DE10249880A1 - Emission control device and emission control method of an internal combustion engine - Google Patents

Abstract

An emission control device comprises a NOx catalytic converter (20), a warming-up device (28) for heating the NOx catalytic converter (20) and an operating state detection device (33, 36) for detecting the state of the operation of the internal combustion engine (1). The warming device (28) heats the NOx catalyst (20) by setting a target temperature based on an operating state of the internal combustion engine (1), which is detected by the operating state detection device (33, 36). If the internal combustion engine (1) is in a high-load state which is not suitable for heating the NOx catalytic converter (20), the heating device (28) does not heat the NOx catalytic converter (20). Therefore, the emission control device is able to control deterioration in fuel economy and is able to rapidly raise the temperature of the NOx catalyst to a temperature that allows sulfur poisoning recovery when a condition necessary for the sulfur poisoning recovery is satisfied.

Description

The invention relates to an emission control device and an emission control method 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 field of internal combustion engines installed in motor vehicles and the like, and particularly in lean-burn gasoline engines and diesel engines capable of burn an air-fuel mixture in a state of excess oxygen (commonly 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 inflow of exhaust gas has a high oxygen concentration, and that releases the stored nitrogen oxides (NOx) and reduces them to nitrogen (N ₂ ) caused 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 air / fuel ratio of the exhaust gas 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 their reduction in nitrogen (N ₂ ).

The storage reduction type NOx catalyst absorbs and also stores sulfur oxides (SOx) through the same Mechanism like NOx. Sulfur oxides (SOx) are caused by the Combustion of sulfur components formed in the Fuel are included. SOx in the catalyst stored is less easy to drain than NOx and is therefore collected on the NOx catalyst. The collection of SOx is called sulfur poisoning (SOx poisoning). If the NOx catalyst of the storage reduction type of the SOx If there is poisoning, the NOx removal rate drops. Therefore it is necessary to change the NOx catalyst Poisoning recovery process to restore the NOx catalyst from the SOx poisoning with a suitable Undergo timing. The Poisoning recovery process is caused by that the exhaust gas with a reduced oxygen concentration flows through the NOx catalyst, achieved while the NOx Catalyst is kept at a high temperature (e.g. approximately 600 ° C to 650 ° C).

However, during lean-burn operation Exhaust gas temperature low, so it is not easy to control the NOx To heat the catalyst to a temperature suitable for the Recovery from SOx poisoning is needed if one normal operating condition is maintained. In this However, the situation becomes the supply of a reducing agent (Fuel) in the exhaust gas the oxygen concentration in the Reduce exhaust gas while the temperature of the catalyst increases.

For example. holds one Engine emission control device used in the Japanese Patent Laid-Open No. 11-343836 is essentially the air / fuel ratio used in the NOx catalyst of the storage reduction type flows in, in the Environment of a stoichiometric air-fuel ratio and makes the air / fuel ratio lower intermittently than the stoichiometric air / fuel ratio when the Restoration of the NOx catalyst Storage reduction design from poisoning becomes necessary. Because of this operation, the air / fuel ratio becomes the environment of the stoichiometric air / fuel ratio for most of the time during the Poisoning recovery process held so that Production of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas can be minimized. Since furthermore that Air / fuel ratio intermittently lower than that stoichiometric air / fuel ratio is made is the average air / fuel ratio during the poisoning recovery process at the fuel-rich side (rich side) of the stoichiometric Air / fuel ratio. Therefore, the NOx catalyst can Storage reduction design from sulfur poisoning within be restored in a relatively short time. According to the the aforementioned disclosure is the Poisoning recovery control on the premise performed that the temperature of the NOx catalyst Storage reduction type is, for example, greater than or equal to 300 ° C and that the amount of sulfur oxides that are in the catalyst is stored greater than or equal to a predetermined amount is.

Although the sulfur poisoning recovery by reducing the exhaust air-fuel ratio is performed as described above results in a reduction in Air / fuel ratio during high load operation of the Internal combustion engine an excessively increased temperature of the NOx catalyst of the storage reduction type and therefore can a thermal deterioration of the NOx catalyst Cause memory reduction design.

According to the above-mentioned patent publication the warm-up control of the NOx catalyst Memory reduction design performed when the temperature of the NOx catalyst of the storage reduction type and the amount of Sulfur oxides stored therein, the conditions for Start poisoning recovery control. However, if the warm-up control is not controlled by the operation of the Internal combustion engine is tracked in a low load range, becomes a deterioration in fuel economy due to a long continuing sequel to one High temperature condition of the catalyst caused.

Furthermore, the sulfur poisoning recovery usually during low load engine operation carried out. However, when the warm-up control is started, after the engine operation to the low load area is switched must take a long time before the NOx Storage reduction type catalyst to one temperature is warmed for sulfur poisoning recovery is needed. If during the course of time the condition the operation of the internal combustion engine to a high load area changes is an opportunity for one Sulfur poisoning recovery lost.

The invention was made to achieve the above To solve problems. It is an object of the invention Technology that is able to create a Deterioration in fuel economy Reduce internal combustion engine with a Emission control device is equipped to the Temperature of a NOx catalyst Emission control device to a temperature quickly which is a sulfur poisoning recovery allowed at the time of fulfilling a condition that is needed for sulfur poisoning recovery.

In order to solve the above-mentioned problem, the Invention an emission control device for a Internal combustion engine as follows. That is, one Emission control device of an internal combustion engine according to of the invention comprises: a NOx catalyst, the NOx from an exhaust gas that flows into the NOx catalytic converter, absorbs and stores when an air / fuel ratio of the Exhaust gas is on a lean side of a stoichiometric Air / fuel ratio, and the stored NOx drains when the exhaust gas air / fuel ratio increases the stoichiometric air / fuel ratio or to the rich side of the stoichiometric air / fuel ratio switches; a warm-up device for performing a Warm-up control of the NOx catalyst when a need for Removal of a sulfur oxide from the NOx catalyst results; and an operating state detection device for Detecting a state of the operation of the internal combustion engine. The Warming device heats the NOx catalyst by setting a target temperature based on the state of the operation the internal combustion engine, which by the Operating state detection device is detected. If the Internal combustion engine is in a high load state that is not is suitable to heat the NOx catalyst, warms the Not warming up the NOx catalyst.

According to another aspect of the invention, a Emission control procedure one Emission control device of an internal combustion engine with a NOx catalyst is provided, the NOx from a in the NOx Catalytic converter inflowing exhaust gas is absorbed and stored when an air / fuel ratio of the exhaust gas is on a lean Side of a stoichiometric air / fuel ratio and that releases the stored NOx when that Air / fuel ratio of the exhaust gas to the stoichiometric Air / fuel ratio or to a rich side of the stoichiometric air / fuel ratio changes, where a warm-up control of the NOx catalyst is carried out, when there is a need to remove a sulfur oxide from the NOx catalyst results. The emissions control process points the following steps: Capture an operating state of the Internal combustion engine; Setting a target temperature of the NOx Catalytic converter based on the operating state; and Heating the NOx catalyst towards the target temperature or avoid heating the NOx catalyst when the Internal combustion engine is in a high-load state, which leads to Heating the NOx catalyst is not suitable.

A main feature of the emission control device and the Emission control method thereof according to the invention in that a target temperature of the NOx catalyst according to the operating state of the internal combustion engine is determined and the heating of the NOx catalyst is performed when there is a need to remove a Sulfur oxide from the NOx catalyst, and in that when the engine is in a high load condition where is a sulfur poisoning recovery cannot be carried out, the heating of the NOx Catalyst is avoided. Therefore, it becomes possible to Deterioration in fuel economy to control and the temperature of the NOx catalyst to a Rapidly raise temperature for that Sulfur poisoning recovery is needed if one Operating state is reached, the Sulfur poisoning recovery allowed.

In the engine emission control device and the emission control method thereof as above is described, the heating of the NOx catalyst avoided when the operating state of the internal combustion engine located in an operating area where the recovery are not carried out by sulfur poisoning, for example in a high load operating area. During the High load operating state can be the execution of the Sulfur poisoning recovery the temperature of the NOx Raise catalyst excessively and may cause thermal Cause deterioration of the NOx catalyst. Therefore it is in some cases, although the temperature of the NOx catalyst is not raised during the high load operating range possible to restore the sulfur poisoning after the To raise the temperature. Furthermore increases the temperature to on during the high load operating range certain level due to the heat from the exhaust gas, so the NOx catalytic converter can be quickly heated to the temperature needed for sulfur poisoning recovery. It is often during a freeway or Expressway 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 considerably long time before you switch to one Operating state run for the Sulfur poisoning recovery is needed. Therefore the heating of the NOx catalyst according to the invention avoided when the internal combustion engine is in the High load operating area is located. Therefore, it becomes possible Fuel consumption and control degradation to reduce fuel economy.

If the engine operation is in a different area, For example, a medium load range, the possibility a change to an operating state that the Sulfur poisoning recovery allowed. If the Operating state reaches the low load range, is a Temperature rise of the NOx catalyst due to the temperature of the exhaust gas less likely. If further the Operating state reaches a low load range, the Possibility of changing to an operating state that the Sulfur poisoning recovery allowed higher, so the need to raise the temperature of the NOx catalyst increases.

Therefore, when the engine operation is in the Medium load range, the set temperature of the NOx Catalyst set so that the temperature of the NOx Catalyst becomes higher when the state of the Internal combustion engine operation reaches the low load range. With With this setting it is possible to adjust the temperature of the NOx Catalyst to quickly raise to the temperature required for the Sulfur poisoning recovery is needed if that Operating state of the sulfur poisoning recovery allowed to be achieved and to reduce the amount of fuel, that before performing the sulfur poisoning recovery is consumed.

If, for example, 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 that is suitable for sulfur poisoning recovery. If hence the temperature of the NOx catalyst to the temperature is raised for sulfur poisoning recovery needed, it is possible to Perform sulfur poisoning recovery immediately.

Therefore, it is preferable to set the target temperature of the NOx Catalyst to set higher when the internal combustion engine is in a low load range as if the Internal combustion engine is located in a high-load area.

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

Thus, when the target temperature of the NOx catalyst is on the Changed basis of the operating range of the internal combustion engine becomes, it becomes possible to see the deterioration in terms of Reduce fuel economy and temperature of the NOx catalyst to quickly raise the temperature for sulfur poisoning recovery is needed if that Operating state of the sulfur poisoning recovery allowed, is reached.

According to another form from each aspect of the invention, described above, the heating of the NOx Catalyst are stopped when an operating condition that removal of the sulfur oxide is not permitted continues at least a predetermined time while the NOx Catalyst is heated.

If the above operating state continues and the sulfur poisoning recovery was not performed becomes a high temperature state of the NOx catalyst maintained with deterioration in terms of Fuel economy is effected. Therefore, during stop the heating of the NOx The deterioration in terms of catalyst Reduce fuel economy.

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

In the engine emission control device and the emission control process that is built up like is described above, the NOx catalyst on the Temperature warmed up for that Sulfur poisoning recovery is needed, though a need to recover the NOx catalyst from one Sulfur poisoning results. If the operating status of the Internal combustion engine changes to a low load range sulfur poisoning recovery performed. If however, the engine operation without a change to continues the above-mentioned operating area Fuel consumed at the temperature of the NOx catalyst maintain. Therefore if the Sulfur poisoning recovery not for the predetermined one Duration is carried out, the warm-up control of the NOx Catalyst performed according to the operating range, so that Deterioration in fuel economy can be reduced.

The above embodiment and others exemplary embodiments task features, Advantages, the technical and industrial importance of this Invention will become apparent by reading the following detailed description the exemplary embodiments of the invention below Understanding of the accompanying drawings better understood.

Fig. 1 shows schematically a combustion engine and its intake and exhaust system is applied to an internal combustion engine emission control apparatus according to the embodiments of the invention;

Fig. 2A is a cross sectional view of a particulate filter of the internal combustion engine emission control apparatus according to the embodiments of the invention;

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

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

Fig. 4 is a graph showing 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 more specific with reference to the exemplary ones Described embodiments.

The following is a specific embodiment of a Emission control device for an internal combustion engine according to the invention described with reference to the drawings. The following description deals with an exemplary case in which the emission control device for the Internal combustion engine according to the invention on a Diesel engine used to power a vehicle is.

First embodiment

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

The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke diesel internal combustion engine with four cylinders 2 .

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

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

In the fuel injection system is constructed so, pushes the fuel pump 6, when a rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel at a pressure corresponding to the rotational torque of which is transmitted from the crankshaft to the input shaft of the fuel pump 6 ,

The fuel ejected from the fuel pump 6 is supplied to the common line 4 through the fuel supply pipe 5 and is stored in the common line 4 up to the predetermined pressure and is distributed to the fuel injection valves 3 of the cylinders 2 . When a driving current is applied to the fuel injection valves 3 , the fuel injection valves 3 are opened. As a result, fuel is injected from each of the fuel injection valves 3 into a corresponding one of the cylinders 2 .

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

The intake manifold 8 is connected to an intake pipe 9 which is connected to an air filter box 10 . An air flow meter 11 is attached to the inlet pipe 9 downstream of the air filter box 10 . The air flow meter 11 outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 9 .

An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is disposed at a location in the intake pipe 9 immediately upstream of the intake manifold 8 . The intake throttle valve 13 is provided with an intake throttle actuator 14 , which is formed, for example, by a stepper motor and the like, and which drives the intake throttle valve 13 in the opening and closing directions.

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

In the intake system thus constructed, intake air that has flown into the air cleaner box 10, dust, dirt or the like. By a (not shown) air cleaner purified in the air cleaner box 10 and then flows into the compressor housing 15a via the intake pipe 9 .

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

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

The exhaust manifold 8 is connected to a turbine housing 15 b of the centrifugal charging device 15 . The turbine housing 15 b is connected to an exhaust pipe or an outlet pipe 19 , which is connected at a downstream portion thereof to a silencer (not shown).

A particulate filter (hereinafter simply referred to as a "filter") 20 , which shows a NOx catalyst, is provided on a central portion of the exhaust pipe 19 . An exhaust gas temperature sensor 24 , which emits an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 , is arranged on the exhaust pipe 19 upstream of the filter 20 .

This embodiment is in connection with a Particle filter described with a NOx catalyst Memory reduction design, commonly referred to as is loaded, which absorbs and stores NOx from the exhaust gas flows when the air / fuel ratio of the exhaust gas increases the lean side of a stoichiometric Air / fuel ratio and the stored NOx drains off for reduction, if that Air / fuel ratio of the exhaust gas that flows to the fuel-rich side (rich side) of the stoichiometric Air / fuel ratio changes.

The above air / fuel ratio, which is based on on the lean side means that Exhaust air / fuel ratio within a range so NOx is not through a three-way catalyst can be reduced. An example of this Air / fuel ratio range in the event of a Diesel engine is 20 to 50.

An exhaust throttle valve 25 for adjusting the flow rate of the exhaust gas flowing through the exhaust pipe 19 is disposed in the exhaust pipe 19 downstream of the filter 20 . An exhaust throttle actuator 22 is attached to the exhaust throttle valve 21 . 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) that is burned in each of the cylinders 2 of the engine 1 is discharged to the exhaust manifold 18 through the exhaust port, and then flows from the exhaust manifold 18 into the turbine housing 15 b of the centrifugal charger 15 . The exhaust gas that has flowed into the turbine housing 15 b rotates a turbine wheel due to its hydrodynamic energy. The turbine wheel is rotatably supported in the turbine housing 15 b. During this operation, a rotational torque of the turbine wheel is transmitted to the compressor wheel in the compressor housing 15 a, which is mentioned above.

Exhaust gas that is expelled from the turbine housing 15 b flows into the filter 20 via the exhaust pipe 19 . Therefore, particulate matter (hereinafter referred to as "PM") contained in the exhaust gas is collected and harmful gas components contained in the exhaust gas are removed or chemically modified. After the PMs are collected and harmful gas components removed or reduced by the filter 20 , the exhaust gas is emitted into the atmosphere via the silencer. If necessary, the exhaust throttle valve 21 adjusts the flow rate of the exhaust gas before the emission of the exhaust gas to the atmosphere.

The exhaust manifold 18 and the intake manifold 8 communicate with each other via an exhaust gas recirculation passage (hereinafter referred to as an "EGR passage") 25 , through which a part of the exhaust gas flowing through the exhaust manifold 18 is recirculated into the intake manifold 8 , A flow rate adjustment valve (hereinafter referred to as "EGR valve") 26 is provided at a central portion of the EGR passage 25 . The EGR valve 26 is formed by an electromagnetic valve or the like, and changes the flow rate of the exhaust gas flowing through the EGR passage 25 (hereinafter referred to as "EGR gas") according to the applied electric power.

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

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

In this case, heat in the EGR cooler 27 is exchanged between the EGR gas flowing through the EGR passage 25 and the engine coolant. As a result, the EGR gas is cooled.

The EGR gas recirculated from the exhaust manifold 18 to the intake manifold 8 via the EGR passage 25 mixes with fresh air flowing from an upstream passage from the intake manifold 8 and is introduced into the combustion chambers of the cylinders 2 .

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 e.g. B. 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 generation of nitrogen oxides (NOx) is reduced.

Furthermore, when the EGR gas is cooled in the EGR cooler 27 , the temperature of the EGR gas drops and its volume decreases. 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 decrease in the amount (volume) of fresh air supplied to each combustion chamber.

The filter 20 according to this embodiment will be described below. Figs. 2A and 2B show cross sections of the filter 20. Fig. 2A is a cross-sectional view of the filter 20. Fig. 2B is a longitudinal sectional view of the filter 20. As shown in FIGS. 2A and 2B, the filter 20 has a generally so called wall flow type having a plurality of exhaust flow passages 50, 51 which extend parallel to each other. These exhaust gas flow passages consist of exhaust gas inflow passages 50 with their downstream ends closed by plugs 52 and exhaust gas flow passages 51 with their upstream ends closed by plugs 53 . Note that hatched areas in FIG. 2A indicate plugs 53 . Accordingly, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are arranged alternately with the interposition of thin separators 54 . The Abgaseinströmungsdurchgänge 50 and the Abgasausströmungsdurchgänge are in other words 51 are arranged so that each Abgaseinströmungsdurchgang 50 is surrounded by four Abgasausströmungsdurchgänge 51 and that each Abgasausströmungsdurchgang 51 is surrounded by four Abgaseinströmungsdurchgänge 50th

The filter 20 is made of a porous material, such as. B. cordierite. Therefore, as indicated by arrows in FIG. 2B, the exhaust gas that has flowed into the exhaust gas inflow passages 50 flows out into their adjacent exhaust gas outflow passages 51 through the partition members 54 .

In the embodiment of the invention, support layers made of alumina or the like are formed on peripheral wall surfaces of the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 , namely on both surfaces of each partition member 54 , and on inner wall surfaces of pores which are in the partition members 54 are formed. The support layers are loaded with a NOx catalyst of the storage reduction type.

An operation of the storage reduction type NOx catalyst supported on the filter 20 according to this embodiment will now be described.

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

The NOx catalyst, which is constructed, absorbs and stores nitrogen oxides (NOx) from the exhaust gas when the exhaust gas, that flows into the NOx catalyst, a high one Acid concentration shows.

On the other hand, 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 as. For example, hydrocarbon (HC), carbon monoxide (CO), etc. are present in the exhaust gas, the nitrogen oxides (NOx) released from the NOx catalyst can be reduced to nitrogen (N ₂ ).

When the engine 1 is in a lean-burn operation, the exhaust gas exhausted from the engine 1 exhibits 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, when the lean-burn operation of the engine 1 continues for a long period of time, the NOx storage capacity of the NOx catalyst becomes saturated. As a result, nitrogen oxides (NOx) are not removed from the exhaust gas by the NOx catalyst, but are discharged into the atmosphere.

Particularly in the case of a diesel engine, such as the internal combustion engine 1 , an air-fuel mixture of a lean air / fuel ratio is burned in most operating ranges and therefore shows the exhaust gas lean air / fuel ratios in most operating ranges. Therefore, the NOx storage capacity of the NOx catalyst tends to be saturated.

Therefore, when the internal combustion engine 1 is in the lean-burn operation, it is necessary to decrease the concentration of oxygen contained in the exhaust gas flowing into the NOx catalyst and to increase the concentration of a reducing agent, and the nitrogen oxides (NOx ) to be released from the NOx 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, adding 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 flowing through the exhaust pipe 19 upstream of the filter 20 . The reducing agent supply mechanism supplies fuel to the exhaust gas to reduce the concentration of oxygen contained in the exhaust gas flowing into the filter 20 and to increase the concentration of the reducing agent.

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

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

The reducing agent injected into the exhaust manifold 18 from the reducing agent injection valve 28 reduces the oxygen concentration of the exhaust gas that has flowed from an upstream portion of the exhaust manifold 18 .

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 the nitrogen oxides to be reduced.

The reductant injector 28 then closes in response to a signal from the ECU 35 , thereby interrupting the addition of the reductant to the exhaust manifold 18 .

In this embodiment, fuel is added to the exhaust gas by injection. However, it is also suitable to carry out the low temperature combustion. In the low-temperature combustion, the amount of soot that is produced increases as the amount of EGR gas is increased, and then the amount of soot that is produced is maximized. Then, if the amount of 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. It is therefore suitable to inject fuel from the fuel injection valves 3 during the expansion stroke, an exhaust stroke or the like of the internal combustion engine 1 .

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

Various sensors, such as B. the pressure sensor 4 a of the common line, the air flow network device 11 , the exhaust gas temperature sensor 24 , a crank position sensor 33 , an accelerator actuation sensor 36 , etc. are connected to the ECU 35 via electrical wiring. Output signals from the various sensors are input to the ECU 35 .

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

As shown in FIG. 3, the ECU 35 has a CPU 351 , a ROM 352 , a RAM 353 , an auxiliary RAM 354 , an input port 356 and an output port 357 which are connected by a bidirectional bus 350 . The ECU 35 also has an A / D converter (A / D) 355 connected to the input port 356 .

The input port 356 receives an input of signals that are output from the sensors that are configured to output digital signals, such as e.g. The crank position sensor 33 and the like, and transmits them to the CPU 351 or the RAM 353 .

The input terminal 356 receives the input of signals that are output by the sensors that are designed to output analog signals, such as. B. the pressure sensor 4 a of the common line, the air flow meter 11 , the temperature sensor 24 , the coolant temperature sensor 34 , the accelerator actuation sensor 36 , etc. via the A / D 355 and transmits these signals to the CPU 351 or the RAM 353 .

The output port 357 is connected 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 , the shutoff valve 31 , etc. through electrical wiring. Control signals output from the CPU 351 are transmitted 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 shutoff valve 31 via the output port 357 .

The ROM 352 stores application programs such as. B., 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 , a NOx purification control routine for discharging absorbed NOx Reducing agent to the filter 20 , a sulfur poisoning recovery control routine to recover the filter 20 from SOx poisoning, and a PM combustion control routine to burn and remove the PMs collected by the filter 20 , etc.

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

Examples of the control pictures include a fuel injection quantity control map indicating the relation between operating states of the internal combustion engine 1 and base fuel injection amounts (base fuel injection periods), a fuel injection timing control map that indicates the relationship between operating conditions of the internal combustion engine 1 and base fuel timings, an intake throttle valve opening control map showing the relation between operational states of the internal combustion engine 1 and target opening degrees of the intake throttle valve 13 indicates an exhaust throttle valve opening control map indicating the relationship between operating states of the engine 1 and target opening degrees of the exhaust throttle valve 21 , an EGR valve opening control map indicating the relationship between operating states of the internal combustion engine 1 and target opening degrees of the EGR valve reducing amount 26 control map indicating the relationship between operating conditions of the internal combustion engine 1 and target amounts of reductant to be added (or target air-fuel ratios of the exhaust gas), a reductant injector control map indicating the relationship between target amounts of the added reductant and valve opening times of the reductant injector 28 , and the like.

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

The auxiliary RAM 354 is a non-volatile memory capable of holding data even when the engine 1 is stopped.

The CPU 351 operates in accordance with the application programs stored in the ROM 352 and performs fuel injector control, intake throttle control, exhaust throttle control, EGR control, NOx elimination control, poisoning recovery control, PM combustion control, and the like.

For example, during the NOx purification control, the CPU 351 performs so-called pulse peak fat control, in which the concentration of oxygen contained in the exhaust gas flowing into the filter 20 is peaked (within a short time) with a relatively short cycle.

In the pulse peak control, the CPU 351 determines in a predetermined cycle whether a condition for performing the pulse peak control has been met. 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 output signal of the exhaust gas temperature sensor 24 (exhaust gas temperature) is less than or equal to a predetermined upper limit value, a condition that the poisoning recovery control is not currently being performed will, etc.

If it is determined that the condition has been met for performing the pulse peak rich control, as has been described above, the CPU 351 controls the reducing agent injection valve 28 to inject pulse peak shape around the fuel as a reducing agent from the reducing agent injection valve 28th Thus, the CPU 351 temporarily makes the air-fuel ratio of the exhaust gas flowing into the filter 20 equal to a predetermined rich target air-fuel ratio.

More specifically, the CPU 351 reads an engine speed stored in the RAM 353 , an output signal of the accelerator operation sensor 36 (the depression amount of the accelerator pedal), an output 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 on.

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

Subsequently, the CPU 351 accesses the reducing agent injection control map stored in the ROM 352 using the target addition amount as a parameter, and calculates a valve opening duration (target valve opening duration) of the reducing agent injection valve 28 that is used to inject the target addition amount of the reducing agent the reducing agent injection valve 28 is required.

When the target valve opening period of the reductant injection valve 28 is calculated, the CPU 351 opens the reductant injection valve 28 .

When the target valve opening period expires following the opening of the reducing agent injection valve 28 , the CPU 351 closes the reducing agent injection valve 28 .

Thus, when the reductant injection valve 28 is opened for the target valve opening period, the target addition amount of fuel is injected from the reductant injection valve 28 into the exhaust manifold 18 . The reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas that has flowed from an upstream portion of the exhaust manifold 18 , and forms a mixture that has the target air-fuel ratio, and then flows into the filter 20th

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

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

Note that the internal combustion engine 1 can use a fuel containing sulfur (S). When such a fuel burns in the internal combustion engine 1 , sulfur oxides (SOx) such as. B. sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), etc. generated.

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

More specifically, when the exhaust gas flowing into the filter 20 shows a high oxygen concentration, sulfur oxides (SOx) contained in the exhaust gas, such as e.g. B. sulfur dioxide (FO ₂ ), sulfur trioxide (SO ₃ ) etc. on the surfaces of platinum (Pt) oxidized and absorbed and stored by the filter 20 in the form of sulfate ions (SO ₄ ^2- ). The sulfate ions (SO ₄ ^2- ), which are thus absorbed by the filter 20 , 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 nitride (Ba (NO ₃ ) ₂ ). Even if the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low, the sulfate (BaSO ₄ ) remains in the filter 20 without being decomposed.

As the amount of sulfate (BaSO ₄ ) in 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 causes deterioration of the NOx absorption ability of the filter 20 .

In an exemplary method of recovering the filter 20 from sulfur poisoning, the atmospheric temperature of the filter 20 is raised to a high temperature range of approximately 600 ° C to 650 ° C and the oxygen concentration of the exhaust gas flowing into the filter 20 is reduced. As a result, barium sulfate (BaSo ₄ ) stored in the filter 20 is thermally decomposed into SO ₃ ^- and SO ₄ ^- . Then SO ₃ ^- and SOC are caused to react with hydrocarbons HC and carbon monoxide CO contained in the exhaust gas and thus reduced to gaseous SO ₂ ^- .

In the poisoning recovery process according to this embodiment, therefore, the CPU 351 first performs catalyst warm-up 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 catalyst warm-up control, the CPU 351 causes the reductant injection valve 28 to inject fuel so that the fuel in the filter 22 is oxidized. The temperature of the filter 20 is raised due to the heat generated by the oxidation. The amount of fuel that is injected from the reductant injector 28 in this case is set so that the injection duration is shorter and the air-fuel ratio is higher compared to the fuel injection from the reductant injector 28 that is performed to discharge and reduce NOx becomes.

In the catalyst warm-up control, the CPU 351 or the like. be configured to inject fuel from each of the fuel injection valves 3 secondary during an expansion stroke of a corresponding cylinder 2 and to add fuel to the exhaust gas from the reducing agent injection valve 28 so that unburned components of the fuel in the filter 20 are oxidized. Due to the heat generated by the oxidation, the catalyst temperature of the filter 20 can be raised.

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

If the catalyst temperature of the filter 20 to a high temperature range of BSW. increases about 630 ° C by the above catalyst warm-up process, the CPU 351 causes the reductant injection valve 28 to inject fuel to decrease the oxygen concentration of the exhaust gas flowing into the filter 20 .

If an excessive amount of fuel is injected from the reductant injection valve 28 , the filter 20 may be overheated by rapid combustion of the fuel. Instead, an excessive amount of fuel injected from the reductant injector 28 may undesirably cool the filter 20 . It is therefore preferable that the CPU 351 perform feedback control of the fuel injection amount from the reductant injection valve 28 based on 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 exhaust gas flowing into the filter 20 lowers under the condition that the catalyst temperature of the filter 20 is high. Therefore, barium sulfate (BaSo ₄ ) stored in the filter 20 is thermally decomposed into SO ₃ ^- and SO ₄ ^- . The SO ₃ ^- and SO ₄ ^- reacts with hydrocarbon HC and carbon monoxide CO contained in the exhaust gas and is reduced, thereby eliminating the sulfur poisoning of the filter 20 .

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

However, if the fueling for the filter 20 is avoided to reduce the deterioration in fuel economy, the temperature of the filter 20 will drop so that the SOx poisoning recovery cannot be performed immediately when the engine operation changes 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 is controlled and maintained in accordance with the engine operating condition to achieve both temperature maintenance of the filter 20 and reduction or prevention of fuel economy deterioration.

Fig. 4 illustrates an image that indicates a relationship between the engine speed, the engine load and the target temperature of the filter 20. This map is stored in advance in the ROM 352 . In the illustration, the hatched area is an area of bsw. 630 ° C and the target temperature of the filter 20 gradually decreases with an increase in the distance from the hatched area. In FIG. 4 is an internal combustion engine operating region in which the target temperature of the filter is 20 to 500 ° C, indicated representatively.

In a high load range, the temperature of the filter 20 becomes high, e.g. 550 ° C, without adding fuel due to the high exhaust gas temperature and the large flow rate of the exhaust gas. When engine operation changes from the high load range to a low load range, the temperature of the filter 20 may be to a temperature required for SOx poisoning recovery, e.g. 630 ° C can be raised 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 changes to another operating range.

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

In this case, the CPU 351 reads an output signal from the crank position sensor 33 (speed) and an output signal from the accelerator operation sensor 36 (load) and calculates a target temperature of the filter 20 by using these values in the map of FIG. 4. Then the CPU 351 reads in Output signal of the exhaust gas temperature sensor 24 and estimates a temperature of the filter 20 . The temperature of the filter 20 is estimated from the intake air amount (output signal of the air flow meter 11 ), the rotational speed, the load, the amount of fuel injected, etc. The temperature of the filter 20 can also be determined using a map prepared in advance from values obtained through experiments. Furthermore, the temperature of the filter 20 can be measured directly by a temperature sensor which is provided for the filter 20 . The actual temperature of the filter 20 determined in this way is compared with 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 fuel added is increased. Examples of the method of decreasing and increasing the amount of fuel added include adjusting the fuel injection interval, adjusting the valve opening duration of the reducing agent injection valve 28 in a fuel injection operation, etc.

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

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

Although the operating areas in this embodiment use terms such as e.g. B. "low load range", "medium load range" and "high load range" are described for simplification in the description, the operating ranges are actually divided according to the speed and the load, as indicated in Fig. 4.

In this embodiment, if an operating range that the SOx poisoning recovery not allowed to sign up for a predetermined time (or 3 min.) continues, the addition of Fuel stopped.

The SOx poisoning recovery control is performed when the load becomes low, as described above. Therefore, there is essentially no opportunity for SOx poisoning recovery control while driving in a suburb, on a highway, or the like. If fuel is added during such an operating condition to maintain a high temperature of the filter 20 , it takes a considerably long time before execution of the SOx poisoning recovery control, so that the fuel consumption increases. Therefore, when such an operating condition continues for a predetermined time (e.g. 3 minutes), the addition of fuel is stopped to reduce the deterioration in fuel economy. The predetermined time before stopping the addition of the fuel can be determined according to the present operating state.

According to the prior art, the warm-up control performed when the amount of SOx contained in the NOx catalyst is stored, a predetermined amount is reached or exceeds. However, if the warm-up control does not go through has followed a low load operation, the SOx Poisoning recovery control not performed, so that the warm-up control does not have to be carried out again, and therefore 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 operating areas with higher possibilities of performing the SOx poisoning recovery so that the fuel consumption can be reduced and the opportunities for the SOx poisoning recovery can be fully used.

As described above, when the possibility of performing the SOx poisoning recovery is higher, the engine emission control device according to the embodiment maintains the higher temperature of the filter 20 to avoid losing an opportunity for the SOx poisoning recovery. When the possibility of performing the SOx poisoning recovery is less, the emission control device lowers the target temperature of the filter 20 to improve the fuel economy and decrease the deterioration of the exhaust gas emissions due to the SOx poisoning of the memory reduction type SOx catalyst.

Second embodiment

A second embodiment differs from the first embodiment in the following respects. That is, in the first embodiment, the temperature setting of the filter 20 is performed in consideration of the operating state of the engine 1 immediately after SOx poisoning recovery becomes necessary. However, in the second embodiment, when SOx poisoning recovery becomes necessary, the filter 20 is heated to a temperature (e.g., 630 ° C) necessary for the SOx poisoning recovery.

If the SOx poisoning recovery is not performed for at least a predetermined time (3 minutes, for example), the warm-up control for the filter 20 is 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 is first heated to a predetermined temperature, the internal combustion engine 1 and other object elements to which the embodiment is applied have basically the same structure as those in the first Embodiment and are not described below.

In general, it is difficult to predict when the area of operation of the engine 1 will change to a low load area. Therefore, in the engine emission control device of the first embodiment, the target temperatures of the filter 20 are set accordingly in operating areas of the engine 1 to allow the filter 20 to be heated after the operating area changes to the low-load area.

However, the operation continues in a high load area some cases, e.g. during a motorway trip or the like, and is immediately by a low load area followed for any other case, e.g. while driving of the vehicle in an urban area or the like.

In this embodiment, when SOx poisoning recovery becomes necessary, the temperature of the filter 20 is raised to a temperature (e.g. 630 ° C) necessary for SOx poisoning recovery. If the operating range does not change to an operating range that allows SOx poisoning recovery to be performed for a predetermined period (e.g., 3 minutes), the temperature of the filter 20 is controlled according to the operating range to control deterioration in fuel economy as in the first embodiment ,

Therefore, when SOx poisoning recovery becomes necessary, the temperature of the filter 20 is immediately raised to allow the SOx poisoning recovery. Then the SOx poisoning recovery can be performed immediately when an operating state that allows the SOx poisoning recovery is reached. If an operating state that does not allow SOx poisoning recovery continues, the temperature of the filter 20 is controlled in accordance with the operating state, so that the deterioration in fuel economy can be reduced, and so when changing to a low load range, the temperature of the filter 20 can be raised quickly.

The engine emission control device of the invention is able to control the deterioration in fuel economy by setting the target temperature of the filter 20 according to the operating state and increase the opportunities for SOx poisoning recovery by quickly heating the NOx catalyst when sulfur poisoning recovery is allowed.

While the invention is described with reference to what currently considered as their preferred embodiments it is understandable that the invention does not apply to the disclosed embodiments or constructions limited is. In contrast, it is intended that the invention various modifications and equivalent arrangements covers. In addition, while the various elements of the disclosed invention in various combinations and Configurations shown that are exemplary are others Combinations and configurations including more, less or a single embodiment also within the Scope of the invention.

Thus, the emission control device includes a NOx catalytic converter 20 , a warming-up device 28 for heating the NOx catalytic converter 20 and an operating state detection device 33 , 36 for detecting the state of the operation of the internal combustion engine 1 . The heating device 28 heats the NOx catalyst 20 by setting a target temperature based on an operating state of the internal combustion engine 1 , which is detected by the operating state detection device 33 , 36 . If the internal combustion engine 1 is in a high-load state that is not suitable for heating the NOx catalytic converter 20 , the warming-up device 28 does not heat the NOx catalytic converter 20 . Therefore, the emission control device is able to control deterioration in fuel economy and is able to rapidly raise the temperature of the NOx catalyst to a temperature that allows sulfur poisoning recovery when a condition necessary for the sulfur poisoning recovery is satisfied.

Claims (10)

1. Emission control device for an internal combustion engine ( 1 ) with:
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-fuel ratio, and the stored NOx emits 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 up means ( 28 ) for performing warming up control of the NOx catalyst ( 20 ) when there is a need 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 the emission control device is characterized in that the heating device ( 28 ) heats the NOx catalyst ( 20 ) by setting a target temperature based on the operating state of the internal combustion engine ( 1 ) detected by the operating state detection device ( 33 , 36 ), or that the heating device ( 28 ) does not heat the NOx catalytic converter ( 20 ) when the internal combustion engine ( 1 ) is in a high-load state which is not suitable for heating the NOx catalytic converter ( 20 ). 2. Emission control device according to claim 1, characterized in that when there is a need to remove the sulfur oxide from the NOx catalyst ( 20 ), the heating device ( 28 ) temporarily raises a temperature of the NOx catalyst ( 20 ) to a temperature which is required for sulfur poisoning recovery, and if the sulfur poisoning recovery is not performed for a subsequent predetermined time, the warmer ( 28 ) heats the NOx catalyst ( 20 ) by setting a target temperature based on the operating state of the internal combustion engine ( 1 ) by the Operating state detection device ( 33 , 36 ) is detected, and when the internal combustion engine ( 1 ) is in the operating state which is not suitable for heating the NOx catalyst ( 20 ), the heating device ( 28 ) heating the NOx catalyst ( 20 ) avoids. 3. 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 located. 4. 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 weakened 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 amplified when the actual temperature of the NOx catalyst ( 20 ) is lower than the target temperature. 5. Emission control device according to one of claims 1 to 4, characterized in that the heating device ( 28 ) stops the heating of the NOx catalyst ( 20 ) when an operating state that does not allow removal of the sulfur oxide continues for at least a predetermined time while the heating device ( 28 ) is heating the NOx catalyst ( 20 ). 6. 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 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 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, with 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 ), characterized in that 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 ) based on the operating state; and
Heating the NOx catalyst ( 20 ) towards the target temperature or avoiding heating of the NOx catalyst ( 20 ) when the internal combustion engine ( 1 ) is in a high-load state that is not suitable for heating the NOx catalyst ( 20 ) , 7. The emission control method according to claim 6, characterized by the step of temporarily raising a temperature of the NOx catalyst ( 20 ) to a temperature required for sulfur poisoning recovery when there is a need to remove the sulfur oxide from the NOx catalyst ( 20 ). results. 8. Emission control method according to claim 6 or 7, characterized in that the target temperature of the NOx catalytic converter ( 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 area. 9. Emission control method according to one of claims 6 to 8, characterized in that a warm-up control of the NOx catalyst ( 20 ) is weakened when an actual temperature of the NOx catalyst ( 20 ) is higher than the target temperature, and that the warm-up control is enhanced when the actual temperature of the NOx catalyst ( 20 ) is lower than the target temperature. 10. 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 state that does not allow removal of the sulfur oxide continues for at least a predetermined time during the NOx -Catalyst ( 20 ) is being warmed up.