Automatic emergency control method and system based on wheel cooperative steering

Abstract

The invention discloses an automatic emergency control method and system based on wheel cooperative steering, electronic signals are used for replacing traditional mechanical connection so that the characteristic that four wheels can rotate in different directions in the braking process of a vehicle can be achieved, an AEB control strategy based on wheel steering cooperation is designed, the actual braking distance is shortened, and the braking efficiency is improved. And the braking effect of the AEB system is improved. The method comprises the steps that in the process that an AEB system triggers braking, when the road adhesion state of a vehicle in the current driving state is a high adhesion state, whether the vehicle speed is smaller than or equal to a speed threshold value or not is judged; wherein the speed threshold value is the speed at which the tire is in a sliding state when the slip rate between the wheel and the ground is too high; when the vehicle speed is smaller than or equal to the speed threshold value, a wheel cooperative steering mode is adopted for assisting in braking so as to reduce the braking distance; according to the wheel auxiliary steering mode, friction force between wheels and the ground is increased through front wheel steering or four-wheel steering, and wheel steering comprises wheel inward deflection or wheel outward deflection.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of vehicle braking control, and in particular to an automatic emergency control method and system based on coordinated wheel steering. Background Art

[0002] Traffic accidents have always been a serious challenge facing the global society, resulting in huge casualties and losses. In order to meet this challenge, automatic emergency braking (AEB) technology has become the focus of research and application, aiming to reduce the incidence and severity of traffic accidents by reducing or avoiding collisions with obstacles ahead, thereby improving the safety of drivers and passengers.

[0003] The control strategy of the longitudinal AEB system mainly includes control algorithms based on safety distance and collision safety time. The safety distance is the minimum distance that the vehicle needs to maintain in order to avoid collision with obstacles in time under the current driving state. The safety time model calculates the collision time through the motion relationship between vehicles, compares it with the safety time threshold, and determines the vehicle braking state.

[0004] Existing research has conducted in-depth studies on automatic emergency braking systems from the aspects of algorithm optimization and controller improvement. However, the impact of tire steering on the AEB system has not been considered in the research on longitudinal braking. Summary of the invention

[0005] In order to overcome the above-mentioned technical defects, this application is based on the characteristic of replacing traditional mechanical connections with electronic signals in wire-controlled steering technology, so that the vehicle can realize the rotation of four wheels in different directions during braking. An AEB control strategy based on wheel steering coordination is designed, and through comparative analysis under various test scenarios, its advantages in improving braking efficiency compared with traditional AEB algorithms are demonstrated.

[0006] The technical solution in this application is as follows:

[0007] An automatic emergency control method based on wheel coordination, comprising:

[0008] During the AEB system triggering braking, when the road adhesion state of the vehicle is high adhesion state in the current driving state, determine whether the vehicle speed is less than or equal to the speed threshold;

[0009] The speed threshold is to prevent the slip rate between the wheel and the ground from being too high, causing the tire to slide;

[0010] When the vehicle speed is less than or equal to the speed threshold, the wheel coordinated steering method is used to assist braking to reduce the braking distance;

[0011] Among them, the wheel-assisted steering method increases the friction between the wheels and the ground by front-wheel steering or four-wheel steering. Wheel steering includes inward deflection of the wheels or outward deflection of the wheels.

[0012] Optionally, in a possible implementation of the above automatic emergency control method, the speed threshold ranges from 5 to 10 m / s, and the wheel steering angle ranges from 10 to 20 degrees.

[0013] Further optionally, the speed threshold value is 6 m / s, 7 m / s or 9 m / s.

[0014] Further optionally, when the speed threshold is 6 m / s, the wheel steering angle is 20 degrees; or, when the speed threshold is 6 m / s, the wheel steering angle is 10 degrees.

[0015] Optionally, in a possible implementation of the automatic emergency control method, the high adhesion state is that the friction coefficient between the tire and the road surface, that is, the road surface adhesion coefficient is greater than 0.8.

[0016] Optionally, in a possible implementation of the automatic emergency control method, using wheel coordinated steering to assist braking includes: sending a braking signal and a steering signal to an on-board ECU.

[0017] A coordinated steering AEB system is used to execute all operations in the above-mentioned automatic emergency control method based on wheel coordination and its possible implementation methods.

[0018] A vehicle is provided with a coordinated steering AEB system for executing all operations in the above-mentioned automatic emergency control method based on wheel coordination and possible implementation methods thereof.

[0019] The above-mentioned technical scheme is adopted in the embodiment of the present application to achieve the following technical effects: when the traditional AEB system is unable to complete the braking task independently, it is ensured that during the automatic emergency braking process, when the speed drops below the speed threshold, the wheel coordinated steering method is used for auxiliary braking, and the four-wheel turning angles are coordinated, including inward deflection or outward deflection of the wheels, so that greater friction is generated between the wheels and the road surface, while avoiding excessive slip rate between the wheels and the ground and the tires being in a sliding state, thereby effectively avoiding collisions, shortening the braking distance, and improving the braking effect of the AEB system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings exemplarily illustrate the embodiments and constitute a part of the specification, and together with the text description of the specification, are used to explain the exemplary implementation of the embodiments. The embodiments shown are for illustrative purposes only and do not limit the scope of the claims. In all drawings, the same reference numerals refer to similar but not necessarily identical elements.

[0021] Figure 1 This is a schematic diagram of the emergency brake wheel deflection in this application;

[0022] Figure 2 Schematic diagram of eight steering modes for coordinated wheel steering;

[0023] Figure 3 A schematic flow chart of an automatic emergency control method based on coordinated wheel steering in this application;

[0024] Figure 4 This is a system framework diagram of the collaborative steering AEB system in this application;

[0025] Figure 5 This is a comparison chart of braking performance in high adhesion scenarios in this application;

[0026] Figure 6 This is a comparison chart of braking performance in low adhesion scenarios in this application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0028] It should be noted that the descriptions involving "first", "second", etc. in the embodiments of the present application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0029] In the description of the present application, it should be understood that the numerical labels before the steps do not indicate the order in which the steps are executed, but are only used to facilitate the description of the present application and to distinguish each step, and therefore should not be understood as a limitation on the present application.

[0030] Generally speaking, traditional automatic emergency braking (AEB) systems use the TTC collision time algorithm. The TTC collision time algorithm issues a danger warning to the driver based on the time dimension, that is, TTC refers to the time required for two vehicles to maintain their current speed until they collide from the current moment. The TTC algorithm is only applied when the speed of the rear vehicle is greater than that of the front vehicle and the two vehicles are driving on the road in front and behind.

[0031] The current AEB system mainly determines whether to activate the brakes based on the relative distance and speed information from the vehicle in front, but this does not fully consider the potential impact of wheel angle on the braking effect. In some extreme braking scenarios, the traditional AEB algorithm cannot ensure sufficient braking safety, which may not be able to effectively avoid collisions with obstacles ahead. To address this problem, this paper takes advantage of the characteristics of the vehicle and proposes a novel automatic emergency braking control strategy based on coordinated wheel steering. This strategy, such as Figure 1 As shown, when the traditional AEB algorithm cannot complete the braking task independently, it can coordinate the four-wheel turning angles to generate greater friction and contact with the ground, thereby shortening the actual braking distance.

[0032] The traditional TTC algorithm can successfully avoid collisions with the vehicle in front in many braking scenarios, but the effect of the traditional AEB system is not satisfactory in dangerous situations such as high-speed driving or when the distance between vehicles is too close. Therefore, when studying the cooperative steering AEB system, this paper first ensures that the traditional AEB-TTC system can effectively avoid collisions at a certain speed to avoid tire wear caused by cooperative steering braking. In an emergency, if the traditional AEB system cannot avoid a collision, full braking is used to reduce the vehicle speed to below the threshold where cooperative steering can take effect, and the friction of the tires is increased by cooperative steering of the front and rear wheels, thereby reducing the braking distance and avoiding the occurrence of a collision. Figure 2 As shown, there are eight coordinated steering modes according to the different turning directions of the four wheels of the vehicle.

[0033] like Figure 3 As shown, the automatic emergency control method based on wheel coordination in this application includes:

[0034] When the vehicle suddenly encounters an obstacle while driving, the automatic emergency control system uses emergency braking to reduce the vehicle's speed and determines whether the speed threshold suitable for turning is reached during the braking process;

[0035] S1. During the AEB system triggering braking process, when the road adhesion state under the current driving state of the vehicle is a high adhesion state, determine whether the vehicle speed is less than or equal to the speed threshold.

[0036] The speed threshold is used to prevent the slip rate between the wheel and the ground from being too high, causing the tire to slide.

[0037] During the driving process, the vehicle obtains the current road conditions and vehicle status information through vehicle sensors such as lidar, camera, accelerometer, etc. When a sudden obstacle occurs, the AEB system will take emergency braking to reduce the speed of the vehicle.

[0038] When the AEB system triggers braking, the vehicle speed will continue to decrease under the action of braking. By implementing coordinated steering of the vehicle tires, the following can be achieved: Figure 2 The eight different steering methods shown in the figure increase the contact area between the wheels and the ground, thereby increasing friction and improving the braking effect. However, as the vehicle speed increases, the effect of this method will gradually weaken or even become unfavorable. This is because after exceeding a certain speed, the form of coordinated steering may cause the slip rate between the wheels and the ground to be too high, the tires to slide, and even cause the risk of vehicle loss of control, thereby reducing the braking effect of AEB. Therefore, it is necessary to set a speed threshold to avoid the above risks.

[0039] Similarly, the road surface adhesion state affects whether to adopt wheel coordinated steering to assist the vehicle in braking. The road surface adhesion state is related to the friction coefficient between the tire and the road surface. Specifically, the greater the friction coefficient between the tire and the road surface, the greater the road surface adhesion, which can be identified as a high adhesion state; otherwise, it can be identified as a low adhesion state. The determination of the high adhesion state is comprehensively determined by the road surface state and the tire condition. In this application, when the friction coefficient between the tire and the road surface is greater than 0.8, it can be identified as a high adhesion state, and the wheel coordinated steering auxiliary braking can be initiated.

[0040] S2. When the vehicle speed is less than or equal to the speed threshold, the wheel coordinated steering method is used to assist braking to reduce the braking distance.

[0041] Among them, the wheel-assisted steering method increases the friction between the wheels and the ground by front-wheel steering or four-wheel steering. Wheel steering includes inward deflection of the wheels or outward deflection of the wheels.

[0042] Optionally, in one implementation of the embodiment of the present application, the speed threshold ranges from 5 to 10 m / s, and the wheel steering angle is 10 to 20 degrees.

[0043] Further optionally, in one implementation of the embodiment of the present application, the speed threshold value is 6 m / s, 7 m / s or 9 m / s.

[0044] Optionally, in one implementation of the embodiment of the present application, when the speed threshold is 6 m / s, the wheel steering angle is 20 degrees; or, when the speed threshold is 6 m / s, the wheel steering angle is 10 degrees.

[0045] In the technical solution of the present application, when the traditional AEB system is unable to complete the braking task independently, it is ensured that during the automatic emergency braking process, at a certain speed (i.e., the speed threshold), the wheel coordinated steering method is used for auxiliary braking, and the four-wheel turning angles are coordinated to generate greater friction and contact with the ground, thereby shortening the actual braking distance and effectively avoiding collisions. At the same time, the tire wear caused by coordinated steering braking can be avoided, which can effectively improve the braking effect of the AEB system.

[0046] This application uses three standardized test conditions described in the "Performance Requirements and Test Methods for Automatic Emergency Braking Systems (AEBS) for Passenger Cars", namely, stationary target conditions (STC), moving target conditions (MTC), and braking target conditions (BTC) to simulate and verify the strategy to ensure its effectiveness.

[0047] The simulation test analysis is as follows:

[0048] During the driving process, the vehicle sensors such as laser radar, camera, accelerometer, etc. obtain the current road conditions and vehicle status information. When a sudden obstacle occurs, the system first uses emergency braking to reduce the vehicle speed, and determines whether the speed threshold suitable for turning is reached during the braking process. When the vehicle decelerates to the appropriate threshold v * Afterwards, the front wheel / four-wheel coordinated steering is used to increase the friction with the ground to improve the braking efficiency of the AEB system. Figure 4 shown.

[0049] 1. Vehicle model

[0050] CarSim software is widely used in the industry for its built-in comprehensive vehicle data and good compatibility interface with platforms such as Matlab / Simulink. This study used CarSim software to configure the vehicle model of the main vehicle and the front vehicle, and optimized the vehicle model in CarSim based on the actual vehicle parameters. For detailed information on vehicle dynamics parameters, see Table 1.

[0051] Table 1

[0052] parameter Numeric Vehicle mass (kg) 1413 Wheelbase(m) 2.910 Distance from center of mass to front axle (m) 1.015 Front wheel track (m) 1.675 Rear wheel track (m) 1.675 Air resistance coefficient 0.3 <![CDATA[Windward area (m 2 )]]> 2.2 Tire rolling radius (m) 0.325 Vehicle length(m) 4.430 Vehicle width(m) 1.916 Vehicle height(m) 1.610

[0053] 2. Wheel deflection angle threshold setting

[0054] In order to determine the optimal speed threshold, experiments are needed to determine at what vehicle speed the cooperative steering method can still effectively increase friction and improve braking effect without causing safety hazards. This test process will involve the evaluation of AEB braking performance at different speeds, including the measurement and analysis of indicators such as braking distance and braking stability, and ultimately determine the optimal speed threshold suitable for vehicle characteristics and road conditions. After testing, it was found that on high-adhesion roads, when the speed is 5m / s or less, there is no significant difference between the traditional TTC method and the TTC method with cooperative steering. However, when the speed is increased to more than 10m / s, the use of cooperative steering will increase the slip rate of the tires, resulting in a longer braking distance. Therefore, compared with the traditional AEB system and Figure 2 The braking effectiveness of the eight cooperative steering AEB systems shown requires analysis of the differences in braking distances at vehicle speeds ranging from 6m / s to 9m / s on high-adhesion roads.

[0055] like Figure 5 The above is shown when the speed is 6-9m / s and the road adhesion coefficient μ is 0.9. Figure 2 The braking effect of eight steering-assisted braking methods is shown in the figure, where part a is at a speed of 6 m / s, part b is at a speed of 7 m / s, part c is at a speed of 6 m / s, and part d is at a speed of 7 m / s. Figure 5 From the braking distance in the figure, it can be seen that the coordinated steering braking method has a better effect when the speed is 6m / s and 7m / s. The best effect is to turn about 20° at a speed of 6m / s, and the best effect is to turn about 10° at a speed of 7m / s. Compared with the traditional AEB system, the braking distance is reduced by about 0.4 meters when the coordinated steering AEB system is adopted. However, as the vehicle speed increases, the effect of the coordinated steering AEB system gradually weakens. At the same time, it is found that the coordinated steering of the rear wheels will increase the braking distance and affect the overall braking efficiency. Based on this finding, and taking into account the wear caused by tire steering, 7m / s is taken as the speed threshold. In the emergency braking simulation, when the vehicle speed drops to this threshold, according to different driving conditions, the front wheels are coordinated to turn outward by about 10° to improve the braking efficiency. The adoption of this strategy is intended to further optimize the braking performance of the vehicle to ensure that the stopping distance is minimized as much as possible in an emergency and to improve driving safety.

[0056] Braking on a low-adhesion road surface is always a dangerous behavior. The lateral adhesion coefficient between the tire and the ground can easily reach the adhesion limit, resulting in side slip. Figure 6 In the low speed condition shown, the road adhesion coefficient μ is also low and is 0.3. Figure 2The braking effect of the eight steering methods for auxiliary braking shown in the figure, when braking on a low-adhesion road, using the coordinated steering method for the wheels will not reduce the braking distance, but will bring the opposite result. Because the road adhesion coefficient is too low, the coordinated steering method will cause the wheels to slide and the grip will be weakened. It is very dangerous, so steering should be avoided on low-adhesion roads.

[0057] 3. Simulation analysis

[0058] In order to verify the effectiveness of the designed AEB control strategy, this paper uses Carsim and Matlab / Simulink platforms for joint simulation. In this simulation, Carsim software provides simulation scenarios and vehicle dynamics models, obtains current road and vehicle information through its own sensors, and passes the distance and speed of the front vehicle to the AEB control strategy in Simulink. The AEB decision module makes decisions based on the current state of the vehicle and the environmental information, and the controller module is responsible for vehicle control. The simulation conditions refer to the AEB test conditions published by the European New Car Assessment Program (Euro-NCAP), the German Automobile Club (ADAC) and GB / T39901-2021, and are divided into three categories: stationary target conditions (STC), moving target conditions (MTC), and braking target conditions (BTC). The performance of the designed strategy is evaluated by comparing the effects of the traditional AEB algorithm (TTC algorithm) and the AEB algorithm with wheel coordinated steering (TTC-cooperative steering algorithm).

[0059] Through Matlab / Simulink and CarSim, simulation verification was carried out under three test conditions: stationary target condition, moving target condition, and braking target condition according to the AEB test conditions specified in GB / T 39901-2021. The simulation results show that:

[0060] 1) When braking on low-adhesion roads, avoid turning the wheels, as this will increase the braking distance of the vehicle.

[0061] 2). The AEB control algorithm that uses wheel coordinated steering can effectively improve the vehicle's braking performance on high-adhesion roads.

[0062] 3) In all three test conditions, collisions were avoided, which to some extent avoided or reduced the severity of accidents. At the same time, its stability was improved by 73.2%, 85.5% and 77.9% respectively. The stability of the vehicle was greatly improved while ensuring the safety of the vehicle.

[0063] Therefore, this paper proposes a wheel coordinated steering AEB control strategy, which can further enhance the braking efficiency of the vehicle.

[0064] Obviously, those skilled in the art should understand that the modules or steps of the above-mentioned embodiments of the present application can be implemented by general-purpose computer devices, they can be concentrated on a single computer device, or distributed on a network composed of multiple computer devices, optionally, they can be implemented by executable program codes of computer devices, so that they can be stored in a storage device and executed by the computer device, and in some cases, the steps shown or described can be executed in a different order from that herein, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. In this way, the embodiments of the present application are not limited to any specific combination of hardware and software.

[0065] It should be noted that the above are only preferred embodiments of the present application, and the patent protection scope of the present application is not limited thereto. Any equivalent structure or equivalent process transformation made using the contents of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An automatic emergency control method based on wheel coordination, characterized in that: include: During the AEB system triggering braking, when the road adhesion state of the vehicle is high adhesion state in the current driving state, determine whether the vehicle speed is less than or equal to the speed threshold; The speed threshold is to prevent the slip rate between the wheel and the ground from being too high, causing the tire to slide; When the vehicle speed is less than or equal to the speed threshold, the wheel coordinated steering method is used to assist braking to reduce the braking distance; Among them, the wheel-assisted steering method increases the friction between the wheels and the ground by front-wheel steering or four-wheel steering. Wheel steering includes inward deflection of the wheels or outward deflection of the wheels.

2. The automatic emergency control method according to claim 1, characterized in that: The speed threshold ranges from 5-10m / s and the wheel steering angle ranges from 10-20 degrees.

3. The automatic emergency control method according to claim 2, characterized in that: The speed threshold value is 6m / s, 7m / s or 9m / s.

4. The automatic emergency control method according to claim 2 or 3, characterized in that: When the speed threshold is 6m / s, the wheel steering angle is 20 degrees; Alternatively, when the speed threshold is 6 m / s, the wheel steering angle is 10 degrees.

5. The automatic emergency control method according to claim 1, characterized in that: The high adhesion state means that the friction coefficient between the tire and the road surface, that is, the road adhesion coefficient, is greater than 0.

8.

6. The automatic emergency control method according to claim 1, characterized in that: The auxiliary braking method using wheel coordinated steering includes: sending a braking signal and a steering signal to the vehicle-mounted ECU.

7. A coordinated steering AEB system, characterized in that: The system is used to execute the automatic emergency control method described in any one of claims 1 to 6.

8. A vehicle, characterized in that: The vehicle is equipped with the cooperative steering AEB system described in claim 7.

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