阅读说明：本技术 一种基于变加速模型的紧急制动方法和系统 (Emergency braking method and system based on variable acceleration model ) 是由 潘元承 王鸿源 沈定彬 林文山 林文畅 杨财有 庄进发 侯学锋 石添华 徐德强 于 2021-08-26 设计创作，主要内容包括：本发明公开了一种基于变加速模型的紧急制动方法和系统,所述方法包括：建立紧急制动的变加速模型,在所述变加速模型中,包括驾驶员反应阶段,减速度由零到最大减速度的减速度上升制动阶段和在最大减速度下的恒定减速度阶段；所述减速度上升制动阶段的刹车力度和时间,通过标定的刹车力度-减速度-时间关系曲线获得；在整个紧急制动阶段,周期性地检测本车速度、前车速度和前车加速度,并将该时刻获得的实际速度和理论制动曲线上同时刻的理论速度进行比较；根据同时刻下的实际速度、理论速度,计算减速度变化量,并根据所述减速度变化量修正下一检测周期的刹车力度；以期在下一检测周期期末时的实际速度和理论速度趋同。(The invention discloses an emergency braking method and system based on a variable acceleration model, wherein the method comprises the following steps: establishing a variable acceleration model of emergency braking, wherein the variable acceleration model comprises a driver reaction stage, a deceleration rising braking stage of which the deceleration is from zero to the maximum deceleration and a constant deceleration stage under the maximum deceleration; the braking force and the time of the deceleration rising braking stage are obtained through a calibrated braking force-deceleration-time relation curve; in the whole emergency braking stage, periodically detecting the speed of the vehicle, the speed of the vehicle ahead and the acceleration of the vehicle ahead, and comparing the actual speed obtained at the moment with the theoretical speed at the same moment on a theoretical braking curve; calculating deceleration variation according to the actual speed and the theoretical speed at the same time, and correcting the braking force of the next detection period according to the deceleration variation; in order to converge the actual speed and the theoretical speed at the end of the next detection period.)

1. An emergency braking method based on a variable acceleration model is characterized by comprising the following steps:

step S1: establishing a variable acceleration model of emergency braking, wherein the variable acceleration model comprises a driver reaction stage, a deceleration rising braking stage of which the deceleration is from zero to the maximum deceleration and a constant deceleration stage under the maximum deceleration; the time of the driver reaction phase is obtained through setting; the braking force and the time of the deceleration rising braking stage are obtained through a calibrated braking force-deceleration-time relation curve;

step S2: inputting the speed of the vehicle, the speed of the front vehicle and the acceleration of the front vehicle, and calculating the collision distance or the collision time according to the variable acceleration model;

step S3: when the distance between the vehicle and the front vehicle is smaller than the collision distance or the collision time is smaller than a set threshold value, triggering emergency braking, and generating a theoretical braking curve according to the variable acceleration model;

step S4: when the manual intervention of the driver is not received in the driver reaction stage, executing automatic emergency braking, and entering the deceleration rising braking stage; in the whole emergency braking stage, periodically detecting the speed of the vehicle, the speed of the vehicle ahead and the acceleration of the vehicle ahead, and comparing the actual speed obtained at the moment with the theoretical speed at the same moment on a theoretical braking curve; calculating deceleration variation according to the actual speed and the theoretical speed at the same time, and correcting the braking force of the next detection period according to the deceleration variation; in order to converge the actual speed and the theoretical speed at the end of the next detection period.

2. The variable acceleration model-based emergency braking method according to claim 1, wherein in step S1, the braking force and time of the deceleration rising braking phase are obtained by: the time for the acceleration of the deceleration rising braking stage to increase from zero to the maximum deceleration, namely the time for the deceleration rising braking stage is given through a calibrated braking force-deceleration-time relation curve under different braking duty ratios.

3. The variable acceleration model-based emergency braking method according to claim 1, wherein in step S4, the deceleration change amount is calculated by the formula: the deceleration change amount is 2 (actual speed-theoretical speed)/detection period, which is the time interval between two speed acquisitions.

4. The variable acceleration model-based emergency braking method according to claim 1, wherein the step S4 of modifying the braking force in the next detection period according to the deceleration variation comprises:

calculating a desired deceleration that is a sum of the deceleration change amount and an actual deceleration;

indexing a brake calibration table according to the sum of the deceleration variable quantity and the actual deceleration and the detection time point to obtain the brake force of the next detection period; and the brake calibration table is generated by taking points according to time for the parameter relation of the brake force-deceleration-time relation curve.

5. The variable acceleration model-based emergency braking method according to claim 4, characterized in that in the method, a deceleration change rate threshold value is further set; the ratio of the deceleration variation amount to the actual deceleration is a deceleration change rate, and when the absolute value of the deceleration change rate is smaller than or equal to a threshold value, the deceleration is expected to be kept unchanged; when the absolute value of the deceleration change rate is larger than the threshold, updating the expected deceleration according to the actual deceleration (1-threshold) when the deceleration change rate is a negative value; or when the deceleration change rate is a positive value, the desired deceleration is updated by the actual deceleration (1+ threshold).

6. The variable acceleration model-based emergency braking method according to claim 5, wherein the deceleration change rate threshold value is between 0% and 5%.

7. The variable acceleration model-based emergency braking method according to claim 1, wherein the detection period has a value in a range of 25-50 ms.

8. The variable acceleration model-based emergency braking method according to claim 1, wherein the parameter corresponding to the braking force is a braking duty cycle of a pneumatic braking system, and the braking duty cycle is used for adjusting the speed of inflation of a braking air pump of the pneumatic braking system.

9. An emergency braking system based on a variable acceleration model, characterized in that the emergency braking system is an air brake braking system, which performs the variable acceleration model based emergency braking method according to any one of claims 1-8.

Technical Field

The invention relates to the field of air brake control of unmanned vehicles, in particular to an emergency braking method and system based on a variable acceleration model.

Background

An automatic emergency braking system (AEB) is an active safety system that activates the brakes of a vehicle when a potential collision is detected. It is automatic and does not require the driver to actually touch the brake pedal. It may also increase the braking force if the driver is stepping on the brakes, but not enough to prevent a collision. All AEB systems are able to detect vehicles, many are also able to detect pedestrians and cyclists. The purpose of the AEB is to activate braking when a dangerous situation arises or the driver has insufficient braking, thereby reducing collisions.

The traditional AEB decision-making braking model generally uses a TTC collision time model (the vehicle acceleration is constant, and the vehicle enters when the vehicle speed is higher than the vehicle speed of a front vehicle) or a safe distance model, and the model is generally modeled according to uniform variable speed movement, but the emergency braking easily causes discomfort to drivers and passengers. In addition, a series of control parameters in the model, including acceleration and brake control parameters, are theoretically continuous curves, but the actual parameter states are discrete, so how to better match and complement the difference between the theory and the reality and reduce the control error, and the industry has no more reasonable and perfect scheme.

Disclosure of Invention

In view of the above-mentioned defects of the prior art, the present invention aims to provide an emergency braking method and system based on a variable acceleration model, which uses the variable acceleration model to perform emergency braking to reduce the uncomfortable influence caused by emergency braking, and provides a discrete parameter control method to reduce the control error.

In order to achieve the above object, the present invention provides an emergency braking method based on a variable acceleration model, comprising the following steps:

step S1: establishing a variable acceleration model of emergency braking, wherein the variable acceleration model comprises a driver reaction stage, a deceleration rising braking stage of which the deceleration is from zero to the maximum deceleration and a constant deceleration stage under the maximum deceleration; the time of the driver reaction phase is obtained through setting; the braking force and the time of the deceleration rising braking stage are obtained through a calibrated braking force-deceleration-time relation curve;

step S2: inputting the speed of the vehicle, the speed of the front vehicle and the acceleration of the front vehicle, and calculating the collision distance or the collision time according to the variable acceleration model;

step S3: when the distance between the vehicle and the front vehicle is smaller than the collision distance or the collision time is smaller than a set threshold value, triggering emergency braking, and generating a theoretical braking curve according to the variable acceleration model;

step S4: when the manual intervention of the driver is not received in the driver reaction stage, executing automatic emergency braking, and entering the deceleration rising braking stage; in the whole emergency braking stage, periodically detecting the speed of the vehicle, the speed of the vehicle ahead and the acceleration of the vehicle ahead, and comparing the actual speed obtained at the moment with the theoretical speed at the same moment on a theoretical braking curve; calculating deceleration variation according to the actual speed and the theoretical speed at the same time, and correcting the braking force of the next detection period according to the deceleration variation; in order to converge the actual speed and the theoretical speed at the end of the next detection period.

Further, in step S1, the method for obtaining the braking force and the time of the deceleration rising braking stage includes: the time for the acceleration of the deceleration rising braking stage to increase from zero to the maximum deceleration, namely the time for the deceleration rising braking stage is given through a calibrated braking force-deceleration-time relation curve under different braking duty ratios.

Further, the deceleration change amount is calculated by the following formula: the deceleration change amount is 2 (actual speed-theoretical speed)/detection period, which is the time interval between two speed acquisitions.

Further, the method for correcting the braking force in the next detection period according to the deceleration variation in step S4 includes:

calculating a desired deceleration that is a sum of the deceleration change amount and an actual deceleration;

indexing a brake calibration table according to the sum of the deceleration variable quantity and the actual deceleration and the detection time point to obtain the brake force of the next detection period; and the brake calibration table is generated by taking points according to time for the parameter relation of the brake force-deceleration-time relation curve.

Furthermore, the parameter corresponding to the braking force is the braking duty ratio of the pneumatic braking system, and the braking duty ratio is used for adjusting the speed of inflation of a braking air pump of the pneumatic braking system.

Further, in the method, a deceleration change rate threshold value is also set; the ratio of the deceleration variation amount to the actual deceleration is a deceleration change rate, and when the absolute value of the deceleration change rate is smaller than or equal to a threshold value, the deceleration is expected to be kept unchanged; when the absolute value of the deceleration change rate is larger than the threshold, updating the expected deceleration according to the actual deceleration (1-threshold) when the deceleration change rate is a negative value; or when the deceleration change rate is a positive value, the desired deceleration is updated by the actual deceleration (1+ threshold).

Furthermore, the value interval of the deceleration degree change rate threshold is between 0 and 5 percent.

Further, the value range of the detection period is 25-50 ms.

The invention also provides an emergency braking system based on the variable acceleration model, wherein the emergency braking system is an air brake braking system, and the air brake braking system executes the emergency braking method based on the variable acceleration model according to any scheme.

The invention realizes the following technical effects:

the emergency braking method based on the variable acceleration model adopts the variable acceleration model to perform emergency braking so as to reduce the uncomfortable influence of the emergency braking on drivers and passengers; in the braking process, the control curve of emergency braking is converged with the theoretical braking curve through discrete parameter control, and the control error is small.

Drawings

FIG. 1 is a velocity-acceleration-time graph of a variable acceleration braking model of the present invention;

FIG. 2 is a graph of acceleration versus time for different duty cycles of braking that is experimentally calibrated;

FIG. 3 is an actual speed and theoretical braking curve;

fig. 4 is a speed-time graph (a) and an acceleration-time graph (b) of the variable acceleration braking example 1;

fig. 5 is a speed-time graph (a) and an acceleration-time graph (b) of the variable acceleration braking example 2.

Detailed Description

To further illustrate the various embodiments, the invention provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures. Elements in the figures are not drawn to scale and like reference numerals are generally used to indicate like elements.

The invention will now be further described with reference to the accompanying drawings and detailed description.

The invention provides an emergency braking method based on a variable acceleration model, which comprises the following steps:

step S1: establishing a variable acceleration model of emergency braking, wherein the variable acceleration model comprises a driver reaction stage, a deceleration rising braking stage of which the deceleration rises from zero to the maximum deceleration and a constant deceleration stage under the maximum deceleration; the time of the driver reaction phase is obtained through setting; the time of the deceleration rising braking stage and a deceleration-time relation curve are obtained by calibration;

step S2: inputting the speed of the vehicle, the speed of the front vehicle and the acceleration of the front vehicle, and calculating the collision distance or the collision time according to the variable acceleration model;

step S3: when the collision distance or the collision time is smaller than a set threshold value, triggering emergency braking, and generating a theoretical braking curve according to the variable acceleration model;

step S4: when the manual intervention of the driver is not received in the driver reaction stage, executing automatic emergency braking, and entering the deceleration rising braking stage; in the whole emergency braking stage, periodically detecting the speed of the vehicle, the speed of the vehicle ahead and the acceleration of the vehicle ahead, and comparing the actual speed obtained at the moment with the theoretical speed at the same moment on a theoretical braking curve; calculating deceleration variation according to the actual speed and the theoretical speed at the same time, and correcting the braking force of the next detection period according to the deceleration variation; in order to converge the actual speed and the theoretical speed at the end of the next detection period.

1. Variable acceleration model construction for emergency braking

In the conventional TTC model, we take: the distance between two vehicles is s (m), the safety stopping distance is d (m), the running time is t(s), and the speed and the acceleration of the vehicle are v₁(m/s)、a₁(m/s²) Front vehicle speed and acceleration v₂(m/s)a₂(m/s²) The safe stopping distance is generally 0.5-3 m. Relative vehicleVelocity v_rel(speed of the vehicle is reduced by speed of the vehicle ahead), and the relative acceleration is a_rel(the acceleration of the vehicle minus the acceleration of the vehicle ahead). The conventional TTC model is based on the following assumed behavior: after the two vehicles travel for t seconds, the speed reaches 0(m/s) at the same time, and the distance between the two vehicles is just the safe stopping distance d. The formula may now be listed:

solving the equation yields:

where TTC is the time to collision.

The conventional TTC model is based on the assumption of constant deceleration, and the time of the deceleration rising phase in which the acceleration increases from zero to the maximum deceleration exists as a fixed amount and does not participate in the calculation of the collision time.

The variable acceleration model of the present embodiment is shown in fig. 1, wherein the interval t0-t1 is the driver reaction stage; the interval t1-t2 is a deceleration rising braking stage from zero deceleration to maximum deceleration; the interval t2-t3 is the period of constant deceleration braking at maximum deceleration.

It can be statistically obtained from the braking test data that when the vehicle brakes at different speeds, the time required for the deceleration of the vehicle to increase from 0 to the maximum deceleration (e.g., -5.3m/s) is about 0.6 seconds, for example, when the vehicle brakes at 100km/h for emergency braking, and the time required for the vehicle to increase from 0 to the maximum deceleration (e.g., -5.3 meters per square second). By extending the time of the variable acceleration phase, discomfort to the driver or passenger under emergency braking can be reduced.

The difference between the variable acceleration model in this embodiment and the conventional TTC crash model is that the braking force and time during the deceleration rising phase in which the acceleration increases from zero to the maximum deceleration can be adjusted, and the braking force and time can be obtained by calibration.

In this embodiment, the collision sets a driver reaction phase. When the driver does not make an active braking reaction in the stage, the follow-up braking action is taken over by the emergency braking system, the emergency braking is started, and the deceleration rising stage is started.

In the variable acceleration model of the present embodiment, braking is performed at the maximum deceleration in the constant deceleration stage in order that the braking distance in this stage is the shortest.

In the present embodiment, the time of the deceleration rising phase is obtained by:

as shown in fig. 2, the time of the acceleration increasing from zero to the maximum deceleration during the deceleration increasing braking period, i.e. the time of the deceleration increasing braking period, is given by calibrating the deceleration-time relationship curve (braking duty cycle-deceleration-time relationship curve) under different braking force levels (e.g. the braking duty cycle of the air brake system). For convenience of searching, the parameter relation of the brake duty ratio-deceleration-time relation curve is subjected to point taking according to time to generate a brake calibration table.

As shown in fig. 2, at a certain braking duty ratio, the deceleration a and the time t have a linear relationship, and the relationship can be expressed by a ═ k × t + C.

In this embodiment, different braking duty ratios can be selected according to the speed of the vehicle, the speed of the vehicle ahead, and the acceleration of the vehicle ahead, so as to obtain different time of deceleration rising braking stage. Generally, when the vehicle travels at a high speed, the vehicle is highly likely to be braked suddenly, and the braking operation is gentler, so that a smaller braking duty ratio can be selected to smooth the deceleration of the vehicle from zero to the maximum deceleration, and when the deceleration is increased to the maximum, the vehicle is braked at the maximum deceleration to minimize the braking distance in the constant deceleration stage. When the vehicle is in low-speed running, the possibility of danger of emergency braking of the vehicle is low, the action of braking can be violent, an increased braking duty ratio can be selected, the deceleration of the vehicle is quickly increased from zero to the maximum deceleration, and then braking is carried out at the maximum deceleration, so that the whole braking distance is as short as possible.

And when the distance between the vehicle and the front vehicle is smaller than the safe distance, triggering an emergency braking system of the vehicle. There are two conditions at this time: a. the speed of the vehicle is already reduced to 0 before the deceleration is increased and does not reach the maximum deceleration; b. the vehicle reaches the maximum deceleration when the deceleration rises, the speed does not drop to 0, and the vehicle travels at a constant deceleration until the relative speed with the preceding vehicle becomes zero. In the two working conditions, the situation that the front vehicle just does not collide with the front vehicle under the theoretical braking distance needs to be ensured.

Calculation of time to collision:

in this model, we take: the distance between two vehicles is s (m), the safety stopping distance is d (m), the running time is t(s), and the speed and the acceleration of the vehicle are v_zhu(m/s)、a_zhu(m/s²) Front vehicle speed and acceleration v_qian(m/s)、a_qian(m/s²) The safe stopping distance is generally 0.5-3 m. Relative vehicle speed v_rel(speed of the vehicle is reduced by speed of the vehicle ahead), and the relative acceleration is a_rel(the acceleration of the vehicle minus the acceleration of the vehicle ahead). Assuming one operating condition: after the two vehicles travel for t seconds, the speed reaches 0(m/s) at the same time, and the distance between the two vehicles is just the safe stopping distance d.

(1) Driver reaction phase (t 1-t 2): the time of this phase is set by the emergency braking system.

(2) Deceleration increasing stage (t1 to t2):

maximum deceleration a_zhumaxGiven by the emergency braking system;

speed v of the host vehicle from 0 to the maximum deceleration_{accup_max}Comprises the following steps:

wherein, t_accupmaxAccording to a calibrated acceleration-time relation curve (a)_zhuK × t + C), where k and C are known, and a_zhumaxSubstitution into a_zhuT is obtained as t_accupmax。

There are two conditions in this crash model:

1. if the vehicle is runningThe speed has dropped to 0 (i.e. calculated v) before the deceleration has risen to less than the maximum value_{accup_max}≦ 0), as shown in fig. 4, the time of the deceleration rising phase is:

t_accup＝t2-t1＝sqrt((2×v_zhu×t_accupmax)/a_zhumax)

wherein v is_zhuIndicates the initial speed, t, of the vehicle at the time of braking_accupIndicating the braking time.

2. When the vehicle reaches the maximum deceleration, the speed v_accupmaxNot reduced to 0 (i.e. calculated v)_accupmax≧ 0), as shown in fig. 5, the safety braking distance is equal to the travel distance S from t0 to t1 and from t1 to t2 (deceleration rising phase)_accupT2-t3 (uniformly decelerating at the maximum deceleration until the vehicle and the front speed are equal) travel distance S_brakeThe distance L traveled by the leading vehicle and the safe stopping distance d are subtracted from the sum.

The time of the deceleration rising phase is:

t_accup＝t2-t1＝t_accupmax

the travel distance from t1 to t2 is S_accup：

(3) Constant deceleration braking phase (t 2-t 3):

the calculation formula is as follows:

a_diff＝a_zhumax-a_qian

v_brake＝(a_zhumax×(v_qian-a_qian×(t_{driver_reaction}+t_accup))-a_qian×(v_zhu-0.5×a_zhumax×t_accup))/a_diff

wherein, a_zhumaxFor the maximum deceleration of the vehicle, a_qianDeceleration of the target vehicle, t_{driver_reaction}Reaction time for the driver; v. of_brakeIn order to obtain the departure speed, the speeds of the host vehicle and the preceding vehicle are equal.

The safe braking distance is as follows: s ═ S_{driver_reaction}+S_accup+S_brake-L-d

And when the braking is started, determining a theoretical braking curve according to the safe braking distance and the initial speed.

In the braking stage, the acceleration is controlled to make the speed of the vehicle approach to a theoretical braking curve (theoretical braking curve). Taking fig. 3 as an example, it is known that the optimal braking force (in this embodiment, the braking duty ratio of the air brake system) corresponding to the theoretical braking curve is first controlled by using the optimal braking force as an initial value. In the whole braking process, data updating is carried out according to a fixed detection period (such as 50ms) to obtain real-time parameter values of braking, therefore, a theoretical braking curve is discretized according to the detection period, namely the whole braking period is divided equally according to the time of actually obtaining the parameter state values, and for example, 50ms is updated once. And updating the actual speed in real time, and when the actual speed is smaller than the theoretical speed, taking 2 (actual speed-theoretical speed)/a detection period as a deceleration variation, and calculating the ratio of the deceleration variation and the actual deceleration to be a deceleration change rate. The braking force for the next detection period can be estimated from the desired deceleration (the sum of the deceleration change amount and the current deceleration). In this embodiment, based on the desired deceleration (sum of the deceleration change amount and the current deceleration) and the detection time point indexed brake calibration table, we can know the corresponding brake force (brake duty ratio) at this time, and brake with the brake force in the next detection period, so that the actual speed and the theoretical speed at the end of the next detection period converge.

In this embodiment, in order to make the control smoother and not allow the deceleration to directly change abruptly, a threshold value of the deceleration change rate is set, and the deceleration change rate can only be increased or decreased by not more than the threshold value (the threshold value is generally less than 5%, and a typical value may be set to 2% or 3%) per detection period.

The invention further provides an emergency braking system based on the variable acceleration model, wherein the emergency braking system is an air brake system, and the air brake system executes the emergency braking method based on the variable acceleration model according to any scheme through the inflation control of a brake air pump.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.