EP1625011B1 - Hydraulic drive - Google Patents

Abstract

Hydraulic drive has an active surface (30) acting in the driving direction and delimiting an annular chamber (32) which is connected to a switching valve (10). The annular chamber is impinged with a supply pressure in the original position of the switching valve and with a lower supply pressure when a predetermined loading pressure is exceeded. An independent claim is also included for a switching valve for the hydraulic drive. Preferred Features: The switching valve prevents the connection of the annular chamber with a tank line (16) and permits a pressure flow in the counter direction. A tank line damper is provided in the tank line.

Description

The invention relates to a hydraulic drive for a punching or forming machine according to the preamble of claim 1.

Such from the US Pat. No. 5,042,362 known hydraulic drives for punching or forming machines, in particular high-speed nibbling machines, have a cylinder designed as a differential cylinder, via which a punching tool is actuated. A circuit diagram of a known, but not described in a document solution of such a hydraulic drive is in the FIG. 1 shown.

A working cylinder 2 is divided by a piston 4 into a piston bottom end cylinder chamber 6 and a piston rod side annular space 8. The cylinder chamber 6 is supplied via a continuously adjustable valve 10 with pressure medium. An input port E of the continuously variable valve 10 is connected to a valve assembly 12. The valve arrangement 12 has a pilot-operated check valve 14 and a counter-blocking check valve 16 connected in parallel thereto. The unlockable check valve 14 can be unlocked via a predetermined load pressure in the cylinder chamber 6. It is connected via a supply line 28 to a high-pressure accumulator HD. The check valve 16 is connected via a supply line 32 with a low-pressure accumulator ND. Like next FIG. 1 can be removed, the annular space 8 is constantly connected to the low-pressure accumulator ND.

For quick extension of the piston 4 are the continuously adjustable valve 10 and the valve assembly 12 in the illustrated basic positions. The cylinder chamber 6 is acted upon by low pressure, so that the piston 4 expands quickly due to its area difference. Upon impact of the piston 4 on a workpiece to be punched, the pressure in the cylinder chamber 6 increases. This load pressure is reported to the pilot operated check valve 14. From a certain load pressure this acts as a switching pressure and the check valve 14 is unlocked. Consequently, the high-pressure accumulator HD is switched on. The high pressure is conducted to the input port E and thus into the cylinder chamber 6, so that a maximum punching force can be applied. The high pressure is also applied to the check valve 16 so that it closes and the pressure medium connection to the low-pressure accumulator ND is shut off. After punching the load pressure in the cylinder chamber 6 decreases, whereby the pilot-operated check valve 14 resumes its basic position and the low-pressure accumulator ND is switched on.

A disadvantage of this known solution is that the check valve in the low pressure line only by means of a time delay of 2ms to 5ms closes, so that the pressurized high pressure fluid flows through the check valve to the low-pressure accumulator. At stroke times of about 10ms to 20ms for the extension of the working cylinder thus creates a significant loss of time and energy.

Another disadvantage of the known solution is that the connection of the high-pressure accumulator and the shutdown of the low-pressure accumulator can not be enforced without load pressure. However, in some modes, such as embossing and forming near the switching pressure, there is a supply of the Working cylinder with a permanently high load pressure required. Accordingly, the illustrated drive unit is not fully suitable for embossing and forming.

Another drive unit is in the DE 37 20 266 C2 disclosed. The drive unit has a working cylinder with a piston which separates an annulus from a cylinder space. The annular space acts in the retraction direction and the cylinder space acts in the extension direction on the piston. About a motor-adjustable valve assembly with two mutually in mechanical operative engagement control valves of two control valves of the cylinder chamber with high pressure, low pressure or a tank pressure can be acted upon. The annulus is constantly subjected to low pressure.

The spools are in contact with each other at the front and are biased by a spring in their basic positions. To move the spool, a cam disc acting on one of the spools is controlled via an electric motor such that, depending on the rotation of the cam disc, the spools are transferred from their basic positions to control positions. For rapid extension of the piston, the cylinder chamber is subjected to low pressure. Due to the difference in the area of the piston, the latter extends until it hits a workpiece to be machined. To apply a high punching force of the cylinder chamber is subjected to high pressure. For rapid retraction of the piston, the cylinder space is depressurized to the tank, so that due to the low pressure acting in the annular space, the piston is moved back to its original position.

A disadvantage of this solution is that the valve arrangement with the two control spools in contact with one another and the motor control is designed to be technically complex.

The object of the present invention is to provide a hydraulic drive for a stamping or forming machine in which no significant time and energy losses occur during pressure switching.

This object is achieved by a hydraulic drive for a stamping or forming machine with the features of claim 1.

The drive unit according to the invention has a working cylinder whose piston acts directly or indirectly on a workpiece to be machined. At least one pressure chamber of the working cylinder is acted upon for retraction and extension of the piston via a continuously adjustable valve with a tank pressure or a supply pressure. Furthermore, a valve arrangement is provided, which is connected upstream of the continuously adjustable valve, and via which an input terminal of the continuously adjustable valve with a higher or lower supply pressure can be acted upon. According to the invention, the valve arrangement has a switching valve which can be switched between a basic position and a switching position as a function of the load pressure on the working cylinder in order to tap the supply pressure from a low-pressure source or a high-pressure source.

The mechanical connection of the control edges of the switching valve, a time loss between the connection of the high pressure and the switching off of the low pressure compared to the solution with the separate check valves is substantially reduced. Thus, under High pressure fluid does not flow into the low pressure accumulator and no energy loss occurs. Consequently, the pressure build-up on the continuously adjustable valve is faster. Furthermore, the valve arrangement according to the invention is simple and inexpensive to implement.

In a preferred embodiment, the working cylinder has a cylinder space and an annulus. The pressure in the cylinder chamber acts in the extension direction, and the pressure in the annulus acts in the retraction direction on the piston. Furthermore, the pressure in the cylinder chamber acts on a large control surface of the switching valve and forms from a certain load pressure, the switching pressure for switching the switching valve in its switching position, in the opposite direction, the pressure in the annular space acts on a small control surface of the switching valve.

In a preferred embodiment, a pilot valve is provided, via which in the direction of the basic position effective small control surface of the switching valve is relieved, so that at reduced load pressure in the cylinder chamber, the switching valve can be switched and high pressure can be performed to the cylinder chamber. Preferably, the pilot valve is electrically operated.

In principle, the annulus can constantly be subjected to high pressure. Preferably, however, the annular space is constantly connected to the low-pressure source, since the annular surface is then larger and higher load capacity as a stop. '

The working cylinder can have two or three pressure chambers.

Other advantageous embodiments of the invention are the subject of further subclaims.

• Figur 1 ein Schaltschema einer bekannte Lösung eines hydraulischen Antriebs für eine Nibbelmaschine, und
• Figur 2 ein Schaltschema einer bevorzugten erfindungsgemäßen Lösung eines hydraulischen Antriebs für eine Nibbelmaschine.

In the following, preferred embodiments of the invention are explained in more detail with reference to schematic representations. Show it

• FIG. 1 a circuit diagram of a known solution of a hydraulic drive for a nibbling machine, and
• FIG. 2 a circuit diagram of a preferred inventive solution of a hydraulic drive for a nibbling machine.

FIG. 2 shows a highly simplified circuit diagram of a drive 1 of a high-speed nibbling machine. In such Nibbelmaschinen the extension movement takes place within 10 ms to 20 ms.

The nibbling machine has a working cylinder 2, which has a piston 4 as in the known solution described above, which separates a cylinder chamber 6 from an annular space 8 and acts directly or indirectly on a punching tool. The piston 4 has a rear piston rod 18 which extends away from the piston crown and the working cylinder 2 passes through the front side.

The cylinder chamber 6 is connected to a working port A of a continuously adjustable valve 10 which in one of its control positions (b) opens a connection between the cylinder chamber 6 and a tank line 20 connected to a tank. In the tank line 20, a tank line damper 22 and a biasing valve 24 are arranged. By the tank line damper 22 pressure fluctuations in the tank line 20 are suppressed and the biasing valve 24, the tank line 20 on biased to the spring of the biasing valve 22 equivalent pressure.

An input port P of the continuously variable valve 12 is connected to a working port B of a switching valve 26, which is connected to a pressure port P or a pressure port P 'of the switching valve 26 depending on the switching position (1), (2) of the switching valve 26. The pressure port P is connected via a feed line 28 to a high pressure accumulator HD, and the pressure port P 'is connected via a branch line 30 and a portion of a feed line 32 with a low pressure accumulator ND. The supply line 32 connects the low-pressure accumulator ND with the annular space 8.

The pressure in the annular space 8 is tapped via a control line 34 and an electrically operated pilot valve 38. In the basic position (x) of the pilot control valve 38, the pressure is led to a small control surface of the switching valve 26 which is effective in the direction of the basic position (1) of the switching valve 26. In a control position (y) of the pilot valve 38, the connection to the small control surface is shut off and a connection of the small control surface to the tank T is opened.

The pressure in the cylinder chamber 6 is tapped off via a control line 36 and led to an effective in the direction of the switching position (2) large control surface of the switching valve 26.

To initiate the punching process, ie for fast feed, the switching valve 26 is in its illustrated basic position (1). The pilot valve 34 is in its home position (x) and the pressure acting in the annulus 8 becomes the small control surface the switching valve 26 out. Likewise, the continuously adjustable valve 10 is in its illustrated basic position (a). Thus, the cylinder chamber 6 is subjected to low pressure. The annular space 8 is also supplied via the supply line 32 with low pressure, so that the piston 4 extends due to its area difference, wherein pressure medium is displaced from the annular space 8 in the low-pressure accumulator ND.

Upon impact of the piston 4 on a workpiece to be punched, the load pressure in the cylinder chamber 6 increases. When a certain load pressure level is exceeded, this acts as a switching pressure and the switching valve 26 is brought against the force of a return spring and a force corresponding to the pressure acting on the small control surface in its switching position (2) in which the working port B to the pressure port P is connected so that high pressure on the piston bottom surface is effective and thus the force applied by the working cylinder 2 punching force is increased. After punching the load pressure decreases and the switching valve 26 switches back to its normal position (1), in which the pressure port P is shut off and the pressure port P 'is turned on, so that at the working port B is again low pressure.

To retract the piston 4, i. for rapid retraction, the continuously adjustable valve 10 is transferred to its designated (b) control positions, in which the cylinder chamber 6 is connected to the tank T. Due to the low pressure acting in the annular space 8, the piston 4 is pushed back to its original position.

For embossing, as an option during the rapid feed, the pilot valve 38 can be brought into its control position (y), in which the control line 34 shut off and the small control surface of the switching valve 26 is relieved of pressure to the tank. Thus, only the force of the return spring acts against the voltage applied to the large control surface load pressure, so that the necessary switching pressure is reduced accordingly. The switching valve 26 is transferred against the force of the return spring from its basic position (1) in its switching position (2), so that the pressure port P 'shut off and the pressure port P is turned on. Accordingly, the cylinder chamber 6 is subjected to high pressure, so that even before the construction of the maximum load pressure, the maximum workforce is available.

The inventive solution with a continuously adjustable valve 10 upstream switching valve 26 can also be used in other cylinder designs, eg. With three pressure chambers.

Disclosed is a hydraulic drive for a punching or forming machine with a plurality of pressure chambers having working cylinder whose piston acts directly or indirectly on a workpiece to be machined, wherein at least one pressure chamber of the working cylinder for retraction or extension of the piston via a continuously adjustable valve with a Tank pressure or a supply pressure can be acted upon, and with a valve assembly which is connected upstream of the continuously variable valve and via which an input port of the continuously variable valve with a higher or lower supply pressure can be acted upon, the valve assembly having a switching valve, which in dependence on the load pressure on Working cylinder between a basic position and a switching position is switchable to tap the supply pressure from a low pressure source or a high pressure source.

LIST OF REFERENCE NUMBERS

1

drive

2

working cylinder

4

piston

6

cylinder space

8th

annulus

10

steadily adjustable valve

12

valve assembly

14

unlockable check valve

16

check valve

18

piston rod

20

tank line

22

Tank line attenuator

24

Pre-load valve

26

switching valve

28

supply line

30

branch line

32

supply line

34

control line

36

control line

38

pilot valve

Claims (7)

1. A hydraulic drive mechanism for a blanking or forming machine comprising a working cylinder (2) having several pressure chambers (6, 8), the piston (4) of which acts directly or indirectly on a workpiece to be processed, wherein at least one pressure chamber (6) of the working cylinder (2) for retracting and extending the piston (4) is adapted to be subjected to a tank pressure or a supply pressure via a continuously adjustable valve (10), and comprising a valve assembly (26) arranged upstream of the continuously adjustable valve (10), whereby an inlet port (E) of the continuously adjustable valve (10) may be subjected to a higher or lower supply pressure, wherein the valve assembly (26) comprises a switching valve (26) adapted to be switched over between a basic position (1) and a switching position (2) in dependence on the load pressure at the working cylinder (2), characterized in that in the basic position (1), the inlet port (E) of the continuously adjustable valve (10) is connected to a low-pressure source (ND), and in the switching position (2) the connection to the low-pressure reservoir (ND) is cut off and the inlet port (E) is connected to a high-pressure source (HD).
2. The hydraulic drive mechanism in accordance with claim 1, wherein the working cylinder (2) comprises an annular chamber (8) acting in the retracting direction and a cylinder chamber (6) acting in the extending direction, and wherein the load pressure acting in the cylinder chamber (6) acts on a large control surface of the switching valve (26).
3. The hydraulic drive mechanism in accordance with claim 2, wherein the large control surface acts in the direction of a switching position (2) of the switching valve (26), and wherein a small control surface of the switching valve (26) acting in the direction of the basic position (1) of the switching valve (26) is connected with the low-pressure source (32) via a control line (34).
4. The hydraulic drive mechanism in accordance with claim 3, wherein a pilot valve (38) is arranged in the control line (34), whereby the small control surface may be subjected to tank pressure for load-independent switching.
5. The hydraulic drive mechanism in accordance with claim 4, wherein the pilot valve (38) is actuated electrically.
6. The hydraulic drive mechanism in accordance with any one of the preceding claims, wherein the annular chamber (8) is constantly connected to the low-pressure source (ND).
7. The hydraulic drive mechanism in accordance with any one of the preceding claims, wherein the working cylinder (2) is designed with two or three pressure chambers.

Images