Planet Gear Rim Thickness Tuning for Benign Failure Modes
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Solution Overview
Problem
Conventional planetary gear systems are prone to catastrophic failure due to planet gear tooth breakage, which can lead to costly and potentially fatal crashes in aircraft propulsion systems, as the broken teeth can lock up and cause system failure.
Innovation Solution
Designing the planetary gear system to prioritize rim breakage over tooth breakage by optimizing the planet gear's rim thickness and tooth depth ratio, allowing for a more benign failure mode where the rim cracks or breaks instead of the teeth, thereby preventing tooth fragments from causing interference and system lockup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If planet gear tooth breakage is promoted as a preferred failure mode, then the planet gear can fail in a controlled manner, but the broken teeth can become enmeshed between gears and cause catastrophic system lockup
Solution Approach 1:
The invention changes the geometric parameters of the planet gear by optimizing the rim thickness to tooth depth ratio. By reducing the rim thickness relative to the tooth depth (creating a thinner rim structure), the design shifts the failure mode from tooth breakage to rim breakage. This parameter change ensures that when failure occurs, the rim breaks in a manner that does not produce interfering fragments, thus resolving the contradiction between controlled failure and system lockup prevention
Solution Approach 2:
Instead of designing the planet gear to fail by tooth breakage (conventional approach), the invention inverts the approach by designing it to fail by rim breakage. This inversion changes the failure mechanism fundamentally - the rim breaks away from the gear body rather than teeth breaking off, eliminating the source of interfering fragments that cause catastrophic lockup while maintaining the benefit of predictable failure mode
2Reliability
If the planet gear rim thickness is reduced to promote rim breakage, then tooth breakage is prevented, but the rim structural strength is reduced
Solution Approach 1:
The invention applies parameter changes by optimizing the rim thickness to tooth depth ratio within a specific range (0.5 to 1.2 times). This controlled reduction in rim thickness achieves the dual benefit of promoting rim breakage as the preferred failure mode while maintaining sufficient structural integrity through the optimized ratio. The specific parameter range ensures the rim is thin enough to break preferentially but strong enough to prevent premature failure
Solution Approach 2:
The invention applies local quality by creating a non-uniform thickness distribution in the planet gear structure. The rim is designed with varying thickness - thinner at critical stress zones to promote controlled breakage, while maintaining adequate thickness in other areas to support the gear's operational loads. This localized optimization allows the rim to fail in a controlled manner without compromising overall gear strength
3Reliability
If the planet gear is designed with optimized rim thickness and tooth depth ratio, then rim breakage is promoted over tooth breakage, but the manufacturing complexity increases
Solution Approach 1:
The invention uses parameter changes by defining specific ranges for rim thickness (0.5 to 1.2 times the tooth depth) that can be directly applied during manufacturing. These parameter specifications provide clear manufacturing guidelines that simplify the production process while achieving the desired failure mode optimization. The standardized parameter ranges allow for straightforward machining and quality control
Solution Approach 2:
The invention applies preliminary action by pre-calculating and specifying the optimal rim thickness to tooth depth ratio during the design phase. This preliminary determination of geometric parameters eliminates the need for complex iterative manufacturing adjustments, as the optimal dimensions are established beforehand based on failure mode analysis. The pre-determined parameters guide the manufacturing process directly, reducing complexity
Data Source
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AI summary
A method of optimizing a planetary gear system (100) for continued operation after failure of a planet gear (106) includes providing a planetary gear system (100) and reducing a backup ratio of a planet gear (106) of the planetary gear system (100) by reducing a rim thickness (204) of the planet gear (106).