EP1924859A1

EP1924859A1 - Device and method for measuring a quantity representing the rotational speed of a motor vehicle and system and method using said device and said method

Info

Publication number: EP1924859A1
Application number: EP06808303A
Authority: EP
Inventors: Zahir Djama; Denis Le Bret
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2005-09-16
Filing date: 2006-09-11
Publication date: 2008-05-28
Also published as: FR2891055B1; FR2891055A1; US20090021242A1; WO2007031675A1

Abstract

The invention concerns a device for measuring a quantity representing the rotational speed of a motor vehicle wheel (14ag, 14ad, 14rg, 14rd), comprising means (22ag, 22ad, 22rg, 22rd) for coding and measuring the rotational speed in the form of electromagnetic pulses, means (24) for determining a time interval including a whole number of said pulses, and means (24) for counting the whole number of said pulses during said time interval. Said device comprises means (24) for determining a quantity representing the radius of the wheel and means (24) for determining said quantity based of the whole number of pulses, on the time interval and on the quantity representing the radius of the wheel.

Description

Device and method for measuring a representative quantity of the rotational speed of a motor vehicle wheel and system and method using such a device and such a method

The present invention relates to a device and a method for measuring the longitudinal velocity of a vehicle wheel.

More particularly, the present invention relates to such a device comprising means for encoding rotational speed in the form of electromagnetic pulses, means for measuring said pulses, means for determining a period of time comprising an integer number of said pulses, and means for counting the integer pulse number during this period of time.

The present invention also relates to a system for determining the condition of tires of the wheels of a vehicle comprising such a device and a method for determining the state of tires of the wheels of a vehicle comprising such a method.

The control of the operation of a vehicle, such as its braking or trajectory, currently uses rotational speed measurements of the wheels of the vehicle. These measurements are delivered by rotational speed sensors mounted on the wheels, generally referred to as "ABS sensors".

An ABS sensor typically includes an encoder disk mounted on the axle of a vehicle wheel and including a plurality of alternating north and south magnetic poles. The ABS sensor also comprises a casing mounted on the spindle of the wheel facing the disc and connected to an information processing unit. This housing houses a printed circuit board on which a Hall effect cell is mounted. This cell produces an electric current according to the magnetic field variations generated by the alternating passage in front of the housing of the north and south poles of the disk rotated by the axle. The ABS sensor thus functions as a magnetic encoder of the rotational speed of the wheel and the current it generates, or an image thereof, is delivered to the information processing unit which calculates the frequency of the current. generated and consequently the speed of rotation of the wheel. However, the calculation of the signal frequency of the ABS sensor implemented by this unit uses a predetermined and constant radius of the wheel. Also, if the latter does not have this constant radius, for example because its tire is not inflated satisfactorily or if a bad tire has been mounted on the wheel, this calculation is distorted. Applications using the calculated frequency, such as anti-wheel lock, tire condition diagnosis, trajectory control, etc., are then based on a bad value, which can be dangerous.

The object of the present invention is to solve the above problem.

For this purpose, the subject of the present invention is a device for measuring a quantity representative of the speed of rotation of a vehicle wheel, of the type comprising:

means for encoding the speed of rotation of the wheel in the form of electromagnetic pulses;

means for measuring said pulses;

means for determining a time period comprising an integer number of said pulses; and

means for counting the integer number of pulses during this period of time, characterized in that it comprises:

means for determining a magnitude representative of the radius of the wheel; and

means for determining said quantity as a function of the integer number of pulses, the period of time and the magnitude representative of the radius of the wheel;

the quantity representative of the speed of rotation of the wheel is the frequency of the electromagnetic pulses encoding said speed;

the means for determining the magnitude representative of the radius of the wheel comprise means for acquiring vertical accelerations in a frame of reference of the vehicle of the wheel and of another wheel arranged on the same side of the vehicle as this one and the means for estimating a coefficient of stiffness of a tire mounted on the wheel; the estimating means comprise means for temporal resetting of one of the accelerations acquired on the other of the accelerations acquired;

the means for estimating the stiffness coefficient are suitable for estimating it from a single-wheel mechanical model of said wheels connected to a vehicle body by means of suspensions and comprising tires similar to springs characterized by coefficients of stiffness;

the means for estimating the stiffness coefficient are suitable for estimating it by relying on discrete time modeling of the recalibrated accelerations of the wheel and the other wheel according to the relation:

Apr where k is the k ^th sampling instant, mrr is the mass of the rear wheel from the wheel and the other wheel, MRA is the mass of the front wheel from the wheel and the other wheel, Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and before respectively in the vehicle reference system, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, and n is a moment of registration corresponding to a time shift between said rear and front wheels undergoing the same portion of roadway;

Ava (k) = where k is the k ^th sampling instant, mrr is the mass of the rear wheel from the wheel and the other wheel, MRA is the mass of the front wheel from the wheel and the other wheel, Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and before respectively in the reference system of the vehicle, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, and n is a time of registration corresponding to a time shift between said rear and front wheels undergoing the same portion of roadway;

the estimation means are capable of estimating the coefficient of stiffness from a bicycle mechanical model of a vehicle body assimilated to a mass connected to the wheel and the other wheel by means of suspensions, the wheel and the other wheel comprising tires similar to springs characterized by coefficients of stiffness;

the means for estimating the coefficient of stiffness are suitable for estimating it by relying on a discrete time modeling of the recalibrated accelerations of the wheel and of the other wheel according to the relation: mra

-Av (k -n) mrr Kpr (k) / Kpa (k)

- (Zva (k - n) - Zvr (k))

Avr (k) = mrr Kpr (k)

-Zva (k - n) (Kpr (k) / Kpa (k)) xKca (k) mnr Kcr (k)

Zvr (k) mrr where k is the k ' ^th moment of sampling, mrr is the mass of the rear wheel among the wheel and the other wheel, mra is the mass of the front wheel among the wheel and the other wheel , Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and respectively respectively in a reference system of the vehicle, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, n is a time of registration corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway, Kca and Kcr are coefficients of stiffness suspensions of said front and rear wheels respectively, and Zva and Zvr are the speeds vertical displacement of the centers of said front and rear wheels respectively;

the means for estimating the coefficient of stiffness are suitable for implementing a recursive least squares algorithm in real time; the magnitude representative of the radius of the wheel is a number that is a function of the ratio of the longitudinal speed of the wheel to the frequency of said pulses, and the means for determining this magnitude comprise means for estimating said number as a function of the coefficient of stiffness estimated tire of the wheel; and

the means for determining the quantity representative of the rotational speed of the wheel comprise means for selecting an abacus of a predetermined set of abacuses as a function of the determined quantity representative of the radius of the wheel and the number of counted pulses and means for estimating said quantity by evaluating the selected chart for the determined period of time.

The subject of the invention is also a system for determining the state of tires of the wheels of a vehicle, characterized in that it comprises: a device of the aforementioned type associated with each wheel of the vehicle and delivering a representative quantity of the speed of rotation of the wheel; and

means for diagnosing the condition of the tires of the wheels of the vehicle as a function of said delivered quantities; - The diagnostic means are adapted to diagnose a tire as underinflated when the amount associated therewith is less than more than a first predetermined value to at least a quantity associated with other tires;

the devices are capable of delivering, in addition, the estimated stiffness coefficients of the wheels, and the diagnostic means are able to diagnose the tire as underinflated if, in addition, its estimated stiffness coefficient is more than a second predetermined value by less than at least one estimated stiffness coefficient of the other tires;

- The diagnostic means are adapted to diagnose under-inflation of the vehicle wheels if said delivered quantities are less than a first predetermined threshold value; - The diagnostic means are adapted to diagnose under-inflation of the vehicle wheels if further said delivered coefficients are less than a second predetermined threshold value.

The invention also relates to a method for measuring a representative quantity of the speed of rotation of a vehicle wheel, of the type comprising:

a step of encoding the speed of rotation of the wheel in the form of electromagnetic pulses;

a step of measuring said pulses; a step of determining a time period comprising an integer of said pulses; and

a step of counting the integer number of pulses during this period of time, characterized in that it comprises: a step of determining a magnitude representative of the radius of the wheel; and

a step of determining said quantity as a function of the integer number of pulses, the period of time and the magnitude representative of the radius of the wheel. The subject of the invention is also a method for determining the state of tires of the wheels of a vehicle, characterized in that it comprises:

a method of the aforementioned type for each wheel of the vehicle and delivering a quantity representative of the speed of rotation of the wheel; and a step of diagnosing the condition of the tires of the wheels of the vehicle according to said delivered quantities.

The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended drawings in which identical references designate identical or similar elements, and in which:

FIG. 1 is a schematic view of a motor vehicle comprising a system for determining the inflation state of tires according to the invention; FIG. 2 is a schematic view of a sensor forming part of the constitution of the system of FIG. 1 associated with a rolling train of the vehicle;

- Figure 3 is a side view of the housing of Figure 1 in an orthogonal reference of the wheel;

FIG. 4 is a schematic perspective exploded view of a first embodiment of the housing of FIG. 2;

FIG. 5 is a schematic exploded perspective view of a second embodiment of the housing of FIG. 2; FIG. 6 is an exploded schematic perspective view of a third embodiment of the housing of FIG. 2;

FIG. 7 is a schematic view of an information processing unit forming part of the constitution of FIG. 1;

FIG. 8 is a diagram illustrating a calculation hypothesis used by the unit of FIG. 7;

FIG. 9 is a schematic view of a module for determining operating points of front and rear wheels forming part of the unit of FIG. 7;

- Figure 10 is a schematic view of a mechanical model of a motor vehicle wheel connected to the body thereof by means of a suspension;

- Figure 11 is a schematic view of a second mechanical model of a front and rear wheel of a motor vehicle arranged on the same side of the vehicle and connected to the body thereof by means of suspensions;

FIG. 12 is a graph of the coefficient of stiffness of a tire mounted on a wheel of the vehicle as a function of the operating point thereof;

FIG. 13 is a schematic view of an electromagnetic pulse frequency determination module forming part of the unit of FIG. 7;

FIG. 14 is a graph illustrating the determination of an electromagnetic pulse address; FIG. 15 is a graph of electromagnetic pulse frequency charts as a function of electromagnetic pulse addresses; and

FIG. 16 is a schematic view of a diagnostic module forming part of the unit of FIG. 7.

In Figure 1, there is schematically illustrated a motor vehicle 10 having two front wheels right and left 14ag, 14ad mounted on a front axle 16 and two rear wheels right and left 14rg, 14rd mounted on a rear axle 18. Each of 14ag, 14ad, 14rg, 14rd wheels is equipped with a tire 20ag, 20ad, 20rg, 20rd. Each of the wheels is associated also associated with a sensor 22ag, 22ad, 22rg, 22rd encoding in the form of magnetic pulses its speed of rotation and measuring an acceleration of the center thereof.

The sensors 22ag, 22ad, 22rg, 22rd are connected to an information processing unit 24 which determines, as a function of the signals delivered by them, the frequencies of the pulses encoding the rotational speeds of the wheels 14ag, 14ad, 14rg, 14rd and the condition of the tires 20ag, 20ad, 20rg,

20rd, as will be described in more detail later.

FIG. 2 is a view in more detail of the running gear of one of the wheels 14ag, 14ad, 14rg, 14rd, for example that of the left front wheel 14ag associated with the corresponding sensor 22ag. The other sensors 22ad, 22rg, 22rd are identical to the sensor 22ag described below.

In a conventional manner, the wheel 14ag is marked by an orthogonal reference OXYZ of a reference frame of the vehicle, the axis OX being the transverse axis of the wheel, the axis OY being the longitudinal axis of the wheel and the axis OZ being the vertical axis of the wheel, as is known per se. The OXY plane is referred to as the horizontal plane of the 14ag wheel.

The sensor 22ag comprises an encoder disk 30 formed of a succession of magnetic poles north 32 and south 34 alternately. This disc 30 is mounted on the axle 16.

The sensor 22ag also includes a sensor housing 36 attached to a rocket 37 of the wheel 14ag opposite the encoder disk 30 and separated therefrom by a gap distance g. The housing 36 is electrically connected to the information processing unit 24 and to the vehicle power supply system (not shown) by electrical wiring 38 for its power supply and for data communication. The housing 36 is of parallelepipedal shape and houses a circuit board on a longitudinal plane C1, as will be explained in more detail later. Active elements are mounted on the printed circuit board and are adapted to measure electromagnetic field variations caused by the scrolling of the north and south poles 32, 34 and an acceleration of the wheel 14a along a predetermined axis.

Due to the arrangement of the various members for driving, braking and steering of the wheel and for questions of ease of assembly and electrical connections well known in the state of the art, the housing 30 is mounted inclined . The longitudinal plane C1 of the housing 36 on which the printed circuit board is arranged thus forms a predetermined and known angle A with respect to the horizontal plane OXY of the wheel 14ag, as can be seen in FIG. 3, which is a side view of the housing in the OXY mark.

FIG. 4 is a diagrammatic exploded perspective view of a first embodiment of the sensor housing 36. This housing 36 is for example a rectangular parallelepiped formed of an upper half-shell 40 and a lower half-shell 42 and housing in its central longitudinal plane a printed circuit board 44 plane. This card 44 is connected to a block 46 of electrical connections for its power supply and the transmission of signals via the electrical wiring 38.

At the front face 48 of the housing 36, which faces the encoder disk 30, a Hall effect encoder cell 50 is mounted on the printed circuit board 44. As is known per se, this cell 50 is sensitive to the magnetic field variations generated by the successive passage of the magnetic poles 32, 34 of the disk 30 in front of the front face 48. The cell 50 thus produces an electric current in the form of pulses substantially in square whose frequency depends on the period spatial poles on the disk 30 and the speed of rotation of the wheel 14ag. The disk 30 and the cell 50 constitute a magnetic encoder of the speed of rotation of the wheel 14ag.

The cell 50 is supplied with electrical energy by a supply line 52 connected to the connection block 46 and the electric current it generates is transmitted to the block 46 by a first data line 54.

A single-axis accelerometer 56, consisting of an electromechanical micro-system in the form of a chip, is also mounted on the card 44 and is capable of measuring the acceleration experienced by the housing 36 along a predetermined axis M, here perpendicular to the plane of the card 44. This accelerometer 44 is provided to measure the acceleration of the center of the wheel 14ag along the axis OZ (Figure 2), hereinafter referred to as vertical acceleration.

Accelerometer 56 is connected to line 52 for their power supply and to a ground line 58 connected to block 46. Accelerometer 56 is further connected to a second data line 60 for transmission to the block. 46 of the acceleration measurement.

It should be noted that only five electrical connections are required for the power supply and the data communication of the card 44.

As mentioned above, because of the mounting of the housing 36 on the wheel 14ag, the plane of the printed circuit board 44 is inclined to the known angle A relative to the horizontal plane OXY of the wheel 14ag. In order to extract from the measurement of the accelerometer 56 the component along the vertical axis OZ of the wheel 14ag, there are provided filtering means capable of extracting the latter. These filtering means are for example provided in the information processing unit 24 and multiply the measurement received from the accelerometer 56 by the cosine of the angle A to extract the vertical acceleration of the wheel 14ag.

In a variant, the filtering means are mounted on the card 44 in the form of a microcontroller chip. FIG. 5 is a schematic view of a second embodiment of the housing 36.

The chip of the accelerometer 56 is here mounted inclined at an angle B, substantially equal to the angle 180 ° -A (in degrees), relative to the plane of the map 44 by resting on appropriate support means 70. Thus, the measurement axis M of the accelerometer 56 is substantially in a vertical plane of the wheel 14ag.

Thus, the accelerometer 56 directly measures the vertical acceleration of the wheel 14ag and it is not necessary to implement a filtering of its measurement.

As a variant, the chip of the accelerometer 56 is not mounted inclined on the card 44 but the accelerometer 56 measures the acceleration that the card undergoes

44 along an axis forming the angle B with the plane of the connection pads of the accelerometer chip 56. This type of accelerometers is generally referred to as "inclined axis accelerometers".

FIG. 6 is a schematic exploded perspective view of a third embodiment of the housing 36.

In this embodiment, the housing 36 is formed of an upper half-shell 80 and a lower half-shell 82 bent from the angle B. The housing 36 houses a printed circuit board 84, also bent from the angle B. The card 84 comprises a first portion P1 on which the encoder cell 50 is mounted and a second portion P2 on which the accelerometer 56 is mounted. The card 84 is for example rigid or is formed of a conformed flexible film to present an elbow at angle B.

The plane of the portion P1 of the card 84 forms with the horizontal plane OXY of the wheel 14ag the angle A. Thus, the portions P1 and P2 being inclined relative to each other of the angle B, the portion P2 on which is mounted the accelerometer 56 is substantially in a horizontal plane of the wheel 14ag.

Thus, the accelerometer 56 directly measures the vertical acceleration of the wheel 14ag and it is therefore not necessary to implement a filtering of its measurement.

As a variant, in the third embodiment, the housing 36 is a rectangular parallelepiped comprising appropriate support and / or fixing means for the bent printed circuit board 84.

Thus, a compact 22ag sensor is obtained, comprising a single housing and a limited number of electrical connections. Although there has been described a connection block 46 integrated in the sensor housing, alternatively, the connection block is remote at the information processing unit 24.

Fig. 7 is a schematic view of the information processing unit 24.

The unit 24 comprises, for each pair of wheels 14ag, 14rg, 14ad, 14rd arranged on the same side of the vehicle 10, a module 90, 92 for determining tire stiffness coefficients and magnitudes representative of the wheel radius. . The module 90, 92 receives sensors 22rg, 22ag, 22rd, 22ad corresponding to the vertical accelerations Avrg, Avag, Avrd, Avad measured of the pair of wheels and determines, according to these measurements, coefficients of stiffness Kprg, Kpag, Kprd, Kpad tires 20rg, 20ag, 20rd, 20ad of the pair of wheels.

The module 90, 92 also determines, as a function of the accelerations received, the operating points Pf rg, Pfag, Pf rd, Pfad of the wheels of the pair of wheels, that is to say the quantities representative of their radii, as will be explained in more detail later.

The unit 24 also comprises, for each of said pairs of wheels, a frequency determining module 94, 96 receiving corresponding sensors the electromagnetic pulses Icrg, Icag, Icrd, Icad, measured. This module 94, 96 is furthermore connected to the modules 90, 92 for determining the stiffness coefficients and the quantities representative of the radius of the wheels and determines, as a function of the inputs it receives, the frequencies fcrg, fcag, fcrd, fcad of the electromagnetic pulses. measured, as will be explained in more detail later.

Finally, the unit 24 comprises a diagnostic module 98 connected to the sensors 22rg, 22ag, 22rd, 22ad and the various modules 90, 92, 94, 96 mentioned above. The diagnostic module 98, according to the inputs it receives, the inflation state of each of the tires 20rg, 20ag, 20rd, 20ad and the operating state of each of the sensors 22rg, 22ag, 22rd, 22ad, like this. will be described in more detail later.

FIG. 8 illustrates a calculation hypothesis used by the modules 90, 92 to determine the stiffness coefficients of the tires. This figure shows the progress of a motor vehicle on a roadway between two instants t and t + Δt.

As illustrated in this figure, the front and rear wheels arranged on the same side of the vehicle undergo with a time shift Δt depending on the speed V and the wheelbase d of the vehicle, the same road profile. This phenomenon can be modeled according to the relation:

Zsa (t) = Zsr (t + Δt) (1) where t is the time, Δt is the time between the passage of the rear wheel on a point of the road, the passage of the front wheel on the same point, Zsa is the altitude of the ground at the level of the front wheel and Zsr is the altitude of the ground at the level of the rear wheel.

Figure 9 is a schematic view of a module 90, 92 for determining the stiffness coefficients and magnitudes representative of the radius of the wheels, for example the module 90 associated with the pair of wheels arranged on the left side of the vehicle. The module 90 described in relation with FIG. 9 corresponds to an embodiment associated with sensors 22ag, 22rg of the type described in relation with one of FIGS. 5 and 6.

The module 92 associated with the pair of wheels arranged on the right side is identical to the module 90. Among the pair of left wheels, there will be distinguished hereinafter the front wheel of the rear wheel.

The module 90 comprises an analog / digital converter 100, for example a 0-order sample-and-hold device, adapted to digitize according to a predetermined sampling period Te, for example between approximately 0.001 seconds and 0.02 seconds, the vertical accelerations Avrg , Avag and thus output numerical vertical accelerations of the front and rear wheels, where k represents the k ' ^th instant of sampling.

The sampler 100 is connected to a bandpass filter 102 adapted to process the digital accelerations delivered by the sampler 100 by applying bandpass filtering thereto. This filtering is implemented in a frequency range in which the power of the modes of the front and rear wheels is concentrated. This frequency range corresponds to the rolling resistance range and is for example substantially equal to the range [8; 20] Hz.

The module 90 also comprises time resetting means 104 connected to the filter 102. These means 104 temporally recalibrate the filtered numerical acceleration Avag (k) of the front wheel on the filtered numerical acceleration Avrg (k) of the rear wheel to deliver at the output of the accelerated accelerations Avrg (k), Avag (kn) of the front and rear wheels, corresponding to the same altitude of the ground in order to apply the hypothesis according to the relation (1) described above. These means 104 of registration include for this purpose means

Computing calculus estimating the digital intercorrelation IC (N) of the accelerations Avrg (k), Avag (k) delivered by the filter 102 according to the relation:

+ OO

IC (N) = ΣAvrg (k) xAvag (Nk) (2)

The calculation means 104 implement an estimator of this intercorrelation, as is known per se in the field of signal processing.

The resetting means 104 also comprise, connected to the calculation means 106, means 108 for determining the maximum of the intercorrelation IC (N) and the sampling instant n corresponding to this maximum. This instant n corresponds to the time shift nxTe between the front and rear wheels undergoing the same portion of roadway.

Time shift means 110 are connected to the means 108 and the filter 102, and apply a delay of n samples to the acceleration Avag (k) of the front wheel and deliver an acceleration Avag (kn) of the front wheel set back temporally on Avrg acceleration (k) of the rear wheel.

The module 90 also comprises means 112 for estimating the coefficients of pneumatic stiffness Kprg, Kpag of the front and rear wheels.

These means 112 are connected to the filter 102 to receive the accelerations

Avrg (k), Avag (k) filtered digital rear and front wheels and 110 resetting means for receiving acceleration Avag (kn) recalibrated the front wheel. The means 112 are based on the mechanical model of FIG. 10 to model the dynamic behavior of each of the front and rear wheels.

In this figure, there is illustrated a single-wheeled mechanical model of a wheel R of a four-wheeled motor vehicle, connected to the body C of the latter by means of a suspension Su, the wheel R being in contact with soil So.

The body C is modeled by a mass brought back to the wheel occupying me, on a vertical axis OZ of the vehicle of a reference system thereof, an altitude Z _c with respect to a reference level NRef, for example the altitude So soil at the front wheel when starting the vehicle.

The suspension Su is modeled by a stiffness coefficient spring Kc in parallel with damper damping coefficient Rc. The wheel R is modeled by a mass Mr occupying on the axis OZ an altitude Zr with respect to the reference level Nref. The tire of this latter is modeled by a stiffness coefficient spring Kp in contact with the ground So which occupies on the axis OZ an altitude Zs with respect to the reference level

Nref.

When the vehicle moves, the behavior of this mechanical system is controlled by the evolution over time of the altitude Zs of the ground. In the following, the letter "a" is added to the designations of the preceding quantities for the quantities associated with a front wheel, the letter

"R" is added to the previous designations for quantities associated with a rear wheel, the letter "g" is added to the previous quantity designations for the quantities associated with the left side of the vehicle, and the letter "d" is added to the designations of the previous quantities for the quantities associated with the right side of the vehicle.

Using the fundamental principle of dynamics applied to this model in relation to the hypothesis according to relation (1), the vertical accelerations Avrg (k), Avag (k) of the wheel centers are modeled in discrete time according to the relations: Avrg (k) = (3)

Avag (k) = ^ - (mrrgxAvrg (k ₊ n) Zvrg (k ₊ n) -Zvag (k)) f ^Kpag f ^V *? " ^{G (k)} l (4) mrag ^ Kpag (k) J where mrrg and mrag are the masses of the rear and front wheels respectively, and Zvrg and Zvag are the altitudes of the centers of the rear and front wheels respectively with respect to the reference level.

Referring again to FIG. 9, estimation means 112 are adapted to implement a recursive algorithm of least squares in real time based on relation (3), according to the relations: θ (k + 1) = θ (k) + K (k + 1) (Avτg (k + 1) - A (k + 1) θ (k)) (5)

K (k + 1) = 03 ^"1 S (k) X ^τ (k + 1) (σ ² (k) + 05 ^" 1At + 1) s (k) A ^τ (k + 1)) ^"1 (6)

S (k + I) = OJ- ¹ (S (k) -K (k + 1) A (k + 1) S (k)) (7)

X (k + 1) = E (A ^τ (k + I) λ 1)) T ¹ (8) σ (k) = Var (e (k)) (9)

where («) ^τ is the symbol of the transpose, θ (k) is the vector estimate

parameters at the instant k, A (k) is the vector of regression at moment k,

E (A ^τ (k) A (k)) is the variance of the vector A ^τ at time k, Var (e (k)) is the variance of the estimation error e (k) = Avrg (k ) -A (k) θ (k) at time k, 03 is a predetermined forgetting factor and κ (k), x (k) and S (k) are vectors or intermediate matrices used during estimation of the vector θ.

Preferably, the means 112 calculate the altitudes Zvrg (k), Zvag (kn) of the centers of the rear and front wheels at each sampling instant as a function of the vertical accelerations Avrg (k) and Avag (kn), for example by realizing a double integration of these after their filtering between 8 Hz and 20 Hz. Another example of a calculation of the altitude of a wheel in function of its vertical acceleration is described in the French patent application FR 2 858 267 in the name of the applicant.

In a variant, the estimation means 112 are adapted to implement a real-time least-squares recursive algorithm based on the relation (4) in a manner similar to that described above.

As a variant, the means 112 are suitable for implementing an inversion or deconvolution algorithm based on the relation (3) or (4) for estimating the stiffness coefficients.

The estimation means 112 are thus adapted to deliver at each sampling instant estimated values Kpag (k) and Kprg (k) of the pneumatic stiffness coefficients of the front and rear wheels.

Alternatively, the means 112 rely on another type of mechanical model to estimate the stiffness coefficients.

For example, alternatively, the system is based on the mechanical model shown in FIG. 11. FIG. 11 is a schematic view of a mechanical model generally referred to as a "bicycle model." This type of model allows in particular to take into account the case of active suspensions equipping the vehicle and applies to front and rear wheels arranged on the same side of the vehicle. The difference with the model of Figure 10 consists in the fact that the body C of the vehicle is likened to a mass suspended me on both the front wheel Ra and the rear wheel Rr.

Based on the fundamental principle of the dynamics applied to this bicycle model as well as the hypothesis according to relation (1), the vertical accelerations Avag (k), Avrg (k) of the front and rear wheels are modeled in discrete time according to the relationship :

where Zvaget Zvrg are the first derivatives of the altitudes of the centers of the front and rear wheels respectively, that is to say the speeds of vertical displacement thereof.

The estimation means 112 are then adapted to implement a recursive least squares algorithm in real time based on the relation (10).

This algorithm is analogous to the one previously described (relations (6) to (10)) with the parameter vector defined by the relation:

Kprg / Kpag Kprg

. (12)

((KKpprrgg // Kpag) x Kcag

Kcrg and the regression vector defined by the relation:

A (k) = ^IDra ^ Avag (k - n) -! - (Zvag (k - n) - Zvrg (k)) -! - Zvag (k - n) - -! - Zvrg (k) (13) I mrrg mrrg mrrg mrrg I

The elevations Zvrg (k), Zvag (k) of the centers of the wheels with respect to the reference level and their first derivatives Zvrg (k), Zvag (k -n) are calculated at each sampling step in a manner similar to the first embodiment, for example by integrating the corresponding vertical accelerations or in a manner described in the French patent application

FR 2,858,267.

As can be seen, the application of the recursive algorithm of the least squares in real time based on the bicycle model makes it possible to simultaneously estimate the pneumatic stiffness coefficients Kpag, Kprg as well as the stiffness coefficients Kcag and Kvrg of the suspensions .

Referring again to FIG. 9, the module 90 finally comprises means 114 for determining operating points connected to the means 112 for estimating the stiffness coefficients. The means 114 determine the operating points Pfrg, Pfag of each of the wheels

Towards the front and rear, and more particularly, the ratio - (k), - (k) of the ferg feag longitudinal speed Vcrg, Vcag of the wheel on the frequency ferg, feag of electromagnetic pulses encoding the rotational speed of the wheel. This ratio is proportional to the radius of the wheel and it is found that it is linked bijectively to the stiffness coefficient Kprg, Kpag of the tire of the wheel, as illustrated in FIG. 12. This FIG. 12 is a graph of a curve of the evolution, over a range P1, of the coefficient of stiffness of a tire of a wheel as a function of the evolution, over a range P2, of the ratio of the longitudinal speed of this wheel to the frequency of the encoding pulses the speed of rotation of the wheel. The ranges P1 and P2 corresponding to the values that can physically take these two quantities. The means 114 for determining comprises a predetermined mapping of ratio values as a function of stiffness coefficient values. The means 114 evaluate, at each instant of sampling, this map for each of the coefficients of stiffness estimated by the means.

To Vcag

112 to determine the ratio - (k), - (k) corresponding. FIG. 13 is a schematic view of a module 94, 96 for determining the frequencies of the electromagnetic pulses, for example the module 94 associated with the pair of wheels arranged on the left side of the vehicle.

The module 96 associated with the pair of wheels arranged on the right side is identical to the module 94.

The module 94 comprises a clock 120 delivering a clock signal CIk of predetermined period TO, for example equal to 7 milliseconds, and means 122, 124 for determining the frequency fcrg, fcag measured pulses associated with each of the rear wheels and before 14rg, 14ag. The means 122 and 124 are identical.

By considering for example the means 122 associated with the left rear wheel 14rg, these comprise means 126 for determining the period of time connected to the clock 120 and receiving the electromagnetic pulses Irg measured from the sensor 22rg associated with the rear wheel 14rg. . The means 126 determine for each period of time TO defined by two successive rising edges of the clock signal CIk, a period of time comprising an integer number of electromagnetic pulses.

Fig. 14 is a timing diagram of measured electromagnetic pulses Irg and clock signal CIk. As illustrated in this figure, the time period TO does not necessarily include an integer number of pulses due to the asynchrony between the measured pulses and the clock signal CIk.

The means 126 take account of this fact by calculating, for the period of time TO, a period TO + Δrg, with Δrg = (T1-T2), where T1 is the period separating the rising edge beginning the period TO from the front of the just preceding pulse this rising edge and T2 the period of time separating the rising edge ending the TO period from the pulse front just preceding this rising edge. The period of time TO + Δrg thus comprises an integer number of pulses. The period of time Δrg will be referred to hereinafter as "address".

The means 122 also comprise means 128 connected to the means 126 for determining the period TO + Δrg, receiving the measured pulses Irg and counting the number of pulses present in the period TO + Δrg. The counting means 122 are connected to selection means 130. The selection means 130 are also connected to the modules 90, 92 for determining the stiffness coefficients and the operating points of the wheels and to the diagnostic module 98. The means 130 receive from these the operating point Pfrg of the left rear wheel 14rg, the operating point of the wheel mounted on the same axle as the left rear wheel, that is to say here the operating point. Pfrd of the right rear wheel 14rd, the operating point of the wheel located diagonally of the left rear wheel 14rg, that is to say here the operating point Prad of the front right wheel 14ad, and a selection signal DC of an operating point among the operating points received by the means 130.

The DC signal is delivered by the diagnostic module 98 and lists the sensors whose accelerometer portion is defective. By default, means 130 select the operating point Pfrg of the left rear wheel. If the accelerometer portion of the sensor associated with the left rear wheel is defective, the means 130 select one or other of the other operating points. The means 130 also select, according to the selected operating point and the number of pulses Irg counted in the time period TO + Δrg, one of a predetermined set of abacuses. As can be seen in FIG. 15, which illustrates a set of pulse frequency charts fc as a function of address values Δ, or in an equivalent manner as a function of value of period T0 + Δ, it can be seen that the frequency fc electromagnetic pulses delivered by a sensor is an affine function of the address Δ associated therewith for an operating point and a given number of counted pulses.

The selection means 130 includes, for each value of one or other of the other operating points of a predetermined set of operating points, a predetermined set of lines. Each of these lines is associated with a predetermined value of number of pulses. The means 130 select the set of lines associated with the selected operating point and then the right of this set associated with the number of pulses counted. The charts of the means 130 are for example stored therein in the form of maps.

Referring again to FIG. 13, the means 122 for determining the frequency fcrg comprise frequency calculation means 132 connected to the selection means 130 for receiving the selected chart and to the means 126 for determining the period TO + Δrg to receive the address Δrg. The means 132 calculate the frequency fcrg of the pulses delivered by the sensor 22rg associated with the left rear wheel 14rg by evaluating the nomogram selected for the address Δrg received.

FIG. 16 is a schematic view of the diagnostic module 98 of the unit 24 of FIG. 7.

The module 98 comprises first comparison means 150 connected to the modules 94, 96 for determining the frequencies frcag, fcad, fcrg, fcrd and comparing these frequencies with each other. If the means 150 determine that these frequencies differ in absolute value by more than a first predetermined threshold value, the means 150 emit a first diagnosis of underinflation of the tire or tires associated with the lowest frequencies. For example, if three frequencies are substantially equal and the fourth frequency is smaller than the absolute value of more than the first threshold value, the means 150 emit that the tire associated with this fourth frequency is underinflated.

The comparison means 150 also compares each of the frequencies with a second predetermined threshold value. The means 150 emit as a first diagnosis that the tires are all underinflated if all the frequencies frcag, fcad, fcrg, fcrd are lower than the second threshold value.

The diagnostic module 98 also comprises second comparison means 152 connected to the modules 90, 92 for determining the stiffness coefficients and the quantities representative of the radius of the wheels for receiving the coefficients of stiffness Kprg, Kpag, Kprd, Kpad and comparing these. between them. If the means 152 determines that these coefficients differ in absolute value by more than a third threshold value, they emit a second diagnosis of underinflation of the tire or tires associated with the lowest coefficients.

Means 152 also compare each of Kprg, Kpag, Kprd, Kpad coefficients to a fourth predetermined threshold value. The means 152 emit as a second diagnosis that the tires are all underinflated if all the coefficients Kprg, Kpag, Kprd, Kpad are lower than the fourth threshold value.

The first means 150 and the second means 152 are connected to means 154 for diagnosing the state of inflation of the tires. These means 154 diagnose that a tire is underinflated if the first and the second diagnosis made by the first and second means 150, 152 of comparison coincide.

The module 98 also comprises, for each pair of wheels arranged on the same side of the vehicle, means 156, 158 for diagnosing the accelerometer portion of the sensors 22ag, 22ad, 22rg, 22rd associated with the pair of wheels.

By considering, for example, the means 156 associated with the pair of left wheels of the vehicle, these test the consistency of the accelerations Avrg (k) and Avag (k) with each other over a predetermined period of time, for example between 5 minutes and 10 minutes. As previously described, it is known that the vertical accelerations of the front and rear wheels are consistent because the wheels undergo the same portion of roadway with a time shift. For example, the means 156 calculate the frequency spectra of these accelerations by means of a fast Fourier transform of the accelerations included in the predetermined period of time and compare the calculated spectra. If these differ by more than a predetermined value, for example in quadratic error, then the accelerometers of the sensors 22ag, 22rg are diagnosed as defective by the means 156.

The diagnostic module 98 also comprises, for each pair of wheels arranged on the same side of the vehicle, means 160, 162 for diagnosing the speed encoding part of the sensors 22ag, 22ad, 22rg, 22rd associated with the pair of wheels. These means 160, 162 are analogous to the means 156, 158 for diagnosing the accelerometer portion of the sensors and test the frequency coherence frequency frcag, fcad, fcrg, fcrd pulses measured by the sensors associated with the pair of wheels. The means 156, 160 diagnose a failure of the speed encoding part of these sensors if these frequencies are not coherent.

For more robustness in the diagnosis of the operating state of the accelerometers of the sensors 22ag, 22rg, as a variant, the means 156 for diagnosing the accelerometer portion of the sensors associated with the pair of left wheels, and correspondingly the means 158 associated with the right wheel pair, are further adapted to predict the vertical acceleration of the left rear wheel as a function of the measured vertical acceleration of the left front wheel from the relation (4) by varying the instant n sampling. The means 156 test the coherence between this predicted acceleration of the rear wheel and the acceleration of the front wheel measured for example in the manner described above.

If, moreover, the coherence between these accelerations is not proven, then the means 156, 158 diagnose a malfunction of the accelerometers of the sensors 22ag, 22rg.

The diagnostic module 98 also comprises, for each pair of wheels arranged on the same side of the vehicle, means 160, 162 for diagnosing the speed encoding part of the sensors 22ag, 22ad, 22rg, 22rd associated with the pair. of wheels. The diagnostic module 98 finally comprises, connected to the means

156, 158 of the accelerometer portion of the sensors, means 164 for forming the DC signal listing the sensors whose part accelerometers is diagnosed as defective.

Although it has been described a motor vehicle wheel, it will be understood that the invention applies to any type of vehicle wheels, for example a motorcycle, multi-train vehicle (truck), or others.

Similarly, although a sensor encoding a rotational speed in the form of magnetic pulses has been described, alternatively, the sensor comprises an optical encoder comprising a toothed disk associated with means for emitting a light beam. disposed opposite the sensor housing on the other side of the disc and the encoder cell is adapted to measure changes in brightness caused by the successive passage of the teeth of the disc.

Claims

Apparatus for measuring a representative quantity of the speed of rotation of a wheel (14ag, 14ad, 14rg, 14rd) of a vehicle, of the type comprising:

means (32, 50) for encoding the speed of rotation of the wheel in the form of electromagnetic pulses;

means (50) for measuring said pulses;

means (126) for determining a period of time comprising an integer number of said pulses; and

means (128) for counting the integer number of pulses during this period of time, characterized in that it comprises:

means (90, 92) for determining a magnitude representative of the radius of the wheel; and

means (94, 96) for determining said quantity as a function of the integer number of pulses, the period of time and the magnitude representative of the radius of the wheel.

2. Device according to claim 1, characterized in that the representative amount of the speed of rotation of the wheel is the frequency of the electromagnetic pulses encoding said speed.

3. Device according to claim 1 or 2, characterized in that the means (90, 92) for determining the magnitude representative of the radius of the wheel comprise means (56) for acquiring vertical accelerations in a reference system of the vehicle the wheel and another wheel arranged on the same side of the vehicle as the latter and means (104, 112) for estimating a stiffness coefficient of a tire mounted on the wheel.

4. Device according to claim 3, characterized in that the means (104, 112) of estimation comprise means (104) of time registration of one of the accelerations acquired on the other accelerations acquired.

5. Device according to claim 3 or 4, characterized by the means

(104, 112) of estimating the stiffness coefficient are able to estimate it from a single-wheel mechanical model of said wheels connected to a vehicle body by means of suspensions and comprising tires comparable to springs characterized by coefficients of stiffness.

6. Device according to claim 5, characterized in that the stiffness coefficient estimating means are adapted to estimate it by relying on a discrete time modeling of the recalibrated accelerations of the wheel and the other wheel according to the invention. the relationship :

Avr (k) = where k is the k ^th sampling instant, mrr is the mass of the rear wheel from the wheel and the other wheel, MRA is the mass of the front wheel from the wheel and the other wheel, Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and before respectively in the vehicle reference system, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, and n is a moment of registration corresponding to a time shift between said rear and front wheels undergoing the same portion of roadway.

7. Device according to claim 5, characterized in that the means for estimating the stiffness coefficient are adapted to estimate it based on a discrete time modeling of the recalibrated accelerations of the wheel and the other wheel according to the relationship :

Ava (k) = where k is the k ^th sampling instant, mrr is the mass of the rear wheel from the wheel and the other wheel, MRA is the mass of the front wheel from the wheel and the other wheel, Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and before respectively in the vehicle reference system, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, and n is a moment of registration corresponding to a time shift between said rear and front wheels undergoing the same portion of roadway.

8. Device according to claim 3 or 4, characterized in that the estimating means are adapted to estimate the coefficient of stiffness from a bicycle mechanical model of a vehicle body assimilated to a mass connected to the wheel and to the other wheel by means of suspensions, the wheel and the other wheel comprising tires similar to springs characterized by coefficients of stiffness.

9. Device according to claim 8, characterized in that the means for estimating the stiffness coefficient are able to estimate it based on a discrete time modeling of the recalibrated accelerations of the wheel and the other wheel according to the relationship: mra

Ava (k -n) mrr Kpr (k) / Kpa (k)

- (Zva (k - n) - Zvr (k))

Avr (k) = mrr Kpr (k)

- Zva (k - n) (Kpr (k) / Kpa (k)) xKca (k) mnr Kcr (k)

Zvr (k) mrr where k is the k ' ^th moment of sampling, mrr is the mass of the rear wheel among the wheel and the other wheel, mra is the mass of the front wheel among the wheel and the other wheel , Avr and Ava are the vertical accelerations of said rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of said rear wheels and respectively respectively in a reference system of the vehicle, Kpr and Kpa are the stiffness coefficients of the tires of said front and rear wheels respectively, n is a time of registration corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway, Kca and Kcr are coefficients of stiffness suspensions of said front and rear wheels respectively, and Zva and Zvr are the speeds vertical displacement of the centers of said front and rear wheels respectively.

10. Device according to any one of claims 3 to 9, characterized in that the means for estimating the stiffness coefficient are adapted to implement a recursive least squares algorithm in real time.

11. Device according to any one of claims 3 to 10, characterized in that the magnitude representative of the radius of the wheel is a number function of the ratio of the longitudinal speed of the wheel to the frequency of said pulses, and in that the means (90, 92) for determining this magnitude comprise means (114) for estimating said number as a function of the estimated stiffness coefficient of the tire of the wheel.

12. Device according to any one of the preceding claims, characterized in that the means (94, 96) for determining the amount representative of the speed of rotation of the wheel comprises means (130) for selecting an abacus d. a predetermined set of abacuses as a function of the determined quantity representative of the radius of the wheel and the number of pulses counted and means (132) for estimating said quantity by evaluating the abacus selected for the determined period of time .

13. A system for determining the state of tires of the wheels of a vehicle, characterized in that it comprises:

- A device according to any one of the preceding claims associated with each wheel of the vehicle and delivering a representative amount of the speed of rotation of the wheel; and means (98) for diagnosing the condition of the tires of the wheels of the vehicle according to said delivered quantities.

System according to claim 13, characterized in that the diagnostic means (98) are suitable for diagnosing a tire as underinflated when the quantity associated with it is less than a first predetermined value by at least a quantity associated with other tires.

15. System according to claim 14 and comprising a device according to any one of claims 3 to 10 associated with each wheel of the vehicle, characterized in that the devices are able to further deliver the estimated stiffness coefficients of the wheels, and in that the diagnostic means (98) are suitable for diagnosing the tire as underinflated if, in addition, its estimated stiffness coefficient is smaller by more than one second predetermined value to at least one estimated stiffness coefficient of the other tires.

16. System according to claim 13, 14 or 15, characterized in that the diagnostic means (98) are adapted to diagnose under-inflation of the wheels of the vehicle if said delivered quantities are less than a first predetermined threshold value.

17. System according to claims 15 and 16, characterized in that the diagnostic means are adapted to diagnose under-inflation of the wheels of the vehicle if further said delivered coefficients are less than a second predetermined threshold value.

18. A method for measuring a representative quantity of the speed of rotation of a vehicle wheel, of the type comprising:

a step of encoding the speed of rotation of the wheel in the form of electromagnetic pulses; a step of measuring said pulses;

a step of determining a time period comprising an integer of said pulses; and

a step of counting the integer number of pulses during this period of time, characterized in that it comprises:

a step of determining a magnitude representative of the radius of the wheel; and

a step of determining said quantity as a function of the integer number of pulses, the period of time and the magnitude representative of the radius of the wheel.

19. A method for determining the state of tires of the wheels of a vehicle, characterized in that it comprises:

a method according to claim 18 for each wheel of the vehicle and delivering a representative quantity of the speed of rotation of the wheel; and

a step of diagnosing the condition of the tires of the wheels of the vehicle according to said delivered quantities.