Ignition device

An ignition device comprising:

• a spark plug that generates a plasma discharge between a pair of discharge electrodes for igniting a combustible mixture in a combustion chamber of an internal combustion engine;
• an ignition coil having a primary coil and a secondary coil that applies a voltage between the pair of discharge electrodes of the spark plug by the secondary coil;
• a measurement value detecting section that detects at least one measurement value among a primary current flowing through the primary coil, a primary voltage applied to the primary coil, a secondary current flowing through the ignition plug, and a secondary voltage applied to the spark plug;
• an electrical breakdown determiner that determines whether or not a discharge between the pair of discharge electrodes has become an electrical breakdown state based on the measurement value detected by the measurement value detecting section;
• an AC voltage applying section that applies an AC voltage of a first predetermined frequency, which causes voltage resonance in a circuit including the spark plug and the secondary coil, in the primary coil;
• and
• a first changing section that changes the frequency of the AC voltage outputted by the AC voltage applying section to a second predetermined frequency that is configured to maintain the electrical breakdown state, and is lower in frequency than the first predetermined frequency when a determination has been made by the electrical breakdown determiner that the discharge has become the electrical breakdown state, wherein,
• the ignition device includes an elongation state determiner that determines whether or not the discharge in an elongated state of which the discharge is elongated based on the measurement value detected by the measurement value detector under a condition that the discharge is determined by the electrical breakdown determination section to have become the electrical breakdown state;
• the AC voltage applying section applies the AC voltage of the first predetermined frequency to the primary coil under a condition that the elongation state determiner determines that the discharge is not in the elongated state;
• and
• the first changing section changes the frequency of the AC voltage to the second predetermined frequency under a condition that the elongation state determiner determines that the discharge is in the elongated state.

An ignition device comprising:

• a spark plug that generates a plasma discharge between a pair of discharge electrodes for igniting a combustible mixture in a combustion chamber of an internal combustion engine;
• an ignition coil having a primary coil and a secondary coil that applies a voltage between the pair of discharge electrodes of the spark plug by the secondary coil;
• a measurement value detecting section that detects at least one measurement value among a primary current flowing through the primary coil, a primary voltage applied to the primary coil, a secondary current flowing through the ignition plug, and a secondary voltage applied to the spark plug;
• an electrical breakdown determiner that determines whether or not a discharge between the pair of discharge electrodes has become an electrical breakdown state based on the measurement value detected by the measurement value detecting section;
• an AC voltage applying section that applies an AC voltage of a first predetermined frequency, which causes voltage resonance in a circuit including the spark plug and the secondary coil, in the primary coil;
• and
• a first changing section that changes the frequency of the AC voltage outputted by the AC voltage applying section to a second predetermined frequency that is configured to maintain the electrical breakdown state, and is lower in frequency than the first predetermined frequency when a determination has been made by the electrical breakdown determiner that the discharge has become the electrical breakdown state, wherein,
• the ignition device includes an elongation state determiner that determines whether or not the discharge in an elongated state of which the discharge is elongated based on the measurement value detected by the measurement value detector under a condition that the discharge is determined by the electrical breakdown determination section to have become the electrical breakdown state;
• a second changing section that changes the frequency of the AC voltage outputted by the AC voltage applying section to a third predetermined frequency that is configured to maintain the electrical breakdown state, and is higher in frequency than the first predetermined frequency when a determination has been made under a condition that the elongation state determiner determines that the discharge is not in the elongated state;
• and
• the first changing section changes the frequency of the AC voltage to the second predetermined frequency under a condition that the elongation state determiner determines that the discharge is in the elongated state.