Bottom Bracket Planetary Gear Layout for Compact E-Bike Drives
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Solution Overview
Problem
The limited installation space in the vicinity of the pedal shaft region of electric bicycles poses a challenge for integrating both an electric motor and a gear mechanism effectively, limiting the hybrid operation of pedelecs.
Innovation Solution
A gear mechanism is integrated into the bottom bracket of the bicycle, utilizing a planetary gear set with three rotatable elements and a freewheeling-element carrier to transmit torque efficiently, reducing the number of components and installation space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a gear mechanism and electric motor are integrated in the pedal shaft region, then torque transmission efficiency is improved, but installation space requirements increase
Solution Approach 1:
The patent combines the gear mechanism and electric motor into a single integrated unit mounted in the bottom bracket. The planetary gear set and motor are merged into one compact assembly, eliminating the need for separate mounting spaces and reducing overall installation footprint while maintaining efficient torque transmission from both pedal and electric power sources.
Solution Approach 2:
The bottom bracket is designed as a multi-functional component that simultaneously serves as the mounting location for the gear mechanism, electric motor, and chain ring. This universal mounting structure allows all torque transmission components to share the same installation space, resolving the contradiction between integration efficiency and space requirements.
2Reliability
If multiple components are used for torque transmission, then transmission reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple torque transmission components into integrated assemblies. The planetary gear set combines sun gear, planet gears, and ring gear into a single mechanism unit. The freewheeling element carrier integrates the freewheeling element with the drive shaft, reducing the number of separate components while maintaining reliable torque transmission in both pedaling and electric drive modes.
Solution Approach 2:
The drive shaft serves multiple functions: it transmits torque from the planetary gear set, supports the freewheeling element carrier, and connects to the chain ring. This multi-functional design reduces component count while ensuring reliable power transmission through a single robust component that handles multiple transmission paths.
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
This configuration allows for a compact, cost-effective, and efficient transmission of both muscle-powered and electrically generated drive power, enhancing the hybrid operation of bicycles while minimizing friction loss and extending the service life of the gear mechanism.
Implementation Method 1
The gear mechanism includes at least one planetary gear set, wherein the planetary gear set includes at least three rotary elements, which are arranged so as to be rotatable relative to one another and are designed for torque transmission
Implementation Method 2
The electric motor can be designed to convert electrical energy into mechanical energy
Data Source
AI summary
An electric drive device for a bicycle includes a transmission, an electric motor, a drive shaft, and a drive wheel arranged coaxially to the drive shaft. A first freewheeling element and a second freewheeling element are arranged in a one-piece freewheeling element carrier. The drive wheel is connectable to the drive shaft via the one-piece freewheeling element carrier by the first freewheeling element, and a rotary element of a planetary gear set of the transmission is connectable to the drive shaft via the one-piece freewheeling element carrier by the second freewheeling element. Another rotary element of the planetary gear set of the transmission is formed in one piece with a power transfer device.