JP3557964B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
In an exhaust passage of an internal combustion engine air-fuel ratio in the combustion chamber is so allowed to combust a mixture of lean air-fuel ratio of the inflowing exhaust gas is stored in the NO _X in the inflowing exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas the _the NO _X storage reduction catalyst that reduces by releasing NO _X are stored and lowered is arranged, the reducing agent from _the NO _X storage reduction catalyst upstream of the exhaust passage arranged reducing agent supply device into the NO _X occluding and reducing catalyst 2. Description of the Related Art There is known an exhaust gas purification device for an internal combustion engine in which NO _X stored in a NO _X storage reduction catalyst is intermittently supplied to release and reduce the NO _X (see JP-A-7-102948). In such a reducing agent supply apparatus, the reducing agent injection pressure is generally maintained constant, and therefore, the amount of the reducing agent injected per unit time is constant.
[0003]
[Problems to be solved by the invention]
When the reducing agent injection pressure is constant, the reducing agent concentration in the exhaust gas flowing into the NO _X storage reduction catalyst decreases as the intake air amount increases, and as a result, the exhaust gas flowing into the NO _X storage reduction catalyst increases. Will change relatively slowly. However, _the NO _X storage reduction catalyst reliably release the NO _X in, and reduced, in order to reduce the amount of reducing agent discharged from _the NO _X storage reduction catalyst at the same time, empty the inflowing exhaust into _the NO _X storage reduction catalyst Preferably, the fuel ratio changes rapidly. Therefore, if the reducing agent injection pressure is constant, there is a problem that NO _X may be satisfactorily released and reduced, and the amount of reducing agent discharged from the NO _X storage reduction catalyst may not be reduced.
[0004]
It is an object of the present invention, _the NO _X storage reduction catalyst reliably release the NO _X in, reduced, the exhaust gas purifying apparatus for an internal combustion engine which can reduce the amount of reducing agent discharged from _the NO _X storage reduction catalyst at the same time To provide.
[0005]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an exhaust passage for an internal combustion engine in which an air-fuel ratio in a combustion chamber is lean. store up _X, the oxygen concentration in the inflowing exhaust gas is arranged _the NO _X storage reduction catalyst that reduces by releasing NO _X are stored and lowered, _the NO _X storage reduction catalyst upstream of the exhaust passage located reducing agent fed into the in the exhaust purification system of an internal combustion engine which is adapted to intermittently supplying the reducing agent to the NO _X occluding and reducing catalyst for reducing NO _X in _the NO _X storage reduction catalyst from the unit, than when less when many intake air amount determine the amount of reducing agent supplied from the reducing agent supply apparatus per unit time to be larger, to a predetermined target air-fuel ratio of the inflowing exhaust gas into _the NO _X storage reduction catalyst when the reducing agent supply operation Required for Determine the amount of reducing agent, and to obtain the reducing agent injection time based on the the required reducing agent amount amount of reducing agent supplied from the reducing agent supply device per these unit time. That is, in the first aspect, is prevented from the reducing agent concentration in the inflowing exhaust gas to the intake air amount is large becomes _the NO _X storage reduction catalyst be reduced, hence reducing agent concentration can vary sharply NO _X , The amount of the reducing agent discharged from the NO _X storage reduction catalyst is reduced. Further, the ratio of the amount of fuel and the amount of reducing agent to the amount of intake air supplied into the engine exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the engine exhaust passage is determined by the air-fuel ratio of the exhaust gas at that position. In the first aspect, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst is quickly made to match the target air-fuel ratio.
[0006]
According to a second aspect, in the first aspect, the reducing agent supply device can change the reducing agent injection pressure, and when the intake air amount is large, the reducing agent injection pressure is set higher than when the intake air amount is small. ing. That is, in the second invention, the reducing agent amount supplied from the reducing agent supply apparatus per unit time by increasing the reducing agent injection pressure is increased.
[0008]
Further, in the first aspect according to the third invention, it is supplied from the reducing agent supply apparatus per unit time with respect to the intake air amount to be maintained within the set range of the reducing agent injection time is predetermined Determines the amount of reducing agent.
Further, in the first aspect according to the fourth invention, the residual reducing agent amount to determine the residual amount of reducing agent remaining in the _the NO _X storage reduction catalyst after the previous reducing agent supply operation is predetermined When the amount becomes smaller than the set amount, the next reducing agent supply operation is performed. That is, in the fourth invention, the reducing agent is supplied to the NO _X storage reduction catalyst without excess or shortage.
[0009]
Further, in the first aspect according to the fifth invention, the average air-fuel ratio is predetermined in obtaining an average air-fuel ratio of the inflowing exhaust into _the NO _X storage reduction catalyst since the previous reducing agent supply operation is initiated When the air-fuel ratio becomes larger than the set air-fuel ratio, it is determined that the amount of the remaining reducing agent in the NO _X storage reduction catalyst has become smaller than the set amount. That is, in the fifth invention, when the average air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst becomes larger than the set air-fuel ratio, the next reducing agent supply operation is started.
[0010]
Further, in the first aspect according to the sixth invention, the previous reducing agent supply operation and the time interval between subsequent reductant supply action for the next so as not shorter than the minimum predetermined time interval The start time of the reducing agent supply action is determined. That is, in the sixth aspect , a sufficient time interval is provided between the previous reducing agent supply operation and the next reducing agent supply operation.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can be applied to a spark ignition type engine.
Referring to FIG. 1, the engine main body 1 includes, for example, four cylinders # 1, # 2, # 3, and # 4. Each cylinder is connected to a surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected to a supercharger, for example, an outlet of a compressor 6 c of an exhaust turbocharger 6 via an intake duct 4 and an intercooler 5. Is done. The inlet of the compressor 6c is connected to an air cleaner 8 via an air suction pipe 7. A throttle valve 10 driven by an actuator 9 is arranged in the intake duct 4 between the surge tank 3 and the intercooler 5. Each cylinder has a fuel injection valve 11 for directly injecting fuel into the combustion chamber. Each fuel injection valve 11 is connected to a fuel pump (not shown) via a common fuel accumulator (not shown).
[0013]
Each cylinder is connected to an inlet of the exhaust turbine 6t of the exhaust turbocharger 6 through an exhaust manifold 12, an outlet portion of the exhaust turbine 6t The casing 15 housing the NO _X reduction catalyst 14 via the exhaust pipe 13 The casing 15 is connected to the exhaust pipe 16.
A reducing agent supply device 17 for supplying a reducing agent to the NO _X reduction catalyst 14 is provided in the exhaust pipe 13. The reducing agent supply device 17 includes a reducing agent injection nozzle 18 disposed on the exhaust inflow surface of the NO _X reduction catalyst 14, and the reducing agent injection nozzle 18 is connected to a fuel tank 21 via a reducing agent supply pipe 19 and an electromagnetic valve 20. Is connected to the discharge side of a fuel pump 22 capable of controlling the discharge amount disposed therein.
[0014]
That is, in this embodiment, fuel (HC) of the internal combustion engine is used as the reducing agent. However, hydrocarbons such as gasoline, isooctane, hexane, heptane, light oil, kerosene, butane, propane, hydrogen, ammonia, urea and the like can also be used as the reducing agent.
FIG. 2 shows the structure of the reducing agent injection nozzle 18 in detail. Referring to FIG. 2, the reducing agent injection nozzle 18 includes a casing 18a, a nozzle port 18b formed at one longitudinal end of the casing 18a, a reducing agent inlet 18c formed at the other longitudinal end of the casing 18a, and a casing. A guide member 18e fixed in the internal space and having a guide groove 18d inclined with respect to the longitudinal axis of the reducing agent injection nozzle 18, and extending in the casing internal space around the guide member 18e from the reducing agent inflow port 18c to the nozzle port 18b. It has a reducing agent passage 18f and a check valve 18g arranged between the reducing agent inlet 18c and the reducing agent supply pipe 19 and capable of flowing only toward the reducing agent inlet 18c.
[0015]
When the solenoid valve 20 is opened and the check valve 18g is opened, the reducing agent flows through the reducing agent passage 18f, and is then injected from the nozzle port 18b. At this time, since the guide groove d is provided in the guide member 18e, the reducing agent is injected while turning, and therefore the reducing agent is injected over a wide range.
Referring to FIG. 1 again, the exhaust manifold 12 and the intake duct 4 downstream of the throttle valve 10 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 23, and an EGR cooler 24 is provided in the EGR passage 23. And an EGR control valve 26 driven by an actuator 25. By opening the EGR passage 23 upstream of the reducing agent supply device 17 in this manner, the returning of the reducing agent together with the EGR gas to the engine intake passage is prevented.
[0016]
An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, and always connected via a bidirectional bus 31. It has a B-RAM (backup RAM) 35, an input port 36, and an output port 37 connected to a power supply. An intake air amount sensor 38 for detecting a mass flow rate of the intake air is disposed in the air intake pipe 7. A temperature sensor 39 that generates an output voltage proportional to the temperature of the exhaust gas flowing into the NO _X reduction catalyst 14 is disposed in the exhaust pipe 13. The depression sensor 40 generates an output voltage proportional to the depression DEP of the accelerator pedal. The output voltages of these sensors 38, 39, 40 are input to the input port 36 via the corresponding AD converters 41, respectively. The input port 36 is connected to a rotation speed sensor 42 that generates an output pulse indicating the engine rotation speed. On the other hand, the output port 37 is connected to the actuator 9, each fuel injection valve 11, the solenoid valve 20, the fuel pump 22, and the actuator 25 via the corresponding drive circuit 43, respectively.
[0017]
In the present embodiment, the NO _X reduction catalyst 14 is formed from a NO _X storage reduction catalyst. The NO _X storage reduction catalyst 14 uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and lanthanum La And at least one selected from rare earths such as yttrium Y and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir. This _the NO _X storage reduction catalyst 14 is stored the NO _X when the air-fuel ratio of the inflowing exhaust is lean, the NO _X absorption emission-reducing effect of the oxygen concentration in the inflowing exhaust gas is reduced by releasing NO _X are stored to be reduced Do. Here, it is considered that the NO _X storage reduction catalyst 14 stores NO _X by absorption.
[0018]
By arranging the _the NO _X storage reduction catalyst 14 described above in the engine exhaust passage this _the NO _X storage reduction catalyst 14 performs actual NO _X absorption emission-reduction action but detailed mechanism of this NO _X absorption emission-reducing action Is not clear. However, it is considered that this NO _X absorption / release / reduction action is performed by a mechanism as shown in FIGS. 3 (A) and 3 (B). Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0019]
That is, when the inflow exhaust gas becomes considerably lean, the oxygen concentration in the inflow exhaust gas greatly increases, and as shown in FIG. 3 (A), these oxygen O ₂ is converted into O ²⁻ or O ₂ ^{− in} the form of platinum Pt. Attaches to surface. On the other hand, NO in the inflowing exhaust gas reacts with O ²⁻ or O ₂ ⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed into the absorbent while being further oxidized on the platinum Pt, 3 nitric acid as shown in (A) ions NO ₃ ^- in It diffuses into the absorbent in form. In this way, NO _X is absorbed in the NO _X storage reduction catalyst 14.
[0020]
As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _X absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ⁻ are generated. You. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent. There are released from the absorbent in the form of NO _2. Namely, when the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X storage reduction catalyst 14 when lowered. The oxygen concentration in the inflowing exhaust gas if the lean degree of the inflowing exhaust is low is reduced, thus resulting in the NO _X is released from _the NO _X storage reduction catalyst 14 if lowering the lean degree of the inflowing exhaust.
[0021]
On the other hand, when a reducing agent such as HC is supplied to the NO _X storage reduction catalyst 14 at this time, the reducing agent HC and HC and CO discharged from the engine react with oxygen O ₂ ⁻ or O ²⁻ on the platinum Pt to be oxidized. Can be Further, NO _X concentration of oxygen storage-reduction catalyst 14 in the inflowing exhaust gas and supplying the reducing agent is released NO ₂ from the absorbent in order to decrease, as the NO ₂ is shown in FIG. 3 (B) HC, It is reduced by reacting with CO. In this way, when NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another and reduced. Therefore, NO _X from NO _X when the reducing agent storage reduction catalyst 14 is supplied _the NO _X storage reduction catalyst 14 is released, it will be reduced.
[0022]
The diesel engine as in the present embodiment, the NO _X in the exhaust gas average air-fuel ratio of the normal in each cylinder during operation is maintained lean, thus discharged from the cylinders during normal operation _the NO _X storage reduction catalyst 14 Is stored in However, the the NO _X storage ability of the NO _X occluding and reducing catalyst 14 is necessary to release the NO _X from _the NO _X storage reduction catalyst 14 before NO _X storage capability of the NO _X occluding and reducing catalyst 14 is saturated because there is a limit . Therefore, in the present embodiment, the reducing agent is intermittently supplied from the reducing agent supply device 17, so that the NO _X amount stored in the NO _X storage reduction catalyst 14 is reduced.
[0023]
In this case, as described at the beginning, it is preferable that the concentration of the reducing agent in the exhaust gas flowing into the NO _X storage reduction catalyst 14 or the air-fuel ratio of the inflow exhaust gas rapidly change. Therefore, in the present embodiment, when the intake air amount Ga is large, the reducing agent injection pressure PR of the reducing agent supply device 17 is set to be higher than when it is small, so that the reducing agent supply amount per unit time is increased. ing. The reducing agent injection pressure PR in this case is stored in the ROM 32 in the form of a map shown in FIG.
[0024]
In the present embodiment, the supply amount of the reducing agent is determined so that the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 14 becomes a predetermined target air-fuel ratio. In this way, it is possible to _the NO _X storage reduction catalyst 14 reliably release the NO _X in, favorably reduces the amount of reducing agent is discharged from the reducing life-and-death _the NO _X storage reduction catalyst 14. The target air-fuel ratio may be determined in any manner as long as the above-described effects are obtained, but in the present embodiment, the target air-fuel ratio is set to the stoichiometric air-fuel ratio.
[0025]
Assuming that the reducing agent supply amount from the reducing agent supply device 17 is QR and the fuel injection amount from the fuel injection valve 11 to the engine 1 is QE, the inflow into the NO _X storage reduction catalyst 14 when the reducing agent supply operation is performed The air-fuel ratio AFRE of the exhaust gas is expressed by the following equation.
AFRE = Ga / (QR + QE)
Therefore, the reducing agent amount QR required to make the air-fuel ratio AFRE of the exhaust gas flowing into the NO _X storage reduction catalyst 14 coincide with the stoichiometric air-fuel ratio AFRS is expressed by the following equation.
[0026]
QR = Ga / AFRS-QE
The reducing agent is supplied from the reducing agent supply device 17 by QR.
When the reducing agent injection pressure PR and the reducing agent supply amount QR are determined in this way, the reducing agent injection time TAUR is determined. The reducing agent injection time TAUR is stored in the ROM 32 in advance in the form of a map shown in FIG. 5 as a function of the reducing agent injection pressure PR and the reducing agent supply amount QR. Therefore, the solenoid valve 20 is opened by TAUR.
[0027]
Even if the reducing agent injection pressure PR is determined according to the intake air amount Ga as described above, the reducing agent injection time TAUR may fluctuate depending on the manner of determination. In this case, as the reducing agent injection time TAUR becomes longer, the amount of the reducing agent discharged from the NO _X storage reduction catalyst 14 increases. Therefore, the upper limit of the reducing agent injection time TAUR is determined so that the amount of reducing agent discharged from the NO _X storage reduction catalyst 14 does not exceed the allowable amount. On the other hand, the reducing agent supply device 17 is provided with a minimum injection time according to its structure. Therefore, the lower limit of the reducing agent injection time TAUR is determined so that the reducing agent injection time TAUR does not become shorter than the minimum injection time. That is, the reducing agent injection pressure PR is determined with respect to the intake air amount Ga such that the reducing agent injection time TAUR is maintained within a predetermined set range. Further, preferably, the reducing agent injection pressure PR is determined such that the reducing agent injection time TAUR is maintained at a substantially constant value.
[0028]
When the reducing agent supply operation is performed, releasing reducing action of the NO _X in _the NO _X storage reduction catalyst 14 is performed. In the present embodiment, the reducing agent is injected in the form of droplets rather than spraying, and the reducing agent in the form of droplets adheres to the surface of the NO _X storage reduction catalyst 14. As a result, the air-fuel ratio locally exhausted is formed a rich region, emission reduction action of the NO _X is quickly and reliably carried out thus.
[0029]
The reducing agent supply operation surface of the NO _X occluding and reducing catalyst 14 be stopped continues to remain in the reducing agent, the residual reducing agent is reduced gradually while releasing reducing the NO _X in _the NO _X storage reduction catalyst 14 . Therefore, it is not necessary to supply the reducing agent while the amount of the remaining reducing agent in the NO _X storage reduction catalyst 14 is large, and it is sufficient to supply the reducing agent when the amount of the remaining reducing agent becomes small.
[0030]
Therefore, in the present embodiment, after the previous reducing agent supply operation, the amount of the remaining reducing agent in the NO _X storage reduction catalyst 14 is obtained, and when the amount of the remaining reducing agent becomes smaller than a predetermined set amount, the next A reducing agent supply operation is performed.
As the elapsed time from the start of the previous reducing agent supply operation becomes longer, the amount of the remaining reducing agent in the NO _X storage reduction catalyst 14 decreases. On the other hand, with respect to the integrated value of the amount of intake air from the start of the previous reducing agent supply operation to a certain time, the amount of the reducing agent supply in the previous reducing agent supply operation and the time after the start of the previous reducing agent supply operation If the ratio of the sum of the fuel injection amount to the engine 1 and the integrated value up to the time is referred to as the average air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 14 at this time, the previous reducing agent supply operation is started. As the elapsed time increases, the average air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 14 increases. Therefore, the average air-fuel ratio of the inflowing exhaust into _the NO _X storage reduction catalyst 14 will be representing the residual amount of reducing agent in _the NO _X storage reduction catalyst 14.
[0031]
Therefore, when the average air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 14 after the previous reducing agent supply operation is performed becomes larger than a predetermined set air-fuel ratio, the NO _X storage reduction catalyst 14 It is determined that the remaining reducing agent amount has become smaller than the set amount, and at this time, the next reducing agent supply operation is performed.
However, the start time of the next reducing agent supply operation is determined so that the time interval between the previous reducing agent supply operation and the next reducing agent supply operation is not shorter than a predetermined minimum time interval. As a result, for example, a control signal to start the next reducing agent supply operation before the previous reducing agent supply operation is completed is prevented from being issued.
[0032]
Next, the present embodiment will be described in detail with reference to FIGS. 6 and 7 while referring to FIG. FIG. 6 shows a routine for calculating the reducing agent injection time TAUR. This routine is executed by interruption every predetermined set time.
Referring to FIG. 6, first, at step 50, it is determined whether or not the exhaust gas temperature TE is higher than a predetermined set temperature T1. When TE ≦ T1, it is determined that the NO _X storage reduction catalyst 14 is not in the active state, and the processing cycle ends. That is, the reducing agent supply operation is stopped. On the other hand, when TE> T1, the routine proceeds to step 51, where it is determined whether or not the flag is set. This flag is set when the reducing agent supply operation of the reducing agent supply device 17 is to be performed, and is reset when the reducing agent supply operation is performed, and is controlled by the routine of FIG. When the flag has been reset, the processing cycle ends. When the flag is set, the routine then proceeds to step 52, where the reducing agent injection pressure PR is calculated from the map of FIG. Thereby, the discharge amount of the reducing agent pump 22 is controlled so that the actual reducing agent injection pressure becomes PR. In the following step 53, the fuel injection amount QE from the fuel injection valve 11 to the engine 1 is read. In the following step 54, the required reducing agent amount QR is calculated (QR = Ga / AFRS-QE). In the following step 55, the reducing agent injection time TAUR is calculated from the map of FIG. Therefore, the solenoid valve 20 is opened by TAUR. In the following step 56, the flag is reset.
[0033]
That is, when the flag is set as shown in FIG. 8, the solenoid valve 20 is opened, and the reducing agent supply operation is started. As a result, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 14 is made to match the stoichiometric air-fuel ratio AFRS that is the target air-fuel ratio.
FIG. 7 shows a flag control routine. This routine is executed by interruption every predetermined set time.
[0034]
Referring to FIG. 7, first, at step 60, it is determined whether or not the flag is set. When the flag is switched from set to reset, that is, when the reducing agent supply operation is performed, the process proceeds to step 61, where the count value INT representing the time interval of the reducing agent supply operation is incremented by one. In the following step 62, the integrated intake air amount SGa and the integrated fuel injection amount SQE since the start of the reducing agent supply operation are calculated (SGa = SGa + Ga, SQE = SQE + QE). In the following step 63, the average air-fuel ratio AFRAVE of the exhaust gas flowing into the NO _X storage reduction catalyst 14 at this time is calculated (AFRAVE = SGa / (SQE + QR)). Here, QR is the reducing agent supply amount in the immediately preceding reducing agent supply operation.
[0035]
In the following step 64, it is determined whether or not the average air-fuel ratio AFRAVE is larger than the set value R1. When AFRAVE ≦ R1, it is determined that the amount of the remaining reducing agent in the NO _X storage reduction catalyst 14 is still large, and the processing cycle ends. On the other hand, when AFRAVE> R1, it is determined that the amount of the remaining reducing agent in the NO _X storage reduction catalyst 14 has become smaller than the set amount, and then the routine proceeds to step 65. In step 65, it is determined whether or not the count value INT is larger than a set value I1 representing the minimum time interval. When INT ≦ I1, the processing cycle ends. If INT> I1, then the routine proceeds to step 66, where a flag is set.
[0036]
That is, as shown in FIG. 8, when the flag is reset, the average air-fuel ratio AFRAVE starts to increase from the stoichiometric air-fuel ratio AFRS. Next, the average air-fuel ratio AFRAVE becomes larger than the set value R1, and at this time, a flag is set if INT> I1.
When the flag is set, the process proceeds from step 60 to step 67, where the integrated intake air amount SGa, the integrated fuel injection amount SQE, and the count value INT are cleared. Then, the processing cycle ends.
[0037]
By the way, as described above with reference to FIG. 4, the reducing agent injection pressure PR increases as the intake air amount Ga increases, and the reducing agent injection pressure PR decreases as the intake air amount Ga decreases. However, the controllable range of the reducing agent injection pressure PR may be limited depending on the reducing agent supply device 17, that is, the reducing agent injection pressure PR may not be very high or low. In such a case, the reducing agent injection pressure PR is maintained at the maximum or minimum possible pressure of the reducing agent supply device 17, but the reducing agent injection time TAUR is increased or decreased.
[0039]
【The invention's effect】
_The NO _X storage reduction catalyst reliably release the NO _X in, reduced, it is possible to reduce the amount of reducing agent discharged from _the NO _X storage reduction catalyst at the same time.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is an enlarged view of a reducing agent injection nozzle.
3 is a diagram illustrating a NO _X absorption emission-reducing action of the NO _X occluding and reducing catalyst.
FIG. 4 is a diagram showing a reducing agent injection pressure PR.
FIG. 5 is a diagram showing a reducing agent injection time TAUR.
FIG. 6 is a flowchart illustrating a routine for calculating a reducing agent injection time TAUR.
FIG. 7 is a flowchart illustrating a flag control routine.
FIG. 8 is a time chart for explaining a reducing agent supply operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine body 13 ... Exhaust pipe 14 ... NO _X storage reduction catalyst 17 ... Reducing agent supply device 38 ... Intake air amount sensor

Claims (6)

In an exhaust passage of an internal combustion engine air-fuel ratio in the combustion chamber is set to be lean, the air-fuel ratio of the inflowing exhaust gas is stored in the NO _X in the inflowing exhaust gas when the lean and stored with the oxygen concentration in the inflowing exhaust gas is lowered to release the NO _X place _the NO _X storage reduction catalyst for which are intermittently supplying reducing agent from the arrangement reducing agent supply device to the NO _X occluding and reducing catalyst upstream in the exhaust passage to the NO _X occluding and reducing catalyst in to _the NO _X storage reduction catalyst exhaust purifying apparatus of an internal combustion engine so as to reduce NO _X in is supplied from the reducing agent supply apparatus per unit time to be larger than when less when many intake air amount The required amount of reducing agent required to bring the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst into a predetermined target air-fuel ratio during the reducing agent supply operation is determined. Reducing agent Exhaust purification system of an internal combustion engine so as to obtain a reducing agent injection time based on the amount of reducing agent supplied from the charging device and the required amount of reducing agent. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reducing agent supply device is capable of changing the reducing agent injection pressure, and when the intake air amount is large, the reducing agent injection pressure is higher than when the intake air amount is small . 2. The internal combustion engine according to claim 1, wherein the amount of reducing agent supplied from the reducing agent supply device per unit time with respect to the amount of intake air is determined so that the reducing agent injection time is maintained within a predetermined setting range. Exhaust gas purification device. The amount of the remaining reducing agent remaining in the NO _X storage reduction catalyst after the previous reducing agent supply operation is obtained, and when the amount of the remaining reducing agent becomes smaller than a predetermined set amount, the next supply of the reducing agent is performed. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus performs an operation. _The NO _X storage when the previous reducing agent supply operation is greater than the set air-fuel ratio by calculating an average air-fuel ratio of the inflowing exhaust into _the NO _X storage reduction catalyst is the average air-fuel ratio predetermined from the start of 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4 , wherein it is determined that the amount of the remaining reducing agent in the reduction catalyst has become smaller than the set amount. According to claim 4, the time interval between the previous reducing agent supply operation and the next of the reducing agent supply operation defining the start timing of the next of the reducing agent supply operation so as not shorter than the minimum predetermined time interval Exhaust purification device for internal combustion engine.

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