Honda RC212V: Transmission Patent | Drawing the Line

Something Old, Something New

In the pre-season MotoGP tests, the new Honda RC212V dominated, setting the fastest lap time on each day. Honda’s Casey Stoner took pole and won the first race at Qatar, then set pole again at Jerez. He might have won there as well had he not been taken out in the wet by Valentino Rossi. There was talk in the pits of a new clutch and shifting mechanism, something new in the drive train that was making the bike easier to ride. Dual-clutch technology like that employed on the VFR1200F isn’t legal in MotoGP, and neither is fully electrical shift control, so those explanations were out.

However, we got a look at a published U.S. patent application showing a new trans-mission credited to a Mr. Matsumoto, who is a Honda engineer. Japanese patent documents verify the Honda connection and show the transmission in what appears to be the RC212V engine, although Honda has made no public statement about it.

The patent application shows the mechanism in great detail, and the first thing I thought was: Hodaka! For those of you without gray hair, Hodaka produced inexpensive trailbikes in Japan that were sold by the Pacific Basin Trading Company (PABATCO) in Oregon from 1964-’80. I sold and worked on Hodakas in the early ’70s, and the trans- mission design stuck with me as a clever and simple mechanism. Other oldsters have also seen the Honda-Hodaka connection.

Hodaka’s five primary-shaft gears were all fixed to the shaft. The countershaft gears were in constant mesh with their corresponding primary-shaft gears, and in neutral were all free to rotate. Under each gear the countershaft had four holes, with a ball resting in each one. Each of the freewheeling gears had four semi-circular indentations on its inner diameter. A small shaft rode in the inside of the hollow countershaft and had a detent collar. The trans shifted by moving the detent collar so that it pushed the four balls out into the pockets in the chosen gear, locking it to the countershaft.

Conceptually, the Honda transmission is the same. The primary-shaft gears are all fixed to the shaft in sequential order, with first to the right and sixth to the left. When the transmisssion is in neutral, all six corresponding countershaft gears, in constant mesh with their counterparts, freewheel on the countershaft.

Under each countershaft gear are four pawls that pivot on axes parallel to the countershaft, with two facing in each direction, in order to take both drive and deceleration torque. Noses on the pawls engage the edges of recesses on the inner diameter of the gear. In neutral the pawls are fully retracted, letting the gear freewheel, and when fully in gear all four pawls are pivoted outward to contact the chosen gear and fix it to the countershaft.

A very clever and complex group of indented metal strips ride inside the countershaft, and are moved back and forth by the shift mechanism. Round-ended pins in holes in the countershaft contact the strips on the inside, and the pawls on the outside, so that when the pin encounters an indentation on the strips, it moves inward. This moves one end of the corresponding pivoting pawl inward (helped by a spring), and the opposite end of the pawl outward, engaging a gear.

What’s particularly interesting is that the four pawls don’t all engage at the same time. If the two drive-torque pawls are engaged, but not the deceleration-torque pawls (or vice versa), the pawls can “ratchet” to allow relative freewheeling in the opposite direction. This would potentially allow two gears to be (partially) selected simultaneously, but with one freewheeling in one direction. It’s easier to follow the hardware shown in the application than it is to interpret the “software” of selection logic, but one can assume the “overlapping” shifts would help speed the gear change.

Honda’s riders (Stoner, Dani Pedrosa and Andrea Dovizioso) say the transmission is very good, but isn’t a “secret weapon.” It doesn’t singlehandedly account for the current relative superiority of the RC212V. But the details make this the most interesting recent development in MotoGP technology, and we hear other teams are looking at building similar gearboxes. All credit, then, to the little trailbike company that pioneered this technology more than 40 years ago. All credit, as well, to Honda’s designers, who could take a device good for maybe 15 horsepower and transform it into one capable of withstanding 250 bhp.

A U.S. patent application details the transmission employed in Honda’s latest RC212V MotoGP racer. Surprisingly, the technology first appeared on Hodaka mini-cycles four decades ago.