JP3775460B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to a technique for reliably preventing emission of harmful substances in exhaust gas.
[0002]
[Related background]
As a catalyst for purifying harmful substances (HC, CO, etc.) in exhaust gas at an early stage even at the time of cold start, a low-temperature active catalyst that becomes active at a low temperature of about 200 ° C. is known in “SAE Paper 980421”.
Thereby, even if the internal combustion engine is at a low temperature, the purification action is exhibited from an early point, and the exhaust gas characteristics in the cold state are better than those of the conventional three-way catalyst.
[0003]
[Problems to be solved by the invention]
By the way, the low-temperature active catalyst disclosed in the above-mentioned “SAE Paper 980421” has a characteristic that the heat-resistant temperature is low because the activation temperature is low. Therefore, if the low-temperature active catalyst is provided in the exhaust passage at a position under the floor of a conventionally arranged vehicle, there is a problem that heat deterioration is likely to occur due to high-temperature exhaust gas.
[0004]
Further, an air supply device for supplying secondary air is provided in the upstream exhaust passage of the low-temperature active catalyst, so that when oxidative removal of harmful substances is promoted, the upstream of the low-temperature active catalyst in the vehicle floor position is provided. In general, the exhaust pressure is large, and therefore, a high-pressure air pump is required as the air supply device, which is not preferable because the air supply device is large and expensive.
[0005]
The present invention has been made to solve such problems, and an object of the present invention is to purify exhaust gas of an internal combustion engine that is inexpensive and can reliably purify harmful substances in exhaust gas regardless of operating conditions. To provide an apparatus.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a low-temperature active catalyst capable of low-temperature activation is provided downstream of a muffler spaced apart from the internal combustion engine in the exhaust passage at the rear of the vehicle. Air supply means for supplying air (secondary air) is provided between the low-temperature active catalyst.
In the invention of claim 2, the low temperature active catalyst can purify harmful substances at a low temperature immediately after the cold start of the internal combustion engine. In the invention of claim 3, harmful substances can be purified at a low temperature of less than 200 ° C.
[0007]
Therefore, the thermal degradation of the low-temperature active catalyst is preferably prevented by being arranged away from the internal combustion engine, and the exhaust pressure is very close to the atmospheric pressure downstream of the muffler. Even if it is constituted by a small air pump, the secondary air can be sufficiently supplied to the low temperature active catalyst, and the low temperature active catalyst can function effectively with high reliability and high purification efficiency. Therefore, taking advantage of the characteristics of the low-temperature active catalyst that has a purification ability even at low temperatures, it is possible to reliably remove harmful substances (HC, CO, etc.) regardless of the operating state of the internal combustion engine, while having an inexpensive configuration.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle 1, and the configuration of the exhaust gas purification apparatus for an internal combustion engine according to the present invention based on the same figure. Will be explained.
[0009]
An engine body 2 (hereinafter simply referred to as an engine) 10 is mounted in the engine room 2 of the vehicle 1, and an exhaust pipe (from the exhaust port of the engine 10 through an exhaust manifold 12 and a small proximity three-way catalyst 14 ( An exhaust passage 16 extends rearward of the vehicle 1.
Here, as the engine 10, for example, a spark ignition gasoline engine is used, but it may be either an intake pipe injection type or an in-cylinder injection type.
[0010]
Further, since the proximity three-way catalyst 14 is close to the exhaust manifold 12, it is configured to be heated and activated relatively early.
Further, a NOx catalyst 20 is interposed as an underfloor catalyst in the exhaust pipe 16 at the back of the floor 4 of the vehicle 1. The NOx catalyst 20 is a catalyst capable of purifying NOx in exhaust gas, and a selective reduction type NOx catalyst and an occlusion type NOx catalyst are known. Note that the NOx catalyst 20 may have a function as a three-way catalyst, or may be a combination of various catalysts such as an HC trap and an electric heating catalyst.
[0011]
A muffler 24 that is a silencer is connected to the exhaust pipe 16 at the rear of the vehicle 1, and a low-temperature active three-way catalyst (low-temperature active catalyst) 30 is connected downstream of the muffler 24 in the exhaust direction. Yes.
As shown in the SAE paper 980421, the low temperature activated three-way catalyst 30 is a catalyst that can exhibit a sufficient exhaust purification ability even at low temperatures. Etc.) can be reliably purified.
[0012]
Further, an electric air pump (air supply means) 40 is provided so as to open at a portion between the muffler 24 of the exhaust pipe 16 and the low temperature active type three-way catalyst 30. The air pump 40 is mounted, for example, in the trunk room 3 and operates according to a drive command from an electronic control unit (ECU) 50. Note that the ECU 50 is connected to the battery 60. Specifically, the power from the battery 60 is supplied to the air pump 40 by turning on and off a relay in the ECU 50.
[0013]
Referring to FIG. 2, a cross-sectional view of the rear portion of the vehicle 1 is shown, and details of the configuration of the present invention will be described based on the same drawing.
As shown in the figure, an air intake 18 is opened in a portion between the muffler 24 downstream of the muffler 24 in the exhaust direction and the low-temperature active type three-way catalyst 30, and the air intake 18 includes One end of the rubber hose 42 is connected.
[0014]
The other end of the rubber hose 42 is connected to the output port 44 of the air pump 40 mounted in the trunk room 3 so as to penetrate the grommet 5 fitted in the hole formed in the floor 4. .
On the other hand, one end of a metal tube 48 is connected to the input port 46 of the air pump 40, and the other end of the metal tube 48 protrudes outside from a hole formed in the rear panel member 6. Specifically, the other end of the metal tube 48 is covered with the bumper fascia 7 and is positioned so that air in the atmosphere enters through a gap between the rear panel member 6 and the bumper fascia 7.
[0015]
Hereinafter, the operation and effect of the present invention of the exhaust emission control device configured as described above will be described.
As described above, the low temperature activated three-way catalyst 30 is activated at a low temperature. Therefore, even if the low-temperature activated three-way catalyst 30 is arranged at a position where the exhaust gas temperature is further downstream from the muffler 24 in this way, the exhaust gas will not be exhausted immediately after the cold start regardless of the operating state of the engine 1. It can be purified.
[0016]
Further, the three-way catalyst 30 that is active at the low temperature has a trade-off relationship that the heat-resistant temperature is low, and thus the low-temperature active three-way catalyst 30 is further downstream than the muffler 24. When arranged, there is an advantage that it is not exposed to high-temperature exhaust gas and thermal deterioration is prevented.
When the air pump 40 is driven by an instruction from the ECU 50 and air in the atmosphere is supplied as secondary air into the exhaust pipe 16 upstream of the low-temperature activated three-way catalyst 30 as indicated by a solid arrow, the secondary air is supplied. The catalytic capacity of the low-temperature active three-way catalyst 30 is further improved by the oxygen therein. That is, harmful substances (HC, CO, etc.) in the exhaust gas are oxidized more satisfactorily by the oxygen in the secondary air.
[0017]
By the way, the exhaust gas flowing through the exhaust pipe 16 becomes lower in pressure, that is, the exhaust pressure, as it goes downstream. Further, when passing through the muffler 24, the pressure is further reduced by the buffer member in the muffler 24, and is indicated by a white arrow. As shown schematically, the pressure is extremely close to atmospheric pressure.
From this, the air pump 40 may be a low-pressure, small-sized one, and secondary air can be introduced with a lightweight and inexpensive configuration.
[0018]
Further, since the exhaust pressure is very close to the atmospheric pressure, the exhaust gas hardly flows to the air pump 40 side. Therefore, it is not necessary to provide a check valve between the output port 44 of the air pump 40 and the air intake port 18, and it is sufficient to connect the output port 44 and the air intake port 18 with the rubber hose 42 in this way, This also makes it possible to configure the introduction of secondary air at a low cost.
[0019]
That is, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, the low-temperature active three-way catalyst 30 is used, and the low-temperature active three-way catalyst 30 is disposed downstream of the muffler 24, thereby In addition to preventing thermal deterioration, secondary air can be introduced at a low cost, and it becomes possible to realize an exhaust purification device having high reliability and high purification efficiency while suppressing cost. Harmful substances (HC, CO, etc.) can be purified very well and reliably from the cold start at a low temperature.
[0020]
In the above embodiment, the proximity three-way catalyst 14 is provided. However, if the low-temperature activated three-way catalyst 30 is arranged as described above, it is sufficiently harmful even if the proximity three-way catalyst 14 is not provided. The substance can be purified.
In the above embodiment, the low-temperature active three-way catalyst 30 is disposed downstream of the muffler 24. However, the low-temperature active catalyst is not limited to the three-way catalyst and has a NOx purification function. It may be a thing. In this case, the NOx catalyst 20 or the like, which is an underfloor catalyst, may not be provided as long as there is a sufficient installation space and a certain amount of capacity can be secured.
[0021]
Further, the low temperature active catalyst may be provided with a water trap catalyst or the like immediately upstream of the catalyst body.
In the above embodiment, the introduction of the secondary air is performed to promote the oxidation treatment of harmful substances in the exhaust gas. For example, to control the temperature of the low-temperature active catalyst, that is, the exhaust gas temperature. You may make it implement in order to adjust. Specifically, for example, a temperature sensor is provided upstream of the low-temperature active catalyst, the catalyst temperature is estimated from the output of the temperature sensor, and the secondary air is introduced so that the temperature efficiency of the low-temperature active catalyst is high. Alternatively, when the temperature of the low-temperature active catalyst is about to enter the temperature range of thermal degradation for some reason, a large amount of secondary air may be introduced to perform forced cooling.
[0022]
Moreover, you may make it employ | adopt an HC trap catalyst as an underfloor catalyst. However, this HC trap catalyst usually has a characteristic of releasing adsorbed HC at about 200 ° C. On the other hand, when the HC trap catalyst reaches about 200 ° C., at least the low-temperature active catalyst having an oxidation function is in an active state as described above. Therefore, when the HC trap catalyst is provided as the underfloor catalyst, the secondary air is introduced into the low temperature active catalyst in accordance with the time when HC is released from the HC trap catalyst. Thereby, even if HC is released from the HC trap catalyst, the released HC can be well and sufficiently purified on the low-temperature active catalyst.
[0023]
【The invention's effect】
As described above in detail, according to the exhaust gas purification apparatus for an internal combustion engine according to the first to third aspects of the present invention, the low temperature active catalyst can be purified with high reliability while preventing thermal deterioration and downsizing the air supply means. Utilizes the characteristics of a low-temperature active catalyst that can function efficiently and effectively, and has a purification ability even at low temperatures, and it is an inexpensive configuration that reliably ensures harmful substances (HC, CO, etc.) regardless of the operating state of the internal combustion engine Can be purified.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an exhaust gas purification apparatus for an internal combustion engine mounted on a vehicle according to the present invention.
FIG. 2 is a detailed cross-sectional view of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
[Explanation of symbols]
1 vehicle 10 engine (internal combustion engine)
16 Exhaust pipe (exhaust passage)
24 Muffler 30 Low-temperature active three-way catalyst (low-temperature active catalyst)
40 Air pump (air supply means)
42 Rubber hose 48 Metal tube 50 Electronic control unit (ECU)

Claims (3)

A muffler that is provided in the exhaust passage at a rear portion of the vehicle so as to be separated from the internal combustion engine, and suppresses exhaust noise;
A low-temperature active catalyst provided in an exhaust passage downstream of the muffler;
Air supply means for supplying air to an exhaust passage between the muffler and the low-temperature active catalyst;
An exhaust emission control device for an internal combustion engine, comprising: The exhaust purification apparatus for an internal combustion engine according to claim 1, wherein the low temperature active catalyst is capable of purifying harmful substances at a low temperature immediately after the internal combustion engine is cold started. The exhaust purification apparatus for an internal combustion engine according to claim 2, wherein the low temperature active catalyst is capable of purifying harmful substances at a low temperature of less than 200 ° C.

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