A method for brake-by-wire and regenerative braking cooperative energy optimization

Abstract

This invention provides a method for optimizing the energy recovery of brake-by-wire and regenerative braking. The method includes the following steps: S1, acquiring vehicle state parameters in real time, including steering wheel angle, yaw rate, and vehicle speed; S2, based on the vehicle state parameters and a preset vehicle dynamics model, calculating in real time the yaw moment safety boundary for maintaining stable vehicle operation under the current conditions; S3, acquiring the total required braking torque corresponding to the driver's braking intention; S4, dynamically distributing the total required braking torque between the vehicle's regenerative braking system and friction braking system. This invention maximizes brake energy recovery while ensuring vehicle dynamic stability.

Description

Technical Field

[0001] This invention relates to a coordinated control method for a brake-by-wire system and a regenerative braking system applied to electric vehicles, specifically a coordinated energy optimization method for brake-by-wire and regenerative braking, belonging to the field of electric vehicle control technology. Background Technology

[0002] With the rapid development of new energy vehicle technology, electric vehicles have become an important direction for the automotive industry. To improve driving range, maximizing the recovery of energy generated during braking is one of the core technologies of electric vehicle energy management systems. Regenerative braking systems convert the drive motor into a generator, transforming the vehicle's kinetic energy into electrical energy and storing it in the battery, thereby achieving energy recovery.

[0003] In an online braking system, the driver's brake pedal input is no longer directly applied to the brakes mechanically or hydraulically. Instead, it is interpreted as a braking request signal, which is then coordinated by the vehicle's central controller to work together with the regenerative braking system and the traditional friction braking system to meet the driver's braking needs.

[0004] However, existing cooperative braking strategies inherently suffer from a technical contradiction: most strategies prioritize maximizing energy recovery efficiency, meaning they preferentially use regenerative braking, supplementing it only with friction braking when regenerative braking force is insufficient or under specific conditions. While this strategy performs well during straight-line braking, it poses serious safety hazards in complex dynamic situations, such as when braking while steering. Specifically, regenerative braking force is typically applied to the drive wheels. During steering, applying excessive regenerative braking force to the drive wheels significantly alters the vehicle's original yaw moment balance, potentially weakening steering ability, reducing driving stability, and in severe cases, even inducing skidding or fishtailing, resulting in a poor driving experience and serious safety risks.

[0005] Therefore, how to design a novel cooperative braking strategy that can balance the relationship between energy recovery efficiency and vehicle driving stability under complex dynamic conditions, while taking into account both safety and efficiency, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] Based on the above background, the purpose of this invention is to provide a method for optimizing the energy of brake-by-wire and regenerative braking in coordination, which can maximize the recovery of braking energy while ensuring the dynamic stability of the vehicle.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for coordinated energy optimization of brake-by-wire and regenerative braking, comprising the following steps:

[0009] S1. Real-time acquisition of vehicle status parameters, including steering wheel angle, yaw rate and vehicle speed;

[0010] S2. Based on the vehicle state parameters and combined with the preset vehicle dynamics model, calculate in real time the yaw moment safety boundary for maintaining stable vehicle driving under the current working conditions.

[0011] S3. Obtain the total required braking torque corresponding to the driver's braking intention;

[0012] S4. Dynamically distribute the total required braking torque between the vehicle's regenerative braking system and friction braking system;

[0013] The regenerative braking system can independently control the regenerative braking torque applied to the left and right drive wheels of the vehicle. The dynamic allocation is optimized in real time to maximize the total regenerative braking torque while simultaneously satisfying a first constraint and a second constraint. The first constraint is that the total yaw moment generated on each wheel by the torque allocated to the regenerative braking system and the friction braking system is within the yaw moment safety boundary. The second constraint is that the sum of the braking torques generated on all wheels by the torque allocated to the regenerative braking system and the friction braking system is equal to the total required braking torque.

[0014] By quantifying the dynamic stability of a vehicle into a yaw moment safety boundary that can be calculated in real time, and using it as a strong constraint on the braking torque distribution optimization problem, the existing strategy of recovering first and then remedying is transformed into a new mode that seeks optimal recovery within the safety boundary, ensuring that the output of any braking strategy will not threaten the vehicle's driving stability.

[0015] Preferably, in step S2, the yaw moment safety boundary is calculated and determined based on the deviation between the expected and actual values ​​of the yaw rate and the estimated value of the tire slip angle.

[0016] The deviation between the expected and actual values ​​of the yaw rate directly reflects whether the vehicle's steering state meets the driver's expectations, while the tire slip angle is a key indicator for measuring whether the tire's lateral force is close to its saturation limit. Combining these two core parameters to calculate the safety boundary ensures that the safety boundary is neither too conservative, which would affect energy recovery, nor too aggressive, which would bring safety risks.

[0017] Preferably, the estimated tire slip angle is obtained in real time by using a Kalman filter algorithm to fuse the vehicle's lateral acceleration, yaw rate, and steering wheel angle data.

[0018] The Kalman filter algorithm can effectively filter out sensor noise and fuse information from multiple relevant physical quantities, thereby obtaining an accurate and fast-responding side slip angle estimate.

[0019] Preferably, in step S2, the vehicle dynamics model is a two-degree-of-freedom or higher-degree-of-freedom vehicle dynamics model that includes the nonlinear characteristics of tire lateral force.

[0020] When a vehicle approaches its instability limit, the lateral force of the tire exhibits a strong nonlinear relationship with the slip angle. That is, after the slip angle increases to a certain extent, the lateral force no longer increases and may even decrease. By using a vehicle dynamics model that can describe this nonlinear characteristic, it can be ensured that the calculated yaw moment safety boundary remains accurate and effective under extreme conditions.

[0021] Preferably, the nonlinear characteristics of the tire lateral force are described by the Magic Formula tire model or the Dugoff tire model.

[0022] Preferably, when the vehicle state parameters obtained in step S1 indicate that the vehicle is in a steering condition, during the dynamic allocation process in step S4, the regenerative braking torque on the inner steering drive wheel is reduced first, and the regenerative braking torque on the outer steering drive wheel and / or the friction braking torque of the front and rear axles are increased accordingly, so that the total yaw moment satisfies the first constraint condition.

[0023] When turning, the vertical load on the inner wheel decreases, and the adhesion it can provide also decreases. Applying excessive regenerative braking torque to this wheel can easily cause it to exceed its adhesion limit, resulting in unstable yaw moment. By using an inner-reduction and outer-compensation distribution strategy, the yaw moment can be adjusted and kept within a safe range without affecting the total braking force.

[0024] Preferably, the real-time optimization of the dynamic allocation is achieved by solving a quadratic programming model with inequality constraints.

[0025] Preferably, the objective function of the quadratic programming model is to minimize the sum of squares of the regenerative braking torque, the inequality constraints of the quadratic programming model are the first constraint conditions, and the equality constraints of the quadratic programming model are the second constraint conditions.

[0026] Preferably, the method further includes the following steps:

[0027] If the vehicle's anti-lock braking system or traction control system is determined to be activated, the regenerative braking torque of the activated side wheel will be set to zero or limited to a preset low safety threshold.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present invention provides a method for optimizing the energy of brake-by-wire and regenerative braking in coordination. By calculating the vehicle's yaw moment safety boundary in real time and using it as a strong constraint, the regenerative braking torque and friction braking torque are optimized and allocated in real time. This solves the inherent contradiction between energy recovery and driving stability under complex dynamic conditions such as steering and braking. It can maximize the recovery of braking energy while ensuring that the vehicle does not lose stability, and significantly improve the overall energy efficiency and active control safety of the vehicle in real driving scenarios. Attached Figure Description

[0030] 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 only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating the energy optimization method for coordinated braking and regenerative braking according to the present invention.

[0032] Figure 2 This is a schematic diagram of the yaw moment safety boundary in this invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0034] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0035] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0036] An embodiment of the present invention discloses a method for coordinated energy optimization of brake-by-wire and regenerative braking, see reference. Figure 1 The method includes the following steps:

[0037] S1. Real-time acquisition of vehicle status parameters, including steering wheel angle, yaw rate and vehicle speed;

[0038] S2. Based on vehicle state parameters and combined with a preset vehicle dynamics model, calculate in real time the yaw moment safety boundary for maintaining stable vehicle driving under the current working conditions.

[0039] S3. Obtain the total required braking torque corresponding to the driver's braking intention;

[0040] S4. Dynamically distribute the total required braking torque between the vehicle's regenerative braking system and friction braking system;

[0041] The regenerative braking system can independently control the regenerative braking torque applied to the left and right drive wheels of the vehicle. It dynamically allocates the torque to maximize the total regenerative braking torque while simultaneously satisfying the first and second constraints. The first constraint is that the total yaw moment generated on each wheel by the torques allocated to the regenerative braking system and the friction braking system is within the yaw moment safety boundary. The second constraint is that the sum of the braking torques generated on all wheels by the torques allocated to the regenerative braking system and the friction braking system is equal to the total required braking torque.

[0042] The following is a detailed explanation of each of the above steps.

[0043] Step S1: Obtain vehicle status parameters in real time.

[0044] During vehicle operation, the controller acquires a series of sensor signals reflecting vehicle dynamics in real time at extremely high frequency via the vehicle's CAN bus. In this embodiment, these essential vehicle state parameters include at least:

[0045] Steering wheel angle δ w The steering wheel angle sensor measures the steering angle and directly reflects the driver's steering intention.

[0046] Yaw rate γ, measured by a gyroscope sensor in an inertial measurement unit (IMU), reflects the actual angular velocity of the vehicle rotating about its vertical axis.

[0047] Vehicle speed v x The average value is calculated from the wheel speed sensor signal or obtained from signals such as GPS.

[0048] Furthermore, for more accurate calculations, the lateral acceleration a can also be obtained. y Wheel speed ω of each wheel i Parameters such as these.

[0049] Step S2: Calculate the yaw moment safety boundary.

[0050] The controller performs real-time calculations based on the vehicle state parameters obtained in step S1 and the vehicle dynamics model preset in the controller's memory to determine a safe range of additional yaw moment that can be applied to the vehicle.

[0051] First, the controller needs to calculate the desired yaw rate γ. des This represents the ideal stable steering response of the vehicle at the current vehicle speed and steering wheel angle. The calculation formula is:

[0052] Where L is the vehicle wheelbase and K is the understeer, which are constants related to the vehicle's own characteristics.

[0053] Then, the controller estimates the slip angle α of each tire. i Since the sideslip angle cannot be directly measured, this embodiment uses the Extended Kalman Filter (EKF) algorithm for estimation. The state variables of the EKF algorithm are set as the vehicle's sideslip angle β and yaw rate γ, while the observed variable is the lateral acceleration a directly measured by the sensor. y And the yaw rate γ. Through prediction and iterative updates using the EKF algorithm, a relatively accurate estimate of the vehicle's sideslip angle β is obtained. Then, based on the vehicle's geometry and kinematics, the sideslip angle α of each tire is calculated. i .

[0054] Next, the safety boundary is calculated using a vehicle dynamics model. This embodiment employs a two-degree-of-freedom vehicle model incorporating tire nonlinear characteristics, specifically the Magic Formula tire model, which accurately describes the tire lateral force F. y With respect to tire slip angle α and vertical load F z Nonlinear relationship between them:

[0055]

[0056] Among them, B, C, D, and E are tire characteristic parameters.

[0057] The controller uses the estimated tire slip angle α i Using tire models, determine whether the lateral force on each tire is close to its adhesion limit. Yaw moment safety boundary. The calculation takes into account both the deviation of the yaw rate and the tire's operating condition. The calculation formula is:

[0058]

[0059] Where μ is an estimated value of the road adhesion coefficient. When the yaw rate deviation increases, or any tire slip angle approaches the saturation zone, the safety boundary... Dynamically narrowing. Please refer to [link / reference]. Figure 2The diagram illustrates that the safety boundary is a dynamic range that varies with vehicle speed and steering angle, and the total yaw moment generated by the vehicle must fall within this safety area.

[0060] This embodiment also includes real-time estimation of the road adhesion coefficient μ. The controller calculates the wheel slip ratio by comparing the theoretical angular acceleration of the drive wheel (calculated based on motor torque and moment of inertia) with the actual angular acceleration measured by the wheel speed sensor. When the slip ratio increases abnormally, it indicates that the road surface is slippery. By establishing a mapping table between slip ratio and adhesion coefficient, μ can be estimated in real time and used to dynamically adjust the yaw moment safety boundary, making this method safe and effective on low-adhesion road surfaces such as those in rain or snow.

[0061] Step S3: Obtain the total required braking torque.

[0062] The controller reads signals from the brake pedal displacement or pressure sensor, combines them with the current vehicle speed, and consults a pre-set braking intent mapping table to translate the driver's physical actions into a specific total braking torque T. req_total .

[0063] Step S4: Constrained real-time optimization and dynamic allocation.

[0064] The problem the controller needs to solve is how to convert the total demand braking torque T req_total Regenerative braking torque T distributed to the four wheels reg_fl T reg_fr (Assuming it's a front-wheel drive vehicle) and friction braking torque T fric_fl T fric_fr T fric_rl T fric_rr Above. This embodiment constructs this problem as a quadratic programming model.

[0065] The optimization objective is to maximize the total regenerative braking torque (equivalent to minimizing the sum of squares of the regenerative braking torques). The calculation formula is:

[0066]

[0067] Where w1 and w2 are weighting coefficients.

[0068] The first constraint is:

[0069]

[0070] Among them, B f B r These are the front and rear track widths, ΔM. z,min ΔM z,max These are the lower and upper limits of the yaw moment safety boundary calculated in step S2. This formula calculates the total yaw moment generated by all braking forces.

[0071] The second constraint is:

[0072]

[0073] Other physical constraints are: the frictional braking torque of each wheel is non-negative and does not exceed its maximum capacity; the regenerative braking torque of each drive wheel is non-negative and does not exceed the maximum generating torque of the motor under the current operating conditions.

[0074] The controller inputs the above model into the solver, and can obtain a set of optimal torque distribution values ​​in each calculation cycle.

[0075] Taking the example of braking while making a left turn, the working principle of this invention will be explained.

[0076] When the vehicle turns left, according to steps S1 and S2, the system determines that the vehicle is in a steering condition and calculates the corresponding yaw moment safety boundary. At this time, if the regenerative braking force is still distributed evenly, the vertical load on the left front wheel (the inner drive wheel of the steering wheel) decreases due to load transfer, and the applied regenerative braking force can easily saturate its lateral force, thereby generating an unwanted yaw moment that interferes with steering and may trigger the safety boundary.

[0077] Finding the optimal solution under the first constraint results in prioritizing the reduction of the regenerative braking torque T of the left front wheel. reg_fl Even reducing it to zero. To satisfy the second constraint (total braking force remains unchanged), this lost braking force will be compensated by increasing the regenerative braking torque T of the right front wheel. reg_fr And / or correspondingly increase the friction braking torque of the four wheels to compensate. As a result of this distribution, the final total yaw moment is precisely controlled within the safety boundary, the vehicle smoothly corners as intended by the driver, and at the same time, the total energy recovery reaches its maximum value under this safety premise.

[0078] In addition, the method includes steps that integrate with the underlying security system.

[0079] For maximum safety, the controller continuously monitors the status flags of the ABS and TCS systems. Once the CAN message indicates that the ABS or TCS of any wheel is activated, the controller will immediately execute an interrupt procedure, forcibly applying the regenerative braking torque T to that wheel. reg_i Set it to zero, and completely hand over all the braking torque required by the wheel to the friction braking system.

[0080] This method calculates the vehicle's yaw moment safety boundary in real time and uses it as a strong constraint to optimize the allocation of regenerative braking torque and friction braking torque in real time. It solves the inherent contradiction between energy recovery and driving stability under complex dynamic conditions such as steering and braking. It can recover braking energy to the maximum extent while ensuring that the vehicle does not lose stability, and significantly improve the vehicle's overall energy efficiency and active control safety in real driving scenarios.

[0081] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for optimizing the energy of coordinated braking and regenerative braking, characterized in that: The method includes the following steps: S1. Real-time acquisition of vehicle status parameters, including steering wheel angle, yaw rate and vehicle speed; S2. Based on the vehicle state parameters and combined with the preset vehicle dynamics model, calculate in real time the yaw moment safety boundary for maintaining stable vehicle driving under the current working conditions. S3. Obtain the total required braking torque corresponding to the driver's braking intention; S4. Dynamically distribute the total required braking torque between the vehicle's regenerative braking system and friction braking system; The regenerative braking system can independently control the regenerative braking torque applied to the left and right drive wheels of the vehicle. The dynamic allocation is optimized in real time to maximize the total regenerative braking torque while simultaneously satisfying the first and second constraints. The first constraint is that the value of the total yaw torque generated on each wheel by the torque allocated to the regenerative braking system and the friction braking system is within the yaw torque safety boundary. The second constraint is that the sum of the braking torques generated on all wheels by the torque allocated to the regenerative braking system and the friction braking system is equal to the total required braking torque. When the vehicle state parameters obtained in step S1 indicate that the vehicle is in a steering condition, during the dynamic allocation process in step S4, the regenerative braking torque on the inner steering drive wheel is reduced, and the regenerative braking torque on the outer steering drive wheel and / or the friction braking torque of the front and rear axles are increased accordingly, so that the total yaw moment satisfies the first constraint condition.

2. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 1, characterized in that: In step S2, the yaw moment safety boundary is calculated and determined based on the deviation between the expected and actual values ​​of the yaw rate and the estimated value of the tire slip angle.

3. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 2, characterized in that: The estimated tire slip angle is obtained in real time by using a Kalman filter algorithm, which integrates data on the vehicle's lateral acceleration, yaw rate, and steering wheel angle.

4. The method for optimizing energy through coordinated braking and regenerative braking according to claim 1, characterized in that: In step S2, the vehicle dynamics model is a two-degree-of-freedom or higher-degree-of-freedom vehicle dynamics model that includes the nonlinear characteristics of tire lateral force.

5. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 4, characterized in that: The nonlinear characteristics of tire lateral force are described by the Magic Formula tire model or the Dugoff tire model.

6. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 1, characterized in that: The real-time optimization of the dynamic allocation is achieved by solving a quadratic programming model with inequality constraints.

7. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 6, characterized in that: The objective function of the quadratic programming model is to minimize the sum of squares of the regenerative braking torque. The inequality constraints of the quadratic programming model are the first constraint conditions, and the equality constraints of the quadratic programming model are the second constraint conditions.

8. The method for optimizing the energy of coordinated braking and regenerative braking according to claim 1, characterized in that: The method also includes the following steps: If the vehicle's anti-lock braking system or traction control system is determined to be activated, the regenerative braking torque of the activated side wheel will be set to zero or limited to a preset low safety threshold.

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