Method and system or central station for monitoring tyre condition, and for detecting the presence of chains or nails, on a vehicle

• US 20040196149A1
• Filed: 03/25/2004
• Published: 10/07/2004
• Est. Priority Date: 09/15/2000
• Status: Active Grant

• Current Assignee: Dufournier Technologies SAS
• Original Assignee: Dufournier Technologies SAS
• Inventors: Dufournier, Arnaud
• Granted Patent: US 7,233,237 B2
• Time in Patent Office: Days
• US Class Current: 340/443
• CPC Class Codes: B60C 23/06 Signalling devices actuated by deformation of the tyre , e.g. tyre mounted deformation sensors or indirect determination of tyre deformation based on wheel speed, wheel-centre to ground distance or inclination of wheel axle
• CPC Class Codes: B60T 2240/03 Tire sensors
• CPC Class Codes: B60T 8/171 Detecting parameters used in the regulation; Measuring values used in the regulation
• CPC Class Codes: B60T 8/1725 Using tyre sensors, e.g. Sidewall Torsion sensors [SWT] for tyre pressure and temperature detection B60C23/00
• CPC Class Codes: G01M 17/02 Tyres

Abstract

According to the invention the method, and the system or corresponding device, consist in measuring a signal proportional to the speed of rotation of the wheel and in calculating a harmonic signal of the round of wheel (rather equal to the energies of the harmonics of this signal) then in comparing the result with a threshold and in activating an alarm when over-passing this threshold.

In a variant of the device, the basic signal comes from an accelerometer and is measured on the wheel, the elements of suspension or any representative element of the body of the vehicle.

Warning the driver and\or information of the security systems such as ABS™ etc.

Claims

1. Process for monitoring the condition of the tires of a vehicle (and, by extension, for detecting the presence or absence of snow chains, studs/nails, or other deforming elements), characterized by the fact that said process consists in measuring a signal that is proportional to the speed of rotation of the wheel and in calculating synchronous (or harmonic) information on the speed of the wheel, and then comparing the results to a threshold and triggering an alarm when this threshold is exceeded.

2. Process according to claim 1, wherein said process consists in measuring, on the wheel, the ground connection, or the chassis of the vehicle, a signal that is proportional to the speed of rotation of the wheel resulting from the generation by said deforming element of harmonic vibrations from the turn of the wheel.

3. Process according to claim 1, wherein the essential characteristic consists of taking the wheel speed information as a basic signal and then calculating the energies of this signal corresponding to the harmonics from the turn of the wheel (from the fundamental harmonic to the harmonic of order 64).

4. Process for monitoring the condition of the tires of a vehicle according to claim 1, wherein the wheel speed measurement may be replaced by:

measurement of the hub, suspension, or even chassis speed or acceleration;

or by measurement of the load on or displacement of the wheels or elements of the chassis or suspension, the entire process being designated for the sake of simplicity, as “

measurement of wheel speeds” and

, wherein, optionally

an effort is made to achieve almost absolute accuracy limited in reality by the accuracy of the sensor(s) by measuring the “

wheel”

speed by a method in which an event associated with the wheel, the wheel rotation in particular, is examined and the same event is examined exactly one turn later;

the event may be a specific wheel azimuth or, even, if use is made of a conventional gear wheel rather than a customary “

tooth to tooth”

measurement (i.e., a single interval between two successive teeth), a measurement is made “

of a tooth with itself one turn later”

;

this in turn permitting, if this measurement “

one turn later”

is made additionally for each tooth No. 1, then No. 2, and so forth, execution of as many very precise measurements per turn of the wheel as there are teeth, such as 48 or 64.

5. Process for monitoring the condition of the tires of a vehicle according to any of claims 1 to 4 claim 1, wherein, especially in the case where an accelerometer or load sensor is used, it is possible to use only one sensor measurement per axle or set of wheels that will be mounted on a representative element of the axle or set of wheels or to use a single sensor measurement for the entire vehicle, which will then preferably be mounted on the chassis.

6. Process according to claim 1, wherein said process essentially involves the use of a BO central electronic unit that is able, using known or readily accessible memory devices and computers, to collect and process signals that are put out by the on-board electronics in series or as desired, such as the ABS™

system, anti-skid system, or path stabilization system and, by processing the signal, to deduce therefrom the condition of the tire (or the presence of chains or studs/nails), i.e., the presence of any element or factor that would locally alter the tire'"'"'s radius R1 (static or dynamic and, especially, the contact radius, i.e., the radius measured in the area of contact) or the roll radius.

7. Process according to claim 1, wherein the device thus calculates this signal'"'"'s energies that correspond to the harmonics of the turn of the wheel (from the fundamental harmonic to the harmonic of order 64).

8. A process as specified in claim 1, wherein the system compares the result to an individual threshold value and initiates an alarm when this threshold value is exceeded.

9. A process as specified in claim 1, wherein such process comprises a “

spatial adjustment”

stage between a front wheel and most preferably a rear wheel during calculation of the C % factor (factor of comparison of the wheel being tested with a reference wheel (or signal standardization)) in order to eliminate the effects of unevenness of the ground and to make a comparison of the two wheels termed “

iso-ground”

comparison. may be dispensed with.

10. A process as specified in claim 1, wherein the wheels situated on the same side of the vehicle are taken into consideration.

11. A process as specified in claim 1, wherein the frequency, or at least one of its harmonics, coincides with a characteristic frequency of the vehicle, such as around 12 Hz for the vertical vibration mode of the body, around 40 Hz for the tire itself, the frequency of vertical movement being of the order of 12 Hz, and is of the order of 40 to 60 depending on the movement of rotation, as a function of the speed, and wherein the frequency or its harmonic corresponding to the defect is then amplified by the resonance (generally stationary) with which it coincides.

12. A process as specified in claim 1, wherein the sum of part or all of the harmonics is compared to a specific threshold value and an alarm is initiated when this threshold is crossed.

13. A process as specified in claim 12, wherein the thresholds correspond to a function of identical measurements made with all or at least one of the wheels of the vehicle, of the total number of wheels of the vehicle, or the wheel on the same side, the same axle, or diagonally thereto.

14. A process as specified in claim 1, wherein the base signal is an accelerometric signal measured at the wheel, the suspension elements, or any element representative of the chassis of the vehicle.

15. A process as specified in claim 1, wherein the base signal is made up of a measurement of the load applied to the wheel, and/or to the suspension elements, and/or to any element representative of the chassis of the vehicle (such as a strain gauge sensor or an accelerometer positioned on the wheel or such element).

16. A process as specified in claim 1, wherein, in another approach, measurement may be made of displacement of the chassis element, suspension element, or other characteristic element.

17. A process as specified in claim 1, wherein the steering angle is used to validate/invalidate the results obtained and/or to weight calculation of C % (t) (action to affect either coefficient k and/or action to affect factor C % (t).

18. Process according to claim 8, wherein said alarm is transmitted to the driver and/or to the safety systems that act on the different wheels (antilock brake system ABS, antiskid system, path monitoring system) and/or within the framework of the vehicle-mounted, transportable or remote maintenance device.

19. Process according to claim 1, wherein said process includes the following stages:

The speeds Vroue(t) of rotation of each of the wheels are continuously measured, especially using the sensors and the packaging used for the antilock braking device or antiskid device;

For each wheel, a criterion A(t) is calculated based on the measurement of the dispersion or variation of Vroue(t), using the standard deviation of Vroue(t) (standard deviation of the variations of the speed of rotation of the front wheel relative to that of the rear wheel) and the mean speed of the wheel over a time period T.

20. Process according to claim 1, wherein said process includes the following stages:

The speeds Vroue(t) of rotation of each of the wheels are continuously measured, especially using the sensors and the conditioning used for the antilock braking device or antiskid device;

For each of the wheels, a criterion A(t) is calculated based on the measurement of the energy of the signal on the frequency bands that are centered on a portion of harmonics 1-64 of the signal Vroue(t) (frequency bands that are centered on the harmonics and are significantly less than 10 Hz in width will be used) and/or on fixed frequency bands located between 1 and 400 Hz.

21. Process according to claim 19, wherein, in all the criteria for calculating A(t), Vroue(t) will be replaced by the phase of the signal Vroue(t).

22. Process according to claim 19, wherein, in all the criteria for calculating A(t), Vroue(t) can also be replaced by its derivative (the angular acceleration of the wheel).

23. Process according to claim 19, wherein weighting is effected of a constant value or function of Vroue(t) Vroue in order to make allowance for the technological differences in the different chassis, and wherein the speed of the vehicle is taken into account, and also, if necessary, of the level of ground excitation (data which can be provided, for example, by the ground connection sensors used to measure the position of the vehicle relative to the horizontal or for controlled suspensions and shock absorbers).

24. A process as specified in claim 1, wherein, whenever the base data are obtained by sensors other than the wheel speed sensors, the search for the harmonics or the phase will be made preferably either by self-correlation of the base signal or by convolution with a signal representative of the wheel speed or the mean speed of a set of wheels of the vehicle, it being permissible for the latter signal to be derived, for example, from speed data available for the set of vehicles or the wheel speed sensors used for the ABS™

25. Process according to claim 1, wherein said process includes a stage for calculating a coefficient of comparison C %

C %=[Art−

k×

Ac−

r]/Ac

in which

Art corresponds to the wheel undergoing testing.

Ac corresponds to one of the other wheels or to the mean of the other wheels of any set of wheels of the vehicle.

k is a coefficient which makes it possible, if necessary, to allow for the distribution of the engine torque or braking torque among the wheels compared, and also of the load, the differences between tires, and the pressure, the technological differences of the chassis compared, or again of the steering lock angle or of specific equipment (such as snow chains).

r is a coefficient which permits allowance for the resistance to rolling associated with the tires, the ground contact elements, and the chassis adjustments.

26. A process as specified in claim 25, wherein there is adopted for Ac a wheel or a set of wheels situated on the same side of the vehicle, each of the wheels being referred to the same reference point in space.

28. A process as specified in claim 1, wherein such process comprises the following stages of final data extraction.

two values D(1) and D(2) are calculated which permit both reactive monitoring of the progress of rapid deterioration and final monitoring of the progress of slow deterioration.

$\mathrm{D1}$

(t)

=x=t-T1x=t

C

%

(x)

 





x$\mathrm{D2}<br><br>\left(t\right)<br><br>{=}_{x=t-\mathrm{T2}}^{x=t}<br><br>C<br><br>\%<br><br>\left(x\right)<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>x$

With T1<

T2

The order of magnitude being;

T1;

several fractions of seconds to several seconds

T2;

several seconds to several hours

and, to simplify calculation, use is made if necessary, in place of the integrals, of sliding totals of the successive values of C % (t) over the numbers of terms corresponding more or less to x periods T1 and T2.

D1 and D2 are then compared both to the respective threshold values S1 and S2 and to the threshold values S3 and S4.

these tests being monitored by counter readings which increase and decrease as a function of the result of the tests;

the counters, Cpt1 and Cpt2, providing the following data;

Cpt1 permits concentration more particularly on rapid and significant deterioration

Cpt2 permits concentration on slight deterioration which is slow to develop.

Lined out on 27-02-03

29. Process according to claim 1, wherein, in order to simplify the processing, the following is adopted as a formula for C %:

C %(t)=A(t)

30. Process according to claim 1, wherein knowledge of the angle of lock or “

steering-wheel angle”

is used in evaluating the comparison coefficient k for the wheel speeds or an additional factor that makes it possible to weight C % (t), or is used to invalidate to the measurement beyond a limiting angle of lock, whereby the measurement results are then considered not to exist during the entire time that the limiting angle is exceeded and the counters Cpt2 and Cpt2 thus remain unincremented.

31. Process according to claim 1, wherein:

During braking phases, knowing the braking torque and and/or its distribution makes it possible to derive final data by weighting the coefficients S1, S2, S3, and S4 based on these latter elements, whereby this knowledge can be obtained from the braking pressures and their distributions, broken down by wheel, and wherein, in cases where a braking distributor is used, allowance will be made, especially in turning, for the braking torque that is actually applied to each wheel;

this makes it possible to refine the evaluation and the evaluation may be done based on the calculation of this ratio using the mean speed of the drive wheels and the speed of the engine.

32. Process according to claim 31, wherein knowing the distribution of the load and/or total load of the vehicle makes it possible to improve the derivation of the final data by weighting the coefficients S1, S2, S3, and S4 based on these latter elements.

33. Process according to claim 1, wherein said process is adapted to designing a detector for determining the presence of snow chains and/or studs and detects the generation of harmonic vibrations from the turn of the wheel that can be measured on the wheel, the ground connection, or the chassis of the vehicle, whereby the detection can then be done either with the aid of the wheel-speed sensors used for the ABS or with the aid of one or more accelerometric sensors or strain gauges mounted on the ground connection or chassis.

34. A process as specified in claim 33, wherein processing of the signal is identical to a fairly inclusive criterion for the function A(t) such as dispersion of the speed signals (for example, the standard deviation of signals measured over one or more turns of the wheel), which is sufficient for achievement of a satisfactory detection level, and wherein the sensitivity of the system may if necessary be improved by use of a criterion which consists of summation of the energy values of the signal centered around the harmonics of the turn of the wheel.

35. A process as specified in claim 34, wherein the chains are designed to emit a particular vibratory signature (for example, harmonic of the turn of the wheel over one or more harmonics ranging from 1 to 64), the detection then being effected preferably over the harmonics generated.

49. Device according to claim 36, wherein said device includes means that are designed to implement the process according to any of claims 1 to 33, and in particular the means for carrying out the following operations:

during the braking phases knowledge of the braking torque and/or its distribution permits improvement in extraction of the final data by weighting the coefficients S1, S2, S3, and S4 as a function of these latter elements, it being possible to obtain such knowledge on the basis of the braking pressures and their distribution per wheel and wherein, in the case of use of a braking distributor, the braking torque actually applied to each wheel, in particular on a curve, is taken into account, this permitting refined evaluation and/or

during the braking phases subjected to engine torque, knowledge of the engine torque and/or its distribution also permits improvement in extraction of the final data by weighting the coefficients S1, S2, S3, and S4 as a function of these latter elements, and/or

measurement or evaluation of the engine torque is effected on the basis of parameters of the engine computer, the engine torque Cm applied to the driving wheels, and/or

the evaluation may be made on the basis of the following measurements or data;

accelerator pedal position or injection output, and/or

engine speed, and/or

transmission ratio (or calculation of such ratio on the basis of the mean speed of the driving wheels and the engine speed) and/or in the case of use of a torque distributor (remote-controlled differential, for example), the torque actually applied to each wheel, on a curve in particular, is taken into account, this permitting refined evaluation and/or

knowledge of the load distribution and/or of the total load of the vehicle permits improvement in extraction of the final data by weighting the coefficients S1, S2, S3, and S4 as a function of these latter elements, it being possible to obtain such knowledge by means of the body height sensors used in particular for adjustment of the headlights and/or

knowledge of the dynamic load on the wheel permits improvement in extraction of the final data by weighting the coefficients S1, S2, S3, and S4 and/or

knowledge of the dynamic load on the wheel may be evaluated, for example, on the basis of an inertial unit, and/or sensors introduced into the ground connection and used in particular for remote control of the shock absorbers and suspensions and/or

knowledge of the external air humidity permits improvement in extraction of the final data by weighting coefficients S1, S2, S3, and S4, it being possible to obtain such knowledge, for example, by means of rain sensors used, for example, for remote control of the windshield wipers and/or

knowledge of the external temperature permits improvement in extraction of the final data by weighting coefficients S1, S2, S3, and S4 it being possible to obtain such knowledge, for example, by means of temperature sensors frequently installed on the vehicles and/or

knowledge of the interior temperature of the tire casing (temperature of the tire or temperature of the enclosed air) permits improvement in extraction of the final data by weighting coefficients S1, S2, S3, and S4, it being possible to obtain such knowledge, for example, by means of temperature sensors installed in the wheels and/or

knowledge of the interior pressure of the tire casing permits improvement in the final data by weighting coefficients S1, S2, S3, and S4, it being possible to obtain such knowledge, for example, by means of pressure sensors installed in the wheels and/or

the threshold values S1, S2, S3, and S4 may also be weighted by the means speed of advance of the vehicle and/or

the threshold values S1, S2, S3, and S4 may also be weighted by a signal derived from all or part of the wheels of the vehicle as the derivative or the variations or dispersions of Vroue(t) or its modulus or its phase.

50. Device according to claim 1, wherein said device is designed to be a detector for detecting the presence of snow chains and/or studs and includes the means for generating harmonic vibrations from the turn of the wheel that can be measured on the wheel, the ground connection, or the chassis of the vehicle, whereby the detection can then be done either with the aid of the wheel-speed sensors used for the ABS or by means of one or more accelerometric sensors or strain gauges mounted on the suspension or the chassis.

27. A process as specified in claim or 25, wherein, whenever a wheel undergoing testing (such as a front or rear wheel) is compared to a reference wheel (such as a rear or a front wheel, the function will be

C %(t)=[Av(t)−

k×

Ar(t+Δ

t)−

r]/Ar(t+Δ

t)

in which

Av corresponds to the wheel undergoing testing (such as a front or a rear wheel)

Ar corresponds to the reference wheel (such as a rear or a front wheel)

e is the difference between the wheel undergoing testing and the reference wheel along the longitudinal axis of the vehicle (=wheelbase in the case of a front wheel compared to a rear wheel)

Δ

t=e/V

in which V=speed of advance of the vehicle

V being calculated, for example, on the basis of the mean speed of the non-driving wheels or of the mean speed of the set of wheels,

wherein the wheel undergoing testing is compared to a reference wheel, these two wheels being “

spatially adjusted”

one relative to the other, that is, being referred for the sake of comparison to a single point situated on the longitudinal axis of the vehicle,

and wherein, in the event of comparison to a set of wheels, each of the wheels is spatially adjusted before calculation of the criterion C %.

36. Device for monitoring the condition of the tires of a vehicle (and, by extension, for detecting the presence or absence of snow chains, studs, or other deforming elements), wherein said device includes the means for measuring a signal that is proportional to the speed of rotation of the wheel and thus for calculating synchronous (or harmonic) information on the speed of the wheel, and then comparing the results to a threshold and triggering an alarm when this threshold is exceeded.

37. Device according to claim 36, wherein said device includes the means for measuring, on the wheel, the ground connection, or the chassis of the vehicle, a signal that is proportional to the speed of rotation of the wheel resulting from the generation by said deforming element of harmonic vibrations of the turn of the wheel.

38. Device according to claim 36, characterized in the fact that it includes means for the measurement of a wheel speed information as basic signal and then to calculate the energies of this signal corresponding to the harmonics of the wheel round (from the 1^st to the 64^th harmonic).

39. Device for monitoring the condition of the tires of a vehicle, according to claim 36, wherein said device includes means for:

measurement of the “

wheel,”

hub, suspension, or even chassis speeds or accelerations

or measurement of the load applied to or of the displacement of the wheel or elements of the chassis or of the suspension systems,

the foregoing as a whole being designated for the sake of simplicity “

wheel speed measurement”

.

40. Device for monitoring the state of the tires of a vehicle, according to claim 36, characterized in the fact that it includes, especially in the case of use of accelerometer or force sensor, only one sensor by axle or group of wheels which will then be setting on a representative element of the axle or the group of wheels, or single sensor for the whole vehicle which will then be setting preferably on the body.

41. Device according to claim 36 characterized in the fact that it mainly includes, according to its general mode, an electronic central unit BO capable of collecting and processing, using memories and processors, signals emitted by the series or optional embedded electronic, such as ABS™

, antiskid system, path control, and similar devices, and to evaluate thanks to data processing of the signal the state of the tire (or the use of snow chains or spikes) which is to say the presence of any element or cause locally modifying the radius R1 (static or dynamic in particular the loaded radius, that is measured in the contact area) of the tire or the rolling radius.

42. Device according to claim 36, wherein said device includes means for:

then calculating the energies of this signal corresponding to the harmonics of the turn of the wheel (from the fundamental harmonic to the harmonic of order

     64);

comparing the results to an individual threshold and triggering an alarm when this threshold is exceeded.

43. A device as specified in claim 36, wherein such device comprises means of “

adjustment in space”

between a front wheel and by preeminent preference a rear wheel during calculation of factor C % (factor for comparison of the wheel undergoing testing to a reference wheel (or signal standardization)), such means being suitable for and capable of eliminating the effects of unevenness of the ground and of making a comparison of the two wheels termed “

iso-ground”

comparison.

44. Device according to claim 36, wherein said device includes means for measuring load on the wheel and/or on the suspension parts and/or on any representative part of the chassis of the vehicle (a strain-gauge sensor or an accelerometer positioned on the wheel or said part) or measuring the displacement of the chassis or suspension part.

45. Device according to claim 36, wherein said device includes means for measuring and using the steering-wheel angle to validate/invalidate the results obtained and/or to weight the calculation of C % (t) (adjusting either the coefficient k and/or adjustment based on C % (t)).

46. Device according to claim 42, wherein said device includes the means for transmitting said alarm to the driver and/or to the safety systems that act on the different wheels (antilock brake system ABS, antiskid system, vehicle stability control) and/or within framework of the vehicle-mounted, transportable, or remote maintenance device.

47. A device as specified in claim 36, wherein, when the base data are obtained by sensors other than the wheel speed sensors, such device comprises means for effecting the search for harmonics or the phase either by autocorrelation of the base signal or by combination with a signal representative of the speed of the wheel or the mean speed of a set of wheels of the vehicle, it being possible for the latter signal to be derived, for example, from the speed data available for the set of wheels of the vehicles or from the wheel speed sensors used for ABS™

.

48. A device as specified in claim 36, wherein such device comprises means for completing a stage of calculation of a comparison coefficient C %

C %=[Art−

k×

Ac−

r]/Ac

in which

Art corresponds to the wheel undergoing testing,

Ac corresponds to one of the other wheels or to the mean of the other wheels or of any set of wheels of the vehicle,

k is a coefficient which permits making any necessary allowance for distribution of the engine torque or braking torque among the wheels compared, but also for the load, differences between tires, and the pressure, technological differences of the chassis compared, or again for the deflection angle of the steering wheel or of specific equipment (such as snow tires),

r is a coefficient which permits making allowance for the resistance to rolling associated with the tires, the ground connection elements, and the chassis adjustments.

and wherein, in the case of a wheel undergoing testing (such as a front or rear wheel), the function is

C %(t)=[Av(t)−

k×

Ar(t+Δ

t)−

r]/Ar(t+Δ

t)

in which

Av corresponds to the wheel undergoing testing (such as a front or rear wheel)

Ar corresponds to the reference wheel (such as a rear or front wheel)

e is the distance between the wheel undergoing testing and the reference wheel along the longitudinal axis of the vehicle (=wheel base in the case of a front wheel relative to a rear wheel)

Δ

t=e/V

with V=speed of advance of the vehicle

V being calculated, for example, on the basis of the mean speed of the non-driving wheels or the mean speed of the set of wheels,

wherein the wheel being tested is compared to a reference wheel, these two wheels being “

spatially adjusted”

one relative to the other, that is, referred for the sake of comparison to a single point situated on the longitudinal axis of the vehicle,

and wherein, in the case of comparison to a set of wheels, each of the wheels is spatially readjusted before criterion C % is calculated.

51. Device according to claim 36, wherein said device is used to generate and measure said signal from the sensors that are premounted on the vehicle (sensors that are used for the antilock brake system ABS, antiskid system, or path monitoring system) or additional sensors such as optical coders, magnetic coders, accelerometers (whereby the optical or magnetic “

coders”

can, as one skilled in the art is aware, be geometric elements that are marked either optically or mechanically and are arranged according to a sensor-readable code) and whereby the signals produced by these sensors are then forwarded to a central box positioned close to the ABS™

computer.

and wherein the central housing is made up of two electronic stages;

the analog stage, which modifies the incoming analog and digital signals, contains the supply (printed circuit) card and the output signal adaptation card (analog;

dashboard indicator, digital;

information concerning the condition of the tires)

the digital stage, assembled around an 8-bit microcontroller and executing all processing.

And if necessary uses a speed regulator which has been modified to modulate its speed as a function of the indication of deterioration and to the ABS.

Or, for determination of the steering angle, devices such as an electronic stability control device.