Electro-hydrostatic drive system

Abstract

The present invention relates to an electro-hydrostatic system (1) with a hydraulic machine (11) which is driven by an electric motor (10) and has a variable volume and/or rotational speed for providing a volumetric flow rate of a hydraulic fluid, a differential cylinder (20) with a piston surface and with an annular surface, and at least one equalization container (30, 37), wherein the drive system (1) has a closed hydraulic circuit and during operation has an overpressure relative to the environment by means of the hydraulic machine (11) and/or a pretensioning source (15, 37), and the drive system (1) provides a movement of the cylinder in a first direction by means of a volumetric flow rate of the hydraulic machine (11) and a volumetric flow rate from the equalization container (30, 37), and provides a movement in a second direction by means of a volumetric flow rate of the hydraulic machine (11) and a volumetric flow rate into the equalization container (30, 37), and a power operating mode and a speed operating mode are provided with the differential cylinder (20).

Claims

1. An electro-hydrostatic drive system comprising: a hydraulic machine driven by an electric motor and having a variable displacement volume and/or rotational speed, operable to provide a volumetric flow rate of a hydraulic fluid, a first differential cylinder including a piston having a front side and a rear side to which a rod is attached, the first differential cylinder having a piston chamber with a piston area on the front side of the piston and having an annular chamber with an annular area on the rear side of the piston; at least one equalization container, and a preload source connected with the piston chamber via a first check-valve and connected with the annular chamber via a second check-valve, wherein during operation, the drive system has a closed hydraulic circuit including a plurality of conduits, and wherein the preload source is operable to provide the drive system with an overpressure relative to the environment, wherein the drive system is operable to provide a movement of the piston of the first differential cylinder in a first direction as a function of a volumetric flow of the hydraulic machine through one of the plurality of conduits into the piston chamber and a volumetric flow from the equalization container through a check-valve conduit to the annular chamber, wherein the check-valve conduit has only a third check valve and has only a single branch conduit positioned between the third check valve and the equalization container, wherein the drive system is operable to provide the movement of the piston of the first differential cylinder in a second direction as a function of a volumetric flow of the hydraulic machine through another of the plurality of conduits into the annular chamber and a volumetric flow through the branch conduit into the equalization container, wherein both sides of the hydraulic machine are connected with the preload source, whereby the hydraulic machine is operable to transmit a preload in the hydraulic fluid of the closed hydraulic circuit, wherein a first side of the hydraulic machine is connected with the piston chamber without any intervening components, and a second side of the hydraulic machine is connected with the annular chamber without any intervening components, and wherein the third check valve connected between the annular chamber and the equalization container provides one-way flow into the annular chamber when pressure in the annular chamber drops below a certain pressure.

2. The electro-hydrostatic system according to claim 1, wherein the equalization container is designed as a second cylinder containing a second piston having a front side and a rear side to which a second piston rod is attached, the second cylinder having a second piston chamber with a second piston area on the front side of the second piston and having a second annular chamber with a second annular area on the rear side of the second piston.

3. The electro-hydrostatic system according to claim 2, wherein the second cylinder is a second differential cylinder, and the second annular area corresponds to the difference between the piston area and the annular area of the first differential cylinder.

4. The electro-hydrostatic system according to claim 2, wherein the piston rod of the first differential cylinder and the piston rod of the second cylinder are mechanically coupled.

5. The electro-hydrostatic system according to claim 2, wherein the annular area of the first differential cylinder is less than or equal to the second annular area of the second cylinder.

6. An electro-hydrostatic drive system comprising: a hydraulic machine driven by an electric motor and having a variable displacement volume and/or rotational speed, operable to provide a volumetric flow rate of a hydraulic fluid; a first differential cylinder including a piston having a front side and a rear side to which a rod is attached, the first differential cylinder having a piston chamber with a piston area on the front side of the piston and having an annular chamber with an annular area on the rear side of the piston; at least one equalization container; and a preload source connected with the piston chamber via a first check-valve and connected with the annular chamber via a second check-valve; wherein during operation, the drive system has a closed hydraulic circuit including a plurality of conduits, and wherein the preload source is operable to provided the drive system with an overpressure relative to the environment; wherein the drive system is operable to provides a movement of the piston of the first differential cylinder in a first direction as a function of a volumetric flow of the hydraulic machine through one of the plurality of conduits into the piston chamber and a volumetric flow from the equalization container through a check-valve conduit to the annular chamber, wherein the check-valve conduit has only a third check valve and has only a single branch conduit positioned between the third check valve and the equalization container, wherein the drive system is operable to provide the movement of the piston of the first differential cylinder in a second direction as a function of a volumetric flow of the hydraulic machine through another of the plurality of conduits into the annular chamber and a volumetric flow through the branch conduit into the equalization container, wherein a first side of the hydraulic machine is connected with the piston chamber without any intervening components, and a second side of the hydraulic machine is connected with the annular chamber without any intervening components, and wherein the piston chamber of the first differential cylinder is connected with the equalization container via the branch conduit, the annular chamber being connected with the equalization container through the check-valve conduit, wherein the check valve connected between the annular chamber and the equalization container provides one-way flow into the annular chamber when pressure in the annular chamber drops below a certain pressure.

7. The electro-hydrostatic system according to claim 6, wherein the equalization container is designed as a second differential cylinder containing a second piston having a front side and a rear side to which a second piston rod is attached, the second differential cylinder having a second piston chamber with a second piston area on the front side of the second piston and having a second annular chamber with a second annular area on the rear side of the second piston.

8. The electro-hydrostatic system according to claim 7, wherein the second cylinder is a second differential cylinder, and the second annular area corresponds to the difference between the piston area and the annular area of the first differential cylinder.

9. The electro-hydrostatic system according to claim 7, wherein the piston rod of the first differential cylinder and the piston rod of the second cylinder are mechanically coupled.

10. The electro-hydrostatic system according to claim 7, wherein the annular area of the first differential cylinder is less than or equal to the second annular area of the second cylinder.

Description

(1) The invention is explained in the following on the basis of various exemplary embodiments, wherein it is noted that this example encompasses modifications or additions as they immediately arise to the person skilled in the art.

(2) Thereby shown are:

(3) FIG. 1a: schematic depiction of the configuration of a system according to the invention during extension in power operating mode;

(4) FIG. 1b: schematic depiction of the configuration of a system according to the invention during retraction in power operating mode;

(5) FIG. 2a: schematic depiction of the configuration of a system according to the invention during extension in speed operating mode;

(6) FIG. 2b: schematic depiction of the configuration of a system according to the invention during retraction in speed operating mode;

(7) FIG. 3a: schematic depiction of the configuration of a system according to the invention during extension, with a check valve;

(8) FIG. 3b: schematic depiction of the configuration of a system according to the invention upon retraction, with a check valve;

(9) FIG. 4a: schematic depiction of the configuration of a system according to the invention during extension in power operating mode, with separate mass and a pretensioning source;

(10) FIG. 4b: schematic depiction of the configuration of a system according to the invention upon retraction in speed operating mode, with separate mass and a pretensioning source;

(11) FIG. 5a: schematic depiction of the configuration of a system according to the invention during extension in speed operating mode, with hydraulic accumulator equalization container;

(12) FIG. 5b: schematic depiction of the configuration of a system according to the invention upon retraction, with hydraulic accumulator equalization container.

(13) FIG. 1a shows an electro-hydrostatic drive system 1 with a first cylinder or master cylinder 20 designed as a differential cylinder. The first cylinder 20 has a master cylinder piston 23 with a piston chamber 21 and an annular chamber 22. On the piston chamber 21 side, the master cylinder piston 23 has a piston rod 24 connected to a pressing tool 40.

(14) The piston chamber 21 is connected to the pump 11 (hydraulic machine) via the conduit 62. The pump 11 is driven by an electric motor 10. The hydraulic machine may have either an electric motor with variable rotational speed and a fixed displacement pump, or an electric motor with constant rotational speed and a variable displacement pump, or an electric motor with variable rotational speed and a variable displacement pump. The annular chamber 22 is connected to the pump 11 via the conduit 61.

(15) The pump 11 is connected to a pressure vessel 15 via the check valves 16 and 17. The check valves 16 or 17 thereby open if there is a lower pressure in the conduit 62 or 61 than in the pressure vessel 15. The dynamics of the system are thereby improved and/or energy is saved. In a variation, the pressure vessel 15 and the check valves 16 and 17 may be omitted, wherein the pretensioning of the system may then be provided by other measures, for example an external pressure source. According to the embodiments depicted here, both terminals of the hydraulic machine 11 are connected with the pretensioning source 15. Cavitation in the hydraulic machine is hereby advantageously avoided in pressure buildup phases or non-ideally balanced cylinder surfaces between master cylinder and cylinder equalization container.

(16) The piston chamber 21 of the first cylinder 20 is connected to the annular chamber 32 of the second cylinder 30 via the conduit 71, the 2/2-port directional control valve 51, and the conduit 72. The annular chamber 22 of the first cylinder 20 is connected to the annular chamber 32 of the second cylinder 30 via the conduit 73, the 2/2-port directional control valve 52, and the conduit 72. A piston rod 34 is arranged in the annular chamber 32 at the piston 33 of the second cylinder 30. The piston rod 34 is connected to the common pressing tool 40, and in this way is mechanically coupled to the piston rod 24 of the first cylinder 20. According to the embodiments shown here, the effective annular surface of the second cylinder 30 is larger than the effective annular surface of the first cylinder 20. In the understanding of the present invention, the second cylinder thereby acts primarily as an equalization container which is able to compensate for volume displacements in the system. Moreover, and due to the coupling to the piston rod of the first cylinder 20, this also contributes to the movement of the pressing tool 40. According to the exemplary embodiments illustrated here, the piston rod diameter 24 is greater than or equal to the piston rod diameter 34. A system is herewith advantageously provided in which the full process force can be transmitted via piston rod 24 in power operating mode, and at the same time the buckling load of the piston rod 24 can be kept low. According to the exemplary embodiment shown here, the piston chamber 31 of the second cylinder 30 is open to the environment; it therefore represents no or only a very slight resistance for the piston 33 of the second cylinder 30.

(17) Given extension of a system 1 according to the invention in power operating mode, the master cylinder piston 23 is driven downwards; see the dotted arrow on the master cylinder piston 23 and the piston rod 24. Since the piston rod 24 of the first cylinder 20 is mechanically coupled to the piston rod 34 of the second cylinder 30 via the common pressing tool 40, the piston 33 of the second cylinder 30 also moves downwards during extension; see the dotted arrow on the piston 33 and piston rod 34. For this purpose, the pump 11 generates a volumetric flow upwards, i.e. in the direction of the piston chamber 21; see the arrow next to the pump 11. The hydraulic fluid thereby flows from the pump 11 via the conduit 62 into the piston chamber 21, and hydraulic fluid flows from the annular chamber 22 into the pump 11.

(18) Furthermore, the valve 51 is closed and the valve 52 is opened. Via this valve position and via the mechanical coupling via the pressing tool 40, hydraulic fluid flows from the annular chamber 32 of the second cylinder 30 via the lower part of the conduit 72—see the arrow arranged there—via the open valve 52 and conduits 73 and 61, into the pump 11. Via this measure, the different volumes of piston chamber 21 and annular chamber 22 of the first cylinder are compensated. Therefore, the hydraulic circuit in the system 1 can be closed.

(19) FIG. 1b shows the configuration of a system 1 according to the invention according to FIG. 1a, upon retraction in power operating mode. The elements used and the reference symbols are thereby the same as in FIG. 1a.

(20) Upon retraction in power operating mode, the master cylinder piston 23 is moved upwards; see the dotted arrow at master cylinder piston 23 and piston rod 24. Due to the common pressing tool 40, piston 33 of the second cylinder 30 likewise moves upwards. A downward volumetric flow, i.e. in the direction of the annular chamber 22, is generated by the pump 11; see the arrow next to the pump 11. Furthermore, the valve 51 is closed and the valve 52 is opened. Hydraulic fluid thereby flows from the piston chamber 21 into the annular chambers 22 and 32 of the first or second cylinder. The power operating mode results from the summary effect of the two annular surfaces of the annular chambers 22 and 32.

(21) FIG. 2a shows the configuration of a system 1 according to the invention according to FIG. 1a, upon extension in speed operating mode. The elements used and the reference symbols are thereby the same as in FIG. 1a.

(22) In speed operating mode, the pump 11 generates a volumetric flow upwards, i.e. in the direction of the piston chamber 21; see the arrow next to the pump 11. The hydraulic fluid thereby flows from the pump 11 via the conduit 62 into the piston chamber 21, and from the annular chamber 22 into the pump 11. In contrast to power operating mode, in speed operating mode the valve 51 is open and the valve 52 is closed. As a result, hydraulic fluid flows from the annular chamber 32 of the second cylinder 30 directly into the piston chamber 21 via the conduit 72, valve 51, and conduit 71.

(23) FIG. 2b shows the configuration of a system 1 according to the invention upon retraction in speed operating mode. The elements used and the reference symbols are thereby the same as in FIG. 1a.

(24) A downward volumetric flow, i.e. in the direction of the annular chamber 22, is thereby generated by the pump 11; see the arrow next to the pump 11. The hydraulic fluid thereby flows from the pump 11 via the conduit 61 into the annular chamber 22. The valve 51 is open and the valve 52 is closed. As a result, hydraulic fluid also flows from the piston chamber 21 of the first cylinder into the annular chamber 32 of the second cylinder 30 via the conduit 71, valve 51, and conduit 72.

(25) FIG. 3a shows the configuration of a system 1 according to the invention upon extension, here in power operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. One exception is the check valve 54, which replaces the valve 52.

(26) According to a particularly preferred embodiment, the pressure vessel 15 may be executed as a low-pressure vessel. Among other things, advantages in terms of a more compact design may hereby be realized, whereby a cost saving results and an easier design may be realized.

(27) The movement sequence is the same as in FIG. 1a; however, the check valve 54 always opens in one direction as of a certain pressure, corresponding to the arrow at conduit 72.

(28) FIG. 3b shows the configuration of a system 1 according to the invention upon retraction, here in speed operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. One exception is again the check valve 54, which replaces the valve 52.

(29) The movement sequence is the same as in FIG. 2b; however, the check valve 54 is always closed in the direction of the annular chamber 32 as of a certain pressure.

(30) FIG. 4a shows the configuration of a system 1 according to the invention upon extension, here in speed operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. One exception is the separate masses 41 and 42, instead of the mechanical coupling of the two piston rods 24 and 34 by the pressing tool 40. Moreover, the pressure accumulator 37 is provided which is connected to the—now closed—piston chamber 31 of the second cylinder. The pressure vessel 15 and the check valves 16 and 17 have been omitted.

(31) The separated masses m.sub.1 41 and m.sub.2 42 no longer force—as was the case with the common mass 40—a coupled movement of the piston rod 24 and 34 of the first and of the second cylinder 20 and 30. However, the mass m.sub.2 42 charges the chamber 32 with a pressure, meaning that the system is hereby at least partially pretensioned. The movement sequence of the piston rod of the first cylinder 20 is also comparable to that in the description regarding FIG. 2a.

(32) The pressure accumulator 37 represents a further increase in the reserve pressure and produces greater dynamics of the system, or further savings in energy consumption. Alternatively, for certain configurations of the system the additional mass m.sub.2 42 can be dispensed with if an additional mass m.sub.2 42—or a larger common mass 40—appears to be disadvantageous.

(33) The optional omission of the pressure vessel 15 and the check valves 16 and 17 may be compensated for either via measures such as an additional mass m.sub.2 42 and/or the pressure accumulator 37. Alternatively, this omission leads to lower costs of the system 1.

(34) In a further alternative embodiment, the pressure accumulator 37 may optionally also be dispensed with, so that the pretensioning is provided by the second cylinder itself. For example, this may be effected in that the pretensioning in the hydraulic fluid is generated by the own weight of the cylinder and/or of the cylinder rod.

(35) The movement sequence of the piston rod of the first cylinder is—with the cited changes—comparable to that in FIG. 2b.

(36) FIG. 4b shows the configuration of a system 1 according to the invention according to FIG. 1a upon retraction in speed operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. One exception is thereby again the separate masses 41 and 42, instead of the mechanical coupling of the two piston rods 24 and 34 by the pressing tool 40. Moreover, a pressure accumulator 37 is provided which is connected to the—now closed—piston chamber 31 of the second cylinder. The pressure vessel 15 and the check valves 16 and 17 have also been omitted.

(37) The movement sequence of the piston rod of the first cylinder 20 is comparable to that of FIG. 2b for the reasons explained in the description of FIG. 4a.

(38) FIG. 5a shows the configuration of a system 1 according to the invention upon extension, in speed operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. One exception is the equalization container 37, which replaces the second cylinder 30, wherein this equalization container provides both a predetermined pressure level and an equalization volume. Furthermore, the pressure vessel 15 and the check valves 16 and 17 have been omitted.

(39) Since, in a system 1 according to the invention, the second cylinder 30 is used as an equalization container which—together with the hydraulic machine 11—provides a volumetric flow, here too the movement sequence of the piston rod of the first cylinder 20 is comparable to FIG. 2a.

(40) FIG. 5b shows the configuration of a system 1 according to the invention upon retraction in speed operating mode. Most of the elements used and the reference symbols are thereby the same as in FIG. 1a. Here, too, the second cylinder 30 has been replaced by the pressure accumulator 37. Furthermore, the pressure vessel 15 and the check valves 16 and 17 have been omitted.

(41) Since, in a system 1 according to the invention, the second cylinder 30 is used as an equalization container which—together with the hydraulic machine 11—provides a volumetric flow, here too the movement sequence of the piston rod of the first cylinder 20 is comparable to FIG. 2b.

(42) In a further embodiment, a check valve 54 as is arranged in FIGS. 3a and 3b may also be adopted analogously into the embodiments according to FIG. 4a, 4b, 5a, 5b.

(43) Furthermore, in particular FIGS. 3b, 5a and 5b show that, in a system according to the invention, the second cylinder 30 is used as equalization container and does not represent a second operative cylinder.

LIST OF REFERENCE CHARACTERS

(44) 1 Electro-hydrostatic system 10 Electric motor 11 Pump 15 Pressure vessel 16, 17 Check valve 20 Master cylinder, first cylinder 21 Piston chamber 22 Annular chamber 23 Master cylinder piston 24 Piston rod 30 Second cylinder, secondary cylinder 31 Piston chamber 32 Annular chamber 33 Secondary cylinder piston 34 Piston rod 37 Equalization container 40 Pressing tool 41 Mass m.sub.1 42 Mass m.sub.2 51 Directional control valve 52 Directional control valve 54 Check valve 61, 62, 65 Conduit 71, 72, 73 Conduit