The Wolfsburg-based company became the first manufacturer to introduce active cylinder management in a four-cylinder last year—a technology that until then had been more familiar in large eight- or twelve-cylinder engines. Active cylinder management made its debut in the Polo and Golf 1.4 TSI.

Active Cylinder Management takes effect whenever the 1.4 TSI’s engine speed lies between 1,250 and 4,000 rpm and its torque lies between 25 and 100 N·m. This applies to nearly 70% of the driving distance in the EU fuel economy driving cycle.

First, the combustion chambers are filled with air; this entrapped fresh air leads to minimal cylinder pressure and therefore to lower energy consumption. Afterwards, the system closes the intake and exhaust valves of cylinders 2 and 3; engine ignition only occurs once per crankshaft revolution. The pistons of the deactivated cylinder are now dragged by the crankshaft. On the other hand, efficiency increases in the two active cylinders, because their operating points are shifted to higher loads.

Active cylinder management (ACT) camshaft module, Polo BlueGT. Click to enlarge.

The valves are closed using a complex set of actuators: on both the intake camshaft and the exhaust camshaft, there are two adjustable sleeves known as cam pieces that are placed on special tooth systems. They are responsible for the eight valves of the second and third cylinders.

At the ends of each cam piece, there are two different profiles adjacent to one another—a conventional full profile and a zero-lift cam. The full profiles actuate the roller cam followers, which in turn actuate the valves in four-cylinder operation; that is, they behave like very conventional cams. However, the zero-lift cams rotate over the followers—i.e. they do not actuate them—and the valve springs hold the valves shut. Engine management simultaneously shuts off fuel injection.

Active cylinder management. Click to enlarge.

Spiral-shaped slots are milled in the outer surfaces of the rotating cam pieces (diagram at right); these slots permit shifting the sleeves a few millimeters along the shafts at lightning speed; when electromagnetic actuators in the valve cover get a signal from the engine controller, two integrated metal pins engage the slots from outside and move them to their end positions. Finally, the cam pieces are locked in place by spring-loaded balls. As soon as the driver presses the accelerator pedal sufficiently, cylinders 2 and 3 are reactivated.

All mechanical switchover processes are executed within one-half camshaft revolution; they last between 13 and 36 milliseconds, depending on engine speed. These processes are smoothed by accompanying interventions in ignition and throttle valve control.

Volkswagen utilizes information from the accelerator pedal sensor to detect the driver’s momentary style of driving. If the driving exhibits a nonuniform pattern—e.g. while driving in roundabout traffic or using a sporty gear-shifting style on a country road—the shut-off functionality is suppressed.

Temporary shutoff of the second and third cylinders—in conjunction with an economical style of driving—reduces fuel consumption by more than 0.5 litres per 100 kilometers.

Even with two cylinders the excellently balanced 1.4 TSI runs just as quietly and with low vibration as with four active combustion chambers.

Altogether, the components of active cylinder management weigh just 3 kg. Their actuators, the camshafts and their bearing frames are integrated in the cylinder heat; two low-friction bearings reduce shaft friction.

In the Polo BlueGT, the TSI with ACT develops a power output of 103 kW / 138 hp, with a combined fuel consumption of 4.7 l/100 km/h (50 mpg US), equivalent to 108 g/km CO₂. If the Polo BlueGT is ordered with the optional 7-speed dual clutch gearbox (DSG), fuel consumption drops further to 4.5 l/100 km (52 mpg US), equivalent to 105 g/km CO₂.

Compared to its predecessor, fuel consumption and CO₂ emission values of the TSI engines were reduced to 9% in part also by such measures as reducing internal friction, lowering weight and optimizing thermal management. The savings potential is as much as 15% in conjunction with the active cylinder management (ACT) feature.

Other 2013 International Engine of the Year Awards. The global jury once again voted for Ford’s 999cc, three-cylinder turbo engine (EcoBoost) as the best engine on the market, and awarded it a second title. This is the third time in 15 years that a manufacturer has secured back-to-back honors for the top spot.

The Best Green Engine award went to Fiat for its 1.4-liter, 875cc, two-cylinder turbo CNG engine—the first ever Awards victory for compressed natural gas technology.