Vehicle Stability Control Methods and Systems During EPB Braking Degradation

Abstract

This invention provides a vehicle stability control method and system during EPB braking degradation. The method includes: (1) when the EPB switch is triggered and the vehicle is in RWU state, detecting whether the wheels are locked. If the detection result is yes, proceed to step (2); otherwise, proceed to step (3); (2) based on the additional yaw moment ΔM generated on the side where the locked wheel is located during braking, determine the braking torque required for the locked wheel, adjust the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the braking torque required for the additional yaw moment ΔM, and proceed to step (1); (3) calculate the desired front wheel steering angle that can maintain vehicle stability, adjust the steering wheel angle so that the front wheel steering angle of the vehicle reaches the desired front wheel steering angle. When facing road conditions with low friction coefficient, even if the ESP function fails and the EPB function is degraded, the RWU function can still ensure that the dynamic stability of the vehicle is not affected.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of brake control, and provides a vehicle stability control method and system when EPB brake degradation occurs. BACKGROUND

[0002] An electrical park brake (EPB) system can perform emergency braking when an electronic stability program (ESP) system fails, and the two systems closely cooperate and jointly play a crucial role in the safety field of a vehicle.

[0003] When a vehicle travels on a low adhesion road surface such as ice and snow, a water-sprinkled ceramic tile, and the like, a driver can transmit a brake signal to an electronic stability control system ESP through an EPB, and control a caliper to realize dynamic parking, so as to ensure the stability of the vehicle; however, when an ESP controller fails to work normally, the brake system of the vehicle will be actively degraded, and enter a rear wheel unlock (RWU) stage.

[0004] Since the RWU cannot clamp and release the caliper at a high frequency like the ESP, the loss of the lateral force of the steering front wheel is directly caused, so that the trajectory direction of the vehicle becomes uncontrollable; at this time, the driver will continue to increase the control on the steering system due to the effect of inertia when he finds that the vehicle deviates from the expected trajectory, and further causes the vehicle to deviate, which seriously threatens the safety of the driver. SUMMARY

[0005] In view of this, the application provides a vehicle stability control method when EPB brake degradation occurs, which aims to improve the above problems.

[0006] Specifically, the technical scheme comprises the following steps:

[0007] On the one hand, the application embodiment provides a vehicle stability control method when EPB brake degradation occurs, and the method comprises the following steps:

[0008] (1) when an EPB switch is triggered and the vehicle is in an RWU state, detecting whether a wheel is locked, if the detection result is yes, executing step (2), and if the detection result is no, executing step (3);

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

[0010] (3) calculating a desired front wheel steering angle capable of maintaining the stability of the vehicle, and adjusting the steering angle of the steering wheel so that the front wheel steering angle of the vehicle reaches the desired front wheel steering angle.

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

[0012] In some embodiments of the present application, when the locked wheel is the left rear wheel, the additional yaw moment ΔM generated when the vehicle brakes 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] wherein F blf , F brf are the braking forces of the left front wheel and the left rear wheel, respectively, F blr , F brr are the braking forces of the right front wheel and the right rear wheel, respectively, T f , T r are the front axle track and the rear axle track of the vehicle, respectively.

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

[0018]

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

[0020]

[0021] wherein F zfr , F zrr are the vertical loads of the right front wheel and the right rear wheel, respectively, T f , T r are the front axle track and the rear axle track of the vehicle, respectively, and R is the wheel radius.

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

[0023] The braking torque required to lock the wheel under the additional yaw moment ΔM is taken as the desired 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 desired braking torque.

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

[0025]

[0026] Where v is the current vehicle speed, L is the wheelbase between the front and rear axles, K is the stability factor, and ω d This represents the yaw rate of the vehicle just before it becomes unstable, obtained from the snail experiment.

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

[0028]

[0029] Where m is the mass of the vehicle, a and b are the distances from the center of gravity to the front and rear axles, respectively, and k r k f These are the lateral 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 as follows:

[0031] The maximum front wheel steering angle δ that can maintain vehicle stability m The desired front wheel steering angle is input to the PID controller. At the same time, the current front wheel steering angle, calculated based on the real-time collected yaw rate, is also input to the PID controller. The PID controller adjusts the steering wheel angle to make the current front wheel steering angle reach the desired front wheel steering angle.

[0032] On the other hand, embodiments of this application provide a vehicle stability control system during EPB braking degrade, the system comprising:

[0033] The acquisition unit is connected to the ESP controller.

[0034] When the EPB switch is triggered and the vehicle is in RWU state, the acquisition unit sends the real-time operating status information of the vehicle to the ESP controller. The ESP controller determines the caliper braking force of the locked wheel based on the vehicle stability control method during EPB braking degradation. After the locked wheel returns to normal rolling state, the front wheel steering angle is corrected to control the vehicle to move along the desired trajectory.

[0035] By precisely controlling the pressure of the brake calipers through the electronic control unit, the front wheel steering angle is immediately corrected when the brake wheel returns to normal rolling state after locking up, controlling the vehicle to move along the desired trajectory, which can give the driver a better road feel and thus create a safer driving experience. In addition, when facing complex road conditions with low friction coefficients such as icy and snowy roads or wet and 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. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a vehicle stability control method during EPB braking degradation provided in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the vehicle stability control system during EPB braking degradation provided in an embodiment of the present invention;

[0039] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

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

[0042] Figure 1 This is a flowchart of a vehicle stability control method during EPB braking degradation provided in an embodiment of the present invention. The method specifically includes the following steps:

[0043] (1) When the EPB switch is triggered (EPB switch is pulled up) and the vehicle is in RWU state, the wheel locks up based on the vehicle's slip ratio. If the detection result is yes, then step (2) is executed; if the detection result is no, then step (3) is executed.

[0044] In this embodiment of the invention, the real-time operating status information of the vehicle is obtained through sensors, including: obtaining wheel speed pulses using a wheel speed pulse sensor, obtaining acceleration signals and yaw rate signals based on data fed back by the IMU, obtaining wheel cylinder pressure values ​​entering the wheel cylinders using a master cylinder pressure sensor, and obtaining steering wheel angle signals using a steering wheel angle sensor.

[0045] The vehicle speed is calculated based on the acceleration signal. An extended Kalman filter algorithm is used to filter the vehicle speed and wheel speed signals to remove noise interference. The slip ratio is then calculated based on the relationship between wheel speed and vehicle speed. The vehicle speed calculation process is as follows:

[0046] v(t)=∫a(t)dt+v0

[0047] In the formula, v(t) represents the vehicle speed at time t, v0 is the vehicle speed at the initial time, and a(t) represents the magnitude of the vehicle's acceleration at time t.

[0048] The read wheel speed pulses are converted from analog to digital signals via digital-to-analog conversion and stored. The vehicle speed is obtained by integrating the acceleration signal. Simultaneously, the speed signal is filtered using an extended Kalman filter algorithm. Through state prediction, observation update, Kalman gain coefficient calculation, state update, and covariance update, noise interference in the speed signal can be eliminated, providing high-quality speed data for subsequent slip ratio calculation. The current slip ratio is calculated based on the current vehicle speed and wheel speed. The specific calculation process is as follows:

[0049]

[0050] Where s represents the slip ratio at the current moment, and v, v w These represent the vehicle speed and wheel speed at the current moment, respectively. Based on the above formula, the slip ratio of all wheels is calculated. Wheels with a slip ratio s < 100 at the current moment are considered not locked; wheels with a slip ratio s = 100 at the current moment are considered locked. When a wheel locks, lateral force is lost, causing the steering function to fail. Due to inertia, the driver, noticing that the vehicle is not following the expected trajectory, will continue to increase the steering wheel angle, leading to further loss of vehicle control.

[0051] (2) Based on the additional yaw moment ΔM generated on the side where the wheel is locked during braking, determine the braking torque required for the wheel to be locked. Adjust the braking torque of the wheel by adjusting the wheel cylinder pressure of the wheel to make the braking torque of the wheel reach the required braking torque of the additional yaw moment ΔM. Execute step (1).

[0052] If a wheel locks up, the braking force of the locked tire should be adjusted to prevent the wheel from remaining locked for an extended period, ensuring the tire has sufficient lateral force to allow the wheel to return to normal steering. Specifically, the required braking torque for the locked wheel is determined based on the additional yaw moment ΔM generated on the side of the locked wheel during braking. This braking torque is adjusted by regulating the wheel cylinder pressure of the locked wheel, ensuring the braking torque reaches the required level for the additional yaw moment ΔM.

[0053] When entering the rear wheel anti-lock braking (RWU) phase, the locked wheels may be the left rear wheel and / or the right rear wheel. The calculation method for the required braking torque of the additional yaw moment ΔM is the same when the left rear wheel locks and the right rear wheel locks. This invention will take the left rear wheel as an example for detailed explanation, as follows:

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

[0055]

[0056] In the formula, F blf F brf The braking forces of the left front wheel and the left rear wheel are T, respectively. f T r These are the front and rear wheelbases of the vehicle, respectively. Assuming the vehicle's turning angle is sufficiently small, the above formula can be transformed into:

[0057]

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

[0059]

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

[0061]

[0062] When the right rear wheel is locked, the braking torque T of the right front wheel and the right rear wheel can be obtained similarly. bfr T brr The specific calculation formula is as follows:

[0063]

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

[0065] In this embodiment of the invention, after determining the required braking torque for the locked wheel based on the additional yaw moment ΔM generated on the side where the locked wheel is located, this braking torque is taken as the desired 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 desired braking torque. Then, it is detected whether the vehicle is still locked. If it is still locked, the braking force of the locked wheel is adjusted according to the above method until the vehicle is delocked.

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

[0067] When the wheels are not locked, the vehicle has steering ability. However, due to driver error during the wheel lock-up phase, the vehicle does not move along the expected trajectory. Frequent left and right steering on low-friction surfaces will seriously affect the stability of the system. At this time, it is necessary to calculate the maximum front wheel steering angle that can meet the vehicle's stable driving needs, while minimizing system intervention to allow the driver to maintain a good road feel.

[0068] The yaw rate ω of the vehicle just before instability was obtained from the snail experiment. d This refers to the critical value of the yaw rate, the critical value of the yaw rate between stability and instability. Combining this with an ideal two-degree-of-freedom model, the maximum front wheel steering angle δ that can maintain vehicle stability can be derived. m The specific 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, reflecting 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 gravity to the front and rear axles, respectively, and k r k f These are the lateral stiffness of the front and rear wheels, respectively.

[0073] This invention enables the maximum front wheel steering angle δ to maintain vehicle stability. m The desired front wheel steering angle is input to the PID controller. At the same time, the yaw rate is collected in real time and the current front wheel steering angle is calculated and also input to the PID controller. The PID controller adjusts the steering wheel angle to make the current front wheel steering angle reach the desired front wheel steering angle.

[0074] By precisely controlling the pressure of the brake calipers through the electronic control unit, the front wheel steering angle is immediately corrected when the brake wheel returns to normal rolling state after locking up, controlling the vehicle to move along the desired trajectory, which can give the driver a better road feel and thus create a safer driving experience. In addition, when facing complex road conditions with low friction coefficients such as icy and snowy roads or wet and 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 This is a schematic diagram of the vehicle stability control system during EPB braking degradation provided in an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown. The system includes:

[0076] The acquisition unit is connected to the ESP controller.

[0077] When the EPB switch is triggered and the vehicle is in RWU state, the acquisition unit will send the real-time operating status information of the vehicle to the ESP controller. The operating status information includes: using the wheel speed pulse sensor to obtain the wheel speed pulse, obtaining the acceleration signal and yaw rate signal based on 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 wheels based on the vehicle stability control method during EPB brake degradation. Once the locked wheels return to normal rolling, the front wheel steering angle is corrected to control the vehicle along the desired trajectory. When the ESP controller malfunctions and cannot function properly, the vehicle's braking system actively degrades, entering the rear-wheel anti-lock braking system (RWU) phase. Even on low-friction surfaces, the vehicle maintains stability to ensure safe driving. Furthermore, by precisely controlling the brake caliper pressure through the electronic control unit, the front wheel steering angle is immediately corrected when the locked wheels return to normal rolling, controlling the vehicle along the desired trajectory. This provides the driver with better road feel, creating a safer driving experience.

[0079] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0080] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A vehicle stability control method at the time of EPB brake degradation, characterized by, The method comprises the following steps: (1) detecting whether the wheels are locked when the EPB switch is triggered and the vehicle is in the RWU state, if the result is yes, executing step (2), if the result is no, executing step (3); (2) determining the required braking torque of 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 required braking torque of the additional yaw moment ΔM, and executing step (1); (3) calculating the desired front wheel angle capable of maintaining the stability of the vehicle, and adjusting the steering angle of the steering wheel so that the front wheel angle of the vehicle reaches the desired front wheel angle; The control method of the steering angle is as follows: The maximum front wheel turning angle δ m As the desired front wheel turning angle, the PID controller is input, and the current front wheel turning angle calculated based on the real-time collected yaw rate is input into the PID controller, and the PID controller adjusts the turning angle of the steering wheel so that the current front wheel turning angle reaches the desired front wheel turning angle. Maximum front wheel turning angle δ that can maintain vehicle stability m The calculation formula is as follows: wherein v is the current vehicle speed, L is the wheelbase between the front and rear axles, K is a stability factor, ω d is the yaw rate at the moment before the vehicle loses stability based on the snail experiment.

2. The vehicle stability control method when the EPB is degraded according to claim 1, characterized by, Calculate the slip rate s of each wheel at the current time, and identify the wheel with a slip rate s = 100 at the current time as the locked wheel.

3. The vehicle stability control method when the EPB is degraded according to claim 1, characterized by, When the locked wheel is the left rear wheel, the additional yaw moment ΔM generated during vehicle braking is: When the locked wheel is the right rear wheel, the additional yaw moment ΔM generated during vehicle braking is: wherein F blf , F brf are the braking forces of the left front wheel and the left rear wheel, respectively, F blr , F brr are the braking forces of the right front wheel and the right rear wheel, respectively, T f , T r are the front axle track and the rear axle track of the vehicle, respectively.

4. The vehicle stability control method when the EPB is degraded according to claim 3, characterized by, When the locked wheel is the left rear wheel, the additional yaw moment ΔM under the braking torque T of the left rear wheel brl The calculation formula is: When the locked wheel is the right rear wheel, the additional yaw moment ΔM is added to the braking torque T of the right rear wheel brr The calculation formula is: wherein F zfr , F zrr are the vertical loads of the right front wheel and the right rear wheel, respectively, T f , T r are the front and rear wheel base of the vehicle, respectively, and R is the wheel radius.

5. The vehicle stability control method when the EPB is degraded according to claim 1, characterized by, The wheel cylinder pressure control method of the locked wheel is as follows: The braking torque required by the locked wheel under the additional yaw moment ΔM is taken as the desired braking torque, which is input into the PID controller, and the real-time collected braking torque of the locked wheel under the current pressure is also input into the PID controller, and the PID controller adjusts the wheel cylinder pressure of the locked wheel so that the braking torque of the locked wheel reaches the desired braking torque.

6. The vehicle stability control method when the EPB is degraded according to claim 1, wherein, The calculation formula of the stability factor K is as follows: Wherein, m is the mass of the vehicle, a, b are the distances from the mass center to the front axle and the rear axle respectively, k r , k f are the cornering stiffness of the front wheel and the rear wheel respectively.

7. A vehicle stability control system in the event of EPB brake degradation, characterized by, The system comprises: A collection unit connected to an ESP controller; When the EPB switch is triggered and the vehicle is in the RWU state, the collection unit sends the real-time running state information of the vehicle to the ESP controller, and the ESP controller determines the caliper braking force of the locked wheel based on the vehicle stability control method during EPB braking degradation according to any one of claims 1 to 6, so that the front wheel angle is corrected after the locked wheel returns to the normal rolling state, and the vehicle is controlled to move along the desired trajectory.

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