Ignition system

An ignition system comprising:

• a spark coil having a primary coil and a secondary coil which are magnetically connected to each other;
• a spark plug having a center electrode projected into a combustion chamber of an internal combustion engine and a ground electrode;
• and
• an ignition control means that produces discharge sparks in a gap between the center electrode and the ground electrode by conducting current supply to the primary coil, followed by applying a high voltage to the gap by cutting off the current supply to the primary coil;
• wherein
• the secondary coil has one end connected to a member having a reference potential via a low-voltage side path and the other end connected to the center electrode via the connecting path;
• the connecting path has an end connected to the secondary coil of the low-voltage side path or to a constant-voltage path which is grounded;
• the constant-voltage path is provided with a constant-voltage element that, when current is supplied to the primary coil, allows current supply to the constant-voltage path in a specified direction in which the polarity of an inductive voltage caused in the secondary coil turns from negative to positive, and, when the current supply to the primary coil is cut off and a voltage across the terminals of itself becomes equal to or larger than a specified voltage, allows current supply to the constant-voltage path in a direction opposite to the specified direction, while causing a voltage drop corresponding to the specified voltage;
• and
• the specified voltage is adjusted to a voltage higher than a discharge voltage at the time of initial use of the spark plug.