WO2024041293A1

WO2024041293A1 - Turning control method and device for four-wheel drive vehicle

Info

Publication number: WO2024041293A1
Application number: PCT/CN2023/109230
Authority: WO
Inventors: 周泽慧; 刘元治; 崔金龙; 吴爱彬; 赵洋
Original assignee: 中国第一汽车股份有限公司
Priority date: 2022-08-25
Filing date: 2023-07-26
Publication date: 2024-02-29
Also published as: CN115285108A

Abstract

A turning control method and device for a four-wheel drive vehicle. The method comprises: acquiring a target turning control mode selected by a user on the basis of a driving scenario; acquiring the current steering information and the current driving torque output by an accelerator pedal; if a non-pavement control mode is selected, distributing the current driving torque to two front wheels for driving control, performing locking control on the inner rear wheel in two rear wheels on the basis of the current steering information, and performing slip control on the outer rear wheel in the two rear wheels; if a pavement control mode is selected, distributing the current driving torque to the two rear wheels for driving control, and performing drift control on the two rear wheels on the basis of the current steering information; and if a turn-around control mode is selected, on the basis of the current steering information, distributing the current driving torque to the two front wheels and the two rear wheels for driving control.

Description

Turning control method and device for four-wheel drive vehicle

This application claims priority to the Chinese patent application with application number 202211026357.8, which was submitted to the China Patent Office on August 25, 2022. The entire content of this application is incorporated into this application by reference.

Technical field

The present application relates to the field of vehicle control technology, for example, to a turning control method and device for a four-wheel drive vehicle.

Background technique

With the advancement of the times and the gradual popularization of automobiles, people's material lives have become increasingly superior. Cars have become the main tool for travel, and people have put forward higher requirements for the convenience and adaptability of vehicles. Cars will have a minimum turning radius. The minimum turning radius of a car is the radius of the circle formed by the trajectory of the contact point between the center of the front outer wheel and the ground when turning at low speed when the front wheel of the car is at the maximum limit turning angle. The turning radius indicates the car's ability to pass through narrow curved areas or avoid obstacles. The smaller the turning radius, the smaller the space required for the car to turn, and the better the car's maneuverability.

The traditional automobile steering system uses a differential and a transfer case to reduce the turning radius. However, for four-wheel drive vehicles that are not equipped with differentials and transfer cases, the steering wheel controls the steering direction when turning, so that the front wheels turn and the rear wheels do not participate in the steering.

In some steering conditions, due to the limitation of the site size, the vehicle cannot complete a one-time turn and must switch gears repeatedly to complete the U-turn or steering, which increases the driver's operational complexity and increases the time it takes for the vehicle to turn; In addition, this method of reducing the turning radius is not suitable for many different working conditions.

Contents of the invention

This application provides a turning control method and device for a four-wheel drive vehicle to solve the problem of reducing the turning radius under different working conditions, reduce the complexity of the steering operation and the time required for steering, and improve the driving experience and use of the vehicle. Convenience.

This application provides a turning control method for a four-wheel drive vehicle. The method includes: obtaining the target turning control mode selected by the user based on the driving scenario; obtaining the current steering information and the current driving torque output through the accelerator pedal; When the control mode is a non-paved road control mode, the current drive torque is distributed to the two front wheels for drive control, and the inner rear wheel of the two rear wheels is locked based on the current steering information. and skidding the outer rear wheel among the two rear wheels. Control; when the target turning control mode is a paved road control mode, allocate the current drive torque to the two rear wheels for drive control, and perform drive control on the two rear wheels based on the current steering information. Tail drift control; when the target turning control mode is a local U-turn control mode, based on the current steering information, the current driving torque is distributed to the two front wheels and the two rear wheels for drive control.

The present application provides a turning control device for a four-wheel drive vehicle. The device includes: a turning mode acquisition module configured to obtain the target turning control mode selected by the user based on the driving scenario; a driving torque acquisition module configured to obtain the current steering information and The current driving torque output through the accelerator pedal; the non-paved road control module is configured to distribute the current driving torque to the two front wheels for driving when the target turning control mode is the non-paved road control mode. control, and based on the current steering information, perform lock control on the inner rear wheel of the two rear wheels and perform slip control on the outer rear wheel of the two rear wheels; the paved road control module is set to When the target turning control mode is a paved road control mode, the current driving torque is distributed to the two rear wheels for drive control, and the two rear wheels are subject to drift control based on the current steering information. ; In-place U-turn control module, configured to distribute the current driving torque to two front wheels and two rear wheels based on the current steering information when the target turning control mode is an in-place U-turn control mode. Perform drive control.

Description of drawings

The drawings needed to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without exerting creative efforts, Under the premise, other drawings can also be obtained based on these drawings.

Figure 1 is a flow chart of a turning control method for a four-wheel drive vehicle provided in Embodiment 1 of the present application;

Figure 2 is a flow chart of a turning control method for a four-wheel drive vehicle provided in Embodiment 2 of the present application;

Figure 3 is a graph showing changes in target speed of the inner rear wheels over time for a turning control method for a four-wheel drive vehicle provided in Embodiment 3 of the present application;

Figure 4 is a schematic structural diagram of a turning control device for a four-wheel drive vehicle provided in Embodiment 4 of the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall within the scope of protection of this application.

It should be noted that the terms "first", "second", etc. in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances so that the embodiments of the application described herein can be practiced in sequences other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, e.g., a process, method, system, product, or apparatus that encompasses a series of steps or units and need not be limited to those explicitly listed. Those steps or elements may instead include other steps or elements not expressly listed or inherent to the process, method, product or apparatus.

Embodiment 1

Figure 1 is a flow chart of a turning control method for a four-wheel drive vehicle provided in Embodiment 1 of the present application. This embodiment can be applied to scenarios of reducing the turning radius under different working conditions, so that users can efficiently and conveniently complete the steering function of the vehicle while driving. The method can be performed by a turning control device of a four-wheel drive vehicle, which can be implemented in the form of hardware and/or software, and the device can generally be integrated in a car. As shown in Figure 1, the method includes the following steps.

S110. Obtain the target turning control mode selected by the user based on the driving scenario;

The driving scene is the environment in which the user drives the target vehicle, such as off-road environments with low ground friction, working conditions such as mud, sand, and snow; paved road environments with large ground friction, asphalt roads, cement roads, etc. Working conditions: Extremely narrow road conditions, the road space only allows vehicles to turn around and turn in place. The target turning control mode is based on different road conditions, and the user selects the corresponding control mode according to the actual working conditions. The control modes can include: non-paved road control mode, paved road control mode and narrow road condition U-turn mode.

According to the current working environment, the user can select the corresponding mode through the vehicle central control menu, or by integrating buttons with corresponding functions on the target vehicle. After the user selects any mode according to the working conditions, the instrument prompts the mode. The activation status reminds the user that the mode has been activated. When a target turning control mode is selected, the vehicle's controller reads the user-selected mode.

For example, the user's current environment is an asphalt road. The surface friction of the asphalt road is relatively large. Through the menu of the target vehicle control surface, the user selects a pavement road control mode suitable for the road surface with large surface friction. The control mode of the vehicle The device reads the pavement control mode selected by the user.

S120: Obtain current steering information and current driving torque output through the accelerator pedal.

The current steering information is the direction in which the user turns and the size of the steering angle. The direction and angle of the user's steering can be indicated by turning the steering wheel of the target vehicle. The steering direction can be to the right or left, depending on the size of the steering angle. Indicates the user's steering intention, which is related to the turning arc of the current road condition. The accelerator pedal is a hardware structure configured on the target vehicle. It can be a floor-type accelerator pedal. It can also be a suspended accelerator pedal, which can control the opening of the engine throttle, thereby controlling the engine's power output. A displacement sensor can be installed on the accelerator pedal. When the user steps on the accelerator pedal, the vehicle controller will collect the opening changes and acceleration of the displacement sensor on the pedal, and calculate the user's driving intention based on the opening changes and acceleration of the displacement sensor. Then a corresponding control signal is sent to the engine throttle control motor to control the engine's power output. The vehicle controller can calculate the current driving torque based on the engine's power output.

When the user encounters road conditions that require the target vehicle to turn while driving, the user determines the direction and angle of the turn based on the actual road conditions. The user turns the steering wheel of the target vehicle to determine the direction and angle of the turn; at the same time, the user steps on the accelerator pedal Pedal, the depth of pressing the accelerator pedal can indicate how fast the user needs to turn.

For example, the user needs to make a small turn to the right while driving. At this time, the user turns the steering wheel to the right at a relatively small angle and lightly steps on the accelerator pedal, which requires a relatively small driving torque. At this time, the user uses the steering wheel and accelerates The pedals express steering intentions, which can be read by the vehicle's controller.

S131. If the target turning control mode is a non-paved road control mode, the current driving torque is distributed to the two front wheels for drive control, and the inner rear wheel of the two rear wheels is locked based on the current steering information. Carry out slip control on the outer rear wheel of the two rear wheels;

The non-paved road control mode is used in off-road conditions, such as mud, sand, snow, etc. This mode is a smooth steering mode that requires the driver to control the accelerator pedal gently. In this mode, the chassis body stability control system (Electronic Stability Program, ESC) needs to exit the control of the rear wheel slip rate to avoid interference with this strategy. The two front wheels are two of the four tires of the target vehicle, and are the two wheels corresponding to the front direction of the target vehicle. Drive control is realized through the electric vehicle drive control system. The electric vehicle drive control system is the core subsystem of electric vehicles. It mainly includes power batteries, drive motors and drive controllers. Its main function is to store the stored data when the electric vehicle is driving normally. The electrical energy in the power battery is converted into the kinetic energy of the electric vehicle through the motor. During braking, part of the vehicle's kinetic energy is converted into electrical energy and stored in the power battery. Locking control means that the vehicle controller controls the braking system of the target vehicle to continuously apply braking force to the wheels. The brakes clamp the tires. The tires have no relative movement to the brakes and the tires slide relative to the ground. Slip control: The target vehicle's rotation distance is less than the vehicle's traveling distance within a certain period of time, and the wheels are in a sliding state where they rotate in place.

S132. If the target turning control mode is the paved road control mode, the current driving torque is distributed to the two rear wheels for drive control, and the two rear wheels are subject to drift control based on the current steering information;

The paved road control mode is used on paved roads, such as asphalt roads and cement roads. This mode is a radical steering mode, which requires the driver to step deeply on the accelerator pedal, complete the steering by flicking, and reduce the turning radius. In this mode, the chassis stability control system (ESC) needs to exit the control of the four-wheel slip rate to avoid interference with this strategy. The two rear wheels are two of the four tires of the target vehicle. are the two wheels corresponding to the rear direction of the target vehicle. Drift control means that the vehicle is in rear-wheel drive mode. When the user presses the accelerator pedal quickly and deeply, the two rear wheels will slip. At this time, the driver controls the steering wheel to achieve drift steering, which can greatly shorten the turning radius.

S133. If the target turning control mode is a local U-turn control mode, based on the current steering information, the current driving torque is distributed to the two front wheels and the two rear wheels for driving control.

The in-situ U-turn control mode is used in extremely narrow road conditions. The road space only allows the vehicle to make an in-situ U-turn and turn. The intensity of this mode is controlled by the driver. If the driver lightly presses the accelerator pedal, the vehicle will slowly make a U-turn; if the driver presses the accelerator pedal deeply, the vehicle will quickly make a U-turn. In this mode, the chassis stability control system (ESC) needs to exit the control of the four-wheel slip rate to avoid interference with this strategy.

In the technical solution of this embodiment, the user selects different target turning control modes according to different working conditions; and expresses the steering intention through the current steering information and the current driving torque output through the accelerator pedal; the target turning control mode can be non-paved road control mode, paved road control mode and in-situ U-turn control mode. Its different target turning control modes correspond to different control methods for reducing the turning radius, thus solving the problem of reducing the turning radius under different working conditions and reducing the complexity and complexity of steering operations. The time taken to turn improves the driving experience of the vehicle and the convenience of using the vehicle.

Embodiment 2

Figure 2 is a flow chart of a turning control method for a four-wheel drive vehicle provided in Embodiment 2 of the present application. Based on the above embodiment, the embodiment of the present application describes the control process in each turning control mode. The application embodiments may be combined with multiple optional solutions in one or more of the above embodiments. The explanation of terms that are the same as or corresponding to the above-mentioned embodiments will not be repeated here. As shown in Figure 2, the turning control method of a four-wheel drive vehicle includes the following steps.

S210. Obtain the target turning control mode selected by the user based on the driving scenario.

S220: Obtain current steering information and current driving torque output through the accelerator pedal.

S230. If the target turning control mode is a non-paved road control mode, the current driving torque is evenly distributed to the two front wheels and the positive torque of each front wheel is determined.

S231. Drive the corresponding front wheel forward based on the positive torque of each front wheel.

In this embodiment, when the user selects the non-paved road control mode through the control panel, the vehicle controller activates the non-paved road control mode. When the user gently controls the accelerator pedal, the current driving torque generated at this time is controlled by the vehicle controller. Evenly distributed to the two front wheels, the driving torque is positive torque and the two front wheels drive forward. For example, if the user depresses the accelerator pedal to generate a driving torque of 500N·m, then the two front wheels respectively obtain a torque of 250N·m, and the front wheels of the target vehicle drive forward.

S232. Determine the current steering direction based on the current steering information, and determine two One of the rear wheels is the inner rear wheel, and the other of the two rear wheels is determined to be the outer rear wheel.

The user turns the steering wheel to determine the steering direction. When the steering wheel turns left, the left rear wheel is determined as the inner rear wheel and the right rear wheel is determined as the outer rear wheel. When the steering wheel turns right, the right rear wheel is determined as the inner rear wheel. , the left rear wheel is determined as the outer rear wheel.

S233, perform locking control on the inner rear wheel.

Locking control means that the brakes clamp the tires and there is no relative movement of the tires to the brakes. In other words, the tires stop spinning and the vehicle slides on the road like a brick. In this embodiment, the wheel speed of the inner rear wheel is set to zero, so that locking control can be achieved; in addition, in order to avoid long-term sliding friction on the same part of the inner rear wheel, the wear amount of different parts of the wheel is inconsistent and affects the driving quality. , the inner rear wheel speed can be set to achieve periodic changes, which can also achieve the locking effect of the inner rear wheel, but can reduce tire wear.

Next, we will explain how to achieve periodic changes in the wheel speed of the inner rear wheel, and then control the locking of the inner rear wheel, including:

Obtain the target wheel speed of the inner rear wheel, where the target wheel speed is a periodically changing wheel speed, the target wheel speed is zero vehicle speed in part of each cycle, and the target wheel speed is non-zero vehicle speed in the remaining time periods;

Based on the target wheel speed of the inner rear wheel, the actual wheel speed of the inner rear wheel is controlled by Proportional Integral Differential (PID) to determine the negative torque of the inner rear wheel, and based on the negative torque of the inner rear wheel, the inner rear wheel Perform a backward drive.

In this embodiment, the target rotation speed of the inner rear wheel is preset. It can be a fixed value or a changing value that changes periodically over time. For example, the target wheel speed of the inner rear wheel changes between [0, 1]km/h, maintains 0km/h for 3 seconds, and then changes to 1km/h.

The target wheel speed of the inner rear wheel of the target vehicle is a preset value that changes periodically. Based on the target wheel speed of the inner rear wheel, PID control is performed on the actual wheel speed of the inner rear wheel, the negative torque of the inner rear wheel is determined, and the inner rear wheel is driven backward based on the negative torque of the inner rear wheel. According to the target wheel speed and the actual wheel speed, the torque output can be controlled by using a PID controller. After obtaining the torque value of the inner rear wheel, the controller of the target vehicle sets the torque of the inner rear wheel to this calculated value. The torque calculation formula is as shown in formula (1):

T _{in_rear} is the torque of the inner rear wheel; kp is the proportional term coefficient, which needs to be determined by actual vehicle calibration; ki is the integral term coefficient, and its value needs to be determined by actual vehicle calibration; kd is the differential term coefficient, and its value needs to be determined by actual vehicle calibration; v _{in_act} is the actual inner rear wheel speed, provided by the wheel speed sensor; v _{in_tgt} is the inner rear wheel target wheel speed.

S234. Determine the target wheel speed of the outer rear wheel when the inner rear wheel is locked. When the inner rear wheel is locked, the target wheel speed of the outer rear wheel can be calculated based on the principles of vehicle dynamics. The calculation formula for the rotation speed of the outer rear wheel when the inner rear wheel is locked is as shown in formula (2):
v _{out_rear} =(v _FR +v _FL )cosδ (2)

v _{out_rear} is the target wheel speed of the outer rear wheel, v _FR is the actual wheel speed of the right front wheel, v _FL is the actual wheel speed of the left front wheel, and δ is the front wheel steering angle. The actual wheel speed of the right front wheel and the actual wheel speed of the left front wheel can be collected through the wheel speed sensor of the corresponding wheel of the target vehicle and transmitted to the vehicle controller. The front wheel steering angle can be collected through the steering angle sensor and transmitted to the vehicle controller.

S235. Based on the target wheel speed of the outer rear wheel, perform PID control on the actual wheel speed of the outer rear wheel, determine the positive torque of the outer rear wheel, and drive the outer rear wheel forward based on the positive torque of the outer rear wheel.

In this embodiment, since the target wheel speed of the outer rear wheel has been determined in S234, the actual wheel speed of the outer rear wheel can be collected through the wheel speed sensor of the corresponding wheel of the target vehicle and transmitted to the vehicle controller. PID control can control the actual wheel speed of the target vehicle near the target wheel speed, thereby determining the positive torque of the outer rear wheel, and driving the outer rear wheel forward based on the positive torque of the outer rear wheel. According to the target wheel speed and the actual wheel speed, the torque output can be controlled by using a PID controller. After obtaining the torque value of the outer rear wheel, the controller of the target vehicle sets the torque of the outer rear wheel to this calculated value.

S240. If the target turning control mode is the paved road control mode, the current driving torque is distributed to the two rear wheels for drive control.

S241. Based on the current steering angle of the steering wheel, determine the target slip rate of each rear wheel.

The initial value of the target slip rate of the rear wheels is related to the driver's steering wheel angle. The steering wheel angle represents the driver's steering intention. The greater the slip rate of the rear wheels, the more fully the vehicle will drift and the greater the steering radius. Small, the steering wheel angle can be collected through sensors. The larger the steering wheel angle, the larger the initial value of the target slip rate of the rear wheels, and the actual parameters of the vehicle need to be determined based on the calibration results.

In this embodiment, the target yaw rate of the vehicle is first calculated based on the vehicle's steering wheel angle signal, vehicle speed signal and lateral acceleration signal. The calculated target yaw rate can represent the driver's steering intention, while ensuring that the target yaw rate does not exceed the physical limits allowed by the vehicle and the road surface. The actual yaw rate of the vehicle can be obtained from the yaw sensor. When the actual yaw rate is in the same direction as the driver's target yaw rate, when the actual yaw rate is greater than the driver's target yaw rate, it means that too much has occurred at this time. When steering, the target slip rate of the rear wheels should be reduced; when the actual yaw rate is less than the driver's target yaw rate, it means that understeer occurs at this time, and the target slip rate of the rear wheels should be increased. The PID controller is used to perform closed-loop adjustment of the target slip rate. The purpose is to calculate and adjust the target slip rate based on the difference between the actual yaw rate and the driver's target yaw rate, as shown in formula (3):

kp is the proportional term coefficient, which needs to be determined by actual vehicle calibration; ki is the integral term coefficient, and its value needs to be determined by actual vehicle calibration; kd is the differential term coefficient, and its value needs to be determined by actual vehicle calibration; γ _act is the actual yaw rate, It is provided by the yaw sensor; γ _tgt is the target yaw rate, calculated from the two-degree-of-freedom model; Δslip is the correction amount of the target slip rate of the rear wheel. The total target slip rate of the rear wheels is the sum of the initial value of the slip rate and the correction amount of the target slip rate of the rear wheels. When the actual yaw rate is opposite to the driver's target yaw rate, it means that the driver needs to reduce the degree of vehicle drift, so the slip rate of the rear wheels needs to be reduced.

S242. Determine the target wheel speed of each rear wheel based on the target slip rate of each rear wheel.

After obtaining the target slip rate, the target speed can be obtained through related technologies. Therefore, after determining the target slip rate of each rear wheel, the target wheel speed of each rear wheel can be obtained.

S243. Based on the target wheel speed of each rear wheel, perform PID control on the actual wheel speed of each rear wheel, determine the positive torque of each rear wheel, and control the direction of each rear wheel based on the positive torque of each rear wheel. Front drive.

The PID controller is also used to control the actual speed of the rear wheels near the target speed, and determine the positive torque of each rear wheel. Based on the positive torque of each rear wheel, each rear wheel is driven forward to achieve drift steering. , greatly reducing the turning radius. The function of this PID controller is to make the actual slip rate of the rear wheel equal to the target slip rate.

S250. If the target turning control mode is a local U-turn control mode, determine the current steering direction based on the current steering information, and determine the two inside wheels and the two outside wheels based on the current steering direction.

In this embodiment, the in-situ U-turn control mode is applied to very narrow road conditions to enable the vehicle to make a U-turn in place. This mode requires the user to keep the steering wheel in the back position, and the user can choose to turn left or right through the buttons, which can be integrated on the control panel of the target vehicle. Because this mode needs to distinguish between the inside wheels and outside wheels of the target vehicle, and then allocate torque, the inside wheels allocate negative torque, and the outside wheels allocate positive torque. For example, when making a U-turn to the left, the two wheels on the right are the outside wheels and the two wheels on the left are the inside wheels; when making a U-turn to the right, the two wheels on the left are the outside wheels and the two wheels on the right are the inside wheels.

S251. According to the principle that the outside wheel drives forward and the inside wheel drives backward, the current driving torque is evenly distributed to the two inside wheels and the two outside wheels, and the negative torque of each inside wheel and the positive torque of each outside wheel are determined.

S252, each inner wheel is driven backward based on the negative torque of each inner wheel, and each outer wheel is driven forward based on the positive torque of each outer wheel.

The torque generated by the user depressing the brake pedal is distributed equally to the four wheels, and is distributed according to the principle that the outer wheel drives forward and the inner wheel drives backward. For example, the torque generated by the user depressing the brake pedal is 1000N·m, then The outer front wheel is 250N·m, the outer rear wheel is 250N·m, the inner front wheel is -250N·m, The inner rear wheel is -250N·m. The two inside wheels then drive rearward and the two outside wheels drive forward.

For example, after S252, it may also include:

If it is detected that the actual yaw rate of the four-wheel drive vehicle is greater than the maximum yaw rate, PID control is performed on the actual yaw rate of the four-wheel drive vehicle based on the maximum yaw rate, the target driving torque corresponding to the four wheels is determined, and the target The drive torque is distributed to the four wheels for drive control.

The maximum yaw rate is a preset yaw rate value, which can be calibrated according to the actual target vehicle. For example, it can be 4rad/s. The target driving torque is the total torque of the four wheels determined by PID control of the actual yaw rate of the four-wheel drive vehicle based on the maximum yaw rate.

When the user depresses the brake pedal and the displacement stroke is relatively large, and the user's demand torque is large enough, the vehicle will yaw on the spot. When the user feels that the vehicle's steering angle meets the demand, the vehicle can be lifted up to accelerate. pedal to stop the steering function. In order to prevent the wheels from violently slipping when the accelerator pedal is depressed too deeply, this mode requires the development of a unique slip rate control function. When the wheel slip rate is too large, it will not only increase tire wear, but also reduce steering ability, so the vehicle slip rate must be controlled. And in this mode, the TCS function of ESC can no longer work properly. If the driver presses the accelerator pedal too deeply, the wheels will slip violently, causing greater tire wear. In addition, violent yaw movement of the vehicle is more dangerous, so the maximum yaw rate of the wheels must be limited.

When the actual yaw rate of the vehicle exceeds the maximum yaw rate, the PID controller is used to reduce the driver's required torque, as shown in the calculation formula (4):

T _driver is the total torque of the target vehicle; kp is the proportional term coefficient, which requires real vehicle calibration to determine its value; ki is the integral term coefficient, which requires real vehicle calibration to determine its value; kd is the differential term coefficient, which requires real vehicle calibration to determine its value ; γ _act is the actual yaw rate, provided by the yaw combination sensor; γ _tgt is the target yaw rate of the outer rear wheel.

With the above technical solution, users can select different target turning control modes according to different working conditions, ensuring that this technical solution covers all paved and non-paved roads. In the non-paved road control mode, the left and right rear wheels simulate an open differential strategy to achieve the effect of reducing the turning radius; in the paved road control mode, the slip rate of the rear wheels is controlled according to the driver's steering angle to achieve Drift steering on paved roads reduces the turning radius; in the in-situ U-turn control mode, the left and right torque distribution strategy is adopted to realize the in-situ steering and U-turn function, and a maximum yaw rate limiting strategy is proposed. The above technical solution can keep the gear position unchanged (for example, D gear), realize one-time U-turn or steering on all paved roads, non-paved roads, and narrow sites, and solve the problem of reducing the turning radius under different working conditions. , reduces the complexity of the steering operation and the time required for steering, sets the limit value during the steering process, ensures the safety of the user and the target vehicle during the steering process, and improves the vehicle's driving experience and vehicle usage convenience.

Embodiment 3

In the embodiment of this application, the process of turning control of a four-wheel drive vehicle is introduced in an implementation manner, including the following steps.

1. Mode setting

This embodiment proposes three modes of shortening the steering radius, which are respectively applied to different working conditions, and the driver needs to choose according to the actual working conditions. The selection method can be designed to select the corresponding mode through the vehicle central control menu. The following three modes can cover all working conditions. Choose which mode to use for small radius steering according to the actual situation.

(1) Small radius steering model under off-road conditions

This mode is used in off-road conditions, such as mud, sand, snow, etc. This mode is a smooth steering mode, which requires the driver to control the accelerator pedal gently. With the assistance of this strategy, the vehicle shows a lower turning radius than the normal mode. In this mode, ESC needs to exit control of the rear wheel slip rate to avoid interference with this strategy.

(2) Paved road small radius steering model

This mode is suitable for paved roads, such as asphalt roads and cement roads. This mode is a radical steering mode, which requires the driver to step deeply on the accelerator pedal. With the assistance of this strategy, the steering is completed by flicking and the steering radius is reduced. In this mode, ESC needs to exit the control of the four-wheel slip rate to avoid interference with this strategy.

(3) U-turn model on narrow road conditions

This mode is used in extremely narrow road conditions, where the road space only allows the vehicle to turn around and turn on the spot. The intensity of this mode is controlled by the driver. If the driver lightly presses the accelerator pedal, the vehicle will slowly make a U-turn; if the driver presses the accelerator pedal deeply, the vehicle will quickly make a U-turn. In this mode, the chassis stability control system (ESC) needs to exit the control of the four-wheel slip rate to avoid interference with this strategy.

After the driver selects any mode, the instrument needs to prompt the activation status of the mode to remind the driver that the mode has been activated.

2. Control strategy

1) Small radius steering mode in off-road conditions

Under off-road conditions, negative torque control is performed on the inner rear wheel and positive torque control is performed on the outer rear wheel, causing the inner rear wheel to lock and the outer rear wheel to slip while causing a yaw torque to the vehicle. Due to the longitudinal slip/slip of the two rear wheels, the lateral adhesion capacity of the two rear wheels is less than the lateral adhesion capacity of the two front wheels. Under the action of yaw torque, the rear wheels are more prone to sideslip than the front wheels, which increases the vehicle load. Excessive steering characteristics, thereby reducing the turning radius.

This mode is suitable for non-paved roads with low adhesion coefficient, such as sand, dirt roads, muddy roads, snow, ice, etc. In this mode, all the driver's requested torque needs to be allocated to the front wheels, and the torque of the rear wheels is calculated by the following strategy.

Negative torque control strategy for the inner rear wheel:

① When the steering wheel turns left, the left rear wheel is determined as the inside rear wheel; when the steering wheel turns right, the right rear wheel is determined as the inside rear wheel.

② Figure 3 is a graph showing the change of the target rotation speed of the inner rear wheel over time in a turning control method for a four-wheel drive vehicle provided in Embodiment 3 of the present application. The target wheel speed of the inner rear wheel changes between [0,1]km/h. After maintaining 0km/h for 3 seconds, it changes to 1km/h (the actual value needs to be finalized according to the calibration). The purpose is to avoid the inner rear wheel from being damaged. Long-term sliding friction in the same part prevents inconsistent wear in different parts of the wheel and affects driving quality.

③The control method adopts PID controller, and the torque calculation formula is as follows:

T _{in_rear} is the torque of the inner rear wheel; kp is the proportional term coefficient, which requires real vehicle calibration to determine its value; ki is the integral term coefficient, which requires real vehicle calibration to determine its value; kd is the differential term coefficient, which requires real vehicle calibration to determine its value ; v _{in_act} is the actual wheel speed of the inner rear wheel, provided by the wheel speed sensor; v _{in_tgt} is the target wheel speed of the inner rear wheel.

Positive torque control strategy for the outer rear wheel:

① Calculation of the target wheel speed of the outer rear wheel

On vehicles with an open differential, a reduced turning radius is achieved by braking control of the inner rear wheel. On models equipped with a transfer case, due to the existence of the differential, when the inner rear wheel locks, the rotation speed of the outer rear wheel increases and the outer rear wheel slips. The reason is that the function of the transfer case is to average the front and rear axle speeds. They are equal, so when the inner rear wheel locks, the outer rear wheel must increase speed. On a distributed four-wheel drive vehicle, there is no open differential. This article simulates the effect of the transfer case plus an open differential through closed-loop control of the outer rear wheel speed. When the outer rear wheel slips, the lateral adhesion of the outer rear wheel decreases, making the rear of the car more prone to sideslip and reducing the turning radius.

According to the principles of vehicle dynamics and combined with the characteristics of the differential, it can be seen that the rotation speed of the outer rear wheel when the inner rear wheel is locked should be:
v _{out_rear} =(v _FR +v _FL )cosδ (6)

v _{out_rear} is the target wheel speed of the outer rear wheel, v _FR is the actual wheel speed of the right front wheel, v _FL is the actual wheel speed of the left front wheel, and δ is the steering angle of the front wheel. The actual wheel speed of the right front wheel and the actual wheel speed of the left front wheel can be collected through the wheel speed sensor of the corresponding wheel of the target vehicle and transmitted to the vehicle controller. The steering angle of the front wheel can be It is collected by the steering angle sensor and sent to the vehicle controller.

② Torque calculation of outer rear wheel

After obtaining the target wheel speed of the outer rear wheel, the PID controller is also used to control the actual speed of the outer rear wheel near the target speed, which can imitate the effect of the developed differential, causing the inner rear wheel to lock while the outer rear wheel slips. change.

Among them, T _{in_rear} is the torque of the inner rear wheel; kp is the proportional term coefficient, which needs to be determined by actual vehicle calibration; ki is the integral term coefficient, which needs to be determined by actual vehicle calibration; kd is the differential term coefficient, which needs to be determined by actual vehicle calibration. Its value; v _{in_act} is the actual wheel speed of the inner rear wheel, provided by the wheel speed sensor; v _{in_tgt} is the target wheel speed of the inner rear wheel.

2) Small radius steering mode on paved roads

Different from off-road conditions, paved roads are mostly roads with high adhesion coefficient. If the inner rear wheel locking control method is adopted, the vehicle will be difficult to start due to the locking of the single rear wheel; and when the inner rear wheel is locked, other The wheels are not prone to sideslip and have no obvious effect on reducing the turning radius, so the inner rear wheel locking control method is not suitable for paved roads.

When the driver chooses to enter the small-radius steering mode on paved roads, this strategy will evenly distribute the driving torque to the two rear wheels, making the vehicle in rear-drive mode. When the driver quickly and deeply steps on the accelerator pedal, the two rear wheels will slip. At this time, the driver controls the steering wheel to achieve drift steering, which can greatly shorten the turning radius.

① Calculation of initial value of target slip rate

In this mode, the initial value of the target slip rate of the rear wheels is related to the driver's steering wheel angle, as shown in the table below. The steering wheel angle represents the driver's steering intention. The greater the slip rate of the rear wheels, the more fully the vehicle will drift and the smaller the turning radius. The larger the steering wheel angle, the larger the initial value of the target slip rate of the rear wheels, and the actual parameters of the vehicle need to be determined based on the calibration results. The principle is that the greater the slip rate of the wheel, the smaller the lateral adhesion force. After obtaining the target slip rate, the target speed can be obtained. The PID controller is also used to control the actual speed of the rear wheel near the target speed, which can realize drift steering and greatly reduce the turning radius. The function of this PID controller is to make the actual slip rate of the rear wheel equal to the target slip rate.

②Yaw closed-loop control

This patent first calculates the target yaw rate of the vehicle based on the vehicle's steering wheel angle signal, vehicle speed signal and lateral acceleration signal. The steps for calculating the target yaw rate can be determined based on methods in related technologies. The calculated target yaw rate can represent the driver's steering intention, while ensuring that the target yaw rate does not Exceeding the physical limits allowed by the vehicle-road surface.

The actual yaw rate of the vehicle can be obtained from the yaw sensor. When the actual yaw rate is in the same direction as the driver's target yaw rate, when the actual yaw rate is greater than the driver's target yaw rate, it means that too much steering has occurred at this time. , the target slip rate of the rear wheels should be reduced; when the actual yaw rate is less than the driver's target yaw rate, it means that understeer occurs at this time, and the target slip rate of the rear wheels should be increased. Use a PID controller to perform closed-loop adjustment of the target slip rate. The purpose is to calculate and adjust the target slip rate based on the difference between the actual yaw rate and the driver's target yaw rate. The formula is as follows:

3) U-turn mode on narrow road conditions

This mode is used in very narrow road conditions to allow the vehicle to turn around on the spot. The center of the vehicle's turning circle is the center symmetry point of the four wheels. Since all four wheels in this mode will slip significantly at the same time, it is recommended to be used on non-paved roads and other road conditions with low adhesion coefficients to prevent greater tire wear.

This mode requires the driver to keep the steering wheel in the return position, and the driver can choose to turn left or right through the buttons. When turning left, the two wheels on the right are outside wheels and the two wheels on the left are inside wheels; when turning right, the two wheels on the left are outside wheels and the two wheels on the right are inside wheels. The strategy proposed in this article distributes the driver's requested torque equally to the four wheels, and distributes it according to the principle that the outer wheel drives forward and the inner wheel drives backward (for example: the driver's requested torque is 1000N·m, then the outer front wheel is 250N ·m, the outer rear wheel is 250N·m, the inner front wheel is -250N·m, the inner rear wheel is -250N·m). When the driver's demand torque is large enough, the vehicle will yaw on the spot. When the driver feels that the vehicle's steering angle meets the demand, he can lift the accelerator pedal and stop the steering function.

In order to prevent the wheels from violently slipping when the accelerator pedal is depressed too deeply, this mode requires the development of a unique slip rate control function. When the wheel slip rate is too large, it will not only increase tire wear, but also reduce steering ability, so the vehicle slip rate must be controlled.

This strategy proposes to limit the maximum yaw rate γ _MAX of the vehicle (for example, 4rad/s, calibrated). The reason is that in this mode, the TCS function of ESC cannot work properly. If the driver depresses the accelerator pedal too deeply, the wheels will Severe slipping occurs, causing greater tire wear. In addition, violent yaw movement of the vehicle is more dangerous, so the maximum yaw rate of the wheels must be limited.

When the actual yaw rate of the vehicle exceeds the maximum yaw rate, a PID controller is used to reduce the driver's required torque. The calculation formula is as follows:

Embodiment 4

FIG. 4 is a schematic structural diagram of a turning control device for a four-wheel drive vehicle provided in the fourth embodiment of the present application. The device can execute the turning control method of the four-wheel drive vehicle provided by the embodiment of the present application. The device includes: a turning mode acquisition module 410, configured to acquire the target turning control mode selected by the user based on the driving scenario; a driving torque acquisition module 420, configured to acquire current steering information and the current driving torque output through the accelerator pedal; non-paved The road surface control module 431 is configured to allocate the current driving torque to the two front wheels for drive control if the target turning control mode is the non-paved road control mode, and control the inner rear wheel of the two rear wheels based on the current steering information. Carry out locking control and slip control on the outer rear wheel of the two rear wheels; the pavement control module 432 is set to distribute the current driving torque to the two if the target turning control mode is the pavement control mode. The rear wheels perform drive control, and perform drift control on the two rear wheels based on the current steering information; the in-situ U-turn control module 433 is set to if the target turning control mode is the in-situ U-turn control mode, based on the current steering information, the current Drive torque is distributed to the two front wheels and the two rear wheels for drive control.

Based on the above multiple technical solutions, the non-paved road control module 431 includes: a front wheel torque determination unit configured to evenly distribute the current driving torque to the two front wheels and determine the positive torque of each front wheel; forward A drive unit configured to forwardly drive the corresponding front wheel based on the positive torque of each front wheel.

On the basis of the above multiple technical solutions, the non-paved road control module 431 also includes: an inner and outer rear wheel determination unit, configured to determine the current steering direction based on the current steering information, and determine one of the two rear wheels according to the current steering direction. the inner rear wheel, and determines that the other of the two rear wheels is the outer rear wheel; the rear wheel locking control unit is configured to lock the inner rear wheel; the target wheel speed determination unit is configured to determine the locking of the inner rear wheel. The target wheel speed of the outer rear wheel at the time of death; the rear wheel control unit is set to be based on the target wheel speed of the outer rear wheel, performs PID control on the actual wheel speed of the outer rear wheel, determines the positive torque of the inner rear wheel, and based on the inner rear wheel The positive torque drives the outer rear wheel forward.

Based on the above multiple technical solutions, the paved road control module also includes: a target slip rate determination unit, which is set to determine the target slip rate of each rear wheel based on the current steering angle of the steering wheel; The standard wheel speed determination unit is configured to determine the target wheel speed of each rear wheel based on the target slip rate of each rear wheel; the rear wheel control unit is configured to determine the target wheel speed of each rear wheel based on the target wheel speed of each rear wheel. The actual wheel speed of each wheel is controlled by PID, the positive torque of each rear wheel is determined, and each rear wheel is driven forward based on the positive torque of each rear wheel.

Based on the above multiple technical solutions, the target slip rate determination unit includes: an initial slip rate determination subunit, which is set to determine the initial slip rate of each rear wheel according to the current steering angle of the steering wheel; the target yaw rate The determination subunit is set to determine the target yaw rate of the four-wheel drive vehicle based on the current steering angle of the steering wheel, driving speed and lateral acceleration; the slip rate correction amount determination subunit is set to determine the target yaw rate of the four-wheel drive vehicle based on the current steering angle of the steering wheel, driving speed and lateral acceleration. The actual yaw rate of the vehicle is controlled by PID to determine the slip rate correction amount; the target slip rate determination subunit is set to determine the target slip rate of each rear wheel based on the initial slip rate and the slip rate correction amount.

Based on the above multiple technical solutions, the in-situ U-turn control module also includes: a drive control sub-module. The drive control submodule includes: an inner and outer wheel determination unit, configured to determine the current steering direction based on the current steering information, and determine two inner wheels and two outer wheels based on the current steering direction; an outer wheel control unit, configured to drive forward according to the outer wheel , the inner wheel rearward driving principle, the current driving torque is evenly distributed to the two inner wheels and the two outer wheels, and the negative torque of each inner wheel and the positive torque of each outer wheel are determined; the inner wheel control unit is set to be based on Negative torque on each inside wheel drives each inside wheel rearward, and positive torque on each outside wheel drives each outside wheel forward.

Based on the above technical solutions, the in-situ U-turn control module also includes: if it is detected that the actual yaw rate of the four-wheel drive vehicle is greater than the maximum yaw rate, based on the maximum yaw rate, the actual yaw rate of the four-wheel drive vehicle will be determined. PID control is performed at a certain rate to determine the target driving torque corresponding to the four wheels, and distribute the target driving torque to the four wheels for drive control.

Based on the above multiple technical solutions, the in-situ U-turn control module also includes: if the target turning control mode is the in-situ U-turn control mode, the user is reminded to keep the steering wheel in the return position and obtains the current steering direction selected by the user through the buttons. .

The turning control device of a four-wheel drive vehicle provided in the embodiment of the present application can execute the turning control method of the four-wheel drive vehicle provided in any embodiment of the present application. The turning control device of the four-wheel drive vehicle in the embodiment of the present application is used to solve the problem The problem of narrowing the turning radius under different working conditions reduces the complexity of steering operations and the time required for steering, and improves the driving experience of the vehicle and the convenience of using the vehicle.

It should be understood that various forms of the process shown above may be used, with steps reordered, added or deleted. For example, multiple steps described in this application can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solution of this application can be achieved.

Claims

A turning control method for a four-wheel drive vehicle, including:

Obtain the target turning control mode selected by the user based on the driving scenario;

Obtain current steering information and current drive torque output through the accelerator pedal;

When the target turning control mode is a non-paved road control mode, the current driving torque is distributed to the two front wheels for driving control, and the inner and rear wheels of the two rear wheels are controlled based on the current steering information. The wheels are locked and the outer rear wheel of the two rear wheels is controlled to slip;

When the target turning control mode is a paved road control mode, the current driving torque is distributed to the two rear wheels for drive control, and the two rear wheels are drifted based on the current steering information. control;

When the target turning control mode is a local U-turn control mode, based on the current steering information, the current driving torque is distributed to two front wheels and two rear wheels for drive control.
The method according to claim 1, wherein the distributing the current driving torque to two front wheels for driving control includes:

Distribute the current driving torque equally to the two front wheels and determine the positive torque of each front wheel;

Based on the positive torque of each front wheel, the corresponding front wheel is driven forward.
The method according to claim 1, wherein the inner rear wheel among the two rear wheels is locked and the outer rear wheel among the two rear wheels is slid based on the current steering information. transfer control, including:

Determine the current steering direction based on the current steering information, determine one of the two rear wheels as an inner rear wheel based on the current steering direction, and determine the other of the two rear wheels as an outer rear wheel;

Perform locking control on the inner rear wheel;

Determine the target wheel speed of the outer rear wheel when the inner rear wheel is locked;

Based on the target wheel speed of the outer rear wheel, the actual wheel speed of the outer rear wheel is controlled by proportional integral differential PID, the positive torque of the outer rear wheel is determined, and the positive torque of the outer rear wheel is controlled based on the positive torque of the outer rear wheel. The outer rear wheels are driven forward.
The method according to claim 3, wherein the locking control of the inner rear wheel includes:

Obtain the target wheel speed of the inner rear wheel, wherein the target wheel speed is a periodically changing wheel speed, the target wheel speed is zero vehicle speed in part of each period, and the target wheel speed is zero in the remaining time periods. is a non-zero vehicle speed;

Based on the target wheel speed of the inner rear wheel, PID control is performed on the actual wheel speed of the inner rear wheel to ensure The negative torque of the inner rear wheel is determined, and the inner rear wheel is driven backward based on the negative torque of the inner rear wheel.
The method according to claim 1, wherein the performing drift control on the two rear wheels based on the current steering information includes:

Determine the target slip rate for each rear wheel based on the current steering angle of the steering wheel;

Determine the target wheel speed of each rear wheel based on the target slip rate of each rear wheel;

Based on the target wheel speed of each rear wheel, perform PID control on the actual wheel speed of each rear wheel, determine the positive torque of each rear wheel, and drive each rear wheel forward based on the positive torque of each rear wheel. .
The method of claim 5, wherein determining the target slip rate of each rear wheel based on the current steering angle of the steering wheel includes:

Determine the initial slip rate of each rear wheel based on the current steering angle of the steering wheel;

Determine the target yaw rate of the four-wheel drive vehicle based on the current steering angle of the steering wheel, driving speed and lateral acceleration;

Based on the target yaw rate, perform PID control on the actual yaw rate of the four-wheel drive vehicle to determine the slip rate correction amount;

Based on the initial slip rate and the slip rate correction amount, a target slip rate for each rear wheel is determined.
The method according to claim 1, wherein, based on the current steering information, allocating the current driving torque to two front wheels and two rear wheels for drive control includes:

The current steering direction is determined based on the current steering information, and two inner wheels and two outer wheels are determined according to the current steering direction, wherein the two inner wheels include the inner front wheel and the inner front wheel of the two front wheels. The inner rear wheel among the two rear wheels, the two outer wheels include the outer front wheel among the two front wheels and the outer rear wheel among the two rear wheels;

According to the principle that the outside wheel drives forward and the inside wheel drives backward, the current driving torque is evenly distributed to the two inside wheels and the two outside wheels, and the negative torque of each inside wheel and the positive torque of each outside wheel are determined;

Each inside wheel is driven rearward based on the negative torque of each inside wheel, and each outside wheel is driven forward based on the positive torque of each outside wheel.
The method of claim 1, after allocating the current driving torque to two front wheels and two rear wheels for drive control based on the current steering information, further comprising:

When it is detected that the actual yaw rate of the four-wheel drive vehicle is greater than the maximum yaw rate, based on the maximum yaw rate, PID control is performed on the actual yaw rate of the four-wheel drive vehicle to determine the corresponding target driving torque, and distributes the target driving torque to the four wheels for drive control.
The method according to claim 1, wherein obtaining current steering information includes:

When the target turning control mode is an in-situ U-turn control mode, the user is reminded to keep the steering wheel in the return position, and the current steering direction selected by the user through buttons is obtained.
A cornering control device for a four-wheel drive vehicle, including:

The turning mode acquisition module is configured to obtain the target turning control mode selected by the user based on the driving scenario;

a driving torque acquisition module, configured to obtain current steering information and current driving torque output through the accelerator pedal;

A non-paved road control module, configured to distribute the current driving torque to the two front wheels for drive control when the target turning control mode is a non-paved road control mode, and based on the current steering information performing locking control on the inner rear wheel among the two rear wheels and performing slip control on the outer rear wheel among the two rear wheels;

The pavement control module is configured to allocate the current drive torque to the two rear wheels for drive control when the target turning control mode is the pavement control mode, and perform drive control on all rear wheels based on the current steering information. The two rear wheels perform drift control;

An in-situ U-turn control module is configured to distribute the current driving torque to the two front wheels and the two rear wheels based on the current steering information when the target turning control mode is the in-situ U-turn control mode. Drive control.