Piston stroke discriminating apparatus for general-purpose engine

An apparatus for discriminating a piston stroke of a general-purpose internal combustion engine connectable to an operating machine to be used as a prime mover of the machine, the engine having a four-stroke operating cycle comprising intake, compression, expansion and exhaust and including a piston moveably accommodated in a cylinder to be connected to a crankshaft, comprising:

• a crank angle sensor that produces an output in response to rotation of the crankshaft at a predetermined crank angular position in synchronism with movement of the piston in the cylinder;
• an intake air temperature sensor that produces an output indicative of a temperature of intake air sucked in to the engine;
• an engine operation condition determiner that determines whether operation of the engine is under a stable condition;
• and
• a stroke discriminator that discriminates based on the intake air temperature detected by the intake air temperature sensor whether a stroke next to the predetermined crank angular position at which the crank angle sensor produces the output is the intake stroke or the expansion stroke, when the operation of the engine is determined to be under the stable condition.