Bicycle Hub Friction Mechanism for Backwards Pedal Decoupling
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Solution Overview
Problem
Backwards rotation of a bicycle hub shell causes the foot pedal to rotate backwards, leading to potential harm and damage, especially when bicycles are parked or moved in tight spaces, as the pedals can hit other parts of the frame or the rider's leg.
Innovation Solution
A friction device is used in conjunction with a control mechanism to disengage the freewheel pawls, allowing the hub shell to rotate backwards without the foot pedal, by engaging a friction spring that prevents the pawl carrier from rotating backwards, thus disengaging the direct gear pawls from the hub shell teeth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a freewheel is used to allow backwards rotation of the hub shell, then the hub shell can rotate backwards without pedal movement, but the torque path is not interrupted and the pedals still move backwards
Solution Approach 1:
A friction device is introduced as an intermediary component between the hub shell and the freewheel pawls. This friction device selectively engages to disengage the pawls from the hub shell teeth during backwards rotation, preventing torque transmission to the pedals while allowing forward rotation to proceed normally through the freewheel mechanism
2Reliability
If the freewheel pawls remain engaged during backwards rotation, then the torque path remains continuous, but the pedals rotate backwards causing harm and damage
Solution Approach 1:
The friction device is positioned and configured to preemptively engage before backwards rotation can transmit torque to the pedals. By applying frictional force to the pawl carrier in the opposite direction of backwards rotation, the system prevents harmful torque transmission before it occurs, while maintaining normal forward rotation functionality
3Object-affected harmful factors
If a friction device is added to disengage the freewheel during backwards rotation, then pedal movement is prevented, but the device complexity increases
Solution Approach 1:
The friction device utilizes changes in friction parameters through spring-loaded engagement. The friction spring adjusts the normal force between the friction surfaces, creating direction-dependent friction characteristics that automatically engage during backwards rotation and disengage during forward rotation, providing the required functionality through parameter variation rather than complex mechanical switching
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
Prevents the backwards rotation of the foot pedal during hub shell rotation, reducing the risk of damage and injury, and maintaining functionality across various gear speeds and configurations.
Implementation Method 1
a friction device is provided, which works together with a control mechanism to disengage the pawls of the freewheel
Data Source
AI summary
A control mechanism for decoupling a drive ratchet on a bicycle hub makes it possible to push the bicycle backwards while the foot pedals of the pedal crank drive remain still. These functions can be applied to folding bicycles, in which pedal movements are harmful when in their folded up state. The control mechanism includes a controlling sleeve coupled to the drive ratchet, which is indirectly connected by means of a frictional device to the unmoving hub axle.