Small-horsepower stepless speed change and power reversing tractor control system and control method

Abstract

The invention relates to a control system and a control method for a low-horsepower stepless speed change and power reversing tractor, which are characterized in that a low-cost and highly-integrated electric control system is designed for the low-horsepower tractor, and the complexity and the manufacturing cost of the system are greatly reduced on the premise of ensuring core functions by sharing a sensing network and optimizing the number of actuators. The control system is suitable for the low-horsepower tractor market sensitive to cost, can realize intelligent identification and switching of dual-mode starting, performs cooperative control on stepless speed change and power reversing functions, optimizes stepless speed change and power reversing control strategies, uses a dual-mode closed-loop control strategy, and improves the control efficiency. Smoothness of torque transmission under different working conditions is guaranteed, the stepless speed change function and the advancing power reversing function of the low-horsepower tractor are achieved, and a new platform is provided for intelligent development of the low-horsepower tractor.

Description

Technical Field

[0001] This invention relates to the field of tractor control, specifically to a control system and control method for a low-horsepower continuously variable transmission (CVT) and power reversing tractor. Background Technology

[0002] As a core power equipment in agriculture and engineering, the transmission system and handling performance of tractors directly affect operating efficiency, fuel economy, and operator comfort. Low-horsepower tractors are mainly used in rural areas where farmland is relatively small, requiring frequent gear shifting and reversing during field operations. Traditional mechanical stepped transmissions require power transmission to be interrupted during gear shifting or reversing, resulting in poor operational continuity. This is particularly true in situations requiring frequent gear changes, such as tilling and sowing, or frequent reversing in confined spaces like orchards and greenhouses, significantly reducing operating efficiency. Furthermore, due to the use of fixed gears, the engine cannot continuously operate within its high-efficiency range, making it difficult to adapt to complex and changing working conditions.

[0003] Currently, continuously variable transmission (CVT) tractors and power-reversing tractors have significant advantages in improving work efficiency and intelligence. However, due to high manufacturing and maintenance costs, they are generally only used in high-horsepower tractors where cost is not a major concern. Meanwhile, low-horsepower tractors are still mainly mechanical tractors, where shifting and reversing functions can only be achieved after the vehicle has stopped, making operation complex and unable to achieve stepless speed regulation. Against this backdrop, there is a need for a system that integrates continuously variable transmission, power reversing, and their intelligent collaborative control to achieve continuous power output, seamless reversing, and intelligent control for low-horsepower tractors. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a control system and method for a low-horsepower continuously variable transmission (CVT) and power reversing tractor, enabling low-horsepower tractors to achieve CVT, power reversing, and their coordinated control, thereby reducing driver workload, improving driving comfort, and increasing tractor efficiency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The control system for a low-horsepower continuously variable transmission (CVT) and power reversing tractor includes a signal source, a CVT controller, and a terminal actuator. The signal source includes a reversing handle, a CVT pushrod, a motor speed sensor, a reversing input speed sensor, a reversing output speed sensor, a vehicle speed sensor, an oil temperature sensor, and a sensitivity knob. The CVT controller integrates a signal acquisition module, a CVT module, a power reversing module, a torque-current conversion module, a fault diagnosis module, and a drive and information transmission module. The terminal actuator includes four proportional solenoid valves and two wet clutches. Two proportional solenoid valves control two oil circuits of the CVT HST to achieve continuously variable transmission; the other two proportional solenoid valves control two wet clutches for power reversing, enabling smooth engagement and disengagement between forward and reverse gears. The driver can automatically start the tractor and perform power reversing by changing the position of the reversing handle. By comprehensively adjusting the engine speed and the CVT pushrod, the tractor can achieve smooth continuous gear changes under different working conditions and loads.

[0006] Furthermore, the continuously variable transmission (CVT) controller determines the tractor's starting and reversing types based on the power reversing module, and determines whether the tractor needs to accelerate or decelerate based on the CVT module; it calculates the actual displacement ratio output by the HST based on the engine speed value sent by the engine controller's CAN bus and the collected motor speed value; it calculates the real-time speed difference between the forward and reverse clutches based on the collected reversing input speed value and reversing output speed value; and it calculates the torque that can be transmitted when each clutch is fully engaged based on the torque signal sent by the engine controller's CAN bus, providing a data basis for subsequent precise control. The control system, combining the characteristics of each proportional solenoid valve and clutch, calculates the corresponding required current value through the torque current conversion module, which is finally executed by the drive and information transmission module to drive the proportional solenoid valves to obtain accurate actual current.

[0007] Furthermore, the fault diagnosis module monitors the status of all signals in real time. Once an abnormality is detected, the continuously variable transmission (CVT) controller will immediately send diagnostic information via the CAN bus and automatically take corresponding measures based on the severity of the fault.

[0008] This invention also provides a control method for a low-horsepower continuously variable transmission (CVT) and power reversing tractor. The tractor employs the aforementioned low-horsepower CVT and power reversing tractor control system, and the control method is as follows: (1) When the driver starts the engine, the control system will perform a self-check: if the reversing lever is not in neutral, the forward / reverse proportional solenoid valve will be locked at the hardware level and will not be able to obtain the requested current. It must be returned to neutral to unlock the direction control function. Similarly, if the continuously variable transmission push rod is not in the zero position, it must be reset to the zero position before the continuously variable transmission function can be enabled. (2) After the control system performs a self-check, if it is determined that there is no serious fault affecting the operation of the vehicle, the tractor performs coordinated control of automatic start, power reversal and continuously variable transmission. The driver operates the reversing handle, and the continuously variable transmission controller will calculate the real-time speed difference based on the speed of the reversing input / output speed sensor to realize the automatic start and power reversal functions of the vehicle; the driver operates the continuously variable transmission push rod position, and the continuously variable transmission controller controls the vehicle to realize the continuously variable transmission function based on the actual displacement ratio and the requested displacement ratio. (3) If the clutch speed difference exceeds the set value and continues for a specific time during the starting, reversing or driving of the tractor, the controller will immediately cut off the clutch current to prevent clutch wear. At the same time, the instrument will display the corresponding fault code and fault warning information. The driver needs to disconnect the tractor and then reconnect the power to operate the vehicle normally.

[0009] Furthermore, the continuously variable transmission (CVT) control process is as follows: After the tractor starts, the engine status and system pressure are first detected. When both the engine speed and system pressure exceed the set threshold, the driver selects the high or low gear range using the high / low gear switching button, and then operates the forward or reverse clutch. If the CVT push lever is not in the zero position at this time, the system will restrict its function, and the driver needs to manually return the push lever to zero to unlock the CVT control function. When the driver pushes the CVT push lever, the controller determines the requested displacement ratio based on the real-time position of the CVT push lever and calculates the actual displacement ratio based on the engine speed and motor output speed. If the difference between the requested value and the actual value exceeds the set threshold, the controller will adjust the current of the two CVT proportional solenoid valves through a PID algorithm to make the actual displacement ratio track the requested displacement ratio, thereby achieving smooth control of the expected vehicle speed. If a power reversal is encountered during the CVT process, the CVT maintains the current state until the reversal is completed and continues to adjust according to the displacement ratio deviation.

[0010] Furthermore, the tractor includes two starting modes: Mode 1: first switch direction, then adjust speed; Mode 2: first preset speed, then switch direction. The control system intelligently distinguishes between the two starting modes based on the driver's operation sequence of the continuously variable transmission push rod and the reversing handle, achieving precise and smooth power connection.

[0011] Furthermore, when the driver has the continuously variable transmission push lever in the zero position, first switch the reversing handle from neutral to forward or reverse gear, and then push the continuously variable transmission push lever to start. The system determines this to be "mode one". At this time, the speed difference between the two ends of the reversing clutch is close to zero, and the clutch can quickly complete the oil filling and mechanical engagement. At the same time, the continuously variable transmission proportional solenoid valve adjusts the starting current according to the preset ramp curve to achieve a linear increase in speed. If the driver first pushes the continuously variable transmission (CVT) push lever to the target percentage position and then operates the reversing handle to switch between forward and reverse gears, the system enters "Mode Two". At this time, the CVT module has already established the target displacement, the hydraulic motor starts to accelerate, and a significant speed difference is generated before the reversing clutch engages. When this speed difference exceeds the system's set threshold, the control system activates the dual closed-loop torque compensation mechanism. The requested current of the reversing clutch proportional solenoid valve is determined by the superposition of two parts: one is the current corresponding to the ramp torque set based on acceleration, and the other is the current corresponding to the torque obtained by PID adjustment based on the speed difference. The CVT controller converts the calculated total torque into the corresponding proportional solenoid valve control current to complete the automatic start. When the speed difference during clutch engagement is lower than the set threshold, or the engagement time exceeds the set limit, the proportional solenoid valve current will rapidly rise to the maximum value with a preset maximum step size to ensure reliable engagement.

[0012] Furthermore, the slope of the ramp torque can be automatically adjusted according to the rotational input shaft speed and continuously increased within the simulation step size, thereby achieving smooth and rapid clutch engagement at different speeds. By introducing the rotational input shaft speed factor Map, the slope of the ramp torque is automatically corrected in real time. Users can also customize the ramp torque slope through the rotational sensitivity knob to adapt to the starting smoothness requirements under different working conditions.

[0013] Furthermore, the power reversing control process is as follows: During tractor travel, the reversing handle is moved from the current travel direction to the opposite direction, at which point the tractor enters the power reversing state. The controller will determine the clutches that need to be disengaged and engaged based on the vehicle status and sensor information, and will acquire the speed difference, vehicle speed, and oil filling time in real time. Subsequently, the clutch to be disengaged enters the pre-opening stage, and its transmitted torque gradually decreases from the maximum value to the actual input torque value of the engine according to the set curve. At the same time, the clutch to be engaged begins pre-engagement, and rapid oil filling is performed until the free stroke is completely eliminated. At this time, its hydraulic pressure can only balance the spring force and does not transmit actual torque. When the torque of the disengaging clutch decreases to the actual input torque value of the engine, the torque curve transmitted by the disengaging clutch will be adjusted by closed-loop control. The total torque value of the disengaging clutch is calculated by the sum of the preset torque defined by acceleration and the torque determined by PID adjustment, ultimately achieving smooth torque transition and speed synchronization. When the speed difference of the engaging clutch is less than the set threshold, or the engagement time is greater than the set value, the engaging clutch quickly increases to the maximum torque to complete the locking, marking the completion of the power reversing process.

[0014] Furthermore, when the control system detects that the continuously variable transmission (CVT) push lever has returned to zero, it will simultaneously cut off the control current of the currently engaged reversing clutch while issuing a displacement ratio request corresponding to zero vehicle speed. This forces the vehicle to stand still at the mechanical transmission level, unaffected by changes in volumetric efficiency. When the driver pushes the CVT push lever again, the system will re-engage the reversing clutch according to the automatic start-up curve and coordinate with the CVT module to ensure a smooth start for the vehicle.

[0015] Beneficial effects: This invention designs a low-cost, highly integrated electronic control system that enables small-horsepower tractors to achieve continuously variable transmission (CVT) and power reversal functions typically found only in high-horsepower, high-end models. This significantly improves the intelligence level and operational efficiency of small agricultural machinery. The continuously variable transmission (CVT) module and power reversal module, originally used in high-end, high-horsepower tractors, are integrated into the vehicle controller. By sharing a sensor network and optimizing the number of actuators (using only four proportional solenoid valves), precise current control enables direct drive of the hydraulic system and wet clutch. While ensuring core functions, this greatly reduces system complexity and manufacturing costs, making it suitable for the cost-sensitive small-horsepower tractor market.

[0016] This invention changes the traditional mechanical operation mode of small-horsepower tractors, which requires the tractor to stop before shifting gears / changing direction. It simplifies the operation to an intuitive electronic handle and push lever, significantly reducing the driver's workload and skill threshold, and facilitating the promotion and modernization of agricultural machinery. This invention enables small-horsepower tractors to achieve continuously variable transmission (CVT) and power reversing functions. Drivers can achieve stepless speed adjustment throughout the entire operation according to different working conditions, effectively solving the technical problems of complex gear shifting and excessive shifting shock during tractor operation. When changing direction at the end of the field, the driver does not need to depress the clutch pedal; they can directly operate the reversing handle to change direction. The entire reversing process is smooth and the power is uninterrupted, shortening the tractor's reversing time and thus improving the tractor's working efficiency.

[0017] This invention enables intelligent identification and switching of dual-mode starting. The control system can automatically switch between two starting modes, "smoothness priority" and "response priority," based on the driver's operation sequence of the continuously variable transmission push lever and the reversing handle. This achieves intelligent selection of starting strategies on a low-horsepower platform, taking into account the different needs of precise field operations and rapid response.

[0018] This invention proposes a unified closed-loop torque control method. In the control of automatic start or power reversal, the core torque control adopts a composite control method that combines "preset ramp curve" and "PID dynamic compensation based on real-time speed difference". This unified control framework ensures the smoothness of torque transmission under different operating conditions, effectively eliminates the reversal jerking feeling, and significantly shortens the clutch slippage time. It has the advantages of strong adaptability and fast and stable response.

[0019] This invention integrates the control of continuously variable transmission (CVT) and power reversing functions. Addressing the industry problem of "drifting" in hydraulic continuously variable transmission (HST) systems at zero speed due to changes in oil temperature and pressure, this invention innovatively proposes an electromechanical collaborative solution: when the HST push rod returns to zero, the system synchronously cuts off the control current of the reversing clutch, forcing the vehicle to come to an absolute stop through the physical disconnection of the mechanical transmission chain, fundamentally ensuring parking reliability.

[0020] This invention introduces a "sensitivity knob," allowing the driver to customize the smoothness of reversing or starting according to actual conditions such as soil conditions and load (e.g., adjusting the clutch engagement slope). This gives the system preliminary adaptability to working conditions and personalized adjustment space, improving the user experience. At the same time, this invention is equipped with a fault diagnosis module, which monitors the tractor's own status in real time through the controller, analyzes faults based on abnormal data, and takes timely corresponding actions to protect the tractor itself and the safety of personnel. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall architecture of the continuously variable transmission and power reversing tractor control system of the present invention; Figure 2 This is a flowchart of the continuously variable transmission (CVT) mode control for the tractor according to the present invention. Figure 3 This is a flowchart of the tractor automatic start mode control for the present invention; Figure 4 This is a flowchart of the tractor power reversal mode control of the present invention; Figure 5 This is a flowchart of the coordinated control of continuously variable transmission and power reversing in a tractor according to the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] This invention takes the Dongfanghong 90-horsepower wheeled continuously variable transmission tractor as the research object. The overall architecture diagram of the tractor control system is shown below. Figure 1As shown, the control system includes a signal source, a continuously variable transmission (CVT) controller, and a terminal actuator. By comprehensively adjusting the engine speed and the CVT push rod, the driver enables the tractor to achieve smooth and continuous speed changes under different working conditions and loads. By changing the position of the reversing handle, the tractor can achieve automatic start-up and power reversal functions.

[0024] Specifically, the signal source collects signals from the reversing handle, continuously variable transmission (CVT) pushrod, motor speed sensor, reversing input speed sensor, reversing output speed sensor, vehicle speed sensor, oil temperature sensor, sensitivity knob, etc. The CVT controller includes a signal acquisition module, a power reversing module, a CVT module, a torque current conversion module, a fault diagnosis module, and a drive and information transmission module. The terminal actuator includes four proportional solenoid valves and two wet clutches. Among them, two proportional solenoid valves, a CVT positive adjustment proportional solenoid valve and a CVT negative adjustment proportional solenoid valve, are used to control the two oil circuits of the CVT HST to realize the vehicle's continuously variable transmission. The other two proportional solenoid valves, an F-gear clutch proportional solenoid valve and an R-gear clutch proportional solenoid valve, are used to control the two wet clutches of the power reversing. Through the proportional solenoid valves, the reversing wet clutches can be precisely controlled, realizing smooth engagement and disengagement between forward and reverse gears, effectively eliminating the jerkiness of power reversing.

[0025] The continuously variable transmission (CVT) controller determines the tractor's starting and reversing types based on the power reversing module, and determines whether the tractor needs to accelerate or decelerate based on the CVT module. It calculates the actual displacement ratio output by the HST based on the engine speed value sent from the engine controller's CAN bus and the collected motor speed value. It calculates the real-time speed difference between the forward and reverse clutches based on the collected reversing input and output speed values. Based on the torque signal from the CAN bus sent by the engine controller, it calculates the torque that can be transmitted when each clutch is fully engaged, providing a data foundation for subsequent precise control. Subsequently, the control system, combining the characteristics of each proportional solenoid valve and clutch, calculates the corresponding required current value through the torque current conversion module. This instruction is ultimately executed by the drive and information transmission module, driving the proportional solenoid valves to obtain precise actual current. Throughout the process, the integrated fault diagnosis module monitors all signal statuses in real time. Once an anomaly is detected, the controller immediately sends diagnostic information via the CAN bus and automatically takes appropriate measures based on the severity of the fault.

[0026] Based on the aforementioned tractor control system, a control method for a low-horsepower continuously variable transmission (CVT) and power reversing tractor is as follows: (1) When the driver starts the engine, the control system will perform a self-check: if the reversing lever is not in neutral, the forward and reverse proportional solenoid valves will not receive the requested current and must be returned to neutral to unlock the direction control function; similarly, if the continuously variable transmission push rod is not in zero position, it must be reset to zero position before the continuously variable transmission function can be activated.

[0027] (2) After the control system performs a self-check, if it is determined that there is no serious fault affecting the operation of the vehicle, the system will control automatic start, continuously variable transmission and power reversal according to the driver's operation. When the driver operates the reversing handle, the controller will realize the automatic start and power reversal functions of the vehicle according to the real-time speed difference of the reversing clutch. When the driver operates the continuously variable transmission push rod position, the controller will control the vehicle to realize the continuously variable transmission function according to the actual displacement ratio and the requested displacement ratio.

[0028] (3) If the clutch speed difference exceeds the set value and continues for a specific time during the starting, reversing or driving of the tractor, the controller will immediately cut off the clutch current to prevent clutch wear. At the same time, the instrument will display the corresponding fault code and fault warning information. The driver needs to disconnect the tractor and then reconnect the power to operate the vehicle normally.

[0029] The control method of the present invention will be described in detail below in conjunction with continuously variable transmission (CVT), automatic start, power reversing, and the coordinated control of CVT and power reversing.

[0030] like Figure 2 As shown, the control flow of the continuously variable transmission (CVT) mode of the tractor in this invention is as follows: After the tractor is started, the engine status and system pressure are checked first to determine whether the engine speed and system pressure are greater than the set threshold, as a safety prerequisite for subsequent operations.

[0031] When the engine speed exceeds 600 rpm and the system pressure is greater than 1.8 MPa, the driver can select the operating mode through the high / low gear switch button. The high gear is suitable for transportation operations, and the low gear is suitable for load operations.

[0032] After the gear is selected, the driver then operates the forward or reverse clutch to physically engage the power transmission path; this step must be performed after the gear is confirmed to ensure that the transmission system is free from shock and reverse load risk.

[0033] After the above steps are completed, the system still requires the continuously variable transmission (CVT) push lever to be in the zero position. If the CVT push lever is not in the zero position at this time, the system will restrict its function, and the driver must manually return the push lever to zero to unlock the CVT control function. This design effectively avoids accidental acceleration or loss of control caused by accidental activation of the push lever, and is a core barrier to ensure human-machine collaborative safety.

[0034] When the driver pushes the continuously variable transmission (CVT) push lever, the controller determines the requested displacement ratio based on the real-time position of the push lever and calculates the actual displacement ratio based on the engine speed and the motor output speed. If the difference between the requested value and the actual value exceeds a set threshold, the controller will adjust the current of the two continuously variable proportional solenoid valves through a PID algorithm to make the actual displacement ratio track the requested displacement ratio, thereby achieving smooth control of the expected vehicle speed.

[0035] When the tractor performs power reversal during continuously variable transmission (CVT), the CVT module will maintain its current state. After the reversal is completed, it will continue to adjust according to the displacement ratio deviation to achieve coordinated control of CVT and power reversal.

[0036] Specifically, the continuously variable transmission (CVT) system in this invention employs a mechanical-hydraulic CVT transmission system, mainly composed of a power splitting mechanism, an HST continuously variable speed control mechanism (including a variable displacement pump and a fixed displacement motor), and a power merging mechanism (differential gear train). The percentage position of the CVT pushrod corresponds linearly to the requested displacement ratio: when the pushrod is at 0%, the variable displacement pump displacement ratio is -1, the hydraulic circuit performs negative work, and after coupling with the mechanical circuit, it outputs the maximum reverse speed, and the vehicle is at zero speed; when the pushrod is at 50%, the displacement ratio is 0, the hydraulic circuit does not work, only the mechanical circuit outputs, and the vehicle speed is zero; when the pushrod is at 100%, the displacement ratio is +1, the hydraulic circuit performs positive work, and the vehicle reaches its maximum speed.

[0037] This continuously variable transmission (CVT) system achieves "mechanical direct drive zero speed" at the 50% push lever position. This is not neutral in the traditional sense, but rather the energy transfer is completely stopped through the hydraulic circuit, so that the output shaft is driven only by the mechanical path. At this time, the engine is still running, but there is no power output to the wheels, providing a new paradigm for energy-saving idle speed control.

[0038] This invention employs a simplified "two-speed + stepless" design: before operation, the user only needs to press a button once to select the high-speed or low-speed working zone; during operation, the vehicle speed can be smoothly and continuously adjusted using a single push rod. The system structure is simple, and even if the hydraulic efficiency fluctuates, the vehicle speed will only change gradually without causing shift shock.

[0039] The aforementioned continuously variable transmission (CVT) control process constructs a four-tiered progressive safety chain of "state detection - mode selection - direction confirmation - safety unlocking," which not only achieves precise control of the CVT but also significantly improves operational safety and system reliability in complex working environments through sequential dependency and physical interlocking mechanisms. The CVT module of this invention supports continuous adjustment of vehicle speed across the entire engine speed range, balancing maximum torque output and fuel economy.

[0040] like Figure 3The diagram shown is a flowchart of the automatic start mode control for the tractor according to the present invention. The automatic start control method for a continuously variable transmission (CVT) tractor of the present invention can be divided into two start modes based on the difference in the operating sequence of the CVT push rod and the reversing handle. The control system intelligently distinguishes between the two start modes based on the driver's operating sequence of the CVT push rod and the reversing handle, achieving precise and smooth power connection.

[0041] Mode 1: Switch direction first, then adjust speed. When the CVT push lever is in the zero position, first push the reversing handle from neutral to forward or reverse, then push the CVT push lever to start. At this time, since the speed difference between the two ends of the reversing clutch is basically zero, the clutch can quickly complete oil filling and engagement without slippage or impact. At the same time, the current of the CVT proportional solenoid valve is adjusted according to... Figure 2 The control flow shown begins to adjust, achieving continuously variable transmission to ensure a smooth, stable, and low-impact start-up process.

[0042] Mode 2: Preset speed first, then switch direction. After unlocking the CVT push lever, push it to the target percentage position, then move the reversing lever from neutral to forward or reverse to start. In this mode, before the reversing clutch engages, the current to the CVT proportional solenoid valve is... Figure 2 The control flow shown begins to adjust, so a speed difference already exists when the reversing clutch engages; when this speed difference exceeds the set threshold, the system starts closed-loop control: the requested current of the reversing clutch proportional solenoid valve is determined by the superposition of two parts: one is the current corresponding to the ramp torque set based on acceleration, and the other is the current corresponding to the torque obtained by PID adjustment based on the speed difference. This torque closed-loop control enables the system to respond quickly when the speed difference changes abruptly, significantly reducing slippage time and avoiding overshoot or oscillation.

[0043] Specifically, the formula for calculating the requested current of the proportional solenoid valve of the reversing clutch is as follows: I total =I AVeh +I PID =0.3474*(Tq) AVeh +Tq PID ); Tq AVeh =Map(ades_ramp)*e(t); Tq PID =K p *Δω(t)+K i *∫Δω(t)dt+K d *dΔω(t) / dt; In the formula, I total I represents the requested current of the proportional solenoid valve of the reversing clutch. AVehThis indicates the current corresponding to the ramp torque set based on acceleration, used to ensure that the engagement process meets driving expectations. PID This represents the current corresponding to the torque obtained through PID adjustment based on the speed difference, used to eliminate the deviation between the actual and target speeds and improve response accuracy; T qAVeh T is the ramp torque calculated from acceleration. qPID The torque is obtained by PID adjustment of the speed difference. The current coefficient 0.3474 is the system calibration constant, which is derived from the hydraulic valve flow-current characteristic curve to ensure that the current and hydraulic pressure are linearly related.

[0044] T qAVeh In the formula, Map(ades_ramp) is a preset acceleration-torque mapping table, and e(t) is the engagement time function. The calculation of the ramp torque can simulate the experience of "manual smooth gear shifting" and make the engagement process conform to ergonomics.

[0045] T qPID In the formula, Δω(t) is the real-time speed deviation before and after the reversing clutch (input / output), K p K i K d These are the proportional gain, integral gain, and derivative gain of the PID controller, respectively. The torque controlled by this PID closed-loop system dynamically compensates for speed deviations caused by sudden load changes, oil temperature variations, or mechanical lag, based on the ramp torque, thus achieving adaptive and precise control.

[0046] To further optimize starting quality, the ramp torque T qAVeh The slope of the ramp torque can be automatically adjusted according to the commutation input shaft speed and continuously increased within the simulation step size, thus achieving smooth and rapid clutch engagement at different speeds and effectively shortening the slippage time. This is because the torque transmission capability of the clutch system is closely related to the commutation input shaft speed: when the commutation input shaft speed is low, the torque required for clutch engagement is small, and the ramp torque slope should be reduced; when the commutation input shaft speed is high, the torque required for clutch engagement is large, and the ramp torque slope should be increased. Therefore, by introducing the commutation input shaft speed factor Map(N)... InterShul _ramp), automatically corrects the slope of the ramp torque in real time. The specific calculation formula is: Tq AVeh =Map(ades_ramp)*e(t)*Map(N InterShul _ramp).

[0047] Furthermore, users can customize the ramp torque slope via the commutation sensitivity knob to adapt to the starting smoothness requirements under different operating conditions and improve the user experience. For example, setting the commutation sensitivity influence factor Map(Sens_ramp) will output a smaller parameter when the sensitivity knob is 0, slowing down the clutch engagement process and making the start slow and comfortable; when the sensitivity knob is 100, it will output a larger parameter, making the start quick and powerful. The specific calculation formula is as follows: Tq AVeh =Map(ades_ramp)*e(t)*Map(N InterShul _ramp)*Map(Sens_ramp).

[0048] Furthermore, in the closed-loop control of the speed difference, the system uses the deviation between the actual difference in speed before and after the clutch and the predefined speed difference (derived from the tractor's acceleration) as the input for PID control. The predefined speed difference calculation formula is as follows: N CluDiffSet =N CluDiffInit / (Map(ades_N InterShul )*1000)*PSCC_FacLdSetp; In the formula, N CluDiffSet For the predefined speed difference, N CluDiffInit To determine the clutch speed difference at the start of automatic start-up adjustment, Map(ades_N) InterShul The preset commutation input shaft speed-acceleration mapping table, with PSCC_FacL-dSetp as the step size adjustment factor, allows for increased request current when the speed difference is large at the initial engagement stage, accelerating the start-up process and reducing slippage time.

[0049] Based on the above, the controller converts the calculated total torque into the corresponding control current of the proportional solenoid valve of the reversing clutch to complete the automatic start. When the speed difference during clutch engagement is lower than the set threshold, or the engagement time exceeds the set limit, the proportional solenoid valve current will rapidly increase to the maximum value in a preset maximum step size to ensure reliable engagement.

[0050] like Figure 4This is a flowchart of the tractor power reversing mode control of the present invention. Power reversing mode refers to the tractor entering a power reversing state when the reversing handle is turned from the current direction of travel to the opposite direction during tractor movement. The controller determines the clutches that need to be disengaged and engaged based on vehicle status and sensor information, and acquires key parameters such as speed difference, vehicle speed, and oil filling time in real time. Subsequently, the clutch to be disengaged enters a pre-opening stage, and its transmitted torque gradually decreases from its maximum value to the actual input torque value of the engine according to a set curve. Simultaneously, the clutch to be engaged begins pre-engagement, undergoing rapid oil filling until the free travel is completely eliminated. At this time, its hydraulic pressure can only balance the spring force and does not transmit actual torque. When the torque of the disengaging clutch decreases to the actual input torque value of the engine, the torque curve transmitted by the disengaging clutch will be adjusted using closed-loop control. The total torque value of the engaging clutch is calculated by the sum of the preset torque defined by acceleration and the torque determined by PID adjustment, achieving a smooth transition. When the speed difference of the engaging clutch is less than a set threshold, or the engagement time is greater than a set value, the engaging clutch rapidly increases to its maximum torque to complete locking, marking the completion of the power reversing process.

[0051] Specifically, when the clutch torque drops to the engine's actual input torque, the torque curve transmitted by the clutch will be adjusted using closed-loop control, based on a preset torque T defined by acceleration. qAVeh_Offgoing The torque T determined by PID adjustment qPID_Offgoing The sum of these values ​​yields the total torque value T of the disengaged clutch. q_OffGoing The specific calculation formula is as follows: Tq _Offgoing =Tq AVeh_Offgoing +Tq PID_Offgoing ; Tq AVeh_Offgoing =PSCC_TqSSP-Map(ades_N InterShul *PSCC_FacTqOffgPreCtl; Tq PID_Offgoing =K p1 *Δv(t)+K i1 *∫Δv(t)dt+K d1 *dΔv(t) / dt; In the formula, Tq AVeh_Offgoing Let Tq be the ramp torque calculated from acceleration. PID_Offgoing The torque is obtained by PID adjustment based on the vehicle speed difference, PSCC_TqSSP is the current actual engine input torque value, and Map(ades_N) is the torque obtained by PID adjustment based on the vehicle speed difference. InterShul ) represents the preset acceleration-torque mapping table, PSCC_FacTqOffgPreCtl is the ramp torque adjustment factor, and K p1 K i1 K d1These are the proportional gain, integral gain, and derivative gain of the PID controller, respectively, and Δv(t) is the vehicle speed difference.

[0052] Through torque control, the speed difference of the disengaging clutch can be increased according to a certain curve to achieve smooth and rapid disengagement; while the engagement clutch, under the premise of maintaining a certain basic torque, after the torque transmitted by the disengaging clutch drops to zero, adjusts the engagement torque according to the sum of the preset torque defined by another acceleration and the torque determined by PID adjustment. The adjustment process is similar to automatic start, and finally achieves smooth torque transition and speed synchronization.

[0053] Meanwhile, users can also adjust the ramp torque slope value of the clutch engagement using the reversing sensitivity knob to ensure a smooth start under different operating conditions.

[0054] like Figure 5 This is a flowchart illustrating the coordinated control of continuously variable transmission (CVT) and power reversing in a tractor according to the present invention. Because the volumetric efficiency of the variable pump in a continuously variable transmission (HST) module is affected by factors such as individual manufacturing differences, system operating pressure, and hydraulic oil temperature, and because there is a fixed linear correspondence between the percentage position of the HST pushrod and the requested displacement ratio, the requested displacement ratio corresponding to the pushrod being in the zero position is theoretically fixed. However, in actual operation, changes in engine speed, system pressure, or oil temperature can cause fluctuations in the volumetric efficiency of the variable pump, resulting in the inability to consistently and accurately achieve the zero-speed vehicle state with a fixed zero-speed requested displacement ratio.

[0055] To address this issue, when the control system detects that the CVT push lever has returned to zero, in addition to issuing a displacement ratio request corresponding to zero vehicle speed, it simultaneously cuts off the control current of the currently engaged reversing clutch. This forces the vehicle to remain stationary at the mechanical transmission level, unaffected by changes in volumetric efficiency. When the driver pushes the CVT push lever again, the system will re-engage the reversing clutch according to the automatic start-up curve and coordinate with the CVT module to ensure a smooth vehicle start.

[0056] This invention deeply integrates the two core functions of continuously variable transmission and power reversing into a single controller. Through a unified control strategy, it achieves continuous speed adjustment and smooth switching between forward and reverse, thus providing an intelligent solution with extremely simplified operation and precise and smooth response for work scenarios such as small plots and orchards that require frequent speed adjustment and steering.

[0057] In the tractor control system of this invention, the three modes of automatic start, power reversal and continuously variable transmission are precisely switched and seamlessly coordinated through "four-stage safety chain + dual-path collaborative control", thus constructing an intelligent operation closed loop with human-machine collaboration and zero operation errors.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A control system for a low-horsepower continuously variable transmission (CVT) and power reversing tractor, the control system comprising a signal source, a CVT controller, and a terminal actuator, characterized in that, The signal source includes a reversing handle, a continuously variable transmission (CVT) push rod, a motor speed sensor, a reversing input speed sensor, a reversing output speed sensor, a vehicle speed sensor, an oil temperature sensor, and a sensitivity knob. The CVT controller integrates a signal acquisition module, a CVT module, a power reversing module, a torque current conversion module, a fault diagnosis module, and a drive and information transmission module. The terminal actuator includes four proportional solenoid valves and two wet clutches. Two proportional solenoid valves control two oil circuits of the CVT HST to achieve continuously variable transmission of the vehicle. The other two proportional solenoid valves control two wet clutches for power reversing, enabling smooth engagement and disengagement between forward and reverse gears. The driver can achieve automatic tractor start and power reversing functions by changing the position of the reversing handle. By comprehensively adjusting the engine speed and the CVT push rod, the tractor can achieve smooth continuous gear shifting under different working conditions and loads.

2. The control system for a low-horsepower continuously variable transmission and power reversing tractor according to claim 1, characterized in that, The continuously variable transmission (CVT) controller determines the tractor's starting and reversing types based on the power reversing module, and determines whether the tractor needs to accelerate or decelerate based on the CVT module. It calculates the actual displacement ratio output by the HST based on the engine speed value sent from the engine controller's CAN bus and the collected motor speed value. It calculates the real-time speed difference between the forward and reverse clutches based on the collected reversing input and output speed values. Based on the torque signal from the CAN bus sent by the engine controller, it calculates the torque that can be transmitted when each clutch is fully engaged, providing a data foundation for subsequent precise control. The control system, combining the characteristics of each proportional solenoid valve and clutch, calculates the corresponding required current value through the torque current conversion module, which is ultimately executed by the drive and information transmission module to drive the proportional solenoid valves to obtain precise actual current.

3. The control system for a low-horsepower continuously variable transmission and power reversing tractor according to claim 1, characterized in that, The fault diagnosis module monitors the status of all signals in real time. Once an abnormality is detected, the continuously variable transmission controller will immediately send diagnostic information through the CAN bus and automatically take corresponding measures according to the severity of the fault.

4. A control method for a low-horsepower continuously variable transmission (CVT) and power reversing tractor, characterized in that, The tractor adopts the low-horsepower continuously variable transmission and power reversing tractor control system as described in any one of claims 1-3, and the control method is as follows: (1) When the driver starts the engine, the control system will perform a self-check: if the reversing lever is not in neutral, the forward / reverse proportional solenoid valve will be locked at the hardware level and will not be able to obtain the requested current. It must be returned to neutral to unlock the direction control function. Similarly, if the continuously variable transmission push rod is not in the zero position, it must be reset to the zero position before the continuously variable transmission function can be enabled. (2) After the control system performs a self-check, if it is determined that there is no serious fault affecting the operation of the vehicle, the tractor performs coordinated control of automatic start, power reversal and continuously variable transmission. The driver operates the reversing handle, and the continuously variable transmission controller will calculate the real-time speed difference based on the speed of the reversing input / output speed sensor to realize the automatic start and power reversal functions of the vehicle; the driver operates the continuously variable transmission push rod position, and the continuously variable transmission controller controls the vehicle to realize the continuously variable transmission function based on the actual displacement ratio and the requested displacement ratio. (3) If the clutch speed difference exceeds the set value and continues for a specific time during the starting, reversing or driving of the tractor, the controller will immediately cut off the clutch current to prevent clutch wear. At the same time, the instrument will display the corresponding fault code and fault warning information. The driver needs to disconnect the tractor and then reconnect the power to operate the vehicle normally.

5. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 4, characterized in that, The continuously variable transmission (CVT) control process is as follows: After the tractor starts, the engine status and system pressure are first detected. When both the engine speed and system pressure exceed the set threshold, the driver selects the high or low gear range using the high / low gear switch button, and then operates the forward or reverse clutch. If the CVT push lever is not in the zero position at this time, the system will restrict its function, and the driver needs to manually return the push lever to zero to unlock the CVT control function. When the driver pushes the CVT push lever, the controller determines the requested displacement ratio based on the real-time position of the CVT push lever and calculates the actual displacement ratio based on the engine speed and motor output speed. If the difference between the requested value and the actual value exceeds the set threshold, the controller will adjust the current of the two CVT proportional solenoid valves through a PID algorithm to make the actual displacement ratio track the requested displacement ratio, thereby achieving smooth control of the expected vehicle speed. If a power reversal occurs during the CVT process, the CVT maintains the current state until the reversal is completed and continues to adjust according to the displacement ratio deviation.

6. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 4, characterized in that, The tractor includes two starting modes: Mode 1: first switch direction, then adjust speed; Mode 2: first preset speed, then switch direction. The control system intelligently distinguishes between the two starting modes based on the driver's operation sequence of the continuously variable transmission push lever and the reversing handle, achieving precise and smooth power connection.

7. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 6, characterized in that, When the driver has the continuously variable transmission (CVT) push lever in the zero position, first switch the reversing handle from neutral to forward or reverse gear, and then push the CVT push lever to start. The system determines this as "Mode 1". At this time, the speed difference between the two ends of the reversing clutch is close to zero, and the clutch can quickly complete the oil filling and mechanical engagement. At the same time, the CVT proportional solenoid valve adjusts the starting current according to the preset ramp curve to achieve a linear increase in speed. If the driver first pushes the continuously variable transmission (CVT) push lever to the target percentage position and then operates the reversing handle to switch between forward and reverse gears, the system enters "Mode Two". At this time, the CVT module has already established the target displacement, the hydraulic motor starts to accelerate, and a significant speed difference is generated before the reversing clutch engages. When this speed difference exceeds the system's set threshold, the control system activates the dual closed-loop torque compensation mechanism. The requested current of the reversing clutch proportional solenoid valve is determined by the superposition of two parts: one is the current corresponding to the ramp torque set based on acceleration, and the other is the current corresponding to the torque obtained by PID adjustment based on the speed difference. The CVT controller converts the calculated total torque into the corresponding proportional solenoid valve control current to complete the automatic start. When the speed difference during clutch engagement is lower than the set threshold, or the engagement time exceeds the set limit, the proportional solenoid valve current will rapidly rise to the maximum value with a preset maximum step size to ensure reliable engagement.

8. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 7, characterized in that, The slope of the ramp torque can be automatically adjusted according to the rotational input shaft speed and continuously increased within the simulation step size, so as to achieve smooth and fast clutch engagement at different speeds. By introducing the rotational input shaft speed factor Map, the slope of the ramp torque is automatically corrected in real time. Users can also customize the ramp torque slope through the rotational sensitivity knob to adapt to the starting smoothness requirements under different working conditions.

9. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 4, characterized in that, The power reversing control process is as follows: During tractor travel, the reversing handle is moved from the current direction of travel to the opposite direction, at which point the tractor enters the power reversing state. The controller will determine the clutches that need to be disengaged and engaged based on the vehicle status and sensor information, and will acquire the speed difference, vehicle speed, and oil filling time in real time. Subsequently, the clutch to be disengaged enters the pre-opening stage, and its transmitted torque gradually decreases from the maximum value to the actual input torque value of the engine according to the set curve. At the same time, the clutch to be engaged begins to pre-engage, and rapid oil filling is carried out until the free stroke is completely eliminated. At this time, its hydraulic pressure can only balance the spring force and does not transmit actual torque. When the torque of the disengaging clutch decreases to the actual input torque value of the engine, the torque curve transmitted by the disengaging clutch will be adjusted by closed-loop control. The total torque value of the disengaging clutch is calculated by the sum of the preset torque defined by acceleration and the torque determined by PID adjustment, and finally the torque smooth transition and speed synchronization are achieved. When the speed difference of the engaging clutch is less than the set threshold, or the engagement time is greater than the set value, the engaging clutch quickly increases to the maximum torque to complete the locking, marking the completion of the power reversing process.

10. The control method for a low-horsepower continuously variable transmission and power reversing tractor according to claim 4, characterized in that, When the control system detects that the continuously variable transmission (CVT) push lever has returned to zero, it will simultaneously cut off the control current of the currently engaged reversing clutch while issuing a displacement ratio request corresponding to zero vehicle speed. This forces the vehicle to stand still at the mechanical transmission level, unaffected by changes in volumetric efficiency. When the driver pushes the CVT push lever again, the system will re-engage the reversing clutch according to the automatic start-up curve and work in coordination with the CVT module to ensure a smooth start for the vehicle.

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