Fault-tolerant control method and system for electronic mechanical braking

Abstract

The invention discloses a fault-tolerant control method and system for electronic mechanical braking. The method comprises the steps that the expected additional yawing moment and the expected braking force of a vehicle are calculated; the failure degree of each wheel side EMB actuator is obtained, and whether a fault-tolerant control mode needs to be entered or not is judged; if the vehicle does not need to enter the fault-tolerant control mode, the braking force of the EMB is distributed by taking the minimum value obtained by a self-adaptive distribution function of the vehicle as a target; otherwise, entering a fault-tolerant control mode, and sequentially judging whether each control mode can meet the requirements of providing the expected additional yawing moment and the expected braking force of the vehicle or not; when any control mode can be met, judging is ended, and the braking force of the EMB is distributed to all the wheels through the corresponding distribution mode under the control mode; and when all the control modes are not met, on the premise that the expected additional yaw moment of the vehicle is met, the actual maximum braking force of the vehicle is applied to brake the vehicle. The electronic mechanical braking stability can be improved, and the driving safety of the vehicle is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic mechanical braking, and in particular to a fault-tolerant control method and system for electronic mechanical braking. Background Art

[0002] As the automotive industry transforms towards electrification, intelligence and digitalization, the importance of brake-by-wire technology is becoming increasingly prominent. Due to the advancement of autonomous driving technology and the increasing proportion of new energy vehicles, brake-by-wire technology will become a key technology in the execution layer of the automotive chassis and will achieve rapid growth in the next few years.

[0003] As an advanced braking technology, the EMB system has the advantages of precise braking response, high integration, integrated advanced intelligent control, simple structure, shorter braking response time and superior performance. However, its commercial application still needs to solve some key problems, such as system reliability, anti-interference ability and power supply redundancy.

[0004] The EMB system uses a large number of electronic circuits, which may be affected by electromagnetic interference. If some electronic control units in the system fail, it will directly lead to abnormalities or failures in the braking system, and even cause unstable conditions such as vehicle skidding or running off the track, affecting the stability and safety of the braking system. Therefore, fault-tolerant control is required to ensure that even when some systems fail, the vehicle can brake safely to ensure vehicle stability.

[0005] Existing technologies mostly focus on single-point failure fault-tolerant control of EMB, and distribute braking force to front and rear axles for such failures, without judging the control potential of each wheel to distribute braking force to each wheel in real time.

[0006] Some methods perform active fault-tolerant control based on fault detection and isolation (FDI) technology, but the control method based on FDI overly relies on the diagnosis results of the fault diagnosis mechanism and cannot control the gain response parameter changes through real-time estimation information of unknown parameters. Summary of the invention

[0007] The main purpose of the present invention is to provide a fault-tolerant control method and system for electronic mechanical braking, so as to ensure the stability of the braking system and the safe braking of the vehicle.

[0008] The technical solution adopted by the present invention is: a fault-tolerant control method for electronic mechanical braking, comprising:

[0009] Obtain the expected parameters and state parameters of the vehicle, and calculate the expected additional yaw moment and expected braking force of the vehicle in combination with the two-degree-of-freedom reference model of the vehicle;

[0010] Obtain the failure degree of each wheel-side EMB actuator to determine whether it is necessary to enter the fault-tolerant control mode;

[0011] If it is not necessary to enter the fault-tolerant control mode, the braking force of the EMB is allocated with the minimum value of the vehicle's adaptive allocation function as the target; if it is necessary to enter the fault-tolerant control mode, the braking control mode is switched in the order of the single control of the EMB actuator that has not failed, the EMB+SBW coordinated control, and the EMB+SBW+AKC coordinated control to determine whether each braking control mode can provide the expected additional yaw moment and expected braking force of the vehicle;

[0012] When any of the braking control modes can provide the expected additional yaw moment and the expected braking force of the vehicle, the judgment is terminated, and the braking force of the EMB is allocated to each wheel through the corresponding allocation method under the braking control mode; when none of the braking control modes can provide the expected additional yaw moment and the expected braking force of the vehicle, the vehicle is braked with the actual braking force of the vehicle as the maximum target, under the premise of meeting the expected additional yaw moment of the vehicle.

[0013] According to the above technical solution, the desired parameters of the vehicle include the desired front wheel turning angle, the desired rear wheel turning angle, the desired longitudinal deceleration, the ideal center of mass sideslip angle and the desired slip rate of the tire;

[0014] The state parameters of the vehicle include the vehicle's center of mass sideslip angle, the vehicle's yaw angular velocity, the vehicle's front wheel sideslip angle, the vehicle's front wheel sideslip stiffness, the vehicle's rear wheel sideslip stiffness, the distance from the vehicle's center of mass to the vehicle's front axle, the distance from the vehicle's center of mass to the vehicle's rear axle, the vehicle's front wheel turning angle, the vehicle's rear wheel turning angle, the vehicle's mass, and the vehicle's speed.

[0015] According to the above technical solution, the method for calculating the expected additional yaw moment of the vehicle includes:

[0016] Designing a yaw moment sliding mode controller with the vehicle's center of mass sideslip angle as a control variable, wherein the controller takes the ideal center of mass sideslip angle as a target, takes the vehicle's two-degree-of-freedom reference model as an expected value, and defines a sliding mode surface;

[0017] Differentiating the sliding surface to obtain a first formula;

[0018] The exponential approach rate of the saturation function is taken as the sliding mode control rate of the sliding surface to obtain the second formula:

[0019] The first formula and the second formula are combined to calculate the expected additional yaw moment of the vehicle;

[0020] The method for calculating the expected braking force of the vehicle includes: the expected braking force of the vehicle is equal to the mass of the vehicle multiplied by the expected longitudinal deceleration of the vehicle.

[0021] According to the above technical solution, the method for determining whether it is necessary to enter the fault-tolerant control mode includes: comparing the acquired failure degree of each EMB actuator with the preset maximum failure degree; if the failure degree of any EMB actuator is greater than the preset maximum failure degree, entering the fault-tolerant control mode; otherwise, not entering the fault-tolerant control mode.

[0022] According to the above technical solution, the adaptive allocation function of the vehicle is J=aJ1+bJ2, where J1 is the dynamic response function of the vehicle, J2 is the tire slip function of the vehicle, a and b are preset weight coefficients and a+b=1;

[0023] The vehicle's dynamic response function J1 = [BF xi -U] T H[BF xi -U], where H=diag(h1,h2),δ f is the actual turning angle of the front wheel, δ r is the actual turning angle of the rear wheel, d is the distance between the front wheel and the rear wheel, l f is the distance from the vehicle's center of mass to the front axle, U = [F xc ΔM z ] is the expected braking force and the expected additional yaw moment, h1 is the weight coefficient related to the vehicle braking force, and h2 is the weight coefficient related to the vehicle additional yaw moment;

[0024] The tire slip function of the vehicle J2 = F xi T WF xi ; Among them, F xi =[F fl F fr F rl F rr ],W=diag(|s fl -s d |,|s fr -s d |,|s rl -s d |,|s rr -s d |), where F fl The braking force distributed to the left front wheel of the vehicle, F fr The braking force distributed to the right front wheel of the vehicle, F rl The braking force distributed to the left rear wheel of the vehicle, F rr Braking force distributed to the right rear wheel of the vehicle, s fl is the slip rate of the left front wheel of the vehicle, s fr is the slip rate of the right front wheel of the vehicle, s rl is the slip rate of the left rear wheel of the vehicle, srr is the slip rate of the right rear wheel of the vehicle, s d is the expected slip ratio of the vehicle tire.

[0025] According to the above technical solution, the allocation method of the single control of the EMB actuator that has not failed includes: allocating the braking force of the EMB to each wheel with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle;

[0026] The EMB+SBW coordinated control allocation method includes: calculating the active front wheel angle according to the expected additional yaw moment, and adding the active front wheel angle to the front wheel angle of the current vehicle; based on the adjusted front wheel angle of the vehicle, with the adaptive allocation function of the vehicle taking the minimum value as the goal, allocating the EMB braking force to each wheel;

[0027] The allocation method of the EMB+SBW+AKC coordinated control includes: setting the front wheel steering angle of the vehicle to the steering angle limit value under physical constraints, calculating the active rear wheel steering angle according to the sideslip angle and yaw rate of the center of mass of the vehicle, and adding the active rear wheel steering angle to the rear wheel steering angle of the current vehicle; based on the front wheel steering angle adjusted to the steering angle limit value and the rear wheel steering angle of the adjusted vehicle, with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle, distributing the braking force of the EMB to each wheel.

[0028] According to the above technical solution, the method for calculating the active front wheel turning angle includes:

[0029] In the vehicle two-degree-of-freedom reference model, the vehicle speed, front wheel steering angle and front wheel sideslip angle are orthogonally decomposed to obtain the longitudinal speed and lateral speed of the vehicle, and the front wheel sideslip angle is calculated according to the longitudinal speed, lateral speed, yaw rate and the distance from the center of mass of the vehicle to the front wheel;

[0030] Calculate the additional yaw moment required to be provided by the SBW according to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle;

[0031] Calculating the lateral force generated by the target front wheel turning angle according to the additional yaw moment required to be provided by the SBW and the distance from the vehicle center of mass to the front axle;

[0032] The active front wheel steering angle is calculated according to the lateral force generated by the target front wheel steering angle, the front wheel sideslip angle of the vehicle and the front wheel sideslip stiffness of the vehicle.

[0033] According to the above technical solution, the method for calculating the active rear wheel turning angle includes:

[0034] Calculating the lateral force generated by the front wheel according to the turning angle limit value under the physical constraint, the lateral speed of the vehicle, the front wheel cornering stiffness of the vehicle, the yaw rate of the vehicle, and the distance from the center of mass of the vehicle to the front wheel;

[0035] Calculate the additional yaw moment required to be jointly provided by SBW and AKC according to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle, and calculate the lateral force generated by the rear wheel according to the additional yaw moment required to be jointly provided by SBW and AKC, the lateral force generated by the front wheel, the distance from the center of mass of the vehicle to the front wheel, and the distance from the center of mass of the vehicle to the rear wheel;

[0036] Calculating a rear wheel slip angle according to the longitudinal velocity, lateral velocity, yaw rate and the distance from the center of mass of the vehicle to the rear wheel;

[0037] The active rear wheel steering angle is calculated according to the rear wheel slip angle, the lateral force generated by the rear wheel, and the rear wheel slip stiffness of the vehicle.

[0038] Another aspect of the present invention provides a fault-tolerant control system for an electronic mechanical brake, which executes the above-mentioned fault-tolerant control method for an electronic mechanical brake.

[0039] Another aspect of the present invention provides a computer storage medium, which stores a computer program executable by a processor, and the computer program executes the above-mentioned fault-tolerant control method of the electronic mechanical brake.

[0040] The beneficial effects of the present invention are as follows: the present invention provides a fault-tolerant control method and system for electronic mechanical braking. In the event of partial or complete failure of an EMB system actuator, it is determined whether the single control of the EMB actuator that has not failed, the EMB+SBW coordinated control that intervenes in the active front wheel steering angle, and the EMB+SBW+AKC coordinated control that intervenes in the active front and rear wheel steering angles can meet the requirements of providing the expected dynamic response of the vehicle, and the braking force is adaptively distributed to each wheel in combination with the control potential of each wheel to ensure the driving safety and driving stability of the vehicle.

[0041] Compared with existing technologies:

[0042] The present invention collects vehicle parameters in real time to participate in the fault-tolerant control of the braking system, and can better control the change of the gain response coefficient;

[0043] The present invention considers the control potential of each wheel when adaptively distributing the braking force, which can improve the stability of the vehicle during braking;

[0044] In the actual vehicle operation process, the present invention couples the dynamic responses of multiple subsystems in the braking system to each other, so as to better obtain the influence of each subsystem in the braking system on the braking of the whole vehicle.

[0045] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 is a flow chart of a fault-tolerant control method of an electronic mechanical brake according to an embodiment of the present invention;

[0048] Figure 2 is a working principle diagram of a fault-tolerant control system of an electronic mechanical brake according to an embodiment of the present invention;

[0049] Figure 3 is a schematic structural diagram of a fault-tolerant control device for an electronic mechanical brake according to an embodiment of the present invention;

[0050] Figure 4 It is a schematic diagram of the orthogonal decomposition of the vehicle speed, front wheel steering angle and front wheel sideslip angle in the vehicle two-degree-of-freedom model of an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0053] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0054] In order to facilitate the understanding of this application document, the following keywords need to be explained as follows:

[0055] IMU: Inertial Measurement Unit.

[0056] EMB: Electronic Mechanical Brake System, electronic mechanical brake system.

[0057] CDCU: Chassis Domain Control Unit, chassis domain controller, is used to identify the driver's braking intention and send it to the brake control unit for execution.

[0058] BCU: Brake Control Unit, brake control unit, receives the braking request from the chassis domain controller and controls the wheel caliper motor to execute.

[0059] SMC: Sliding Mode Control, a nonlinear control method based on sliding surface.

[0060] Fault-tolerant control: A technology that ensures that the control system can maintain stable operation and meet performance indicators when some components fail. It is divided into passive fault-tolerant control and active fault-tolerant control.

[0061] ASIL: Automotive Safety Integrity Level, a classification system defined in the ISO 26262 standard for measuring the risk level of specific system components in an automotive system. This standard is a functional safety standard used in the automotive industry that ensures the safety of automotive equipment and systems throughout their life cycle based on risk assessment.

[0062] SBW: Steer-by-wire.

[0063] AKC: Active Kinematics control, active rear-wheel steering.

[0064] Example 1

[0065] This embodiment provides a fault-tolerant control method for an electronic mechanical brake. In the case of partial or complete failure of an EMB system actuator, adaptive fault-tolerant control is performed based on the control potential of the chassis EMB, SBW, and AKC. The process is as follows: Figure 1 As shown, including:

[0066] S1. Obtaining expected parameters and state parameters of a vehicle, combining the expected parameters and state parameters of the vehicle with a two-degree-of-freedom reference model of the vehicle, and calculating an expected additional yaw moment and an expected braking force of the vehicle.

[0067] Specifically, the desired parameters of the vehicle include a desired front wheel steering angle, a desired rear wheel steering angle, a desired longitudinal deceleration, an ideal sideslip angle of the center of mass, and a desired slip rate of the tires.

[0068] The state parameters of the vehicle include the vehicle's center of mass sideslip angle, the vehicle's yaw angular velocity, the vehicle's front wheel sideslip angle, the vehicle's front wheel sideslip stiffness, the vehicle's rear wheel sideslip stiffness, the distance from the vehicle's center of mass to the vehicle's front axle, the distance from the vehicle's center of mass to the vehicle's rear axle, the vehicle's front wheel turning angle, the vehicle's rear wheel turning angle, the vehicle's mass, and the vehicle's speed.

[0069] Specifically, since the center of mass slip angle of the vehicle has a significant impact on the stability of the vehicle, the size of the center of mass slip angle needs to be strictly controlled during the operation of the vehicle to prevent the vehicle from becoming unstable. Therefore, a yaw moment sliding mode controller with the center of mass slip angle of the vehicle as the control variable is designed. The controller takes the ideal center of mass slip angle as the target and the two-degree-of-freedom reference model of the vehicle as the expected value to define the sliding mode surface.

[0070] The vehicle two-degree-of-freedom reference model is:

[0071]

[0072] Among them, β is the sideslip angle of the center of mass, γ is the yaw rate, k f is the front wheel cornering stiffness, k r is the rear wheel cornering stiffness, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle center of mass to the rear axle, δ f is the front wheel turning angle, δ r is the rear wheel turning angle, I z is the yaw moment of inertia, m is the vehicle mass, V x is the longitudinal velocity of the vehicle, ΔM z The additional yaw moment is expected.

[0073] The sliding surface is:

[0074]

[0075] Among them, β d is the ideal center of mass sideslip angle.

[0076] Differentiate the sliding surface to obtain the first formula:

[0077]

[0078] The exponential approach rate of the saturation function is taken as the sliding film control rate of the sliding surface to obtain the second formula:

[0079]

[0080] Among them, ε β , k β are preset center of mass sideslip angle control parameters, and are all greater than 0.

[0081] The expected additional yaw moment of the vehicle is calculated by combining the first and second equations:

[0082]

[0083] The method for calculating the expected braking force of the vehicle includes: xc =ma xd .

[0084] That is, the expected longitudinal force of the vehicle is equal to the vehicle mass multiplied by the expected longitudinal deceleration of the vehicle, where m is the vehicle mass and a is xd is the desired longitudinal deceleration of the vehicle.

[0085] S2. Obtain the failure degree of each wheel-side EMB actuator and determine whether it is necessary to enter the fault-tolerant control mode.

[0086] The method for determining whether to enter the fault-tolerant control mode includes: comparing the acquired failure degree of each EMB actuator with a preset maximum failure degree, and if the failure degree of any EMB actuator is greater than the preset maximum failure degree, entering the fault-tolerant control mode. Otherwise, not entering the fault-tolerant control mode.

[0087] S3. If it is not necessary to enter the fault-tolerant control mode, the braking force of the EMB is allocated with the minimum value of the vehicle's adaptive allocation function as the target; if it is necessary to enter the fault-tolerant control mode, the braking control mode is switched in the order of single control of the EMB actuator that has not failed, EMB+SBW coordinated control, and EMB+SBW+AKC coordinated control to determine whether each braking control mode can provide the expected additional yaw moment and expected braking force of the vehicle.

[0088] The adaptive distribution of braking force mainly realizes the following two functions: ensuring the dynamics and stability of the vehicle; improving the adhesion margin of the vehicle so that each tire force is far away from the adhesion limit of the tire. Based on the above-mentioned target function of adaptive distribution of braking force, the adaptive distribution function of the vehicle is designed as J=aJ1+bJ2, where J1 is the dynamic response function of the vehicle, J2 is the tire slip function of the vehicle, a and b are preset weight coefficients and a+b=1.

[0089] The vehicle's dynamic response function J1 = [BF xi -U] T H[BF xi -U], where B is a constant coefficient matrix related to tire steering angle and vehicle parameters,

[0090] H is J 21 The weight coefficient matrix, H = diag (h1, h2), δ f is the actual turning angle of the front wheel, δ r is the actual turning angle of the rear wheel, d is the distance between the front wheel and the rear wheel, l f is the distance from the vehicle's center of mass to the front axle, U = [F xc ΔM z ] is the expected braking force and the expected additional yaw moment, h1 is the weight coefficient related to the vehicle braking force, and h2 is the weight coefficient related to the vehicle additional yaw moment. The size of the weight coefficient can be adjusted according to the specific driving conditions. For example, when the vehicle accelerates urgently, the longitudinal speed requirement is high, and h1 is increased; when the vehicle is unstable, the requirement for yaw moment control is higher, and h2 should be increased.

[0091] The tire slip function of the vehicle J2 = F xi T WF xi ; Among them, F xi =[F fl F fr F rl F rr ],W=diag(|s fl -s d |,|s fr -s d |,|s rl -s d |,|s rr -s d |), where F fl The braking force distributed to the left front wheel of the vehicle, F fr The braking force distributed to the right front wheel of the vehicle, F rl The braking force distributed to the left rear wheel of the vehicle, F rr Braking force distributed to the right rear wheel of the vehicle, s fl is the slip rate of the left front wheel of the vehicle, s fr is the slip rate of the right front wheel of the vehicle, s rl is the slip rate of the left rear wheel of the vehicle, s rr is the slip rate of the right rear wheel of the vehicle, s d is the expected slip ratio of the vehicle tire.

[0092] S4. When any of the braking control modes can provide the expected additional yaw moment and expected braking force of the vehicle, the judgment is terminated, and the braking force of the EMB is allocated to each wheel through the corresponding allocation method under the braking control mode; when none of the braking control modes can provide the expected additional yaw moment and expected braking force of the vehicle, the vehicle is braked with the actual braking force of the vehicle as the maximum target, under the premise of satisfying the expected additional yaw moment of the vehicle.

[0093] Furthermore, the allocation method of the single control of the EMB actuator that has not failed includes: allocating the braking force of the EMB to each wheel with the goal of obtaining a minimum value of the adaptive allocation function of the vehicle.

[0094] The EMB+SBW coordinated control allocation method includes: calculating the active front wheel angle according to the expected additional yaw moment, adding the active front wheel angle to the front wheel angle of the current vehicle, and allocating the EMB braking force to each wheel based on the front wheel angle of the adjusted vehicle with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle.

[0095] The allocation method of the EMB+SBW+AKC coordinated control includes: setting the front wheel steering angle of the vehicle to the steering angle limit value under physical constraints, calculating the active rear wheel steering angle according to the center of mass sideslip angle and yaw rate of the vehicle, and adding the active rear wheel steering angle to the rear wheel steering angle of the current vehicle. Based on the front wheel steering angle adjusted to the steering angle limit value and the rear wheel steering angle of the adjusted vehicle, the EMB braking force is allocated to each wheel with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle.

[0096] The method for calculating the active front wheel turning angle includes:

[0097] In the vehicle two-degree-of-freedom reference model, the vehicle speed, front wheel steering angle and front wheel sideslip angle are orthogonally decomposed, such as Figure 4 As shown, the longitudinal velocity V of the vehicle is obtained. x With the lateral velocity V y , and V y =V x tanβ, calculate the front wheel slip angle based on the longitudinal velocity, lateral velocity, yaw rate and the distance from the vehicle's center of mass to the front wheel. The calculation formula is: Among them, θ vf is the front wheel slip angle, l f is the distance from the center of mass of the vehicle to the front wheel.

[0098] According to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle, the additional yaw moment required by SBW is calculated. The calculation formula is: ΔM z1 =ΔM z -M z . ΔM z1 Additional yaw moment required for SBW, ΔM z is the expected additional yaw moment of the vehicle, M z is the actual yaw moment of the vehicle.

[0099] The lateral force generated by the target front wheel steering angle is calculated based on the additional yaw moment required by the SBW and the distance from the vehicle center of mass to the front axle. In the current control mode, the active rear wheel steering does not contribute, so the lateral force generated by the rear wheel steering angle is F yr = 0. The calculation formula of the lateral force generated by the front wheel turning angle is: F yf =2·k f ·(δ fd -θ vf ). Among them, δ fd is the desired front wheel steering angle, k f is the front wheel cornering stiffness.

[0100] The active front wheel steering angle is calculated based on the lateral force generated by the target front wheel steering angle, the front wheel sideslip angle of the vehicle and the front wheel sideslip stiffness of the vehicle. The calculation formula is:

[0101] The allocation method of the EMB+SBW+AKC coordinated control includes: setting the front wheel steering angle of the vehicle to the steering angle limit value under physical constraints, calculating the active rear wheel steering angle according to the center of mass sideslip angle and the yaw angular velocity, and adding the active rear wheel steering angle to the current rear wheel steering angle of the vehicle; based on the current front wheel steering angle of the vehicle and the rear wheel steering angle of the adjusted vehicle, with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle, distributing the braking force of the EMB healthy actuator to each wheel.

[0102] The calculation method of the active rear wheel turning angle includes:

[0103] The lateral force generated by the front wheel is calculated according to the turning angle limit value under the physical constraint, the lateral speed of the vehicle, the front wheel cornering stiffness of the vehicle, the yaw rate of the vehicle, and the distance from the center of mass of the vehicle to the front wheel. The calculation method includes: Among them, δ fmax is the rotation angle limit under physical constraints.

[0104] According to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle, the additional yaw moment required to be provided by SBW and AKC is calculated. The calculation formula is: ΔM z1 =ΔM z -M z . ΔM z1 Additional yaw moment required for SBW and AKC, ΔM z is the expected additional yaw moment of the vehicle, M z is the actual yaw moment of the vehicle.

[0105] The lateral force generated by the rear wheel is calculated based on the additional yaw moment required to be provided by the SBW and AKC, the lateral force generated by the front wheel, the distance from the vehicle's center of mass to the front wheel, and the distance from the vehicle's center of mass to the rear wheel. The calculation formula is: ΔM z1= l f ·F yf -l r ·F yr Among them, F yr is the lateral force generated by the rear wheel, l r is the distance from the vehicle's center of mass to the rear wheels.

[0106] The rear wheel slip angle is calculated based on the longitudinal speed, lateral speed, yaw rate and the distance from the vehicle's center of mass to the rear wheel. The calculation formula is:

[0107] The active rear wheel steering angle is calculated based on the rear wheel slip angle, the lateral force generated by the rear wheel, and the rear wheel slip stiffness of the vehicle. The calculation formula is:

[0108] This embodiment further provides a computer storage medium, which stores a computer program executable by a processor, and the computer program executes the above-mentioned fault-tolerant control method of the electronic mechanical brake.

[0109] Example 2

[0110] This embodiment provides a fault-tolerant control system for electronic mechanical braking, which executes the fault-tolerant control method for electronic mechanical braking described in Example 1. The system includes: a parameter acquisition and analysis module, a mode selection module, a braking force distribution module and a braking execution module.

[0111] Among them, the parameter acquisition and analysis module includes an upper-level controller, which is used to obtain the expected parameters and state parameters of the vehicle, and calculate the expected additional yaw moment and expected braking force of the vehicle in combination with the vehicle's two-degree-of-freedom reference model, and transmit the expected additional yaw moment and expected braking force of the vehicle to the braking force distribution module.

[0112] Furthermore, the calculation method of the expected additional yaw moment and the expected braking force of the vehicle has been described in Example 1 and will not be repeated here.

[0113] The mode selection module is used to determine whether it is necessary to enter the fault-tolerant control mode according to the failure degree of each wheel-side EMB actuator. If it is not necessary to enter the fault-tolerant control mode, a distribution instruction is issued to the braking force distribution module. If it is necessary to enter the fault-tolerant control mode, the mode selection module determines in turn whether the single control of the EMB actuator that has not failed, the EMB+SBW coordinated control, and the EMB+SBW+AKC coordinated control can meet the expected additional yaw moment and expected braking force of the vehicle. When any of the control modes can meet the expected additional yaw moment and expected braking force of the vehicle, the judgment is terminated, and the distribution instructions corresponding to the different control modes are issued to the braking force distribution module. When all control modes do not meet the expected additional yaw moment and expected braking force of the vehicle, it is determined to enter the emergency braking mode, and the actual maximum braking force of the vehicle is applied to brake the vehicle on the premise of meeting the expected additional yaw moment of the vehicle.

[0114] The method for determining whether each braking control mode can provide the desired additional yaw moment and desired braking force of the vehicle has been described in Embodiment 1 and will not be repeated here.

[0115] The braking force distribution module is used to distribute the EMB braking force to each wheel according to the distribution instruction issued by the braking control mode selection module and the expected additional yaw moment and expected braking force calculated by the parameter acquisition and analysis module.

[0116] Furthermore, the allocation method of the different control modes has been introduced in Example 1 and will not be repeated here.

[0117] The brake actuation module is used to brake the vehicle through the wheel-side EMB actuator according to the braking force distributed to each wheel.

[0118] This embodiment also provides a fault-tolerant control device for an electronic mechanical brake, which executes the fault-tolerant control method for an electronic mechanical brake described in Embodiment 1, and has a structure as follows: Figure 3 As shown, including:

[0119] Chassis domain controller CDCU, wheel-side brake control unit BCU, wheel-end EMB assembly, front wheel steer-by-wire SBW, rear wheel active steering AKC, power supply BAT1 and redundant power supply BAT2, vehicle CAN bus, electronic pedal E-Pedal, EPB switch and four-wheel speed sensors.

[0120] The CDCU includes a main control unit MECU and a redundant control unit SECU, both of which have the same functional model and serve as backup for each other.

[0121] The wheel-end EMB assembly includes a motor, a transmission mechanism, a motion conversion mechanism and a sensor.

[0122] The principle of the fault-tolerant control method for electronic mechanical braking described in Example 1 is as follows: Figure 2 As shown. Among them, δ fd is the desired front wheel steering angle, δ f is the actual front wheel turning angle, δ rd is the desired rear wheel steering angle, δ r is the actual rear wheel turning angle, a xd is the expected longitudinal deceleration, a x is the current longitudinal deceleration of the vehicle, ΔM z is the expected additional yaw moment, F xic is the expected braking force of each wheel, F xi Actual distribution of braking force to each wheel.

[0123] In summary, the present invention provides a fault-tolerant control method and system for electronic mechanical braking. In the event of partial or complete failure of the EMB system actuator, it is determined whether each control method can provide the expected dynamic response of the vehicle, and the braking force is adaptively distributed to each wheel in combination with the control potential of each wheel to ensure the driving safety and driving stability of the vehicle.

[0124] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0125] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0126] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A fault-tolerant control method for an electronic mechanical brake, characterized in that: include: Obtain the expected parameters and state parameters of the vehicle, and calculate the expected additional yaw moment and expected braking force of the vehicle in combination with the two-degree-of-freedom reference model of the vehicle; Obtain the failure degree of each wheel-side EMB actuator to determine whether it is necessary to enter the fault-tolerant control mode; If it is not necessary to enter the fault-tolerant control mode, the braking force of the EMB is allocated with the minimum value of the vehicle's adaptive allocation function as the target; if it is necessary to enter the fault-tolerant control mode, the braking control mode is switched in the order of the single control of the EMB actuator that has not failed, the EMB+SBW coordinated control, and the EMB+SBW+AKC coordinated control to determine whether each braking control mode can provide the expected additional yaw moment and expected braking force of the vehicle; When any of the braking control modes can provide the expected additional yaw moment and the expected braking force of the vehicle, the judgment is terminated, and the braking force of the EMB is allocated to each wheel through the corresponding allocation method under the braking control mode; when none of the braking control modes can provide the expected additional yaw moment and the expected braking force of the vehicle, the vehicle is braked with the actual braking force of the vehicle as the maximum target, under the premise of meeting the expected additional yaw moment of the vehicle.

2. The fault-tolerant control method of electronic mechanical braking according to claim 1, characterized in that: The desired parameters of the vehicle include a desired front wheel steering angle, a desired rear wheel steering angle, a desired longitudinal deceleration, an ideal center of mass sideslip angle, and a desired slip rate of the tire; The state parameters of the vehicle include the vehicle's center of mass sideslip angle, the vehicle's yaw angular velocity, the vehicle's front wheel sideslip angle, the vehicle's front wheel sideslip stiffness, the vehicle's rear wheel sideslip stiffness, the distance from the vehicle's center of mass to the vehicle's front axle, the distance from the vehicle's center of mass to the vehicle's rear axle, the vehicle's front wheel turning angle, the vehicle's rear wheel turning angle, the vehicle's mass, and the vehicle's speed.

3. The fault-tolerant control method of electronic mechanical braking according to claim 2, characterized in that: The method for calculating the expected additional yaw moment of a vehicle includes: designing a yaw moment sliding mode controller with the vehicle's center of mass sideslip angle as a control variable, wherein the controller takes the ideal center of mass sideslip angle as a target and the vehicle's two-degree-of-freedom reference model as an expected value, and defines a sliding mode surface; differentiating the sliding mode surface to obtain a first formula; taking the exponential approach rate of a saturation function as the sliding mode control rate of the sliding mode surface to obtain a second formula; and combining the first formula and the second formula to obtain the expected additional yaw moment of the vehicle; The method for calculating the expected braking force of the vehicle includes: the expected braking force of the vehicle is equal to the mass of the vehicle multiplied by the expected longitudinal deceleration of the vehicle.

4. The fault-tolerant control method of electronic mechanical braking according to claim 1, characterized in that: The method for determining whether it is necessary to enter the fault-tolerant control mode includes: comparing the acquired failure degree of each EMB actuator with the preset maximum failure degree, if the failure degree of any EMB actuator is greater than the preset maximum failure degree, entering the fault-tolerant control mode; otherwise, not entering the fault-tolerant control mode.

5. The fault-tolerant control method of electronic mechanical braking according to claim 1, characterized in that: The adaptive allocation function of the vehicle J=aJ1+bJ2, wherein J1 is the dynamic response function of the vehicle, J2 is the tire slip function of the vehicle, a and b are preset weight coefficients and a+b=1; The vehicle's dynamic response function J1 = [BF xi -U] T H[BF xi -U], where H=diag(h1,h2),δ f is the front wheel turning angle, δ r is the rear wheel turning angle, d is the distance between the front wheel and the rear wheel, l f is the distance from the vehicle's center of mass to the front axle, U = [F xc ΔM z ] is the expected braking force and the expected additional yaw moment, h1 is the weight coefficient related to the vehicle braking force, and h2 is the weight coefficient related to the vehicle additional yaw moment; The tire slip function of the vehicle J2 = F xi T WF xi Among them, F xi =[F fl F fr F rl F rr ],W=diag(|s fl -s d |,|s fr -s d |,|s rl -s d |,|s rr -s d |), where F fl The braking force distributed to the left front wheel of the vehicle, F fr The braking force distributed to the right front wheel of the vehicle, F rl The braking force distributed to the left rear wheel of the vehicle, F rr Braking force distributed to the right rear wheel of the vehicle, s fl is the slip rate of the left front wheel of the vehicle, s fr is the slip rate of the right front wheel of the vehicle, s rl is the slip rate of the left rear wheel of the vehicle, s rr is the slip rate of the right rear wheel of the vehicle, s d is the expected slip ratio of the vehicle tire.

6. The fault-tolerant control method of electronic mechanical braking according to claim 5, characterized in that: The allocation method of the single control of the EMB actuator that has not failed includes: allocating the braking force of the EMB to each wheel with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle; The EMB+SBW coordinated control allocation method includes: calculating the active front wheel angle according to the expected additional yaw moment, and adding the active front wheel angle to the front wheel angle of the current vehicle; based on the adjusted front wheel angle of the vehicle, with the adaptive allocation function of the vehicle taking the minimum value as the goal, allocating the EMB braking force to each wheel; The allocation method of the EMB+SBW+AKC coordinated control includes: setting the front wheel steering angle of the vehicle to the steering angle limit value under physical constraints, calculating the active rear wheel steering angle according to the sideslip angle and yaw rate of the center of mass of the vehicle, and adding the active rear wheel steering angle to the rear wheel steering angle of the current vehicle; based on the front wheel steering angle adjusted to the steering angle limit value and the rear wheel steering angle of the adjusted vehicle, with the goal of obtaining the minimum value of the adaptive allocation function of the vehicle, distributing the braking force of the EMB to each wheel.

7. The fault-tolerant control method of electronic mechanical braking according to claim 6, characterized in that: The method for calculating the active front wheel turning angle includes: In the vehicle two-degree-of-freedom reference model, the vehicle speed, front wheel steering angle and front wheel sideslip angle are orthogonally decomposed to obtain the longitudinal speed and lateral speed of the vehicle, and the front wheel sideslip angle is calculated according to the longitudinal speed, lateral speed, yaw rate and the distance from the center of mass of the vehicle to the front wheel; Calculate the additional yaw moment required to be provided by the SBW according to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle; Calculating the lateral force generated by the target front wheel turning angle according to the additional yaw moment required to be provided by the SBW and the distance from the vehicle center of mass to the front axle; The active front wheel steering angle is calculated according to the lateral force generated by the target front wheel steering angle, the front wheel sideslip angle of the vehicle and the front wheel sideslip stiffness of the vehicle.

8. The fault-tolerant control method of electronic mechanical braking according to claim 7, characterized in that: The calculation method of the active rear wheel turning angle includes: Calculating the lateral force generated by the front wheel according to the turning angle limit value under the physical constraint, the lateral speed of the vehicle, the front wheel cornering stiffness of the vehicle, the yaw rate of the vehicle, and the distance from the center of mass of the vehicle to the front wheel; Calculate the additional yaw moment required to be jointly provided by SBW and AKC according to the expected additional yaw moment of the vehicle and the actual yaw moment of the vehicle, and calculate the lateral force generated by the rear wheel according to the additional yaw moment required to be jointly provided by SBW and AKC, the lateral force generated by the front wheel, the distance from the center of mass of the vehicle to the front wheel, and the distance from the center of mass of the vehicle to the rear wheel; Calculating a rear wheel slip angle according to the longitudinal velocity, lateral velocity, yaw rate and the distance from the center of mass of the vehicle to the rear wheel; The active rear wheel steering angle is calculated according to the rear wheel slip angle, the lateral force generated by the rear wheel, and the rear wheel slip stiffness of the vehicle.

9. A fault-tolerant control system for an electromechanical brake, characterized in that: The system executes the fault-tolerant control method of the electronic mechanical brake as described in any one of claims 1-8.

10. A computer storage medium, characterized in that: A computer program executable by a processor is stored therein, and the computer program executes the fault-tolerant control method for an electronic mechanical brake according to any one of claims 1 to 8.

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