Fuel control system for internal combustion engine

Internal-combustion engines – Charge forming device – Fuel injection system

Reexamination Certificate

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Details

C123S435000, C123S490000

Reexamination Certificate

active

06199540

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a system for deciding the combustion state of each cylinder in an internal combustion engine, and a fuel control system which optimizes a fuel injection quantity while suppressing the combustion change of each cylinder after starting of engine and reduces a non-combustion composition in an engine exhaust gas.
Generally, a multi-cylinder engine having a fuel injection system has different combustion states due to different injection characteristics of fuel injection valves and different intake air distributions for the respective cylinders.
Particularly, when a cooled engine is started, in order to compensate for the attenuation of the vaporizing characteristic of fuel, a fuel injection quantity is increased according to the temperature of engine coolant. The quantity of fuel to be increased in starting of engine is set for a prescribed value for all cylinders relative to the cylinder having the poorest fuel contribution.
Therefore, a large quantity of incomplete combustive fuel is exhausted from a cylinder to which excessive fuel has been supplied when the engine is started, thus giving rise to a problem of air pollution.
In order to solve such a problem, it is necessary to control the distribution of fuel to be injected for each cylinder to supply an optimum quantity of injection fuel to each cylinder so that the combustion states of the respective cylinders are averaged and the fuel injection quantity set according to a coolant temperature and others is reduced within a range not deteriorating the combustion state.
In order to detect fuel distributed properly, means for directly measuring the combustion state of each cylinder is required. As an example thereof, a technique using an ion current is disclosed in JP-A-7-293306.
Such a combustion control technique for each cylinder (also referred to as cylinder-individual combustion control technique) is to control fuel for each cylinder on the basis of the comparison of an ion current output maximum value and an integrated value of each cylinder with a reference value so as to reduce the fuel injection quantity for each cylinder.
The above conventional cylinder-individual combustion control technique controls the fuel injection quantity for each cylinder by reducing a difference in the combustion state among the respective cylinders. Therefore, it can suppress engine vibration due to a difference in the combustion state among the respective cylinders. But it does not necessarily reduce the fuel injection quantity for all the cylinders and hence does not perform an optimum control.
Further, the above conventional cylinder-individual combustion control technique decides the combustion state on the basis of the maximum value and integrated value of the ion current acquired from the combustion state in a present cycle of each cylinder. However, the combustion state of each cylinder varies for each cycle. Therefore, the conventional control technique cannot provide a correct value of the combustion state only from the combustion state in the present cycle, thus making it impossible to make appropriate decision.
SUMMARY OF THE INVENTION
The present invention has been accomplished in order to solve such a problem.
The present invention intends to provide a fuel control system which corrects the fuel injection quantity for all cylinders and also for each cylinder so that the fuel injection quantity is reduced in average while the combustion change among the cylinders is suppressed, thereby reducing a quantity of exhaust gas. The present invention also intends to provide a fuel control system which can provide an appropriate combustion state even when the combustion state varies in each cycle by taking the combustion state in a cycle prior to a present cycle.
The fuel control system for an internal combustion engine according to the present invention comprises: a cylinder-individual fuel injection quantity correcting means for correcting the fuel quantity injection quantity in each cylinder so that the sum of fuel injection quantities to be supplied to the cylinders of the internal combustion engine having a plurality of cylinders decreases in each combustion cycle of each the cylinder and a difference between the combustion state value of the first cylinder of the internal combustion engine and that of the second cylinder thereof decreases; and a fuel injecting means for injecting into each cylinder the fuel injection quantity for each cylinder of the internal combustion engine corrected by the fuel injection quantity correcting means for each cylinder.
The fuel control system for an internal combustion engine according to the present invention comprises: a cylinder-common fuel injection quantity correcting means for each cylinder for correcting the fuel injection quantity to be supplied to each cylinder so that the sum of fuel quantity injection quantities to be supplied to the cylinders of the internal combustion engine having a plurality of cylinders varies in each combustion cycle of each the cylinder; a cylinder-individual fuel injection quantity correcting means for correcting the fuel quantity in each cylinder so that a difference in the combustion state value between the first cylinder of the internal combustion engine and that of the second cylinder thereof decreases; and a fuel injecting means for injecting into each cylinder the fuel injection quantity for each cylinder of the internal combustion engine corrected by the cylinder-individual fuel injection quantity correcting means and the cylinder-common fuel injection quantity correcting means, wherein the cylinder-common fuel injection quantity correcting means corrects the fuel injection quantity to be supplied to each the cylinder in accordance with the fuel injection quantity for each cylinder corrected by the cylinder-individual fuel injection quantity correcting means.
The cylinder-common fuel injection quantity correcting means changes the fuel injection quantity supplied to each the quantity by a degree-corresponding to the fuel injection quantity for each cylinder corrected by the cylinder-individual fuel injection quantity correcting means.
The fuel injection quantity supplied to each the cylinder for each combustion cycle of each cylinder is corrected in accordance with the environmental condition of the internal combustion engine.
The environmental condition for the internal combustion engine is at least one of a cooled water temperature of the internal combustion engine, intake air temperature, atmospheric pressure, battery, and fuel quantity supplied to the internal combustion engine.
The cylinder-individual fuel injection quantity correcting means comprises: a combustion state quantity computing means for computing the combustion state quantity for each cylinder from each combustion state of at least two cylinders of the internal combustion engine; and a combustion change quantity computing means for computing the combustion change quantity in each the cylinder on the basis of the combustion state quantity in a present cycle and a cycle prior to the present cycle computed by the combustion state quantity computing means, wherein the fuel injection quantity for each the cylinder is corrected so that a difference in the combustion change quantity among the cylinders computed by the combustion change quantity computing means decreases.
The fuel injecting means corrects the fuel injection quantity of a cylinder with a larger deviation from the average value of the combustion change quantities of the cylinders.
The fuel control system for an internal combustion engine according to the present invention comprises: a combustion state quantity computing means for computing the combustion state quantity of each cylinder from each combustion state of at least two cylinders of an internal combustion engine having a plurality of cylinders; and a combustion change quantity computing means for computing the combustion change quantity of each the cylinder on the basis of the combustion state quantities in a present

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