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 ANOMALY IN A DEPOLLUTED ENGINE SECONDARY AIR CIRCUIT

[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 depolluted by means of a catalytic converter. The subject of interest here is an isolation valve or "stop valve" arranged in said so-called secondary air circuit.

[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 a catalytic converter engine 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. For the record, the primary air circuit designates the air flow which passes into the cylinders.

[0006] Furthermore, this is an early heating system, which is implemented before the engine is started. A diagnosis can thus be carried out before the engine is started, in particular to comply with anti-pollution regulations.

[0007] In another phase of 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 going back up through the secondary air circuit. This is the role of the stop valve. This stop valve is piloted, so we also call it a solenoid valve. This stop valve can be formed as a quarter-turn flap, a guillotine, a valve or any other type of valve piloted by an electrical element, eg either a motor or an inductive coil, or a mechanical element, eg a vacuum lung as used for turbocharger controls for example.

[0008] Failure to close this shut-off valve could be detrimental, because 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 stop valve.

[0010] For this purpose, 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 pipe portion upstream of the shut-off valve, a second pipe portion downstream of the shut-off valve, a temperature sensor arranged on the first pipe portion, an air pump arranged on the first pipe portion, the second pipe portion being configured to deliver air pushed by the pump onto a heating grid to heat a catalyst pot, characterized in that the method comprises: a- a step of acquiring a temperature prevailing in the first portion of the pipe, b- a step of periodic calculation of a temporal temperature 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, continuously for a predefined duration.

[0011] Thanks to the provisions promoted above, it is possible to detect an abnormal rise in temperature upstream of the shut-off valve, which is indicative of a shut-off valve in an incompletely closed or not closed at all state. In the event of the presence of such an anomaly, it is the very hot burnt gases which 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 shut-off valve fault.

[0013] It is noted that during the diagnostic steps, the internal combustion engine is rotating and the air pump is non-rotating.

[0014] It is noted that the predefined duration for declaring / confirming the fault can be small, for example of 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 trigger threshold may depend on the engine speed and the torque delivered by the engine.

[0016] Such a cartographic trigger threshold 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.

[0017] According to one embodiment, the first trigger threshold further depends on an environmental temperature. The environmental temperature may be an outside temperature, a temperature under the engine hood, a coolant temperature or any other temperature measurement.

[0018] By means of which, the robustness of the method can be further improved and the occurrence of possible false detections can be reduced.

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

[0020] By means of tests on an air flow bench, or on an engine, or even on a vehicle, it is possible to obtain a single parameter value which makes it possible to significantly detect temperature increases while avoiding cases of false detections. This solution makes it possible to have simpler software and a very low requirement for memory resources.

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

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

[0023] As a result, the temperature of the burnt gases leaving 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 feature, 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 pipe is obtained from a temperature sensor arranged on the first portion of 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 makes it possible to avoid having to use a temperature sensor on the intermediate pipe upstream of the valve. It is possible to use a temperature sensor placed on an element which is located in the vicinity of the first portion of pipe, and reconstruct the estimated temperature 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 method 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 portion of the pipe (the inlet pipe and the intermediate pipe) may be made of synthetic or polymer material. The second portion of the pipe (the blowing pipe) 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 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 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 relating to the stop 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 steps of the process.

[0035] 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 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 towards the catalytic converter 55 then towards the exhaust pipe downstream exhaust 56.

[0036] 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 the present invention; the engine may be without it. It should be noted that the present 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 that it may have, in addition to the internal combustion engine, an electric traction motor and an on-board electrical energy storage device.

[0038] Now concerning 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 comprises 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, marked 4. The intermediate pipe 12 can be equipped with a pressure sensor marked 44. The 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 temperature sensor 4 can be mounted on a tapping 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 comprises a stop valve 3 and a blowing pipe 13 downstream of the stop valve 3. The blowing pipe 13 opens upstream of the heating grid 5. It can be noted that the outlet of the blowing pipe 13 can be equipped with a diffuser to direct and / or homogenize the air flow on the grid.

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

[0043] The pressure prevailing in the inlet pipe 11 is denoted P1, 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.

[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 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 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 line to the blow-off line 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 stop valve may be monostable, i.e. require an electrical supply while it is in the open state. In this case, the stop valve may be controlled at the same time as the pump and the grid is heated. The stop 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.

[0048] The stop valve can be bistable, that is to say that it needs to be electrically powered only 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 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.

[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 rotating. The proposed method is preferably carried out with the air pump not activated, i.e. not rotating.

[0053] The proposed method comprises a step of periodic acquisition of a temperature prevailing in the first portion of pipe, this is the step noted a-. The temperature value acquired using the temperature sensor 4 is generically noted TC. The values ​​acquired successively over time are noted TC(i), i being a sampling index or are noted TC(ti), ti being a sampling instant.

[0054] The proposed method comprises a step of calculating a temperature time gradient, this is the step noted b-.

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

[0056] Moving into the digital 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 different from the frequency / recurrence for calculating the gradient.

[0059] The temperature time gradient GD is compared to a trigger threshold noted GDS, called in the present context “first trigger threshold”.

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

[0061] Figures 3, 4, 5 and 6 all illustrate the same scenario concerning the operational conditions of the engine, illustrated in the respective upper part of each figure. We start, at time t1, from an operating point called PF1 with an engine speed noted RPM1 and a delivered torque noted TQ1. A rapid change in operating conditions brings the engine operating point to a point noted PF2 at time t2 with an engine speed noted RPM2 and a delivered torque noted TQ2. We observe that the torque increases as well as the engine speed, we therefore understand that the thermal energy transmitted in the exhaust gases increases very significantly. The reference outside temperature is 25°C.

[0062] The first operating point PF1 may correspond to a situation where the engine is idling or the engine is already under load. The second operating point PF2 corresponds to a situation where the first operating point PF1 is more loaded, therefore a thermal load of the burnt gases is clearly increasing.

[0063] In [Fig. 3], we see a rather moderate and rather slow increase in the temperature TC recorded in the intermediate pipe 12 of the secondary air circuit 6.

[0064] By examining curve 93, plotted from the succession of acquired TC temperature values, we observe low amplitude oscillations. The temperature value remains around 30°C on average. The temperature changes at this location are the consequence of thermal radiation from neighboring parts, but we are not in the hot part of the engine.

[0065] Curve 73, at the bottom of the figure and in long dotted lines, represents the gradient over time, the graduation is on the right of the figure, in degrees per second. We note that curve 73 remains in the vicinity of 0 and well below the GDS gradient threshold discussed below.

[0066] [Fig.4] illustrates a scenario where valve 3 is not correctly closed (eg presence of a leak). We can immediately see 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 engine operating point PF2 at time t2.

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

[0068] Curve 74, at the bottom of the figure and in long dotted lines, represents the gradient over time. We note 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 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 temperature time gradient GD exceeds the first GDS trigger threshold.

[0071] According to the method, this condition must be verified during the time delay noted TS. The condition GD>GDS must be verified continuously during the time delay TS. This avoids reacting too quickly to an aberrant value. If the condition becomes false again before this time delay, then it is necessary to wait until the fault condition reappears to recount the time from zero, and only confirm the fault if this condition lasts at least TS. To return 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 operational conditions of the engine which remains at the operating point PF2. It can be seen that the temperature TC increases to a value between 90°C and 100°C.

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

[0074] According to the method, an action on the operational conditions of the engine is also provided, this functionality will now be described in relation to figures 5 and 6.

[0075] [Fig.5] shows the curve 95 of the evolution of the temperature recorded in the first section of the pipe. The start of the sequence is identical to what was explained for [Fig.4],

[0076] Curve 75, at the bottom of the figure and in long dotted 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 passes below 0 just after time t6.

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

[0078] Here we must understand by reduction of engine performance a particular mode of derating (we say in English 'derating'). For strong performance limitations we can speak of 'live 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 burnt gases is lower than that observed in [Fig.4] which would have given the dotted line marked 94'. Curve 95 follows a bell oriented downwards and does not exceed the TCS threshold in this case.

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

[0081] [Fig.6] shows the temperature evolution curve 96 recorded in the first section of the pipe. The start of the sequence is identical to what was explained for [Fig.4]. The rest is identical to what was explained for [Fig.5], namely the first reduction in engine performance.

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

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

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

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

[0086] According to a non-limiting example, the GDS trigger threshold relating to the criterion on the temperature time gradient can be a fixed predefined parameter, independent of the operational conditions of the engine and the outside temperature. For example, a GDS trigger threshold can be chosen at a value between 0.1°C per second and 0.5°C per second, depending on the 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 time gradient can depend on the engine speed and the torque delivered by the engine. This can be a fairly simple mapping that tolerates larger gradient values ​​for high speeds and torques and has smaller threshold gradient values ​​for a stabilized idle speed, for example.

[0088] According to a non-limiting example, the GDS trigger threshold relating to the criterion on the temperature time gradient may also depend on an environmental temperature. This may for example be the outside temperature information or the coolant temperature information. The mapping of the trigger threshold values ​​may thus be multidimensional.

[0089] In the absence of a physical sensor on the first portion of pipe, the prevailing temperature can be estimated from a mathematical model from another source of temperature information such as a temperature taken from an element neighboring the first portion of pipe. This indirect information is introduced into a mathematical compensation model, resulting from the calibration tests, to give an estimated temperature prevailing in the first portion 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 keeps track 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 case of leakage from the shut-off valve. In the case of a shut-off valve that remains completely open, the temperature ramp is much steeper and detection is the easiest. A small leak from the shut-off valve is the most difficult case to detect since it differs only slightly from the normal temperature changes observed in all cases of life on the pipe upstream of the shut-off valve.

[0092] It should also be noted that, for the presentation of the invention, we have taken a case of simple and theoretical change of engine load (PF1->PF2), but in the real life of the engine the operating point is constantly evolving. The fact remains that the method promoted here works whatever the operating points and their evolution over time.

[0093] It is noted that the air circuit comprises, in this order: the inlet pipe, the air pump, the intermediate pipe, the shut-off valve and the blowing pipe.

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

[0095] It should also be noted that the torque reduction can be constant or mapped as a function of the engine speed and the temperature gradient for example.

[0096] It should also be noted that the torque reductions can be successive so as 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.

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