The Dual Clutch Transmission (DCT): Grab a coffee and a snack, because this one’s a doozy. The Dual-Clutch Transmission (DCT) is marketed under different names by different automakers, though they all work on the same principle to deliver higher performance and fuel efficiency than a conventional automatic or manual. Craziest thing about the DCT? It’s virtually impossible to explain.

In very simple terms, a DCT amounts to two manual transmissions contained within a single housing. Let’s call these two separate transmissions “sub-transmissions”.

One of the sub-transmissions contains the odd-numbered gears, for instance, 1, 3 and 5. The other sub-transmission contains even gears, for instance 2, 4 and 6. Like any other transmission, there’s an input shaft from the engine, and an output shaft, which sends power to the wheels.

But here’s the neat part – each of the sub-transmissions has its own input shaft, meaning there are two input shafts, not one. In a DCT, the input shafts from both of the sub-transmissions fit inside of one another, since one is slightly larger than the other, and hollow. This allows them to operate like a single unit. The nutshell? A DCT basically allows two transmissions to turn from the same input shaft, at the same time.

At the end of the input shafts are two clutches. One is attached to the outer, hollow shaft, the other, to the slightly smaller inner one. Remember – each of these shafts is attached to a different sub-transmission. The clutches, therefore, control which shaft, and therefore, which sub-transmission, is currently driving the wheels. These special clutches are computer controlled, so there’s no clutch pedal to press. There’s also no torque converter, as the clutches open on their own when the vehicle is stopping.

Say you’re accelerating slightly in third gear. The sub-transmission that houses the odd-numbered gears is engaged, in third, and the sub-transmission that houses the even gears is disengaged, but has fourth-gear pre-selected and waiting. Shifting up simply disengages the clutch from the odd-numbered sub-transmission, and simultaneously engages the clutch on the even-number sub-transmission, where fourth gear is ready to go.

This happens in milliseconds. In the process, the outer, hollow input shaft stops spinning, and the inner, thinner one starts spinning, simultaneously. Key word? Simultaneously. This two-in-one input shaft design allows gears to change without any slowing down of the power delivery to the wheels.

So now, cruising along in fourth gear with the even-number sub-transmission engaged, the odd-number sub-transmission pre-selects fifth gear in the meantime, so it’s ready when needed.

Here’s the key: with two sub-transmissions acting on the two-in-one input shaft, an upshift actually just changes the currently-engaged sub-transmission at some point after the gear change has already occurred. Drivers get smoother and faster shifts, and no interruption in power flow.

Notable DCT’s: Common in performance cars, and making their way into the mainstream, there’s no shortage of DCT transmissions in the market. Your writer’s very favourite belongs to the last-generation BMW M3. Advanced controls allow drivers to set gear shift speed and force, with the most aggressive mode changing up at full throttle so fast, it ignites the rear tires upon a full-throttle shift into second gear. Lightning-fast gear changes with beautiful rev-matching are also characteristic of the DCT transmissions used by Porsche, Volkswagen and Audi.

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