An Active Braking Control Method and System for Electric Vehicles Based on Obstacle Distance

Abstract

The present invention provides an active braking control method and system for an electric vehicle based on the distance to an obstacle. First, radar sensors are arranged on the front and rear bumpers of the vehicle to measure the distance between the vehicle and the obstacles in the traffic environment, and the measured distance is compared with a preset safe distance threshold to determine whether the vehicle needs to brake. When braking is required, the torque to be corrected required for vehicle braking is calculated based on the current speed of the vehicle and the measured distance. Then, a slip ratio differential equation and a sliding surface differential equation are designed, and the torque to be corrected is corrected according to the slip ratio differential equation and the sliding surface differential equation to obtain the corrected target torque. Finally, the corrected target torque is distributed to the front and rear wheels of the vehicle for braking torque distribution to complete the braking control of the vehicle. The present invention intelligently distributes the braking torque through a torque adaptive control algorithm, effectively ensuring the personal safety of the driver and other personnel in the traffic scenario.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle control, and particularly relates to an active braking control method and system for an electric vehicle based on obstacle distance. Background Art

[0002] Compared with traditional vehicles, electric vehicles have the advantages of zero emissions, simple structure, ultra-low noise, high energy efficiency, easy realization of stepless speed change, and relatively high economy. Although electric vehicles have many advantages, they have not become the mainstream means of transportation because their weaknesses and limitations are also obvious, specifically including long charging time, short driving range, inability to quickly achieve energy replenishment, and expensive power batteries. In the research of electric vehicles, how to improve the energy utilization rate is a very crucial issue in all research.

[0003] Research on braking energy recovery is very meaningful for improving the energy utilization rate of electric vehicles. During the braking process of a vehicle, the kinetic energy of the vehicle is converted into heat energy through friction and dissipated, resulting in a large amount of energy being wasted. Research shows that under several typical urban driving conditions, the energy dissipated by friction braking during vehicle braking accounts for about 50% of the total driving energy of the vehicle.

[0004] Braking energy recovery of an electric vehicle means that during the braking or deceleration process of the electric vehicle, the drive motor should be in the operating state of a generator at this time, so that the kinetic energy during the vehicle's driving can be converted into electrical energy and stored in the energy storage device (battery or supercapacitor). In the energy storage device, the electrical energy is converted into chemical energy for storage, and the purpose is to use the reverse torque generated by the motor to provide a braking torque to decelerate and brake the vehicle. This is crucial for improving the energy utilization efficiency of the vehicle and extending the driving distance of the electric vehicle. Relevant foreign research shows that under the operating conditions of urban driving with frequent braking and starting, effectively recovering braking energy can reduce the energy consumption of an electric vehicle by about 15% and extend the driving distance of the electric vehicle by 10% - 30%.

[0005] The core components of the electric vehicle power system are the motor and the battery. During the process of driving an electric vehicle, the battery on the electric vehicle supplies power to the drive motor, and the drive motor drives the vehicle through the transmission mechanism; during the braking process, the drive motor is converted into a generator for power generation, and a part of the kinetic energy during the driving process is converted into electrical energy and stored in the battery to achieve the purpose of energy conservation and efficiency improvement. When braking when the speed of the drive motor is greater than the base speed, the drive motor will supply the electrical energy converted from the energy to the battery and provide a braking torque. This situation belongs to the downhill situation; when decelerating and braking when the speed of the drive motor is less than the base speed, the drive motor is in the generator state, and the braking electrical energy can only be charged to the battery when the conversion voltage is higher than the battery voltage.

[0006] The existing electric vehicle braking systems mainly rely on the driver to manually step on the brake pedal according to the actual traffic scenario during normal driving. At this time, the control unit obtains relevant information on the braking intensity based on the pedal depression speed signal. Then, according to the set control strategy, the control unit intelligently distributes the front and rear axle braking forces, frictional braking forces, and regenerative braking forces to achieve the braking operation of the electric vehicle. However, if the driver fails to perform the braking operation in a timely manner according to the actual traffic scenario due to certain reasons, it will pose a hazard to the driver and even other people in the traffic scenario, and in severe cases, it may endanger lives. Summary of the Invention

[0007] To solve the problems in the prior art that the driver cannot perform the braking operation in a timely manner according to the actual traffic scenario, resulting in the control unit not receiving the brake pedal speed signal in time for braking operation, which may cause harm to the driver and even other people in the traffic scenario, the present invention provides an active braking control method for electric vehicles based on the obstacle distance. By combining millimeter-wave radar and ultrasonic radar with a torque adaptive control algorithm, a specific calculation method is used to correct the target torque, and the corrected target torque is combined with the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle. There is no need for the driver to perform the braking operation manually, effectively ensuring the personal safety of the driver and other people in the traffic scenario, and at the same time improving the energy utilization efficiency of electric vehicles. The present invention also relates to an active braking control system for electric vehicles based on the obstacle distance.

[0008] The technical solution of the present invention is as follows:

[0009] An active braking control method for electric vehicles based on the obstacle distance, characterized by comprising the following steps:

[0010] S1: Arrange radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle and obstacles in the traffic environment during driving;

[0011] S2: Compare the distance between the vehicle and the obstacle with a preset safety distance threshold to determine whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than the preset safety distance threshold, it is determined that the vehicle needs to brake; if the distance between the vehicle and the obstacle is greater than or equal to the safety distance threshold, it is determined that the vehicle does not need to brake;

[0012] S3: When braking is required, calculate the torque to be corrected for vehicle braking based on the current vehicle speed and the distance between the vehicle and the obstacle. Then, using the adaptive control algorithm, calculate the tire slip ratio based on the current vehicle speed, wheel radius, and wheel speed. Differentiate the slip ratio to obtain the slip ratio differential equation. Then, based on the error equation formed by the slip ratio and the desired slip ratio, obtain the sliding mode surface equation. Differentiate the sliding mode surface equation to obtain the sliding mode surface differential equation. Correct the torque to be corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque;

[0013] S4: According to the vehicle speed and the battery SOC, use the braking force distribution curve to distribute the corrected target torque to the front and rear wheels of the vehicle for braking torque distribution, so as to complete the braking control of the vehicle.

[0014] Preferably, in step S4, the braking torque distribution is to judge and adopt different braking force distribution curves to distribute the braking torques of the front and rear wheels of the vehicle according to the comparison results of the vehicle speed and the power battery SOC with the preset thresholds,

[0015] When the vehicle speed is less than the preset vehicle speed threshold or the power battery SOC is less than the preset SOC threshold, use the conventional braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle;

[0016] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the power battery SOC is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is not triggered, use the economic braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle;

[0017] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the power battery SOC is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is triggered, use the ideal braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle.

[0018] Preferably, in step S2, during the process of braking the vehicle, when the radar sensor detects that the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the radar controller will continuously send out braking signals to control the motor to run faster until the front and rear wheels stop rotating, so that the vehicle reaches a stop state;

[0019] When the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the preset safety distance threshold, the radar controller sends out a brake release signal to control the motor to reverse and release the brake, and the vehicle resumes normal driving.

[0020] Preferably, in step S1, the radar sensor includes a millimeter-wave radar sensor and an ultrasonic radar sensor.

[0021] Preferably, in the step S2, when the distance between the vehicle and the obstacle is less than a preset safety distance threshold, the motor is also started to recover the braking energy in the form of a generator.

[0022] An active braking control system for an electric vehicle based on the distance to an obstacle, characterized by comprising a distance measurement module, a braking judgment module, a torque correction module, and a braking torque distribution module that are connected in sequence.

[0023] The distance measurement module arranges radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle during driving and the obstacles in the traffic environment.

[0024] The braking judgment module compares the distance between the vehicle and the obstacle with a preset safety distance threshold to judge whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than the preset safety distance threshold, it is judged that the vehicle needs to brake. If the distance between the vehicle and the obstacle is greater than or equal to the safety distance threshold, it is judged that the vehicle does not need to brake.

[0025] The torque correction module, when braking is required, calculates the torque to be corrected required for vehicle braking according to the current vehicle speed and the distance between the vehicle and the obstacle, and uses an adaptive control algorithm to calculate the tire slip ratio according to the current vehicle speed, wheel radius, and wheel speed. The slip ratio is differentiated to obtain a slip ratio differential equation, and then a sliding mode surface equation is obtained according to the error equation composed of the slip ratio and the desired slip ratio. The sliding mode surface equation is differentiated to obtain a sliding mode surface differential equation, and the torque to be corrected is corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque.

[0026] The braking torque distribution module distributes the corrected target torque to the front and rear wheels of the vehicle according to the vehicle speed and the battery SOC by using a braking force distribution curve to complete the braking control of the vehicle.

[0027] Preferably, in the braking torque distribution module, the braking torque distribution judges whether to use different braking force distribution curves to distribute the braking torques of the front and rear wheels of the vehicle according to the comparison results of the vehicle speed and the battery power SOC with preset thresholds.

[0028] When the vehicle speed is less than a preset vehicle speed threshold or the battery power SOC is less than a preset SOC threshold, a conventional braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle.

[0029] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and meanwhile when the anti-lock braking system is not triggered, the economic braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle;

[0030] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and meanwhile when the anti-lock braking system is triggered, the ideal braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle.

[0031] Preferably, during the process of braking the vehicle, when the radar sensor detects that the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the radar controller continuously sends out braking signals to control the motor to run faster until the front and rear wheels stop rotating, so that the vehicle reaches a stopped state to complete the braking process;

[0032] When the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the preset safety distance threshold, the radar controller sends out a braking release signal to control the motor to reverse and release the braking, and the vehicle resumes normal driving.

[0033] Preferably, the radar sensor includes a millimeter-wave radar sensor and an ultrasonic radar sensor.

[0034] Preferably, in the braking judgment module, when the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the motor is also started to recover braking energy in the form of a generator.

[0035] The beneficial effects of the present invention are:

[0036] The present invention provides an active braking control method for electric vehicles based on the distance to obstacles. First, millimeter-wave radars and ultrasonic radars are arranged on the front and rear bumpers of the vehicle to measure the distance between the electric vehicle and the obstacles in the traffic environment during driving. Then, the distance between the vehicle and the obstacles is compared with a preset safety distance threshold to determine whether the vehicle needs to brake. If the distance between the vehicle and the obstacles is less than the preset safety distance threshold, it is determined that the vehicle needs to brake, and the control unit will start the motor to perform braking energy recovery work in the form of a generator, improving the energy utilization efficiency of the electric vehicle. When braking is required, the torque to be corrected required for vehicle braking is calculated based on the current speed of the vehicle and the distance between the vehicle and the obstacles. A specific calculation method (adaptive control algorithm) is used to correct the torque to be corrected to obtain the corrected target torque, realizing the adaptive control of the braking torque of the electric vehicle. Finally, the corrected target torque is combined with the braking force distribution curve, and the braking torque is distributed to the front and rear wheels of the vehicle according to the vehicle speed and the battery SOC to complete the braking control of the vehicle, ensuring the braking stability and braking effect of the electric vehicle and effectively solving the safety problem during vehicle braking. This method intelligently distributes the braking torque through the torque adaptive control algorithm. On the one hand, it can force the vehicle to decelerate and ultimately achieve the goal of stopping the electric vehicle without the driver having to perform braking operations manually, effectively protecting the personal safety of the driver and other people in the traffic scenario. On the other hand, the kinetic energy of the vehicle drives the generator to convert the kinetic energy of the vehicle into electrical energy and store it in the energy storage device. When the vehicle starts or accelerates, the motor works in the form of a motor to convert the electrical energy stored in the energy storage device into mechanical energy for the vehicle, thus effectively improving the energy utilization efficiency of the electric vehicle.

[0037] The present invention also relates to an active braking control system for electric vehicles based on the distance to obstacles. This system corresponds to the above-mentioned active braking control method for electric vehicles based on the distance to obstacles and can be understood as a system for implementing the above-mentioned active braking control method for electric vehicles based on the distance to obstacles. It includes a distance measurement module, a braking judgment module, a torque correction module, and a braking torque distribution module connected in sequence. Each module works in coordination with each other, using torque adaptive control to intelligently distribute the braking torque, without the driver having to perform braking operations manually, effectively solving problems such as the driver being unable to perform braking operations in a timely manner according to the actual traffic scenario, resulting in the control unit not being able to receive the braking pedal speed signal in a timely manner for braking operations, causing harm to the driver and even other people in the traffic scenario. Description of the Drawings

[0038] Figure 1 is a flowchart of the active braking control method for electric vehicles based on the distance to obstacles of the present invention.

[0039] Figure 2 It is a schematic diagram of the braking force distribution curve of the present invention.

[0040] Figure 3 It is the working principle diagram of the braking torque distribution of the present invention. Specific embodiments

[0041] The present invention will be described below with reference to the accompanying drawings.

[0042] The present invention relates to an active braking control method for an electric vehicle based on the distance to an obstacle. The flowchart of this method is as Figure 1 shown, and successively includes the following steps:

[0043] S1. Arrange radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle during driving and the obstacles in the traffic environment. This step can also be called the distance measurement step. Specifically, the millimeter-wave radar realizes the task of detecting targets by emitting electromagnetic waves with a wavelength in the millimeter range. The electromagnetic waves are reflected by the detected targets and received by the receiving device, and the distance and relative speed of the measured target are obtained by analyzing the information in the echo. The ultrasonic radar emits ultrasonic waves through the ultrasonic wave emitting device. Using the known propagation speed of ultrasonic waves in the air, it measures the time when the ultrasonic wave encounters an obstacle and reflects back after being emitted, and calculates the actual distance from the emission point to the obstacle according to the time difference between emission and reception.

[0044] S2. After the radar obtains the distance information between the vehicle and the obstacle, the control unit in the electric vehicle will compare the distance between the vehicle and the obstacle with a pre-set safety distance threshold to determine whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than or equal to the safety distance threshold, it is determined that the vehicle needs to brake. If the distance between the vehicle and the obstacle is greater than the safety distance threshold, it is determined that the vehicle does not need to brake. This step can also be called the braking judgment step.

[0045] Among them, the safety distance refers to the distance that the electric vehicle travels from that speed to a stop after starting to brake when driving at different speeds. According to relevant research, the safety distance K of the electric vehicle is judged according to the following formula:

[0046] K = M 0 + M 1 (1)

[0047] In the above formula, M 0 is the reserved distance, generally a fixed value; M 1 is the braking distance.

[0048] The control unit of the electric vehicle obtains the corresponding safe distance based on the vehicle speed, compares this safe distance with the distance between the vehicle and the obstacle measured by the radar sensor, and determines whether the vehicle needs to brake. When the distance between the vehicle and the obstacle measured by the radar sensor is less than the safe distance, it is determined that the vehicle needs to brake. At this time, the radar controller will give a braking signal, and the motor of the braking mechanical device rotates to brake, and the vehicle decelerates. Among them, during the braking process, the radar sensor will continuously compare the distance between the vehicle and the obstacle with the safe distance.

[0049] When the radar sensor detects that the distance between the vehicle and the obstacle is still less than the safe distance during the deceleration process, the radar controller will give a signal to continue braking, and the motor of the braking mechanical device will further accelerate its operation until the front and rear wheels stop rotating, that is, the vehicle speed is 0, reaching a stop state.

[0050] When the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the safe distance during the deceleration process, the radar controller will give a signal to release the brake, the motor rotates in reverse to release the electric brake, and the electric brake pedal returns to the normal state, and the vehicle resumes normal driving.

[0051] Preferably, when the distance between the vehicle and the obstacle is less than the preset safe distance threshold, the motor is also started to recover the braking energy in the form of a generator. During the braking process of the electric vehicle, part of the kinetic energy of the vehicle is converted into braking energy, which is transmitted from the wheels through the transmission system to the motor, driving the motor to generate electricity, and the generated electric energy is stored by the energy storage device. When the vehicle starts or accelerates, the motor converts the electric energy stored in the energy storage device into mechanical energy to the vehicle in the form of a motor, thereby improving the energy utilization efficiency of the electric vehicle.

[0052] S3: When braking is required, calculate the torque to be corrected required for vehicle braking according to the current vehicle speed and the distance between the vehicle and the obstacle, and use the adaptive control algorithm to calculate the tire slip ratio according to the current vehicle speed, wheel radius and wheel speed, perform differential processing on the slip ratio to obtain the slip ratio differential equation, then obtain the sliding mode surface equation according to the error equation composed of the slip ratio and the desired slip ratio, perform differential processing on the sliding mode surface equation to obtain the sliding mode surface differential equation, and correct the torque to be corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque. This step can also be called the torque correction step.

[0053] Specifically, when braking is required, first calculate the torque to be corrected for vehicle braking according to the current vehicle speed and the distance between the vehicle and the obstacle using an adaptive control algorithm. This torque is the optimal torque to ensure safety and recovery efficiency during braking. However, there is an error in this torque at this time, and the error needs to be corrected. During the braking process of an electric vehicle, part of the vehicle's kinetic energy is converted into braking energy, which is transmitted from the wheels through the transmission system to the motor, driving the motor to generate electricity, and the generated electric energy is stored by the energy storage device. According to vehicle dynamics theory, the vehicle driving equation is:

[0054] F t = F f + F w + F i + F j (2)

[0055] In the above formula, F t is the driving force acting on the wheels; F f is the rolling resistance; F w is the air resistance, F i is the gradient resistance; F j is the acceleration resistance.

[0056] When the vehicle brakes, the acceleration resistance F j becomes the braking force F b for vehicle driving, then the vehicle driving equation changes to:

[0057] F t = F f + F w + F i + F b (3)

[0058] Ignoring the rolling resistance F f couple moment, air resistance F w and the inertia couple moment generated during the deceleration of the rotating mass, the ground normal reaction forces on the front and rear axles of the vehicle during braking are:

[0059]

[0060] When the electric vehicle brakes on a road surface with different adhesion coefficients, when both the front and rear wheels are locked, at this time, the ground normal reaction forces acting on the front and rear wheels by the ground are:

[0061]

[0062] In the above formula, G is the gravity of the vehicle; F z1 is the ground normal reaction force on the front wheel; F z2 is the ground normal reaction force on the rear wheel; h gis the center of gravity height; a is the distance from the center of mass to the front axle; b is the distance from the center of mass to the rear axle; z is the braking intensity, and L is the wheelbase.

[0063] Meanwhile, during the vehicle braking process, the slip ratio λ of the tire is calculated according to the following formula:

[0064]

[0065] In the above formula, v is the vehicle speed; R is the wheel radius; w represents the wheel rotational speed; and λ is the slip ratio of the tire.

[0066] During braking, the slip ratio largely determines the target torque required for the vehicle braking process. To calculate the torque to be corrected more accurately, the following differential equation related to the slip ratio is designed by differentiating the slip ratio and using an adaptive control algorithm:

[0067]

[0068] In the above formula, w v is the linear speed of the wheel, w w is the angular speed of the wheel, J is the moment of inertia, f v is the speed factor, f a is the acceleration factor, T b is the target braking torque acting on the wheel, m is the vehicle mass, and g is the acceleration due to gravity.

[0069] The purpose of the adaptive control of the electric vehicle braking torque is to make the slip ratio close to the target torque value. The specific error equation is as follows:

[0070] e = λ - λ d (8)

[0071] In the above formula, e is the slip ratio error, λ is the slip ratio of the tire, and λ d is the desired slip ratio of the tire.

[0072] Since the torque adaptive control may include unexpected disturbances such as ice and snow sliding in the actual control process, to solve the problem of unexpected disturbances, the following proportional integral sliding mode surface s is proposed according to Equation (8):

[0073] s = e + α∫edt (9)

[0074] In the above formula, α is the sliding mode reaching law coefficient.

[0075] By differentiating Equation (9), the following formula can be obtained:

[0076]

[0077] Substituting Equation (7) into Equation (10) gives:

[0078]

[0079] To meet the requirements of precise adaptive control, the differential equation of the sliding mode surface is designed as follows:

[0080]

[0081] In the above formula, β is the sliding mode parameter and τ is the time constant.

[0082] Therefore, according to equations (11) and (12), the torque to be corrected required for the electric vehicle braking can be corrected to obtain the corrected target torque. Among them, the corrected target torque T b is calculated according to the following formula:

[0083]

[0084] In addition, to prove the stability of the designed sliding mode surface s, the Lyapunov function is selected for verification as follows:

[0085]

[0086] Derive equation (14), and the result is as follows:

[0087]

[0088] Among them:

[0089]

[0090] In the above formula, is the road surface adhesion coefficient, sgn is the sign function, and else represents other cases.

[0091] In this case, the torque adaptive control system is stable. Therefore, during the actual driving process of the electric vehicle, the vehicle control unit can estimate the road conditions according to the designed adaptive law through the wheel speed.

[0092] S4. After obtaining the corrected target torque, according to the vehicle speed and the battery SOC, the corrected target torque is distributed to the front and rear wheels of the vehicle by using the braking force distribution curve for braking torque distribution to complete the braking control of the vehicle. This step can also be called the braking torque distribution module.

[0093] Specifically, when performing vehicle braking torque distribution, the most important thing is to solve the safety problem during vehicle braking. To ensure the braking stability and braking effect of the electric vehicle, the braking method of the Economic Commission of Europe (ECE) can be expressed as follows:

[0094]

[0095] In the above formula, G is the total weight of the electric vehicle, L is the vehicle length, z is the braking intensity, h is the height of the center of mass, and F F is the braking force of the front wheels, and F R is the braking force of the rear wheels. During the braking process of the electric vehicle, the locking of the front or rear wheels will make the vehicle unstable. If the adhesion coefficient is close to the braking intensity, the ground adhesion condition will be more fully utilized. According to automotive theory, the ideal braking force distribution method can be expressed as follows:

[0096]

[0097] In the above formula, a is the distance from the vehicle's center of mass to the center line of the front axle, and b is the distance from the vehicle's center of mass to the center line of the rear axle.

[0098] During the actual driving process of the electric vehicle, the braking torque of the front and rear wheels of the vehicle can be judged and allocated according to the comparison results of the vehicle speed and the SOC of the power battery with the preset thresholds. Among them, the braking force distribution curves include the I curve, the ECE curve, and the β curve. As Figure 2 shown, the I curve is the ideal braking force distribution curve, which refers to the torque distribution strategy of the front and rear wheels when they lock simultaneously. It can ensure safety and comfort to a great extent, but it is not the best choice for energy recovery. The ECE curve is the economic braking force distribution curve, which is the best choice for braking energy recovery because it allows the front wheels to provide as much torque as possible, but the comfort is average. As for the β curve, it is the conventional braking force distribution curve, which is the most commonly used torque distribution method in current vehicles, that is, the front and rear wheels are distributed proportionally. Compared with the first two torque distribution strategies, the β curve is simpler, and its effectiveness is a compromise between the I curve and the ECE curve.

[0099] The specific distribution method is as Figure 3 shown. When the vehicle speed v is less than the preset vehicle speed threshold v 0 , or when the vehicle speed v is greater than or equal to the preset vehicle speed threshold v 0 and the SOC of the power battery is less than the preset SOC threshold SOC 0 , at this time, the first braking mode is selected, that is, the β curve is used to distribute the braking torque of the front and rear wheels of the vehicle;

[0100] When the vehicle speed v is greater than or equal to the preset vehicle speed threshold v 0 and the SOC of the power battery is greater than or equal to the preset SOC threshold SOC 0 , and at the same time when the Antilock Brake System (ABS) is not triggered, at this time, the second braking mode is selected, that is, the ECE curve is used to distribute the braking torque of the front and rear wheels of the vehicle;

[0101] When the vehicle speed v is greater than or equal to the preset vehicle speed threshold v 0 and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold SOC 0 and at the same time when the anti-lock braking system (ABS) is triggered, the third braking mode is selected at this time, that is, the I curve is used to distribute the braking torques of the front and rear wheels of the vehicle.

[0102] The present invention also relates to an active braking control system for an electric vehicle based on the obstacle distance. This system corresponds to the above-mentioned active braking control method for an electric vehicle based on the obstacle distance and can be understood as a system for implementing the above method. The system includes a distance measurement module, a braking judgment module, a torque correction module, and a braking torque distribution module that are connected in sequence. Specifically,

[0103] The distance measurement module arranges radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle and obstacles in the traffic environment during driving;

[0104] The braking judgment module compares the distance between the vehicle and the obstacle with a preset safety distance threshold to judge whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than the preset safety distance threshold, it is judged that the vehicle needs to brake;

[0105] The torque correction module, when braking is required, calculates the torque to be corrected required for vehicle braking according to the current vehicle speed and the distance between the vehicle and the obstacle, and uses an adaptive control algorithm to calculate the tire slip ratio according to the current vehicle speed, wheel radius, and wheel speed. The slip ratio is differentiated to obtain the slip ratio differential equation, and then the sliding mode surface equation is obtained according to the error equation composed of the slip ratio and the desired slip ratio. The sliding mode surface equation is differentiated to obtain the sliding mode surface differential equation, and the torque to be corrected is corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque, so as to realize the adaptive control of the braking torque of the electric vehicle;

[0106] The braking torque distribution module distributes the corrected target torque to the front and rear wheels of the vehicle according to the vehicle speed and the battery SOC by using a braking force distribution curve to complete the braking control of the vehicle.

[0107] Preferably, in the braking torque distribution module, the braking torque distribution is to judge whether to use different braking force distribution curves to distribute the braking torques of the front and rear wheels of the vehicle according to the comparison results of the vehicle speed and the SOC of the power battery with the preset thresholds.

[0108] When the vehicle speed is less than the preset vehicle speed threshold or the SOC of the power battery is less than the preset SOC threshold, the conventional braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle;

[0109] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is not triggered, the economic braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle;

[0110] When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is triggered, the ideal braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle.

[0111] Preferably, during the process of braking the vehicle by the braking judgment module, when the radar sensor detects that the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the radar controller will continuously send out braking signals to control the motor to run faster until the front and rear wheels stop rotating, so that the vehicle reaches a stop state to complete the braking process;

[0112] When the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the preset safety distance threshold, the radar controller sends out a braking release signal to control the motor to reverse and release the braking, and the vehicle resumes normal driving.

[0113] Preferably, the radar sensor includes a millimeter-wave radar sensor and an ultrasonic radar sensor.

[0114] Preferably, in the braking judgment module, when the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the motor is also started to recover the braking energy in the form of a generator.

[0115] The present invention provides an objective and scientific active braking control method and system for electric vehicles based on the distance to obstacles. The braking torque is intelligently distributed through a torque adaptive control algorithm, without the need for the driver to perform braking operations manually, effectively ensuring the personal safety of the driver and other personnel in the traffic scenario, and at the same time greatly improving the energy utilization efficiency of electric vehicles.

[0116] It should be noted that the above specific embodiments can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. Therefore, although this specification has described the present invention in detail with reference to the drawings and embodiments, those skilled in the art should understand that the present invention can still be modified or equivalently replaced. In short, all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered by the protection scope of the patent of the present invention.

Claims

1. An active braking control method for electric vehicles based on the distance to obstacles, characterized in that, it includes the following steps: S1: Arrange radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle during driving and the obstacles in the traffic environment; S2: Compare the distance between the vehicle and the obstacle with a preset safety distance threshold to determine whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than the preset safety distance threshold, it is determined that the vehicle needs to brake. If the distance between the vehicle and the obstacle is greater than or equal to the safety distance threshold, it is determined that the vehicle does not need to brake; S3: When braking is required, calculate the torque to be corrected required for vehicle braking based on the current vehicle speed and the distance between the vehicle and the obstacle, and use the adaptive control algorithm to calculate the tire slip ratio based on the current vehicle speed, wheel radius, and wheel speed. Differentiate the slip ratio to obtain the slip ratio differential equation, then obtain the sliding mode surface equation based on the error equation composed of the slip ratio and the desired slip ratio, differentiate the sliding mode surface equation to obtain the sliding mode surface differential equation, correct the torque to be corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque, and verify the stability of the sliding mode surface through the Lyapunov function and its derivative to achieve adaptive control of the braking torque of the electric vehicle; S4: According to the vehicle speed and the battery SOC, use the braking force distribution curve to intelligently distribute the corrected target torque to the front and rear wheels of the vehicle to complete the braking control of the vehicle.

2. The active braking control method for electric vehicles based on the distance to obstacles according to claim 1, characterized in that, in step S4, the braking torque distribution is to judge whether to use different braking force distribution curves to distribute the braking torques of the front and rear wheels of the vehicle according to the comparison results of the vehicle speed and the power battery SOC with the preset thresholds. When the vehicle speed is less than the preset vehicle speed threshold or the power battery SOC is less than the preset SOC threshold, use the conventional braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle; When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the power battery SOC is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is not triggered, use the economic braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle; When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the power battery SOC is greater than or equal to the preset SOC threshold, and at the same time when the anti-lock braking system is triggered, use the ideal braking force distribution curve in the braking force distribution curve to distribute the braking torques of the front and rear wheels of the vehicle.

3. The active braking control method for electric vehicles based on the distance to obstacles according to claim 1 or 2, characterized in that, during the process of braking the vehicle in step S2, when the radar sensor detects that the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the radar controller will continuously send out braking signals to control the motor to run faster until the front and rear wheels stop rotating, so that the vehicle reaches a stopped state; When the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the preset safe distance threshold, the radar controller issues a brake release signal to control the motor to reverse and release the brake, and the vehicle resumes normal driving.

4. The active braking control method for an electric vehicle based on the obstacle distance according to claim 1 or 2, characterized in that, in the step S1, the radar sensor includes a millimeter-wave radar sensor and an ultrasonic radar sensor.

5. The active braking control method for an electric vehicle based on the obstacle distance according to claim 1 or 2, characterized in that, in the step S2, when the distance between the vehicle and the obstacle is less than the preset safe distance threshold, the motor is also started to recover the braking energy in the form of a generator.

6. An active braking control system for an electric vehicle based on the obstacle distance, characterized in that, it includes a distance measurement module, a braking judgment module, a torque correction module and a braking torque distribution module connected in sequence, the distance measurement module arranges radar sensors on the front and rear bumpers of the vehicle to measure the distance between the vehicle in the driving process and the obstacles in the traffic environment; the braking judgment module compares the distance between the vehicle and the obstacle with the preset safe distance threshold to judge whether the vehicle needs to brake. If the distance between the vehicle and the obstacle is less than the preset safe distance threshold, it is judged that the vehicle needs to brake. If the distance between the vehicle and the obstacle is greater than or equal to the safe distance threshold, it is judged that the vehicle does not need to brake; the torque correction module, when braking is required, calculates the torque to be corrected required for vehicle braking according to the current vehicle speed and the distance between the vehicle and the obstacle, and uses an adaptive control algorithm to calculate the tire slip ratio according to the current vehicle speed, wheel radius and wheel speed, differentiates the slip ratio to obtain the slip ratio differential equation, then obtains the sliding mode surface equation according to the error equation composed of the slip ratio and the desired slip ratio, differentiates the sliding mode surface equation to obtain the sliding mode surface differential equation, corrects the torque to be corrected according to the slip ratio differential equation and the sliding mode surface differential equation to obtain the corrected target torque, and verifies the stability of the sliding mode surface through the Lyapunov function and its derivative to realize the adaptive control of the braking torque of the electric vehicle; the braking torque distribution module distributes the corrected target torque to the front and rear wheels of the vehicle according to the vehicle speed and the battery SOC, and performs intelligent distribution of the braking torque to complete the braking control of the vehicle.

7. The active braking control system for an electric vehicle according to claim 6, characterized in that, in the braking torque distribution module, the braking torque distribution is to judge according to the comparison result of the vehicle speed and the power battery SOC with the preset threshold value, and different braking force distribution curves are used to distribute the braking torque of the front and rear wheels of the vehicle. When the vehicle speed is less than the preset vehicle speed threshold or the power battery SOC is less than the preset SOC threshold, the conventional braking force distribution curve in the braking force distribution curve is used to distribute the braking torque of the front and rear wheels of the vehicle; When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and meanwhile when the anti-lock braking system is not triggered, the economic braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle; When the vehicle speed is greater than or equal to the preset vehicle speed threshold and the state of charge (SOC) of the power battery is greater than or equal to the preset SOC threshold, and meanwhile when the anti-lock braking system is triggered, the ideal braking force distribution curve in the braking force distribution curve is used to distribute the braking torques of the front and rear wheels of the vehicle.

8. The active braking control system for an electric vehicle according to claim 6 or 7, characterized in that, during the process of braking the vehicle by the braking judgment module, when the radar sensor detects that the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the radar controller will continuously send out braking signals to control the motor to run faster until the front and rear wheels stop rotating, so that the vehicle reaches a stopped state to complete the braking process; when the radar sensor detects that the distance between the vehicle and the obstacle is greater than or equal to the preset safety distance threshold, the radar controller sends out a braking release signal to control the motor to reverse and release the braking, and the vehicle resumes normal driving.

9. The active braking control system for an electric vehicle according to claim 6 or 7, characterized in that, the radar sensor includes a millimeter-wave radar sensor and an ultrasonic radar sensor.

10. The active braking control system for an electric vehicle according to claim 6 or 7, characterized in that, in the braking judgment module, when the distance between the vehicle and the obstacle is less than the preset safety distance threshold, the motor is also started to recover the braking energy in the form of a generator.

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