston 36 is arranged. The hydraulic piston 36 divides the cylinder housing 34 into a cylinder chamber 38 and an annular space 39. It thus forms, together with the cylinder housing 34, a double-acting differential hydraulic cylinder. On the piston rod 37 of the hydraulic piston 36 of the tool holder 16 is 25 introduced.

It should be noted that a press brake is often equipped with several pressing cylinders. In this case, the drive device 1 is supplemented by further differential cylinders, which are connected in parallel to the differential cylinder formed by the piston 36 and the housing 34.

A fluid line 40 connects the cylinder chamber 30 permanently with the cylinder chamber 38. A further fluid line 41, 42 leads from the limited by the annular piston 28 annular space 31 via a switching valve 44 to the hydraulic piston 36 limited annular space 39. At the 35 line section 41 is also a Hydro accumulator 46 connected. The switching valve 44 is designed as a seat valve. It controls a fluidic connection between the annular space 31 and the reservoir 46 or the annular space 39.

The active surface with which the piston 36 delimits the cylinder space 38 corresponds in this embodiment to the surface with which the annular piston 28 adjoins the cylinder space 30, plus the rod cross-sectional area of the plunger 24. The surface with which the piston 36 engages the annular space 39 This is due to the fact that the piston rod 37 is designed to accommodate the usual high pressure loads in the press operation, while the piston 24 and the threaded rod 14 are dimensioned 14 weaker. The rod cross-sectional area of the plunger 24 is 1/5 of the circular area of the piston 36, so that a force transmission by about a factor of 5 can be achieved.

The operation of the drive device shown in Figure 1 will be explained below. 50

In order to put the drive in an upper holding position of the tool holder 16 in a resting state, the switching valve 44 is brought into a closed valve position, as shown in Fig. 1. The hydraulic accumulator 46 is biased to a certain pressure, e.g. 20 bar. This pressure creates an upward force on the annular surface of the piston 36 that is approximately equal to 55% of the weight of the tool holder 16 with the upper tool. The force surplus is compensated by a pressure which occurs in the pressure chambers 38 and 30. This pressure is lower than the preload pressure of the hydraulic accumulator 46. The pressure in the pressure chambers 38, 30 is based on the pressure chamber 30 facing annular surface of the annular piston 28 from. In the annular space 31 there is a pressure which corresponds to at least the pressure in the rooms 5 and 30. This pressure is based on the closed switching valve 44. The annular piston 28 is to be in abutment with the stop formed by the shoulder 26, or at most be displaced within the scope of the compressibility of the hydraulic fluid in the annular space 31 in the direction of a reduction of the same. A force exerted by the pressure in the cylinder chamber 30 on the hydraulic piston 24 force can be easily by the An-io drive motor 10 hold or possibly on an end stop (not shown) support the threaded rod 14.

To end the idle state, the switching valve 44 is switched to the open valve position. Now, the bias pressure of the hydraulic accumulator 46 is also in the pressure chamber 31. 15 The pressure in the chambers 38 and 30 is lower than the bias pressure of the hydraulic accumulator 46, because it is still determined by the excess force on the piston 36 in the upward direction. On the annular piston 28 there is an excess of force in the direction of the shoulder 26, to which he now rests. At the threaded rod 14 thus acts a tensile force. The force required to hold the threaded rod consists of the weight of the tool holder 16, the tool 20 and the piston 36 together and from an additional force. This additional force is based on the difference of the forces, which causes the biasing pressure of the memory 46 on the one hand on the annular surface of the piston 36 and on the other hand on the annular surface of the piston 28. The larger the annular surface of the piston 28 relative to the annular surface of the piston 36, the greater is the additional force to be applied to the threaded rod. 25

If the electric motor 10 is now controlled in such a way that the piston 24 attached to the threaded rod 14 is pushed into the cylinder 22, the annular piston 28 follows it due to the pressures acting on it. The displaced from the space 30 pressure fluid flows into the cylinder chamber 38 and the cylinder 36 lowers. The displaced from the annular space 39 30 hydraulic fluid is supplied via the line 41 and 42 and the open switching valve 44 to the annular space 31. In addition, a compensating amount of pressure fluid flows from the reservoir 46 into the annular space 31.

The cylinder chamber 38 facing surface of the piston 36 corresponds to the sum of the force acting on the cylinder chamber 30 surfaces of the piston 28 and 24. Therefore, the path traveled by the piston 36 is the same as the distance traveled by the threaded rod 14 way. The path ratio is 1/1, once the low compressibility of the hydraulic fluid is ignored. Such a long translation is also referred to as rapid traverse and allows a quick lowering of the hydraulic piston 36. Since according to the Wegüber-40 setting the force transmission is 1/1, and since the annular piston 28 the plunger 24 in any case only follows as long as the pressure in the cylinder chambers 38 and 30 does not exceed the accumulator pressure, this mode is particularly suitable for fast positioning movements, where no large forces are applied. 45 In order to obtain a shorter path ratio, which allows exerting high pressing forces by the hydraulic piston 36, the switching valve 44 is brought into the closed position. The annular space 31 is thereby shut off. A pending in him pressure is based on the closed switching valve 46. With continued insertion movement of the piston 24, the annular piston 28 follows this initially until the pressure in the cylinder chamber 30 exceeds the pressure in the annular space 31 so. Then, the annular piston 28 stops and it moves only the piston 24 in the sense of reducing the volume of the cylinder chamber 30. The displaced therefrom pressure fluid is pushed into the space 38 and causes a further downward movement of the piston 36. The displaced from the annular space 39 Pressure fluid is absorbed by the memory 46. The displacement or force transmission is measured in accordance with the ratio of the circular area of the piston 36 adjacent to the pressure chamber 38 and the rod cross-sectional area 7 AT 502 339 B1 of the piston 24. In this example, there is an area ratio of 5/1. This results in a path ratio of 1/5, i. the piston 24 travels a five times longer travel than the piston 36, and a power ratio of 5/1. This means that a five times greater pressing force can be applied to the piston 36 than a force applied to the threaded rod 14 by the electric motor drive.

To raise the piston 36 again after the downward movement, i. E. In order to perform a return movement, the plunger 24 must first be moved out of the cylinder 22 with the valve 44 closed until its shoulder 26 abuts again on the annular piston 28. Assuming that there is no leakage, so is the way that the piston 24 was retracted with the valve 44 closed, the same way that the piston 24 must be moved out again with the valve 44 closed. As soon as due to the extension movement of the piston 24, a pressure built up in the pressure chambers 38, 30 and 31 has fallen back to a pressure on the piston 36, the pressure on the piston 36 and the weight of the tool holder 16, the upper tool and piston 36 compensates, so moves with continued extension movement of the piston 24, the piston 36 under the influence of the pending in the annulus 39 biasing pressure of the memory 46 upwards. The previously recorded amount of liquid is now discharged again from the memory 46 into the annular space 39. The path ratio is 1/5. However, no great force is built up on the piston 36 in the upward direction because it is limited to the pressure equivalent of the storage biasing pressure. If one were to open the valve 44, while in the pressure chambers 38, 30 and 31, there is still a higher pressure than the storage bias pressure, the piston 28 would retreat until the pressure has dropped to the storage pressure. However, if the piston 36 is loaded in the extension direction of the piston rod 37, the annular piston 28 would slide against the stop 26 and the piston 36 and the tool holder 16 would sag correspondingly.

As soon as the plunger 24 has moved out of the cylinder 22 so far that its school 30 ter abuts the annular piston 28, the valve 44 can be opened. In the further extension movement of the piston 24 takes the annular piston 28 positively by the system on the shoulder 26 with. The displaced from the annular space 31 hydraulic fluid is the annular space 39 and the memory 46 is supplied. Under the action of the biasing pressure of the accumulator 46, the piston 36 moves upward. The resulting in the cylinder chamber 30 volume 35 is filled by pressure fluid from the space 38. The path ratio is 1/1. The force which can be applied by the piston 36 is in turn limited by the accumulator pre-load pressure or its permissible operating pressure.

Thus, the described cycle of operation of the piston 36 consists of a long translated first downward movement, which is executable as a rapid steep movement, a short translated second downward movement, in which a large pressing force is available, a short translated first retraction movement and a long translated and thus faster executable second withdrawal movement. Accordingly, the electric motor 10 via the screw 12 consecutively two retraction movements of the piston 24 and then two 45 Ausfahrbewegungen of the piston 24 from. Stopping the electric motor between the two retracting or extending motions is not required. The movements are rather distinguishable by the switching of the valve 44.

FIG. 2 shows a hydraulic force transmission device 50, which is slightly modified in comparison with the force transmission device 20 shown in FIG. Reference numerals for components of the power transmission device 50 corresponding to those of the power transmission device 20 have been retained. The difference between the power transmission device 50 and the power transmission device 20 is that in the power transmission device 50, the pressure chambers 30 and 38 to a common pressure chamber 54 to-55 are summarized. Accordingly, the hydraulic pistons 24, 28 and 36 can all be arranged in a single cylinder housing 52. The connecting line 40 is omitted. In this way, a more compact, simpler construction of the power transmission device can be achieved. The cost of piping and sealing is reduced compared to the power transmission device 20. 5

Apart from the mentioned difference, the remaining structure and the operation of the power transmission device 50 of the power transmission device 20th

FIG. 3 shows a further force transmission device 60, which is likewise a modification of the force transmission device 20. There are three hydraulic pistons 64, 72 and 36 available. Hydraulic piston 36, cylinder housing 34 and piston rod 37 correspond to the respective components of the force transmission device 20. The hydraulic piston 64 forms, together with the cylinder housing 62 and the piston rod 67, a double-acting differential hydraulic cylinder. The interior of the cylinder housing 62 is divided by the piston 64 in FIG. 15 into an annular space, 66 and a cylinder space 65. The piston rod 67 is rigidly coupled to the threaded rod of the electromotive drive. The hydraulic piston 72 also forms with its cylinder housing 70 and the piston rod 75 a differential hydraulic cylinder. In the interior of the cylinder housing 70, a cylinder chamber 73 and an annular space 74 are formed. 20

The cylinder chambers 65 and 73 are constantly connected via fluid lines 80 and 81 with the cylinder chamber 38. From the annular space 39, a fluid line 82 leads to the annular space 66. A further fluid line 83 leads with the interposition of the switching valve 44 to the annular space 74. 25 Between the piston rod 67 and the piston rod 75, a coupling element is provided that in the extension direction of the piston rod 67 a positive entrainment of the piston rod 75 allowed. The coupling element is here formed by a coupling bar 77 which is fixed to the piston rod 67. The piston rod 75 is guided through a receiving bore in the coupling bar 77. A trained on the piston rod 75 stopper 78 forces a 30 entrainment of the piston rod 75 in the extension direction. Apart from that, the coupling bar 77 is displaceably guided on the piston rod 75.

The pistons 64 and 72 are dimensioned so that the ratio of the circular area which defines the respective cylinder space 65 and 73, to the annular surface which limits the respective annular space 66 35 and 74, the area ratio of the cylindrical space 38 facing circular area and the the annular space 39 facing annular surface on the piston 36 corresponds. This also applies to the sum of the cylinder spaces 65 and 73 bounding circular surfaces of the pistons 64 and 72 in relation to the sum of the annular spaces 66 and 74 bounding annular surfaces. 40

The sum of the cylinder spaces 65 and 73 bounding circular surfaces of the pistons 64 and 72 corresponds to the circular area of the piston 36, which limits the cylinder space 38. The cylinder space 65 facing the circular surface of the piston 64 is 1/5 of the area with which the piston 36 limits the space 38. Because of these area ratios results in a path ratio 45 of 1/1 when the movement of the pistons 64 and 72 is coupled. If only the piston 64 is displaced while the piston 72 is stationary, then a displacement ratio of 1/5 and thus a power ratio of 5/1 is achieved.

If the switching valve 44 is opened, the piston 72 follows the piston 64 in a movement in such a direction of a reduction of the cylinder chambers 65 and 73 due to an attacking on the piston 36 in the direction of the annular space 39 directed weight force of the tool holder 16, the tool, etc. By the pressure generated by the weight in the annular space 39 continues in the annular space 66 and via the open switching valve 44 also in the annular space 74 and thus ensures that the piston 72 follows the piston 64 under abutment against the stop 78. This allows a lowering of the piston 36 with a long travel ratio of 1/1. For a 9 AT 502 339 B1

Extending movement of the piston rod 67, the piston 64 takes the piston 72 via the stop 78 with. The displaced from the annular spaces 66 and 74 hydraulic fluid is supplied to the annular space 39. This leads to an upward movement of the piston 36. 5 When the switching valve 44 is closed, the annular space 74 is shut off. A pressure acting on it from the cylinder chamber 73 is supported via the locked cylinder chamber 74. Upon a retraction movement of the piston rod 67 and the piston 64, the piston 72 stops. The coupling bar 77 lifts off from the stop 78. From the cylinder chamber 65 displaced hydraulic fluid is passed into the cylinder chamber 38. Accordingly, pressure fluid is displaced from the annular space 39 into the annular space 66. The piston 36 lowers. By the ratio of the effective areas of the piston 64 and the piston 36, the force transmission is determined as indicated above. To raise the piston 36 again, the piston 64 is first moved in the direction of the annular space 66 until the coupling bar rests against the stop 78. Then, the valve 44 can be opened and carried out under displacement of hydraulic fluid 15 from both chambers 66 and 74, a further lifting of the piston 36.

The described mode of action of the force transmission device 60 differs only insignificantly from the mode of operation of the force transmission device 20. Because the piston 64 is arranged in a differential hydraulic cylinder, an upward movement of the piston 36 can also be performed by applying high forces. The force transmission achieved corresponds to the area ratio of the pistons 36 and 64 when the valve 44 is closed.

Due to the choice of the same ratio of the circular areas and the annular surfaces on the pistons 36, 64 and 72, a memory can be omitted. However, if it is appropriate to choose the ratio of the 25 circular and annular surfaces of the piston 64 or 72 different from the area ratio of the circular and annular surface of the piston 36, so connected via the fluid line 83 to the annular space 39 memory compensate for the differences. As already described in connection with the force transmission device 20, such a reservoir can additionally cause a biasing force of the piston 72 in the direction of reducing the cylinder space 73, so that the piston 72 reliably follows the piston 64 even in the absence of a tensile force acting on the piston rod 37 , In addition, as with the power transmission device 20, such a reservoir supplies the piston 36 with a biasing force in the upward direction. Thus, the tool holder 16 is supported with a closed valve 44 against sagging, without the piston rod 67 must be applied with a tensile force 35 must. A thrust on the piston rod 67 could possibly be supported by an end stop.

A modification of the force transmission device 60 shown in FIG. 3 is shown in FIG. The components of the power transmission device 90, which correspond to the components of the power transmission device 60, are given the same reference numerals and will not be discussed separately. The following description illustrates the differences between the force translating device 90 and the force translating device 60. The piston 64 with the housing 62 and the piston rod 67 is replaced by the plunger 93 which is guided in the housing 92. On the plunger 93, a piston rod 94 is attached. At this piston rod 94 of the coupling bar 77 is attached. The space 91 bounded by the hydraulic piston 93 is connected to the cylinder space 38 via the fluid line 80. The cylinder chamber 73 is constantly connected to the cylinder chamber 91 and thus also the cylinder chamber 38. The limited by the hydraulic piston 36 annular space 39 is connected to a hydraulic accumulator 96. The limited by the hydraulic piston 72 annular space 74 is connected via the switching valve with a further hydraulic accumulator 98. A return between the annular space 39 and the annular space 74 is eliminated. The mode of operation of the force transmission device 90 essentially corresponds to that in FIG

Claims (10)

Pressure transmission fluid can be displaced into the cylinder chamber 38 from the cylinder chambers 91 and 73. When the switching valve 44 is opened, the cylinder 72 follows the cylinder 93 in the direction of a reduction of the pressure chambers 91 and 73 under the action of the biasing pressure prevailing in the memory 98. In the other direction 5, the piston 72 is taken by the stop 78. The memory 98 is depending on the direction of movement, the required amount of pressure fluid from or absorbs them. If the valve 44 is closed, the annular space 74 is shut off and the cylinder 92 is blocked against a reduction of the annular space 74. The piston 93 can now be displaced in the direction of a reduction of the space 91 without taking the piston 72 with it. By the pressure surface 91 adjacent to the small surface of the piston 93 can be with a small force on the piston rod 94, a high pressure in the pressure chambers 91 and 38 generate. Thus, a downward movement of the piston 36 to produce a high pressing force on the piston rod 37 is feasible. In order to raise the piston 36 again, when the valve 15 is closed, the piston 93 is initially moved back out of the housing 92 until the coupling bar 77 bears against the stop 78. Then, the valve 44 is opened and another retraction movement involving both pistons 93 and 72 is performed. From the annular space 39 during the downward movement of the piston 36 displaced hydraulic fluid 20 is received by the hydraulic accumulator 96. Upon an extension movement of the pistons 93 and 72, the pressure in the pressure chamber 38 is lowered. The pressure in the hydraulic accumulator 96 raises the piston 36 thereupon. The previously displaced pressure fluid is fed back from the hydraulic accumulator 96 into the annular space 39. The biasing pressure of the hydraulic accumulator 96 must be selected in comparison to the bias pressure of the hydraulic accumulator 98 and taking into account the annular surfaces of the pistons 36 and 72 so that when the open switching valve 44 is ensured that the piston 72 follows a retraction movement of the piston rod 94. Are e.g. the annular areas of the pistons 36 and 72 equal, the bias pressure of the memory 96 must be below the bias pressure of the memory 98. In the described embodiment and its modifications, the force transmission ratio for the downward movement of the piston 36 with closed switch 44 has been given as 5/1. However, one skilled in the art can readily choose a different gear ratio that appears appropriate to him. For this purpose, only the surface of the piston 36, which adjoins the cylinder chamber 38, and the surface of the piston 24, 64 or 93, which is effective relative to this pressure chamber and which is coupled directly to the threaded rod, need to be dimensioned according to the desired ratio. 40 Patent claims: 1. 45 50 drive device for a movable component (16), in particular for an upper tool of a press brake, with an electromotive drive unit, which has an electric motor (10) and a rectilinearly movable output element (14), and with a hydraulic force transmission device ( 20) disposed in a force chain between the output member (14) and the movable member (16) and comprising: a first hydraulic piston (36) having a first effective area adjacent to a first pressure space (38) filled with pressurized fluid; a second hydraulic piston (24; 64; 93) rigidly coupled to the output member (14) and fluidly connected to a second pressure surface (30; 54; 65; 91) in fluid communication with the first pressure chamber (38) is, adjacent, a third hydraulic piston (28; 72), which is adjacent to a third effective area to a third pressure chamber (30; 54; 73) and with a dr the fourth active surface oppositely directed active surface to a fourth pressure chamber (31; 74), wherein the second active area is substantially smaller than the first effective area and as the third active area, a one-sided mechanical stop (26; 78) through which the third hydraulic piston (28; 72) in the direction an enlargement of the third pressure chamber (30; 54; 73) is entrained by the second hydraulic piston (24), the third hydraulic piston (28r 72) being directed toward the second hydraulic piston (24; 64; 93) in the direction of reducing the third pressure chamber (30; 54; 73) up to a certain pressure in the third pressure chamber (30; 54; 73) follows, and a switching valve (44) through which in a first switching position to the third hydraulic piston (28) adjacent pressure chamber is shut off and by in a second switching position pressure fluid in this pressure chamber can be supplied or pressure fluid from this pressure chamber is displaced, characterized in that also the third pressure chamber (30; 54; 73) continuously with the first pressure chamber (38) flui is connected, and that with the switching valve (44) of the fourth pressure chamber (31; 74) is lockable. 2. Drive device according to claim 1, characterized in that at least two of the three permanently fluidly connected pressure chambers to a single pressure chamber (30, 54) are summarized. 3. Drive device according to claim 2, characterized in that the second hydraulic piston (24) and the third hydraulic piston (28) in a common cylinder housing (22, 52) are arranged. 4. Drive device according to claim 3, characterized in that the second hydraulic piston (24) is designed as a plunger and that the third hydraulic piston (28) annularly shaped, is pushed onto the second hydraulic piston (24) and guided axially movable on this. 5. Drive device according to claim 4, characterized in that the mechanical stop is formed by a shoulder (26) on a in the cylinder housing (22; 52) projecting end of the second hydraulic piston (24). 6. Drive device according to one of claims 1 to 5, characterized in that a hydraulic accumulator (46; 98) is present and that the switching valve (44) has a connection between the fourth pressure chamber (31; 74) and the hydraulic accumulator (46; 98) controls. 7. Drive device according to one of claims 1 to 6, characterized in that the first hydraulic piston (36) with a first active surface oppositely directed fifth effective surface bounds a fifth pressure chamber (39). 8. Drive device according to claim 7, characterized in that the switching valve (44) controls a fluidic connection between the fifth pressure chamber (39) and the fourth pressure chamber (31, 74). 9. Drive device according to claim 7, characterized in that the fifth pressure chamber (39) with a second memory (96) is connected. 10. Drive device according to one of claims 1 to 9, characterized in that the switching valve (44) is designed as a seat valve. Including 4 sheets of drawings