Carburetor for an internal combustion engine

Claim 1

In a carburetor for an internal combustion engine having an ignition circuit with an ignition switch, an air cleaner, a main mixture circuit adapted to supply an air-fuel mixture to a carburetor induction passage for high-speed and heavy load operations of the engine, an idling and slow-running mixture circuit adapted to supply an air-fuel mixture to said carburetor induction passage for idling and light load operations of the engine, a throttle valve operatively disposed in said carburetor induction passage for controlling the quantity and air-fuel ratio of the mixture to be supplied to said engine, and a fuel supply reservoir which supplies fuel to said two mixture circuits, an auxiliary mixture supply control system which is operative during starting and warm-up operations of the engine to control the quantity and air-fuel ratio of an additional air-fuel mixture to be introduced into said carburetor induction passage in dependence on engine temperature to effect satisfactory starting and warm-up operations of the engine, said auxiliary fuel supply circuit leading from said fuel supply reservoir and communicating with said carburetor induction passage downstream of said throttle valve, and adapted to admit additional fuel thereinto, an auxiliary air supply circuit leading from said air cleaner and communicating with said carburetor induction passage downstream on said throttle valve and adapted to admit additional air thereinto, a needle valve element located in said auxiliary fuel supply circuit for controlling the quantity of said additional fuel to be introduced into said carburetor induction passage, an air control valve element located in said auxiliary air supply circuit for controlling the quantity of said additional air to be introduced into said carburetor induction passage, said needle valve element being operatively connected to said air control valve element and cooperating therewith, an actuating device for simultaneously moving said air control valve element and said needle valve element for thereby controlling the quantities of said additional fuel and said additional air to be introduced into said carburetor induction passage to provide an enriched air-fuel mixture, and an electronic control circuit electrically connected to said actuating means and including a source of d.c. voltage supply, a first switching transistor connected to said source of d.c. voltage supply and conductive when the ignition switch is switched on, a relay switch connected to said first switching transistor and closed when said first switching transistor is conductive, a thermostatic switch connected to said relay switch and closed when the engine temperature is below a first predetermined value, a second switching transistor connected to said source of d.c. voltage supply and to said relay switch and conductive when said ignition switch is switched on, a third switching transistor connected to said second switching transistor through said relay switch and said thermostatic switch, said third switching transistor being also connected to said actuating device, and a thermistor connected to said second transistor for varying the base potential of said third switching transistor in dependence on the engine temperature, whereby said actuating means is energized to a varying degree to correspondingly move said air control valve element and said needle valve element to different positions to control the quantities of said additional fuel and said additional air for thereby varying the air-fuel ratio of said additional air-fuel mixture in dependence on said engine temperature.