U.S. patent application number 14/418594 was filed with the patent office on 2015-07-23 for method for estimating the weight of a vehicle.
This patent application is currently assigned to RENAULT s.a.s. The applicant listed for this patent is RENAULT s.a.s.. Invention is credited to Francois Desnoyer, Guillaume Martin, Guillermo Pita-Gil.
Application Number | 20150204715 14/418594 |
Document ID | / |
Family ID | 48771484 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150204715 |
Kind Code |
A1 |
Pita-Gil; Guillermo ; et
al. |
July 23, 2015 |
METHOD FOR ESTIMATING THE WEIGHT OF A VEHICLE
Abstract
A method estimating weight of a motor vehicle including front
and rear wheel assemblies using a smart communication device after
loading the vehicle, including: (i) identifying the vehicle in the
smart communication device; (ii) using a camera of the smart
communication device, capturing and processing a photograph of at
least one vehicle wheel after loading to determine displacement of
a corresponding wheel assembly; (iii) using at least one
accelerometer or inclinometer of the smart communication device,
measuring at least one tilt angle of the vehicle after loading to
determine displacement of the opposite wheel assembly and the
corresponding wheel assembly; (iv) using a calculation unit of the
smart communication device, calculating load values on the
corresponding and opposite wheel assemblies based on respective
displacements of the wheel assemblies, to determine a total load
vehicle value; and (v) indicating by the smart communication device
a vehicle load state to the user.
Inventors: |
Pita-Gil; Guillermo; (Paris,
FR) ; Martin; Guillaume; (Versailles, FR) ;
Desnoyer; Francois; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RENAULT s.a.s. |
Boulogne-Billancourt |
|
FR |
|
|
Assignee: |
RENAULT s.a.s
Boulogne-Billancourt
FR
|
Family ID: |
48771484 |
Appl. No.: |
14/418594 |
Filed: |
July 24, 2013 |
PCT Filed: |
July 24, 2013 |
PCT NO: |
PCT/FR2013/051783 |
371 Date: |
January 30, 2015 |
Current U.S.
Class: |
382/104 |
Current CPC
Class: |
G01G 23/3735 20130101;
G01G 19/02 20130101; G01G 23/01 20130101; G01G 19/022 20130101 |
International
Class: |
G01G 19/02 20060101
G01G019/02; G01G 23/37 20060101 G01G023/37; G01G 23/01 20060101
G01G023/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2012 |
FR |
1257425 |
Claims
1-12. (canceled)
13. A method for estimating weight of a motor vehicle including a
front wheel assembly and a rear wheel assembly, using a smart
communication device, after loading of the vehicle, the method
comprising: (i) identifying the vehicle in the smart communication
device; (ii) using a camera of the smart communication device to
capture and process a photograph of at least one wheel of the
vehicle after loading to determine clearance of the wheel assembly
of the photographed wheel as a function of the identified vehicle;
(iii) determining clearance of the wheel assembly opposite the
wheel photographed in (ii), either by measuring an angle of
inclination of the vehicle after loading, using at least one
accelerometer or inclinometer of the smart communication device, or
by capturing and processing a photograph of at least one wheel of
the wheel assembly opposite the wheel assembly of the wheel
photographed in (ii), using the camera of the smart communication
device; (iv) using a calculation unit of the smart communication
device to calculate a load value on the wheel assembly of the
photographed wheel and a load value on the opposite wheel assembly
as a function of respective clearances of the wheel assemblies, to
determine a total load value of the vehicle; (v) using the smart
communication device to inform a user of a load state of the
vehicle.
14. The method for estimating the weight of a vehicle as claimed in
claim 13, wherein the vehicle includes a load space arranged at a
rear of the vehicle, the photographed wheel is a rear wheel of the
vehicle, enabling clearance of the rear wheel assembly to be
determined, and the opposite wheel assembly is the front wheel
assembly.
15. The method for estimating the weight of a vehicle as claimed in
claim 14, wherein a photograph of each rear wheel of the vehicle is
taken and processed, and clearance of the rear wheel assembly is
determined from an average clearance for each rear wheel
photographed.
16. The method for estimating the weight of a vehicle as claimed in
claim 13, wherein (v) informing the user is executed by an
illuminated and/or audible indicator at three levels, a first level
corresponding to information that the vehicle is overloaded
relative to the permitted maximum, a second level corresponding to
information that there is a risk of overloading the vehicle
relative to the permitted maximum, and a third level corresponding
to information that the load is below the permitted maximum.
17. The method for estimating the weight of a vehicle as claimed in
claim 13, wherein (ii) taking a photograph of a wheel is dependent
on vertical positioning of the smart communication device, detected
by an accelerometer.
18. The method for estimating the weight of a vehicle as claimed in
claim 13, wherein (i) identifying the vehicle comprises: (i1)
determining, before loading, a distance between a wheel center and
a center of the wheel housing of the wheel to be photographed in
(ii); (i2) determining the angle of inclination of the vehicle
before loading; (i3) determining a total permissible load of the
identified vehicle.
19. The method for estimating the weight of a vehicle as claimed in
claim 18, wherein (ii) capturing and processing the image
comprises: (ii0) taking a photograph of a wheel of the vehicle;
(ii1) converting the taken photograph of the wheel to a grayscale
image; (ii2) using a first filter of fuzzy Gaussian type to improve
sharpness of the image; (ii3) using a second filter of Sobel type
to obtain contours of the image; (ii4) breaking down the image into
two parts, a first part relating to the wheel and a second part
relating to the wheel housing; (ii5) calculating a center and
radius of the wheel housing by least squares method; (ii6)
calculating values of the minimum and maximum radii of the wheel as
a function of the radius of the wheel housing and of the identified
vehicle; (ii7) using a third filter of Mexican hat wavelet type to
improve concentration of points near the center of the wheel; (ii8)
calculating the center of the wheel on the basis of accumulation of
points in the wheel center, and calculating the distance after
loading between the wheel center and the center of the wheel
housing; (ii9) calculating the clearance of the wheel assembly of
the photographed wheel, using the difference in distance between
the wheel center and the center of the wheel housing after and
before loading.
20. The method for estimating the weight of a vehicle as claimed in
claim 18, wherein (iii) determining the clearance of the opposite
wheel assembly is based on a measurement of the difference in the
angle of inclination before and after loading, the angle of
inclination being chosen as the angle between a terrestrial
reference frame and a vehicle reference frame along the axis of the
vehicle.
21. The method for estimating the weight of a vehicle as claimed in
claim 20, wherein, during (iii) measuring the angle of inclination,
any detection of an acceleration beyond a certain predetermined
threshold is considered to indicate that the smart communication
device has been dropped, and (iii) must be repeated.
22. The method for estimating the weight of a vehicle as claimed in
claim 13, wherein (iv) calculating the load value on the front and
rear wheel assemblies is executed by interpolation in a
load/clearance map.
23. A smart communication device for execution of the method as
claimed in claim 13, the smart communication device comprising: an
application programmed to activate a method for estimating the
weight of a vehicle; a human-machine interface for starting the
application for estimating the weight of a vehicle; means for
identifying the vehicle; a camera for taking a photograph of at
least one wheel of the vehicle; at least one accelerometer and/or
inclinometer for measuring an angle of inclination between the
terrestrial reference frame and the vehicle reference frame; a
calculation unit programmed to execute image processing and
calculation of clearance values and load values, and at least one
graphic and/or audio interface to alert the user to the load state
of the vehicle.
24. An application for a smart communication device as claimed in
claim 23, comprising from a viewpoint of a user of the application:
a) identifying the user's vehicle; b) taking a photograph of at
least one wheel indicated by the application; c) placing the smart
communication device in a docking station of the vehicle and
validation after the placing placement; d) informing the user of
the load state of the vehicle.
Description
[0001] The present invention relates in a general way to a method
for estimating the total weight of a motor vehicle. More
specifically, the invention relates to a method for estimating the
total weight of a vehicle after loading.
[0002] A knowledge of the total weight of a motor vehicle is
necessary for the correct operation of numerous on-board systems in
the vehicle, such as shock absorber systems, underinflation
detection systems, engine control systems (for electric, combustion
or hybrid engines), hill starting systems, overload detection
systems, lighting systems, braking and/or energy recovery systems,
and the like.
[0003] At present, there are two groups of methods for evaluating
the weight of a motor vehicle. A first group comprises direct
systems, which use supplementary sensors such as ground to body
clearance sensors, ground to axle clearance sensors, sensor
bearings, and the like. A second group comprises indirect systems,
which use only the sensors present in a vehicle to estimate the
total weight of the vehicle. This family includes methods which,
for example, estimate the weight using techniques of the recursive
least squares type.
[0004] For example, FR 2 857 090 describes a method for estimating
the total weight of a vehicle in which the weight of the vehicle is
estimated by a recursive least squares algorithm. This method bases
all the estimations on a single instant at a time. Problems arise
with this estimation because of the number, complexity and
dispersion of the various forces and vehicle parameters which are
present in the vehicle dynamics equation and which must be
estimated or have values assigned to them.
[0005] A similar approach is considered in U.S. Pat. No. 6,249,735.
This document describes a method which uses measurements of the
engine torque and the acceleration of the vehicle. The acceleration
is calculated by discrete approximation of the derivative of the
speed, and by filtering, which gives rise to problems of noise and
has an effect on the accuracy and robustness of the estimation.
[0006] Furthermore, although methods which do not use the vehicle
acceleration are less subject to noise, they do not take into
account the gradient of the surface on which the vehicle is
operated.
[0007] There is a further aspect of the problem, in that very high
costs are incurred for both the direct solutions (for additional
parts) and the indirect solutions (for adjustment and validation
tests). Moreover, these systems are difficult to adjust and have
low robustness.
[0008] One object of the present invention is to respond to the
aforementioned drawbacks of the prior art documents, in the first
place by proposing a method for estimating the weight of a motor
vehicle after loading which will enable the user to detect
overloading of his vehicle in a simple way without the need for
supplementary sensors.
[0009] For this purpose, a first aspect of the invention relates to
a method for estimating the weight of a motor vehicle comprising a
front wheel assembly and a rear wheel assembly, using a smart
communication device, after the loading of the vehicle, the method
comprising the steps of: (i) identifying the vehicle in the smart
communication device; (ii) using a camera of the smart
communication device to capture and process a photograph of at
least one wheel of the vehicle after loading to determine the
clearance of the wheel assembly of the photographed wheel as a
function of the identified vehicle; (iii) determining the clearance
of the wheel assembly opposite the wheel photographed in step (ii),
either by measuring the angle of inclination of the vehicle after
loading, using at least one accelerometer or inclinometer of the
smart communication device, or by capturing and processing a
photograph of at least one wheel of the wheel assembly opposite the
wheel assembly of the wheel photographed in step (ii), using the
camera of the smart communication device; (iv) using a calculation
unit of the smart communication device to calculate the load value
on the wheel assembly of the photographed wheel and the load value
on the opposite wheel assembly as a function of the respective
clearances of these wheel assemblies, so as to determine the total
load value of the vehicle; (v) using the smart communication device
to inform the user of the load state of the vehicle.
[0010] This method for estimating the load of the vehicle can be
very rapidly and easily executed by a user in possession of a smart
communication device such as an intelligent mobile phone or
computerized phone, also known as a "smartphone" in the English
terminology, equipped with a suitable application. This solution is
highly competitive in terms of cost, since it does not require any
additional parts in the vehicle, and is reliable because it does
not depend on any element in the vehicle. Thus it allows any user
to check the load state of his vehicle after loading, and to
prevent any risk of overload which may, notably, lead to excess
consumption, degraded roadholding, or infringement of the safety
regulations for the type of vehicle concerned (notably in terms of
the gross vehicle weight rating or GVWR).
[0011] Advantageously, the vehicle comprises a loading space
arranged at the rear of the vehicle, and the photographed wheel is
a rear wheel of the vehicle, enabling the clearance of the rear
wheel assembly to be determined, the opposite wheel assembly being
the front wheel assembly. The photographing of the rear wheel
increases the reliability of the measurement of the clearance of
the rear wheel assembly for vehicles having a rear load space,
since the load is essentially applied in this area. Advantageously,
a photograph of each rear wheel of the vehicle is taken and
processed, and the clearance of the rear wheel assembly is
determined from the average clearance for each rear wheel
photographed. This increases the reliability of the measurement of
the clearance of the rear wheel assembly, particularly if the load
is not distributed along the X axis of the vehicle.
[0012] According to an advantageous variant, step (v) of informing
the user is executed by means of an illuminated and/or audible
indicator at three levels, the first level corresponding to the
information that the vehicle is overloaded relative to the
permitted maximum, the second level corresponding to the
information that there is a risk of overloading the vehicle
relative to the permitted maximum, and the third level
corresponding to the information that the load is below the
permitted maximum. For example, a red display will indicate
overloading of the vehicle, an orange display will indicate a risk
of overload, and a green display will indicate a permitted loading
level.
[0013] According to another advantageous variant, step (ii) of
taking a photograph of a wheel is dependent on the vertical
positioning of the smart communication device, detected by means of
an accelerometer. The detection of the vertical positioning of the
smart communication device during the taking of a wheel photograph
simplifies the processing, by avoiding problems of parallax in the
image and increasing the reliability in terms of the value of the
clearance of the wheel assembly of the photographed wheel.
[0014] According to another advantageous variant, step (i) of
identifying the vehicle comprises the steps of: (i.1) determining,
before loading, the distance between the wheel center and the
center of the wheel housing of the wheel to be photographed in step
(ii); (i.2) determining the angle of inclination of the vehicle
before loading; (i.3) determining the total permissible load of the
identified vehicle. This initial step of identifying the vehicle
increases the reliability of the weight estimation, while
simplifying the calculations in the subsequent steps. Step (i.3) is
also essential in cases in which the vehicle to be weighed is not
parked on a flat surface in the terrestrial reference frame.
[0015] According to another advantageous variant, step (ii) of
image processing comprises the following substeps of: (ii.0) taking
a photograph of a wheel of the vehicle; (ii.1) converting the
captured photograph of the wheel to a grayscale image; (ii.2) using
a first filter of the fuzzy Gaussian type to improve the sharpness
of the image; (ii.3) using a second filter of the Sobel type to
obtain the contours of the image; (ii.4) breaking down the image
into two parts, namely a first part relating to the wheel and a
second part relating to the wheel housing; (ii.5) calculating the
center and the radius of the wheel housing by the least squares
method; (ii.6) calculating the values of the minimum and maximum
radii of the wheel as a function of the radius of the wheel housing
and of the identified vehicle; (ii.7) using a third filter of the
Mexican hat wavelet type to improve the concentration of points
near the center of the wheel; (ii.8) calculating the center of the
wheel on the basis of the accumulation of points in the wheel
center, and calculating the distance after loading between the
wheel center and the center of the wheel housing; (ii.9)
calculating the clearance of the wheel assembly of the photographed
wheel, using the difference in distance between the wheel center
and the center of the wheel housing after and before loading.
[0016] This image processing method is highly reliable if the
vehicle is correctly identified at the outset. Notably, it can be
used for the precise detection of the radius of the wheel housing
and the minimum and maximum wheel radii, as well as the center of
the wheel and the center of the wheel housing.
[0017] According to another advantageous variant, step (iii) of
determining the clearance of the opposite wheel assembly is based
on a measurement of the difference in the angle of inclination
before and after loading, the angle of inclination being chosen as
the angle between a terrestrial reference frame and a vehicle
reference frame along the X axis of the vehicle. In particular,
this step of determining the clearance by measuring the angle of
inclination is particularly simple and reliable for the wheel
assembly opposite the load space. Advantageously, during step (iii)
of measuring the angle of inclination, any detection of an
acceleration beyond a certain predetermined threshold is considered
to indicate that the smart communication device has been dropped,
and step (iii) must be repeated. This variant can be used to
prevent an unrealistic measurement of the angle of inclination
caused by the dropping of the device.
[0018] According to another advantageous variant, step (iv) of
calculating the load value on the front and rear wheel assemblies
is executed by interpolation in a load/clearance map. This map is
plotted for each vehicle model and must be correctly identified at
the start of the application. It enables the load value on the
wheel assembly concerned to be determined in a direct and simple
manner, without the need for calculation.
[0019] A second aspect of the invention relates to a smart
communication device for the execution of the method according to
the first aspect of the invention, characterized in that the smart
communication device comprises an application programmed to
activate a method for estimating the weight of a vehicle, means for
identifying the vehicle, a camera for taking a photograph of at
least one wheel of the vehicle, at least one accelerometer and/or
inclinometer for measuring an angle of inclination between the
terrestrial reference frame and the vehicle reference frame, a
calculation unit programmed to execute steps of image processing
and calculation of clearance values and load values, and at least
one graphic and/or audio interface to alert the user to the load
state of his vehicle.
[0020] A third aspect of the invention relates to an application
for a smart communication device according to the second aspect of
the invention, for the execution of the method according to the
first aspect, characterized in that it comprises the following
steps from the viewpoint of the user of the application: a)
identifying the user's vehicle; b) taking a photograph of at least
one wheel indicated by the application; c) placing the smart
communication device in a docking station of the vehicle and
validation after this placement; d) informing the user of the load
state of the vehicle.
[0021] Other features and advantages of the present invention will
be more evident from a reading of the following detailed
description of an embodiment of the invention, provided by way of
non-limiting example and illustrated in the appended drawings, in
which:
[0022] FIG. 1 is a schematic representation of a smart
communication device according to an embodiment of the
invention;
[0023] FIG. 2 shows a diagram of the method for estimating the
weight of a vehicle according to an embodiment of the
invention;
[0024] FIG. 3 is a schematic representation of the clearance of the
front and rear wheel assemblies after the loading of the
vehicle;
[0025] FIG. 4 shows a detailed diagram of the step of image
processing according to an embodiment of the invention;
[0026] FIGS. 4A-4D show some substeps of the image processing
performed;
[0027] FIG. 5A shows an example of the load/clearance relationship
for a wheel suspension for a predetermined vehicle model;
[0028] FIG. 5B shows the experimental results of the determination
of the total load of a vehicle;
[0029] FIG. 6 shows an example of the definition of the axes for a
smart communication device.
[0030] FIG. 1 is a schematic representation of a smart
communication device according to an embodiment of the invention.
The smart communication device 10 comprises a programmable central
unit 12. An application 14 for estimating the weight of a vehicle
is programmed into this central unit 12. A human-machine interface
16 is used to start the application 14 for estimating the weight of
a vehicle. Means for identifying the vehicle are provided, for
example, in the form of the selection, via the human-machine
interface 16, of a vehicle model from a list of models recorded
previously in a non-volatile memory 18. A camera 20 is also
provided, for taking a photograph of at least one wheel of the
vehicle, together with at least one accelerometer 22 and/or an
inclinometer 24 for measuring the angle of inclination of the smart
communication device, the central unit 12 being programmed to
execute steps of image processing and calculation of clearance
values and load values. At least one graphic and/or audio interface
26 is also provided, to alert the user to the load state of his
vehicle. This graphic and/or audio interface 26 may be partially or
completely connected to the human-machine interface 16. For
information, the axes x, y and z as generally defined for a
communication device of this kind are shown in FIG. 6.
[0031] FIG. 2 shows a diagram of the method for estimating the
weight of a vehicle according to an embodiment of the invention. A
preliminary step is that of starting the application for estimating
the load of a vehicle.
[0032] When the application has been started, the user must
identify his vehicle in a first step (i) so that the weight of the
vehicle can be estimated.
[0033] For this purpose, he may, for example, be invited via the
human-machine interface to select his vehicle model from a
previously recorded list. The previously recorded vehicle model
must include at least the information relating to the distance
between the wheel center and the center of the wheel housing of the
wheel to be photographed (step i.1), together with the total
permissible load for this model of vehicle (step i.3).
Alternatively, the distance between the wheel center and the center
of the wheel housing of the wheel to be photographed (step i.1) may
be determined manually by taking a photograph of a wheel of the
vehicle before loading, the subsequent processing of which will be
similar to that explained in detail in FIG. 4 in respect of steps
(ii.1) to (ii.8). Additionally, the identification of the vehicle
may include the determination of an angle of inclination of the
vehicle before its loading (step i.2). This measurement of
inclination will preferably be made along the X axis of the
vehicle, that is to say along the longitudinal axis of the vehicle,
between the terrestrial reference frame (based on gravity) and the
vehicle reference frame (based on the vehicle). To this end, the
smart communication device will preferably be positioned in a
location in the vehicle provided for this purpose, for example in
the form of a docking station having a known orientation.
[0034] In a second step (ii), the user is invited to take a
photograph of at least one wheel of his vehicle after loading.
Preferably, the user is invited to take a photograph of a wheel
located at the load space end. Thus, for most vehicles, the load
space is located at the rear of the vehicle, and the user will
therefore be invited to take a photograph of a rear wheel of his
vehicle. This photograph is then processed by an image processing
method described in detail with reference to FIG. 4. On the basis
of the image processing that is executed, the application
determines the clearance of the wheel assembly of the photographed
wheel, which, as a general rule, will be the clearance of the rear
wheel assembly.
[0035] In a third step (iii), the user preferably positions the
smart communication device in his docking station to make at least
one measurement of the inclination of the vehicle along the X axis
between the terrestrial reference frame and the vehicle reference
frame after the loading of the vehicle. For this purpose, provision
is made to position the communication device correctly in its
location, to ensure that the measured inclination is indeed the
inclination along the X axis of the vehicle. If a similar
measurement has been made before loading, during the identification
of the vehicle, it will be possible to calculate the precise
difference in inclination before and after loading, so as to
compensate for any gradient in the ground on which the vehicle is
parked while being loaded. On the basis of the inclination measured
after loading, and advantageously both before and after loading,
the application determines the clearance of the wheel assembly
opposite that of the photographed wheel, for example the front
wheel assembly.
[0036] In a fourth step (iv), the application calculates the load
value on the front and rear wheel assemblies of the vehicle, from
which it deduces the total load value of the vehicle by adding the
two loads together. This total load value can then be displayed by
the communication device.
[0037] In a fifth step (v), the application operates the graphic
and/or audio interface of the communication device to alert the
user to the load state of his vehicle. Thus, for example, the
communication device displays a red alert if the weight is more
than 0.95*maxweight, where "maxweight" is a calibration constant
corresponding to the maximum permitted load. The device displays a
yellow alert if the weight is in the range from 0.8*maxweight to
0.95*maxweight. The device displays a green alert if the weight is
below 0.8*maxweight. The levels 0.8 and 0.95 are two thresholds
which are also calibration parameters. Clearly, they may be
modified to meet requirements. The number of alert levels may be
variable and may depend on the type of application. It is also
possible to display the probability of overload, or the load and
the confidence level at 95% or 99%, for example.
[0038] FIG. 3 is a schematic representation of the clearance of the
front wheel assembly .DELTA..sub.AV and rear wheel assembly
.DELTA..sub.ARR after the loading of the vehicle. In the example
shown in the figure, the vehicle is parked on horizontal ground.
The vehicle is represented schematically by two points representing
the front wheel center CR.sub.AV and rear wheel center CR.sub.ARR
of the vehicle, and by the front wheel housing center CP.sub.AV and
the rear wheel housing center CP.sub.ARR of the vehicle, these
points being used to determine the clearances of the wheel
assemblies of the vehicle. However, it will be evident that points
on the vehicle other than the centers of the wheel housings can be
considered, where these other points are subject to being pushed
inward together with the wheel suspension when the vehicle is
loaded. The distance between the front wheel center CR.sub.AV and
rear wheel center CR.sub.ARR of the vehicle is the wheelbase L of
the vehicle.
[0039] Additionally, the term "clearance" will generally be taken
to mean the distance corresponding to the vertical oscillation of
an axle with respect to the chassis, due to the flexibility of the
suspension during loading. In the remainder of this example, the
clearance will signify the vertical oscillation of the center of
the wheel housing with respect to the corresponding wheel
center.
[0040] Before loading, the identification makes it possible,
notably, to determine the distance at the rear before loading
d.sub.avc.sup.arr between the wheel center CR.sub.ARR and the wheel
housing center CP.sub.ARR, particularly in the case where the load
space is located at the rear of the vehicle, and, if required, the
angle of inclination along the X axis of the vehicle between the
terrestrial reference frame and the vehicle reference frame, if
this angle is not zero. This measurement may be automatically made
and recorded by the smart communication device if the latter
detects a non-zero inclination during the initial identification
step.
[0041] During step (iii), which is detailed below with reference to
FIG. 4, the communication device determines the distance at the
rear after loading d.sub.apc.sup.arr between the wheel center
CR.sub.ARR and the center of the wheel housing CP.sub.ARR which has
been pushed inwards.
[0042] During step (iv), the communication device calculates the
clearance of the wheel assembly opposite the photographed wheel,
that is to say the front wheel assembly in the present example. To
this end, the communication device is preferably placed in the
docking station provided for this purpose in the vehicle. When the
communication device is in the predetermined position, it can make
a measurement of the inclination of the vehicle either
automatically or manually (that is to say, by the user's action).
Thus, for example, during three seconds the communication device
averages the three components measured by its accelerometer. The
values gxiPh, gyiPh and gziPh are obtained. If the communication
device falls down during the three seconds of measurement, at least
one of the acceleration components exceeds 1.5 g, and it is then
considered that the device has moved and the measurement will have
to be repeated. The same procedure can be followed if one of the
angular velocities exceeds the threshold of 0.1 rad/s in absolute
value. Advantageously, the communication device displays a progress
bar during the measurement. During this measurement, it must also
check that the communication device is being held in the correct
direction, which may be indicated by a negative value of the
parameters gyiPh and gziPh.
[0043] When the calculation has finished, the communication device
estimates the angle of inclination after loading .alpha..sub.apc
along the X axis of the vehicle between the terrestrial reference
frame and the vehicle reference frame, by calculating, for
example:
.alpha..sub.apc=0.5(.alpha. cos(|gyiPh|)+.alpha. sin(|gziPh|))
[0044] The communication device then deduces the distance at the
front d.sub.apc.sup.av after loading between the wheel center
CR.sub.AV and the wheel housing center CP.sub.AV which has been
pushed inwards, using the following formula:
d.sub.apc.sup.av=d.sub.apc.sup.arr+L.tan(.alpha..sub.apc)
[0045] If the gradient of the ground is to be taken into account,
the following general formula may be used:
d.sub.apc.sup.av=d.sub.apc.sup.arr-L.tan(.DELTA..alpha.)
where .DELTA..alpha.=.alpha..sub.avc-.alpha..sub.apc,
.alpha..sub.avc being the inclination before loading, defined
during the identification of the vehicle. L is the wheelbase of the
vehicle, also defined during the identification of the vehicle.
[0046] FIG. 4 shows a detailed diagram of step (ii) of image
capture and processing according to a preferred embodiment of the
invention.
[0047] As mentioned above, the user is invited by the application
to take a photograph (step ii.0) of at least one wheel of his
vehicle, for example a rear wheel. The photograph is preferably
taken in conditions in which the communication device is "upright",
that is to say when the measurements of the accelerometers
contained in it indicate x and z components close to zero and a y
component of less than zero (the telephone is not upside down).
Components x, y and z of the smart communication device are shown
in FIG. 6.
[0048] An illuminated and/or audible and/or vibration signal may
inform the user that these conditions are present, so that he can
initiate the photograph capture. In a variant, automatic capture of
the photograph may be provided when the conditions are met.
[0049] The communication device then commences the processing of
the photograph of the rear wheel taken by the user, enabling the
clearance of the corresponding suspension to be calculated. When
the photograph has been taken, if the communication device does not
allow the grayscale photograph to be taken directly, the photograph
is converted to grayscale (step ii.1, only if necessary). This
conversion may be carried out, for example, with the following
weights applied at each RGB level of the signal:
gray_image=0.3*photo_red+0.59*photo_green0.11*photo_blue;
[0050] where photo_red is the red luminous intensity, photo_green
is the green luminous intensity, and photo_blue is the blue
luminous intensity. When the image has been converted to grayscale,
the processing starts with blurring of the image with a Gaussian
filter (step ii.2). This processing enables artificial image
gradients, defects, and the like to be reduced.
[0051] "Sobel" filtering is then applied (step ii.3) to calculate
the derivative of the image in the direction of the width and of
the height, and then in both directions combined. This processing
enables the contours present in the image to be obtained (see FIG.
4A).
[0052] The image is then broken down into two parts, namely the
wheel housing and the wheel (step ii.4).
[0053] For the separated wheel housing, the circle containing the
points forming the contour is calculated by the least squares
method (step ii.5). Thus the center (Xc.sub.pix.sup.PdR,
Yc.sub.pix.sup.PdR) and the radius R.sub.pix.sup.PdR of the wheel
housing in pixels are found (see FIG. 4B).
[0054] For the separated wheel, the first stage is the calculation
of the direction map, which is a matrix containing the directions
normal to the intensity gradient calculated during the Sobel
filtering. The points in the direction indicated by this vector,
the distance of which varies from r_min to r_max, are then
cumulated in the image. These values r_min and r_max are calculated
(step ii.6) using the value of the radius R.sub.pix.sup.PdR of the
wheel housing estimated in the preceding step in pixels and the
theoretical ratio R.sub.J/PR (known) between the rim radius and the
radius of the wheel housing (see FIG. 4C).
[0055] The processing is continued by filtering the resulting image
with a Mexican hat filter or a Mexican hat wavelet filter (step
ii.7), similar to a cardinal sine. This makes it possible to
improve the concentration of points near the center of the wheel
(see FIG. 4D).
[0056] The center of the wheel (Xc.sub.pix.sup.R, Yc.sub.pix.sup.R)
is then calculated (step ii.8) on the basis of the accumulation of
points in the wheel center.
[0057] In the context of the present invention, other forms of
image processing may be used to define both the wheel center and
the wheel housing center.
[0058] To complete the processing, the distance in pixels between
the wheel center and the wheel housing center is calculated, after
which it is converted into meters, using the ratio between the
radius of the wheel housing in pixels and in meters (the
theoretical radius). The experimental results are shown in FIG. 5B.
The result of the calculations is the distance d.sub.apc.sup.arr
between the wheel center and the wheel housing center after
loading. This distance decreases with an increase in the loading of
the vehicle.
[0059] Therefore, an initial step of calibration in the factory
makes it possible to plot a map showing this distance
d.sub.apc.sup.arr as a function of a known weight of the vehicle,
and subsequently to determine this weight by estimating
d.sub.apc.sup.arr.
[0060] More advanced versions of the application can be imagined,
in which the user is requested to photograph both rear wheels in
order to calculate a distance d.sub.apc.sup.arr which is the
average of the two wheels.
[0061] However, in order to allow for ageing, and notably the
phenomena of creep in the linkage between the chassis and the
suspensions, the application subsequently deduces (step ii.9) the
clearance of the rear wheel assembly by performing the following
operation
.DELTA.d.sub.arr=d.sub.avc.sup.arr-d.sub.apc.sup.arr
[0062] where d.sub.avc.sup.arr represents the front distance before
loading (in the empty state). This value will be deduced during the
stage of vehicle identification: for example, either by asking the
user to photograph the vehicle in the empty state, or by accessing
a database and interrogating it with the vehicle identifier.
[0063] The user may also be requested to photograph the vehicle
regularly in the empty state (once or twice a year, for example),
in order to allow for variations in this empty distance, due
essentially to the ageing of the various members of the
suspension.
[0064] FIG. 5A shows an example of the load/clearance relationship
of a wheel suspension for a predetermined vehicle model. The rear
clearance value found on completion of processing step (ii) can be
used during the step to calculate, by interpolation in a map (such
as that shown in FIG. 5A, for example), the value of the loading on
the rear wheel assembly.
[0065] This figure exhibits hysteresis: when the vehicle is
progressively loaded, the clearance follows the curve a.sub.1,
whereas the relationship follows the curve a.sub.2 when the vehicle
is unloaded.
[0066] To limit the uncertainties, the median curve, shown as a
broken line, is used.
[0067] According to another embodiment of the invention, the user
is requested to photograph the four wheels of the vehicle, enabling
the precision of the weight estimation to be increased, notably by
improving the evaluation of the loading conditions.
[0068] The photographing of each of the wheels and the image
processing as defined, or any other image processing that results
in the determination of the wheel centers and wheel housing
centers, then enables the clearance of each wheel to be determined
for each wheel assembly. During the identification of the vehicle,
if it is specified that the clearance of each wheel is to be
determined, making it necessary to photograph each of the wheels,
it is no longer necessary to determine the angles of longitudinal
and transverse inclination of the vehicle, since the unloaded
clearance of each wheel is then solely dependent on the known
characteristics of the vehicle, and on the gradient of the road,
which can therefore be easily determined, by interpolation of the
known clearances on flat ground, for example.
[0069] A simplified variant is that of measuring only one of the
wheels in each wheel assembly for the determination of the
clearance of the wheel assemblies.
[0070] Clearly, various modifications and/or improvements which
will be evident to those skilled in the art may be made to the
different embodiments of the invention described in the present
description, without departing from the scope of the invention
defined by the attached claims.
[0071] Notably, the identification of the vehicle may be used on
the use of the VIN (for "Vehicle Identification Number"), which is
the unique alphanumeric code assigned to each vehicle. If the VIN
is used, the parameters required for the various calculations can
be obtained from a central server.
[0072] This VIN could be obtained by a request sent by the smart
communication device to the vehicle, for example via the OBD (On
Board Diagnostic) diagnostic interface, and the response could then
be transmitted in its turn to a database, which would return the
parameters required for the various calculations.
[0073] Additionally, in order to improve the precision of the
device, during the vehicle identification step (step (iii)), in
which the user is requested to position the smart communication
device in his docking station to make at least one measurement of
the inclination of the vehicle along the X axis between the
terrestrial reference frame and the vehicle reference frame before
the loading of the vehicle, provision is also advantageously made
to determine the inclination along the Y axis of the vehicle (the
transverse inclination) in order to correct the subsequent
determination of the distance between the wheel housing center and
the wheel center for this inclination.
[0074] Advantageously, provision is also made, during the
determination of the inclination after loading along the X axis, to
determine the inclination along the Y axis, this determination
being advantageously coupled with the measurement of a single wheel
of each wheel assembly.
[0075] Thus the difference in inclination is measured with even
greater precision.
[0076] The inclination of the vehicle along the Y axis may be due
to the banking of the ground, or may occur when the vehicle is
parked with one of the wheels, or both wheels on one side, placed
on a sidewalk, while the other two wheels are on the road.
* * * * *