A tractor load adaptive gear shifting and brake coordination control system and method

Abstract

The application relates to a tractor load-adaptive gear shifting and brake coordination control system and method, and relates to the technical field of tractor control, which comprises a four-state state machine of a parking state, a starting transition state, a running state and a parking transition state, state migration is carried out according to operation parameters; in the parking state, brake pressure target values are determined according to clutch output shaft torque, and brakes are applied to inhibit self-walking caused by oil viscosity changes; when starting, brake pressure is synchronously released with clutch pre-oil; in the running state, gear shifting decisions are determined by inquiring into a gear shifting MAP table according to engine speed and clutch output shaft torque, a hysteresis interval and a minimum gear shifting interval are set to prevent frequent gear shifting; and pre-oil time, joint pressure and pressure change rate are compensated according to hydraulic oil temperature. The application realizes unified and coordinated control of brake coordination, load-adaptive gear shifting and temperature compensation, and improves the safety and smoothness of the tractor.

Description

Technical Field

[0001] This invention relates to the field of tractor control technology, and in particular to a control system and method for tractor load adaptive shifting and braking coordination. Background Technology

[0002] As an important piece of agricultural machinery, the power shift gearbox of a tractor plays a crucial role in transmitting and changing power during operation. Hi-Lo two-speed power shift gearboxes achieve gear switching through the alternating engagement of high-gear and low-gear clutches, offering the advantage of uninterrupted power during gear changes and are widely used in medium and large tractors. However, in practical use, existing power shift control systems still have many shortcomings, affecting the tractor's operational safety, shifting smoothness, and clutch lifespan.

[0003] When the tractor is stationary, it typically relies on clutch disengagement to cut off power transmission. However, the viscosity of hydraulic oil increases significantly in low-temperature environments or after prolonged standing. Even when the clutch friction plates and steel plates are disengaged, the viscosity of the oil can increase the drag torque, leading to sudden shifting or self-propelled movement. This drag torque, transmitted through the transmission system to the drive wheels, may cause the tractor to move slowly, i.e., self-propelled movement. Self-propelled movement not only poses safety hazards but can also lead to accidental collisions on slopes or in confined spaces. In existing technologies, braking control when the tractor is stationary is usually manually operated by the driver, lacking an automatic braking compensation mechanism based on the drag torque, and thus failing to effectively suppress self-propelled movement when unattended or when the driver fails to react in time.

[0004] In terms of shift control, existing technologies mostly employ fixed shift strategies based on vehicle speed and throttle opening, failing to fully reflect the actual load conditions of the tractor. When a tractor is operating in the field, the load fluctuates significantly with changes in soil conditions, tillage depth, and operating speed. When the load suddenly increases, the fixed shift strategy may fail to downshift in time, causing a sharp drop in engine speed or even stalling; conversely, when the load suddenly decreases, it may fail to upshift in time, resulting in excessively high engine speed and increased fuel consumption. Furthermore, existing shift control typically uses fixed parameters for filling time, engagement point pressure, and pressure change rate, without considering the impact of hydraulic oil temperature on viscosity. In low-temperature environments, oil viscosity increases, resulting in a slower filling speed and lower engagement point pressure under fixed parameters, leading to insufficient clutch engagement or excessively long engagement time. In high-temperature environments, oil viscosity decreases, resulting in a faster filling speed and higher engagement point pressure under fixed parameters, easily causing engagement shock and pressure overshoot. These problems result in poor consistency in shift quality across a wide temperature range for existing shift control systems.

[0005] During start-up, the coordinated control of brake release and clutch engagement also has shortcomings. In existing technologies, brake release and clutch pre-filling are often controlled independently, and their completion times lack precise synchronization. If the braking force is released before the clutch engages, the tractor may briefly roll or slip before the clutch has delivered sufficient torque; if the braking force is released after the clutch engages, noticeable start-up jerking occurs, affecting driving smoothness. Furthermore, under conditions of frequent load fluctuations, existing control strategies lack effective mechanisms to prevent frequent gear shifting, easily leading to continuous rapid gear shifts, accelerating clutch friction plate wear, and shortening its service life.

[0006] In summary, existing tractor power shift control technology has significant shortcomings in areas such as parking brake coordination, load adaptive shifting, temperature compensation, and start-up coordination control, making it difficult to meet the comprehensive requirements of tractors for safety, smoothness, and durability under complex working conditions. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention discloses a control system and method for tractor load adaptive shifting and braking coordination.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A control method for adaptive shifting and braking coordination of a tractor under load includes the following steps:

[0010] A1. State machine management steps: Establish a four-state state machine including parking state, start transition state, driving state and parking transition state, and perform state transition between each state according to the tractor operating parameters;

[0011] A2. Braking Coordination Steps: In the parking state, the clutch output shaft torque is obtained, the target value of the braking pressure is determined based on the clutch output shaft torque, and braking is applied to suppress self-propelled movement caused by the increase in clutch drag torque due to the increase in oil viscosity; in the starting transition state, the braking pressure is released synchronously with the execution of clutch pre-charging.

[0012] A3. Load-adaptive shifting steps: In driving mode, obtain engine speed and clutch output shaft torque, determine shifting decisions based on preset shifting MAP table, and execute shifting control;

[0013] A4. Temperature compensation steps: Obtain the hydraulic oil temperature and compensate the control parameters during the gear shifting process based on the hydraulic oil temperature.

[0014] Preferably, in the braking coordination step:

[0015] The target value of braking pressure is linearly related to the clutch output shaft torque. The clutch output shaft torque is divided into multiple torque ranges, and each torque range corresponds to a target value of braking pressure.

[0016] During the start-up transition, the braking pressure is released linearly in stages as the clutch pre-filling is performed, so that the completion time of brake release is synchronized with the completion time of clutch pre-filling.

[0017] When the driver is detected to have pressed the brake pedal, the braking coordination steps immediately cease execution, transferring braking control to the driver.

[0018] Preferably, in the load adaptive shifting step:

[0019] The shift MAP uses engine speed and clutch output shaft torque as input dimensions, and upshift, downshift or hold as output decisions;

[0020] The shift MAP table has a hysteresis range set. When the engine speed is within the hysteresis range, the current gear is maintained.

[0021] Set an interval timer so that if the time interval between two shift commands is less than the preset minimum interval, the second shift command is ignored.

[0022] Preferably, in the load adaptive shifting step, the shifting control process includes four stages executed sequentially:

[0023] Pre-filling stage: Fill the clutch corresponding to the target gear with oil, so that the clutch pressure rises to the engagement point pressure;

[0024] Torque phase stage: The clutch pressure of the target gear gradually increases, while the clutch pressure of the current gear gradually decreases. The two clutch pressures cross at the midpoint, keeping the total transmitted torque constant.

[0025] Inertial phase stage: The clutch pressure of the target gear continues to rise, while the clutch pressure of the current gear continues to decrease until disengagement;

[0026] Locking phase: The clutch pressure of the target gear rises to the locking pressure, completing the gear shift.

[0027] Preferably, in the temperature compensation step:

[0028] The temperature range is divided into multiple temperature zones, with a compensation coefficient set for each temperature zone, using a preset reference temperature as the boundary.

[0029] The compensation coefficients are applied to three control parameters: oil filling time, joint pressure, and pressure change rate.

[0030] Based on the actual detected hydraulic oil temperature, linear interpolation is performed using the compensation coefficients of adjacent temperature ranges to obtain the compensation coefficient at the current temperature, which is then applied.

[0031] Preferably, the transition conditions for each state in the state machine are as follows:

[0032] When the tractor is stationary and its speed is zero, it enters the parking state;

[0033] When a start request is detected, the system transitions from the stop state to the start transition state and simultaneously activates the braking coordination step.

[0034] When the start-up transition is completed and the vehicle speed is greater than the preset threshold, the vehicle transitions from the start-up transition state to the driving state, and at the same time, the load adaptive shifting step is activated.

[0035] When a parking request is detected, the system transitions from driving state to parking transition state, and disables the load adaptive shifting step.

[0036] When the parking transition is completed and the vehicle speed drops to zero, the vehicle transitions from the parking transition state to the parking state.

[0037] A tractor load-adaptive shifting and braking coordination control system includes:

[0038] The state machine management module is used to execute state machine management steps;

[0039] Braking coordination module, used to execute braking coordination steps;

[0040] The load adaptive shifting module is used to execute the load adaptive shifting steps;

[0041] The temperature compensation module is used to perform the temperature compensation steps.

[0042] Preferably, it further includes:

[0043] The sensor group includes an engine speed sensor, a clutch output shaft torque sensor, a clutch output shaft speed sensor, a gear position sensor, an oil temperature sensor, a vehicle speed sensor, a brake pressure sensor, and a brake switch;

[0044] The controller is connected to the sensor group, the braking coordination module and the load adaptive shifting module. The controller stores a shifting MAP table and a temperature compensation coefficient table.

[0045] The braking actuator is connected to the braking coordination module via signals and is used to perform braking actions according to the braking pressure command output by the braking coordination module.

[0046] Preferably, the load adaptive shifting module includes:

[0047] The shift decision unit is used to query the shift MAP table based on the engine speed and clutch output shaft torque, and output a shift decision of upshifting, downshifting or holding.

[0048] The shift execution unit is used to control the pressure of the high-gear clutch and the low-gear clutch to change according to a preset curve after receiving the shift decision, so as to complete the shift.

[0049] The anti-frequent shifting unit is used to set a hysteresis range and a minimum shift interval. When the engine speed is within the hysteresis range or the interval between two shift commands is less than the minimum shift interval, shifting is prohibited.

[0050] Preferably, the temperature compensation module includes:

[0051] Temperature detection unit for real-time monitoring of hydraulic oil temperature;

[0052] The compensation coefficient determination unit is used to determine the current temperature range based on the hydraulic oil temperature within a preset temperature range, and to calculate the compensation coefficient at the current temperature through linear interpolation.

[0053] The parameter correction unit is used to apply the compensation coefficient to the oil filling time, engagement point pressure and pressure change rate to correct the control parameters during the shift control process.

[0054] By employing the technical solution described above, the present invention has the following beneficial effects:

[0055] (1) This invention automatically determines the target value of braking pressure based on the clutch output shaft torque and applies braking while the vehicle is stationary. This can compensate in real time for the increase in drag torque caused by the increase in oil viscosity, effectively suppressing the self-driving phenomenon of the tractor after being stationary for a long time at low temperatures, and eliminating the safety hazard of the vehicle driving on its own when the driver forgets to disengage the main and auxiliary gears and does not engage the handbrake. At the same time, in the transition state of starting, the braking pressure is released synchronously with the execution of clutch pre-filling, ensuring that the moment of brake release is precisely synchronized with the moment of clutch engagement. This avoids both the brief slippage caused by premature release of braking force and the start-up jerking caused by delayed release of braking force, significantly improving the smoothness and safety of the starting process.

[0056] (2) This invention constructs a shift MAP table with engine speed and clutch output shaft torque as input dimensions, enabling shift decisions to reflect the actual load status of the tractor in real time. When the load increases, it automatically downshifts to obtain greater torque output capability, and when the load decreases, it automatically upshifts to improve transmission efficiency and reduce fuel consumption, overcoming the shortcomings of traditional fixed shift strategies that cannot adapt to load changes. At the same time, by setting a dual anti-frequent shifting mechanism of hysteresis interval and minimum shift interval in the MAP table, it effectively avoids the phenomenon of continuous rapid shifting under field working conditions with frequent load fluctuations, protects the clutch friction plates, and extends their service life.

[0057] (3) This invention divides multiple temperature ranges with a preset reference temperature as the boundary, and sets compensation coefficients for three dimensions—filling time, engagement point pressure, and pressure change rate—for each temperature range, thereby achieving systematic compensation for the viscosity of hydraulic oil as a function of temperature. At low temperatures, the filling time is automatically extended, the engagement point pressure is increased, and the pressure change rate is reduced; at high temperatures, the filling time is shortened, reduced, and increased accordingly, ensuring consistent shifting quality and clutch engagement reliability across the entire temperature range from -40℃ to 100℃. Linear interpolation of the compensation coefficients between adjacent temperature ranges further eliminates parameter abrupt changes at the temperature range boundaries, ensuring a continuous and smooth control process.

[0058] (4) This invention establishes a four-state state machine comprising parking state, starting transition state, driving state, and parking transition state, integrating the three major functions of braking coordination, load adaptive shifting, and temperature compensation into a unified control framework. Each functional module is activated or disabled only in its corresponding state, avoiding logical conflicts and mutual interference between functions and ensuring the orderliness and rigor of the control process. Multiple judgment criteria, such as vehicle speed threshold and pedal signal, are introduced into the state transition conditions, effectively preventing state misjudgment and jitter caused by sensor noise or transient disturbances, thereby improving the robustness and reliability of the system. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the control system structure in an embodiment of the present invention;

[0060] Figure 2 This is a state transition diagram in an embodiment of the present invention;

[0061] Figure 3 This is a graph showing the relationship between braking coordination pressure and clutch output shaft torque in an embodiment of the present invention.

[0062] Figure 4 This is a schematic representation of the shift MAP in the embodiments of the present invention;

[0063] Figure 5 This is a schematic diagram of the temperature compensation coefficient in an embodiment of the present invention;

[0064] Figure 6 This is a flowchart of the control system implementation method of the present invention. Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0066] Combined with appendix Figures 1-6 The present invention discloses a tractor load adaptive shifting and braking coordination control system and method according to some embodiments, comprising the following steps:

[0067] A1. State machine management steps: Establish a four-state state machine including parking state, start transition state, driving state and parking transition state, and perform state transition between each state according to the tractor operating parameters;

[0068] A2. Braking Coordination Steps: In the parking state, the clutch output shaft torque is obtained, the target value of the braking pressure is determined based on the clutch output shaft torque, and braking is applied to suppress self-propelled movement caused by the increase in clutch drag torque due to the increase in oil viscosity; in the starting transition state, the braking pressure is released synchronously with the execution of clutch pre-charging.

[0069] A3. Load-adaptive shifting steps: In driving mode, obtain engine speed and clutch output shaft torque, determine shifting decisions based on preset shifting MAP table, and execute shifting control;

[0070] A4. Temperature compensation steps: Obtain the hydraulic oil temperature and compensate the control parameters during the gear shifting process based on the hydraulic oil temperature.

[0071] See Figure 1 In this embodiment, the control method operates within the tractor's electronic control unit (ECU). This ECU is communicatively connected to the engine speed sensor, clutch output shaft torque sensor, clutch output shaft speed sensor, gear position sensor, oil temperature sensor, vehicle speed sensor, accelerator pedal position sensor, brake pressure sensor, and brake switch, collecting signals from these sensors in real time. In this embodiment, the tractor uses a Hi-Lo two-speed power shift gearbox, where the high-speed clutch corresponds to Hi gear and the low-speed clutch corresponds to Lo gear, ensuring uninterrupted power during gear switching. In the state machine management steps, the four-state state machine is as follows: Figure 2 As shown, including parking status Start-up and transition state Driving status and parking transition status There are four states, and the states switch between each other according to preset transition conditions. In the parking state... At this point, the tractor is stationary with zero speed and the engine idling. The braking coordination function is active, while the load adaptive shifting function and temperature compensation function are in standby mode. This is during the start-up transition phase. When the driver requests to start, the brake coordination function continues to synchronously release the brake pressure, while the clutch begins to pre-fill with oil in preparation for power engagement. During driving... Under normal tractor operation, the load adaptive shifting function is activated, the temperature compensation function is activated simultaneously, and the braking coordination function is deactivated. During the stop transition state... The driver issues a stop request, the load adaptive shift function is disabled, the clutch gradually disengages, the vehicle speed gradually decreases to zero, and then returns to a stop state. The aforementioned four-state machine configuration ensures that the three main functions—braking coordination, load-adaptive shifting, and temperature compensation—operate in a coordinated manner within a unified control framework. Each functional module is activated only in its corresponding state, avoiding conflicts and interference between functions. For example, in the parking state, only the braking coordination function is activated to prevent the tractor from self-propelling due to an unexpected increase in drag torque caused by increased oil viscosity; in the driving state, only the load-adaptive shifting and temperature compensation functions are activated to ensure the accuracy of shifting decisions and the smoothness of shifting execution. Furthermore, the transitions between states have clear directions and conditional constraints, guaranteeing the logical rigor of the control process.

[0072] In some embodiments, during the braking coordination step: the target value of the braking pressure is linearly related to the clutch output shaft torque, and the clutch output shaft torque is divided into multiple torque ranges, each torque range corresponding to a target value of braking pressure; during the start-up transition state, the braking pressure is released linearly in stages as the clutch pre-filling is executed, so that the completion time of braking release is synchronized with the completion time of clutch pre-filling; when the driver is detected to have pressed the brake pedal, the braking coordination step immediately stops executing, and the braking control is transferred to the driver.

[0073] See Figure 3 The specific implementation process of the braking coordination step is as follows. In the parking state... The electronic control unit continuously collects the torque signal output by the clutch output shaft torque sensor. Because the viscosity of hydraulic oil increases at low temperatures or after prolonged standing, even when the clutch friction plates and steel plates are separated, the viscosity of the oil will increase the drag torque. This drag torque, transmitted to the output shaft, may drive the tractor to move slowly, resulting in self-propelled movement. To suppress this self-propelled movement, the electronic control unit determines the target value of the braking pressure to be applied based on the magnitude of the clutch output shaft torque. Specifically, the clutch output shaft torque is divided into three torque ranges: when the clutch output shaft torque is in the first torque range (i.e., the torque value is greater than or equal to zero and less than the first torque threshold)... When ), the first braking pressure is applied. When the clutch output shaft torque is in the second torque range (i.e., the torque value is greater than or equal to...) And less than the second torque threshold When ), a second braking pressure is applied. When the clutch output shaft torque is in the third torque range (i.e., the torque value is greater than or equal to...) And less than the third torque threshold When ), apply the third braking pressure. .in, , , The preset torque boundary value, and < < Accordingly, < < Within each torque range, there is a linear relationship between braking pressure and clutch output shaft torque; that is, braking pressure increases linearly with increasing clutch output shaft torque. This is especially true during the initial transition phase. When the driver presses the accelerator pedal to initiate a start-up request, the electronic control unit (ECU) immediately activates the clutch pre-filling procedure. Simultaneously, the brake coordination function begins to execute a graded linear release of brake pressure. The release rate of the brake pressure matches the filling rate of the clutch pre-filling, ensuring that the moment the brake pressure drops to zero is synchronized with the moment the clutch pre-filling is completed. Through this synchronized control, the braking force is completely released precisely at the instant the clutch begins to transmit torque, avoiding start-up jerks caused by residual braking force and preventing brief periods of self-driving due to premature release of braking force before the clutch is fully engaged. When the ECU detects that the driver has actively pressed the brake pedal, regardless of the current stage of the brake coordination function, it immediately stops brake coordination control, completely transferring control of the braking system to the driver. This ensures that the driver has complete control over the braking system at all times, guaranteeing driving safety.

[0074] In some embodiments, in the load-adaptive shifting step: the shift MAP table takes engine speed and clutch output shaft torque as input dimensions and upshift, downshift, or hold as output decisions; the shift MAP table is set with a hysteresis interval, and when the engine speed is within the hysteresis interval, the current gear is maintained; an interval timer is set, and when the time interval between two shift commands is less than a preset minimum interval, the latter shift command is ignored.

[0075] See Figure 4 The specific implementation process of the load-adaptive shifting step is as follows. During driving... The electronic control unit (ECU) simultaneously acquires the engine speed signal from the engine speed sensor and the torque signal from the clutch output shaft torque sensor at preset intervals. The ECU internally stores a two-dimensional shift map, where the horizontal axis represents engine speed and the vertical axis represents clutch output shaft torque. Each grid cell in the map stores the corresponding shift decision, including upshifting (from low to high), downshifting (from high to low), or maintaining the current gear. Specifically, the engine speed is divided into multiple speed ranges, with a first speed threshold... Second speed threshold and the third speed threshold The clutch output shaft torque is divided into multiple torque ranges, with a first torque threshold as the boundary. Second torque threshold and the third torque threshold As a boundary. When the engine speed is lower than And the clutch output shaft torque is greater than When the engine speed is higher than a certain value, the MAP outputs a downshift decision; when the engine speed is higher than a certain value... And the clutch output shaft torque is less than When the tractor load increases, the clutch output shaft torque increases, and the engine speed decreases due to the increased load. In this case, the MAP output decides to downshift, causing the transmission to switch to the Lo gear, which has a stronger torque amplification capability. Conversely, when the tractor load decreases, the clutch output shaft torque decreases, and the engine speed increases due to the reduced load. In this case, the MAP output decides to upshift, causing the transmission to switch to the Hi gear, which has higher transmission efficiency. To prevent frequent shifting under critical operating conditions, the shift MAP includes a hysteresis range with a width of ±50 rpm. This hysteresis range creates a 50 rpm speed hysteresis band between the upshift and downshift boundaries. When the engine speed falls within this hysteresis band, regardless of the clutch output shaft torque level, the current gear is maintained, and no shifting action is performed. In addition, the electronic control unit is equipped with an interval timer, which records the time when the last gear shift was completed. When a new gear shift decision is made, the electronic control unit determines whether the time interval between the current time and the time when the last gear shift was completed is less than a preset minimum interval. In this embodiment, the minimum interval is 3 seconds. If the time interval is less than 3 seconds, the current gear shift decision is ignored, and the gear shift operation is not performed until the time interval meets the minimum interval requirement before the next gear shift can be performed. The dual setting of the hysteresis interval and the interval timer effectively avoids the phenomenon of continuous rapid gear shifts under conditions of frequent load fluctuations, protects the service life of the clutch friction plates, and improves driving smoothness.

[0076] In some embodiments, the load-adaptive shifting step includes four sequentially executed stages: pre-filling stage: filling the clutch corresponding to the target gear with oil, causing the clutch pressure to rise to the engagement point pressure (i.e., the kisspoint pressure); torque phase stage: the clutch pressure of the target gear gradually increases, while the clutch pressure of the current gear gradually decreases, and the two clutch pressures cross at the midpoint, keeping the total transmitted torque constant; inertia phase stage: the clutch pressure of the target gear continues to rise, while the clutch pressure of the current gear continues to decrease until disengagement; locking stage: the clutch pressure of the target gear rises to the locking pressure, completing the shift.

[0077] Taking shifting from Lo to Hi as an example, the four stages of the shift control process are as follows: In the pre-filling stage, the electronic control unit sends a filling command to the proportional solenoid valve corresponding to the high-gear clutch. Hydraulic oil enters the cylinder of the high-gear clutch through the proportional solenoid valve, pushing the piston to move and eliminating the gap between the clutch friction plates and steel plates. The pressure of the high-gear clutch gradually rises from zero to the engagement point pressure. In this stage, the low-gear clutch remains fully engaged, and power transmission is uninterrupted. In the torque phase, the pressure of the high-gear clutch gradually rises from the engagement point pressure, while the pressure of the low-gear clutch gradually decreases from its current operating pressure. The two pressure change curves intersect at the midpoint. At the intersection, the sum of the torque transmitted by the high-gear clutch and the torque transmitted by the low-gear clutch equals the total transmitted torque before the shift. That is, the total transmitted torque remains constant throughout the entire torque phase, and power is uninterrupted. This intersection ensures that the torque output of the transmission system is continuous and smooth during the shift, and the driver will not feel any significant power interruption or shock. In the inertia phase, the pressure of the high-gear clutch continues to rise, and the pressure of the low-gear clutch continues to decrease until complete disengagement. The proportional solenoid valve corresponding to the low-gear clutch de-energizes and releases pressure. During this process, the inertial torque of the transmission system is gradually borne by the high-gear clutch, and the engine speed and output shaft speed gradually approach the synchronous speed corresponding to the Hi gear. In the locking phase, the pressure of the high-gear clutch continues to rise to the preset locking pressure, the high-gear clutch is fully engaged, and the shifting process ends. At this time, the electronic control unit updates the current gear status to Hi gear and records the moment the shift is completed for use by the interval timer. The downshifting process (switching from Hi gear to Lo gear) is symmetrical to the upshifting process described above; that is, the target gear is the low-gear clutch, and the current gear is the high-gear clutch. The pressure change direction in each stage is opposite to that in the upshifting process, but the control logic is the same.

[0078] In some embodiments, in the temperature compensation step: the temperature range is divided into multiple temperature intervals with a preset reference temperature as the boundary, and a compensation coefficient is set for each temperature interval; the compensation coefficients are applied to three control parameters: oil filling time, contact pressure, and pressure change rate; based on the actual detected hydraulic oil temperature, linear interpolation is performed using the compensation coefficients of adjacent temperature intervals to obtain the compensation coefficient at the current temperature and apply it.

[0079] See Figure 5The specific implementation process of the temperature compensation step is as follows: The oil temperature sensor detects the temperature of the transmission hydraulic oil in real time and transmits the temperature signal to the electronic control unit. Since the viscosity of hydraulic oil changes significantly with temperature (increasing at low temperatures and decreasing at high temperatures), without compensation, it will lead to clutch filling time deviation, engagement point pressure offset, and inaccurate pressure change rate, thus affecting shifting quality. In this embodiment, 50℃ is used as the preset reference temperature, and the operating temperature range is divided into seven temperature intervals: -40~-20℃, -20~0℃, 0~20℃, 20~40℃, 40~60℃, 60~80℃, and 80~100℃, covering the complete operating temperature range from -40℃ to 100℃. Each temperature interval corresponds to a set of compensation coefficients, which includes three components: filling time compensation coefficient, engagement point pressure compensation coefficient, and pressure change rate compensation coefficient.

[0080] Specifically, in the seven temperature ranges of -40~-20℃, -20~0℃, 0~20℃, 20~40℃, 40~60℃, 60~80℃, and 80~100℃, the oil filling time compensation coefficients are respectively... , , , 0 , The pressure compensation coefficients at the joint points are respectively , , , 0 , The pressure change rate compensation coefficients are respectively , , , 0 , The 40–60℃ temperature range includes a preset reference temperature of 50℃. All three compensation coefficients for this range are 0, indicating that no compensation correction is needed near the reference temperature. The compensation coefficients for temperatures below the reference temperature range (…) ~ , ~ , ~ ) is used to compensate for the effect of increased oil viscosity at low temperatures; the compensation coefficient is higher than the reference temperature range ( , , , , , It is used to compensate for the effect of reduced oil viscosity at high temperatures.

[0081] When the actual detected hydraulic oil temperature is exactly equal to the boundary value of a certain temperature range, the compensation coefficient corresponding to that range is directly used. When the actual detected hydraulic oil temperature is between the boundaries of two adjacent temperature ranges, a linear interpolation method is used to calculate the compensation coefficient at the current temperature. Let the actual oil temperature be... It is located at the boundary of two adjacent temperature ranges. and Between, the compensation coefficients for the corresponding two intervals are respectively and The compensation coefficient at the current temperature Calculate using the following formula:

[0082]

[0083] The calculated compensation coefficients are applied to three parameters in the shift control process: the oil filling time compensation coefficient corrects the oil filling duration during the pre-filling phase. At low temperatures, increased viscosity slows the oil filling speed, requiring a longer filling time; at high temperatures, the filling time is shortened. The engagement point pressure compensation coefficient corrects the target value of the engagement point pressure. At low temperatures, increased viscous resistance necessitates a higher engagement point pressure to ensure reliable clutch engagement; at high temperatures, the engagement point pressure is reduced to avoid engagement shock. The pressure change rate compensation coefficient corrects the slope of clutch pressure changes in the torque and inertial phases. At low temperatures, the change rate is reduced to compensate for the response lag caused by increased oil flow resistance; at high temperatures, the change rate is increased to match the actual response of enhanced oil flowability. Through the combined compensation of these three parameters, shift control maintains consistent shift quality across the entire temperature range from -40℃ to 100℃.

[0084] In some embodiments, the transition conditions for each state in the state machine are as follows: when the tractor is stopped and its speed is zero, it enters the parking state; when a start request is detected, it transitions from the parking state to the start transition state, and simultaneously activates the braking coordination step; when the start transition is completed and the speed is greater than a preset threshold, it transitions from the start transition state to the driving state, and simultaneously activates the load adaptive shifting step; when a stop request is detected, it transitions from the driving state to the parking transition state, and simultaneously disables the load adaptive shifting step; when the parking transition is completed and the speed drops to zero, it transitions from the parking transition state to the parking state.

[0085] See Figure 2 and 6 The state machine transition conditions are implemented as follows: Parking state. The entry conditions are: the vehicle speed detected by the vehicle speed sensor is zero, and both the high-gear clutch and the low-gear clutch are fully disengaged. In a stationary state... In this state, the electronic control unit activates the braking coordination function, continuously monitoring the clutch output shaft torque and applying corresponding braking pressure. The start-up request is detected as follows: the electronic control unit detects that the accelerator pedal position signal is greater than a preset start-up threshold, and the gear selection signal is valid. Once these conditions are met, the state machine transitions from the stop state. Migration to the initial transition state In the initial transition phase Under these conditions, the braking coordination function performs a graded linear release of braking pressure, and the clutch pre-charging procedure is executed synchronously. When the clutch pre-charging is complete, the braking pressure drops to zero, and the vehicle speed detected by the vehicle speed sensor is greater than a preset threshold, the start-up transition is determined to be complete, and the state machine transitions from the start-up transition state. Transfer to driving status In driving condition Under these conditions, the load-adaptive shifting function and temperature compensation function are activated, and the electronic control unit executes shifting decisions and shifting control according to a preset cycle. The detection method for a stop request is as follows: the electronic control unit detects that the brake pedal position signal is greater than a preset stop threshold, or the accelerator pedal position signal drops to zero and the vehicle speed continues to decrease. After these conditions are met, the state machine transitions from the driving state. Move to parking transition state During the parking transition period Under these conditions, the load-adaptive shifting function is disabled, and no new shift decisions are generated; the clutch gradually disengages, and the engine speed drops back to idle. When the vehicle speed detected by the vehicle speed sensor drops to zero, the parking transition is determined to be complete, and the state machine transitions from the parking transition state. Return to parking status The braking coordination function is then reactivated. The aforementioned state transition conditions ensure the orderly activation and disabling of each functional module, avoiding logical conflicts such as performing gear shifting during start-up or while stationary. Simultaneously, a vehicle speed threshold is set as the judgment criterion in the state transition conditions to avoid misjudgments and state fluctuations caused by sensor noise or transient disturbances.

[0086] A tractor load adaptive shifting and braking coordination control system disclosed in some embodiments of the present invention includes: a state machine management module configured to execute the state machine management steps in the above control method; a braking coordination module configured to execute the braking coordination steps in the above control method; a load adaptive shifting module configured to execute the load adaptive shifting steps in the above control method; and a temperature compensation module configured to execute the temperature compensation steps in the above control method.

[0087] The control system in this embodiment comprises four functional modules: a state machine management module, a braking coordination module, a load adaptive shifting module, and a temperature compensation module. All four modules operate within the electronic control unit (ECU). The state machine management module, as the system's top-level scheduling module, is responsible for maintaining the current state, determining transition conditions, executing state transitions, and sending activation or deactivation commands to the other three modules during state transitions. Upon receiving the activation command from the state machine management module, the braking coordination module calculates the target braking pressure value based on the signal from the clutch output shaft torque sensor and applies or releases the braking pressure through the braking execution unit. Upon receiving the activation command from the state machine management module, the load adaptive shifting module queries the shifting MAP table based on engine speed and clutch output shaft torque, outputs a shifting decision, and executes shifting control. The temperature compensation module continuously operates, providing the load adaptive shifting module with temperature-corrected control parameters. The four modules coordinate through data exchange within the ECU, and the state machine management module controls the enabling of each module's operation through state flags. The modular design of this system ensures that each function is independent yet coordinated. When one module needs to adjust parameters or upgrade its control strategy, it does not affect the normal operation of other modules, which is beneficial for system maintenance and expansion.

[0088] In some embodiments, the system further includes: a sensor group, including an engine speed sensor, a clutch output shaft torque sensor, a clutch output shaft speed sensor, a gear position sensor, an oil temperature sensor, a vehicle speed sensor, a brake pressure sensor, and a brake switch; a controller, connected to the sensor group, the brake coordination module, and the load adaptive shifting module, the controller storing a shifting MAP table and a temperature compensation coefficient table; and a brake execution unit, connected to the brake coordination module, for executing braking actions according to the brake pressure command output by the brake coordination module.

[0089] See Figure 1The sensor array includes an engine speed sensor to detect the engine's real-time speed. A clutch output shaft torque sensor, installed on the gearbox output shaft, detects the transmitted torque in real-time. A clutch output shaft speed sensor, also installed on the gearbox output shaft, detects the output shaft's speed in real-time. A gear position sensor detects the current gear. An oil temperature sensor detects the real-time temperature of the hydraulic oil. A vehicle speed sensor detects the tractor's real-time speed. A brake pressure sensor, installed in the brake hydraulic lines, detects the real-time pressure of the braking system. A brake switch detects whether the user is braking. The controller, the core processing component of the electronic control unit, stores a shift MAP table and a temperature compensation coefficient table in its internal memory. The shift MAP table is a two-dimensional data table indexed by engine speed and clutch output shaft torque, storing corresponding shift decisions. The temperature compensation coefficient table contains multiple sets of data, each corresponding to a temperature range, including three components: oil filling time compensation coefficient, engagement point pressure compensation coefficient, and pressure change rate compensation coefficient. The controller receives signals from the sensor array, performs internal calculations, and outputs control commands to the brake actuator and proportional solenoid valve. The brake actuator unit is connected to the brake coordination module. The brake pressure command output by the brake coordination module is converted into a drive signal for the brake actuator unit via a controller. The brake actuator unit adjusts the brake pressure according to the drive signal, thereby controlling the braking force on the tractor. When the brake coordination module outputs a brake release command, the brake actuator unit gradually reduces the brake pressure, and the braking force is gradually released. The independent setting of the brake actuator unit allows the brake coordination function to be implemented without changing the original brake pipeline structure of the tractor, reducing the system's modification cost and integration difficulty.

[0090] In some embodiments, the load-adaptive shifting module includes: a shifting decision unit, configured to query a shifting MAP table based on engine speed and clutch output shaft torque, and output a shifting decision of upshifting, downshifting, or holding; a shifting execution unit, configured to control the pressure of the high-gear clutch and the low-gear clutch to change according to a preset curve after receiving the shifting decision, thereby completing the shifting; and an anti-frequent shifting unit, configured to set a hysteresis range and a minimum shifting interval, and to prohibit shifting when the engine speed is within the hysteresis range or the interval between two shifting commands is less than the minimum shifting interval.

[0091] See Figure 4The three units within the load-adaptive shift module work collaboratively. The shift decision unit reads the current values ​​from the engine speed sensor and the clutch output shaft torque sensor in each control cycle, uses these values ​​as indexes to look up the corresponding shift decision in the shift MAP table, and outputs it. The shift execution unit receives the decision signal from the shift decision unit. If the decision is to upshift or downshift, it follows a four-stage control process—pre-filling stage, torque phase stage, inertia phase stage, and locking stage—outputting pressure control commands to the proportional solenoid valves corresponding to the high-gear clutch and the low-gear clutch, respectively. This causes the pressure of the two clutches to change according to a preset curve, completing the shift. In the torque phase stage, the shift execution unit controls the high-gear clutch pressure rise curve and the low-gear clutch pressure fall curve to intersect at the midpoint, ensuring that the total transmitted torque remains constant during the shift. The anti-frequent shifting unit makes a judgment after the shift decision unit outputs its decision and before the shift execution unit executes it. The anti-frequent shifting unit first determines whether the current engine speed is within the hysteresis range. If it is, regardless of the decision output by the shift MAP table, it forcibly modifies the current gear and does not perform a shift. If the engine speed is not within the hysteresis range, the anti-frequent shifting unit further determines whether the time interval between the current moment and the last shift completion moment is less than a preset minimum interval. If it is less than the minimum interval, it also forcibly modifies the current gear. Only when neither of the above two conditions is met is the shift decision transmitted to the shift execution unit for execution. The anti-frequent shifting unit filters unreasonable shift requests from both the decision-making and execution levels, avoiding misjudgments caused by transient sensor fluctuations and frequent clutch actuation caused by rapid load changes, thus extending the service life of the clutch friction plates.

[0092] In some embodiments, the temperature compensation module includes: a temperature detection unit for real-time detection of hydraulic oil temperature; a compensation coefficient determination unit for determining the current temperature range based on the hydraulic oil temperature within a preset temperature range, and calculating the compensation coefficient at the current temperature through linear interpolation; and a parameter correction unit for applying the compensation coefficient to the oil filling time, engagement point pressure, and pressure change rate respectively to correct the control parameters during the gear shifting control process.

[0093] The temperature compensation module consists of three units that operate sequentially. The temperature detection unit reads the signal from the oil temperature sensor in each control cycle to obtain the current hydraulic oil temperature. The compensation coefficient determination unit receives the temperature value output by the temperature detection unit and determines the current temperature's position within one of seven preset temperature ranges (-40~-20℃, -20~0℃, 0~20℃, 20~40℃, 40~60℃, 60~80℃, 80~100℃). If the current temperature falls exactly on the boundary of a range, the compensation coefficient for that range is directly used; if the current temperature lies between the boundaries of two adjacent ranges, the compensation coefficient for the current temperature is calculated using a linear interpolation formula. The parameter correction unit receives the compensation coefficients output by the compensation coefficient determination unit and applies them to three parameters in the shift control process: the filling time compensation coefficient is superimposed with the reference filling time to obtain the corrected filling time; the engagement point pressure compensation coefficient is superimposed with the reference engagement point pressure to obtain the corrected engagement point pressure; and the pressure change rate compensation coefficient is superimposed with the reference pressure change rate to obtain the corrected pressure change rate. The three corrected parameters are transmitted to the shift execution unit, replacing the original reference parameters for shift control. The continuous operation of the temperature compensation module allows the shift control to adapt to changes in ambient temperature and viscosity variations caused by the hydraulic oil's own temperature rise. During cold starts in winter, the hydraulic oil viscosity is high, resulting in longer filling time, increased engagement point pressure, and a reduced pressure change rate, ensuring reliable clutch engagement and a smooth engagement process. During continuous operation in summer at high temperatures, the hydraulic oil viscosity is low, resulting in shorter filling time, lower engagement point pressure, and a increased pressure change rate, avoiding engagement shock and pressure overshoot caused by excessive oil fluidity. Through the combined correction of these three parameters, the shift control maintains consistent shift quality and clutch engagement reliability across the entire operating temperature range.

[0094] See Figure 2 The overall workflow of the control system and control method in this embodiment is as follows: After the tractor is powered on and started, the electronic control unit completes a self-test, and the state machine is initialized to the parking state. The braking coordination module is activated. (In parking state) Under these conditions, the braking coordination module applies braking pressure based on the clutch output shaft torque to suppress self-propelled movement. After the driver depresses the accelerator pedal to request a start, the state machine transitions to the start-up transition state. The braking coordination module performs graded linear release of braking pressure, while the clutch pre-charging is performed synchronously. After starting, the state machine transitions to the driving state. The load-adaptive shift module and temperature compensation module are activated. The electronic control unit makes shift decisions in real time based on engine speed and clutch output shaft torque, and executes four-stage shift control when a shift is needed. The temperature compensation module simultaneously corrects the control parameters. After the driver presses the brake pedal to request a stop, the state machine transitions to the stop transition state. The load-adaptive shift module is disabled, the clutch disengages, and the vehicle speed decreases. After the vehicle speed drops to zero, the state machine transitions back to the stationary state. The braking coordination module is then reactivated, completing a full work cycle. Throughout the process, the state machine management module acts as the top-level scheduler, ensuring that each functional module operates in the correct state, that there are no logical conflicts between modules, and that the control process is continuous, stable, and reliable.

[0095] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0096] The parts of this invention not described in detail are prior art. It will be apparent to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and are intended to encompass all changes falling within the meaning and scope of equivalents within this invention.

Claims

1. A control method for adaptive shifting and braking coordination under load in a tractor, characterized in that, Includes the following steps: A1. State machine management steps: Establish a four-state state machine including parking state, start transition state, driving state and parking transition state, and perform state transition between each state according to the tractor operating parameters; A2. Braking Coordination Steps: In the stationary state, the clutch output shaft torque is obtained, the target value of the braking pressure is determined based on the clutch output shaft torque, and braking is applied to suppress self-propelled movement caused by the increase in clutch drag torque due to the increase in oil viscosity; in the starting transition state, the braking pressure is released synchronously with the execution of clutch pre-charging. A3. Load-adaptive shifting steps: In driving mode, obtain engine speed and clutch output shaft torque, determine shifting decisions based on preset shifting MAP table, and execute shifting control; A4. Temperature compensation steps: Obtain the hydraulic oil temperature and compensate the control parameters during the shifting control process based on the hydraulic oil temperature; In the A2 braking coordination step: The target value of braking pressure is linearly related to the clutch output shaft torque. The clutch output shaft torque is divided into multiple torque ranges, and each torque range corresponds to a target value of braking pressure. During the start-up transition, the braking pressure is released linearly in stages as the clutch pre-filling is performed, so that the completion time of brake release is synchronized with the completion time of clutch pre-filling. When the driver is detected to have pressed the brake pedal, the braking coordination steps immediately cease execution and transfer braking control to the driver. In the A4 temperature compensation step: The temperature range is divided into multiple temperature zones, with a compensation coefficient set for each temperature zone, using a preset reference temperature as the boundary. The compensation coefficients are applied to three control parameters: oil filling time, joint pressure, and pressure change rate. Based on the actual detected hydraulic oil temperature, linear interpolation is performed using the compensation coefficients of adjacent temperature ranges to obtain the compensation coefficient at the current temperature, which is then applied.

2. The tractor load adaptive shifting and braking coordination control method as described in claim 1, characterized in that, In the load adaptive shifting step: The shift MAP uses engine speed and clutch output shaft torque as input dimensions, and upshift, downshift or hold as output decisions; The shift MAP table has a hysteresis range set. When the engine speed is within the hysteresis range, the current gear is maintained. Set an interval timer so that if the time interval between two shift commands is less than the preset minimum interval, the second shift command is ignored.

3. The tractor load adaptive shifting and braking coordination control method as described in claim 1, characterized in that, The load-adaptive shifting step includes four stages executed sequentially: Pre-filling stage: Fill the clutch corresponding to the target gear with oil, so that the clutch pressure rises to the engagement point pressure; Torque phase stage: The clutch pressure of the target gear gradually increases, while the clutch pressure of the current gear gradually decreases. The two clutch pressures cross at the midpoint, keeping the total transmitted torque constant. Inertial phase stage: The clutch pressure of the target gear continues to rise, while the clutch pressure of the current gear continues to decrease until disengagement; Locking phase: The clutch pressure of the target gear rises to the locking pressure, completing the gear shift.

4. The tractor load adaptive shifting and braking coordination control method as described in claim 1, characterized in that, The transition conditions for each state in the state machine are as follows: When the tractor is stationary and its speed is zero, it enters the parking state; When a start request is detected, the system transitions from the stop state to the start transition state and simultaneously activates the braking coordination step. When the start-up transition is completed and the vehicle speed is greater than the preset threshold, the vehicle transitions from the start-up transition state to the driving state, and the load adaptive shifting step is activated at the same time. When a parking request is detected, the system transitions from driving state to parking transition state, and disables the load adaptive shifting step. When the parking transition is completed and the vehicle speed drops to zero, the vehicle transitions from the parking transition state to the parking state.

5. A control system for adaptive shifting and braking coordination under tractor load, characterized in that, include: The state machine management module is used to execute state machine management steps, establish a four-state state machine including parking state, start transition state, driving state and parking transition state, and perform state transition between states according to the tractor's operating parameters. The braking coordination module executes braking coordination steps. In a stopped state, it acquires the clutch output shaft torque, determines the target value of the braking pressure based on the clutch output shaft torque, and applies the brakes to suppress self-propelled movement caused by increased clutch drag torque due to increased fluid viscosity. The target braking pressure value is linearly correlated with the clutch output shaft torque, dividing the clutch output shaft torque into multiple torque ranges, each corresponding to a target braking pressure value. In a start-up transition state, the braking pressure is released linearly in stages as clutch pre-charging is performed, synchronizing the brake release completion time with the clutch pre-charging completion time. When the driver is detected pressing the brake pedal, the braking coordination steps immediately cease execution, transferring braking control to the driver. The load-adaptive shift module is used to execute the load-adaptive shift procedure. In driving mode, it obtains the engine speed and clutch output shaft torque, determines the shift decision according to the preset shift MAP table, and executes the shift control. The temperature compensation module is used to perform temperature compensation steps, obtain the hydraulic oil temperature, and compensate the control parameters in the shift control process based on the hydraulic oil temperature. The temperature range is divided into multiple temperature intervals with a preset reference temperature as the boundary, and a compensation coefficient is set for each temperature interval. The compensation coefficients are applied to three control parameters: oil filling time, engagement point pressure, and pressure change rate. Based on the actual detected hydraulic oil temperature, the compensation coefficient at the current temperature is obtained by linear interpolation using the compensation coefficients of adjacent temperature intervals and then applied.

6. The tractor load adaptive shifting and braking coordination control system as described in claim 5, characterized in that, Also includes: The sensor group includes an engine speed sensor, a clutch output shaft torque sensor, a clutch output shaft speed sensor, a gear position sensor, an oil temperature sensor, a vehicle speed sensor, a brake pressure sensor, and a brake switch; The controller is connected to the sensor group, the braking coordination module and the load adaptive shifting module. The controller stores a shifting MAP table and a temperature compensation coefficient table. The braking actuator is connected to the braking coordination module via signals and is used to perform braking actions according to the braking pressure command output by the braking coordination module.

7. The tractor load adaptive shifting and braking coordination control system as described in claim 5, characterized in that, The load adaptive shifting module includes: The shift decision unit is used to query the shift MAP table based on the engine speed and clutch output shaft torque, and output shift decisions such as upshifting, downshifting, or holding. The shift execution unit is used to control the pressure of the high-gear clutch and the low-gear clutch to change according to a preset curve after receiving the shift decision, so as to complete the shift. The anti-frequent shifting unit is used to set a hysteresis range and a minimum shift interval. When the engine speed is within the hysteresis range or the interval between two shift commands is less than the minimum shift interval, shifting is prohibited.

8. The tractor load adaptive shifting and braking coordination control system as described in claim 5, characterized in that, The temperature compensation module includes: Temperature detection unit is used to detect the hydraulic oil temperature in real time; The compensation coefficient determination unit is used to determine the current temperature range based on the hydraulic oil temperature within a preset temperature range, and to calculate the compensation coefficient at the current temperature through linear interpolation. The parameter correction unit is used to apply the compensation coefficients to the oil filling time, engagement point pressure, and pressure change rate to correct the control parameters during the shift control process.

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