Multi-Stage Planetary Bicycle Transmission for High Gear Density
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Solution Overview
Problem
Existing bicycle and pedelec transmission systems, particularly those with hub motors and derailleur gears, suffer from low power density and efficiency due to high weight and complex maintenance requirements, affecting handling characteristics and power distribution.
Innovation Solution
A multi-stage planetary transmission system with at least three coaxially arranged planetary gear sets, including a main gear set and front/rear-mounted gear sets, along with free-wheel clutches and brakes, designed for high power density and efficiency, allowing for a high number of gears and integration with electric assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If derailleur gears or hub gears are used in bicycles and pedelecs, then the transmission can provide multiple gears, but the system suffers from low power density, high weight, and poor efficiency
Solution Approach 1:
The patent combines multiple planetary gear sets (first and second planetary gear sets) into a single integrated transmission unit, merging their functions to achieve multiple gear ratios while maintaining compact size and high power density. The sun gear of the first planetary gear set is connected to the planet carrier of the second planetary gear set, creating a unified structure that provides both versatility and efficiency.
Solution Approach 2:
The patent employs nested planetary gear sets where the first planetary gear set is arranged within or alongside the second planetary gear set in a coaxial configuration. This nesting allows multiple gear stages to be compactly integrated, achieving high gear multiplicity without increasing overall size, thereby maintaining high power density.
2Device complexity
If hub motors are installed in the front wheel, then the transmission can be simplified, but the handling characteristics deteriorate due to high weight
Solution Approach 1:
The patent replaces the need for complex hub motor integration with a mechanically efficient planetary gear transmission system. By using multiple planetary gear sets with appropriate gear ratios, the system achieves the necessary torque multiplication and speed reduction without requiring heavy hub motors, thereby maintaining good handling characteristics while simplifying the overall drive system.
3Adaptability or versatility
If bottom bracket transmissions of countershaft design are used, then the electric motor can be integrated, but the power density and efficiency decrease due to low rolling power
Solution Approach 1:
The patent merges the electric motor integration capability with a planetary gear transmission system, combining the advantages of both approaches. The electric motor can be coupled to the transmission input shaft, and the planetary gear sets provide efficient torque transmission with rolling power, achieving both adaptability and high power density simultaneously.
Solution Approach 2:
The patent employs a dynamic transmission system where the electric motor can operate in different modes (assisting pedaling, providing full power, or regenerative braking) and the planetary gear sets can engage different gear ratios dynamically. This dynamic capability allows the system to maintain high power density and efficiency across varying operating conditions while integrating electric motor assistance.
4Power
If multiple planetary gear sets are arranged coaxially, then the power density and efficiency increase, but the device complexity increases
Solution Approach 1:
The patent uses nested planetary gear sets arranged coaxially, where the first planetary gear set is integrated within or alongside the second planetary gear set. This nesting reduces the overall axial length and radial space required, making the complex multi-stage transmission more compact and manageable while maintaining high power density and efficiency.
Solution Approach 2:
The patent designs the planetary gear sets with universal components that serve multiple functions. For example, the sun gear of the first planetary gear set serves as both a gear element and a connection point to the planet carrier of the second planetary gear set. This multi-functionality reduces the number of separate components needed, thereby reducing device complexity while maintaining high power density.
Data Source
AI summary
A multi-stage planetary transmission for a bicycle or a pedelec includes a transmission input shaft (1), a transmission output shaft (2), and at least three planetary gear sets (VRS, VR1, VR2, RS1, RS2, NRS, NR1, NR2). A first planetary gear set (RS1) and a second planetary gear set (RS2) are configured as a main gear set and at least one further planetary gear set (VRS, VR1, VR2, NRS, NR1, NR2) is configured as a front-mounted gear set and/or as a rear-mounted gear set. At least three free-wheel clutches (F1, F2, F3, F4) and at least three brakes (B1, B2, B3, B4) are provided for implementing at least eight gears (G1, G2, G3, G4, G5, G6, G7, G8, G9, G10, G11, G12, G13, G14, G15, G16). Moreover, the multi-stage transmission may be a bottom bracket transmission. In addition, a bicycle or pedelec with the multi-stage transmission is proposed.