EP2150446A1

EP2150446A1 - Prevention of a rear crash during an automatic braking intervention by a vehicle safety system

Info

Publication number: EP2150446A1
Application number: EP08717249A
Authority: EP
Inventors: Stephan Stabrey
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-04-27
Filing date: 2008-02-29
Publication date: 2010-02-10
Also published as: JP2010525975A; JP5108939B2; US20100280726A1; DE102007019991A1; WO2008131982A1

Abstract

The invention relates to a method for preventing a rear crash following activation of an automatic braking intervention by a vehicle safety system. The danger and degree of a possible rear crash by a vehicle (2) following behind can be significantly reduced if a model for the approach of a hypothetical following vehicle is used, and a condition for the activation of the brakes is determined, based on this model and, finally, if the brakes are at least partially activated when this condition occurs.

Description

27.02.2008

ROBERT BOSCH GMBH; 70442 Stuttgart

description

title

Avoiding a rear-end collision during an automatic braking intervention of a vehicle safety system

State of the art

The invention relates to a method for avoiding a rear-end collision after triggering of an automatic brake intervention by a vehicle safety system according to the preamble of patent claim 1 and to a control device having a brake algorithm according to the preamble of patent claim 7.

Various vehicle safety systems are known from the prior art, which initiate automatic emergency braking (ANB) in critical driving situations in which the vehicle, for example, approaches an obstacle. Such collision avoidance systems usually comprise a "forward-looking" sensor system which monitors the area in front of the vehicle and automatically triggers the service brake in the event of an impending head-on collision with another object In the case of interventions of this kind, there is always the danger that a following vehicle or its driver will not be able to brake fast enough and, in the absence of sufficient safety distance, a rear-end collision will occur.

Disclosure of the invention

It is therefore the object of the present invention, in the case of an automatic emergency braking to reduce the risk of collision with a subsequent vehicle. This object is achieved by the features specified in the patent claim 1 and 7 features. Further embodiments of the invention are the subject of dependent claims.

An essential aspect of the invention is to perform an automatic braking intervention assuming a hypothetical follow-up vehicle that approaches the own vehicle in a certain, theoretically assumed manner, and to perform the braking so that there is no or only a very weak rear-end collision comes. According to the

Invention is carried out at the beginning of the automatic braking intervention strong braking with high braking torque, and in a second phase, the brake at least partially solved to reduce the risk or the severity of the collision. The time for releasing the brake is determined in particular by the initial distance and the theoretically assumed behavior of the following vehicle. The use of a model for the approach of the follower vehicle has the advantage that no sensor for monitoring the rear space of the vehicle is necessary. However, the brake is released during an automatic braking, even if no subsequent vehicle exists. Between the safety of your own

Vehicle and the subsequent vehicle is therefore to be found in the design of the system a compromise.

The release condition for the brake of the front vehicle is preferably dependent on the assumed initial distance of the following vehicle to the own vehicle, the initial speed of the following vehicle, a theoretical reaction time of the driver of the following vehicle and / or a theoretically possible deceleration of the following vehicle.

For example, the rule of thumb "half tacho" or an arbitrary multiple of the airspeed may be used for the initial distance of the following vehicle The assumed distance of the following vehicle is preferably speed-dependent For example, for the initial speed of the following vehicle can be the speed of the own vehicle any multiple thereof, and for the delay a fraction, eg 80%, of the deceleration of the forward vehicle are assumed. To determine the release time, an algorithm is preferably provided which takes into account one or more of the variables mentioned. Instead of an analytical algorithm, of course, a corresponding function or set of curves can be stored in the system, which defines the desired braking function. Both variants should be understood here by the term "model".

According to a preferred embodiment of the invention, an algorithm is provided which during an automatic emergency braking a

Calculated speed (release speed) for the front vehicle, at which the vehicle brake must be automatically released again. Optionally, of course, another dissolution condition, such as e.g. a specific time or a certain theoretically assumed distance to the following vehicle can be determined as a release condition. The

However, release speed can be relatively easily and accurately measured by the wheel speed sensors. In the case of a brake function stored in the system, this preferably specifies a release speed at which the vehicle brake is to be released. The release speed is dependent in particular on the initial speed of the own vehicle.

For the determination of the release condition it is assumed that after release of the brake, a certain distance between both vehicles does not fall below, or, in the case that both vehicles touch, a certain speed difference should not be exceeded. According to a preferred embodiment of the invention, the condition is chosen such that at the time when both vehicles touch, the speed difference is equal to zero.

A vehicle system according to the invention comprises a control unit which is connected to an environment sensor system and has an algorithm which operates as described above.

In the case of a collision avoidance system, the system includes "predictive" sensing that monitors the area in front of the vehicle and automatically triggers the service brake in the event of an impending head-on collision with another object Initial collision initiates automatic emergency braking, the control unit z. B. equipped with acceleration sensors or receives the information about a collision from the airbag system.

Brief description of the drawings

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

Fig. 1 is a schematic representation of two vehicles which move at a predetermined distance;

Figure 2a shows the time course of the acceleration of the two vehicles.

Figure 2b shows the time course of the speed of the two vehicles.

Fig. 2c shows the time course of the distance between the two vehicles; and

Fig. 3 is a schematic function diagram for calculating the trigger condition.

Embodiments of the invention

Fig. 1 shows two vehicles 1, 2, located on a roadway 3 with a

Move speed vi (t) or v ₂ (t). The distance between the two vehicles is denoted by d (t).

At least the front vehicle 1 comprises a vehicle safety system 5, which in certain driving situations, for. B. in an imminent frontal collision or after a first collision can initiate automatic emergency braking. The entire system including the sensors and the controller is shown schematically as block 5 here.

Upon detection of a critical situation, an automatic braking is triggered and the vehicle brakes initially operated with high braking force. At some point, the brakes will be at least partially solved in order to reduce the risk or the severity of an impending rear-end collision. The time at which the brakes are released is calculated by means of a theoretical model for the approach of a hypothetical following vehicle based on assumptions for the initial distance and a specific driving behavior of the following vehicle 2. The

Collision avoidance system 5 therefore does not require any sensors for monitoring the rear space of vehicle 1. There is thus no information about speed v ₂ (t) or distance d (t) of the following vehicle available. The existence of a subsequent vehicle is not known. Rather, the system 5 is based on a typical driving behavior or driver characteristics that can be determined from statistical evaluations of the traffic situation.

In the embodiment described below, for the behavior of the follower vehicle 2, a certain reaction time t _{r of} the driver, a maximum deceleration a _ma χ, 2 of the following vehicle 2 and a certain initial distance do, which depends on the speed vi of the first vehicle, assumed. The driving behavior of the two vehicles 1, 2 and the change of different driving state variables are shown in an illustrative manner in FIGS. 2a-2c.

Fig. 2a shows the time course of the longitudinal acceleration a _{x of} the two vehicles after triggering an automatic emergency braking, Fig. 2b shows the time course of the longitudinal velocities vi or V ₂ and Fig. 2c shows the time course of the distance d between the two vehicles 1 and 2. The index "1" designates in each case a size of the first vehicle and "2" a size of the second vehicle 2. The illustrated variables of the vehicle 1 can be measured by means of the existing sensors, the illustrated variables of the vehicle 2 are based on the above assumptions with the aid of the approximation model of the safety system 5.

At time t ₀ an automatic emergency braking is triggered. The speed vi of the vehicle 1 decreases accordingly. In addition, it is assumed that the driver of the following vehicle 2 needs a reaction time t _r until he also operates the brake. The following vehicle then decelerates with a _max , 2- This acceleration a _max , 2 is here in terms of magnitude smaller than that of the first vehicle 1 assumed as a average driver usually does not reach the full, physically realizable deceleration of the vehicle. As can be seen in Fig. 2b, the speed V _{2 of} the second vehicle slows down more slowly than that of the first vehicle 1. The distance d (t) between the two vehicles 1, 2 is thus always smaller, as in Fig. 2c recognize.

At the time ti, the brake of the front vehicle 1 is automatically released to avoid a rear-end collision. The first vehicle 1 then moves on at a constant speed vi (see Fig. 2b). The time ti is calculated here so that at time t ₂ , in which touch the two vehicles (the distance d is zero), the speed vi, V _{2 of} the two vehicles 1, 2 is the same size. That is, the subsequent vehicle 2 approaches the own vehicle 1 to touch, but it does not come to a rear-end collision, since both vehicles have the same speed at this time.

Optionally, of course, could be tolerated a start-up of the following vehicle with low energy or even be determined that the two vehicles do not touch at all and a predetermined minimum distance should be maintained.

In the following, an algorithm is explained which determines a vehicle speed vi at which the brake must be released in order for the vehicles 1 and 2 to have the same speed at the time of the touch, thus avoiding a collision.

The algorithm initially assumes that the two vehicles 1, 2 drive at the same speed before the automatic braking. This is approximately the case in the rules in normal follow-up traffic. After a reaction time t _r , the vehicle then decelerates with a _ma χ, 2 Thus, for the speed V _{2 of} the following vehicle 2 (for t> t _o + t _r ):

v ₂ (t) = V ₀ + lnt (a _{max, 2} (t)) - dt. (1 )

Here, V _{0 is} the speed of the two vehicles 1, 2 at the beginning of the automatic braking.

The relative speed of both vehicles is thus: V _r e _l (t) = V i (t) - V ₂ (t) (2)

where vi can be measured directly in the vehicle 1.

The relative speed is then numerically integrated, which results in the reduction d _re d (t) of the distance between the two vehicles:

d _red (t) = lnt (v _re ι (t)) - dt (3)

The remaining distance d (t) thus results in:

d (t) = do + d _red (t). (4)

Since the following vehicle 2 is faster than the first vehicle because of the lesser deceleration a _x , ₂ , d _re d (t) is less than zero. The remaining distance d (t) thus decreases.

As described above, it is defined for the release speed v _L that both vehicles are just touching and imaginary

Touch time t _{2 should have} the same speed. For the contact time dt, the following applies, assuming a constant deceleration of the following vehicle:

vi (dt) = v ₂ (dt) = V ₂ (W) ⁺ a _x , ₂ (W) -dt (5)

In this case, V ₂ (W) is the theoretical assumed current speed of the follower vehicle 2 at the current time W- If the current distance d (W) of the two vehicles after a time dt should be reduced to zero, can for the difference of the two vehicles. 1 , 2 distance traveled following equation:

v ₂ (t _act ) -dt + 1/2-a ₂ (W) -dt ² -vi (t _act ) -dt = d (W) (6)

From the two equations (5), (6) one obtains the duration until the touch.

dt = -1 / a ₂ (W) - V (-2 - ^ ('. J ^■ <* (' *)) (7) and the speed v _{L of} the first vehicle 1, at which the brakes must be released, to:

v _L = V ₂ (U) - 4 2 - a ₂ (t _act ) - d (t _act ) (8)

3 shows a schematic block diagram of a collision avoidance system with an algorithm for reducing the risk of a rear-end collision. The overall system 5 includes various sensors 10 for monitoring the front space of the first vehicle 1, such as radar sensors, and wheel speed sensors. Those sensor signals which are necessary for triggering an automatic braking are read out by a safety function 13. When a critical driving situation occurs, the brake system 11 is automatically actuated by the function 13.

A unit 12 calculates z. Based on the deceleration of the vehicle 1, and possibly the estimated coefficient of friction assuming a reaction time a theoretical delay a _{x, 2 of} the assumed subsequent vehicle 2. The latter is integrated by means of an integrator 14 according to equation (1) and thus taking into account Initial speed, a speed V _{2 of} the follower vehicle 2 calculated. The velocities vi and V ₂ are fed to a unit 19 for calculating the release speed v _L according to equation (8). From the difference of the two velocities vi and V ₂ , which is calculated at a node 15, the relative velocity v _re ι, which is integrated by means of an integrator 16, to the change of the distance d of both vehicles 1, 2 according to equation (3 ) to calculate. From this value d _re d and a starting distance do determined by a unit 17, the instantaneous distance d of the two vehicles 1, 2 results (see equation (4)). The latter is also supplied to the unit 19, which calculates the release speed v _L from the various input variables. If the

Speed vi of the front vehicle reaches the release speed v _L , the braking process is automatically interrupted. The front vehicle 1 then continues to move at a constant speed.

Claims

27.02.2008ROBERT BOSCH GMBH; 70442 Stuttgart claims

A method for avoiding a possible collision after triggering an automatic braking intervention by a vehicle safety system, characterized in that - in a first phase of the automatic braking intervention braking with high braking torque is carried out - using a model for the approximation of a hypothetical

Following the vehicle is a condition for releasing the brake is determined and - when the condition occurs, the brake is at least partially released to prevent a collision or limit its severity.

2. The method according to claim 1, characterized in that the model assumes an initial distance (do) of the follower vehicle (2) to the own vehicle (1) and determines the release condition as a function of this distance (do).

3. The method of claim 1 or 2, characterized in that the model assumes an initial speed (v ₀ ) of the follower vehicle (2) and determines the release condition in dependence on this speed (v ₀ ).

4. The method according to any one of the preceding claims, characterized in that the model assumes a theoretical reaction time (t _r ) of the driver of the following vehicle (2) and determines the release condition as a function of this reaction time (t _r ).

5. The method according to any one of the preceding claims, characterized in that the model assumes a theoretical deceleration (a _{x 2} ) of the following vehicle (2) and determines the release condition in response to this delay (a _{x 2} ).

6. The method according to any one of the preceding claims, characterized in that the release condition is selected so that after release the brake does not fall below a certain distance (d) between the two vehicles (1, 2), or that at the time (t ₂ ) in which both vehicles (1, 2) touch, a certain speed difference of the vehicles (1, 2 ) is not exceeded.

7. Control device comprising means for performing one of the aforementioned methods.