FR3150306A1 - METHOD FOR DETECTING A LEAK IN A DEPOLLUTED ENGINE SECONDARY AIR CIRCUIT - Google Patents

Abstract

The invention relates to a method for detecting a leak in an air circuit 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 blowing pipe (13) delivering air to a heating grid (5) to heat a catalyst pot (55), the method comprising: a step of controlling the pump, a step of calculating a first air flow rate based on the characteristics of the pump, from information on the rotation speed of the pump and information on the pressure prevailing in the intermediate pipe, a step of calculating a second parameter based on airflow conditions prevailing downstream of the air pump, and a step of comparing with a predetermined threshold. Figure 2

Description

METHOD FOR DETECTING A LEAK IN A DEPOLLUTED ENGINE SECONDARY AIR CIRCUIT

The invention relates to a method for detecting a possible leak in an air circuit, in particular in a so-called secondary air circuit, in an engine depolluted by means of a catalytic converter.

In low-emission internal combustion engines, a pollutant-reducing exhaust system, known as a catalytic converter, is provided. In order to perform its function properly, 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.

Typically, when the vehicle engine is started, the temperature in the catalytic converter is below the optimum operating temperature. The temperature increases as the engine runs and reaches a sufficient level after a few dozen seconds, or even a little longer depending on the low ambient starting temperatures.

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

This heating system includes 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.

Since this is a system that contributes 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 Anglo-Saxon terminology "On Board Diagnostic").

In addition, this is an advance heating system, which is implemented before the engine is started. The diagnosis can thus be carried out before the engine is started.

The present invention is particularly concerned with the detection of a possible leak in the air ducts which carry the air flow from the secondary circuit to the heating grid.

For this purpose, the present invention provides a method for detecting a leak in an air circuit, in an internal combustion engine, the air circuit comprising 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 line being configured to deliver air onto a heating grid to heat a catalyst pot,
characterized in that the method comprises:
a- a step of controlling the pump up to a predetermined speed setpoint value,
b- a step of first calculation of a first air flow rate based on the characteristics of the air pump, from information on the rotation speed of the pump and information on the pressure prevailing in the intermediate pipe, giving a first estimated air flow rate,
c- a second calculation step of a second parameter based on air conditions prevailing downstream of the air pump,
d- a step of comparing a third value, calculated from the first estimated air flow and/or the second parameter, with a predetermined threshold,
e- a step of signaling a fault if the third value exceeds the predetermined threshold.

Thanks to the provisions promoted above, it is possible to detect an anomaly in relation to the expected air flow, said anomaly being able to be representative of an air leak. Said air leak can be partial, for example a crack in a pipe or can be total, for example a disconnected, or cut or even missing pipe.

As will be seen later, the second parameter can be a second estimate of the air flow or an estimate of the apparent cross section.

Note that during the diagnostic steps, the engine is stopped.

Note that the air circuit includes, in this order: the inlet pipe, the air pump, the intermediate pipe, the shut-off solenoid valve and the blowing pipe.

According to one embodiment, the second parameter is an estimate of an air flow rate based on pressure and temperature information prevailing downstream of the air pump, as a function of an effective section, giving a second estimated air flow rate, the third value being a difference between the first and second estimated flow rates.

A significant difference in estimated flow rates is indicative of a defect in the air piping downstream of the pump. The first estimated flow rate is calculated from the intrinsic characteristics of the pump and the pressure downstream of the pump, while the second estimated flow rate is calculated from the airflow conditions downstream of the pump to the heating grid. If everything is normal, the two flow rates are substantially equivalent, while if the two flow rates are substantially different, this indicates the presence of an air leak.

According to one embodiment, generally speaking, the second air flow rate Q2 is estimated by Q2 = F (P2,T2,Seff), where P2 and T2 are respectively the pressure and the temperature prevailing in the intermediate pipe and Seff is a parameter representative of the effective section.

The effective section Seff is a predetermined parameter resulting from the preparatory calibration and validation measurements of the function. The effective section is representative of the smallest section obstructing the air path between the pump and the grid outlet. In practice, this can be the passage section presented by the stop valve (in its open state), or the passage section presented by the reheating grid. Note that the pressure losses in the current section of the pipes are neglected here given the relatively modest air flows.

According to one embodiment, the second air flow is estimated by the expression:
where Q2 is the second estimated air flow rate, CFE is a flow coefficient linked in particular to the nature of the gas and the configuration of the pipe circuit, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by atmospheric pressure, T2 is the temperature downstream of the pump.

We thus use an equation derived from the equations governing the flow of compressible gases, in particular the application to a simple pipe of the Navier Stokes and Barré de Saint Venant equations.

According to one embodiment, the second parameter is an estimate of an apparent effective section, based on aeraulic conditions prevailing in the intermediate pipe, from pressure and temperature information prevailing in the intermediate pipe, the apparent effective section being estimated by the expression:
where Q1 is the first estimated air flow, CFE is a flow coefficient linked in particular to the nature of the gas, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by atmospheric pressure, T2 is the temperature downstream of the pump. We use the same equation but in reverse mode.

In one embodiment, the process steps are performed while the shutoff solenoid valve is open. This tests the entire pump piping up to the heating grid.

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.

According to one embodiment, the steps of the method can be carried out while the shutoff solenoid valve is closed.

This allows you to diagnose only the part of the pipes between the air pump and the shut-off solenoid valve.

According to one embodiment, it may be provided to adjust the pump rotation speed setpoint according to the flow rate estimated via the airflow conditions. This achieves a control of the pump rotation speed.

The invention further relates to an internal combustion engine, comprising a secondary air circuit, and a control unit, in which the method as described above is implemented, while the engine is not rotating.

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

The cross-sectional diameter of the pipes can be between 12 millimeters and 16 millimeters, without these dimensions being limiting.

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.

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:
is a schematic representation of an exemplary internal combustion engine with a secondary air circuit in which the present invention is implemented,
is a more localized schematic representation of the secondary air circuit,
represents an example of an abacus illustrating operating characteristics of the pump.
is a schematic representation showing flow information as a function of a leakage ratio.
represents an example of a flowchart showing tests.

We now describe, with reference to the , 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 and further downstream a throttle valve marked 53 are shown. 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 to the catalytic converter 55 then to the downstream exhaust pipe 56.

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 mandatory within the meaning of this convention, the engine may be devoid of it. It should also be noted that the present invention remains valid for a diesel engine or any other fuel source.

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

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

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

Downstream of the air pump 2, an intermediate line 12 directs the air pressurized by the pump to a solenoid shut-off valve. The intermediate line 12 is equipped with a pressure and temperature sensor, marked 4. The pressure and temperature sensor 4 is arranged on the intermediate line, 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 transverse tapping to the intermediate line or directly in an orifice of the intermediate line 12.

Downstream of the intermediate pipe 12, the secondary air circuit 6 comprises a shut-off solenoid valve 3 and a blowing pipe 13 downstream of the shut-off solenoid 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 direct/homogenize the air flow on the heating grid.

The pressure in the inlet pipe 11 is denoted P1, the pressure in the intermediate pipe 12 is denoted P2, and the pressure in the blowing pipe 13 is denoted P3. The pressure in the catalytic converter 55 downstream of the heating grid 5 is denoted P4. When the engine is not running, which is the case of interest here, P4 is equal to atmospheric pressure Patmo.

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 stop solenoid valve 3 via its inductive coil 30. The control unit 8 can be specific to the heating function of the catalytic converter or the control unit 8 can form a part or a function of a general engine management and control computer.

Shut-off solenoid valve 3 is open during the warm-up 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 shut-off solenoid valve 3 is closed, it prevents any air from flowing from the intermediate line to the blow-off line and vice versa.

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 shutoff solenoid valve can remain open or closed.

The shut-off solenoid valve can be monostable, i.e. require a power supply while it is in the open state. In this case, the shut-off solenoid valve can be controlled at the same time as the pump and the grid is heated.

The shut-off solenoid valve can be bistable, meaning that it only needs to be electrically powered for a change of state, from open to closed, or closed to open.

Typically, the air pump must be operated at the same time as the heating grid is electrically powered to produce calories by Joule effect.

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

The cross-sectional diameter of the pipes can be between 12 mm and 16 mm, without these dimensions being limiting.

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 air losses in the current section can be neglected.

The method first provides a step of controlling the pump up to a predetermined speed setpoint value (step denoted a-). The predetermined speed setpoint value can be calculated as a function of the more or less early anticipation of 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 that will be dissipated in the heating grid.

Then, at step b-, we take advantage of the known characteristics of the air pump, which are for example known from an abacus, such as that shown in .

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

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

In the case of secondary air circuit application, the pump inlet pressure is P1 and the pump outlet pressure is P2.

Since the air flow considered here is relatively low, the air filter does not cause a significant pressure loss, and it is neglected so that P1 can be approximated by the atmospheric pressure Patmo.

An initial calculation of an air flow rate is carried out based on the characteristics of the air pump, from information on the rotation speed of the pump VR and information on the pressure P2 prevailing in the intermediate pipe. This calculation gives an initial estimated air flow rate denoted Q1. The rotation speeds VR1, VR2, VR3, VR4, VR5 and VR6 are six speed setpoint values in increasing notation. With reference to the , if the set rotation speed is VR5, and the compression ratio is P2a/P1a, then the chart allows us to find the expected flow rate noted Qa.

Then, at step c1-, a second flow calculation is carried out, based on pressure information P2 and temperature information T2 prevailing downstream of the air pump. This second flow calculation also uses an effective section noted Seff as a parameter known from preparatory work (calibration on reference engine).

In this document, with regard to units, temperatures, including T2, are expressed in degrees Kelvin and pressures, including P2, are expressed in Pascal.

This calculation gives a second estimated air flow Q2.

More precisely, we start from a fluid mechanics equation applied to the simplified case of flow of a compressible gas in a tube expressed as follows:

CFE is a surface flow coefficient specific to the flow of a gas (here air) in a given pipe. It can be a mapping datum, defined for example by mapping measurements on an aeraulic test bench.

Applied to our particular case, this gives:

Q2 is the second estimated air flow (in ^m3 /s), CFE is a flow coefficient linked in particular to the nature of the gas and the configuration of the pipe circuit, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by the atmospheric pressure Patmo, T2 is the temperature downstream of the pump.

More generally, the second air flow rate can be calculated by any 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.

After having carried out the two different flow estimation calculations Q1, Q2, we then calculate (step d1-) a difference between the first estimated flow Q1 and the second estimated flow Q2, as a third value.

There illustrates the effect of a leak on flow rates, with the x-axis representing the ratio of leak diameter to pipe diameter, and the y-axis showing flow rates.

Curve 91 represents the calculation of the flow rate according to the first calculation based on the intrinsic characteristics of the pump. It is noted that when the leakage ratio increases, then the compression ratio decreases, and then the flow rate increases.

Curve 92 represents the calculation of the flow rate according to the second flow rate calculation (flow rate equation). Here it is the opposite, when the leakage ratio increases, then the pressure decreases and it follows that the flow rate decreases.

Curve 94 represents the difference between the two results, namely the first estimated flow rate minus the second estimated flow rate.

The DPS threshold value represents the maximum value that curve 94 must not exceed to validate the integrity of the air line. If the difference between the two flow rates is greater than the DPS threshold value, then the method provides for a fault signalling step (step e-). In this case, a flag is mounted in the fault memory, and the MIL (Malfunction Indication Lamp) lamp on the instrument cluster signals the incident to encourage the vehicle to be taken to a repair garage.

Thanks to the estimation of the flow rate Q2, we can carry out a feedback of the rotation speed of the pump, thus forming a control on the speed control of the pump.

Thus, the control unit 8 can adjust the pump rotation speed setpoint according to the flow rate estimated 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.

According to a second embodiment, steps a- and b- are identical but the following two steps differ. Turning to the , the first embodiment proceeds to steps c1- and d1- while in the second embodiment proceeds to steps c2- and d2-.

In step c2-, the second parameter is an estimate of an apparent cross-section, calculated from pressure and temperature information prevailing in the intermediate pipe, the apparent cross-section being estimated by the expression:

This is the same equation as before but used in reverse. Q1 is the first air flow calculated in step b-, CFE is the flow coefficient, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by the atmospheric pressure Patmo, T2 is the temperature downstream of the pump.

In the case of the second embodiment, the 3rd value mentioned in the generic step called d- is the estimated apparent cross section Seffest.

At step d2-, if the Seffest value is too different from a configurable value contained in the memory, in particular higher, then this means that the pipes suffer from an anomaly.

According to a variant of application of the method, the steps of the method can be carried out while the shut-off solenoid valve is closed. For the implementation of step c-, this case corresponds to a very small, or even zero, effective section parameter Seff. Similarly, a different threshold can be chosen to trigger the alert than the threshold chosen for the case of the open valve.

Furthermore, the control unit 8 can be configured to interrupt the catalytic converter heating 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.

It should be noted that the actual speed of the pump rotation is not necessarily known.

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

Claims (10)

Method for detecting a leak in an air circuit (6), in an internal combustion engine, the air circuit comprising an inlet pipe (11), an air pump (2), an intermediate pipe (12) downstream of the air pump, with a pressure and temperature sensor (4) arranged on the intermediate pipe, a shut-off solenoid valve (3), a blowing pipe (13) downstream of the shut-off solenoid valve,
the blowing line being configured to deliver air onto a heating grid (5) to heat a catalyst pot (55),
characterized in that the method comprises:
a- a step of controlling the pump up to a predetermined speed setpoint value,
b- a step of first calculation of a first air flow rate based on the characteristics of the air pump, from information on the rotation speed of the pump and information on the pressure prevailing in the intermediate pipe, giving a first estimated air flow rate,
c- a second calculation step of a second parameter based on air conditions prevailing downstream of the air pump,
d- a step of comparing a third value, calculated from the first estimated air flow and/or the second parameter, with a predetermined threshold,
e- a step of signaling a fault if the third value exceeds the predetermined threshold.
Method according to claim 1, characterized in that the second parameter is an estimate of an air flow rate based on pressure and temperature information prevailing downstream of the air pump, as a function of an effective section (Seff), giving a second estimated air flow rate, the third value being a difference between the first and second estimated flow rates.
Method according to claim 2, characterized in that the second air flow estimated by the expression:
where Q2 is the second estimated air flow rate, CFE is a flow coefficient linked in particular to the nature of the gas and the configuration of the pipe circuit, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by atmospheric pressure, T2 is the temperature downstream of the pump.
Method according to claim 1, characterized in that the second parameter is an estimate of an apparent effective section, based on aeraulic conditions prevailing in the intermediate pipe, from pressure and temperature information prevailing in the intermediate pipe, the apparent effective section being estimated by the expression:

where Q1 is the first estimated air flow, CFE is a flow coefficient linked in particular to the nature of the gas, P2 is the pressure downstream of the pump, P4 is the pressure downstream of the heating grid approximated by atmospheric pressure, T2 is the temperature downstream of the pump.
Method according to any one of claims 1 to 4, characterized in that the steps of the method are carried out while the shut-off solenoid valve is open.
Method according to any one of claims 1 to 5, characterized in that 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.
Method according to any one of claims 1 to 4, characterized in that the steps of the method are carried out while the shut-off solenoid valve is closed.
Method according to any one of claims 1 to 3, characterized in that provision is made to adjust the pump rotation speed setpoint as a function of the flow rate estimated via the airflow conditions.
Internal combustion engine, comprising a secondary air circuit and a control unit (8), in which the method according to any one of claims 1 to 8 is implemented, while the engine is not rotating.
Vehicle comprising an engine according to claim 9, characterized in that provision is made for detecting an event anticipated in relation to starting the engine.