An integrated hydraulic system for a hydrostatic transmission tractor

Abstract

This invention relates to an integrated hydraulic system for hydrostatic transmission tractors in the field of agricultural machinery hydraulic transmission technology. The system includes an oil tank, a steering gear, a PTO unit, a first solenoid valve, a second solenoid valve, a sequence valve, and an HST device. The oil tank is connected to oil supply branch one and oil supply branch two via pump one and pump two, respectively. The oil inlet and outlet of the steering gear are connected to the lubrication chamber of oil supply branch two and the PTO unit, respectively. Oil supply branch one is connected to the normally open port of solenoid valve one. The switching port I of solenoid valve one is connected to the switching port I of solenoid valve two and the oil inlet of the sequence valve. The switching port II of solenoid valve one and the oil outlet of the sequence valve are both connected to the replenishment port of the HST device. The normally open port of solenoid valve two is connected to the engagement chamber of the PTO unit. The switching port II of solenoid valve two, the external drain port of the sequence valve, and the drain port of the HST device are all connected to the oil tank. This system can achieve safe, smooth, efficient, and reliable operation with limited resources.

Description

Technical Field

[0001] This invention relates to the field of agricultural machinery hydraulic transmission technology, and in particular to an integrated hydraulic system for hydrostatic transmission tractors. Background Technology

[0002] As is well known, low-horsepower multi-functional tractors are equipped with a hydrostatic transmission (HST) for walking, a power take-off unit (PTO) for drive implements, a steering system, and auxiliary working devices such as front loaders and lawn mowers. Due to the prominent contradiction between compact space layout, strict cost control, and the demand for multi-functional operation, existing low-horsepower tractor hydraulic systems often adopt simplified single-pump or simple parallel dual-pump solutions when a compromise cannot be reached. However, this often has the following main drawbacks:

[0003] First, the system has poor interference and maneuverability. The travel drive, steering and working device (such as loader) share the same oil source or are simply connected in parallel. During compound actions, flow competition is easy to occur, which leads to short-term loss of steering force or sluggish action, which poses a safety hazard and reduces work efficiency.

[0004] Secondly, the thermal management capability is weak. In traditional single cooling circuits, the hydraulic oil temperature tends to rise rapidly during continuous heavy-load operations (such as rotary tillage and mowing), leading to a decrease in HST efficiency, premature aging of seals, and reduced system reliability.

[0005] In addition, due to the large rotational inertia of the supporting agricultural implements (such as lawnmowers and rotary tillers), the engagement process of the existing mechanical or simple hydraulically controlled PTO clutch is fast and abrupt, generating huge impact loads, which can easily lead to engine stalling, damage to transmission components or agricultural implements; at the same time, there are problems such as redundant layout and low reliability. Summary of the Invention

[0006] To overcome the shortcomings of the prior art and solve the existing technical problems, this invention discloses an integrated hydraulic system for hydrostatic transmission tractors. Through optimized dual-pump independent oil supply, priority and multiplexing control, and an actuator with embedded buffer function, it achieves safe, smooth, efficient and reliable operation with limited resources.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An integrated hydraulic system for a hydrostatic transmission tractor includes an oil tank, a steering gear, a PTO unit, a solenoid valve one, a solenoid valve two, a sequence valve, and an HST device. Solenoid valve one and solenoid valve two each have a normally open port, and switching ports I and II, respectively, which are connected to the corresponding normally open ports depending on whether they are powered on or off. The oil tank is connected to oil supply branch one and oil supply branch two via pump one and pump two, respectively. The oil inlet and outlet of the steering gear are respectively connected to the lubrication chamber of oil supply branch two and the PTO unit. Oil supply branch one is connected to the normally open port of solenoid valve one. Switching port I of solenoid valve one is connected to the switching port I of solenoid valve two and the oil inlet of the sequence valve. Switching port II of solenoid valve one and the oil outlet of the sequence valve are both connected to the replenishment port of the HST device. The normally open port of solenoid valve two is connected to the engagement chamber of the PTO unit. Switching port II of solenoid valve two, the external drain port of the sequence valve, and the drain port of the HST device are all connected to the oil tank.

[0009] Furthermore, the solenoid valve one, solenoid valve two, and sequence valve are integrated to form an integrated control valve block, and the oil outlet of the steering gear is connected to the lubricating oil chamber of the PTO unit through the LR flow channel set in the integrated control valve block.

[0010] Furthermore, the switching port I of the solenoid valve one is connected to the main channel in the integrated control valve block. The main channel is divided into two branch channels and connected to the switching port I of the solenoid valve two and the oil inlet of the sequence valve, respectively. The branch channel connected to the solenoid valve two is provided with a fixed throttling orifice.

[0011] Furthermore, the system also includes a priority valve and a working device multi-way valve. The oil inlet and priority outlet of the priority valve are connected in series to the second oil supply branch. The oil inlet and return outlet of the working device multi-way valve are respectively connected to the bypass outlet of the priority valve and the oil tank.

[0012] Furthermore, the oil tank is connected to an oil suction filter, the oil outlet of which is connected to the oil inlet of pump one and pump two respectively, and a fine filter one and a fine filter two are connected in series near the oil outlets of pump one and pump two respectively.

[0013] Furthermore, a radiator is connected in series on the oil supply branch between the pump and the fine filter.

[0014] Furthermore, the first solenoid valve and the second solenoid valve are synchronously controlled to turn on and off.

[0015] Furthermore, both pump one and pump two are gear pumps, and the steering gear is a fully hydraulic steering gear.

[0016] Furthermore, pump one and pump two are installed below the tractor cab, corresponding to the front and rear positions of the engine gear compartment; the integrated control valve block is installed above the tractor transmission box, and the oil suction filter is installed on one side of the transmission box; the radiator is a plate-fin radiator, installed in front of the engine coolant tank; the priority valve, fine filter one, and fine filter two are installed on the side of the engine compartment, with the priority valve installed near pump two.

[0017] Furthermore, the control method for the operation of the integrated control valve block and the PTO unit includes the following cases:

[0018] PTO unit in non-working state: Solenoid valve 1 and solenoid valve 2 are not energized by default. The normally open port is connected to switching port II. The oil supplied by pump 1 directly enters the HST device. The PTO unit's connection chamber is connected to the oil tank and there is no pressure.

[0019] PTO unit combined working state: Solenoid valve 1 and solenoid valve 2 are both energized, and the normally open port is connected to switching port I. The oil supplied by pump 1 is pressure adjusted by the sequence valve and then slowly enters the PTO unit combined chamber through the fixed throttle orifice; at the same time, oil flows out of the oil outlet of the sequence valve and enters the HST device.

[0020] PTO unit disengagement state: Both solenoid valve one and solenoid valve two are de-energized, the system returns to the "PTO unit non-working state", and the pressure oil in the engagement chamber of the PTO unit is quickly discharged back to the oil tank, realizing the rapid disengagement of the clutch;

[0021] PTO lubrication status: The oil supplied by pump 2 enters the PTO lubrication chamber from the return oil of the steering gear.

[0022] By employing the technical solution described above, the present invention has the following beneficial effects:

[0023] The integrated hydraulic system for hydrostatic transmission tractors disclosed in this invention separates the hydraulic systems of the walking drive and the working device from the source through a dual-pump source design, eliminating mutual interference and making each action independent and responsive. Furthermore, the return oil from the steering gear does not return directly to the oil tank but is directly introduced into the PTO unit for lubrication, achieving efficient reuse of return oil within the system, simplifying the lubrication system, and improving energy efficiency. Simultaneously, the system is designed with an efficient continuous cooling scheme for the HST unit. Regardless of whether the PTO is working, the cooling oil from pump one can continuously supply the HST unit's oil replenishment circuit, providing crucial temperature control and lubrication for the HST unit's walking system. This design fully utilizes hydraulic oil and solves the problem of limited heat dissipation capacity in low-horsepower tractors.

[0024] Furthermore, the integrated control valve block, connected via internal oil passages, significantly reduces external high-pressure pipelines and joints, resulting in a compact layout and low leakage risk. This makes it particularly suitable for space-constrained conditions in low-horsepower tractors. The fixed throttle orifice design allows for slow oil filling of the clutch engagement chamber, enabling smooth engagement of the PTO unit for soft starts and significantly reducing the starting shock when docking with high-inertia implements such as lawnmowers and rotary tillers. Simultaneously, rapid oil draining during power failure ensures quick clutch disengagement. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the hydraulic system of the present invention.

[0026] Figure 2 This is a front view schematic diagram showing the installation positions of the various components of the present invention on the tractor;

[0027] Figure 3 This is a rear view schematic diagram showing the installation positions of the various components of the present invention on the tractor.

[0028] In the diagram: 1. Oil tank; 2. Suction filter; 3. Pump 1; 4. Pump 2; 5. Radiator; 6. Fine filter 2; 7. Fine filter 1; 8. Integrated control valve block; 8a. Solenoid valve 1; 8b. Solenoid valve 2; 8c. Sequence valve; 8d. Fixed throttle orifice; 9. HST device; 10. PTO unit; 11. Priority valve; 12. Diverter; 13. Working device multi-way valve. Detailed Implementation

[0029] The technical solution of the present invention will be described below with reference to the accompanying drawings of the embodiments of the present invention. In the description, it should be understood that if there are terms such as "upper", "lower", "front", "rear", "left", "right" indicating the orientation or positional relationship, they are only corresponding to the accompanying drawings of the present invention for the convenience of describing the present invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation.

[0030] Combined with appendix Figure 1 The integrated hydraulic system for a hydrostatic transmission tractor includes an oil tank 1, a steering gear 12, a PTO unit 10, solenoid valve 8a, solenoid valve 8b, a sequence valve 8c, and an HST device 9. Solenoid valves 8a and 8b each have a normally open port, and switching ports I and II that connect to the corresponding normally open port depending on whether the power is on or off. That is, when energized, the normally open port is connected to switching port I; when de-energized, the normally open port is connected to switching port II. Currently... Figure 1In the diagram, the normally open ports of solenoid valve 8a and solenoid valve 8b are located near points P and K, respectively, and are in a de-energized state. They are connected to switching port II as shown in the diagram. Depending on the requirements, pumps 3 and 4 are both gear pumps, offering high reliability and low cost. Steering gear 12 generally refers to a fully hydraulic steering gear. Specifically, solenoid valves 8a and 8b are synchronously controlled for on / off states, making synchronous control simpler and more convenient in application.

[0031] Oil tank 1 is connected to oil supply branch 1 and oil supply branch 2 via pump 3 and pump 4 respectively. The dual-pump source design separates the travel drive and the hydraulic system of the working device from the source, eliminating mutual interference and making each action independent and responsive. The oil inlet and outlet of steering gear 12 are respectively connected to oil supply branch 2 and the lubrication chamber of PTO unit 10. The oil return from the outlet of steering gear 12 does not return directly to oil tank 1, but is directly introduced into PTO unit 10 for lubrication, realizing efficient reuse of return oil within the system, simplifying the lubrication system and improving energy efficiency. As needed, the system also includes priority valve 11 and working device multi-way valve 13. Working device multi-way valve 13 is usually used to control operations such as front loading or lawnmower lifting. The oil inlet and priority outlet of priority valve 11 are connected in series to oil supply branch 2, and working device multi-way valve 13... The oil inlet and outlet of the pump are respectively connected to the bypass outlet of the priority valve 11 and the oil tank 1. That is, the oil supplied by pump 2 4 will pass through the priority valve 11 and be preferentially supplied to the steering gear 12, ensuring that the steering flow is guaranteed with absolute priority when any working device is in operation, which greatly improves the operating safety of the small horsepower tractor during compound actions. In addition, the oil tank 1 is connected to the suction filter 2 through the suction pipe. The outlet of the suction filter 2 is connected to the oil inlet of pump 1 3 and pump 2 4 respectively, which performs primary filtration of the oil. The oil supply branch 1 and oil supply branch 2 near the oil outlet of pump 1 3 and pump 2 4 are respectively connected in series with fine filter 1 7 and fine filter 2 6, which can perform secondary filtration. In addition, a radiator 5 is connected in series on the oil supply branch 1 between pump 1 3 and fine filter 1 7 for heat dissipation, reducing the oil temperature and achieving a cooling effect.

[0032] The first oil supply branch is connected to the normally open port of solenoid valve 8a. The switching port I of solenoid valve 8a is connected to the switching port I of solenoid valve 8b and the oil inlet of sequence valve 8c. The switching port II of solenoid valve 8a and the oil outlet of sequence valve 8c are both connected to the replenishment port of HST device 9. The normally open port of solenoid valve 8b is connected to the engagement cavity of PTO unit 10. The switching port II of solenoid valve 8b, the external drain port of sequence valve 8c, and the drain port of HST device 9 are all connected to oil tank 1. This connection method enables... Figure 1When neither solenoid valve 8a nor solenoid valve 8b is energized, oil is supplied directly to the HST device 9. When energized, oil is supplied first to the PTO unit 10, and then to the HST device 9. That is, regardless of whether the PTO unit 10 is working or not, the cooling oil from pump 3 is continuously supplied to the HST device 9's oil supply circuit, providing crucial temperature control and lubrication for the HST device 9. In particular, when the PTO unit 10 is not working, the cooling oil is directly replenished; when the PTO is working, the oil at the outlet of the sequence valve 8c is still continuously replenished. This design makes full use of hydraulic oil and solves the problem of limited heat dissipation capacity of small horsepower tractors.

[0033] As needed, in other embodiments, solenoid valve 8a, solenoid valve 8b, and sequence valve 8c are integrated to form an integrated control valve block 8. The oil outlet of the steering gear 12 is connected to the lubrication chamber of the PTO unit 10 through the LR flow channel provided in the integrated control valve block 8; as shown in the attached figure. Figure 1 As shown, the integrated control valve block 8 includes several interfaces such as H, P, K, R, and L points, which can be directly connected to the outside via pipelines. This allows for the high-level integration of the complex electro-hydraulic control logic of the PTO unit 10, oil circuit switching, and steering return oil lubrication channel into a single valve block. Through internal oil passage connections, it significantly reduces external high-pressure pipelines and joints, resulting in a compact layout and low leakage risk, making it particularly suitable for the space-constrained working conditions of low-horsepower tractors. Furthermore, and more importantly, the internal structure of the valve body allows the switching port I of the solenoid valve 8a to connect to the main channel within the integrated control valve block 8. Two branch channels are connected to the switching port I of solenoid valve 2 8b and the oil inlet of sequence valve 8c, respectively. The branch channel connected to solenoid valve 2 8b is provided with a fixed throttling orifice 8d. This fixed throttling orifice 8d can be formed by the reduction of the diameter of the corresponding section of the branch channel, or it can be fixedly installed in the corresponding section of the branch channel as a detachable throttling component. This realizes the slow filling of the clutch engagement chamber with oil, so that the PTO unit 10 can be smoothly engaged, that is, soft start, which significantly reduces the starting shock of large inertia implements such as lawnmowers and rotary tillers. At the same time, the rapid oil discharge when the power is cut off ensures the rapid disengagement of the clutch of PTO unit 10.

[0034] Specifically, the control method for the operation of the integrated control valve block 8 and the PTO unit 10 includes the following:

[0035] PTO not working status: see attached. Figure 1 As shown, both solenoid valve 8a and solenoid valve 8b are not energized by default. Their normal ports are connected to switching port II. The oil supplied by pump 3 flows directly into point P, passes through solenoid valve 8a, and flows out from point H into HST device 9 to replenish it and provide continuous cooling and lubrication. The engagement chamber of PTO unit 10 is connected to oil tank 1 through point K and solenoid valve 8b, and there is no pressure.

[0036] PTO engagement state: When PTO unit 10 needs to be started, both solenoid valve 8a and solenoid valve 8b are energized, and the normally open port is connected to the switching port I. The oil supplied by pump 3 passes through solenoid valve 8a, the pressure is adjusted by sequence valve 8c, and then flows slowly through fixed throttle orifice 8d. It then enters the engagement chamber of PTO unit 10 through solenoid valve 8b and point K to achieve smooth engagement. At the same time, the oil outlet of sequence valve 8c is opened under pressure and oil flows out into HST device 9 for continuous oil replenishment and cooling.

[0037] PTO Disengagement State: When PTO unit 10 needs to be stopped, both solenoid valve 8a and solenoid valve 8b are de-energized, and the system instantly returns to the "PTO unit 10 non-working state". The pressure oil in the engagement chamber of PTO unit 10 is quickly discharged back to oil tank 1 through point K and solenoid valve 8b, realizing the rapid disengagement of the clutch.

[0038] PTO lubrication status: The oil supplied by pump 2 4 returns from the steering gear 12 and enters the lubrication chamber of the PTO unit 10 through the internal dedicated channel connected by points L and R, supplying lubrication points such as bearings and gears of the PTO unit 10, realizing direct and efficient reuse of steering return oil.

[0039] As attached Figure 2-3 As shown, in other embodiments, pump 3 and pump 4 are installed below the tractor cab and positioned corresponding to the front and rear positions of the engine gearbox, as needed. The integrated control valve block 8 is installed above the tractor transmission box. The oil tank 1 is designed for combined oil supply, drawing oil directly from the transmission system via a pump. The oil suction filter 2 is installed on one side of the transmission box. The radiator 5 is a plate-fin radiator installed in front of the engine coolant tank. The priority valve 11, fine filter 7, and fine filter 6 are installed on the side of the engine compartment, with the priority valve 11 installed near pump 4. The steering gear 12 is generally installed below the steering wheel. The HST device 9 is installed below the steering gear 12. The PTO unit 10 is installed below the integrated control valve block 8. The working device multi-way valve 13 is installed on the side of the driver's seat. Through the above compact and reasonable component layout, the present invention significantly reduces external connection pipelines, achieves a high degree of system integration, and is very suitable for installation environments with limited space for small-horsepower tractors.

[0040] The overall working principle of the integrated hydraulic system for hydrostatic transmission tractors described in this invention is as follows:

[0041] Driving and Steering (PTO Off): After being cooled and filtered, the oil from pump 13 is directly replenished to the HST device 9 through the integrated control valve block 8; the oil from pump 24 is prioritized to power the steering gear 12, with excess oil reserved; the return oil from the steering gear 12 lubricates the PTO unit 10.

[0042] Start PTO operation: Solenoid valve 1 8a and solenoid valve 2 8b are energized; the oil circuit of pump 1 3 is changed to drive PTO unit 10 to slowly engage, while the oil return of sequence valve 8c continues to be for HST device 9; the lubrication path of pump 2 4 and steering remains unchanged.

[0043] Stop PTO operation: Solenoid valve 18a and solenoid valve 28b are de-energized; PTO unit 10 is quickly depressurized and separated, and the oil circuit of pump 13 is restored to directly replenish oil to HST unit 9.

[0044] Operating the working device: When operating the multi-way valve 13 of the working device, the remaining flow of pump 2 4 is supplied to the working device; due to the action of the priority valve 11, the steering oil supply always takes priority and does not affect the steering performance.

[0045] This invention effectively solves the contradictions in space, heat dissipation, smoothness and reliability of the hydraulic system of small horsepower tractors through a highly integrated and efficient reusable oil circuit design, and significantly improves the overall performance of the machine.

[0046] The parts of this invention not described in detail are prior art. It will be apparent to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the above embodiments should be regarded as exemplary and non-limiting in all respects. The scope of this invention is defined by the appended claims rather than the foregoing description. Therefore, it is intended to include all changes that fall within the meaning and scope of the equivalents of the claims within this invention, and no reference numerals in the claims should be regarded as limiting the content of the claims.

Claims

1. An integrated hydraulic system for a hydrostatic transmission tractor, characterized in that: The system includes an oil tank (1), a steering gear (12), a PTO unit (10), a solenoid valve 1 (8a), a solenoid valve 2 (8b), a sequence valve (8c), and an HST device (9). Both solenoid valve 1 (8a) and solenoid valve 2 (8b) have a normally open port, and switching ports I and II, respectively, which connect to the corresponding normally open ports when the power is on or off. The oil tank (1) is connected to oil supply branch 1 and oil supply branch 2 via pump 1 (3) and pump 2 (4), respectively. The oil inlet and outlet of the steering gear (12) are respectively connected to oil supply branch 2 and the lubrication chamber of the PTO unit (10). The oil branch is connected to the normal port of the first solenoid valve (8a). The switching port I of the first solenoid valve (8a) is connected to the switching port I of the second solenoid valve (8b) and the oil inlet of the sequence valve (8c). The switching port II of the first solenoid valve (8a) and the oil outlet of the sequence valve (8c) are connected to the oil replenishment port of the HST device (9). The normal port of the second solenoid valve (8b) is connected to the connection cavity of the PTO unit (10). The switching port II of the second solenoid valve (8b), the external oil drain port of the sequence valve (8c), and the oil drain port of the HST device (9) are all connected to the oil tank (1).

2. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 1, characterized in that: The solenoid valve one (8a), solenoid valve two (8b) and sequence valve (8c) are integrated to form an integrated control valve block (8). The oil outlet of the steering gear (12) is connected to the lubricating oil chamber of the PTO unit (10) through the LR flow channel set in the integrated control valve block (8).

3. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 2, characterized in that: The switching port I of the solenoid valve one (8a) is connected to the main channel in the integrated control valve block (8). The main channel is divided into two branch channels and connected to the switching port I of the solenoid valve two (8b) and the oil inlet of the sequence valve (8c) respectively. The branch channel connected to the solenoid valve two (8b) is provided with a fixed throttling orifice (8d).

4. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 2, characterized in that: The system also includes a priority valve (11) and a working device multi-way valve (13). The oil inlet and priority outlet of the priority valve (11) are connected in series to the second oil supply branch. The oil inlet and return outlet of the working device multi-way valve (13) are respectively connected to the bypass outlet of the priority valve (11) and the oil tank (1).

5. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 4, characterized in that: The oil tank (1) is connected to an oil suction filter (2). The oil outlet of the oil suction filter (2) is connected to the oil inlet of pump one (3) and pump two (4) respectively. The oil supply branch one and oil supply branch two near the oil outlet of pump one (3) and pump two (4) are respectively connected in series with fine filter one (7) and fine filter two (6).

6. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 5, characterized in that: A radiator (5) is connected in series on the oil supply branch between the pump (3) and the fine filter (7).

7. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 1, characterized in that: The solenoid valve one (8a) and solenoid valve two (8b) are synchronously controlled to turn on and off.

8. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 1, characterized in that: Both pump one (3) and pump two (4) are gear pumps, and the steering gear (12) is a fully hydraulic steering gear.

9. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 6, characterized in that: Pump 1 (3) and Pump 2 (4) are installed below the tractor cab and correspond to the front and rear positions of the engine gear compartment; the integrated control valve block (8) is installed above the tractor transmission box, and the oil suction filter (2) is installed on one side of the transmission box; the radiator (5) is a plate-fin radiator and is installed in front of the engine coolant tank; the priority valve (11), the fine filter 1 (7) and the fine filter 2 (6) are installed on the side of the engine compartment, wherein the priority valve (11) is installed near Pump 2 (4).

10. The integrated hydraulic system for a hydrostatic transmission tractor according to claim 3, characterized in that: The control method for the operation of the integrated control valve block (8) and the PTO unit (10) includes the following cases: PTO unit (10) in non-working state: Solenoid valve 1 (8a) and solenoid valve 2 (8b) are not energized by default. The normal port is connected to the switching port II. The oil supplied by pump 1 (3) directly enters the HST device (9). The connecting chamber of PTO unit (10) is connected to the oil tank (1) and there is no pressure. PTO unit (10) in working state: Solenoid valve 1 (8a) and solenoid valve 2 (8b) are both energized, and the normally open port is connected to the switching port I. The oil supplied by pump 1 (3) is adjusted by the sequence valve (8c) and then slowly enters the PTO unit (10) connection chamber through the fixed throttle orifice (8d). At the same time, oil flows out of the oil outlet of the sequence valve (8c) and enters the HST device (9). PTO unit (10) separation state: Solenoid valve one (8a) and solenoid valve two (8b) are both de-energized, the system returns to "PTO unit (10) non-working state", the pressure oil in the engagement chamber of PTO unit (10) is quickly discharged back to the oil tank (1), and the clutch is quickly separated; PTO lubrication status: The oil supplied by pump 2 (4) returns from the steering gear (12) into the PTO lubrication chamber.

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