Wolfrom Bicycle Drive Layout for Compact Bottom Bracket Integration
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Solution Overview
Problem
Existing bicycle drives for electrically drivable bicycles require significant installation space, limiting the compactness and efficiency of the design, especially in the radial direction, which hinders the integration of additional components and increases the axial space requirement.
Innovation Solution
The Wolfrom transmission system, which features a planet gear meshing with two axially adjacent ring gears instead of a single ring gear, allows for a compact design by maximizing the transmission ratio and reducing installation space requirements, enabling the arrangement of components in a radially outer area without additional planet carriers or sun gears, thus allowing for radial nesting and reduced axial extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a classic planetary transmission is used, then the structure is simple with a single ring gear, but the transmission ratio cannot be maximized and installation space is not efficiently utilized
Solution Approach 1:
The single ring gear is divided into two annular halves (first and second ring gears) that are axially adjacent, allowing the planet gear to mesh with both simultaneously. This segmentation enables the transmission ratio to be maximized while keeping one ring gear fixed in motion, without significantly increasing structural complexity
Solution Approach 2:
The transmission system transitions from a single-plane planetary gear arrangement to a two-dimensional axial stacking configuration, where two ring gears are positioned adjacent to each other in the axial direction. This allows the planet gear to engage both ring gears simultaneously, maximizing the transmission ratio while efficiently utilizing installation space
2Productivity
If additional planet carriers or sun gears are added to increase transmission ratio, then the transmission ratio improves, but the radial installation space requirement increases
Solution Approach 1:
Instead of increasing the radial extent by adding more planet carriers or sun gears, the solution stacks two ring gears in the axial direction. This allows the planet gear to mesh with both ring gears simultaneously, achieving maximum transmission ratio while keeping the radial installation space requirement determined only by the single annular electric machine
3Productivity
If the axial installation space is increased to accommodate additional transmission components, then the transmission ratio can be increased, but the overall compactness of the bicycle drive is reduced
Solution Approach 1:
The first and second ring gears are merged into a single compact axial assembly, with the planet gear bridging both ring gears. This configuration maximizes the transmission ratio while minimizing the axial space requirement, as the two ring gears occupy the same radial envelope and are positioned adjacent to each other rather than requiring separate axial spaces
Solution Approach 2:
The transmission system uses axial stacking of ring gears rather than radial or longitudinal expansion, efficiently utilizing the radial installation space that is already determined by the electric machine's annular configuration around the pedal crankshaft
4Adaptability or versatility
If the bicycle drive is electrified with an electric machine and transmission system, then the functionality improves, but the installation space requirement increases compared to conventional bicycles
Solution Approach 1:
The electric machine is configured in an annular shape that surrounds the pedal crankshaft in the radial direction, which determines the radial installation space requirement. The Wolfrom transmission with two axially stacked ring gears then utilizes this radial space efficiently, creating radially inner free space that allows compact axial arrangement of components without significantly increasing the overall installation space
Solution Approach 2:
The electric machine forms an annular structure that nests around the central pedal crankshaft, creating a compact radial arrangement. The Wolfrom transmission components are then nested within the space defined by the electric machine's annular configuration, with the two ring gears positioned in the radial outer area and the planet gear bridging them, achieving efficient space utilization
Data Source
AI summary
In an embodiment a bicycle drive includes a pedal crankshaft configured to input mechanical drive power, an electric machine coupleable to the pedal crankshaft configured to input electric drive power and/or output generator power and a Wolfrom transmission interposed in a torque flow between the electric machine and the pedal crankshaft.