Hydraulic system for a hydro-mechanical continuously variable transmission of a high horse-power tractor

Abstract

The application provides a hydraulic system of a hydraulic mechanical continuously variable transmission suitable for a large-horsepower tractor, and belongs to the technical field of tractor hydraulic systems. The hydraulic system comprises an oil pan, a lubricating hydraulic system, a working hydraulic system and a compensation system. The oil pan is connected with an oil inlet of a coarse filter. A lubricating pump of the lubricating hydraulic system, a system pump of the working hydraulic system and a compensation pump of the compensation system are connected in parallel and share an oil suction port. The oil suction port is connected with an oil outlet of the coarse filter. A PTO control hydraulic system, a direction gear control hydraulic system, a speed gear control hydraulic system and a double-station unit control hydraulic system are sequentially arranged on a working hydraulic pipeline. The hydraulic system is responsible for controlling the combination and disconnection of five groups of wet clutches to form gear intervals, controlling the combination and disconnection of a PTO clutch, controlling the change of a static liquid unit swing angle, controlling the flow distribution of a three-union oil pump, controlling the oil compensation of the static liquid unit and the forced lubrication of the entire transmission.

Description

Technical Field

[0001] This invention belongs to the technical field of tractor hydraulic systems, specifically relating to a hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors. Background Technology

[0002] Agricultural tractor transmissions mainly include traditional mechanical transmissions, power shift transmissions, and hydraulic mechanical continuously variable transmissions (CVTs). Hydraulic mechanical CVTs are more technologically advanced than the other two types. They utilize a hydraulic control system to control a wet clutch for shifting, and incorporate a closed hydrostatic unit to achieve stepless speed changes across various shift ranges. This effectively improves tractor operating efficiency, fuel efficiency, and operator comfort. Currently, existing hydraulic mechanical CVTs are compatible with tractors of lower horsepower; transmissions for high-horsepower tractors are currently unavailable. With the increasing demand for high-horsepower tractors, developing transmissions for even higher horsepower tractors is essential.

[0003] The hydraulic system of a hydraulic continuously variable transmission (CVT) is responsible for the oil replenishment circuit and circulation cooling of the hydrostatic unit, the engagement and disengagement of the wet clutch to achieve the shifting function, and the forced cooling and lubrication of the mechanical transmission system. It is a key design element of the transmission product and will greatly affect the transmission efficiency, reliability and safety of the transmission product.

[0004] Currently, hydraulic continuously variable transmissions (CVTs) are generally designed for lower horsepower ranges and typically use a single hydrostatic unit for continuously variable transmission. However, for high-horsepower tractors, the maximum torque transmitted by a single hydrostatic unit is limited and cannot meet the requirements of high-horsepower tractors. Furthermore, during the transmission design process, to ensure the safe operation of the entire transmission, the oil pump's supply capacity is often selected to be slightly greater than the transmission's normal operating capacity to meet certain extreme conditions. However, this selection results in wasted oil pump power and oil pump placement problems due to the larger pump size. Therefore, improvements to the transmission's oil supply system are necessary. Additionally, traditional PTO (Pulse-Torque Transmission) control systems consist of a PTO clutch valve, PTO clutch, mechanical anti-rotation device, and related oil circuits and transmission components. While effectively performing PTO transmission control and anti-rotation functions, the high slippage at the contact point between the anti-rotation device and the PTO clutch easily causes wear on related components, affecting product reliability and safety. Therefore, improvements to the PTO transmission control system are required. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors. This system addresses the technical problems of limited maximum torque transmitted by a single hydrostatic unit, which cannot meet the requirements of high-horsepower tractors; wasted oil pump power; oil pump layout problems caused by oil pump selection; and high slippage at the contact point between the anti-rotation device and the PTO clutch, which easily causes wear on related components and affects the reliability and safety of the product.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention provides a hydraulic system for a hydraulic continuously variable transmission (CVT) suitable for high-horsepower tractors, comprising an oil pan, a lubrication hydraulic system, a working hydraulic system, and a compensation system; the oil pan is connected to the oil inlet of a coarse filter, the lubrication pump of the lubrication hydraulic system, the system pump of the working hydraulic system, and the compensation pump of the compensation system are connected in parallel and share a common suction port, and the suction port is connected to the oil outlet of the coarse filter.

[0008] The working hydraulic system includes a system pump, a fine filter, a main pressure regulating valve, and a control hydraulic system. The outlet of the system pump is connected to the inlet of the working hydraulic pipeline. The fine filter is installed on the working hydraulic pipeline, which is connected in parallel with the first oil circuit equipped with the main pressure regulating valve. A branch outlet is provided on the working hydraulic pipeline, and the branch outlet is connected to the compensation system. The control hydraulic system includes a PTO control hydraulic system, a steering gear control hydraulic system, a speed gear control hydraulic system, and a dual hydrostatic unit control hydraulic system. The PTO control hydraulic system, steering gear control hydraulic system, speed gear control hydraulic system, and dual hydrostatic unit control hydraulic system are sequentially installed on the working hydraulic pipeline.

[0009] The PTO control hydraulic system includes a PTO safety switch valve, a PTO clutch valve, a PTO anti-rotation device drive cylinder, and a PTO clutch; the PTO safety switch valve and the PTO clutch valve are sequentially arranged on the PTO control main line, the PTO safety switch valve is connected to the PTO anti-rotation device drive cylinder, and the PTO clutch valve is connected to the PTO clutch.

[0010] The dual hydrostatic unit control hydraulic system includes a first hydrostatic unit and a second hydrostatic unit that are symmetrically arranged and interconnected.

[0011] In specific implementation, the steering gear control hydraulic system includes a CF clutch valve, a CR clutch valve, a steering gear accumulator, and a CF clutch and a CR clutch.

[0012] The steering gear accumulator is installed on the steering gear control main circuit, which connects the steering gear first control branch circuit and the steering gear second control branch circuit. The steering gear first control branch circuit is provided with a CR clutch valve and a CR clutch in sequence; the steering gear second control branch circuit is provided with a CF clutch valve and a CF clutch in sequence.

[0013] In specific implementation, the speed gear control hydraulic system includes a C1 clutch valve, a C2 clutch valve, a C3 clutch valve, a speed gear accumulator, and clutches C1, C2, and C3.

[0014] The speed accumulator is installed on the speed control main circuit, which connects the speed first control branch, the speed second control branch, and the speed third control branch. The speed first control branch is provided with a C2 clutch valve and a C2 clutch in sequence. The speed second control branch is provided with a C1 clutch valve and a C1 clutch in sequence. The speed third control branch is provided with a C3 clutch valve and a C3 clutch in sequence.

[0015] In specific implementation, the compensation system includes a compensation pump, a pilot-operated compensation pump control valve, a first solenoid valve, and a second solenoid valve. The outlet of the compensation pump is connected to the inlet of the pilot-operated compensation pump control valve. The first solenoid valve and the second solenoid valve are respectively connected to both sides of the pilot-operated compensation pump control valve. The inlets of the first solenoid valve and the second solenoid valve are connected to the branch outlets of the working hydraulic pipeline. The first port of the pilot-operated compensation pump control valve is connected to the lubrication hydraulic system. The second port of the pilot-operated compensation pump control valve is connected to the outlet of the coarse filter.

[0016] In the specific implementation process, the oil circuit between the compensation pump and the pilot-operated compensation pump control valve and the working hydraulic pipeline between the system pump and the fine filter are connected through the first branch.

[0017] In the specific implementation process, an overflow valve is installed on the first branch.

[0018] In specific implementation, the lubrication hydraulic system includes a lubrication pump, an oil cooler, a lubrication check valve, and a lubrication system circuit; the coarse filter is connected to the second oil circuit, the oil outlet of the lubrication pump is connected to the oil inlet of the lubrication hydraulic pipeline, the oil cooler is installed on the lubrication hydraulic pipeline, the lubrication hydraulic pipeline is connected in parallel with the second oil circuit equipped with the lubrication check valve, and the lubrication system circuit is connected to the oil outlet of the lubrication hydraulic pipeline; the lubrication check valve is used to control the lubrication oil pressure.

[0019] In the specific implementation process, a second branch is connected to the lubrication hydraulic pipeline between the lubrication pump and the oil cooler; the lubrication hydraulic pipeline of the lubrication hydraulic system is connected to the compensation system through the second branch.

[0020] In the specific implementation process, a third branch is opened on the lubrication hydraulic pipeline, and a temperature-controlled bypass valve is installed on the third branch.

[0021] In the specific implementation process, a fourth branch is provided on the working hydraulic pipeline, and a cold start valve is provided on the fourth branch.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention discloses a hydraulic system for a hydraulic continuously variable transmission (CVT) suitable for high-horsepower tractors. It employs a triple-pump design combined with a pilot valve. The system pump and lubrication pump meet the transmission's fluid requirements under normal operating conditions. In extreme situations, the third pump automatically replenishes fluid to the system or lubrication circuit as needed. This oil supply system design significantly reduces the power consumption of the system and lubrication pumps. When selecting the system and lubrication pumps, only those meeting the transmission's normal operating fluid requirements need to be chosen, avoiding the problems of traditional dual-pump systems where pump power exceeds normal operating requirements and the resulting large pump size and space constraints. The use of dual hydrostatic units in parallel allows for greater horsepower while ensuring dynamic power balance through external oil circuit connections between the two units.

[0024] This invention improves the PTO transmission control system by replacing the traditional mechanical anti-rotation device with a hydraulically controlled anti-rotation device. This makes the opening and closing of the anti-rotation device controllable, and the PTO clutch is connected in series after the PTO safety switch valve. Furthermore, when PTO operation is required, the PTO safety switch valve is opened first, disengaging the PTO anti-rotation device, and then the PTO clutch valve is opened. When PTO operation needs to be stopped, the PTO clutch valve is closed first, and after the PTO speed decreases, the PTO safety switch valve is closed, engaging and locking the PTO anti-rotation device to prevent PTO idling. This effectively reduces the slippage work on the contact surfaces of the PTO anti-rotation device, reducing wear and improving the reliability and safety of the transmission.

[0025] Furthermore, the transmission has three speed ranges each for forward and reverse. It internally houses five wet clutches, which engage and disengage to achieve gear shifting and speed range transitions. The transmission also features two variable displacement piston pumps, a fixed displacement piston motor, and a closed-loop hydrostatic unit. Within each speed range, continuously variable transmission (CVT) is achieved by adjusting the swashplate angle of the variable displacement pumps. For ease of use with agricultural implements, the transmission is also equipped with a PTO interface flange. This hydraulic system controls the engagement and disengagement of the five wet clutches to form gear ranges, controls the engagement and disengagement of the PTO clutch, controls the swashplate angle of the hydrostatic unit, controls the flow distribution of the three-pronged oil pump, controls the oil replenishment of the hydrostatic unit, and provides forced lubrication for the entire transmission.

[0026] Furthermore, the design of using a triple pump combined with a pilot control valve allows the first two pumps to meet the transmission's fluid requirements under normal operating conditions, while the third pump can supplement the lubrication or pressure hydraulic system under more extreme or necessary conditions, thus saving pump power.

[0027] Furthermore, the hydraulic systems for steering gear control and speed gear control use accumulators to ensure stable system pressure during gear shifting. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the hydraulic system of the hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to the present invention.

[0029] Wherein: 1-Oil pan; 2-Coarse filter; 3-Lubrication pump; 4-System pump; 5-Compensation pump; 6-Cold start valve; 7-Relief valve; 8-Oil cooler; 9-Temperature control bypass valve; 10-Fine filter; 11-Lubrication check valve; 12-Main pressure regulating valve; 13-First solenoid valve; 14-Second solenoid valve; 15-Pilot-operated compensation pump control valve; 16-PTO safety switch valve; 17-PTO clutch valve; 18-PTO anti-rotation device drive cylinder; 1 9-PTO clutch; 20-CF clutch valve; 21-CR clutch valve; 22-Directional gear accumulator; 23-CF clutch; 24-CR clutch; 25-C2 clutch valve; 26-C1 clutch valve; 27-C3 clutch valve; 28-Speed ​​gear accumulator; 29-C2 clutch; 30-C1 clutch; 31-C3 clutch; 32-First hydrostatic unit; 33-Second hydrostatic unit; 34-Lubrication system circuit. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0031] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0032] The present invention will now be described in further detail with reference to the accompanying drawings:

[0033] like Figure 1 As shown, this application provides a hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors. The hydraulic system is supplied with oil by a lubrication pump 3, a system pump 4, and a compensation pump 5. The three pumps are connected in parallel and share the oil filtered from the coarse filter 2. When the coarse filter 2 is blocked, the bypass valve of the coarse filter 2 will open to overflow.

[0034] The aforementioned hydraulic system includes an oil pan 1, a lubrication hydraulic system, a working hydraulic system, and a compensation system; the lubrication hydraulic system includes a lubrication pump 3, an oil cooler 8, a lubrication check valve 11, and a lubrication system circuit 34; the compensation system includes a compensation pump 5, a pilot-operated compensation pump control valve 15, a first solenoid valve 13, and a second solenoid valve 14; the working hydraulic system includes a system pump 4, a fine filter 10, a cold start valve 6, a main pressure regulating valve 12, and various control hydraulic systems arranged sequentially on the working hydraulic pipeline.

[0035] The oil pan 1 is connected to the inlet of the coarse filter 2. The lubrication pump 3 of the lubrication hydraulic system, the system pump 4 of the working hydraulic system, and the compensation pump 5 of the compensation system are connected in parallel and share a common suction port. The outlet of the coarse filter 2 is connected to the suction port, the inlet of the first oil circuit, and the inlet of the second oil circuit. The outlet of the lubrication pump 3 is connected to the inlet of the lubrication hydraulic pipeline. The oil cooler 8 is installed on the lubrication hydraulic pipeline. The lubrication check valve 11 is installed on the second oil circuit. The lubrication hydraulic pipeline is connected in parallel with the second oil circuit. The outlet of the lubrication hydraulic pipeline is connected to the lubrication system circuit 34. A second branch is connected to the lubrication hydraulic pipeline between the lubrication pump 3 and the oil cooler 8, and the compensation system is connected through the second branch. The outlet of the system pump 4 is connected to the inlet of the working hydraulic pipeline. The fine filter 10 is installed on the working hydraulic pipeline. A fourth branch is installed on the working hydraulic pipeline. A cold start valve 6 is installed on the fourth branch. The system pump 4 and the cold start valve 6 are connected to the lubrication system circuit 34. Valve 6 is configured in parallel, and the working hydraulic line is connected in parallel with the first oil line equipped with the main pressure regulating valve 12. The working hydraulic line is sequentially connected to the PTO control hydraulic system, the direction gear control hydraulic system, the speed gear control hydraulic system, and the dual hydrostatic unit control hydraulic system. The oil outlet of the compensation pump 5 is connected to the P port of the pilot-operated compensation pump control valve 15. The oil line between the compensation pump 5 and the pilot-operated compensation pump control valve 15 is connected to the working hydraulic line between the system pump 4 and the fine filter 10 through the first branch. An overflow valve 7 is installed on the first branch. The two sides of the pilot-operated compensation pump control valve 15 are respectively connected to the first solenoid valve 13 and the second solenoid valve 14. The P ports of the first solenoid valve 13 and the second solenoid valve 14 are connected to the working hydraulic line. The A1 port of the pilot-operated compensation pump control valve 15 is connected to the lubrication hydraulic system through the second branch. The A2 port of the pilot-operated compensation pump control valve 15 is connected to the oil outlet of the coarse filter 2.

[0036] In a specific embodiment, a third branch is provided on the lubrication hydraulic pipeline, and a temperature-controlled bypass valve 9 is installed on the third branch. Specifically, an oil cooler 8 is connected after the lubrication pump 3, and the temperature-controlled bypass valve 9 is connected in parallel with the oil cooler 8. When the temperature is low, the bypass valve 9 is opened, and the lubricating oil directly enters the lubrication system through the temperature-controlled bypass valve 9 without passing through the oil cooler 8, allowing the system to heat up quickly. When the temperature is high, the temperature-controlled bypass valve 9 is closed, and the lubricating oil passes through a heat exchanger to cool the oil and ensure the system's lubrication requirements. After passing through the oil cooler 8, the lubricating oil flows into the lubrication system circuit 34, and a lubrication check valve 11 is connected in parallel to control the lubricating oil pressure. The pipeline between the lubrication pump 3 and the oil cooler 8 is connected to the A1 port of the pilot-operated compensating pump control valve 15, which is connected to the pilot-operated compensating pump control valve 15 in the compensation system via the second branch.

[0037] A fine filter 10 is connected after system pump 4. The fine filter 10 is connected in parallel with a differential pressure sensor and a bypass valve. When the differential pressure between the inlet and outlet of the fine filter 10 reaches a preset value due to blockage, the differential pressure sensor will alarm. If the differential pressure continues to rise, the bypass valve will open to overflow. The oil circuit between system pump 4 and fine filter 10 is connected to the first branch circuit, which originates from the overflow valve 7. After the fine filter 10, the PTO control hydraulic system, the direction gear control hydraulic system, the speed gear control hydraulic system, and the dual hydrostatic unit control hydraulic system are connected in sequence. Two thin oil passages, i.e., branch ports, and corresponding pipelines, are led out from the fine filter 10 and connected to the compensation system, allowing the oil to enter the P ports of the two-position three-way valves, namely the first solenoid valve 13 and the second solenoid valve 14. The first solenoid valve 13 and the second solenoid valve 14 serve as pilot controls for the pilot-operated compensation pump control valve 15. Simultaneously, the system oil circuit is connected to the main pressure regulating valve 12 to adjust the system working oil pressure.

[0038] The aforementioned PTO control hydraulic system includes a PTO safety switch valve 16, a PTO clutch valve 17, a PTO anti-rotation device drive cylinder 18, and a PTO clutch 19. The PTO safety switch valve 16 and PTO clutch valve 17 are sequentially arranged on the main PTO control line. The PTO safety switch valve 16 is connected to the PTO anti-rotation device drive cylinder 18, and the PTO clutch valve 17 is connected to the PTO clutch 19. The PTO clutch valve 17 is connected in series after the PTO safety switch valve 16. When the PTO is not in operation, the PTO safety switch valve 16 is normally closed to prevent the PTO from idling. Using the improved PTO transmission control system and strategy, while effectively preventing PTO idling, the slippage work at the contact points of the PTO anti-rotation device can be greatly reduced, reducing wear and improving product reliability and safety.

[0039] The steering gear control hydraulic system includes a CF clutch valve 20, a CR clutch valve 21, and a steering gear accumulator 22. The speed gear control hydraulic system includes a C1 clutch valve 26, a C2 clutch valve 25, a C3 clutch valve 27, and a speed gear accumulator 28. The accumulator helps stabilize system pressure under specific operating conditions, such as gear shifting. Port A of each clutch valve connects to the corresponding clutch. When the solenoid valve is energized, system fluid enters the clutch piston chamber from port A, engaging the clutch and achieving gear shifting. When the solenoid valve is de-energized, the fluid in the clutch piston chamber is discharged into the oil tank through port T.

[0040] The dual hydrostatic unit control hydraulic system consists of two symmetrically arranged hydrostatic units, namely the first hydrostatic unit 32 and the second hydrostatic unit 33, and related oil circuits. The two hydrostatic units are connected through external oil circuits, ensuring that the pressure difference and swing angle of the two hydrostatic units are consistent during operation, thereby achieving the purpose of ensuring symmetrical power balance of the hydrostatic units.

[0041] The compensating pump 5 is connected to the P port of the pilot-operated compensating pump control valve 15. The oil circuit between the compensating pump 5 and the pilot-operated compensating pump control valve 15 is connected to the first branch equipped with the relief valve 7, and is connected to the working hydraulic line between the system pump 4 and the fine filter 10 through the first branch. The pilot-operated compensating pump control valve 15 is connected to the A ports of the first solenoid valve 13 and the second solenoid valve 14 on both sides and is controlled by these two valves. The A1 port of the pilot-operated compensating pump control valve 15 is connected to the oil circuit between the lubrication pump 3 and the oil cooler 8, and the A2 port of the pilot-operated compensating pump control valve 15 is connected to the oil outlet of the coarse filter 2. When both solenoid valves are working, the pilot-operated compensating pump control valve 15 is in the neutral position, and its P port is not connected to its A1 and A2 ports. When the oil pressure reaches a certain value, it will overflow into the system oil circuit. At this time, the compensating pump 5 supplies oil to the system oil circuit. When the first solenoid valve 13 is working and the second solenoid valve 14 is not working, the pilot valve is in the left position, and its P port is connected to its A1 port. At this time, the compensating pump 5 supplies oil to the lubrication circuit. When the first solenoid valve 13 is not working and the second solenoid valve 14 is working, the control valve is in the right position, and its P port is connected to its A2 port. At this time, the pump oil of the compensating pump 5 returns to the outlet of the coarse filter 2, that is, the compensating pump 5 runs dry.

[0042] The specific implementation method is as follows:

[0043] This invention provides a hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors, the hydraulic system comprising a lubrication hydraulic system, a working hydraulic system, and a compensation system;

[0044] The aforementioned lubrication hydraulic system includes a lubrication pump 3, an oil cooler 8, a temperature-controlled bypass valve 9, a lubrication check valve 11, a lubrication system circuit 34, and related oil circuits; wherein the lubrication pump 3 supplies oil to the lubrication hydraulic system.

[0045] The oil circuit sequence is as follows: the lubrication pump 3 draws oil from the suction port, and then connects to the oil cooler 8. The oil cooler 8 is connected in parallel to the lubrication check valve 11 and the temperature control bypass valve 9. The function of the temperature control bypass valve 9 is to allow some oil to enter the lubrication system through the bypass valve at low oil temperatures so that the system can heat up quickly. When the temperature exceeds the set value, all the oil passes through the oil cooler 8 to ensure the lubrication needs of the system. The oil circuit after the oil cooler 8 is connected in parallel to the lubrication check valve 11 and then connected to the lubrication circuit 34 of the gearbox, which includes the lubrication of each wet clutch, the oil pump drive shaft, the front drive shaft, the sun gear shaft, the planetary carrier, the output intermediate shaft, the PTO shaft, and the bearings, gears and splines of the output shafts of the two hydrostatic units.

[0046] The aforementioned working hydraulic system consists of a system pump 4, a fine filter 10, a cold start valve 6, a main pressure regulating valve 12, and various control hydraulic systems and related oil circuits sequentially arranged on the working hydraulic pipeline.

[0047] System pump 4 supplies oil to the working hydraulic system. Oil from the outlet of coarse filter 2 enters the working hydraulic system via system pump 4, followed by a cold start valve 6 connected in parallel. This valve's function is to allow oil to overflow into the oil tank when the system pressure is too high during low-temperature starts. The oil then connects to fine filter 10, which is connected in parallel to a differential pressure sensor and a bypass valve. When the differential pressure exceeds a set value, the system prompts for replacement of the fine filter element, further increasing the overflow from the bypass valve. After filtration by fine filter 10, the oil circuit is connected in parallel to a main pressure regulating valve 12 to adjust the system pressure and maintain stability. Overflow oil returns to the oil tank along the pipeline. Simultaneously, two oil passages are led out, allowing the oil to enter the P ports of two-position three-way valves, namely the first solenoid valve 13 and the second solenoid valve 14. Then, the pressurized oil sequentially enters the PTO control hydraulic system, the direction gear control hydraulic system, the speed gear control hydraulic system, and the dual hydrostatic unit control hydraulic system.

[0048] In practical implementation, the PTO control hydraulic system includes a PTO safety switch valve 16 and a PTO clutch valve 17, as well as correspondingly connected PTO anti-rotation device drive cylinders 18 and PTO clutches 19. The PTO clutch valve 17 is connected in series after the PTO safety switch valve 16 and is controlled by it. The PTO safety switch valve 16 is normally closed when the PTO is not in operation. At this time, the PTO anti-rotation device drive cylinder 18 engages under its own spring force to prevent the PTO from idling. When the PTO is operating, the PTO safety switch valve 16 and the PTO clutch valve 17 are opened sequentially, causing the PTO anti-rotation device to disengage under the action of hydraulic oil before the PTO clutch 19 engages. Similarly, when the PTO stops operating, the PTO clutch valve 17 and the PTO safety switch valve 16 are closed sequentially, causing the PTO anti-rotation device to engage before the PTO clutch 19 disengages. PTO safety switch valve 16 and PTO clutch valve 17 are sequentially installed on the PTO control main line. PTO safety switch valve 16 is connected to PTO anti-rotation device drive cylinder 18, and PTO clutch valve 17 is connected to PTO clutch 19.

[0049] The steering gear control hydraulic system includes a CF clutch valve 20, a CR clutch valve 21, a steering gear accumulator 22, and CF clutches 23 and CR clutches 24. All clutch valves are proportional solenoid valves to ensure precise control of clutch filling and emptying. An accumulator is added to the system to ensure pressure stability during gear shifting. CF clutch valve 20, CR clutch valve 21, and steering gear accumulator 22 are connected in parallel to the main pressure oil circuit. The use of accumulators in both the steering gear control hydraulic system and the speed gear control hydraulic system ensures stable system pressure during gear shifting. In some embodiments, the main steering gear control circuit is connected to the working hydraulic pipeline and the steering gear accumulator 22. A first steering gear control branch and a second steering gear control branch are established on the main steering gear control circuit, connected in parallel. CR clutch valve 21 and CR clutch 24 are sequentially installed on the first steering gear control branch; CF clutch valve 20 and CF clutch 23 are sequentially installed on the second steering gear control branch.

[0050] The speed gear control hydraulic system includes clutch valve 26 (C1), clutch valve 25 (C2), clutch valve 27 (C3), speed gear accumulator 28, clutches 30 (C1), 29 (C2), and 31 (C3). The speed gear accumulator 28 is located on the main speed gear control circuit. The main speed gear control circuit includes a first speed gear control branch, a second speed gear control branch, and a third speed gear control branch, all connected in parallel. Clutch valves 25 and 29 are sequentially installed on the first speed gear control branch, clutch valves 26 and 30 are sequentially installed on the second speed gear control branch, and clutch valves 27 and 31 are sequentially installed on the third speed gear control branch.

[0051] All clutch valves are proportional solenoid valves to ensure precise control of clutch filling and draining. An accumulator is added to the system to ensure pressure stability during gear shifting. Clutch valves 26 (C1), 25 (C2), 27 (C3), and accumulator 28 (speed gear) are connected in parallel to the main pressure oil circuit.

[0052] The dual hydrostatic unit control hydraulic system consists of two symmetrically arranged hydrostatic units, namely the first hydrostatic unit 32 and the second hydrostatic unit 33, and related oil circuits. The two hydrostatic units are connected in parallel to the main system oil circuit. The two hydrostatic units are connected through an external oil circuit, ensuring that the pressure difference and swing angle of the two hydrostatic units are consistent during operation, thereby achieving symmetrical power balance. Using a parallel arrangement of dual hydrostatic units can provide greater horsepower while ensuring dynamic symmetrical power balance through external oil circuit connections.

[0053] The aforementioned compensation system includes a compensation pump 5, a pilot-operated compensation pump control valve 15, a first solenoid valve 13, a second solenoid valve 14, and related oil circuits. A relief valve 7 is connected in parallel at the outlet of the compensation pump 5. The outlet of the relief valve 7 is connected to the oil circuit between the system pump 4 and the fine filter 10, and then to the P port of the pilot-operated compensation pump control valve 15. The pilot-operated compensation pump control valve 15 is a three-position three-way valve controlled by two first solenoid valves 13 and second solenoid valves 14. Its two sides are respectively connected to the A ports of the first solenoid valve 13 and the second solenoid valve 14. The A1 port of the pilot-operated compensation pump control valve 15 is connected to the oil circuit between the lubrication pump 3 and the oil cooler 8, and the A2 port of the pilot-operated compensation pump control valve 15 is connected to the oil outlet of the coarse filter 2.

[0054] The compensation pump 5 can supply oil to the lubrication system or pressure oil circuit or run idle as needed. The lubrication pump 3 and system pump 4 meet the oil requirements of the gearbox during normal operation. Under special operating conditions, the compensation pump 5 is required to supplement the flow of the working oil circuit or lubrication oil circuit.

[0055] This invention proposes a hydraulic system for a hydraulic-mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors. This system features dual hydrostatic units and internally houses only five wet clutches, enabling three speed ranges each for forward and reverse. The parallel dual hydrostatic units further facilitate continuously variable transmission within each speed range. The system adapts to the simple internal mechanical structure of the high-horsepower tractor transmission while ensuring the hydrostatic units can achieve continuously variable transmission across all speed ranges. Furthermore, the hydraulic system satisfies the requirements for oil supply to the wet clutches, oil replenishment and circulation cooling of the hydrostatic units, and cooling and lubrication of other internal mechanical components. This hydraulic system simplifies the internal mechanical transmission structure of the transmission while also meeting the cooling, lubrication, and operational requirements of various internal components.

[0056] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors, characterized in that, It includes an oil pan (1), a lubrication hydraulic system, a working hydraulic system and a compensation system; the oil pan (1) is connected to the oil inlet of the coarse filter (2), the lubrication pump (3) of the lubrication hydraulic system, the system pump (4) of the working hydraulic system and the compensation pump (5) of the compensation system are connected in parallel and share a common oil suction port, and the oil suction port is connected to the oil outlet of the coarse filter (2). The working hydraulic system includes a system pump (4), a fine filter (10), a main pressure regulating valve (12), and a control hydraulic system; the outlet of the system pump (4) is connected to the inlet of the working hydraulic pipeline, the fine filter (10) is installed on the working hydraulic pipeline, and the working hydraulic pipeline is connected in parallel with the first oil circuit where the main pressure regulating valve (12) is installed; a branch outlet is opened on the working hydraulic pipeline, and the branch outlet is connected to the compensation system; the control hydraulic system includes a PTO control hydraulic system, a steering gear control hydraulic system, a speed gear control hydraulic system, and a dual hydrostatic unit control hydraulic system; the PTO control hydraulic system, the steering gear control hydraulic system, the speed gear control hydraulic system, and the dual hydrostatic unit control hydraulic system are sequentially installed on the working hydraulic pipeline; The PTO control hydraulic system includes a PTO safety switch valve (16), a PTO clutch valve (17), a PTO anti-rotation device drive cylinder (18), and a PTO clutch (19); the PTO safety switch valve (16) and the PTO clutch valve (17) are sequentially arranged on the PTO control main line, the PTO safety switch valve (16) is connected to the PTO anti-rotation device drive cylinder (18), and the PTO clutch valve (17) is connected to the PTO clutch (19); The dual hydrostatic unit control hydraulic system includes a first hydrostatic unit (32) and a second hydrostatic unit (33) that are symmetrically arranged and interconnected.

2. The hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors according to claim 1, characterized in that, The steering gear control hydraulic system includes a CF clutch valve (20), a CR clutch valve (21), a steering gear accumulator (22), and a CF clutch (23) and a CR clutch (24); The steering gear accumulator (22) is installed on the steering gear control main line, which connects the steering gear first control branch and the steering gear second control branch. The steering gear first control branch is provided with a CR clutch valve (21) and a CR clutch (24) in sequence; the steering gear second control branch is provided with a CF clutch valve (20) and a CF clutch (23) in sequence.

3. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 1, characterized in that, The speed gear control hydraulic system includes a C1 clutch valve (26), a C2 clutch valve (25), a C3 clutch valve (27), a speed gear accumulator (28), and C1 clutches (30), C2 clutches (29) and C3 clutches (31); The speed accumulator (28) is installed on the speed control main circuit, which connects the first speed control branch, the second speed control branch and the third speed control branch. The first speed control branch is provided with a C2 clutch valve (25) and a C2 clutch (29) in sequence. The second speed control branch is provided with a C1 clutch valve (26) and a C1 clutch (30) in sequence. The third speed control branch is provided with a C3 clutch valve (27) and a C3 clutch (31) in sequence.

4. The hydraulic system for a hydraulic mechanical continuously variable transmission suitable for high-horsepower tractors according to claim 1, characterized in that, The compensation system includes a compensation pump (5), a pilot-operated compensation pump control valve (15), a first solenoid valve (13), and a second solenoid valve (14). The outlet of the compensation pump (5) is connected to the inlet of the pilot-operated compensation pump control valve (15). The first solenoid valve (13) and the second solenoid valve (14) are connected to the two sides of the pilot-operated compensation pump control valve (15), respectively. The inlet of the first solenoid valve (13) and the inlet of the second solenoid valve (14) are connected to the branch outlet of the working hydraulic pipeline. The first port of the pilot-operated compensation pump control valve (15) is connected to the lubrication hydraulic system. The second port of the pilot-operated compensation pump control valve (15) is connected to the outlet of the coarse filter (2).

5. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 4, characterized in that, The oil circuit between the compensation pump (5) and the pilot-operated compensation pump control valve (15) is connected to the working hydraulic line between the system pump (4) and the fine filter (10) through the first branch.

6. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 5, characterized in that, An overflow valve (7) is installed on the first branch.

7. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 1, characterized in that, The lubrication hydraulic system includes a lubrication pump (3), an oil cooler (8), a lubrication check valve (11), and a lubrication system circuit (34); the coarse filter (2) is connected to the second oil circuit, the oil outlet of the lubrication pump (3) is connected to the oil inlet of the lubrication hydraulic pipeline, the oil cooler (8) is installed on the lubrication hydraulic pipeline, the lubrication hydraulic pipeline is connected in parallel with the second oil circuit equipped with the lubrication check valve (11), and the lubrication system circuit (34) is connected to the oil outlet of the lubrication hydraulic pipeline; the lubrication check valve (11) is used to control the lubrication oil pressure.

8. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 7, characterized in that, A second branch is connected to the lubrication hydraulic pipeline between the lubrication pump (3) and the oil cooler (8); the lubrication hydraulic pipeline of the lubrication hydraulic system is connected to the compensation system through the second branch.

9. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for high-horsepower tractors according to claim 7, characterized in that, A third branch is provided on the lubrication hydraulic pipeline, and a temperature-controlled bypass valve (9) is provided on the third branch.

10. The hydraulic system for a hydraulic mechanical continuously variable transmission (CVT) suitable for a high-horsepower tractor according to claim 1, characterized in that, A fourth branch is provided on the working hydraulic pipeline, and a cold start valve (6) is provided on the fourth branch.

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