New Accord not firing on all cylinders

The idea's not new. Cadillac pioneered it and Chrysler -- the only company to offer the system in Australia up to this point -- has refined it for the 21st Century.

Now, Honda is adopting what is variously known as 'Displacement on Demand', 'Active Fuel Management' and 'Multi Displacement System' by other manufacturers. In Honda's terms, the new technology is known as Variable Cylinder Management (VCM).

VCM will be introduced with the new Accord V6, built in Thailand and due for release in Australia around February of next year.

The SOHC V6 displaces 3.5 litres and produces over 200kW of power. Being able to run on all six cylinders, just four or even as few as three, the engine will record fuel consumption figures as low as the fuel consumption of a four-cylinder car, according to feedback from Honda's American customers.

Honda has spent a long time developing this technology and claims that the operational cylinder deactivation occurs "seamlessly".

VCM cuts back from six to four cylinders when the driver requires just light acceleration and the engine will change operation to one bank of three cylinders when the vehicle is cruising.

Cylinder deactivation takes place when the engine's VTEC system closes the intake and exhaust valves simultaneously for two or three cylinders (depending on the driving mode). Even with the piston reciprocating inside the deactivated cylinder, there is relatively little loss of efficiency due to pumping losses, since the deactivated cylinder is closed.

With VTEC closing the intake and exhaust valves, the engine's 'Powertrain Control Module' also curtails the fuel supply to the deactivated cylinder, but keeps the spark plug firing in the deactivated cylinder. This ensures that the plug's temperature doesn't decline and the plug itself isn't fouled when the cylinder reactivates.

In the two modes, the same cylinders are deactivated in each case. For four-cylinder mode, the deactivated cylinders are right-front and left-rear. In three-cylinder mode, the front bank of three cylinders is deactivated.

VCM coordinates the cylinder deactivation by monitoring throttle input, speed, engine revs and gear selection (in the automatic transmission), to determine which mode of operation should apply at any given time. By adjusting engine ignition, electronic throttle setting and the torque converter's damper clutch, VCM can keep the transition from one mode to another virtually undetectable.