Hydraulic press drive with energy recovery

Abstract

A hydraulic die cushion drive (2) for a press device (10), comprising a multi-surface cylinder and a multi-surface piston arranged axially displaceably therein, characterized in that the multi-surface piston (8) has a rapid traverse pressure surface (48), a reverse traverse pressure surface (52) acting counter to the rapid traverse pressure surface, a counter-holding pressure surface (56), and a working pressure surface (60) acting counter to the rapid traverse pressure surface, and in that an rapid traverse pressure chamber (50) delimited by the rapid traverse pressure surface (48), a reverse traverse pressure chamber (54) delimited by the reverse traverse pressure surface (52) and acting counter to the rapid traverse pressure chamber (50), a counter-holding pressure chamber (58) delimited by the counter-holding pressure surface (56), and a working pressure chamber (62) delimited by the working pressure surface (60) and acting counter to the counter-holding pressure chamber (58) are formed in the multi-surface cylinder (6). with a working and counterholding arrangement (66), in which the counterholding pressure chamber (58), a first working pressure line (84), a hydraulic machine (68), a second working pressure line (86), and the working pressure chamber (62) form a lockable hydraulic circuit, in particular a hydraulic circuit that is essentially closed during operation of the die cushion drive, wherein the working and counterholding arrangement (66), in addition to the first working pressure line (84), the hydraulic machine (68), and the second working pressure line (86), comprises an electric motor (70) that is directly or indirectly coupled to the hydraulic machine (68) in a torque-transmitting manner, wherein the working and counterholding arrangement (66) is designed such that, upon an externally driven movement of the multi-surface piston (8) in an axial direction, in particular in the drawing direction (144), the hydraulic machine (68) can be driven in motor mode,wherein pressure medium can be conveyed from the counter-pressure chamber (58) into the working pressure chamber (62), the counter-pressure chamber (58) can be subjected to the counter-pressure and the electric motor (70) can be driven by the hydraulic machine (68) as a generator, and that when the multi-surface piston (8) is moved in an opposite axial direction, in particular in the retraction direction (146), the hydraulic machine (68) can be driven by the electric motor (70) in a pumping operation with a conveying direction reverse to that of the motor operation, wherein pressure medium can be conveyed from the working pressure chamber (62) into the counter-pressure chamber (58), and with a rapid traverse arrangement (102) which is designed to controllably supply either the rapid traverse pressure chamber (50) with a pressure medium for driving the movement a) or the reverse rapid traverse pressure chamber (54) with a pressure medium for driving the movement d).

Description

[0001] The invention relates to a hydraulic press drive with energy recovery according to the preamble of patent claim 1.

[0002] The published patent application DE 10 2009 058 407 A1 discloses a hydraulic press drive with a rapid traverse cylinder and a counter-holding cylinder arranged axially offset therefrom, which together form a die cushion and are each arranged in its own hydraulic circuit together with a hydraulic machine. Each of the hydraulic machines operates as a pump in one movement cycle of the cylinder assigned to it and as a motor in the other movement cycle. If one of the hydraulic machines operates as a motor, the power generated can be used to supply a consumer with energy. A disadvantage of this press drive is that each hydraulic circuit containing a hydraulic machine contains a throttle control in which a significant portion of the mechanical energy supplied by a pressing device is converted into heat and is lost.Another disadvantage is the large overall length of the die cushion caused by the axial displacement of the rapid traverse cylinder and the counter-holding cylinder.

[0003] DE 10 2010 019 324 A1 discloses a hydraulic die cushion drive with a multi-surface cylinder. DE 10 2006 025 463 A1 discloses a hydraulic press drive with a multifunctional cylinder with a piston. CN 2 02 628 634 U relates to a hydraulic drive for a high-speed CNC turret punch press.

[0004] Compared to the known devices, the object of the invention is to provide a hydraulic die cushion drive with reduced energy losses and a compact design of the die cushion and a method for its operation.

[0005] According to a first aspect of the invention, to achieve this object, a hydraulic die cushion drive for a press device is provided, wherein the die cushion drive comprises a multi-surface cylinder and a multi-surface piston arranged axially displaceably therein. According to the invention, the multi-surface piston has a rapid traverse pressure surface, a reverse traverse pressure surface counteracting said rapid traverse pressure surface, a counter-holding pressure surface, and a working pressure surface counteracting said rapid traverse pressure surface. Formed in the multi-surface cylinder are an rapid traverse pressure chamber delimited by the rapid traverse pressure surface, a reverse traverse pressure chamber delimited by the reverse traverse pressure surface and counteracting the rapid traverse pressure chamber, a counter-holding pressure chamber delimited by the counter-holding pressure surface, and a working pressure chamber delimited by the working pressure surface and counteracting the counter-holding pressure chamber.The multi-surface cylinder proposed here for use in a die cushion drive can be a multi-surface differential cylinder with a dual function, namely a rapid traverse and a working traverse function, and in particular a four-surface differential cylinder. The multi-surface piston can be a four-surface piston. The proposed design of the die cushion drive with the proposed multi-surface cylinder allows the pressure chambers required to control the movements of the multi-surface piston to be accommodated in a single cylinder housing of the multi-surface cylinder, thus enabling a compact design.

[0006] The die cushion drive can be designed to interact with a pressing device to repeatedly execute cycles with the following movements: a) accelerated movement of the multi-surface piston, in particular in a rapid traverse of the same, in a drawing direction from a press-side dead center to a die cushion-side dead center until the press ram driven in the drawing direction acts on a press-side end of the multi-surface piston, b) joint movement of the press ram and the multi-surface piston in the drawing direction in a drawing passage driven by the press ram, while applying a counter-pressure to the multi-surface piston until it approaches or reaches its dead center on the die cushion side, wherein the counter-pressure counteracts a contact pressure of the press ram in a retraction direction opposite to the drawing direction, c) reversing the direction of movement of the multi-surface piston and, in a retraction stroke driven by the die cushion, with the multi-surface piston moving back in the retraction direction until it approaches or reaches its press-side dead center and thereby pushes in the direction of the press ram, and d) Approaching the press-side dead center, particularly in a rapid traverse of the multi-surface piston, in the retraction direction.

[0007] In this case, an axial direction of the multi-surface cylinder can be aligned parallel to the drawing direction. The rapid traverse pressure chamber and the rapid traverse pressure surface can be designed to drive movement a), the counter-holding pressure chamber and the counter-holding pressure surface can be designed to apply the counter-holding pressure during movement b), the working pressure chamber and the working pressure surface can be designed to drive movement c), and the reverse rapid traverse pressure chamber can be designed to be the reverse rapid traverse pressure surface to drive movement d). The counter-holding pressure surface can be larger than the rapid traverse pressure surface and the working pressure surface can be larger than the reverse rapid traverse pressure surface. This design of the die cushion drive makes it suitable for interaction with the press device, so that the advantage of the compact design achievable with the die cushion drive also enables an overall more compact design of the press device.

[0008] The die cushion drive can comprise a working and counterholding arrangement in which the counterholding pressure chamber, a first working pressure line, a hydraulic machine, a second working pressure line, and the working pressure chamber form a lockable hydraulic circuit. This can be a substantially closed hydraulic circuit during operation of the die cushion drive. This hydraulic circuit can also be subjected to hydraulic preload. Such a closed circuit enables the hydraulic control of the counterholding pressure chamber to apply the counterholding pressure during movement b) or the hydraulic control of the working pressure chamber to drive movement c) to be carried out by displacing pressure medium from the counterholding pressure chamber into the working pressure chamber and vice versa, i.e., by a displacement control.With this type of displacement control, thermal energy loss is significantly lower, if not negligible, compared to previously known die cushions with throttle controls. The working stroke and counterholding arrangement is referred to below as the counterholding arrangement.

[0009] In addition to the first working pressure line, the hydraulic machine, and the second working pressure line, the counterholding arrangement can comprise an electric motor that is directly or indirectly coupled to the hydraulic machine in a torque-transmitting manner. The counterholding arrangement can be designed such that, upon an externally driven movement of the multi-surface piston in an axial direction, in particular in the retraction direction, such as when performing movement b), the hydraulic machine can be driven in motor mode, that pressure medium can be conveyed from the counterholding pressure chamber into the working pressure chamber, that the counterholding pressure chamber can be subjected to the counterholding pressure, and that the electric motor can be driven by the hydraulic machine as a generator.Furthermore, the counterholding arrangement can be designed such that when the multi-surface piston is moved in an opposite axial direction, in particular in the retraction direction, such as when moving c), the hydraulic machine can be driven by the electric motor in pump mode with a conveying direction opposite to that of the motor mode, such that pressure medium can be conveyed from the working pressure chamber into the counterholding pressure chamber, and the counterholding pressure chamber can be subjected to a retraction working pressure. The hydraulic machine can be an adjustable hydraulic machine, which can be designed, in particular, as an adjustable axial piston machine. The electric motor can be controlled at a variable speed and can, in particular, be a synchronous motor or an asynchronous motor.The torque-transmitting coupling of the electric motor with the hydraulic machine enables a compact arrangement of these two components and that the electric motor can be driven as a generator, particularly when performing movement b), whereby electrical power is generated which can be supplied to another consumer to increase energy efficiency.

[0010] The counter-holding arrangement can comprise a hydraulic machine with a drive shaft, a first pressure connection and a second pressure connection, the electric motor with a drive shaft, the first working pressure line connecting the first pressure connection of the hydraulic machine to the counter-holding pressure chamber, and the second working pressure line connecting the second pressure connection of the hydraulic machine to the working pressure chamber. The drive shaft of the hydraulic machine can be coupled to the drive shaft of the electric motor in a torque-transmitting manner, in particular by means of a connecting shaft. This embodiment with a torque-transmitting coupling of the electric motor and the hydraulic machine also enables a compact arrangement of these components and the drive of the electric motor during movement b) as a generator for generating electrical power that can be supplied to other consumers.

[0011] In the aforementioned embodiments of the counterholding arrangement, the hydraulic machine and the electric motor can be designed such that they can run essentially continuously during operation. In particular, the hydraulic machine and the electric motor can be designed such that they run with a constant direction of rotation and a substantially constant speed while executing movements a) to d). These operating modes are particularly energy-efficient because they largely avoid the need for additional power to accelerate and / or decelerate the rotating elements.

[0012] If the electric motor operates as a generator, the electrical power generated by the generator for driving the press ram can be electrically fed, in particular, into the main drive motor of the press ram. The die cushion drive can comprise a regenerative power line that electrically connects the electric motor to a main drive power line for supplying electrical power to the main drive motor, and an electrical converter arranged in the regenerative power line. The converter can be designed to convert the electrical power generated by the electric motor operating as a generator into electrical power that can be fed into the main drive power line and supplied to the main drive motor for driving the press ram. Thus, the generated electrical power is supplied to a consumer located near the die cushion drive, which can be done with low losses due to the short feed path.

[0013] The counterholding arrangement can also comprise more than one unit consisting of a hydraulic machine and an electric motor coupled thereto to transmit torque, these units being integrated parallel to one another in the lockable hydraulic circuit. In this way, the stress acting on the hydraulic machines and the electric motors, i.e. the load, such as when performing movement b), and the workload to be performed, such as when performing movement c), can be distributed across several machines, so that the stress on a single machine can be comparatively low and the service life of the machines is increased. In addition, the use of several small units offers advantages with regard to the achievable dynamics and manufacturing costs.

[0014] The counterholding arrangement can comprise a bypass line that connects the counterholding pressure chamber through a section of the first working pressure line and the retraction pressure chamber through a section of the second working pressure line, serving as a bypass line to the hydraulic machine. A first 2 / 2-way control valve can be arranged in the bypass line, which is designed to open, interrupt, or block this bypass line. When the first 2 / 2-way control valve is in a closed position and the bypass line is interrupted, the pressure medium can be conveyed in the closed hydraulic circuit to control the displacement of the retraction pressure chamber and the retraction pressure chamber, respectively, during movements b) and c).When the first 2 / 2-way control valve is in an open position and the bypass line is open, the displacement control of the pull pressure chamber and the retract pressure chamber is deactivated, and the movement of the multi-surface piston can be controlled via hydraulic controls of the first and second rapid traverse pressure chambers, respectively.

[0015] The multi-surface piston can comprise the following: a first piston rod, a second piston rod arranged opposite the first piston rod and on the press drive side, a connecting rod arranged between the first piston rod and the second piston rod, a first piston section formed at the transition from the first piston rod to the connecting rod, the surface of which facing the first piston rod is annular and forms the second rapid traverse pressure surface and the surface of which facing the connecting rod is annular and forms the working pressure surface, and a second piston section formed at the transition from the second piston rod to the connecting rod, the surface of which facing the second piston rod is annular and forms the first rapid traverse pressure surface and the surface of which facing the connecting rod is annular and forms the counter-pressure surface.In this case, the multi-surface piston can be pushed in the pulling direction by applying pressure to the first rapid traverse pressure surface and in the retracting direction by applying pressure to the counter-holding pressure surface, i.e. it can be subjected to a force. In this case, the multi-surface piston can also be pushed in the retracting direction by applying pressure to the second rapid traverse pressure surface and in the pulling direction by applying pressure to the working pressure surface. The second rapid traverse pressure surface can be essentially the same size as the first rapid traverse pressure surface and the working pressure surface can be essentially the same size as the counter-holding pressure surface. Finally, the rapid traverse pressure chamber, the retracting pressure chamber, the counter-holding pressure chamber and the working pressure chamber can each be an annular pressure chamber arranged around a piston rod section of the multi-surface piston.In these configurations of the multi-surface cylinder and the multi-surface piston guided within it, the multi-surface cylinder is a double-acting double-action cylinder or a differential cylinder with double action. This configuration enables the realization of a particularly compact design.

[0016] The die cushion drive can comprise a rapid traverse arrangement configured to controllably supply either the rapid traverse pressure chamber with a pressure medium to drive movement a) or the reverse rapid traverse pressure chamber with a pressure medium to drive movement d). Due to the rapid traverse arrangement provided separately by the counter-holding arrangement, movements a) and d) can be hydraulically controlled independently of movements b) and c).

[0017] The rapid traverse arrangement can comprise the following: a controllable 4 / 3-way control valve configured to control the first and second rapid traverse pressures, and comprising a first and a second control valve output and a first and a second control valve input; a rapid traverse pressure line connecting the control valve output to the rapid traverse pressure chamber; a reverse traverse pressure line connecting the second control valve output to the reverse traverse pressure chamber; and a pressure medium supply for supplying the first control valve input with pressure medium. With such a rapid traverse arrangement, movements a) and d) can be hydraulically controlled essentially independently of one another.

[0018] In this embodiment, (i) the third pressure line for supplying the pressure medium from the pressure medium supply, the rapid traverse pressure line and the rapid traverse pressure chamber, (ii) the third pressure line, the reverse traverse pressure line and the reverse traverse pressure chamber, and (iii) the third pressure line, the rapid traverse pressure line, the bypass line, and the reverse traverse pressure line can each be hydraulic circuits controllable by throttling the 4 / 3-way control valve. By means of these circuits, the movements a) and d) of the multi-surface piston, executed in rapid traverse and at successive time intervals, can be hydraulically controlled independently of one another.

[0019] In the aforementioned embodiments, the rapid-action arrangement can further comprise a hydraulic accumulator for storing pressure medium and a hydraulic pump, which is connected to the first control valve inlet via a third pressure line and is designed to convey pressure medium provided from the hydraulic accumulator to the first control valve inlet of the 4 / 3-way control valve. Furthermore, the rapid-action arrangement can comprise a tank, which is connected to the second control valve inlet of the 4 / 3-way control valve via a discharge line. The tank enables the pressure medium to be collected, treated, and reused as required.

[0020] The rapid traverse arrangement can comprise a bypass line which connects the rapid traverse pressure chamber through a section of the rapid traverse pressure line and the reverse traverse pressure chamber through a section of the reverse traverse pressure line as a bypass line to the 4 / 3-way control valve. A second 2 / 2-way control valve can be arranged in the bypass line and is designed to open or interrupt the bypass line. When the 2 / 2-way control valve is in an open position, so that the bypass line is open, hydraulic controls of the rapid traverse and reverse traverse pressure chambers are deactivated and control of the movement of the multi-surface piston can be taken over by the counter-holding arrangement. When the 2 / 2-way control valve is in a closed position, so that the bypass line is interrupted oris shut off, independent hydraulic controls of the first and second rapid traverse pressure chambers are possible via a throttle control effected by the 4 / 3-way control valve.

[0021] According to a second aspect of the invention, a method for operating a die cushion drive according to the first aspect of the invention is provided. The die cushion drive comprises a multi-surface cylinder and a multi-surface piston, and is designed to interact with a press device having a press ram drivable via a main drive motor. The method comprises the following steps: b) joint movement of the press ram and the multi-surface piston in the drawing direction in a drawing direction driven by the press ram, while applying a counter-pressure to the multi-surface piston until it approaches or reaches its dead center on the die cushion side, wherein the counter-pressure counteracts a contact pressure of the press ram in a retraction direction opposite to the drawing direction, wherein pressure medium is conveyed from a counter-pressure chamber of the multi-surface cylinder through a substantially closed hydraulic circuit by a hydraulic machine operating in motor mode into a working pressure chamber of the multi-surface cylinder, and wherein the hydraulic machine drives an electric motor coupled to it in a torque-transmitting manner as a generator, and c) Reversing the direction of movement of the multi-surface piston and retracting the multi-surface piston in the retraction direction until it approaches or reaches its press-side dead center, while pushing in the direction of the press ram, whereby pressure medium is conveyed from the working pressure chamber through the closed hydraulic circuit into the counterpressure chamber by means of the hydraulic machine driven by the electric motor and now operating in pump mode. This method enables the same advantages mentioned above for the die cushion drive according to the first aspect of the invention to be achieved, including the energy-saving hydraulic control of movements b) and c) by means of the die cushions that can be realized in a compact design.

[0022] In the procedure, the following step may be carried out before step b): a) Accelerated movement of the multi-surface piston, in particular in a rapid traverse, in a drawing direction from a press-side dead center to a die-cushion-side dead center, until the press ram driven in the drawing direction acts on a press-side end of the multi-surface piston, by applying pressure medium to a rapid traverse pressure chamber of the multi-surface cylinder delimited by a rapid traverse pressure surface of the multi-surface piston. Furthermore, after step c), the following step can be carried out: d) Approaching the press-side dead center, in particular in a rapid traverse of the multi-surface piston, in the retraction direction by applying pressure medium to a retraction pressure chamber of the multi-surface cylinder delimited by a retraction pressure surface of the multi-surface piston.By sequentially performing steps a), b), c) and d), the corresponding movements a), b), c) and d) can be hydraulically controlled independently of one another.

[0023] During the execution of step b), the electric motor can operate as a generator, and the electrical power generated by the generator to drive the press ram can be electrically fed into the press ram's main drive motor. This allows the generated electrical power to be supplied to a consumer located near the die cushion drive, with minimal losses due to the short feed path.

[0024] Embodiments of the invention are explained in more detail below with reference to a schematic drawing. It shows: Fig. 1 a schematic hydraulic circuit diagram of an embodiment of the hydraulic die cushion drive according to the invention.

[0025] The invention is explained below using a hydraulic sheet metal forming or deep-drawing press and a drawing process carried out therewith; however, it is in principle also applicable to other types of presses or machine tools. Such a press device 10 has a two-part tool (not shown) in which a workpiece to be formed (also not shown) is formed. An upper part of the tool, fastened to a press ram 12, is designed as a die. The press device 10 has a main drive with an electric main drive motor 20, which drives a crank mechanism 18 via a main drive shaft 22, to which one end of a crank rod 16 is pivotally connected, the other end of the crank rod 16 being connected to a (in Fig. 1 upper) end of a push rod 14, and at the other (in Fig. 1 lower) end of the push rod 14, a press ram 12 is formed, to which the upper part of the tool is fastened. The crank rod 16 transmits a rotary movement of the crank drive 18 into an up and down movement of the push rod 14 and the press ram 12 with the upper part of the tool. The movement from an upper to a lower reversal point, i.e. in a drawing direction 144, is referred to as the forward stroke or drawing stroke, and the subsequent movement from the lower to the upper reversal point, i.e. in a retraction direction 146 opposite to the drawing direction 144, is referred to as the return stroke or retraction stroke. The movement of the press ram 12 driven by the crank drive 18 is predetermined by the structural design of the crank drive 18 and its rotational speed. During a complete working cycle of the drawing process consisting of the drawing and the retraction stroke, the crank drive 18 performs a full revolution.

[0026] A lower part of the tool (not shown) is attached to one end of a piston rod 42 of a multi-surface piston 8 driven by a hydraulic multi-surface cylinder 6. The movement of the multi-surface piston 8 is controlled by a pressure medium supply to a corresponding first pressure chamber of the multi-surface cylinder 6 and by a pressure medium discharge from another pressure chamber of the cylinder 6. The movement of the lower part of the tool attached to the piston rod 42 is ultimately influenced by controlling the pressure medium flow to and from the corresponding pressure chambers of the multi-surface cylinder 6, independently of the movement of the crank drive 18.

[0027] A movement cycle of the multi-surface piston 8 carried out during a working cycle of the pressing device 10 comprises a sequence of four movements a) to d) carried out in successive time intervals. During the first time interval, the movement a) takes place as an accelerating movement of the multi-surface piston 8 in a rapid traverse in the drawing direction 144 from a press-side (in the Fig. 1 upper) dead center to a die cushion side (in Fig. 1 bottom) dead center until the multi-surface piston 8 moves at practically the same speed as the press ram 12 moving in the drawing direction 144 is driven, and the press ram 12 acts on the press-side end of the piston rod 42 of the multi-surface piston 8. In the second time interval following the first time interval, movement b) is carried out, in which the upper part and the lower part of the tool rest on opposite sides of the workpiece and deform it, and during the deformation they approach each other even further. Movement b) is therefore a joint movement of the press ram 12 and the multi-surface piston 8 in the drawing direction 144 in a drawing pass driven by the press ram 12. Movement b) takes place under the application of a counter-pressure in a pressure chamber of the multi-surface cylinder 6 to the multi-surface piston 8 until its die cushion-side (in Fig. 1 bottom) dead center. The counter-pressure counteracts the contact pressure of the press ram 12 in a retraction direction 146 opposite to the drawing direction 144. Due to the action of the counter-pressure counteracting the contact pressure of the press ram 12, the workpiece is deformed between the two parts of the tool. A third time interval follows, in which movement c) is carried out. This comprises a reversal of the direction of movement of the multi-surface piston 8 and a retraction movement driven by the die cushion 4 with a retraction of the multi-surface piston 8 in the retraction direction 146 until it approaches its press-side dead center and thereby pushes in the direction of the press ram 12. Then the fourth time interval follows, in which movement d) is carried out.This movement d) of the multi-surface piston 8 optionally includes moving to a removal position in which the workpiece can be removed from the area between the upper part and the lower part of the tool, and in any case moving to the press-side (in . Fig. 1 top) dead center in a rapid traverse of the multi-surface piston 8 in the retraction direction 146.

[0028] The present invention now relates to the Fig. 1. This comprises a die cushion 4 with the multi-surface cylinder 6, the multi-surface piston 8 arranged therein so as to be displaceable in the axial direction, a working movement and counter-holding arrangement (hereinafter referred to as counter-holding arrangement) 66 for controlling the movements b) and c) of the multi-surface piston 8 and a rapid traverse arrangement 102 for controlling the movements a) and d) of the multi-surface piston 8.

[0029] The multi-surface cylinder 6 comprises a cylinder housing 24 which has a substantially cylindrical jacket wall, a first end wall 28 facing away from the pressing device 10 and having an opening 30 formed in the center thereof, a second end wall 32 facing the pressing device 10 and having an opening 34 formed in the center thereof, and a partition wall 36 arranged in the axial direction in the center between the first and second end walls 28, 32 and having an opening 38 formed in the center thereof.The multi-surface piston 8 comprises a first piston rod 40, which is guided axially displaceably in the opening 30 of the first end wall 28, a second piston rod 42, which is arranged opposite the first piston rod 40 and on the press drive side and is guided axially displaceably in the opening 34 of the second end wall 32, and a connecting rod 64 arranged between the first and second piston rods 40 and 42 and is guided axially displaceably in the opening 38 of the partition wall 36. The multi-surface piston 8 further comprises a first piston section 44 formed at the transition from the first piston rod 40 to the connecting rod 64, the surface of which facing the first piston rod 40 is annular and forms a reverse travel pressure surface 52, and the surface of which facing the connecting rod 64 is also annular and forms a working pressure surface 60.Furthermore, the multi-surface piston 8 comprises a second piston section 46 formed at the transition from the second piston rod 42 to the connecting rod 64, the surface of which second piston section 46 facing the second piston rod 42 is annular and forms a rapid traverse pressure surface 48, and the surface of which connecting rod 64 is annular and forms a counter-pressure surface 56. An outer circumferential surface of the first piston section 44 is slidably guided in the axial direction on an inner wall surface of the jacket wall of the cylinder housing 24 in the axial region between the first end wall 28 and the partition wall 36. Analogously, an outer circumferential surface of the second piston section 46 is slidably guided in the axial direction on the inner wall surface of the jacket wall of the cylinder housing 24 in the axial region between the second end wall 32 and the partition wall 36.The rapid traverse and reverse traverse pressure surfaces 48 and 52, as well as the counter-holding pressure surface 56 and the retracting pressure surface 60, are each annular pressure surfaces. Within the cylinder housing 24, the rapid traverse pressure surface 48 defines an annular rapid traverse pressure chamber 50, the reverse traverse pressure surface 52 defines an annular reverse traverse pressure chamber 54, the counter-holding pressure surface 56 defines an annular counter-holding pressure chamber 58, and the working pressure surface 60 defines an annular working pressure chamber 62. The rapid traverse and reverse traverse pressure surfaces 48 and 52 are essentially the same size. The counter-holding pressure surface 56 and the working pressure surface 60 are also essentially the same size. However, the counter pressure surface 56 is larger than the rapid traverse pressure surface 48 and the working pressure surface 60 is larger than the reverse traverse pressure surface 52. Due to this design, the multi-surface cylinder 6 is a double-acting differential orDouble-action cylinder in which the multi-surface piston 8 can execute working strokes in working steps, controlled by pressure medium supply to or pressure medium discharge from the pressure chambers 58 and 62, and rapid strokes in rapid traverses, controlled by pressure medium supply to or pressure medium discharge from the pressure chambers 50 and 54.

[0030] The counterholding arrangement 66 comprises an adjustable hydraulic machine 68, such as an adjustable axial piston machine, with a first pressure port 68a, a second pressure port 68b, and a drive shaft, a first working pressure line 84 connecting the first pressure port 68a to the counterholding pressure chamber 58 of the multi-surface differential cylinder 6, and a second working pressure line connecting the second pressure port 68b to the working pressure chamber 62 of the multi-surface cylinder 6, and a variable-speed electric motor 70 configured as a synchronous motor with a drive shaft. The drive shaft of the hydraulic machine 68 and the drive shaft of the electric motor 70 are coupled to one another in a torque-transmitting manner and are arranged coaxially with one another, forming a connecting shaft 72 that couples the hydraulic machine 68 and the electric motor 70 in a torque-transmitting manner.The arrangement 66 further comprises a bypass line 88 which connects the first working pressure line 84 to the second working pressure line 86 and in this way connects the counter-pressure chamber 58 through a section of the first working pressure line 84 and the retraction pressure chamber 62 through a section of the second working pressure line 86, specifically as a bypass line to the hydraulic machine 68. A first 2 / 2-way control valve 78 is arranged in the bypass line 88 and is designed to open or interrupt this bypass line 88. For this purpose, the first 2 / 2-way control valve 78 has a first switching position in which an inlet of the valve 78 is connected to an outlet of the valve 78 (in . Fig. 1 not switched) and a second switching position in which the input and output of the valve 78 are not connected to each other (in the Fig. 1 switched).

[0031] The counter-holding arrangement 66 further comprises a first pressure relief line 90, in which a first pressure relief valve 80 is arranged, and a second pressure relief line 92, in which a second pressure relief valve 82 is arranged. The first pressure relief line 90 connects the second working pressure line 86 to the first working pressure line 84 via the first pressure relief valve 80, wherein the first pressure relief valve 80 opens only in the direction from the second working pressure line 86 to the first working pressure line 84 and only when a predetermined, e.g. pre-adjustable, pressure threshold is exceeded. The second pressure relief line 92 connects the first working pressure line 84 to the second working pressure line via the second pressure relief valve 82, which opens only in the direction from the first working pressure line 84 to the second working pressure line 86 and only when a predetermined, e.g.presettable pressure threshold. The first pressure relief valve 80 or the second pressure relief valve 82 serves to protect the second working pressure line 86 or the first working pressure line 84 against overpressure.

[0032] The counter-holding arrangement 66 comprises a pressure pump 76 with an intake inlet connected to a pressure medium reservoir (not shown) and a delivery outlet, furthermore a first pressure line 94 in which a first check valve 96 is arranged and via which the delivery outlet of the pressurization pump 76 is connected to the second working pressure line 86, and a second pressure line 98 in which a second check valve 100 is arranged and via which the delivery outlet of the pressurization pump 76 is connected to the first working pressure line 84. The first check valve 96 opens only in its flow direction from the pressure pump 76 to the second working pressure line 86 and closes in the opposite direction. The second check valve 100 opens only in the direction from the pressurization pump 76 to the first working pressure line 84 and closes in the opposite direction.When the pressure pump 76 is put into operation, it first pumps pressure medium from the pressure medium reservoir and through the first and second pressure lines 94 and 98 into the first and second working pressure lines 84 and 86 and through these into the counter-pressure chamber 58 and the working pressure chamber 62 of the multi-surface cylinder 6, until a pressure, i.e. a hydraulic preload, has built up in the lines 94, 98, 84 and 86 as well as in the pressure chambers 58 and 62, which corresponds to the maximum delivery pressure of the pressure pump 76. After this pressure or this hydraulic preload has been reached, the pressure pump 76 only pumps pressure medium to compensate for any leakage losses in the lines 94, 98, 84, 86, in the pressure chambers 58 and 62 and in the hydraulic machine 68.Because of the first and second check valves 96 and 100 blocking in the direction towards the pressure boosting pump 76, the counter pressure chamber 58, the first working pressure line 84, the hydraulic machine 68, the second working pressure line 86 and the retraction pressure chamber 62 form a closable hydraulic circuit which is closed during operation by the check valves 96 and 100 and which can be placed under hydraulic prestress by means of the pressure pump 76.

[0033] When the first 2 / 2-way control valve 78 is in the closed position and the bypass line 88 is interrupted accordingly, the counter pressure chamber 58 and the working pressure chamber 62 are pressurized with the hydraulically prestressed pressure medium depending on the conveying direction and the conveying capacity of the hydraulic machine 68. If now during the movement b) the multi-surface piston 8 is moved in the drawing direction 144 (in Fig. 1 downwards), the pressure medium is displaced out of the counter-pressure chamber 58 by the counter-pressure surface 56 driven in the pulling direction 144 and through the first working pressure line 84, the hydraulic machine 68 and the second working pressure line 86 (i.e. through a closed hydraulic circuit) into the working pressure chamber 52. The hydraulic machine 68 is driven by the displaced pressure medium and operates as a hydraulic motor. Via the torque-transmitting coupling with the electric motor 70, the hydraulic machine 68 transmits a torque to the electric motor 70 and drives it as an electrical generator. In the process, electrical power is generated which can be supplied to another consumer.

[0034] In the die cushion drive 2, the electrical power generated by the electric motor 70, which functions as a generator, is supplied to the main drive motor 20 of the press and fed electrically. For this purpose, a regenerative power line 140 is provided, which electrically connects the electrical generator output of the electric motor 70 to a main drive power line 142, which supplies the main drive motor 20 with working current. An electrical converter 138 is arranged in this regenerative power line 140, which serves to convert the electrical power generated by the electric motor 70, which functions as a generator, into electrical power that is fed into the main drive power line 142 and through this into the main drive motor 20.

[0035] During the movement b) of the multi-surface piston 8, with the first 2 / 2-way control valve 78 on the working piston unit of the hydraulic machine 68 closed, a controlled counter-pressure (pulling pressure) is built up in the counter-pressure chamber 58 via a torque control and, if necessary, superimposed with a swivel angle control. This counter-pressure acts on the multi-surface piston 8 via the counter-pressure surface 56 in the retraction direction 146 (ie in the Fig. 1 upwards) as long as the multi-surface piston 8 performs the movement b) until it reaches its die cushion side (in Fig. 1 bottom) dead center.

[0036] When the dead center on the die cushion side is reached, movement b) ends and movement c) begins. The conveying direction and the operating mode of the hydraulic machine 68 are changed by changing the swivel angle, and the pressure medium is thus conveyed by the hydraulic machine 68, now operating as a pump, in the reverse conveying direction, now from the working pressure chamber 62 through the closed hydraulic circuit into the counter-pressure chamber 58. Accordingly, the direction of movement of the multi-surface piston 8 is reversed, and the piston 8 is moved in the retraction direction 146 (in Fig. 1 upwards). As mentioned, the hydraulic machine 68 operates as a pump and is driven by the electric motor 70, which now operates as a motor. During the transition from movement b) to movement c) of the multi-surface piston 8, i.e. before, during and after its reversal of movement direction, the electric motor 70, and due to the torque-transmitting coupling also the hydraulic machine 68, run with the same direction of rotation and essentially a constant speed of the drive shaft 72. This has the advantage that no superfluous energy is required for braking or accelerating the speed of the electric motor 70 and the hydraulic machine 68. The multi-surface piston 8 is driven in the retraction direction 146 until it approaches its press-side (in Fig. 1 top) dead center and movement c) ends. At this time, the 2 / 2-way control valve 78 moves to its open position and opens the bypass line 88, so that the pressure medium can now flow through the working chamber bypass line 88 with almost no resistance and the hydraulic machine 68 runs without load, whereby the control of the movement of the multi-surface piston 8 by the hydraulic machine 68 or the displacement of the pressure medium from the counter-pressure chamber 58 into the working pressure chamber 62 or vice versa caused by this is also prevented. The control of the movement of the multi-surface piston 8 is transferred to the rapid traverse arrangement 102 after the end of movement c) and for the duration of the subsequent movement d) and movement a) of a subsequent movement cycle of the multi-surface piston 8.

[0037] The rapid traverse arrangement 102 is designed to controllably and selectively either pressurize the rapid traverse pressure chamber 50 with a pressure medium, thereby driving movement a), or pressurize the reverse rapid traverse pressure chamber 54 with the pressure medium, thereby driving movement d). The rapid traverse arrangement 102 comprises a controllable 4 / 3-way control valve 104, which is designed to regulate or control the pressure (rapid traverse pressure) in the rapid traverse or reverse rapid traverse pressure chambers 50 and 54, respectively. The 4 / 3-way control valve 104 has a first and a second control valve output 104a and 104b, and a first and a second control valve inlet 104c and 104d. The rapid traverse arrangement 102 further comprises a rapid traverse pressure line 124 which connects the first control valve outlet 104a to the rapid traverse pressure chamber 50, a reverse rapid traverse pressure line 126 which connects the second control valve outlet 104b to the reverse rapid traverse pressure chamber 54, and a pressure medium supply (not designated) for supplying pressure medium.This pressure medium supply supplies the first control valve inlet 104c of valve 104 and, via valve 104, the rapid traverse and reverse traverse pressure lines 124 and 126, and through these, the rapid traverse and reverse traverse pressure chambers 50 and 54 of the multi-surface cylinder 6 with the pressure medium. For this purpose, the pressure medium supply comprises a hydraulic pump 118 with a delivery outlet, a third pressure line 134 connecting the delivery outlet of the hydraulic pump 118 to the first control valve inlet 104c, a hydraulic accumulator 116 for storing pressure medium, and an accumulator supply line 136 connecting the hydraulic accumulator 116 to the third pressure line 134, so that pressure medium provided from the hydraulic accumulator 116 can be quickly pumped by means of the hydraulic pump 118 to the 4 / 3-way control valve 104 and the hydraulic circuits connected to its outputs.

[0038] The 4 / 3-way control valve 104 has three switching positions, a first switching position (in Fig. 1), in which the control valve inputs 104c and 104d are separated from the control valve outputs in 104a and 104b, a switching position with parallel connection, wherein the first control valve input 104c is connected to the second control valve output 104b and the second control valve input 104d is connected to the first control valve output 104a (in Fig. 1 in the valve 104 indicated below and not switched), and a switching position with crossed connections, wherein the first control valve inlet 104c is connected to the first control valve outlet 104a and the second control valve inlet 104d is connected to the second control valve outlet 104b (in Fig. 1 in valve 104 shown above and not switched). The arrangement 102 further comprises a bypass line 128, which connects the rapid traverse pressure line 124 with the reverse traverse pressure line 126 and in which a second 2 / 2-way control valve 106 is arranged. This can be switched between a closed position (in Fig. 1) and an opening position (in Fig. 1 not switched) so that the bypass line 128 can be controllably interrupted or opened. By means of this second 2 / 2-way control valve 106, the rapid traverse pressure chamber 50 can be connected to or interrupted by the reverse traverse pressure chamber 54 of the multi-surface cylinder 6 via a portion of the rapid traverse pressure line 124, the bypass line 128, and a portion of the reverse traverse pressure line 126.

[0039] The rapid traverse arrangement 102 further comprises a third 2 / 2-way valve 110, which is arranged in the first rapid traverse pressure line 124 in the section between the second control valve outlet 104a of the valve 104 and the branch point of the bypass line 128 from the rapid traverse pressure line 124, and a fourth 2 / 2-way valve 108, which is arranged in the reverse rapid traverse pressure line 126 between the first control valve outlet 104b of the valve 104 and the branch point of the bypass line 128 from the reverse rapid traverse pressure line 126. The third 2 / 2-way valve 110 has a closed position (in Fig. 1), in which the rapid traverse pressure line 124 is interrupted, and an opening position (in Fig. 1 not switched), in which the rapid traverse pressure line 124 is opened. The fourth 2 / 2-way valve 108 has a closed position (in Fig. 1), in which the reverse pressure line 126 is interrupted, and an opening position (in Fig. 1 not switched), is open in the reverse rapid traverse pressure line 126. By means of the third 2 / 2-way valve 110 or the fourth 2 / 2-way valve 108, the rapid traverse pressure line 124 or the reverse rapid traverse pressure line 126 can be controlled in addition to the control by means of the 4 / 3-way control valve 104.

[0040] The rapid traverse arrangement 102 further comprises a third pressure relief line 130 with a third pressure relief valve 112 arranged therein, and a fourth pressure relief line 132 with a fourth pressure relief valve 114 arranged therein. The third pressure relief line 130 connects the reverse rapid traverse pressure line 126 to the rapid traverse pressure line 124 via the third pressure relief valve 112, which is permeable to pressure medium only in this direction and blocks in the opposite direction. The third pressure relief valve 112 opens only when the pressure in the reverse rapid traverse pressure line 126 exceeds a predetermined pressure threshold of the third pressure relief valve 112 and blocks in the opposite direction. The fourth pressure relief line 132 connects the rapid traverse pressure line 124 to the reverse traverse pressure line 126 via the fourth pressure relief valve 114, which is permeable to pressure medium only in this direction and blocks in the opposite direction.The fourth pressure relief valve 114 opens only when the pressure in the rapid traverse pressure line 124 exceeds a predetermined pressure threshold of the fourth pressure relief valve 114, and closes in the opposite direction. The third and fourth pressure relief valves 112 and 114 serve to protect the reverse and rapid traverse pressure lines 126 and 124, respectively, against excess pressure. The rapid traverse arrangement 102 further comprises a tank 120 for collecting pressure medium and a discharge line 122 connecting the second control valve inlet 104d to the tank 120.

[0041] In the rapid traverse arrangement 102, (i) the third pressure line 134, the rapid traverse pressure line 124 and the rapid traverse pressure chamber 50, (ii) the third pressure line 134, the reverse rapid traverse pressure line 126 and the reverse rapid traverse pressure chamber 54, and (iii) the third pressure line 134, the rapid traverse pressure line 124, the bypass line 128 and the reverse rapid traverse pressure line 126, each form hydraulic circuits that can be selected alternatively depending on the switching position of the 4 / 3-way control valve 104 and can each be controlled by throttling the 4 / 3-way control valve 104 with regard to the applied pressure medium pressure.

[0042] When the second 2 / 2-way control valve 106 is closed, the following controls of the rapid traverse and reverse traverse pressure chambers 50 and 54 can be carried out in the rapid traverse arrangement 102.

[0043] Execution of movement a): The third and fourth 2 / 2-way valves 108 and 110 are open and the 4 / 3-way control valve 104 is in its crossed switching position. The rapid traverse pressure chamber 50 is supplied with pressure medium via the rapid traverse pressure line 124, the valve 104 and the third pressure line 134 from the hydraulic pump 118, whereby a control or regulation of the pressure is possible via the controllability of the valve 104. By applying pressure medium to the rapid traverse pressure chamber 50, the rapid traverse pressure surface 48 of the multi-surface piston 8 is moved in the drawing direction 144 (in Fig. 1 downwards) with a pressure medium pressure that can be regulated or controlled by the throttling on the control valve 104.

[0044] Execution of movement d): The valves 108 and 110 are opened and the 4 / 3-way control valve is switched to its parallel switching position. The reverse travel pressure chamber 54 is supplied with pressure medium via the reverse travel pressure line 126, the 4 / 3-way control valve 104 and the third pressure line 134 from the hydraulic pump 118, whereby a control or regulation of the pressure is possible via the controllability of the valve 104. By supplying the pressure medium to the reverse travel pressure chamber 54, the reverse travel pressure surface 52 of the multi-surface piston 8 is moved in the retraction direction 146 (in Fig. 1 upwards) with a pressure medium pressure that can be regulated or controlled by the throttling on the control valve 104.

[0045] When the second 2 / 2-way control valve 106 is open and the third and fourth 2 / 2-way valves 108 and 110 are each closed, pressure medium can flow with virtually no resistance through the bypass line 128 from the rapid traverse pressure chamber 50 into the reverse rapid traverse pressure chamber 54, or in the opposite direction. In this case, the control of the movement of the multi-surface piston 8 by the rapid traverse and reverse rapid traverse pressure chambers 50 and 54 is deactivated, and the movement control of the multi-surface piston 8 can be transferred to the working movement and counterholder arrangement 66 to control movements b) and c).

[0046] A complete working cycle of the die cushion comprises the movements a) to d) of the multi-surface piston 8 and is controlled by the die cushion drive 2, as described below. The (small) rapid traverse pressure surface 48 or the first pressure chamber 50 delimited by it serve to pre-accelerate the multiple piston 8 in the drawing direction 144 during movement a). The (small) reverse traverse pressure surface 52 or the reverse traverse pressure chamber 54 delimited by it serve to position the multi-surface piston 8 in its starting position on the press-side (in Fig. 1 upper) dead center during movement d). The (large) counter-pressure surface 56 or the counter-pressure chamber 58 delimited by it serve during movement b) to apply the desired, specific counter-pressure (pulling pressure) which in the retraction direction 146 (in Fig. 1 upwards). The (large) working pressure surface 60 or the working pressure chamber 62 delimited by it serve, after completion of the pulling movement (movement b)), to move the multi-surface piston 8 back to the vicinity of the starting position by means of the hydraulic machine 68 acting as a feed pump during movement c).

[0047] At the beginning of the movement a), ie when the multi-surface piston 8 is in its press-side position (in Fig. 1 top) dead center, the valves are switched as follows. The first 2 / 2-way control valve 78 in the bypass line 88 is open, so that the counter-pressure chamber 58 and the working pressure chamber 62 are short-circuited by the bypass line 88, whereby the closed hydraulic circuit of the arrangement 66 is pre-stressed. The hydraulic machine 68 and the electric motor 70 are operated together essentially at a nominal speed, and the hydraulic machine 68 is set for a conveying direction of the pressure medium from the counter-pressure chamber 58 to the working pressure chamber 62. The nominal speed is the speed required to achieve the drawing speed of the multi-surface piston 8 upon impact of the press ram 12. The valves 108 and 110 in the rapid traverse arrangement 102 are open, and the 4 / 3-way control valve 104 is in the control position.

[0048] Upon a predetermined start signal, movement a) begins. The 4 / 3-way control valve 104 is moved to the crossed position, so that the rapid traverse pressure chamber 50 is supplied with pressure medium and the rapid traverse pressure surface 48 is subjected to pressure medium pressure. The multi-surface piston 8 is accelerated in the drawing direction 144. This continues until the multi-surface piston 8 has reached the speed of the press ram 12 moving in the drawing direction 144 and the press ram 12 begins to act on the multi-surface piston 8. Then movement b) begins.

[0049] To initiate movement b), the 2 / 2-way control valve 106 opens, so that the first and second rapid traverse pressure chambers 50 and 54 are short-circuited via the bypass line 128 and the control of the movement of the multi-surface piston 8 is transferred from the rapid traverse arrangement 102 to the counter-holding arrangement 66. In this case, the valves 108 and 110 of the rapid traverse arrangement 102 close and interrupt the pressure medium supply from the hydraulic pump 118. The first 2 / 2-way control valve 78 of the counter-holding arrangement 66 closes, so that the working piston unit in the hydraulic machine 68 builds up a controlled counter-holding pressure (drawing pressure) via a displacement control or a torque control, and if necessary superimposed by a swivel angle control of the hydraulic machine 68, while the multi-surface cylinder 8 is moved by the press ram 12 in the drawing direction 144 (in Fig. 1 downwards). Because a force is exerted on the multi-surface piston 8 from the outside via the press ram 12 and the multi-surface piston 8 is driven, pressure medium from the counter-pressure chamber 58 is displaced into the working pressure chamber 62 by the hydraulic machine 68 acting as a motor and drives the hydraulic machine 68. This in turn drives the electric motor 70 due to the torque-transmitting coupling, which acts as an electric generator and generates electrical power. This electrical power is converted by the inverter 138 and supplied and fed to the main drive motor 20 of the press drive (drive of the press ram 12). In order to keep the dead volume in the closed hydraulic circuit, i.e. in the first and second working pressure lines 84 and 86, as small as possible, the hydraulic machine 68 is installed as close as possible to the multi-surface cylinder 6 orarranged at the pressure chambers 58 and 62, and the lines 84 and 86 are designed to be correspondingly short. Upon reaching the die cushion side (in . Fig. 1 bottom) dead center, the movement b) ends and the actual drawing process of the workpiece to be formed is completed.

[0050] The subsequent movement c) is initiated by a reversal of the direction of movement of the multi-surface piston 8. For this purpose, the pump operation is switched on and the delivery direction of the hydraulic machine 68 is switched on by changing the swivel angle, so that the pumping action of the hydraulic machine 68 displaces pressure medium from the working pressure chamber 62 into the counter-pressure chamber 58. If necessary, the speed of the hydraulic machine 68 and the electric motor 70 is slightly adjusted in order to achieve the desired retraction speed of the multiple piston 8. When the multiple piston 8 approaches its press-side (in Fig. 1 upper) dead center the movement ends c).

[0051] At the beginning of movement d), valve 78 of arrangement 66 opens and opens bypass line 88, so that pressure chambers 58 and 62 are short-circuited and the movement control of the multiple piston 8 on the counter-holding arrangement 66 is transferred to the rapid traverse arrangement 102. Valves 108 and 110 open, and valve 106 closes and interrupts bypass line 128. The 4 / 3-way control valve 104 is placed in the parallel switching position, so that the reverse rapid traverse pressure chamber 54 is controllably supplied with pressure medium by the throttling on valve 104, and the multi-surface piston 8 is moved to the press-side dead center via this throttling control.

[0052] The die cushion 4 according to the invention with the multi-surface cylinder 6 and the multi-surface piston 8 movable therein, and the described working stroke and counterholding arrangement 66, make it possible to recover up to 70% of the work supplied externally to the multiple piston 8 via the press ram 12 during movement b), while the electric motor 70 is operated as an electric generator. The work supplied via the press ram 12 would be converted almost completely (almost 100%) into thermal energy if the movement of the multiple piston 8 were throttled. Furthermore, the energy required for the retraction stroke (movement c)) is reduced by approximately 30% compared to the energy required for throttled control, since displacement control is also used for this movement c).

[0053] By designing the working and counter-holding arrangement 66 with the lockable or, in operation, closed hydraulic circuit, it is possible to arrange the hydraulic machine 68 or a unit formed by the hydraulic machine 68 and the electric motor 70 close to the multi-surface cylinder 6 and to minimize the dead volumes in the first and second working pressure lines 84 and 86 by designing them short. Therefore, a much smaller hydraulic tank can be selected as the storage tank (pressure medium reservoir) for the pressure pump 76 than would be necessary with throttle control of movements b) and c). Due to the smaller hydraulic tank size and its significantly reduced tank volume, the complex cooling systems otherwise required for larger tank volumes can be dispensed with or made much smaller. Since during movements b), iethe drawing process, and during movement c) the rapid and reverse traverse pressure surfaces 48 and 52 are not effective, a net force on the (large) pressure surfaces 76 and 60 is greater, so that with a similar net drawing force or a net drawing force required for the drawing process, a smaller counter-pressure surface 56 and a smaller working pressure surface 60 can be selected. List of reference symbols: 2 die cushion drive 4 draw cushions 6 multi-surface cylinders 8 multi-surface pistons 10 Pressing device 12 press rams 14 Pushrod 16 Crank rod 18 Crank drive 20 Main drive motor 22 Main drive shaft 24 cylinder housings 26 Cylinder wall 28 first front wall 30 Opening 32 second end wall 34 Opening 36 Partition wall 38 Opening 40 first piston rod 42 second piston rod 44 first piston section 46 second piston section 48 rapid traverse printing area 50 rapid traverse printing chamber 52 return pressure surface 54 Return pressure chamber 56 Counter pressure surface 58 Counter pressure chamber 60 working print area 62 Working pressure chamber 64 connecting rod 66 Working process and counter-holding arrangement 68 Hydromachine 68a first pressure connection 68b second pressure connection 70 electric motor 72 connecting shaft 74 Pressurization device 76 pressure pump 78 first 2 / 2-way control valve 80 first pressure relief valve 82 second pressure relief valve 84 first working pressure line 86 second working pressure line 88 Bypass line 90 first pressure relief line 92 second pressure relief line 94 first pressure line 96 first check valve 98 second pressure line 100 second check valve 102 Rapid traverse arrangement 104 4 / 3-way control valve 104a first control valve output 104b second control valve output 104c first control valve inlet 104d second control valve inlet 106 second 2 / 2-way control valve 108 third 2 / 2-way valve 110 fourth 2 / 2-way valve 112 third pressure relief valve 114 fourth pressure relief valve 116 hydraulic accumulators 118 Hydraulic pump 120 tanks 122 discharge line 124 Rapid traverse pressure line 126 Reverse speed pressure line 128 Bypass line 130 third pressure relief line 132 fourth pressure relief line 134 third pressure line 136 storage supply line 138 inverters 140 regenerative power line 142 Main propulsion power line 144 Pulling direction 146 Retraction direction

Claims

[1] Hydraulic die cushion drive (2) for a pressing device (10), with a multi-surface cylinder and a multi-surface piston arranged axially displaceably therein, characterized by that the multi-surface piston (8) has a rapid traverse pressure surface (48), a reverse traverse pressure surface (52) acting counteracting the rapid traverse pressure surface, a counter-holding pressure surface (56) and a working pressure surface (60) acting counteracting the rapid traverse pressure surface, and that in the multi-surface cylinder (6) there are formed a rapid traverse pressure chamber (50) delimited by the rapid traverse pressure surface (48), a reverse traverse pressure chamber (54) delimited by the reverse traverse pressure surface (52) and acting counteracting the rapid traverse pressure chamber (50), a counter-holding pressure chamber (58) delimited by the counter-holding pressure surface (56) and a working pressure chamber (62) delimited by the working pressure surface (60) and acting counteracting the counter-holding pressure chamber (58), with a working and counterholding arrangement (66), in which the counterholding pressure chamber (58), a first working pressure line (84), a hydraulic machine (68), a second working pressure line (86), and the working pressure chamber (62) form a lockable hydraulic circuit, in particular a hydraulic circuit that is essentially closed during operation of the die cushion drive, wherein the working and counterholding arrangement (66), in addition to the first working pressure line (84), the hydraulic machine (68), and the second working pressure line (86), comprises an electric motor (70) that is directly or indirectly coupled to the hydraulic machine (68) in a torque-transmitting manner, wherein the working and counterholding arrangement (66) is designed such that, upon an externally driven movement of the multi-surface piston (8) in an axial direction, in particular in the drawing direction (144), the hydraulic machine (68) can be driven in motor mode,wherein pressure medium can be conveyed from the counter-pressure chamber (58) into the working pressure chamber (62), the counter-pressure chamber (58) can be subjected to the counter-pressure and the electric motor (70) can be driven by the hydraulic machine (68) as a generator, and that when the multi-surface piston (8) is moved in an opposite axial direction, in particular in the retraction direction (146), the hydraulic machine (68) can be driven by the electric motor (70) in a pumping operation with a conveying direction reverse to that of the motor operation, wherein pressure medium can be conveyed from the working pressure chamber (62) into the counter-pressure chamber (58), and with a rapid traverse arrangement (102) which is designed to controllably supply either the rapid traverse pressure chamber (50) with a pressure medium for driving the movement a) or the reverse rapid traverse pressure chamber (54) with a pressure medium for driving the movement d). [2] Die cushion drive according to claim 1, which is designed to cooperate with the pressing device (10) for the repeated execution of cycles with the following movements: a) accelerated movement of the multi-surface piston (8), in particular in a rapid traverse, in a drawing direction (144) from a press-side dead center to a die cushion-side dead center, until a press ram (12) driven in the drawing direction (144) acts on a press-side end of the multi-surface piston (8), b) joint movement of the press ram (12) and the multi-surface piston (8) in the drawing direction (144) in a drawing passage driven by the press ram (12) while applying a counter-pressure to the multi-surface piston (8) until it approaches its dead center on the die cushion side, the counter-pressure counteracting a contact pressure of the press ram (12) in a retraction direction (146) opposite to the drawing direction (144), c) reversing the direction of movement of the multi-surface piston (8) and, in a retraction movement driven by the die cushion drive (2), with a retraction of the multi-surface piston (8) in the retraction movement direction (146) until it approaches or reaches its press-side dead center and thereby presses in the direction of the press ram (12), and d) Approaching the press-side dead center, in particular in a rapid traverse of the multi-surface piston (8), in the retraction direction (146). [3] Die cushion drive according to claim 2, wherein an axial direction of the multi-surface cylinder (6) can be aligned parallel to the drawing direction (144), and wherein the rapid traverse pressure chamber (50) and the rapid traverse pressure surface (48) are designed to drive the movement a), the counter-holding pressure chamber (58) and the counter-holding pressure surface (56) are designed to apply the counter-holding pressure during the movement b), the counter-holding pressure chamber (58) and the counter-holding pressure surface (56) are designed to drive the movement c), and the reverse traverse pressure chamber (54) and the reverse traverse pressure surface (52) are designed to drive the movement d). [4] Die cushion drive according to one of claims 1 to 3, wherein the counter-pressure surface (56) is larger than the rapid traverse pressure surface (48) and the working pressure surface (60) is larger than the reverse traverse pressure surface (52). [5] Die cushion drive according to one of claims 1 to 4, wherein the hydraulic circuit can be placed under a hydraulic preload. [6] Die cushion drive according to one of the preceding claims, wherein the hydraulic machine (68) is an adjustable hydraulic machine, in particular designed as an axial piston machine. [7] Die cushion drive according to one of the preceding claims, wherein the hydraulic machine (68) and the electric motor (70) are designed such that they can run substantially continuously, in particular during the movements a) to d) with a constant direction of rotation and a substantially constant speed. [8] Die cushion drive according to one of the preceding claims, designed so that when the electric motor (70) operates as a generator, the electrical power generated by the generator for driving the press ram (12) can be electrically fed into the main drive motor (20) of the press ram (12). [9] Die cushion drive according to one of the preceding claims, wherein the working and counter-holding arrangement (66) comprises a bypass line (88) which connects the counter-holding pressure chamber (58) through a section of the first working pressure line (84) and the retraction pressure chamber (62) through a section of the second working pressure line (86) as a bypass line to the hydraulic machine (68), and in which a first 2 / 2-way control valve (78) is arranged which is designed to open or interrupt the bypass line (88). [10] Die cushion drive according to one of the preceding claims, wherein the rapid traverse arrangement (102) comprises the following: a controllable 4 / 3-way control valve (104) which is designed to regulate or control the pressure for the rapid traverse or the reverse traverse and which comprises a first and a second control valve output (104a, 104b) and a first and a second control valve input (104c, 104d), a rapid traverse pressure line (124) which connects the first control valve output (104a) to the rapid traverse pressure chamber (50), a reverse traverse pressure line (126) which connects the second control valve output (104b) to the reverse traverse pressure chamber (54), and a pressure medium supply (116, 118, 134, 136) for supplying the first control valve input (104c) with pressure medium, and wherein (i) the third pressure line (134) for supplying the pressure medium from the pressure medium supply, the rapid traverse pressure line (124) and the rapid traverse pressure chamber (50), (ii) the third pressure line (134), the reverse speed pressure line (126) and reverse speed pressure chamber (54), and (iii) the third pressure line (134), the rapid traverse pressure line (124), a bypass line (128) and the reverse rapid traverse pressure line (126) are each hydraulic circuits controllable by throttling on the 4 / 3-way control valve (104). [11] Method for operating a die cushion drive (2) according to one of claims 1 to 10, which comprises a multi-surface cylinder (6) and a multi-surface piston (8) and which cooperates with a pressing device (10) with a drivable press ram (12), comprising the following steps: b) joint movement of the press ram (12) and the multi-surface piston (8) in the drawing direction (144) in a drawing direction driven by the press ram (12) while applying a counter-pressure to the multi-surface piston (8) until it approaches or reaches its dead center on the die cushion side, wherein the counter-pressure counteracts a contact pressure of the press ram (12) in a retraction direction (146) opposite to the drawing direction (144), wherein pressure medium is conveyed from a counter-pressure chamber (58) of the multi-surface cylinder (24) through a substantially closed hydraulic circuit by a hydraulic machine (68) operating in motor mode into a working pressure chamber (62) of the multi-surface cylinder (24), and wherein the hydraulic machine (68) drives an electric motor (70) coupled to it in a torque-transmitting manner as a generator, and c) reversing the direction of movement of the multi-surface piston (8) and moving the multi-surface piston (8) back in the retraction direction (146) until it approaches or reaches its press-side dead center and thereby presses in the direction of the press ram (12), whereby pressure medium is conveyed from the working pressure chamber (62) through the closed hydraulic circuit into the counter-pressure chamber (58) by means of the hydraulic machine (68) driven by the electric motor (70) and now operating in pump mode. [12] Method according to claim 11, wherein before step b) the following step is carried out: a) accelerated movement of the multi-surface piston (8), in particular in a rapid traverse of the multi-surface piston (8) in a drawing direction (144), from a press-side dead center to a die cushion-side dead center, until the press ram (12) driven in the drawing direction (144) acts on a press-side end of the multi-surface piston (8), by applying pressure medium to a rapid traverse pressure chamber (50) of the multi-surface cylinder (6) delimited by a rapid traverse pressure surface (48) of the multi-surface piston (8), and wherein after step c) the following step is carried out: d) approaching the press-side dead center, in particular in a rapid traverse of the multi-surface piston (8) in the retraction direction (146), by applying pressure medium to a retraction pressure chamber (54) of the multi-surface cylinder (6) delimited by a retraction pressure surface (52) of the multi-surface piston (8). [13] Method according to claim 11 or 12, wherein during the execution of step b) the electric motor (70) operates as a generator and the electrical power generated by the generator for driving the press ram (12) is electrically fed into the main drive motor (20) of the press ram (12).

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