Alternating Bicycle Drive with Spiral Spring Rope Biasing
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Solution Overview
Problem
Alternating drives for bicycles face issues such as high twisting loads on the frame, rope breakage due to bending loads, and difficulty in adjusting transmission ratios, especially with the use of plastic ropes and complex bearing systems, which limit their applicability and efficiency.
Innovation Solution
The design incorporates a swinging arm system with a spiral spring for rope biasing, allowing the rope to withstand bending loads and featuring a Bowden wire mechanism for easy adjustment of transmission ratios, reducing the twisting load on the frame and enhancing durability and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a cam disc is used to change transmission ratio, then the driving characteristic can be changed within a wide range, but the cam disc has a big size and weight and substantially limits the applicability of the swinging element for traction purposes
Solution Approach 1:
The invention extracts the transmission ratio change function from a separate cam disc and integrates it into the swinging arm structure itself. The swinging arm's geometry and positioning directly provide the transmission characteristics, eliminating the need for a heavy separate cam disc component while maintaining the ability to adjust driving characteristics.
Solution Approach 2:
The invention merges the transmission ratio adjustment function with the swinging arm structure. The swinging arm serves dual purposes: providing the alternating motion and simultaneously determining the transmission characteristics through its geometric configuration and positioning on the bicycle frame.
2Power
If pressing forces are applied by the cam disc on the shaft of the two-armed lever, then the driving force is transmitted, but the forces are very high which tried to twist the frame and a specially designed strong bearing had to be provided
Solution Approach 1:
Instead of applying forces through a cam disc that creates twisting moments on the frame, the invention inverts the approach by using the swinging arm's natural alternating motion and gravitational forces. The drive forces are applied in a direction that aligns with the frame's strong axis, avoiding twisting loads.
Solution Approach 2:
The invention converts the potentially harmful twisting forces into beneficial forces by aligning the force application with the frame's strong vertical axis. The alternating downward forces on the swinging arms create driving torque without inducing twisting moments that would harm the frame structure.
3Device complexity
If a single rope wheel is used to transfer the forward-backward motion of the swinging arm to the rope drum, then the structure is simplified, but the number of turns on the rope wheel changes during swinging motion creating transverse forces that tried to bend the swinging arm
Solution Approach 1:
The invention segments the rope wheel system into multiple independent rope wheels, each handling specific portions of the alternating motion. This segmentation allows each rope wheel to operate with more consistent rotational characteristics, reducing the variation in turns and minimizing transverse bending forces on the swinging arm.
4Device complexity
If a plastic rope is used for driving, then the system is simple, but the rope could not resist the high bending loads and got broken after each 600-800 km of operation
Solution Approach 1:
The invention changes the operational parameters of the rope system by reducing the bending loads through the multi-rope wheel configuration. This parameter change allows plastic ropes to operate within their load capacity, dramatically extending their service life from 600-800 km to potentially unlimited operation while maintaining system simplicity.
5Ease of operation
If a separate rope-biasing assembly is provided to return the swinging arm into its original position, then the swinging arm returns to position, but the assembly required a substantial space on the frame and on the rope drum and increased manufacturing costs
Solution Approach 1:
The invention makes the swinging arm system self-servicing for the return motion. The alternating downward forces applied to both swinging arms during the driving cycle naturally propel the arms back to their starting positions without requiring any separate biasing assembly, springs, or additional space on the frame and rope drum.
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 provides a robust and adjustable drive system that can withstand high mileage without rope breakage, offers a lighter driving sensation by eliminating twisting torque, and allows for easy transmission ratio changes, enhancing the overall efficiency and reliability of the bicycle drive mechanism.
Implementation Method 1
The design incorporates a swinging arm system with a spiral spring for rope biasing, allowing the rope to withstand bending loads
Implementation Method 2
a ball bearing was provided that rolled along an internal linear recess of the swinging arm designed as a link-bar
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
Alternating drive primarily for bicycles and similar driven vehicles, in which the rotation of driven pedals are converted into reciprocating swinging motion of swinging arms, and the swinging arms have respective driving arms (16, 16') coupled to a head portion (14, 14') surrounding the swinging shaft (11) of the pedals from which a traction arm (17, 17') is extending out that closes an angle with the driving arm and the remote ends of the driving and traction arms (16, 17) are interconnected by a connection arm (20, 20'). A substantially triangular opening is formed between these arms, and the shaft of a driving wheel (15, 15') is positioned in this opening, the traction arm defines a traction path (19, 19'), and a flexible pulling rope (28) that rotates the driven wheel of the vehicle is led around at least one rope wheel (26) that has a shaft (35) guided and led along the traction path for adjusting the transmission ratio.