Electrohydraulic drive unit

Abstract

An electrohydraulic drive unit is provided, comprising a cylinder-piston assembly having a piston-side first hydraulic working chamber and a piston-rod-side second hydraulic working chamber, a tank, a hydraulic pump, which can be driven at variable rotational speed and which has a tank connection point and a working connection point, a valve assembly, which is connected between the working connection point of the hydraulic pump and the cylinder-piston assembly, and an anti-cavitation valve, which is connected between the tank and the first hydraulic working chamber; and a machine controller. Switching valves of the valve assembly can be switched between loading of the first hydraulic working chamber and loading of the second hydraulic working chamber of the cylinder-piston assembly during pumping operation of the hydraulic pump from the working connection point of the hydraulic pump by the machine controller.

Claims

1. An electrohydraulic drive unit, especially for use on a machine press, having a cylinder-piston arrangement (1) having a first hydraulic working chamber (5) on the piston side and a second hydraulic working chamber (6) on the piston-rod side a tank (4) as a hydraulic-fluid reservoir, a hydraulic pump (3) driven at variable rpm by an electric motor (2) and having a tank port (T) and a working port (P), a valve arrangement connected between the working port (P) of the hydraulic pump (3) and the cylinder-piston arrangement (1) and comprising several electrically activatable switching valves (S1-S6), a servo-suction valve (8) connected between the tank (4) and the first hydraulic working chamber (5) of the cylinder-piston arrangement (1), and a machine controller acting on the switching valves (S1-S6) and on the electric motor (2), by means of which the switching valves (S1-S6) can be reversed between pressurization of the first hydraulic working chamber (5) and of the second hydraulic working chamber (6) of the cylinder-piston arrangement (1) in pumping mode of the hydraulic pump (3) from its working port (P), wherein a hydraulic decompression module (9) having a hydraulic accumulator (10), which can be placed in communication with the second hydraulic working chamber (6) via a first connecting line (11) having a pressure-limiting valve (15) having flow direction from the second hydraulic working chamber (6) to the hydraulic accumulator (10) and via a second connecting line (12) having a check valve (16) opening in flow direction from the hydraulic accumulator (10) to the second hydraulic working chamber (6).

2. The electrohydraulic drive unit of claim 1, wherein the hydraulic decompression module (9) comprises a loading/unloading valve (14).

3. The electrohydraulic drive unit of claim 2, wherein the loading/unloading valve (14) is disposed in a line section (13) common to the first connecting line (11) and the second connecting line (12).

4. The electrohydraulic drive unit of claim 2, wherein the loading/unloading valve (14) opens in pressure-controlled manner, wherein the control-pressure line (17) communicates with the first hydraulic working chamber (5).

5. The electrohydraulic drive unit of claim 4, wherein the loading/unloading valve (14) is of pressure-actuated design.

6. The electrohydraulic drive unit of claim 4, wherein the loading/unloading valve (14) can be actuated by a pressure-controlled positioning drive.

7. The electrohydraulic drive unit of claim 2, wherein the loading/unloading valve (14) can be actuated by a sequence-controlled positioning drive, which communicates with the machine controller.

8. The electrohydraulic drive unit of claim 2, wherein the loading/unloading valve (14) can be manually actuated.

9. The electrohydraulic drive unit of claim 1, wherein the cylinder-piston arrangement (1) is oriented with at least substantially vertical axis of movement (X) of piston (7), wherein the first hydraulic working chamber (5) is disposed above second hydraulic working chamber (6).

10. The electrohydraulic drive unit of claim 1, wherein a filter unit (18) is connected between the working port (P) of the hydraulic pump (3) and the valve arrangement.

11. The electrohydraulic drive unit of claim 1, wherein the hydraulic pump (3) is designed as a 2-quadrant pump and can be reversed by means of the machine controller in braking mode such that the directions of rotation and flow are reversed compared with pumping mode.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The present invention will be explained in more detail hereinafter on the basis of a preferred exemplary embodiment illustrated in the drawing, wherein

(2) FIG. 1 shows a hydraulic diagram of connections and

(3) FIG. 2 shows a functional diagram of the exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The electrohydraulic drive unit according to the exemplary embodiment corresponds to a considerable extent to that drive unit described and explained in detail in DE 202015106161 U1. Within the scope of this agreement with the prior art, a separate detailed explanation is not needed at this point, but instead reference is made to DE 202015106161 U1, the entire disclosure content of which is included by reference in the content of the present patent application.

(5) The illustrated electrohydraulic drive unit, as is suitable in particular for use on a machine press such as a straightening or bending press, a press brake or else a powder press, for example, comprises a hydraulic cylinder-piston arrangement 1, a hydraulic pump 3 (2-quadrant pump) driven at variable rpm by an electric motor 2 and having a tank port T and a working port P, a tank 4 as a hydraulic-fluid reservoir, a valve arrangement connected between working port P of hydraulic pump 3 and hydraulic cylinder-piston arrangement 1 and comprising several electrically activatable switching valves S1, S2, S3, S4, S5 and S6 andnot showna machine controller acting on switching valves S1 to S6 and on electric motor 2. Cylinder-piston arrangement 1 is of double-acting design; it has a first hydraulic working chamber 5 on the piston side and a second hydraulic working chamber 6 on the piston-rod side. The said cylinder-piston arrangement 1 is oriented in such a way with vertical axis of movement X of piston 7 that first hydraulic working chamber 5 is disposed above second hydraulic working chamber 6. Pressurization of first hydraulic working chamber 5 by means of hydraulic pump 3 results in a downward movement and pressurization of second working chamber 6 in an upward movement of piston 7. A servo-suction valve 8, through which first hydraulic working chamber 5 is filled with hydraulic fluid during a downward movement of piston 7 in rapid traverse, is connected between tank 4 and first hydraulic working chamber 5 of cylinder-piston arrangement 1.

(6) The drive unit is provided with a hydraulic decompression module 9. This comprises a hydraulic accumulator 10, which can be placed in communication with the second hydraulic working chamber 6 via two different connecting lines 11 and 12, part of which, however, is a shared, common line section 13 having a loading/unloading valve 14 disposed therein. On the one hand, hydraulic accumulator 10 of hydraulic decompression module 9 can be placed in communication with second hydraulic working chamber 6 via a first connecting line 11 having a pressure-limiting valve 15 having flow direction from second hydraulic working chamber 6 to hydraulic accumulator 10; thus first connecting line 11 represents a loading line for hydraulic accumulator 10. And, on the other hand, hydraulic accumulator 10 can be placed in communication, via a second connecting line 12, with a check valve 16 opening in flow direction from hydraulic accumulator 10 to second hydraulic working chamber 6; thus second connecting line 12 represents an unloading line for hydraulic accumulator 10.

(7) The said loading/unloading valve 14 opens (and closes) in pressure-controlled manner, i.e. in dependence on a control pressure, and in fact is actuated directly by the control pressure. The said control pressure is the pressure prevailing in first hydraulic working chamber 5. For this purpose, control-pressure line 17 of loading/unloading valve 14which is designed as a hydraulically actuatable valvecommunicates with first hydraulic working chamber 5. The switching-pressure threshold of loading/unloading valve 14 is adjusted such that the said valve already opens at the pressure established (due to pressure-limiting valve 15) in first hydraulic working chamber 5 at the beginning of the power mode.

(8) The actuation of switching valves S1 to S6 of the valve arrangement as well as of electric motor 2 by the machine controller and also the resulting movement of piston 7 between top dead center (TDC) and bottom dead center (BDC) during a complete working cycle are illustrated in the functional diagram according to FIG. 2. The switched situation of loading/unloading valve 14 that results during the working cycle due to its pressure-controlled actuation is likewise illustrated in FIG. 2. By appropriate activation of switching valves S1 to S6 and of electric motor 2with optional pressurization of first hydraulic working chamber 5 or of second hydraulic working chamber 6 of cylinder-piston arrangement 1 in pumping or else in braking mode of hydraulic pump 3it is therefore possible, during one working cycle, to execute the following phases for the illustrated electrohydraulic drive unit I: Holding of the piston at top dead center, II: Downward rapid traverse of the piston, III: Changeover phase IV: Downward power mode of the piston, V: Holding of the piston at bottom dead center and VI: Decompression (together with active upward creep mode) and VII: Upward movement of the piston in fast traverse.

(9) This diagram of the switched and operating states is partly schematic, namely in the sense that an abrupt change is shown instead of the gradual change of rpm of the electric motor as explained in the foregoing. Accordingly, the piston movement is also impacted by unsteady phenomena.

(10) If necessary, an additional Slow upward phase may be provided between the decompression phase (VI) and the upward movement of the piston in rapid traverse (VII). For this purpose, electric motor 2 driving hydraulic pump 3 is operated at first at rpm reduced compared with the upward rapid transverse phase (VII); and servo-suction valve 8 is not yet switched to passing state at first, by the fact that switching valve S5 remains energized at first, just as during phases II to VI, and so hydraulic fluid is displaced through the valve arrangement out of first hydraulic working chamber 5 and into tank 4.

(11) For effective cleaning of the hydraulic fluid, a filter unit 18, by means of which the entire hydraulic fluid being conveyed by hydraulic pump 3 in pumping mode thereof is cleaned by filter 19, is connected between working port P of hydraulic pump 3 and the valve arrangement. It is only if filter 19 is clogged that the hydraulic fluid being conveyed by hydraulic pump 3 flows via the small bypass 20, in which check valve 21 acts as a pressure-limiting valve and opens when filter 19 is loaded or clogged, in order to prevent filter rupture. In braking mode of hydraulic pump 3, the hydraulic fluid flows via the large bypass 22 containing check valve 23 around filter unit 18.

(12) In the embodiment of the invention illustrated in the drawing, the hydraulic decompression module, as explained, is connecteddue to the abrupt pressure rise then occurring in the first hydraulic working chamberat the beginning of the power mode, i.e. during the changeover phase, wherein simultaneouslyby controlled closing of switching valve S2the outflow of fluid displaced from the second hydraulic working chamber to the tank is suppressed. A shift, explained in the foregoing, of the connection of the hydraulic decompression module to a later operating point (for example the clamping point characterized by setting of the tool on the workpiece), by specification of an accordingly higher switching-pressure threshold for the loading/unloading valve, would go hand-in-hand with a modification of the hydraulic system. And, in fact, switching valve S2 would remain open correspondingly longer in this case, i.e. for at least during a first part of the power mode; and the outflow of the fluid displaced from the second hydraulic working chamber to the tank would be expediently suppressed simultaneously with the connection of the hydraulic decompression module (by hydraulic opening of the loading/unloading valve) by means of a valve that is likewise pressure-controlled and connected in series with switching valve S2.

(13) If the loading/unloading valve of the hydraulic decompression module were to be actuated not hydraulically, as in the exemplary embodiment, but instead in electrically controlled manner, a corresponding coordinated connection of the hydraulic decompression module with simultaneous shutoff of the discharge to the tank (e.g. in position-controlled manner) could be realized particularly simply at any desired operating point of the power mode. In this case, the respective process control could be optimized in the sense of greatest possible efficiency without problems as a function of need.