CVT Casing Shape Around the Secondary Pulley to Avoid Belt Contact
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Solution Overview
Problem
Belt-type continuously variable transmissions face challenges in preventing an increase in casing size while maintaining the internal surface position not in contact with the radially outside end of the belt, which can lead to extra radial gaps and increased casing dimensions.
Innovation Solution
The internal surface of the casing is formed in an elliptical shape that follows the trajectory of the belt's radially outside end, with a radial distance from the secondary pulley's rotation center to the internal surface being shorter in one direction than in another, preventing contact with the belt's radially outside end and thus avoiding extra radial gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the internal surface of the casing is positioned to not contact the radially outside end of the belt, then vibration and noise are prevented, but the casing size increases due to extra radial gaps
Solution Approach 1:
The patent applies asymmetry by positioning the internal surface of the casing at different radial distances from the rotation center of the secondary pulley depending on the direction. Specifically, the radial distance is shorter in the direction orthogonal to the line connecting the rotation centers of the primary and secondary pulleys, and longer in the direction along that line. This asymmetric configuration allows the casing to closely follow the belt's trajectory without contact in critical areas while maintaining adequate clearance in other areas, thereby preventing vibration and noise without unnecessarily increasing overall casing size.
Solution Approach 2:
The patent applies local quality by varying the radial distance of the casing's internal surface from the rotation center based on the specific direction. Instead of maintaining a uniform radial gap around the entire secondary pulley, the design provides different clearance characteristics in different directions - shorter distance in the orthogonal direction and longer distance along the line connecting pulley centers. This localized adjustment optimizes the balance between preventing belt contact (reducing vibration and noise) and minimizing casing volume.
2Volume of stationary object
If the radial distance from the secondary pulley rotation center to the casing internal surface is reduced, then casing size is minimized, but the internal surface may contact the radially outside end of the belt
Solution Approach 1:
The patent resolves this contradiction by implementing an asymmetric radial distance configuration. The radial distance from the secondary pulley rotation center to the casing internal surface is set to be shorter in the direction orthogonal to the line connecting the rotation centers, and longer in the direction along that line. This asymmetric arrangement ensures that the casing internal surface follows the belt's trajectory without contact in the critical orthogonal direction while maintaining adequate clearance in the longitudinal direction, thereby achieving compact casing size without compromising reliability.
Solution Approach 2:
The patent addresses the contact prevention issue by considering the three-dimensional trajectory of the belt and the casing internal surface. By analyzing the belt's path in multiple directions from the rotation center and setting different radial distances accordingly, the design ensures that the casing accommodates the belt's movement in all directions without contact, while minimizing overall volume. This dimensional approach allows precise control over clearance characteristics.
Data Source
AI summary
A belt-type continuously variable transmission includes: a primary pulley; a secondary pulley; a belt wound along the primary pulley and the secondary pulley; and a casing accommodating the primary pulley and the secondary pulley. Further, the belt has, in a portion being wound along the secondary pulley, a radially outside end which may be located further radially outside than an outer circumference portion of the secondary pulley, and a distance from a rotation center of the secondary pulley to an internal surface of the casing in a first direction, which is along a straight line passing through rotation centers of the primary pulley and the secondary pulley, is shorter than a distance from the rotation center of the secondary pulley to the internal surface of the casing in a second direction which is orthogonal to the first direction at the rotation center of the secondary pulley.