DE10143780A1 - Emission control device and method for an internal combustion engine - Google Patents

Abstract

A lean-burn type internal combustion engine emission control device includes a NOx catalyst (20) disposed in an exhaust passage (18) of the engine for absorbing nitrogen oxides when the exhaust gas is lean on fuel and releasing the absorbed Nitrogen oxides when the exhaust gas is rich in fuel. The emission control device performs a NOx removal process to release and reduce nitrogen oxides absorbed in the NOx catalyst, and performs a poisoning elimination process to eliminate poisoning of the NOx catalyst due to oxides. The device further includes an air-fuel ratio sensor (23), which is configured in the exhaust passage, for checking an air-fuel ratio of the exhaust gas. An output signal of the air-fuel sensor is corrected based on an output signal generated by the air-fuel ratio sensor during the execution of the poisoning elimination process, and the corrected output signal is used for subsequent control by the Emission control device is executed.

Description

The invention relates to an emission control device and a method of controlling exhaust gases from a Internal combustion engine are ejected, and especially one Emission control device and method to essentially remove nitrogen oxides from exhaust gases from an engine.

In the field of internal combustion engines used in motor vehicles and the like are installed, in particular by Diesel engines or lean or lean burning Gasoline engines that are an air-fuel mixture in one Can burn excess oxygen state (what as "Lean" or "lean air-fuel mixture" called there has been a need in recent years improved technique to reduce or remove Nitrogen oxides (NOx), which are contained in exhaust gases from the engine.

In order to meet this need described above, is been proposed in a slim NOx catalyst to provide an exhaust system of the internal combustion engine. A well-known example of a lean NOx catalyst is one Storage reduction type NOx catalyst which Nitrogen oxides (NOx) are absorbed from the exhaust gas when the Exhaust gas oxygen concentration is high, and which releases absorbed nitrogen oxides (NOx) and the oxides too Nitrogen (N2) reduces when the oxygen concentration of the exhaust gas is low and a reducing agent around the Catalyst around.

With the storage reduction type NOx catalyst installed in the engine exhaust system, nitrogen oxides (NOx) contained in the exhaust gas are absorbed into the NOx catalyst when the engine is operating in a lean-burn mode, and thus the air-fuel Exhaust gas ratio high. When the air-fuel ratio of the exhaust gas entering the storage reduction type NOx catalyst is decreased or enriched, the nitrogen oxides (NOx) stored in the NOx catalyst are released and become nitrogen (N ₂ ) reduced.

Because there is a limit to the NOx absorption capacity of the storage reduction type NOx catalyst, the NOx absorption capacity of the NOx catalyst is ge saturates when the internal combustion engine is in a lean Combustion mode is operated for a long time, and the Nitrogen oxides (NOx) contained in the exhaust gas are sent to the Atmosphere released without being removed by the NOx catalyst to become.

It is therefore necessary if the NOx catalyst is from Storage reduction type in a lean-burning interior Internal combustion engine is applied in the NOx catalyst absorbed nitrogen oxides (NOx) are released and reduced by using a so-called enrichment peak control is performed at which an air-fuel ratio of the exhaust gas entering the NOx catalyst is reduced before the NOx absorption capacity of the NOx catalyst is saturated.

In an example of a method of enrichment peak Control is a fuel that acts as a reducing agent serves to the exhaust gas, which is upstream of the NOx Storage-reduction type catalyst flows.

In the case where the reducing agent to the exhaust gas is added, which is upstream of the NOx catalyst flows, it is equally important to add the amount of To control the reducing agent precisely in accordance with the stored in the storage reduction type NOx catalyst Nitrogen oxides (NOx).  

If an excessive amount of the reducing agent is added with respect to that in the NOx catalyst Storage reduction type stored nitrogen oxides (NOx) to be precise, an excess or an unnecessary amount of Reducing agent released into the atmosphere. When a insufficient amount of the reducing agent is added in Reference to the nitrogen oxides stored in the NOx catalytic converter (NOx), the NOx absorption capacity of the NOx catalyst saturated, and nitrogen oxides (NOx) in the exhaust gas to the Atmosphere released without being removed by the NOx catalyst to become.

In view of the problem described above is one Emission control device for an internal combustion engine as proposed in the Japanese patent 2,845,056. The one disclosed in this patent Emission control device determines an amount of to add giving reducing agent, the amount of the reducing means that through reductions with that contained in the exhaust gas Oxygen is consumed, and the amount of reducing agent means for reducing the ge in the NOx catalyst stored nitrogen oxides (NOx) are required to be pulled. Because of the excess amount determined in this way the device tries to find excess or insufficient Prevent supply of the reducing agent, and suppressed thereby affecting the exhaust emissions due to the Release of reducing agents or nitrogen oxides (NOx) to the The atmosphere.

In the known emission tax pre-described above the amount of gas contained in the exhaust gas Oxygen and that in the NOx catalyst from the storage Reduction-type stored amount of NOx required for maintenance the amount of reducing agent which is caused by the reaction with the oxygen in the exhaust gas consumed by the NOx catalyst  was, as well as the amount of reducing agent to reduce adorn the nitrogen oxides stored in the NOx catalyst (NOx) is required.

To increase the amount of oxygen contained in the exhaust gas get an oxygen sensor or air-fuel Ratio sensor designed in a part of the exhaust gas path, which downstream of the NOx catalyst from the storage Reduction type lies, and during the execution of the series peak control is the amount added Reducing agent controlled by a feedback that on a value of an output signal of the oxygen sensor or the air-fuel ratio sensor (where the value is indicates actual exhaust air-fuel ratio).

The output signal of the oxygen sensor or the air However, the fuel ratio sensor can vary from the nominal value deviate due to z. B. Chronological changes or damage to the sensor. If the amount of sour substance or the amount of reducing agent, which from the Output of the sensor is obtained from the actual one Amount of oxygen or the actual amount of reduk deviates, it becomes difficult to determine the amount of control the given reducing agent, and in some Cases can be affected due to exhaust emissions of excess or insufficient supply of the reduction means.

The object of the invention is to provide an engine emission control direction to provide the nitrogen oxides (NOx) Exhaust gases essentially removed by a combination of one lean NOx catalyst and an enrichment peak Control where an output value of the in an exhaust path designed air-fuel ratio sensor suitable is corrected so that the air-fuel ratio can be adequately controlled by feedback,  thereby avoiding deterioration in exhaust emissions becomes.

To achieve this object, the invention provides an emission control device for a lean-burn type internal combustion engine capable of burning an air-fuel mixture having a lean air-fuel ratio, the device comprising:

• 1. one in an exhaust gas path of the internal combustion engine provided NOx catalyst, the NOx catalyst so is designed that nitrogen oxides contained in the exhaust gas be absorbed when the exhaust gas is a high air-fuel Has ratio, and nitrogen oxides stored therein be released when the exhaust gas has a low air Has fuel ratio;
• 2. a NOx removal control device for executing a NOx removal process to be absorbed in the NOx catalyst dispose of and reduce nitrogen oxides;
• 3. a poisoning elimination control device for Running a poisoning elimination process so that poisoning of the NOx catalyst due to oxides is eliminated;
• 4. an air-fuel ratio sensor device for Perceiving an air-fuel ratio of the exhaust gas, which is established in the exhaust path; and
• 5. an air-fuel ratio correction device for Correcting an Output Signal of Air-Fuel Ratio sensor device based on an output signal from the air-fuel ratio sensor establishment during the execution of the poisoning elimination process was created, with the corrected output signal is used for the subsequent control, the is carried out by the emission control device.

In the emission tax constructed as described above device for internal combustion engines when the engine is in  is operating in a lean burning mode that Exhaust gas fuel ratio increases (i.e., the exhaust gas becomes Low in fuel), and therefore that is contained in the exhaust gas NOx absorbed into the NOx catalyst. If that in the NOx To release and reduce catalyst-absorbed NOx the NOx removal controller performs the NOx removal process to determine the NOx stored in the NOx catalytic converter deliver and reduce.

If necessary, poisoning of the NOx catalyst due to eliminating oxides, the poisoning leads Elimination Control Device The Poisoning Elimination development process. Since it is necessary that in the NOx catalyst there is a reducing atmosphere around which the NOx Eliminating catalyst poisoning oxides reduces the Poisoning Elimination Controller That Air Force Substance ratio of the exhaust gas, which is in the NOx catalyst enters, down, e.g. B. on the stoichiometric value or continue to maintain a high air-fuel ratio.

If NOx and / or stored O _{2 is released} from the NOx catalyst during an early phase of the poisoning elimination process, the air-fuel ratio of the exhaust gas flowing out of the NOx catalyst changes to a predetermined one Value close to the stoichiometric air-fuel ratio. It is thus understood that the air-fuel ratio sensor device is assumed to be in a deteriorated or damaged condition when the output value is given by the air-fuel ratio sensor device during the early phase of the poisoning elimination process is generated, is not the same or deviates substantially from the predetermined value.

Because the poisoning elimination process lasts for a long time Duration when the NOx removal process is carried out  also apparent changes in the exhaust air / fuel Ratio due to emissions from the NOx catalyst NOx probably observed.

When the output value of the air-fuel ratio sensor establishment during the early phase of poisoning elimi nation process with the predetermined value (which corresponds to the Output value of the air-fuel ratio sensor device corresponds if it is new), and there is one Deviation or difference between these two Values, the output value of the air-fuel Ratio sensor device based on the thus obtained Deviation can be corrected.

As a result, the air-fuel ratio can be sufficient high accuracy can be measured, and control measures, z. B. Adding a reducing agent to the NOx catalyst or injecting fuel into the engine, can on the Basis of the air-fuel ratio obtained in this way be carried out in a suitable manner.

The above and other tasks, features and pre parts of the invention will become apparent from the following description of the preferred embodiments with reference to the at attached drawings, in which like reference numerals for same elements are used, clearly:

Fig. 1 is a schematic diagram illustrating the structure of an internal combustion engine and its entry and exhaust gas systems, in which an emission control apparatus of the invention is applied in accordance with;

Fig. 2A is a diagram of an NOx catalyst by the control-reduction type NOx illustrates a Absorptionsmechanis mus;

Fig. 2B is a diagram of the NOx discharge mechanism of the storage reduction type NOx catalyst;

Figure 3 is a block diagram illustrating the internal structure of an ECU.

Fig. 4 is a graph showing the predetermined values and tatsäch rior value of the exhaust gas air-fuel ratio on the downstream side during the poisoning elimination process indicates; and

Fig. 5 is a flow diagram illustrating a poisoning elimination control routine illustrated.

An emission control device of an internal combustion engine according to a preferred embodiment of the invention hereinafter with reference to the accompanying drawings described.

In the preferred embodiment, the emission Control device in a diesel engine for driving a Motor vehicle, such as a motor vehicle, applied.

Fig. 1 is a schematic diagram illustrating the construction of an internal combustion engine using the emission control device of the invention and its intake and exhaust systems. The Ver shown in FIG. 1 brennungsmotor 1 is a water-cooled diesel engine has four-stroke cycle, the four cylinder 2.

The engine 1 has fuel injection valves 3 for injecting fuel directly into the combustion chamber of the corresponding cylinder 2 . The fuel injection valves 3 are connected to an accumulator or a common rail 4 in which the pressure of the fuel is raised to a predetermined level. The common rail 4 is equipped with a pressure sensor for the common rail 4 a, which outputs an electronic signal that indicates the pressure of the fuel in the common rail 4 .

The common rail 4 is connected via a fuel supply line 5 to the fuel pump 6 . The fuel pump 6 is operated using the torque of an output shaft (crankshaft) of the engine 1 as its drive source. A pump pulley 6 a, which is saddled on an input shaft of the fuel pump 6 , is connected via a belt 7 to a crank belt 1 a, which is saddled on the output shaft (crankshaft) of the engine 1 . In the fuel injection system constructed as described above, the torque of the crankshaft is transmitted to the input shaft of the fuel pump 6 , so that the fuel pump 6 delivers fuel at a pressure corresponding to the torque from the crankshaft to the input shaft of the Fuel pump 6 is transmitted.

The fuel supplied by the fuel pump 6 is supplied to the common rail 4 via the fuel supply line 5 . After the fuel pressure is raised to a predetermined level in the common rail 4 , fuel is distributed to the fuel injection valves 3 of the respective cylinders 2 . When a drive current is applied to a specific fuel injection valve 3 , the fuel injection valve 3 is opened so that fuel from the injection valve 3 is injected into a specific one of the combustion chambers of the cylinder 2 .

An inlet duct 8 is connected to the engine 1 . The inlet duct 8 has branch pipes which are connected to the respective combustion chambers of the cylinder 2 via corresponding inlet connection points (not shown).

The inlet duct 8 is connected to an inlet pipe 9 , which in turn is connected to an air cleaning box 10 . An air flow meter 11 and an inlet air temperature sensor 12 are arranged downstream of the air cleaning box 10 in the inlet line 9 . The air flow meter 11 generates an electrical signal corresponding to the mass of the air entry flowing through the inlet line 9 and the air inlet temperature sensor 12 generates an electrical signal corresponding to the temperature of the air entry flowing through the inlet line 9 .

An inlet throttle valve 13 for adjusting the amount of the air inlet flowing through the inlet line 9 is provided on a part of the inlet line 9 which is located directly above the inlet duct 8 . The intake throttle valve 13 is fitted with the throttle switch 14 which consists of a stepping motor or the like and can operate so that the throttle valve 13 is driven to open or close the valve. 13

A compressor housing 15 a is designed in the inlet line 9 between the air flow meter 11 and the inlet throttle valve 13 . The housing 15 a houses a centrifugal supercharger (turbocharger), which is operated using the thermal energy of the exhaust gas as a drive source. An intercooler 16 is also configured in the inlet line 9 so that it is located downstream of the compressor housing 15 a. The intercooler 16 is used to cool the intake air, the temperature of which was increased while it was compressed in the compressor housing 15 a.

In the intake system constructed as described above, the intake air passes through the air cleaning box 10 , so that dust, dirt and the like are removed from the intake air by means of an air cleaner (not shown), which is configured in the air cleaning box 10 , and then into the compressor housing 15 a flows through the inlet line 9 .

The intake air that has entered into the compressor housing 15a is a housing within the compressor a compressor blade designed compressed by rotation of 15 °. The intake air, which is compressed and heated in the compressor housing 15 a, is cooled by the intercooler 16 and then flows into the intake duct 8 , its amount being adjusted as required by the intake throttle valve 13 . The intake air that has entered the intake port 8 is distributed to the respective combustion chambers of the cylinders 2 via corresponding branch pipes. In each combustion chamber, the intake air is burned with fuel which serves as an ignition source and which is injected from one of the corresponding fuel injection valves 3 .

On the other hand, an exhaust duct 18 is connected to the engine 1 . Branch pipes of the exhaust gas channel 18 communicate with the respective combustion chambers of the cylinder 2 via corresponding exhaust gas connections.

The exhaust duct 18 is connected to a turbine housing 15b of the centrifugal supercharger 15, respectively. The turbine housing 15 b is connected to an exhaust pipe 19 , which in turn is connected at its downstream end to a silencer (not shown).

An exhaust gas purification catalytic converter 20 for removing harmful gas components from the exhaust gases is provided halfway along the exhaust gas line 19 . In addition, an air-fuel ratio sensor 23 and an exhaust gas temperature sensor 24 are arranged on a part of the exhaust pipe 19 located downstream of the catalytic converter 20 . The air-fuel ratio sensor 23 outputs an electrical signal that is indicative of the air / fuel ratio of the exhaust gas flowing through the exhaust pipe 19 , and the exhaust gas temperature sensor 24 outputs an electrical signal that is indicative of the Temperature of the exhaust gas flowing through the exhaust pipe 19 .

An exhaust throttle valve 21 for adjusting the amount of air flowing through the exhaust pipe 19 exhaust gas is arranged in the exhaust pipe 19 so that the air-fuel ratio sensor 23 and the exhaust temperature sensor 24 is located downstream. The exhaust throttle valve 21 is provided with an exhaust throttle switch 22 consisting of a stepping motor or the like, and can operate to drive the exhaust throttle valve 21 to open or close the valve 21 .

In the exhaust system constructed as described above, the air-fuel mixture that has been burned in the cylinders 2 of the engine 1 , ie, burned gas, is discharged into the exhaust duct 18 via exhaust gas connection points and then flows out of the exhaust duct 18 into the turbine housing 15 b of the centrifugal supercharger 15 . The exhaust gas, which enters the turbine housing 15 b, rotatably drives a turbine blade, which is rotatably mounted within the turbine housing 15 b, by utilizing the thermal energy contained in the exhaust gas. The torque of the turbine blade rotating in this way is then transmitted to the compressor blade, which is set up in the compressor housing 15 a. After leaving the turbine housing 15 b, the exhaust gas flows through the exhaust pipe 19 and enters the exhaust gas purification catalyst 20 , in which harmful components contained in the exhaust gas are removed or eliminated. The exhaust gas, which has been freed from the harmful components by the catalytic converter 20 , then passes through the exhaust gas throttle valve 21 in such a way that the flow rate of the exhaust gas is adjusted as required by the throttle valve 21 . After this, the exhaust gas is released to the atmosphere via the silencer.

The exhaust duct 18 and the inlet duct 8 are connected to one another via the exhaust gas recirculation path (EGR path) 25 , through which part of the exhaust gas in the exhaust duct 18 is recirculated into the inlet duct 8 . A flow regulation valve (EGR valve) 26 , which consists of an electromagnetic valve or the like, is provided in the middle of the EGR path 25 . The flow regulating valve 26 serves to vary the amount of exhaust gas flowing through the EGR path 25 (hereinafter referred to as "EGR gas") according to the amount of electrical energy supplied to the valve 26 .

An EGR cooler 27 for cooling the air flowing through the EGR path 25 EGR gas is arranged upstream in the EGR path 25 EGR valve 26th

In the exhaust gas recirculation system constructed as described above, when the EGR valve 26 is opened, the EGR path 25 is brought into communicating state, which allows the EGR gas to pass therethrough, so that part of the exhaust gas in the Exhaust duct 18 flows into EGR path 25 and leads to intake duct 8 via EGR cooler 27 . During this operation, the EGR cooler 27 cools the EGR gas in the EGR path 25 by heat exchange between the EGR gas and an appropriate coolant.

The EGR gas, which is circulated from the exhaust passage 18 into the intake passage 8 via the EGR path 25 , is then drawn into the combustion chambers of the cylinders 2 while being mixed with fresh air which is on an upstream part of the intake passage 8 streams. In each combustion chamber, the mixture of the air intake and the EGR gas is burned with fuel, which serves as an ignition source and was injected from one of the corresponding fuel injection valves 3 .

The EGR gas contains inactive gas components, such as water (H ₂ O) and carbon dioxide (CO ₂ ), which are non-combustible and have heat-absorbing properties. Therefore, when the EGR gas is contained in the mixture to be burned in the combustion chamber, the combustion temperature of the mixture is reduced and the amount of nitrogen oxides (NOx) thus generated is reduced accordingly.

Furthermore, the cooling of the EGR gas by the EGR cooler 27 leads to a reduction in the temperature of the EGR gas and further to a volume reduction in the EGR gas. Therefore, when the EGR gas is supplied to the combustion chamber, the temperature of the atmosphere in the combustion chamber is not raised to an unnecessarily high level, and the amount of fresh air supplied to the combustion chamber is not unnecessarily reduced even in the presence of the EGR gas.

The exhaust gas purifying catalyst 20 used in the emission control device of this embodiment will be described below.

The exhaust gas purifying catalyst 20 is a NOx catalyst that removes or reduces nitrogen oxides (NOx) contained in the exhaust gases in the presence of a reducing agent. While examples of the NOx catalyst include selective reduction type NOx catalysts, storage reduction type NOx catalysts, etc., the following description will be made in connection with the storage reduction type NOx catalyst. Hereinafter, the exhaust gas purifying catalyst 20 will be referred to as "storage reduction type NOx catalyst 20 ".

The storage reduction type NOx catalyst 20 is obtained by loading a carrier e.g. B. is made of aluminum oxide, with at least one substance consisting of alkali metals such as potassium (K), sodium (Na), lithium (Li) and cesium (Cs), alkaline earth metals such as barium (Ba) and calcium (Ca), and rare earth metals such as lanthanum (La) and yttrium (Y) is selected, as well as formed with a noble metal such as platinum (Pt). In the following description of the embodiment, the storage reduction type NOx catalyst is formed by loading an alumina support with barium (Ba) and platinum (Pt).

The storage reduction type 20 NOx catalyst constructed as described above absorbs nitrogen oxides (NOx) contained in the exhaust gas when exhaust gas entering the NOx catalyst 20 has a high oxygen concentration. Conversely, the NOx catalyst 20 releases the nitrogen oxides (NOx) stored therein when the oxygen concentration of the exhaust gas entering the NOx catalyst 20 is reduced.

If a reducing component such as hydrocarbon (HC), carbon monoxide (CO), etc. is present in the exhaust gas at the time of releasing the nitrogen oxides (NOx), the storage reduction type NOx catalyst 20 is capable of reducing the NOx -Catalyst 20 cause released nitrogen oxides (NOx) to nitrogen (N ₂ ).

Although the functions of the storage reduction type NOx catalyst 20 for absorbing and releasing NOx have not been fully understood, it can be considered that the NOx catalyst 20 absorbs and releases NOx according to the following mechanism.

When an exhaust gas entering the storage reduction type NOx catalyst has a low-fuel air / fuel ratio and therefore has a high oxygen concentration, oxygen (O ₂ ) contained in the exhaust gas is formed on the surface of the platinum ( Pt) precipitated in the form of O ₂ or O ² as illustrated in Fig. 2A. Also if nitrogen monoxide (NO) contained in the exhaust gas reacts with O _2- or O ^2- on the surface of the platinum (Pt) to form nitrogen dioxide (NO ₂ ) (2NO + 2O ₂ → 2NO ₂ ). The nitrogen dioxide (NO ₂ ) is further oxidized on the surface of the platinum (Pt) and absorbed into the storage reduction type 20 NOx catalyst to be stored in the form of nitrate ions (NO ³ ). The nitrate ions (NO ₃ ) thus absorbed in the storage reduction type 20 NOx catalyst combine with barium oxide (BaO) to form barium nitrate (Ba (NO ₃ ) ₂ ).

If the exhaust gas entering the storage reduction type 20 NOx catalytic converter has a low-fuel air / fuel ratio, nitrogen oxides (NOx) in the exhaust gas are absorbed into the storage reduction type 20 NOx catalytic converter and in the form of nitrate ions ( NO _3- ) saved.

The storage reduction type NOx catalyst 20 continues to absorb NOx as long as the incoming exhaust gas has a lean air / fuel ratio and the NOx absorption ability of the NOx catalyst 20 is not saturated. Therefore, when the exhaust gas entering the NOx catalyst of storage reduction type 20, a fuel-lean has air / fuel ratio, which contained tene in the exhaust gas NOx absorbed and the NOx catalyst 20 is from the exhaust gas as long removed how the NOx absorbency of the NOx catalyst is not saturated.

Conversely, when the oxygen concentration of the exhaust gas entering the storage reduction type NOx catalyst 20 is reduced, the amount of nitrogen dioxide (NO ₂ ) generated on the surface of the platinum (Pt) is reduced. As a result, the counter reactions proceed, namely, nitrate ions (NO ₃ ^- ) associated with barium oxide (Ba) are converted into nitrogen dioxide (NO ₂ ) or nitrogen monoxide (NO), which is then released or separated from the storage reduction type 20 NOx catalyst ,

If a reducing component, such as a hydrocarbon (HC) and carbon monoxide (CO), is present in the exhaust gas, as illustrated in FIG. 2B, the reducing component partially reacts with oxygen (O ₂ ^- ) or (O ^2- ) on the exhaust gas Platinum (Pt) thus forms an active species. The active species reduces nitrogen dioxide (NO ₂ ) or nitrogen monoxide (NO) released from the storage reduction type 20 NOx catalyst in nitrogen (N ₂ ).

Therefore, when the exhaust gas entering the storage reduction type 20 NOx catalyst has a stoichiometric air / fuel ratio or a fuel-rich air / fuel ratio and therefore has a reduced oxygen concentration and an increased reducing agent concentration, nitrogen oxides ( NOx) stored in the storage reduction type 20 NOx catalyst is released and reduced. As a result, the NOx absorbency of the storage reduction type 20 NOx catalyst is regained.

During the lean-burn operation of the internal combustion engine 1, the engine 1 emits exhaust gas having a lean air / fuel ratio and an increased oxygen concentration, and therefore, the nitrogen oxides contained in the exhaust gas (NOx) by the NOx catalyst of storage reduction type 20 are absorbed , However, when the lean combustion operation of the engine 1 continues for a long time, the NOx absorbency of the storage reduction type NOx catalyst 20 becomes saturated, and nitrogen oxides (NOx) contained in the exhaust gas are released into the atmosphere without being released by the NOx -Catalyst 20 to be removed.

Particularly in diesel engines such as engine 1 , an air / fuel mixture with a lean air / fuel ratio is burned during most of the operating range of the engine so that the air / fuel ratio of the resulting exhaust gas becomes lean in most of the engine - operating area. Therefore, the NOx absorbency of the storage reduction type 20 NOx catalyst used in diesel engines tends to become saturated.

Therefore, when the engine 1 is normally operated in a lean-burn mode, it is necessary to reduce the oxygen concentration of the exhaust gas and increase the concentration of the reducing agent before the NOx absorption ability of the storage reduction type NOx catalyst 20 is saturated whereby nitrogen oxides (NOx) stored in the storage reduction type 20 NOx catalyst are released and reduced.

In order to meet this requirement, the emission control device of this embodiment is equipped with a reducing agent supply mechanism for adding fuel (light oil) serving as a reducing agent to the exhaust gas passing through the exhaust path upstream of the storage reduction type NOx catalyst 20 flows. By adding fuel to the exhaust gas through the reducing agent supply mechanism, the emission control device of the embodiment lowers the oxygen concentration of the exhaust gas entering the storage reduction type 20 NOx catalyst and, at the same time, increases the concentration of the reducing agent in the exhaust gas.

The reducing agent supply mechanism includes a reducing agent injection valve 28 , a flow control valve 30 , a shutoff valve 31, and a reducing agent pressure sensor 32 as shown in FIG. 1. The reducing agent injection valve 28 is saddled on a cylinder head of the engine 1 so that its nozzle opening faces the interior of the exhaust passage 18 . The reducing agent injection valve 28 is opened to inject fuel when the valve 28 receives fuel at a pressure that is equal to or higher than a predetermined valve opening pressure. A reducing agent supply path 29 leads fuel coming from the fuel pump 6 to the reducing agent injection valve 28 . The flow control valve 30 , which is designed in the middle of the reducing agent supply path 29 , is used to adjust the amount of fuel that flows through the reducing agent supply path 29 . The shutoff valve 31 is configured in the reducing agent supply path 29 so that it is upstream of the flow control valve 30 . The cutoff valve 31 blocks or inhibits the flow of fuel through the reducing agent supply path 29 when it is brought into a closed position. The reducing agent pressure sensor 32 is attached to the reducing agent supply path 29 upstream of the flow control valve 30 . The reducing agent pressure sensor 32 outputs an electrical signal that corresponds to the pressure in the reducing agent supply path 29 .

The reducing agent injection valve 28 is preferably mounted on the cylinder head in such a way that the nozzle opening of the valve 28 is located downstream of a common part of the exhaust gas duct 18 with the EGR path 25 . The reducing agent injection valve 28 is also oriented so that the nozzle opening protrudes into the exhaust port of the cylinder 2 , which is a connecting part of the exhaust passage 18 , where the four branch lines come together, and so that the nozzle opening for connection part of the exhaust duct 18 is directed.

With the thus applied reducing agent injection valve 28, the reducing agent (unburned Kraftstoffkompo component), which is injected from the reducing agent injection valve 28 is prevented from flowing into the EGR passage 25, and the reducing agent, the turbine housing 15b of the centrifugal Reach supercharger 15 without remaining in the exhaust duct 18 .

In the embodiment shown in FIG. 1, in the direction from the left to the right side shown in FIG. 1, the four cylinders 2 are numbered as # 1, # 2, # 3 and # 4. Since the No. 2 cylinder # 1 is closest to the connection area of the exhaust passage 18 among the four cylinders 2 , the reducing agent injection valve 28 is attached to the wall of the exhaust port of the No. 2 cylinder 2 (# 1). However, when a different cylinder 2 no. 1 (# 1) cylinder 2 is the connection portion of the exhaust passage 18 closest to the reducing agent injection valve is attached to the wall of the exhaust gas output from the cylinder 28.

The reductant injector 28 may extend or be located near a water jacket (not shown) formed in the cylinder head so that the reductant injector 28 is cooled by cooling water flowing through the water jacket.

In the reducing agent supply mechanism as described above, fuel supplied from the fuel pump 6 is applied under high pressure to the reducing agent injection valve 28 via the reducing agent supply passage 29 when the flow control valve 30 is opened. When the pressure applied to the reductant injector 28 reaches or exceeds the valve opening pressure, the reductant injector 28 is opened to inject fuel into the exhaust passage 18 serving as the reductant.

The reducing agent injected from the reducing agent injection valve 28 into the exhaust duct 18 flows into the turbine housing 15 b together with the exhaust gas that flows from an upstream region of the exhaust duct 18 . After flowing into the turbine housing 15 b, the reducing agent and the exhaust gas are stirred and mixed together by rotating the turbine wheel, thus forming an exhaust gas with a high air / fuel ratio.

The thus formed exhaust gas with a fuel-rich air / fuel ratio flows from the turbine housing 15 b into the NOx catalyst of the storage reduction type 20 through the exhaust pipe 19 and causes nitrogen oxides (NOx) stored in the NOx catalyst of the storage reduction type 20. are released from the catalyst 20 and reduced to nitrogen (N ₂ ).

Then, when the flow control valve 30 is closed to stop the supply of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 , the fuel pressure applied to the reducing agent injection valve 28 becomes lower than the above-mentioned valve opening pressure. As a result, the reducing agent injection valve 28 is closed, so that the addition of the reducing agent into the exhaust passage 18 is completed.

The engine 1 as described above is equipped with an electronic control unit (ECU) 35 for controlling the engine 1 . The ECU 35 controls the operating state of the engine 1 according to the operating conditions of the engine 1 and a request or a command made by an automobile operator or driver.

The ECU 35 is electrically connected to various sensors, including the pressure sensor for the common rail 4 a, the air flow meter 11 , the air entry temperature sensor 12 , an inlet line pressure sensor 17 , the air-fuel ratio sensor 23 , the exhaust gas Temperature sensor 24 , the reducing agent pressure sensor 32 , a crank position sensor 33 , a water temperature sensor 34 , an accelerator position sensor 36 , etc. In operation, the ECU 35 receives output signals from these sensors.

The ECU 35 is also electrically connected to the fuel injection valves 3 , the intake throttle switch 14 of the exhaust gas throttle switch 22 , the EGR valve 26 , the flow control valve 30 , the shutoff valve 31, etc., and is capable of these valves and control other components.

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

The input port 356 receives output signals from sensors, such as the crank position sensor 33 , which generate signals in digital format, and transmits the digital signals to the CPU 351 , RAM 353, or the like.

The entry connection point 356 receives via the A / D converter 355 output signals from the sensors, which generate signals in analog format, the sensors being the pressure sensor for the common rail 4 a, the air flow meter 11 , the air entry temperature sensor 12 , the entry line Include pressure sensor 17 , air-fuel ratio sensor 23 , exhaust gas temperature sensor 24 , reducing agent pressure sensor 32 , water temperature sensor 34 , accelerator position sensor 36, etc.

The output port 357 is electrically connected to the fuel injection valves 3 , the intake throttle switch 14 , the exhaust throttle switch 22 , the EGR valve 26 , the flow control valve 30 , the shutoff valve 31, etc. In operation, the output port 357 allows control signals from the CPU 351 to the fuel injectors 3 , the intake throttle switch 14 , the exhaust throttle switch 22 , the EGR valve 26 , the flow control valve 30 , the shutoff valve 31 etc. to transfer.

The ROM 352 controls various application programs, including 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 gas throttle control routine for controlling the exhaust gas throttle valve 21 , an EGR Control routine for controlling the EGR valve 26 , a NOx removal control routine for removing or reducing nitrogen oxides (NOx) stored in the storage reduction type 20 NOx catalyst, a poisoning elimination control routine for eliminating the poisoning of the NOx Storage reduction type catalyst by oxides etc.

In addition to the application programs listed above, the ROM 352 stores various control plans. The tax plans include z. B. a fuel injection quantity control schedule indicating a relationship between the mode 1 operating state and the basic quantity of injection fuel (basic fuel injection duration), a fuel injection timing card showing a relationship between the operating state of the Engine 1 and the basic timing of fuel injection indicates a control card for opening the intake throttle valve, which indicates a relationship between the operating state of the engine 1 and the target amount of opening of the intake throttle valve 13 , and a control card for opening the exhaust throttle indicating a relationship between the operating state of the engine 1 and the target amount of opening of the exhaust throttle valve 21 . The control cards further include a control card for opening the EGR valve, which indicates a relationship between the operating state of the engine 1 and the target amount of opening of the EGR valve 26 , a control card for the reducing agent amount, which shows a relationship between the operating state of the engine 1 and indicates the target amount of the reducing agent to be added (or the intended exhaust air-fuel ratio), a control card for the flow control valve indicating a relationship between the target amount of the reducing agent added and the period during which the flow control valve 30 is kept open will, etc., a.

The RAM 353 temporarily stores output signals from various sensors, operating results of the CPU 351 etc. The results of the operations of the CPU 351 include e.g. B. the engine speed, which are calculated from the time interval between course signals generated by the crank position sensor 33 . Such data is rewritten as the latest data every time the crank position sensor 33 outputs a pulse signal.

The backup RAM 354 is a permanent memory that can hold data even when the engine 1 stops operating.

The CPU 351 operates in accordance with a currently selected one or more selected application programs stored in the ROM 352 to perform one or more selected types of fuel injector control, intake throttle control, exhaust throttle control, EGR control, etc. Output NOx removal control, poisoning elimination control, etc.

In the fuel injector control z. For example, the CPU 351 first determines an amount of fuel to be injected from each fuel injection valve 3 , and then determines the timing of fuel injection from each fuel injection valve 3 .

To determine the amount of fuel to be injected, the CPU 351 reads the engine speed and the output of the acceleration position sensor 36 (ie, the amount of depression of the accelerator pedal) from the RAM 353 . The CPU 351 then responds to the fuel injection amount control card and calculates a basic amount of fuel injection (basic fuel injection duration) according to the engine speed and the position of the accelerator pedal. The CPU 351 then corrects the basic fuel injection period using values of the output signals of the air flow meter 11 , the air intake temperature sensor 12 , the water temperature sensor 34 , the air-fuel ratio sensor 23, etc. as parameters, thereby providing a final fuel injection duration is determined.

To determine the timing of the fuel injection, the CPU 351 addresses a start timing control card for the fuel injection and calculates the basic fuel injection timing that corresponds to the engine speed and the position of the accelerator pedal. Using values of the output signals of the air flow meter 11 , the air intake temperature sensor 12 , the water temperature sensor 34 , the air-fuel ratio sensor 23, etc. as parameters, the CPU 351 corrects the basic timing for fuel injection to the final timing to determine the fuel injection.

After the fuel injection duration and the timing for the fuel injection are determined, the CPU 351 compares the timing of the fuel injection with the output signal of the piston position sensor 33 . At a time when the output signal of the crank position sensor 33 coincides with the start timing of the fuel injection, the CPU 351 starts to supply drive power to the appropriate fuel injection valve. The CPU 351 then stops supplying the drive power to the fuel injection valve 3 at a time when the elapsed time after the start of the supply of the drive power to the fuel injection valve 3 becomes equal to the fuel injection duration.

When the engine 1 is idling during the fuel injection control, the CPU 351 calculates a target idling speed using a value of an output signal of the water temperature sensor 34 , the operating conditions of companion parts such as a compressor of an automobile room air conditioner, about use the rotational force of the crankshaft is operated, etc. as a parameter. The CPU 351 then performs feedback control on the amount of fuel injection so that the actual idle speed becomes substantially the same as the target idle speed.

To execute the entry throttle control, the CPU 351 reads e.g. B. a motor speed and an accelerator pedal position from the RAM 353 . The CPU 351 then responds to the above control card for opening the intake throttle valve and calculates a target amount of opening of the intake throttle valve according to the engine speed and the position of the accelerator pedal. The CPU 351 then supplies drive power, which corresponds to the target amount of opening of the entry throttle valve, to the entry throttle switch 14 . The CPU 351 can detect an actual opening degree of the intake throttle valve 13 and perform feedback control on the entry throttle switch 14 based on a difference between the actual opening amount of the entry throttle valve 13 and the target opening amount of the Entry throttle valve 13 .

To perform the exhaust throttle control, the CPU 351 controls the exhaust throttle switch 22 to turn the exhaust throttle valve 21 z. B. to move in the valve closing direction when the engine 1 is in an operating state of warming up immediately following the cold start, or when a heater is operated to heat a vehicle compartment.

In this case, the load on the engine 1 is increased, and the amount of fuel injected is increased accordingly. As a result, the amount of heat generated by the engine increases, so that the warming-up of the engine 1 is accelerated and a heat source for the automotive space heater is surely provided.

To perform the EGR control, the CPU 351 reads an engine speed, an output of the water temperature sensor 34 (indicating the temperature of the cooling water), an output of the acceleration position sensor 36 (indicating a position of the accelerator pedal), etc. from the RAM 353 out. The CPU 351 then determines whether conditions for executing EGR control are established.

The aforementioned conditions for performing EGR control include e.g. B. ( 1 ) a condition that the cooling water temperature is equal to or higher than a predetermined temperature, ( 2 ) a condition that the engine 1 has been operated continuously for at least a predetermined period of time since its start, ( 3 ) a condition that the amount of change in the position of the accelerator pedal (ie, the amount of operation of the accelerator pedal) takes a positive value, etc. When it is determined that the above EGR control execution conditions are satisfied, the CPU 351 responds to the EGR valve opening control card using the engine speed and the position of the accelerator pedal as parameters, and calculates a target EGR valve opening amount that is the engine speed and corresponds to the position of the accelerator pedal. The CPU 351 then supplies drive power to the EGR valve 26 corresponding to the intended EGR valve opening. Conversely, if it is determined that any of the EGR control execution conditions are not met, the CPU 351 controls the EGR valve 26 so that a fully closed state of the EGR valve 26 is maintained.

Further, under the EGR control, the CPU 351 can perform EGR valve feedback control, generally speaking, in which the amount of opening of the EGR valve 26 is controlled in a feedback manner using the amount of the intake air of the engine 1 as a parameter.

In the EGR feedback control, the CPU 351 determines e.g. B. a target amount of the intake air of the engine 1 using the position of the accelerator pedal, the engine speed, etc. as a parameter. Thus, it is possible to determine in advance a relationship between the position of the accelerator pedal, the engine speed and the target amount of entry air in the form of a map, and a target amount of entry air from the position of the accelerator pedal and the engine speed with reference to the map receive.

After the target amount of intake air is determined by the above-mentioned procedure, the CPU 351 reads an output value of the air flow meter 11 (indicating the actual amount of the intake air) from the RAM 353 and compares the actual amount of the intake air with the target amount of the intake air.

If the actual amount of intake air is less than the target amount of intake air, the CPU 351 drives the EGR valve 26 by an appropriate amount in the valve closing direction. In this case, the amount of EGR gas flowing into the intake passage 8 from the EGR passage 25 decreases, and the amount of EGR gas drawn into the cylinders 2 of the engine 1 decreases accordingly. As a result, the amount of fresh air drawn into the cylinders 2 of the engine 1 increases by an amount corresponding to the decrease in the amount of EGR gas.

Conversely, when the actual amount of intake air is larger than the target amount of intake air, the CPU 351 drives the EGR valve 26 by an appropriate amount in the valve opening direction. In this case, the amount of EGR gas flowing from the EGR passage 25 into the intake port 8 increases , and the amount of EGR gas drawn into the cylinders 2 of the engine 1 increases accordingly. As a result, the amount of fresh air drawn into the cylinders 2 of the engine 1 is reduced by an amount corresponding to the increase in the amount of EGR gas.

In the NOx removal control, the CPU 351 executes a so-called enrichment peak control in which the air-fuel ratio of the exhaust gas entering the storage reduction type 20 NOx catalyst is set to a high air-fuel ratio for one controls for a short time in a relatively short cycle.

In order to execute the spike control, the CPU 351 determines at predetermined time intervals whether conditions for executing the spike control are satisfied. The conditions for the enrichment peak control include: (1) a condition that the storage reduction type NOx catalyst 20 is in an activated state, (2) a condition that an output value of the exhaust gas temperature sensor 24 (the exhaust gas temperature Display) is equal to or less than a predetermined upper limit, (3) a condition that the poisoning elimination control is not executed, etc.

When it is determined that the above-mentioned conditions for the enrichment peak control are satisfied, the CPU 351 temporarily controls the air / fuel ratio of the exhaust gas entering the storage reduction type 20 NOx catalyst to a target high air / Fuel ratio by controlling the flow control valve so that fuel serving as a reducing agent is injected from the reducing agent injection valve 28 for a short time.

Specifically, the CPU 351 reads an engine speed, an output signal of the acceleration position sensor 36 (indicating the position of the accelerator pedal), an output signal of the air flow meter 11 (indicating the amount of air intake), an output signal of the air-fuel ratio sensor 23 , one Amount of fuel injected, etc. from RAM 353 . Using the engine speed, the position of the accelerator pedal, the amount of intake air and the amount of injected fuel as parameters, the CPU 351 addresses the control card of the amount of reducing agent stored in the ROM 352 and calculates an amount of the reducing agent (target amount the reducing amount to be added) required to control the air / fuel ratio of the exhaust gas to a preset target of the high air / fuel ratio.

Using the above-mentioned target amount of reducing agent as a parameter, the CPU 351 then addresses the control card of the flow control valve which is stored in the ROM 352 and calculates a period of time of the valve opening (target duration of the valve opening) of the flow control valve 30 which is required to inject the target amount of the reducing agent from the reducing agent injection valve 28 .

After the target time period for valve opening of the flow control valve 30 is calculated, the CPU 351 opens the flow control valve 30 for the calculated duration. In this case, fuel under high pressure, which is supplied from the fuel pump 6 , is supplied to the reducing agent injection valve 28 through the reducing agent supply passage 29 , so that the fuel pressure supplied to the reducing agent injection valve 28 is a valve opening pressure or one more reached higher, whereby the reducing agent injection valve 28 is opened.

The CPU 351 closes the flow control valve 30 after lapse of the above-mentioned target duration for valve opening from the time at which the flow control valve 30 is opened. With the so-closed flow control valve 30, the supply is of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 is interrupted, so that the injection valve reducing agent is 28 Fuel pressure supplied reduced so to that it ge is ringer than the opening pressure of the valve. As a result, the reducing agent injection valve 28 is closed.

Thus, when the flow control valve 30 is kept open for the target duration of the valve opening, the target amount of fuel is injected from the reducing agent injection valve 28 into the exhaust passage 18 . The reducing agent injected from the reducing agent injection valve 28 is then mixed with exhaust gas flowing from an upstream portion of the exhaust passage 18 , and forms a mixture of the reducing agent and the exhaust gas, which has an intentionally high air / fuel ratio. The mixture thus formed flows into the storage reduction type 20 NOx catalyst.

As a result, the air / fuel ratio of the exhaust gas entering the storage reduction type NOx catalyst 20 is changed in a relatively short cycle between a lean air / fuel ratio to a high target air / fuel ratio so that the high air / fuel ratio only occurs for a short duration. In this way, the storage reduction type 20 NOx catalyst alternatively performs the absorption of the nitrogen oxides (NOx) and the release and reduction of the nitrogen oxides (NOx) repeatedly in a short cycle.

To execute the poisoning elimination control, the CPU 351 executes the poisoning elimination process to eliminate the poisoning of the storage reduction type 20 NOx catalyst caused by oxides.

In some cases, the fuel used in the engine 1 contains sulfur (S). Therefore, when such a fuel is burned in the engine 1 , sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), etc. are produced.

The sulfur oxides (SOx) flow together with the exhaust gas in the NOx catalyst of the storage reduction type 20 and be absorbed into the NOx catalyst of the storage reduction type 20 by a mechanism which is substantially the same as the mechanism of absorption of nitrogen oxides ( NOx).

Specifically, when exhaust gas entering the storage reduction type 20 NOx catalyst has a lean air / fuel ratio, oxygen (O ₂ ) on the surface of platinum (Pt) in the form of O ₂ ^- or O ^2- , as noted above, in conjunction with the NOx absorption mechanism. Therefore, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), etc., which are contained in the exhaust gas, react with O ₂ ^- or O ^2- on the surface of the platinum (Pt), thereby causing SO ₃ ^- , SO ₄ ^- etc. to form.

SO ₃ ^- and SO ₄ ^- are further oxidized on the surface of the platinum (Pt) and are absorbed in the form of sulfate ions (SO ₄ ^2- ) by the storage reduction type NOx catalyst. The sulfate ions (SO ₄ ^2- ) absorbed in the storage reduction type 20 NOx catalyst then combine with barium oxide (BaO) to form a sulfate (BaSO ₄ ).

Thus, when the air / fuel ratio of the exhaust gas entering the storage reduction type NOx catalyst 20 is a lean air / fuel ratio, sulfur oxides (SOx) are generated in the exhaust gas in the form of sulfate ions (SO ₄ ^2- ) is absorbed into the storage reduction type 20 NOx catalyst.

It should be noted that the sulfate (BaSO ₄ ) is more stable and decomposes less easily than barium nitrate (Ba (NO ₃ ) ₂ ). Therefore, even if the air / fuel ratio of the exhaust gas entering the NOx catalyst 20 is set to a stoichiometric or high air / fuel ratio, the sulfate (BaSO ₄ ) tends to be in the storage reduction type NOx catalyst 20 to remain without being decomposed.

When the amount of the sulfate (BaSO ₄ ) in the storage reduction type NOx catalyst 20 increases, the amount of barium oxide (BaO) used for absorbing nitrogen oxides (NOx) is reduced accordingly, thereby reducing the NOx absorbency of the NOx catalyst 20 deteriorates, so that the so-called SOx poisoning occurs.

As an example of a method for eliminating the SOx poisoning of the storage reduction type 20 NOx catalyst, the temperature of the atmosphere to which the NOx catalyst is exposed is raised to a high temperature range of about 500 ° C to about 700 ° C , and the air / fuel ratio of the exhaust gas entering the NOx catalyst 20 is set to a high air / fuel ratio. As a result, the barium sulfate (BaSO ₄ ) stored in the NOx catalyst 20 is thermally decomposed to form SO ₃ ^- or SO ₄ ^- , and the ions SO ₃ ^- or SO ₄ are caused to be mixed with hydrocarbons (HC) and carbon monoxide ( CO), which is present in the exhaust gas, so as to be reduced in SO ₂ ^- in gaseous form.

Therefore, in the detoxification process according to this embodiment, the CPU 351 first executes a catalyst temperature raising process to raise the catalyst temperature of the storage reduction type 20 NOx catalyst, and then controls the air / fuel ratio of the exhaust gas entering the NOx catalyst 20 high air / fuel ratio.

In the catalyst temperature raising process, the CPU 351 can raise the center bed temperature of the storage reduction type NOx catalyst 20 in the following manner. Namely, the CPU 351 performs subsidiary post-injection of fuel from each fuel injection valve 3 during the expansion stroke of the cylinder 2 and supplies fuel from the reductant injection valve 28 into the exhaust gas, so that unburned fuel components in the NOx catalyst are stored -Reduction type 20 can be oxidized.

Due to the heat generated during the oxidation, the middle bed temperature of the NOx catalyst 20 is raised. However, an excessively elevated temperature of the storage reduction type 20 NOx catalyst may possibly cause thermal damage to the NOx catalyst 20 . Therefore, it is preferable to control the amount of post-fuel injection and the amount of fuel added in a feedback manner based on the output signal of the exhaust gas temperature sensor 24 .

After the center bed temperature of the storage reduction type 20 NOx catalyst is raised to a high temperature range of about 500 ° C to about 700 ° C by the catalyst temperature raising method described above, the CPU 351 causes the reducing agent injection valve 28 to inject fuel to control the air / fuel ratio of the exhaust gas entering the NOx catalyst 20 to a high air / fuel ratio.

However, if an excessive amount of fuel is injected from the reductant injection valve 28 , the injected fuel may burn into the storage reduction type 20 NOx catalyst very quickly, causing the NOx catalyst 20 to overheat or the NOx catalyst from the storage Reduction type 20 may be unnecessarily cooled by the excessive amount of fuel injected from the reductant injector 28 . Therefore, it is preferable that the CPU 351 perform feedback control on the amount of fuel injected from the reducing agent injection valve 28 based on the output signal of the air-fuel ratio sensor 23 .

When the detoxification process is carried out as described above, the air-fuel ratio of the exhaust gas entering the storage reduction type 20 NOx catalyst is changed to a high air-fuel ratio under a condition that the NOx catalyst is removed from the storage Reduction type 20 has a high middle bed temperature. Therefore, barium sulfide (BaSO ₄ ) stored in the storage reduction type 20 NOx catalyst is thermally decomposed to form SO ₃ or 50 ₄ , and the ions SO ₃ ^- or SO ₄ ^- are caused to coexist to react hydrocarbons (HC) and carbon monoxide (CO) present in the exhaust gas in order to be reduced in SO ₂ ^- in gaseous form. In this way, SOx poisoning the storage reduction type 20 NOx catalyst is eliminated.

When executing the NOx removal control described above, the CPU 351 executes an enrichment peak control in a predetermined cycle so that the air-fuel ratio of the exhaust gas entering the storage reduction type 20 NOx catalyst is set to a targeted high air. The fuel ratio is only controlled for a short period of time, so that nitrogen oxides (NOx) stored in the NOx catalytic converter are released and reduced.

The targeted high air-fuel ratio for use in the peaking control is a fixed value, which is determined based on the assumption that the storage reducing type 20 reducing agent supply mechanism and NOx catalyst are configured for their typical conditions , If there are any changes in the operation of the NOx catalyst 20 , the characteristic of the reducing agent supply mechanism, the characteristic of the fuel injection valves 3, and the like with the lapse of time of use or due to changes in circumstances, the amount of reducing agent supplied may change become excessive or insufficient in the amount of nitrogen oxides (NOx) stored in the storage reduction type 20 NOx catalyst.

In view of the problem described above, it is considered to detect the amount of nitrogen oxides released from the NOx catalyst 20 based on the output signal of the air-fuel ratio sensor 23 during the execution of the peaking control and perform a feedback check regarding the targeted high air-fuel ratio (in other words, the amount of the reducing agent added) in correspondence with the detected amount of nitrogen oxides (NOx).

Furthermore, the air-fuel ratio is calculated based on an output signal generated by the air-fuel ratio sensor 23, which is assumed to be in a completely new state. Therefore, if there is any change in the output characteristic of the sensor 23 due to changes in time or damage, e.g. B. the air-fuel ratio can be detected incorrectly or incorrectly, which makes it difficult to perform an accurate feedback control.

Therefore, in this embodiment, the CPU 351 compares the air-fuel ratio obtained from the output signal of the air-fuel ratio sensor 23 with a predetermined value during the detoxification process, in which the air-fuel ratio is shown in FIGS NOx catalyst 20 entering exhaust gas is set to a high air-fuel ratio for a relatively long time, and corrects the output signal of the air-fuel ratio sensor 23 based on a deviation of the obtained air-fuel ratio from the predetermined Value. Here, the predetermined value is equivalent to the air-fuel ratio obtained during an early period of the detoxification process when the air-fuel ratio sensor 23 is new.

That is, since the air-fuel ratio of the exhaust gas entering the storage reduction type 20 NOx catalyst is set to a high air-fuel ratio during the detoxification process, nitrogen oxides or O ₂ stored in the NOx catalyst 20 become released during the early period of execution of the detoxification process. When nitrogen oxides (NOx) are released from the NOx catalyst 20 , the air-fuel ratio of the exhaust gas that is on the downstream side of the NOx catalyst 20 (hereinafter referred to as "air-fuel ratio on the downstream side" approaches referred to) is measured based on the stoichiometric value due to oxygen contained in the released nitrogen oxides (NOx) and oxygen (generally referred to as O ₂ storage) which is absorbed and stored in the NOx catalyst 20 ,

Therefore, by calculating the deviation of the exhaust air-fuel ratio on the downstream side from the predetermined air-fuel ratio during an early period of executing the detoxification process, the amount of change in the output of the air-fuel ratio sensor 23 , that is, the Value by which the sensor output should be corrected should be determined.

After the output value of the air-fuel ratio sensor 23 is corrected as described above, the CPU 351 stores the corrected value in a predetermined area of the RAM 353 or in the backup RAM 354 .

When the NOx removal control is carried out after the completion of the poisoning elimination control, the CPU 351 executes the enrichment of the peak control based on the corrected value of the air-fuel ratio sensor 23 , which is in the RAM 353 or the backup RAM 354 is saved.

In this case, the amount of reducing agent injected from the reducing agent injection valve 28 during the enrichment peak control reflects the air-fuel ratio of the exhaust gas that is actually released from the storage reduction type 20 NOx catalyst. Therefore, the amount of the reducing agent added can be set to an optimal value even if the output characteristic of the air-fuel ratio sensor 23 changes, e.g. B. due to changes in time or damage to the sensor 23 .

Consequently, during the spike control, the with the detoxification process or the NOx removal process is associated with the amount of reducing agent supplied not overly high or insufficient, and another possible deterioration of exhaust emissions due to excessive or insufficient supply of the reducing agent can advantageously be prevented.

Even if the spike control is not is carried out, the amount of other Fuel delivered to the internal combustion engine via feedback be controlled based on the exhaust gas / fuel Ratio, and worsening of exhaust emissions can be prevented in a similar manner.  

The poisoning elimination control according to this embodiment will be described in more detail with reference to the flowchart shown in FIG. 5.

The flowchart of FIG. 5 illustrates a control routine for poisoning elimination. The poisoning elimination control routine is repeatedly executed by the CPU 351 at predetermined time intervals (e.g., each time the curve position sensor 33 generates a pulsed signal). The poisoning elimination control routine is pre-stored in the ROM 352 .

In step S501 of the poisoning elimination control routine, the CPU 351 initially determines whether conditions for executing the detoxification process are satisfied. The conditions for performing the poisoning eliminations may e.g. For example, include: (1) a condition that the storage reduction type NOx catalyst 20 is in an activated state, (2) a condition that the exhaust gas temperature sensor 24 output value (indicating the exhaust gas temperature) is equal to or less than an upper limit, (3) a condition that an extent of SOx poisoning of the storage reduction type NOx catalyst 20 exceeds an allowable range, etc.

If it is determined in step S501 that any of the conditions for executing the poisoning elimination is not met, the CPU 351 temporarily completes the execution of this routine.

If it is determined in step S501 that the conditions for executing the poisoning elimination are met, the CPU 351 proceeds to step S502. In step S502, the CPU 351 reads out an engine speed, an output value of the acceleration position sensor 36 (indicating a position of the accelerator pedal) and an output value of the air-fuel ratio sensor 23 from the RAM 353 . Using the engine speed, the accelerator pedal position, and the air-fuel ratio as parameters, the CPU 351 calculates an amount of reducing agent (fuel) required to determine the air-fuel ratio of the exhaust gas entering the NOx catalyst 20 to change to a predetermined reference value of high air-fuel ratio.

To allow the above operations, it is possible to empirically determine a relationship between the engine speed, the accelerator pedal position and the amount of reducing agent added, and to pre-store the relationship in the form of a map in the ROM 352 or the like.

In step S503, the CPU 351 controls the flow control valve 30 in accordance with the amount of reducing agent determined in step S502 to start adding the reducing agent from the reducing agent injection valve 28 to the exhaust gas.

In step S504, the CPU 351 stores the output value of the air-fuel ratio sensor 23 (exhaust air-fuel ratio on the downstream side) in the RAM 353 .

In step S505, the CPU 351 determines whether conditions for ending the poisoning elimination process are met. The conditions for stopping the poisoning elimination can e.g. B. Include a condition that the time or duration of executing the poisoning elimination process has reached an at least predetermined time or duration.

If it is determined in step S505 that the conditions for ending the poisoning elimination are not met, the CPU 351 repeatedly executes steps S504 and S505 until an affirmative decision (YES) is obtained in step S505.

Conversely, if it is determined in step S505 that the conditions for ending the poisoning elimination are satisfied, the CPU 351 proceeds to step S506, in which the CPU351 controls the flow control valve 30 to stop the addition of the reducing agent.

In step S507, the CPU 351 determines whether the exhaust air-fuel ratio on the downstream side during an early period of detoxification control is equal to a predetermined air-fuel ratio.

If it is determined in step S507 that the exhaust air-fuel ratio on the downstream side is equal to the predetermined air-fuel ratio, the CPU 351 temporarily completes the execution of the routine.

Conversely, if it is determined in step S507 that the exhaust air-fuel ratio on the downstream side is different from the predetermined air-fuel ratio, the CPU 351 proceeds to step S508.

In step S508, the CPU 351 calculates a deviation of the downstream-side exhaust air-fuel ratio from the predetermined air-fuel ratio during the poisoning elimination control stored in the RAM 353 , and stores the calculated value as a corrected value in a predetermined one Area of backup RAM 354 . The CPU 351 then temporarily completes execution of the routine.

In the NOx removal control that follows the execution of the poisoning elimination control routine described above, the CPU 351 executes the enrichment peak control while assuming as an actual downstream exhaust air-fuel ratio a value obtained by adding the correction value, which is stored in the predetermined area of the backup RAM 354 to the air-fuel ratio determined from the output signal of the air-fuel ratio sensor 23 .

According to the emission control device of the internal combustion engine of the embodiment, the amount of the reducing agent injected from the reducing agent injection valve 28 during the peaking control reflects the air-fuel ratio of the exhaust gas actually released from the storage reduction type 20 NOx catalyst contrary.

Therefore, the amount of reducing agent added can be controlled to an optimum value even if there is any change in the characteristic of the output signal of the air-fuel ratio sensor 23 , e.g. B. due to changes in time and damage.

Consequently, during the enrichment spike control The amount of the reducing agent supplied is not excessively large or insufficient, and another possible injury to the Exhaust emissions due to excessive or insufficient Supply of the reducing agent can be advantageous be prevented.

While the invention is described with reference to that was what is currently their preferred embodiments is considered, it is clear that the invention is not based on the disclosed embodiments or constructions limited is. On the contrary, the invention is intended  various modifications and equivalent arrangements includes.

In the emission control device according to the invention the air-fuel ratio of the exhaust gas during the Execution of the poisoning elimination process for the NOx catalyst is detected, and the output value of the air Fuel ratio sensor device is based on a deviation between the detected air-fuel Ratio and a predetermined value corrected.

The above arrangement enables the air-fuel Check or improve ratio with improved accuracy analyze and an optimal NOx removal process itself in the case when the output signal of the air Fuel ratio sensor device from the nominal Value differs, e.g. B. due to changes over time or damage to the sensor device.

In the emission control device in which a reduction is added to the exhaust gas to make the air-fuel Ratio of the exhaust gas entering the NOx catalyst to a predetermined target level in the NOx removal process adjust, the arrangement described above is particularly effective to prevent the deterioration of the Exhaust emissions due to excessive or insufficient Supply of the reducing agent due to errors in the Air-fuel ratio measurement results.

In addition, it makes the exact measurement of air Fuel ratio achieved by the invention is possible, a feedback control with a sufficiently high level Execute accuracy when the amount of in the Internal combustion engine injected fuel from the NOx Removal process different situations is determined.  

In this case too, deterioration of the Exhaust emissions are prevented.

Claims (20)

1. An emission control device for a lean-burn type internal combustion engine capable of burning an air-fuel mixture having a lean air-fuel ratio, the device comprising:
a NOx catalytic converter ( 20 ) which is provided in an exhaust gas path ( 18 ) of the internal combustion engine ( 1 ), the NOx catalytic converter ( 20 ) being adapted to absorb nitrogen oxides contained in the exhaust gas when the exhaust gas is a high air-fuel Ratio, and release the nitrogen oxides stored therein when the exhaust gas has a low air-fuel ratio;
NOx removal control means for performing a NOx removal process to release and reduce the nitrogen oxides absorbed in the NOx catalyst ( 20 );
poisoning elimination control means for performing a poisoning elimination process to eliminate poisoning of the NOx catalyst ( 20 ) due to the oxides;
air-fuel ratio sensor means ( 23 ) provided in the exhaust path ( 18 ) for checking the air-fuel ratio of the exhaust gas; and
air-fuel ratio correction means for correcting an output signal of the air-fuel ratio sensor means ( 23 ) based on an output signal generated by the air-fuel ratio sensor means ( 23 ) during execution of the poisoning elimination process , the corrected output signal being used for the subsequent control performed by the emission control device. 2. The emission control device according to claim 1, wherein during the execution of the poisoning elimination process, the temperature of the atmosphere to which the NOx catalyst ( 20 ) is exposed is raised. 3. Emission control device according to claim 2, wherein the Temperature to a temperature of about 500 ° C to 700 ° C is raised. 4. Emission control device according to one of claims 1 to 3, while during the execution of the poisoning Elimination process the air-fuel ratio of the in the exhaust gas entering the NOx catalyst to a rich one Range is set 5. Emission control device according to claim 4, wherein the air-fuel ratio is made rich by adding a reducing agent to the exhaust gas via a reducing agent injection valve ( 28 ) which injects the reducing agent into the exhaust gas path ( 18 ). 6. Emission control device according to claim 5, wherein the reducing agent injection valve ( 28 ) is arranged in the exhaust gas path ( 18 ) so that the nozzle opening of the valve ( 28 ) faces the interior of the path ( 18 ). 7. The emission control device according to claim 5 or 6, wherein the nozzle opening of the reducing agent injection valve ( 28 ) is located downstream of a connection region of the exhaust gas path ( 18 ) with an exhaust gas recirculation passage. 8. Emission control device according to one of claims 1 to 7, whereby the poisoning elimination process is only completed leads if at least one predetermined condition for the execution is fulfilled. 9. The emission control device of claim 8, wherein at least one predetermined condition for performing the poisoning elimination process comprises at least one of the following conditions:
the NOx catalyst ( 20 ) is in an activated state;
an exhaust gas temperature is equal to or lower than an upper limit; and
the amount of NOx poisoning of the NOx catalyst ( 20 ) exceeds an allowable range. 10. The emission control device according to one of claims 1 to 9, wherein the air-fuel ratio correction device outputs an output signal generated by the air-fuel ratio sensor device ( 23 ) during an early period of the poisoning elimination process. is compared with a predetermined value, and if there is a deviation of the output signal from the predetermined value, the air-fuel ratio correction device corrects the output signal of the air-fuel ratio sensor device ( 23 ) on the basis of the deviation. 11. The emission control device according to claim 10, wherein the predetermined value corresponds to an output signal generated by an air-fuel ratio sensor means ( 23 ) during an early period of the poisoning elimination process when the air-fuel ratio Sensor device ( 23 ) is new. 12. Emission control device according to one of claims 1 to 11, wherein the air-fuel ratio sensor device ( 23 ) is located downstream of the NOx catalyst ( 20 ) for checking the air-fuel ratio of the exhaust gas, which the NOx -Catalyst ( 20 ) has passed. 13. Emission control device according to one of claims 1 to 12, wherein the corrected output signal of the air-fuel ratio sensor device ( 23 ) is used in the subsequent check for determining an amount of reducing agent which is during the NOx removal process or Poisoning elimination process is added. 14. Emission control device according to one of claims 1 to 13, where fuel is the reducing agent or Is reducing agent. 15. Emission control device according to one of claims 1 to 14, wherein a temperature sensor ( 24 ) is arranged downstream of the NOx catalyst ( 20 ) for checking the temperature of the exhaust gas that has passed through the NOx catalyst. 16. Emission control method of an emission control device of a lean-burn type internal combustion engine capable of burning an air-fuel mixture with a lean air-fuel ratio, the internal combustion engine including a NOx catalyst ( 20 ) which is arranged in an exhaust gas path ( 18 ) of the internal combustion engine ( 1 ), the NOx catalytic converter ( 20 ) being adapted to absorb nitrogen oxides contained in the exhaust gas when the exhaust gas has a high air-fuel ratio and the nitrogen oxides stored therein to release when the exhaust gas has a low air-fuel ratio, the method comprising the following steps:
Performing a NOx removal process to release and reduce nitrogen oxides absorbed in the NOx catalyst ( 20 );
Performing a poisoning elimination process to eliminate poisoning of the NOx catalyst ( 20 ) due to oxides;
Checking the air-fuel ratio of the exhaust gas by an air-fuel ratio sensor ( 23 ) provided in the exhaust passage ( 18 ); and
Correcting an output signal of the air-fuel ratio sensor ( 23 ) based on an output signal generated by the air-fuel ratio sensor ( 23 ) during the execution of the poisoning elimination process, the corrected output signal for the subsequent control is used, which is carried out by the emission control device. 17. The emission control method according to claim 16, wherein an output signal generated by the air-fuel ratio sensor ( 23 ) during an early period of the poisoning elimination process is compared with a predetermined value and if there is a deviation of the From output signals of the predetermined value there, the output signal of the air-fuel ratio sensor ( 23 ) is corrected based on the deviation. The emission control method according to claim 17, wherein the predetermined value corresponds to an output signal generated by the air-fuel ratio sensor ( 23 ) during an early period of the poisoning elimination process when the air-fuel ratio sensor ( 23 ) is new. 19. The emission control method according to any one of claims 16 to 18, wherein the air-fuel ratio sensor ( 23 ) is located downstream of the NOx catalyst ( 20 ) for checking the air-fuel ratio of the exhaust gas which is the NOx Catalyst ( 20 ) has passed. 20. Emission control method according to one of claims 16 to 19, wherein the corrected output signal of the air-fuel ratio sensor ( 23 ) is used in the subsequent control for determining an amount of reducing agent which is present during the NOx removal process or the poisoning -Elimination process is added.