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 malfunction of a shut-off valve (3) in an air circuit in a gasoline internal combustion engine. The air circuit comprises 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, and an air pump (2) interposed between the first and second sections of pipe, which is configured to deliver air onto a heating grid (5) to heat a catalytic converter (55). The method comprises: a) acquiring temperatures prevailing in the first section of pipe; b) calculating a temperature gradient over time; c) determining a fault if the temperature gradient exceeds a first trigger threshold; d) reducing engine load in case of a fault. 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 'catalyst', 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 controls, 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 malfunction of 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 warm a catalytic converter, characterized in that the method comprises: a- a stage of acquiring a temperature prevailing in the first section of the pipe, b- a step of periodic calculation of a temporal temperature gradient, based on the temperature values ​​acquired in the acquisition step, c- a step of determining a fault if the temporal gradient exceeds a first triggering threshold, continuously for a predefined duration.

[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 positive temperature gradient.

[0012] Monitoring a temperature gradient rather than an absolute temperature value allows for a faster response to such a fault in the shut-off valve.

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

[0014] It is noted that the predefined duration for declaring / confirming the fault can be small, for example on the order of 1 second, but in practice the predefined duration in question can be between 2 seconds and 5 seconds.

[0015] According to one embodiment, the first triggering threshold may depend on the engine speed and the torque delivered by the engine.

[0016] Such a cartographic trigger threshold makes it more robust to hazards and to avoid certain false detections, which could appear due to pronounced and sudden changes in engine speed or torque.

[0017] According to one embodiment, the first triggering threshold also depends on an ambient temperature. The ambient temperature can be an outside temperature, a temperature under the engine hood, a coolant temperature, or any other temperature measurement.

[0018] Wherefore, the robustness of the process can be further improved and the occurrences of possible false detections reduced.

[0019] According to one embodiment, the first triggering threshold can be a predetermined parameter independent of the engine speed and the torque delivered by the engine. This predetermined parameter can be dependent on the material used for the air line.

[0020] 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.

[0021] According to one embodiment, a step of reducing engine performance (reducing engine load) may also be provided in the event of the determination of a fault relating to the shut-off valve.

[0022] According to one embodiment, the reduction in engine performance may depend on the engine speed and the temperature gradient.

[0023] 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.

[0024] According to one embodiment, the method may further comprise: d- a step of determining a fault if the temperature prevailing in the first portion of the pipe exceeds a second absolute temperature threshold.

[0025] This is an additional safety measure, which could intervene if the temperature gradient-based logic did not work.

[0026] 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.

[0027] The values ​​obtained by the acquisition step are real values.

[0028] According to one embodiment, the prevailing temperature is estimated from a mathematical model.

[0029] This avoids the need for a temperature sensor on the intermediate pipe upstream of the valve. A temperature sensor can be used on a component located near the first section of pipe, and the temperature estimated in the pipe from a transfer function or a mathematical model.

[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; [Fig.7] schematically illustrates the steps of the process.

[0035] A general diagram of an internal combustion engine of a motor vehicle is now described with reference to [Fig. 1], comprising an engine block 7 including 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 exhaust. downstream exhaust 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 in the intermediate pipe 12 is denoted P2, and the pressure in the blow-off pipe 13 is denoted P3. The pressure in the catalytic converter 55 downstream of the preheating grid 5 is denoted 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 can be specific to the catalytic converter heating function or the control unit 8 may form part or 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 of calculating a time gradient of temperature, this is the step denoted b-.

[0055] For the calculation of the temporal temperature gradient, we start from the formula of the derivative of the temperature expressed as follows: GD = [TC(t+dt)-TC(t)] / dt.

[0056] In passing into the numerical domain, this gives GD = [TC(tb)-TC(ta)] / [tb-ta] where ta is a first sampling instant and tb is a second sampling instant.

[0057] The control unit 8 can calculate a time gradient each time it acquires a new temperature value TC.

[0058] However, it is also possible to have a sampling frequency for acquisition that is different from the frequency / recurrence for calculating the gradient.

[0059] The temporal temperature gradient GD is compared to a triggering threshold denoted GDS, referred to in this context as the "first triggering threshold".

[0060] Figure [Fig. 3] graphically illustrates the temperature reading in a normal case where the shut-off valve is correctly closed.

[0061] 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. It is observed that both the torque and the engine speed increase, thus indicating a very significant increase in the thermal energy transmitted in the exhaust gases. The reference ambient temperature is 25°C.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] Curve 73, at the bottom of the figure and shown in long dashed lines, represents the gradient over time; the graduation is located on the right of the figure, in degrees per second. It can be seen that curve 73 remains close to 0 and well below the GDS gradient threshold discussed below.

[0066] Figure 4 illustrates a scenario where valve 3 is not properly closed (e.g. presence of a leak). We can see immediately that the temperature curve (trace 94) increases very strongly after the operating conditions of the engine have changed from the first operating point PF1 to the second operating point of the engine PF2 at time t2.

[0067] Figure 4 also graphically illustrates the temporal gradient that corresponds to the substance 94 is related to the slope of curve 94, which is plotted from the succession of acquired temperature values ​​TC. Three calculation instances, GDI, GD2, and GD3, are illustrated in [Fig. 4]. The temperature temperature gradient mathematically represents the rate of temperature rise, i.e., the slope of curve 94. In the illustrated example, the iteratively calculated value is compared to a trigger threshold, identified as GDS.

[0068] Curve 74, at the bottom of the figure and shown in long dashed lines, represents the gradient over time. It can be seen that curve 74 exceeds the GDS threshold at time t3 and remains above the GDS threshold until a time after t5. After t5, curve 94 flattens out and curve 74 of the gradient reaches 0.

[0069] In the example of [Fig.4], we have GD2 < GDS and GD3 > GDS.

[0070] At time t3, we therefore have the condition that the temporal temperature gradient GD exceeds the first triggering threshold GDS.

[0071] According to the method, this condition must be verified during the time interval denoted TS. The condition GD>GDS must be verified continuously during the time interval TS. This prevents reacting too quickly to an outlier. If the condition becomes false again before this time interval, then it is necessary to wait for the fault condition to reappear before restarting the time from zero, and to confirm the fault only if this condition lasts for at least TS. Returning to the example in [Fig. 4], the fault condition is confirmed at time t4.

[0072] In the example illustrated in [Fig.4], there is no particular action on the operating conditions of the engine, which remains at operating point PF2. It can be seen that the temperature TC increases to a value between 90°C and 100°C.

[0073] It is noted that at time t5, the curve 94 crosses a threshold denoted TCS (here 75°C as a non-limiting example), which it is desirable not to exceed.

[0074] 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.

[0075] 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.

[0076] Curve 75, at the bottom of the figure and shown in long dashed lines, represents the gradient over time. Note that curve 75 exceeds the GDS threshold at time t3 and remains at- above the GDS threshold until a time after t4. After t6, the 95 curve bends and the 75 curve of the gradient goes below 0 just after time t6.

[0077] When the determination of a fault is confirmed, namely that the time gradient of temperature has been greater than the first trigger threshold GDS for at least the time delay TS, which occurs at time t4 on the [Fig.5], then the control unit 8 causes a reconfiguration of the motor, here represented by a reduction in motor performance, i.e. a reduction in motor load.

[0078] 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 'limping home' mode.

[0079] Here we have illustrated a torque reduction implemented from time t4. 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 dashed line labeled 94'. The curve 95 follows a downward-pointing bell curve and does not exceed the TCS threshold in this case.

[0080] At time t6, the engine operates according to a third operating point named PF3 with an engine speed noted RPM3 and a delivered torque noted TQ3.

[0081] 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.

[0082] In this case, it turns out that the temperature TC still exceeds the TCS threshold, called here the second threshold.

[0083] According to this condition, the process optionally provides for the following step d-: a step of determining a fault if the temperature prevailing in the first portion of the pipe exceeds a second TCS absolute temperature threshold.

[0084] It can be provided that the control unit then triggers, at time t7, a second reduction in engine performance, for example a larger reduction in the torque delivered, as shown in [Fig.6].

[0085] At time t8, the engine operates according to a fourth operating point named PF4 with an engine speed noted RPM4 and a delivered torque noted TQ4.

[0086] By way of non-limiting example, the GDS trigger threshold relating to the temperature time gradient criterion can be a fixed predefined parameter, independent of the engine's operating conditions and the ambient temperature. For example, a GDS trigger threshold can be chosen with a value between 0.1 °C per second and 0.5 °C per second, depending on measurements and tests carried out on validation engines or vehicles.

[0087] According to a non-limiting example, the GDS trigger threshold relating to the criterion on The temperature gradient over time can depend on the engine speed and the torque delivered by the engine. This can be a fairly simple map that tolerates higher gradient values ​​for high speeds and torques and has lower threshold gradient values ​​for a steady speed at idle, for example.

[0088] By way of example, the GDS trigger threshold for the temperature time gradient criterion may also depend on an ambient temperature. This could be, for example, the outside temperature or the coolant temperature. The mapping of the trigger threshold values ​​can thus be multidimensional.

[0089] 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 in the first section of pipe. This indirect information is fed into a mathematical compensation model, derived from calibration tests, to provide an estimated temperature prevailing in the first section of pipe upstream of the shut-off valve.

[0090] The method may provide that a detected 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 garage.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] It should also be noted that the reduction in torque can be more or less significant, even leading to the engine cutting out in the worst case.

[0095] It should also be noted that the torque reduction can be constant or mapped according to engine speed and temperature gradient, for example.

[0096] It should also be noted that torque reductions can be successive in order to limit the drop in torque felt by the customer.

Claims

Claims

1. Method for detecting a malfunction of 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 calculating a temperature time gradient, from the temperature values ​​acquired in the acquisition step,c- a step of determining a fault if the time gradient exceeds a first trigger threshold (GDS), continuously for a predefined duration (TS).,

2. Method according to claim 1, characterized in that the first trigger threshold depends on the engine speed and the torque delivered by the engine.

3. Method according to claim 2, characterized in that the first trigger threshold further depends on an environmental temperature.

4. Method according to any one of claims 1 to 3, characterized in that the first trigger threshold is a predetermined parameter independent of the engine speed and the torque delivered by the engine.

5. Method according to any one of claims 1 to 4, characterized in that a step of reducing the performance of the engine is further provided in the event of determination of a fault relating to the shut-off valve.

6. Method according to any one of claims 1 to 5, characterized in that it further comprises: d- a step of determining a fault if the temperature prevailing in the first portion of pipe exceeds a second absolute temperature threshold.

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 section 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. A gasoline 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 carried out, while the engine is running and the air pump is not activated.

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

Images