JP2000282843A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively disperse reducing agent in an exhaust emission control device for performing exhaust emission control through the supply of the reducing agent. SOLUTION: This exhaust emission control device comprises a first exhaust passage 2a for discharging exhaust gas from a lean-burn internal combustion engine, a second exhaust passage 2b branching from the first exhaust passage 2b and passing exhaust gas, having a volume which is smaller than that of exhaust gas flowing through the first exhaust passage 3a, urea selecting reduction catalyst 4 as exhaust purifying catalyst, and a reducing agent supply means 6 for feeding reducing agent for purifying the exhaust gas into the second exhaust passage 2b. With this arrangement, the reducing agent can be easily dispersed in the second exhaust passage 2 through the exhaust gas flows at a low flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an apparatus for purifying NOx and the like in exhaust gas discharged from a lean burn type internal combustion engine.

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for a lean-burn internal combustion engine, for example, an apparatus disclosed in Japanese Patent Application Laid-Open No. 3-213614 is known.

This device is an exhaust gas purifying device for a diesel engine provided with an injector for injecting an aqueous urea solution at a predetermined timing toward one of a combustion chamber of the diesel engine and an exhaust passage near the combustion chamber.

[0004]

In the above-described apparatus, when the reducing agent is added, the reducing agent is added to the catalyst without being sufficiently dispersed due to the influence of the exhaust gas flow. May not be dispersed.

The present invention has been made in view of the above points, and an exhaust gas purifying apparatus for an internal combustion engine capable of sufficiently dispersing and supplying a reducing agent to a selective reduction catalyst that purifies exhaust gas by adding a reducing agent. To provide

[0006]

The present invention adopts the following means in order to solve the above-mentioned problems. That is, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a first exhaust passage for discharging exhaust gas from a lean burn internal combustion engine, and an amount of exhaust gas branched from the first exhaust passage and flowing into the first exhaust passage. A second exhaust passage through which a smaller amount of exhaust gas flows;
An exhaust purification catalyst provided in the exhaust passage for purifying exhaust gas flowing in the second exhaust passage; and a reducing agent for the exhaust gas purification catalyst provided in the second exhaust passage upstream of the exhaust gas purification catalyst. And a reducing agent supply means for supplying the reducing agent into the second exhaust passage.

The internal combustion engine to which the present invention is applied is a lean burn type diesel engine or gasoline engine, and includes a direct injection type engine. In the present invention, since the first exhaust passage forms the main flow of the exhaust gas and the second exhaust passage forms the sub-flow of the exhaust gas, the amount of the exhaust gas flowing through the second exhaust passage is reduced by the amount of the exhaust gas flowing through the first exhaust passage. Less than the amount of gas. Therefore, the reducing agent supplied from the reducing agent supply means is sufficiently dispersed in the exhaust gas. For this purpose, the flow velocity of the exhaust gas flowing in the second exhaust passage may be lower than the flow velocity of the exhaust gas flowing in the first exhaust passage.

When a heating means is provided between the exhaust gas purifying catalyst and the reducing agent supply means, the upper limit of exhaust gas saturation is increased by heating by the heating means, so that more reducing agent is dispersed and Of the exhaust gas, that is, the exhaust gas purification rate can be improved.

Further, in the present invention, it is needless to say that an exhaust gas purifying catalyst may be provided in the first exhaust gas passage for purifying the exhaust gas flowing through the first exhaust gas passage. Is preferable. That is, when the end of the second exhaust passage is connected to the first exhaust passage, and when the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is lean, the NOx enters the first exhaust passage downstream of the connection point. Occlude,
The system is provided with a NOx storage-reduction catalyst that releases and reduces the stored NOx when the oxygen concentration in the exhaust gas decreases.

Here, the exhaust gas purifying catalyst provided in the second exhaust passage may be of any type as long as it can perform a reducing action for purifying exhaust gas by supplying a reducing agent. The catalyst is preferably a selective reduction catalyst in which selective reduction is performed by addition, and more preferably an ammonia compound selective reduction catalyst in which selective reduction is performed by addition of an ammonia compound such as urea.
In this case, the reducing agent supply means may be a means for supplying an ammonia compound such as urea as a reducing agent. Examples of the ammonia compound as the reducing agent include urea, ammonium carbamate and the like.

In the NOx storage-reduction catalyst, when the internal combustion engine is operated under high-speed, high-load, lean combustion, NOx absorbed by the NOx absorbent is not reduced by the catalyst, and
Since the Ox absorbent is not reduced, NOx purification becomes impossible. However, under high-rotation, high-load operating conditions, the urea selective reduction catalyst functions to purify NOx. Therefore, NOx
As compared with the case where only the storage reduction catalyst is provided, the operating range in which NOx can be purified is widened.

If a flow rate adjusting means for adjusting the flow rate of the exhaust gas flowing in the second exhaust passage is provided, the dispersion of the reducing agent in the second exhaust passage can be controlled. Further, when a urea (ammonia compound) selective reduction catalyst is provided in the second exhaust passage, the urea (ammonia compound)
Based on the NOx amount in the exhaust gas flowing into the selective reduction catalyst and the intake air amount of the internal combustion engine, the urea (ammonia compound)
If the exhaust gas purification apparatus having the above-mentioned configuration is provided with an added urea (ammonia compound) amount determining means for estimating the amount of urea (ammonia compound) to be added to the selective reduction catalyst, the amount of urea (ammonia compound) to be added can be easily determined. Can decide.

Further, urea (ammonia compound) detecting means for detecting urea (ammonia compound) flowing out from the urea (ammonia compound) selective reduction catalyst, and urea (ammonia compound) detected by the urea (ammonia compound) detecting means By providing a control means for correcting the amount of urea (ammonia compound) to be added from the detected amount to an appropriate amount, the amount of added urea (ammonia compound) can be controlled more accurately, and more effective exhaust gas purification It can be performed.

A catalyst temperature detecting means for detecting a temperature state of the urea (ammonia compound) selective reduction catalyst, and the amount of urea (ammonia compound) added to the urea (ammonia compound) selective reduction catalyst is increased or decreased according to the detected catalyst temperature. Urea (ammonia compound) addition amount controlling means may be provided. Note that the above configurations can be combined with each other as much as possible.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> In the example shown in FIG. 1, the exhaust pipe 2 of the in-cylinder injection lean-burn gasoline engine 1 is branched into a first exhaust passage 2a and a second exhaust passage 2b.
Further, the second exhaust passage 2b is connected to the first exhaust passage 2a at the end of the second exhaust passage 2b. And the second
The urea selective reduction catalyst 4 is disposed in the exhaust passage 2b, and the NOx storage reduction catalyst 3 is disposed in the first exhaust passage downstream of the connection point between the end of the second exhaust passage and the first exhaust passage. .

At the entrance of the second exhaust passage 2b branched from the first exhaust passage 2a, the vortex flow of the exhaust gas is reduced by making the second exhaust passage orthogonal to the first exhaust passage or at the entrance of the second exhaust passage. The amount of exhaust gas flowing through the second exhaust passage is smaller than the amount of exhaust gas flowing through the first exhaust passage, and the amount of exhaust gas flowing through the second exhaust passage is reduced by means such as forming a stagnation portion such as a depression to be formed. The speed of the exhaust gas is lower than the speed of the exhaust gas flowing through the first exhaust passage.

In the engine 1, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = TP · K Here, TP indicates a basic fuel injection time, and K indicates a correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained in advance by an experiment, and the engine load Q / N
As a function of (intake air amount Q / engine speed N) and engine speed N, they are stored in the ROM in advance in the form of a map.

The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder.
If it is 1.0, the air-fuel mixture supplied to the engine cylinder has a stoichiometric air-fuel ratio. On the other hand, K <1.0
, The air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, becomes lean, and K>
At 1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

In the engine 1, in the engine low-medium load operation range, the value of the correction coefficient K is set to a value smaller than 1.0 to perform lean air-fuel ratio control, and the engine 1 operates in the engine high load operation range and the engine 1 starts. During warm-up operation, acceleration, and at a constant speed operation of, for example, 120 km / h or more, the value of the correction coefficient K is set to 1.0 and stoichiometric control is performed. Is set to a value larger than 1.0 and rich air-fuel ratio control is performed.

In an internal combustion engine, low-medium load operation is usually performed most frequently, and therefore, during most of the operation period, the value of the correction coefficient K is made smaller than 1.0, and the lean mixture is burned. become.

The NOx storage reduction type catalyst 3 uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, and an alkaline earth such as barium Ba and calcium Ca. And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage and the exhaust passage upstream of the NOx storage reduction catalyst 3 is referred to as the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 3, this NOx The storage reduction type catalyst 3 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases.

When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx storage reduction catalyst 3, the air-fuel ratio of the inflowing exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber. Therefore, in this case, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is lean, the NOx storage reduction catalyst 3 absorbs NOx and the oxygen concentration in the air-fuel mixture supplied to the combustion chamber decreases. Releases and reduces absorbed NOx.

NOx absorption and reduction in the NOx storage reduction catalyst 3
It is believed that the reduction is performed by a mechanism as shown in FIG. This mechanism is a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

First, when the exhaust gas becomes considerably lean, the exhaust gas is exhausted.
Since the oxygen concentration in the gas greatly increases, FIG.
Oxygen O as shown in_TwoIs O_Two ^-Or O^2-In the form of platinum Pt
Attaches to surface. Next, NO contained in the exhaust gas is white.
O on the surface of gold Pt_Two ^-Or O ^2-Reacts with NO_TwoBecomes
(2NO + O_Two→ 2NO_Two).

[0026] Then, the generated NO ₂ as long as the NOx absorbing capability of the NOx storage reduction catalyst 3 is not saturated, is absorbed in the catalyst bonding with the barium oxide BaO while being oxidized on platinum Pt, FIG. 2 ( nitrate ions NO as shown in a) ₃ ^- diffuses in the NOx storage reduction catalyst 3 in the form of. In this way, NOx is absorbed in the NOx storage reduction type catalyst 3.

On the other hand, when the oxygen concentration in the exhaust gas decreases, the amount of generated NO ₂ decreases, and the nitrate ion NO ₃ ⁻ in the NOx storage-reduction catalyst 3 is reduced by the reverse reaction. Is released from the NOx storage reduction catalyst 3 in the form of NO ₂ or NO.

That is, NOx is released from the NOx storage reduction catalyst 3 when the oxygen concentration in the exhaust gas decreases. As shown in FIG. 3, when the lean degree of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases. Therefore, when the leanness of the inflowing exhaust gas decreases, even if the inflowing exhaust gas becomes empty, Even when the fuel ratio is lean, NOx is released from the NOx storage reduction catalyst 3.

On the other hand, at this time, when the air-fuel mixture supplied to the combustion chamber is made stoichiometric or rich, and the air-fuel ratio of the exhaust gas becomes stoichiometric or rich, a large amount of unburned HC and CO is produced as shown in FIG. Emitted from 1.
These unburned HC and CO are converted to oxygen O ₂ ^- or O ₂ on platinum Pt.
^2- Reacts immediately and is oxidized.

When the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich, the oxygen concentration in the exhaust gas extremely decreases, and the NOx storage reduction catalyst 3 releases NO ₂ or NO. This NO ₂ or NO is shown in FIG.
As shown in (B), it is reduced by reacting with unburned HC and CO. When NO ₂ or NO on the platinum Pt is no longer present, NO ₂ or NO is released from the catalyst one after another. Therefore, when the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx storage reduction catalyst 3 within a short time. Platinum Pt on the O ₂ ^- or O ^2- unburned be consumed HC, any remaining CO is, NOx released from the NOx storage reduction catalyst 3 also, even NOx discharged from the engine 1, the It is reduced by unburned HC and CO.

Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, the NOx absorbed in the NOx storage-reduction catalyst 3 is released within a short time, and the released NOx is released.
NOx can be prevented from being discharged into the atmosphere due to reduction of x.

Since the NOx storage-reduction catalyst 3 has a function of a reduction catalyst, the NOx released from the NOx storage-reduction catalyst 3 is reduced even if the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio. You. However, when the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NOx is gradually released from the NOx storage-reduction catalyst 3, so that all the NOx absorbed by the NOx storage-reduction catalyst 3 is released. Takes a long time.

If the air-fuel ratio of the inflowing exhaust gas is made lower, the NOx is released from the NOx storage reduction catalyst 3 even if the air-fuel ratio of the inflowing exhaust gas is lean. Therefore, in order to release NOx from the NOx storage reduction catalyst 3, the oxygen concentration in the inflowing exhaust gas should be reduced.

Next, the urea selective reduction catalyst 4
The selective reduction is performed by adding urea to the catalyst. The NOx catalyst mentioned here can be exemplified by a zeolite catalyst containing an oxide of a transition element and / or a rare earth oxide in the fourth, fifth and sixth cycles. Particularly preferably, T ₂ is added to Al ₂ O ₃ .
A catalyst supporting i and V can be exemplified.

When an aqueous urea solution is added to the catalyst,
At a predetermined exhaust temperature, nitrogen oxides in the exhaust are reduced according to the following reaction formula.

(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ ^X + CO ₂ (1) 4NH ₃ ^X + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2) The NOx storage reduction catalyst 3 and the urea selective reduction described above. In this embodiment, a NOx sensor 5 is provided in the first exhaust passage on the upstream side of the NOx storage-reduction catalyst 3 and the urea selective reduction catalyst 4 so that the catalyst 4 functions. A urea addition control valve 6 is provided in the second exhaust passage on the upstream side of the urea selective reduction catalyst.

Further, a catalyst-input gas temperature sensor 7 is disposed immediately upstream of the NOx storage reduction catalyst 3.
An ammonia sensor 8 is provided downstream of the NOx storage-reduction catalyst 3.
Is arranged.

The NOx sensor 5, the urea addition control valve 6, the catalyst-containing gas temperature sensor 7, and the ammonia sensor 8 are each electrically connected to a control unit (ECU) 9 composed of a computer. Further, although not shown, a speed sensor for detecting the engine speed is provided, and this sensor is also connected to the control device (ECU) 9.

The urea addition control valve 6 has a pump 10
And a reducing agent storage tank 12 for storing a reducing agent via a pressure regulator 11. The urea aqueous solution as a reducing agent pumped up from the reducing agent storage tank 12 by the pump 10 is pressurized by the pressure regulator 11 and supplies the urea aqueous solution from the urea addition control valve 6 to the second exhaust passage 2b.

The reducing agent to be supplied may be not an aqueous solution but a powder or a gas. Further, a reducing agent remaining amount sensor 13 is provided in the reducing agent storage tank 12. This is constituted by a liquid level sensor or the like. Further, a canister 14 is connected to the reducing agent storage tank 12 so that the reducing agent gasified in the reducing agent storage tank 12 is returned to the intake system of the internal combustion engine.

Based on the information from the above-described sensors and the like, the state of each catalyst, and thus the operating state of the internal combustion engine, is detected. Operating state detecting means 15 for detecting the operating state of the internal combustion engine from data input from these sensors and the like is realized on a computer of the control device (ECU) 9. Further, according to the detected operating state, the urea addition control valve 6 issues a urea addition command to the urea addition control valve 6, and the urea addition amount control means 16 for controlling the addition amount also includes the control device (E
CU) 9. When urea is added by the urea addition amount control means 16, a reducing agent indicator 17 for indicating to the driver that urea is being added is provided on a meter panel 18 or the like.

The NOx sensor 5 detects the NOx concentration in the exhaust gas passing through the NOx occlusion reduction type catalyst 3, that is, the NOx concentration in the gas entering the urea selective reduction catalyst 4. The urea addition amount control means 16 obtains the NOx amount discharged from the internal combustion engine based on the NOx concentration detected by the NOx sensor 5 and the air amount detected by the air flow meter 19 provided in the intake system. There is added urea amount determining means (not shown) for estimating the amount of urea to be added to the urea selective reduction catalyst 4 from the amount, and instructs to add an amount of urea according to the estimated value.

Here, in order to estimate the amount of urea, a map in which the relationship between the detected amount of NOx and the amount of urea to be added is predetermined may be stored in the ROM. It should be noted that, instead of the NOx sensor 5, the accelerator opening, the fuel injection amount, the engine speed, the EGR amount by the EGR control device, etc.
The x amount may be estimated. Further, the intake air amount of the internal combustion engine may be determined by other means instead of the detection by the air flow meter 19, for example, by a throttle opening.

The catalyst-containing gas temperature sensor 7 functions as catalyst temperature detection means for detecting the temperature of the exhaust gas flowing into the NOx storage reduction catalyst 3, and determines the activation state of the urea selective reduction catalyst 4 from this temperature. be able to. When the temperature of the gas entering the catalyst is low, the purification capacity of the catalyst is low, and the urea addition amount control means 16 reduces the urea addition amount. The relationship between the temperature of the gas entering the catalyst (catalyst temperature) and the amount of urea added is stored in the ROM in advance as a map.

The ammonia sensor 8 is used for correcting the amount of urea added. That is, detecting ammonia by the ammonia sensor 8 downstream of the urea selective reduction catalyst 4 means that the added urea is too much more than the NOx amount. Therefore, a feedback control unit is provided which feeds back the detected amount of ammonia detected by the ammonia sensor 8 to the urea addition amount control unit 16 and corrects the amount of urea to be added to an appropriate target value. This control means is also realized on a computer of the control device (ECU) 9 as a part of the urea addition amount control means 16.

Hereinafter, the exhaust gas purification control according to this embodiment will be described. When the internal combustion engine is operated, fuel is burned in the cylinder to discharge exhaust gas, and the discharged gas flows through the exhaust pipe 2 and flows through the first exhaust passage 2a through the NOx storage reduction catalyst 3. Through a muffler (not shown), the gas is discharged to the atmosphere. A part of the exhaust gas is supplied to the second exhaust passage 2.
The fuel gas returns to the first exhaust passage 2a via the urea selective reduction catalyst 4 via b, passes through a muffler (not shown) via the NOx storage reduction catalyst 3, and is discharged to the atmosphere.

First, the exhaust gas that has passed through the first exhaust passage 2a is subjected to NOx storage and reduction in the NOx storage reduction type catalyst 3 according to the above-described principle, whereby exhaust gas is purified. That is, when NOx is released from the NOx storage reduction catalyst 3, the air-fuel ratio of the inflowing exhaust gas is made rich to reduce the released NOx in the NOx storage reduction catalyst 3.

On the other hand, the exhaust gas passing through the second exhaust passage 2b is purified by the urea selective reduction catalyst 4. The urea selective reduction catalyst 4 functions in a high-load, high-speed engine operation region beyond the purification region of the NOx storage-reduction catalyst 3, so that the region as wide as possible beyond the purification region of the NOx storage-reduction catalyst 3 can be used. It is possible to purify exhaust gas at the same time.

The urea addition amount control means 16 issues a urea addition command to the urea addition control valve 6 in response to the detection of the operation state by the operation state detection means 15. An aqueous urea solution is injected from the urea addition control valve 6, whereby the exhaust gas is purified according to the above-described principle.

The amount of the exhaust gas flowing through the second exhaust passage 2b is smaller than that of the first exhaust passage 2a, and has a lower flow rate, so that the added urea does not flow in the exhaust gas flow. , Are dispersed throughout the exhaust gas. As a result, it is sufficiently dispersed also in the urea selective reduction catalyst 4.

This is particularly effective when the exhaust gas is at a low temperature. During this time, the NOx sensor 5 detects the concentration of NOx discharged from the internal combustion engine, and in response to the detected value, the urea addition amount control means 16 of the control unit (ECU) 9 controls the NOx concentration and the intake to the internal combustion engine. The amount of NOx exhausted from the internal combustion engine is determined from the amount of air, the amount of urea to be added to the urea selective reduction catalyst 4 is estimated from the value, and the amount of urea is added according to the estimated value. To the urea addition control valve 6.

Further, the temperature of the gas entering the urea selective reduction catalyst 4 is measured by the catalyst entering gas temperature sensor 7, and the urea addition amount control means 16 of the control unit (ECU) 9 Increase or decrease the amount of urea added.

Further, the ammonia sensor 8 detects the concentration of ammonia in the exhaust gas passing through the urea selective reduction catalyst 4, and receives this detected value,
The feedback control means in (1) corrects the added urea amount in a direction in which the ammonia concentration in the exhaust gas passing through the urea selective reduction catalyst 4 decreases.

In this way, the NOx storage reduction catalyst 3
The exhaust gas purification is performed by the NOx storage reduction catalyst 3 and the urea selective reduction catalyst 4. The complementary relationship between the NOx storage reduction catalyst 3 and the urea selective reduction catalyst 4 is shown in FIG. FIG. 4A shows a purifiable region by the NOx storage reduction catalyst 3, and FIG. 4B shows a purifiable region by the urea selective reduction catalyst 4.

FIG. 5 shows the relationship between the exhaust gas temperature and the purification rate in the NOx storage reduction catalyst 3 and the urea selective reduction catalyst 4. FIG. 5A shows a purifiable region by the NOx storage reduction catalyst 3, and FIG. 5B shows a purifiable region by the urea selective reduction catalyst 4. As is clear from FIG. 5, it is understood that the NOx occlusion reduction type catalyst 3 functions in a region where the exhaust gas temperature is low, and the urea selective reduction catalyst 4 functions in a region where the exhaust gas temperature is high.

In this embodiment, the urea selective reduction catalyst is disposed in the second exhaust passage. However, instead of the urea selective reduction catalyst, an HC-added catalyst or NO for injecting fuel as a reducing agent is used.
x A selective reduction catalyst may be provided.

<Embodiment 2> Next, another embodiment will be described with reference to FIG. 6, in the configuration shown in the first embodiment, the urea selective reduction catalyst 4 and the urea addition control valve 6
And a heating means 21 provided between them. Heating means 2
By providing 1 in the second exhaust passage 2b having a slow exhaust gas flow, the exhaust gas can be efficiently heated. Further, the urea saturation upper limit of the exhaust gas is increased by the heating, so that more urea can be dispersed, and the activation by the heating of the catalyst, that is, the exhaust gas purification rate can be improved.

<Embodiment 3> As shown in FIG. 7, the exhaust gas purifying apparatus shown in this embodiment uses a plugging catalyst in the configuration shown in FIG.

The plugged catalyst has a structure in which the end face of the catalyst cell is packed, and is used by spraying a liquid or powdery reducing agent on the end face.

<Fourth Embodiment> As shown in FIG. 8, in this example, the flow rate of the exhaust gas flowing through the second exhaust passage is adjusted at the inlet and the outlet of the second exhaust passage connected to the first exhaust passage. The flow control valves 41 are provided respectively as flow control means.

The flow control valve 41 is driven by a command from the control device 9, and its control amount is determined, for example, when the operating state detecting means 15 determines that the engine is in cold operation.
In order to activate urea at a lower temperature, the flow control valve 41 is throttled when the temperature of the exhaust gas is low, so that the flow rate of the exhaust gas flowing through the second exhaust passage is reduced.

[Other Embodiments] In the above-described embodiment, the present invention is applied to the gasoline engine 1. However, it goes without saying that the present invention can be applied to a diesel engine. In the case of a diesel engine, the combustion in the combustion chamber is performed in a much leaner region than the stoichiometric condition, so that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 3 is very lean under a normal engine operating condition. , NOx is absorbed, but NOx is hardly released.

Therefore, in a diesel engine, for example, an exhaust gas recirculation device (a so-called EGR device) is introduced, and a large amount of exhaust gas recirculation gas is introduced into the combustion chamber to make the air-fuel ratio of the exhaust gas stoichiometric or rich. In addition, NOx absorbed by the catalyst can be released.

[0064]

According to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the first exhaust passage for discharging the exhaust gas of the lean burn internal combustion engine, and the first exhaust passage branched from the first exhaust passage. A second exhaust passage through which an amount of exhaust gas smaller than the amount of exhaust gas flowing through the second exhaust passage is provided. An exhaust gas purifying catalyst is disposed in the second exhaust passage. Since the reducing agent for the gas purification catalyst is supplied, it is sufficiently dispersed in the exhaust gas as compared with the case where the reducing agent is supplied into the first exhaust passage.

Further, when a urea selective reduction catalyst is provided in the second exhaust passage, if urea is added as an additive, in the second exhaust passage, when the urea is effectively dispersed, it is converted into a highly reactive ammonia as a reducing agent. Can be converted effectively. This means that urea is sufficiently dispersed even in a low temperature state in the second exhaust passage through which the exhaust gas flows slowly, and the reduction can be effectively performed.

Further, by providing heating means between the exhaust gas purifying catalyst and the reducing agent supply means, the upper limit of the exhaust gas saturation is increased by heating by the heating means, and more reducing agent is dispersed. Activation by heating the catalyst, that is, an improvement in the exhaust gas purification rate can be achieved. Therefore, it is more effective to disperse the reducing agent at a low temperature.

When a flow rate adjusting means for adjusting the flow rate of the exhaust gas flowing in the second exhaust passage is provided, the dispersion of the reducing agent in the second exhaust passage can be more effectively controlled.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
It is a schematic structure figure of an embodiment.

FIG. 2 is a diagram for explaining the NOx absorbing / releasing action of a storage reduction type NOx catalyst.

FIG. 3 Unburned HC in exhaust gas discharged from the engine,
FIG. 3 is a diagram schematically showing the concentrations of CO and oxygen.

FIG. 4 is a graph showing an exhaust gas purification region using a catalyst in relation to an engine speed and an engine load.

FIG. 5 is a diagram showing a relationship between an exhaust gas temperature and an exhaust gas purification rate.

FIG. 6 is a diagram showing a second embodiment.

FIG. 7 is a diagram showing a third embodiment.

FIG. 8 is a diagram showing a fourth embodiment.

[Explanation of symbols]

Reference Signs List 1 engine 2 exhaust pipe 2a first exhaust passage 2b second exhaust passage 3 storage reduction catalyst 4 urea selective reduction catalyst (exhaust purification catalyst) 5 NOx sensor 6 urea addition control valve (reducing agent supply means) 7 catalyst input gas temperature sensor Reference Signs List 8 ammonia sensor 9 control device (ECU) 10 pump 11 pressure regulator 12 reducing agent storage tank 13 reducing agent remaining amount sensor 14 canister 15 operating state detecting means 16 urea addition amount controlling means 17 reducing agent indicator 18 meter panel etc. 19 air flow meter 21 Heating means 41 Flow control valve (flow control means)

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Iwa ▲ saki ▼ ▲ English ▼ 2 Toyota Motor, Toyota City, Aichi Prefecture 1 Toyota Town F-term (reference) 3G091 AA02 AA11 AA17 AA18 AA24 AB05 AB06 BA03 BA14 CA03 CA12 CA13 CA16 CA17 CA27 CB02 CB08 DA01 DA02 DA05 DB10 DC01 EA01 EA05 EA07 EA17 EA22 EA33 FA02 FA04 FA09 FA12 FA13 FA14 FA17 FA18 FB02 FB10 FB11 FB12 FC04 FC05 FC07 GB01W GB01X GB02W GB03W GB04W GBXB GB03 GB06W GBX GB03 GB06 4D048 AA06 AA13 AA18 AB01 AB02 AC04 AC09 BA03Y BA07Y BA11Y BA13X BA14Y BA15Y BA18Y BA23Y BA30Y BA41Y CC26 CC32 CC46 CC52 CC61 CD08 DA01 DA02 DA05 DA06 DA08 DA09 DA10 EA04

Claims (8)

[Claims] 1. A first exhaust passage for discharging exhaust gas of a lean-burn internal combustion engine, and an amount of exhaust gas branched from the first exhaust passage and flowing through the first exhaust passage is smaller than the amount of exhaust gas. Flowing second
An exhaust passage, an exhaust gas purification catalyst provided in the second exhaust passage for purifying exhaust gas flowing in the second exhaust passage, and an exhaust gas purification catalyst provided in the second exhaust passage on an upstream side of the exhaust gas purification catalyst. Second reduction agent for exhaust gas purification catalyst
An exhaust gas purifying apparatus for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent into an exhaust passage. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a flow velocity of the exhaust gas flowing through the second exhaust passage is lower than a flow velocity of the exhaust gas flowing through the first exhaust passage. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising heating means between said exhaust gas purifying catalyst and said reducing agent supply means. 4. An end of the second exhaust passage is connected to the first exhaust passage, and a first exhaust passage downstream of the connection point is provided with a lean air-fuel ratio of exhaust gas discharged from the internal combustion engine. The internal combustion engine according to any one of claims 1 to 3, further comprising a NOx storage-reduction catalyst that stores NOx and releases and reduces the stored NOx when the oxygen concentration in the exhaust gas decreases. Exhaust purification equipment. 5. The exhaust gas purifying catalyst provided in the second exhaust passage is a selective reduction catalyst in which selective reduction is performed by adding a reducing agent.
An exhaust gas purification device for an internal combustion engine according to any one of the above. 6. An exhaust gas purifying catalyst provided in the second exhaust passage is an ammonia compound selective reduction catalyst in which selective reduction is performed by adding an ammonia compound, and the reducing agent supply means uses the ammonia compound as a reducing agent. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas is supplied. 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 6, wherein the ammonia compound is urea. 8. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising a flow rate adjusting means for adjusting a flow rate of the exhaust gas flowing in the second exhaust passage.