JP2003090211A - Exhaust gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To well purify exhaust gas by using a small capacity of NOx absorbent. SOLUTION: NOx absorbents NA1, NA2 are arranged in a pair of branch exhaust passages, respectively. The exhaust gas from an internal combustion engine is introduced into both NOx absorbents to cause NOx contained in the exhaust gas at this time to be absorbed by both NOx absorbents. When the NOx absorbing amount of one NOx absorbent exceeds an upper limit amount, exhaust gas from a combustion heater 30 is temporarily supplied to one NOx absorbent while temporarily shutting off the flow of the exhaust gas to one NOx absorbent, and the exhaust gas from the internal combustion engine is introduced into the other NOx absorbent to cause NOx contained in the exhaust gas at this time to be absorbed by the other NOx absorbent. When the NOx absorbing amount of both NOx absorbents exceeds an upper limit amount, the exhaust gas from the internal combustion engine is introduced into both NOx absorbents and the air/fuel ratio of the exhaust gas from the internal combustion engine is temporarily changed from lean state to rich state.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification method.

[0002]

2. Description of the Related Art An exhaust gas flowing into a pair of branch exhaust passages formed by branching an exhaust passage of an internal combustion engine in which combustion is performed under a lean air-fuel ratio flows when the air-fuel ratio of the exhaust gas is lean. evacuated to absorb NO _X in the gas, the air-fuel ratio of the inflowing exhaust gas is the _the NO _X absorbent to release and reduce NO _X that is absorbed becomes the stoichiometric air-fuel ratio or rich is arranged, one of the NO _X absorbent directing exhaust gas discharged from the internal combustion engine while blocking the exhaust gas flow to the agent on the other of the NO _X absorbent, allowed absorb this case NO _X contained in the exhaust gas to the other of _the NO _X absorbent, When the NO _X absorption amount of the other NO _X absorbent exceeds the upper limit value, the other N _X
While blocking the exhaust gas flow to the other of the NO _X absorbent to reduce to release NO _X absorbed in the inside O _X absorbent supplies reducing agent to the other of _the NO _X absorbent, internal combustion An exhaust gas purification method is known in which exhaust gas exhausted from an engine is guided to one NO _X absorbent so that NO _X contained in the exhaust gas at this time is absorbed by this one NO _X absorbent (Japanese Patent Laid-Open No. 2000-2000). -345831 gazette).

When a large amount of exhaust gas is flowing into the NO _X absorbent, an extremely large amount of reducing agent is required to switch the air-fuel ratio of this exhaust gas from lean to rich.
Therefore, in this exhaust gas purification method, and so as to supply the reducing agent to the NO _X absorbent while blocking the exhaust gas flow to _the NO _X absorbent. The way to be able to reduce the amount of reducing agent necessary for reducing to release NO _X that is absorbed in the NO _X absorbent.

[0004]

In this exhaust gas purification method, almost all of the exhaust gas discharged from the internal combustion engine is introduced into either one of the NO _X absorbents. Therefore, each NO
_{The X-} absorbent must have the capacity necessary to absorb or reduce almost all of the NO _X emitted from the internal combustion engine. In other words, two NO _X absorbents with the same capacity as the NO _X absorbent used in the exhaust gas purification method using a single NO _X absorbent are required. That is, in order to adopt the above exhaust gas purification method, NO
There is a problem that a large space is required to arrange the _X absorbent. Alternatively, the above-mentioned exhaust gas purification method cannot be adopted unless this wide space can be secured.

Therefore, an object of the present invention is to provide an exhaust gas purification method capable of purifying exhaust gas satisfactorily with a small amount of NO _X absorbent.

[0006]

[Means for Solving the Problems] To solve the above problems
According to the first invention, the air-fuel ratio of the inflowing exhaust gas is
NO in the exhaust gas that flows in when lean_XAbsorbs
The air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich.
NO absorbed_XNO to release and reduce _XAbsorbent
A pair of branch exhausts formed by branching the engine exhaust passage
Place each in the passage and each NO_XAbsorbing agent with reducing agent
Equipped with a reducing agent supply device that can be supplied secondarily, and lean air-fuel
In an internal combustion engine in which combustion is performed at a ratio,
Exhaust gas exhausted from both NO_XGuide to the absorbent
NO contained in the exhaust gas at this time_XBoth NO_XSucking
Absorb with a collecting agent, NO_XNO for each absorbent_XAbsorption
Determines whether the amount exceeds a predetermined upper limit and
One of the NO_XAbsorbent NO_XAbsorption exceeds the upper limit
If it is determined that the_XAbsorbed in the absorbent
NO_XThe NO to release and reduce_XTo absorbent
Reductant supply device while temporarily shutting off the exhaust gas flow
To the NO_XWhen the reducing agent is temporarily supplied to the absorbent,
The exhaust gas discharged from the internal combustion engine to the other NO_XSucking
NO contained in the exhaust gas at this time by leading to the collecting agent_XThe
Other NO_XAbsorb with an absorbent, NO of both_XAbsorbent
NO_XWhen it is determined that the absorption amount exceeds the upper limit amount
Exhaust gas emitted from the internal combustion engine is NO_XAbsorbent
And both NO_XN absorbed in the absorbent
O_XEmitted from the internal combustion engine to release and reduce
Temporarily switch the exhaust gas air-fuel ratio from lean to rich
I am. That is, in the first invention, the emission from the internal combustion engine
Exhaust gas is two NO at the same time_XGuided by absorbent
And NO_XThe capacity of the absorbent can be reduced, thus
NO_XDoes not require a large space for the absorbent.

According to the second invention, in the first invention, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is the stoichiometric air-fuel ratio or the rich air-fuel ratio regardless of the NO _X absorption amount of each NO _X absorbent. When switched to, the exhaust gas discharged from the internal combustion engine is guided to both NO _X absorbents. That is, in the second invention, it is possible to reduce to release NO _X even without supplying reducing agent secondarily in the NO _X absorbent is absorbed in the NO _X absorbent.

According to the third invention, the first invention
The air-fuel ratio of the exhaust gas discharged from the internal combustion engine is
After switching from lean to rich, one of either
NO _XAbsorbent NO_XThe absorption amount is below the predetermined lower limit amount.
It is judged whether or not it has become less than
_XAbsorbent NO_XAbsorption is less than the predetermined lower limit
When it is determined that the amount has decreased, it is discharged from the internal combustion engine.
The air-fuel ratio of the exhaust gas is returned from rich to lean.
It That is, in the third invention, NO_XSupplied to absorbent
The amount of reducing agent is reduced.

According to a fourth aspect of the present invention, in the first aspect, the reducing agent supply device comprises a combustion device for performing combustion under a rich air-fuel ratio, and either one of the NO
Exhaust of the reducing agent supply device to the _the NO _X absorbent to reduce to release NO _X absorbed in the within the _the NO _X absorbent when the NO _X absorption of _X absorbent is determined to exceed the upper limit amount Gas is being supplied temporarily.

According to a fifth aspect of the present invention, in the first aspect, the reducing agent supply device comprises a reducing agent supply valve disposed in each branch exhaust passage upstream of the NO _X absorbent, and either one of them is provided. reducing agent corresponding to the _the NO _X absorbent to reduce to release NO _X absorbed in the within the _the NO _X absorbent when the NO _X absorption of the NO _X absorbent is determined to exceed the upper limit amount The reducing agent is temporarily supplied from the supply valve.

According to a sixth aspect of the present invention, in the first aspect, a shutoff valve is arranged in each branch exhaust passage, and when the exhaust gas flow to the NO _X absorbent should be shut off, the corresponding shutoff valve is provided. Is closed.

According to the seventh aspect, in the sixth aspect, the shutoff valve is closed so that a slight amount of exhaust gas flows through the corresponding NO _X absorbent.

[0013]

FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.

Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston,
5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve,
Reference numeral 8 is an intake port, 9 is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing in the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is the cooling device 1.
8, the intake air is cooled by the engine cooling water.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 1.
9 and the exhaust pipe 20 are connected to the exhaust turbine 21 of the exhaust turbocharger 14, and the outlet of the exhaust turbine 21 is connected to the first and second upstream exhaust ducts DU1 and DU2 via the branch pipe 22. These upstream side exhaust ducts DU1 and DU2 have first and second casings CA1 and CA1.
These casings CA1 and C are respectively connected to A2.
A2 is the first and second downstream exhaust ducts DL1, DL2
The downstream exhaust ducts DL1 and DL2 are connected to a common exhaust pipe 23.

The first and second upstream exhaust ducts DU1,
The first and second upstream side shutoff valves VU1 and VU are provided in the DU2.
2 are respectively arranged, and the first and second downstream cutoff valves V1 and DL2 are provided in the first and second downstream exhaust ducts DL1 and DL2.
L1 and VL2 are arranged respectively. These shutoff valves are respectively driven by corresponding actuators. Further, the first and second NO _X absorbents NA1 and NA2 are housed in the first and second casings CA1 and CA2, respectively. Here, the first upstream exhaust duct DU1 and the first downstream exhaust duct DL1 are referred to as a first exhaust duct, and the first upstream cutoff valve VU1 and the first downstream cutoff portion VL1 are referred to as a first exhaust duct. When referred to as a shutoff valve, it means that the first NO _X absorbent NA1 and the first shutoff valve are arranged in the first exhaust duct. Similarly, the second upstream exhaust duct DU2 and the second downstream exhaust duct D
L2 is referred to as a second exhaust duct, and a second upstream cutoff valve V
When the U2 and the second downstream side cutoff portion VL2 are referred to as a second cutoff valve, the second NO _X absorbent NA is provided in the second exhaust duct.
2 and the second shutoff valve are arranged.

The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electric control type EGR control valve 25 is arranged in the EGR passage 24. In addition, the EGR passage 24
A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is arranged around the device. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the engine cooling water cools the EGR gas. On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 27, via a fuel supply pipe 6a. This common rail 2
The fuel is supplied to the inside of the fuel cell 7 from an electrically controlled variable discharge fuel pump 28, and the fuel supplied to the common rail 27 is supplied to the fuel injection valve 6 through each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and the fuel pump 28 is arranged so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 29. Is controlled.

The internal combustion engine shown in FIG. 1 has a NO _X absorbent NA.
1, a combustion type heater 30 for supplying a reducing agent to NA2
It is equipped with. Air passage 31 of this combustion heater 30
Is connected to the discharge side of an air pump 33 via an electrically controlled air throttle valve 32 whose valve opening ratio can be changed. on the other hand,
The exhaust passage 34 of the combustion heater 30 has first and second exhaust passages DU1 and DU2 arranged in the first and second upstream exhaust ducts DU1 and DU2 downstream of the first and second upstream cutoff valves VU1 and VU2. It is connected to the electrically controlled exhaust gas injection nozzles NG1 and NG2. In addition, the combustion chamber 35 of the combustion heater 30
A glow plug 36 is arranged inside. Further, the air passage 31 downstream of the air throttle valve 32 and the exhaust pipe 23 are connected via an EGR passage 37, and an electric control for controlling the amount of EGR gas flowing in the EGR passage 37 is provided in the EGR passage 37. A formula EGR valve 38 is arranged. The fuel in the fuel tank is supplied to the combustion chamber 35 of the combustion heater 30.

When the reducing agent is to be supplied to the NO _X absorbents NA1 and NA2, the combustion heater 30 is operated and the exhaust gas supply nozzles NG1 and NG2 are opened, so that the exhaust gas of the combustion heater 30 absorbs NO _X. It is supplied to the agents NA1 and NA2. That is, the air pump 33 is operated, the air throttle valve 32 is opened, the glow plug 36 is operated, and the fuel is supplied into the combustion chamber 35 so that the air-fuel ratio in the combustion chamber 35 becomes rich. The combustion heater 30 is activated. In this case, unburned HC and carbon monoxide CO contained in the exhaust gas from the combustion heater 30 act as a reducing agent. Here, the reducing power of CO is stronger than HC, therefore the NO _X that is absorbed in the NO _X absorbent NA1, the NA2 can efficiently to release reduction.
In the embodiment shown in FIG. 1, when the combustion type heater 30 should be operated, the EGR valve 38 is opened and the combustion type heater 3
At 0, the amount of fuel required for combustion under a rich air-fuel ratio is reduced.

The electronic control unit 40 is composed of a digital computer, and has a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, and an input port 45 which are connected to each other by a bidirectional bus 41. The output port 46 is provided. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. A temperature sensor 49 for detecting the temperature of the exhaust gas flowing in the exhaust pipe 23 is attached to the inside of the exhaust pipe 23, and the output signal of the temperature sensor 49 is input through the corresponding AD converter 47 to the input port. 45 is input. In the first and second upstream exhaust ducts DU1 and DU2 downstream of the first and second exhaust gas supply nozzles NG1 and NG2, first and second NOs are provided.
Air-fuel ratio sensors S1 and S2 for detecting the air-fuel ratio of the exhaust gas flowing into the _X absorbents NA1 and NA2 are attached, and the output signals of these air-fuel ratio sensors S1 and S2 are passed through the corresponding AD converter 47. Input to the input port 45.

On the other hand, a load sensor 51 for generating an output voltage proportional to the amount L of depression of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port via a corresponding AD converter 47. 45 is input. Further, the input port 45 is connected to a crank angle sensor 52 that generates an output pulse each time the crankshaft rotates, for example, 30 °. On the other hand, the output port 46, via the corresponding drive circuit 48, the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, the shutoff valves VU1, VU2, VL1 and VL2, and the combustion. It is connected to the air throttle valve 32, the air pump 33, the glow plug 36, the EGR valve 38, and the exhaust gas supply nozzles NG1 and NG2 of the device 30, respectively.

Each of the NO _X absorbents NA1 and NA2 uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, an alkaline earth such as barium Ba, calcium Ca are supported on the carrier. At least one selected from the group consisting of rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported. The NO _X absorbents NA1 and NA2 may be carried on a particulate filter for collecting fine particles made of solid carbon contained in the exhaust gas.

[0023] The _the NO _X absorbent absorbs NO _X when the average air-fuel ratio of the inflowing exhaust gas lean, absorption emission of the NO _X which the oxygen concentration in the exhaust gas flowing to release NO _X absorbed to decrease To act. In this specification, the exhaust passage, the combustion chamber 5, and the exhaust passage upstream of a certain position of the exhaust passage,
The ratio of the air supplied to the intake passage to the hydrocarbon HC and carbon monoxide CO is called the air-fuel ratio of the exhaust gas at that position.

The detailed absorption and desorption mechanism of the NO _X absorbent has not been completely clarified. However, the currently considered absorption and release mechanism will be briefly described as follows, taking a case where platinum Pt and barium Ba are supported on a carrier as an example.

That is, NO_XOf exhaust gas flowing into the absorbent
Inflow when the air-fuel ratio becomes considerably leaner than the theoretical air-fuel ratio
Oxygen concentration in the exhaust gas greatly increases_TwoIs O
_Two ⁻Or O^2-It adheres to the surface of platinum Pt in the form of. one
On the other hand, NO in the inflowing exhaust gas is O on the surface of platinum Pt.
_Two ⁻Or O^2-Reacts with NO_TwoBecomes (2NO + O_Two
→ 2 NO_Two). NO generated next_TwoPart of the platinum P
On the other hand, it is further oxidized on the t
Nitrate ion NO while binding with BaO_Three ⁻Form of
It diffuses into the absorbent. NO in this way_XIs NO_X
It is absorbed in the absorbent.

On the other hand, when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent becomes rich or becomes the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas decreases, the amount of NO ₂ produced decreases, and the reaction is reversed. In the direction (NO ₃ ⁻ → NO ₂ ), the nitrate ions NO ₃ ⁻ in the absorbent are thus released from the absorbent in the form of NO ₂ . The released NO _X is the HC in the exhaust gas,
It is reduced by reacting with CO. When NO ₂ is no longer present on the surface of platinum Pt in this way, NO ₂ is released from the absorbent one after another and is reduced.

Next, the embodiment according to the present invention will be described in detail with reference to FIGS. Note the air-fuel ratio of the exhaust gas A / F in FIG. 4 to FIG. 2 is discharged from the internal combustion engine, QA1 is the amount of the NO _X absorbed in the first of the NO _X absorbent NA1, QA2 second represents of the NO _X absorbent NA2 amount of absorbed in which NO _X in each.

In the internal combustion engine of FIG. 1, as shown by the arrow (a) in FIG. 2, the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine is basically leaned to the z level. Shutoff valves VU1, VL1 and second shutoff valves VU2, V
Since L2 is fully opened, the exhaust gas discharged from the internal combustion engine at this time is the same as the first NO _X absorbent NA1 and the second NO _X absorbent NA1.
Of the NO _X absorbent NA2. At this time, the combustion heater 30 is stopped (OFF) and the exhaust gas supply nozzles NG1 and NG2 are closed. Therefore, the reducing agent supply action from the combustion heater 30 to the NO _X absorbents NA1 and NA2 is performed. Has been stopped. Therefore, NO _X in the exhaust gas is absorbed in the first and second NO _X absorbents NA1, NA2.

[0029] Here, is discharged from approximately half of the amount of flow, so that each _the NO _X absorbent NA1, NA2 internal combustion engine of the _the NO _X absorbent NA1, exhaust gas discharged from the internal combustion engine is within NA2 It suffices to have a capacity capable of absorbing almost half the amount of NO _X. Therefore, a single N
The capacity of each of the NO _X absorbents NA1 and NA2 can be reduced as compared with the case where the exhaust gas purifying action is performed by the O _X absorbent, and therefore the space required for arranging the NO _X absorbent can be reduced. it can.

Then, as shown by the arrow (b) in FIG.
For example, the first NO_XAbsorbent NA1 NO_XAbsorption QA
When 1 exceeds the predetermined upper limit UL, the first NO
_XNO absorbed in the absorbent NA1_XRelease and return
In order to recover, the first shutoff valves VU1 and VL1 are closed,
The combustion heater 30 is operated (ON), and the first exhaust gas
The supply nozzle NG1 is opened. As a result, combustion type heat
30 to the first NO _XSupplying reducing agent to absorbent NA1
Is started and the first as shown by the arrow (c) in FIG.
NO_XAbsorbent NA1 NO_XAbsorption amount QA1 gradually decreases
Less.

In this case, since the first shutoff valves VU1 and VL1 are closed, the space velocity of the exhaust gas in the first NO _X absorbent NA1 is reduced, and therefore the first NO _X absorbent NA1 flows into the first NO _X absorbent NA1. The amount of reducing agent required to make the air-fuel ratio of the exhaust gas rich can be reduced. Further, since the downstream cutoff valve VL1 is closed, it is possible to prevent the exhaust gas flowing in the second downstream exhaust duct DL2 from flowing backward in the first downstream exhaust duct DL1. Further, at this time, the first shut-off valves VU1, VL are arranged so that a slight amount of exhaust gas flows through the first NO _X absorbent NA1.
1 is slightly open. In this way, the reducing agent supplied to the first of the NO _X absorbent NA1 first of the NO _X
It can be diffused throughout the absorbent NA1.

On the other hand, at this time, the second cutoff valves VU2, VL
2 continues to be opened and is therefore discharged from the internal combustion engine
All exhaust gases are second NO_XInflow into the absorbent NA2
To do. Therefore, as shown by the arrow (c) in FIG.
NO_XAbsorbent NA2 NO _XAbsorption QA2 promptly
Increase. It should be noted that in this way,
Exhaust gas has a small capacity NO_XThe time to flow into the absorbent is
It's quite short, so the second NO_XAbsorbent NA2
NO to pass_XThe amount of is much smaller.

Then, as shown by the arrow (d) in FIG.
To the first NO_XAbsorbent NA1 NO _XAbsorption QA1
If it becomes smaller than the lower limit LL specified for
The shut-off valves VU1 and VL1 are returned to full open, and the combustion heater 30
Is stopped (OFF) and the first exhaust gas supply nozzle NG
1 is closed. Therefore, the exhaust gas emitted from the internal combustion engine
Gas is the first and second NO_XIn the absorbent NA1, NA2
Inflowed, first and second NO_XAbsorbent NA1,
NA2 NO_XThe absorption amounts QA1 and QA2 increase.

Then, as shown by the arrow (e) in FIG.
Second NO_XAbsorbent NA2 NO _XAbsorption QA2 is high
If the limit UL is exceeded, the second NO_XAbsorb in the absorbent NA2
NO is stored_XSecond shield to release and reduce
The shutoff valves VU2 and VL2 are closed, and the combustion heater 30 is operated.
Is activated (ON), the second exhaust gas supply nozzle NG2 is opened.
Be spoken. As a result, the second NO from the combustion heater 30
_XThe action of supplying the reducing agent to the absorbent NA2 is started. Next
Then, as shown by the arrow (f) in FIG._XSucking
NO of collecting agent NA2_XAbsorption amount QA2 is smaller than the lower limit amount LL
When the temperature drops, the second shutoff valves VU2 and VL2 are returned to full open.
Then, the combustion heater 30 is stopped (OFF), and the second exhaust gas is discharged.
The gas gas supply nozzle NG2 is closed. Therefore, the internal combustion engine
Exhaust gas discharged from Seki is the first and second NO_Xabsorption
It is made to flow into the agents NA1 and NA2.

As shown by the arrow (a) in FIG. 3, while the first shutoff valves VU1 and VL1 are closed, the reducing agent is supplied from the combustion heater 30 to the first NO _X absorbent NA1. While the second NO _X absorbent NA2 is NO
_{When the X} absorption amount QA2 exceeds the upper limit amount UL, that is, the NO _X absorption amounts Q of the first and second NO _X absorbents NA1 and NA2.
When both A1 and QA2 exceed the upper limit UL, the first
The shutoff valves VU1 and VL1 are fully opened, the combustion heater 30 is stopped (OFF), and the first exhaust gas supply nozzle NG1 is closed. Therefore, the reducing agent supply action from the combustion heater 30 to the first NO _X absorbent NA1 is stopped, and the exhaust gas discharged from the internal combustion engine flows into the first and second NO _X absorbents NA1 and NA2. Be punished. At this time, the rich air-fuel ratio A / F of the exhaust gas discharged from an internal combustion engine for reducing to release NO _X absorbed in the first and second of the NO _X absorbent NA1, the NA2 from lean Switched, thus the first and second NO _x
The air-fuel ratio of the exhaust gas flowing into the absorbents NA1, NA2 is switched to rich. As a result, the arrow (b) in FIG.
The first and second NO _x absorbents NA1,
The NO _X absorption amounts QA1 and QA2 of NA2 gradually decrease. By doing so, the first and second shutoff valves VU1,
VL1, VU2, VL2 without closing the can be reduced to release the NO _X absorbed in the first and second of the NO _X absorbent NA1, the NA2. Further, it is not necessary to operate the combustion heater 30.

Next, as shown by the arrow (c) in FIG. 3, for example, the NO _X absorption amount QA of the first NO _X absorbent NA1.
When 1 becomes less than the lower limit amount LL, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is returned from rich to lean. As a result, it is possible to shorten the time for which the air-fuel ratio of the exhaust gas discharged from the internal combustion engine should be made rich. The air-fuel ratio A / F can also be kept rich until the NO _X absorption amount QA2 of the second NO _X absorbent NA2 becomes smaller than the lower limit amount LL.

Therefore, generally speaking, the exhaust gas from the internal combustion engine is
The exhaust gas emitted is both NO_XAbsorbent NA1, NA2
NO contained in the exhaust gas at this time_XBoth
NO _XAbsorb by the absorbents NA1, NA2, NO_Xabsorption
NO for each agent_XAbsorption amount QA1, QA2 is the upper limit amount UL
It is judged whether or not it exceeds, and either one of the NO_XAbsorbent
NO_XWhen it is determined that the absorption amount exceeds the upper limit amount UL
Is this NO_XNO absorbed in the absorbent_XEmitted
This NO to reduce_XThe exhaust gas flow to the absorbent
NO from the reducing agent supply device while temporarily shutting off_XAbsorbent
The reducing agent is temporarily supplied to and discharged from the internal combustion engine.
The exhaust gas discharged to the other NO_XGuide to the absorbent at this time
NO contained in exhaust gas_XThe other NO_XAbsorb with absorbent
Hold it, both NO_XAbsorbent NO_XAbsorption QA1,
When it is determined that QA2 exceeds the upper limit UL, the internal combustion
Exhaust gas exhausted from the engine is both NO_XAbsorbent NA
1, leading to NA2 and both NO_XAbsorbent NA1, N
NO absorbed in A2_XTo release and reduce
The air-fuel ratio of the exhaust gas discharged from the internal combustion engine
Switch from lean to rich, then either N
O_XAbsorbent NO_XAbsorption amount is less than the lower limit amount LL
It is determined whether or not the result is NO_XAbsorbent N
O_XIt is determined that the absorption amount is less than the lower limit amount LL
The air-fuel ratio of the exhaust gas discharged from the internal combustion engine
It means returning from rich to lean.

By the way, the exhaust gas discharged from the internal combustion engine contains sulfur, for example, SO _X , and NO _X.
Not only NO _X but also SO _X is absorbed by the absorbents NA1 and NA2. Therefore, in the internal combustion engine shown in FIG.
_The NO _X absorbent NA1 as indicated by the arrow (a), N
In order to release SO _X from A2, the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine is temporarily switched to rich.

Thus, even if the NO _X absorption amounts QA1, QA2 of the first and second NO _X absorbents NA1, NA2 do not exceed the upper limit amount UL, the air-fuel ratio A / of the exhaust gas discharged from the internal combustion engine. F may be switched to rich or stoichiometric. In this case, in the embodiment according to the present invention, the first
Also, the second cutoff valves VU1, VL1, VU2, VL2 are held fully open, the combustion heater 30 is stopped (OFF), and the first and second exhaust gas supply nozzles NG1, NG2 are closed. As a result, the reducing agent supply action from the combustion heater 30 to the NO _X absorbents NA1 and NA2 is stopped, and the exhaust gas discharged from the internal combustion engine flows into the first and second NO _X absorbents NA1 and NA2. Be punished. as a result,
As shown by the arrow (b) in FIG. 4, the first and second NO
NO _X absorption amount QA1 of _X absorbent NA1, NA2, QA2
Gradually decreases. Next, as shown by the arrow (c) in FIG. 4, the air-fuel ratio A / of the exhaust gas discharged from the internal combustion engine
When F is returned to lean, NO _X absorption amount QA1, QA2
Begins to increase again.

There are various methods for temporarily changing the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine from lean to rich. For example, there are a method of making the average air-fuel ratio in the combustion chamber 5 rich, and a method of injecting additional fuel into the combustion chamber 5 in the latter half of the expansion stroke or during the exhaust stroke.

[0041] In addition, of _the NO _X absorbent NO _X absorption amount QA
1, QA2 exceeds the upper limit amount UL, or the lower limit amount L
There are various methods for determining whether or not the value is smaller than L. For example, NO when it exceeds _the NO _X absorbent NA1, the NO _X concentration sensor arranged NA2 in the downstream of the exhaust passage, NO _X concentration threshold in the exhaust gas flowing out from _the NO _X absorbent NA1, NA2 _X absorption QA1, QA2
It is also possible to determine that has exceeded the upper limit amount UL, or when the NO _X absorption amounts QA1, QA2 have reached the lower limit amount L when a predetermined time has elapsed after operating the combustion heater 30.
It can also be determined that it has become smaller than L. Alternatively, NO _X absorption QA1, increase amount per unit of time QA2 or based on decrease NO _X absorption amount of the NO _X absorbent QA1, QA2 whether exceeds the upper limit amount UL, or than the lower limit amount LL It is also possible to determine whether or not it has become smaller.

In the embodiment shown in FIG. 1, a method based on the amount of increase or decrease of the NO _X absorption amounts QA1 and QA2 per unit time is used. Therefore, this method will be briefly described.

[0043] In this way, when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is lean, the amount of the NO _X discharged from the internal combustion engine per unit time, i.e., only discharge amount of NO _X QI, NO _X absorption It is considered that the quantities QA1 and QA2 increase per unit time. Therefore, when the exhaust gas discharged from the internal combustion engine is caused to flow into both NO _X absorbents NA1, NA2, the NO _X absorption amounts QA1, QA
2 increases by QI / 2 per unit time, and when the exhaust gas discharged from the internal combustion engine is caused to flow into one NO _X absorbent, the NO _X absorption amounts QA1 and QA2 increase by QI per unit time.

Although the exhausted NO _X amount QI depends on the average air-fuel ratio in the combustion chamber 5, the required torque TQ, and the engine speed N, the average air-fuel ratio in the combustion chamber 5 is required in the internal combustion engine shown in FIG. It is determined according to the torque TQ and the engine speed N, and therefore the exhausted NO _X amount QI is a function of the required torque TQ and the engine speed N. Specifically, increases the higher the discharge amount of NO _X QI required torque TQ becomes higher, the engine speed N becomes higher discharge amount of NO _X QI is increased higher.
The exhausted NO _X amount QI has been previously obtained by an experiment, and is shown as a function of the required torque TQ and the engine speed N in FIG.
It is stored in advance in the ROM 42 in the form of the map shown in FIG. It should be noted that the NO _X absorbent is upstream of the NO _X
It is also possible to dispose a concentration sensor and calculate the exhausted NO _X amount QI from the detected NO _X concentration and the amount of exhaust gas flowing into the NO _X absorbent.

On the other hand, NO_XAbsorbent NA1, NA2
The air-fuel ratio of the exhaust gas flowing into the engine is rich or has a stoichiometric air-fuel ratio
NO when done_XUnit time from absorbent NA1, NA2
NO released per hit and reduced_XAmount of NO_XRelease
Output is NO_XAbsorbent NA1, NA2 per unit time
The larger the amount of reducing agent supplied, the larger. NO _X
Exhaust gas of the combustion heater 30 is applied to the absorbents NA1 and NA2.
NO if supplied _XUnit time for absorbents NA1, NA2
The amount of reducing agent supplied per unit of time is stored in the combustion heater 30.
Amount of supplied air and combustion in combustion heater 30
Although it depends on the air-fuel ratio, the internal combustion engine shown in FIG.
Rich air whose combustion air-fuel ratio in the heater 30 is almost constant
Is maintained at the fuel ratio, so NO in this case_XRelease amount
QRH is the amount QB of air supplied to the combustion heater 30.
It becomes a function. Specifically, it is supplied to the combustion heater 30.
NO as the amount of air QB increases_XIncreased release amount QRH
Big NO_XThe amount of release QRH is obtained in advance by experiments.
As a function of the supply air amount QH of the combustion heater 30
In advance, it is recorded in the ROM 42 in the form of the map shown in FIG.
It is remembered.

On the other hand, when the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine is switched to rich, the amount of the reducing agent supplied to the NO _X absorbents NA1, NA2 per unit time is the combustion chamber 5 Mean air-fuel ratio within the, required torque T
Although it depends on Q and the engine speed N, in the internal combustion engine shown in FIG. 1, the average air-fuel ratio in the combustion chamber 5 is maintained at a substantially constant rich air-fuel ratio, so NO in this case.
_{The X} release amount QRR is a function of the required torque TQ and the engine speed N. Specifically, increases the higher the NO _X release amount QRR required torque TQ becomes higher, the engine speed N becomes higher NO _X emissions QRR increases higher. NO in this case
_{The X} release amount QRR has been previously obtained by an experiment, and is shown as a function of the required torque TQ and the engine speed N in FIG.
It is previously stored in the ROM 42 in the form of the map shown in FIG.

The NO _X absorption amount Q calculated in this way
The NO _X absorption amounts QA1 and QA2 can be calculated by integrating the increase amount or decrease amount of A1 and QA2 per unit time, and the calculated NO _X absorption amounts QA1 and QA2 are used as the upper limit amount UL or the lower limit amount LL. By comparison, the NO _X absorption amount QA1,
It is possible to determine whether QA2 has exceeded the upper limit amount UL or has become smaller than the lower limit amount LL.

[0048] The first to reduction to release for example a first of the NO _X in the absorbent within NA1 are absorbed NO _X
Even though the shutoff valve of 1 is closed, the first shutoff valve is slightly opened as described above. Therefore, N at this time
O increase amount per unit time of the _X absorption QA2 is discharged NO
_It is slightly less than the _X amount QI. At this time a part of the first of the NO _X absorbent NA1 supplied reducing agent is consumed by oxygen or NO _X in the exhaust gas flowing into the first of the NO _X absorbent in NA1, NO at this time The decrease amount of the _X absorption amount QA1 per unit time is slightly smaller than that of QRH. However, in the above-described method, such an error is negligible, and the increase amount or decrease amount of the NO _X absorption amounts QA1 and QA2 is calculated. Naturally, the amount of increase or decrease of the NO _X absorption amounts QA1, QA2 per unit time should be corrected according to the amount of exhaust gas flowing through the first or second shutoff valve so as to eliminate such an error. You can also

6 to 10 show a routine for executing the above-mentioned embodiment. This routine is executed by interruption every predetermined set time.

Referring to FIGS. 6 to 10, first, at step 100, it is judged if the first flag F1 is set and the second flag F2 is set.
The first flag F1 is set when the NO _X absorption amount QA1 of the first NO _X absorbent NA1 exceeds the upper limit amount UL (F
1 = 1), QA1 is reset when the amount becomes less than the lower limit amount LL (F1 = 0), and the second flag F2 indicates that the NO _X absorption amount QA2 of the second NO _X absorbent NA2 has the upper limit amount UL. Set when crossing (F2 = 1), QA2
Is reset when the amount becomes less than the lower limit amount LL (F2
= 0). If the first flag F1 is not set or the second flag F2 is not set, then the routine proceeds to step 101, where it is judged if the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine is lean. To be done. When the air-fuel ratio A / F is lean, then step 1
In 02, it is determined whether or not the first flag F1 is set. If the first flag F1 is not set, then the routine proceeds to step 103, where it is judged if the second flag F2 is set. Second flag F2
Is not set, that is, the first flag F1 is also set to the second
When the flag F2 is not set either, the routine proceeds to step 104, where the exhausted NO _X amount QI is calculated from the map of FIG. 5 (A). In the following step 105, the NO _X absorption amount QA of the first and second NO _X absorbents NA1, NA2.
1, QA2 is increased by QI / 2 (QA1 =
QA1 + QI / 2, QA2 = QA2 + QI / 2). In the following step 106, it is judged if the NO _X absorption amount QA1 of the first NO _X absorbent exceeds the upper limit amount UL. QA
When 1 ≦ UL, the process jumps to step 108 and QA
When 1> UL, the routine proceeds to step 107, where the first flag F1 is set, and then the routine proceeds to step 108. In step 108, it is judged if the NO _X absorption amount QA2 of the second NO _X absorbent exceeds the upper limit amount UL. QA2 ≦ UL
In case of, the processing cycle is ended, and in case of QA2> UL, the routine proceeds to step 109 to set the second flag F2, and then ends the processing cycle.

When only the first flag F1 is set, the routine proceeds from step 102 to step 110, where the parameter i is set to 1 and the parameter j is set to 2, and then the routine proceeds to step 112. On the other hand, when only the second flag F2 is set, the process proceeds from step 103 to step 111, the parameter i is set to 2 and the parameter j is set to 1, and then the process proceeds to step 112.

At step 112, the shutoff valves VUi, VLi
Is closed, the combustion heater 30 is operated, the exhaust gas supply nozzle NGi is opened, and the EGR valve 38 is opened. In the following step 113, N is selected from the map of FIG.
O _X release amount QRH is calculated, In the following step 114 NO _X absorption QAi is made to decrease by NO _X emissions QRH (QAi = QAi-QRH). Continued Step 1
At 15, it is judged if the NO _X absorption amount QAi is smaller than the lower limit amount LL. When QAi ≧ LL, the routine jumps to step 118, and when QAi <LL, the routine proceeds to step 116, where the shutoff valves VUi and VLi are returned to full open, the combustion heater 30 is stopped, and the exhaust gas supply nozzle NGi is closed. , EGR valve 38 is closed. In the following step 117, the flag Fi is reset. Then, it proceeds to step 118.

At step 118, the exhausted NO _X amount QI is calculated from the map of FIG. 5 (A). Continued Step 119
Then, the NO _X absorption amount QAj is increased by QI (QAj = QAj + QI). In the following step 120, N
O _X absorption QAj whether exceeds the upper limit amount UL is determined. When QAj ≦ UL, the processing cycle is ended,
When QAj> UL, the routine proceeds to step 121, where the flag Fj is set, and then the processing cycle is ended.

That is, for example, taking i = 1 and j = 2 as an example,
To explain, in step 112, the first shut-off valve V
U1 and VL1 are closed and the combustion heater 30 is activated.
Then, the first exhaust gas supply nozzle NG1 is opened and EG
The R valve 38 is opened. In the following step 113, NO_X
The release amount QRH is calculated, and in the subsequent step 114, NO
_XAbsorption amount QA1 is NO_XThe amount of emission QRH is reduced.
(QA1 = QA1-QRH). Continued Step 115
Then NO_XWhether the absorption amount QA1 is less than the lower limit amount LL
Is determined. When QA1 ≧ LL, step 11
Jump to step 8. If QA1 <LL, then step
Proceed to 116 and open the first shutoff valves VU1, VL1 fully.
The combustion type heater 30 is stopped and the first exhaust gas is returned.
The supply nozzle NG1 is closed and the EGR valve 38 is closed.
It In the following step 117, the first flag F1 is reset
To be done. Then, it proceeds to step 118. Step 118
Then discharge NO_XThe quantity QI is calculated and the following step 119
Then NO_XAbsorption amount QA2 is increased by QI
(QA2 = QA2 + QI). In the following step 120, N
O_XIt is determined whether or not the absorption amount QA2 exceeds the upper limit amount UL.
Be done. When QA2 ≦ UL, the processing cycle ends,
If QA2> UL, proceed to step 121
After setting the lag F2, the processing cycle is ended.

The first flag F1 is set and the second flag F1 is set.
When F2 is set, step 100 is started.
Proceed to Step 122, and first and second shutoff valves VU1, VL
1, VU2, VL2 are fully opened, combustion type heater 30
When stopped, the first and second exhaust gas supply nozzles NG1,
NG2 is closed and EGR valve 38 is closed. Continued
At step 123, the exhaust gas discharged from the internal combustion engine is empty.
The fuel ratio A / F is switched to rich. Continued Step 1
24, NO from the map of FIG. 5 (C)_XThe release amount QRR is
Calculated and NO in the following step 125_XAbsorption QA
1, QA2 is NO _XRelease amount can be reduced by QRR
(QA1 = QA1-QRR, QA2 = QA2-QR
R). In the following step 126, NO_XAbsorption QA1 or
It is determined whether QA2 is less than the lower limit amount LL.
Processing cycle when QA1 ≧ LL and QA2 ≧ LL
When QA1 <LL or QA2 <LL,
Then, proceed to step 127, where the exhaust gas discharged from the internal combustion engine
The air-fuel ratio A / F of the gas gas is returned to lean. Continued step
In step 128, the first flag F1 and the second flag F2 are reset.
Is set. Then, the processing cycle is ended.

On the other hand, the air-fuel ratio A / F of the exhaust gas discharged from the internal combustion engine regardless of the NO _X absorption amounts QA1 and QA2.
Is set to a rich or stoichiometric air-fuel ratio, the routine proceeds from step 100 and step 101 to step 129, where the first and second cutoff valves VU1, VL1, VU2, V
L2 is fully opened, the combustion heater 30 is stopped, and the first
Also, the second exhaust gas supply nozzles NG1 and NG2 are closed, and the EGR valve 38 is closed. In the following step 130, the NO _X release amount QRR is calculated from the map of FIG. 5C, and in the following step 131, the NO _X absorption amounts QA1, QA.
2 is reduced by the amount of NO _X release QRR (QA1
= QA1-QRR, QA2 = QA2-QRR). In the following step 132, it is judged if the NO _X absorption amount QA1 or QA2 is smaller than the lower limit amount LL. QA1 ≧ LL
When QA2 ≧ LL, the routine jumps to step 134, and when QA1 <LL or QA2 <LL, the routine proceeds to step 133, where the first flag F1 and the second flag F are entered.
After resetting 2, proceed to step 134. At step 134, it is judged if the NO _X absorption amount QA1 is smaller than zero. If QA1 ≧ 0, then jump to step 136, and if QA1 <0, then proceed to step 135 to set QA1 = 0 and then step 13
Go to 6. At step 136, it is judged if the NO _X absorption amount QA2 is smaller than zero. When QA2 ≧ 0, the processing cycle is ended. When QA2 <0, the routine proceeds to step 137, where QA2 = 0 is set, and then the processing cycle is ended.

Next, a low temperature combustion method suitable for carrying out the present invention will be briefly described with reference to FIGS. 11 to 13.

In the internal combustion engine shown in FIG. 1, the EGR rate (E
When the amount of GR gas / (the amount of EGR gas + the amount of intake air) is increased, the amount of smoke generated gradually increases and reaches a peak, and when the EGR rate is further increased, the amount of smoke generated suddenly increases. descend. This will be described with reference to FIG. 11 showing the relationship between the EGR rate and smoke when the cooling degree of EGR gas is changed. In addition, in FIG. 11, a curve A shows a case where the EGR gas is strongly cooled to maintain the EGR gas temperature at about 90 ° C., and a curve B shows a case where the EGR gas is cooled with a small cooling device. Curve C shows the case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 11, when the EGR gas is strongly cooled, the amount of smoke generated peaks when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Smoke hardly occurs if it is set above the percentage. On the other hand, FIG.
When the EGR gas is cooled a little as shown by the curve B in No. 1, the amount of smoke generated peaks when the EGR rate is slightly higher than 50%, and in this case E
Smoke hardly occurs when the GR rate is set to about 65% or more. Further, as shown by the curve C in FIG. 11, when the EGR gas is not forcibly cooled, the amount of smoke generated peaks near the EGR rate of 55%, and in this case, the EGR rate is almost 70%. Smoke hardly occurs if it is set above the percentage.

As described above, when the EGR gas ratio is set to 55% or more, the smoke is not generated because the endothermic action of the EGR gas does not raise the temperature of the fuel and the surrounding gas so much, that is, low temperature combustion is performed. As a result, hydrocarbons do not grow to soot.

This low-temperature combustion is characterized in that it is possible to reduce the amount of NO _X produced while suppressing the production of smoke regardless of the air-fuel ratio. That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excessive fuel does not grow to soot, and thus smoke does not occur. Also, at this time N
O _{X is} also generated in a very small amount. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature rises, but under low temperature combustion the combustion temperature is suppressed to a low temperature. No smoke is generated and NO _X is also generated in a very small amount.

By the way, when the required torque TQ of the engine becomes high, that is, when the fuel injection amount becomes large, the temperature of the fuel and the surrounding gas at the time of combustion becomes high, so that it becomes difficult to perform low temperature combustion. That is, low-temperature combustion can be performed only during engine low load operation in which the calorific value due to combustion is relatively small.
In FIG. 12 (A), the region I is the operating region where the first combustion, that is, the low temperature combustion, in which the amount of the inert gas in the combustion chamber 5 is larger than the amount of the inert gas at which the amount of soot is peaked, is performed. The region II shows the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot is peaked, that is, the operating region in which only normal combustion can be performed. There is.

FIG. 12B shows the target air-fuel ratio A / F when low temperature combustion is performed in the operating region I, and FIG.
Is the opening degree of the throttle valve 17 according to the required torque TQ for low temperature combustion in the operating region I, the EGR control valve 2
5, the EGR rate, the air-fuel ratio, the injection start timing θS, the injection completion timing θE, and the injection amount are shown. Note that FIG. 13 also shows the opening degree of the throttle valve 17 during normal combustion performed in the operation region II.

From FIG. 12 (B) and FIG. 13, the operating range I
The EGR rate is 5 when low temperature combustion is performed in
It can be seen that the air-fuel ratio A / F is 5% or more, and the lean air-fuel ratio is about 15.5 to 18. As described above, there is an advantage that smoke, that is, fine particles are hardly emitted when low temperature combustion is performed.

When low temperature combustion is used, the air-fuel ratio in the combustion chamber 5 can be made rich without generating a large amount of soot, that is, a large amount of fine particles. Therefore, when the operating condition of the engine is in the second operating region II shown in FIG. 12, N
O _X absorption QA1, the operating state of the engine when the QA2 are both exceeded the upper limit amount UL is not an air-fuel ratio A / F until shifts to the first operating region I to the rich operating state of the engine is the first
It is preferable to make the air-fuel ratio A / F rich after shifting to the operating region II.

In the embodiment shown in FIG. 1, the first shutoff valve is the first
The upstream cutoff valve VU1 and the first downstream cutoff valve VL1 are formed, and the second cutoff valve is formed of the second upstream cutoff valve VU2 and the second downstream cutoff valve VL2. However, as shown in FIG. 14, it is also possible to form the first shutoff valve only from the first downstream side VL1 and the second shutoff valve only from the second downstream side shutoff valve VL2.

Further, in the embodiment shown in FIG. 1, the combustion type heater 3 in which the reducing agent is burned under the rich air-fuel ratio is used.
0 exhaust gas, and this exhaust gas is used as the first and second exhaust gases.
From the exhaust gas injection nozzles NG1, NG2 of the first and second
Are supplied to the NO _X absorbents NA1 and NA2, respectively. However, as shown in FIG. 14, the reducing agent is formed from the fuel, and the first and the second are arranged in the first and the second upstream exhaust ducts DU1 and DU2, respectively.
It is also possible to supply the fuel to the first and second NO _X absorbents NA1 and NA2 from the electrically controlled fuel injection nozzles NF1 and NF2, respectively. In this case, the fuel in the fuel tank is supplied to the first and second fuel injection nozzles NF1 and NF2 by the additional fuel pump 53.

[0068]

The exhaust gas can be satisfactorily purified with a small capacity NO _X absorbent.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining exhaust gas purification control.

FIG. 3 is a diagram for explaining exhaust gas purification control.

FIG. 4 is a diagram for explaining exhaust gas purification control.

FIG. 5 is a diagram showing the amount of exhausted NO _{X and the} amount of NO _X released.

FIG. 6 is a flow chart for executing exhaust gas purification control.

FIG. 7 is a flowchart for executing exhaust gas purification control.

FIG. 8 is a flow chart for executing exhaust gas purification control.

FIG. 9 is a flowchart for executing exhaust gas purification control.

FIG. 10 is a flowchart for executing exhaust gas purification control.

FIG. 11 is a diagram showing the amount of smoke generated.

FIG. 12 is a diagram showing an operating region and the like of the engine.

FIG. 13 is a diagram showing changes in throttle valve opening and the like.

FIG. 14 is a diagram showing another embodiment.

[Explanation of symbols]

1 ... Engine body NA1, NA2 ... NO _X absorbent 30 ... Combustion heater

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) F01N 3/36 F01N 3/36 B (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd. (72) Inventor Takamitsu Asanuma 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Koichi Kimura 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Invention Person Koichiro Nakatani 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Akira Aichi Prefecture, Toyota City, Toyota City 1, Toyota Town, F Term (reference) 3G091 AA10 AA11 AA18 AB06 BA01 BA14 BA33 CA16 DB10 FB07 FB12 FC01 GA06 GB02W GB03W GB04W GB06W GB07W GB10X

Claims (7)

[Claims] 1. When the air-fuel ratio of the inflowing exhaust gas is lean
NO in the exhaust gas flowing in_XAbsorbs and inflows
Absorbs when the air-fuel ratio of air gas becomes stoichiometric or rich.
NO_XNO to release and reduce_XRemove the absorbent from the engine
A pair of branch exhaust passages formed by branching the air passages
Arranged individually, each NO_XSecondary supply of reducing agent to absorbent
Equipped with a possible reducing agent supply device, under lean air-fuel ratio
In an internal combustion engine in which combustion occurs, the emissions from the internal combustion engine
Exhausted exhaust gas to both NO_XGuide it to the absorbent and remove it at this time
NO contained in air gas_XBoth NO_XAbsorbed in absorbent
No, no_XNO for each absorbent_XAbsorption amount is predetermined
It is determined whether the upper limit amount has been exceeded, and either
NO_XAbsorbent NO_XIt is judged that the absorption amount exceeds the upper limit amount.
If the_XNO absorbed in the absorbent_X
The NO to release and reduce_XExhaust gas to absorbent
The NO from the reducing agent supply device while temporarily interrupting the flow
_XThe reducing agent is temporarily supplied to the absorbent and the internal combustion engine
Exhaust gas discharged from the other NO_XGuide to the absorbent
NO contained in the exhaust gas at this time _XTo the other NO_X
Absorb with an absorbent, NO of both_XAbsorbent NO_Xabsorption
When it is determined that the amount exceeds the upper limit, the internal combustion engine
Exhausted exhaust gas is both NO_XLeading to absorbent
Both NO_XNO absorbed in the absorbent_XEmitted
Of exhaust gas emitted from the internal combustion engine to reduce
Exhaust gas that temporarily changes the fuel ratio from lean to rich
Purification method. 2. The exhaust gas discharged from the internal combustion engine when the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is switched to the stoichiometric air-fuel ratio or the rich air-fuel ratio regardless of the NO _X absorption amount of each NO _X absorbent. The exhaust gas purification method according to claim 1, wherein the exhaust gas is led to both NO _x absorbents. 3. After the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is switched from lean to rich, the NO _X absorption amount of either one of the NO _X absorbents becomes smaller than a predetermined lower limit amount. If it is determined that the NO _X absorption amount of one of the NO _X absorbents has become smaller than the predetermined lower limit amount, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is changed from rich to rich. The exhaust gas purification method according to claim 1, wherein the exhaust gas is returned to lean. 4. The reducing agent supply device comprises a combustion device for performing combustion under a rich air-fuel ratio, and it is determined that the NO _X absorption amount of either one of the NO _X absorbents exceeds the upper limit amount. NO _X which is sometimes absorbed within the _the NO _X absorbent
The exhaust gas purification method according to claim 1, wherein the exhaust gas of the reducing agent supply device is temporarily supplied to the NO _X absorbent in order to release and reduce the NOx. Wherein said reducing agent supply device comprises a reducing agent supply valve disposed in the branch exhaust passage of the NO _X absorbent upstream, NO _X absorption of the upper limit amount of either of the NO _X absorbent the NO _X to reduce to release NO _X absorbed in the within the _the NO _X absorbent when it is determined that exceeds the
The exhaust gas purification method according to claim 1, wherein the reducing agent is temporarily supplied from a reducing agent supply valve corresponding to the absorbent. 6. The exhaust gas purifying according to claim 1, wherein a cutoff valve is arranged in each branch exhaust passage, and when the flow of the exhaust gas to the NO _X absorbent should be cut off, the corresponding cutoff valve is closed. Method. 7. The exhaust gas purification method according to claim 6, wherein the shutoff valve is closed so that a slight amount of exhaust gas flows through the corresponding NO _X absorbent.