Variable Cylinder Management (VCM) - iVTEC Accord V6
i-VTEC with Variable Cylinder Management (VCM)
What is VCM?
VCM (Variable Cylinder Management) is fuel-saving technology that automatically deactivates 1/3 or 1/2 of the cylinders, according to the driving conditions.
Cylinder deactivation idle image
Combustion halted to deactivate the cylinder
VCM, installed in a 6-cylinder engine, shuts off the valves and halts fuel supply in two cylinders when 1/3 of the cylinders are deactivated and in three cylinders when 1/2 of the cylinders are deactivated.
Engine operation with cylinder deactivation
Deactivating the Cylinders means that when VCM is in operation, it’s the same as driving a car with a smaller, lower-displacement engine, emitting less CO2.
When does VCM Operate?
VCM operates during everyday driving.
You can also expect VCM to contribute to fuel savings especially at long distance driving when driving at a consistent speed.
VCM technology combines the excitement of a luxury vehicle's ample acceleration with outstanding fuel economy, enhancing both economic and environmental performances.
The VCM cylinder deactivation mechanism
VCM deactivates the cylinder by keeping the intake and exhaust valves in the closed position to halt fuel supply.
To accomplish this, it uses Honda’s original VTEC (Variable Valve Timing and Lift Electronic Control) technology.
To deactivate the cylinder, the pin is moved hydraulically to disengage the rocker arm that pushes down the valves. In this mode, even though the cam pushes up the rocker arm, it has no effect and the valves remain closed.
The reason why the cylinder deactivation improves fuel economy
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:
1. It eliminates pumping losses in the deactivated cylinders.
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 a 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 the 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.
2. Pumping losses in active cylinders are also reduced
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.
4- cylinder combustion added to enhance the cylinder deactivation effect
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
VCM was materialised by combining Honda's original VTEC system with other advanced Honda technologies.
The VCM system combines two characteristics that don't typically coexist in conventional engines: maximum performance and maximum fuel economy
From the world's largest engine manufacturer comes the next iteration of i-VTEC. At the heart of the eighth generation V6 Accord is the all-new 3.5 litre i-VTEC engine with Variable Cylinder Management (VCM). Delivering 202kW of power and 340Nm of torque the V6 engine intelligently adapts to suit your current driving situation, seamlessly deactivating engine cylinders when not required. The VCM system combines two characteristics that don't typically coexist in conventional engines: maximum performance and maximum fuel economy. VCM deactivates specific cylinders by using the i-VTEC (Variable Valve Timing and Lift, Electronic Control) system to close the intake and exhaust valves while the Powertrain Control Module simultaneously cuts fuel to those cylinders. By monitoring throttle position, vehicle speed, engine revs, automatic transmission gear selection and other factors, the VCM system intuitively determines the correct cylinder activation scheme for the operating conditions.
Variable Cylinder Management in operation
During start-up, acceleration, when climbing hills or when high power output is required, the engine operates on all six cylinders. During moderate speed cruising and at low engine loads, the system operates just one bank of three cylinders. For high speed cruising and moderate acceleration including mild hills, the engine operates on only four cylinders.
Overtaking and accelerating. Unleash
the full 202kW.
High speed cruising and easy acceleration.
It's there, but you don’t need it right now.