Not all technologies depicted are used in all markets.
Basically, deactivating the cylinders improves fuel economy because it creates a smaller, lower-displacement engine.
Explained in mechanical terms, it is effective for the following three reasons.
Keeping the valves closed in the cylinder to stop fuel supply also prevents aspiration in that cylinder. This eliminates pumping loss, the greatest source of resistance in engine operation. This is the main reason why deactivating the cylinders contributes to improved fuel economy.
What is pumping loss?
Pumping loss is the air resistance incurred when the pistons pump intake and exhaust gases through the cylinder. It is particularly high during intake with the throttle closed.
Isn’t resistance higher when the valves are closed?
While it is true that resistance is incurred when the piston compresses the air in the sealed cylinder, this is almost completely offset during the down-stroke when the expanding air presses back on the piston. As a result, the loss is minimal.
As is shown in the above diagram, the throttle is open wider during 3-cylinder combustion. This makes intake easier for the active cylinders, reducing intake pumping losses for improved fuel economy.
What is a throttle?
The throttle is the valve that controls engine intake. The picture shows a DBW electronically controlled throttle. A motor rotates the valve (the gold-colored disc) around the hinge (the black, horizontal pin) to open and close it.
What is DBW?
DBW is the acronym for Drive-By-Wire, or electronic throttle control. A sensor detects the amount the gas pedal is depressed, and the throttle is operated by an electric motor based on that information. This allows a computer to be used to ensure optimum control.
Because the valves are deactivated, losses shown in the diagram to the left are largely reduced, allowing the engine to operate more efficiently. This contributes to improved fuel economy.
For the above three reasons, more frequent engine operation in the combustion range with high thermal efficiency during cylinder deactivation, also contributes to improved fuel economy.
When Honda initially developed its VCM, it featured a 3.0L V6 engine that switched between 3- and 6-cylinder combustion. Now, to further enhance the cylinder-deactivation effect, we have developed a 3.5L V6 engine capable of operating in three stages to deliver 6-, 3-, and 4-cylinder combustion.
The new 3-stage switching makes full use of Honda’s original VTEC (Variable Valve Timing and Lift Electronic Control) technology. This achievement has demanded high-precision engineering, including implementation of four hydraulic pathways in the rocker shafts for the rear cylinder bank where up to three cylinders are deactivated.
V6 engine - rocker shafts for rear cylinder bank