Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1998-08-04
2001-04-10
Chapman, Jeanette (Department: 3747)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S284000, C060S285000, C123S429000, C123S429000
Reexamination Certificate
active
06212879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control system for an internal combustion engine equipped with a catalytic converter for purifying exhaust gas from the engine, and, more particularly, to a fuel combustion control system for providing combustion stability when an ignition timing is retarded in order to rise the temperature of a catalyst of the catalytic converter during a cold start of the engine.
2. Description of the Related Art
Typically, there have been known various types of catalytic converters for purifying exhaust gas from an engine. Such an catalytic converter incorporates a three way catalyst to purify or significantly lower emission levels of unburnt hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and the like which can pose a health problem for the nation if uncontrolled. The three way catalyst is hard to present desired catalytic conversion efficiency if it is at lower temperatures and is, however, activated to present catalytic conversion efficiency when heated higher than a specific temperature sufficiently.
In this type of engine control system, it has been known to accelerate a rise in catalyst temperature by significantly retarding an ignition timing after top dead center to present desired catalytic conversion efficiency which is dictated by a temperature of engine cooling water while the catalyst has not yet attained an activated condition necessary. One of the engine control systems of this type is known from, for example, Japanese Unexamined Patent Publication No. 8-232645. This engine control system causes a large retard of an ignition timing to provide a large exhaust heat loss with an effect of rising an exhaust gas temperature, as a result of which the catalyst is quickly heated and activated sufficiently. Further, in order to prevent fuel combustion from being made unstable due to a retard of ignition timing, the engine control system is designed and adapted to improve ignitability and combustibility of an air-fuel mixture by generating a swirl of intake air in the combustion chamber, increasing a speed of an intake air stream or rising ignition energy.
The prior art engine control system has a necessity to have much scope for controlling an engine, so that the engine does not exceed a limit on necessary combustion stability. This imposes a restraint on retarding an ignition timing to its limit. In view of this, it is desired to improve activation of the catalyst by rising the temperature of exhaust gas.
As a practical matter, fuel is varies in quality such as heaviness to some extent, so that it is the possibility that the engine is deprived of combustion stability if a fuel of inferior ignitability and combustibility is used. When a limit to combustion stability is exceeded, the engine encounters an increase in vibration and a sharp increase in harmful emission level.
SUMMARY OF THE INVENTION
It is an objective of the invention to provide a fuel combustion control system which provides greater acceleration of a rise in catalyst temperature as well as ensuring combustion stability during a cold engine start by feedback controlling actual combustion within limits on combustion stability.
The foregoing object of the present invention is achieved by detecting a state of combustion based on fluctuations of engine speed and controlling engine operation according to the state of combustion. Specifically, the fuel combustion control system for an engine equipped with an exhaust gas purifying catalyst installed in an exhaust line for controlling acceleration of a rise in catalyst temperature by retarding an ignition timing from a point at which the engine produces maximum output torque while the exhaust gas purifying catalyst remains inactive or is not yet warmed sufficiently determines fluctuations of engine speed and controls fuel combustion by controlling at least one control value of an ignition timing, an air-fuel ratio and an air flow in an combustion chamber of the engine so as to maintain the fluctuations within limits on combustion stability while the catalyst remains inactive giving the ignition timing control priority. The fuel combustion control system incorporates a crankangle sensor to monitor a crankangular velocity based on which a fluctuation of engine speed is determined.
With the fuel combustion control system, when there is a demand for accelerating a rise in catalyst temperature while the catalyst is not yet warmed up nor activated, the control system determines fluctuations of engine speed based on crankangular velocity and performs fuel combustion control so as to maintain the fluctuations of engine speed within a limit on desired combustion stability. The fuel combustion control develops stable combustion by advancing an ignition timing, changing an air-fuel ratio toward the richer side, producing a swirl of intake air in the combustion chamber, or rising a velocity of intake air flow. Because the determination of an actual state of combustion based on fluctuations of engine speed is precise, an ignition timing can be advanced as large as possible so as to provide the greatest acceleration of a rise in catalyst temperature within limits on combustion stability as well as ensuring engine combustion stability. Further, the determination of an actual state of combustion based on fluctuations of engine speed also realizes greater acceleration of a rise in catalyst temperature as well as engine combustion stability even if there are changes in fuel ignitability and combustibility due to difference in fuel quality such as heaviness.
Giving the ignition timing control priority leads to satisfactory stabilization of fuel combustion. Concurrently, it is possible, for example, to deliver an air-fuel mixture leaner than a stoichiometric mixture, which is always desirable to rise a catalyst temperature with an effect of lowering the emission level of hydrocarbons (HC) and carbon monoxide (CO).
Variable air intake means for varying intake air quantity bypassing an engine throttle valve and admitted to the engine and idle detection means for detecting idling of the engine may be incorporated to the fuel combustion control system. In this instance, the fuel combustion control system controls an ignition timing to perform engine speed feedback control so as to attain a predetermined idle engine speed while the idle detection means detects idling of the engine, and interrupts the engine speed feedback control during the control of the variable air intake means to provide an increase in intake air quantity while performing acceleration of a rise in catalyst temperature when the idle detection means detects idling of the engine.
When acceleration of a rise in catalyst temperature by retarding an ignition timing is interrupted during idling, the engine speed is feedback controlled to a predetermined idle speed in quick response to a change in ignition timing. On the other hand, while acceleration of a rise in catalyst temperature by retarding an ignition timing is executed, a change in ignition timing is not caused, so that the engine is prevented from suffering unstable operation such as hunting. Further, the variable air intake means is controlled to provide an increase in intake air quantity so as to remain a desired air charging efficiency or a desired engine speed such as a predetermined idle speed. This prevents the engine from dropping its speed due to retarding an ignition timing. In this instance, the variable air intake means may be controlled to provide an increase in intake air quantity so that an engine speed ascends higher than the predetermined idle speed, with an effect of stabilizing engine operation and accelerating a rise in catalyst temperature due to an increase in exhaust heat energy.
The detection of fluctuations of engine speed and the combustion control are made for each cylinder. Generally, because there are variations of fuel injection quantity, combustion temperature, intake air flow and so forth among cylinders, if controlling fuel combustion for the cylinder
Ishihara Takahisa
Nishimura Eiji
Nishimura Hirofumi
Taga Junichi
Abrams Hugh A.
Chapman Jeanette
Mazda Motor Corporation
Sidley & Austin
Varma Sueh
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