JP3075214B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

In the internal combustion engine in which the air-fuel mixture as allowed to combustion, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _X when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease place _the NO _X absorbent in the engine exhaust passage, the internal combustion engine so as to absorb by _the NO _X absorbent to NO _X generated when burned lean mixture, long air-fuel ratio is in a lean state Once operated, NO _X absorbing capacity of the NO _X absorbent is saturated, NO _X can no longer be absorbed.

[0003] Therefore, the temporary air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent to temporarily rich air-fuel mixture fed into the engine cylinder before the NO _X absorbing capacity of the NO _X absorbent is saturated made rich, whereby internal combustion engine so as to reduce the released NO _X with the release of NO _X from _the NO _X absorbent is already proposed by the present applicant (see Japanese Patent application No. Hei 3-284095) .

[0004]

When the air-fuel mixture fed into the engine cylinder in order to release the NO _X from however _the NO _X absorbent [0005] rich, shock to the output torque of the engine increases abruptly generated In addition, there is a problem that fuel efficiency deteriorates.

[0005]

According to the present invention in order to solve the above problems SUMMARY OF THE INVENTION, it absorbs NO _X in the inflowing exhaust gas when the air-fuel ratio is lean of inflow exhaust gas in the inflowing exhaust gas the _the NO _X absorbent oxygen concentration emits NO _X which is absorbed to decrease a plurality arranged in an engine exhaust passage, NO
The exhaust gas when the air-fuel ratio is lean of the exhaust gas flowing into the _X absorbent allowed absorb NO _X in _the NO _X absorbent is guided to at least one of these _the NO _X absorbent, NO _X
NO _X exhaust gas is directed sequentially led by a predetermined number of air-fuel ratio of exhaust gas flowing into the absorbent is stoichiometric or these _the NO _X absorbent exhaust gas when the rich
It is provided sequentially exhaust gas introduction means for releasing NO _X that is absorbed from the absorbent. That is, in at least one guided NO _X in _the NO _X absorbent by absorption of _the NO _X absorbent air-fuel ratio these _the NO _X absorbent exhaust gas when the lean exhaust gas flowing into <br/>I'm sullen. NO _X
NO air-fuel ratio of the exhaust gas flowing into the absorbent is guided sequentially guided to the exhaust gas exhaust gas when the stoichiometric or rich by several predetermined Of these _the NO _X absorbent
NO _X which is absorbed from the _X absorbent is sequentially released.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment will be described. Referring to FIG. 1, 1 indicates an engine body, 2 indicates a piston, 3 indicates a combustion chamber, 4 indicates a spark plug, 5 indicates an intake valve, 6 indicates an intake port, 7 indicates an exhaust valve, and 8 indicates an exhaust port. The intake port 6 is connected to a surge tank 10 via a corresponding branch pipe 9, and a fuel injection valve 11 for injecting fuel into the intake port 6 is attached to each branch pipe 9. The surge tank 10 is connected to an air cleaner 14 via an intake duct 12 and an air flow meter 13, and a throttle valve 15 is arranged in the intake duct 12.

On the other hand, the exhaust port 8 is connected via a first exhaust pipe 17 to a casing 19 containing a NO _X absorption / decomposition agent 18, and the casing 19 is further connected to a second exhaust pipe 20. A first valve 21 is disposed in the second exhaust pipe 20,
And the second exhaust pipe 20 is first bypass passage 26 branching between the casing 19 and the first valve 21, is connected to the casing 28 with a built-in _the NO _X absorbent 27. Further, the casing 28 is connected to the first valve 21 via the second bypass passage 29.
It is merged with the second exhaust pipe 20 downstream. The second valve 22 is disposed in the first bypass passage 26 and the second bypass passage 29
Is provided with a third valve 23. A lean sensor 30 is disposed in the first exhaust pipe 17 and generates an output voltage proportional to the oxygen concentration in the exhaust gas. A first recirculation passage 31 branches from the first exhaust pipe 17 between the lean sensor 30 and the casing 19 and is connected to a discharge side of a pump 32. The suction side of the pump 32 is connected to a second bypass passage 29 between the casing 28 and the third valve 23 via a second return passage 33. A fourth valve 24 is disposed in the first recirculation passage 31,
The fifth valve 25 is disposed in the return passage 33.

An electronic control unit 40 comprising a digital computer controls the first to fifth valves 21 to 25 and the pump 32 based on the output signal of the lean sensor 30. The air-fuel ratio of the mixture supplied to the engine cylinder is
Except during warm-up operation, acceleration operation and full-load operation, a constant lean air-fuel ratio is maintained, so that the lean mixture is burned in most engine operation regions.

FIG. 2 schematically shows the concentration of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 2, the amounts of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increase as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 increases, and the amount of the exhaust gas discharged from the combustion chamber 3 increases The amount of oxygen O ₂ in the exhaust gas increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

[0010] NO _X contained in the casing 19
The absorption / decomposition agent 18 uses, for example, alumina as a carrier and, for example, potassium K, sodium Na, lithium L
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earths such as yttrium Y and a noble metal such as platinum Pt are supported. Engine intake passage, NO _X absorption of Toko called air-fuel ratio of exhaust gas flowing the ratio of the combustion chamber and NO _X absorbent decomposer 18 upstream of the exhaust passage supplying air and fuel into the NO _X absorbent decomposer 18 NO decomposition agent 18 that the air-fuel ratio of the inflowing exhaust gas to absorb NO _X when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease
_X absorbs and releases. The air-fuel ratio of the inflowing exhaust gas when the fuel or air is not supplied to the NO _X absorbent decomposer 18 in the exhaust passage upstream of the match to the air-fuel ratio of the mixture supplied into the combustion chamber 3, thus in this case air-fuel ratio of the mixture gas NO _X absorbent decomposer 18 is supplied into the combustion chamber 3 when the lean absorb NO _X, the oxygen concentration in the mixture fed into the combustion chamber 3 decreases to the absorption It will emit the NO _X.

If the above-mentioned NO _X absorption / decomposition agent 18 is disposed in the engine exhaust passage, the NO _X absorption / decomposition agent 18 is actually N
O _X absorption and release performs the action of, but is also not clear portion detailed mechanism of action out this absorbing and releasing. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. 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 other noble metals, alkali metals,
The same mechanism can be obtained by using alkaline earths and rare earths.

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 ⁻ . On the other hand, N
O is O ₂ on the surface of the platinum Pt ^- reacted with, and _{NO 2 (2NO + O 2 →} 2NO 2). NO ₂ generated
3A is absorbed in the absorbent while being further oxidized on platinum Pt and combined with barium oxide BaO, while FIG.
It is diffused in the absorbent in the form of nitrate ions NO ₃ ^- as shown in the. In this way, NO _X is converted to NO _X absorption decomposer 1
8 is absorbed.

[0013] oxygen concentration in the inflowing exhaust gas is generated NO ₂ on the surface of as high as platinum Pt, 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 inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ), thus the nitrate ion NO ₃ ⁻ in the absorbent. There are released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflowing exhaust gas is lowered NO _X absorbent from decomposer 18 NO _X is to be released. Figure 2 is the oxygen concentration of the inflowing exhaust gas when the degree of leanness becomes lower in the inflowing exhaust gas as shown in drops, thus the NO _X absorbent decomposer 18 if lowering the degree of lean of the inflowing exhaust gas NO _X Will be released.

On the other hand, at this time, the air-fuel ratio of the inflowing exhaust gas is reset.
As shown in Fig. 2, a large amount of
Fuel HC and CO are discharged, and these unburned HC and CO are converted to platinum.
Oxygen O on Pt_Two ^-And oxidize. Ma
When the air-fuel ratio of the inflow exhaust gas is made rich, the inflow exhaust gas
NOx from the absorbent because the oxygen concentration in the
_TwoIs released and this NO_TwoIs as shown in FIG.
And reacts with unburned HC and CO to be reduced. This
NO on the surface of platinum Pt_TwoIs no longer present
NO from next to next from absorbent_TwoIs released. Therefore the flow
If the air-fuel ratio of the incoming and exhaust gas is made rich, N
O_XNO from absorption decomposer 18_XIs released and reduced
Will be.

[0015] Thus the air-fuel ratio of the inflowing exhaust gas becomes lean NO _X is absorbed in the NO _X absorbent decomposer 18, a short air-fuel ratio of the inflowing exhaust gas when the rich NO _X from NO _X absorbent decomposer 18 Released and reduced in time. _The NO _X absorbent 2 accommodated in the casing 28
7 is made of, for example, alumina as a carrier, on which potassium K, sodium Na, lithium Li, cesium C
alkali metals such as s, barium Ba, calcium C
a at least one selected from alkaline earths such as a, lanthanum La, and rare earths such as yttrium Y;
and a metal such as u. The NO _X absorbent 27 absorbs or releases NO _X by the same mechanism as the NO _X absorption / decomposition agent 18 described above.

FIG. 4 shows a routine for controlling the first to fifth valves 21 to 25 and the pump 32. This routine is executed by interruption every predetermined time. FIG.
First, at step 50, the lean sensor 3
It is determined whether the air-fuel ratio is lean based on the 0 detection signal. If it is determined to be lean, the process proceeds to step 52, where it is determined whether or not the duration _TL of the lean state is equal to or longer than a predetermined time α. α is NO when the continuation time _TL of the lean state has continued for a predetermined time or more in a predetermined engine operating state.
_This is the time until the NO _X absorption capacity of the _X absorption decomposer 18 is saturated. Since this time changes according to the engine operating state, it is preferable to change α according to the engine operating state.

When T _L <α, that is, when the NO _X absorption capacity of the NO _X absorption decomposer 18 is not saturated,
Proceeding to step 54, only the first valve 21 is opened and the second valve 21 is opened.
The fifth to fifth valves 25 to 25 are closed, and the pump 32 is turned off. Therefore the exhaust gas flows only to the NO _X absorbent decomposer 18, NO _X is absorbed in the NO _X absorbent decomposer 18.

On the other hand, if it is determined in step 52 that T _L ≧ α, that is, if the NO _X absorbing ability of the NO _X absorbing / decomposing agent 18 is saturated,
_To release _X to the atmosphere, the process proceeds to step 56, where the second valve 22 and the third valve 23 are opened, and the first valve 2 is opened.
The first, fourth and fifth valves 24 and 25 are closed,
The pump 32 is turned off. Therefore, the exhaust gas that has flowed through the NO _x absorbing / decomposing agent 18 flows into the NO _x absorbing agent 27, and the NO _x is not released to the atmosphere because the NO _x is absorbed by the NO _x absorbing agent 27.

On the other hand, when the air-fuel ratio is stoichiometric or rich,
If yes, go to step 58,
State duration T_SRIs longer than a predetermined time β.
It is. β is the stoichiometric
Or rich state duration T _SRContinued for more than a predetermined time
NO_XNO absorbed by the absorbent 18_XBut ten
Time to release in minutes. This time,
Β in response to the engine
It is preferable to change the same.

In the case of T _SR <beta, that is, when the NO _X absorbed in the NO _X absorbent decomposer 18 is not sufficiently released, the process proceeds to step 54, only the first valve 21 is opened, The second to fifth valves 22 to 25 are closed, and the pump 32 is turned off. Therefore, the exhaust gas is N
O _X absorbent decomposer 18 flows only, NO _X absorbent decomposing agent 1
8 NO _X is reduced is released from the.

On the other hand, at step 58, T_SR≧ β
In other words, NO_XAbsorbed and decomposed by absorbent 18
NO_XIf it is determined that
Proceeding to step 60, first valve 21, second valve 22, fourth valve 2
The fourth and fifth valves 25 are opened, and the third valve 23 is opened.
The valve is closed, and the pump 32 is turned on. this
Exhaust gas is NO_XFlows into the absorbent 27,_XSucking
NO absorbed by the absorbent 27_XIs released. This released
NO_XThe exhaust gas containing
NO via passages 31 and 33_XFlow into absorption decomposer 18
Sir, no _XReduced by absorption decomposer
You.

As described above, according to this embodiment, the lean
NO for a long time in the state_XNO of absorption decomposer 18_X
If the absorption capacity is saturated, NO_XBy the absorbent 27
NO_XIs absorbed because NO is absorbed_XIs released into the atmosphere
Never. Also, if the air-fuel ratio is stoichiometric or rich
Sometimes, first, NO_XNO of absorption decomposer 18_XIs released
And, when this is completed, NO_XAbsorbent 27
NO _XIs released and reduced. That is, absorbed
NO_XIs released in two stages. Therefore, NO_X
Absorbing decomposer 18 and NO_XLarge amount at the same time from absorbent 27
NO_XIs not released, so NO_XAbsorption
NO of dissolving agent 18_XNO beyond reduction ability_XIs released
Nothing. Therefore, NO_XNO reduction ability_XTotal absorption of
Can be smaller than ability.

Further, in this embodiment, necessary to increase the degree of richness of the air-fuel ratio of the exhaust gas necessary to release the NO _X is eliminated. In other words, it is possible to release the NO _X in the air-fuel ratio of the inflowing exhaust gas only to stoichiometric or slightly rich. Therefore, it is not necessary to forcibly make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder rich as in the conventional internal combustion engine described above,
Thus, torque shock can be reduced and fuel economy can be prevented from deteriorating.

FIG. 5 shows a second embodiment. Engine body 1
The exhaust pipe 70 extending from the first exhaust branch pipe 72 is provided with a switching valve 71.
And the second exhaust branch pipe 73, and then merges again in the exhaust merge pipe 74. First exhaust branch pipe 72 and second exhaust branch pipe 7
3 respectively first 1NO _X absorbent 75 and the 2NO _X absorbent 76 is disposed in, it is arranged reduction catalyst 77 in the exhaust collecting pipe 74. The switching valve 71 can take two positions. When the switching valve 71 is in the first position, the exhaust pipe 70 is connected to the first exhaust branch pipe 72, and when in the second position, the exhaust pipe 70 is connected to the second exhaust branch. It is communicated with the tube 73.

FIG. 6 shows a routine for controlling the switching valve 71. This routine is executed by interruption every predetermined time. Referring to FIG. 6, first, step 80
Then, it is determined whether the air-fuel ratio is lean based on the detection signal of the lean sensor 30. If it is determined to be lean, the routine proceeds to step 82, where it is determined whether or not the duration _TL of the lean state is equal to or longer than a predetermined time α.

In the case of T _L <alpha, that is, when the NO _X absorbing capacity of the 1NO _X absorbent 75 is not saturated, the process proceeds to step 84, the exhaust pipe 70 switching valve 71 is a first position, the 1 is connected to the exhaust branch pipe 72. Therefore, the exhaust gas flows into the first 1NO _X absorbent 75, NO _X is absorbed in the first 1NO _X absorbent 75. On the other hand, at step 82, T
If it is determined that _L ≧ alpha, that is, when the NO _X absorbing capacity of the 1NO _X absorbent 75 becomes saturated, the process proceeds to step 88, the exhaust pipe 70 switching valve 71 is a second position, the second
It is communicated with the exhaust branch pipe 72. For this reason, the exhaust gas
Flows into _the NO _X absorbent 76, N to a 2NO _X absorbent 76
O _X is absorbed.

On the other hand, when the air-fuel ratio is stoichiometric or rich, the processing proceeds to step 86, the duration T _SR stoichiometric or rich state is determined whether more than a predetermined time period beta. In the case of T _SR <β, that is, the first 1NO _X absorbent 7
5 to absorb the NO _X is when not fully released, the process proceeds to step 84, switching valve 71 and an exhaust pipe 70 are a first position is communicated to the first exhaust branch pipe 72. Therefore, the exhaust gas flows into the first 1NO _X absorbent 75, the 1N
The NO _X absorbed by the O _X absorbent 75 is released. The exhaust gas containing the released NO _X flows into the reduction catalyst 77, and the NO _X is reduced by the reduction catalyst 77.

On the other hand, if it is determined that T _SR ≧ beta in step 86, that is, when the NO _X absorbed in the first 1NO _X absorbent 75 is judged to have been fully released, the process proceeds to step 88, The switching valve 71 is set to the second position, and the exhaust pipe 70 is communicated with the second exhaust branch pipe 73. Therefore, the exhaust gas flows into the first 2NO _X absorbent 76, the 2N
The NO _X absorbed by the O _X absorbent 76 is released. The exhaust gas containing the released NO _X flows into the reduction catalyst 77, and the NO _X is reduced by the reduction catalyst 77.

As described above, also in the present embodiment, the first
The same operation and effect as the embodiment can be achieved.
In this embodiment, the pump 32 of the first embodiment is unnecessary.
You. FIG. 7 shows a third embodiment. Extending from the engine body 1
The first exhaust pipe 90 is connected to a switching valve 92, and the switching valve 92
The second exhaust pipe 93 and the bypass pipe 94 are branched from
You. In the second exhaust pipe 93, NO_Xabsorption
Agent 95 and NO_XAn absorption decomposer 96 is provided.
The bypass pipe 94 has NO_XAbsorbent 95 and NO _XAbsorption decomposition
The second exhaust pipe 93 is connected to the agent 96. Switching
The valve 92 can be in two positions, the first position
The first exhaust pipe 90 communicates with the bypass pipe 94
When in the second position, the first exhaust pipe 90 is
It is communicated with the trachea 93.

FIG. 8 shows a routine for controlling the switching valve 92. This routine is executed by interruption every predetermined time. Referring to FIG. 8, first, at step 10
At 0, it is determined whether the air-fuel ratio is lean based on the detection signal of the lean sensor 30. If it is determined to be lean, the process proceeds to step 102, where it is determined whether or not the duration _TL of the lean state is equal to or longer than a predetermined time α.

If T _L <α, that is, if the NO _X absorption capacity of the NO _X absorption / decomposition agent 96 is not saturated, the routine proceeds to step 104, where the switching valve 92 is set to the first position and the first position is set.
An exhaust pipe 90 communicates with the bypass pipe 94. For this reason,
Exhaust gas flows only to the NO _X absorbent decomposer 96, NO _X
NO _X is absorbed by the absorption decomposer 96. On the other hand, if it is determined in step 102 that T _L ≧ α, that is, NO _X
If NO _X absorbing capacity of the absorbent decomposer 96 is saturated, the process proceeds to step 108, the by switching valve 92 is a second position 1
An exhaust pipe 90 communicates with the second exhaust pipe 93. For this reason,
Exhaust gas flows into _the NO _X absorbent 95, _the NO _X absorbent 9
5 NO _X is absorbed.

On the other hand, when the air-fuel ratio is stoichiometric or rich, the processing proceeds to step 106, the duration T _SR stoichiometric or rich state is determined whether more than a predetermined time period beta. For T _SR <beta, that is, when the NO _X absorbed in the NO _X absorbent decomposer 96 is not sufficiently released, the process proceeds to step 104, the first and the switching valve 92 is a first position exhaust The pipe 90 is connected to the bypass pipe 94.
Therefore, the exhaust gas flows only to the NO _X absorbent decomposer 96, NO _X absorbed in the NO _X absorbent decomposer 96 is made to reduction is released.

On the other hand, at step 106, T_SR≧ β
If it is, that is, NO_XAbsorbed by the absorption decomposer 96
NO_XIf it is determined that
Proceeding to step 108, the switching valve 92 is set to the second position and
The first exhaust pipe 90 is communicated with the second exhaust pipe 93. This
Exhaust gas is NO_XFlows into the absorbent 95, NO _X
NO absorbed by absorbent 95_XIs released. This release
NO_XExhaust gas containing NO_XFor absorption decomposer 96
Inflow, NO_XIs NO_XBy the absorbent 96
To be reduced.

As described above, also in this embodiment, the first
The same operation and effect as those of the embodiment can be obtained.

[0035]

Richness of the air-fuel ratio of the exhaust gas is not necessary to increase the required NO _X according to the present invention in order to release. In other words, it is possible to release the NO _X in the air-fuel ratio of the inflowing exhaust gas only to stoichiometric or slightly rich. Therefore, it is not necessary to forcibly make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder rich, so that the torque shock can be reduced and the fuel efficiency can be prevented from deteriorating.

Further, the action of releasing the absorbed NO _X is to be done in multiple steps, never NO _X is released beyond the NO _X reduction capability.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 shows unburned HC and C in exhaust gas discharged from an engine.
FIG. 3 is a diagram schematically showing the concentrations of O and oxygen.

3 is a diagram for explaining the absorbing and releasing action of NO _X.

FIG. 4 is a flowchart for controlling first to fifth valves and a pump according to the first embodiment of the present invention.

FIG. 5 is a view showing an exhaust system of an internal combustion engine according to a second embodiment of the present invention.

FIG. 6 is a flowchart for controlling a switching valve according to a second embodiment of the present invention.

FIG. 7 is a view showing an exhaust system of an internal combustion engine according to a third embodiment of the present invention.

FIG. 8 is a flowchart for controlling a switching valve according to a third embodiment of the present invention.

[Explanation of symbols]

18,96 ... NO _X absorbent decomposer 21 to 25 ... first to fifth valves 27,95 ... NO _X absorbent 71,92 ... changeover valve 75 ... first 1NO _X absorbent 76 ... first 2NO _X absorbent 77 ... reducing catalyst

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ identification code FI F01N 3/24 B01D 53/36 101B 3/28 301 (58) Investigated field (Int.Cl. ⁷ , DB name) F01N 3 / 08-3/28 B01D 53/56 B01D 53/81 B01D 53/94

Claims (1)

(57) [Claims] Air-fuel ratio of 1. A inflows exhaust gas absorbs NO _X in the inflowing exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X which is absorbed to decrease N
The O _X absorbent plurality disposed engine exhaust passage, NO _X absorption
The exhaust gas when the air-fuel ratio of the exhaust gas flowing into agent is lean allowed absorb NO _X in _the NO _X absorbent is guided to at least one of these _the NO _X absorbent, _the NO _X absorbent <br/> NO _X when the air-fuel ratio of the inflowing exhaust gas when the stoichiometric or rich is absorbed exhaust gas from _the NO _X absorbent to advance sequentially led to the exhaust gas by several defined has led among these _the NO _X absorbent to An exhaust gas purification device for an internal combustion engine, comprising exhaust gas introduction means for sequentially releasing the exhaust gas.