EP1907227A2

EP1907227A2 - System for determining inflating pressures of tyres mounted on a motor vehicle wheels

Info

Publication number: EP1907227A2
Application number: EP06779017A
Authority: EP
Inventors: Zahir Djama
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2005-07-26
Filing date: 2006-07-05
Publication date: 2008-04-09
Also published as: WO2007012772A3; US20080177498A1; WO2007012772A2; FR2889112B1; FR2889112A1; US7657393B2

Abstract

The invention concerns a system for determining inflating pressures of tyres mounted on a motor vehicle wheels, said system comprising means (12, 14) for acquiring vertical accelerations of a front wheel and of a rear wheel of the vehicle and means (34) for estimating coefficients of stiffness of the tyres of said wheels based on the acquired accelerations. Said system is characterized in that it comprises means (26) for temporal resetting of one of the acquired accelerations on another of the acquired accelerations, and in that the estimation means (34) are adapted to estimate said coefficients of stiffness based on the thus temporally reset accelerations.

Description

System for determining the inflation pressure of tires mounted on motor vehicle wheels

The present invention relates to a system for determining the inflation pressure of tires mounted on motor vehicle wheels.

Such systems are known in the state of the art which use the vertical acceleration of one or more wheels of the vehicle to determine the stiffness coefficients of the tires thereof, and their inflation pressures from these coefficients.

However, these systems determine the profile of the roadway to determine the coefficients of stiffness, which poses problems of precision because of the imperfect reconstruction of this profile.

The invention aims to solve these problems by proposing a system of the aforementioned type that does not use a reconstruction of the road profile to calculate the tire inflation pressure.

To this end, the subject of the invention is a system for determining the inflation pressure of tires mounted on motor vehicle wheels, the system comprising: means for acquiring the vertical accelerations of a front wheel and of a rear wheel of the vehicle; and

means for estimating coefficients of stiffness of the tires of these wheels as a function of the accelerations acquired, characterized in that it furthermore comprises means for time registration of one of the accelerations acquired on the other of the accelerations acquired, and in that the estimation means are adapted to estimate said stiffness coefficients as a function of the accelerations thus time-corrected.

According to particular embodiments, the system comprises one or more of the following characteristics:

the means of time registration comprise means for calculating the intercorrelation of the accelerations acquired and means for applying a delay corresponding to the maximum of the calculated correlation to the acceleration gained from the front wheel; the estimation means are adapted to implement a recursive least squares algorithm in real time to estimate said stiffness coefficients;

the estimation means are adapted to implement an inversion or deconvolution algorithm for estimating said stiffness coefficients;

the system further comprises means for bandpass filtering the acquired accelerations arranged between means for acquiring the accelerations and the time resetting means; the band-pass filtering means are adapted to implement a filtering in a frequency range substantially equal to [8, 20] Hz;

the estimation means are adapted to estimate said stiffness coefficients from a single-wheel mechanical model of the front and rear wheels; the estimation means are capable of estimating said stiffness coefficients based on discrete time modeling of the corrected accelerations of the front and rear wheels according to the relation:

Avr (k) = where k is the k ^th time of sampling, ^Avr and Ava are the vertical accelerations of the rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of the rear wheels and respectively before, Kpr and

Kpa are the stiffness coefficients of the tires of the front and rear wheels respectively, and n is a sampling instant corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway;

the estimation means are capable of estimating said stiffness coefficients based on discrete time modeling of the corrected accelerations of the front and rear wheels according to the relation:

Ava (k) = where k is the kth sampling time, Avr and Ava are the vertical accelerations of the rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of the rear and front wheels respectively, Kpr and Kpa are the stiffness coefficients of the tires of the front and rear wheels respectively, and n is a sampling instant corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway;

the estimation means are adapted to estimate said stiffness coefficients from a bicycle mechanical model thereof;

where k is the kth sampling time, Avr and Ava are the vertical accelerations of the rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of the rear wheels and before respectively, Kpr and Kpa are the coefficients of stiffness of the front and rear wheel tires respectively, n is a sampling instant corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway, Ra and Rr are stiffness coefficients of the front and rear wheel suspensions respectively, and Zva and Zvr are the first derivatives of the altitudes of the centers of the front and rear wheels respectively;

- It further comprises means for diagnosing the operating state of the means for acquiring vertical accelerations of the rear front wheels adapted to diagnose the operating state thereof by testing their consistency over a predetermined period of time;

the means are adapted to calculate the frequency spectra of the accelerations delivered by the acquisition means, to compare these spectra and to diagnose a defective state of the acquisition means if the spectra differ by more than a predetermined value; and

- The diagnostic means are further adapted to predict one of the accelerations of the front and rear wheels depending on the other of these accelerations delivered by the acquisition means and to diagnose a defective state of the acquisition means if furthermore the predicted acceleration and the acceleration used for this prediction are not coherent.

The invention will be better understood on reading the following description, given solely by way of example and with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a mechanical model used in a first embodiment of a system according to the invention;

FIG. 2 is a diagram illustrating the calculation hypothesis used by the system according to the invention;

FIG. 3 is a schematic view of a first embodiment of the system according to the invention;

FIG. 4 is a schematic view of a second mechanical model used by a second embodiment of a system according to the invention; and - Figures 5 to 7 are graphs of temporal variation of the pneumatic stiffness coefficients of front and rear wheels estimated by the system according to the invention.

The system according to the invention is based on a mechanical model of the interactions between the body C of a vehicle, mass Mc, the wheels R thereof and the ground S.

A first example of mechanical modeling of these interactions is illustrated in FIG. 1, which is a schematic view of a "single-wheel" type of model, of the interactions between a vehicle wheel Ro, the vehicle body C and the vehicle. As shown in this figure, in this model with two degrees of freedom, the body C of the vehicle is likened to a mass Mc suspended from the wheel Ro mass Mr by a suspension Su assimilated to a spring / damping stiffness Kc and damping coefficient R.

The wheel Ro and the body C move in a vertical direction and occupy respective attitudes Zr and Zc with respect to a reference level, for example the altitude of the ground when the vehicle is started.

The wheel Ro carries a pneumatic tire Pn resting on the ground S and similar to a stiffness spring K composed of a spring modeling the tire envelope Pn of structural stiffness Ks in parallel with a spring Modeling the gas contained in the pneumatic stiffness tire Kp, all in series with a spring modeling the gum of the tire of rubber stiffness Kg.

The behavior of this mechanical system is controlled by the evolution over time of the altitude Zs of the ground relative to the reference level, that is to say the profile of the roadway.

It is also known that the inflation pressure Pg of the tire is directly related to the pneumatic stiffness Kp thereof, this dependence being for example modeled according to the relation:

where c and α are predetermined constants, for example substantially equal to 6.7 and 0.85 respectively for a given tire.

The system according to the invention is also based on the following observation presented in FIG. 2 which illustrates the progress of a vehicle on a roadway between two instants t and t + Δt.

As illustrated in this figure, the front and rear wheels of the vehicle undergo, most of the time, with a time shift Δt depending on the speed V and the wheelbase of the vehicle, the same road profile. The system according to the invention is then advantageously based on the following relationship to determine the stiffness coefficients of the tires and therefore the inflation pressure thereof, as will appear in more detail below:

Z _sa (t) = Z _sr (t + Δt) (2) where t is the time, Δt is the time between the passage of a rear wheel on a point of the road, the passage of a front wheel on this same point, Z _sa is the ground altitude at the front wheel and Z _sr is the ground altitude at the rear wheel.

FIG. 3 schematically illustrates, under the general reference 10, a first embodiment of the system according to the invention for determining the inflation pressure of the tires mounted on a wheel. front and a rear wheel of a motor vehicle, arranged on the same side thereof.

This system 10 comprises an accelerometer 12, 14 fitted to each of these wheels to measure the vertical acceleration Avr, Ava thereof at its center. This accelerometer 12, 14 is for example a single-axis accelerometer or tri-axis mounted in the center of the wheel and comprising means 16, 18 forming a transmission antenna for the delivery of a high frequency electromagnetic signal representative of the vertical acceleration Apr, Ava in the center of the wheel. Receiving antenna means 20 are provided in the system 10 for receiving the signals emitted by the accelerometers 12, 14 and extracting from these signals the accelerations Avr, Ava measured by them.

The means 20 are connected to a bandpass filter 22 adapted to process the accelerations Avr, Ava of the wheels delivered by the means 20 by applying a band-pass filtering. 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 bandpass filter 22 is moreover connected to an analog / digital converter 24, for example an order 0, a buffer sampler adapted to digitize at a predetermined sampling frequency fe, for example between about 50 Hz and 1000 Hz. , filtered accelerations and thus outputting digital acceleration Avr (k), Ava (k) of the front and rear wheels, where k represents the k sampling instant ^ιeme. Of course, a different arrangement of the elements just described is possible. The sampling of the accelerations may be, for example, applied previously to a bandpass filtering performed in discrete time.

The system 10 according to the invention also comprises means 26 of time registration connected to the converter 24 and adapted to time shift the digital acceleration Ava (k) of the front wheel on the digital acceleration Avr (k) of the rear wheel for outputted accelerations Avr (k), Ava (k -n) of the front and rear wheels, corresponding to the same altitude of the ground in order to apply the hypothesis according to the relation (2) described above.

These adjustment means 26 comprise, for this purpose, calculation means 28 adapted to estimate the digital intercorrelation IC (N) of the accelerations Avr (k), Ava (k) delivered by the converter 24 according to the relation:

+ OO

IC (N) = ΣAvr (k) xAva (N -k) (3) k = -oo

The calculation means 28 are adapted to implement an estimator of this cross-correlation, as is known per se in the field of signal processing. The retiming means 26 also comprise, connected to the calculation means 28, means 30 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 difference between the front and rear wheels undergoing the same portion of roadway. Time-shift means 32 are connected to the means 30 and to the converter 24, and are suitable for applying a delay of n samples to the acceleration Ava (k) of the front wheel and thus to deliver an acceleration Ava (kn) set back temporally on the acceleration Avr (k) of the rear wheel.

The system 10 further comprises means 34 for estimating the pneumatic stiffness coefficients Kpn, Kpa of the front and rear wheels. These means 34 are connected to the converter 24 to receive the accelerations

Avr (k), Ava (k) of the rear and front wheels and the means 26 of registration for receiving the acceleration Ava (k-n) recaled the front wheel. The means 34 are suitable for estimating said coefficients of stiffness Kpa, Kpn as a function of the accelerations they receive.

The means 34 are based on the mechanical model of Figure 1 to model the dynamic behavior of the front and rear wheels.

More particularly, using the fundamental principle of dynamics applied to this model in relation to the hypothesis according to the relation (2), it can be shown that the vertical accelerations Avr (k), Ava (k) of the wheel centers can be modeled in discrete time according to the relations:

Avr (k) = (4)

Ava (k) = (5) where mrr and mra are the masses of the rear and front wheels respectively, and Zvret Zva are the altitudes of the centers of the rear and front wheels respectively with respect to the reference level.

The estimation means 34 are adapted to implement a recursive algorithm of least squares in real time based on the relation (4), according to the relations: θ (k + 1) = θ (k) + K (k + 1) ) (Avr (k + 1) - A (k + 1) θ (k)) (6)

K (k + l) = 05 ^{~ 1} S (k) X ^τ (k + l) (σ ² (k) + Oi ^"1 A (k + l) s (k) ^τ (k + l)) ^{~ 1} (7) S (k + I) = OJ ^{- 1} (S (k) - K (k + 1) A (k + 1) s (k)) (8)

X (k + l) = E (A ^τ (k + l ^ k + l) ^ ¹ (9) σ (k) = Var (e (k)) (10) where (») ^τ is the symbol of the transposed, θ (k) is the vector estimate

parameters θ = at time k, A (k) is the regression vector at the instant 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) = Avr (k) -A (k) θ (k) at the moment k, 05 is a predetermined forgetting factor and κ (k), x (k) and s (k) are vectors or intermediate matrices used in estimating the vector θ.

Preferably, the means 34 are capable of calculating the altitudes Zvr (k), Zva (k -n) of the centers of the rear wheels and before each sampling instant as a function of the vertical accelerations Avr (k) and Ava (k - n), for example by carrying out 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.

Alternatively, the estimation means 34 are adapted to implement a recursive least squares algorithm in real time based on the relation (5) in a manner similar to that described above.

In a variant, the means 34 are suitable for implementing an inversion or deconvolution algorithm based on the relation (4) or (5) for estimating the stiffness coefficients.

The estimation means 34 are thus adapted to deliver at each sampling instant estimated values Kpa (k) and Kpr (k) of the pneumatic stiffness coefficients of the front and rear wheels.

The system 10 also comprises means 36 for determining the inflation pressure Pa (k), Pr (k) of the tires of the front and rear wheels connected to the estimating means 34. These means 36 receive the estimated values Kpa (k) and Kpr (k) and are adapted to calculate, as a function of these, the inflation pressures Pa (k) and Pb (k) of the front and rear wheels, for example from of the relation (1).

For example, the inflation pressures Pa and Pr are tabulated in the means 36 as a function of the pneumatic stiffness coefficients Kpa and Kpn respectively, or the means 36 are adapted to evaluate the function according to the relation (1) as a function of the values of the coefficients. of stiffness that they receive.

The system 10 finally comprises means 40 for diagnosing the state of inflation of the tires of the front and rear wheels. These means 40 are for example connected to the estimation means 34, the converter 24 and the determination means 36 for receiving the estimated stiffness coefficients, the vertical accelerations Avr (k), Ava (k) of the rear and front wheels and the inflation pressures Pa (k), Pr (k) and are adapted to determine, according to these, the operating state of the accelerometers 12, 14 as well as the inflation state of the tires (under-inflation, over-inflation , puncture ...). More particularly, the means 40 comprise means 42 for diagnosing the operating state of the accelerometers adapted to test the coherence of the accelerations Avr (k) and Ava (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 42 are adapted to 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 to compare the calculated spectra. If these differ by more than a predetermined value, for example in quadratic error, then the accelerometers are diagnosed as defective by the means 42. For more robustness in diagnosing the operating state of the accelerometers, alternatively, the means 42 are further adapted to predict the vertical acceleration of the rear wheel as a function of the vertical acceleration of the front wheel delivered by the converter 24 and the stiffness coefficients of the front and rear wheels calculated by the means 34, to from relation (4) by varying the sampling instant n. The means 44 are also adapted to test the coherence between this predicted acceleration of the rear wheel and the acceleration of the front wheel delivered by the converter 24, for example in the manner previously described for the accelerations delivered by the converter 24. If, in addition, the coherence between these accelerations is not proven, then the means 42 diagnose a malfunction of the accelerometers 12, 14.

The means 40 also comprise means 44 for diagnosing the state of inflation of the tires as a function of the inflation pressures Pa (k), Pr (k) estimated.

For example, the means 44 are able to compare each of these pressures to a predetermined set of pressure intervals each representative of a state of inflation of the tire (puncture, under-inflation, normal inflation, over-inflation). The means 44 thus determine the state of inflation of the tire associated with this pressure as a function of the membership of the latter at one of the pressure intervals.

The means 40 may furthermore comprise means for supplying the driver of the vehicle with this information, for example light indicators arranged on the dashboard of the vehicle and / or audible warning of incorrect tire inflation or defective condition of accelerometers.

It has just been described an embodiment based on a single-wheel mechanical model of a motor vehicle wheel as shown in Figure 1.

Other embodiments of the system according to the invention based on other models are of course possible. Such embodiments are structurally identical to that illustrated in FIG. 3, only the algorithm implemented by the estimation means 34 being modified.

For example, alternatively, the system is based on the mechanical model shown in Figure 4. Figure 4 is a schematic view of a mechanical model generally referred to as the "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 1 consists in the fact that the body C of the vehicle is likened to a mass Mc suspended both on the front wheel Roa and the rear wheel Ror.

Based on the fundamental principle of the dynamics applied to this bicycle model as well as the hypothesis according to relation (2), it can be shown that the vertical accelerations Ava (k), Avr (k) of the front and rear wheels are Modeling in discrete time according to the relation: mra

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

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

Avr (k) = mrr (H)

Zva (k -n) (Kpr (k) / Kpa (k)) xRa (k) mnr Rr (k)

1

Zvr (k) mrr where Ra and Rr are stiffness coefficients of the suspensions of the front and rear wheels respectively, and Z va and Zv are the first derivatives of the altitudes of the centers of the front and rear wheels respectively, i.e. speeds of vertical displacement thereof. The estimation means 34 are then adapted to implement a recursive algorithm of the least squares in real time based on the relation (11).

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

Kpr / Kpa Kpr θ = (12)

((KKpprr // Kpa) x Ra

Rr and the regression vector defined by the relation:

A (k) =

The elevations Zvr (k), Zva (k -n) of the centers of the wheels relative to the reference level and their first derivatives Zvr (k), Zva (k -n) are calculated at each sampling step in a manner analogous 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 least squares recursive algorithm in real time based on the bicycle model can simultaneously estimate the pneumatic stiffness coefficients Kpa, Kpr and the stiffness coefficients Ra and Rr suspensions.

Examples of estimation of the stiffness coefficients Kpa, Kpr of the front and rear wheels by the first embodiment of the system according to the invention are illustrated in the graphs of FIGS. 5 to 7.

FIGS. 5A and 5B are graphs of temporal variations of the pneumatic stiffness coefficients Kpa, Kpr of the front and rear wheels arranged on the left side of the vehicle and the front and rear wheels arranged on the right side of the vehicle respectively, the tires of the wheels. front of the vehicle being inflated to a pressure of 2.4 bar, the tire of the left rear wheel being inflated to a pressure of 3 bar and the tire of the right rear wheel being inflated to a pressure of 2.4 bar. FIG. 6 is a graph of temporal variations of the pneumatic stiffness coefficients Kpa, Kpr of the front and rear wheels arranged on the right side of the vehicle, the tires of which are initially inflated to a pressure of 2.5 bars and the tire of the front wheel undergoing a pressure drop of 4 mbar / s over 400 s from time t = 300s.

FIG. 7 is a graph of the temporal variations of the pneumatic stiffness coefficients Kpa, Kpr of the front and rear wheels arranged on the right side of the vehicle, the tires of which are initially inflated to a pressure of 2.5 bars and the tire the front wheel undergoing a pressure drop of 1, 6 bar quasi-instant, here over a period of 1s at time t = 300s.

It is then conceivable that the system according to the invention reliably determines the pneumatic stiffness coefficients and the associated inflation pressures. It has been described a system according to the invention applied to a pair of front and rear wheels of a motor vehicle arranged on the same side thereof. Of course, it will be understood that this system can also be applied to each pair of front and rear wheels arranged on the same side of the vehicle.

Claims

1. A system for determining the tire pressure of tires mounted on motor vehicle wheels, the system comprising:

means (12, 14) for acquiring the vertical accelerations of a front wheel and a rear wheel of the vehicle; and

means (34) for estimating stiffness coefficients of the tires of these wheels as a function of the accelerations acquired, characterized in that it furthermore comprises means (26) for temporal registration of one of the accelerations acquired on the other accelerations acquired, and in that the estimating means (34) are adapted to estimate said stiffness coefficients as a function of the accelerations thus adjusted in time.

2. System according to claim 1, characterized in that the means

(26) comprise means (28) for calculating the intercorrelation of the acquired accelerations and means (30, 32) for applying a delay corresponding to the maximum of the calculated intercorrelation to the acquired acceleration of the front wheel.

3. System according to any one of the preceding claims, characterized in that the estimation means (34) are adapted to implement a recursive least squares algorithm in real time to estimate said stiffness coefficients.

4. System according to any one of claims 1 to 3, characterized in that the estimating means (34) are adapted to implement an inversion or deconvolution algorithm for estimating said stiffness coefficients.

5. System according to any one of the preceding claims, characterized in that it further comprises means (22) for bandpass filtering acquired accelerations arranged between means (12, 14) for acquisition accelerations and the means (26) for time registration.

6. System according to claim 5, characterized in that the means (22) bandpass filter are adapted to implement a filter in a frequency range substantially equal to [8, 20] Hz.

7. System according to any one of the preceding claims, characterized in that the estimation means (34) are adapted to estimate said stiffness coefficients from a single-wheel mechanical model of the front and rear wheels.

8. System according to claim 7, characterized in that the means

(34) are able to estimate said stiffness coefficients based on discrete time modeling of the recalibrated accelerations of the front and rear wheels according to the relation:

Avr (k) = where k is the k ^th time of sampling, ^Avr and Ava are the vertical accelerations of the rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of the rear and front wheels respectively, Kpr and Kpa are the stiffness coefficients of the tires front and rear wheels respectively, and n is a sampling time corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway.

9. System according to claim 7, characterized in that the estimating means (34) are adapted to estimate said stiffness coefficients based on a discrete time modeling of the recalibrated accelerations of the front and rear wheels according to the relation:

Ava (k) = where k is the kth sampling time, Avr and Ava are the vertical accelerations of the rear and front wheels respectively, Zvr and Zva are the altitudes of the centers of the rear wheels and before respectively, Kpr and Kpa are the coefficients of stiffness of the tires of the front and rear wheels respectively, and n is a sampling instant corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway.

10. System according to any one of claims 1 to 6, characterized in that the estimating means (34) are adapted to estimate said stiffness coefficients from a bicycle mechanical model thereof.

11. System according to claim 10, characterized in that the estimating means (34) are adapted to estimate said stiffness coefficients based on a discrete time modeling of the recalibrated accelerations of the front and rear wheels according to the relation:

a (k)

where k is the k ^ι J è ^e ^m e ^th sampling instant, Avr and Ava are the vertical accelerations of the rear and front wheels, respectively, and Zvr Zva are the altitudes of the rear wheels and front centers, respectively, and Kpr Kpa are the stiffness coefficients of the tires of the front and rear wheels respectively, n is a sampling instant corresponding to a time shift between the rear and front wheels undergoing the same portion of roadway, Ra and Rr are stiffness coefficients of the suspensions of the front and rear wheels respectively, and Zva and Zvr are the first derivatives of the altitudes of the centers of the front and rear wheels respectively.

12. System according to any one of the preceding claims, characterized in that it comprises means (42) for diagnosing the operating state of the means (12, 14) for acquiring the vertical accelerations of the adapted front wheels. to diagnose the operating state of these by testing their consistency over a predetermined period of time.

13. System according to claim 12, characterized in that the means (42) are adapted to calculate the frequency spectra of the accelerations delivered by the acquisition means (12, 14), to compare these spectra and to diagnose a defective state of the means of acquisition. acquisition (12, 14) if the spectra differ by more than a predetermined value.

14. System according to claim 12 or 13, characterized in that the means (42) of diagnosis are further adapted to predict one of the accelerations of the front and rear wheels depending on the other of these accelerations delivered by the means of acquisition and to diagnose a condition defective acquisition means (12, 14) if furthermore the predicted acceleration and acceleration used for this prediction are not consistent.