Zero Torque Membrane Seal for Rotating Shafts
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Solution Overview
Problem
Conventional dynamic seals apply significant torque loads to rotating shaft systems, hindering performance and requiring additional components like garter springs, which increase cost and torque load.
Innovation Solution
A zero torque membrane seal design featuring an inner and outer case with a seal element that flexes under centrifugal forces at high rotational speeds, reducing torque load to zero by lifting off the outer case, utilizing a flexible membrane and seal lip configuration with a high length-to-thickness ratio and optional features like dust lips and shielding to manage debris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dynamic seal designs are used to prevent water and dirt ingress, then sealing function is adequate, but torque loads are high (3.4 Nm or larger)
Solution Approach 1:
The seal element incorporates a flexible membrane that dynamically responds to rotational speed. At low speeds, the membrane maintains contact with the outer case for effective sealing. At high speeds, centrifugal forces cause the membrane to flex outward, reducing contact pressure and torque load to near zero, thus dynamically adapting the seal's mechanical characteristics to operating conditions.
Solution Approach 2:
The seal design changes the contact pressure parameter as a function of rotational speed. The flexible membrane allows the contact pressure to decrease naturally as speed increases due to centrifugal effects, transforming the seal from a high-torque conventional design to a variable-torque design that approaches zero torque at high speeds while maintaining sealing effectiveness.
2Reliability
If garter springs are added to conventional seals to apply forces to the seal lip, then sealing capability is improved, but torque load and cost increase
Solution Approach 1:
The design extracts and eliminates the garter spring component from the seal assembly. Instead of using an elastic element to apply sealing force, the invention relies on the flexible membrane's inherent ability to conform to the outer case surface and the natural contact pressure generated by the seal's geometry, thereby removing the source of additional torque load and cost.
Solution Approach 2:
The flexible membrane serves its own sealing function without requiring external assistance from garter springs. The membrane's flexibility allows it to self-adjust and maintain contact with the outer case through its own structural properties and the operational dynamics of the seal, making the system self-sufficient and eliminating the need for additional force-applying components.
3Reliability
If seal lip contact pressure is increased to improve sealing, then sealing effectiveness improves, but friction and torque load increase
Solution Approach 1:
The seal transitions from a static contact pressure design to a dynamic one where contact pressure varies with rotational speed. The flexible membrane allows contact pressure to be high at low speeds for effective sealing, then automatically reduces at high speeds, creating a dynamic balance between sealing effectiveness and frictional energy loss that adapts to operating conditions.
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 membrane seal achieves significantly lower torque loads at low speeds and reduces or eliminates torque at high rotational speeds (500-800 rpm), compared to conventional seals, thereby enhancing system performance and reducing costs.
Implementation Method 1
As the shaft rotates, the centrifugal forces tend to cause the membrane portion to flex and the torque loads applied by the dynamic seal are reduced to the point that the seal lifts off of the outer case and applies zero torque load.
Data Source
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AI summary
A low friction seal (10) for sealing between a shaft (12) and a bore (14) and includes an inner case (18) adapted to be mounted on the shaft (12). An outer case (20) is adapted to be mounted within the bore (14). A seal element (22) is mounted to the inner case and includes a base portion attached to the inner case. A membrane (22b) extends from the base portion (22a) and an axially extending leg (22c) extends from the membrane. A seal lip (22d) extends from the axially extending leg (22c) and sealingly engages a radially extending portion (20b) of the outer case. As the shaft rotates, the centrifugal forces tend to cause the membrane to flex and the torque loads applied by the dynamic seal are reduced to the point that the seal lip (22d) can lift off and apply zero torque load.