Aircraft Actuator Planetary Gearbox Position Transducer
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Solution Overview
Problem
The transition from hydraulic to electric actuation in aircraft control surfaces faces challenges with oversized motors due to gearbox inertia amplification, leading to increased weight and cost, and design complexities with planetary gearboxes, particularly in positioning and protecting position resolvers.
Innovation Solution
Aircraft control surface actuation using a planetary gearbox assembly with an input sun gear, intermediate planetary gear, and output ring gear, where a position transducer is driven by the planet carrier via a resolver drive arm, allowing for a compact and protected arrangement that reduces radial forces on the transducer and housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high gear ratio gearbox is used to reduce motor speed and increase torque, then the motor can be smaller, but the reflected inertia of the motor armature increases substantially, requiring oversized motors
Solution Approach 1:
The patent segments the actuation function into two independent single-stage planetary gearboxes instead of one high-ratio gearbox. Each gearbox handles one motor's torque requirement independently, avoiding the inertia amplification problem. The first gearbox has a gear ratio of approximately 10:1 and the second has approximately 5:1, both much lower than the several hundreds to one ratio in conventional designs.
Solution Approach 2:
Instead of using one motor to drive a high-inertia gearbox output, the patent inverts the approach by using two motors with reduced inertia that directly drive separate gearboxes. The standby motor can easily back-drive the active motor through the low-ratio gearbox without requiring oversized motor dimensions.
2Measurement precision
If the position transducer is positioned at the output ring gear, then it can measure output position directly, but the transducer is exposed to external forces and contaminants
Solution Approach 1:
The patent nests the position transducer within the internal structure of the gearbox housing, specifically within the planetary gear assembly area. The transducer is mounted on the housing and its measurement axis is aligned with the planet carrier rotation, allowing it to measure output position indirectly through the gear ratio relationship while being protected from external environmental factors.
Solution Approach 2:
The patent uses the planet carrier as an intermediary element. The transducer measures the position of the planet carrier, which is mechanically linked to the output ring gear through the planetary gear set. This intermediary measurement approach allows accurate output position detection while keeping the transducer isolated from external forces and contaminants.
3Volume of moving object
If a single high-ratio gearbox is used, then the system is more compact, but the standby motor inertia reflected through the gearbox requires oversized motors
Solution Approach 1:
The patent divides the single high-ratio gearbox into two separate low-ratio gearboxes, each driven by its own motor. This segmentation eliminates the inertia amplification effect that would otherwise require oversized motors, while the overall actuator assembly remains compact due to the efficient planetary gearbox design and integrated housing.
Data Source
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AI summary
An aircraft control surface actuation assembly comprises a first electromechanical actuator assembly (44) driven by two independent motors (48, 50) for redundancy, with a damping assembly (46) provided to mitigate flutter.