Ignition device for internal combustion engine

An ignition device of an internal combustion engine comprising:

• an ignition coil having a primary coil through which a primary current flows and a secondary coil in which a secondary current is produced with a change in the primary current;
• an ignition plug to which a secondary voltage generated at the secondary coil is applied to produce a discharge;
• and
• an ignition control unit that controls ignition operation of the ignition plug,
• wherein
• the ignition control unit includes:
• a secondary voltage detecting unit that detects the secondary voltage;
• a secondary current adjusting unit that adjusts, in each cycle, an amount of the secondary current after initiating the discharge;
• a discharge extension detecting unit that detects an amount of extension of the discharge;
• and
• a short determination unit that determines whether a discharge-short has occurred based on the secondary voltage detected by the secondary voltage detecting unit,
• the ignition control unit is configured to control, in each cycle, the secondary current adjusting unit to repeatedly perform a first step that decreases the secondary current when the extension amount detected by the discharge extension detecting unit is a predetermined extension amount or more, and a second step that increases the secondary current when the short determination unit determines that a discharge-short has occurred;
• and
• the ignition control unit is configured to decrease, in the first step, the secondary current while keeping the secondary current higher than a predetermined lower current limit.