METHOD FOR DETECTING A TRAFFIC CONGESTION SITUATION IN A MOTOR VEHICLE

Abstract

Method for detecting traffic congestion using a motor vehicle radar system, comprising multi-beam radar sensors (21-24) in the rear and front corners of the vehicle, the method comprising the steps of: dividing the radar sensors (Df_l, Df_r, Dr_l, Dr_r) into four angular sectors (Zfront, Zrear, Zleft, Zright) extending to the front, to the rear, to the right and to the left of the vehicle respectively, selecting for each angular sector, from the beams for which no target is detected, the (Dfront, Drear, Dleft, Dright) beam having the shortest reach distance, detecting the amplitude of reflected beams corresponding respectively to the selected beams, and—analysing the period during which the amplitude of the reflected beams is maintained relative to a predefined time threshold for each angular sector respectively, the method detecting a traffic congestion situation when the analysing step determines simultaneously for the four angular sectors that the period during which the amplitude of the reflected beams is maintained is greater than or equal to the predefined time threshold.

Claims

1. A method for detecting a traffic congestion situation by means of a radar system equipping a host automobile vehicle, said radar system comprising multi-beam radar sensors arranged at the rear and front corners of the host vehicle, the radar beams being emitted in various given targeted directions in such a manner as to cover, for each radar sensor, a detection zone extending between a radial direction oriented obliquely toward the front and a radial direction oriented obliquely toward the rear, each radar sensor being capable of supplying, for each given targeted direction, the range of the radar beam emitted in said direction, the method being characterized in that it comprises steps for: of all of the radar beams (D.sub.f_l, D.sub.f_r, D.sub.r_l, D.sub.r_r) emitted by the radar sensors according to a division of the environment of the vehicle into four angular sectors (Z.sub.front, Z.sub.rear, Z.sub.left, Z.sub.right), in opposing pairs, respectively extending toward the front and toward the rear of the vehicle and toward the right side and toward the left side of the vehicle, selection for each of four angular sectors, from amongst the beams distributed into each of them for which no target is detected, of the beam (D.sub.front, D.sub.rear, D.sub.left, D.sub.right) having the shortest range, detection of the amplitude of the reflected beams corresponding respectively to said beams selected within the four angular sectors, and analysis of the period of time for which the amplitude of said reflected beams is maintained with respect to a predefined time threshold for each angular sector, respectively, the method detecting a traffic congestion situation when the analysis step determines, simultaneously for the four angular sectors, that said period of time for which the amplitude is maintained is greater than or equal to said predefined time threshold.

2. The method as claimed in claim 1, wherein the analysis step furthermore comprises a step for comparing the range of each beam selected within the four angular sectors with a predefined distance threshold for each angular sector respectively, the method detecting a traffic congestion situation when the comparison step determines, simultaneously for the four angular sectors, that said range is less than or equal to said predefined distance threshold.

3. The method as claimed in claim 2, wherein said predefined distance threshold is fixed at less than or equal to 5 m, for the angular sectors extending toward the front and toward the rear of the host vehicle.

4. The method as claimed in claim 2, wherein said predefined distance threshold is fixed at less than or equal to 2 m for the angular sectors extending from the right side and from the left side of the host vehicle.

5. The method as claimed in claim 1, further comprising a step for activating an autonomous driving mode of the host vehicle when a traffic congestion situation is detected.

6. The method as claimed in claim 3, wherein said autonomous driving mode is designed to provide all of the operational driving tasks of the host vehicle.

7. A device for detecting a traffic congestion situation comprising a radar system on board a host automobile vehicle, said radar system comprising multi-beam radar sensors arranged at the rear and front corners of said vehicle, the radar beams being emitted in various given targeted directions in such a manner as to cover, for each radar sensor, a detection zone extending between a radial direction oriented obliquely toward the front and a radial direction oriented obliquely toward the rear, each radar sensor being capable of supplying, for each given targeted direction, the range of the radar beam emitted in said direction, the device comprising: a unit for processing the emitted radar beams, designed to apply a distribution of all of the radar beams (D.sub.f_l, D.sub.f_r, D.sub.r_l, D.sub.r_r) emitted by the radar sensors according to a division of the environment of the vehicle into four angular sectors (Z.sub.front, Z.sub.rear, Z.sub.left, Z.sub.right), in opposing pairs, respectively extending toward the front and toward the rear of the vehicle and toward the right side and toward the left side of the vehicle, and to select for each of said four angular sectors, from amongst the beams distributed into each of them for which no target is detected, the beam (D.sub.front, D.sub.rear, D.sub.left, D.sub.right) having the shortest range, said processing unit comprising an analysis module designed to verify the period of time for which the amplitude of the reflected beams, corresponding respectively to said beams selected within the four angular sectors, is maintained with respect to a predefined time threshold for each angular sector respectively, said device detecting a traffic congestion situation when said analysis module determines, simultaneously for the four angular sectors, that said period of time for which the amplitude is maintained is greater than or equal to said predefined time threshold.

8. The device as claimed in claim 7, further comprising a module for comparing the range of each beam selected within the four angular sectors with a predefined distance threshold for each angular sector respectively, the device detecting a traffic congestion situation when the comparison module determines simultaneously for the four angular sectors that said range is less than or equal to said predefined distance threshold.

9. The device as claimed in claim 7, further comprising means for activating a system for controlling the autonomous mode of the vehicle when a traffic congestion situation is detected.

10. An automobile vehicle comprising: the device according to claim 7.

11. The method as claimed in claim 2, wherein said predefined distance threshold is fixed at less than or equal to 3 m for the angular sectors extending toward the front and toward the rear of the host vehicle.

12. The method as claimed in claim 2, wherein said predefined distance threshold is fixed at less than or equal to 1.5 m for the angular sectors extending from the right side and from the left side of the host vehicle.

Description

[0026] In the present description, the terms front, rear, right, left are denoted with respect to the front and rear directions of the vehicle and with respect to the normal direction of travel of this vehicle.

[0027] With reference to FIG. 1, this illustrates an object detection system installed on a host automobile vehicle 10. The object detection system comprises four object detection sensors arranged at the four corners of the vehicle, respectively a front left corner sensor 21, a front right corner sensor 22, a rear left corner sensor 23 and a rear right corner sensor 24. These corner sensors are for example positioned at the lateral ends of a face of the front and rear fenders of the vehicle. These object detection sensors 21-24 may for example be radar sensors and, in particular, multi-beam radar sensors designed to emit radar beams in various given targeted directions in such a manner that each radar sensor 21-24 can scan a detection zone extending over a given angular range, for example of substantially 180°, between a radial direction oriented obliquely toward the front and a radial direction oriented obliquely toward the rear. The detection zone of each radar sensor 21-24 has substantially the shape of a semi-circle.

[0028] The detection zone of the radar sensor 21 disposed on the front left corner extends over an angular range of substantially 180° bounded between a radial direction oriented obliquely toward the front right and a radial direction substantially opposite, oriented obliquely toward the rear left, such that the detection zone covered by the radar sensor 21 disposed on the front left corner extends over the front of the vehicle and the left side of the vehicle.

[0029] Similarly, the detection zone of the radar sensor 22 disposed on the front right corner extends over an angular range of substantially 180° bounded between a radial direction oriented obliquely toward the front left and a radial direction oriented obliquely toward the rear right, such that the detection zone covered by the radar sensor 22 disposed on the front right corner extends over the front of the vehicle and the right side of the vehicle.

[0030] Similarly again, the detection zone of the radar sensor 23 disposed on the rear left corner extends over an angular range of substantially 180° bounded between a radial direction oriented obliquely toward the front left and a radial direction oriented obliquely toward the rear right, such that the detection zone covered by the radar sensor 23 disposed on the rear left corner extends over the rear of the vehicle and the left side of the vehicle.

[0031] Lastly, the detection zone of the radar sensor 24 disposed on the rear right corner extends over an angular range of substantially 180° bounded between a radial direction oriented obliquely toward the front left and a radial direction oriented obliquely toward the rear right, such that the detection zone covered by the radar sensor 24 disposed on the rear right corner extends over the rear of the vehicle and the right side of the vehicle.

[0032] Thus, the corner radar sensors 21-24 are capable of detecting objects in the environment of the vehicle both on the right and left sides of the vehicle and on the front and the rear of the vehicle.

[0033] The detection zones of the radar sensors disposed on the front left and right corners partially overlap on the front of the vehicle, the detection zones of the radar sensors disposed on the front left and rear left corners partially overlap on the left side of the vehicle, the detection zones of the radar sensors disposed on the rear left and right corners partially overlap on the rear of the vehicle and the detection zones of the radar sensors disposed on the rear right and front right corners partially overlap on the right side of the vehicle.

[0034] Each radar sensor 21-24 emits beams of electromagnetic waves, respectively D.sub.f_l, D.sub.f_r, D.sub.r_l, D.sub.r_r, in a given targeted direction of space, in such a manner as to cover the corresponding detection zone of the radar sensor. When a radar beam encounters an object situated in the detection zone the beam is reflected. By measuring the time of flight (time needed for the beam to go from the radar sensor to the object then to return), the distance between the sensor and the object is determined. Furthermore, if the reflecting object is moving at a certain speed, the resulting shift in frequency between the emitted beam and the reflected beam allows a measurement of the speed of the reflecting object to be obtained.

[0035] Thus, the detection system installed on the host vehicle allows detection information to be received relating to an assembly of mobile objects positioned inside of the detection zones of the radar sensors of the detection system. In particular, the distance between an object and the radar sensor and the speed of an object are associated with each mobile object detected.

[0036] In contrast, as explained in the introduction, when an object is immobile, it is not detected by the radar sensor. However, each radar sensor supplies, for each radar beam emitted in a given targeted direction, a distance to which its beam reaches if it does not detect a target, either the emitted beam does not encounter any obstacle, or it encounters an obstacle, but this is an immobile obstacle, not therefore generating any detection information. Accordingly, this distance to which the beam reaches if it does not detect a target may be either the maximum range to which the emitted radar beam reaches, corresponding to the case where it does not encounter any obstacle, or the distance at which the emitted radar beam encounters an obstacle, corresponding to the case of an immobile obstacle, without it being possible, in the absence of a detection, to distinguish between these various possible cases.

[0037] Accordingly, rather than exploiting detection information resulting from the encounters of a radar beam with a mobile object situated in the detection zone, the method of the invention exploits the information relating to the range of the beams by targeted direction when the emitted beam does not detect any target, in order to allow an immobile object to be detected in the environment of the vehicle, typically a stationary vehicle, or a barrier running along the roadside.

[0038] For this purpose, in a first step, a distribution of all of the radar beams D.sub.f_l, D.sub.f_r, D.sub.r_l, D.sub.r_r, emitted by the radar sensors 21-24, is carried out according to a division of the environment of the vehicle 10 into four angular sectors Z.sub.front, Z.sub.rear, Z.sub.left, Z.sub.right, these angular sectors being in opposing pairs and respectively extending toward the front and toward the rear of the vehicle, and toward the left side and toward the right side of the vehicle. More precisely, the front Z.sub.front and rear Z.sub.rear angular sectors each extend to the front and to the rear of the vehicle, preferably symmetrically on either side of the longitudinal median axis X of the vehicle, the angular sector Z.sub.left, extends from the left side of the vehicle between the front and rear angular sectors and the angular sector Z.sub.right extends from the right side of the vehicle between the front and rear angular sectors. As illustrated in FIG. 1, the radar beams Df_l and Df_r grouped within the angular sector Z.sub.front extending toward the front of the vehicle 10 are shown according to a first graphic code, the radar beams Dr_l and Dr_r grouped within the angular sector Z.sub.rear extending toward the rear of the vehicle 10 are shown according to a second graphic code, the radar beams Df_l and Dr_l grouped in the angular sector Z.sub.left extending toward the left side of the vehicle 10 are shown according to a third graphic code and the radar beams Df_r and Dr_r grouped within the angular sector Z.sub.right extending toward the right side of the vehicle 10 are shown according to a fourth graphic code. The radar beams thus distributed into these four angular sectors Z.sub.front, Z.sub.rear, Z.sub.left, Z.sub.right allow new detection zones to be defined covering specifically the front, the rear, the left side and the right side of the vehicle, respectively.

[0039] The configuration of the four angular sectors may be adjusted by means of two adjustment parameters, allowing the extent of the front angular sector Z.sub.front, and of the rear angular sector Z.sub.rear to be respectively adjusted. Thus, the front angular sector Z.sub.front has an angular extent defined by the angle α between the longitudinal median axis X of the vehicle and a radial edge of the front angular sector Z.sub.front. Similarly, the rear angular sector Z.sub.rear has an angular extent defined by the angle β between the longitudinal median axis X of the vehicle and a radial edge of the rear angular sector Z.sub.rear.

[0040] Then, for each of the four angular sectors thus defined, a selection of the radar beam which has the shortest range is subsequently made from amongst the radar beams distributed into each of them for which no target is detected.

[0041] D.sub.front thus denotes the beam having the shortest range from amongst the beams grouped within the angular sector Z.sub.front extending to the front of the vehicle, D.sub.rear, the beam having the shortest range from amongst the beams grouped within the angular sector Z.sub.rear extending to the rear of the vehicle, D.sub.left, the beam having the shortest range from amongst the beams grouped within the angular sector Z.sub.left extending from the left side of the vehicle and D.sub.right, the beam having the shortest range from amongst the beams grouped within the angular sector Z.sub.right extending from the right side of the vehicle.

[0042] In a following step, the amplitude of the reflected beams, corresponding respectively to the beams selected within the four angular sectors, is detected and the period of time for which the amplitude of these beams is maintained with respect to a predefined time threshold for each angular sector, respectively, is analyzed. In other words, it is sought to verify whether, for each of the four angular sectors, the reflected amplitude of the selected beam which does not detect a target and has the shortest range is maintained for a minimum time corresponding to the predefined time threshold. If this is the case, it is considered that there is an immobile obstacle, which can typically be a stationary vehicle, for the angular sector in question. In this way, a traffic congestion situation is detected when the analysis step determines, simultaneously for the four angular sectors Z.sub.front, Z.sub.rear, Z.sub.left, Z.sub.right, that the period of time for which the amplitude is maintained is greater than or equal to the predefined time threshold for the corresponding angular sector.

[0043] For this purpose, as illustrated in FIG. 2, a module 30 for analyzing the period of time for which the amplitude of the selected beams is maintained with respect to values of predefined time thresholds may consist of a low-pass filter, whose time constant T.sub.i is of the same order of magnitude as the time threshold predefined for each angular sector Z.sub.i (i=front, rear, left, right). Thus, the low-pass filter 30 filters the selected beams having the shortest range whose reflected amplitude is maintained for a duration greater than or equal to the predefined time threshold for each angular sector being considered.

[0044] According to one preferred embodiment of the invention illustrated in FIG. 2, when it has been verified that the amplitude of the selected beams having the shortest range stays the same for a predefined time threshold, the idea is then to compare the range of each beam selected within the four angular sectors with a predefined distance threshold for each angular sector respectively. The information relating to this comparison for each angular sector Z.sub.i, denoted Info_Z.sub.i (i=front, rear, left, right), which is preferably a Boolean value, is determined by a comparison module 40, by comparing, for each angular sector, the range of the selected beams previously filtered with at least one threshold. According to the exemplary embodiment in FIG. 2, two thresholds are used corresponding to a hysteresis function, as follows:

[0045] Info_Z.sub.i=0 if the range of the beam selected for the corresponding angular sector is greater than a first low threshold D.sub.down i defined for the angular sector in question, or

[0046] Info_Z.sub.i=1 if said range is less than or equal to a second high threshold D.sub.up i defined for the angular sector in question and higher than the low threshold D.sub.down i.

[0047] Alternatively, where the two thresholds are equal to a single distance threshold, then:

[0048] Info_Z.sub.i=0 if the range of the beam selected for the corresponding angular sector is greater than the single distance threshold predefined for the angular sector in question,

[0049] Info_Z.sub.i=1 if said range is less than or equal to said threshold.

[0050] For example, this predefined distance threshold is fixed at less than or equal to 5 m, preferably equal to 3 m, for the angular sectors Z.sub.front and Z.sub.rear extending toward the front and toward the rear of the host vehicle 10. With regard to the angular sectors Z.sub.right and Z.sub.left extending from the right side and from the left side of the host vehicle 10, this distance threshold is for example fixed at less than or equal to 2 m, preferably equal to 1.5 m.

[0051] It is therefore considered that, if the range of the beam selected for an angular sector in question is below this threshold, there is an immobile obstacle corresponding to a stationary vehicle for this angular sector in the immediate vicinity of the vehicle.

[0052] The state of the Boolean values info_Z.sub.i thus determined by the comparison module 40 is used at the input of an AND gate 50, whose output TJD_Flag is used to validate the detection of a traffic congestion situation. Thus, if the condition on the comparison of the ranges of the selected beams with the predefined distance threshold is met simultaneously in the four angular sectors, the output signal TJD_Flag goes to 1, which allows the detection of a traffic congestion situation to be validated. This information on traffic congestion detection validation TJD_Flag is supplied at an enable input of a system for controlling the autonomous mode of the vehicle and, in particular, of a system for controlling the autonomous mode of the vehicle designed to operate at level 3 of autonomy, so as to activate this system. Given that the method just described allows a traffic congestion situation to be detected even when the surrounding vehicles are stationary, the availability of such a system is consequently significantly improved.