A method for optimizing distribution of braking torque of a multi-axle wheeled vehicle suitable for non-planar roads

Abstract

This invention relates to a method for optimizing the allocation of braking torque for multi-axle wheeled vehicles on non-planar roads, comprising: defining a coordinate system for the multi-axle vehicle; calculating the vertical loads of each axle of the multi-axle vehicle based on the coordinate system; constructing a dynamic model of the multi-axle vehicle based on the vertical loads of each axle; calculating the total braking force requirement based on the dynamic model and incorporating the vehicle's current state information; constructing an objective function by combining tire adhesion constraints, braking torque constraints, energy optimization objectives, and braking stability optimization objectives; and solving for the target braking torque using a hybrid particle swarm optimization algorithm based on the total braking force requirement and the objective function. This invention can generate dynamic and coordinated braking torque allocation results under complex road conditions.

Description

Technical Field

[0001] This invention relates to the field of vehicle braking force distribution technology, and in particular to a method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads. Background Technology

[0002] Heavy-duty 8x8 multi-axle wheeled vehicles are commonly used in off-road transportation, engineering operations, and unmanned platforms. Their braking process is affected not only by vehicle speed, load, and braking requirements, but also by road gradient, roll angle, road surface adhesion coefficient, and the combined effects of vertical load transfer on each axle. Especially on non-planar roads, slopes, lateral slopes, and conditions where the adhesion conditions of the left and right wheels are inconsistent, the available adhesion forces of each axle and wheel differ significantly. If a fixed ratio or empirical rule is still used for braking force distribution, problems such as local wheel lock-up, uncoordinated braking forces between axles, increased braking distance, and vehicle instability are likely to occur.

[0003] Existing braking force distribution methods for multi-axle vehicles are mostly based on planar road models or the static load ratio between the front and rear axles. They typically focus on braking intensity and axle load distribution, but fail to adequately consider vertical load variations caused by non-planar roads, the influence of road angles, and differences in adhesion on off-road surfaces. For four-axle, eight-wheel vehicles, there are coupling relationships between multiple axles, and simply distributing braking force according to axle load or braking pressure makes it difficult to simultaneously consider braking efficiency, vehicle stability, and even wear of tires / brake components.

[0004] Therefore, there is a need for an optimized braking torque distribution method for multi-axle wheeled vehicles on non-planar roads. This method should be able to combine vehicle motion state, road slope angle, roll angle, vertical load, and road surface adhesion conditions to establish a multi-axle vehicle dynamics model and calculate the total braking force demand. Then, an optimization algorithm should be used to solve for the target braking torque of each axle or wheel, so that the braking force distribution can be dynamically adjusted according to road conditions and vehicle state, thereby improving braking safety, stability, and braking efficiency under complex road conditions. Summary of the Invention

[0005] The purpose of this invention is to provide an optimized braking torque distribution method for multi-axle wheeled vehicles on non-planar roads, in order to solve the problems existing in the prior art. This method combines the slope angle, roll angle, vehicle vertical load variation and road surface adhesion conditions under non-planar road conditions to establish a dynamic model of multi-axle vehicles and calculate the total braking force demand. By optimizing the objective function and using a hybrid particle swarm optimization algorithm, the braking torque distribution results of each axle are solved, thereby improving the braking stability and braking efficiency of vehicles under complex road conditions and reducing tire and brake component wear caused by uneven braking force distribution.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads includes: Define the coordinate system for multi-axle vehicles; Based on the coordinate system, calculate the vertical load on each axle of the multi-axle vehicle; Based on the vertical loads of each axle, a dynamic model of the multi-axle vehicle is constructed; Based on the dynamic model, the total braking force requirement is calculated by incorporating the vehicle's current state information. An objective function is constructed by combining tire adhesion constraints, braking torque constraints, energy optimization objectives, and braking stability optimization objectives. Based on the total braking force requirement and objective function, the target braking torque is solved using a hybrid particle swarm optimization algorithm.

[0007] Optionally, defining the coordinate system for a multi-axle vehicle includes: East is taken as the positive direction of the X-axis in the world coordinate system, north is taken as the positive direction of the Y-axis in the world coordinate system, and the plane perpendicular to the X-axis and Y-axis and pointing upwards is taken as the positive direction of the Z-axis. With the center of mass of the sprung mass as the origin of the vehicle coordinate system (Ob), the positive direction of vx is aligned with the direction of vehicle travel, the left side of the vehicle's forward direction is defined as the positive direction of vy, and the vehicle's yaw rate is... The direction perpendicular to the road surface upwards is considered positive. The vehicle's coordinate system consists of vx, vy, and Confirmed; vx represents the vehicle's longitudinal velocity, vy represents the vehicle's lateral velocity, and ω represents the yaw rate. The coordinate system also represents: the longitudinal distance of the i-th axis from the vehicle's center of gravity, the vehicle's wheelbase, the longitudinal force of the tires on the i-th axis, and the lateral force of the tires.

[0008] Optionally, calculating the vertical load on each axle of a multi-axle vehicle includes: Obtain the static and dynamic suspension forces of each axle of the vehicle; Based on the static suspension force and dynamic suspension force, the resultant vertical force of each suspension is obtained; Based on the vertical resultant force of each suspension and combined with the unsprung mass of the corresponding axle, the vertical resultant force of each tire is obtained; By combining the vertical resultant forces of each tire, the vertical resultant forces of each axle are obtained.

[0009] Optionally, obtaining the static suspension forces of each axle of the vehicle includes: The static equilibrium state of the vehicle is determined using the displacement method: in, This represents the suspension force under static equilibrium conditions on each axle. i =1, 2, 3, 4, R The rotation matrix represents the state of the vehicle. GR This represents the component of the vehicle's weight in the z-direction. mbIndicates the sprung mass of the vehicle. g Represents gravitational acceleration. Li This represents the longitudinal distance of the i-th axis from the vehicle's center of mass; Based on geometric relationships, obtain the deformation ratios of each suspension component: in, fi This represents the deformation ratio coefficient of the i-th axle suspension relative to the first axle suspension; Based on the vehicle's static balance state and the deformation ratio of each suspension component, calculate the corresponding static suspension force: in, La This represents the algebraic sum of the longitudinal positions of each axle relative to the vehicle's center of gravity. La = L 1+ L 2- L 3- L 4, Lb This represents the sum of the squares of the longitudinal positions of each axle relative to the vehicle's center of gravity. Lb = L 1²+ L 2²+ L 3²+ L 4².

[0010] Optionally, obtaining the dynamic suspension force includes: Obtain the vehicle's current pitch angle θ; Assuming the relative height between the vehicle body coordinate system and the ground remains constant, the relative deformation of each wheel and suspension relative to the static equilibrium state in the vehicle body coordinate system is calculated based on geometric relationships: in, This represents the deformation of the suspension on the j-th side of the i-th axis relative to the static equilibrium state. B Indicates the wheelbase of the vehicle; Based on the relative deformation, the dynamic suspension force is obtained: in, This represents the dynamic suspension force of the suspension on the j-th side of the i-th axis. This represents the single-sided stiffness of the suspension on the j-th side of the i-th axis. This indicates the single-sided damping of the suspension on the j-th side of the i-th axis. j A value of 1 indicates the left side. j 2 indicates the right side. This represents the deformation rate of the suspension on the j-th side of the i-th axis relative to the static equilibrium state.

[0011] Optionally, the dynamic model of the multi-axle vehicle is: in, m Indicates the overall weight of the vehicle. This represents the longitudinal acceleration at the vehicle's center of gravity. This indicates the vehicle's drag coefficient. This indicates the vehicle's frontal area. Indicates air density, Indicates the rolling resistance coefficient. R The rotation matrix represents the state of the vehicle. This represents the longitudinal braking force between the wheel on the j-th side of the i-th axle and the road surface, where j=1 represents the left side and j=2 represents the right side.

[0012] Optionally, based on the dynamic model, and by incorporating the vehicle's current state information, the total braking force requirement is calculated, including: in, Indicates the lateral speed of the vehicle. Indicates yaw rate. Indicates the longitudinal speed of the vehicle. Indicates the expected acceleration. This indicates the total braking force requirement.

[0013] Optionally, the tire adhesion constraint is: in, express i The braking force corresponding to the shaft, express i The axis corresponds to the road surface adhesion coefficient. This represents the vertical load on the wheel of the i-th axle. This represents the road adhesion coefficient corresponding to the left wheel of the i-th axis. This represents the road surface adhesion coefficient corresponding to the right wheel of the i-th axis; The braking torque constraint is: in, Indicates transmission efficiency. Indicates the tire's rolling radius. Indicates braking torque; The tire adhesion constraint and braking torque constraint are constraints in the objective function optimization process, used to limit the feasible range of braking force and braking torque for each axle; the objective function, under the condition of satisfying the tire adhesion constraint and braking torque constraint, comprehensively optimizes the energy optimization objective and the braking stability objective; the objective function is: in, This represents the energy optimization objective, used to achieve the minimum torque output while satisfying constraints. This represents the braking stability optimization objective, used to achieve the smoothest braking under the given constraints. 1, 2 represents a parameter used to balance the priorities of different objectives. Represents the constraint function; constraint functions for: in, x ( i Let x(i) represent the i-th optimization variable; when allocated by axle, x(i) represents the target braking torque of the i-th axle; when allocated by wheel, x(i) represents the target braking torque of the i-th wheel.

[0014] Optionally, the hybrid particle swarm optimization algorithm is used to solve for the target braking torque, including: Initialize particle swarm: randomly generated N There are 10 particles, each representing a braking torque allocation scheme, and the particle velocity is initialized. Calculate the fitness value: For each particle, calculate the objective function value and the penalty function, and use the penalty function to incorporate the constraints into the objective function; Update the individual optimal solution and the global optimal solution; Update particle velocity and position; The iteration terminates when the maximum number of iterations is reached or the rate of change of the objective function is less than a preset threshold, and the target braking torque is obtained.

[0015] The beneficial effects of this invention are as follows: (1) Improve braking stability and safety: This method introduces road slope angle, roll angle, vehicle vertical load and road surface adhesion conditions during the braking torque distribution process, so that the braking force distribution can adapt to load transfer and adhesion changes in non-planar roads and off-road scenarios, reducing the risk of tire lock-up and braking instability.

[0016] (2) Improve the effect of multi-axle coordinated braking: This method calculates the total braking force demand based on the 8×8 multi-axle vehicle dynamics model and optimizes the distribution of braking torque of each axle, so that the braking forces of the front and rear axles and each wheel are more coordinated and the overall vehicle braking efficiency is improved.

[0017] (3) Reduce uneven wear of braking components: By dynamically adjusting the braking torque of each axle, excessive braking force on a single axle or local wheels can be avoided, thereby reducing uneven wear of brake pads and tires and lowering maintenance costs.

[0018] (4) Adapting to complex road conditions: This method can perform braking force constraints and optimization solutions for working conditions such as slopes, side-sloping roads, off-road terrain and different adhesion conditions of left and right wheels, thereby improving the braking adaptability of multi-axle vehicles under complex road conditions. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of an 8×8 vehicle planar dynamics model according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the execution environment for the braking torque optimization allocation method according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a method for optimizing the distribution of braking torque of multi-axle wheeled vehicles applicable to non-planar roads, according to an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 3 As shown in the figure, this embodiment proposes a method for optimizing the distribution of braking torque of multi-axle wheeled vehicles applicable to non-planar roads, which mainly includes: Define the coordinate system for multi-axle vehicles; Based on the coordinate system, calculate the vertical load on each axle of the multi-axle vehicle; Based on the vertical loads of each axle, a dynamic model of the multi-axle vehicle is constructed; Based on the dynamic model, the total braking force requirement is calculated by incorporating the vehicle's current state information. An objective function is constructed by combining tire adhesion constraints, braking torque constraints, energy optimization objectives, and braking stability optimization objectives. Based on the total braking force requirement and objective function, a hybrid particle swarm optimization algorithm is used to solve for the target braking torque of each axle or wheel.

[0024] This embodiment proposes a method for optimizing the distribution of braking torque applicable to heavy-duty 8×8 multi-axle wheeled vehicles. This method combines the slope angle, roll angle, vehicle vertical load variations, and road adhesion conditions under non-planar road conditions to establish a multi-axle vehicle dynamics model and calculate the total braking force demand. The method then uses an optimized objective function and a hybrid particle swarm optimization algorithm to solve for the braking torque distribution results for each axle, thereby improving vehicle braking stability and efficiency under complex road conditions and reducing tire and brake component wear caused by uneven braking force distribution.

[0025] The method in this embodiment is executed by a control unit with data processing and control output capabilities, such as a vehicle controller, brake controller, or vehicle controller. The control unit receives state information such as vehicle speed, longitudinal acceleration, yaw rate, vehicle attitude, road slope angle, road roll angle, wheel speed, braking request, vehicle load, and road adhesion coefficient, calculates the total braking force requirement of the vehicle on non-planar roads, and decomposes the total braking force requirement into target braking torques for each axle or wheel.

[0026] The method includes at least the following steps: establishing an 8×8 multi-axle wheeled vehicle coordinate system; calculating the vertical loads of each axle and wheel based on road angles and suspension deformation; establishing longitudinal dynamic equations considering slope, roll, and vehicle motion; calculating the total braking force demand based on the desired deceleration or braking request; establishing an optimization objective function by combining tire adhesion constraints, braking torque upper limit, inter-axle stability constraints, and braking energy consumption targets; solving for the target braking torque of each axle or wheel using a hybrid particle swarm optimization algorithm; and outputting the obtained target braking torque to the braking execution system, which then converts it into braking pressure, motor torque, or other braking execution commands.

[0027] In this embodiment, the optimization variable can be the target braking torque for four axles, or it can be further extended to the target braking torque for eight wheels. When the adhesion coefficients of the left and right wheels are inconsistent, the upper limit of the available braking force for that axle or wheel is determined by the smaller adhesion coefficient, thereby avoiding local tire lock-up. The control unit can execute the above steps cyclically, so that the braking torque distribution result is updated in real time according to the vehicle attitude, load transfer, and road adhesion conditions.

[0028] Since the application scenarios of heavy multi-axle vehicles are different from those of passenger vehicles, including complex road surfaces and off-road scenarios, the impact of road angles on vehicle dynamics must be considered in addition to the vehicle model when modeling.

[0029] Specifically, in this embodiment, step 1: establish the coordinate system of the unmanned 8×8 multi-axis drive vehicle; The coordinate system definition for the 8×8 multi-axis drive vehicle (planar) dynamics model is as follows: East is defined as the positive X-axis direction of the world coordinate system, North is defined as the positive Y-axis direction, and the plane perpendicular to the X and Y axes and pointing upwards is defined as the positive Z-axis direction. The origin of the vehicle body coordinate system, Ob, is defined by the center of mass of the sprung mass. The positive direction of vx is consistent with the direction of vehicle travel. The left side of the vehicle's forward direction is defined as the positive direction of vy. The vehicle's yaw rate is... The direction perpendicular to the road surface upwards is considered positive. The vehicle's coordinate system consists of vx, vy, and Determine; Li represents the longitudinal distance of the i-th axis from the vehicle's center of gravity, and B represents the vehicle's track width. Based on this, establish as follows: Figure 1 The vehicle dynamics model shown is as follows. Here, Fxij represents the longitudinal tire force on the i-th axis, and Fyij represents the lateral tire force on the i-th axis. j=1 indicates the left wheel, and j=2 indicates the right wheel.

[0030] Furthermore, calculating the vertical loads on each axle of a multi-axle vehicle includes: Obtain the static and dynamic suspension forces of each axle of the vehicle; Based on the static suspension force and dynamic suspension force, the resultant vertical force of each suspension is obtained; Based on the vertical resultant force of each suspension and combined with the unsprung mass of the corresponding axle, the vertical resultant force of each tire is obtained; By combining the vertical resultant forces of each tire, the vertical resultant forces of each axle are obtained.

[0031] Obtaining the static suspension forces of each axle of the vehicle includes: The static equilibrium state of the vehicle is solved using the displacement method; Based on geometric relationships, obtain the deformation ratio of each suspension component; Based on the vehicle's static balance and the deformation ratio of each suspension component, the corresponding static suspension force is calculated.

[0032] Obtaining the dynamic suspension force includes: Obtain the vehicle's current pitch angle. Pitch angle θ; Assuming that the relative height between the vehicle body coordinate system and the ground remains constant, the relative deformation of each wheel and each suspension relative to the static equilibrium state in the vehicle body coordinate system is calculated based on geometric relationships. The dynamic suspension force is obtained based on the relative deformation.

[0033] Specifically, in this embodiment, step 2: vertical load analysis and calculation; (1) Static suspension force analysis: Multi-axle vehicles are typical statically indeterminate systems, therefore they can only be solved using the displacement method. Assuming the vehicle is symmetric about the xOz plane of the vehicle body, the suspension stiffness of each axle is equivalent to the sum of the stiffnesses of the suspensions on both sides, that is... The components of gravity in the x and y coordinate systems are considered under the dynamic equilibrium state of the vehicle, while the component of gravity in the z direction is considered under the static equilibrium state of the vehicle. GR Under static equilibrium conditions, based on the balance of vertical forces and pitch moments of the entire vehicle, the static suspension forces of each axle can be solved using the displacement method, and can be expressed by the following formula: in, This represents the suspension force under static equilibrium conditions on each axle.

[0034] R represents the rotation matrix of the vehicle's current state. ,in: Where a represents the road's roll angle, b represents the road's slope angle, and c represents the road's heading angle. The sign of the road angle is determined according to the right-hand rule of the vehicle coordinate system. Based on geometric relationships, specifically, using the longitudinal distance Li from the i-th axis to the vehicle's center of gravity, the vehicle's track width B, the vehicle's pitch angle θ, and the roll angle φ, the height changes of the left and right wheels of the i-th axis relative to the static equilibrium state are calculated respectively. Here, the pitch angle θ characterizes the height change in the vehicle's longitudinal direction, and the roll angle φ and track width B characterize the height change in the vehicle's lateral direction. These height changes are then used as the relative deformation or deformation ratio of the corresponding suspension. The deformation ratio of each suspension is then obtained. By combining suspension mechanics and the proportional relationships of deformation of each suspension element, the corresponding static suspension force can be calculated: in, (2) Dynamic suspension force analysis: The vehicle's current pitch angle is read from the onboard sensors. Let the pitch angle θ be a constant, neglecting the vertical dynamics of the vehicle and wheels (i.e., the relative height between the vehicle body coordinate system and the ground remains constant, and the wheels are always in tangential contact with the ground). Assuming that both the roll and pitch angles are small, the relative deformation of each wheel and suspension relative to the static equilibrium state in the vehicle body coordinate system can be calculated using geometric relationships: In the formula, the variable sign term ±B / 2 is positive for the left suspension and negative for the right suspension; the variable sign term ± Li The first two axes are negative, and the last two axes are positive.

[0035] Further, the dynamic suspension forces of each axle are obtained: in This represents the stiffness of the suspension on one side along the i-axis. This represents the damping of the suspension on one side of the i-axis, where j = 1 indicates the left side and j = 2 indicates the right side.

[0036] (3) Calculate the resultant vertical force of each suspension: This represents the suspension force on one side of the i-axis, where j = 1 indicates the left side and j = 2 indicates the right side.

[0037] (4) Calculate the resultant vertical force of each tire: This indicates the unsprung mass of the corresponding shaft. This represents the vertical force of the tire on one side of the i-axis, where j = 1 indicates the left side and j = 2 indicates the right side.

[0038] (5) Calculate the resultant vertical force on each axis. : This represents the total vertical force exerted on the i-th axis by the road surface.

[0039] Specifically, in this embodiment, step 3: establish the vehicle's dynamic equations; The longitudinal dynamics equations of the vehicle are established. Considering the relatively small roll, pitch, and vertical motions, these are neglected in the longitudinal, lateral, and yaw dynamics. Furthermore, considering the small front wheel steering angle during braking, the lateral tire forces are ignored. Therefore, the longitudinal dynamics of the vehicle can be expressed as: in, m For the overall vehicle weight, This represents the longitudinal acceleration at the vehicle's center of gravity. CD This indicates the vehicle's drag coefficient. A This indicates the vehicle's frontal area. Indicates air density, This represents the rolling resistance coefficient.

[0040] Specifically, in this embodiment, step 4: calculation of total braking force requirement; Tire adhesion constraints and braking torque constraints are the constraints in the optimization process of the objective function, used to limit the feasible range of braking force and braking torque for each axle; the objective function performs comprehensive optimization of energy optimization objective and braking stability objective under the condition of satisfying the tire adhesion constraints and braking torque constraints.

[0041] Based on the vehicle dynamics model, the vehicle's current state information measured by onboard sensors, including the vehicle's lateral velocity, is incorporated. yaw rate longitudinal velocity and expected acceleration The total braking force requirement is calculated as follows: .

[0042] Specifically, in this embodiment, step 5: Optimize the allocation of braking torque; Tire adhesion constraints: The core relationship between braking force and road adhesion coefficient can be expressed as: in, This represents the braking force (in N) corresponding to the i-axis. This represents the road adhesion coefficient corresponding to the i-axis. Since the maximum braking force of a tire is limited by the road adhesion conditions, if the braking force demand exceeds this value, the tire will lock up (100% slip), leading to brake failure. Considering the presence of off-road terrain in multi-axle vehicle driving environments, the left and right wheels may be on surfaces with different adhesion coefficients; therefore: Take the smaller value between the left and right wheels.

[0043] Braking torque constraint: The braking torque and braking force have the following mathematical relationship: in Indicates transmission efficiency. This indicates the tire's rolling radius.

[0044] Tire adhesion constraints limit the braking force of each axle to no more than the adhesion capacity provided by the road surface, while braking torque constraints limit the target braking torque to be within the allowable range of the actuator; both serve as constraints when solving the objective function.

[0045] Set the target function: in 1, 2. Used to balance the priorities of different objectives (satisfying) 1+ 2=1), optimization variables This is the braking torque for the four axles.

[0046] This represents the energy optimization objective, which aims to achieve the minimum torque output while satisfying constraints.

[0047] This indicates the braking stability optimization objective, which aims to achieve the smoothest braking while meeting constraints and reducing inter-axle parasitic torque.

[0048] The constraint function is defined as follows: .

[0049] Furthermore, the solution for the target braking torque using the hybrid particle swarm optimization algorithm includes: Initialize particle swarm: randomly generated N There are 10 particles, each representing a braking torque allocation scheme, and the particle velocity is initialized. Calculate the fitness value: For each particle, calculate the objective function value and the penalty function, and use the penalty function to incorporate the constraints into the objective function; Update the individual optimal solution and the global optimal solution; Update particle velocity and position; The iteration terminates when the maximum number of iterations is reached or the rate of change of the objective function is less than a preset threshold, and the target braking torque is obtained.

[0050] Specifically, in this embodiment, step 6: solve using the hybrid particle swarm algorithm; (1) Initialize the particle swarm: N particles are randomly generated, and each particle represents a braking torque distribution scheme. .

[0051] Initialize particle velocity vi exist[- v max, v The value is randomly set within the [max] range.

[0052] (2) Calculate the fitness value: For each particle, calculate the objective function value J and the penalty function C: Incorporate constraints into the objective function using a penalty function: in This represents the penalty coefficient.

[0053] (3) Update the individual optimal solution pi and the global optimal solutiong : If the current particle's Jtotal If it is better than its historical best value, then update. pi .

[0054] If the current particle's Jtotal If it is better than the global optimum, then update. g .

[0055] (4) Update particle velocity and position: Update speed: Where w represents the inertia weight (linearly decreasing, taking...) ); This represents the learning factor, which is set to 2.0. Represents a random number.

[0056] Update location: And on Perform boundary violation handling.

[0057] (5) Iteration termination: Reaching the maximum number of iterations kmax Or the rate of change of the objective function is less than the threshold. .

[0058] (6) Optimize the solution for braking torque: The calculated target braking torque is output to the vehicle braking system, which then generates a corresponding braking force based on the target braking torque. The vehicle braking system can be an electro-pneumatic braking system, a hydraulic braking system, an electric motor braking system, or a combined braking system. This method focuses on the calculation and optimized allocation of the target braking torque on non-planar roads, and does not limit the specific structural form of the braking system.

[0059] The method in this embodiment can be executed by a control unit with data processing and control output capabilities, such as a vehicle controller, brake controller, or vehicle controller. Figure 2 As shown, the control unit receives vehicle status information, road surface status information, and braking demand information. The vehicle status information includes one or more of the following: vehicle speed, wheel speed, yaw rate, longitudinal acceleration, vehicle attitude, and suspension status. The road surface status information includes one or more of the following: road slope angle, roll angle, and road surface adhesion coefficient. The braking demand information includes the driver's brake pedal signal or the desired deceleration output by the automatic driving controller.

[0060] The control unit executes the aforementioned braking torque optimization allocation method, calculating the total braking force requirement based on vehicle status, road surface conditions, and braking demand, and solving for the target braking torque for each axle or wheel. The control unit outputs the target braking torque to the braking execution interface module, which converts the target braking torque into target braking pressure, electric motor torque, valve control command, or other braking execution command according to different actuator types.

[0061] In one optional embodiment, the brake execution interface module is connected to an electro-pneumatic braking system and converts the target braking torque into target braking pressure for each axle; in other embodiments, the brake execution interface module may also be connected to a hydraulic braking system, an electric motor braking system, or a combined braking system. The above execution environment is only used to illustrate the implementation of this method, and this method does not require a specific electro-pneumatic braking system as a necessary condition.

[0062] Based on the above-described non-planar road perception, vertical load analysis, and multi-axis braking torque optimization solution process, the method in this embodiment can generate dynamic and coordinated braking torque distribution results under complex road conditions. The main technical effects are as follows: (1) Improve braking stability and safety: This method introduces road slope angle, roll angle, vehicle vertical load and road surface adhesion conditions during the braking torque distribution process, so that the braking force distribution can adapt to load transfer and adhesion changes in non-planar roads and off-road scenarios, reducing the risk of tire lock-up and braking instability.

[0063] (2) Improve the effect of multi-axle coordinated braking: This method calculates the total braking force demand based on the 8×8 multi-axle vehicle dynamics model and optimizes the distribution of braking torque of each axle, so that the braking forces of the front and rear axles and each wheel are more coordinated and the overall vehicle braking efficiency is improved.

[0064] (3) Reduce uneven wear of braking components: By dynamically adjusting the braking torque of each axle, excessive braking force on a single axle or local wheels can be avoided, thereby reducing uneven wear of brake pads and tires and lowering maintenance costs.

[0065] (4) Adapting to complex road conditions: This method can perform braking force constraints and optimization solutions for working conditions such as slopes, side-sloping roads, off-road terrain and different adhesion conditions of left and right wheels, thereby improving the braking adaptability of multi-axle vehicles under complex road conditions.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads, characterized in that, include: Define the coordinate system for multi-axle vehicles; Based on the coordinate system, calculate the vertical load on each axle of the multi-axle vehicle; Based on the vertical loads of each axle, a dynamic model of the multi-axle vehicle is constructed; Based on the dynamic model, the total braking force requirement is calculated by incorporating the vehicle's current state information. An objective function is constructed by combining tire adhesion constraints, braking torque constraints, energy optimization objectives, and braking stability optimization objectives. Based on the total braking force requirement and objective function, the target braking torque is solved using a hybrid particle swarm optimization algorithm.

2. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 1, characterized in that, Defining the coordinate system for a multi-axle vehicle includes: East is taken as the positive direction of the X-axis in the world coordinate system, north is taken as the positive direction of the Y-axis in the world coordinate system, and the plane perpendicular to the X-axis and Y-axis and pointing upwards is taken as the positive direction of the Z-axis. With the center of mass of the sprung mass as the origin of the vehicle coordinate system (Ob), the positive direction of vx is aligned with the direction of vehicle travel, the left side of the vehicle's forward direction is defined as the positive direction of vy, and the vehicle's yaw rate is... The direction perpendicular to the road surface upwards is considered positive. The vehicle's coordinate system consists of vx, vy, and Confirmed; vx represents the vehicle's longitudinal velocity, vy represents the vehicle's lateral velocity, and ω represents the yaw rate; The coordinate system also represents: the longitudinal distance of the i-th axis from the vehicle's center of gravity, the vehicle's wheelbase, the longitudinal force of the tires on the i-th axis, and the lateral force of the tires.

3. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 1, characterized in that, Calculating the vertical load on each axle of a multi-axle vehicle includes: Obtain the static and dynamic suspension forces of each axle of the vehicle; Based on the static suspension force and dynamic suspension force, the resultant vertical force of each suspension is obtained; Based on the vertical resultant force of each suspension and combined with the unsprung mass of the corresponding axle, the vertical resultant force of each tire is obtained; By combining the vertical resultant forces of each tire, the vertical resultant forces of each axle are obtained.

4. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 3, characterized in that, Obtaining the static suspension forces of each axle of the vehicle includes: The static equilibrium state of the vehicle is determined using the displacement method: in, This represents the suspension force under static equilibrium conditions on each axle. i =1, 2, 3, 4, R The rotation matrix represents the state of the vehicle. GR This represents the component of the vehicle's weight in the z-direction. mb Indicates the sprung mass of the vehicle. g Represents gravitational acceleration. Li This represents the longitudinal distance of the i-th axis from the vehicle's center of mass; Based on geometric relationships, obtain the deformation ratios of each suspension component: in, fi This represents the deformation ratio coefficient of the i-th axle suspension relative to the first axle suspension; Based on the vehicle's static balance state and the deformation ratio of each suspension component, calculate the corresponding static suspension force: in, La This represents the algebraic sum of the longitudinal positions of each axle relative to the vehicle's center of gravity. Lb This represents the sum of squares of the longitudinal positions of each axle relative to the vehicle's center of gravity.

5. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 3, characterized in that, Obtaining the dynamic suspension force includes: Obtain the vehicle's current pitch angle θ; Assuming the relative height between the vehicle body coordinate system and the ground remains constant, the relative deformation of each wheel and suspension relative to the static equilibrium state in the vehicle body coordinate system is calculated based on geometric relationships: in, This represents the deformation of the suspension on the j-th side of the i-th axis relative to the static equilibrium state. B Indicates the wheelbase of the vehicle; Based on the relative deformation, the dynamic suspension force is obtained: in, This represents the dynamic suspension force of the suspension on the j-th side of the i-th axis. This represents the single-sided stiffness of the suspension on the j-th side of the i-th axis. This indicates the single-sided damping of the suspension on the j-th side of the i-th axis. j A value of 1 indicates the left side. j 2 indicates the right side. This represents the deformation rate of the suspension on the j-th side of the i-th axis relative to the static equilibrium state.

6. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 1, characterized in that, The dynamic model of the multi-axle vehicle is as follows: in, m Indicates the overall weight of the vehicle. This represents the longitudinal acceleration at the vehicle's center of gravity. This indicates the vehicle's drag coefficient. This indicates the vehicle's frontal area. Indicates air density, Indicates the rolling resistance coefficient. R The rotation matrix represents the state of the vehicle. This represents the longitudinal braking force between the wheel on the j-th side of the i-th axle and the road surface, where j=1 represents the left side and j=2 represents the right side.

7. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 6, characterized in that, Based on the aforementioned dynamic model, and incorporating the vehicle's current state information, the total braking force requirement is calculated as follows: in, Indicates the lateral speed of the vehicle. Indicates yaw rate. Indicates the longitudinal speed of the vehicle. Indicates the expected acceleration. This indicates the total braking force requirement.

8. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 1, characterized in that, The tire adhesion constraint is: in, express i The braking force corresponding to the shaft, express i The axis corresponds to the road surface adhesion coefficient. This represents the vertical load on the wheel of the i-th axle. This represents the road adhesion coefficient corresponding to the left wheel of the i-th axis. This represents the road surface adhesion coefficient corresponding to the right wheel of the i-th axis; The braking torque constraint is: in, Indicates transmission efficiency. Indicates the tire's rolling radius. Indicates braking torque; The tire adhesion constraint and braking torque constraint are constraints in the objective function optimization process, used to limit the feasible range of braking force and braking torque for each axle; the objective function, under the condition of satisfying the tire adhesion constraint and braking torque constraint, comprehensively optimizes the energy optimization objective and the braking stability objective; the objective function is: in, This represents the energy optimization objective, used to achieve the minimum torque output while satisfying constraints. This represents the braking stability optimization objective, used to achieve the smoothest braking under the given constraints. 1, 2 represents a parameter used to balance the priorities of different objectives. Represents the constraint function; constraint functions for: in, x ( i Let x(i) represent the i-th optimization variable; when allocated by axle, x(i) represents the target braking torque of the i-th axle; when allocated by wheel, x(i) represents the target braking torque of the i-th wheel.

9. The method for optimizing the distribution of braking torque for multi-axle wheeled vehicles on non-planar roads according to claim 1, characterized in that, Solving for the target braking torque using a hybrid particle swarm optimization algorithm includes: Initialize particle swarm: randomly generated N There are 10 particles, each representing a braking torque allocation scheme, and the particle velocity is initialized. Calculate the fitness value: For each particle, calculate the objective function value and the penalty function, and use the penalty function to incorporate the constraints into the objective function; Update the individual optimal solution and the global optimal solution; Update particle velocity and position; The iteration terminates when the maximum number of iterations is reached or the rate of change of the objective function is less than a preset threshold, and the target braking torque is obtained.

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