The present invention relates to an idling operation control apparatus for an internal combustion engine, more particularly to an idling operation control, apparatus for regulating fuel supply for every cylinder so as to minimize the dispersion of the output among the respective cylinders of a multiple cylinder engine and to assure the stable engine operation.
In the control of the amount of fuel injection in a multiple cylinder engine according to the prior art, the fuel injection amount is uniformly controlled for all the cylinders. Accordingly, the output of the respective cylinders is not equal due to differences within the manufacturing tolerance of the internal combustion engine and/or the fuel injection pump and the like.
In particular, non-uniform output among the cylinders causes striking degradation in the stability of the engine operation during the idling operation of the engine, and this in turn increases the amount of harmful components included in the exhaust gas, thus producing engine vibration. In addition, disadvantages such as noise are liable to be generated by the vibration of the engine.
In order to overcome the above disadvantages, there have been proposed various apparatuses for controlling the fuel to be injected into each cylinder of the engine by means of an individual cylinder control system.
The inventors have also been proposed an improved individual control system in which the system has a closed-loop system for controlling an average engine speed and a second closed-loop system for controlling the fuel to be injected into each cylinder of the engine and the second closed-loop system can selectively be used (U.S. patent application Ser. No. 779,222).
However, since the control constants in the first closed-loop system is set a constant in the proposed system regardless of whether or not the second closed-loop system is used, it sometimes occurs that the stability of the operation of the individual control system is lowered even further when the second closed-loop system is used.