Jack Luke, an assistant editor at BikeRadar, routinely scours the US Patent Office for cycling-related filings. This one was tucked away under the ubiquitous title, "Sliding Component and Bicycle Internal Transmission Device" by Shimano Inc. in Japan. (See the patent application here
In his comprehensive article
, Luke mentions that the word "gearbox" never appeared in the patent. No doubt an intentional ploy to hide the monstrously huge news that the world's largest component maker in cycling has been developing a comprehensive strategy to produce a sequential-shifting 13-speed hybrid transmission that substitutes heavy, draggy gears with lighter, more efficient roller chain, sealed from the elements and bathed in an engineered lubricant. All this, including advanced drawings of how the gearbox will be mounted in production and its programmable electronic shifting controls, are described in detail.
Big news? I'd say so, but the concept isn't new. The famous Honda DH bikes used a similar gearbox. Honda's transmission featured a chain and cassette, sealed from the elements inside an aluminum and carbon shell. It was shifted by a modified derailleur which slid laterally on a shaft to provide a perfect chain line. Rumors point to another large drivetrain maker that "may" have developed and tested a roller-chain hybrid gearbox as well in the not too distant past. What makes Shimano's patent application so important is, um, Shimano.
Shimano Isn't Bluffing
The smoking gun in Shimano's application can be found in the details. The abstract drawings depict a concept that is near production, not a bunch of cut-and-paste bicycle parts adorned with play school cogs and components. The side shot of the bike,
for instance, depicts a high level of integration and shows how the drive sprocket could be correctly aligned for a modern high-pivot suspension. The three-quarter view of the transmission further illustrates an evolved, working concept.
Why Roller Chain?
Shimano's application also describes in detail, a special lubricating fluid that when combined with a surface treatment that traps the substance in the metal, will shear at a prescribed thickness and prevent metal-to-metal contact at high pressures. Both the lubricant and the technical details of the surface treatment are detailed in the application. Does that sound speculative? I didn't get that impression either.
Shimano's proposed lubricant and surface treatment work together to eliminate the possibility of metal-to-metal contact.
Why roller chain? No other strategy can compete with a roller chain for low friction losses in rotary power transfer at low RPM and high torque loads - especially at low power inputs. The enemy of roller chain drives is dirt. Tests at the University of Utah proved that friction losses in roller chain drives were minimal, regardless of the type of lubricant, even when lubricant was absent. Dirt, and angular misalignment, however, contributed to large friction losses in the trials. Shimano's transmission handily solves both of those issues and then some.
According to the application, Shimano's gearbox pairs opposing seven-cog cassettes. A small "derailleur" slides on an angular shaft between them to shift the chain to each gear, while maintaining a perfect chain line in each selection. To extract 13 speeds from only seven pairs, one of the cassettes can be shuttled laterally, which presents six more gearing options. This strategy ensures low friction, because only one pair of sprockets are engaged at any moment, and keeps the transmission simpler, lighter weight and also, minimizes its width.
Shifting to the next gear is proposed in the application to be either electric, or cable operated, but either way, you wouldn't have to figure out which gear you were in. You'd only be pushing one of two levers on the right side of the handlebar. Another plus is that the transmission would be moving as long as the bicycle was in motion, so you would be able to effortlessly change as many gears as you wanted while coasting.
A "derailleur" device moves the chain between two mirror-image cassettes (left image). After seven shifts (middle image), the lower cassette is moved over one space (right image) and offers six additional gears - 13 speeds in total.
What Lies Ahead?
Is there a future for this? Absolutely. Gearboxes that use toothed gears must be constructed from the finest materials, with aerospace tolerances in order to approach the efficiency of roller chain drives on bikes sold at the department store level. Shimano's concept bridges that gap with a protected, permanently lubricated transmission that will operate efficiently when constructed with average quality bearings and moving parts. That means this gearbox will eventually be scalable and thus
appear at a number of price points. Conventional gearboxes are not - which is why the gearbox bike has never been moved into mass production.
We'll keep an eye on Shimano and report further developments.