Air-fuel ratio control system utilizing oxygen sensor and pressure differential sensor

A method for controlling the air-fuel ratio in an internal combustion engine having a combustion chamber arranged to operate at subatmospheric pressures, an intake manifold communication with the combustion chamber for providing a flow of air to the combustion chamber, adjustable throttle means in the intake manifold for controlling the flow of air through the intake manifold, a relative vacuum thereby being produced in the intake manifold and fuel pumping means for providing a flow of fuel into the intake manifold, and producing an air-fuel mixture, the method comprising the steps of:

• providing a flow of air through an air intake means which is spaced apart from the intake manifold, the ratio of the cross-sectional area of the intake manifold to that of the air intake means being K.sub.1, a constant;
• providing a flow of fuel into the air intake means to produced an air-fuel mixture the ratio of rate of flow of fuel into the intake manifold to that into the air intake being K.sub.2, a constant which is less than K.sub.1, as long as the relative vacuum in the intake manifold exceeds a preselected amount;
• continuously maintaining the air-fuel ratio in the air intake at a predetermined value;
• continuously equalizing the respective pressures in the air intake means and the intake manifold, and
• adjusting the ratio of the rate of flow of fuel into the intake manifold to that into the air intake to K.sub.3, a constant which is greater than K.sub.1 only when and as long as the relative vacuum in the intake is less than the preselected amount.

In combination, an air-fuel ratio control system and an internal combustion engine, the engine having a combustion chamber arranged to operate at subatmospheric pressures, an intake manifold communicating with the combustion chamber for providing a flow of air to the combustion chamber, adjustable throttle means in the intake manifold for controlling the flow of air through the intake manifold, a relative vacuum thereby being produced in the intake manifold, and fuel pumping means for providing a flow of fuel into the intake manifold and producing an air-fuel mixture, the control system comprising:

• an adjustable vacuum pump communicating with the combustion chamber, having an inlet orifice and being arranged to produce a subatmospheric pressure adjacent the inlet orifice;
• an air intake conduit, spaced-apart from the intake manifold, having a throttle means which is adjustable together with the throttle means in the intake manifold and communicating with the inlet orifice of the adjustable vacuum pump for producing a flow of air in the intake conduit, the ratio of the cross-sectional area of the intake manifold to that of the intake conduit being K.sub.1, a constant;
• second fuel pumping means for providing a flow of fuel into the intake conduit and producing an air-fuel mixture, the rate of flow of fuel into the intake manifold to that into the intake conduit being K.sub.2, a constant which is significantly less than K.sub.1, as long as the relative vacuum in the intake manifold exceeds a preselected amount;
• first control means for maintaining the air-fuel ratio of the mixture in the intake conduit at a predetermined value;
• second control means for continuously equalizing the respective pressures in the intake conduit and the intake manifold, and
• third fuel pumping means for increasing the ratio of the rate of flow of fuel into the intake manifold to that flowing into the intake conduit to K.sub.3, a constant which is significantly greater than K.sub.1, only when and as long as the relative vacuum in the intake manifold is less than the preselected amount.