For those of you (and there have been a few) who have dreamed of and/or actually tried your hand at DIY cylinder deactivation (mechanically), VW has provided data on the fuel economy improvement achieved by switching from 4 to 2 cylinders at various speeds in their 1.4 L gasoline engine which will be in this year's "Polo Blue GT" model:
Driving at a constant speed (load):
(Note baseline mpg for putting these figures in perspective: the car is rated either 50 or 52 mpg on the Euro cycle depending on transmission choice.)
- @ 50 km/h (31 mph) in 3rd or 4th gear = up to 16 mpg improvement
- @ 70 km/h (43 mph) in 5th gear = 11 mpg improvement
- On the European combined driving cycle (ie. variable load, and switching between 4 & 2 cylinders): about 8 mpg.
Quote:
The cylinder deactivation feature becomes active at engine speeds from 1,250 to 4,000 rpm, and at torque outputs from 18 to approximately 74 pound-feet--a broad swath of the operating map that includes nearly 70 percent of most driving states, according to Volkswagen’s own research.
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Source:
Volkswagen Polo Blue GT Is First Car With Four-Cylinder Deactivation Tech
The article doesn't say how VW accomplishes deactivation, but presumably it's by shutting both the intake & exhaust valves on the cylinders.
EDIT: found a video demonstrating VW's approach...
EDIT 2: here's VW's press release (edited to remove some unrelated topics & shameless marketing-speak):
Quote:
Wolfsburg / Geneva, 06 March 2012 - The new Polo BlueGT...
The technical highlight of this compact car is the cylinder deactivation system, which is being introduced for the first time in a Volkswagen – also known as active cylinder management or ACT. The system was realised with the new 1.4-litre TSI of the Polo BlueGT. The torque-strong TSI develops a power output of 103 kW / 140 PS, yet has a combined fuel consumption of just 4.7 l/100 km/h* (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* – and, bear in mind, this is a petrol, not a diesel (105 g/km* CO2). Nonetheless, this car, with a top speed of 210 km/h, accelerates to 100 km/h in 7.9 seconds. The new car will be available on the market in July.
New generation of engines.
The 1.4 TSI in the Polo BlueGT is the top engine of the entirely new EA211 series of petrol engines.
Fuel savings by ACT.
Volkswagen is the first carmaker to introduce active cylinder management as a fuel-saving technology in smaller engines – they were previously only known in larger eight or twelve cylinder units. [Edit: this isn't true if VW is referring to all automakers - Honda has been doing cylinder deactivation in some of its V6's for years.]
Shutting down the second and third cylinders under low and medium load states reduces fuel consumption in the EU driving cycle by about 0.4 l/100 km. In constant speed driving at 50 km/h in third or fourth gear, fuel savings are as much as one litre per 100 km. But even when driving at 70 km/h in fifth gear, fuel consumption is still reduced by 0.7 l/100 km.
ACT mode of operation.
ACT becomes active at engine speeds from 1,250 to 4,000 rpm, and at torque outputs from 25 to approx. 100 Nm – a broad swath of the operating map that includes nearly 70 per cent of all driving states in the EU driving cycle. When the driver presses the accelerator pedal, the two cylinders are reactivated. Even with two cylinders, the balanced 1.4 TSI of the Polo BlueGT runs just as quietly with as little vibration as it does when all four combustion chambers are active.
All mechanical switchover actions are completed within one half of a camshaft revolution; this only takes between 13 and 36 milliseconds, depending on engine speed. The transitions are smoothed by supporting interventions to the ignition and throttle valve.
Thanks to an accelerator pedal sensor and intelligent monitoring software, the system can also detect non-uniform driving profiles – such as while driving through traffic or in a sporty manner when driving on a country road. In such cases, cylinder shutoff is disabled. The driver is informed whether two or four cylinders are active by an indication in the multifunction display located between the speedometer and tachometer.
ACT camshaft adjustment.
To further reduce emission and fuel consumption values and improve torque in the lower engine speed range, the intake camshaft was designed to be adjustable over a range of 50 degree crank angle on all EA211 engines; in the 1.4 TSI of the Polo BlueGT, an exhaust camshaft adjuster is added. It adjusts to the desired spread of control times, thereby ensuring more spontaneous response from low revs; at the same time, it also improves torque at high revs.
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