Saving fuel by selectively reducing the number of cylinders in operation at any given time has become a fairly widespread and well-proven technology. However, to date, no manufacturer has applied this efficiency-enhancing system to any series-production engine with fewer than six pistons. Now Volkswagen has decided to adapt it for use on the firm’s new 1.4-liter TSI, a turbocharged/direct-injected four-banger that’s already quite adept at wringing an impressive number of miles out of every gallon of gasoline. According to VW, combining cylinder deactivation and Start/Stop technology helps improve the overall economy by nearly one liter/100km on the Euro cycle when a suitably scaled vehicle is being driven at around 30 mph in 3rd of 4th gears.
The VW deactivation system relies on a series of computer-controlled electro-magnetic actuators linked to mechanical elements on the intake and exhaust camshafts to suspend movement of the valves on the engine’s number two and three cylinders. This process, which takes place within one half a rotation of each cam, can occur any time the vehicle is in a constant-speed cruise mode with the engine turning between 1,400-4,000 rpm and developing 18-55 lb-ft of torque — conditions that VW says occur during nearly 70 percent of the European Union’s testing regimen.
According to Volkswagen, the 1.4 TSI retains its smooth, quiet character, even when running in mileage-maxing two-cylinder mode. Out in the real world, reactivation is a seamless process that takes place whenever the driver does step back into the throttle. For the record, a sensor on the accelerator pedal also precludes any shutdown when it recognizes a “non-uniform” application pattern, so there’s no danger of it swinging into action when the car is negotiating more challenging road situations – like being tossed about on your favorite twisty two-lane.
