EP0551495A1

EP0551495A1 - Method for processing signals in a tyre monitoring system

Info

Publication number: EP0551495A1
Application number: EP19920917209
Authority: EP
Inventors: Jacques Hebert
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1991-08-08
Filing date: 1992-07-20
Publication date: 1993-07-21
Also published as: JPH06501903A; WO1993002875A1; FR2680135A1

Abstract

Le système de surveillance de la pression des pneumatiques fonctionne selon un mode normal de détection des crevaisons et sous-gonflages, et selon un mode d'assistance au regonflage des pneumatiques. Le basculement entre les deux modes (P1; P2) ne requiert aucune intervention de l'utilisateur: par détection d'une élévation de la masse d'air dans un pneumatique, on peut en déduire que le pneumatique en question est en cours de regonflage.The tire pressure monitoring system operates in a normal puncture and under-inflation detection mode, and in a tire inflation assistance mode. Switching between the two modes (P1; P2) requires no user intervention: by detecting an increase in the air mass in a tire, it can be deduced that the tire in question is being re-inflated .

Description

METHOD FOR EXPLOITING SIGNALS IN A TIRE MONITORING SYSTEM

The present invention relates to tire monitoring systems. More particularly, it relates to the use of the measurements made on tires with a view to providing the driver with as complete a help as possible.

The primary purpose of tire monitoring systems is to alert the driver of any abnormality that may occur with the tires, or with one of these tires. For this, it is impossible to be satisfied with displaying the values of pressure, and temperature if necessary, recorded in the tires. The permanent consultation of these indications is likely to be tedious, and especially their interpretation by the driver remains very problematic because these measurements are influenced by various disturbances like the heating of the tire while driving, due to its hysteretic losses. This is why a processor takes charge of the overall processing of the signals, according to an appropriate processing program to give the driver an alert when one or more of his tires are no longer in a state of normal operation, or even enters a danger zone for the safe use of the vehicle.

The object of the present invention is to be able not only to provide the "alert" function in the event of a fault, but also to be able to provide assistance when the tires are being re-inflated. The classic approach to this problem is to ask the driver to indicate to the system, by an appropriate command to the dashboard for example, that we are going to re-inflate, or else to add a sensor, for example on the valve, making it possible to detect the use of a re-inflator, as proposed in application EP 0 284 895.

According to the invention, the method of processing the signals in a system for monitoring the tires of a vehicle, said system delivering an estimate N of the quantity of air contained in each tire, the monitoring system having an operating mode normal consisting in giving the driver of the vehicle an alert when one of the tires does not have the desired quantity of air, is characterized in that, at all times t,

a) a filtered value N of N is calculated, representative of the previous states of the tire existing before time t, b) we compare N to N „, c) we detect that the observed tire is being re-inflated if N - N is greater than a threshold value determined experimentally and one automatically switches to an operating mode in assistance with re-inflation of the tire considered.

Based on the observation that, by the cause of leaks or porosity of materials, a tire in use can only lose air, that is to say, can only see its amount of air decrease, it is proposed to build a monitoring system capable of automatically switching from a normal operating mode to a re-inflation assistance mode when the start of re-inflation is detected. This changeover is not only automatic, but it is spontaneous since it only uses its own knowledge of the amount of air, without having to resort to additional information specific to the reinflation situation. A monitoring system thus developed not only makes it possible to provide the driver with assistance when he actually wants to reinflate his tires, but it also makes it possible to alert him when, for example when the tires are swapped on a vehicle having pressures. different inflation at the front and rear, we forget to readjust the pressures. In this case, on at least one of the axles, the system will detect an unnatural evolution, namely a re-inflation, and the one who has carried out the changeover operation, or the driver, may be notified by the automatic change in re-inflation assistance mode. Similarly, when the spare tire is placed after a puncture, the system will automatically switch to re-inflation assistance mode, and in general will give an over-inflation alarm since the spare tire must always be inflated to a pressure higher than the higher of the nominal tire pressures of each axle.

Preferably, in order to estimate the air mass in each tire, account is taken of the pressure measurement and the temperature measurement, recorded substantially at the same time for each tire. Variations in the volume of the tire can be neglected.

The following description sets out an embodiment of the invention which is particularly effective by virtue of the filter chosen to calculate N _p , and is illustrated by the attached figures, in which:

Figure 1 is a timing diagram to illustrate the operation of the filter, Figure 2 gives the signal processing algorithm.

In the following description, the estimate N. of the quantity of air contained in each tire i is calculated by the ratio of the absolute pressure P. expressed in bars divided by the absolute temperature T. expressed in Kelvin. For each measurement cycle, i.e. at any time t, the ratio is expressed:

N (t) = —i

T. (t)

Knowing for each tire i the nominal quantity of air N. which it must contain, generally expressed by vehicle manufacturers in an inflation pressure established when cold (in a normalized atmosphere of 17 ° C.), it is possible to construct a dimensionless estimator:

It is necessary to build a filter making it possible to erase all the fluctuations of the measurements NR. (T). This filter must be representative of the history of the amounts of inflation air of a tire. We will therefore calculate, for each tire i, a filtered value N „(or NR _p if dimensionless estimators are used) which embodies a representation of all the inflation states of the tire, preferably since the last inflation. This filtered value is calculated as follows:

NR _Fi (t) = _χ NR _pi (t-1) + K- NR _jL (t) with K _χ + K ₂ = 1

In FIG. 1, the abscissa represents the elapsed time expressed in months during the period P .. elapsing between two adjustments of the inflation pressure, then expressed in number of cycles of the monitoring system during the period „which is the phase re-inflation. The ordinates represent the air quantity estimator, equal to 1 for a tire in nominal condition. The solid line curve represents the NR estimator and the broken line curve the filtered value NR „F of this estimator.

We see in Figure 1 that this filtered value NR_1. (t) makes it possible to give a continuously decreasing pressure ramp, during phase P .., and that this filtered value rises only very slightly during the start of phase P ₂ . The re-inflation detection consists in locating only the last value of the NR estimator. (t) has deviated by excess of the filtered value NR „. (t). We choose experimentally a threshold ε.

Experiments have shown that the values

K ₁ = 0.98 and K ₂ = 0.02 give excellent results. The sensitivity of the filter, that is to say its reaction speed from the moment that inflation is effectively started, depends on the flow of air blown into the tire. The proposed filter is an excellent compromise making it possible to use both high-flow re-inflation stations and manual pumps. K. can be chosen between 0.9 and 0.995 to give sufficient weight to the previous states of the tire while reducing transient fluctuations. The weight K. should be reduced especially as the flow rate of the re-inflation pump is high. By associating the filtered value NR F_ with a detection threshold ε = 5%, preferably, we will choose K .. between 0.97 and 0.985

In re-inflation assistance, we cannot be content to reuse the same range of air quantity monitoring as that used by the same system when working in normal mode. It is necessary to re-inflate respecting a narrow tolerance (for example ± 1.3%) finely framing the nominal value, which possibly takes into account the conditions of use of the vehicle (load sensor for example), while in normal mode performing the actual monitoring, we will tolerate a greater loss of air (for example - 12%).

The re-inflation assistance offered consists in providing a first alarm as long as the quantity of air measured N. (t) is less than a minimum threshold Ni. mi.n, and to provide a second alarm distinct from the first when the quantity of air measured N. (t) is greater than a maximum threshold N. N. (t).

With the operator outside the vehicle, the first alarm activates a buzzer continuously, and the second alarm activates the same buzzer discontinuously. The operator knows that he must re-inflate until the buzzer has not gone out, and at most until the buzzer operates discontinuously.

We have just explained how the system is capable of automatically switching to inflation assistance mode for a given tire. This is symbolized by the condition M. = Seated, on the flowchart of FIG. 2. It is now necessary to establish the conditions to be fulfilled so that the system automatically leaves this assistance mode for the tire i. We propose to check the following three conditions:

1) switching to assistance mode for another tire j: M. = assist. ;

2) long period of time in assistance mode without air supply on the same tire: θ _{M ± = Assistance} >

3) starting the vehicle: for example solicitation of the starter or better still, information obtained from a speed sensor.

When at least one of these conditions is met, the When at least one of these conditions is met, the system switches to normal mode for tire i, which is illustrated by switching to mode M. = Normal in FIG. 2.

After switching to re-inflation assistance mode, NR _F is no longer calculated, and therefore does not change level on the curve in broken lines in FIG. 1. The period P corresponds to switching to normal mode for the tire in question. The new reference value for tire i is memorized (Memorization of Ni. Nom) 'and the filter NR. is reset by clearing the history. The filter conventionally takes the value 1 (RESET of NR_.).

Since the monitoring system itself consumes electrical energy, it will generally be provided that it is automatically shut down when the engine is not running. If a re-inflation assistance mode is incorporated into the system as proposed by the present invention, then the system must be able to operate when the vehicle ignition key is in a position other than the ignition off position. Preferably, the data relating to the history of the tires must be stored in non-volatile memory.

Claims

1. A method of processing the signals in a system for monitoring the tires of a vehicle, said system delivering an estimate N of the quantity of air contained in each tire, the monitoring system having a normal operating mode consisting in giving to the driver of the vehicle an alert when one of the tires does not have the desired amount of air, characterized in that at all times t,

a) a filtered value N_ of N is calculated, representative of the previous states of the tire existing before time t, b) one compares N to N_, c) one detects that the observed tire is being re-inflated if N - N_, is greater than a threshold value determined experimentally and one automatically switches to an operating mode in assistance with re-inflation of the tire considered.

2. Method according to claim 1, characterized in that the system performs a measurement of the pressure and of the temperature recorded substantially at the same time for each tire.

3. Method according to claim 2, characterized in that the estimate N of the quantity of air is calculated by the ratio of the absolute pressure divided by the absolute temperature recorded for the tire considered.

4. Method according to claim 3, characterized in that the estimate N of the quantity of air is expressed as a percentage relative to the nominal quantity of air for the tire considered.

5. Method according to claim 1, characterized in that the filtered value is calculated as follows:

N _p (t) = K _± N _F (tl) + K ₂ N (t) with K _χ + K ₂ = 1

6. Method according to claim 5, characterized in that 0.90 ≤ K ₁ ≤ 0.995.

7. Method according to claim 6, characterized in that 0.97 ≤ K ₁ ≤ 0.985 and in that the threshold value corresponds to an evolution of N of more than 5% between the instants t-1 and t.

8. Method according to one of claims 1 to 7, characterized in that the re-inflation assistance consists in providing a first alarm as long as the quantity of air measured N (t) is less than a minimum threshold Ni. mi.n, and to provide a second alarm distinct from the first when the quantity of air measured N. (t) is greater than a maximum threshold N. _maχ >

9. Method according to one of claims 1 to 8, characterized in that one leaves the mode of assistance for re-inflating a tire when the re-inflation of another tire is detected, or when the operating time in mode d re-inflation assistance for a given tire has exceeded a predetermined period, or when other predetermined conditions are met.