GB2478721A

GB2478721A - Method for managing a desulphurization phase of a catalyst device

Info

Publication number: GB2478721A
Application number: GB1004262A
Authority: GB
Inventors: Roberto Argolini; Nicola Pio Sacco; Alessandra Chianale
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-03-15
Filing date: 2010-03-15
Publication date: 2011-09-21
Anticipated expiration: 2030-03-15
Also published as: GB201004262D0; GB2478721B

Abstract

Disclosed is a method for managing a desulphurization phase of a catalyst device 12 of an internal combustion engine 10) wherein the method comprises the steps of. sampling the temperature Tiof the catalyst device 12 during a rich combustion mode of the desulphurization phase, of correlating each temperature measure Tito a weight factor WFi, of multiplying the weight factor WFiby the rich time tispent by the catalyst device 12 at the correspondent temperature Ti, in order to calculate a weighted rich time WRTiof adding the weighted rich times WRTicalculated from the beginning of the desulphurization phase, in order to calculate a cumulative weighted rich time CWRT, and of ending the desulphurization phase when the cumulative weighted rich time CWRT reaches a predetermined level CWRT. The method basically sets a desired amount of energy necessary for desulphurisation, the desired cumulative weighted rich time value, and sums the energy released over all temperature ranges. Different temperature ranges vary in efficiency of removing the sulphur from the convertor and this is represented by the weighting factor. Also disclosed is a computer program for carrying out the method, a computer program product with the computer program stored on it, an internal combustion engine having the necessary devices and an ECU with the computer program stored on a data carrier associated with the ECU and an electromagnetic signal modulated as a carrier of data bits representing the computer program.

Description

METhOD 10 NA A DESULPHtJRIZATION PHASE OF A CATALYST DEVICE OF AN INTERNAL CCZv1BUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a method to manage a desuiphuriza-tion phase of a catalyst device of an internal combustion engine, typically a Diesel engine.

The present invention is mainly directed towards the internal combus-tion engine of the motor vehicles.

BACOU

In order to comply with tighter emission regulations, the internal combustion engine of the motor vehicles are conventionally equipped with a plurality of catalyst devices, each of which is located in an exhaust line for cleaning the exhaust gas.

Due to the sulphur contained in the Diesel fuel and engine lubricat-ing oil, the exhaust gas produced by the Diesel engines generally contains sulphur oxides (SOs), which can be responsible of a progres-sive poisoning of sorre catalyst devices.

As a consequence, this catalyst devices must be periodically sub-jected to a desulphurization phase, also referred as DeSO phase, in order to restore their original efficiency.

A catalyst device of this kind is the lean NO trap (LNT), which is provided for trapping and reducing the nitrogen oxides (NO) contained in the exhaust gas.

The DeSO phase of the LNT is conventionally obtained heating up the LNT (typically up to 600-650°C) and operating the Diesel engine in a rich combustion mode, namely by operating the Diesel engine with a fuel mixture having the mass ratio of air to fuel lower than the stoichiometric ratio (lambda <1).

As a matter of fact, the desuiphurization rate of the LNT, also re-ferred as efficiency of the DeSO phase, depends on the temperature reached by the LNT during this phase, so that the final desuiphuriza-tion degree of the UT, at the end of the DeSO phase, depends in turn on said LNT temperature and on the total duration of the rich combus-tion mode.

At present, the DeSO phase is managed according to a fixed time ap-proach, namely by imposing a fixed duration of the rich combustion mode, wherein said fixed duration is deteimined on the base of a tem-perature target that is supposed to be reached and maintained by the LNT during the rich combustion mode of the DeSO phase.

However, it has been found that the LNT temperature during the desul- phurization phase can oscillate below or above the mentioned tempera-ture target, so that the DeSO phase could result too short or too long in order to keep a desired final desuiphurization degree.

In case the DeSOx phase is too short, the LNT does not reach the de- sired desuiphurization degree, because it has not remained at the es- timated target temperature for the time needed to reach that thre-shold.

In case the DeSOx phase is too long, the rich combustion mode contin- ues for a certain period even if the UJT has already reached the de- sired desuiphurization degree, thereby causing an excessive fuel con-sumption and increasing the LNT thermal stress.

An object of the present invention is to solve, or at least positive-ly reduce, the above mentioned drawbacks.

Another object of the present invention is to reach this goal with a simple, rational and rather inexpensive solution.

DISISURE

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous fea-tures of the embodiments of the invention.

An embodiment of the invention provides a method to manage a desul- phurization phase of a catalyst device of an internal combustion en-gine, wherein the method catiprises the steps of: -initiating a desulphurization phase by entering into a rich combus- tion mode of the combustion engine and by heating up the catalyst de-vice, -sampling the temperature of the catalyst device, -associating a weight factor with each measurement value of the tern-perature, -determining a rich time (ti), said rich time being defined to be the time during which the catalyst device has the associated tempera-ture, -multiplying the weight factor by the rich time (ti), thereby calcu-lating a weighted rich time, -adding the weighted rich times calculated from the beginning of the desuiphurization phase, thereby calculating a cumulative weighted rich time, -ending the desuiphurization phase when the cumulative weighted rich time (CWRT) reaches a determined threshold.

Thanks to the weighted times, this managing strategy takes into con- sideration the impact of different temperatures of the catalyst de-vice on the desuiphurization efficiency, in order to properly adjust the actual duration of the DeSO phase.

As a consequence, this managing strategy can effectively reach a de- sired desuiphurization degree of the catalyst device, without involv-ing an excessive fuel consumption and/or an excessive thermal stress for the catalyst device itself.

According to an aspect of the invention, the weight factor increases as the temperature of the catalyst device increases, so that high catalyst device temperatures are associated to high weight factors and vice versa.

In this way, the managing strategy reproduces the real behaviour of the DeS phase, wherein high temperatures of the catalyst device pro-mote and speed up the desuiphurization process of the catalyst device itself.

According to another aspect of the invention, the weight factor is determined through a data set correlating the weight factors to the catalyst device temperatures.

This aspect has the advantage that the data set can be determined with a experimental activity and then stored in a data carrier of an engine control unit (ECU), thereby allowing the latter to manage the DeSO phase of the catalyst device.

According to still another aspect of the invention, the data set is determined with the steps of assigning a different weight factor to each different temperature value, in a substantially continuous man-ner.

This aspect has the advantage of considering with great precision the impact of the different temperatures on the desuiphurization effi-ciency of the catalyst device.

According to a further aspect of the invention, the data set is de-termined with the seeps of defining a plurality of contiguous and not overlapping temperature ranges and of assigning to each temperature range a correspondent weight factor.

This aspect has the advantage of reducing the number of weigh factors to be determined, in order to simplify the experimental activity and reducing the data carrier footprint.

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 a computer program product comprising the computer program.

The computer program product can be embodied as an internal combus-tion engine comprising a catalyst device, a temperature sensor for sampling the temperature of the catalyst device, an ECU connected to the temperature sensor, a data carrier associated to the ECU, and the computer program stored in the data carrier, so that, when the ECU executes the computer program, all the steps of the method described above are carried out.

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

BRIEF DESCR.IPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 is a schematic illustration of a Diesel engine system.

Figure 2 is a flowchart representing a managing method according to an embodiment of the invention.

Figure 3 is a table that correlates LNT temperature ranges and weight factors.

DETAILED DESCRIPTION

11⁄2n embodiment of the invention is hereinafter described referring to a Diesel engine 10 of a motor vehicle (see fig.1), which comprises an exhaust line 11 for discharging the exhaust gas into the environment, and a LNT 12 located in the exhaust line 11, for trapping and reduc- ing the NO contained in the exhaust gas and thus preventing their en-vironmental release.

The present embodiment relates to a method for managing the DeSO phase of the LNT 12.

The DeSO phase of the LNT 12 is conventionally obtained heating up the LNT (typically up to 600-650°C) and operating the Diesel engine in a rich combistion mode, namely by operating the Diesel engine with a fuel mixture having the mass ratio of air to fuel lower than the stoichiometric ratio (lambda <1).

Temperature and rich exhaust gas environment promote the sulphur re-moval.

According to the present embodiment (see fig.2), the managing method of the DeSO phase firstly provides for setting at zero a cumulative parameter, which is hereinafter referred as cumulative weighted rich time CWRT.

Subsequently, the managing method provides for sampling the tempera-ture of the LNT 12 during the DeSO phase, by means of a temperature sensor 13 associated to the LNT 12 itself.

The LNT temperature is measured from the beginning of the DeSO, phase, namely from the beginning of the rich combustion mode, with a con-stant frequency.

By way of example, the LNT temperature can be measured once per second.

Each temperature measure T is used for determining a nuirrical weight factor WF that is related to the efficiency of the DeSO phase when the LNT 12 is at that measured temperature T1.

The weight factor WF can be determined through an empirically deter-mined data set correlating the weight factors to the temperature of the LNT 12.

As a matter of fact, the data set can be determined by quantizing the temperature magnitude in a plurality of contiguous and not overlap-ping temperature ranges TR, and by assigning to each temperature range a different weight factor WF determined on the base of an expe-rimental activity.

Since the efficiency of the DeSO phase generally increases as the temperature of the LNT increases, also the weight factor WF should increase as the temperature of the LNT increases.

By way of example, it is possible to quantize the temperature magni-tude T in three contiguous and not overlapping temperature ranges, which are respectively indicated as TR1, TR0 and TR1 in the table of figure 3.

The temperature ranges TR1, TR0 and TR1 have preferably the same size, thereby quantizing the temperature magnitude T in levels having the same distance from each other.

The intermediate temperature range TP is centered on a given tempera-ture target which is supposed to be reached and maintained longer by the LNT 12 during the DeSc& phase.

In order to take into consideration the effect of the different tem- peratures on the desulphurization efficiency, the intermediate tern-perature range TRQ is correlated to a weight factor WF equal to one, while the preceding temperature range TR.1 is correlated to a weight factor WF smaller than one, and the following temperature range TR1 is correlated to a weight factor WF greater than one.

Notwithstanding the present example refers to only three temperature ranges having a wide size, it should be appreciated that the size of each temperature range can be reduced at will while contemporaneously increasing their total number, up to even assigning a different weight factor WF to each different temperature value, in a substan-tially continuous manner.

Returning to the managing method (see fig.2), the weight factor WF is multiplied for the time t. spent during the rich combustion mode by the LNT 12 at the corresponding temperature T, in order to calculate a weighted rich time WRT.

As a matter of fact, the time t is the period between the jth tempera-ture measure and the next one.

In the present example, the time t can be calculated as the reciproc- al of the sampling frequency, hence it is constant for each tempera-ture measure.

The weighted rich time WRT is then added to the cumulative weighted richtime CWRT.

The cumulative weighted rich time CWRT is finally compared with a predetermined threshold CWRT* at which the desulphurization of the LJT 12 should be considered complete.

The threshold CWRT* can be empirically determined during the experi-mental activity.

Until the cumulative weighted rich time CWRT is smaller than the threshold CWRT*, the managing method provides for maintaining the De-SO phase active, and for performing the next temperature measure, in order to repeat the subroutine by means of which the cumulative weighted rich time CWRT is progressively increased.

Conversely, when the cumulative weighted rich time is equal or great-er than the threshold CWRT*, the managing method provides for ending the DeSO phase.

According to an aspect of the invention, the DeS phase can be ma-naged with the help of a computer program comprising a program-code for carrying out all the steps of the method described above.

The computer program is stored in a data carrier 14 associated to an engine control unit (ECU) 15, which is in turn connected to the tem-perature sensor 13.

In this way, when the ECU 15 executes the computer program, all the steps of the method described above are carried out.

While at least one exemplary embodiment has been presented in the foregoing summary 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 summary 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 errbodirrent without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERENCE NUMBERS

Diesel engine 11 Exhaust line 12 LNT 13 Temperature sensor 14 Data carrier

ECU

CWRT Cumulative weighted rich time CWRT* Threshold ti Rich time T Temperature magnitude Ti Temperature measure WFi weight factor Generic weight factor WRTi Weighted rich time TR Generic temperature range TR+1 Temperature range TRO Temperature range TR-1 Data set or map Ttgt Temperature target

Claims

CLIMS1. Method for managing a desuiphurization phase of a catalyst device (12) of an internal combustion engine (10), wherein the method com-prises the steps of: -initiating a desulphurization phase by entering into a rich cornbus- tion mode of the combustion engine and by heating up the catalyst de-vice, -sampling the temperature (Ti) of the catalyst device (12), -associating a weight factor (WF) with each measurement value of the temperature (T1), -detennining a rich time (ti), said rich time being defined to be the time during which the catalyst device (12) has the associated temperature (Ti), multiplying the weight factor (WE'1) by the rich time (t1), thereby calculating a weighted rich time (WRT1), -adding the weighted rich times (WRT1) calculated from the beginning of the desuiphurization phase, thereby calculating a cumulative weighted rich time (CWRT), -ending the desuiphurization phase when the cumulative weighted rich time (CWR) reaches a detennined threshold (CWRT*).
2. Method according to claim 1, wherein the weight factor (WF) in-creases as the temperature of the catalyst device (12) increases.
3. Method according to claim 1, wherein the weight factor (WE'1) is determined through a data set correlating the weight factors to the catalyst device temperatures.
4. Method according to claim 3, wherein the data set is determined with the steps of assigning a different weight factor (WF1) to each different temperature value.
5. Method according to claim 3, wherein the data set is determined with the steps of defining a plurality of contiguous and not overlap-ping temperature ranges (TR) and of assigning to each temperature range (TR) a correspondent weight factor (WF).
6. Computer program comprising a computer-code for carrying out a method according to any of the preceding claims.
7. Computer program product on which the computer program according to claim 6 is stored.
8. Internal combustion engine (10) comprising a catalyst device (12), a temperature sensor (13) for sampling the temperature of the catalyst device (12), an ECU (15) connected to the temperature sensor (13), a data carrier (14) associated to the ECU (15), and a computer program according to claim 6 stored in the data carrier (14).
9. ?n electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 6.