DE10249880B4 - Emission control device and emission control method of an internal combustion engine - Google Patents

Abstract

An emission control device for an internal combustion engine (1) comprising: a NOx catalyst (20) that absorbs and stores NOx from an exhaust gas flowing into the NOx catalyst when an air-fuel ratio of the exhaust gas is on a lean side of a stoichiometric air pressure. Fuel ratio is, and releases the stored NOx when the air-fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or to a rich side of the stoichiometric air-fuel ratio; warming means (28) for performing warm-up control of the NOx catalyst (20) when a need arises to remove a sulfur oxide from the NOx catalyst (20); and an operating state detection device (33, 36) for detecting an operating state of the internal combustion engine (1), wherein, if the internal combustion engine (1) is in a low load state, the warm-up device (28) sets a target temperature of the NOx catalyst (20) to a temperature which is necessary for removing the sulfur oxide if the internal combustion engine (1) is in a high load state which is not suitable for heating the NOx catalyst (20), the warming device (28) the NOx catalyst ...

Description

The invention relates to an emission control device according to the preamble of claim 1 and an emission control method according to the preamble of claim 6 for an internal combustion engine.

In the past, a technology in which a NOx catalyst is disposed in an exhaust system of an internal combustion engine has been proposed in the range of internal combustion engines installed in motor vehicles and the like, and particularly lean-burn gasoline engines and diesel engines capable of to burn an air-fuel mixture in a state of excess oxygen (generally referred to as a lean air-fuel ratio mixture). A known NOx catalyst is a storage-reduction type NOx catalyst that absorbs and stores nitrogen oxides (NOx) from the exhaust gas when the exhaust gas inlet has a high oxygen concentration, and discharges the stored nitrogen oxides (NOx) and reduces them to nitrogen (N ₂ ) when the exhaust gas inflow has a low oxygen concentration and a reducing agent is present.

When such a storage-reduction type NOx catalyst is disposed in the exhaust system of an internal combustion engine, the storage-reduction type NOx catalyst absorbs nitrogen oxides (NOx) from the exhaust gas when the internal combustion engine is operated in a lean combustion mode and therefore the exhaust gas air-fuel ratio becomes high , When the air-fuel ratio of the exhaust gas flowing into the storage-reduction type NOx catalyst becomes low, the storage-reduction type NOx catalyst releases nitrogen oxides (NOx) and causes its reduction into nitrogen (N ₂ ).

The storage-reduction type NOx catalyst also absorbs and stores sulfur oxides (SOx) by the same mechanism as NOx. Sulfur oxides (SOx) are formed by the combustion of sulfur components contained in the fuel. SOx stored in the catalyst is discharged less easily than NOx and is therefore collected on the NOx catalyst. The collection of SOx is called sulfur poisoning (SOx poisoning). When the NOx reduction catalyst undergoes the SOx poisoning, the NO x removal rate drops. Therefore, it is necessary to subject the NOx catalyst to a poisoning recovery process for restoring the NOx catalyst from SOx poisoning with an appropriate timing. The poisoning recovery process is achieved by causing the exhaust gas having a reduced oxygen concentration to flow through the NOx catalyst while keeping the NOx catalyst at a high temperature (for example, about 600 ° C to 650 ° C).

However, during the lean-burn operation, the exhaust gas temperature is low, so that it is not easy to heat the NOx catalyst to a temperature required for the recovery from SOx poisoning when a normal operating condition is maintained. In this situation, however, the supply of a reducing agent (fuel) into the exhaust gas will reduce the oxygen concentration in the exhaust gas as the temperature of the catalyst increases.

For example. holds an engine emission control device disclosed in Japanese Laid-Open Patent Publication JP-A 11-343836 basically, the air-fuel ratio flowing into the storage-reduction type NOx catalyst is in the vicinity of a stoichiometric air-fuel ratio, and makes the air-fuel ratio intermittently lower than the stoichiometric air-fuel ratio when restoring the storage-reduction type NOx catalyst from poisoning becomes necessary. Due to this operation, the air-fuel ratio is kept around the stoichiometric air-fuel ratio for most of the time during the poisoning recovery process, so that the generation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas can be minimized. Further, since the air-fuel ratio is made intermittently lower than the stoichiometric air-fuel ratio, the average air-fuel ratio during the poisoning recovery process is at the fuel-rich side (rich side) of the stoichiometric air-fuel ratio. Therefore, the storage-reduction type NOx catalyst can be recovered from the sulfur poisoning within a relatively short time. According to the above-mentioned publication, poisoning recovery control is performed on the assumption that the temperature of the storage-reduction type NOx catalyst is, for example, greater than or equal to 300 ° C and that the amount of sulfur oxides stored in the catalyst is greater than or equal to a predetermined one Amount is.

Although the sulfur poisoning recovery is performed by decreasing the exhaust gas air-fuel ratio as described above, a reduction in the air-fuel ratio during a high-load operation of the internal combustion engine results in an excessively increased temperature of the NOx catalyst Memory reduction type and therefore may cause a thermal deterioration of the storage-reduction type NOx catalyst.

According to the above-mentioned patent publication, the warm-up control of the storage-reduction type NOx catalyst is performed when the temperature of the storage-reduction type NOx catalyst and the amount of sulfur oxides stored therein satisfy the conditions for starting poisoning recovery control. However, if the warm-up control is not tracked by the operation of the engine in a low-load range, deterioration of fuel economy due to a long-term continuation of a high-temperature state of the catalyst is caused.

Furthermore, the sulfur poisoning recovery is normally performed during a low load engine operation. However, if the warm-up control is started after the engine operation is switched to the low load region, it takes a long time before the storage-reduction type NOx catalyst is heated to a temperature needed for sulfur poisoning recovery. If, during the passage of time, the state of operation of the internal combustion engine changes to a high load region, an opportunity for sulfur poisoning recovery is lost.

In EP 0 971 101 A1 is an exhaust purification device for an internal combustion engine explained, in which a warm-up device is provided for the catalyst. In this prior art, the heating of the catalyst is decided depending on the impurity components contained in the catalyst.

In the document JP 2000 130 223 A An emission control apparatus and related method is disclosed as the closest prior art that represents the generic art of the present invention.

The invention has been made to solve the above-mentioned problems. It is an object of the invention to provide a technology capable of reducing a deterioration of the fuel economy of an internal combustion engine equipped with an emission control device for rapidly raising the temperature of a NOx catalyst of the emission control device to a temperature allows sulfur poisoning recovery at the time of meeting a condition needed for sulfur poisoning recovery.

The object is achieved by an emission control device with the combination of the features of claim 1 and an emission control method with the combination of the features of claim 6. Further advantageous developments of the invention are defined in the dependent claims.

An emission control device of an internal combustion engine includes: a NOx catalyst that absorbs and stores NOx from an exhaust gas flowing into the NOx catalyst when an air-fuel ratio of the exhaust gas is on a lean side of a stoichiometric air-fuel ratio, and discharging the stored NOx when the air-fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or to the rich side of the stoichiometric air-fuel ratio; a warming-up means for performing a warm-up control of the NOx catalyst when there is a need to remove a sulfur oxide from the NOx catalyst; and operating condition detecting means for detecting a state of operation of the internal combustion engine. The warm-up means heats the NOx catalyst by setting a target temperature based on the state of operation of the internal combustion engine detected by the operating condition detecting means. When the engine is in a high load condition that is not capable of warming the NOx catalyst, the warm-up device does not heat the NOx catalyst.

According to another aspect, there is provided an emission control method of an emission control apparatus of an internal combustion engine having a NOx catalyst that absorbs and stores NOx from exhaust gas flowing into the NOx catalyst when an air-fuel ratio of the exhaust gas is on a lean side of a stoichiometric air-fuel ratio and which discharges the stored NOx when the air-fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or to a rich side of the stoichiometric air-fuel ratio, wherein a warm-up control of the NOx catalyst is performed, if there is a need to remove a Sulfur oxide of the NOx catalyst results. The emission control method comprises the steps of: detecting an operating state of the internal combustion engine; Setting a target temperature of the NOx catalyst based on the operating condition; and heating the NOx catalyst toward the target temperature or avoiding heating of the NOx catalyst NOx catalyst, when the internal combustion engine is in a high load state, which is not suitable for heating the NOx catalyst.

A main feature of the emission control device and the emission control method thereof according to the invention is that a target temperature of the NOx catalyst is determined according to the operating state of the internal combustion engine and the heating of the NOx catalyst is performed when there is a need to remove a sulfur oxide from the NOx Catalyst results, and in that, when the internal combustion engine is in a high load state in which a sulfur poisoning restoration can not be performed, the heating of the NOx catalyst is avoided. Therefore, it becomes possible to control the deterioration in fuel economy and to rapidly raise the temperature of the NOx catalyst to a temperature required for the sulfur poisoning recovery when an operation state allowing the sulfur poisoning recovery is achieved.

In the engine emission control apparatus and the emission control method thereof, as described above, the heating of the NOx catalyst is avoided when the operating state of the engine is in an operating region where recovery from sulfur poisoning is not performed, for example, in a high load operation region , During the high load operation, the execution of sulfur poisoning recovery may excessively raise the temperature of the NOx catalyst and may cause thermal deterioration of the NOx catalyst. Therefore, in some cases, although the temperature of the NOx catalyst is raised during the high load operation range, it is not possible to perform the sulfur poisoning recovery after the temperature is raised. Further, during the high load operation range, the temperature rises to a certain level due to the heat from the exhaust gas, so that the NOx catalyst can be rapidly heated to the temperature needed for sulfur poisoning recovery. Often it is during highway driving or the like that the high load operating state continues. In such a case, despite the execution of the heating of the NOx catalyst, a considerably long time may elapse before a change to an operation state required for sulfur poisoning recovery. Therefore, the heating of the NOx catalyst according to the invention is avoided when the engine is in the high load operating range. Therefore, it becomes possible to reduce fuel consumption and control deterioration in terms of fuel economy.

When the engine operation is in another range, for example, a medium load range, the possibility of switching to an operating state allowing sulfur poisoning recovery becomes high. When the operating state approaches the low-load region, a temperature rise of the NOx catalyst due to the temperature of the exhaust gas becomes less likely. Further, when the operating state reaches a low-load range, the possibility of switching to an operating state allowing the sulfur poisoning recovery becomes higher, so that the demand for raising the temperature of the NOx catalyst increases.

Therefore, when the engine operation is in the middle-load range, the set temperature of the NOx catalyst is set so that the temperature of the NOx catalyst becomes higher as the state of the engine operation approaches the low-load region. With this setting, it becomes possible to rapidly raise the temperature of the NOx catalyst to the temperature needed for the sulfur poisoning recovery, to reach the operating state allowing the sulfur poisoning recovery, and to reduce the amount of fuel before the sulfur poisoning recovery is carried out is consumed.

For example, when the internal combustion engine is in the low-load range, it is possible to perform sulfur poisoning recovery immediately, provided that the NOx catalyst has a temperature suitable for sulfur poisoning recovery. Therefore, when the temperature of the NOx catalyst is raised to the temperature needed for the sulfur poisoning recovery, it is possible to directly carry out the sulfur poisoning recovery.

Therefore, it is preferable to set the target temperature of the NOx catalyst higher when the internal combustion engine is in a low-load region than when the internal combustion engine is in a high-load region.

It is also preferable to mitigate the warm-up control when an actual temperature of the NOx catalyst is higher than the target temperature, and to enhance the warm-up control when the actual temperature of the NOx catalyst is lower than the target temperature.

Thus, when the target temperature of the NOx catalyst is based on the operating range of the internal combustion engine, it becomes possible to reduce the deterioration in fuel economy and to rapidly raise the temperature of the NOx catalyst to the temperature needed for the sulfur poisoning recovery when the operating state permitting the sulfur poisoning recovery is reached.

According to another form from every point of view. According to the invention described above, the heating of the NOx catalyst can be stopped when an operation state that does not allow removal of the sulfur oxide continues for at least a predetermined time while the NOx catalyst is being heated.

When the above-mentioned operation state continues and the sulfur poisoning recovery is not performed, a high-temperature state of the NOx catalyst is maintained, causing a deterioration in fuel economy. Therefore, during this operating state, stopping the heating of the NOx catalyst can reduce the deterioration in fuel economy.

According to another form of the invention, it is possible to adopt a construction in which, when there is a need to remove the sulfur oxide from the NOx catalyst, the temperature of the NOx catalyst is raised to a temperature needed for sulfur poisoning recovery and when the sulfur poisoning recovery is not performed for a subsequent predetermined time, the NOx catalyst is heated by setting a target temperature based on the detected operating state of the internal combustion engine, and when the internal combustion engine is in an operating state that is not suitable for heating the NOx catalyst is, the heating of the NOx catalyst is avoided.

In the engine emission control apparatus and the emission control method constructed as described above, the NOx catalyst is heated to the temperature required for sulfur poisoning restoration when there is a need to recover the NOx catalyst from sulfur poisoning. Thereafter, when the operating state of the internal combustion engine changes to a low load region, sulfur poisoning recovery is performed. However, if engine operation continues without a change to the above operating range, fuel is consumed to maintain the temperature of the NOx catalyst. Therefore, when the sulfur poisoning recovery is not performed for the predetermined period of time, the warming up control of the NOx catalyst is performed according to the operating range, so that the deterioration in fuel economy can be reduced.

The above embodiment and other exemplary embodiments, objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of exemplary embodiments of the invention, with reference to the accompanying drawings.

1 schematically shows an internal combustion engine and its intake and exhaust system, to which an engine emission control device according to the embodiments of the invention is applied;

2A FIG. 12 is a cross-sectional view of a particulate filter of the engine emission control apparatus according to embodiments of the invention; FIG.

2 B Fig. 15 is a longitudinal sectional view of the particulate filter of the engine emission control apparatus according to the embodiments of the invention;

3 Fig. 10 is a block diagram showing the internal structure of an ECU of the engine emission control apparatus according to the embodiments of the invention; and

4 Fig. 15 is a diagram indicating the set temperature of the filter in the first embodiment of the invention.

In the following description and the accompanying drawings, the invention will be described in more detail with reference to the exemplary embodiments.

Hereinafter, a specific embodiment of an emission control device for an internal combustion engine according to the invention will be described with reference to the drawings. The following description deals with an exemplary case where the emission control device for the internal combustion engine according to the invention is applied to a diesel engine for driving a vehicle.

(First embodiment)

1 schematically shows the structure of a diesel internal combustion engine (hereinafter referred to as " Internal combustion engine ") 1 on which an emission control device according to this embodiment is applied.

The internal combustion engine 1 who in 1 shown is a water-cooled four-stroke four-cylinder diesel engine 2 ,

The internal combustion engine 1 has fuel injectors 3 , each of which feeds fuel directly into a combustion chamber of a corresponding cylinder 2 injects. Each of the fuel injection valves 3 is with a collector (common rail) 4 connected, which stores the fuel until a predetermined pressure is reached. The common management 4 is with a pressure sensor 4a the common line, which provides an electrical signal corresponding to a fuel pressure in the common line 4 emits.

The common management 4 is in connection with a fuel pump 6 via a fuel supply pipe 5 , The fuel pump 6 operates by using a rotational torque of an output shaft (crankshaft) of the internal combustion engine 1 as a drive power source. A pump pulley 6a connected to an input shaft of the fuel pump 6 attached is via a belt 7 with a crankshaft pulley 1a connected to the output shaft (crankshaft) of the internal combustion engine 1 is appropriate.

In the fuel injection system thus constructed, the fuel pump bumps 6 when a rotational torque of the crankshaft to the input shaft of the fuel pump 6 is transferred, the fuel at a pressure corresponding to the rotational torque from the crankshaft to the input shaft of the fuel pump 6 is transmitted.

The from the fuel pump 6 expelled fuel becomes the common conduit 4 over the fuel supply pipe 5 fed and is in the common line 4 stored to the predetermined pressure and becomes the fuel injection valves 3 the cylinder 2 distributed. When a drive current to the fuel injectors 3 is applied, the fuel injectors 3 open. As a result, fuel from each of the fuel injection valves 3 into a corresponding one of the cylinders 2 injected.

An intake manifold 8th is with the internal combustion engine 1 connected. Each branch pipe of the intake manifold 8th communicates with the combustion chamber of a corresponding one of the cylinders 2 via an inlet port (not shown).

The intake manifold 8th is with an inlet pipe 9 connected with an air filter box 10 connected is. An air flow meter 11 is at the inlet pipe 9 downstream of the air filter box 10 appropriate. The air flow meter 11 gives an electrical signal corresponding to the mass of the through the inlet pipe 9 flowing inlet air.

An intake throttle valve 13 for adjusting the flow rate of the intake air passing through the inlet pipe 9 is at a location in the inlet pipe 9 immediately upstream of the intake manifold 8th arranged. The intake throttle valve 13 is with an intake throttle actuator 14 provided, for example, by a stepping motor and the like. Is formed, and that the intake throttle valve 13 drives in the opening and closing directions.

A compressor housing 15a a centrifugal loader (turbocharger) 15 That works by using hydrodynamic energy of the exhaust gas as a driving power source is at the intake pipe 9 between the air flow meter 11 and the intake throttle valve 13 arranged. An intercooler 16 for cooling the intake air, which is a high temperature as a result of compression in the compressor housing 15a has is at the inlet pipe 9 downstream of the compressor housing 15a arranged.

In the intake system thus constructed, intake air is introduced into the air cleaner box 10 from dust, dirt or the like through an air cleaner (not shown) in the air cleaner box 10 cleaned and then flows into the compressor housing 15a over the inlet pipe 9 ,

The intake air entering the compressor housing 15a is flowed, is compressed by a rotation of a compressor wheel, which in the compressor housing 15a is adjusted. The intake air, which is a high temperature as a result of compression in the compressor housing 15a has, gets in the intercooler 16 cooled and flows into the intake manifold 8th , The intake air entering the intake manifold 8th has flowed, becomes the combustion chambers of the cylinder 2 is distributed over the respective branch pipes and is subjected to combustion using fuel injection valves 3 is caused as an ignition source of injected fuel.

An exhaust manifold 18 is with the internal combustion engine 1 connected. Each branch pipe of the exhaust manifold 18 communicates with the combustion chamber of a corresponding one of the cylinders 2 via an outlet port (not shown).

The exhaust manifold 8th is with a turbine housing 15b the centrifugal loader 15 connected. The turbine housing 15b is with an exhaust pipe or an outlet pipe 19 connected to a silencer (not shown) at a downstream portion thereof.

A particle filter (hereinafter simply referred to as "filter") 20 showing a NOx catalyst is at a middle portion of the exhaust pipe 19 intended. An exhaust gas temperature sensor 24 which provides an electrical signal corresponding to the temperature of the exhaust pipe 19 flowing exhaust gas is at the exhaust pipe 19 upstream of the filter 20 arranged.

This embodiment will be described in connection with a particulate filter loaded with a storage-reduction type NOx catalyst so generally called, which absorbs and stores NOx from the exhaust gas flowing when the air-fuel ratio of the exhaust gas is on the exhaust gas fuel lean side of a stoichiometric air / fuel ratio and which dumps stored NOx for reduction as the air / fuel ratio of the exhaust gas flowing changes to the fuel rich side (rich side) of the stoichiometric air / fuel ratio.

The above air-fuel ratio, which is on the lean side, means that the air-fuel ratio of the exhaust gas is within a range such that NOx can not be reduced by a three-way catalyst. An example of this air / fuel ratio range for the case of a diesel engine is 20 to 50.

An exhaust throttle valve 25 for adjusting the flow rate of the exhaust gas passing through the exhaust pipe 19 flows is in the exhaust pipe 19 downstream of the filter 20 arranged. An exhaust throttle actuator 22 is at the exhaust throttle valve 21 appropriate. The exhaust throttle actuator 22 is formed by a stepping motor or the like and drives the exhaust throttle valve 21 in opening and closing directions.

In the exhaust system thus constructed, a mixture (burned gas) is generated in each of the cylinders 2 of the internal combustion engine 1 is burned to the exhaust manifold 18 ejected via the outlet port and then flows from the exhaust manifold 18 in the turbine housing 15b the centrifugal loader 15 , The exhaust gas that enters the turbine housing 15b has flowed, a turbine wheel rotates due to its hydrodynamic energy. The turbine wheel is rotatable in the turbine housing 15b trimmed. During this operation, a rotational torque of the turbine wheel is applied to the compressor wheel in the compressor housing 15a transferred, which is mentioned above.

Exhaust gas from the turbine housing 15b is ejected, flows into the filter 20 over the exhaust pipe 19 , Therefore, particulate matters (hereinafter referred to as "PM") contained in the exhaust gas are collected, and harmful gas components contained in the exhaust gas are removed or chemically changed. After the PMs are collected and harmful gas components through the filter 20 removed or reduced, the exhaust gas is emitted into the atmosphere via the muffler. If necessary, set the exhaust throttle valve 21 the flow rate of the exhaust gas before the emission of the exhaust gas into the atmosphere.

The exhaust manifold 18 and the intake manifold 8th communicate with each other via an exhaust gas recirculation passage (hereinafter referred to as "EGR passage") 25 through which a portion of the exhaust gas passing through the exhaust manifold 18 flows into the intake manifold 8th is recirculated or returned. At a middle section of the EGR passage 25 is a flow rate adjusting valve (hereinafter referred to as "EGR valve") 26 intended. The EGR valve 26 is formed by an electromagnetic valve or the like, and changes the flow rate of the exhaust gas passing through the EGR passage 25 (hereinafter referred to as "EGR gas") flows according to the applied electric power.

An EGR cooler 27 for cooling the EGR gas passing through the EGR passage 25 is at a middle portion of the EGR passage upstream of the EGR valve 26 arranged. The EGR cooler 27 is provided with a coolant passage (not shown) through which a part of the coolant for cooling the engine 1 circulated.

On the exhaust gas recirculation mechanism thus constructed becomes the EGR passage 25 passable if the EGR valve 26 is open. Then, part of the exhaust gas flows through the exhaust manifold 18 flows into the EGR passage 25 and flows through the EGR cooler 27 and gets into the intake manifold 8th introduced.

In this case, heat is generated in the EGR cooler 27 between the EGR gas passing through the EGR passage 25 flows, and replaced the internal combustion engine coolant. As a result, the EGR gas is cooled.

The EGR gas coming from the exhaust manifold 18 to the intake manifold 8th over the EGR passage 25 is recirculated, mixes with one Fresh air coming from a passage upstream of the intake manifold 8th flows, and gets into the combustion chambers of the cylinders 2 introduced.

It should be noted that the EGR gas contains inert gas components which do not burn and which have a high thermal capacity, such as. As water (H ₂ O) and carbon dioxide (CO ₂ ). Therefore, when the EGR gas is contained in the air-fuel mixture, the combustion temperature of the mixture becomes relatively low. As a result, the production of nitrogen oxides (NOx) is reduced.

Furthermore, if the EGR gas in the EGR cooler 27 is cooled, the temperature of the EGR gas decreases and reduces its volume. Thus, supplying the EGR gas to a combustion chamber does not cause an undesirable increase in the atmospheric temperature in the combustion chamber and does not cause an undesirable reduction in the amount (volume) of the fresh air supplied to each combustion chamber.

The filter 20 according to this embodiment will be described below. The 2A and 2 B show cross sections of the filter 20 , 2A is a cross-sectional view of the filter 20 , 2 B is a longitudinal sectional view of the filter 20 , As in the 2A and 2 B shown is the filter 20 a generally so-called Wandströmungsbauart with a plurality of exhaust gas flow passages 50 . 51 which extend parallel to each other. These exhaust flow passages consist of exhaust gas inflow passages 50 with their downstream ends plugged 52 are closed, and from Abgasausströmungsdurchgängen 51 with their upstream ends plugged 53 are closed. It should be noted that hatched areas in 2A the trunks 53 suggest. Accordingly, the exhaust gas inflow passages 50 and the exhaust outflow passages 51 alternating with the interposition of thin separating elements 54 arranged. In other words, the exhaust gas inflow passages 50 and the exhaust outflow passages 51 arranged so that each exhaust gas inflow passage 50 through four exhaust outflow passages 51 is surrounded and that each Abgasausströmungsdurchgang 51 through four exhaust gas inflow passages 50 is surrounded.

The filter 20 consists of a porous material, such as. B. cordierite. Therefore, the exhaust gas flows as indicated by arrows in FIG 2 B indicated in the exhaust gas inflow passages 50 has flowed into their adjacent Abgasausströmungsdurchgänge 51 through the dividing elements 54 out.

In the embodiment of the invention, supporting layers made of alumina or the like are provided on peripheral wall surfaces of the exhaust gas inflow passages 50 and the exhaust outflow passages 51 namely on both surfaces of each separating element 54 , and formed on inner wall surfaces of pores, which are in the separating elements 54 are formed. The backing layers are loaded with a storage-reduction type NOx catalyst.

In the following, an operation of the storage-reduction type NOx catalyst attached to the filter will be described 20 is supported, described according to this embodiment.

For example. has the filter 20 a support consisting of alumina or alumina, and at least one material consisting of alkali metals, such as. As potassium (K), sodium (Na), lithium (Li), cesium (Cs), etc., alkaline earth metals, such as. As barium (Ba), calcium (Ca), etc., and rare earths such. As lanthanum (La), yttrium (Y), etc., and a noble metal such. As platinum (Pt) and the like. Is selected, is supported on the support. This embodiment adopts a storage-reduction type NOx catalyst formed by charging an alumina support with barium (Ba) and platinum (Pt) and adding cerium (Ce ₂ O ₃ ) capable of O ₂ save.

The NOx catalyst thus constructed absorbs and stores nitrogen oxides (NOx) from the exhaust gas when the exhaust gas flowing into the NOx catalyst shows a high acid concentration.

In contrast, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst is low, the NOx catalyst releases stored nitrogen oxides (NOx). If in this case the reducing components, such. Hydrocarbon (HC), carbon monoxide (CO), etc. In the exhaust gas, the nitrogen oxides (NOx) discharged from the NOx catalyst can be reduced to nitrogen (N ₂ ).

When the internal combustion engine 1 is in a lean-burn operation, shows the exhaust gas from the engine 1 is discharged, a lean air / fuel ratio and a high oxygen concentration, so that the NOx catalyst absorbs and stores nitrogen oxides (NOx) from the exhaust gas. However, if the lean burn operation of the internal combustion engine 1 continues for a long period, the NOx storage capacity of the NOx catalyst is saturated. As a result, nitrogen oxides (NOx) are not removed from the exhaust gas by the NOx catalyst, but are discharged into the atmosphere.

Especially in the case of a diesel engine, as in the internal combustion engine 1 , an air-fuel mixture of a lean air Fuel ratio burned in most operating areas and therefore the exhaust gas shows lean air / fuel ratios in most operating areas. Therefore, the NOx storage capacity of the NOx catalyst tends to saturate.

If therefore the internal combustion engine 1 is in the lean-burn operation, it is necessary to decrease the concentration of the oxygen contained in the exhaust gas flowing into the NOx catalyst and increase the concentration of a reducing agent, and the nitrogen oxides (NOx) from the NOx Release catalyst for reduction before the NOx absorption capacity of the NOx catalyst is saturated.

Conceivable methods of reducing the oxygen concentration described above include, for example, the addition of fuel to the exhaust gas, low-temperature combustion as mentioned above, fuel injection into the cylinders 2 during the expansion stroke and the like. This embodiment employs a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to the exhaust gas passing through the exhaust pipe 19 flows upstream of the filter 20 one. The reductant delivery mechanism supplies fuel to the exhaust gas to reduce the concentration of oxygen in the filter 20 flowing exhaust gas, and to increase the concentration of the reducing agent.

As in 1 is shown, the reducing agent supply mechanism has a nozzle hole, which is towards the inside of the exhaust manifold 18 is directed. The reductant supply mechanism further includes a reductant injection valve 28 , a reducing agent supply passage 29 and a shut-off valve 31 , The reducing agent injection valve 21 opens to fuel in response to a signal from the ECU 35 inject. The reductant supply passage 29 conducts fuel from the fuel pump 6 into the reducing agent injection valve 28 , The shut-off valve 31 is in the reductant supply passage 29 for shutting off the flow of the fuel in the reducing agent supply passage 29 arranged.

In such a reductant supply mechanism, high pressure fuel coming from the fuel pump 6 is discharged to the reducing agent injection valve 28 via the reductant supply passage 29 promoted. Then it opens in response to a signal from the ECU 35 the reducing agent injection valve 28 to deliver fuel as a reductant into the exhaust manifold 18 inject.

The reducing agent supplied by the reducing agent injection valve 28 in the exhaust manifold 18 is injected, reduces the oxygen concentration of the exhaust gas from an upstream portion of the exhaust manifold 18 has flowed.

The low oxygen concentration exhaust gas thus formed flows into the filter 20 and causes the nitrogen oxides (NOx) to be released from the filter 20 and a reduction of nitrogen oxides.

Then the reducing agent injection valve closes 28 in response to a signal from the ECU 35 , thereby adding the reducing agent to the exhaust manifold 18 is interrupted.

In this embodiment, fuel is added by injection into the exhaust gas. However, it is also suitable to carry out the low-temperature combustion. In the low-temperature combustion, the amount of soot that is generated is increased as the amount of EGR gas is increased, and then the amount of soot produced is maximized. Then, when the amount of the EGR gas is further increased, soot is hardly generated because the temperatures of the fuel and the ambient gas are lower than the temperature at which soot can be generated. So it is suitable to fuel from the fuel injectors 3 during the expansion stroke, an exhaust stroke or the like of the internal combustion engine 1 inject.

The internal combustion engine 1 , which is constructed as described above, is connected to an electronic control unit (ECU). 35 for controlling the internal combustion engine 1 Mistake. The ECU 35 controls the operating state of the internal combustion engine 1 according to an operating condition of the internal combustion engine 1 or a request from the driver.

Various sensors, such. B. the pressure sensor 4a the common line, the air flow network device 11 , the exhaust temperature sensor 24 , a crank position sensor 33 , an accelerator operation sensor 36 etc. are with the ECU 35 connected via electrical wiring. Output signals from the various sensors become the ECU 35 entered.

The fuel injectors 3 , the intake throttle actuator 14 , the exhaust throttle actuator 22 , the reducing agent injection valve 28 , the EGR valve 26 , the shut-off valve 31 and the like are with the ECU 35 connected via electrical wiring. The ECU 35 is able to control these components.

As in 3 shown has the ECU 35 a CPU 351 , a ROM 352 , a ram 353 , an auxiliary RAM 354 , an input port 356 and an output port 357 passing through a bidirectional bus 350 are connected. The ECU 35 also has an A / D converter (A / D) 355 that with the input connector 356 connected is.

The input port 356 Takes an input of signals that are output from the sensors that are designed to deliver digital signals, such. B. the crank position sensor 33 and the like, and transmits them to the CPU 351 or the RAM 353 ,

The input port 356 accepts the input of signals output from the sensors designed to emit analog signals, such as those shown in FIG. B. the pressure sensor 4a the common line, the air flow meter 11 , the temperature sensor 24 , the coolant temperature sensor 34 , the accelerator actuation sensor 36 etc. over the A / D 355 and transmits these signals to the CPU 351 or the RAM 353 ,

The output port 357 is with the fuel injectors 3 , the intake throttle actuator 14 , the exhaust throttle actuator 22 , the EGR valve 26 , the reducing agent injection valve 28 , the shut-off valve 31 , etc. connected via electrical wiring. Control signals coming from the CPU 351 are delivered to the fuel injection valves 3 , the intake throttle actuator 14 , the exhaust throttle actuator 22 , the EGR valve 26 , the reducing agent injection valve 28 and the shut-off valve 31 via the output port 357 transfer.

The ROM 352 stores application programs, such as For example, a fuel injection control routine for controlling the fuel injection valves 3 , an intake throttle control routine for controlling the intake throttle valve 13 , an exhaust throttle control routine for controlling the exhaust throttle valve 21 , an EGR control routine for controlling the EGR valve 26 , an NOx purifying control routine for discharging absorbed NOx by adding a reducing agent to the filter 20 , a sulfur poisoning recovery control routine for restoring the filter 20 from SOx poisoning and a PM combustion control routine for burning and removing the PMs passing through the filter 20 collected, etc.

In addition to the above-mentioned application programs, the ROM stores 352 various control maps or control field fields.

Examples of the control maps include a fuel injection amount control map showing the relationship between operating conditions of the internal combustion engine 1 and indicate basic fuel injection amounts (basic fuel injection durations), a fuel injection timing control map representing the relationship between operating conditions of the internal combustion engine 1 and basic fuel timings, an intake throttle valve opening control map indicating the relationship between operating conditions of the internal combustion engine 1 and target opening degrees of the intake throttle valve 13 An exhaust throttle valve opening control map indicates the relationship between operating conditions of the internal combustion engine 1 and target opening degrees of the exhaust throttle valve 21 indicates an EGR valve opening control map showing the relationship between operating conditions of the internal combustion engine 1 and target opening degrees of the EGR valve 26 indicates a reducing agent addition amount control map showing the relationship between operating conditions of the internal combustion engine 1 and target amounts of reductant added (or target air-fuel ratios of the exhaust gas) indicates a reductant injector control map representing the relationship between target amounts of the added reductant and valve opening durations of the reductant injector 28 indicates, and the like.

The RAM 353 stores output signals from the sensors, calculation results obtained by the CPU 351 are obtained, and the like. Examples of the calculation results include an engine speed calculated on the basis of a time interval at which the crank position sensor 33 outputs a pulse signal. This data is updated each time the crank position sensor 33 emits a pulse signal.

The auxiliary RAM 354 is a non-volatile memory that is able to retain data even when the internal combustion engine is running 1 is stopped.

The CPU 351 works according to the application programs included in the ROM 352 and performs fuel injection valve control, intake throttle control, exhaust throttle control, EGR control, NOx removal control, poisoning recovery control, PM combustion control, and the like.

For example, the CPU performs 351 during the NOx purge control, a so-called pulse peak fat control, in which the concentration of oxygen in the filter 20 flowing exhaust gas is included, impulsive peak shape (within a short time) is reduced at a relatively short cycle.

In pulse peaking control, the CPU detects 351 in a predetermined cycle, whether a condition for performing the pulse peak fat control has been satisfied. Examples of this condition for performing the pulse peak fat control is a condition that the filter 21 has been activated, a condition that the value of the exhaust gas temperature sensor output signal 24 (Exhaust gas temperature) is less than or equal to a predetermined upper limit, a condition that poisoning recovery control is not being performed, etc.

When it is determined that the condition for performing the pulse peaking control has been satisfied, as described above, the CPU controls 351 the reducing agent injection valve 28 to fuel as a reducing agent from the reducing agent injection valve 28 Inject impulsively. Thus, the CPU does 351 the air-fuel ratio of the exhaust gas into the filter 20 inflows, temporarily equal to a predetermined rich target air-fuel ratio.

More specifically, the CPU reads 351 one in the RAM 353 stored engine speed, a delivery signal of the accelerator operation sensor 36 (the amount of depression of the accelerator pedal), a discharge signal value of the air flow meter 11 (Intake air amount), an output signal of the air-fuel ratio sensor, a fuel injection amount, and the like.

Using the engine speed, the accelerator operation amount, the intake air amount and the fuel injection amount as parameters, the CPU intervenes 351 to the reductant addition amount control map stored in the ROM 352 and calculates a reducing agent amount to be added to make the air-fuel ratio of the exhaust gas a preset target air-fuel ratio (target addition amount).

Subsequently, the CPU attacks 351 using the target addition amount as a parameter to the reducing agent injection valve control map included in the ROM 352 is stored, and calculates a valve opening periods (target valve opening period) of the reducing agent injection valve 28 for injecting the target addition amount of the reducing agent from the reducing agent injection valve 28 is needed.

When the target valve opening period of the reducing agent injection valve 28 calculated, the CPU opens 351 the reducing agent injection valve 28 ,

At the expiration of the target valve opening period of the opening of the reducing agent injection valve 28 Next, the CPU will close 351 the reducing agent injection valve 28 ,

When the reducing agent injection valve 28 thus, is open for the target valve opening period, the target addition amount of the fuel from the reducing agent injection valve becomes 28 in the exhaust manifold 18 injected. The reducing agent supplied by the reducing agent injection valve 28 is injected, mixes with the exhaust gas from an upstream portion of the exhaust manifold 18 has flowed, and forms a mixture having the target air-fuel ratio, and then flows into the filter 20 ,

As a result, the oxygen concentration of the exhaust gas that changes in the filter changes 20 flows, in a relatively short cycle. Therefore, the filter repeats 20 the absorption of nitrogen oxides NOx and the emission / reduction of nitrogen oxides (NOx) alternately into a short cycle.

In the poison recovery control, the CPU performs 351 a poisoning recovery process through to the filter 20 from poisoning by oxides.

It should be noted that the internal combustion engine 1 can use a fuel containing sulfur (S). If such a fuel in the internal combustion engine 1 burns, sulfur oxides (SOx), such as. As sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), etc. produced.

Sulfur oxides SOx flow into the filter 20 along with the exhaust and are through the filter 20 absorbed and stored by the same mechanism as in the case of nitrogen oxides (NOx).

If more specifically that in the filter 20 flowing exhaust gas shows a high oxygen concentration, sulfur oxides (SOx) contained in the exhaust gas, such. For example, sulfur dioxide (FO ₂ ), sulfur trioxide (SO ₃ ), etc. are oxidized on the surfaces of the platinum (Pt) and through the filter 20 in the form of sulfate ions (SO ₄ ^2- ) absorbed and stored. The sulfate ions (SO ₄ ^2- ), which pass through the filter 20 are absorbed, combine with barium oxide (BaO) and form a sulfate (BaSO ₄ ).

It should be noted that the sulfate (BaSO ₄ ) is more stable and less likely to decompose than barium nitrate (Ba (NO ₃ ) ₂ ). Even if the oxygen concentration of the filter 20 flowing low, the sulfate (BaSO4) remains in the filter 20 without being decomposed.

When the amount of sulfate (BaSO4) in the filter 20 increases, the amount of barium oxide (BaO) that can contribute to the absorption of nitrogen oxides (NOx) decreases accordingly. This leads to the so-called SOx poisoning, which is a deterioration of the NOx absorbing ability of the filter 20 caused.

In an exemplary method for restoring the filter 20 Sulfur poisoning becomes the atmospheric temperature of the filter 20 is raised to a high temperature range of about 600 ° C to 650 ° C and the oxygen concentration of the exhaust gas that enters the filter 20 flows, decreases. As a result, barium sulfate (BaSo ₄ ), which is in the filter 20 stored thermally in SO ₃ ^- and SO ₄ ^- decomposed. Then, SO ₃ ^- and SO ₄ ^- are caused to react with hydrocarbons HC and carbon monoxide CO contained in the exhaust gas, thus being reduced to gaseous SO ₂ ^- .

In the poisoning recovery process according to this embodiment, therefore, the CPU performs 351 first, a catalyst heating control of raising the catalyst temperature of the filter 20 and reduces the oxygen concentration of the exhaust gas flowing into the filter.

In the catalyzer warm-up control, the CPU causes 351 in that the reducing agent injection valve 28 Fuel is injected so that the fuel in the filter 22 is oxidized. Due to the heat generated by the oxidation, the temperature of the filter 20 raised. The amount of fuel flowing from the reductant injector 28 is injected in this case is set so that the injection duration is shorter and a higher air-fuel ratio in comparison with the fuel injection from the reducing agent injection valve 28 resulting in discharging and reducing NOx.

In the catalyzer warm-up control, the CPU 351 bsw. be designed to receive fuel from each of the fuel injection valves 3 secondarily during an expansion stroke of a corresponding cylinder 2 to inject and fuel the exhaust gas from the reducing agent injection valve 28 Add so that unburned components of the fuel in the filter 20 be oxidized. Due to the heat generated by the oxidation, the catalyst temperature of the filter 20 be raised.

However, if the filter 20 is heated excessively, can cause thermal deterioration of the filter 20 be induced. It is therefore preferable to feedback control the secondary injection amount of the fuel and the addition amount of the fuel on the basis of the value of a discharge signal of the exhaust gas temperature sensor 24 perform.

When the catalyst temperature of the filter 20 to a high temperature range of bsw. rises about 630 ° C through the above-mentioned catalyst warm-up process causes the CPU 351 in that the reducing agent injection valve 28 Fuel injects to the oxygen concentration of the filter 20 to reduce incoming exhaust gas.

When an excessive amount of fuel from the reducing agent injection valve 28 the filter can be injected 20 be overheated by rapid combustion of the fuel. Instead, an excessive amount of injected fuel may be discharged from the reducing agent injection valve 28 undesirable the filter 20 cool. It is therefore preferable that the CPU 351 a feedback control of the fuel injection amount from the reducing agent injection valve 28 on the basis of an output signal of an air-fuel ratio sensor (not shown).

When the poisoning recovery process is performed as described above, the oxygen concentration of the one in the filter decreases 20 flowing exhaust gas under the condition that the catalyst temperature of the filter 20 is high. Therefore, barium sulfate (BaSo ₄ ), which is in the filter 20 stored thermally in SO ₃ ^- and SO ₄ ^- decomposed. The SO ₃ ^- and SO ₄ ^- react with hydrocarbon HC and carbon monoxide CO, which are contained in the exhaust gas, and is reduced, whereby the sulfur poisoning of the filter 20 is eliminated.

It should be noted that when the addition of fuel for recovery from SOx poisoning is performed in a medium to high engine load operating range, the filter 20 can be heated excessively and can be thermally deteriorated. Therefore, if the execution of the warm-up control is not caused by the operation of the internal combustion engine 1 in a low load range, fuel addition for SOx poisoning recovery is avoided. If this situation continues, the temperature of the filter will drop 20 so that the warm-up control must be performed again to perform SOx poisoning recovery. Thus, a large amount of fuel is consumed, so that the fuel economy will deteriorate.

However, if the fuel addition for the filter 20 is avoided, to reduce the deterioration of fuel economy, the temperature of the filter 20 fall off, so that the SOx poisoning recovery can not be performed immediately when engine operation shifts to a low load range. Thus, the opportunity for SOx poisoning recovery may be lost.

Therefore, in this embodiment, the temperature of the filter 20 regulated and maintained in accordance with the engine operating condition to maintain both a temperature maintenance of the filter 20 as well as to reduce or prevent fuel economy degradation.

4 FIG. 12 is a graph showing a relationship between the engine speed, the engine load, and the target temperature of the filter 20 suggests. This picture is in advance in the ROM 352 saved. In the figure, the hatched area is a range of bsw. 630 ° C and decreases the target temperature of the filter 20 gradually with an increase in the distance from the hatched area. In 4 is an engine operating range where the target temperature of the filter 20 500 ° C, representatively indicated.

In a high load range, the temperature of the filter 20 high, bsw 550 ° C, without the addition of fuel due to the high exhaust gas temperature and the large flow rate of the exhaust gas. When the engine operation shifts from the high load range to a low load range, the temperature of the filter may increase 20 to a temperature required for SOx poisoning recovery, eg. 630 ° C, within a short time, and therefore the fuel economy deterioration is reduced or controlled by avoiding the addition of the fuel until the engine operation shifts to another operating range.

On the other hand, when the engine operation is in a medium load range, a target temperature of the filter becomes 20 is determined in accordance with the engine speed and the engine load and addition of fuel is performed with a feedback control of the added amount of fuel.

In this case, the CPU reads 351 an output signal of the crank position sensor 33 (Speed) and an output signal of the accelerator operation sensor 36 (Load) and calculates a target temperature of the filter 20 by putting these values into the picture of 4 , Then the CPU reads 351 a discharge signal of the exhaust gas temperature sensor 24 and estimates a temperature of the filter 20 , The temperature of the filter 20 is determined by the intake air quantity (emission signal of the air flow meter 11 ), the number of revolutions, the load, the amount of injected fuel, etc. are estimated. The temperature of the filter 20 can also be determined by using a map which is prepared in advance from values obtained through experiments. Furthermore, the temperature of the filter 20 can be measured directly by a temperature sensor, for the filter 20 is provided. The thus determined actual temperature of the filter 20 is compared to the target temperature. If the actual temperature of the filter 20 is higher than the target temperature, the amount of fuel added is reduced. If the actual temperature of the filter 20 is lower than the target temperature, the amount of added fuel is increased. Examples of the method of reducing and increasing the amount of added fuel include adjusting the fuel injection interval, adjusting the valve opening duration of the reducing agent injection valve 28 in a process of fuel injection, etc.

When the engine operation is in a low load range, the temperature of the filter becomes 20 maintained at a temperature required for SOx poisoning recovery, bsw. 630 ° C to allow immediate onset of SOx poisoning recovery. In such an operating range, the temperature of the filter 20 maintained at a temperature that allows immediate onset of SOx poisoning recovery to avoid losing an opportunity for SOx poisoning recovery.

In this way, it becomes possible to control the deterioration in fuel economy by decreasing the amount of added fuel during a high load operation range and the deterioration of the exhaust emission by maintaining a high temperature of the filter 20 to avoid losing an opportunity for SOx poisoning recovery.

Although the operating areas in this embodiment are defined using terms such as. For example, as "low load range", "medium load range" and "high load range" are described for the sake of simplicity in the description, the operating ranges are actually divided according to the rotational speed and the load as in 4 is indicated.

In this embodiment, when an operating range that does not allow the SOx poisoning recovery continues for a predetermined time (for example, 3 minutes), the addition of fuel is stopped.

The SOx poisoning recovery control is performed when the load becomes low, as described above. Therefore, there is substantially no opportunity for the SOx poisoning recovery control during a suburban drive, on a highway, or the like. If fuel is added during such an operating condition to a high temperature of the filter 20 Maintaining a considerable time before the execution of SOx poisoning recovery control, so that the fuel consumption increases. Therefore, when such an operating condition continues for a predetermined time (for example, 3 minutes), the addition of fuel is stopped to reduce the deterioration of the fuel economy. The predetermined time before stopping the addition of the fuel may be determined according to the present operating condition.

According to the prior art, the warm-up control is performed when the amount of SOx stored in the NOx catalyst reaches or exceeds a predetermined amount. However, if the warm-up control has not been followed by a low-load operation, the SOx poisoning recovery control is not performed, so that the warm-up control does not have to be performed again, and therefore the fuel consumption increases.

However, the engine emission control device according to this embodiment sets the target temperature of the filter 20 at elevated temperatures for higher SOX poisoning recovery capabilities, so that fuel consumption can be reduced and the opportunities for SOx poisoning recovery fully exploited.

As described above, if the possibility of executing SOx poisoning recovery is higher, the engine emission control apparatus according to the embodiment obtains the higher temperature of the filter 20 upright to avoid losing an opportunity for SOx poisoning recovery. When the possibility of performing SOx poisoning recovery is lower, the emission control device reduces the target temperature of the filter 20 in order to improve the fuel economy and reduce the deterioration of the exhaust emission due to the SOx poisoning of the storage reduction type SOx catalyst.

Second Embodiment

A second embodiment differs from the first embodiment in the following respect. This heals that in the first embodiment, the temperature setting of the filter 20 taking into account the operating condition of the internal combustion engine 1 is performed immediately after the SOx poisoning recovery becomes necessary. However, in the second embodiment, when SOx poisoning recovery becomes necessary, the filter becomes 20 heated to a temperature (eg, 630 ° C) necessary for SOx poisoning recovery.

If the SOx poisoning recovery is not performed at least for a predetermined time (3 min., For example), the warm-up control for the filter becomes 20 performed according to the operating state as in the first embodiment.

Although the second embodiment differs from the first embodiment in that the filter 20 first heated to a predetermined temperature, have the internal combustion engine 1 and other objective elements to which the embodiment is applied basically have the same structure as those in the first embodiment and will not be described below.

In general, it is difficult to predict when the area of operation of the internal combustion engine 1 switch to a low load range. Therefore, in the engine emission control apparatus of the first embodiment, the target temperatures of the filter are 20 correspondingly in operating areas of the internal combustion engine 1 set to the heating of the filter 20 after changing the operating range to the low load range.

However, operation in a high load range continues in some cases, bsw. during a highway trip or the like, and is immediately followed by a low load range for any other case, bsw. during a journey of the vehicle in an urban area or the like.

In this embodiment, when SOx poisoning recovery becomes necessary, the temperature of the filter becomes high 20 raised to a temperature (bsw 630 ° C) necessary for SOx poisoning recovery. If, for a predetermined period of time (3 min., For example), the operating range does not change to an operating range permitting the SOx poisoning recovery to be performed, the temperature of the filter will become 20 according to the operating range for controlling the deterioration of the fuel economy as in the first embodiment controlled.

Therefore, when the SOx poisoning recovery becomes necessary, the temperature of the filter becomes 20 immediately raised to allow SOx poisoning restoration. Then, the SOx poisoning recovery can be performed immediately when an operating state allowing SOx poisoning recovery is achieved. When an operating condition that does not permit the SOx poisoning recovery continues, the temperature of the filter becomes 20 controlled according to the operating state, so that the deterioration in fuel economy can be reduced, and so that when changing to a low load range, the temperature of the filter 20 can be raised quickly.

The engine emission control apparatus of the invention is capable of reducing the deterioration in fuel economy by setting the target temperature of the filter 20 to control in accordance with the operating condition and to increase the opportunities for SOx poisoning recovery by rapidly heating the NOx catalyst when sulfur poisoning recovery is permitted.

While the invention has been described with reference to what is presently considered to be its preferred embodiments, it will be understood that the invention is not limited to the disclosed embodiments or constructions. By contrast, it is intended that the invention cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations including more, less, or a single embodiment are also within the scope of the invention.

Thus, the emission control device includes a NOx catalyst 20 , a warm-up device 28 for heating the NOx catalyst 20 and an operating condition detecting means 33 . 36 for detecting the state of operation of the internal combustion engine 1 , The warm-up device 28 heats the NOx catalyst 20 by setting a target temperature based on an operating condition of the internal combustion engine 1 by the operating state detecting means 33 . 36 is detected. If he is an internal combustion engine 1 is in a high load condition that is not for heating the NOx catalyst 20 is suitable, heats the warm-up device 28 the NOx catalyst 20 Not. Therefore, the emission control device is capable of controlling deterioration in fuel economy, and is capable of rapidly raising the temperature of the NOx catalyst to a temperature that permits sulfur poisoning recovery when a condition required for sulfur poisoning recovery is satisfied.

Claims (10)

Emission control device for an internal combustion engine ( 1 ) with: a NOx catalyst ( 20 ) that absorbs and stores NOx from exhaust gas flowing into the NOx catalyst when an air-fuel ratio of the exhaust gas is on a lean side of a stoichiometric air-fuel ratio and discharges NOx stored when the air-fuel ratio. The fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or to a rich side of the stoichiometric air-fuel ratio; a warm-up device ( 28 ) for performing a warm-up control of the NOx catalyst ( 20 ), when the need to remove a sulfur oxide from the NOx catalyst ( 20 ) results; and an operating state detecting device ( 33 . 36 ) for detecting an operating state of the internal combustion engine ( 1 ), where, if the internal combustion engine ( 1 ) is in a low load state, the warm-up device ( 28 ) a target temperature of the NOx catalyst ( 20 ) is set to a temperature which is necessary for the removal of the sulfur oxide, if the internal combustion engine ( 1 ) is in a high load condition that is not for heating the NOx catalyst ( 20 ), the warm-up device ( 28 ) the NOx catalyst ( 20 ) not heated, characterized in that if the internal combustion engine ( 1 ) is in a medium load condition when the operating condition is approaching a low load region, the warm-up means (15 28 ) the temperature of the NOx catalyst ( 20 ) so that when entering the low load range, the target temperature necessary to remove the sulfur oxide is present. Emission control device according to claim 1, characterized in that when the need to remove the sulfur oxide from the NOx catalyst ( 20 ), the warm-up device ( 28 ) a temperature of the NOx catalyst ( 20 ) temporarily raises to a temperature required for sulfur poisoning recovery, and if the sulfur poisoning recovery is not performed for a subsequent predetermined time, the warm-up means (FIG. 28 ) the NOx catalyst ( 20 by setting a target temperature on the basis of the operating state of the internal combustion engine ( 1 ) heated, the by the operating state detection device ( 33 . 36 ) is detected, and when the internal combustion engine ( 1 ) is in the operating condition that is not for heating the NOx catalyst ( 20 ), the warm-up device ( 28 ) heating the NOx catalyst ( 20 ) avoids. Emission control device according to claim 1 or 2, characterized in that the target temperature of the NOx catalyst ( 20 ), when the internal combustion engine ( 1 ) is in a low-load range, is set higher than when the internal combustion engine ( 1 ) is in a high load range. Emission control device according to one of claims 1 to 3, characterized in that the warm-up control by the warm-up device ( 28 ) is attenuated when an actual temperature of the NOx catalyst ( 20 ) is higher than the target temperature, and that the warm-up control by the warm-up device ( 28 ) is increased when the actual temperature of the NOx catalyst ( 20 ) is lower than the target temperature. Emission control device according to one of claims 1 to 4, characterized in that the warm-up device ( 28 ) the warm-up of the NOx catalyst ( 20 ) stops when an operating condition that does not permit the removal of the sulfur oxide continues for at least a predetermined time while the warm-up device ( 28 ) just the NOx catalyst ( 20 ) is heated. Emission control method of an emission control device of an internal combustion engine ( 1 ) with a NOx catalyst ( 20 ) that absorbs and stores NOx from exhaust gas flowing into the NOx catalyst when an air-fuel ratio of the exhaust gas is on a lean side of a stoichiometric air-fuel ratio and discharges NOx stored when the air-fuel ratio. A fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or a rich side of the stoichiometric air-fuel ratio changes, wherein a warm-up control of the NOx catalyst ( 20 ) is performed when there is a need to remove a sulfur oxide from the NOx catalyst ( 20 ), wherein the emission control method comprises the following steps: detecting an operating state of the internal combustion engine ( 1 ); Setting a target temperature of the NOx catalyst ( 20 ) to a temperature which is necessary for the removal of the sulfur oxide, if the internal combustion engine ( 1 ) is in a low load state; not heating the NOx catalyst ( 20 ), if the internal combustion engine ( 1 ) is in a high load condition that is not for heating the NOx catalyst ( 20 ), characterized by increasing the temperature of the NOx catalyst ( 20 ), if the internal combustion engine ( 1 ) is in a medium load condition when the operating condition is approaching a low load region, so that when entering the low load range, there is the target temperature necessary to remove the sulfur oxide. Emission control method according to claim 6, characterized by the step of temporarily raising a temperature of the NOx catalyst ( 20 ) to a temperature needed for sulfur poisoning recovery when there is a need to remove the sulfur oxide from the NOx catalyst ( 20 ). Emission control method according to claim 6 or 7, characterized in that the target temperature of the NOx catalyst ( 20 ), when the internal combustion engine ( 1 ) is in a low-load range, is set higher than when the internal combustion engine ( 1 ) is located in a high load area. Emission control method according to one of claims 6 to 8, characterized in that a warm-up control of the NOx catalyst ( 20 ) is attenuated when an actual temperature of the NOx catalyst ( 20 ) is higher than the target temperature, and that the warm-up control is boosted when the actual temperature of the NOx catalyst ( 20 ) is lower than the target temperature. Emission control method according to one of claims 6 to 9, characterized in that the heating of the NOx catalyst ( 20 ) is stopped when an operating condition that does not allow the removal of the sulfur oxide continues for at least a predetermined time, while the NOx catalyst ( 20 ) is just warmed up.

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