Engine control unit operable with different clocks based on crank signal system operation

An engine control unit comprising:

• pulse interval measuring means for receiving a crank signal of a pulse train of a predetermined angle interval corresponding to rotation of a crankshaft of an engine and measuring a pulse interval;
• frequency multiplication signal generating means for generating frequency multiplication signals of an integer times a next pulse in accordance with the pulse interval measured by the pulse interval measuring means;
• a counter which operates in accordance with the frequency multiplication signals;
• failure detecting means for detecting a failure in a crank signal system which supplies the crank signal;
• switching means for switching the counter so as to be used as a free-run counter which operates in accordance with time clocks when the failure in the crank signal system is detected by the failure detecting means;
• and
• means for generating a control signal for controlling the engine in accordance with a value of the counter.