Control apparatus for internal combustion engine

A control apparatus for an ignition system of an internal combustion engine, wherein the ignition system includes a spark coil having a primary coil and a secondary coil being electro-magnetically connected to the primary coil, and a spark plug that produces discharge sparks in between its center electrode and its ground electrode by applying a high voltage across both electrodes on the basis of the magnetic energy stored in the spark coil, comprising:

• one of two ends of the secondary coil is connected to the center electrode via a connecting path, while another end of the secondary coil is grounded via a low-voltage side path or connected to a member having a standard electric potential via a low-voltage side path;
• one of two ends of a constant-voltage path is connected to the connecting path, wherein another end of the constant-voltage path is grounded or connected to a secondary coil;
• and
• the constant-voltage path includes a constant-voltage element, wherein the constant-voltage element, in an occasion where current is supplied to the primary coil, allows current to flow through the constant-voltage path in a specified direction that permits the polarity of the inductive voltage generated in the secondary coil to turn from negative to positive, and, in an occasion where current supplied to the primary coil is cut off and the voltage applied across the terminals of the element becomes equal to or higher than a specified voltage, allows current to flow through the constant-voltage path in a direction opposite to the specified direction and decreases voltage corresponds to the level of the specified voltage;
• wherein
• the control apparatus further includes
• a current detecting means which detects a current passing through the constant-voltage path in the specified direction when current is supplied to the primary coil, and
• an open failure judging means which determines the occurrence of an open failure in the constant-voltage path on the basis of the fact that no current has been detected by the current detecting means when current is supplied to the primary coil.