Tech Special: Why we all need Honda’s DCT gearbox, maybe
Honda’s DCT gearbox makes use of clever engineering and a dash of witchcraft
The new Gold Wing, which is landing in dealers shortly, brings a host of innovations with it including the first seven-speed DCT gearbox on a bike. It begs the question: what on earth is DCT and how does it work? DCT stands for Dual Clutch Transmission and it’s a system that allows for both manual and automatic shifting. DCT has been popular in cars for decades, but Honda have only been fitting them to bikes since 2009. So far we’ve seen it on the NC750, Africa Twin (pictured right) and VFR1200.
The biggest difference between DCT and conventional transmission is the clutch: ordinary systems use a single clutch for the entire gearbox whereas a DCT has two clutches: one for the odd gears and one for the evens. DCTs differ from automatics because they do not have torque converters. Only one clutch is ever active at any one time. On the Gold Wing, when you select ‘Drive’ the computer-controlled actuator in the gearbox selects first but it does not engage the clutch. As you twist the throttle, the first clutch begins to engage and you pull away. The gearbox then selects second (as that’s the only way you could go) but this time it does not engage the second clutch. When you speed up the computer disengages the clutch for first gear and simultaneously engages the clutch for second, meaning the drive is uninterrupted. This process of pre-selecting the gear then engaging the clutch continues throughout the gearbox. DCT has many advantages including ease of use, increased shift speed and increased economy but there are a few disadvantages. A second clutch and the associated electronics are heavy, so the DCT Wing is 4kg heavier than the manual one. Not so much of a problem on the 380kg Wing but it does present a problem for Honda’s desire to see a DCT sportsbike. DCT also struggles at slow speed, which is why Honda add torque converters to some of their cars but this isn’t feasible on a bike. Instead, for the Gold Wing, Honda added walking mode buttons, which crawl the bike forwards and backwards using the two clutches. DCT is also more expensive than conventional transmission but the biggest problem of all seems to be convincing red-blooded bikers that having a computer doing the shifting isn’t a bad thing. Oh and yes, they still wheelie!
Honda wants to fit DCT to its sportsbikes