A method of dynamic braking force control for a multi-axle vehicle

Abstract

This invention relates to a dynamic braking force control method for multi-axle vehicles, belonging to the field of vehicle dynamic control technology. The method includes the following steps: acquiring static load, wheel speed, and vehicle speed information for each wheel, and calculating the slip ratio of each wheel; establishing a braking dynamics equation for a multi-axle vehicle while preserving suspension constraint characteristics, and calculating the dynamic load of each wheel; reducing the braking force distribution ratio of the wheel with the maximum slip ratio, normalizing the braking force distribution ratio of each wheel according to the braking force ratio between each wheel, and calculating the required dynamic braking force for each wheel. This invention proposes a braking force control method for multi-axle vehicles that preserves suspension constraint characteristics, transforming the dynamic load of each axle into the dynamic load of each wheel, allowing for accurate and simple calculation; estimating the slip ratio of each wheel based on the dynamic load and state of each wheel, achieving the purpose of suppressing the maximum slip ratio and synchronizing the slip ratios of each wheel, and rationally distributing the braking force of each wheel, effectively reducing the probability of premature wheel lock-up.

Description

Technical Field

[0001] This invention relates to the field of vehicle power control technology, and in particular to a dynamic braking force control method for multi-axle vehicles. Background Technology

[0002] Anti-lock braking system (ABS) prevents wheel lock-up by adjusting braking force, thus avoiding dangerous situations such as skidding and sideslip. In this process, ABS maintains the vehicle's maximum road grip performance, keeping the wheel slip ratio within a small range to provide greater longitudinal and lateral forces, achieving the goal of obtaining maximum braking force, minimum lateral slip, and best braking and steering performance.

[0003] Current ABS systems only control each wheel individually during vehicle braking. While this effectively prevents wheel lock-up, it has significant shortcomings in brake force distribution from the perspective of overall vehicle motion and force analysis. Taking a four-axle commercial vehicle as an example, its long body and uneven mass distribution cause significant variations in the dynamic load on each wheel due to the shifting center of gravity. This also results in unequal ground adhesion for each axle, causing some wheels to fail to meet the braking intensity requirements of ABS. Consequently, the time it takes for each wheel to reach its optimal slip ratio is inconsistent. From the perspective of overall braking performance, a four-axle commercial vehicle cannot fully utilize ground adhesion to achieve the best braking effect. Furthermore, from a comfort perspective, if there is a large difference in slip ratio between the front and rear axles during braking, the braking states of each wheel will be completely different, significantly impacting passenger comfort.

[0004] For the reasons mentioned above, in order to improve braking force distribution and comfort, reduce the probability of ABS triggering, and with the iterative upgrades of brake-by-wire systems, electronic brake force distribution (EBD) has become an important braking safety measure to improve and enhance ABS and has been widely used.

[0005] In summary, the primary challenge in brake force distribution for four-axle commercial vehicles lies in accurately determining the dynamic load on each wheel. This is crucial for achieving high performance in multi-axle vehicles, particularly in terms of maneuverability and braking safety. Various equivalent calculation methods proposed for classic braking dynamics models of two-axle vehicles have yielded less than ideal results when applied to multi-axle vehicles. Therefore, simply borrowing theories and methods from two-axle vehicles is insufficient to solve these problems. my country's design and manufacturing of high-performance multi-axle vehicles remains largely based on empirical design. Secondly, traditional brake force distribution relies on fixed brake force distribution coefficients, and later, fixed slip ratio control thresholds were used to control the braking torque of the front and rear wheels. While this approach offers advantages such as low computational complexity and ease of control, it suffers from drawbacks including significant differences in slip ratios between wheels, insufficient flexibility in slip ratio control, and an inability to effectively reduce the possibility of premature wheel lock-up.

[0006] Therefore, it is necessary to improve one or more of the problems existing in the above-mentioned related technical solutions.

[0007] It should be noted that this section is intended to provide background or context for the embodiments of this disclosure set forth in the claims. The description herein does not constitute an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0008] The purpose of this invention is to provide a dynamic braking force control method for multi-axle vehicles, thereby overcoming, at least to some extent, one or more problems caused by the limitations and defects of related technologies.

[0009] This invention provides a dynamic braking force control method for a multi-axle vehicle, comprising the following steps:

[0010] Obtain information on the static load, wheel speed, and vehicle speed of each wheel, and calculate the slip ratio of each wheel;

[0011] Establish braking dynamics equations for multi-axle vehicles that retain suspension constraint characteristics, and calculate the dynamic load on each wheel;

[0012] The braking force distribution ratio of the wheel with the largest slip ratio is reduced. The braking force distribution ratio of each wheel is normalized according to the braking force ratio between each wheel. The required dynamic braking force of each wheel is then calculated.

[0013] Preferably, the multi-axle vehicle has 2, 3, 4 or 6 axles.

[0014] Preferably, the step of establishing the braking dynamics equations for a multi-axle vehicle while retaining suspension constraint characteristics and calculating the dynamic load on each wheel includes:

[0015] Estimate the longitudinal and lateral positions of the vehicle's center of gravity;

[0016] Based on the forces acting in the vertical direction, we derive independent force balance equations and moment balance equations for each wheel.

[0017] Considering the suspension constraint characteristics, we take the deformation compatibility equations;

[0018] The dynamic load of each wheel is calculated based on the independent force balance equation, moment balance equation, and deformation compatibility equation for each wheel.

[0019] Preferably, the slip ratio κ of each wheel is calculated. i The calculation formula is as follows:

[0020]

[0021] Where i is the wheel number corresponding to each axle. When the vehicle has 4 axles, i = 1 to 8, which refer to the left wheel of axle 1, the right wheel of axle 1, the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4, respectively; V X For longitudinal vehicle speed, ω i Let r be the angular velocity of the i-th wheel, and r be the wheel radius.

[0022] Preferably, when the vehicle has 4 axles, the calculation process for estimating the longitudinal and lateral positions of the vehicle's center of gravity is as follows:

[0023] The longitudinal distance L from the center of mass to the first axle is estimated based on the static load of each wheel. cx The calculation formula is as follows:

[0024]

[0025] Where L1, L2, and L3 are the longitudinal distances from axle 1 to axle 2, from axle 2 to axle 3, and from axle 3 to axle 4, respectively; m1 to m8 are the static loads of the left wheel of axle 1, the right wheel of axle 1, the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4, respectively, in kg.

[0026] Estimate the lateral distance L from the center of mass to the line connecting the midpoints of each axle. cy The calculation formula is as follows:

[0027]

[0028] Where Lw refers to the wheelbase of the left and right wheels of each axle. In this formula, the wheelbase of the left and right wheels of each axle is equal. G is the vehicle's weight, and g is the acceleration due to gravity.

[0029] Preferably, the calculation process for deriving the independent force balance equations and moment balance equations for each wheel based on the vertical force conditions is as follows:

[0030] The formula for calculating the vehicle's weight G is as follows:

[0031]

[0032] Based on the vertical force equilibrium, the first independent force equilibrium equation is obtained, as shown below:

[0033] A1·F=b1 (5)

[0034] Wherein, the coefficient matrix A1 = [1, 1, 1, 1, 1, 1, 1, 1], and F is the dynamic load matrix, F = [F1, F2, F3, F4, F5, F6, F7, F8]. TF1 to F8 correspond to the dynamic loads of the left wheel of the first axle, the right wheel of the first axle, the left wheel of the second axle, the right wheel of the second axle, the left wheel of the third axle, the right wheel of the third axle, the left wheel of the fourth axle, and the right wheel of the fourth axle, with the unit being N, and b1 = G;

[0035] Taking the right-side contact point of the axle as the origin, the line connecting the right wheel contact points as the x-axis, and the forward longitudinal direction as the positive x-axis of the coordinate system, with the direction perpendicular to the x-axis pointing to the left as the positive y-axis, we perform torque balance about the x-axis to obtain the second independent equilibrium equation, as shown below:

[0036] A²·F=b² (6)

[0037] Where, the coefficient matrix A2 = [1, 0, 1, 0, 1, 0, 1, 0], For lateral acceleration, h g The height of the center of mass is in meters (m).

[0038] By applying torque balance about the y-axis, we obtain the third independent equilibrium equation, as shown below:

[0039] A3·F=b3 (7)

[0040] Wherein, the coefficient matrix Longitudinal acceleration, in m / s² 2 .

[0041] Preferably, the calculation process for taking the deformation compatibility equation considering the suspension constraint characteristics is as follows:

[0042] Based on the suspension constraint characteristics, the following formula is obtained:

[0043]

[0044] Where, Δz i’ It is the suspension deformation on one side of the i'-th axis, i'=1~4, Δz i’+1 It is the suspension deformation on the same side of the i'+1th axis, Δz i’+n This refers to the suspension deformation on the same side of the (i'+n)th axis. Let the stiffness of the suspension on the i'th axis side be K. i’ Here, it is assumed that the suspension stiffness on the left and right sides of the same axle is the same. The unit is m; F is the dynamic load of the wheel on the same side of the axle, in N; L i’ It represents the distance between the i'-th axis and the (i'+1)-th axis; n represents the nth axis excluding the i'-th axis starting from the i'-th axis; j represents values ​​from 0 to n-1; L i’+j It is the distance between the i'+j-th axis and the i'+j+1-th axis; when i'=1, n takes 2 or 3, and j takes 0, 1 or 2.

[0045] Preferably, according to formula (8), when n takes the values ​​of 3 and 2 respectively, a fourth independent equation can be obtained for the left wheel and a fifth independent equation can be obtained for the right wheel, as shown below:

[0046] A4·F=b4 (9)

[0047] A5·F=b5 (10)

[0048] Wherein, the coefficient matrix coefficient matrix K1, K2, K3, and K4 represent the stiffness of the suspension on one side of the first, second, third, and fourth axles, respectively. Here, it is assumed that the stiffness of the suspension on the left and right sides of the same axle is the same.

[0049] Preferably, the calculation process for calculating the dynamic load of each wheel based on the independent force balance equation, moment balance equation, and deformation compatibility equation of each wheel is as follows:

[0050] Solving equations (2)-(10) simultaneously, we obtain the following formula:

[0051] A·F=b (11)

[0052] in,

[0053] Multiply both sides of the equation (11) by the inverse of matrix A to obtain the dynamic load matrix of each wheel, as shown below:

[0054] F = A -1 ·b (12)

[0055] The initial value of the braking force distribution coefficient D is obtained by calculating the ratio matrix of dynamic load to vehicle mass of each wheel according to the following formula, as shown below:

[0056]

[0057] Preferably, the reduction of the braking force distribution ratio of the wheel with the maximum slip ratio involves normalizing the braking force distribution ratio of each wheel based on the braking force ratio between each wheel, and the calculation process for obtaining the required dynamic braking force for each wheel is as follows:

[0058] Based on the slip ratio of each wheel, the step size of the actuator feedback signal is defined as T, and the slip ratio control coefficient is defined as σ.

[0059] Find the maximum slip ratio κ of each wheel within the k-th step of the continuous feedback step. max_t+kT As shown below:

[0060] κ max_t+kT =max(κ) 1_t+kT κ 2_t+kT κ3_t+kT κ 4_t+kT κ 5_t+kT κ 6_t+kT κ 7_t+kT κ 8_t+kT (14)

[0061] Where k = 0, 1, 2, ..., n', n' represents a total of n' feedback steps, and the subscript t+kT represents the k-th feedback step starting from time t; max(*) represents the maximum function, κ *_t+kt This indicates the slip ratio of the *th wheel;

[0062] Within the k-th step of the continuous feedback step, the braking force distribution ratio at the maximum slip ratio is reduced, and the braking force ratio S of that step is reduced accordingly. t+kT As shown below:

[0063]

[0064] By solving equations (13) and (15) simultaneously, the braking force distribution ratio of each wheel is normalized to obtain the normalized braking force Ds of each wheel at step k. t+kT As shown below:

[0065]

[0066] The present invention can achieve the following beneficial effects:

[0067] This invention proposes a braking force control method for multi-axle vehicles that retains suspension constraint characteristics. The dynamic load of each axle is converted into the dynamic load of each wheel, which can be calculated accurately and simply. Based on the calculated dynamic load and state of each wheel, the slip ratio of each wheel is estimated, thereby suppressing the maximum slip ratio and synchronizing the slip ratio of each wheel. The braking force of each wheel is reasonably distributed, effectively reducing the probability of premature wheel lock-up. Attached Figure Description

[0068] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0069] Figure 1 A flowchart illustrating the dynamic braking force control method for a multi-axle vehicle in an embodiment of the present invention is shown.

[0070] Figure 2 This document illustrates a flowchart of establishing the braking dynamics equations for a multi-axle vehicle while retaining suspension constraint characteristics, and calculating the dynamic load on each wheel, in an embodiment of the present invention.

[0071] Figure 3 This diagram illustrates a four-axle vehicle braking dynamics model incorporating suspension deformation coordination in an embodiment of the present invention.

[0072] Figure 4 This diagram illustrates the force analysis of a four-axle vehicle frame considering suspension deformation and linear constraints in an embodiment of the present invention.

[0073] Figure 5 This diagram illustrates the braking force ratio allocation architecture based on slip ratio synchronization in an embodiment of the present invention. Detailed Implementation

[0074] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0075] This invention provides a dynamic braking force control method for multi-axle vehicles, such as... Figure 1 As shown, it includes the following steps:

[0076] Step S100: Obtain information on the static load, wheel speed, and vehicle speed of each wheel, and calculate the slip ratio of each wheel;

[0077] Step S200: Establish the braking dynamics equations for a multi-axle vehicle while retaining suspension constraint characteristics, and calculate the dynamic load on each wheel;

[0078] Step S300: Reduce the braking force distribution ratio of the wheel with the maximum slip ratio. Normalize the braking force distribution ratio of each wheel according to the braking force ratio between each wheel. Calculate the required dynamic braking force for each wheel.

[0079] In this embodiment of the invention, a braking force control method for multi-axle vehicles that retains suspension constraint characteristics is proposed. The dynamic load of each axle is converted into the dynamic load of each wheel, which can be calculated accurately and simply. Based on the calculated dynamic load and state of each wheel, the slip ratio of each wheel is estimated, thereby suppressing the maximum slip ratio and synchronizing the slip ratio of each wheel. The braking force of each wheel is reasonably distributed, effectively reducing the probability of premature wheel lock-up.

[0080] In some embodiments, the number of axles in the multi-axle vehicle can be 2, 3, 4, or 6, but is not limited to these. Calculations only need to be performed based on the number of axles.

[0081] It is understandable that, such as Figure 2As shown, step S200 may further include steps S201-S204:

[0082] Step S201: Estimate the longitudinal and lateral positions of the vehicle's center of gravity.

[0083] Step S202: Based on the forces acting in the vertical direction, list the independent force balance equations and torque balance equations for each wheel.

[0084] Step S203: Consider the suspension constraint characteristics and derive the deformation compatibility equation.

[0085] Step S204: Calculate the dynamic load of each wheel based on the independent force balance equation, moment balance equation, and deformation compatibility equation for each wheel.

[0086] The following describes in detail the specific steps of the dynamic braking force control method for multi-axle vehicles of the present invention, taking a four-axle vehicle as an example.

[0087] In step S100, before performing dynamic load calculation and dynamic distribution of braking force, the static load of each wheel is obtained, and the wheel speed and vehicle speed information are obtained in real time on the Controller Area Network (CAN) bus to calculate the slip ratios κ1, κ2, κ3, κ4, κ5, κ6, κ7, and κ8 of each wheel. The calculation formula is as follows:

[0088]

[0089] Where i is the wheel number corresponding to each axle. When the vehicle has 4 axles, i = 1 to 8, which refer to the left wheel of axle 1, the right wheel of axle 1, the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4, respectively; V X For longitudinal vehicle speed, ω i Let r be the angular velocity of the i-th wheel, and r be the wheel radius.

[0090] The static loads of each wheel are denoted as m1, m2, m3, m4, m5, m6, m7, and m8, respectively, in kg. The subscript numbers 1-8 refer to the left wheel of axle 1, the right wheel of axle 1, the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4 in sequence.

[0091] In step S200, the calculation of the dynamic load for all the wheels above must take into account the suspension deformation compatibility condition. Here, they are represented by F1, F2, F3, F4, F5, F6, F7, and F8 respectively. The subscripts have the same meaning as those for static loads, and the unit is N. The calculation is simplified using matrix form; let the dynamic load matrix be F = [F1, F2, F3, F4, F5, F6, F7, F8].T Next, we will introduce the dynamic load calculation step by step.

[0092] (1) First, estimate the longitudinal distance L from the center of mass to the first axis based on the static load. cx The unit is meters (m), and the calculation formula is as follows:

[0093]

[0094] Where L1, L2, and L3 are the longitudinal distances from axis 1 to axis 2, from axis 2 to axis 3, and from axis 3 to axis 4, respectively.

[0095] Similarly, estimate the lateral distance L from the centroid to the midpoints of each axis. cy The calculation formula is as follows:

[0096]

[0097] Where Lw refers to the wheelbase of the left and right wheels of each axle. In this formula, the wheelbase of the left and right wheels of each axle is equal. G is the vehicle's weight, and g is the acceleration due to gravity.

[0098] (2) Figure 3 As shown, X represents the longitudinal displacement, and the second derivative of X represents the acceleration. Figure 3 The direction to the left is the direction of travel. Figure 3 The four circles in the diagram, from left to right, represent the first axis, second axis, third axis, and fourth axis, respectively. F x1 F x2 F x3 F x4 These represent the longitudinal forces exerted by the ground on the wheels corresponding to axles 1 through 4, F. z1 F z2 F z3 F z4 Let each axle (1-4) represent the vertical force exerted on the wheel by that axle. The formula for calculating the total vehicle weight G is shown below:

[0099]

[0100] Based on the vertical force equilibrium, the first independent force equilibrium equation is obtained, as shown below:

[0101] A1·F=b1 (5)

[0102] Wherein, the coefficient matrix A1=[1,1,1,1,1,1,1,1,1],b1=G,F is the dynamic load of the wheel on the same side of the axle, in N.

[0103] (3) Taking the right-side contact point of the axle as the origin, the line connecting the right wheel contact points as the x-axis, and the forward longitudinal direction as the positive x-axis of the coordinate system, with the direction perpendicular to the x-axis pointing to the left as the positive y-axis. Performing torque balance along the x-axis yields the second independent torque balance equation as follows:

[0104] A²·F=b² (6)

[0105] Where, the coefficient matrix A2 = [1, 0, 1, 0, 1, 0, 1, 0], ρ is the lateral acceleration, hg is the height of the center of mass, and the unit is m.

[0106] Similarly, taking the torque balance with respect to the y-axis, we can obtain the third independent torque balance equation as follows:

[0107] A3·F=b3 (7)

[0108] Wherein, the coefficient matrix Longitudinal acceleration, in m / s² 2 .

[0109] (4) Figure 4 As shown, considering the deformation coordination conditions of the suspension, the suspension is appropriately simplified. The constraint characteristics of the suspension structure are retained, and the suspension is simplified to a spring with a stiffness equal to the equivalent stiffness of the suspension and tires; the vehicle body and wheels are both simplified to rigid bodies; because the deformation of the frame is much smaller than that of the suspension, the deformation of the frame can be ignored, and therefore the frame can be considered a rigid body. At the same time, the deformation of the suspension is constrained by the frame (…). Figure 4 They believed that the connection points between each suspension and the frame always remain on a straight line.

[0110] Based on the deformation compatibility conditions, the formula can be obtained:

[0111]

[0112] Where, Δz i’ It is the suspension deformation on one side of the i'-th axis, i'=1~4, Δz i’+1 It is the suspension deformation on the same side of the i'+1th axis, Δz i’+n This refers to the suspension deformation on the same side of the (i'+n)th axis. Let the stiffness of the suspension on the i'th axis side be K. i’ Here, it is assumed that the suspension stiffness on the left and right sides of the same axle is the same. The unit is m; L i’ It represents the distance between the i'-th axis and the (i'+1)-th axis; n represents the nth axis excluding the i'-th axis starting from the i'-th axis; j represents values ​​from 0 to n-1; L i’+j It is the distance between the i'+j-th axis and the i'+j+1-th axis; when i'=1, n takes 2 or 3, and j takes 0, 1 or 2.

[0113] Based on the deformation compatibility condition formula, when n takes the values ​​of 3 and 2 respectively, the fourth independent equation can be obtained for the left wheel, and the fifth independent equation can be obtained for the right wheel, as shown below:

[0114] A4·F=b4 (9)

[0115] A5·F=b5 (10)

[0116] Wherein, the coefficient matrix coefficient matrix K1, K2, K3, and K4 represent the stiffness of the suspension on one side of the first, second, third, and fourth axles, respectively. Here, it is assumed that the stiffness of the suspension on the left and right sides of the same axle is the same.

[0117] (5) Combining formulas (2) and (10), we can obtain the following formula:

[0118] A·F=b (11)

[0119] In the above formula, Since both matrices A and b are eight-dimensional matrices, the dynamic load matrix can be obtained by multiplying both sides of the above equation by the inverse of matrix A, as shown in the following equation:

[0120] F = A -1 ·b (12)

[0121] (6) After obtaining the dynamic load of each wheel, the proportion matrix of the dynamic load of each wheel to the total vehicle mass can be calculated according to the following formula, that is, the initial value of the braking force distribution coefficient D:

[0122]

[0123] The D matrix is ​​also an eight-dimensional matrix.

[0124] In step S300, dynamic braking force distribution is based on slip ratio synchronization. Step S200 has already obtained the ratio matrix of dynamic loads on each wheel. Since braking force is positively correlated with dynamic load, the distribution ratio of braking force to each wheel can be calculated based on this ratio. Combined with... Figure 5 Based on the slip ratios κ1, κ2, κ3, κ4, κ5, κ6, κ7, and κ8 of each wheel observed in the condition, the actuator feedback signal step size is defined as T, and the slip ratio control coefficient σ is defined as (T = 0.001, σ = 0.0003 can be taken, and can be adjusted according to the actual effect). Figure 5 S in Chinese i D represents the braking force ratio in the i-th round. i This represents the dynamic load ratio in the i-th round.

[0125] (1) Calculate the maximum slip ratio κ of each wheel within the k-th step of the continuous feedback step.max_t+kT The formula is as follows:

[0126] κ max_t+kT =max(κ) 1_t+kT κ 2_t+kT κ 3_t+kT κ 4_t+kT κ 5_t+kT κ 6_t+kT κ 7_t+kT κ 8_t+kT (14)

[0127] In the formula, k = 0, 1, 2, ..., n', where n' represents a total of n' feedback steps, and the subscript t+kT indicates the k-th feedback step starting from time t; max(★) represents taking the maximum function, κ ★_t+kt This indicates the slip ratio of the wheel with the ★ symbol.

[0128] (2) Reducing the braking force distribution ratio of the wheel with the maximum slip ratio aims to avoid excessive differences in slip ratios among the wheels, achieve synchronization of slip ratios, and prevent premature ABS triggering by any wheel. This is achieved by suppressing the maximum slip ratio to bring the slip ratios of each wheel closer together. The method involves reducing the braking force distribution ratio of the wheel with the maximum slip ratio within the k-th step of the continuous feedback step. After the reduction, the braking force ratio S for that step is... t+kT The calculation results are shown in the following formula:

[0129]

[0130] (3) To obtain the dynamic braking force of each wheel that meets the final braking force requirement, by combining formulas (13) and (15), the distribution ratio of braking force of each wheel at the k-th step of the continuous feedback step can be obtained. After reducing the distribution ratio of dynamic braking force of a certain wheel, in order to meet the final braking force requirement, the reduced braking force of that wheel needs to be distributed to other wheels according to the braking force ratio between each wheel, which is the normalization process, so that the sum of the current braking forces still meets the total braking force requirement. Then the normalized braking force DS of each wheel at the k-th step is... t+kT The calculation formula is as follows:

[0131]

[0132] In formula (16), the pair of double vertical lines and its right subscript 1 represent the operation symbol of the first norm.

[0133] The final braking force matrix DS for each wheel t+kT It is an 8×1 matrix. From the first row to the last row, it refers to the dynamic braking force assigned to the left wheel of the first axle, the right wheel of the first axle, the left wheel of the second axle, the right wheel of the second axle, the left wheel of the third axle, the right wheel of the third axle, the left wheel of the fourth axle, and the right wheel of the fourth axle.

[0134] It should be noted that the above calculation method uses a four-axle, eight-wheel configuration as an example. However, the calculation method of this invention is not limited to the four-axle, eight-wheel configuration. For those skilled in the art, the specific calculation process can be deduced when the number of axles of the vehicle can be 2, 3, or 6, using the above four-axle, eight-wheel configuration as an example.

[0135] This invention uses the static wheel load of a four-axle commercial vehicle as a basis and considers suspension constraints to establish a longitudinal braking dynamic model of the four-axle vehicle. The dynamic load of each wheel obtained in this way has the advantages of accurate results and simple calculation.

[0136] The dynamic braking force distribution control method proposed in this invention can estimate the slip ratio based on the real-time calculated dynamic load values ​​and states of each wheel, and compare and suppress the maximum slip ratio to achieve near synchronization of the slip ratios of each wheel. By adjusting the braking force distribution ratio of each wheel, the possibility of premature wheel lock-up is reduced, making full use of road adhesion conditions and effectively reducing the probability of ABS triggering. The system has good response; simulation verification shows that the time for each wheel to enter ABS control is delayed by a maximum of 1-2 seconds.

[0137] In summary, this invention firstly changes the braking force distribution of four-axle commercial vehicles from axle-based to wheel-based, resulting in more precise braking force control; secondly, it addresses the shortcomings of threshold-based braking force distribution, which leads to inaccurate braking force distribution, conservative braking force distribution, and insufficient braking efficiency due to the inability to effectively utilize road adhesion; finally, the method of this invention can be applied as a pre-distribution method in the field of regenerative braking, ensuring maximum recovery of braking energy while fully utilizing road adhesion conditions, thus guaranteeing the safety of commercial vehicles and expanding the scope of application.

[0138] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" in the above description indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0139] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0140] In the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0141] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0142] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0143] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A method for dynamic braking force control of a multi-axle vehicle, characterized in that, The control method includes the following steps: Obtain information on the static load, wheel speed, and vehicle speed of each wheel, and calculate the slip ratio of each wheel; Establish braking dynamics equations for multi-axle vehicles that retain suspension constraint characteristics, and calculate the dynamic load on each wheel; The braking force distribution ratio of the wheel with the largest slip ratio is reduced. The braking force distribution ratio of each wheel is normalized according to the braking force ratio between each wheel, and the dynamic braking force required for each wheel is calculated. Since the dynamic braking force of each wheel is positively correlated with the dynamic load of each wheel, the braking force distribution ratio of each wheel is determined based on the ratio matrix of the dynamic load of each wheel. The steps for establishing the braking dynamics equations for a multi-axle vehicle while preserving suspension constraint characteristics and calculating the dynamic load on each wheel include: Estimate the longitudinal and lateral positions of the vehicle's center of gravity; Based on the forces acting in the vertical direction, we derive independent force balance equations and moment balance equations for each wheel. Considering the suspension constraint characteristics, we take the deformation compatibility equations; The dynamic load of each wheel is calculated based on the independent force balance equation, moment balance equation, and deformation compatibility equation for each wheel.

2. The dynamic braking force control method for multi-axle vehicles according to claim 1, characterized in that, The number of axles in the multi-axle vehicle is 2, 3, 4 or 6.

3. The dynamic braking force control method for multi-axle vehicles according to claim 1, characterized in that, Calculate the slip ratio of each wheel The calculation formula is as follows: （1） Where i is the sequence number of the wheel corresponding to each axle. When the vehicle has 4 axles, i = 1 to 8, which refer to the left wheel of axle 1, the right wheel of axle 1, the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4 in sequence. VX For longitudinal vehicle speed, ωi Let be the angular velocity of the i-th wheel. r The radius is the wheel radius.

4. The dynamic braking force control method for multi-axle vehicles according to claim 3, characterized in that, When the vehicle has 4 axles, the calculation process for estimating the longitudinal and lateral positions of the vehicle's center of gravity is as follows: Estimate the longitudinal distance from the center of mass to the first axle based on the static load of each wheel. The calculation formula is as follows: （2） in, These represent the longitudinal distances from axle 1 to axle 2, from axle 2 to axle 3, and from axle 3 to axle 4, respectively. m3~m8 correspond to the static loads of the left wheel of axle 2, the right wheel of axle 2, the left wheel of axle 3, the right wheel of axle 3, the left wheel of axle 4, and the right wheel of axle 4, respectively, in kg. Estimate the lateral distance from the center of mass to the line connecting the midpoints of each axle. The calculation formula is as follows: （3） in, This refers to the wheel track width of the left and right wheels on each axle. m1~m8 correspond to the static load of the left wheel on axle 1, the right wheel on axle 1, the left wheel on axle 2, the right wheel on axle 2, the left wheel on axle 3, the right wheel on axle 3, the left wheel on axle 4, and the right wheel on axle 4, respectively. In this formula, the wheel track width of the left and right wheels on each axle is equal. G For vehicle weight, g This is the acceleration due to gravity.

5. The dynamic braking force control method for multi-axle vehicles according to claim 4, characterized in that, The calculation process for establishing the independent force balance equations and moment balance equations for each wheel based on the vertical force conditions is as follows: Determine vehicle weight G The calculation formula is as follows: （4） m i This indicates the static load of wheel number i; Based on the vertical force equilibrium, the first independent force equilibrium equation is obtained, as shown below: （5） Wherein, the coefficient matrix F is the dynamic load matrix. F1~F8 correspond to the dynamic loads of the left and right wheels of axle 1, axle 1, axle 2, axle 2, axle 3, axle 4, and axle 5, respectively, in N (unit: N). ; Taking the right-side contact point of the axle as the origin, the line connecting the right wheel contact points as the x-axis, and the forward longitudinal direction as the positive x-axis of the coordinate system, with the direction perpendicular to the x-axis pointing to the left as the positive y-axis, we perform torque balance about the x-axis to obtain the second independent equilibrium equation, as shown below: （6） Wherein, the coefficient matrix , , For lateral acceleration, h g The height of the center of mass is in meters (m). By applying torque balance about the y-axis, we obtain the third independent equilibrium equation, as shown below: （7） Wherein, the coefficient matrix , , The longitudinal acceleration is expressed in m / s². m2i represents the static load of wheel number 2i, and m2i-1 represents the static load of wheel number 2i-1.

6. The dynamic braking force control method for multi-axle vehicles according to claim 5, characterized in that, The calculation process for taking the deformation compatibility equation considering the suspension constraint characteristics is as follows: Based on the suspension constraint characteristics, the following formula is obtained: （8） in, It refers to the suspension deformation on one side of the i'-th axis, where i' = 1~4. It is the suspension deformation on the same side of the i'+1th axis. This represents the suspension deformation on the same side of the (i'+n)th axis. Let the stiffness of the suspension on the i'th axis side be... If the suspension stiffness on the left and right sides of the same axle is set to be the same, then The unit is m, and F is the dynamic load of the wheel on the same side of the axle, in N; is the distance between the i'-th axis and the (i'+1)-th axis; n represents the nth axis excluding the i'-th axis starting from the i'-th axis; j represents values ​​from 0 to n-1; It is the distance between the i'+j-th axis and the i'+j+1-th axis; when i'=1, n takes the values ​​2 or 3, and j takes the values ​​0, 1, or 2.

7. The dynamic braking force control method for multi-axle vehicles according to claim 6, characterized in that, According to formula (8), when n takes the values ​​of 3 and 2 respectively, the fourth independent equation can be obtained for the left wheel and the fifth independent equation can be obtained for the right wheel, as shown below: （9） （10） Wherein, the coefficient matrix , coefficient matrix , , K 1. K 2. K 3. K 4 represents the stiffness of the suspension on one side of the first, second, third, and fourth axles, respectively, and the stiffness of the suspension on the left and right sides of the same axle is set to be the same.

8. The dynamic braking force control method for a multi-axle vehicle according to claim 7, characterized in that, The calculation process for calculating the dynamic load of each wheel based on the independent force balance equation, moment balance equation, and deformation compatibility equation for each wheel is as follows: Solving equations (2)-(10) simultaneously, we obtain the following formula: （11） in, , ; Multiply both sides of the equation (11) by the inverse of matrix A to obtain the dynamic load matrix of each wheel, as shown below: （12） The initial value of the braking force distribution coefficient is obtained by calculating the ratio matrix of dynamic load to vehicle mass of each wheel according to the following formula. D As shown below: （13）。 9. The dynamic braking force control method for a multi-axle vehicle according to claim 8, characterized in that, The process of reducing the braking force distribution ratio of the wheel with the maximum slip ratio, normalizing the braking force distribution ratio of each wheel based on the braking force ratio between each wheel, and calculating the required dynamic braking force for each wheel is as follows: Based on the slip ratio of each wheel, the step size of the actuator feedback signal is defined as T, and the slip ratio control coefficient is... σ ; Find the maximum slip ratio of each wheel within the k-th step of the continuous feedback step. As shown below: （14） in, k =0, 1, 2...n', where n' represents a total of n' feedback steps, and the subscript t+kT indicates the k-th feedback step starting from time t; max(*) indicates taking the maximum function. κ *_ t+kt This indicates the slip ratio of the *th wheel; Within the k-th step of the continuous feedback step, the braking force distribution ratio at the maximum slip ratio is reduced, and the braking force ratio for that step is reduced accordingly. As shown below: （15） By solving equations (13) and (15) simultaneously, the braking force distribution ratio of each wheel is normalized to obtain the normalized braking force of each wheel at step k. As shown below: （16）。

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