METHOD FOR DETECTING ANOMALY IN A SECONDARY AIR CIRCUIT SYSTEM OF A DEPOLLUTED ENGINE

Abstract

The invention relates to a method for detecting an anomaly in an air circuit system in an internal combustion engine, the air circuit comprising an inlet pipe (11), an air pump (2), an intermediate pipe (12) with a pressure and temperature sensor (4) arranged on the intermediate pipe, a shut-off solenoid valve (3), a blow-off pipe (13) delivering air onto a heating grid (5) to heat a catalytic converter (55), the method comprising steps for checking various parameters related to the pump, steps for detecting leaks in the intermediate pipe and in the blow-off pipe, and identifying a component that may be malfunctioning. Figure 2

Description

Title of the invention: METHOD FOR DETECTING AN ANOMALY IN A DEPOLUTED ENGINE SECONDARY AIR CIRCUIT SYSTEM

[0001] The invention relates to a method for detecting a possible anomaly in an air circuit system, in particular relating to a so-called secondary air circuit, in an engine depolluted by means of a catalytic converter.

[0002] In low-pollutant internal combustion engines, a pollutant-reducing exhaust system, called a catalytic converter, is provided. To properly perform its function, such a catalytic converter must be at least at a required minimum temperature. Such an engine with a catalytic converter is installed in a motor vehicle.

[0003] Generally, when the vehicle engine is started, the temperature in the catalytic converter is lower than the optimum operating temperature. The temperature increases as the engine operates and reaches a sufficient level after a few tens of seconds, or even a little longer depending on the low starting ambient temperatures.

[0004] The inventors therefore proposed working on a system for heating the catalytic converter in order to minimize the emission of pollutants during the first seconds of engine operation.

[0005] This heating system comprises a grid of electrical resistors subjected to an air flow which then passes through the internal elements of the catalytic converter in order to heat the latter. Here, the air flow in question is part of the so-called secondary air circuit.

[0006] Given that this is a system contributing to compliance with pollutant gas emission levels, this system must be diagnosed and any malfunction must be reported by the so-called OBD system (from the English terminology "On Board Diagnostic").

[0007] Furthermore, this is an early heating system, which is implemented before the engine is started. The diagnosis can thus be carried out before the engine is started.

[0008] The present invention is particularly concerned with the detection of a possible anomaly concerning the air pump or the air ducts which generate and respectively conduct the air flow from the secondary circuit to the heating grid.

[0009] To this end, the present invention provides a method for detecting an anomaly in an air circuit system, in an internal combustion engine, the system of air circuit comprising a control unit, an inlet pipe, an air pump, an intermediate pipe downstream of the air pump, with a pressure and temperature sensor arranged on the intermediate pipe, a shut-off solenoid valve, a blowing pipe downstream of the shut-off solenoid valve, the blowing pipe being configured to deliver air to a heating grid to heat a catalyst pot, the method comprising: SI- a shutoff solenoid valve closing step of closing the shutoff solenoid valve or keeping the shutoff solenoid valve in the closed state, S2- a step of controlling the pump up to a predetermined speed setpoint value, S3- a step of checking the pressure rise in the intermediate pipe, giving a normal or abnormal result, S4- a step of verifying the rotation speed measured by a sensor delivering information representative of the rotation speed of the pump, giving a normal or abnormal result, S5- a first step of checking for the absence of leaks with the solenoid valve closed, giving a normal or abnormal result, S6- a step of opening the shut-off solenoid valve, and a second check for the absence of leaks with the solenoid valve open, giving a normal or abnormal result, S7- a step of checking the pump's electrical consumption, giving a normal or abnormal result, S8- a step for determining a type of anomaly and a step for reporting the type of anomaly if one of the anomaly criteria is verified.

[0010] Thanks to the provisions promoted above, it is possible to discriminate which component or organ of the system is suspected of an anomaly. This is a valuable aid for maintenance operators who can have relevant information about the component that they must exchange to contribute to the repair of the secondary air circuit system.

[0011] For the verification steps, a normal result corresponds to an expected situation, i.e. a value or values ​​that are within a range of nominal or normal values. Conversely, an abnormal result corresponds to a problematic situation with one or more values ​​that are outside a range of nominal or normal values.

[0012] It is noted that during the diagnostic steps, the engine is stopped, at least for steps S3- to S7-.

[0013] It is noted that the air circuit comprises, in this order: the inlet pipe, the air pump, the intermediate pipe, the shut-off solenoid valve and the outlet pipe. blowing.

[0014] In step S7-, the electrical consumption of the pump motor is for example delivered by a current sensor, or by information returned from the power switches (MOSFETs) inside the control unit.

[0015] According to one embodiment, in step S3-, the pressure value reached after a predetermined time is checked with respect to a chart of intrinsic characteristics of the pump and the rotation speed of the pump. The measured pressure is compared with the expected pressure with respect to the chart.

[0016] According to one embodiment, in step S3-, the pressure value reached after a predefined time is checked with regard to a map dependent on the pump speed.

[0017] According to one embodiment, in step S3-, the pressure value is checked with respect to a pressure threshold value and said pressure threshold value further depends on the temperature and the ambient pressure.

[0018] According to one embodiment, the characteristics of the air pump are given in the form of an abacus in a diagram with the air flow rate on the abscissa and the compression ratio on the ordinate, with pump rotation iso-speed curves which make it possible to establish a correspondence between a compression ratio and an expected flow rate for a given rotation speed.

[0019] According to one embodiment, in step S8-, a pump fault is declared in response to one of the following combinations: - verification S3 gives an abnormal result, then verification S4 gives an abnormal result, - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives an abnormal result, then check S7 gives a normal result, - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives a normal result.

[0020] Under these conditions, an indication is given for vehicle maintenance, this indication specifying that the pump appears to be defective.

[0021] According to one embodiment, in step S8-, an intermediate driving fault is declared in response to the following combination: - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives an abnormal result, then check S7 gives an abnormal result.

[0022] Under these conditions, an indication is given for the maintenance of the vehicle, this indication specifying that the intermediate pipe, between the pump and the stop valve, appears to be defective.

[0023] According to one embodiment, in step S8-, a blowing duct fault is declared in response to one of the following combinations: - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives an abnormal result, - check S3 gives a normal result, then check S6 gives an abnormal result.

[0024] Under these conditions, an indication is given for the maintenance of the vehicle, this indication specifying that the blowing pipe, between the stop valve and the heating grille, appears to be defective.

[0025] According to one embodiment, in step S6-, a flow rate estimate calculated from the aeraulic conditions in the intermediate pipe is compared with an expected flow rate estimate calculated from a chart of the pump characteristics.

[0026] This makes it possible to determine the presence of a leak concerning a pipe, for example the presence of a crack in the pipe or a disconnected state of the pipe.

[0027] According to one embodiment, in step S7-, a pump power is calculated and compared to a theoretical power from a chart.

[0028] According to one option, said theoretical power of the pump further depends on the pressure delivered by the pump and the ambient atmospheric conditions (pressure and temperature).

[0029] According to one embodiment, the method may comprise a step of prior verification of the absence of rotation of the internal combustion engine, and provision may be made to terminate said method as soon as the start of the engine start sequence is detected.

[0030] As a result, the diagnostic steps of the method are prevented from being disturbed by the rotation of the engine or the engine start sequence.

[0031] According to one embodiment, the method can be carried out at each new cycle of use of the vehicle.

[0032] Thus, a fault occurring during the life of the vehicle is detected as soon as possible.

[0033] According to one embodiment, the method provides that a detected anomaly is recorded in the memory of the control unit. Whereby the memory of the control unit keeps track of the anomaly in question and can be read by a diagnostic tool in a repair garage.

[0034] According to one embodiment, the activation of the heating resistors of the heating grid is delayed until after the tests mentioned above have been carried out.

[0035] The invention further relates to an internal combustion engine, comprising a secondary air circuit system, in which the method as described above is implemented, while the engine is running.

[0036] In the secondary air circuit, the inlet pipe and the intermediate pipe may be made of synthetic or polymer material. The blowing pipe may be made of metal.

[0037] The transverse diameter of the pipes can be between 12 millimeters and 16 millimeters, without these dimensions being limiting.

[0038] The invention further relates to a vehicle comprising an engine as described above, characterized in that provision is made for detecting an event anticipated in relation to starting the engine.

[0039] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: [Fig.l] is a schematic representation of an exemplary internal combustion engine with a secondary air circuit in which the present invention is implemented, [Fig.2] is a more localized schematic representation of the secondary air circuit, [Fig.3] represents an example of an abacus illustrating the operating characteristics of the pump. [Fig.4] is a schematic representation showing a power consumption of the pump motor; [Fig.5] represents an example of a flowchart showing the sequence of tests; [Fig.6] represents an example of a timeline illustrating the sequence of actions.

[0040] We will now describe, with reference to [Fig.l], a general diagram of an internal combustion engine of a motor vehicle, which comprises an engine block 7 including the cylinders (here four). The main air circuit extends from the air filter 51 arranged upstream to the downstream exhaust pipe 56. On this main air circuit, a compressor 81 of a turbocharger is shown and further downstream a throttle valve marked 53. Downstream of the throttle valve 53, the intake manifold 58 distributes the air into the cylinders. Downstream of the cylinders, an exhaust manifold 59 collects the burnt gases which first pass through the turbine 82 of the turbocharger, the burnt gases then being directed towards the catalytic converter 55 then towards the downstream exhaust pipe 56.

[0041] The internal combustion engine presented here is a gasoline engine, i.e. spark ignition. It should be noted that the presence of the turbocharger is not obligatory within the meaning of this convention; the engine may be without it. It should also be noted that the present invention remains valid for a diesel engine or one operating with any other source of fuel.

[0042] The motor vehicle may be a hybrid vehicle, that is to say that it may have, in addition to the internal combustion engine, an electric traction motor and an on-board electrical energy storage device.

[0043] Now concerning the secondary air circuit 6, this extends from the air filter 51 to a heating grid 5 of the catalytic converter 55.

[0044] As also illustrated in [Fig.2], the secondary air circuit 6 comprises an inlet pipe 11 bringing air from the air filter to an air pump 2.

[0045] Downstream of the air pump 2, an intermediate pipe 12 directs the air pressurized by the pump to a shut-off valve. The intermediate pipe 12 is equipped with a pressure and temperature sensor, marked 4. The pressure and temperature sensor 4 is arranged on the intermediate pipe, at an intermediate position as illustrated, but it can also be arranged just at the outlet of the pump or just at the inlet of the shut-off valve. The pressure and temperature sensor 4 can be mounted on a connection transverse to the intermediate pipe or directly in an orifice of the intermediate pipe 12.

[0046] Downstream of the intermediate pipe 12, the secondary air circuit 6 comprises a stop valve 3 and a blowing pipe 13 downstream of the stop valve 3. The blowing pipe 13 opens onto the heating grid 5. It should be noted that the blowing pipe 13 can be equipped with a diffuser to optimize / homogenize the air flow on the heating grid.

[0047] The pressure prevailing in the inlet pipe 11 is denoted PI, the pressure prevailing in the intermediate pipe 12 is denoted P2, and the pressure prevailing in the blowing pipe 13 is denoted P3. The pressure prevailing in the catalytic converter 55 downstream of the heating grid 5 is denoted P4. When the engine is not running, this is the case which interests us here, P4 is equal to the atmospheric pressure Patmo.

[0048] The stop valve 3 may be a valve controlled by electrical means in which case it is a valve that can be called a solenoid valve, but the stop valve 3 could be controlled by a non-electrical means, such as by a vacuum lung.

[0049] The shut-off solenoid valve 3 may be an induction-moved valve as shown. The shut-off solenoid valve 3 can also be a flap or a shutter moved by an electric motor. The shutter can be, for example, a quarter-turn shutter, but any other type of valve technology can be used.

[0050] The air pump is for example a vane pump, but any technological type of air pump can be used within the scope of the present invention. The pump is driven by an electric motor 20. Said electric motor 20 is controlled by a control unit 8. Said control unit 8 also controls the shut-off solenoid valve 3 via its inductive coil 30. The control unit 8 can be specific to the catalytic converter heating function or the control unit 8 may form part or a function of a general engine management and control computer.

[0051] The shut-off valve 3 is open during the heating sequence to allow air to flow from the secondary air circuit, but it must be closed when the engine is running to prevent exhaust gases from flowing back up to the air filter. When the shut-off valve 3 is closed, it prevents any air from passing from the intermediate pipe to the blow-off pipe and vice versa. The shut-off valve 3 may be formed as a piloted flap, for example a quarter-turn flap.

[0052] The rest of the time, i.e. when the engine is not running and there is no need to blow air into the secondary air circuit, the shut-off valve can remain open or closed.

[0053] The shut-off valve may be monostable, i.e. require an electrical supply while it is in the open state. In this case, the shut-off valve may be controlled at the same time as the pump and the heating grid 5. The shut-off valve 3 may be returned by a spring to its closed position, and moved away from the closed position to an open position by supplying electrical or mechanical energy.

[0054] Alternatively, the shut-off valve may be bistable, i.e. it requires being actively moved (e.g. electrically powered) only for a change of state, either open to closed, or closed to open.

[0055] Generally, the air pump must be controlled at the same time as the heating grid is electrically powered to produce calories by Joule effect. However, the activation of the heating grid can be delayed until after diagnostic tests to discriminate possible component failures.

[0056] The inlet pipe 11 and the intermediate pipe 12 can be made of synthetic material or plastic polymer. The blowing pipe 13 can be made of metal, in particular due to the hot environment since it is in contact with the catalytic converter 55.

[0057] The air flow circulating in the pipes in question 11, 12, 13 for the heating function of the catalytic converter 55 remains moderate and in practice the airflow losses in the current section can be neglected.

[0058] The method first provides a step, called SI-, of closing the shut-off solenoid valve 3 consisting of closing the shut-off solenoid valve or maintaining the shut-off solenoid valve 3 in the closed state.

[0059] The method then provides a step of controlling the pump up to a predetermined speed setpoint value (step denoted S2-). The predetermined speed setpoint value VRi can be calculated as a function of the more or less early anticipation of the heating in relation to an estimated future use of the catalytic converter. The predetermined speed setpoint value can also be calculated as a function of the electrical power which will be dissipated in the heating grid.

[0060] Then, in step denoted S3-, we take advantage of the known characteristics of the air pump, which are for example known from an ACP chart, such as that shown in [Fig.3],

[0061] In this example, for a given rotation speed of the pump, there is a correspondence between the flow rate delivered by the pump and the compression ratio (pressure ratio between the pump outlet and the pump inlet).

[0062] We note that for a given rotation speed, if the compression ratio decreases then the flow rate increases according to this chart.

[0063] In the case of application of the secondary air circuit, the inlet pressure of the pump is PI and the outlet pressure of the pump is P2.

[0064] As the air flow considered here is relatively low, the air filter does not cause a significant pressure loss, consequently it is neglected so that PI is approximated by the atmospheric pressure Patmo.

[0065] The rotation speeds VR1, VR2, VR3, VR4, VR5 and VR6 are six speed setpoint values ​​with increasing notation, VRi being a generic notation. With reference to [Fig.3], generally speaking, if the setpoint rotation speed is VR5, and the compression ratio is P2a / Pla, then the chart allows the expected flow rate noted Qa to be found.

[0066] In particular, when the stop valve is closed, the flow rate delivered by the pump is zero Q=0, and the ACP chart makes it possible to estimate the pressure normally expected at the pump outlet as a function of its rotation speed VRi, for example PR5 if the rotation speed is VR5.

[0067] The method provides for waiting for a predefined time DTI after starting the pump to determine whether the pressure measurement made at that time substantially corresponds or not to the expected pressure. With reference to [Fig.6], the control of the pump starts at time t0 and the acquisition of the pressure of interest occurs at time tl after a duration DTI.

[0068] For example, in the illustrated case, if the pressure P2 is between 95% of PR5 and 105% of PR5, then the verification of the pressure rise gives a normal result.

[0069] Conversely, if the pressure P2 is not between 95% of PR5 and 105% of PR5, then the verification of the pressure rise gives an abnormal result.

[0070] Then, in step denoted S4-, the method provides a step of verifying the rotation speed cop. The rotation speed cop is for example measured by a sensor delivering information representative of the rotation speed of the pump. This sensor can be arranged opposite the rotor shaft of the pump or another part linked in rotation to the pump.

[0071] If the observed rotational speed is substantially equal to the rotational speed setpoint as controlled by the control unit 8, then the test carried out in step S4- gives a normal result. Otherwise the test carried out in step S4- gives an abnormal result.

[0072] Then, in step denoted S5-, the method provides a step of checking for the absence of leaks with the solenoid valve in the closed state. The aim of this step is to detect a possible leak in the intermediate pipe, in particular by calculating the estimated flow rate in two ways.

[0073] The control unit 8 estimates an air flow rate noted QF which can be calculated by a theoretical or empirical function which is written in the form: QF = F (P2,T2,Seff), where P2 and T2 are the temperatures prevailing in the intermediate pipe and Seff is a parameter representative of the effective section.

[0074] According to one option, if the air flow rate noted QF is lower than a predetermined threshold value, this is representative of an absence of substantial leakage and in this case the result of the test is normal.

[0075] According to another option, the control unit 8 estimates a second flow rate noted QF2 which is calculated from the pump characteristics. As a function of this, the control unit 8 calculates a delta between the two previously calculated flow rates noted DQF, i.e. QF2-QF.

[0076] If the flow delta DQF is greater than a predetermined threshold value, this is representative of the existence of a leak in the pipes, in particular in the intermediate pipe 12, and in this case the result of the test is abnormal.

[0077] After step S5-, the method comprises a step named S6- comprising an action of opening the shut-off solenoid valve 3, then a step of second verification of absence of leakage with solenoid valve open.

[0078] Advantageously, a first air flow rate Q1 is calculated, estimated from the characteristics of the air pump, from information on the rotation speed of the pump VRi and from information on the pressure P2 prevailing in the intermediate pipe. For this first calculation, the ACP chart is used, for example.

[0079] In parallel, a second air flow rate Q2 can be calculated by a theoretical or empirical function which is written in the form: Q2 = F (P2,T2,Seff), where P2 and T2 are the temperatures prevailing in the intermediate pipe and Seff is a parameter representative of the effective section.

[0080] In other words, in step S6-, an estimate of flow rate Q2 calculated from the aeraulic conditions in the intermediate pipe is compared with an estimate of expected flow rate Q1 calculated from a chart of the pump characteristics.

[0081] Thanks to the estimation of the flow rate Q2, it is possible to carry out a feedback of the rotation speed of the pump, thus forming a control on the speed control of the pump.

[0082] Thus, the control unit 8 can adjust the rotation speed setpoint of the pump according to the estimated flow rate via the airflow conditions by controlling the current delivered to the motor 20. This makes it possible to compensate for any drop in pump performance linked to wear or an incident on a vane.

[0083] The method provides a step S7 for verifying the electrical consumption of the pump. [Fig.4] illustrates the power consumed by the pump as a function of the pressure at its outlet with a curve for the case of the open valve and a curve for the case of the closed valve.

[0084] The electric current consumed by the pump can be measured either by a specific current sensor or can be calculated by the control unit 8 which knows, via internal sensors, the currents circulating in the power switches connected to the poles of the electric motor 20. The intelligent power switches (Smart MOSFETs) can in fact return the value of the current flowing through them.

[0085] As illustrated in [Fig.6], at the bottom is the pump control C2, in the middle the valve control C3 and at the top the heating resistors control C5. The pump control begins at time t0, and the pressure test at step S3 is carried out at time t1, after a duration DTI. At time t2, the control unit 8 controls the closing of the valve, which switches to the open state, releasing the passage of air downstream to the heating resistor grid. At time t3, the tests are finished and the control unit activates the electric current in the heating resistors. Note that the heating of the grid can also be done before the diagnostic sequence previously explained.

[0086] All of the tests can be carried out in a duration typically between 1 second and 3 seconds, preferably less than 2 seconds.

[0087] As visible in [Fig.5], if step S3 gives a normal result, the flowchart is finished ('end' box 90), and conversely if test S3 gives an abnormal result then the flowchart continues with test S4.

[0088] If step S4 gives a normal result, then the flowchart continues with test S5, and conversely if test S4 gives an abnormal result, then the flowchart arrives at a conclusion of a pump fault.

[0089] If step S5 gives a normal result, then the flowchart continues with an opening of the valve then with test S6, and conversely if test S5 gives an abnormal result then the flowchart continues with test S7.

[0090] If step S6 gives a normal result, then the logic diagram arrives at a conclusion of pump fault, more precisely rotation information failure. Conversely, if test S6 gives an abnormal result, then the logic diagram arrives at a conclusion of blowing pipe fault.

[0091] If step S7 gives a normal result, then the flowchart arrives at a conclusion of pump fault, more precisely failure of rotating elements of the pump. conversely, if the S7 test gives an abnormal result, then the flowchart arrives at a conclusion of an intermediate driving fault.

[0092] We note that only one arrival box of the flowchart corresponds to no fault, it is marked by 90 ('end').

[0093] Thus, generally, the method provides a step S8- of determining a type of anomaly and a step of signaling the type of anomaly if one of the anomaly criteria is verified.

[0094] An anomaly criterion corresponds to all the arrival boxes of the flowchart except the box marked 90.

[0095] A pump fault is declared in response to one of the following combinations: - verification S3 gives an abnormal result, then verification S4 gives an abnormal result (box 95), - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives an abnormal result, then check S7 gives a normal result (box 93), - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives a normal result (box 91).

[0096] An intermediate conduct fault is declared in response to the following combination: - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives an abnormal result, then check S7 gives an abnormal result (box 94).

[0097] A blowing pipe fault is declared in response to the following combination: - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives an abnormal result (box 92).

[0098] Furthermore, the control unit 8 can be configured to interrupt the test sequence in the event of the start of the engine start sequence, for example on an active flywheel tooth signal information. Such an interruption causes the solenoid valve 3 to close and the air pump motor 2 to stop.

[0099] It is noted that the secondary air circuit as promoted here is devoid of a flow sensor itself, i.e. there is no flow meter in the secondary air circuit.

Claims

Claims

1. Method for detecting an anomaly in an air circuit system (6), in an internal combustion engine, the air circuit system comprising a control unit (8), an inlet line (11), an air pump (2), an intermediate line (12) downstream of the air pump, with a pressure and temperature sensor (4) arranged on the intermediate line, a shut-off solenoid valve (3), a blow-off line (13) downstream of the shut-off solenoid valve, the blow-off line being configured to deliver air onto a heating grid (5) to heat a catalyst pot (55), characterized in that the method comprises: S1- a step of closing the shut-off solenoid valve consisting of closing the shut-off solenoid valve or keeping the shut-off solenoid valve in the closed state, S2- a step of controlling the pump up to a predetermined speed setpoint value (VRi),S3- a step of verifying the pressure rise in the intermediate pipe (12), giving a normal or abnormal result, S4- a step of verifying the rotation speed (cop) measured by a sensor delivering information representative of the rotation speed of the pump, giving a normal or abnormal result, S5- a step of first verification of absence of leak with solenoid valve closed, giving a normal or abnormal result, S6- a step of opening the stop solenoid valve, and second verification of absence of leak with solenoid valve open, giving a normal or abnormal result, S7- a step of verifying the electrical consumption of the pump, giving a normal or abnormal result, S8- a step of determining a type of anomaly and a step of signaling the type of anomaly if one of the anomaly criteria is verified.,

2. Method according to claim 1, characterized in that in step S3-, the pressure value reached after a predetermined time (DTI) is checked with regard to an abacus (ACP) of intrinsic characteristics of the pump and the rotation speed of the pump.

3. Method according to any one of claims 1 to 2, characterized in that, in step S8-, a pump fault is declared in response to one of the following combinations: - verification S3 gives an abnormal result, then verification S4 gives an abnormal result, - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives an abnormal result, then check S7 gives a normal result, - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives a normal result.

4. Method according to any one of claims 1 to 3, characterized in that, in step S8-, an intermediate driving fault is declared in response to the following combination: - verification S3 gives an abnormal result, then verification S4 gives a normal result, then verification S5 gives an abnormal result, then verification S7 gives an abnormal result.

5. Method according to any one of claims 1 to 4, characterized in that, in step S8-, a blowing pipe fault is declared in response to one of the following combinations: - check S3 gives an abnormal result, then check S4 gives a normal result, then check S5 gives a normal result, then check S6 gives an abnormal result, - check S3 gives a normal result, then check S6 gives an abnormal result.

6. Method according to any one of claims 1 to 5, characterized in that in step S6-, a flow rate estimate calculated from the aeraulic conditions in the intermediate pipe is compared with an expected flow rate estimate calculated from a chart of the pump characteristics.

7. Method according to any one of claims 1 to 6, characterized in that it comprises a step of prior verification of the absence of rotation of the internal combustion engine, and in that it is provided to terminate said method as soon as the start of the engine starting sequence is detected.

8. Method according to any one of claims 1 to 7, characterized in that it is carried out at each new cycle of use of the vehicle.

9. A gasoline internal combustion engine, comprising a secondary air circuit system, in which the method according to any one of claims 1 to 8 is carried out, while the engine is running.

10. A vehicle comprising an engine according to claim 9.

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