JP2000145433A - Exhaust gas purifier for internal combustion engines - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply reducing agent uniformly in the direction of exhaust flow, and in the radial direction, in the exhaust purifying catalyst. SOLUTION: An NOx absorber 17 that absorbs NOx when the inflowing fuel-air ratio is lean and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas drops, is installed in the engine exhaust passage. An oxidizing catalyst 16 is installed upstream of the NOx absorber in the exhaust passage. Primary and secondary reducing agent injection nozzles 21, 22 are installed in the exhaust passage upstream of the oxidizing catalyst 16 in order to release and reduce the NOx within the NOx absorber 17. The particle size of the reducing agent injected from the primary reducing agent injection nozzle 21 is larger than that of the reducing agent injected from the secondary reducing agent injection nozzle. When the temperature of the NOx absorber is low, a reducing agent is supplied through the secondary reducing agent injection nozzle 22 only, and when the temperature of the NOx reducing agent is high, a reducing agent is supplied through the primary reducing agent injection nozzle 21 only.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

BACKGROUND OF THE INVENTION engine combustion chamber internal combustion engine in which the air-fuel ratio of the mixture burned in the lean in, along with arranging the NO _X reducible exhaust gas purifying catalyst in the engine exhaust passage in an oxidizing atmosphere containing a reducing agent A first HC injection nozzle disposed in the engine exhaust passage upstream of the exhaust purification catalyst, and a first HC injection nozzle adjacent to the exhaust purification catalyst; place the oxidation catalyst in the exhaust passage between the second HC injection nozzle of the nozzle upstream, NO _X in the exhaust purification catalyst by HC supplies HC to the exhaust purification catalyst from these HC injection nozzle
There is known an exhaust gas purifying apparatus for an internal combustion engine that reduces the pressure (see JP-A-5-214926).

[0003] In the exhaust gas purifying apparatus, at the time of engine high load operation so that the reduction of NO _X in the exhaust purification catalyst by the HC by injecting HC from only the first HC injection nozzle. On the other hand, during low engine load operation, the second
By injecting HC from the HC injection nozzle oxidized reaction in the oxidation catalyst, to increase the temperature of the exhaust gas purifying catalyst thereby, the NO _X in the exhaust purification catalyst by the HC by injecting HC from the first HC injection nozzle I try to give back. In this case, almost all of the HC injected from the second HC injection nozzle is completely oxidized by the oxidation catalyst, and even when the HC reaches the exhaust purification catalyst, the degree of oxidation is considerably large. Therefore, HC injected from the second HC injection nozzle reacts at the exhaust upstream end of the exhaust purification catalyst and does not reach the exhaust downstream end of the exhaust purification catalyst.
Therefore, in order to supply HC to the exhaust gas downstream end of the exhaust gas purifying catalyst in this exhaust gas purifying device, it is necessary to use HC injected from the first HC injection nozzle.

[0004]

However, for example, when the temperature of the exhaust purification catalyst is high, HC particles injected from the first HC injection nozzle are supplied so that HC is supplied to the exhaust downstream end of the exhaust purification catalyst. If the diameter is set to be large, there is a problem that HC having a large particle diameter adheres to the exhaust purification catalyst when the temperature of the exhaust purification catalyst is low, and thus the exhaust purification catalyst is poisoned by HC. On the other hand, if the particle size of HC injected from the first HC injection nozzle is set small so that the exhaust gas purification catalyst is not poisoned by HC when the temperature of the exhaust gas purification catalyst is low, when the temperature of the exhaust gas purification catalyst is high, There is a problem that most of the HC is consumed around the exhaust upstream end of the exhaust purification catalyst, and is not supplied to the exhaust downstream end of the exhaust purification catalyst. The above publication does not consider this problem at all.

[0005]

According to a first aspect of the present invention, an exhaust purification catalyst is disposed in an engine exhaust passage, and a plurality of reducing agent injection nozzles are arranged in the exhaust flow direction. Is disposed in the engine exhaust passage upstream of the exhaust purification catalyst, and the reducing agent injection nozzle is configured to supply the reducing agent to the exhaust purification catalyst from the reducing agent injection nozzle. The particle diameter of the reducing agent injected from the reducing agent injection nozzle is increased as the value of. That is, in the first invention, for example, when the temperature of the exhaust purification catalyst is low, the reducing agent is supplied from the reducing agent injection nozzle on the exhaust downstream side, and when the temperature of the exhaust purification catalyst is high, the reducing agent is supplied from the reducing agent injection nozzle on the exhaust upstream side. Is supplied, the reducing agent can be supplied to the exhaust downstream end of the exhaust purification catalyst while the poisoning of the exhaust purification catalyst is prevented. In other words, the reducing agent is supplied uniformly in the exhaust gas flow direction of the exhaust purification catalyst. Further, as the reducing agent having a larger particle diameter at the time of injection is used, the distance from the reducing agent injection nozzle to the exhaust purification catalyst is longer, so that the reducing agent is uniformly supplied in the radial direction of the exhaust purification catalyst.

According to a second aspect, in the first aspect, an oxidation catalyst is disposed in an exhaust passage between a pair of reducing agent injection nozzles adjacent to each other. That is, in the second invention, except for the reducing agent injection nozzle immediately upstream of the exhaust purification catalyst, the reducing agent injected from the reducing agent injection nozzle is supplied to the exhaust purification catalyst after being oxidized by the oxidation catalyst. In this case, since the particle size of the reducing agent injected from the reducing agent injection nozzle is larger as the position of the reducing agent injection nozzle is on the exhaust upstream side, it is possible to reach the exhaust purification catalyst even if oxidized by the oxidation catalyst. Becomes

According to a third aspect, in the second aspect, the reducing agent injection nozzle for performing the reducing agent injection is changed according to the engine operating state. That is, in the third aspect, it is possible to supply the reducing agent in an optimal form according to the operating state of the engine.

[0008]

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, 1 is an engine body, 2 is a combustion chamber, 3 is an intake port, 4 is an intake valve, 5 is an exhaust port, 6 is an exhaust valve, and 7 is fuel injection for directly injecting fuel into the combustion chamber 2. Each nozzle is shown.
The intake port 3 of each cylinder is connected to a common surge tank 9 via a corresponding intake branch pipe 8, and the surge tank 9 is connected to an air cleaner 11 via an intake duct 10. An intake control valve 13 driven by an actuator 12 is arranged in the intake duct 10. On the other hand, the exhaust port 5 of each cylinder is connected to a casing 18 which accommodates an oxidation catalyst 16NO _X absorbent 17 via a common exhaust manifold 14 and exhaust pipe 15, the casing 17 is connected to the exhaust pipe 19.

[0009] NO _X in the absorbent 17 in the exhaust passage upstream of N
Reducing agent supply device 20 for supplying a reducing agent to O _X absorbent 17 is provided. In the present embodiment, the reducing agent supply device 20 includes first and second reducing agent injection nozzles 21 and 22 arranged in the exhaust pipe 15 with a gap in the exhaust gas flow direction.
Is provided. These reducing agent injection nozzles 21 and 22 are connected to the discharge side of a reducing agent pump 24 via corresponding solenoid valves 21a and 22a, respectively, and the suction side of the reducing agent pump 24 is connected to a reducing agent tank (not shown). The particle size of the reducing agent injected from the first reducing agent injection nozzle 21 is determined to be larger than the particle size of the reducing agent injected from the second reducing agent injection nozzle 22, and therefore, the position of the reducing agent injection nozzle Is closer to the exhaust upstream side, the particle diameter of the reducing agent injected from the reducing agent injection nozzle is larger. The actuator 12, the solenoid valves 21a and 22a, and the reducing agent pump 24 are controlled based on output signals from the electronic control unit 30, respectively.

[0010] The reducing agent can be selected from hydrocarbons, hydrogen and alcohols and can be gaseous or liquid. In this embodiment, engine fuel (light oil) is used as the reducing agent. Thus, the reductant tank is formed from a fuel tank and does not require an additional reductant tank. The electronic control unit (ECU) 30 comprises a digital computer,
A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, a B-RAM (backup RA) connected to a power source at all times via a bidirectional bus 31
M) 35, an input port 36, and an output port 37. A pressure sensor 38 for generating an output voltage proportional to the absolute pressure PM in the surge tank 9 is attached to the surge tank 9, and an output voltage proportional to the temperature of exhaust gas flowing out of the NO _X absorbent 17 is provided in the exhaust pipe 19. Is mounted. Temperature of the exhaust represents _the NO _X absorbent temperature TNA. Further, the depression amount sensor 40 generates an output voltage proportional to the depression amount 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 has a rotation speed sensor 4 for generating an output pulse representing the engine rotation speed N.
2 are connected. On the other hand, the output ports 37 are respectively connected to the actuator 12 and the reducing agent pump 24 via the corresponding drive circuits 43.

NO _X stored in casing 17
The absorbent 17 is made of, for example, alumina as a carrier. On this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y are used. At least one selected from such rare earths and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported. The ratio of the total air amount to the total fuel amount and the total reducing agent amount supplied into the exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the exhaust passage is determined by the air-fuel ratio of the exhaust flowing through the position. when called, the air-fuel ratio of the _the NO _X absorbent 17 flows exhaust gas absorbs the NO _X when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed and reduced N
Absorption and desorption of O _X out perform the action. Note that matches the ratio of the air quantity for the air-fuel ratio is the amount of fuel supplied to the engine of the exhaust gas flowing to the NO _X absorbent 17 when the fuel or air to _the NO _X absorbent 17 in the exhaust passage upstream of is not supplied .

If the above-mentioned NO _X absorbent 17 is disposed in the engine exhaust passage, the NO _X absorbent 17 actually performs the NO _X absorption / release operation, but the detailed mechanism of this absorption / release operation is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIGS. 2 (A) and 2 (B). Next, regarding this mechanism, platinum Pt and barium Ba are deposited on the carrier.
Will be described as an example in the case of carrying other precious metals,
The same mechanism is obtained by using an alkali metal, an alkaline earth, or a rare earth.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases.
As shown in (A), these oxygens O ₂ adhere to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO in the exhaust gas that flows in reacts with O ₂ ⁻ or O ²⁻ on the surface of 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, 2 nitrate ions NO ₃ as shown in (A) ^- of It diffuses into the absorbent in form. Thus N
O _X is absorbed in the NO _X absorbent 17.

[0014] NO ₂ is produced on the surface of the oxygen concentration is as high as platinum Pt in the inflowing exhaust gas, as long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- Is generated. On the other hand, when the oxygen concentration in the exhaust gas that flows in decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ions NO ₃ ⁻ There are released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflowing exhaust gas decreases _the NO _X absorbent as shown in FIG. 2 (B) 17
NO _X is to be released from the. The oxygen concentration in the exhaust gas lean degree of the exhaust gas flowing to flow the lower the lowered, thus NO _X from _the NO _X absorbent 17 when lowering the lean degree of the exhaust gas flowing is to be released.

Meanwhile, when supplying a reducing agent (HC) in this case _the NO _X absorbent 17 unburned H in the reducing agent and the exhaust
C and CO react with oxygen O ₂ ^- or O ^2- on platinum Pt to be oxidized. Also, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 is supplied a certain amount of reducing agent to the NO _X absorbent 17 is a lean, because the oxygen concentration around the platinum Pt is lowered locally NO ₂ is released from the absorbent, and this NO ₂ is reduced by reacting with the reducing agent and unburned HC and CO as shown in FIG. 2 (B).
In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Accordingly, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 be supplied a certain amount of reducing agent to the NO _X absorbent 17 is NO _X is released from _the NO _X absorbent 17 even lean, is released and NO _X is to be reduced.

In a diesel engine as shown in FIG.
Usually reduces smoke and particulates emitted from engines
Therefore, the average air-fuel ratio of the air-fuel mixture burned in the combustion chamber 2 is
It is maintained leaner than the stoichiometric air-fuel ratio. Therefore
NO during normal operation_XAir-fuel ratio of exhaust gas flowing into absorbent 17
Is lean, so the NO discharged from the engine at this time _X
Is NO_XAbsorbed by the absorbent 17.

However, NO_XNO of absorbent 17_Xabsorption
NO because the ability is limited_XNO of absorbent 17_Xabsorption
NO before capacity saturates_XNO from absorbent 17_XRelease
Need to be done. NO_XNO from absorbent 17_XRelease
NO to let_XWhen the reducing agent is supplied to the absorbent 17
NO_XNO of absorbent 17_XRelease rate, and NO_XReturn
Original reaction rate is NO_XDepends on the absorbent temperature TNA, but
NO_XNO of absorbent 17_XThe purification rate R is shown in FIG.
So no_XDepends on the absorbent temperature TNA. From FIG.
As you can see, NO_XAbsorbent temperature TNA is NO_XAbsorbent
It should be higher than the threshold temperature T1 determined according to the type of 17
NO_XPurification rate R is higher than allowable minimum purification rate R1
You. NO_XAbsorbent temperature TNA is equal to threshold temperature T1
NO when low _XIf it cannot be released and reduced
NO_XThe reducing agent supplied to the absorbent 17 is an acid
NO without being converted_XIt flows out of the absorbent 17.

Therefore, in this embodiment, NO_XAbsorbent temperature
When the TNA is lower than the threshold temperature T1, the reducing agent supply
The reducing agent supply operation of the device 20 is stopped and NO_XAbsorbent temperature T
When the NA becomes higher than the threshold temperature T1, the reducing agent is supplied.
A predetermined set time for the reducing agent supply operation of the supply device 20
Just go and no_XNO absorbed from absorbent 17 _X
And released NO_XTo reduce
You.

[0019] In this case, _the NO _X absorbent rapidly released air-fuel ratio of the exhaust gas flowing into the NO _X in _the NO _X absorbent 17 needs to supply the reducing agent so that the stoichiometric air-fuel ratio or rich to 17, reduced be able to. However, in order to make the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 in the diesel engine shown in FIG. 1 to the stoichiometric air-fuel ratio or rich requires a large amount of reducing agent, whereas, as described above NO _X air-fuel ratio of the exhaust gas flowing into the absorbent 17 is NO _X is released from _the NO _X absorbent 17 even lean, released NO _X is reduced. Therefore, in this embodiment, NO
Releasing NO _X in the _X absorbent 17, so that the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 is maintained lean when performing a reducing agent supply serves to reduction.

The reducing agent supplied from the reducing agent supply device 20 first reaches the oxidation catalyst 16, where the reducing agent is partially oxidized, and then flows into the NO _x absorbent 17. As a result, N
Temperature of the exhaust gas flowing into the O _X absorbent 17 is raised, NO _X emission rate and the reduction rate of the NO _X absorbent 17 is kept high. Further, the oxygen concentration in the exhaust gas flowing to the NO _X absorbent 17 is made to decrease by the reducing agent is partially oxidized and further a reducing agent is made to more easily reacts with state NO _X, also NO _X by these Absorbent 17
NO _X emission rate and the reduction ratio of can be maintained high.

[0021] _the NO _X absorbent release the NO _X in the 17, only qN per unit time from the reducing agent supply device 20 reducing agent is supplied to the time to reduction. This qN is favorably emits NO _X in _the NO _X absorbent 17 while maintaining a small reducing agent consumption ratio is optimal amount of reducing agent to be reduced, are obtained by experiments in advance. qN is stored in the ROM 32 in advance in the form of a map shown in FIG. 4 as a function of the absolute pressure PM in the surge tank 9 and the engine speed N.

In this embodiment, when the reducing agent is supplied from the reducing agent supply device 20, the reducing agent injection nozzle for performing the injection of the reducing agent is changed according to the operating state of the engine. Next, this will be described. When _the NO _X absorbent temperature TNA first switching temperature TS1 (> T1) lower than a predetermined reducing agent is supplied from only the second reducing agent injection nozzle 22. When supplying a reducing agent from the first reducing agent injection nozzle 21 when the first particle size of the reducing agent injected from the reducing agent injection nozzle 21 is relatively large because _the NO _X absorbent temperature TNA is low, the particle size big reducing agent is NO _X of
There is a possibility that so-called HC poisoning may occur by adhering and remaining on the surface of the absorbent 17. Therefore, when TNA <TS1, the reducing agent is supplied only from the second reducing agent injection nozzle 22 and N
HC of O _X absorbent 17 so as to prevent poisoning.
In this case, the particle size of the reducing agent injected from the second reducing agent injection nozzle 22 is determined to be just completely oxidized in the exhaust downstream end of the NO _X absorbent 17, therefore N
Uniformly reducing agent relates to an exhaust flow direction of O _X absorbent 17 is supplied. Further, since the particle diameter of the reducing agent injected from the second reducing agent injection nozzle 22 is relatively small, the reducing agent injected from the second reducing agent injection nozzle 22 is easily diffused in the radial direction, and therefore NO _X The reducing agent is also supplied uniformly in the radial direction of the absorbent 17.

On the other hand, NO_XAbsorbent temperature TNA is the first cut
Second switching temperature TS2 higher than switching temperature TS1
(> TS1), the first reducing agent injection nozzle
The reducing agent is supplied only from the fuel tank 21. NO_XAbsorbent temperature
When the TNA is high, return from the second reducing agent injection nozzle 22
When the base agent is supplied, the particle size of the reducing agent is small, so NO _X
Most is consumed on the exhaust upstream side of the absorbent 17,
NO_XIt cannot reach the exhaust downstream end of the absorbent 17. There
When TS2> TNA> TS1, the first reducing agent injection
The reducing agent having a relatively large particle diameter is changed to NO
_XTo the absorbent 17, whereby the exhaust flow direction
The reducing agent is supplied uniformly. Also, the first
NO from the reducing agent injection nozzle 21_XDistance to absorbent 22
Due to the long separation, the reducing agent with a relatively large particle size can be filled in the radial direction.
Diffuser, and thus uniformly in the radial direction
Is supplied.

[0024] _the NO _X absorbent temperature TNA is when higher than the second switching temperature TS2 reducing agent is supplied from the first and second reducing agent injection nozzle 21, thereby a large amount in _the NO _X absorbent 17 A reducing agent can be supplied. In this case, for example, the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is qN · m (m is a constant value smaller than 1) with respect to the total reducing agent amount qN to be supplied from the reducing agent supply device 20. And the second reducing agent injection nozzle 2
The reducing agent injection amount q2 of 2 is qN · (1-m).

[0025] be provided by changing the reducing agent injection nozzle to be injected reducing agent in accordance with this way the engine operating condition, the reducing agent optimal properties regardless the engine operating condition in the NO _X absorbent 17 Can be. Incidentally, as described above in this embodiment, releasing the NO _X in _the NO _X absorbent 17, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 when to be reduced is a lean, _the NO _X absorbent 17 _the NO _X absorbent 17 by the oxygen concentration of the surface of the drops locally
NO _X is released, it is reduced from. NO _X like this
It has been confirmed that it is more preferable to supply the reducing agent in the form of droplets than to supply the sufficiently vaporized reducing agent to the NO _x absorbent 17 in order to effectively perform the release and reduction actions of NO. On the other hand, the more the position of the reducing agent injection nozzle is the exhaust upstream side, i.e. the reducing agent injection nozzle and _the NO _X absorbent 1
As the distance from the reducing agent 7 increases, the reducing agent injected from the reducing agent injection nozzle is more likely to be vaporized and lightened.

Therefore, in the present embodiment, the particle size of the reducing agent injected from the reducing agent injection nozzle is increased as the position of the reducing agent injection nozzle is on the exhaust upstream side, whereby the reducing agent is vaporized and lightened. Is to be suppressed. Therefore, the NO _X releasing and reducing actions of the NO _X absorbent 17 can be performed efficiently. FIG. 5 shows an interruption routine executed by interruption every predetermined time.

Referring to FIG. 5, first, at step 50, it is determined whether or not a flag is set. This flag is set when the reducing agent is to be supplied from the reducing agent supply device 20, and is reset when the supply of the reducing agent is to be stopped. Flag routine goes to step 51 when it is reset, NO _X absorbent temperature TNA whether higher than the threshold temperature T1 is determined. TNA> T1
The routine goes to step 52, whether _the NO _X absorbent temperature TNA was a T1 or less in the last processing cycle is determined at the time of. T in the previous processing cycle
When NA ≦ T1, i.e. _the NO _X absorbent temperature TNA is routine goes to step 53 when the rise above the threshold temperature T1, the flag is set. On the other hand, when TNA ≦ T1 in step 51, or in step 52, TNA> T in the previous processing cycle.
If it is 1, the processing cycle ends.

Step 5 when the flag is set
From 0, the process proceeds to step 54, where the counter value C representing the time during which the flag is set is incremented by one. In a succeeding step 55, it is determined whether or not the count value C is larger than the set value C1. When C ≦ C1, the processing cycle ends. When C> C1, it is determined that the reducing agent supply operation of the reducing agent supply device 20 has been performed for a predetermined time, and the routine proceeds to step 56, where the flag is reset. In the following step 57, the counter value C is cleared.

FIG. 6 shows a routine for calculating the reducing agent injection amounts q1 and q2 of the first and second reducing agent injection nozzles 21 and 22. This routine is executed by interruption every predetermined set time. Referring to FIG. 6, first, in step 60, it is determined whether a flag is set. When the flag is reset, the routine proceeds to step 61, where the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 and the reducing agent injection amount q2 of the second reducing agent injection nozzle 22 are both made zero. That is, the reducing agent supply operation from the reducing agent supply device 20 is stopped. On the other hand, when the flag is set, the routine proceeds to step 62, where qN is calculated from the map of FIG. The following step 63 the _the NO _X absorbent temperature TNA whether high is determined than the second switching temperature TS2. TNA
If ≦ TS2, the routine proceeds to step 64, where NO _X
It is determined whether the absorbent temperature TNA is higher than the first switching temperature TS1. When TNA ≦ TS1, the routine proceeds to step 65, where the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is set to zero, and the reducing agent injection amount q2 of the second reducing agent injection nozzle 22 is set to qN. That is, the reducing agent is injected only from the second reducing agent injection nozzle 22. On the other hand, when TNA> TS1, step 6
4 to step 66, where the first reducing agent injection nozzle 2
The first reducing agent injection amount q1 is set to qN, and the reducing agent injection amount q2 of the second reducing agent injection nozzle 22 is set to zero. That is, the reducing agent is injected only from the first reducing agent injection nozzle 21. On the other hand, when the flag is set, the process proceeds from step 63 to step 67, where the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is set to qN · m, and the reducing agent injection amount of the second reducing agent injection nozzle 22 is set. The quantity q2 is qN · (1
-M).

FIG. 7 shows another embodiment. Referring to FIG. 7, this embodiment and the embodiment shown in FIG. 1 in that the third reducing agent injection nozzle 23 is disposed in a casing 18 which is formed between the oxidation catalyst 16 and _the NO _X absorbent 17 structure Is different. The third reducing agent injection nozzle 23 is connected to a reducing agent pump 24 via a corresponding solenoid valve 23a. The particle size of the reducing agent injected from the third reducing agent injection nozzle 23 is smaller than the particle size of the reducing agent injected from the second reducing agent injection nozzle 22, and therefore, the position of the reducing agent injection nozzle is located upstream of the exhaust gas. The closer to the side, the larger the particle size of the reducing agent injected from the reducing agent injection nozzle.

[0031] In the present embodiment, NO _X absorbent temperature TNA
Is lower than the first switching temperature TS1, the reducing agent is supplied only from the second reducing agent injection nozzle 22 and NO
_{When the X} absorbent temperature TNA is higher than the first switching temperature TS1 and lower than the second switching temperature TS2, the first
The reducing agent is supplied only from the reducing agent injection nozzle 21.
As a result, the reducing agent is supplied uniformly in the exhaust flow direction and the radial direction of the NO _X absorbent 17.

On the other hand, NO _X absorbent temperature TNA is when higher than the second switching temperature TS2 in addition to the first reducing agent injection nozzle 21, the reducing agent is supplied from the third reducing agent injection nozzle 23. NO when _X absorbent temperature TNA is considerably higher are difficult to reach reducing agent to the exhaust downstream end of the NO _X absorbent 17, it is injected from the first reducing agent injection nozzle 21 for example in order to make this possible When the particle size of the reducing agent is very large, a large amount of the reducing agent adheres to and remains on the oxidation catalyst 16, or when TNA <TS2, N
O _X absorbent 17 to adhere a large amount of reducing agent, which may remain. Therefore, the particle size of the reducing agent injected from the third reducing agent injection nozzle 23 is determined to be larger than the particle size of the reducing agent when flowing out of the oxidation catalyst 16, and TNA> TS
And when two third of the reducing agent injection nozzle 23 as a reducing agent to the exhaust downstream end of the NO _X absorbent 17 even when _the NO _X absorbent temperature is considerably higher by injecting reducing agent can reach ing. On the other hand, the third reducing agent injection nozzle 2
The particle size of the reducing agent injected from the third reducing agent injection nozzle 22 is smaller than the particle size of the reducing agent injected from the second reducing agent injection nozzle 22, and therefore, the reducing agent injected from the third reducing agent injection nozzle 23 Can be diffused very easily.

FIG. 8 shows the first to third reducing agent injection nozzles 2.
A routine for calculating the reducing agent injection amounts q1, q2, q3 of 1, 22, and 23 is shown. This routine is executed by interruption every predetermined set time. Note that, also in this embodiment, the interrupt routine shown in FIG. 5 is executed. Referring to FIG. 8, first, at step 160, it is determined whether or not the flag is set. When the flag has been reset, the routine then proceeds to step 161, where the reducing agent injection amounts q1, q2, q3 of the first to third reducing agent injection nozzles 21, 22, 23 are both set to zero. That is, the reducing agent supply operation from the reducing agent supply device 20 is stopped.
On the other hand, when the flag is set, the process proceeds to step 162, where qN is calculated from the map of FIG. Following step 163 in _the NO _X absorbent temperature TNA whether high is determined than the second switching temperature TS2. When the TNA ≦ TS2 then proceeds to step 164, NO _X absorbent temperature TNA first switching temperature T
It is determined whether it is higher than S1. When TNA ≦ TS1, the process proceeds to step 165, where the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is set to zero, and the reducing agent injection amount q2 of the second reducing agent injection nozzle 22 is set to qN.
The reducing agent injection amount q3 of the third reducing agent injection nozzle 23 is set to zero. That is, the reducing agent is injected only from the second reducing agent injection nozzle 22. On the other hand, when TNA> TS1, the process proceeds from step 164 to step 166, where the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is set to qN, and the reducing agent injection amount q2 of the second reducing agent injection nozzle 22 is set to qN.
Is set to zero, and the reducing agent injection amount q3 of the third reducing agent injection nozzle 23 is set to zero. That is, the reducing agent is injected only from the first reducing agent injection nozzle 21. On the other hand, when the flag is set, the steps 163 to 1
Proceeding to 67, the reducing agent injection amount q1 of the first reducing agent injection nozzle 21 is set to qN · m, and the second reducing agent injection nozzle 22
Is set to zero, and the reducing agent injection amount q3 of the third reducing agent injection nozzle 23 is set to qN · (1-m).

As shown in FIG. 9, the oxidation catalyst 16 is formed from a pair of oxidation catalysts 16a and 16b separated in the exhaust flow direction, and the second reducing agent injection nozzle 22 is interposed between the pair of oxidation catalysts 16a and 16b. Can also be arranged. In this case, reducing agent injected from the second reducing agent injection nozzle 22 flows into _the NO _X absorbent 17 through the oxidation catalyst 16b, the first reducing agent reducing agent injected from the injection nozzle 21 of the pair oxidation catalyst 16a, via 16b flowing into _the NO _X absorbent 17. Therefore, the properties of the reducing agent injected from the first reducing agent injection nozzle 21 and the properties of the reducing agent injected from the second reducing agent injection nozzle 22 can be made different.

[0035] In the embodiment described so far, to form an exhaust gas purifying catalyst from _the NO _X absorbent 17, _the NO _X absorbent 1
Releasing NO _X in 7, the reducing agent supply device 2 in order to reduce
The present invention is applied when the reducing agent is supplied from zero.
However, the NO _X in the inflowing exhaust gas in an oxygen atmosphere containing a reducing agent to form an exhaust gas purifying catalyst from the selective reduction catalyst capable of reducing, NO _X in the selective reduction catalyst
The present invention can also be applied to a case where a reducing agent is supplied from the reducing agent supply device 20 in order to reduce the amount. Or,
The present invention can also be applied to a case where a reducing agent is supplied from the reducing agent supply device 20 in order to regenerate an exhaust purification catalyst poisoned by sulfur or an SOF (organic soluble component).

[0036]

As described above, the reducing agent can be supplied uniformly in the exhaust gas flowing direction and the radial direction of the exhaust gas purifying catalyst.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram for explaining the NO _X absorbing / releasing action of a NO _X absorbent.

FIG. 3 is a view showing a NO _X purification rate R of a NO _X absorbent;

FIG. 4 is a diagram showing a reducing agent supply amount qN.

FIG. 5 is a flowchart showing an interrupt routine.

FIG. 6 is a flowchart for calculating a reducing agent injection amount q1, q2.

FIG. 7 is an overall view of an internal combustion engine showing another embodiment.

FIG. 8 is a flowchart for calculating a reducing agent injection amount q1, q2, q3.

FIG. 9 is an overall view of an internal combustion engine showing another embodiment.

[Explanation of symbols]

1 ... engine body 15 ... exhaust pipe 16 ... oxidizing catalyst 17 ... NO _X absorbent 21, 22, 23 ... reducing agent injection nozzle

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) F01N 3/36 F01N 3/36 K F term (reference) 3G091 AA18 AB02 AB05 AB06 BA01 BA11 BA14 BA15 BA19 BA33 CA16 CA17 CA18 CA19 CB07 DB06 DB10 EA01 EA06 EA07 EA17 EA18 EA30 FB10 FC01 GB02W GB03W GB04W GB05W GB06W GB07W GB16X HA10 HA37 HA47

Claims (3)

[Claims] An exhaust purifying catalyst is disposed in an engine exhaust passage, and a plurality of reducing agent injection nozzles arranged in the exhaust flow direction are disposed in an engine exhaust passage upstream of the exhaust purifying catalyst. In an exhaust gas purifying apparatus for an internal combustion engine in which a reducing agent is supplied from a nozzle to an exhaust gas purifying catalyst, the particle size of the reducing agent injected from the reducing agent injection nozzle increases as the position of the reducing agent injection nozzle is on the exhaust upstream side. An exhaust purification device for an internal combustion engine. 2. An oxidation catalyst is disposed in an exhaust passage located between a pair of reducing agent injection nozzles adjacent to each other.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein a reducing agent injection nozzle for performing a reducing agent injection is changed according to an engine operating state.