An ignition control system includes a spark plug including a cylindrical ground electrode, a cylindrical insulator having a protruding portion held inside the ground electrode and protruding toward a tip side the spark plug relative to the ground electrode, and a center electrode held inside the insulator and exposed from the insulator, an ignition coil including a primary coil and a secondary coil, and a primary current control unit performing creeping discharge control for generating a creeping discharge along a surface of the insulator, and air discharge transition control for stopping the creeping discharge occurring in the spark plug after the creeping discharge control is performed, and cutting off primary current after a discharge stop period ends, in one combustion cycle of the engine.

An ignition control system includes a spark plug including a cylindrical ground electrode, a cylindrical insulator having a protruding portion held inside the ground electrode and protruding toward a tip side the spark plug relative to the ground electrode, and a center electrode held inside the insulator and exposed from the insulator, an ignition coil including a primary coil and a secondary coil, and a primary current control unit performing creeping discharge control for generating a creeping discharge along a surface of the insulator, and air discharge transition control for stopping the creeping discharge occurring in the spark plug after the creeping discharge control is performed, and cutting off primary current after a discharge stop period ends, in one combustion cycle of the engine.

An internal combustion engine ignition system includes: a primary coil provided with a center tap; a third switching element that interrupts and conducts a primary current flowing from a voltage application unit to the center tap; a first switching element connected to one end on a first winding side; a second switching element connected to the other end on a second winding side; an ignition control circuit that controls operation of each of the above switching elements, thereby performing discharge generation control that allows an ignition plug to generate a spark discharge, and thereby interrupting and conducting the primary current flowing to the second winding to perform discharge maintenance control that maintains the spark discharge generated in the ignition plug; and a current circulation path that circulates a current flowing from the second winding to the second switching element.

An internal combustion engine ignition system includes: a primary coil provided with a center tap; a third switching element that interrupts and conducts a primary current flowing from a voltage application unit to the center tap; a first switching element connected to one end on a first winding side; a second switching element connected to the other end on a second winding side; an ignition control circuit that controls operation of each of the above switching elements, thereby performing discharge generation control that allows an ignition plug to generate a spark discharge, and thereby interrupting and conducting the primary current flowing to the second winding to perform discharge maintenance control that maintains the spark discharge generated in the ignition plug; and a current circulation path that circulates a current flowing from the second winding to the second switching element.

An internal combustion engine ignition system includes: a primary coil provided with a center tap; a third switching element that interrupts and conducts a primary current flowing from a voltage application unit to the center tap; a first switching element connected to one end on a first winding side; a second switching element connected to the other end on a second winding side; an ignition control circuit that controls operation of each of the above switching elements, thereby performing discharge generation control that allows an ignition plug to generate a spark discharge, and thereby interrupting and conducting the primary current flowing to the second winding to perform discharge maintenance control that maintains the spark discharge generated in the ignition plug; and a current circulation path that circulates a current flowing from the second winding to the second switching element.

An internal combustion engine ignition system includes: a primary coil provided with a center tap; a third switching element that interrupts and conducts a primary current flowing from a voltage application unit to the center tap; a first switching element connected to one end on a first winding side; a second switching element connected to the other end on a second winding side; an ignition control circuit that controls operation of each of the above switching elements, thereby performing discharge generation control that allows an ignition plug to generate a spark discharge, and thereby interrupting and conducting the primary current flowing to the second winding to perform discharge maintenance control that maintains the spark discharge generated in the ignition plug; and a current circulation path that circulates a current flowing from the second winding to the second switching element.

An ignition control system includes a spark plug including a cylindrical ground electrode, a cylindrical insulator having a protruding portion held inside the ground electrode and protruding toward a tip side the spark plug relative to the ground electrode, and a center electrode held inside the insulator and exposed from the insulator, an ignition coil including a primary coil and a secondary coil, and a primary current control unit performing creeping discharge control for generating a creeping discharge along a surface of the insulator, and air discharge transition control for stopping the creeping discharge occurring in the spark plug after the creeping discharge control is performed, and cutting off primary current after a discharge stop period ends, in one combustion cycle of the engine.

A piston of an internal combustion engine is provided and includes a piston skirt enclosing at least a portion of an underside of a piston crown. A cooling oil passageway is provided on the underside of the piston and extends from a first part to a second part of the underside, where the first part is closer than the second part to a fluid flow from a cooling oil source. The cooling oil passageway may include a main channel and a branch channel extending from the main channel at an angle.