At the beginning of 2012, Volkswagen’s latest efficiency technology, the cylinder shut-off, will make its premiere in the new 1.4 TSI engine. Of course, we have seen these techniques being used already decades ago in large V8 engines, but Volkswagen is the first manufacturer in the world to implement cylinder shut-off on a four-cylinder TSI engine in high-volume production. Reason enough to mention this here on our columns.
Hans Knol ten Bensel
The high-tech system reduces fuel consumption considerably by temporarily shutting off two of the four cylinders during low to medium engine loads. In fact, cylinder shut-off reduces fuel consumption of the 1.4 TSI by 0.4 litre per 100 km in the NEDC driving cycle. When the Stop/Start functionality is integrated, which stops the engine in neutral gear, the savings effect adds up to about 0.6 litre per 100 km.
The best use of this cutting edge technology are made while driving at constant moderate speeds. At 50 km/h, in third or fourth gear, savings amount to nearly one litre per 100 km.
This also means that the new fuel efficient TSI will meet the future EU6 emissions standard effortlessly.
On the first photo above, we show the condition when the cylinder shut off mechanism is not active. The camshaft moves between lobe profiles suited for partial or full load.
High efficiency does not go at the expense of any driving comfort: even when running on just two cylinders, the 1.4 TSI – thanks to its excellent engine balance – is still very quiet and runs virtually vibrationless.
Cylinder shut-off is active whenever the engine speed of the 1.4 TSI is between 1,400 and 4,000 rpm and torque is very low, between 25 and 75 Nm.
The graph above shows fuel consumption improvement in % on the vertical axis, with speed in kph on the horzontal axis: in low gears and low vehicle speeds one benefits most from the cylinder shut off technology...
This applies to nearly 70 per cent of the driving distance in the EU fuel economy driving cycle. We all know it, driving at slow speeds with virtually no engine load in lower gears, this is the condition where petrol engines are very inefficient. So if we can make fewer cylinders work more efficiently, then this efficiency improves markedly.
The second photo here below shows the camshaft position when cylinder desactivation is active, and cylinders 2 and 3 are indeed deactivated: the tappets just run on round rings, and are therefore not actuated.
As soon as the driver presses the accelerator pedal sufficiently, cylinders 2 and 3 are reactivated, completely unfelt by the driver.
Volkswagen uses information from the gas pedal sensor to detect the driving style of the man (or woman) at the wheel.
If the driving style is not smooth, and/or sporting, the shut-off functionality is suppressed.
We are anxious to drive this innovation next year, and see whether the driver’s “feel” of the engine remains indeed unchanged…
Hans Knol ten Bensel