Second Prototype

Preliminary design work has begun on a second prototype (see cross-section view below):

prototype 2 Model (1)

Objective

The main objectives of the design are to:

  • Reduce the size of the hub, particularly the overall diameter
  • Reduce the weight
  • Simplify the hub architecture
  • Allow the use of standard bearings throughout
  • Reduce the number of rollers
  • Eliminate the sprocket tooth profile anomaly (see first prototype page)
  • Improve manufacturing and assembly efficiency

Solution

To best meet these objectives, the following has been become clear from a design analysis of the first prototype:

  • Eliminating the monoblade mounting option reduces the hub size considerably by removing the large cantilever internal bearing for the axle, thus reducing the mounting height of the bevel planet gears on the planet carrier.
  • The first embodiment of the patent (the design with planet gear clusters) has greater scope for reducing the hub overall diameter because the planet gears within each identical planet cluster can have different diameters so as to increase the ratio for a given planet gear cluster height. This is achieved by placing smaller bevel planet gears at the top of the cluster and larger ones further down the cluster. The planet gears are still all much larger than in a regular hub, retaining all the advantages of large planet gears.
  • Stress analysis indicates that only two planet gear clusters are required, rather than three. This means that the lowest number of rollers is attained with the rollers on the planet gears, rather than on the ring gears.
  • The sprocket tooth profile anomaly is not present in the first embodiment since there is only one planet gear in the cluster that meshes with two ring gears, and these two ring gears have the same diameter. In addition, mounting the rollers on the planet gears rather than the ring gear always eliminates this problem.
  • Cantilevering the hub shell on the crank axle eliminates a large bearing on the ring gear carrier side of the hub, but this advantage is more than offset by complex bearings within the hub which interfere with the ideal planet cluster mounting. Given the smaller overall diameter attainable, it is better simply to mount the hub shell conventionally on a large bearing on the ring gear carrier.

The second prototype design therefore embodies the above features.

Overview

The second prototype design has four speeds and an overall ratio range of 350%. The configuration of the hub follows the principles of the first embodiment presented in the patent. The bevel planet gears are arranged in two clusters each comprising three bevel gears of slightly different diameters. Each bevel gear gives a specific ratio, so, along with the 1:1 direct ratio, this gives the four speeds. The rollers are mounted to the planet elements, and the sprocket teeth are on the ring and output elements. Gear change is accomplished by holding individual ring gears stationary, using a sliding clutch stopper mechanism. The axle and hub shell are not cantilever-mounted, but rather mounted on two opposing bearings. Thus the hub is configured for dual-blade mounting only. However the right side of the hub (ring gear carrier side) is mounted directly, and thus the hub requires no separate torque reaction bar.

Gear ratios

  • First:       1:1.00
  • Second:  1:2.00
  • Third:     1:2.73
  • Fourth:   1:3.50

For direct-drive with a 27 inch front wheel (700C – 622-32) this gives in gear inches and meters development [in square brackets]:

  • First:       27 [2.15]
  • Second:  54 [4.31]
  • Third:     74 [5.88]
  • Fourth:  95 [7.54]

… more to come