Method for correcting a measurement of the speed of a vehicle

Abstract

Disclosed is a computer-implemented method for correcting a measurement of the speed of a vehicle, in particular in a driver-assistance system, the method comprising: receiving data representing a relative speed of the vehicle with respect to a fixed target obtained by a radar sensor of the vehicle; receiving data representing an azimuth of said fixed target with respect to the radar sensor of the vehicle; correcting the relative speed of the vehicle with said azimuth in order to obtain a radar speed of the vehicle; and receiving a rolling-circumference-related speed of the vehicle obtained by a speed sensor of the vehicle.

Description

Description _ Title of the invention: Method for correcting the measurement of the speed of a vehicle Technical field of the invention

[0001] The present invention relates to the field of vehicle speed measurements, in particular in a driving assistance system. State of the art

[0002] It is known to equip modern motor vehicles with one or more driver assistance systems. These driver assistance systems may include, for example, an automatic emergency braking system intended to automatically brake the vehicle if an obstacle is detected in the vehicle's path, for example, a pedestrian crossing. Another type of driver assistance system is, for example, a cruise adaptor or cruise control intended to regulate the speed of the vehicle and adapt it to the speed of a vehicle in front. Another example of a driver assistance system is an automatic parking system which is intended to assist the driver in parking the vehicle by taking control of the steering wheel, acceleration and / or braking during parking maneuvers.These different systems require the presence on the vehicle of one or more sensors positioned at the front or rear of the vehicle, for example radars, ultrasonic sensors or cameras which are intended to detect a position and / or a relative speed of the vehicle in relation to its environment.

[0003] It is also known to measure the absolute speed of a vehicle in a conventional way, based on an average of the number of revolutions made by each of the vehicle's wheels per minute and to deduce from this an estimate of the position of the vehicle relative to its starting position, which is called odometry. This speed is generally displayed on the vehicle's dashboard, preferably in a slightly modified form, for example by adding a percentage and / or a constant in order to display an overestimated speed to compensate for possible inaccuracies in the speed measurement. These measurement inaccuracies may be due to an imperfect knowledge of the radius of the vehicle's wheel. Indeed, this radius can be influenced by the mass of the vehicle, the tire pressure, the tire wear and / or by the engine or braking torque applied to the wheel.Even if these inaccuracies in measuring speed and / or estimated position are generally limited to only a few percent, these inaccuracies can lead to a malfunction of driver assistance systems, in particular a (semi-)automatic parking system.

[0004] The present invention therefore aims to respond at least partially to one or more disadvantages mentioned above. In particular, the objective of the invention is to provide a method for correcting the speed measurement of a vehicle, in particular for a driving assistance system, which makes it possible to improve the accuracy of this driving assistance system, in particular of a (semi-)automatic parking system. Summary of the invention

[0005] To this end, a first aspect of the present invention relates to a computer-assisted method for correcting a speed measurement of a vehicle, in particular for a driving assistance system, the method being characterized by the elements cited in claim 1. In particular, the method or process comprises a first step A of receiving data representing a relative speed of the vehicle with respect to a fixed target obtained by a radar sensor of the vehicle. This radar sensor is configured to measure a relative speed of the vehicle with respect to a fixed target by Doppler effect. The fixed target may for example be a tree, a house, or any other fixed object along the trajectory of the vehicle.

[0006] Then, the computer-implemented method comprises step B of receiving data representing an azimuth of said fixed target relative to the radar sensor of the vehicle. The azimuth of said fixed target may be defined as the angle in the horizontal plane between the direction of said target and a reference direction which may be the direction in which the vehicle is moving and / or a central direction of the radar sensor.

[0007] The computer-assisted method then comprises step C of correcting the relative speed of the vehicle by said azimuth in order to obtain a radar speed of the vehicle. This step makes it possible to obtain a measurement of the speed of the vehicle without contact with the ground which is independent of a speed linked to the length of the wheel development which is for example indicated on a dashboard of the vehicle.

[0008] The method further comprises step D of receiving a vehicle speed obtained by a vehicle speed sensor. This vehicle speed sensor is configured to provide a vehicle speed linked to the length of the speed of one or more wheels of the vehicle. This sensor may for example be placed at the gearbox output or be connected to the wheels. This speed is generally displayed on the vehicle dashboard.

[0009] The method then comprises step E of determining a correction coefficient which is proportional to the ratio between the vehicle's developed speed and the vehicle's radar speed. In an innovative manner, the method finally comprises step F of correcting the vehicle's developed speed by said correction coefficient. This step makes it possible to obtain an improvement in the accuracy of the vehicle speed measurement.

[0010] Unlike the prior art, this computer-implemented method makes it possible, for example in a driver assistance system, to obtain a vehicle speed and / or position accuracy of the order of a few centimeters instead of the previous several tens of centimeters. This improvement in accuracy by a factor of 10 may prove particularly significant, for example, in a (semi-)automatic parking system, where this improvement can make the difference between aborted or successful parking.

[0011] Advantageously, steps A to D can be repeated during a sequence of instants t, preferably by a given time step, for example every 40 milliseconds, or by another time step. Step E of determining a correction coefficient can then take into account all of the data collected during this sequence of instants t. This repetition of steps A to D can stabilize the correction coefficient.

[0012] Advantageously, step E of determining a correction coefficient may comprise the application of a time filter to said sequence of instants t. This time filter may for example be a first-order or higher-order low-pass filter. Alternatively, this filter may also be a time-weighted average. The application of a time filter may contribute to stabilizing the correction coefficient.

[0013] Advantageously, the relative speed of the vehicle at time t can be filtered by a low-pass filter as a function of a value of the relative speed at a time preceding time t of the sequence of times t. In this way, an influence of measurement errors or inaccuracies, for example due to poor capture by the radar of the reflected waves, or due to another specific cause, can be limited.

[0014] Advantageously, the method may further comprise a step of receiving data representing a change in direction of movement of the vehicle. This data may for example come from a yaw sensor, a steering wheel angle sensor of the vehicle, and / or a speed sensor of the four wheels of the vehicle. This data may allow the determination of periods when the vehicle is moving substantially in a straight line.

[0015] Advantageously, the application of a time filter may be limited to times when the change in direction of movement of the vehicle is less than a predetermined threshold. In other words, in determining a correction coefficient, it has been found advisable to consider only data obtained during one or more periods of substantially rectilinear movement of the vehicle. A yaw angle of less than plus or minus 2 degrees may provide an example of a predetermined threshold below which a movement of the vehicle may be considered as being substantially rectilinear. Other thresholds, or a threshold based on one or more other parameters, are also possible. This limitation of the application of a time filter can simplify the calculation of this correction coefficient and therefore the IT infrastructure necessary to implement this method.

[0016] Advantageously, step C of correcting the relative speed of the vehicle by said azimuth may also comprise a correction of a difference between an axis of the radar sensor and a direction of movement of the vehicle. An axis of the radar sensor, i.e. the central axis of the radar beam, is preferably positioned in parallel with a straight-line direction of movement of the vehicle. If the central axis of the radar sensor deviates slightly from this preferred position, the method may apply a correction that corrects this deviation, thereby improving the accuracy of the radar speed of the vehicle.

[0017] Advantageously, the data representing the relative speed of the vehicle with respect to a fixed target may be data representing a relative speed of approach of the vehicle with respect to said fixed target. In other words, the data captured by the radar sensor of the vehicle preferably comes from a radar sensor placed at the front of the vehicle if the vehicle is moving forward. Alternatively, data from a radar sensor placed at the rear of the vehicle may also be used, for example when the vehicle is in reverse. When the vehicle is moving forward, the data from a sensor placed at the rear of a vehicle may also be data representing a relative speed of departure of the vehicle with respect to said fixed target.

[0018] A second aspect of the invention relates to a data processing device comprising the means for implementing the method described above. This device can provide one or more of the advantages cited above.

[0019] A third aspect of the invention relates to a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to implement the method characterized by the elements cited in claims 1 to 8. This computer program product can provide one or more of the advantages cited above.

[0020] A fourth aspect of the invention relates to a computer-readable medium, on which is recorded the computer program product characterized by the elements cited in claim 11.

[0021] A fifth aspect of the invention relates to a motor vehicle characterized by the elements cited in claim 12 - 13. This motor vehicle can provide one or more advantages cited above. Brief description of the drawings

[0022] A preferred embodiment of the invention will be described with reference to the accompanying drawings in which - [Fig.l] represents a schematic view of a preferred embodiment of a motor vehicle according to one aspect of the invention; - [Fig.2] represents a diagram of a preferred embodiment of a computer-implemented method according to one aspect of the invention; - [Fig.3] represents a computer system adapted to the execution of various steps of the method of correcting a measurement of the speed of a vehicle, according to one aspect of the invention. Detailed description of the invention

[0023] [Fig.l] represents a schematic view of a preferred embodiment of a motor vehicle 1 according to one aspect of the invention. This motor vehicle 1 comprises a radar sensor 2 which is preferably positioned at the front of the vehicle 1. This radar sensor 2 is adapted to determine a relative speed of the vehicle with respect to a fixed target 3, preferably with an accuracy of up to, for example, 0.05 m / s. This fixed target 3 may for example be a house along the path of the vehicle 1 or any other fixed object, such as, for example, a tree, a parked vehicle, etc. This fixed target may preferably be located within a radius between + / - 0.2 m and + / - 200 m of the radar sensor 2. The motor vehicle 1 further comprises a speed measuring system 4 having at least one speed sensor adapted to determine a speed of the vehicle by a development of at least one wheel 5 of the vehicle.This speed measurement system 4 may include one or more sensors linked to the wheels 5 of the vehicle 1 and / or to the output of the gearbox. The speed measurement of the motor vehicle 1 by this system 4 is generally displayed on the dashboard of said motor vehicle 1. The motor vehicle 1 also comprises a data processing device 6 configured to implement the method for correcting a speed measurement of a vehicle, in particular in a driver assistance system, the method being as described with reference to [Fig.2]. An example of such a data processing device is shown in [Fig.3] and described with reference thereto. The motor vehicle 1 moves in a direction indicated by the arrow 7, preferably forward and in a substantially straight line. The central direction 8 of a wave beam emitted by the radar sensor 2 may make an angle 9 with the direction of movement 7 of the motor vehicle 1.The radar sensor 2 is configured to receive the reflection of this wave beam by the fixed target 3, and to deduce therefrom the azimuth 10 of this fixed target 3, the azimuth 10 being the angle in the horizontal plane between the direction 11 of said fixed target 3 and a reference direction which is the central direction of the wave beam. The azimuth 10 of this fixed target is. preferably within a margin of + / - -50° to + / - +50°.

[0024] [Fig. 2] represents a diagram of a preferred embodiment of a computer-implemented method according to one aspect of the invention. Step 100 represents receiving data representing a relative speed of the vehicle 1 with respect to a fixed target 3 obtained by a radar sensor 2 of the motor vehicle. Step 110 represents receiving data representing an azimuth 10 of said fixed target 3 with respect to the radar sensor 2 of the motor vehicle 1. In step 120, a radar speed is calculated, which is a correction of the relative speed of the vehicle 1 by said azimuth 10. If the central axis 8 of the radar sensor 2 deviates slightly from the direction of movement 7 of the vehicle 1, this deviation 9 is generally known and can be taken into account in calculating the radar speed of the motor vehicle 1. The radar speed can then be obtained by

[0025] V radar = relative speed -cos(angle 9 + angle 10) •

[0026] These steps 100, 110 and 120 may be repeated. In other words, the relative speed measurements by the radar sensor 2 and by the speed measuring system 4 by the wheel evolute may be repeated for a series of times t, for example by a predetermined time step, such as every 40 milliseconds or other for for example about ten minutes or for another period of time. This data will then comprise a series of n relative speed measurements and n speed measurements by evolute at n different times t. In this case, in step 120, the radar speed may be based on the relative speed of the vehicle at time t filtered by a low-pass filter as a function of a value of the relative speed at a time preceding time t of the series of times t:

[0028] with a being a weighting factor.

[0029] Then, in step 140, a correction coefficient is determined. This coefficient C is proportional to the ratio between the vehicle's developed speed and the vehicle's radar speed:

[0031] The determination of this correction coefficient C may comprise the application of a time filter on said sequence of instants t to obtain a filtered correction coefficient Cfn tri s. This time filter may for example be a first-order or higher-order low-pass filter. Alternatively, this filter may also be a time-weighted average. The application of a time filter may advantageously be limited to times when the change in direction of movement of the vehicle is less than a predetermined threshold so that only the data captured during a substantially rectilinear movement of the vehicle 1 are taken into account. This change of direction can for example be deduced from data coming from a yaw sensor with which the motor vehicle 1 can be equipped. The method finally comprises step 150 of correcting the vehicle's developed speed by said correction coefficient:

[0032] TZ > TZ > C filtered 'corrected' developed' JQQ

[0033] This corrected developed speed V corrected P cul a ^ ors be used in step 160 in a driver assistance system, for example in a (semi-)automatic parking system, in which an improvement in the accuracy of the odometry based on this developed speed can make the difference between a successful or aborted parking maneuver.

[0034] [Fig. 3] shows a suitable computer system 500 comprising circuitry for performing the steps of embodiments of the method for correcting a vehicle speed measurement, particularly in a driver assistance system, according to one aspect of the invention. The computer system 500 may generally be in the form of a suitable general-purpose computer and include a bus 510, a processor 502, a local memory 504, one or more optional input interfaces 514, one or more optional output interfaces 516, a communication interface 512, a storage element interface 506, and one or more storage elements 508. The bus 510 may include one or more conductors for communication between components of the computer system 500. The processor 502 may include any type of conventional processor or microprocessor that interprets and executes programming instructions.The local memory 504 may include random access memory (RAM) or another type of dynamic storage device that stores information and instructions to be executed by the processor 502 and / or a read only memory (ROM) or another type of static storage device that stores information and static instructions to be used by the processor 502. The input interface 514 may include one or more conventional mechanisms for an operator or user to input information into the computer system 500, such as a keyboard 520, a mouse 530, a pen, voice and / or biometric recognition mechanisms, a camera, etc. The output interface 516 may include one or more conventional mechanisms that transmit information to the operator or user, such as a display 540, etc.The communication interface 512 may comprise any transceiver type mechanism, such as, for example, one or more Ethernet interfaces, which allows the computer system 500 to communicate with other devices and / or systems, for example with other computer devices 581, 582, 583. The communication interface 512 of the computer system 500 may be connected to. another computer system by means of a local area network (LAN) or a wide area network (WAN), such as, for example, the Internet. The storage element interface 506 may comprise a storage interface such as, for example, a Serial Advanced Technology Attachment (SATA) interface or a Small Computer System Interface (SCSI) interface for connecting the bus 510 to one or more storage elements 508, such as one or more local disks, for example, SATA disk drives, and controlling the reading and writing of data to and / or from these storage elements 508. Although the storage element(s) 508 above are described as a local disk, in general, any other suitable computer-readable medium, such as a removable magnetic disk, an optical storage medium such as a CD or DVD, a disk-ROM, solid-state drives, flash memory cards, ... could be used.

[0035] As used herein, the term "circuit" may refer to one or more or all of the following:

[0036] (a) hardware-only circuit implementations such as implementations in analog and / or digital-only circuits and

[0037] (b) combinations of hardware and software circuits, such as (as applicable):

[0038] (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and

[0039] (ii) any portion of hardware processor(s) with software (including digital signal processor(s), software and memory(s) that work together to enable a device, such as a mobile phone or a server, to perform various functions) and

[0040] (c) hardware circuit(s) and / or processor(s), such as a microprocessor or part of a microprocessor, that requires software (e.g., firmware) to operate, but the software may not be present when it is not necessary for the operation of the device.

[0041] This definition of circuits applies to all uses of this term in this application, including in the claims. By way of further example, as used in this application, the term "circuit" also covers an implementation of a single hardware circuit or processor (or multiple processors) or part of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term "circuit" also covers, for example and if applicable to the particular claimed element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, cellular network device or other computing or networking device.

[0042] Although the present invention has been illustrated with reference to embodiments specific, it will be understood by those skilled in the art that the invention is not limited to the details of the illustrative embodiments, and that the present invention may be embodied with numerous modifications without departing from the scope of the invention. The embodiments are to be considered illustrative and not restrictively, the scope of the invention being defined by the claims which follow rather than by the foregoing description. Any modification which falls within the meaning or equivalence of the claims is intended to be understood. That is, it is intended to cover all modifications, variations or equivalences which fall within the scope of the basic principles underlying and the essential features of which are claimed in this patent application.The reader of this patent application will understand that the words “comprising” or “comprises” do not exclude any other element or step, and that the words “a” or “an” do not exclude a plurality. The reference signs in the claims cannot be considered as limiting the claim concerned. The terms “first”, “second”, “third”, “a”, “b”, “c”, etcetera are introduced to distinguish different elements or steps and do not necessarily describe a sequential or chronological order. Similarly, the terms “upper”, “lower”, “above”, “below”, etcetera are introduced for descriptive purposes and not necessarily to designate relative positions. It will be understood that these terms are interchangeable under appropriate conditions and that embodiments of the invention are capable of being operable according to the present invention in other sequences or in orientations which differ from those described or illustrated above.

Claims

Claims

1. A computer-implemented method for correcting a vehicle speed measurement, particularly in a driver assistance system, the method comprising • A) receiving data representing a relative speed of the vehicle with respect to a fixed target obtained by a radar sensor of the vehicle; • B) receiving data representing an azimuth of said fixed target relative to the vehicle's radar sensor; • C) correcting the relative speed of the vehicle by said azimuth in order to obtain a radar speed of the vehicle; • D) receiving a vehicle speed obtained by a vehicle speed sensor; • E) the determination of a correction coefficient which is proportional to the ratio between the developed speed of the vehicle and the radar speed of the vehicle; • F) the correction of the vehicle's developed speed by said correction coefficient.

2. Method according to claim 1, in which steps A to D are repeated during a sequence of times t.

3. Method according to claim 2, in which step E of determining a correction coefficient comprises applying a temporal filter to said sequence of instants t.

4. A method according to any one of the preceding claims 2 - 3, wherein the relative speed of the vehicle at time t is filtered by a low-pass filter as a function of a value of the relative speed at a time preceding time t of the sequence of times t.

5. A method according to any preceding claim, further comprising a step of receiving data representing a change in direction of movement of the vehicle.

6. Method according to at least claims 3 and 5, wherein the application of a temporal filter is limited to the instants when the change in direction of movement of the vehicle is less than a predetermined threshold.

7. A method according to any preceding claim, in wherein step C of correcting the relative speed of the vehicle by said azimuth also comprises correcting a difference between an axis of the radar sensor and a direction of movement of the vehicle.

8. A method according to any preceding claim, wherein the data representing the relative speed of the vehicle relative to a fixed target is data representing a relative speed of approach of the vehicle relative to said fixed target.

9. Data processing device comprising the means for implementing the method according to any one of the preceding claims.

10. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to implement the method according to any one of the preceding claims 1 to 8.

11. Computer-readable medium, on which the computer program product according to claim 10 is recorded.

12. Motor vehicle comprising • a radar sensor adapted to determine a relative speed of the vehicle with respect to a fixed target; • a speed measuring system having at least one speed sensor adapted to determine a speed of the vehicle by a development of at least one wheel of the vehicle; • a data processing device configured to implement the method according to any one of the preceding claims 1 to 8.

13. A motor vehicle according to claim 12, wherein the radar sensor is positioned at the front of the vehicle.

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