阅读说明：本技术 一种基于驾驶员风格的直行跟车安全距离预警方法 (Straight-going following safety distance early warning method based on driver style ) 是由 郭洪艳 张永达 赵小明 赵伟 孟庆瑜 陈虹 高振海 胡云峰 于 2020-07-27 设计创作，主要内容包括：本发明公开了一种基于驾驶员风格的直行跟车安全距离预警方法,第一步,建立车辆道路关系模型；第二步,拟合前方车辆紧急制动的最小安全距离模型；第三步,拟合本车紧急制动减速到与前车保持同速的最小安全距离模型；第四步,建立基于驾驶员风格的安全距离模型；第五步,进行安全距离预警；本方法拟合了两种极限情况下的最小安全距离,即前方车辆紧急制动情况以及本车紧急制动将本车速度调整到与前方车辆速度相同的情况；同时,结合了驾驶员的驾驶风格和心理安全距离,进行了符合驾驶员风格的安全距离预警；本方法采用分等级预警,给驾驶员提供了对外界情况作出反应的时间,提前对本车速度做出调整,能有效减少追尾事故发生,达到安全驾驶的目的。(The invention discloses a straight-driving following safety distance early warning method based on the style of a driver, which comprises the following steps of firstly, establishing a vehicle road relation model; secondly, fitting a minimum safe distance model of the front vehicle for emergency braking; thirdly, fitting a minimum safe distance model for the vehicle to be decelerated to the same speed as the previous vehicle in emergency braking; fourthly, establishing a safe distance model based on the style of the driver; fifthly, carrying out safety distance early warning; the method fits the minimum safe distance under two limit conditions, namely the emergency braking condition of the front vehicle and the condition that the speed of the vehicle is adjusted to be the same as the speed of the front vehicle by the emergency braking of the vehicle; meanwhile, the driving style and the psychological safety distance of the driver are combined, and safety distance early warning conforming to the style of the driver is carried out; the method adopts grading early warning, provides time for a driver to react to external conditions, adjusts the speed of the vehicle in advance, can effectively reduce rear-end accidents and achieves the aim of safe driving.)

1. A straight-driving following safety distance early warning method based on driver style is characterized in that in the driving process of a driving vehicle, the real-time speed of the driving vehicle and a front vehicle and the distance between the driving vehicle and the front vehicle are measured through a vehicle speed measuring system and a sensing device, three levels of safety early warnings are given according to different speeds of the two vehicles, the distance between the driving vehicle and the front vehicle and the driver style of the driving vehicle, rear-end collision accidents can be effectively reduced, and the purpose of safe driving is achieved, and the method is characterized by comprising the following specific steps:

step one, establishing a vehicle road relation model:

establishing a geodetic coordinate system, wherein an origin O of the geodetic coordinate system is fixedly connected to the position of the centroid of the vehicle at the current moment, an X axis points to the front of the vehicle body of the vehicle at the current moment, and the direction of the X axis rotating 90 degrees along the counterclockwise direction is the positive direction of a Y axis;

step two, fitting a minimum safe distance model for emergency braking of a front vehicle:

when the vehicle runs in a straight-going following manner and the front vehicle is subjected to emergency braking in case of emergency, the deceleration of the front vehicle is subjected to a linear rising stage from the perspective of the rear vehicle, namely a driver of the vehicle, and the deceleration of the front vehicle is kept unchanged until the vehicle speed is reduced to 0m/s after the deceleration of the front vehicle reaches the maximum deceleration; the deceleration a of the front vehicle in the emergency braking process of the front vehicle_pre,1Is represented by formula (1):

in the formula, a_pre,1The real-time deceleration of the front vehicle in the X-axis direction from the emergency braking moment is measured in m/s²；a_{max pre}The maximum deceleration of the front vehicle during emergency braking is calculated in m/s²；t_preaupFor deceleration during emergency braking of the preceding vehicleFrom 0m/s²Linearly up to a_{max pre}Time of (d), in units of s;

according to the formula (1), the displacement X in the X-axis direction of the front vehicle from emergency braking to 0m/s can be obtained_pre,1As shown in formula (2):

in the formula, x_pre,1The displacement of the front vehicle in the X-axis direction is measured from the beginning of emergency braking to the speed of 0m/s, and the unit is m; when the driver of the vehicle finds that the vehicle is braked suddenly before, the driver of the vehicle takes emergency braking treatment, the deceleration of the vehicle does not rise immediately because the driver takes braking after a reaction time, after braking, the braking device also has a short delay time, then braking is acted, the deceleration of the vehicle rises linearly until the maximum deceleration of the vehicle is increased, and then the deceleration is kept unchanged until the speed of the vehicle is reduced to 0m/s, therefore, in the emergency braking condition of the vehicle before, the deceleration a of the vehicle is reduced to 0m/s_tar,1Is represented by formula (3):

in the formula, a_tar,1The real-time deceleration of the vehicle in the X-axis direction from the emergency braking moment of the front vehicle is measured in m/s²；a_maxtarThe maximum deceleration of the vehicle during emergency braking is in m/s²；t_taraupThe deceleration of the vehicle during emergency braking is from 0m/s²Linearly up to a_{max tar}Time of (d), in units of s; t is t_reactionIs the driver reaction time in units of s; t is t_delayDelay time for brake application in units of s;

from the change in acceleration of the vehicle in the equation (3), the displacement X of the vehicle in the X-axis direction from the time of sudden braking of the preceding vehicle to the time when the vehicle speed is 0m/s can be obtained_tar,1As shown in formula (4):

in the formula x_tar,1The unit is m, and the displacement of the vehicle in the X-axis direction is measured in the process from the time of emergency braking of the front vehicle to the time when the speed of the vehicle is 0 m/s; in order to ensure that two vehicles do not collide in the process, the two vehicles are ensured to have a large enough initial distance, namely the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle, on the basis, the psychological safety distance of a driver is considered, and the minimum safety distance L between the vehicle and the front vehicle under the condition of emergency braking of the front vehicle can be obtained by combining the factors and the formula (2) and the formula (4)₁As shown in formula (5):

L₁＝x_tar,1-x_pre,1+l_safe(5)

in the formula, L₁Namely, under the condition of emergency braking of the front vehicle, the unit of the minimum safe distance between the vehicle and the front vehicle is m; l_safeIs the psychological safety distance of the driver, and the unit is m;

step three, fitting a minimum safe distance model for the vehicle to be decelerated to the same speed as the previous vehicle in emergency braking:

when the vehicle runs with the vehicle, when the current vehicle speed is less than the vehicle and the vehicle distance is not large enough, the two vehicles are in danger of collision, the vehicle needs to adopt emergency braking to reduce the speed, and when the vehicle speed is adjusted to be the same as the front vehicle, the two vehicles can be prevented from collision_reactionSo that from the moment the driver of the vehicle assumes braking, the vehicle will experience a short braking delay and then the deceleration will rise linearly to the maximum deceleration until the speed is reduced to the same speed as the preceding vehicle; if the speed of the vehicle is reduced to be the same as that of the front vehicle and two vehicles do not collide with each other, the two vehicles do not have collision danger, so the vehicle adopts the acceleration a during the emergency speed reduction_tar,2As shown in formula (6):

in the formula, a_tar,2The change of deceleration during the taking of an emergency deceleration for the vehicle is in m/s²(ii) a The speed v of the vehicle during the emergency deceleration can be obtained by the equation (6)_tar,2Is represented by formula (7):

in the formula, v_tar,2The real-time speed of the vehicle during the emergency deceleration is m; since the speed variation of the vehicle is a piecewise function, the time when the speeds of the two vehicles are the same is determined, let v_tar,2＝v_preThe time t when the speed of the vehicle is reduced to be the same as the speed of the vehicle ahead can be obtained_sThe unit is s; thereby obtaining the displacement X of the vehicle in the X-axis direction during the period from the emergency braking deceleration to the same speed as the previous vehicle_tar,2As shown in formula (8):

in the formula, x_tar,2Namely the displacement of the vehicle in the X-axis direction from the emergency deceleration to the same speed as the previous vehicle, and the unit is m; during the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, the displacement X of the front vehicle in the X-axis direction_pre,2As shown in formula (9):

x_pre,2＝v_pret_s(9)

in the formula, x_pre,2Namely the displacement of the front vehicle in the X-axis direction in the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, and the unit is m; in order to ensure that two vehicles do not collide in the process, the two vehicles are ensured to have a large enough initial distance, namely the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle, and meanwhile, the psychological safety distance of a driver is considered, the emergency braking deceleration of the vehicle can be obtained by combining the factors and the formula (8) and the formula (9), and the speed of the vehicle is adjusted to the minimum safety distance L for keeping the same speed as the front vehicle₂As shown in formula (10):

in the formula L₂The minimum safe distance is the minimum safe distance of the vehicle which is decelerated to the same speed as the front vehicle in an emergency, and the unit is m; in consideration of the completeness of the speed states of the front and rear vehicles, v is added to the formula (10)_pre≥v_tarThe case (1);

step four, establishing a safe distance model based on the style of the driver:

the style of the driver is divided into an aggressive type and a conservative type, the aggressive type driver is more aggressive in performance when driving, and the required driving distance is smaller; on the contrary, the conservative driver is more conservative in performance when driving, and the required driving distance is larger; l_safeThe relationship with the driver style is shown in equation (11):

empirical and statistical studies give the values of the following parameters as shown in table one:

table-value of constant parameter

Parameter(s) Dimension line t_reaction 0.8s t_delay 0.2s t_preaup 0.1s t_taraup 0.2s a_{max pre} 7m/s² a_maxtar 7m/s²

The speed measuring system and the sensor system can detect the speed v of the vehicle in real time_tarAnd the speed v of the front vehicle_preSo that L is calculated in real time₁And L₂The actual distance to the preceding vehicle detected by the radar of the vehicle and the driving safety relationship are as follows:

in the formula S_pre,tarThe unit of the actual distance between the head of the vehicle and the tail of the front vehicle detected by the radar of the vehicle is m;

fifthly, carrying out safety distance early warning:

according to the safety class, the system can give the driver safety precaution, and the early warning method has two kinds, and one kind is through the suggestion sound of difference suggestion driver, and another kind is through early warning safety pilot lamp, according to different safety classes, early warning safety pilot lamp can show different colours, and the method selects to combine above two kinds of modes, specifically as follows:

the current safe state of driver can be reminded to different pilot lamp colours and early warning prompt tone, and the driver can make the adjustment in advance to reach safe driving's purpose.

Technical Field

The invention belongs to the technical field of automobile driving control, and relates to a straight-driving following safety distance early warning method based on a driver style.

Background

In recent years, as the number of people who drive automobiles increases, traffic accidents become a common phenomenon. Studies have shown that rear-end collisions are the most common traffic accidents, and over 90% of rear-end collisions are caused by the lack of concentration or the lack of a safe distance between the vehicle and the preceding vehicle by the following driver. Therefore, the early warning method for the safe distance between the following vehicles has great practical significance. Meanwhile, with continuous innovation of the vehicle-mounted sensing technology, powerful support is provided for research of the vehicle following safety distance early warning method. However, most of researches on following safety distance warning methods are based only on the speed of a vehicle and the distance between vehicles, and rarely consider the driving style of a driver and the psychological safety distance of the driver, and safety distance warning conforming to the driving style of the driver is not performed.

Disclosure of Invention

The invention provides a straight-driving following safe distance early warning method based on driver style, which measures the distance between a vehicle and a front vehicle through a vehicle-mounted sensing system and provides a safe distance early warning problem for a driver of the vehicle according to the speed of the vehicle, the speed of the front vehicle and the driver style

The invention is realized by adopting the following technical scheme:

a straight-driving following safety distance early warning method based on driver style is characterized in that in the driving process of a driving vehicle, the real-time speed of the driving vehicle and a front vehicle and the distance between the driving vehicle and the front vehicle are measured through a vehicle speed measuring system and a sensing device, three levels of safety early warnings are given according to different speeds of the two vehicles, the distance between the driving vehicle and the front vehicle and the driver style of the driving vehicle, rear-end collision accidents can be effectively reduced, and the purpose of safe driving is achieved, and the method specifically comprises the following steps:

step one, establishing a vehicle road relation model:

establishing a geodetic coordinate system, wherein an origin O of the geodetic coordinate system is fixedly connected to the position of the centroid of the vehicle at the current moment, an X axis points to the right front of the vehicle body of the vehicle at the current moment, and the direction of the X axis rotating 90 degrees along the counterclockwise direction is the positive direction of a Y axis;

step two, fitting a minimum safe distance model for emergency braking of a front vehicle:

when the vehicle runs in a straight-going following manner and the front vehicle is subjected to emergency braking in case of emergency, the deceleration of the front vehicle is subjected to a linear rising stage from the perspective of the rear vehicle, namely a driver of the vehicle, and the deceleration of the front vehicle is kept unchanged until the vehicle speed is reduced to 0m/s after the deceleration of the front vehicle reaches the maximum deceleration; the deceleration a of the front vehicle in the emergency braking process of the front vehicle_pre,1Is represented by formula (1):

in the formula, a_pre,1The real-time deceleration of the front vehicle in the X-axis direction from the emergency braking moment is measured in m/s²；a_maxpreThe maximum deceleration of the front vehicle during emergency braking is calculated in m/s²； t_preaupFor deceleration during emergency braking of the front vehicle from 0m/s²Linearly up to a_maxpreTime of (d), in units of s;

according to the formula (1), the displacement X in the X-axis direction of the front vehicle from emergency braking to 0m/s can be obtained_pre,1As shown in formula (2):

in the formula, x_pre,1The displacement of the front vehicle in the X-axis direction is measured from the beginning of emergency braking to the speed of 0m/s, and the unit is m; when the driver of the vehicle finds that the vehicle is braked suddenly before, the driver of the vehicle takes emergency braking treatment, the deceleration of the vehicle does not rise immediately because the driver takes braking after a reaction time, after braking, the braking device also has a short delay time, then braking is acted, the deceleration of the vehicle rises linearly until the maximum deceleration of the vehicle is increased, and then the deceleration is kept unchanged until the speed of the vehicle is reduced to 0m/s, therefore, in the emergency braking condition of the vehicle before, the deceleration a of the vehicle is reduced to 0m/s_tar,1Is represented by formula (3):

in the formula, a_tar,1The real-time deceleration of the vehicle in the X-axis direction from the emergency braking moment of the front vehicle is measured in m/s²；a_maxtarThe maximum deceleration of the vehicle during emergency braking is in m/s²；t_taraupThe deceleration of the vehicle during emergency braking is from 0m/s²Linearly up to a_maxtarTime of (d), in units of s; t is t_reactionIs the driver reaction time in units of s; t is t_delayDelay time for brake application in units of s;

from the change in acceleration of the vehicle in the equation (3), the displacement X of the vehicle in the X-axis direction from the time of sudden braking of the preceding vehicle to the time when the vehicle speed is 0m/s can be obtained_tar,1As shown in formula (4):

in the formula x_tar,1The unit is m, and the displacement of the vehicle in the X-axis direction is measured in the process from the time of emergency braking of the front vehicle to the time when the speed of the vehicle is 0 m/s; to ensure that the two vehicles do not collide in the process, the two vehicles have a large enough initial distance, i.e. the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle,on the basis, the psychological safety distance of the driver is also considered, and the minimum safety distance L between the vehicle and the front vehicle under the condition of emergency braking of the front vehicle can be obtained by combining the factors and the expressions (2) and (4)₁As shown in formula (5):

L₁＝x_tar,1-x_pre,1+l_safe(5)

in the formula, L₁Namely, under the condition of emergency braking of the front vehicle, the unit of the minimum safe distance between the vehicle and the front vehicle is m; l_safeIs the psychological safety distance of the driver, and the unit is m;

step three, fitting a minimum safe distance model for the vehicle to be decelerated to the same speed as the previous vehicle in emergency braking:

when the vehicle runs with the vehicle, when the current vehicle speed is less than the vehicle and the vehicle distance is not large enough, the two vehicles are in danger of collision, the vehicle needs to adopt emergency braking to reduce the speed, and when the vehicle speed is adjusted to be the same as the front vehicle, the two vehicles can be prevented from collision_reactionSo that from the moment the driver of the vehicle assumes braking, the vehicle will experience a short braking delay and then the deceleration will rise linearly to the maximum deceleration until the speed is reduced to the same speed as the preceding vehicle; if the speed of the vehicle is reduced to be the same as that of the front vehicle and two vehicles do not collide with each other, the two vehicles do not have collision danger, so the vehicle adopts the acceleration a during the emergency speed reduction_tar,2As shown in formula (6):

in the formula, a_tar,2The change of deceleration during the taking of an emergency deceleration for the vehicle is in m/s²(ii) a The speed v of the vehicle during the emergency deceleration can be obtained by the equation (6)_tar,2Is represented by formula (7):

in the formula, v_tar,2The real-time speed of the vehicle during the emergency deceleration is m; since the speed variation of the vehicle is a piecewise function, the time when the speeds of the two vehicles are the same is determined, let v_tar,2＝v_preThe time t when the speed of the vehicle is reduced to be the same as the speed of the vehicle ahead can be obtained_sThe unit is s; thereby obtaining the displacement X of the vehicle in the X-axis direction during the period from the emergency braking deceleration to the same speed as the previous vehicle_tar,2As shown in formula (8):

in the formula, x_tar,2Namely the displacement of the vehicle in the X-axis direction from the emergency deceleration to the same speed as the previous vehicle, and the unit is m; during the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, the displacement X of the front vehicle in the X-axis direction_pre,2As shown in formula (9):

x_pre,2＝v_pret_s(9)

in the formula, x_pre,2Namely the displacement of the front vehicle in the X-axis direction in the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, and the unit is m; in order to ensure that two vehicles do not collide in the process, the two vehicles are ensured to have a large enough initial distance, namely the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle, and meanwhile, the psychological safety distance of a driver is considered, the emergency braking deceleration of the vehicle can be obtained by combining the factors and the formula (8) and the formula (9), and the speed of the vehicle is adjusted to the minimum safety distance L for keeping the same speed as the front vehicle₂As shown in formula (10):

in the formula L₂The minimum safe distance is the minimum safe distance of the vehicle which is decelerated to the same speed as the front vehicle in an emergency, and the unit is m; in consideration of the completeness of the speed states of the front and rear vehicles, v is added to the formula (10)_pre≥v_tarThe case (1);

step four, establishing a safe distance model based on the style of the driver:

the style of the driver is divided into an aggressive type and a conservative type, the aggressive type driver is more aggressive in performance when driving, and the required driving distance is smaller; on the contrary, the conservative driver is more conservative in performance when driving, and the required driving distance is larger; l_safeThe relationship with the driver style is shown in equation (11):

empirical and statistical studies give the values of the following parameters as shown in table one:

table-value of constant parameter

The speed measuring system and the sensor system can detect the speed v of the vehicle in real time_tarAnd the speed v of the front vehicle_preSo that L is calculated in real time₁And L₂The actual distance to the preceding vehicle detected by the radar of the vehicle and the driving safety relationship are as follows:

in the formula S_pre,tarThe unit of the actual distance between the head of the vehicle and the tail of the front vehicle detected by the radar of the vehicle is m;

fifthly, carrying out safety distance early warning:

according to the safety class, the system can give the driver safety precaution, and the early warning method has two kinds, and one kind is through the suggestion sound of difference suggestion driver, and another kind is through early warning safety pilot lamp, according to different safety classes, early warning safety pilot lamp can show different colours, and the method selects to combine above two kinds of modes, specifically as follows:

the current safe state of driver can be reminded to different pilot lamp colours and early warning prompt tone, and the driver can make the adjustment in advance to reach safe driving's purpose.

Compared with the prior art, the invention has the beneficial effects that:

1. the method fits the acceleration curves of the front vehicle and the rear vehicle under two limit conditions, namely the condition that the front vehicle stops in an emergency braking mode and the speed of the front vehicle is reduced in the emergency braking mode so that the speed of the front vehicle is adjusted to be the same as the speed of the front vehicle.

2. The method adopts three safety distance grades for early warning, and provides time for a driver to react to external conditions to adjust the vehicle speed.

3. When the safety distance is calculated, the driving style of the driver and the psychological safety distance of the driver are considered, and safety distance early warning is provided according to different driver styles.

Drawings

Fig. 1 is a simplified flow chart of a straight-driving following safety distance early warning method based on a driver style according to the present invention.

Fig. 2 is a schematic diagram of a vehicle road relationship model established in the straight-driving following safety distance early warning method based on the driver style.

Fig. 3 is a fitted acceleration change curve of a preceding vehicle under an emergency braking condition in the straight-ahead following safety distance early warning method based on the driver style.

FIG. 4 is a curve of acceleration change of the vehicle under the condition of emergency braking of the vehicle ahead, which is fitted in the straight-ahead vehicle following safety distance early warning method based on the driver style.

Fig. 5 is an acceleration change curve of the vehicle when the vehicle is decelerated to the same speed as the preceding vehicle in emergency braking according to the straight-driving following safety distance early warning method based on the driver style.

Detailed Description

The invention is described in detail below with reference to the attached drawing figures:

a straight-driving following safety distance early warning method based on driver style is disclosed, as shown in figure 1, in the driving process of a driving vehicle, the real-time speed of the vehicle and a front vehicle and the distance between the vehicle and the front vehicle are measured by a vehicle speed measuring system and a sensing device, three levels of safety early warnings are given according to different speeds of the two vehicles, the distance between the vehicle and the front vehicle and the driver style of the vehicle, the occurrence of rear-end collision accidents can be effectively reduced, and the purpose of safe driving is achieved, and the method is characterized by comprising the following specific steps:

step one, establishing a vehicle road relation model:

establishing a geodetic coordinate system, wherein FIG. 2 is a schematic diagram of a vehicle road relation model, an origin O of the geodetic coordinate system is fixedly connected to the position of the centroid of the vehicle at the current moment, an X axis points to the front of the vehicle body of the vehicle at the current moment, the direction of the X axis rotating 90 degrees along the counterclockwise direction is the positive direction of the Y axis, tar represents the vehicle, and pre represents the front vehicle;

step two, fitting a minimum safe distance model for emergency braking of a front vehicle:

FIG. 3 is a curve of the acceleration variation of the front vehicle under the emergency braking condition of the front vehicle, when the front vehicle is subjected to emergency braking while the vehicle is traveling straight with the following vehicle, the deceleration of the front vehicle will go through a linear rising stage from the perspective of the driver of the rear vehicle, i.e., the vehicle, and after the deceleration of the front vehicle reaches the maximum deceleration, the deceleration of the front vehicle will remain unchanged until the vehicle speed drops to 0 m/s; the deceleration a of the front vehicle in the emergency braking process of the front vehicle_pre,1Is represented by formula (1):

in the formula, a_pre,1The real-time deceleration of the front vehicle in the X-axis direction from the emergency braking moment is measured in m/s²；a_maxpreFor maximum of preceding vehicle during emergency brakingDeceleration in m/s²；t_preaupFor deceleration during emergency braking of the front vehicle from 0m/s²Linearly up to a_maxpreTime of (d), in units of s;

according to the formula (1), the displacement X in the X-axis direction of the front vehicle from emergency braking to 0m/s can be obtained_pre,1As shown in formula (2):

in the formula, x_pre,1The displacement of the front vehicle in the X-axis direction is measured from the beginning of emergency braking to the speed of 0m/s, and the unit is m; as shown in fig. 4, when the driver of the vehicle is in emergency braking with the front vehicle, the emergency braking processing is also adopted, the deceleration of the vehicle does not rise immediately, because the driver does not adopt the braking after a reaction time, after the braking, the braking device has a short delay time, then the braking is acted, the deceleration of the vehicle rises linearly until the maximum deceleration of the vehicle rises, and then the deceleration is kept unchanged until the speed of the vehicle drops to 0m/s, therefore, in the emergency braking of the front vehicle, the deceleration a of the vehicle is reduced to 0m/s_tar,1Is represented by formula (3):

in the formula, a_tar,1The real-time deceleration of the vehicle in the X-axis direction from the emergency braking moment of the front vehicle is measured in m/s²；a_maxtarThe maximum deceleration of the vehicle during emergency braking is in m/s²；t_taraupThe deceleration of the vehicle during emergency braking is from 0m/s²Linearly up to a_maxtarTime of (d), in units of s; t is t_reactionIs the driver reaction time in units of s; t is t_delayDelay time for brake application in units of s;

the change in acceleration of the vehicle is obtained from the equation (3), and the vehicle speed is 0m/s from the time of sudden braking of the preceding vehicle,displacement X of the vehicle in the X-axis direction_tar,1As shown in formula (4):

in the formula x_tar,1The unit is m, and the displacement of the vehicle in the X-axis direction is measured in the process from the time of emergency braking of the front vehicle to the time when the speed of the vehicle is 0 m/s; in order to ensure that two vehicles do not collide in the process, the two vehicles are ensured to have a large enough initial distance, namely the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle, on the basis, the psychological safety distance of a driver is considered, and the minimum safety distance L between the vehicle and the front vehicle under the condition of emergency braking of the front vehicle can be obtained by combining the factors and the formula (2) and the formula (4)₁As shown in formula (5):

L₁＝x_tar,1-x_pre,1+l_safe(5)

in the formula, L₁Namely, under the condition of emergency braking of the front vehicle, the unit of the minimum safe distance between the vehicle and the front vehicle is m; l_safeIs the psychological safety distance of the driver, and the unit is m;

step three, fitting a minimum safe distance model for the vehicle to be decelerated to the same speed as the previous vehicle in emergency braking:

fig. 5 is an acceleration change curve of the host vehicle when the host vehicle is decelerated by sudden braking until the host vehicle keeps the same speed as the preceding vehicle. When the vehicle runs with the vehicle, when the current vehicle speed is less than the vehicle and the vehicle distance is not large enough, the two vehicles are in danger of collision, the vehicle needs to adopt emergency braking to reduce the speed, and when the vehicle speed is adjusted to be the same as the front vehicle, the two vehicles can be prevented from collision_reactionSo that from the moment the driver of the vehicle assumes braking, the vehicle will experience a short braking delay and then the deceleration will rise linearly to the maximum deceleration until the speed is reduced to the same speed as the preceding vehicle; if the speed of the vehicle is reduced to be the same as that of the front vehicle, the two vehicles do not collide, and the two vehicles do not have collision danger, so that the vehicle adoptsTaking the acceleration a during an emergency deceleration_tar,2As shown in formula (6):

in the formula, a_tar,2The change of deceleration during the taking of an emergency deceleration for the vehicle is in m/s²(ii) a The speed v of the vehicle during the emergency deceleration can be obtained by the equation (6)_tar,2Is represented by formula (7):

in the formula, v_tar,2The real-time speed of the vehicle during the emergency deceleration is m; since the speed variation of the vehicle is a piecewise function, the time when the speeds of the two vehicles are the same is determined, let v_tar,2＝v_preThe time t when the speed of the vehicle is reduced to be the same as the speed of the vehicle ahead can be obtained_sThe unit is s; thereby obtaining the displacement X of the vehicle in the X-axis direction during the period from the emergency braking deceleration to the same speed as the previous vehicle_tar,2As shown in formula (8):

in the formula, x_tar,2Namely the displacement of the vehicle in the X-axis direction from the emergency deceleration to the same speed as the previous vehicle, and the unit is m; during the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, the displacement X of the front vehicle in the X-axis direction_pre,2As shown in formula (9):

x_pre,2＝v_pret_s(9)

in the formula, x_pre,2Namely the displacement of the front vehicle in the X-axis direction in the period from the emergency deceleration of the vehicle to the same speed as the front vehicle, and the unit is m; in order to ensure that two vehicles do not collide in the process, the two vehicles are ensured to have a large enough initial distance, namely the initial distance is larger than the difference between the displacement of the vehicle and the displacement of the front vehicle, and meanwhile, the psychological safety distance of a driver is considered, and the factors are combinedAnd the equations (8) and (9) can obtain the speed reduction of the vehicle by emergency braking, and adjust the speed of the vehicle to the minimum safe distance L keeping the same speed with the previous vehicle₂As shown in formula (10):

in the formula L₂The minimum safe distance is the minimum safe distance of the vehicle which is decelerated to the same speed as the front vehicle in an emergency, and the unit is m; in consideration of the completeness of the speed states of the front and rear vehicles, v is added to the formula (10)_pre≥v_tarThe case (1);

step four, establishing a safe distance model based on the style of the driver:

the style of the driver is divided into an aggressive type and a conservative type, the aggressive type driver is more aggressive in performance when driving, and the required driving distance is smaller; on the contrary, the conservative driver is more conservative in performance when driving, and the required driving distance is larger; l_safeThe relationship with the driver style is shown in equation (11):

empirical and statistical studies give the values of the following parameters as shown in table one:

table-value of constant parameter

Parameter(s)	Dimension line
		treaction	0.8s
tdelay	0.2s
		tpreaup	0.1s
ttaraup	0.2s
		amaxpre	7m/s2
amaxtar	7m/s2

The speed measuring system and the sensor system can detect the speed v of the vehicle in real time_tarAnd the speed v of the front vehicle_preSo that L is calculated in real time₁And L₂The actual distance to the preceding vehicle detected by the radar of the vehicle and the driving safety relationship are as follows:

in the formula S_pre,tarThe unit of the actual distance between the head of the vehicle and the tail of the front vehicle detected by the radar of the vehicle is m;

fifthly, carrying out safety distance early warning:

according to the safety class, the system can give the driver safety precaution, and the early warning method has two kinds, and one kind is through the suggestion sound of difference suggestion driver, and another kind is through early warning safety pilot lamp, according to different safety classes, early warning safety pilot lamp can show different colours, and the method selects to combine above two kinds of modes, specifically as follows:

the current safe state of driver can be reminded to different pilot lamp colours and early warning prompt tone, and the driver can make the adjustment in advance to reach safe driving's purpose.