Dumping the DSG?

[Cossor]

The argument for the 7speed dry clutch was for energy efficiency re transmission power loss compared to 6speed oil clutch .
With 7Speed Golf clutch, had several occasions where DSG suddenly disengaged (due to over temperature? while slowly into position uphill)
However re the 6 speed DSG fitted to my Passat, this is so much better than older cars I have driven with conventional torque converters. Unless one watches the Tacho' one is not aware if any change has taken place. BUT and I mean BUT, re BlueMotion, this is a Bugger. Many times I pull up at a roundabout then I see my opportunity. What happens? The car stalls at the most critical moment!

[trojon]

The DSG is nothing like a preselector gearbox - a la Armstrong Siddeley, Daimler and some modern buses.

The preselector box has a series of epicyclic (planetary) gear trains just like a conventional auto box. A specific gear is selected electrically in advance (preselected) and engaged mechanically when needed by pressing a "clutch" pedal. The "clutch" pedal applies a brake band to the preselected planetary gear with a big spring. Preselector boxes often have a fluid flywheel (like a modern torque converter) or a centrifically engaged mechanical clutch. In modern applications, the mechanical engagement can be power actuated.

A DSG is two parallel conventional gear sets, with two co-axial clutches - operated, as Umai Naa says, by electrickery and hydraullickery.

[Martin]

Who said you could? The DSG is in fact a pre-selector style of box, not a conventional two shaft manual.

It certainly is a conventional style box
It's just that the two shafts are not parallel, one is inside the other
Our hand and foot have been replaced by electrickery and hydraullickery

Don't get me wrong - the electrics managing the box are very smart
VW had to create a faster diverter valve to handle the fast gear changes

The clutches are interesting to see (for ages I could not work out how that part worked)

[Ryeman]

I still want to know how the rotating mass of crank, rods and pistons can be moved 500rpm in 6 milliseconds (a fifth of a blink of the eye) unless the tacho is fibbing of course.
Multiples of clutches have nothing to do with the basic physics of controlling the rotational mass.

[Idle]

I still want to know how the rotating mass of crank, rods and pistons can be moved 500rpm in 6 milliseconds (a fifth of a blink of the eye) unless the tacho is fibbing of course.
Multiples of clutches have nothing to do with the basic physics of controlling the rotational mass.

The rotating mass changes speed in whatever time it takes — as does the flipping of an electronic switch.
Whilst not necessarily the same, both are virtually imperceptible in terms of human comprehension, and moving the tacho needle itsalf also takes time.

[Ryeman]

The rotating mass changes speed in whatever time it takes — as does the flipping of an electronic switch.
Whilst not necessarily the same, both are virtually imperceptible in terms of human comprehension, and moving the tacho needle itsalf also takes time.

Stuff happens is not an answer.
The energy required is not explained anywhere that I can find.

[Umai Naa!!]

Where do you want to start?

At how the tacho motor is slow to respond?

[Ryeman]

Where do you want to start?

At how the tacho motor is slow to respond?

What has a tacho needle got to do with the spectacular change in rotational mass which we are supposed to believe is accurately depicted by it?.

[Idle]

Very little, I should think.

The time — 6ms or whatever the figure is to swap a gear, would be the time take to activate a solenoid (possibly more than one, I've not seen the internals of a DSG and mechatronics,) compress one spring and release the other.

The time to dissipate the kinetic energy should be immaterial — the just-released clutch and its associated shaft could just spin down, but probably has a brake.

[Martin]

I still want to know how the rotating mass of crank, rods and pistons can be moved 500rpm in 6 milliseconds (a fifth of a blink of the eye) unless the tacho is fibbing of course.

Fair question

1) The tacho is most certainly lying
It's damped to appear nice and smooth for consumers
The actual engine RPM changes are much faster

2) Cars with DSG and sequential shifts all run a much lighter flywheel - to reduce inertia and allow faster changes
(faster changes in RPM hence faster gear changes)

3) Cars with DSG and sequential shifts all have an ECU managing the engine,
The ECU cuts the power HARD for a precise period of time - this significantly slows the engine inertia
(if you've ever hit the limiter on a track you know what I mean)

On turbo cars this presents special/additional problems,
Closing the throttle on a turbo engine at 6,500rpm causes a massive pressure spike in the inlet manifold
The ECU triggers the diverter valve to deal with this

4) Track cars with sequential shifts have narrow power bands and close ratio gearboxes
The RPM difference from gear to gear is not huge

Have you ever watched V8 supercars on TV?
Seen them "flat-shifting" - pulling on the sequential gear level at full throttle and not using the clutch?
The gear lever has a stress sensor to detect flex - it triggers the ECU to cut the engine for the gear change
These changes are lightening fast against a 5 litre V8 engine - which manages to change inertia very quickly
If a 5 litre V8 can change inertia that fast then a 2 litre 4 cylinder can also
It's actually been around for 15 years or so (in racing)

In summary, engines are able to change RPM much faster than we expect/anticipate
But it's not the same as blipping the throttle in neutral and waiting for the RPM to decrease,
the ECU cuts the engine hard to make it slow down - then there are other factors (flywheel, etc)

I would also add - don't read too much into VW's 8ms claim which is faster than Ferrari
Never the less, DSG changes are very fast as we all know
(I love it when a Commodore has a go at me, as soon as he puts the clutch down it's all over!)

[stefcio007]

I'm currently driving a car with a Getrag 6DCT450 (wet) and it shifts nicely and very quick, downshifting goes nicely too. Not VW obviously.
The 6DCT450 is used by Ford, Volvo, Chrysler, Dodge.
On the other hand the DCT250 is riddled with problems.

Are the high torque rated DCTs generally more reliable?

[Snail Style]

Timing pull reduces the RPM quickly, the same thing that gives your DSG the fart sounds on shift.

[Ryeman]

I didn't even add the flywheel to the rotating mass equation either......still beats me.

[Umai Naa!!]

It's a dual-mass flywheel (just like a manual!) too, if that helps you at all.

[Ryeman]

I WOULD understand if there were two crankshafts each with their own rods and pistons but a change of 500rpm in six thousandths of a second remains a mystery to me.