Method for actuating a hydrostatic drive

Abstract

The present invention relates to a method for operating a hydraulic system (100) of a mobile working machine, wherein the hydraulic system (100) is provided with a hydraulic pump (2) which is connected to a hydraulic motor (4) via a first line (10) and a second line (11), wherein a bypass valve (99) is also provided which is positioned between the first line (10) and the second line (11) and is designed to prevent and permit hydraulic connection between the first and the second line (10, 11); wherein the hydraulic system (100) also comprises a charge pump (13) which is designed to supply pressurised fluid to the first and / or the second line (11) in order to compensate for fluid losses occurring during operation of the hydraulic system (100); characterised in that the method comprises the following steps: a) establishing a hydraulic connection between the charge pump (12) and the bypass valve (99) such that the bypass valve (99) can be controlled taking into account a charge pressure provided by the charge pump (12).

Description

[0001] R. 410715

[0002] Robert Bosch GmbH

[0003] 410715 - Tagliabue

[0004] METHOD FOR CONTROLLING A HYDROSTATIC DRIVE

[0005] TECHNICAL AREA

[0006] The invention relates to a method for operating a hydraulic system of a hydrostatic drive, preferably of a machine. Furthermore, this invention relates to a control unit, a machine comprising the control unit, and a computer program.

[0007] STATE OF THE ART

[0008] This invention relates to a hydraulic system, in particular a closed system, which uses a bypass valve to ensure a minimum pressure on the low-pressure side.

[0009] Such a hydraulic system is known, among other places, from patent DE 10 2018 205 194 A1. In such a closed circuit, energy is transferred from a source connected to the pump shaft to a load coupled to the motor shaft. The hydraulic fluid flows from the pump to the motor and then directly back to the pump, thus keeping the circuit closed.

[0010] For the pump to efficiently transfer energy to the motor, the hydraulic fluid pressure must be higher on one side of the circuit than on the other. The side with the higher pressure is called the high-pressure side, and the side with the lower pressure is called the low-pressure side. A feed pump is often used to compensate for fluid losses on the low-pressure side.

[0011] During the operation of a closed-loop system, it is often necessary to maintain a minimum low pressure. This becomes particularly critical when a sudden shock load leads to a rapid pressure increase. In such cases, the hydraulic fluid is compressed, causing the lines to expand and forcing more fluid to the high-pressure side. Simultaneously, less fluid is returned from the motor to the pump, resulting in a pressure drop on the low-pressure side, as the

[0012] Page 1 of 12 R. 410715

[0013] The feed pump cannot supply sufficient liquid. This so-called low-loop event can lead to damage to the pump and motor.

[0014] To compensate for fluctuations on the low-pressure side, accumulators and high-performance feed pumps are used. Accumulators are pressure storage tanks that hold fluid under pressure. Although useful, they are expensive to purchase and maintain and require qualified personnel. Furthermore, they are susceptible to leaks, making them unreliable. Alternatively or additionally, larger feed pumps are integrated into the system. However, these pumps are less efficient because they generate more heat in the system.

[0015] To avoid these disadvantages, a device was developed in patent DE 10 2018 205 194 A1 in which a flushing system is connected between the high-pressure and low-pressure sides, communicating with both. The flushing system includes a changeover valve and a limiting valve. Also communicating with both the high-pressure and low-pressure sides, and connected in parallel to the flushing system, is a bypass valve. When opened or moved, the bypass valve directs fluid from the high-pressure side to the low-pressure side. The bypass valve has a setpoint pressure that is above a minimum pressure on the low-pressure side, and is configured to open when the pressure in the low-pressure line falls below a preset pressure.

[0016] This described solution is particularly complex, as several additional components (the bypass valve and the changeover valve) must be installed to guarantee a minimum pressure on the low-pressure side. While this solution is more cost-effective compared to a pressure accumulator, it results in higher costs compared to a system that does not include this feature.

[0017] The main goal of this invention is therefore to improve the current state of the art.

[0018] SUMMARY

[0019] According to one embodiment of the present invention, a method for operating a hydraulic system (100) of a mobile working machine is provided, wherein the hydraulic system (100) is provided with a hydraulic pump (2) which is connected to a hydraulic motor (4) via a first line (10) and a second line (11), further comprising a bypass valve (99) which is located between the first line (10) and the second line (11).

[0020] Page 2 of 12 R. 410715

[0021] Line (11) is positioned and configured to prevent and enable a hydraulic connection between the first and second lines (10, 11), respectively; wherein the hydraulic system (100) further comprises a feed pump (13) configured to supply the first and / or the second line (11) with hydraulic fluid so that fluid losses occurring during the operation of the hydraulic system (100) can be compensated for; wherein the method comprises the following steps: establishing a (preferably hydraulic) connection between the feed pump (12) and the bypass valve (99) so that the bypass valve (99) can be controlled taking into account a feed pressure provided by the feed pump (12). It is noted that the phrase "taking into account a feed pressure provided by the feed pump (12)" means that the feed pressure can be taken into account either directly or indirectly.Direct consideration means that the supply pressure is used directly at the outlet of the feed pump to control the bypass valve. Conversely, indirect consideration means that the supply pressure is not considered directly at the outlet of the feed pump, but at another point in the hydraulic system (e.g., after the hydraulic fluid has been filtered, etc.). This invention is particularly advantageous because it eliminates the need for certain hydraulic components (e.g., the changeover valve known from German patent DE 10 2018 205 194 A1), thus effectively reducing the cost of the hydraulic system.

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures:

[0024] Fig. 1 shows a hydraulic circuit diagram of a hydrostatic drive according to a first embodiment of the present invention,

[0025] Fig. 2 shows a hydraulic circuit diagram of a hydrostatic drive according to a second embodiment of the present invention,

[0026] Fig. 3 shows a hydraulic circuit diagram of a hydrostatic drive according to a third embodiment of the present invention,

[0027] Fig. 4 shows a hydraulic circuit diagram of a hydrostatic drive according to a fourth embodiment of the present invention,

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[0029] Fig. 5 shows a hydraulic circuit diagram of a hydrostatic drive according to a fifth embodiment of the present invention.

[0030] DETAILED DESCRIPTION

[0031] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0032] Further modifications and variations of the present invention are obvious to a person skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims.

[0033] As shown in Figure 1, the hydraulic system 100 includes a hydraulic pump 2, which is driven by a drive motor (not shown). Preferably, the hydraulic pump 2 is a variable displacement pump. The hydraulic pump 2 is connected to a hydraulic motor 4 via a first line 10 and a second line 11, thus forming a closed circuit. When the hydraulic pump is operating as a pump, the first line 10 functions as a high-pressure line and the second line 11 as a low-pressure line. Conversely, when the hydraulic pump 2 is operating as a motor during deceleration of the mobile machine, the first line 10 functions as a low-pressure line and the second line 11 as a high-pressure line.

[0034] As shown in Figure 1, a feed pump 12 is coupled to the hydraulic pump 2 to compensate for fluid losses that occur during operation in the closed circuit. A feed pressure relief valve 13 limits the feed pressure. The feed pressure is then supplied to the first or second line 10, 11, depending on which line is currently the low-pressure line. This is done by means of the pressure relief valves 88 and 89, which are configured to allow a flow of the feed fluid towards the first or second line 10, 11 if the pressure difference between the feed pressure and the low-pressure side pressure is greater than a predetermined value.

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[0036] The pressure relief valve 88 or 89 can be opened. The line connecting the feed pump 12 to the first and second pressure relief valves 88 and 89 (where the pressure is essentially constant) will be referred to as the feed pressure line in the following description.

[0037] As shown in Figure 1, the supply pressure is fed to two pressure control valves 21 and 22, which are responsible for controlling the swivel angle of the hydraulic pump 2. The pressure control valves 21 and 22 then supply a control pressure to the two chambers of a hydraulic cylinder 20. As already mentioned, the hydraulic cylinder 20 has a first cylinder chamber and a second cylinder chamber that counteracts the first. The first cylinder chamber is connected to the outlet of the first pressure control valve 21 via a first control pressure line. Similarly, the second cylinder chamber is connected to the second pressure control valve 22 via a second control pressure line, which is connected to the control pressure line 23. The pressure reducing valves 21 and 22 are electromagnetically actuated, with the resulting control pressure p in the respective control pressure line being... a (X1) or pb (X2) according to a valve characteristic curve proportional to a control current l aor Ib of the electromagnet a or b. The electromagnetic actuation of the pressure regulating valves 21, 22 thus allows the control currents l to be specified. a , Ib the actuating pressures p a (X1 ), pb (X2) of the cylinder chambers are controlled. For this purpose, the electromagnets a, b of the pressure reducing valves 21 ,22 are connected to an electronic control unit (not shown) via a respective signal line.

[0038] As already mentioned, the control pressure line 23 is connected to the feed pump 12, with the feed pump 12 sitting on the same drive shaft as the hydraulic pump 2, so that the control pressure line 23 can be supplied with control pressure fluid from the feed pump 12.

[0039] A bypass valve 99 is arranged between the high-pressure line 10 and the low-pressure line 11 and is connected to both sides. The bypass valve is a 2 / 2-way valve that is closed in the normal state (i.e., when a certain supply pressure is present in the supply line) and prevents the flow of hydraulic fluid from the first line to the second line (and, of course, in the reverse direction). When the bypass valve 99 is opened (in the illustrated embodiment, when the supply pressure drops below a certain level), it will allow a flow of fluid between the two lines 10 and 11, thus short-circuiting the hydraulic motor 4.

[0040] Page 5 of 12 R. 410715

[0041] With reference to Figures 1 to 5, various methods corresponding to different embodiments of the present invention, which describe different ways of actuating the bypass valve 99, will now be described. The various embodiments have in common that a pressure provided by the feed pump is used directly or indirectly for actuating the bypass valve 99. In particular, in each embodiment, the bypass valve 99 will be controlled taking into account a feed pressure provided by the feed pump 12.

[0042] As shown in Figure 1, according to a first embodiment of the present invention, the supply pressure is used directly to influence the bypass valve 99, so that the hydraulic connection between the bypass valve 99 and the supply pressure line is established when the supply pressure drops below a predetermined pressure. In particular, a hydraulic connection is established between a control pressure port of the bypass valve 30 and the feed pump 12. The control pressure port of the bypass valve 30 is configured, taking into account a pressure at the control pressure port, to determine a position between an open position, in which the bypass valve 99 allows a hydraulic connection between the first and second lines 10, 11, and a closed position, in which the bypass valve 99 prevents a hydraulic connection between the first and second lines 10, 11.Compared to the state of the art, this solution is not only more cost-effective but also more efficient. In particular, the pressure relief valves 88 and 89, which ensure low-pressure replenishment via check valves, provide a certain damping effect / delay of the supply pressure drop. This damping behavior prevents oscillation, fluctuation, and unnecessary activation of the bypass valve 99 between the low-pressure and high-pressure sides 10 and 11.

[0043] As shown in Figure 2, the hydraulic system 100 further comprises a filter device 77, which is configured to filter hydraulic fluid from the supply pressure line and return it to the supply pressure line. Figure 3 shows the hydraulic connection between an inlet of the filter device 77 and the bypass valve 99. Figure 3 also shows the hydraulic connection between an outlet of the filter device 77 and the bypass valve 99.

[0044] As already mentioned, the hydraulic system 100 has a control pressure line 23 that extends from the supply pressure line and is configured to provide pressure from the

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[0046] The supply pressure line is to be routed to a hydraulic cylinder 20. As shown in Figure 4, the hydraulic connection between the control pressure line 23 and the bypass valve 99 is established.

[0047] As shown in Figure 5, according to a fifth embodiment of the present invention, a sequence valve 66 can be arranged along the control pressure line 23. The sequence valve 66 is a 3 / 2-way valve, wherein, without actuation of the sequence valve 66, flow along the control pressure line 23 is prevented and a section of the control pressure line between the hydraulic cylinder 10 and the sequence valve 66 is allowed to drain, and wherein, with actuation of the sequence valve 66, flow along the control pressure line 23 from the feed pump 12 to the hydraulic cylinder 10 is allowed and a section of the control pressure line between the hydraulic cylinder 10 and the sequence valve 66 is prevented from draining. According to this embodiment, the hydraulic connection is established between a section of the control pressure line 23, which is arranged between the sequence valve 66 and the hydraulic cylinder 10, and the bypass valve 99.This solution is particularly advantageous because it allows for the safe shutdown of hydraulic system 100. In fact, if the system needs to be shut down, the sequence valve 66 is no longer actuated, causing the control pressure line 23 to drain, thus reducing the control pressure to near zero. Simultaneously, this low control pressure automatically opens the bypass valve, connecting the first and second lines 10 and 11 together, thereby enabling the safe shutdown of hydraulic system 100 without any additional effort.

[0048] It should be noted that although the five different embodiments always depict hydraulic actuation of the bypass valve 99 (the bypass valve 99 will open when the feed pressure in the feed line drops below a predetermined value), this type of actuation is not necessary. In fact, alternatively, in another embodiment, the pressure in the feed line could be directly detected, and this information could be used by a control unit to electrically actuate the bypass valve (of the same type as in the illustrated embodiments). For this specific embodiment, a logical (or electronic) connection is established between the feed pump 12 and the bypass valve 99, rather than a hydraulic one, so that the bypass valve 99 can be controlled taking into account the feed pressure provided by the feed pump 12.Therefore, this patent application also discloses a control unit (not shown in the images) which is configured to execute a method of the first five described embodiments.

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[0050] Furthermore, a computer program is disclosed which is configured to execute a method according to one of the embodiments. In addition, a machine-readable storage medium containing the computer program is disclosed.

[0051] The described method can be used in various types of machinery. Essentially, it can be used in all machinery that has a hydrostatic drive and a controllable drive motor (such as a diesel engine). Examples of applications include forage harvesters, combine harvesters, snow blowers, and road milling machines.

[0052] While the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to implement various modifications, variations and improvements of the present invention in light of the teaching described above and within the scope of the attached claims without deviating from the scope of protection of the invention.

[0053] Furthermore, the areas in which experts are likely to be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention.

[0054] Accordingly, the invention should not be limited by the specific illustrative embodiments, but only by the scope of protection of the attached claims.

[0055] Page 8 of 12

Claims

R. 410715 1. A method for operating a hydraulic system (100) of a mobile working machine, wherein the hydraulic system (100) is provided with a hydraulic pump (2) which is connected to a hydraulic motor (4) via a first line (10) and a second line (11), further comprising a bypass valve (99) which is positioned between the first line (10) and the second line (11) and is configured to prevent and allow a hydraulic connection between the first and the second line (10, 11) respectively; wherein the hydraulic system (100) further comprises a feed pump (13) which is configured to supply the first and / or the second line (11) with hydraulic fluid so that hydraulic fluid losses which occur during the operation of the hydraulic system (100) can be compensated for;characterized in that the method comprises the following steps: a) Controlling the bypass valve (99) taking into account a feed pressure prevailing downstream of the feed pump (12).

2. Method according to claim 1, wherein in step a) a hydraulic connection is established between a control pressure port of the bypass valve (30) and the feed pump (12), wherein the control pressure port of the bypass valve (99) is configured to determine, taking into account a pressure at the control pressure port, a position of the bypass valve (99) between an open position, in which the bypass valve (99) enables a hydraulic connection between the first and the second line (10, 11), and a closed position, in which the bypass valve (99) prevents a hydraulic connection between the first and the second line (10, 11).

3. Method according to one of claims 1 to 2, wherein the hydraulic system (100) further comprises a first valve (88) arranged between the feed pump and the first line (10), wherein the hydraulic system (100) further comprises a second valve (89) arranged between the feed pump and the second line (11), wherein the first and second valves (88, 89) are configured to provide a hydraulic connection between the feed pump (12) and the first and second lines (10, 11), respectively.

4. Method according to claim 3, wherein the hydraulic system (100) further comprises a feed pressure line connecting the feed pump (2) to the first and the second Page 9 of 12 R. 410715 Valve (88, 89) connects, with the pressure along the feed pressure line being essentially constant.

5. Method according to claim 4, wherein in step a) a hydraulic connection is established between the bypass valve (99) and the feed pressure line.

6. Method according to claim 4, wherein the hydraulic system (100) further comprises a filter device (77) configured to filter pressure medium from the supply pressure line and return it to the supply pressure line, wherein in step a) a hydraulic connection is established between an inlet or an outlet of the filter device (77) and the control pressure port of the bypass valve (99).

7. Method according to claim 4, wherein the hydraulic system (100) further comprises a control pressure line (23) extending from the supply pressure line and configured to direct pressure from the supply pressure line to a hydraulic cylinder (20) responsible for adjusting the hydraulic pump (2), wherein in step a) a hydraulic connection is established between the control pressure line (23) and the control pressure port of the bypass valve (99).

8. Method according to claim 7, wherein a sequence valve (66) is arranged along the control pressure line (23), which is preferably a 3 / 2 way valve, wherein without actuation of the sequence valve (66) flow along the control pressure line (23) is prevented and a section of the control pressure line (23) between the hydraulic cylinder (10) and the sequence valve (66) is allowed to drain, and wherein with actuation of the sequence valve (66) flow along the control pressure line (23) from the feed pump (12) to the hydraulic cylinder (10) is allowed and a section of the control pressure line between the hydraulic cylinder (10) and the sequence valve (66) is prevented from draining, wherein in step (a) the hydraulic connection between a section of the control pressure line (23), which is between the sequence valve (66) and the hydraulic cylinder, and the control pressure port of the bypass valve (99) is established.

9. Control unit which is configured to execute a method according to any one of claims 1 to 8. Page 10 of 12 R. 410715 10. Working machine comprising a hydraulic system (100), wherein the hydraulic system (100) is provided with a first hydraulic machine (2) having an adjustable displacement volume and with a second hydraulic machine, wherein the hydraulic machines (2) are fluidically connected, and wherein the first hydraulic machine (2) can be coupled to a drive machine and the second hydraulic machine can be coupled to at least one driven wheel or chain or axle, wherein the working machine comprises a control unit according to claim 9 11. Computer program configured to execute and / or control the method according to any one of claims 1 to 8.

12. Machine-readable storage medium with a computer program stored thereon according to claim 11. Page 11 of 12

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