Returning an appropriate amount of the exhaust gases leaving the engine to the intake by means of the EGR valve in response to vehicle driving conditions lowers combustion temperatures and reduces NOx. In addition, supplying uninflammable gas in proportion to the cylinder capacity reduces engine pumping loss due to the throttle valve and improves fuel efficiency.

Returning an appropriate amount of the exhaust gases leaving the engine to the intake by means of the EGR valve in response to vehicle driving conditions lowers combustion temperatures and reduces NOx. In addition, supplying uninflammable gas in proportion to the cylinder capacity reduces engine pumping loss due to the throttle valve and improves fuel efficiency.