Disengageable Speed Reducer Ring Gear for Fan Anti-Blocking
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Solution Overview
Problem
Conventional speed reducers in aircraft turbomachines face issues with blocking due to bearing drag, foreign body ingestion, or vane breaks, leading to increased turbomachine drag and reduced aircraft controllability, which existing fusible devices attempt to address but introduce flexible zones detrimental to dynamic behavior.
Innovation Solution
A speed reducer design featuring annular half-ring gears with helical teeth and a support plate that allows uncoupling when a predefined unclutching action is exceeded, maintaining a rigid system without introducing flexible zones, using retaining means like deformable stop rings and thrust bearings to facilitate the mechanical fuse function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fusible devices are introduced in the low pressure line to prevent blocking, then safety and reliability are improved, but flexible zones are introduced which worsen the dynamic behavior of the line
Solution Approach 1:
The ring gear is divided into two separate half-ring gears that can move independently relative to each other along the low pressure line. This segmentation allows one half-ring gear to remain stationary (maintaining rigidity) while the other can move to create separation (providing flexibility for uncoupling). The planet gears are also segmented into two sets, each engaging with a different half-ring gear, enabling independent movement and preventing the need for a flexible zone throughout the entire line.
Solution Approach 2:
The invention introduces dynamic capability selectively: the half-ring gears are designed to be movable relative to each other along the low pressure line axis, allowing them to separate when blocking occurs. This dynamic feature is localized to specific components rather than introducing flexibility throughout the entire low pressure line, thus maintaining overall system rigidity while enabling safety uncoupling functionality.
2Reliability
If half-ring gears are made movable to enable uncoupling function, then safety and reliability are improved, but device complexity increases
Solution Approach 1:
The ring gear is segmented into two half-ring gears that can move independently, allowing the uncoupling function to be achieved through relative movement of these segments rather than through complex mechanisms. Each half-ring gear is engaged by its own set of planet gears, simplifying the control of the uncoupling action.
Solution Approach 2:
Instead of making the entire ring gear movable or introducing complex fusible devices, the invention inverts the approach by making the support structure (half-ring gears) movable relative to each other while keeping the planet gears stationary in their carriers. This inversion simplifies the mechanism: the half-ring gears simply slide along the low pressure line axis when uncoupling is needed, rather than requiring complex actuation systems.
3Reliability
If retaining means are added to hold half-ring gears in coupled position, then reliability is improved, but device complexity increases
Solution Approach 1:
The retaining means are designed to automatically engage and disengage based on the operational state of the system. During normal operation, the retaining means (such as deformable stop rings or thrust bearings) automatically hold the half-ring gears in their coupled position without requiring active control. When blocking occurs and the unclutching action exceeds the retention force, the retaining means automatically disengage, allowing the half-ring gears to separate. This self-service mechanism improves reliability without adding complex control systems.
Solution Approach 2:
The retaining means utilize changes in force parameters to maintain reliability. The retaining force is designed to be sufficient under normal operating conditions but is intentionally set below the force that occurs during blocking events. This parameter-based approach allows the same structural components to serve dual purposes: maintaining coupled position during normal operation and allowing separation when needed, without requiring additional complexity.
Data Source
AI summary
A speed-reducing unit, particularly for transferring torque between a gas turbine and a fan in a turbine engine, includes an annular ring, at least one gear that is coupled to the ring, the ring including two annular half-rings that are offset relative to each other along the main axis of the speed-reducing unit and that are coupled with at least one gear, and a plate for supporting the two half-rings, in relation to which the two half-rings are rotationally fixed about the main axis of the speed-reducing unit. Each half-ring includes an internal helical tooth. Each half-ring is connected to the support plate so as to be able to be uncoupled from at least one gear when at least one gear exerts a disengaging action on each half-ring, with the amplitude of the action being greater than a determined amplitude value.