Hydraulic Tension Spring Structure for Long Stroke Without Buckling
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Solution Overview
Problem
Conventional springs, including torsion and compression springs, fail to provide sufficient force to enhance knee extension and resist buckling in knee braces, especially for applications requiring precise force curves over thousands of cycles, and hydraulic compression springs are unsuitable due to low compression ratio and potential buckling issues.
Innovation Solution
A hydraulic tension spring design featuring a moving cylinder with a liquid-impermeable cavity filled with a compressible hydraulic fluid, precision-guided piston, and a flexible cord for loading, which allows for a longer stroke length and consistent force curve, preventing buckling through precise axial alignment and high-strength materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic compression springs are used, then the force curve is smooth and compression ratio is low, but the stroke length is insufficient and buckling occurs under high load
Solution Approach 1:
The patent inverts the conventional hydraulic spring configuration by switching from compression to tension mode. The piston moves outward to extend the spring rather than inward to compress it, allowing the piston rod to be supported at the base preventing buckling while achieving extended stroke length.
Solution Approach 2:
The patent changes the operational dimension from compression (piston moving into the cylinder) to tension (piston moving out of the cylinder). This dimensional change allows the piston rod to be positioned in a stable support configuration at the base, enabling longer stroke without buckling.
2Reliability
If the piston is carefully guided to prevent buckling, then buckling is avoided, but the piston, seal, or both may be damaged or destroyed
Solution Approach 1:
The patent uses the base structure as a counterweight/support for the piston rod, positioning the heavy, stable base at the fixed end to provide continuous support against buckling forces throughout the extended stroke, eliminating the need for delicate guidance mechanisms.
3Device complexity
If conventional springs are used in knee braces, then the structure is simple, but the force is insufficient to enhance knee extension and resist buckling
Solution Approach 1:
The patent replaces conventional mechanical springs with a hydraulic tension spring system using incompressible fluid in a sealed cylinder. This hydraulic mechanism generates significantly higher forces for knee extension assistance while maintaining a relatively simple overall structure.
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 hydraulic tension spring effectively enhances knee extension and maintains a consistent force curve over multiple cycles, reducing the risk of buckling and damage, while being compact and lightweight for use in knee braces and other applications.
Implementation Method 1
a piston compresses a liquid to load the spring, and the potential energy of the spring is released when the compressive force is removed from the piston
Implementation Method 2
Liquid die springs have a very low compression ratio and a smooth force curve
Data Source
Figure 1~5
Figure 6~8
Figure 9A~12
AI summary
A hydraulic tension spring comprises a block comprising at least one liquid-impermeable cylinder and at least one piston disposed through an open end of the cylinder. The piston provides a piston guide within a liquid containment space within the cylinder filled with hydraulic fluid. A tensioning member moves the piston or the cylinder relative to the other to compress the hydraulic fluid and load the spring, while the piston guide keeps the piston axially aligned to prevent buckling.