Ball-Clutch Speed Limiter for Aircraft Door Power-Loss Closure
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Solution Overview
Problem
Existing power door opening systems (PDOS) for aircraft lack a mechanism to control the retraction of the actuator in the event of power loss, leading to uncontrolled door closure.
Innovation Solution
A one-way speed limiter is introduced, comprising a ball housing with a one-way clutch and a friction clutch, which allows controlled door closure by engaging the friction clutch when the motor shaft reaches a certain speed, preventing uncontrolled rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a no-back unit is used to prevent free rotation of the actuator, then the actuator can be retracted only by the motor, but without the no-back unit the actuator/door will retract at an uncontrolled rate
Solution Approach 1:
A one-way clutch is introduced as an intermediary component between the motor shaft and the actuator mechanism. This clutch allows free rotation in the extension direction while preventing uncontrolled rotation in the retraction direction, thereby providing controlled retraction without requiring a complex no-back unit with resistive torque proportional to axial load.
2Reliability
If power is lost to the motor, then the PDOS does not allow retraction of actuator, but the door cannot be lowered or closed
Solution Approach 1:
The clutch mechanism is segmented into two functional directions: one way for free rotation (extension) and another way for controlled engagement (retraction). This segmentation allows the system to provide power loss protection while still enabling manual door closure by simply removing the pin, as the one-way clutch design inherently allows controlled rotation in both directions when disengaged.
3Reliability
If a one-way clutch is used to allow free rotation in extension direction, then retraction is controlled, but the system lacks speed limitation during uncontrolled rotation
Solution Approach 1:
A friction clutch is introduced as an intermediary between the one-way clutch and the motor shaft. This friction clutch acts as a speed limiter by providing friction-based resistance during uncontrolled rotation, preventing the motor shaft from rotating at excessive speeds and thereby eliminating the harmful effects of uncontrolled rotation while maintaining the one-way clutch's retraction control functionality.
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 one-way speed limiter ensures that the aircraft door closes in a controlled manner even if power is lost, preventing damage and ensuring safety by limiting the rotational speed of the motor shaft.
Implementation Method 1
The ball member selectively engages the stop feature to generate an axial force on the ball housing
Implementation Method 2
A friction clutch is disposed between the ball housing and the first housing. The friction clutch selectively retards rotation of the ball housing
Data Source
AI summary
A one-way speed limiter includes a first housing including an inner surface. defining a speed limiter receiving zone. A second housing includes a flange and a second wall including an inner surface portion that includes a stop feature. A ball housing including a ball member is rotatably supported in the speed limiter receiving zone. The ball member selectively engages the stop feature. A friction clutch is disposed between the ball housing and the first housing. The friction clutch selectively retards rotation of the ball housing. A motor shaft is selectively rotatably connected to the ball housing. The motor shaft including a first end supported at the ball housing and a second end. The motor shaft is rotatable relative to the ball housing in a first direction and selectively rotatably constrained relative to the ball housing in a second direction to selectively engage the friction clutch.