Hydrostatic linear drive system

Abstract

A linear drive system, in particular for a closure unit of a blow mold installation, with a simpler and more compact structure, a higher retraction and expansion speed in rapid mode, higher forces in power mode, and reduced energy consumption, than the prior art includes a cylinder arrangement which brings about a retraction and extension movement in rapid mode by separate hydraulically active faces which are independent of a larger hydraulically active face which is acted on with pressurized hydraulic fluid only in power mode. During the extension movement in power mode, however, the hydraulically active faces cooperate which contributes to high forces with a compact structure of the drive system.

Claims

1. A hydrostatic linear drive system, comprising: a single-action cylinder having a cylinder component and a piston component with a first hydraulically active face; a first fluid connection through which a hydraulic fluid can act on the first hydraulically active face in an extension direction of the single-action cylinder; a synchronous cylinder having a cylinder component and a piston component with a second hydraulically active face and a third hydraulically active face, wherein an area of the second hydraulically active face corresponds to an area of the third hydraulically active face; a second fluid connection and a third fluid connection, wherein the second hydraulically active face can be acted on with the hydraulic fluid through the second fluid connection in the extension direction and the third hydraulically active face can be acted on with the hydraulic fluid through the third fluid connection in a retraction direction counter to the extension direction, wherein an area of the first hydraulically active face of the single-action cylinder is greater than the area of the second hydraulically active face and the area of the third hydraulically active face of the synchronous cylinder; a first hydraulic pump having a first pressure connection and a second pressure connection for providing a volume flow of the hydraulic fluid, wherein a flow direction of the volume flow between the pressure connections is reversible; a closed hydraulic circuit under a pretensioning pressure including the synchronous cylinder and the first hydraulic pump, wherein the first pressure connection is connected to the second fluid connection and the second pressure connection is connected to the third fluid connection in a fluid-conducting manner, respectively; an equalizing tank for the hydraulic fluid open towards the environment and a fluid-conducting connection between the equalizing tank and the first fluid connection of the single-action cylinder; a first shut-off member in the fluid-conducting connection between the equalizing tank and the single-action cylinder, wherein the first shut-off member enables a throughflow of the hydraulic fluid into and out of the equalizing tank; a second hydraulic pump having a low-pressure connection and a high-pressure connection configured for temporarily providing a volume flow of the hydraulic fluid, wherein the low-pressure connection is connected in a fluid-conducting manner to the equalizing tank and the high-pressure connection is connected in a fluid-conducting manner to the first fluid connection of the single-action cylinder; and a mechanical coupling connecting the piston component of the single-action cylinder to the piston component of the synchronous cylinder.

2. A hydrostatic linear drive system, comprising: a cylinder having a cylinder pipe with a first end side and an opposing end side, a cylinder base arranged at and closing the first end side of the cylinder pipe, and a piston rod guide arranged at the opposing end side of the cylinder pipe, a guiding pin extending from the cylinder base into the cylinder pipe, an annular piston surrounding the guiding pin, the annular piston having a first annular piston face and a second annular piston face, and a piston rod having a hollow space surrounding the guiding pin and connected to the annular piston; a first hydraulically active face formed by the first annular first piston face facing the cylinder base and delimiting a first cylinder chamber between the annular piston and the cylinder base; a second hydraulically active face formed by a partial surface of the hollow space in the piston rod and which is opposite the end side of the guiding pin; a third hydraulically active face formed by the annular second piston face facing the piston rod guide and delimiting a second cylinder chamber between the annular piston and the piston rod guide, wherein an area of the second hydraulically active face corresponds to an area of the third hydraulically active face; a first fluid connection through which a hydraulic fluid can act on the first hydraulically active face in an extension direction of the cylinder; a second fluid connection and a third fluid connection, wherein the second hydraulically active face can be acted on with the hydraulic fluid through the second fluid connection in the extension direction and the third hydraulically active face can be acted on with the hydraulic fluid through the third fluid connection in a retraction direction counter to the extension direction; wherein an area of the first hydraulically active face is larger than the area of the second hydraulically active face and larger than the area of the third hydraulically active face; a first hydraulic pump having a first pressure connection and a second pressure connection for providing a volume flow of the hydraulic fluid, wherein a flow direction of the volume flow between the pressure connections is reversible; a closed hydraulic circuit under a pretensioning pressure and comprising the first hydraulic pump, wherein the first pressure connection is connected to the second fluid connection and the second pressure connection is connected to the third fluid connection in a fluid-conducting manner, respectively; an equalizing tank for the hydraulic fluid open towards the environment and a fluid-conducting connection between the equalizing tank and the first fluid connection; a first shut-off member in the fluid-conducting connection between the equalizing tank and the first fluid connection, wherein the first shut-off member enables a throughflow of the hydraulic fluid into and out of the equalizing tank; and a second hydraulic pump having a low-pressure connection and a high-pressure connection configured for temporarily providing a volume flow of the hydraulic fluid, wherein the low-pressure connection is connected in a fluid-conducting manner to the equalizing tank and the high-pressure connection is connected in a fluid-conducting manner to the first fluid connection.

3. The hydrostatic linear drive system according to claim 1, further comprising: a fluid-conducting connection between the high-pressure connection of the second hydraulic pump and the second pressure connection of the first hydraulic pump; a non-return valve in the fluid-conducting connection between the high pressure connection of the first hydraulic pump and the second pressure connection of the second hydraulic pump that prevents a return flow of the hydraulic fluid toward the second hydraulic pump; and a fluid-conducting connection between the first pressure connection and the first fluid connection; and a second shut-off member in the fluid-conducting connection between the first pressure connection and the first fluid connection.

4. The hydrostatic linear drive system according to claim 1, wherein at least one from the group of a displacement volume of the first hydraulic pump, a drive speed of the first hydraulic pump, a displacement volume of the second hydraulic pump, and a drive speed of the second hydraulic pump can be changed.

5. The hydrostatic linear drive system according to claim 1, wherein at least one from the group of the pressure connections of the first hydraulic pump and the high-pressure connection of the second hydraulic pump are connectable to a pressure store.

6. The hydrostatic linear drive system according to claim 1, wherein at least one from the group of the first shut-off member and the second shut-off member is a non-return valve.

7. The hydrostatic linear drive system according to claim 1, wherein the pretensioning pressure is higher than an ambient pressure.

8. The hydrostatic linear drive system according to claim 7, wherein the pretensioning pressure is between 5 and 50 bar.

9. The hydrostatic linear drive system according to claim 1, wherein a throttle is arranged in the fluid-conducting connection between the equalizing tank and the first fluid connection.

10. The hydrostatic linear drive system according to claim 1, wherein the single-action cylinder is a plunger cylinder.

11. The hydrostatic linear drive system according to claim 1, wherein the first hydraulic pump, the second hydraulic pump, and the first shut-off member are each controllable to be operated in a rapid mode in an extension direction and a retraction direction in which the first hydraulic pump is active, the first shut-off member is open, and the second hydraulic pump is inactive, and in a power mode in the extension direction in which both the first hydraulic pump and the second hydraulic pump are active and the first shut-off member is closed.

12. The hydrostatic linear drive system according to claim 2, further comprising: a fluid-conducting connection between the high-pressure connection of the second hydraulic pump and the second pressure connection of the first hydraulic pump; a non-return valve in the fluid-conducting connection between the high pressure connection of the first hydraulic pump and the second pressure connection of the second hydraulic pump that prevents a return flow of the hydraulic fluid toward the second hydraulic pump; and a fluid-conducting connection between the first pressure connection and the first fluid connection; and a second shut-off member in the fluid-conducting connection between the first pressure connection and the first fluid connection.

13. The hydrostatic linear drive system according to claim 2, wherein at least one from the group of a displacement volume of the first hydraulic pump, a drive speed of the first hydraulic pump, a displacement volume of the second hydraulic pump, and a drive speed of the second hydraulic pump can be changed.

14. The hydrostatic linear drive system according to claim 2, wherein at least one from the group of the pressure connections of the first hydraulic pump and the high-pressure connection of the second hydraulic pump are connectable to a pressure store.

15. The hydrostatic linear drive system according to claim 2, wherein at least one from the group of the first shut-off member and the second shut-off member is a non-return valve.

16. The hydrostatic linear drive system according to claim 2, wherein the pretensioning pressure is higher than an ambient pressure.

17. The hydrostatic linear drive system according to claim 16, wherein the pretensioning pressure is between 5 and 50 bar.

18. The hydrostatic linear drive system according to claim 2, wherein a throttle is arranged in the fluid-conducting connection between the equalizing tank and the first fluid connection.

19. The hydrostatic linear drive system according to claim 2, wherein the first hydraulic pump, the second hydraulic pump, and the first shut-off member are each controllable to be operated in a rapid mode in an extension direction and a retraction direction in which the first hydraulic pump is active, the first shut-off member is open, and the second hydraulic pump is inactive, and in a power mode in the extension direction in which both the first hydraulic pump and the second hydraulic pump are active and the first shut-off member is closed.

20. A hydrostatic linear drive system, comprising: a cylinder including a piston component having a first hydraulically active face, a second hydraulically active face, and a third hydraulically active face, wherein an area of the second hydraulically active face corresponds to an area of the third hydraulically active face, and wherein an area of the first hydraulically active face is larger than the area of the second hydraulically active face and larger than the area of the third hydraulically active face; a first fluid connection through which a hydraulic fluid can act on the first hydraulically active face in an extension direction of the piston component; a second fluid connection and a third fluid connection, wherein the second hydraulically active face can be acted on with the hydraulic fluid through the second fluid connection in the extension direction and the third hydraulically active face can be acted on with the hydraulic fluid through the third fluid connection in a retraction direction counter to the extension direction; a first hydraulic pump having a first pressure connection and a second pressure connection for providing a volume flow of the hydraulic fluid, wherein a flow direction of the volume flow between the pressure connections is reversible; a closed hydraulic circuit under a pretensioning pressure including the first hydraulic pump, wherein the first pressure connection is connected to the second fluid connection and the second pressure connection is connected to the third fluid connection in a fluid-conducting manner, respectively; an equalizing tank for the hydraulic fluid open towards the environment and a fluid-conducting connection between the equalizing tank and the first fluid connection; a first shut-off member in the fluid-conducting connection between the equalizing tank and the first fluid connection, wherein the first shut-off member enables a throughflow of the hydraulic fluid into and out of the equalizing tank; and a second hydraulic pump having a low-pressure connection and a high-pressure connection configured for temporarily providing a volume flow of the hydraulic fluid, wherein the low-pressure connection is connected in a fluid-conducting manner to the equalizing tank and the high-pressure connection is connected in a fluid-conducting manner to the first fluid connection, wherein the piston component is configured so that: the first hydraulically active face, the second hydraulically active face and the third hydraulically active face are arranged in a single cylinder, or the first hydraulically active face is arranged in a single-action cylinder and the second hydraulically active face and the third hydraulically active face are arranged in a synchronous cylinder separate from the single-action cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, wherein like reference characters denote similar elements throughout the several views:

(2) FIG. 1 is a schematic diagram of a first embodiment of the hydrostatic linear drive system having a single-action cylinder and a synchronous cylinder,

(3) FIG. 1A is a schematic diagram of the first embodiment during an extension in a rapid mode,

(4) FIG. 1B is a schematic diagram of the first embodiment during an extension in a power mode,

(5) FIG. 1C is a schematic diagram of the first embodiment during cancellation of a force,

(6) FIG. 1D is a schematic diagram of the first embodiment during a retraction in the rapid mode,

(7) FIG. 2 is a schematic diagram of a second embodiment of the hydrostatic linear drive system with a single-action cylinder and a synchronous cylinder,

(8) FIG. 2A is a schematic diagram of the second embodiment during an extension in a rapid mode,

(9) FIG. 2B is a schematic diagram of the second embodiment during an extension in a power mode,

(10) FIG. 2C is a schematic diagram of the second embodiment during cancellation of the force,

(11) FIG. 2D is a schematic diagram of the second embodiment during the retraction in rapid mode,

(12) FIG. 3 is a schematic diagram of the first embodiment of the hydrostatic linear drive system with a 3-face cylinder,

(13) FIG. 3A is a schematic diagram of the system of FIG. 3 during the extension in the rapid mode,

(14) FIG. 3B is a schematic diagram of the system of FIG. 3 during the extension in the power mode,

(15) FIG. 3C is a schematic diagram of the system of FIG. 3 during cancellation of the force,

(16) FIG. 3D is a schematic diagram of the system of FIG. 3 during the retraction in the rapid mode,

(17) FIG. 4 is a schematic diagram of the second embodiment of the hydrostatic linear drive system having a 3-face cylinder,

(18) FIG. 4A is a schematic diagram of the system of FIG. 4 during the extension in the rapid mode,

(19) FIG. 4B is a schematic diagram of the system of FIG. 4 during the extension in the power mode,

(20) FIG. 4C is a schematic diagram of the system of FIG. 4 during cancellation of the force, and

(21) FIG. 4D is a schematic diagram of the system of FIG. 4 during the retraction in the rapid mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(22) FIG. 1 shows a first embodiment of a hydrostatic linear drive system 1 having a single-action cylinder 2 which is constructed as a plunger cylinder. The plunger cylinder comprises a piston rod 3, a first hydraulically active face 4 and a first cylinder chamber 5 having a first fluid connection 6 for a hydraulic fluid 7. As a result of the construction of the single-action cylinder 2 as a plunger cylinder, the piston rod 3 is at the same time the piston. The end side of the piston rod 3 facing the cylinder chamber 5 is the piston face and is hydraulically active.

(23) The first hydraulically active face 4 of the single-action cylinder 2 can be acted on with the hydraulic fluid 7 via the first fluid connection 6 in an extension direction 8 (see FIG. 1A).

(24) Referring back to FIG. 1, the linear drive system 1 further has a synchronous cylinder 9 which has at both sides of the piston 10 a piston rod 11, 12. The annular piston faces which surround the piston rods 11, 12 form a second hydraulically active face 13 and a third hydraulically active face 14 which correspond in terms of size/area. The synchronous cylinder 9 has a second fluid connection 15 and a third fluid connection 16, wherein the second fluid connection 15 opens in an annular second cylinder chamber 35 at the left side of the piston 10 and the third fluid connection 16 opens in an annular third cylinder chamber 36 at the right side of the piston 10.

(25) The second hydraulically active face 13 can be acted on with hydraulic fluid 7 via the second fluid connection 15 in the extension direction 8 (see FIG. 1A). The third hydraulically active face 14 can be acted on with hydraulic fluid 7 via the third fluid connection 16 in the retraction direction 17 (see FIG. 1D).

(26) A closed hydraulic circuit 18 which is under pretensioning pressure comprises the synchronous cylinder 9 and a first hydraulic pump 19 with a first and a second pressure connection 21, 22. An electric motor 20 drives the first hydraulic pump 19 at a constant or variable motor speed. The first hydraulic pump 19 is preferably an axial piston variable-displacement pump of the swash plate construction type. As a result of the adjustment of a pivot angle the swash plate, the volume flow of the first hydraulic pump 19 can be changed in a stepless manner. When the swash plate is adjusted through the zero position, the flow direction 23.1, 23.2 (see FIGS. 1A, 1B, and 1D) of the volume flow changes. The adjustment of the pivot angle of the swash plate is carried out in this instance hydraulically by an actuating piston.

(27) Depending on the flow direction 23.1/23.2, the first pressure connection 21 is the high-pressure side and the second pressure connection 22 is the low-pressure side of the first hydraulic pump 19, or vice versa.

(28) The first pressure connection 21 is connected to the second fluid connection 15 and the second pressure connection 22 is connected to the third fluid connection 16 in a fluid-conducting manner by a hydraulic line 24, 25, respectively. The pretensioning of the hydraulic fluid in the closed hydraulic circuit 18 may, for example, be produced by a pressure source which is not illustrated and which is connected to the pressure connections 21, 22 (for example, feed oil pump). Since the pretensioning of a closed hydraulic circuit 18 is known to the person skilled in the art, an illustration of the components required for this has been omitted for the sake of clarity.

(29) In order to act on the first hydraulically active face 4 of the single-action cylinder 2 with hydraulic fluid 7, a second hydraulic pump 26 is provided with a low-pressure connection 27 and a high-pressure connection 28. The low-pressure connection 27 is connected in a fluid-conducting manner via a hydraulic line 29 to an equalizing tank 30 and the high-pressure connection 28 is connected in a fluid-conducting manner via a hydraulic line 31 to the first fluid connection 6 of the single-action cylinder 2.

(30) The equalizing tank 30 which is open towards the environment receives hydraulic fluid 7 and is further connected in a fluid-conducting manner to the first fluid connection 6 of the single-action cylinder 2 via a hydraulic line 32. A 2/2-way valve 33.1 is arranged as a first shut-off member 33 in the hydraulic line 32 between the equalizing tank 30 and the single-action cylinder 2.

(31) Finally, the piston rod 3 of the single-action cylinder 2 and the piston rod 12 of the synchronous cylinder 9 are mechanically connected to each other by a coupling member 34 in such a manner that both cylinders move exclusively in a synchronous manner.

(32) When the linear drive system 1 is extended in rapid mode as shown in FIG. 1A, the second hydraulically active face 13 is acted on with hydraulic fluid 7 through the second fluid connection 15 by the first hydraulic pump 19 operating in the flow direction 23.1, whereby the piston 10 of the synchronous cylinder 9 moves in the extension direction 8. The piston rod 3 of the single-action cylinder 2 which is connected to the piston rod 12 of the synchronous cylinder 9 by the coupling member 34 is also moved in the extension direction 8 without the hydraulically active face 4 thereof being acted on with hydraulic fluid 7. The hydraulic fluid 7 passes through the open 2/2-way valve 33.1 from the equalizing tank 30 via the first fluid connection 6 into the cylinder chamber 5 of the single-action cylinder 2 (extraction). The second hydraulic pump 26 which is also connected to the first fluid connection 6 is not active.

(33) When the linear drive system 1 is retracted in rapid mode as shown in FIG. 1D, the third hydraulically active face 14 is acted on with hydraulic fluid 7 through the third fluid connection 16 by the first hydraulic pump 19 which is now operating in the opposite flow direction 23.2, whereby the piston 10 of the synchronous cylinder 9 moves in the retraction direction 17. The piston rod 3 of the single-action cylinder 2 which is connected to the piston rod 12 of the synchronous cylinder 9 via the coupling member 34 is also moved in the retraction direction 17 without the hydraulically active face 4 thereof being acted on with hydraulic fluid 7. The hydraulic fluid 7 is displaced through the open 2/2-way valve 33.1 from the cylinder chamber 5 of the single-action cylinder 2 into the equalizing tank 30. The second hydraulic pump 26 which is connected to the first fluid connection 6 is not active.

(34) When the linear drive system 1 is extended in power mode as shown in FIG. 1B, the first hydraulically active face 4 of the single-action cylinder 2 is acted on with hydraulic fluid 7 through the first fluid connection 6 by the activated second hydraulic pump 26, whereby the single-action cylinder 2 moves in the extension direction 8. During extension in power mode, the first hydraulic pump 19 is further activated in the flow direction 23.1 so that through the second fluid connection 15 the second hydraulically active face 13 of the synchronous cylinder 9 is acted on with hydraulic fluid 7. The synchronous cylinder moves synchronously with the single-action cylinder 2, to which it is coupled via the coupling member 34, in the extension direction 8. A flow of the hydraulic fluid 7 via the hydraulic line 32 into the equalizing tank 30 is prevented by the closed 2/2-way valve 33.1. The force produced during extension in power mode is produced by the cooperation of the single-action cylinder 2 and the synchronous cylinder 9 which is acted on in the extension direction 8.

(35) In order to end the power mode, the first hydraulic pump 19 and the second hydraulic pump 26 are deactivated and the 2/2-way valve 33.1 is opened so that the hydraulic fluid 7 can flow from the first cylinder chamber 5 via the open 2/2-way valve 33.1 in the hydraulic line 32 into the equalizing tank 30 as shown in FIG. 1C.

(36) FIG. 2 shows a second embodiment of a hydrostatic linear drive system 1 having a single-action cylinder 2, which is constructed as a plunger cylinder. The plunger cylinder comprises a piston rod 3, a first hydraulically active face 4 and a first cylinder chamber 5 with a first fluid connection 6 for a hydraulic fluid 7. As a result of the construction of the single-action cylinder 2 as a plunger cylinder, the piston rod 3 is at the same time the piston. The end side of the piston rod 3 facing the cylinder chamber 5 is the first hydraulically active face 4.

(37) The first hydraulically active face 4 of the single-action cylinder 2 can be acted on with the hydraulic fluid 7 in an extension direction 8 via the first fluid connection 6.

(38) The linear drive system 1 further has a synchronous cylinder 9 which has at both sides of the piston 10 a piston rod 11, 12. The annular piston faces which surround the piston rods 11, 12 form a second hydraulically active face 13 and a third hydraulically active face 14 which correspond to each other in terms of size/area. The synchronous cylinder 9 has a second fluid connection 15 and a third fluid connection 16, wherein the second fluid connection 15 opens in an annular second cylinder chamber 35 at the left side of the piston 10 and the third fluid connection 16 opens in a third annular cylinder chamber 36 at the right side of the piston 10.

(39) The second hydraulically active face 13 can be acted on in the extension direction 8 with hydraulic fluid 7 via the second fluid connection 15. The third hydraulically active face 14 can be acted on with hydraulic fluid 7 in the retraction direction 17 via the third fluid connection 16.

(40) A closed hydraulic circuit 18 which is under a pretensioning pressure comprises the synchronous cylinder 9 and a first hydraulic pump 19 with a first and a second pressure connection 21, 22. An electric motor 20 drives the hydraulic pump 19 at a constant or variable motor speed. The hydraulic pump 19 is preferably an axial piston variable-displacement pump of the swash plate construction type as in the embodiment according to FIG. 1.

(41) The first pressure connection 21 is connected to the second fluid connection 15 and the second pressure connection 22 is connected to the third fluid connection 16 in a fluid-conducting manner by a hydraulic line 24, 25, respectively. The pretensioning of the hydraulic fluid in the closed hydraulic circuit 18 may, for example, be produced by a pressure source which is not illustrated and which is connected to the pressure connections 21, 22.

(42) In order to act on the first hydraulically active face 4 of the single-action cylinder 2 with hydraulic fluid 7, the first fluid connection 6 of the single-action cylinder 2 is connected by a hydraulic line 38 in a fluid-conducting manner to the first pressure connection 21 of the first hydraulic pump 19. A second shut-off member 39 which is constructed as a 2/2-way valve 39.1 is arranged in the hydraulic line 38. A high-pressure connection 28 of a second hydraulic pump 26 is connected in a fluid-conducting manner via a hydraulic line 31 to the second pressure connection 22 of the first hydraulic pump 19. A non-return valve 40 in the hydraulic line 31 prevents a return flow of the hydraulic fluid 7 in the direction of the second hydraulic pump 26.

(43) A low-pressure connection 27 of the second hydraulic pump 26 is connected in a fluid-conducting manner by a hydraulic line 29 to the equalizing tank 30. In contrast to the embodiment according to FIG. 1, however, the high-pressure connection 28 of the second hydraulic pump 26 is not directly connected to the first fluid connection 6 of the single-action cylinder 2 in a fluid-conducting manner, but instead indirectly by the flow path released by the open 2/2-way valve 39.1 and the first hydraulic pump 19 which is activated in the flow direction 23.1.

(44) The equalizing tank 30 which is open in the direction towards the environment receives hydraulic fluid 7 and is further connected in a fluid-conducting manner via a hydraulic line 32 to the first fluid connection 6 of the single-action cylinder 2. A 2/2-way valve 33.1 is arranged in the hydraulic line 32 between the equalizing tank 30 and the single-action cylinder 2 as a first shut-off member 33.

(45) Finally, the piston rod 3 of the single-action cylinder 2 and the piston rod 12 of the synchronous cylinder 9 are mechanically connected to each other by a coupling member 34 in such a manner that both cylinders move exclusively in a synchronous manner.

(46) When the linear drive system 1 is extended in the rapid mode, the second hydraulically active face 13 is acted on with hydraulic fluid 7 through the second fluid connection 15 by the first hydraulic pump 19 operating in the flow direction 23.1 as shown in FIG. 2A, whereby the piston 10 of the synchronous cylinder 9 moves in the extension direction 8. The piston rod 3 of the single-action cylinder 2 which is connected to the piston rod 12 of the synchronous cylinder 9 via the coupling member 34 is also moved in the extension direction 8 without the hydraulically active face 4 thereof being acted on with hydraulic fluid 7. The hydraulic fluid 7 from the equalizing tank 30 reaches the cylinder chamber 5 of the single-action cylinder 2 by the open 2/2-way valve 33.1 through the first fluid connection 6 (extraction). The first hydraulically active face 4 of the single-action cylinder 2 is not acted on since the 2/2-way valve 39.1 is closed in the hydraulic line 38.

(47) When the linear drive system 1 is retracted in rapid mode, the third hydraulically active face 14 is acted on with hydraulic fluid 7 through the third fluid connection 16 by the first hydraulic pump 19 which is operated in the opposite flow direction 23.2 as shown in FIG. 2D, whereby the piston 10 of the synchronous cylinder 9 moves in the retraction direction 17. The piston rod 3 of the single-action cylinder 2, which is connected to the piston rod 12 of the synchronous cylinder 9 by the coupling member 34, is also moved in the retraction direction 17 without the hydraulically active face 4 being acted on with hydraulic fluid 7. The hydraulic fluid 7 is displaced through the open 2/2-way valve 33.1 from the cylinder chamber 5 of the single-action cylinder 2 into the equalizing tank 30. The 2/2-way valve 39.1 in the hydraulic line 38 is closed.

(48) When the linear drive system 1 is extended in power mode, the first hydraulically active face 4 of the single-action cylinder 2 is acted on with hydraulic fluid 7 through the first fluid connection 6 as shown in FIG. 2B, whereby the single-action cylinder 2 moves in the extension direction 8. The 2/2-way valve 39.1 in the hydraulic line 38 is now open. Both the first hydraulic pump 19 and the second hydraulic pump 26 are activated and convey the hydraulic fluid 7 in a corresponding flow direction 23.1 in the direction of the first fluid connection 6 of the single-action cylinder 2. The activated second hydraulic pump 26 provides the required additional volume of hydraulic fluid 7 from the equalizing tank 30 in order to act with hydraulic fluid 7 on the first hydraulically active face 4 of the single-action cylinder 2 through the first fluid connection 6 and to act with hydraulic fluid 7 on the second hydraulically active face 13 of the synchronous cylinder 9 through the second fluid connection 15. The synchronous cylinder 9 moves synchronously in the extension direction 8 with the single-action cylinder 2, to which it is coupled via the coupling member 34. A flow of the hydraulic fluid 7 via the hydraulic line 32 into the equalizing tank 30 is prevented by the closed 2/2-way valve 33.1.

(49) In order to end the power mode, the first hydraulic pump 19 and the second hydraulic pump 26 are deactivated, the 2/2-way valve 33.1 is opened, and the 2/2-way valve 39.1 in the hydraulic line 38 is closed as shown in FIG. 2C so that the hydraulic fluid 7 flows from the first cylinder chamber 5 via the open 2/2-way valve 33.1 in the hydraulic line 32 into the equalizing tank 30.

(50) FIG. 3 shows a third embodiment of a hydrostatic linear drive system 1 having a 3-face cylinder 42, which integrates the functions of the single-action cylinder 2 and the synchronous cylinder 9 of the embodiments according to FIGS. 1 and 2 in a sub-assembly. Components of the 3-face cylinder 42 which correspond in terms of function to the embodiments according to FIGS. 1 and 2 are given corresponding reference numerals. The 3-face cylinder 42 has a cylinder pipe 43, a cylinder base 44 which terminates the cylinder pipe 43 at an end side and a piston rod guide 45 which is arranged at the opposite end side. The piston rod guide 45 guides a piston rod 46 in an axial direction. An annular piston 47 is arranged at one end of the piston rod 46. From the cylinder base 44, a guiding pin 48 extends into the cylinder pipe 43. The annular piston 47 surrounds the guiding pin 48 and is moved in a sliding manner along the guiding pin 48 in an extension direction 8 (see FIGS. 3A and 3B) and a retraction direction 17 (see FIG. 3D).

(51) The piston rod 46 has a hollow space 49 in the form of a blind hole which extends from the central passage in the annular piston 47 into the piston rod 46 and which surrounds the guiding pin 48.

(52) The 3-face cylinder has first, second, and third hydraulically active faces 4, 13, 14. The first hydraulically active face 4 is formed by the first annular piston face 47.1 facing the cylinder base 44 and delimits a first annular cylinder chamber 5. The second hydraulically active face 13 is formed by a partial surface 50 of the hollow space 49, which is opposite the end side of the guiding pin 48. The third hydraulically active face 14 is formed by the second annular piston face 47.2 facing the piston rod guide 45.

(53) A second annular cylinder chamber 51 is formed by the annular piston face 47.2, the cover (outer surface) of the piston rod 46, the inner face of the cylinder pipe 43 and at the end side by the piston rod guide 45.

(54) The second and third hydraulically active faces 13, 14 correspond to each other in terms of size/area.

(55) The first cylinder chamber 5 has a first fluid connection 6, through which the first hydraulically active face 4 can be acted on with a hydraulic fluid 7 in the extension direction 8 of the 3-face cylinder 42.

(56) The second hydraulically active face 13 can be acted on with the hydraulic fluid 7 through a second fluid connection 15 in the extension direction 8. The second fluid connection 15 is located on the cylinder base 44. From the second fluid connection 15, the hydraulic fluid 7 reaches a discharge opening arranged at the end side of the guiding pin 48 through a fluid channel 52.

(57) The third hydraulically active face 14 can be acted on with the hydraulic fluid 7 through the third fluid connection 16 in a retraction direction 17. The third fluid connection 16 opens in the second annular cylinder chamber 51.

(58) The first hydraulically active face 4 can be acted on with the hydraulic fluid 7 in the extension direction 8 through the first fluid connection 6.

(59) The second hydraulically active face 13 can be acted on with the hydraulic fluid 7 in the extension direction 8 through the second fluid connection 15.

(60) The third hydraulically active face 14 can be acted on with hydraulic fluid 7 in the retraction direction 17 Via the third fluid connection 16.

(61) A closed hydraulic circuit 18 which is under a pretensioning pressure comprises the first hydraulic pump 19, wherein the first pressure connection 21 is connected to the second fluid connection 15 via the hydraulic line 24 and the second pressure connection 22 is connected via the hydraulic line 25 to the third fluid connection 16 in a fluid-conducting manner.

(62) An electric motor 20 drives the first hydraulic pump 19 at a constant or variable motor speed. The hydraulic pump 19 is preferably an axial piston variable-displacement pump of the swash plate construction type. As a result of the adjustment of the swash plate, the volume flow of the first hydraulic pump can be steplessly changed and reversed.

(63) The pretensioning of the hydraulic fluid in the closed hydraulic circuit 18 may, for example, be produced by a pressure container which is not illustrated and which is connected to the pressure connections 21, 22 or by an external hydraulic pump.

(64) In order to act on the first hydraulically active face 4 of the 3-face cylinder 42 with hydraulic fluid 7, a second hydraulic pump 26 with a low-pressure connection 27 and a high-pressure connection 28 is provided. The low-pressure connection 27 is connected to an equalizing tank 30 in a fluid-conducting manner by a hydraulic line 29 and the high-pressure connection 28 is connected in a fluid-conducting manner to the first fluid connection 6 by a hydraulic line 31.

(65) The equalizing tank 30 which is open towards the environment receives hydraulic fluid 7 and is further connected in a fluid-conducting manner to the first fluid connection 6 of the 3-face cylinder 42 by a hydraulic line 32. In the hydraulic line 32 between the equalizing tank 30 and the first fluid connection 6, a 2/2-way valve 33.1 is arranged. When the linear drive system 1 is extended in rapid mode, the second hydraulically active face 13 is acted on with hydraulic fluid 7 through the second fluid connection 15 by the first hydraulic pump 19 which operates in the flow direction 23.1 according to FIG. 3A, whereby the annular piston 47 with the piston rod 46 moves in an extension direction 8. The hydraulically active face 4 is not acted on with hydraulic fluid 7 in rapid mode. The hydraulic fluid 7 from the equalizing tank 30 reaches the first cylinder chamber 5 of the 3-face cylinder 42 through the open 2/2-way valve 33.1 through the first fluid connection 6 (extraction). The second hydraulic pump 26 which is also connected to the first fluid connection 6 is not active.

(66) When the linear drive system 1 is retracted in rapid mode, the third hydraulically active face 14 is acted on with hydraulic fluid 7 through the third fluid connection 16 by the first hydraulic pump 19 which now operates in the opposite flow direction 23.2 according to FIG. 3D, whereby the annular piston 47 moves with the piston rod 46 in the retraction direction 17. The hydraulically active face 4 is not acted on with hydraulic fluid 7. The hydraulic fluid 7 is displaced through the open 2/2-way valve 33.1 from the cylinder chamber 5 of the first cylinder chamber 5 into the equalizing tank 30. The second hydraulic pump 26 which is connected to the first fluid connection 6 is not active.

(67) When the linear drive system 1 is extended in power mode, the first hydraulically active face 4 of the 3-face cylinder 42 is acted on with hydraulic fluid 7 through the first fluid connection 6 by the activated second hydraulic pump 26, whereby the 3-face cylinder 42 moves in the extension direction 8 as shown in FIG. 3B. When extending in power mode, the first hydraulic pump 19 is further activated in the flow direction 23.1 so that, through the second fluid connection 15, the second hydraulically active face 13 is acted on with hydraulic fluid 7. A flow of the hydraulic fluid 7 from the first cylinder chamber 5 via the hydraulic line 32 into the equalizing tank 30 is prevented by the closed 2/2-way valve 33.1. The force produced during extension in power mode is produced by the cooperation of the larger first hydraulically active face 4 and the smaller second hydraulically active face 13.

(68) In order to end the power mode, the first hydraulic pump 19 and the second hydraulic pump 26 are deactivated and the 2/2-way valve 33.1 is opened as shown in FIG. 3C so that the hydraulic fluid 7 can flow from the first cylinder chamber 5 via the open 2/2-way valve 33.1 in the hydraulic line 32 into the equalizing tank 30.

(69) FIG. 4 shows a fourth embodiment of a hydrostatic linear drive system 1 with a 3-face cylinder 42 which integrates the functions of the single-action cylinder 2 and the synchronous cylinder 9 of the embodiments according to FIGS. 1 and 2 in a sub-assembly. The 3-face cylinder 42 is constructed in accordance with the 3-face cylinder 42 of the third embodiment so that, in order to prevent repetition, reference may be made to the explanations of FIG. 3.

(70) The fourth embodiment is different from the third embodiment with regard to the hydraulic supply of the 3-face cylinder 42 and will be explained in greater detail below. The differences correspond to the differences of the second embodiment compared with the first embodiment.

(71) In order to act on the first hydraulically active face 4 with hydraulic fluid 7, the first fluid connection 6 of the 3-face cylinder 42 is connected via a hydraulic line 38 in a fluid-conducting manner to the first pressure connection 21 of the first hydraulic pump 19. In the hydraulic line 38, there is arranged a second shut-off member 39 which is constructed as a 2/2-way valve 39.1. A high-pressure connection 28 of a second hydraulic pump 26 is connected via a hydraulic line 31 in a fluid-conducting manner to the second pressure connection 22 of the first hydraulic pump 19. A non-return valve 40 in the hydraulic line 31 prevents a return flow of the hydraulic fluid 7 in the direction of the second hydraulic pump 26.

(72) The low-pressure connection 27 of the second hydraulic pump 26 is connected to the equalizing tank 30 in a fluid-conducting manner via the hydraulic line 29. In contrast to the embodiment according to FIG. 3, however, the high-pressure connection 28 of the second hydraulic pump 26 is not directly connected in a fluid-conducting manner to the first fluid connection 6 of the 3-face cylinder 42, but instead indirectly via the flow path which has been released by the open 2/2-way valve 39.1 and the first hydraulic pump 19 which is activated in the flow direction 23.1.

(73) The equalizing tank 30 which is open in the direction towards the environment receives hydraulic fluid 7 and is connected in a fluid-conducting manner to the first fluid connection 6 of the 3-face cylinder 42 by a hydraulic line 32. A 2/2-way valve 33.1 is arranged in the hydraulic line 32.

(74) When the linear drive system 1 is extended in rapid mode, the second hydraulically active face 13 is acted on with hydraulic fluid 7 via the second fluid connection 15 by the first hydraulic pump 19 which functions in the flow direction 23.1 as shown in FIG. 4A, whereby the annular piston 47 moves with the piston rod 46 in the extension direction 8.

(75) The hydraulic fluid 7 from the equalizing tank 30 reaches the cylinder chamber 5 of the 3-face cylinder 42 through the open 2/2-way valve 33.1 via the first fluid connection 6 (extraction). The first hydraulically active face 4 is not acted on since the 2/2-way valve 39.1 in the hydraulic line 38 is closed.

(76) When the linear drive system 1 is retracted in rapid mode, the third hydraulically active face 14 is acted on with hydraulic fluid 7 through the third fluid connection 16 by the first hydraulic pump 19 which is now operating in the opposite flow direction 23.2 as shown in FIG. 4D, whereby the annular piston 47 together with the piston rod 46 moves in the retraction direction 17. The hydraulic fluid 7 is displaced through the open 2/2-way valve 33.1 from the cylinder chamber 5 of the 3-face cylinder 42 into the equalizing tank 30. The 2/2-way valve 39.1 in the hydraulic line 38 is closed.

(77) When the linear drive system 1 is extended in power mode, the first hydraulically active face 4 is acted on with hydraulic fluid 7 via the first fluid connection 6 as shown in FIG. 4B, whereby the 3-face cylinder 42 moves in the extension direction 8. The 2/2-way valve 39.1 in the hydraulic line 38 is now open. Both the first hydraulic pump 19 and the second hydraulic pump 26 are activated and convey the hydraulic fluid 7 in a corresponding flow direction 23.1 in the direction of the first fluid connection 6. The activated second hydraulic pump 26 provides the required additional volume of hydraulic fluid 7 from the equalizing tank 30 in order to act with hydraulic fluid 7 on the first hydraulically active face 4 of the 3-face cylinder 42 via the first fluid connection 6 and to act with the hydraulic fluid on the second hydraulically active face 13 via the second fluid connection 15. A flow of the hydraulic fluid 7 via the hydraulic line 32 into the equalizing tank 30 is prevented by the closed 2/2-way valve 33.1.

(78) In order to end the power mode, the first hydraulic pump 19 and the second hydraulic pump 26 are deactivated, the 2/2-way valve 33.1 is opened and the 2/2-way valve 39.1 in the hydraulic line 38 is closed as shown in FIG. 4C so that the hydraulic fluid 7 flows from the first cylinder chamber 5 via the open 2/2-way valve 33.1 in the hydraulic line 32 into the equalizing tank 30.

(79) Thus, while there has been shown and described and pointed out the fundamental novel features of the invention is applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

LIST OF REFERENCE NUMERALS

(80) 1 Linear drive system 2 Single-action cylinder 3 Piston rod of single-action cylinder 4 First hydraulically active face 5 First cylinder chamber 6 First fluid connection 7 Hydraulic fluid 8 Extension direction 9 Synchronous cylinder 10 Piston 11 Piston rod synchronous cylinder 12 Piston rod synchronous cylinder 13 Second hydraulically active face 14 Third hydraulically active face 15 Second fluid connection 16 Third fluid connection 17 Retraction direction 18 Closed hydraulic circuit 19 First hydraulic pump 20 Electric motor 21 First pressure connection 22 Second pressure connection 23.1 Flow direction 23.2 Opposite flow direction 24 Hydraulic line 25 Hydraulic line 26 Second hydraulic pump 27 Low-pressure connection 28 High-pressure connection 29 Hydraulic line 30 Equalizing tank 31 Hydraulic line 32 Hydraulic line 33 First shut-off member 33.1 2/2-way valve 34 Coupling member 35 Second cylinder chamber 36 Third cylinder chamber 38 Hydraulic line 39 Second shut-off member 39.1 2/2-way valve 40 Non-return valve 42 3-face cylinder 43 Cylinder pipe 44 Cylinder base 45 Piston rod guide 46 Piston rod 47 Annular piston 47.1 First piston face 47.2 Second piston face 48 Guiding pin 49 Hollow space 50 Partial surface 51 Second cylinder chamber 52 Fluid channel