Honda's MotoGP gearbox explained

Patent drawings reveal the workings of the new gearbox that has caused a stir in MotoGP

Posted: 5 April 2011
by Visordown News

Recently acquired patent drawings have allowed us to examine the workings of Honda’s new MotoGP gearbox. It’s clever. Very clever.

It uses gears that spin freely on the output shaft when they’re not engaged, with internal ratchet mechanisms in each gear. There are four pawls on each ratchet – two take drive loads when the ratchet is engaged and the other two are used to limit backlash. During engine braking, the backlash-limiting pawls take the load.

These pawls are normally held in the “neutral” position, so the gear isn’t engaged, by sliding rods inside the output shaft. These rods have indentations in them, so when they’re slid into a particular position, they allow the pawls for one gear to engage (the pawls are sprung, so they will pop out and try to engage the ratchets on the inner circumference of each gear as soon as the selector shaft allows them to). Honda’s DCT twin-clutch system (banned by MotoGP rules) uses hollow output shaft technology to run one shaft within another to drive both clutch baskets.

On changing up to the next gear, first the backlash pawls in the first gear are disengaged (but not the drive ones) and the drive pawls in the second ratio are engaged. As the 2nd gear pawls connect with the ratchet inside 2nd gear, they take the load and accelerate the output shaft. Because the ones in 1st gear act as a ratchet, they can remain engaged right up to that moment – when the output shaft starts spinning faster than the 1st gear output ratio, the pawls will get pushed out of the way. Then, in the second stage of engagement, the backlash pawls in 2nd gear will be released and slot into place while the drive pawls in 1st gear are locked out of the way.

This new take on gear engagement has a couple of key advantages: First, it’s a seamless-shift arrangement (1st will be driving right until the moment 2nd gear takes over, and so on) so there’s no loss of drive. Second, there’s no conventional selector forks or gearshift drum, so it’s ultra-compact (the selection process is done via the rods inside the hollow output shaft). A corollary of that is that the gears themselves can be wider, and therefore stronger.

Finally, whenever you’re changing gear, the parts are moved in a sequence that means you’re never moving a part that’s under load. That means it’s easy to shift gear and doesn’t need powerful hydraulics (which MotoGP prohibits anyway).

The downsides are that it could really do with an electronically-controlled clutch to make the most of the system – allowing a modicum of slip as the gears are shifted to smooth the transition from gear to gear. Downshifts will rely totally on the slipper clutch to soften the torque loadings.

At the recent Jerez MotoGP race, several Honda riders did mention that downshifts were sometimes a problem. This system, as far as we know, is in its development infancy but the potential appears to be huge and for such a revolutionary departure the bugs appear to be minimal.

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Discuss this story

Coming soon to a Fireblade near you..?

Posted: 05/04/2011 at 14:30

I think that will bump the price up somewhat........

Posted: 05/04/2011 at 15:05


In manufacturing terms I wouldn’t have thought it would cost much more than the DCT option on the VFR1200, maybe even a little less? They could put it out in a limited RR version for Superbike/Superstock homologation and gain a significant advantage. It’s clearly strong and reliable, so far. I really wouldn’t be surprised to see it appear in one form or another in the next couple of years

Posted: 05/04/2011 at 16:38

Posted: 05/04/2011 at 17:29

Imagine the cost if it goes wrong? not sure your standard honda mechanic would be able to sort that thing out, and thats not saying anything against honda garage mechanics by the way

Posted: 05/04/2011 at 17:32

I don't understand... my gear box has my gloves & boots in it

Posted: 06/04/2011 at 13:06

......oh yeah I get it. Well no I dont. I love listening to technically apt people trying to explain things. Its like listening toa Chemistry prof explaing elementary science, they just cant do it because all is so obvious to them.

One other thing I don't get is why do they ban the double clutch thing? Isnt GP supposed to be about the quickest way to get around a track?

Speaking of technology, what has happened to the bike in moto2 with the funky front end / no forks set up? Dont hear too much about it.

Posted: 07/04/2011 at 08:20

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