A fault-tolerant control method and system for electromechanical braking

Abstract

The application discloses a fault-tolerant control method and system of an electromechanical brake, and the method comprises the following steps: calculating a desired additional yaw moment and a desired braking force of a vehicle; obtaining the failure degree of each wheel-side EMB actuator, and judging whether it is necessary to enter a fault-tolerant control mode; if it is not necessary to enter the fault-tolerant control mode, the braking force of the EMB is distributed by taking the minimum value of a self-adaptive distribution function of the vehicle as a target; otherwise, the fault-tolerant control mode is entered, and it is judged in turn whether each control mode can meet the desired additional yaw moment and the desired braking force of the vehicle; when any control mode can meet the requirements, the judgment is ended, and the braking force of the EMB is distributed to each wheel by a corresponding distribution mode under the control mode; when all control modes cannot meet the requirements, the vehicle is braked by using the actual maximum braking force of the vehicle on the premise of meeting the desired additional yaw moment of the vehicle. The application can improve the stability of the electromechanical brake and ensure the driving safety of the vehicle.

Description

Technical Field

[0001] This invention relates to the field of electromechanical braking technology, and in particular to a fault-tolerant control method and system for electromechanical braking. Background Technology

[0002] As the automotive industry transforms towards electrification, intelligentization, and digitalization, the importance of brake-by-wire technology is becoming increasingly prominent. Due to advancements in autonomous driving technology and the increasing proportion of new energy vehicles, brake-by-wire technology will become a key technology in the automotive chassis actuator layer and is expected to experience rapid growth in the coming years.

[0003] As an advanced braking technology, the EMB system has advantages such as precise braking response, high integration, integration with 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 capability, and power redundancy.

[0004] The EMB system uses a large number of electronic circuits, which may be susceptible to electromagnetic interference. If some electronic control units in the system malfunction, it will directly lead to abnormal or failed braking systems, or even cause unstable conditions such as vehicle skidding or veering, affecting the stability and safety of the braking system. Therefore, fault-tolerant control is needed to ensure that the vehicle can brake safely even when some systems malfunction, thus ensuring the vehicle's stability.

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

[0006] Some methods rely on fault detection and isolation (FDI) technology for active fault-tolerant control. However, FDI-based control methods are overly dependent on the diagnostic results of fault diagnosis agencies and cannot control changes in gain response parameters through real-time estimation information of unknown parameters. Summary of the Invention

[0007] The main objective of this invention is to provide a fault-tolerant control method and system for electromechanical braking, ensuring the stability of the braking system and the safe braking of the vehicle.

[0008] The technical solution adopted in this invention is: a fault-tolerant control method for electromechanical braking, comprising:

[0009] Obtain the desired parameters and state parameters of the vehicle, and calculate the desired additional yaw moment and desired braking force of the vehicle by combining the two-degree-of-freedom reference model of the vehicle.

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

[0011] If there is no need to enter the fault-tolerant control mode, the EMB braking force is allocated with the minimum value obtained by 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 non-failed EMB actuator, EMB+SBW coordinated control, and EMB+SBW+AKC coordinated control, and it is determined whether each braking control mode can meet the requirements of providing the vehicle's expected additional yaw moment and expected braking force.

[0012] When any of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the judgment ends, and under the braking control method, the EMB braking force is distributed to each wheel through the corresponding distribution method; when none of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the vehicle is braked with the target of maximizing the vehicle's actual braking force, provided that the vehicle's desired additional yaw moment is satisfied.

[0013] According to the above technical solution, the desired parameters of the vehicle include the desired front wheel steering angle, the desired rear wheel steering angle, the desired longitudinal deceleration, the ideal center of gravity sideslip angle, and the desired slip ratio of the tires.

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

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

[0016] Design a yaw moment sliding mode controller with the vehicle's center of gravity sideslip angle as the control variable. The controller uses the ideal center of gravity sideslip angle as the target and the vehicle's two-degree-of-freedom reference model as the expected value, and defines a sliding surface.

[0017] Differentiate the sliding surface to obtain the first formula;

[0018] Using the exponential reaching rate of the saturation function as the sliding control rate of the sliding surface, we obtain the second formula:

[0019] The expected additional yaw moment of the vehicle is calculated by combining the first and second equations.

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

[0021] According to the above technical solution, the method for determining whether to enter the fault-tolerant control mode includes: comparing the 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, then enter the fault-tolerant control mode; otherwise, do not enter the fault-tolerant control mode.

[0022] According to the above technical solution, the adaptive allocation function of the vehicle ,in Let be the vehicle's dynamic response function. Let be the tire slip ratio function of the vehicle, where a and b are preset weighting coefficients and a+b=1;

[0023] The vehicle's dynamic response function ,in, , , This is the actual steering angle of the front wheels. This is the actual steering angle of the rear wheels. The distance between the front and rear wheels. This is the distance from the vehicle's center of gravity to the front axle. For the desired braking force and the desired additional yaw moment, The weighting coefficients related to vehicle braking force. Add a weighting factor related to the yaw moment to the vehicle;

[0024] The vehicle's tire slip ratio function ;in, , ,in, Braking force distributed to the left front wheel of the vehicle. Braking force distributed to the right front wheel of the vehicle. The braking force distributed to the left rear wheel of the vehicle, Braking force distributed to the right rear wheel of the vehicle. The slip ratio of the vehicle's left front wheel. The slip ratio of the vehicle's right front wheel. The slip ratio of the vehicle's left rear wheel. The slip ratio of the vehicle's right rear wheel. This represents the expected slip ratio of the vehicle's tires.

[0025] According to the above technical solution, the allocation method for single control of the non-failed EMB actuator includes: allocating EMB braking force to each wheel with the goal of obtaining the minimum value of the vehicle's adaptive allocation function;

[0026] The EMB+SBW coordinated control allocation method includes: calculating the active front wheel steering angle based on the desired additional yaw moment, and adding the active front wheel steering angle to the current vehicle's front wheel steering angle; based on the adjusted vehicle's front wheel steering angle, and with the vehicle's adaptive allocation function achieving the minimum value as the objective, allocating EMB braking force to each wheel.

[0027] The EMB+SBW+AKC coordinated control allocation method 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 based on the vehicle's center of gravity sideslip angle and yaw rate; and adding the active rear wheel steering angle to the current rear wheel steering angle of the vehicle. Based on the front wheel steering angle adjusted to the steering angle limit value and the adjusted rear wheel steering angle of the vehicle, the EMB braking force is allocated to each wheel with the goal of obtaining the minimum value of the vehicle's adaptive allocation function.

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

[0029] In the two-degree-of-freedom reference model of the vehicle, the vehicle's velocity, front wheel steering angle, and front wheel sideslip angle are orthogonally decomposed to obtain the vehicle's longitudinal velocity and lateral velocity. Based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of mass to the front wheel, the front wheel sideslip angle is calculated.

[0030] Calculate the additional yaw moment required by the SBW based on the vehicle's expected additional yaw moment and the vehicle's actual yaw moment.

[0031] 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's center of gravity to the front axle.

[0032] The active front wheel steering angle is calculated based on the lateral force generated by the target front wheel steering angle, the vehicle's front wheel slip angle, and the vehicle's front wheel slip stiffness.

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

[0034] The lateral force generated by the front wheel is calculated based on the turning angle limit value under the physical constraints, the lateral velocity of the vehicle, the lateral stiffness of the front wheel of the vehicle, the yaw rate of the vehicle, and the distance from the center of gravity of the vehicle to the front wheel.

[0035] Based on the vehicle's expected additional yaw moment and the vehicle's actual yaw moment, calculate the additional yaw moment that SBW and AKC need to provide together. Based on the additional yaw moment that SBW and AKC need to provide together, the lateral force generated by the front wheel, the distance from the vehicle's center of gravity to the front wheel, and the distance from the vehicle's center of gravity to the rear wheel, calculate the lateral force generated by the rear wheel.

[0036] Calculate the rear wheel slip angle based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of gravity to the rear wheel;

[0037] 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.

[0038] Another aspect of the present invention provides a fault-tolerant control system for electromechanical braking, which executes the above-described fault-tolerant control method for electromechanical braking.

[0039] Another aspect of the present invention provides a computer storage medium storing a computer program executable by a processor, the computer program performing the above-described fault-tolerant control method for electromechanical braking.

[0040] The beneficial effects of this invention are as follows: This invention provides a fault-tolerant control method and system for electromechanical braking. In the event of partial or complete failure of the EMB system actuator, it determines whether the single control of the undisturbed EMB actuator, the EMB+SBW coordinated control involving active front wheel steering angle, and the EMB+SBW+AKC coordinated control involving active front and rear wheel steering angle can meet the desired dynamic response of the vehicle. Combining the control potential of each wheel, it adaptively distributes braking force to each wheel to ensure the vehicle's driving safety and stability.

[0041] Compared with existing technologies:

[0042] This invention collects vehicle parameters in real time to participate in the fault-tolerant control of the braking system, which can better control the changes in the gain response coefficient;

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

[0044] In actual vehicle operation, this invention couples the dynamic responses of multiple subsystems in the braking system to each other, which can better obtain the influence of each subsystem on the overall vehicle braking.

[0045] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1This is a flowchart of the fault-tolerant control method for electromechanical braking according to an embodiment of the present invention;

[0048] Figure 2 This is a schematic diagram of the working principle of the fault-tolerant control system of electromechanical braking according to an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the fault-tolerant control device for electromechanical braking according to an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the orthogonal decomposition of the vehicle's speed, front wheel steering angle, and front wheel sideslip angle in a two-degree-of-freedom vehicle model according to an embodiment of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0052] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0053] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

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

[0055] IMU: Inertial Measurement Unit.

[0056] EMB: Electronic Mechanical Brake System.

[0057] CDCU: Chassis Domain Control Unit, used to identify the driver's braking intentions and send them to the brake control unit for execution.

[0058] BCU: Brake Control Unit, which receives braking requests from the chassis domain controller and controls the wheel-side caliper motors to perform the braking.

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

[0060] Fault-tolerant control: a technology that ensures that a control system can still 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, is a classification system defined in ISO 26262 that measures the risk level of specific system components in a vehicle system. This standard is a functional safety standard used in the automotive industry, based on risk assessment, to ensure the safety of automotive equipment and systems throughout their entire lifecycle.

[0062] SBW: Steer-by-wire.

[0063] AKC: Active Kinematics control.

[0064] Example 1

[0065] This embodiment provides a fault-tolerant control method for electromechanical braking. In the event of partial or complete failure of the 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, it includes:

[0066] S1. Obtain the desired parameters and state parameters of the vehicle, and combine the desired parameters and state parameters of the vehicle with the two-degree-of-freedom reference model of the vehicle to calculate the desired additional yaw moment and desired braking force of the vehicle.

[0067] Specifically, the vehicle's desired parameters include the vehicle's desired front wheel steering angle, desired rear wheel steering angle, desired longitudinal deceleration, ideal center of gravity sideslip angle, and desired tire slip ratio.

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

[0069] Specifically, since the sideslip angle of a vehicle's center of gravity has a significant impact on vehicle stability, it is necessary to strictly control the size of the sideslip angle during vehicle operation to prevent vehicle instability. Therefore, a yaw moment sliding mode controller is designed with the vehicle's sideslip angle as the control variable. The controller uses the ideal sideslip angle as the target and the two-degree-of-freedom reference model of the vehicle as the expected value, and defines a sliding surface.

[0070] The two-degree-of-freedom reference model for the vehicle is as follows:

[0071]

[0072] in, β The angle of sideslip is the center of mass, γ is the yaw rate, and k is the angular velocity. f For the front wheel lateral stiffness, k r For the rear wheel lateral stiffness, l f l is the distance from the vehicle's center of gravity to the front axle. r δ is the distance from the vehicle's center of gravity to the rear axle. f For the front wheel steering angle, δ r For the rear wheel steering angle, I z Let m be the yaw moment of inertia, and V be the total mass of the vehicle. x For the longitudinal speed of the vehicle, To add a yaw moment as desired.

[0073] The sliding surface is:

[0074]

[0075] in, β d The ideal centroid sideslip angle.

[0076] Differentiating the sliding surface yields the first formula:

[0077]

[0078] Using the exponential reaching rate of the saturation function as the sliding control rate of the sliding surface, we obtain the second formula:

[0079]

[0080] Where, ε β k βThese are preset centroid sideslip angle control parameters, and all are greater than 0.

[0081] By combining the first and second equations, the expected additional yaw moment of the vehicle can be calculated:

[0082]

[0083] The method for calculating the desired braking force of the vehicle includes: .

[0084] That is, the desired longitudinal force of the vehicle is equal to the vehicle's mass multiplied by its desired longitudinal deceleration, where, For the overall vehicle quality, The desired longitudinal deceleration of the vehicle.

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

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

[0087] S3. If it is not necessary to enter the fault-tolerant control mode, the EMB braking force is allocated with the minimum value obtained by 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 non-failed EMB actuator, EMB+SBW coordinated control, and EMB+SBW+AKC coordinated control, and it is determined whether each braking control mode can meet the requirements of providing the vehicle's expected additional yaw moment and expected braking force.

[0088] Adaptive braking force distribution primarily achieves two functions: ensuring vehicle dynamics and stability; and increasing the vehicle's grip margin, keeping the forces of each tire away from their grip limits. Based on these objectives, an adaptive distribution function for the vehicle is designed. ,in Let be the vehicle's dynamic response function. Let be the tire slip ratio function of the vehicle, where a and b are preset weighting coefficients and a+b=1.

[0089] The vehicle's dynamic response function Where B is a constant coefficient matrix related to tire steering angle and vehicle parameters. H is J 21 The weight coefficient matrix, , This is the actual steering angle of the front wheels. This is the actual steering angle of the rear wheels. The distance between the front and rear wheels. This is the distance from the vehicle's center of gravity to the front axle. For the desired braking force and the desired additional yaw moment, The weighting coefficients related to vehicle braking force. A weighting coefficient related to the yaw moment is added to the vehicle. The magnitude of the weighting coefficient can be adjusted according to the specific driving conditions. For example, when the vehicle is accelerating urgently, the longitudinal speed requirement is high, so h1 is increased; when the vehicle is unstable, the requirement for yaw moment control is even higher, so h2 should be increased.

[0090] The vehicle's tire slip ratio function ;in, , ,in, Braking force distributed to the left front wheel of the vehicle. Braking force distributed to the right front wheel of the vehicle. The braking force distributed to the left rear wheel of the vehicle, Braking force distributed to the right rear wheel of the vehicle. The slip ratio of the vehicle's left front wheel. The slip ratio of the vehicle's right front wheel. The slip ratio of the vehicle's left rear wheel. The slip ratio of the vehicle's right rear wheel. This represents the expected slip ratio of the vehicle's tires.

[0091] S4. When any of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the judgment ends, and under the braking control method, the EMB braking force is allocated to each wheel through the corresponding allocation method; when none of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the vehicle is braked with the vehicle's actual braking force as the target, provided that the vehicle's desired additional yaw moment is satisfied.

[0092] Furthermore, the allocation method for single control of the non-failed EMB actuator includes: allocating EMB braking force to each wheel with the goal of minimizing the adaptive allocation function of the vehicle.

[0093] The EMB+SBW coordinated control allocation method includes: calculating the active front wheel steering angle based on the desired additional yaw moment, and adding the active front wheel steering angle to the current vehicle's front wheel steering angle. Based on the adjusted vehicle's front wheel steering angle, and with the vehicle's adaptive allocation function aiming to achieve the minimum value, the EMB braking force is allocated to each wheel.

[0094] The EMB+SBW+AKC coordinated control allocation method includes: setting the front wheel steering angle of the vehicle to the physical constraint's steering angle limit value; calculating the active rear wheel steering angle based on the vehicle's center of gravity sideslip angle and yaw rate; and adding the active rear wheel steering angle to the current rear wheel steering angle of the vehicle. Based on the front wheel steering angle adjusted to the steering angle limit value and the adjusted rear wheel steering angle, and aiming to achieve the minimum value of the vehicle's adaptive allocation function, the braking force of EMB is allocated to each wheel.

[0095] The calculation method for the active front wheel steering angle includes:

[0096] In the aforementioned two-degree-of-freedom reference model of the vehicle, the vehicle's velocity, front wheel steering angle, and front wheel slip angle are orthogonally decomposed, as follows: Figure 4 As shown, the longitudinal velocity of the vehicle is obtained. With lateral velocity ,and The front wheel slip angle is calculated based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of gravity to the front wheel. The calculation formula is: .in, The front wheel slip angle, This is the distance from the vehicle's center of gravity to the front wheels.

[0097] The additional yaw moment required by the SBW is calculated based on the vehicle's desired additional yaw moment and the vehicle's actual yaw moment. The calculation formula is as follows: . Additional yaw moment required for SBW To add the desired yaw moment to the vehicle, This represents the actual yaw moment of the vehicle.

[0098] 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's center of gravity to the front axle. In the current control mode, active rear wheel steering does not contribute, therefore the lateral force generated by the rear wheel steering angle... The formula for calculating the lateral force generated by the front wheel steering angle is: .in, To achieve the desired front wheel steering angle, This refers to the front wheel lateral stiffness.

[0099] The active front wheel steering angle is calculated based on the lateral force generated by the target front wheel steering angle, the vehicle's front wheel slip angle, and the vehicle's front wheel slip stiffness. The calculation formula is: .

[0100] The EMB+SBW+AKC coordinated control allocation method 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 based on the center of gravity sideslip angle and yaw rate; 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 and the adjusted rear wheel steering angle, and with the minimum value of the vehicle's adaptive allocation function as the objective, the braking force of the EMB health actuator is allocated to each wheel.

[0101] The calculation method for the active rear wheel steering angle includes:

[0102] The lateral force generated by the front wheels is calculated based on the steering angle limit under the aforementioned physical constraints, the vehicle's lateral velocity, the front wheel lateral stiffness, the vehicle's yaw rate, and the distance from the vehicle's center of gravity to the front wheels. The calculation method includes: .in, This represents the rotation limit value under physical constraints.

[0103] Calculate the additional yaw moment required jointly by SBW and AKC based on the vehicle's expected additional yaw moment and actual yaw moment. The calculation formula is: . The additional yaw moment required by both SBW and AKC To add the desired yaw moment to the vehicle, This represents the actual yaw moment of the vehicle.

[0104] The lateral force generated by the rear wheels is calculated based on the additional yaw moment required by the SBW and AKC, the lateral force generated by the front wheels, the distance from the vehicle's center of gravity to the front wheels, and the distance from the vehicle's center of gravity to the rear wheels. The calculation formula is as follows: .in, The lateral force generated by the rear wheels, This is the distance from the vehicle's center of gravity to the rear wheel.

[0105] The rear wheel slip angle is calculated based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of gravity to the rear wheel. The calculation formula is: .

[0106] 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: .

[0107] This embodiment also provides a computer storage medium storing a computer program that can be executed by a processor, the computer program executing the above-described fault-tolerant control method for electromechanical braking.

[0108] Example 2

[0109] This embodiment provides a fault-tolerant control system for electromechanical braking. The system executes the fault-tolerant control method for electromechanical braking described in Embodiment 1. The system includes: a parameter acquisition and analysis module, a mode selection module, a braking force distribution module, and a braking execution module.

[0110] The parameter acquisition and analysis module includes an upper-level controller, which is used to acquire the vehicle's desired parameters and state parameters, and calculate the vehicle's desired additional yaw moment and desired braking force in conjunction with the vehicle's two-degree-of-freedom reference model, and transmit the vehicle's desired additional yaw moment and desired braking force to the braking force distribution module.

[0111] Furthermore, the calculation methods for the desired additional yaw moment and desired braking force of the vehicle have been described in Example 1, and will not be repeated here.

[0112] The mode selection module determines whether to enter the fault-tolerant control mode based on the failure level of each wheel-side EMB actuator. If entering the fault-tolerant control mode is not required, a distribution command is issued to the brake force distribution module. If entering the fault-tolerant control mode is required, the mode selection module sequentially determines whether single control of the undisturbed EMB actuator, EMB+SBW coordinated control, and EMB+SBW+AKC coordinated control can meet the desired additional yaw moment and desired braking force of the vehicle. When any of the control methods can meet the desired additional yaw moment and desired braking force of the vehicle, the determination ends, and a distribution command corresponding to the different control methods is issued to the brake force distribution module. When all control methods fail to meet the desired additional yaw moment and desired braking force of the vehicle, the emergency braking mode is entered, and the vehicle's actual maximum braking force is applied to brake the vehicle, provided that the desired additional yaw moment of the vehicle is met.

[0113] The method for determining whether each braking control mode can meet the requirements of providing the vehicle with the desired additional yaw moment and desired braking force has been described in Example 1 and will not be repeated here.

[0114] The braking force distribution module is used to distribute the EMB braking force to each wheel according to the distribution command 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.

[0115] Furthermore, the allocation method for the different control modes has been described in Embodiment 1, and will not be repeated here.

[0116] The braking execution module is used to brake the vehicle via wheel-side EMB actuators according to the braking force distributed to each wheel.

[0117] This embodiment also provides a fault-tolerant control device for electromechanical braking. This device executes the fault-tolerant control method for electromechanical braking described in Embodiment 1, and its structure is as follows: Figure 3 As shown, it includes:

[0118] Chassis Domain Controller (CDCU), Wheel-side Brake Control Unit (BCU), Wheel-end EMB Assembly, Front Wheel Steering-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 Wheel Speed ​​Sensors.

[0119] The CDCU includes a main control unit (MECU) and a redundant control unit (SECU), both of which have the same function and model and serve as backups for each other.

[0120] The wheel-end EMB assembly includes a motor, a transmission mechanism, a motion conversion mechanism, and sensors.

[0121] The principle of the fault-tolerant control method for electromechanical braking described in Example 1 is as follows: Figure 2 As shown. Where, δ fd To determine the desired front wheel steering angle, δ f δ is the actual front wheel steering angle. rd For the desired rear wheel steering angle, δ r a is the actual rear wheel steering angle. xd For the desired longitudinal deceleration, a x The vehicle's current longitudinal deceleration, To add the desired yaw moment, F xic For the desired braking force of each wheel, F xi The actual braking force is allocated to each wheel.

[0122] In summary, this invention provides a fault-tolerant control method and system for electromechanical braking. In the event of partial or complete failure of the actuator in the EMB system, it determines whether each control method can meet the desired dynamic response of the vehicle, and adaptively distributes braking force to each wheel based on the control potential of each wheel, thereby ensuring the vehicle's driving safety and stability.

[0123] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0124] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0125] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A fault-tolerant control method for electromechanical braking, characterized in that, include: Obtain the desired parameters and state parameters of the vehicle, and calculate the desired additional yaw moment and desired braking force of the vehicle by combining the two-degree-of-freedom reference model of the vehicle. Obtain the failure level of the EMB actuators on each wheel side and determine whether it is necessary to enter the fault-tolerant control mode; If there is no need to enter the fault-tolerant control mode, the EMB braking force is allocated with the minimum value obtained by 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 non-failed EMB actuator, EMB+SBW coordinated control, and EMB+SBW+AKC coordinated control, and it is determined whether each braking control mode can meet the requirements of providing the vehicle's expected additional yaw moment and expected braking force. The vehicle's adaptive allocation function ,in Let be the vehicle's dynamic response function. Let be the tire slip ratio function of the vehicle, where a and b are preset weighting coefficients and a+b=1; The vehicle's dynamic response function ,in, , , For the front wheel steering angle, For the rear wheel steering angle, The distance between the front and rear wheels. This is the distance from the vehicle's center of gravity to the front axle. For the desired braking force and the desired additional yaw moment, The weighting coefficients related to vehicle braking force. Add a weighting factor related to the yaw moment to the vehicle; The vehicle's tire slip ratio function ;in, , ,in, Braking force distributed to the left front wheel of the vehicle. Braking force distributed to the right front wheel of the vehicle. The braking force distributed to the left rear wheel of the vehicle, Braking force distributed to the right rear wheel of the vehicle. The slip ratio of the vehicle's left front wheel. The slip ratio of the vehicle's right front wheel. The slip ratio of the vehicle's left rear wheel. The slip ratio of the vehicle's right rear wheel. The desired slippage of the vehicle's tires; When any of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the judgment ends, and under the braking control method, the EMB braking force is distributed to each wheel through the corresponding distribution method; when none of the braking control methods can satisfy the requirement of providing the vehicle's desired additional yaw moment and desired braking force, the vehicle is braked with the target of maximizing the vehicle's actual braking force, provided that the vehicle's desired additional yaw moment is satisfied.

2. The fault-tolerant control method for electromechanical braking according to claim 1, characterized in that, The desired parameters of the vehicle include the desired front wheel steering angle, desired rear wheel steering angle, desired longitudinal deceleration, ideal center of gravity sideslip angle, and desired tire slip ratio. The vehicle's state parameters include the vehicle's center of gravity sideslip angle, vehicle's yaw rate, vehicle's front wheel sideslip angle, vehicle's front wheel sideslip stiffness, vehicle's rear wheel sideslip stiffness, distance from the vehicle's center of gravity to the front axle, distance from the vehicle's center of gravity to the rear axle, vehicle's front wheel steering angle, vehicle's rear wheel steering angle, vehicle mass, and vehicle speed.

3. The fault-tolerant control method for electromechanical 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 gravity sideslip angle as the control variable, wherein the controller takes the ideal center of gravity sideslip angle as the target and the vehicle's two-degree-of-freedom reference model as the expected value, and defining a sliding surface; differentiating the sliding surface to obtain a first formula; taking the exponential approach rate of the saturation function as the sliding mode control rate of the sliding surface to obtain a second formula; and combining the first and second formulas to obtain the expected additional yaw moment of the vehicle. The method for calculating the desired braking force of the vehicle includes: the desired braking force of the vehicle is equal to the total mass of the vehicle multiplied by the desired longitudinal deceleration of the vehicle.

4. The fault-tolerant control method for electromechanical braking according to claim 1, characterized in that, The method for determining whether to enter the fault-tolerant control mode includes: comparing the failure level of each EMB actuator with the preset maximum failure level; if the failure level of any EMB actuator is greater than the preset maximum failure level, then enter the fault-tolerant control mode; otherwise, do not enter the fault-tolerant control mode.

5. The fault-tolerant control method for electromechanical braking according to claim 1, characterized in that, The allocation method for single control of the non-failed EMB actuator includes: allocating EMB braking force to each wheel with the goal of obtaining the minimum value of the vehicle's adaptive allocation function; The EMB+SBW coordinated control allocation method includes: calculating the active front wheel steering angle based on the desired additional yaw moment, and adding the active front wheel steering angle to the current vehicle's front wheel steering angle; based on the adjusted vehicle's front wheel steering angle, and with the vehicle's adaptive allocation function achieving the minimum value as the objective, allocating EMB braking force to each wheel. The EMB+SBW+AKC coordinated control allocation method 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 based on the vehicle's center of gravity sideslip angle and yaw rate; and adding the active rear wheel steering angle to the current rear wheel steering angle of the vehicle. Based on the front wheel steering angle adjusted to the steering angle limit value and the adjusted rear wheel steering angle of the vehicle, the EMB braking force is allocated to each wheel with the goal of obtaining the minimum value of the vehicle's adaptive allocation function.

6. The fault-tolerant control method for electromechanical braking according to claim 5, characterized in that, The method for calculating the active front wheel steering angle includes: In the two-degree-of-freedom reference model of the vehicle, the vehicle's velocity, front wheel steering angle, and front wheel sideslip angle are orthogonally decomposed to obtain the vehicle's longitudinal velocity and lateral velocity. Based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of mass to the front wheel, the front wheel sideslip angle is calculated. Calculate the additional yaw moment required by the SBW based on the vehicle's expected additional yaw moment and the vehicle's actual yaw moment. 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's center of gravity to the front axle. The active front wheel steering angle is calculated based on the lateral force generated by the target front wheel steering angle, the vehicle's front wheel slip angle, and the vehicle's front wheel slip stiffness.

7. The fault-tolerant control method for electromechanical braking according to claim 6, characterized in that, The calculation method for the active rear wheel steering angle includes: The lateral force generated by the front wheel is calculated based on the turning angle limit value under the physical constraints, the lateral velocity of the vehicle, the lateral stiffness of the front wheel of the vehicle, the yaw rate of the vehicle, and the distance from the center of gravity of the vehicle to the front wheel. Based on the vehicle's expected additional yaw moment and the vehicle's actual yaw moment, calculate the additional yaw moment that SBW and AKC need to provide together. Based on the additional yaw moment that SBW and AKC need to provide together, the lateral force generated by the front wheel, the distance from the vehicle's center of gravity to the front wheel, and the distance from the vehicle's center of gravity to the rear wheel, calculate the lateral force generated by the rear wheel. Calculate the rear wheel slip angle based on the vehicle's longitudinal velocity, lateral velocity, yaw rate, and the distance from the vehicle's center of gravity to the rear wheel; 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.

8. A fault-tolerant control system for electromechanical braking, characterized in that, The system performs the fault-tolerant control method of electromechanical braking as described in any one of claims 1-7.

9. A computer storage medium, characterized in that, It contains a computer program that can be executed by a processor, which performs the fault-tolerant control method of electromechanical braking according to any one of claims 1-7.

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