Diagnostic method for an outdoor air quality measurement sensor in a vehicle passenger compartment

Abstract

The invention relates to a diagnostic method for at least a first sensor (2a) intended to measure a first variable Text representative of the quality of the outside air passing through an air supply circuit (1) of a motor vehicle passenger compartment (3), comprising: a first step of measuring the first variable Text by the first sensor, a second step of measuring the second variable Tint by the second sensor, the valve being in the open position of the outside air supply duct during the first and second steps, and a third comparison step during which the first sensor is considered to be functioning correctly if the second variable Tint is less than or equal to the first variable Text and if the first variable Text is less than or equal to the second variable Tint multiplied by a coefficient representative of an average filtration level of the filtration device. Abstract figure: Fig. 1

Description

Title of the invention: Method for diagnosing a sensor for measuring the quality of outside air in a vehicle interior

[0001] The present invention relates to the field of managing the monitoring of the proper functioning of a sensor for the quality of the outside air entering a motor vehicle passenger compartment.

[0002] The invention relates more particularly to a method for diagnosing a first sensor or external sensor intended to measure a variable representative of the quality of the external air passing through an air supply circuit of a motor vehicle passenger compartment.

[0003] A motor vehicle conventionally comprises a passenger compartment supplied with air via an air supply circuit.

[0004] The supply circuit comprises an aerator, through which air from outside the motor vehicle is admitted and a first air intake duct, called "external air inlet duct", which connects the aerator to an air pulsation fan, diffusing the air into the passenger compartment.

[0005] The exterior air intake duct further comprises a filter (or several filters, depending on the level of finish of the motor vehicle), through which the admitted air passes in order to be purified.

[0006] The filtered air is conveyed through the outside air intake duct to the air pulsation fan, which draws in the filtered air and diffuses it into the passenger compartment.

[0007] The supply circuit further comprises a second air intake duct, called the “passenger compartment duct”, forming a loop between the passenger compartment of the motor vehicle and the exterior air intake duct.

[0008] The outside air inlet duct comprises a sensor (called an internal sensor) positioned downstream of the filters and which is responsible for carrying out measurements representative of the quality of the filtered air passing through the outside air inlet duct.

[0009] Document FR3076491B1 describes, for example, a method for determining the level of at least one pollutant in the air inside and outside the passenger compartment of a motor vehicle. The vehicle comprises a sensor adapted to determine the level of at least one pollutant in the air inside the passenger compartment of the vehicle, and an air management system adapted to ventilate outside air inside the passenger compartment. The level of the pollutant in the outside air is determined from the determined quantity of renewed air and the variation between the first and second values ​​of the measured level of the pollutant in the inside air.

[0010] We also know the document FR2305652 which describes a diagnostic method of at least one sensor intended to measure a variable representative of the quality of the interior air passing through an air supply circuit of a motor vehicle passenger compartment. The sensor is positioned downstream of a filtration device.

[0011] However, the prior art does not describe a sensor positioned upstream of the filtering device to measure pollutants in the air coming from outside the passenger compartment and even less a method for verifying the correct operation of the sensor.

[0012] However, this type of sensor can malfunction and lead to false measured pollutant level values ​​without the user noticing it immediately. The opening of the outside air intake duct can be controlled while the outside air is very polluted, causing a risk to the health of the vehicle occupants.

[0013] There is therefore a need to be able to control the correct operation of the sensor positioned upstream of the filtering device. Otherwise, the malfunction of the sensor could only be detected during vehicle maintenance, which is too late and this detection can take time.

[0014] The aim of the invention is therefore to overcome the drawbacks of the prior art by proposing a method for diagnosing a sensor intended to measure a variable representative of the quality of the outside air passing through an air supply circuit of a motor vehicle passenger compartment, making it possible to easily and quickly detect a faulty outside sensor.

[0015] To do this, the invention thus relates, in its broadest sense, to a diagnostic method, a diagnostic method for at least a first sensor intended to measure a first variable Text representative of the quality of the outside air passing through an air supply circuit of a motor vehicle passenger compartment. The supply circuit comprises an outside air supply duct connecting the interior to the exterior of the passenger compartment. The outside air supply duct comprises a filtration device positioned downstream of the first sensor, an air flow control valve positioned downstream of the filtration device and intended to close or open the outside air supply duct and at least a second sensor positioned downstream of the valve and intended to measure a second variable Tint representative of the quality of the inside air passing through the supply circuit.

[0016] According to the invention, the method comprises: - A first step of measuring the first Text variable by the first sensor, - A second step of measuring the second variable Tint by the second sensor, the valve being in the open position of the outside air supply duct during the first and second steps, the first sensor and the second sensor measuring the same type of variable representative of the air quality, and - A third comparison step during which the first sensor is considered to be functioning correctly if the second variable Tint is less than or equal to the first variable Text and if the first variable Text is less than or equal to the second variable Tint multiplied by a coefficient representative of an average filtration level of the filtration device.

[0017] The invention thus provides a method for diagnosing a sensor intended to measure a variable representative of the quality of the outside air passing through an air supply circuit of a motor vehicle passenger compartment, making it possible to easily and quickly detect a faulty outside sensor.

[0018] The method consists of verifying that the first sensor or external sensor positioned upstream of the filtration device detects a higher level of pollutant than the second sensor or internal sensor positioned downstream of the filtration device.

[0019] Thus, the after-sales service is able to diagnose a failure of one of the first sensors in a minimum of time.

[0020] A time saving is therefore achieved in after-sales service, resulting in an economic gain.

[0021] Since a failure of the first sensor is detected quickly, the risk to the health of the vehicle occupants is reduced.

[0022] According to a variant, the average filtration level corresponds to a ratio between a value of the second variable Tint and a value of the first variable Text. The average filtration level is calculated before the first step. The coefficient is equal to the average filtration level multiplied by 10.

[0023] This solution provides a reliable method for verifying the consistency of the first sensor.

[0024] According to a variant, the first sensor is a particle rate sensor measuring particle sizes contained in the air flow passing through the outside air supply duct or a sensor measuring the level of ozone or nitrogen dioxygen or sulfur dioxide or carbon monoxide in the air flow passing through the outside air supply duct. The first and second variables are a particle rate or an ozone rate or a nitrogen dioxygen rate or a sulfur dioxide rate or a carbon monoxide rate.

[0025] According to a variant, the outside air supply duct comprises several first sensors including a particle rate sensor measuring particle sizes, a sensor measuring the ozone rate, a sensor measuring the nitrogen dioxide rate, a sensor measuring the sulfur dioxide rate and a sensor measuring the carbon monoxide rate. The first, second and third steps are applied simultaneously for each first sensor in order to diagnose all

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[0037] the first sensors simultaneously. This helps reduce diagnostic time. According to one variant, the vehicle includes openings in the closed position during the first and second measurement steps. This allows for more accurate measurement of pollutants. According to one variant, two successive test series each comprising at least the first and second measurement steps are carried out after a time interval of at least 10 seconds. This allows time for the new air flow to circulate in the outside air supply duct and ensures a variation in the pollutant level. Alternatively, the number of malfunctions is counted for each first sensor. A fault code is stored in a memory when the number of malfunctions exceeds a counting threshold. Each first sensor includes a separate fault code. This allows rapid detection of malfunction of one of the first sensors. According to a variant, a diagnostic method is also carried out for the second sensor before the first and second measurement steps carried out for the first sensor. This ensures that the second sensor is reliable to make the diagnostic process of the first sensor more reliable. According to a variant, the diagnostic method for the second sensor comprises: - A first step of measuring a first variable representative of the air quality by the second sensor, the valve being in a first position of closing or opening of the outside air supply duct, - A second step of measuring a second variable representative of the air quality by the second sensor, the valve being in a second position of closing or opening of the outside air supply duct, different from the first position, - A third step of calculating the difference between the second variable and the first variable to deduce a gap, and - A fourth step of comparison between the deviation and a threshold value to check if the second sensor is working correctly. The invention also relates to a vehicle implementing the diagnostic method as defined above. The first and second sensors and the valve are connected to a computer of the vehicle. An embodiment of the present invention will be described below, by way of non-limiting examples, with reference to the single appended figure in which:

[0038] [Fig. 1] schematically illustrates an air supply circuit for a motor vehicle passenger compartment.

[0039] In the remainder of the description, elements having an identical structure or similar functions are designated by the same reference.

[0040] [Fig.l] illustrates an air supply circuit 1 for a passenger compartment 3 of a motor vehicle.

[0041] The supply circuit 1 comprises an aerator, for example positioned in the upper part of the passenger compartment 3, in particular at the level of the awning of the motor vehicle.

[0042] The supply circuit 1 comprises an outside air supply duct 4, called an “outside air inlet duct”, which connects the aerator to an air pulsation fan 7, diffusing the air into the passenger compartment 3.

[0043] The outside air supply duct 4 comprises a filtration device 5 comprising at least one filter, for example, chosen from the group containing: a pollen filter, an activated carbon filter, an anti-allergen filter, a particle filter.

[0044] Depending on the level of finish, equipment or options of the motor vehicle, the motor vehicle includes one or more of the filters listed in the aforementioned group.

[0045] More generally, the filter designates equipment designed to filter, in the air which feeds it, at least one chemical species in solid form, for example fine particles or dust, or in gaseous form, comprising for example carbon monoxide (CO), sulfur dioxide (SO2), ozone (03), nitrogen dioxide (NO2), carbon dioxide (CO2), oxygen (02).

[0046] The filter may also include, as a supplement or alternative, a function for dehumidifying the air passing through it.

[0047] The filtered air is conveyed through the outside air supply duct 4 to the air pulsation fan 7, designed to suck in the filtered air and distribute it into the passenger compartment 3.

[0048] The supply circuit 1 further comprises a passenger compartment duct 8, forming a loop between the passenger compartment 3 of the motor vehicle and the exterior air supply duct 4 for recycling the air from the passenger compartment 3.

[0049] In the exemplary embodiment of the supply circuit 1 illustrated in [Fig.l], the passenger compartment duct 8 comprises a filtration assembly 9 designed to filter the air circulating from the passenger compartment 3 to the outside air supply duct 4.

[0050] For example, the filtration assembly 9 comprises a small filter which has the function of cleaning the air coming from the passenger compartment 3.

[0051] According to an alternative embodiment not shown, the passenger compartment duct 8 does not include any filtration assembly 9.

[0052] The outside air supply duct 4 comprises a valve 6 for controlling the air flow, for example a three-way valve, called a “Y valve”, designed and arranged For : • Close the passenger compartment duct 8 so that all the air entering the motor vehicle is admitted via the outside air supply duct 4, or • Close the outside air supply duct 4 to prevent outside air from entering the passenger compartment 3, for example when the user of the motor vehicle operates the supply circuit in “recycling” mode, for example when the motor vehicle passes through a polluted tunnel, or • Admit into the outside air supply duct 4 air from both outside the motor vehicle and air from the passenger compartment 3 in order to allow partial renewal of the air and to begin to bring the air from outside the motor vehicle to the temperature of the passenger compartment 3.

[0053] In the embodiment illustrated in [Fig.l], the air flow control valve 6 is mounted downstream of the filtration device 5, the upstream and downstream being understood relative to the direction of air flow in the supply circuit 1, i.e. from the outside to the inside of the passenger compartment 3.

[0054] The supply circuit 1 comprises at least one first sensor 2a (called external sensor) intended to measure a variable representative of the quality of the outside air passing through the air supply circuit 1 of the passenger compartment 3 of the motor vehicle. The first sensor 2a is mounted in the outside air supply duct 4, downstream of the valve 6, that is to say between the valve 6 and the air pulsation fan 7.

[0055] The first sensor 2a may be a particle rate sensor measuring particle sizes contained in the air flow passing through the outside air supply duct 4.

[0056] The particle rate sensor is an optical sensor designed to measure the content of particles less than 2.5 pm or less than 10 pm contained in the air passing through it.

[0057] In this regard, the particle rate sensor is also called a “PM2.5” sensor or a “PM 10” sensor.

[0058] The operating principle is as follows: air passes through a housing containing an infrared light emitter and the particle rate sensor measures the content of these particles contained in the air by measuring the quantity of light reflected by the particles. The wavelength of the light source makes it possible to distinguish the particle sizes, this distinction being materialized on the pulse pattern of the output voltage of the optical sensor, which makes it possible to distinguish between the particles.

[0059] The first sensor 2a may also be a sensor measuring the level of ozone (03) or nitrogen dioxide (NO2) or sulfur dioxide (SO2) or carbon monoxide (CO) in the air flow passing through the outside air supply duct 4, for example.

[0060] The first sensor 2a may be an air quality control sensor, known under the name “AQS”, an English acronym for “Air Quality System”.

[0061] The air quality monitoring sensor is capable of measuring the levels of carbon monoxide (CO), sulfur dioxide (SO2), ozone (03), and nitrogen dioxide (NO2) at the same time.

[0062] Preferably, the outside air supply duct 4 comprises several first sensors 2a including a particle rate sensor measuring particle sizes of 2.5 μm and 10 μm, and an air quality control sensor measuring the levels of carbon monoxide (CO), sulfur dioxide (SO2), ozone (03), and nitrogen dioxide (NO2).

[0063] The supply circuit 1 also comprises at least one second sensor 2b (called internal sensor) intended to measure a variable representative of the quality of the interior air passing through the air supply circuit 1 of the passenger compartment 3, i.e. the air filtered by the filtration device 5. The first sensor 2a is mounted in the exterior air supply duct 4, upstream of the filtration device 5.

[0064] Thus, the air passing through the first sensor 2a is not filtered by the filtration device 5 whereas the air passing through the second sensor 2b is filtered by the filtration device 5.

[0065] As for the first sensor 2a, the second sensor 2b may be a particle rate sensor measuring particle sizes contained in the air flow passing through the outside air supply duct 4 or a sensor measuring the rate of ozone (03) or nitrogen dioxide (NO2) or sulfur dioxide (SO2) or carbon monoxide (CO) in the air flow passing through the outside air supply duct 4, for example.

[0066] Preferably, the outside air supply duct 4 comprises several second sensors 2b including a particle rate sensor measuring particle sizes of 2.5 μm and 10 μm, and an air quality control sensor measuring the levels of carbon monoxide (CO), sulfur dioxide (SO2), ozone (03), and nitrogen dioxide (NO2).

[0067] The first and second sensors 2a, 2b are of the same nature, that is to say they measure the same type of variable representative of the air quality. If the first sensor 2a measures particle rates of 2.5 p and 10 p, then the second sensor 2b also measures particle rates of 2.5 p and 10 p, for example.

[0068] The invention relates to a method for diagnosing at least one first sensor 2a intended to measure a variable representative of the quality of the outside air passing through the air supply circuit 1 of the passenger compartment 3 of the motor vehicle.

[0069] The diagnostic method is implemented by hardware and software means integrated into the motor vehicle.

[0070] For this purpose, the software means include in particular the algorithm implemented to execute the method of the invention.

[0071] The software means are for example integrated into a motor vehicle computer, for example in the electronic management box known under the name “BSI”, acronym for “Intelligent Servitude Box”.

[0072] The diagnostic method comprises: • A first step of measuring the first variable Text by the first sensor 2a, • A second step of measuring the second variable Tint by the second sensor 2b, the valve 6 being in the open position of the outside air supply duct 4 during the first and second steps, the first sensor 2a and the second sensor 2b measuring the same type of variable representative of the air quality, and • A third comparison step during which the first sensor 2a is considered to be operating correctly if the second variable Tint is less than or equal to the first variable Text and if the first variable Text is less than or equal to the second variable Tint multiplied by a coefficient representative of an average filtration level of the filtration device 5.

[0073] The average filtration level corresponds to that of commonly used filtration devices 5. The average filtration level is equal to the ratio between a value of the second variable Tint and a value of the first variable Text. Several ratios can be calculated to obtain an average. The average filtration level is calculated before the first step. The coefficient is equal to the average filtration level multiplied by 10.

[0074] The first and second variables are a particle rate if the first and second sensors 2a, 2b are particle rate sensors or an ozone rate if the first and second sensors 2a, 2b are sensors measuring the ozone rate or a nitrogen dioxide rate if the first and second sensors 2a, 2b are sensors measuring the nitrogen dioxide rate or a sulfur dioxide rate if the first and second sensors 2a, 2b are sensors measuring the sulfur dioxide rate or a carbon monoxide rate if the first and second sensors 2a, 2b are sensors measuring the carbon monoxide rate.

[0075] As previously stated, preferably, the outside air supply duct 4 comprises first and second particle rate sensors 2a, 2b measuring particle sizes of 2.5 p and 10 p, first and second sensors 2a, 2b measuring the ozone level, first and second sensors 2a, 2b measuring the nitrogen dioxide level, first and second sensors 2a, 2b measuring the sulfur dioxide level and first and second sensors 2a, 2b measuring the carbon monoxide level.

[0076] The diagnostic method is applied for all the first sensors 2a. In other words, the first, second and third steps are carried out simultaneously for each first sensor 2a in order to diagnose all the first sensors 2a simultaneously.

[0077] Two successive test series each comprising at least the first and second measurement steps are carried out at a time interval of at least 10 seconds. The time interval is calibratable.

[0078] Alternatively, the first sensors 2a can be diagnosed successively. The diagnostic method is then carried out sensor by sensor.

[0079] The vehicle includes openings which are closed during the first and second measurement steps. The computer must receive information that the openings are closed, otherwise these steps are not carried out.

[0080] An example of operation is given below.

[0081] The vehicle's openings are all closed and valve 6 is open.

[0082] During the first measurement step, pollutant levels are measured in the air outside upstream of the filtration device 5. The first particle rate sensor measures first particle rates of 2.5 p and 10 p. The first air quality control sensor measures first rates of ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide which are transmitted to the computer.

[0083] In this example, six first rates and therefore six first variables representative of the quality of the outside air are measured.

[0084] The calculator thus receives a first particle rate of 2.5 p (TextP2.5), a first particle rate of 10 p (TextPIO), a first ozone rate (TextO3), a first nitrogen dioxide rate (TextNO2), a first sulfur dioxide rate (TextSO2) and a first carbon monoxide rate (TextCO).

[0085] During the second measurement step, pollutant levels are measured downstream of the filtration device 5. The second particle level sensor measures second particle levels of 2.5 p and 10 p and the second air quality control sensor measures second levels of ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide which are transmitted to the computer.

[0086] In this example, six second rates and therefore six second variables representative of indoor air quality are also measured.

[0087] The calculator thus receives a second particle rate of 2.5 p (TintP2.5), a second particle rate of 10 p (TintPIO), a second ozone rate (TintO3), a second nitrogen dioxide rate (TintNO2), a second sulfur dioxide rate (TintSO2) and a second carbon monoxide rate (TintCO).

[0088] During the third comparison step, the indoor pollutant levels are compared to the outdoor pollutant levels using a multiplying coefficient representative of the average filtration level of the filtration device 5.

[0089] The average filtration levels are defined as follows: - Average filtration level of a 2.5 p particle filter: approximately 0.8 (= 2.5 p particle rate downstream of filtration device 5 / 2.5 p particle rate upstream of filtration device 5); - Average filtration level of a 10 p particle filter: approximately 0.9 (= 10 p particle rate downstream of filtration device 5 / 10 p particle rate upstream of filtration device 5); - Average filtration level of an O3 filter: approximately 0.4 (= O3 rate downstream of filtration device 5 / O3 rate upstream of filtration device 5); - Average filtration level of a NO2 filter: approximately 0.4 (= NO2 level downstream of filtration device 5 / NO2 level upstream of filtration device 5); - Average filtration level of a SO2 filter: approximately 0.8 (= SO2 rate in downstream of the filtration device 5 / SO2 level upstream of the filtration device 5); - Average filtration level of a CO filter: approximately 0.4 (= CO level in downstream of the filtration device 5 / CO level upstream of the filtration device 5).

[0090] To obtain the multiplier coefficient, each average filtration level is multiplied by 10: - CoefP2.5 = Coefficient associated with the particle rate of 2.5 p = average filtration level of a 2.5 px particle filter 10 = 0.8 x 10 = 8; - CoefPlO = Coefficient associated with the particle rate of 10 p = average filtration level of a 10 px particle filter 10 = 0.9 x 10 = 9; - CoefO3 = Coefficient associated with the ozone rate = average filtration level of an ozone filter = 0.4 x 10 = 4; - CoefNO2 = Coefficient associated with the nitrogen dioxide rate = average filtration level of a nitrogen dioxide filter = 0.4 x 10 = 4; - CoefSO2 = Coefficient associated with the sulfur dioxide rate = average filtration level of a sulfur dioxide filter = 0.8 x 10 = 8; - CoefCO = Coefficient associated with the carbon monoxide level = level filtration rate of a carbon monoxide filter = 0.4 x 10 = 4.

[0091] These coefficients are given as an example because they depend on the filtering device 5 used, the average filtration level of which can vary. The coefficients are calibrated during the function development on the vehicle.

[0092] The first sensor of the particle rate of 2.5 p is valid if TintP2.5 < TextP2.5 < coefP2.5 x TintP2.5;

[0093] The first 10 p particle rate sensor is valid if TintPIO < TextPIO < coefPlO x TintPMIO;

[0094] The first ozone rate sensor is valid if TintO3 < TextO3 < coefO3 x TintO3;

[0095] The first sensor of the nitrogen dioxygen rate is valid if TintNO2 < TextNO2 < coefNO2 x TintNO2 ;

[0096] The first sulfur dioxide rate sensor is valid if TintSO2 < TextSO2 < coefSO2 x TintSO2 ;

[0097] The first carbon monoxide level sensor is valid if TintCO < TextCO < coefCO x TintCO.

[0098] Otherwise, for each variable representative of the quality of the outside air, if this relationship is not satisfied, the first sensor 2a is considered to be malfunctioning.

[0099] The first, second and third steps are repeated several times. The number of malfunctions is counted for each first sensor 2a. A fault code is stored in a vehicle memory when the number of malfunctions is greater than a counting threshold. Each first sensor 2a includes a separate fault code.

[0100] The counting threshold may be identical for all the first sensors 2a or different for each first sensor 2a.

[0101] The counting threshold can be three for all the first sensors 2a, for example.

[0102] The number of malfunctions is counted for the first sensor of the particle rate of 2.5 p, for example.

[0103] If the number of malfunctions for the first 2.5 p particle rate sensor is greater than 3, a first fault code is stored in the memory.

[0104] If the number of malfunctions for the first 10 p particle rate sensor is greater than 3, a second fault code is stored in the memory.

[0105] If the number of malfunctions for the first ozone level sensor is greater than 3, a third fault code is stored in the memory.

[0106] If the number of malfunctions for the first nitrogen dioxygen rate sensor is greater than 3, a fourth fault code is stored in the memory.

[0107] If the number of malfunctions for the first sulfur dioxide sensor is greater than 3, a fifth fault code is stored in the memory.

[0108] If the number of malfunctions for the first carbon monoxide sensor is greater than 3, a sixth fault code is stored in the memory.

[0109] Alternatively, the vehicle service indicator light may be illuminated when a fault code is stored.

[0110] To reset the first sensor(s) 2a, the associated counters are reset to zero. The first sensor(s) 2a can continue to carry out pollutant measurements.

[0111] Preferably, this reset is carried out by an after-sales service.

[0112] According to a variant, a diagnostic method is carried out for the second sensor 2b before the first and second measurement steps carried out for the first sensor 2a.

[0113] Preferably, the diagnostic method for the second sensor 2b is carried out as described in document FR2305652.

[0114] The diagnostic method for the second sensor 2b comprises: - A first step of measuring a first variable representative of the air quality by the second sensor 2b, the valve 6 being in a first position of closing or opening of the outside air supply duct 4, - A second step of measuring a second variable representative of the air quality by the second sensor 2b, the valve 6 being in a second position of closing or opening of the outside air supply duct 4, different from the first position, - A third step of calculating the difference between the second variable and the first variable to deduce a gap, and - A fourth step of comparison between the deviation and a threshold value to check if the second sensor 2b is working correctly.

[0115] According to a variant, during the first measurement step, the valve 6 is closed, the valve 6 being open during the second measurement step. The measurements of the second sensor 2b are considered consistent if the difference between the second variable and the first measured variable is strictly greater than the threshold value.

[0116] According to another variant, during the first measurement step, the valve 6 is open, the valve 6 being closed during the second measurement step. The measurements of the second sensor 2b are considered consistent if the difference between the second variable and the first measured variable is strictly less than the threshold value.

Claims

Claims

1. Method for diagnosing at least one first sensor (2a) intended to measure a first variable Text representative of the quality of the outside air passing through an air supply circuit (1) of a passenger compartment (3) of a motor vehicle, the supply circuit (1) comprising an outside air supply duct (4) connecting the interior to the exterior of the passenger compartment (3), the outside air supply duct (4) comprising a filtration device (5) positioned downstream of the first sensor (2a), a valve (6) for controlling the air flow positioned downstream of the filtration device (5) and intended to close or open the outside air supply duct (4) and at least one second sensor (2b) positioned downstream of the valve (6) and intended to measure a second variable Tint representative of the quality of the inside air passing through the supply circuit (1),characterized in that the method comprises: • A first step of measuring the first variable Text by the first sensor (2a), • A second step of measuring the second variable Tint by the second sensor (2b), the valve (6) being in the open position of the outside air supply duct (4) during the first and second steps, the first sensor (2a) and the second sensor (2b) measuring the same type of variable representative of the air quality, and • A third comparison step during which the first sensor (2a) is considered to be functioning correctly if the second variable Tint is less than or equal to the first variable Text and if the first variable Text is less than or equal to the second variable Tint multiplied by a coefficient representative of an average filtration level of the filtration device (5).,

2. Diagnostic method according to claim 1, characterized in that the average filtration level corresponds to a ratio between a value of second variable Tint and a value of first variable Text, the average filtration level being calculated before the first step, the coefficient being equal to the average filtration level multiplied by 10.

3. A diagnostic method according to any one of claims 1 or 2, characterized in that the first sensor (2a) is a particle rate sensor measuring particle sizes contained in the air flow passing through the outside air supply duct (4) or a sensor measuring the level of ozone or nitrogen dioxide or sulfur dioxide or carbon monoxide in the air flow passing through the outside air supply duct (4), the first and second variables being a particle rate or an ozone rate or a nitrogen dioxide rate or a sulfur dioxide rate or a carbon monoxide rate.

4. A diagnostic method according to any one of claims 1 or 2, characterized in that the outside air supply duct (4) comprises several first sensors (2a) including a particle rate sensor measuring particle sizes, a sensor measuring the ozone rate, a sensor measuring the nitrogen dioxide rate, a sensor measuring the sulfur dioxide rate and a sensor measuring the carbon monoxide rate, the first, second and third steps being applied simultaneously for each first sensor (2a) in order to diagnose all the first sensors (2a) simultaneously.

5. Diagnostic method according to any one of claims 1 to 4, characterized in that the vehicle comprises openings in the closed position during the first and second measurement steps.

6. Diagnostic method according to any one of claims 1 to 5, characterized in that two successive test series each comprising at least the first and second measurement steps are carried out after a time interval of at least 10 seconds.

7. Diagnostic method according to any one of claims 1 to 6, characterized in that the number of malfunctions is counted for each first sensor (2a), a fault code being stored in a memory when the number of malfunctions is greater than a counting threshold, each first sensor (2a) comprising a distinct fault code.

8. Diagnostic method according to any one of claims 1 to 7, characterized in that a diagnostic method is carried out for the second sensor (2b) before the first and second measuring steps carried out for the first sensor (2a).

9. Diagnostic method according to claim 8, characterized in that the diagnostic method for the second sensor (2b) comprises: • A first step of measuring a first variable representative of the air quality by the second sensor (2b), the valve (6) being in a first position of closing or opening the outside air supply duct (4), • A second step of measuring a second variable representative of the air quality by the second sensor (2b), the valve (6) being in a second position of closing or opening the outside air supply duct (4), different from the first position, • A third step of calculating the difference between the second variable and the first variable to deduce a deviation therefrom, and • A fourth step of comparing the deviation and a threshold value to check whether the second sensor (2b) is working correctly.

10. Vehicle, characterized in that it implements the diagnostic method as defined according to any one of claims 1 to 9, the first and second sensors (2a, 2b) and the valve (6) being connected to a computer of the vehicle.

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