METHOD FOR CALCULATING A QUANTITY OF NITROGEN EFFLUENTS IN AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to a method for calculating a cumulative quantity of nitrogen effluents in an exhaust system of an internal combustion engine, with a nitrogen effluent probe arranged on the exhaust line, the probe requiring at least to be heated to be operational, an operating sequence of the engine comprising a first phase (PH1) while the probe is not yet ready and a second phase (PH2) while the probe is at the appropriate temperature, with a mathematical model for estimating the quantities of nitrogen effluents emitted during the first phase, as a function of operating parameters of the engine and of the post-treatment systems, the method providing for determining a deviation between the mathematical model and the actual behavior, when operational conditions for determining (CD1) this deviation prevail,and correct the output of the mathematical model by means of a correction coefficient in order to obtain a corrected cumulative quantity. Figure 2,

Description

Title of the invention: METHOD FOR CALCULATING A QUANTITY OF NITROGEN EFFLUENTS IN AN INTERNAL COMBUSTION ENGINE

[0001] The invention relates to a method for calculating a cumulative quantity of polluting nitrogen effluents, in particular nitrogen oxides and ammonia, discharged by an exhaust system of an internal combustion engine of a motor vehicle.

[0002] Certain provisions of the standard under discussion known as 'EURO7' provide that vehicles are capable of measuring the quantities of polluting nitrogen effluents emitted per kilometer traveled and of making the corresponding information available by means of an electronic query using a diagnostic tool with which maintenance garages and inspectors from official bodies are equipped.

[0003] For this purpose, vehicles intended to meet certain provisions of the so-called 'EURO7' standard must be equipped on their exhaust line with a polluting nitrogen effluent probe, capable of determining the concentration and / or quantities, in particular of nitrogen oxides and ammonia, which pass into a downstream portion of the exhaust pipe and which are then released into the atmosphere.

[0004] It turns out that in practice the polluting nitrogen effluent probe cannot deliver reliable information from the start of engine operation, particularly for a driving sequence which begins cold, i.e. the probe is not ready to operate immediately after the engine has started cold.

[0005] While waiting for the nitrogen effluent probe to be ready, the engine control system uses a mathematical model to estimate the nitrogen effluent emissions. The mathematical model takes into account the engine operating parameters and the operating parameters of post-treatment systems (catalytic reductions of pollutants) provided in the exhaust line.

[0006] However, the mathematical model cannot take into account all the parameters, in particular those linked to the aging of the vehicle and to certain drifts which may occur, without this being provided for in the mathematical model. In particular, the mathematical model remains imperfect for taking into account dispersions between vehicles which are theoretically identical, but which in practice evolve differently depending on the stresses to which they are subjected and depending on certain intrinsic dispersions.

[0007] Furthermore, the operation of the engine in the moments immediately following its start-up involves multiple transients, and this initial transient phase is more likely to generate nitrogen pollutants than the later phases. Therefore, a good estimate of nitrogen pollutant emissions during this start-up phase is very important in order to be able to accurately establish a pollution index per kilometer for the vehicle of interest.

[0008] The inventors therefore sought to improve the accuracy of estimation of nitrogen effluents during the initial operating phase, while waiting for the nitrogen effluent probe to be ready to deliver a reliable measurement.

[0009] To this end, the present invention provides a method for calculating a cumulative quantity of nitrogen effluents in an exhaust system of an internal combustion engine, the exhaust system comprising a pollutant probe configured to measure a concentration of nitrogen effluents and arranged on a terminal portion of an exhaust line, the pollutant probe needing at least to be heated to begin delivering a reliable measurement, an operating sequence of the engine comprising a first operating phase while the pollutant probe is not yet at an adequate temperature and a second operating phase while the pollutant probe is at the adequate temperature and delivers a reliable measurement, the method comprising a mathematical model for estimating quantities of nitrogen effluents emitted during the first phase, as a function of engine operating parameters and as a function of post-treatment system operating parameters, characterized in that the method provides for determining a model deviation between an estimate given by the mathematical model and a measurement of the actual behavior given by the pollutant probe, when operational conditions for determining this model deviation prevail, and the method further provides for correcting a first cumulative quantity given by the mathematical model during the first operating phase (probe not ready) by means of a correction coefficient obtained from the model deviation, in order to obtain a first corrected cumulative quantity for the first operating phase.

[0010] Thanks to the provisions promoted above, it is possible to provide a more precise estimate of the quantity of nitrogen compounds emitted during the first phase of operation while waiting for the pollutant probe to be ready. This makes it possible to provide a nitrogen pollution index that is as close to reality as possible.

[0011] The adjustment made by the correction coefficient makes it possible to take into account drift phenomena of certain elements of the combustion engine or of the catalytic reduction post-treatment systems, which are not or cannot be taken into account by the mathematical model.

[0012] In other words, instead of using the open loop mathematical model, a closed feedback loop is created from the measurements made using the probe. pollutants, under adequate comparison conditions which will be seen later.

[0013] It is noted that the internal combustion engine is installed on board a hybrid vehicle or a conventional vehicle with a thermal engine.

[0014] It is noted that to prepare the pollutant probe, an initial phase of ventilation of the probe is provided, before triggering a reheating phase, all this in order to prepare the probe for its operational operation.

[0015] Here, the term "engine operating sequence" is understood to mean a vehicle driving sequence or a driving cycle from the engine starting until it is stopped by the vehicle driver. In the case where the engine is temporarily stopped by a stop / start type sequence or in the zero-emission hybrid vehicle configuration, the pollutant sensor remains operational and can reliably and accurately measure the concentrations of nitrogen components.

[0016] According to one embodiment, the method provides a calculation of total effluents consisting of adding the first corrected cumulative quantity and a second cumulative quantity measured by the pollutant probe for the second operating phase. This total calculation makes it possible to establish the total quantity of nitrogen component emissions which come out of the exhaust pipe for the driving sequence carried out.

[0017] According to one embodiment, the method provides for dividing the total effluent by a cumulative distance traveled during the engine operating sequence, to obtain an index called here “kilometer pollution index”.

[0018] In other words, the total effluent is divided by the distance traveled during the vehicle's driving sequence. The kilometer pollution index is official information that must be made available to the authorities by means of an electronic interrogation tool (via the diagnostic socket known as the 'OBD' socket).

[0019] Advantageously, the nitrogenous effluents of interest here include in particular nitrogen oxides and ammonia. Nitrogen oxides include nitrogen monoxide and nitrogen dioxide, without excluding other more complex compounds.

[0020] According to one embodiment, the operational determination conditions correspond to at least one engine load condition greater than a predefined threshold, with nitrogen oxides produced by combustion.

[0021] The operational conditions for determining the model deviation are achieved when engine torque is called upon, at least for a minimum period, for example it may be an acceleration phase, an uphill portion of the route, etc.

[0022] The nitrogen oxides produced by combustion are partially reduced by the aftertreatment systems and the remainder is measured by the pollutant probe. In parallel, the mathematical model also provides a cumulative result for this charging phase and the two results are compared.

[0023] According to one embodiment, the first cumulative quantity given by the mathematical model is corrected a posteriori, over a given sequence of operation of the engine, with a correction coefficient determined during the second phase of the given sequence of operation of the engine. For this purpose, the first cumulative quantity is temporarily stored while waiting for it to be corrected.

[0024] According to one embodiment, the first cumulative quantity is corrected using the correction coefficient most recently established in the previous sequences. The logic is then quite simple, and considers that parameter drifts are slow phenomena and that the difference between two consecutive rolling sequences is minimal and the resulting error remains almost negligible. In addition, this can be useful if, during the current rolling sequence, the comparison conditions for determining the model deviation do not occur.

[0025] According to one embodiment, the last N kilometer pollution indices relating to the last N engine operating sequences are stored in memory, the last N kilometer pollution indices being readable using a diagnostic tool.

[0026] In other words, the latest kilometer pollution indices are made available for a diagnostic tool (in English 'scan tool') in particular for reasons of market surveillance by the authorities.

[0027] According to one embodiment, it is provided that when a kilometer pollution index value exceeds a reference threshold, an engine malfunction indicator light is illuminated on the dashboard.

[0028] In practice, this involves lighting up a so-called MIL ('Malfunction Indication Lamp') warning light, and this malfunction must be reported in accordance with regulations. The lighting of this warning light therefore encourages the driver to go to a garage to have the malfunction repaired.

[0029] The invention further relates to a control system comprising a nitrogen effluent probe and an engine control unit, characterized in that the engine control unit is configured to implement the method as described above.

[0030] The invention further relates to a vehicle comprising a control system as described above.

[0031] 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 partial schematic representation of an internal combustion engine with its exhaust line and control unit; [Fig.2] shows a timing diagram illustrating an engine operating sequence with a first phase during which the pollutant probe is not ready and a second phase during which the pollutant probe is operational; [Fig.3] shows an example of a functional flowchart of the method implemented in the present invention, with correction based on knowledge of the previous sequences; [Fig.4] shows another example of a functional flowchart of the method implemented in the present invention, with a posteriori correction based on the same sequence.

[0032] In the various figures, the same references designate identical or similar elements.

[0033] In [Fig. 1], the system represented symbolically comprises an internal combustion engine marked 1, known per se and therefore not described in detail here. An exhaust manifold 12 collects the burnt gases in the engine to direct them towards an exhaust line 2.

[0034] The internal combustion engine is installed in a hybrid vehicle or in a vehicle with a conventional thermal engine. There is no limitation on the type of vehicle in the context of the present invention: it can be a private vehicle, a utility vehicle, a recreational vehicle, etc.

[0035] The internal combustion engine is for example a spark-ignition engine, in other words a gasoline engine.

[0036] The present invention is however particularly aimed at vehicles which are presented as conforming to a provision of the 'EURO 7' pollution control standard, also called 'EURO 7 standard'.

[0037] The vehicle comprises a control unit 3 responsible for controlling the operation of the internal combustion engine. As known per se, the control unit 3 manages multiple functions linked to the engine, in particular it controls the opening of the injectors, it controls the ignition timing, it manages, if necessary, a camshaft offset position, etc.

[0038] The control unit 3 also manages the pollution control systems which are of interest here.

[0039] The exhaust line 2 comprises a first treatment chamber 21 comprising catalyst elements known per se, with oxygen sensors 51, 52 as known per se to allow the computer to manage the richness of the mixture.

[0040] The exhaust line 2 comprises a second treatment chamber 22 comprising other catalyst elements. Another probe marked 4, which will be detailed below, is arranged in the second treatment chamber 22.

[0041] Said probe 4 is capable of determining a concentration of polluting nitrogen effluents; it is more simply called a “pollutant probe” in this document.

[0042] The pollutant probe 4 comprises a sensitive part 41 (capture portion) in the flow of burnt gases and local processing electronics 40 arranged nearby. The local processing electronics shapes signals captured by the sensitive part. The local processing electronics 40 indicates whether the pollutant probe is in an operational state, i.e. ready to deliver reliable nitrogen gas concentration information.

[0043] The exhaust line 2 further comprises, downstream of the second treatment chamber, a silencer (not shown in the figures) which has no chemical function but simply an acoustic reduction function.

[0044] It is noted that in addition to the first two treatment chambers described, there may be additional chemical treatment chambers.

[0045] The pollutant probe measuring the concentrations of nitrogen compounds is located on the most downstream chemical treatment chamber, it is therefore arranged on a terminal portion of an exhaust line in the sense of pollutant treatment.

[0046] The pollutant probe 4 measures the concentration of nitrogen oxides which include nitrogen monoxide NO and nitrogen dioxide NO2, and the concentration of ammonia NH3.

[0047] The pollutant probe 4 requires at least to be warmed up to begin delivering a reliable measurement. More specifically, to prepare the pollutant probe, an initial ventilation phase of the probe is provided to eliminate water or dew that may be present on the capture part of the probe, before triggering a warming phase, all this in order to prepare the probe for its operational operation. The ventilation is provided by the passage of the first exhaust gases.

[0048] As visible in [Fig.2], in view of the operation of the nitrogen pollutant probe 4, an engine operating sequence (i.e. a vehicle running sequence) comprises a first operating phase PHI while the pollutant probe is not yet at an adequate temperature (not yet ready) and a second operating phase PH2 while the pollutant probe is at the adequate temperature and delivers a reliable measurement.

[0049] The method uses a mathematical model to estimate the quantities of nitrogen effluents emitted during the first PHI phase, as a function of engine operating parameters and as a function of post-treatment system operating parameters.

[0050] In the service of the mathematical model, one or more calibration tables may be provided which give, as a function of the engine speed, the engine load and the injection times, an estimate of the nitrogen oxides which arrive in the exhaust manifold. Furthermore, other calibration tables may be provided which give, as a function of the temperature and, where appropriate, other parameters, the estimated efficiency of the nitrogen oxide post-treatment systems in the exhaust chambers. exhaust line treatment 2.

[0051] From these calibration tables, the mathematical model gives an estimate of an instantaneous emission rate of nitrogen gases, and the mathematical model performs a summation to give a cumulative emission of nitrogen gases.

[0052] Advantageously according to the present invention, the method provides for determining a model deviation between an estimate given by the mathematical model and a measurement of the actual behavior given by the pollutant probe. This determination is a comparison which is carried out when particular conditions prevail, called here operational conditions for determining CD1 this model deviation.

[0053] The conditions CD1 occur during the second operating phase PH2 while the pollutant probe 4 is operational, therefore after the first operating phase PHI. We will see later how we can correct a posteriori the calculation produced by the mathematical model concerning the first operating phase.

[0054] With reference to [Fig. 3], which illustrates the process implemented for a driving cycle (implemented only once for the driving cycle considered), the box 87 'SenseR' represents the operational state of the pollutant probe 4, e.g. either it is not yet ready, or it is ready. When it is ready, it causes the switch marked 91 to switch, which then switches to the count coming from the actual measurement 88 'NoxMES' by the pollutant probe 4.

[0055] While the probe is not yet ready, the switch 91 selects the result from the mathematical model (box 89) 'NoxMC', with already a correction described below.

[0056] In other words, during the first operating phase PHI, the switch 91 selects the output of the mathematical model, then after switching (time t2 in [Fig.2]) and during the second operating phase PH2, the switch 91 selects the measurement output made available by the pollutant probe.

[0057] The small boxes containing 'X' represent multiplication. The small box containing '&' represents an 'AND' condition. The small box containing '7' represents division. The small box containing '+' and represents subtraction.

[0058] As already mentioned, the mathematical model combines the result of the engine model 82 'NoxMB' and the model of the aftertreatment systems 81 'PTEF'. The raw result of this combination is then affected by a correction using a correction coefficient noted CoeffCorr. The output and therefore a corrected NoxMC emission rate in box 89.

[0059] The operational conditions for determining CD1 are represented by the box 83. When these conditions are met and at the same time the pollutant probe 4 is ready to operate, then the output of box 90 switches to an active value.

[0060] The comparison between the result given by the corrected NoxMC model and the measurements given by the NoxMES pollutant probe is then evaluated by a ratio (NoxMES / NoxMC) at box 84. A current correction ratio or coefficient 'CoeffCorrC' is deduced from this at box 85. This information multiplied by the previous value stored at box 86 is stored in a non-volatile memory 'Memo' so that it can be used during a subsequent operating sequence.

[0061] Before any allocation resulting from calculation, the memory is initialized to the value 1.

[0062] The new stored correction coefficient 'CoeffCorr' replaces the previous correction coefficient.

[0063] In addition, the correction coefficient CoeffCorr multiplies the result of the raw mathematical model, to the multiplier box 80.

[0064] The output of switch 91 enters box 93 which represents the cumulative quantity of nitrogenous effluents 'S Nox' which have been continuously counted either from the mathematical model or from the pollutant probe.

[0065] The box marked 92 represents the cumulative distance traveled 'Km' for the driving sequence considered.

[0066] The box marked 94 collects the result of dividing the cumulative nitrogen effluents by the distance traveled. The result therefore forms an index called here the kilometer pollution index.

[0067] Advantageously, the last N kilometer pollution indices relating to the last N engine operating sequences are stored in memory, the last N kilometer pollution indices being readable using a diagnostic tool. The last N kilometer pollution indices can also be transmitted remotely via a data link to a server or a service center.

[0068] The number N can be chosen according to specific needs, it can be a predetermined fixed number or N can be calculated to cover the last M kilometers, or to cover the last K days.

[0069] Optionally, it is provided that, if a kilometer pollution index value exceeds a reference threshold, the lighting of an engine malfunction alert is generated on the dashboard (for example a warning light called 'MIL' in the jargon of the trade or a specific 'emission' warning light called EEDWS ('Excess Emissions Driver Warning System' provided for by the Euro7 standard). This makes it possible to inform the driver of an abnormal situation and the need to repair the malfunction. This information can be transmitted remotely via a data link to a service center.

[0070] In [Fig.4], a variant of the flowchart is presented. Only the differences compared to [Fig.3] are commented on, the rest is considered identical or similar.

[0071] A calculation of the cumulative emissions estimated by the mathematical model after correction is also provided: the box marked 96 collects this cumulative figure. This is the cumulative figure of emissions estimated by the corrected mathematical model (first correction) over the current driving sequence. This cumulative figure is retained and reused after a new comparison between the model and the actual measurement has been carried out for this current driving sequence.

[0072] For this purpose, in the upper part of the flowchart, this accumulation 'S Nox' enters a multiplier box where a new correction coefficient value corrects it. The output of the subtractive box 95 thus provides a complementary correction compared to the correction resulting from the knowledge of the previous cycles. This delta is added to or subtracted from the general accumulation box 93.

[0073] Returning to [Fig.2], the lower portion of the graph illustrates instantaneous concentrations of nitrogen compounds while the upper portion of the graph illustrates cumulative emissions of nitrogen compounds.

[0074] The rolling sequence starts at time t1 with the engine starting. The first phase PHI occurs from time t1 until time t2 and has a duration DTI. The second phase PH2 occurs from time t2. During the first phase PHI, the pollutant sensor 4 is not ready 'Sense-OFF' and during the second phase PH2 the pollutant sensor is operational 'Sense-ON'. The duration DTI can be a few seconds, for example 5 to 10 seconds in a nominal case. DTI can be longer in cases of starting in sustained cold, eg 0°C or below.

[0075] At time t3, the conditions CD1 are met to carry out a relevant comparison between the results given by the measurement and the results given by the mathematical model.

[0076] Curve 61 illustrates the nitrogen emission rate calculated from the mathematical model. Curve 62 illustrates the nitrogen emission rate measured by the pollutant probe 4 from time t2.

[0077] Curve 63 illustrates the cumulative calculated from the mathematical model.

[0078] Curve 64 illustrates the true cumulative nitrogen emissions.

[0079] It should be noted that the difference between the 2 curves 63,64 has been exaggerated to facilitate the explanation of the present invention.

[0080] At time t3, the system notes the difference 70 between the estimate given by the mathematical model and the actual measurement given by the pollutant probe.

[0081] As mentioned above, this gives a new correction coefficient which is applied to the cumulative nitrogen emissions which were calculated by the mathematical model on the first phase of PHI operation and stored in the memory.

[0082] The resulting correction is represented by the jump 71 on the cumulative curve. At this moment, the estimated cumulative curve joins the true cumulative curve 64.

[0083] All the steps of the method presented above are preferably implemented in the control unit 3 of the engine.

[0084] It is noted that in the case of a temporary interruption of the operation of the engine, for example for a stop / start sequence, or in a zero-emission phase of a hybrid vehicle, we are always in the second phase PH2 within the meaning of the present invention.

[0085] It is also noted that for short journeys, the cumulative nitrogen emissions produced during the first phase of operation may prove to be more significant than the overall cumulative figure, hence the interest in having the most precise and faithful estimate possible of the emissions of nitrogen compounds in this first phase of operation.

Claims

Claims

1. Method for calculating a cumulative quantity of nitrogen effluents (NOx, NH3) in an exhaust system of an internal combustion engine, the exhaust system comprising a pollutant probe configured to measure a concentration of nitrogen effluents and arranged on a terminal portion of an exhaust line, the pollutant probe needing at least to be heated to start delivering a reliable measurement, an operating sequence of the engine comprising a first phase (PHI) of operation while the pollutant probe is not yet at an adequate temperature and a second phase (PH2) of operation while the pollutant probe is at the adequate temperature and delivers a reliable measurement, the method comprising a mathematical model for estimating quantities of nitrogen effluents emitted during the first phase, as a function of engine operating parameters and as a function of post-treatment system operating parameters,characterized in that the method provides for determining a model deviation between an estimate given by the mathematical model and a measurement of the actual behavior given by the pollutant probe, when operational conditions for determining (CD1) this model deviation prevail, and the method further provides for correcting a first cumulative quantity given by the mathematical model during the first operating phase by means of a correction coefficient obtained from the model deviation in order to obtain a first corrected cumulative quantity for the first operating phase.,

2. Method according to claim 1, characterized in that the method provides a calculation of total effluents consisting of adding the first corrected cumulative quantity and a second cumulative quantity measured by the pollutant probe for the second operating phase.

3. Method according to claim 2, characterized in that the method provides for dividing the total effluent by a cumulative distance traveled during the engine operating sequence, to obtain a kilometer pollution index.

4. Method according to any one of claims 1 to 3, characterized in that the nitrogenous effluents include in particular nitrogen oxides (NO,NO2) and ammonia (NH3).

5. Method according to any one of claims 1 to 4, characterized in that the operational determination conditions (CD1) correspond at least to an engine load condition greater than a predefined threshold, with nitrogen oxides produced by combustion.

6. Method according to any one of claims 1 to 5, characterized in that the first cumulative quantity given by the mathematical model is corrected a posteriori, over a given sequence of operation of the engine, with a correction coefficient determined during the second phase of the given sequence of operation of the engine.

7. Method according to claim 3, characterized in that the last N kilometer pollution indices relating to the last N engine operating sequences are stored in memory, the last N kilometer pollution indices being readable using a diagnostic tool.

8. Method according to claim 3, characterized in that when a kilometer pollution index value exceeds a reference threshold, an engine malfunction indicator light is illuminated on the dashboard.

9. A control system comprising a nitrogen effluent probe and an engine control unit, characterized in that the engine control unit is configured to implement the method according to one of claims 1 to 8.

10. A motor vehicle comprising a control system according to claim 9.

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