Air-fuel ratio control apparatus

An air-fuel ratio control apparatus for use in an internal combustion engine having a fixed Venturi type carburetor, an exhaust conduit and an exhaust emission control device including a ternary catalyst, said carburetor including a primary air suction conduit having mounted therein a choke valve, a primary fixed Venturi and a primary throttle valve adapted to be operated by a driver, a secondary air suction conduit having mounted therein a secondary throttle valve adapted to open when the negative pressure introduced into the engine increases, a fuel bowl, a main fuel supply passage for supplying fuel from said fuel bowl into the air in said primary fixed Venturi, a low speed fuel supply passage for supplying fuel from said fuel bowl into the air in the vicinity of said primary throttle valve, and a power valve for increasing the volume of fuel supplied to said main fuel supply passage from said fuel bowl when the negative pressure introduced into the engine decreases, said air-fuel ratio control apparatus comprising:

• means provided in said exhaust conduit for detecting the concentration of one constituent of exhaust emissions;
• first fuel control means for effecting control of the rate of fuel flowing through said main fuel supply passage;
• second fuel control means for effecting control of the rate of fuel flowing through said low speed fuel supply passage;
• and
• electric circuit means which inputs a signal from said detecting means and outputs a common signal for controlling said first and second fuel control means;
• said first fuel control means and said second fuel control means being constructed in such a manner that the region of the air-fuel ratios that can be controlled thereby for the low engine speed range is substantially equal to the region of the air-fuel ratios that can be controlled thereby for the intermediate engine speed range, wherein said first fuel control means comprises an air passage communicating with said main fuel supply passage, and a first electromagnetic valve for controlling the flow rate of air passing through said air passage, and said second fuel control means comprises an air passage communicating with said low speed fuel supply passage, and a second electromagnetic valve for controlling the flow rate of air passing through said air passage, wherein said first electromagnetic valve and said second electromagnetic valve each comprise an on-off electromagnetic valve for opening and closing the respective air passage, and wherein said electric circuit means comprises a control circuit which outputs to each of said electromagnetic valves voltage pulses of a square wave form having a duty ratio consistent with a signal from said detecting means, further comprising:
• first switch means combined with said choke valve for detecting the movement of the choke valve toward a closed position in an amount which is greater than a predetermined value;
• second switch means combined with said secondary throttle valve for detecting the movement of the secondary throttle valve toward an open position in an amount which is greater than a predetermined value;
• and
• third switch means combined with said power valve for detecting the movement of the power valve toward an open position in an amount which is greater than a predetermined value;
• and
• wherein said electric circuit means further comprises:
• a circuit which outputs voltage pulses of a swuare wave form having a predetermined duty ratio;
• and
• a selector circuit for selectively connecting one of said constant duty ratio square wave voltage pulse generating circuit and said control circuit with each of said electromagnets;
• said selector circuit being connected to said switch means in a manner to connect said control means with said electromagnets when said switch means all remain inoperative and to connect said constant duty ratio square wave voltage pulse generating circuit with said electromagnets when at least one of said switch means is rendered operative.

An air-fuel ratio control apparatus for use in an internal combustion engine having a fixed Venturi type carburetor and an exhaust conduit, said carburetor including an air suction conduit, a throttle valve, a fixed Venturi, a fuel bowl, a main fuel supply passage for supplying fuel from said fuel bowl into the air in the fixed Venturi, and a low speed fuel supply passage for supplying fuel from said fuel bowl into the air in the vicinity of said throttle valve, said air-fuel ratio control apparatus comprising:

• detector means provided in said exhaust conduit for detecting the concentration of one constituent of exhaust emissions;
• first fuel control means for effecting control of the flow rate of the fuel through said main fuel supply passage;
• second fuel control means for effecting control of the flow rate of the fuel through said low speed fuel supply passage;
• switch means for detecting the condition of operation of said carburetor;
• and
• electric circuit means which inputs an output signal from said detector means and an output signal from said switch means and which outputs one of a square wave form signal having a duty ratio which is a function of the output signal from said detector means and a square wave form signal having a constant duty ratio, which is arbitrarily selected with regard to said detector means, to said first fuel control means and said second fuel control means depending on said output signal from said switch means.

An air-fuel ratio control apparatus for use in an internal combustion engine having a fixed Venturi type carburetor, an exhaust conduit, and an exhaust emission control device including a ternary catalyst, said carburetor including a primary air suction conduit having mounted therein a choke valve, a primary fixed Venturi and a primary throttle valve adapted to be operated by a driver, a fuel bowl, a primary main fuel passage for supplying fuel from said fuel bowl into the air in said fixed Venturi, a primary low speed fuel passage for supplying fuel from said fuel bowl into the air in the vicinity of said primary throttle valve, a secondary air suction conduit having mounted therein a secondary fixed Venturi and a secondary throttle valve adapted to open when the negative pressure introduced into the engine increases, a secondary main fuel passage for supplying fuel from said fuel bowl into the air in said secondary fixed Venturi, a secondary low speed fuel passage for supplying fuel from said fuel bowl into the air in the vicinity of said secondary throttle valve, and a power valve for increasing the volume of fuel supplied from said fuel bowl to said primary main fuel passage when the negative pressure introduced into the engine decreases, said air-fuel ratio control apparatus comprising:

• detector means provided in said exhaust conduit for detecting the concentration of one consituent of exhaust emissions;
• first fuel control means for effecting control of the flow rate of the fuel through said primary main fuel passage;
• second fuel control means for effecting control of the flow rate of the fuel through said primary low speed fuel passage;
• switch means for detecting whether or not the displacement of a movable member has reached a predetermined value, the displacement of said movable member varying depending on the condition of operation of said carburetor;
• and
• electric circuit means which inputs an output signal from said detector means and an output signal from said switch means and which outputs, to said first fuel control means and said second fuel control means, a square wave form signal having a duty ratio consistent with the output signal from said detector means when the output signal from said switch means is below a predetermined value and a swuare wave form signal having a constant duty ratio, which is arbitrarily selected with respect to the output signal from said detector means, when the output signal from said switch means has reached said predetermined value.