A method for estimating an amount of particulate matter in a particulate filter for a spark-ignition engine

Abstract

There is described a method for estimating an amount of particulate matter accumulated in a particulate filter of a spark-ignition internal combustion engine, the method comprising: • providing a first estimate (2) of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine, on the basis of a pressure difference between an inlet and an outlet of the filter, • providing a second estimate (6) of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine, on the basis of an accumulation map, defining the estimate (SL) of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine by summing a product of said first estimate (2) by a first coefficient (16) to a product of said second estimate (6) by a second coefficient (16), wherein the first coefficient and the second coefficient are variable as a function of operating parameters of the internal combustion engine.

Description

[0001] "A method for estimating an amount of particulate matter in a particulate filter for a spark-ignition engine"

[0002] ★ ★ ★ ★

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention refers to internal combustion engines . Speci fically, the invention was developed with reference to spark-ignition, gasoline- fueled internal combustion engines provided with a particulate filter ( GPF, Gasoline Particulate Filter ) .

[0006] Prior Art

[0007] The estimate of the amount of particulate matter trapped in a particulate filter for a spark-ignition, gasoline- fuelled internal combustion engine is obtained based on two di f ferent calculation techniques , which are used for di f ferent operating modes . A first calculation technique is based on the measure of a pressure di f ference acros s the particulate filter (upstreamdownstream) , while a second calculation technique is based on an accumulation model ( or map ) as a function of the engine speed of rotation, the metering, the engine load etc .

[0008] The first calculation technique is essentially employed at high loads and in stationary or nearly stationary conditions . At low loads , the gas flow rate traversing the f ilter is very low, and therefore the pressure drop across the particulate filter is accordingly low . In such circumstances , the resolution of the measure by pressure di f ference across the filter is insuf ficient , and therefore it is impossible to determine the origin (which may be kinetic or dependant on the presence of particulate matter ) of the pressure drop .

[0009] Similarly, in non-stationary conditions there are great variations in the exhaust gas flow rate traversing the particulate filter, and therefore it is very likely to have high pressure drop values - mainly due to an increase of the upstream pressure - in the early steps of the transition, this having no direct relationship with the presence of particulate matter in the filter .

[0010] The accumulation model or map, of course , is not influenced by such ef fects , and for this reason it is employed at low or middle-to-low loads and in trans ient conditions .

[0011] The problem of a combined and alternate use of both calculation techniques is an overestimate or an underestimate of the amount of particulate matter in the filter . Tests show that , after a few combustion cycles , wherein the estimate of the load of particulate matter is operated based on the pressure di f ference across the particulate filter , the passage to an estimate based on the accumulation map leads to amounts of particulate matter which are definitely smaller ( a step discontinuity is observed) . Of course , the reverse may occur .

[0012] I f there is an overestimate o f the amount o f particulate matter ( combined with a high temperature of the exhaust gases ) the control system would inhibit the filter regeneration, in order to prevent the combustion of the high amount of particulate matter to lead to exceeding the limit temperature of the GPF, and therefore in order to prevent the latter from being damaged . Normally, in spark-ignition engines the regeneration is passive , and therefore it is not controlled by a speci fic inj ection strategy, as is the case for instance in compression-ignition engines by means of postinj ections . Regeneration is therefore performed in the deceleration steps of the vehicle , wherein the driver completely releases the accelerator pedal ( ceasing the request of useful torque from the engine ) and the control system inhibits the inj ection of fuel ( cut-of f ) . The inj ection cut-of f leads to a high concentration of free oxygen in the exhaust gases ( essentially, the engine behaves as a supercharger, by pumping air to the exhaust ) which oxygen performs the function of a comburent of the particulate matter accumulated in the filter .

[0013] The regeneration inhibition due to an overestimate of the amount of particulate matter causes an inhibition of the gasoline inj ection cut-of f in a condition of released accelerator pedal , thereby creating a slight ef fect of an increase of torque and a reduction of the engine brake .

[0014] In the case of an underestimate of the amount of particulate matter, there would be the risk of damaging the filter, as the control system might not recogni ze the need to inhibit the passive regeneration ( and therefore the inj ection cut-of f during deceleration) . This would result in a high exothermia in the GPF, due to the combustion of the high amount of particulate matter, with the consequence of exceeding the limit temperature of the GPF .

[0015] However, it is not possible to eliminate either calculation technique in favour of the other in order to eliminate the problem of overestimates or underestimates , precisely due to the applicability limits of both techniques .

[0016] Obj ect of the Invention

[0017] The present invention aims at solving the technical problems outlined in the foregoing . Speci fically, the present invention aims at providing a method for estimating an amount of particulate matter in a particulate filter for a gasoline-fuelled engine , which is substantially exempt from over- and underestimate errors of the amount of particulate matter accumulated in the particulate filter .

[0018] Summary of the Invention

[0019] The obj ect of the invention is achieved by means of a method having the features provided in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention .

[0020] Brief Description of the Figures

[0021] The present invention will now be described with reference to the annexed Figures , which are provided by way of non-limiting example only and wherein :

[0022] - Figure 1 shows a general flow diagram of a method according to the invention, and

[0023] - Figure 2 shows , again in the form of a diagram, a detail of a block of the flow diagram of Figure 1 .

[0024] The text matter provided in the Figures in addition to the references is to be construed as a support o f the description, without necessarily constituting a limitation thereof .

[0025] Detailed Description

[0026] Reference 1 in Figure 1 generally denotes a diagram of a method for estimating an amount of particulate matter accumulated in a particulate filter of a sparkignition internal combustion engine according to the invention .

[0027] In general , in various embodiments of the invention, the method 1 comprises :

[0028] - providing a first estimate of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine , on the basis of a pressure di f ference between an inlet and an outlet of the filter,

[0029] - providing a second estimate of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine , on the basis of an accumulation map, and defining the estimate of the amount of particulate matter accumulated in the particulate filter o f the internal combustion engine by summing a first product of the first estimate by a first coef ficient to a second product of the second estimate by a second coef ficient , wherein the first coef ficient and the second coef ficient are variable as a function of operating parameters of the internal combustion engine .

[0030] Speci fically, the input data for implementing the method according to the invention comprise :

[0031] - the first estimate of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine on the basis of a pressure di f ference between an inlet and an outlet of the filter, denoted by reference 2 ;

[0032] - an enable condition for the use of the first estimate , denoted by reference 4 ; the enable condition essentially corresponds to an indicator of a fault in a di f ferential pressure sensor, which enables operating the first estimate 2 ( or, generally speaking, in pressure sensors adapted to detect the pressure upstream and downstream of the particulate filter ) . In preferred embodiments , the enable condition requires , in order to be true ( logic state " 1" = true ) , meeting simultaneously (AND) four requirements : i ) absence of faults in a di f ferential pressure sensor which enables providing the first estimate 2 ( or, generally speaking, in pressure sensors adapted to detect the pressure upstream and downstream of the particulate filter ) ; ii ) exceeding the dew point of the exhaust gas , in order to avoid the presence of liquid water in the exhaust gas , which would alter the pressure reading; iii ) stability ( or stationarity ) of the operating point of the engine , as regards the pressure drop across the particulate filter and the flow rate of the exhaust gas ; iv) a contribution to the pressure di f ference between an inlet and an outlet of the particulate f ilter, given by the presence of ashes in the particulate filter (produced by the combustion of the particulate matter ) shall be lower than a maximum threshold;

[0033] - the second estimate of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine , on the basis of an accumulation map ( denoted by reference 6 ) , wherein the accumulation map is a function of one or more operating parameters of the engine , comprising for example a number of revolutions of the engine , a metering, an engine load ( i . e . a torque request to the same engine ) ,

[0034] - a calibration variable 8 , which is normally not active , except during the calibration of the method,

[0035] - a data item 10 of the volume flow rate of the engine exhaust gas through the particulate filter, and a data item 12 corresponding to a pressure drop between the inlet and the outlet of the particulate filter, wherein data 10 and 12 are used - in the preferred embodiment shown in the Figures - as input data for the reading of a map of coef ficient values 14 ( speci fically a three-dimensional map, with two input data items and one output data item) and determining a multiplication coef ficient 16 . It will be appreciated that the data 10 , 12 correspond to operating parameters of the engine , and therefore the coef ficient 16 does not have a fixed value , but a value which depends on said parameters . The coef ficient 16 is involved in the estimate of the accumulated amount of particulate matter according to the following procedure , even though in alternative embodiments other procedures may be envisaged .

[0036] Referring to Figure 1 and Figure 2 , the data 2 , 16 , 6 and SL, the latter representing the latest calculated value of the estimate of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine , are sent to a block 18 the function whereof is to assign a weight to each contribution to the estimate (by means of multiplication) and to operate a sum of the various contributions . It shall be noted that the data 6 and SL are used alternatively : i f an estimate SL of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine is already available from a previous calculation cycle , then such a value is used; otherwise , an estimate is used which is operated on the basis of the accumulation map, and therefore data item 6 .

[0037] In block 18 , a first calculation path 181 aims at providing the first product mentioned in the foregoing, i . e . a product of the first estimate 2 of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine on the basis of a pressure di f ference between an inlet and an outlet of the filter by the first coef ficient . In the preferred embodiment , the first coef ficient corresponds to coef ficient 16 . The first estimate 2 and the coef f icient 16 are processed by means of a first multiplication operator Ml and sent to a summation operator S I .

[0038] A second calculation path 182 aims at providing the second product mentioned in the foregoing, i . e . a product of the second estimate 6 , SL by a second coef ficient, which in the preferred embodiment is complementary to 1 of the first coef ficient 16 ( therefore , the first coef ficient and the second coef ficient are variable as a function of operating parameters of the internal combustion engine , as they both depend on coef ficient 16 ) . In more detail , the coefficient 16 is sent to a subtraction operator DI , wherein it is subtracted from the unit, and the second coefficient so defined (1 - coefficient 16) is processed by means of a second multiplication operator M2 in combination with the output of a first switch SW1, in order to be subsequently sent to operator SI. The switch SW1 comprises - as alternative inputs - the data 2 and 6, SL. The selection of either data item depends on the value of an initialization variable INIT. The variable INIT represents the need of a transition in the estimate of the amount of particulate matter, from a calculation based on an accumulation map to a calculation based on a pressure difference. The condition shown in the Figure (which corresponds to the logic state "1" of the variable INIT) shows such need, and corresponds to deleting the stored data, which are based on the accumulation map, and to imposing the first estimate based on the pressure difference as the latest value of the second estimate. It is easy to see that, in the case shown in Figure 2, an output 22 of block 18 corresponds to "coefficient 16 * 2 + (1 - coefficient 16) * 2", therefore to the data item 2, which is the first estimate.

[0039] If the logic state of the variable INIT is "0", then the switch SW1 enables the input 6, SL, so that the output 22 corresponds to "coefficient 16 * 2 + (1 - coefficient 16) * (6, SL) , therefore to the sum of the first product to the second product (data item 6 is used in the first iteration of the calculation, data item SL is used from the second iteration onwards) .

[0040] Referring to Figure 1, the output 22 is further processed by means of a second switch SW2, which is controlled based on data item 4. In other words, if no fault is present in the differential pressure sensor (or in the sensors across the particulate filter) , the output 22 is sent to a processing block 24 which is active only during the calibration step (and which receives as input the data item 8 , in addition to output 22 ) . I f a mal function takes place in the di f ferential pressure sensor ( or in the sensors across the particulate fi lter ) the switch SW2 imposes the estimate of the amount of particulate matter in the filter only by means of the accumulation map, leaving only the second estimate 6 active . This is due to the fact that the first estimate 2 is evidently unreliable and because - as described in the foregoing - it is impossible to calculate the value of coef ficient 16 .

[0041] The block 24 in turn comprises an output 26 , which corresponds to the output 22 provided that a calibration step is not taking place . The output 26 is then distributed on various levels of the control system, speci fically :

[0042] - it is made available , 26_OUT , on the CAN network ( or another communication network) of the vehicle ;

[0043] - it is stored, block SVC and output SVC_OUT , for future service or maintenance operation on the vehicle ;

[0044] - it is written in memory, WRT , as an initial value of the following calculation cycle ;

[0045] - it is sent as a data item SL to block 18 - precisely - in each following calculation cycle .

[0046] The method thus described is iterated for a number of times ( the value of coefficient 16 being adapted to vary from one iteration to the other, as a function of the engine operating parameters ) , which number may vary according to circumstances . For example , the iterations may cease when a maximum number thereof is achieved, or else - as described in the foregoing - i f conditions occur due to which the estimate of the amount of particulate matter must be based on a traditional calculation, based on only one of both techniques (pressure di f ference and accumulation map ) , for example due to a fault of the pressure sensor or to operational limits of the accumulation map .

[0047] Moreover, although in the preferred embodiment provided herein the coef ficient 16 has values lower than the unit , and therefore , as a consequence , both the first and the second coef ficient have values smaller than the unit ( the first coef ficient is coef ficient 16 , whereas the second coef ficient is the complementary to 1 thereof ) , embodiments are possible wherein, due for example to a normali zation of the estimate data obtained with the first and second estimates , the coef ficients may be chosen greater than the unit and / or not necessarily dependent on the relationship provided in the foregoing; on the contrary, they may be chosen independently by means of speci fic maps for each coef ficient . In such cases it is possible to select the coef ficients also on the basis of engine operating parameters other than data 10 , 12 .

[0048] It will therefore be appreciated that , thanks to the method according to the invention, it is possible to improve the accuracy of the estimate of the amount of particulate matter accumulated in a particulate filter for spark-ignition ( gasoline- fuelled) internal combustion engines , by attributing individual weights , which may vary as a function of the engine operating parameters , to the estimates 2 and 6 , therefore overcoming the respective limits thereof as described in the state of the art .

[0049] Of course , the implementation details and the embodiments may amply vary with respect to what has been described and illustrated, without departing from the scope of the present invention as defined by the annexed claims .

Claims

CLAIMS1. A method for estimating an amount of particulate matter accumulated in a particulate filter of a sparkignition internal combustion engine, the method comprising :- providing a first estimate (2) of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine, on the basis of a pressure difference between an inlet and an outlet of the particulate filter,- providing a second estimate (6) of the amount of particulate matter accumulated in the particulate filter of said internal combustion engine, on the basis of an accumulation map; defining the estimate (SL) of the amount of particulate matter accumulated in the particulate filter of the internal combustion engine by summing a product of said first estimate (2) by a first coefficient (16) to a product of said second estimate (6) by a second coefficient (16) , wherein the first coefficient and the second coefficient are variable as a function of operating parameters of the internal combustion engine.

2. The method according to claim 1, wherein each coefficient (16) has a value lower than the unit.

3. The method according to claim 2, wherein the second coefficient (16) is the complementary to 1 of the first coefficient.

4. The method according to any of the previous claims, wherein said operating parameters comprise a volume flow rate of the exhaust gas of the engine through the particulate filter and a pressure difference between an inlet and an outlet of the particulate filter.

5. The method according to claim 1, further comprising defining an enable condition (4) of said firstestimate (2) , wherein said enable condition corresponds to an enable condition of the first estimate (2) when the following requirements are met simultaneously: i) absence of faults in one or more of the pressure sensors which enable providing the first estimate (2) ; ii) exceeding the dew point of the exhaust gas which traverses the particulate filter; iii) stability or stationarity of the operating point of the engine, as regards the pressure drop across the particulate filter and the flow of the exhaust gas therethrough; iv) a contribution to the pressure difference between an inlet and an outlet of the particulate filter, given by the presence of ashes in the particulate filter, is lower than a maximum threshold.

6. The method according to any of the previous claims, wherein said internal combustion engine is gasoline- fuelled.

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