The DCT Transmission


By Staff

Is This Really An Automatic?


Are you a die-hard manual transmission enthusiast?  Does it break your heart that most major automotive companies are putting the age-old stick shift in the closet for replacement of paddle shifters and automatic clutches?  Before you jump off a bridge, you may want to look what's really inside the inner workings of a DCT transmission.  How similar it is to the traditional manual may surprise you.


First off is the gear box. Just as the standard manual transmission has, the DCT has nearly identical helical cut gears, shift synchronizers and shift forks. Overall, the entire mechanical operation of changing gears is the same concept as the manual transmission. The major difference is using the hydraulic clutches and solenoids to assist in shifting the gears instead of your foot and hand. So how does that work you ask?


It starts with the DCT, which stands for Dual Clutch Transmission. Note! This is not the same as a twin disk clutch in the traditional manual transmission (where there are two disks, back to back within the clutch pressure plate).  The two clutches in the DCT are actually two separate clutches.


Now here is where things get tricky. There is a main input shaft that the main gears are attached to and spin to drive the secondary gears. But the main shaft is hollow with another shaft inside. In most cases the outer shaft usually spins the even gears, and then the inner shaft spins the odd gears. Depending on which clutch is engaged, spins the appropriate shaft. For example, if the first clutch is engaged will spin the outer gear shaft, and if the second clutch is engaged will spin the inner gear shaft.



And how are the clutches engaged? Simple. With hydraulic solenoids. So every time the car needs to shift, instead of you pushing your foot to engage a clutch, a solenoid does that for you.


Next is the fact of shifting gears, and that's where the secondary gears come into play.  Those are moved by a shift fork to align them up to the appropriate main shaft gear that is engaged by the clutch. But instead of using a stick shift and your hand to change the gear, again this is performed by solenoids. Pretty cool right?


So now that you know the basics of a DCT transmission and how it works; it's not entirely different in function. As you can see, it's just a lot more complex. But this isn't not a bad thing. A DCT transmission can shift in a fraction of a section. Plus, with the dual clutch system and the dual input shaft, can do it seamlessly without separating the engine engagement from the drive line.  Which creates a smooth seamless shift versus a traditional manual, that every time the clutch is disengaged, the engine is disconnected from the drive-line.


But in retrospect, it also disconnects the driver from the transmission and the spirited feeling of shifting the car. In a modern world, we are always going to have machines doing things quicker and more effectively. Not at all should the traditional manual transmission go away -- but hopefully this gives those passionate about the gear lever, a different perspective on the DCT; which is an offspring of the old tech and new.





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