Variable-Lever Crank Drive for Oval Pedal Torque Delivery
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Solution Overview
Problem
Existing crank drives fail to effectively change the effective lever length, particularly on an oval pedal path, leading to inefficient torque delivery and ergonomically unfavorable movement sequences, with known solutions being complex, prone to wear, and lacking a natural movement axis alignment.
Innovation Solution
A crank drive design featuring gear levers with a 2:1:1 gear ratio, comprising external spur gears, which are arranged to extend the effective lever length during force delivery, providing a compact, stable, and durable configuration that mimics natural movement axes, while minimizing dead point zones and allowing for adjustable pedal path shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a telescopic extension of the crank arm is used to increase lever length during force delivery, then torque is increased, but the construction becomes complex and susceptible to wear
Solution Approach 1:
The patent applies dynamics by making the crank arm length variable through a telescopic mechanism. The inner crank arm can extend relative to the outer crank arm during the power delivery phase, dynamically adjusting the lever length to maximize torque when force is applied, while retracting during other phases to minimize complexity and wear.
Solution Approach 2:
The telescopic extension operates periodically, extending only during the force delivery phase when the pedal is in the optimal position for power transfer. This periodic action ensures that the complex telescopic mechanism is engaged only when needed for torque multiplication, reducing unnecessary wear and complexity exposure during other parts of the pedal cycle.
2Force
If an elliptical pedal path is used to change lever length, then torque delivery improves, but the movement sequence becomes ergonomically unfavorable due to dead centers
Solution Approach 1:
The patent employs asymmetry by using an oval-shaped pedal path instead of a symmetric circular path. The oval geometry provides a longer lever arm during the forward power delivery phase while maintaining a more favorable pedal angle during the return stroke, eliminating dead centers and improving ergonomic efficiency without sacrificing torque delivery.
Solution Approach 2:
The patent changes the geometric parameters of the pedal path from a circle to an oval, and further optimizes it to an egg-shaped curve. This parameter change allows the pedal to maintain a more natural angle throughout the cycle while providing extended lever length precisely when force is applied, eliminating dead centers and improving overall ergonomics.
3Force
If the effective lever length is increased significantly, then torque increases, but the size and weight of the crank drive increase
Solution Approach 1:
The patent applies the nested doll principle by placing the inner telescopic crank arm inside the outer crank arm structure. This nesting allows significant lever length extension during power delivery without proportionally increasing the overall size or weight of the crank drive, as the extended portion is housed within the existing structural envelope.
Solution Approach 2:
By making the lever length dynamic rather than static, the system achieves high torque only when needed during power delivery, rather than continuously. This dynamic extension reduces the average weight and size requirements compared to a permanently extended crank arm, as the extension mechanism is compact when retracted.
4Device complexity
If conventional crank drives are used, then the design is simple, but dead point zones are present and natural movement sequences are not supported
Solution Approach 1:
The patent implements periodic action through the oscillating lever mechanism, which periodically adjusts the pedal path geometry during each rotation. This periodic adjustment eliminates dead point zones by maintaining optimal force angles throughout the cycle, improving efficiency without requiring a completely complex redesign of the basic crank drive structure.
Solution Approach 2:
The patent introduces dynamic elements to the conventional crank drive through the oscillating lever and telescopic crank arm. These dynamic components allow the system to adapt the pedal path in real-time, eliminating dead centers and supporting natural movement sequences while maintaining relatively simple overall design principles.
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 design achieves a significant increase in torque and power output by varying the effective lever length, enhancing ergonomics and efficiency, and supports natural movement sequences, while being lightweight and durable, suitable for various applications including bicycles and power generation systems.
Implementation Method 1
A crank drive (1) with a periodic change in the effective lever length, in particular on an oval pedal path, wherein a gear lever (4, 7) is mounted at both ends for each crank (2), which is preferably rotated by a gearwheel drive (4a, 4b, 4c, 4a', 4b', 4c'), so as to increase the length of the effective overall lever (crank arm+gear lever) when kicking down
Implementation Method 2
The gear levers preferably consist of at least three external spur gears, which periodically (during force delivery) are largely arranged in the extension of the respective crank arm, and preferably have a gear ratio (number of teeth) of 2:1:1
Implementation Method 3
so as to increase the length of the effective overall lever (crank arm+gear lever) when kicking down
Data Source
AI summary
In order to form a largely oval circulatory path, in particular a pedal (1a), a crank drive (1) is described which periodically changes the effective lever length of a crank (2). In this case, gear levers (4′ or 7) are mounted on a crank (2) at both ends (2a, 2b) which rotate in opposite directions with respect to one another and thus form two further movement axes within the pedal path and are thus adapted to the natural human leg movement in a force-saving and ergonomic manner.