PURPOSE: To reduce the number of times of a charge-up and to reduce the cost by amplifying in order the signal charge only of the specified cylinder meeting an expansion stroke via a switching means.
CONSTITUTION: The pressure detecting circuit of a six cylinder engine, for instance, is consisted of the pressure sensor 10 fitted to the ignition plug 11 of each cylinder, a pair of switching means 20, 30 having respectively the same number of switching elements 21W26, 31W36 with the number of cylinders, a charge amplifier 40, a changeover indicating device 60, etc. Then when No.1 cylinder meets an expansion stroke, the switching element 21 only is made conductive for the prescribed crank angle period of before and behind the compression upper dead point by the indication of the changeover indicating device 60 and the switching element 31 is shut off and the charge amplifier 40 amplifies the charge quantity caused by the pressure sensor 10 of No.1 cylinder. The pressure detection of all cylinders can be thus performed based on the ignition order with a single charge amplifier 40.
SAWAMOTO KUNIAKI
TAKEUCHI KIYOSHI
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