Spark ignited internal combustion engines

In a spark ignited engine employing exhaust gas recirculation and stratification of the recirculated exhaust gas, and having at least one cylinder accommodating a piston, at least one inlet port cooperating with an inlet valve for introducing air into said cylinder, a fuel supply for introducing fuel into said cylinder, and at least one exhaust port cooperating with an exhaust valve for discharging exhaust gas from said cylinder, wherein the improvement comprises:

• an exhaust gas recirculation duct connecting said exhaust port to the first inlet port;
• first valve means located at the juncture of said exhaust gas recirculation duct and said first inlet port, and having a first valve state and a second valve state;
• said valve means being operable in its first valve state, at low engine loads, to introduce solely recirculated exhaust gas through said first inlet port into said cylinder during an induction stroke of said piston, and being operable in its second valve state, at high engine loads, to introduce air through said first inlet port into said cylinder during an induction stroke of said piston;
• the introduction of air through said first inlet port occurring at a time which does not overlap with that during which exhaust gas is recirculated therethrough;
• a second inlet port cooperating with a second inlet valve communicating with said cylinder;
• second valve means operatively associated with said second inlet port for controlling the introduction of air into said cylinder through said second inlet port during an induction stroke of said piston;
• and
• said fuel supply being operative to permit fuel to be introduced into said second inlet port.

A method of employing exhaust gas recirculation and stratification of the recirculated exhaust gas in a spark ignited engine having at least one cylinder accommodating a piston, a first inlet port cooperating with a first inlet valve for introducing air into said cylinder, a second inlet port cooperating with a second inlet valve communicating with said cylinder, the first and second inlet ports being of the tumbling type whereby gas flowing in through said inlet ports swirls within a respective portion of said cylinder about an axis substantially perpendicular to the axis of said cylinder, a fuel supply for introducing fuel into said cylinder, and at least one exhaust port cooperating with an exhaust valve for discharging exhaust gas from said cylinder, comprising the steps of:

• introducing solely recirculated exhaust gas into said cylinder through said first inlet port during an induction stroke of said piston, at low engine load;
• introducing air into said cylinder through said first inlet port during an induction stroke of said piston, at high engine load;
• and
• introducing air into said cylinder through said second inlet port during an induction stroke of said piston.