Patent Publication Number: US-11643058-B2

Title: Method and device for controlling emergency braking distance

Description:
The present invention relates to a driver assistance method and system, known to the person skilled in the art by the acronym ADAS (“Advanced Driver Assistance System”). It relates more particularly to an emergency braking method and module for a motor vehicle known to the person skilled in the art by the acronym AEBS (“Autonomous Emergency Braking System”). 
     An emergency braking module AEB makes it possible to trigger an automatic braking of a motor vehicle equipped with such a system. 
       FIG.  1    illustrates the architecture of an emergency braking module  3  incorporated in a driver assistance system  2  of a vehicle  1  according to the state of the art which interacts with a target  6 . 
     The vehicle  1  comprises perception means  4 , notably distance sensors, linked to an input E 2  of the driver assistance system  2 . An output S 2  of the driver assistance system  2  is linked to braking means  5  of the vehicle  1 , for example disk brakes. 
     The driver assistance system  2  comprises the braking module  3  of which an input E 3  is linked to the input E 2  of the system  2  and an output S 3  is connected to the output S 2  of the system  2 . 
     The perception means  4  transmit to the module  3  distance and relative speed information between the vehicle  1  and the target  6 , for example a car, a pedestrian or a cyclist. 
     When the braking module  3  perceives a definite risk of collision between the target  6  and the vehicle  1 , the module  3  actuates the braking means  5  bringing about an automatic braking of the vehicle  1  so as to prevent the collision between the target  6  and the vehicle  1 . 
     The automatic braking is driven by the module  3  to the maximum of the capabilities of the braking means  5 . In other words, the braking is driven in such a way that the stopping distance of the vehicle  1  is the shortest possible. The braking driven in this way is an emergency braking. 
     In some situations, the braking driven in this way outperforms, that is to say that the maximum braking brings about a stopping of the vehicle  1  at a distance of several meters from the target  6 . 
     The outperforming braking results in the failure of the system  2  to take account of the characteristics of the vehicles, notably of the engine brake and of the weight of the vehicle, and of the environmental conditions in which the vehicle  1  is moving, notably the characteristics of the roadway on which the vehicle  1  is moving, for example the slope of the roadway, and the behavior of the target  6 , for example a slight acceleration of the target  6 . This effect can be felt by the user of the vehicle as a defect of the driver assistance system  2 , and when the vehicle  1  is in front of another vehicle, an emergency braking generates a risk of collision of the two vehicles following one another. 
     In order to enhance the feeling of the driver of the vehicle and minimize the risks of collision in emergency braking phases, the aim is to drive the braking power of the braking means  5  according to the imminence of the risk of collision and by taking account of the environmental conditions in which the vehicle is moving, that is to say that the aim is to manage the stopping conditions of the vehicle when the braking is sufficiently early and/or effective to avoid the collision between the vehicle and the target according to the characteristics of the roadway on which the vehicle is moving. 
     In this respect, reference can be made to the document US2016221549 which proposes an electronic control unit which will modulate the braking force of the vehicle as a function of the distance and of the relative speed between the vehicle and a target. 
     Reference will also be able to be made to the document CN104139781 which presents a method based on the communication of data between two vehicles to regulate the deceleration of the vehicle in an emergency braking situation. 
     The document US2014156157 describes an AEBS system that allows the driver to override the AEBS system in specific conditions. 
     The document CA2860892 seeks to enhance the decision-making as to the triggering of the emergency braking by implementing, among other things, motion equations. 
     In the document DE102011085585, the speed regulation system of the vehicle is directly linked to the brake pedal in order to take account of all the situations brought by the operation of the brake pedal. 
     Reference will also be able to be made to the document DE102010029223 which illustrates a method in which the relative speed between a followed vehicle and a following vehicle is calculated. The braking is driven by the relative speed. 
     The methods and devices according to the state of the art set out above are alternative emergency braking methods and devices but do not take account of the characteristics of the vehicles and the environmental conditions in which the vehicle is moving. 
     The aim of the invention is to overcome these drawbacks. 
     In light of the above, the invention proposes a method for controlling an emergency braking distance for a motor vehicle comprising a driver assistance system comprising a braking module and a module for controlling emergency braking distance. 
     According to a feature of the method according to the invention, when the braking module delivers an emergency braking setpoint at the input of said module for controlling distance, said module for controlling distance generates a braking setpoint that is variable according to time and intended for the braking means of said vehicle. 
     According to another feature, the generation of said braking setpoint uses a one-dimensional dynamic model of said vehicle. 
     Advantageously, the stopping distance of the vehicle is estimated for a maximum braking setpoint of the braking means and said setpoint is determined. 
     Preferably, said setpoint is generated in open loop mode. 
     According to another feature which said setpoint generated in open loop mode is corrected by incorporating correction means forming a closed loop. 
     Advantageously, an estimation of the acceleration of a target identified by detection means linked to said driver assistance system is determined. 
     Another subject of the invention is a driver assistance system comprising a braking module and a module for controlling emergency braking distance, the braking module being intended to be linked to braking means. 
     According to a feature of the system according to the invention, the module for controlling braking distance is linked to an output of the braking module. 
     Preferably, the system further comprises an embedded processing unit. 
     Another subject of the invention is a motor vehicle comprising a driver assistance system as defined above. 
    
    
     
       Other aims, features and advantages of the invention will become apparent on reading the following description, given purely by way of nonlimiting example, and with reference to the attached drawings in which: 
         FIG.  1   , which has already been mentioned, shows the general architecture of an emergency braking device incorporated in a vehicle according to the state of the art; 
         FIG.  2    shows the general architecture of an emergency braking device incorporated in a vehicle according to the invention; 
         FIG.  3    shows an example of braking setpoint generated by the driver assistance device according to the invention; and 
         FIGS.  4  and  5    show examples of braking setpoint on approaching a target generated by the driver assistance device according to the invention. 
     
    
    
     Reference is now made to  FIG.  2    which illustrates the architecture of a driver assistance system  8  implementing an emergency braking management method incorporated in a vehicle  7  according to an embodiment of the invention and which interacts with the target  6 . 
     The elements that are identical to those of  FIG.  1    are designated by the same numerical references. 
     The vehicle  7  comprises the perception means  4  and the braking means  5 . 
     The perception means  4  transmit distance and relative speed information between the vehicle  1  and the target  6  to the system  8 , and when they are actuated, the braking means  5  brake the vehicle  7 . 
     An input E 8  of the driver assistance system  8  is linked to an output of the perception means, and an output S 8  of the system  8  is linked to the braking means  5 . 
     The driver assistance system  8  comprises the braking module  3  and a module for controlling emergency braking distance  9 . 
     The input E 3  of the braking module  3  is linked to the input E 8  and the output S 3  of the device  3  is linked to an input E 9  of the module for controlling emergency braking distance  9 . An output S 9  of the module  9  is linked to the output S 8 . 
     A signal s 1  circulates between the output S 3  and the input E 9 , and a signal s 2  circulates between the output S 8  and the braking means  5 . 
     The signal s 1  comprises the braking setpoint emitted by the module  3  and the signal s 2  comprises the braking setpoint T Brk  emitted by the module  9 . 
     The determination of the setpoint T Brk  will be explained hereinbelow. 
     The module  9  is situated downstream of the braking module  3  and can be deactivated at any instant. Advantageously, the module  9  has no impact on the tuning of the module  3 . 
     When the module  8  allows only the reduction of speed of the vehicle  7  and not the avoidance of the target  6 , the module  9  behaves as a “wire”, that is to say that it transmits the signal received at its input E 9  to its output S 9  without modification, in other words the signals s 1  and s 2  are identical. 
     The driver assistance system  8  comprises an embedded processing unit implementing the braking module  3  and the module for controlling emergency braking distance  9 . 
     For example, the processing unit is implemented on the basis of a computer, but it can be any embedded device making it possible to implement the modules  3  and  9 . 
     As will be described in detail hereinbelow, such computation means are for example intended to implement control laws by implementing a dynamic model of the vehicle  7  and of the target  6  incorporated in the module  9  to determine the braking setpoint T Brk . 
     The computation means implement an example of method for controlling a braking distance which is now described. 
     The method for controlling braking distance comprises a dynamic model that makes it possible to calculate the physical quantities necessary to the execution of the method. 
     The dynamic model is one-dimensional according to the axis X of an absolute reference frame R linked to the road. The vehicle  7  and the target  6  are assumed rigid without bodywork motion. The different calculations are projected into a relative reference frame linked to the front of the vehicle Rrel. 
     In the absolute reference frame R, the following notations apply:
         a ego (t): the acceleration of the vehicle  7  as a function of time t;   V ego (t): the speed of the vehicle  7  as a function of time t;   X ego (t): the position of the vehicle  7  as a function of time t;   a tgt (t): the acceleration of the target  6  as a function of time t;   V tgt (t): the speed of the target  6  as a function of time t; and   X_tgt(t): the position of the target  6  as a function of time t.       

     The relative acceleration a rel (t), the relative speed V rel (t) and the relative position X rel (t) between the target  6  and the vehicle  7  are given by the following equations:
 
 a   rel ( t )= a   tgt ( t )− a   ego ( t )  (equation 1)
 
 V   rel ( t )= V   tgt ( t )− V   ego ( t )  (equation 2)
 
 X   rel ( t )= X   tgt ( t )− X   ego ( t )  (equation 3)
 
     By considering the equations of the dynamics, the acceleration a ego (t) of the vehicle  7  is described by the following equation: 
                       a   ego     ⁡     (   t   )       =           -   g     ·   sin     ⁢           ⁢   α     -     F   Pert     -     g   ·       m   0     m     ·     [     1   -   ɛ     ]     ·         T   Brk     ⁡     (   t   )         T   MAX                   (     equation   ⁢           ⁢   3     )               
in which:
         g is the acceleration of gravity;   α is the slope of the roadway counted positive in climbing, on which the vehicle  7  is moving;   F Pert  is a disruptive braking, for example the engine brake of the vehicle  7 ;   m is the current weight of the vehicle  7 ;   m 0  is the nominal weight of the vehicle  7  in the tuning of the module  8 ;   ε is the braking loss factor linked to the road grip of the vehicle  7 , for example a is equal to 0.2 on a wet roadway;   T Brk (t) is the variable braking setpoint that is variable according to time t delivered by the module  9 ; and   T MAX  is the maximum braking setpoint.       

     Consequently, the signal s 2  is equal to T Brk  (t). 
     The acceleration of the target according to in the absolute reference frame R is given by the following equation:
 
 a   tgt ( t )= A   tqt   +Δa   tgt ( t )  (equation 4)
         in which:
           A tgt  is the constant acceleration of the target  6  during the emergency braking; and   
           Δa tgt (t) is the variable acceleration of the target  6  during the emergency braking as a function of time t.       

     The relative acceleration a rel  in the absolute reference frame R is described by the following equation:
 
 a   rel ( t )= A   Pert ( t )− K ( t )  (equation 5)
         in which:       

     
       
         
           
             
               
                 
                   
                     
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                       ⁡ 
                       
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                         - 
                         g 
                       
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                       · 
                       
                         [ 
                         
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                           - 
                           ɛ 
                         
                         ] 
                       
                       · 
                       
                         
                           
                             T 
                             Brk 
                           
                           ⁡ 
                           
                             ( 
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                             ) 
                           
                         
                         
                           T 
                           MAX 
                         
                       
                     
                   
                   ; 
                   and 
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
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                       A 
                       Pert 
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       A 
                       tgt 
                     
                     + 
                     
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                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           a 
                           tgt 
                         
                         ⁡ 
                         
                           ( 
                           t 
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                         g 
                         . 
                         sin 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       α 
                     
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                       F 
                       Pert 
                     
                   
                 
               
               
                 
                   ( 
                   
                     equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ) 
                 
               
             
           
         
       
     
     The quantities measured by the perception means  4  are denoted as follows:
         V rel   mes (t) is the relative speed measured at the instant t; and   X rel   mes (t) is the relative position measured at the instant t.       

     V ego   mes (t) denotes the absolute speed of the vehicle  7  measured at the instant t by measuring means incorporated in the vehicle, notably in the CAN of the vehicle. 
     The following notations also apply:
         D Stop  the relative distance between the target  6  and the vehicle  7  for which the relative speed is zero;   t Stop  the time at the end of which the relative speed D Stop  is canceled out;   {circumflex over (D)} T max,Vrel=0  is an estimation of the stopping distance of the vehicle  7  for the braking setpoint T MAX  applied to the braking means  5 ; and   Â relMAX  is an estimation of the relative acceleration a rel (t) for the braking setpoint T MAX  applied to the braking means  5 .       

       FIG.  3    shows the procedure of an example of method for controlling an emergency braking distance implemented in the module  9 . The method comprises five logic tests T 1 , T 2 , T 3 , T 4  and T 5 , and eight steps  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6  and  7 . 
     A first step  0  is the initial step of the method. In this step, the module  9  behaves as a wire. The signals s 1  and s 2  are identical. The system  8  behaves like the system  2 , as known from the state of the art. 
     The next step  1  is activated if the set of two conditions is fulfilled, that is to say if the test T 1  is validated. 
     If the test T 1  is not validated, the procedure remains at the step  0 . 
     A first condition of the logic test T 1  requires the module  3  to generate a signal s 1  corresponding to the maximum braking setpoint T MAX , the aim of which is a stopping of the vehicle  7 . 
     A second condition requires the method for controlling an emergency braking distance to be authorized for the target  6  detected by the detection means  4 . The distance control system is triggered only for targets of chosen type (e.g.: system active for the target vehicles, inactive for pedestrians or cyclists). 
     In the step  1 , the module  9  still behaves as a wire and delivers a signal s 2  equal to the signal s 1 , in other words the braking setpoint s 2  is equal to T MAX . 
     This is a waiting step, the duration of which is variable and depends on the state of the braking means  5 . 
     For a maximum braking setpoint T MAX , the braking means  5  have a response dynamic range that is variable according to their preceding state. For example, if a moderate braking was ordered previously, the time to reach the maximum braking power corresponding to the setpoint T MAX  is reduced by the order of 150 ms. 
     In the step  2 , the stopping distance {circumflex over (D)} T max,Vrel=0  of the vehicle  7  is calculated for the braking setpoint T MAX . In this step, the setpoint T Brk (t) delivered to the braking means is equal to T MAX . 
     It is assumed:
         that the acceleration of the target  6  is constant:
 
Δ a   tgt ( t )=0  (equation 8)
   that the braking setpoint is constant:
 
 T   Brk ( t )= T   MAX   (equation 9);
   and that the relative speed between the target  6  and the vehicle  7  is zero:
 
 V   rel ( t )=0  (equation 10)
       

     By using the measured values defined previously, the following equations are obtained: 
     
       
         
           
             
               
                 
                   
                     
                       D 
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                         T 
                         ⁢ 
                         
                             
                         
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                         max 
                       
                       , 
                       
                         Vrel 
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                         0 
                       
                     
                   
                   = 
                   
                     
                       - 
                       
                         
                           
                             
                               V 
                               rel 
                               mes 
                             
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                               ( 
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                           2 
                         
                         
                           2 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
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                               ^ 
                             
                             relMAX 
                           
                         
                       
                     
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                         X 
                         rel 
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                     equation 
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                     11 
                   
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                     12 
                   
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     The estimation D T max,Vrel=0  of the stopping distance of the vehicle  7  is dependent on the estimation Â relMAX  of the relative acceleration a rel (t) for the setpoint T MAX  supplied by the speed measurement over a time interval Δt. The interval Δt depends on the quality of the perception means  4 , and the interval is of the order of 100 ms. 
     The estimation {circumflex over (D)} T max,Vrel=0  is compared to a threshold P in the test T 2 , P is for example equal to 1 m. The threshold P is the minimum stopping distance of the vehicle  7  before striking the target  6 . 
     If the estimation D T max,Vrel=0  is above the threshold P, it is considered that the safety conditions are sufficient for a regulation of the braking setpoint. The test T 2  is validated and the variable braking setpoint T Brk (t) is authorized, to be determined in the step  4 . 
     If the estimation {circumflex over (D)} T max,Vrel=0  is below the threshold P, the test T 2  is not validated and the procedure goes to the step  3 . 
     In the step  3 , the braking setpoint s 2  equal to the maximum braking set point T MAX  is maintained. The setpoint T Brk (t) is equal to T MAX  for a predetermined time T out  then, at the end of this time, the procedure reverts to the initial step  0 . 
     In the step  4 , the estimation {circumflex over (D)} T max,Vrel=0  is recalculated as a function of the relative positions and speeds X rel   mes (t) and V rel   mes (t). 
     The braking setpoint T Brk (t) that makes it possible to cancel the relative speed V rel  at a distance D Stop  from the target  6 , for example D Stop  is equal to 0.5 m, is calculated in open loop mode on each calculation step. 
     It is assumed that the engine brake, the slope and the behavior of the target  6  remain similar to those of the preceding states. 
     The precise data on weight m and state of the road s not being available, conditions giving the maximum braking setpoint T Brk (t) are considered, i.e.:
 
 m=m   0 ; and  (equation 13)
 
ε=0  (equation 14)
 
     Under these assumptions, the expression of the braking setpoint T Brk (t) in open loop mode is described by the following equations: 
                       T   Brk     ⁡     (   t   )       =       T   MAX     -         T   MAX     g     ·     (         A   ^     relMAX     -         A   ^     rel   cmd     ⁡     (   t   )         )                 (     equation   ⁢           ⁢   15     )               
in which
 
                         A   ^     rel   cmd     ⁡     (   t   )       =           V   rel   mes     ⁡     (   t   )       2           2   ·     (       X   rel   mes     ⁡     (   t   )       )       -     D   Stop       )               (     equation   ⁢           ⁢   16     )               
and
         Â relMAX  is calculated as described previously in the step  2 .       

     The use of the setpoint T Brk (t) in open loop mode comprising the estimation Â relMAX  of the relative acceleration a rel (t) for the braking setpoint T MAX  makes it possible to take account of the environmental conditions. Indeed, the estimation Â relMAX  is determined according to the measured relative speed V rel   mes (t). 
     Then, in the step  5 , the setpoint T Brk (t) is corrected so as to take account of the disturbances caused notably by the engine brake of the vehicle  7 . 
     After a predefined time, for example 100 ms, the setpoint T Brk (t) calculated in the preceding step by using an estimation of the acceleration Â rel   cmd (t) is recalculated by using a closed loop regulation based on the error of relative acceleration E Acmd (t) by incorporating correction means. The correction means comprise a regulator of PI (proportional integral) type for proportional gain k p  and integral gain k i  coefficients in the regulation loop. The gain coefficients k p  and k i  are determined by the usual methods known to the person skilled in the art. 
     In fact, the desired braking setpoint T Brk (t) is different from the corresponding braking power developed by the braking means  5  by virtue of disturbances, notably caused by the engine brake of the vehicle  7 , the dynamics of the braking means  5 . It is necessary to take account of this deviation to correct the setpoint value T Brk (t). 
     The following equation gives the error E Acmd (t) of relative acceleration: 
                       E   Acmd     ⁡     (   t   )       =             V   rel   mes     ⁡     (   t   )       2       2   ·     (         X   rel   mes     ⁡     (   t   )       -     D   Stop       )         -     [           V   rel   mes     ⁡     (     t   -     Δ   ⁢           ⁢   t       )       -       V   rel   mes     ⁡     (   t   )           Δ   ⁢           ⁢   t       ]               (     equation   ⁢           ⁢   17     )               
in which Δt is a time interval necessary to perform an estimation of the real acceleration, for example Δt is equal to 100 ms.
 
     By using the relative acceleration error formula E Acmd (t) defined in the equation 17, the closed loop control becomes: 
     
       
         
           
             
               
                 
                   
                     
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                     18 
                   
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     The summer ΣE Acmd (t) is reset to zero as soon as the procedure is at the step  5 . Moreover, the state of the summer ΣE Acmd (t) is maintained if the setpoint T Brk (t) is saturated, that is to say if T Brk  (t) is equal to T MAX  or if T Brk (t) is equal to the minimum braking value T MIN  determined according to the characteristics of the braking means  5 . 
     According to the equation 16, the relative acceleration Â rel   cmd (t) allowing the vehicle  7  to stop at the desired distance depends on the position measurement X rel   mes (t). 
     On approaching the target  6 , the position measurement errors of the detection means  4  are significant and the estimation of the relative speed X rel   mes (t) is difficult. 
     When the method is at the step  4  or  5  and the target  6  is at a distance less than a threshold H, for example 0.4 m, the test T 3  is validated and the procedure goes to the step  6 . 
     In this step, the braking setpoint T Brk (t) in the preceding step, that is to say in the step  4  or  5 , is maintained until the end of the braking. The braking setpoint is constant and unregulated. At the end of the braking, the procedure returns to the step  0 . 
     In all the preceding steps, the braking setpoint T Brk (t) was determined by assuming that the acceleration a tgt (t) of the target  6  is constant, that is to say that Δa tgt (t) is zero. 
     To some extent, the module  9  is capable of making up absolute acceleration variations Δa tgt (t) of the target  6 . Nevertheless, if the target  6  brakes suddenly while the module  9  is in a step other than the steps  0  and  1  the time necessary for the braking setpoint T Brk (t) to be saturated, that is to say in this case equal to T MAX , is too long. 
     The estimation {circumflex over (D)} T max,Vref=0  comprising the calculation of the estimation Â relMAX  of the relative acceleration a rel (t) for the braking setpoint T MAX  is no longer valid. Indeed, the calculation of the estimation Â relMAX  takes as assumption a movement of the target  6  according to a constant acceleration, that is to say that Δa tgt (t) is zero. This assumption is no longer borne out in the event of sudden braking. 
     When a sudden braking of the target  6  is detected in one of the steps  2 ,  4  or  5 , that is to say when the test T 4  is validated, the procedure goes to the step  7 . The determination of a sudden braking of the target  6  will be explained hereinbelow. 
     In the step  7 , the braking setpoint T Brk (t) is equal to T MAX  for the duration of the braking then the procedure goes to the step  0 . The module  9  behaves as a wire. 
     To detect a sudden braking of the target  6 , an estimator Â tgt (t) of the acceleration a tgt (t) of the target  6  is determined. 
     The estimator Â tgt (t) is described by the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       
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     To estimate the acceleration of the target  6  at the instant t, the relative speed V rel   mes  and the absolute speed V ego   mes  of the vehicle  7  are measured at the instant t−Δt and at the instant t, Δt being a fixed time equal for example to 100 ms. 
     If the estimator Â tgt (t) gives a value at the instant t below a threshold T, for example −2.5 m/s 2 , it is deduced therefrom that the target  6  is braking suddenly. 
     In the steps  2 ,  4  and  5 , the relative acceleration a rel (t) is determined according to the trend of the relative speed V rel   mes . 
     Upon a change of target, there can be an abrupt jump in the relative speed that can disrupt the regulation loops. To avoid this phenomenon, a change of target generates a return to the initial state that is to say to the step  0 . 
     The braking module  3  operates with a waiting time, or “timeout”. When the braking is triggered, the braking will be stopped after a determined time, for example 2 seconds. 
     When the braking setpoint is maximal, that is to say T Brk (t) is equal to T MAX , that does not present any problem. 
     However, since the module  9  varies the value of the braking setpoint T Brk (t), notably by reducing the value of the braking power demanded s 1  from the module  3 , it is probable that the module  3  will stop supplying a braking setpoint before the relative speed V rel   mes (t) is zero. 
     To eliminate this risk, the module  9  adjusts the minimum braking setpoint T MIN  for the relative speed V rel   mes (t) to be zero at the end of a predetermined time counted from the triggering of the braking. This time is for example equal to 5 seconds. In this case, the final distance constraint is then considered secondary and will no longer be observed. 
     In order to secure the module  9 , at each calculation step in the different steps of the method described previously, the estimation {circumflex over (D)} T max,Vrel=0  of the stopping distance of the vehicle  7  for the braking setpoint T MAX  is recalculated. If this distance becomes less than a threshold R, for example the value of R is equal to 0.4 m, the setpoint T Brk (t) is equal to T MAX  for the duration of braking, then the procedure goes to the initial step  0 . 
       FIG.  4    illustrates a braking phase according to the procedure described previously in the case where the value of the estimation {circumflex over (D)} T max,Vrel=0  is above the threshold value R for all the calculation steps and the value of the estimator Â tgt (t) of the acceleration a tgt (t) of the target  6  is above the threshold T, that is to say that the target  6  is not braking suddenly. 
     It represents the braking setpoint T Brk (t) that is variable according to time t delivered by the module  9  to the braking means  5 . 
     In the step  0  of the method, the module  9  behaves as a wire. 
     At the instant t 1 , the braking module  3  delivers a signal s 1  equal to T MAX  following the detection of a risk of collision with the target  6  by the driver assistance system  8 . 
     The target  6  is authorized, the test  1  is validated. The method goes to the step  1 . The module  9  still behaves as a wire, T Brk (t) is equal to s 1 , that is to say that T Brk (t) is equal to T MAX . 
     Then, the method goes to the step  2  at the instant t 2 . The setpoint T Brk (t) is equal to T MAX  and the value of the estimation {circumflex over (D)} T max,Vrel=0  is estimated. The estimated value is above the threshold P, the test T 2  is validated. 
     The method goes to the step  4  at the instant t 3 . The braking setpoint T Brk (t) is recalculated in open loop mode so as to take account of the conditions of the roadway. 
     Then, at the instant t 4 , the braking setpoint T Brk (t) is recalculated in the step  5  in closed loop mode so as to correct the setpoint determined in open loop mode by taking account of the disturbances linked to the vehicle  7 , notably the disturbances caused by the engine brake of the vehicle  7 . 
     Then, at the instant t 5 , the vehicle  7  is close to the target  6 , that is to say at a distance below the threshold H. The test T 4  is validated and the method goes to the step  6 . 
     In this step, the braking setpoint T Brk (t) in the preceding step, that is to say in the step  5 , is maintained until the end of the braking. The vehicle  7  stops at the instant t 6 . 
       FIG.  5    illustrates a braking phase according to the procedure described previously in the case where the value of the estimation {circumflex over (D)} T max,Vrel=0  is below the threshold value R for a calculation step at the end of the step  3  at the instant t 7 . 
     The steps  0 ,  1 ,  2  and  3  of  FIG.  4    apply once again and proceed as described previously. 
     At the instant t 7 , the setpoint T Brk (t) is equal to T MAX  for the duration of braking, then the procedure goes to the initial step  0 . 
     Advantageously, in the event of an emergency braking, the method for controlling an emergency braking distance generates a control law for the braking means of the vehicle  7  that takes account of the characteristics of the vehicle and the environmental conditions in which the vehicle is moving so as to optimize the braking stopping distance of the vehicle, while guaranteeing at each instant of the emergency braking phase procedure, that a risk of collision between the vehicle  7  and the detected target  6  is eliminated.