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Hello everybody,
English is my third language and it's not that good but I will give it a try.
I have a lot of experience in technology, worked on gearboxes, engines, helped to produce wings for the F-16 Fighter, Airbus parts, helicopter parts and much more......
I drove all kind of cars, Jags, BMW, Mercedes, Porsche, Audi, Cadillac, Lincoln, small cars etc..... All kind of engines, from a 402 cc 2 cylinder up to a 7.6 liter, 460 cubic inches V8, even a 12 cylinder car. All kinds of transmissions from manual, automatic with torque convector, DCT, CVT and centrifugal. So I think I may say to understand how a DCT works and what the potential problems could be.
I own several cars and I bought the Tucson 1.6 l turbo Executive with the DCT cause I wanted a cheap fully loaded SUV for daily use. It's a beast of a car, unbelievable fast for a 1.6 liter Turbo, handles well, shifts fast without shocks etc... Almost everybody love their Tucson.
But that DCT 
......................
'There is nothing wrong with that DCT gear box, it works fast, sharp and the right way it's designed for.. But it's different from the classic automatic and people should understand how it works.
The DCT contains 2 shafts with each shaft his own clutch, dubble axes egals dubble clutch.... You can find a perfect movie on YouTube about the Kia DCT. It helps to understand the working of the gearbox
Shaft #1 holds for example gear 1, 3, 5 and 7. Shaft #2 hold the gears or sprockets for gear 2, 4, 6 and Reverse. The reverse works different from a manual gearbox because in the DCT they use a combination of several sprockets to back up the car but that's not the point of discussion. But it proves the simplicty and posibilities from a piece of art what a DCT is.
People should know that there is always a gear in the DCT that is selected when in Drive (few exceptions in abnormal conditions, will tell later), for example 3th gear on shaft#1 you are driving in and while accelerating the transmission knows that it has to shift to 4th gear on shaft #2 as you want to go faster. Gear 4 is already selected on forehand by the TCU and it will shift when the TCU ( Transmision Control or Computer Unit) gives the order to shift.
This is done by disengaging the clutch on shaft#1 with gear 3 and engaging-locking the clutch from shaft #2 with the 4th gear. And so further on......
In the opposite, when slowing down, the transmission will (has to) go into a lower gear when the TCU gives the order. For example driving in 4th gear on shaft #2 and braking the TCU knows that it has to downshift to 3 or even lower, and will on forehand select and hold that 3th gear on shaft #1 till it shifts.
This is how the transmission works in ideal ( easy ) circumstances.
Now, people think because a gear is selected in the gearbox the gearbox is also " engaged "........ Not..... !!!!!!! NOT !!!!!!
No matter which gear is selected in a DCT, the transmission becomes only effective when clutch #1 or #2 is engaged, locked. Clutch #1 engaged means clutch #2 is disengaged, unlocked and vice versa......
There are 3 possibilities, clutch #1 is engaged OR clutch # 2, >>>>>>> OR NONE of the 2 CLUTCHES are engaged and here is where the misunderstanding, problems begin......... if or when you do not understand why none clutch is locked !!!!!!
In a standard automatic transmission there is always a form of connection between the driven shaft ( engine) and the transmission, you can step brutally on the throttle pedal, the torque convector handles the torque with a " slip " (remember that word for later) - that's why a hydraulic torque converter transmission is less fuel effective-efficient than a locked gear from a manual gearbox or a DCT. You loose energy by that slip......
And from now on we can talk about the DCT problems.......
I will end for now to see if I can post it and will start the next post with the things you should never do with a DCT, AND WHY the clutch is NOT engaging in the Tucson or Sportage DCT and the car DOES NOT MOVE from where it stays, even if you rev the engine up to 3000, 4000, 5000, or even 6000 RPM as you can see in some movies on YouTube......
I will also explain why in the middle of a freeway your Hyundai or Sportage can slow down suddenly.......
How to blow up a DCT in a few 100 miles or kilometers....
From my first post we should remember 2 important things :
1) EACH shaft, with the designated gears, has his OWN clutch. In our DCT we have an inner shaft that goes through a hollow shaft so the 2 clutches are in the same center-line using the same counter party disc. This is a very compact design.
2) Or clutch #1 is locked-closed (and #2 unlocked-open) OR clutch #2 is locked-closed (and #1 unlocked-open)......... OR NONE of the 2 clutches !!!!! None of them means there is NO connection between the engine and the gearbox at that moment, opposite to the classic hydraulic gearbox where there is ALWAYS a connection, the torque converter !
And here is the FIRST mistake of those drivers : the gearbox was in DRIVE with a selected gear (which you can see on your dashboard). It is an AUTOMATIC TRANSMISSION..... BUT it didn"t move........ even if I rev it up to 3000 RPM or even higher?????.....
Of course it didn"t move, THE CLUTCH WAS OPEN..... It is a MANUAL gearbox, be automated !!!!!!
BUT..... the clutch should not be open at the moment you push the accelerator...... What happened??????
We saw that there are 2 possibilities for a clutch : locked-closed OR unlocked-open.
When a clutch is fully locked-closed there is no slip between the 2 discs, because they are at the same RPM.
When the clutch is unlocked-open there is no friction between the discs, in theory.... In the practice there is a light form of friction and we will see later that this is important in how to treat a DCT !!
So, the ideal position for the clutch is at " fully locked-closed ", that's the working environment for our clutch. No slip....
The second one is unlocked-open due to the light friction.
The worst is when we take off and the clutch HAS to slip as the speed of the car is zero and without the slip the engine would stall or the transmission would shock at the time the clutch engages and the RPM of the 2 clutch discs is different. The slip adds to the smoothness of the transmission.
When I was young we raced our Alfa-Romeo's, BMW, Fiat, MG, Triumph, VW, Porsche, Renauts, lots of brands, all with manual transmissions. Small engines, 1300 cc, 1600 cc, max 2 liters with at that time only torque and power in higher RPM's. So we had to "let slip" the clutch to gain some smoothnesss and power. But even if you won, people where laughing at you if you slipped the clutch too much.
It ended mostly with a burned, smelling, full smoking clutch.... sparks.....
Why am I telling this..... you can not imagine the wear and heat for your clutch when it slips.... and people who don't know how the DCT works do slip their transmission more than you think.
That's the reason for the Heat Fail-Safe system in our DCT...... and as we can see it works, the fail-safe........
Drivers should know now that slipping the clutch is very deadly for it, it's not done, out of style..........
I will explain later the damages you can expect to the clutch, actuators (parts that command the pressure on the disc of the clutch, open or close the clutch), even ending in damaging the entire gearbox.
As we know, the clutch has to slip every time the gearbox shifts caused by the difference in RPM of he driven disc (engine) and the disc of one of the 2 gear-shafts to add some smoothness in the process of shifting, specially when the car is standing still and we are taking off. The slips from gear 2 up to 3 and so on is irrelevant in our story, so let us focus of what's happens between speed zero to gear 2 and what's more important here, when the car slows down and comes to a stop.......
I would like to ask a question first : would you dare to put your hand against a spinning, rotating (polished) disc in a drilling machine for example, that turns at 900~1200 RPM ( some drivers even like 6000 RPM) or 15 to 20 rotations ( 100 !!) per SECOND ?? NO, well that's what our clutch is going through.... every time we bring the car in movement.
I subdivide it in several points.....
You start the engine, the clutch performs a calibration you can hear by the clicks and clacks. Same for when you turn your engine off.
1) Stick in Park or Neutral, engine running at idle, around 850 RPM. The clutch discs are at maximum gap, no need to engage. No slip or friction.
2) stick in Drive, foot on brake pedal. The gearbox is in 1 st gear, the clutch is OPEN, the discs are close to each other to minimalize the time to engage.
3) foot COMPLETE OFF the brake pedal, we don't touch the accelerator. The car starts to move forward, the clutch engages by allowing a slip for smoothness till the clutch locks fully, the 2 RPM's of both discs are equal.
Let's see in slow motion.... the clutch engages, disengages, allows more or less slip by more or less pressure between both discs, kind of an on and off...., till they are locked. The faster the clutch is locked, the less slip, wear and heat.
But we have to go faster....
So, the initial engine RPM will go up to 1250 ~1750 RPM, even higher as we pull of very fast or push the accelerator hard, the clutch has to allow many slips......
The job of the TCU AND the driver is to close the clutch as soon as possible. In a hydraulic converter you can allow more and longer slip, it's a fluid..... in our DCT high spinnning discs..... remember your hand......
Let's see what happens in traffic jam, when you inches forward, creeping...
Zero speed. With a MANUAL transmission you have your gearbox in neutral, foot OFF the clutch pedal, WAITING to move. Right foot is on the brake pedal.
Moving : You engage first gear by pushing the clutch pedal, shift the stick into first gear, release the clutch pedal and at THE SAME TIME your right foot OFF the brake pedal. Sounds logical......
Would you release your clutch pedal, so engaging the clutch, while holding your right foot on the brake....... Hahaha, yes it's a stupid question...... but a lot of drivers do that ALL THE TIME...... in their DCT.
Engaging the clutch in a manual gearbox is done by releasing the clutch pedal so it can engage.
In our DCT it's the TCU that gives the order, but we can influence that TCU.
When we release the brake pedal we give order to the clutch to start to engage. When we brake we give order to disengage. (in the zero speed to fully engaged clutch and vice versa)
So, while inching forward, creeping, the clutch has to open and "close" all the time when applying different pressure on the brake pedal. Friction, wear and heat.....
Or you have your foot on the pedal or complete OFF the pedal.
When you want to go forward wait a little bit so you can release the pedal fully and LET THE CLUTCH COME TO A FULL LOCK.
When you want to pull off fast let your clutch engage and step then hard on the gas pedal..... or help your clutch to lock faster......
If your clutch can/does not engage, it will NOT help to let your engine REV up, even to 6000 RPM ?????? Foolish..... Next post.....
This story can not come to an end
(Courtesy Hyundai’s Forum)
