Emergency valve for closed pump, closed pump, engineering machinery and fault diagnosis method

Abstract

The invention discloses an emergency valve for a closed pump, the closed pump, engineering machinery and a fault diagnosis method. The emergency valve comprises an emergency valve block, an emergency valve element installed in the emergency valve block, an emergency valve electromagnet and an emergency valve spring, wherein the emergency valve electromagnet and the emergency valve spring are used for adjusting the emergency valve element to work at different working positions so as to control connection and disconnection between the pilot oil source and the control valve or the variable piston. The emergency valve block is provided with a first working oil port, a second working oil port, a third working oil port, an oil return port used for being connected with an oil tank and a pilot oil inlet used for receiving pilot oil. The first working oil port is used for being connected with a left cavity of a variable piston in the closed pump. The second working oil port is used for being connected with a right cavity of a variable piston in the closed pump. The third working oil port is used for being connected with an inlet of a control valve in the closed pump. According to the method, reliable return-to-zero control over the displacement of the closed pump can be achieved, the fault point can be rapidly recognized, and the problem solving efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering machinery, and in particular relates to an emergency valve for a closed pump, a closed pump, engineering machinery and a fault diagnosis method. Background Art

[0002] A closed pump refers to an axial piston pump used in a closed circuit. In the wheeled walking machinery industry, the walking drive system is mostly a closed hydraulic system, with the motor directly driven by a closed pump. In actual working conditions, when the vehicle needs to stop, if the closed pump displacement cannot return to zero in time (referring to the position where the closed pump displacement is zero), the vehicle will slip, which is likely to cause a safety accident. At present, it is mainly solved by adjusting the piston pump displacement to zero at the factory, but when the control valve fails or fails (the control valve is stuck, the control valve feedback spring fails due to fatigue), the piston pump displacement cannot be returned to zero in time, and the vehicle will slip. Summary of the invention

[0003] In order to solve the deficiencies in the prior art, the present invention provides an emergency valve for a closed pump, a closed pump, engineering machinery and a fault diagnosis method, which can not only realize reliable zeroing control of the closed pump displacement, but also quickly identify the fault point and improve the efficiency of solving the problem.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: In a first aspect, an emergency valve for a closed pump is provided, the emergency valve comprising: an emergency valve block, an emergency valve core installed in the emergency valve block, an emergency valve solenoid and an emergency valve spring for adjusting the emergency valve core to work in different working positions to control the on-off between a pilot oil source and a control valve or a variable piston; the emergency valve block is provided with a working oil port one, a working oil port two, a working oil port three, an oil return port for connecting to an oil tank, and a pilot oil inlet for receiving pilot oil; the working oil port one is used to connect to a left chamber of a variable piston in a closed pump; the working oil port two is used to connect to a right chamber of a variable piston in a closed pump; the working oil port three is used to connect to an inlet of a control valve in a closed pump.

[0005] In a second aspect, a closed pump is provided, comprising an emergency valve for a closed pump as described in the first aspect.

[0006] Furthermore, the emergency valve block is directly connected to the control valve block of the control valve or adopts an integrated design.

[0007] Furthermore, the control valve includes: a control valve block, a control valve spool installed in the control valve block, a fulcrum pin installed on the control valve block, a control valve solenoid 1 and a control valve solenoid 2 for adjusting the control valve block to work in different working positions; one end of shift fork 1, one end of shift fork 2, and a middle part of a feedback rod are respectively hinged to the fulcrum pin; the other end of shift fork 1 and the other end of shift fork 2 are respectively connected to the two ends of a control valve spring; one end of the feedback rod is transmission connected to the variable piston, and the other end of the feedback rod is transmission connected to shift fork 1 or shift fork 2 through the feedback rod pin; the control valve spool is transmission connected to shift fork 1 or shift fork 2 through the spool pin.

[0008] Furthermore, the variable piston is transmission-connected to the swash plate via a slider, and is used to change the swing angle of the swash plate, thereby controlling the flow of the closed pump.

[0009] Furthermore, under normal circumstances, the emergency valve works in the right position, and the control valve solenoid 1 is energized, pushing the control valve core to move left, allowing the pilot oil to enter the right chamber of the variable piston. At the same time, the control valve core moves to the left, driving the shift fork 2 to open to the left around the fulcrum pin. The variable piston moves to the left under the action of the pressure oil, and the slider drives the swash plate to change the swing angle of the swash plate. At the same time, the variable piston drives the feedback rod to rotate to the right around the fulcrum pin, and pushes the shift fork 1 to open to the right around the fulcrum pin through the feedback rod pin. At this time, the spring force on the shift fork 1 and the shift fork 2 is greater than the electromagnetic force. Under the action of the spring force, the shift fork 2 moves to the right, driving the valve core pin to push the control valve core to move until the spring force and the electromagnetic force are balanced, the control valve core stops moving, and the oil circuit between the pilot oil source and the variable piston is disconnected, so that the displacement of the variable piston is stabilized at a certain set position, the swash plate stops at a certain set swing angle, and the hydraulic pump outputs a stable flow rate.

[0010] Furthermore, when the control valve solenoid 1 loses power, the spring force drives the shift fork 2 to push the control valve spool to the right, the valve port opens, the right chamber of the variable piston is connected to the oil tank, and the variable piston moves to the right under the action of its internal return spring. At the same time, the variable piston drives the feedback rod to rotate left around the fulcrum pin, and the feedback rod pin disengages from the shift fork 1. The shift fork 1 moves to the right under the action of the spring force, the control valve spring returns to its initial length, the control valve spool returns to its initial position, the valve port gradually closes, and the variable piston stops moving. At this time, the displacement of the closed pump returns to zero.

[0011] According to a third aspect, there is provided an engineering machine, wherein the engineering machine is equipped with the closed pump according to the second aspect.

[0012] In a fourth aspect, a method for diagnosing engineering machinery faults is provided, wherein the engineering machinery is the engineering machinery described in the third aspect, and the method comprises: judging the cause of the fault according to whether the engineering machinery has a slipping phenomenon and the state of the emergency valve after the engineering machinery has a slipping phenomenon.

[0013] Furthermore, when the solenoid of the control valve is de-energized but slippage occurs, it means that the displacement of the closed pump has not returned to zero. At this time, the emergency valve solenoid is energized, so that the emergency valve spool is in the middle position, cutting off the oil circuit between the control valve and the pilot oil source, and connecting the inlet of the control valve back to the oil tank; if the problem is solved, it means that when the oil circuit between the control valve and the pilot oil source is not cut off, the pilot oil enters the variable piston through the control valve, and the variable piston moves and finally maintains a certain position under the action of the pilot oil and the built-in return spring, the swash plate is at a certain angle, and the closed pump displacement is not zero; the cause of the fault is: the closed pump is inaccurately zeroed at the factory or the control valve spring is attenuated, resulting in the control valve spool being unable to reset, resulting in the control valve port being unable to close.

[0014] Furthermore, if the problem is still not solved, the current signal is switched to make the emergency valve work in the left position, cutting off the oil circuit between the control valve and the pilot oil source, and at the same time, connecting the pilot oil source with the oil chambers at both ends of the variable piston; in this case, if the problem is solved, the cause of the fault is: the control valve is stuck, the control valve spool cannot move, and the valve port is not opened, resulting in the oil chamber of the variable piston unable to relieve pressure, the variable piston cannot move, and the swash plate is always at a certain angle; if the problem is not solved, the cause of the fault is: the variable piston is stuck, and the closed pump cannot be variable.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention arranges an emergency valve, which includes: an emergency valve block, an emergency valve core installed in the emergency valve block, an emergency valve solenoid and an emergency valve spring for adjusting the emergency valve core to work in different working positions to control the on-off between the pilot oil source and the control valve or the variable piston; the emergency valve block is provided with a working oil port 1 for connecting to the left chamber of the variable piston in the closed pump, a working oil port 2 for connecting to the right chamber of the variable piston in the closed pump, a working oil port 3 for connecting to the inlet of the control valve in the closed pump, an oil return port for connecting to the oil tank and a pilot oil inlet for receiving the pilot oil; not only can the reliable zeroing control of the closed pump displacement be achieved, but also the fault point can be quickly identified, thereby improving the efficiency of problem solving. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the structure of a closed pump in an embodiment of the present invention; Figure 2 is a schematic diagram of the connection structure between the variable piston and the slant plate in an embodiment of the present invention; Figure 3 is a schematic diagram of the connection structure between the emergency valve and the control valve in an embodiment of the present invention; Figure 4 is a schematic diagram of the connection structure between the control valve and the variable piston in an embodiment of the present invention; Figure 5is a schematic cross-sectional structure diagram of a variable displacement piston in an embodiment of the present invention; Figure 6 Schematic diagram of the structure of the emergency valve core in an embodiment of the present invention, wherein (a) is a schematic diagram of the three-dimensional structure of the emergency valve core, and (b) is a schematic diagram of the cross-sectional structure of the emergency valve core; Figure 7 It is a schematic diagram of the working principle of the emergency valve in the embodiment of the present invention when it works in the right position; Figure 8 It is a schematic diagram of the working principle of the emergency valve in the embodiment of the present invention when it works in the middle position; Fig. 9 It is a schematic diagram of the working principle of the emergency valve in the embodiment of the present invention when it works in the left position; In the figure: 1. Emergency valve; 2. Control valve; 3. Feedback rod; 4. Variable piston; 5. Slider; 6. Swash plate; 7. Variable pump; 8. Oil replenishment pump; 11. Emergency valve solenoid; 12. Emergency valve spool; 13. Emergency valve spring; 14. Emergency valve block; 15. Filter 2; 21. Control valve solenoid 1; 22. Control valve solenoid 2; 23. Control valve spool; 24. Feedback rod pin; 25. Shift fork 1; 26. Valve spool pin; 27. Pivot pin; 28. Shift fork 2; 29. ​​Control valve block; 30. Control valve spring; 81. Filter 1; 82. Cold start valve; 83. Oil replenishment relief valve; 84. High-pressure relief oil replenishment valve 1; 85. High-pressure relief oil replenishment valve 2; 86. Pressure cut-off valve. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0018] Embodiment 1 like Figure 1 to Figure 9 As shown, an emergency valve for a closed pump, the emergency valve 1 includes: an emergency valve block 14, an emergency valve spool 12 installed in the emergency valve block 14, an emergency valve solenoid 11 and an emergency valve spring 13 for adjusting the emergency valve spool 12 to work in different working positions to control the on-off between the pilot oil source and the control valve 2 or the variable piston 4.

[0019] The emergency valve block 14 is provided with working oil port 1, working oil port 2, working oil port 3, an oil return port for connecting to the oil tank and a pilot oil inlet for receiving pilot oil; working oil port 1 is used to connect to the left chamber of the variable piston 4 in the closed pump; working oil port 2 is used to connect to the right chamber of the variable piston 4 in the closed pump; working oil port 3 is used to connect to the inlet of the control valve 2 in the closed pump.

[0020] By setting the emergency valve described in the present invention, not only can the closed pump displacement be reliably returned to zero, the problem of slipping during emergency braking can be effectively solved, and the safety of the whole machine can be improved; the fault point can also be quickly identified during slipping, and the efficiency of problem solving can be improved. The emergency valve core structure in the present invention is simple, easy to process, and easy to assemble; and the emergency valve can adopt different control forms, such as manual, electric control, etc., which can quickly and conveniently match the host requirements.

[0021] Embodiment 2 Based on the emergency valve for a closed pump described in Example 1, this embodiment provides a closed pump, which includes a variable pump 7, an oil replenishing pump 8, a control valve 2, a feedback rod 3, a variable piston 4, a slider 5, a swash plate 6, the emergency valve 1 described in Example 1 and other components; the variable pump 7 is the main pump of the closed pump; the oil replenishing pump 8 provides supplementary hydraulic oil to the variable pump 7 and the system, and at the same time, the oil replenishing pump 8 serves as a pilot oil source for the closed pump to provide pilot oil for the closed pump.

[0022] The control valve 2 includes a control valve block 29, a control valve core 23 installed in the control valve block 29, a fulcrum pin 27 installed on the control valve block 29, and a control valve solenoid 1 21 and a control valve solenoid 22 for adjusting the control valve block 29 to work in different working positions.

[0023] One end of the shift fork 1 25, one end of the shift fork 28, and the middle part of the feedback rod 3 are respectively hinged to the fulcrum pin 27; the other end of the shift fork 1 25 and the other end of the shift fork 28 are respectively connected to the two ends of the control valve spring 30; one end of the feedback rod 3 is transmission connected to the variable piston 4, and the other end of the feedback rod 3 is transmission connected to the shift fork 1 25 or the shift fork 2 28 through the feedback rod pin 24; the control valve spool 23 is transmission connected to the shift fork 1 25 or the shift fork 2 28 through the spool pin 26.

[0024] The variable piston 4 is transmission-connected to the swash plate 6 via the slider 5, and is used to change the swing angle of the swash plate 6, thereby controlling the flow rate of the closed pump.

[0025] The inlet of the replenishing oil pump 8 is connected to the oil tank, and the outlet of the replenishing oil pump 8 is connected to the inlet of the filter 1 81 and the inlet of the cold start valve 82; the outlet of the cold start valve 82 is connected to the inlet of the replenishing oil pump 8; the outlet of the filter 1 81 is connected to the pilot oil inlet of the emergency valve 1, and at the same time, it is also connected to the oil tank through the replenishing oil relief valve 83, and is also connected to the inlet of the variable pump 7 through the high-pressure relief replenishing oil valve 1 84, and is also connected to the outlet of the variable pump 7 through the high-pressure relief replenishing oil valve 2 85. The outlet of the variable pump 7 and the working oil port 3 of the emergency valve 1 are connected to the oil tank through the pressure cut-off valve 86 respectively. The working oil port 3 of the emergency valve 1 is connected to the inlet of the control valve 2 through the filter 2 15.

[0026] Under normal circumstances, the emergency valve 1 works in the right position, the control valve solenoid 21 is energized, pushing the control valve spool 23 to move left, allowing the pilot oil to enter the right chamber of the variable piston 4. At the same time, the control valve spool 23 moves leftward and drives the shift fork 28 to open leftward around the fulcrum pin 27. The variable piston 4 moves leftward under the action of the pressure oil, and the slider 5 drives the swash plate 6 to change the swing angle of the swash plate 6. At the same time, the variable piston 4 drives the feedback rod 3 to rotate rightward around the fulcrum pin 27 and pushes the feedback rod pin 24. The shift fork 1 25 opens to the right around the fulcrum pin 27. At this time, the spring force on the shift fork 1 25 and the shift fork 28 is greater than the electromagnetic force. Under the action of the spring force, the shift fork 28 moves to the right, driving the valve core pin 26 to push the control valve core 23 to move until the spring force is balanced with the electromagnetic force. The control valve core 23 stops moving, and the oil circuit between the pilot oil source and the variable piston 4 is disconnected, so that the displacement of the variable piston 4 is stabilized at a certain set position, the swash plate 6 stops at a certain set swing angle, and the hydraulic pump outputs a stable flow rate.

[0027] When the control valve solenoid 21 loses power, the spring force drives the shift fork 28 to push the control valve spool 23 to move rightward, the valve port opens, the right chamber of the variable piston 4 is connected to the oil tank, and the variable piston 4 moves rightward under the action of its internal return spring. At the same time, the variable piston 4 drives the feedback rod 3 to rotate leftward around the fulcrum pin 27, and the feedback rod pin 24 disengages from the shift fork 25. The shift fork 25 moves rightward under the action of the spring force, and the control valve spring 30 returns to its initial length, the control valve spool 23 returns to its initial position, the valve port gradually closes, and the variable piston 4 stops moving. At this time, the displacement of the closed pump (variable pump 7) returns to zero.

[0028] When the control valve solenoid 21 is powered off but the pump slips, it means that the closed pump displacement has not returned to zero. The possible reasons for the pump displacement not returning to zero are as follows: 1. The pump is not adjusted to zero accurately before leaving the factory; 2. The control valve spring 30 is attenuated, causing the control valve core 23 to be unable to reset; 3. The control valve core 23 is stuck, and the pump cannot be variable; 3. The variable piston 4 is stuck.

[0029] When the vehicle slips, the emergency valve solenoid 11 is energized, so that the emergency valve spool 12 is in the middle position, cutting off the oil circuit between the control valve 2 and the pilot oil source, and connecting the inlet of the control valve 2 back to the oil tank.

[0030] If the problem is solved, it means that when the oil circuit between the control valve 2 and the pilot oil source is not cut off, the pilot oil enters the variable piston 4 through the control valve 2, and the variable piston 4 moves and finally maintains a certain position under the action of the hydraulic oil and the built-in return spring. The swash plate 6 is at a certain angle, and the closed pump displacement is not zero; the cause of the fault is: the closed pump is not accurately zeroed at the factory or the control valve spring 30 is attenuated, resulting in the control valve spool 23 cannot be reset, resulting in the control valve port cannot be closed.

[0031] If the problem is still not solved, switch the current signal to make the emergency valve 1 work in the left position, cut off the oil circuit between the control valve 2 and the pilot oil source, and at the same time, connect the pilot oil source with the oil chambers at both ends of the variable piston 4; in this case, if the problem is solved, the cause of the fault is: the control valve 2 is stuck, the control valve spool 23 cannot move, and the valve port is not opened, resulting in the oil chamber of the variable piston 4 unable to relieve pressure, the variable piston 4 cannot move, and the swash plate is always at a certain angle; if the problem is not solved, the cause of the fault is: the variable piston 4 is stuck, and the closed pump cannot be variable.

[0032] In the present invention, the emergency valve core 12 can be built into the control valve cover plate of the closed pump (that is, the emergency valve block 14 is directly connected to the control valve block 29 of the control valve 2 or adopts an integrated design), and there is no need to add additional components to the hydraulic system. The emergency valve can adopt different control forms such as manual and electric control, which can quickly and conveniently match the needs of the host. In the present invention, the emergency valve is a three-position four-way sliding valve structure, and several deformations can be generated based on this structure, such as exchanging the left position and the right position of the three-position four-way valve, or splitting the three-position four-way valve into two two-position valves, which can realize the function of the emergency valve described in the present invention.

[0033] Embodiment 3 Based on the closed pump described in the second embodiment, this embodiment provides an engineering machine, and the engineering machine is equipped with the closed pump described in the second embodiment.

[0034] Embodiment 4 Based on the closed pump described in Example 2 and the engineering machinery described in Example 3, this embodiment provides a method for diagnosing a fault of a closed pump or engineering machinery. The method includes: judging the cause of the fault according to whether the engineering machinery has a slipping phenomenon and the state of the emergency valve 1 after the engineering machinery has a slipping phenomenon.

[0035] When the solenoid of the control valve is powered off but slipping occurs, it means that the displacement of the closed pump has not returned to zero. At this time, the emergency valve solenoid 11 is powered, so that the emergency valve spool 12 is in the middle position, cutting off the oil circuit between the control valve 2 and the pilot oil source, and connecting the inlet of the control valve 2 back to the oil tank; If the problem is solved, it means that when the oil circuit between the control valve 2 and the pilot oil source is not cut off, the pilot oil enters the variable piston 4 through the control valve 2. Under the action of the pilot oil and the built-in return spring, the variable piston 4 moves and finally maintains a certain position, the swash plate 6 is at a certain angle, and the closed pump displacement is not zero; the cause of the fault is: the closed pump is not accurately zeroed at the factory or the control valve spring 30 is attenuated, resulting in the control valve spool 23 cannot be reset, resulting in the control valve port cannot be closed; If the problem is still not solved, switch the current signal to make the emergency valve 1 work in the left position, cut off the oil circuit between the control valve 2 and the pilot oil source, and at the same time, connect the pilot oil source with the oil chambers at both ends of the variable piston 4; in this case, if the problem is solved, the cause of the fault is: the control valve 2 is stuck, the control valve spool 23 cannot move, and the valve port is not opened, resulting in the oil chamber of the variable piston 4 unable to relieve pressure, the variable piston 4 cannot move, and the swash plate is always at a certain angle; if the problem is not solved, the cause of the fault is: the variable piston 4 is stuck, and the closed pump cannot be variable.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An emergency valve for a closed pump, characterized in that: The emergency valve (1) comprises: an emergency valve block (14), an emergency valve core (12) installed in the emergency valve block (14), an emergency valve solenoid (11) and an emergency valve spring (13) for adjusting the emergency valve core (12) to work in different working positions to control the on-off between the pilot oil source and the control valve (2) or the variable piston (4); The emergency valve block (14) is provided with a working oil port 1, a working oil port 2, a working oil port 3, an oil return port for connecting to an oil tank, and a pilot oil inlet for receiving pilot oil; The working oil port 1 is used to connect to the left chamber of the variable displacement piston (4) in the closed pump; The working oil port 2 is used to connect to the right chamber of the variable displacement piston (4) in the closed pump; The working oil port 3 is used to connect to the inlet of the control valve (2) in the closed pump.

2. A closed pump, characterized in that: Including the emergency valve for a closed pump as described in claim 1.

3. The closed pump according to claim 2, characterized in that: The emergency valve block (14) is directly connected to the control valve block (29) of the control valve (2) or is designed as an integrated unit.

4. The closed pump according to claim 2, characterized in that: The control valve (2) comprises: a control valve block (29), a control valve core (23) installed in the control valve block (29), a fulcrum pin (27) installed on the control valve block (29), and a control valve solenoid first (21) and a control valve solenoid second (22) for adjusting the control valve block (29) to work in different working positions; One end of the first shift fork (25), one end of the second shift fork (28), and the middle of the feedback rod (3) are respectively hinged to the fulcrum pin (27); the other end of the first shift fork (25) and the other end of the second shift fork (28) are respectively connected to the two ends of the control valve spring (30); one end of the feedback rod (3) is transmission-connected to the variable piston (4), and the other end of the feedback rod (3) is transmission-connected to the first shift fork (25) or the second shift fork (28) via the feedback rod pin (24); the control valve core (23) is transmission-connected to the first shift fork (25) or the second shift fork (28) via the core pin (26).

5. The closed pump according to claim 4, characterized in that: The variable piston (4) is transmission-connected to the swash plate (6) via a slider (5) and is used to change the swing angle of the swash plate (6), thereby controlling the flow rate of the closed pump.

6. The closed pump according to claim 5, characterized in that: Under normal circumstances, the emergency valve (1) works in the right position, the control valve solenoid 1 (21) is energized, pushing the control valve spool (23) to move leftward, causing the pilot oil to enter the right chamber of the variable piston (4). At the same time, the control valve spool (23) moves leftward, driving the second shift fork (28) to open leftward around the fulcrum pin (27). The variable piston (4) moves leftward under the action of the pressure oil, and the slider (5) drives the swash plate (6) to change the swing angle of the swash plate (6). At the same time, the variable piston (4) drives the feedback rod (3) to rotate rightward around the fulcrum pin (27), and the feedback rod pin (2 4) Pushing the shift fork 1 (25) to open rightward around the fulcrum pin (27), at which time the spring force on the shift fork 1 (25) and the shift fork 2 (28) is greater than the electromagnetic force. Under the action of the spring force, the shift fork 2 (28) moves rightward, driving the valve core pin (26) to push the control valve core (23) to move until the spring force and the electromagnetic force are balanced, the control valve core (23) stops moving, the oil path between the pilot oil source and the variable piston (4) is disconnected, so that the displacement of the variable piston (4) is stabilized at a certain set position, the swash plate (6) stops at a certain set swing angle, and the hydraulic pump outputs a stable flow rate.

7. The closed pump according to claim 5, characterized in that: When the control valve solenoid 1 (21) loses power, the spring force drives the shift fork 2 (28) to push the control valve core (23) to move rightward, the valve port opens, the right chamber of the variable piston (4) is connected to the oil tank, and the variable piston (4) moves rightward under the action of its internal return spring. At the same time, the variable piston (4) drives the feedback rod (3) to rotate leftward around the fulcrum pin (27), the feedback rod pin (24) is separated from the shift fork 1 (25), and the shift fork 1 (25) moves rightward under the action of the spring force. The control valve spring (30) returns to its initial length, the control valve core (23) returns to its initial position, the valve port gradually closes, and the variable piston (4) stops moving. At this time, the displacement of the closed pump returns to zero.

8. An engineering machine, characterized in that: The engineering machinery is equipped with a closed pump as described in any one of claims 2 to 7.

9. A method for diagnosing engineering machinery faults, characterized in that: The engineering machinery is the engineering machinery according to claim 8, and the method comprises: judging the cause of the fault according to whether the engineering machinery has a slipping phenomenon and the state of the emergency valve (1) after the engineering machinery has a slipping phenomenon.

10. The engineering machinery fault diagnosis method according to claim 9, characterized in that: When the solenoid of the control valve is powered off but slipping occurs, it means that the displacement of the closed pump has not returned to zero. At this time, the emergency valve solenoid (11) is powered, so that the emergency valve spool (12) is in the middle position, cutting off the oil path between the control valve (2) and the pilot oil source, and connecting the inlet of the control valve (2) back to the oil tank; If the problem is solved, it means that when the oil circuit between the control valve (2) and the pilot oil source is not cut off, the pilot oil enters the variable piston (4) through the control valve (2). Under the action of the pilot oil and the built-in return spring, the variable piston (4) moves and finally maintains a certain position. The swash plate (6) is at a certain angle, and the closed pump displacement is not zero. The cause of the fault is: the closed pump is not accurately zeroed at the factory or the control valve spring (30) is attenuated, resulting in the control valve spool (23) cannot be reset, resulting in the control valve port cannot be closed.

11. The engineering machinery fault diagnosis method according to claim 10, characterized in that: If the problem is still not solved, the current signal is switched to make the emergency valve (1) work in the left position, cutting off the oil path between the control valve (2) and the pilot oil source, and at the same time connecting the pilot oil source with the oil chambers at both ends of the variable piston (4); in this case, if the problem is solved, the cause of the fault is: the control valve (2) is stuck, the control valve spool (23) cannot move, the valve port is not opened, resulting in the oil chamber of the variable piston (4) being unable to release pressure, the variable piston (4) being unable to move, and the swash plate always being at a certain angle; if the problem is not solved, the cause of the fault is: the variable piston (4) is stuck, and the closed pump cannot be variable.

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