Honda’s Secret MotoGP Transmission
Ever since the beginning of pre-season MotoGP testing, trackside observers noticed that the factory Honda RC212Vs sounded different—notably, that their gearshifting was almost imperceptible. Instead of the usual “pop” during shifts caused by powershifters momentarily cutting spark to interrupt power (which allows a conventional transmission to accomplish an upshift without backing out of the throttle or using the clutch), the Hondas simply changed engine note. There were initial misguided claims that Honda was using the electronic DCT gearbox found on its VFR1200F production sportbike, but the problem there is that not only is the unit heavy, but MotoGP regulations specifically prohibit twin-clutch transmissions.
Numerous theories and conjecture were thrown around about how the new transmission was constructed, but thanks to the U.S. Patent and Trademark Office’s website (www.uspto.gov/) as well as Google Patents (www.google.com/patents), the patents applied for by Honda regarding this transmission were found. A patent describing a “multi-stage transmission” shows a motorcycle transmission utilizing an innovative cam/pawl setup inside the countershaft itself to engage transmission gears (similar to the Xtrac IGS, a company that works with Honda’s IndyCar engine program) rather than sliding the gears across a mainshaft as with a conventional constant mesh sequential motorcycle transmission.
A conventional motorcycle transmission changes gears by sliding one gearwheel across a mainshaft until it locks into a driven gearwheel via internal “dogs”—lugs cast into one gear that fit into holes in another gearwheel. Moving the gears across the shaft is accomplished by yokes or shift forks, which are controlled by a shift “drum”. Because the dogs are made so that the gears lock together under power, power must be interrupted so that the gear wheels can be disengaged. Sliding the gearwheels across the shaft requires time as well.
With the Honda multi-stage transmission, there are no shift forks, and there is no lateral movement of the gearwheels. Instead of using dogs cast into the gears to lock them to the countershaft, the Honda setup uses a series of cam-type rods that slide back and forth inside the countershaft itself. The cam-type control rods actuate swingable pawls inside each gear that lock them to the countershaft when a gear change is enabled. The pawls and the steps machined into the inner portion of the gears are designed in such a way that when the next gear becomes engaged, the pawls on the previous gear detach naturally. This means that there is no power cut needed, power is continuously transmitted, and no clutch actuation is necessary.
Because there is no large shift drum to control the shift forks, and since the gearwheels do not slide laterally on the countershaft/mainshaft, the gear cluster can be made more compact. The gears can be made stronger as well, since there is more room for gear teeth width.
Will we see this transmission setup on a future Honda sportbike? It’s very likely. -KK