Strain Wave Gearing Oil-Repellent Coating for Lower Loss Torque
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Solution Overview
Problem
Strain wave gearings experience increased loss torque due to high stirring resistance near the input shaft and wave bearing, primarily caused by grease contact and adherence, which is difficult to balance with lubricity considerations.
Innovation Solution
The strain wave gearing employs a rigid internally toothed gear with a flexible externally toothed gear, a wave generator, and oil-repellent coatings on the input shaft and wave bearing components to reduce grease adherence and stirring resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large amount of grease is applied near the input shaft and wave bearing to maintain long-term lubrication, then lubricity is improved, but stirring resistance increases and loss torque increases
Solution Approach 1:
The patent applies oil-repellent coatings specifically to the input shaft outer circumferential surface portion and wave bearing surfaces where grease adherence causes excessive stirring resistance. This localized treatment allows grease to be retained in areas where lubrication is critical while repelling it from areas where it causes excessive drag, thus maintaining lubrication durability without increasing loss torque.
2Loss of energy
If the viscosity of the grease base oil is lowered to reduce stirring resistance, then loss torque is reduced, but lubricity deteriorates
Solution Approach 1:
Instead of changing the viscosity parameter of the grease, the patent modifies the surface properties of contact surfaces by applying oil-repellent coatings. This allows the use of higher viscosity grease that provides better lubricity while the coating prevents excessive grease adherence that would increase stirring resistance, thus resolving the contradiction without compromising lubricity.
3Loss of energy
If oil-repellent coating is applied to reduce grease adherence, then stirring resistance is reduced, but lubricant retention in meshing area may be affected
Solution Approach 1:
The oil-repellent coating is applied selectively to specific surfaces (input shaft outer circumferential surface portion and wave bearing surfaces) rather than throughout the entire gearing system. This localized application ensures that grease is repelled from areas causing excessive stirring resistance while maintaining adequate grease retention in the meshing area between gears, thus reducing stirring resistance without compromising lubrication reliability.
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 oil-repellent coatings facilitate grease removal by centrifugal force, reducing the amount applied and lowering shear rates, thereby decreasing stirring resistance and overall torque loss.
Implementation Method 1
a first oil-repellent coating such as a fluorine resin coating that covers the input-shaft outer circumferential surface portion and has oil-repellent properties against a lubricant applied or supplied to the wave bearing
Implementation Method 2
The oil-repellent coating makes it easier for the lubricant to be shaken off by centrifugal force
Implementation Method 3
The oil-repellent coating causes slippage between the lubricant and the surface in contact with the lubricant, lowering the lubricant shear rate and reducing stirring resistance
Data Source
AI summary
A strain wave gearing (1) has a hollow input shaft (5). A wave generator (4), which makes an externally toothed gear (3) flex in the radial direction so as to engage an internally toothed gear (2), has a wave bearing (43) that has a ball retainer (47). An input-shaft outer circumferential surface portion of the hollow input shaft (5) that is positioned on the inside of the externally toothed gear (3) is coated with an oil-repellent coating (14). The surface of the ball retainer (47) is also coated with an oil-repellent coating (15). The oil-repellent coatings (14, 15) lower the grease stirring resistance of the hollow input shaft (5) and the ball retainer (47) and make it possible to reduce loss torque at the strain wave gearing (1).