JP2000240429A - Exhaust gas emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform efficient regeneration of an NOX occlusion reduction catalyst regardless of an exhaust gas temperature. SOLUTION: An NOX occlusion reduction catalyst 7 is arranged in the exhaust passage 3 of an engine 1 and absorbs NOX contained in exhaust gas from an engine under lean air-fuel ratio operation. When an NOX occlusion amount of the catalyst 7 is increased, a liquid reducing agent (diesel oil) is injected in an exhaust passage on the upper stream side of the catalyst 7 through a reducing agent injection valve 91 and NOX is emitted from the catalyst 7 for reduction purification. An electronic control unit(ECU) 30 calculates the temperature of exhaust gas flowing in the catalyst 7 based on an engine running state and the more a calculated exhaust gas temperature is lower, the more an injection pressure of the reducing agent injection valve is increased and the grain size of injected reducing agent particles is decreased. By decreasing the grain size, the injected reducing agent particles are easily evaporated even at a low exhaust gas temperature. Since liquid reducing agent particles are prevented from reaching the catalyst 7, the reduction agent supplied to the catalyst 7 is effectively utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Relates to an exhaust purifying apparatus of the present invention is an internal combustion engine TECHNICAL FIELD OF THE INVENTION The exhaust air-fuel ratio flows into the details absorbs NO _X in the exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas drops The present invention relates to an exhaust gas purification device for an internal combustion engine provided with a NO _X storage reduction catalyst that releases sometimes absorbed NO _X.

[0002]

BACKGROUND ART exhaust air-fuel ratio of the inflowing absorbs NO _X in the exhaust gas when the lean, NO _X occluding and reducing catalyst the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed when reduced intellectual Have been. _The NO _X storage reduction catalyst absorbs NO _X in the exhaust gas under a lean air-fuel ratio atmosphere, but absorbed N
When O _X amount is reaches the saturation amount increases can not be absorbed any more NO _X. Therefore, it is necessary to release periodically _the NO _X storage reduction catalyst to reduce the oxygen concentration of the exhaust gas flowing into the by _the NO _X storage NO _X absorbed from the reduction catalyst in an exhaust gas purification apparatus using the _the NO _X storage reduction catalyst . When the NO _X storage reduction catalyst is used as an exhaust gas purification device of a gasoline engine, when the operating air-fuel ratio of the engine is reduced (that is, when the engine is operated at a rich air-fuel ratio), the oxygen concentration in the exhaust is reduced and the exhaust gas is reduced. unburned HC, since the CO component is increased, the _the NO _X storage reduction catalyst from the NO _X is released, the released NO _X is HC on _the NO _X storage reduction catalyst,
Reduced by CO.

[0003] However, when using _the NO _X storage reduction catalyst as an exhaust gas purification device for a diesel engine, reduces the oxygen concentration in the exhaust gas by other means since it is difficult to operate the engine at a rich air-fuel ratio It is necessary. When the NO _X storage reduction catalyst is used as an exhaust gas purification device for a diesel engine, the NO _X
As a method of releasing the NO _X absorbed from the _X storage reduction catalyst, a method of supplying a reducing agent such as liquid hydrocarbon to an exhaust passage upstream of the NO _X storage reduction catalyst is usually used.
When the reducing agent supplied to the exhaust passage on the upstream side is dispersed in the exhaust gas and flows into the NO _X storage reduction catalyst together with the exhaust gas, the reducing agent reacts with the oxygen in the exhaust gas on the NO _X storage reduction catalyst and is oxidized. , atmospheric oxygen concentration of the NO _X occluding and reducing catalyst is decreased, the absorbed NO _X is released from _the NO _X storage reduction catalyst. The released NO _X is reduced and purified by the reducing agent in the exhaust gas on the NO _X storage reduction catalyst.

[0004] does not relate to _the NO _X storage reduction catalyst, but those examples of devices for supplying a reducing agent to the upstream side of the exhaust passage is arranged in an exhaust passage catalysts described in JP-A-5-44434 is there. In the device disclosed in the publication, a particulate filter carrying an oxidation catalyst is disposed in an exhaust passage of a diesel engine, and when burning exhaust particulates collected by the particulate filter, fuel (fuel) is supplied to an exhaust passage upstream of the particulate filter. By injecting a reducing agent), the injected fuel is burned on the oxidation catalyst to raise the temperature of the particulate filter. Further, in the device of the publication, in order to supply an appropriate amount of fuel in accordance with the activation of the oxidation catalyst, while calculating the amount of fuel to be supplied to the catalyst based on the temperature of exhaust gas flowing into the catalyst and the amount of engine intake air, The fuel amount calculated based on the exhaust gas temperature at the catalyst outlet is corrected.

In general, when a reducing agent is supplied to an exhaust passage on the upstream side of the catalyst, the entire amount of the supplied reducing agent is reacted by the catalyst to prevent the unreacted reducing agent from flowing to the downstream side of the catalyst. There is a need to. In addition, since the catalyst performance decreases as the temperature of the catalyst decreases, when the same amount of reducing agent is supplied when the exhaust temperature is low and when the exhaust temperature is high, part of the supplied reducing agent remains unreacted downstream of the catalyst. In some cases. The apparatus of the above publication determines the amount of the reducing agent to be supplied in accordance with the exhaust gas temperature (that is, the capacity of the catalyst) in order to prevent the unpurified reducing agent from flowing downstream of the catalyst due to a change in the exhaust gas temperature. The entire amount of the supplied reducing agent is reacted on the catalyst.

[0006]

However, the above-mentioned Japanese Patent Application Laid-Open
The exhaust gas flowing into the catalyst as in the device disclosed in Japanese Patent Publication No.
Even if an appropriate amount of reducing agent is supplied to the catalyst according to the
That the entire amount of the reducing agent may not react on the catalyst.
It is known. For example, supply the exhaust passage upstream of the catalyst.
The liquid reductant such as fuel supplied does not vaporize enough
Reach the catalyst with relatively large liquid particles
And the reducing agent particles adhere to the catalyst surface or
In some cases, the particles pass through the catalyst cell as they are.
NO_XNO from storage reduction catalyst_XRelease and reduction purification operations
(Hereinafter NO_XNO absorbed from the storage reduction catalyst_XRelease
The operation for reducing and purifying is "NO _XRegeneration operation of storage reduction catalyst
), The catalyst of the liquid reducing agent particles
Reduction provided when surface adhesion or passage (slip through) occurs
Agent is not used effectively and NO_XReleased from storage reduction catalyst
NO_XMay not be reduced and purified.
To prevent this, NO_XSupply to storage reduction catalyst
Increase the amount of reducing agent to supply a sufficient amount of reducing agent to the catalyst.
It is possible to do so, but in this case
NO for missing_XUnreacted water flowing downstream of the storage reduction catalyst
The amount of reducing agent increases, and the amount of reducing agent consumed increases
In addition, there arises a problem that the exhaust properties deteriorate.

[0007] In view of the above problems, the present invention appropriately controls the atomization state of the reducing agent when supplying the liquid reducing agent to the NO _X storage reduction catalyst, thereby increasing the consumption of the reducing agent and deteriorating the exhaust characteristics. It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can prevent the occurrence of the exhaust gas.

[0008]

Means for Solving the Problems] According to the invention described in claim 1, disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas flowing flows to absorb NO _X in the exhaust gas when the lean with a _the NO _X storage reduction catalyst the oxygen concentration of the exhaust gas to release the absorbed NO _X when reduced, and a reducing agent supply device to the upstream side of the exhaust passage of the _the NO _X storage reduction catalyst for injecting the liquid reducing agent In the exhaust gas purifying apparatus for an internal combustion engine, atomizing control means for changing an atomizing state of a reducing agent injected into an exhaust passage from the reducing agent supply device according to an exhaust gas temperature flowing into the NO _X storage reduction catalyst is provided. An exhaust gas purification device for an internal combustion engine is provided.

That is, in the first aspect of the present invention, NO
_The atomization state of the reducing agent is changed according to the exhaust gas temperature on the upstream side of the _X storage reduction catalyst. When the liquid reducing agent is injected into the exhaust passage, if the exhaust temperature is low, the exhaust temperature is high even if the atomization state is the same (for example, even if the particle diameter of the injected reducing agent is the same). In comparison with the case, the amount of the reducing agent that reaches the NO _X storage reduction catalyst in the form of liquid particles without being vaporized in the exhaust gas increases. On the other hand, when the temperature of the exhaust gas is high, the amount of the reducing agent that reaches the NO _X storage reduction catalyst as liquid particles since the reducing agent evaporates in the high-temperature exhaust gas even if the atomized state of the injected reducing agent is somewhat poor. Decreases. For this reason, by changing the atomization state of the reducing agent injected according to the exhaust gas temperature,
It is possible to prevent the aforementioned reducing agent from adhering to the catalyst surface and bleeding through.

According to the invention described in claim 2, wherein the atomizing control means, the reducing agent by decreasing the particle size of the reducing agent the exhaust gas temperature flowing into the _the NO _X storage reduction catalyst is lower the injection An exhaust purification device for an internal combustion engine according to claim 1, wherein the atomization state of the exhaust gas is changed. In other words, according to the second aspect of the present invention, as the temperature of the exhaust gas flowing into the NO _X storage reduction catalyst decreases, the particle diameter of the liquid reducing agent injected into the exhaust passage decreases. When the particle size of the liquid reducing agent is small, the reducing agent is easily vaporized, so that the reducing agent injected into the exhaust gas is sufficiently vaporized even at a low exhaust gas temperature and reaches the NO _X storage reduction catalyst in a gaseous state. I do. For this reason, even when the exhaust gas temperature is low, the NO _X storage-reduction catalyst does not cause attachment or slippage of the liquid reducing agent particles,
The total amount of the supplied reducing agent is N from the NO _X storage reduction catalyst.
O _X emissions, will be effectively used for reduction and purification.
For this reason, the consumption of the reducing agent is reduced and the NO _X
The amount of unreacted reducing agent flowing downstream of the storage reduction catalyst is reduced.

According to the third aspect of the present invention, the reducing agent supply device includes an injection valve for injecting the reducing agent into an exhaust passage, and the atomization control unit performs injection of the reducing agent from the injection valve. An exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the particle diameter of the injected reducing agent is changed by changing the pressure. That is, in the third aspect of the present invention, the reducing agent is injected into the exhaust passage through the injection valve, and the particle diameter of the reducing agent is adjusted by changing the injection pressure of the reducing agent. Thereby, the atomization state of the injected reducing agent can be easily changed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment of the exhaust gas purification apparatus of the present invention. In FIG. 1, reference numeral 1 denotes an internal combustion engine. In this embodiment, a diesel engine is used as the internal combustion engine 1, and each cylinder exhaust port of the engine is connected to a common exhaust passage 3 via an exhaust manifold 31. Further, a NO _X storage reduction catalyst 7 described later is arranged on the exhaust passage 3. Shown in 9 in Figure 1 is _the NO _X storage reduction catalyst 7 during the regenerating operation NO _X
This is a reducing agent supply device that supplies a reducing agent to the storage reduction catalyst 7. Reducing agent supply device, _the NO _X storage reduction by injecting reducing agent into the exhaust gas flowing to the NO _X occluding and reducing catalyst 7 provided with _the NO _X storage reduction the reducing agent injection valve 91 disposed in the exhaust inlet vicinity of the catalyst 7 The concentration of oxygen in the exhaust gas flowing into the catalyst 7 is reduced, the NO _X absorbed from the catalyst 7 is released, and the released NO _X is reduced and purified. As described below, in the present embodiment, the fuel (diesel oil) of the engine 1 is used as the reducing agent. The reducing agent supply device 9 includes an electric motor-driven fuel pump 92 that pressurizes fuel supplied from an engine fuel system (not shown), and pressurizes the fuel to inject the fuel from the reducing agent injection valve 91 into the exhaust passage 3.

In FIG. 1, reference numeral 30 denotes an electronic control unit (ECU) of the engine 1. In the present embodiment, the ECU 3
Reference numeral 0 denotes a microcomputer having a known configuration including a RAM, a ROM, and a CPU. The microcomputer 0 performs basic control such as a fuel injection amount and a fuel injection timing of the engine 1 and also controls a reducing agent supply device 9 to be described below. N from _X storage reduction catalyst 7
O _X release and reduction purification operation (NO _X catalyst regeneration operation of the reduction catalyst) is carried out.

In order to perform the regeneration operation of the NO _X storage reduction catalyst 7, an input port of the ECU 30 is provided with a driver's accelerator pedal depression amount (accelerator opening, ACCP)
, And a rotation pulse signal from the crank rotation angle sensor 35 disposed near the engine crankshaft at every constant rotation angle of the crankshaft. ECU3
0 is the rotation speed N of the engine 1 at regular intervals based on the time interval of the pulse signal input from the crank rotation angle sensor 35.
Calculate E.

An output port of the ECU 30 is connected to a power supply control circuit 9 of the fuel pump 92 via a drive circuit (not shown).
2a is connected to the reducing agent injection valve 91, and controls the rotation speed (discharge pressure) of the pump 92 and the valve opening time (injection amount) of the injection valve 91. _The NO _X storage reduction catalyst 7 in this embodiment
Are prepared on a carrier such as alumina, for example, alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La, cerium Ce and yttrium Y. And a noble metal such as platinum Pt. NO _X
When the air-fuel ratio of the inflowing exhaust gas is lean, the storage reduction catalyst converts NO _x (NO ₂ , NO) in the exhaust gas into nitrate ions N
O ₃ ^- absorbed in the form of, performing absorption and release action of the NO _X that releases NO _X concentration of oxygen absorbed to decrease the inflow exhaust gas.

The mechanism of the absorption and release will be described below by taking platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths. When the oxygen concentration in the inflowing exhaust gas increases (that is, when the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio), these oxygens become
₂ ^- or deposited at O ^2- form, NO _X in the exhaust gas platinum P
O ₂ on t ^- or react with O ^2-, thereby NO ₂ is produced. Further, NO ₂ and NO ₂ produced by the above in the inflowing exhaust gas is barium oxide BaO which acts as an absorbent is absorbed by the catalyst while being further oxidized on the platinum Pt
Diffuses in the catalyst in the form of ^- bound nitrate ions NO ₃ while the. Therefore, in a lean atmosphere, NO _X in the exhaust gas is absorbed in the NO _X storage reduction catalyst in the form of nitrate.

Further, when the oxygen concentration in the inflowing exhaust gas decreases (ie, when the air-fuel ratio of the exhaust gas decreases), the amount of NO ₂ generated on the platinum Pt decreases, so that the reaction proceeds in the reverse direction, and the catalyst proceeds. The nitrate ion NO ₃ ⁻ in the inside is released from the NO _X storage reduction catalyst in the form of NO ₂ . In this case, if components such as HC and CO are present in the exhaust gas, platinum Pt
Above, these components reduce NO ₂ .

[0018] In this embodiment, the exhaust air-fuel ratio of the engine for diesel engine is used as the engine 1 is lean, the normal operation of the exhaust passage 3 NO _X occluding and reducing catalyst 7
NO _X in the exhaust gas flowing the exhaust of a lean air-fuel ratio in the NO
It is absorbed by the _X storage reduction catalyst 7. When the reducing agent is supplied to the exhaust passage 3 on the upstream side of the NO _X storage reduction catalyst 7, NO
The _X occluding and reducing catalyst 7 flows is contained reductant exhaust, part of the reducing agent reacts with oxygen on the platinum Pt of the NO _X occluding and reducing catalyst 7. Thereby, the oxygen concentration in the atmosphere of the NO _X storage reduction catalyst 7 decreases, and components such as unburned HC and CO are generated by oxidation of the reducing agent. When the atmospheric oxygen concentration of the NO _X occluding and reducing catalyst 7 by oxidation of the reducing agent decreases, HC of _the NO _X storage NO _X from the reducing catalyst 7 is released in the exhaust by a mechanism mentioned above, it is reduced by CO component.

[0019] The _the NO _X storage reduction and release of the NO _X from the catalyst, the reducing agent used in the reduction purification operation (reproducing operation of the NO _X occluding and reducing catalyst), the reducing components and HC such as H ₂ in the exhaust, A substance that generates a CO component is used, and for example, a gas such as hydrogen and carbon monoxide, a liquid or gaseous hydrocarbon such as propane, propylene, and butane, and a liquid fuel such as gasoline, light oil, and kerosene can be used. In the present embodiment, since a diesel engine is used as the internal combustion engine 1, the fuel (diesel oil) of the engine 1 is used as a reducing agent in consideration of the convenience of replenishment and storage.

As will be described later, in this embodiment, the ECU 3
0 is the engine load state (accelerator opening ACCP and engine speed N
E), the exhaust gas temperature flowing into the NO _X storage reduction catalyst 7 is calculated, and the power supply voltage of the fuel pump 92 is controlled based on the exhaust temperature at the time of the regeneration operation of the NO _X storage reduction catalyst 7 to thereby inject the reducing agent. The reducing agent injection pressure from the valve 91 is controlled, and the opening time of the reducing agent injection valve 91 is controlled to control the injection amount of the reducing agent from the injection valve 91.

When the liquid reducing agent (diesel oil in this embodiment) is injected into the exhaust passage upstream of the NO _X storage reduction catalyst 7 as in this embodiment, the injection is performed particularly when the exhaust gas temperature is low. In some cases, the reducing agent is not used effectively for the regeneration of the NO _X storage reduction catalyst 7. A diesel engine generally has a low exhaust temperature, and the exhaust temperature may be 200 ° C. or less in a low load operation. In such a case, there is a case where the fuel injected from the reducing agent injection valve 91 does not sufficiently vaporize in the exhaust gas and reaches the NO _X storage reduction catalyst 7 in the form of liquid particles. When the reducing agent reaches the NO _X occluding and reducing catalyst 7 remains liquid, the liquid reducing agent will adhere to the inlet portion of the NO _X occluding and reducing catalyst, or reduced contact area between the exhaust catalyst of this portion, the liquid Particles of the reducing agent pass through the NO _X storage reduction catalyst without contacting the cell wall surface and flow out to the downstream side, so-called so-called reducing agent slippage occurs. In this case, the reducing agent adhering to the NO _X occluding and reducing catalyst 7, or the reducing agent having passed through the _the NO _X storage reduction catalyst 7 is not used in the regeneration of the NO _X occluding and reducing catalyst, NO
_{In the X} storage reduction catalyst 7, regeneration is not sufficiently performed due to a shortage of the reducing agent. In order to prevent this problem, if the supply amount of the reducing agent to the NO _X storage-reduction catalyst 7 during the regeneration operation is increased in advance in consideration of slip-through or the like, a shortage of the reducing agent on the NO _X storage-reduction catalyst may occur. However, in this case, not only does the amount of reducing agent required for the regenerating operation increase and the engine fuel consumption rate deteriorates, but also there arises a problem that the exhaust properties deteriorate due to the reducing agent flowing out downstream due to slip-through or the like.

Therefore, in the present embodiment, the above problem is solved by making the particle diameter of the fuel injected from the reducing agent injection valve 91 smaller as the engine exhaust temperature becomes lower. That is, when the particle diameter of the injected fuel becomes small, the surface area per unit volume of the fuel particle increases, so that the fuel is easily vaporized even when the exhaust gas temperature is low. Therefore, by reducing the particle size of the injected fuel when the exhaust gas temperature is low, the injected fuel reaches the NO _X storage reduction catalyst 7 in a vaporized state, and the supplied fuel (reducing agent) NO
It is used effectively on the _X storage reduction catalyst 7. Therefore, the exhaust gas temperature can also be completely carried out the regeneration of the NO _X occluding and reducing catalyst 7 with a small amount of fuel when low, with the increase of the fuel (reducing agent) consumed is suppressed, slipping of the liquid fuel particles Deterioration of the exhaust properties due to the above is prevented.

Next, a method for changing the particle size of the supplied fuel will be described. In the present embodiment, the reducing agent injection valve 9
As 1 a swirl injector is used. FIG. 2 is a diagram illustrating a schematic structure of the swirl injection valve of the present embodiment.
2, the injection valve 91 includes a nozzle 91a and a control valve 91.
b and a connection pipe 91c for connecting them.
The nozzle 91a is installed so as to penetrate the exhaust passage 3. The control valve 91 functions as a shutoff valve that shuts off pressurized fuel supplied from the fuel pump 92 to the nozzle 91a.

FIG. 3 is a sectional view for explaining the schematic structure of the nozzle 91a. FIG. 3A shows a cross section along the axis of the nozzle 91 (A). In FIG. 3A, reference numeral 911 denotes a nozzle body, and 913 denotes a substantially cylindrical nozzle piece fitted into the nozzle body 911. At the center of the nozzle piece 913, a fuel passage 913a to which pressurized fuel is supplied from the control valve 91b via the connection pipe 91c is provided in the axial direction. In FIG. 3A, reference numeral 913b denotes a check ball urged by a spring 913c in a direction to close the fuel passage 913a, and 913d has a radius so as to connect to the fuel passage 913a below the check ball 913b. It is a fuel passage drilled in the direction.

FIG. 3B shows the nozzle piece 913 shown in FIG.
FIG. 5 is a view taken in the direction of arrows BB in FIG. As shown in FIG.
The nozzle piece 913 has flat notches formed on both side surfaces, and is connected to the radial fuel passage 913d between the inner circumference of the nozzle body 911 and the outer circumference of the nozzle piece 913 by this flat notch. A fuel passage 913e is formed.

The lower part of the nozzle piece 913 is mounted so that its outer peripheral part is in close contact with the inner peripheral part of the nozzle body 911. As shown in FIG. 3B, a groove 913f is formed in the lower surface of the nozzle piece 913, and a fuel passage 913e is formed.
And an injection passage connecting the nozzle hole 915 at the center of the nozzle body 911. As shown in FIG. 3B, the injection passage 913f is provided from the outer periphery of the lower surface of the nozzle piece 913 so as to be directed at a position slightly eccentric with respect to the central axis of the nozzle piece 913.

When the control valve 91b is opened, the fuel pump 9
2 from the fuel passage 913 of the nozzle piece 913
flows into a. If the force due to the supplied fuel pressure exceeds the urging force of the spring 913c, the check ball 913b
Moves downward, and the fuel passage 913a communicates with the radial fuel passage 913d. As a result, the pressurized fuel flows from the radial fuel passage 913d into the fuel passage 913e formed by the planar cutouts on both sides of the nozzle piece, and the injection passage 9
The fuel is injected from 13f into the exhaust passage 3 through the injection hole 915. As described above, the injection passage 9 of the nozzle piece 913
Since 13 f is directed in a direction eccentric with respect to the central axis of the nozzle piece 913, the fuel passing through the injection passage 913 f is given a tangential velocity to the injection hole 915.
Therefore, the injected fuel is injected into the exhaust passage 3 while turning inside the injection hole 915, and the injected fuel is atomized.

In the swirl nozzle 91a as described above,
As the fuel injection pressure increases, a large tangential velocity is applied to the fuel at the outlet of the injection passage 913f. Therefore, as the fuel injection pressure increases, the atomization of the fuel injected from the injection holes 915 improves. As a result, the diameter of the injected fuel particles becomes smaller. In the present embodiment, the atomization state (particle size) of the fuel particles is controlled by changing the fuel injection pressure using the swirl injection valve 91 described above. That is, the ECU 30 sets the NO _X storage reduction catalyst 7
The exhaust gas temperature at the inlet is calculated, and the voltage applied to the electric motor of the fuel pump 92 is adjusted by driving the power supply control circuit 92a of the fuel pump 92 of the reducing agent supply device 9 according to the exhaust gas temperature. When the motor voltage increases, the discharge pressure of the fuel pump 92 increases, and the fuel injection pressure of the injection valve 91 increases, so that the particle size of the injected fuel decreases. When the motor voltage decreases, the discharge pressure of the fuel pump 92 decreases.
The particle size of the fuel injected from No. 1 increases.

FIG. 4 is a flowchart specifically illustrating the above-mentioned regeneration operation of the NO _X storage reduction catalyst 7 in the present embodiment. This operation is performed by a routine executed by the ECU 30 at regular time intervals. In FIG.
In step 401, the engine speed NE calculated based on the output of the crank angle sensor 35 and the accelerator opening ACCP detected by the accelerator opening sensor 33 are read. Then, NO _X in the current of the NO _X occluding and reducing catalyst 7 on the basis of and the NE ACCP step 403
The storage amount CNOX is calculated.

[0030] In this embodiment, NO _X storage amount CNOX is calculated based on the operating state of the engine. N generated per unit time (for example, the execution interval of the operation in FIG. 4) from the institution
The O _X amount is determined by the engine load condition (for example, accelerator opening and rotation speed). Therefore, in this embodiment, pre-engine was operated by changing the load conditions, and measuring the NO _X generation amount in each load conditions, for example the ECU30 in the form of a numerical table using the accelerator opening and the rotational speed It is stored in ROM. In step 403, it calculates the amount of NO _X generated from the engine by the time this operation execution from the last operation performed by using the numerical table from an accelerator opening ACCP and the rotational speed NE read in step 401. A value obtained by multiplying this generation amount by a predetermined constant (the ratio of NO _X absorbed by the NO _X storage reduction catalyst 7 to NO _{X in} the exhaust gas) is defined as CN.
Add to OX. As a result, the value of CNOX becomes a value corresponding to the amount of NO _X stored in the NO _X storage reduction catalyst 7.

[0031] In the present embodiment, a value calculated based on the accelerator opening and the rotational speed of the NO _X occluding and reducing catalyst 7 N
Is used as the O _X storage amount CNOX, for example, the integrated value of the fuel injection amount of the previous regeneration operation performed after the engine, when the integrated value of the rotational speed, or engine relatively high rotation, as is normal operation the last regeneration operation after completion of engine operation time of the may simplify the calculation is used as _the NO _X storage amount CNOX to.

[0032] According to the above, NO of _the NO _X storage reduction catalyst 7
After calculating the _X storage amount CNOX, it is determined in step 405 whether or not the calculated NO _X storage amount CNOX has reached a predetermined value CNOX ₀ . Here, CNOX ₀ is NO _X
The value is set to a value with a sufficient margin for the maximum NO _X amount (saturation amount) that can be absorbed by the storage reduction catalyst 7, and in the present embodiment, CNOX ₀ is set to a value of about 70% of the saturation amount. I have.

If CNOX ≧ CNOX ₀ in step 405, the NO _X storage amount of the NO _X storage reduction catalyst 7 has increased, and it is necessary to execute the regeneration operation of the NO _X storage reduction catalyst. Perform the following operations.
That is, in step 407, the present exhaust temperature T _EX flowing into the NO _X storage reduction catalyst 7 is calculated based on the engine load state (accelerator opening, rotation speed).

The engine exhaust temperature changes in accordance with the engine load condition. Therefore, in the present embodiment, operating the pre-engine at different load conditions, NO _X occluding and reducing catalyst 7 actually measured exhaust gas temperature at the inlet, for example, the ECU30 in the form of a numerical table using the accelerator opening and the rotational speed It is stored in ROM. In step 407, the current exhaust gas temperature T _EX is calculated from the accelerator opening ACCP and the rotational speed NE read in step 401 using the above numerical table.

[0035] In the present exemplary embodiment calculates the exhaust temperature T _EX flowing to the NO _X occluding and reducing catalyst 7 based on the engine load condition, the exhaust gas temperature detected an _the NO _X storage and reduction catalyst 7 inlet exhaust temperature It is also possible to arrange a sensor to directly detect the exhaust gas temperature T _EX . Step 407
In the exhaust gas temperature T _EX is calculated, in the next step 409, the injection pressure target value of the fuel pump 92 is set from a predetermined relationship based on the exhaust gas temperature T _EX. In the present embodiment, the relationship between the particle size of the injected fuel at each exhaust temperature (that is, the injection pressure of the injection valve 91) and the vaporized state of the fuel is previously obtained by an experiment through experiments. Is set as a function of the exhaust gas temperature. In step 407, a target injection pressure is set based on the calculated exhaust temperature T _EX using the above relationship. The target injection pressure is set higher as the exhaust gas temperature is lower, and the particle diameter of the fuel injected from the injection valve 91 is smaller.

In step 411, the amount of the reducing agent (fuel) required for the regeneration operation is calculated based on the exhaust gas temperature _TEX . Since the catalytic activity of the NO _X storage reduction catalyst 7 changes according to the temperature, it is preferable to change the amount of the reducing agent (fuel) to be supplied according to the exhaust temperature T _EX even during the regeneration operation. In the present embodiment, Yes found through experiments amount of reducing agent the amount of the NO _X corresponding to CNOX beforehand catalyst is required playback operation in a state of being absorbed by the exhaust temperature conditions, in step 411, the The required fuel injection amount is calculated based on the relationship.

In step 413, the power supply control circuit 92a is controlled so that the discharge pressure of the fuel pump 92 becomes the injection pressure calculated in step 409.
Then, the opening time of the injection valve 91 (the opening time of the control valve 91b) required to inject the amount of the reducing agent calculated in step 411 under the set injection pressure is set, and the injection valve 91 is opened. Is ventured. As a result, a required amount of fuel having a particle size adjusted according to the exhaust gas temperature T _EX is injected from the injection valve 91.

After the above operation is completed, step 417 is NO.
The value of the _X storage amount CNOX is reset, and this operation ends. As described above, by changing the particle size of the fuel particles injected from the injection valve 91 in accordance with the temperature of the exhaust gas flowing into the NO _X storage reduction catalyst 7, almost all the injected fuel is vaporized regardless of the exhaust gas temperature. and is on _the NO _X storage reduction catalyst 7 to become to reach the NO _X occluding and reducing catalyst 7 in the state were now fuel supplied is used to effectively play operation, the amount of fuel required for the regenerating operation (Reducing agent amount) can be reduced, and the deterioration of the exhaust properties due to the passage of fuel particles, which tends to occur particularly when the exhaust temperature is low, is prevented.

It should be noted that, as in this embodiment, the reducing agent injection valve
NO_XWhen supplying the reducing agent to the storage reduction catalyst, the injection valve
And NO_XIf the distance to the storage reduction catalyst is large,
The injected reducing agent diffuses in the front and rear direction of the exhaust flow,
May not be able to form an exhaust layer with a high concentration of reducing agent
There is. For this reason, the reducing agent injection valve _X
It is preferable to install at a position close to the storage reduction catalyst. When
If the distance between the injection valve and the reducing agent is set short,
If the exhaust temperature is too low, the injected reducing agent will not evaporate
NO as liquid particles_XEasy to reach storage reduction catalyst
Problem. In the present embodiment, the injection is performed according to the exhaust gas temperature.
By changing the particle size of the reducing agent particles
Almost all of the reducing agent is vaporized regardless of the temperature.
O_XIt is possible to reach the storage reduction catalyst. this
Therefore, according to this embodiment, the liquid reducing agent particles_X
Injecting reducing agent while preventing it from reaching the storage reduction catalyst
NO valve_XTo be located close to the storage reduction catalyst
That the supplied reductant is diluted by the exhaust gas.
Is prevented, so NO_XRegeneration of storage reduction catalyst
It can be performed efficiently.

In the above embodiment, the fuel injection pressure (fuel particle size) and the injection amount are continuously changed according to each value of the exhaust gas temperature.
(About 50 ° C.), the control can be simplified by switching the fuel injection pressure and the injection amount between the high temperature side and the low temperature side.

[0041]

According to the present invention, since the atomization state of the reducing agent supplied to the NO _X storage reduction catalyst is controlled in accordance with the exhaust gas temperature, a small amount of reduction can be performed regardless of the exhaust gas temperature. It is possible to efficiently regenerate the NO _X storage reduction catalyst with the catalyst, and to prevent deterioration of the exhaust properties due to the unreacted reducing agent flowing out downstream of the catalyst.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel engine.

FIG. 2 is a diagram illustrating a configuration of a reducing agent injection valve in FIG. 1;

FIG. 3 is a sectional view illustrating a configuration of a reducing agent injection valve of FIG. 1;

FIG. 4 is a flowchart illustrating a NO _X storage reduction catalyst regeneration operation of the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Diesel engine 3 ... Exhaust passage 7 ... NO _X storage reduction catalyst 9 ... Reducing agent supply device 30 ... Electronic control unit (ECU) 91 ... Reducing agent injection valve

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Terms (reference) 3G091 AA12 AA18 AA28 AB06 BA03 BA14 BA33 CA18 CA19 CB02 CB08 DB06 DB08 DB10 EA01 EA07 EA17 EA31 FA02 FA04 FA12 FA13 FB02 FB10 FB11 FB12 GB01X GB02W GB03W GB04W GB05W GB06W GB10X GB16X GB16X

Claims (3)

[Claims] An N disposed in an exhaust passage of an internal combustion engine absorbs NO _X in the exhaust gas when the inflowing exhaust gas has a lean air-fuel ratio, and absorbs the NO _X when the oxygen concentration of the inflowing exhaust gas decreases.
And _the NO _X storage reduction catalyst to release the O _X, in the exhaust purification apparatus for an internal combustion engine having a reducing agent supply apparatus that injects the liquid reducing agent to the upstream side of the exhaust passage of the _the NO _X storage reduction catalyst, the NO _X An exhaust gas purification device for an internal combustion engine, comprising: atomization control means for changing an atomization state of a reducing agent injected into an exhaust passage from the reducing agent supply device according to an exhaust gas temperature flowing into a storage reduction catalyst. 2. The atomization control means changes the atomization state of the reducing agent by reducing the particle size of the injected reducing agent as the temperature of the exhaust gas flowing into the NO _X storage reduction catalyst decreases. 2. The exhaust gas purification device for an internal combustion engine according to claim 1. 3. The reducing agent supply device includes an injection valve that injects the reducing agent into an exhaust passage, and the atomization control unit is injected by changing an injection pressure of the reducing agent from the injection valve. 3. The exhaust gas purification device for an internal combustion engine according to claim 2, wherein the particle size of the reducing agent is changed.