How do DCTs work?
12-06-2018, 11:23 AM
#81
Le Mans Master
Originally Posted by Atomic Fred
[left]Have you ever driven one? It is surely automated but drives NOTHING like a traditional slush box. Why is it so difficult for certain very obstinate folks on this Forum to comprehend that these dual-clutch trannies are really a hybrid?
12-06-2018, 11:41 AM
#82
Race Director
No one said they are. Pretty much the same guts as most manuals; completely different, and automated, clutching actuation. So why all the arguing?
Last edited by Rapid Fred; 12-06-2018 at 11:42 AM.
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ByByBMW (12-06-2018)
12-06-2018, 11:43 AM
#83
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Porsche’s PDK is pretty well regarded as the best DCT on the market. What you should know is that the internal gear sets of the PDK are identical to the manual 7 speed transmission. In fact one transmission was designed that could work with a manually activated single clutch AND a dual clutch version where the clutches are under electro-mechanical control, that control either being purely driven by the ECU/TCU or the driver, per paddles on the steering wheel or by movement of the gear lever.
It is far better to call the PDK transmission a manual transmission with ‘automated features’, than a true ‘Automatic’. I’m not sure why you keep contesting this.
BTW: I have a DCT in my AMG GT R. I can be in say 5th gear and high speed; brake hard for a corner and by pulling and holding the left hand (downshift) paddle, the transmission will almost instantly change down to the lowest acceptable gear. These transmissions are able to change gears in as little as 80 milliseconds when in ‘Race/Sport +’ mode, so for all intents and purposes they are capable of instant gear changes. Certainly they the DCT in my car will change down from 5th to say 2nd far, far quicker than you could ever shift a manual from 5 down to 2, and it does so incredibly smoothly without upsetting the balance of the car. If you do not understand the above you have never driven in a car with a good DCT.
Bish
For example. having only had a standard trans in all my DDs for ~60 years, when skipping a gear on a downshift I usually put the trans in the skipped gear with the clutch depressed, it spooled up the cluster gear. Doing that with Rev Match logic assumed I was wanting to go into that gear and matched accordingly. Now I go directly to the lower gear, i.e. most common 5th to 3rd and also 7th to direct drive 4th and let those triple synchros handle speed changes! Also have to be careful where the shift lever is moved. Found I could duplicate the overrevving some complain even when in the neutral gate. For example on a downshift from 5th to 3rd, if the shift level is in the neutral gate but moved toward the 1st/2nd gear slot it will match as if 2nd is where the planned shift will be! Rev Match uses sensors to anticipate what gear is desired!
Last edited by JerryU; 12-06-2018 at 11:46 AM.
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thebishman (12-06-2018)
12-06-2018, 11:50 AM
#84
Porsche’s PDK is pretty well regarded as the best DCT on the market. What you should know is that the internal gear sets of the PDK are identical to the manual 7 speed transmission. In fact one transmission was designed that could work with a manually activated single clutch AND a dual clutch version where the clutches are under electro-mechanical control, that control either being purely driven by the ECU/TCU or the driver, per paddles on the steering wheel or by movement of the gear lever.
It is far better to call the PDK transmission a manual transmission with ‘automated features’, than a true ‘Automatic’. I’m not sure why you keep contesting this.
BTW: I have a DCT in my AMG GT R. I can be in say 5th gear and high speed; brake hard for a corner and by pulling and holding the left hand (downshift) paddle, the transmission will almost instantly change down to the lowest acceptable gear. These transmissions are able to change gears in as little as 80 milliseconds when in ‘Race/Sport +’ mode, so for all intents and purposes they are capable of instant gear changes. Certainly they the DCT in my car will change down from 5th to say 2nd far, far quicker than you could ever shift a manual from 5 down to 2, and it does so incredibly smoothly without upsetting the balance of the car. If you do not understand the above you have never driven in a car with a good DCT.
Bish
Speednet is talking definitions. The term "automated manual" is a contradiction. How can something be both automatic and manual? They are opposites. A manual transmission is not defined by what gear sets or clutches it has. It is defined by requiring manual operation. As in, shifting gears by hand, rather than automatically. I could create a CVT that requires the driver to adjust the ratios by hand, and appropriately call it a manual transmission. If your transmission shifts gears for you, it is an automatic. Definitions don't care if it "feels way better than a slushbox."
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Speednet (12-06-2018)
12-06-2018, 12:31 PM
#85
Race Director
Thread Starter
Come on guys, who really cares if the DCT is an automatic or a manual transmission? The DCT is a transmission that transmits power from the engine onwards towards the drive wheels. If it works it does not matter if you call it an auto or a standard.
Last edited by Tom73; 12-06-2018 at 12:32 PM.
12-06-2018, 12:32 PM
#86
Melting Slicks
For the record, a DCT is an automatic transmission, FULL STOP, because an automatic transmission means it can be shift autonomously (without driver interaction). It doesn't matter than it can optionally use paddles, it doesn't matter how many clutches it has, whether it has a torque converter or not, or if the gears are the exact same ratio as a transmission offered in manual. All that stuff doesn't matter to whether it's classified as an automatic transmission or not. If it can shift without you telling it to, it's an automatic. I don't think this can be made any clearer.
12-06-2018, 01:52 PM
#87
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Are you guys missing the point on purpose??
Speednet is talking definitions. The term "automated manual" is a contradiction. How can something be both automatic and manual? They are opposites. A manual transmission is not defined by what gear sets or clutches it has. It is defined by requiring manual operation. As in, shifting gears by hand, rather than automatically. I could create a CVT that requires the driver to adjust the ratios by hand, and appropriately call it a manual transmission. If your transmission shifts gears for you, it is an automatic. Definitions don't care if it "feels way better than a slushbox."
Speednet is talking definitions. The term "automated manual" is a contradiction. How can something be both automatic and manual? They are opposites. A manual transmission is not defined by what gear sets or clutches it has. It is defined by requiring manual operation. As in, shifting gears by hand, rather than automatically. I could create a CVT that requires the driver to adjust the ratios by hand, and appropriately call it a manual transmission. If your transmission shifts gears for you, it is an automatic. Definitions don't care if it "feels way better than a slushbox."
In welding we have a term for when a welder (as in person) moves a MIG gun, it's called and referred to as semi-automatic. (MIG is what some call a "wire welder" and it's formally called and "defined" as GMAW (Gas Metal Arc Welding" by the purists.) That is opposed to "fully automatic" which I could teach all of you how to weld in minutes, Just "push the Green start button and when at the end of the plates being welded the Red stop button!" Often had folks who visited our R&D Lab do that so they could say they welded!"
As Shakespeare said in Romeo and Juliet", "A rose by any other name would smell as sweet." So a transaxle transmits power. I'll continue to think of it as a computer controlled (if I elect not to use the paddles) manual! If I use the paddles I'm just replacing the mechanical shift linkage with a hydraulic piston and letting the clutchs operate based on when I pull a lever!
We can each have our own definition!
Last edited by JerryU; 12-06-2018 at 02:00 PM.
12-06-2018, 02:49 PM
#88
Safety Car
I think part of the thing is confusing the "manual" and "automatic" terminology as being terminology for the type of gear sets used. There's two types of gear sets used to drive automobiles.
One gear technology is a stack of constantly meshed ratio gear pairs (usually helical cut, sometimes straight cut spur gears), with sliders and dogs/synchronizers used to connect exactly one ratio pair through from input to output, and one or more clutches used to engage/disengage power from the thing.
The other gear technology is planetary gears (ring, sun, planetary gear set).
In recent history, "automatic transmissions" have always been implemented with planetary gear sets, and "manual transmissions" have been implemented with stacks of constantly meshed ratio gear pairs and sliders.
However, there are definitely manual transmissions that use planetary gears. Has anyone here ever driven (or ridden in and watched the driver of) a model T Ford? That's definitely not an "automatic transmission," it's one of the most manual of manual transmissions, and somewhat complex to operate. But it has planetary gears.
On the other end of the spectrum is the current DCT technology, which uses a stack of constant mesh ratio gears and sliders with dogs/synchros, but controlled automatically by a computer and electro-mechanical devices.
One gear technology is a stack of constantly meshed ratio gear pairs (usually helical cut, sometimes straight cut spur gears), with sliders and dogs/synchronizers used to connect exactly one ratio pair through from input to output, and one or more clutches used to engage/disengage power from the thing.
The other gear technology is planetary gears (ring, sun, planetary gear set).
In recent history, "automatic transmissions" have always been implemented with planetary gear sets, and "manual transmissions" have been implemented with stacks of constantly meshed ratio gear pairs and sliders.
However, there are definitely manual transmissions that use planetary gears. Has anyone here ever driven (or ridden in and watched the driver of) a model T Ford? That's definitely not an "automatic transmission," it's one of the most manual of manual transmissions, and somewhat complex to operate. But it has planetary gears.
On the other end of the spectrum is the current DCT technology, which uses a stack of constant mesh ratio gears and sliders with dogs/synchros, but controlled automatically by a computer and electro-mechanical devices.
12-06-2018, 02:54 PM
#89
Le Mans Master
If you go to the ZF website, the manufacture of DCTs actually refers to them as automatics. It is beyond comprehension how someone can claim otherwise with a straight face. This thread is like the twilight zone .
12-06-2018, 03:41 PM
#90
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Reminded of what we used in the early 1960's making clutchless shifts of a 4 speed! . Just cut some of the blocker ring teeth and pull or push very hard! Then we didn't expect the trans to last without a rebuild for more than a few races!
12-06-2018, 03:47 PM
#91
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r
Hmm better write to Sundar Pichai, Google's CEO as this is came up as the first answer to the question, "Is a DCT a Manual or Automatic?" Quoting:
"Essentially, a DCT is an automated manual transmission which uses two separate clutches, one of each odd and even gear sets. ... They can also work just like an automatic transmission, shifting gears on their own, or can be manually controlled, via paddle shifters or a separate gate on the gear selector."
Boy that Google is overly influencing the gullible young generation! We "Old Folks" can make our own definition without their help!
But then again those Google folks are much smarter than any of us- Just ask them!
"Essentially, a DCT is an automated manual transmission which uses two separate clutches, one of each odd and even gear sets. ... They can also work just like an automatic transmission, shifting gears on their own, or can be manually controlled, via paddle shifters or a separate gate on the gear selector."
Boy that Google is overly influencing the gullible young generation! We "Old Folks" can make our own definition without their help!
But then again those Google folks are much smarter than any of us- Just ask them!
Last edited by JerryU; 12-06-2018 at 03:58 PM.
12-06-2018, 04:12 PM
#92
Safety Car
Yep, have watched the Lenco folks rebuild customer transmissions in their booth at national drag events. . They use sun and planetary gears but instead of hydraulics and slipping clutches to engage the next gear they just just brute force! I recall asking a Lenco Tech what causes parts failure and he said folks not pulling it into gear quick enough! But they don't expect to have the trans last 50,000 miles and don't care about efficiency!
Reminded of what we used in the early 1960's making clutchless shifts of a 4 speed! . Just cut some of the blocker ring teeth and pull or push very hard! Then we didn't expect the trans to last without a rebuild for more than a few races!
Reminded of what we used in the early 1960's making clutchless shifts of a 4 speed! . Just cut some of the blocker ring teeth and pull or push very hard! Then we didn't expect the trans to last without a rebuild for more than a few races!
Slowly wandering back to the topic of this thread, it had a very well tuned 455 cubic inch V8, turbohydramatic 400 transmission, but I replaced the torque converter with a clutch and put the Lenco pro-stock shifter package from that era on it. It was definitely a manual transmission with planetary gears.
Would take it to places with valet parking sometimes. When I'd get back from dinner or whatever, It was always right where I left it, with the keys still in it, untouched and unmoved. I heard more than one valet guy say something like "Awwww, hell no!" when getting into the thing.
Last edited by C6_Racer_X; 12-06-2018 at 04:13 PM.
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JerryU (12-06-2018)
12-06-2018, 04:34 PM
#93
Race Director
Thread Starter
Moderators, can you close this thread? I started this thread to find out how a DCT works. It has now devolved into a shouting match about if a DCT is an automatic or a manual transmission.
Time me to shut it down.
Time me to shut it down.
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ByByBMW (12-06-2018)
12-06-2018, 04:37 PM
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