GB2479122A

GB2479122A - Determining soot rate in an exhaust by measuring its oxygen concentration

Info

Publication number: GB2479122A
Application number: GB1005188A
Authority: GB
Inventors: Federico Luigi Guglielmone; Stefano Cassani; Giuseppe Schiavone
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-03-29
Filing date: 2010-03-29
Publication date: 2011-10-05
Also published as: GB201005188D0

Abstract

A method for determining the soot rate Se in an exhaust stream based on measuring the oxygen concentration value As in the exhaust stream. Preferably the estimation of the soot rate comprises determining a soot rate reference value Sr, determining a correction Cf on the base of the oxygen concentration value and applying the correction to the soot rate reference value. The correction may be determined by determining a reference value Ar of the oxygen concentration in the exhaust stream, calculating the difference Ae between it and the oxygen concentration value and determining the correction on the base of the oxygen concentration value and its difference. Preferably the soot rate reference value, the correction and the oxygen concentration reference value are determined from an empirically determined data set, where the correction is correlated to the oxygen concentration value and its difference and the soot rate reference value and the oxygen concentration reference value are correlated to one or more engine operating parameters. The oxygen concentration value may be measure by a lambda sensor. A method for managing and regenerating a DPF is also claimed.

Description

METHOD DETERMINING THE SCOT R'E IN AN EXHAUST STRE7M F1 AN IN-TERNAL CV1BUSTION ENGINE

TECHNICAL FIElD

The present invention relates to a method for determining the soot rate in an exhaust stream flowing from an internal combustion engine of a vehicle, typically from a Diesel engine, and to a method for managing a Diesel Particulate Filter, which is located in an exhaust pipe of the internal combustion engine for treating said exhaust stream.

BACKDUND

It is known that the exhaust pipe of a modern Diesel engine is gener-ally equipped with a Diesel Particulate Filter, also referred as DPF in the present description, which is designed to trap the soot con- tained in exhaust stream that flows fran the Diesel engine, to there- by cleaning the exhaust stream in order to comply with specific regu-lation emission limits.

The DPF is conventionally located downstream a Diesel Oxidation Cata- lyst, also referred as DOC in the present description, which is pro-vided for degrading residual hydrocarbons and carbon oxides contained in the exhaust stream.

During the normal engine functioning, the soot contained in the ex-haust stream is progressively accumulated within the DPF, so that the pressure drop across the DPF gradually increases as its clogging raises.

If the clogging of the DPF becomes excessive, the pressure drop may affect the efficiency of the Diesel engine and even cause the DPF to crack.

In order to avoid excessive clogging of the DPF, the latter is ertp- tied-out by means of a dedicated engine management, known as DPF re- generation, that generally provides for heating the DPF to a tempera-ture at which the accumulated soot burns off (typically up to 630°C), leaving the DEF clean again.

In greater details, the DPF regeneration provides for inducing a spe-cific combustion mode within the Diesel engine, by means of which a certain amount of late-injected fuel is discharged unburnt from the Diesel engine and is channeled by the exhaust pipe towards the DOC.

The DCC is effective to oxidize the unburnt fuel, to thereby heating the exhaust stream that subsequently passes through the DPF, whereby the latter is heated.

From the above, it follows that the DPF regeneration requires the in-jection of a greater amount of fuel than a normal engine management, and involves also a greater oil dilution, since part of the late-injected fuel adheres to the internal walls of the cylinders and is drawn within the crankcase by the pistons.

The DPF regeneration is automatically conanded by the Engine Control Unit, also referred as ECU in the present description, every tir the soot loading level within the DPF exceeds a predetermined maximum threshold, to thereby causing a certain DPF regeneration frequency along the vehicle life.

An optimal DPF regeneration frequency must be such as to avoid exces-sive fuel consumption and oil dilution, which can be caused by a DPF regeneration frequency higher than necessary, and must also avoid DEF clogging and overloading occurrences, which can be caused by a DPF regeneration frequency lower than necessary.

The DPF regeneration frequency actually depends on the accuracy of the strategy used by the ECU for determining the soot loading level within the DPF.

At present, the ECU estimates the soot loading level within the DPF by means of a statistical model that correlates the soot rate in the exhaust stream to the driving conditions to which the vehicle is sub-ject, coninonly known as Mission Profile.

The driving conditions are determined by many driving parameters, in-cluding engine operating parameters, such as engine speed and engine load, as well as other characteristic parameters, such as vehicle speed.

The statistical model is empirically calibrated by means of experi- mental activities that provides for inducing different driving condi-tions, and to measure the soot rate in the exhaust stream for each driving condition.

Due to the so many driving parameters involved in determining the driving conditions, said calibration activity generally involves a great effort.

Moreover, the calibration activity generally considers only a limited number of stationary driving conditions, so that the soot rate esti- mation model does not cover the entire gairma of possible driving con-ditions.

As a matter of fact, the transient driving conditions are typically not considered.

The calibration activity is performed on fully functional test ye- hides, so that system variations, due for example to engine produc-tion spread, sub-systems production spread and drifts, are generally not considered at all.

Therefore, the soot rate estimating strategy is blind to any differ-ence between reality and the reference experimental conditions used to calibrate the statistical model.

Furthermore, the calibration activity is performed on test vehicle fleets that are representative only of a small portion of the entire vehicle production.

The above mentioned drawbacks globally cause a low accuraöy of the soot rate estimation.

One object of an embodiment of the present invention is to provide a new strategy for estimating the soot rate in the exhaust stream from an internal combustion engine.

A further object of an embodiment of the present invention is to pro-vide an estimating strategy that needs an easy and quick calibration activity and that provides a good soot estimation accuracy.

Another object of an embodiment of the present invention is to pro-vide an estimating strategy that is sensitive to engine properties variations, including engine production spread, engine sub-systems production spread, sub-systems faulty conditions, such as for example EGR valve stuck, and sub-systems drift due to ageing effect, such as for example injector drifts or air flow meter drift.

A further object is to provide an estirreting strategy capable to mon- itor driving conditions not considered as experimental reference con-ditions in the calibration activity, such as for example transitory conditions.

Another object is to provide a strategy for estimating the soot load-ing level within the DPF, in order to achieve an optimal regeneration frequency that prevents excessive fuel consumption and oil dilution, as well as DPF overloading and clogging occurrences.

These and other objects are attained by the characteristics of the embodiments of the invention as reported in the independent claims.

The dependent claims recite preferred and/or especially advantageous features of other embodiments of the invention.

DISClOSURE

An embodiment of the invention provides a method for determining the soot rate in an exhaust stream from an internal combustion engine, wherein the method comprises the steps of maasuring oxygen concentra-tion value in the exhaust stream, and of estimating the soot rate in the exhaust stream on the base of said oxygen concentration value.

This method is based on the principle that the soot production de- pends on air/fuel ratio during the combustion process within the en-gine cylinders, and that the air/fuel ratio is directly correlated to the oxygen concentration in the exhaust stream.

Hence, by measuring oxygen concentration in the exhaust stream, it is effectively possible to provide an accurate estimation of the soot rate.

According to an embodiment of the invention, the estimation of the soot rate comprises the steps of determining a soot rate reference value, of determining a correction thereto on the base of the oxygen concentration value, and of applying said correction to said soot rate reference value.

In particular, the soot rate reference value represents the expected soot rate in a reference driving condition, typically in an experi-mental stationary driving condition, and the correction represents the adjustment to be applied to the reference soot rate value, in or-der to consider the real driving condition.

In other words, the soot rate reference value provides the expected soot rate for a stationary and known driving condition (reference condition), and the correction globally accounts for most of the driving parameters, whose variations, with respect to the reference condition, have effect on the soot rate and are responsible that it deviates from the expected one.

Thanks to the correction, the soot rate reference value can depend on engine operating parameters only, such as for example engine speed and engine load, so that the soot rate reference values are generally easy and quick to be calibrated.

At the same time, the correction responds to engine properties varia-tions, including production spreads, sub-systems faulty conditions and sub-systems drift, and is capable to account driving conditions not considered as reference conditions, such as for example transi- tory conditions, to thereby allowing a good soot rate estimation ac-curacy.

According to an embodiment of the invention, the soot rate reference value can be determined from an empirically determined data set or map correlating the soot rate reference value to one or more engine operating parameters, such as for example engine speed and engine load.

In this way, said data set or map can be stored in a memory module of the ECU, to thereby allowing the latter to automatically perform the estimating method.

According to another embodiment of the invention, the determination of the correction comprises the steps of determining a reference val-ue of the oxygen concentration in the exhaust stream, of calculating the difference between said oxygen concentration reference value and the oxygen concentration value, and of determining the correction on the base of said oxygen concentration value and said difference.

In particular, said reference value represents the oxygen concentra-tion that is expected in the exhaust stream for the reference driving condition, so that the oxygen concentration value and its difference with respect to the reference value uniquely identify the real driv-ing condition.

In this way, the estimating method results particularly effective and simple to be calibrated.

According to an embodiment of the invention, the oxygen concentration reference value can be determined from an empirically determined data set or map correlating the oxygen concentration reference value to one or more engine operating parameters, such as engine speed and en-gine load.

According to another embodiment of the method, the correction can be determined from an empirically determined data set or map correlating the correction to said oxygen concentration measureirent and said dif-ference.

Each of the preceding embodiments has the advantage that the respec-tive data set or map can be stored in a memory module of an ECU, to thereby allowing the latter to automatically perform the estimating method.

According to a further embodiment of the invention, the oxygen con-centration value is measured by means of a lambda sensor.

Since a lambda sensor is conventionally located in the exhaust pipe of any internal combustion engine system, this erribodirrient has the ad-vantage of not increasing the cost.

Another aspect of the invention provides a method for managing a DPF located in an exhaust pipe of an internal combustion engine, wherein the method comprises the steps of determining, as explained above, the soot rate in the exhaust stream flowing from the engine, and of estimating the soot loading level within the DPF on the base of said determined soot rate.

Thanks to the accuracy of the soot rate estimation method, the DPF managing method achieves in turn an accurate soot loading level esti-mation within the DPF.

According to an embodiment of the invention, the estimation of the soot loading level within the DPF provides for time integrating the determined soot rate.

In this way, the DPF managing method results particularly simple and easy to be performed.

According to another embodiment of the invention, the DPF managing method further comprises the step of performing a DPF regeneration process, when the estimated soot loading level within the DPF exceeds a predetermined threshold.

Thanks to the accurate soot loading level estimation, this embodiment provides an optimal regeneration frequency that prevents excessive fuel consumption and oil dilution, as well as DPF overloading and clogging occurrences.

The method according to the invention can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of com-puter program product comprising the computer program.

The computer progam product can be embodied as a control apparatus for an internal combustion engine, comprising the ECU, a data carrier associated to the ECU, and the computer program stored in a data car rier, so that the control apparatus defines the invention in the same way as the method. In this case, when the control apparatus executes the corruter program all the steps of the method described above are carried out.

The method can also be embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent computer program to carry out all steps of the method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accanpanying drawings, in which: figure 1 is a schematic illustration of a Diesel engine system; figure 2 is a schematic flowchart of a method according to an erribodi-ment of the invention.

DETAILED DESCRIPTION

An embodiment of the present invention provides a method for managing a DPF associated to a Diesel engine system of a vehicle.

The Diesel engine system generally comprises a Diesel engine 1 and an exhaust pipe 2 for channeling the exhaust stream from the Diesel en-gine 1 into the environment.

The exhaust pipe 2 is equipped with a lambda sensor 3 for sensing the oxygen concentration in the exhaust stream; with a DOC 4, located downstream the lambda sensor 3, for degrading residual hydrocarbons and carbon oxides contained in the exhaust stream; and with the above mentioned DPF 5, located downstream the DOC 4, for trapping the soot contained in exhaust stream.

The Diesel engine system further comprises a microprocessor based controller 6, also referred as ECU, which is connected to the Diesel engine 1 and to the lambda sensor 3, in order to perform the DPF man-aging method described hereinafter.

As shown in figure 2, the DPF managing method provides for monitoring a plurality of engine operating parameters, in this case engine speed Es and engine load El.

In reference conditions, that is in stationary and known driving con-ditions, engine speed Es can be directly related to the intake air mass flow and engine load El can be directly related to the fuel mass injected into the Diesel engine 1.

The intake air mass flow and the fuel mass injected determine the air/fuel ratio during the combustion process, which in turn deter-mines the quantity of soot and other residuals that is produced by the Diesel engine 1.

Hence, in reference conditions, any couple of values of engine speed Es and engine load El can be directly related to an expected soot rate in the exhaust stream.

According to this principle, the method provides for determining a reference value Sr of the soot rate in the exhaust stream, which represents the soot rate that is expected in the exhaust stream, in reference conditions, for the sensed values of engine speed Es and engine load El.

The reference value Sr is determined through a first map 10, which correlates any couple of values of engine speed Es and engine load El to a correspondent reference value Sr of the soot rate in the exhaust stream.

The first map 10 can be empirically determined by means of a calibra-tion activity.

Since the first map 10 depends on engine speed Es and engine load El only, the calibration activity is generally quite easy and quick to be performed.

In principle, the air/fuel ratio during the combustion process within the Diesel engine 1 is directly linked also to the oxygen concentra-tion in the exhaust stream.

Hence, in reference conditions, any couple of values of engine speed Es and engine load El can be directly related also to an expected oxygen concentration in the exhaust stream.

According to this principle, the method further provides for deter- mining a reference value Ar of the oxygen concentration in the ex- haust stream, which represents the oxygen concentration that is ex-pected in the exhaust stream, in reference conditions, for the sensed values of engine speed Es and engine load El.

The reference value Ar is determined through a second map 20 that correlates any couple of values of engine speed Es and engine load El to a correspondent reference value Ar of the oxygen concentration in the exhaust stream.

The second map 20 can be empirically determined by means of a cali-bration activity.

Since the second map 20 depends on engine speed Es and engine load El only, the calibration activity is generally quite easy and quick to be performed.

Furthermore, the method provides for monitoring the actual oxygen concentration value As in the exhaust stream, by means of the lambda sensor 3.

The measured oxygen concentration value As is sent to an adder 30, which calculates the difference Xe between the previously determined oxygen concentration reference value Ar and the measured oxygen con-centration value Xs.

As a matter of fact, this difference Xe is globally determined by all the driving parameters, whose variations, with respect to the refer-ence conditions, affects the intake air mass flow and/or the fuel mass injected, to thereby deviating the air/fuel ratio fran the ex-pected one.

In particular, the difference Xe depends on engine properties varia-tions, including for example production spreads, sub-systems faulty conditions and sub-systems drifts, and on engine operating condition variations, such as for example transitory conditions.

In this way, the difference Xe identifies the real driving conditions and is directly related to a deviation of the actual soot rate with respect to that expected in reference conditions.

Accordingly, the method uses the sensed oxygen concentration value As and the difference Xe for determining a correction factor Cf to be applied to the soot rate reference value Sr.

The correction factor Cf is detenniried through a third map 40 that correlates any couple of values As and Xe to a correspondent correc-tion factor Cf.

The third map 40 can be empirically determined by means of a calibra-tion activity.

Since the third map 40 depends on As and Xe only, the calibration ac-tivity is generally quite easy and quick to be perfonred.

The soot rate correction factor Cf is sent to a multiplier 50 that applies the soot rate correction factor Cf to the previously deter-mined soot rate reference value Sr, in order to obtain an accurate estimation Se of the soot rate in the exhaust stream.

The estimated soot rate Se is then sent to an integrator 60 that time integrates the estimated soot rate Se, in order to achieve the total amount of soot, also referred as soot loading level Sli, that is sup-posed to be stored in the DPF 5.

Eventually, it is possible to consider the efficiency of the DPF 5 by multiplying the estimated soot rate Se, or the soot loading level Sli, for the efficiency factor of the DPF 5 itself.

The soot loading level Sil is finally sent to a comparator 70 that compares the estimated soot loading level Sli with a predetermined soot threshold St. When the estimated soot loading level Sll exceeds said soot threshold St, the managing method provides for performing a regeneration process of the DPF 5.

While at least one exemplary embodiment has been presented in the foregoing sumnary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing surrmary and detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodinnt without departing from the scope as set forth in the appended claims and in their legal equivalents. ID4S

Claims

1. Method for determining the soot rate in an exhaust stream from an internal combustion engine, wherein the method comprises the steps of measuring oxygen concentration value (Xs) in the exhaust stream, and of estimating the soot rate (Se) in the exhaust stream on the base of said oxygen concentration value (Xs).

2. Method according to claim 1, wherein the estimation of the soot rate comprises the steps of determining a soot rate reference value (Sr), of determining a correction (Cf) thereto on the base of said oxygen concentration value (2s), and for applying said correction (Cf) to said soot rate reference value (Sr).

3. Method according to claim 2, wherein said soot rate reference value (Sr) is determined from an empirically determined data set (10) correlating the soot rate reference value (Sr) to one or more engine operating parameters (Es, El).

4. Method according to claim 2, wherein the determination of said correction (Of) comprises the steps of determining a reference value (Xr) of the oxygen concentration in the exhaust stream, of calculat-ing the difference (Xe) between said oxygen concentration reference value (Ar) and the oxygen concentration value (As), and of determin-ing the correction (Of) on the base of said oxygen concentration val ue (As) and said difference (Xe).

5. Method according to claim 4, wherein said correction (Of) is de-termined from an empirically determined data set (40) correlating the correction (Of) to said oxygen concentration value (As) and said dif-ference (le).

6. Method according to claim 4, wherein said oxygen concentration reference value (Ar) is determined from an empirically determined da-ta set (20) correlating the oxygen concentration reference value (Ar) to one or more engine operating parameters.

7. Method according to claim 1, wherein the oxygen concentration value (As) is rreasured by rreans of a lambda sensor (3).

8. Method for managing a DPF (5) located in an exhaust pipe (2) of an internal combustion engine, wherein the method comprises the steps of determining, according to any of the preceding claims, the soot rate (Se) in the exhaust stream flowing from the engine, and of esti-mating the soot loading level (Sli) within the DPF (5) on the base of said determined soot rate (Se).

9. Method according to claim 8, wherein the estimation of the soot loading level (Sli) within the DPF (5) provides for time integrating said determined soot rate (Se).

10. Method according to claim 8, further canprising the step of per-forming a DPF regeneration process when the estimated soot loading level (Sll) within the DPF (5) exceeds a threshold.

11. Computer program comprising a computer-code for carrying out a method according to any of the preceding claims.

12. Computer program product on which the computer program according to claim 11 is stored.

13. Control apparatus for an internal combustion engine, ccnprising an ECU (6), a data carrier associated to the ECU and a computer pro gram according to claim 11 stored in the data carrier.

14. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 11.REFERENCES1 Diesel engine 2 Exhaust pipe 3 Lambda sensor 4 DCCDPF 6 ECUFirst map 20 Second map Adder Third map multiplier Integrator 70 Comparator Es Engine speed El Engine load Xs Oxygen concentration value Xr Oxygen concentration reference value Xe Difference Sr Soot rate reference value Se Estimated soot rate Sil Soot loading level St Soot threshold