Shape Memory Preload for Temperature-Stable Pressure Relief Valves
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Solution Overview
Problem
Existing pressure relief valves (PRVs) for high temperature applications, such as those used in aircraft engines and nacelles, suffer from inconsistent performance due to the degradation of spring stiffness with temperature changes, leading to variations in cracking pressure and pressure regulation.
Innovation Solution
Incorporation of a variable preload mechanism using shape memory materials, such as Nickel/Titanium alloys, to adjust the biasing force of the spring based on temperature, compensating for the degradation in spring stiffness and maintaining consistent performance across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple mechanical PRV is used, then the device complexity is reduced and weight is minimized, but the performance consistency across wide temperature ranges deteriorates due to spring stiffness degradation
Solution Approach 1:
The patent changes the physical state of the preload means by utilizing the phase transition of shape memory alloy from martensite to austenite at elevated temperatures. This phase change causes a significant increase in the preload applied to the spring, compensating for spring stiffness degradation and maintaining consistent cracking pressure across wide temperature ranges without adding electronic components or complex control systems
Solution Approach 2:
The patent employs shape memory alloy, a composite material with unique thermomechanical properties, as the preload means. This material combines elastic deformation capability with phase-transition-induced shape recovery, enabling it to automatically adjust preload based on temperature while maintaining a simple mechanical structure
2Reliability
If electronically actuated PRV is used, then performance consistency across temperature ranges is improved, but the device complexity and weight increase due to additional sensors, control and wiring
Solution Approach 1:
The shape memory alloy preload means automatically adjusts the preload on the spring based on the temperature of the fluid passing through the PRV. The material's inherent phase transition properties enable it to sense temperature changes and mechanically adjust the preload without requiring external sensors, control systems, or power sources, thus maintaining simple mechanical structure while achieving consistent performance
Solution Approach 2:
The patent replaces electronic control mechanisms with a purely mechanical solution based on shape memory alloy's thermomechanical properties. The phase transition of the material provides an automatic mechanical adjustment of preload, eliminating the need for electronic sensors, actuators, and control circuits while maintaining performance consistency
3Device complexity
If conventional spring biasing means is used, then the PRV structure remains simple, but the biasing force degrades at higher temperatures leading to cracking pressure variation
Solution Approach 1:
The shape memory alloy preload means undergoes a parameter change in its mechanical properties through phase transition. Below the transformation temperature, the material is in martensite phase with lower stiffness; above the temperature, it transforms to austenite phase with higher stiffness and generates increased preload, thereby compensating for spring force degradation at elevated temperatures
Solution Approach 2:
The patent utilizes the solid-phase transition of shape memory alloy from martensite to austenite as the temperature increases. This phase transition causes a significant increase in the material's stiffness and shape recovery capability, which in turn increases the preload on the spring to compensate for thermal degradation of the spring's biasing force
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 provides a simple and lightweight PRV with improved temperature compensation, reducing cracking pressure variation and pressure regulation decay by up to 6% across varying temperatures, ensuring reliable operation.
Implementation Method 1
a variable preload means, the variable preload means configured to apply a preload to the biasing means so as to increase the biasing force, wherein the variable preload means comprises a shape memory material such that, above a transition temperature of the shape memory material, the variable preload means changes shape so as to apply a higher preload to the biasing means
Data Source
AI summary
A pressure relief valve, PRV, includes an inlet and an outlet defining a fluid flow path therebetween and a plunger. The plunger is moveable between a closed position and an open position, wherein, in the closed position, the plunger blocks the fluid flow path, and, in the open position, fluid may flow through the fluid flow path, wherein pressure at the inlet applies an opening force on the plunger, urging the plunger towards the open position. The PRV also includes a biasing means configured to apply a biasing force to the plunger, thereby biasing the plunger towards the closed position such that, when the biasing force is greater than the opening force, the plunger remains in the closed position, and when the opening force is greater than the biasing force and the plunger moves to the open position.