阅读说明：本技术 一种闭式液压系统、闭式液压系统的控制方法及工程机械 (Closed hydraulic system, control method of closed hydraulic system and engineering machinery ) 是由 张平 薛德森 杨乐 杨典作 石常增 卞秀强 王雷 于 2020-12-14 设计创作，主要内容包括：本发明涉及工程机械技术领域,具体公开了一种闭式液压系统、闭式液压系统的控制方法及工程机械,该闭式液压系统包括变量泵、伺服油缸、马达和制动组件,变量泵与动力源连接,伺服油缸与变量泵的斜盘连接,且用于控制斜盘的摆角；变量泵和马达通过第一油路和第二油路构成闭式循环,马达与转动负载连接,制动组件能够将第一油路和第二油路同时打开,变量泵可正常驱动马达工作,以输出动力,并驱动转动负载转动；且制动组件能够将第一油路及第二油路同时断开,闭式循环的油路被截止,可有效保证回转负载停止,避免出现转动漂移或者回转停不住的情况。(The invention relates to the technical field of engineering machinery, and particularly discloses a closed hydraulic system, a control method of the closed hydraulic system and the engineering machinery, wherein the closed hydraulic system comprises a variable pump, a servo oil cylinder, a motor and a brake assembly; the variable pump and the motor form closed circulation through a first oil way and a second oil way, the motor is connected with a rotating load, the braking assembly can open the first oil way and the second oil way simultaneously, and the variable pump can normally drive the motor to work so as to output power and drive the rotating load to rotate; and the brake assembly can disconnect the first oil way and the second oil way simultaneously, and the closed-cycle oil way is cut off, so that the rotation load can be effectively guaranteed to stop, and the conditions of rotation drift or rotation stop failure are avoided.)

1. A closed hydraulic system, comprising:

the variable pump (1) is connected with a power source;

the servo oil cylinder (2) is connected with a swash plate of the variable pump (1) and is used for controlling the swing angle of the swash plate;

the variable pump comprises a motor (3), wherein a first oil port of the variable pump (1) is connected with a second oil port of the motor (3) through a first oil path (6), and a second oil port of the variable pump (1) is connected with a first oil port of the motor (3) through a second oil path (7);

and the brake assembly can control the first oil path (6) and the second oil path (7) to be simultaneously conducted or simultaneously disconnected.

2. Closed hydraulic system according to claim 1, characterized in that the brake assembly comprises a first solenoid valve (16) arranged in the first oil passage (6) and a second solenoid valve (17) arranged in the second oil passage (7).

3. The closed hydraulic system according to claim 1, wherein the brake assembly includes a first pilot check valve (18) disposed in the first oil passage (6) and a second pilot check valve (19) disposed in the second oil passage (7), the pilot oil passage of the first pilot check valve (18) is connected to the second oil passage (7) and a connection point is located between a second oil port of the variable pump (1) and the second pilot check valve (19), and the pilot oil passage of the second pilot check valve (19) is connected to the first oil passage (6) and a connection point is located between the first oil port of the variable pump (1) and the first pilot check valve (18).

4. The closed hydraulic system according to claim 1, wherein the brake assembly comprises an electromagnetic control valve (22), a first pilot valve (20) arranged in the first oil path (6) and a second pilot valve (21) arranged in the second oil path (7), and the electromagnetic control valve (22) is used for controlling the pilot oil path of the first pilot valve (20) and the pilot oil path of the second pilot valve (21) to be simultaneously connected or disconnected.

5. Closed hydraulic system according to claim 4, characterized in that the solenoid control valve (22) is a proportional pressure reducing valve.

6. The closed hydraulic system according to claim 4, further comprising an oil replenishment pump (4), wherein the oil replenishment pump (4) is connected to the power source, and the oil replenishment pump (4) is connected to the first oil passage (6) through a first oil replenishment oil passage (8), and the oil replenishment pump (4) is connected to the second oil passage (7) through a second oil replenishment oil passage (9); and the oil supplementing pump (4) is connected with the electromagnetic control valve (22) and is used for supplying oil to the pilot oil path of the first pilot valve (20) and the pilot oil path of the second pilot valve (21).

7. The closed hydraulic system according to claim 1, further comprising an electro-hydraulic proportional valve (10), wherein 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 swash plate, the servo piston (201) divides the servo oil chamber into a left chamber (202) and a right chamber (203), and the electro-hydraulic proportional valve (10) can control one of the left chamber (202) and the right chamber (203) to be supplied with oil and the other to be drained with oil, or to be drained with oil at the same time.

8. Closed hydraulic system according to any one of claims 1 to 7, characterized in that the brake assembly and the variable displacement pump (1) are provided integrally.

9. A control method of a closed hydraulic system according to any one of claims 1-8, characterized in that during braking, the controller (5) controls the electromagnetic control end of the electro-hydraulic proportional valve (10) to lose power so as to gradually reset the servo cylinder (2), and after an interval of time Δ t, the brake assembly controls the first oil passage (6) and the second oil passage (7) to be simultaneously disconnected.

10. A working machine, characterized in that it comprises a closed hydraulic system according to any one of claims 1-8.

Technical Field

The invention relates to the technical field of engineering machinery, in particular to a closed hydraulic system, a control method of the closed hydraulic system and the engineering machinery.

Background

The swing mechanism is an important part of a hydraulic excavator and is used for driving an upper vehicle part of a working vehicle such as the hydraulic excavator to perform swing motion.

For an engineering machine using closed system rotation, when the rotation stops, the braking is realized mainly by an overflow valve in the system. However, when the moment of inertia of getting on the vehicle is large or the system leaks, the situation of rotational drift or rotation stop is easy to occur.

Disclosure of Invention

The invention aims to: the closed type hydraulic system, the control method of the closed type hydraulic system and the engineering machinery are provided, and the problem that in the related art, the closed type system rotating engineering machinery is used, braking is achieved mainly by means of an overflow valve in the system, and when the rotational inertia of a vehicle is large or the system leaks, the situation that rotational drift or rotation cannot be stopped easily occurs is solved.

In one aspect, the present invention provides a closed hydraulic system comprising:

the variable pump is connected with the 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 first oil port of the variable pump is connected with the second oil port of the motor through a first oil path, and the second oil port of the variable pump is connected with the first oil port of the motor through a second oil path;

and the brake assembly can control the first oil path and the second oil path to be simultaneously connected or disconnected.

As a preferable technical scheme of the closed hydraulic system, the brake assembly includes a first solenoid valve disposed in the first oil passage and a second solenoid valve disposed in the second oil passage.

As a preferable technical solution of the closed hydraulic system, the brake assembly includes a first pilot check valve disposed in the first oil passage and a second pilot check valve disposed in the second oil passage, the pilot oil passage of the first pilot check valve is connected to the second oil passage and a connection point of the first pilot check valve is located between the second oil port of the variable displacement pump and the second pilot check valve, and the pilot oil passage of the second pilot check valve is connected to the first oil passage and a connection point of the second pilot check valve is located between the first oil port of the variable displacement pump and the first pilot check valve.

As a preferable technical solution of the closed hydraulic system, the brake assembly includes an electromagnetic control valve, a first pilot valve disposed in the first oil path, and a second pilot valve disposed in the second oil path, and the electromagnetic control valve is configured to control the pilot oil path of the first pilot valve and the pilot oil path of the second pilot valve to be simultaneously turned on or turned off.

As a preferred technical scheme of the closed hydraulic system, the electromagnetic control valve is a proportional pressure reducing valve.

As a preferred technical scheme of the closed hydraulic system, the closed hydraulic system further comprises an oil supplementing pump, the oil supplementing pump is connected with the power source, and is connected with the first oil path through a first oil supplementing oil path, and is connected with the second oil path through a second oil supplementing oil path; and the oil supplementing pump is connected with the electromagnetic control valve and is used for supplying oil to the pilot oil path of the first pilot valve and the pilot oil path of the second pilot valve.

As the preferred technical scheme of the closed hydraulic system, the closed hydraulic system further comprises an electro-hydraulic proportional valve, the servo oil cylinder is provided with a servo oil cavity and a servo piston located in the servo oil cavity, the servo piston is connected with the swash plate, the servo piston divides the servo oil cavity into a left cavity and a right cavity, and the electro-hydraulic proportional valve can control oil supplementing and oil draining of one of the left cavity and the right cavity or oil draining of the other cavity simultaneously.

As a preferable technical scheme of the closed hydraulic system, the brake assembly and the variable pump are integrally arranged.

On the other hand, the invention provides a control method of the closed hydraulic system in any one of the above schemes, during braking, the controller controls the electromagnetic control end of the electro-hydraulic proportional valve to lose power so as to gradually reset the servo oil cylinder, and after the interval time delta t, the brake assembly controls the first oil path and the second oil path to be simultaneously disconnected.

In another aspect, the invention provides a construction machine, which includes the closed hydraulic system in any one of the above aspects.

The invention has the beneficial effects that:

the invention provides a closed hydraulic system, a control method of the closed hydraulic system and engineering machinery. The variable pump is connected with the power source, and the servo oil cylinder is connected with a swash plate of the variable pump and used for controlling the swing angle of the swash plate; the variable displacement pump and the motor form closed circulation through the first oil path and the second oil path, the motor is connected with a rotating load, the braking assembly can disconnect the first oil path and the second oil path simultaneously, and the braking assembly can open the first oil path and the second oil path simultaneously. When the brake assembly opens the first oil path and the second oil path simultaneously, the variable displacement pump can normally drive the motor to work so as to output power and drive the rotating load to rotate. When the brake assembly cuts off the first oil way and the second oil way simultaneously, the closed-cycle oil way is cut off, so that the rotation load can be effectively guaranteed to stop, and the rotation drift or rotation stop failure is avoided.

Drawings

Fig. 1 is a schematic structural diagram of a closed-center hydraulic system according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a closed hydraulic system according to a second embodiment of the present invention;

fig. 3 is a second structural schematic diagram of a closed hydraulic system in the second embodiment of the invention;

fig. 4 is a first structural schematic diagram of a closed hydraulic system in a third embodiment of the invention;

fig. 5 is a schematic structural diagram of a closed hydraulic system in a third embodiment of the present invention.

In the figure:

1. a variable displacement pump; 2. a servo cylinder; 201. a servo piston; 202. a left lumen; 203. a right lumen; 3. a motor; 4. an oil replenishing pump; 5. a controller; 6. a first oil passage; 7. a second oil passage; 8. a first oil supply path; 9. a second oil supply path; 10. an electro-hydraulic proportional valve; 11. a first oil-supplementing one-way valve; 12. a second oil-supplementing one-way valve; 13. a first overflow valve; 14. a second overflow valve; 15. a third overflow valve; 16. a first solenoid valve; 17. a second solenoid valve; 18. a first pilot check valve; 19. a second pilot check valve; 20. a first pilot valve; 21. a second pilot valve; 22. an electromagnetic control valve.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Where the terms "first position" and "second position" are two different positions, and where a first feature is "over", "above" and "on" a second feature, it is intended that the first feature is directly over and obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

Example one

As shown in fig. 1, the present embodiment provides a closed type hydraulic system including a variable displacement pump 1, a servo cylinder 2, a motor 3, and a brake assembly. The variable displacement pump 1 is connected with a power source, and is driven to rotate by the power source, wherein the power source can be an engine, a motor and the like. The servo oil cylinder 2 is connected with a swash plate of the variable displacement pump 1 and is used for controlling the swing angle of the swash plate; the first oil port of the variable pump 1 and the second oil port of the motor 3 are connected through a first oil path 6, the second oil port of the variable pump 1 and the first oil port of the motor 3 are connected through a second oil path 7, so that the variable pump 1 and the motor 3 form closed circulation through the first oil path 6 and the second oil path 7, and the motor 3 is connected with a rotary load. The brake assembly can simultaneously open or close the first oil passage 6 and the second oil passage 7. When the brake assembly conducts the first oil path 6 and the second oil path 7 at the same time, the variable displacement pump 1 can normally drive the motor 3 to work so as to output power and drive the rotating load to rotate. When the brake assembly disconnects the first oil way 6 and the second oil way 7 at the same time, the closed-cycle oil way is cut off, so that the rotation load can be effectively guaranteed to stop, and the conditions of rotation drift or rotation stop failure are avoided.

It should be noted that, in the present embodiment, either one of the first port of the variable displacement pump 1 and the second port of the variable displacement pump 1 may be used as an input end, and the other may be used as an output end.

Optionally, the closed hydraulic system further includes an oil supply pump 4, the oil supply pump 4 is connected to the power source, the oil supply pump 4 is connected to the first oil path 6 through a first oil supply path 8, the oil supply pump 4 is connected to the second oil path 7 through a second oil supply path 9, when the motor 3 operates, one of the first oil path 6 and the second oil path 7 is a high-pressure oil path, the other is a low-pressure oil path, and the oil supply pump 4 supplies hydraulic oil for the low-pressure oil path.

Optionally, the closed hydraulic system further includes a first oil-replenishing check valve 11 disposed in the first oil-replenishing oil path 8 and a second oil-replenishing check valve 12 disposed in the second oil-replenishing oil path 9, the first oil-replenishing check valve 11 only allows hydraulic oil to flow from the oil-replenishing pump 4 to the first oil path 6, and the second oil-replenishing check valve 12 only allows hydraulic oil to flow from the oil-replenishing pump 4 to the second oil path 7. By providing the first oil compensation check valve 11 and the second oil compensation check valve 12, the hydraulic oil in the first oil passage 6 and the second oil passage 7 can be prevented from flowing back.

Optionally, the closed hydraulic system further includes a first overflow valve 13 provided between the first oil path 6 and the oil pan, a second overflow valve 14 provided between the second oil path 7 and the oil pan, and a third overflow valve 15 provided between the oil replenishment pump 4 and the oil pan. When the high-pressure oil in the first oil path 6 or the second oil path 7 exceeds the first limit value, the high-pressure oil can overflow through the corresponding first overflow valve 13 or the corresponding second overflow valve 14, and when the oil pressure in the oil supply pump 4 exceeds the second limit value, the high-pressure oil can overflow to the oil pan through the third overflow valve 15.

Optionally, the closed hydraulic system further comprises 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 with a swash plate, the servo oil chamber is divided into a left chamber 202 and a right chamber 203 by the servo piston 201, the electro-hydraulic proportional valve 10 can enable the oil supply pump 4 to be communicated with one of the left chamber 202 and the right chamber 203, the oil pan is communicated with the other of the left chamber 202 and the right chamber 203, and the electro-hydraulic proportional valve 10 can enable the oil supply pump 4 to be simultaneously disconnected with the left chamber 202 and the right chamber 203. The hydraulic oil flow direction of the left cavity 202 and the right cavity 203 is controlled through the electro-hydraulic proportional valve 10 to drive the servo piston 201 to move, and then the swing angle of the swash plate is adjusted through the servo piston 201 to adjust the pump displacement of the variable displacement pump 1.

Specifically, the electro-hydraulic proportional valve 10 is a three-position four-way valve having two electromagnetic control ends and four ports. The two electromagnetic control ends are connected with the controller 5, and the controller 5 controls the electro-hydraulic proportional valve 10 to switch among a left position, a middle position and a right position by controlling the two electromagnetic control ends to be powered on or powered off. When only the electromagnetic control end on the right side is electrified, the electromagnetic control end on the right side attracts the valve core to move towards the right side, and the electro-hydraulic proportional valve 10 is located at the left position; when only the electromagnetic control end on the left side is electrified, the electromagnetic control end on the left side attracts the valve core to move towards the left side, and the electro-hydraulic proportional valve 10 is in the right position; when the two electromagnetic control ends are both de-energized, the electro-hydraulic proportional valve 10 is in the middle position. The four interfaces are respectively a port P, a port T, a port A and a port B. Wherein, P mouth and the oil supplementing pump 4 intercommunication, T mouth and oil pan intercommunication, A mouth and B mouth are connected to left chamber 202 and right chamber 203 respectively. When the electro-hydraulic proportional valve 10 is in the left position, the port A is communicated with the port P, the port B is communicated with the port T, at the moment, oil enters the left cavity 202, and oil is drained from the right cavity 203; when the electro-hydraulic proportional valve 10 is in the right position, the port A is communicated with the port T, the port B is communicated with the port P, oil is drained from the left cavity 202 at the moment, and oil is fed into the right cavity 203; when the electro-hydraulic proportional valve 10 is in the middle position, the port A and the port B are both disconnected with the port P, the port A and the port B are both communicated with the port T, oil is drained from the left cavity 202 and the right cavity 203, the swash plate swing angle is minimum, and the displacement of the variable displacement pump 1 is minimum. And, taking the electro-hydraulic proportional valve 10 in the left position as an example, at this time, the controller 5 controls the voltage flowing into the left electromagnetic control end, so as to control the opening degree of the electro-hydraulic proportional valve 10, thereby adjusting the oil amount of the hydraulic oil entering the left chamber 202, and further adjusting the position of the servo piston 201. In other embodiments, the electro-hydraulic proportional valve 10 may be replaced by a two-position four-way valve or the like.

Alternatively, referring to fig. 1, the brake assembly includes a first solenoid valve 16 disposed in the first oil passage 6 and a second solenoid valve 17 disposed in the second oil passage 7. The first electromagnetic valve 16 and the second electromagnetic valve 17 are both connected with the controller 5, and the controller 5 controls the first electromagnetic valve 16 and the second electromagnetic valve 17 to be powered on or powered off. Specifically, the first solenoid valve 16 and the second solenoid valve 17 are both two-position two-way valves, and when the first solenoid valve 16 and the second solenoid valve 17 are both energized, the first solenoid valve 16 opens the first oil passage 6, and the second solenoid valve 17 opens the second oil passage 7. When both the first solenoid valve 16 and the second solenoid valve 17 are de-energized, the first solenoid valve 16 disconnects the first oil passage 6, and the second solenoid valve 17 disconnects the second oil passage 7. Because the electro-hydraulic proportional valve 10 has a dead zone when the variable displacement pump 1 is started, in the dead zone, the voltage of the electromagnetic control end is increased, so that the displacement of the variable displacement pump 1 is not increased, and the displacement of the variable displacement pump 1 is zero. Therefore, when the closed hydraulic system is started, the controller 5 controls one electromagnetic control end of the electro-hydraulic proportional valve 10 to be electrified, when the electro-hydraulic proportional valve 10 is still in a dead zone, the controller 5 controls the first electromagnetic valve 16 and the second electromagnetic valve 17 to be electrified, the closed loop of the variable displacement pump 1 and the closed loop of the motor 3 are communicated, when the electro-hydraulic proportional valve 10 crosses the dead zone, the operation can be normally carried out, and the motor 3 drives the rotary load to operate.

In the embodiment, a control method of the closed hydraulic system is further provided, during braking, the controller 5 controls the electromagnetic control end of the electro-hydraulic proportional valve 10 to lose power so as to gradually reset the servo oil cylinder 2, and after an interval time Δ t, the brake assembly controls the first oil path 6 and the second oil path 7 to be simultaneously disconnected. Specifically, in this embodiment, the electro-hydraulic proportional valve 10, the first electromagnetic valve 16 and the second electromagnetic valve 17 are all connected with the controller, when the closed hydraulic system brakes, the controller 5 controls the electromagnetic control end of the electro-hydraulic proportional valve 10 to lose power, and the controller 5 delays time Δ t to control the first electromagnetic valve 16 and the second electromagnetic valve 17 to be powered off, so as to disconnect the closed loop between the variable displacement pump 1 and the motor 3, thereby effectively ensuring that the rotary load stops and preventing the drift phenomenon from occurring. Wherein, Δ t is the time required for the motor 3 to stop rotating after the electromagnetic control end of the electro-hydraulic proportional valve 10 is powered on and powered off. When the vehicle is flamed out, the electromagnetic control end of the electro-hydraulic proportional valve 10 is de-energized, the first electromagnetic valve 16 and the second electromagnetic valve 17 are de-energized, the rotation load can be effectively guaranteed to stop, and the drifting phenomenon is prevented.

As shown in fig. 1, the brake assembly may be provided separately from the variable displacement pump 1, and the brake assembly may be provided outside the variable displacement pump 1. Certainly, the brake assembly can also be integrated with the variable pump 1 and set up, and the brake assembly can set up in the variable pump 1 inside, and it is higher to set up the integrated level like this, can effectively reduce outside connecting line.

Example two

Referring to fig. 2 and 3, the difference between the first embodiment and the second embodiment is that only the structure of the braking assembly is different. Specifically, the brake assembly includes a first pilot check valve 18 disposed on the first oil path 6 and a second pilot check valve 19 disposed on the second oil path 7, the pilot oil path of the first pilot check valve 18 is connected to the second oil path 7, and a connection point is located between the second oil port of the variable displacement pump 1 and the second pilot check valve 19, the pilot oil path of the second pilot check valve 19 is connected to the first oil path 6, and a connection point is located between the first oil port of the variable displacement pump 1 and the first pilot check valve 18. Specifically, a first end of first pilot check valve 18 is connected to the pump side of first oil passage 6, a second end of first pilot check valve 18 is connected to the motor side of first oil passage 6, a first end of second pilot check valve 19 is connected to the pump side of second oil passage 7, and a second end of second pilot check valve 19 is connected to the motor side of second oil passage 7. When the oil pressure on the pump side of the first oil passage 6 is greater than the oil pressure on the motor side of the first oil passage 6, the first pilot check valve 18 is opened, and at this time, hydraulic oil can flow from the variable displacement pump 1 to the motor 3 in a one-way manner through the first oil passage 6; when the pump-side oil pressure of the second oil passage 7 is greater than the motor-side oil pressure of the second oil passage 7, the second pilot check valve 19 opens, and hydraulic oil can flow from the variable displacement pump 1 to the motor 3 in one direction through the second oil passage 7. When the pump-side oil pressure of the second oil passage 7 is greater than the set oil pressure, the first pilot check valve 18 is opened, and the first oil passage 6 is conducted in both directions; when the pump-side oil pressure of first oil passage 6 is greater than the set oil pressure, second pilot check valve 19 opens, and second oil passage 7 is bidirectionally communicated at this time. 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 path 6 as low-pressure oil and the second oil path 7 as high-pressure oil as an example, the oil pressure of the second oil path 7 is higher than the set oil pressure, so that the first pilot check valve 18 is opened, the first oil path 6 is conducted in two directions, the pump-side oil pressure of the second oil path 7 is greater than the motor-side oil pressure of the second oil path 7, and the second pilot check valve 19 is opened in one direction, so that 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 path 7, the motor 3, the first oil path 6 and the first oil port of the variable pump 1. At the moment, the closed cycle can work normally, and the motor 3 can drive the rotating load to work; when the closed hydraulic system brakes, the controller 5 controls the electromagnetic control end of the electro-hydraulic proportional valve 10 to lose power, the oil pressures of the first oil path 6 and the second oil path 7 are both low and lower than the starting oil pressures of the first pilot check valve 18 and the second pilot check valve 19, so that the first pilot check valve 18 disconnects the first oil path 6, the second pilot check valve 19 disconnects the second oil path 7, a closed loop between the variable displacement pump 1 and the motor 3 is disconnected, the rotation load can be effectively guaranteed to stop, and the drift phenomenon is prevented from occurring. When the vehicle is flamed out, the electromagnetic control end of the electro-hydraulic proportional valve 10 loses power, the first pilot check valve 18 disconnects the first oil path 6, the second pilot check valve 19 disconnects the second oil path 7, and the rotation load can be effectively guaranteed to stop.

The brake assembly can be arranged in a split mode with the variable pump 1, and the brake assembly is arranged outside the variable pump 1 and is convenient to maintain. Preferably, as shown in fig. 2, the brake assembly, the first oil supplementing check valve 11, the second oil supplementing oil path 9, the first overflow valve 13, the second overflow valve 14 and the third overflow valve 15 are integrated to be an external valve set. Certainly, the brake assembly can also be integrated with the variable pump 1 and set up in the variable pump 1, so set up the integrated level higher, can effectively reduce outside connecting line. Preferably, as shown in fig. 3, the brake assembly, the first oil-replenishing check valve 11, the second oil-replenishing oil passage 9, the first relief valve 13, the second relief valve 14, and the third relief valve 15 are all integrated inside the variable displacement pump 1.

EXAMPLE III

Referring to fig. 4 and 5, the difference between the first embodiment and the second embodiment is that only the structure of the braking assembly is different. Specifically, the brake assembly includes an electromagnetic control valve 22, a first pilot valve 20 disposed in the first oil path 6, and a second pilot valve 21 disposed in the second oil path 7, a first oil port of the electromagnetic control valve 22 is connected to the oil replenishment pump 4, and a second oil port of the electromagnetic control valve 22 respectively provides pilot oil for the first pilot valve 20 and the second pilot valve 21. Specifically, the electromagnetic control valve 22 is connected to the controller 5, and the controller 5 may control the electromagnetic control valve 22 to open, so as to connect the pilot oil path of the pilot valve of the first pilot valve 20 and the pilot oil path of the second pilot valve 21 to the oil replenishing pump 4, under the oil pressure of the hydraulic oil provided by the oil replenishing pump 4, the first pilot valve 20 opens the first oil path 6, the second pilot valve 21 opens the second oil path 7, and then the controller 5 controls the electromagnetic control end of the electro-hydraulic proportional valve 10 to be energized, so as to open the closed cycle, and the motor 3 may drive the rotary load to work. When the closed circulation needs braking, the controller 5 controls the voltage of the electromagnetic control end of the electro-hydraulic proportional valve 10 to be gradually reduced to zero, meanwhile, the controller 5 controls the control voltage of the electromagnetic control valve 22 to be gradually reduced to zero so as to gradually disconnect the first oil path 6 and the second oil path 7, the rotating load can be guaranteed to stop stably without generating impact, and finally the closed circulation is closed, at the moment, the first oil path 6 and the second oil path 7 are disconnected, and the closed loop between the variable displacement pump 1 and the motor 3 is disconnected, so that the rotating load can be effectively guaranteed to stop, and the drifting phenomenon is prevented. When the vehicle is shut down, the electromagnetic control end of the electro-hydraulic proportional valve 10 is de-energized, the electromagnetic control valve 22 is de-energized, the first oil way 6 is disconnected by the first pilot valve 20, the second oil way 7 is disconnected by the second pilot valve 21, and the turning load can be effectively guaranteed to stop. Preferably, the solenoid control valve 22 is a proportional pressure reducing valve. In other embodiments, the solenoid control valve 22 may be replaced with a combination of a solenoid valve and a relief valve.

The brake assembly can be arranged in a split mode with the variable pump 1, and the brake assembly is arranged outside the variable pump 1 and is convenient to maintain. Preferably, as shown in fig. 4, the brake assembly, the first oil supplementing check valve 11, the second oil supplementing oil path 9, the first overflow valve 13, the second overflow valve 14 and the third overflow valve 15 are integrated to be an external valve set. Certainly, the brake assembly can also be integrated with the variable pump 1 and set up in the variable pump 1, so set up the integrated level higher, can effectively reduce outside connecting line. Preferably, as shown in fig. 5, the brake assembly, the first oil-replenishing check valve 11, the second oil-replenishing oil passage 9, the first relief valve 13, the second relief valve 14, and the third relief valve 15 are all integrated inside the variable displacement pump 1.

Example four

The embodiment also provides engineering machinery comprising the closed hydraulic system in any one of the first embodiment to the third embodiment.

It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.