Fuel control system for internal combustion engine

In a fuel control system for an internal combustion engine including an intake tube, an exhaust pipe, a throttle valve disposed within said intake tube for controlling the flow rate of the intake air flowing therethrough, means for delivering the fuel to be mixed with the intake air, and means for metering the fuel delivered, said fuel control system of the type further including a sensing vane disposed within said intake pipe in series to said throttle valve for rotation, the angle of which is dependent upon the flow rate of the intake air flowing through said intake tube, a fuel metering shaft attached to said sensing vane for rotation therewith and operatively coupled to said fuel metering means so that said fuel metering means may meter the fuel in quantity depending upon the angle of rotation of said metering shaft, a pressure-difference-responsive valve mechanism for detecting the pressure difference across said sensing vane and generating a first output signal representative of the difference between a predetermined reference pressure difference and said pressure difference across said sensing vane, and pressure-responsive actuating means operatively coupled to said sensing vane for controlling the angular position of said sensing vane in response to said first output signal in such a way that said pressure difference across said sensing vane may become substantially equal to said predetermined pressure difference, the improvement comprising:

• (a) an air-fuel ratio sensor means mounted in the exhaust pipe of the engine for sensing the air-fuel ratio based on the composition of the exhaust gases and generating a second output signal when the detected air-fuel ratio is deviated from a predetermined air-fuel ratio;
• and
• (b) means operatively coupled to said air-fuel ratio sensor means and said pressure-difference-responsive valve mechanism for changing said reference pressure difference to be set on and regulated by said pressure-difference-responsive valve mechanism in response to said second output signal, and wherein said pressure-difference-responsive valve mechanism comprises:
• (a) a housing,
• (b) a diaphragm disposed within said housing, defining within said housing a first pressure chamber in communication with said intake tube at the upstream side of said sensing vane and a second pressure chamber in communication with said intake tube at the downstream side of said sensing vane,
• (c) a negative pressure chamber provided with an intake port in communication with a negative pressure source of the engine, an outlet port through which the negative pressure in said negative pressure control chamber is transmitted as said first output signal to said pressure-responsive actuating means, and a valve port in communication with the surrounding atmosphere,
• (d) a control valve element fixed to said diaphragm for displacement therewith so as to control the opening area of said valve port, and
• (e) spring means disposed in said second pressure chamber for biasing said diaphragm toward said first pressure chamber;
• and
• said means for changing the reference pressure difference to be set on said pressure-difference-responsive valve mechanism comprises:
• (a) spring retaining means slidably disposed within said housing for receiving the end of said spring means remote from the end attached to said diaphragm, and
• (b) means for shifting said spring retaining means in response to said second output signal.