A closed-loop control method applied to an automobile anti-lock braking system (ABS)

Abstract

The application relates to the technical field of engine system control safety, in particular to a closed-loop control method applied to an automobile anti-lock braking system (ABS). The closed-loop control method calls a wheel brake closed-loop control model based on braking torque Ta of a braking system, obtains real-time braking torque Ta of a brake, calculates real-time slip rate lambda and ground braking force Fs currently borne by the wheel, thereby calculates the first derivative F_s' of the ground braking force Fs, dynamically adjusts the braking torque Ta by taking the first derivative F_s' of the ground braking force Fs proportional to the adhesion coefficient as a feedback factor, so as to adjust the slip rate lambda to a preset range of optimal slip rate lambda k, indirectly estimates the current ground braking force Fs by taking the adhesion coefficient as a feedback factor, and introduces the first derivative of the ground braking force Fs proportional to the adhesion coefficient as a feedback factor, so as to dynamically adjust the braking torque, effectively prevents vehicle out-of-control caused by road surface mutation, and improves driving safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of engine system control safety technology, in particular to a closed-loop control method applied to an automobile anti-lock braking system (ABS). BACKGROUND

[0002] In modern automobile safety technology, the anti-lock braking system (ABS) plays a crucial role. It can effectively prevent the wheels from locking during emergency braking, thereby maintaining the vehicle's steering ability and stability, greatly improving the safety of driving. The traditional ABS system mainly monitors the wheel speed through a wheel speed sensor and adjusts the braking torque accordingly to avoid wheel locking. However, with the continuous advancement of technology, ABS employs more and more complex control strategies. Currently, the ABS scheme mainly sets a threshold speed to increase (or decrease) the speed, but this scheme requires multiple experimental data when setting the value. Or it takes a certain fixed slip rate (such as 20%) as the adjustment target, but the optimal slip rate is different on different road surfaces. If a certain fixed slip rate is used as the adjustment target, it cannot cope with different road conditions. In addition, the vehicle body speed is also a necessary condition for calculating the slip rate, but the vehicle body speed is difficult to measure, requiring higher sensor requirements.

[0003] According to the research of the prior art, see Figure 1 The force analysis diagram of a single wheel during braking, where w is the wheel angular velocity, V is the vehicle speed, r is the wheel radius, Ta is the brake torque, and Fs is the ground braking force. Ignoring the relatively small factors such as air resistance, the wheel dynamics equation is:

[0004] Jw'=F_s r-T_a(1)

[0005] In the formula, J is the rotational inertia of the wheel, and the ground braking force Fs satisfies the following formula:

[0006] F_S=μ(λ)mg (2)

[0007] In the formula, m is the weight of the vehicle, the longitudinal adhesion coefficient µ is a function of the slip rate λ, which increases first and then decreases with the increase of the slip rate, and reaches the maximum value at the optimal slip rate λ_k, as shown in Figure 2 The optimal slip rate λ_k is not a fixed value and varies with different road conditions. That is, the ground braking force Fs also increases first and then decreases with the increase of the slip rate, and has different maximum braking force F_smax on different road surfaces.

[0008] The slip rate is calculated by the following formula: λ=(v-wr) / v×100%

[0009] Based on the prior art, the present application has the following improvements: Figure 2Analyzing the relationship between the adhesion coefficient and slip ratio, we find that the longitudinal adhesion coefficient is maximized when the slip ratio λ is at the optimal slip ratio λk. Therefore, when braking, it is desirable to maintain the slip ratio near λk, which is the shaded area in the figure.

[0010] Combining formulas (1), (2), and (3) with Figure 2 , it can be concluded that when the brake torque Ta is too large, the wheel angular velocity w decreases rapidly, and the slip ratio λ increases rapidly, resulting in an insufficient ground braking force Fs, or even locking (wheel angular velocity is 0). When the brake torque is too small, the wheel decelerates slowly, and the braking time is prolonged, increasing the possibility of danger. Therefore, existing technologies use the wheel angular velocity w and the braking torque Ta provided by the brake as feedback to adjust the slip ratio to maintain it near λk. However, this solution still suffers from accuracy issues in practical applications.

[0011] Therefore, how to confirm the ABS control scheme relatively conveniently and accurately has become an urgent problem that needs to be solved in the industry. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a relatively convenient and accurate ABS control method.

[0013] In order to solve the above technical problems, the inventors came up with the idea of ​​collecting the current wheel angular velocity w and the braking torque Ta provided by the brake, and calculating the angular acceleration. Then, the ground braking force F_s and its derivative F_s' on the current wheel are calculated by formula (1). Finally, F_s' is introduced into the control system, and the braking torque is adjusted according to F_s' to keep the slip ratio always near λk. The control block diagram is shown as follows: Figure 3 shown.

[0014] The present invention provides a closed-loop control method for an automobile anti-lock braking system (ABS), comprising the following steps:

[0015] A wheel brake closed-loop control model based on the braking torque Ta of the braking system is called to obtain the real-time braking torque Ta of the brake. Based on this, the real-time slip rate λ and the ground braking force Fs currently acting on the wheel are calculated, thereby calculating the first-order derivative F_s' of the ground braking force Fs. The calculated first-order derivative F_s' is used as the feedback factor of the wheel brake closed-loop control model to dynamically adjust the braking torque Ta to adjust the slip rate λ to within the preset range of the optimal slip rate λk.

[0016] Furthermore, the dynamic adjustment refers to:

[0017] S1. If the first-order derivative of the ground braking force Fs is positive and the wheel angular acceleration is less than 0, increase the braking torque.

[0018] S2. If the first-order derivative of the ground braking force Fs is negative and the wheel angular acceleration is greater than 0, increase the braking torque.

[0019] S3. If the first-order derivative of the ground braking force Fs is positive and the wheel angular acceleration is greater than 0, reduce the braking torque.

[0020] S4. If the first-order derivative of the ground braking force Fs is negative and the wheel angular acceleration is less than 0, reduce the braking torque.

[0021] Furthermore, the degree to which S1 increases the braking torque is greater than that of S2.

[0022] Furthermore, the degree to which S3 reduces the braking torque is smaller than that of S4.

[0023] Furthermore, the vehicle parameters include wheel parameters and brake output parameters, and the wheel parameters include rotation speed and acceleration.

[0024] Furthermore, the adhesion coefficient is calculated according to the real-time slip ratio λ, and the current ground braking force Fs is proportional to the adhesion coefficient.

[0025] The present invention has the following beneficial effects: the closed-loop control method of the present invention uses the adhesion coefficient as a feedback factor, calculates the real-time slip rate λ and the ground braking force Fs currently exerted on the wheel based on the braking torque and the resulting deceleration effect, thereby calculating the first-order derivative F_s' of the ground braking force Fs, and uses the calculated first-order derivative F_s' as a feedback factor of the wheel brake closed-loop control model to dynamically adjust the braking torque Ta, so as to adjust the slip rate λ to within a preset range of the optimal slip rate λk. By using the adhesion coefficient as a feedback factor, the current ground braking force Fs is indirectly estimated, and the first-order derivative of the ground braking force Fs, which is proportional to the adhesion coefficient, is introduced as a feedback factor to achieve dynamic adjustment of the braking torque, thereby controlling the vehicle's braking force to maintain the maximum adhesion coefficient, preventing wheel locking, effectively preventing vehicle loss of control due to sudden changes in road surface, and further improving driving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the wheel force model in the prior art.

[0027] Figure 2 It is the relationship curve between adhesion coefficient and slip rate of the existing technology.

[0028] Figure 3 The present invention is a control block diagram of a brake system using the ABS closed-loop control method. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific embodiments.

[0030] The closed-loop control method of the present embodiment is applied to the anti-lock braking system ABS of an automobile. Figure 3 Using the adhesion coefficient as a feedback factor, the system indirectly estimates the current ground braking force Fs (proportional to the adhesion coefficient) by real-time monitoring of the braking torque and its resulting deceleration effect. The first derivative (i.e., rate of change) of this ground braking force Fs, which is proportional to the adhesion coefficient, is then introduced as a feedback factor to dynamically adjust the braking torque. Specifically, the current ground braking force Fs (proportional to the adhesion coefficient) is estimated and its first derivative is used as a feedback factor to adjust the braking torque. As shown in Table 1 below, if the first derivative of the ground braking force Fs is positive (i.e., the adhesion coefficient is increasing) and the wheel angular acceleration is less than 0, or if it is negative (i.e., the adhesion coefficient is decreasing) and the wheel angular acceleration is greater than 0, the braking torque is increased. If the first derivative of the ground braking force Fs is positive (i.e., the adhesion coefficient is increasing) and the wheel angular acceleration is greater than 0, or if it is negative (i.e., the adhesion coefficient is decreasing) and the wheel angular acceleration is less than 0, the braking torque is reduced.

[0031] Table 1 Braking force control scheme

[0032]

[0033] by Figure 2 The specific implementation process of the closed-loop control method applied to the automobile anti-lock braking system ABS of this embodiment is specifically described by taking the relationship curve of Figure 2 Point A represents the case where λ < λ_k, and Point B represents the case where λ > λ_k. Based on the current braking torque and the longitudinal ground braking force Fs, four scenarios can be discussed. The first two cases increase the braking torque, while the latter two cases decrease it.

[0034] 1. Adhesion coefficient increases and wheel deceleration (the first derivative of the ground braking force Fs is positive and the wheel angular acceleration is less than 0): At this time, the road conditions are improving and the vehicle has greater potential for more efficient braking. Therefore, the system increases the braking torque to fully utilize the increased ground braking force Fs. Specifically, T_a<F_s r(即 ω^'> 0), and λ < λ_k: Since ω^' > 0 (ω is increasing), λ decreases, and λ is less than the optimal slip ratio, the longitudinal adhesion also decreases, meaning F_s' < 0. According to the control scheme, T_a increases. When the braking torque increases to a value greater than the longitudinal adhesion, ω^' < 0 (ω is decreasing), and λ increases, approaching the optimal slip ratio.

[0035] 2. Adhesion coefficient decreases and wheel acceleration (the first-order derivative of the ground braking force Fs is negative and the wheel angular acceleration is greater than 0): This situation usually occurs when transitioning from a high-friction road surface to a low-friction road surface. In order to prevent the wheels from slipping suddenly, the system will also increase the braking torque to maintain vehicle stability. Specifically, T_a<F_s r(即 ω^'> 0), and λ>λ_k: Since ω^'>0, that is, ω is increasing, λ is decreasing, and λ is greater than the optimal slip ratio, the longitudinal adhesion is increasing, that is, F_s'>0. According to the control scheme, T_a will decrease, so ω^'>0 is still satisfied, and λ continues to decrease, that is, approaching the optimal slip ratio.

[0036] 3. Adhesion coefficient increases and wheels accelerate (the first-order derivative of the ground braking force Fs is positive and the wheel angular acceleration is greater than 0): Although road conditions are improving, wheel acceleration indicates that the current braking torque may be insufficient or excessive. Braking torque should be appropriately reduced according to the specific situation to avoid discomfort or tire wear caused by excessive braking. Specifically, T_a > F_s r (i.e., ω^' < 0), and λ < λ_k: Since ω^' < 0, i.e., ω is decreasing, λ increases. At this time, λ is less than the optimal slip ratio, and longitudinal adhesion increases, i.e., F_s' > 0. According to the control scheme, T_a will increase, so ω^' > 0 is still satisfied, and λ continues to increase, approaching the optimal slip ratio.

[0037] 4. Adhesion coefficient decreases and wheel deceleration occurs (the first derivative of the ground braking force Fs is negative, and the wheel angular acceleration is less than 0): Road conditions deteriorate, and continuing to apply the same braking torque may cause wheel lock. Therefore, the system should reduce the braking torque to maintain the wheel's rolling state. Specifically, T_a>F_s r (i.e., ω^'<0), and λ>λ_k: Since ω^'<0, i.e., ω is decreasing, λ increases, and λ is greater than the optimal slip ratio, the longitudinal adhesion also decreases, i.e., F_s'<0. According to the control scheme, T_a will decrease. When the braking torque decreases to less than the longitudinal adhesion, ω^'>0, i.e., ω is increasing, and λ decreases, approaching the optimal slip ratio.

[0038] This embodiment not only improves the ABS system's response speed and accuracy, but more importantly, it intelligently adjusts braking torque based on complex and changing road conditions, maximizing the utilization of the ground braking force Fs between the tire and the road surface, thereby providing optimal braking performance under various road conditions. Furthermore, by monitoring changes in the adhesion coefficient in real time, this method effectively prevents vehicle loss of control due to sudden road surface changes, further enhancing driving safety.

[0039] Furthermore, the adhesion coefficient (μ), a key parameter describing the ground braking force Fs between the tire and the road, directly impacts the vehicle's braking performance. A high adhesion coefficient means a greater ground braking force Fs between the tire and the road, resulting in better braking. Conversely, a low adhesion coefficient (such as on wet, icy, or snowy roads) increases braking distance and may even cause skidding. Therefore, accurately assessing and adapting to current road adhesion conditions is crucial for optimizing ABS control strategies.

[0040] This embodiment uses real-time monitored environmental parameters to provide early warnings for the ABS control logic. Specifically, the system acquires ABS control strategies under different environmental parameters over a period of time, builds a classification model, and trains the model using the different environmental parameters as input and the corresponding ABS control strategies as output. This model is then trained to output the corresponding ABS control strategies based on the input environmental parameters. While the vehicle is in motion, the current environmental parameters are acquired in real time, and the corresponding ABS control logic for these parameters is output. Increasing braking torque in the ABS control logic is associated with a brake-tightening voice warning, while decreasing braking torque is associated with a brake-weakening voice warning, which is then output to the vehicle's voice control system.

[0041] The environmental parameters monitored in this embodiment include road surface type, road surface condition, and weather conditions. Road surface type: Different types of road surfaces (such as asphalt, concrete, and dirt roads) have different adhesion coefficients. Dry, hard roads generally have higher adhesion coefficients, while wet, soft roads have lower adhesion coefficients. Road surface condition: Whether there is water accumulation, ice, snow, oil stains, etc. on the road surface, all of which will significantly affect the grip of the wheels. For example, wet and slippery roads will reduce the adhesion coefficient and increase braking distance. Weather conditions: Severe weather such as rainy, snowy, and foggy days will affect the adhesion conditions of the road surface. Rainy days will make the road surface slippery, snowy days will make the road surface icy, and foggy days will affect visibility.

[0042] The training model used in this embodiment is a general classification model, such as a naive Bayes model, a K-nearest neighbor (KNN) classification model, or a support vector machine (SVM) classification model.

[0043] The above is only an embodiment of the present invention and does not limit the scope of patent protection. Those skilled in the art can make non-substantial changes or substitutions based on the present invention and still fall within the scope of patent protection.

Claims

1. A closed-loop control method for an automobile anti-lock braking system (ABS) is characterized by: Invoking a wheel brake closed-loop control model based on the braking system's braking torque Ta to obtain real-time vehicle parameters and the brake's braking torque Ta, and based on these, calculating the current wheel's ground braking force Fs, which is proportional to the adhesion coefficient, and the slip ratio λ. This first-order derivative F_s' of the ground braking force Fs is then calculated. The calculated first-order derivative F_s' is used as a feedback factor in the wheel brake closed-loop control model to dynamically adjust the braking torque Ta to keep the slip ratio λ within a preset range of the optimal slip ratio λk. The dynamic adjustment refers to: S1. If the first-order derivative of the ground braking force Fs is positive and the wheel angular acceleration is less than 0, increase the braking torque. S2. If the first-order derivative of the ground braking force Fs is negative and the wheel angular acceleration is greater than 0, increase the braking torque. S3. If the first-order derivative of the ground braking force Fs is positive and the wheel angular acceleration is greater than 0, reduce the braking torque. S4. If the first-order derivative of the ground braking force Fs is negative and the wheel angular acceleration is less than 0, reduce the braking torque.

2. The closed-loop control method for an automobile anti-lock braking system (ABS) according to claim 1, wherein: The degree to which S1 increases the braking torque is greater than that of S2.

3. The closed-loop control method for an automobile anti-lock braking system (ABS) according to claim 1, wherein: The extent to which S3 reduces the braking torque is smaller than that of S4.

4. The closed-loop control method for an automobile anti-lock braking system (ABS) according to claim 1, wherein: The vehicle parameters include wheel parameters and brake output parameters, and the wheel parameters include rotation speed and acceleration.

5. The closed-loop control method for an automobile anti-lock braking system (ABS) according to claim 1, wherein: The adhesion coefficient is calculated based on the adjusted real-time slip ratio λ.

Images