A segmented compound anti-lock braking control method

Abstract

The present invention discloses a segmented composite anti-lock braking control method. During a braking process, the following steps are cyclically executed: calculating a real-time slip rate; comparing the real-time slip rate with a slip rate threshold; if the real-time slip rate is greater than the slip rate threshold, selecting an anti-lock composite braking mode in combination with the brake pedal opening; when the brake pedal opening is less than α1, adopting motor braking control, and adopting fuzzy PID control to realize anti-lock control; when the brake pedal opening is greater than or equal to α1 and less than α2, adopting anti-lock hybrid braking using electric braking force and hydraulic / pneumatic braking force; when the brake pedal opening is greater than or equal to α2, adopting hydraulic / pneumatic anti-lock braking control, and the electric braking force is withdrawn according to a certain slope based on the original torque; and executing mechanical braking force and electric braking force distribution according to the selected anti-lock composite braking mode.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle braking control, in particular to a segmented composite anti-lock braking control method. Background Art

[0002] With the development of new energy vehicles, braking safety is receiving increasing attention. Unlike fuel-powered vehicles, new energy vehicles must consider not only braking performance but also brake energy recovery. Their braking systems incorporate not only hydraulic / pneumatic braking (including service braking and emergency braking) but also electric braking for energy recovery. Coordinating the hydraulic / pneumatic braking force with the electric braking force to achieve anti-lock braking on low-grip surfaces has become a current research focus. Summary of the Invention

[0003] In view of the above requirements of the prior art, the purpose of the present invention is to provide a segmented composite anti-lock braking control method, which realizes anti-lock control of electric vehicles on low-adhesion roads through the cooperation of hydraulic / pneumatic braking and motor braking.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A segmented compound anti-lock braking control method, during the braking process, cyclically performs the following steps:

[0006] Step S1: Calculate the real-time slip rate;

[0007] Step S2: Compare the real-time slip rate with the slip rate threshold. If the real-time slip rate is greater than the slip rate threshold, go to step S3 to select the anti-lock combined braking mode; otherwise, go to step S5.

[0008] Step S3: Detecting the brake pedal opening. When the brake pedal opening is less than or equal to α1, executing step S31; when the brake pedal opening is greater than α1 and less than or equal to α2, executing step S32; when the brake pedal opening is greater than α2, executing step S33;

[0009] Step S31: Hydraulic / pneumatic braking force is not involved; electric motor force is involved, and the first motor braking anti-lock braking control strategy is executed: a fuzzy PID controller is used to adjust the electric motor force of each wheel end based on the target slip rate, so that the real-time slip rate is controlled near the target value; then the process goes to step S5;

[0010] Step S32: Hydraulic / pneumatic braking force intervenes and executes the hydraulic / pneumatic anti-lock braking control strategy; at the same time, electric braking force intervenes and executes the second electric motor anti-lock braking control strategy: the electric braking force of each wheel end is calculated with reference to the current road adhesion coefficient and vehicle axle load distribution; then the process goes to step S5;

[0011] Step S33: Hydraulic / pneumatic pressure force intervenes and executes the hydraulic / pneumatic anti-lock braking control strategy; at the same time, the motor force of each wheel end is withdrawn according to a certain slope based on the original torque; then the process goes to step S5;

[0012] Step S4: Execute the conventional service brake control strategy; then go to step S5;

[0013] Step S5: Execute the distribution of hydraulic / pneumatic compressive force and electric motor compressive force, and apply the hydraulic / pneumatic compressive force and electric motor compressive force to each wheel end of the vehicle.

[0014] Furthermore, the value of the brake pedal opening α2 is determined according to the set vehicle fully loaded braking deceleration. When the measured vehicle fully loaded braking deceleration is equal to the set value, the brake pedal opening is equal to α2.

[0015] Furthermore, the relationship between the output u and the input e of the fuzzy PID controller in step S31 is:

[0016] e(t)=λ ref -λ real

[0017]

[0018] The PID controller parameter K p , K i , K d The relationship is:

[0019]

[0020] Where ΔK p , ΔK i , ΔK d is the output of the fuzzy controller, K p0 , K i0 , K d0 is the initial value of the PID controller, λ ref is the target slip ratio, λ real is the real-time slip rate.

[0021] Furthermore, the calculation formula of the real-time slip ratio S is:

[0022]

[0023] Where V x is the longitudinal velocity of the wheel, r is the rolling radius of the wheel, and ω is the angular velocity of the wheel.

[0024] Furthermore, the target slip rate is the optimal slip rate of the road surface to be estimated, and the calculation formula is:

[0025]

[0026]

[0027]

[0028] Among them, μ max,b 、μ lock,b 、s opt,b are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the road to be estimated; μ max,1 、μ lock,1 、s opt,1 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the known typical road surface 1; μ max,2 、μ lock,2 、s opt,2 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the known typical road surface 2; μ s,b 、μ s,1 、μ s,2 are the adhesion coefficients of the road to be estimated, typical road 1, and typical road 2 when the slip rate is S.

[0029] Furthermore, the μ-S relationship of the road surface is:

[0030]

[0031] Where S is the real-time slip rate of the road surface; μ max 、μ lock 、S opt They are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the road surface respectively.

[0032] Furthermore, the motor braking anti-lock braking control strategy in step S31 and step S32 is:

[0033] Calculate the front and rear axle load F zf 、F zr :

[0034]

[0035] Where m is the mass of the vehicle; g is the acceleration due to gravity; l f 、l r are the distances from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the distance from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the vehicle's wheelbase g is the height of the vehicle's center of mass; a x is the longitudinal acceleration;

[0036] The motor-assisted braking force at each wheel end is:

[0037]

[0038] Where, Fx is the total motor force; F xf 、F xr Respectively, the front and rear axle electric motor power; F zfl 、F zfr 、F zrl 、F zrr F is the vertical load on each wheel end of the front and rear axles; xfl 、F zfr 、F zrl 、F zrr are the electric motor motive forces of the front and rear driving wheels respectively; i is the adjustment coefficient.

[0039] Furthermore, the adjustment coefficient i ranges from 0.7 to 0.85.

[0040] Furthermore, the process of step S33 is as follows:

[0041] Check whether the hydraulic / pneumatic ABS system is involved;

[0042] When the hydraulic / pneumatic ABS system is detected to be involved, the hydraulic / pneumatic ABS system controls the output of the hydraulic / pneumatic pressing force;

[0043] The motor force exits at a certain slope based on the original torque as the braking time progresses, and the motor force is zero after exiting.

[0044] During the exit process of the electric brake force, it is continuously detected whether the vehicle has exited the braking process. If the vehicle has not exited the braking process, the electric brake force continues to exit or is in the exit state.

[0045] The present invention achieves the following technical effects:

[0046] The segmented composite anti-lock braking control method of the present invention can be applied to new energy vehicles with composite braking functions. It can control the distribution of hydraulic / pneumatic braking force and electric braking force according to the different opening degrees of the brake pedal during service braking. This method does not affect traditional emergency braking habits and can also take into account the cost of the braking system and the efficient recovery of braking energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is the structural form of the composite braking system of new energy vehicles;

[0048] Figure 2 This is the structural form of the coordinated braking control system of the present invention;

[0049] Figure 3 It is the segmented compound anti-lock braking control strategy of the present invention;

[0050] Figure 4It is the fuzzy PID control under the motor braking control at a small brake pedal opening;

[0051] Figure 5 It is the compound anti-lock braking adjustment process under large brake pedal opening;

[0052] Figure 6 This is the anti-lock braking control process under large brake pedal opening;

[0053] Figure 7 It is the μ-S bilinear curve relationship diagram of the road surface;

[0054] Figure 8 It is the μ-S bilinear curve relationship diagram of two typical road surfaces: snow road and wet asphalt road. DETAILED DESCRIPTION

[0055] To further illustrate various embodiments, the present invention provides accompanying drawings. These drawings form part of the present disclosure and are primarily used to illustrate the embodiments and, in conjunction with the relevant description in the specification, to explain the operating principles of the embodiments. By referring to these drawings, those skilled in the art will be able to understand other possible implementations and the advantages of the present invention.

[0056] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0057] According to the different combinations of hydraulic / pneumatic pressing power and electric motor power of new energy vehicles, the compound braking structure can usually be divided into parallel compound braking and series compound braking, such as Figure 1 shown.

[0058] Parallel compound braking does not interfere with the existing hydraulic / pneumatic braking system; it simply adds the electric motor force to the existing friction braking force, without any coordinated control between the two. Series compound braking flexibly and rationally distributes the two different braking forces simultaneously, allowing for greater recovery of braking energy while also ensuring better braking performance.

[0059] In order to balance the cost of the braking control system and the goal of efficiently recovering braking energy, the present invention proposes a coordinated braking control system, such as Figure 2As shown, the system can be based on either parallel or series compound braking, but incorporates coordination between the output of hydraulic / pneumatic and electric braking forces. The coordinated braking system's brake pedal has a predetermined amount of idle travel. During this idle travel, the hydraulic / pneumatic braking force does not intervene in braking control, while only the electric braking force participates. When the brake pedal opening reaches a first set value, the hydraulic / pneumatic braking force intervenes, synchronously participating in the braking process with the electric braking force. During normal service braking, the electric braking force increases with increasing brake pedal opening, remaining constant after reaching a maximum value. The hydraulic / pneumatic braking force increases with increasing brake pedal opening. In emergency braking, anti-lock braking control, combining hydraulic / pneumatic and electric braking forces, is implemented based on the brake pedal opening, switching from normal service braking mode to emergency braking mode, known as anti-lock braking control (ABS).

[0060] Example 1

[0061] For the coordinated braking control system, the present invention proposes a segmented composite anti-lock braking control method. Based on the brake pedal opening and the hydraulic / pneumatic pressure intervention, the anti-lock braking control strategy is formulated in segments by fully utilizing the characteristics of the motor such as fast response and high precision. The method is explained using a four-wheel distributed drive electric bus as an example. Figure 3 The specific implementation steps are as follows.

[0062] Step S1: Calculate the real-time slip ratio S. The real-time slip ratio is expressed as:

[0063]

[0064] Where V x is the longitudinal velocity of the wheel, r is the rolling radius of the wheel, and ω is the angular velocity of the wheel.

[0065] Step S2: Compare the real-time slip rate S with the slip rate threshold. If the real-time slip rate is greater than the slip rate threshold, go to step S3 to select the anti-lock combined braking mode.

[0066] Step S3: Detect the brake pedal opening. When the brake pedal opening is less than or equal to α1, perform anti-lock control under a small brake pedal opening (0<α≤α1); when the brake pedal opening is greater than α1 and less than or equal to α2, perform anti-lock control under a medium brake pedal opening (α1<α≤α2); when the brake pedal opening is greater than α2, perform anti-lock control under a large brake pedal opening (α>α2).

[0067] Step S31, anti-lock control under small brake pedal opening (0<α≤α1):

[0068] In the small brake pedal opening stage (0<α≤α1), the hydraulic / pneumatic pressure force does not intervene, and the brake adjustment is performed only by the electric brake force. In this case, if emergency braking occurs, the electric brake force will execute the first motor braking anti-lock braking control strategy. Specifically, Figure 4 As shown in the figure, the first motor anti-lock braking control strategy in this stage adopts a fuzzy PID controller based on the target slip rate λ ref Adjust the motor force so that the real-time slip rate λ real Controlled near the target value. Specifically expressed as:

[0069] The input of the fuzzy PID controller is the slip error e(t). The relationship between the output u(t) and the input e(t) is as follows:

[0070] e(t)=λ ref -λ real

[0071]

[0072] The PID controller parameter K p , K i , K d for:

[0073]

[0074] Where ΔK p , ΔK i , ΔK d is the output of the fuzzy controller, K p0 , K i0 , K d0 is the initial value of the PID controller.

[0075] Step S32, anti-lock control at a medium brake pedal opening (α1 < α ≤ α2):

[0076] At moderate brake pedal opening (α1 < α ≤ α2), hydraulic / pneumatic compressive force is minimally applied. During service braking, the hydraulic / pneumatic compressive force increases with increasing brake pedal opening, according to the fixed pedal opening-hydraulic / pneumatic compressive force relationship curve. At this point, hydraulic / pneumatic service braking is primarily controlled, with electric braking force providing auxiliary braking. In the event of emergency braking, hydraulic / pneumatic anti-lock braking (ABS) control strategies are implemented based on brake pedal opening, and a secondary electric motor ABS strategy is implemented. The magnitude of the electric braking force is determined by the road adhesion coefficient and vehicle load transfer.

[0077] The value of the brake pedal opening α2 is determined according to the set vehicle fully loaded braking deceleration. For example, in this embodiment, the vehicle fully loaded braking deceleration is set to -0.1g, where g is the acceleration due to gravity.

[0078] Step S33, anti-lock control under large brake pedal opening (α>α2):

[0079] In the stage of large brake pedal opening (α>α2), the hydraulic / pneumatic compressive force intervenes in large quantities, and the size of the hydraulic / pneumatic compressive force has fully met the braking force requirements. At this time, emergency braking occurs, and the hydraulic / pneumatic ABS system is activated. The hydraulic / pneumatic anti-lock braking control strategy is executed according to the brake pedal opening, and anti-lock adjustment can be performed only by relying on the hydraulic / pneumatic compressive force. In order not to destroy the adjustment rules and consistency of the original hydraulic / pneumatic braking system, and to prevent the sudden withdrawal of the electric braking force from seriously affecting the vehicle state, the electric braking force at each wheel end will exit according to a certain slope based on the original torque. After exiting, the electric braking force is zero. Preferably, the exit time of the electric braking force can refer to the braking adjustment cycle of the original hydraulic / pneumatic ABS system. Usually, the exit is completed within one braking cycle. The process is as follows Figure 5 .exist Figure 5 During the time t from 0 to t1 to t2, the brake pedal opening angle α is adjusted from α equal to 0 to α greater than α2, which corresponds to the anti-lock control under small and medium brake pedal openings, and the ABS system's anti-lock control is activated. From t2 to t3, the ABS system completes a braking control, and the electric motor force is completely disengaged within one braking control cycle of the ABS system's anti-lock control.

[0080] In order to avoid frequent activation and deactivation of hydraulic / pneumatic ABS, the electric brake force will not intervene again after the electric brake force is deactivated during a complete braking process. The control process is as follows: Figure 6 , including: brake pedal opening detection. When the brake pedal opening detection is in the state of large-opening brake pedal compound braking, and the hydraulic / pneumatic ABS system intervenes (that is, the ABS system is activated), the electric brake force exits at a certain slope. During the electric brake force exit process, the brake pedal opening is continuously checked to detect whether the vehicle has exited the braking process. If the braking process has not been exited, the electric brake force continues to exit or is in the exit state; if it has already exited, the electric brake force is re-intervened according to the brake pedal opening detection and enters the cycle.

[0081] Step S4: Execute the conventional service brake control strategy; then go to step S5.

[0082] Specifically, in this step, the brake pedal opening must be detected first. When the brake pedal opening is less than or equal to α1, the hydraulic / pneumatic pressing force is not intervened, the electric brake force is intervened, and only the electric brake force is used for service braking, and the electric brake force increases with the increase of the pedal opening; when the brake pedal opening is greater than α1, the hydraulic / pneumatic pressing force is intervened, and the hydraulic / pneumatic pressing force increases with the increase of the brake pedal opening, the electric brake force is intervened, and the electric brake force remains unchanged.

[0083] Step S5: Execute the electric motor braking force and the hydraulic / pneumatic braking force distribution to distribute the braking force to each wheel end of the vehicle.

[0084] In this embodiment, in step S32, the coordinated control of the braking forces on the four drive wheels is performed. Since the braking forces of each wheel-end motor of a distributed drive electric bus are independently controllable and the left and right wheels are susceptible to locking to varying degrees during vehicle operation, a significant difference in road adhesion between the left and right wheels will lead to a sharp increase in the difference in braking forces, resulting in a significant, undesirable additional yaw moment and causing the vehicle to veer under braking. Force analysis also shows that when the front axle locks, the vehicle tends to travel straight and maintain stability, while when the rear axle locks, the vehicle becomes increasingly unstable. Therefore, the front axle utilizes an independent control method that improves braking efficiency, while the rear axle utilizes a low-selection control method that helps maintain braking stability.

[0085] Due to the high center of gravity of some vehicles (such as buses), the axle load is prone to forward shift during braking, which makes the rear axle wheels more likely to lock. In order to take into account both braking stability and braking efficiency, the present invention transfers part of the rear axle motor braking force to the front axle based on the front and rear axle load transfer and road adhesion conditions.

[0086] Front and rear axle load F zf 、F zr The calculations are:

[0087]

[0088] Where m is the mass of the vehicle; g is the acceleration due to gravity; l f 、l r are the distances from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the distance from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the vehicle's wheelbase g is the height of the vehicle's center of mass; a x is the longitudinal acceleration (positive for acceleration drive and negative for deceleration braking).

[0089] Assume that the road adhesion coefficients of the front and rear wheel ends are μ fl 、μ fr 、μ rl 、μ rr , then the maximum braking force that the ground can provide to each wheel is F zflμ fl 、F zfr μ fr 、F zrl μ rl 、F zrr μ rr Combining the axle load transfer and road adhesion conditions, the motor-assisted braking force at each wheel end is:

[0090]

[0091] Where, F x is the total motor power; F xf 、F xr Respectively, the front and rear axle electric motor power; F zfl 、F zfr 、F zrl 、F zrr F is the vertical load on each wheel end of the front and rear axles; xfl 、F xfr 、F xrl 、F xrr are the front and rear driving wheel motor forces respectively; i is the adjustment coefficient, preferably, the adjustment coefficient ranges from 0.7 to 0.85, with a typical value of 0.8.

[0092] Target slip ratio estimation:

[0093] Anti-lock braking control with electric braking force at a small brake pedal opening requires a target slip ratio determined based on road conditions. Meanwhile, the required electric braking force for anti-lock control at a medium brake pedal opening also needs to be determined based on the current road surface adhesion coefficient. In this embodiment, the currently unknown road surface adhesion coefficient is estimated by referring to the adhesion characteristics of a typical road surface.

[0094] Considering that the road surface on urban roads where wheel locking tends to occur is basically between wet asphalt and snowy roads, and the adhesion characteristics of these typical roads are highly similar, in this embodiment, two typical roads, wet asphalt and snowy roads, are selected as reference roads to estimate the peak adhesion coefficient of the unknown road surface. Referring to the most commonly used Burckhardt model, the optimal slip ratio S for the two typical roads can be obtained respectively. opt , Peak road adhesion coefficient μ max , locking adhesion coefficient μ lock Here, the snow road surface is recorded as road surface 1, and the wet asphalt road surface is recorded as road surface 2. In order to further simplify the estimation process, the Burckhardt model is replaced by a bilinear model, and the μ-S relationship of the road surface is obtained as follows, and the relationship curve is as follows: Figure 7 .

[0095]

[0096] The real-time slip ratio S is calculated as follows:

[0097]

[0098] Where V x is the longitudinal velocity of the wheel, r is the rolling radius of the wheel, and ω is the angular velocity of the wheel.

[0099] The bilinear model is used to obtain the μ-S relationship diagram of two typical reference roads, such as Figure 8 .

[0100] Road adhesion coefficient μ b It can be approximately calculated from the ground longitudinal force and vertical load as follows:

[0101]

[0102] Where, F x is the tire longitudinal force, F z is the vertical load, a x is the longitudinal braking deceleration, and g is the acceleration due to gravity.

[0103] Assuming that the unknown road surface when the wheel locks is between a snowy road surface (Road 1) and a wet asphalt road surface (Road 2), the key characteristic parameters of the unknown road surface are estimated based on the linear analogy and weight distribution, referring to the curve data of the two typical roads, as shown below.

[0104]

[0105]

[0106]

[0107] Where μ max,b 、μ lock,b 、s opt,b are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the road to be estimated; μ max,1 、μ lock,1 、s opt,1 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of typical road surface 1; μ max,2 、μ lock,2 、s opt,2 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip ratio of typical road surface 2; μ s,b 、μ s,1 、μ s,2 are the adhesion coefficients of the road to be estimated, typical road 1, and typical road 2 when the slip rate is S.

[0108] The peak adhesion coefficient, locking adhesion coefficient and optimal slip ratio of the unknown road surface can be obtained respectively through the above formulas, thereby uniquely determining the adhesion characteristic curve of the road surface to be estimated.

[0109] In the fuzzy PID controller based on the target slip rate λ ref When adjusting the motor force, the target slip rate is the optimal slip rate of the road surface to be estimated.

[0110] Although the present invention has been particularly shown and described in conjunction with preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the present invention without departing from the spirit and scope of the invention as defined in the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. A segmented compound anti-lock braking control method, characterized in that: During the braking process, the following steps are executed cyclically: Step S1: Calculate the real-time slip rate; Step S2: Compare the real-time slip rate with the slip rate threshold. If the real-time slip rate is greater than the slip rate threshold, go to step S3 to select the anti-lock combined braking mode; otherwise, go to step S4. Step S3: Detecting the brake pedal opening. When the brake pedal opening is less than or equal to α1, executing step S31; when the brake pedal opening is greater than α1 and less than or equal to α2, executing step S32; when the brake pedal opening is greater than α2, executing step S33; Step S31: Hydraulic / pneumatic braking force is not involved; electric motor force is involved, and the first motor braking anti-lock braking control strategy is executed: a fuzzy PID controller is used to adjust the electric motor force of each wheel end based on the target slip rate, so that the real-time slip rate is controlled near the target value; then the process goes to step S5; Step S32: Hydraulic / pneumatic braking force intervenes and executes the hydraulic / pneumatic anti-lock braking control strategy; at the same time, electric braking force intervenes and executes the second electric motor anti-lock braking control strategy: the electric braking force of each wheel end is calculated with reference to the current road adhesion coefficient and vehicle axle load distribution; then the process goes to step S5; Step S33: Hydraulic / pneumatic pressure force intervenes and executes the hydraulic / pneumatic anti-lock braking control strategy; at the same time, the motor force of each wheel end is withdrawn according to a certain slope based on the original torque; then the process goes to step S5; Step S4: Execute the conventional service brake control strategy; then go to step S5; Step S5: executing hydraulic / pneumatic compressing force and electric motor compressing force distribution, applying the hydraulic / pneumatic compressing force and electric motor compressing force to each wheel end of the vehicle; The relationship between the output u(t) and the input e(t) of the fuzzy PID controller in step S31 is: e(t)=S ref -S The PID controller parameter K p , K i , K d The relationship is: Where ΔK p , ΔK i , ΔK d is the output of the fuzzy controller, K p0 , K i0 , K d0 is the initial value of the PID controller, S ref is the target slip rate, S is the real-time slip rate; The second motor braking anti-lock braking control strategy in step S32 is: Calculate the front and rear axle load F zf 、F zr : Where m is the mass of the vehicle; g is the acceleration due to gravity; l f 、l r are the distances from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the distance from the vehicle's center of mass to the front and rear axles, respectively; l is the vehicle's wheelbase; h is the vehicle's wheelbase g is the height of the vehicle's center of mass; a x is the longitudinal acceleration; The motor-assisted braking force at each wheel end is: Where, F x is the total motor power; F xf 、F xr Respectively, the front and rear axle electric motor power; F zfl 、F zfr 、F zrl 、F zrr F is the vertical load on each wheel end of the front and rear axles; xfl 、F xfr 、F xrl 、F xrr are the electric motors for the front and rear driving wheels respectively; μ fl 、μ fr 、μ rl 、μ rr are the road adhesion coefficients of the front and rear wheel ends respectively; i is the adjustment coefficient.

2. The segmented compound anti-lock braking control method according to claim 1, characterized in that: The value of the brake pedal opening α2 is determined according to the set vehicle fully loaded braking deceleration. When the measured vehicle fully loaded braking deceleration is equal to the set value, the brake pedal opening is equal to α2.

3. The segmented compound anti-lock braking control method according to claim 1, characterized in that: The calculation formula of the real-time slip ratio S is: Where V x is the longitudinal velocity of the wheel, r is the rolling radius of the wheel, and ω is the angular velocity of the wheel.

4. The segmented compound anti-lock braking control method according to claim 1, characterized in that: The target slip rate is the optimal slip rate of the road surface to be estimated, and the calculation formula is: Among them, μ max,b 、μ lock,b 、s opt,b are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the road to be estimated; μ max,1 、μ lock,1 、s opt,1 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the known typical road surface 1; μ max,2 、μ lock,2 、s opt,2 are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the known typical road surface 2; μ s,b 、μ s,1 、μ s,2 are the adhesion coefficients of the road surface to be estimated, typical road surface 1, and typical road surface 2 at the real-time slip rate S, respectively. The typical road surface 1 is a snowy road surface, and the typical road surface 2 is a wet asphalt road surface.

5. The segmented compound anti-lock braking control method according to claim 4, characterized in that: The μ-S relationship of the road surface is: Where S is the real-time slip rate of the road surface; μ max 、μ lock 、S opt They are the peak adhesion coefficient, locking adhesion coefficient and optimal slip rate of the road surface respectively.

6. The segmented compound anti-lock braking control method according to claim 1, characterized in that: The adjustment coefficient i ranges from 0.7 to 0.

85.

7. The segmented compound anti-lock braking control method according to claim 1, wherein: The process of step S33 is as follows: Check whether the hydraulic / pneumatic ABS system is involved; When the hydraulic / pneumatic ABS system is detected to be involved, the hydraulic / pneumatic ABS system controls the output of the hydraulic / pneumatic pressing force; The motor force exits at a certain slope based on the original torque as the braking time progresses, and the motor force is zero after exiting. During the exit process of the electric brake force, it is continuously detected whether the vehicle has exited the braking process. If the vehicle has not exited the braking process, the electric brake force continues to exit or is in the exit state.

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