Catalyst warming apparatus of internal combustion engine

Details Catalyst warming apparatus of internal combustion engine Catalyst warming apparatus of internal combustion engine

2000-10-17

2002-11-19

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S286000, C060S324000, C422S183000

Reexamination Certificate

active

06481200

ABSTRACT:

BACKGROUND ART
The present invention generally relates to a technology for purifying the exhaust gas of internal combustion engines mounted in automobiles and the like, and in particular, relates to a technology for improving exhaust emissions by activating early on an exhaust-purifying catalyst disposed in an exhaust passage of the internal combustion engine.
In recent years, internal combustion engines mounted in automobiles and the like are required to remove harmful gas components contained in the exhaust gas before discharging the exhaust gas into the air. With respect to such requirement, there has been proposed a technology in which an exhaust-purifying catalyst that removes the harmful gas components contained in the exhaust gas is provided in an exhaust passage of an internal combustion engine.
As an exhaust-purifying catalyst described above, a wide variety of exhaust-purifying catalysts have been developed including, for example, a three-way catalyst, an NO
x
occlusion reduction catalyst, a selective reduction NO
x
catalyst, an oxidation catalyst, and an exhaust-purifying catalyst formed from an appropriate combination of these exhaust-purifying catalysts. These exhaust-purifying catalysts are generally capable of purifying the harmful gas components of the exhaust gas when activated at or higher than a predetermined temperature. Therefore, these exhaust-purifying catalysts cannot sufficiently purify the harmful gas components of the exhaust gas at a temperature less than the predetermined temperature, for example, when the internal combustion engine is cold-started.
Particularly, when the internal combustion engine is cold-started, combustion of the mixture is likely to become unstable due to low temperature within the cylinders. Therefore, the internal combustion engine discharges a relatively large quantity of unburned fuel components. If the exhaust-purifying catalyst is inactive, a large quantity of unburned fuel components is discharged into the air without being purified.
Accordingly, when the internal combustion engine is cold-started, it is important to activate the exhaust-purifying catalyst early on to suppress degradation of the exhaust emissions during and immediately after starting.
Regarding such a requirement, Japanese Patent No. 2710269 discloses a proposal for a catalyst-heating burner for a spark-ignition engine.
This catalyst-heating burner for the spark-ignition engine described in the Patent Publication of the above-mentioned patent includes an exhaust-purifying catalyst disposed in an exhaust passage of the internal combustion engine, and a combustor disposed in the exhaust passage upstream of the exhaust-purifying catalyst. When the internal combustion engine is warmed up after cold starting, half of the cylinders of the internal combustion engine are operated with a rich mixture to produce a combustible gas, and fuel injection to the other half is discontinued. The combustible gas discharged from the former half cylinders and the air discharged from the latter half cylinders are mixed and burned in the combustor, thereby quickly heating the exhaust-purifying catalyst.
The combustor used in such a catalyst-heating burner for the spark-ignition engine has a chamber for mixing and burning the combustible gas and the air. However, this chamber has a larger cross-sectional area as compared to that of the exhaust passage and a larger heat capacity. Therefore, the heat of the exhaust gas would be transferred to the combustor when the combustor is not in operation.
Then, when the heat of the exhaust gas is transferred to the combustor, the exhaust-purifying catalyst located downstream of the combustor is cooled by the low-temperature exhaust gas, resulted in a possibility of lowering the temperature of the exhaust-purifying catalyst to a temperature less than the activation temperature.
Moreover, the combustor of the above-described catalyst-heating burner for the spark ignition engine is located immediately downstream of the exhaust branch pipes. Therefore, the combustible mixture within the combustor is liable to be affected by pulsation of the exhaust gas, whereby combustion of the combustible mixture is liable to become unstable. Moreover, an atmosphere.temperature of the exhaust passage and the combustor becomes low immediately after cold-starting of the internal combustion engine, so that combustion of the combustible mixture is apt to become unstable.
Such unstable combustion of the combustible mixture in the combustor makes it difficult for the combustible mixture to be completely burned up, and, it is possible to result in rather increasing quantity of unburned fuel components to be discharged into the air.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing conventional problems. A first object of the present invention is to prevent an undesirable temperature decrease of an exhaust-purifying catalyst during normal operation and suppress degradation of exhaust emissions, by providing a technology capable of mixing the combustible gas and air, without providing a special combustion chamber dedicated for mixing the combustible gas and air, in an apparatus for warming an exhaust-purifying catalyst by burning the combustible mixture in an exhaust passage upstream of the exhaust-purifying catalyst.
A second object of the present invention is to prevent degradation of exhaust emissions caused by combustion of the combustible mixture and activate an exhaust-purifying catalyst early on, by providing a technology for stabilizing combustion of the combustible mixture in an apparatus for warming an exhaust-purifying catalyst by burning the combustible mixture in an exhaust passage upstream of the exhaust-purifying catalyst.
First, the present invention employs the following means to achieve the foregoing first object.
More specifically, a catalyst warming apparatus of an internal combustion engine according to the present invention includes: an exhaust passage connected to the internal combustion engine; a main exhaust-purifying catalyst provided in the exhaust passage for purifying exhaust gas flowing in the exhaust passage; a sub exhaust-purifying catalyst provided in the exhaust passage upstream of the main exhaust-purifying catalyst for purifying the exhaust gas flowing in the exhaust passage; ignition means provided in the exhaust passage between the main and sub exhaust-purifying catalysts; and combustible-component supply means for supplying fuel and air to the exhaust passage upstream of the sub exhaust-purifying catalyst.
In a catalyst warming apparatus constructed as described above, the combustible-component supply means and the ignition means are actuated when the main exhaust-purifying catalyst needs to be heated.
When the combustible-component supply means is actuated, fuel and air are supplied to the exhaust passage upstream of the sub exhaust-purifying catalyst and enter the sub exhaust-purifying catalyst.
The sub exhaust-purifying catalyst has a plurality of flow passages each having a much smaller diameter as compared to that of the exhaust passage. Therefore, the fuel and air flowing in such small flow passages are sufficiently mixed together. As a result, the gas flowing out from the sub exhaust-purifying catalyst is a combustible gas consisting of a pre-mixed fuel and air, namely, a combustible mixture.
The combustible mixture discharged from the sub exhaust-purifying catalyst is ignited for combustion by the ignition means disposed in the exhaust passage between the sub and main exhaust-purifying catalysts. Hot burned gas produced by the combustion of the combustible mixture enters the main exhaust-purifying catalyst located downstream of the ignition means. When the burned gas flows through the main exhaust-purifying catalyst, a large amount of heat is transferred from the burned gas to the main exhaust-purifying catalyst, whereby the main exhaust-purifying catalyst is rapidly warmed up to an activation temperature range.
Therefore, according to the catalyst warming apparatus of the internal

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