Carburetion

In combination with an air-fuel intake system for internal combustion engines comprising a downdraft carburetor which forms the only restricting device in the flow of the air-fuel mixture to the engine, said carburetor having an air-fuel outlet passage in its lower portion, a throttle valve disposed in said outlet passage for controlling the amount of finalized air-fuel mixture flowing to said engine, an intake manifold having an air-fuel passage therein which communicates with said carburetor outlet passage adapted to deliver said air-fuel mixture to said engine, and an intake valve and cooperating intake port disposed between said intake manifold passage and the combustion chamber of said engine, said intake manifold

• said upper inlet opening and said lower outlet passage in said air-fuel mixing chamber being substantially on the same vertical axis,
• said air-fuel mixing chamber being adapted in one mode to cause an upper horizontally and radially extending divergence of flow of said air-fuel mixture in said mixing chamber as said mixture enters said mixing chamber through said upper inlet opening with said mixture being caused to turn downwardly at the perimeter of said mixing chamber, and further causing said air-fuel mixture to converge below the upper diverging flow to exit through the lower outlet passage in said mixing chamber and into said intake manifold passage,
• said divergence and convergence flow pattern also being effective to cause any heavier liquid fuel particles to impinge on the upper floor surface of said lower horizontal wall member where said particles are evaporated from said surface,
• said divergence and convergence flow pattern being minimized in another mode during periods of acceleration when the throttle valve is suddenly moved to a more open position and the vacuum in said mixing chamber is caused to drop appreciably during said periods of acceleration, the flow path in said mixing chamber being substantially and unrestrictedly "straight through" between the inlet opening and the outlet passage of said mixing chamber,
• said air-fuel mixing chamber being substantially devoid of any members therein which would cause divergence and convergence passage and said intake valve port comprising a substantially unrestricted air-fuel passage from said carburetor outlet passage to said combustion chamber;
• wherein an air-fuel mixing chamber is provided in said intake manifold passage downstream of said throttle valve, said air-fuel mixing chamber including a substantially horizontally disposed upper wall member, said upper wall member having an air-fuel inlet opening which communicates with said carburetor air-fuel outlet passage, a substantially horizontally disposed lower wall member, said lower wall member having an air-fuel outlet passage communicating with said intake manifold air-fuel passage, said lower wall member having an upper floor surface which angles downwardly toward said air-fuel outlet passage for draining any residual liquid fuel into said intake manifold passage,
• means for joining said upper and lower wall members at their perimeters to form a leakproof housing which encompasses said air-fuel mixing chamber,
• said upper air-fuel inlet opening being substantially the same diameter as said outlet passage of said carburetor,
• said lower air-fuel outlet passage of said mixing chamber being substantially the same diameter as said carburetor outlet passage,
• the height of said mixing chamber between said upper inlet opening and said lower outlet passage of said mixing chamber being at least greater than the diameter of said upper inlet opening,
• the width of said air-fuel mixing chamber being at least greater than the diameter of said upper inlet opening of said air-fuel mixing chamber, flow pattern, and having unrestricted air-fuel passages therein, and being devoid of functional elements therein other than structural members which would tend to obstruct the natural divergence and convergence flow pattern in said air-fuel mixing chamber,
• the diameter of said upper inlet opening of said air-fuel mixing chamber being substantially the same size as the diameter of the carburetor air-fuel outlet passage downstream of said throttle valve, said upper inlet opening serving as a functional reference diameter, the horizontal cross-sectional area of said air-fuel mixing chamber at all horizontal levels being at least greater than the area of said reference diameter, and the height of said air-fuel mixing chamber between said inlet opening and said outlet passage being at least greater than said reference diameter.