A Shift In Changing Gears
A SHIFT IN CHANGING GEARS
ROUNDUP
A look at Honda's new MotoGP racing transmission
KEVIN CAMERON
ADD HONDA'S ZERO-SHIFT-DELAY MotoGP transmission to the novel shift systems that have appeared on motorcycles lately. Honda introduced its pushbutton-or-automatic Dual-Clutch Transmission on the VFR1200F DCT, and Yamaha's FJR1300AE uses the foot-or-pushbutton-shift YCC-S system. Honda's DN-01 has a multi-mode hydrostatic transmission, and Aprilia gives its Mana 850 V-Twin a snowmobile-style belt CVT.
Do modern marketeers think us so fatigued by gear-changing that we need this help? Is it the eternal hope that new buyers will appear when bikes become as automated as cars? Or is this more blurring of the difference between mo torcycles and scooters?
Quite a few cars have adopted more transmission speeds lately to let smaller, niore-economical engines heave
four-wheel living rooms away from stoplights yet still cruise the freeway at friction-reducing low revs. So far, bikes carry no governmental pressure to deliver economy; anyone wanting super mileage can buy a scooter or a 250.
Honda's 201 1 MotoGP transmission is neither automatic nor automated; it is just a new way to select the con ventional six speeds permitted by the FIM. A conventional gearbox must first disengage the current ratio, after which it can select the next one. Even using a racing-style shitler switch, this two-step process involves a power outage" of .04 to .06 second per upshift. which, on many tracks, can result in the loss of close to a second a lap. Honda's new transmission operates the other way around. It selects the next gear with zero delay and only then does it kick out the previous gear.
The mechanics of this are contained inside one of the two transmission shafts. Forward and reverse torques are transmitted by separate sets of tilting dogs that engage features on the inner diameters of the gears. The tilting dogs are operated by rods and cams inside the shaft. This gearbox is very compact be cause its "interior engagement" system requires neither dogs on the faces of gears nor any axial sliding of gears.
b I Because engagement takes place at the ID of each gear, the `engagement radius" is smaller than in the case of conventional face dogs, so the forces are larger. This may mean that the tilting dogs will accumulate wear or become damaged too rapidly for this to become other than a racing system that needs frequent parts replacement. On the other hand. because this system does not pass through a neutral during gear-changing,
shift impacts are significantly reduced.
One gear shaft is splined and six splined gears are stacked onto it. The other shaft, containing within it the gear selection apparatus, carries six gears as well, all of which are free to spin on the shaft until selected.
Older readers may remember the “ball-lock” selector mechanism used on some smaller-displacement bikes during the late 1960s and early ’70s; Hodakas and smaller Pentons were among the more popular. Under each gear on one of the shafts were multiple holes, in each of which was a steel ball. Movable through the center of the hollow shaft was a slender rod with an enlarged end. By sliding this rod to place its enlarged end at one gear, the engagement balls were pushed outward to lock the gear to
the shaft by means of scallops cut into the gear’s inner diameter.
This system lacked parts durability, and because the actuating rod had to move the full length of the gear stack, “stick-out clearance” was required at one end. The new Honda system, by contrast, moves its control rod only a bit more than an inch, using a spiral groove cut into a small “shift drum.”
Honda’s system exploits a loophole in the present MotoGP engine life rule, which allows only six engines per rider, per season. Because gear-ratio alterations are necessary from circuit to circuit, the rule allows the gearbox to be changed at will. Thus, even if the transmission’s parts last only one race, they can legally be renewed.
But will this system soon appear on a production bike? Durability is a legitimate question, but you can never count
Honda out when it comes to innovative engineering. E
