2 cylinder mode

[zx6rick]

Hi how do I know when my karoq is running on 2 cylinders.

Is there a setting on the display that would tell me?

[Kenny R]

The Eco symbol illuminates  on the dash when ACT in operation.

Edited 16 October, 2020 by Kenny R

[shyVRS245]

Also you need to be doing at least 1,400rpm on level ground or going downhill. The engine will need all 4 cylinders pumping when under load going uphill.

[Sanqhar]

I get notification on the centre console on the fuel consumption screen (not the 'Average'). 

 

tom

[Tim1631]

Isn't there a very noticeably vibration and noise during the two cylinder mode? 

[Ootohere]

Only with the lemons, it is not a design feature or characteristic that the VW engineers aimed for.

[Quickasaquickthing]

I’ve noticed that it depends on what you have selected on the display  screen between the dials. If you just have the MPH in numerals for example you just get the ‘eco mode’ indication. If you have selected constant fuel usage you actually get the words ‘2 cylinder mode’ on the display.

 

But here’s something I’m probably too thick to understand. I can be cruising along at 40 in a 40 limit in 4th gear and I get the ‘2 cylinder mode’  display.great fuel efficiency- excellent!  But... the wee indicator at the top left is telling me to change from 4th to 5th and I can understand that because surely the highest possible gear is best for the car and fuel efficiency? But.... as soon as I change out of 4 th gear to 5th the ‘2 cylinder mode’  goes off, not just for a second but for quite a long while , maybe miles ‘till I’m settled in sixth. So it’s more efficient in 4th than 6 th at a constant speed cruise.

 

Am I being stupid or is this odd? 

 

[xman]

Cylinder deactivation works only between 1,400 and 4,000 rpm and when the engine torque (presumably taken from the ecu map) lies in the range of 25 Nm to 75 Nm. Bear in mind that max torque for 1.5tsi/1.4tsi is much greater, 250 Nm,  so ACT is only activated between 10% and 30% of max available torque 

 

In practice I find it needs 1500 sometimes 1600 rpm to trigger and will hold on to 1400 rpm only if the revs drop slowly enough without dipping below the threshold. It will also remain active even if you lift the throttle completely (zero torque) subject to rpm and the the caveat I explain later in this post.

 

Its important to understand the relationship between torque and power.

 

Power = Torque x rpm

 

So for the same power output, torque is 33% lower at 2000rpm than at 1500rpm.........and so on......

 

When you are in 4th gear, you may satisfy the criterea for 2 cylinder mode, but when you change up to 5th, either the rpm drops too low, or the torque demand increases too high, even though the power developed is the same or lower.

 

I have found there is at least another condition where ACT deactivates. If going downhill, and it is steep enough for the car to start accelerating on its own without any throttle, and the braking provided by the micro hybrid energy recovery is not enough to stop it accelerating, then ACT will deactivate to increase engine braking.

 

Other factors are also taken into account. A minimum time after an engine start, it will delay after deactivating before reactivating, it will stop for a  longer period if its being asked to activate/deactivate too frequently. And no doubt other factors too.

 

Despite what the gear suggestion may say, its often more economical to hold onto a lower gear to keep rpm well above 1500rpm and keep torque low.

 

Another big advantage to keep rpm high and so torque at the lower end is that it reduces the vibration caused by the inherent imbalance of 2 cylinder operation. This not only is more pleasant from a NVH point of view, it also reduces the stress/work demanded from the DMF and reduces torsional vibration through the gearbox and driveline, possibly leading to less wear on components 

 

Its easy to see the advantage using the instantaneous mpg display. I find the fuel saving at 1500 rpm can be marginal between the 2 modes, but change down and take it up to 1800 and higher and the saving is much more substantial and obvious (as well as being more pleasant). 

 

2 cylinder mode gains most of its economy advantage by allowing a wider throttle plate opening which reduces pumping losses (and engine braking). Note this is all done automatically and is not related to the throttle position under your foot .

 

Gear suggestion doesn't seem to take any account of ACT in my experience.

 

Hope you understand all this.

Edited 17 October, 2020 by xman

[Quickasaquickthing]

Thanks Xman for a helpful and detailed explanation! Now I do understand it. ( had to read it three times though😀) Appreciate your help. 

[edbostan]

What balances the crankshaft when 2 pots are working and the others are passengers?

[Ootohere]

 

 

[xman]

5 hours ago, edbostan said:

What balances the crankshaft when 2 pots are working and the others are passengers?

 

Explained in this pdf

 

SSP-510_Active_Cylinder_Management_ACT_in_the_1_4_l_103_kW_TSI_engine.pdf

 

[smipx]

When my 1.5 DSG is in 2-cyl mode I have to say I would not be able to tell apart from the "ECO mode" illumination on the dash.  No vibration due to any imbalance or rough sounds at all.

I also don't get any issues at cold start (aka Kangaroo)  - I think my car had the software update.   My 3rd gear in slowish traffic can sometimes feel a touch jerky - not badly so - just feels a bit like I lifted quickly off and back on to the gas with the resultant bit of jerkiness (had I been driving in a manual car) .  It annoyed me to begin with but I'm kind of used to it now and put it down to "DSG quirks".  All I do know is the DSG is one hell of a lot smoother than I am when driving my wife's 1.0 Fabia (manual). That is something else.  Whoever decided the gear ratios on that gearbox should be taken out and shot by a firing sqaud.  The 1st gear is really short and the 2nd gear really long so it constantly feels like its about to stall in slow traffic in 2nd but if I were to go into 1st it would scream and be jerkier than a jerky thing - calling it a a kangaroo would not do it justice  - horrible!

Edited 26 October, 2020 by smipx