Stepless speed change mode switching control method for HMCVT tractor

Abstract

The invention relates to an HMCVT tractor stepless speed change mode switching control method. The method comprises the steps that current operation parameters are read through a TCU; judging a switching signal type according to the current operation parameter; and multi-control-stage control is conducted on clutch control pressure and electromagnetic valve current corresponding to the switching signal type, and switching control is completed. The precision and stability of stepless speed change switching control can be improved, and the stability and reliability of a transmission system are enhanced.

Description

Technical Field

[0001] The present invention belongs to the field of power shift control, and particularly relates to a control method for continuously variable transmission mode switching of an HMCVT tractor. Background Art

[0002] A tractor using a bidirectional variable pump and a fixed-displacement motor for stepless speed regulation can use either the HST transmission route or the HMT transmission route alone for power transmission during forward driving, or can automatically select and switch between the HST mode and the HMT mode according to different vehicle speeds and different loads.

[0003] Currently, most tractor models on the market use the HMT transmission route for forward gears alone. The single working mode is easy to control and implement with low difficulty. However, the single HMT transmission route has great defects under vehicle starting and low vehicle speed conditions: the circulation is too large, and the reason for this situation is determined by the characteristics of the planetary gear mechanism itself. Since the engine speed of an agricultural tractor is constant during operation, in low-speed conditions, in order to balance the vehicle speed, it is necessary to use a hydraulic system to dissipate the excess power, resulting in power waste.

[0004] Therefore, there is an urgent need in this field for a control strategy for HST / HMT adaptive switching. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the purpose of the invention is to provide a control method for continuously variable transmission mode switching of an HMCVT tractor.

[0006] The present invention provides a control method for continuously variable transmission mode switching of an HMCVT tractor, including:

[0007] S1: Read the current operating parameters through the TCU;

[0008] S2: Judge the type of switching signal according to the current operating parameters;

[0009] S3: Complete the switching control by performing multi-control stage control on the clutch control pressure and solenoid valve current corresponding to the type of switching signal.

[0010] According to the control method for continuously variable transmission mode switching of an HMCVT tractor provided by the present invention, the current operating parameters in step S1 are the direction of the speed control handle and the opening of the speed control handle.

[0011] According to the control method for continuously variable transmission mode switching of an HMCVT tractor provided by the present invention, the type of switching signal specifically includes:

[0012] The first switching type, when the direction of the speed control handle is increasing, the opening of the speed control handle is adjusted from less than or equal to 45 degrees to greater than 45 degrees;

[0013] The second switching type, when the direction of the speed control handle is decreasing, the opening of the speed control handle is adjusted from greater than 42 degrees to less than or equal to 42 degrees.

[0014] According to a method for controlling the stepless speed change mode switching of an HMCVT tractor provided by the present invention, the control stage in step S3 specifically includes:

[0015] The first control stage, the second control stage, and the third control stage.

[0016] According to a method for controlling the stepless speed change mode switching of an HMCVT tractor provided by the present invention, the control steps of the first control stage further include:

[0017] S311: Pre-fill the second clutch after switching to the oil pressure at the KP point;

[0018] S312: Reduce the oil pressure of the first clutch before switching and maintain the torque capacity of the first clutch greater than the input torque;

[0019] S313: Maintain the current of the second solenoid valve to maintain torque input.

[0020] According to a method for controlling the stepless speed change mode switching of an HMCVT tractor provided by the present invention, the second control stage specifically includes:

[0021] The second control stage for speed increase corresponding to the first switching type, and the control steps of the second control stage for speed increase further include:

[0022] S3211: Boost the second clutch according to a preset first rate;

[0023] S3212: Reduce the pressure of the first clutch according to a preset second rate and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value;

[0024] S3213: Control the second solenoid valve to reduce the current according to a preset third rate;

[0025] The second control stage for deceleration corresponding to the second switching type, and the control steps of the second control stage for deceleration further include:

[0026] S3221: Reduce the pressure of the first clutch to 0 according to a preset fourth rate;

[0027] S3222: Taking the difference between the actual slip and the target slip of the first clutch as the input, correct the pressure value of the first clutch through the PID control method;

[0028] S3223: Control the second solenoid valve to reduce the current to the target displacement.

[0029] According to a control method for HMCVT tractor continuously variable transmission mode switching provided by the present invention, after step S3222, it further includes:

[0030] S32221: Detect the rotational speed of the active end and the rotational speed of the driven end of the second clutch;

[0031] S32222: When the rotational speed of the active end is greater than the rotational speed of the driven end, switch to the third control stage for control.

[0032] According to a control method for HMCVT tractor continuously variable transmission mode switching provided by the present invention, the third control stage specifically includes:

[0033] The third control stage of speed increase corresponding to the first switching type, the control steps of the third control stage of speed increase further include:

[0034] S3311: Reduce the pressure of the first clutch to 0 according to the preset fourth rate;

[0035] S3312: Taking the difference between the actual slip and the target slip of the second clutch as the input, correct the pressure value of the second clutch through the PID control method;

[0036] S3313: Control the second solenoid valve to reduce the current to the target displacement;

[0037] The third control stage of speed decrease corresponding to the second switching type, the control steps of the third control stage of speed decrease further include:

[0038] S3321: Increase the pressure of the second clutch according to the preset first rate;

[0039] S3322: Reduce the pressure of the first clutch according to the preset second rate, and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value;

[0040] S3323: Control the second solenoid valve to reduce the current according to the preset third rate.

[0041] According to a control method for HMCVT tractor continuously variable transmission mode switching provided by the present invention, when the switching signal type is the first switching type, the first clutch is an HST clutch, and the second clutch is an HMT clutch;

[0042] When the switching signal type is the second switching type, the first clutch is an HMT clutch and the second clutch is an HST clutch.

[0043] According to a method for controlling the continuously variable transmission mode switching of an HMCVT tractor provided by the present invention, after step S3323, it further includes:

[0044] Monitor the slip value of the second clutch, and when the monitored slip value is lower than the preset slip value, press the second clutch.

[0045] A method for controlling the continuously variable transmission mode switching of an HMCVT tractor provided by the present invention, through refined multi-stage control (the first control stage, the second control stage, the third control stage), can ensure that during the continuously variable transmission mode switching of the HMCVT tractor, the changes in the oil pressure of the clutch and the solenoid valve current are smoother, thereby reducing the power interruption or mutation caused by mode switching, and improving the driving smoothness and comfort; during the switching process, the present invention ensures the continuity and efficiency of power transmission by maintaining the torque capacity of the clutch greater than the input torque and compensating the oil pressure according to the rotational speed change rate of the output shaft, which helps to improve the overall performance of the tractor, especially under working conditions that require quick response; in addition, the present invention accurately corrects the pressure value of the clutch through advanced control strategies such as the PID control method, avoiding system failures caused by improper oil pressure or abnormal solenoid valve current, and helping to improve the reliability and durability of the system; by monitoring the direction and opening of the speed control handle, the present invention can automatically judge the switching signal type and adopt corresponding control strategies, simplifying the operation process of the driver and improving the operation convenience and intelligent level; through refined control strategies, the present invention can also reduce the energy loss and emission pollution generated by mode switching, which is of great significance for improving the environmental protection performance and energy-saving effect of the tractor.

[0046] The present invention is applicable to the continuously variable transmission mode switching control of different types of HMCVT tractors, including both speed increase and speed decrease situations. By flexibly adjusting the control parameters of the clutch and the solenoid valve, the present invention can meet the requirements under different working conditions. In summary, through improvements in aspects such as improving driving smoothness, optimizing power transmission efficiency, enhancing system reliability, improving operation convenience, reducing energy consumption and emissions, and enhancing adaptability, the present invention can significantly improve the user experience and satisfaction. Brief Description of the Drawings

[0047] The accompanying drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals represent the same components. Obviously, the drawings in the following description are only some embodiments described in the embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings.

[0048] Figure 1 A control method for switching the stepless speed change mode of an HMCVT tractor provided by an embodiment of the present invention;

[0049] Figure 2 A control curve graph of the first switching type provided by an embodiment of the present invention;

[0050] Figure 3 A control curve graph of the second switching type provided by an embodiment of the present invention. Detailed implementation manners

[0051] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. It should be understood that these descriptions are only exemplary and are not used to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts disclosed in the present invention.

[0053] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. The terms "mounted", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] Exemplary embodiments will be described in detail herein, and examples thereof are shown in the accompanying drawings. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are merely examples of methods and systems consistent with some aspects of the present invention as detailed in the appended claims.

[0055] To better understand the present invention, the nouns appearing in the embodiments of the present invention will be explained first below.

[0056] HMCVT transmission: Hydraulic Mechanical Continuously Variable Transmission (HMCVT), a new technology that combines hydraulic drive and mechanical drive proposed to meet the variable operating conditions of high-power agricultural machinery, and can achieve stepless speed change within a gear.

[0057] TCU (Transmission control Unit): Automatic transmission control unit.

[0058] HMT clutch: The clutch used in the power split gear.

[0059] HST clutch: The clutch used for pure hydraulic flow drive.

[0060] Alpha and beta solenoid valves: The present invention uses a two-way variable pump plus a fixed-displacement motor for stepless speed regulation. The displacement of the pump is controlled by the beta and alpha solenoid valves. The displacement range is 0 to 1. When the displacement is 0, the speed of the motor is 0. When the displacement is 1, the speed of the motor is the same as that of the pump, and the direction depends on the controlled valve. Since the pump is directly connected to the engine, the speed of the pump is always equal to the engine speed. For example, if the displacements of the beta and alpha valves are both 1 and the pump speed is 1000 rpm at this time, if the Alpha displacement is 1, the motor speed is also 1000 rpm. If the beta displacement is 1, the motor speed is -1000 rpm.

[0061] HST: Hydrostatic unit, composed of a two-way variable pump and a fixed-displacement motor. The displacement of the pump is adjusted by controlling beta and alpha. The two solenoid valves control the forward and reverse rotation of the motor respectively.

[0062] The embodiments of the present invention will be described below with reference to the drawings.

[0063] As Figure 1 shown, the present invention provides a method for switching the stepless speed change mode of an HMCVT tractor, including:

[0064] S1: Read the current operating parameters through the TCU.

[0065] Among them, the current operating parameters in step S1 are the direction of the speed control handle and the opening of the speed control handle.

[0066] In step S1, the TCU judges the timing of the whole machine working mode switching based on the input signal and the internal preset algorithm, and controls the hydraulic pump to cooperate with the clutch to complete the gear shift. The shift control adopts the control method of power shift. The TCU obtains the vehicle state information in real time, and receives signals such as the speed control handle, the shift handle, the oil pump displacement, the vehicle speed, the HST clutch opening, and the HMT clutch opening in real time. The TCU controller calculates the HST clutch control pressure, the HMT clutch control pressure, and the β solenoid valve current in real time based on the internal preset algorithm.

[0067] S2: Judge the type of switching signal according to the current operating parameters.

[0068] Among them, the specific types of switching signals include:

[0069] The first switching type, when the direction of the speed control handle is increasing, the opening of the speed control handle is adjusted from less than or equal to 45 degrees to greater than 45 degrees;

[0070] The second switching type, when the direction of the speed control handle is decreasing, the opening of the speed control handle is adjusted from greater than 42 degrees to less than or equal to 42 degrees.

[0071] Further, during the working process of the tractor, the engine speed remains unchanged, and the opening of the speed control handle is adjusted to control the transmission for stepless speed regulation. The forward gear HST speed regulation ratio range is 0 to 0.784, and the HMT speed regulation ratio range is 0 to 1.6. The speed regulation ratio is equal to the input shaft speed divided by the output shaft speed. During the process of increasing the handle opening, the HST route is used to output power in the range of 0 to 45 of the handle opening, and the HMT route is used to output power in the range of 45 - 100 (excluding 45). When the opening reaches 45 during the process of increasing the opening, power shift is performed, and the shift type is HST→HMT, and the power is gradually transferred from the HST clutch to the HMT clutch; during the process of decreasing the handle opening, the HST route is used to output power in the range of 0 - 42 (excluding 42), and the HMT route is used to transmit power in the range of 42 - 100. When the opening decreases to 42, power shift HMT→HST is performed, and the power is gradually transferred from the HMT clutch to the HST clutch. The hysteresis control is used to prevent the clutch from being worn due to the fluctuation of the speed control handle opening signal causing the gear to switch back and forth.

[0072] S3: Complete the switching control by performing multi-control stage control on the clutch control pressure and solenoid valve current corresponding to the switching signal type.

[0073] Among them, the control phase in step S3 specifically includes:

[0074] The first control phase, the second control phase, and the third control phase.

[0075] In step S3, first, when the internal algorithm of the TCU detects that the opening of the speed control handle increases and exceeds 45% and the vehicle speed and motor speed reach the preset values, the HST to HMT shift control logic is activated; the entire switching process is divided into three stages, namely the above-mentioned first, second, and third control phases, corresponding to the switching preparation stage, the switching torque exchange stage, and the switching speed regulation stage respectively.

[0076] When the internal algorithm of the TCU detects that the opening of the speed control handle decreases and is lower than 42%, the HST to HMT shift control logic is activated, and the entire switching process is also divided into three stages. However, since the gear ratio of the HMT is higher than that of the HST, it results in the inability of the HST to transmit positive torque at the initial stage of shifting. It is necessary to first control the slip grinding of the HMT clutch until the speed of the output shaft of the gearbox is lower than the speed of the HST clutch before starting torque exchange. Therefore, the timing of the latter two stages is adjusted, and the shifting process is: the switching preparation stage, the switching speed regulation stage, and the switching torque exchange stage.

[0077] The control steps of the first control phase further include:

[0078] S311: Pre-fill the second clutch after switching to the KP point oil pressure;

[0079] S312: Reduce the oil pressure of the first clutch before switching and maintain the torque capacity of the first clutch greater than the input torque;

[0080] S313: Maintain the current of the second solenoid valve to maintain torque input.

[0081] In the switching preparation stage when the opening of the shift handle increases, the HMT first enters the pre-fill oil control, quickly eliminates the piston gap and keeps the oil pressure near the KISSPOINT oil pressure, improves the torque response speed. At the same time, the HST clutch quickly reduces the oil pressure and monitors the engine torque in real time to ensure that the torque capacity of the HST clutch is always higher than the input torque. During this stage, the current of the β solenoid valve always remains unchanged, staying near 0.9987, ensuring the stability of torque input.

[0082] During the switching preparation stage of reducing the opening of the shift lever, the HST first enters the pre-oiling control to quickly eliminate the piston clearance and maintain the oil pressure near the KISSPOINT oil pressure, improving the torque response speed. At the same time, the HMT clutch quickly reduces the oil pressure and monitors the engine torque in real time to ensure that the torque capacity of the HMT clutch is always higher than the input torque. During this stage, the current of the β solenoid valve remains unchanged to ensure the stability of torque input.

[0083] Among them, the specific second control stage includes:

[0084] The second control stage for speed increase corresponding to the first switching type, and the control steps of the second control stage for speed increase further include:

[0085] S3211: Boost the second clutch according to a preset first rate;

[0086] S3212: Reduce the pressure of the first clutch according to a preset second rate, and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value;

[0087] S3213: Control the second solenoid valve to reduce the current according to a preset third rate.

[0088] During the switching torque exchange stage of increasing the opening of the shift lever, the HMT pressure rises at a fixed slope, the HST clutch drops at a fixed slope, the rotational speed change rate of the output shaft is monitored in real time, and the HST oil pressure is compensated in real time based on the change rate to ensure that the rotational speed change rate of the output shaft is always within the upper and lower limit values. During this stage, the current of the β solenoid valve drops slowly at a fixed slope with a small change rate.

[0089] The second control stage for deceleration corresponding to the second switching type, and the control steps of the second control stage for deceleration further include:

[0090] S3221: Reduce the pressure of the first clutch to 0 according to a preset fourth rate;

[0091] S3222: Use the difference between the actual slip and the target slip of the first clutch as the input, and correct the pressure value of the first clutch through the PID control method;

[0092] S3223: Control the second solenoid valve to reduce the current to the target displacement.

[0093] During the switching torque exchange stage where the shift lever reduces its opening, the HMT clutch descends at a lower slope until it reduces to zero. The HMT clutch adopts PID control, takes the difference between the HMT clutch target slip and the actual slip as the input, and corrects the HMT clutch pressure value in real time through PID control. Meanwhile, the β solenoid valve rises with a three-stage slope and gradually reduces to reach the target displacement.

[0094] Wherein, after step S3222, it further includes:

[0095] S32221: Detect the rotational speed of the driving end and the driven end of the second clutch;

[0096] S32222: When the rotational speed of the driving end is greater than that of the driven end, switch to the third control stage for control.

[0097] During the process where the β solenoid valve rises with a three-stage slope, it is also necessary to continuously detect the rotational speed of the driving end (connected to the hydraulic motor) and the driven end (connected to the output shaft) of the HST clutch at the same time. When the rotational speed of the driving end exceeds that of the driven end, this stage ends and enters the next stage, namely the torque exchange stage.

[0098] Wherein, the third control stage specifically includes:

[0099] The third control stage of speed increase corresponding to the first switching type, and the control steps of the third control stage of speed increase further include:

[0100] S3311: Reduce the pressure of the first clutch to 0 according to a preset fourth rate;

[0101] S3312: Take the difference between the actual slip and the target slip of the second clutch as the input, and correct the pressure value of the second clutch through the PID control method;

[0102] S3313: Control the second solenoid valve to reduce the current to the target displacement.

[0103] During the switching speed regulation stage where the shift lever increases its opening, the HST clutch descends at a lower slope until it reduces to zero. The HMT clutch adopts PID control, takes the difference between the HMT clutch target slip and the actual slip as the input, and corrects the HMT clutch pressure value in real time through PID control. Meanwhile, the β solenoid valve descends with a three-stage slope and gradually reduces to reach the target displacement.

[0104] The third control stage of deceleration corresponding to the second switching type, and the control steps of the third control stage of deceleration further include:

[0105] S3321: Increase the pressure of the second clutch according to a preset first rate;

[0106] S3322: Reduce the pressure of the first clutch according to a preset second rate, and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft, so as to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value;

[0107] S3323: Control the second solenoid valve to reduce the current according to a preset third rate.

[0108] In the switching torque exchange stage where the shift lever reduces the opening, the HST pressure rises at a fixed slope, the HMT clutch drops at a fixed slope, the rotational speed change rate of the output shaft is monitored in real time, and the HMT oil pressure is compensated in real time based on the change rate to ensure that the rotational speed change rate of the output shaft is always within the upper and lower limit values. In this stage, the current of the β solenoid valve drops slowly at a fixed slope with a small change rate.

[0109] Among them, after step S3323, it further includes:

[0110] Monitor the slip value of the second clutch, and when the monitored slip value is lower than the preset slip value, compress the second clutch.

[0111] Specifically, when in the switching torque exchange stage where the shift lever reduces the opening, the oil pressure of the second clutch gradually increases at a preset rate, while the oil pressure of the first clutch gradually decreases at another preset rate, the system needs to carefully control the states of these two clutches to ensure the continuity and smoothness of power transmission.

[0112] Monitor the rotational speed change rate of the output shaft in real time, and compensate the oil pressure of the first clutch in real time according to this change rate, in order to ensure that the rotational speed change of the output shaft remains within the predetermined upper and lower limit values, avoiding excessive impact or jerks, which is crucial for improving the driving experience and vehicle performance.

[0113] When the slip value of the second clutch (i.e., the relative rotational speed difference between the driving disk and the driven disk of the clutch) drops below the preset slip value, it indicates that the second clutch has approached or reached the fully engaged state. At this time, compressing the second clutch can ensure that it fully undertakes the task of transmitting torque, thus smoothly completing the shifting process. This step ensures a smooth transition of torque transmission from the first clutch to the second clutch, avoiding problems that may be caused by torque interruption or sudden changes, such as power loss, vibration, or noise.

[0114] According to a HMCVT tractor continuously variable transmission mode switching control method provided by the present invention, when the switching signal type is the first switching type, the first clutch is the HST clutch, and the second clutch is the HMT clutch;

[0115] When the switching signal type is the second switching type, the first clutch is an HMT clutch and the second clutch is an HST clutch.

[0116] As Figure 2 shown, this is the first switching type of the present invention, that is, the HST-to-HMT reverse control curve. Among them, Figure 2 curve ① in it adopts a conventional power shift control curve. Figure 2 Curve ② in it is an innovative hydraulic pump control method. In the torque exchange stage ab, the displacement of the pump is adjusted at a lower change rate to gradually improve the shifting process. In the bc stage, a three-stage slope control method is adopted to quickly and smoothly enhance the shifting process. By the time point c, 90% of the shifting process has been completed. For the last 10%, the displacement of the pump is further controlled at a lower change rate. The entire shifting process has a short duration and is smooth.

[0117] As Figure 3 shown, this is the second control stage in the present invention, that is, the HMT-to-HST control curve. This figure shows the control process of HMT-to-HST. The difference compared with Figure 2 is that the gear shifting stage is before the torque exchange stage. Because the HST clutch cannot transmit positive torque at the initial stage of shifting, in the gear shifting stage, the displacement of the pump adopts a three-stage slope control method, which is combined with the slip control of the HMT clutch to enhance the shifting process. When reaching point c, the shifting process has exceeded 80%. Subsequently, it enters the torque exchange stage. The determination condition for entering the torque exchange stage is that the HST clutch has the ability to transmit positive torque. When the shifting process exceeds 95%, a pressure of 2 MPA is applied to the HST clutch to complete the shifting. The entire shifting process has a rapid response and little impact.

[0118] Finally, based on the shift lever, oil pump displacement, vehicle speed, and governor lever opening obtained from the CAN network or sensors, through the control method of the present invention, signals of HMT solenoid valve current, HST solenoid valve current, α solenoid valve current, and β solenoid valve current will be output to the actuator, and then vehicle control will be performed accordingly.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A control method for the stepless speed change mode switching of an HMCVT tractor, characterized in that, Including: S1: Read the current operating parameters through the TCU; S2: Determine the type of switching signal according to the current operating parameters; S3: Complete the switching control by performing multi-control stage control on the clutch control pressure and solenoid valve current corresponding to the switching signal type.

2. The HMCVT tractor stepless speed change mode switching control method according to claim 1, characterized in that, The current operating parameters in step S1 are the direction of the speed control handle and the opening of the speed control handle.

3. A method for controlling the shift of the stepless speed change mode of an HMCVT tractor according to claim 2, characterized in that, The specific types of switching signals include: The first switching type, when the direction of the speed control handle is increasing, the opening of the speed control handle is adjusted from less than or equal to 45 degrees to greater than 45 degrees; The second switching type, when the direction of the speed control handle is decreasing, the opening of the speed control handle is adjusted from greater than 42 degrees to less than or equal to 42 degrees.

4. A control method for switching the continuously variable transmission mode of an HMCVT tractor according to claim 1, characterized in that, The control stages in step S3 specifically include: The first control stage, the second control stage, and the third control stage.

5. A control method for switching the stepless transmission mode of an HMCVT tractor according to claim 4, characterized in that, The control steps of the first control stage further include: S311: Pre-fill the second clutch after switching to the oil pressure at the KP point; S312: Reduce the oil pressure of the first clutch before switching and maintain the torque capacity of the first clutch greater than the input torque; S313: Maintain the current of the second solenoid valve to maintain torque input.

6. A control method for the stepless speed change mode switching of an HMCVT tractor according to claim 5, characterized in that, The second control stage specifically includes: The second control stage for speed increase corresponding to the first switching type, and the control steps of the second control stage for speed increase further include: S3211: Increase the pressure of the second clutch according to a preset first rate; S3212: Reduce the pressure of the first clutch according to a preset second rate and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value; S3213: Control the second solenoid valve to reduce the current according to a preset third rate; The second control stage for speed reduction corresponding to the second switching type, and the control steps of the second control stage for speed reduction further include: S3221: Reduce the pressure of the first clutch to 0 according to a preset fourth rate; S3222: Use the difference between the actual slip and the target slip of the first clutch as the input, and correct the pressure value of the first clutch through the PID control method; S3223: Control the second solenoid valve to reduce the current to the target displacement.

7. A control method for switching the stepless speed change mode of an HMCVT tractor according to claim 6, characterized in that, After step S3222, it further includes: S32221: Detect the rotational speed of the active end and the driven end of the second clutch; S32222: When the rotational speed of the active end is greater than the rotational speed of the driven end, switch to the third control stage for control.

8. A method for controlling the shift of the stepless speed change mode of an HMCVT tractor according to claim 7, characterized in that, The third control stage specifically includes: The third control stage for speed increase corresponding to the first switching type, and the control steps of the third control stage for speed increase further include: S3311: Reduce the pressure of the first clutch to 0 according to a preset fourth rate; S3312: Use the difference between the actual slip and the target slip of the second clutch as the input, and correct the pressure value of the second clutch through the PID control method; S3313: Control the second solenoid valve to reduce the current to the target displacement; The third control stage for speed reduction corresponding to the second switching type, and the control steps of the third control stage for speed reduction further include: S3321: Supercharge the second clutch according to a preset first rate; S3322: Reduce the pressure of the first clutch according to a preset second rate, and compensate the oil pressure of the first clutch according to the rotational speed change rate of the output shaft to maintain the rotational speed of the output shaft less than the upper limit value and greater than the lower limit value; S3323: Control the second solenoid valve to reduce the current according to a preset third rate.

9. A method for controlling the seamless shift of an HMCVT tractor's continuously variable transmission mode, characterized in that, When the switching signal type is the first switching type, the first clutch is an HST clutch and the second clutch is an HMT clutch; When the switching signal type is the second switching type, the first clutch is an HMT clutch and the second clutch is an HST clutch.

10. A method for controlling the seamless shift of an HMCVT tractor's continuously variable transmission mode according to claim 8, characterized in that, After step S3323, it further includes: Monitor the slip value of the second clutch, and when the monitored slip value is lower than the preset slip value, compress the second clutch.

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