1. Field of the Invention
This invention relates to an internal combustion engine of the split type operable on less than all of the cylinders when the engine load is below a given value and, more particularly, to improvements in such an engine where engine operation is shifted to a full engine mode at a fast speed in response to rapid engine acceleration.
2. Description of the Prior Art
It is generally known that internal combustion engines demonstrate higher fuel combustion and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engine have already been proposed as automotive vehicle engines or the like. Such split type internal combustion engines include an active cylinder unit having at least one cylinder being always active and an inactive cylinder unit having at least one cylinder being inactive when the engine load is below a given value. At low load conditions, the flow of fuel to the inactive cylinder unit is cut off so that the engine operates only on the active cylinder unit for relatively increased active cylinder loads resulting in high fuel economy. In such an engine, control means is provided for shifting engine operation between its full and split engine modes in response to fuel injection pulses determined by the intake air flow rate indicative directly of engine load.
One difficulty with such an engine is that the speed which engine operation is shifted to its full engine mode from its split engine mode is too slow to achieve required engine output when rapid engine acceleration occurs. The reason for this is that the intake air flow rate does not increase with an increase in the degree of opening of the throttle valve during rapid acceleration but increases at a time after the throttle valve rapidly opens.