Actuator Fail-Fix Assembly for Last-Position Hold
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Solution Overview
Problem
Actuator assemblies in turbo machines experience undesired movement and operational failures due to loss of input signal or pressure, leading to uncommanded changes in vane angle, which can cause stalls or surges, and existing fail fix systems are heavy and complex.
Innovation Solution
An actuator assembly with a fail-fix system that includes a piston assembly with a spring and friction mechanism, coupled with a control valve assembly to maintain or disable motive fluid flow, preventing undesired movement by engaging the piston with the input drive assembly via a friction mechanism when the signal is lost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fail fix system is added to prevent undesired movement after actuator failure, then reliability is improved, but device complexity increases
Solution Approach 1:
The fail fix system merges the piston assembly with the input drive assembly by integrating a friction mechanism directly into the piston structure. The piston includes a friction surface that engages with a corresponding friction surface on the input drive assembly, combining multiple functions (actuation and fail-safe positioning) into a single integrated component rather than adding separate fail-safe mechanisms.
Solution Approach 2:
The friction mechanism acts as an intermediary between the piston assembly and the input drive assembly. During normal operation, the friction surfaces are disengaged allowing free movement. Upon failure, the spring pushes the piston forward to engage the friction surfaces, which then serve as the mediating mechanism to prevent undesired rotation without requiring complex locking or braking systems.
2Reliability
If a fail fix system with multiple separate components is used, then reliability is improved, but weight increases
Solution Approach 1:
The design combines the fail-safe function with the existing piston assembly structure. The friction surfaces are integrated into the piston and input drive assembly rather than being separate components. This merging approach achieves the fail-safe function while minimizing additional weight compared to systems that use separate brakes, locks, or positioning mechanisms.
3Device complexity
If a friction mechanism is integrated into the piston assembly, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The friction surfaces are designed with specific local geometric features (such as tapered surfaces or designated contact zones) that concentrate the friction engagement in controlled areas. This local quality approach ensures that precise manufacturing is required only in specific zones rather than throughout the entire component, making the precision requirements more manageable while maintaining the simplicity of the integrated design.
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 system effectively mitigates undesired movement and maintains the last commanded position of the output shaft, reducing the risk of stalls and surges in turbo machines by engaging the piston with the input drive assembly through a friction mechanism after loss of signal, thus stabilizing the system.
Implementation Method 1
The piston assembly includes a spring disposed at the first end between the body and the piston
Implementation Method 2
The friction mechanism includes a friction disc configured to engage together the piston and the input drive assembly
Data Source
AI summary
An actuator assembly including a fail-fix system is provided. The actuator assembly includes an output shaft, an input drive assembly, and a piston assembly. The piston assembly includes a body surrounding a piston moveable within the body. The body defines a first end and a second end opposite thereof between which the piston is moveable within the body. The piston assembly includes a spring disposed at the first end between the body and the piston. The piston assembly includes a friction mechanism disposed at the second end of the piston opposite of the first end. An adjustable area is defined within the body between the second end of the piston and the input drive assembly.