Electronic control system for air fuel ratio compensation in highlands

An electronic control system for high-ground compensation of the air fuel ratio of an air-fuel mixture for a gasoline engine of the type including a carburetor having a venturi and a throttle valve, the system comprising:

• a passage for supplying secondary air to a zone downstream of the throttle valve of said carburetor;
• an orifice device arranged across said passage and including an orifice having a variable opening;
• first electronic control means for regulating the orifice opening of said orifice device, the first electronic control means having a program recorded therein for controlling the orifice opening of the orifice device as a function of atmospheric pressure and engine temperature, the first electronic control means being responsive to an actual atmospheric pressure and an actual engine temperature to drive the orifice device in accordance with the program to adjust the orifice opening thereof, to thereby provide a reference pressure corresponding to said actual atmospheric pressure and said actual engine temperature in a zone downstream of said orifice device in said passage;
• a differential pressure detector for detecting the difference between said reference pressure and an actual pressure present in the venturi of said carburetor to produce a detected differential pressure signal;
• a valve arranged downstream of said orifice device in said passage for controlling the quantity of secondary air being supplied to said zone downstream of the throttle valve;
• and
• second electronic control means responsive to a differential pressure signal produced by said differential pressure detector to drive said secondary air supply control valve in accordance with a predetermined operating characteristic pattern, the second electronic control means being adapted to operate so that the difference between the base pressure and the actual pressure in the venturi becomes zero;
• whereby an air-fuel mixture obtained by the carburetor has an optimum air fuel ratio corresponding to the actual atmospheric pressure, engine temperature and engine load.