Variable-Lever Crank Drive for Uniform Torque Output
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Solution Overview
Problem
Existing bicycle crank drives with oval or elliptical chain rings are costly due to high technical device expenses, and they fail to provide uniform torque over a rotational range less than one revolution.
Innovation Solution
A crank device with a crankshaft that introduces a variable force through a transmission element with a variable lever spacing, where the lever spacing is designed to compensate for the force change, ensuring uniform torque over a rotational range, using a spring force and a mechanism like a chain or rack to maintain constant torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oval or elliptical chain ring is used to equalize torque, then the torque on the rear wheel hub is equalized, but the technical device cost increases
Solution Approach 1:
The patent extracts the torque equalization function from the complex oval chain ring system and implements it through a simpler mechanism: a cam-shaped lever arm with variable lever spacing that directly modulates the force transmission to the crankshaft, eliminating the need for oval chain rings while maintaining the torque equalization effect
Solution Approach 2:
Instead of modifying the chain ring geometry to achieve torque equalization (as in prior art), the patent inverts the approach by modifying the lever arm geometry (cam shape) to achieve the same effect, thereby simplifying the overall device structure and reducing cost
2Reliability
If a variable lever spacing mechanism is used to compensate for force changes, then uniform torque is achieved over a rotational range, but the device complexity increases
Solution Approach 1:
The patent employs a cam-shaped (curved) lever arm where the distance from the rotation axis to the force application point varies continuously along the curvature. This geometric curvature inherently provides the variable lever spacing needed for torque equalization without requiring complex mechanical adjustment mechanisms
Solution Approach 2:
The lever spacing parameter is designed to change systematically with the rotation angle through the cam profile, allowing the mechanism to automatically adapt the lever arm length to compensate for spring force variations and maintain uniform torque output
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 reduces technical device costs and achieves uniform torque over a rotational range, minimizing bearing forces and allowing for reduced component count, thus lowering overall costs while maintaining efficient energy transfer.
Implementation Method 1
the first force is a first spring force transmissible from a tensioned first spring of the crank device to the first lever spacing and can be introduced into the crankshaft via the first lever spacing. This spring force decreases as the force is applied and the associated length change of the spring towards an output length.
Implementation Method 2
an effect of change in the first variable force on the crankshaft is at least partially, preferably completely, compensated for. the comparative or uniform torque results from the product of the force (component) and the lever spacing.
Data Source
AI summary
A crank device or crank drive is disclosed which has a crankshaft, into which a variable first force can be introduced by way of a transmission element over a variable first lever spacing. Here, the first variable force has a predefined profile and/or predefined change. A profile of the first variable lever spacing is designed in a manner which is dependent on the predefined profile of the first variable force in such a way that an effect of change in the first variable force on the crankshaft is at least partially compensated for. The compensation is provided over a rotational range of the crankshaft, which is preferably less than one revolution of the crankshaft.