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Aiming for higher output power, greater fuel economy and reduced exhaust emissions, a new V-6 3.5-liter i-VTEC Variable Cylinder Management (VCM) engine has been developed. This engine uses a cylinder-deactivation mechanism with VTEC technology that allows the number of cylinders to be controlled in three modes (three, four or all six cylinders), according to the operating conditions. This adds a four-cylinder mode to the conventional cylinder- deactivation engine. In addition to increasing the number of cylinder- deactivation modes, the new hydraulic circuits, a hydraulic pressure switching mechanism and a switchover control were also developed. These make it possible to instantaneously switch the active cylinders without impairing drivability, in the same manner as a conventional engine.

In the cities of the U.S. the worsening ozone problem has attracted attention and prompted reinforcement of regulations against emissions of hydrocarbons (HC) from automobiles. To cope with this situation, a reduction of HC is a vital challenge for the automotive industry. HC emission comes mainly from a cold engine, which usually uses a richer air-fuel mixture to achieve stable combustion and secure good driveability. The purpose of this paper is to show that using a engine with variable valv1e timing and lift system (VTEC) (1)∼(2) it is possible to reduce considerably HC emission in cold-start conditions. In other words, it is able to employ a leaner mixture than in existing engines (A/F=15.5) by using the VTEC system to alter the valve timing and lift according to various driving conditions, thereby considerably reducing HC emissions due to the improvement and stabilization of engine combustion.