Bottom-Bracket Planetary Transmission for High-Gear Pedelec Drivetrains
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Solution Overview
Problem
Existing bicycle and pedelec transmission systems, particularly those with hub motors and bottom bracket gears, face challenges such as low power density, poor efficiency, and unfavorable handling due to high weight, especially when combined with maintenance-unfriendly derailleur gears.
Innovation Solution
A multi-stage planetary transmission design with at least three coaxially arranged planetary gear sets, overrunning clutches, and brakes, allowing for a high number of gears with high power density and efficiency, integrated as a bottom bracket gear, and optionally incorporating an electric machine for enhanced support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a hub motor is integrated into the front wheel, then the pedelec can provide electric assistance, but the handling is negatively impacted due to the weight
Solution Approach 1:
The patent moves the transmission system from a lateral distribution (front/rear wheel hub motors) to a centralized bottom bracket position. By integrating the multi-stage planetary gear system into the bottom bracket, the electric motor's power is transmitted through a centralized gearbox, redistributing the weight centrally rather than at the wheel extremes, thereby improving handling while maintaining electric assistance capability
2Power
If derailleur gears are used with rear-wheel hub motors, then the pedelec can provide electric assistance, but the system is difficult to maintain and has unfavorable handling due to weight
Solution Approach 1:
The patent merges the electric motor drive, multi-stage planetary gear transmission, and gear selection functionality into a single integrated bottom bracket gearbox. This consolidation eliminates the need for separate derailleur mechanisms and multiple external cables, creating a sealed, self-contained unit that is significantly easier to maintain while providing the same electric assistance capability
Solution Approach 2:
The patent extracts the complex derailleur gear system and its associated maintenance requirements from the drivetrain. By removing the derailleur mechanism entirely and replacing it with an internally integrated planetary gear system, the design eliminates the external components that are difficult to maintain, while still achieving multiple gear ratios through the planetary sets
3Power
If multiple planetary gear sets are integrated coaxially in the bottom bracket, then the power density and efficiency are increased, but the device complexity increases
Solution Approach 1:
The patent nests the first, second, and third planetary gear sets within each other in a coaxial arrangement. The gear sets are positioned concentrically around the input shaft, with each subsequent gear set nested within the dimensional envelope of the previous one. This nesting approach allows multiple complex gear stages to be integrated into a compact bottom bracket housing without proportionally increasing the external dimensions or overall complexity
4Adaptability or versatility
If at least three freewheel clutches and at least three brakes are used to realize at least eight gears, then the number of gears is increased, but the device complexity increases
Solution Approach 1:
The patent designs the freewheel clutches and brakes to serve multiple functions simultaneously. Each clutch and brake component is integrated into the planetary gear set structure, where they not only control gear selection but also provide overrunning clutch functionality, locking mechanisms, and torque transmission paths. This multi-functionality allows the system to achieve at least eight distinct gear ratios without proportionally increasing the number of discrete components, thereby managing device complexity while maximizing adaptability
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 achieves a high power density and efficiency, enabling a high number of gears with improved handling and system integration, suitable for various bicycle types, including off-road and sports bikes, while minimizing drag torques and allowing for seamless gear shifting.
Implementation Method 1
a first planetary gear set (RS1) and a second planetary gear set (RS2), which are designed as the main gear set
Implementation Method 2
at least three overrunning clutches (F1, F2, F3) and at least three brakes (B1, B2, B3)
Data Source
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AI summary
The invention relates to a planet-type multi-stage transmission for a bicycle or a pedelec, comprising a transmission input shaft (1) as the drive, a transmission output shaft (2) as the output, and at least three planetary gear sets (VRS, VR1, VR2, RS1, RS2, NRS, NR1, NR2), wherein a first planetary gear set (RS1) and a second planetary gear set (RS2) are designed as the main gear set, and at least one additional planetary gear set (VRS, VR1, VR2, NRS, NR1, NR2) is designed as a front-end gear set and/or as a back-end gear set, wherein at least three freewheel clutches (F1, F2, F3, F4) and at least three brakes (B1, B2, B3, B4) are provided in order to implement at least eight gears (G1, G2, G3, G4, G5, G6, G7, G8, G9, G10, G11, G12, G13, G14, G15, G16). Furthermore, the multi-stage transmission is provided as a bottom-bracket transmission. The invention additionally relates to a bicycle or a pedelec comprising the multi-stage transmission.