A closed hydraulic control system and engineering machinery

Abstract

The invention provides a closed hydraulic control system and engineering machinery, belonging to the field of hydraulic control technology. The closed hydraulic control system includes a closed main system, an oil replenishing system and an oil unloading system. The oil replenishing system is connected to the closed main system and is used to replenish oil to the closed main system. The oil unloading system is connected to the closed main system through a control valve group, and the control valve group is suitable for connecting or disconnecting the closed main system and the oil unloading system. Energy saving effect is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic control, and in particular to a closed hydraulic control system and engineering machinery. Background Art

[0002] Closed hydraulic system has the advantages of smooth switching, small impact, high efficiency, etc., and is widely used in construction machinery. In some construction machinery, such as hydraulic boom tower cranes, crawler cranes, etc., there are often multiple actuators such as luffing, lifting, slewing, etc. These actuators are generally controlled by closed hydraulic subsystems.

[0003] In a closed hydraulic system, the hydraulic oil flows from the variable pump to the actuator and then back to the variable pump, circulating inside the system without flowing back to the oil tank. In theory, the total amount of oil remains unchanged, but in the actual working process, leakage and loss are inevitable (continuous internal leakage of high-pressure oil is an inherent product of component design), so an oil replenishment circuit is often set up to replenish the leaked and lost hydraulic oil in time through the oil replenishment pump. Especially when the system is on standby, in order to ensure the lubrication of the main oil pump and actuator inside the closed hydraulic system, the oil replenishment pump needs to replenish oil to the closed hydraulic system at all times. In addition to replenishing the leakage and loss of the closed hydraulic system, the rest of the hydraulic oil overflows from the oil replenishment overflow valve of the oil replenishment pump. This part of the power loss is all converted into heat, resulting in a large amount of energy loss. Summary of the invention

[0004] The invention aims to reduce the energy loss of an oil replenishment pump when replenishing oil to a closed system.

[0005] In order to solve the above problems, the present invention provides a closed hydraulic control system, comprising:

[0006] Closed main system;

[0007] an oil replenishment system, the oil replenishment system being connected to the closed main system and being used to replenish oil to the closed main system; and

[0008] An oil unloading system is connected to the closed main system through the control valve group, and the control valve group is suitable for connecting or disconnecting the closed main system with the oil unloading system.

[0009] Compared with the prior art, the closed hydraulic control system provided by the present invention has the following beneficial effects but is not limited to them:

[0010] In the present invention, no matter the closed main system is in standby state or in working state, the closed main system will have leakage and loss, so the oil replenishment system replenishes oil to the closed main system at all times. And in order to ensure that the flow rate supplemented by the oil replenishment system to the closed main system can offset the flow rate leaked from the closed main system, it is necessary to make the flow rate supplemented by the oil replenishment system to the closed main system greater than the flow rate leaked from the closed main system, and then a part of the excess flow is left. When the closed main system is working, the excess flow can overflow back to the oil tank by the oil replenishment system. For example, when the closed main system is on standby, the control valve group can connect the closed main system with the oil unloading system, and then the oil unloading system unloads this part of the excess flow to the oil tank. Compared with the traditional overflow that can only be caused by the oil replenishment system itself, when the closed main system is on standby in the present invention, the oil replenishment system does not need to overflow and reduce pressure by itself, which reduces the oil replenishment back pressure (the back pressure generated during overflow) and achieves energy saving.

[0011] Furthermore, one end of the oil unloading system away from the control valve group is connected to the oil tank through a filter.

[0012] Furthermore, the closed main system includes a closed circuit, a main oil pump and an actuator, the closed circuit includes a high-pressure side circuit and a low-pressure side circuit, the main oil pump is connected to the actuator through the high-pressure side circuit and the low-pressure side circuit respectively, and the main oil pump is suitable for being driven and connected to the actuator.

[0013] Furthermore, the oil replenishment system includes an oil replenishment circuit, an oil replenishment pump and an oil replenishment overflow valve arranged on the oil replenishment circuit, the oil replenishment circuit is connected to a closed circuit, and the oil replenishment overflow valve is located between the oil replenishment pump and the closed circuit.

[0014] Furthermore, the main oil pump is a bidirectional variable displacement pump, and the actuator is a hydraulic motor.

[0015] Furthermore, the closed hydraulic control system also includes a shunt pipe, and the oil replenishment system is connected to the high-pressure side circuit and the low-pressure side circuit respectively through two shunt pipes, and a one-way valve is arranged on the shunt pipe, and the one-way valve limits the oil flow from the oil replenishment system to the high-pressure side circuit and the low-pressure side circuit.

[0016] Furthermore, the oil unloading system includes an oil unloading circuit and an electromagnetic unloading valve arranged on the oil unloading circuit, the oil unloading circuit is connected to the closed circuit through the control valve group, the high-pressure oil in the high-pressure side circuit flows into the oil outlet of the electromagnetic unloading valve through the control valve group, and the low-pressure oil in the low-pressure side circuit flows into the control oil port of the electromagnetic unloading valve through the control valve group.

[0017] Further, the control valve group includes a shuttle valve and a hydraulically controlled reversing valve, the electromagnetic unloading valve includes an electromagnetic reversing valve and a hydraulically controlled one-way valve, the high-pressure oil in the high-pressure side circuit flows into the oil outlet of the hydraulically controlled one-way valve through the shuttle valve, and the low-pressure oil in the low-pressure side circuit flows into the oil inlet of the electromagnetic reversing valve through the hydraulically controlled one-way valve, the first oil outlet of the electromagnetic reversing valve is connected to the piston push rod of the hydraulically controlled one-way valve, when the electromagnetic reversing valve is energized, the oil inlet of the electromagnetic reversing valve is connected to the first oil outlet of the electromagnetic reversing valve, wherein the oil outlet of the hydraulically controlled one-way valve is the oil outlet of the electromagnetic unloading valve, the oil inlet of the hydraulically controlled one-way valve is the oil inlet of the electromagnetic unloading valve, and the oil inlet of the electromagnetic reversing valve is the control oil port of the electromagnetic unloading valve.

[0018] Furthermore, the first oil inlet of the shuttle valve is communicated with the high-pressure side circuit, the second oil inlet of the shuttle valve is communicated with the low-pressure side circuit, and the oil outlet of the shuttle valve is communicated with the oil outlet of the hydraulically controlled one-way valve.

[0019] In addition, the present invention also provides an engineering machine, comprising the closed hydraulic control system as described above.

[0020] Since the technical improvements and technical effects of the engineering machinery are the same as those of the closed hydraulic control system, the technical effects of the engineering machinery will not be described in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a closed hydraulic control system according to an embodiment of the present invention.

[0022] Description of reference numerals:

[0023] 1-closed main system, 11-closed circuit, 111-high-pressure side circuit, 112-low-pressure side circuit, 12-main oil pump, 13-actuator, 2-oil replenishment system, 21-oil replenishment circuit, 22-oil replenishment pump, 23-oil replenishment overflow valve, 3-oil unloading system, 31-oil unloading circuit, 32-electromagnetic unloading valve, 321-hydraulic control one-way valve, 322-electromagnetic reversing valve, 4-filter, 5-diverter pipe, 51-one-way valve, 6-control valve group, 61-shuttle valve, 62-hydraulic control reversing valve. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "up", "down", "left", "right", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0026] Moreover, the Z-axis in the accompanying drawings represents the vertical direction, that is, the up and down position, and the positive direction of the Z-axis (that is, the direction of the arrow of the Z-axis) represents the top, and the negative direction of the Z-axis (that is, the direction opposite to the positive direction of the Z-axis) represents the bottom; the Y-axis in the accompanying drawings represents the horizontal direction, that is, the left and right position, and the positive direction of the Y-axis (that is, the direction of the arrow of the Y-axis) represents the left, and the negative direction of the Y-axis (that is, the direction opposite to the positive direction of the Y-axis) represents the right.

[0027] It should also be noted that the aforementioned Z and Y axes are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0028] See also Figure 1 A closed hydraulic control system according to an embodiment of the present invention comprises a closed main system 1, an oil replenishment system 2 and an oil unloading system 3. The oil replenishment system 2 is connected to the closed main system 1 and is used to replenish oil to the closed main system 1. The oil unloading system 3 is connected to the closed main system 1 through the control valve group 6. The control valve group 6 is suitable for connecting or disconnecting the closed main system 1 and the oil unloading system 3.

[0029] In this embodiment, no matter whether the closed main system 1 is in standby state or in working state, the closed main system 1 will have leakage and loss, so the oil replenishment system 2 replenishes the closed main system 1 at all times. In order to ensure that the flow rate supplemented by the oil replenishment system 2 to the closed main system 1 can offset the flow rate leaked from the closed main system 1, it is necessary to make the flow rate supplemented by the oil replenishment system 2 to the closed main system 1 greater than the flow rate leaked in the closed main system 1, and then a part of the excess flow rate remains. For example, when the closed main system is working, the excess flow rate can overflow back to the oil tank by the oil replenishment system 2, and when the closed main system 1 is on standby, the control valve group 6 can connect the closed main system 1 with the oil unloading system 3, and then the oil unloading system 3 unloads this part of the excess flow rate. Compared with the traditional method that can only overflow by the oil replenishment system 2 itself, in this embodiment, when the closed main system 1 is on standby, the oil replenishment system 2 does not need to overflow and reduce pressure by itself, which reduces the oil replenishment back pressure (the back pressure generated during overflow, and the back pressure causes energy loss), and achieves energy saving.

[0030] Alternatively, see Figure 1The end of the oil unloading system 3 away from the control valve group 6 is connected to the oil tank through the filter 4.

[0031] Here, when the closed main system 1 is on standby, the oil in the closed main system 1 is unloaded and the hydraulic oil is filtered through the filter 4 to filter out impurities in the pipeline. That is, when the closed main system 1 is on standby, it plays a filtering role, improves the cleanliness of the hydraulic oil, and increases the service life of the equipment.

[0032] It is understandable that a filter may also be provided at the initial end of the oil replenishment system 2 .

[0033] Alternatively, see Figure 1 The closed main system 1 includes a closed circuit 11, a main oil pump 12 and an actuator 13. The closed circuit includes a high-pressure side circuit 111 and a low-pressure side circuit 112. The main oil pump 12 is connected to the actuator 13 through the high-pressure side circuit 111 and the low-pressure side circuit 112 respectively. The main oil pump 12 is suitable for driving connection with the actuator 13.

[0034] Here, the closed main system 1 at least has a closed circuit 11 and a main oil pump 12 and an actuator 13 arranged on the closed circuit 11 .

[0035] It can be understood that the input end of the main oil pump 12 is connected to the output end of the actuator 13 , and the output end of the main oil pump 12 is connected to the input end of the actuator 13 , thus forming a closed main system 1 .

[0036] Alternatively, see Figure 1 The oil replenishment system 2 includes an oil replenishment circuit 21, an oil replenishment pump 22 and an oil replenishment overflow valve 23 arranged on the oil replenishment circuit 21. The oil replenishment circuit 21 is connected to the closed circuit 11, and the oil replenishment overflow valve 23 is located between the oil replenishment pump 22 and the closed circuit 11.

[0037] Here, as mentioned above, when the closed main system 1 is working, the excess flow overflows from the oil replenishment relief valve 23 back to the oil tank.

[0038] Alternatively, see Figure 1 The oil unloading system 3 includes an oil unloading circuit 31 and an electromagnetic unloading valve 32 arranged on the oil unloading circuit 31. The oil unloading circuit 31 is connected to the closed circuit 11 through the control valve group 6.

[0039] Here, when the oil unloading system 3 unloads the closed main system 1 , specifically, the excess flow input into the closed main system 1 by the oil replenishment system 2 is unloaded through the electromagnetic unloading valve 32 .

[0040] Furthermore, the main oil pump 12 is a bidirectional variable displacement pump, and the actuator 13 is a hydraulic motor.

[0041] Here, if the actuator 13 in the closed main system 1 adopts a double-acting single-piston rod hydraulic cylinder, the power utilization rate will decrease during operation due to the unequal flow rates of the large and small chambers. Therefore, the actuator 13 in the closed main system 1 in this embodiment is selected as a hydraulic motor.

[0042] Secondly, the variable pump is easy to operate and can reduce the displacement according to the working conditions, thereby reducing the power consumption of the engine and reducing heat. The advantage of the quantitative motor is that it is cheap, because the working range of the motor is wide and can adapt to the flow change. In this way, the system layout is simple. When the speed of the motor needs to be adjusted, the displacement of the main oil pump is directly changed to gradually approach the required speed. On the other hand, the starting torque of the main oil pump 12 is proportional to the displacement under constant pressure, and the general prime mover (engine, motor, etc.) is required to start at a small torque, which requires the pump to be variable. Therefore, the main oil pump here is a variable pump.

[0043] The main oil pump 12 is preferably a bidirectional variable pump, which not only has the function of regulating flow, but also has the dual function of changing flow direction. It can continuously adjust the speed and rotation direction of the hydraulic motor without setting a reversing valve in the main oil circuit, and the flow loss of the hydraulic oil is small.

[0044] It should be noted that the closed main system 1 is in standby mode, which means that the main oil pump 12 is in idle mode and does not displace oil, that is, the main oil pump 12 does not supply oil to the motor. The idling main oil pump 12 and the motor need oil lubrication. Since the main oil pump 12 does not displace oil, the pressure of the pipelines on both sides of the main oil pump 12 will gradually balance. At this time, the oil replenishment system 2 replenishes oil to the pipelines on both sides of the main oil pump 12. Part of the replenished oil enters the main oil pump 12 and the motor for lubrication and leaks into the oil tank, and the other part of the excess flow enters the oil unloading system 3 for unloading. When the closed main system 1 is in standby mode, the oil replenished by the oil replenishment system 2 will not pass through the oil replenishment overflow valve 23.

[0045] It can be understood that when the closed main system 1 is working, since the main oil pump 12 works to drive the motor to rotate through high-pressure oil, the oil replenishment system 2 replenishes oil to the pipeline between the input end of the main oil pump 12 and the discharge end of the motor, and the excess flow overflows from the oil replenishment overflow valve 23 back to the oil tank.

[0046] See also Figure 1 Optionally, the closed hydraulic control system further includes a shunt pipe 5, the oil replenishment system 2 is connected to the high-pressure side circuit 111 and the low-pressure side circuit 112 through two shunt pipes 5, and a one-way valve 51 is provided on the shunt pipe 5, and the one-way valve 51 limits the oil from the oil replenishment system 2 to the high-pressure side circuit 111 and the low-pressure side circuit 112;

[0047] When the closed main system 1 is on standby, the control valve group 6 is suitable for unloading the high-pressure oil in the high-pressure side circuit 111 through the electromagnetic unloading valve 32 .

[0048] It should be noted that the high-pressure side circuit 111 refers to at least the pipeline between the output end of the main oil pump 12 and the input end of the motor, while the low-pressure side circuit 112 refers to at least the pipeline between the input end of the main oil pump 12 and the output end of the motor. Figure 1 The upper pipeline of the closed main system 1 is the high-pressure side circuit 111, and the lower pipeline is the low-pressure side circuit 112, which is only an example. Since the main oil pump 12 is a bidirectional variable pump, when the oil port at the upper end of the main oil pump 12 is the oil discharge port and the oil port at the lower end is the oil inlet, the main oil pump 12 drives the motor on the right to rotate clockwise. At this time, the upper pipeline is the high-pressure side circuit 111, and the lower pipeline is the low-pressure side circuit 112; when the lower end oil port of the main oil pump 12 is the oil discharge port and the upper end oil port is the oil inlet, the motor on the right is driven to rotate counterclockwise. At this time, the lower pipeline is the high-pressure side circuit 111, and the upper pipeline is the low-pressure side circuit 112.

[0049] Here, one end of the closed loop 11 is connected to the low-pressure side loop 112 and the high-pressure side loop 111 respectively through two shunt pipes 5. The upper pipeline is the high-pressure side loop 111 and the lower pipeline is the low-pressure side loop 112. When the closed main system 1 is working, due to the high oil pressure in the high-pressure side loop 111, the oil added in the oil replenishment loop 21 enters the low-pressure side loop 112 from the lower one-way valve 51 for oil replenishment, and the excess flow overflows back to the oil tank from the oil replenishment overflow valve 23. When the closed main system 1 is on standby, the main oil pump 12 does not discharge into the upper high-pressure side loop 111, and the oil pressure in the high-pressure side loop 111 and the oil pressure in the low-pressure side loop will gradually tend to balance. Most of the oil added in the oil replenishment loop 21 enters the high-pressure side loop 111, and a part of the flow enters the main oil pump 12 and the motor for lubrication, and the other part of the excess flow is unloaded through the electromagnetic unloading valve 32 under the control of the control valve group 6. Ensure energy saving when the closed main system 1 is in standby mode.

[0050] Alternatively, see Figure 1The control valve group 6 includes a shuttle valve 61 and a hydraulically controlled reversing valve 62, and the electromagnetic unloading valve 32 includes an electromagnetic reversing valve 322 and a hydraulically controlled one-way valve 321. The high-pressure oil in the high-pressure side circuit 111 flows into the oil outlet of the hydraulically controlled one-way valve 321 through the shuttle valve 61, and the low-pressure oil in the low-pressure side circuit 112 flows into the oil inlet of the electromagnetic reversing valve 322 through the hydraulically controlled reversing valve 62. The first oil outlet of the electromagnetic reversing valve 322 is connected to the oil outlet of the hydraulically controlled one-way valve 321. The piston push rod of the hydraulically controlled one-way valve 321 is connected. When the electromagnetic reversing valve 322 is energized, the oil inlet of the electromagnetic reversing valve 322 is connected to the first oil outlet of the electromagnetic reversing valve 322, wherein the oil outlet of the hydraulically controlled one-way valve 321 is the oil outlet of the electromagnetic unloading valve 32, the oil inlet of the hydraulically controlled one-way valve 321 is the oil inlet of the electromagnetic unloading valve 32, and the oil inlet of the electromagnetic reversing valve 322 is the control oil port of the electromagnetic unloading valve 32.

[0051] Here, in the closed main system 1, when the upper pipeline is the high-pressure side circuit 111 and the lower pipeline is the low-pressure side circuit 112, the oil pressure in the high-pressure side circuit 111 will drive the upper position of the hydraulic control reversing valve 62 to move downward, and then the hydraulic control reversing valve 62 connects the low-pressure side circuit 112 with the oil inlet of the electromagnetic reversing valve 322, then the low-pressure oil in the low-pressure side circuit 112 enters the oil inlet of the electromagnetic reversing valve 322 as the pilot control oil, and controls the electromagnetic reversing valve 322 to be energized, and then the electromagnetic The reversing valve 322 moves from the left position to the right, and the low-pressure oil serving as the pilot control oil flows out from the first oil outlet of the electromagnetic reversing valve and acts on the piston push rod of the hydraulically controlled one-way valve 321 to move, thereby controlling the oil outlet (B port) of the hydraulically controlled one-way valve 321 to be connected with the oil inlet (A port) of the hydraulically controlled one-way valve. Then, the high-pressure oil in the high-pressure side circuit 111 is unloaded to the oil tank through the hydraulically controlled one-way valve 321 until the oil pressure in the high-pressure side circuit 111 gradually tends to balance with the oil pressure in the low-pressure side circuit 112. Among them, it can be understood that the excess flow of the oil added to the high-pressure side circuit 111 is unloaded through the hydraulically controlled one-way valve along with the high-pressure oil until the oil pressure in the high-pressure side circuit 111 is balanced with the oil pressure in the low-pressure side circuit 112. Among them, through Figure 1 From the specific structure of the middle hydraulically controlled reversing valve, it can be seen that under the action of oil pressure, no matter whether the main oil pump 12 is rotating forward or reverse, the oil in the low-pressure side circuit 112 serves as the pilot control oil to control the oil outlet and oil inlet of the hydraulically controlled one-way valve 321 to be connected.

[0052] It should be noted that when the closed main system 1 is on standby, the low-pressure oil in the low-pressure side circuit 112 serves as the pilot control oil to control the oil outlet and oil inlet of the hydraulically controlled one-way valve 321 to be connected. However, the low-pressure oil in the low-pressure side circuit 112 will not return to the oil tank through the hydraulically controlled one-way valve 321. Instead, the high-pressure oil in the high-pressure side circuit 111 will be unloaded through the hydraulically controlled one-way valve 321 and return to the oil tank. Therefore, the oil in the high-pressure side circuit 111 is lost more than the oil in the low-pressure side circuit 112. Therefore, when replenishing oil, more oil is replenished into the high-pressure side circuit 111.

[0053] Alternatively, see Figure 1 The first oil inlet of the shuttle valve 61 is connected to the high-pressure side circuit 111, the second oil inlet of the shuttle valve 61 is connected to the low-pressure side circuit 112, and the oil outlet of the shuttle valve 61 is connected to the oil outlet of the hydraulically controlled one-way valve 321.

[0054] Here, the oil inlet at the left end of the shuttle valve 61 is the first oil inlet, the oil inlet at the right end is the second oil inlet, and the upper end is the oil outlet. Through the setting of the shuttle valve 61, it is always ensured that regardless of whether the main oil pump 12 is reversed, the high-pressure oil can always be connected to the oil outlet of the hydraulically controlled one-way valve 321 through the shuttle valve 61.

[0055] In addition, another embodiment of the present invention further provides an engineering machine, comprising the closed hydraulic control system as described above.

[0056] Since the technical improvements and technical effects of the engineering machinery are the same as those of the closed hydraulic control system, the technical effects of the engineering machinery will not be described in detail.

[0057] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0058] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A closed hydraulic control system, characterized in that: include: Closed main system (1); an oil replenishment system (2), the oil replenishment system (2) being connected to the closed main system (1) and being used to replenish oil to the closed main system (1); as well as An oil unloading system (3), the oil unloading system (3) being connected to the closed main system (1) via a control valve group (6), the control valve group (6) being suitable for connecting or disconnecting the closed main system (1) and the oil unloading system (3); an end of the oil unloading system (3) away from the control valve group (6) being connected to the oil tank via a filter (4); The closed main system (1) comprises a closed circuit (11), a main oil pump (12) and an actuator (13); the closed circuit comprises a high-pressure side circuit (111) and a low-pressure side circuit (112); the main oil pump (12) is connected to the actuator (13) via the high-pressure side circuit (111) and the low-pressure side circuit (112), respectively; the main oil pump (12) is a two-way variable pump, and the actuator (13) is a hydraulic motor; and the closed main system (1) further comprises a shunt pipe (5); the oil replenishment system (2) is connected to the high-pressure side circuit (111) and the low-pressure side circuit (112) via two shunt pipes (5), and a one-way The one-way valve (51) limits the flow of oil from the oil replenishment system (2) to the high-pressure side circuit (111) and the low-pressure side circuit (112); the oil unloading system (3) comprises an oil unloading circuit (31) and an electromagnetic unloading valve (32) arranged on the oil unloading circuit (31); the oil unloading circuit (31) is connected to the closed circuit (11) through the control valve group (6); the high-pressure oil in the high-pressure side circuit (111) flows into the oil outlet of the electromagnetic unloading valve (32) through the control valve group (6); and the low-pressure oil in the low-pressure side circuit (112) flows into the control oil port of the electromagnetic unloading valve (32) through the control valve group (6).

2. The closed hydraulic control system according to claim 1, characterized in that: The oil replenishment system (2) comprises an oil replenishment circuit (21), an oil replenishment pump (22) and an oil replenishment overflow valve (23) arranged on the oil replenishment circuit (21); the oil replenishment circuit (21) is connected to the closed circuit (11); and the oil replenishment overflow valve (23) is located between the oil replenishment pump (22) and the closed circuit (11).

3. The closed hydraulic control system according to claim 1, characterized in that: The control valve group (6) comprises a shuttle valve (61) and a hydraulically controlled reversing valve (62); the electromagnetic unloading valve (32) comprises an electromagnetic reversing valve (322) and a hydraulically controlled one-way valve (321); the high-pressure oil in the high-pressure side circuit (111) flows into the oil outlet of the hydraulically controlled one-way valve (321) through the shuttle valve (61); the low-pressure oil in the low-pressure side circuit (112) flows into the oil inlet of the electromagnetic reversing valve (322) through the hydraulically controlled reversing valve (62); the first oil outlet of the electromagnetic reversing valve (322) is connected to the oil outlet of the electromagnetic reversing valve (322). The piston push rod of the hydraulically controlled one-way valve (321) is connected, and when the electromagnetic reversing valve (322) is energized, the oil inlet of the electromagnetic reversing valve (322) is connected to the first oil outlet of the electromagnetic reversing valve (322), wherein the oil outlet of the hydraulically controlled one-way valve (321) is the oil outlet of the electromagnetic unloading valve (32), the oil inlet of the hydraulically controlled one-way valve (321) is the oil inlet of the electromagnetic unloading valve (32), and the oil inlet of the electromagnetic reversing valve (322) is the control oil port of the electromagnetic unloading valve (32).

4. The closed hydraulic control system according to claim 3, characterized in that: The first oil inlet of the shuttle valve (61) is in communication with the high-pressure side circuit (111), the second oil inlet of the shuttle valve (61) is in communication with the low-pressure side circuit (112), and the oil outlet of the shuttle valve (61) is in communication with the oil outlet of the hydraulically controlled one-way valve (321).

5. An engineering machine, characterized in that: It comprises a closed hydraulic control system as described in any one of claims 1 to 4.

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