Series-parallel hybrid power tractor driving system and control method

Abstract

The invention provides a series-parallel hybrid power tractor driving system. The series-parallel hybrid power tractor driving system comprises an engine, a P1 motor used for generating electricity or starting the engine, a PS motor used for independent or coupled driving and a series-parallel hybrid power tractor transmission system. The invention further provides a control method of the driving system. Confluence and diversion of engine power and speed change of the tractor are controlled through the P1 motor, the PS motor, the rotating speed coupling mechanism, the torque coupling mechanism, the clutch and the brake. According to the series-parallel connection type hybrid power tractor driving system, a multi-mode driving mode can be achieved to adapt to operation in a complex environment, the dynamic property and economical efficiency of a tractor are improved, and the series-parallel connection type hybrid power tractor driving system has the advantages of interval stepless speed change, precise control and the like.

Description

Technical Field

[0001] The present invention relates to the field of hybrid tractors, and particularly relates to a series-parallel hybrid tractor drive system and a control method therefor. Background Art

[0002] At present, most tractors on the market still use diesel engines as power sources. Moreover, the operating environment of tractors is complex and changeable, and the energy utilization efficiency of the drive system is relatively poor. Under high-load conditions, the engine fuel cannot be fully burned, and a large amount of pollutants are contained in the exhaust emissions. Problems such as high fuel consumption and high pollution of traditional tractors have become particularly prominent. Therefore, carrying out research on energy-saving and environmentally friendly agricultural special vehicles, especially tractors in the form of electromechanical coupling, is of great significance for improving energy utilization efficiency and environmental protection.

[0003] In the research of hybrid tractors, drive modes such as series, parallel speed coupling, or parallel torque coupling are mostly adopted. These three modes are difficult to meet the complex working conditions of tractors. For the series drive mode, due to the large power range of tractors, the motor needs to maintain a high efficiency within a large range, which requires high performance of the motor, and the energy loss is large after multiple conversions, resulting in a low overall efficiency; for the parallel speed coupling drive mode, stepless speed change in sections of the tractor can be achieved, but under high-load conditions of the tractor, high performance of the motor and the power battery pack is required, and the total cost is relatively high; for the parallel torque coupling drive mode, high-load coupling drive of the tractor can be achieved, but under the condition of the tractor traveling at high speed, high performance of the motor and the power battery pack is required, and the total cost is relatively high. The hybrid tractors disclosed in the prior art generally have problems such as overly single operation modes, insufficient power performance, and low energy utilization efficiency. Summary of the Invention

[0004] The object of the present invention is to provide a series-parallel hybrid tractor drive system and a control method therefor. Among them, the drive system can decouple the engine from the traveling system, improve its fuel economy by adjusting the engine operating point and the energy flow path. Since the drive system adopts a combination of easy control of electric drive and high efficiency of mechanical drive, it can effectively improve the overall vehicle performance and achieve stepless speed change within a range.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A series-parallel hybrid tractor driving system, comprising a whole machine controller, a power battery pack, a distribution box, a P1 motor, a PS motor and an engine installed on a hybrid tractor, wherein the whole machine controller is connected to an engine controller, a transmission system controller, an energy management unit, a P1 motor controller and a PS motor controller respectively, and the whole machine controller is connected to a control circuit of the distribution box, the whole machine controller is used to control the whole machine operation of the series-parallel hybrid tractor, the engine controller, the P1 motor controller and the PS motor controller respectively control the driving of the engine, the P1 motor and the PS motor; the energy management unit controls the charging and discharging of the power battery pack, and the power battery pack supplies power to the P1 motor, the PS motor and a low-voltage battery through the distribution box; the transmission system controller controls the operation of the tractor transmission system;

[0007] The transmission system includes a central transmission shaft, an intermediate planetary carrier shaft, a torque coupling device, an engine output shaft, a power reversing device, a power output speed change device, a power output shaft, a reduction device, a PS motor output shaft, an intermediate sun gear shaft and a speed coupling device;

[0008] The engine output shaft is coupled to the power reversing device, the power reversing device is connected to the torque coupling device, and both the power reversing device and the torque coupling device are coupled to the intermediate planetary carrier shaft, and the torque coupling device is coupled to the central transmission shaft; the engine output shaft is coupled to the power output shaft through the power output transmission device, and the power output shaft is connected to the agricultural implement; the front end of the engine output shaft is connected to the engine, and the rear end of the engine output shaft is connected to the P1 motor;

[0009] The intermediate planet carrier shaft is connected to the intermediate sun gear shaft through a speed coupling device, and the intermediate sun gear shaft is connected to the output shaft of the PS motor through a reduction device; the intermediate planet carrier shaft is connected to the central transmission shaft through a torque coupling device; the intermediate planet carrier shaft and the intermediate sun gear shaft are connected to the central transmission shaft through a speed coupling device;

[0010] The central transmission shaft is connected to the tractor central transmission.

[0011] The speed coupling device includes a speed four-speed driving gear, a speed three-speed driving gear, a first planetary row sun gear, a first planetary row planetary carrier, a first planetary row planetary gear, a first planetary row ring gear, a second planetary row planetary gear, a second planetary row planetary carrier, a speed two-speed driving gear, a speed one-speed driving gear, a speed one-speed driven gear, a speed one-speed clutch, a speed two-speed driven gear, a speed two-speed clutch, a brake, a second planetary row sun gear, a speed three-speed clutch, a speed three-speed driven gear, a speed four-speed driven gear and a speed four-speed clutch;

[0012] The first planetary carrier is fixedly connected to the intermediate planetary carrier shaft. The fourth-speed driving gear, the third-speed driving gear, and the ring gear of the first planetary gear set are all sleeved on the intermediate planetary carrier shaft, and the fourth-speed driving gear, the third-speed driving gear, and the ring gear of the first planetary gear set are fixedly connected. The ring gear of the second planetary gear set is fixedly connected to the planetary carrier of the first planetary gear set. The sun gear of the first planetary gear set and the sun gear of the second planetary gear set are both fixedly connected to the intermediate sun gear shaft. The planetary carrier of the second planetary gear set, the second-speed driving gear, and the first-speed driving gear are all sleeved on the intermediate sun gear shaft, and the planetary carrier of the second planetary gear set, the second-speed driving gear, and the first-speed driving gear are fixedly connected.

[0013] The first-speed driven gear, the second-speed driven gear, the third-speed driven gear, and the fourth-speed driven gear are all sleeved on the central transmission shaft. The brake is connected to the tractor frame.

[0014] The fourth-speed driving gear meshes with the fourth-speed driven gear. By controlling the fourth-speed clutch, the connection or disconnection between the fourth-speed driven gear and the central transmission shaft is achieved. The third-speed driving gear meshes with the third-speed driven gear. By controlling the third-speed clutch, the connection or disconnection between the third-speed driven gear and the central transmission shaft is achieved. The second-speed driving gear meshes with the second-speed driven gear. By controlling the second-speed clutch, the connection or disconnection between the second-speed driven gear and the central transmission shaft is achieved. The first-speed driving gear meshes with the first-speed driven gear. By controlling the first-speed clutch, the connection or disconnection between the first-speed driven gear and the central transmission shaft is achieved.

[0015] The planetary gears of the first planetary gear set respectively mesh with the ring gear and the sun gear of the first planetary gear set. The planetary gears of the second planetary gear set respectively mesh with the ring gear and the sun gear of the second planetary gear set. By controlling the brake, the connection or separation between the ring gear of the second planetary gear set and the frame is achieved. The speed coupling device can increase or decrease the gear according to the power demand of the tractor.

[0016] The power reversing device includes a forward gear clutch, a forward gear driving gear, a reverse gear driving gear, a reverse gear clutch, a reverse gear transmission gear, an intermediate planetary carrier shaft clutch, a reverse gear driven gear, and a forward gear driven gear. The forward gear driving gear meshes with the forward gear driven gear. By controlling the forward gear clutch, the connection or disconnection between the forward gear driving gear and the engine output shaft is achieved. The reverse gear driving gear meshes with the reverse gear transmission gear. By controlling the reverse gear clutch, the connection or disconnection between the reverse gear driving gear and the engine output shaft is achieved. The reverse gear driven gear meshes with the reverse gear transmission gear.

[0017] The torque coupling device described above includes a first-gear torque driving gear, a second-gear torque driving gear, a third-gear torque driving gear, a third-gear torque clutch, a third-gear torque driven gear, a second-gear torque driven gear, a first-gear torque driven gear, a second-gear torque clutch, and a first-gear torque clutch;

[0018] The first-gear torque driving gear meshes with the first-gear torque driven gear. By controlling the first-gear torque clutch, the connection or disconnection between the first-gear torque driven gear and the central transmission shaft can be achieved. The second-gear torque driving gear meshes with the second-gear torque driven gear. By controlling the second-gear torque clutch, the connection or disconnection between the second-gear torque driven gear and the central transmission shaft can be achieved. The third-gear torque driving gear meshes with the first-gear torque driven gear. By controlling the first-gear torque clutch, the connection or disconnection between the first-gear torque driven gear and the central transmission shaft can be achieved. The first-gear torque driving gear, the second-gear torque driving gear, and the third-gear torque driving gear of the torque coupling device are coaxial with the forward-gear driven gear and the reverse-gear driven gear of the power reversing device. By controlling the intermediate planet carrier shaft clutch, the connection or disconnection between the above gears and the intermediate planet carrier shaft can be achieved. The torque coupling device can increase or decrease the gear positions according to the power demand of the tractor;

[0019] The front end of the intermediate sun gear shaft is connected to the sun gear of the first planetary row and the sun gear of the second planetary row of the torque coupling device.

[0020] The power take-off speed change device described above includes a second-gear power take-off clutch, a second-gear power take-off driven gear, a first-gear power take-off driven gear, a first-gear power take-off clutch, a first-gear power take-off driving gear, and a second-gear power take-off driving gear;

[0021] The first-gear power take-off driving gear and the second-gear power take-off driving gear are connected to the engine output shaft. The first-gear power take-off driving gear meshes with the first-gear power take-off driven gear. By controlling the first-gear power take-off clutch, the connection or disconnection between the first-gear power take-off driven gear and the power take-off shaft can be achieved. The second-gear power take-off driving gear meshes with the second-gear power take-off driven gear. By controlling the second-gear power take-off clutch, the connection or disconnection between the second-gear power take-off driven gear and the power take-off shaft can be achieved. The power take-off speed change device can increase or decrease the gear positions according to the requirements of the tractor agricultural implements.

[0022] The reduction device described above includes a third planetary carrier, a third ring gear, third planetary gears, and a third sun gear. The third planetary gears are installed on the third planetary carrier, and the third planetary gears mesh with the third ring gear and the third sun gear. The third ring gear is connected to the tractor frame. The rear end of the intermediate sun gear shaft is connected to the third planetary carrier of the reduction device. The front end of the PS motor output shaft is connected to the third sun gear of the reduction device, and the rear end of the PS motor output shaft is connected to the PS motor.

[0023] The engine includes a diesel engine, a natural gas engine, and a hydrogen fuel engine.

[0024] The engine controller, the whole machine controller, the transmission system controller, the energy management unit, the P1 motor controller, the PS motor controller, and the distribution box constitute the control system of the series-parallel hybrid tractor; the whole machine controller obtains the engine controller information, the transmission system controller information, the energy management unit information, the P1 motor controller information, the PS motor controller information, and the distribution box information through the high-speed CAN bus; the whole machine controller sends control signals to the engine controller, the transmission system controller, the energy management unit, the P1 motor controller, the PS motor controller, and the distribution box through the high-speed CAN bus; the whole machine controller obtains the instrument and lighting information of the series-parallel hybrid tractor through the low-speed CAN bus; the energy management unit controls the power battery pack, and the power battery pack supplies power to the P1 motor, the PS motor, and the low-voltage battery through the distribution box; the operation information of the series-parallel hybrid tractor includes key signal, mode signal, position signal, torque signal, and speed signal.

[0025] The present invention also provides a control method for the drive system of a series-parallel hybrid tractor as described above, specifically as follows: SOCh is preset as the upper limit value of the high-efficiency area of the power battery pack SOC, SOCl is preset as the lower limit value of the high-efficiency area of the power battery pack SOC, Treq,cd is the demand torque of the tractor equivalent to the central drive shaft; Te_l,cd is the lower limit of the high-efficiency working interval torque of the engine equivalent to the central drive shaft, Te_h,cd is the upper limit of the high-efficiency working interval torque of the engine equivalent to the central drive shaft, ne_l,cd is the lower limit of the high-efficiency working interval speed of the engine equivalent to the central drive shaft, ne_h,cd is the upper limit of the high-efficiency working interval speed of the engine equivalent to the central drive shaft; after the control system of the series-parallel hybrid tractor is started, the whole vehicle enters the self-check of the control system. After the self-check of the control system passes, the whole machine controller obtains the key signal, mode signal, position signal, torque signal, and speed signal. The whole machine controller determines the drive system start mode according to the obtained information, and at the same time sends control signals to the engine controller, the transmission system controller, the energy management unit, the P1 motor controller, the PS motor controller, and the distribution box. After the drive system starts, the whole machine controller sends control signals according to the tractor power demand information and operation information, so as to control the tractor to switch to different drive modes.

[0026] The drive modes and the corresponding switching methods are specifically as follows:

[0027] A. Pure electric drive mode: When the power demand of the tractor cannot enable the engine to operate in the high-efficiency region, and the SOC of the power battery pack satisfies SOC > SOCl, the tractor demand torque satisfies Treq,cd ≤ Te_l,cd, and the demand speed satisfies nreq,cd ≤ ne_h,cd, switch to the pure electric drive mode; at this time, turn off the engine, and the power battery pack alone provides energy to the PS motor to drive the tractor running system to run.

[0028] B. Series drive mode: When the power demand of the tractor cannot enable the engine to operate in the high-efficiency region, and the state of charge SOC of the power battery pack ≤ SOCl, the tractor demand torque satisfies Treq,cd ≤ Te_l,cd, and the demand speed satisfies nreq,cd ≤ ne_h,cd, switch to the series drive mode; at this time, decouple the engine output shaft from the power reversing device, start the engine by the P1 motor, and then the engine drives the P1 motor to generate electricity. The power battery pack and the P1 motor simultaneously or the P1 motor alone provide energy for the PS motor drive; when the SOC of the power battery pack reaches SOCl, carry out charging protection, the engine drives the P1 motor to generate electricity, and the P1 motor provides energy for the PS motor and the power battery pack simultaneously. When it reaches SOCh, carry out trickle charging protection; in this mode, the engine can operate under the best working conditions to drive the P1 motor to generate electricity, provide energy for the PS motor and the power battery pack, and provide power for the tractor running system in series.

[0029] C. Engine independent drive mode: When the power demand of the tractor reaches the best working condition range of the engine and the tractor running speed and the external working environment change little, and the tractor demand torque satisfies Te_l,cd <

[0030] Treq,cd ≤ Te_h,cd, and the demand speed satisfies ne_l,cd < nreq,cd ≤ ne_h,cd, switch to the engine independent drive mode; at this time, neither the P1 motor nor the PS motor works, and the power of the engine is all transmitted to the tractor running system by mechanical transmission. Since the power does not pass through the electric drive device, the energy loss caused by energy conversion can be avoided, and the system efficiency is the highest in this mode.

[0031] D. Parallel torque coupling drive mode: When the tractor torque demand changes greatly, and the SOC of the power battery pack satisfies SOC > SOCl, the tractor demand torque satisfies Treq,cd > Te_h,cd, and the demand speed satisfies ne_l,cd < nreq,cd ≤ ne_h,cd, switch to the parallel torque coupling drive mode. The P1 motor absorbs the excess power output by the engine to convert it into electric energy and store it in the power battery pack or provide it to the PS motor. The engine and the PS motor provide power for the tractor running system by torque coupling.

[0032] E. Parallel speed coupling drive mode: When the speed demand of the tractor changes significantly, and the SOC of the power battery pack satisfies SOC > SOCl, the demand torque of the tractor satisfies Te_l,cd < Treq,cd ≤ Te_h,cd, and the demand speed satisfies nreq,cd > ne_h,cd, switch to the parallel speed coupling drive mode; The P1 motor absorbs the excess power output by the engine to convert it into electrical energy and store it in the power battery pack or supply it to the PS motor, and the engine and the PS motor provide power for the tractor running system through the speed coupling method;

[0033] F. Energy recovery mode: When the tractor brakes or decelerates, the demand torque of the tractor Treq,cd < 0, and the mechanical energy of the tractor running system drives the PS motor in reverse to generate electricity, realizing braking / deceleration energy recovery. At this time, the engine stops or decouples from the tractor running system.

[0034] The specific method for the series-parallel hybrid tractor to select the drive system startup method includes the following steps:

[0035] Step S1.1. First, the control system is based on the SOC of the power battery pack. If SOC > SOCl, go to step S1.2, otherwise go to step S1.3;

[0036] Step S1.2. If the demand torque of the tractor satisfies Treq,cd ≤ Te_l,cd, the tractor starts purely electrically and directly goes to step S1.4; otherwise go to step S1.3;

[0037] Step S1.3. The tractor starts the engine first. If the demand torque of the tractor satisfies Treq,cd ≤ Te_l,cd, the tractor performs a series startup; otherwise, only start the engine;

[0038] Step S1.4. The startup of the tractor drive system is completed.

[0039] The beneficial effects brought by the present invention are:

[0040] 1. The series-parallel hybrid drive system described in the present invention can make the engine operate in the optimal working area by adjusting the dual motors, improve its fuel economy through the energy flow path, combine the easy control of electric drive with the high efficiency of mechanical drive, and can effectively improve the performance of the whole vehicle and achieve stepless speed change in the range.

[0041] 2. The series-parallel hybrid drive system consists of an engine, two motors, and a series-parallel hybrid transmission system. Through control, six modes can be achieved, namely pure electric drive, series drive, independent engine drive, parallel torque coupling drive, parallel speed coupling drive, and energy recovery. The multi-mode drive method is beneficial for the tractor to operate in various complex environments and improves the power performance, economy, and adaptability of the whole vehicle.

[0042] 3. The power reversing device of the transmission system can make the number of forward gears and reverse gears of the tractor the same, improve the working ability of the tractor when reversing, and is beneficial to improving the flexibility of the tractor in field operations.

[0043] 4. The torque coupling device of the transmission system can achieve the torque coupling between the engine and the PS motor, reduce the complexity of the tractor transmission system, and at the same time meet the operating requirements of the tractor for low speed and large torque; it can effectively improve the traction characteristics of the tractor.

[0044] 5. The speed coupling device of the transmission system can achieve the speed coupling between the engine and the PS motor, reduce the complexity of the tractor transmission system, and at the same time meet the operating requirements of the tractor for stepless speed change in a certain range.

[0045] 6. When the hybrid tractor is in a short-term stop in place or braking while moving, the system enters the energy recovery mode to improve the overall energy utilization rate of the machine. Description of the Drawings

[0046] Figure 1 is the structural schematic diagram of the series-parallel hybrid tractor drive system;

[0047] Figure 2 is the structural schematic diagram of the transmission system;

[0048] Figure 3 is the structural schematic diagram of the torque coupling device of the transmission system;

[0049] Figure 4 is the structural schematic diagram of the reversing device of the transmission system;

[0050] Figure 5 is the structural schematic diagram of the power output speed change device of the transmission system;

[0051] Figure 6 is the structural schematic diagram of the reduction device of the transmission system;

[0052] Figure 7 is the structural schematic diagram of the speed coupling device of the transmission system;

[0053] Figure 8 is the circuit connection relationship diagram of the series-parallel hybrid tractor drive system;

[0054] Figure 9It is the control method flowchart of the series-parallel hybrid tractor drive system.

[0055] The description of the reference numerals in the attached drawings is as follows:

[0056] 1. Engine, 2. Transmission system, 3. Engine controller, 4. Whole machine controller, 5. Transmission system controller, 6. Energy management unit, 7. P1 motor controller, 8. Power battery pack, 9. PS motor controller, 10. Distribution box, 11. P1 motor, 12. PS motor, 13. Central transmission shaft, 14. Intermediate planetary carrier shaft, 15. Torque coupling device, 1501. Torque first gear driving gear, 1502. Torque second gear driving gear, 1503. Torque third gear driving gear, 1504. Torque third gear clutch, 1505. Torque third gear driven gear, 1506. Torque second gear driven gear, 1507. Torque first gear driven gear, 1508. Torque second gear clutch, 1509. Torque first gear clutch, 16. Engine output shaft, 17. Power reversing device, 1701. Forward gear clutch, 1702. Forward gear driving gear, 1703. Reverse gear driving gear, 1704. Reverse gear clutch, 1705. Reverse gear transmission gear, 1706. Intermediate planetary carrier shaft clutch, 1707. Reverse gear driven gear, 1708. Forward gear driven gear, 18. Power take-off speed change device, 1801. Power take-off second gear clutch, 1802. Power take-off second gear driven gear, 1803. Power take-off first gear driven gear, 1804. Power take-off first gear clutch, 1805. Power take-off first gear driving gear, 1806. Power take-off second gear driving gear, 19. Power take-off shaft, 20. Reduction device, 2001. Reduction clutch, 2002. Third planetary carrier, 2003. Third planetary ring gear, 2004. Third planetary planet gear, 2005. Third planetary sun gear, 21. PS motor output shaft, 22. Intermediate sun gear shaft, 23. Speed coupling device, 2301. Fourth gear driving gear, 2302. Speed third gear driving gear, 2303. First planetary sun gear, 2304. First planetary carrier, 2305. First planetary planet gear, 2306. First planetary ring gear, 2307. Second planetary ring gear, 2308. Second planetary planet gear, 2309. Second planetary carrier, 2310. Speed second gear driving gear, 2311. Speed first gear driving gear, 2312. Speed first gear driven gear, 2313. Speed first gear clutch, 2314. Speed second gear driven gear, 2315. Speed second gear clutch, 2316. Brake, 2317. Second planetary sun gear, 2318. Speed third gear clutch, 2319. Speed third gear driven gear, 2320. Speed fourth gear driven gear, 2321. Speed fourth gear clutch. Specific embodiments

[0057] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the "first", "second" and "third" in the following embodiments are only used to distinguish the names of the devices and do not have specific meanings.

[0058] Referring to Figure 1 , the present invention provides a series-parallel hybrid tractor drive system, which includes a power battery pack 8, a distribution box 10, a P1 motor 11 and a PS motor 12 installed on the hybrid tractor. The whole machine controller 4 is respectively connected to the engine controller 3, the transmission system controller 5, the energy management unit 6, the P1 motor controller 7 and the PS motor controller 9 by signals. The whole machine controller 4 is also connected to the control circuit of the distribution box 10. The whole machine controller 4 is used to control the normal operation of the series-parallel hybrid tractor. The engine controller 3, the P1 motor controller 7 and the PS motor controller 9 respectively control the drives of the engine 1, the P1 motor 11 and the PS motor 12. The energy management unit 6 controls the charge and discharge of the power battery pack 8. The transmission system controller 5 controls the operation of the tractor transmission system 2.

[0059] Referring to Figure 2 , the transmission system 2 includes a central transmission shaft 13, an intermediate planet carrier shaft 14, a torque coupling device 15, an engine output shaft 16, a power reversing device 17, a power output speed change device 18, a power output shaft 19, a reduction device 20, a PS motor output shaft 21, an intermediate sun gear shaft 22 and a speed coupling device 23;

[0060] The central transmission shaft 13 is connected to the tractor central transmission;

[0061] The intermediate planet carrier shaft 14 is connected to the first planet carrier 2304 and the second planet gear ring 2307 of the speed coupling device 23;

[0062] Referring to Figure 3, the torque coupling device 15 includes a first-gear torque driving gear 1501, a second-gear torque driving gear 1502, a third-gear torque driving gear 1503, a third-gear torque clutch 1504, a third-gear torque driven gear 1505, a second-gear torque driven gear 1506, a first-gear torque driven gear 1507, a second-gear torque clutch 1508, and a first-gear torque clutch 1509; the first-gear torque driving gear 1501 meshes with the first-gear torque driven gear 1507, and the connection or disconnection between the first-gear torque driven gear 1507 and the central transmission shaft 13 is achieved by controlling the first-gear torque clutch 1509; the second-gear torque driving gear 1502 meshes with the second-gear torque driven gear 1506, and the connection or disconnection between the second-gear torque driven gear 1506 and the central transmission shaft 13 is achieved by controlling the second-gear torque clutch 1508; the third-gear torque driving gear 1503 meshes with the third-gear torque driven gear 1505, and the connection or disconnection between the third-gear torque driven gear 1505 and the central transmission shaft 13 is achieved by controlling the third-gear torque clutch 1504; the first-gear torque driving gear 1501, the second-gear torque driving gear 1502, and the third-gear torque driving gear 1503 of the torque coupling device 15 are coaxial with the forward-gear driven gear 1708 and the reverse-gear driven gear 1707 of the power reversing device 17, and the connection or disconnection between the above gears and the intermediate planet carrier shaft 14 is achieved by controlling the intermediate planet carrier shaft clutch 1706; the torque coupling device 15 can increase or decrease the gear according to the power demand of the tractor;

[0063] The front end of the engine output shaft 16 is connected to the engine 1, and the rear end of the engine output shaft 16 is connected to the P1 motor 11; the engine includes a diesel engine, a natural gas engine, and a hydrogen fuel engine;

[0064] Refer to Figure 4 , the power reversing device 17 includes a forward-gear clutch 1701, a forward-gear driving gear 1702, a reverse-gear driving gear 1704, a reverse-gear clutch 1704, a reverse-gear transmission gear 1705, an intermediate planet carrier shaft clutch 1706, a reverse-gear driven gear 1707, and a forward-gear driven gear 1708; the forward-gear driving gear 1702 meshes with the forward-gear driven gear 1708, and the connection or disconnection between the forward-gear driving gear 1702 and the engine output shaft 16 is achieved by controlling the forward-gear clutch 1701; the reverse-gear driving gear 1704 meshes with the reverse-gear transmission gear 1705, and the connection or disconnection between the reverse-gear driving gear 1704 and the engine output shaft 16 is achieved by controlling the reverse-gear clutch 1704; the reverse-gear driven gear 1707 meshes with the reverse-gear transmission gear 1705;

[0065] Refer to Figure 5, the power output speed change device 18 includes a power output second gear clutch 1801, a power output second gear driven gear 1802, a power output first gear driven gear 1803, a power output first gear clutch 1804, a power output first gear driving gear 1805, and a power output second gear driving gear 1806; the power output first gear driving gear 1805 and the power output second gear driving gear 1806 are connected to the engine output shaft 16; the power output first gear driving gear 1805 meshes with the power output first gear driven gear 1803, and by controlling the power output first gear clutch 1804, the power output first gear driven gear 1803 is connected to or disconnected from the power output shaft 19; the power output second gear driving gear 1806 meshes with the power output second gear driven gear 1802, and by controlling the power output second gear clutch 1801, the power output second gear driven gear 1802 is connected to or disconnected from the power output shaft 19; the power output speed change device 18 can increase or decrease the gear according to the requirements of the tractor agricultural implements;

[0066] The power output shaft 19 is connected to the agricultural implements;

[0067] Refer to Figure 6 , the reduction device 20 includes a third planetary carrier 2001, a third planetary ring gear 2002, a third planetary gear 2003, and a third planetary sun gear 2004; the third planetary gear 2003 is installed on the third planetary carrier 2001, and the third planetary gear 2003 meshes with the third planetary ring gear 2002 and the third planetary sun gear 2004; the third planetary ring gear 2002 is connected to the tractor frame;

[0068] The front end of the PS motor output shaft 21 is connected to the third planetary sun gear 2004 of the reduction device 20, and the rear end of the PS motor output shaft 21 is connected to the PS motor 12;

[0069] The front end of the intermediate sun gear shaft 22 is connected to the first planetary sun gear 2303 and the second planetary sun gear 2317 of the torque coupling device 23, and the rear end is connected to the third planetary carrier 2001 of the reduction device 20;

[0070] Refer to Figure 7, the rotational speed coupling device 23 includes a fourth-gear rotational speed driving gear 2301, a third-gear rotational speed driving gear 2302, a first planetary gear train sun gear 2303, a first planetary gear train planet carrier 2304, a first planetary gear train planet gear 2305, a first planetary gear train ring gear 2306, a second planetary gear train ring gear 2307, a second planetary gear train planet gear 2308, a second planetary gear train planet carrier 2309, a second-gear rotational speed driving gear 2310, a first-gear rotational speed driving gear 2311, a first-gear rotational speed driven gear 2312, a first-gear rotational speed clutch 2313, a second-gear rotational speed driven gear 2314, a second-gear rotational speed clutch 2315, a brake 2316, a second planetary gear train sun gear 2317, a third-gear rotational speed clutch 2318, a third-gear rotational speed driven gear 2319, a fourth-gear rotational speed driven gear 2320, and a fourth-gear rotational speed clutch 2321;

[0071] The fourth-gear rotational speed driving gear 2301 meshes with the fourth-gear rotational speed driven gear 2320, and connection or disconnection between the fourth-gear rotational speed driven gear 2320 and the central transmission shaft 13 is achieved by controlling the fourth-gear rotational speed clutch 2321; the third-gear rotational speed driving gear 2302 meshes with the third-gear rotational speed driven gear 2319, and connection or disconnection between the third-gear rotational speed driven gear 2319 and the central transmission shaft 13 is achieved by controlling the third-gear rotational speed clutch 2318; the first planetary gear train planet carrier 2304 is fixed to the first planetary gear train planet gear 2305, and the first planetary gear train planet gear 2305 meshes with the first planetary gear train ring gear 2306 and the first planetary gear train sun gear 2303; the first planetary gear train planet carrier 2304 is fixed to the second planetary gear train ring gear 2307; the second planetary gear train planet carrier 2309 is fixed to the second planetary gear train planet gear 2308, and the second planetary gear train planet gear 2308 meshes with the second planetary gear train ring gear 2307 and the second planetary gear train sun gear 2317; the second-gear rotational speed driving gear 2310 meshes with the second-gear rotational speed driven gear 2314, and connection or disconnection between the second-gear rotational speed driven gear 2314 and the central transmission shaft 13 is achieved by controlling the second-gear rotational speed clutch 2315; the first-gear rotational speed driving gear 2311 meshes with the first-gear rotational speed driven gear 2312, and connection or disconnection between the first-gear rotational speed driven gear 2312 and the central transmission shaft 13 is achieved by controlling the first-gear rotational speed clutch 2313; connection or separation between the second planetary gear train ring gear 2307 and the machine frame is achieved by controlling the brake 2316; the rotational speed coupling device 23 can increase or decrease gears according to the power demand of the tractor;

[0072] Referring to Figure 8 , the engine controller 3, the whole machine controller 4, the transmission system controller 5, the energy management unit 6, the P1 motor controller 7, the PS motor controller 9, and the distribution box 10 constitute the control system of the series-parallel hybrid tractor drive system;

[0073] The overall machine controller 4 obtains the information of the engine controller 3, the transmission system controller 5, the energy management unit 6, the P1 motor controller 7, the PS motor controller 9, and the distribution box 10 through the high-speed CAN bus; sends control signals to the engine controller 3, the transmission system controller 5, the energy management unit 6, the P1 motor controller 7, the PS motor controller 9, and the distribution box 10 through the high-speed CAN bus; the overall machine controller 4 obtains information such as the hybrid tractor instrument and lighting through the low-speed CAN bus.

[0074] The energy management unit 6 controls the power battery pack 8, and the power battery pack 8 supplies power to the P1 motor 11, the PS motor 12, and the low-voltage battery through the distribution box 5.

[0075] The operating information of the hybrid tractor includes key signal, mode signal, position signal, torque signal, and speed signal.

[0076] Refer to Figure 9 : The series hybrid tractor has a total of 6 driving modes, namely pure electric drive, series drive, engine independent drive, parallel torque coupling drive, parallel speed coupling drive, and energy recovery.

[0077] After the hybrid tractor starts, the whole vehicle enters the self-check of the control system. After the self-check of the control system passes, the overall machine controller 4 obtains the key signal, mode signal, position signal, torque signal, and speed signal. The overall machine controller 4 determines the starting method of the drive system according to the obtained information, and at the same time sends control signals to the engine controller 3, the transmission system controller 5, the energy management unit 6, the P1 motor controller 7, the PS motor controller 9, and the distribution box 10, so that the hybrid tractor selects to operate in different drive modes:

[0078] 1) Pure electric drive mode: When the power demand of the tractor cannot enable the engine 1 to operate in the high-efficiency area, and the SOC of the power battery pack 8 satisfies SOC > SOC l , the tractor demand torque satisfies T req,cd ≤T e_l,cd , the demand speed satisfies n req,cd ≤n e_h,cd , it switches to the pure electric drive mode. At this time, the engine 1 can be controlled to be turned off, and the power battery pack 8 alone provides energy to the PS motor 12 to drive the walking system of the tractor to walk. This mode can utilize the advantages of the motor's low-speed high torque and pure electric drive being green and pollution-free. For example, working conditions such as the tractor starting without load, walking at low speed without load, and short-distance transfer.

[0079] 2) Series drive mode: When the power demand of the tractor cannot enable the engine 1 to operate in the high-efficiency area, and the state of charge SOC of the power battery pack 8 ≤ SOC l, the required torque of the tractor satisfies T req,cd ≤T e_l,cd , the required speed satisfies n req,cd ≤n e_h,cd , switch to the series drive mode. At this time, the P1 motor 11 drives the engine 1 to start, and then drives the P1 motor 11 to generate electricity. The power battery pack 8 and the P1 motor 11 simultaneously or the P1 motor 11 alone provide energy for the drive of the PS motor 12. When the SOC of the power battery pack 8 reaches SOC l , charging protection is performed. The engine 1 drives the P1 motor 11 to generate electricity, and the P1 motor 11 provides energy for the PS motor 12 and the power battery pack 8 simultaneously. When reaching SOC h , trickle charging protection is performed. In this mode, the engine 1 is decoupled from the tractor running system, allowing the engine 1 to operate under the best working conditions to drive the P1 motor 11 to generate electricity, providing energy for the PS motor 12 and the power battery pack 8, and providing power for the tractor running system in series. For example, working conditions such as the tractor starting without load, traveling at low speed without load, and transferring fields.

[0080] 3) Engine independent drive mode: When the power demand of the tractor reaches the best working condition range of the engine 1 and the traveling speed of the tractor and the external working environment change little, and the required torque of the tractor satisfies T e_l,cd <T req,cd ≤T e_h,cd , the required speed satisfies n e_l,cd <n req,cd ≤n e_h,cd , switch to the engine independent drive mode. At this time, both the P1 motor 11 and the PS motor 12 do not work, and the power of the engine 1 is all transmitted to the tractor running system by mechanical transmission. Since the power does not pass through the electric drive device, the energy loss caused by energy conversion can be avoided, and the system efficiency is the highest in this mode. For example, working conditions such as plowing, sowing, and harvesting.

[0081] 4) Parallel torque coupling drive mode: When the torque demand of the tractor changes greatly, and the SOC of the power battery pack 8 satisfies SOC > SOC l , the required torque of the tractor satisfies T req,cd >T e_h,cd , the required speed satisfies n e_l,cd <n req,cd ≤n e_h,cd , switch to the parallel torque coupling drive mode. The P1 motor 11 absorbs the excess power output by the engine 1 to convert it into electrical energy and store it in the power battery pack 8 or provide it to the PS motor 12. The engine 1 and the PS motor 12 provide power for the tractor running system through torque coupling. For example, working conditions such as getting out of trouble, plowing, harrowing, rotary tillage, and low-speed transportation with load.

[0082] 5) Parallel speed coupling drive mode: When the speed demand of the tractor changes greatly and the SOC of the power battery pack 8 satisfies SOC > SOC l , the required torque of the tractor satisfies T e_l,cd < T req,cd ≤ T e_h,cd , and the required speed satisfies n req,cd > n e_h,cd , switch to the parallel speed coupling drive mode. The P1 motor 11 absorbs the excess power output by the engine 1 to convert it into electrical energy and store it in the power battery pack 8 or supply it to the PS motor 12. The engine 1 and the PS motor 12 provide power for the tractor running system through the speed coupling method. For example, in working conditions such as intertillage, harvesting, light-load transportation, medium-load transportation, and long-distance transfer.

[0083] 6) Energy recovery mode: When the tractor brakes or decelerates, the required torque T of the tractor req,cd < 0, the mechanical energy of the running system reversely drives the PS motor 12 to generate electricity, realizing the recovery of braking / deceleration energy. At this time, the engine 1 stops or decouples from the tractor running system. For example, when the tractor is in working conditions such as transportation and transfer braking / deceleration.

[0084] The SOC h is the upper limit value of the high-efficiency area of the SOC of the power battery pack 8; SOC l is the lower limit value of the high-efficiency area of the SOC of the power battery pack 8; T req,cd is the required torque of the tractor equivalent to the central drive shaft 13; T e_l,cd is the lower limit of the high-efficiency working range torque of the engine 1 equivalent to the central drive shaft 13; T e_h,cd is the upper limit of the high-efficiency working range torque of the engine 1 equivalent to the central drive shaft 13; n e_l,cd is the lower limit of the high-efficiency working range speed of the engine 1 equivalent to the central drive shaft 13; n e_h,cd is the upper limit of the high-efficiency working range speed of the engine 1 equivalent to the central drive shaft 13.

[0085] In addition, according to actual needs, those skilled in the art can also select other possible working states.

[0086] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes, but as long as it does not depart from the technical content of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

[0087] The parts not described in detail in the present invention are the prior art.

Claims

1. A series-parallel hybrid tractor drive system, comprising an overall machine controller (4), a power battery pack (8), a distribution box (10), a P1 motor (11), a PS motor (12) and an engine, which are installed on a hybrid tractor, and is characterized in that: The whole machine controller (4) is respectively connected to the engine controller (3), the transmission system controller (5), the energy management unit (6), the P1 motor controller (7) and the PS motor controller (9). The control circuit of the whole machine controller (4) is connected to the distribution box (10). The whole machine controller (4) is used to control the operation of the whole series-parallel hybrid tractor. The engine controller (3), the P1 motor controller (7) and the PS motor controller (9) respectively control the drives of the engine (1), the P1 motor (11) and the PS motor (12). The energy management unit (6) controls the charge and discharge of the power battery pack (8). The power battery pack (8) supplies power to the P1 motor (11), the PS motor (12) and the low-voltage battery through the distribution box (5). The transmission system controller (5) controls the operation of the tractor transmission system (2). The described transmission system (2) includes a central transmission shaft (13), an intermediate planet carrier shaft (14), a torque coupling device (15), an engine output shaft (16), a power reversing device (17), a power take-off speed change device (18), a power take-off shaft (19), a reduction device (20), PS motor output shaft (21) , an intermediate sun gear shaft (22) and a speed coupling device (23); The engine output shaft (16) is coupled to the power reversing device (17). The power reversing device (17) is connected to the torque coupling device (15), and both the power reversing device (17) and the torque coupling device (15) are coupled to the intermediate planet carrier shaft (14). The torque coupling device (15) is coupled to the central transmission shaft (13). The engine output shaft (16) is coupled to the power take-off shaft (19) through the power take-off speed change device (18), and the power take-off shaft (19) is connected to the agricultural implement. The front end of the engine output shaft (16) is connected to the engine (1), and the rear end of the engine output shaft (16) is connected to the P1 motor (11). The intermediate planet carrier shaft (14) is drivingly connected to the intermediate sun gear shaft (22) through a speed coupling device (23), and the intermediate sun gear shaft (22) is drivingly connected to PS motor output shaft (21) a driving connection; the intermediate planet carrier shaft (14) is coupled to the central transmission shaft (13) through a torque coupling device (15); both the intermediate planet carrier shaft (14) and the intermediate sun gear shaft are coupled to the central transmission shaft (13) through a speed coupling device (23); The central transmission shaft (13) is connected to the tractor central transmission.

2. The series-parallel hybrid tractor drive system according to claim 1, wherein: The described speed coupling device (23) includes a four-speed main gear (2301), a three-speed main gear (2302), a first planetary gear set sun gear (2303), a first planetary gear set planet carrier (2304), a first planetary gear set planet gear (2305), a first planetary gear set ring gear (2306), a second planetary gear set ring gear (2307), a second planetary gear set planet gear (2308), a second planetary gear set planet carrier (2309), a two-speed main gear (2310), a first-speed main gear (2311), a first-speed driven gear (2312), a first-speed clutch (2313), a two-speed driven gear (2314), a two-speed clutch (2315), a brake (2316), a second planetary gear set sun gear (2317), a three-speed clutch (2318), a three-speed driven gear (2319), a four-speed driven gear (2320) and a four-speed clutch (2321). The first planetary gear carrier (2304) is fixedly connected to the intermediate planetary gear carrier shaft (14). The fourth-speed driving gear (2301), the third-speed driving gear (2302), and the ring gear of the first planetary gear set (2306) are all sleeved on the intermediate planetary gear carrier shaft (14), and the fourth-speed driving gear (2301), the third-speed driving gear (2302), and the ring gear of the first planetary gear set (2306) are fixedly connected. The ring gear of the second planetary gear set (2307) is fixedly connected to the first planetary gear carrier (2304). The sun gear of the first planetary gear set (2303) and the sun gear of the second planetary gear set (2317) are both fixedly connected to the intermediate sun gear shaft (22). The second planetary gear carrier (2309), the second-speed driving gear (2310), and the first-speed driving gear (2311) are all sleeved on the intermediate sun gear shaft (22), and the second planetary gear carrier (2309), the second-speed driving gear (2310), and the first-speed driving gear (2311) are fixedly connected. The first-speed driven gear (2312), the second-speed driven gear (2314), the third-speed driven gear (2319), and the fourth-speed driven gear (2320) are all sleeved on the central transmission shaft (13). The brake (2316) is connected to the tractor frame. The fourth-speed driving gear (2301) meshes with the fourth-speed driven gear (2320), and the connection or disconnection between the fourth-speed driven gear (2320) and the central transmission shaft (13) is achieved by controlling the fourth-speed clutch (2321). The third-speed driving gear (2302) meshes with the third-speed driven gear (2319), and the connection or disconnection between the third-speed driven gear (2319) and the central transmission shaft (13) is achieved by controlling the third-speed clutch (2318). The second-speed driving gear (2310) meshes with the second-speed driven gear (2314), and the connection or disconnection between the second-speed driven gear (2314) and the central transmission shaft (13) is achieved by controlling the second-speed clutch (2315). The first-speed driving gear (2311) meshes with the first-speed driven gear (2312), and the connection or disconnection between the first-speed driven gear (2312) and the central transmission shaft (13) is achieved by controlling the first-speed clutch (2313). The planetary gears of the first planetary gear set (2305) mesh with the ring gear of the first planetary gear set (2306) and the sun gear of the first planetary gear set (2303) respectively. The planetary gears of the second planetary gear set (2308) mesh with the ring gear of the second planetary gear set (2307) and the sun gear of the second planetary gear set (2317) respectively. The connection or separation between the ring gear of the second planetary gear set (2307) and the frame is achieved by controlling the brake (2316). The speed coupling device (23) can increase or decrease the gear according to the power demand of the tractor.

3. A series-parallel hybrid tractor drive system according to claim 1, characterized in that: The described power shift device (17) includes a forward gear clutch (1701), a forward gear driving gear (1702), a reverse gear driving gear (1704), a reverse gear clutch (1704), a reverse gear transmission gear (1705), an intermediate planet carrier shaft clutch (1706), a reverse gear driven gear (1707), and a forward gear driven gear (1708); the forward gear driving gear (1702) meshes with the forward gear driven gear (1708), and the connection or disconnection between the forward gear driving gear (1702) and the engine output shaft (16) is achieved by controlling the forward gear clutch (1701); the reverse gear driving gear (1704) meshes with the reverse gear transmission gear (1705), and the connection or disconnection between the reverse gear driving gear (1704) and the engine output shaft (16) is achieved by controlling the reverse gear clutch (1704); the reverse gear driven gear (1707) meshes with the reverse gear transmission gear (1705). The described torque coupling device (15) includes a torque first gear driving gear (1501), a torque second gear driving gear (1502), a torque third gear driving gear (1503), a torque third gear clutch (1504), a torque third gear driven gear (1505), a torque second gear driven gear (1506), a torque first gear driven gear (1507), a torque second gear clutch (1508), and a torque first gear clutch (1509). The torque first gear driving gear (1501) meshes with the torque first gear driven gear (1507), and the connection or disconnection between the torque first gear driven gear (1507) and the central transmission shaft (13) is achieved by controlling the torque first gear clutch (1509); the torque second gear driving gear (1502) meshes with the torque second gear driven gear (1506), and the connection or disconnection between the torque second gear driven gear (1506) and the central transmission shaft (13) is achieved by controlling the torque second gear clutch (1508); the torque third gear driving gear (1503) meshes with the torque third gear driven gear (1505), and the connection or disconnection between the torque third gear driven gear (1505) and the central transmission shaft (13) is achieved by controlling the torque third gear clutch (1504); the torque first gear driving gear (1501), the torque second gear driving gear (1502), and the torque third gear driving gear (1503) of the torque coupling device (15) are coaxial with the forward gear driven gear (1708) and the reverse gear driven gear (1707) of the power shift device (17), and the connection or disconnection between the above gears and the intermediate planet carrier shaft (14) is achieved by controlling the intermediate planet carrier shaft clutch (1706); the torque coupling device (15) can increase or decrease the gear according to the power demand of the tractor. The front end of the described intermediate sun gear shaft (22) is connected to the first planetary row sun gear (2303) and the second planetary row sun gear (2317) of the torque coupling device (23).

4. A series-parallel hybrid tractor drive system according to claim 1, characterized in that: The described power output speed change device (18) includes a power output second gear clutch (1801), a power output second gear driven gear (1802), a power output first gear driven gear (1803), a power output first gear clutch (1804), a power output first gear driving gear (1805), and a power output second gear driving gear (1806); The power output first gear driving gear (1805) and the power output second gear driving gear (1806) are connected to the engine output shaft (16); the power output first gear driving gear (1805) meshes with the power output first gear driven gear (1803), and by controlling the power output first gear clutch (1804), the connection or disconnection between the power output first gear driven gear (1803) and the power output shaft (19) is achieved; the power output second gear driving gear (1806) meshes with the power output second gear driven gear (1802), and by controlling the power output second gear clutch (1801), the connection or disconnection between the power output second gear driven gear (1802) and the power output shaft (19) is achieved; the power output speed change device (18) can increase or decrease the gear according to the requirements of the tractor agricultural implements.

5. A series-parallel hybrid tractor drive system according to claim 1, characterized in that: The described reduction device (20) includes a third planetary carrier (2001), a third planetary ring gear (2002), a third planetary gear (2003), and a third planetary sun gear (2004); the third planetary gear (2003) is installed on the third planetary carrier (2001), and the third planetary gear (2003) meshes with the third planetary ring gear (2002) and the third planetary sun gear (2004); the third planetary ring gear (2002) is connected to the tractor frame; the rear end of the intermediate sun gear shaft (22) is connected to the third planetary carrier (2001) of the reduction device (20); The front end of the PS motor output shaft (21) is connected to the third planetary sun gear (2004) of the reduction device (20), and the rear end of the PS motor output shaft (21) is connected to the PS motor (12).

6. The series-parallel hybrid tractor drive system according to claim 1, characterized in that: The described engine (1) includes a diesel engine, a natural gas engine, and a hydrogen fuel engine.

7. A series-parallel hybrid tractor drive system according to claim 1, characterized in that: The control system of the series-parallel hybrid tractor consists of the engine controller (3), the whole-machine controller (4), the transmission system controller (5), the energy management unit (6), the P1 motor controller (7), the PS motor controller (9), and the distribution box (10); the whole-machine controller (4) obtains the information of the engine controller (3), the transmission system controller (5), the energy management unit (6), the P1 motor controller (7), the PS motor controller (9), and the distribution box (10) through the high-speed CAN bus; the whole-machine controller (4) sends control signals to the engine controller (3), the transmission system controller (5), the energy management unit (6), the P1 motor controller (7), the PS motor controller (9), and the distribution box (10) through the high-speed CAN bus; the whole-machine controller (4) obtains the instrument and lighting information of the series-parallel hybrid tractor through the low-speed CAN bus; the energy management unit (6) controls the power battery pack (8), and the power battery pack (8) supplies power to the P1 motor (11), the PS motor (12), and the low-voltage battery through the distribution box (5); the operation information of the series-parallel hybrid tractor includes key signal, mode signal, position signal, torque signal, and speed signal.

8. The control method of a series-parallel hybrid tractor drive system according to any one of claims 1-7, characterized in that: Specifically as follows: Preset the SOC h is the upper limit value of the high-efficiency region of the SOC of the power battery pack, and SOC l is the lower limit value of the high-efficiency region of the SOC of the power battery pack, and T req,cd is the required torque of the tractor equivalent to the central drive shaft; T e_l,cd is the lower limit of the high-efficiency working range torque of the engine equivalent to the central drive shaft, and T e_h,cd is the upper limit of the high-efficiency working range torque of the engine equivalent to the central drive shaft, and n e_l,cd is the lower limit of the high-efficiency working range speed of the engine equivalent to the central drive shaft, and n e_h,cd is the upper limit of the high-efficiency working range speed of the engine equivalent to the central drive shaft; After the control system of the series-parallel hybrid tractor is started, the whole vehicle enters the self-check of the control system. After the self-check of the control system passes, the whole-machine controller (4) obtains the key signal, mode signal, position signal, torque signal, and speed signal. The whole-machine controller (4) determines the starting method of the drive system according to the obtained information, and at the same time sends control signals to the engine controller (3), the transmission system controller (5), the energy management unit (6), the P1 motor controller (7), the PS motor controller (9), and the distribution box (10). After the drive system starts successfully, the whole-machine controller (4) sends control signals according to the power demand information and operation information of the tractor, so as to control the tractor to switch to different drive modes. The specific drive modes and the corresponding switching methods are as follows: A. Pure electric drive mode: When the power demand of the tractor cannot achieve the engine (1) operating in the high-efficiency area and the SOC of the power battery pack (8) satisfies SOC > SOC l , the required torque of the tractor satisfies T req,cd ≤T e_l,cd , the required speed satisfies n req,cd ≤n e_h,cd , switch to the pure electric drive mode; at this time, turn off the engine (1), and the power battery pack (8) alone provides energy to the PS motor (12) to drive the walking system of the tractor to move forward; B. Series drive mode: When the power demand of the tractor cannot enable the engine (1) to operate in the high-efficiency region and the state of charge (SOC) of the power battery pack (8) is ≤ SOC l , and the required torque of the tractor satisfies T req,cd ≤ T e_l,cd , and the required speed satisfies n req,cd ≤ n e_h,cd , switch to the series drive mode; at this time, the output shaft (16) of the engine is decoupled from the power reversing device (17), and the P1 motor (11) drives the engine (1) to start. Subsequently, the engine (1) drives the P1 motor (11) to generate electricity, and the power battery pack (8) and the P1 motor (11) simultaneously or the P1 motor (11) alone provide energy for the drive of the PS motor (12); when the SOC of the power battery pack (8) reaches SOC l , carry out charging protection. The engine (1) drives the P1 motor (11) to generate electricity, and the P1 motor (11) provides energy for both the PS motor (12) and the power battery pack (8) simultaneously. When it reaches SOC h , carry out trickle charging protection; in this mode, the engine (1) can operate under the best working conditions to drive the P1 motor (11) to generate electricity, provide energy for the PS motor (12) and the power battery pack (8), and provide power for the tractor running system in series; C. Engine independent drive mode: When the power demand of the tractor reaches the optimal operating range of the engine (1), and the traveling speed of the tractor and the external working environment change little, and the required torque of the tractor satisfies T e_l,cd <T req,cd ≤T e_h,cd , the required speed satisfies n e_l,cd <n req,cd ≤n e_h,cd At this time, switch to the engine independent drive mode; at this time, both the P1 motor (11) and the PS motor (12) do not work, and the power of the engine (1) is all transmitted to the tractor traveling system by mechanical transmission. Since the power does not pass through the electric drive device, the energy loss caused by energy conversion can be avoided, and the system efficiency is the highest in this mode; D. Parallel torque coupling drive mode: When the torque demand of the tractor changes greatly and the SOC of the power battery pack (8) satisfies SOC > SOC l , the required torque of the tractor satisfies T req,cd > T e_h,cd , the required speed satisfies n e_l,cd < n req,cd ≤ n e_h,cd When this condition is met, switch to the parallel torque coupling drive mode. The P1 motor (11) absorbs the excess power output by the engine (1) to convert it into electrical energy and store it in the power battery pack (8) or supply it to the PS motor (12). The engine (1) and the PS motor (12) provide power to the tractor running system through torque coupling; E. Parallel speed coupling drive mode: When the speed demand of the tractor changes greatly and the SOC of the power battery pack (8) satisfies SOC > SOC l , the required torque of the tractor satisfies T e_l,cd < T req,cd ≤ T e_h,cd , the required speed satisfies n req,cd > n e_h,cd When, switch to the parallel speed coupling drive mode; The P1 motor (11) absorbs the excess power output by the engine (1) to convert it into electric energy and store it in the power battery pack (8) or supply it to the PS motor (12), and the engine (1) and the PS motor (12) provide power for the tractor running system through the speed coupling method; F. Energy recovery mode: When the tractor brakes or decelerates, the required torque T of the tractor req,cd <0, the mechanical energy of the tractor running system reversely drives the PS motor (12) to generate electricity, realizing the recovery of braking / deceleration energy. At this time, the engine (1) stops or is decoupled from the tractor running system.

9. The control method of a series-parallel hybrid tractor drive system according to claim 8, characterized in that: The specific method for the series-parallel hybrid tractor to select the starting method of the drive system includes the following steps: Step S1.

1. First, the control system is based on the SOC of the power battery pack (8). If SOC > SOC l , go to step S1.2; otherwise, go to step S1.

3. Step S1.

2. If the required torque of the tractor satisfies T req,cd ≤T e_l,cd , the tractor starts purely electrically and directly proceeds to Step S1.4; otherwise, it proceeds to Step S1.3; Step S1.3: The tractor first starts the engine (1). If the required torque of the tractor satisfies T req,cd ≤T e_l,cd , the tractor performs a series start; otherwise, only the engine (1) is started; Step S1.4, the starting of the tractor drive system is completed.

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