A tractor dual-source power transmission system and a gear shifting method thereof

Abstract

A tractor dual-source power transmission system and a shifting method thereof, the system comprises a housing, the housing is provided with a speed change input shaft, a first speed change intermediate shaft, a second speed change intermediate shaft and a speed change output shaft, the speed change input shaft is connected to the output end of the engine through a clutch transmission device, a first speed change transmission mechanism is provided between the speed change input shaft and the first speed change intermediate shaft, a second speed change transmission mechanism is provided between the first speed change intermediate shaft and the second speed change intermediate shaft, and a third speed change transmission mechanism is provided between the second speed change intermediate shaft and the speed change output shaft, the shifting is smooth and impact-free, the cost is low, the control is simple, and the transmission reliability is high. The method is to first disconnect the power of the speed change input shaft, then the hydraulic stepless speed regulation drive device drives the speed change output shaft to rotate at a speed corresponding to a target gear position, then convert to a transmission ratio corresponding to the target gear position, then engage the clutch transmission device, stop the hydraulic stepless speed regulation drive device, and realize uninterrupted power and smooth shifting and skipping gear shifting.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle engineering, and in particular to a dual-source power transmission system for a tractor and a gear shifting method thereof. Background Art

[0002] The transmission of a tractor is similar to that of a car. Both achieve speed change and torque change and deceleration and torque increase by adjusting the transmission ratio of different gear sets, and adjust the driving speed by controlling the engine speed and gear changes. However, the car transmission mainly adjusts the driving speed by dynamic gear shifting, while the tractor transmission is mainly for power output, multi-condition operation and low-speed traction. In addition, the tractor needs more gears and does not need frequent gear switching. Therefore, the MT, AMT, CVT, AT, and DCT transmissions that are maturely used in cars cannot meet the needs of tractors.

[0003] The existing tractor transmissions mainly include MT with pure mechanical shifting, HST with hydrostatic continuously variable drive, and PST with power shifting. Among them, MT has a high transmission efficiency, but it is inconvenient to operate and cannot be upgraded intelligently. HST is convenient to operate and intelligently upgrade, but the transmission efficiency is low. PST has two types: full power shifting and partial power shifting. Full power shifting has the characteristics of convenient operation and intelligent upgrading, high transmission efficiency, but it has a complex structure and high cost; partial power shifting has poor operation and intelligent upgrading. At present, there is no transmission that can combine the advantages of the above-mentioned transmissions, and it cannot meet the needs of convenient control of tractors and even unmanned driving. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a tractor dual-source power transmission system with smooth gear shifting without impact, low cost, simple control and high transmission reliability. A corresponding gear shifting method for the tractor dual-source power transmission system is also provided, which can achieve uninterrupted power and smooth gear shifting and can achieve skip gear shifting.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A dual-source power transmission system for a tractor comprises an engine and a transmission connected to the engine, the transmission comprising a housing, a speed change input shaft, a first speed change intermediate shaft, a second speed change intermediate shaft and a speed change output shaft are mounted on the housing, the speed change input shaft is connected to the output end of the engine via a clutch transmission device, a first speed change transmission mechanism capable of performing two transmission ratio selection conversions is provided between the speed change input shaft and the first speed change intermediate shaft, a second speed change transmission mechanism capable of performing two transmission ratio selection conversions is provided between the first speed change intermediate shaft and the second speed change intermediate shaft, and a third speed change transmission mechanism capable of performing two transmission ratio selection conversions and having a transmission disconnection function is provided between the second speed change intermediate shaft and the speed change output shaft.

[0007] As a further improvement of the above technical solution:

[0008] The output end of the engine is also connected to a PTO device, which includes a PTO input shaft and a PTO output shaft. The PTO input shaft is connected to the output end of the engine through a PTO clutch. A PTO speed change transmission mechanism capable of selecting and switching between two transmission ratios is provided between the PTO input shaft and the PTO output shaft.

[0009] The PTO speed transmission mechanism includes a PTO intermediate shaft, a first PTO gear, a second PTO gear, a third PTO gear, a fourth PTO gear, a fifth PTO gear, a sixth PTO gear and a PTO coupling sleeve. The first PTO gear and the second PTO gear are fixedly mounted on the PTO input shaft, the third PTO gear and the fourth PTO gear are rotatably mounted on the PTO intermediate shaft, the first PTO gear is meshed with the third PTO gear, the second PTO gear is meshed with the fourth PTO gear, the fifth PTO gear is fixedly mounted on the PTO intermediate shaft, the sixth PTO gear is fixedly mounted on the PTO output shaft and is meshed with the fifth PTO gear, the PTO coupling sleeve is axially slidably mounted on the PTO intermediate shaft and can selectively engage with the third PTO gear and the fourth PTO gear by sliding, and the PTO coupling sleeve is connected to a PTO control component for controlling the sliding of the PTO coupling sleeve.

[0010] The first speed transmission mechanism comprises a first gear, a second gear, a third gear, a fourth gear and a first engagement sleeve, the first gear and the second gear are rotatably mounted on the speed input shaft, the third gear and the fourth gear are fixedly mounted on the first speed intermediate shaft, the third gear is meshed with the first gear, the fourth gear is meshed with the second gear, the first engagement sleeve is axially slidably mounted on the speed input shaft and can selectively engage with the first gear and the second gear by sliding, and the first engagement sleeve is connected to a first control assembly for controlling the sliding of the first engagement sleeve;

[0011] The second speed transmission mechanism comprises a fifth gear, a sixth gear, a seventh gear, an eighth gear and a second engagement sleeve, wherein the fifth gear and the sixth gear are fixedly mounted on the first speed intermediate shaft, the seventh gear and the eighth gear are rotatably mounted on the second speed intermediate shaft, the fifth gear is meshed with the seventh gear, the sixth gear is meshed with the eighth gear, the second engagement sleeve is axially slidably mounted on the second speed intermediate shaft and can selectively engage with the seventh gear and the eighth gear by sliding, and the second engagement sleeve is connected to a second control assembly for controlling the sliding of the second engagement sleeve;

[0012] The third speed transmission mechanism includes a ninth gear, a tenth gear, an eleventh gear, a twelfth gear, a first friction clutch and a second friction clutch. The ninth gear and the tenth gear are rotatably mounted on the second speed intermediate shaft, the eleventh gear and the twelfth gear are fixedly mounted on the speed output shaft, the eleventh gear is meshed with the ninth gear, the twelfth gear is meshed with the tenth gear, the second speed intermediate shaft is connected to the ninth gear via the first friction clutch, and the second speed intermediate shaft is connected to the tenth gear via the second friction clutch.

[0013] The PTO control assembly, the first control assembly and the second control assembly all include a shift fork driven to reciprocate by a double-acting oil cylinder; the clutch transmission device includes an input driving gear and an input driven gear fixedly mounted on the speed change input shaft and meshing with the input driving gear, the input driving gear is connected to the output end of the engine through an input clutch, and the input clutch, the PTO clutch, the first friction clutch and the second friction clutch are all friction clutches driven to reciprocate by a single-acting oil cylinder and a spring; the tractor dual-source power transmission system also includes a pressure oil source generating device connected to the output end of the engine and driven by the engine to generate pressure oil, each double-acting oil cylinder is connected to the pressure oil source generating device through an independent electromagnetic control valve, and each single-acting oil cylinder is connected to the pressure oil source generating device through an independent electromagnetic control valve.

[0014] The electromagnetic control valves of the input clutch, PTO clutch, first friction clutch and second friction clutch are configured so that when power is lost, the corresponding double-acting cylinders drive the input clutch, PTO clutch, first friction clutch and second friction clutch to be in a disengaged state.

[0015] The pressure oil source generating device includes an oil tank and an oil pump connected to the output end of the engine, the inlet of the oil pump is connected to the oil tank through a filter, the outlet of the oil pump is connected to a pressure oil output pipe, and the pressure oil output pipe is connected to an oil source pressure reducing valve and an oil source overflow valve.

[0016] The speed input shaft, the second speed intermediate shaft and the PTO output shaft are coaxially arranged, the first speed intermediate shaft, the speed output shaft and the PTO intermediate shaft are coaxially arranged, the speed input shaft, the first speed intermediate shaft and the PTO input shaft are arranged side by side, and the first speed intermediate shaft is located between the speed input shaft and the PTO input shaft.

[0017] The dual-source power transmission system of the tractor also includes a hydraulic stepless speed regulation drive device, and the output end of the hydraulic stepless speed regulation drive device is connected to the speed change output shaft.

[0018] The hydraulic stepless speed regulation drive device includes a variable pump and a bidirectional fixed-displacement motor, which are arranged in series in a closed circulation pipeline. The variable pump is connected to the output end of the engine and is driven by the engine. The shaft of the bidirectional fixed-displacement motor serves as the output end of the hydraulic stepless speed regulation drive device and is connected to the speed-changing output shaft through a transmission mechanism.

[0019] The two inlets and outlets of the bidirectional quantitative motor are respectively a first inlet and an inlet and a second inlet. The first inlet and outlet are connected to an inlet and outlet of a variable pump through a first pipeline, and the second inlet and outlet are connected to another inlet and outlet of the variable pump through a second pipeline to form the closed circulation pipeline. An intermediate pipeline is connected between the first pipeline and the second pipeline, and the intermediate pipeline is provided with a neutral control solenoid valve for controlling the opening and closing of the intermediate pipeline.

[0020] The neutral control solenoid valve is connected to the intermediate pipeline when power is lost, and is disconnected from the intermediate pipeline when power is obtained.

[0021] The hydraulic stepless speed regulation drive device also includes a flushing oil inlet pipeline connected to the pressure oil source, the intermediate pipeline between the neutral control solenoid valve and the first pipeline is connected to the flushing oil inlet pipeline through the first flushing pipeline, the second pipeline between the neutral control solenoid valve and the variable pump is connected to the flushing oil inlet pipeline through the second flushing pipeline, the second pipeline between the neutral control solenoid valve and the two-way quantitative motor is connected to the flushing oil inlet pipeline through the third flushing pipeline, the first flushing pipeline and the second flushing pipeline are both provided in parallel with a first one-way valve for preventing the pressure oil from flowing to the flushing oil inlet pipeline and a flushing overflow valve for overflowing to the flushing oil inlet pipeline, the third flushing pipeline is provided with a second one-way valve for preventing the pressure oil from flowing to the flushing oil inlet pipeline; the intermediate pipeline between the neutral control solenoid valve and the first pipeline is provided with an electromagnetic overflow valve.

[0022] A shifting method for the above-mentioned tractor dual-source power transmission system, the shifting method is that when the transmission needs to be shifted to a target gear, the clutch transmission device is firstly used to disconnect the power transmission between the output end of the engine and the speed input shaft, and then the hydraulic stepless speed regulation drive device is started to drive the speed output shaft to rotate at a speed corresponding to the target gear, and then the first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism are shifted to a transmission ratio corresponding to the target gear, and then the clutch transmission device is engaged and the driving action of the hydraulic stepless speed regulation drive device is stopped.

[0023] As a further improvement of the above technical solution:

[0024] The speed corresponding to the target gear is preset based on the actual speed of the transmission output shaft when the transmission is in the target gear at different speeds of the engine.

[0025] The first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism are controlled by a shift handle to select and convert the transmission ratio to achieve gear shifting of the transmission. The clutch transmission device, the first speed transmission mechanism, the second speed transmission mechanism, the third speed transmission mechanism and the hydraulic stepless speed regulation drive device are automatically controlled by a control device, and the control device is provided with a detector for detecting the position of the shift handle in each gear position; the starting timing of the hydraulic stepless speed regulation drive device is that after the shift handle is switched to the position corresponding to the target gear position, the control device obtains the residence time of the shift handle at the position corresponding to the target gear position through the detector, and when the residence time reaches the preset time, the control device automatically starts the hydraulic stepless speed regulation drive device to drive the speed output shaft to rotate at the speed corresponding to the target gear position.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] The dual-source power transmission system for a tractor of the present invention adopts a speed input shaft, a first speed intermediate shaft, a second speed intermediate shaft and a speed output shaft, and is combined with a first speed transmission mechanism, a second speed transmission mechanism and a third speed transmission mechanism to form a series shifting system, which can realize mechanical shifting of eight working gears and one neutral gear. The shifting range is large and can meet the use requirements of the tractor. Only the third speed transmission mechanism is provided with a transmission disconnection function. The first speed transmission mechanism and the second speed transmission mechanism do not need to be provided with a neutral gear, and a shift interlocking mechanism and a neutral gear actuator are not required. The structure of the first speed transmission mechanism and the second speed transmission mechanism can be simplified, the cost and control difficulty can be reduced, and the reliability of the transmission system can be improved. When the transmission shifts gears, the first speed transmission mechanism and the second speed transmission mechanism can be converted to the transmission ratio of the target gear first, and then the third speed transmission mechanism can be converted, so that the gear shifting can be smooth and impact-free.

[0028] The shifting method of the dual-source power transmission system of the tractor of the present invention can realize uninterrupted power shifting and smooth shifting in all speed sections of the dual-source power transmission system of the tractor, and the transmission does not need to follow the requirements of sequential shifting, and skip gear shifting can be realized, which greatly improves the convenience of shifting. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the schematic diagram of the tractor's dual-source power transmission system.

[0030] Figure 2 This is the schematic diagram of the PTO device.

[0031] Figure 3 This is the schematic diagram of the transmission.

[0032] Figure 4 It is the schematic diagram of the transmission control components and the hydraulic stepless speed regulation drive device.

[0033] Figure 5 This is the schematic diagram of the various control components of the transmission control.

[0034] Figure 6 This is the schematic diagram of the hydraulic stepless speed regulation drive device.

[0035] Figure 7 This is a schematic diagram for presetting the speed corresponding to each gear when the engine is at maximum throttle.

[0036] Legend:

[0037] 1. Engine; 11. Input driving gear; 12. Input driven gear; 13. Input clutch; 2. Transmission; 21. Case; 3. PTO device; 31. PTO input shaft; 32. PTO output shaft; 33. PTO intermediate shaft; 34. PTO clutch; 35. First PTO gear; 36. Second PTO gear; 37. Third PTO gear; 38. Fourth PTO gear; 39. Fifth PTO gear; 310. Sixth PTO gear; 311. PTO coupling sleeve; 312. PTO control assembly; 4 , hydraulic stepless speed regulation drive device; 41, variable pump; 42, bidirectional quantitative motor; 421, first inlet and outlet; 422, second inlet and outlet; 43, first pipeline; 44, second pipeline; 45, intermediate pipeline; 46, neutral control solenoid valve; 47, flushing oil inlet pipeline; 48, first flushing pipeline; 49, second flushing pipeline; 410, third flushing pipeline; 411, first non-return valve; 412, flushing overflow valve; 413, second non-return valve; 414, electromagnetic overflow valve; 101, speed change input shaft; 102, first speed change intermediate shaft ; 103, second speed change intermediate shaft; 104, speed change output shaft; 201, first gear; 202, second gear; 203, third gear; 204, fourth gear; 205, fifth gear; 206, sixth gear; 207, seventh gear; 208, eighth gear; 209, ninth gear; 210, tenth gear; 211, eleventh gear; 212, twelfth gear; 213, thirteenth gear; 301, first engagement sleeve; 302, second engagement sleeve; 303, first friction clutch; 304, second friction clutch Clutch; 401, first control component; 402, second control component; 501, oil tank; 502, oil pump; 503, filter; 504, pressure oil output pipe; 505, oil source pressure reducing valve; 506, oil source overflow valve; 601, first single-acting cylinder; 602, second single-acting cylinder; 603, third single-acting cylinder; 604, fourth single-acting cylinder; 605, two-position three-way solenoid valve; 701, first double-acting cylinder; 702, second double-acting cylinder; 703, third double-acting cylinder; 704, two-position four-way solenoid valve. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] like Figure 1As shown, the dual-source power transmission system of the tractor of this embodiment includes an engine 1 and a transmission 2 connected to the engine 1, the transmission 2 includes a housing 21, on which a speed change input shaft 101, a first speed change intermediate shaft 102, a second speed change intermediate shaft 103 and a speed change output shaft 104 are installed, the speed change input shaft 101 is connected to the output end of the engine 1 through a clutch transmission device, a first speed change transmission mechanism capable of performing two transmission ratio selection conversion is provided between the speed change input shaft 101 and the first speed change intermediate shaft 102, a second speed change transmission mechanism capable of performing two transmission ratio selection conversion is provided between the first speed change intermediate shaft 102 and the second speed change intermediate shaft 103, and a third speed change transmission mechanism capable of performing two transmission ratio selection conversion and having a transmission disconnection function is provided between the second speed change intermediate shaft 103 and the speed change output shaft 104. The dual-source power transmission system of the tractor adopts a speed input shaft 101, a first speed intermediate shaft 102, a second speed intermediate shaft 103 and a speed output shaft 104, and is combined with a first speed transmission mechanism, a second speed transmission mechanism and a third speed transmission mechanism to form a series shifting system, which can realize mechanical shifting of eight working gears and one neutral gear. The shifting range is large and can meet the use requirements of the tractor. Only the third speed transmission mechanism is provided with a transmission disconnection function, and the first speed transmission mechanism and the second speed transmission mechanism do not need to be provided with a neutral gear, and a shift interlocking mechanism and a neutral gear actuator are not required. The structure of the first speed transmission mechanism and the second speed transmission mechanism can be simplified, the cost and control difficulty can be reduced, and the reliability of the transmission system can be improved. When the transmission 2 is shifted, the first speed transmission mechanism and the second speed transmission mechanism can be firstly converted to the transmission ratio of the target gear, and then the third speed transmission mechanism is converted, so that the gear shift can be smooth and impact-free.

[0040] In this embodiment, Figure 1 and Figure 2 As shown, the output end of the engine 1 is also connected to a PTO device 3, and the PTO device 3 includes a PTO input shaft 31 and a PTO output shaft 32. The PTO input shaft 31 is connected to the output end of the engine 1 through a PTO clutch 34, and a PTO speed change transmission mechanism capable of selecting and switching two transmission ratios is provided between the PTO input shaft 31 and the PTO output shaft 32. By controlling the engagement and disengagement of the PTO clutch 34, the power of the engine 1 can be selectively transmitted to the PTO input shaft 31, and by adjusting the transmission ratio of the PTO speed change transmission mechanism, the output speed and torque of the PTO output shaft 32 can be adjusted. The PTO device 3 is provided, so that the tractor dual-source power transmission system has the function of PTO power output, which expands the function of the tractor dual-source power transmission system and increases the scope of application.

[0041] In this embodiment, Figure 3As shown, the PTO speed transmission mechanism includes a PTO intermediate shaft 33, a first PTO gear 35, a second PTO gear 36, a third PTO gear 37, a fourth PTO gear 38, a fifth PTO gear 39, a sixth PTO gear 310 and a PTO coupling sleeve 311. The first PTO gear 35 and the second PTO gear 36 are fixedly mounted on the PTO input shaft 31, the third PTO gear 37 and the fourth PTO gear 38 are rotatably mounted on the PTO intermediate shaft 33, and the first PTO gear 35 is meshed with the third PTO gear 37. The second PTO gear 36 meshes with the fourth PTO gear 38, the fifth PTO gear 39 is fixedly mounted on the PTO intermediate shaft 33, the sixth PTO gear 310 is fixedly mounted on the PTO output shaft 32 and meshes with the fifth PTO gear 39, the PTO engagement sleeve 311 is axially slidably mounted on the PTO intermediate shaft 33 and can selectively engage with the third PTO gear 37 and the fourth PTO gear 38 by sliding, and the PTO engagement sleeve 311 is connected with a PTO control component 312 for controlling the sliding of the PTO engagement sleeve 311. When the PTO control component 312 controls the PTO engagement sleeve 311 to slide to engage with the third PTO gear 37, the power transmission route input to the PTO input shaft 31 is: PTO input shaft 31→first PTO gear 35→third PTO gear 37→PTO engagement sleeve 311→PTO intermediate shaft 33→fifth PTO gear 39→sixth PTO gear 310→PTO output shaft 32, so as to realize the power output of the first transmission ratio. When the PTO control component 312 controls the PTO coupling sleeve 311 to slide to engage with the fourth PTO gear 38, the power transmission route input to the PTO input shaft 31 is: PTO input shaft 31→second PTO gear 36→fourth PTO gear 38→PTO coupling sleeve 311→PTO intermediate shaft 33→fifth PTO gear 39→sixth PTO gear 310→PTO output shaft 32, realizing the power output of the second transmission ratio. The PTO speed transmission mechanism has the advantages of simple and compact structure, stable and reliable operation, and easy control. The power of the PTO input shaft 31 is transmitted to the PTO output shaft 32 through the PTO intermediate shaft 33, which can realize a large transmission ratio output with two-stage reduction, and make the direction of the PTO output shaft 32 consistent with the direction of the engine 1, which meets the relevant standard requirements and design requirements.

[0042] In this embodiment, the first speed transmission mechanism includes a first gear 201, a second gear 202, a third gear 203, a fourth gear 204 and a first engagement sleeve 301. The first gear 201 and the second gear 202 are rotatably mounted on the speed input shaft 101, the third gear 203 and the fourth gear 204 are fixedly mounted on the first speed intermediate shaft 102, the third gear 203 is meshed with the first gear 201, the fourth gear 204 is meshed with the second gear 202, and the first engagement sleeve 301 is axially slidably mounted on the speed input shaft 101 and can pass through the first gear. The first engagement sleeve 301 can be selectively engaged with the first gear 201 and the second gear 202 by sliding, and the first engagement sleeve 301 is connected with a first control component 401 for controlling the sliding of the first engagement sleeve 301; when the first control component 401 controls the first engagement sleeve 301 to slide to engage with the first gear 201, the power transmission route input to the speed change input shaft 101 is: the speed change input shaft 101→the first engagement sleeve 301→the first gear 201→the third gear 203→the first speed change intermediate shaft 102, so as to realize the power output of the first transmission ratio of the first speed change transmission mechanism. When the first control component 401 controls the first engagement sleeve 301 to slide to engage with the second gear 202, the power transmission route input to the speed change input shaft 101 is: the speed change input shaft 101→the first engagement sleeve 301→the second gear 202→the fourth gear 204→the first speed change intermediate shaft 102, so as to realize the power output of the second transmission ratio of the first speed change transmission mechanism.

[0043] The second speed transmission mechanism includes a fifth gear 205, a sixth gear 206, a seventh gear 207, an eighth gear 208 and a second engagement sleeve 302. The fifth gear 205 and the sixth gear 206 are fixedly mounted on the first speed intermediate shaft 102, the seventh gear 207 and the eighth gear 208 are rotatably mounted on the second speed intermediate shaft 103, the fifth gear 205 is meshed with the seventh gear 207, the sixth gear 206 is meshed with the eighth gear 208, and the second engagement sleeve 302 is axially slidably mounted on the second speed intermediate shaft 103 and can be slidably mounted on the second speed intermediate shaft 103. The second engagement sleeve 302 can be selectively engaged with the seventh gear 207 and the eighth gear 208, and is connected to a second control assembly 402 for controlling the sliding of the second engagement sleeve 302; when the second control assembly 402 controls the second engagement sleeve 302 to slide to engage with the seventh gear 207, the power transmission route input to the first speed-changing intermediate shaft 102 is: the first speed-changing intermediate shaft 102 → the fifth gear 205 → the seventh gear 207 → the second engagement sleeve 302 → the second speed-changing intermediate shaft 103, so as to realize the power output of the first transmission ratio of the second speed-changing transmission mechanism. When the second control assembly 402 controls the second engagement sleeve 302 to slide to engage with the eighth gear 208, the power transmission route input to the first speed-changing intermediate shaft 102 is: the first speed-changing intermediate shaft 102 → the sixth gear 206 → the eighth gear 208 → the second engagement sleeve 302 → the second speed-changing intermediate shaft 103, so as to realize the power output of the second transmission ratio of the second speed-changing transmission mechanism.

[0044] The third speed transmission mechanism includes a ninth gear 209, a tenth gear 210, an eleventh gear 211, a twelfth gear 212, a first friction clutch 303 and a second friction clutch 304. The ninth gear 209 and the tenth gear 210 are rotatably mounted on the second speed intermediate shaft 103, the eleventh gear 211 and the twelfth gear 212 are fixedly mounted on the speed output shaft 104, the eleventh gear 211 is meshed with the ninth gear 209, the twelfth gear 212 is meshed with the tenth gear 210, the second speed intermediate shaft 103 is connected to the ninth gear 209 via the first friction clutch 303, and the second speed intermediate shaft 103 is connected to the tenth gear 210 via the second friction clutch 304. When the first friction clutch 303 is engaged and the second friction clutch 304 is disengaged, the power transmission route input to the second speed-changing intermediate shaft 103 is: the second speed-changing intermediate shaft 103 → the first friction clutch 303 → the ninth gear 209 → the eleventh gear 211 → the speed output shaft 104, so as to realize the power output of the first transmission ratio of the third speed-changing transmission mechanism. When the first friction clutch 303 is disengaged and the second friction clutch 304 is engaged, the power transmission route input to the second speed-changing intermediate shaft 103 is: the second speed-changing intermediate shaft 103 → the second friction clutch 304 → the tenth gear 210 → the twelfth gear 212 → the speed output shaft 104, so as to realize the power output of the second transmission ratio of the third speed-changing transmission mechanism. When the first friction clutch 303 is disengaged and the second friction clutch 304 is disengaged, the power input from the second speed-changing intermediate shaft 103 to the second speed-changing intermediate shaft 103 cannot be transmitted to the speed output shaft 104, and at this time, the third speed-changing transmission mechanism is disengaged.

[0045] The first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism each have two transmission ratios, and the third speed transmission mechanism can also disconnect the transmission. Through the combination of different transmission ratios, the transmission 2 can be switched between eight gears, and the transmission can be disconnected as a whole to realize the neutral function. The first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism have simple and compact structures, stable and reliable operation, and are easy to control.

[0046] In this embodiment, the PTO control component 312, the first control component 401 and the second control component 402 all include a shift fork driven to reciprocate by a double-acting cylinder; the clutch transmission device includes an input driving gear 11 and an input driven gear 12 fixedly mounted on the speed change input shaft 101 and meshing with the input driving gear 11, the input driving gear 11 is connected to the output end of the engine 1 through an input clutch 13, the input clutch 13, the PTO clutch 34, the first friction clutch 303 and the second friction clutch 304 are all friction clutches driven to reciprocate by a single-acting cylinder and a spring; the tractor dual-source power transmission system also includes a pressure oil source generating device connected to the output end of the engine 1 and driven by the engine 1 to generate pressure oil, each double-acting cylinder is connected to the pressure oil source generating device through an independent electromagnetic control valve, and each single-acting cylinder is connected to the pressure oil source generating device through an independent electromagnetic control valve. The fork driven to reciprocate by the double-acting cylinder, the cooperation between the fork and the coupling sleeves, the assembly of the coupling sleeves, the friction clutch driven to reciprocate by the single-acting cylinder and the spring, and the electromagnetic control valve can all be configured with reference to the existing technology.

[0047] like Figures 4 to 6 As shown, in this embodiment, the single-acting cylinder corresponding to the input clutch 13 is the first single-acting cylinder 601, the single-acting cylinder corresponding to the PTO clutch 34 is the second single-acting cylinder 602, the single-acting cylinder corresponding to the first friction clutch 303 is the third single-acting cylinder 603, and the single-acting cylinder corresponding to the second friction clutch 304 is the fourth single-acting cylinder 604. The first single-acting cylinder 601, the second single-acting cylinder 602 and the fourth single-acting cylinder 604 are respectively connected to the pressure oil source generating device through an independent two-position three-way solenoid valve 605. The double-acting cylinder corresponding to the first control component 401 is the first double-acting cylinder 701, the double-acting cylinder corresponding to the second control component 402 is the second double-acting cylinder 702, and the double-acting cylinder corresponding to the PTO control component 312 is the third double-acting cylinder 703. The first double-acting cylinder 701, the second double-acting cylinder 702 and the third double-acting cylinder 703 are respectively connected to the pressure oil source generating device through an independent two-position four-way solenoid valve 704.

[0048] In this embodiment, the electromagnetic control valves of the input clutch 13, the PTO clutch 34, the first friction clutch 303 and the second friction clutch 304 are configured so that when power is lost, the corresponding double-acting cylinders drive the input clutch 13, the PTO clutch 34, the first friction clutch 303 and the second friction clutch 304 to be in a disengaged state, so as to avoid safety accidents caused by the engagement of the clutches in the event of a power failure or other fault.

[0049] In this embodiment, the pressure oil source generating device includes an oil tank 501 and an oil pump 502 connected to the output end of the engine 1. The inlet of the oil pump 502 is connected to the oil tank 501 through a filter 503. The outlet of the oil pump 502 is connected to a pressure oil output pipe 504. The pressure oil output pipe 504 is connected to an oil source pressure reducing valve 505 and an oil source overflow valve 506. The oil pump 502 is directly connected to the output end of the engine 1 and works synchronously with the engine 1. The filter 503 plays a role in filtering the hydraulic oil. The oil source overflow valve 506 releases pressure when overpressure occurs to prevent system overload. The oil source pressure reducing valve 505 controls the output oil pressure to make the pressure of each oil cylinder appropriate.

[0050] In this embodiment, the speed change input shaft 101, the second speed change intermediate shaft 103 and the PTO output shaft 32 are coaxially arranged, the first speed change intermediate shaft 102, the speed change output shaft 104 and the PTO intermediate shaft 33 are coaxially arranged, the speed change input shaft 101, the first speed change intermediate shaft 102 and the PTO input shaft 31 are arranged side by side, and the first speed change intermediate shaft 102 is located between the speed change input shaft 101 and the PTO input shaft 31. This arrangement makes the transmission 2 compact in structure, easy to manufacture and assemble, and low in cost.

[0051] In this embodiment, the tractor dual-source power transmission system further includes a hydraulic stepless speed regulation drive device 4, and the output end of the hydraulic stepless speed regulation drive device 4 is connected to the speed output shaft 104. The hydraulic stepless speed regulation drive device 4 is provided, so that the tractor dual-source power transmission system has a hydraulic stepless speed regulation function at the same time, and can cooperate with the transmission 2 to flexibly switch between mechanical gear shifting and hydraulic stepless speed shifting. In special cases, it can be driven by the hydraulic stepless speed regulation drive device 4 alone, which increases the range of the tractor's stable output speed and improves the adaptability of the tractor to multiple working conditions. At the same time, dual-power source mixed shifting can also be achieved. When the transmission 2 performs mechanical shifting, the hydraulic stepless speed regulation drive device 4 can be used to drive the speed output shaft 104 to operate at a speed corresponding to the target gear or a speed close to the speed corresponding to the target gear, and then the transmission 2 is switched to the target gear, which can achieve full-speed shifting power uninterrupted and smooth shifting of the tractor dual-source power transmission system, and the transmission 2 does not need to follow the requirements of sequential shifting, and can achieve skipping gear shifting, which greatly improves the convenience of shifting.

[0052] In this embodiment, the hydraulic stepless speed regulation drive device 4 includes a variable pump 41 and a bidirectional quantitative motor 42, which are arranged in series in a closed circulation pipeline, and the variable pump 41 is connected to the output end of the engine 1 and driven by the engine 1, and the shaft of the bidirectional quantitative motor 42 is connected to the variable speed output shaft 104 through a transmission mechanism as the output end of the hydraulic stepless speed regulation drive device 4. The flow rate and direction of the variable pump 41 can be adjusted by controlling the deflection angle of its swash plate, so that the speed and direction of the hydraulic oil in the closed circulation pipeline can be adjusted, and the pressure oil is not output (when the swash plate is in the middle position), and the bidirectional quantitative motor 42 is arranged in series in the closed circulation pipeline, so that the variable pump 41 can control the direction and speed of the bidirectional quantitative motor 42, thereby realizing the bidirectional stepless speed regulation drive of the variable speed output shaft 104. Preferably, the transmission mechanism includes a thirteenth gear 213, which is connected to the output shaft of the bidirectional quantitative motor 42, and meshes with the tenth gear 210, which is conducive to simplifying the structure, reducing costs, and facilitating control.

[0053] In this embodiment, the two inlets and outlets of the bidirectional quantitative motor 42 are respectively the first inlet and outlet 421 and the second inlet and outlet 422. The first inlet and outlet 421 is connected to one inlet and outlet of the variable pump 41 through the first pipeline 43, and the second inlet and outlet 422 is connected to the other inlet and outlet of the variable pump 41 through the second pipeline 44 to form a closed circulation pipeline. An intermediate pipeline 45 is connected between the first pipeline 43 and the second pipeline 44. The intermediate pipeline 45 is provided with a neutral control solenoid valve 46 for controlling the opening and closing of the intermediate pipeline 45. When the neutral control solenoid valve 46 disconnects the intermediate pipeline 45, the variable pump 41 will directly drive the bidirectional quantitative motor 42 to rotate accordingly. When the neutral control solenoid valve 46 connects the intermediate pipeline 45, the pressure oil output by the variable pump 41 will directly return to the variable pump 41 through the intermediate pipeline 45. At this time, the pressure oil generated by the variable pump 41 does not drive the bidirectional quantitative motor 42, the bidirectional quantitative motor 42 rotates, and the hydraulic stepless speed regulation drive device 4 is in a neutral state. The neutral control solenoid valve 46 is provided to facilitate the control of the hydraulic stepless speed regulation drive device 4 to switch to a neutral state.

[0054] In this embodiment, the neutral control solenoid valve 46 is connected to the intermediate pipeline 45 when it is powered off, and is disconnected from the intermediate pipeline 45 when it is powered on. When the variable pump 41 is controlled by a controller, the signal accuracy of its zero output (the swash plate is in the middle position) is difficult to ensure, and there may be controller failure, power failure and other failures. When the neutral control solenoid valve 46 is powered off, it is connected to the intermediate pipeline 45, and in the above case, the hydraulic stepless speed regulation drive device 4 can be placed in absolute neutral, avoiding driving safety accidents caused by failure to place the neutral gear.

[0055] In this embodiment, the hydraulic stepless speed regulation drive device 4 further includes a flushing oil inlet pipeline 47 connected to the pressure oil source, the intermediate pipeline 45 between the neutral control solenoid valve 46 and the first pipeline 43 is connected to the flushing oil inlet pipeline 47 through the first flushing pipeline 48, the second pipeline 44 between the neutral control solenoid valve 46 and the variable pump 41 is connected to the flushing oil inlet pipeline 47 through the second flushing pipeline 49, and the second pipeline 44 between the neutral control solenoid valve 46 and the bidirectional quantitative motor 42 is connected to the flushing oil inlet pipeline 47 through the third flushing pipeline 48. The flushing pipeline 410 is connected to the flushing oil inlet pipeline 47. The first flushing pipeline 48 and the second flushing pipeline 49 are both provided with a first non-return valve 411 to prevent the pressure oil from flowing to the flushing oil inlet pipeline 47 and a flushing overflow valve 412 for overflowing to the flushing oil inlet pipeline 47 in parallel. The third flushing pipeline 410 is provided with a second non-return valve 413 to prevent the pressure oil from flowing to the flushing oil inlet pipeline 47; the intermediate pipeline 45 between the neutral control solenoid valve 46 and the first pipeline 43 is provided with an electromagnetic overflow valve 414. Since the variable pump 41 and the two-way quantitative motor 42 are connected to form a closed circulation pipeline, the hydraulic oil is prone to heat up and fail. The above arrangement can flush and cool the closed circulation pipeline. Figure 6 As shown, the process and principle of flushing and cooling are: when the neutral control solenoid valve 46 and the flushing relief valve 412 are closed and disconnected, when the variable pump 41 rotates forward, the pressure oil generated by the variable pump 41 is transmitted from the output point A to the forward flushing connection point B, and is transmitted to the input point E of the two-way fixed-displacement motor 42 through the connection points C and D, and then transmitted to the two-way fixed-displacement motor 42, and then converges into the variable pump 41 through the output point F of the two-way fixed-displacement motor 42. Since the hydraulic oil cannot be compressed, the hydraulic oil output by the variable pump 41 drives the two-way fixed-displacement motor 42 to rotate, and its speed and direction are controlled by adjusting the swash plate angle of the variable pump 41. When the variable pump 41 drives the bidirectional quantitative motor 42 to rotate forward, the pressure oil from the pressure oil source to the flushing oil inlet pipeline 47 flows from the flushing connection point H through the first flushing pipeline 48 and its first non-return valve 411 to the forward flushing connection point J, and the pressure oil of the reverse flushing connection point B flows to the flushing connection point H through the second flushing pipeline 49 and its flushing overflow valve 412, thereby replacing part of the pressure oil in the closed circulation pipeline to achieve flushing and cooling. The principle of flushing and cooling when the variable pump 41 is reversed is the same as that of flushing and cooling when it is forward. At the same time, since the bidirectional quantitative motor 42 will rotate with the mechanical gear when it is in pure mechanical gear transmission, in order to prevent low internal pressure and poor flushing and cooling effect, when the neutral control solenoid valve 46 is closed and disconnected, the flushing overflow valve 412 can also be controlled to gain and lose power according to a certain rule, and cooperate with the first non-return valve 411 on the second flushing pipeline 49 to perform flushing and cooling.

[0056] A shifting method for the dual-source power transmission system of a tractor of the present embodiment, the shifting method is that when the transmission 2 needs to be shifted to the target gear, the clutch transmission device is firstly used to disconnect the power transmission between the output end of the engine 1 and the speed input shaft 101, and then the hydraulic stepless speed regulation drive device 4 is started to drive the speed output shaft 104 to rotate at the speed corresponding to the target gear, and then the first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism are shifted to the transmission ratio corresponding to the target gear, and then the clutch transmission device is engaged, and the driving action of the hydraulic stepless speed regulation drive device 4 is stopped. The shifting method can realize the full-speed shifting power of the dual-source power transmission system of the tractor without interruption and smooth shifting, and the transmission 2 does not need to follow the requirements of sequential shifting, and can realize skipping gear shifting, which greatly improves the convenience of shifting.

[0057] In this embodiment, the speed corresponding to the target gear is preset according to the actual speed of the transmission output shaft 104 when the transmission 2 is in the target gear at different speeds of the engine 1. For example, the speed corresponding to each gear when the engine 1 is at maximum throttle is preset. Figure 7 , the x-axis represents the engine speed and the position of the gear lever, and the y-axis represents the vehicle speed. The line segments s1 to s8 represent the speed lines of the 1st to 8th gears, s0 represents the maximum throttle speed line, and s n Indicates other throttle speed lines, s n It only appears on the lower right side of s0. The intersection points of s0 and the line segments s1 to s8 are a to h, which correspond to the optimal shifting time of the corresponding gear when the engine 1 is at maximum throttle. Its x-coordinate position is the position corresponding to the gear lever, which is p1 to p8 respectively, and the y-coordinate position corresponds to the vehicle speed v1 to v8 at this time.

[0058] In this embodiment, the first speed transmission mechanism, the second speed transmission mechanism and the third speed transmission mechanism are controlled by a shift handle to perform transmission ratio selection and conversion to realize the gear shifting of the transmission 2. The clutch transmission device, the first speed transmission mechanism, the second speed transmission mechanism, the third speed transmission mechanism and the hydraulic stepless speed regulation drive device 4 are automatically controlled by the control device. The control device is provided with a detector for detecting the position of the shift handle in each gear position. The starting timing of the hydraulic stepless speed regulation drive device 4 is that after the shift handle is switched to the position corresponding to the target gear position, the control device obtains the residence time of the shift handle in the position corresponding to the target gear position through the detector. When the residence time reaches the preset time, the control device automatically starts the hydraulic stepless speed regulation drive device 4 to drive the speed change output shaft 104 to rotate at the speed corresponding to the target gear position.

[0059] In this embodiment, the hydraulic stepless speed regulation driving device 4 and the speed corresponding to each gear are preset, so that when the hydraulic stepless speed regulation driving device 4 is used alone, it has both the smoothness of stepless gear shifting and the rhythm of stepped gear shifting.

[0060] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and changes obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A dual-source power transmission system for a tractor, comprising an engine (1) and a transmission (2) connected to the engine (1), characterized in that: The transmission (2) comprises a housing (21), on which a speed change input shaft (101), a first speed change intermediate shaft (102), a second speed change intermediate shaft (103) and a speed change output shaft (104) are mounted; the speed change input shaft (101) is connected to the output end of the engine (1) via a clutch transmission device; a first speed change transmission mechanism capable of performing two transmission ratio selection conversions is provided between the speed change input shaft (101) and the first speed change intermediate shaft (102); a second speed change transmission mechanism capable of performing two transmission ratio selection conversions is provided between the first speed change intermediate shaft (102) and the second speed change intermediate shaft (103); and a third speed change transmission mechanism capable of performing two transmission ratio selection conversions and having a transmission disconnection function is provided between the second speed change intermediate shaft (103) and the speed change output shaft (104); The tractor dual-source power transmission system further comprises a hydraulic stepless speed regulation drive device (4), the output end of the hydraulic stepless speed regulation drive device (4) being connected to the speed change output shaft (104); the hydraulic stepless speed regulation drive device (4) comprising a variable pump (41) and a bidirectional fixed-displacement motor (42), the variable pump (41) and the bidirectional fixed-displacement motor (42) being arranged in series in a closed-loop pipeline, the two inlets and outlets of the bidirectional fixed-displacement motor (42) being respectively a first inlet and outlet (421) and a second inlet and outlet (422), the first inlet and outlet (421) being connected to one inlet and outlet of the variable pump (41) through a first pipeline (43), and the second inlet and outlet (422) being connected to the other inlet and outlet of the variable pump (41) through a second pipeline (44) to form the closed-loop pipeline, an intermediate pipeline (45) being connected between the first pipeline (43) and the second pipeline (44), the intermediate pipeline (45) being provided with a neutral control solenoid valve (46) for controlling the on and off of the intermediate pipeline (45); The hydraulic stepless speed regulation drive device (4) further comprises a flushing oil inlet pipeline (47) connected to a pressure oil source, an intermediate pipeline (45) between the neutral control solenoid valve (46) and the first pipeline (43) being connected to the flushing oil inlet pipeline (47) via a first flushing pipeline (48), a second pipeline (44) between the neutral control solenoid valve (46) and the variable displacement pump (41) being connected to the flushing oil inlet pipeline (47) via a second flushing pipeline (49), and a second pipeline (44) between the neutral control solenoid valve (46) and the bidirectional quantitative motor (42) being connected to the flushing oil inlet pipeline (47) via a third flushing pipeline (48). The pipeline (410) is connected to the flushing oil inlet pipeline (47); the first flushing pipeline (48) and the second flushing pipeline (49) are both provided in parallel with a first check valve (411) for preventing the pressure oil from flowing into the flushing oil inlet pipeline (47) and a flushing overflow valve (412) for overflowing into the flushing oil inlet pipeline (47); the third flushing pipeline (410) is provided with a second check valve (413) for preventing the pressure oil from flowing into the flushing oil inlet pipeline (47); and the intermediate pipeline (45) between the neutral control solenoid valve (46) and the first pipeline (43) is provided with an electromagnetic overflow valve (414).

2. The tractor dual-source power transmission system according to claim 1, characterized in that: The output end of the engine (1) is also connected to a PTO device (3), the PTO device (3) comprising a PTO input shaft (31) and a PTO output shaft (32), the PTO input shaft (31) being connected to the output end of the engine (1) via a PTO clutch (34), and a PTO speed change transmission mechanism capable of selecting and switching between two transmission ratios being provided between the PTO input shaft (31) and the PTO output shaft (32).

3. The tractor dual-source power transmission system according to claim 2, characterized in that: The PTO speed transmission mechanism comprises a PTO intermediate shaft (33), a first PTO gear (35), a second PTO gear (36), a third PTO gear (37), a fourth PTO gear (38), a fifth PTO gear (39), a sixth PTO gear (310) and a PTO coupling sleeve (311); the first PTO gear (35) and the second PTO gear (36) are fixedly mounted on the PTO input shaft (31); the third PTO gear (37) and the fourth PTO gear (38) are rotatably mounted on the PTO intermediate shaft (33); the first PTO gear (35) meshes with the third PTO gear (37) The second PTO gear (36) is meshed with the fourth PTO gear (38), the fifth PTO gear (39) is fixedly mounted on the PTO intermediate shaft (33), the sixth PTO gear (310) is fixedly mounted on the PTO output shaft (32) and is meshed with the fifth PTO gear (39), the PTO engagement sleeve (311) is axially slidably mounted on the PTO intermediate shaft (33) and can be selectively engaged with the third PTO gear (37) and the fourth PTO gear (38) by sliding, and the PTO engagement sleeve (311) is connected to a PTO control assembly (312) for controlling the sliding of the PTO engagement sleeve (311).

4. The dual-source power transmission system for a tractor according to claim 3, characterized in that: The first speed change transmission mechanism comprises a first gear (201), a second gear (202), a third gear (203), a fourth gear (204) and a first engagement sleeve (301); the first gear (201) and the second gear (202) are rotatably mounted on the speed change input shaft (101); the third gear (203) and the fourth gear (204) are fixedly mounted on the first speed change intermediate shaft (102); the third gear (203) meshes with the first gear (201); the fourth gear (204) meshes with the second gear (202); the first engagement sleeve (301) is axially slidably mounted on the speed change input shaft (101) and can selectively engage with the first gear (201) and the second gear (202) by sliding; the first engagement sleeve (301) is connected to a first control component (401) for controlling the sliding of the first engagement sleeve (301); The second speed transmission mechanism comprises a fifth gear (205), a sixth gear (206), a seventh gear (207), an eighth gear (208) and a second engagement sleeve (302); the fifth gear (205) and the sixth gear (206) are fixedly mounted on the first speed intermediate shaft (102); the seventh gear (207) and the eighth gear (208) are rotatably mounted on the second speed intermediate shaft (103); the fifth gear (205) is meshed with the seventh gear (207); the sixth gear (206) is meshed with the eighth gear (208); the second engagement sleeve (302) is axially slidably mounted on the second speed intermediate shaft (103) and can be selectively engaged with the seventh gear (207) and the eighth gear (208) by sliding; the second engagement sleeve (302) is connected to a second control component (402) for controlling the sliding of the second engagement sleeve (302); The third speed transmission mechanism comprises a ninth gear (209), a tenth gear (210), an eleventh gear (211), a twelfth gear (212), a first friction clutch (303) and a second friction clutch (304); the ninth gear (209) and the tenth gear (210) are rotatably mounted on the second speed intermediate shaft (103); the eleventh gear (211) and the twelfth gear (212) are fixedly mounted on the speed output shaft (104); the eleventh gear (211) meshes with the ninth gear (209); the twelfth gear (212) meshes with the tenth gear (210); the second speed intermediate shaft (103) is connected to the ninth gear (209) via the first friction clutch (303); and the second speed intermediate shaft (103) is connected to the tenth gear (210) via the second friction clutch (304).

5. The tractor dual-source power transmission system according to claim 4, characterized in that: The PTO control assembly (312), the first control assembly (401) and the second control assembly (402) all include a shift fork driven to reciprocate by a double-acting oil cylinder; the clutch transmission device includes an input driving gear (11) and an input driven gear (12) fixedly mounted on a speed change input shaft (101) and meshing with the input driving gear (11); the input driving gear (11) is connected to the output end of the engine (1) via an input clutch (13); the input clutch (13), the PTO clutch (34), the first friction clutch (303) and the second friction clutch (304) are all friction clutches driven to reciprocate by a single-acting oil cylinder and a spring; the tractor dual-source power transmission system also includes a pressure oil source generating device connected to the output end of the engine (1) and driven by the engine (1) to generate pressure oil; each double-acting oil cylinder is connected to the pressure oil source generating device via an independent electromagnetic control valve; and each single-acting oil cylinder is connected to the pressure oil source generating device via an independent electromagnetic control valve.

6. The dual-source power transmission system for a tractor according to claim 5, characterized in that: The electromagnetic control valves of the input clutch (13), the PTO clutch (34), the first friction clutch (303) and the second friction clutch (304) are configured so that when power is lost, the corresponding double-acting cylinders drive the input clutch (13), the PTO clutch (34), the first friction clutch (303) and the second friction clutch (304) to be in a disengaged state.

7. The dual-source power transmission system for a tractor according to claim 5, characterized in that: The pressure oil source generating device comprises an oil tank (501) and an oil pump (502) connected to the output end of the engine (1); the inlet of the oil pump (502) is connected to the oil tank (501) via a filter (503); the outlet of the oil pump (502) is connected to a pressure oil output pipe (504); and the pressure oil output pipe (504) is connected to an oil source pressure reducing valve (505) and an oil source overflow valve (506).

8. The tractor dual-source power transmission system according to claim 3, characterized in that: The speed change input shaft (101), the second speed change intermediate shaft (103) and the PTO output shaft (32) are coaxially arranged, the first speed change intermediate shaft (102), the speed change output shaft (104) and the PTO intermediate shaft (33) are coaxially arranged, the speed change input shaft (101), the first speed change intermediate shaft (102) and the PTO input shaft (31) are arranged side by side, and the first speed change intermediate shaft (102) is located between the speed change input shaft (101) and the PTO input shaft (31).

9. The dual-source power transmission system for a tractor according to claim 1, characterized in that: The variable displacement pump (41) is connected to the output end of the engine (1) and is driven by the engine (1); the shaft of the bidirectional quantitative motor (42) serves as the output end of the hydraulic stepless speed regulation drive device (4) and is connected to the variable speed output shaft (104) through a transmission mechanism.

10. The tractor dual-source power transmission system according to claim 1, characterized in that: The neutral control solenoid valve (46) is connected to the intermediate pipeline (45) when power is lost, and is disconnected from the intermediate pipeline (45) when power is supplied.

11. A shifting method for the dual-source power transmission system of a tractor according to claim 1, characterized in that: The gear shifting method is as follows: when the transmission (2) needs to be shifted to a target gear position, the clutch transmission device is firstly used to disconnect the power transmission between the output end of the engine (1) and the speed change input shaft (101), and then the hydraulic stepless speed regulation drive device (4) is started to drive the speed change output shaft (104) to rotate at a speed corresponding to the target gear position, and then the first speed change transmission mechanism, the second speed change transmission mechanism and the third speed change transmission mechanism are shifted to a transmission ratio corresponding to the target gear position, and then the clutch transmission device is engaged, and the driving action of the hydraulic stepless speed regulation drive device (4) is stopped.

12. The tractor dual-source power transmission system according to claim 11, characterized in that: The speed corresponding to the target gear position is preset based on the actual speed of the transmission output shaft (104) when the transmission (2) is in the target gear position at different speeds of the engine (1).

13. The dual-source power transmission system for a tractor according to claim 12, characterized in that: The first speed change transmission mechanism, the second speed change transmission mechanism and the third speed change transmission mechanism are controlled by a shift handle to select and convert the transmission ratio so as to realize the gear shifting of the transmission (2); the clutch transmission device, the first speed change transmission mechanism, the second speed change transmission mechanism, the third speed change transmission mechanism and the hydraulic stepless speed regulation drive device (4) are automatically controlled by a control device, and the control device is provided with a detector for detecting the position of the shift handle in each gear position; the hydraulic stepless speed regulation drive device (4) is started when, after the shift handle is switched to the position corresponding to the target gear position, the control device obtains the stay time of the shift handle at the position corresponding to the target gear position through the detector, and when the stay time reaches a preset time, the control device automatically starts the hydraulic stepless speed regulation drive device (4) to drive the speed change output shaft (104) to rotate at the speed corresponding to the target gear position.

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