One-Way Clutch Segmentation for Electric Bicycle Drive Units
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Solution Overview
Problem
The existing drive units in electric-motor-assisted bicycles with a one-way clutch positioned coaxially with the crank axle experience a time lag between pedal input and power transmission to the rear wheel, and increasing the number of engagement teeth to reduce this lag results in a larger clutch size, compromising stability and durability.
Innovation Solution
A drive unit design with a one-way clutch featuring an outer and inner member, where the number of clutch lugs is an even number not smaller than 4, and the number of clutch teeth is an even number not a multiple of the lugs, with springs biasing adjacent lugs for engagement, and pins restricting spring movement to enhance biasing force when lugs are pushed by clutch teeth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the number of engagement teeth is increased to reduce time lag, then the time lag between pedal input and power transmission is reduced, but the size (radial dimension) of the one-way clutch increases
Solution Approach 1:
The one-way clutch is segmented into multiple independent engagement units, each consisting of a clutch lug and corresponding engagement teeth. By distributing the engagement across multiple segments (lugs and teeth pairs), the system achieves smoother and faster power transmission without requiring a single large clutch structure, thus reducing time lag while maintaining compact size.
2Loss of time
If the number of engagement teeth is increased to reduce time lag, then the time lag between pedal input and power transmission is reduced, but the stability of operation deteriorates
Solution Approach 1:
The clutch design employs asymmetric engagement geometry where clutch lugs and engagement teeth are positioned at specific non-uniform intervals. This asymmetric arrangement ensures that engagement occurs at optimal points in the rotational cycle, providing stable and reliable power transmission while minimizing time lag. The asymmetric design prevents simultaneous engagement of all teeth, distributing load more effectively.
3Loss of time
If the number of engagement teeth is increased to reduce time lag, then the time lag between pedal input and power transmission is reduced, but the durability of the one-way clutch deteriorates
Solution Approach 1:
The engagement teeth and clutch lugs are designed with optimized local geometric properties, including specific tooth profiles, contact surface areas, and material distributions. This local quality optimization ensures that stress is concentrated at designed contact points rather than distributed across the entire clutch structure, reducing wear on individual engagement elements and extending the overall durability of the one-way clutch while maintaining fast engagement.
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 time lag while maintaining a compact clutch size, stabilizing operation, and improving durability by ensuring consistent engagement and reduced load on clutch lugs.
Implementation Method 1
a plurality of springs, each capable of exerting a biasing force on two of the plurality of clutch lugs that are adjacent as determined along the circumferential direction
Implementation Method 2
The plurality of pins are provided on the other of the inner peripheral portion of the outer member and the outer peripheral portion of the inner member. Each of the plurality of pins is in contact with one of the plurality of springs to restrict movement of this spring.
Data Source
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AI summary
Time lag is reduced and, at the same time, an increase in the size of the one-way clutch is avoided and the operation of the one-way clutch is stabilized. The one-way clutch (233) includes an outer member (2331), an inner member (2332), a plurality of clutch lugs (233F), a plurality of springs (238), and a plurality of pins (237). The clutch teeth (233C) are provided on one of the inner peripheral portion (233B) of the outer member and the outer peripheral portion (233D) of the inner member. The clutch lugs are provided on the other of the inner peripheral portion and the outer peripheral portion. The springs are provided on the other of the inner peripheral portion and the outer peripheral portion. The number of clutch lugs is an even number not smaller than 4 (four). The number of clutch teeth is an even number that is not a multiple of the number of the clutch lugs. The number of springs is half the number of clutch lugs. Each spring is capable of exerting a biasing force on two of the clutch lugs that are adjacent as determined along the circumferential direction. Each pin is in contact with one of the springs.