SE514288C2 - Apparatus and process for sulfur regeneration of NOx adsorbent catalyst - Google Patents

Abstract

The invention relates to a method for sulphur regeneration of a NOx adsorbing exhaust catalyst (18) by means of raising of its temperature, wherein the exhaust catalyst (18) is installed in an exhaust system (16, 17) which is connected to a combustion engine (1), which method comprises generation of an air/fuel mixture to the respective cylinder (3) of the engine (1). The invention is characterized in that it comprises alternating control of the combustion engine (1) between a first condition during which a comparatively rich exhaust gas mixture is supplied to the exhaust catalyst (18), wherein oxygen that is stored in the exhaust catalyst (18) is consumed at least partly during combustion of combustible compounds in the exhaust system (16, 17), for generation of heat, and a second condition during which a comparatively lean exhaust gas mixture is supplied to the exhaust catalyst (18), for storage of oxygen to said exhaust catalyst (18), and closure of said alternating control following the desorption of a predetermined amount of sulphur compounds from said exhaust catalyst (18). The invention also relates to an arrangement for such a sulphur regeneration. By means of the invention, an improved sulphur regeneration of a NOx adsorbing exhaust catalyst (18) in a motor vehicle is provided.

Description

, 14 288 2 stems, among other things, from increasingly stringent legislation in different countries, with requirements for extremely low emissions of N0; v C0 and HC compounds.

Furthermore, in connection with vehicles, there is a general requirement to reduce the engine's fuel consumption as much as possible. For this purpose, in recent years, engines with new types of combustion chambers of the engine cylinders have been developed, in particular to be able to drive the engine with increasingly leaner fuel mixtures, i.e. where Ä> l. Such engines are commonly referred to as "lean-burn" engines. In a so-called DI engine (ie a direct-injected Otto engine), the respective combustion chambers of the engine are arranged in such a way that the supplied fuel can be concentrated to a large extent at respective spark plugs. Such engines can be operated in continuous operation with a very lean air / fuel mixture, of the order of Ä = 4. For this reason, a considerable saving in fuel consumption is obtained with this type of engine.

Since a DI engine is normally powered by a very lean air / fuel mixture, a correspondingly lean exhaust mixture will flow through the three-way catalytic converter. This means that the three-way catalyst is not able to reduce the NO; compounds in the exhaust gases (due to the fact that it is designed for optimal purification ability in stoichiometric mixing). For this reason, an ordinary three-way catalyst can be combined with a nitrogen oxide adsorbent (also called NO3 adsorbent, or "NO trap"), which is a device known per se for absorbing lüg compounds, eg in the exhaust gases. The NO2 adsorbent can thus be used as a complement to a conventional NOx adsorbent. A three-way catalyst can be arranged. Either as a separate unit upstream of an ordinary alternative or a three-way catalyst can be arranged, integrated with the three-way catalyst, ie together with the three-way catalyst. catalytic materials å514.2s, p 3 The NOX adsorbent is such that it absorbs (adsorbs) NOx compounds in the exhaust gases if the engine is run on a lean air / fuel mixture and emits (desorbs) the NO, compounds if the engine during a certain Furthermore, the NOX adsorbent has the property that it can only adsorb NOx compounds up to a certain limit, ie it is "filled" eventually. and thus reaches a limit of adsorption. In this mode, the NOX adsorbent must be regenerated, i.e. it must be allowed to desorb and thus release the stored NOx compounds. If then a conventional three-way catalyst is provided downstream of a NOx adsorbent, or if alternatively a three-way catalyst is integrally formed with a NO 1 adsorbent, the desorbed NOx compounds can be eliminated by the three-way catalyst, provided that the latter has reached its ignition temperature.

In accordance with the prior art, an NO 1 adsorbent can be regenerated by making the exhaust gas mixture flowing through the NO 1 adsorbent relatively greasy for a certain period of time, of the order of a few seconds. This can be achieved by running the engine with a relatively greasy air / fuel mixture during this period. In this way, the NO 1 adsorbent is "emptied" so that it can then adsorb NOX compounds for a certain period of time until a new regeneration becomes necessary.

A problem with the use of a NOX adsorbent is that sulfur compounds (eg sulfur dioxide, SO2) present in the exhaust gases flowing through the NO2 adsorbent give rise to a coating on the active material of the NOX adsorbent. This coating in turn blocks the ability of the NOx adsorbent to adsorb NO 2 compounds. The sulfur compounds originate from the engine fuel, and can vary e.g. depending on current fuel quality. As a result of such a sulfur coating, the adsorption capacity of the NO 3 adsorbent will gradually decrease over time.

To solve the problem of such a sulfur coating, the NQ; adsorbent must be regenerated at regular intervals also with respect to sulfur compounds, i.e. "emptied" of sulfur compounds so that the sulfur coating on the fl g adsorbent can be removed. According to the prior art, such a sulfur regeneration can be carried out by operating the tower for a certain period of time so that it produces a fatty exhaust mixture (ie Å <1) at the same time as a relatively high exhaust temperature is generated, more specifically an exhaust temperature higher than cza 650 ° C. In this way sulfur compounds can be desorbed, ie released from the NQ; adsorbent. According to the prior art, a sulfur regeneration is preferably carried out at an interval determined on the basis of the lost NO; storage capacity of the NO; adsorbent, which in turn can be estimated on the basis of the sulfur content in the fuel of the fuel consumption of the vehicle in question. The problem with the above-mentioned known technique for sulfur regeneration is that it is difficult to reconcile the desired exhaust gas temperature during lean driving (approx. 250-450 ° C) with the requirement of a temperature of at least 650 ° C in the NQ fadsorbent for to perform a sulfur regeneration. In principle, this can be solved in the respective cylinders by raising the exhaust gas temperature in a manner known per se in a manner known per se by postponing the ignition time for the engine problems. However, such a measure is not sufficient to raise the exhaust gas temperature to the required level in cases where the vehicle in question is in principle never driven with a high load, which may be relevant in certain types of driving environments and for certain types of drivers. Such a measure is also normally not sufficient in the types of exhaust systems which include e.g. a precatalyst and a 514 288 exhaust cooler, as these components will have a cooling effect on the exhaust gases from the engine before they reach the NO; adsorbent. Even if the temperature of the exhaust gases from the engine were to be raised to compensate for the cooling effect of, for example, an exhaust radiator, there is also a risk of damage to, for example, the precatalyst or the exhaust radiator at too high an exhaust temperature.

SUMMARY OF THE INVENTION: The object of the present invention is to provide an improved method for purifying harmful emissions from an internal combustion engine. In particular, it is an object of the invention to provide an improved sulfur regeneration of an NO 2 adsorbent exhaust catalyst which is arranged in connection with an internal combustion engine. This is achieved by means of a method, the characterizing features of which are set out in the appended claims 1. This is also achieved by means of an arrangement, the characterizing features of the appended claims 6.

The invention relates to a process for sulfur regeneration of a NO 2 adsorbent exhaust catalyst by raising its temperature, wherein the exhaust catalyst is mounted in an exhaust system and is connected to an internal combustion engine.

The method involves generating an air / fuel mixture to the respective engine cylinders. The invention is characterized in that it comprises alternating control of the internal combustion engine between a first state in which a relatively oily exhaust gas mixture is delivered to the exhaust catalyst, an oxygen buffer of the exhaust catalyst being burned at least in part in the presence of hydrocarbons a relatively lean exhaust gas mixture is supplied to the exhaust catalyst, for storing oxygen to said oxygen buffer, and shutting off said alternating control after a predetermined amount of 514 zss 6 sulfur compounds have been desorbed from said exhaust catalyst.

In accordance with the invention, a sulfur regeneration of an NO 2 adsorbent exhaust catalyst can be done by the above-mentioned alternating control, whereby a predetermined amount of sulfur compounds in the exhaust catalyst are removed from the exhaust catalyst. With the aid of the invention, this sulfur regeneration can take place even at relatively low loads, more particularly at loads where it is difficult to achieve sufficiently high exhaust gas temperatures with known temperature-raising measures. According to the invention, reduced emissions of harmful pollutants in the engine exhaust are obtained, which is an advantage.

The term "N2-adsorbent exhaust catalyst" as used herein refers to an integrated component which includes both NO2-adsorbent materials and provides conventional three-way catalyst. materials as the function of an Advantageous Embodiments of the Invention are set forth in the appended dependent claims.

DESCRIPTION OF THE DRAWINGS: The invention will be explained in more detail below with reference to a preferred exemplary embodiment and the accompanying drawings, in which: Figure 1 is a principal diagram of an arrangement in which the present invention may be used, and Figure 2 is a somewhat simplified flow chart describing - ver function of the invention. 514 yzss PREFERRED EMBODIMENTS = Figure 1 shows in schematic form an arrangement according to the present invention. According to a preferred embodiment, the invention is arranged in connection with an internal combustion engine 1 which may be a conventional petrol or diesel engine, but which preferably consists of a so-called

DI motor, i.e. an engine of the direct-injection Otto engine type, where the injection of fuel into the engine 1 is arranged for "stratified" operation, i.e. where the supplied fuel can be concentrated in the engine's respective combustion chamber so that in certain predetermined operating cases the engine can be operated with a very lean air / fuel mixture, of the order of A = 4. With such an engine, significant fuel savings are obtained compared to engines powered by stoichiometric mixing, i.e. where A = 1. Such a motor is also set up for "homogeneous" operation in certain operating cases, i.e. with a stoichiometric or relatively oily mixture.

The engine 1 is fed in the usual way with inflowing air via an air inlet 2. Furthermore, the engine 1 is provided with a number of cylinders 3 and a corresponding number of injection devices 4 for fuel. The respective injection device 4 is connected to a central control unit 5 via an electrical connection 6. The control unit 5 is preferably computer-based and is arranged to control the fuel supply to the respective injection device 4 with fuel from a fuel tank (not shown) so that a air / fuel mixture is fed to the engine 1. The engine 1 according to the embodiment is designed according to the type "multi-point" injection, where the correct amount of fuel to the engine 1 can be supplied individually to the respective injection device 4. During operation of the engine 1 is the control unit 5 arranged to control the air / fuel mixture to the engine 1 so that in each current operating condition. moment is adapted to 514 zss 8 The control of the engine 1 takes place in a substantially known manner depending on various parameters which reflect the operating condition of the engine 1 and the vehicle in question. For example, the engine control can take place depending on the current throttle, the engine speed, the amount of air fed to the engine and the oxygen concentration in the exhaust gases. For this purpose, the engine 1 is provided with, for example, a position sensor 7 for the vehicle accelerator pedal (not shown), a speedometer 8 for detecting the engine 1 speed and an air flow meter 9 for detecting the amount of air supplied to the engine 1, all of which are connected to the control unit 5 via corresponding electrical connections 10, 11 and 12 respectively.

In addition, the system also comprises a gas throttle 13, which is preferably electrically controllable and for this reason arranged with a controllable adjusting motor 14 by means of which the gas throttle 13 can be set in a certain desired position so that a suitable amount of air is fed to the engine 1 depending on drift case. Thus, the actuator motor 14 is connected to the control unit 5 via a further connection 15.

The engine 1 shown in the figure is of a five-cylinder type. It should be noted, however, that the invention can be used with engines with different cylinder numbers and cylinder configurations. Preferably, the injection devices 4 are of the type in which the fuel is injected directly into the respective cylinder 3, but the invention can also be used in so-called In addition, the invention can in principle also be used in so-called "single-point" injection, where a single fuel injection device is located in the inlet to the engine.

The exhaust gases from the engine 1 are led out of the cylinders 3 via a manifold 16 and further to an exhaust pipe 17 which is connected to the manifold 16. Further downstream along the exhaust pipe 17 a NO 2 adsorbent exhaust catalyst 18 is arranged, the embodiment is built up according to 51.4 288 9 three-way catalyst that is integrally designed together with a NO 1 adsorbent. This means that the exhaust catalyst 18 comprises partly NQ; adsorbent material and partly a noble metal which provides the function of a per se conventional three-way catalyst. In the following, the term "w fl g-adsorbent exhaust catalyst", alternatively (in abbreviated form) "exhaust catalyst", is used to describe such an integrated component.

During stoichiometric driving cases with the motor 1 (i.e. Å = 1), the exhaust catalyst 18 functions as a conventional three-way catalyst, i.e. for the elimination of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide compounds (NO,). In case of lean operating conditions (ie Å> 1) within a certain temperature window, more specifically about 250-450 ° C, most of the the NQ compounds emitted from the engine 1 by means of the NO; adsorbent material in the exhaust catalyst 18.

According to the embodiment, the engine 1 is provided with a pre-catalyst 19 which is located upstream of the exhaust catalyst 18.

The precatalyst 19 is in particular arranged for rapid heating at cold starts with the engine 1, i.e. so that its catalytic coating quickly becomes active. This provides a significant elimination of 'HC-, CO- and. NO¿ compounds in the exhaust gases at particularly low idle flows. Because the flowing exhaust gases can be heated quickly with the aid of the precatalyst 19, a relatively short ignition time is also obtained for the subsequent exhaust catalyst 18, i.e. a relatively short time which elapses until the exhaust catalyst 18 is heated to a temperature at which it is able to reduce a predetermined proportion of the harmful substances in the exhaust gases. This provides efficient exhaust purification for the engine 1, especially during cold starts. In accordance with the invention, both the exhaust catalyst 18 and the precatalyst 19 are designed with a certain predetermined oxygen storage capacity. On. so can these. components absorb and store an oxygen buffer, i.e. a "reserve" of stored oxygen. Designing a three-way catalyst in this way is known per se and is based on the fact that a certain oxygen storage capacity in its catalytic material means that the catalytic reactions in the three-way catalyst (ie oxidation of HC and CO compounds and reduction of NO; compounds) can take place even in the conditions where a certain excess of either air or fuel is present in the exhaust gases in relation to the stoichiometric ratio (ie Å = 1). g As will be described in detail below, the exhaust catalyst 18 is preferably designed with a oxygen storage capacity that is significantly greater than the precatalyst 19. Closer to the oxygen storage capacity of particular, the precatalyst 19 and the exhaust catalyst 18 are designed so that their respective oxygen storage capacity is at least 1: 2, and preferably in the range 1: 5-1: 30.

Furthermore, the arrangement according to the invention comprises a sensor 20 for detecting the oxygen concentration in the exhaust gases. The sensor 20 is preferably of the linear lambda probe type and is connected to the control unit 5 'via an electrical connection 21. The sensor 20 is preferably located in the exhaust pipe 17, upstream of the precatalyst 19.

However, other locations of the sensor 20 are possible, for example downstream of the precatalyst 19 or downstream of the exhaust catalyst 18.

In addition, an exhaust cooler 22 is preferably provided along the exhaust pipe 17, more particularly between the precatalyst 19 and the exhaust catalyst 18. The purpose of this component is to adjust the exhaust temperature so that light adsorption in the exhaust catalyst 18 is allowed at a suitably adjusted temperature during lean operation. the engine 1. However, the invention is not limited to only those exhaust systems which comprise such an exhaust cooler.

Furthermore, the arrangement according to the invention comprises a temperature sensor 23 which is arranged along the exhaust pipe, preferably between the precatalyst 19 and the exhaust cooler 22. The temperature sensor 23 is connected to the control unit 5 via a further electrical connection 24, and emits a signal which measures the temperature of the exhaust stream through the exhaust pipe. 17.

The function of the invention will now be described in detail. In the case that the engine 1 consists of a DI engine, it can during normal, continuous operation be run with a very lean air / fuel mixture, more specifically a mixture whose lambda value is of the order of 1 = 4. This means that the exhaust mixture flowing through the exhaust pipe 17 and reaching the exhaust catalyst 18 will also be lean. According to known principles, then, the majority of the NO compounds present in the exhaust mixture will be adsorbed by the exhaust catalyst 18.

After a certain time of running with lean exhaust mixture, normally about 1-2 minutes, the exhaust catalyst 18 will be "full", i.e. its catalytic material will be saturated. This means that the exhaust catalyst 18 can no longer take up NO compounds from the exhaust mixture. At this stage, the exhaust catalyst 18 must be regenerated. According to the prior art, the regeneration can take place by making the exhaust mixture through the exhaust catalyst 18 for a certain period of time relatively greasy, which in turn can be achieved by the engine 1 being driven by means of the control unit 5 with a relatively greasy air / fuel mixture for a short period. .111 zss 12 e.g. a few seconds. In this way, NO 2 compounds previously desorbed in the exhaust catalyst 18 are desorbed, so that it is again allowed to adsorb NO 2 compounds for a certain period of time until a new regeneration becomes necessary. Once the NO compounds have been desorbed from the exhaust catalyst 18, they will also be reduced by the catalytic coating which forms an integral part of the exhaust catalyst 18.

According to what soul was initially mentioned, over time a sulfur compound occurs on the exhaust catalyst 18.

This successively blocks the adsorption capacity of the exhaust gas catalyst 18. For this reason, the invention is designed for an improved sulfur regeneration of the exhaust catalyst 18, in particular for solving the initially mentioned problem of insufficient sulfur regeneration due to an excessively low exhaust gas temperature. For this purpose, it is a basic principle behind the invention that a sulfur regeneration is carried out by repeated combustion of a certain amount of oxygen which is stored in the oxygen buffer of the exhaust catalyst 18. More particularly, the invention is based on the fact that unburned hydrocarbons in the exhaust gases are first allowed to burn in the exhaust catalyst 18 in the presence of oxygen stored in the oxygen buffer while the tower 1 is operated so that a fatty exhaust mixture is generated. In this way, heat is generated while the oxygen buffer is gradually consumed. When the oxygen buffer has been consumed (at least in part), according to the invention, the engine 1 is adjusted so that it instead generates a relatively lean exhaust gas mixture, i.e. an exhaust mixture with an excess of oxygen. This means that a new amount of oxygen is allowed to be stored in the oxygen buffer in the exhaust catalyst 18.

Thereafter, the engine 1 is switched to grease again, whereby the process is restarted so that the oxygen buffer in the exhaust catalyst 18 is consumed during heat generation. Taken together, the heat evolution obtained during the repeated combustion of the unburned 514. zss k, 13 hydrocarbons gives rise to an increase in the exhaust gas temperature above the limit (cza 650 ° C) at which a sulfur regeneration can take place. This alternating process continues for a certain period of time which corresponds to the fact that the sulfur accumulated in the exhaust catalyst 18 has mainly been emptied. This time period can in turn be estimated e.g. based on the sulfur content of the fuel used in the engine 1 and the fuel consumption of the vehicle in question, which are parameters stored in the control unit 5. For this purpose, the signal from the temperature sensor 23 can also be used, together with pre-stored algorithms in the control unit 5. These algorithms then define a relationship between the temperature measured by the temperature sensor 23 and the temperature present in the exhaust catalyst 18. These algorithms then take into account, for example, the amount of oxygen stored in the exhaust catalyst 18 and the time period during which combustion of unburned hydrocarbons occur in the exhaust catalyst 18 during the above process. In this way, the control unit 5 can be used for determining the amount of heat evolved in the exhaust catalyst 18 and for determining whether the temperature in the exhaust catalyst 18 has a current limit value of approximately 650 ° C for a sufficiently long time for the sulfur regeneration to have taken place. exceeded it A corresponding combustion of stored oxygen also takes place in the precatalyst 19 during fatty operating cases. In accordance with what has been mentioned above, however, the invention is based on the fact that the oxygen storage capacity of the precatalyst 19 is significantly lower than the oxygen storage capacity of the exhaust catalyst 18.

As a result, only a small portion of the unburned hydrocarbons discharged from the engine 1 will be burned in the precatalyst 19. Most of the unburned hydrocarbons will instead pass along the exhaust pipe 17 and be combusted in the exhaust catalyst 18. This means that the main the heat development generated by means of the invention according to the invention will take place where it is really needed, i.e. in the exhaust catalyst 18. This provides efficient sulfur regeneration of the exhaust catalyst 18.

Figure 2 is a flow chart describing the operation of the invention. It is assumed here that a continuous NO¿ regeneration of the exhaust catalyst 18 is made, which in itself is previously known and is not described further here. The invention is particularly suitable for use in cases where the motor 1 consists of a DI motor which is arranged so that in certain operating cases, e.g. during operation of the engine 1 for continuous operation at medium loads, is operated with a relatively lean exhaust gas mixture (box 25) ¿During such operation, a check is made as to whether a sulfur regeneration is necessary (box 26). This is allowed by the control unit 5 being set up to determine a value of the lost NO; chasing capacity of the exhaust catalyst 18, which in turn can be done on the basis of, for example, the sulfur content of the engine 1 fuel, the vehicle's fuel consumption and the time since the last regeneration. .

Thus, when the N0¿ storage capacity of the exhaust catalyst 18 has fallen below a predetermined value, a sulfur regeneration must take place. This sulfur regeneration begins with the control unit 5 controlling the air and fuel supply to the engine so that a greasy exhaust mixture is obtained (box 27).

In this case, the fuel supply to the injection device 14 so that the desired mixture is obtained in dependence also on other operating parameters of the engine, e.g. current throttle, engine speed and the amount of air injected into the engine. In this way, the engine 1 is placed in an operating state where an oily exhaust mixture (i.e. Å <1) flows through the exhaust catalyst 18. As explained above, this results in oxygen stored in an oxygen buffer in the exhaust catalyst 18 being burned together with unburned hydrocarbon compounds in the exhaust stream. This gives rise to control and 514 288 heat generation, respectively, so that the exhaust gas stream and the exhaust catalyst 18 can be heated to at least about 650 ° C.

When the oxygen buffer present in the exhaust catalyst 18 has been consumed (which in normal applications in passenger cars takes place after a few seconds of operation with greasy exhaust mixture), the control unit 5 converts the engine 1 to a state where the engine 1 is supplied with a relatively lean air / fuel mixture and where a relatively lean exhaust gas mixture (ie Å> 1) is fed through the exhaust catalyst (box 28). In this way an excess of oxygen will be present in the exhaust gases, which leads to new oxygen being stored in the oxygen buffer in the exhaust catalyst 18. Thereafter it is checked with the aid of the control unit 5 whether a sufficient combustion of stored oxygen in the exhaust catalyst 18 has taken place, i.e. if sufficient sulfur regeneration has taken place for the exhaust gas catalyst 18 to be considered to have regained its NO¿ storage capacity (Box 29).

In the event that the sulfur generation can be considered sufficient, the engine is allowed to return to its original state with lean driving (box 25) and in the event that the sulfur generation is not considered sufficient, the engine is switched. to grease operation (box 27), whereupon the process described above with an alternating grease. and lean exhaust mixture in the exhaust catalyst 18 is repeated.

The value of the time period required for the exhaust gas catalyst 18 to be completely sulfur regenerated depends on various factors, such as the sulfur content of the engine 1 fuel, the vehicle fuel consumption, the size of the exhaust catalyst 18, the size of the oxygen catalyst 18 oxygen buffer and the extent of previous sulfur regenerations.

In the process described above, it is assumed that the oxygen buffer in the exhaust catalyst 18 is in principle completely emptied when the engine 514 288 16 is operated with greasy exhaust mixture (box 27). In the subsequent operation with lean exhaust gas mixture (box 28), a certain amount of oxygen is then stored in the oxygen buffer of the exhaust catalyst 18 (i.e. the oxygen buffer is then partially filled).

Thereafter, the process returns to operation with a greasy exhaust mixture (box 27). According to an alternative, reverse process, the state with lean exhaust gas mixture (box 28) can instead cause the oxygen buffer to be filled in principle completely, while the state with fat exhaust gas mixture (box 27) then means that only a small part of the oxygen buffer is burned.

The combustion of the oxygen buffer in the exhaust gas catalyst 18 according to the invention can also be used in combination with other measures for raising the exhaust gas temperature, e.g. a delayed ignition of the fuel in the respective cylinder 3.

As an alternative to the above mode of operation, the invention can also be arranged so that a partial regeneration of the exhaust catalyst 18 is done, i.e. a regeneration which does not necessarily have to continue until the exhaust catalyst 18 is completely emptied of sulfur compounds. This may be relevant, for example, if a certain operating case would require that a relatively greasy air / fuel mixture can only be delivered to the engine for a certain limited time.

However, the control unit 5 is arranged to continuously store a value of the sulfur coating, which then forms the basis for the next regeneration of the exhaust catalyst 18.

The invention can in particular be used for a rapid heating of the exhaust catalyst 18 in connection with cold start of the engine 1. For this purpose a periodic process takes place as described above, but with a period time which is adjusted according to the size of the oxygen buffer present in the precatalyst 19. , ie the periodic course is controlled (514 zss 17 with a relatively fast period time. In this way a very fast heating of the precatalyst 19 is obtained, which in turn shortens the ignition time of the exhaust catalyst 18.

Furthermore, the invention can be used to selectively raise the exhaust gas temperature in those situations where the temperature of the exhaust catalyst 18 or the precatalyst 19 has dropped (or is in danger of falling) below a value corresponding to these components having full purification capacity. Such a condition can be detected by means of the temperature sensor 23, and then according to the invention entails that the periodic course described above with change between fat exhaust mixture (box 27) and nmger exhaust mixture (box 28) is initiated.

This results in a rapid increase in the exhaust gas temperature so that the exhaust catalyst 18 and the precatalyst 19, respectively, can be reheated to the correct operating temperature.

The invention is not limited to the embodiments described above and shown in the drawings, but can be varied within the scope of the following claims. For example, the invention can in principle be used without either a precatalyst 19 or an exhaust cooler 22. If a precatalyst is used, it can alternatively consist of an electrically heatable starting catalyst. In addition, the invention can be used with both a conventional gas throttle and with an electrically controlled gas throttle.

Other locations of, for example, the temperature sensor 23 than the one described above are possible. For example, a temperature sensor can be placed after the exhaust catalyst 18. In this way, a check can be made as to whether the exhaust temperature has reached the limit temperature of 650 ° C.

Finally, the invention can also be used in cases where a NO; adsorbent and a conventional three-way catalyst are arranged as two separate components, instead of the above-mentioned embodiment where these two components have been integrated into a single component in the form of a NOx adsorbent exhaust catalyst.

Claims (10)

10 15 20 25 30 35 S14,2ss 19 PATENTKRAVZ A process for sulfur regeneration of a NOK adsorbing exhaust catalyst (18) by raising its temperature, the exhaust catalyst (18) being mounted in an exhaust system (16, 17) soul is connected to an internal combustion engine (1), the method comprising generating an air / fuel mixture for cylinders (3), characterized by comprising: adjusting the temperature of the exhaust gases in said engine (1) and from it, respectively, that the method indoor exhaust system (16, 17) by means of an exhaust cooler (22 ) which is arranged upstream of the exhaust catalyst (18), alternating control of the internal combustion engine (1) between a first state at. which a relatively fatty exhaust mixture is supplied to the exhaust catalyst (18), an oxygen buffer of the exhaust catalyst (18) being burned at least in part in the presence of hydrocarbons in the exhaust gas generating system (16, 17), and a second condition in which a relatively lean exhaust mixture is supplied to the exhaust catalyst (18), for storing oxygen to said oxygen buffer, and shutting off said alternating control after a predetermined amount of sulfur compounds has been desorbed from said exhaust catalyst (18). A method according to claim 1, characterized in that it comprises: calculating the degree. of coating sulfur compounds in the exhaust catalyst (18), and controlling between said first and second states for a period of time corresponding to said coating having dropped to a predetermined level. 10 15 20 25 30 35 514 2.88 10 A process according to claim 1 or 2, wherein a precatalyst (19) is arranged in said exhaust system (16, 17), upstream of the exhaust catalyst (18), characterized in that said alternating control is tuned for combustion of a considerably less amount of oxygen stored in. a. oxygen buffer in the precatalyst (19) relative to the exhaust catalyst (18). the combustion of stored oxygen in A method according to any one of the preceding claims, wherein a temperature sensor (23) is arranged in said exhaust system (16, 17), characterized in that the method comprises determining whether the temperature of the exhaust catalyst (18) has reached a limit value at which said sulfur regeneration can take place, by means of said temperature sensor (23) and stored algorithms which define a relationship between the temperature measured with the temperature sensor (23) and the amount of heat developed in the exhaust catalyst (18). Process according to the preceding claim, according to any one of the features, which comprises a periodic NOX regeneration of said exhaust catalyst (18). Arrangement 'for sulfur regeneration' of a. NO 3 adsorbent exhaust catalyst (18) through. raising its temperature, the exhaust catalyst (18) being mounted in an exhaust system (16, 17) and said arrangement comprising an internal combustion engine (1) connected to means (4, 5, 13) for generating an air / fuel mixture exhaust system (1) and to the engine (1) cylinders (3), characterized in that the arrangement comprises a respective exhaust cooler (22) arranged upstream of said exhaust catalyst (18), for adjusting the temperature of the exhaust gases in said 51.4 288 ll. exhaust system. (16, 17), and that said means (4, 5, 13) comprises a control unit (5) arranged for alternating control between a first state in which a relatively fatty exhaust mixture is delivered to the exhaust catalyst (18), an oxygen buffer of the exhaust catalyst (18) is at least partially combusted in the presence of hydrocarbons in the exhaust gas generating system (16, 17), and a second state in which a relatively lean exhaust gas mixture is supplied to the exhaust catalyst (18), for storing oxygen in said oxygen buffer, said control unit (5) is arranged to turn off said alternating control after a predetermined one. amount. sulfur compounds have been desorbed from said exhaust catalyst (18). Arrangement according to claim 6, wherein a precatalyst (19) is arranged in said exhaust system (16, 17), upstream of the exhaust catalyst (18), characterized in another substantially V, that the oxygen storage capacity of the precatalyst (19) ) associated oxygen buffer lower than the oxygen storage capacity of the oxygen buffer of the exhaust catalyst (18). Arrangement according to claim 7, characterized in that the ratio between the oxygen storage capacity of the precatalyst (19) and the oxygen storage capacity of the exhaust catalyst (18) is at least 1: 2. Arrangement according to any one of claims 6-8, characterized in that said motor (1) is of the type DI motor, direct-injection Otto motor. Arrangement according to one of Claims 6 to 9, characterized in that the temperature sensor (23) arranged as an exhaust system (16, 17) comprises a i connected to the control unit (5), the control unit (5) being set up to determine whether the temperature of the exhaust catalyst (18) 514 288 .ZZ has reached a limit value at. which. said sulfur regeneration can take place, by means of the temperature sensor (23) and algorithms stored in the control unit (5) which define a relationship between the temperature measured with the temperature sensor (23) and the amount of heat developed in the exhaust catalyst (18).