12-07-2015, 05:27 AM
(12-07-2015, 02:58 AM)The ferret_imp Wrote: ok..trying to learn here..old dog and all
If this is common practice and won't hurt the tranny..why was it such a big deal that Yamaha didn't have a seamless tranny in MotoGP year before last (allowing clutchless shifts) while Honda did? (and Suzuki is behind because they still don't)
It was claimed clutchless shifts with the seamless gearboxes were responsible for a gain of 2/10s or 3/10ths per lap.
Though still a constant mesh manual gearbox, the seamless shift transmission is a different beast. You have two gears selected at any one time (the current one and the predicted next one), but only one is actually powering the bike and the other is queued up waiting for a hand-off.
On a normal bike, even if you shift without the clutch, you are coming off power momentarily and physically disengaging the shift dogs from one gear and locking another set onto the next gear you want -- this takes time (even if only a few hundred milliseconds).
In the seamless you have the gear you are in powering the bike and the next one pre-selected, but not being used. To pre-select the bike likely either 'guesses' which gear is next by monitoring what is occurring (rev's, throttle position,acceleration, decelerating, braking, etc...) or has the rider pre-select by picking his/her next gear (likely by lightly pushing up or down on the shift lever between shifts).
When you go to shift then there is no power to cut and no dogs to release and re-engage, as it's already done in the 'down time' between shifts. All you need to is hand-off power from one gear to the other using a more efficient form of mechanical switching. In a car (and a DCT bike actually) this is usually done by having two wet clutches (one for even and one for odd gears) that can be engaged/disengaged in about 50ms. On the GP bike, it's speculated that there is a mechanical system that instantly disengages the previous gear as soon as the next one is engaged. This is where the time-savings per lap come in -- as forward acceleration remains uninterrupted for a few milliseconds less per shift and this accrues over the course of the entire race. The chassis is also upset way less by the seamless, as the shifts are 'perfect' every time and there is no jarring or motion created by the power variation of switching gears.
The hand-off portion is really the secrecy is about, it wouldn't be hard to build a pre-selector box for a motorcycle (as said above, motorcycle DCTs are basically this), but miniaturizing it and making the engagement purely mechanical is pure engineering genius.