JP3518391B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to purification of exhaust gas from an internal combustion engine.
Regarding the device, specifically, the inflow exhaust air-fuel ratio is lean.
NO in exhaust_XAbsorb oxygen, and oxygen concentration in the exhaust
NO absorbed when temperature drops_XReleases NO_XSucking
The present invention relates to an exhaust gas purification device for an internal combustion engine having a storage reduction catalyst. [0002] 2. Description of the Related Art When an inflowing exhaust air-fuel ratio is lean, exhaust gas is exhausted.
NO in the air_XAbsorbs low oxygen concentration in the exhaust gas
NO absorbed when dropped_XReleases NO_XOcclusion reduction
Catalysts are known. NO_XThe storage reduction catalyst is lean air-fuel
NO in exhaust at specific atmosphere_XBut absorbed N
O_XWhen the amount increases and reaches the saturation amount, NO_XSuck
It cannot be collected. Therefore, NO_XUsing storage reduction catalyst
Exhaust gas purifier periodically_XFlow into storage reduction catalyst
Reducing the oxygen concentration of the exhaust gas_XOcclusion reduction catalyst
NO absorbed from_XMust be released. NO_XOcclusion
A reduction catalyst was used as a gasoline engine exhaust purification system.
In such a case, if the operating air-fuel ratio of the engine is reduced (ie,
When the engine is operated at a rich air-fuel ratio), the oxygen concentration in the exhaust
Unburned HC and CO components in exhaust gas increase as well as decrease
Therefore, the above NO_XNO from storage reduction catalyst_XIs released
NO released_XIs NO_XHC on the storage reduction catalyst,
Reduced by CO. However, NO_XDize for storage reduction catalyst
When used as an exhaust purification device for
Other means due to the difficulty of driving with rich air-fuel ratio
It is necessary to reduce the oxygen concentration in the exhaust
You. NO_XThe storage reduction catalyst is equipped with exhaust purification equipment for diesel engines.
When used as a storage device, the exhaust oxygen concentration is reduced and NO
_XNO absorbed from the storage reduction catalyst_XHow to release
Usually NO_XIn the exhaust passage upstream of the storage reduction catalyst
A method of supplying a reducing agent such as a liquid hydrocarbon is used.
The reducing agent supplied to the upstream exhaust passage is dispersed in the exhaust
NO with exhaust_XWhen flowing into the storage reduction catalyst, it is reduced
No agent_XOxidation by reaction with oxygen in exhaust gas on storage reduction catalyst
NO_XLow atmospheric oxygen concentration of the storage reduction catalyst
Down, no_XNO absorbed from the storage reduction catalyst_XIs released
It is. In addition, the released NO_XIs NO_XOn storage reduction catalyst
And is reduced and purified by the reducing agent in the exhaust gas. [0004] NO_XNot related to storage reduction catalyst
Returns to the exhaust passage upstream of the catalyst placed in the exhaust passage
An example of a device for supplying the agent is disclosed in JP-A-5-44434.
Some are described in the gazette. The device of the publication is
Particulates carrying an oxidation catalyst in the exhaust passage of the diesel engine
And place it on the particulate filter.
Particulates when burning collected exhaust particulates
Inject fuel (reducing agent) into the exhaust passage upstream of the filter
This allows the injected fuel to burn on the oxidation catalyst
Increase the temperature of the particulate filter
It is something. Also, in the device of the publication, the activity of the oxidation catalyst is
Flows into the catalyst to supply the appropriate amount of fuel
Supply to catalyst based on exhaust temperature and engine intake air amount
The fuel amount is calculated based on the exhaust gas temperature at the catalyst outlet.
Then, the calculated fuel amount is corrected. In general, a reducing agent is supplied to an exhaust passage on the upstream side of a catalyst.
When supplying, the entire amount of the supplied reducing agent reacts with the catalyst.
Unreacted reducing agent flows downstream of the catalyst
It is necessary to prevent that. Also, as the temperature of the catalyst becomes
When the exhaust temperature is low, the exhaust
Supplied when supplying the same amount of reducing agent as when the temperature is high
Part of the reducing agent flows out downstream of the catalyst without reacting.
May be. The device disclosed in the above publication is based on a change in exhaust gas temperature.
To prevent unpurified reducing agent from flowing out downstream of the catalyst.
Supply according to the exhaust temperature (ie, the capacity of the catalyst)
The amount of reducing agent to be used is determined, and the total amount of supplied reducing agent
It reacts on a medium. [0006] However, the above-mentioned Japanese Patent Application Laid-Open
The exhaust gas flowing into the catalyst as in the device of JP-A-5-44434 is disclosed.
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 the supplied fuel does not vaporize sufficiently
Reach the catalyst with relatively large liquid particles
And the reducing agent particles adhere to the catalyst surface or
The particles may pass through the catalyst cell as they are.
NO_XNO from storage reduction catalyst_XRelease, reduction purification operation
(Hereinafter NO_XNO absorbed from the storage reduction catalyst_XRelease
The operation of reducing and purifying _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 the 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. SUMMARY OF THE INVENTION In view of the above problems, the present invention_XOcclusion reduction
When supplying the liquid reducing agent to the catalyst, the atomization state of the reducing agent
Control to increase the consumption of reducing agent and deteriorate exhaust characteristics.
To provide an exhaust purification device for an internal combustion engine capable of preventing
The purpose is. [0008] [Means for Solving the Problems]The present inventionAccording to the internal combustion engine
Located in the exhaust passage of the Seki, the air-fuel ratio of the
NO during exhaust_XAbsorbs and flows in the exhaust oxygen
NO absorbed when the concentration decreases_XReleases NO_XSucking
Storage reduction catalyst and the NO_XExhaust passage upstream of the storage reduction catalyst
And a reducing agent supply device for injecting a liquid reducing agent into the path.
Oh, beforeNote NO_XAccording to the temperature of exhaust gas flowing into the storage reduction catalyst
Reducing agent injected into the exhaust passage from the reducing agent supply device
Equipped with atomization control means for changing the atomization state of theTauchiFuel engine
Exhaust purification equipmentWherein the reducing agent supply device comprises:
An injection valve for injecting a reducing agent into an exhaust passage;
The control means increases the injection pressure of the reducing agent from the injection valve.
The above-mentioned NO _X Exhaust flowing into the storage reduction catalyst
The lower the gas temperature, the smaller the particle size of the injected reducing agent
Change the atomization state of the reducing agent,Exhaust purification equipment for internal combustion engine
Device is provided. That is,The present inventionThen NO_XStorage reduction catalyst
Change the atomization state of the reducing agent according to the upstream exhaust temperature
You. When injecting liquid reducing agent into the exhaust passage,
If the air temperature is low, even if the atomization state is the same (for example, injection
High exhaust temperature (even if the particle size of the applied reducing agent is the same)
NO in the form of liquid particles without vaporization in exhaust compared to the case
_XThe amount of the reducing agent reaching the storage reduction catalyst increases. one
On the other hand, if the exhaust gas temperature is high,
Even if the condition is somewhat bad, the reducing agent evaporates in the high-temperature exhaust gas,
NO as liquid particles_XOf the reducing agent reaching the storage reduction catalyst
The amount decreases. Therefore, the fuel is injected according to the exhaust gas temperature.
By changing the atomization state of the reducing agent, the aforementioned reduction
Agent is prevented from adhering to the catalyst surface and slipping through
You. [0010]In addition, the present inventionThen, NO_XFor storage reduction catalyst
The lower the temperature of the incoming exhaust gas, the lower the liquid injected into the exhaust passage
The particle diameter of the body reducing agent is reduced. Liquid reducing agent
When the particle size of is small, the reducing agent is likely to evaporate,
The reducing agent injected into the exhaust is charged even when the exhaust temperature is low.
NO in gaseous state_XReach the storage reduction catalyst
You. Therefore, even when the exhaust gas temperature is low, NO_XOcclusion reduction
The catalyst can cause the liquid reductant particles to adhere and slip through
And the total amount of supplied reducing agent is NO_XOcclusion reduction
NO from medium_XIt is used effectively for emission and reduction purification.
Swell. Therefore, if the consumption of the reducing agent is reduced,
NO_XUnreacted reduction flowing downstream of the storage reduction catalyst
The amount of agent is reduced. [0011]Furthermore, the present inventionThen, the reducing agent passes through the injection valve
Is injected into the exhaust passage, and the particle size of the reducing agent is
It is adjusted by changing the force. This allows
It is possible to easily change the atomization state of the injected reducing agent.
Wear. [0012] BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment will be described. FIG. 1 shows the exhaust gas purification of the present invention.
1 is a diagram showing a schematic configuration of an embodiment of a chemical conversion device. In FIG.
Here, 1 indicates an internal combustion engine. In the present embodiment, the internal combustion engine
Diesel engines are used as Seki 1.
Cylinder exhaust ports share a common exhaust via exhaust manifold 31.
It is connected to the air passage 3. Furthermore, there is a rear
NO to state_XThe storage reduction catalyst 7 is provided. In FIG.
9 is NO_XNO during regeneration operation of storage reduction catalyst 7_X
A reducing agent supply device for supplying a reducing agent to the storage reduction catalyst 7;
You. The reducing agent supply device is NO_XExhaust of storage reduction catalyst 7
NO with a reducing agent injection valve 91 arranged near the mouth_XOcclusion
Injecting a reducing agent into the exhaust gas flowing into the reduction catalyst 7
More no_XOxygen concentration in exhaust gas flowing into storage reduction catalyst 7
And the NO absorbed from the catalyst 7_XRelease
Both released NO_XTo purify. I'll explain later
As described above, in the present embodiment, the fuel of the engine 1 (D
Oil) is used. The reducing agent supply device 9 is illustrated
Motor pressurizes fuel supplied from the engine fuel system
A driving fuel pump 92 is provided, which pressurizes the fuel and injects a reducing agent.
The fuel is injected from the discharge valve 91 into the exhaust passage 3. In FIG. 1, reference numeral 30 denotes the electronic control of the engine 1.
Unit (ECU). In the present embodiment, the ECU 3
0 is a microcomputer having a known configuration including a RAM, a ROM, and a CPU.
Is configured as a microcomputer and fuel injection of the engine 1
In addition to performing basic control of the amount, fuel injection timing, etc.,
NO 9 to be described later by controlling_XN from the storage reduction catalyst 7
O_XRelease and reduction purification operation (NO_XReuse of storage reduction catalyst
Raw operation). NO_XThe regeneration operation of the storage reduction catalyst 7 is performed.
Therefore, the accelerator pedal of the engine is connected to the input port of the ECU 30.
From the accelerator opening sensor 33 located near the
Accelerator pedal depression amount (accelerator opening, ACCP)
Voltage signal is also located near the engine crankshaft.
From the detected crank rotation angle sensor 35,
A rotation pulse signal is input for each rotation angle. ECU3
0 is a pulse signal input from the crank rotation angle sensor 35.
Number of revolutions N of the engine 1 at regular intervals based on the time interval of the
Calculate E. The output port of the ECU 30 is shown in FIG.
Power supply control circuit 9 of the fuel pump 92 via a non-driving circuit
2a and the reducing agent injection valve 91,
Number of rotations (discharge pressure) and valve opening time (injection amount) of the injection valve 91
Is controlling. NO of this embodiment_XStorage reduction catalyst 7
Can be made on a carrier such as alumina, for example, potassium K, sodium
Alkaline such as Na, lithium Li, cesium Cs
Alkali such as metal, barium Ba, calcium Ca
Earth, lanthanum La, cerium Ce, yttrium Y
At least one component selected from rare earths
It carries a noble metal such as gold Pt. NO_X
When the air-fuel ratio of the inflowing exhaust gas is lean,
NO in exhaust_X(NO_Two, NO) with nitrate ion N
O_Three ^-To reduce the oxygen concentration of the incoming exhaust gas.
And absorbed NO_XReleases NO_XPerform the absorption and release action of
U. The mechanism of the absorption and release is described below.
Taking platinum Pt and barium Ba as an example
Explain other precious metals, alkali metals, alkaline earth
The same mechanism can be obtained by using rare earths. Inflow and outflow
When the oxygen concentration in the air increases (that is, the air-fuel ratio of the exhaust
(At a lean air-fuel ratio), these oxygens
_Two ^-Or O^2-NO in the exhaust_XIs platinum P
O on t_Two ^-Or O^2-With NO_TwoBut
Generated. Also, NO in the inflow exhaust_TwoAnd by the above
NO generated_TwoIn the catalyst while being oxidized further on platinum Pt
Barium Oxide BaO Absorbed in Water and Acts as an Absorbent
Nitrate ion NO while binding with_Three ^-Diffusion into the catalyst in the form of
I do. Therefore, in a lean atmosphere, NO_XBut
NO_XBe absorbed in the form of nitrate in the storage reduction catalyst
Become. Further, when the oxygen concentration in the inflow exhaust gas decreases,
(That is, when the air-fuel ratio of the exhaust gas decreases),
NO at_TwoThe reaction proceeds in the opposite direction because the amount of production decreases
Swelling, nitrate ion NO in the catalyst_Three ^-Is NO_TwoIn the form of
NO_XIt is released from the storage reduction catalyst. This place
If the exhaust gas contains components such as HC and CO, platinum Pt
Above these components make NO_TwoIs reduced. In this embodiment, the engine 1 is a diesel engine.
Because the engine is used, the exhaust air-fuel ratio of the engine is lean
During normal operation, NO in the exhaust passage 3_XStorage reduction catalyst 7
Exhaust gas with a lean air-fuel ratio flows into the_XIs NO
_XIt is absorbed by the storage reduction catalyst 7. NO_XOcclusion reduction
When the reducing agent is supplied to the exhaust passage 3 on the upstream side of the catalyst 7, NO
_XExhaust gas containing a reducing agent flows into the storage reduction catalyst 7,
Part of base agent is NO_XOxygen on the platinum Pt of the storage reduction catalyst 7
Reacts with. Thereby, NO_XAtmosphere of storage reduction catalyst 7
As the oxygen concentration in the air decreases, oxidation of the reducing agent
Unburned components such as HC and CO are generated. For oxidation of reducing agent
More no_XAtmospheric oxygen concentration of the storage reduction catalyst 7 decreases.
And NO by the mechanism described above_XStorage reduction catalyst 7
NO_XIs released and reduced by HC and CO components in the exhaust
Is done. The above NO_XNO from storage reduction catalyst_XRelease
Out, reduction purification operation (NO_XRegeneration operation of the storage reduction catalyst)
The reducing agent used is H in the exhaust gas._TwoReduction components such as
And those that produce HC and CO components, such as water
Gases such as carbon dioxide and carbon monoxide, propane, propylene, and pig
Liquid or gaseous hydrocarbons such as gasoline, gasoline, light oil, kerosene
And the like can be used. In the present embodiment, the internal combustion engine
Because a diesel engine is used as Seki 1
Considering the convenience of supply and storage, the fuel (de-
Diesel oil). As described later, in this embodiment, the ECU 3
0 is the engine load state (accelerator opening ACCP and engine speed N
E) NO based on_XExhaust gas flowing into the storage reduction catalyst 7
While calculating the temperature, NO_XRegeneration of storage reduction catalyst 7
Power supply voltage of fuel pump 92 based on exhaust temperature during operation
To control the reducing agent injection pressure from the reducing agent injection valve 91.
In addition, the valve opening time of the reducing agent injection valve 91 is controlled to perform injection.
The injection amount of the reducing agent from the injection valve 91 is controlled. By the way, as in this embodiment, NO_XOcclusion
In the exhaust passage upstream of the reduction catalyst 7, a liquid reducing agent (this embodiment
In particular, when injecting diesel oil), exhaust temperature
Is low when the reducing agent injected is NO_XOf the storage reduction catalyst 7
There is a case where it is not used effectively for reproduction. Diesel machine
In general, the exhaust temperature is low in the Seki area.
It may be 200 ° C or lower. In such a case return
The fuel injected from the base agent injection valve 91 is sufficiently
NO as liquid particles without forming_XReach the storage reduction catalyst 7
May occur. NO while the reducing agent is liquid_XOcclusion reduction
Upon reaching the medium 7, the liquid reducing agent becomes NO_XOcclusion reduction catalyst
It adheres to the inlet part, and the exhaust of the catalyst in this part
If the contact area decreases or the reducing agent remains as liquid particles,
NO without contacting the wall_XAfter passing through the storage reduction catalyst
The so-called reducing agent that escapes downstream is generated.
I will. In this case, NO_XReduction attached to storage reduction catalyst 7
Agent or NO_XThe reducing agent that has passed through the storage reduction catalyst 7 is
NO_XSince it is not used for regeneration of the storage reduction catalyst, NO
_XWith the storage reduction catalyst 7, regeneration is sufficient due to the lack of reducing agent.
No longer. To prevent this problem,
NO at the time of reproduction operation in consideration of_XTo the storage reduction catalyst 7
NO if the reducing agent supply amount is increased_XReturn on storage reduction catalyst
There is no shortage of base agent, but in this case the regeneration operation
The amount of reducing agent required for the engine increases and the engine fuel consumption rate deteriorates
In addition to the reducing agent that has flowed downstream due to slippage, etc.
There is a problem that the exhaust properties are further deteriorated. Therefore, in this embodiment, the engine exhaust temperature is low.
The particle size of the fuel injected from the reducing agent injection valve 91 is reduced
The above-mentioned problem is solved by reducing the size. Sand
That is, when the particle size of the injected fuel becomes smaller, the unit volume of the fuel particles becomes smaller.
Even when the exhaust temperature is low because the surface area per unit increases
The fuel vaporizes easily. Therefore, the exhaust temperature
By reducing the particle size of the injected fuel when it is low,
The injected fuel is vaporized and NO_XFor the storage reduction catalyst 7
And the supplied fuel (reducing agent) becomes NO
_XThe storage reduction catalyst 7 is effectively used. This
Therefore, even when the exhaust temperature is low, NO_XSucking
The regeneration of the storage reduction catalyst 7 can be completely performed, and the fuel (return
Base agent) In addition to suppressing the increase in consumption,
Deterioration of the exhaust properties due to slippage of the child is prevented. Next, the method of changing the particle size of the supplied fuel
The method will be described. In the present embodiment, the reducing agent injection valve 9
As 1 a swirl injector is used. FIG.
It is a figure explaining the schematic structure of the swirl injection valve of a form.
In FIG. 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. control
The valve 91 is supplied from the fuel pump 92 to the nozzle 91a.
It functions as a shutoff valve that shuts off pressurized fuel. FIG. 3 illustrates a schematic structure of the nozzle 91a.
It is sectional drawing. FIG. 3A is along the axis of the nozzle 91A.
2 shows a cross section taken along the line. In FIG. 3A, reference numeral 911 denotes a nozzle body.
D, 913 is a substantially cylindrical shape fitted into the nozzle body 911
FIG. Inside nozzle piece 913
Connect the connection pipe 91c from the control valve 91b to the center in the axial direction.
A fuel passage 913a through which pressurized fuel is supplied is provided.
Have been. In FIG. 3A, reference numeral 913b denotes a spring.
913c pushes the fuel passage 913a in the closing direction.
Check ball 913d is check bo
So that it connects to the fuel passage 913a below the
It is a fuel passage drilled in the radial 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.
Nozzle piece 913 has flat notches on both sides
The inner circumference of the nozzle body 911 and the nozzle piece
913 with the flat notch between the outer periphery
The fuel passage 913e connected to the direction fuel passage 913d is shaped.
Has been established. The lower part of the nozzle piece 913 is located on the outer periphery.
The part is mounted so that it is in close contact with the inner circumference of the nozzle body 911.
ing. The lower surface of the nozzle piece 913 is shown in FIG.
Thus, a groove 913f is formed, and the fuel passage 913e is formed.
And the injection hole 915 in the center of the nozzle body 911
An injection passage is formed. As shown in FIG.
The passage 913f is formed from the outer periphery of the lower surface of the nozzle piece 913 with a nozzle.
Finger at a position slightly eccentric with respect to the center axis of
It is provided to face. 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. The power from the supplied fuel pressure causes the spring
Check ball 913b when pushing force of 913c
Moves downward, and the fuel passage 913a moves in the radial fuel passage.
913d. This allows the pressurized fuel to move radially
From the fuel passage 913d to the flat notch on both sides of the nozzle piece
Flows into the fuel passage 913e formed by the
13f is injected into the exhaust passage 3 through the injection hole 915
You. As described above, the injection passage 9 of the nozzle piece 913
13f is eccentric with respect to the central axis of the nozzle piece 913.
The fuel flowing through the injection passage 913f.
The material is given a tangential velocity to the injection holes 915.
Therefore, the injected fuel is swirled in the injection hole 915 and discharged.
The fuel is injected into the air passage 3 and the injected fuel is slightly
Granulate. In the swirl nozzle 91a as described above,
As the fuel injection pressure increases, the injection passage 913f exits.
Large tangential velocity is given to fuel at the mouth
Therefore, as the fuel injection pressure increases, the injection holes 915
The atomization of the fuel injected from the
The particle size of the particles becomes smaller. In the present embodiment, the above-described swath is used.
The fuel injection pressure using the fuel injection valve 91
Control the atomization state (particle size) of fuel particles
ing. That is, the ECU 30_XStorage reduction catalyst 7
Calculate the exhaust temperature at the inlet, and use the reducing agent according to this exhaust temperature.
The power supply control circuit 92a of the fuel pump 92 of the supply device 9 is driven.
To adjust the voltage applied to the motor of the fuel pump 92.
You. When the motor voltage increases, the discharge pressure of the fuel pump 92 increases.
Increases, and the fuel injection pressure of the injection valve 91 increases.
The particle size of the propellant decreases. Also, the motor voltage drops
And the discharge pressure of the fuel pump 92 decreases, the injection valve 9
The particle size of the fuel injected from 1 increases. FIG. 4 is a graph showing the relationship between NO and_XOcclusion return
A flow chart specifically explaining the regeneration operation of the source catalyst 7
It is. This operation is performed at fixed time intervals by the ECU 30.
Is performed by a routine executed by In FIG.
In step 401, the output of the crank rotation angle sensor 35
Engine speed NE calculated based on
The accelerator opening ACCP detected by the sensor 33 is
Is read. Then, in step 403, ACCP and
The current NO based on the NE_XNO of the storage reduction catalyst 7_X
The storage amount CNOX is calculated. In this embodiment, NO_XThe storage amount CNOX is
It is calculated based on the operating state of the engine. Institutional unit
N generated during the interval (for example, the execution interval of the operation in FIG. 4)
O_XThe amount depends on the engine load conditions (for example, accelerator opening and engine speed).
And). Therefore, in the present embodiment, the engine
Is operated under different load conditions, and NO under each load condition_XDeparture
Actual production was measured and, for example, the accelerator opening and rotation speed were used.
It is stored in the ROM of the ECU 30 in the form of a numerical table.
You. In step 403, the data read in step 401
The above numerical value table is obtained from the accelerator opening ACCP and the rotational speed NE.
From the previous operation execution to the current operation execution
NO generated by the engine_XCalculate the amount. And this departure
A predetermined constant (NO in exhaust_XNO_XOcclusion return
NO absorbed by the source catalyst 7_XMultiplied by CN)
Add to OX. As a result, the value of CNOX becomes NO_XSucking
NO stored in the storage reduction catalyst 7_XValue corresponding to the quantity
You. In this embodiment, the accelerator opening and the rotation
The value calculated based on the number is NO_XN of the storage reduction catalyst 7
O_XIt is used as the storage amount CNOX.
The integrated value of the fuel injection amount of the engine after the regeneration operation
Integrated value, or the engine is running at a relatively high speed
Engine operating time since the last regeneration operation
NO etc._XSimplify calculation by using as storage amount CNOX
May be. According to the above, NO_XNO of the storage reduction catalyst 7
_XAfter calculating the storage amount CNOX, in step 405, the calculation is performed.
NO_XThe storage amount CNOX is equal to a predetermined value CNOX.₀Reached
Is determined. Here, CNOX₀Is NO_X
Maximum NO that can be absorbed by the storage reduction catalyst 7_XAmount (saturation amount)
The value is set to a value with a sufficient margin for
Is CNOX₀Is set to a value of about 70% of the saturation
Is defined. At step 405, CNOX ≧ CNOX₀so
If there is, NO_XNO of the storage reduction catalyst 7_XOcclusion amount
Is increasing and NO_XExecute the regeneration operation of the storage reduction catalyst
Therefore, the operation after step 407 is performed.
That is, in step 407, the current NO_XOcclusion reduction
Exhaust temperature T flowing into the medium 7_EXIs the engine load condition (accelerator
(Opening degree, rotation speed). The engine exhaust temperature varies according to the engine load condition.
Become For this reason, in the present embodiment, the engine is different in advance.
Operate under load, NO_XAt the inlet of the storage reduction catalyst 7
Measure the exhaust gas temperature and use, for example, the accelerator opening and rotation speed.
Stored in the ROM of the ECU 30 in the form of a numerical table
is there. In step 407, the data is read in step 401.
From the accelerator opening ACCP and the rotational speed NE.
Current exhaust temperature T_EXIs calculated. In this embodiment, based on the engine load condition,
And NO_XExhaust temperature T flowing into storage reduction catalyst 7_EXIs calculated
Is out but no_XExhaust gas temperature at inlet of storage reduction catalyst 7
An exhaust temperature sensor for detecting the exhaust temperature T_EXDirectly
It is also possible to make it detect. Step 407
And the exhaust temperature T_EXIs calculated, then in step 409
Is the exhaust temperature T_EXFrom the relationship determined in advance based on
An injection pressure target value of the pump 92 is set. In this embodiment
Is the particle size of the injected fuel at each exhaust temperature
That is, the relationship between the injection pressure of the injection valve 91) and the fuel vaporization state.
The relationship is determined by actual measurement.
Injection pressure as a function of exhaust gas temperature for good vaporization of fuel
Is set. In step 407, the calculated exhaust gas
Temperature T_EXBased on the above, the target injection pressure is
Is set. Note that the target injection pressure is lower when the exhaust gas temperature is lower.
The particle size of the fuel injected from the injection valve 91
Becomes smaller. In step 411, it is necessary to perform a playback operation.
The amount of reducing agent (fuel) to be discharged depends on the exhaust gas temperature T_EXCalculated based on
Is done. NO_XThe storage reduction catalyst 7 has a catalytic activity depending on the temperature.
Changes, so the reducing agent supplied even during the regeneration operation
(Fuel) amount is the exhaust temperature T_EXIt is better to change according to
Good. In this embodiment, the catalyst corresponds to CNOX in advance.
Amount of NO_XIs needed for playback operation in the absorbed state
The amount of reducing agent to be used is determined experimentally under each exhaust temperature condition.
In step 411, it is necessary based on this relationship.
The fuel injection amount to be calculated is calculated. In step 413, the discharge of the fuel pump 92 is performed.
The output pressure becomes the injection pressure calculated in step 409.
As described above, the power supply control circuit 92a is controlled, and
Now, the amount calculated in step 411 under the set injection pressure
Of the injection valve 91 required to inject the reducing agent
The valve time (valve opening time of the control valve 91b) is set, and the injection valve
The valve 91 is opened. As a result, exhaust gas is discharged from the injection valve 91.
Air temperature T_EXOnly the required amount of fuel of the particle size adjusted according to
It will be injected. After the above operation is completed, step 417 is NO.
_XThe value of the storage amount CNOX is reset, and this operation ends.
You. As described above, NO_XExhaust flowing into the storage reduction catalyst 7
Particle size of fuel particles injected from injection valve 91 according to air temperature
By changing the fuel injection temperature
Regardless, almost all gas is vaporized and NO_XOcclusion reduction
NO because it reaches medium 7_XAbove the storage reduction catalyst 7
To ensure that the supplied fuel is used effectively for regeneration operations
And the amount of fuel (reducing agent) required for the regeneration operation
Can be reduced, and especially when the exhaust temperature is low.
Poor exhaust properties due to fuel particles slipping through
Is prevented. It should be noted that, as in this embodiment, the reducing agent injection valve
NO_XWhen supplying a 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 exhaust gas.
Is prevented, so that NO_XRegeneration of storage reduction catalyst
It can be performed efficiently. In the above embodiment, the exhaust gas temperature
The fuel injection pressure (fuel particle size) and the injection amount are continuously
Although it is changed, for example, a predetermined value (for example, 2
(About 50 ° C) at the higher and lower temperatures
Control by switching between fuel injection pressure and injection amount
Simplification is also possible. [0041] 【The invention's effect】The present inventionAccording to the above, NO
_XThe atomization state of the reducing agent supplied to the storage reduction catalyst is controlled.
Efficiency with small amount of reducing agent regardless of exhaust temperature
NO_XWhen it becomes possible to regenerate the storage reduction catalyst
In both cases, unreacted reducing agent flows out downstream of the catalyst.
This can prevent deterioration of the exhaust properties.

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 of 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. [Description of Signs] 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

Continuation of the front page (72) Inventor Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-6-129237 (JP, A) JP-A-7-279649 (JP, A) JP-A-6-235318 (JP, A) JP-A-9-13946 (JP, A) JP-A-61-164017 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) F01N 3/08-3/36

Claims (1)

(57) is disposed in an exhaust passage of the Claims 1 an internal combustion engine, the oxygen concentration of the exhaust gas absorbed flowing NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the lean decrease N absorbed when
And _the NO _X storage reduction catalyst to release the O _X, e Bei a reducing agent supply apparatus that injects liquid reducing agent into the exhaust passage upstream of the _the NO _X storage reduction catalyst, flows before Symbol _the NO _X storage reduction catalyst a exhaust gas purification device of the combustion engine within which includes atomizing control means for changing the atomization state of the reducing agent injected into the exhaust passage from the reducing agent supply device in accordance with the exhaust temperature, the reducing agent supply device Injecting the reducing agent into the exhaust passage
An injection valve, and the atomization control means includes an injection pressure of a reducing agent from the injection valve.
By increasing the force, the _the NO _X storage reduction catalyst
The lower the temperature of the exhaust gas, the smaller the particle size of the injected reducing agent
An exhaust gas purification device for an internal combustion engine that changes the atomization state of a reducing agent by making it smaller .