Abstract: A rotor of a crankshaft has protrusions. A timing sensor produces a rotation leading signal and a rotation trailing signal. A control unit measures a previous signal production interval and a present signal production interval based on the rotation signals, and determines that the rotor is in the forward rotation if an inequality of Tn/Tn−1≧K holds alternately but consecutively by four times on the side of the rotation trailing signal. As a result, at the time of manufacturing the rotor, the degree of freedom of design in the positional relations of the protrusions can be enhanced to control the ignition timing precisely and stably.

Abstract: A rotor has teeth on a rotor body. The teeth indicate fixed ignition timings for both of normal and reverse rotations. The teeth also indicate beginning positions of a calculation ignition sequence and an excess advanced ignition sequence for both of the normal and reverse rotations. One of the teeth is longer than the other teeth to provide a signal for determining a rotating direction based on a detected signal from a timing sensor. In a stable rotating condition, a countdown process begins when the beginning position located on the forward side in the rotating direction from the cylinder to be ignited is detected, and the spark plug of the target cylinder sparks when the counting process finished.

Abstract: A rotor of a crankshaft has protrusions. A timing sensor produces a rotation leading signal and a rotation trailing signal. A control unit measures a previous signal production interval and a present signal production interval based on the rotation signals, and determines that the rotor is in the forward rotation if an inequality of Tn/Tn−1≧K holds alternately but consecutively by four times on the side of the rotation trailing signal. As a result, at the time of manufacturing the rotor, the degree of freedom of design in the positional relations of the protrusions can be enhanced to control the ignition timing precisely and stably.

Abstract: A rotor has teeth on a rotor body. The teeth indicate fixed ignition timings for both of normal and reverse rotations. The teeth also indicate beginning positions of a calculation ignition sequence and an excess advanced ignition sequence for both of the normal and reverse rotations. One of the teeth is longer than the other teeth to provide a signal for determining a rotating direction based on a detected signal from a timing sensor. In a stable rotating condition, a countdown process begins when the beginning position located on the forward side in the rotating direction from the cylinder to be ignited is detected, and the spark plug of the target cylinder sparks when the counting process finished.