CN108437805A - Regenerating braking energy recycling control based on wheel hub motor four-wheel drive vehicle and computational methods - Google Patents

Abstract

The invention provides a regenerative braking energy recovery control method for a four-wheel drive vehicle based on in-wheel motors. When the SOC of the power battery is greater than the saturation threshold, the braking force of the entire vehicle comes from the mechanical hydraulic braking system; otherwise, it is judged: when the vehicle speed is greater than the starting threshold, according to the brake pedal opening and its rate of change, it is judged that the working condition is a small braking condition, a medium braking intensity working condition or an emergency braking working condition; Mechanical hydraulic braking system; under small braking conditions, the braking force of the entire vehicle comes from the regenerative braking system, and the hub motor outputs regenerative braking torque; under medium braking intensity conditions, the braking force of the entire vehicle is controlled by mechanical hydraulic braking The coordinated work of the braking system and the regenerative braking system is obtained. The hub motor outputs the maximum regenerative braking torque, and the rest is supplemented by the mechanical hydraulic braking system. The invention can reasonably recycle and control the energy generated by the hub motor during braking according to working conditions, so as to avoid damage to the power battery.

Description

Control and Calculation of Regenerative Braking Energy Recovery Based on In-wheel Motor Four-Wheel Drive Vehicle method

technical field

The invention belongs to the field of automobile control, and in particular relates to a regenerative braking energy recovery control and calculation method for a four-wheel drive vehicle based on an in-wheel motor.

Background technique

As the energy problem of the oil crisis becomes more and more prominent, electric vehicles with low emission and low pollution are becoming more and more competitive in the market. Among them, the hub motor drives the vehicle to integrate the power device, transmission device and braking device into the hub, which greatly simplifies the mechanical part of the vehicle and increases the space flexibility of the chassis layout. At the same time, the torque of each wheel of the hub motor-driven vehicle is distributed by the vehicle controller and is independently controllable. Therefore, compared with traditional vehicles, the dynamic control of the hub motor-driven electric vehicle can be better applied, and the driver can experience better power. performance, handling stability and braking performance. Another huge advantage of in-wheel motor-driven vehicles is the use of in-wheel motor regenerative braking systems. When the vehicle brakes, the in-wheel motor is in the power generation mode, and the power battery is in the charging mode. The braking energy is recovered through regenerative braking, which is of great significance to improve the driving range of the vehicle.

Contents of the invention

The technical problem to be solved by the present invention is to provide a regenerative braking energy recovery control and calculation method for a four-wheel drive vehicle based on in-wheel motors.

The technical solution adopted by the present invention to solve the above technical problems is: a regenerative braking energy recovery control method for four-wheel drive vehicles based on in-wheel motors, which is characterized in that: when the SOC of the power battery is greater than the saturation threshold, the use of regenerative braking is stopped system, the braking force of the whole vehicle comes from the mechanical hydraulic braking system; when the SOC of the power battery is less than or equal to the saturation threshold, the following judgments are made:

When the vehicle speed is greater than the start threshold, according to the range of the brake pedal opening and its rate of change, it is determined that the working condition is a small braking condition, a medium braking intensity working condition or an emergency braking working condition;

In the case of emergency braking, the braking force of the whole vehicle comes from the mechanical hydraulic braking system; in the case of small braking, the braking force of the whole vehicle comes from the regenerative braking system, and the hub motor outputs regenerative braking torque; Under the condition of dynamic intensity, the braking force of the whole vehicle is obtained by the coordinated work of the mechanical hydraulic braking system and the regenerative braking system, the hub motor outputs the maximum regenerative braking torque, and the rest is supplemented by the mechanical hydraulic braking system;

When the mechanical hydraulic braking system is working, if the wheels are locked, the ABS system of the vehicle will be activated to output the hydraulic braking force of the vehicle;

When the regenerative braking system is working, if the wheels are locked or the charging rate of the power battery reaches 3C, the output of the regenerative braking torque will be reduced;

The braking force of the whole vehicle controls the vehicle to decelerate, stop or go downhill at a constant speed until the vehicle speed is less than the minimum threshold or the brake pedal opening is equal to 0, the braking ends, otherwise the braking continues.

According to the above solution, the regenerative braking system outputs the regenerative braking torque by using the in-wheel motor as a generator to overcome the reluctance torque when the vehicle is braking, and the inner rotor of the in-wheel motor cuts the magnetic induction line to generate induced current and store it in the power battery.

According to the above solution, the saturation threshold of the power battery SOC is 0.95.

According to the above scheme, when the opening of the brake pedal is greater than 0.7 and the rate of change of the opening of the brake pedal is greater than 0.875, it is determined as an emergency braking condition; when the opening of the brake pedal is less than 0.3, it is determined as a small braking condition; When the brake pedal opening is between 0.3 and 0.7, or when the brake pedal opening is greater than 0.7 and the rate of change of the brake pedal opening is less than or equal to 0.875, it is determined to be a medium braking intensity working condition.

The calculation method based on the regenerative braking energy recovery of the hub motor four-wheel drive vehicle is characterized in that: based on the described regenerative braking energy recovery control method based on the hub motor four-wheel drive vehicle,

When the vehicle is in the braking state and the regenerative braking system of the hub motor is working, the regenerative braking torque output by the hub motor is obtained according to the actual braking characteristic curve of the hub motor. The braking power P _regi of a single hub motor is:

The total braking power P _reg of the hub motor is:

P _reg =ΣP _regi (2)

The charging power P _ch of the battery is:

P _ch =P _reg ·η _ge ·η _ch (3)

The charging current I _ch of the battery is:

Among them, i=(fl, fr, rl, rr), fl is the left front wheel, fr is the right front wheel, rl is the left rear wheel, rr is the right rear wheel; T _regi means that a single hub motor according to its actual braking characteristics The regenerative braking torque obtained from the curve; w _i represents the rotational angular velocity of a single in-wheel motor; η _ge represents the discovery efficiency of the in-wheel motor; η _ch represents the charging efficiency of the battery; _U represents the bus voltage; , it is necessary to overcome the power output of the battery to the vehicle accessories, which is a constant;

According to the charging power P _ch integral of the battery, the energy E _b recovered during the braking process is obtained:

The kinetic energy △E ₁ consumed by the vehicle during the braking process is:

If the vehicle is going downhill, there will be consumption of gravitational potential energy, and the consumed potential energy △E ₂ is:

ΔE ₂ =mg·h=mg·s·sinβ=mg·∫Vdt·sinβ

During the whole braking process, the energy consumption △ _E3 of the vehicle accessories is:

ΔE ₃ ＝∫P _f dt

Therefore, the total energy △E consumed by the vehicle during braking is:

ΔE＝ΔE ₁ +ΔE ₂ +ΔE ₃

So the regenerative braking energy recovery rate ε is:

Among them, R _b represents the internal resistance of the power battery; V ₁ and V ₂ represent the speed of the vehicle at the end and initial stages of braking respectively; h represents the vertical distance of the center of mass of the vehicle when the vehicle is going downhill; s represents the distance traveled by the vehicle on the slope ; β represents the slope angle of the ramp.

The beneficial effect of the invention is that the energy generated by the hub motor during braking can be reasonably recovered and controlled according to the working conditions, and the damage of the power battery can be avoided.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Figure 2 shows the ideal and actual braking characteristic curves of the hub motor.

Fig. 3 is a flowchart of a control method according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific examples and accompanying drawings.

Figure 1 shows the braking system scheme of the in-wheel motor four-wheel drive vehicle. The main components of the regenerative braking system are the in-wheel motor, brake controller, motor controller, power battery and power battery management system, etc. When the vehicle is driving, The hub motor is in the electric drive state, and the hub motor relies on the power battery to drive the vehicle; when the vehicle brakes, the hub motor is in the power generation state, and the vehicle will continue to move forward due to inertia, so the hub motor will continue to rotate, and it will be used as a generator to overcome The reluctance torque is the regenerative braking torque. At the same time, the inner rotor of the motor cuts the magnetic induction line to generate an induced current. After a series of processing such as filtering and rectification, the electric energy is finally stored in the power battery to achieve the recovery of regenerative energy.

For small braking intensity conditions, the regenerative braking torque that the hub motor can provide fully meets the braking torque required by the vehicle; but for medium braking intensity conditions, the motor immediately provides the maximum regenerative braking torque, which is still not enough. To meet the demand, the braking system of the whole vehicle also needs the traditional hydraulic braking system to work at the same time; in emergency braking conditions, in order to ensure braking efficiency and braking stability, under the premise of safety, the wheel hub will be withdrawn Motor regenerative braking, the braking torque of the vehicle is all provided by the traditional hydraulic braking system.

Figure 2 shows the ideal and actual braking characteristic curves of the hub motor, that is, the relationship curve between the hub motor speed and the output torque. However, when the speed of the hub motor is too low, the regenerative braking will fail due to the low counter electromotive force generated by the hub motor.

In the actual braking characteristic curve of the in-wheel motor, in consideration of protecting the power battery and preventing the instantaneous charging current from being too large, the maximum braking force provided by the regenerative braking of the motor is set when all the braking torque of the vehicle is provided by the in-wheel motor. Deceleration limit (generally z=0.2g～0.3g), at this time, the braking torque required by the whole vehicle can be obtained, which is the actual peak regenerative braking torque of the in-wheel motor.

A regenerative braking energy recovery control method based on in-wheel motor four-wheel drive vehicles, as shown in Figure 3, when the SOC of the power battery is greater than the saturation threshold (0.95), in order to protect the power battery, prevent overcharging, and cause danger, stop using it With the regenerative braking system, the braking force of the entire vehicle comes from the mechanical hydraulic braking system.

When the power battery SOC is less than or equal to the saturation threshold (0.95), the following judgments are made:

When the vehicle speed is greater than the start threshold (10km/h), according to the range of the brake pedal opening and its rate of change, it is determined that the working condition is a small braking condition, a medium braking intensity working condition or an emergency braking working condition. In this embodiment, when the opening of the brake pedal is greater than 0.7 and the rate of change of the opening of the brake pedal is greater than 0.875, it is determined as an emergency braking condition; when the opening of the brake pedal is less than 0.3, it is determined as a small braking condition ; When the brake pedal opening is between 0.3 and 0.7, or when the brake pedal opening is greater than 0.7 and the rate of change of the brake pedal opening is less than or equal to 0.875, it is determined to be a medium braking intensity working condition. 0.3 and 0.7 are set values, which may vary slightly depending on the type of car.

In emergency braking conditions, in order to ensure safety, based on the stability and braking efficiency of the vehicle, the braking force of the entire vehicle comes from the mechanical hydraulic braking system.

In small braking conditions, the regenerative braking torque provided by the regenerative braking system of the in-wheel motor fully meets the braking requirements of the vehicle. The braking force of the entire vehicle comes from the regenerative braking system, and the in-wheel motor outputs the regenerative braking torque.

When the braking intensity is moderate, the maximum regenerative braking torque provided by the hub motor is not enough to meet the braking requirements of the whole vehicle. The braking force of the whole vehicle is obtained by the coordinated work of the mechanical hydraulic braking system and the regenerative braking system. The hub motor outputs the maximum regenerative braking torque to fully recover the braking energy, and the remaining part is supplemented by the mechanical hydraulic braking system.

When the mechanical hydraulic braking system is working, if the wheels are locked, in order to avoid danger, the ABS system of the vehicle is activated to output the hydraulic braking force of the vehicle.

When the regenerative braking system is working, if the wheels are locked, in order to avoid danger, the output of the hub motor regenerative braking torque will be appropriately reduced. If the charging rate of the power battery reaches 3C, in order to prevent the instantaneous charging current of the power battery from over If it is too large, the power battery will be damaged, and the output of the in-wheel motor's regenerative braking torque will also be appropriately reduced, so as to output the regenerative braking torque of the vehicle.

The braking force of the whole vehicle controls the vehicle to decelerate, stop or go downhill at a constant speed until the vehicle speed is less than the minimum threshold (1km/h) or the brake pedal opening is equal to 0, then the braking ends, otherwise the braking continues.

Under the above control method, the calculation method of regenerative braking energy recovery is introduced.

When the vehicle is in the braking state and the hub motor regenerative braking system is working, according to the actual hub motor braking characteristic curve, the regenerative braking torque T _regi output by the hub motor can be obtained, so the braking power P _regi of a single motor is :

Therefore, the total braking power P _reg of the hub motor is:

P _reg =ΣP _regi (2)

The charging power P _ch of the battery is:

P _ch =P _reg ·η _ge ·η _ch (3)

The charging current I _ch of the battery is:

Among them, i=(fl, fr, rl, rr), T _regi represents the regenerative braking torque (N m) obtained by a single hub motor according to its actual braking characteristic curve. w _i represents the rotational angular velocity of a single hub motor (rad/ s), η _ge represents the discovery efficiency of the hub motor, η _ch represents the charging efficiency of the battery, and U represents the bus voltage (V). Note: P _f means that no matter the vehicle is braking, it needs to overcome the power output of the battery to the vehicle accessories (for easy calculation, p _f can be regarded as a constant, generally 2 ~ 4kW).

Only energy can be recovered during the braking process. Excluding the energy loss of vehicle accessories and the internal resistance (R _b ) consumption of the power battery, only the energy recovered into the power battery can be counted as the truly recovered energy. According to the above Introduction, the energy _Eb recovered during braking can be obtained according to the integral of the charging power _Pch of the battery:

The kinetic energy △E ₁ consumed by the vehicle during the braking process is:

If the vehicle is going downhill, there will be consumption of gravitational potential energy, and the consumed potential energy △E ₂ is:

ΔE ₂ =mg·h=mg·s·sinβ=mg·∫Vdt·sinβ

Note: P _f means that no matter the vehicle is braking, it needs to overcome the power output of the battery to the vehicle accessories (for easy calculation, p _f can be regarded as a constant, generally 2 ~ 4kW). During the whole braking process, the energy consumption △ _E3 of the vehicle accessories is:

ΔE ₃ ＝∫P _f dt

Therefore, the total energy △E consumed by the vehicle during braking is:

ΔE＝ΔE ₁ +ΔE ₂ +ΔE ₃

So the regenerative braking energy recovery rate ε is:

Among them, R _b represents the internal resistance of the power battery (Ω), V ₁ and V ₂ represent the vehicle speed (m/s) at the end and initial stages of the vehicle’s braking respectively, and h represents the vertical drop distance of the vehicle’s center of mass when the vehicle is going downhill (m ), s represents the distance (m) that the vehicle travels on the slope, and β represents the slope angle (°) of the slope.

In the present invention, first: a unique regenerative braking control strategy for four-wheel-drive vehicles with in-wheel motors is proposed, the theoretical braking characteristics of in-wheel motors are compared with the actual braking characteristics, and SOC is added to the control strategy to The limitation of motor regenerative braking intervention includes the limitation of wheel slip rate on braking, and the limitation of power battery charging rate on regenerative braking force;

Second: In the calculation method of regenerative braking energy recovery of in-wheel motor four-wheel drive vehicles, the power loss of vehicle accessories is added, and the calculation method of energy recovery when the vehicle goes down a long slope at a constant speed is introduced for the first time.

The above embodiments are only used to illustrate the design concept and characteristics of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims (5)

1. A regenerative braking energy recovery control method based on an in-wheel motor four-wheel drive vehicle, characterized in that: when the SOC of the power battery is greater than the saturation threshold, the regenerative braking system is stopped, and the braking force of the entire vehicle comes from mechanical hydraulic braking system; when the power battery SOC is less than or equal to the saturation threshold, the following judgments are made: When the vehicle speed is greater than the start threshold, according to the range of the brake pedal opening and its rate of change, it is determined that the working condition is a small braking condition, a medium braking intensity working condition or an emergency braking working condition; In the case of emergency braking, the braking force of the whole vehicle comes from the mechanical hydraulic braking system; in the case of small braking, the braking force of the whole vehicle comes from the regenerative braking system, and the hub motor outputs regenerative braking torque; Under the condition of dynamic intensity, the braking force of the whole vehicle is obtained by the coordinated work of the mechanical hydraulic braking system and the regenerative braking system, the hub motor outputs the maximum regenerative braking torque, and the rest is supplemented by the mechanical hydraulic braking system; When the mechanical hydraulic braking system is working, if the wheels are locked, the ABS system of the vehicle will be activated to output the hydraulic braking force of the vehicle; When the regenerative braking system is working, if the wheels are locked or the charging rate of the power battery reaches 3C, the output of the regenerative braking torque will be reduced; The braking force of the whole vehicle controls the vehicle to decelerate, stop or go downhill at a constant speed until the vehicle speed is less than the minimum threshold or the brake pedal opening is equal to 0, the braking ends, otherwise the braking continues. 2. The regenerative braking energy recovery control method for four-wheel drive vehicles based on in-wheel motors according to claim 1, characterized in that: the regenerative braking system overcomes magnetic The resistance torque outputs the regenerative braking torque, and the inner rotor of the hub motor cuts the magnetic induction line to generate an induced current and store it in the power battery. 3. The regenerative braking energy recovery control method for a four-wheel drive vehicle based on in-wheel motors according to claim 1, wherein the saturation threshold of the SOC of the power battery is 0.95. 4. The regenerative braking energy recovery control method for four-wheel drive vehicles based on in-wheel motors according to claim 1, characterized in that: when the opening of the brake pedal is greater than 0.7 and the rate of change of the opening of the brake pedal is greater than 0.875, it is determined that It is an emergency braking condition; when the brake pedal opening is less than 0.3, it is judged as a small braking condition; when the brake pedal opening is between 0.3 and 0.7, or the brake pedal opening is greater than 0.7 and the brake pedal When the rate of change of the opening degree is less than or equal to 0.875, it is judged as a medium braking intensity working condition. 5. The calculation method based on the regenerative braking energy recovery of the in-wheel motor four-wheel drive vehicle is characterized in that: based on the regenerative braking energy recovery control method of the in-wheel motor four-wheel drive vehicle according to claim 1, When the vehicle is in the braking state and the regenerative braking system of the hub motor is working, the regenerative braking torque output by the hub motor is obtained according to the actual braking characteristic curve of the hub motor. The braking power P _regi of a single hub motor is: The total braking power P _reg of the hub motor is: P _reg =ΣP _regi (2) The charging power P _ch of the battery is: P _ch =P _reg ·η _ge ·η _ch (3) The charging current I _ch of the battery is: Among them, i=(fl, fr, rl, rr), fl is the left front wheel, fr is the right front wheel, rl is the left rear wheel, rr is the right rear wheel; T _regi means that a single hub motor according to its actual braking characteristics The regenerative braking torque obtained from the curve; w _i represents the rotational angular velocity of a single in-wheel motor; η _ge represents the discovery efficiency of the in-wheel motor; η _ch represents the charging efficiency of the battery; _U represents the bus voltage; , it is necessary to overcome the power output of the battery to the vehicle accessories, which is a constant; According to the charging power P _ch integral of the battery, the energy E _b recovered during the braking process is obtained: The kinetic energy △E ₁ consumed by the vehicle during the braking process is: If the vehicle is going downhill, there will be consumption of gravitational potential energy, and the consumed potential energy △E ₂ is: ΔE ₂ =mg·h=mg·s·sinβ=mg·∫Vdt·sinβ During the whole braking process, the energy consumption △ _E3 of the vehicle accessories is: ΔE ₃ ＝∫P _f dt Therefore, the total energy △E consumed by the vehicle during braking is: ΔE＝ΔE ₁ +ΔE ₂ +ΔE ₃ So the regenerative braking energy recovery rate ε is: Among them, R _b represents the internal resistance of the power battery; V ₁ and V ₂ represent the speed of the vehicle at the end and initial stages of braking respectively; h represents the vertical distance of the center of mass of the vehicle when the vehicle is going downhill; s represents the distance traveled by the vehicle on the slope ; β represents the slope angle of the ramp.