This invention generally relates to a method and apparatus for controlling energizing interval of an ignition coil of an internal combustion engine, and more particularly, the present invention relates to such a method and apparatus for increasing the energizing interval during acceleration of the engine which is equipped with an electronic control device.
Generally speaking, conventional electronic control systems for internal combustion engines comprise various sensors, such as a rotational angle sensor, a reference position sensor, coolant temperature sensor, suction vacuum sensor, ambient air pressure sensor, acceleration sensor and the like, which detect the operating condition of the engine; a control unit for obtaining various amounts to be controlled, such as ignition timing, energizing interval of the ignition coil, fuel injecting interval, the amount of exhaust gas recirculation (EGR) and the like by using, for instance, a microcomputer, in accordance with the information from the sensors; and various actuators, such as an ignition device, an EGR control valve, a fuel injection device and the like, which control the operating condition of the engine in accordance with the control amounts from the control unit.
In the above-mentioned conventional electronic control system, the energizing interval of the ignition coil is determined by detecting the rotational speed of the engine crankshaft. Namely, the energizing interval decreases as the engine rpm increases. However, when the engine is accelerated, the actual energizing interval is apt to be shorter than a desired interval, as will be described hereinlater, in the conventional devices. Because of the shorter energizing interval, the ignition coil cannot produce a sufficient voltage for properly igniting the air/fuel mixture in the cylinders of the engine. Although it is theoretically possible to set a basic value of the energizing interval longer in advance so that the energizing interval during acceleration is sufficient, such a longer energizing interval may cause the final stage transistor and the ignition coil, both included in the ignition device, to generate undesirable heat, resulting in deterioration of these elements because an electric current flows through the transistor and the ignition coil for an interval longer than required during normal or steady operating condition of the engine.