Centre-Biased Actuator Bellows Chamber for Bias Force Stability
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Solution Overview
Problem
Self-contained centre biased actuators face issues with loss of bias force and complex maintenance due to hydraulic fluid and gas leakage across dynamic seals, which can lead to operational failures and increased maintenance needs, particularly in aircraft landing gear applications.
Innovation Solution
A centre biased actuator with a sealed gas chamber defined by an expandable metal bellows chamber that accommodates fluid loss while preventing fluid transfer, maintaining bias force and simplifying maintenance by isolating gas and hydraulic fluid compartments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealed gas chamber with expandable metal bellows is used, then the reliability of bias force is improved, but the device complexity increases
Solution Approach 1:
The patent employs an expandable metal bellows chamber that can flexibly expand and contract to accommodate hydraulic fluid volume changes while maintaining gas containment. This flexible shell structure allows the gas chamber to adapt to actuator movement without requiring complex rigid mechanical linkages or adjustment mechanisms, thereby improving reliability while controlling complexity.
Solution Approach 2:
The gas chamber defined by the metal bellows is nested within the actuator housing, with the bellows containing the gas and being surrounded by the hydraulic fluid environment. This nested arrangement allows compact integration of multiple functional elements (gas containment, fluid isolation, volume compensation) within a single structure, improving reliability without proportionally increasing overall device complexity.
2Reliability
If dynamic seals are used to contain hydraulic fluid, then fluid containment is improved, but maintenance complexity increases due to seal degradation
Solution Approach 1:
The patent extracts the gas containment function into a separate sealed metal bellows chamber that is isolated from the hydraulic fluid system. This separation means that hydraulic fluid degradation or contamination does not affect the gas chamber integrity, and vice versa. The dynamic seals are confined to specific interfaces where they can be independently monitored and replaced without affecting the entire actuator system, simplifying maintenance.
Solution Approach 2:
The actuator is segmented into distinct functional zones: a gas-containing metal bellows chamber and a hydraulic fluid chamber, separated by dynamic seals at defined interfaces. This segmentation allows each system (gas and hydraulic fluid) to be independently managed, with seals positioned at controlled transition points that can be accessed and replaced without disassembling the entire actuator, reducing maintenance complexity.
3Device complexity
If gas and hydraulic fluid are allowed to interact, then volume compensation is simplified, but substance loss increases due to transfer between chambers
Solution Approach 1:
The metal bellows chamber acts as an intermediary structure that allows volume compensation without direct mixing of gas and hydraulic fluid. The bellows expands and contracts in response to hydraulic fluid volume changes, providing mechanical coupling between the two substances while maintaining their separation. This eliminates the need for complex check valves or controlled transfer mechanisms, simplifying the volume compensation system while preventing substance loss through direct contact interfaces.
Solution Approach 2:
The metal bellows serves as a flexible barrier that mechanically transmits volume changes between the gas and hydraulic fluid systems without allowing substance transfer. The bellows expands when hydraulic fluid volume increases and contracts when volume decreases, providing seamless volume compensation while the metallic barrier prevents diffusion or leakage of either substance into the other chamber, eliminating substance loss.
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 solution reduces the likelihood of bias force degradation and simplifies maintenance by containing gas within an expandable chamber, ensuring reliable operation and reducing the risk of operational failures like aborted take-offs.
Implementation Method 1
a sealed gas chamber defined by an elastic vessel or expandable chamber, the volume of which can vary in an elastic nature
Implementation Method 2
the working fluid comprises a virtually incompressible liquid and a compressible gas, the liquid being pressurised by the stored energy in the compressed gas
Implementation Method 3
pressurised fluid which acts on internal surfaces of the actuator such that a pressure differential causes the actuator to adopt the intermediate condition
Data Source
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AI summary
A centre biased actuator (10) comprising: an outer cylinder (102); a slave cylinder (14) linearly transposed within the outer cylinder; a rod assembly (120, 122), the piston (122) of which is linearly transposed within the slave cylinder and the rod (120) of which extends from the outer cylinder; one or more first dynamic seals (121) arranged to act on a sidewall of the rod to inhibit hydraulic fluid leaking from the outer cylinder; one or more second dynamic seals (117) arranged to act on a sidewall of the slave cylinder or an inner surface of the outer casing to inhibit hydraulic fluid leaking from the outer cylinder; and a gas chamber (13, 23) comprising a sealed expandable chamber (14, 24) containing gas, the expandable chamber being arranged to act on hydraulic fluid within the centre biased actuator to bias the centre biased actuator to assume an intermediate condition which lies between a compressed condition and an extended condition.