GB2402892A

GB2402892A - Method and device for operating an internal combustion engine in whose exhaust-gas region a catalyst is disposed

Info

Publication number: GB2402892A
Application number: GB0410851A
Authority: GB
Inventors: Christian Schiller; Markus Widenmeyer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-05-15
Filing date: 2004-05-14
Publication date: 2004-12-22
Anticipated expiration: 2024-05-14
Also published as: FR2854926A1; GB0410851D0; GB2402892B; DE10321873A1

Abstract

A method and a device for operating an internal combustion engine 10 is proposed in the exhaust-gas region 11 of which device a catalyst 12 is disposed and in which method a control 16 provides at least one control signal msk, dr, agr for at least one component 14, 19, 20 assigned to the internal combustion engine. The control signal modifies the temperature of the catalyst. The control signal is defined as a function of a measure of a sulfur concentration in the exhaust gas and/or in the fuel of the internal combustion engine , which measure is determined by a sulfur sensor 24, 27 disposed in the exhaust-gas region and/or in a fuel region 19, 23.

Description

Method and device for operating an internal combustion engine in whose

exhaust-gas region a catalyst is disposed

Prior art

The invention proceeds from a method and a device for operating an internal combustion engine in whose exhaust gas region a catalyst is disposed, according to the generic kind of the independent claims.

DE 198 43 859 Al describes a regeneration method for a three-way storage catalyst or an NOx storage catalyst that has been poisoned by sulfur. The sulfur loads are caused by sulfur components of the fuel, which turn up again as sulfur oxides in the exhaust gas. The sulfur loads are temperature dependent. The sulfur poisoning can be detected from a decrease in the oxygen-storage capability of the catalyst since the sulfur occupies those storage locations in the catalyst that are otherwise occupied by oxygen or nitrogen oxides. The sulfur poisoning consequently reduces the serviceability of the catalyst, in particular the serviceability of an NOx storage catalyst.

Regeneration of the catalyst from sulfur is possible at elevated temperatures by supplying a reducing agent, which can be provided, for example, in the engine by a rich mixture having an air/fuel ratio < 1. The regeneration takes place in a temperature range of, for example, 400-800 C, preferably 500-700 C. At such high temperatures, damage to the catalyst cannot be completely eliminated.

Furthermore, the regeneration increases the fuel consumption of the internal combustion engine. A high sulfur content of the fuel may even irreversibly damage the catalyst, in particular at high operating temperatures.

High sulfur concentrations in the exhaust gas and high catalyst temperatures promote the growth of metal sulfate crystallites from the active components (predominantly Ba and Sr). The metal sulfate crystallites could be removed only at very high catalyst temperatures at which the danger of damage to the catalyst would be appreciable.

DE 44 26 020 Al describes a method of monitoring the serviceability of a catalyst in which the expected temperature increase due to an exothermic reaction in the catalyst is evaluated. An exhaust-gas temperature determined using a temperature sensor is compared with the exhaust-gas temperature calculated on the basis of a model.

In the model of the exhaust-gas temperature, account is taken of the air mass flow that is measured by an air mass flow sensor in accordance with a first embodiment. In accordance with another embodiment, a load signal, for example the opening angle of a throttle valve, is taken into account. Optionally, the rotational speed of the internal combustion engine is included.

EP 865 595 describes a method of desulfurizing an NOx storage catalyst in which a time integration of an SOx absorption rate is provided. The regeneration is started if the integration result exceeds a predetermined threshold value. The SOx absorption rate is determined on the basis of a functional relationship in the dependence of the content of sulfur components in the fuel used, the actual fuel mass flow and the actual exhaust-gas temperature at the NOx storage catalyst.

WO 92/03728 describes a sulfur sensor for detecting gaseous sulfur components. The sensor can be used in the exhaust gas of the combustion processes.

DE 100 45 939 Al describes a sulfur sensor for detecting sulfur components in liquids. The sensor may be disposed in the fuel that is provided for operating the internal combustion engines.

The object of the invention is to provide a method and a device for operating an internal combustion engine, in which poisoning with sulfur of a catalyst disposed in the exhaust-gas region of the internal combustion engine is reduced.

The object is achieved in each case by the features specified in the independent claims.

Advantages of the invention According to the invention, provision is made that at least one control signal is defined for a component assigned to the internal combustion engine as a function of the measure of sulfur concentration in the fuel region and/or in the exhaust-gas region of the internal combustion engine. The measure of the sulfur concentration is provided by a sulfur sensor that is disposed in the fuel region and/or in the exhaust-gas region of the internal combustion engine.

The method according to the invention has the advantage that the operating state of the internal combustion engine can be modified at least as a function of the sulfur concentration in the exhaust-gas region and/or in the fuel region. In particular, the method according to the invention can avoid those operating states of the internal combustion engine in which a high exhaust-gas temperature or a high catalyst temperature would occur.

The at least approximate knowledge of the sulfur concentration or a measure of the sulfur concentration in the exhaust-gas/fuel makes it possible at least to reduce or completely prevent sulfur poisoning of the catalyst by avoiding such critical operating states of the internal combustion engine. The danger of damage to the catalyst due to excessively high temperatures during regeneration is minimized, as is the additional fuel requirement for the regeneration.

The at least one control signal can be continuously modified as a function of the magnitude of the measure of the sulfur concentration. The modification increases with increasing sulfur concentration.

Advantageous developments and embodiments of the method according to the invention emerge from the dependent claims.

One development envisages that a measure of the temperature of the catalyst is determined and that the at least one control signal is additionally modified as a function of the measure of the temperature. The knowledge of the temperature or a measure of the temperature of the catalyst makes possible a still more controlled definition of the at least one control signal since the danger of poisoning the catalyst with sulfur depends on temperature and, in particular, increases considerably at high temperatures of, for example, more than 400 C. In accordance with said development, the at least one control signal can likewise be continuously defined.

One embodiment envisages that the measure of the sulfur concentration in the exhaust-gas and/or fuel is compared with a sulfur threshold and that a definition of the at least one control signal is provided as a function of the measure of the sulfur concentration only when the threshold is exceeded.

One embodiment envisages that the measure of the temperature of the catalyst is compared with a temperature threshold value and that a definition of the at least one control signal is provided as a function of the measure of the sulfur concentration only in the event of exceeding both the sulfur threshold value and the temperature threshold value.

One embodiment envisages that the temperature of the catalyst is determined using a temperature sensor. The temperature sensor may be disposed at a suitable point in the exhaust-gas region of the internal combustion engine.

For example, an arrangement upstream of the catalyst is suitable. At this point, the temperature sensor determines the temperature of the exhaustgas flow flowing into the catalyst. An arrangement downstream of the catalyst is also suitable because, at that point, account can additionally be taken of the catalyst temperature due to an exothermic reaction in the catalyst. Ideally, the temperature sensor is disposed directly in the catalyst or at it since, at that point the actual temperature of the catalyst can be determined with the smallest error.

Another embodiment envisages that the measure of the temperature of the catalyst is calculated on the basis of a model. The temperature can be determined, for example, at least approximately from an internal combustion engine load. In its turn, the load results at least approximately from the amount of fuel supplied to the internal combustion engine and the air mass flowing into the internal combustion engine. In the case of a diesel internal combustion engine, the amount of fuel supplied to the internal combustion engine is essentially available. In the case of a petrol internal combustion engine, both signals are generally available.

One embodiment envisages that the at least one control signal modifies the output of the internal combustion engine. Intervention in the control signal that defines the amount of fuel fed to the internal combustion engine is suitable. A reduction in the amount of fuel fed to the internal combustion engine results in a limitation of the output and, consequently, in a limitation of the catalyst temperature by limiting the exhaust-gas temperature. An alternative, which can be used in particular in petrol internal combustion engines, provides a limitation of the air mass flowing into the internal combustion engine, whereby a reduction in the output of the internal combustion engine can likewise be achieved. In the case of internal combustion engines that have an exhaust-gas feedback, the exhaust-gas feedback rate can be reduced by means of the control signal. The reduction in the exhaust- gas feedback rate likewise reduces the catalyst temperature by reducing the exhaust-gas temperature.

One development envisages that the catalyst is designed as an NOx storage catalyst and that the internal combustion engine is operated in a first operating phase with an air/fuel ratio of > 1 and in a second operating phase with an air/fuel ratio of ≤ 1. The development finds application both in the case of diesel internal combustion engines and in the case of petrol internal combustion engines that contain an NOx storage catalyst in the exhaust gas region that stores the nitrogen oxide produced with a leaner air/fuel mixture of the internal combustion engine in the first operating phase.

The device according to the invention has all the features that are necessary for performing the method. The device accordingly has the same advantages as the method according to the invention.

Further advantageous developments and embodiments of the method according to the invention and of the device according to the invention emerge from further dependent

claims and from the following description.

Drawing The sole figure shows a block circuit diagram of a technical environment in which a method according to the invention proceeds.

The figure shows an internal combustion engine 10 in whose exhaust-gas region 11 a catalyst 12 is disposed. A throttle valve 14 that modifies an airflow measured by an air mass flow sensor 15 is disposed in the intake region 13 of the internal combustion engine 10.

The air mass flow sensor 15 delivers an air mass flow signal msl both to a control 16 and to a signal selector 17.

To modify the position of the throttle valve 14, the control 16 delivers a throttle-valve signal dr to the throttle valve 14.

The control 16 is supplied with a rotational-speed signal n provided by the internal combustion engine 10, which signal is also applied to a temperature characteristic diagram 18.

The control 16 delivers a fuel apportionment signal msk to a fuel apportionment system 19. The fuel apportionment signal msk is furthermore fed to the signal selector 17.

The control 16 delivers an exhaust-gas feedback signal agr to an exhaustgas feedback valve 20. The exhaust-gas feedback signal agr is furthermore applied to the temperature characteristic diagram 18. The exhaust-gas feedback valve 20 defines an amount of exhaust gas fed-back 21.

A lambda sensor 22 disposed in the exhaust-gas region 11 delivers a A signal lam to the control 16. To set the output of the internal combustion engine 10, an output setting signal ps is fed to the control 16. The output of the internal combustion engine 10 is obtained from a fuel that is stored in the fuel tank 23. The fuel flows from the fuel tank 23 to the fuel apportionment system 19.

Disposed in the fuel tank 23 is a first sulfur sensor 24 that delivers a first sulfur-sensor signal ssl both to the signal evaluation system 25 and to a first comparator 26. A second sulfur sensor 27 in the exhaust gas region 11 delivers a second sulfur-sensor signal ss2 likewise both to the signal evaluation system 25 and to the first comparator 26. The first comparator 26 compares the first and second sulfur-sensor signals ssl, ss2 with a sulfur threshold value sws and, if a threshold is exceeded, delivers a digital sulfur signal ssd to an AND gate 30.

A temperature sensor 28 assigned to the catalyst 12 delivers a measured temperature signal temps both to the signal evaluation system 25 and to a second comparator 29.

Fed to the second comparator 29 is furthermore a calculated temperature signal tempm that determines the temperature characteristic diagram 18 from the exhaust-gas feedback signal agr, the rotational-speed signal n, a load signal pm provided by the signal selector 17 and also from a further input signal wm. The second comparator 29 compares the measured temperature signal temps and the calculated temperature signal tempm with a temperature threshold value nut and, if a threshold is exceeded, delivers a digital temperature signal tempd to the AND gate 30. The signal evaluation system 25 delivers an analog limit signal a to the control 16 and the AND gate 30 delivers a digital limit signal d to it.

The method according to the invention proceeds as follows: Control signals are by the control 16 applied to the internal combustion engine 10 and to the components assigned to the internal combustion engine 10, in particular the throttle valve 14, the fuel apportionment system 19 and the exhaust-gas feedback valve 20. Provided as control signals are the throttle-valve signal dr, the fuel apportionment signal msk and the exhaust-gas feedback signal agr. Further control signals may be provided that control further components, not shown in greater detail, of the internal combustion engine 10.

The control signals msk, dr, agr are first defined in particular as a function of the output setting signal ps.

In the case of a diesel internal combustion engine, in particular, the fuel apportionment signal msk is defined and defines the fuel rate or the amount of fuel per working stroke of the internal combustion engine 10. In the case of a petrol internal combustion engine, the throttle-valve signal dr is first defined and the fuel apportionment signal msk matched thereto is determined, the signal lam provided by the lambda sensor 22 being taken into account.

In the case of directly injecting internal combustion engines, the control 16 can predetermine at least two different operating phases. In a first operating phase, a lean air/fuel mixture having an air/fuel ratio A of > 1 is fed to the internal combustion engine 10. In a first operating phase, an increased proportion of nitrogen oxide occurs in the exhaust gas in the exhaust-gas region 11 of the internal combustion engine 10. The nitrogen oxide is intercalated in the catalyst 12, which is designed, for this purpose, as an NOx storage catalyst. In a subsequent second operating phase of the internal combustion engine 10, the NOx storage catalyst is regenerated by the nitrogen oxide. The reagent necessary for this purpose may be produced in the engine by operating the internal combustion engine 10 with an at least stoichiometric, preferably, however, rich air/fuel mixture corresponding to an air/fuel ratio A of < 1.

A reduction of the nitrogen oxides in the exhaust gas can be achieved by an exhaust-gas feedback. The amount of exhaust gas fed-back 21 is modified by the exhaust-gas feedback valve 20. The amount of exhaust gas fed-back 21 depends, furthermore, on the air pressure in the intake region 13 and on the pressure in the exhaust-gas region 11.

To control the exhaust-gas feedback valve 20, the exhaust- gas feedback signal agr is provided as control signal. In the event of an increase in the exhaust-gas feedback rate, the peak temperature increases during the combustion of the fuel and the mean exhaust-gas temperature increases.

During the combustion of the fuel in the internal combustion engine 10, sulfur oxides that are produced from the sulfur components contained in the fuel are furthermore encountered in addition to the nitrogen oxides produced from the nitrogen in the air. The sulfur component of the fuel has an appreciable fluctuation range. Low-sulfur fuel contains a sulfur component of, for example 10-20 ppm. The sulfur component of conventional fuel may be in the range of 100-300 ppm. The sulfur component in bad fuel may be up to 2000 ppm. The sulfur oxides in the exhaust gas are produced in addition from combustion of sulfur-containing engine oil that enters the combustion chamber of the internal combustion engine 10 as a result of passing the piston rings. The sulfur component in the exhaust gas can therefore be in a range from 1-200 ppm and may result in a sulfur poisoning of the catalyst 12, in particular at high catalyst temperatures. The intercalation of the sulfur oxides takes place, in particular, in a temperature range above 400 C. The catalyst 12 can be regenerated from the intercalated sulfur oxide by supplying a reagent. In this connection, increased temperatures in a temperature range of, for example, 400-800 C are necessary compared with a regeneration from nitrogen oxides. The preferred temperature range is approximately 500-700 C.

The measurement of the sulfur component is provided in the fuel region and/or in the exhaust-gas region 11 of the internal combustion engine 10. The sulfur component in the fuel region is measured by the first sulfur sensor 24, which is disposed, for example, in the fuel apportionment system 19 or in the fuel tank 23. Alternatively or additionally, the second sulfur sensor 27 is provided that is disposed in the exhaust-gas region 11 of the internal combustion engine 10, preferably upstream of the catalyst 12.

The first sulfur-sensor signal ssl delivered by the first sulfur sensor 24 and the second sulfur sensor signal ss2 provided by the second sulfur sensor 27 are processed in the signal evaluation system 25 to form an analog limit signal a. The analog limit signal a modifies at least one control signal msk, dr, agr of the internal combustion engine 10 or a control signal msk, dr, agr at least of one of the components 14, 19, 20 assigned to the internal combustion engine 10. The modification is all the more considerable, the higher the sulfur concentration measured by the at least one sulfur sensor 24, 27 is.

A reduction in the amount of fuel that is fed to the internal combustion engine 10 by influencing the amount-of fuel signal msk reduces the output of the internal combustion engine 10 with the result that a lower exhaust gas temperature is established that results in a reduction in the temperature of the catalyst 12. If the throttle valve 14 is present, the airflow flowing into the internal combustion engine 10 is reduced by influencing the throttle-valve signal dr, with the result that the output of the internal combustion engine 10 likewise decreases as a result of a necessary adjustment of the amount-of-fuel signal msk. A modification of the exhaust-gas feedback signal agr reduces the amount of exhaust gas fedback 21, with the result that the exhaust-gas temperature also decreases as a result of this measure. Furthermore, influencing the rotational speed n of the internal combustion engine 10, for example a limitation to a maximum value, is conceivable, which maximum value preferably depends on the existing operating state of the internal combustion engine 10.

The analog limit signal a may additionally depend on the temperature of the catalyst 12. The temperature of the catalyst 12 can be measured, for example, by a temperature sensor 28. The temperature sensor 28 may be disposed immediately upstream of the catalyst 12. An arrangement of the temperature sensor 28 in the exhaust-gas flow downstream of the catalyst 12 makes it possible to determine the temperature of the catalyst 12, likewise with sufficient accuracy, in which case even the temperature increase is determined by means of an exothermic reaction in the catalyst 12. Optionally, an arrangement in the exhaust-gas flow upstream of the catalyst 12 is possible.

The temperature of the catalyst 12 may be calculated, alternatively or additionally, on the basis of a model. The temperature may be stored, for example, in the temperature characteristic diagram 18, which is addressed as a function of characteristic variables. The load signal pm, which is obtained from the air mass flow signal msl or from the amount-of-fuel signal msk, is provided as characteristic value. The signal selector 17 passes either the air mass flow signal msl or the amount-of-fuel signal msk to the temperature characteristic diagram 18 as an input variable.

This embodiment is provided, in particular, in a petrol internal combustion engine 10 since both variables are available. In the case of a diesel internal combustion engine 10, only the amount-of-fuel signal msk is generally available and can be used as load signal pm.

The calculated temperature signal tempm can already be determined using the load signal pm alone. An increase in the accuracy achieved in the calculation of the temperature of the catalyst 12 can be achieved using the rotational speed n of the internal combustion engine 10. If an exhaust-gas feedback is available, the inclusion of the exhaust-gas feedback signal agr increases the accuracy in calculating the temperature of the catalyst 12 further. An expected exothermic reaction in the catalyst 12, which results in an increase in the temperature in the catalyst 12, can be taken into account using the further input signal wm, which depends, for example, on the lambda signal lam.

The calculation of the temperature signal tempm comprises in the exemplary embodiment shown, only the reading-out of that storage point in the temperature characteristic diagram 18 addressed by the load signal pm, optionally by the rotational-speed signal n, optionally by the exhaustgas feedback signal agr and optionally by the further input signal wm.

The measured temperature signal temps provided by the temperature sensor 28 and/or the calculated temperature signal tempm are/is likewise fed to the signal evaluation system 25 and taken into account in determining the analog limit signal a. The signal evaluation system 25 takes account of the measured temperature signal hemps and/or the calculated temperature signal tempm as a result of the fact that the influence on the at least one manipulated variable msk, dr, agr increases with increasing temperature. Taking account of the temperature of the catalyst 12 or at least a measure of the temperature of the catalyst 12 is particularly expedient since the intercalation of sulfur oxides and, consequently, the sulfur poisoning increases with increasing temperature.

The analog limit signal a makes possible an analog intervention in the at least one control signal msk, dr, agr. Alternatively or additionally, the digital limit signal d may be provided. The digital limit signal d is defined by the AND gate 30 as a function of the logical state of the digital sulfur signal ssd and the digital temperature signal tempd. The digital limit signal d occurs only if both the digital sulfur signal ssd and the digital temperature signal tempd are logically one. The first comparator 26 determines the digital sulfur signal sad from the first and/or second sulfur-sensor signal ssl, ss2 by comparison with the sulfur threshold value sws. The second comparator 29 determines the digital temperature signal tempd from the measured and/or the calculated temperature signal temps, tempm by comparison with the temperature threshold value nut. The digital limit signal d limits at least a control signal msk, dr, agr to a predetermined value.

The digital limit signal d may be provided in addition to the analog limit signal a. If the digital limit signal d does not yet have the logic one state, the at least one control signal msk, dr, agr is modified only by the analog limit signal a. If the logic one state of the digital limit signal d is present, the at least one control signal msk, dr, agr is set to the predetermined value.

The internal combustion engine 10 may, for example, be operated in at least two different operating phases. In a first operating phase, the internal combustion engine 10 is operated with a lean air/fuel mixture corresponding to an air/fuel ratio A of > 1. The nitrogen oxides increasingly produced in said operating phase cannot be removed to the desired extent by the amount of exhaust gas fed-back 21 via the exhaustgas feedback valve 20. The residual nitrogen oxides are stored in the first operating phase in the catalyst 12, which is configured as an NOx storage catalyst to perform this task. During the first operating phase, the undesired sulfur poisoning of the NOx storage catalyst 12 occurs as a function of the sulfur content of the fuel or of the sulfur content of the exhaust gases.

When the storage capacity of the NOx storage capacity is exhausted or substantially exhausted, a change is made to the second operating phase, in which the NOx storage catalyst 12 is regenerated. The regeneration is performed by adding a reagent, which can be provided, for example in the engine, by at least a stoichiometric, preferably, however, a rich operation of the internal combustion engine 10 with an air/fuel ratio of < 1.

The increased operating temperature of the NOx storage catalyst 12 present during the regeneration of the NOx storage catalyst in the range of, for example, 300-500 C is not quite sufficient to free the NOx storage catalyst 12 equally of the sulfur poisoning. If sulfur poisoning is detected, regeneration is necessary at a temperature increased further, which is, for example, in a range of 400-800 C, preferably in a range of 500-700 C. The regeneration of a sulfur poisoning is therefore associated with a fuel consumption increased yet again compared with a regeneration from nitrogen oxides. The method according to the invention that avoids sulfur poisoning, or at least reduces it, results in a reduction in the fuel consumption.

The device according to the invention has the features that are necessary for performing the method according to the invention.

Claims

Claims 1. Method for operating an internal combustion engine (10) in whose

exhaust-gas region (11) a catalyst (12) is disposed and in which a control (16) provides at least one control signal (msk, dr, agr) for a component (14, 19, 20) assigned to the internal combustion engine (10), which control signal modifies the temperature of the catalyst (12), characterized in that there is provided a sulfur sensor (24, 27) that is disposed in the exhaust-gas region (11) and/or in a fuel region (19, 23) that provides a sulfur-sensor signal (ssl, ss2) that is a measure of the sulfur concentration in the exhaust gas/in the fuel, and in that the at least one control signal (msk, dr, agr) is defined as a function of the measure of the sulfur concentration.
2. Method according to Claim 1, characterized in that a measure of the temperature of the catalyst (10) is determined and in that the at least one control signal (msk, dr, agr) is defined additionally as a function of the measure of the temperature.
3. Method according to Claim 1 or 2, characterized in that the measure of the sulfur concentration in the exhaust gas/in the fuel is compared with a sulfur threshold (sws) and in that the at least one control signal (msk, dr, agr) is defined as when the threshold value (sws) is exceeded.
4. Method according to Claims 2 and 3, characterized in that the measure of the temperature of the catalyst (12) is compared with a temperature threshold value (nut) and in that the at least one control signal (msk, dr, agr) is defined as when the sulfur threshold value (sws) and the temperature threshold value (nut) are exceeded.
5. Method according to Claim 2, characterized in that the measure of the temperature of the catalyst (12) is determined by measurement with a temperature sensor (23).
6. Method according to Claim 2, characterized in that the measure of the temperature of the catalyst (12) is calculated.
7. Method according to any one of the preceding claims, characterized in that the at least one control signal (msk, dr, agr) limits the output of the internal combustion engine (10) or an exhaust-gas feedback rate (agr).
8. Method according to Claim 6, characterized in that the control signal (msk) modifies the amount of fuel fed to the internal combustion engine (10).
9. Method according to Claim 6, characterized in that the control signal (dr) modifies the airflow flowing into the internal combustion engine (10) .
10. Method according to any one of the preceding claims, characterized in that the catalyst (12) is designed as an NOx storage catalyst, and in that the internal combustion engine (10) is operated in a first operating phase with an air/fuel ratio A of > 1 and in a second operating phase with an air/fuel ratio A of ≤ 1.
11. Device for performing the method according to any one of Claims 1 to 10.
12. Method substantially as hereinbefore described with reference to the accompanying drawings.
13. Device substantially as hereinbefore described with reference to the accompanying drawings.