Engine control system

Claim 1

An engine control system for controlling an engine control value, at which an internal combustion engine is operated, according to a grade of gasoline delivered into said internal combustion engine, said control system comprising: a knock sensor for detecting knockings caused in said internal combustion engine; engine operating condition detecting means for detecting if an engine operating condition, over a predetermined engine load, falls in a first operating zone for knocking detection ranging under a predetermined engine speed or in a second operating zone for knocking detection ranging over said predetermined engine speed; grade determining means for determining, only when said engine operating condition detecting means detects an engine operating condition in said first operating zone, if gasoline delivered in said internal combustion engine has a high grade or a low grade, based on frequency levels of knockings continually detected by said knock sensor; first control value changing means for setting said engine control value to a first standard engine control value suitable for gasoline having a high grade and changing said engine control value from said first standard control value every time said knock sensor detects knockings, when said engine operating condition detecting means detects an engine operating condition in said first operating zone; and second control value changing means for setting said engine control value to a second standard engine control value suitable for gasoline having a low grade when said engine operating condition detecting means detects an engine operating condition in said second operating zone, and when said knock sensor detects knockings within a predetermined period from a transition of said engine operating condition to said first operating zone.