Asymmetric Planetary Gear Teeth for Pitting-Resistant Power Transfer
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Solution Overview
Problem
Conventional gear teeth in planetary gear systems are prone to pitting and wear, which can lead to functional loss and failure in extreme operating conditions, limiting the maximum horsepower, weight, and form factor of aircraft transmissions.
Innovation Solution
The design incorporates gear teeth with asymmetrical pressure angles, where the drive side has a greater pressure angle than the coast side, enhancing the strength and reducing contact stress, allowing for improved lubrication and reduced risk of pitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetrical gear teeth are used, then the gear design is simpler and manufacturing is easier, but the gear teeth are prone to pitting and wear under extreme operating conditions
Solution Approach 1:
The gear teeth are designed with asymmetrical pressure angles where the drive side has a different pressure angle than the coast side. This asymmetry optimizes the contact stress distribution and reduces pitting resistance on the drive side where the majority of wear occurs during operation
Solution Approach 2:
Different portions of the gear tooth are given different pressure angles tailored to their specific functional requirements. The drive side uses one pressure angle optimized for power transmission, while the coast side uses another pressure angle optimized for reverse motion handling
2Reliability
If gear teeth are designed to withstand extreme operating conditions, then reliability improves, but the gear train generates more heat and requires better lubrication
Solution Approach 1:
The pressure angle parameter is changed differently on the drive side versus the coast side of each gear tooth. This parameter modification alters the contact mechanics to reduce sliding velocity and contact stress, thereby reducing heat generation while maintaining reliability under extreme conditions
3Strength
If the pressure angle on the drive side is increased, then contact stress is reduced and pitting resistance improves, but the coast side performance may be affected
Solution Approach 1:
The gear tooth is designed with differentiated local properties where the drive side has a higher pressure angle for improved contact stress resistance, while the coast side maintains a lower pressure angle for smooth operation during reverse motion. Each side is locally optimized for its specific operational role
Data Source
AI summary
A gear train includes a first gear having teeth meshed with teeth of a second gear. Each tooth of the first gear includes a coast side and a drive side opposed to the coast side. The drive side has a pressure angle that is greater than that of the coast side. The gear train can be part of a powertrain system for a rotorcraft, and can replace a traditional gear train in a retrofit or new build. The first gear is a planet gear and the second gear is a ring gear wherein the planet gear and ring gear are in a planetary gear train configuration.