A turning control method and device for four-wheel drive vehicle

Abstract

The present invention discloses a turning control method and device for a four-wheel drive vehicle. The target turning control mode selected by the user based on the driving scenario is obtained; the current steering information and the current driving torque output through the accelerator pedal are obtained; if the unpaved road control mode is selected, the current driving torque is distributed to the two front wheels for drive control, and the inner rear wheel is locked and the outer rear wheel is slipped based on the current steering information; if the paved road control mode is selected, 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; if the in-situ U-turn control mode is selected, the current driving torque is distributed to the four wheels for drive control based on the current steering information. The present invention solves the problem of reducing the turning radius under different working conditions, reduces the complexity of the steering operation and the time taken for steering, and improves the driving experience and the convenience of the vehicle.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle control, and in particular to a turning control method and device for a four-wheel drive vehicle. Background Art

[0002] With the advancement of the times and the increasing popularity of automobiles, people's material lives have become increasingly better. Cars have become the primary means of transportation, and people have placed higher demands on vehicle convenience and adaptability. Every car has a minimum turning radius. This is the radius of the circle formed by the contact point between the center of the front outer wheel and the ground when turning at low speed, with the front wheels at their maximum turning angle. The turning radius indicates a car's ability to negotiate narrow curves or circumvent obstacles. The smaller the turning radius, the less space the car needs to turn, and the better the car's maneuverability.

[0003] Traditional automotive steering systems rely on a differential and transfer case to reduce the turning radius. However, for four-wheel drive vehicles that lack a differential or transfer case, the steering wheel controls the direction of the turn, allowing the front wheels to steer while the rear wheels remain uninvolved.

[0004] In some turning situations, due to limited space, the vehicle cannot complete a single turn, requiring repeated gear changes to complete a U-turn or turn. This increases the driver's operational complexity and increases steering time. Furthermore, this method of reducing the turning radius is not applicable to all different operating conditions. Therefore, how to efficiently, conveniently, and comprehensively reduce the turning radius of four-wheel drive vehicles is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The present invention 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 taken for steering, and improve the vehicle's driving experience and vehicle convenience.

[0006] In a first aspect, the present invention provides a turning control method for a four-wheel drive vehicle, the method comprising:

[0007] Obtain the target turning control mode selected by the user based on the driving scenario;

[0008] Obtain current steering information and current driving torque output through the accelerator pedal;

[0009] If the target turning control mode is the unpaved road control mode, the current driving torque is distributed to the two front wheels for driving control, and the inner rear wheel is locked and the outer rear wheel is slipped based on the current steering information;

[0010] If the target turning control mode is the paved road control mode, the current driving torque is distributed to the two rear wheels for driving control, and the two rear wheels are controlled to drift based on the current steering information;

[0011] If the target turning control mode is the pivot point control mode, the current driving torque is distributed to the four wheels for driving control based on the current steering information.

[0012] In a second aspect, the present invention provides a turning control device for a four-wheel drive vehicle, the device comprising:

[0013] A turning mode acquisition module is used to obtain the target turning control mode selected by the user based on the driving scenario;

[0014] A driving torque acquisition module is used to obtain current steering information and current driving torque output through the accelerator pedal;

[0015] an unpaved road control module, configured to distribute the current driving torque to the two front wheels for driving control if the target turning control mode is the unpaved road control mode, and to perform locking control on the inner rear wheel and slip control on the outer rear wheel based on the current steering information;

[0016] a paved road control module, configured to distribute the current driving torque to the two rear wheels for driving control if the target turning control mode is the paved road control mode, and to perform drift control on the two rear wheels based on the current steering information;

[0017] The pivot point control module is configured to distribute the current driving torque to the four wheels for driving control based on the current steering information if the target turning control mode is the pivot point control mode.

[0018] The technical solution of the embodiment of the present invention obtains the target turning control mode selected by the user based on the driving scenario; obtains the current steering information and the current driving torque output by the accelerator pedal; if the target turning control mode is the unpaved road control mode, the current driving torque is distributed to the two front wheels for driving control, and the inner rear wheel is locked and the outer rear wheel is slipped based on the current steering information; if the target turning control mode is the paved road control mode, the current driving torque is distributed to the two rear wheels for driving control, and the two rear wheels are drifted based on the current steering information; if the target turning control mode is the spot turn control mode, the current driving torque is distributed to the four wheels for driving control based on the current steering information. The above technical solution can 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 vehicle's driving experience and vehicle convenience.

[0019] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 This is a flow chart of a turning control method for a four-wheel drive vehicle provided in Example 1 of the present invention;

[0022] Figure 2 This is a flow chart of a turning control method for a four-wheel drive vehicle provided in the second embodiment of the present invention;

[0023] Figure 3 A graph showing changes in the target speed of the inner rear wheel over time in a turning control method for a four-wheel drive vehicle provided in the third embodiment of the present invention;

[0024] Figure 4 This is a structural schematic diagram of a turning control device for a four-wheel drive vehicle provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0026] It should be noted that the terms "first precondition," "second precondition," and the like in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatuses.

[0027] Example 1

[0028] Figure 1 This is a flow chart of a turning control method for a four-wheel drive vehicle provided in the first embodiment of the present invention. This embodiment is applicable to scenarios where the turning radius is reduced under different working conditions, so that the user can efficiently and conveniently complete the vehicle's steering function while driving. The method can be executed by a turning control device for a four-wheel drive vehicle, which can be implemented in the form of hardware and / or software, and the device can generally be integrated into a car. Figure 1 As shown, the method includes:

[0029] S110: Obtaining a target turning control mode selected by the user based on a driving scenario;

[0030] The driving scenario represents the environment in which the user drives the target vehicle, including low-friction off-road conditions such as mud, sand, and snow; high-friction paved roads such as asphalt and concrete; and extremely narrow roads where the road space only allows for a U-turn or turn. The target turning control mode is selected based on the actual driving conditions. The control modes include: unpaved road control mode, paved road control mode, and narrow road U-turn mode.

[0031] Specifically, users can select the appropriate mode based on their current operating environment through the vehicle's central control menu or by using the corresponding function button integrated into the target vehicle. After the user selects any mode based on the operating conditions, the instrument panel will indicate the activation status of the mode, reminding the user that the mode has been activated. Once a target turning control mode is selected, the vehicle controller reads the user's selected mode.

[0032] For example, the user's current environment is an asphalt road, which has a large surface friction. The user selects a paved road control mode suitable for a road with a large surface friction through the menu of the target vehicle control surface, and the vehicle controller reads the paved road control mode selected by the user.

[0033] S120: Acquire current steering information and current driving torque output through the accelerator pedal.

[0034] The current steering information refers to the user's steering direction and steering angle. This can be indicated by turning the target vehicle's steering wheel. The steering direction can be right or left, and the steering angle indicates the user's steering intention, which is related to the turning arc of the current road conditions. The accelerator pedal is a hardware structure installed on the target vehicle and can be either floor-mounted or suspended. The accelerator pedal controls the opening of the engine throttle, thereby controlling the engine's power output. The current driving torque is the result of the user pressing the accelerator pedal. The accelerator pedal may be equipped with a displacement sensor. When the driver presses the accelerator pedal, the vehicle controller collects the displacement sensor's opening change and acceleration. Based on this displacement sensor's opening change and acceleration, the vehicle controller determines the user's driving intention and sends a corresponding control signal to the engine throttle control motor to control the engine's power output. The vehicle controller calculates the current driving torque based on the engine's power output.

[0035] Specifically, when the user encounters a road condition that requires the target vehicle to turn while driving, the user determines the direction and steering 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, and the depth of the accelerator pedal step can indicate how fast the user needs to turn.

[0036] 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 expresses the steering intention through the steering wheel and accelerator pedal, and the vehicle controller can read this information.

[0037] S131: If the target turning control mode is the unpaved road control mode, distribute the current driving torque to the two front wheels for driving control, and perform locking control on the inner rear wheel and slip control on the outer rear wheel based on the current steering information;

[0038] The off-road control mode is designed for off-road driving, such as in mud, sand, and snow. This mode is a smooth steering mode, requiring the driver to gently apply the accelerator pedal. In this mode, the Electronic Stability Program (ESC) disengages rear wheel slip control to prevent interference with the strategy. The two front wheels are two of the target vehicle's four tires, corresponding to the front direction of the target vehicle. Drive control is achieved through the electric vehicle drive control system, a core subsystem of the electric vehicle. It primarily includes the power battery, drive motor, and drive controller. Its primary function is to convert the electrical energy stored in the power battery into kinetic energy through the motor during normal driving and to convert a portion of the vehicle's kinetic energy into electrical energy stored in the power battery during braking. Lock control involves the vehicle controller controlling the target vehicle's braking system to continuously apply braking force to the wheels. The brakes clamp the tires, preventing relative motion relative to the brakes and causing the tires to slide relative to the ground. Slip control involves rotating the target vehicle within a certain period of time, resulting in the wheels sliding in place.

[0039] S132: If the target turning control mode is the paved road control mode, distributing the current driving torque to the two rear wheels for driving control, and performing tailswing control on the two rear wheels based on the current steering information;

[0040] Among them, the paved road control mode is applied to paved roads, such as asphalt roads and cement roads. This mode is an aggressive steering mode, which requires the driver to step deeply on the accelerator pedal and complete the steering by drifting to reduce the turning radius. In this mode, the chassis body stability control system (ESC) is required 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, and are the two wheels corresponding to the rear direction of the target vehicle. The drift control is when the vehicle is in rear-wheel drive form. When the user quickly and deeply steps on the accelerator pedal, the two rear wheels slip. At this time, the driver controls the steering wheel to achieve drift steering, which can greatly shorten the turning radius.

[0041] S133: If the target turning control mode is the pivot point control mode, the current driving torque is distributed to the four wheels for driving control based on the current steering information.

[0042] The Pivot Control mode is designed for extremely narrow road conditions where the road space only allows the vehicle to turn or swerve in place. The driver controls the intensity of this mode. A light accelerator pedal press results in a slow pivot; a deeper accelerator pedal press results in a faster pivot. In this mode, the chassis stability control system (ESC) disengages from all-wheel slip control to avoid interfering with the strategy.

[0043] According to 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 by the accelerator pedal; the target turning control mode can be an unpaved road control mode, a paved road control mode and an on-the-spot U-turn control mode, and its different target turning control modes correspond to different control methods for reducing the turning radius, thereby solving the problem of reducing the turning radius under different working conditions, reducing the complexity of the steering operation and the time required for steering, and improving the vehicle's driving experience and vehicle convenience.

[0044] Example 2

[0045] Figure 2 This is a flowchart of a turning control method for a four-wheel drive vehicle provided by the second embodiment of the present invention. Based on the above embodiments, the embodiment of the present invention describes in detail the specific control process under each turning control mode. The embodiment of the present invention can be combined with various optional solutions in one or more of the above embodiments. The explanations of the terms that are the same or corresponding to the above embodiments are not repeated here. Figure 2 As shown, the turning control method of a four-wheel drive vehicle specifically includes the following steps:

[0046] S210: Obtain a target turning control mode selected by the user based on a driving scenario.

[0047] S220: Obtain current steering information and current driving torque output through the accelerator pedal.

[0048] S230: If the target turning control mode is the unpaved road control mode, evenly distribute the current driving torque to the two front wheels to determine the positive torque of each front wheel.

[0049] S231 : Drive the corresponding front wheel forward based on the positive torque of each front wheel.

[0050] In this embodiment, when the user selects the unpaved road control mode via the control panel, the vehicle controller activates the unpaved road control mode. When the user gently applies the accelerator pedal, the current driving torque generated is evenly distributed by the vehicle controller to both front wheels, resulting in positive driving torque, driving both front wheels forward. For example, if the user applies the accelerator pedal to generate 500 N·m of driving torque, each front wheel receives 250 N·m of torque, driving the front wheels of the target vehicle forward.

[0051] S232: Determine the inner rear wheel and the outer rear wheel based on the current steering direction.

[0052] Specifically, the user turns the steering wheel to determine the steering direction. When the steering wheel is turned 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 is turned right, the right rear wheel is determined as the inner rear wheel and the left rear wheel is determined as the outer rear wheel.

[0053] S233: Perform locking control on the inner rear wheel.

[0054] Lock control involves the brakes clamping the tires, preventing relative movement of the tires with respect to the brakes. In other words, the tires stop rotating, and the vehicle slides on the road like a brick. In this embodiment, the inner rear wheel speed is set to zero to achieve lock control. Furthermore, to prevent prolonged sliding friction on the same part of the inner rear wheel, which would cause uneven wear across different parts of the wheel and affect ride quality, the inner rear wheel speed can be set to vary periodically. This also achieves the same locking effect, but with reduced tire wear.

[0055] The following explains in detail how to achieve periodic changes in the inner rear wheel speed and thus control the locking of the inner rear wheel, including:

[0056] Obtaining a target wheel speed for the inner rear wheel, wherein the target wheel speed is a periodically varying wheel speed, with a portion of each period being zero speed and the remaining period being non-zero speed;

[0057] 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, a 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.

[0058] In this embodiment, the inner rear wheel target speed is pre-set. It can be a fixed value or a value that changes periodically over time. For example, the inner rear wheel target speed varies between [0, 1] km / h, remains at 0 km / h for 3 seconds, and then changes toward 1 km / h.

[0059] Specifically, the target wheel speed of the inner rear wheel of the target vehicle is a pre-set periodically changing value. 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 determine the negative torque of the inner rear wheel, 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 output of the torque 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 shown in formula (1):

[0060]

[0061] Among them, T in_rearis the inner rear wheel torque; kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle to determine its value; v in_act is the actual inner rear wheel speed, provided by the wheel speed sensor; v in_tgt is the target wheel speed of the inner rear wheel.

[0062] S234: Determine the target wheel speed of the outer rear wheel when the inner rear wheel is locked.

[0063] When the inner rear wheel is locked, the target wheel speed of the outer rear wheel can be calculated based on the vehicle dynamics principle. The formula for calculating the speed of the outer rear wheel when the inner rear wheel is locked is shown in formula (2):

[0064] v out_rear =(v FR +v FL )cosδ (2)

[0065] Among them, 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 left front wheel speed, and δ is the front wheel steering angle. The actual right and left front wheel speeds can be acquired by the wheel speed sensors of the corresponding wheels of the target vehicle and transmitted to the vehicle controller. The front wheel steering angle can be acquired by the steering angle sensor and transmitted to the vehicle controller.

[0066] 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 inner rear wheel forward based on the positive torque of the outer rear wheel.

[0067] 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 by 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 to be close to the target wheel speed. The positive torque of the outer rear wheel is then determined, and the inner rear wheel is driven forward based on the positive torque of the outer rear wheel. Based on the target wheel speed and the actual wheel speed, the torque output can be controlled by a PID controller. After the torque value of the outer rear wheel is obtained, the controller of the target vehicle sets the torque of the outer rear wheel to this calculated value.

[0068] 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 driving control.

[0069] S241: Determine a target slip rate for each rear wheel based on the current steering angle of the steering wheel.

[0070] The initial value of the rear wheel target slip rate is related to the driver's steering wheel angle. The steering wheel angle represents the driver's steering intention. A greater rear wheel slip rate indicates a more complete vehicle drift and a smaller steering radius. The steering wheel angle can be detected by sensors. A greater steering wheel angle increases the initial value of the rear wheel target slip rate. Actual vehicle parameters must be determined based on calibration results.

[0071] In this embodiment, the vehicle target yaw rate is first calculated based on the vehicle steering wheel angle signal, vehicle speed signal, and lateral acceleration signal. The calculated target yaw rate can represent the driver's steering intention and ensure that the target yaw rate does not exceed the physical limit range 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 indicates that oversteering has occurred and the rear wheel target slip rate should be reduced; when the actual yaw rate is less than the driver's target yaw rate, it indicates that understeering has occurred and the rear wheel target slip rate should be increased. A PID controller is used to perform closed-loop adjustment on 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):

[0072]

[0073] Among them, kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle to determine its value; γ act is the actual yaw rate, provided by the yaw sensor; γ tgt is the target yaw rate, calculated from the two-degree-of-freedom model; Δslip is the correction for the rear wheel target slip rate. The total rear wheel target slip rate is the sum of the initial slip value and the correction for the rear wheel target slip rate. When the actual yaw rate is opposite to the driver's target yaw rate, it indicates that the driver needs to reduce the vehicle's drift and, therefore, the rear wheel slip rate needs to be reduced.

[0074] S242: Determine a target wheel speed for each rear wheel based on the target slip rate of each rear wheel.

[0075] After the target slip rate is obtained, the target rotational speed can be obtained through existing technology. Therefore, after the target slip rate of each rear wheel is determined, the target wheel speed of each rear wheel can be obtained.

[0076] 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 drive each rear wheel forward based on the positive torque of each rear wheel.

[0077] A PID controller is also used to control the actual speed of the rear wheels near the target speed, and to 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 tail-swing steering and significantly reduce the turning radius. The function of this PID controller is to make the actual slip rate of the rear wheels equal to the target slip rate.

[0078] S250: If the target turning control mode is the pivot point control mode, determine the two inner wheels and the two outer wheels based on the current steering direction.

[0079] In this embodiment, the on-the-spot U-turn control mode is used in very narrow road conditions, allowing the vehicle to make a U-turn in place. This mode requires the user to keep the steering wheel in the center position and select a left or right turn using a button that can be integrated into the control panel of the target vehicle. Because this mode requires distinguishing between the inner and outer wheels of the target vehicle and then allocating torque, the inner wheels are allocated negative torque and the outer wheels are allocated positive torque. For example, when turning left, the two right wheels are the outer wheels and the two left wheels are the inner wheels; when turning right, the two left wheels are the outer wheels and the two right wheels are the inner wheels.

[0080] S251: Distribute the current driving torque evenly to the two inner wheels and the two outer wheels, and determine the negative torque of each inner wheel and the positive torque of each outer wheel.

[0081] S252: Drive each inner wheel backward based on the negative torque of each inner wheel, and drive each outer wheel forward based on the positive torque of each outer wheel.

[0082] The torque generated by the user pressing the brake pedal is evenly distributed to all four wheels, with the outer wheels driving forward and the inner wheels driving backward. For example, if the torque generated by the user pressing the brake pedal is 1000N·m, the outer front wheel will be 250N·m, the outer rear wheel will be 250N·m, the inner front wheel will be -250N·m, and the inner rear wheel will be -250N·m. The two inner wheels will then drive backward, and the two outer wheels will drive forward.

[0083] Exemplarily, after S252, the following steps may also be included:

[0084] 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 driving torque is distributed to the four wheels for drive control.

[0085] The maximum yaw rate is a preset yaw rate value that can be calibrated based on the actual target vehicle, and can be, for example, 4 rad / s. The target driving torque is the total torque at all four wheels determined by performing PID control on the actual yaw rate of the four-wheel drive vehicle based on the maximum yaw rate.

[0086] Specifically, when the user depresses the brake pedal through a relatively large amount of travel and the required torque is sufficiently high, the vehicle will yaw in place. When the user feels the steering angle meets their requirements, they can lift the accelerator pedal to deactivate the steering function. To prevent excessive wheel slip caused by excessive accelerator pedal depression, this mode requires the development of a unique slip control function. Excessive wheel slip not only increases tire wear but also reduces steering ability, so the vehicle's slip must be controlled. Furthermore, in this mode, the ESC's TCS function is no longer functioning properly. If the driver depresses the accelerator pedal too deeply, the wheels will slip violently, causing significant tire wear. Furthermore, the vehicle will experience dangerous yaw movements, so the maximum wheel yaw rate is limited.

[0087] 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 formula (4):

[0088]

[0089] Among them, T driver is the total torque of the target vehicle; kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle 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.

[0090] With the above technical solution, users can select different target turning control modes based on different operating conditions, ensuring that this technical solution covers all paved and unpaved roads. In the unpaved road control mode, the left and right rear wheels simulate an open differential strategy to achieve a reduced turning radius. In the paved road control mode, the rear wheel slip rate is controlled according to the driver's steering angle, achieving a tail-swinging turn on paved roads and reducing the turning radius. In the spot turn control mode, a left-right torque distribution strategy is adopted to achieve a spot turn function and propose a maximum yaw rate limit strategy. The above technical solution can achieve a single turn or steering on all paved and unpaved roads, as well as in narrow spaces, while maintaining the same gear position (for example, D gear). This solves the problem of reducing the turning radius under different operating conditions, reduces the complexity and time of steering operations, sets limits 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 convenience.

[0091] Example 3

[0092] In an embodiment of the present invention, a process of turning control of a four-wheel drive vehicle is described in a specific implementation manner, which specifically includes the following steps:

[0093] 1. Mode Setting

[0094] This embodiment proposes three modes for shortening turning radius, each applicable to different operating conditions. The driver needs to select the mode based on the actual operating conditions. This selection can be designed to be made through the vehicle's central control menu. The following three modes cover all operating conditions; the choice of which mode for shortening turning radius is based on the actual situation.

[0095] (1) Small radius turning model for off-road conditions

[0096] This mode is intended for off-road driving, such as in mud, sand, and snow. This mode provides smooth steering, requiring the driver to gently apply the accelerator pedal. With this strategy, the vehicle exhibits a turning radius lower than in normal mode. In this mode, ESC disengages rear wheel slip control to avoid interfering with the strategy.

[0097] (2) Paved road small radius turning model

[0098] This mode is for use on paved roads, such as asphalt and concrete. This aggressive steering mode requires the driver to deeply depress the accelerator pedal. With the assistance of this strategy, the vehicle will steer by drifting, narrowing the turning radius. In this mode, ESC must disengage all-wheel slip control to avoid interfering with the strategy.

[0099] (3) U-turn model in narrow road conditions

[0100] This mode is designed for extremely narrow roads where the road space only allows the vehicle to turn or swerve in place. The driver controls the intensity of this mode. A light accelerator pedal press results in a slow, stationary turn; a deeper accelerator pedal press results in a faster, stationary turn. In this mode, the chassis stability control system (ESC) must disengage all-wheel slip control to avoid interfering with this strategy.

[0101] After the driver selects any mode, the instrument panel will indicate the activation status of the mode to remind the driver that the mode has been activated.

[0102] 2. Control Strategy

[0103] (1) Small radius steering mode for off-road conditions

[0104] In off-road conditions, negative torque control is applied to the inner rear wheel and positive torque to the outer rear wheel, causing the inner rear wheel to lock and the outer rear wheel to spin, simultaneously creating a yaw torque for the vehicle. Due to the longitudinal slip / spin of the rear wheels, their lateral adhesion is less than that of the front wheels. Under the influence of the yaw torque, the rear wheels are more prone to sideways slipping than the front wheels, increasing the vehicle's oversteer characteristics and thus reducing the turning radius.

[0105] This mode is suitable for unpaved roads with low adhesion coefficients, such as sand, dirt roads, muddy roads, snow, ice, etc. In this mode, the driver's required torque is fully distributed to the front wheels, and the rear wheel torque is calculated according to the following strategy.

[0106] Inner rear wheel negative torque control strategy:

[0107] ① When the steering wheel turns left, the left rear wheel is determined as the inner rear wheel; when the steering wheel turns right, the right rear wheel is determined as the inner rear wheel.

[0108] ② Figure 3 This graph shows the target speed of the inner rear wheel changing over time for a turning control method for a four-wheel drive vehicle, provided in Example 3 of the present invention. The target speed of the inner rear wheel varies between [0, 1] km / h, remaining at 0 km / h for 3 seconds before changing toward 1 km / h (the actual value is subject to final calibration). This is to avoid prolonged sliding friction on the same part of the inner rear wheel, preventing inconsistent wear on different parts of the wheel and affecting ride quality.

[0109] ③ The control method adopts PID controller, and the torque calculation formula is as follows:

[0110]

[0111] Among them, T in_rearis the inner rear wheel torque; kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle to determine its value; v in_act is the actual inner rear wheel speed, provided by the wheel speed sensor; v in_tgt is the target wheel speed of the inner rear wheel.

[0112] Outer rear wheel positive torque control strategy:

[0113] ① Calculation of target wheel speed of outer rear wheel

[0114] On vehicles equipped with an open differential, the turning radius is reduced by braking the inner rear wheel. On vehicles equipped with a transfer case, due to the presence of the differential, when the inner rear wheel locks, the outer rear wheel's speed increases, causing it to slip. This is because the transfer case's function is to equalize the average speeds of the front and rear axles, so when the inner rear wheel locks, the outer rear wheel inevitably increases in speed. On distributed four-wheel drive vehicles, which lack an open differential, this paper simulates the effects of a transfer case and an open differential by implementing closed-loop control of the outer rear wheel's speed. When the outer rear wheel slips, its lateral adhesion decreases, making the rear end of the vehicle more susceptible to sideways sliding and reducing the turning radius.

[0115] According to the principles of vehicle dynamics and the characteristics of the differential, when the inner rear wheel is locked, the speed of the outer rear wheel should be:

[0116] v out_rear =(v FR +v FL )cosδ (6)

[0117] Among them, 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 left front wheel speed, and δ is the front wheel steering angle. The actual right and left front wheel speeds can be acquired by the wheel speed sensors of the corresponding wheels of the target vehicle and transmitted to the vehicle controller. The front wheel steering angle can be acquired by the steering angle sensor and transmitted to the vehicle controller.

[0118] ②Outer rear wheel torque calculation

[0119] 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 simulate the effect of the open differential, causing the inner rear wheel to lock while the outer rear wheel slips.

[0120]

[0121] Among them, T in_rearis the inner rear wheel torque; kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle to determine its value; v in_act is the actual inner rear wheel speed, provided by the wheel speed sensor; v in_tgt is the target wheel speed of the inner rear wheel.

[0122] (2) Small radius steering mode on paved roads

[0123] Unlike off-road conditions, paved roads mostly have a high adhesion coefficient. If the inner rear wheel lock control method is used, the vehicle will be difficult to start due to the locking of the single rear wheel. Moreover, when the inner rear wheel is locked, the other wheels are not prone to side skidding, and there is no obvious effect on reducing the turning radius. Therefore, the inner rear wheel lock control method is not suitable for paved roads.

[0124] 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, putting the vehicle in rear-wheel drive mode. When the driver quickly and deeply steps on the accelerator pedal, the two rear wheels will slip. At this time, the driver can control the steering wheel to achieve tail-swing steering, which can significantly shorten the turning radius.

[0125] ① Calculation of the initial value of the target slip rate

[0126] In this mode, the initial value of the rear wheel target slip is related to the driver's steering wheel angle, as shown in the table below. The steering wheel angle represents the driver's steering intent. A greater rear wheel slip results in a more complete vehicle drift and a smaller turning radius. The larger the steering wheel angle, the larger the initial value of the rear wheel target slip. The actual vehicle parameters must be determined based on calibration results. The principle is that greater wheel slip results in less lateral adhesion. Once the target slip is determined, the target speed can be determined. Similarly, a PID controller is used to control the actual rear wheel speed near the target speed, enabling drift steering and significantly reducing the turning radius. The purpose of this PID controller is to ensure that the actual rear wheel slip equals the target slip.

[0127] ② Yaw closed-loop control

[0128] This patent first calculates the vehicle's target yaw rate based on the vehicle's steering wheel angle, vehicle speed, and lateral acceleration. The detailed steps for calculating the target yaw rate can be determined based on existing methods. 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 of the vehicle-road relationship.

[0129] The yaw sensor can determine the vehicle's actual yaw rate. When the actual yaw rate is in the same direction as the driver's target yaw rate, a greater yaw rate indicates oversteer and the rear wheel target slip rate should be reduced. A lesser yaw rate indicates understeer and the rear wheel target slip rate should be increased. A PID controller is used to perform closed-loop adjustment of the target slip rate. This calculation adjusts 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:

[0130]

[0131] Among them, kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle to determine its value; γ act is the actual yaw rate, provided by the yaw sensor; γ tgt is the target yaw rate, calculated from the two-degree-of-freedom model; Δslip is the correction for the rear wheel target slip rate. The total rear wheel target slip rate is the sum of the initial slip value and the correction for the rear wheel target slip rate. When the actual yaw rate is opposite to the driver's target yaw rate, it indicates that the driver needs to reduce the vehicle's drift and, therefore, the rear wheel slip rate needs to be reduced.

[0132] (3) U-turn mode in narrow road conditions

[0133] This mode is designed for very narrow roads, allowing the vehicle to turn around on the spot, with the center of the vehicle's turning circle being the center of symmetry of the four wheels. Because all four wheels simultaneously experience significant slippage in this mode, it is recommended for use on unpaved roads and other roads with low adhesion to prevent significant tire wear.

[0134] This mode requires the driver to maintain the steering wheel in the center position and select a left or right turn using a button. When turning left, the right two wheels become the outer wheels, and the left two wheels become the inner wheels; when turning right, the left two wheels become the outer wheels, and the right two wheels become the inner wheels. The proposed strategy distributes the driver's requested torque equally among all four wheels, driving the outer wheels forward and the inner wheels backward (for example, if the driver requests a torque of 1000 N·m, the outer front wheel receives 250 N·m, the outer rear wheel receives 250 N·m, the inner front wheel receives -250 N·m, and the inner rear wheel receives -250 N·m). When the driver's requested torque is sufficient, the vehicle will yaw in place. When the driver feels the steering angle meets the requirement, they can release the accelerator pedal to deactivate the steering function.

[0135] To prevent excessive wheel slippage caused by pressing the accelerator too deeply, a unique slip control function was developed for this mode. Excessive wheel slip not only increases tire wear but also reduces steering ability, so the vehicle's slip rate must be controlled.

[0136] This strategy proposes to limit the maximum yaw rate of the vehicle γ MAX (For example, 4 rad / s, calibrable). This is because in this mode, the ESC's TCS function no longer works properly. If the driver depresses the accelerator pedal too deeply, the wheels will spin violently, causing significant tire wear. The vehicle will also experience violent yaw motion, which is dangerous. Therefore, the maximum yaw rate of the wheels must be limited.

[0137] 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. The calculation formula is as follows:

[0138]

[0139] Among them, T driver is the total torque of the target vehicle; kp is the proportional term coefficient, which needs to be calibrated on the actual vehicle to determine its value; ki is the integral term coefficient, which needs to be calibrated on the actual vehicle to determine its value; kd is the differential term coefficient, which needs to be calibrated on the actual vehicle 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.

[0140] Example 4

[0141] Figure 4 This is a schematic diagram of the structure of a turning control device for a four-wheel drive vehicle provided in the fourth embodiment of the present invention. The device can execute the turning control method for a four-wheel drive vehicle provided in the embodiment of the present invention. The device includes:

[0142] The turning mode acquisition module 410 is used to obtain the target turning control mode selected by the user based on the driving scenario;

[0143] A driving torque acquisition module 420 is used to acquire current steering information and current driving torque output through the accelerator pedal;

[0144] an unpaved road control module 431 for distributing the current driving torque to the two front wheels for driving control if the target turning control mode is the unpaved road control mode, and performing locking control on the inner rear wheel and slip control on the outer rear wheel based on the current steering information;

[0145] a paved road control module 432 configured to distribute the current driving torque to the two rear wheels for driving control if the target turning control mode is the paved road control mode, and to perform drift control on the two rear wheels based on the current steering information;

[0146] The pivot control module 433 is configured to distribute the current driving torque to the four wheels for driving control based on the current steering information if the target turning control mode is the pivot control mode.

[0147] Based on the above technical solutions, the unpaved road control module 431 includes:

[0148] a front wheel torque determination unit, configured to distribute the current driving torque equally to the two front wheels and determine the positive torque of each front wheel;

[0149] a forward drive unit for driving each front wheel forward based on the positive torque of the corresponding front wheel;

[0150] Based on the above technical solutions, the unpaved road control module 431 further includes:

[0151] an inner and outer rear wheel determination unit, configured to determine an inner rear wheel and an outer rear wheel based on a current steering direction;

[0152] Rear wheel lock control unit, used to control the lock of the inner rear wheel;

[0153] a target wheel speed determination unit, used to determine the target wheel speed of the outer rear wheel when the inner rear wheel is locked;

[0154] The rear wheel control unit is used to perform PID control on the actual wheel speed of the outer rear wheel based on the target wheel speed of the outer rear wheel, determine the positive torque of the inner rear wheel, and drive the inner rear wheel forward based on the positive torque of the inner rear wheel.

[0155] Based on the above technical solutions, the pavement control module also includes:

[0156] a target slip rate determination unit, configured to determine a target slip rate for each rear wheel based on a current steering angle of the steering wheel;

[0157] a target wheel speed determination unit, configured to determine a target wheel speed of each rear wheel according to a target slip rate of each rear wheel;

[0158] The rear wheel control unit is configured to perform PID control on the actual wheel speed of each rear wheel based on the target 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.

[0159] Based on the above technical solutions, the target slip ratio determination unit includes:

[0160] an initial slip rate determination subunit, configured to determine an initial slip rate of each rear wheel according to a current steering angle of the steering wheel;

[0161] a target yaw rate determination subunit, for determining a target yaw rate of the four-wheel drive vehicle based on a current steering wheel angle, vehicle speed, and lateral acceleration;

[0162] a slip rate correction amount determination subunit, configured to perform PID control on the actual yaw rate of the four-wheel drive vehicle based on the target yaw rate to determine the slip rate correction amount;

[0163] The target slip rate determination subunit is used to determine the target slip rate of each rear wheel according to the initial slip rate and the slip rate correction amount.

[0164] On the basis of the above technical solutions, the turn-around control module further includes: a drive control submodule. The drive control submodule includes:

[0165] an inner and outer wheel determining unit, configured to determine two inner wheels and two outer wheels based on a current steering direction;

[0166] an outer wheel control unit for equally distributing the current drive torque to the two inner wheels and the two outer wheels, determining a negative torque for each inner wheel and a positive torque for each outer wheel;

[0167] The inner wheel control unit is configured to drive each inner wheel rearward based on the negative torque of each inner wheel and to drive each outer wheel forward based on the positive torque of each outer wheel.

[0168] Based on the above technical solutions, the stationary U-turn control module also includes:

[0169] 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 driving torque is distributed to the four wheels for drive control.

[0170] Based on the above technical solutions, the stationary U-turn control module also includes:

[0171] If the target turning control mode is the pivot point control mode, the user is reminded to keep the steering wheel in the center position and the current steering direction selected by the user is obtained.

[0172] A turning control device for a four-wheel drive vehicle provided in an embodiment of the present invention can execute the turning control method for a four-wheel drive vehicle provided in any embodiment of the present invention. The turning control device for a four-wheel drive vehicle in an embodiment of the present invention is used 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 vehicle's driving experience and the convenience of vehicle use.

[0173] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0174] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A turning control method for a four-wheel drive vehicle, characterized in that: include: Obtain the target turning control mode selected by the user based on the driving scenario; Obtain current steering information and current driving torque output through the accelerator pedal; If the target turning control mode is the unpaved road control mode, the current driving torque is distributed to the two front wheels for driving control, and the inner rear wheel is locked and the outer rear wheel is slipped based on the current steering information; If the target turning control mode is the paved road control mode, the current driving torque is distributed to the two rear wheels for driving control, and the two rear wheels are subjected to tailswing control based on the current steering information; If the target turning control mode is the pivot point control mode, the current driving torque is distributed to the four wheels for driving control based on the current steering information; The step of performing tail-swing control on the two rear wheels based on the current steering information 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 wheel angle, vehicle speed, and lateral acceleration; Based on the target yaw rate, performing PID control on the actual yaw rate of the four-wheel drive vehicle to determine a slip rate correction amount; determining a target slip rate of each rear wheel according to the initial slip rate and the slip rate correction amount; determining a target wheel speed of each rear wheel according to a target slip rate of each rear wheel; Based on the target wheel speed of each rear wheel, PID control is performed on the actual wheel speed of each rear wheel, a positive torque of each rear wheel is determined, and each rear wheel is driven forward based on the positive torque of each rear wheel.

2. The method according to claim 1, characterized in that The method of distributing the current driving torque to the 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 applied to each front wheel, the corresponding front wheel is driven forward.

3. The method according to claim 1, characterized in that The locking control of the inner rear wheel and the slip control of the outer rear wheel based on the current steering information include: Based on the current steering direction, determine the inner rear wheel and the outer rear wheel; performing locking control on the inner rear wheel; determining a 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, PID control is performed on the actual wheel speed of the outer rear wheel, a positive torque of the outer rear wheel is determined, and the inner rear wheel is driven forward based on the positive torque of the outer rear wheel.

4. The method according to claim 3, characterized in that The locking control of the inner rear wheel includes: Obtaining a target wheel speed of the inner rear wheel, wherein the target wheel speed is a periodically varying wheel speed, with a portion of time periods within each cycle being zero speed and the remaining time periods being non-zero 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, a 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.

5. The method according to claim 1, wherein The method of distributing the current driving torque to the four wheels for driving control based on the current steering information includes: Based on the current steering direction, determine the two inner wheels and the two outer wheels; Distribute the current driving torque equally to the two inner wheels and the two outer wheels, determine a negative torque for each inner wheel and a positive torque for each outer wheel; Each inside wheel is driven rearward based on the negative torque at each inside wheel, and each outside wheel is driven forward based on the positive torque at each outside wheel.

6. The method according to claim 1, characterized in that After distributing the current driving torque to the four wheels for driving control based on the current steering information, the following steps are also included: 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 driving torque is distributed to the four wheels for drive control.

7. The method according to claim 1, characterized in that Get the current steering information, including: If the target turning control mode is the pivot point control mode, the user is reminded to keep the steering wheel in the centering position, and the current steering direction selected by the user through the button is obtained.

8. A turning control device for a four-wheel drive vehicle, characterized in that: include: A turning mode acquisition module is used to obtain the target turning control mode selected by the user based on the driving scenario; A driving torque acquisition module is used to obtain current steering information and current driving torque output through the accelerator pedal; an unpaved road control module, configured to distribute the current driving torque to the two front wheels for driving control if the target turning control mode is the unpaved road control mode, and to perform locking control on the inner rear wheel and slip control on the outer rear wheel based on current steering information; a paved road control module, configured to distribute the current driving torque to the two rear wheels for driving control if the target turning control mode is the paved road control mode, and perform drift control on the two rear wheels based on the current steering information; a pivot control module configured to distribute the current driving torque to the four wheels for driving control based on the current steering information if the target turning control mode is the pivot control mode; Wherein, the pavement control module includes: a target slip rate determination unit, configured to determine an initial slip rate for each rear wheel based on a current steering wheel angle; determine a target yaw rate for the four-wheel drive vehicle based on the current steering wheel angle, vehicle speed, and lateral acceleration; perform PID control on the actual yaw rate of the four-wheel drive vehicle based on the target yaw rate to determine a slip rate correction; and determine a target slip rate for each rear wheel based on the initial slip rate and the slip rate correction; a target wheel speed determination unit, configured to determine a target wheel speed of each rear wheel according to a target slip rate of each rear wheel; The rear wheel control unit is configured to perform PID control on the actual wheel speed of each rear wheel based on the target 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.

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