Vehicle stability control method and system during EPB braking degradation

Abstract

The invention provides a vehicle stability control method and system during EPB braking degradation, and the method comprises the steps: (1) detecting whether wheels are locked or not when an EPB switch is triggered and a vehicle is in an RWU state, if yes, executing a step (2), and if not, executing a step (3); (2) determining the braking torque required for locking the wheels on the basis of the additional yawing torque delta M generated on the side where the locked wheels are located during braking, adjusting the wheel cylinder pressure of the locked wheels to enable the braking torque of the locked wheels to reach the braking torque required by the additional yawing torque delta M, and executing the step (1); and (3) calculating an expected front wheel steering angle capable of keeping the vehicle stable, and adjusting the steering angle of a steering wheel to enable the vehicle front wheel steering angle to reach the expected front wheel steering angle. Under the road condition with a low friction coefficient, even if the ESP function fails and the EPB function is degraded, the dynamic stability of the vehicle can still be ensured not to be influenced through the RWU function.

Description

Technical Field

[0001] The invention relates to the technical field of brake control, and provides a vehicle stability control method and system when EPB brake is degraded. Background Art

[0002] The Electronic Park Brake (EPB) system can perform emergency braking when the Electronic Stability Program (ESP) system fails. The two work closely together and play a vital role in vehicle safety.

[0003] When the vehicle is driving on low-adhesion roads such as ice, snow, and sprinkler tiles, the driver can transmit a braking signal to the electronic stability control system ESP through EPB to control the caliper to achieve dynamic parking, thereby ensuring the stability of the vehicle; however, when the ESP controller fails and cannot work normally, the vehicle's braking system will actively downgrade and enter the rear wheel anti-lock (RearWheel Unlock, RWU) stage.

[0004] Since RWU cannot clamp and release the caliper at a high frequency like ESP, it directly leads to the loss of lateral force on the steering front wheels, making the vehicle's trajectory and direction uncontrollable. At this time, due to inertia, the driver will continue to increase control over the steering system when he finds that the vehicle deviates from the expected trajectory, further causing the vehicle to yaw, posing a serious threat to the driver's safety. Summary of the invention

[0005] In view of this, the present application provides a vehicle stability control method when EPB brake degradation occurs, aiming to improve the above-mentioned problem.

[0006] Specifically, the following technical solutions are included:

[0007] On the one hand, an embodiment of the present application provides a vehicle stability control method when EPB braking is degraded, the method comprising the following steps:

[0008] (1) When the EPB switch is triggered and the vehicle is in the RWU state, detect whether the wheels are locked. If the detection result is yes, execute step (2); if the detection result is no, execute step (3);

[0009] (2) determining the braking torque required for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located during braking, adjusting the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the braking torque required by the additional yaw moment ΔM, and executing step (1);

[0010] (3) Calculate the desired front wheel steering angle that can maintain vehicle stability, and adjust the steering wheel angle so that the vehicle's front wheel steering angle reaches the desired front wheel steering angle.

[0011] In some embodiments of the present invention, the slip rate s of each wheel at the current moment is calculated, and the wheel with the slip rate s=100 at the current moment is identified as a locked wheel.

[0012] In some embodiments of the present invention, when the locked wheel is the left rear wheel, the additional yaw moment ΔM generated when the vehicle is braked is:

[0013]

[0014] When the locked wheel is the right rear wheel, the additional yaw moment ΔM generated when the vehicle brakes is:

[0015]

[0016] Among them, F blf 、F brf are the braking forces of the left front wheel and the left rear wheel, respectively, and F blr 、F brr are the braking forces of the right front wheel and the right rear wheel, respectively, T f 、T r They are the front axle wheelbase and rear axle wheelbase of the vehicle respectively.

[0017] In some embodiments of the present invention, when the locked wheel is the left rear wheel, the braking torque T of the left rear wheel under the additional yaw moment ΔM is brl The calculation formula is:

[0018]

[0019] When the locked wheel is the right rear wheel, the braking torque T of the right rear wheel under the additional yaw moment ΔM brr The calculation formula is:

[0020]

[0021] Among them, F zfr 、F zrr are the vertical loads on the right front wheel and the right rear wheel, respectively, T f 、T r They are the front axle wheelbase and rear axle wheelbase of the vehicle respectively, and R is the wheel radius.

[0022] In some embodiments of the present invention, the wheel cylinder pressure control method of the locked wheel is specifically as follows:

[0023] The braking torque required for the locked wheel under the additional yaw moment ΔM is taken as the expected braking torque and input into the PID controller. At the same time, the braking torque of the locked wheel under the current pressure collected in real time is input into the PID controller. The PID controller adjusts the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the expected braking torque.

[0024] In some embodiments of the present invention, the maximum front wheel turning angle δ that can maintain vehicle stability is m The calculation formula is as follows:

[0025]

[0026] Among them, v is the current vehicle speed, L is the wheelbase between the front and rear axles, K is the stability factor, ω d is the yaw angular velocity of the vehicle just before it becomes unstable, obtained based on the snail experiment.

[0027] In some embodiments of the present invention, the calculation formula of the stability factor K is as follows:

[0028]

[0029] Among them, m is the mass of the vehicle, a and b are the distances from the center of mass to the front axle and rear axle respectively, and k r , k f are the cornering stiffness of the front and rear wheels respectively.

[0030] In some embodiments of the present invention, the method for controlling the steering wheel angle is specifically as follows:

[0031] The maximum front wheel turning angle δ that can maintain vehicle stability m The desired front wheel angle is input into the PID controller, and the current front wheel angle calculated based on the real-time collected yaw angular velocity is input into the PID controller. The PID controller adjusts the steering wheel angle so that the current front wheel angle reaches the desired front wheel angle.

[0032] On the other hand, an embodiment of the present application provides a vehicle stability control system when EPB braking is degraded, the system comprising:

[0033] A collection unit connected to an ESP controller connected to the collection unit;

[0034] When the EPB switch is triggered and the vehicle is in the RWU state, the collection unit will collect the real-time operating status information of the vehicle and send it to the ESP controller. The ESP controller determines the caliper braking force of the locked wheel based on the vehicle stability control method when the EPB brake is degraded. After the locked driving wheel returns to the normal rolling state, the front wheel steering angle is corrected to control the vehicle to move along the desired trajectory.

[0035] The electronic control unit accurately controls the pressure of the brake caliper. When the brake wheel locks and returns to a normal rolling state, the front wheel angle is immediately corrected to control the vehicle to move along the desired trajectory, which can give the driver a better sense of the road and create a safer driving experience for the driver. In addition, when facing complex road conditions with a low friction coefficient such as icy roads or slippery tiles, even if the ESP function fails and the EPB function is downgraded, the RWU function can still ensure that the dynamic stability of the vehicle is not affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 A flow chart of a vehicle stability control method when EPB braking is degraded provided by an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the structure of a vehicle stability control system when EPB braking is degraded provided by an embodiment of the present invention;

[0039] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] Unless otherwise defined, all technical terms used in the embodiments of the present application have the same meanings as commonly understood by those of ordinary skill in the art.

[0042] Figure 1 A flow chart of a vehicle stability control method when EPB braking is degraded provided by an embodiment of the present invention, the method specifically comprises the following steps:

[0043] (1) When the EPB switch is triggered (the EPB switch is pulled up) and the vehicle is in the RWU state, whether the wheels are locked is detected based on the vehicle's slip rate. If the detection result is yes, step (2) is executed; if the detection result is no, step (3) is executed;

[0044] In an embodiment of the present invention, real-time operating status information of the vehicle is obtained through sensors, including: using a wheel speed pulse sensor to obtain wheel speed pulses, obtaining acceleration signals and yaw angular velocity signals based on data fed back by an IMU, using a master cylinder pressure sensor to obtain the wheel cylinder pressure value entering the wheel cylinder, and obtaining a steering wheel angle signal through a steering wheel angle sensor.

[0045] The vehicle speed is calculated based on the acceleration signal, and the extended Kalman filter algorithm is used to filter the vehicle speed and wheel speed signals to eliminate the influence of noise interference. The slip rate is calculated based on the relationship between the wheel speed and the vehicle speed. The vehicle speed calculation process is as follows:

[0046] v(t)=∫a(t)dt+v0

[0047] Where v(t) represents the vehicle speed at time t, v0 represents the vehicle speed at the initial time, and a(t) represents the acceleration of the vehicle at time t.

[0048] The wheel speed pulses read are converted from analog signals to digital signals through digital-to-analog conversion and stored; the acceleration signal is integrated to obtain the vehicle speed, and the speed signal can be filtered according to the extended Kalman filter algorithm. Through state prediction, observation update, Kalman gain coefficient calculation, state update and covariance update, the noise interference in the speed signal can be eliminated to provide high-quality speed data for subsequent slip rate calculation. The current slip rate is calculated based on the current vehicle speed and wheel speed. The specific calculation formula is as follows:

[0049]

[0050] Among them, s represents the slip rate at the current moment, v, v w Respectively represent the vehicle speed and wheel speed at the current moment. Based on the above formula, the slip rate of all wheels is calculated. If the slip rate s is less than 100 at the current moment, the corresponding wheel is deemed not to be locked; if the slip rate s is 100 at the current moment, the corresponding wheel is deemed to be locked. When the wheel is locked, the lateral force is lost, resulting in the loss of steering function. Due to inertial thinking, the driver will continue to increase the steering wheel angle when he finds that the vehicle is not driving according to the expected trajectory, causing the vehicle to further lose control.

[0051] (2) determining the braking torque required for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located during braking, adjusting the braking torque of the locked wheel by adjusting the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the required braking torque of the additional yaw moment ΔM, and executing step (1);

[0052] If a wheel is locked, the braking force of the locked tire should be adjusted to prevent the wheel from being locked for a long time, ensure that the tire has a certain lateral force, and thus restore the wheel to a normal steering state. The specific method is to determine the braking torque required for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located during braking, and adjust the braking torque of the locked wheel by adjusting the wheel cylinder pressure, so that the braking torque of the locked wheel reaches the required braking torque of the additional yaw moment ΔM.

[0053] When entering the rear wheel anti-lock (RWU) stage, the locked wheel may be the left rear wheel and / or the right rear wheel. When the left rear wheel is locked and the right rear wheel is locked, the calculation method of the required braking torque of the additional yaw moment ΔM is the same. The present invention takes the locked wheel as the left rear wheel as an example for detailed description, which is as follows:

[0054] When the locked wheel is the left rear wheel, the additional yaw moment ΔM generated when the vehicle brakes is:

[0055]

[0056] In the formula, F blf 、F brf are the braking forces of the left front wheel and the left rear wheel respectively, T f 、T r are the front axle wheelbase and rear axle wheelbase of the vehicle respectively. Assuming the turning angle of the vehicle is small enough, the above formula can be transformed into:

[0057]

[0058] Since the vertical load of the tire is approximately proportional to the braking force, the braking torque F of the left front wheel and the left rear wheel is blf 、F brf The allocation is as follows:

[0059]

[0060] In the formula, F zfl 、F zrl are the vertical loads on the left front wheel and the left rear wheel respectively. Considering the tire radius R, we can get the braking torque T of the left front wheel and the left rear wheel: blf 、T brf The expression is as follows:

[0061]

[0062] When the locked wheel is the right rear wheel, the braking torque T between the right front wheel and the right rear wheel can be obtained by the same logic. bfr 、T brr The calculation formula is as follows:

[0063]

[0064] In the formula, F blr 、F brr are the braking forces of the right front wheel and the right rear wheel, respectively, and F zfr 、F zrr are the vertical loads on the right front wheel and the right rear wheel respectively.

[0065] In an embodiment of the present invention, after determining the braking torque required for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located, the braking torque is used as the expected braking torque and input into the PID controller. At the same time, the braking torque of the locked wheel under the current pressure is collected in real time and input into the PID controller. The PID controller adjusts the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the expected braking torque. Then, it is detected whether the vehicle is still in a locked state. If it is still in a locked state, the braking force of the locked wheel is continuously adjusted based on the above method until the vehicle is released from the locked state.

[0066] (3) Calculate the desired front wheel steering angle that can maintain vehicle stability with minimal intervention, and adjust the steering wheel angle so that the vehicle's front wheel steering angle reaches the desired front wheel steering angle.

[0067] When the wheels are not locked, the vehicle has the ability to steer. However, due to driver misoperation during the wheel locking stage, the vehicle does not move along the expected trajectory. Frequent left and right steering on low-adhesion roads will seriously affect the stability of the system. At this time, it is necessary to calculate the maximum front wheel turning angle that can meet the vehicle's stable driving, while minimizing system intervention as much as possible to allow the driver to maintain a good sense of the road.

[0068] The yaw angular velocity ω of the vehicle before instability obtained from the snail experiment d , which is the critical value of the yaw rate, is the critical value of the yaw rate between stability and instability. Combined with the ideal two-degree-of-freedom model, the maximum front wheel turning angle δ that can maintain vehicle stability can be derived m , the calculation formula is as follows:

[0069]

[0070] In the formula, v is the current vehicle speed, L is the wheelbase between the front and rear axles, and K is the stability factor, which reflects the steady-state response of the vehicle. The specific calculation is as follows:

[0071]

[0072] In the formula, m is the mass of the vehicle, a and b are the distances from the center of mass to the front axle and rear axle respectively, and k r , k f are the cornering stiffness of the front and rear wheels respectively.

[0073] The present invention will be able to maintain the maximum front wheel turning angle δ of the vehicle stable m The desired front wheel angle is input into the PID controller. At the same time, the yaw angular velocity is collected in real time and the current front wheel angle is calculated and also input into the PID controller. The PID controller adjusts the steering wheel angle so that the current front wheel angle reaches the desired front wheel angle.

[0074] The electronic control unit accurately controls the pressure of the brake caliper. When the brake wheel locks and returns to a normal rolling state, the front wheel angle is immediately corrected to control the vehicle to move along the desired trajectory, which can give the driver a better sense of the road and create a safer driving experience for the driver. In addition, when facing complex road conditions with a low friction coefficient such as icy roads or slippery tiles, even if the ESP function fails and the EPB function is downgraded, the RWU function can still ensure that the dynamic stability of the vehicle is not affected.

[0075] Figure 2 The schematic diagram of the structure of the vehicle stability control system when the EPB brake is degraded provided by the embodiment of the present invention. For the convenience of explanation, only the part related to the embodiment of the present invention is shown. The system includes:

[0076] A collection unit connected to an ESP controller connected to the collection unit;

[0077] When the EPB switch is triggered and the vehicle is in the RWU state, the acquisition unit will collect the real-time running status information of the vehicle and send it to the ESP controller. The running status information includes: using the wheel speed pulse sensor to obtain the wheel speed pulse, obtaining the acceleration signal and the yaw rate signal according to the data fed back by the IMU, using the master cylinder pressure sensor to obtain the wheel cylinder pressure value entering the wheel cylinder, and obtaining the steering wheel angle signal through the steering wheel angle sensor;

[0078] The ESP controller determines the caliper braking force of the locked wheel based on the vehicle stability control method when the EPB brake is downgraded, so that after the locked side wheel returns to the normal rolling state, the front wheel steering angle is corrected to control the vehicle to move along the desired trajectory. When the ESP controller fails and cannot work normally, the vehicle's braking system actively downgrades and enters the rear wheel anti-lock RWU stage. The vehicle can still maintain vehicle stability when working on low-adhesion road conditions to ensure the safe driving of the car on low-adhesion roads; in addition, the pressure of the brake caliper is accurately controlled by the electronic control unit. When the brake wheel is locked and returns to the normal rolling state, the front wheel steering angle is immediately corrected to control the vehicle to move along the desired trajectory, which can give the driver a better sense of the road, thereby creating a safer driving experience for the driver.

[0079] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the present application disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only.

[0080] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A vehicle stability control method when EPB braking is degraded, characterized in that: The method comprises the following steps: (1) When the EPB switch is triggered and the vehicle is in the RWU state, detect whether the wheels are locked. If the detection result is yes, execute step (2); if the detection result is no, execute step (3); (2) determining the braking torque required for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located during braking, adjusting the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the braking torque required by the additional yaw moment ΔM, and executing step (1); (3) Calculate the desired front wheel steering angle that can maintain vehicle stability, and adjust the steering wheel angle so that the vehicle's front wheel steering angle reaches the desired front wheel steering angle.

2. The vehicle stability control method when EPB brake is degraded as claimed in claim 1, characterized in that: The slip ratio s of each wheel at the current moment is calculated, and the wheel with the slip ratio s=100 at the current moment is identified as a locked wheel.

3. The vehicle stability control method when EPB brake is degraded as claimed in claim 1, characterized in that: When the locked wheel is the left rear wheel, the additional yaw moment ΔM generated when the vehicle brakes is: When the locked wheel is the right rear wheel, the additional yaw moment ΔM generated when the vehicle brakes is: Among them, F blf 、F brf are the braking forces of the left front wheel and the left rear wheel, respectively, and F blr 、F brr are the braking forces of the right front wheel and the right rear wheel, respectively, T f , T r They are the front axle wheelbase and rear axle wheelbase of the vehicle respectively.

4. The vehicle stability control method when EPB brake is degraded as claimed in claim 3, characterized in that: When the locked wheel is the left rear wheel, the braking torque T of the left rear wheel under the additional yaw moment ΔM brl The calculation formula is: When the locked wheel is the right rear wheel, the braking torque T of the right rear wheel under the additional yaw moment ΔM brr The calculation formula is: Among them, F zfr 、F zrr are the vertical loads on the right front wheel and the right rear wheel, respectively, T f , T r They are the front axle wheelbase and rear axle wheelbase of the vehicle respectively, and R is the wheel radius.

5. The vehicle stability control method when EPB brake degradation occurs as claimed in claim 1, characterized in that: The wheel cylinder pressure control method of the locked wheel is as follows: The braking torque required for the locked wheel under the additional yaw moment ΔM is taken as the expected braking torque and input into the PID controller. At the same time, the braking torque of the locked wheel under the current pressure collected in real time is input into the PID controller. The PID controller adjusts the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the expected braking torque.

6. The vehicle stability control method when EPB brake degradation occurs as claimed in claim 1, characterized in that: The maximum front wheel turning angle δ that can maintain vehicle stability m The calculation formula is as follows: Among them, v is the current vehicle speed, L is the wheelbase between the front and rear axles, K is the stability factor, ω d is the yaw angular velocity of the vehicle just before it becomes unstable, obtained based on the snail experiment.

7. The vehicle stability control method when EPB brake is degraded as claimed in claim 6, characterized in that: The calculation formula of the stability factor K is as follows: Among them, m is the mass of the vehicle, a and b are the distances from the center of mass to the front axle and rear axle respectively, and k r , k f are the cornering stiffness of the front and rear wheels respectively.

8. The vehicle stability control method when EPB brake is degraded as claimed in claim 6, characterized in that: The control method of the steering wheel angle is as follows: The maximum front wheel turning angle δ that can maintain vehicle stability m The desired front wheel angle is input into the PID controller, and the current front wheel angle calculated based on the real-time collected yaw angular velocity is input into the PID controller. The PID controller adjusts the steering wheel angle so that the current front wheel angle reaches the desired front wheel angle.

9. A vehicle stability control system when EPB brake is degraded, characterized in that: The system comprises: A collection unit connected to an ESP controller connected to the collection unit; When the EPB switch is triggered and the vehicle is in the RWU state, the collection unit collects the real-time operating status information of the vehicle and sends it to the ESP controller. The ESP controller determines the caliper braking force of the locked wheel based on the vehicle stability control method when the EPB brake is degraded as described in any one of claims 1 to 8, so that after the locked driving wheel returns to a normal rolling state, the front wheel steering angle is corrected to control the vehicle to move along a desired trajectory.

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