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School me on the DCT #4660844
02/09/18 11:54 AM
02/09/18 11:54 AM
Joined: Sep 2004
Posts: 8,009
Marshfield , MA
andyd Offline OP
andyd  Offline OP

Joined: Sep 2004
Posts: 8,009
Marshfield , MA
Ever since I first encountered the term dual clutch transmission I've wondered what was good about having 2 clutches? What makes a DCT work? . TIA


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2
Re: School me on the DCT [Re: andyd] #4660861
02/09/18 12:08 PM
02/09/18 12:08 PM
Joined: Dec 2013
Posts: 3,989
Manchester, England
Olas Offline
Olas  Offline

Joined: Dec 2013
Posts: 3,989
Manchester, England
You know about input shaft/lay shaft/output shaft and the sliding mesh gears?
Well imagine two concentric input shafts, one has gears 1,3,5 other shaft has gears 2,4,6. Each shaft has its own clutch and can 'preselected' the next gear so it only has to change from one concentric input shaft to the next.

There's some cool animations on YouTube


Cable ties should hold it
Re: School me on the DCT [Re: andyd] #4660866
02/09/18 12:10 PM
02/09/18 12:10 PM
Joined: Dec 2013
Posts: 3,989
Manchester, England
Olas Offline
Olas  Offline

Joined: Dec 2013
Posts: 3,989
Manchester, England


Cable ties should hold it
Re: School me on the DCT [Re: andyd] #4660903
02/09/18 12:46 PM
02/09/18 12:46 PM
Joined: Jan 2013
Posts: 2,496
Texas
WyrTwister Offline
WyrTwister  Offline

Joined: Jan 2013
Posts: 2,496
Texas
I have read up on the problems with the Dual Clutch Transmissions on the Ford Escape and Focus .

Those transmissions give the appearance of an automatic , but are more a semi-automatic transmission under electronic control . Do not think they have the torque converter , like the traditional automatic . Maybe no planateraries or " wet clutches " .

This last summer when we were shopping for a used car , I ruled out the Focus because of the history of problems with the transmissions .

I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?


Wyr
God bless
Re: School me on the DCT [Re: WyrTwister] #4660912
02/09/18 12:58 PM
02/09/18 12:58 PM
Joined: Nov 2008
Posts: 13,150
NH
supton Offline
supton  Offline

Joined: Nov 2008
Posts: 13,150
NH
Originally Posted By: WyrTwister
I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?


Yep. Never in a slippage region like an unlocked torque convertor. I think all the controls are electromechanical? conventional automatics use a fluid pump to generate pressure; but in order to have sufficient pressure at low engine rpm means it's bleeding lots of pressure off at high rpm. [Pump is driven off the engine, so that the transmission will work at idle.]

IIRC first & reverse are usually pretty low, so as to get around having to slip the clutch a lot.

It's a pretty cool idea. Just one that seems to have had a few teething issues--good idea, and some bad implementations it seems.


2011 Toyota Camry, base, 2.5L/6MT, 179k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 146k, ours
1999 Toyota Camry LE, 2.2L/4AT, 202k, his
Re: School me on the DCT [Re: andyd] #4660919
02/09/18 01:08 PM
02/09/18 01:08 PM
Joined: Aug 2008
Posts: 3,461
Where the wind comes sweepin'
Reddy45 Offline
Reddy45  Offline

Joined: Aug 2008
Posts: 3,461
Where the wind comes sweepin'
I think the biggest problem with DCTs is that people get them and drive them like traditional automatics (with the same expectations).

A lot of the complaints probably have to do with how the DCT prepares the next gear. If you drive in a manner that is not consistent with how a DCT is programmed then you're going to think it's clunky and inefficient.

Burnt clutches would be another issue. The mfrs should only use wet clutch DCTs for consumer vehicles. This might give it a fighting chance to survive when the car is held up on a hill with just the gas pedal.

Re: School me on the DCT [Re: andyd] #4660925
02/09/18 01:14 PM
02/09/18 01:14 PM
Joined: Sep 2004
Posts: 8,009
Marshfield , MA
andyd Offline OP
andyd  Offline OP

Joined: Sep 2004
Posts: 8,009
Marshfield , MA
Thank you, Olas. I kept waiting for the the guy's beard to get caught in the gears. And DCT are "good" because they shift faster? Further wikipedia informs me that they are used in everything on wheels.


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2
Re: School me on the DCT [Re: andyd] #4660938
02/09/18 01:27 PM
02/09/18 01:27 PM
Joined: Aug 2003
Posts: 11,229
Buffalo, NY
JTK Online content
JTK  Online Content

Joined: Aug 2003
Posts: 11,229
Buffalo, NY
I think they've got some good things going for them, such as needing gear oil for a lube as opposed to expensive, unit-specific ATF/CVT fluid. Not a lot of heat generated, nor the need for fluid coolers/heaters either.

Like said, I think with the right driver and driving conditions, DCTs could be a great thing.

Last edited by JTK; 02/09/18 01:27 PM.

2017 Ram 1500 4x4, 3.6L. 2016 Nissan Quest SV (Babe magnet IV)
Re: School me on the DCT [Re: andyd] #4661008
02/09/18 02:30 PM
02/09/18 02:30 PM
Joined: Dec 2011
Posts: 5,650
North Carolina
rooflessVW Offline
rooflessVW  Offline

Joined: Dec 2011
Posts: 5,650
North Carolina
Which DCT doesn't need a special oil?


"Zed's dead baby, Zed's dead."
Re: School me on the DCT [Re: rooflessVW] #4661027
02/09/18 02:42 PM
02/09/18 02:42 PM
Joined: Dec 2006
Posts: 8,366
Canuck living in California
KrisZ Online content
KrisZ  Online Content

Joined: Dec 2006
Posts: 8,366
Canuck living in California
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?


Dry clutch units should not need anything special.


2015 Grand Caravan 3.6L - 31k miles.
2006 Mazda 3 2.0L - 171k miles
Re: School me on the DCT [Re: KrisZ] #4661048
02/09/18 03:07 PM
02/09/18 03:07 PM
Joined: Dec 2011
Posts: 5,650
North Carolina
rooflessVW Offline
rooflessVW  Offline

Joined: Dec 2011
Posts: 5,650
North Carolina
Originally Posted By: KrisZ
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?

Dry clutch units should not need anything special.

And yet...

Porsche, BMW, VW, Audi, Ford, etc. all use special oils in their dual clutch gearboxes.


"Zed's dead baby, Zed's dead."
Re: School me on the DCT [Re: rooflessVW] #4661063
02/09/18 03:41 PM
02/09/18 03:41 PM
Joined: Dec 2006
Posts: 8,366
Canuck living in California
KrisZ Online content
KrisZ  Online Content

Joined: Dec 2006
Posts: 8,366
Canuck living in California
Originally Posted By: rooflessVW
Originally Posted By: KrisZ
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?

Dry clutch units should not need anything special.

And yet...

Porsche, BMW, VW, Audi, Ford, etc. all use special oils in their dual clutch gearboxes.


I'm talking from a technical point of view, not marketing and revenue generation. If the clutches are dry, the only reason I can think of is some special and exotic materials used in synchros to cope with the computer controlled actuators. But I think it's a stretch.

Last edited by KrisZ; 02/09/18 03:41 PM.

2015 Grand Caravan 3.6L - 31k miles.
2006 Mazda 3 2.0L - 171k miles
Re: School me on the DCT [Re: andyd] #4661064
02/09/18 03:42 PM
02/09/18 03:42 PM
Joined: Jun 2002
Posts: 19,753
Iowegia - USA
MolaKule Offline
Global Moderator
MolaKule  Offline
Global Moderator

Joined: Jun 2002
Posts: 19,753
Iowegia - USA
Most DCT fluids are MTF-type formulations with an [email protected] viscosity.

https://www.youtube.com/watch?v=lFAtc-zOKZs

Last edited by MolaKule; 02/09/18 03:57 PM.

"I can't change the direction of the wind, but I can adjust my sails to always reach my destination." Jimmy Dean
Re: School me on the DCT [Re: WyrTwister] #4661161
02/09/18 05:16 PM
02/09/18 05:16 PM
Joined: Oct 2010
Posts: 1,856
.
Danh Offline
Danh  Offline

Joined: Oct 2010
Posts: 1,856
.
Originally Posted By: WyrTwister
I have read up on the problems with the Dual Clutch Transmissions on the Ford Escape and Focus .

Those transmissions give the appearance of an automatic , but are more a semi-automatic transmission under electronic control . Do not think they have the torque converter , like the traditional automatic . Maybe no planateraries or " wet clutches " .

This last summer when we were shopping for a used car , I ruled out the Focus because of the history of problems with the transmissions .

I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?


The Escape has a conventional 6 speed automatic. DCTs are on the Focus and Fiesta.

There are DCTs and there are DCTs. The Focus/Fiesta version sold in the US is a dry-clutch unit designed for lower torque applications. This version is sold elsewhere too, but more common is a wet-clutch, high torque DCT mated to Diesel engines.

Fordís was and is a mess. First, itís a dry clutch that is inherently more challenging. Second, itís uncomfortably close to its torque capacity in the Focus. Third, Ford did an abysmal job of testing, Fourth, quality control over the gearbox and clutches was lousy. Having owned one and gone through 3 clutch packs and countless program updates over 45k, I can confidently advise people to stay away.

I now have an Acura with both wet clutches and a torque converter and itís great.

DCTs are more engaging to drive than a conventional automatic and can be more efficient. Properly designed, they can also be trouble free. But stay away from dry-clutch variants.

Re: School me on the DCT [Re: supton] #4661210
02/09/18 06:37 PM
02/09/18 06:37 PM
Joined: Dec 2016
Posts: 8,006
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,006
Waco, TX
Originally Posted By: supton
conventional automatics use a fluid pump to generate pressure; but in order to have sufficient pressure at low engine rpm means it's bleeding lots of pressure off at high rpm. [Pump is driven off the engine, so that the transmission will work at idle.


This is no longer true.

All modern auto transmissions vary pressure to the clutches depending on RPM & Load.

Under light cruise, very little hyd pressure is to the clutches.
Under heavy load and acceleration, the pressure increases to keep the clutches tight.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
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