Method, device and storage medium for distributing braking torque of front and rear axles of electric vehicles under combined braking

Abstract

The present invention discloses a method, computer device, and storage medium for distributing front and rear axle braking torques of an electric vehicle under combined braking. Based on the distribution of regenerative braking and mechanical braking torques, the present invention further distributes the regenerative braking torque and mechanical braking torque to the front and rear wheels. The method distributes the braking torque to the front and rear wheels based on the OABC line in the front and rear wheel braking force coordinate system, thereby meeting the requirements of an optimal braking energy recovery strategy when the maximum regenerative braking force meets the front wheel non-lock requirement. The method distributes the braking torque to the front and rear wheels based on the OBC line in the front and rear wheel braking force coordinate system, thereby meeting the requirements of a front and rear wheel distribution strategy when both regenerative braking torque and mechanical braking torque exist simultaneously, i.e., meeting the requirements of a parallel braking energy recovery strategy. The method maintains braking stability and increases recovered energy, thereby reducing the risk of sideslip of the electric vehicle and ensuring driving safety. The present invention has broad application in the automotive technology field.

Description

Technical Field

[0001] The present invention relates to the field of automobile technology, and in particular to a method for distributing braking torque of front and rear axles of an electric vehicle under combined braking, a computer device, and a storage medium. Background Art

[0002] Electric vehicle braking methods include regenerative braking and mechanical braking. Regenerative braking converts the electric vehicle's kinetic energy back into electricity and charges it back into the battery. Mechanical braking, similar to the braking method of traditional fuel vehicles, converts the electric vehicle's kinetic energy into heat energy for dissipation through brake friction. Therefore, regenerative braking can achieve the following effects: reducing energy consumption and extending driving range. Therefore, current electric vehicle braking technology generally incorporates the components required for both regenerative braking and mechanical braking. The total braking force of an electric vehicle is equal to the sum of the braking force provided by the regenerative braking components and the braking force provided by the mechanical brakes.

[0003] Current electric vehicle braking technology adopts a control strategy for optimal energy recovery, that is, when the required total braking force is greater than the regenerative braking force, only regenerative braking is used and the mechanical braking components do not work; when the required total braking force is greater than the regenerative braking force, the regenerative braking components output braking force at full load, and the braking force provided by the mechanical braking components is equal to the difference between the total braking force and the regenerative braking force.

[0004] Although the optimal energy recovery control strategy can maintain a high energy recovery rate, which is beneficial to improving the endurance of electric vehicles, electric vehicles face complex environments during driving. For example, when emergency braking is required, under the optimal energy recovery control strategy, regenerative braking is used first, and mechanical braking intervenes later. There is a risk of insufficient braking force before mechanical braking intervenes. In actual driving, electric vehicles may also slip and other phenomena. These phenomena may make the optimal energy recovery control strategy lose its safety. Summary of the Invention

[0005] In response to technical problems such as the lack of safety of the optimal energy recovery control strategy used in current electric vehicle braking technology, the purpose of the present invention is to provide a method, computer device and storage medium for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking.

[0006] In one aspect, an embodiment of the present invention includes a method for distributing braking torque between front and rear axles of an electric vehicle under combined braking, comprising:

[0007] Establishing a front and rear wheel braking force coordinate system; wherein the first coordinate axis of the front and rear wheel braking force coordinate system represents the front wheel braking torque, and the second coordinate axis represents the rear wheel braking torque;

[0008] Generate an f-line and an I-line based on the front and rear wheel braking force coordinate system; the f-line is a curve corresponding to the front and rear axle braking torque distribution when the front wheels of the electric vehicle are locked and the rear wheels are not locked; the I-line is a curve corresponding to the front and rear axle braking torque distribution when both the front and rear wheels of the electric vehicle are locked;

[0009] Determine points O, A, B, and C based on the front and rear wheel braking force coordinate system, the f-line, and the I-line;

[0010] When executing the optimal braking energy recovery strategy, the braking torque is distributed to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system;

[0011] When the parallel braking energy recovery strategy is executed, the braking torque is distributed to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system.

[0012] Furthermore, the method for distributing the braking torque of the front and rear axles of the electric vehicle under combined braking further includes:

[0013] Obtain the total braking torque, braking strength, power battery state of charge and slip rate of the electric vehicle;

[0014] When the braking intensity is less than an intensity threshold, the state of charge of the power battery is less than a charge threshold, and the slip rate is less than a slip rate threshold, executing the optimal braking energy recovery strategy;

[0015] When the braking intensity is less than an intensity threshold, the power battery state of charge is less than a charge threshold, and the slip ratio is greater than or equal to the slip ratio threshold, the parallel braking energy recovery strategy is executed.

[0016] Furthermore, under the optimal braking energy recovery strategy, a maximum regenerative braking torque of the electric vehicle is obtained, a braking torque required by the wheels of the electric vehicle is obtained, and a regenerative braking torque and a mechanical braking torque are determined based on a magnitude relationship between the maximum regenerative braking torque and the braking torque required by the wheels;

[0017] Under the parallel braking energy recovery strategy, the braking torque when the motor speed of the electric vehicle is at the base speed is obtained, the regenerative braking torque is determined according to the braking torque when the motor speed is at the base speed, and the mechanical braking torque is determined according to the total braking torque and the regenerative braking torque.

[0018] Furthermore, generating the f-line and the I-line according to the front and rear wheel braking force coordinate system includes:

[0019] According to the equation

[0020]

[0021] Generate the f line; where F f Indicates the front wheel braking force, represents the coefficient, G represents the weight of the electric vehicle, L represents the distance between the front axle and the rear axle of the electric vehicle, b represents the distance between the rear axle and the center of mass of the electric vehicle in the direction parallel to the ground, Z represents the braking strength of the electric vehicle, h represents the height of the center of mass of the electric vehicle, and F r Indicates the rear wheel braking force.

[0022] Furthermore, generating the f-line and the I-line according to the front and rear wheel braking force coordinate system includes:

[0023] According to the equation

[0024]

[0025] Generate the I line; wherein, F f represents the front wheel braking force, G represents the weight of the electric vehicle, L represents the distance between the front axle and the rear axle of the electric vehicle, b represents the distance between the rear axle and the center of mass of the electric vehicle in the direction parallel to the ground, Z represents the braking strength of the electric vehicle, h represents the height of the center of mass of the electric vehicle, F r Indicates the rear wheel braking force.

[0026] Furthermore, determining point O, point A, point B, and point C based on the front and rear wheel braking force coordinate system, the f-line, and the I-line includes:

[0027] Determine the origin of the front and rear wheel braking force coordinate system as point O;

[0028] Determine the point on the first coordinate axis that has the same value as the maximum regenerative braking torque of the electric vehicle as the point A;

[0029] Draw a line perpendicular to the first coordinate axis from point A, and determine the intersection of the line and line I as point B;

[0030] The intersection of the f line and the I line is determined as the C point.

[0031] Furthermore, distributing the braking torque to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system includes:

[0032] In the OA segment of the OABC line, according to the formula F u1 =mgZ,F u2 =0 for allocation; where F u1 Indicates the braking torque distributed to the front wheels, F u2 Indicates the braking torque distributed to the rear wheels; m represents the vehicle mass of the electric vehicle, g represents the acceleration due to gravity, and Z represents the braking strength of the electric vehicle;

[0033] In the AB segment of the OABC line, according to the formula To allocate; among them, Z A Indicates the system strength of regenerative braking torque;

[0034] In the BC segment of the OABC line, according to the formula To allocate; among them, Z B Indicates the system strength generated by the mechanical braking torque, K BC Represents the slope of the BC segment of the OABC connecting line in the front and rear wheel braking force coordinate system.

[0035] Furthermore, distributing the braking torque to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system includes:

[0036] In the OB segment of the OBC line, according to the formula To allocate; where F u1 Indicates the braking torque distributed to the front wheels, F u2 Indicates the braking torque distributed to the rear wheels; m represents the vehicle mass of the electric vehicle, g represents the acceleration of gravity, Z represents the braking strength of the electric vehicle, and Z A Indicates the system strength of the regenerative braking torque, Z B Indicates the system strength generated by the mechanical braking torque;

[0037] In the BC section of the OBC line, according to the formula To allocate; among them, K BC Represents the slope of the BC segment of the OABC connecting line in the front and rear wheel braking force coordinate system.

[0038] On the other hand, an embodiment of the present invention also includes a computer device, including a memory and a processor, wherein the memory is used to store at least one program, and the processor is used to load the at least one program to execute the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in the embodiment.

[0039] On the other hand, an embodiment of the present invention also includes a storage medium storing a program executable by a processor, which is used to execute the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in the embodiment when executed by the processor.

[0040] The beneficial effects of the present invention are as follows: the front and rear axle braking torque distribution method of an electric vehicle under combined braking in the embodiment, on the basis of realizing the regenerative braking and mechanical braking torque distribution of the electric vehicle, further distributes the regenerative braking torque and the mechanical braking torque to the front and rear wheels, wherein the braking torque is distributed to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system, and can meet the requirements of the optimal braking energy recovery strategy when the maximum regenerative braking force meets the front wheel non-locking requirement; the braking torque is distributed to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system, and can meet the front and rear wheel distribution requirements when the regenerative braking torque and the mechanical braking torque exist at the same time, or when the mechanical braking torque exists alone, that is, meets the requirements of the parallel braking energy recovery strategy, so that the optimal braking energy recovery strategy and the parallel braking energy recovery strategy can be realized, thereby achieving the technical effects of the optimal braking energy recovery strategy of maintaining braking stability and improving recovered energy, and achieving the technical effects of the parallel braking energy recovery strategy of recovering energy and reducing the risk of electric vehicle skidding, ensuring driving safety, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of an electric vehicle to which the regenerative braking and mechanical braking torque distribution method of the electric vehicle can be applied in an embodiment;

[0042] Figure 2 Schematic diagram of the steps of the method for distributing regenerative braking and mechanical braking torque of an electric vehicle in an embodiment;

[0043] Figure 3 Schematic diagram of a flow chart of a method for distributing regenerative braking and mechanical braking torque of an electric vehicle in an embodiment;

[0044] Figure 4 Schematic diagram of the relationship between the weighting coefficient w1 and the state of charge SOC of the power battery of the electric vehicle in the embodiment;

[0045] Figure 5 Schematic diagram of the relationship between the weighting coefficient w2 and the real-time speed v of the electric vehicle in the embodiment;

[0046] Figure 6 Schematic diagram of the steps of the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in an embodiment;

[0047] Figure 7 Schematic diagram of the front and rear wheel braking force coordinate system and the curves and points therein in the embodiment. DETAILED DESCRIPTION

[0048] In this embodiment, before describing a method for distributing the braking torques of the front and rear axles of an electric vehicle under combined braking, a method for distributing the regenerative braking and mechanical braking torques of an electric vehicle is described.

[0049] The regenerative braking and mechanical braking torque distribution method of electric vehicles can be applied to Figure 1 In the electric vehicle shown. Figure 1 The front wheels of an electric vehicle are driven by the battery management system (BMS), motor control system (MCU), vehicle control unit (VCU), and electronic hydraulic brake controller (EHB). The BMS controls the power output from the traction battery to power the motor, which, under the control of the motor control system MCU, drives the electric vehicle forward.

[0050] Regenerative braking has the following characteristics:

[0051] 1. As the braking process continues, the speed becomes lower and lower, and the recyclable braking energy becomes smaller and smaller. It is not easy to stop the car in an emergency at low speeds. Therefore, when emergency braking is required, regenerative braking alone cannot stop the car quickly.

[0052] 2. The slip rate should be considered when starting and stopping regenerative braking and mechanical braking to fully utilize ground adhesion and improve braking efficiency. When the slip rate is high, braking safety should be considered.

[0053] Traditionally, regenerative braking has employed an optimal energy recovery control strategy. Specifically, when the total braking force is less than the regenerative braking force, only regenerative braking is used, with mechanical braking disabled. When the total braking force is greater than the regenerative braking force, the mechanical braking force is the total braking force minus the regenerative braking force. This traditionally employed a fixed ratio between the front and rear axles, resulting in poor braking efficiency and safety.

[0054] Regarding the above issues, refer to Figure 2 , a method for distributing regenerative braking and mechanical braking torque of an electric vehicle comprises the following steps:

[0055] S1. Obtain the total braking torque T of the electric vehicle brake , braking intensity Z and power battery state of charge SOC;

[0056] S2. When the braking intensity is greater than or equal to the intensity threshold, or the power battery state of charge is greater than or equal to the charge threshold, mechanical braking is performed;

[0057] S3. When the braking intensity is less than the intensity threshold and the power battery state of charge is less than the charge threshold, perform combined braking.

[0058] The process of steps S1-S3 is as follows Figure 3 In this embodiment, unless otherwise specified, the “wheel” mentioned may refer to the driving wheel of an electric vehicle, such as the front wheel of a current mainstream electric vehicle.

[0059] In step S1, Figure 1The electronic hydraulic brake controller EHB detects the action of the brake pedal, detects the depth of the brake pedal through the displacement sensor set on the brake pedal, and calculates the required total system torque T brake And the braking intensity Z. In this embodiment, the total system torque T brake It can be linearly related to the depth of the brake pedal, the braking intensity Z = T brake / mgr, where m is the weight of the electric vehicle, g is the acceleration due to gravity, and r is the wheel radius. Data such as m, g and r can be stored as constants in the electronic hydraulic brake controller EHB.

[0060] In step S1, Figure 1 The battery management system (BMS) in the system detects and records the status of the power battery to obtain the state of charge (SOC) of the power battery at each moment.

[0061] In step S2, refer to Figure 3 When the braking intensity Z is greater than or equal to the intensity threshold (which can be set to 0.75 in this embodiment), or the power battery state of charge SOC is greater than or equal to the charge threshold (which can be set to 85% in this embodiment), mechanical braking is performed.

[0062] Among them, when the braking intensity Z ≥ 0.75, it can be judged as an emergency brake. To ensure driving safety, the motor does not provide feedback resistance for deceleration. The entire vehicle distributes the hydraulic braking force of the front and rear axles according to the preset VSA control strategy, and the total braking torque is determined as mechanical braking torque, that is, only mechanical braking is performed, and no regenerative braking is performed.

[0063] When the power battery's state of charge (SOC) is ≥85%, it can be considered too high. Because the power battery's charging efficiency is limited by the battery's SOC, temperature, and charging current, braking energy recovery should not be used when the SOC is too high. During braking, the motor's braking torque decreases as the braking process progresses. At this time, the regenerative braking torque is small and only serves a supplementary purpose, so it can be considered as only mechanical braking.

[0064] Reference Figure 3 When the braking intensity Z is less than 0.75 and the power battery state of charge SOC is less than 85%, EHB combined braking can be performed. The steps of combined braking specifically include:

[0065] S301. Detecting the slip rate S of the electric vehicle;

[0066] S302. When the slip rate S is less than the slip rate threshold (which can be set to 15% in this embodiment), the maximum regenerative braking torque T of the electric vehicle is obtained. regen , obtain the braking torque T required by the wheels of the electric vehicle front , according to the maximum regenerative braking torque T regenThe required braking torque T of the wheel front The relationship between the magnitudes of the two determines the regenerative braking torque F. regen and mechanical braking torque F friction ;

[0067] S303. When the slip rate is greater than or equal to the slip rate threshold (15%), obtain the braking torque T0 when the motor speed of the electric vehicle is the base speed, and determine the regenerative braking torque F according to the braking torque T0 when the motor speed is the base speed. regen , according to the total braking torque T brake and regenerative braking torque F regen Determine the mechanical braking torque F friction .

[0068] When executing step S301, Figure 1 The vehicle stability control system VSA detects the slip rate S of the electric vehicle.

[0069] Reference Figure 3 In step S302, when the slip ratio S is less than 15%, the anti-lock braking control in the vehicle stability control system VSA is not triggered because the slip ratio S is less than the slip ratio threshold. The mechanical braking and regenerative braking forces can be distributed with the maximum braking energy recovery strategy. The combined braking performed in step S302 (simultaneously performing regenerative braking and mechanical braking) is the optimal braking energy recovery strategy.

[0070] Specifically, in step S302, by formula T regen =T m .i0.μ m .μ t .w1.w2 calculates the maximum regenerative braking torque T regen Among them, T m is the electric vehicle's motor braking torque; i0 is the electric vehicle's main reduction ratio; μ m is the electric motor power generation efficiency of the electric vehicle; μ t is the transmission efficiency of the electric vehicle; w1 is the weighted coefficient of the state of charge of the electric vehicle's power battery on the regenerative braking torque; w2 is the weighted coefficient of the electric vehicle's real-time speed on the regenerative braking torque.

[0071] In this embodiment, the electric vehicle's motor braking torque T m , the main reduction ratio i0 of the electric vehicle, the motor power generation efficiency μ of the electric vehicle m and the transmission efficiency μ of electric vehicles t Parameters such as Figure 1 In the motor control system MCU.

[0072] In this embodiment, the relationship between the weighted coefficient w1 and the state of charge SOC of the power battery of the electric vehicle is as follows: Figure 4As shown, it satisfies the following relationship:

[0073]

[0074] In this embodiment, the relationship between the weighted coefficient w2 and the real-time speed v of the electric vehicle is as follows: Figure 5 As shown, it satisfies the following relationship:

[0075]

[0076] Among them, you can Figure 1 The motor control system MCU detects the motor speed and calculates the real-time speed v of the electric vehicle, or the vehicle control system VCU calls the data measured by the positioning system to obtain the real-time speed v of the electric vehicle.

[0077] Specifically, in step S302, the regenerative braking torque F is calculated by the following formula: regen and mechanical braking torque F friction :

[0078] (1) When the wheel braking torque T front ≤Maximum regenerative braking torque T regen hour:

[0079] Regenerative braking torque F regen =T front / r;

[0080] Mechanical braking torque F friction =0;

[0081] (2) When the wheel braking torque T front >Maximum regenerative braking torque T regen hour:

[0082] Regenerative braking torque F regen =T regen / r;

[0083] Mechanical braking torque F friction =(T front -T regen ) / r;

[0084] Where r is the wheel radius of the electric vehicle.

[0085] Reference Figure 3 In step S303, when the slip rate S is greater than or equal to the slip rate threshold, the anti-lock braking control in the vehicle stability control system VSA is triggered. The combined braking performed in step S303 (simultaneously performing regenerative braking and mechanical braking) is a parallel braking energy recovery strategy.

[0086] Specifically, in step S303, according to formula F regen =T0.i0.μ m .μ t .w1.w2 / r calculates the regenerative braking torque F regen Among them, T0 is the braking torque when the motor speed is the base speed, i0 is the main reduction ratio of the electric vehicle, μ m is the electric vehicle motor power generation efficiency, μ t is the transmission efficiency of the electric vehicle, w1 is the weighted coefficient of the state of charge of the electric vehicle's power battery on the regenerative braking torque, w2 is the weighted coefficient of the electric vehicle's real-time speed on the regenerative braking torque, and r is the wheel radius of the electric vehicle.

[0087] In this embodiment, the braking torque T0 when the motor speed is the base speed, the main reduction ratio i0 of the electric vehicle, and the motor power generation efficiency μ of the electric vehicle are m and the transmission efficiency μ of electric vehicles t Parameters such as the wheel radius r of the electric vehicle can be stored as constants in Figure 1 In the motor control system MCU.

[0088] In step S303, after obtaining the total braking torque T brake And calculate the regenerative braking torque F regen Then, by formula F friction =(T brake -T regen ) / r to calculate the mechanical braking torque F friction .

[0089] In this embodiment, refer to Figure 3 , by executing step S302 or step S303, the regenerative braking torque F is obtained. regen and mechanical braking torque F friction Afterwards, by Figure 1 The braking force distribution unit in the regen Control the action of the regenerative braking components according to the mechanical braking torque F friction Control the mechanical brake components to brake the electric vehicle.

[0090] In this embodiment, after executing the regenerative braking and mechanical braking torque distribution method of the electric vehicle, namely steps S1-S3, the front and rear axle braking torque distribution method of the electric vehicle under combined braking can be executed. Figure 6 The method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking comprises the following steps:

[0091] P1. Establish the front and rear wheel braking force coordinate system;

[0092] P2. Generate the f-line and I-line based on the front and rear wheel braking force coordinate systems;

[0093] P3. Determine points O, A, B, and C based on the front and rear wheel braking force coordinate systems, line f, and line I.

[0094] P4. When executing the optimal braking energy recovery strategy, the braking torque is distributed to the front and rear wheels based on the OABC line in the front and rear wheel braking force coordinate system.

[0095] P5. When executing the parallel brake energy recovery strategy, the braking torque is distributed to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system.

[0096] In step P1, the front and rear wheel braking force coordinate system is established as follows: Figure 7 As shown. Figure 7 The front and rear wheel braking force coordinate system is a rectangular coordinate system, in which the first coordinate axis, i.e. the horizontal axis, represents the front wheel braking torque F u1 The second coordinate axis, the vertical axis, represents the rear wheel braking torque F u2 .

[0097] In the front and rear wheel braking force coordinate system established in step P1, curves such as the f line, r line, I line and β line can be generated.

[0098] When studying automobile braking safety, there are three states of braking:

[0099] ① The front wheels lock first, but the rear wheels do not lock, and the vehicle loses its steering function;

[0100] For case ①, the curve corresponding to the critical state of the front and rear wheel braking force distribution is called f-line, which can be described by the following formula:

[0101]

[0102] ② If the rear wheels lock first and the front wheels do not lock, the vehicle may easily skid or spin out.

[0103] For situation ②, the curve corresponding to the critical state of the front and rear wheel braking force distribution is called the r-line, which can be described by the following formula:

[0104]

[0105] ③ The front and rear wheels are locked at the same time. This situation is the most ideal, relatively safe and can maximize the use of the road adhesion coefficient.

[0106] For case ③, the curve corresponding to the critical state of the front / rear wheel distribution method is usually called the I line. The I line can be described by the following formula:

[0107]

[0108] In the above formulas, Ff Indicates the front wheel braking force, represents the coefficient, G represents the weight of the electric vehicle, L represents the distance between the front axle and the rear axle of the electric vehicle, b represents the distance between the rear axle and the center of mass of the electric vehicle in the direction parallel to the ground, Z represents the braking strength of the electric vehicle, h represents the height of the center of mass of the electric vehicle, and F r Indicates the rear wheel braking force.

[0109] Due to factors such as control cost and difficulty, most vehicles currently use the β line to complete the braking force distribution. The synchronous adhesion coefficient is determined by the vehicle structure, and the β value can be calculated from the vehicle parameters. The front and rear wheel braking forces are distributed according to the following formula:

[0110]

[0111] R f Indicates the front wheel radius (m); R r Indicates the rear wheel radius (m); r bf Indicates the effective radius of the front wheel under braking (m); r br Indicates the effective radius of the rear wheel under braking (m); d wf Indicates the effective radius of the front wheel cylinder piston (m); d wr Indicates the effective radius of the rear wheel cylinder piston (m).

[0112] During design, in order to prevent the rear axle from locking and skidding, the front and rear braking force distribution lines (β lines) of the automobile braking system should always be below the ideal braking force distribution line (I curve); in order to reduce the chance of the front wheels locking and losing steering ability during braking, the β line can be as close to the I curve as possible.

[0113] In the above formulas, the front wheel braking force F f and the front wheel braking torque F u1 The relationship between them can be expressed as F u1 =F f R f , where R f is the front wheel radius, rear wheel braking force F r and rear wheel braking torque F u2 The relationship between them can be expressed as F u2 =F r R r , where R r is the rear wheel radius. Since the front wheel radius R f and rear wheel radius R r They are all constants, that is, the front wheel braking force F f and the front wheel braking torque F u1 There is a constant factor between them, and the rear wheel braking force F r and rear wheel braking torque F u2There is a constant factor difference between them, so we only need to scale the coordinates of formulas ①, ②, ③, etc. to get Figure 7 The f line and I line in the front and rear wheel braking force coordinate system are shown.

[0114] In this embodiment, when executing step P3, that is, determining point O, point A, point B, and point C based on the front and rear wheel braking force coordinate systems, line f, and line I, the following steps may be specifically performed:

[0115] P301. Determine the origin of the front and rear wheel braking force coordinate system as point O;

[0116] P302. The point on the first coordinate axis with the same value as the maximum regenerative braking torque of the electric vehicle is determined as point A;

[0117] P303. Draw a line perpendicular to the first coordinate axis from point A. The intersection of the line and line I is determined as point B.

[0118] P304. Determine the intersection of line f and line I as point C.

[0119] Reference Figure 7 , where point O is the origin of the front and rear wheel braking force coordinate system; point A is on the first coordinate axis, and the value is consistent with the maximum regenerative braking torque T of the electric vehicle. regen The same point; point B is the intersection of the line drawn from point A and perpendicular to the first coordinate axis with line I; point C is the intersection of line f and line I, and point C corresponds to the synchronous adhesion coefficient.

[0120] In this embodiment, when executing step P4, that is, when executing the optimal braking energy recovery strategy and distributing the braking torque to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system, the following steps may be specifically performed:

[0121] P401. In the OA segment of the line OABC, according to the formula F u1 =mgZ,F u2 =0 for allocation;

[0122] P402. In the AB segment of the line OABC, according to the formula To allocate; among them, Z A Indicates the system strength of regenerative braking torque;

[0123] P403. In the BC segment of the OABC line, according to the formula In steps P401-P403, for ease of explanation, the maximum regenerative braking torque of the electric vehicle can be set to Take i0.μ m .μ t.w1.w2=0.8;where P is the rated power of the motor (KW), n is the rated speed of the motor (rad / s). When the braking intensity is Z, the required braking torque T brake =mgZr.

[0124] In steps P401-P403, F u1 Indicates the braking torque distributed to the front wheels, F u2 Indicates the braking torque distributed to the rear wheels; m represents the vehicle mass of the electric vehicle, g represents the acceleration of gravity, Z represents the braking strength of the electric vehicle, and Z A Indicates the strength of the regenerative braking torque (for example, the regenerative braking torque F is obtained by executing step S302 or step S303). regen Produce, satisfy F regen =mgZ A r), Z B Indicates the system strength of the mechanical braking torque (for example, the mechanical braking torque F is obtained by executing step S302 or step S303). friction Produce, satisfy F friction =mgZ B r), K BC It represents the slope of the BC segment of the OABC line in the front and rear wheel braking force coordinate system.

[0125] In step P401, since the optimal braking energy recovery strategy is executed, T regen ≥T brake Taking a current electric vehicle and its permanent magnet synchronous motor as an example, its performance parameters are P = 37KW, n = 3926rpm, m = 1500kg, r = 0.35m, and the braking strength is calculated by substituting them into Right now Figure 7 The braking intensity Z of point A is 0.137. At this time, the braking force required by the electric vehicle can be fully provided by the regenerative braking force. Therefore, in the OA segment: F u1 =mgZ,F u2 =0.

[0126] In step P402, since the regenerative braking torque F regen Has increased to the maximum value T regen , when the braking intensity Z increases further, the increased braking force is provided by the mechanical brake. Draw a straight line perpendicular to the X axis through point A and intersect line I at point B. In segment AB, the braking force that increases with the braking intensity is applied to the rear wheel by the mechanical brake, satisfying:

[0127] In step P403, in the BC section, when the braking intensity Z increases again, the regenerative braking torque F regen When the braking torque required by the front wheels is insufficient, the brake force distribution unit will apply the mechanical braking torque Ffriction Distribute to the front and rear wheels according to the BC line. At this time:

[0128]

[0129] In this embodiment, when executing step P5, that is, when executing the parallel braking energy recovery strategy, the braking torque is distributed to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system, the following steps P501 can be specifically performed. In the OB segment of the OBC line, according to the formula Make an allocation;

[0130] P502. In the BC segment of the OBC line, according to the formula Make an allocation;

[0131] In steps P501-P502, due to the parallel braking energy recovery strategy, the slip ratio S ≥ 15%, and the braking system requiring anti-lock braking. Regenerative braking alone cannot provide the required braking force for the rear wheels. Therefore, mechanical braking is added in parallel at the very beginning. At this time, the front and rear axle braking force distribution curve follows the OBC curve in the front and rear wheel braking force coordinate system.

[0132] Specifically, in step P501, the braking torque F distributed to the front wheels is distributed according to the OB segment of the OBC line. u1 The braking torque F that is satisfied and distributed to the rear wheels u2 satisfy:

[0133] In step P502, the braking torque F is distributed to the front wheels according to the BC segment of the OBC line. u1 The braking torque F that is satisfied and distributed to the rear wheels u2 satisfy:

[0134]

[0135] The front and rear axle braking torque distribution method of an electric vehicle under combined braking in this embodiment further distributes the regenerative braking torque and the mechanical braking torque to the front and rear wheels on the basis of executing the regenerative braking and mechanical braking torque distribution method of the electric vehicle (steps S1-S3), wherein the braking torque is distributed to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system, which can meet the requirements of the optimal braking energy recovery strategy when the maximum regenerative braking force meets the front wheel non-locking requirement; the braking torque is distributed to the front and rear wheels according to the OBC line in the front and rear wheel braking force coordinate system, which can meet the front and rear wheel distribution requirements when the regenerative braking torque and the mechanical braking torque exist at the same time, or when the mechanical braking torque exists alone, that is, it meets the requirements of the parallel braking energy recovery strategy.

[0136] A computer program that executes the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in this embodiment can be written and written into a storage medium or a computer device. When the computer program is read out and run, the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in this embodiment is executed, thereby achieving the same technical effect as the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking in the embodiment.

[0137] It should be noted that, unless otherwise specified, when a feature is referred to as being "fixed" or "connected" to another feature, it may be directly fixed or connected to the other feature, or it may be indirectly fixed or connected to the other feature. In addition, the descriptions of up, down, left, right, etc. used in this disclosure are only relative to the relative positional relationship of the components of the present disclosure in the accompanying drawings. The singular forms of "a", "said" and "the" used in this disclosure are also intended to include the plural forms, unless the context clearly indicates otherwise. In addition, unless otherwise defined, all technical and scientific terms used in this embodiment have the same meaning as those generally understood by those skilled in the art. The terms used in the description of this embodiment are only for describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in this embodiment includes any combination of one or more related listed items.

[0138] It should be understood that, although the present disclosure may adopt the term first, second, third etc. to describe various elements, these elements should not be limited to these terms.These terms are only used to distinguish the elements of the same type from each other.For example, without departing from the scope of the present disclosure, the first element may also be referred to as the second element, and similarly, the second element may also be referred to as the first element.The use of any and all examples or exemplary language ("for example", "such as" etc.) provided by the present embodiment is only intended to better illustrate embodiments of the present invention, and unless otherwise required, the scope of the present invention will not be limited.

[0139] It should be appreciated that embodiments of the present invention can be implemented or practiced by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer-readable memory. The methods can be implemented in a computer program using standard programming techniques, including a non-transitory computer-readable storage medium configured with a computer program, wherein the storage medium so configured causes the computer to operate in a specific and predefined manner, according to the methods and figures described in the specific embodiments. Each program can be implemented in a high-level procedural or object-oriented programming language to communicate with the computer system. However, if desired, the program can be implemented in assembly or machine language. In any case, the language can be a compiled or interpreted language. In addition, the program can be run on a programmed application-specific integrated circuit for this purpose.

[0140] In addition, the operations of the processes described in this embodiment may be performed in any suitable order, unless otherwise indicated in this embodiment or otherwise clearly contradicted by the context. The processes described in this embodiment (or variations and / or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions, and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) that is executed collectively on one or more processors, by hardware, or a combination thereof. The computer program includes a plurality of instructions that can be executed by one or more processors.

[0141] Furthermore, the methods can be implemented in any type of computing platform that is operably connected to a suitable computer, including but not limited to a personal computer, a minicomputer, a mainframe, a workstation, a network or distributed computing environment, a separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, etc. Various aspects of the present invention can be implemented as machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, an optical read and / or write storage medium, RAM, ROM, etc., so that it can be read by a programmable computer, and when the storage medium or device is read by the computer, it can be used to configure and operate the computer to perform the processes described herein. In addition, the machine-readable code, or portions thereof, can be transmitted over a wired or wireless network. When such media includes instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor, the invention described in this embodiment includes these and other different types of non-transitory computer-readable storage media. When programmed according to the methods and techniques of the present invention, the present invention also includes the computer itself.

[0142] The computer program can be applied to input data to perform the functions described in the present embodiment, thereby converting the input data to generate output data that is stored in a non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the present invention, the converted data represents a physical and tangible object, including a specific visual depiction of the physical and tangible object produced on the display.

[0143] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the aforementioned embodiments. As long as the technical effects of the present invention are achieved by the same means, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention. Within the scope of protection of the present invention, various modifications and variations of the technical solutions and / or implementation methods are possible.

Claims

1. A method for distributing braking torque between front and rear axles of an electric vehicle under combined braking, characterized in that: The method for distributing the braking torque of the front and rear axles of the electric vehicle under combined braking comprises: Establishing a front and rear wheel braking force coordinate system; wherein the first coordinate axis of the front and rear wheel braking force coordinate system represents the front wheel braking torque, and the second coordinate axis represents the rear wheel braking torque; Generate an f-line and an I-line based on the front and rear wheel braking force coordinate system; the f-line is a curve corresponding to the front and rear axle braking torque distribution when the front wheels of the electric vehicle are locked and the rear wheels are not locked; the I-line is a curve corresponding to the front and rear axle braking torque distribution when both the front and rear wheels of the electric vehicle are locked; Determine points O, A, B, and C based on the front and rear wheel braking force coordinate system, the f-line, and the I-line; When executing the optimal braking energy recovery strategy, the braking torque is distributed to the front and rear wheels according to the OABC line in the front and rear wheel braking force coordinate system; When executing the parallel braking energy recovery strategy, the braking torque is distributed to the front and rear wheels according to the OBC connecting line in the front and rear wheel braking force coordinate system; Obtain the total braking torque, braking strength, power battery state of charge and slip rate of the electric vehicle; When the braking intensity is less than an intensity threshold, the state of charge of the power battery is less than a charge threshold, and the slip ratio is less than a slip ratio threshold, the optimal braking energy recovery strategy is executed; under the optimal braking energy recovery strategy, a maximum regenerative braking torque of the electric vehicle is obtained, a braking torque required by a wheel of the electric vehicle is obtained, and a regenerative braking torque and a mechanical braking torque are determined based on a magnitude relationship between the maximum regenerative braking torque and the braking torque required by the wheel; When the braking intensity is less than an intensity threshold, the state of charge of the power battery is less than a charge threshold, and the slip ratio is greater than or equal to the slip ratio threshold, the parallel braking energy recovery strategy is executed; under the execution of the parallel braking energy recovery strategy, the braking torque of the electric vehicle when the motor speed is a base speed is obtained, the regenerative braking torque is determined according to the braking torque when the motor speed is the base speed, and the mechanical braking torque is determined according to the total braking torque and the regenerative braking torque; Determining point O, point A, point B, and point C based on the front and rear wheel braking force coordinate system, the f-line, and the I-line includes: Determine the origin of the front and rear wheel braking force coordinate system as point O; Determine the point on the first coordinate axis that has the same value as the maximum regenerative braking torque of the electric vehicle as the point A; Draw a line perpendicular to the first coordinate axis from point A, and determine the intersection of the line and line I as point B; The intersection of the f line and the I line is determined as the C point; The distributing the braking torque to the front wheel and the rear wheel according to the OABC line in the front and rear wheel braking force coordinate system includes: In the OA segment of the OABC line, according to the formula , To allocate; among them, Indicates the braking torque distributed to the front wheels, Indicates the braking torque distributed to the rear wheels; Indicates the vehicle mass of the electric vehicle, represents the acceleration due to gravity, Indicates the braking strength of the electric vehicle; In the AB segment of the OABC line, according to the formula To allocate; among them, Indicates the system strength of regenerative braking torque; In the BC segment of the OABC line, according to the formula To allocate; among them, Indicates the system strength generated by the mechanical braking torque, Represents the slope of the BC segment of the OABC connecting line in the front and rear wheel braking force coordinate system; The distributing the braking torque to the front wheels and the rear wheels according to the OBC line in the front and rear wheel braking force coordinate system includes: In the OB segment of the OBC line, according to the formula To allocate; among them, Indicates the braking torque distributed to the front wheels, Indicates the braking torque distributed to the rear wheels; Indicates the vehicle mass of the electric vehicle, represents the acceleration due to gravity, Indicates the braking strength of the electric vehicle. Indicates the system strength of the regenerative braking torque, Indicates the system strength generated by the mechanical braking torque; In the BC section of the OBC line, according to the formula To allocate; among them, Represents the slope of the BC segment of the OABC connecting line in the front and rear wheel braking force coordinate system.

2. The method for distributing braking torque between front and rear axles of an electric vehicle under combined braking according to claim 1, characterized in that: Generating the f-line and the I-line according to the front and rear wheel braking force coordinate system includes: According to the equation Generate the f line; wherein, Indicates the front wheel braking force, represents the coefficient, Indicates the total weight of the electric vehicle. Indicates the distance between the front and rear axles of an electric vehicle. It represents the distance between the rear axle and the center of mass of the electric vehicle in the direction parallel to the ground. Indicates the braking strength of the electric vehicle. represents the center of mass height of the electric vehicle, Indicates the rear wheel braking force.

3. The method for distributing braking torque between front and rear axles of an electric vehicle under combined braking according to claim 1, characterized in that: Generating the f-line and the I-line according to the front and rear wheel braking force coordinate system includes: According to the equation Generate the I line; wherein, Indicates the front wheel braking force, Indicates the total weight of the electric vehicle. Indicates the distance between the front and rear axles of an electric vehicle. It represents the distance between the rear axle and the center of mass of the electric vehicle in the direction parallel to the ground. Indicates the braking strength of the electric vehicle. represents the center of mass height of the electric vehicle, Indicates the rear wheel braking force.

4. A computer device, characterized in that: It includes a memory and a processor, the memory is used to store at least one program, and the processor is used to load the at least one program to execute the front and rear axle braking torque distribution method of an electric vehicle under combined braking according to any one of claims 1 to 3.

5. A computer-readable storage medium storing a program executable by a processor, characterized in that: The program executable by the processor is used to execute the method for distributing the braking torque of the front and rear axles of an electric vehicle under combined braking as described in any one of claims 1 to 3 when executed by the processor.

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