Variable Diameter Pulley Assembly for CVT
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Solution Overview
Problem
Conventional continuously variable transmissions for human-powered vehicles and machines are complex, unreliable, heavy, and lack intuitive control, with high mechanical complexity and weight, making them unsuitable for widespread use and retrofitting into existing systems.
Innovation Solution
A variable diameter pulley assembly with a power transfer element, such as a belt or chain, that allows for stepless adjustment of the input-output rotational power ratio through a mechanism involving guided pulley segments and an actuator system, enabling precise control and minimizing the number of mechanical parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-ratio drive with chain, front and rear gear clusters, and derailleurs is used, then a wide range of selectable ratios is provided, but the mechanical complexity, weight, and unreliability increase
Solution Approach 1:
The pulley is divided into multiple segments that can move independently relative to each other. These segments are arranged radially around the axis and can be positioned at different radial distances to create variable effective diameters. The segmentation allows the complex multi-ratio functionality to be achieved through simpler radial positioning mechanisms rather than multiple gear clusters and derailleurs.
Solution Approach 2:
The pulley system transitions from static gear ratios to dynamic continuous variation. The pulley segments can be positioned continuously along radial guideways, enabling smooth transition between ratios without discrete steps. This dynamic positioning is controlled by actuators that move segments radially, providing continuously variable transmission ratios.
2Adaptability or versatility
If a multi-ratio drive with derailleurs is used, then multiple gear ratios are available, but the reliability decreases due to sensitive mechanisms that may misalign or become damaged
Solution Approach 1:
The design incorporates guideways that constrain pulley segment movement to precise radial paths, preventing misalignment before it can occur. The segments are guided along predetermined trajectories, ensuring they remain properly positioned during ratio changes. This preemptive guidance mechanism eliminates the alignment issues that plague derailleur systems.
Solution Approach 2:
The invention extracts and eliminates the derailleur mechanism entirely from the drive system. Instead of using derailleurs to shift chains between sprockets, the system uses directly actuated pulley segments that move radially on guideways. This removal of the sensitive derailleur component fundamentally improves reliability by eliminating the source of misalignment and damage.
3Ease of operation
If a conventional continuously variable transmission is used, then smooth ratio changes are achieved, but the weight and complexity increase making it unsuitable for human-powered vehicles
Solution Approach 1:
The pulley is segmented into multiple independently positionable elements rather than using a complex continuous mechanism. These segments can be positioned radially to achieve continuous ratio variation, but the segmented approach allows for a lighter, more discrete structure compared to conventional CVT designs with continuous belts and variable diameter sheaves.
Solution Approach 2:
The system achieves continuous ratio variation by changing the radial position parameter of pulley segments along guideways. Instead of using complex mechanical linkages or continuous belts, the invention varies the effective diameter by translating segments radially, controlled by actuators. This parameter-based approach (radial position) simplifies the mechanism and reduces weight while maintaining smooth ratio changes.
Data Source
AI summary
Provided is a continuously variable transmission including a variable diameter first pulley assembly, a second pulley assembly, coupled with an endless power transfer element. The first pulley assembly includes: a first side member having a plurality of first guideways coupled to rotate on a first axle; a second side member having a plurality of a second guideways, separated from the first side member, coupled to rotate freely about the first axle; a plurality of pulley segments engaged with the endless power transfer element coupled with the first and second guideways arranged in the circle about the first axis of rotation; an actuator for rotating the first and second side member relative to each other about the first axis of rotation, producing radial displacement of the pulley segments and changing the effective diameter of the first pulley assembly; and a tensioner for tensioning the endless power transfer element.