Hydraulic drive with rapid stroke and load stroke

Abstract

A hydraulic drive including at least one hydraulic cylinder that includes a piston chamber, an annulus, and a piston that separates the piston chamber from the annulus. The hydraulic drive also includes a first hydraulic pump hydraulically connected with the piston chamber, a second hydraulic pump hydraulically connected with the annulus, a third hydraulic pump, and a directional control valve that has a first switching position and a second switching position. The third hydraulic pump in the first switching position of the directional control valve is hydraulically connected with the piston chamber, and the third hydraulic pump in the second switching position of the directional control valve is not hydraulically connected with the piston chamber.

Claims

1. A hydraulic drive for a hydraulic press, said hydraulic drive comprising: at least one hydraulic cylinder, including: a piston chamber and an annulus; and a piston that separates said piston chamber from said annulus; a first hydraulic pump configured to supply pressurized fluid to said piston chamber, and wherein said first hydraulic pump cannot supply pressurized fluid to said annulus; a second hydraulic pump configured to supply pressurized fluid to said annulus; a third hydraulic pump configured to supply pressurized fluid to said piston chamber; and a directional control valve that has a first switching position and a second switching position, wherein in said first switching position of the directional control valve said third hydraulic pump is able to supply pressurized fluid to said piston chamber and wherein in said second switching position of the directional control valve said third hydraulic pump does not supply pressurized fluid to said piston chamber, wherein said directional control valve is hydraulically controllable in such a way that a pressure in said piston chamber is used for shifting said directional control valve from the first switching position into the second switching position, and a pressure in said annulus is used for shifting the directional control valve from the second switching position into the first switching position.

2. The hydraulic drive according to claim 1, wherein said second hydraulic pump cannot supply a pressurized fluid to said piston chamber.

3. The hydraulic drive according to claim 1, wherein the first hydraulic pump and the third hydraulic pump rotate together in the same rotational direction, and the second pump rotates together with the first hydraulic pump and the second hydraulic pump in the opposite direction relative to the rotational direction of the first hydraulic pump and the third hydraulic pump.

4. The hydraulic drive according to claim 1, further comprising an electric motor that drives the first hydraulic pump, the second hydraulic pump, and the third hydraulic pump.

5. The hydraulic drive according to claim 1, further including at least one of a position sensor and at least one pressure sensor.

6. The hydraulic drive according to claim 1, wherein said piston chamber has a hydraulic effective surface and said annulus has a hydraulic effective surface.

7. The hydraulic drive according to claim 6, wherein a joint fluid delivery volume of the first hydraulic pump and the third hydraulic pump is adapted to the hydraulic effective surface of the piston chamber, and a fluid delivery volume of the second hydraulic pump is adapted to the hydraulic effective surface of the annulus.

8. The hydraulic drive according to claim 7, wherein a ratio of said joint fluid delivery volume of the first hydraulic pump and the third hydraulic pump, relative to the fluid delivery volume of the second hydraulic pump, is consistent with a surface ratio of the hydraulic effective surface of the piston chamber, relative to the hydraulic effective surface of the annulus.

9. The hydraulic drive according to claim 1, further including a tank that is hydraulically connected with said first hydraulic pump and said second hydraulic pump.

10. The hydraulic drive according to claim 9, wherein said tank is in the form of a pressure tank.

11. The hydraulic drive according to claim 9, further including a plurality of check valves and a plurality of pressure relief valves which are arranged respectively between said first hydraulic pump and said third hydraulic pump and said piston chamber in such a way that a hydraulic fluid can be diverted into said tank in order to avoid at least one excess pressure and that the hydraulic fluid can be moved out of said tank in order to avoid at least one vacuum.

12. The hydraulic drive according to claim 9, further including a plurality of check valves and a plurality of pressure relief valves which are arranged respectively between said second hydraulic pump and said annulus in such a way that a hydraulic fluid can be diverted into said tank in order to avoid at least one excess pressure and that the hydraulic fluid can be moved out of said tank in order to avoid at least one vacuum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following descriptions of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a diagram that illustrates a first embodiment of a hydraulic drive according to the present invention; and

(3) FIG. 2 is a diagram that illustrates a second embodiment of a hydraulic drive according to the present invention.

(4) Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring now to FIG. 1, there is shown a hydraulic circuit diagram of a hydraulic drive 10 according to the present invention.

(6) Drive 10 includes a hydraulic cylinder 12, which may be designed as a differential cylinder, as well as three hydraulic pumps 14, 16, 18 that are driven entirely by an electric motor 62.

(7) Hydraulic cylinder 12 includes a piston 22 that separates a piston chamber 24 from an annulus 26. Piston chamber 24 has a hydraulic effective surface 28, whereby annulus 26 has a hydraulic effective surface 30. Because of piston rod 32 the hydraulic effective surface 30 of annulus 26 which is designed as a circular ring is smaller than hydraulic effective surface 28 of piston chamber 24.

(8) Hydraulic pump 14 is hydraulically connected with piston chamber 24 of hydraulic cylinder 12 via a pump connection that is described as pump outlet 15 by a hydraulic line 34, whereas hydraulic pump 16 is hydraulically connected with annulus 26 of hydraulic cylinder 12 via a pump connection that is described as pump intake 17 by a second hydraulic line 36. The two hydraulic pumps 14, 16 deliver thereby in opposite directions and fulfil the function of a four-quadrant pump which has one pump intake and one pump outlet and with whichdepending on the direction of deliveryhydraulic fluid can be sucked in at the pump intake and hydraulic fluid can be moved out of the pump at the pump outlet, and vice versa. For this reason the two hydraulic pumps 14, 16 are also referred to herein in part as first hydraulic pump 14, 16. Second hydraulic pump 18 can also be connected via directional control valve 40 with piston chamber 24 of the hydraulic cylinder by a third hydraulic line 38. Directional control valve 40 has a first switching position which is illustrated on the right in FIG. 1, as well as a second switching position which is illustrated on the left in FIG. 1. Directional control valve 40 is shown in its first switching position in FIG. 1.

(9) Directional control valve 40 can be hydraulically controllable, whereby a first control line 42 is provided, whereby the pressure in piston chamber 24 is used to feed back to directional control valve 40 and for changeover from the first switching position into the second switching position. If the pressure in piston chamber 24 exceeds a pressure limit, a counter force can be overcome that is adjustable via a return spring 44, and directional control valve 40 is moved into the second switching position. When the pressure in piston chamber 24 drops again below the pressure limit, the directional control valve can again be moved by return spring 44 into the first switching position.

(10) A second control line 46 may furthermore be provided, whereby the pressure from annulus 26 is used to feed back to directional control valve 40 and for changeover from the second switching position into the first switching position. This function is explained in further detail later in this text.

(11) The three hydraulic pumps 14, 16, 18 are each connected with a hydraulic tank 48. Hydraulic pumps 14, 16, 18 can moreover be protected against vacuum or excess pressure via check valves 50, 52, 54 as well as pressure relief valves 56, 58, 69.

(12) The three hydraulic pumps 14, 16, 18 can be driven by an electric motor 62 via a shaft 63. Hydraulic pump 14 and second hydraulic pump 18 have a direction of delivery corresponding with each other, whereas hydraulic pump 16 has a delivery direction in the opposite direction. The direction of rotation or respectively delivery direction in the opposite direction of hydraulic pump 16 is indicated by intersecting segment 66 of shaft 64.

(13) The joint delivery volume of hydraulic pump 14 and second hydraulic pump 18 is adapted to hydraulic effective surface 28 of piston chamber 24, whereby the delivery volume of hydraulic pump 16 is adapted to hydraulic effective surface 30 of annulus 26. Consequently, the ratio of the joint delivery volume of hydraulic pump 14 and second hydraulic pump 18 relative to the delivery volume of hydraulic pump 16 is approximately consistent with the surface ratio of hydraulic effective surface 28 of piston chamber 24 relative to hydraulic effective surface 30 of annulus 26.

(14) The inventive hydraulic drive 10 can function as follows:

(15) If, during operation of hydraulic drive 10, for example when used in a hydraulic press that is not illustrated here, electric motor 62 rotates and directional control valve 40 is in its first switching position illustrated in FIG. 1, hydraulic pump 14 as well as also second hydraulic pump 18 are hydraulically connected with piston chamber 24 of hydraulic cylinder 12. If electric motor 62 rotates in the direction of arrow 68, pump 14 delivers hydraulic fluid at pump outlet 15, and second hydraulic pump 18 out of tank 48 into piston chamber 24. Hydraulic pump 16 again moves hydraulic fluid at pump intake 17 out of annulus 26 into tank 48. Due to delivery volume of hydraulic pumps 14, 16, 18 that is adapted to the surface ratio of hydraulic effective surfaces 28, 30 no, or almost no hydraulic fluid needs to be sucked back via check valves 50, 52, whereby also no or almost no hydraulic fluid is delivered via pressure relief valve 60 to tank 48.

(16) When electric motor 62 rotates in the direction of arrow 68 and directional check valve 40 is in its first switching position, piston 22 or respectively piston rod 32 of hydraulic cylinder 12 moves in the direction of arrow 70 in a so-called rapid stroke at high speed.

(17) If now, during operation of hydraulic drive 10, piston rod 32 or respectively a pressing tool that is arranged on piston rod 32 impinges on an obstacle, for example, a work piece that is to be processed, the pressure in piston chamber 24 increases. If the pressure in piston chamber 24 increases to above a preset pressure limit of directional control valve 40, a hydraulically forced guidance can be provided via control line 42. Directional control valve 40 is moved against the force of return spring 44 into the second switching position.

(18) In the second switching positionat an unchanged rotational direction of electric motor 62second hydraulic pump 18 moves hydraulic fluid without pressure or almost without pressure from tank 48 back into tank 48. It consequently does not participate in the fluid exchange with hydraulic cylinder 12.

(19) Thus, only hydraulic pump 14 still moves (pumps) hydraulic fluid into piston chamber 24, whereby hydraulic pump 16 moves (sucks) hydraulic fluid out of annulus 26. Electric motor 62 can nowat an unchanged motor torqueprovide a higher pressure for a machining operation due to hydraulic pumps 14, 16 acting by themselves. Piston 22 or respectively piston rod 32 can thus be moved in a so-called load stroke at lower speed, however with greater force in the direction of arrow 70.

(20) In the load stroke, the delivery volumes of hydraulic pumps 14, 16 are no longer adapted to the surface ratio of hydraulic effective surfaces 28, 30 since second hydraulic pump 18 moves hydraulic fluid only in the circuit. Additional hydraulic fluid is consequently subsequently sucked via check valve 54 since otherwise hydraulic pump 16 would create a vacuum in annulus 26.

(21) After completion of the load stroke or respectively after completion of a machining operation, the pressure in piston chamber 24 drops off again. If the pressure in piston chamber 24 drops below the pressure limit of directional control valve 40 that is set by return spring 44, directional control valve 40 is again moved back into its first switching position that is illustrated in FIG. 1. If the direction of rotation of electric motor 62 is reversed, in other words if electric motor 62 or respectively shaft 64 rotate in opposite direction than that indicated by arrow 68, hydraulic pump 14 at pump outlet 15, and second hydraulic pump 18 move (suck) hydraulic fluid out of piston chamber 24 into tank 48, whereas hydraulic pump 16 at pump intake 17 moves (pumps) hydraulic fluid out of tank 48 into annulus 26 of hydraulic cylinder 12. On a reversal of the direction of rotation of electric motor 62, piston 22 or respectively piston rod 32 can thus again be moved back in a rapid stroke against the direction of arrow 70.

(22) An exception can occur if the load in a machining operation is present until the return point of the movement of piston 22. A high pressure continues to prevail in piston chamber 24, so that directional control valve 40 cannot be moved into the first switching position by return spring 44 due to the pressure prevailing in first control line 42. If the direction of rotation of electric motor 62 is reversed in this condition against the direction of arrow 68, hydraulic pump 16 moves (pumps) hydraulic fluid out of tank 48 into annulus 26, whereby only hydraulic pump 14 pumps (sucks) hydraulic fluid out of piston chamber 24 into tank 48. Since also in this operational condition the delivery volumes of hydraulic pumps 14, 16 are not adapted to the surface volume of hydraulic effective surfaces 28, 20, the pressure in annulus 26 increases. If the pressure in annulus 26 which also prevails in second control line 46, together with the force of spring 44 exceeds the pressure prevailing in control line 42 or respectively in piston chamber 24, directional control valve 40 switches from the second switching position through hydraulically forced guidance back into the first switching position, whereby again second hydraulic pump 18 is hydraulically connected with piston chamber 24.

(23) The delivery volumes of the three pumps 14, 16, 18 are now again adapted to the surface ratio of hydraulic effective surfaces 28, 30 and piston 22 or respectively piston rod 26 can be moved back in a rapid stroke against the direction of arrow 70.

(24) Referring now FIG. 2, there is shown a second embodiment of an inventive hydraulic drive 100. Corresponding elements are identified with corresponding reference numbers, whereby the functionality of hydraulic drive 100 is fundamentally consistent with the functionality of hydraulic drive 10 which is illustrated in FIG. 1.

(25) Drive 100 includes a hydraulic cylinder 12 that may be designed as a differential cylinder, as well as a first hydraulic pump 102 that may be designed as a four-quadrant pump, and a second hydraulic pump 18, whereby hydraulic pumps 18, 102 can be driven entirely by an electric motor 62.

(26) Hydraulic cylinder 12 comprises a piston 22 that separates a piston chamber 24 from an annulus 26. Piston chamber 24 has a hydraulic effective surface 28, whereby annulus 26 has a hydraulic effective surface 30. Because of piston rod 32, hydraulic effective surface 30 of annulus 26 which is round is smaller than hydraulic effective surface 28 of piston chamber 24.

(27) Hydraulic pump 102 is hydraulically connected with piston chamber 24 of hydraulic cylinder 12 with a pump connection that is identified as pump outlet 104 by a hydraulic line 34, whereas hydraulic pump 102 is hydraulically connected with annulus 26 of hydraulic cylinder 12 with a pump connection that is identified as pump intake 106 by a hydraulic line 36. Hydraulic pump 102 which can be designed as four-quadrant pump delivers hereby in opposite directions at pump intake 106 and at pump outlet 104, whereby depending on the direction of delivery at pump intake 106 hydraulic fluid can be sucked in and hydraulic fluid can be moved out of pump 102 at pump outlet 104, and vice versa.

(28) Second hydraulic pump 18 can also be connected via directional control valve 40 with piston chamber 24 of the hydraulic cylinder by a third hydraulic line 38. Directional control valve 40 has a first switching position that is illustrated on top of FIG. 2, as well as a second switching position that is shown on the bottom of FIG. 2. Directional control valve 40 is shown in its first switching position in FIG. 2.

(29) Directional control valve 40 is hydraulically controllable, whereby a first control line 42 is provided, whereby the pressure in piston chamber 24 is used to feed back to directional control valve 40 and for changeover from the first switching position into the second switching position. If the pressure in piston chamber 24 exceeds a pressure limit, a counter force can be overcome that is adjustable via a return spring 44, and directional control valve 40 can be moved into the second switching position. When the pressure in piston chamber 24 drops again below the pressure limit, the directional control valve can again be moved by return spring 44 into the first switching position.

(30) A second control line 46 is furthermore provided, whereby the pressure from annulus 26 is used to feed back to directional control valve 40 and for changeover from the second switching position into the first switching position. This function is explained in further detail later in this text.

(31) Hydraulic pump 18 is hydraulically connected with a tank 48. Hydraulic pumps 18, 102 are driven by an electric motor 62 via a shaft 64.

(32) The joint delivery volume of hydraulic pump 102 at pump outlet 104 and of second hydraulic pump 18 is adapted to hydraulic effective surface 28 of piston chamber 24, where the delivery volume of hydraulic pump 102 at pump intake 106 is adapted to hydraulic effective surface 30 of annulus 26. Consequently, the ratio of the joint delivery volume of hydraulic pump 102 at pump outlet 104 and of second hydraulic pump 18 relative to the delivery volume of hydraulic pump 102 at pump intake 106 is approximately consistent with the surface ratio of hydraulic effective surface 28 of piston chamber 24 relative to hydraulic effective surface 30 of annulus 26.

(33) The inventive hydraulic drive 100 can function as follows:

(34) If, during operation of hydraulic drive 100, for example, when used in a hydraulic press that is not illustrated here, electric motor 62 rotates and directional control valve 40 is in its first switching position illustrated in FIG. 2, pump outlet 104 of hydraulic pump 104 as well as also second hydraulic pump 18 are hydraulically connected with piston chamber 24 of hydraulic cylinder 12. If electric motor 62 rotates in the direction of arrow 68, hydraulic pump 102 at pump outlet 104, and second hydraulic pump 18 deliver hydraulic fluid, into piston chamber 24. Hydraulic pump 102 again moves hydraulic fluid out of annulus 26 at pump intake 106.

(35) When electric motor 62 rotates in the direction of arrow 68 and directional check valve 40 is in its first switching position, piston 22 or respectively piston rod 32 of hydraulic cylinder 12 moves in the direction of arrow 70 in a so-called rapid stroke at high speed.

(36) If now, during operation of hydraulic drive 100, piston rod 32 or respectively a pressing tool that is arranged on piston rod 32 impinges on an obstacle, for example, a work piece that is to be processed, the pressure in piston chamber 24 increases. If the pressure in piston chamber 24 increases to above a preset pressure limit of directional control valve 40, a hydraulically forced guidance can be provided via control line 42. Directional control valve 40 is moved against the force of return spring 44 into the second switching position.

(37) In the second switching positionat unchanged rotational direction of electric motor 62second hydraulic pump 18 moves hydraulic fluid without pressure or almost without pressure from tank 48 back into tank 48. It consequently does not participate in the fluid exchange with hydraulic cylinder 12.

(38) Thus, only hydraulic pump 102 still moves (pumps) hydraulic fluid at pump outlet 104 into piston chamber 24, whereby hydraulic pump 102 moves (sucks) hydraulic fluid at pump intake 106 out of annulus 26. Electric motor 62 can nowat unchanged motor torqueprovide a higher pressure for a machining operation due to hydraulic pump 102 acting alone. Piston 22 or respectively piston rod 32 can thus be moved in a so-called load stroke at lower speed, however with greater force in the direction of arrow 70.

(39) In the load stroke the delivery volumes of hydraulic pump 102 is no longer adapted to the surface ratio of hydraulic effective surfaces 28, 30 since second hydraulic pump 18 moves hydraulic fluid only in the circuit. Additional hydraulic fluid must consequently subsequently be sucked via a feed line 108 since otherwise hydraulic pump 102 would create a vacuum in annulus 26.

(40) After completion of the load stroke or respectively after completion of a machining operation the pressure in piston chamber 24 drops off again. If the pressure in piston chamber 24 drops below the pressure limit of directional control valve 40 that is set by return spring 44, directional control valve 40 is again moved back into its first switching position that is illustrated in FIG. 2. If the direction of rotation of electric motor 62 is reversed, in other words if electric motor 62 or respectively shaft 64 rotate in opposite direction than that indicated by arrow 68, hydraulic pump 102 at pump outlet 104, and second hydraulic pump 18 move (suck) hydraulic fluid out of piston chamber 24 into tank 48, whereas hydraulic pump 102 at pump intake 106 moves (pumps) hydraulic fluid out of tank 48 into annulus 26 of hydraulic cylinder 12. On a reversal of the direction of rotation of electric motor 62, piston 22 or respectively piston rod 32 can thus again be moved back in a rapid stroke against the direction of arrow 70.

(41) An exception can occur if the load in a machining operation is present until the return point of the movement of piston 22. The high pressure then continues to prevail in piston chamber 24, so that directional control valve 40 cannot be moved into the first switching position by return spring 44 due to the pressure prevailing in first control line 42. If the direction of rotation of electric motor 62 is reversed in this condition against the direction of arrow 68, hydraulic pump 102 moves (pumps) hydraulic fluid out of tank 48 into annulus 26, whereby only hydraulic pump 102 pumps (sucks) hydraulic fluid out of piston chamber 24 into tank 48. Since also in this operational condition the delivery volumes of hydraulic pump 102 are not adapted to the surface volume of hydraulic effective surfaces 28, 20, the pressure in annulus 26 increases. If the pressure in annulus 26 which also prevails in second control line 46, together with the force of spring 44 exceeds the pressure prevailing in control line 42 or respectively in piston chamber 24, directional control valve 40 switches from the second switching position through hydraulically forced guidance back into the first switching position, whereby again second hydraulic pump 18 is hydraulically connected with piston chamber 24.

(42) The delivery volumes of pumps 18, 102 are now again adapted to the surface ratio of hydraulic effective surfaces 28, 30 and piston 22 or respectively piston rod 32 can be moved back in a rapid stroke against the direction of arrow 70.

(43) While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.