A regenerative braking method and electromechanical system suitable for all working conditions

Abstract

The present invention provides a regenerative braking method and electromechanical system applicable to all operating conditions. The brake control unit receives brake pedal opening, vehicle speed, and wheel speed signals, calculates braking intensity using a fuzzy controller, obtains motor torque and hydraulic torque using a braking torque optimization distribution module, and determines whether a downshift is necessary using a downshift strategy module. The motor controller receives control instructions from the brake control unit and controls the motor to output the corresponding torque. The hydraulic controller receives control instructions from the brake control unit and controls the hydraulic brake system to output the corresponding hydraulic torque. The DHT controller receives control instructions from the brake control unit and controls the clutch and synchronizer to implement mode / gear switching. The downshift strategy module includes a downshift switching function consisting of the inverse of the objective function increment and a periodic penalty switching index to determine the downshift switching conditions. This invention effectively prevents frequent mode / gear switching and upshifting.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile braking energy recovery, and in particular to a regenerative braking method and an electromechanical system applicable to all working conditions. Background Art

[0002] In recent years, the greenhouse effect has intensified. my country has set the strategic goals of peaking CO2 emissions by 2030 and achieving carbon neutrality by 2060. Automobiles are a major emitter of greenhouse gases, accounting for over 80% of my country's transportation sector and approximately 7.5% of total societal emissions. The high number of traditional fuel vehicles and their extensive use of fossil fuels contribute to these high levels of carbon emissions. To achieve this goal, accelerating the research and development and sales of new energy vehicles is a key measure for emission reduction. my country is currently experiencing rapid development of new energy vehicles. Data released by the Ministry of Industry and Information Technology indicates that in 2021, production and sales of new energy vehicles reached 3.545 million and 3.521 million, respectively, a 1.6-fold year-on-year increase, with a market penetration rate of 13.4%.

[0003] Among new energy vehicles, hybrid vehicles are an important one. Before fully moving towards pure electric vehicles, hybrid vehicles are very important products. Hybrid vehicles have the advantages of low fuel consumption and low pollution emissions. At the same time, because they have dual kinetic energy, they give full play to the advantages of the engine and motor, and choose to use different power sources in different situations, which further improves the performance of the car and is favored by consumers. The "New Energy Vehicle Industry Development Plan (2021-2035)" issued by my country clearly proposes to make pure electric vehicles, plug-in hybrid vehicles, and fuel cell vehicles as the "three vertical" research and development layout, and the "Energy Saving and New Energy Vehicle Technology Route" Figure 2 .0》also identifies the “low-carbonization” of electromechanical coupling systems as a development focus for new energy vehicles.

[0004] Most ordinary family passenger cars are driven on urban roads, where driving is characterized by low speeds and frequent braking. Under typical operating conditions (FTP7, UDDS, and Japan 1015), braking energy accounts for 43.2%, 49.8%, and 51.2%, respectively. If this energy is not recovered during the braking process, it will be dissipated as heat, resulting in energy waste. For new energy vehicles, efficient, stable, and reliable regenerative braking systems and their control strategies are important ways to reduce vehicle energy loss during braking and increase pure electric driving range. During regenerative braking in plug-in hybrid vehicles, braking energy flows through the DHT and ultimately generates regenerative energy through the motor. How to fully improve the regenerative braking energy recovery rate of hybrid vehicles while ensuring safety and reliability is one of the key technical issues that urgently needs to be addressed. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a regenerative braking method and electromechanical system suitable for all operating conditions. Taking into full consideration vehicles with multi-mode / gear structures, a downshift strategy is proposed to fully utilize the structural characteristics to recover more braking energy while taking into account braking stability, thereby increasing the mileage of new energy vehicles. At the same time, a downshift switching function Φ is proposed, including the inverse of the objective function increment J1 and the periodic penalty switching index J2, which effectively avoids frequent mode / gear switching and even upshifting.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A regenerative braking method applicable to all working conditions comprises the following steps:

[0008] S1: If the vehicle speed v = 0 km / h, execute S2; if v ≤ 20 km / h, v > 20 km / h and the SOC value ≥ 85%, execute S3; otherwise, execute S4;

[0009] S2, exit without braking;

[0010] S3, the braking mode is hydraulic braking, and the braking force is distributed according to the I curve;

[0011] S4: If the brake pedal opening angle P is less than or equal to 0, execute S2; otherwise, execute S5.

[0012] S5, identifying the driver’s braking intention through the braking intensity z output by the fuzzy controller;

[0013] S6: When the current mode / gear position of the hybrid power transmission DHT is 1, execute S7; otherwise, execute S10.

[0014] S7, keep the current mode / gear mode unchanged;

[0015] S8, according to the current vehicle speed signal v and braking intensity z, the weight coefficients λ1, λ2 and λ3 are obtained according to the offline table lookup module, and then the braking torque optimization coefficients β and α are obtained based on the optimization objective function. mh , α m12 and α f ;

[0016] S9, a braking torque distribution module calculates the braking torque of motor M1, the braking torque of motor M2, the left front wheel hydraulic braking torque, the right front wheel hydraulic braking torque, the left rear wheel hydraulic braking torque, and the right rear wheel hydraulic braking torque based on the braking force distribution coefficient; and controls the motors and the hydraulic braking system to operate according to the braking torque;

[0017] S10, calculating the downshift switching function Φ:

[0018]

[0019] Where: J1 is the inverse of the optimization objective function increment, J2 is the periodic switching penalty function, Γ(x) t is the optimization objective function at the current moment, is the optimization objective function of the previous gear switching time, t0 is the previous gear switching time, t is the current time, t d Indicates the penalty function action time;

[0020] S11, determining a downshift switching condition Ψ based on the downshift switching function:

[0021]

[0022] Where: Φ t is the downshift switching function at the current moment, Φ t＝t0 is the downshift switching function at the previous gear switching moment;

[0023] S12, if Ψ≤20%, return to S7, otherwise execute S13;

[0024] S13, the DHT controller controls the clutch and synchronizer to perform a downshift operation, mode = mode-1;

[0025] S14, after downshifting, updates t0 to t, and determines the braking torque of motor M1, motor M2, left front wheel hydraulic braking torque, right front wheel hydraulic braking torque, left rear wheel hydraulic braking torque, and right rear wheel hydraulic braking torque through the current vehicle speed and braking intensity, offline table lookup and braking torque distribution, and controls the action of the motor and hydraulic braking system.

[0026] Furthermore, the t d satisfy:

[0027]

[0028] Among them: c1, c2, c3 are all constants, and their values ​​are all less than t-t0.

[0029] Furthermore, the fuzzy controller inputs the brake pedal opening P and the pedal opening change rate dP / dt, and outputs the braking intensity z.

[0030] Furthermore, the selection criteria of the weight coefficients λ1, λ2 and λ3 are: at low speed and low braking intensity, focus on braking energy recovery; at high speed and high braking intensity, focus on longitudinal braking stability and lateral stability.

[0031] Further:

[0032] When z < 0.15 and 20 km / h < v ≤ 40 km / h, λ1 = 1, λ2 = 0, λ3 = 0;

[0033] When z < 0.15 and 40 km / h < v ≤ 60 km / h, λ1 = 1, λ2 = 0, λ3 = 0;

[0034] When z < 0.15 and 60 km / h < v ≤ 80 km / h, λ1 = 0.9, λ2 = 0, λ3 = 0.1;

[0035] When z < 0.15 and v > 80 km / h, λ1 = 0.8, λ2 = 0, λ3 = 0.2;

[0036] When 0.15 ≤ z < 0.45 and 20 km / h < v ≤ 40 km / h, λ1 = 0.9, λ2 = 0.1, λ3 = 0;

[0037] When 0.15 ≤ z < 0.45 and 40 km / h < v ≤ 60 km / h, λ1 = 0.8, λ2 = 0.1, λ3 = 0.1;

[0038] When 0.15 ≤ z < 0.45 and 60 km / h < v ≤ 80 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25;

[0039] When 0.15 ≤ z < 0.45 and v > 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3;

[0040] When 0.45 ≤ z < 0.61 and 20 km / h < v ≤ 40 km / h, λ1 = 0.8, λ2 = 0.1, λ3 = 0.1;

[0041] When 0.45 ≤ z < 0.61 and 40 km / h < v ≤ 60 km / h, λ1 = 0.6, λ2 = 0.2, λ3 = 0.2;

[0042] When 0.45 ≤ z < 0.61 and 60 km / h < v ≤ 80 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25;

[0043] When 0.45 ≤ z < 0.61 and v > 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3;

[0044] When 0.61 ≤ z < 0.8 and 20 km / h < v ≤ 40 km / h, λ1 = 0.6, λ2 = 0.2, λ3 = 0.2;

[0045] When 0.61 ≤ z < 0.8 and 40 km / h < v ≤ 60 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25;

[0046] When 0.61 ≤ z < 0.8 and 60 km / h < v ≤ 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3;

[0047] When 0.61 ≤ z < 0.8 and v > 80 km / h, λ1 = 0.2, λ2 = 0.3, λ3 = 0.4;

[0048] When 0.8 ≤ z and 20 km / h < v ≤ 40 km / h, λ1 = 0, λ2 = 0.8, λ3 = 0.2;

[0049] When 0.8 ≤ z and 40 km / h < v ≤ 60 km / h, λ1 = 0, λ2 = 0.7, λ3 = 0.3;

[0050] When 0.8 ≤ z and 60 km / h < v ≤ 80 km / h, λ1 = 0, λ2 = 0.6, λ3 = 0.4;

[0051] When 0.8 ≤ z and v > 80 km / h, λ1 = 0, λ2 = 0.5, λ3 = 0.5.

[0052] Furthermore, the optimization objective function is:

[0053] Γ(x) = λ1f1 + λ2f2 + λ3f3

[0054] Where: f1 is the braking energy recovery rate, f2 represents longitudinal stability, and f3 represents lateral stability. <​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0058] Furthermore, the optimization objective function is optimized using a Grey Wolf optimization algorithm, and the constraints of the Grey Wolf optimization algorithm include motor operating characteristics and ECU braking regulations.

[0059] An electromechanical system for implementing a regenerative braking method applicable to all operating conditions, comprising:

[0060] The electronic control unit includes a brake control unit BCU, a motor controller MCU, a hydraulic controller HCU and a DHT controller. The brake control unit BCU includes a fuzzy controller, a braking torque distribution module and a downshift strategy module. The brake control unit BCU receives the brake pedal opening P, the vehicle speed signal v and the wheel speed signal n. w The fuzzy controller calculates the braking intensity, the braking torque optimization distribution module obtains the motor torque and hydraulic torque, and the downshift strategy module determines whether downshifting is required; the motor controller MCU receives control instructions from the brake control unit BCU and controls the motor to output the corresponding torque; the hydraulic controller HCU receives control instructions from the brake control unit BCU and controls the hydraulic brake system to output the corresponding hydraulic torque; the DHT controller receives control instructions from the brake control unit BCU and controls the clutch and synchronizer to achieve mode / gear switching.

[0061] The above technical solution also includes:

[0062] The vehicle mechanical unit includes a regenerative braking system, a hydraulic braking system and a hybrid-specific transmission DHT. The regenerative braking system includes a motor M1, a motor M2 and a battery pack. The hydraulic braking system includes a vacuum booster, a brake master cylinder, a brake wheel cylinder, a solenoid valve, an accumulator and a brake pedal.

[0063] The beneficial effects of the present invention are:

[0064] (1) The downshift switching function Φ of the present invention includes the inverse of the objective function increment J1 and the periodic penalty switching index J2. The downshift switching condition Ψ is determined based on the downshift switching function. If the downshift switching condition Ψ satisfies the gear switching condition, the gear switching is performed; otherwise, the gear switching is not performed. The present invention effectively avoids the situation where frequent mode / gear switching leads to reduced vehicle stability, and also effectively avoids the situation where upshifting leads to reduced energy recovery rate. The present invention increases energy recovery while taking into account braking stability during vehicle braking, thereby improving the vehicle's economy and increasing the vehicle's mileage.

[0065] (2) The optimization objective function of the present invention comprehensively considers the braking energy recovery rate, longitudinal stability and lateral stability, and sets weight coefficients for each of them. The weight coefficients are obtained by looking up the current vehicle speed signal and braking intensity according to an offline table, ensuring that at low speed and low braking intensity, the focus is on braking energy recovery, and at high speed and high braking intensity, the focus is on braking stability. The Gray Wolf optimization algorithm is based on the determined vehicle speed and braking intensity and the optimization objective function, and obtains the braking force distribution coefficient by searching for the best solution, and then determines the motor torque and hydraulic pressure torque, controls the motor and hydraulic brake system to perform actions, and ensures braking stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a structural block diagram of the regenerative braking electromechanical system applicable to all working conditions according to the present invention;

[0067] Figure 2 This is a structural diagram of the braking torque optimization distribution module of the present invention;

[0068] Figure 3 This is a flow chart of the regenerative braking method applicable to all working conditions according to the present invention. DETAILED DESCRIPTION

[0069] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0070] like Figure 1 As shown, the present invention provides a regenerative braking electromechanical system suitable for all working conditions, including an electronic control unit and a vehicle mechanical unit.

[0071] The electronic control unit includes a brake control unit BCU, a motor controller MCU, a hydraulic controller HCU and a DHT controller; the brake control unit BCU includes a fuzzy controller, a braking torque distribution module and a downshift strategy module. The brake control unit BCU receives the brake pedal opening P, the vehicle speed signal v and the wheel speed signal n sent by the wheel speed sensor. w The braking intensity is calculated by the fuzzy controller, the motor torque and hydraulic torque are obtained by the braking torque optimization distribution module, and the downshift strategy module determines whether downshifting is required; the brake control unit BCU sends control instructions to the motor controller MCU, and the motor controller MCU controls the motor to output the corresponding torque; the brake control unit BCU sends control instructions to the hydraulic controller HCU, and the hydraulic controller HCU controls the hydraulic brake system to output the corresponding hydraulic torque; the brake control unit BCU sends control instructions to the DHT controller, and the DHT controller controls the clutch and synchronizer to achieve mode / gear switching.

[0072] The vehicle mechanical unit includes a regenerative braking system, a hydraulic braking system and a hybrid-specific transmission DHT. The regenerative braking system includes a motor M1, a motor M2 and a battery pack. The battery pack is used to power the motor M1, the motor M2, the motor controller MCU, the hydraulic controller HCU, the DHT controller and the brake control unit BCU; the hydraulic braking system includes a vacuum booster, a brake master cylinder, a brake wheel cylinder, a solenoid valve, an accumulator and a brake pedal. The force acting on the brake pedal is amplified by the vacuum booster and pushes the push rod. The push rod pushes the brake master cylinder piston to increase the brake fluid. The brake fluid is transmitted to the brake wheel cylinder through the brake line. The brake fluid squeezes the wheel cylinder piston to achieve braking. The solenoid valve controls the rise and fall of the oil to achieve precise control of the braking torque. The accumulator is used to store excess oil when the hydraulic braking system is depressurized.

[0073] The fuzzy controller inputs the brake pedal opening P and the pedal opening change rate dP / dt, and outputs the braking intensity z. The fuzzy rules of the fuzzy controller can be found in Chinese patent CN112550256A.

[0074] Figure 2 This is a schematic diagram of the braking torque optimization distribution module, which includes an offline table lookup module and a braking torque distribution module. The offline table lookup module inputs the braking intensity, vehicle speed, and battery SOC value. When the battery SOC is ≤ 85%, the gray wolf optimization algorithm is used to optimize the braking force distribution coefficients β and α based on the optimization objective function. mh , α m12 , α f , respectively representing the ratio of the total front wheel braking torque to the required total braking torque, the ratio of the front wheel electric motor braking torque to the total front wheel braking torque, the ratio of the motor M1 braking torque to the total electric motor braking torque, and the ratio of the left front wheel braking torque to the front wheel braking torque; when the battery SOC is greater than 85%, hydraulic braking is directly used for braking torque distribution, and the distribution method adopts the I curve.

[0075] The constraints of the Gray Wolf optimization algorithm include motor operating characteristics and ECU braking regulations. The constraints are existing technologies and will not be described in detail here.

[0076] The optimization objective function is:

[0077] Γ(x)=λ1f1+λ2f2+λ3f3

[0078] Among them, f1 is the braking energy recovery rate, and its expression is:

[0079]

[0080] Among them, T m1 、T m2 Represents the regenerative braking torque of motor M1 and motor M2 respectively, and the total required braking torque T b_totAnd the distribution coefficient is obtained; n w Indicates the wheel speed, i0, i g1 、i g2 、i m2 They represent the transmission ratio of the main reducer, the transmission ratio of the motor M1 to the wheel end, the transmission ratio of the motor M2 to the wheel end, and the reduction ratio of the motor M2 respectively; η1 and η2 represent the power generation efficiency of the motor M1 and the motor M2 respectively, v and v0 represent the current vehicle speed and the initial vehicle speed respectively, P los represents the battery loss, m represents the vehicle mass, g represents the acceleration of gravity, and f v Indicates the rolling resistance coefficient, C d Indicates the drag coefficient, A v Indicates the frontal area of ​​the vehicle;

[0081] f2 represents longitudinal stability, which is expressed as the difference between the front and rear wheel adhesion coefficient and the braking strength:

[0082]

[0083] Among them, h g represents the height of the center of mass, L represents the vehicle wheelbase, L a Indicates the distance from the center of mass to the front axle, L b represents the distance from the center of mass to the rear axle, represents the front wheel adhesion coefficient, Indicates the rear wheel adhesion coefficient;

[0084] f3 represents lateral stability, which is expressed as:

[0085]

[0086] The ideal reference yaw rate of the vehicle ω ref for:

[0087]

[0088] Where, is the stability factor, unit is s 2 / m 2 , used to represent the steady-state steering characteristics of the vehicle; μ max is the peak road adhesion coefficient; κ is the stability factor, which is 0.9 in this embodiment; δ represents the heading angle; k1 represents the front wheel camber stiffness, and k2 represents the rear wheel camber stiffness, and k1 and k2 satisfy the following vehicle two-degree-of-freedom dynamic equation:

[0089]

[0090] where ω r is the yaw angular velocity, is the yaw angular acceleration, Iz is the lateral moment of inertia, is the vehicle acceleration; ΔM represents the additional yaw moment, which is expressed as:

[0091]

[0092] Where, F xfr 、F xfl 、F xrr 、F xrl They are respectively expressed as the longitudinal right front wheel braking torque, the longitudinal left front wheel braking torque, the longitudinal right rear wheel braking torque, and the longitudinal rear front wheel braking torque, and B is expressed as the wheelbase.

[0093] The optimization objective function weight coefficients λ1, λ2, and λ3 are selected based on the following criteria: at low speeds and low braking intensity, the focus is on brake energy recovery; at high speeds and high braking intensity, the focus is on braking stability, including longitudinal braking stability and lateral stability. For specific values, refer to Table 1:

[0094] Table 1 Selection criteria for weight coefficients

[0095]

[0096] The Gray Wolf optimization algorithm is used to optimize the braking force distribution coefficients β and α based on the determined vehicle speed, braking intensity and objective function. mh , α m12 , α f .

[0097] The braking torque distribution module is based on the braking force distribution coefficients β and α mh , α m12 , α f , determine the motor torque and hydraulic torque, specifically:

[0098] T bF_m1 =T b_tot β α mh α m12

[0099] T bF_m2 =T b_tot β α mh (1-α m12 )

[0100] T bF_h =T b_tot ·β·(1-α mh )

[0101] T bR_h =T b_tot (1-β)

[0102] T xfl =Tb_tot β α f

[0103] T xfr =T b_tot ·β·(1-α f )

[0104] T xrl =T xrr =0.5·T b_tot (1-β)

[0105] Among them, T bF_m1 、T bF_m2 、T bF_h 、T bR_h 、T xfr 、T xfl 、T xrr 、T xrl They represent the braking torque of motor M1, the braking torque of motor M2, the total braking torque of the front wheels, the total braking torque of the rear wheels, the braking torque of the right front wheel, the braking torque of the left front wheel, the braking torque of the right rear wheel, and the braking torque of the rear front wheels, respectively. b_tot Represents the total required braking torque.

[0106] The downshift strategy module determines whether downshifting is required. The judgment condition J1 is the inverse of the increment of the optimization objective function:

[0107]

[0108] Where t0 represents the last gear shift time, and t represents the current time;

[0109] Judgment condition J2 is a periodic switching penalty function:

[0110]

[0111] Where, t d It represents the penalty function action time, which is affected by the braking intensity. The relationship is:

[0112]

[0113] Where c1, c2, and c3 are all constants, and their values ​​are all less than t-t0;

[0114] Combining J1 and J2, we get the downshift switching function:

[0115]

[0116] Determine the downshift switching condition Ψ based on the downshift switching function:

[0117]

[0118] Figure 3 This is a flow chart of a regenerative braking method applicable to all working conditions. The specific control process is as follows:

[0119] Step (1): The brake control unit BCU collects the brake pedal opening signal P, the vehicle speed signal v, and the wheel speed signal n. w and battery SOC value; if the vehicle speed signal v=0km / h is detected, go to step (2); if the vehicle speed signal v≤20km / h, v>20km / h and the SOC value ≥85% is detected, go to step (3), otherwise go to step (4);

[0120] Step (2), exit without braking;

[0121] Step (3), the braking mode is hydraulic braking, and the braking force is distributed according to the I curve;

[0122] Step (4): if the brake pedal opening P≤0, proceed to step (2); otherwise proceed to step (5);

[0123] Step (5), identifying the driver's braking intention through the braking intensity z output by the fuzzy controller;

[0124] Step (6), the brake control unit BCU collects the current mode / gear mode of the hybrid power transmission DHT. If mode=1, go to step (7), otherwise go to step (10);

[0125] Step (7), the DHT controller sends an instruction to the hybrid power transmission DHT to keep the current mode / gear mode unchanged;

[0126] Step (8): Based on the current vehicle speed signal v and the braking intensity z, the weight coefficients λ1, λ2, and λ3 are obtained according to the offline table lookup module, and then the braking torque optimization coefficients β and α are obtained based on the optimization objective function. mh , α m12 , α f ;

[0127] Step (9): the braking torque distribution module is based on the braking force distribution coefficients β and α mh , α m12 , α f , calculating the braking torques of the motor M1, the motor M2, the left front wheel hydraulic pressure, the right front wheel hydraulic pressure, the left rear wheel hydraulic pressure, and the right rear wheel hydraulic pressure; based on the braking torques, the motor controller MCU and the hydraulic controller HCU respectively control the motors and the hydraulic brake system to perform actions, and executing step (15);

[0128] Step (10), enter the downshift strategy module, according to the braking torque optimization coefficient (β, α mh , αm12 , α f )、DHT current mode / gear mode (used to determine i g1 、i g2 ), braking intensity z, vehicle speed v and penalty function action time t d , calculate the downshift switching function Φ:

[0129]

[0130] Step (11), calculate the downshift switching condition Ψ:

[0131]

[0132] Step (12), if Ψ≤20%, return to step (7), i.e., t0 remains unchanged, otherwise go to step (13);

[0133] Step (13), downshifting is implemented, the brake control unit BCU sends a command to the DHT controller, and the DHT controller controls the clutch and synchronizer to implement the downshift operation, mode = mode-1;

[0134] Step (14): after downshifting, update t0 to t, and determine the braking torque of motor M1, motor M2, left front wheel hydraulic braking torque, right front wheel hydraulic braking torque, left rear wheel hydraulic braking torque, and right rear wheel hydraulic braking torque at this time through the current vehicle speed and braking intensity, and control the action of the motor and hydraulic braking system;

[0135] Step (15), the simulation of this step is completed, and the next simulation step is entered, and the process returns to step (1).

[0136] The embodiments described are preferred implementations of the present invention, but the present invention is not limited to the above implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention.

Claims

1. A regenerative braking method applicable to all working conditions, characterized in that: It includes the following steps: S1. If the vehicle speed v = 0 km / h, execute S2; if v ≤ 20 km / h, v > 20 km / h and the SOC value ≥ 85% are satisfied, execute S3, otherwise execute S4; S2. Exit without braking; S3. The braking mode is hydraulic braking, and the braking force is distributed according to the I curve; S4. If the braking pedal opening P ≤ 0, execute S2, otherwise execute S5; S5. Identify the driver's braking intention through the braking intensity z output by the fuzzy controller; S6. When the current mode / gear position mode of the dedicated hybrid transmission DHT = 1, execute S7, otherwise execute S10; S7. Keep the current mode / gear position mode unchanged; S8, according to the current vehicle speed signal v and braking intensity z, the weight coefficients λ1, λ2 and λ3 are obtained according to the offline table lookup module, and then the braking torque optimization coefficients β and α are obtained based on the optimization objective function. mh , α m12 and α f ; S9. The braking torque distribution module calculates the braking torque of motor M1, the braking torque of motor M2, the hydraulic braking torque of the left front wheel, the hydraulic braking torque of the right front wheel, the hydraulic braking torque of the left rear wheel, and the hydraulic braking torque of the right rear wheel based on the braking force distribution coefficient; control the motor and the hydraulic braking system to act according to the braking torque; S10. Calculate the downshift switching function Φ: Where: J1 is the inverse of the optimization objective function increment, J2 is the periodic switching penalty function, Γ(x) t is the optimization objective function at the current moment, is the optimization objective function of the previous gear switching time, t0 is the previous gear switching time, t is the current time, t d Indicates the penalty function action time; S11. Determine the downshift switching condition Ψ based on the downshift switching function; Where: Φ t is the downshift switching function at the current moment, Φ t＝t0 is the downshift switching function at the previous gear switching moment; S12. If Ψ ≤ 20%, return to S7, otherwise execute S13; S13. The DHT controller controls the clutch and the synchronizer to perform a downshift operation, mode = mode - 1; S14. After downshifting, update t0 to t, and determine the braking torque of motor M1, the braking torque of motor M2, the hydraulic braking torque of the left front wheel, the hydraulic braking torque of the right front wheel, the hydraulic braking torque of the left rear wheel, and the hydraulic braking torque of the right rear wheel at this time through off-line look-up table and braking torque distribution according to the current vehicle speed and braking intensity, and control the motor and the hydraulic braking system to act.

2. The regenerative braking method applicable to all working conditions according to claim 1, characterized in that: The t d satisfy: Where: c1, c2, and c3 are all constants, and their values are all less than t - t0.

3. The regenerative braking method applicable to all working conditions according to claim 1, characterized in that: The fuzzy controller inputs the braking pedal opening P and the change rate of the pedal opening dP / dt, and the output is the braking intensity z.

4. The regenerative braking method applicable to all working conditions according to claim 1, characterized in that: The selection criteria for the weight coefficients λ1, λ2, and λ3 are: at low speed and low braking intensity, emphasizing braking energy recovery; at high speed and high braking intensity, emphasizing longitudinal braking stability and lateral stability.

5. The regenerative braking method applicable to all working conditions according to claim 4, wherein: When z < 0.15 and 20 km / h < v ≤ 40 km / h, λ1 = 1, λ2 = 0, λ3 = 0; When z < 0.15 and 40 km / h < v ≤ 60 km / h, λ1 = 1, λ2 = 0, λ3 = 0; When z < 0.15 and 60 km / h < v ≤ 80 km / h, λ1 = 0.9, λ2 = 0, λ3 = 0.1; When z < 0.15 and v > 80 km / h, λ1 = 0.8, λ2 = 0, λ3 = ​ ​ When 0.15 ≤ z < 0.45 and 60 km / h < v ≤ 80 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25; When 0.15 ≤ z < 0.45 and v > 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3; When 0.45 ≤ z < 0.61 and 20 km / h < v ≤ 40 km / h, λ1 = 0.8, λ2 = 0.1, λ3 = 0.1; When 0.45 ≤ z < 0.61 and 40 km / h < v ≤ 60 km / h, λ1 = 0.6, λ2 = 0.2, λ3 = 0.2; When 0.45 ≤ z < 0.61 and 60 km / h < v ≤ 80 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25; When 0.45 ≤ z < 0.61 and v > 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3; When 0.61 ≤ z < 0.8 and 20 km / h < v ≤ 40 km / h, λ1 = 0.6, λ2 = 0.2, λ3 = 0.2; When 0.61 ≤ z < 0.8 and 40 km / h < v ≤ 60 km / h, λ1 = 0.5, λ2 = 0.25, λ3 = 0.25; When 0.61 ≤ z < 0.8 and 60 km / h < v ≤ 80 km / h, λ1 = 0.4, λ2 = 0.3, λ3 = 0.3; When 0.61 ≤ z < 0.8 and v > 80 km / h, λ1 = 0.2, λ2 = 0.3, λ3 = 0.4; When 0.8 ≤ z and 20 km / h < v ≤ 40 km / h, λ1 = 0, λ2 = 0.8, λ3 = 0.2; When 0.8 ≤ z and 40 km / h < v ≤ 60 km / h, λ1 = 0, λ2 = 0.7, λ3 = 0.3; When 0.8 ≤ z and 60 km / h < v ≤ 80 km / h, λ1 = 0, λ2 = 0.6, λ3 = 0.4; When 0.8 ≤ z and v > 80 km / h, λ1 = 0, λ2 = 0.5, λ3 = 0.

5.

6. The regenerative braking method applicable to all working conditions according to claim 1, characterized in that: The optimization objective function is: Γ(x) = λ1f1 + λ2f2 + λ3f3 Where: f1 is the braking energy recovery rate, f2 represents longitudinal stability, and f3 represents lateral stability.

7. The regenerative braking method applicable to all working conditions according to claim 6, characterized in that: The expression of the braking energy recovery rate is: Where: T m1 Represents the regenerative braking torque of motor M1, T m2 Represents the regenerative braking torque of motor M2, n w represents the wheel speed, i0 represents the transmission ratio of the main reducer, i g1 Indicates the transmission speed ratio from motor M1 to the wheel end, i g2 Indicates the transmission speed ratio from motor M2 to the wheel end, i m2 represents the reduction ratio of motor M2, η1 represents the power generation efficiency of motor M1, η2 represents the power generation efficiency of motor M2, v represents the current vehicle speed, v0 represents the initial vehicle speed, P los represents the battery loss, m represents the vehicle mass, g represents the acceleration of gravity, and f v Indicates the rolling resistance coefficient, C d Indicates the drag coefficient, A v Indicates the vehicle's frontal area.

8. The regenerative braking method applicable to all working conditions according to claim 1, characterized in that: The optimization of the objective function is performed using the Grey Wolf Optimization Algorithm, and the constraints of the Grey Wolf Optimization Algorithm include motor operating characteristics and ECU braking regulations.

9. An electromechanical system for implementing the regenerative braking method applicable to all working conditions as claimed in any one of claims 1 to 8, characterized in that: Including: The electronic control unit includes a brake control unit BCU, a motor controller MCU, a hydraulic controller HCU and a DHT controller. The brake control unit BCU includes a fuzzy controller, a braking torque distribution module and a downshift strategy module. The brake control unit BCU receives the brake pedal opening P, the vehicle speed signal v and the wheel speed signal n sent by the wheel speed sensor. w The fuzzy controller calculates the braking intensity, the braking torque optimization distribution module obtains the motor torque and hydraulic torque, and the downshift strategy module determines whether downshifting is required; the motor controller MCU receives control instructions from the brake control unit BCU and controls the motor to output the corresponding torque; the hydraulic controller HCU receives control instructions from the brake control unit BCU and controls the hydraulic brake system to output the corresponding hydraulic torque; the DHT controller receives control instructions from the brake control unit BCU and controls the clutch and synchronizer to achieve mode / gear switching.

10. The electromechanical system according to claim 9, characterized in that Also including: The vehicle mechanical unit includes a regenerative braking system, a hydraulic braking system, and a dedicated hybrid transmission DHT. The regenerative braking system includes motors M1, M2, and a battery pack. The hydraulic braking system includes a vacuum booster, a brake master cylinder, brake wheel cylinders, solenoid valves, an accumulator, and a brake pedal.

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