Coaxial Planetary Bicycle Transmission for Seamless E-Assist Shifting
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Solution Overview
Problem
Current transmission devices for electrically assisted cycles face issues of inefficiency and bulkiness, with existing configurations either reducing electric assistance motor efficiency at low speeds or requiring temporary disengagement during gear changes, leading to user inconvenience and parasitic torques.
Innovation Solution
A compact transmission device featuring epicyclic gear trains and an intermediate coaxial transmission element with interconnection devices, allowing seamless gear changes without interrupting electric assistance and reducing parasitic torques, while maintaining motor efficiency through electronic control of the assistance torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric assistance motor is coupled upstream of the transmission device with gear change, then the motor can operate at optimal rotational speed with higher torque and power, but the assistance must be temporarily cut off during each gear change causing user inconvenience and efficiency loss
Solution Approach 1:
The transmission device is divided into two independent subassemblies: a first subassembly handling gear changes and a second subassembly handling motor torque transmission. This segmentation allows gear changes to occur in the first subassembly without interrupting the continuous operation of the motor through the second subassembly, eliminating the need to cut off assistance during gear changes.
Solution Approach 2:
A torque storage element acts as an intermediary between the motor and the transmission system. This element temporarily stores motor torque during gear changes, allowing the motor to continue operating and maintaining assistance without interruption. The storage element mediates the torque transmission, decoupling the gear change process from the motor operation.
2Adaptability or versatility
If a simple gear train with offset countershaft is used, then transmission ratios can be achieved, but the structure becomes bulky and requires complex machining
Solution Approach 1:
The transmission device employs nested epicyclic gear trains where planetary gears are positioned around a central sun gear, with ring gears enclosing the entire assembly. This nested configuration allows multiple transmission ratios to be achieved within a compact radial space, significantly reducing the overall volume compared to linear gear train arrangements with offset shafts.
Solution Approach 2:
The patent transitions from a one-dimensional linear gear train with offset shafts to a two-dimensional epicyclic arrangement where gears are distributed radially around a central axis. This dimensional change enables multiple gear ratios to be achieved simultaneously or sequentially within a compact footprint, reducing the transmission device volume while maintaining versatility.
3Device complexity
If the electric assistance motor is coupled in direct drive on the vehicle wheel, then the structure is simple, but the motor efficiency is reduced at low vehicle speeds
Solution Approach 1:
The transmission device incorporates dynamically selectable gear ratios that can be changed during motor operation. This dynamic capability allows the system to maintain the motor at optimal operating speeds across varying vehicle speeds, preventing energy loss at low speeds while keeping the overall structure relatively simple through the use of epicyclic gear trains.
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
The solution provides a compact, efficient transmission system that maintains electric assistance motor efficiency across varying speeds and reduces user inconvenience by minimizing losses during gear changes, ensuring optimal performance and extended vehicle autonomy.
Implementation Method 1
the first transmission subassembly and the second transmission subassembly each comprise an epicyclic gear train
Implementation Method 2
the intermediate transmission element comprises a first clutch device capable of selectively coupling the first output to the first input of the first transmission subassembly
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A transmission device (1) for a human-powered vehicle, comprising a first planetary gear transmission sub-assembly (5) with a plurality of transmission ratios, which has a first input (13) coupled to a rotary shaft (2) receiving a drive torque applied by a user and which has a first output (14), a second planetary gear transmission sub-assembly (6) with a plurality of transmission ratios which has a second input (18) and an output shaft (19), and an intermediate transmission member (7) operatively coupling the first output (14) to the second input (18) in a rotatable manner. Coupling means (26) transmit an auxiliary torque generated on the shaft (24) of an auxiliary motor (25) to the intermediate transmission member (7).