DE10011612B4 - Emission control device for an internal combustion engine - Google Patents

Abstract

Emission control device for an internal combustion engine, comprising the following components:
a NOx absorption-reduction catalyst (3) provided in an exhaust pipe (2) of a lean-burn internal combustion engine (1), the NOx absorption-reduction catalyst (3) absorbing NOx when an air-fuel ratio of an exhaust gas from the internal combustion engine is on a lean side of a theoretical air-fuel ratio, and wherein the NOx absorption-reduction catalyst (3) releases NOx and causes a reduction of NOx when an oxygen concentration in the exhaust gas by shifting the air / fuel ratio of the Exhaust gas is reduced to the rich side by means of the control of the internal combustion engine; and
a selective ammonia compound reduction catalyst (4) which causes a selective reduction due to the supply of an ammonia compound, the amount of the ammonia compound to be supplied being determined by an ammonia compound adding amount determining device (11a) which detects the NOx concentration in the exhaust gas upstream of the selective ammonia compound reduction catalyst (4) taken into account, which is determined by means of a NOx sensor (5).

Description

The present invention relates an emission control device for an internal combustion engine, in particular for converting NOx from the exhaust gas of a lean-burn engine.

An emission control device for a lean-burn engine is disclosed, for example, in Japanese Patent JP 02-605580 A described.

The emission control device, the described in the Japanese patent has in an exhaust line an absorbent that absorbs NOx when the air-fuel ratio of the Exhaust gas that flows in on the lean side of the theoretical air-fuel ratio lies, and that the absorbed NOx releases when the oxygen concentration in the inflowing Exhaust gas decreases. To reduce the oxygen concentration in the exhaust gas leads the Device a greased pulse control by the fuel is injected into the internal combustion engine to produce unburned gas to generate (reducing agent). That means that due to the enriched pulse control a reducing agent for reducing from NOx via the internal combustion engine is delivered to the NOx absorbent.

Regarding an emission control device, which supplies a reducing agent from an internal combustion engine it is desirable that if the engine is a lean engine, the engine is operated in a lean-burning state, even at high ones Speeds and high loads. However, it is in one Operating state impossible, the reducing agent through the enriched pulse to the NOx absorbent (NOx catalyst) to deliver.

To achieve a fuel-rich air-fuel ratio to achieve it is necessary to reduce the amount of intake air by reducing a throttle valve opening to reduce. However, if such a fuel-rich condition is produced when the internal combustion engine at high speed and a high load works in the lean-burn mode, prevents the combustion of fuel, so that smoke is generated becomes.

To solve this problem, you can the lean fuel combustion will be abandoned and instead can do the stoichiometric Air-fuel ratio (theoretical air-fuel ratio) can be set. This solution moves away from the improvement of economical use with fuel obtained from lean combustion i.e. by adapting a lean-burn internal combustion engine.

It may also be conceivable to provide a selective reduction catalyst, the HCs or H used as a reducing agent. However, the selective reduction catalyst the HCs or H used as a reducing agent in a high speed range and a high load condition, only a low NOx removal rate.

It was therefore difficult to get NOx above the sufficient to remove the entire combustion engine operating area.

From the DE 197 40 702 C1 an exhaust gas purification system for lean-burn engines is known, which is equipped with an adsorption catalyst and with a Denox catalyst. Furthermore, a changeover valve is provided with which the exhaust gas flow can be passed through both catalysts either in parallel or in series. The adsorption catalyst is said to adsorb NOx under lean conditions and release it again under rich conditions. These rich conditions are achieved by means of fuel injection upstream of the catalytic converter via an injection valve.

From the document DE 42 27 741 A1 a method for converting NOx from the exhaust gas of an internal combustion engine is known. According to this document, NOx is reduced by means of an exhaust gas purification device which comprises a catalytic converter, by means of a reducing agent which is supplied upstream of the catalytic converter. For regulating the device, in particular for controlling the amount of reducing agent supplied, NOx sensors are provided, which are arranged upstream and downstream of the catalytic converter. Furthermore, a sensor can be used which detects the amount of reducing agent downstream of the catalytic converter.

The document EP 07 02 134 A2 describes an emission control device for an internal combustion engine, in particular a lean-burn internal combustion engine, which comprises a NOx absorption catalytic converter. This emission control device also has a device for regulating the air / fuel ratio in order to achieve absorption and reduction of the emitted NOx by a suitable choice of the air / fuel ratio.

Accordingly, it is an object of the present Invention, an emission control device for an internal combustion engine create that is able to NOx over the widest possible operating range to convert compared to the prior art.

This task is due to the characteristics of claim 1 solved.

The internal combustion engine in which the Invention applied appropriately is a lean-burn diesel or gasoline engine that contains a direct injection into the cylinder.

During the operation of the internal combustion engine in a lean combustion state, the NOx absorption-reduction catalyst device becomes unable to remove NOx because NOx that is in an egg is absorbed, is not released, and therefore the NOx in the absorbent is not reduced. However, the selective ammonia compound reduction catalyst serves to substantially eliminate NOx during an engine operating condition in the high load range. Therefore, the emission control device of the invention extends the operating range in which NOx is removed compared to a device that uses a NOx absorption-reduction catalyst and no other catalyst.

Although the device of the invention is intended to typically be embodied in a construction be in which a reducing agent via the internal combustion engine the NOx absorption reduction catalyst is supplied Invention also applicable to a device of a type at which delivers a reducing agent into an exhaust line, which is connected to an internal combustion engine without any Problem occurs.

The emission control device can an operating state detection device for detection have an operating state of the internal combustion engine, and a Switching device for changing the direction of flow of the exhaust gas either to the NOx absorption-reduction catalyst device or the selective ammonia compound catalyst device in dependence from the operating state of the internal combustion engine, which is detected by the operating state detection device has been.

For example, if the operating status of the Internal combustion engine by the operating state detection device is detected, a state that is below a predetermined high speed and a predetermined high load, the NOx absorption reduction catalyst selected, and when the detected operating state of the internal combustion engine is a state at the predetermined high speed and the predetermined high Load exceeds becomes the selective ammonia compound reduction catalyst device selected.

The operating state that is captured is to be in an operating range in which the NOx absorption-reduction catalyst is not is able to carry out the reduction. In the invention when the internal combustion engine is in a predetermined high load and high speed operating condition is contemplated that the Reduction impracticable and the emission control is performed using the selective ammonia compound reduction catalyst device becomes. To the aforementioned Operating state, it is therefore possible to use parameters which directly or indirectly the impracticable reduction range of NOx absorption-reduction catalyst display, such as engine speed and / or engine load, or the air intake amount, or the degree of throttle opening, or like.

The NOx absorption reduction catalyst and the selective ammonia compound reduction catalyst can be used in the exhaust line can be arranged in series.

With this arrangement, it is possible to selective ammonia compound reduction catalyst downstream of to arrange the NOx absorption reduction catalyst in the exhaust system. It is possible, too, the selective ammonia compound reduction catalyst upstream of the NOx absorption reduction catalyst to be arranged in the exhaust line.

Along with the serial arrangement of the catalysts, a bypass passage can be provided, which an upstream Bypasses the catalytic converter and directs the exhaust gas to the downstream catalytic converter. The flow direction of the exhaust gas is changed by a switching device which the bypass passage opens and closes.

The NOx absorption reduction catalyst and the selective ammonia compound reduction catalyst can further be arranged in parallel in the exhaust line.

If the catalysts are arranged in parallel, the emission control device can also have a construction, in which the exhaust line into a first exhaust line and one second exhaust line forks, the NOx absorption reduction catalyst is arranged in the first exhaust line, and the selective ammonia compound reduction catalyst is arranged in the second exhaust line, a changeover valve as a switching device at the branching point between the first exhaust line and the second exhaust line is arranged. Dependent on from the operating state at least one of the first and second exhaust lines selected by the changeover valve.

The construction described above allows it the NOx absorption-reduction catalyst and the selective ammonia compound reduction catalyst complementary to each other dependent on to function from the operating state. That is why the emission control device able to regulate emissions across the widest possible Operating area, compared to a device that uses only one of the emission control catalysts used.

The emission control device may further include an added ammonia compound amount determining device to estimate an amount of the ammonia compound to be added to the selective ammonia compound reduction catalyst based on an amount of NOx flowing in the exhaust gas flowing into the selective ammonia compound reduction catalyst , and an intake air amount that is drawn into the internal combustion engine. That's why it will possible to easily determine an amount of ammonia compound to be added.

The emission control device can further include an ammonia compound detection device, an ammonia compound resulting from the selective ammonia compound reduction catalyst is dismissed, and a control device for correction an amount of the ammonia compound in an appropriate amount added to be based on an amount of the ammonia compound which was detected by the ammonia compound detection device. Therefore it becomes possible regulating the amount of ammonia compound to be added, to regulate more precisely, and therefore the emissions regulation more effectively perform.

Examples of the ammonia compound, i.e., a reducing agent which is used together with the selective ammonia compound reduction catalyst used contains urea, ammonium carbamate and the like.

The constructions according to the invention described above can essentially combined with each other in any way.

The above task and features and advantages of the present invention will become apparent from the following Description of preferred embodiments with reference on the attached Drawings obvious, using the same reference numerals to represent the same elements.

1 is a schematic representation of a first embodiment of the emission control device for an internal combustion engine of the invention.

2A FIG. 12 is a graph showing NOx absorption and release performed by the NOx absorption-reduction catalyst with the air-fuel ratio of the incoming exhaust gas on the lean side of the stoichiometric air-fuel ratio.

2 B is a diagram; which shows the NOx absorption and release performed by the NOx absorption-reduction catalyst, wherein the air-fuel ratio of the inflowing exhaust gas is on the stoichiometric air-fuel ratio or on the rich side thereof.

3 FIG. 12 is a diagram schematically showing the concentrations of unburned HCs, CO and oxygen in the exhaust gas that is emitted from the internal combustion engine.

4 FIG. 12 is a diagram illustrating emission control ranges of the catalysts versus engine speed and engine load.

5 FIG. 12 is a graph showing a relationship between the exhaust gas temperature and the emission control rate.

6 represents a second embodiment of the invention.

7 represents a third embodiment.

8th represents a fourth embodiment.

The following are preferred embodiments the invention in detail with reference to the accompanying drawings described. In the embodiments can e.g. Urea can be used as an ammonia compound.

A first embodiment of the invention will be described with reference to FIG 1 to 5 described.

According to 1 are a NOx absorption-reduction catalyst 3 and a selective ammonia compound reduction catalyst 4 in series in an exhaust pipe 2 of a direct-injection lean-burn petrol engine 1 arranged.

Regarding the internal combustion engine 1 a fuel injection duration TAU is calculated according to the following equation: TAU = TPK

In the above equation, TP represents represents a basic fuel injection period and K represents a correction coefficient The basic fuel injection duration TP is a fuel injection duration, who needs the theoretical air-fuel ratio in the mixture contained in the cylinder is delivered to achieve. The basic fuel injection duration TP is determined beforehand through experiments and is stored in a ROM as a function of engine load Q / N (amount of intake air Q / engine speed N) and the engine speed N previously stored in the form of a table.

The correction coefficient K is a Coefficient for controlling the air-fuel ratio of the mixture supplied in the cylinder of the internal combustion engine becomes. If K = 1.0, then the air-fuel ratio of the Mixture delivered in the cylinder of the internal combustion engine becomes equal to the theoretical air-fuel ratio. If K <1.0, it will Air-fuel ratio of the mixture supplied in the cylinder of the internal combustion engine becomes greater than the theoretical air-fuel ratio, i.e., the mixture skinny. If K> 1.0 the air-fuel ratio of the mixture that is in the cylinder of the internal combustion engine is delivered less than the theoretical air-fuel ratio, i.e., the mixture becomes fat.

In the internal combustion engine 1 the correction coefficient K is set to a value lower than 1.0 to perform lean air-fuel ratio control in a low to medium engine load operating range. In a high load operating area of the engine during the warm-up phase. of the internal combustion engine after Starting, during acceleration or during a constant speed of the vehicle of, for example, 120 km / h or more, the correction coefficient K is set to 1.0 in order to carry out stoichiometric operation. In a full-load operating range of the internal combustion engine, the correction coefficient K is set to a value larger than 1.0 to perform rich air-fuel ratio control.

Usually the internal combustion engine is on common operated at low to medium loads, so for the most part while the operation of the internal combustion engine, the correction coefficient K is set to less than 1.0 and therefore a lean fuel mixture is burned.

The NOx absorption reduction catalyst 3 has a carrier, for example an aluminum carrier, which is coated with a noble metal such as platinum Pt or the like and with at least one element from the group of, for example, alkali metals, such as potassium (K), sodium (Na), lithium (Li), cesium (Cs ) and the like, is selected from alkaline earths such as barium (Ba), calcium (Ca) and the like and from rare earths such as lanthanum (La), yttrium (Yi) and the like. The following is the relationship between the air and the fuel (carbon dioxide) entering the intake passage of the internal combustion engine 1 and in a portion of the exhaust line upstream of the NOx absorption-reduction catalyst 3 is referred to as the air-fuel ratio of the exhaust gas entering the NOx absorption-reduction catalyst. 3 flows. When the air-fuel ratio of the inflowing exhaust gas is on the lean side of the theoretical air-fuel ratio, the NOx absorption-reduction catalyst absorbs 3 the NOx. When the oxygen concentration in the inflowing exhaust gas decreases, the NOx absorption reduction catalyst sets 3 the NOx absorbed freely.

In a case where no fuel (hydrocarbons) or no air in the section of the exhaust line upstream of the NOx absorption-reduction catalyst 3 is supplied, the air-fuel ratio of the inflowing exhaust gas equals the air-fuel ratio of the mixture that is supplied into the combustion chamber. In this case, therefore, the NOx absorption-reduction catalyst absorbs 3 the NOx when the air-fuel ratio of the mixture supplied into the combustion chamber is on the lean side of the theoretical air-fuel ratio, and the NOx absorption-reduction catalyst 3 releases the absorbed NOx when the oxygen concentration in the mixture supplied to the combustion chamber decreases.

It is considered that the absorption and reduction of the NOx by the NOx absorption-reduction catalyst 3 are caused by a mechanism such as that described in the 2A and 2 B is shown. Although the mechanism is illustrated in the case of a catalyst device in which a support is charged with platinum (Pt) or barium (Ba), the same mechanism applies essentially to a catalyst that uses a noble metal other than platinum or an alkaline metal, a contains alkaline earth, or a rare earth.

When the exhaust gas becomes noticeably lean, the oxygen concentration in the exhaust gas increases considerably, so that oxygen (O ₂ ) is deposited on the surfaces of platinum (Pt) in the form of O ₂ ^_ or O ² - as in FIG 2A is shown. Nitrogen oxides No contained in the exhaust gas react with O ₂ ^- or O ^2- on the surfaces of platinum (Pt) to produce NO ₂ (2NO + O ₂ → 2NO ₂ ).

As long as the NOx absorption capacity of the NOx absorption-reduction catalyst 3 is not saturated, NO ₂ generated as described above is absorbed in the catalyst while oxidation is taking place on the platinum (Pt), and it binds to barium oxide (BaO) and then diffuses in the form of nitrate ions (NO ₃ ) in the NOx absorption-reduction catalyst 3 , In this way, NOx becomes in the NOx absorption-reduction catalyst 3 absorbed.

However, when the oxygen concentration in the exhaust gas decreases, the production of NO ₂ also decreases, so that through a reaction in the opposite direction to that described above, nitrate ions (NO ₃ ^- ) from the NOx absorption-reduction catalyst 3 are released in the form of NO ₂ or NOx.

That is, NOx is from the NOx absorption-reduction catalyst 3 released when the oxygen concentration in the exhaust gas decreases. As in 3 is shown, the oxygen concentration in the incoming exhaust gas decreases when the degree of leanness of the exhaust gas, which is in the NOx absorption-reduction catalyst 3 flows, decreases. That is, by reducing the leanness of the inflowing exhaust gas NOx from the NOx absorption-reduction catalyst 3 is released even if the air-fuel ratio of the inflowing exhaust gas is on the lean side of the theoretical air-fuel ratio.

When the air-fuel ratio of the mixture supplied into the combustion chamber changes to the stoichiometric air-fuel ratio or the rich side thereof, and accordingly the air-fuel ratio of the exhaust gas changes to the stoichiometric air-fuel ratio or the rich side thereof large amounts of unburned HCs and CO are emitted from the internal combustion engine, as in 3 is shown. In this case, unburned HCs and CO oxidize directly through reactions with O ₂ ^- or O ^{2 -} on the platinum (Pt).

Furthermore, the oxygen concentration in the exhaust gas becomes very low when the air-fuel ratio of the exhaust gas that is in the NOx absorption-reduction catalyst 3 flows to the stoichiometric air-fuel ratio or the rich side thereof, so that the NOx absorption-reduction catalyst 3 Releases NO ₂ or NO. The NO ₂ or NO released in this way is reduced by the reactions with unburned HCs and CO, as in 2 B is shown. If NO ₂ or NO on platinum (Pt) is removed in this way, the catalyst releases NO ₂ or NO successively. Therefore, the NOx absorption-reduction catalyst 3 NOx released in a short time by changing the air-fuel ratio of the exhaust gas flowing into the NOx absorption-reduction catalyst 3 to the rich side of the theoretical air-fuel ratio. If unburned HCs and CO remain after the O ^{2 -} or O ^{2 -} on the platinum (Pt) is consumed, NOx is released from the NOx absorption-reduction catalyst 3 was released, and NOx from the internal combustion engine 1 is emitted, reduced by the remaining unburned HCs and CO.

Therefore, it becomes in the NOx absorption-reduction catalyst 3 absorbed NOx released in a short time by the air-fuel ratio of the exhaust gas entering the NOx absorption-reduction catalyst 3 flows in, is shifted to the rich side. Furthermore, the NOx released in this way is reduced, so that the emission of NOx into the atmosphere is prevented.

Furthermore, NOx generated by the NOx absorption-reduction catalyst 3 was also released by shifting the air-fuel ratio of the exhaust gas into the catalytic converter 3 inflows can be reduced to the theoretical air-fuel ratio, because the NOx absorption reduction catalyst 3 also has the function of a reduction catalyst. However, when the air-fuel ratio of the inflowing exhaust gas is shifted to the theoretical air-fuel ratio, the NOx absorption-reduction catalyst sets 3 the NOx is only gradually released so that it takes a long time to remove the entire amount of the NOx absorption-reduction catalyst 3 to release absorbed NOx.

By reducing the leanness of the in the NOx absorption reduction catalyst 3 Incoming exhaust gas becomes NOx from the NOx absorption-reduction catalyst 3 released even if the air-fuel ratio of the exhaust gas flowing therein is on the lean side of the theoretical air-fuel ratio. Therefore, NOx from the NOx absorption-reduction catalyst 3 are released by only the oxygen concentration in the exhaust gas entering the catalyst 3 flows in, is reduced.

The selective ammonia compound reduction catalyst 4 is formed by adding urea to a NOx catalyst for selective reduction. An example of the NOx catalyst mentioned here is a zeolite catalyst which contains an oxide of a transition element of the fourth, fifth or sixth period and / or an oxide of a rare earth. A more preferred example is a catalyst in which Al ₂ O _{3 is} charged with Ti and V.

When an aqueous solution of the urea is added to the catalyst, oxides of nitrogen in the exhaust gas are reduced at a predetermined exhaust gas temperature according to the following reaction equations: (NH ₂ ) 2CO + H ₂ O → 2NH ₃ ^x + CO ₂ 4NH ₃ ^x + 4NO + O ₂ → 4N ₂ 6H ₂ O

To cause the NOx absorption reduction catalyst 3 and the selective ammonia compound reduction catalyst 4 Function complementary to each other, this embodiment uses a NOx sensor 5 and an ammonia compound addition control valve 6 that are in a section of the exhaust line 2 are provided, which is downstream of the NOx absorption-reduction catalyst 3 and upstream of the selective ammonia compound reduction catalyst 4 located. The NOx sensor 5 is immediately downstream of the NOx absorption-reduction catalyst 3 and upstream of the ammonia compound addition control valve 6 arranged. Furthermore, a catalyst temperature detection device 7 immediately upstream of the selective ammonia compound reduction catalyst 4 arranged and an ammonia sensor 8th is downstream of the selective ammonia compound reduction catalyst 4 arranged.

The NOx sensor 5 , the ammonia compound addition control valve 6 , the catalyst temperature detection device 7 and the ammonia sensor 8th are electrical with a control unit (ECU) 9 connected, which is formed by a computer. An engine speed sensor for detecting the speed of the internal combustion engine 1 is also provided and with the control unit (ECU) 9 connected.

Based on the information of these sensors and the like, the states of the catalysts and therefore the operation of the internal combustion engine 1 detected. An operating state detection device 10 for detecting the operating state of the internal combustion engine 1 based on the data input from the sensors and the like, in the computer of the control unit (ECU) 9 realized. Furthermore, an ammonia compound adding amount control device 11 for issuing an ammonia compound addition instruction to the ammonia compound addition control valve 6 depending on the detected operating state and under control of the amount of added ammonia compound in the computer of the control unit (ECU) 9 realized. A reducing agent indicator 12 . which is when an ammonia compound by the ammonia compound addition amount control device 11 13, which indicates to a driver that an ammonia compound is being added, is provided in a display panel or the like.

The NOx sensor 5 detects the concentration of NOx in the exhaust gas from the NOx absorption-reduction catalyst 3 is output, ie, the NOx concentration in the exhaust gas that is in the selective ammonia compound reduction catalyst 4 flows. The ammonia compound addition amount control device 11 includes an ammonia compound adding amount determining device 11a for determining an amount of NOx emitted by the internal combustion engine 1 is released on the basis of the NOx sensor 5 sensed NOx concentration and the amount of air detected by an air flow meter (not shown) and intended to estimate, based on the amount of NOx detected, an amount of ammonia compound that the selective ammonia compound reduction catalyst 4 must be added. The ammonia compound addition amount control device 11 issues an instruction, an amount of ammonia compound depending on that by the ammonia compound adding amount determining device 11a add estimated value.

To the amount of ammonia compound estimate it is advantageous to save them in advance as a table in a ROM, which is a predetermined relationship between the detected amount of NOx and the amount of ammonia compound, who inflicted should be represents.

Instead of using the NOx sensor 5 it is also possible to use an accelerator pedal depression degree (which can therefore be replaced by the fuel injection amount), the engine speed, and the amount of EGR (exhaust gas recirculation) provided by an EGR control device to estimate the amount of NOx. The amount of in the internal combustion engine 1 Intake air may also be determined based on the extent of the throttle opening, rather than the detection by the air flow meter.

The catalyst inflow gas temperature sensor 7 serves as a catalyst temperature detection device for detecting the temperature of the exhaust gas entering the selective ammonia compound reduction catalyst 4 flows. Based on the detected exhaust gas temperature, an activation state of the selective ammonia compound reduction catalyst can 4 be determined. If the temperature of the in the catalyst 4 inflowing exhaust gas is relatively low, the exhaust gas control ability of the catalyst 4 low, so that the amount of ammonia compound added by the urea adding amount control device 11 is reduced. A ratio between the temperature of the exhaust gas entering the catalyst 4 flows in, and the amount of ammonia compound added is previously stored as a table in the ROM.

The ammonia sensor 8th is used to correct the amount of ammonia compound to be added. Ie, if ammonia through the ammonia sensor 8th is detected, the downstream of the selective ammonia compound reduction catalyst 4 is arranged, the detection means that the amount of ammonia compound added is too large compared to the amount of NOx. Therefore, a feedback control device is provided to control the amount of ammonia passed through the ammonia sensor 8th was detected, back to the urea adding amount control device 11 and thereby correct the amount of urea to be added to a suitable setpoint. The feedback control device is implemented as a portion of the urea adding amount control device 11 in the computer of the control unit (ECU). 9 realized.

Below is an emission control according to the embodiment described.

As a result of the fuel combustion in the cylinder during the operation of the internal combustion engine 1 becomes exhaust gas from the internal combustion engine 1 ejected and flows through the exhaust pipe 2 sequentially over the NOx absorption reduction catalyst 3 and the selective urea reduction catalyst 4 and then flows through the silencer, not shown. Thus, exhaust gas is released into the atmosphere.

This exemplary embodiment cleans the emissions over the widest possible operating range of the internal combustion engine by means of the selective urea reduction catalyst 4 that works in a high load and high speed range that is behind the emission control range of the NOx absorption-reduction catalyst 3 lies.

While the operating state of the internal combustion engine is not in a predetermined high-load and high-speed range, the emission control is accomplished by repeatedly causing the absorption and reduction of NOx in the NOx absorption-reduction catalyst 3 performed according to the principle described above. That is, when NOx is from the NOx absorption-reduction catalyst 3 is released, the air-fuel ratio of the exhaust gas is shifted to the rich side, so that NOx that is released by the NOx absorption-reduction catalyst 3 is reduced.

When the air-fuel ratio is set on the rich side, for example, by reducing the throttle valve opening to reduce the amount of intake air when the operation of the engine 1 is in the predetermined high-load and high-speed range, the reduced amount of intake air thus discharges (Amount of oxygen) a little unburned fuel, so that a smoke commonly referred to as smoke is fathered. Therefore, the reduction of NOx in the predetermined high-load and high-speed operating range cannot be in the NOx absorption-reduction catalyst 3 be performed.

In response to the operating condition detection device 10 who finds that the engine 1 is in the above-described operating state, the ammonia compound addition amount control device 11 an ammonia compound addition instruction to the ammonia compound addition control valve 6 so that the aqueous solution of the ammonia compound from the ammonia compound addition control valve 6 is injected. Therefore, the emission control is carried out according to the principle described above.

Meanwhile, the concentration of the NOx absorption-reduction catalyst 3 escaping, not treated by him, NOx through the NOx sensor 5 detected. As a result of entering the NOx sensor 5 of the detected value is determined by the ammonia compound addition amount control device 11 the control unit (ECU) 9 the amount of NOx emitted by the internal combustion engine 1 based on the NOx concentration and the amount of in the internal combustion engine 1 sucked air was expelled. Based on the thus determined amount of NOx, the ammonia compound addition amount control device estimates 11 an amount of ammonia compound from the selective ammonia compound reduction catalyst 4 to be added by the ammonia compound adding amount determining device 11a is used. The ammonia compound addition amount control device 11 then has the ammonia compound addition control valve 6 to add an amount of ammonia compound depending on the estimated value.

Furthermore, the temperature of the in the NOx sensor 5 inflowing gas through the catalyst temperature detection device 7 measured. Depending on the magnitude of the inflow gas temperature detected, the ammonia compound addition amount control device changes 11 the control unit (ECU) 9 the amount of ammonia compound to be added.

Furthermore, the ammonia concentration in the gas resulting from the selective ammonia compound reduction catalyst 4 flows through the ammonia sensor 8th detected. On the basis of the ammonia sensor 8th of the detected value is corrected by the feedback control device of the ammonia compound addition amount control device 11 the amount of fuel to be added in such a direction that the ammonia concentration in the exhaust gas coming from the selective ammonia compound reduction catalyst 4 flows out, will decrease.

In the manner described above, the emission control by the NOx absorption-reduction catalyst 3 and the selective ammonia compound reduction catalyst 4 carried out. The complementary ratio between the NOx absorption-reduction catalyst 3 and the selective ammonia compound reduction catalyst 4 is in 4 shown. In 4 “A” indicates an area where the NOx absorption-reduction catalyst 3 is able to perform emission control, and "B" indicates an area where the selective ammonia compound reduction catalyst 4 is able to control emissions.

5 shows relationships between the exhaust gas temperature and the control rate in the NOx absorption-reduction catalyst 3 and the selective ammonia compound reduction catalyst 4 , In 5 “A” denotes an area in which the NOx absorption-reduction catalyst 3 is able to perform emission control, and "B" shows an area where the selective ammonia compound reduction catalyst 4 is able to control emissions. As with 5 can be understood, the NOx absorption-reduction catalyst works 3 in a relatively low exhaust gas temperature range and the selective ammonia compound reduction catalyst 4 works in a relatively high exhaust gas temperature range.

In this embodiment, the positional relationship between the NOx absorption-reduction catalyst 3 and the selective ammonia compound reduction catalyst 4 be reversed.

A second exemplary embodiment according to the invention is described with reference to FIG 6 described.

The embodiment that in 6 has a starting catalyst device 21 , in addition to a construction as described in connection with the first embodiment. The starting catalyst device 21 is a NOx catalyst in a section of an exhaust pipe 2 is provided, which is as close as possible to the internal combustion engine. The starting catalyst device 21 is able to substantially remove NOx from the exhaust gas of the internal combustion engine before the NOx absorption-reduction catalyst 3 is warmed up after starting the internal combustion engine. Because the starting catalyst device 21 in a section of the exhaust pipe adjacent to the internal combustion engine 2 is arranged, which is upstream of a NOx absorption-reduction catalyst 3 extends, the starting catalyst device 21 quickly heated to a control temperature range by the exhaust gas after the engine was started.

A third embodiment of the invention is described below with reference to FIG 7 be wrote.

An emission control device of the embodiment shown in 7 has a bypass line 31 that have an upstream, side-mounted NOx absorption reduction catalyst 3 bypasses and directs exhaust to a downstream catalytic converter, in addition to a construction as shown in 1 is shown. A branch point between the bypass line 31 and an exhaust pipe 2 is with a switching device 32 provided, that is, a changeover valve that the exhaust flow path by closing and opening the bypass line 31 changes.

The changeover valve 32 is an electromagnetic valve that is electrically connected to a control unit (ECU) 9 connected and controlled thereby. If by an operating condition detection device 10 It is determined that the present operating range of an internal combustion engine is such a range in which the NOx absorption-reduction catalyst 3 is able to function, the switching valve closes 32 the bypass line 31 so that the exhaust gas to the NOx absorption-reduction catalyst 3 flows. When it detects that engine operation has been shifted to a high load and high speed range, the switch valve opens 32 the bypass line 31 and closes the exhaust pipe leading to the NOx absorption-reduction catalyst 3 extends so that the exhaust gas via the bypass line 31 to the selective ammonia compound reduction catalyst 4 flows.

Therefore, the control unit (ECU) 9 the changeover valve 32 on, the bypass line 31 close when the operating state of the internal combustion engine by the operating state detection device 10 Was detected, is not the high-load and high-speed range, so that the exhaust gas in the NOx absorption reduction catalyst 3 flows. When the operating state of the internal combustion engine by the operating state detection device 10 is detected, is in the high-load and high-speed range, the control unit (ECU) 9 the changeover valve 32 on, the bypass line 31 to open and close the exhaust pipe leading to the NOx absorption reduction catalyst 3 extends so that the exhaust gas via the bypass line 31 directly to the selective ammonia compound reduction catalyst 4 flows. In response to the determination by the operating condition detection device 10 that the operating state of the internal combustion engine is in the high-load and high-speed range is given by the ammonia compound addition amount control device 11 an ammonia compound addition instruction to the ammonia compound addition control valve 6 so that an aqueous solution of ammonia compound from the ammonia compound addition control valve 6 is injected. In this way, emission control is carried out depending on the principle described above.

Next, a fourth embodiment of the invention will be described with reference to FIG 8th described.

In an emission control device of the embodiment shown in 8th is shown, an exhaust pipe branches into a first exhaust pipe 41 and a second exhaust pipe 42 that are arranged in parallel. The first exhaust pipe 41 is with a NOx absorption-reduction catalyst 3 Mistake. The second exhaust pipe 42 is with a selective ammonia compound reduction catalyst 4 Mistake.

A changeover valve, ie a changeover device 32 , is at a branch point between the first exhaust pipe 41 and the second exhaust pipe 42 arranged.

As in the in 1 shown construction is a NOx sensor 5 upstream of the selective ammonia compound reduction catalyst 4 provided, and a catalyst temperature detection device 7 is immediately upstream of the selective ammonia compound reduction catalyst 4 intended. There is also an ammonia sensor 8th downstream of the selective ammonia compound reduction catalyst 4 and an ammonia compound addition control valve 6 is immediately upstream of the selective ammonia compound reduction catalyst 4 intended.

The changeover valve 32 is an electromagnetic valve that is electrically connected to a control unit (ECU) 9 connected and controlled thereby. If by the operating condition detection device 10 It is determined that the present operating range of an internal combustion engine is such a range in which the NOx absorption-reduction catalyst 3 is able to function, selects the switching valve 32 the first exhaust pipe 41 off, so that the exhaust gas to the NOx absorption reduction catalyst 3 flows. The NOx absorption reduction catalyst 3 performs emission control as described above.

If it is determined that the operation of the internal combustion engine has shifted to the high-load and high-speed range, the changeover valve selects 32 the second exhaust pipe 42 off so that the exhaust gas in the selective ammonia compound reduction catalyst 4 flows. If the selective ammonia compound reduction catalyst 4 is selected in this way, the ammonia compound addition amount control device outputs 11 an ammonia compound addition instruction to the ammonia compound addition control valve 6 so that an aqueous solution of ammonia compound from the ammonia compound addition control valve 6 is injected. In this way, the emission control is carried out according to the principle described above.

Although the foregoing embodiments of the invention are in connection with a gasoline-powered internal combustion engine 1 , it should be understood that the invention is also applicable to a diesel engine. In the case of a diesel engine, fuel combustion in the combustion chambers is performed in a lean (or high) air-fuel ratio range that is far from the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio of the exhaust gas entering the NOx absorption-reduction catalyst 3 flows very lean (or high) during a normal operating state of the diesel engine, so that NOx flows through the catalytic converter 3 absorbed, but is hardly released from it.

Therefore, when using in an exhaust gas recirculation device for a diesel engine (commonly referred to as an EGR device) is used as an example so that the NOx that is absorbed in the catalyst by shifting the air-fuel ratio of the exhaust gas to the stoichiometric Air-fuel ratio or to the fat side of it by introducing a large amount of recirculated exhaust gas be released into the combustion chambers.

Claims (12)

Emission control device for an internal combustion engine comprising the following components: a NOx absorption reduction catalyst ( 3 ) in an exhaust pipe ( 2 ) a lean-burn internal combustion engine ( 1 ) is provided, the NOx absorption reduction catalyst ( 3 ) Absorbs NOx when an air-fuel ratio of an exhaust gas from the internal combustion engine is on a lean side of a theoretical air-fuel ratio, and wherein the NOx absorption-reduction catalyst ( 3 ) Releases NOx and causes a reduction in NOx when an oxygen concentration in the exhaust gas is decreased by shifting the air / fuel ratio of the exhaust gas toward the rich side by the control of the internal combustion engine; and a selective ammonia compound reduction catalyst ( 4 ) which causes a selective reduction due to the supply of an ammonia compound, the amount of the ammonia compound to be supplied from an ammonia compound adding amount determining device ( 11a ) which determines the NOx concentration in the exhaust gas upstream of the selective ammonia compound reduction catalyst ( 4 ) taken into account by means of a NOx sensor ( 5 ) is determined. Emission control device according to claim 1, characterized by: an operating state detection device ( 10 ) for detecting an operating state of the internal combustion engine ( 1 ); and a switching device ( 32 ) to switch a flow direction of the exhaust gas from either the NOx absorption-reduction catalyst ( 3 ) or the selective ammonia compound reduction catalyst ( 4 ), depending on the operating state of the internal combustion engine ( 1 ) by the operating state detection device ( 10 ) was recorded. Emission control device according to claim 1, characterized in that the NOx absorption reduction catalyst ( 3 ) and the selective ammonia compound reduction catalyst ( 4 ) in series in the exhaust pipe ( 2 ) are arranged. Emission control device according to claim 3, characterized in that the selective ammonia compound reduction catalyst ( 4 ) downstream of the NOx absorption reduction catalyst ( 3 ) in the exhaust duct ( 2 ) is arranged. Emission control device according to claim 3, characterized in that the selective ammonia compound reduction catalyst ( 4 ) upstream of the NOx absorption reduction catalyst ( 3 ) in the exhaust pipe ( 2 ) is arranged. Emission control device according to claim 1 or 2, characterized in that the NOx absorption reduction catalyst ( 3 ) and the selective ammonia compound reduction catalyst ( 4 ) parallel in the exhaust pipe ( 2 ) are arranged. Emission control device according to claim 2 or 3, characterized by a bypass line ( 31 ) that bypasses an upstream catalyst and directs the exhaust gas to a downstream catalyst, the switching device ( 32 ) the flow direction of the exhaust gas by opening and closing the bypass line ( 31 ) changed. Emission control device according to claim 6, characterized in that the exhaust pipe ( 2 ) in a first exhaust pipe ( 41 ) and a second exhaust pipe ( 42 ) forks that are arranged in parallel; that the NOx absorption reduction catalyst ( 3 ) in the first exhaust pipe ( 41 ) is arranged, and that the selective ammonia compound reduction catalyst ( 4 ) in the second exhaust pipe ( 42 ) is arranged; and that a switching valve as a switching device ( 32 ) at a branch point between the first exhaust pipe ( 41 ) and the second exhaust pipe ( 42 ) is arranged. Emission control device according to one of Claims 1 to 8, characterized by an additional ammonia compound addition quantity determination device ( 11a ) for estimating an amount of the ammonia compound that the selective ammonia compound reduction catalyst ( 4 ) to be added based on an amount of NOx present in the exhaust gas flow that is in the selective ammonia compound reduction catalyst ( 4 ) flows, and on the basis of the intake air that enters the internal combustion engine ( 1 ) is sucked in. Emission control device according to claim 9, characterized by an ammonia sensor ( 8th ) for the detection of an ammonia compound that results from the selective ammonia compound reduction catalyst ( 4 ) was let out; and a control device for correcting an amount of the ammonia compound to be added in an appropriate amount based on an amount of the ammonia compound detected by the ammonia sensor ( 8th ) is recorded. Emission control device according to one of claims 1 to 10, characterized by a catalyst temperature detection device ( 7 ) for detecting a temperature state of the selective ammonia compound reduction catalyst ( 4 ); and an ammonia compound addition amount control device ( 11 ) to change an ammonia compound addition amount required for the selective ammonia compound reduction catalyst ( 4 ) is provided depending on the detected catalyst temperature. Emission control device according to one of Claims 1 to 11, characterized by a third catalytic converter which is located in a section of the exhaust pipe ( 2 ) is provided which is upstream of the NOx absorption-reduction catalyst ( 3 ) and the selective ammonia compound reduction catalyst ( 4 ) extends.