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
School me on the DCT
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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
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
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 ?
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 ?
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.
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.
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.
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.
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.
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.
Like said, I think with the right driver and driving conditions, DCTs could be a great thing.
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Which DCT doesn't need a special oil?
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?
Dry clutch units should not need anything special.
Which DCT doesn't need a special oil?
Dry clutch units should not need anything special.
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.
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.
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.
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.
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MolaKule
Staff member
Most DCT fluids are MTF-type formulations with an 8.0cSt@100C viscosity.
https://www.youtube.com/watch?v=lFAtc-zOKZs
https://www.youtube.com/watch?v=lFAtc-zOKZs
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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.
Ford’s was and is a mess. First, it’s a dry clutch that is inherently more challenging. Second, it’s 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 it’s 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.
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.
Ford’s was and is a mess. First, it’s a dry clutch that is inherently more challenging. Second, it’s 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 it’s 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.
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.
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 DCT is two 3-speed manuals tied together with 2 clutches. Typically, one set controls the odd gears (1/3/5), while the other set controls the even number gears (2/4/6). One of them also runs the reverse gear.
The problems with DCT transmissions is that using the paddles is REQUIRED to get any decent behavior out of them because they're not quite the same thing as a normal automatic transmission. Even though it looks like there's a D like a regular automatic, even though it looks like P/R/N/D like a regular automatic, it's not. A DCT with no paddles is just downright awful. Neither of Ford's DCTs in the Fiesta and Focus have paddles, just D and L, for 6 gears. And you know they wouldn't DARE put a DCT in the Ecosport or Escape or any crossover or large car.
Ford sells the Fiesta overseas with a regular 4-speed automatic, and with all the recalls on the DCT, it would've been cheaper for Ford to just swap in the 4-speed auto. The Focus is available with a 6-speed automatic in the US, but only on the SE sedan with the 1.0T. Ford should use that automatic on all Focus models.
Honda makes a DCT with a torque converter on the TLX and RLX, and it's better than other DCTs, but it's still not as good as a regular automatic. They are still AWFUL in daily driving in the city.
Amalie makes a good DCT fluid at a great price when bought by the case, so if I had a DCT, I'd change the fluid every year if not every OCI. So special fluid is the least of your problems.
Theoretically the DCT is supposed to give you better mileage and be more efficient, but for this purpose, a CVT is best because it has an infinite number of gears/ratios. Also, regular torque converter automatics have gotten so good there's no need to put up with the many downsides of the DCT.
The DCT DOES NOT belong in normal regular economy cars and family cars. These poor designs should be restricted to high performance cars where the difference is actually meaningful and more likely to be driven in a way that actually benefits from a DCT.
The problems with DCT transmissions is that using the paddles is REQUIRED to get any decent behavior out of them because they're not quite the same thing as a normal automatic transmission. Even though it looks like there's a D like a regular automatic, even though it looks like P/R/N/D like a regular automatic, it's not. A DCT with no paddles is just downright awful. Neither of Ford's DCTs in the Fiesta and Focus have paddles, just D and L, for 6 gears. And you know they wouldn't DARE put a DCT in the Ecosport or Escape or any crossover or large car.
Ford sells the Fiesta overseas with a regular 4-speed automatic, and with all the recalls on the DCT, it would've been cheaper for Ford to just swap in the 4-speed auto. The Focus is available with a 6-speed automatic in the US, but only on the SE sedan with the 1.0T. Ford should use that automatic on all Focus models.
Honda makes a DCT with a torque converter on the TLX and RLX, and it's better than other DCTs, but it's still not as good as a regular automatic. They are still AWFUL in daily driving in the city.
Amalie makes a good DCT fluid at a great price when bought by the case, so if I had a DCT, I'd change the fluid every year if not every OCI. So special fluid is the least of your problems.
Theoretically the DCT is supposed to give you better mileage and be more efficient, but for this purpose, a CVT is best because it has an infinite number of gears/ratios. Also, regular torque converter automatics have gotten so good there's no need to put up with the many downsides of the DCT.
The DCT DOES NOT belong in normal regular economy cars and family cars. These poor designs should be restricted to high performance cars where the difference is actually meaningful and more likely to be driven in a way that actually benefits from a DCT.
Originally Posted By: slacktide_bitog
Honda makes a DCT with a torque converter on the TLX and RLX, and it's better than other DCTs, but it's still not as good as a regular automatic. They are still AWFUL in daily driving in the city.
The RLX has a conventional automatic. And, do you own an Acura with a DCT? I do. And it’s just fine in city driving, virtually indistinguishable from a conventional automatic. While it has paddle shifters I rarely use them; really no need.
I know this is BITOG and we hate CVTs, DCTs, low viscosity oils, Frams (or Purolators, depending on day), direct injection, et al, but sometimes we go overboard. Well, except for DI maybe...
Honda makes a DCT with a torque converter on the TLX and RLX, and it's better than other DCTs, but it's still not as good as a regular automatic. They are still AWFUL in daily driving in the city.
The RLX has a conventional automatic. And, do you own an Acura with a DCT? I do. And it’s just fine in city driving, virtually indistinguishable from a conventional automatic. While it has paddle shifters I rarely use them; really no need.
I know this is BITOG and we hate CVTs, DCTs, low viscosity oils, Frams (or Purolators, depending on day), direct injection, et al, but sometimes we go overboard. Well, except for DI maybe...
Bought a '14 Focus without realizing what I was getting into. At first I was delighted by the low price of the car, then dismayed and sad about the DCT.
But a couple of months in, I'm really just fine with it. It feels like an automated manual, and that's a great thing. It's like the opposite of a CVT. You have to drive it sort of the same way you ride a horse: you need to signal with your throttle and brake applications what you intend to do and give it 1/4 second to respond appropriately. Being an inconsistent and jerky operator will give you inconsistent and jerky performance.
I haven't quite demystified the whole shift algorithm, but I'm pretty ok with it. It likes to slip into 2nd way longer than I would with a third pedal. But it's not the monster it's made out to be.
But a couple of months in, I'm really just fine with it. It feels like an automated manual, and that's a great thing. It's like the opposite of a CVT. You have to drive it sort of the same way you ride a horse: you need to signal with your throttle and brake applications what you intend to do and give it 1/4 second to respond appropriately. Being an inconsistent and jerky operator will give you inconsistent and jerky performance.
I haven't quite demystified the whole shift algorithm, but I'm pretty ok with it. It likes to slip into 2nd way longer than I would with a third pedal. But it's not the monster it's made out to be.
Originally Posted By: Linctex
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.
Sure, but how does it vary the pressure? Do they alter the vanes (or similar) so as to reduce pumping loss; or do they just bleed it off? I'm thinking there is still loss there, loss that a DCT or MT wouldn't have.
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.
Sure, but how does it vary the pressure? Do they alter the vanes (or similar) so as to reduce pumping loss; or do they just bleed it off? I'm thinking there is still loss there, loss that a DCT or MT wouldn't have.
Originally Posted By: supton
Originally Posted By: Linctex
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.
Sure, but how does it vary the pressure? Do they alter the vanes (or similar) so as to reduce pumping loss; or do they just bleed it off? I'm thinking there is still loss there, loss that a DCT or MT wouldn't have.
I too wonder how does this supposedly constant-rpm 'variable-line-pressure' pump works ?
Awaiting to be educated.
Originally Posted By: Linctex
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.
Sure, but how does it vary the pressure? Do they alter the vanes (or similar) so as to reduce pumping loss; or do they just bleed it off? I'm thinking there is still loss there, loss that a DCT or MT wouldn't have.
I too wonder how does this supposedly constant-rpm 'variable-line-pressure' pump works ?
Awaiting to be educated.
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