1. Field of the Invention
The present invention relates to an apparatus to control the ratio of air to fuel of the air-fuel mixture which is supplied to an internal combustion engine, and more particularly to an apparatus provided for controlling the amount of air supplied to the main system fuel passage and the slow system fuel passage of a carburetor for supplying an air-fuel mixture to an internal combustion engine by means of a single proportional control solenoid valve.
2. Description of the Prior Art
It is known to incorporate a catalytic converter have ternary catalytically active substances into the exhaust system of the internal combustion engine of an automobile in order to simultaneously reduce the injurious components of the exhaust gas, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). It is required to supply an air-fuel mixture of an air-fuel ratio corresponding to the stoichiometric air-fuel ratio into the cylinders of an internal combustion engine, since the maximum cleaning efficiency of the ternary catalytically active substances is attained when the exhaust gas is produced by the combustion of an air-fuel mixture of the stoichiometric air-fuel ratio. An air-fuel ratio controller to meet such a requirement is proposed, which includes a main system air-bleeding passage connected to the main system fuel passage connecting to the main jet of a carburetor, a slow system air-bleeding passage connected to the slow system fuel passage connecting to the slow system fuel supply port of the carburetor, and a main system proportional control solenoid valve for controlling the main air bleeder and a slow system proportional control solenoid valve for controlling the slow air bleeder, which are disposed within the main system air-bleeding passage and the slow system air-bleeding passage, respectively, and are adapted to be controlled by a control signal provided by converting the output signal of an oxygen sensor disposed within the exhaust passage of the engine by means of an electronic control unit. It is proposed to control the rate of air to be supplied to the main system fuel passage and to the slow system fuel passage through the main system air-bleeding passage and through the slow system air-bleeding passage, respectively, with an air-fuel ratio controller as described above, so that the air-fuel ratio of the air-fuel mixture which is supplied into the cylinders of an engine is controlled so as to be close to the stoichiometric air-fuel ratio.
However, heretofore known air-fuel ratio controllers of this type for carburetor are provided with individual proportional control solenoid valves in the main system air-bleeding passage and the slow system air-bleeding passage, respectively, and are adapted to control both proportional control solenoid valves simultaneously with the control signal of a single system provided by the control signal producing circuit of an electronic control unit. Accordingly, the electronic control unit is required to supply an electric current simultaneously to the main system and the slow system proportional control solenoid valves. Therefore, the electronic control unit is necessary to be capable of supplying an electric current twice as much as that to be supplied to a single solenoid. Thus such conventional air-fuel ratio controllers have a disadvantage that the control signal producing circuit of the electronic control unit must consist of elements which have superior current capacities.