Bicycle CVT with Coaxial Planetary Gearset and Traction Rings
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Solution Overview
Problem
There is a need for a continuously variable transmission (CVT) system that can be integrated into a bicycle's frame forward of the rear wheel or rear wheel hub, providing adjustable speed ratios and efficient power transfer.
Innovation Solution
A CVT system featuring a coaxially mounted planetary gear set with a ring gear, sun gear, and traction rings, along with a shift screw and shift pin hub for adjusting transmission ratios, and a cage to support and transfer power to the traction planets, allowing for axial and radial support and power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a CVT is integrated into the bicycle frame forward of the rear wheel, then the transmission system becomes more compact and integrated, but the device complexity increases
Solution Approach 1:
The patent combines the CVT mechanism with the bicycle frame structure by integrating the transmission housing into the frame members. The crankshaft is coupled directly to the planetary gear set carrier, and the entire assembly is mounted coaxially about the crankshaft within the frame, merging what were previously separate components into a unified integrated structure.
Solution Approach 2:
The patent employs nested arrangement where the planetary gear set is positioned within the CVT housing, which is in turn integrated into the bicycle frame. The traction planets are supported by a cage that is coupled to the crankshaft, creating concentric nested arrangements that maximize space utilization and reduce overall volume.
2Loss of energy
If a planetary gear set is coupled coaxially to the crankshaft, then power transfer efficiency is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent achieves equipotentiality in terms of rotational alignment by coupling the planetary gear set carrier directly to the crankshaft in a coaxial arrangement. This direct coupling eliminates misalignment issues that would occur with flexible couplings or offset mounts, ensuring that all rotating components share the same rotational axis and potential, thereby minimizing power loss due to misalignment.
3Ease of operation
If traction planets are supported by a cage coupled to the crankshaft, then the ease of operation is improved, but the device complexity increases
Solution Approach 1:
The cage serves multiple functions simultaneously: it supports the traction planets axially and radially, transfers power from the crankshaft to the traction planets, and provides structural support for the entire CVT mechanism. This multi-functionality reduces the need for separate components for each function, simplifying the overall structure while maintaining ease of operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient adjustment of speed ratios and power transfer in a compact, integrated bicycle transmission system, enhancing the performance and versatility of bicycle drivetrains.
Implementation Method 1
Power is transferred sequentially from the crankshaft to the planetary gear set carrier, to the planetary gears, to the sun gear
Implementation Method 2
A first traction ring is operationally coupled to the sun gear, and a plurality of traction planets are coupled to the traction ring. A second traction ring is coupled to the traction planets.
Data Source
AI summary
Traction planets and traction rings can be operationally coupled to a planetary gearset to provide a continuously variable transmission (CVT). The CVT can be used in a bicycle. In one embodiment, the CVT is mounted on the frame of the bicycle at a location forward of the rear wheel hub of the bicycle. In one embodiment, the CVT is mounted on and supported by members of the bicycle frame such that the CVT is coaxial with the crankshaft of the bicycle. The crankshaft is configured to drive elements of the planetary gearset, which are configured to operationally drive the traction rings and the traction planets. Inventive component and subassemblies for such a CVT are disclosed. A shifting mechanism includes a plurality of pivot arms arranged to pivot about the centers of the traction planets as a shift pin hub moves axially.