Variable Cylinder Management (VCM) is Honda's term for a variable displacement technology. It uses the i-VTEC system to disable one bank of cylinders during specific driving conditions (for example, highway driving) to save fuel. The 2008 Accord takes this a step further allowing the engine to go from 6 cylinders, down to 4, and further down to 3 as the computer sees fit. Honda's VCM uses overhead cams as opposed to DaimlerChrysler's Multi-Displacement System and General Motors' Active Fuel Management pushrod systems.
It uses a solenoid to unlock the cam followers on one bank from their respective rockers, so the cam follower floats freely while the valve springs keep the valves closed. The engine's drive by wire throttle allows the engine management computer to smooth out the engine's power delivery, making the system nearly imperceptible on some vehicles. Vehicles equipped with VCM are equipped with an "ECO" indicator on the dashboard which corresponds to the VCM system's operation. Vehicles equipped with VCM also include Active Noise Cancellation (ANC) and Honda's Active Control Engine Mount (ACM) system. The ANC and ACM systems work in cooperation to cancel both noise and vibration that could occur in relation to the cylinder deactivation process. The ANC system uses the audio speakers to cancel out noise by using an opposite phase sound.
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