Cross-Bleed Spool Mechanism for Stalled Hydraulic Actuator Loads
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Solution Overview
Problem
Hydraulic actuators in aircraft systems face damage due to excessive loads when kinematic devices become inoperable or experience high friction, leading to potential damage to the actuator, linking mechanisms, and mounting structures, which traditional safety mechanisms like shear pins result in inoperability.
Innovation Solution
A cross-bleed safety mechanism with a bilaterally moveable spool within a hydraulic cylinder that blocks and unblocks hydraulic bypass channels in response to pressure differentials, limiting excessive loads on the actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a shear pin is used to disconnect the actuator from the kinematic device when load exceeds threshold, then damage to components is prevented, but the kinematic device becomes inoperable
Solution Approach 1:
A bilaterally moveable spool valve is introduced as an intermediary component between the actuator and kinematic device. The spool valve monitors load conditions and selectively connects or disconnects hydraulic chambers, providing protective mediation without permanent damage to the kinematic device or linking mechanism
Solution Approach 2:
The safety mechanism transitions from a static sacrificial shear pin to a dynamic spool valve that can move between positions. The spool responds to differential pressure changes in real-time, dynamically adjusting hydraulic connections to protect against excessive loads while maintaining system operability
2Ease of operation
If the actuator operates a stalled kinematic device beyond sizing limit, then the kinematic device can be moved, but damage occurs to the actuator, linking mechanism, or mounting
Solution Approach 1:
The spool valve is pre-configured with bypass channels that activate before excessive damage can occur. When differential pressure reaches a threshold indicating a stalled condition, the spool automatically shifts to bypass hydraulic fluid, cushioning the system against damaging pressure spikes before they can compromise the actuator or mounting structures
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
Prevents damage to hydraulic actuators and associated components by passively relieving pressure, maintaining control of kinematic devices without mechanical disconnection, thus avoiding inoperability.
Implementation Method 1
The bilaterally moveable spool blocks the second hydraulic bypass channel and begins to unblock the first hydraulic bypass channel in response to a first differential pressure between the first and second chambers exceeding a first differential cracking pressure
Data Source
AI summary
Apparatus and associated methods relate to passively limiting a load of a stalled linear hydraulic actuator that actuates a kinematic device. Damage to a stalled linear hydraulic actuator, associated mounting structure(s), any associated linking mechanism(s), and/or a kinematic device controlled thereby can be prevented quickly and without necessarily forfeiting control of the kinematic device. Such damage prevention can be performed using a cross-bleed safety mechanism connected in parallel with the linear hydraulic actuator. The cross-bleed safety mechanism includes a bilaterally moveable spool within a hydraulic cylinder. The bilaterally moveable spool is located between hydraulic chambers that are in fluid communication with corresponding chambers of the linear hydraulic actuator. In response to being sufficiently displaced from an equilibrium position in each direction of movement by a pressure difference thereacross, the bilaterally moveable spool unblocks bypass channels thereby limiting the stalled linear actuator.