阅读说明：本技术 自动驾驶车辆的横向控制安全监测方法及系统 (Lateral control safety monitoring method and system for automatic driving vehicle ) 是由 王天培 张凯 和林 甄龙豹 葛建勇 鲁宁 张健 曹增 张露 高莎莎 于 2019-03-18 设计创作，主要内容包括：本发明涉及智能交通技术领域,提供一种自动驾驶车辆的横向控制安全监测方法及系统。所述方法包括：建立车辆的侧翻稳定性评价指标,包括横向载荷转移率；确定影响横向载荷转移率的因子,包括侧向加速度,以及将侧向加速度作为横向载荷转移率对应的稳定性控制目标；根据车辆运动学模型及车辆参数,建立侧向加速度与纵向车速及方向盘转角之间的对应关系；根据所述对应关系,获取不同车速下给定的最大侧向加速度对应的最大方向盘转角作为转角阈值；以及实时监测方向盘转角,在其大于转角阈值时,将方向盘转角限制在转角阈值,否则正常输出方向盘转角。本发明相比于传统的直接给出极值限制值的方案,更加适应不同的工况和不断变化的车辆状态。(The invention relates to the technical field of intelligent traffic, and provides a transverse control safety monitoring method and system for an automatic driving vehicle. The method comprises the following steps: establishing rollover stability evaluation indexes of the vehicle, including a transverse load transfer rate; determining factors influencing the transverse load transfer rate, including lateral acceleration, and taking the lateral acceleration as a stability control target corresponding to the transverse load transfer rate; establishing a corresponding relation between lateral acceleration and longitudinal speed as well as between steering wheel corners according to a vehicle kinematics model and vehicle parameters; acquiring the maximum steering wheel corner corresponding to the given maximum lateral acceleration at different vehicle speeds as a corner threshold value according to the corresponding relation; and monitoring the steering wheel angle in real time, limiting the steering wheel angle to the steering wheel threshold value when the steering wheel angle is larger than the steering wheel threshold value, and otherwise, normally outputting the steering wheel angle. Compared with the traditional scheme of directly providing the extreme limit value, the method is more suitable for different working conditions and continuously changing vehicle states.)

1. A lateral control safety monitoring method for an autonomous vehicle, the lateral control safety monitoring method comprising:

establishing a rollover stability evaluation index of the vehicle, wherein the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle;

determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle, including:

determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and

taking the lateral acceleration as the stability control target corresponding to the transverse load transfer rate;

establishing a corresponding relation between the lateral acceleration and the longitudinal speed as well as the steering wheel corner according to a vehicle kinematics model and vehicle parameters;

according to the corresponding relation, obtaining the maximum steering wheel corner corresponding to the given maximum lateral acceleration under different vehicle speeds, and taking the maximum steering wheel corner as a corner threshold value; and

and monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.

2. The lateral-control safety monitoring method for an autonomous vehicle of claim 1, wherein the rollover stability assessment indicators further comprise one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.

3. The lateral-control safety monitoring method for autonomous vehicles of claim 1, wherein the determining a factor that affects the lateral load transfer rate comprises:

establishing a mathematical model expressing the transverse load transfer rate as follows:

wherein LTR represents the lateral load transfer rate, a_yRepresenting the lateral acceleration, h representing the height of the centre of mass, h_sThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;

determining factors that affect the lateral load transfer rate include any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.

4. The lateral-control safety monitoring method for autonomous vehicles according to claim 1, characterized in that the correspondence between the lateral acceleration and the longitudinal vehicle speed and the steering wheel angle is:

wherein the content of the first and second substances,_swrepresenting the steering wheel angle, L representing the vehicle wheelbase, a_yRepresents the lateral acceleration, u represents the longitudinal vehicle speed, and i represents the steering system gear ratio.

5. The lateral-control safety monitoring method for an autonomous vehicle as claimed in claim 1, characterized in that the lateral-control safety monitoring method for an autonomous vehicle further comprises:

and controlling the maximum lateral acceleration corresponding to different vehicle speeds to be less than or equal to a given limit lateral acceleration value, wherein the limit lateral acceleration value is any value of 0.2-0.3 g, and g is gravity acceleration.

6. A machine-readable storage medium having instructions stored thereon for causing a machine to perform the lateral control safety monitoring method of an autonomous vehicle of any of claims 1 to 5.

7. A lateral control safety monitoring system for an autonomous vehicle, the lateral control safety monitoring system comprising:

the index establishing module is used for establishing a rollover stability evaluation index of the vehicle, and the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle;

a target determination module for determining a factor affecting the rollover stability evaluation index as a stability control target for the vehicle, comprising:

determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and

taking the lateral acceleration as the stability control target corresponding to the transverse load transfer rate;

the relation establishing module is used for establishing a corresponding relation between the lateral acceleration and the longitudinal speed as well as the steering wheel corner according to a vehicle kinematics model and vehicle parameters;

the threshold value determining module is used for acquiring the maximum steering wheel corner corresponding to the given maximum lateral acceleration under different vehicle speeds according to the corresponding relation and taking the maximum steering wheel corner as a corner threshold value; and

and the monitoring module is used for monitoring the steering wheel angle in real time and judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, the steering wheel angle is limited to be output after the steering wheel angle threshold value for vehicle transverse control, otherwise, the steering wheel angle is normally output for vehicle transverse control.

8. The lateral-control safety monitoring system for an autonomous vehicle of claim 7, wherein the rollover stability assessment indicators further comprise one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.

9. The lateral-control safety monitoring system for autonomous vehicles of claim 7, wherein the determining a factor that affects the lateral load transfer rate comprises:

establishing a mathematical model expressing the transverse load transfer rate as follows:

wherein LTR represents the lateral load transfer rate, a_yRepresenting the lateral acceleration, h representing the height of the centre of mass, h_sThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;

determining factors that affect the lateral load transfer rate include any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.

10. The lateral-control safety monitoring system for autonomous vehicles of claim 7, wherein the correspondence between lateral acceleration and longitudinal vehicle speed and steering wheel angle is:

wherein the content of the first and second substances,_swrepresenting the steering wheel angle, L representing the vehicle wheelbase, a_yRepresents the lateral acceleration, u represents the longitudinal vehicle speed, and i represents the steering system gear ratio.

Technical Field

The invention relates to the technical field of intelligent traffic, in particular to a transverse control safety monitoring method and system for an automatic driving vehicle.

Background

The design and development of an autonomous driving (also called unmanned, intelligent driving) system can be roughly divided into four modules: environmental perception, data fusion, decision planning and motion control. To realize automatic driving, an automatic driving vehicle needs to fully understand surrounding environment like human, including all environmental information affecting driving behaviors, such as surrounding vehicles, pedestrians, road signs, road surfaces, weather and the like, namely environment perception. Secondly, the automatic driving system processes all the acquired sensor information, including extraction, screening, filtering, comparison and the like, and finally obtains stable signals which can truly reflect the information of the surrounding environment of the vehicle, namely data fusion. And then, the automatic driving system makes corresponding judgment and planning according to the fused information, and the judgment and planning comprise the steps of keeping the contents of current road running, lane change, running track, running speed and the like, namely decision planning. And finally, controlling the vehicle to complete corresponding actions by the automatic driving system according to the received decision-making instruction, wherein the actions comprise keeping running in the current lane, changing lanes, running at a specified speed, following the previous vehicle, and the like, namely motion control.

The motion control module is used as a bottom module of the automatic driving control system, and is very easily influenced when other modules are in error operation. For example, a sudden failure or signal abnormality of a certain sensor causes an input abnormality of the automatic driving system, thereby causing erroneous calculation, and finally resulting in erroneous output. This erroneous output may cause the vehicle to suddenly turn or suddenly brake and accelerate, which may cause the passenger to feel uncomfortable at a light rate and cause the vehicle to sideslip and roll over at a heavy rate, thus seriously defeating the purpose of the automatic driving system.

Therefore, in order to ensure the safety of the control of the automatic driving system, a safety monitoring function needs to be added in a motion control module of the automatic driving system so as to realize the safety monitoring of the transverse and longitudinal control quantity. According to the output of the motion control module, the related safety monitoring function comprises two parts: one part is used for safety monitoring of longitudinal control, and the other part is used for safety monitoring of transverse control. The aim of safety monitoring for transverse control is mainly to ensure that the moving vehicle does not have the risks of side turning, sideslip and the like.

However, the current lateral control safety monitoring scheme directly limits the control quantity to the output (e.g., u_min≤u≤u_maxWhere u is the output value, u_minIs the upper limit of output, u_maxLower limit of output). Although the scheme can achieve a certain monitoring purpose, the method is too general and simple and cannot adapt to different working conditions and continuously changing vehicle states. The end result is often: the safety monitoring effect cannot be achieved under some working conditions; and under other working conditions, the control action of the control system is restricted. Therefore, new lateral control safety monitoring strategies need to be designed to improve safe driving of autonomous vehicles.

Disclosure of Invention

In view of the above, the present invention is directed to a lateral control safety monitoring method for an autonomous vehicle, so as to at least partially solve the above technical problems.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a lateral control safety monitoring method for an autonomous vehicle, comprising: establishing a rollover stability evaluation index of the vehicle, wherein the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle; determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle, wherein the factor influencing the lateral load transfer rate comprises the lateral acceleration of the vehicle, and the lateral acceleration is used as the stability control target corresponding to the lateral load transfer rate; establishing a corresponding relation between the lateral acceleration and the longitudinal speed as well as the steering wheel corner according to a vehicle kinematics model and vehicle parameters; according to the corresponding relation, obtaining the maximum steering wheel corner corresponding to the given maximum lateral acceleration under different vehicle speeds, and taking the maximum steering wheel corner as a corner threshold value; and monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.

Further, the rollover stability evaluation index further includes one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.

Further, the determining a factor that affects the lateral load transfer rate includes:

first, a mathematical model expressing the lateral load transfer rate is established as follows:

wherein LTR represents the lateral load transfer rate, a_yRepresenting said lateral accelerationH denotes the height of the centroid, h_sThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;

secondly, determining factors that affect the lateral load transfer rate includes any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.

Further, the corresponding relationship between the lateral acceleration and the longitudinal vehicle speed and the steering wheel angle is as follows:

wherein the content of the first and second substances,_swrepresenting the steering wheel angle, L representing the vehicle wheelbase, a_yRepresents the lateral acceleration, u represents the longitudinal vehicle speed, and i represents the steering system gear ratio.

Further, the lateral control safety monitoring method for the autonomous vehicle further comprises: and controlling the maximum lateral acceleration corresponding to different vehicle speeds to be less than or equal to a given limit lateral acceleration value, wherein the limit lateral acceleration value is 0.25g, and g is gravity acceleration.

Compared with the prior art, the transverse control safety monitoring method based on the vehicle kinematic design can achieve the purpose of safety monitoring, particularly can ensure the safe driving of the vehicle under the high-speed working condition, and further improves the safety of an automatic driving system, so that the transverse control safety monitoring method is more suitable for different working conditions and continuously changing vehicle states compared with the traditional scheme of directly providing an extreme value limiting value.

Another object of the present invention is to propose a machine readable storage medium to at least partially solve the above technical problem.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a machine-readable storage medium having instructions stored thereon for causing a machine to perform the lateral control safety monitoring method for an autonomous vehicle described above.

The machine-readable storage medium has the same advantages as the above-mentioned lateral control safety monitoring method over the prior art, and is not described herein again.

Another object of the present invention is to propose a lateral control safety monitoring system of an autonomous vehicle to at least partially solve the above technical problem.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a lateral control safety monitoring system for an autonomous vehicle, comprising: the index establishing module is used for establishing a rollover stability evaluation index of the vehicle, and the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle; the target determination module is used for determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle, determining a factor influencing the transverse load transfer rate, wherein the factor comprises the lateral acceleration of the vehicle, and taking the lateral acceleration as the stability control target corresponding to the transverse load transfer rate; the relation establishing module is used for establishing a corresponding relation between the lateral acceleration and the longitudinal speed as well as the steering wheel corner according to a vehicle kinematics model and vehicle parameters; the threshold value determining module is used for acquiring the maximum steering wheel corner corresponding to the given maximum lateral acceleration under different vehicle speeds according to the corresponding relation and taking the maximum steering wheel corner as a corner threshold value; and the monitoring module is used for monitoring the steering wheel angle in real time and judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, the steering wheel angle is limited to be output after the steering wheel angle threshold value for vehicle transverse control, otherwise, the steering wheel angle is normally output for vehicle transverse control.

Further, the rollover stability evaluation index further includes one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.

Further, the determining a factor that affects the lateral load transfer rate includes:

first, a mathematical model expressing the lateral load transfer rate is established as follows:

wherein LTR represents the lateral load transfer rate, a_yRepresenting the lateral acceleration, h representing the height of the centre of mass, h_sThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;

secondly, determining factors that affect the lateral load transfer rate includes any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.

Further, the corresponding relationship between the lateral acceleration and the longitudinal vehicle speed and the steering wheel angle is as follows:

wherein the content of the first and second substances,_swrepresenting the steering wheel angle, L representing the vehicle wheelbase, a_yRepresents the lateral acceleration, u represents the longitudinal vehicle speed, and i represents the steering system gear ratio.

Compared with the prior art, the transverse control safety monitoring system and the transverse control safety monitoring method have the same advantages, and are not described again.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic flow diagram of a lateral control safety monitoring method for an autonomous vehicle in accordance with an embodiment of the present invention;

FIG. 2 is a schematic diagram of a physical model of lateral load transfer rate for an embodiment of the present invention;

FIG. 3 is a graph of maximum steering wheel angle at different vehicle speeds in an actual measurement example of an embodiment of the present invention; and

fig. 4 is a schematic structural diagram of a lateral control safety monitoring system of an autonomous vehicle according to an embodiment of the present invention.

Description of reference numerals:

410. index establishing module 420 and target determining module

430. Relationship establishing module 440 and threshold determining module

450. Monitoring module

Detailed Description

In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Fig. 1 is a schematic flow chart of a lateral control safety monitoring method for an autonomous vehicle according to an embodiment of the present invention. As shown in fig. 1, the self-lateral control safety monitoring method may include the steps of:

and step S110, establishing a rollover stability evaluation index of the vehicle.

Among them, rollover is an important index of vehicle stability, and is also a control index that needs to be paid attention to in the lateral control of an autonomous vehicle. Rollover stability has only developed over 20 years, but casualties and economic losses caused by rollover are the most serious. Therefore, the rollover stability evaluation index is determined in the lateral control safety monitoring, and the introduction of the vehicle rollover control is considered to be imperative.

When the vehicle rollover is researched, an evaluation index for measuring the vehicle rollover risk degree needs to be provided, and whether the vehicle reaches a critical rollover point needs to be judged according to the evaluation index. First, rollover refers to a dangerous situation in which a vehicle turns over more than a large right angle around its driving direction as an axis during movement, resulting in collision of the vehicle body with the ground. Under actual conditions, particularly for vehicle rollover caused by curvilinear motion, due to the fact that high-speed moving vehicles have large inertia, rollover accidents of the vehicles occur in most cases when one side wheel is away from the ground. Only a few drivers driving a particular vehicle can keep running and return to a steady state at the moment when the wheels lift off the ground. Therefore, the evaluation index of the rollover stability is different for different situations.

Because the vertical load of the wheel on one side is 0 basically during high-speed movement, a rollover accident can happen, so that the vertical load of each wheel of the vehicle during high-speed movement needs to be measured in real time when the vehicle is researched to rollover. However, it is difficult to measure the load on the wheels when the vehicle is moving, so the parameters need to be converted, and the conversion process is to convert the mechanical conditions of the whole vehicle with the wheels on one side off the ground. The evaluation indexes finally used are different according to different condition changes.

Based on this, the rollover stability evaluation index in the embodiment of the present invention includes one or more of a roll angle threshold, a Lateral acceleration threshold, a rollover time, and a Lateral-Load Transfer Rate (LTR). The roll angle threshold and the lateral acceleration threshold can be used for describing the rollover state of the vehicle, and the two indexes can be obtained through static tests. Specifically, the roll angle and the lateral acceleration at different stages can be obtained by measurement or calculation while the vehicle is in motion, and compared with a threshold value, if the more closely equals or exceeds the threshold value, the rollover is more likely to occur. The problem of the two evaluation indexes is that static tests of different vehicle types are required to obtain closed values of corresponding parameters.

The lateral load transfer rate is a commonly used index for expressing the vertical load change condition of the wheel, and in the embodiment of the invention, the lateral load transfer rate can also be used for evaluating the rollover stability of the whole vehicle. The lateral load transfer rate is the ratio of the difference and the sum of vertical loads of the left wheel and the right wheel of the vehicle, and the expression is as follows:

wherein LTR represents the lateral load transfer rate, and F_zlAnd F_zrRespectively, represents vertical loads acting on left and right wheels, and satisfies the following equation:

F_zl+F_zr＝mg (2)

in the formula (2), m is the total mass of the vehicle, and g is the gravitational acceleration. Considering the driving condition of the vehicle, when the vehicle turns, the vertical load of the turning wheel is reduced and the vertical load of the turning wheel is correspondingly increased. From the definition of rollover, it is clear that:

the magnitude of the lateral load transfer rate is irrelevant to vehicle types, vehicle body parameters and the like, and the absolute value is about 1, so that the lateral load transfer rate is easy to compare, therefore, the lateral load transfer rate is suitable for all types of vehicles (including automatic driving vehicles), and has certain universality for researching vehicle types which are easy to roll over, such as SUVs, semi-trailer trains and the like.

In specific practice, based on the above equations (1) to (3), Simulink simulation software can be used to establish an anti-rollover model of the vehicle, so that the simulation process can measure some vehicle operation parameters which are difficult to obtain in real time, such as roll angle, LTR and other parameters. The LTR can evaluate the rollover prevention performance of the vehicle from different aspects, so that the LTR is used as the rollover stability evaluation index in the embodiment of the present invention, and the following steps are all taken as examples.

And step S120, determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle.

Taking the lateral load transfer rate as an example, the step S120 specifically includes: determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and taking the lateral acceleration as the stability control target corresponding to the lateral load transfer rate.

More specifically, a mathematical model is first established that can express the influence of which parameter the lateral load transfer rate LTR is influenced, and the physical model is shown in fig. 2. Based on a physical model, in the construction of a data model, the road surface is assumed to be smooth and neglectedSlightly rolling the mass of the axle and assuming the same track for the front and rear axles, i.e. B_r＝B_l. Suppose that the sprung mass is m_sH is the height of the center of mass, h_sIs the distance from the center of mass to the center of rollover, g is the gravitational acceleration, phi is the equivalent roll angle,in order to be equivalent in roll stiffness,

for equivalent roll damping, a moment balance equation is taken for the ground reaction point of the roll inner side wheel (the inner side wheel is the right side wheel in fig. 2) of the vehicle, and then:

by the same method, the moment of the vehicle roll outer side wheel is obtained, and the following can be obtained:

because phi is smaller, sin phi is taken as phi; when taking LTR value, the model ignores unsprung mass, i.e. m is taken_sM. From formulae (1), (2), (4), and (5), it is possible to obtain:

from the formula (6), the lateral load transfer rate of the vehicle rollover can be influenced by the vehicle structural parameters and the driving parameters, and the rollover state of the vehicle can be controlled by effectively controlling the parameters. According to equation (6), to lower the value of LTR, the following method is possible:

1) lowering the vehicle centroid height h, thereby also enabling h_sDecrease;

2) increasing the vehicle wheel track B;

3) reducing the vehicle roll angle phi; and

4) reducing vehicle lateral acceleration a_y。

These are four approaches that are the subject of rollover research. Since the structural parameters of a vehicle model are already determined in the vehicle design stage, the structural parameters such as the centroid height and the vehicle wheel track of the method 1) and the method 2) are not changed after the vehicle is produced. Therefore, the rollover prevention control effect which can be achieved by the two methods is determined in the vehicle design stage, so that the technology for controlling rollover by optimizing the structural parameters belongs to passive rollover prevention technology. The magnitude of the roll angle Φ is determined mainly by a coefficient and a parameter that determine the degree of rolling of the sprung mass, such as a suspension system of the vehicle, when the lateral acceleration is constant, and therefore, it is necessary to consider the influence of the suspension in order to reduce the equivalent roll angle. It is obvious that the main reason for the rollover is due to a_yAnd exceeding the limit, and reducing the vertical load of the wheels at the inner side of the curve to 0. Lateral acceleration a of vehicle_yThe lateral force is generated, and the control on the lateral force usually adopts active control technology, such as active steering, differential braking and the like, so that the lateral acceleration when the vehicle turns is controlled by adopting one or more control modes.

Therefore, to lower the value of LTR, it is necessary to consider the influence of the suspension and to select an active control technique for controlling the lateral force. Method 3) is also not considered by embodiments of the present invention, since the type of suspension is also basically determined at the time of vehicle design. Thus, embodiments of the present invention address the important issue of rollover prevention in reducing the lateral acceleration of a vehicle turning.

And step S130, establishing a corresponding relation between the lateral acceleration and the longitudinal speed as well as the steering wheel angle according to the vehicle kinematic model and the vehicle parameters.

In other embodiments, the vehicle dynamics model may also be considered to establish the correspondence between the lateral acceleration and the longitudinal vehicle speed and the steering wheel angle, but the vehicle dynamics model needs to consider a plurality of vehicle parameters, including tire longitudinal stiffness, tire lateral stiffness, wheel slip rate, wheel slip angle, centroid height, etc., which are generally difficult to obtain and often change with the change of vehicle conditions. It is therefore difficult to obtain a reasonable turning angle output limit by a dynamic model.

Based on the above analysis, the embodiment of the present invention calculates the turning angle threshold value (or the limit turning angle value) of the vehicle in the moving state from the kinematic model. Since the lateral acceleration of the vehicle exceeds the limit lateral acceleration value of the vehicle when the vehicle rolls over, the important quantity for ensuring safety and comfort is to determine the limit lateral acceleration of the vehicle. Most studies have shown that rollover occurs at extreme lateral acceleration values of the vehicle exceeding 0.4g (where g is the acceleration of gravity) with good road adhesion coefficients. The embodiment of the invention takes into account that the vehicle does not always run under the condition of good road adhesion coefficient and also takes into account the comfort of lateral control, thereby setting the limit lateral acceleration value of the vehicle to any value of 0.2g-0.3g, including 0.2g and 0.4g, and preferably 0.25 g.

The lateral acceleration of the vehicle during turning can be known from the kinematic principle:

in the formula, a_yThe vehicle lateral acceleration is represented by u, the longitudinal vehicle speed is represented by R, and the turning radius of the vehicle is represented by R.

And according to the Ackerman steering principle:

in the formula, the front wheel deflection angle is shown, and L is the vehicle wheelbase.

The vehicle front wheel deflection angle and the steering wheel angle are known to satisfy the following conditions:

_sw＝i (9)

in the formula:_swthe steering wheel angle is the front wheel slip angle, and i is the steering system transmission ratio.

According to equations (7), (8) and (9), the correspondence between the lateral acceleration and the vehicle speed, the steering wheel angle can be easily established, that is:

step S140, according to the corresponding relation, obtaining the maximum steering wheel angle corresponding to the given maximum lateral acceleration under different vehicle speeds, and taking the maximum steering wheel angle as a steering angle threshold value.

Specifically, according to equation (10), a limit vehicle lateral acceleration a is given at different vehicle speeds_ymaxThen, the maximum steering wheel angle can be obtained_swmaxThe calculation formula is as follows:

the maximum steering wheel angle_swmaxIs the corner threshold.

In addition, the maximum lateral acceleration corresponding to different vehicle speeds is controlled to be less than or equal to a given limit lateral acceleration value (any value of 0.2g-0.3g, preferably 0.25g as mentioned above).

And S150, monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.

Specifically, the automatic driving system may utilize an Electric Power Steering (EPS) for lateral control, so after the environmental awareness module, the data fusion module or the decision planning module obtains the target Steering wheel angle, the Steering wheel angle is sent to the EPS by using the Steering angle threshold before being sent to the EPS_swmaxLimiting, and when the calculated target steering wheel angle is larger than the steering angle threshold value at a certain moment, making the target steering wheel angle equal to the steering angle threshold value_swmaxOtherwise, outputting normally.

Regarding the above steps S110 to S150, the actual measurement results of the lateral control safety monitoring method according to the embodiment of the present invention are described by way of example. In this example, the parameters are set according to a certain model of vehicle, wherein the axisDistance L is 2.85 m, transmission ratio i is 17.23, and maximum lateral acceleration a_ymaxIs 2.5m/s²As shown in fig. 3, it can be seen that the larger the vehicle speed is, the smaller the corresponding maximum steering wheel angle is, thereby preventing the vehicle from rolling over due to the excessively large vehicle speed.

The actual measurement result shown in fig. 3 shows that the lateral control safety monitoring method based on the vehicle kinematics design can achieve the purpose of safety monitoring, especially can ensure the safe driving of the vehicle under the high-speed working condition, and further improves the safety of the automatic driving system.

Fig. 4 is a schematic structural diagram of a lateral control safety monitoring system of an autonomous vehicle according to an embodiment of the present invention. As shown in fig. 4, the lateral control safety monitoring system may include: the index establishing module 410 is configured to establish a rollover stability evaluation index of the vehicle, where the rollover stability evaluation index includes a lateral load transfer rate of the vehicle; a target determining module 420, configured to determine a factor affecting the rollover stability evaluation index as a stability control target of the vehicle, including determining a factor affecting the lateral load transfer rate, where the factor includes a lateral acceleration of the vehicle, and using the lateral acceleration as the stability control target corresponding to the lateral load transfer rate; the relationship establishing module 430 is used for establishing a corresponding relationship between the lateral acceleration and the longitudinal speed and the steering wheel angle according to a vehicle kinematics model and vehicle parameters; a threshold determining module 440, configured to obtain, according to the corresponding relationship, a maximum steering wheel angle corresponding to the given maximum lateral acceleration at different vehicle speeds, and use the maximum steering wheel angle as a steering angle threshold; and a monitoring module 450, configured to monitor the steering wheel angle in real time, and determine whether the monitored steering wheel angle is greater than the steering angle threshold, if so, limit the steering wheel angle to the steering angle threshold, and then output the steering wheel angle for vehicle lateral control, otherwise, normally output the steering wheel angle for vehicle lateral control.

It should be noted that, for other implementation details and effects of the lateral control safety monitoring system of the autonomous vehicle according to the embodiment of the present invention, reference may be made to the above-mentioned embodiment of the lateral control safety monitoring method of the autonomous vehicle, and details are not described herein again.

In the embodiment of the invention, the lateral control safety monitoring method and the lateral control safety monitoring system can be configured in a motion control module of an automatic driving system so as to monitor the stability of lateral control of a vehicle. Compared with the conventional vehicle which can predict rollover depending on the experience of a driver, the automatic driving vehicle has higher requirement on control precision due to rollover control depending on the motion control module, and needs a perfect safety monitoring scheme.

Another embodiment of the present invention also provides a machine-readable storage medium having instructions stored thereon for causing a machine to perform the lateral control safety monitoring method for an autonomous vehicle described above. The machine-readable storage medium includes, but is not limited to, various media capable of storing program code such as Phase Change random access Memory (PRAM, also known as RCM/PCRAM), Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM), Flash Memory (Flash Memory) or other Memory technologies, compact disc read only Memory (CD-ROM), Digital Versatile Disc (DVD) or other optical storage, magnetic cassettes, magnetic tape storage or other magnetic storage devices.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.