CV Joint Boot Seal Structure for Lower Insertion Load
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Solution Overview
Problem
Conventional boots for constant velocity joints face a trade-off between securing surface pressure and reducing insertion load, as increasing seal lip height increases surface pressure but also increases insertion load, while decreasing seal lip height reduces surface pressure but not insertion load effectively.
Innovation Solution
A boot design with an elastic body featuring a large-diameter tubular portion, a small-diameter tubular portion, and a bellows portion, including a fastening groove and protrusions on the inner circumferential surface to distribute insertion load and maintain surface pressure, where the protrusion height is set to be smaller than the seal lip height to reduce insertion load without compromising surface pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the height of the seal lips is increased to secure surface pressure, then the surface pressure provided by the seal lips to the outer case becomes higher, but the insertion load of the outer case to the large-diameter tubular portion becomes larger
Solution Approach 1:
The seal lip is divided into multiple segments along its height: a first seal lip portion extending from the inner circumferential surface to a first height, and a second seal lip portion extending from the first height to a second height. This segmentation allows different portions of the seal lip to engage with different portions of the outer case, distributing the sealing function across multiple contact zones and reducing the concentration of insertion load at any single point.
Solution Approach 2:
The seal lip is designed with varying heights at different locations: the first seal lip portion has a first height and the second seal lip portion has a second height that is greater than the first height. This local variation in geometry allows the lower portion (first seal lip portion) to engage earlier during insertion, distributing the load, while the upper portion (second seal lip portion) provides enhanced sealing pressure at the final position.
2Force
If the height of the seal lips is decreased to reduce insertion load, then the insertion load is reduced, but the surface pressure by the seal lips is lowered
Solution Approach 1:
The segmented seal lip structure enables the first seal lip portion to engage with the outer case at a lower height, reducing the initial insertion load required. Simultaneously, the second seal lip portion extends higher to provide sufficient sealing pressure at the final mounted position, ensuring both low insertion load and adequate surface pressure are achieved through the distributed engagement of multiple segments.
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 boot effectively reduces the maximum insertion load while maintaining surface pressure by distributing the load through protrusions and seal lips, ensuring uniform surface pressure and efficient sealing.
Implementation Method 1
The boot includes an elastic body. After the outer case is inserted into the protrusion provided over the entire circumference so that the large-diameter tubular portion is slightly expanded to the outside in the radial direction, the outer case is further inserted into the seal lip so that the large-diameter tubular portion is expanded to the outside in the radial direction.
Data Source
AI summary
A boot includes a large-diameter tubular portion, a small-diameter tubular portion, and a bellows portion. The large-diameter tubular portion includes a fastening groove into which a fastening member is fitted, an opening end to which the bellows portion is coupled and into which an outer case is inserted, at least one seal lip having an annular shape and protruding from an inner circumferential surface of the large-diameter tubular portion at the position where the fastening groove is projected to the inside in the radial direction, so as to be continuous over the entire circumference, and a protrusion protruding from the inner circumferential surface on the opening end side with respect to the seal lip so as to be provided over the entire circumference. A height of the protrusion is set to be smaller than a height of the seal lip.