Bicycle Bottom Bracket Drive with Planetary Gear Shifting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bottom bracket drives for electric bicycles, particularly those with a central motor, face inefficiencies in power transmission due to friction, low torque density, and lack of seamless gear shifting, leading to reduced battery range and noticeable pedal crank idle travel during gear changes.
Innovation Solution
A bottom bracket drive system featuring a linearly movable shift gate that blocks and releases individual planetary gear degrees of freedom, allowing for automatic shifting under load, with radially extending shift fingers and blocking elements that enable varying torque flow and multiple gear combinations without load interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a friction ring transmission is used for continuous variable gear shifting, then gear ratio can be continuously adjusted, but power transmission efficiency decreases significantly
Solution Approach 1:
The patent replaces the friction-based mechanical transmission system with a planetary gear system that uses positive engagement through gear teeth. This substitution eliminates the sliding friction losses inherent in friction ring transmissions while maintaining the ability to provide multiple gear ratios through the planetary gear arrangement and selective blocking mechanisms.
2Ease of operation
If pawls are used to block and release gears, then gear shifting can be achieved, but shifting requires holding or releasing gears which causes interruption in traction
Solution Approach 1:
The patent employs a dynamic shifting gate mechanism that can rapidly move between positions to engage different planetary gear configurations. This dynamic approach allows for quick gear changes without the need to hold or release gears, maintaining continuous power transmission and eliminating the traction interruptions associated with traditional pawl-based systems.
Solution Approach 2:
The shifting gate acts as an intermediary mechanism that selectively blocks or releases the rotation of specific planetary gears. By using this intermediate blocking element rather than direct pawl engagement, the system achieves smooth gear transitions without interrupting the power flow from the crankshaft to the output.
3Adaptability or versatility
If traditional gear blocking mechanisms are used, then gear changes can be made, but noticeable idle travel of the pedal cranks occurs during shifting
Solution Approach 1:
The planetary gear system is pre-configured with multiple possible gear ratios through its structural arrangement. The shifting gate is positioned to selectively engage different planetary gear configurations in advance, allowing for rapid gear changes without requiring the pedal cranks to travel through an idle position. The system prepares multiple gear states simultaneously through its mechanical architecture.
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 seamless, automatic gear shifting with minimal load interruption and increased efficiency, improving battery range and pedaling assistance by varying the transmission ratio through the displacement of the shift gate, thus enhancing the overall drivability of electric bicycles.
Implementation Method 1
a gear assembly (3) which is located on the pedal crankshaft (2) and includes a plurality of interconnected planetary gears (4, 6)
Implementation Method 2
The planetary gears in particular define a plurality of degrees of freedom of the gear arrangement, so that different transmission ratios of the gear arrangement can be implemented by blocking individual degrees of freedom
Implementation Method 3
there is a linearly movable shift gate which can block and release individual gears by linear displacement
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
The present invention relates to a bottom bracket drive (1) of a bicycle, comprising a crankshaft (2) designed for operation by a rider, a gear arrangement (3) mounted on the crankshaft (2) comprising a plurality of interconnected planetary gears (4, 5), a shift gate (7) arranged rotationally fixed relative to the crankshaft (2) and displaceable along an axial direction (100) of the crankshaft (2), wherein sun gears (8, 9, 10, 11) of the planetary gears (4, 5) each have a shift finger (12, 13, 14, 15) extending radially outwards with respect to the crankshaft (7), wherein the shift gate (7) has locking elements (16), and wherein the locking elements (16) overlap with at least one shift finger (8, 9, 10, 11) in the radial direction of the crankshaft (2), such that by displacement of the Shift gate (7) by overlapping shift fingers (8, 9, 10,11) and blocking elements (16) prevent the rotation of one or more shift fingers (8, 9, 10, 11) around the pedal crank shaft (2) in both the axial and radial directions of the pedal crank shaft (7).