Cylinder Deactivation: Best of both worlds

Cylinder deactivation or variable cylinder management systems, as the names imply, control the number of cylinders in use by the engine. This technology has been used by big displacement motors, like Honda Accord's 3.5l V6, to reduce fuel consumption. It has also been used in hybrid’s like the Civic Hybrid to shut off the engine when running in electric mode or during braking.

The cylinder de-activation system monitors the driving conditions and when it senses that the full torque of the engine is not required it shuts off fuel and air from entering a pre-decided cylinder/s. So what happens? The piston inside the cylinder keeps moving up and down. But now it experiences very little load as the trapped inside air acts as a spring that pushes against the piston when it is compressed. The ECU also cuts off the fuel supply to the cylinders. The use of this system has pitfalls - such as resonance and mechanical imbalance. Manufacturers have found different ways of working around these using active acoustics to control drone and active engine mounts to absorb vibrations.

However, Volkswagen has just announced the use of this system on a turbocharged, 4-cylinder in-line motor. During low load conditions the 1.4 TSI motor will "switch off" the 2nd and 3rd cylinders by keeping the intake and exhaust valves closed. The two active cylinders will now run at higher loads and this improves efficiency.  This is done when the motor is running between 1,400 and 4,000 rpm and its torque is between 25 and 75 Nm. VW claims that these parameters apply to nearly 70 per cent of European driving distance in the EU driving cycle. The cylinders then spring back to life as soon as the driver presses the accelerator pedal hard enough. Notably, here the engine runs either in 2 cylinder or 4-cylinder mode. Watch the video to understand how it works.  

The Accord in comparison can go from 6 to 4 and even down to 3 cylinders. However, the I4 motor's by sticking to 2-cylinder or 4-cylinder operation will keep vibrations and harshness under check. Turbocharged fours are the next wave across classes of cars so you can expect the 1.4TSI with cylinder de-activation to power a wide range of cars in the VW family. The engine is expected to debut in 2012.