A dual-clutch transmission is an automated manual transmission with two sets of gears, each operated by a separate clutch. 2020 Porsche 911 Specs & Reviews Find a 2020 Porsche 911 Near You One. The dual-clutch transmission, also known as the Direct Shift Gearbox (DSG) or twin-clutch transmission, is an automated transmission that can change gears faster than any other geared transmission. Dual clutch transmissions deliver more power and better control than a traditional automatic transmission and faster performance than a manual.
Clutch; - Perfect, Exactly what is needed, (also used like 'score' or 'awesome', as an exclamation.). A double clutch is a method of shifting gears primarily used for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. A double clutch is not necessary in a vehicle that has a synchronized manual transmission.
“Granny shifting instead of double clutching like you should”
Words made famous by ‘Dom’ (Vin Diesel) in 2001 film The Fast and the Furious. Maybe the low expectations of the movie led the makers to deem fact checking unnecessary, but this line stands out as a glaring error amongst a host of them relating to motor vehicles and their operation.
Subsequently the Fast & Furious franchise has gone on to become the sixth highest grossing in cinema history taking over $5billion worldwide, mistakes and all. Proving everyone loves fast cars regardless of whether the people driving them know what they’re talking about or not.
The reason this supposed criticism is such a mistake is that double clutching is a technique typically used for shifting down through the gears, and since they had just completed a drag race this was not what ‘Brian’ (the late Paul Walker) should have been doing at all.
Technique
‘Granny shifting’ describes the process of methodically sequencing up or down through the gears – as taught by your driving instructor. Other techniques to change gears in certain situations have been devised through the years to speed up or otherwise improve upon the action of changing gears in the quest for more speed.
Double clutching is one such technique, but it is not used to shift up. This is because the process involves matching the engine speed with the gear you want to change into - but as you can only directly affect an engines speed when it isn’t in gear by increasing it (using the accelerator), double clutching isn’t used for accelerating as you would need to drop the engines speed relative to the wheels instead. The only way to do that is to wait for the engine speed to drop.
When looking to change up gears, the process of pressing the clutch and lifting off the accelerator drops your engine speed sufficiently to change into a higher gear and then continue accelerating afterwards. Your transmission speed is almost unchanged; the wheels are still travelling nearly as fast as they were, but by dropping the engine speed you have matched it to the gear you want to engage.
When changing down, the speed of your engine needs to be higher in relation to the speed of the wheels and transmission – which is why if you change down when travelling at speed you will feel the car decelerate noticeably as the engine isn’t rotating fast enough to maintain the current transmission and wheel speed.
Here’s where double clutching comes in. As you look to change down, instead of immediately putting it into the next gear, you instead put it in neutral and release the clutch. This meshes the clutch with the engine but not the transmission, at which point you tap the accelerator to increase both the engine speed and now enmeshed clutch speed as well.
Double Clutch Meaning In Car
Now they are rotating at a faster speed than before, you can depress the clutch again and change down into the next gear as normal having matched the engine speed to the gear you want to change into rather than the one you were in.
This all happens very quickly – barely half a second with practice – and when done correctly will speed up how fast you can change down gears as you don’t have to wait for the transmission/wheel speed to drop before making the change.
redundant
Not that you would notice however - this technique is now largely redundant. Transmissions have advanced to the point where they incorporate the process into their mechanics through the use of synchronisers, which sit between the gears and the clutch and help match their speeds without the need of advanced shifting techniques.
We have talked here about how different types of manual transmissions work, including the synchromesh which uses synchronisers, and it provides a better understanding of the processes double clutching affects.
So now you know what it is, you can…not bother with it. Double clutching is now primarily utilised by certain large vehicles and older cars with transmissions that don’t have synchronisers.
There are a few instances where it could be used, but all involve racing and not everyday road use - such as powering into a corner where you need to change down quickly, and when overtaking and need to quickly accelerate by shifting down into a lower gear. But there's no harm in knowing what it is and how to do it.
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Despite what is undoubtably very clever and complex engineering, the Double (or Dual) Clutch Transmission (DCT), has a mixed reputation with drivers and has not achieved the level of ubiquity many thought it would.
Sitting in the middle ground between an automatic and a manual transmission, the simplest way of describing their operation, is that they’re an automatically operated manual transmission – achieved by using two clutches.
Doing away with the torque converter of a normal automatic transmission, they utilise the traditional gearing methods of a manual - but then split that gearing across two output shafts to allow power flow to shift between them incredibly quickly.
ORIGINS
Also referred to as a Direct Shift Gearbox (DSG), most car manufacturers have their own version or versions, but use them selectively across their ranges of vehicles – with the Volkswagen group the most invested in their implementation.
Like so many ‘new’ developments for automobiles, the double clutch transmission is an idea that had been around for a significant amount of time before finally being put to use, having been experimented with pre-World War two.
Its realisation had to wait until the 80’s, and it was Porsche who eventually became the first major adopter having worked on their own version since the 60’s.
The Porsche 956 released in 1983 received the distinction of being the first to feature one, and their complexity and expense kept them in the realm of motor racing and high-end super cars for the most part.
Space was also a considerable restriction. The electronics needed for the computerised control module had not yet reached the miniaturisation levels of modern times and so were quite sizeable and took up valuable engine bay space.
It wasn’t until 2003 that a production road car featured a DCT, in Volkswagen’s Mk4 Golf R32.
ADVANTAGES
The purpose behind a DCT is to reduce the gap between gear shifts to a minimum, with the benefits being improved performance and fuel efficiency.
The less time spent off the power changing gear during acceleration the faster the vehicle can accelerate - and by reducing the time spent off the power during gear changes in general, the better fuel economy will be as engine power isn’t wasted.
Double Clutch Meaning In English
Gear changes on DCTs can now be measured in the milliseconds, faster than any driver is capable of, and still retain the advantages a manual gearbox has over an automatic.
How it achieves these lightning fast changes is by anticipating what the next gear needed will be, based on factors such as rate of acceleration or deceleration, current speed of travel and engine speed.
This allows the computer to have the predicted gear already engaged before the change is made.
OPERATION
Unless you’re already familiar with how a DCT works, you’re probably already questioning how this type of transmission can have two different gears selected simultaneously without exploding into a shower of shrapnel.
The clue is in the name but that’s only describing part of the process. Yes, there are two clutches, but simply having an extra clutch doesn’t really explain how a transmission can select more than one gear at a time.
The twin clutches are arranged concentrically – meaning one sits within the circumference of the other, crucially enabling them to both work on the same input shaft.
However, the input shaft connected to both the clutches is not one shaft, but two - with one of them sitting within the other and allowing each clutch to contact and act upon a different one.
The gears are split across the split input shaft by odds and evens, allowing the transmission to switch back and forth between them as the car accelerates and decelerates – pre-selecting each gear on the opposite input shaft to the one engaged.
The gears themselves are no longer engaged purely mechanically by the gear level either and are instead actuated by shift forks powered by pistons, engaging and disengaging as necessary.
When you shift gears, the gear level is signalling for these pistons to actuate and engage the synchronisers onto the chosen gear, and not mechanically engaging them itself.
In this simplified diagram you can see how the input shaft is divided in two via a hollow shaft, with one running through the other and both controlled by the double clutch switching between them.
The gears work as a normal synchromesh transmission would, by utilising synchronisers to connect the gears to the output shafts.
Tracing a line from the blue clutch on the left, along the input shaft, up onto first gear on the first output shaft, and then continuing along and down onto the transmission output gives you first gear.
While this is happening, the computer is deciding which gear you’ll be wanting next. If you are accelerating it will almost certainly opt for second gear and connect this gear on other half of the input shaft so that it is ready as soon as you want to shift up into second.
On shifting, the clutches switch over and power transfers to the grey section of the input shaft, tracing a line along and down onto second gear and out onto the transmission output as before.
There’s a slight overlap between the two as the clutches engage and disengage, but the change is incredibly fast with almost no gap between the two speeds, giving the impression of a near seamless gear change.
It’s a very sophisticated system - but not one without its problems or detractors.
PROBLEMS
The system does run into problems when going from stationary to very slow speeds, where there’s a delay in engaging first gear but the driver is still depressing the accelerator waiting for power delivery. Once the system catches up and the gear is engaged, the car will then accelerate according to how fast the engine speed is - and if the driver has given it too much power it can cause the car to shoot forwards unexpectedly.
This problem can be largely attributed to unfamiliarity with the system, but other complaints are more directly related to its mechanical processes - although this is usually relevant for earlier model DCT/DSGs.
These include having to wait for the system to shift down gears when decelerating rapidly, as it is unable to skip gears due to the alternating method of operation between input shafts; and problems with reversing up hills where the system can get confused by which gear it should be engaging next.
Like any system, continued refinement and improvement eliminates problems and improves operation, and this could be the case here if given the development time. However, the writing could already be on the wall as some automotive manufacturers have already cast doubt over the future of the complex transmissions.
Advances made in automatic transmission technology have closed the gap to DCT/DSGs, and with automatics already selling in increasing numbers over manuals we could well see a time in the near future where manual transmissions phase out completely – leaving them to the enthusiasts.
Clutch Urban Dictionary
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