difference between Steptronic vs Double Clutch

[jayce]

apologies for such noob question

BMW announced that they will equipt the 7-speed Double Clutch DKG on the 2009 3series coupe&converts.

I've seen this 'double clutch technology' on a Volkswagen and they call it the DCT(double clutch transmission)

according to wikipedia,
http://en.wikipedia.org/wiki/Twin-clutch_gearbox
DCT is just another semi-auto trans, just like step(correct me if im wrong)

I'm totally confused.

To me, seems like DCT or DKG trans have no clutch, shifts instantly in manual mode.
That sounds just like a steptronic.

[mtla4]

DSG-DCT=twin clutch while the Steptronic is a fancy name for a regular auto tranny.
People will argue that the 1 is faster in auto(but the test werent done the same day..different conditions etc). Steptronic has a torque converter and is like any other Tiptronic,Autostick,E-Shift etc.
DCT-DSG are faster than manual but the thing is that you always feel like its missing something(3rd pedal)

[atr_hugo]

No - and don't worry about being alone, most folks don't understand the difference.

The double clutch tranny uses a clutch (two actually - and they are 'wet'), like a manual transmission, to couple the engine output to the transmission. It uses software to control the shifts (like a modern automatic) but there is no clutch pedal (because of the electronic operation of the clutch/gear-change). So it is, in essence, a 'clutch pedalless', 'stickless', manual tranmission that has a pretty passable automatic mode built in.

The Steptronic transmission (and the other so-called manu-matic trannies) have torque converters. There is no direct physical coupling (other than transmission fluid) between the output of the engine and the transmission. But because modern automatics are electronically controlled they can deliver a reasonable facsimile of a manual transmission (minus the clutch pedal and the gear-change, of course).

Now don't confuse either of those with the SMG. It's a horse of a different color. ; -)

[jayce]

thanks to both for good answers.
then i guess the F1 cars use double clutch.

undoubtly, if this is the case, i would call the DCT a true automatic trans. God i regret ordering that steptronic on my 135

[atr_hugo]

No the F1 cars use an SMG (it may be a multiplate clutch though, not unlike a lot of motorcycles - I've got a recent F1 tech book around here somewhere that'll tell me what type clutch it uses).

Bear this in mind when thinking about a DCT - it has two clutches each attached to a separate shaft (they are concentric however) - one shaft contains the odd-numbered gears, the other the even. It pre-selects the next gear based on observed conditions (throttle position, brake, steering angle und so weiter). That's one of the reasons the shifts are so quick. (Now for those truly interested, pre-selector gearboxes date back to WW I - the Cotal, nee Wilson pre-selector gearbox was first used in tanks then in some pretty special French cars.)

An SMG is a single shaft input gearbox. It is sequentially shifted which means to get to sixth from third you have to go through fourth and fifth - you have to row all the way up and all the way down that's why you hear the multiple blips whilst an F1/Indy car corners, and why you sometimes hear one MASSIVE blip when a 'regular' manual tranny (which can go from sixth to second skipping fifth, fourth, and third) racing car is under braking for a corner.

Now, if that doesn't confuse the hell out of you, let's talk about derivatives and the banking crisis. ; -)

[atr_hugo]

What we really need here are pictures. Let me dig around I think I have a cutaway pic of the Audi DSG.

Had to steal one off the intertubes. ; -)

[ru with me drhoo]

Originally Posted by jayce

undoubtly, if this is the case, i would call the DCT a true automatic trans.

Not quite. Look at it like this:

Steptronic is an auto trans (has a torque convertor, not a direct link) that you can control (like any auto trans, really).

DSG/DCT is a manual trans where a computer manages the clutch "pedal" and throttle while you control the gears, but can also be used "automatically".

[jayce]

Originally Posted by ru with me drhoo

Not quite. Look at it like this:

Steptronic is an auto trans (has a torque convertor, not a direct link) that you can control (like any auto trans, really).

DSG/DCT is a manual trans where a computer manages the clutch "pedal" and throttle while you control the gears, but can also be used "automatically".

yes i mean the DCT is a transmission that normal auto trans ought to be.
it's just brilliant and so efficient.

but then i see DCT provided in only M3
and SMG provided in only M6

i see how SMG is better than DCT and DCT than Steptronic,
but just wondering does it really cost much more to make SMG and DCT than steptronic?

[Mad Dragon]

SMG isn't better than the DCT.

[Rye]

Originally Posted by jayce

...but just wondering does it really cost much more to make SMG and DCT than steptronic?

Newer technology almost always costs more than what traditionally has been produced.

[JohnnyTT]

I don't want to start up an automatic vs .... war.

But I've driven manuals my whole life, I've driven auto-clutches, and I'm driving my 135i with steptronic.

I would put this steptronic up against all the DSG/DCT trans out there and say the 135's steptronic shifts faster than everyone I've been in. The shifts are INSTANT!!!!..and lock up is INSTANT!!!!

Yes, as soon as a DSG/DCT comes out that is lightning fast, I will definitley jump on board. But I havn't driven one yet. I'm honestly extremely happy with my instant shifts.

Yes everybody, I do understand the feel of having a direct line to the engine. I do appreciate that raw feeling. But I'm all smiles in manual mode when I hit a turn in 3rd or 4th...and come flying out in 2nd, WithOut A Hint Of Hesitation.

[Buschy]

Originally Posted by JohnnyTT

I don't want to start up an automatic vs .... war.

But I've driven manuals my whole life, I've driven auto-clutches, and I'm driving my 135i with steptronic.

I would put this steptronic up against all the DSG/DCT trans out there and say the 135's steptronic shifts faster than everyone I've been in. The shifts are INSTANT!!!!..and lock up is INSTANT!!!!

Yes, as soon as a DSG/DCT comes out that is lightning fast, I will definitley jump on board. But I havn't driven one yet. I'm honestly extremely happy with my instant shifts.

Yes everybody, I do understand the feel of having a direct line to the engine. I do appreciate that raw feeling. But I'm all smiles in manual mode when I hit a turn in 3rd or 4th...and come flying out in 2nd, WithOut A Hint Of Hesitation.

if you go flying out of a turn in second and the tires spin, doesnt the tranny kick it at redline, shift, lose power, and bog a bit?

in a manual, your in total control?

this is a question,not a disput.

[JohnnyTT]

Originally Posted by Buschy

if you go flying out of a turn in second and the tires spin, doesnt the tranny kick it at redline, shift, lose power, and bog a bit?

in a manual, your in total control?

this is a question,not a disput.

Buschy, I'm not sure what you mean. I'm assuming I'm coming out of the turn in 2nd in the 3500-5000 rpm range, and pull near red and shift. Where do I lose power or bog?

Can you better clarify the order of events for me. Thanks.

[Buschy]

Just wondering if your flying out a corner or drifting or whatever if your in say second gear and you get to redline, you have to shift or the car shifts for you, right>?
when you shift the tires go from spinning to gripping, and well I guess you dont lose power or bog. I guess you take off.
so what if you want to keep spinning, say in a drift? can you?
I dont know how to drift but I know that when even I "fishtailed" in my 335 it would have to shift and then I would not spin any more.

I am jsut wondering.

[Wraith]

Originally Posted by Mad Dragon

SMG isn't better than the DCT.

Correct !

SMG stands for 'Sequential Manual Gearbox' and is previous technology from BMW now replaced with their 'automated manual trans' they call DCT...or 'Double Clutch Transmission'

The actual precise specific designation or as the mech. heads refer to it for the BMW 7sp DCT is: GS7D36SG Twin-Clutch-Gearbox.

The VW DSG stands for 'Double Shift Gearbox' and they now have 3 main versions of this transmission, the 6spd we all know of in most of their range, the 6spd upgraded/strengthened model in the Veyron and a new 7spd introduced recently.

Porsche were the 1st to produce and use 'automated manuals' pity they are amongst the last hi-po car manufacturers to introduce them for their street cars...their new 7spd unit is the 'PDK'

atr_hugo has nailed the rest with his posts !

Automated manuals were made to incorporate the best features of 'both' auto and manuals into one transmission, they will continue to evolve and eventually will totally replace all other transmissions - some hi-po vehicles are already being released with automated manual trans only ! eg: R35 GT-R, so the stick shift bridgade had better get used to them :wink:

[jayce]

far as i know, no matter what your situation is, if the rpm hits rev meter, it shifts. it's just designed like that.

honestly, after test driving a couple more steps and sticks and DCT,
i have to say steps are not that great in delivering the power. the torque converter def has a limit on tranferring power

[atr_hugo]

Software determines whether it upshifts at the rev limiter. And that goes for manu-matics and DCT gearboxes.

I seem to remember driving a Lincoln LS on an autocross course a few years back and the manu-matic allowed you to bounce off the rev-limiter. It would not upshift until you instructed it to by slapping the gearlever. But, thank goodness, it wouldn't let you downshift past the red line. ; -)

[jeremyc74]

For me the real attraction to the DCT is the fact that it offers the best of both worlds. It's a direct connection system like a normal manual transmission, so you don't loose any of the feel when you're driving hard, but it has the lightening fast shifts and the ability to let it take care of the gear selection when you're in traffic.

I'm not sure I would like it as much as a standard transmission after a while, but it's certainly better than having a torque converter between the engine and drive wheels.

(And I don't mean that as a dig on the automatic that's in the 135i. It's about as good as any auto I've ever driven, but there's still a fluid coupling)

[Robert]

Money shift is no fun

[Mad Dragon]

Originally Posted by Wraith

The VW DSG stands for 'Double Shift Gearbox'

Direct Shift Gearbox

[jkp1187]

I was impressed with the shifts in the steptronic 128i as well as the Volkswagen GTI's DSG.

I was disappointed, however, that neither of them held the gear and let me bounce off the redline, even when in "manual" mode.

[JohnnyTT]

Originally Posted by Buschy

Just wondering if your flying out a corner or drifting or whatever if your in say second gear and you get to redline, you have to shift or the car shifts for you, right>?
when you shift the tires go from spinning to gripping, and well I guess you dont lose power or bog. I guess you take off.
so what if you want to keep spinning, say in a drift? can you?
I dont know how to drift but I know that when even I "fishtailed" in my 335 it would have to shift and then I would not spin any more.

I am jsut wondering.

Now I gotcha. First, I don't ever really drift turns. I'm not really driving in places that I would try to. For me, I tend to keep the 1st lvl of traction control on....and when I'm coming out of the turn, I'll chirp the tires if I'm high enough rpms in second and the traction will bring bring me back into line. With the traction off, all I do is partially let off the gas so the tires are with less power, but I'm not really giving up much boost.

But what you're saying about your 335.. when you shift, you have a brief moment where there is no power to your tires, I wouldn't call it a loss of power... it's just a brief shift with boost partially maintained and rebuilt as the car engages the next gear.