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

The spool valve switches the variable valve timing and lift electronic control (VTEC) mechanism by switching oil passages in the rocker arm in the engine according to commands from the ECU. The consumption flow rate is reduced by using a three-way valve solenoid, delivering a stable response even when hydraulic pressure is low.