Control method for electric vehicle, braking system and electric vehicle

Abstract

The invention discloses a control method for an electric vehicle, a braking system and the electric vehicle, and relates to the technical field of new energy automobiles. The control method is used for controlling the driving system and the braking system to achieve safe braking of the electric vehicle after braking of one wheel of the electric vehicle fails, and comprises the steps that in the running process of the electric vehicle, before the electric vehicle is braked, the driving torque output by the driving system is controlled to change along with the opening degree change of an accelerator pedal; the direction of the driving torque is the same as the rotating speed direction of wheels of the electric vehicle. In the braking process that braking of one front wheel of the electric vehicle fails, the braking system is controlled to output braking force to two rear wheels of the electric vehicle, the driving system is controlled to output reverse torque to the two front wheels, and the direction of the reverse torque is opposite to the rotating speed direction of the two front wheels. According to the scheme, effective braking can be achieved, no obvious yawing exists, and the braking safety and stability of the electric vehicle are improved.

Description

Technical Field

[0001] This application relates to the field of electric vehicles, and more specifically, to a control method, braking system, and electric vehicle for electric vehicles. Background Technology

[0002] Electromechanical brake (EMB) systems completely replace the hydraulic force transmission medium in traditional hydraulic or pneumatic braking systems with electronically controlled braking. EMB systems combine electronic technology with mechanical braking principles, using an electronic control unit to control the brake's action and achieve vehicle braking. When the wheel-end braking device or wheel speed sensor fails, causing braking failure, the wheel with the failed brake loses braking force, and braking can only be achieved by the normally functioning wheel. This affects the braking force, making the EMB system unable to meet the driver's braking needs. During braking, when the brakes of one wheel fail, the imbalance of braking torque on both sides of the vehicle can cause the braking vehicle to yaw or skid, and may even lead to vehicle instability, causing serious driving safety problems.

[0003] Therefore, how to achieve safe braking when the brakes of one wheel of an electric vehicle fail is a problem that needs to be solved. Summary of the Invention

[0004] This application provides a control method, braking system, and electric vehicle for electric vehicles. When the braking of one wheel fails, the drive system outputs reverse torque for braking, while the two wheels on the normal axle output braking force, which can effectively brake without significant yaw, thus improving the safety and stability of electric vehicle braking.

[0005] Firstly, this application provides a control method for an electric vehicle. The control method controls the drive system and braking system to achieve safe braking of the electric vehicle after the braking of one wheel fails. The control method includes, during the operation of the electric vehicle and before braking, controlling the drive torque output by the drive system to change with the opening of the accelerator pedal, with the direction of the drive torque being the same as the rotational speed direction of the electric vehicle's wheels. During the braking process when the braking of one front wheel of the electric vehicle fails, the braking system is controlled to output braking force to the two rear wheels of the electric vehicle, and the drive system is controlled to output a reverse torque to the two front wheels, with the direction of the reverse torque being opposite to the rotational speed direction of the two front wheels.

[0006] In this application, brake failure of a single wheel refers to the inability of the wheel-end braking device in the braking system to properly output braking force to that wheel. Causes of brake failure of a single wheel include actuator failure, brake motor failure, controller failure, and wheel speed sensor failure. When brake failure occurs on a single wheel, the braking system cannot output braking force to that wheel, resulting in a reduction in the total braking force generated by the braking system, thus affecting the braking safety and stability of the electric vehicle.

[0007] During the operation of an electric vehicle, before braking begins, brake failure of one wheel has minimal impact. The control drive system outputs the drive torque indicated by the accelerator pedal opening. This drive torque drives the wheel, and its direction is the same as the wheel's rotational speed. If brake failure of one wheel occurs before or after braking begins, the braking system detects the failure and coordinates with the drive system for control. During braking in the event of brake failure of one wheel, the control braking system outputs braking force to the wheel on the same side and the diagonally opposite wheel, while the control drive system outputs reverse torque to the wheel on the same axle and the wheel on the same side. The direction of this reverse torque is opposite to the wheel's rotational speed. The left front wheel and right rear wheel of an electric vehicle are diagonally opposite each other, or the right front wheel and left rear wheel are diagonally opposite each other. The two left wheels or two right wheels are on the same side, and the two front wheels or two rear wheels are on the same axle.

[0008] In this application, the magnitude of the reverse torque is the absolute value of the output torque of the drive system; increasing the reverse torque output is equivalent to increasing the absolute value of the output torque. During the forward motion of the electric vehicle, positive torque is used to drive the vehicle, and negative torque is used to brake the vehicle. At this time, the driving torque is positive, and the reverse torque is negative. The drive system changes the phase of the three-phase current output by the motor controller to the drive motor, causing the rotor to cut the magnetic field generated by the stator windings. The rotor's kinetic energy is converted into electrical energy and input into the power battery. At this time, the drive motor outputs negative torque. By changing the magnitude of the three-phase current output to the motor, the motor controller can increase or decrease the positive or negative torque output by the drive system. It should be understood that during the reversing process of the electric vehicle, positive torque is used to brake the vehicle, and negative torque is used to drive the vehicle. This application uses the forward motion of the electric vehicle as an example for explanation; a similar description can be used in the reversing scenario, and the direction of the torque output by the drive motor can be modified accordingly, but the function of the torque should remain consistent.

[0009] The accelerator pedal in this application is also called the power pedal or throttle pedal. The opening degree of the accelerator pedal indicates the amount of driving force required by the driver. The larger the opening degree of the accelerator pedal, the greater the driver's demand for driving force, and the greater the torque required from the drive motor. The drive system controls the amount of current output to the drive motor according to the opening degree of the accelerator pedal, so that the drive motor outputs the torque indicated by the throttle pedal opening degree. The larger the opening degree of the accelerator pedal, the greater the current, and thus the greater the torque output by the drive motor. The smaller the opening degree of the accelerator pedal, the smaller the current, and thus the smaller the torque output by the drive motor. The driving torque output by the drive system varies with the opening degree of the accelerator pedal.

[0010] The braking system includes four wheel-end brakes, each of which outputs braking force to the wheels of the electric vehicle. Each of the four wheel-end brakes corresponds one-to-one with one of the four wheels, and each brake applies braking force independently. Under normal conditions, the four wheel-end brakes output the braking force indicated by the brake pedal opening. When one wheel fails, the wheel-end brake used to brake that wheel cannot output braking force. In this case, the braking system controls the output of braking force to the wheels on the same side as the failed wheel and the wheels diagonally opposite the failed wheel.

[0011] Specifically, when the left front wheel brake fails, during the braking process, the braking system is controlled to output braking force to both rear wheels, and the drive system is controlled to output reverse torque to both front wheels. The direction of the reverse torque is opposite to the rotational speed of the two front wheels. When the right front wheel brake fails, during the braking process, the braking system is controlled to output braking force to both rear wheels, and the drive system is controlled to output reverse torque to both front wheels. The direction of the reverse torque is opposite to the rotational speed of the two front wheels.

[0012] It should be understood that, because it is necessary to control the drive system to output reverse torque to the two front wheels, the drive system includes at least one drive motor for driving the two front wheels. When the two front wheels are driven by two drive motors respectively, the two drive motors are controlled to simultaneously output reverse torque to brake the two front wheels.

[0013] In another embodiment, the wheel whose braking fails is a rear wheel. During the braking process when the braking of one rear wheel of the electric vehicle fails, the braking system is controlled to output braking force to the two front wheels of the electric vehicle, and the drive system is controlled to output reverse torque to the two rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels.

[0014] Specifically, when the left rear wheel brake fails, during the braking process, the braking system is controlled to output braking force to both front wheels, and the drive system is controlled to output reverse torque to both rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels. When the right rear wheel brake fails, during the braking process, the braking system is controlled to output braking force to both front wheels, and the drive system is controlled to output reverse torque to both rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels.

[0015] It should be understood that, because it is necessary to control the drive system to output reverse torque to the two rear wheels, the drive system includes at least one drive motor for driving the two rear wheels. When the two rear wheels are driven by two drive motors respectively, the two drive motors are controlled to simultaneously output reverse torque to brake the two rear wheels.

[0016] According to the solution of this application, by controlling the drive system to output reverse torque to the two wheels of the wheel axle where braking has failed to compensate for the failure of braking force, and cooperating with the braking system to output braking force to the two wheels of the normal axle, the yaw of the electric vehicle caused by braking of one side of the wheel is avoided. At the same time, a larger braking force is output, the braking distance is shortened, and the safety and stability of the electric vehicle braking are improved.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the braking force output by the braking system to the two rear wheels of the electric vehicle to vary with the opening of the brake pedal during a braking process in which the front wheel brake fails, and controlling the reverse torque output by the drive system to vary with the opening of the brake pedal.

[0018] In this application, the brake pedal is also referred to as the brake or brake pedal. The opening degree of the brake pedal indicates the amount of braking force required by the driver. The larger the opening degree of the brake pedal, the greater the driver's demand for braking, and the greater the braking force required from the braking system. During normal driving of an electric vehicle, the braking system controls the wheel-end braking devices according to the opening degree of the brake pedal, thereby outputting the braking force indicated by the brake pedal opening degree. The larger the opening degree of the brake pedal, the greater the braking force output by the wheel-end braking devices; the smaller the opening degree of the brake pedal, the smaller the braking force output by the wheel-end braking devices. The braking force output by the braking system varies with the opening degree of the brake pedal.

[0019] During braking when one wheel's brakes fail, the braking force output by the control braking system to the two rear wheels of the electric vehicle varies with the opening of the brake pedal, and the reverse torque output by the control drive system also varies with the opening of the brake pedal. During the electric vehicle's operation, before braking, the drive torque output by the control drive system varies with the opening of the accelerator pedal. After braking begins and one wheel's brakes fail, the control drive system outputs reverse torque to that wheel and the wheel on the same axle, and the magnitude of the reverse torque is determined by the opening of the brake pedal, varying with its opening. The braking force output by the braking system to the two normally braked wheels on the same axle varies with the opening of the brake pedal.

[0020] According to the solution of this application, during the braking process when the brake of one wheel fails, the reverse torque output by the control drive system and the braking force output by the braking system change with the opening of the brake pedal. The braking force is adjusted according to the driver's instructions, which improves the operability of the electric vehicle and maintains the responsiveness and effectiveness of braking.

[0021] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during a braking process in which the front wheel brakes fail, first controlling the braking system to output braking force to the two rear wheels of the electric vehicle, and controlling the drive system to output reverse torque to the two front wheels, and then controlling the braking system to output braking force to the other front wheel.

[0022] During braking when one wheel fails to brake, the reverse torque output by the drive system to that wheel and its coaxial wheel can brake them. However, the maximum braking capacity generated by this reverse torque is less than the maximum braking effect of the braking force output by the braking system. Therefore, when a large braking force is required, the reverse torque output by the drive system to that wheel and its coaxial wheel alone is insufficient to produce a adequate braking effect. In this case, the braking system outputs braking force to the third wheel that is braking normally, thereby effectively improving the braking capacity.

[0023] Specifically, when the left rear wheel brake fails, during the braking process when the left front wheel brake fails, the braking system is first controlled to output braking force to both rear wheels of the electric vehicle, and the drive system is controlled to output reverse torque to both front wheels. Then, the braking system is controlled to output braking force to the right front wheel. When the right front wheel brake fails, during the braking process when the right front wheel brake fails, the braking system is first controlled to output braking force to both rear wheels of the electric vehicle, and the drive system is controlled to output reverse torque to both front wheels. Then, the braking system is controlled to output braking force to the left front wheel.

[0024] In another embodiment, the wheel whose braking fails is a rear wheel. During the braking process when the braking of a rear wheel fails, the braking system is first controlled to output braking force to the two front wheels of the electric vehicle, and the drive system is controlled to output reverse torque to the two rear wheels. Then, the braking system is controlled to output braking force to the other rear wheel.

[0025] Specifically, when the left rear wheel brake fails, during the braking process of the left rear wheel brake failure, the braking system is controlled to output braking force to both front wheels, and the drive system is controlled to output reverse torque to both rear wheels, and then the braking system is controlled to output braking force to the right rear wheel. When the right rear wheel brake fails, during the braking process of the right rear wheel brake failure, the braking system is controlled to output braking force to both front wheels, and the drive system is controlled to output reverse torque to both rear wheels, and then the braking system is controlled to output braking force to the left rear wheel.

[0026] According to the scheme of this application, by controlling the braking system to output braking force to the third wheel that is in normal braking condition, the braking capacity is further improved, thereby improving the braking capacity of the electric vehicle when the braking of one wheel fails.

[0027] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes, during a braking process in which the front wheel brakes fail, when the brake pedal opening is less than a preset opening, controlling the braking force output by the braking system to the other front wheel to be zero. When the brake pedal opening increases to be greater than or equal to the preset opening, controlling the braking force output by the braking system to the other front wheel to be greater than zero.

[0028] After the braking system outputs braking force to the third wheel that is functioning normally, this third wheel, which is coaxial with the wheel that has failed to brake, will be subjected to both the reverse torque and the braking force output by the braking system. This results in the total braking force on the third wheel being greater than the braking force on the coaxial wheel that has failed to brake. The unequal braking forces on both sides of the electric vehicle generate yaw torque, causing the electric vehicle to yaw. However, in emergency braking situations, the demand for braking force is more urgent. Therefore, generating a controllable range of yaw torque is permissible to ensure safe braking of the electric vehicle.

[0029] The driver's need for emergency braking is determined by the brake pedal opening. If the brake pedal opening is less than the preset opening, the driver does not need emergency braking. In this case, the braking system outputs braking force to the two rear wheels of the electric vehicle, while the drive system outputs reverse torque to the two front wheels. The required braking force can be compensated by the reverse torque output by the drive system. The braking system does not output braking force to the normally braking third wheel. The braking force output to the two rear wheels and the reverse torque output to the two front wheels are symmetrical, preventing yaw and achieving both sufficient braking capacity and vehicle stability during braking. When the brake pedal opening increases to greater than or equal to the preset opening, it is determined that the driver needs emergency braking. In this case, the required braking force cannot be fully compensated by the reverse torque output by the drive system. Therefore, the braking system outputs braking force to the normally braking third wheel, further increasing the braking force and effectively achieving emergency braking.

[0030] The preset opening is pre-calibrated based on actual vehicle experiments and / or model calculations, or it is preset by comprehensively considering the needs and performance of the entire vehicle.

[0031] According to the solution of this application, the opening degree of the brake pedal determines whether the electric vehicle is undergoing emergency braking, thereby controlling whether the braking system outputs braking force to the third wheel that is braking normally. Under non-emergency braking, the drive system is controlled to output reverse torque to the two wheels of the wheel axle where braking has failed to compensate for the failure of braking force. This, combined with the braking system outputting braking force to the two wheels of the normal axle, avoids the electric vehicle from swaying due to braking on one side of the wheel. Under emergency braking, the braking system is controlled to output braking force to the third wheel that is braking normally, further improving the braking capacity and enhancing the safety and stability of the electric vehicle's braking.

[0032] In conjunction with the first aspect, in certain implementations of the first aspect, the control method specifically includes, during the braking process when the left front wheel brake fails, controlling the braking force output by the braking system to the right front wheel to be zero before the reverse torque output by the drive system to both front wheels increases to a preset torque. After the reverse torque output by the drive system to both front wheels increases to the preset torque, controlling the braking force output by the braking system to the right front wheel to be greater than zero.

[0033] When the braking system directs braking force to the third wheel that is functioning normally, the total braking force on that wheel will be greater than that on the wheel on the same axle where the brakes have failed. This unequal braking force on both sides of the electric vehicle generates yaw torque, causing the vehicle to yaw. Therefore, in non-essential situations, symmetrical control should be prioritized for emergency braking. Before the reverse torque output by the drive system to the wheel that has failed braking and its coaxial wheel falls below a preset torque, increasing the reverse torque output can enhance braking force without needing to direct braking force to the third wheel. Once the reverse torque output by the drive system to the wheel that has failed braking and its coaxial wheel reaches the preset torque, it becomes impossible to further enhance braking force by increasing the reverse torque output, thus preventing the system from directing braking force to the third wheel to improve braking capability.

[0034] The preset torque is pre-calibrated based on real vehicle experiments and / or model calculations, or it is preset by taking into account the overall vehicle requirements and vehicle performance.

[0035] According to the solution in this application, the braking system is controlled to output braking force to the third wheel that is braking normally based on whether the output torque of the drive system reaches the maximum braking effect, thereby improving the braking safety and stability of electric vehicles.

[0036] In conjunction with the first aspect, in certain implementations of the first aspect, the control method specifically includes, during a braking process in which the front wheel brakes fail, controlling the braking force output by the braking system to the other front wheel to be zero before the reverse torque output by the drive system to the two front wheels increases to a preset torque. After the reverse torque output by the drive system to the two front wheels increases to the preset torque, when the average slip ratio of the two front wheels is less than a preset value, controlling the braking force output by the braking system to the other front wheel to be greater than zero.

[0037] The drive system includes a resolver sensor, whose resolver signal can be used to obtain the rotational speed of the drive motor. By combining the drive motor's rotational speed with the electric vehicle's transmission ratio, the angular velocity of the wheels can be calculated. Further combining this with the wheel radius and the electric vehicle's speed yields the slip ratio of each wheel. The wheel slip ratio affects the braking effect; when the slip ratio is too high, the wheel slips, and it cannot generate effective braking force.

[0038] Therefore, when the average slip ratio of the two wheels is greater than the preset value, the braking force output by the control braking system to the normally braking third wheel cannot further improve the braking effect. Only after the reverse torque output by the drive system to the two front wheels increases to the preset torque, and when the average slip ratio of the two front wheels is less than the preset value, does the braking force output by the control braking system to the other front wheel become greater than zero.

[0039] This preset value is pre-calibrated based on real vehicle experiments and / or model calculations, or it is pre-set by comprehensively considering the vehicle's requirements and performance.

[0040] According to the solution in this application, the braking system is controlled to output braking force to the third wheel that is braking normally based on the wheel slip ratio, thereby improving the braking safety and stability of electric vehicles.

[0041] In conjunction with the first aspect, in some implementations of the first aspect, during the process of controlling the drive system to increase the reverse torque output to the two front wheels to a preset torque, the control method further includes controlling the reverse torque output to the two front wheels by the drive system to vary with the change in the average slip ratio of the two front wheels.

[0042] Since wheel slip ratio directly affects braking performance, the drive system regulates wheel slip ratio by controlling the magnitude of the output reverse torque. Specifically, when the average slip ratio of the two wheels is less than a preset slip ratio, the drive system increases the reverse torque output to the two wheels; conversely, when the average slip ratio of the two wheels is greater than the preset slip ratio, the drive system decreases the reverse torque output to the two wheels. This ensures that the reverse torque output by the drive system produces an effective braking effect.

[0043] The preset slip ratio is pre-calibrated based on real vehicle experiments and / or model calculations, or it is preset by comprehensively considering the vehicle's requirements and performance.

[0044] According to the solution of this application, the magnitude of the reverse torque output by the drive system is adjusted according to the average slip ratio of the two wheels, so that the slip ratio of the two wheels is within a suitable range, which enables the reverse torque output by the drive system to produce a better braking effect and improves the braking safety and stability of electric vehicles.

[0045] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the braking system to output equal braking forces to the two rear wheels of the electric vehicle during a braking process in which the front wheel brakes fail.

[0046] To prevent yaw torque caused by unequal braking forces on both sides of an electric vehicle, which could lead to yaw, the braking force output by the braking system to the two wheels on the same axle should be controlled to be equal, thus preventing yaw torque.

[0047] According to the solution of this application, by controlling the braking system to output equal braking force to the two wheels of the normal axle, the yaw of the electric vehicle caused by excessive braking on one side of the wheel is avoided, thereby improving the braking safety and stability of the electric vehicle.

[0048] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the braking force output by the braking system to the other front wheel to always be less than the braking force output to either of the two rear wheels during a braking process in which the front wheel brake fails.

[0049] When the braking system directs braking force to the third wheel that is functioning normally, the total braking force on that third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. This unequal braking force on both sides of the electric vehicle generates yaw torque, causing the electric vehicle to yaw. The greater the braking force output by the braking system to the third wheel that is functioning normally, the greater the yaw torque generated by the electric vehicle. Therefore, it is necessary to limit the magnitude of the braking force output by the braking system to the third wheel that is functioning normally.

[0050] Specifically, during a braking process where one front wheel brake fails, the braking force output by the braking system to the other front wheel is always less than the braking force output to either of the two rear wheels. Similarly, during a braking process where one rear wheel brake fails, the braking force output by the braking system to the other rear wheel is always less than the braking force output to either of the two front wheels.

[0051] According to the solution in this application, the amount of braking force output by the braking system to the third wheel that is braking normally is limited, which avoids the electric vehicle from losing control due to excessive braking on one side of the wheel, thus improving the safety and stability of the electric vehicle's braking.

[0052] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, after controlling the braking force output by the braking system to the other front wheel to be greater than zero, controlling the braking force output by the braking system to the other front wheel to vary with the yaw angle of the electric vehicle.

[0053] When the braking system directs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than that on the wheel on the same axle where the brakes have failed. This unequal braking force on both sides of the electric vehicle generates yaw torque, causing the electric vehicle to yaw. Adjusting the braking force directed to the third wheel based on its yaw angle prevents excessive yaw and loss of control.

[0054] According to the solution in this application, the braking system outputs braking force to the third wheel that is braking normally according to the yaw angle of the electric vehicle, which avoids the electric vehicle from losing control due to excessive yaw torque caused by excessive braking on one side of the wheel, and improves the braking safety and stability of the electric vehicle.

[0055] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, after controlling the braking force output by the braking system to the other front wheel to be greater than zero, controlling the braking force output by the braking system to the other front wheel to vary with the steering wheel angle of the electric vehicle.

[0056] When the control braking system outputs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. The unequal braking forces generated on both sides of the electric vehicle will produce yaw torque, causing the electric vehicle to yaw. At this time, the driver may adjust the steering wheel angle because he perceives the change in the vehicle's posture. When the steering wheel angle changes, the electric vehicle's steering system will adjust the direction of the wheels, which can offset the yaw torque generated by the electric vehicle to a certain extent. At this time, the control braking system outputs more braking force to the third wheel that is braking normally, thus obtaining greater braking force.

[0057] According to the solution in this application, when the driver controls the steering wheel to adjust the vehicle's yaw attitude, the braking system can output greater braking force to the third wheel that is braking normally, further improving braking capability and enhancing the safety and stability of electric vehicle braking.

[0058] Secondly, this application provides a braking system for an electric vehicle. This braking system adjusts the braking force output to the other three wheels to achieve safe braking of the electric vehicle after the braking of one wheel fails. During the operation of the electric vehicle, before braking, the braking system controls the output of braking force to all four wheels of the electric vehicle as indicated by the brake pedal opening. During braking when the left front wheel of the electric vehicle fails, the braking system controls the output of braking force to the right front wheel and left rear wheel, and controls the braking force output to the left rear wheel to vary with the yaw angle of the electric vehicle.

[0059] When the drive system consists of only one drive motor, and that drive motor is used to drive a wheel that has failed to brake, safe braking control can be achieved solely through the braking system.

[0060] When the brakes on one front wheel of an electric vehicle fail, the braking system controls the output of braking force to the wheel on the same side and the wheel on the same axle of the failed wheel, achieving diagonal braking. At the same time, the difference in braking force between the two rear wheels is controlled to adjust the yaw angle of the electric vehicle.

[0061] Specifically, during the braking process when the left front wheel brake of an electric vehicle fails, the control braking system outputs braking force to the right front wheel and left rear wheel of the electric vehicle. When the yaw angle of the electric vehicle increases to the left, the control braking system reduces the braking force output to the left rear wheel, and when the yaw angle of the electric vehicle increases to the right, the control braking system increases the braking force output to the left rear wheel.

[0062] Specifically, during the braking process when the right front wheel brake of an electric vehicle fails, the control braking system outputs braking force to the left front wheel and right rear wheel of the electric vehicle. When the yaw angle of the electric vehicle increases to the left, the control braking system increases the braking force output to the right rear wheel. When the yaw angle of the electric vehicle increases to the right, the control braking system decreases the braking force output to the right rear wheel.

[0063] According to the solution in this application, when the braking of one front wheel of an electric vehicle fails, diagonal braking combined with the yaw angle control of the rear axle dual-wheel braking force is adopted, which effectively improves the braking capacity and enhances the braking safety and stability of the electric vehicle.

[0064] In conjunction with the second aspect, in some implementations of the second aspect, the braking system is further configured to, during braking after the failure of the left front wheel's brakes, control the braking force output by the braking system to the right rear wheel of the electric vehicle to be zero when the brake pedal opening increases and is less than a preset opening. When the brake pedal opening increases to be greater than or equal to the preset opening, control the braking force output by the braking system to the right rear wheel to be greater than zero, and control the braking force output by the braking system to the left rear wheel to be greater than the braking force output to the right rear wheel.

[0065] The system determines whether the driver needs emergency braking by monitoring the brake pedal opening. If the brake pedal opening is less than a preset opening, the driver does not need emergency braking, and the braking force output by the braking system to the diagonal wheel opposite the wheel that has failed braking is zero. When the brake pedal opening increases to be greater than or equal to the preset opening, it is determined that the driver needs emergency braking. At this time, the braking system outputs braking force to the diagonal wheel opposite the wheel that has failed braking, thereby further increasing the braking force and effectively achieving emergency braking.

[0066] In conjunction with the second aspect, in some implementations of the second aspect, the braking system is also used to, during the braking process in which the left rear wheel brake of the electric vehicle fails, first control the braking system to output braking force to the two front wheels of the electric vehicle, and then control the braking system to output braking force to the right rear wheel of the electric vehicle.

[0067] In conjunction with the second aspect, in some implementations of the second aspect, the braking system is specifically used to, during the braking process when the left rear wheel brake of the electric vehicle fails, control the braking system to output braking force to the two front wheels of the electric vehicle when the brake pedal opening increases and is less than a preset opening. When the brake pedal opening increases to be greater than or equal to the preset opening, control the braking system to output braking force to the right rear wheel of the electric vehicle, and control the braking force output by the braking system to the right rear wheel to vary with the yaw angle of the electric vehicle.

[0068] The system determines whether the driver needs emergency braking by monitoring the brake pedal opening. If the brake pedal opening is less than a preset opening, the driver does not need emergency braking. When the brakes on one rear wheel of the electric vehicle fail, the braking system directs braking force to both front wheels to achieve front axle braking. When the brake pedal opening increases to be greater than or equal to the preset opening, it indicates that the driver needs emergency braking. At this time, the braking system directs braking force to the other rear wheel, further increasing the braking force and effectively achieving emergency braking. Simultaneously, the difference in braking force between the two rear wheels is controlled to adjust the yaw angle of the electric vehicle.

[0069] Specifically, during the braking process when the left rear wheel brake of an electric vehicle fails, the control braking system outputs braking force to the two front wheels of the electric vehicle. When the yaw angle of the electric vehicle increases to the left, the control braking system increases the braking force output to the right rear wheel. When the yaw angle of the electric vehicle increases to the right, the control braking system decreases the braking force output to the right rear wheel.

[0070] Specifically, during the braking process when the right rear wheel brake of an electric vehicle fails, the control braking system outputs braking force to the two front wheels of the electric vehicle. When the yaw angle of the electric vehicle increases to the left, the control braking system reduces the braking force output to the left rear wheel. When the yaw angle of the electric vehicle increases to the right, the control braking system increases the braking force output to the left rear wheel.

[0071] Thirdly, this application provides an electric vehicle including a brake pedal, an accelerator pedal, a braking system, a drive system, and four wheels. The opening of the brake pedal is used to indicate that the braking system outputs braking force, and the accelerator pedal is used to indicate that the drive system outputs drive torque. The braking system and the drive system are used to perform the control methods described in the first aspect and its various implementations.

[0072] Other beneficial effects can be found in the description of the first aspect, and will not be repeated here. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of an electric vehicle provided in an embodiment of this application;

[0074] Figure 2This is a schematic diagram of the braking system architecture provided in an embodiment of this application;

[0075] Figure 3 This is a schematic diagram of the electric vehicle architecture provided in an embodiment of this application;

[0076] Figure 4 This is a schematic diagram of a drive system and braking system control for a single-wheel braking failure braking process provided in an embodiment of this application;

[0077] Figure 5 This is a schematic diagram of a single-wheel brake failure braking process scenario provided in an embodiment of this application;

[0078] Figure 6 This is another schematic diagram of the drive system and braking system control for a single-wheel braking failure braking process provided in an embodiment of this application;

[0079] Figure 7 This is a schematic diagram of another single-wheel brake failure braking process scenario provided in an embodiment of this application;

[0080] Figure 8 This is a schematic diagram of the braking system control during a single-wheel brake failure braking process provided in an embodiment of this application;

[0081] Figure 9 This is a schematic diagram of another single-wheel brake failure braking process scenario provided in an embodiment of this application;

[0082] Figure 10 This is another schematic diagram of the braking system control during a single-wheel brake failure braking process provided in an embodiment of this application;

[0083] Figure 11 This is a schematic diagram of a single-wheel brake failure braking process scenario provided in an embodiment of this application;

[0084] Figure 12 This is a schematic diagram of a drive system and braking system control for a dual-wheel brake failure braking process provided in an embodiment of this application;

[0085] Figure 13 This is a schematic diagram of a dual-wheel brake failure braking process scenario provided in an embodiment of this application;

[0086] Figure 14 This is another schematic diagram of the drive system control during a dual-wheel brake failure braking process provided in an embodiment of this application;

[0087] Figure 15 This is a schematic diagram of another dual-wheel brake failure braking process scenario provided in an embodiment of this application;

[0088] Figure 16This is another schematic diagram of the drive system and braking system control during a dual-wheel brake failure braking process provided in an embodiment of this application;

[0089] Figure 17 This is a schematic diagram of another dual-wheel brake failure braking process scenario provided in an embodiment of this application;

[0090] Figure 18 This is a schematic diagram of a dual-wheel brake failure braking control process provided in an embodiment of this application;

[0091] Figure 19 This is a schematic diagram of the control of a drive system for a multi-wheel braking failure braking process provided in an embodiment of this application;

[0092] Figure 20 This is another schematic diagram of the drive system control for a multi-wheel brake failure braking process provided in an embodiment of this application;

[0093] Figure 21 This is another schematic diagram of the drive system control for a multi-wheel brake failure braking process provided in an embodiment of this application;

[0094] Figure 22 This is a schematic diagram of a multi-wheel brake failure braking process scenario provided in an embodiment of this application;

[0095] Figure 23 This is a schematic diagram of another multi-wheel brake failure braking process scenario provided in an embodiment of this application;

[0096] Figure 24 This is a schematic diagram of a multi-wheel braking failure braking control process provided in an embodiment of this application. Detailed Implementation

[0097] The technical solutions in this application will now be described in conjunction with the accompanying drawings. The detailed descriptions and drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments.

[0098] The braking capability of electric vehicles is a crucial factor affecting their safety. Electromechanical braking systems typically involve braking each of the four wheels of an electric vehicle. When the wheel-end brake of a wheel fails or the wheel speed sensor malfunctions, resulting in brake failure, that wheel loses braking force, and braking relies solely on the normally functioning wheels. This compromises the braking power, preventing the electromechanical braking system from meeting the driver's braking needs. During braking, if one wheel fails to brake, the resulting imbalance in braking torque between the two sides of the vehicle can cause the vehicle to yaw, veer, or even become unstable, leading to serious driving safety issues.

[0099] Based on the above problems, this application provides a control method, braking system and electric vehicle for electric vehicles. When the braking of a certain wheel fails, the drive system outputs reverse torque for braking, and at the same time, the two wheels on the normal axle output braking force, which can effectively brake without obvious yaw, thus improving the safety and stability of electric vehicle braking.

[0100] Figures 1-3 This is a schematic diagram of the architecture of the electric vehicle 10 provided in the embodiments of this application.

[0101] like Figure 1 As shown, the electric vehicle 10 includes a vehicle controller 20, a drive system 50, and a braking system 60. The drive system 50 includes a motor controller 40 and a drive motor 30. The motor controller 40 is used to output current to the drive motor 30 to control the drive motor 30 to output torque to drive the electric vehicle 10. The braking system 60 is used to output braking force to brake the four wheels of the electric vehicle 10.

[0102] like Figure 2 As shown, the braking system 60 includes a brake pedal and four wheel-end brake devices. During the operation of the electric vehicle 10, when braking is required, the driver presses the brake pedal, and the braking system 60 controls the four wheel-end brakes to output braking force to brake the electric vehicle 10.

[0103] In this application, the brake pedal is also referred to as the brake or brake pedal. The opening degree of the brake pedal indicates the amount of braking force required by the driver. The larger the opening degree of the brake pedal, the greater the driver's demand for braking, and the greater the braking force required from the braking system 60. When the electric vehicle 10 is in normal driving, the braking system 60 controls the wheel-end braking devices according to the opening degree of the brake pedal, thereby outputting the braking force indicated by the brake pedal opening degree. The larger the opening degree of the brake pedal, the greater the braking force output by the wheel-end braking devices; the smaller the opening degree of the brake pedal, the smaller the braking force output by the wheel-end braking devices. The braking force output by the braking system 60 varies with the opening degree of the brake pedal.

[0104] For example, the braking system includes four wheel-end braking devices, namely wheel-end braking device 61, wheel-end braking device 62, wheel-end braking device 63, and wheel-end braking device 64. Wheel-end braking device 61 is used to brake wheel 51, wheel-end braking device 62 is used to brake wheel 52, wheel-end braking device 63 is used to brake wheel 53, and wheel-end braking device 64 is used to brake wheel 54.

[0105] In one embodiment, the electric vehicle 10 has a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers 40. In another embodiment, the electric vehicle 10 also has a centralized drive motor architecture, where drive motors for driving two front wheels or two rear wheels are arranged together. There are one or more motor controllers 40. Each motor controller 40 corresponds one-to-one with a drive motor, or one motor controller 40 corresponds to multiple drive motors. The motor controllers 40 control the output torque of one or more drive motors to drive the electric vehicle 10.

[0106] In one embodiment, such as Figure 3 As shown in (a), the electric vehicle 10 has a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers. The electric vehicle 10 is also as follows... Figure 3 The centralized four-drive motor drive architecture shown in (b) has two drive motors for driving the two front wheels or the two rear wheels set together.

[0107] For example, the electric vehicle 10 includes four motor controllers: motor controller 41, motor controller 42, motor controller 43, and motor controller 44. The four motors include drive motor 31, drive motor 32, drive motor 33, and drive motor 34. Motor controller 41 controls drive motor 31 to drive wheel 51, motor controller 42 controls drive motor 32 to drive wheel 52, motor controller 43 controls drive motor 33 to drive wheel 53, and motor controller 44 controls drive motor 34 to drive wheel 54.

[0108] In one embodiment, the electric vehicle 10 still... Figure 3 The centralized drive motor architecture shown in (c) uses one drive motor to drive the two front wheels of the electric vehicle 10, and two drive motors to drive the two rear wheels of the electric vehicle 10 respectively.

[0109] In one embodiment, the various architectures mentioned above can also be combined, for example, the front drive adopts a distributed drive motor architecture and the rear drive adopts a centralized drive motor architecture.

[0110] The electric vehicle 10 also includes an accelerator pedal and a steering wheel. The accelerator pedal is used to instruct the drive system to output drive torque to the wheels of the electric vehicle 10. The steering wheel angle is used to instruct the steering angle of the two front wheels.

[0111] The accelerator pedal in this application is also called the power pedal or throttle pedal. The opening degree of the accelerator pedal indicates the amount of driving force required by the driver. The larger the opening degree of the accelerator pedal, the greater the driver's demand for driving force, and the greater the torque required from the drive motor. The drive system controls the amount of current output to the drive motor according to the opening degree of the accelerator pedal, so that the drive motor outputs the torque indicated by the throttle pedal opening degree. The larger the opening degree of the accelerator pedal, the greater the current, and thus the greater the torque output by the drive motor. The smaller the opening degree of the accelerator pedal, the smaller the current, and thus the smaller the torque output by the drive motor. The driving torque output by the drive system varies with the opening degree of the accelerator pedal.

[0112] In one embodiment, each motor controller 40 is directly connected to the accelerator pedal and controls the output torque of the corresponding drive motor according to the torque signal output by the accelerator pedal.

[0113] In one embodiment, each motor controller 40 is connected to a resolver sensor. The resolver sensor is used to detect the rotational speed of the drive motor 30 controlled by the motor controller 40, and the motor controller 40 is used to receive signals from the resolver sensor. The resolver sensor can accurately detect the position, direction, and speed of the motor rotor, and is responsible for monitoring and extracting the rotational speed of the drive motor. It has a high sampling rate and is directly connected to the motor controller 40, resulting in short signal transmission time and higher stability.

[0114] In one embodiment, the motor controller 40 also obtains the vehicle speed, yaw rate and center of gravity sideslip angle of the electric vehicle 10 from the vehicle controller 20 or other sensors of the electric vehicle 10 through a signal interface.

[0115] Braking system failure 60 includes various scenarios, such as brake failure of a single wheel, brake failure of two wheels, brake failure of three wheels, and brake failure of four wheels.

[0116] The following provides different control methods for electric vehicles 10 based on different failure scenarios.

[0117] The following is combined with Figures 4-7 The control method, braking system 60, and electric vehicle 10 for electric vehicle 10 when single-wheel braking fails according to the embodiments of this application will be described. Figure 4 and Figure 6 This is a signal timing diagram of electric vehicle 10 during operation. Figure 4 and Figure 6 This includes the relationship between the drive system 50, the brake system 60, and the brake pedal opening during the process of controlling the drive system 50 and the brake system 60 to achieve safe braking of the electric vehicle 10 after the brake of one wheel of the electric vehicle 10 fails. Figure 5 and Figure 7 This is a schematic diagram of an electric vehicle 10 during the braking process.

[0118] The control method provided in this application is used to control the drive system 50 and the braking system 60 to achieve safe braking of the electric vehicle 10 after the braking of one wheel fails. When the braking of a certain wheel fails, the drive system 50 outputs reverse torque for braking, while the two wheels on the normal axle output braking force, which can effectively brake without obvious yaw, thereby improving the safety and stability of the braking of the electric vehicle 10.

[0119] like Figure 4 and Figure 6 As shown, the control method includes, during the operation of the electric vehicle 10, before braking, controlling the drive torque output by the drive system 50 to change with the opening of the accelerator pedal, with the direction of the drive torque being the same as the rotational speed direction of the wheels of the electric vehicle 10. During braking when one front wheel of the electric vehicle 10 fails to brake, the control braking system 60 outputs braking force to the two rear wheels of the electric vehicle 10, and controls the drive system 50 to output reverse torque to the two front wheels, with the direction of the reverse torque being opposite to the rotational speed direction of the two front wheels.

[0120] During the operation of electric vehicle 10, before braking begins, brake failure of one wheel has minimal impact. The control drive system 50 outputs the drive torque indicated by the accelerator pedal opening. This drive torque drives the wheel, and its direction is the same as the wheel rotation direction of electric vehicle 10. If brake failure of one wheel of electric vehicle 10 occurs before or after braking begins, the braking system 60 detects the failure and coordinates with the drive system 50 for control. During braking when one wheel of electric vehicle 10 fails, the control braking system 60 outputs braking force to the wheel on the same side and the diagonally opposite wheel of the failed wheel, and the control drive system 50 outputs reverse torque to the failed wheel and the wheel on the same axle. The direction of the reverse torque is opposite to the wheel rotation direction. The left front wheel and right rear wheel of electric vehicle 10 are diagonally opposite wheels, or the right front wheel and left rear wheel are diagonally opposite wheels. The two left wheels or two right wheels of electric vehicle 10 are on the same side, and the two front wheels or two rear wheels of electric vehicle 10 are on the same axle.

[0121] The braking system 60 includes four wheel-end braking devices, each of which outputs braking force to the wheels of the electric vehicle 10. Each of the four wheel-end braking devices corresponds one-to-one with one of the four wheels, and each device outputs braking force separately. Under normal conditions, the four wheel-end braking devices output the braking force indicated by the brake pedal opening. When one wheel fails, the wheel-end braking device used to brake that wheel cannot output braking force. In this case, the braking system 60 outputs braking force to the wheels on the same side as the failed wheel and to the wheels diagonally opposite the failed wheel.

[0122] Specifically, when the left front wheel brake fails, during the braking process of the left front wheel brake failure, the control braking system 60 outputs braking force to both rear wheels, and the control drive system 50 outputs reverse torque to both front wheels. The direction of the reverse torque is opposite to the rotational speed of the two front wheels. When the right front wheel brake fails, during the braking process of the right front wheel brake failure, the control braking system 60 outputs braking force to both rear wheels, and the control drive system 50 outputs reverse torque to both front wheels. The direction of the reverse torque is opposite to the rotational speed of the two front wheels.

[0123] It should be understood that, because it is necessary to control the drive system 50 to output reverse torque to the two front wheels, the drive system 50 includes at least one drive motor 30 for driving the two front wheels. When the two front wheels are driven by the two drive motors 30 respectively, the two drive motors 30 are controlled to simultaneously output reverse torque to brake the two front wheels.

[0124] In another embodiment, such as Figure 6 As shown, the wheel that fails to brake is a rear wheel. During the braking process when the brake of one rear wheel of the electric vehicle 10 fails, the control braking system 60 outputs braking force to the two front wheels of the electric vehicle 10, and controls the drive system 50 to output reverse torque to the two rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels.

[0125] Specifically, when the left rear wheel brake fails, during the braking process of the left rear wheel brake failure, the control braking system 60 outputs braking force to both front wheels, and the control drive system 50 outputs reverse torque to both rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels. When the right rear wheel brake fails, during the braking process of the right rear wheel brake failure, the control braking system 60 outputs braking force to both front wheels, and the control drive system 50 outputs reverse torque to both rear wheels. The direction of the reverse torque is opposite to the rotational speed of the two rear wheels.

[0126] It should be understood that, because it is necessary to control the drive system 50 to output reverse torque to the two rear wheels, the drive system 50 includes at least one drive motor 30 for driving the two rear wheels. When the two rear wheels are driven by two drive motors 30 respectively, the two drive motors 30 are controlled to simultaneously output reverse torque to brake the two rear wheels.

[0127] According to the solution of this application, by controlling the drive system 50 to output reverse torque to the two wheels of the wheel axle where braking has failed to compensate for the failure of braking force, and cooperating with the braking system 60 to output braking force to the two wheels of the normal axle, the electric vehicle 10 is prevented from swaying due to braking of one side of the wheel. At the same time, a larger braking force is output, the braking distance is shortened, and the safety and stability of braking of the electric vehicle 10 are improved.

[0128] In one embodiment, the control method specifically includes controlling the braking force output by the braking system 60 to the two rear wheels of the electric vehicle 10 to vary with the opening of the brake pedal during a braking process in which the front wheel brakes fail, and controlling the reverse torque output by the drive system 50 to vary with the opening of the brake pedal.

[0129] During braking when one wheel's brakes fail, the braking force output by the control braking system 60 to the two rear wheels of the electric vehicle 10 varies with the opening of the brake pedal, and the reverse torque output by the control drive system 50 also varies with the opening of the brake pedal. During the operation of the electric vehicle 10, before braking, the drive torque output by the control drive system 50 varies with the opening of the accelerator pedal. After braking begins and one wheel's brakes fail, the control drive system 50 outputs reverse torque to that wheel and the wheel on the same axle as that wheel. The magnitude of the reverse torque is determined by the opening of the brake pedal and varies with the opening of the brake pedal. The braking force output by the braking system 60 to the two wheels on the same axle that are normally braked varies with the opening of the brake pedal.

[0130] In one embodiment, the control method specifically includes controlling the braking system 60 to output equal braking forces to the two rear wheels of the electric vehicle 10 during a braking process in which the front wheel brakes fail.

[0131] In order to avoid the unequal braking forces generated on both sides of the electric vehicle 10, which would cause the electric vehicle 10 to yaw, the braking force output by the braking system 60 to the two wheels on the same axle should be controlled to be equal, so as not to generate yaw torque.

[0132] In one embodiment, the control method further includes, during a braking process in which the front wheel brakes fail, first controlling the braking system 60 to output braking force to the two rear wheels of the electric vehicle 10, and controlling the drive system 50 to output reverse torque to the two front wheels, and then controlling the braking system 60 to output braking force to the other front wheel.

[0133] During braking when one wheel fails to brake, the reverse torque output by the drive system 50 to that wheel and its coaxial wheel can brake them. However, the maximum braking capacity generated by this reverse torque is less than the maximum braking effect of the braking force output by the braking system 60. Therefore, when the braking force demand is high, the reverse torque output by the drive system 50 to that wheel and its coaxial wheel alone is insufficient to produce a sufficient braking effect. In this case, the braking system 60 outputs braking force to the third wheel that is braking normally, thereby effectively improving the braking capacity.

[0134] Specifically, when the left rear wheel brake fails, during the braking process when the left front wheel brake fails, the braking system 60 is first controlled to output braking force to both rear wheels of the electric vehicle 10, and the drive system 50 is controlled to output reverse torque to both front wheels. Then, the braking system 60 is controlled to output braking force to the right front wheel. When the right front wheel brake fails, during the braking process when the right front wheel brake fails, the braking system 60 is first controlled to output braking force to both rear wheels of the electric vehicle 10, and the drive system 50 is controlled to output reverse torque to both front wheels. Then, the braking system 60 is controlled to output braking force to the left front wheel.

[0135] In another embodiment, the wheel whose braking fails is a rear wheel. During the braking process when the braking of a rear wheel fails, the braking system 60 is first controlled to output braking force to the two front wheels of the electric vehicle 10, and the drive system 50 is controlled to output reverse torque to the two rear wheels. Then, the braking system 60 is controlled to output braking force to the other rear wheel.

[0136] Specifically, when the left rear wheel brake fails, during the braking process of the left rear wheel brake failure, the braking system 60 is controlled to output braking force to both front wheels, and the drive system 50 is controlled to output reverse torque to both rear wheels, and then the braking system 60 is controlled to output braking force to the right rear wheel. When the right rear wheel brake fails, during the braking process of the right rear wheel brake failure, the braking system 60 is controlled to output braking force to both front wheels, and the drive system 50 is controlled to output reverse torque to both rear wheels, and then the braking system 60 is controlled to output braking force to the left rear wheel.

[0137] In one embodiment, the control method specifically includes controlling the braking force output by the braking system 60 to the other front wheel to always be less than the braking force output to either of the two rear wheels during a braking process in which the front wheel brakes fail.

[0138] When the braking system 60 outputs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. This unequal braking force on both sides of the electric vehicle 10 generates yaw torque, causing the electric vehicle 10 to yaw. The greater the braking force output by the braking system 60 to the third wheel that is braking normally, the greater the yaw torque generated by the electric vehicle 10. Therefore, it is necessary to limit the magnitude of the braking force output by the braking system 60 to the third wheel that is braking normally.

[0139] Specifically, during a braking process where one front wheel brake fails, the braking force output by the control braking system 60 to the other front wheel is always less than the braking force output to either of the two rear wheels. Similarly, during a braking process where one rear wheel brake fails, the braking force output by the control braking system 60 to the other rear wheel is always less than the braking force output to either of the two front wheels.

[0140] In one embodiment, the control method specifically includes, during a braking process in which the front wheel brakes fail, when the brake pedal opening is less than a preset opening, controlling the braking system 60 to output zero braking force to the other front wheel. When the brake pedal opening increases to be greater than or equal to the preset opening, controlling the braking system 60 to output greater than zero braking force to the other front wheel.

[0141] After the braking system 60 outputs braking force to the third wheel that is normally braking, this third wheel is the same wheel as the wheel that failed to brake. This wheel will be subjected to the reverse torque and the braking force output by the braking system 60. This will result in the total braking force on the third wheel being greater than the braking force on the wheel that failed to brake. The unequal braking forces generated on both sides of the electric vehicle 10 will produce yaw torque, causing the electric vehicle 10 to yaw. However, in emergency braking situations, the demand for braking force is more urgent. Therefore, it is permissible to generate a controllable range of yaw torque in order to ensure safe braking of the electric vehicle 10.

[0142] The driver's need for emergency braking is determined by the brake pedal opening. If the brake pedal opening is less than the preset opening, the driver does not need emergency braking. In this case, the braking system 60 outputs braking force to the two rear wheels of the electric vehicle 10, and the drive system 50 outputs reverse torque to the two front wheels. The braking force required by the electric vehicle 10 can be compensated by the reverse torque output by the drive system 50. At this time, the braking system 60 does not output braking force to the third wheel that is braking normally. The braking force output by the braking system 60 to the two rear wheels and the reverse torque output by the drive system 50 to the two front wheels are symmetrical, preventing the electric vehicle 10 from yawing. This achieves sufficient braking capacity while maintaining the vehicle's stability during braking. When the brake pedal opening increases to greater than or equal to the preset opening, it is determined that the driver needs emergency braking. In this case, the braking force required by the electric vehicle 10 cannot be fully compensated by the reverse torque output by the drive system 50. Therefore, the braking system 60 outputs braking force to the third wheel that is braking normally, thereby further increasing the braking force and effectively achieving emergency braking.

[0143] In one possible implementation, the preset opening is 80%.

[0144] In one embodiment, the control method specifically includes, during the braking process when the left front wheel brake fails, controlling the braking force output by the braking system 60 to the right front wheel to be zero before the reverse torque output by the drive system 50 to both front wheels increases to a preset torque. After the reverse torque output by the drive system 50 to both front wheels increases to the preset torque, controlling the braking force output by the braking system 60 to the right front wheel to be greater than zero.

[0145] When the braking system 60 outputs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. This unequal braking force on both sides of the electric vehicle 10 generates yaw torque, causing the electric vehicle 10 to yaw. Therefore, in non-essential situations, emergency braking should be prioritized through symmetrical control. Before the reverse torque output by the drive system 50 to the wheel that has failed to brake and its coaxial wheel is less than a preset torque, the braking force can be increased by increasing the reverse torque output without needing to control the braking system 60 to output braking force to the third wheel that is braking normally. Once the reverse torque output by the drive system 50 to the wheel that has failed to brake and its coaxial wheel increases to the preset torque, it will be impossible to increase the braking force by increasing the reverse torque output, thus preventing the braking system 60 from outputting braking force to the third wheel that is braking normally to further improve braking capability.

[0146] In one embodiment, the control method specifically includes, during a braking process in which the front wheel brakes fail, controlling the braking force output by the braking system 60 to the other front wheel to be zero before the reverse torque output by the drive system 50 to the two front wheels increases to a preset torque. After the reverse torque output by the drive system 50 to the two front wheels increases to the preset torque, when the average slip ratio of the two front wheels is less than a preset value, controlling the braking force output by the braking system 60 to the other front wheel to be greater than zero.

[0147] The drive system 50 includes a resolver sensor, through which the rotational speed of the drive motor 30 can be obtained. The angular velocity of the wheels can be calculated from the rotational speed of the drive motor 30 and the transmission ratio of the electric vehicle 10. Further combining this with the wheel radius and the speed of the electric vehicle 10 yields the slip ratio of each wheel. The wheel slip ratio affects the braking effect; when the wheel slip ratio is too high, the wheel slips, and in this case, the wheel cannot generate effective braking force.

[0148] Therefore, when the average slip ratio of the two wheels is greater than the preset value, the braking force output by the control braking system 60 to the normally braking third wheel cannot further improve the braking effect. Only after the reverse torque output by the drive system 50 to the two front wheels increases to the preset torque, and when the average slip ratio of the two front wheels is less than the preset value, does the braking force output by the control braking system 60 to the other front wheel become greater than zero.

[0149] In one embodiment, during the process of controlling the drive system 50 to increase the reverse torque output to the two front wheels to a preset torque, the control method further includes controlling the reverse torque output by the drive system 50 to the two front wheels to vary with the change in the average slip ratio of the two front wheels.

[0150] Since the wheel slip ratio directly affects the braking effect, the drive system 50 regulates the wheel slip ratio by controlling the magnitude of the output reverse torque. Specifically, when the average slip ratio of the two wheels is less than a preset slip ratio, the drive system 50 increases the reverse torque output to the two wheels; when the average slip ratio of the two wheels is greater than the preset slip ratio, the drive system 50 decreases the reverse torque output to the two wheels. This ensures that the reverse torque output by the drive system 50 produces an effective braking effect.

[0151] In one embodiment, the control method further includes, after controlling the braking force output by the braking system 60 to the other front wheel to be greater than zero, controlling the braking force output by the braking system 60 to vary with the yaw angle of the electric vehicle 10.

[0152] When the braking system 60 outputs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. This unequal braking force on both sides of the electric vehicle 10 generates yaw torque, causing the electric vehicle 10 to yaw. The braking force output by the braking system 60 to the third wheel that is braking normally is adjusted according to the yaw angle of the electric vehicle 10, thereby preventing the electric vehicle 10 from yawing excessively and causing loss of control.

[0153] In one embodiment, the control method further includes, after the braking force output by the control braking system 60 to the other front wheel is greater than zero, controlling the braking force output by the control braking system 60 to the other front wheel to vary with the steering wheel angle of the electric vehicle 10.

[0154] After the control braking system 60 outputs braking force to the third wheel that is braking normally, the total braking force on the third wheel will be greater than the braking force on the wheel on the same axle that has failed to brake. The braking forces generated on both sides of the electric vehicle 10 are not equal, which will generate yaw torque and cause the electric vehicle 10 to yaw. At this time, the driver may adjust the steering wheel angle because he perceives the change in the vehicle's posture. When the steering wheel angle changes, the steering system of the electric vehicle 10 will adjust the direction of the wheels, which can offset the yaw torque generated by the electric vehicle 10 to a certain extent. At this time, the control braking system 60 increases the braking force output to the third wheel that is braking normally, and can obtain greater braking force.

[0155] The braking system 60 provided in this application embodiment is used to implement the operation of the braking system 60 in the above control method.

[0156] When the drive system 50 includes only one drive motor 30, and the drive motor 30 is used to drive a wheel that has failed to brake, safe braking control can be performed solely through the braking system 60.

[0157] The following is combined with Figure 8 and Figure 10 Another braking system 60 control method provided in the embodiments of this application will be described. Figure 8 and Figure 10 This is a signal timing diagram of electric vehicle 10 during operation. Figure 8 and Figure 10 This includes the relationship between the braking system 60 and the brake pedal opening during the process of adjusting the braking force output by the braking system 60 to achieve safe braking of the electric vehicle 10 after the braking of one wheel of the electric vehicle 10 fails.

[0158] The braking system 60 is used to control the output of braking force indicated by the brake pedal opening to the four wheels of the electric vehicle 10 before braking, during the operation of the electric vehicle 10. During braking when the left front wheel brake fails, the braking system 60 is controlled to output braking force to the right front wheel and left rear wheel of the electric vehicle 10, and the braking force output to the left rear wheel varies with the yaw angle of the electric vehicle 10.

[0159] When the brakes on one front wheel of the electric vehicle 10 fail, the braking control system 60 outputs braking force to the wheel on the same side and the wheel on the same axle of the failed wheel to achieve diagonal braking. At the same time, the difference in braking force between the two rear wheels is controlled to adjust the yaw angle of the electric vehicle 10.

[0160] Specifically, such as Figure 8 As shown, during the braking process when the left front wheel brake of the electric vehicle 10 fails, the control braking system 60 outputs braking force to the right front wheel and left rear wheel of the electric vehicle 10. When the yaw angle of the electric vehicle 10 increases to the left, the control braking system 60 reduces the braking force output to the left rear wheel. When the yaw angle of the electric vehicle 10 increases to the right, the control braking system 60 increases the braking force output to the left rear wheel.

[0161] Specifically, during the braking process when the right front wheel brake of the electric vehicle 10 fails, the control braking system 60 outputs braking force to the left front wheel and right rear wheel of the electric vehicle 10. When the yaw angle of the electric vehicle 10 increases to the left, the control braking system 60 increases the braking force output to the right rear wheel. When the yaw angle of the electric vehicle 10 increases to the right, the control braking system 60 decreases the braking force output to the right rear wheel.

[0162] In one embodiment, the braking system 60 is further configured to, during braking after the left front wheel brake failure, control the braking force output by the braking system 60 to the right rear wheel of the electric vehicle 10 to be zero when the brake pedal opening increases and is less than a preset opening. When the brake pedal opening increases to a value greater than or equal to the preset opening, control the braking force output by the braking system 60 to the right rear wheel to be greater than zero, and control the braking force output by the drive system 50 to the left rear wheel to be greater than the braking force output to the right rear wheel.

[0163] The brake pedal opening is used to determine whether the driver needs emergency braking. If the brake pedal opening is less than a preset opening, the driver does not need emergency braking, and the braking force output by the control system to the diagonal wheel opposite the wheel that has failed braking is zero. When the brake pedal opening increases to be greater than or equal to the preset opening, it is determined that the driver needs emergency braking. At this time, the control system outputs braking force to the diagonal wheel opposite the wheel that has failed braking, thereby further increasing the braking force and effectively achieving emergency braking.

[0164] In one embodiment, such as Figure 10 As shown, the braking system 60 is also used to, during the braking process when the left rear wheel brake of the electric vehicle 10 fails, first control the braking system 60 to output braking force to the two front wheels of the electric vehicle 10, and then control the braking system 60 to output braking force to the right rear wheel of the electric vehicle 10.

[0165] In one embodiment, the braking system 60 is specifically used to, during the braking process when the left rear wheel brake of the electric vehicle 10 fails, control the braking system 60 to output braking force to the two front wheels of the electric vehicle 10 when the brake pedal opening increases and is less than a preset opening. When the brake pedal opening increases to be greater than or equal to the preset opening, control the braking system 60 to output braking force to the right rear wheel of the electric vehicle 10, and control the braking force output by the braking system 60 to the right rear wheel to vary with the yaw angle of the electric vehicle 10.

[0166] The driver's need for emergency braking is determined by the brake pedal opening. If the brake pedal opening is less than a preset opening, the driver does not need emergency braking. When the brakes on one rear wheel of the electric vehicle 10 fail, the braking system 60 outputs braking force to both front wheels to achieve front axle braking. When the brake pedal opening increases to be greater than or equal to the preset opening, it is determined that the driver needs emergency braking. At this time, the braking system 60 outputs braking force to the other rear wheel, thereby further increasing the braking force and effectively achieving emergency braking. Simultaneously, the difference in braking force between the two rear wheels is controlled to adjust the yaw angle of the electric vehicle 10.

[0167] Specifically, during the braking process when the left rear wheel brake of the electric vehicle 10 fails, the control braking system 60 outputs braking force to the two front wheels of the electric vehicle 10. When the yaw angle of the electric vehicle 10 increases to the left, the control braking system 60 increases the braking force output to the right rear wheel. When the yaw angle of the electric vehicle 10 increases to the right, the control braking system 60 decreases the braking force output to the right rear wheel.

[0168] Specifically, during the braking process when the right rear wheel brake of the electric vehicle 10 fails, the control braking system 60 outputs braking force to the two front wheels of the electric vehicle 10. When the yaw angle of the electric vehicle 10 increases to the left, the control braking system 60 reduces the braking force output to the left rear wheel. When the yaw angle of the electric vehicle 10 increases to the right, the control braking system 60 increases the braking force output to the left rear wheel.

[0169] According to the above-described solution of this application, when one wheel on the front axle fails, the braking system 60 controls the yaw torque by outputting braking force to the diagonally opposite wheels and adjusting the braking force output to the two rear axle wheels according to the yaw angle and acceleration; when one wheel on the rear axle fails, the braking system 60 controls the yaw torque by outputting braking force to the two front axle wheels and adjusting the braking force output to the rear axle wheels according to the yaw angle and acceleration, which can effectively improve braking capability.

[0170] The following is combined with Figures 12-17 The present application describes a control method for an electric vehicle 10 and an electric vehicle 10 when the braking of two wheels fails. Figure 12 , Figure 14 and Figure 16 This is a signal timing diagram of electric vehicle 10 during operation. Figure 12 , Figure 14 and Figure 16 This includes the relationship between the drive system 50, the brake system 60, and the brake pedal opening during the process of controlling the drive system 50 and the brake system 60 to achieve safe braking of the electric vehicle 10 after the brakes of two wheels of the electric vehicle 10 fail. Figure 13 , Figure 15 and Figure 17 This is a schematic diagram of an electric vehicle 10 during the braking process.

[0171] Braking failure of two wheels includes braking failure of two wheels on the same axle, braking failure of two wheels on the same side, and braking failure of two wheels diagonally opposite each other. The two front wheels or two rear wheels of the electric vehicle 10 are on the same axle, the two left wheels or two right wheels of the electric vehicle 10 are on the same side, and the left front wheel and right rear wheel of the electric vehicle 10 are diagonally opposite each other, or the right front wheel and left rear wheel are diagonally opposite each other.

[0172] like Figure 12 and Figure 13 As shown, the control method includes, during the operation of the electric vehicle 10, before braking, controlling the drive torque output by the drive system 50 to change with the opening of the accelerator pedal, with the direction of the drive torque being the same as the rotational speed direction of the wheels of the electric vehicle 10. During braking when the left front wheel and right rear wheel of the electric vehicle 10 fail to brake, the control drive system 50 outputs reverse torque to the two front wheels and two rear wheels of the electric vehicle 10, respectively, with the direction of the reverse torque being opposite to the rotational speed direction of the two front wheels.

[0173] During the operation of electric vehicle 10, before braking begins, brake failure of two wheels has minimal impact. The control drive system 50 outputs the drive torque indicated by the accelerator pedal opening. This drive torque is used to drive the wheels, and its direction is the same as the wheel rotation direction of electric vehicle 10. If brake failure of two wheels of electric vehicle 10 occurs before or after braking begins, the braking system 60 detects the failure and coordinates with the drive system 50 for control. During braking when the left front wheel and right rear wheel of electric vehicle 10 fail to brake, the control drive system 50 outputs reverse torque to the two front wheels and two rear wheels of electric vehicle 10, respectively. The direction of this reverse torque is opposite to the wheel rotation direction.

[0174] When the braking of the left front wheel and the right rear wheel fails, during the braking process when the braking of the left front wheel and the right rear wheel fails, the control drive system 50 outputs reverse torque to the two front wheels and the two rear wheels respectively.

[0175] It should be understood that, because it is necessary to control the drive system 50 to output reverse torque to the two front wheels and the two rear wheels, the drive system 50 includes at least two drive motors 30, with the two front wheels driven by at least one drive motor 30 and the two rear wheels driven by at least one drive motor 30. When the two wheels on the same axle are driven by the two drive motors 30 respectively, the two drive motors 30 are controlled to simultaneously output reverse torque to brake the two wheels on the same axle.

[0176] In another embodiment, when the braking of the right front wheel and the left rear wheel fails, during the braking process when the braking of the right front wheel and the left rear wheel fails, the control drive system 50 outputs reverse torque to the two front wheels and the two rear wheels respectively.

[0177] According to the solution of this application, when the braking of the diagonal wheels fails, the drive system 50 is controlled to output reverse torque to the two front wheels and the two rear wheels to compensate for the failure of braking force, thereby achieving the output of greater braking force, shortening the braking distance, and improving the braking safety and stability of the electric vehicle 10.

[0178] In one embodiment, the control method further includes, during the braking process in which the left front wheel and right rear wheel brakes fail, first controlling the drive system 50 to output reverse torque to the two front wheels and the two rear wheels respectively, and then controlling the braking system 60 to output braking force to the right front wheel and left rear wheel of the electric vehicle 10.

[0179] During braking when the left front wheel and right rear wheel brakes fail, the drive system 50 outputs reverse torque to the two front wheels and two rear wheels. However, the maximum braking capacity generated by the reverse torque is less than the maximum braking effect of the braking force output by the braking system 60. Therefore, when the braking force demand is high, the reverse torque output by the drive system 50 to the two front wheels and two rear wheels alone is insufficient to produce a sufficient braking effect. At this time, the control system 60 outputs braking force to the two wheels that are braking normally, thereby effectively improving the braking capacity by adding diagonal braking.

[0180] Specifically, when the braking of the left front wheel and the right rear wheel fails, during the braking process when the braking of the left front wheel and the right rear wheel fails, the drive system 50 is first controlled to output reverse torque to the two front wheels and the two rear wheels respectively, and then the braking system 60 is controlled to output braking force to the right front wheel and the left rear wheel of the electric vehicle 10.

[0181] In another embodiment, when the braking of the right front wheel and the left rear wheel fails, during the braking process when the braking of the right front wheel and the left rear wheel fails, the drive system 50 is first controlled to output reverse torque to the two front wheels and the two rear wheels respectively, and then the braking system 60 is controlled to output braking force to the left front wheel and the right rear wheel of the electric vehicle 10.

[0182] In one embodiment, the control method specifically includes, during braking when the left front wheel and right rear wheel brakes fail, controlling the braking force output by the braking system 60 to be zero when the opening of the brake pedal of the electric vehicle 10 is less than a preset opening. When the opening of the brake pedal increases to be greater than or equal to the preset opening, controlling the braking system 60 to output braking force to the right front wheel and left rear wheel of the electric vehicle 10.

[0183] The driver's need for emergency braking is determined by the opening of the brake pedal. If the opening of the brake pedal is less than the preset opening, the driver does not need emergency braking. At this time, the drive system 50 outputs reverse torque to the two front wheels and two rear wheels of the electric vehicle 10. The braking force required by the electric vehicle 10 can be compensated by the reverse torque output by the drive system 50. At this time, the braking system 60 does not output braking force to the two wheels that are braking normally.

[0184] When the brake pedal opening increases to a value greater than or equal to a preset opening, it is determined that the driver needs to brake urgently. At this time, the braking force required by the electric vehicle 10 cannot be fully compensated by the reverse torque output by the drive system 50. Therefore, the braking system 60 is controlled to output braking force to the two wheels that are braking normally, and the braking force is further increased by utilizing the braking of the diagonal wheels, effectively achieving emergency braking. This preset opening is pre-calibrated based on actual vehicle experiments and / or model calculations, or is preset by comprehensively considering the overall vehicle requirements and vehicle performance.

[0185] In one embodiment, the control method specifically includes, during braking when the left front wheel and right rear wheel brakes fail, controlling the braking force output by the braking system 60 to be zero before the reverse torque output by the drive system 50 to the two front wheels and two rear wheels increases to a preset torque. After the reverse torque output by the drive system 50 to the two front wheels and two rear wheels increases to the preset torque, controlling the braking system 60 to output braking force to the right front wheel and left rear wheel of the electric vehicle 10.

[0186] During the process of the drive system 50 outputting reverse torque to the two front wheels and two rear wheels, the braking force on both sides of the electric vehicle 10 is equal, preventing yaw during braking and resulting in greater stability. Before the reverse torque output by the drive system 50 to the left front wheel and right rear wheel (which have failed braking) is less than the preset torque, the braking force can be increased by increasing the reverse torque output without needing to control the braking system 60 to output braking force to the two normally braking wheels. Once the reverse torque output by the drive system 50 to the left front wheel and right rear wheel (which have failed braking) increases to the preset torque, it becomes impossible to increase the braking force by increasing the reverse torque output. Therefore, the braking capacity is further improved by controlling the braking system 60 to output braking force to the diagonally opposite normally braking wheels. This preset torque is pre-calibrated based on actual vehicle experiments and / or model calculations, or is pre-set considering overall vehicle requirements and performance.

[0187] In one embodiment, as the reverse torque output by the drive system 50 to the two front wheels and the two rear wheels increases to a preset torque, the control method further includes controlling the reverse torque output by the drive system 50 to the two front wheels to change with the change of the average slip ratio of the two front wheels, and controlling the reverse torque output by the drive system 50 to the two rear wheels to change with the change of the average slip ratio of the two rear wheels.

[0188] The drive system 50 includes a resolver sensor, which transmits the resolver signal to obtain the rotational speed of the drive motor 30. The angular velocity of the wheels can be calculated from the rotational speed of the drive motor 30 and the transmission ratio of the electric vehicle 10. Further combining this with the wheel radius and the speed of the electric vehicle 10 yields the slip ratio of each wheel. The wheel slip ratio affects the braking effect; when the slip ratio is too high, the wheels slip, and effective braking force cannot be generated. Since the wheel slip ratio directly affects the braking effect, the drive system 50 regulates the wheel slip ratio by controlling the magnitude of the output reverse torque. Specifically, when the average slip ratio of the two wheels is less than a preset slip ratio, the drive system 50 increases the reverse torque output to the two wheels; when the average slip ratio of the two wheels is greater than the preset slip ratio, the drive system 50 decreases the reverse torque output to the two wheels. This ensures that the reverse torque output by the drive system 50 produces an effective braking effect.

[0189] In one embodiment, the control method specifically includes controlling the drive system 50 to output a reverse torque to the two front wheels and the two rear wheels in a braking process where the left front wheel and the right rear wheel brakes fail, so as to vary with the opening of the brake pedal, and controlling the reverse torque output by the drive system 50 to vary with the opening of the brake pedal.

[0190] During braking when the left front wheel and right rear wheel brakes fail, the reverse torque output by the control drive system 50 varies with the opening of the brake pedal. During the operation of the electric vehicle 10, before braking, the drive torque output by the control drive system 50 varies with the opening of the accelerator pedal. After braking begins and both wheels fail to brake, the control drive system 50 outputs a reverse torque, the magnitude of which is determined by the opening of the brake pedal and varies with the opening of the brake pedal.

[0191] In one embodiment, the control method specifically includes controlling the reverse torque output by the drive system 50 to the two front wheels to always be greater than the reverse torque output to the two rear wheels during the braking process when the left front wheel and right rear wheel brakes fail, and controlling the braking force output by the braking system 60 to always be greater than the braking force output to the left rear wheel.

[0192] When the electric vehicle 10 brakes, its center of gravity shifts forward, resulting in greater downforce on the two front wheels and increased load on the front wheels, thus providing greater grip and braking force. Conversely, the downforce on the rear wheels decreases, and the load on the rear wheels also decreases. If the two rear wheels are given the same or greater braking force as the two front wheels, the rear wheels will lock up before the front wheels due to insufficient positive pressure. Once the rear wheels lock up, the electric vehicle 10 will lose lateral grip, making it prone to fishtailing or skidding and loss of control. Since the front wheels are steering wheels, even if they lock up, it will only lead to steering failure, and the electric vehicle 10 will slide in a straight line, making it relatively easier to control. Therefore, in controlling the output of reverse torque by the drive system 50 or the output of braking force by the braking system 60, the reverse torque output by the drive system 50 to the front wheels is greater than the reverse torque output to the rear wheels, and the braking force output by the braking system 60 to the front wheels is greater than the braking force output to the rear wheels, resulting in a greater braking force on the two front wheels than on the two rear wheels.

[0193] like Figure 14 and Figure 15 As shown, the control method also includes controlling the drive system 50 to output reverse torque to the two front wheels and the two rear wheels during the braking process when the left front wheel and left rear wheel of the electric vehicle 10 fail to brake, or during the braking process when the right front wheel and right rear wheel of the electric vehicle 10 fail to brake.

[0194] When two wheels on the same side fail, if the braking system 60 outputs braking force, it will cause unequal braking forces on both sides of the electric vehicle 10, resulting in yaw torque and affecting the vehicle's stability. Therefore, the braking system 60 cannot output braking force to the wheels of the electric vehicle 10. At this time, the drive system 50 is controlled to output reverse torque to the two front wheels and the two rear wheels.

[0195] In one embodiment, the control method specifically includes controlling the reverse torque output by the drive system 50 to change with the opening of the brake pedal during the braking process when the left front wheel and left rear wheel of the electric vehicle 10 fail to brake, or during the braking process when the right front wheel and right rear wheel of the electric vehicle 10 fail to brake.

[0196] During braking when the left front and left rear wheels fail to brake, or during braking when the right front and right rear wheels fail to brake, the reverse torque output by the control drive system 50 varies with the opening of the brake pedal. During the operation of the electric vehicle 10, before braking, the drive torque output by the control drive system 50 varies with the opening of the accelerator pedal. After braking begins and the brakes on both wheels on the same side fail, the control drive system 50 outputs a reverse torque, the magnitude of which is determined by the opening of the brake pedal and varies with the opening of the brake pedal.

[0197] In one embodiment, during the process of controlling the drive system 50 to output reverse torque to the two front wheels and the two rear wheels, the control method further includes controlling the sum of the reverse torques output by the drive system 50 to the two front wheels to always be greater than the sum of the reverse torques output to the two rear wheels.

[0198] like Figure 16 and Figure 17 As shown, the control method also includes controlling the braking system 60 to output braking force to the two rear wheels of the electric vehicle 10 during the braking process when the two front wheels of the electric vehicle 10 fail to brake, and controlling the drive system 50 to output reverse torque to the two front wheels.

[0199] When the braking of two wheels on the same axle fails, the drive system 50 outputs reverse torque to the two wheels of the axle with the failed braking, and the braking system 60 outputs braking force to the two wheels of the axle with normal braking, thereby braking.

[0200] In another embodiment, during the braking process when the brakes of the two rear wheels of the electric vehicle 10 fail, the braking system 60 is controlled to output braking force to the two front wheels of the electric vehicle 10, and the drive system 50 is controlled to output reverse torque to the two rear wheels.

[0201] According to the solution of this application, by controlling the drive system 50 to output reverse torque to the two wheels of the wheel axle where braking has failed to compensate for the failure of braking force, and cooperating with the braking system 60 to output braking force to the two wheels of the normal axle, the electric vehicle 10 is prevented from swaying due to braking of one side of the wheel. At the same time, a larger braking force is output, the braking distance is shortened, and the safety and stability of braking of the electric vehicle 10 are improved.

[0202] In one embodiment, the control method specifically includes controlling the braking force output by the braking system 60 to the two rear wheels to vary with the opening of the brake pedal during the braking process when the brakes of the two front wheels fail, and controlling the reverse torque output by the drive system 50 to vary with the opening of the brake pedal.

[0203] During braking when both front wheels fail to brake, the reverse torque output by the control drive system 50 varies with the opening of the brake pedal. During the operation of the electric vehicle 10, before braking, the drive torque output by the control drive system 50 varies with the opening of the accelerator pedal. After braking begins and the brakes of the two wheels on the same axle fail, the control drive system 50 outputs a reverse torque, the magnitude of which is determined by the opening of the brake pedal and varies with the opening of the brake pedal.

[0204] In another embodiment, during braking when the brakes of the two rear wheels fail, the braking force output by the control braking system 60 to the two front wheels varies with the opening of the brake pedal, and the reverse torque output by the control drive system 50 varies with the opening of the brake pedal.

[0205] In one embodiment, during the process of controlling the drive system 50 to output reverse torque to the two front wheels, the control method further includes controlling the reverse torque output by the drive system 50 to the two front wheels to vary with the change in the average slip ratio of the two front wheels.

[0206] The wheel slip ratio affects the braking effect of the wheel. When the wheel slip ratio is too large, the wheel slips, and the wheel cannot generate effective braking force. Since the wheel slip ratio directly affects the braking effect generated by the wheel, the drive system 50 regulates the wheel slip ratio by controlling the magnitude of the output reverse torque.

[0207] In another embodiment, during braking when the brakes of the two rear wheels fail, the braking force output by the control braking system 60 to the two front wheels varies with the opening of the brake pedal, and the reverse torque output by the control drive system 50 to the two rear wheels varies with the average slip ratio of the two rear wheels.

[0208] Figure 18 A flowchart illustrating the control methods for the two wheel braking failures provided in this application is shown.

[0209] like Figure 18 As shown, during operation, signals from the electric vehicle 10 are collected, such as the brake pedal opening, battery charge, yaw rate, and acceleration. When the braking system 60 detects brake failure at two wheels, it determines the positions of the two wheels that have failed to brake. If brake failure occurs at the two wheels on the front axle, the drive system 50 outputs reverse torque to the two wheels on the front axle and the braking system 60 outputs braking force to the two wheels on the rear axle; if brake failure occurs at the two wheels on the rear axle, the drive system 50 outputs reverse torque to the two wheels on the rear axle and the braking system 60 outputs braking force to the two wheels on the front axle; if brake failure occurs at two diagonally opposite wheels, the drive system 50 outputs reverse torque to both the two wheels on the front axle and the two wheels on the rear axle; when emergency braking is required, the braking system 60 outputs braking force to the wheels that are braking normally; if brake failure occurs at two wheels on the same side, the drive system 50 outputs reverse torque to both the two wheels on the front axle and the two wheels on the rear axle.

[0210] According to the above-mentioned solution of this application, when the brakes of two wheels of the electric vehicle 10 fail, the drive system 50 outputs reverse torque to produce an effective braking effect without obvious yaw. In the scenario where the brakes of the diagonal wheels fail, the braking of the normally braking diagonal wheels is superimposed during emergency braking to provide additional braking force, which can effectively improve the safety and braking stability of the electric vehicle 10.

[0211] The following is combined with Figures 19-23 The control method, drive system 50, and electric vehicle 10 for electric vehicle 10 when multiple wheels (e.g., three or four wheels) of the electric vehicle provided in the embodiments of this application fail to brake are described. Figures 19-21 This is a signal timing diagram of electric vehicle 10 during operation. Figure 19 The electric vehicle 10 includes four drive motors 30, each of which drives one wheel; Figure 20 The electric vehicle 10 includes three drive motors 30, two of which are used to drive the two rear wheels respectively, and one drive motor 30 is used to drive the two front wheels. Figure 21 The electric vehicle 10 includes two drive motors 30, one drive motor 30 for driving the two front wheels and the other drive motor 30 for driving the two rear wheels. Figures 19-21 This includes the relationship between the drive torque output by the drive system 50, the reverse torque, the vehicle speed of the electric vehicle 10, and the brake pedal opening. Figure 22 and Figure 23 This is a schematic diagram of an electric vehicle 10 during the braking process.

[0212] like Figures 19-23 As shown, the control method includes controlling the drive system 50 to output drive torque during the driving process of the electric vehicle 10 when the accelerator pedal is depressed and the brake pedal is not depressed. The drive torque output by the drive system 50 is controlled to change with the opening of the accelerator pedal, and the direction of the drive torque is the same as the rotational speed direction of the wheels of the electric vehicle 10. After the accelerator pedal is released and the brake pedal is depressed, the drive system 50 stops outputting drive torque and outputs reverse torque, and the reverse torque changes with the opening of the brake pedal. The direction of the reverse torque is opposite to the rotational speed direction of the wheels.

[0213] The drive system 50 enables the electric vehicle 10 to perform both driving and braking functions by outputting driving torque or reverse torque to its four wheels. During the driving process of the electric vehicle 10, where the accelerator pedal is depressed and the brake pedal is not depressed (i.e., the accelerator pedal opening is greater than zero and the brake pedal opening is equal to zero), the drive system 50 is controlled to output driving torque, and the driving torque output by the drive system 50 varies with the accelerator pedal opening. After the accelerator pedal is released and the brake pedal is depressed (i.e., the accelerator pedal opening is equal to zero and the brake pedal opening is greater than zero), the drive system 50 stops outputting driving torque and instead outputs reverse torque, and the reverse torque output by the drive system 50 varies with the brake pedal opening. The drive system 50 performs the driving function when controlled in response to the accelerator pedal opening and the braking function when controlled in response to the brake pedal opening.

[0214] According to the solution of this application, the drive system 50 can replace the braking system 60 to realize the braking function of the electric vehicle 10, and adjust the output torque to brake in response to the change of the opening of the brake pedal, thus realizing the backup of the braking function at low cost and improving the safety and stability of the electric vehicle 10.

[0215] In one embodiment, the control method is used to control the drive system 50 to achieve braking when the braking system 60 of the electric vehicle 10 fails. Specifically, after the accelerator pedal is released and the brake pedal is depressed, when the braking system 60 of the electric vehicle 10 fails, the control method controls the drive system 50 to stop outputting drive torque and controls the drive system 50 to output reverse torque, and controls the reverse torque to change with the opening of the brake pedal.

[0216] Braking system 60 detects a failure, which means that multiple wheel-end braking devices in the four wheel-end braking devices of braking system 60, used to brake the four wheels, fail to output braking force to their corresponding wheels normally. Braking system 60 failure can include three-wheel braking failure or four-wheel braking failure. Causes of braking failure include actuator failure, brake motor failure, controller failure, and wheel speed sensor failure. When multiple wheels fail to brake, braking system 60 cannot output braking force to those wheels, resulting in a reduction in the total braking force generated by braking system 60, affecting the braking safety and stability of electric vehicle 10.

[0217] When the electric vehicle 10 is in normal operation, the braking system 60 controls the wheel-end braking devices according to the opening of the brake pedal, thereby outputting the braking force indicated by the brake pedal opening. The larger the opening of the brake pedal, the greater the braking force output by the wheel-end braking devices; the smaller the opening of the brake pedal, the smaller the braking force output by the wheel-end braking devices. The braking force output by the braking system 60 varies with the opening of the brake pedal.

[0218] During the operation of the electric vehicle 10, the failure of the braking system 60 before braking begins has minimal impact. The drive system 50 outputs the drive torque indicated by the accelerator pedal opening. This drive torque drives the wheels, and its direction is the same as the rotational speed of the wheels of the electric vehicle 10. If the failure of the braking system 60 occurs before or after braking begins, the electric vehicle 10 will control the drive system 50 after time t2, when the accelerator pedal is released and the brake pedal is depressed. If the braking system 60 fails, the drive system 50 will stop outputting drive torque and output reverse torque, which will vary with the brake pedal opening, thus achieving braking.

[0219] In one embodiment, the control method is further configured to control the drive torque output by the drive system 50 to change with the speed of the electric vehicle 10 when the braking system 60 of the electric vehicle 10 fails during driving when the accelerator pedal is depressed and the brake pedal is not depressed.

[0220] During the driving process, before time t2, when the accelerator pedal of the electric vehicle 10 is depressed and the brake pedal is not depressed, the drive system 50 is controlled to output drive torque and the drive torque output by the drive system 50 is controlled to change with the opening of the accelerator pedal. The direction of the drive torque is the same as the rotational speed direction of the wheels of the electric vehicle 10.

[0221] When the braking system 60 detects a failure, it immediately limits the speed of the entire vehicle. Since a failure of the braking system 60 reduces the braking capability of the electric vehicle 10, the speed of the electric vehicle 10 should be limited for the safety of the occupants to prevent excessive speed from causing loss of control or failure to stop in time. Therefore, when the braking system 60 of the electric vehicle 10 fails, the drive torque output by the control drive system 50 changes with the speed of the electric vehicle 10, thereby limiting the speed and acceleration of the electric vehicle 10.

[0222] In one embodiment, the control method is specifically used to control the drive system 50 to increase the drive torque output as the accelerator pedal opening increases during the driving process of the electric vehicle 10 when the accelerator pedal is depressed and the brake pedal is not depressed, and to control the drive system 50 to decrease the output drive torque when the vehicle speed is less than a preset speed.

[0223] After the braking system 60 of the electric vehicle 10 fails, when the speed of the electric vehicle 10 is less than the preset speed, the drive torque output by the control drive system 50 increases as the opening of the accelerator pedal increases, ensuring a certain acceleration and driving capability for the electric vehicle 10. After time t1, when the speed of the electric vehicle 10 exceeds the preset speed, the speed exceeds the speed limit. At this time, the control drive system 50 reduces the output drive torque to prevent the speed of the electric vehicle 10 from increasing further.

[0224] In one embodiment, the control method specifically includes controlling the sum of the reverse torques output by the drive system 50 to the two front wheels to be greater than the sum of the reverse torques output to the two rear wheels during the process of controlling the drive system 50 to output reverse torques.

[0225] When the electric vehicle 10 brakes, its center of gravity shifts forward, resulting in greater downforce on the two front wheels and increased load on the front wheels, thus providing greater grip and braking force. Conversely, the downforce on the rear wheels decreases, and the load on the rear wheels also decreases. If the two rear wheels were to receive the same or greater braking force as the two front wheels, they would lock up before the front wheels due to insufficient positive pressure. Once the rear wheels lock up, the electric vehicle 10 will lose lateral grip, making it prone to fishtailing or skidding and loss of control. Since the front wheels are steering wheels, even if they lock up, it will only result in steering failure, and the electric vehicle 10 will slide in a straight line, making it relatively easier to control. Therefore, during the process of controlling the reverse torque output of the drive system 50, the sum of the reverse torques output by the drive system 50 to the two front wheels is greater than the sum of the reverse torques output to the two rear wheels, resulting in a greater braking force on the two front wheels than on the two rear wheels.

[0226] In one embodiment, the control method further includes controlling the reverse torque output by the drive system 50 to increase to a preset torque and then maintaining the output preset torque after the accelerator pedal is released and the brake pedal is depressed.

[0227] The reverse torque output of the drive system 50 is limited by the influence of the drive motor 30, the power battery, and the wheel grip. After the driver depresses the brake pedal, the reverse torque output of the drive system 50 is initially controlled to change linearly with the opening of the brake pedal; the larger the brake pedal opening, the larger the reverse torque output of the drive system 50. When the reverse torque output of the drive system 50 increases to a preset torque, the reverse torque that the drive system 50 can output reaches its limit. At this point, the maximum reverse torque that the drive system 50 can output, or the maximum reverse torque that can produce a braking effect, is reached. Then, the drive system 50 is controlled to maintain the output of the preset torque.

[0228] In one embodiment, the control method specifically includes, during the process of controlling the drive system 50 to output reverse torque, controlling the reverse torque output by the drive system 50 to the two front wheels to vary with the change in the average slip ratio of the two front wheels, and controlling the reverse torque output by the drive system 50 to the two rear wheels to vary with the change in the average slip ratio of the two rear wheels.

[0229] The drive system 50 includes a resolver sensor, whose resolver signal can be used to obtain the rotational speed of the drive motor 30. The angular velocity of the wheels can be calculated from the rotational speed of the drive motor 30 and the transmission ratio of the electric vehicle 10. Further combining this with the wheel radius and the speed of the electric vehicle 10 yields the slip ratio of each wheel. The wheel slip ratio affects the braking effect; when the wheel slip ratio is too high, the wheel slips, and the wheel cannot generate effective braking force. Since the wheel slip ratio directly affects the braking effect, the drive system 50 regulates the wheel slip ratio by controlling the magnitude of the output reverse torque.

[0230] The average slip ratio of the two front wheels refers to the average of the slip ratios of the left front wheel and the right front wheel, while the average slip ratio of the two rear wheels refers to the average of the slip ratios of the left rear wheel and the right rear wheel.

[0231] It should be understood that, for example Figure 4 The drive system 50 shown includes four drive motors 30, which individually controls the output reverse torque according to the slip ratio of each wheel. For example... Figure 5 The drive system 50 shown includes three drive motors 30. The drive system 50 controls the reverse torque output to the two front wheels based on the average slip ratio of the two front wheels, and controls the reverse torque output to the left and right rear wheels based on the slip ratio of the two rear wheels, respectively. For example... Figure 6 The drive system 50 shown includes two drive motors 30. The drive system 50 controls the reverse torque output to the two front wheels based on the average slip ratio of the two front wheels, and controls the reverse torque output to the two rear wheels based on the average slip ratio of the two rear wheels.

[0232] In one embodiment, the control method specifically includes, during the process of controlling the drive system 50 to output reverse torque, controlling the drive system 50 to adjust the reverse torque output to the four wheels so that the average slip ratio of the two front wheels is greater than the average slip ratio of the two rear wheels.

[0233] When the average slip ratio of the two front wheels is greater than a first slip ratio, the control drive system 50 reduces the reverse torque output to the two front wheels; when the average slip ratio of the two front wheels is less than the first slip ratio, the control drive system 50 increases the reverse torque output to the two front wheels. When the average slip ratio of the two rear wheels is greater than a second slip ratio, the control drive system 50 reduces the reverse torque output to the two rear wheels; when the average slip ratio of the two rear wheels is less than the second slip ratio, the control drive system 50 increases the reverse torque output to the two rear wheels.

[0234] The target slip ratios for the two front wheels (first slip ratio) and the two rear wheels (second slip ratio) are set separately, with the target slip ratio of the front wheels always being greater than that of the rear wheels. During the output of reverse torque, the drive system 50 controls the magnitude of the reverse torque output to the two front wheels and the two rear wheels based on their average slip ratios, ensuring that the slip ratios of all four wheels are within a suitable range. This allows the reverse torque output by the drive system 50 to produce an effective braking effect. The first and second slip ratios are pre-calibrated based on real-vehicle experiments and / or model calculations, or are pre-set considering overall vehicle requirements and performance.

[0235] In one embodiment, the control method further includes, during the process of controlling the drive system 50 to output reverse torque, when the yaw angle of the electric vehicle 10 is greater than zero, controlling the reverse torque output by the drive system 50 to the left wheel to be unequal to the reverse torque output to the right wheel, and controlling the difference between the reverse torque output by the drive system 50 to the left wheel and the reverse torque output to the right wheel to change with the change of the yaw angle.

[0236] During braking, the electric vehicle 10 may yaw, shifting to one side. If the two wheels on the same axle are driven by two separate drive motors 30, the counter-torques output by the left and right drive motors 30 are unequal based on the yaw angle of the electric vehicle 10. This torque difference between the two drive motors 30 is used to suppress the yaw of the electric vehicle 10. When the yaw angle of the electric vehicle 10 is greater than zero, it indicates that the electric vehicle 10 is yawing. At this time, the counter-torque output by the control drive system 50 to the left wheel is unequal to the counter-torque output to the right wheel, and the difference between the counter-torque output to the left wheel and the counter-torque output to the right wheel varies with the yaw angle. The larger the yaw angle, the greater the difference between the counter-torque output to the left wheel and the counter-torque output to the right wheel.

[0237] In one embodiment, the control method further includes, during the process of controlling the drive system 50 to output reverse torque, before the steering wheel angle of the electric vehicle 10 changes, the electric vehicle 10 deviates to the left, and the drive system 50 reduces the reverse torque output to a left wheel and increases the reverse torque output to a right wheel coaxial with a left wheel.

[0238] During braking, the electric vehicle 10 may yaw. When the steering wheel angle of the electric vehicle 10 does not change but the driving path of the electric vehicle 10 deviates to the left, the control drive system 50 reduces the reverse torque output to one left wheel and increases the reverse torque output to one right wheel that is coaxial with one left wheel. As a result, the reverse torques on both sides of the electric vehicle 10 are unequal, generating yaw torque and suppressing the yaw of the electric vehicle 10 to the left.

[0239] For example, such as Figure 8 As shown, when the steering wheel angle of the electric vehicle 10 remains unchanged and the driving path of the electric vehicle 10 deviates to the left, the control drive system 50 reduces the reverse torque output to the left rear wheel and increases the reverse torque output to the right rear wheel.

[0240] When the steering wheel angle of the electric vehicle 10 remains unchanged but the driving path of the electric vehicle 10 deviates to the right, the control drive system 50 reduces the reverse torque output to one right wheel and increases the reverse torque output to one left wheel that is coaxial with one right wheel. As a result, the reverse torques on both sides of the electric vehicle 10 are unequal, generating yaw torque and suppressing the yaw of the electric vehicle 10 to the right.

[0241] For example, when the steering wheel angle of the electric vehicle 10 remains unchanged but the driving path of the electric vehicle 10 deviates to the right, the control drive system 50 reduces the reverse torque output to the right rear wheel and increases the reverse torque output to the left rear wheel.

[0242] In one embodiment, the control method specifically includes controlling the preset torque output by the drive system 50 to vary with the charge level of the power battery of the electric vehicle 10 after the accelerator pedal is released and the brake pedal is depressed.

[0243] When the drive system 50 outputs reverse torque, it supplies current to the power battery to charge it. Therefore, the power battery's charge directly affects the preset torque that the drive system 50 can output; when the power battery's charge increases, the preset torque that the drive system 50 can output decreases.

[0244] In one embodiment, the control method is specifically used to control the drive system 50 to output a preset torque when the power battery charge of the electric vehicle 10 is less than a preset value, wherein the higher the power battery charge, the lower the preset torque output. When the power battery charge is greater than the preset value, the drive system 50 is controlled to stop outputting reverse torque.

[0245] When the remaining charge of the power battery is low, the battery management system allows the drive system 50 to output reverse torque at maximum power, resulting in a larger preset torque output. When the remaining charge of the power battery is high, in order to protect the power battery from overcharging, the battery management system will strictly limit or even prohibit the current input to the power battery. The electrical energy generated by the drive motor 30 cannot be effectively received by the power battery, and the drive system 50 must reduce the power generation output. In this case, the preset torque output by the drive system 50 is smaller.

[0246] When the power battery's charge level is lower than a preset value, the preset torque output by the drive system 50 decreases as the power battery's charge level increases. When the power battery's charge level is higher than the preset value, the battery management system stops charging the power battery to prevent overcharging and controls the drive system 50 to stop outputting reverse torque.

[0247] Figure 9 A flowchart illustrating the control method provided in this application is shown.

[0248] like Figure 9 As shown, during operation, signals from the electric vehicle 10 are collected, such as the brake pedal opening, battery charge, yaw rate, and acceleration. When the braking system 60 detects a failure, it determines whether the drive system 50 can output reverse torque and the magnitude of the reverse torque based on the battery charge. When the braking system 60 fails, the drive system 50 outputs reverse torque to replace the braking system 60 for braking. Before the reverse torque output by the drive system 50 reaches a preset torque, the reverse torque output by the drive system 50 is linearly related to the brake pedal opening, limiting vehicle acceleration. If the average slip ratio of the two wheels is greater than the target slip ratio, the magnitude of the reverse torque output by the drive system 50 to the two wheels is adjusted.

[0249] For two wheels on the same axle, such as the left front wheel and the right front wheel or the left rear wheel and the right rear wheel, if there are two drive motors 30 driving them separately, the drive system 50 will control the magnitude of the reverse torque output by the left and right drive motors 30 according to the yaw angle and acceleration of the electric vehicle 10, and use the difference in the reverse torque output by the left and right drive motors 30 to suppress yaw.

[0250] According to the solution of this application, when the braking system 60 fails, the vehicle acceleration is limited and the drive system 50 is used to replace the braking system 60 to achieve deceleration or stopping. When the wheel slip ratio increases, the drive system 50 can control the wheel slip ratio to achieve the anti-lock braking system (ABS) function.

[0251] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method for electric vehicles, characterized in that, The control method is used to control the drive system and braking system to achieve safe braking of the electric vehicle after the braking of one wheel of the electric vehicle fails. The control method includes: During the operation of the electric vehicle, before the electric vehicle brakes, the drive torque output by the drive system is controlled to change with the opening of the accelerator pedal, and the direction of the drive torque is the same as the rotational speed direction of the wheels of the electric vehicle. During the braking process when one front wheel of the electric vehicle fails to brake, the braking system is controlled to output braking force to the two rear wheels of the electric vehicle, and the drive system is controlled to output reverse torque to the two front wheels. The direction of the reverse torque is opposite to the rotational speed direction of the two front wheels.

2. The control method according to claim 1, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, the braking force output by the braking system to the two rear wheels of the electric vehicle varies with the opening of the brake pedal, and the reverse torque output by the drive system varies with the opening of the brake pedal.

3. The control method according to claim 1 or 2, characterized in that, The control method further includes: During the braking process when one front wheel brake fails, the braking system is first controlled to output braking force to the two rear wheels of the electric vehicle, and the drive system is controlled to output reverse torque to the two front wheels. Then, the braking system is controlled to output braking force to the other front wheel.

4. The control method according to claim 3, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, if the opening of the brake pedal is less than a preset opening, the braking force output by the braking system to the other front wheel is controlled to be zero. When the opening of the brake pedal increases to be greater than or equal to the preset opening, the braking force output by the braking system to the other front wheel is greater than zero.

5. The control method according to claim 3 or 4, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, before the reverse torque output by the drive system to the two front wheels increases to a preset torque, the braking force output by the braking system to the other front wheel is controlled to be zero. After the reverse torque output by the drive system to the two front wheels increases to a preset torque, the braking force output by the braking system to the other front wheel is controlled to be greater than zero.

6. The control method according to any one of claims 3-5, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, before the reverse torque output by the drive system to the two front wheels increases to a preset torque, the braking force output by the braking system to the other front wheel is controlled to be zero. After the reverse torque output by the drive system to the two front wheels increases to a preset torque, when the average slip ratio of the two front wheels is less than a preset value, the braking force output by the braking system to the other front wheel is controlled to be greater than zero.

7. The control method according to claim 6, characterized in that, In the process of controlling the drive system to increase the reverse torque output to the two front wheels to a preset torque, the control method further includes: The reverse torque output by the drive system to the two front wheels varies with the average slip ratio of the two front wheels.

8. The control method according to any one of claims 3-7, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, the braking system is controlled to output equal braking force to both rear wheels of the electric vehicle.

9. The control method according to any one of claims 3-8, characterized in that, The control method specifically includes: During the braking process when one front wheel brake fails, the braking force output by the braking system to the other front wheel is always less than the braking force output to either of the two rear wheels.

10. The control method according to any one of claims 3-9, characterized in that, The control method further includes: After controlling the braking force output by the braking system to the other front wheel to be greater than zero, the braking force output by the braking system to the other front wheel varies with the yaw angle of the electric vehicle.

11. The control method according to any one of claims 3-9, characterized in that, The control method further includes: After controlling the braking system to output a braking force greater than zero to the other front wheel, the braking force output by the braking system to the other front wheel varies with the steering wheel angle of the electric vehicle.

12. A braking system for an electric vehicle, characterized in that, The braking system is used to adjust the braking force output to the other three wheels of the electric vehicle to achieve safe braking of the electric vehicle after the braking of one wheel fails. The braking system is used to: During the operation of the electric vehicle, before the electric vehicle brakes, the braking system is controlled to output braking force indicated by the opening of the brake pedal to the four wheels of the electric vehicle. During the braking process when the left front wheel brake of the electric vehicle fails, the braking system is controlled to output braking force to the right front wheel and left rear wheel of the electric vehicle, and the braking force output by the braking system to the left rear wheel is controlled to change with the yaw angle of the electric vehicle.

13. The braking system according to claim 12, characterized in that, The braking system is also used for: During the braking process after the left front wheel brake fails, when the brake pedal opening increases and the brake pedal opening is less than a preset opening, the braking force output by the braking system to the right rear wheel of the electric vehicle is controlled to be zero. When the opening of the brake pedal increases to be greater than or equal to the preset opening, the braking force output by the braking system to the right rear wheel is controlled to be greater than zero, and the braking force output by the braking system to the left rear wheel is controlled to be greater than the braking force output to the right rear wheel.

14. The braking system according to claim 12 or 13, characterized in that, The braking system is also used for: During the braking process when the left rear wheel brake of the electric vehicle fails, the drive system is first controlled to output braking force to the two front wheels of the electric vehicle, and then the drive system is controlled to output braking force to the right rear wheel of the electric vehicle.

15. The braking system according to claim 14, characterized in that, The braking system is specifically used for: During the braking process when the left rear wheel brake of the electric vehicle fails, when the brake pedal opening increases and the brake pedal opening is less than a preset opening, the drive system is controlled to output braking force to the two front wheels of the electric vehicle. When the opening of the brake pedal increases to be greater than or equal to the preset opening, the drive system is controlled to output braking force to the right rear wheel of the electric vehicle, and the torque output by the drive system to the right rear wheel is controlled to change with the yaw angle of the electric vehicle.

16. An electric vehicle, characterized in that, The electric vehicle includes a brake pedal, an accelerator pedal, a braking system, a drive system, and four wheels. The opening of the brake pedal is used to indicate that the braking system outputs braking force, and the accelerator pedal is used to indicate that the drive system outputs drive torque. The braking system and the drive system are used to perform the control method as described in any one of claims 1-11.

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