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Looking for a bit of info please.

mjcairney Apr 23, 2019

  1. mjcairney

    mjcairney Active Member Gold Supporter

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    Hi, part of the specification on my A4 TFSi 252PS is MHEV. I have been trying to figure something out since I purchased the car, second-hand, as follows. When I'm driving along at say 70mph the rev counter is showing approximately 2,000rpm. If I lift my foot off the throttle, sometimes nothing happens except of course the speed begins to drop, other times the autostop cuts in and the car coasts along, all fair enough. However, other times the revs drop back to around 700/800rpm with the speed still around the 70mph mark - what is actually happening here I continually wonder, so decided to ask on here as I have no doubt some of you very knowledgeable folk will be able to help me out.

    Thanks for reading. :icon thumright:
     
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  3. cuke2u

    cuke2u Well-Known Member

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  4. Daggerit

    Daggerit Registered User

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  5. cuke2u

    cuke2u Well-Known Member

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    sketch-1556040541572.png
     
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  6. Philio

    Philio Registered User

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    Pretty sure you can disable it if you want, there is an option under Car -> Driver assist -> Efficiency assist.

    Sent from my Pixel 3 using Tapatalk
     
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  7. Daggerit

    Daggerit Registered User

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    Yeah, it’s just a shame you can’t see those and signatures if you’re using the app on your phone...


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  8. Spearo

    Spearo Registered User

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    I must say I’ve never seen mine completely shut off the engine. I just assumed that coasting just uncoupled the gearbox and the revs dropped to 800 or so rpm.
    Do you guys really have the engine shut off completely? What sort of screen am I expecting to see in the VC when this happens ? Is the complete shut off thing S tronic only ?
     
  9. Daggerit

    Daggerit Registered User

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    Yeah the new ones do shut off the engine when coasting in some situations. I think it’s something like 29-50mph tang or thereabouts if I remember rightly?


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  10. JRF

    JRF Registered User

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    My shuts off at any speed, coasting under settings on the MMI. I think it is clever saves fuel
     
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  11. mjcairney

    mjcairney Active Member Gold Supporter

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    Thanks for all the replies guys but I must say I'm still unsure - I thought it was coasting when the revs dropped to zero like @JRF in the previous post, as they often do, but wonder why, at other times, they drop to, as mentioned in my opening post, 700/800rpm. Having said that, I haven't had time to read the link kindly provided by @cuke2u where I might get the full answer.
     
    Last edited: Apr 23, 2019
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  13. MOA4B9

    MOA4B9 Registered User

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    Does anyone know how much fuel (and money) do you actually save due to coasting? For me it only comes on once or twice in a day and for a 50-100 meter stretch. The difference between lifting foot of the accelerator in old car and intelligent coasting must be so minuscule. I will be surprised if it saved me 1 penny each time. It will probably cost me more in the long run if this clever technology decides to break one day and Audi will charge you a fortune to fix it.

    I'm also confused how it decides when to coast. On my way to work it always tells me to lift of the accelerator in exactly the same spot on quite a flat road but in other places which are more downhill it stays in gear and it doesn't even do engine breaking.
     
  14. mjcairney

    mjcairney Active Member Gold Supporter

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    When the car tells you to lift your foot of the accelerator, I'm presuming you mean by the "green foot" showing, that is activated by the navigation system warning that you are approaching a 'hazard' like e.g. a junction, roundabout or the likes, and has nothing to do with coasting.
     
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  15. DaveW

    DaveW Registered User

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    It can initiate coasting with the engine off, if it recognizes the need, it does this for me when travelling downhill etc. You know the engine is shut down as the "Ready" symbol and the green start/stop "A" indicator is displayed inside the tachometer.
     
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  16. cuke2u

    cuke2u Well-Known Member

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    I doubt if the feature is only aimed at owners saving money, more to do with meeting emission targets probably...
     
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  17. DaveW

    DaveW Registered User

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    If you put the virtual cockpit to driver assist view, it'll tell you the reason e.g. speed limit/roundabout for asking you to lift off.
     
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  18. mjcairney

    mjcairney Active Member Gold Supporter

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    Hi, thanks for that but I really have no wish to disable it, I just want to know what it's doing with the car running at 70mph when the revs are only at 700/800rpm, near enough tickover. I know it's coasting when the engine is off but can't really figure the 700/800rpm part.
     
  19. Philio

    Philio Registered User

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    I've never had the engine turn off at speed, but I mostly drive on dynamic which seems to disable most of the efficiency systems. Have had this though, I assume it's just disengaged the clutch.

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  20. DaveW

    DaveW Registered User

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    Coasting only works when the gearbox is in D or E modes, dynamic defaults the box to S unless you override it to D,then the coasting should kick in.
     
  21. Daggerit

    Daggerit Registered User

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    This is coasting as well. Exactly the same as if you’d just depressed the clutch on a manual car while going downhill. The engine will still be at those revs because it’s idling.


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  22. mjcairney

    mjcairney Active Member Gold Supporter

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    I've wondered if that is the case and I think that you have just confirmed that it is, so thank you for that. I now just wonder what criteria are used to decide whether the engine should be stopped or just idle. Thanks.
     
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  23. Daggerit

    Daggerit Registered User

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    Now that part I definitely can’t answer for sure. If I had to guess I imagine that it would take some fixed aspects like the gradient and distance as well as dynamic ones like current speed, battery voltage, engine temp, etc. so it may not activate the same on a given section road day to day.


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  24. mjcairney

    mjcairney Active Member Gold Supporter

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    Yes, I would guess that it's probably a decision made from a concoction of different criteria. I can definitely say that it does not always activate similarly on a given section of road.

    Thanks to everyone who has chipped in here. That's what I really appreciate about forums such as this one, there are always lots of people looking to offer help and advice when it's asked for.

    Thanks again. :thumbs up:
     
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  25. MOA4B9

    MOA4B9 Registered User

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    I thought the green foot meant that the car will coast if you take your foot of the accelerator.
    I never had the engine turn off or go to "ready" when at speed. When it happens when stationary the I loose all the steering. I wouldn't want that to happen at any speed.
     
  26. SMI77

    SMI77 Australia

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    Maybe I'm barking up the wrong tree, but have serious difficulty believing Bosch's claim 'During the average trip, according to Bosch, around 30 per cent of the time is spent coasting'. Even going over a familiar section of road trying to replicate coasting conditions (revs/speed etc) sometimes it coasts and sometimes it doesn't, even when using tricks, e.g. lightly tapping the '+' paddle. We've done trips 400m to 4000m & lucky to get 10% coasting. Perhaps if they were 'economy runs', like car clubs hold, totally different scenario. On that basis the fuel economy may well be to the point where it has a significant affect, but I have difficulty in how, in the real world, Audi can convince EU authorities that any portion of the fuel economy benchmarks can be attained through coasting. Until S4/S5 TFSI's go hybridisation with the electric coasting function, coasting is only based on gravity.

    This is an excerpt from the recent Audi-Media Centre release this month on the Audi S5 TDI:
    'MHEV technology: recuperate or coast

    The mild hybrid system in the S models, which is also integrated into the new 48-volt electrical system, has the potential to reduce customer fuel consumption by as much as 0.4 liters per
    100 kilometers. Mounted on the end face of the 3.0 TDI is a water-cooled belt alternator starter (BAS), which is connected to the crankshaft via a particularly high-load poly-V belt. The BAS generates a recuperation power of up to 8 kW and 60 Nm (44.3 lb-ft) of torque. It interacts closely with the TDI engine, which in many situations can be operated more closely to its ideal load point as a result. That enhances efficiency.

    When drivers take their foot off the accelerator pedal at a speed between 55 and 160 km/h (34.2 to 99.4 mph), the car can coast for up to 40 seconds with the engine shut off completely. The lithium-ion battery continues to supply electricity. The engine management system decides anew in every situation whether coasting, freewheeling or recuperation, i.e. the recovery of kinetic energy, is most efficient. It does this using information from the navigation system and the onboard sensors. The energy recovered by the BAS during coasting and braking flows into the 48-volt storage unit or directly to the electrical consumers.

    * Fuel consumption and CO2 emission figures given in ranges depend on the tires/wheels used as well as the selected equipment

    The mild hybrid system not only reduces fuel consumption; it also provides greater comfort and convenience. The conventional starter is only used to start the car initially, when cold engine oil requires high forces. When the driver presses the accelerator pedal again after a coasting phase or a stop, the BAS restarts the combustion engine. The system does this as required by the driver’s wishes and the situation, from very smoothly to very quickly. Start-stop operation begins at 22 km/h (13.7 mph). When stopped, the engine restarts as soon as the car in front starts to move, even if the brake is depressed."
     
  27. DaveW

    DaveW Registered User

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    You can steer while coasting as the mild hybrid system will provide enough power for the electrically powered power steering.
     
  28. SMI77

    SMI77 Australia

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    Can't remember anytime, when coasting, that the motor has switched off itself, and have been able to steer during this period.
     
  29. Daggerit

    Daggerit Registered User

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    I think it’s only the newer ones with the mild hybrid systems that do it. Our model S4 doesn’t.


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  30. SMI77

    SMI77 Australia

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    Yeah, our engines, in technology, are fast becoming boat anchors. Although the last real petrol engines.

    Still confused when MOA4B9 says he loses steering when stationary???
     
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  31. Daggerit

    Daggerit Registered User

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    I think he just means when the stop start kicks in. Mines the same, but since you’re stationary it doesn’t matter! And if you force the steering wheel round like you’re actually trying to turn the wheels then the car starts again to give you the assistance in the case of an emergency or something.


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  32. MOA4B9

    MOA4B9 Registered User

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    Yes, when the stop start kicks in the engine goes off, needle goes to 'ready' and you cannot turn the steering wheel. As mentioned earlier, it is designed differently in cars where engine cuts out during coasting.
     

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