A hydrostatic drive system for a pressure balance with two parallel control surfaces.

Abstract

The present invention relates to a hydraulic drive system (10) with a plurality of actuators (20), wherein each actuator (20) is provided with a pressure balance (30) having a continuously adjustable first baffle (40), wherein a maximum load pressure is applied in a load communication line (16), and wherein a third baffle (40) is arranged between a second and a third control section (12; 13). According to the invention, the pressure balance (30) has a first and a separate second control surface (31; 32), wherein the pressure balance can be adjusted along the closing direction of the first baffle (40) by pressure loading of the first and second control surfaces (31; 32).

Description

Technical Field

[0001] The present invention relates to a hydraulic drive system as described in the preamble of claim 1. Background Technology

[0002] A hydraulic drive system is known from US 5,305,789. This hydraulic drive system has a pump that supplies pressurized fluid to multiple actuators in parallel. The speed of motion of each actuator is adjusted by a continuously adjustable main baffle. A pressure balance with a continuously adjustable first baffle is connected downstream of the main baffle. The pressure balance is configured such that it regulates the pressure at a second control point between the main baffle and the first baffle to the highest load pressure. The highest load pressure in this system is not obtained by cascading directional valves. Rather, it is achieved by fully utilizing the pressure balance with the highest load when it is fully open. Only this fully open pressure balance establishes a connection between the pressure and load communication line downstream of the fully open first baffle, thus applying the maximum load pressure in the load communication line. Summary of the Invention

[0003] The advantage of this invention is that the pressure balance responds more quickly to pressure changes at the third control point downstream of the first baffle. Furthermore, cavitation is avoided when the actuator is subjected to a dragging load.

[0004] According to the invention, the pressure balance has a first and a separate second control surface, wherein the pressure balance can be adjusted along the closing direction of a first baffle by pressure loading of the first and second control surfaces, wherein the first control surface is fluidly connected to a third control unit via a load communication line and further through an adjustable second baffle, wherein the second baffle is opened in a third position, wherein the second baffle is closed in the first and second positions, and wherein the second control surface is fluidly connected to the third control unit in the second position by passing through the third baffle and avoiding the load communication line. Thus, the load signal from the third control unit to the pressure balance is accelerated along the closing direction of the first baffle. Shortly before the second baffle opens, a large volume of the load communication line is briefly avoided.

[0005] The hydraulic drive system preferably operates using a pressurized liquid fluid, and most preferably hydraulic oil. The pump preferably has a continuously adjustable displacement volume. A pump regulator is preferably provided to the pump, which adjusts the pressure at the first control location to a rated pressure by adjusting the displacement volume. The rated pressure depends on the pressure in the load communication line. The rated pressure is, for example, higher than the pressure in the load communication line by a predetermined pressure differential. When multiple pressure balances according to the invention are present, the corresponding fluid flow paths preferably coincide at the first control location, wherein the fluid flow paths then branch in parallel, so that the pump supplies pressurized fluid to the actuator in parallel. Besides actuators with pressure balances according to the invention, actuators with other pressure balances, particularly those according to US 5,305,789, may also exist, especially lacking a third baffle and a separate second control surface. The pressure balances are preferably configured such that they substantially regulate the pressure at the second control location to the pressure in the load communication line. It is important to note that the present invention eliminates the precise adjustment behavior required in US 5305 789, instead selectively and slightly distorting this adjustment behavior using a second control surface. It is also important to note that the connection between the first control surface and the load communication line facilitates the pressure loading of the first control surface into the load communication line.

[0006] Advantageous extended designs and improvements of the invention are described in this invention.

[0007] It can be stipulated that the flow resistance of the third baffle is essentially independent of the position of the pressure balance. The corresponding pressure balance is constructed to be particularly simple and cost-effective. It is possible that the third baffle has different flow resistance in the first and third positions compared to the second position.

[0008] It can be specified that the first and second control surfaces are in a fluid exchange connection via a fourth baffle. In the second position, the fluid exchange connection between the load communication line and the third control location is preferably only present via the fourth baffle. The third and fourth baffles together form a pressure divider between the pressure in the load communication line or the pressure at the first control surface and the pressure at the third control location, wherein the corresponding average pressure chamber of the pressure divider is the pressure at the second control surface. This pressure divider is effective when the pressure balance is in the second position. In the third position, the pressure in the load communication line and the pressure at the third control location are equal to and therefore equal to the average pressure at the second control surface. The third baffle then, compared to the prior art, only contributes to the suppression of movement of the pressure balance in the direction of the third position. In the first position, the pressure divider is ineffective because the actuator cannot move based on the closed first baffle. Compared to the known pressure balance of US 5,305,789, the pressure divider in the second position causes the first baffle to close slightly less extensively with respect to the pressure at the third control location compared to its situation in the prior art. The corresponding actuator is therefore less prone to cavitation during rapid load changes, rapid pressure changes at the third control point, or under traction loads. Thus, it is no longer necessary to continuously supply the actuator with slightly excessive pressure fluid to avoid cavitation. This achieves energy savings.

[0009] It can be stipulated that the flow resistance of the fourth baffle is essentially independent of the position of the pressure balance. The corresponding pressure balance is constructed to be particularly simple and cost-effective. It is worth considering that the fourth baffle has different flow resistance in the first and third positions compared to the second position.

[0010] The pressure balance can be specified to include a control slide valve movable along the longitudinal axis and a substantially immobile stator, wherein a third and / or fourth baffle is formed by the gap between the control slide valve and the stator. The corresponding pressure balance is constructed to be particularly compact. The fluid connection according to the invention can be implemented with particular simplicity.

[0011] It can be specified that the control slide valve has a stator recess, wherein the stator is elongated and extends into the stator recess, and wherein a third and / or fourth baffle is arranged in the region of the stator recess. The third and / or fourth baffles may each be formed by at least one annular gap between the stator and the stator recess. At least in the region of the annular gap, the stator and the stator recess are preferably constructed to be cylindrical. The gap width of the annular gap or the corresponding gap between the stator and the stator recess is preferably designed in such a way that the desired flow resistance is generated. The stator is preferably elongated along the longitudinal axis. The stator is preferably substantially cylindrical.

[0012] It can be specified that the stator recess is constructed in the form of a blind bore, wherein the corresponding base of the blind bore forms a second control surface. This allows for the provision of the second control surface in a particularly simple and cost-effective manner. The stator also facilitates the sealing of the first control surface relative to the second control surface.

[0013] It can be specified that the third and / or fourth baffles each include at least one notch extending along the longitudinal axis at the stator or at the control slide valve. The notch is preferably constructed so narrow relative to the adjacent portion of the corresponding fluid flow path that the notch essentially defines the flow resistance of the corresponding baffle alone. Based on its longer friction path for pressurized fluids, such a fourth baffle is also referred to as a throttle.

[0014] It can be specified that the stator is formed by a separate component, which is held in place at the housing by means of a retaining ring, wherein a control slide valve is movably accommodated at the housing, and wherein the stator is persistently pressure-loaded on its end face pointing in the direction of the longitudinal axis. The cost-effective fixing by means of the retaining ring typically leaves a gap. The pressure loading on the end face causes the stator to be persistently pressed into its final position in the gap region during operation, thus preventing stator movement.

[0015] It can be specified that the stator end faces are pressure-loaded in the load communication pipeline. This allows for particularly simple and cost-effective establishment of the corresponding fluid connections. Alternatively, the stator end faces can be pressure-loaded at the first, second, or third control points.

[0016] It can be stipulated that the sum of the hydraulically effective areas of the first and second control surfaces is equal to such hydraulically effective area, and the pressure acting on the pressure balance at the second control point acts on such hydraulically effective area.

[0017] Of course, the foregoing and subsequent features can be used not only in the corresponding combinations described, but also in other combinations or individually, without departing from the scope of the invention. Attached Figure Description

[0018] The invention will now be explained in more detail with reference to the accompanying drawings. In the drawings:

[0019] Figure 1 This is a wiring diagram of the hydraulic drive system according to the present invention;

[0020] Figure 2 This is a longitudinal section of the pressure balance according to the present invention, wherein the control slide valve is in the first position;

[0021] Figure 2a This is a longitudinal section of the pressure balance according to the present invention, wherein the control slide valve is in the third position;

[0022] Figure 3 It is a three-dimensional view of the sealing screw, stator, and control slide valve;

[0023] Figure 4 It is a three-dimensional view of the stator; and

[0024] Figure 5 It is a three-dimensional sectional view of the control slide valve. Detailed Implementation

[0025] Figure 1 A wiring diagram of a hydraulic drive system 10 according to the invention is shown. The hydraulic drive system 10 includes a pump 14 that draws pressurized fluid from a tank 15 and delivers it to a pump line 18, where the pressure is substantially the same throughout the pump line. The pump line 18 forms a first control section 13. The pressurized fluid preferably involves a liquid and most preferably hydraulic oil. Figure 1 All bins marked with 15 are labeled as belonging to the same bin.

[0026] Pump 14 preferably has an adjustable displacement volume, which can be adjusted by pump regulator 17 according to adjustment parameters. The actual parameters of pump regulator 17 are the pressure at the first control point 11 or in the pump line 18. The rated parameters of pump regulator 17 depend on the pressure in the load communication line 16, for example, the rated parameters are higher than the pressure in the load communication line 16 by a predetermined pressure difference.

[0027] The hydraulic drive system 10 preferably includes a plurality of actuator sections 19, wherein, in Figure 1 Only one actuator section 19 is shown in the image. This actuator section is... Figure 1 The area is bordered with dotted lines. Actuator sections 19 each include actuators 20, which can be designed as hydraulic cylinders or hydraulic motors. The remaining actuator sections 19 are often formed by separate valve discs, wherein all the valve discs of the hydraulic drive system 10 are assembled into a valve body such that pump lines 18 and load communication lines 16 each have uninterrupted lines extending through the valve body. Actuators 20 are thus supplied with pressurized fluid in parallel by pump 14. Load communication line 16 is preferably fluid-tightly closed at its end opposite pump regulator 17. Pump line 18 is preferably fluid-tightly closed at its end opposite pump 14.

[0028] Each actuator 20 is equipped with a continuously adjustable main baffle 21, a pressure balance 30, and a directional control valve 22. The main baffle 21 and the directional control valve 22 are preferably formed from a common valve core and... Figure 1 The images are shown separately for easy viewing only. The speed of the actuator 20 is adjusted by the main baffle 21, and its direction of movement is adjusted by the directional control valve 22.

[0029] Each actuator 20 is provided with a fluid flow path, which extends from the tank 15 through the pump 14, through the first control unit 11, through the associated main baffle 21, through the second control unit 12, through the first baffle 40 of the associated pressure balance 30, through the third control unit 13, and through the associated directional control valve 22 to the actuator 20. The pressurized fluid flowing back from the actuator 20 flows back to the tank 15 through the directional control valve 22.

[0030] The pressure balance 30 has first, second, and third positions 41, 42, and 43, which are arranged side-by-side in the order described. In the first position 41, the first baffle 40 is completely closed. In the second position 42, the first baffle 40 is partially open. In the third position 42, the first baffle 40 is fully open. The first and third positions 41 and 43 essentially refer to two opposing final positions of the pressure balance 30, wherein the second position 42 refers to the adjustment region of the pressure balance in which the opening cross-section of the first baffle 40 always changes from completely closed to fully open.

[0031] The pressure balance 30 is loaded in the opening direction of the first baffle 40 by pressure at the second control point 12. Currently, the pressure balance 30 is not equipped with a spring. However, it is conceivable that the pressure balance 30 is equipped with a spring that preloads the pressure balance 30 into the first position 41. This spring is preferably designed to be so weak that it is essentially only effective in the unpressurized state.

[0032] In the closing direction of the first baffle 40, the pressure balance 30 is equipped with first and separate second control surfaces 31 and 32. The pressure balance 30 can be adjusted in the closing direction of the first baffle 40 by applying pressure to each of these two individual control surfaces 31 and 32. The first control surface 31 is pressure-loaded in the load communication line 16. This connection causes the pressure balance 30 to adjust the pressure at the second control location 12 to the pressure in the load communication line 16 at a first approximation. The higher the pressure at the third control location 13, the wider the first baffle 40 opens. When multiple actuators 20 are present, the pressure balance 30 is in a third position 43, where the pressure at the third control location 13 is the highest.

[0033] The second baffle 52 is open only in the third position 43; it is closed in the first and second positions 41 and 42. The second baffle 52 establishes a connection between the third control section 13 and the load communication line 16. Correspondingly, the maximum pressure of all pressures applied to the third control section 13 in the load communication line 16 is always present. This pressure is also called the maximum load pressure.

[0034] According to the invention, the second control surface 32 is loaded with the average pressure of a pressure divider formed by third and fourth baffles 53 and 54. This pressure divider is connected between the pressure in the load communication line 16 and the pressure at the third control point 13. Correspondingly, the pressure at the second control surface 32 is between the two pressures. As a result, in the pressure balance 30 according to the invention, the first baffle 40, in the second position 42, opens slightly less dramatically than in the pressure balance known in US 5,305,789. This prevents cavitation in the actuator 20 in an energy-efficient manner. Furthermore, only the third baffle 53 causes the pressure balance to respond more quickly to changes in pressure at the third control point 13, a behavior particularly important at the actuator 20 under maximum load.

[0035] The flow resistance of the third and fourth baffles 53 and 54 is preferably independent of the position of the pressure balance 30. However, within the scope of the invention, it is only important that the third and fourth baffles 53 and 54 are effective in the second position 42. The third baffle 53 can also be completely closed, especially in the first position 41. The third baffle 53 can also be opened more fully in the third position 43 than it is in the second position 42.

[0036] Figure 2 A longitudinal section of the pressure balance 30 according to the invention is shown, with the control slide valve 33 in the first position 41. Figure 2a A longitudinal section of the pressure balance 30 according to the invention is shown, wherein the control slide valve 33 is in the third position 43. Figure 2 and 2a The only difference is the position of the control slide valve 33.

[0037] The pressure balance 30 includes a control slide valve 33 housed in a housing 39 in a manner that allows linear movement about the longitudinal axis 38. A corresponding bore is fluid-tightly closed by a retaining screw 35 and a sealing screw 36, wherein a sealing ring 37 is inserted between the retaining screw 35 and the housing 39. A separate stator 50 is held in the retaining screw 35 by means of a retaining ring 51. The sealing screw 36 causes the stator 50 and the retaining ring 51 to be inserted into the retaining screw 35, so that the retaining ring 51 abuts against a protrusion of the retaining screw 35. The sealing screw 36 is tensioned toward the retaining screw 35, wherein a gap is left between the sealing screw 36 and the stator 50. Within this gap, pressure is substantially applied to the load communication line 16, regardless of the position of the pressure balance 30. The cylindrical annular gap 57 between the stator 50 and the retaining screw 35 is designed to be so large that a corresponding fluid exchange is achieved. The end side 56 of the stator 50 is thus permanently subjected to pressure loading in the control line 16, so that the stop ring 51 is permanently pressed against the additional protrusion at the retaining screw 35 during operation.

[0038] The stator 50 extends into the stator recess 44 of the control slide valve 33, wherein the stator recess 44 fluidly and sealably mates with the stator 50 except for the third and third baffles 53; 54, which will be explained below. The stator recess 44 is substantially constructed as a blind bore cylindrical about the longitudinal axis 38. The base of the stator recess 44 forms the second control surface 32. A first control surface 31 is formed on the cylindrical surface of the control slide valve 33 facing the end of the retaining screw 35. The first and second control surfaces 31; 32 are sealed to each other by the stator 50, wherein the stator 50 and the stator recess 44 together form a defined fourth baffle 54, which fluidly connects the first and second control surfaces to each other. The flow resistance of the fourth baffle 54 is independent of the position of the control slide valve 33, wherein, referring to Figure 4 To elaborate on further details.

[0039] A first baffle 40 is arranged at the end of the control slide valve 33 opposite to the stator 50. Figure 2 and 2a Reference numeral 40 in the figure refers here to the corresponding control edge at the housing 39 that is circular about the longitudinal axis 38. (See Figure 40 for reference.) Figure 5 The mating profile at the control slide valve 33 is explained in more detail. The first baffle 40 is... Figure 2 The first position shown is completely closed. In this position, the control slide valve 33 is inserted into the longitudinal end of the first baffle 40 located on the housing 39. Figure 2a In the third position shown, the first baffle 40 is fully opened, with the control slide valve 33 resting against the retaining screw 35 at its longitudinal end, which is associated with the stator 50. It should be noted here that the perforation at the first control surface 31 ( Figure 3 (as shown in number 80). This prevents full-scale contact from occurring. More precisely, at least a portion of the first control surface 31 is always subjected to pressure in the load communication line 16, even when the control slide valve 31 is in the third position.

[0040] The housing 39 is provided with a third annular groove 63, which surrounds the control slide valve 33 in each position. A load communication line 16 is permanently connected to the third annular groove 63. The corresponding pressure is transmitted through a fourth longitudinal groove (…). Figure 3 and 4 The fourth longitudinal groove (number 74) is externally guided to the first control surface at the control slide valve 33. The fourth longitudinal groove is designed such that fluid connection exists at each position of the pressure balance 30, where the corresponding throttling effect is small. The fourth longitudinal groove can also be arranged at the housing 39, where it is more difficult to manufacture.

[0041] The third annular groove 63 also forms the control edge of the second baffle 52 at the housing 39. The mating profile at the control slide valve 33 is formed by the third longitudinal groove on the outer circumferential surface of the control slide valve 33. Figure 3 and 5 The third longitudinal groove is formed by number 73 in the diagram. This arrangement positions the end of the third longitudinal groove facing the stator 50 such that this end is only located at... Figure 2 The third position shown covers the third annular groove 63. The second baffle 52 is open only in this position. In all other positions, this coverage is absent, and therefore the second baffle 52 is closed.

[0042] The third control section 13 is formed by a channel in the housing 39 that annularly surrounds the control slide valve 33 in each position. This channel is preferably manufactured in a casting process. A control edge of the first baffle 40 is machined into the sidewall of this channel. The aforementioned third longitudinal groove (in...) Figure 3 and 5 The third longitudinal groove (number 73) is constructed to be so long that it covers the passage in every position of the control slide valve 33. Correspondingly, the second baffle 52 is permanently connected to the third control part 13.

[0043] The second control section 12 is formed by a channel within the housing 39, which exits at the end of the control slide valve 33. Pressure at the second control section 12 loads the control slide valve 33 toward the stator 50, wherein the first baffle 40 opens during the corresponding movement. A fluid exchange connection then exists between the second and third control sections 12 and 13 via the first baffle 40.

[0044] A connecting channel 60 is arranged internally in the stator 50. This connecting channel permanently connects the end face of the stator 50 opposite to the second control surface 32 to the second annular groove (in the outer circumferential surface of the stator 50) Figure 4 The connecting channel 60 includes a first borehole along the longitudinal axis 38 and at least one second borehole radially to the longitudinal axis 38. The second borehole leads into the second annular groove and the first borehole.

[0045] Figure 3 A perspective view of the sealing screw 36, the stator 50, and the control slide valve 33 is shown. The previously mentioned fourth longitudinal groove 74 can be seen, extending from the first control surface 31 on the end side along the longitudinal axis 38 to the fourth annular groove 64 on the outside of the control slide valve 33. Figure 2 and 2a The comparison shows that the fourth annular groove 64 covers the third annular groove in each position of the control slide valve 33 (in Figure 2 and 2a (as shown in number 63), thus applying pressure there persistently to the load communication line 16.

[0046] The stator 50 and the control slide valve 33 are each provided with a plurality of circular grooves 81 extending around the longitudinal axis 38 on their outer circumferential surfaces. This avoids clamping of the control slide valve 33.

[0047] Figure 4 A perspective view of the stator 50 is shown. This stator has a second, elongated groove 72 on its outer circumferential surface, extending parallel to the longitudinal axis 38. The second groove 72 is connected to a second annular groove 62 via a notch 55, wherein the flow resistance of the notch 55 is much greater than that of the second longitudinal groove 72. Correspondingly, the flow resistance of the fourth baffle 54 is substantially determined by the notch 55, which is surrounded by stator grooves (…). Figure 2 and 2a The cylindrical section (number 44) about the longitudinal axis 38 covers, more precisely, the control slide valve ( Figure 2 and 2a In each position of number 33 in the diagram. The flow resistance of the fourth baffle 54 is therefore independent of the position of the control slide valve.

[0048] exist Figure 3 As can be seen, the second longitudinal groove 72 extends to the first control surface 31. An application is made at the first control surface 31 to the load communication pipeline ( Figure 1 The pressure (number 16 in the text) is also applied to the second longitudinal groove 72, more precisely, regardless of the position of the pressure balance. The fourth baffle 54 connects this pressure to the second annular groove 62, which guides the pressure to the second control surface ( Figure 1 The pressure at point 32 in the diagram is as explained above.

[0049] Shipped at the end facing the control surface, the stator 50 has a first annular groove 61 on its outer circumferential surface, into which a first longitudinal groove 71 passes. The first longitudinal groove 71 terminates at a certain distance from the second annular groove 62. This region is cylindrical about the longitudinal axis 38 and designed to be smooth. This region is located in the stator recess ( Figure 2 and 2a The same cylindrical and smooth area is covered at point 44 (in the diagram), more precisely at each position of the control slide valve. A defined gap is provided there, forming the first portion of the third baffle 53. Another portion of the third baffle 53 is formed by a similar annular gap between the first annular groove 61 and the longitudinal ends of the stator 50 facing the second control surface. Correspondingly, the flow resistance of the third baffle 53 is related to the control slide valve (…). Figure 2 and 2a The position of number 33 in the text is irrelevant.

[0050] Figure 5A perspective sectional view of the control slide valve 33 is shown. The sectional plane extends through the longitudinal axis 38 and through the third and fourth longitudinal grooves 73 and 74.

[0051] The longitudinal end of the crown-shaped structure of the control slide valve 33 can be seen, which is part of a continuously adjustable first baffle 40. A blind drill hole 84 is provided there. A corresponding radial wall is penetrated by a larger first groove 40a, which defines the rough control area of ​​the first baffle 40. The first groove 40a is configured as a circular notch or a U-shaped groove. A smaller second groove 40b, designed as a circular notch, is formed in the fine control area near the closed first baffle 40.

[0052] Furthermore, it should be noted that the radial bore 83 connects the associated third longitudinal groove 73 to the fifth annular groove 65 on the inner circumferential surface of the stator groove 44. Correspondingly, a third control portion is applied in the fifth annular groove 65. Figure 2 and 2a The pressure at point 13 (in the diagram) is constant, regardless of the position of the control valve 33. The fifth annular groove 65 covers the first longitudinal groove (in each position of the control valve 33) Figure 4 (as in number 71), thus applying pressure there for an equally sustained period at the third control point.

[0053] List of reference numerals

[0054] 10. Hydraulic drive system

[0055] 11 First control point

[0056] 12 Second control area

[0057] 13 Third control area

[0058] 14 pumps

[0059] 15 material bins

[0060] 16 Load communication pipelines

[0061] 17 Pump Regulator

[0062] 18 Pump pipeline

[0063] 19. Actuator Section

[0064] 20 actuators

[0065] 21 Main baffle

[0066] 22 Directional control valve

[0067] 30 Pressure Balance

[0068] 31 First Control Surface

[0069] 32 Second Control Surface

[0070] 33 Control slide valve

[0071] 35 Retaining screw

[0072] 36 Sealing screws

[0073] 37 Sealing ring

[0074] 38. Vertical axis

[0075] 39. Shell

[0076] 40 First baffle

[0077] 40a First Groove

[0078] 40b Second Groove

[0079] 41 First position

[0080] 42 Second position

[0081] 43 Third position

[0082] 44 Stator Groove

[0083] 50 stators

[0084] 51 Retaining ring

[0085] 52 Second baffle

[0086] 53 Third baffle

[0087] 54 Fourth baffle

[0088] 55 Notch

[0089] 56. End face of stator

[0090] 57 Annular gap

[0091] 60 connection channels

[0092] 61 First annular groove

[0093] 62 Second annular groove

[0094] 63 Third annular groove

[0095] 64 Fourth annular groove

[0096] 65 Fifth annular groove

[0097] 71 First longitudinal groove

[0098] 72 Second longitudinal groove

[0099] 73 Third longitudinal groove

[0100] 74 Fourth longitudinal groove

[0101] 80 perforations

[0102] 81 Trench

[0103] 83 Radial drilling

[0104] 84 Blind Drilling

Claims

1. A hydraulic drive system (10) comprising a pump (14) and at least one actuator (20), wherein, At least one actuator (20) is provided with a continuously adjustable main baffle (21) and a pressure balance (30), wherein the pressure balance (30) has a continuously adjustable first baffle (40), wherein the pressure balance (30) has first, second and third positions (41; 42; 43) arranged side by side in the described order, wherein in the first position (41), the first baffle (40) is completely closed, wherein in the second position (42), the first baffle (40) is partially open, wherein in the third position (43), the first baffle (41; 42; 43) is partially closed. 0) Fully open, wherein at least one actuator (20) is provided with a fluid flow path, the fluid flow path extending from the pump (14) via a first control unit (11) via a related main baffle (21), via a second control unit (12), via a related first baffle (40), and via a third control unit (13) to the related actuator (20), wherein the pressure at the second control unit (12) is applied to a pressure balance (30) in the opening direction of the first baffle (40), wherein a load communication line (16) is provided. The pressure balance (30) is characterized by having a first and a separate second control surface (31; 32), wherein the pressure balance is adjustable along the closing direction of the first baffle (40) by pressure loading of the first and second control surfaces (31; 32), wherein the first control surface (31) is fluidly connected to the third control part (13) via the load communication line (16) and the adjustable second baffle (52), wherein the second baffle (52) is opened in the third position (43), wherein it is closed in the first and second positions (41; 42), wherein the second control surface (32) is fluidly connected to the third control part (13) via the third baffle (53) and in the second position (42) in any case while avoiding the load communication line (16).

2. The hydraulic drive system according to claim 1, wherein, The flow resistance of the third baffle (53) is independent of the position of the pressure balance (30).

3. The hydraulic drive system according to any one of the preceding claims, wherein, The first and second control surfaces (31; 32) are in fluid exchange connection via a fourth baffle (54).

4. The hydraulic drive system according to claim 3, wherein, The flow resistance of the fourth baffle (54) is independent of the position of the pressure balance (30).

5. The hydraulic drive system according to claim 1 or 2, wherein, The pressure balance (30) includes a control slide valve (33) that can move along the longitudinal axis (38) and a stationary stator (50) that cannot move, wherein a third and / or fourth baffle (53; 54) are formed by the gap between the control slide valve (33) and the stator (50), respectively.

6. The hydraulic drive system according to claim 5, wherein, The control slide valve (33) has a stator groove (44), wherein the stator (50) is elongated and extends into the stator groove (44), wherein a third and / or fourth baffle (53; 54) is arranged in the region of the stator groove (44).

7. The hydraulic drive system according to claim 6, wherein, The stator groove (44) is configured as a blind bore, wherein the corresponding base of the blind bore forms the second control surface (32).

8. The hydraulic drive system according to claim 5, wherein, The third and / or fourth baffles (53; 54) each include at least one recess (55) extending in the direction of the longitudinal axis (38) at the stator (50) or at the control slide valve (33).

9. The hydraulic drive system according to claim 5, wherein, The stator (50) is formed by a single component held in the housing (39) by means of a stop ring (51), in which a control slide valve (33) is movably housed, and the stator (50) is perpetually pressure-loaded on its end face (56) pointing in the direction of the longitudinal axis (38).

10. The hydraulic drive system according to claim 9, wherein, The end face (56) of the stator (50) is pressure-loaded in the load communication line (16).

11. The hydraulic drive system according to claim 1 or 2, wherein, The sum of the hydraulically effective areas of the first and second control surfaces (31; 32) is equal to such hydraulically effective area that the pressure acting on the pressure balance (30) at the second control part (12) acts on the hydraulically effective area.

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