Method of diagnosing glow plug and glow plug drive control device

A glow plug drive control device comprising:

• an operational control unit that performs drive control of a glow plug;
• and
• an energization drive circuit that energizes the glow plug according to the drive control of the glow plug performed by the operational control unit,
• wherein the operational control unit is configured to calculate a resistance value of the glow plug, when energization current and an applied voltage of the glow plug are acquired, as a latest resistance value on a basis of the energization current and the applied voltage, is configured to determine whether or not a rate of the change of the latest resistance value with respect to an initial resistance value of the glow plug exceeds a first predetermined value, is configured to determine whether or not the rate of the change of the latest resistance value with respect to a last resistance value that is a resistance value of the glow plug, which has been recently measured at a time of acquisition of the latest resistance value, exceeds a second predetermined value when determining that the rate of the change of the latest resistance value with respect to the initial resistance value of the glow plug exceeds the first predetermined value, and is configured to determine that the glow plug is in an abnormal degradation state when the rate of the change of the latest resistance value with respect to the last resistance value exceeds the second predetermined value and the rate of the change of the latest resistance value with respect to the initial resistance value of the glow plug exceeds the first predetermined value;
• wherein the operational control unit is adapted to determine that the glow plug is in a common degradation state when determining that the rate of the change of the latest resistance value with respect to the last resistance value is smaller than the second predetermined value.

A glow plug drive control device comprising:

• an operational control unit that performs drive control of a glow plug;
• and
• an energization drive circuit that energizes the glow plug according to the drive control of the glow plug performed by the operational control unit,
• wherein the operational control unit is configured to:
• calculate a resistance value of the glow plug, when energization current and an applied voltage of the glow plug are acquired, as a latest resistance value on a basis of the energization current and the applied voltage,
• determine that a degradation state of the glow plug is normal when the rate of the change of the latest resistance value with respect to an initial resistance value of the glow plug is smaller than a first predetermined value, and
• when the rate of the change of the latest resistance value with respect to the initial resistance value of the glow plug exceeds the first predetermined value, determine whether or not the rate of the change of the latest resistance value with respect to a last resistance value that is a resistance value of the glow plug, which has been recently measured at a time of acquisition of the latest resistance value, exceeds a second predetermined value, wherein the glow plug is in an abnormal degradation state when the rate of the change of the latest resistance value with respect to the last resistance value exceeds the second predetermined value, and wherein the glow plug is in a common degradation state when the rate of the change of the latest resistance value with respect to the last resistance value is smaller than the second predetermined value.