A skid steer hydraulic system and control method

Abstract

The present application belongs to the field of loaders, and particularly relates to a hydraulic system and control method of a skid steer loader. The hydraulic system comprises a multi-way valve, an oil outlet of a hydraulic pump I is connected to an oil inlet of the multi-way valve; the oil inlet of the multi-way valve is connected to a pressure-adjustable overflow valve, and the pressure-adjustable overflow valve is connected to a hydraulic oil tank; an oil outlet of a hydraulic pump II is connected to a hydraulic control reversing valve group, and the hydraulic control reversing valve group is connected to a confluence port of the multi-way valve; an oil outlet of a hydraulic pump III is connected to an electromagnetic reversing valve I, and the oil outlet of the electromagnetic reversing valve I is respectively connected to a control port of the hydraulic control reversing valve group and a control port of the pressure-adjustable overflow valve; the electromagnetic reversing valve I is connected to a low-pressure overflow valve, and the low-pressure overflow valve is connected to the hydraulic oil tank. The present application controls the pressure and flow of the hydraulic system, so that the whole machine realizes four basic working states, keeps the hydraulic system of the whole machine within the power range of an engine, and can realize balanced or high-pressure or high-flow working states according to selection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of loaders, and particularly relates to a hydraulic system and control method of a skid steer loader. BACKGROUND

[0002] The skid steer loader is a special chassis equipment of the wheeled type, which realizes the steering of the vehicle by using the linear speed difference of the wheels on both sides. It is mainly used in the occasions where the work site is narrow, the ground is uneven, and the work content is frequently changed. In order to meet different working conditions, the skid steer loader is configured with various implements, such as a sweeper, a milling machine, etc. Different implements have different requirements for the hydraulic system. Some implements have a large requirement for the system flow, and require the implement to work quickly. Some implements have a large requirement for the system pressure, and require the implement to overcome heavy load. Generally, the skid steer loader can only meet the high flow requirement, and cannot meet the high pressure requirement. At the same time, the traveling system of the skid steer loader is a closed hydrostatic system, which also needs to consume power when traveling. Generally speaking, the skid steer loader prioritizes the working system. When the working system occupies a large power, the traveling system will have a power control valve to control the power of the traveling system, so as to ensure that the engine does not stall. However, the common result is that the whole machine can only work, and cannot travel. If you want to travel, you must reduce the power of the working system. This brings inconvenience to the actual work. SUMMARY

[0003] In order to overcome the shortcomings of the prior art, the present application provides a hydraulic system and control method of a skid steer loader. The present application controls the pressure and flow of the hydraulic system, so that the whole machine realizes four basic working states, and keeps the hydraulic system of the whole machine within the engine power range at all times. The balanced or high pressure or high flow working state can be realized according to the selection.

[0004] The present application is realized by the following technical scheme: a hydraulic system of a skid steer loader, comprising a multi-way valve, a working device connected to the oil outlet of the multi-way valve, and a hydraulic oil tank connected to the oil return port of the multi-way valve; further comprising a hydraulic pump I, a hydraulic pump II, and a hydraulic pump III connected to the output port of the engine, the oil suction ports of the hydraulic pump I, the hydraulic pump II, and the hydraulic pump III being connected to the hydraulic oil tank; the oil outlet of the hydraulic pump I being connected to the oil inlet of the multi-way valve; the oil inlet of the multi-way valve being connected to a pressure-adjustable overflow valve, the pressure-adjustable overflow valve being connected to the hydraulic oil tank; the oil outlet of the hydraulic pump II being connected to a hydraulic control reversing valve group, the hydraulic control reversing valve group being connected to the confluence port of the multi-way valve; the oil outlet of the hydraulic pump III being connected to an electromagnetic reversing valve I, the oil outlets of the electromagnetic reversing valve I being respectively connected to the control port of the hydraulic control reversing valve group and the control port of the pressure-adjustable overflow valve; the electromagnetic reversing valve I being connected to a low-pressure overflow valve, the low-pressure overflow valve being connected to the hydraulic oil tank.

[0005] Further, the pilot valve and the shuttle valve are further included, the oil inlet of the pilot valve is connected with the walking pilot oil source, the oil outlet of the pilot valve is connected with the control port of the walking system and the oil inlet of the shuttle valve group respectively, and the oil return port of the pilot valve is connected with the hydraulic oil tank; the oil outlet of the shuttle valve group is connected with the electromagnetic reversing valve II, the oil outlet of the electromagnetic reversing valve II is connected with the second oil inlet of the shuttle valve; the oil outlet of the electromagnetic reversing valve I is connected with the first oil inlet of the shuttle valve, and the oil outlet of the shuttle valve is connected with the control port of the hydraulic control reversing valve group.

[0006] Further, the electromagnetic reversing valve II is a two-position two-way reversing valve; the electromagnetic reversing valve II is in the initial position when no electricity is supplied, the oil inlet of the electromagnetic reversing valve II is communicated with the oil outlet of the electromagnetic reversing valve II when the electromagnetic reversing valve II is in the initial position; the electromagnetic reversing valve II is in the working position when electricity is supplied, and the oil outlet of the electromagnetic reversing valve II is unidirectionally communicated with the oil inlet of the electromagnetic reversing valve II when the electromagnetic reversing valve II is in the working position.

[0007] Further, the hydraulic control reversing valve group includes the hydraulic control reversing valve and the check valve, the oil inlets of the hydraulic control reversing valve and the check valve are connected with the oil outlet of the hydraulic pump II respectively, the oil outlet of the hydraulic control reversing valve is connected with the hydraulic oil tank, and the oil outlet of the check valve is connected with the confluence port of the multi-way valve.

[0008] Further, the hydraulic control reversing valve is a two-position two-way reversing valve; the hydraulic control reversing valve is in the initial position under the spring pressure, the oil outlet of the hydraulic control reversing valve is unidirectionally communicated with the oil inlet of the hydraulic control reversing valve when the hydraulic control reversing valve is in the initial position; the hydraulic control reversing valve is in the working position when the control port of the hydraulic control reversing valve has pressure and can overcome the spring pressure to push the valve core to change position, and the oil inlet of the hydraulic control reversing valve is communicated with the oil outlet of the hydraulic control reversing valve when the hydraulic control reversing valve is in the working position.

[0009] Further, the oil outlet of the check valve is connected with the overflow valve, and the overflow valve is connected with the hydraulic oil tank.

[0010] Further, the electromagnetic reversing valve I is a two-position three-way reversing valve; the electromagnetic reversing valve I is in the initial position when no electricity is supplied, the oil outlet of the electromagnetic reversing valve I is communicated with the oil return port of the electromagnetic reversing valve I when the electromagnetic reversing valve I is in the initial position; the electromagnetic reversing valve I is in the working position when electricity is supplied, and the oil inlet of the electromagnetic reversing valve I is communicated with the oil outlet of the electromagnetic reversing valve I when the electromagnetic reversing valve I is in the working position.

[0011] Further, the hydraulic pump I, the hydraulic pump II and the hydraulic pump III are connected in parallel through the connecting shaft.

[0012] The application further provides a control method of the hydraulic system of the skid steer loader, when the vehicle engine is started, the hydraulic pump I supplies oil to the multi-way valve.

[0013] When the working device needs high pressure work, the inlet of electromagnetic reversing valve I is communicated with the outlet of electromagnetic reversing valve I, the hydraulic oil outputted by hydraulic pump III acts on the control port of pressure adjustable overflow valve, at this time, the control port of hydraulic control reversing valve group also receives the hydraulic oil from shuttle valve, the hydraulic oil outputted by hydraulic pump II returns to hydraulic oil tank through hydraulic control reversing valve group, and the pressure of pressure adjustable overflow valve is increased; at this time, the working device works under the flow provided by hydraulic pump I, and the working pressure is the sum of the initial pressure of pressure adjustable overflow valve and the set pressure of low pressure overflow valve;

[0014] When the walking system does not work:

[0015] The inlet of electromagnetic reversing valve I is not communicated with the outlet of electromagnetic reversing valve I, the hydraulic oil outputted by hydraulic pump II and the hydraulic oil outputted by hydraulic pump I are combined to provide the multi-way valve, and the flow is increased; at this time, the working device works under the flow provided by hydraulic pump I and hydraulic pump II, and the working pressure is the initial pressure of pressure adjustable overflow valve;

[0016] When the walking system works:

[0017] The inlet of electromagnetic reversing valve I is not communicated with the outlet of electromagnetic reversing valve I, and the inlet of electromagnetic reversing valve II is not communicated with the outlet of electromagnetic reversing valve II, the hydraulic oil outputted by hydraulic pump II and the hydraulic oil outputted by hydraulic pump I are combined to provide the multi-way valve, and the flow is increased; at this time, the working device works under the flow provided by hydraulic pump I and hydraulic pump II, and the working pressure is the initial pressure of pressure adjustable overflow valve;

[0018] The inlet of electromagnetic reversing valve I is not communicated with the outlet of electromagnetic reversing valve I, and the inlet of electromagnetic reversing valve II is communicated with the outlet of electromagnetic reversing valve II, the hydraulic oil outputted by hydraulic pump II returns to hydraulic oil tank through hydraulic control reversing valve group; at this time, the working device works under the flow provided by hydraulic pump I, and the working pressure is the initial pressure of pressure adjustable overflow valve.

[0019] The working device of the hydraulic system can provide working oil source by hydraulic pump I and hydraulic pump II, the whole machine works under high flow and standard pressure, and has high working efficiency. Meanwhile, in order to meet different working conditions, for the machine tool with high system pressure requirement, the hydraulic system can be switched to standard flow and high pressure working state.

[0020] The hydraulic system also takes into account the use of the traveling system; when the traveling system works, it can be automatically switched to make the whole machine work under standard flow and standard pressure, and the remaining power can be used by the traveling system, so that the whole machine is in the working condition of taking into account work and travel. At the same time, the direct connection between the traveling system and the working system can also be cut off, so that the whole machine working system continues to work under large flow and standard pressure, and the remaining power can be used by the traveling system. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The hydraulic schematic diagram of the present application;

[0022] In the figure, 1, hydraulic pump I, 2, hydraulic pump II, 3, hydraulic pump III, 4, hydraulic oil tank, 5, electromagnetic reversing valve I, 51, low-pressure overflow valve, 6, hydraulic control reversing valve group, 61, hydraulic control reversing valve, 62, check valve, 63, overflow valve, 7, multi-way valve, 71, working device, 8, pilot valve, 81, pilot oil source, 82, traveling system, 9, shuttle valve group, 10, electromagnetic reversing valve II, 11, shuttle valve, 12, pressure-adjustable overflow valve. DETAILED DESCRIPTION

[0023] The present application will be further described below according to the drawings and examples.

[0024] Example one

[0025] As Figure 1 shown, a hydraulic system of a skid steer loader, comprising a multi-way valve 7, the oil outlet of the multi-way valve 7 is connected with a working device 71, and the oil return port of the multi-way valve 7 is connected with a hydraulic oil tank 4.

[0026] The hydraulic pump I 1, the hydraulic pump II 2 and the hydraulic pump III 3 are connected in parallel through a connecting shaft and are connected with the output port of an engine. The oil suction ports of the hydraulic pump I 1, the hydraulic pump II 2 and the hydraulic pump III 3 are connected with the hydraulic oil tank 4.

[0027] The oil outlet of the hydraulic pump I 1 is connected with the oil inlet of the multi-way valve 7, the oil inlet of the multi-way valve 7 is connected with a pressure-adjustable overflow valve 12, and the pressure-adjustable overflow valve 12 is connected with the hydraulic oil tank 4.

[0028] The oil outlet of the hydraulic pump II 2 is connected with a hydraulic control reversing valve group 6, and the hydraulic control reversing valve group 6 is connected with the converging port of the multi-way valve 7. Specifically, the hydraulic control reversing valve group 6 comprises a hydraulic control reversing valve 61, a check valve 62 and an overflow valve 63. The oil inlets of the hydraulic control reversing valve 61 and the check valve 62 are respectively connected with the oil outlet of the hydraulic pump II 2, the oil outlet of the hydraulic control reversing valve 61 is connected with the hydraulic oil tank 4, and the oil outlet of the check valve 62 is connected with the converging port of the multi-way valve 7. The oil outlet of the check valve 62 is also connected with the overflow valve 63, and the overflow valve 63 is connected with the hydraulic oil tank 4.

[0029] The hydraulic control reversing valve 61 is a two-position two-way reversing valve; the hydraulic control reversing valve 61 is in the initial position under the spring pressure, when the hydraulic control reversing valve 61 is in the initial position, the oil outlet of the hydraulic control reversing valve 61 is one-way communicated to the oil inlet of the hydraulic control reversing valve 61. When the control port of the hydraulic control reversing valve 61 has pressure and can overcome the spring pressure to push the valve core to change position, the hydraulic control reversing valve 61 is in the working position, when the hydraulic control reversing valve 61 is in the working position, the oil inlet of the hydraulic control reversing valve 61 is communicated with the oil outlet of the hydraulic control reversing valve 61.

[0030] The oil outlet of the hydraulic pump III 3 is connected with the electromagnetic reversing valve I 5, the oil outlet of the electromagnetic reversing valve I 5 is connected with the control port of the hydraulic control reversing valve group 6 (the control port of the hydraulic control reversing valve group 6 is the control port of the hydraulic control reversing valve 61) and the control port of the pressure adjustable overflow valve 12 respectively; the electromagnetic reversing valve I 5 is connected with the low pressure overflow valve 51, and the low pressure overflow valve 51 is connected with the hydraulic oil tank 4.

[0031] The electromagnetic reversing valve I 5 is a two-position three-way reversing valve; the electromagnetic reversing valve I 5 is in the initial position when not powered, when the electromagnetic reversing valve I 5 is in the initial position, the oil outlet of the electromagnetic reversing valve I 5 is communicated with the oil return port of the electromagnetic reversing valve I 5; the electromagnetic reversing valve I 5 is in the working position when powered, when the electromagnetic reversing valve I 5 is in the working position, the oil inlet of the electromagnetic reversing valve I 5 is communicated with the oil outlet of the electromagnetic reversing valve I 5.

[0032] The hydraulic system further comprises a pilot valve 8 and a shuttle valve 11. The oil inlet of the pilot valve 8 is connected with the walking pilot oil source 81, the oil outlet of the pilot valve 8 is connected with the control port of the walking system 82 and the oil inlet of the shuttle valve group 9 respectively, and the oil return port of the pilot valve 8 is connected with the hydraulic oil tank 4. The oil outlet of the shuttle valve group 9 is connected with the electromagnetic reversing valve II 10, and the oil outlet of the electromagnetic reversing valve II 10 is connected with the second oil inlet of the shuttle valve 11. The oil outlet of the electromagnetic reversing valve I 5 is connected with the first oil inlet of the shuttle valve 11, and the oil outlet of the shuttle valve 11 is connected with the control port of the hydraulic control reversing valve group 6 (the control port of the hydraulic control reversing valve group 6 is the control port of the hydraulic control reversing valve 61).

[0033] The electromagnetic reversing valve II 10 is a two-position two-way reversing valve; the electromagnetic reversing valve II 10 is in the initial position when not powered, when the electromagnetic reversing valve II 10 is in the initial position, the oil inlet of the electromagnetic reversing valve II 10 is communicated with the oil outlet of the electromagnetic reversing valve II 10; the electromagnetic reversing valve II 10 is in the working position when powered, when the electromagnetic reversing valve II 10 is in the working position, the oil outlet of the electromagnetic reversing valve II 10 is one-way communicated to the oil inlet of the electromagnetic reversing valve II 10.

[0034] Embodiment two

[0035] The application further provides a control method of the hydraulic system of the skid steer loader, when the vehicle engine is started; the hydraulic pump I 1 supplies oil to the multi-way valve 7.

[0036] When the work device 71 needs high pressure work, the electromagnetic reversing valve I 5 is powered, the electromagnetic reversing valve I 5 is in the working position, and the oil inlet of the electromagnetic reversing valve I 5 is in communication with the oil outlet of the electromagnetic reversing valve I 5. At this time, the hydraulic oil output by the hydraulic pump III 3 acts on the control port of the pressure adjustable overflow valve 12, and the pressure of the pressure adjustable overflow valve 12 rises. At this time, the working pressure of the hydraulic system is the sum of the initial pressure of the pressure adjustable overflow valve 12 and the pressure set by the low pressure overflow valve 51. At the same time, the control port of the hydraulic control reversing valve group 6 (the control port of the hydraulic control reversing valve group 6 is the control port of the hydraulic control reversing valve 61) receives the hydraulic oil from the shuttle valve 11, and the hydraulic oil output by the outlet of the shuttle valve 11 acts on the control port of the hydraulic control reversing valve 61, so that the spool of the hydraulic control reversing valve 61 moves against the spring pressure. When the hydraulic control reversing valve 61 is in the working position, the oil inlet of the hydraulic control reversing valve 61 is in communication with the oil outlet of the hydraulic control reversing valve 61. The hydraulic oil output by the hydraulic pump II 2 returns to the hydraulic oil tank 4 through the oil outlet of the hydraulic control reversing valve 61, and the work device 71 works only under the flow provided by the hydraulic pump I 1. At this time, the whole machine works under standard flow and high pressure, and the remaining power can be used by the walking system, which is controlled by the walking system power control valve. The whole machine is in the standard flow and high pressure working condition, and works preferentially.

[0037] The hydraulic oil acting on the control port of the hydraulic control reversing valve 61 is the hydraulic oil output by the hydraulic pump III 3 through the outlet of the shuttle valve 11 when the walking system does not work. When the walking system works, if the electromagnetic reversing valve II 10 is in the initial position, the oil inlet of the electromagnetic reversing valve II 10 is in communication with the oil outlet of the electromagnetic reversing valve II 10, and at this time, the hydraulic oil with greater pressure selected by the shuttle valve 11 acts on the control port of the hydraulic control reversing valve 61 through the outlet of the shuttle valve 11. In actual work, the hydraulic pressure of the hydraulic oil output by the hydraulic pump III 3 is greater than the hydraulic pressure of the hydraulic oil output from the walking system through the electromagnetic reversing valve II 10, that is, the hydraulic oil output by the hydraulic pump III 3 acts on the control port of the hydraulic control reversing valve 61 through the outlet of the shuttle valve 11. If the electromagnetic reversing valve II 10 is in the working position, the oil outlet of the electromagnetic reversing valve II 10 is unidirectionally communicated to the oil inlet of the electromagnetic reversing valve II 10, and at this time, the hydraulic oil output by the hydraulic pump III 3 acts on the control port of the hydraulic control reversing valve 61 through the outlet of the shuttle valve 11.

[0038] In the case that the walking system does not work:

[0039] When the electromagnetic reversing valve 15 is in the initial position without electricity, the inlet of the electromagnetic reversing valve 15 is not communicated with the outlet of the electromagnetic reversing valve 15. At this time, the control port of the hydraulic control reversing valve 61 is not acted by the hydraulic pressure, and the hydraulic control reversing valve 61 is in the initial position, and the outlet of the hydraulic control reversing valve 61 is communicated with the inlet of the hydraulic control reversing valve 61 in one way. The hydraulic oil outputted by the hydraulic pump 12 is combined with the hydraulic oil outputted by the hydraulic pump 11 to provide the multi-way valve 7, so as to realize the increase of the flow. At this time, the working device 71 works under the flow provided by the hydraulic pump 11 and the hydraulic pump 12. Since the control port of the pressure adjustable overflow valve 12 is not acted by the hydraulic pressure, the pressure value of the pressure adjustable overflow valve 12 is unchanged, and the working pressure of the hydraulic system is the initial pressure of the pressure adjustable overflow valve 12. The hydraulic pump 1 and the hydraulic pump 2 provide the working oil source, and the whole machine works under the high flow and the standard pressure, and has high working efficiency.

[0040] When the walking system works:

[0041] When the electromagnetic reversing valve 15 is in the initial position without electricity, the inlet of the electromagnetic reversing valve 15 is not communicated with the outlet of the electromagnetic reversing valve 15. At the same time, the electromagnetic reversing valve 110 is in the working position with electricity, and the inlet of the electromagnetic reversing valve 110 is not communicated with the outlet of the electromagnetic reversing valve 110. At this time, the control port of the hydraulic control reversing valve 61 is not acted by the hydraulic pressure, and the hydraulic control reversing valve 61 is in the initial position, and the outlet of the hydraulic control reversing valve 61 is communicated with the inlet of the hydraulic control reversing valve 61 in one way. The hydraulic oil outputted by the hydraulic pump 12 is combined with the hydraulic oil outputted by the hydraulic pump 11 to provide the multi-way valve 7, so as to realize the increase of the flow. At this time, the working device 71 works under the flow provided by the hydraulic pump 11 and the hydraulic pump 12. Since the control port of the pressure adjustable overflow valve 12 is not acted by the hydraulic pressure, the pressure value of the pressure adjustable overflow valve 12 is unchanged, and the working pressure of the hydraulic system is the initial pressure of the pressure adjustable overflow valve 12. At this time, the hydraulic pump 1 and the hydraulic pump 2 provide the working oil source, and the whole machine works under the high flow and the standard pressure, and the remaining power can be used by the walking system, which is controlled by the walking system power control valve. The whole machine works under the high flow and the standard pressure, and works preferentially.

[0042] When the electromagnetic reversing valve 15 is not powered and is in the initial position, the oil inlet of the electromagnetic reversing valve 15 is not communicated with the oil outlet of the electromagnetic reversing valve 15, and at the same time, the electromagnetic reversing valve 110 is not powered and is in the initial position, and the oil inlet of the electromagnetic reversing valve 110 is communicated with the oil outlet of the electromagnetic reversing valve 110. The hydraulic oil of the traveling system flows to the control port of the hydraulic control reversing valve 61 through the electromagnetic reversing valve 110 and the shuttle valve 11 in sequence, the hydraulic oil output by the oil outlet of the shuttle valve 11 acts on the control port of the hydraulic control reversing valve 61, the spool of the hydraulic control reversing valve 61 moves against the spring pressure, and when the hydraulic control reversing valve 61 is in the working position, the oil inlet of the hydraulic control reversing valve 61 is communicated with the oil outlet of the hydraulic control reversing valve 61. The hydraulic oil output by the hydraulic pump 2 returns to the hydraulic oil tank 4 through the hydraulic control reversing valve group 6. At this time, the working device 71 works only under the flow provided by the hydraulic pump 11. Since the control port of the pressure-adjustable overflow valve 12 is not subjected to the hydraulic pressure, the pressure value of the pressure-adjustable overflow valve 12 is unchanged, and at this time, the working pressure of the hydraulic system is the initial pressure of the pressure-adjustable overflow valve 12. At this time, the whole machine working system works under the standard flow and the standard pressure, and the remaining power can be used by the traveling system, and the whole machine is in the working condition of giving consideration to work and travel.

[0043] The technical effect of the embodiment is exemplified as follows:

[0044] In a conventional vehicle, if the selected hydraulic rated power is 60 kW and the hydraulic system set pressure is 20 MPa, the hydraulic system flow must be below 180 L / min, otherwise the maximum hydraulic power will be greater than the engine power, which will cause the engine to drop speed until it is turned off. For example, if the vehicle standard flow is 90 L / min and the combined flow is 90 L / min, when the vehicle works under the standard flow and the standard pressure, the hydraulic system power is 30 kW; when the vehicle works under the large flow and the standard pressure, the hydraulic system power is 60 kW.

[0045] With the system of the embodiment, when the vehicle does not need to travel, the large flow and the standard pressure working state can be selected, that is, if the selected hydraulic system rated power is 60 kW, the hydraulic system flow is 180 L / min, and the set pressure of the overflow valve is 20 MPa. When the vehicle needs to travel, the system can automatically switch to the standard flow state, that is, the hydraulic system flow is 90 L / min, the set pressure of the overflow valve is 20 MPa, and the working hydraulic system power is 30 kW, at this time, the traveling system can obtain 30 kW, when the vehicle does not need to travel, the system automatically switches to the large flow state. When it is desired to maintain the large flow working state while traveling, the automatic switching function can be closed, at this time, the system gives priority to work, and the remaining power is used by the traveling system. When high pressure is needed, the working system pressure is increased, the system can automatically switch to the standard flow state, that is, the hydraulic system flow is 90 L / min, the set pressure of the overflow valve is 26 MPa, and the working hydraulic system power is 39 kW, at this time, the traveling system can still obtain 21 kW, ensuring the operation of the traveling system.

[0046] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present application are within the scope of the technical solution of the present application.

Claims

1. A hydraulic system for a skid steer loader, comprising a multi-way valve (7), the outlet of which is connected to a working device (71), and the return port of which is connected to a hydraulic oil tank (4); further comprising hydraulic pump I (1), hydraulic pump II (2), and hydraulic pump III (3) connected to the engine output port, the suction ports of which are connected to the hydraulic oil tank (4); the outlet of the hydraulic pump I (1) is connected to the inlet of the multi-way valve (7); characterized in that: The inlet of the multi-way valve (7) is connected to a pressure-adjustable relief valve (12), which is connected to the hydraulic oil tank (4); the outlet of the hydraulic pump II (2) is connected to a hydraulic control directional valve group (6), which is connected to the confluence port of the multi-way valve (7); the outlet of the hydraulic pump III (3) is connected to a solenoid directional valve I (5), which is connected to the control port of the hydraulic control directional valve group (6) and the control port of the pressure-adjustable relief valve (12) respectively; the solenoid directional valve I (5) is connected to a low-pressure relief valve (51), which is connected to the hydraulic oil tank (4); It also includes a pilot valve (8) and a shuttle valve (11). The inlet of the pilot valve (8) is connected to the travel pilot oil source (81). The outlet of the pilot valve (8) is connected to the control port of the travel system (82) and the inlet of the shuttle valve group (9). The return port of the pilot valve (8) is connected to the hydraulic oil tank (4). The outlet of the shuttle valve group (9) is connected to the solenoid directional valve II (10). The outlet of the solenoid directional valve II (10) is connected to the second inlet of the shuttle valve (11). The outlet of the solenoid directional valve I (5) is connected to the first inlet of the shuttle valve (11). The outlet of the shuttle valve (11) is connected to the control port of the hydraulic directional valve group (6).

2. The hydraulic system for a skid steer loader according to claim 1, characterized in that: The electromagnetic directional valve II (10) is a two-position two-way directional valve. When the electromagnetic directional valve II (10) is not energized, it is in the initial position. When the electromagnetic directional valve II (10) is in the initial position, the oil inlet of the electromagnetic directional valve II (10) is connected to the oil outlet of the electromagnetic directional valve II (10). When the electromagnetic directional valve II (10) is energized, it is in the working position. When the electromagnetic directional valve II (10) is in the working position, the oil outlet of the electromagnetic directional valve II (10) is unidirectionally connected to the oil inlet of the electromagnetic directional valve II (10).

3. The hydraulic system for a skid steer loader according to claim 1, characterized in that: The hydraulic directional valve group (6) includes a hydraulic directional valve (61) and a check valve (62). The oil inlet of the hydraulic directional valve (61) and the oil inlet of the check valve (62) are respectively connected to the oil outlet of the hydraulic pump II (2). The oil outlet of the hydraulic directional valve (61) is connected to the hydraulic oil tank (4), and the oil outlet of the check valve (62) is connected to the confluence port of the multi-way valve (7).

4. The hydraulic system for a skid steer loader according to claim 3, characterized in that: The hydraulic control directional valve (61) is a two-position two-way directional valve. The hydraulic control directional valve (61) is in the initial position under the action of spring pressure. When the hydraulic control directional valve (61) is in the initial position, the oil outlet of the hydraulic control directional valve (61) is unidirectionally connected to the oil inlet of the hydraulic control directional valve (61). When the control port of the hydraulic control directional valve (61) is pressurized and can overcome the spring pressure to push the valve core to change position, it is in the working position. When the hydraulic control directional valve (61) is in the working position, the oil inlet of the hydraulic control directional valve (61) is connected to the oil outlet of the hydraulic control directional valve (61).

5. A skid steer loader hydraulic system according to claim 3, characterized in that: The outlet of the one-way valve (62) is connected to an overflow valve (63), and the overflow valve (63) is connected to the hydraulic oil tank (4).

6. A skid steer loader hydraulic system according to claim 1, characterized in that: The solenoid directional valve I (5) is a two-position three-way directional valve; when the solenoid directional valve I (5) is not energized, it is in the initial position. When the solenoid directional valve I (5) is in the initial position, the oil outlet of the solenoid directional valve I (5) is connected to the oil return port of the solenoid directional valve I (5); when the solenoid directional valve I (5) is energized, it is in the working position. When the solenoid directional valve I (5) is in the working position, the oil inlet of the solenoid directional valve I (5) is connected to the oil outlet of the solenoid directional valve I (5).

7. A skid steer loader hydraulic system according to claim 1, characterized in that: The hydraulic pumps I (1), II (2), and III (3) are connected in parallel via a connecting shaft.

8. A control method for a skid steer loader hydraulic system, employing the skid steer loader hydraulic system as described in any one of claims 1-7, characterized in that: When the vehicle engine is started, hydraulic pump I (1) supplies oil to the multi-way valve (7); Regardless of whether the walking system is working, when the working device (71) needs to work under high pressure, the oil inlet of the solenoid directional valve I (5) is connected to the oil outlet of the solenoid directional valve I (5), and the hydraulic oil output by the hydraulic pump III (3) acts on the control port of the pressure adjustable relief valve (12). At this time, the control port of the hydraulic control directional valve group (6) also receives hydraulic oil from the shuttle valve (11). The hydraulic oil output by the hydraulic pump II (2) returns to the hydraulic oil tank (4) through the hydraulic control directional valve group (6), and the pressure of the pressure adjustable relief valve (12) increases. At this time, the working device (71) works under the flow provided by the hydraulic pump I (1), and the working pressure is the sum of the initial pressure of the pressure adjustable relief valve (12) and the pressure set by the low-pressure relief valve (51). When the walking system is not working: The oil inlet of the electromagnetic reversing valve I (5) and the oil outlet of the electromagnetic reversing valve I (5) are not connected. The hydraulic oil output by the hydraulic pump II (2) and the hydraulic oil output by the hydraulic pump I (1) are combined and supplied to the multi-way valve (7) to increase the flow rate. At this time, the working device (71) works under the flow rate provided by the hydraulic pump I (1) and the hydraulic pump II (2), and the working pressure is the initial pressure of the pressure adjustable relief valve (12). When the walking system is working: The oil inlet of the electromagnetic directional valve I (5) is not connected to the oil outlet of the electromagnetic directional valve I (5), and at the same time, the oil inlet of the electromagnetic directional valve II (10) is not connected to the oil outlet of the electromagnetic directional valve II (10). The hydraulic oil output by the hydraulic pump II (2) and the hydraulic oil output by the hydraulic pump I (1) are combined and supplied to the multi-way valve (7) to increase the flow rate. At this time, the working device (71) works under the flow rate provided by the hydraulic pump I (1) and the hydraulic pump II (2), and the working pressure is the initial pressure of the pressure adjustable relief valve (12). The oil inlet of the electromagnetic directional valve I (5) is not connected to the oil outlet of the electromagnetic directional valve I (5), while the oil inlet of the electromagnetic directional valve II (10) is connected to the oil outlet of the electromagnetic directional valve II (10). The hydraulic oil output by the hydraulic pump II (2) returns to the hydraulic oil tank (4) through the hydraulic control directional valve group (6). At this time, the working device (71) works under the flow provided by the hydraulic pump I (1), and the working pressure is the initial pressure of the pressure adjustable relief valve (12).

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