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Old 03-12-2012, 02:23 PM   #1 (permalink)
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VW quantifies MPG gain of 4- to 2-cylinder deactivation at 31 mph = +16 mpg

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.
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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Old 03-12-2012, 02:34 PM   #2 (permalink)
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IMHO it would be more effective to disable the appropriate injector and leave the valves alone, it seems to me that by shutting both intake and exhaust valves the piston would essentially be creating a vacuum causing even more issues.
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Old 03-12-2012, 02:58 PM   #3 (permalink)
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Leaving both valves open would pump oxygen into the exhaust stream and mess with O2 sensor.

I think just leaving intake valves open would work better, if they deativated the same 2 cylinders all the time and the pistons are 180 off each other I wonder about connecting the intake runners between them to push the air back and forth between the 2 cylinders.
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Old 03-12-2012, 03:07 PM   #4 (permalink)
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Quote:
Originally Posted by WD40 View Post
IMHO it would be more effective to disable the appropriate injector and leave the valves alone, it seems to me that by shutting both intake and exhaust valves the piston would essentially be creating a vacuum causing even more issues.
Leaving the valves closed basically uses the air as a spring. The piston uses energy to compress it, but the air pushes the piston back down on the other side of the stroke. Leaving the valves open would waste the compression energy.
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Old 03-12-2012, 03:54 PM   #5 (permalink)
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wd, rooster: there are articles here and online explaining cylinder deactivation. Would the manufacturers close off both valves if closing one or none worked better? Really? You are missing a major part of the whole theory and that is reduction in pumping losses. Think about why air compressors require so much power.

I've played with this at home and was hoping someday they'd get it to work on a 4 cylinder. Mine sounded like it wanted to start but it just couldn't quite do it. Of course one of the key things might be to start on 4 then switch off at higher rpm as there just isn't quite enough inertia to get 'er going on 2, but I had to try starting on 2 because my deac scheme was under the hood, not on the go.

Thanks for the figures metro; some rough extrapolating says maybe +15% could be expected on average... that's about what DoD for larger engines gets too... so for the Tempo I'd be looking at +5 or 6 mpg. Nice, but perhaps I won't be pulling those two pistons after all. :/
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Old 03-12-2012, 04:52 PM   #6 (permalink)
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Frank: maybe you needed another battery inline on the starter circuit, so you could have spun the engine up to a higher RPM with the key.
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Old 03-12-2012, 09:45 PM   #7 (permalink)
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Ha- it was spinning over pretty good. Gee I wish I had a 48 volt system! errrrrr.... Next time I'll get Cletus to gimme a tow up to 55 mph or so and then see if it starts/stays running.

We all know that 2 cylinder engines start, run, and work. I think if mine had more flywheel it would have gone. Or, if it had a 2 piston delete. Or an active deac system for high rpm deac.

rooster: I haven't seen it mentioned (or, I forgot ) about if the timing of the valve closing event is critical. I would think that since piston rings don't make a PERFECT seal, that cylinder pressure- or vacuum as the case may be- would reach some sort of equilibrium in short order. After all that piston will have gone up and down thousands of times in the space of one minute...
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Old 03-12-2012, 09:57 PM   #8 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
I've played with this at home and was hoping someday they'd get it to work on a 4 cylinder. Mine sounded like it wanted to start but it just couldn't quite do it. Of course one of the key things might be to start on 4 then switch off at higher rpm as there just isn't quite enough inertia to get 'er going on 2, but I had to try starting on 2 because my deac scheme was under the hood, not on the go.

:/
I inadvertently found that a Volvo B18 engine will start and run on two cylinders. Fortunately, it was the middle two cylinders.

Rush fixit job just before the welding supply store closed. Made it to the store, then hooked everything up to get home on four cylinders.
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Old 03-12-2012, 10:10 PM   #9 (permalink)
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Mine'll run on two if I just pull the spark plug or injector wires, but I went the distance and disabled the valves.
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Old 03-13-2012, 12:39 AM   #10 (permalink)
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for a 1500 cc engine, that is 15 percent or so.

which is EXACTLY the math we came up with in the bsfc thread.

pretty amazing stuff, because the math suggests it is 15 percent for ANY gasoline engine.

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