FR2854201A1 - Automobile engine management method, useful in lean burn operation, uses catalyst storage capacity value determined from point of inflection in NOx flow rate curve - Google Patents

Abstract

A predefined NOx storage capacity is determined by the point of inflection (W) in the NOx vs. time graph, from a signal representing the mass flow rate of NOx downstream of the storage catalyst (21). The mass flow rate of NOx is determined as a function of this storage capacity. The storage catalyst is regenerated as a function of the NOx mass flow rate. The relative rate of increase at the point of inflection (W) is predefined, and the mass flow rate is determined as a function of it. In a variant method, the storage capacity and/or the relative rate of growth is measured previously for a reference storage catalyst, and this information is recorded. The capacity or relative rate of growth is measured as a function of the temperature and/or mass flow rate of exhaust gas and/or NOx mass flow rate. The mass flow rate of NOx downstream of the catalyst, may be determined in accordance with equations provided. Independent claims are included for; (1) A computer program product; (2) A corresponding control equipment; and (3) An engine including the above components.

Description

Field of the invention

  The present invention relates to a method for managing an internal combustion engine, in particular of a motor vehicle, according to which the combustion chamber is fed with a lean fuel / air mixture, and whose nitrogen oxides NO. released by combustion are supplied to an accumulator catalyst which is regenerated.

  The invention also relates to a computer program, a control apparatus and an internal combustion engine for carrying out the above method. State of the art Such a method is known, for example, applied to direct injection internal combustion engines. In this case, it is necessary to ensure, in case of lean air / fuel mixture, an intermediate storage of the nitrogen oxides for releasing this storage of the accumulator catalyst again during operation with a rich air / fuel mixture. The instant of the execution of such a regeneration of the accumulator catalyst must be chosen as a function of a large number of operating parameters of the internal combustion engine and this operation can therefore frequently be carried out only with a implementation of important means.

  OBJECT OF THE INVENTION The object of the present invention is to develop a method making it possible to determine, as optimally as possible, the time of execution of a regeneration of an accumulator catalyst, without necessitating the implementation of large quantities. means as is currently the case.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION To this end, the invention relates to a method of the above-defined type, characterized in that predefines an accumulation capacity 30 at the point of inflection of the timing diagram of a mass flow signal. NO., Downstream of the accumulator catalyst, the mass flow NOx is determined as a function of this accumulation capacity and the storage catalyst is regenerated as a function of this NOx mass flow.

  The accumulation capacity at the point of inflection of the chronogram of the mass flow NOx represents a characteristic quantity of the accumulator catalyst. This size makes it possible to determine in a very precise manner the storage capacity of the accumulator catalyst.

  A NO mass flow is very accurately deduced. downstream of the accumulator catalyst and thus the regeneration of the accumulator catalyst can be determined. The invention thus makes it possible to determine the instant of the execution of a regeneration of the accumulator catalyst without requiring significant means.

  According to an advantageous development of the invention, a growth rate relative to the point of inflection of the chronogram of the mass flow NO is predefined. and this mass flow is determined as a function of this relative growth rate. The relative growth rate at the inflection point of the mass flow diagram NOx is another characteristic of the accumulator catalyst. This size makes it possible to determine in an even more precise manner the accumulation capacity of the accumulator catalyst.

  According to another development of the invention, the accumulation capacity and / or the relative growth rate in the case of a reference storage catalyst are measured beforehand and these values are recorded. It is particularly advantageous that the accumulator capacity and / or the relative growth rate are measured as a function of a temperature and / or a mass flow rate of exhaust gas and / or a mass flow NO,.

  According to other advantageous characteristics: the mass flow NO- (msnohkm) is determined downstream of the accumulator catalyst according to the following equation (G1): msnohkm = msnovhk 1 + exp I mnospm RWRNO

MNODB

  in which msnohkm = mass flow NOx downstream of the accumulator catalyst (21) in mg / s, msnovhk = mass flow NO. upstream of the accumulator catalyst (21) in mg / s, mnospm = mass NOx accumulated in the accumulator catalyst (21) in mg, MNODB = reference accumulation capacity in mg at the point of inflection (W) of the msnohkm signal , RWRNO = relative reference growth rate or slope of the msnohkm signal at its inflection point, - the mass NO, accumulated (mnospm) in the accumulator catalyst is determined with the following equation (G2): mnospm = I (msnovhk - msnohkm) dt ..

  The present invention will be described in more detail below with the aid of exemplary embodiments shown in the accompanying drawings, in which: FIG. 1 is a diagrammatic presentation of an embodiment of a combustion engine. FIG. 2 is a block diagram of an exemplary embodiment of a method according to the invention for the management of the internal combustion engine of FIG. 1; FIG. 3 shows a geometric chronogram. signals for describing the method and the internal combustion engine of Figures 1 and 2.

  Description of embodiments

  Figure 1 shows an internal combustion engine 10 in particular for equipping a motor vehicle. The internal combustion engine 10 is a gasoline internal combustion engine with direct injection. The invention described below, however, can be applied correspondingly to a diesel internal combustion engine or to an internal combustion engine with injection into the intake duct.

  The internal combustion engine 10 comprises a cylinder 11 equipped with a piston 12 movable reciprocatingly in the cylinder. The cylinder 11 and the piston 12 delimit a combustion chamber 13. An intake pipe 14 is connected to the combustion chamber 13 to supply air to the combustion chamber 13. The combustion chamber 13 is also connected to an exhaust pipe 15 for exhausting the exhaust gas from the combustion chamber 13. The control of the air supply and the flow of the exhaust gas is provided by valves 16. The combustion chamber 13 is further equipped with an injector 17 and a spark plug 18. The injector 17 is used to inject fuel into the combustion chamber 13 and the spark plug 18 ignites the fuel injected into the combustion chamber 13 to burn it.

  The exhaust line 15 is connected to a three-way catalyst 19 provided for converting the HC, CO and NO 2 polluting components into H 2 O, CO 2 and N 2 components. The three-way catalyst is connected via a pipe 20 to an accumulator catalyst 21. The pipe 20 is equipped with a temperature sensor 22 which determines the temperature TSK of the exhaust gas arriving in the accumulator catalyst 21. The catalyst accumulator 21 is further connected to a pipe 23 equipped with a nitrogen oxide sensor NO, 24. The NO. 24 determines the NOX concentration of nitrogen oxides NO. contained in the exhaust gas passing through the pipe 23.

  If the internal combustion engine 10 operates with a stoichiometric air / fuel mixture, i.e., a lambda coefficient = 1, the pollutant components are converted by the three-way catalyst 19. To save fuel, however, operating the internal combustion engine 10 with a lean mixture air / fuel, that is to say with a coefficient lamnbda> 1. As a result, the nitrogen oxides NOx contained in the exhaust gas can no longer reduced because of excess air at the three-way catalyst 19.

  For this purpose, there is provided an accumulator catalyst 21 for storing nitrogen oxides NO. Intermediately. The storage capacity of the accumulator catalyst 21 is limited. Thus, its storage capacity decreases from a certain degree of filling of the accumulator catalyst 2 1. In addition, the limit of the specific capacity depends on operating parameters of the internal combustion engine 10.

  The accumulator catalyst 21 must always be discharged, that is to say regenerated. For this purpose, the internal combustion engine 10 is briefly operated with a rich fuel / air mixture, that is to say with a lambda coefficient <1. The nitrogen oxides NO-, accumulated in the accumulator catalyst 21 are thus converted to N2 and CO2. After such regeneration of the accumulator catalyst 21, the latter can again store NOS nitrogen oxides.

  The instant at which a regeneration of the accumulator catalyst 21 is performed can be determined by means of the NO sensor. 24. For example, it is possible, for example, to initiate a regeneration precisely when the NOX concentration of the NOx contained in the exhaust gas exceeds a first predefined threshold and / or the combined concentration or integrated NOX nitrogen NO. contained in the exhaust gas exceeds a given second threshold.

  In particular, during the cold start of the internal combustion engine 10, the NO sensor. 24 is ready to operate only after a waiting time. During this waiting time, it is impossible to carry out the determination described above of the instant for the execution of a regeneration of the accumulator catalyst 21. Amongst others, during this waiting time, the method can be applied. according to the invention, described below.

  FIG. 2 shows a method of managing the internal combustion engine 10. This method is performed by a control apparatus receiving sensor input signals, for example those of the temperature sensor 22 or the sensor NO, 24 and providing output signals for the actuators, for example for the injector 17 or the spark plug 18 for controlling the internal combustion engine 10.

  The control apparatus is adapted to perform the method described below. The control apparatus can be realized in the same conditions either in circuit technology and / or as a digital processor with memories. In the latter case we use a program designed to execute the process.

  According to the method, a crude mass flow model of nitrogen oxide NO is available. and we run it. This model is represented by block 25 in FIG. 2. This crude mass flow model NO. 25 determines a mass flow of nitrogen oxide NO. msnovhk upstream of the accumulator catalyst 21 at least as a function of the load L applied to the internal combustion engine 10 and the speed (rotational speed) N of the internal combustion engine 10. The NOx gross mass flow model may for example be realized in the form of a field of characteristics or an equation. As shown in FIG. 1, the mass flow NOS, msnovhk passes through the pipe 21 of the three-way catalyst 19 in the accumulator catalyst 21.

  The process also provides a cumulative catalyst model and runs it. This model is represented in FIG. 2 by block 26. This model of accumulator catalyst 26 determines a mass flow of nitrogen oxide NO, msnohkm downstream of the accumulator catalyst 21 according to the equation which will be described next. As shown in FIG. 1, this mass flux NOx msnohkm passes through the pipe 23 coming out of the accumulator catalyst 21. The mass flux NO. msnohkm is the NOx mass flux that has not been converted by the accumulator catalyst 21 and thus comes out of the internal combustion engine 10 as a pollutant.

  The accumulator catalyst model 26 further determines the nitrogen oxide mass NO. accumulated mnospm. This is the mass accumulated temporarily in the accumulator catalyst 21.

  This mass NO. accumulated mnospm is also indicated in Figure 1 as the content of the accumulator catalyst 21. The mass NO. accumulated mnospm is determined using an equation that will be described next.

  As a function of mass flow NO- msnohkm and / or as a function of mass NO. accumulated mnospm, the process executes a regeneration command. This process is represented by the block 27 of FIG. 2. This regeneration control 27 determines the time at which the regeneration of the storage catalyst 21 must be made. As will be described later, this determination is independent of the NOX oxide concentration. nitrogen NO, exhaust gas, concentration measured by NO sensor. 24. In addition, the regeneration control 27 can also provide the NOX concentration of the NOx nitrogen oxides measured by the NO sensor. 24 in the exhaust. The regeneration control 27 can also determine the time of execution of regeneration of the accumulator catalyst as a function of this measured NOX concentration of nitrogen oxides NO. A combination of these two possibilities can also be envisaged.

  To determine the mass flux NO., Msnohkm we apply the following equation G1: msnovhk msnohkm =. 1+ exp 1 mnospm RWRNO t MNODB R msnohkm = NOx mass flow downstream of the accumulator catalyst 21 in mg / s, msnovhk = mass flow NOx upstream of the accumulator catalyst 21 30 mg / s, mnospm = mass NOx accumulated in the catalyst accumulator 21 in mg, MNODB = reference accumulation capacity in mg at point of inflection W of the msnohkm signal, RWRNO = relative reference growth rate or slope of the msnohkm signal at its point of inflection W. The mass flux NO ., msnovhk is provided by the NO mass flow model. As described. The accumulated NOx mass mnospm is determined using the equation G2 as already indicated: mnospm = f (msnovhk - msnohkm) dt The reference accumulation capacity MNODB and the relative reference growth rate, RWRNO, will be described hereinafter using i0 of FIG.

  FIG. 3 represents the chronograms of the mass flow NOS, msnovhk upstream of the accumulator catalyst 21, of the mass flow NO. msnohkm downstream of the accumulator catalyst 21 and the mass NO. mnospm accumulated in the accumulator catalyst 21 as a function of time t. It is assumed that at time t = 0, the accumulator catalyst 21 is discharged and the NO.sub.0 mass flow, upstream of the catalyst 21, is substantially constant.

  The mass flow NOS, msnovhk represents a continuous accumulation of nitrogen oxides NO. in the accumulator catalyst 21. As a result, the mass NO, accumulated, mnospm increases. As the accumulator catalyst 21 has in principle all its accumulation capacity, the mass flow NO.sub.o, msnohkm is substantially zero downstream of the accumulator catalyst 21. In the zone bearing the reference D in FIG. . This means that the mass flux NO, msnohkm is now starting to increase. This results from the fact that the accumulation capacity of the accumulator catalyst 21 decreases slowly as it approaches its capacity limit. In the following, the mass NO. accumulated, mnospm and mass flow NO., msnohkm continue to increase.

  The mass flow diagram NO., Msnohkm has a point of inflection with the reference W in Figure 3. This point has been mentioned in connection with equation 1. At the point of inflection W, the second derivative of the signal of the NOS mass flow, msnohkm is equal to zero.

  Then, after the point of inflection W, the mass flow NOS, 35 msnohkm and mass NOx accumulated, mnospm approach saturation; the saturation is designated by the reference S in FIG. 3. At the saturation level S. the accumulator catalyst 21 is completely charged so that its storage capacity is practically zero. As a result, the mass flow NO ,, msnovhk upstream of the accumulator catalyst 21 is equal to the mass flow NO., Msnohkm downstream of the accumulator catalyst 21.

  At the inversion point W, the accumulator catalyst 21 has a certain remaining capacity of accumulation and a certain relative growth rate to continue to accumulate NO.sub.2 nitrogen oxides. This accumulation capacity and this relative growth rate are not known for the accumulator catalyst 21 actually used in the internal combustion engine 10.

  The accumulation capacity and the relative growth rate are, however, determined beforehand for a reference storage catalyst of the same type using measurements. These measurements are thus made as a function of the temperature of the reference accumulator catalyst and / or as a function of the mass flow of exhaust gas and / or of the mass flow NO ,. From these measurements one obtains the reference accumulation capacity MNODB and the reference growth rate RWTRNO according to the equation G1. The measured values of the reference accumulation capacity MNODB and the reference growth rate RVWRNO are recorded in the control apparatus in two fields of characteristics as a function of the temperature of the reference storage catalyst and / or the mass flow. exhaust gas.

  The reference accumulation capacity MNODB and the corresponding reference growth rate RWVRNO will then be used as the accumulation capacity and as the relative growth rate of the actual accumulator catalyst 21. For this purpose, the accumulator catalyst model 26 receives the temperature TSK of the accumulator catalyst 21; this temperature is measured by a measurement sensor or is determined in another way, for example by modeling. Then, the accumulator catalyst model 26, if necessary, provides a general mass flow of exhaust gas AMS which can be generated in particular by means of modeling. Instead of the mass flow signal of the exhaust gas AMS, the mass flow NO., Msnovhk can also be used. This makes it possible to extract from the two fields of characteristics indicated above, both the MNODB reference accumulation capacity and the relative reference growth rate, RWRNO.

  In the process, the accumulated nitrogen oxide mass NOx, mnospm is determined in the first step, for a time t> 0 and using the equation G2, starting from the instant t = 0 at which the accumulator catalyst 21 is discharged; thus, the NO.sub.0 mass flow, msnohkm, is essentially zero downstream of the accumulator catalyst 21. In a second step, the mass flow NO is determined. msnohkm using the equation G1 and mass NO. accumulated and calculated pre-alable, that is to say the mass mnospm. From the mass flow NO.

  existing now, that is to say msnohkm, one can, in another step and using the equation G2, again determine the mass NO. accumulated, that is to say mnospm. The process can be continued with the second and third steps.

  As a result of the process, the accumulator catalyst model 26 continuously generates the current values for the mass flow NO.sub.o, msnohkm and for mass NO.sub.b. accumulated, mnospm. As already indicated, these values are used for the regeneration control 27 to determine the instant at which the generation of the accumulator catalyst 21 is to be made. As already indicated, the current values of the mass flux NO.sub.e, ie msnohkm. , and the accumulated mass NO, i.e., mnospm, are values independent of the NO sensor. 24. These values obtained from the accumulator catalyst model 26 can, among other things, be used if the sensor NO. 24 is not ready for operation after a cold start.

  The values provided by the accumulator catalyst model 26 for NO.sub.0 mass flux, msnohkm and for NO mass. accumulated, mnospm, can also be used to completely replace the NO sensor. 24. These values can also be used to detect a defect or phenomena of aging of the NO sensor, 24 and if necessary to adapt it. The same applies to a defect or aging phenomenon of the accumulator catalyst 21. This finding can also be obtained in particular by an adaptation factor combined with the MNODB reference accumulation capacity. O10

Claims (9)

  1) A method of managing an internal combustion engine (10) including a motor vehicle, wherein the combustion chamber (13) is fed with a lean fuel / air mixture, and whose nitrogen oxides NOx generated by the combustion are supplied to an accumulator catalyst (21) which is regenerated, characterized in that an accumulation capacity (MNODB) is predefined at the point of inflection (W) of the timing diagram of a mass flow signal. NOx, (msnohkm) downstream of the accumulator catalyst (21), the mass flow NOx (msnohkm) is determined as a function of this accumulation capacity (MNODB) and the accumulator catalyst (21) is regenerated as a function of this mass flow. NOx (msnohkm).   2) Process according to claim 1, characterized in that a relative growth rate (RWRNO) is predefined at the point of inflection (W) of the NOx mass flow diagram (msnohkm) and this NOx mass flux (msnohkm) is determined. ) based on this relative growth rate (RWRNO).   3) Process according to claim 1, characterized in that the accumulation capacity (MNODB) and / or the relative growth rate (RWRNO) are measured beforehand for a reference storage catalyst and this information is recorded.   4) Process according to claim 3, characterized in that the accumulation capacity (MNODB) or the relative growth rate (RWRNO) is measured as a function of a temperature (TSK) and / or a mass flow. exhaust gas and / or NOx mass flow.   5) Process according to claim 1, characterized in that the mass flow NOx (msnohkm) downstream of the accumulator catalyst (21) is determined according to the following equation (G 1): msnovhk msnohkm msnovhk l + exp [/ 1 mnospm 'RWRNO [(MNODB RWRNO] in which msnohkm = NOx mass flow downstream of the accumulator catalyst (21) in mg / s, msnovhk = mass flow NOx upstream of the accumulator catalyst (21) in mg / s, mnospm = accumulated NOx mass in the accumulator catalyst (21) in mg, MNODB = reference accumulation capacity in mg at the point of inflection () of the signal msnohkm, RWRNO = relative reference growth rate or slope of the signal S5 msnohkm at its point of inflection ().   6) Process according to claim 5, characterized in that the accumulated NOx mass (mnospm) in the accumulator ac20 catalyst (21) is determined with the following equation (G2): mnospm = f (msnovhk - msnohkm) dt.   7) Computer program for the application of the method according to one of claims 1 to 6.   8) Control apparatus for applying the method according to one of claims 1 to 6.   9) Internal combustion engine (10) equipped with a control apparatus for the application of the method according to one of claims 1 to 6.