METHOD FOR DETECTING A VALVE FAULT IN A SECONDARY AIR CIRCUIT OF A DEPOLLUTED ENGINE

Abstract

The invention relates to a method for detecting a fault in a shut-off valve in an air circuit in a gasoline internal combustion engine. The air circuit comprises a shut-off valve (3), a first section of pipe (11, 12) upstream of the shut-off valve, a second section of pipe (13) downstream of the shut-off valve, a temperature sensor (4) arranged on the first section of pipe (11, 12), and an air pump (2). The second section of pipe is configured to deliver air pushed by the pump onto a heating grid (5) to heat a catalytic converter (55). The method comprises: a) a step of periodically acquiring the temperature prevailing in the first section of pipe; b) a step of determining a first fault if temperature values ​​acquired in the acquisition step exceed a first triggering threshold. Figure 2

Description

Title of the invention: METHOD FOR DETECTING A VALVE FAULT IN A SECONDARY AIR CIRCUIT OF A DEPOLLUTED ENGINE

[0001] The invention relates to a method for detecting a possible anomaly in an air circuit, in particular in a so-called secondary air circuit, in an engine with emissions control provided by means of a catalytic converter. The focus here is on an isolation valve or "shut-off valve" arranged in said secondary air circuit.

[0002] In low-emission internal combustion engines, an exhaust system for reducing pollutant gases, known as a 'catalytic converter' or 'catalytic converter', is provided. To function correctly, such a catalytic converter must be at least at a minimum required temperature. Such an engine with a catalytic converter is installed in a motor vehicle.

[0003] Generally, when the vehicle's engine is started, the temperature inside the catalytic converter is below the optimal operating temperature. The temperature increases as the engine runs and reaches a sufficient level after a few tens of seconds, or even slightly longer depending on the low ambient temperatures at startup.

[0004] The inventors therefore proposed to work on a catalytic converter heating system 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 airflow that then passes through the internal elements of the catalytic converter to heat it. Here, the airflow in question is part of the so-called secondary air circuit. As a reminder, the primary air circuit refers to the airflow that passes through the cylinders.

[0006] Furthermore, this is an advance heating system, which is activated before the engine starts. A diagnostic can therefore be carried out before the engine is started, particularly for compliance with anti-pollution regulations.

[0007] In another phase of its life, when the engine is running, burnt gases pass through the catalytic converter and the downstream exhaust, and it is necessary to prevent these burnt gases from flowing back up through the secondary air circuit. This is the role of the shut-off valve. This shut-off valve is pilot-operated, hence we also call it a solenoid valve. This shut-off valve can be shaped like a quarter-turn flap, a guillotine, a valve, or any other type of valve operated by an electrical element, e.g., either a motor or an inductive coil, or a mechanical element, e.g., a vacuum actuator such as those used for the turbocharger control, for example.

[0008] A failure to close this shut-off valve could be detrimental, as very hot burnt gases rising up the pipes could cause excessive heating, damage, or even the start of combustion of certain components located upstream of the shut-off valve and / or upstream of the pump, but also in the environment under the engine hood in the worst case.

[0009] The present invention is particularly concerned with the detection of a malfunction or anomaly of this shut-off valve.

[0010] To this end, the present invention proposes a method for detecting a fault in a shut-off valve in an air circuit in an internal combustion engine, the air circuit comprising a shut-off valve, a first section of pipe upstream of the shut-off valve, a second section of pipe downstream of the shut-off valve, a temperature sensor arranged on the first section of pipe, an air pump arranged on the first section of pipe, the second section of pipe being configured to deliver air pushed by the pump onto a heating grid to heat a catalytic converter, characterized in that the method comprises: a- a step of periodically acquiring a temperature prevailing in the first section of the pipe, b- a step to determine a first fault if temperature values ​​acquired in the acquisition step exceed a first triggering threshold.

[0011] Thanks to the provisions described above, it is possible to detect an abnormal temperature rise upstream of the shut-off valve, which indicates that the shut-off valve is incompletely closed or not closed at all. In the presence of such an anomaly, the very hot combustion gases cause a significant temperature rise.

[0012] Under normal operating conditions, the temperature recorded at the first section of the pipe does not exceed 50°C. When the recorded temperatures exceed the first triggering threshold, which can be set, for example, around 60° or 70°, this indicates a fault that allows burnt gases to rise inside the pipe.

[0013] It is noted that during the diagnostic steps, the internal combustion engine is rotating and the air pump is not rotating.

[0014] According to one embodiment, the process may further comprise: c- a step to determine a second fault if temperature values ​​acquired in the acquisition step exceed a second triggering threshold continuously for a predefined duration

[0015] The second defect is more critical than the first defect because the second threshold of If the activation threshold is higher than the first threshold, the warning given to the vehicle driver can be more pronounced. Furthermore, the actions taken to reduce the upward heat flow in the pipes can be more drastic.

[0016] According to one embodiment, it may also be provided for a step of reducing the performance of the engine in the event of the determination of a first fault (DF1) or a second fault (DF2) relating to the shut-off valve.

[0017] By which means, the temperature of the burnt gases exiting the exhaust manifold is reduced, which reduces the impact of the leak which allows gases to rise upstream of the secondary circuit.

[0018] According to one embodiment, the first triggering threshold (TTH1) and / or the second triggering threshold (TTH2) may depend on the engine speed and the torque delivered by the engine

[0019] Such a mapping trigger threshold (first and / or second) makes it possible to be more robust to hazards and to avoid certain false detections, which could appear due to pronounced and sudden changes in engine speed or torque.

[0020] According to one embodiment, the first triggering threshold and / or the second triggering threshold may further depend on an ambient temperature. The ambient temperature may be an outside temperature, a temperature under the engine hood, a coolant temperature, or any other temperature measurement.

[0021] Wherefore, the robustness of the process can be further improved and the occurrences of possible false detections reduced.

[0022] R6 According to one embodiment, the first trigger threshold and / or the second trigger threshold may be a predetermined parameter independent of the engine speed and the torque delivered by the engine. This predetermined parameter may depend on the material used for the air line.

[0023] By means of tests on an air test bench, or on an engine, or even on a vehicle, a single parameter value can be obtained that makes it possible to reliably detect temperature increases while avoiding false readings. This solution allows for simpler software and very low memory resource requirements.

[0024] According to one embodiment, the temperature prevailing in the first portion of the pipe is obtained from a temperature sensor arranged on the first portion of the pipe.

[0025] The values ​​obtained by the acquisition step are real values.

[0026] According to one embodiment, the prevailing temperature is estimated from a mathematical model.

[0027] This avoids the need for a temperature sensor on the intermediate pipe upstream of the valve. A temperature sensor can be placed on a component located near the first section of pipe, and the estimated temperature in the pipe can be reconstructed from a transfer function or a mathematical model.

[0028] According to one embodiment, the method may provide that the first triggering threshold or respectively the second triggering threshold is exceeded for at least a short predefined period of time to declare the (or confirm the declaration of the) first fault or respectively the second fault.

[0029] This makes it possible to strengthen the strategy and to further reduce the occurrences of possible false detections.

[0030] The invention further relates to an internal combustion engine, comprising a secondary air circuit and a control unit, in which the process as described above is implemented, while the engine is running and the air pump is not activated.

[0031] In the secondary air circuit, the first section of the duct (the supply duct and the intermediate duct) may be made of synthetic or polymer material. The second section of the duct (the supply duct) may be made of metal.

[0032] The transverse diameter of the pipes can be between 12 mm and 16 mm, without these dimensions being limiting.

[0033] The invention further relates to a vehicle comprising an engine as described above.

[0034] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: [Fig. 1] is a schematic representation of an example of an 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 a timing diagram illustrating a normal case without failure of the shut-off valve; [Fig.4] represents another example of a timing diagram illustrating an abnormal case, i.e. with an anomaly related to the shut-off valve; [Fig.5] is analogous to [Fig.4] and further illustrates corrective actions in response to the detection of an anomaly on the shut-off valve; [Fig.6] is analogous to [Fig.4] and further illustrates additional corrective actions in response to the detection of an anomaly on the shut-off valve.

[0035] A general diagram of a motor is now described with reference to [Fig. 1]. Internal combustion of a motor vehicle, which includes an engine block 7 comprising the cylinders (here, four). The main air circuit extends from the upstream air filter 51 to the downstream exhaust manifold 56. On this main air circuit, a turbocharger compressor 81 is shown, and further downstream, a throttle valve 53. Downstream of the throttle valve 53, the intake manifold 58 distributes the air to the cylinders. Downstream of the cylinders, an exhaust manifold 59 collects the exhaust gases, which first pass through the turbocharger turbine 82. The exhaust gases are then directed to the catalytic converter 55 and then to the downstream exhaust manifold 56.

[0036] The internal combustion engine presented here is a gasoline engine, i.e., a spark-ignition engine. It should be noted that the presence of a turbocharger is not mandatory for the purposes of this invention; the engine may be without one. It should also be noted that this invention remains valid for a diesel engine or any other fuel source.

[0037] 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.

[0038] Now, regarding the secondary air circuit 6, this extends from the air filter 51 to a heating grid 5 of the catalytic converter 55.

[0039] As also illustrated in [Fig.2], the secondary air circuit 6 includes an inlet pipe 11 bringing air from the air filter to an air pump 2.

[0040] Downstream of the air pump 2, an intermediate pipe 12 directs the air pressurized by the pump to a shut-off valve 3. The intermediate pipe 12 is equipped with a temperature sensor, designated 4. The intermediate pipe 12 may also be equipped with a pressure sensor, designated 44. The temperature sensor 4 is arranged on the intermediate pipe, at an intermediate position as illustrated, but it may also be arranged directly at the outlet of the pump or directly at the inlet of the shut-off valve. The temperature sensor 4 may be mounted on a branch transverse to the intermediate pipe or directly in an orifice of the intermediate pipe 12.

[0041] Downstream of the intermediate pipe 12, the secondary air circuit 6 includes a shut-off valve 3 and a blow-off pipe 13 downstream of the shut-off valve 3. The blow-off pipe 13 opens upstream of the heating grid 5. It can be noted that the outlet of the blow-off pipe 13 can be equipped with a diffuser to direct and / or homogenize the airflow over the grid.

[0042] What is referred to in this document as the first portion of the conduit includes the inlet conduit 11 and the intermediate conduit 12. What is referred to in this document as the second portion of the conduit corresponds to the blowing conduit 13.

[0043] The pressure in the inlet pipe 11 is denoted PI, the pressure The pressure in the intermediate pipe 12 is noted as P2, and the pressure in the blow-off pipe 13 is noted as P3. The pressure in the catalytic converter 55 downstream of the preheating grid 5 is noted as P4.

[0044] 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 valve 3 via its inductive coil 30 (or via its motor). The control unit 8 may 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.

[0045] The shut-off valve 3 is open during the heating sequence to allow air from the secondary air circuit to flow, but it must be closed when the engine is running to prevent exhaust gases from flowing back towards the air filter. When the shut-off valve 3 is closed, it prevents any airflow from the intermediate duct to the blow-off duct and vice versa.

[0046] 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.

[0047] The shut-off valve can be monostable, i.e., require a power supply while it is in the open state. In this case, the shut-off valve can be activated simultaneously with the pump and the heating grid. The shut-off valve 3 can be returned to its closed position by a spring and moved from the closed position to an open position by the application of electrical or mechanical energy.

[0048] The stop valve can be bistable, that is to say, it only needs to be electrically powered for a change of state, open to closed, or closed to open.

[0049] Generally, the air pump must be controlled at the same time as the heating grid is electrically powered to produce calories by Joule effect.

[0050] The inlet pipe 11 and the intermediate pipe 12 can be made of synthetic material or plastic polymer. The outlet pipe 13 can be made of metal, particularly due to the hot environment as it is in contact with the catalytic converter 55.

[0051] The transverse diameter of the pipes can be between 12 mm and 16 mm, without these dimensions being limiting.

[0052] The proposed method is carried out when the internal combustion engine is running. The proposed method is preferably carried out with the air pump not activated, i.e., not rotating.

[0053] The proposed method includes a step of periodically acquiring a temperature prevailing in the first section of the pipe; this is the step denoted a-. The temperature value acquired by means of the temperature sensor 4 is generically denoted TC. The values ​​acquired successively over time are denoted TC(i), i being a sampling index, or alternatively, are denoted TC(ti), ti being a sampling instant.

[0054] The proposed method includes a step, denoted b-, consisting of comparing the acquired temperature values ​​TC(i) with respect to a first triggering threshold.

[0055] The control unit 8 is responsible for performing this comparison, after the analog-to-digital conversion of the signal representing the temperature. The control unit 8 can smooth the sequence of TC(i) values, for example with a digital low-pass filter, to eliminate any outliers.

[0056] It is possible to have a sampling frequency for acquisition that is different from the frequency / recurrence for the comparison calculation.

[0057] Figure 3 graphically illustrates the temperature reading in a normal case where the shut-off valve is correctly closed.

[0058] Figures 3, 4, 5, and 6 all illustrate the same scenario concerning the engine's operating conditions, shown in the upper part of each figure. At time t1, the engine is operating at point PF1 with an engine speed of RPM1 and a delivered torque of TQ1. A rapid change in operating conditions brings the engine's operating point to point PF2 at time t2, with an engine speed of RPM2 and a delivered torque of TQ2. As the torque and engine speed increase, the thermal energy transmitted in the exhaust gases increases significantly. The reference ambient temperature is 25°C.

[0059] The first operating point PF1 can correspond to a situation where the engine is idling or already under load. The second operating point PF2 corresponds to a situation with a higher load than the first operating point PF1, therefore a significantly increased thermal load of the exhaust gases.

[0060] On [Fig.3], we observe a rather moderate and rather slow increase in the temperature TC recorded in the intermediate pipe 12 of the secondary air circuit 6.

[0061] Examining curve 93, plotted from the sequence of acquired temperature values ​​TC, reveals small amplitude oscillations. The temperature value remains close to 30°C on average. The temperature changes at this point are a consequence of thermal radiation from neighboring parts, but this area is not in the hot part of the engine.

[0062] It is noted that curve 93 remains well below the TTH1 and TTH2 thresholds mentioned below.

[0063] Figure 4 illustrates a scenario where valve 3 is not properly closed (e.g., presence of a leak). It is immediately apparent that the temperature curve (trace 94) increases very sharply after the engine operating conditions have changed from the first operating point PF1 to the second operating point PF2 at time t2.

[0064] Fig. 4 also graphically illustrates the first triggering threshold noted TTH1 and the second triggering threshold noted TTH2.

[0065] By way of example, the first activation threshold is between 50°C and 60°C, and the second activation threshold is between 70°C and 80°C. Of course, the invention also applies to thresholds set differently or thresholds dependent on an engine map or an environmental parameter, as will be seen below.

[0066] The temperature curve 94 crosses the first triggering threshold at point 71 at time t3. At this time t3, the first DEFI fault is declared. The temperature curve 94 crosses the second triggering threshold at point 72 at time t4. At this time t3, the second DEFI fault is declared.

[0067] In the example illustrated in [Fig.4], there is no particular action on the operating conditions of the engine, which remain at the operating point PF2. It can be seen that the temperature TC increases to a value between 90°C and 100°C.

[0068] According to the method, it is further envisaged that an action on the operating conditions of the engine will be described now in relation to figures 5 and 6.

[0069] Figure 5 shows the temperature evolution curve 95 recorded in the first section of the pipe. The beginning of the sequence is identical to what was explained for Figure 4.

[0070] When the determination of a first DEFI fault is confirmed, namely that the temperature has become above the first triggering threshold TTH1, which occurs at time t3 on the [Fig.5], then the control unit 8 causes a reconfiguration of the motor, here represented by a reduction in motor performance.

[0071] Here, a reduction in engine performance should be understood as a specific mode of derating (called 'derating' in English). For severe performance limitations, this can be referred to as 'limp home' mode.

[0072] According to one variant, any other reconfiguration of the engine management allowing a reduction of the engine outlet temperature can be used, e.g. a modification of the camshaft phasers, a cut-off of injection for example.

[0073] Here we have illustrated a torque reduction implemented from time t3. The consequence of applying the engine performance reduction is that the thermal load of the exhaust gases is lower than that observed in [Fig. 4] which would have given the dotted line marked 94'. The curve 95 follows a downward-pointing bell and does not exceed the second TTH2 triggering threshold in this case.

[0074] At time t5, the engine operates according to a third operating point named PF3 with an engine speed noted RPM3 and a delivered torque noted TQ3.

[0075] Figure 6 shows the temperature evolution curve 96 recorded in the first section of the drive. The beginning of the sequence is identical to what was explained for Figure 4. The remainder is identical to what was explained for Figure 5, namely the initial reduction in engine performance.

[0076] In this case, it turns out that the temperature TC still exceeds the second triggering threshold TTH2.

[0077] According to this condition, the process optionally provides that the control unit then triggers, at time t4, a second reduction in engine performance, for example a larger reduction in the torque delivered, as shown in [Fig.6].

[0078] At time t5, the engine operates according to a fourth operating point named PF4 with an engine speed noted RPM4 and a delivered torque noted TQ4.

[0079] According to a non-limiting example, the first triggering threshold TTH1 and the second triggering threshold TTH2 can be fixed predefined parameters, independent of the operating conditions of the engine and the outside temperature.

[0080] For example, a value between 50°C and 65°C can be chosen for the first GDS trigger threshold, depending on measurements and tests carried out on validation engines or vehicles. For example, a value between 70°C and 85°C can be chosen for the second GDS trigger threshold.

[0081] By way of example, the first trigger threshold TTH1 and the second trigger threshold TTH2 may depend on the engine speed and the torque delivered by the engine. This could be a fairly simple map that tolerates higher values ​​for high speeds and torques and has lower threshold values ​​for a steady speed at idle, for example.

[0082] By way of non-limiting example, the first triggering threshold TTH1 and the second triggering threshold TTH2 may also depend on an ambient temperature. This could be, for example, the outside temperature or the coolant temperature. The mapping of threshold values ​​can thus be multidimensional.

[0083] In the absence of a physical sensor on the first section of pipe, the prevailing temperature can be estimated from a mathematical model using another source of temperature information, such as a temperature reading taken from a nearby element of the first section of pipe. This indirect information is introduced in a mathematical compensation model, derived from calibration tests, to give an estimated temperature prevailing in the first section of pipe upstream of the shut-off valve.

[0084] The method may provide that a detected fault or anomaly is recorded in the memory of the control unit. Whereby the memory of the control unit retains a record of the anomaly in question and can be read later by a diagnostic tool in a repair shop.

[0085] It should be understood that Figures 3 to 6 illustrate a scenario of a shut-off valve leak. In the case of a shut-off valve that remains fully open, the temperature rise is much steeper, making detection easiest. A small leak in the shut-off valve is the most difficult to detect since it differs little from the normal temperature changes observed in all operating conditions on the pipeline upstream of the shut-off valve.

[0086] It should also be noted that, for the description of the invention, we have considered a simple and theoretical case of motor load change (PF1->PF2), but in real-world motor operation, the operating point is constantly evolving. Nevertheless, the method promoted here works regardless of the operating points and their evolution over time.

[0087] It is noted that the air circuit comprises, in this order: the supply line, the air pump, the intermediate line, the shut-off valve and the blowing line.

Claims

Claims

1. Method for detecting a fault in a shut-off valve in an air circuit (6), in an internal combustion engine, the air circuit comprising a shut-off valve (3), a first pipe portion (11, 12) upstream of the shut-off valve, a second pipe portion (13) downstream of the shut-off valve, a temperature sensor (4) arranged on the first pipe portion (11, 12), an air pump (2) arranged on the first pipe portion, the second pipe portion being configured to deliver air pushed by the pump onto a heating grid (5) to heat a catalyst pot (55), characterized in that the method comprises: a- a step of periodically acquiring a temperature prevailing in the first pipe portion, b- a step of determining a first fault (DF1) if temperature values ​​acquired in the acquisition step exceed a first trigger threshold (TTH1).

2. Method according to claim 1, characterized in that it further comprises: c- a step of determining a second fault (DF2) if temperature values ​​acquired in the acquisition step exceed a second trigger threshold (TTH2) continuously for a predefined duration.

3. Method according to any one of claims 1 to 2, characterized in that a step of reducing the performance of the engine is further provided in the event of determination of a first fault (DF1) or a second fault (DF2) relating to the shut-off valve.

4. Method according to any one of claims 1 to 3, characterized in that the first trigger threshold (TTH1) and / or the second trigger threshold (TTH2) depend on the engine speed and the torque delivered by the engine.

5. Method according to claim 4, characterized in that the first trigger threshold (TTH1) and / or the second trigger threshold (TTH2) further depend on an ambient temperature.

6. Method according to any one of claims 1 to 3, characterized in that the first trigger threshold (TTH1) and / or the second trigger threshold (TTH2) is a predetermined parameter independent of the engine speed and the torque delivered by the engine.

7. Method according to any one of claims 1 to 6, characterized in that the temperature prevailing in the first portion of pipe is obtained from a temperature sensor arranged on the first portion of pipe.

8. Method according to any one of claims 1 to 6, characterized in that the prevailing temperature is estimated from a mathematical model.

9. 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 running and the air pump is not activated.

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

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