Spark ignition timing control system for internal combustion engine

Claim 1

A spark ignition timing control system for an internal combustion engine adapted for combustioning with a blended fuel composed of more than one mutually different fuels, comprising: first sensor means for monitoring a preselected basic engine operating parameters to produce a first sensor signal representative of the monitored engine operating condition; second sensor means for monitoring concentration of a specific one of fuels in the blended fuel to produce a specific fuel concentration indicative second sensor signal; third sensor means for monitoring variation of internal pressure in an engine cylinder to produce a third sensor signal indicative of the monitored internal pressure; fourth means for deriving a basic fuel advance angle on the basis of said fist sensor signal; fifth means for deriving a first correction value on the basis of said third sensor signal; sixth means for deriving a second correction value on the basis of the concentration of the specific fuel, said specific fuel concentration normally corresponding to said second sensor signal value; seventh means for correcting said basic fuel advance angle with said first and second correction values for deriving a spark advance angle to control the spark ignition timing; and eighth means for detecting lag period between spark ignition and occurrence of the maximum pressure in said engine cylinder to predict concentration of the specific fuel, and comparing the predicted specific fuel concentration with the specific fuel concentration represented by said second sensor signal for detecting failure of said second sensor means on the basis of the difference therebetween, said eighth means replacing said specific fuel concentration represented by said second sensor signal with a given value for derivation of said second correction value.