Road surface adhesion coefficient identification method, storage medium and system

Abstract

The application discloses a road surface adhesion coefficient identification method, a storage medium and a system, and the method comprises the following steps: S1, comparing the brake pedal displacement of two time points to determine whether the brake pedal is stepped on; S2, reading the working state of the ESP system, and if the brake pedal is stepped on and the ESP system is not working, entering step S3; S3, establishing a following wheel speed for each wheel, which changes with the fixed acceleration and the change trend of the original wheel speed of the corresponding wheel, and the value when the following wheel speed changes from acceleration to deceleration is the following wheel speed peak value; S4, calculating the ratio of the difference value of two adjacent following wheel speed peak values of each wheel to the interval time, and then multiplying the ratio by a preset conversion coefficient to obtain the road surface adhesion coefficient of each wheel; and S5, calculating the road surface adhesion coefficient of the road according to the road surface adhesion coefficient values of the four wheels. The method can obtain the road surface adhesion coefficient without relying on the ABS supplier, and can assist the research and development of other system component suppliers.

Description

Technical Field

[0001] This invention relates to the field of braking system control, and in particular to a method, storage medium and system for identifying road surface adhesion coefficient. Background Technology

[0002] Most ABS control methods on the market currently use threshold control. This method performs closed-loop control based on thresholds such as slip ratio and acceleration, resulting in zero control delay and a relatively simple principle. However, this method does not require precise road surface identification and only uses four wheel speeds for calculation, failing to comprehensively consider the vehicle's actual motion. Secondly, ABS manufacturers keep the calculation parameters in the control algorithm relatively closed, not transmitting them externally via CAN. Furthermore, OEMs or other suppliers, during the development of AEB and steering systems, cannot consider the impact of road adhesion coefficient on control, leading to inaccurate control. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to propose a method for identifying the road surface adhesion coefficient, which can identify the road surface adhesion coefficient, and help to achieve more comprehensive ABS control or assist automotive OEMs or other suppliers in developing more precise control systems.

[0004] Another object of the present invention is to provide a system capable of implementing the above-described method and a storage medium storing instructions or computer programs for the above-described method.

[0005] Technical solution: The pavement coefficient identification method of the present invention includes the following steps:

[0006] S1: Compare the brake pedal displacement at two different moments to determine whether the brake pedal has been depressed.

[0007] S2: Read the working status of the ESP system. If the brake pedal is depressed and the ESP system is not working, proceed to step S3.

[0008] S3: Establish a following wheel speed for each wheel with a fixed acceleration, which changes according to the original wheel speed of the corresponding wheel. The value when the following wheel speed changes from acceleration to deceleration is the peak value of the following wheel speed.

[0009] S4: Calculate the ratio of the difference between two adjacent peak following wheel speeds of each wheel to the interval time, and then multiply the ratio by a preset conversion coefficient to obtain the road adhesion coefficient of each wheel.

[0010] S5: Calculate the road surface adhesion coefficient based on the road surface adhesion coefficient values ​​of the four wheels.

[0011] Furthermore, step S1 includes:

[0012] S1.1: Compare the brake pedal displacement at the current moment with the previous moment. If the brake pedal displacement at the current moment is greater than the brake pedal displacement at the previous moment, then the brake pedal is in the outward stroke; if the brake pedal displacement at the current moment is less than the brake pedal displacement at the previous moment, then the brake pedal is in the return stroke.

[0013] S1.2: After a delay, repeat step S1.1. If the two judgment results are consistent, the two judgment results are the current state of the brake pedal; if the two judgment results are inconsistent, the state of the brake pedal remains unchanged.

[0014] Furthermore, in step S3, the following wheel speed follows the trend of the original wheel speed of the corresponding wheel in the following manner: when the following wheel speed is greater than the original wheel speed of the corresponding wheel, the following wheel speed decelerates with a fixed acceleration; when the following wheel speed is less than the original wheel speed of the corresponding wheel, the following wheel speed accelerates with a fixed acceleration.

[0015] Furthermore, in step S3, the following wheel speed tracks the corresponding original wheel speed change with a fixed acceleration gradient.

[0016] Furthermore, step S5 includes:

[0017] S5.1: When the absolute difference between the road surface adhesion coefficients of the two front wheels is less than the first threshold, the average of the road surface adhesion coefficients of the two front wheels shall be taken as the road surface adhesion coefficient.

[0018] S5.2: When the absolute difference between the road surface adhesion coefficients of the two front wheels is greater than the second threshold, and the absolute difference between the road surface adhesion coefficients of the two rear wheels is greater than the second threshold, and the original wheel speeds of the left and right wheels are in the same direction, then the road surface is a mating road surface with two different road surface adhesion coefficients. The first road surface adhesion coefficient is the average of the road surface adhesion coefficients of the two left wheels, and the second road surface adhesion coefficient is the average of the road surface adhesion coefficients of the two right wheels.

[0019] S5.3: When the situation does not fall under the categories described in S5.1 and S5.2, the average of the three larger values ​​of the road surface adhesion coefficients of the four wheels shall be taken as the road surface adhesion coefficient.

[0020] The storage medium of the present invention stores a computer program, characterized in that the computer program is configured to implement the above-mentioned road surface adhesion coefficient identification method when executed.

[0021] The road surface coefficient identification method of the present invention includes: a brake pedal state identification module for identifying the state of the brake pedal; a wheel speed following module for establishing a following wheel speed that changes according to the original wheel speed change trend of each wheel, and controlling the following wheel speed to follow the corresponding original wheel speed change; and a road surface adhesion coefficient calculation module for collecting the following wheel speed peak value, and calculating the road surface adhesion coefficient of each wheel and the road surface adhesion coefficient of the road.

[0022] The storage medium of the present invention stores a computer program, characterized in that the computer program is configured to execute the above-described autonomous driving trajectory tracking method at runtime.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following advantages: 1. It can obtain the road adhesion coefficient without relying on the ABS supplier to calculate it alone, which can assist the development activities of OEMs and component manufacturers and other suppliers; 2. It considers the road adhesion coefficient of each of the four wheels, making the identification results more accurate; 3. It tracks the rise or fall of wheel speed gradient and eliminates singularities in the collected wheel speed signals; 4. It identifies conditions that exclude active control of wheels such as ESP, preventing the identification of incorrect data. Attached Figure Description

[0024] Figure 1 This is a flowchart of the road surface coefficient identification method according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart illustrating the brake pedal state determination process according to an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram illustrating the calculation principle of the road surface adhesion coefficient of the wheel in an embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] Reference Figure 1 and Figure 3 The road surface coefficient identification method according to an embodiment of the present invention specifically includes the following steps:

[0029] S1: Compare the brake pedal displacement at two different moments to determine whether the brake pedal has been depressed.

[0030] S2: Read the working status of the ESP system. If the brake pedal is depressed and the ESP system is not working, proceed to step S3.

[0031] S3: Establish a following wheel speed for each wheel with a fixed acceleration, which changes according to the original wheel speed of the corresponding wheel. The value when the following wheel speed changes from acceleration to deceleration is the peak value of the following wheel speed.

[0032] S4: Calculate the ratio of the difference between the peak values of the following wheel speeds of each wheel in two adjacent times to the interval time, and then multiply the ratio by a preset conversion coefficient to obtain the road surface adhesion coefficient of each wheel;

[0033] S5: Calculate the road surface adhesion coefficient of the road according to the road surface adhesion coefficient values of the four wheels.

[0034] According to the road surface coefficient identification method of the above technical solution, by establishing a following wheel speed that changes with the original wheel speed, the road surface adhesion coefficient of the road is calculated independently without relying on the ABS supplier, which is convenient for the host manufacturer, parts and other system manufacturers to independently obtain the road surface adhesion coefficient and assist their R & D work. At the same time, during the identification process, the situations of active control of wheel conditions such as ESP will be actively excluded, ensuring that the measured road surface adhesion coefficient is more real and accurate.

[0035] Refer to Figure 2 , in this embodiment, the state of the brake pedal is determined in the manner shown in the figure. Denote the obtained brake pedal displacement as pedal_location, compare the brake pedal displacements at two adjacent sampling moments. If the brake pedal displacement at this moment is greater than the brake pedal displacement at the previous moment, that is, pedal_location(n)>pedal_location(n - 1), then the direction of the brake pedal is the forward stroke, that is, the brake pedal is depressed; if the brake pedal displacement at this moment is less than the brake pedal displacement at the previous moment, that is, pedal_location(n)<pedal_location(n - 1), then the direction of the brake pedal is the return stroke, that is, the brake pedal is bouncing back. Delay a detection cycle after each detection is completed and then perform the detection again. If the results of two consecutive detections are the same and the direction of the brake pedal is the forward stroke, then record pedal_direction = 1; if the results of two consecutive detections are the same and the direction of the brake pedal is the return stroke, then record pedal_direction = 0; if the results of the two detections are different, then pedal_direction maintains the original value. Obtain the working state of the ESP system and denote it as ESP_flag. When pedal_direction = 1 and ESP_flag = 0, the subsequent steps can be continued to obtain the road surface adhesion coefficient of the road.

[0036] Refer to Figure 3In this embodiment, the tracked wheel speed uses gradient tracking to track changes in the original wheel speed, which can effectively identify singularities in the collected wheel speed signals and further improve the accuracy of the obtained road surface adhesion coefficient. The original wheel speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel are denoted as fl_wheel, fr_wheel, rl_wheel, and rr_wheel, respectively, and the corresponding tracked wheel speeds are fl_verf, fr_verf, rl_verf, and rr_verf, respectively. Taking the relationship between the tracked wheel speed and the original wheel speed of the left front wheel as an example, when the value of fl_verf is detected to be greater than fl_wheel, it is determined that the original wheel speed begins to decrease, and the tracked wheel speed will decelerate with a fixed acceleration gradient; when the value of fl_verf is detected to be less than fl_wheel, it is determined that the original wheel speed begins to increase, and the tracked wheel speed will increase with a fixed acceleration gradient. The acceleration for the change in tracked wheel speed is generally taken as 0.7g, and technicians can adjust the acceleration value according to the actual situation.

[0037] Similarly, refer to Figure 3 Taking the left front wheel as an example, the value at which the following wheel speed begins to decrease each time is recorded as the peak tracking wheel speed fl_record. The time count value between the peak tracking wheel speeds fl_record and fl_record_old on both adjacent sides is recorded as fl_counter. Then, the road adhesion coefficient of the left front wheel is calculated as fl_grad = (fl_record_old - fl_record) / fl_counter * i, where i is a conversion coefficient. The specific value of i is mainly determined based on the original wheel speed and the unit of the time count value, or it can be an empirical value obtained from multiple tests. The calculation methods for the road adhesion coefficients fr_grad, rl_grad, and rr_grad of other wheels such as the right front wheel, left rear wheel, and right rear wheel can be deduced in the same way.

[0038] The road surface adhesion coefficient can be the average value or weighted average of the road surface adhesion coefficients of the four wheels, and can be adjusted accordingly according to the actual situation. In this embodiment, if |fl_grad - fr_grad| < m, where m is generally taken as 0.1, the average of the left front wheel and the right front wheel is taken as the road surface adhesion coefficient, that is, grad = (fl_grad + fr_grad) / 2; if |fl_grad - fr_grad| > k and |rl_grad - rr_grad| > k and the original wheel speed directions of the left and right wheels are the same, it is determined as a butt joint road surface, which is composed of the left and right splicing of road surfaces with two different road surface adhesion coefficients. The road surface adhesion coefficients of the butt joint road surface are: grad1 = (fl_grad + rl_grad) / 2, grad2 = (fr_grad + rr_grad) / 2, where k is generally taken as 0.4; in other cases, the average of the three larger values among fl_grad, fr_grad, rr_grad, and rl_grad is used as the road surface adhesion coefficient of the road.

[0039] According to the computer-readable storage medium of the embodiment of the present invention, a computer program instantiated with the above road surface adhesion coefficient identification method is stored internally. According to the road surface adhesion coefficient identification system of the embodiment of the present invention, the above road surface adhesion coefficient identification method can be implemented, including a brake pedal state identification module, a wheel speed tracking module, and a road surface adhesion coefficient calculation module. The brake pedal state identification module is used to identify the state of the brake pedal; the wheel speed following module is used to establish a following wheel speed that changes with the change trend of the original wheel speed of each wheel, and control the following wheel speed to follow the corresponding original wheel speed change; the road surface adhesion coefficient calculation module is used to collect the following wheel speed peak value of the following wheel speed, and calculate the road surface adhesion coefficient of each wheel and the road surface adhesion coefficient of the road.

Claims

1. A method for identifying road surface adhesion coefficient, characterized in that, Includes the following steps: S1: Compare the brake pedal displacement at two different moments to determine whether the brake pedal has been depressed. S2: Read the working status of the ESP system. If the brake pedal is depressed and the ESP system is not working, proceed to step S3. S3: Establish a following wheel speed for each wheel with a fixed acceleration, which changes according to the original wheel speed of the corresponding wheel. The value when the following wheel speed changes from acceleration to deceleration is the peak value of the following wheel speed. S4: Calculate the ratio of the difference between two adjacent peak following wheel speeds of each wheel to the interval time, and then multiply the ratio by a preset conversion coefficient to obtain the road adhesion coefficient of each wheel. S5: Calculate the road surface adhesion coefficient based on the road surface adhesion coefficient values ​​of the four wheels.

2. The method for identifying road surface adhesion coefficient according to claim 1, characterized in that, Step S1 includes: S1.1: Compare the brake pedal displacement at the current moment with the previous moment. If the brake pedal displacement at the current moment is greater than the brake pedal displacement at the previous moment, then the brake pedal is in the outward stroke; if the brake pedal displacement at the current moment is less than the brake pedal displacement at the previous moment, then the brake pedal is in the return stroke. S1.2: After a delay, repeat step S1.

1. If the two judgment results are consistent, the two judgment results are the current state of the brake pedal; if the two judgment results are inconsistent, the state of the brake pedal remains unchanged.

3. The method for identifying road surface adhesion coefficient according to claim 1, characterized in that, In step S3, the following wheel speed follows the trend of the original wheel speed of the corresponding wheel in the following manner: when the following wheel speed is greater than the original wheel speed of the corresponding wheel, the following wheel speed decelerates with a fixed acceleration; when the following wheel speed is less than the original wheel speed of the corresponding wheel, the following wheel speed accelerates with a fixed acceleration.

4. The method for identifying road surface adhesion coefficient according to claim 1, characterized in that, In step S3, the following wheel speed tracks the corresponding original wheel speed change with a fixed acceleration gradient.

5. The method for identifying road surface adhesion coefficient according to claim 1, characterized in that, Step S5 includes: S5.1: When the absolute difference between the road surface adhesion coefficients of the two front wheels is less than the first threshold, the average of the road surface adhesion coefficients of the two front wheels shall be taken as the road surface adhesion coefficient. S5.2: When the absolute difference between the road surface adhesion coefficients of the two front wheels is greater than the second threshold, and the absolute difference between the road surface adhesion coefficients of the two rear wheels is greater than the second threshold, and the original wheel speeds of the left and right wheels are in the same direction, then the road surface is a mating road surface with two different road surface adhesion coefficients. The first road surface adhesion coefficient is the average of the road surface adhesion coefficients of the two left wheels, and the second road surface adhesion coefficient is the average of the road surface adhesion coefficients of the two right wheels. S5.3: When the conditions in S5.1 and S5.2 are not met, the average of the three larger values ​​of the road surface adhesion coefficients of the four wheels shall be taken as the road surface adhesion coefficient.

6. The method for identifying road surface adhesion coefficient according to claim 1, characterized in that, The fixed acceleration in step S3 is 0.7g.

7. The method for identifying road surface adhesion coefficient according to claim 5, characterized in that, The first threshold in step S5.1 is 0.

1.

8. The method for identifying road surface adhesion coefficient according to claim 5, characterized in that, The second threshold in step S5.2 is 0.

4.

9. A computer-readable storage medium storing a computer program, characterized in that, The computer program is configured to implement the road surface adhesion coefficient identification method according to any one of claims 1 to 8 when executed.

10. A road surface adhesion coefficient identification system, characterized in that, include: The brake pedal status recognition module is used to identify the status of the brake pedal and compare the brake pedal displacement at two different times to determine whether the brake pedal has been pressed. The wheel speed following module is used to read the working status of the ESP system. If the brake pedal is pressed and the ESP system is not working, a following wheel speed is established for each wheel with a fixed acceleration, which follows the original wheel speed change trend of the corresponding wheel. The value when the following wheel speed changes from acceleration to deceleration is the peak value of the following wheel speed. The road surface adhesion coefficient calculation module is used to collect the peak value of the following wheel speed and calculate the road surface adhesion coefficient of each wheel and the road surface adhesion coefficient of the road. The road surface adhesion coefficient of each wheel is obtained by calculating the ratio of the difference between two adjacent peak values ​​of the following wheel speed of each wheel to the interval time, and then multiplying the ratio by a preset conversion coefficient. The road surface adhesion coefficient of the road is calculated based on the road surface adhesion coefficient values ​​of the four wheels.

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