Eccentric Gear Crank Drive Space Reduction
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Solution Overview
Problem
Electric bicycle pedal crank drives have a large installation space, which restricts ground clearance and makes off-road riding difficult, especially with mountain bikes, due to the size of the drive motor and gearbox.
Innovation Solution
The design incorporates a high-ratio eccentric gear stage arranged kinematically behind a low-ratio gear stage, with the low-ratio gear stage positioned between the drive motor and the high-ratio gear stage, allowing for a high reduction ratio and efficient power transmission while minimizing installation space, using a fast-rotating drive motor with reduced torque and a compact configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional gearbox with multiple gear stages is used to achieve high reduction ratio, then the transmission efficiency is improved, but the installation space increases
Solution Approach 1:
The patent combines multiple gear stages (low-ratio gear stage and high-ratio gear stage) into a single integrated gearbox structure. The drive motor, low-ratio gear stage, and high-ratio gear stage are rigidly mounted together to form a compact unit, merging functions that would traditionally require separate components and reducing overall installation space while maintaining transmission efficiency.
Solution Approach 2:
The patent employs a nested arrangement where the high-ratio gear stage is positioned kinematically behind the low-ratio gear stage within the same gearbox housing. The output shaft of the low-ratio gear stage serves as the input for the high-ratio gear stage, creating a nested configuration that maximizes space utilization and minimizes the overall footprint of the drive system.
2Force
If the drive motor is made larger to generate sufficient torque, then the torque output is improved, but the installation space increases
Solution Approach 1:
The patent segments the torque multiplication function into two distinct gear stages: a low-ratio gear stage and a high-ratio gear stage. This segmentation allows the drive motor to operate at higher speeds with lower individual torque requirements, while the combined effect of both gear stages achieves the necessary total torque output for the pedal crankshaft, thereby reducing motor size and installation space.
Solution Approach 2:
The patent changes the operating parameters of the drive motor by using a high-speed motor configuration rather than a high-torque, low-speed motor. The two-stage gear reduction system compensates for the lower motor torque by providing additional mechanical advantage through the sequential gear stages, allowing the system to achieve the required torque output with a more compact motor design.
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 reduces the installation space of the pedal crank drive, enhancing ground clearance and ease of integration into bicycle frames while maintaining a familiar riding experience by minimizing the width of the pedal crank drive and reducing noise and vibration.
Implementation Method 1
the high-ratio gear stage is designed as an eccentric gear
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to an electric bicycle pedal drive with an electric drive motor (12) which is coupled to a pedal crank shaft (60) via a low-ratio gear stage (20) and a high-ratio gear stage (30), wherein the high-ratio gear stage (30) is formed by an eccentric gear (31), and wherein the high-ratio gear stage (30) is kinematically arranged behind the low-ratio gear stage (20). Such a bicycle pedal drive reduces the installation space required for the bicycle pedal drive.