Series transmission control method of hybrid power tractor

Abstract

The invention belongs to the technical field of tractors, and particularly relates to a series transmission control method of a hybrid tractor, which comprises a generator and a driving motor, a power output shaft is in transmission connection with a four-wheel drive transmission mechanism comprising a four-wheel drive wet clutch, and service brakes are arranged on a left half shaft and a right half shaft of a differential assembly. The PTO input shaft is in transmission connection with a hydraulic output shaft through a gear assembly, the hydraulic output shaft is in transmission connection with a load-sensitive variable pump, and the PTO input shaft is in transmission connection with a PTO executing mechanism through a PTO wet clutch; the transmission control method comprises the steps of S1, energy recovery brake control; s2, four-wheel-drive cooperative braking control is carried out; s3, PTO starting control is carried out; and S4, PTO wet clutch anti-misoperation overrunning control is carried out. Real-time and reasonable distribution of regenerative braking and hydraulic braking is achieved on series hybrid power of the tractor, four-wheel-drive automatic connection can be achieved during emergency braking, the connection curve of the PTO wet clutch can be determined according to actual machines and tools, and anti-misoperation overrunning control is achieved.

Description

Technical Field

[0001] This invention belongs to the field of tractor technology, and specifically refers to a series drive control method for a hybrid tractor. Background Technology

[0002] A tractor combined motor intelligent control transmission system disclosed in a current Chinese invention patent application (application publication number CN119189711A) includes an engine, the crankshaft output end of the engine being drivenly connected to the input shaft of a generator, the generator being electrically connected to a drive motor and a power battery respectively through a high-voltage power distribution assembly, and the output shaft of the drive motor being drivenly connected to the input end of a gearbox assembly. When the generator's power output is greater than the power required by the drive motor, a portion of the generator's power output is transmitted to the drive motor and the other portion is transmitted to the power battery; when the generator's power output is less than the power required by the drive motor, both the generator's power output and the power battery's power are transmitted to the drive motor.

[0003] Meanwhile, a tractor combined motor gearbox assembly disclosed in an existing Chinese utility model patent (authorization publication number CN223203598U) includes a gearbox housing. A generator and a drive motor are coaxially arranged on the side wall of the gearbox housing. The outer end of the input shaft of the generator is connected to the output end of the crankshaft of the engine. An input shaft is supported on the gearbox housing. The input shaft is a hollow shaft. One end of the PTO shaft axially passes through the output shaft of the drive motor and is splinedly connected to the inner end of the input shaft of the generator. The other end of the PTO shaft is supported in the inner hole of the input shaft by a bushing. The input shaft is connected to the inner end of the output shaft of the drive motor by a spline sleeve. An output shaft is supported on the gearbox housing. A gear transmission assembly is provided between the input shaft and the output shaft.

[0004] It is evident that the two existing technologies mentioned above mainly focus on the integration of physical structures and the optimization of electronic control foundations. Their invention points are to provide a hardware foundation and electronic control foundation for hybrid power, but their control logic is relatively simple and isolated. In essence, they still follow the traditional mechanical transmission control thinking and fail to fully realize the huge potential of series hybrid power systems in terms of intelligent and integrated control. Summary of the Invention

[0005] The purpose of this invention is to provide a series drive control method for a hybrid tractor. By utilizing a load-sensitive variable pump, an electro-hydraulic proportional valve, a four-wheel drive wet clutch, and a PTO wet clutch, the method achieves real-time and reasonable distribution of regenerative braking and hydraulic braking in a series hybrid tractor. During emergency braking, the four-wheel drive can automatically engage to improve braking stability and safety. Furthermore, the engagement curve of the PTO wet clutch can be determined according to the actual implement, and it also has overrun control to prevent misoperation, thereby greatly protecting the reliable operation and safety of the entire machine and achieving efficient automated and intelligent operation.

[0006] This invention is implemented as follows: A series drive control method for a hybrid tractor includes a generator and a drive motor coaxially arranged. The drive motor is powered by the generator and a power battery. The input end of the generator is driven to the output end of the engine. The output end of the drive motor is driven to the power input shaft. The PTO input shaft passes through the inner hole of the power input shaft and the output shaft of the drive motor and is splined to the input end of the generator. A power gear transmission assembly is provided between the power input shaft and the power output shaft. The power output shaft is driven to a four-wheel drive transmission mechanism including a four-wheel drive wet clutch, and its end is driven to a differential assembly through a power bevel gear. Service brakes are provided on the left and right half shafts of the differential assembly. The PTO input shaft is driven to a hydraulic output shaft through a gear assembly. The hydraulic output shaft is driven to a load-sensitive variable pump. The outer end of the PTO input shaft is driven to a PTO actuator through a PTO wet clutch. The load-sensitive variable pump is connected to an electro-hydraulic proportional valve through a hydraulic circuit. The electro-hydraulic proportional valve is connected to two service brakes through a hydraulic circuit. The transmission control method is executed by the gearbox controller and includes: S1, Energy Recovery Braking Control: Real-time acquisition of braking demand F req (t), vehicle speed signal v(t) and the state of charge (SOC) signal of the power battery are used by the gearbox controller to control the opening of the electro-hydraulic proportional valve and the braking force of the drive motor to achieve synchronous execution of hydraulic braking and electric braking. S2, Four-wheel drive cooperative braking control: Real-time acquisition of brake pedal travel, and the transmission controller controls the engagement of the four-wheel drive wet clutch according to the brake pedal travel; S3, PTO start control: Two or more pressure-current control curves for PTO wet clutches are preset. The machine inertia and load of each PTO wet clutch pressure-current control curve are different. The current machine inertia and load are obtained in real time. The pressure-current control curve of the corresponding PTO wet clutch is calculated by interpolation. The transmission controller controls the PTO wet clutch to engage according to the pressure-current control curve of the PTO wet clutch. S4. PTO wet clutch anti-misoperation overrun control: When the transmission controller receives the PTO wet clutch engagement command, it obtains the speed of the input and output ends of the PTO wet clutch in real time, calculates the speed difference between the two, and when the speed difference is higher than the predetermined safety threshold, the transmission controller controls the engine or drive motor to synchronize with the speed of the output end of the PTO wet clutch, and then the transmission controller controls the PTO wet clutch to perform engagement.

[0007] In the series transmission control method of the hybrid tractor described above, the power gear transmission assembly includes a field operation drive gear and a road transport drive gear fixedly mounted on the power input shaft. A field operation driven gear meshing with the field operation drive gear and a road transport driven gear meshing with the road transport drive gear are rotatably mounted on the power output shaft. A transmission engagement sleeve or transmission synchronizer is fixedly mounted on the power output shaft between the field operation driven gear and the road transport driven gear. The transmission engagement sleeve or transmission synchronizer is driven by a DC motor shift actuator to achieve its engagement with the field operation driven gear or the road transport driven gear. The DC motor shift actuator is electrically connected to the gearbox controller. The gearbox controller includes a three-core heterogeneous microcontroller, a low-side driver and a high-side driver. The microcontroller generates two PWM signals to control the H-bridge circuit to drive the DC motor shift actuator through the low-side driver and the high-side driver respectively. The H-bridge circuit consists of MOSFET Q1, MOSFET Q2, MOSFET Q3, MOSFET Q4, a 24V power supply and a main relay.

[0008] In the series drive control method of the hybrid tractor described above, S1, energy recovery braking control, includes the following steps in sequence: Step L1: The transmission controller acquires the braking demand F in real time. req (t), vehicle speed signal v(t) and state of charge (SOC) signal of the power battery; Step L2: Calculate the regenerative braking force F according to the following formula. regen (t): F regen (t) = min[F] req (t), η motor × η battery × P max (SOC)] × 1 / v(t); Where, η motor = 0.92 is the motor efficiency, η battery = 0.95 represents the battery charge / discharge efficiency, P max (SOC) is the maximum charging power function of the battery determined based on the SOC signal; Step L3: Calculate the hydraulic braking force F according to the following formula. hydraulic (t): F hydraulic (t) = F req (t)-F regen (t); Step L4: The drive motor is controlled by the gearbox controller to generate F. regen(t), and the opening of the electro-hydraulic proportional valve is controlled by the transmission controller, which in turn drives the hydraulic system of the load-sensitive variable pump to generate F. hydraulic (t).

[0009] In the series drive control method of the hybrid tractor described above, S1, energy recovery braking control, has a braking force distribution strategy table: The transmission controller determines the ratio of hydraulic braking to electric braking according to the braking force distribution strategy table, so as to control the opening of the electro-hydraulic proportional valve.

[0010] In the aforementioned series transmission control method for a hybrid tractor, the four-wheel drive transmission mechanism includes a four-wheel drive intermediate shaft and a four-wheel drive output shaft. A four-wheel drive drive gear is fixedly mounted on the power output shaft, an intermediate gear meshing with the four-wheel drive drive gear is fixedly mounted on the four-wheel drive intermediate shaft, a four-wheel drive driven gear is rotatably mounted on the four-wheel drive output shaft, and the four-wheel drive driven gear is connected to the four-wheel drive output shaft via a four-wheel drive wet clutch. A parking brake is provided between the four-wheel drive driven gear and the tractor body.

[0011] In the series drive control method of the hybrid tractor described above, S2, the four-wheel drive coordinated braking control, includes the following steps in sequence: Step L1: Obtain the brake pedal travel in real time; Step L2: Determine if the brake pedal travel is ≥70%; Step a: Brake pedal travel <70%, normal braking; Step b: If the brake pedal travel is ≥70%, proceed to step L3; Step L3: The four-wheel drive wet clutch is engaged by the transmission controller.

[0012] In the series drive control method of the hybrid tractor described above, the S4 and PTO wet clutch anti-misoperation overrun control include the following steps in sequence: Step L1: The transmission controller receives the PTO wet clutch engagement command; Step L2: Real-time acquisition of the rotational speed n at the input end of the PTO wet clutch. in The rotational speed n at the output end of the PTO wet clutch out ; Step L3: Calculate the speed difference Δn = |n in -n out |; Step L4: Determine if Δn > safety threshold; Step a, △n≤safety threshold, the transmission controller controls the PTO wet clutch to engage; Step b, △n > safety threshold, interrupt PTO wet clutch engagement command and proceed to step L5; Step L5: The transmission controller synchronizes the speed of the engine or drive motor with the output speed of the PTO wet clutch. Step L6: Determine if Δn ≤ synchronization threshold at this time; Step c, Δn > synchronization threshold, repeat step L5; Step d, Δn ≤ synchronization threshold, proceed to step L7; Step L7: The transmission controller controls the PTO wet clutch to engage.

[0013] In the series drive control method of the hybrid tractor described above, the safety threshold is 150 rpm and the synchronization threshold is 30 rpm.

[0014] In the series drive control method of the hybrid tractor described above, the PTO actuator includes a PTO intermediate shaft and a PTO output shaft. The PTO input shaft is driven and linked with the PTO intermediate shaft through a PTO wet clutch. The PTO intermediate shaft and the PTO output shaft are driven and linked through a PTO gear transmission assembly.

[0015] In the aforementioned series transmission control method for a hybrid tractor, the PTO gear transmission assembly includes a PTO low-gear drive gear and a PTO high-gear drive gear fixedly mounted on the PTO intermediate shaft. A PTO low-gear driven gear meshing with the PTO low-gear drive gear and a PTO high-gear driven gear meshing with the PTO high-gear drive gear are rotatably mounted on the PTO output shaft. A PTO engagement sleeve or a PTO synchronizer is fixedly mounted on the PTO output shaft between the PTO low-gear driven gear and the PTO high-gear driven gear. The PTO low-gear driven gear or the PTO high-gear driven gear can engage with the PTO engagement sleeve or the PTO synchronizer to achieve synchronous rotation between the PTO low-gear driven gear or the PTO high-gear driven gear and the PTO output shaft.

[0016] The outstanding advantages of this invention compared to the prior art are: This invention utilizes a load-sensitive variable pump, an electro-hydraulic proportional valve, a four-wheel drive wet clutch, and a PTO wet clutch to achieve real-time and rational distribution of regenerative braking and hydraulic braking in a tractor series hybrid power system. During emergency braking, the four-wheel drive can automatically engage to improve braking stability and safety. Furthermore, the engagement curve of the PTO wet clutch can be determined according to the actual implement, and it also has overrun control to prevent misoperation, which greatly protects the reliable operation and safety of the entire machine, and achieves efficient automated and intelligent operation. Attached Figure Description

[0017] Figure 1This is a simplified diagram of the transmission principle of the present invention; Figure 2 This is a schematic diagram of the gearbox controller and its H-bridge circuit of the present invention; Figure 3 This is the control flowchart of the S2 and four-wheel drive cooperative braking control of the present invention; Figure 4 This is the control flowchart of the S4 and PTO wet clutch anti-misoperation overrun control of the present invention.

[0018] In the diagram: 1. Generator; 2. Drive motor; 3. Power battery; 4. Power input shaft; 5. PTO input shaft; 6. Power output shaft; 7. Four-wheel drive wet clutch; 8. Differential assembly; 9. Service brake; 10. Hydraulic output shaft; 11. Load-sensitive variable pump; 12. PTO wet clutch; 13. Gearbox controller; 14. Field operation drive gear; 15. Road transport drive gear; 16. Field operation driven gear; 17. Road transport driven gear; 18. Transmission synchronizer; 19. Four-wheel drive intermediate shaft; 20. Four-wheel drive output shaft; 21. Four-wheel drive drive gear; 22. Intermediate gear; 23. Four-wheel drive driven gear; 24. Parking brake; 25. PTO intermediate shaft; 26. PTO output shaft; 27. PTO low-gear drive gear; 28. PTO high-gear drive gear; 29. ​​PTO low-gear driven gear; 30. PTO high-gear driven gear; 31. PTO synchronizer. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments. See also: Figure 1 —4: Example 1: A series drive control method for a hybrid tractor includes a generator 1 and a drive motor 2 coaxially arranged. The drive motor 2 is powered by the generator 1 and a power battery 3. The input end of the generator 1 is drive-connected to the output end of the engine. The output end of the drive motor 2 is drive-connected to a power input shaft 4. A PTO input shaft 5 passes through the inner hole of the power input shaft 4 and the output shaft of the drive motor 2 and is splinedly linked to the input end of the generator 1. A power gear transmission assembly is provided between the power input shaft 4 and the power output shaft 6. The power output shaft 6 is drive-connected to a four-wheel drive transmission mechanism including a four-wheel drive wet clutch 7, and its end is drive-connected to a differential assembly 8 through a power bevel gear. The left and right half-shafts of the PTO assembly 8 are each equipped with a service brake 9. The PTO input shaft 5 is driven by a gear assembly and connected to the hydraulic output shaft 10, which is driven by a load-sensitive variable pump 11. The outer end of the PTO input shaft 5 is driven by a PTO wet clutch 12 and connected to the PTO actuator. The load-sensitive variable pump 11 is connected to an electro-hydraulic proportional valve through a hydraulic circuit, and the electro-hydraulic proportional valve is connected to the two service brakes 9 through a hydraulic circuit. This invention allows for precise adjustment of braking pressure through the combined application of the load-sensitive variable pump 11 and the electro-hydraulic proportional valve. Furthermore, the use of wet clutches in both the PTO and four-wheel drive systems enables smooth and rapid torque control. This also solves the fundamental problem of isolated braking systems, PTO systems, and four-wheel drive systems in traditional mechanical or hydraulic transmission systems, making coordinated electronic control difficult.

[0020] S1, Energy Recovery Braking Control: Real-time acquisition of braking demand F req (t), vehicle speed signal v(t) and the state of charge (SOC) signal of the power battery are used by the gearbox controller 13 to control the opening of the electro-hydraulic proportional valve and the braking force of the drive motor 2 to achieve synchronous execution of hydraulic braking and electric braking. The S1 energy recovery braking control includes the following steps in sequence: Step L1: The transmission controller 13 acquires the braking demand F in real time. req (t), vehicle speed signal v(t) and state of charge (SOC) signal of the power battery; Step L2: Calculate the regenerative braking force F according to the following formula. regen (t): F regen (t) = min[F] req (t), η motor × η battery × P max (SOC)] × 1 / v(t); Where, η motor = 0.92 is the motor efficiency, η battery = 0.95 represents the battery charge / discharge efficiency, Pmax (SOC) is the maximum charging power function of the battery determined based on the SOC signal; Step L3: Calculate the hydraulic braking force F according to the following formula. hydraulic (t): F hydraulic (t) = F req (t)-F regen (t); Step L4: The drive motor 2 is controlled by the gearbox controller 13 to generate F. regen (t), and the opening degree of the electro-hydraulic proportional valve is controlled by the gearbox controller 13, which in turn drives the hydraulic system of the load-sensitive variable pump 11 to generate F. hydraulic (t).

[0021] In this embodiment, electric braking and hydraulic braking are coordinated. By dynamically calculating the maximum regenerative braking force, electric braking and hydraulic braking are performed simultaneously during braking to maximize the recovery of braking energy, improve the overall energy utilization rate of the machine, and ensure that the braking efficiency is not reduced. This effectively solves the technical problems of low braking energy recovery efficiency and poor coordination with mechanical braking in hybrid tractors.

[0022] S2, Four-wheel drive cooperative braking control: The brake pedal travel is acquired in real time, and the gearbox controller 13 controls the engagement of the four-wheel drive wet clutch 7 according to the brake pedal travel; The S2, four-wheel drive coordinated braking control, includes the following steps in sequence: Step L1: Obtain the brake pedal travel in real time; Step L2: Determine if the brake pedal travel is ≥70%; Step a: Brake pedal travel <70%, normal braking; Step b: If the brake pedal travel is ≥70%, proceed to step L3; Step L3: The four-wheel drive wet clutch 7 is engaged by the transmission controller 13.

[0023] In this embodiment, the pedal travel of ≥70% is set as emergency braking. When the brake pedal travel of ≥70% is detected, the transmission controller 13 automatically engages the four-wheel drive wet clutch 7 and distributes the driving force to the front axle. This can switch to four-wheel braking during emergency braking, effectively increasing the adhesion utilization rate of the drive wheels, effectively suppressing the sideslip and instability that may be caused by emergency braking of the rear wheels, significantly improving the directional stability and safety of the vehicle during braking, and solving the problem of lack of coordination between the traditional tractor four-wheel drive system and the braking system.

[0024] S3, PTO start control: Two or more pressure-current control curves of PTO wet clutch 12 are preset. The machine inertia and load of each PTO wet clutch 12 are different. The current machine inertia and load are obtained in real time. The pressure-current control curve of the corresponding PTO wet clutch 12 is calculated by interpolation. The gearbox controller 13 controls the PTO wet clutch 12 to engage according to the pressure-current control curve of the PTO wet clutch 12. By pre-setting multiple engagement curves corresponding to different loads and using interpolation calculations to match the current implement in real time, the PTO start-up control achieves self-adaptability and wide applicability. It effectively solves the problems of start-up impact and engagement slippage caused by large differences in inertia when different implements start up, effectively protects the PTO transmission system, generator shaft structure and implements, and improves the smoothness and speed of the PTO start-up process.

[0025] S4, PTO wet clutch anti-misoperation overrun control: When the transmission controller 13 receives the PTO wet clutch 12 engagement command, it acquires the speed of the input and output ends of the PTO wet clutch 12 in real time, calculates the speed difference between the two, and when the speed difference is higher than the predetermined safety threshold, the transmission controller 13 controls the engine or drive motor 2 to synchronize with the speed of the output end of the PTO wet clutch 12, and then the transmission controller 13 controls the PTO wet clutch 12 to perform engagement. The S4 and PTO wet clutch anti-misoperation overrun control includes the following steps in sequence: Step L1: The transmission controller 13 receives the PTO wet clutch 12 engagement command; Step L2: Real-time acquisition of the rotational speed n at the input end of the PTO wet clutch. in The rotational speed n at the output end of the PTO wet clutch out ; Step L3: Calculate the speed difference Δn = |n in -n out |; Step L4: Determine if Δn > safety threshold, where the safety threshold is 150 rpm; Step a, △n≤safety threshold, the transmission controller 13 controls the PTO wet clutch 12 to engage; Step b, △n > safety threshold, interrupt PTO wet clutch 12 engagement command and proceed to step L5; Step L5: The transmission controller 13 controls the engine or drive motor 2 to synchronize with the output speed of the PTO wet clutch 12. Step L6: Determine if Δn ≤ synchronization threshold, which is 30 rpm; Step c, Δn > synchronization threshold, repeat step L5; Step d, Δn ≤ synchronization threshold, proceed to step L7; Step L7: The transmission controller 13 controls the PTO wet clutch 12 to engage.

[0026] This invention acquires and compares the rotational speeds of the input and output terminals of the PTO wet clutch 12 in real time. When the speed difference between the two is too large, the transmission controller 13 will automatically interrupt the dangerous engagement command and actively control the engine or drive motor 2 to synchronize the speed. This avoids severe mechanical shock and component damage caused by driver misoperation during engagement, providing good operational safety and setting a key safety guarantee for PTO output.

[0027] Therefore, by utilizing the combined application of a load-sensitive variable pump 11, an electro-hydraulic proportional valve, a four-wheel drive wet clutch 7, and a PTO wet clutch 12, this invention achieves real-time and reasonable distribution of regenerative braking and hydraulic braking in a tractor series hybrid power system. During emergency braking, the four-wheel drive can automatically engage to improve braking stability and safety. At the same time, the engagement curve of the PTO wet clutch 12 can be determined according to the actual implement, and it also has overrun control to prevent misoperation, which greatly protects the reliable operation and safety of the whole machine, and realizes efficient automated and intelligent operation.

[0028] Furthermore, the power transmission assembly includes a field operation drive gear 14 and a road transport drive gear 15 fixedly mounted on the power input shaft 4. A field operation driven gear 16 meshing with the field operation drive gear 14 and a road transport driven gear 17 meshing with the road transport drive gear 15 are rotatably mounted on the power output shaft 6. A transmission engagement sleeve or transmission synchronizer 18 is fixedly mounted on the power output shaft 6 between the field operation driven gear 16 and the road transport driven gear 17. The transmission engagement sleeve or transmission synchronizer 18 is driven by a DC motor shift actuator to achieve its engagement with the field operation driven gear 16 or the road transport driven gear 17. The DC motor shift actuator is electrically connected to the gearbox controller 13. In other words, the power transmission assembly is designed with corresponding transmission ratios for two common working conditions of tractors: low-speed, high-torque field operations and high-speed road transport. This allows the drive motor 2 to effectively improve the overall efficiency of the transmission system while meeting the traction requirements of different working conditions, thus expanding the tractor's applicability.

[0029] In this embodiment, the transmission controller 13 includes a three-core heterogeneous microcontroller, a low-side driver, and a high-side driver. The microcontroller generates two PWM signals to control the H-bridge circuit to drive the DC motor shift actuator through the low-side driver and the high-side driver, respectively. The H-bridge circuit consists of MOSFETs Q1, Q2, Q3, and Q4, a 24V power supply, and a main relay. The three-core heterogeneous microcontroller directly drives the DC motor shift actuator through the H-bridge circuit, achieving high reliability, high response speed, and direct drive in shift control. This solves the problems of slow response, easy leakage, and complex control in traditional hydraulic or pneumatic shift systems, providing a reliable execution foundation for the vehicle's intelligent shift strategy.

[0030] Furthermore, in this embodiment, the specific structure of the four-wheel drive transmission mechanism is as follows: the four-wheel drive transmission mechanism includes a four-wheel drive intermediate shaft 19 and a four-wheel drive output shaft 20. A four-wheel drive drive gear 21 is fixedly mounted on the power output shaft 6. An intermediate gear 22 that meshes with the four-wheel drive drive gear 21 is fixedly mounted on the four-wheel drive intermediate shaft 19. A four-wheel drive driven gear 23 is rotatably mounted on the four-wheel drive output shaft 20. The four-wheel drive driven gear 23 is connected to the four-wheel drive output shaft 20 through a four-wheel drive wet clutch 7. A parking brake 24 is provided between the four-wheel drive driven gear 23 and the tractor body.

[0031] Furthermore, the PTO actuator includes a PTO intermediate shaft 25 and a PTO output shaft 26. The PTO input shaft 5 is driven and linked to the PTO intermediate shaft 25 via a PTO wet clutch 12. The PTO intermediate shaft 25 and the PTO output shaft 26 are driven and linked via a PTO gear transmission assembly. In this embodiment, the PTO gear transmission assembly provides two different transmission ratios. Specifically, the PTO gear transmission assembly includes a PTO low-gear drive gear 27 and a PTO high-gear drive gear 28 fixedly mounted on the PTO intermediate shaft 25. The PTO output shaft 26 is rotatably fitted with a PTO low-gear driven gear 29 that meshes with the PTO low-gear drive gear 27 and a PTO high-gear driven gear 30 that meshes with the PTO high-gear drive gear 28. Additionally, a PTO low-gear driven gear 29 located at the PTO high-gear drive gear 28 is fixedly mounted on the PTO output shaft 26. The PTO engagement sleeve or PTO synchronizer 31 between the low-gear driven gear 29 and the high-gear driven gear 30 allows the low-gear driven gear 29 or the high-gear driven gear 30 to engage with the PTO engagement sleeve or PTO synchronizer 31 to achieve synchronous rotation between the low-gear driven gear 29 or the high-gear driven gear 30 and the PTO output shaft 26. This enables the tractor to adapt to more types of PTO-driven implements, meet the speed requirements of different operations, and improve the tractor's versatility and operating efficiency.

[0032] Example 2: This embodiment is basically the same as the mechanical structure and control method in Embodiment 1 above. The main difference is that this embodiment provides an alternative solution for S1, energy recovery braking control, namely, S1, energy recovery braking control, which has a braking force distribution strategy table: The transmission controller 13 determines the ratio of hydraulic braking to electric braking according to the braking force distribution strategy table, thereby controlling the opening of the electro-hydraulic proportional valve. That is, by directly looking up the table based on three key parameters—SOC, braking demand, and vehicle speed—using a pre-calibrated braking force distribution strategy table, the braking ratio is determined. Its advantages are that the control logic is simpler and more intuitive, the requirements for the controller's computing power are lower, and it is easy to quickly calibrate and optimize for different vehicle models.

[0033] The above embodiments are merely one of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, all equivalent changes made in accordance with the shape, structure and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A series drive control method for a hybrid tractor, characterized in that: The system includes a generator (1) and a drive motor (2) coaxially mounted. The drive motor (2) is powered by the generator (1) and a power battery (3). The input end of the generator (1) is connected to the output end of the engine. The output end of the drive motor (2) is connected to the power input shaft (4). The PTO input shaft (5) passes through the inner hole of the power input shaft (4) and the output shaft of the drive motor (2) and is splinedly linked to the input end of the generator (1). A power gear transmission assembly is provided between the power input shaft (4) and the power output shaft (6). The power output shaft (6) is connected to a four-wheel drive system including a four-wheel drive wet clutch (7). The transmission mechanism is connected to the differential assembly (8) via a power bevel gear. The left and right half shafts of the differential assembly (8) are equipped with service brakes (9). The PTO input shaft (5) is connected to the hydraulic output shaft (10) via a gear assembly. The hydraulic output shaft (10) is connected to the load-sensitive variable pump (11). The outer end of the PTO input shaft (5) is connected to the PTO actuator via a PTO wet clutch (12). The load-sensitive variable pump (11) is connected to the electro-hydraulic proportional valve via a hydraulic circuit. The electro-hydraulic proportional valve is connected to the two service brakes (9) via a hydraulic circuit. The transmission control method is executed by the gearbox controller (13) and includes: S1, Energy recovery braking control: Real-time acquisition of braking demand Freq(t), vehicle speed signal v(t) and state of charge (SOC) signal of power battery (3), and control of the opening degree of electro-hydraulic proportional valve and the braking force of drive motor (2) by transmission controller (13) to realize the synchronous execution of hydraulic braking and electric braking. S2, Four-wheel drive coordinated braking control: The brake pedal travel is acquired in real time, and the gearbox controller (13) controls the engagement of the four-wheel drive wet clutch (7) according to the brake pedal travel; S3, PTO start control: two or more pressure-current control curves of PTO wet clutch (12) are preset. The machine inertia and load of each pressure-current control curve of PTO wet clutch (12) are different. The current machine inertia and load are obtained in real time. The pressure-current control curve of the corresponding PTO wet clutch (12) is calculated by interpolation. The gearbox controller (13) controls the PTO wet clutch (12) to engage according to the pressure-current control curve of the PTO wet clutch (12). S4, PTO wet clutch (12) anti-misoperation overrun control: When the transmission controller (13) receives the PTO wet clutch (12) engagement command, it obtains the speed of the input end and output end of the PTO wet clutch (12) in real time, calculates the speed difference between the two, and when the speed difference is higher than the predetermined safety threshold, the transmission controller (13) controls the engine or drive motor (2) to synchronize with the output end speed of the PTO wet clutch (12), and then the transmission controller (13) controls the PTO wet clutch (12) to perform engagement.

2. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The power gear transmission assembly includes a field operation drive gear (14) and a road transport drive gear (15) fixedly mounted on the power input shaft (4). The power output shaft (6) is rotatably fitted with a field operation driven gear (16) meshing with the field operation drive gear (14) and a road transport drive gear (15) meshing with the road transport drive gear (15). The power output shaft (6) is also fitted with a transmission engagement sleeve or transmission synchronizer (18) located between the field operation driven gear (16) and the road transport driven gear (17). The transmission engagement sleeve or transmission synchronizer (18) is driven by a DC motor shift actuator to achieve its engagement with the field operation driven gear (16) or the road transport driven gear (17). The DC motor shift actuator is electrically connected to the gearbox controller (13). The gearbox controller (13) includes a three-core heterogeneous microcontroller, a low-side driver and a high-side driver. The microcontroller generates two PWM signals to control the H-bridge circuit to drive the DC motor shift actuator through the low-side driver and the high-side driver respectively. The H-bridge circuit consists of MOSFET Q1, MOSFET Q2, MOSFET Q3, MOSFET Q4, a 24V power supply and a main relay.

3. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The S1 energy recovery braking control includes the following steps in sequence: Step L1: The transmission controller (13) acquires the braking demand F in real time. req (t), vehicle speed signal v(t) and the state of charge (SOC) signal of the power battery (3); Step L2: Calculate the regenerative braking force F according to the following formula. regen (t): F regen (t)=min[F req (t), η motor × η battery × P max (SOC)] × 1 / v (t); Where, η motor = 0.92 is the motor efficiency, η battery = 0.95 represents the battery charge / discharge efficiency, P max (SOC) is the maximum charging power function of the battery determined based on the SOC signal; Step L3: Calculate the hydraulic braking force F according to the following formula. hydraulic (t): F hydraulic (t)= F req (t)- F regen (t); Step L4: The gearbox controller (13) controls the drive motor (2) to generate F. regen (t), and the opening of the electro-hydraulic proportional valve is controlled by the gearbox controller (13), which in turn drives the hydraulic system of the load-sensitive variable pump (11) to generate F. hydraulic (t).

4. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The S1, energy recovery braking control, has a braking force distribution strategy table: The gearbox controller (13) determines the ratio of hydraulic braking to electric braking according to the braking force distribution strategy table in order to control the opening of the electro-hydraulic proportional valve.

5. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The four-wheel drive transmission mechanism includes a four-wheel drive intermediate shaft (19) and a four-wheel drive output shaft (20). A four-wheel drive drive gear (21) is fixedly mounted on the power output shaft (6). An intermediate gear (22) that meshes with the four-wheel drive drive gear (21) is fixedly mounted on the four-wheel drive intermediate shaft (19). A four-wheel drive driven gear (23) is rotatably mounted on the four-wheel drive output shaft (20). The four-wheel drive driven gear (23) is connected to the four-wheel drive output shaft (20) through a four-wheel drive wet clutch (7). A parking brake (24) is provided between the four-wheel drive driven gear (23) and the tractor body.

6. A series drive control method for a hybrid tractor according to claim 1 or 5, characterized in that: The S2, four-wheel drive coordinated braking control, includes the following steps in sequence: Step L1: Obtain the brake pedal travel in real time; Step L2: Determine if the brake pedal travel is ≥70%; Step a: Brake pedal travel <70%, normal braking; Step b: If the brake pedal travel is ≥70%, proceed to step L3; Step L3: The four-wheel drive wet clutch (7) is engaged by the transmission controller (13).

7. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The S4 and PTO wet clutch anti-misoperation overrun control includes the following steps in sequence: Step L1: The transmission controller (13) receives the PTO wet clutch (12) engagement command; Step L2: Real-time acquisition of the rotational speed n at the input end of the PTO wet clutch. in The rotational speed n at the output end of the PTO wet clutch out ; Step L3: Calculate the speed difference Δn = |n in -n out |; Step L4: Determine if Δn > safety threshold; Step a, △n≤safety threshold, the transmission controller (13) controls the PTO wet clutch (12) to engage; Step b, △n > safety threshold, interrupt PTO wet clutch (12) engagement command, and proceed to step L5; Step L5: The transmission controller (13) controls the engine or drive motor (2) to synchronize the output speed with the PTO wet clutch (12); Step L6: Determine if Δn ≤ synchronization threshold at this time; Step c, Δn > synchronization threshold, repeat step L5; Step d, Δn ≤ synchronization threshold, proceed to step L7; Step L7: The transmission controller (13) controls the PTO wet clutch (12) to engage.

8. The series drive control method for a hybrid tractor according to claim 7, characterized in that: The safety threshold is 150 rpm, and the synchronization threshold is 30 rpm.

9. The series drive control method for a hybrid tractor according to claim 1, characterized in that: The PTO actuator includes a PTO intermediate shaft (25) and a PTO output shaft (26). The PTO input shaft (5) is driven and linked with the PTO intermediate shaft (25) through a PTO wet clutch (12). The PTO intermediate shaft (25) and the PTO output shaft (26) are driven and linked through a PTO gear transmission assembly.

10. The series drive control method for a hybrid tractor according to claim 9, characterized in that: The PTO gear transmission assembly includes a PTO low gear drive gear (27) and a PTO high gear drive gear (28) fixedly mounted on the PTO intermediate shaft (25). The PTO output shaft (26) is rotatably fitted with a PTO low gear driven gear (29) meshing with the PTO low gear drive gear (27) and a PTO high gear driven gear (30) meshing with the PTO high gear drive gear (28). The PTO output shaft (26) is also fitted with a PTO engagement sleeve or a PTO synchronizer (31) located between the PTO low gear driven gear (29) and the PTO high gear driven gear (30). The PTO low gear driven gear (29) or the PTO high gear driven gear (30) can engage with the PTO engagement sleeve or the PTO synchronizer (31) to achieve synchronous rotation of the PTO low gear driven gear (29) or the PTO high gear driven gear (30) and the PTO output shaft (26).

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