[legaleye3000]

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As the thread title says... Thanks.

[jdong]

The 2014 BMWs equipped with a ZF 8 speed transmission support a special coasting mode where the transmission disengages the engine (e.g. goes into neutral), the engine drops to idle speed, and the car coasts.

This allows you to lose less speed when coasting, which may prevent you from needing to hit the gas again.

Normally, the transmission back drives the engine while coasting, downshifting to keep the engine above 1000RPM. In this mode, no fuel is injected to the engine while coasting, at the cost of higher frictional losses and hence your car slowing down quicker.

[legaleye3000]

Oh ok. So this improves the fuel savings compared to a 2012 F30? Thanks.

[olinjohnston]

Correct...It essentially decouples the engine from the rest of the drivetrain so you can "idle" at highway speeds as long as your foot is off the gas.

[jdong]

Originally Posted by legaleye3000

Oh ok. So this improves the fuel savings compared to a 2012 F30? Thanks.

It has the potential to save fuel by allowing you to drive with your foot off the gas on slight downhill terrains where you otherwise would need to apply throttle to maintain your speed.

As I mentioned, coasting before already did not require any gas -- it just caused you to lose speed a lot more rapidly.

[nicknaz]

When I spent a day with a 2014 328 it seemed like the "coasting" would only work when I lifted my foot off the gas, and it did not work when I was using the cruise control.

Does anyone know if the "coasting" will work with speed control?

I thought the most efficient way to drive on the highway was to use the cruise control to minimize speed changes, but if it negates the "coasting" feature, will it be better not to use the cruise control and try to coast?

[jdong]

It's worth experimenting with but somehow I don't think the gas savings are significant enough to really matter.

[Feanor]

I thought the whole point in leaving the engine in gear was to save fuel, as no (or less) fuel is needed to keep the engine turning over?

If you put the car into neutral, I thought more fuel is needed in order to keep the engine idling?

[tturedraider]

Originally Posted by nicknaz

When I spent a day with a 2014 328 it seemed like the "coasting" would only work when I lifted my foot off the gas, and it did not work when I was using the cruise control.

Does anyone know if the "coasting" will work with speed control?

I thought the most efficient way to drive on the highway was to use the cruise control to minimize speed changes, but if it negates the "coasting" feature, will it be better not to use the cruise control and try to coast?

"Coasting" does not work with the cruise control. It's primary intended purpose is to allow the car to coast when slowing to a stop.

[Fille]

Originally Posted by tturedraider

"Coasting" does not work with the cruise control. It's primary intended purpose is to allow the car to coast when slowing to a stop.

No that can't be true, that would mean that BMW engineers are idiots, which they probably arn't.
If you WANT to come to a stop you SHOULD engine break because the car doesn't use fuel and it slows down a lot faster than in neutral WITH the engine still pumping fuel.

[PabloK]

Originally Posted by Fille

No that can't be true, that would mean that BMW engineers are idiots, which they probably arn't.
If you WANT to come to a stop you SHOULD engine break because the car doesn't use fuel and it slows down a lot faster than in neutral WITH the engine still pumping fuel.

I don't think your grasping the concept of coasting.

The car is using more fuel when you engine brake opposed to a decoupled drivetrain / idling engine. Period.

The concept of coasting... Think about a red stop light a quarter of a mile in front of you on a 55mph road. You let off the gas and you can easily coast to the light without the engine slowing you down so fast.

[Feanor]

Originally Posted by PabloK

I don't think your grasping the concept of coasting.

The car is using more fuel when you engine brake opposed to a decoupled drivetrain / idling engine. Period.

The concept of coasting... Think about a red stop light a quarter of a mile in front of you on a 55mph road. You let off the gas and you can easily coast to the light without the engine slowing you down so fast.

The AA (a UK breakdown service and driver organisation) seems to disagree: http://www.theaa.com/motoring_advice...ive-smart.html

With changes in vehicle fuel systems coasting won't save you fuel these days either.

Old car with a carburettor – take your foot off the accelerator pedal with the car in gear and fuel is still drawn through into the engine. Fuel savings could be made by coasting out of gear.
Modern car with electronic engine management – fuel and ignition systems are effectively combined and controlled by one Electronic Control Unit (ECU). Take your foot off the accelerator and the ECU cuts the fuel supply to the injectors anyway so there's nothing to be gained by coasting.
Modern diesel engines also have the ability to shut off the fuel when you take your foot off the accelerator.

[Fille]

Originally Posted by PabloK

I don't think your grasping the concept of coasting.

The car is using more fuel when you engine brake opposed to a decoupled drivetrain / idling engine. Period.

The concept of coasting... Think about a red stop light a quarter of a mile in front of you on a 55mph road. You let off the gas and you can easily coast to the light without the engine slowing you down so fast.

Sure, coasting is better if the light is way ahead and you know it takes a while to change. But if it's a short cycle light, the best thing to do is to let off the gas and engine break with downshifts.

[gomichaelkgo]

The manual says that coasting only activates in ECO pro mode and not when any of the following conditions exist:

Cruise control
Foot on brake
Foot on gas
Speed below threshold

I've also found there to be a refractory period for it. If you hit the brakes once on a downhill, it won't coast again for some time. Maybe until you hit the gas again and then keep your feet off both pedals.

[jdong]

Also, remember that the F30 has regenerative braking for alternator recharging. When you use Coasting, the car can no longer regeneratively brake since the driveline is no longer connected to the engine belt, where the alternator resides.

(This is one situation that the ActiveHybrid handles a ton better, where the equivalent of "coasting" mode actually turns off the engine, and the electric motor is still connected to the driveline for regeneration and also slight boost)

[BavarianFanatic]

This would be beneficial in situations where you are traveling a long slight downgrade where there's no concern about scrubbing speed at any point. It will eliminate the normal losses associated with spinning the mass of the trans gear train. The gains associated with approaching lights on high speed roadways would be nominal. As noted, an injected motor doesn't add fuel when there's no load (i.e. coasting). The transmission spins the crank if the torque converter is locked. If it's not, it's fluid coupled which is a huge waste of energy.

[raleedy]

So the normal coupled mode, which provides engine braking, uses no fuel but takes you only a limited distance. Coasting uses the fuel required to keep the engine turning over at idle, but lets you go farther, without adding power, than the coupled mode would. Which will be better in terms of fuel savings will depend on the specific circumstances.

[BavarianFanatic]

Don't over think this. I'm pretty sure we're speaking ounces of fuel per tank here (if even).

[jdong]

Originally Posted by BavarianFanatic

Don't over think this. I'm pretty sure we're speaking ounces of fuel per tank here (if even).

And that's the point. As much as everyone makes fun of how little fuel the ActiveHybrid system saves, all this brake alternator and coasting stuff is a joke compared to what the hybrid F30 can do.

We are arguing over a really trivial (1%? Less than 5% for sure) fuel savings here.

[HighlandPete]

Originally Posted by BavarianFanatic

Don't over think this. I'm pretty sure we're speaking ounces of fuel per tank here (if even).

But enough to get better fuel consumption figures in the European NEDC test cycle.

All part of BMW's Eco-Pro push, to get the 25% improvement in figures by 2020.

Same for innovations such as Predictive Driving Assistant and Eco-Pro Routes, all about improving mpg potential.

We take for granted such features as NIC (Neutral Idle Control) these days, do many even know it's there disengaging the transmission while we sit with the footbrake on? A feature along with better torque converter lock up which improved AT fuel efficiency by 3 - 6%.

Every little helps. Reasons why our UK 3.0d engines are now into 50+ mpg (imperial gallons).

HighlandPete

[BavarianFanatic]

I agree everything cumulatively helps with the drive cycle testing, but real world is generally less effective. I'm not sure about the testing on your side of the pond, but the US drive cycle regimen is ridiculous.

[gomichaelkgo]

What do you all think has a worse long term effect on the power train?

If you coast, the engine turns at a lower RPM. --Less wear on the cylinder walls and spinning parts of the engine, but the transmission cycles more between neutral and drive. More transmission wear?