Hydraulic control system and corresponding mobile work equipment

Abstract

A hydraulic control system comprises: a first hydraulic actuator; at least one second hydraulic actuator with an oil inlet and a feedback port; a pressure flow control variable pump as a first pump, having a variable pump outlet and a flow control port; a second pump, whose outlet is hydraulically connected to the oil inlet through a one-way valve; and a logic control hydraulic subsystem, which at least includes a 2 / 2 proportional valve, a throttle and a pressure relief valve, the first hydraulic port of the 2 / 2 proportional valve is hydraulically connected between the second pump outlet and the one-way valve, the second hydraulic port is hydraulically connected to the oil return pipeline, the first control port is hydraulically connected between the one-way valve and the oil inlet or the first hydraulic connection point, the second control port is hydraulically connected to the feedback port or the second hydraulic connection point through the throttle, the predetermined displacement state of the first pump is detected based on the pressure difference between the first and second hydraulic connection points, one end of the pressure relief valve is hydraulically connected between the second control port and the throttle, and the other end is hydraulically connected to the oil return pipeline. It is reliable and comfortable.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic control system and a corresponding mobile work equipment. BACKGROUND

[0002] Compared with other types of transmission devices such as mechanical transmission devices, hydraulic transmission devices have many advantages such as small size, light weight, sensitive action, frequent start and reversal, simple operation and easy control. Therefore, they are widely used in many mechanical devices at present.

[0003] Especially in loaders, excavators, forklifts and the like, the use of hydraulic control systems has more obvious advantages. In such a hydraulic control system, two parallel hydraulic pumps are usually provided to reduce throttling loss and overflow loss. One of them is preferably a gear pump with a fixed displacement, and the other is a variable pump. These pumps can deliver hydraulic oil to a plurality of hydraulic actuators. The hydraulic actuators include, for example, a travel drive device, a hydraulic cylinder of a hydraulic arm, and a steering device for adjusting the travel direction.

[0004] For safety reasons and the like, each hydraulic actuator has a different priority level. For example, the steering device must be supplied with hydraulic oil in priority to other hydraulic actuators, so that the vehicle can always be steered.

[0005] However, in the current hydraulic control system, there are still problems such as poor comfort for the operator and low fuel efficiency. Therefore, further improvement is needed for the existing hydraulic control system. SUMMARY

[0006] The purpose of the present application is to provide a hydraulic control system which is efficient and reliable, simple in structure, and better in operation comfort, and a corresponding mobile work equipment.

[0007] According to a first aspect of the present application, there is provided a hydraulic control system, comprising: a first hydraulic actuator; at least one second hydraulic actuator having an oil inlet and a feedback port adapted to feedback a load condition of the second hydraulic actuator; a pressure-flow control variable pump as a first pump having a variable pump outlet and a flow control port; a second pump, an outlet of which is hydraulically connected to the oil inlet of the second hydraulic actuator through a check valve to allow hydraulic oil to flow from the second pump to the second hydraulic actuator only; and a logic control hydraulic subsystem for controlling the first hydraulic actuator and / or the second hydraulic actuator, which at least comprises a 2 / 2 proportional valve, a restrictor and a pressure relief valve, wherein the 2 / 2 proportional valve has a first hydraulic port, a second hydraulic port, a first control port and a second control port, the first hydraulic port is hydraulically connected between the outlet of the second pump and the check valve, the second hydraulic port is hydraulically connected to a return oil line, the first control port is hydraulically connected between the check valve and the oil inlet of the second hydraulic actuator or is hydraulically connected to a first hydraulic connection point, the second control port is hydraulically connected to the feedback port of the second hydraulic actuator through the restrictor or is hydraulically connected to a second hydraulic connection point, a pressure difference between the first hydraulic connection point and the second hydraulic connection point is adapted to detect a predetermined displacement state of the pressure-flow control variable pump, one end of the pressure relief valve is hydraulically connected between the second control port and the restrictor, and the other end of the pressure relief valve is hydraulically connected to the return oil line.

[0008] According to an optional embodiment of the present application, the hydraulic control system further comprises a priority valve having an inlet, a first outlet and a second outlet, wherein the variable pump outlet is hydraulically connected to the inlet of the priority valve, the first outlet of the priority valve is hydraulically connected to the oil inlet of the first hydraulic actuator, and the second outlet of the priority valve is hydraulically connected to the oil inlet of the second hydraulic actuator; and the logic control hydraulic subsystem further comprises a shuttle valve, a first inlet of the shuttle valve is hydraulically connected between the restrictor and the feedback port of the second hydraulic actuator or the second hydraulic connection point, a second inlet of the shuttle valve is hydraulically connected to a feedback port of the first hydraulic actuator adapted to feedback a load condition of the first hydraulic actuator, and an outlet of the shuttle valve is hydraulically connected to the flow control port.

[0009] According to an optional embodiment of the present application, the first hydraulic connection point is the variable pump outlet or the inlet of the priority valve; and / or the second hydraulic connection point is the flow control port or the second outlet of the priority valve; and / or the predetermined displacement state is a maximum displacement state.

[0010] According to an optional embodiment of the present application, the second pump is a variable pump; and / or a hydraulic system for supplying hydraulic oil to the first hydraulic actuator is hydraulically separated from a hydraulic system for supplying hydraulic oil to the second hydraulic actuator.

[0011] According to a second aspect of the present application, there is provided a mobile working machine equipped with the hydraulic control system.

[0012] The hydraulic control system of the present application is simple in structure, high in reliability, good in operation comfort, and capable of avoiding throttling loss and overflow loss. BRIEF DESCRIPTION OF DRAWINGS

[0013] The principles, features and advantages of the present application will be better understood by referring to the following detailed description in conjunction with the accompanying drawings in which:

[0014] Figure 1 A system diagram of a hydraulic control system according to an exemplary embodiment of the present application is shown by way of example for a loader. DETAILED DESCRIPTION

[0015] In order to make the technical problems to be solved by the present application, the technical solutions and the beneficial technical effects more clear, the present application will be further described in detail below in conjunction with the drawings and multiple embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the protection scope of the present application.

[0016] Figure 1 A system diagram of a hydraulic control system according to an exemplary embodiment of the present application is shown by way of example for a loader.

[0017] As shown in Figure 1 , the hydraulic control system of the loader mainly comprises a load-sensing pressure flow control variable pump 1, a steering unit 2, a fixed flow pump 3, preferably a gear pump, a priority valve 4, a pilot valve 5, at least one hydraulic working unit 6, and a logic control hydraulic subsystem 7. The steering unit 2 is used to adjust the driving direction of the loader. The at least one hydraulic working unit 6 can be, for example, a hydraulic cylinder on a boom of the loader. Obviously, the number and type of the at least one hydraulic working unit 6 are not limited, but can be any number and any suitable type. The steering unit 2 and the hydraulic working unit 6 are actually both hydraulic actuators.

[0018] The steering unit 2 comprises a steering valve 21. The steering valve 21 has two steering cylinder interfaces 22, 23, which are connected with two steering cylinders 24, 25, which are used to realize steering. The steering valve 21 also has a pump interface 26, a return port 27, and a feedback port 28. The return port 27 is connected to an oil tank 8, the pump interface 26 is connected with a first outlet 41 of the priority valve 4, and the feedback port 28 is connected with a first port 71 of the logic control hydraulic subsystem 7 and a feedback port 42 of the priority valve 4.

[0019] Preferably, the steering valve 21 is center closed. When the steering unit 2 is operated, the feedback port 28 is hydraulically connected with the steering cylinder interfaces 22, 23. When the steering unit 2 is not operated, the feedback port 28 is connected with the return port 27.

[0020] In addition to the first outlet 41 and the feedback port 42 mentioned above, the priority valve 4 has a second outlet 43 and an inlet 44. The second outlet 43 is connected to an oil inlet port 62 of a master valve 61 of the hydraulic working unit 6, and the inlet 44 is connected to an outlet 101 of the load-sensing pressure-flow control variable pump 1. In a state in which the priority valve 4 is not supplied with oil, a spool of the priority valve 4 is held in a first position by a spring 45. In this first position, the inlet 44 is in communication with the first outlet 41, and the second outlet 43 is shut off. A feedback pressure is applied to the spring side of the spool through the feedback port 42, and a pressure at the first outlet 41 is applied to the opposite side of the spring. A pre-tightening force of the spring 45 corresponds to a priority pressure difference, which can be adjusted to, for example, 15 bar. If the difference between the pressure at the first outlet 41 and the feedback pressure at the feedback port 42 is higher than the priority pressure difference by a predetermined value, the spool moves to a second position. In this case, the inlet 44 is in communication with the second outlet 43, and the passage between the inlet 44 and the first outlet 41 is slightly throttled (but not shut off to ensure that the hydraulic supply to the steering unit 2 is not interrupted in any case).

[0021] The fixed-flow pump 3 has a constant displacement (flow rate). The outlet 31 of the fixed-flow pump 3 is connected to a second port 72 of the logic control hydraulic subsystem 7. The fixed-flow pump 3 delivers hydraulic oil from the tank 8 to the hydraulic working unit 6 via the logic control hydraulic subsystem 7 in predetermined cases, and does not deliver to the steering unit 2 in any case.

[0022] The load-sensing pressure-flow control variable pump 1 has a continuously adjustable flow rate, and can be implemented as, for example, a swash plate type pump. The flow rate of the load-sensing pressure-flow control variable pump 1 is adjusted using an adjustment cylinder 102 and a return cylinder 103. The return cylinder 103 is connected to the outlet 101 of the load-sensing pressure-flow control variable pump 1. In this case, once the load-sensing pressure-flow control variable pump 1 is rotated by a drive device (not shown), the load-sensing pressure-flow control variable pump 1 moves in the direction of the maximum flow rate (maximum swing angle). A spring is also provided in the return cylinder 103, so that the maximum flow rate can be adjusted even if the load-sensing pressure-flow control variable pump 1 is not rotated.

[0023] The adjusting cylinder 102 acts in the opposite way to the return cylinder 103, which tends to reduce the flow of the load-sensing pressure-flow controlled variable pump 1 (swing angle reduction). The adjusting cylinder 102 is actuated by a first adjusting valve 104 and a second adjusting valve 105. The first adjusting valve 104 is pressed in a first position by a preferably manually adjustable spring 106. In this first position, the adjusting cylinder 102 is connected to the tank 8 and to the second adjusting valve 105. On the opposite side of the spring 106, the output pressure of the load-sensing pressure-flow controlled variable pump 1 is applied to the first adjusting valve 104, so that at a sufficiently high output pressure the first adjusting valve 104 can be moved into a second position. In this second position, the adjusting cylinder 102 is pressurized by the load-sensing pressure-flow controlled variable pump 1. When the output pressure of the load-sensing pressure-flow controlled variable pump 1 is higher than the pressure value set by the spring 106, the load-sensing pressure-flow controlled variable pump 1 will be adjusted in the direction of reduced flow, so that an upper limit for the output pressure of the load-sensing pressure-flow controlled variable pump 1 can be defined.

[0024] The second adjusting valve 105 is pressed in a first position by a spring 107. In this first position, the adjusting cylinder 102 is connected to the tank 8 via the first adjusting valve 104. On the opposite side of the spring of the second adjusting valve 105, the output pressure of the load-sensing pressure-flow controlled variable pump 1 is applied to the second adjusting valve 105, so that at a sufficiently high output pressure the second adjusting valve 105 can be moved into a second position. In this second position, the adjusting cylinder 102 is pressurized by the load-sensing pressure-flow controlled variable pump 1 via the first adjusting valve 104. On the side of the spring 107, a flow control port 108 is provided, which is connected to the third port 73 of the logic control hydraulic subsystem 7. Thus, the smaller the difference between the output pressure of the load-sensing pressure-flow controlled variable pump 1 and the pressure at the flow control port 108, the more the adjusting cylinder 102 is moved in the direction of increased flow.

[0025] The pilot valve 5 is preferably configured as an operating handle. The ports a1, b1, a2, b2 of the pilot valve 5 are connected to the ports a1, b1, a2, b2 of the hydraulic working unit 6, respectively.

[0026] The hydraulic working unit 6 also has output ports A1, B1, A2, B2, which are connected to the respective hydraulic cylinders 63, 64, 65, in order to control the operation of the hydraulic cylinders.

[0027] The hydraulic control system of the loader also comprises a pilot oil filter 9 and a pilot oil supply valve 10, wherein one end of the pilot oil filter 9 is connected to the outlet 101 of the load-sensing pressure-flow controlled variable pump 1 and the other end is connected to the pilot oil supply valve 10. The output port 11 of the pilot oil supply valve 10 is connected to the oil inlet port 12 of the pilot valve 5, in order to supply hydraulic oil to the pilot valve 5. The oil return port 13 of the pilot oil supply valve 10 and the oil return port 14 of the pilot valve 5 are both connected to the oil return line 15.

[0028] A return oil filter 16 is installed near the oil tank 8 in the return oil line 15 to filter out impurities in the oil.

[0029] The return port 66 of the hydraulic working unit 6 is also connected to the return oil line 15. A radiator 17 is provided on the return oil line 15 to cool the heated return oil.

[0030] The composition and function of the logic control hydraulic subsystem 7 will be described in detail below.

[0031] like Figure 1 As shown, the logic control hydraulic subsystem 7, in addition to the first port 71, second port 72, and third port 73 mentioned above, also has a fourth port 74, a fifth port 75, and a sixth port 76. The fourth port 74 is hydraulically connected to the oil supply line 18 leading to the oil inlet 62 of the main control valve 61, the fifth port 75 is connected to the feedback port 67 of the main control valve 61, and the sixth port 76 is hydraulically connected to the return line 15 as a return port.

[0032] The logic-controlled hydraulic subsystem 7 has a shuttle valve 77, which has a first inlet 771, a second inlet 772, and an outlet 773. The outlet 773 is connected to the flow control port 108, the first inlet 771 is connected to the fifth port 75 and hydraulically connected to the feedback port 67, and the second inlet 772 is connected to the feedback port 28 of the steering valve 21.

[0033] The logic-controlled hydraulic subsystem 7 also has a check valve 78 connected between the second port 72 and the fourth port 74 so as to allow hydraulic oil to flow only from the second port 72 to the fourth port 74.

[0034] In addition, the logic control hydraulic subsystem 7 also includes a 2 / 2 proportional valve 79, a pressure relief valve 80, and a throttle 81. The first hydraulic port 791 of the 2 / 2 proportional valve 79 is connected between the second port 72 and the check valve 78, and is hydraulically connected to the outlet 31 of the fixed flow pump 3. The first control port 792 of the 2 / 2 proportional valve 79 is connected between the check valve 78 and the fourth port 74, and is hydraulically connected to the supply line 18. The second hydraulic port 793 of the 2 / 2 proportional valve 79 is connected to the sixth port 76, and is hydraulically connected to the return line 15. The second control port 794 of the 2 / 2 proportional valve 79 is connected to the fifth port 75 via the throttle 81. One end of the pressure relief valve 80 is connected between the second control port 794 of the 2 / 2 proportional valve 79 and the throttle 81, and is hydraulically connected to both the second control port 794 and the throttle 81. The other end is connected to the sixth port 76, and is hydraulically connected to the return line 15.

[0035] The throttle 81 can be designed to control the pressure difference across the throttle 81 to a predetermined value.

[0036] It must be noted that the logic control hydraulic subsystem 7 can be connected by hydraulic elements as described above, so it can not be a truly independent device, but the hydraulic elements included therein can jointly play a logic control role. These ports can also not be actual existing connection ports, for example, the second port 72 can not exist, instead, the outlet 31 of the fixed displacement pump 3 can be directly connected to the one-way valve 79 through a pipeline, and of course at this time the input port of the one-way valve 79 can be regarded as the second port 72. However, according to a preferred exemplary embodiment, the logic control hydraulic subsystem 7 can be integrated as a first connection device on the master valve 61.

[0037] Below, the working process and control principle of the hydraulic control system shown, in particular the logic control hydraulic subsystem, will be described in detail. Figure 1

[0038] When only the steering unit 2 is operated (i.e., the hydraulic working unit 6 is not operated), the priority valve 4 keeps the outlet 101 of the load-sensing pressure-flow control variable pump 1 in communication with the pump interface 26, so that the hydraulic oil output by the load-sensing pressure-flow control variable pump 1 is directly pumped to the steering unit 2 to drive the steering unit 2 to achieve the desired steering. On the other hand, when the steering unit 2 is operated, the feedback port 28 applies a feedback pressure to the second inlet 772 of the shuttle valve 77 of the logic control hydraulic subsystem 7, and at this time the first inlet 771 is at low pressure due to being connected with the feedback port 67 of the master valve 61, so the outlet 773 of the shuttle valve 77 will output the feedback pressure and apply it to the flow control port 108, while the feedback pressure of the feedback port 28 is directly applied to the feedback port 42 of the priority valve 4. The output flow of the load-sensing pressure-flow control variable pump 1 can be adjusted through the flow control port 108. In this sense, the steering unit 2, the load-sensing pressure-flow control variable pump 1, the priority valve 4, and the shuttle valve 77 of the logic control hydraulic subsystem 7 at this time constitute a load-sensing hydraulic system. In other words, the load-sensing pressure-flow control variable pump 1 provides the required flow to the steering unit 2 according to the feedback pressure at the feedback port 28, so that overflow loss can be avoided.

[0039] ​When only the hydraulic working unit 6 (i.e. the pilot valve 5) is operated or the steering unit 2 is operated simultaneously with the hydraulic working unit 6, the feedback port 67 of the master valve 61 applies a feedback pressure to the first inlet port 771 of the shuttle valve 77, at this time, the shuttle valve 77 selects the greater one between the feedback pressure of the master valve 61 and the feedback pressure of the steering unit 2, and feeds back to the flow control port 108 of the load-sensing pressure-flow control variable pump 1 through its outlet port 773. In this case, the load-sensing pressure-flow control variable pump 1 adjusts towards the maximum displacement direction. When the displacement of the load-sensing pressure-flow control variable pump 1 is sufficient to move the spool of the priority valve 4 to the second position, the inlet port 44 of the priority valve 4 communicates with the second outlet port 43 to allow the hydraulic oil to be supplied to the hydraulic working unit 6. In this case, the priority valve 4 can distribute the flow between the steering unit 2 and the hydraulic working unit 6. If the system pressure of the hydraulic control system exceeds the set pressure of the load-sensing pressure-flow control variable pump 1, the load-sensing pressure-flow control variable pump 1 will automatically reduce the output flow, thus there is no overflow loss. At this time, due to the high system pressure, the check valve 78 of the logic control hydraulic subsystem 7 is squeezed and closed, so the hydraulic oil output by the fixed-flow pump 3 is not delivered to the oil inlet port 62 of the master valve 61. On the other hand, since the second control port 794 of the 2 / 2 proportional valve 79 is connected to the feedback port 67 of the master valve 61 through the throttle 81, the pressure at the second control port 794 is usually lower than the pressure at the feedback port 67 under the throttling effect, while the first control port 792 of the 2 / 2 proportional valve 79 communicates to the oil supply line 18 and is under a higher pressure than the pressure at the second control port 794, when the pressure difference between them is greater than the predetermined opening pressure of the 2 / 2 proportional valve 79, the 2 / 2 proportional valve 79 is opened, the hydraulic oil output by the fixed-flow pump 3 will flow directly from the first hydraulic port 791 to the second hydraulic port 793 of the 2 / 2 proportional valve 79, and then bypass the pressure relief valve 80 to return to the oil return line 15.

[0040] When the load-sensing pressure-flow control variable pump 1 reaches its maximum displacement and still cannot meet the demand of the hydraulic working unit 6 alone or the combined demand of the hydraulic working unit 6 and the steering unit 2 (both are operated), the system pressure will decrease, so the check valve 78 will open under the output pressure of the fixed-flow pump 3 to allow the hydraulic oil from the fixed-flow pump 3 to flow to the oil supply line 18 to make up for the insufficient flow demand. In other words, the fixed-flow pump 3 only participates in supplying hydraulic oil to the hydraulic working unit 6 when the load-sensing pressure-flow control variable pump 1 reaches or approaches the maximum displacement, otherwise the hydraulic oil output by the fixed-flow pump 3 will return to the tank 8 through the 2 / 2 proportional valve 79 with low pressure loss.

[0041] It is obvious to the person skilled in the art that the fixed displacement pump 3 can also be designed in such a way that it participates in the oil supply to the hydraulic working unit 6 when the load-sensing pressure flow control variable pump 1 reaches a certain predetermined displacement, for example 90% of the maximum displacement, below the maximum displacement.

[0042] By introducing the throttle 81, the relationship between the pressure at the second control port 794 of the 2 / 2 proportional valve 79 and the pressure at the feedback port 67 of the main control valve 61 can be controlled, and even the pressure at the second control port 794 of the 2 / 2 proportional valve 79 can be made independent of or isolated from the feedback pressure at the feedback port 67 of the main control valve 61, which makes it possible to control the 2 / 2 proportional valve 79 more flexibly.

[0043] Furthermore, by introducing the pressure relief valve 80, the hydraulic oil flowing from the feedback port 67 of the main control valve 61 through the throttle 81 is returned to the tank 8 when a certain pressure is reached. Even if the pressure relief valve 80 is opened, due to the throttle 81, it can be ensured that the feedback pressure at the feedback port 67 of the main control valve 61 is correctly introduced into the first inlet 711 of the shuttle valve 77 in order to be able to correctly regulate the displacement of the load-sensing pressure flow control variable pump 1.

[0044] It is obvious that the pressure relief valve 80 and the 2 / 2 proportional valve 79 together limit the maximum value of the output pressure of the fixed displacement pump 3, which also provides more flexibility for the design of the hydraulic control system.

[0045] According to an exemplary embodiment of the present application, a pressure compensator can be provided before or after the spool of the main control valve 61 of the hydraulic working unit 6, so that the oil distribution to the hydraulic working unit 6 depends only on the opening area of the spool and no longer on the load.

[0046] It is obvious to the person skilled in the art that the fixed displacement pump 3 can also be replaced by a variable pump.

[0047] Furthermore, according to the present application, the steering hydraulic system, which supplies oil to the steering unit 2, and the actuating hydraulic system, which supplies oil to the hydraulic working unit 6, can be hydraulically separated, so that the priority valve 4 can be dispensed with.

[0048] As mentioned above, Figure 1 The illustrated embodiment uses the pressure difference between the oil inlet 62 and the feedback port 67 of the hydraulic working unit 6 to detect whether the load-sensing pressure flow control variable pump 1 has reached a predetermined displacement, in particular the maximum displacement. However, there are also different methods to detect the displacement state of the load-sensing pressure flow control variable pump 1.

[0049] According to another exemplary embodiment of the present application, the first control port 792 and the second control port 794 of the 2 / 2 proportional valve 79 are connected to the outlet 101 and the flow control port 108 of the load sensing pressure flow control variable pump 1, respectively. If the pressure difference between the first control port 792 and the second control port 794 of the 2 / 2 proportional valve 79 is less than a predetermined setting of the load sensing pressure flow control variable pump 1, the load sensing pressure flow control variable pump 1 is in a maximum displacement state.

[0050] According to yet another exemplary embodiment of the present application, the first control port 792 and the second control port 794 of the 2 / 2 proportional valve 79 are connected to the inlet 44 and the second outlet 43 of the priority valve 4, respectively.

[0051] According to another exemplary embodiment of the present application, it is apparent that the first control port 792 and the second control port 794 of the 2 / 2 proportional valve 79 can also be connected to the outlet 101 of the load sensing pressure flow control variable pump 1 and the second outlet 43 of the priority valve 4, respectively.

[0052] It is apparent to those skilled in the art that the hydraulic control system of the present application can also be applied to other devices requiring such a hydraulic control system, such as forklifts, excavators, etc., and is not limited to loaders only.

[0053] Moreover, other advantages and alternative embodiments of the present application will be apparent to those skilled in the art from the foregoing description. The present application is therefore not to be restricted, in its broader aspects, to the specific details shown and described. Rather, working substitutions and modifications are to be expected from the disclosure herein, which is for purposes of illustration and description. Accordingly, various modifications and changes can be made thereto without departing from the broader spirit and scope of the application as set forth in the appended claims.

Claims

1. A hydraulic control system, comprising: a first hydraulic actuator (2) ; at least one second hydraulic actuator (6) having an oil inlet (62) and a first feedback port adapted to feedback a load condition of the second hydraulic actuator (6) ; a pressure flow control variable pump (1) as a first pump having a variable pump outlet (101) and a flow control port (108) ; a second pump (3), an outlet (31) of which is hydraulically connected to the oil inlet (62) of the second hydraulic actuator (6) through a one-way valve (78) to allow hydraulic oil to flow from the second pump (3) to the second hydraulic actuator (6) only; and a logic control hydraulic subsystem (7) for controlling the first hydraulic actuator (2) and / or the second hydraulic actuator (6), which at least comprises a 2 / 2 proportional valve (79), a restrictor (81) and a pressure relief valve (80), wherein the 2 / 2 proportional valve (79) has a first hydraulic port (791), a second hydraulic port (793), a first control port (792) and a second control port (794), the first hydraulic port (791) is hydraulically connected between the outlet (31) of the second pump (3) and the one-way valve (78), the second hydraulic port (793) is hydraulically connected to a return oil line (15), the first control port (792) is hydraulically connected between the one-way valve (78) and the oil inlet (62) of the second hydraulic actuator (6) or hydraulically connected to a first hydraulic connection point, the second control port (794) is hydraulically connected to the first feedback port of the second hydraulic actuator (6) through the restrictor (81) or hydraulically connected to a second hydraulic connection point, which is adapted to detect a predetermined displacement state of the pressure flow control variable pump (1) based on a pressure difference between the first hydraulic connection point and the second hydraulic connection point, one end of the pressure relief valve (80) is hydraulically connected between the second control port (794) and the restrictor (81), and the other end is hydraulically connected to the return oil line (15). 2.The hydraulic control system of claim 1, wherein: the hydraulic control system further comprises a priority valve (4) having an inlet (44), a first outlet (41) and a second outlet (43), wherein the variable pump outlet (101) is hydraulically connected to the inlet (44) of the priority valve (4), the first outlet (41) of the priority valve (4) is hydraulically connected to the oil inlet of the first hydraulic actuator (2), and the second outlet (43) of the priority valve (4) is hydraulically connected to the oil inlet (62) of the second hydraulic actuator (6) ; and the logic control hydraulic subsystem (7) further comprises a shuttle valve (77), a first inlet (771) of the shuttle valve (77) is hydraulically connected between the restrictor (81) and the first feedback port of the second hydraulic actuator (6) or the second hydraulic connection point, a second inlet (772) of the shuttle valve (77) is hydraulically connected to a second feedback port of the first hydraulic actuator (2) adapted to feedback a load condition of the first hydraulic actuator (2), and an outlet (773) of the shuttle valve (77) is hydraulically connected to the flow control port (108). 3.The hydraulic control system of claim 2, wherein: the first hydraulic connection point is an outlet (101) of the variable pump or an inlet (44) of the priority valve (4); and / or the second hydraulic connection point is a flow control port (108) or a second outlet (43) of the priority valve (4); and / or the predetermined displacement state is a maximum displacement state.

4. The hydraulic control system according to any one of claims 1-3, wherein the first hydraulic actuator (2) is a steering unit; and / or the second pump (3) is a fixed displacement pump; and / or the logic control hydraulic subsystem (7) is integrated as a pilot device to a main control valve (61) of the second hydraulic actuator (6).

5. The hydraulic control system according to any one of claims 1-3, wherein the hydraulic control system further comprises a pilot valve (5) having a plurality of ports hydraulically connected to corresponding ports of the main control valve (61) of the second hydraulic actuator (6); and / or the second pump (3) is a gear pump.

6. The hydraulic control system according to claim 2 or 3, wherein the priority valve (4) further has a third feedback port hydraulically connected to a second feedback port of the first hydraulic actuator (2) to communicate the inlet (44) and the second outlet (43) of the priority valve (4) when an output pressure of the pressure flow controlled variable pump (1) reaches a set value.

7. The hydraulic control system according to any one of claims 1-3, wherein a pressure compensator is provided before or after a spool of the main control valve (61) of the second hydraulic actuator (6).

8. The hydraulic control system according to claim 4, wherein a pressure compensator is provided before or after a spool of the main control valve (61) of the second hydraulic actuator (6).

9. The hydraulic control system according to claim 5, wherein a pressure compensator is provided before or after a spool of the main control valve (61) of the second hydraulic actuator (6).

10. The hydraulic control system according to claim 6, wherein a pressure compensator is provided before or after a spool of the main control valve (61) of the second hydraulic actuator (6).

11. The hydraulic control system according to claim 1, wherein the second pump (3) is a variable pump; and / or a hydraulic system supplying oil to the first hydraulic actuator (2) is hydraulically separated from a hydraulic system supplying oil to the second hydraulic actuator (6).

12. A mobile work apparatus characterized by comprising: The mobile work equipment is equipped with the hydraulic control system according to any one of claims 1-11.

13. The mobile work equipment according to claim 12, wherein the mobile work equipment is a loader or a fork lift or an excavator.

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