Patent Application
20190024775
Since the beginning of bicycle usage, bicycles have typically been propelled by a chain, belt, or shaft. Shaft drive for bicycles was pursued by a good number of manufacturers in the late 1800's. Due to performance and reliability issues associated with system weight, imprecise gear meshing friction, lack of multiple gear drivetrains, etc., the chain driven bicycle became the favored form of final drive configuration for the majority of bicycling applications. Shaft drive is a final drivetrain type offered on certain bicycles available for sale currently where it enjoys the advantage of easy isolation from the moisture and abrasives in the environment and reduction in exposure to the end user to a grimy chain and pull-in points. However, many design deficiencies remain that prevent widespread use across all bicycle applications and brands. Pinnacle Motion, LLC, has identified the root cause of these deficiencies and leveraged advancements in materials science and manufacturing, along with a fresh look at machine design to eliminate these issues and allow bicycle companies (and end user consumers alike) to trust and have confidence in shaft drive as a final drivetrain choice and preference.
A drive shaft, driveshaft, driving shaft, propeller shaft (prop shaft), or Cardan shaft to be used for various types of bicycles, tricycles, quadracycles, unicycles, infinitely wheeled cycles, mopeds, and motorized bicycles (whether propelled solely by human input and/or partial/full input by human input, electricity, gas, or other energy means). All cycle type terms now referred to as “bicycles”.
Materials may include, but are not limited to: aluminum, steel, titanium, carbon fiber. The most popular driveshaft bicycle system on the market until about 2 years ago was the Sussex branded driveshaft (ultimately owned by Dynamic Bicycles company). Dynamic Bicycles no longer sells the bicycle driveshaft. There are some design flaws that were exposed through actual field riding. Our design aims to improve upon these deficiencies. Beixo is the only main brand of bicycle shaft drive still on the market, but shares many of the same fundamental design flaws as the Sussex design. We feel we should be granted a full utility patent based upon these improvements summarized below.
Bearings wore out quickly. Gear meshing inherently induces residual loading beyond the tangential portion which is the useful portion responsible for transmitting power through the gear set. The radial portion creates moments at the bearing when the bearing is offset from the gear. The Sussex design uses two radial bearings placed back to back on the front pinion gear, but the bearing type is not correct to handle axial loads and thus can lead to premature system failure. The single row radial bearing used in Sussex was not designed to react out these moments. We consider this a design flaw which we've resolved in our design by using two rows, separated by some distance, per gear to react out these moments. In addition, the axial (thrust) load into the bearing is relatively high compared to the radial load. The deep groove radial ball bearing is not the best selection for this. We chose an angular contact bearing as one of the two bearings in our set. A spherical tapered roller bearing or other style of tapered roller bearing is optimal in handling radial and thrust loads. In regards to lubrication, an oil bath should allow for more consistent lubrication than grease. Gear alignment is critical for efficiency and longevity.
The tolerance on gear offset for a nice set of bevel gears can be in the thousandths of an inch. This has to be maintained while under load. The gears themselves have to minimize flex and the supporting structure must be rigid. In particular, the rear triangle of a bike can flex maybe 0.250″. Let's assume the center to center distance between the rear axle and bottom bracket changes 0.125″. The Sussex design rigidly mounts the rear gear set to the front gear set thru the drive shaft. They bolt the pinion gear directly to the driveshaft, so as the frame flexes and rear axle comes closer to the bottom bracket, it could drive the front pinion into the front gear. We've eliminated any axial load transmission through the shaft by allowing the shaft to “float”. See claims section for more information regarding this. The gear set is positioned using the several other parts which have their accompanying manufacturing tolerances. These tolerances are additive. In our design we've eliminated parts in this tolerance stack to help reduce the assembly's effect on the gear meshing. In particular, we employ what we call “alignment boxes” which are both the bottom bracket and front pinion housings machined out of a single block of aluminum eliminating a tolerance stack and fasteners. The Sussex design chainstay is threaded into the bearing housing. This effectively leaves the chainstay length undetermined leading to potential user error when trying to install the system with proper gear offset. Even though the Beixo brand shaft drive doesn't thread the chainstay into the bearing housing, their design doesn't allow any float of the driveshaft and thus can experience the same effect of the pinion gear driving into the front gear.
Retrofitting is the next topic area. The Sussex and Beixo system were designed to retrofit to an existing 1.37″ bottom bracket instead of designing from the ground up. The way they clamp into the bottom bracket is susceptible to loosening, creaking and shifting under each pedal stroke. Our system would be welded to traditional frame tubes. The alignment boxes were designed to eliminate deflection at the gear set so we're not constrained by the existing bottom bracket.
