Hydraulic drive system

Abstract

A hydraulic drive system (24), in particular for a self-propelled construction machine, comprises at least one hydraulic pump (28) which can be driven by a drive assembly (26) to deliver hydraulic fluid, a hydraulic circuit (30) which receives the hydraulic fluid delivered by the at least one hydraulic pump (28) and conducts the hydraulic fluid back to the at least one hydraulic pump, at least one hydraulic motor (32, 34) which is supplied via the hydraulic circuit (30) with the hydraulic fluid delivered by the at least one hydraulic pump (28), a discharge line arrangement (52) for discharging hydraulic fluid from the hydraulic circuit (30) to a hydraulic fluid reservoir (42), and at least one flushing line (64) which is supplied by the hydraulic circuit (30) for flushing at least one hydraulic component of the hydraulic drive system (40) with hydraulic fluid, wherein the at least one flushing line (64) branches off from the discharge line arrangement (52) and / or constitutes a line region of the discharge line arrangement (52).

Description

Technical Field

[0001] This invention relates to a hydraulic drive system for use in construction machinery, such as ground compactors, to drive the machinery to move on a foundation and / or to supply hydraulic fluid to the machinery's working equipment for its operation. Background Technology

[0002] Hydraulic drive systems for powering construction machinery typically include: at least one hydraulic pump, which can be driven by a drive unit (e.g., a diesel engine or an electric motor) to deliver hydraulic fluid; a hydraulic circuit that receives the hydraulic fluid delivered by the at least one hydraulic pump and guides the hydraulic fluid back to the at least one hydraulic pump; and at least one hydraulic motor, which is supplied with the hydraulic fluid delivered by the at least one hydraulic pump via the hydraulic circuit and drives, for example, one or more drive wheels or one or more ground processing rollers. During the operation of the unit comprised of such hydraulic components (e.g., hydraulic pumps or hydraulic motors) in the hydraulic drive system, heat is generated, and this heat must be dissipated from the areas of these hydraulic components. For this purpose, hydraulic fluid can be drawn from the hydraulic circuit to guide it, for example, in parallel with the hydraulic fluid delivered to the one or more hydraulic motors through the hydraulic components to be cooled. As a result, the amount of hydraulic fluid delivered by the one or more hydraulic pumps to the hydraulic circuit depends on the amount of hydraulic fluid required to drive the one or more hydraulic motors and the amount of hydraulic fluid required to cool the one or more hydraulic components.

[0003] Because the hydraulic fluid supplied by at least one hydraulic pump or to the hydraulic circuit has a relatively high fluid pressure, diverting a portion of this relatively high-pressure hydraulic fluid to cool one or more hydraulic components of the hydraulic drive system results in significant power loss. Furthermore, to prevent excessively high internal pressure in the hydraulic components through which the hydraulic fluid used for flushing or cooling flows, especially during cold starts, the amount of high-pressure fluid that can be directed through the hydraulic components to be cooled or flushed is limited, particularly when using a high-viscosity hydraulic fluid (typically hydraulic oil). Due to the pressure limitations during cold starts, limiting the amount of hydraulic fluid diverted from the hydraulic circuit is necessary, thus posing a risk that insufficient hydraulic fluid may be delivered through the hydraulic components to be cooled at higher temperatures. Summary of the Invention

[0004] The purpose of this invention is to provide a hydraulic drive system, particularly for engineering machinery such as ground compactors, which can achieve efficient cooling of hydraulic components with low power loss.

[0005] According to the present invention, this objective is achieved by a hydraulic drive system specifically designed for self-propelled engineering machinery, the system comprising: - At least one hydraulic pump, which can be driven by a drive unit to deliver hydraulic fluid; - A hydraulic circuit that receives hydraulic fluid supplied by at least one hydraulic pump and directs the hydraulic fluid back to at least one hydraulic pump; - At least one hydraulic motor, which is supplied with hydraulic fluid delivered by at least one hydraulic pump via a hydraulic circuit; - Discharge piping device for discharging hydraulic fluid from the hydraulic circuit to the hydraulic fluid reservoir; - At least one flushing line, supplied by a hydraulic circuit, for flushing at least one hydraulic component of a hydraulically driven system with hydraulic fluid.

[0006] At least one flushing line branches off from the discharge line assembly and / or forms part of the discharge line assembly's piping area.

[0007] In the hydraulic drive system designed according to the present invention, hydraulic fluid discharged towards the hydraulic fluid reservoir is used to flush or cool one or more hydraulic components. This hydraulic fluid typically has a relatively low pressure. Therefore, the risk of mechanical overload on the hydraulic components to be cooled due to excessively high pressure of the hydraulic fluid used for cooling can be significantly reduced. Furthermore, since the hydraulic fluid used according to the present invention is itself discharged from the hydraulic circuit, i.e., led from the hydraulic circuit towards the hydraulic fluid reservoir, there is no need to correspondingly increase the delivery rate of at least one hydraulic pump to provide hydraulic fluid for cooling the hydraulic components. This results in relatively low power loss required for cooling one or more hydraulic components.

[0008] In a particularly advantageous design, primarily considering hydraulic fluid pressure, it is suggested that the discharge piping assembly includes a discharge cooling line and a discharge bypass line. The discharge cooling line contains a hydraulic fluid cooler and leads to a hydraulic fluid reservoir. The discharge bypass line runs parallel to the discharge cooling line and also leads to the hydraulic fluid reservoir. Furthermore, at least one flushing line branches off from the discharge cooling line assembly and / or constitutes a piping region of the discharge cooling line. The hydraulic fluid cooler located in this discharge cooling line is also a pressure-sensitive component and cannot withstand excessively high hydraulic fluid pressures. Because this drive system ensures that the pressure of the hydraulic fluid input to the discharge cooling line and introduced into the hydraulic fluid reservoir via it does not exceed a predetermined pressure, it also ensures that the hydraulic fluid used to cool at least one hydraulic component has a relatively low hydraulic fluid pressure, thereby eliminating the potential risk of damage to that component.

[0009] At least one flushing line can branch off from the discharge cooling line upstream of the hydraulic fluid cooler and / or form a piping region of the discharge cooling line upstream of the hydraulic fluid cooler. This allows at least one flushing line to be arranged parallel to the hydraulic fluid cooler in such a configuration, such that both the flushing line and the hydraulic fluid cooler are traversed by a portion of the hydraulic fluid flowing through the discharge cooling line. This further reduces the hydraulic fluid pressure acting on the hydraulic components to be cooled.

[0010] Alternatively or additionally, at least one flushing line may branch off from the discharge cooling line downstream of the hydraulic fluid cooler, and / or form a piping region of the discharge cooling line located downstream of the hydraulic fluid cooler. A particular advantage of this design is that the hydraulic fluid flowing into the flushing line has already been cooled in the hydraulic fluid cooler located further upstream, and therefore can be used particularly efficiently to cool at least one hydraulic component associated with the flushing line.

[0011] Regardless of whether the flushing line branches off from the exhaust cooling line upstream or downstream of the hydraulic fluid cooler, at least one flushing line can be connected in series with the hydraulic fluid cooler.

[0012] In order to enable the discharge bypass line to be released in a defined manner to allow flow or to close the discharge bypass line to block flow, thereby enabling the regulation of the proportion of hydraulic fluid flowing through the discharge cooling line and thus mechanically loading the hydraulic fluid cooler, a bypass valve can be provided on the discharge bypass line, wherein the bypass valve is adjustable between a closed position and an open position, wherein the closed position closes (preferably completely closes) the discharge bypass line to block the flow of hydraulic fluid, and the open position releases (preferably releases to the maximum extent) the discharge bypass line to allow the flow of hydraulic fluid.

[0013] In order to avoid mechanical overload of the hydraulic fluid cooler due to excessive hydraulic fluid pressure, it is advantageous if the bypass valve can be adjusted according to the hydraulic fluid temperature (e.g., the hydraulic fluid temperature of the hydraulic fluid flowing through the discharge line device).

[0014] Specifically, the bypass valve can be configured such that it opens (preferably to its maximum extent) to allow flow when the hydraulic fluid temperature is below the switching temperature, and closes at least partially (preferably completely) to prevent flow when the hydraulic fluid temperature is above the switching temperature. If the hydraulic fluid temperature is relatively high, its lower viscosity typically results in lower fluid pressure, thus substantially preventing mechanical overload of the hydraulic fluid cooler at higher hydraulic fluid temperatures. Because most of the discharged hydraulic fluid can flow through the discharge bypass line at lower hydraulic fluid temperatures via the opening of the bypass valve, even if the hydraulic fluid viscosity is relatively high, the pressure of the hydraulic fluid in the discharge line device can be reduced or maintained at a low pressure level, preventing any possible portion of the relatively cold and therefore viscous hydraulic fluid that might still flow through the hydraulic fluid cooler and cause mechanical overload of the hydraulic fluid cooler.

[0015] Alternatively or additionally, the bypass valve can be configured to adjust between a closed position and an open position based on the hydraulic fluid pressure (e.g., the hydraulic fluid pressure in an outlet line arrangement).

[0016] Therefore, the bypass valve can open (preferably to its maximum extent) when the hydraulic fluid pressure is higher than the switching pressure to allow flow, and close at least partially (preferably completely) when the hydraulic fluid pressure is lower than the switching pressure to prevent flow. This ensures that, especially during the cold start phase when the hydraulic fluid viscosity is relatively high, no excessive load is placed on the hydraulic fluid cooler.

[0017] Bypass valves may include, for example: - Thermostatic valve, i.e., a valve that switches when a switching temperature is reached; or - Check valve, i.e., a valve that switches when, for example, the switching pressure is reached; or - A valve that can be electrically switched based on pressure and / or temperature, that is, a valve that takes the pressure and / or temperature of the hydraulic fluid as input variables for control and switches accordingly based on pressure and / or temperature.

[0018] According to the hydraulic drive system of the present invention, at least one hydraulic pump may be a hydraulic component that performs flushing via at least one flushing line. Alternatively or additionally, at least one hydraulic motor may be a hydraulic component that performs flushing via at least one flushing line.

[0019] It should be noted that, in the context of this invention, a hydraulic motor is understood not only as a unit that generates driving torque for driving wheels (e.g., drive wheels or sprockets), but also as any type of unit that generates driving force or driving torque by applying pressurized fluid. For example, in the context of this invention, a hydraulic piston / cylinder unit for moving components or working equipment of engineering machinery should also be considered as a drive motor supplied with hydraulic fluid by means of one or more hydraulic pumps.

[0020] The present invention also relates to a ground processing machine, preferably a surface compactor, which includes a hydraulic drive system designed according to the present invention. Attached Figure Description

[0021] The present invention will now be described in detail with reference to the accompanying drawings. The drawings show: Figure 1 A side view of a self-propelled construction machine designed as a ground compactor is shown. Figure 2 An example of using Figure 1 The circuit diagram of the hydraulic drive system of the engineering machinery shown is shown. Figure 3 An example of using Figure 1 The circuit diagram shows an alternative design for the hydraulic drive system of the engineering machinery. Detailed Implementation

[0022] Figure 1 A side view of a self-propelled construction machine 10 designed as a ground compactor is shown. The construction machine 10 includes drive wheels 14 located on both sides of a rear carriage 12, which can be driven to rotate by a drive unit also mounted on the rear carriage 12. An operator's platform 16 for operating the construction machine 10 is also provided on the rear carriage 12.

[0023] A ground processing roller 20 is mounted on the front vehicle 18, which is pivotally connected to the rear vehicle 12 to enable steering of the construction machinery 10. As the construction machinery 10 moves on the foundation 22 to be processed, the ground processing roller 20 rolls on the foundation. Depending on the surface design of the ground processing roller, it can compact the foundation 22 being driven over, or, for structured surfaces, the ground processing roller can be used to break up hard foundations, such as concrete foundations.

[0024] See below for reference. Figure 2 and Figure 3 Before describing in detail the hydraulic drive system used in this floor processing machine 10, it should be noted that, Figure 1The self-propelled construction machinery 10 shown is merely one example of such machinery. If the machinery 10 is designed as a ground compactor, it may also have ground processing rollers on its rear vehicle 12, wherein one or both ground processing rollers can be driven to rotate, allowing the machinery 10 to move on the foundation 22. Furthermore, the machinery may also be designed as a steering articulated ground compactor, a wheel loader, or a similar type. For example, when designed as a bulldozer, such machinery 10 may also have a tracked chassis.

[0025] Figure 2 A hydraulic drive system 24 for this type of self-propelled construction machinery 10 and its main system areas are shown. The hydraulic drive system 24 includes a hydraulic pump 28 driven by a drive unit 26. In a conventional design, the drive unit 26 may be powered, for example, by a diesel engine. In a design as an electro-hydraulic drive system, the drive unit may also include an electric motor.

[0026] The hydraulic drive system 24 also includes a hydraulic circuit 30, in which two hydraulic motors 32 and 34 are hydraulically connected to a hydraulic pump 28 via the hydraulic circuit 30 to supply pressurized hydraulic fluid (typically hydraulic oil) to the hydraulic motors or to return hydraulic fluid from the hydraulic motors.

[0027] Hydraulic circuit 30 includes a first conduit region 36 connecting hydraulic pump 28 and two hydraulic motors 32, 34, and a second conduit region 38 connecting hydraulic pump 28 and two hydraulic motors 32, 34. According to a preset direction of motion and the corresponding rotational direction of the hydraulic motors 32, 34, hydraulic fluid discharged from hydraulic pump 28 can be guided to hydraulic motors 32, 34 via conduit region 36, and then returned to hydraulic pump 28 via second conduit region 38; alternatively, hydraulic fluid can be guided to the two hydraulic motors 32, 34 via second conduit region 38 (e.g., in...). Figure 1 In the engineering machinery 10 shown, each hydraulic motor can be assigned to a drive wheel 14 arranged on the side of the rear vehicle 12, and then fed back to the hydraulic pump 28 via the first pipeline area 36.

[0028] although Figure 2 The hydraulic circuit 30 shown is essentially a closed circuit, but in various states of the hydraulic drive system 24, it is necessary to replenish hydraulic fluid to the hydraulic circuit 30 from the hydraulic fluid reservoir 42 or the associated pressure fluid reservoir 44, or to drain hydraulic fluid from the hydraulic circuit 30. For example, if the pressure in the hydraulic circuit 30 (especially on the low-pressure side) drops below an associated threshold due to unavoidable leakage in, for example, the hydraulic motors 32, 34 or the hydraulic pump 28, or if hydraulic fluid is actively drained due to, for example, excessively high temperature of the hydraulic fluid in the hydraulic circuit, then it is necessary to replenish hydraulic fluid.

[0029] To replenish the hydraulic fluid, a supply valve assembly, generally designated 46, is provided. This supply valve assembly 46 includes two first supply valves 461 and 462 associated with a first conduit region 36 of the hydraulic circuit 30, and two second supply valves 463 and 464 associated with a second conduit region 38 of the hydraulic circuit 30. According to the shut-off valves 68 and 70 of the service brake 72, [the following information is provided]. Figure 2 and Figure 3 Whether in the locked state (where the service brake is active) or in the released state (where hydraulic fluid supplied by hydraulic pump 28 can flow through hydraulic motors 32 and 34 via pipeline areas 36 and 38), hydraulic fluid from hydraulic fluid reservoir 42 via hydraulic pump (not shown) or hydraulic fluid replenished from pressure fluid reservoir 44 is supplied to hydraulic circuit 30 via supply valves connected to the low-pressure side of four supply valves 461, 462, 463, and 464 in their respective operating states.

[0030] To discharge hydraulic fluid, a discharge valve assembly, generally designated 48, is provided. This discharge valve assembly includes a shut-off valve 50 that releases or closes the flow path to a discharge piping assembly, generally designated 52, and upstream of the shut-off valve 50 is a control valve 54, which optionally connects the shut-off valve 50 to a first piping region 36, a second piping region 38, or neither. In this way, it is ensured that the discharge of hydraulic fluid always occurs on the low-pressure side of the hydraulic circuit 30, i.e., from one of the piping regions 36 and 38, which is used to guide the hydraulic fluid delivered by the hydraulic pump 28 back to the hydraulic pump 28 after flowing through the two hydraulic motors 32 and 34. The discharge valve assembly 48 also includes pressure-holding valves 74 and 76 located between the two valves 50 and 54 and downstream of the shut-off valve 50 in the flow direction. These pressure-holding valves ensure that the fluid pressure in the hydraulic circuit 30 does not drop below a certain minimum pressure level during discharge.

[0031] The discharge piping device 52 includes a discharge cooling line 56 and a parallel discharge bypass line 58. Both the discharge cooling line 56 and the discharge bypass line 58 lead to the hydraulic fluid reservoir 42.

[0032] A hydraulic fluid cooler 60 is provided in the exhaust cooling line 56, in which the hydraulic fluid discharged from the hydraulic circuit 30 can transfer heat, for example, to the surrounding air, thereby cooling at least a portion of the discharged hydraulic fluid before entering the hydraulic fluid reservoir 42.

[0033] A bypass valve 62 is provided in the discharge bypass line 58. In the closed position, the bypass valve 62 preferably completely seals the discharge bypass line 58 to prevent hydraulic fluid flow, thereby directing all discharged hydraulic fluid through the discharge cooling line 56 and the hydraulic fluid cooler 60 disposed therein. In its open position, the discharge bypass line 58 is maximally released to allow hydraulic fluid flow. Since the flow resistance of the bypass valve 62 is relatively low compared to the flow resistance of the hydraulic fluid cooler 60 in this state, when the bypass valve 62 is in the open position, most of the discharged hydraulic fluid flows through the discharge bypass line 58 to the hydraulic fluid reservoir 42.

[0034] For example, the bypass valve can be designed as a thermostatic valve. When the switching temperature of the hydraulic fluid is reached (e.g., about 60°C), the bypass valve 62 switches from its open position to its closed position, ensuring that when the temperature of the hydraulic fluid is below the switching temperature, the bypass line 58 is released to allow flow, thereby preventing the hydraulic fluid cooler 60 from being overloaded by excessively high fluid pressure when the hydraulic fluid is relatively viscous (i.e., not easily flowing). When the switching temperature is reached (i.e., the temperature of the hydraulic fluid is higher and the viscosity is lower), the bypass valve 62 switches to its closed position, thereby ensuring that the hydraulic fluid guided towards the hydraulic fluid reservoir 42 is adequately cooled when the hydraulic fluid cooler 60 is subjected to a relatively small pressure load.

[0035] In an alternative design, bypass valve 62 can be designed as a check valve. When the temperature of the hydraulic fluid is low and therefore the viscosity of the hydraulic fluid is high, the check valve switches to its open position due to the relatively high pressure drop. As the temperature of the hydraulic fluid rises and therefore the viscosity decreases, the check valve switches to its closed position due to the reduced pressure drop. This ensures that as the temperature of the hydraulic fluid rises, the hydraulic fluid is directed to the hydraulic fluid cooler 60 for flow and then into the exhaust cooling line 56.

[0036] Furthermore, the bypass valve 62 can also be designed as an electrically switchable valve controlled by a control unit. Similarly, the pressure and / or temperature of the hydraulic fluid can be considered as input variables for switching this valve, ensuring that when the temperature of the hydraulic fluid is relatively low and the pressure drop at the hydraulic fluid cooler 60 is correspondingly high, the opening of this valve releases the discharge bypass line 58, thus preventing excessive pressure at the hydraulic fluid cooler 60, with a significant portion of the hydraulic fluid being drawn out via the discharge bypass line 58. When the temperature of the hydraulic fluid is sufficiently high and the viscosity is low, and the pressure at the hydraulic fluid cooler 60 is correspondingly low, the electrically switchable valve can be adjusted to its closed position to ensure that the hydraulic fluid discharged from the hydraulic circuit 30 is adequately cooled.

[0037] The bypass valve 62 may also be configured, regardless of its design, to make substantially continuous transitions between its open and closed positions based on temperature and / or pressure, such that, starting from the cold start phase with a relatively cold and therefore highly viscous hydraulic fluid, the bypass valve 62 gradually transitions from its open position to its closed position as the temperature of the hydraulic fluid increases and its viscosity decreases accordingly, and thus an increased portion of the discharged hydraulic fluid flows through the hydraulic fluid cooler 60.

[0038] Since the bypass valve 62, adjusted based on pressure or temperature, is primarily used to protect the hydraulic fluid cooler 60 from overload and potential damage, the parameters considered for adjusting the bypass valve 62 (i.e., temperature or pressure) can be detected, for example, within the region of the hydraulic fluid cooler 60. For instance, pressure sensors can be installed upstream and downstream of the hydraulic fluid cooler 60 in the exhaust cooling line 56 to detect the pressure difference present at the hydraulic fluid cooler 60 and accordingly open or close the bypass valve 62. If the temperature of the hydraulic fluid is considered as a control variable, the temperature of the hydraulic fluid can also be detected within the region of the hydraulic fluid cooler 60 (e.g., upstream). Of course, temperature and / or pressure values ​​in other regions of the hydraulic circuit 30 (e.g., within the region of the hydraulic fluid reservoir 42) can also be considered, provided these values ​​allow sufficient conclusions to be drawn regarding the temperature- or pressure-related mechanical loads on the hydraulic fluid cooler 60.

[0039] The hydraulic drive system 40 also includes a flushing line 64, in Figure 2 In the illustrated design example, the flushing line branches off from the discharge cooling line 56 upstream of the hydraulic fluid cooler 60, or provides a drain line assembly 52 or discharge cooling line 56 in a piping region upstream of the hydraulic fluid cooler 60. Hydraulic fluid flowing through the discharge cooling line 56 is guided via the flushing line 64 to the hydraulic components of the hydraulic drive system 40 that require flushing and therefore cooling. Figure 2 In the design example shown, the hydraulic pump 28 constitutes a hydraulic component to which the discharged hydraulic fluid is supplied by the hydraulic circuit 30 to dissipate the heat generated in the area of ​​the hydraulic pump 28 and to cool the heat-absorbing liquid in the hydraulic fluid cooler 60 before being introduced into the hydraulic flushing reservoir 42.

[0040] Since the hydraulic pump 28 in the illustrated design example is also a hydraulic component, it is necessary to prevent it (especially in the system area through which the hydraulic fluid flows) from being subjected to excessive pressure. Therefore, it is particularly advantageous to integrate the flushing line 64 into or branch from the discharge cooling line 56, because, through the aforementioned function of the bypass valve 62, the discharged hydraulic fluid, or at least most of it, will only flow through the discharge cooling line 56 and the flushing line 64 if the temperature of the discharged hydraulic fluid is sufficiently high or its viscosity is sufficiently low. For this reason, for example, when the bypass valve 62 performs a temperature-dependent or pressure-dependent switch, it is also advantageous to detect the temperature or pressure of the discharged hydraulic fluid upstream of the flushing line 64 or upstream of the hydraulic component to be flushed or cooled by means of the flushing line 64. For example, a temperature sensor or pressure sensor can be placed at the branch point 66—that is, in the discharge line assembly 52, where the discharge bypass line 58 on one hand and the discharge cooling line 56 or flushing line 64 on the other hand—to detect the relevant parameters to be considered.

[0041] Figure 3 Alternative design approaches for the hydraulic drive system 40 are shown. These approaches are particularly relevant to the design of the hydraulic circuit 30. Figure 2 The design methods shown are corresponding, so please refer to the previous description.

[0042] and Figure 2 A significant difference in the design shown is that the flushing line 64 branches off from the discharge cooling line 56 downstream of the hydraulic fluid cooler 60, or forms a section of the discharge cooling line 56 downstream of the hydraulic fluid cooler 60. The advantage of this variation is that the hydraulic fluid discharged from the hydraulic circuit 30 and introduced into the discharge cooling line 56 is cooled in the hydraulic fluid cooler 60 before flowing through the hydraulic component to be cooled (hydraulic pump 28 in this example), enabling the hydraulic component (hydraulic pump 28) to achieve higher cooling efficiency.

[0043] In principle, the flushing line 64 can also be parallel to the hydraulic fluid cooler 60, and therefore can certainly be parallel to the hydraulic bypass line 58. For example... Figure 2 As shown, flushing line 64 can branch off from the discharge cooling line 56 upstream of the hydraulic fluid cooler 60, such as... Figure 3 As shown, the discharge cooling line 56 rejoins downstream of the hydraulic fluid cooler 60. Similarly, in this variant, the system area through which the hydraulic fluid cooler 60 and the hydraulic pump 28 flow in parallel is only traversed when the discharge cooling line 56 is released to allow most of the discharged hydraulic fluid to flow, or when the discharge bypass line 58 is closed by the bypass valve 62 to prevent flow.

[0044] You can also Figure 2 and Figure 3 The two variations shown are combined to utilize the discharged hydraulic fluid to cool multiple hydraulic components of the hydraulic drive system 40. Furthermore, multiple hydraulic components to be cooled can be connected in series and / or in parallel to each other in a flushing line 64 so that the discharged hydraulic fluid can cool not only the hydraulic pump 28, but also, for example, the hydraulic motors 32, 34.

Claims

1. A hydraulic drive system, particularly a hydraulic drive system for self-propelled construction machinery, comprising: - At least one hydraulic pump (28) is capable of being driven by a drive unit (26) to deliver hydraulic fluid; - A hydraulic circuit (30) that receives hydraulic fluid delivered by at least one of the hydraulic pumps (28) and directs the hydraulic fluid back to at least one of the hydraulic pumps; - At least one hydraulic motor (32, 34) is supplied with hydraulic fluid delivered by at least one of the hydraulic pumps (28) via the hydraulic circuit (30); - Discharge line device (52) for discharging hydraulic fluid from the hydraulic circuit (30) to the hydraulic fluid reservoir (42); - At least one flushing line (64), supplied by the hydraulic circuit (30), for flushing at least one hydraulic component of the hydraulic drive system (40) with hydraulic fluid; At least one of the flushing lines (64) branches from the discharge line device (52) and / or constitutes a line area of ​​the discharge line device (52).

2. The hydraulic drive system according to claim 1, characterized in that, The discharge piping device (52) includes a discharge cooling pipe (56) and a discharge bypass pipe (58). The discharge cooling pipe (56) includes a hydraulic fluid cooler (60) and leads to the hydraulic fluid reservoir (42). The discharge bypass pipe (58) is parallel to the discharge cooling pipe (56) and leads to the hydraulic fluid reservoir (42). Furthermore, at least one flushing pipe (64) branches off from the discharge piping device (52) and / or constitutes a piping area of ​​the discharge cooling pipe (56).

3. The hydraulic drive system according to claim 2, characterized in that, At least one flushing line (64) branches off from the discharge cooling line (56) upstream of the hydraulic fluid cooler (60) and / or forms a piping area of ​​the discharge cooling line (56) located upstream of the hydraulic fluid cooler (60).

4. The hydraulic drive system according to claim 3, characterized in that, At least one flushing line is arranged in parallel with the hydraulic fluid cooler (60).

5. The hydraulic drive system according to any one of claims 2 to 4, characterized in that, At least one flushing line (64) branches off from the discharge cooling line (56) downstream of the hydraulic fluid cooler (60) and / or forms a piping area of ​​the discharge cooling line (56) located downstream of the hydraulic fluid cooler (60).

6. The hydraulic drive system according to any one of claims 2 to 5, characterized in that, At least one flushing line (64) is arranged in series with the hydraulic fluid cooler (60).

7. The hydraulic drive system according to any one of claims 2 to 6, characterized in that, A bypass valve (62) is assigned to the discharge bypass line (58), wherein the bypass valve (62) is adjustable between a closed position and an open position, wherein the closed position closes the discharge bypass line (58), preferably completely closing the discharge bypass line (58) to prevent the flow of hydraulic fluid, and the open position releases the discharge bypass line (58), preferably releasing the discharge bypass line (58) to the maximum extent to allow the flow of hydraulic fluid.

8. The hydraulic drive system according to claim 7, characterized in that, The bypass valve (62) can be adjusted between the closed position and the open position according to the temperature of the hydraulic fluid, preferably according to the temperature of the hydraulic fluid flowing through the discharge pipeline device (52).

9. The hydraulic drive system according to claim 8, characterized in that, When the temperature of the hydraulic fluid is below the switching temperature, the bypass valve (62) opens, preferably to the maximum extent, to allow flow; and when the temperature of the hydraulic fluid is above the switching temperature, the bypass valve (62) closes at least partially, preferably completely, to prevent flow.

10. The hydraulic drive system according to any one of claims 7 to 9, characterized in that, The bypass valve (62) can be adjusted between the closed position and the open position according to the hydraulic fluid pressure, preferably the hydraulic fluid pressure in the discharge pipeline device (52).

11. The hydraulic drive system according to claim 10, characterized in that, When the hydraulic fluid pressure is higher than the switching pressure, the bypass valve (62) opens, preferably to the maximum extent, to allow flow; and when the hydraulic fluid pressure is lower than the switching pressure, the bypass valve (62) closes at least partially, preferably completely, to prevent flow.

12. The hydraulic drive system according to any one of claims 7 to 11, characterized in that, The bypass valve (62) includes: -Thermostatic valve, or - Check valve or - A valve capable of being electrically switched based on pressure and / or temperature.

13. The hydraulic drive system according to any one of claims 1 to 12, characterized in that, At least one hydraulic pump (28) is a hydraulic component that performs flushing via at least one flushing line (64).

14. The hydraulic drive system according to any one of claims 1 to 13, characterized in that, At least one hydraulic motor (32, 34) is a hydraulic component that performs flushing via at least one flushing line (64).

15. A ground processing machine, preferably a ground compactor, comprising a hydraulic drive system (24) according to any one of claims 1 to 14.

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