FR2781251A1 - METHOD AND DEVICE FOR DETERMINING THE LOAD OF A PARTICLE FILTER - Google Patents

Abstract

Method for determining the load in soot of a particulate filter, of the type used downstream of an internal combustion engine, the filter having to be regenerated periodically by combustion of soot before reaching a too high load, by which the load (c) is deduced from the differential pressure DELTA P upstream-downstream of the particle filter and from a quantity A representative of the gas flow in the engine. Said quantity A is representative of the only gas flow passing through the particle filter and in that said quantity A is obtained from the mass flow of fresh air entering the engine (Mair) and the mass flow of fuel (Mc) supplying engine.

Description

Method and device for determining the soot loading of a

particle filter.

  The present invention relates to the field of purification of exhaust gases from an internal combustion engine, for example from a motor vehicle, and more particularly to a method and a device.

  to determine the soot loading of a particulate filter.

  The presence of a particulate filter in the exhaust line of an internal combustion engine, in particular a diesel engine, makes it possible to considerably reduce the quantity of particles, dust and other soot emitted into the atmosphere and to satisfy as well as anti-pollution standards, During the operation of the internal combustion engine, the particulate filter is gradually loaded with unburnt hydrocarbons, the accumulation of which eventually degrades the performance of the filter and that of the engine because resulting in an increase in the differential pressure between the upstream and downstream of the filter and therefore of the engine exhaust back pressure. It is therefore necessary to periodically regenerate the filter, an operation which is carried out by setting

  combustion of particles in the filter.

  This thermal regeneration is preferably carried out only when the filter reaches a certain load which can be determined as a function of the loss of efficiency of the filter, as a function of the increase in the differential pressure or as a function of a risk of destruction of the filter by excessive heating during regeneration by

  burning too much soot particles.

  Conventionally, a regeneration operation is triggered after a certain time interval, or distance traveled, but without taking into account the actual charge of the filter, which results in taking account of the

  worst conditions that can occur and regenerate the filter frequently.

  Methods and devices have therefore been developed to optimize the regeneration operations using an estimate of the actual loading of the filter, estimation of the load in particular deduced from the

  nature of the differential pressure prevailing between the upstream and downstream of the filter.

  Document EP-587,146 thus discloses a process for regenerating a particulate filter fitted to an atmospheric or turbocharged engine. According to this document, the regeneration of the filter is triggered as soon as the loading of the filter exceeds a predetermined value. This loading is deduced from the differential pressure prevailing between the input and the output of the filter, noted A P, by the following relation A P = c. A, c = loading of the filter A = quantity characteristic of the flow of gases through the

engine.

  A being a function of the ratio between the product of the engine speed by the pressure in the intake manifold and the average temperature between the upstream and downstream of the particulate filter, and the product of the temperature in the manifold d pressure inlet upstream of

particle filter.

  It appeared to the applicant that the quantity retained as a characteristic of the flow of gases through the engine is not really representative of the gases passing through the particle filter, in particular in the event of recirculation of the exhaust gases, and that by therefore the filter loading estimate could not be

deducted with precision.

  Besides, this EPl document? 587 146 does not mention any methodology for acquiring the information necessary for calculating the loading of the gold filter, given the measurement dispersions of the various sensors required, it seems important to adopt a precise procedure

  to guarantee the reliability of the chosen method.

  The object of the present invention is to determine the loading of a particle filter more precisely than the known prior art and

  for various types of internal combustion engines.

  The method for determining the soot loading, according to the invention, is intended for a particulate filter, of the type used downstream of an internal combustion engine, the filter having to be regenerated periodically by combustion of the soot before reaching a loading

too high.

  The loading c is deduced from the differential pressure A P upstream-downstream of the particle filter and from a quantity A representative of the gas flow in the engine. Said quantity A is representative of the only gas flow passing through the particle filter and is obtained from the mass flow of fresh air entering the Mair engine and the flow

  mass of fuel Mc supplying the engine.

  We can deduce the loading of the following formulas (I) AP = cA + b (II) A = (Mair + Mc) NPT with b constant T: temperature of the exhaust gases upstream of the filter P pressure of the exhaust gases upstream the engine speed N filter; The exhaust gas pressure upstream of the filter can be given by À P = AP + Po Po = atmospheric pressure. It is thus possible to determine the soot loading of an internal combustion engine, including an engine equipped with a combustion gas recirculation system thanks to the fact that the gases actually entering the particle filter are taken into account. In fact, at a high rate of recirculation of the exhaust gases, the flow which arrives at the particle filter is represented by the flow of incoming air added to the flow of fuel. The higher the exhaust gas recirculation rate, the more the fresh air flow decreases and therefore the more the flow of gases arriving on the

particle filter decreases.

  In one embodiment of the invention, the parameter c is compared to a predetermined maximum value cmax and a regeneration of the filter is triggered if the parameter c is greater than said predetermined maximum value cmax. A filter regeneration can be triggered if, in addition, conditions of exhaust temperature, engine speed and fuel flow are met, in order to obtain a

good combustion of soot.

  In one embodiment of the invention, the proportionality parameter c is calculated from at least those

separate measurement points.

  Advantageously, each measurement point is chosen so as to have two values of the differential pressure AP, each of these values being measured within a predetermined range of the parameter A, the

  ranges being provided without overlap.

  In one embodiment of the invention, the duration At elapsed between the first measurement point and the last measurement point is measured, the duration At is compared to a maximum limit, and if the duration At is less than the maximum limit , we admit that the soot loading remained constant

  from the first to the last measurement point.

  The device for determining the soot loading, according to the invention, is provided for a particulate filter, of the type used downstream of an internal combustion engine, the filter having to be regenerated periodically by combustion of the soot before reaching a loading

too high.

  The device comprises means for deducing the charge c from the differential pressure A P upstream-downstream of the particle filter and from a quantity A representative of the flow of gases in the engine. Said quantity A is representative of the only gas flow passing through the particle filter and in that said quantity A is obtained from the mass flow of fresh air entering the Mair engine and the mass flow of

fuel Mc feeding the engine.

  The device may include a means for deducing the loading of the following formulas (I) AP = cA + b (II) A = (Mair + Mc) TNP with b constant T temperature of the exhaust gases upstream of the filter P gas pressure exhaust upstream of filter N: engine speed; The pressure of the exhaust gases upstream of the filter can be given by: P = A P + Po Po = atmospheric pressure The present invention also relates to a motor vehicle comprising a device for determining the loading in

  soot from the particulate filter as above.

  There is thus a precise determination of the loading of the filter, which makes it possible to trigger regeneration by combustion wisely, that is to say when the filter reaches the maximum loading limit fixed and this, without overestimation of the loading due exhaust gas recirculation, which reduces the frequency of regeneration by combustion and increases service life

of the particle filter.

  The present invention will be better understood on studying the

  detailed description of an exemplary embodiment

  in no way limiting and illustrated by the appended drawings, in which: FIG. 1 is a diagram of installation of a particle filter and of the elements arranged upstream; FIG. 2 is a curve representing the evolution of the differential pressure as a function of parameter A; and Figure 3 is a block diagram of a system

according to the invention.

  As can be seen in FIG. 1, an engine 1 provided with an intake manifold 2, an exhaust manifold 3, and an injection system 4, is supplied with air by a compressor 5 upstream of which is located an air flow meter 6 capable of measuring the mass flow rate of fresh air entering Mair. The engine 1 is equipped with an exhaust gas recirculation system which is in the form of a bypass 7 disposed between the exhaust manifold 3 and the intake manifold 2, which makes it possible to introduce into the intake manifold 2 a fraction of the gases from combustion located in the exhaust manifold 3. The bypass 7 is controlled by an electronic engine control unit, not shown, capable of varying the rate of gas recycling exhaust according to the engine needs to reduce the

  formation of polluting compounds and in particular nitrogen oxides.

  The exhaust manifold 3 is connected to a turbine 8 driving the compressor 5 in rotation. The turbine 8 and the compressor 5 are generally coaxial. They have been shown on this diagram separately to facilitate understanding. The turbine 8 is provided with a

bypass 9.

  A particle filter 10 is disposed at the outlet of the turbine 8.

  The upstream of the filter 10 carries the reference 10a and the downstream of the filter 10 carries the reference 10b. The downstream part 10b is connected to other devices such as an exhaust pipe, not shown. On the upstream side

  1 Oa, an upstream temperature sensor 11 is installed.

  A differential pressure sensor 12 AP between the upstream part a and the downstream part lOb of the filter 10 is also provided and connected to said 1 5 upstream parts 10Oa and downstream 10Ob. An electronic computer, not shown, is also provided, which receives the information coming from the air flow meter 6, from the injection system 4 which supplies it with a quantity relating to the mass flow of fuel Mc, from the temperature sensor 11, and of the differential pressure sensor 12. Of course, instead of the differential pressure sensor 12, one could provide an upstream pressure sensor and a downstream pressure sensor and calculate

  then the differential pressure AP.

  The computer comprises storage means and calculation means by which it uses the aforementioned information to estimate the loading of the particulate filter and trigger means of regeneration not shown of the latter when this loading exceeds a

predetermined value.

  According to the invention, this estimate of the loading of the filter is given by the formula: (I) A P = c. A + B o A P is the upstream-downstream differential pressure of the

particle filter.

  c: loading of the filter A: volume flow of the gases passing through the filter b: offset of the differential pressure sensor A being defined by (II) A = (Mair + Mc): TN p Mc: fuel flow T temperature of the gases exhaust upstream of the filter P: pressure of the exhaust gases upstream of the filter. In the case where there is no upstream pressure sensor, we take: (III) P = A P + Po o Po is the atmospheric pressure considered to be the

  pressure downstream of the particulate filter.

  The loading of the particulate filter being deduced from the only flow of gases passing through the filter and not from the flow of gases passing through the engine, a very precise value of this loading is obtained, and therefore whatever the exhaust gas recirculation rates. Of course, this determination can also be made for an engine without an exhaust gas recirculation system and / or atmospheric type dP = e. The loading of the filter given by the formula (I) AP = c A + B We therefore see that two measurement points (AP1 A1) (A P2 A2) are enough, or even one if b is predetermined to get c. To increase the precision on c, we can also take a larger

  number of measurement points and obtain c by linear regression.

  According to the invention, the loading is deduced from at least two points of

  measurement corresponding to appreciably distinct values of A.

  It should be noted that whatever the number of measurement points selected, these measurement points must be sufficiently close in time to correspond well to the same load. Indeed, loading the filter

  increases continuously during engine operation.

  FIG. 2 shows three measurement points 13, 14 and, arranged in a two-axis coordinate system, with the parameter A on the abscissa and the differential pressure AP on the ordinate. Each of the points 13 to 15 was taken in a range of variations of the parameter A limited by values 16 to 19. It could of course be provided for ranges separated from each other. But we will avoid choosing overlapping ranges which would make it difficult to draw a straight line as close as possible to points 13 to 15. We then deduce the equation of the first degree: AP = c * A + b. b is representative of an offset at the origin and c is representative of the loading

soot from the particulate filter.

  The straight line 20 that has been drawn from the points 13 to 15 is placed under a limit line 21 representative of the admissible limit load of the particle filter. As long as the line 20 remains disposed under the line 21, the filter is able to operate without regeneration. On the contrary, if the three measurement points defined a straight line, for example the straight line 22 disposed above the theoretical straight line 21, then the regeneration of the particle filter would be triggered, which would be

excessively charged.

  The steps of the method for determining the soot loading of the particulate filter are represented in FIG. 3. The vehicle is started up in step 23. An acquisition of the parameter A takes place in step 24. In step 25, it is checked whether this acquisition has taken place in the first measurement area, that is to say between the values 16 and 17 in FIG. 2. Otherwise, we go to step 26 in which we check whether this acquisition was carried out in the second measurement zone, that is to say between the values 17 and 18 in FIG. 2. Otherwise, we go to step 27 where the same verification is carried out for the third measurement zone, that is to say between the values 18 and 19 of FIG. 2. Otherwise, we return to step 24 of acquisition of the parameter A. If one of the steps 25, 26 or 27 allowed an acquisition in one of the three zones, the current values of differential pressure AP and of parameter A are saved and we go to step 28. At the step 28 it is checked whether three acquisitions in three different areas were carried out for a duration At less than a maximum limit and if the parameter c which is the slope of the line 20 of Figure 2 is greater than a predetermined value cmax. If one of these two conditions is not satisfied, one returns to step 24 of acquisition of the parameter A. If these two conditions are satisfied, one starts the regeneration by combustion of soot

  trapped in the particle filter (step 29).

  Thanks to the invention, the loading of the particulate filter is precisely determined, which makes it possible to space regenerations, without risking an excessive loading of the filter leading to a deterioration in the performance of the engine and to an excessive thermal release during

  combustion of soot which could damage the filter.

Claims (12)

  1. Method for determining the loading in soot of a particulate filter, of the type used downstream of an internal combustion engine, the filter having to be regenerated periodically by combustion of soot before reaching a too high loading, by which the charge (c) is deduced from the differential pressure AP upstream-downstream of the particulate filter and of a quantity A representative of the flow of gases in the engine, characterized in that said quantity A is representative of the gas flow alone passing through the particle filter and in that said quantity A is obtained from the mass flow of fresh air entering the engine (Mair)   and the mass flow of fuel (Mc) feeding the engine.   2. Method according to claim 1, characterized in that the loading is deduced from the following formulas (I) A P = c A + b (II) A = (Mair + Mc) T N P   with b constant T temperature of the exhaust gases upstream of the filter   P exhaust gas pressure upstream of the filter.   N: engine speed 3. Method according to claim 2, characterized in that the pressure of the exhaust gases upstream of the filter is given by: P = A P + Po Po = atmospheric pressure   4. Method according to any one of the claims   previous in which we compare the parameter c to a predetermined maximum value cmax and we trigger a regeneration of the filter if the   paraleter c is greater than said predetermined maximum value cmax.   5. The method of claim 4 wherein a regeneration of the filter is triggered if, in addition, conditions of exhaust temperature, engine speed and fuel flow are met. 1!   6. Method according to any one of the claims   previous, in which the calculation of the proportionality parameter c is   made from at least two separate measurement points.   7. The method of claim 6, wherein each measurement point is chosen so that there are two values of the differential pressure AP, each of the values being measured within a predetermined range of parameter A, the ranges being provided without overlap. . 8. Method according to claim 7, in which the duration At elapsed between the first measurement point and the last measurement point is measured, the duration At is compared to a maximum limit, and if the duration At is less than the maximum limit , we admit that the soot load is   remained constant from the first to the last measurement point.   9. Device for determining the load in soot of a particulate filter, of the type used downstream of an internal combustion engine, the filter having to be regenerated periodically by combustion of soot before reaching a too high load, comprising a means for deducing the loading (c) of the differential pressure AP upstream-downstream of the particulate filter and of a quantity A representative of the flow of gases in the engine, characterized in that said quantity A is representative of the flow rate of the gas passing through the particle filter and in that said quantity A is obtained from the mass flow rate of fresh air entering the engine (Mair) and the mass flow rate of the fuel (Mc) supplying the engine. 10. Device according to claim 9, characterized in that it comprises a means for deducing the loading of the following formulas: (I) AP = c A + b (II) A = (Mair + Mc) TNP pu with b constant T : exhaust gas temperature upstream of the filter   P: exhaust gas pressure upstream of the filter.   N: engine speed 11. Device according to claim 10, characterized in that the pressure of the exhaust gases upstream of the filter is given by: P = A P + Po Po = atmospheric pressure 12. Vehicle comprising a device according to one of claims 9 to 11.