Compact E-Bike Drive Using Nested Planetary Gears
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Solution Overview
Problem
Existing drive devices for electric bicycles are bulky, noisy, and prone to shock loads due to the use of single or multi-stage spur gears or chain drives, which increase material usage and reduce efficiency, and protrude from the frame, compromising ground clearance and increasing the risk of collisions during transport.
Innovation Solution
A compact drive device with a housing frame that integrates the electric motor and reduction gear within the bicycle frame, using a traction mechanism such as a belt or chain drive, allowing for a high reduction ratio with minimal external dimensions and weight, and featuring a planetary gear stage for efficient torque transmission and shock absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If single or multi-stage spur gears or chain drives are used, then torque transmission is achieved, but the drive device becomes bulky, noisy, and protrudes from the frame
Solution Approach 1:
The patent implements a nested planetary gear system where planet gears are arranged around a sun gear within a compact housing. The planet carrier and ring gear are concentrically arranged, allowing multiple gear stages to be nested within a small volume, achieving high reduction ratios without protruding from the bicycle frame
Solution Approach 2:
The patent transitions from linear/sequential gear arrangements to a radial/dimensional arrangement by using planetary gears. The sun gear, planet gears, and ring gear are arranged in concentric circles, utilizing radial space efficiently to achieve compact torque transmission with high reduction ratios
2Power
If single or multi-stage spur gears are used, then torque transmission is achieved, but material usage increases and efficiency decreases
Solution Approach 1:
The planetary gear system nests multiple gear elements (sun gear, planet gears, ring gear) within a single compact assembly, eliminating the need for separate housing and mounting structures required by conventional gear trains, thereby reducing overall material consumption
Solution Approach 2:
The patent combines multiple gear functions into a single integrated planetary gear unit that achieves high reduction ratios in one stage, eliminating the need for multiple separate gear stages and their associated housings, bearings, and shafts, thus reducing total material usage
3Power
If spur gears with rigid connection are used, then torque transmission is achieved, but susceptibility to shock loads increases
Solution Approach 1:
The patent employs a planetary gear system where the planet gears can dynamically distribute shock loads across multiple contact points with the sun gear and ring gear. The flexible arrangement allows for load redistribution during shock events, reducing stress concentration compared to rigid single-point gear contacts
4Power
If chain drives routed outside housing are used, then torque transmission is achieved, but susceptibility to external influences and injury risk increases
Solution Approach 1:
The patent encloses all chain drive components within a compact planetary gear housing, nesting the chains and sprockets inside the protected assembly. This eliminates external chain routing that would be exposed to dirt, water, and physical damage, while also preventing contact with the rider's clothing or skin
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 results in a lightweight, compact, and efficient drive system with reduced noise and enhanced shock absorption, maintaining the frame geometry and ground clearance of a standard bicycle, enabling easy integration and minimal protrusion, thus improving the overall performance and transportability of electric bicycles.
Implementation Method 1
a planetary gear whose sun gear (50) is connected to the motor shaft (40) of the electric motor (4) and meshes with planet gears (51, 52, 53) which are mounted on a planet gear carrier (55) and run on the internal teeth of a ring gear (54)
Implementation Method 2
using a traction mechanism such as a belt or chain drive
Implementation Method 3
using a traction mechanism such as a belt or chain drive
Implementation Method 4
a hollow shaft (3) arranged coaxially with the pedal crankshaft (2)
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Drive device (1) for an electric bicycle, comprising a drive housing (7) in which a hollow shaft (3) is mounted, said hollow shaft being connected to a sprocket wheel of a chain drive for the electric bicycle, comprising a pedal crankshaft (2) connected at both ends to pedal cranks, wherein said pedal crankshaft is arranged coaxially with the hollow shaft (3) and can be coupled to said hollow shaft (3), and comprising an electric motor (4), the output shaft of which can be coupled to the hollow shaft (3) via a traction gear mechanism (6) constructed as a belt drive with a flat belt, a toothed belt or a V-belt as a flexible traction means (60) or as a chain drive with a single or double roller chain as a flexible traction means (60). The traction gear mechanism (6) can form a multi-stage transmission (5, 6) for reducing the speed of the electric motor (4) with a straight-toothed or helical-toothed spur gear or planetary gear mechanism (5).