Closed hydraulic system, method for controlling a closed hydraulic system and engineering machine

Abstract

The application relates to the technical field of engineering machinery, and particularly discloses a closed hydraulic system, a control method of the closed hydraulic system and engineering machinery. The closed hydraulic system comprises a variable pump, a servo oil cylinder, a motor and a brake assembly. The variable pump is connected with a power source. The servo oil cylinder is connected with a swash plate of the variable pump and is used for controlling the swing angle of the swash plate. The variable pump and the motor constitute a closed circulation through a first oil path and a second oil path. The motor is connected with a rotating load. The brake assembly can simultaneously open the first oil path and the second oil path. The variable pump can normally drive the motor to work, so as to output power and drive the rotating load to rotate. The brake assembly can simultaneously disconnect the first oil path and the second oil path. The oil path of the closed circulation is cut off, so that the rotating load can be effectively guaranteed to stop, and the problems of rotating drift or non-stopping of the rotating load can be avoided.

Description

Technical Field

[0001] This invention relates to the field of engineering machinery technology, and in particular to a closed hydraulic system, a control method for the closed hydraulic system, and engineering machinery. Background Technology

[0002] The slewing mechanism is an important component of a hydraulic excavator, used to drive the upper part of the hydraulic excavator and other engineering vehicles to rotate. Existing slewing mechanisms usually use a closed hydraulic system to control the start, stop and reverse rotation of the slewing mechanism.

[0003] For construction machinery using a closed-loop slewing system, braking is primarily achieved by the system's internal relief valve when slewing stops. However, when the machine's moment of inertia is large, or when there are leaks in the system, slewing drift or inability to stop the machine from rotating can easily occur. Summary of the Invention

[0004] The purpose of this invention is to provide a closed-loop hydraulic system, a control method for the closed-loop hydraulic system, and engineering machinery, in order to solve the problem that engineering machinery using closed-loop systems for rotation mainly relies on the relief valve inside the system for braking. When the rotational inertia of the upper vehicle is large, or when there is leakage in the system, it is easy to experience rotational drift or inability to stop rotation.

[0005] On one hand, the present invention provides a closed-loop hydraulic system, the closed-loop hydraulic system comprising:

[0006] Variable displacement pump, connected to a power source;

[0007] A servo cylinder is connected to the swashplate of the variable pump and is used to control the swing angle of the swashplate.

[0008] The motor, wherein the first oil port of the variable pump and the second oil port of the motor are connected through a first oil passage, and the second oil port of the variable pump and the first oil port of the motor are connected through a second oil passage;

[0009] A braking assembly capable of controlling the simultaneous opening or closing of the first and second oil circuits.

[0010] As a preferred technical solution for a closed hydraulic system, the braking assembly includes a first solenoid valve disposed in the first oil circuit and a second solenoid valve disposed in the second oil circuit.

[0011] As a preferred technical solution for a closed hydraulic system, the braking assembly includes a first pilot check valve disposed in the first oil circuit and a second pilot check valve disposed in the second oil circuit. The pilot oil circuit of the first pilot check valve is connected to the second oil circuit, and the connection point is located between the second port of the variable pump and the second pilot check valve. The pilot oil circuit of the second pilot check valve is connected to the first oil circuit, and the connection point is located between the first port of the variable pump and the first pilot check valve.

[0012] As a preferred technical solution for a closed hydraulic system, the braking assembly includes an electromagnetic control valve, a first pilot valve disposed in the first oil circuit, and a second pilot valve disposed in the second oil circuit. The electromagnetic control valve is used to control the pilot oil circuit of the first pilot valve and the pilot oil circuit of the second pilot valve to be simultaneously opened or simultaneously closed.

[0013] As a preferred technical solution for a closed hydraulic system, the electromagnetic control valve is a proportional pressure reducing valve.

[0014] As a preferred technical solution for the closed hydraulic system, the closed hydraulic system further includes a replenishing pump, which is connected to the power source and connected to the first oil circuit through a first replenishing oil circuit and to the second oil circuit through a second replenishing oil circuit; the replenishing pump is connected to the solenoid control valve and is used to supply oil to the pilot oil circuit of the first pilot valve and the pilot oil circuit of the second pilot valve.

[0015] As a preferred technical solution for a closed hydraulic system, the closed hydraulic system further includes an electro-hydraulic proportional valve. The servo cylinder has a servo oil chamber and a servo piston located in the servo oil chamber. The servo piston is connected to the swashplate. The servo piston divides the servo oil chamber into a left chamber and a right chamber. The electro-hydraulic proportional valve can control one of the left chamber and the right chamber to replenish oil while the other drains oil, or drain oil simultaneously.

[0016] As a preferred technical solution for a closed hydraulic system, the braking assembly and the variable pump are integrated.

[0017] On the other hand, the present invention provides a control method for a closed hydraulic system of any of the above-mentioned schemes. During braking, the controller controls the electromagnetic control terminal of the electro-hydraulic proportional valve to de-energize so that the servo cylinder gradually resets, and after an interval of time Δt, the braking component controls the first oil circuit and the second oil circuit to disconnect simultaneously.

[0018] In another aspect, the present invention provides an engineering machine, including the closed hydraulic system of any of the above-mentioned solutions.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention provides a closed-loop hydraulic system, a control method for the closed-loop hydraulic system, and engineering machinery. The closed-loop hydraulic system includes a variable displacement pump, a servo cylinder, a motor, and a braking assembly. The variable displacement pump is connected to a power source, and the servo cylinder is connected to the swashplate of the variable displacement pump and is used to control the swashplate's angle. The variable displacement pump and the motor form a closed loop through a first oil circuit and a second oil circuit. The motor is connected to a rotating load. The braking assembly can disconnect the first oil circuit and simultaneously disconnect the second oil circuit, and it can also open the first oil circuit and simultaneously open the second oil circuit. When the braking assembly opens the first and second oil circuits simultaneously, the variable displacement pump can normally drive the motor to work, output power, and drive the rotating load to rotate. When the braking assembly disconnects the first and second oil circuits simultaneously, the closed-loop oil circuit is cut off, effectively ensuring that the rotating load stops and avoiding rotational drift or inability to stop rotation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the closed hydraulic system in Embodiment 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of the closed hydraulic system in Embodiment 2 of the present invention. Figure 1 ;

[0023] Figure 3 This is a schematic diagram of the closed hydraulic system in Embodiment 2 of the present invention. Figure 2 ;

[0024] Figure 4 This is a schematic diagram of the closed hydraulic system in Embodiment 3 of the present invention. Figure 1 ;

[0025] Figure 5 This is a schematic diagram of the closed hydraulic system in Embodiment 3 of the present invention. Figure 2 .

[0026] In the picture:

[0027] 1. Variable displacement pump; 2. Servo cylinder; 201. Servo piston; 202. Left chamber; 203. Right chamber; 3. Motor; 4. Make-up pump; 5. Controller; 6. First oil circuit; 7. Second oil circuit; 8. First make-up oil circuit; 9. Second make-up oil circuit; 10. Electro-hydraulic proportional valve; 11. First make-up check valve; 12. Second make-up check valve; 13. First relief valve; 14. Second relief valve; 15. Third relief valve; 16. First solenoid valve; 17. Second solenoid valve; 18. First pilot check valve; 19. Second pilot check valve; 20. First pilot valve; 21. Second pilot valve; 22. Solenoid control valve. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions. Furthermore, "above," "on top of," and "over" the first feature in relation to the second feature includes the first feature directly above and diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "under," and "below" the first feature in relation to the second feature includes the first feature directly below and diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0032] Example 1

[0033] like Figure 1As shown, this embodiment provides a closed-loop hydraulic system, which includes a variable displacement pump 1, a servo cylinder 2, a motor 3, and a braking assembly. The variable displacement pump 1 is connected to a power source, which drives its rotation. The power source can be an engine, an electric motor, etc. The servo cylinder 2 is connected to the swashplate of the variable displacement pump 1 and is used to control the swashplate's angle. The first port of the variable displacement pump 1 and the second port of the motor 3 are connected through a first oil passage 6, and the second port of the variable displacement pump 1 and the first port of the motor 3 are connected through a second oil passage 7, thus forming a closed loop between the variable displacement pump 1 and the motor 3 through the first oil passage 6 and the second oil passage 7. The motor 3 is connected to the rotating load. The braking assembly can simultaneously disconnect or connect the first oil passage 6 and the second oil passage 7. When the braking assembly simultaneously connects the first oil passage 6 and the second oil passage 7, the variable displacement pump 1 can normally drive the motor 3 to work, output power, and drive the rotating load to rotate. When the braking assembly simultaneously disconnects the first oil passage 6 and the second oil passage 7, the closed-loop oil passage is cut off, which can effectively ensure that the rotating load stops and avoid rotational drift or inability to stop rotation.

[0034] It should be noted that in this embodiment, either the first port or the second port of the variable pump 1 can be used as an input terminal, and the other can be used as an output terminal.

[0035] Optionally, the closed hydraulic system also includes a replenishing pump 4, which is connected to the power source. The replenishing pump 4 is connected to the first oil circuit 6 through the first replenishing oil circuit 8 and to the second oil circuit 7 through the second replenishing oil circuit 9. When the motor 3 is working, one of the first oil circuit 6 and the second oil circuit 7 is a high-pressure oil circuit and the other is a low-pressure oil circuit. The replenishing pump 4 replenishes hydraulic oil to the low-pressure oil circuit.

[0036] Optionally, the closed-loop hydraulic system further includes a first replenishing check valve 11 located in the first replenishing oil circuit 8 and a second replenishing check valve 12 located in the second replenishing oil circuit 9. The first replenishing check valve 11 only allows hydraulic oil to flow from the replenishing pump 4 to the first oil circuit 6, and the second replenishing check valve 12 only allows hydraulic oil to flow from the replenishing pump 4 to the second oil circuit 7. By providing the first replenishing check valve 11 and the second replenishing check valve 12, backflow of hydraulic oil in the first oil circuit 6 and the second oil circuit 7 can be prevented.

[0037] Optionally, the closed-loop hydraulic system further includes a first relief valve 13 disposed between the first oil passage 6 and the oil pan, a second relief valve 14 disposed between the second oil passage 7 and the oil pan, and a third relief valve 15 disposed between the replenishing pump 4 and the oil pan. When the high-pressure oil in the first oil passage 6 or the second oil passage 7 exceeds a first limit, it can overflow through the corresponding first relief valve 13 or second relief valve 14. When the oil pressure in the replenishing pump 4 exceeds a second limit, it can overflow to the oil pan through the third relief valve 15.

[0038] Optionally, the closed-loop hydraulic system also includes an electro-hydraulic proportional valve 10. The servo cylinder 2 has a servo oil chamber and a servo piston 201 located within the servo oil chamber. The servo piston 201 is connected to the swashplate and divides the servo oil chamber into a left chamber 202 and a right chamber 203. The electro-hydraulic proportional valve 10 enables the replenishing pump 4 to connect to one of the left chamber 202 and the right chamber 203, and the oil pan to connect to the other of the left chamber 202 and the right chamber 203. The electro-hydraulic proportional valve 10 can also simultaneously disconnect the replenishing pump 4 from both the left chamber 202 and the right chamber 203. The flow direction of the hydraulic oil in the left chamber 202 and the right chamber 203 is controlled by the electro-hydraulic proportional valve 10 to drive the servo piston 201 to move. In turn, the swashplate angle is adjusted by the servo piston 201 to regulate the pump displacement of the variable pump 1.

[0039] Specifically, the electro-hydraulic proportional valve 10 is a three-position four-way valve with two electromagnetic control terminals and four ports. Both electromagnetic control terminals are connected to the controller 5. The controller 5 controls the electro-hydraulic proportional valve 10 to switch between left, center, and right positions by energizing or de-energizing the two electromagnetic control terminals. Specifically, when only the right electromagnetic control terminal is energized, it draws the valve core to the right, placing the electro-hydraulic proportional valve 10 in the left position; when only the left electromagnetic control terminal is energized, it draws the valve core to the left, placing the electro-hydraulic proportional valve 10 in the right position; and when both electromagnetic control terminals are de-energized, the electro-hydraulic proportional valve 10 is in the center position. The four ports are designated P, T, A, and B. Port P is connected to the replenishing pump 4, port T is connected to the oil pan, and ports A and B are connected to the left chamber 202 and right chamber 203, respectively. When the electro-hydraulic proportional valve 10 is in the left position, ports A and P are connected, and ports B and T are connected. At this time, oil enters the left chamber 202, and oil exits the right chamber 203. When the electro-hydraulic proportional valve 10 is in the right position, ports A and T are connected, and ports B and P are connected. At this time, oil exits the left chamber 202, and oil enters the right chamber 203. When the electro-hydraulic proportional valve 10 is in the middle position, ports A and B are disconnected from port P, and both ports A and B are connected to port T. Oil exits from both the left and right chambers 202, the swashplate angle is at its minimum, and the displacement of the variable pump 1 is at its minimum. Furthermore, taking the electro-hydraulic proportional valve 10 in the left position as an example, the voltage flowing into the left electromagnetic control terminal can be controlled by the controller 5, thereby controlling the opening of the electro-hydraulic proportional valve 10, thus adjusting the amount of hydraulic oil entering the left chamber 202, and consequently adjusting the position of the servo piston 201. In other embodiments, the electro-hydraulic proportional valve 10 can also be replaced by a two-position four-way valve, etc.

[0040] Alternatively, please refer to Figure 1The braking assembly includes a first solenoid valve 16 located in the first hydraulic circuit 6 and a second solenoid valve 17 located in the second hydraulic circuit 7. Both the first solenoid valve 16 and the second solenoid valve 17 are connected to a controller 5, which controls the energization or de-energization of these valves. Specifically, both the first solenoid valve 16 and the second solenoid valve 17 are two-position, two-way valves. When both are energized, the first solenoid valve 16 opens the first hydraulic circuit 6, and the second solenoid valve 17 opens the second hydraulic circuit 7. When both are de-energized, the first solenoid valve 16 disconnects the first hydraulic circuit 6, and the second solenoid valve 17 disconnects the second hydraulic circuit 7. Because the electro-hydraulic proportional valve 10 has a dead zone when the variable pump 1 starts, within this dead zone, an increase in voltage at the electromagnetic control terminal will not cause an increase in the displacement of the variable pump 1, and the displacement of the variable pump 1 remains zero. Therefore, when the closed hydraulic system is started, the controller 5 controls one of the solenoid control terminals of the electro-hydraulic proportional valve 10 to be energized. When the electro-hydraulic proportional valve 10 is still in the dead zone, the controller 5 controls the first solenoid valve 16 and the second solenoid valve 17 to be energized, and the closed circuit of the variable pump 1 and the motor 3 is connected. When the electro-hydraulic proportional valve 10 passes the dead zone, it can work normally, and the motor 3 drives the rotary load to operate.

[0041] This embodiment also provides a control method for a closed-loop hydraulic system. During braking, the controller 5 de-energizes the electromagnetic control terminal of the electro-hydraulic proportional valve 10 to gradually reset the servo cylinder 2. After an interval Δt, the braking assembly simultaneously disconnects the first oil circuit 6 and the second oil circuit 7. Specifically, in this embodiment, the electro-hydraulic proportional valve 10, the first solenoid valve 16, and the second solenoid valve 17 are all connected to the controller. When the closed-loop hydraulic system brakes, the controller 5 de-energizes the electromagnetic control terminal of the electro-hydraulic proportional valve 10. The controller 5 then delays for Δt to de-energize the first solenoid valve 16 and the second solenoid valve 17, thereby disconnecting the closed loop between the variable pump 1 and the motor 3. This effectively ensures that the rotary load stops and prevents drift. Here, Δt is the time required for the motor 3 to stop rotating after the electromagnetic control terminal of the electro-hydraulic proportional valve 10 is energized and de-energized. When the vehicle is turned off, the electromagnetic control terminal of the electro-hydraulic proportional valve 10 is de-energized, and the first solenoid valve 16 and the second solenoid valve 17 are de-energized, which also effectively ensures that the rotary load stops and prevents drift.

[0042] like Figure 1 As shown, the braking assembly can be installed separately from the variable pump 1, with the braking assembly located outside the variable pump 1. Alternatively, the braking assembly can be integrated with the variable pump 1, with the braking assembly located inside the variable pump 1. This arrangement results in a higher degree of integration and effectively reduces the number of external connecting pipelines.

[0043] Example 2

[0044] Please refer to Figure 2 and Figure 3The difference between this embodiment and Embodiment 1 lies only in the structure of the braking assembly. Specifically, the braking assembly includes a first pilot check valve 18 disposed in the first oil circuit 6 and a second pilot check valve 19 disposed in the second oil circuit 7. The pilot oil circuit of the first pilot check valve 18 is connected to the second oil circuit 7, and the connection point is located between the second oil port of the variable pump 1 and the second pilot check valve 19. The pilot oil circuit of the second pilot check valve 19 is connected to the first oil circuit 6, and the connection point is located between the first oil port of the variable pump 1 and the first pilot check valve 18. Specifically, the first end of the first pilot check valve 18 is connected to the pump side of the first oil circuit 6, and the second end of the first pilot check valve 18 is connected to the motor side of the first oil circuit 6. The first end of the second pilot check valve 19 is connected to the pump side of the second oil circuit 7, and the second end of the second pilot check valve 19 is connected to the motor side of the second oil circuit 7. When the pump-side oil pressure in the first oil circuit 6 is greater than the motor-side oil pressure in the first oil circuit 6, the first pilot check valve 18 opens, allowing hydraulic oil to flow unidirectionally from the variable pump 1 to the motor 3 via the first oil circuit 6. When the pump-side oil pressure in the second oil circuit 7 is greater than the motor-side oil pressure in the second oil circuit 7, the second pilot check valve 19 opens, allowing hydraulic oil to flow unidirectionally from the variable pump 1 to the motor 3 via the second oil circuit 7. When the pump-side oil pressure in the second oil circuit 7 is greater than the set oil pressure, the first pilot check valve 18 opens, allowing the first oil circuit 6 to be bidirectionally open. When the pump-side oil pressure in the first oil circuit 6 is greater than the set oil pressure, the second pilot check valve 19 opens, allowing the second oil circuit 7 to be bidirectionally open. Therefore, a hydraulic lock can be formed by the first pilot check valve 18 and the second pilot check valve 19. Taking the first oil circuit 6 as low-pressure oil and the second oil circuit 7 as high-pressure oil as an example, the oil pressure in the second oil circuit 7 is higher than the set oil pressure, so the first pilot check valve 18 opens and the first oil circuit 6 is bidirectionally connected. The pump side oil pressure in the second oil circuit 7 is greater than the motor side oil pressure in the second oil circuit 7, so the second pilot check valve 19 opens unidirectionally. Thus, the hydraulic oil can flow back to the variable pump 1 from the second oil port of the variable pump 1 through the second oil circuit 7, the motor 3, the first oil circuit 6, and the first oil port of the variable pump 1. At this time, the closed-loop system can operate normally, and motor 3 can drive the rotating load. When the closed-loop hydraulic system brakes, the controller 5 de-energizes the electromagnetic control terminal of the electro-hydraulic proportional valve 10. The oil pressure in the first oil circuit 6 and the second oil circuit 7 will both be low pressure, lower than the opening oil pressure of the first pilot check valve 18 and the second pilot check valve 19. Thus, the first pilot check valve 18 disconnects the first oil circuit 6, and the second pilot check valve 19 disconnects the second oil circuit 7, thereby disconnecting the closed loop between the variable pump 1 and the motor 3. This effectively ensures that the rotating load stops and prevents drift. When the vehicle is turned off, the electromagnetic control terminal of the electro-hydraulic proportional valve 10 is de-energized, the first pilot check valve 18 disconnects the first oil circuit 6, and the second pilot check valve 19 disconnects the second oil circuit 7, which also effectively ensures that the rotating load stops.

[0045] The braking assembly can be separately installed from the variable displacement pump 1, with the braking assembly located outside the variable displacement pump 1 for easy maintenance. Preferably, as shown below... Figure 2 As shown, the braking assembly, the first replenishing check valve 11, the second replenishing oil passage 9, the first overflow valve 13, the second overflow valve 14, and the third overflow valve 15 are integrated into an external valve group. Alternatively, the braking assembly can be integrated with the variable displacement pump 1, with the braking assembly housed inside the variable displacement pump 1. This arrangement results in a higher degree of integration and effectively reduces the number of external connecting pipelines. Preferably, as shown... Figure 3 As shown, the braking assembly, the first replenishing check valve 11, the second replenishing oil circuit 9, the first overflow valve 13, the second overflow valve 14, and the third overflow valve 15 are all integrated inside the variable pump 1.

[0046] Example 3

[0047] Please refer to Figure 4 and Figure 5 The difference between this embodiment and Embodiment 1 lies only in the structure of the braking assembly. Specifically, the braking assembly includes an electromagnetic control valve 22, a first pilot valve 20 disposed in the first oil circuit 6, and a second pilot valve 21 disposed in the second oil circuit 7. The first port of the electromagnetic control valve 22 is connected to the replenishing pump 4, and the second port of the electromagnetic control valve 22 provides pilot oil to the first pilot valve 20 and the second pilot valve 21 respectively. Specifically, the electromagnetic control valve 22 is connected to the controller 5. The controller 5 can control the electromagnetic control valve 22 to open, so as to connect the pilot oil circuit of the first pilot valve 20 and the pilot oil circuit of the second pilot valve 21 to the replenishing pump 4. Under the oil pressure of the hydraulic oil provided by the replenishing pump 4, the first pilot valve 20 opens the first oil circuit 6, and the second pilot valve 21 opens the second oil circuit 7. Then, the controller 5 controls the electromagnetic control terminal of the electro-hydraulic proportional valve 10 to be energized, so that the closed-loop is opened, and the motor 3 can drive the rotating load to work. When the closed-loop braking is required, the controller 5 gradually reduces the voltage at the electromagnetic control terminal of the electro-hydraulic proportional valve 10 to zero. Simultaneously, the controller 5 gradually reduces the control voltage of the electromagnetic control valve 22 to zero, thus gradually disconnecting the first oil circuit 6 and the second oil circuit 7. This ensures a smooth stop of the rotating load without impact and ultimately closes the closed-loop system. At this point, the first oil circuit 6 and the second oil circuit 7 are disconnected, and the closed circuit between the variable pump 1 and the motor 3 is broken, effectively ensuring the stopping of the rotating load and preventing drift. When the vehicle is turned off, the electromagnetic control terminal of the electro-hydraulic proportional valve 10 is de-energized, and the electromagnetic control valve 22 is de-energized. The first pilot valve 20 disconnects the first oil circuit 6, and the second pilot valve 21 disconnects the second oil circuit 7, similarly effectively stopping the rotating load. Preferably, the electromagnetic control valve 22 is a proportional pressure reducing valve. In other embodiments, the electromagnetic control valve 22 can also be replaced by a combination of a solenoid valve and a relief valve.

[0048] The braking assembly can be separately installed from the variable displacement pump 1, with the braking assembly located outside the variable displacement pump 1 for easy maintenance. Preferably, as shown below... Figure 4As shown, the braking assembly, the first replenishing check valve 11, the second replenishing oil passage 9, the first overflow valve 13, the second overflow valve 14, and the third overflow valve 15 are integrated into an external valve group. Alternatively, the braking assembly can be integrated with the variable displacement pump 1, with the braking assembly housed inside the variable displacement pump 1. This arrangement results in a higher degree of integration and effectively reduces the number of external connecting pipelines. Preferably, as shown... Figure 5 As shown, the braking assembly, the first replenishing check valve 11, the second replenishing oil circuit 9, the first overflow valve 13, the second overflow valve 14, and the third overflow valve 15 are all integrated inside the variable pump 1.

[0049] Example 4

[0050] This embodiment also provides an engineering machine, including the closed hydraulic system in any one of the embodiments one to three.

[0051] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A closed-loop hydraulic system, characterized in that, include: Variable pump (1), connected to power source; Servo cylinder (2) is connected to the swashplate of the variable pump (1) and is used to control the swing angle of the swashplate; The first oil port of the variable pump (1) and the second oil port of the motor (3) are connected through the first oil passage (6), and the second oil port of the variable pump (1) and the first oil port of the motor (3) are connected through the second oil passage (7). The braking assembly is capable of controlling the first oil circuit (6) and the second oil circuit (7) to be simultaneously turned on or off; The braking assembly includes a first solenoid valve (16) disposed in the first oil circuit (6) and a second solenoid valve (17) disposed in the second oil circuit (7); or The braking assembly includes a first pilot check valve (18) disposed in the first oil circuit (6) and a second pilot check valve (19) disposed in the second oil circuit (7). The pilot oil circuit of the first pilot check valve (18) is connected to the second oil circuit (7) and the connection point is located between the second oil port of the variable pump (1) and the second pilot check valve (19). The pilot oil circuit of the second pilot check valve (19) is connected to the first oil circuit (6) and the connection point is located between the first oil port of the variable pump (1) and the first pilot check valve (18); or The braking assembly includes an electromagnetic control valve (22), a first pilot valve (20) disposed in the first oil circuit (6) and a second pilot valve (21) disposed in the second oil circuit (7). The electromagnetic control valve (22) is used to control the pilot oil circuit of the first pilot valve (20) and the pilot oil circuit of the second pilot valve (21) to be simultaneously opened or simultaneously closed. The closed hydraulic system also includes an electro-hydraulic proportional valve (10). The servo cylinder (2) has a servo oil chamber and a servo piston (201) located in the servo oil chamber. The servo piston (201) is connected to the swashplate. The servo piston (201) divides the servo oil chamber into a left chamber (202) and a right chamber (203). The electro-hydraulic proportional valve (10) can control one of the left chamber (202) and the right chamber (203) to replenish oil while the other drains oil, or drain oil simultaneously.

2. The closed-loop hydraulic system according to claim 1, characterized in that, The closed hydraulic system also includes a replenishing pump (4), which is connected to the power source. The replenishing pump (4) is connected to the first oil circuit (6) through the first replenishing oil circuit (8), and the replenishing pump (4) is connected to the second oil circuit (7) through the second replenishing oil circuit (9).

3. The closed-loop hydraulic system according to any one of claims 1-2, characterized in that, The braking assembly and the variable pump (1) are integrated.

4. A control method for a closed hydraulic system as described in any one of claims 1-3, characterized in that, During braking, the controller (5) de-energizes the electromagnetic control terminal of the electro-hydraulic proportional valve (10) to gradually reset the servo cylinder (2), and after an interval of Δt, the braking assembly controls the first oil circuit (6) and the second oil circuit (7) to disconnect simultaneously.

5. An engineering machinery, characterized in that, Includes the closed hydraulic system as described in any one of claims 1-3.

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