CYLINDER DEACTIVATION: PURSUING EVEN BETTER GAS MILEAGE

Wolfsburg, Germany -  Volkswagen continues to make great strides in improving the fuel economy of its vehicles. The latest technology to be employed for greater efficiency is cylinder shut-off, which will debut in the new 1.4L TSI engine in early 2012 in Europe.

High-tech solution

The high-tech cylinder cut-off system temporarily deactivates two of the four cylinders under low to mid-load situations. In the EU (European) driving cycle, this saves 0.4 liters of gasoline per 100 km, equivalent to about three mpg. Fuel savings may increase to more than 1.0 liter per 100 km under certain driving situations. Volkswagen breaks ground as the first carmaker to implement this technology in a turbocharged four-cylinder engine in large-scale production.

Smooth running

Drivers are only informed of the two-cylinder status if they select the readout for instantaneous fuel economy in the multifunction display. Otherwise, they would hardly notice the change. Even when running on just two cylinders, the 1.4L TSI—with its excellent engine balance—is still very quiet and smooth.

Broad characteristics

Cylinder shut-off is active when the 1.4L TSI is operating between 1400 and 4000 rpm and is producing between 18 and 55 pound-feet of torque. This applies to nearly 70 percent 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 two and three; engine ignition only occurs once per crankshaft revolution. The pistons of the deactivated cylinders 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.

Sophisticated technology

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

At the ends of each cam piece, there are two different lobes adjacent to one another—a conventional full profile and a so-called ”zero lift cam”. The full profiles actuate the roller cam followers, which in turn operate the valves when all four cylinders are working. In other words, the cam pieces behave like conventional cams. In two-cylinder operation, 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 the fuel injection.

Spiral-shaped slots are milled in the outer surfaces of the rotating cam pieces; these slots permit the sleeves to shift 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 gas pedal sufficiently, cylinders two and three 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 throttle pedal sensor to detect the driver’s momentary driving style. If the driving exhibits a non-uniform pattern—e.g. during sporty driving—the shut-off functionality is suppressed.

In total, the components for cylinder shut-off weigh a total of about seven pounds. The actuators, the camshafts and their bearing carriers are integrated in the cam cover. Two roller bearings reduce the friction of the shafts.

Potential for nearly 1 liter less fuel consumption

In the NEDC driving cycle, cylinder shut-off reduces the 1.4L TSI’s fuel consumption by 0.4 l/100 km—a CO2 equivalent of 8g/km. If the Stop/Start system that deactivates the engine while in neutral is also factored in, the savings total about 0.6 l/100 km. The greatest benefits of the new technology occur while driving at moderate and constant speeds. At 30 mph in third or fourth gear, savings amount to nearly one liter per 100 km. At 43 mph in fifth gear, for example, fuel consumption is still reduced by 0.7l/100 km.
The new turbocharged 1.4L TSI produces 138 horsepower and makes 185 pound-feet of torque between 1500 and 4,000 rpm. Volkswagen is currently the first carmaker to implement cylinder shut-off in a mass produced four-cylinder TSI engine.
The TSI combustion method—direct fuel injection plus turbocharging—is essential in implementing cylinder shut-off technology in its current form, because it eliminates complications in gas exchange that would otherwise occur in multi-point injection engines.

This new TSI engine will also be able to fulfill the future EU6 emissions standard. Volkswagen will introduce cylinder shut-off on Volkswagen production cars, starting in early 2012.