A load-limited speed control method and system for a tractor engine

Abstract

The present invention discloses a load-limited speed control method and system for a tractor engine. The specific steps are as follows: S1 obtains the expected output engine load-limited speed based on the activation gear switching situation; S2 obtains the sum of the engine load speed in the previous cycle and the difference between the engine load speed when the maximum accelerator pedal is activated; S3 compares the above sum with the expected output engine load-limited speed, and takes the minimum value as the final output engine load-limited speed. The present invention utilizes the final output engine load-limited speed to maintain stable operation of the engine under different working conditions, and has high control accuracy and good economy.

Description

Technical Field

[0001] The present invention belongs to the field of engine control, and in particular to a load-limited speed control method and system for a tractor engine. Background Art

[0002] To ensure sufficient engine output power, stable speed, and good economic efficiency, a suitable engine load speed limit control method is required. When a tractor equipped with a mechanical hydraulic power split continuously variable transmission tows a large plow, the complex soil and terrain conditions cause drastic changes in external load, resulting in frequent fluctuations in the tractor's engine operating point, unstable speed, and high fuel consumption. Existing technologies achieve engine operating point stability by matching the engine power to the load's required power, but this results in low speed control accuracy and stability. For mechanical hydraulic power split continuously variable transmissions, drastic load fluctuations can lead to unstable continuous speed ratios, and frequent speed adjustments can cause engine alarms or damage. For example, excessive loads can cause engine overload. Summary of the Invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a load-limited speed control method and system for a tractor engine, which can maintain stable operation of the engine under different working conditions, and has high control accuracy and good economy.

[0004] To achieve the above object, the present invention provides the following technical solution: a load-limited speed control method for a tractor engine, comprising the following specific steps:

[0005] S1 obtains the desired output engine load limit speed according to the activation gear switching situation;

[0006] S2 obtains the sum of the engine load speed of the previous cycle and the difference between the engine load speed when the maximum accelerator pedal is activated;

[0007] S3 compares the sum with the expected output engine load limit speed, and takes the minimum value as the final output engine load limit speed.

[0008] Furthermore, in S1, when the gear shift is activated, the minimum value of the engine speed limit after the gear shift and the actual engine speed is taken as the engine load speed limit of the desired output;

[0009] When the gear shift is not activated, the expected input engine load limit speed is taken as the expected output engine load limit speed;

[0010] Specifically, when upshifting is activated, the engine load limit speed before the gear shift is subtracted from the engine speed difference used to determine the gear shift to obtain the engine limit speed after the gear shift;

[0011] When downshifting is activated, the engine speed difference after the gear shift is determined is multiplied by the sampling period and added to the engine load limit speed before the gear shift to obtain the engine speed limit after the gear shift.

[0012] Furthermore, in S1 , a desired input engine load limit speed is obtained according to the desired engine load limit speed, the desired engine speed, and the PTO control mode.

[0013] Furthermore, when the PTO control mode is activated: the desired engine load limit speed value is subtracted from the desired engine speed maximum difference in the PTO mode and the engine idle speed reduction value to obtain the desired input engine load limit speed;

[0014] When PTO control mode is not activated:

[0015] 1) Add the difference between the engine speed corresponding to the maximum engine torque and the engine load limit speed corresponding to the shuttle operation, compare the difference with the engine load limit speed corresponding to the start of the vehicle, and take the minimum value;

[0016] 2) Subtract the one-dimensional linear piecewise function table value of the engine speed corresponding to the actual vehicle speed from the minimum value to obtain the difference;

[0017] 3) Compare the difference with the expected engine load limit speed value, and take the minimum value as the expected input engine load limit speed.

[0018] Furthermore, the engine idle speed reduction value is the minimum engine idle speed minus the minimum engine speed at idle.

[0019] Furthermore, 1. Obtain the engine speed corresponding to the maximum engine torque under different driving modes:

[0020] 1) When the driving mode is road mode, a one-dimensional linear piecewise function is used to dynamically look up the desired engine speed table to obtain the engine speed lookup value for road mode. The engine speed lookup value for road mode is compared with the engine speed corresponding to the maximum torque in road mode, and the minimum value is taken as the engine speed corresponding to the maximum engine torque;

[0021] 2) When the driving mode is off-road mode, a one-dimensional linear piecewise function is used to dynamically look up the desired engine speed to obtain an off-road mode engine speed lookup value. The off-road mode engine speed lookup value is compared with the engine speed corresponding to the maximum torque in the off-road mode, and the minimum value is taken as the engine speed corresponding to the maximum engine torque;

[0022] 2. Obtain the engine load limit speed difference corresponding to the shuttle under the load delay time condition:

[0023] 1) Perform a one-dimensional linear piecewise function lookup table based on the desired engine speed to obtain the engine speed difference during shuttle switching;

[0024] 2) multiplying the difference by the load limit speed gradient to obtain the engine load limit speed difference corresponding to the shuttle operation;

[0025] 3. Obtain the corresponding engine load limit speed when starting the vehicle based on the vehicle speed:

[0026] When the vehicle speed is less than or equal to 3 km / h:

[0027] 1) The speed difference is obtained by subtracting the minimum idle speed from the engine speed corresponding to the maximum engine torque and then subtracting the minimum engine speed drop at idle;

[0028] 2) multiplying the speed difference by a one-dimensional linear piecewise function lookup table value of the actual vehicle speed to obtain the engine speed value under the coefficient corresponding to the vehicle speed;

[0029] 3) The sum of the engine speed value under the vehicle speed corresponding coefficient, the minimum engine idle speed, and the minimum engine speed drop at idle speed is used as the engine load limit speed corresponding to starting the vehicle;

[0030] When the vehicle speed is greater than 3 km / h:

[0031] The engine speed corresponding to the maximum engine torque is used as the engine load limit speed corresponding to starting and driving the vehicle.

[0032] Furthermore, in S1 , a desired engine load limit speed is obtained based on the driving mode, the engine fault flag, and the actual engine speed;

[0033] When the engine fault flag is detected, the desired engine load limit speed is the minimum of the speed parameter value selected for the currently active driving mode and the difference between the current actual engine speed and the engine load limit minimum speed.

[0034] When the engine fault flag is not detected, the expected engine load limit speed value is the speed parameter selected by the currently activated driving mode;

[0035] The speed parameter values selected for the currently active driving mode are:

[0036] When the actual driving mode is manual mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load; when the actual driving mode is automatic mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load.

[0037] Furthermore, in S2 , when the maximum accelerator pedal flag is detected, the engine load speed difference is 10 rpm; otherwise, the engine load speed difference is 0.

[0038] The present invention provides a load-limiting speed control system for a tractor engine, comprising:

[0039] The module for calculating the engine load limit speed of the expected output is used to obtain the engine load limit speed of the expected output according to the activation gear switching;

[0040] An engine load speed difference calculation module is used to obtain the sum of the engine load speed of the previous cycle and the engine load speed difference when the maximum accelerator pedal is activated;

[0041] The data comparison output module is used to compare the engine load speed difference and the sum obtained by the calculation module with the expected output engine load limit speed, and output the minimum value, which is the final output engine load limit speed.

[0042] Furthermore, the engine load limit speed calculation module of the expected output includes:

[0043] An activation gear switching calculation module is used to, when the gear switching is activated, take the minimum value of the engine speed limit after the gear switching and the actual engine speed as the desired output engine load limit speed;

[0044] When the gear shift is not activated, the expected input engine load limit speed is taken as the expected output engine load limit speed;

[0045] An expected input engine load limit speed calculation module is used to obtain the expected input engine load limit speed according to the expected engine load limit speed, the expected engine speed and the PTO control mode;

[0046] The expected engine load limit speed calculation module is used to obtain the expected engine load limit speed according to the driving mode, the engine fault flag and the actual engine speed.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] The present invention provides a load-limited speed control method for a tractor engine, which limits actual speed ratio changes by limiting the engine load-limited speed that is ultimately output, so that when the tractor's load changes dramatically, the speed ratio fluctuation of the mechanical hydraulic power split continuously variable transmission is small, thereby preventing the speed ratio fluctuation from affecting the engine speed, controlling the engine speed to operate stably in a short period of time, and achieving a stable engine operating point, high speed control accuracy, and high reliability. The control method of the present invention can be used in mechanical hydraulic continuously variable transmission tractors, can maintain stable operation of the engine under different working conditions, and has reduced fuel consumption and good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of load-limiting speed control logic for tractor engines; DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0051] In order to maintain the stable operation of the engine under different working conditions, it is necessary to configure an appropriate engine load speed limit control method. Therefore, the present invention provides a load limit speed control method for a tractor engine. Figure 1 As shown, the engine load limit speed control logic is divided into three parts, namely the desired engine load limit speed control logic, the desired input engine load limit speed control logic and the final output engine load limit speed control logic.

[0052] (1) Expected engine load limit speed control logic. This control logic calculates the engine speed when the engine is not loaded. The specific control logic is as follows:

[0053] If the tractor engine is at a reduced rated power due to a fault (amber warning light), avoid switching back to idle. When a fault occurs, the fault flag is set to 1 and the expected engine load limit speed is:

[0054] The speed parameter value selected by the currently active driving mode, or the difference between the current actual engine speed and the engine load limit minimum speed (the load limit minimum speed is 20 rpm);

[0055] The minimum of the two values is the desired engine load limit speed value;

[0056] Otherwise, the desired engine load limit speed value is the speed parameter selected by the currently active driving mode.

[0057] Among them, the speed parameter value selected by the currently activated driving mode is:

[0058] When the actual driving mode is manual mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load, which is 1400rpm; when the actual driving mode is automatic mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load, which is 2310rpm.

[0059] (2) Engine load limit speed control logic with expected input. This control logic generates a target value of the engine load limit speed, which is derived from the maximum engine torque curve and defines the engine speed at full load. The specific control logic is as follows:

[0060] When the tractor PTO control mode is activated, the expected input engine load limit speed is:

[0061] The desired engine load limit speed value obtained by the desired engine load limit speed control logic is subtracted from the maximum difference in desired engine speed in PTO mode and the engine idle speed reduction value;

[0062] Specifically, the engine idle speed reduction value is the minimum engine idle speed (750 rpm) minus the minimum engine speed at idle (30 rpm);

[0063] When the tractor PTO control mode is not activated, the expected input engine load limit speed is:

[0064] 1) Add the difference between the engine speed corresponding to the maximum engine torque and the engine load limit speed corresponding to the shuttle operation, compare the difference with the engine load limit speed corresponding to the start of the vehicle, and take the minimum value;

[0065] 2) Subtract the one-dimensional linear piecewise function table value of the engine speed corresponding to the vehicle speed from the minimum value to obtain the difference;

[0066] 3) Compare the difference with the expected engine load limit speed value obtained by the expected engine load limit speed control logic, and take the minimum value, which is the expected input engine load limit speed.

[0067] Among them, the one-dimensional linear piecewise function of the engine speed corresponding to the actual vehicle speed is:

[0068] Actual speed (km / h) 0 50 Speed (rpm) 0 400

[0069] (When the vehicle speed is between 0 and 50 km / h, it has a one-dimensional linear relationship with the rotational speed; when the vehicle speed is greater than 50 km / h, the rotational speed is a fixed value of 400 rpm)

[0070] The engine speed calculation logic for maximum engine torque is as follows: 1) When the driving mode is Road mode, the engine speed lookup value for Road mode is obtained by dynamically looking up the desired engine speed table using a one-dimensional linear piecewise function. This engine speed lookup value for Road mode is then compared with the engine speed corresponding to the maximum torque in Road mode (1820 rpm). The minimum value is the engine speed corresponding to the maximum engine torque.

[0071] 2) When the driving mode is off-road mode, the engine speed lookup value in the off-road mode is obtained by dynamically looking up the desired engine speed using a one-dimensional linear piecewise function. The off-road mode engine speed lookup value is compared with the engine speed corresponding to the maximum torque in the off-road mode (1900 rpm). The minimum value is the engine speed corresponding to the maximum engine torque.

[0072] The one-dimensional linear piecewise function is:

[0073] Desired engine speed (rpm) 750 900 1000 1300 1600 2100 2250 Engine speed in mode (rpm) 720 850 950 1200 1500 1950 2100

[0074] (When the desired engine speed is between 0 and 2100 rpm, the engine speed in the mode is between 0 and 720 rpm, forming a one-dimensional linear relationship; when the desired engine speed is greater than 2250 rpm, the engine speed in the mode is a fixed value of 2100 rpm)

[0075] The calculation logic of the engine load limit speed difference corresponding to the shuttle is as follows:

[0076] (Because the engine speed is low, that is, at the maximum torque of the engine, the allowed engine speed drop is small, which leads to a lower gearbox ratio. During the shuttle, the allowed gearbox ratio can be increased by controlling the engine load limit speed logic.)

[0077] A one-dimensional linear piecewise function table lookup is performed using the desired engine speed to determine the engine speed difference during shuttle switching. This difference is multiplied by the load limit speed gradient (0.005) to obtain the corresponding engine load limit speed difference for shuttle switching. The duration is determined by the load delay time (1s). The one-dimensional linear piecewise function is:

[0078] Desired engine speed (rpm) 1000 1400 1900 2000 Engine speed difference during shuttle switching (rpm) -50 -100 -100 -50

[0079] (When the desired engine speed is between 0 and 1000 rpm, the engine speed difference during shuttle switching is -50 constant value. When the desired engine speed is greater than 2000 rpm, the engine speed difference during shuttle switching is -50 constant value.)

[0080] The calculation logic of the engine load limit speed corresponding to starting the vehicle is as follows:

[0081] (By setting the vehicle speed proportional coefficient, the engine load limit speed can be reduced, which helps to start the vehicle and eliminate the impact of engine speed drop.)

[0082] When the vehicle speed is less than or equal to 3 km / h, 1) subtract the engine's minimum idle speed (750 rpm) from the engine speed corresponding to the maximum engine torque, and then subtract the minimum engine speed drop at idle (30 rpm) to obtain the speed difference;

[0083] 2) Multiplying the speed difference by the one-dimensional linear piecewise function lookup table value of the vehicle speed to obtain the engine speed value under the corresponding coefficient of the vehicle speed;

[0084] 3) The sum of the engine speed value under the vehicle speed corresponding coefficient, the minimum engine idle speed, and the minimum engine speed drop at idle is used as the engine load limit speed corresponding to starting the vehicle.

[0085] When the vehicle speed is greater than 3 km / h, the engine speed corresponding to the maximum engine torque is directly used as the engine load limit speed corresponding to starting the vehicle. The one-dimensional linear piecewise function is:

[0086] Actual speed (km / h) 0 3 Vehicle speed corresponding coefficient 0 1

[0087] (When the actual vehicle speed is greater than 3km / h, the speed corresponding coefficient is a fixed value of 1)

[0088] (3) The final output of the engine load limit speed control logic is:

[0089] Obtain the sum of the difference between the engine load speed in the previous cycle and the engine load speed when the accelerator pedal is fully activated. Compare this sum with the desired output engine load limit speed, and take the minimum value as the final output engine load limit speed:

[0090] The control logic of the engine load speed difference when the maximum accelerator pedal is activated is:

[0091] When the maximum accelerator pedal flag is detected (i.e. the accelerator pedal is fully depressed), the engine load speed difference is 10 rpm; otherwise, the engine load speed difference is 0. This is used to adjust the engine load limit speed increase rate.

[0092] The expected output engine load limit speed control logic is:

[0093] When the gear shift is activated (the gear here refers to the mechanical gear), the expected output engine load limit speed is the minimum value of the engine limit speed after the gear shift and the actual engine speed;

[0094] Otherwise (ie, the mechanical gear switching is not activated and the current mechanical gear is kept unchanged), the expected output engine load limit speed is the expected input engine load limit speed.

[0095] Among them, the engine speed limit control logic after gear switching is:

[0096] (The control logic always makes the engine speed above the engine load limit speed, that is, the engine speed is greater than or equal to the engine load limit speed)

[0097] If upshifting is activated, the engine load limit speed before the gear shift is subtracted from the engine speed difference of 100 rpm used to determine the gear shift to obtain the engine speed limit after the gear shift;

[0098] If downshifting is activated, the engine speed limit after the gear shift is obtained by adding the value obtained by multiplying the engine speed difference after the gear shift by 400 rpm and the sampling period of 0.01 s to the engine load limit speed before the gear shift.

[0099] Implementation Cases:

[0100] When the driver starts a tractor equipped with a mechanical-hydraulic power-split continuously variable transmission, the actual driving mode defaults to automatic. In this case, the tractor is operating in field PTO control mode. If the amber warning light on the engine instrument panel illuminates while the tractor is operating in the field, the fault flag in the software model is set to 1. The expected engine load limit speed is the minimum of the two values: the maximum engine load limit speed in automatic mode, 2310 rpm, and the difference between the current actual engine speed and the minimum engine load limit speed, 20 rpm. The expected engine load limit speed calculated here is the speed when the engine is not loaded.

[0101] The expected engine load limit speed is further calculated if the tractor is operating in field conditions and using PTO control mode. The expected engine load limit speed value obtained by the expected engine load limit speed control logic is subtracted from the maximum expected engine speed difference of 150 rpm in PTO mode and the engine idle speed reduction value of 720 rpm.

[0102] The sum of the engine load speed of the previous cycle and the difference between the engine load speed when the maximum accelerator pedal is activated is further obtained, that is, when the maximum accelerator pedal flag is detected, the engine load speed difference is 10 rpm, and the sum is compared with the expected output engine load limit speed. Specifically, when the gear switch is activated, the expected output engine load limit speed is the minimum value of the engine limit speed after the gear switch and the actual engine speed. The minimum value of the two compared values is the final output engine load limit speed.

[0103] The engine speed is limited by the final output engine load, and the engine speed is controlled to operate stably in the field PTO mode, with high control accuracy and good economy.

Claims

1. A load-limited speed control method for a tractor engine, characterized in that: The specific steps are as follows: S1 obtains the desired output engine load limit speed according to the activation gear switching situation; In S1, when the gear shift is activated, the minimum of the engine speed limit after the gear shift and the actual engine speed is taken as the desired output engine load limit speed; When the gear shift is not activated, the expected input engine load limit speed is taken as the expected output engine load limit speed; In S1, a desired input engine load limit speed is obtained according to the desired engine load limit speed, the desired engine speed, and the PTO control mode; When PTO control mode is activated: The desired engine load limit speed value is subtracted from the desired engine load limit speed value, the maximum difference of the desired engine speed in the PTO mode and the engine idle speed reduction value to obtain the desired input engine load limit speed; When PTO control mode is not activated: 1) Add the difference between the engine speed corresponding to the maximum engine torque and the engine load limit speed corresponding to the shuttle operation, and compare it with the engine load limit speed corresponding to starting the vehicle, and take the minimum value; 2) Subtract the one-dimensional linear piecewise function table value of the engine speed corresponding to the actual vehicle speed from the minimum value to obtain the engine speed value with actual vehicle speed compensation; 3) comparing the actual vehicle speed compensated engine speed value with the desired engine load limit speed value, and taking the minimum value as the desired input engine load limit speed; S2 obtains the sum of the engine load speed of the previous cycle and the difference between the engine load speed when the maximum accelerator pedal flag is detected; In S2, when the maximum accelerator pedal flag is detected, the engine load speed difference is 10 rpm; otherwise, the engine load speed difference is 0; S3 compares the sum with the expected output engine load limit speed, and takes the minimum value as the final output engine load limit speed.

2. The load-limited speed control method for a tractor engine according to claim 1, characterized in that: In S1, When upshifting is activated, the engine load limit speed before the gear shift is subtracted from the engine speed difference used to determine the gear shift to obtain the engine limit speed after the gear shift; When downshifting is activated, the engine speed difference after the gear shift is determined is multiplied by the sampling period and added to the engine load limit speed before the gear shift to obtain the engine speed limit after the gear shift.

3. The load-limited speed control method for a tractor engine according to claim 1, characterized in that: The engine idle speed reduction value is the minimum engine idle speed minus the minimum engine speed at idle.

4. The load-limited speed control method for a tractor engine according to claim 1, characterized in that:

1. Obtain the engine speed corresponding to the maximum engine torque under different driving modes: 1) When the driving mode is road mode, a one-dimensional linear piecewise function is used to dynamically look up the desired engine speed to obtain the engine speed lookup value for road mode. This engine speed lookup value is then compared with the engine speed corresponding to the maximum torque in road mode, and the minimum value is taken as the engine speed corresponding to the maximum engine torque. 2) When the driving mode is off-road mode, a one-dimensional linear piecewise function is used to dynamically look up the desired engine speed to obtain the off-road mode engine speed lookup value. The off-road mode engine speed lookup value is compared with the engine speed corresponding to the maximum torque in the off-road mode, and the minimum value is taken as the engine speed corresponding to the maximum engine torque.

2. Obtain the engine load limit speed difference corresponding to the shuttle under the load delay time condition: 1) Perform a one-dimensional linear piecewise function lookup table based on the desired engine speed to obtain the engine speed value during shuttle switching; 2) multiplying the engine speed value during the shuttle reversal by the load limit speed gradient to obtain the engine load limit speed difference corresponding to the shuttle reversal; 3. Obtain the corresponding engine load limit speed when starting the vehicle based on the vehicle speed: When the vehicle speed is less than or equal to 3 km / h: 1) The engine speed corresponding to the maximum engine torque minus the minimum engine idle speed minus the minimum engine speed drop at idle to obtain the speed value; 2) multiplying the speed value by a one-dimensional linear piecewise function lookup table value of the actual vehicle speed to obtain the engine speed value at the coefficient corresponding to the vehicle speed; 3) The sum of the engine speed value under the vehicle speed corresponding coefficient, the minimum engine idle speed, and the minimum engine speed drop at idle speed is used as the engine load limit speed corresponding to starting the vehicle; When the vehicle speed is greater than 3 km / h: The engine speed corresponding to the maximum engine torque is used as the engine load limit speed corresponding to starting and driving the vehicle.

5. A load-limited speed control method for a tractor engine according to any one of claims 1 to 4, characterized in that: In S1, the desired engine load limit speed is obtained according to the driving mode, the engine fault flag and the actual engine speed; When the engine fault flag is detected, the desired engine load limit speed is the minimum of the speed parameter value selected for the currently active driving mode and the difference between the current actual engine speed and the engine load limit minimum speed. When the engine fault flag is not detected, the expected engine load limit speed value is the speed parameter selected by the currently activated driving mode; The speed parameter values selected for the currently active driving mode are: When the actual driving mode is manual mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load; when the actual driving mode is automatic mode, the speed parameter value selected by the currently activated driving mode is the maximum speed limit of the engine load.

6. A load-limited speed control system for a tractor engine, characterized in that: include: The module for calculating the engine load limit speed of the expected output is used to obtain the engine load limit speed of the expected output according to the activation gear switching; An engine load speed difference calculation module is used to obtain the sum of the engine load speed of the previous cycle and the engine load speed difference when the maximum accelerator pedal is activated; A data comparison and output module is used to compare the engine load speed difference and the sum obtained by the calculation module with the expected output engine load limit speed, and output the minimum value, which is the final output engine load limit speed; The engine load limit speed calculation module of the expected output includes: An activation gear switching calculation module is used to, when the gear switching is activated, take the minimum value of the engine speed limit after the gear switching and the actual engine speed as the desired output engine load limit speed; When the gear shift is not activated, the expected input engine load limit speed is taken as the expected output engine load limit speed; An expected input engine load limit speed calculation module is used to obtain the expected input engine load limit speed according to the expected engine load limit speed, the expected engine speed and the PTO control mode; The expected engine load limit speed calculation module is used to obtain the expected engine load limit speed according to the driving mode, the engine fault flag and the actual engine speed.

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