JP2722982B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to an exhaust purifying apparatus for an internal combustion engine, in particular, to effectively removable exhaust purification apparatus NO _X in the exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art An example of this type of exhaust gas purifying apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of this publication is to connect a vessel containing an absorbent (catalyst) for absorbing NO _X in the presence of oxygen in an exhaust passage of a diesel engine, NO _X in the exhaust gas to the _the NO _X absorbent
Is absorbed, and when the NO _X absorption efficiency of the absorbent decreases, the inflow of exhaust gas into the container is shut off to supply a gaseous reducing agent into the container, thereby generating a reducing atmosphere to generate NO _X from the absorbent. together to release, it is to reduce and purify the released NO _X.

[0003]

Problems to be Solved by the Invention
6826 JP devices, shut off the flow of exhaust gas into the vessel using a shut-off valve provided in the container upstream housing the _the NO _X absorbent, thereby preventing the oxygen contained in the exhaust gas flowing by supplying the reducing agent into the container from, and the inside of the container to a reducing atmosphere _the NO _X absorbent of the NO _X emission reduction purification (hereinafter, referred to as "regeneration") is performed. Therefore, the apparatus of the above publication when reproducing operation of the NO _X absorbent during the engine operation, the exhaust must have caused to flow by bypassing the _the NO _X absorbent vessel, air in the NO _X in the exhaust gas without being purified The problem arises that is released.

In order to prevent this, a plurality of containers containing the NO _X absorbent are connected in parallel to the engine exhaust passage so that one NO _X absorbent can be regenerated while another NO _X absorbent is being regenerated. It is necessary to be able to purify the exhaust gas through the agent, and the provision of a plurality of containers results in an increase in the size of the device.

Further, after the shut-off valve is a relatively long period of time it is the open-valve state hold stop exhaust flowing into the container of the NO _X absorbent, to become intermittent operation state only briefly closed operation during the reproduction operation, There is a problem that a movable portion sticks due to fine particles or oil components in the exhaust gas, which easily causes malfunction. on the other hand,
In order to avoid the problem of the above-mentioned device enlargement, for example, NO
Instead of completely shutting off the exhaust flowing into the _X absorbent,
By the flow rate of the exhaust gas flowing by reducing to a predetermined flow rate to supply the reducing agent, it is also possible configurations so as to ensure the flow of the engine exhaust even during reproduction operation while using a single of the NO _X absorbent container .

However, during the regenerating operation of the NO _X absorbent in this case, the output of the engine for it is necessary to narrow the entire exhaust flow of an engine by a diaphragm valve or the like provided in the exhaust passage decreases rapidly, while the vehicle is traveling There is a problem that drivability deteriorates. The present invention has been made in view of the above circumstances, and has as its object to provide an exhaust gas purifying apparatus for an internal combustion engine, which can reduce the size of the apparatus, and can prevent the influence on the drivability of a vehicle and the occurrence of stick of a movable part. And

[0007]

According to the present invention, when the air-fuel ratio of the inflow exhaust gas, which is disposed in the engine exhaust passage, is lean, N
And _the NO _X absorbent concentration of oxygen absorbs O _X inflow exhaust emits the absorbed NO _X when reduced, a reducing agent to _the NO _X absorbent by blocking the flow of exhaust gas into the _the NO _X absorbent in the exhaust purification apparatus for an internal combustion engine having a reducing agent introduction means for reducing and purifying the released NO _X with the release of NO _X absorbed from the supply to _the NO _X absorbent, the NO _X
Absorber is supported on each of the channel wall surface of the carrier having a plurality of independent flow path through the exhaust performs absorption of the NO _X in the exhaust gas passing through the flow paths, the reducing agent introducing means the of the NO _X from _the NO _X absorbent wall of said plurality of exhaust flow path exhaust passage temporarily sequentially whole by performing blocking and supply of the reducing agent flowing into the exhaust by a portion of the flow path of the carrier There is provided an exhaust gas purification device for an internal combustion engine, which performs emission and reduction purification.

[0008]

[Action] reducing agent introducing means, for supplying blocking and reducing agent temporarily exhaust the only part of the channel inlet of the plurality of channels of the NO _X absorbent carrier. Exhaust flows through other unblocked flow paths because all the flow paths of the NO _X absorbent are not blocked at the same time, and NO _X in the exhaust is purified by the NO _X absorbent on the flow path wall. Is done. The reducing agent introducing means since the supply of blocking and reducing agent temporarily sequential exhaust by part of the flow passage, the regeneration of the NO _X absorbent of all the flow path walls after a certain amount of time to complete.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Figures 1 to 3 show an embodiment of an exhaust gas purifying apparatus of the present invention, an exhaust pipe of an engine 3 is not shown in FIG, 5 shows the carrier of the NO _X absorbent. _The NO _X absorbent carrier 5 in this embodiment is formed of metal, a heat-resistant material such as ceramic in a cylindrical shape, many fine exhaust passage 5b in the axial direction
Was provided, which is a monolithic carrier and a similar structure of the conventional catalysts, _the NO _X absorbent to be described later to the wall surface of the respective exhaust passage 5b is supported. In this embodiment, N
O _X absorbent carrier 5 is rotatably held about an axis in the exhaust pipe 3, and is rotated by a driving shaft 7 passing through the exhaust pipe wall.

Reference numeral 8 designates an appropriate type of variable speed motor such as a DC servo motor connected to the drive shaft 7, which rotates in response to a control signal from an engine control circuit (ECU) 20, which will be described later. It adapted to rotate the drive shaft 7 and _the NO _X absorbent carrier 5 at a rate. Reference numeral 11 denotes a reducing agent supply device that supplies a reducing agent to the NO _x absorbent carrier 5. The reducing agent supply device 11 includes a reducing agent supply unit 12 fixed to the inner surface of the exhaust pipe 3 and a reducing agent supply source 13.
And a flow control valve 14. In this example, hydrogen, a reducing gas such as carbon monoxide, propane,
Liquid or gaseous hydrocarbons such as propylene and butane can be used, and the reducing agent is a reducing agent supply source 13 such as a pressurized container.
The flow rate is adjusted by a flow control valve 14 that operates in response to a control signal from the ECU 20 and supplied to the supply unit 12.

[0011] As shown in FIG.
Has a sector covering a portion of the upstream-side end face 5a of the _X absorbent carrier 5, and the edge portion 12a at a portion facing the NO _X absorbent carrier 5 as shown in the cross section in FIG. 3, the edge 12a
A concave portion 12b surrounded by is formed, and the reducing agent is injected into the concave portion 12b through the fixed pipe 15. Also, the edge 12a is disposed while maintaining the upstream-side end surface 5a with a small gap of the NO _X absorbent carrier 5, the recess 12
b, and the flow of the reducing agent in the recess 12b into the exhaust pipe 3 is substantially prevented.

Therefore, the flow of the exhaust gas into the flow channel 5b of the carrier 5 at the portion covered by the reducing agent supply section 12 is cut off, and the reducing agent is supplied from the concave portion 12a. When the carrier 5 rotates, the reducing agent supply unit 12 sequentially covers the flow path 5b, and while the carrier 5 makes one rotation, the exhaust inflow of all the flow paths 5b is blocked and the reducing agent is supplied. In FIG. 2, reference numeral 16 denotes an exhaust gas temperature sensor disposed downstream of the NO _x absorbent carrier 5 for detecting the exhaust gas temperature.

In FIG. 2, reference numeral 20 denotes an engine control circuit (ECU). The ECU 20 has a CPU, RA
M, ROM, and a well-known digital computer having a configuration in which an input port and an output port are connected to each other by a bidirectional bus, and performs basic control such as fuel injection amount control of an engine. Such as the speed control of the valve and the opening control of the flow control valve 14 of the reducing agent supply device 11
Control of _X absorbent regeneration operation. For these controls, an input port of the ECU 20 is connected to the exhaust temperature sensor 16.
, An engine temperature, an accelerator opening, and other signals are also input from sensors (not shown).

[0014] Next, N of the NO _X absorbent for use in the present invention
O _X absorbing and releasing the operation will be explained. _The NO _X absorbent is used a supported layer, for example alumina or the like, the carrier layer, for example, potassium K, sodium Na, lithium Li, cesium C
Alkali metals such as s, barium Ba, calcium C
At least one selected from alkaline earths such as a, lanthanum La, and rare earths such as yttrium Y, and a noble metal such as platinum Pt are supported. In this embodiment, the wall surface of the flow paths 5b of the support 5 is supported layer such as alumina carrying the component is coated, to form a _the NO _X absorbent layer. This _the NO _X absorbent absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

The above-mentioned exhaust air-fuel ratio is defined as N
O _X absorbent upstream side of the exhaust passage and the engine combustion chamber is intended to mean the ratio of the total sum and the fuel respectively supplied amount of air in the intake passage or the like. Therefore, the fuel in the upstream side exhaust passage of the NO _X absorbent, the exhaust air-fuel ratio in the case of the reducing agent or air is not supplied is equal to the operating air-fuel ratio of the engine (air-fuel ratio in the combustion in the engine combustion chamber).

There is a part where the detailed mechanism of the above-mentioned absorption / release action is not clear. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, regarding this mechanism, platinum P
The case where t and barium Ba are supported will be described as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

That is, the inflow exhaust gas becomes considerably lean.
And the oxygen concentration in the inflow and outflow greatly increased, as shown in Fig. 4 (A).
These oxygen O_TwoIs O_Two ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, NO in the inflow exhaust gas is
This O on the surface of platinum Pt_Two ^-Or O^2-Reacts with N
O_Two(2NO + O_Two→ 2NO_Two ). Then generated
NO_TwoSome of the oxygen is oxidized on platinum Pt and
While being combined with barium oxide BaO while being absorbed by
As shown in (A), nitrate ion NO_Three ^-Absorbent in the form of
Spreads in. NO in this way_XIs NO_XIn the absorbent
Is absorbed by

Therefore, as long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent becomes NO ₂ Released from the absorbent in the form of That is, the oxygen concentration in the inflowing exhaust gas is NO _X is released from _the NO _X absorbent when lowered.

On the other hand, if reducing components such as HC and CO are present in the inflowing exhaust gas, these components become oxygen O ₂ on platinum Pt.
^- or it is reacted with oxide and O ^2-, lowering the oxygen concentration in the exhaust to consume oxygen in the exhaust. Further, NO ₂ released from the NO _X absorbent due to a decrease in the oxygen concentration in the exhaust gas is reduced by reacting with HC and CO as shown in FIG. 4 (B). When NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another.

[0020] That is, HC in the inflowing exhaust gas, CO, first O ₂ on the platinum Pt ^- immediately react with oxidized or O ^2-, and then on the platinum Pt O ₂ ^- or O ^2- is consumed the HC, NO _X released from the absorbent by CO is reduced even yet HC, any remaining CO is. In this embodiment, since the engine for combustion of lean air-fuel ratio is used, the air-fuel ratio of the normal passing through the flow path 5b of the NO _X absorbent carrier 5 during operation exhaust is lean, the passage 5b
NO _X absorbent of the wall to absorb the NO _X in the exhaust gas.

[0021] Then, NO _X absorbent carrier 5 is rotated by the motor 8, the exhaust gas inlet of the flow path 5b flows into the flow path 5b come to the position covered by the reducing agent supply unit 12 by the reducing agent supplying unit 12 The blocking agent is shut off, and the reducing agent supplied into the concave portion 12b flows into the flow path 5b. Therefore, the flow path 5b
The exhaust gas inside is replaced by a reducing agent from the inlet side, and the flow path 5
A significantly rich atmosphere is formed in b. _The NO _X absorbent in the passage 5b wall releases NO _X absorbed under the rich atmosphere, regeneration of the NO _X absorbent is carried out.

[0022] rotates and _the NO _X absorbent carrier 5 further flow path 5
When the inlet of b goes out of the reducing agent supply section 12, exhaust gas flows again into the flow path 5b, and the reducing agent in the flow path 5b is pushed out from the flow path outlet, so that the inside of the flow path 5b becomes lean and NO _X
The absorbent starts to absorb NO _X again in a regenerated state. In this embodiment, the rotational speed of the NO _X absorbent carrier 5 and the amount of the reducing agent supplied to the reducing agent supply unit 12 are set to values proportional to the NO _X emission amount of the engine. That is, the aforementioned EC
U20 is stored emissions of the NO _X from the engine per unit time in advance the engine load (accelerator opening) in the ROM as a function of engine speed, NO _X by the function of the accelerator opening and the rotational speed calculating the emissions, respectively are multiplied by certain coefficients and sets as the reducing agent supply amount from the rotational speed and the reducing agent supply device 11 of the NO _X absorbent carrier 5 in this so as to obtain the set value The speed of the variable speed motor 8 and the opening of the flow control valve 14 are adjusted.

[0023] As described above, the flow path 5b wall until regenerating operation is initiated by rotating the _the NO _X absorbent carrier 5 at a rate proportional to the NO _X emissions the engine NO _X
The amount of NO _X absorbed by the absorbent becomes substantially constant regardless of the operating conditions. Further, by setting the reducing agent supply amount to a value proportional to the NO _X emission amount of the engine (that is, a value proportional to the rotation speed of the NO _X absorbent carrier 5), the flow path 5 during the regeneration operation is reduced.
The amount of reducing agent supplied to _the NO _X absorbent in b wall becomes substantially constant regardless of the operating conditions, NO _X absorption of the NO _X absorbent, regardless of the playback condition is the operating condition such as the reducing agent supply amount It is kept at a certain optimal value.

[0024] In this embodiment, performs during engine operation and the rotation of the constantly _the NO _X absorbent carrier 5 and the supply of the reducing agent in principle. Further, ECU 20 is an exhaust temperature is monitored by the output of the exhaust gas temperature sensor 16, the exhaust gas temperature is below a predetermined value, i.e., when _the NO _X absorbent temperature is below the exhaust temperature is determined to be equal to or less than the activation temperature Stops the supply of the reducing agent to the NO _x absorbent, and prevents the excess reducing agent from being released to the atmosphere.

[0025] Thus, the movable portions such as _the NO _X absorbent carriers are always active, operation failure due stick of the moving part because member for intermittent operation of a long distance as in such a conventional shut-off valve is not present And the like are prevented from occurring. In the _the NO _X absorbent carrier 5 in this embodiment performs continuous rotation, but may be caused to intermittently rotate at relatively short intervals by a constant rotation angle instead of continuously rotating the _the NO _X absorbent carrier 5 .

In this embodiment, of the entire flow path of the NO _x absorbent carrier 5, a flow path of a fixed ratio is always opened in the exhaust pipe 3, and the exhaust flow is accompanied by the regeneration of the NO _x absorbent. since the road area does not vary, the occurrence of torque shock due to fluctuation of the engine output has been caused by the conventional _the nO _X absorbent opening and closing the exhaust throttle like shut-off valve at the time of reproduction can be prevented.

Further, in this embodiment, as described above, NO_X
Absorbent regeneration operation did not affect engine output
NO_XThe rotation speed of the absorbent carrier 5 is set to be large overall.
NO in short cycle_XRepeat the absorbent regeneration cycle
It can be returned. Generally NO_XAbsorbent is NO_XSucking
If the yield is large, it takes a long time to regenerate,
NO_XAbsorption capacity also tends to not recover sufficiently,
To perform the playback operation in a short cycle as described above
Than NO_XNO at early stage when absorption is low _XAbsorbent
Complete playback in a short time.
No_XIt is possible to completely restore the absorption capacity of the absorbent
It works.

Furthermore in addition to the above, to perform the regeneration of _the NO _X absorbent at a short period there is a great effect in the prevention of sulfur poisoning of the NO _X absorbent. In an engine using a fuel such as light oil having a relatively high sulfur content, exhaust gas contains a large amount of sulfur oxides.
For _X and be absorbed at all in the NO _X absorbent by the same mechanism to produce a BaSO ₄ in combination with BaO. This Ba
Since SO ₄ is a relatively stable compound, it is hardly decomposed once generated, and there is a problem that the absorption capacity of NO _X decreases when BaSO ₄ in the NO _X absorbent increases. To prevent the occurrence of sulfur poisoning performs reproduction operation of the NO _X absorbent before absorbed sulfate ions to the NO _X absorbent is combined with BaO to produce the stable BaSO _4, described above the sulfur oxides in the case of the NO _X similar mechanisms need to be released from _the NO _X absorbent. In this embodiment it is possible to reproduce of the NO _X absorbent at a short period as described above, it is possible to effectively prevent the occurrence of sulfur poisoning of the NO _X absorbent.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical scope of the present invention. For example, in the above-described embodiment, the variable speed motor 8
The NO _X and the absorbent carrier 5 driven to rotate, but the gear from the output shaft of the engine without using a variable speed motor, NO _X via a belt or the like at a rate proportional to the engine speed
A configuration in which the absorbent carrier 5 is driven to rotate is also possible.

In the above embodiment, the reducing agent supply unit 12
Is fixed and the NO _X absorbent carrier 5 is rotated. Similarly, the NO _X absorbent carrier 5 is fixed in the exhaust pipe 3 and the reducing agent supply unit 12 is rotated with respect to the NO _X absorbent carrier 5. It is also possible to adopt a configuration in which it is performed. In this case, for example, as shown in FIG. 5, the reducing agent supply unit 12 is driven to rotate using the drive shaft 7, and the reducing agent is supplied to the recess 12b from the reducing agent supply passage 18 provided in the drive shaft. At the same time, an annular member 19 that slides around the drive shaft is provided, and the reducing agent can be supplied to the reducing agent supply passage 18 from the fixed pipe via the member 19 and the radial inlet port 22 in the drive shaft 7. .

[0031]

Exhaust purification apparatus of the present invention exhibits, NO by which is adapted sequentially to supply the blocking and reducing agent in the exhaust for each part of the flow path of the NO _X absorbent carrier as described above _X
It is possible to prevent the problem of fluctuation of the engine output and generation of sticks of the movable member during the operation of regenerating the absorbent.
Further, continuously NO _X using a single of the NO _X absorbent carrier
Since the operation of regenerating the absorbent can be performed, the size of the device can be reduced, and there is an effect that the production on a vehicle is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a sectional view showing one embodiment of the present invention.

FIG. 3 is an enlarged view of a portion A in FIG. 2;

FIG. 4 is a view for explaining the NO _X absorbing / releasing action of the NO _X absorbent of the present invention.

FIG. 5 is a diagram illustrating another embodiment of the present invention.

[Explanation of symbols]

3 ... exhaust pipe 5 ... NO _X absorbent 5a ... upstream end surface 5b ... exhaust passage 7 ... drive shaft 8 ... motor 11 ... reducing agent supply device 12 ... reducing agent supply unit 13 ... reducing agent supply 14 ... flow control valve 16. Exhaust gas temperature sensor 20: Engine control circuit (ECU)

Claims (1)

(57) [Claims] 1. A and _the NO _X absorbent when the air-fuel ratio of the disposed engine exhaust passage inflow exhaust gas oxygen concentration of the inflowing exhaust absorbs NO _X when the lean releases the absorbed NO _X when lowered, the shut off the flow of exhaust gas into _the NO _X absorbent NO
N absorbed from supplying reducing agent to the _X absorbent _the NO _X absorbent
In the exhaust purification apparatus for an internal combustion engine having a reducing agent introduction means for reducing and purifying the released NO _X with the release of O _X, wherein _the NO _X absorbent carrier having a plurality of independent flow paths exhaust passes each is carried on the flow path wall surface, subjected to absorption of the NO _X in the exhaust gas passing through the respective flow path, wherein the reducing agent introducing means part of the flow to a temporary out of the plurality of exhaust flow path of the carrier the exhaust gas of the internal combustion engine, characterized by performing the release of the NO _X from _the NO _X absorbent sequential whole of the wall surface of the exhaust passage by performing blocking and supply of the reducing agent flowing into the exhaust by the road and reduce and purify Purification device.