1. Field of the Invention
This invention relates to an ignition system for an internal combustion engine, and more particularly to an ignition system for an internal combustion engine of the current interruption type.
2. Description of the Prior Art
Such an ignition system of the current interruption type in which a battery is used for its power supply is typically disclosed in, for example, Japanese Utility Model Publication No. 10812/1963. The conventional ignition system disclosed generally includes a transistor switch which is turned off at an ignition position of an internal combustion engine and constantly turned on at an position other than the ignition position, a pulse signal generating device for generating a pulse signal at the ignition position, and a circuit for turning off the transistor switch when the pulse signal generating device generates the pulse signal.
In the conventional ignition system constructed as described above, when the transistor switch is turned off, a high voltage is induced across a primary winding of the ignition coil. The so-induced high voltage is further increased by the ignition coil, so that a high voltage for ignition may be induced across a secondary winding of the ignition coil.
In the above-described construction of the conventional ignition system, the transistor switch which functions to control the primary current of the ignition coil is turned off for a short period of time at the ignition position, however, it is turned on at any position other than the ignition position. This causes the primary current flowing through the ignition coil to lead to the generation of much heat from the ignition coil, thereby increasing power consumption. In order to solve such a problem, an ignition system is proposed which includes a time control circuit for controlling the time for which a primary current flows from a battery to an ignition coil, as disclosed in, for example, U.S. Pat. No. 3,605,713. Unfortunately, such a conventional time control circuit is highly complicated to a degree sufficient to complicate a circuit structure of the ignition system. Thus, the conventional time control circuit is not suitable for use for an ignition system in which a decrease in the number of parts is required for a reduction of its manufacturing cost.
Also, the conventional ignition system is encountered with a problem that the ignition coil is overheated when the primary current continues to flow therethrough after a stop of the internal combustion engine. In view of such a problem, an ignition system is proposed which is adapted to interrupt the flow of a primary current through an ignition coil when an internal combustion engine is stopped, as disclosed in U.S. Pat. No. 3,884,208. However, the ignition system fails to control a time for which the primary current flows.