JPH06108828A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent exhaust emission from being deteriorated and eliminate the need for using a large amount of reducing agent. CONSTITUTION:An NOX adsorption/discharge catalyst 10 is arranged at the exhaust passage 6 of a diesel engine body 2. If the NOX adsorption/discharge catalyst 10 is not in an NOX reducing condition, the opening of an intake throttle valve 8 is reduced, and even when theta=0 is formed, fuel supply amount from a fuel supply device 14 is increased, provided that the catalyst is not in the NOX reducing condition. If the catalyst 10 is in the NOX reducing condition, the opening of the intake throttle valve 8 is increased, and then the fuel supply amount form the fuel supply device 14 is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art The applicant of the present invention absorbs NO _X when the air-fuel ratio of the exhaust gas is lean, releases the absorbed NO _X when the air-fuel ratio of the exhaust gas is stoichiometric or rich, and reduces the released NO _X. the NO _X absorption and release catalyst disposed in the diesel engine exhaust passage, to supply the reducing agent to the NO _X absorbing and releasing catalyst when allowed to reduce NO _X absorption and release NO _X emitted by allowed releasing NO _X from the catalytic combustion of An exhaust gas purification device for an internal combustion engine is proposed (Japanese Patent Application No. 4-TSN92-2166 (TYT92436).
9)).

[0003]

By the way, the amount of NO _X released from the NO _X storage and release catalyst changes depending on the temperature and oxygen concentration at the time of release. However, in the conventional apparatus described above, for not controlling the oxygen or reducing agent supply amount according to the NO _X emissions, there is a problem that the exhaust emission is required a large amount of reducing agent deteriorates.

[0004]

In order to solve the above problems, according to the present invention, NO _x is absorbed when the air-fuel ratio of the exhaust gas is lean, and NO is absorbed when the air-fuel ratio of the exhaust gas is stoichiometric or rich. NO _X absorption and release placing the catalyst into the engine exhaust passage, the reducing agent to the NO _X absorbing and releasing catalyst when allowed to reduction brought releasing NO _X from the NO _X absorption and release catalyst for reducing the released NO _X while emitting _X It is provided with a supply amount control means for supplying and burning and supplying the oxygen or the reducing agent to the NO _x absorbing and releasing catalyst according to the NO _x releasing amount from the NO _x absorbing and releasing catalyst.

[0005]

[Action] reducing agent to the NO _X absorbing and releasing catalyst when allowed to reducing the NO _X absorption and release catalyst allowed releasing NO _X is burned is supplied. Thus, the oxygen concentration decreases is consumed oxygen in the exhaust gas in the catalyst out NO _X absorbing and therefore, NO _X absorbing and releasing NO _X from the catalyst is reduced by the reducing agent is released.

[0006] NO _X absorbing and releasing N depending on the amount of NO _X in the catalyst
O supply amount of oxygen or a reducing agent to the _X absorption and release catalyst is made to control. Therefore, it is possible to prevent the exhaust emission from deteriorating and requiring a large amount of reducing agent.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 2 is a diesel engine body, 4 is an intake passage, and 6 is an exhaust passage. An intake throttle valve 8 is provided in the intake passage 4, and the intake throttle valve 8 is normally fully opened. In the middle of the exhaust passage 6, N
O _X absorption and release casing 12 with a built-in catalyst 10 is arranged. A fuel supply device 14 for supplying fuel as a reducing agent is arranged in the exhaust passage 6 upstream of the casing 12.

A first exhaust temperature sensor 20 is arranged in the exhaust passage 6 between the casing 12 and the fuel supply device 14, and a detection signal of the first exhaust temperature sensor 20 is input to an electronic control unit (ECU) 30. It A second exhaust temperature sensor 22 is arranged in the exhaust passage 6 near the casing 12 and on the downstream side, and a detection signal of the second exhaust temperature sensor 22 is EC.
Input to U30. A limiting current type oxygen concentration sensor (hereinafter referred to as “lean mixture sensor”) 24 that detects the oxygen concentration in the exhaust gas is arranged in the exhaust passage 6 near the second exhaust temperature sensor 22 and on the downstream side. The detection signal of is input to the ECU 30.

The ECU 30 also controls the actuator 16 for driving the intake throttle valve 8 and the fuel supply device 14. The NO _X adsorption / desorption catalyst 10 housed in the casing 12 uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba, calcium Ca are used on the carrier. At least one selected from alkaline earths, lanthanum La, rare earths such as yttrium Y, and a noble metal such as platinum Pt are carried. NO
_x absorption and release catalyst 10 absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, perform absorption and release action of the NO _X that releases NO _X concentration of oxygen absorbed to decrease in the inflowing exhaust gas.

If the above-mentioned NO _X intake / release catalyst 10 is arranged in the engine exhaust passage, the NO _X intake / release catalyst 10 will actually be 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 absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the 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 earth or 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 oxygen O ₂ attaches to the surface of platinum Pt in the form of O ₂ ⁻ . On the other hand, N in the inflowing exhaust gas
O reacts with O ₂ ⁻ on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). NO ₂ produced next
Part of the oxygen is absorbed and released by the catalyst 10 while being further oxidized on platinum Pt.
While being absorbed inside and bound to barium oxide BaO, it diffuses into the adsorption / desorption catalyst 10 in the form of nitrate ions NO ₃ ⁻ as shown in FIG. 2 (A). In this way NO _x is N
It is absorbed in the O _X adsorption / desorption catalyst 10.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is produced on the surface of platinum Pt, and NO ₂ of the adsorption / desorption catalyst 10 is generated.
_As long as the _X absorption capacity is not saturated, NO ₂ is absorbed in the adsorption / desorption catalyst 10 to generate nitrate ion NO ₃ ⁻ . In contrast the reaction with the amount of NO ₂ oxygen concentration is lowered in the inflowing exhaust gas is lowered backward (NO ₃ ^- → NO ₂₎ proceeds to, thus to absorption and release nitrate ions NO in the catalyst 10 ₃ ^-
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 absorbing and releasing from leaving the catalyst 10 NO _X is to be released. Flowing oxygen concentration of the inflowing exhaust gas when the degree becomes lower in lean exhaust gas decreases, thus if a low degree of lean of the inflowing exhaust gas NO _X absorbing and releasing NO _X from the catalyst 10 is to be released .

On the other hand, at this time, the air-fuel ratio of the inflowing exhaust gas is
HC and CO are oxygen O on platinum Pt.₂ ^-When
It reacts and is oxidized. Also, the air-fuel of the inflowing exhaust gas
When the ratio is made rich, the oxygen concentration in the inflowing exhaust gas becomes extremely high.
NO from the intake / release catalyst 10 to decrease₂Is released,
This NO₂Is the unburned HC, C as shown in FIG.
It reacts with O and is reduced and purified. In this way white
NO on the surface of gold Pt ₂Absorption and release catalyst
NO from 10 to next₂Is released. Therefore inflow
If the air-fuel ratio of exhaust gas is made rich, NO
_XNO from adsorption / release catalyst 10_XIs released and reduced and purified
Will be.

As described above, when the air-fuel ratio of the inflowing exhaust gas becomes lean, NO _X is absorbed by the NO _X intake / release catalyst 10, and when the air-fuel ratio of the inflowing exhaust gas is made rich, NO _X becomes short from the NO _X intake / release catalyst 10. It is released and reduced in time. Meanwhile, according to the NO _X emissions from NO _X absorption and release catalyst 10, if not controlled amount of air supplied to the NO _X absorbing and releasing catalyst 10 (oxygen) or fuel quantity, the following problems Occurs.

[0015] That is, when the amount of many air amount of fuel is small, although NO _X is released from the NO _X absorbing and releasing catalyst 10 causes problems that not reduced NO _X is released into the atmosphere. On the other hand, when a large amount of fuel is supplied, there arises a problem that fuel efficiency deteriorates. Therefore, in this embodiment,
NO based on the detection signals of the first exhaust temperature sensor 20, the second exhaust temperature sensor 22, and the lean mixture sensor 24.
Estimating a reduced state of the NO _X in the _X absorption and release catalyst 10 (indirectly estimates the NO _X emissions from NO _X absorption and release catalyst 10), NO _X absorption and release catalyst based on reduced state of the NO _X The amount of air and the amount of fuel supplied to 10 are controlled.

This makes it possible to prevent NO _X from being released to the atmosphere or consuming a large amount of fuel. Here, the reduction state of NO _X is determined as follows, for example. That is, when NO _X is being reduced, the output Ao of the lean mixture sensor 24 is substantially equal to 0, that is, the oxygen concentration in the output gas is almost 0%. Further, at this time, since the fuel is burned in the NO _X intake / release catalyst 10, the outgas temperature To detected by the second exhaust temperature sensor 22 is obtained.
ut becomes higher than the inlet gas temperature Tin detected by the first exhaust gas temperature sensor 20, but does not become higher than the predetermined temperature T _A because oxygen does not exist in a large amount.
In cases other than when these conditions are satisfied, it is determined that NO _X has not been reduced.

FIGS. 3 and 4 show a NO _x absorption / release catalyst 1.
2 shows a routine for controlling the amount of air and the amount of fuel supplied to zero. This routine is executed by interruption at regular time intervals. Referring to FIGS. 3 and 4, first,
At step 40, it is judged if the flag F is reset to 0 or not. Since the flag F is initially reset, an affirmative decision is made and the routine proceeds to step 42. In step 42, the catalyst regeneration start condition, that is, the NO _X intake / release catalyst 10 is used.
It is determined whether or not the conditions for releasing NO _x and reducing NO _x are satisfied. The catalyst regeneration start conditions are, for example, deceleration, the NO _X absorption / release catalyst 10 is at a catalyst activation temperature or higher, and a predetermined time or more has elapsed since the catalyst regeneration was last started. If it is determined that the catalyst regeneration start condition is not satisfied, the routine proceeds from step 52 to step 56, and this routine is ended. In step 52, the flag F is reset to 0, in step 54 the intake throttle valve 8 is fully opened, and in step 56, the fuel supply device 1
Fuel supply from 4 is prohibited.

On the other hand, if it is determined in step 42 that the catalyst regeneration start condition is satisfied, the routine proceeds to step 44, where the flag F is set to 1. Therefore, in the subsequent processing cycles, since the negative determination is made in step 40, steps 42 to 48 are skipped.
In step 46, the opening degree θ of the intake throttle valve 8 is set to 0 and the intake throttle valve 8 is closed. As a result, the maximum air flow into the NO _X intake / release catalyst 10 is reduced to the minimum flow rate. Next, at step 48, a predetermined amount of fuel is supplied from the fuel supply device 14. The predetermined fuel amount is a fuel amount that makes the air-fuel ratio slightly rich.

At step 50, it is judged if the catalyst regeneration stop condition is satisfied. When it is determined that the catalyst regeneration stop condition is satisfied, the routine proceeds from step 52 to step 56, where the catalyst regeneration of the NO _X intake / release catalyst 10 is stopped. If a negative decision is made in step 50, step 58
Then, it is determined whether or not the state is the NO _x reduction state. This determination is made based on the detection signals of the first exhaust temperature sensor 20, the second exhaust temperature sensor 22, and the lean mixture sensor 24, as described above. If it is determined that the NO _x reduction state is not established, that is, if the amount of reducing agent is insufficient, the routine proceeds to step 60, where it is determined whether the opening θ of the intake throttle valve 8 is 0, that is, the intake It is determined whether the throttle valve 8 is closed. When it is determined that θ = 0, the routine proceeds to step 62, where θ is decreased by Δθ, the opening of the intake throttle valve 8 is decreased, and NO _x
The amount of air flowing into the intake / release catalyst 10 is reduced.
On the other hand, when θ = 0 is determined in step 60, the process proceeds to step 64, and the fuel supply amount supplied to the NO _X intake / release catalyst 10 is increased.

On the other hand, if it is determined in step 58 that the NO _x reduction state is present, that is, if the amount of reducing agent is sufficient, the routine proceeds to step 66, where the opening θ of the intake throttle valve 8 is preset. It is determined whether or not the opening degree is equal to or greater than the determined opening θ ₀ . If it is determined that θ <θ ₀ , the routine proceeds to step 68, where θ
Is increased by Δθ, the opening of the intake throttle valve 8 is increased, and the amount of air flowing into the NO _X intake / release catalyst 10 is increased. The reason why the amount of air is increased in the NO _X reducing state is that the combustion temperature in the NO _X intake / release catalyst 10 increases as the amount of air increases, and the release and reduction of NO _X is promoted.

When it is judged at step 66 that θ ≧ θ ₀ , the routine proceeds to step 70, where NO is sent from the fuel supply device 14.
_The amount of fuel supplied to the _X adsorption / desorption catalyst 10 is reduced. As a result, the fuel consumption amount can be reduced. Although the diesel engine has been described in this embodiment, the present invention can also be applied to a gasoline engine.

[0022]

EFFECTS OF THE INVENTION It is possible to prevent the exhaust emission from deteriorating and requiring a large amount of reducing agent.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the absorption and release action of NO _X.

FIG. 3 is a flowchart for controlling the amount of air and the amount of fuel supplied to the NO _X intake / release catalyst.

FIG. 4 is a flowchart for controlling the amount of air and the amount of fuel supplied to the NO _X intake / release catalyst.

[Explanation of symbols]

2 ... Diesel engine body 6 ... Exhaust passage 8 ... Intake throttle valve 10 ... NO _X intake / release catalyst 14 ... Fuel supply device

Claims (1)

[Claims] 1. When the air-fuel ratio of the exhaust gas is lean, N
Air-fuel ratio of absorbing the O _X exhaust gas is arranged NO _X absorption and release catalyst for reducing the released NO _X in the engine exhaust passage with the time of stoichiometric or rich to release NO _X absorbed, the NO _X absorption When releasing NO _x from the releasing catalyst to reduce it, a reducing agent is supplied to the NO _x absorbing and releasing catalyst to burn it, and N from the NO _x absorbing and releasing catalyst is burned.
An exhaust emission control device for an internal combustion engine, comprising a supply amount control means for controlling the supply amount of oxygen or a reducing agent to the NO _X absorption / release catalyst according to the O _X release amount.