Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-02-19
2001-03-27
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...
C060S284000, C060S276000, C060S274000, C123S492000, C123S692000, C123S673000
Reexamination Certificate
active
06205776
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-42417 filed on Feb. 24, 1998 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air-fuel ratio control system for a multi-cylinder internal combustion engine and, more particularly, relates to an air-fuel ratio control system that is employed in a multi-cylinder internal combustion engine and is designed to reduce an amount of fuel injected into some cylinders during engine start and to activate a catalyst at an early stage.
2. Description of the Related Art
According to a conventionally employed control method intended to activate a catalyst at an early stage, fuel injection into some cylinders of a multi-cylinder internal combustion engine is stopped during a cold start thereof. Thus, exhaust gas that is discharged from those cylinders is supplied to a catalytic converter as secondary air, which exhibits a high concentration of oxygen and contains no fuel at all. As a result, the catalyst is urged to further promote reactions for oxidizing HC and CO.
For example, Japanese Patent Application Laid-Open No. HEI 7-83148 discloses an art intended to activate a catalyst at an early stage while maintaining good idling stability. According to this art, during cold start of a multi-cylinder internal combustion engine with a plurality of cylinders, some of those cylinders are subjected to rich-state operation wherein the air-fuel ratio assumes a value on the rich side, and other cylinders are subjected to lean-state operation wherein the air-fuel ratio assumes a value on the lean side. Lean-state operation of those cylinders is accomplished by either reducing an amount of is fuel injected thereto or completely stopping fuel injection thereto. While the ignition timing is retarded with respect to those cylinders which are to be subjected to rich-state operation, it is advanced with respect to those cylinders which are to be subjected to lean-state operation. These ignition timing correcting operations are alternately performed in each of the cylinders.
However, according to the air-fuel ratio control system for the multi-cylinder internal combustion engine disclosed in Japanese Patent Application Laid-Open No. HEI 7-83148, some of the cylinders undergo lean-state operation, which results in a drop in temperature of an exhaust system. Hence, it takes a long time for the catalyst to reach a temperature at which the catalyst starts to be activated (hereinafter referred to as an activation start temperature), that is, a temperature at which the catalyst temperature starts rising sharply (hereinafter referred to as a catalytic reaction promoting temperature).
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an air-fuel ratio control system that is installed in a multi-cylinder internal combustion engine and is capable of solving the aforementioned problem and activating a catalyst at an early stage by reducing an amount of fuel injected into some cylinders.
An air-fuel ratio control system according to the present invention is applied to a multi-cylinder internal combustion engine that has a plurality of cylinders. This air-fuel ratio control system is provided with an exhaust emission control catalyst disposed in an exhaust passage of the internal combustion engine, air-fuel ratio control means for controlling an air-fuel ratio of at least one of the plurality of cylinders, and catalyst temperature detection means for detecting a temperature of the exhaust emission control catalyst. If the temperature of the exhaust emission control catalyst is lower than a first predetermined temperature, the air-fuel ratio control means reduces an upper limit of an air fuel ratio for at least one cylinder of the plurality of cylinders, in comparison with an upper limit of the air-fuel ratio for the at least one cylinder used if the temperature of the exhaust emission control catalyst is equal to or higher than the first predetermined temperature. Furthermore, during cold start of the internal combustion engine, the air-fuel ratio control means achieves rich-state operation or stoichiometric operation in all the cylinders until the temperature of the exhaust emission control catalyst detected by the exhaust gas temperature sensor reaches a first predetermined temperature. After the temperature of the exhaust emission control catalyst exceeds the first predetermined temperature, the air-fuel ratio control means controls air-fuel ratios in the respective cylinders in such a manner as to achieve lean-state operation in a first portion of the plurality of cylinders and rich-state operation in a second portion of the plurality of cylinders.
In the aforementioned construction, an increased amount of fuel is injected into all the cylinders with a view to warming up the engine, until the exhaust emission control catalyst reaches an activation start temperature. After the exhaust emission control catalyst reaches the activation start temperature, the first portion of the plurality of cylinders start undergoing lean-state operation and the second portion of the plurality of cylinders start undergoing rich-state operation. Therefore, the time period required to complete a warm-up process of the exhaust emission control catalyst after engine start is shortened.
In the air-fuel ratio control system for the multi-cylinder internal combustion engine according to the present invention, the air-fuel ratio control means may gradually increase the number of cylinders included in the first portion of the plurality of cylinders in accordance with an operational state of the internal combustion engine.
In this case, when the exhaust emission control catalyst reaches the activation start temperature, the aforementioned air-fuel ratio control means gradually increases the number of cylinder included in the first portion of the plurality of cylinders, instead of simultaneously starting lean-state operation of a plurality of cylinders. Accordingly, the temperature of the exhaust emission control catalyst is prevented from dropping due to an abrupt inflow of secondary air therein, and the time period required to complete a warm-up process of the exhaust emission control catalyst after engine start is reduced.
In the air-fuel ratio control system for the multi-cylinder internal combustion engine according to the present invention, the air-fuel ratio control means may reduce the number of cylinders included in the first portion of the plurality of cylinders when the temperature of the exhaust emission control catalyst detected by the catalyst temperature detection means reaches a second predetermined temperature.
In this case, the aforementioned air-fuel ratio control means reduces the number of cylinders included in the first portion of the plurality of cylinders when the exhaust emission control catalyst reaches the second predetermined temperature, wherein maintaining the catalyst below the second predetermined temperature prevents the exhaust emission control catalyst from becoming overheated and deteriorating in performance. Thus, the exhaust emission control catalyst is prevented from becoming overheated and deteriorating in performance.
Further, the air-fuel ratio control system for the multi-cylinder internal combustion engine according to the present invention may be provided with fuel injection amount correction means for correcting an amount of fuel injected into cylinders under rich-state operation in accordance with an amount of air that is discharged from cylinders under lean-state operation, so that the air-fuel ratio of exhaust gas that is discharged from the internal combustion engine and flows into the exhaust emission control catalyst substantially maximizes a warm-up efficiency of the exhaust emission control catalyst.
In this case, by means of the aforementioned fuel injection amount correction means, exhaust gas with an air-fuel ratio that substantially m
Denion Thomas
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
Trieu Thai Ba
LandOfFree
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