Compact Linear Hydraulic Actuator Triplex Cylinder Design
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Solution Overview
Problem
Conventional linear hydraulic actuators for rotorcraft, particularly in tiltrotor applications, face challenges in achieving a compact design with sufficient stroke length and adequate failure tolerance, as they often require longer envelopes and lack sufficient column stability to prevent uncontrolled motions during flight control system failures.
Innovation Solution
The use of triplex cylinders with inverted unbalanced-area pistons, which provide a larger retract piston area in a shorter envelope, enhancing column stability and failure tolerance by venting the conventional extend piston area to atmosphere and utilizing a pressurized balance tube to create an inverted unbalanced cylinder configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dual parallel or dual tandem actuator configurations are used, then reliability is improved through redundancy, but device complexity and envelope length increase
Solution Approach 1:
The patent combines three single-rod cylinders into a single integrated actuator assembly, merging multiple functions into one unified structure. This triplex configuration provides redundancy and failure tolerance while eliminating the need for separate dual parallel or dual tandem actuators, thereby reducing overall device complexity and integration burden.
Solution Approach 2:
The triplex cylinder assembly serves multiple functions simultaneously: it provides primary actuation, redundancy for failure tolerance, and compact integration in a single envelope. Each cylinder can independently contribute to the overall stroke, allowing the system to maintain functionality even if one cylinder fails, while occupying less space than multiple separate actuators.
2Length of moving object
If conventional hydraulic actuators are used, then sufficient stroke length is achieved, but actuator envelope length increases and column stability decreases
Solution Approach 1:
The patent nests the piston rods and cylinders in a compact triplex arrangement where the three cylinders are positioned concentrically or in close proximity, allowing their piston rods to nest within the overall actuator envelope. This nesting configuration enables the accumulation of stroke lengths from multiple cylinders while maintaining a compact overall envelope length, effectively providing a long stroke without a proportionally long actuator.
Solution Approach 2:
Instead of extending stroke length in a single linear dimension (which increases envelope length), the patent distributes the stroke accumulation across multiple cylinders arranged in a three-dimensional configuration. The triplex arrangement allows stroke lengths to be combined vectorially or through mechanical linkage, achieving extended effective stroke while maintaining a compact envelope by utilizing spatial arrangement rather than linear extension.
3Reliability
If conventional hydraulic actuators are used, then basic actuation function is provided, but column stability is insufficient to prevent uncontrolled motions during flight control system failures
Solution Approach 1:
The patent employs a triplex cylinder configuration where the three cylinders are arranged to provide mutual support and balance. The symmetric or balanced arrangement of the three cylinders creates inherent stability, where the load and forces are distributed evenly across all three units, preventing uncontrolled motions or seizures that could occur with conventional dual configurations during flight control system failures.
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
This configuration allows for a 40% increase in stroke length within the same actuator envelope length, improving failure tolerance and preventing actuator seizures by increasing column stability, thus ensuring reliable operation in tiltrotor aircraft.
Implementation Method 1
utilizing a pressurized balance tube to create an inverted unbalanced cylinder configuration
Implementation Method 2
triplex cylinders with inverted unbalanced-area pistons
Data Source
AI summary
In some embodiments, an actuator includes a chamber, a piston disposed within the chamber, and a tube. The chamber has a first port and a second port. The piston comprises a first surface, a second surface, and an elongated conduit coupling the first surface to the second surface. The first surface is disposed between the first port and the second port. The second surface is offset from the first surface. The tube is disposed at least partially within the elongated conduit of the piston. The tube comprises a third port disposed within the elongated conduit of the piston and a fourth port disposed outside of the elongated conduit of the piston.