Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-12-27
2004-05-04
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...
C060S274000, C060S295000, C123S090110, C123S090150
Reexamination Certificate
active
06729126
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Applications No. 2000-078986 filed on Mar. 21, 2000 and No. 2000-107101 filed on Apr. 7, 2000, each including the specification, drawings and abstract, are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to an internal combustion engine installed on a vehicle, such as an automotive vehicle, and more particularly to an internal combustion engine which includes a variable valve control system capable of changing the opening and closing timing and/or a lift of each of intake and exhaust valves mounted in the engine.
2. Description of Related Art
Internal combustion engines installed on automobiles have recently been desired to purify exhaust gases emitted from the engines of harmful gaseous components such as hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) contained therein, before the exhaust gases are released into the atmosphere.
In order to meet the above-indicated demand, a known technique provides a three-way catalyst in the exhaust passage of the internal combustion engine. The three-way catalyst is arranged to reduce or remove hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) contained in exhaust gases that have a predetermined air/fuel ratio equal to or close to the stoichiometric air/fuel ratio. For controlling the air/fuel ratio of the exhaust gases to which the three-way catalyst is exposed, the air/fuel ratio of an air-fuel mixture to be introduced into the engine is controlled in a feedback fashion, so that the exhaust gases emitted from the engine have the predetermined air-fuel ratio, enabling the three-way catalyst to purify the exhaust gases of desired harmful gaseous components.
On the other hand, internal combustion engines of lean-burn type have been developed for use on automobiles, in an effort to reduce the required amount of consumption of the fuel by the engine. The lean-burn type engine is capable of burning a fuel-lean air-fuel mixture the air/fuel ratio of which is higher than the stoichiometric value.
The exhaust gases to be emitted from such lean-burn type internal combustion engines have a relatively high air/fuel ratio, and contain a relatively small amount of reducing components such as hydrocarbon (HC), so that nitrogen oxides (NOx) contained in the exhaust gases can not be sufficiently reduced or removed by the three-way catalyst alone.
In view of the above situation, it has been proposed to use an occlusion-reduction type NOx catalyst disposed in the exhaust passage of the internal combustion engine. The occlusion-reduction type NOx catalyst is adapted to occlude or absorb nitrogen oxides (NOx) contained in fuel-lean exhaust gases to which the NOx catalyst is exposed when the exhaust gases have a fuel-lean air/fuel ratio, and to release the occluded nitrogen oxides (NOx) when the exhaust gases have a stoichiometric or fuel-rich air/fuel ratio. The released nitrogen oxides (NOx) are reduced into nitrogen (N
2
) by reaction with the reducing agents or components such as hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gases.
With the NOx catalyst of the occlusion-reduction type disposed in the exhaust passage of the lean-burn internal combustion engine, nitrogen oxides (NOx) contained in the exhaust gases are occluded or absorbed in the NOx catalyst, when the fuel-lean exhaust gases are emitted as a result of combustion of a fuel-lean air-fuel mixture within the engine.
When the internal combustion engine is operated with a stoichiometric or fuel-rich air-fuel mixture having the stoichiometric air/fuel ratio or an air/fuel ratio lower than the stoichiometric value, and the exhaust gases emitted from the engine are stoichiometric or fuel-rich, the occlusion-reduction type NOx catalyst releases the occluded nitrogen oxides (NOx), and the released nitrogen oxides are reduced into nitrogen (N
2
).
The amount of nitrogen oxides (NOx) that can be occluded or stored in the occlusion-reduction type NOx catalyst is limited, and the capacity of the NOx catalyst to occlude nitrogen oxides (NOx) is saturated after a long period of operation of the engine with a fuel-lean air-fuel mixture, leading to a possibility of releasing the nitrogen oxides into the atmosphere without being reduced.
To avoid the above-indicated possibility, it has been practiced to perform so-called “rich spike” control when the NOx occlusion capacity of the occlusion-reduction type NOx catalyst is saturated during the lean-burn operation of the engine. In the “rich spike” control, the mode of operation of the engine is switched from the lean-burn mode to the rich-burn mode so that the NOx catalyst is exposed to fuel-rich exhaust gases having a relatively low air/fuel ratio.
However, merely increasing the amount of fuel injection into the engine undesirably causes a sudden increase of the output torque of the engine. To prevent this sudden increase, the fuel injection amount must be increased while the amount of air to be drawn into the engine is reduced. Accordingly, the rich spike control requires both of the fuel injector valve and the throttle valve to be controlled so as to increase the fuel injection amount while reducing the intake air amount.
The throttle valve is located some distance apart from the combustion chamber in each cylinder, and therefore the actual reduction of the air amount in the combustion chamber to a desired value requires a certain time after the moment at which the opening of the throttle valve was reduced. Thus, the switching of the engine operation mode from the lean-burn mode to the rich-burn mode requires a relatively long time due to a delayed control response of the throttle valve.
Further, the throttle valve and the fuel injector valve must be controlled again after the termination of the rich-spike control, in order to increase the air amount to be drawn into the cylinder of the engine and reduce the fuel amount to be injected into the cylinder. Like the switching of the engine operation upon initiation of the rich-spike control, the switching of the engine operation mode from the rich-burn mode to the lean-burn mode requires a relatively long time due to a delayed response of the throttle valve after the termination of the rich-spike control.
Thus, the rich-spike control requires a considerably long time due to the long periods of time required for switching the mode of operation of the engine operation between the lean-burn and rich-burn modes upon initiation and termination of the rich-spike control. This may cause undesired deterioration of the driveability of the vehicle and an unnecessary increase in the amount of consumption of the fuel.
Some of the lean-burn internal combustion engines such as diesel engines and lean-burn gasoline engines use the above-described NOx catalyst of the occlusion-reduction type or selective reduction type or other exhaust emission purifying device for purifying the exhaust gases emitted therefrom.
The selective reduction type NOx catalyst is a catalyst capable of reducing or decomposing nitrogen oxides (NOx) in an oxygen-rich atmosphere, in the presence of hydrocarbon (HC). For this selective reduction type NOx catalyst to be able to reduce or remove NOx, an appropriate amount of HC component is required. When the selective reduction type NOx catalyst is used to purify exhaust gases emitted from the above-indicated lean-burn internal combustion engines, the selective reduction type NOx catalyst needs to be supplied with the hydrocarbon (HC) component, since the amount of the HC component in the exhaust gases emitted during a normal lean-burn operation of the engine is extremely small. The supply of the HC component may be achieved by operating the engine with a fuel-rich or stoichiometric air-fuel mixture so that the exhaust gases emitted from the engine have the stoichiometric air/fuel ratio or an air/fuel ratio lower than the stoichiometric value.
As discussed above, the occlusion-reduction type NOx catalyst is a
Asanuma Takamitsu
Iwashita Yoshihiro
Katsumata Shouji
Nakanishi Kiyoshi
Nishida Hideyuki
Denion Thomas
Nguyen Tu M.
Toyota Jidosha & Kabushiki Kaisha
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