Method for correcting vehicle speed measurements

Abstract

Method for correcting a vehicle speed measurement. A computer-implemented method for correcting a vehicle speed measurement, particularly in a driver assistance system. The method comprises receiving data representing the relative speed of the vehicle with respect to a fixed target obtained by a radar sensor on the vehicle; receiving data representing the azimuth of said fixed target with respect to the vehicle's radar sensor; correcting the relative speed of the vehicle by said azimuth to obtain a radar speed of the vehicle; and receiving a vehicle speed obtained by a speed sensor on the vehicle. Fig. 1

Description

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

[0001] The present invention relates to the field of vehicle speed measurements, in particular in a driver 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 designed to automatically brake the vehicle if an obstacle is detected in the vehicle's path, such as a pedestrian crossing. Another type of driver assistance system is, for example, a speed adapter or cruise control designed to regulate the vehicle's speed and adapt it to the speed of a vehicle in front. Another example of a driver assistance system is an automatic parking system designed to assist the driver in parking the vehicle by taking control of the steering wheel, acceleration, and / or braking during parking maneuvers.These various 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 relative speed of the vehicle with respect to its environment.

[0003] It is also known to measure the absolute speed of a vehicle in a conventional manner, 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 vehicle's position relative to its starting position; this 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 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 vehicle's wheel radius. Indeed, this radius can be influenced by the vehicle's mass, tire pressure, tire wear, and / or the engine or braking torque applied to the wheel.Even though these inaccuracies in speed measurement and / or estimated position are generally limited to only a few percent, these inaccuracies can lead to malfunctions in driver assistance systems, particularly in (semi-)automatic parking systems.

[0004] The present invention therefore aims to address at least partially 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 driver assistance system, which makes it possible to improve the accuracy of this driver assistance system, in particular 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 vehicle speed measurement, particularly for a driver assistance system. The invention thus relates to a computer-implemented method for correcting a vehicle speed measurement, particularly in a driver assistance system, the method comprising: • A) the reception of data representing a relative speed of the vehicle with respect to a fixed target obtained by a radar sensor of the vehicle; • B) the reception of data representing an azimuth of said fixed target with respect to the vehicle's radar sensor; • C) the correction of the relative speed of the vehicle by said azimuth in order to obtain a radar speed of the vehicle; • D) the reception of a vehicle development speed obtained by a vehicle speed sensor; • E) the determination of a correction coefficient which is proportional to the ratio between the vehicle's developed speed and the vehicle's radar speed; • F) the correction of the vehicle's developed speed by said correction coefficient.

[0006] In particular, the method or process includes a first step A of receiving data representing the relative speed of the vehicle with respect to a fixed target obtained by a radar sensor on the vehicle. This radar sensor is configured to measure the relative speed of the vehicle with respect to a fixed target using the Doppler effect. The fixed target can, for example, be a tree, a house, or any other fixed object along the vehicle's path.

[0007] Then, the computer-implemented method includes step B of receiving data representing an azimuth of said fixed target relative to the vehicle's radar sensor. The azimuth of said fixed target can 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.

[0008] The computer-assisted process then includes step C of correcting the The relative speed of the vehicle is determined by the azimuth in order to obtain a radar speed of the vehicle. This step allows for a measurement of the vehicle's speed without contact with the ground, which is independent of a speed related to the wheel circumference, such as that indicated on a vehicle dashboard.

[0009] The method further includes step D of receiving a vehicle speed obtained by a vehicle speed sensor. This vehicle speed sensor is configured to provide a vehicle speed related to the wheelbase of one or more of the vehicle's wheels. This sensor can, for example, be located at the gearbox output or be connected to the wheels. This speed is generally displayed on the vehicle's instrument panel.

[0010] The method then includes step E of determining a correction coefficient that is proportional to the ratio between the vehicle's undulating speed and the vehicle's radar speed. Innovatively, the method finally includes step F of correcting the vehicle's undulating speed by said correction coefficient. This step improves the accuracy of the vehicle speed measurement.

[0011] Unlike the prior art, this computer-implemented method makes it possible, for example in a driver assistance system, to obtain a speed and / or vehicle position accuracy on the order of a few centimeters instead of the several tens of centimeters previously required. This tenfold improvement in accuracy can prove particularly important, for example in a (semi-)automatic parking system, where this improvement can make the difference between a failed or successful parking maneuver.

[0012] Advantageously, steps A to D can be repeated over a sequence of time intervals t, preferably at a given time step, for example every 40 milliseconds, or at another time step. Step E of determining a correction coefficient can then take into account all the data collected during this sequence of time intervals t. This repetition of steps A to D can stabilize the correction coefficient.

[0013] Advantageously, step E of determining a correction coefficient may include applying a time filter to said sequence of time intervals 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. Applying a time filter can help stabilize the correction coefficient.

[0014] Advantageously, the relative speed of the vehicle at time t can be filtered by a low-pass filter based on a value of the relative speed at a time preceding time t in the sequence of times t. In this way, an influence of errors or measurement inaccuracies, for example due to poor radar capture of reflected waves, or due to another specific cause, can be limited.

[0015] Advantageously, the method may further include a step for receiving data representing a change in the direction of movement of the vehicle. This data may, for example, come from a yaw sensor, a steering wheel angle sensor, and / or a four-wheel speed sensor. This data may allow the determination of periods when the vehicle is moving substantially in a straight line.

[0016] Advantageously, the application of a time filter can be limited to times when the change in the vehicle's direction of motion is less than a predetermined threshold. In other words, when determining a correction factor, it has proven advantageous to consider only data obtained during one or more periods of substantially rectilinear vehicle motion. A yaw angle of less than plus or minus 2 degrees can provide an example of a predetermined threshold below which vehicle motion can be considered substantially rectilinear. Other thresholds, or a threshold based on one or more other parameters, are also conceivable. This limitation on the application of a time filter can simplify the calculation of this correction factor and thus the computing infrastructure required to implement this method.

[0017] Advantageously, step C of the correction of the relative speed of the vehicle by said azimuth may also include a correction for 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 parallel to 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.

[0018] Advantageously, the data representing the relative speed of the vehicle with respect to a fixed target can be data representing the relative speed of the vehicle approaching said fixed target. In other words, the data captured by the vehicle's radar sensor preferably comes from a radar sensor located at the front of the vehicle if the vehicle is moving forward. Alternatively, data from a radar sensor located at the rear of the vehicle can also be used, for example, when the vehicle is reversing. When the vehicle is moving forward, the data from a sensor located at the rear of the vehicle can also be data representing the relative speed of the vehicle moving away from said fixed target.

[0019] A second aspect of the invention relates to a data processing device including the means to implement the method described above. This device can provide one or more of the advantages mentioned above.

[0020] 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 according to the invention. This computer program product may provide one or more of the advantages mentioned above.

[0021] A fourth aspect of the invention relates to a computer-readable medium on which the computer program product according to the invention is recorded.

[0022] A fifth aspect of the invention relates to a motor vehicle comprising: • a radar sensor adapted to determine a relative speed of the vehicle with respect to a fixed target; • a speed measurement system having at least one suitable speed sensor to determine a vehicle speed by a development of at least one wheel of the vehicle; • a data processing device configured to implement the method according to the invention.

[0023] The radar sensor of said motor vehicle may be positioned at the front of the vehicle.

[0024] This motor vehicle may provide one or more of the advantages mentioned above. Brief description of the drawings

[0025] A preferred embodiment of the invention will be described with reference to the accompanying drawings in which - Fig. 1 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 speed measurement of a vehicle, according to one aspect of the invention. Detailed description of the invention

[0026] Figure 1 shows a schematic view of a preferred embodiment of a motor vehicle 1 according to one aspect of the invention. This motor vehicle 1 includes a radar sensor 2 which is preferably positioned at the front of the vehicle 1. This radar sensor 2 is adapted to determine the relative speed of the vehicle with respect to a fixed target 3, preferably with an accuracy of, for example, 0.05 m / s. This fixed target 3 can, for example, be a house along the path of the vehicle 1 or any other fixed object, such as a tree, a parked vehicle, etc. This fixed target can preferably be located within a radius between + / - 0.2 m and + / - 200 m from radar sensor 2. The motor vehicle 1 further includes a speed measurement system 4 having at least one speed sensor adapted to determine the vehicle's speed by the circumference of at least one wheel 5 of the vehicle. This speed measurement system 4 may include one or more sensors connected to the wheels 5 of the vehicle 1 and / or to the gearbox output. The speed measurement of the motor vehicle 1 by this system 4 is generally displayed on the instrument panel of said motor vehicle 1. The motor vehicle 1 also includes a data processing device 6 configured to implement the method for correcting a vehicle speed measurement, particularly 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 arrow 7, preferably forwards 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 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 range from + / - -50° to + / - +50°.

[0027] Figure 2 shows a diagram of a preferred embodiment of a computer-implemented method according to one aspect of the invention. Step 100 represents the reception of data representing the relative speed of vehicle 1 with respect to a fixed target 3 obtained by a radar sensor 2 of the motor vehicle. Step 110 represents the reception of 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 vehicle 1 by said azimuth 10. If the central axis 8 of the radar sensor 2 deviates slightly from the direction of motion 7 of vehicle 1, this deviation 9 is generally known and can be taken into account in the calculation of the radar speed of the motor vehicle 1. The radar speed can then be obtained by

[0028] raiiar= relative speed -cos (angle 9 + angle 10).

[0029] These steps 100, 110, and 120 can be repeated. In other words, the relative speed measurements taken by the radar sensor 2 and by the speed measurement system 4 using the wheel's development can be repeated over a sequence of instants t, for example, at a predetermined time step, such as every 40 milliseconds, or for, for example, ten minutes or another period of time. This data will then comprise a sequence of n relative speed measurements and n measurements of speed by developing at n different instants t. In this case, at step 120, the radar speed can 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 an instant preceding time t of the sequence of instants t:

[0030] Vradarfiltered (0;) — (1“ reidarfiltered n-ï) 'V radar^C')

[0031] with a being a weighting factor.

[0032] Next, 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:

[0033] _ æg raddMff titled (. developed

[0034] Determining this correction coefficient C may involve applying a time filter to said sequence of instants t to obtain a filtered correction coefficient C. 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 the instants when the change in the direction of movement of the vehicle is less than a predetermined threshold so that only data captured during substantially rectilinear movement of the vehicle 1 are taken into account. This change in direction may, for example, be deduced from data coming from a yaw sensor with which the motor vehicle 1 may be equipped. The method finally includes step 150 of correcting the vehicle's developed speed by said correction coefficient:

[0035] y , . _ y , . F corrected K developed jqq

[0036] This corrected development speed Vcorrj<^e can then be used in step 160 in a driver assistance system, for example in a (semi-)automatic parking system, in which an improvement in odometry accuracy based on this development speed can make the difference between a successful or aborted parking maneuver.

[0037] Figure 3 shows a suitable computer system 500 comprising circuits for executing the steps of the 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 can generally be in the form of a suitable multipurpose computer and include a bus 510, a processor 502, 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 enabling communication between the 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 read-only memory (ROM) or another type of static storage device that stores static information and instructions to be used by the processor 502. The input interface 514 may include one or more conventional mechanisms enabling an operator or user to input information into the computer system 500, such as a keyboard 520, a mouse 530, a pen, speech 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 screen 540, etc. The communication interface 512 may include 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 can be connected to another computer system via a local area network (LAN) or a wide area network (WAN), such as the internet. The storage element interface 506 can include a storage interface such as, for example, a SATA (Serial Advanced Technology Attachment) interface or a SCSI (Small Computer System Interface) interface to connect the bus 510 to one or more storage elements 508, such as one or more local disks, for example, SATA disk drives, and control the reading and writing of data to and / or from these storage elements 508.Although the 508 storage element(s) 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 ROM disk, solid-state drives, flash memory cards, etc., could be used.

[0038] As used in this application, the term "circuit" may refer to one or more or all of the following:

[0039] (a) purely hardware circuit implementations such as the mentations in purely analog and / or digital circuits and

[0040] (b) combinations of hardware circuits and software, such as (as appropriate):

[0041] (i) a combination of analog and / or digital hardware circuit(s) with a software / firmware and

[0042] ii) any portion of hardware processor(s) with software (including digital signal processor(s)), software and memory that work together to enable a device, such as a mobile phone or a server, to perform various functions) and

[0043] (c) hardware circuit(s) and / or processor(s), such as a microprocessor or a part of a microprocessor, which requires software (e.g., firmware) to function, but the software may not be present when it is not needed for the device to function.

[0044] This definition of circuits applies to all uses of this term in the present application, including in the claims. By way of further example, as used in the present 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 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 a processor integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or networking device.

[0045] Although the present invention has been illustrated with reference to specific embodiments, those skilled in the art will understand that the invention is not limited to the details of the illustrative embodiments, and that the present invention can be carried out with numerous modifications without departing from the scope of the invention. The embodiments are to be considered illustrative and not restrictive, the scope of the invention being defined by the following claims rather than by the preceding description. Any modification that falls within the meaning or equivalence of the claims is intended to be understood. In other words, it is intended to cover all modifications, variations, or equivalences that fall within the scope of the underlying basic principles and whose essential features are claimed in this patent application.The reader of this patent application will understand that the words “comprising” or “includes” do not exclude any other element or step, and that the words “a” or “an” do not exclude a plurality. Reference signs in the claims cannot be considered as limiting the claim in question. The terms “first,” “second,” “third,” “a,” “b,” “c,” etc., 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,” etc., are introduced for descriptive purposes and not necessarily to denote relative positions. It will be understood that these terms are interchangeable under certain conditions. proprieties and that embodiments of the invention are capable of being operated according to the present invention in other sequences or in orientations which differ from those described or illustrated above.

Claims

Demands

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 with respect to the radar sensor of the vehicle; • C) correcting the relative speed of the vehicle by said azimuth to obtain a radar speed of the vehicle; • D) receiving a vehicle speed obtained by a speed sensor of the vehicle; • E) determining a correction coefficient that is proportional to the ratio between the vehicle speed and the vehicle radar speed; • F) correcting the vehicle speed by said correction coefficient.

2. Method according to claim 1, wherein steps A to D are repeated for a sequence of times t.

3. Method according to claim 2, wherein step E of the determination of a correction coefficient includes the application of a time filter on said sequence of instants t.

4. 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. Method according to any one of the preceding claims, further comprising a data reception step representing a change in the direction of movement of the vehicle.

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

7. Method according to any one of the preceding claims, in which step C of the correction of the relative speed of the vehicle by said azimuth also includes a correction of a difference between an axis of the radar sensor and a direction of movement of the vehicle.

8. A method according to any one of the preceding claims, wherein the data representing the relative speed of the vehicle with respect to a fixed target are data representing a relative speed of approach of the vehicle with respect to said fixed target.

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

10. Product computer program 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 measurement 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. Motor vehicle according to claim 12, wherein the radar sensor is positioned at the front of the vehicle.

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