Speed control method and system for electrically driven bulldozer

Abstract

The invention discloses a speed control method and system for an electrically-driven bulldozer. The method comprises the steps that the actual vehicle speed of the bulldozer is obtained, the actual speed difference obtained by subtracting the actual vehicle speed from the target vehicle speed is input into a PID controller, the PID controller outputs a torque value, and the bulldozer is controlled based on the obtained torque value; in the calculation processing process of the PID controller, the integral part in the PID controller is controlled as follows: if the actual speed difference is greater than the first positive deviation value, the integral gain is improved; if the actual speed difference is smaller than the second negative deviation value, the integral accumulated value is reduced. By the adoption of the technical scheme, when the soil load capacity of the bulldozer changes greatly, the integral gain or the integral accumulated value of the integral part of the PID controller is adjusted, control over the speed of the bulldozer is accelerated, and the operation stability of the bulldozer is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric drive bulldozer control, and in particular to a speed control method and system for an electric drive bulldozer. Background Art

[0002] With the country's strong support for the new energy industry in recent years and the rapid improvement of new energy technology, traditional fuel bulldozers have been subject to many constraints due to high energy consumption and exhaust emissions. Therefore, traditional fuel bulldozers have gradually developed into electric-driven bulldozers.

[0003] Bulldozers are mainly used for bulldozing operations in complex working conditions such as mining, farmland reclamation and road construction. Therefore, during the operation, the soil load borne by the bulldozer may change dramatically. For electric drive bulldozers, in order to cope with such changes, improve operating efficiency and ensure the driving stability of the bulldozer, a torque control strategy is needed to meet different working conditions and avoid loss of driving speed.

[0004] In the prior art, in the electronic control system, PID (Proportional-Integral-Derivative Control) controller is often used to make the controlled quantity tend to the target value. However, PID controller also has certain shortcomings. Since PID control belongs to feedback closed-loop control, feedback control has a certain hysteresis, which means that when the soil load changes drastically, it takes a certain amount of time to control the speed. Bulldozers are large heavy machinery. If the speed deviation time is long, there will be certain dangers. Summary of the invention

[0005] Purpose of the invention: The present invention provides a speed control method and system for an electric-driven bulldozer, aiming to solve the problem in the prior art that when the soil load of the bulldozer changes drastically, the speed control time of the bulldozer based on feedback control is relatively long.

[0006] Technical solution: The present invention provides a speed control method for an electric-driven bulldozer, comprising: obtaining the actual vehicle speed of the bulldozer, inputting the actual speed difference obtained by subtracting the actual vehicle speed from the target vehicle speed into a PID controller, the PID controller outputting a torque value, and controlling the bulldozer based on the obtained torque value; during the calculation and processing of the PID controller, the integral part in the PID controller is controlled as follows: if the actual speed difference is greater than a first positive deviation value, the integral gain is increased; if the actual speed difference is less than a second negative deviation value, the integral accumulated value is reduced.

[0007] Specifically, if the actual speed difference is greater than the first positive deviation value and the torque value output by the PID controller is greater than the load change threshold, the integral gain is increased.

[0008] Specifically, under the working conditions of the first soil load and the second soil load, the first function curve and the second function curve between the vehicle speed and the corresponding torque of the bulldozer are respectively obtained; the first soil load is greater than the second soil load; based on the current torque of the bulldozer, and the first function curve and the second function curve, the corresponding first theoretical vehicle speed and the second theoretical vehicle speed are calculated, and the first theoretical vehicle speed is subtracted from the second theoretical vehicle speed to obtain the first theoretical speed difference, and the first theoretical speed difference is used as the first positive deviation value; based on the current vehicle speed of the bulldozer and the first function curve and the second function curve, the corresponding first theoretical torque and the second theoretical torque are obtained, and the second theoretical torque is used as the load change threshold.

[0009] Specifically, improving the integral gain includes: comparing the current torque of the bulldozer with the first theoretical torque; if the current torque is greater than the first theoretical torque, multiplying the integral gain by a first improvement coefficient; if the current torque is not greater than the first theoretical torque, multiplying the integral gain by a second improvement coefficient; the first improvement coefficient is greater than the second improvement coefficient, and both the first improvement coefficient and the second improvement coefficient are greater than 1.

[0010] Specifically, increasing the integral gain includes: until the actual speed difference is not greater than the first positive deviation value, or the torque value output by the PID controller is not greater than the load change threshold, the integral gain stops being increased.

[0011] Specifically, if the actual speed difference is less than the second negative deviation value and the integral accumulated value is greater than 0, the integral accumulated value is reduced.

[0012] Specifically, under the working conditions of the first soil load and the second soil load, the first function curve and the second function curve between the vehicle speed and the corresponding torque of the bulldozer are respectively obtained; the first soil load is greater than the second soil load; based on the current torque of the bulldozer, and the first function curve and the second function curve, the corresponding first theoretical vehicle speed and second theoretical vehicle speed are calculated, and the second theoretical speed is subtracted from the first theoretical vehicle speed to obtain the second theoretical speed difference, and the second theoretical speed difference is used as the second negative deviation value.

[0013] Specifically, reducing the integral accumulated value includes: obtaining the corresponding first theoretical torque and second theoretical torque based on the current vehicle speed of the bulldozer and the first function curve and the second function curve; comparing the current torque of the bulldozer with the first theoretical torque, if the current torque is greater than the first theoretical torque, multiplying the integral gain by a first reduction coefficient; if the current torque is not greater than the first theoretical torque and greater than the second theoretical torque, multiplying the integral gain by a second reduction coefficient; the first reduction coefficient is less than the second reduction coefficient, and both the first reduction coefficient and the second reduction coefficient are less than 1.

[0014] Specifically, reducing the integral accumulated value includes: until the actual speed difference is not less than the second negative deviation value, or the integral accumulated value is not greater than 0, then the integral accumulated value stops being reduced.

[0015] The present invention also provides a speed control device for an electric-driven bulldozer, comprising: a speed execution unit and a PID control unit, wherein: the speed execution unit is used to obtain the actual vehicle speed of the bulldozer, and the actual speed difference obtained by subtracting the target vehicle speed from the actual vehicle speed is input into a PID controller, the PID controller outputs a torque value, and the bulldozer is controlled based on the obtained torque value; the PID control unit is used to control the integral part in the PID controller as follows: if the actual speed difference is greater than the first positive deviation value, the integral gain is increased; if the actual speed difference is less than the second negative deviation value, the integral accumulated value is reduced.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: when the soil load of the bulldozer changes significantly, the integral gain or integral accumulated value of the integral part of the PID controller is adjusted to accelerate the control of the bulldozer speed and improve the stability of the bulldozer operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic flow chart of a speed control method for an electric-driven bulldozer provided by the present invention;

[0018] Figure 2 The present invention provides a schematic flow chart of the integral part control in the PID controller. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0020] See also Figure 1 , which is a flow chart of the speed control method of the electric drive bulldozer provided by the present invention.

[0021] In an embodiment of the present invention, the actual speed of the bulldozer is obtained, and the actual speed difference obtained by subtracting the actual speed from the target speed is input into a PID controller. The PID controller outputs a torque value, and the bulldozer is controlled based on the obtained torque value. During the calculation and processing of the PID controller, the integral part in the PID controller is controlled.

[0022] In a specific implementation, the torque value output by the PID controller can be executed by the motor of the electric bulldozer.

[0023] In practice, the PID controller, or proportional-integral-derivative controller, is a widely used feedback control mechanism in the field of automation control. It calculates the error between the set value (target value) and the actual measured value, and adjusts the control signal according to this error to minimize the error, thereby achieving precise control of the system. The PID controller consists of three independent parts, including proportional control, integral control, and derivative control.

[0024] Proportional control adjusts the output directly in proportion to the error. The proportional gain determines how quickly and how strongly the controller responds to the error. A higher proportional gain can speed up the response. Integral control accumulates past errors to eliminate steady-state errors, which are errors that remain after the system reaches a steady state. The integral gain affects the strength of the integral action, which helps improve control accuracy. Derivative control: Adjusts based on the rate of change of the error to provide predictive control to slow the system's response and reduce overshoot. The differential gain determines the strength of the differential action, which can help smooth the controller's output.

[0025] In the specific implementation, the present invention mainly adjusts and controls the integral part of the PID controller, mainly the integral gain and the integral cumulative value. A higher integral gain can eliminate steady-state errors faster, but this often makes the system too sensitive, and the adjustment amplitude and speed of the controlled variable are too high; a lower integral gain means that the integral action is weaker and the correction speed of the steady-state error is slower. The integral cumulative value is a key component of the integral term in the PID controller, reflecting the accumulation of errors over time. Specifically, the integral cumulative value is the sum of the errors at all times in the past. After being weighted by the integral gain, it is used to adjust the output of the controller to help eliminate steady-state errors. The integral cumulative value continues to accumulate until the error between the actual output of the system and the set value is zero. Even if the error is very small, as long as it exists, the integral action will continue to increase the output until the error is completely eliminated. When the integral accumulation value is high, under the action of the gain, the controller will continue to increase the output to try to eliminate the error. Even if the current error is very small, it means that the system needs more time to stabilize because a large amount of previously accumulated integral action must be consumed first. When the integral accumulation value is low, the integral action is not enough to completely eliminate the error, and the system may have a steady-state error, that is, there is still a non-zero error in the stable state, which means that the integral action is weak and the system responds to the error slowly.

[0026] Therefore, different adjustment methods need to be applied when the bulldozer undergoes different load changes.

[0027] In the embodiment of the present invention, if the actual speed difference is greater than the first positive deviation value, the integral gain is increased; if the actual speed difference is less than the second negative deviation value, the integral accumulated value is reduced.

[0028] In a specific implementation, when the actual speed difference between the target vehicle speed and the actual vehicle speed is greater than the first positive deviation value (greater than 0), it indicates that the system deviation is large at this time and the actual vehicle speed is relatively small, which means that a sudden increase in soil load may have occurred at this time, and the system sensitivity needs to be increased to increase the torque change amplitude and rate, thereby increasing the integral gain.

[0029] In a specific implementation, when the actual speed difference between the target vehicle speed and the actual vehicle speed is less than the second negative deviation value (less than 0), it also indicates that the system deviation is large at this time, but the actual vehicle speed is too high, which means that the soil load may have suddenly decreased at this time, and the system needs to reduce the torque output. Therefore, the integral accumulated value is reduced.

[0030] See also Figure 2 , which is a schematic flow chart of the integral part control in the PID controller provided by the present invention.

[0031] In the embodiment of the present invention, if the actual speed difference is greater than the first positive deviation value and the torque value output by the PID controller is greater than the load change threshold, the integral gain is increased.

[0032] In the specific implementation, when the actual speed difference is greater than the first positive deviation value, the torque value output by the PID controller is greater than the load change threshold, indicating that the current torque output has reached a certain level, while the actual speed difference is still large. This further indicates that due to a sudden increase in soil load, the original output torque is no longer sufficient to support the increase in bulldozer speed, and it is necessary to increase the torque change amplitude and rate by increasing the integral gain.

[0033] In the embodiment of the present invention, if the actual speed difference is less than the second negative deviation value and the integral accumulated value is greater than 0, the integral accumulated value is reduced.

[0034] In a specific implementation, when the actual speed difference is less than the second negative deviation value, the integral accumulated value is greater than 0, indicating that the bulldozer was originally processing a large soil load and continuously outputting high torque, so that the actual vehicle speed is close to the target vehicle speed, rather than braking or decelerating (the integral accumulated value part will have a value less than 0), but the actual speed is too high. This further indicates that the bulldozer may have pushed the soil to a certain place to complete the bulldozing operation, and the soil load suddenly decreased or even became 0, but the bulldozer speed did not decrease rapidly, so the accumulated value of the integral part decreased rapidly, thereby reducing the torque output by the system.

[0035] In the embodiment of the present invention, under working conditions of a first soil load and a second soil load, a first function curve and a second function curve between the vehicle speed and the corresponding torque of the bulldozer are respectively obtained; the first soil load is greater than the second soil load.

[0036] In a specific implementation, in order to further accurately calculate the first positive deviation value, the second negative deviation value, the load change threshold and other related parameters for measuring when to adjust and control the integral part, the present invention introduces a function curve of the relationship between vehicle speed and torque under a certain soil load.

[0037] In a specific implementation, there are many ways to obtain the function curve. For example, multiple sets of vehicle speeds and torques can be sampled under a certain soil load, and the corresponding function curve can be obtained by fitting.

[0038] In a specific implementation, since the numerical values ​​calculated by the first function curve and the second function curve are used as parameters for when to adjust and control the integral part, and as a threshold for when the degree of adjustment of the integral part changes, the difference between the first soil load and the second soil load needs to be reasonably arranged. Typically, the first soil load can be set to 1.5 to 2 times the second soil load.

[0039] In an embodiment of the present invention, based on the current torque of the bulldozer, and the first function curve and the second function curve, the corresponding first theoretical vehicle speed and the second theoretical vehicle speed are calculated, and the first theoretical vehicle speed is subtracted from the second theoretical vehicle speed to obtain a first theoretical speed difference, and the first theoretical speed difference is used as the first positive deviation value; based on the current vehicle speed of the bulldozer and the first function curve and the second function curve, the corresponding first theoretical torque and the second theoretical torque are obtained, and the second theoretical torque is used as the load change threshold.

[0040] In a specific implementation, the current torque of the bulldozer is the torque value output by the current PID controller. Based on the torque value and the first function curve and the second function curve, the first theoretical vehicle speed and the second theoretical vehicle speed can be calculated, which characterize the vehicle speed that can be reached by the current torque value under the first soil load and the second soil load. The first theoretical vehicle speed is subtracted from the second theoretical vehicle speed to obtain the first theoretical speed difference, and the first theoretical speed difference is used as the first positive deviation value. When the actual speed difference is greater than the first theoretical speed difference, it indicates that the soil load change exceeds the difference between the first soil load and the second soil load, indicating that a more drastic increase in soil load has occurred.

[0041] In a specific implementation, based on the current speed of the bulldozer and the first function curve and the second function curve, the corresponding first theoretical torque and the second theoretical torque can be calculated, which characterize the torque value required for the actual speed of the current bulldozer under the first soil load and the second soil load. The second theoretical torque is used as the load change threshold, indicating that the soil load actually handled by the current bulldozer is greater than the second soil load and is at a higher level. The speed of torque increase can be increased by increasing the integral gain, avoiding increasing the sensitivity of the system when the soil load is not high, which may easily lead to excessive torque increase and difficulty in controlling the speed, causing the bulldozer to work unstably.

[0042] In an embodiment of the present invention, the current torque of the bulldozer is compared with the first theoretical torque. If the current torque is greater than the first theoretical torque, the integral gain is multiplied by a first improvement coefficient; if the current torque is not greater than the first theoretical torque, the integral gain is multiplied by a second improvement coefficient; the first improvement coefficient is greater than the second improvement coefficient, and both the first improvement coefficient and the second improvement coefficient are greater than 1.

[0043] In a specific implementation, if the current torque is greater than the first theoretical torque, it indicates that the current torque is already at a very high level, but the actual speed difference is still large, indicating that the soil load has increased to a high degree, so the corresponding torque increase amplitude and rate should also match it, so the integral gain is multiplied by the first increase coefficient; when the current torque is not greater than the first theoretical torque, that is, between the second theoretical torque and the first theoretical torque, it indicates that the current torque is not very high, and there is no need to significantly increase the torque increase amplitude and rate, so the integral gain is multiplied by the second increase coefficient.

[0044] In the embodiment of the present invention, the integral gain is stopped from being increased until the actual speed difference is not greater than the first positive deviation value, or the torque value output by the PID controller is not greater than the load change threshold.

[0045] In an embodiment of the present invention, under working conditions of a first soil load and a second soil load, a first function curve and a second function curve between the vehicle speed and the corresponding torque of the bulldozer are respectively obtained; the first soil load is greater than the second soil load; based on the current torque of the bulldozer, and the first function curve and the second function curve, the corresponding first theoretical vehicle speed and second theoretical vehicle speed are calculated, and the second theoretical vehicle speed is subtracted from the first theoretical vehicle speed to obtain a second theoretical speed difference, and the second theoretical speed difference is used as the second negative deviation value.

[0046] In a specific implementation, correspondingly, based on the torque value and the first function curve and the second function curve, a first theoretical vehicle speed and a second theoretical vehicle speed can be calculated, which characterize the vehicle speed that can be reached by the current torque value under the first soil load and the second soil load. The second theoretical speed difference is obtained by subtracting the first theoretical vehicle speed from the second theoretical vehicle speed, and the second theoretical speed difference is used as the first positive deviation value. When the actual speed difference is less than the second theoretical speed difference, it indicates that the change in soil load exceeds the gap between the second soil load and the first soil load, and also indicates that a more drastic change in soil load reduction has occurred.

[0047] In an embodiment of the present invention, based on the current vehicle speed of the bulldozer and the first function curve and the second function curve, the corresponding first theoretical torque and the second theoretical torque are obtained; the current torque of the bulldozer is compared with the first theoretical torque, and if the current torque is greater than the first theoretical torque, the integral gain is multiplied by the first reduction coefficient; if the current torque is not greater than the first theoretical torque and greater than the second theoretical torque, the integral gain is multiplied by the second reduction coefficient; the first reduction coefficient is less than the second reduction coefficient, and the first reduction coefficient and the second reduction coefficient are both less than 1.

[0048] In specific implementation, similarly, if the current torque is greater than the first theoretical torque, it indicates that the current torque is already at a very high level, and at the same time the actual speed difference is large, indicating that the soil load reduction is high, but the torque output is high and the vehicle speed is fast, so the amplitude and rate of torque reduction should also match it, and the integral accumulated value is multiplied by the first reduction coefficient; when the current torque is between the second theoretical torque and the first theoretical torque, it indicates that the current torque is not very high, and there is no need to significantly reduce the amplitude and rate of torque increase to avoid the bulldozer suddenly losing torque output and causing loss of force, so the integral gain is multiplied by the second reduction coefficient.

[0049] In the embodiment of the present invention, until the actual speed difference is not less than the second negative deviation value, or the integral accumulated value is not greater than 0, the integral accumulated value is stopped from being reduced.

[0050] In the specific implementation, the first function curve and the second function curve corresponding to the first soil load and the second soil load standards are introduced. The advantages are mainly reflected in that the first positive deviation value, the second negative deviation value, the load change threshold, the first theoretical vehicle speed, the second theoretical vehicle speed, the first theoretical torque and the second theoretical torque, which are used to dynamically adjust the reference parameters for measuring when to start adjusting the integral part, and the reference parameters for adjusting the nodes where the control force changes. Compared with fixed parameters, dynamically changing parameters have stronger adaptability to various application scenarios, and can better choose whether to adjust the integral part under different vehicle speeds, different torques and different soil load changes, and make larger or smaller adjustments.

[0051] The present invention also provides a speed control device for an electric-driven bulldozer, comprising: a speed execution unit and a PID control unit, wherein: the speed execution unit is used to obtain the actual vehicle speed of the bulldozer, and the actual speed difference obtained by subtracting the target vehicle speed from the actual vehicle speed is input into a PID controller, the PID controller outputs a torque value, and the bulldozer is controlled based on the obtained torque value; the PID control unit is used to control the integral part in the PID controller as follows: if the actual speed difference is greater than the first positive deviation value, the integral gain is increased; if the actual speed difference is less than the second negative deviation value, the integral accumulated value is reduced.

[0052] In a specific implementation, the speed control device for an electric bulldozer provided by the present invention includes an execution unit for executing a method, step or function, and the method, step or function executed by the execution unit may refer to the speed control method for an electric bulldozer provided by the present invention.

Claims

1. A speed control method for an electric drive bulldozer, characterized in that: include: The actual speed of the bulldozer is obtained, and the actual speed difference obtained by subtracting the actual speed from the target speed is input into the PID controller. The PID controller outputs the torque value, and the bulldozer is controlled based on the obtained torque value. During the calculation process of the PID controller, the integral part of the PID controller is controlled as follows: If the actual speed difference is greater than the first positive deviation value, the integral gain is increased; If the actual speed difference is less than the second negative deviation value, the integral accumulation value is reduced.

2. The speed control method of an electric bulldozer according to claim 1, characterized in that: Control of the integral part of the PID controller, including: If the actual speed difference is greater than the first positive deviation value and the torque value output by the PID controller is greater than the load change threshold, the integral gain is increased.

3. The speed control method of an electric bulldozer according to claim 2, characterized in that: include: Under working conditions of a first soil load and a second soil load, respectively obtaining a first function curve and a second function curve between a vehicle speed and a corresponding torque of the bulldozer; the first soil load is greater than the second soil load; Based on the current torque of the bulldozer, and the first function curve and the second function curve, a corresponding first theoretical vehicle speed and a second theoretical vehicle speed are calculated, and a first theoretical speed difference is obtained by subtracting the first theoretical vehicle speed from the second theoretical vehicle speed, and the first theoretical speed difference is used as a first positive deviation value; Based on the current vehicle speed of the bulldozer and the first function curve and the second function curve, the corresponding first theoretical torque and second theoretical torque are acquired, and the second theoretical torque is used as the load change threshold.

4. The speed control method of an electric bulldozer according to claim 3, characterized in that: The above method improves the integral gain, including: The current torque of the bulldozer is compared with the first theoretical torque. If the current torque is greater than the first theoretical torque, the integral gain is multiplied by the first improvement coefficient; if the current torque is not greater than the first theoretical torque, the integral gain is multiplied by the second improvement coefficient; the first improvement coefficient is greater than the second improvement coefficient, and both the first improvement coefficient and the second improvement coefficient are greater than 1.

5. The speed control method of an electric bulldozer according to claim 4, characterized in that: The above method improves the integral gain, including: When the actual speed difference is not greater than the first positive deviation value, or the torque value output by the PID controller is not greater than the load change threshold, the integral gain is stopped from being increased.

6. The speed control method of an electric bulldozer according to claim 1, characterized in that: Control of the integral part of the PID controller, including: If the actual speed difference is less than the second negative deviation value and the integral accumulated value is greater than 0, the integral accumulated value is reduced.

7. The speed control method of an electric bulldozer according to claim 6, characterized in that: include: Under working conditions of a first soil load and a second soil load, respectively obtaining a first function curve and a second function curve between a vehicle speed and a corresponding torque of the bulldozer; the first soil load is greater than the second soil load; Based on the current torque of the bulldozer, and the first function curve and the second function curve, the corresponding first theoretical vehicle speed and second theoretical vehicle speed are calculated, and the second theoretical speed difference is obtained by subtracting the second theoretical vehicle speed from the first theoretical vehicle speed, and the second theoretical speed difference is used as the second negative deviation value.

8. The speed control method of an electric bulldozer according to claim 7, characterized in that: The method of reducing the integral accumulated value comprises: Based on the current speed of the bulldozer and the first function curve and the second function curve, obtaining the corresponding first theoretical torque and second theoretical torque; The current torque of the bulldozer is compared with the first theoretical torque. If the current torque is greater than the first theoretical torque, the integral gain is multiplied by the first reduction coefficient. If the current torque is not greater than the first theoretical torque but greater than the second theoretical torque, the integral gain is multiplied by the second reduction coefficient. The first reduction coefficient is less than the second reduction coefficient, and both the first reduction coefficient and the second reduction coefficient are less than 1.

9. The speed control method of an electric bulldozer according to claim 8, characterized in that: The method of reducing the integral accumulated value comprises: When the actual speed difference is not less than the second negative deviation value, or the integral accumulated value is not greater than 0, the integral accumulated value is stopped from being reduced.

10. A speed control device for an electric bulldozer, characterized in that: include: Speed ​​execution unit and PID control unit, where: The speed execution unit is used to obtain the actual speed of the bulldozer, and input the actual speed difference obtained by subtracting the actual speed from the target speed into the PID controller, and the PID controller outputs the torque value, and controls the bulldozer based on the obtained torque value; The PID control unit is used to control the integral part of the PID controller as follows: If the actual speed difference is greater than the first positive deviation value, the integral gain is increased; If the actual speed difference is less than the second negative deviation value, the integral accumulation value is reduced.

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