HYDRAULIC SYSTEM

Description

[0001] The present invention relates to a hydraulic system, in particular of a self-propelled harvesting machine, according to the preamble of claim 1.

[0002] A hydraulic system of the type mentioned above is known from EP 3 617 562 B1. The hydraulic system comprises at least one hydraulic motor assembly and a hydraulic fluid reservoir hydraulically coupled to this hydraulic motor assembly, wherein a venting device for venting a hydraulic fluid is assigned to the at least one hydraulic motor assembly. The venting device has a suction device designed as a Venturi nozzle for suctioning the hydraulic fluid from the at least one hydraulic motor assembly. To provide a driving medium, EP 3 617 562 B1 provides for the driving medium to be branched off from a pressurized section of the hydraulic system, wherein the driving medium can be provided by an external pressure source or the driving medium is branched off from pre-pressurized flushing oil of the hydraulic motor assembly.

[0003] When the flushing oil of at least one hydraulic motor arrangement is used as the driving medium of the suction device designed as a Venturi nozzle, requirements arise which result from the need for the flushing oil volume and which are not addressed in EP 3 617 562 B1. For example, a coordination of oil temperature and suction power is necessary. In particular, to safeguard the feed pressure in the closed circuit, the Venturi nozzle must be regulated in the event of an insufficient supply of driving medium. When the hydraulic motor arrangement is stationary and load-free, the flushing of the hydraulic motor arrangement is switched off and suction by the suction device is interrupted. This leads to the motor housing filling up again due to the lack of driving medium volume flow. When the system is started up, the driving medium volume flow is reactivated for flushing and the motor housing empties again. The fastest possible emptying of the motor housing must be guaranteed.

[0004] Based on the above-mentioned prior art, the object of the invention is to further develop a hydraulic system which avoids the disadvantages of the prior art, in particular that meets the above-mentioned requirements when using flushing oil as a driving medium.

[0005] This object is achieved by a hydraulic system having the features of independent patent claim 1. Advantageous embodiments and further developments can be found in the dependent claims.

[0006] According to claim 1, a hydraulic system, in particular of a self-propelled harvesting machine, is proposed, which is designed as a closed-circuit system, wherein the hydraulic system comprises at least one hydraulic motor assembly and a hydraulic fluid reservoir hydraulically coupled to this hydraulic motor assembly. A venting device for venting a hydraulic fluid is assigned to the at least one hydraulic motor assembly. The venting device has a suction device designed as a Venturi nozzle for suctioning the hydraulic fluid from the at least one hydraulic motor assembly. The suction device uses negative pressure to discharge hydraulic fluid from the at least one hydraulic motor assembly integrated into at least one motor housing through a return line into the hydraulic fluid reservoir.According to the invention, a branch line is provided for supplying pre-pressurized flushing oil to the at least one hydraulic motor arrangement as the drive medium for the suction device, wherein a pilot-operated pressure relief valve is arranged in the branch line and is connected to the motor housing via a signaling line, the negative pressure in the motor housing serving to control the pressure relief valve. In order to have the maximum available feed pressure to drive the suction device, the flushing oil must flow from the motor housing to the suction device, i.e. to the Venturi nozzle, with as little restriction as possible. In order to protect the hydraulic system, which is designed as a closed circuit, against inadmissible pressure drops, a feed pressure protection device is required. For this purpose, the pilot-operated pressure relief valve is used with its signaling line connected to the motor housing in order to use the motor housing pressure for control.This ensures that the pressure relief valve is fully open and throttle-free as soon as the required minimum pressure of the closed-circuit hydraulic system is exceeded. If a drop in feed pressure occurs in the hydraulic system, the pressure relief valve closes.

[0007] In particular, the pressure relief valve can be configured to regulate the venting device in the event of an insufficient supply, particularly when the hydraulic motor arrangement is stationary and load-free, with the drive medium provided by the at least one hydraulic motor arrangement. This ensures that when the hydraulic motor arrangement is stationary and load-free, the flushing of the hydraulic motor arrangement is switched off and the suction is interrupted. When the hydraulic motor arrangement is started up, the flushing is activated so that the drive medium volume flow or flushing oil volume is available to empty the motor housing. When the hydraulic motor arrangement is load-free, a motor-side flushing valve can switch off the drive medium. The pressure relief valve can prevent inadmissible drops in feed pressure when the flushing valve is open during operation under load.

[0008] In particular, the venting device can comprise a mixing chamber arranged downstream of the suction device, wherein the mixing chamber is connected to the hydraulic fluid reservoir via the return line. The mixing chamber can have a diffuser on the outlet side, which is either molded into the mixing chamber or connected directly to it as a separate element, for example, via a flange connection. The diffuser connects the mixing chamber to the return line.

[0009] Preferably, the pressure relief valve can be integrated into the venting device, with the pressure relief valve being connected upstream of the suction device designed as a Venturi nozzle. This enables a compact and space-optimized design of the venting device.

[0010] According to a preferred development, the at least one hydraulic motor arrangement can be connected to the hydraulic fluid reservoir by at least one air intake line, wherein an air reservoir is provided for re-ventilation when the at least one hydraulic motor arrangement is transferred to a load state or after constant pressure operation. To ventilate the at least one motor housing to be extracted, a very small orifice is required in the respective air intake line in order to keep the amount of air to be separated as low as possible. To ensure rapid oil extraction when the load-free hydraulic motor arrangement starts up, additional measures are therefore required in addition to the pure air supply. If more than one hydraulic motor arrangement is to be extracted, each must be equipped with its own individual air intake line and orifice.

[0011] For this purpose, the air reservoir can be designed as a container arranged in the air intake line and / or formed by oversizing a section of the air intake line, with the section being delimited by two check valves. By storing a volume of air in the air intake line or the container, rapid re-ventilation can be ensured when the hydraulic motor assembly starts up or after constant-pressure operation, for example, when a work vehicle driven by the hydraulic motor assembly as a hydrostatic drive is traveling at full speed.

[0012] Furthermore, a number of ventilation valves corresponding to the number of hydraulic motors of the at least one hydraulic motor arrangement can be connected upstream of the air reservoir arranged in the air intake line, which ventilation valves are arranged between the hydraulic fluid reservoir and the air reservoir.

[0013] The respective ventilation valve can be designed as a combination of an orifice plate and a check valve, the functions of which are combined in a common valve housing.

[0014] For this purpose, the respective venting valve can comprise a connection on the hydraulic fluid reservoir side and a connection on the motor housing side, wherein the orientation of the respective venting valve in the installed position is perpendicular to a component covering the hydraulic fluid reservoir.

[0015] In particular, the respective vent valve can have a relatively movable tappet, which has an upper sealing cone facing the hydraulic fluid reservoir connection and a sealing cone with a notch facing the motor housing connection. As soon as the hydraulic motor starts up again and the suction is activated, the reservoir volume can expand synchronously with the rapidly decreasing housing pressure. Due to the vertical installation of the respective vent valve, the respective motor housing is initially supplied with a relatively large amount of air without any restriction. Only as the motor housing pressure continues to drop is the tappet sucked upwards against the weight of the tappet, so that the desired smaller amount of air, which is determined by the dimensioning of the notch, is supplied.

[0016] By designing the vent valve as a combination of an orifice and a check valve, the motor housing can be prevented from filling up under no-load conditions. The tappet in the valve housing rests with its lower sealing cone against the seal seat of the hydraulic fluid reservoir-side connection, preventing the hydraulic oil in the motor housing from flowing back through the air intake line into the hydraulic fluid reservoir. Under load, the tappet rests with its upper sealing cone against the seal seat of the motor housing-side connection, so the notch determines the magnitude of the intake air flow.

[0017] The actuation of the tappet of a respective ventilation valve can take place depending on the build-up of negative pressure in the engine housing.

[0018] According to a further development, the venting device can be assigned a filter unit located in the hydraulic fluid reservoir, which is arranged essentially vertically in the hydraulic fluid reservoir. Compared to an inclined arrangement in the hydraulic fluid reservoir, the filter unit protrudes further above the hydraulic oil level, which has a positive effect on air separation.

[0019] The filter unit can comprise an air separation filter and a hydraulic oil return filter, which are arranged on a common filter support frame of the filter unit. The air separation filter should extend as far as possible above the hydraulic oil level. In particular, the air separation filter should have a large filtering surface. As an additional effect of such an enlarged design, lower backpressure is ensured at the inlet of the mixing chamber, which increases the efficiency of the extraction by the extraction device designed as a Venturi nozzle. In addition to the effective air separation of the filter unit arrangement, the filtering effect of the air separation filter protects the working hydraulics from particles in the event of a damage event in the extracted hydraulic motor assembly.

[0020] Furthermore, an outlet filter module containing an open-pore material can be installed downstream of the hydraulic oil return filter. This filter module effectively reduces the oil outlet velocity and prevents turbulence. Air bubbles in the hydraulic oil from the air separation filter can more easily rise to the surface. Steel wool or polyamide fibers, especially polyamide fiber balls, can be used as open-pore materials.

[0021] Preferably, the air separation filter can be designed as a coarse filter.

[0022] The present invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0023] They show: Fig. 1 schematically shows a side view of a self-propelled harvesting machine designed as a forage harvester; Fig. 2 a simplified schematic view of a hydraulic system of the forage harvester; Fig. 3 a schematic partial view of a hydraulic fluid reservoir of the hydraulic system according to Fig. 2 ; Fig. 4 a schematic view of a suction device of a venting device of a hydraulic motor arrangement of the hydraulic system according to Fig. 2 ; and Fig. 5 a schematic representation of a filter unit of the venting device.

[0024] In Fig. 1 is a schematic side view of a self-propelled harvesting machine 1 designed as a forage harvester 2 during harvesting in the field. The forage harvester 2 harvests or collects plants from the field by means of an attachment 4 in order to distribute the resulting crop in the form of a crop stream - in Fig. 1The material is guided—indicated by the arrowed line 3—through working elements designed as processing and conveying elements of the forage harvester 2, and deposited by means of a transfer device into a loading container of a transport vehicle (not shown). The processing and conveying elements of the forage harvester 2 include, among other things, an intake element 5, which consists of several pairs of rollers arranged one behind the other in an intake housing.The forage harvester 2 further comprises a chopping device 6, which chops the crop by means of a rotating chopping drum equipped with knives in conjunction with a counter-blade, a conditioning device 7 arranged downstream of the chopping device 6 in a conveyor shaft in the direction of the crop flow, and an ejection accelerator 8 arranged downstream of the conditioning device 7 in the conveyor shaft in the direction of the crop flow, which accelerates the crop 3 by means of rotating throwing paddles for safe ejection through the transfer device. The front attachment 4, the intake element 5, the chopping device 6, the conditioning device 7, and the ejection accelerator 8 are hereinafter referred to as working elements. An internal combustion engine 9, which serves to drive the forage harvester 2, is arranged in the rear area of ​​the forage harvester 2.

[0025] In Fig. 2A simplified schematic view of a hydraulic system 10 of the self-propelled harvesting machine 1 designed as a forage harvester 2 is shown. The hydraulic system 10 of the forage harvester 2 is designed as a closed-circuit system. The hydraulic system 10 comprises at least one hydraulic motor arrangement 11, 11a, 11b and a hydraulic fluid reservoir 12 hydraulically coupled to the at least one hydraulic motor arrangement 11, 11a, 11b. In the illustrated embodiment, only three hydraulic motor arrangements 11, 11a and 11b are indicated by way of example. The hydraulic motor arrangements 11, 11a and 11b can be designed as a hydrostatic drive of the forage harvester 2, as a drive motor of the front attachment 4, and as a drive motor of the intake member 5. Here, and preferably, the hydraulic motor arrangements 11, 11a and 11b are designed as single-motor arrangements.It is also conceivable to design one of the hydraulic motor arrangements 11, 11a, 11b as a double motor arrangement.

[0026] A supply line 33 supplies the at least one hydraulic motor arrangement 11 with high-pressure hydraulic oil 50 from the hydraulic fluid reservoir 12 from a hydraulic pump (not shown), which flows back into the reservoir through a discharge line 34.

[0027] A venting device 13 for venting a hydraulic fluid is assigned to the at least one hydraulic motor assembly 11. The venting device 13 has a suction device 14 designed as a Venturi nozzle 15 for suctioning the hydraulic fluid from the at least one hydraulic motor assembly 11. For simplification, the venting device 13 is explicitly shown only for the hydraulic motor assembly 11. Each additional hydraulic motor assembly 11a, 11b should be equipped with an individual venting device 13. The following statements apply accordingly to each additional hydraulic motor assembly 11a, 11b.

[0028] The suction device 14 uses negative pressure Δp to discharge hydraulic fluid from the at least one hydraulic motor assembly 11 integrated into at least one motor housing 16 through a return line 17 into the hydraulic fluid reservoir 12. To build up the negative pressure, a driving medium 18 flowing through the Venturi nozzle 15 is branched off from a pressurized section of the hydraulic system 10. For this purpose, a branch line 19 is provided, which serves to supply pre-pressurized flushing oil to the at least one hydraulic motor assembly 11 as the driving medium 18 of the suction device 14. The hydraulic fluid is sucked out of the motor housing 16 through a suction line 17a due to the suction effect generated by the Venturi nozzle.

[0029] The hydraulic motor assembly 11 is connected to the hydraulic fluid reservoir 12 via an air intake line 20. An air reservoir 21 is provided for re-ventilation when the at least one hydraulic motor assembly 11 is transferred to a load state or after constant pressure operation. A check valve 24 provided in the air intake line 20 is connected upstream of the hydraulic motor assembly 11, which prevents hydraulic oil 50 from flowing back from the motor housing 16 toward the hydraulic fluid reservoir 1. The air reservoir 21 is arranged between the hydraulic fluid reservoir 12 and the hydraulic motor assembly 11. The air reservoir 21 can be designed as a container 22 arranged in the air intake line 20. Alternatively or additionally, the air reservoir 21 can be formed by oversizing a section 23 of the air intake line 20.If the air reservoir 21 is designed as an oversized section 23 in the air intake line 20, this is limited by a second check valve 25 shown in dashed lines.

[0030] Upstream of the air reservoir 21 arranged in the air intake line 20, there is a number of vent valves 26, 26a, 26b corresponding to the number of hydraulic motors of the at least one hydraulic motor arrangement 11, 11a, 11b. The vent valves 26, 26a, 26b are arranged between the hydraulic fluid reservoir 12 and the air reservoir 21. The orientation of the respective vent valve 26, 26a, 26b in its installed position is perpendicular to a component 29 covering the hydraulic fluid reservoir 12, in this case a tank cap. A connection unit 30 arranged on the component 29 accommodates the ventilation valves 26, 26a, 26b, which are fluidly connected to the hydraulic fluid reservoir 12 by means of their respective hydraulic fluid reservoir-side connection 31 through the connection unit 30 in order to be able to suck air from the hydraulic fluid reservoir 12, which is indicated by the flow direction arrow 32.

[0031] The venting device 13 further comprises a filter unit 27 located in the hydraulic fluid reservoir 12, which is arranged vertically in the hydraulic fluid reservoir 12. Reference numeral 28 denotes a hydraulic oil level, which represents the fill level of hydraulic oil 50 in the hydraulic fluid reservoir 12. The filter unit 27 is arranged essentially vertically in the hydraulic fluid reservoir 12.

[0032] In Fig. 3 is a schematic partial view of the hydraulic fluid reservoir 12 of the hydraulic system 10 according to Fig. 2 The vent valves 26, 26a, 26b are preferably identical here. However, it is also conceivable that they have different dimensions if this should be necessary due to the respective design of one of the hydraulic motor assemblies 11, 11, 11b.

[0033] The respective vent valve 26, 26a, 26b comprises a motor housing-side connection 35 opposite the hydraulic fluid reservoir-side connection 31. The orientation of the respective vent valve 26, 26a, 26b in the installed position is perpendicular to the component 29 covering the hydraulic fluid reservoir 12. The respective vent valve 26, 26a, 26b is designed as a combination of an orifice 36 and a check valve 37, whose functions are combined in a common valve housing 38. A very small orifice is required to ventilate the respective motor housing 16 to be extracted in order to keep the amount of air to be separated in the filter unit 27 as low as possible.

[0034] In the valve housing 38 of the respective vent valve 26, 26a, 26b, a tappet 39 is arranged, which extends in sections between a sealing seat 40 on the side of the hydraulic fluid reservoir connection 31 and the orifice 36 on the side of the motor housing connection 35. On its underside, the tappet 39 has a lower sealing cone 41, which rests on the sealing seat 40 due to its weight in the load-free state of the hydraulic motor assembly 11, as shown in Fig. 3shown. On its upper side, the tappet 39 has a groove or notch 42, in particular a semicircular one, in the upper sealing cone 43, the diameter of which is less than one third, in particular approximately one tenth, of the opening diameter of the orifice 36. If a negative pressure Δp generated by the Venturi nozzle in the motor housing 16 occurs, this leads to air being sucked in through the air intake line 20, wherein depending on the negative pressure Δp building up in the motor housing 16, i.e. when a threshold value for the pressure difference between the interior of the hydraulic fluid reservoir 12 and the motor housing 16 is exceeded, a movement of the tappet 39 is effected in a vertical direction until the tappet 39 rests with its upper sealing cone 43 against the opening of the orifice 36 in a sealing manner. Only the groove or notch 42 in the upper sealing cone 43 allows air to flow through the remaining gap between the aperture 36 and the groove or notch 42.

[0035] The representation in Fig. 4 shows a schematic view of the suction device 14 of the venting device 13 of one of the hydraulic motor arrangements 11, 11a, 11b of the hydraulic system 10 according to Fig. 2 . The venting device 13 comprises, in addition to the suction device 14 designed as a Venturi nozzle 15, a mixing chamber 44 arranged downstream of the latter. The mixing chamber 44 is connected to the hydraulic fluid reservoir 12 via the return line 17. The mixing chamber 44 can have a diffuser 45 on the outlet side, which is integrated into the mixing chamber 44, as shown in Fig. 4shown, or is directly connected to it, for example, by a flange connection. The diffuser 45 then connects the mixing chamber 44 to the return line 17. The branch line 19 connects the venting device 13 to the motor housing 16, from which the pre-pressurized flushing oil is branched off as the driving medium 18. The branch line 19 is connected to a motor housing-side connection 46 of the venting device 13.

[0036] A pilot-operated pressure relief valve 47 is arranged in the branch line 19 and is connected to the motor housing 16 via a signaling line 48. The negative pressure Δp prevailing in the motor housing, depending on the operating situation, serves to control the pressure relief valve. The pressure relief valve 47 is integrated into the suction device 14, with the pressure relief valve 47 being connected upstream of the suction device 14, which is designed as a Venturi nozzle 15. The signaling line 48 is connected to the pressure relief valve 47 via a connection 49. Using the motor housing pressure instead of the ambient pressure is advantageous from a design perspective, since the signaling line 48 can be implemented as a small transverse bore within the installation space of the pressure relief valve 47. This eliminates the need for an additional tank line.

[0037] The hydraulic oil 50 sucked out of the motor housing 16 flows through the motor housing-side connection 46 to the mixing chamber 44, in which it mixes with the driving medium 18 and returns to the hydraulic fluid reservoir 12 through the return line 17.

[0038] An essential aspect is that the pressure relief valve 47 is configured to regulate the venting device 13 in the event of an undersupply, particularly when the hydraulic motor assembly 11, 11a, 11b is stationary and unloaded, with the propellant 18 provided by the at least one hydraulic motor assembly 11, 11a, 11b to be extracted. This ensures that, when the hydraulic motor assembly 11, 11a, 11b is stationary and unloaded, the flushing of the hydraulic motor assembly 11, 11a, 11b is switched off and the extraction is interrupted.

[0039] When the hydraulic motor arrangement 11, 11a, 11b is started up, the flushing is activated so that the driving medium volume flow or flushing oil volume is available to empty the motor housing 16. In order to have the maximum available feed pressure to drive the suction device 14, the flushing oil must flow from the motor housing 16 to the suction device 14, i.e. to the Venturi nozzle 15, with as little restriction as possible. In order to protect the hydraulic system 10, which is designed as a closed circuit, against inadmissible pressure drops, the pilot-operated pressure relief valve 47 with its signal line 48 is connected to the motor housing 16 in order to use the negative pressure Δp in the motor housing 16 for control. This ensures that the pressure relief valve 47 is fully open and without restriction as soon as the required minimum pressure of the hydraulic system 10, which is designed as a closed circuit, is exceeded.If there is a drop in feed pressure in the hydraulic system 10, the pressure relief valve 47 closes.

[0040] When the hydraulic motor assembly 11, 11a, 11b is stationary, the respective motor housing 16 can refill due to the lack of drive medium flow. Upon startup, drive medium 18 is again supplied to the suction device 14, so that the suction of the housing 16 is activated by the suction device 14. It must be ensured that the motor housing 16 is vented as quickly as possible.

[0041] To prevent the motor housing 16 from filling up under no-load conditions, a return valve 24 is provided in the air intake line 20. To ensure rapid re-ventilation when the hydraulic motor assembly 11, 11a, 11b starts up or after constant-pressure operation at full speed, an air volume is stored in the air reservoir 21 of the air intake line 20. As soon as the respective hydraulic motor assembly 11, 11a, 11b starts up again and the suction is activated, the storage volume can expand synchronously with the rapidly decreasing pressure in the motor housing 16.

[0042] Through the vertically installed ventilation valves 26, 26a, 26b, the respective motor housing 16 is initially supplied with a relatively large amount of air without any restriction. Only when the pressure in the motor housing 16 continues to drop is the tappet 39 drawn upwards, and the desired small amount of air is supplied by drawing the air only through the groove or notch 42. This reduces the air volume flow required to ventilate the motor housing 16 to be extracted, in order to keep the amount of air to be separated in the filter unit 27 as low as possible. During this run-up time, which depends on the negative pressure Δp building up in the motor housing 16, the motor housing 16 can be sufficiently emptied for continued operation.

[0043] In Fig. 5A schematic representation of the filter unit 27 of the venting device 13 is shown. The venting device 13 is assigned the filter unit 27 located in the hydraulic fluid reservoir 12, which is arranged essentially vertically in the hydraulic fluid reservoir 12. The filter unit 27 comprises an air separation filter 51 and a hydraulic oil return filter 52, which are arranged in a common filter support frame 53. On the outlet side, an outlet filter module 54 is connected downstream of the hydraulic oil return filter 52, which contains polyamide fibers, in particular at least one polyamide fiber ball, as filter material. This effectively reduces the exit velocity of the hydraulic oil 50 and prevents turbulence. The air bubbles in the hydraulic oil 50 from the air separation filter 51 can rise more easily to the surface.

[0044] A volume flow 55 coming from the suction device 14, which contains the flushing oil or propellant 18 and air, is fed to the air separation filter 51. An air volume flow 56 is sucked in through the vent valves 26, 26a, 26b arranged on the component 29 covering the hydraulic fluid reservoir 12, and enters the air intake line 20. List of reference symbols

[0045] 1 Harvester 29 component 2 forage harvester 30 Connection unit 3 Crop flow 31 Connection 4 Attachment 32 Flow direction arrow 5 intake organ 33 supply line 6 Chopping device 34 Derivation 7 Conditioning device 35 Connection 8 Ejection accelerator 36 aperture 9 combustion engine 37 Check valve 10 hydraulic system 38 valve housing 11 Hydraulic motor arrangement 39 pestle 11a Hydraulic motor arrangement 40 Seal seat 11b Hydraulic motor arrangement 41 Lower sealing cone 12 Hydraulic fluid reservoir 42 groove, notch 13 venting device 43 Upper sealing cone 14 Extraction device 44 Mixing chamber 15 Venturi nozzle 45 diffuser 16 Engine housing 46 Connection 17 Return line 47 pressure relief valve 17a Suction line 48 Reporting line 18 Propellant 49 Connection 19 branch line 50 hydraulic oil 20 Air intake line 51 Air separation filter 21 Air storage 52 Hydraulic oil return filter 22 container 53 Filter support frame 23 Section of 20 54 Outlet filter module 24 Check valve 55 Volume flow 25 Check valve 56 Air volume flow 26 ventilation valve 26a ventilation valve Δp negative pressure 26b ventilation valve 27 filter unit 28 Hydraulic oil level

Claims

1. A hydraulic system (10) which is configured as a closed circuit system, wherein the hydraulic system (10) comprises at least one hydraulic motor assembly and a hydraulic fluid reservoir (12) hydraulically coupled to this hydraulic motor assembly (11, 11a, 11b), wherein a deaeration device (13) for deaerating a hydraulic fluid (50) is associated with the at least one hydraulic motor assembly (11, 11a, 11b), wherein the deaeration device (13) has a suction means (14) configured as a Venturi nozzle (15) in order to aspirate the hydraulic fluid (50) of the at least one hydraulic motor assembly (11, 11a, 11b), wherein the suction means (14) removes hydraulic fluid (50) from the at least one hydraulic motor assembly (11, 11a, 11b) integrated into at least one motor housing (16) through a return line (17) into the hydraulic fluid reservoir (12) by means of a partial vacuum (Δp), characterized in that a supply of pre-pressurized scavenging oil of the at least one hydraulic motor assembly (11, 11a, 11b) is provided through a branch line (19) as the working medium (18) of the suction means (14), wherein a pilot-controlled pressure limiting valve (47) is disposed in the branch line (19) and is connected to the motor housing (16) by a signal line (48), wherein the partial vacuum (Δp) in the motor housing (16) serves to control the pressure limiting valve (47).

2. The hydraulic system (10) according to claim 1, characterized in that, in the case of an insufficient supply of the working medium (18) provided from the at least one hydraulic motor assembly (11, 11a, 11b), in particular in the case of a stationary, load-free hydraulic motor assembly, the pressure limiting valve (47) is configured to slow down the deaeration device (13).

3. The hydraulic system (10) according to claim 1 or claim 2, characterized in that the deaeration device (13) comprises a mixing chamber (44) downstream of the suction means (14), wherein the mixing chamber (44) is connected to the hydraulic fluid reservoir (12) by the return line (17).

4. The hydraulic system (10) according to one of claims 1 to 3, characterized in that the pressure limiting valve (47) is integrated into the deaeration device (13), wherein the pressure limiting valve (47) is upstream of the suction means (14) configured as a Venturi nozzle (15).

5. The hydraulic system (10) according to one of claims 1 to 4, characterized in that the at least one hydraulic motor assembly (11, 11a, 11b) is connected to the hydraulic fluid reservoir (41) by an air intake line (20), wherein a reservoir of air (21) is provided for re-aeration when the at least one hydraulic motor assembly (11, 11a, 11b) is transposed into a load condition or after a constant pressure operation.

6. The hydraulic system (10) according to claim 5, characterized in that the air reservoir (21) is configured as a container (22) disposed in the air intake line (20) and / or by an oversizing of a section (23) of the air intake line (20), wherein the section (23) is delimited by two non-return valves (24, 25).

7. The hydraulic system (10) according to one of claims 5 or 6, characterized in that a number of aeration valves (26, 26a, 26b) which corresponds to the number of hydraulic motors of the at least one hydraulic motor assembly (11, 11a, 11b) and which are disposed between the hydraulic fluid reservoir (12) and the air reservoir (21) are installed upstream of the air reservoir (21) disposed in the air intake line (20).

8. The hydraulic system (10) according to claim 7, characterized in that the respective aeration valve (26, 26a, 26b) is configured as a combination of an orifice plate (36) and a non-return valve (37), the functions of which are combined in a common valve housing (38).

9. The hydraulic system (10) according to claim 8, characterized in that the respective aeration valve (26, 26a, 26b) comprises a connector (31) on the hydraulic fluid reservoir side and a connector (35) on the motor housing side, wherein the orientation of the respective aeration valve (26, 26a, 26b) in the installed position is perpendicular to a component (29) covering the hydraulic fluid reservoir (12).

10. The hydraulic system (10) according to claim 9, characterized in that the respective aeration valve (26, 26a, 26b) has a relatively movable plunger (39) which has a lower conical nipple (41) facing the connector (31) on the hydraulic fluid reservoir side and an upper conical nipple (43) provided with a notch (42) facing the connector (35) on the motor housing side.

11. The hydraulic system (10) according to claim 10, characterized in that the plunger (39) of a respective aeration valve (26, 26a, 26b) can be actuated as a function of the buildup of the partial vacuum (Δp) in the respective motor housing (16).

12. The hydraulic system (10) according to one of the preceding claims, characterized in that a filter unit (27) located in the hydraulic fluid reservoir (12) and which is disposed substantially vertically upright in the hydraulic fluid reservoir (12) is associated with the deaeration device (13).

13. The hydraulic system (10) according to claim 12, characterized in that the filter unit (27) comprises an air separator filter (51) and a hydraulic oil return filter (52) which are disposed on a common filter support frame (53).

14. The hydraulic system (10) according to claim 13, characterized in that an exit filter module (54) which contains an open-pored material as the filter material is installed on the outlet side downstream of the hydraulic oil return filter (52).

15. The hydraulic system (10) according to claim 13 or claim 14, characterized in that the air separator filter (51) is configured as a coarse filter.