Shifting from D to N when stopping in a DSG - same principle as MT?

[Diesel_vert]

There are moments in driving when you have to stop and know beforehand that you're not going to take off for a while.

A recent thread at Golfmkv got me thinking - for example, say you're coming up to a traffic queue on a motorway (bloody M4!!). Probably an accident ahead, nothing is moving, traffic has been stationary for some time, no one's behind you for miles, and you're the last car to arrive. What I normally do in these situations is during the last couple of metres before coming to a halt, I shift into neutral, hence using only the right foot to come to a complete stop (and engage the handbrake or whatever).

Just out of sheer curiosity, given the same scenario, is there a reason why you couldn't or shouldn't do likewise on a DSG?

[Axis]

There's no reason you couldn't. But you probably shouldn't because the DSG does it for you already (basically).

See this thread: http://www.golfmkv.com/forums/showthread.php?t=69511

Specifically this bit:

One of the ways in which the DSG allows better fuel consumption over a manual gearbox is the ability to disconnect it's clutches when no engine effort is required. This occurs when the brake pedal is depressed (e.g. at stop light) and also when driving on a straight road when no pedal input is detected. When braking the clutches do not disengage unless the car is at a complete standstill.

The fuel injectors are also cut when no pedal input is detected also saving fuel. It is easy to see when you have the "instantaneous" fuel consumption figure in your MFD showing - it will be 0.0 when you take your foot off the pedal whilst moving.

[Big Yellow]

If you RTFM you will actually find that it advises against this as when you have brakes pressed the clutches are disengaged already like above post mentions.

[Diesel_vert]

... the ability to disconnect it's clutches when no engine effort is required. This occurs... when driving on a straight road when no pedal input is detected.

Y'see, I've always had a problem with that statement (which he highlights in bold). Correct me if I'm wrong, but if you (or the mechatronics unit) disengage the clutch, doesn't that mean the revs fall to idle speed? I thought the DSG keeps the clutch engaged on the overrun, like a manual.


He then (correctly) contradicts himself on the next sentence by saying;

When braking the clutches do not disengage unless the car is at a complete standstill.

And he confirms my argument by saying;

The fuel injectors are also cut when no pedal input is detected...

which is what happens on most direct injection engines on the overrun, petrol and diesel.


And to the user who made this post;

Some folks claim 100% fuel cut off and stand by this claim because of the MFD readout of 0.0 l/100km when coasting.

I'd maintain that the injectors switch to an 'idle' phase (ie not cut off) and use VERY LITTLE fuel rather than none at all. After all, what would run your A/C, your GPS, your CD player, lights &c?

The answer to that is in an overrun situation, nothing but the wheels are turning the engine, thus powering the ancillaries without consuming fuel.



Anyway, when you're just about to come to a halt in Drive, I know the clutches disengage. But is it any different than shifting into neutral yourself? (in the context of my scenario)

[gregozedobe]

Unless I've been driving enthusiastically (or uphill) just before the stoppage I'd go one step further and switch off the engine when I stopped behind the last car. No point burning fuel when you are going nowhere.

[zach]

in my Skoda manual it specificly states there is no need to use neutral in terms of saving fuel.

[Diesel_vert]

What if want to give your right foot a break?

Because unlike a traditional auto, where constantly shifting to-and-fro D and N creates wear (supposedly because you are engaging/disengaging something every time you do), doing that on a DSG wouldn't really affect anything as you're not engaging/disengaging anything, just like a manual, right?

[chowi]

I do the same as you Diesel_vert.

I swear the clutch is still engaged right up until the car goes below roughly 1,000 rpm as you can often feel a slight shudder, and a change in engine load as neutral is selected (even with the brakes lightly applied). You can also feel the reduction in decleration when you select neutral while lightly braking.

You also need to shift into neutral to apply the handbrake anyway.

[bazzle]

What if want to give your right foot a break?

Thats what the handbrake is for.

Bazzle

[CatonaPC©]

. . . there is no need to use neutral in terms of saving fuel.

I'm sceptical about this. With my foot on the brake, the fuel flow rate on the MFD might indicate 0.9-1.1 Litre per hour. Put it in N and that figure drops to 0.7-0.8 l/hr.

Plus the fact you can actually feel the car release itself from drive would suggest that there is some load on the transmission with your foot on the brake.