METHOD FOR DIAGNOSING THE OPERATION OF THE PURGING OF A CANISTER

Abstract

A method for diagnosing operation of a valve to purge a canister of an internal combustion engine, the method, carried out during a purge, including: a) detecting, at an instant to, that the purge valve is open; b) executing a forced closing of the valve at an instant t2; c) measuring a pressure P1m of the intake manifold and calculating a corresponding modelled pressure P1c, at an instant t1 between the instant t0 and the instant t2; d) measuring a pressure of the manifold P2m and calculating a corresponding modelled pressure P2c, at an instant t3 after the instant t2; e) calculating a deviation E1 between P1m and P1c and calculating a deviation E2 between P2m and P2c; f) calculating a criterion C=E1−E2; and g) diagnosing malfunction of the purge valve if the criterion C is lower than a predetermined threshold value Cs.

Claims

1-13. (canceled)

14: A method for diagnosing operation of a purge valve for a fuel vapor filter of an internal combustion engine, the purge valve establishing a fluidic communication on request between a reserve chamber of the filter and an intake manifold of the engine, the method, carried out in a course of a purge, comprising: a) detecting, at an instant to, a certain level of opening of the purge valve, established beforehand, based on which the purge valve is considered to be sufficiently open; b) executing a forced and instantaneous closing of the purge valve at an instant t2; c) measuring a first pressure P1m of the intake manifold, prevailing in an interior of the intake manifold, and calculating a first modeled value P1c for the pressure of the intake manifold according to an operating point of the engine, at an instant t1 between the instant t0 the instant t2; d) measuring a second pressure P2m of the intake manifold and calculating a second modeled value P2c for the pressure of the intake manifold according to an operating point of the engine, at an instant t3 after the instant t2; e) calculating a first deviation E1 between the measured pressure P1m and the calculated pressure P1c and calculating a second deviation E2 between the measured pressure P2m and the calculated pressure P2c; f) calculating a criterion corresponding to the difference between the first deviation E1 and the second deviation E2; g) diagnosing malfunction of the purge valve if the criterion is lower than a predetermined threshold value.

15: The method for diagnosing as claimed in claim 14, wherein the level of opening from which the purge valve is considered to be sufficiently open is greater than or equal to 70% opening of the purge valve.

16: The method for diagnosing as claimed in claim 14, wherein the level of opening from which the purge valve is considered to be sufficiently open is less than 90% opening of the purge valve.

17: The method for diagnosing as claimed in claim 14, wherein the deviation between the instant t0 and the instant t1 corresponds to a stabilization time for the manifold pressure.

18: The method for diagnosing as claimed in claim 14, wherein the time between the instant t0 and the instant t1 is between 1 s and 3 s.

19: The method for diagnosing as claimed in claim 14, wherein the deviation between the instant t2 and the instant t3 corresponds to a stabilization time for the manifold pressure following the forced and instantaneous closing.

20: The method for diagnosing as claimed in claim 14, wherein the time between the instant t2 and the instant t3 is between 0.5 s and 2 s.

21: The method for diagnosing as claimed in claim 14, wherein, between the instant t0 and the instant t1, it is verified that the manifold pressure is lower than a previously determined maximum value Pmax and that the operating point of the engine is stable.

22: The method for diagnosing as claimed in claim 14, wherein, between the instant t2 and the instant t3, it is verified that the manifold pressure is lower than a previously determined maximum value Pmax and that the operating point of the engine is stable.

23: The method for diagnosing as claimed in claim 14, wherein the instant t1 is equal to the instant t2, the forced and instantaneous closing of the purge valve being executed just after recording of the measured pressure P1m and the calculated pressure P1c.

24: The method for diagnosing as claimed in claim 14, wherein a) to f) are repeated at least once, and a malfunction of the purge valve is concluded to exist if the criterion on each occasion is lower than the threshold value.

25: The method for diagnosing as claimed in claim 14, wherein the modeled pressure includes a theoretical part and a corrective part, the corrective part being determined by a learning process according to the deviation between the theoretical part and the pressure measured outside purge phases.

26: An internal combustion engine comprising: an intake manifold, a fuel vapor filter, a purge valve establishing a fluidic communication on request between a reserve chamber of the filter and of the engine, means of measuring a manifold pressure prevailing in the interior of the intake manifold, the engine implementing a method as claimed in claim 14.

Description

[0033] The invention will be more easily understood, and other features and advantages will be appreciated from a perusal of the following description with reference to the drawings, in which:

[0034] FIG. 1 is a schematic view of an internal combustion engine containing a fuel vapor filter implementing a method for diagnosing according to the invention;

[0035] FIG. 2 is a time diagram showing the development of the manifold pressure, measured and modeled in the course of a purge with forced closing according to a preferred embodiment of the method.

[0036] The internal combustion engine 1 as represented in FIG. 1 is of the positive-ignition type. It contains a series of combustion chambers 10 supplied with a mixture of air and fuel through an air filter 11, followed by a butterfly valve 12 and by an intake manifold 13. Other functional elements of the engine 1 are without relevance to the invention and are not represented here.

[0037] The engine 1 includes in addition a reservoir 14 for fuel and a filter for fuel vapors 15. The filter for fuel vapors 15 contains a reserve chamber 150, which is connected via a first pipe 16 to the upper part of the reservoir 14. The reserve chamber 150 is likewise connected to an air intake 151 and to the intake manifold 13 by means of a second pipe 17 and a purge valve 152.

[0038] The engine 1 includes a control unit 18 which is, for example, an electronic microprocessor card. A suchlike control unit 18 is conventional and is not described in detail here.

[0039] The control unit 18 receives information from sensors positioned on the engine 1, in particular with a sensor for the speed of rotation of the engine crankshaft, temperature sensors, an oxygen probe, which are not represented here, and a pressure sensor 19 for measuring the pressure inside the intake manifold 13.

[0040] The control unit 18 likewise controls the purge valve 152. When a purge is controlled and lies outside the implementation of the diagnostic method according to the invention, the purge valve 152 opens progressively until it is completely open. It is kept open for a certain time and is then reclosed, likewise progressively. When the valve is open, a gas flow is established between the air intake 151 and the intake manifold 13, such that the fuel vapors contained in the reserve chamber 150 are carried towards the intake manifold 13 and are burned in the combustion chambers 10.

[0041] FIG. 2 shows the position of the purge valve 152, as a percentage of its opening, in the course of the implementation of the method according to the invention during a purge phase, as the curve 20. The change in the position of this purge valve 152 includes a phase 201 of progressive opening until total opening, a phase 202 of maintaining in the open position and an instantaneous closing 203.

[0042] During this change in the position of the purge valve 152, the control unit 18 determines a modeled pressure, which corresponds theoretically to the pressure inside the intake manifold 13 outside the purge phases. The modeled pressure is represented by the curve 21 in FIG. 2. The modeled pressure contains a theoretical part and corrective part, obtained by a learning process outside the purge periods. At the same time, the pressure sensor 19 measures the pressure inside the intake manifold 13. The result of this measurement is indicated by the curve 22 in FIG. 2.

[0043] When the purge valve 152 is blocked, the pressure measured inside the intake manifold does not change in the same way. The curve 23 represents the change in the measured pressure when the purge valve 152 is blocked in the closed position. In this case, the pressure inside the intake manifold 13 remains very close to the modeled pressure. A deviation D may exist between the modeled pressure and the measured pressure, although this deviation is substantially constant.

[0044] In order to perform a diagnosis according to the invention, the control unit 18 detects, at an instant t0, that the purge valve is open when the opening thereof reaches a certain percentage of opening beyond which the opening is considered to be sufficient. This percentage opening is preferably between 70% and 90% opening. This will make it possible both to have an accurate measurement of P1m and not to limit the number of possible diagnoses in the course of a single purge.

[0045] A first delay is then initiated in order to permit the stabilization of the pressure in the intake manifold. The duration of this delay is from is to 3 s, for example. At the end of this first delay, at the instant t1, the control unit 18 memorizes the value of the pressure P1m measured inside the manifold and the calculated value P1c for the modeled pressure according to the operating point of the engine 1. These two values will then serve to calculate a first deviation E1=P1m−P1c.

[0046] Forced and instantaneous closing of the purge valve 152 is subsequently performed at an instant t2 situated slightly after the instant t1, such that the control unit 18 has already memorized the pressure values P1m and P1c during this interval. As a variant, not represented here, the instant t2 could also be the same as the instant t1.

[0047] A second delay is initiated after this instantaneous closing of the purge valve at the instant t2, in order to permit the stabilization of the manifold pressure. The duration of this delay lies between 0.5 s and 2 s, for example. At the end of this delay, at the instant t3, the control unit 18 memorizes the value of the measured pressure P2m inside the manifold and the calculated value of the modelized pressure P2c according to the new operating point of the engine 1, and then calculates a second deviation E2=P2m−P2c. The control unit 18 then establishes a criterion C according to the formula:

C=E1−E2,

and the criterion C is then compared to a predetermined threshold Cs. If the criterion C is greater than Cs, the valve has functioned correctly. Otherwise, the diagnosis is repeated one or more times. If the result remains unchanged after a certain number of times, for example between 2 and 4 times, that is to say if the criterion C on each occasion is below the threshold Cs, it is then concluded that a malfunction of the purge valve 152 has occurred. If, on the other hand, the criterion C is at least once greater than the threshold Cs, it is concluded that no malfunction has taken place.