Fuel injection control system for a two-cycle engine

Claim 1

In an air-fuel ratio control system for a two-cycle engine having a cylinder with a scavenge port and an exhaust port, an intake passage communicating with said scavenge port, an exhaust passage communicating with said exhaust port, a fuel injector directly injecting an amount of fuel and air into said cylinder, a scavenge pump i said intake passage for supplying compressed air into said cylinder through said scavenge port as scavenge air, and a throttle valve disposed in a bypass, around said scavenge pump, of said intake passage, the improvement in the system comprising: a feedback control for controlling the air-fuel ratio comprising: means comprising an O 2 -sensor having a linear characteristic provided in said exhaust passage for detecting actual air-fuel ratio in exhaust gases in which a part of the scavenge air is induced and for generating a corresponding actual air-fuel ratio signal; an engine speed sensor for detecting engine speed and for producing a corresponding engine speed signal; an accelerator position sensor for detecting depressing degree of an accelerator pedal operatively connected with said throttle valve and for producing a corresponding degree signal; calculating means responsive to said engine speed and degree signals for deriving a desired air-fuel ratio stored as a function of said engine speed and said depressing degree of said accelerator pedal and for producing a corresponding desired air-fuel ratio signal; a comparator responsive to said actual air-fuel ratio signal and said desired air-fuel ratio signal for comparing said actual and said desired air-fuel ratios and for producing a correction signal when ratios are different in order to correct the amount of fuel or air to be injected into said cylinder; and control means responsive to said correction signal for controlling the amount of fuel or air injected into said cylinder so as to immediately converge said actual air-fuel ratio to said desired air-fuel ratio, thereby stabilizing optimum combustion of the fuel in said cylinder and improving emission of said exhaust gases and controlability of said engine.