Servo Valve Spool Adjustable Joint Wear Reduction
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Solution Overview
Problem
Existing servo valve designs with ball-in-slot joints suffer from premature wear and lack adjustability for the null-bias position of the feedback member, leading to reduced performance and lifetime, and are costly due to the use of materials like tungsten carbide or sapphire for wear protection.
Innovation Solution
An adjustable joint within the spool of a servo valve, comprising displaceable jaw arms with clamping surfaces that secure a feedback member in a central opening, allowing for off-centre positioning and reducing wear by holding the feedback member in pure shear, eliminating the need for costly materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a ball-in-slot joint is used to connect the feedback member to the spool, then binding problems are alleviated, but premature wear occurs and the lifetime is reduced
Solution Approach 1:
The invention transitions from a static ball-in-slot connection to a dynamic jaw arm mechanism that can adjust and clamp. The jaw arms can move relative to each other to accommodate assembly tolerances and then clamp down to secure the feedback member, providing both ease of operation and wear resistance through a movable clamping action rather than a fixed connection
Solution Approach 2:
The invention uses a composite structure combining metal jaw arms with a clamping mechanism. The jaw arms themselves are made of durable metal material that provides both mechanical strength and wear resistance, eliminating the need for expensive materials like tungsten carbide or sapphire while maintaining reliability
2Device complexity
If a ball-in-socket joint is used to connect the feedback member to the spool, then the structure is simple, but adjustability of the null-bias position is not possible
Solution Approach 1:
The jaw arm mechanism incorporates dynamic adjustability through the relative displacement capability of the jaw arms. Before clamping, the jaw arms can be positioned to accommodate different null-bias requirements, and after clamping, they maintain the adjusted position. This provides adaptability without significantly increasing overall structural complexity
Solution Approach 2:
The joint is segmented into multiple components: first and second jaw arms that can move independently, a feedback member, and a clamping mechanism. This segmentation allows the null-bias position to be adjusted by repositioning the jaw arms relative to each other before clamping, providing adaptability while keeping each individual component relatively simple
3Reliability
If expensive materials like tungsten carbide or sapphire are used for the ball, then wear protection is extended, but the production cost increases
Solution Approach 1:
The invention replaces expensive, long-lasting materials like tungsten carbide or sapphire with more economical metal materials for the jaw arms. While the jaw arms may require replacement sooner than expensive materials, the overall system cost is reduced, and the clamping mechanism compensates for wear through its adjustable nature, effectively providing extended service life at lower cost
Solution Approach 2:
The invention extracts the wear protection function from the ball material itself and relocates it to the clamping mechanism. Instead of relying on expensive hard materials to prevent wear, the adjustable clamping mechanism compensates for wear by allowing repositioning and re-clamping, thereby eliminating the need for costly materials while maintaining reliability
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 adjustable joint extends the lifespan of the servo valve by reducing wear and accommodating assembly tolerances, while being easier to manufacture and maintain, with improved contact surface area and stress distribution compared to traditional ball-in-socket configurations.
Implementation Method 1
holding the feedback member in pure shear
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A spool assembly (100) for a second stage of a servo valve comprises a spool (110) having an axis (L) and an opening (112) for a feedback member (200) provided in a central region (114) of the spool extending perpendicular to the axis. An adjustable joint (120) is provided within the spool for securing a feedback member relative to the spool, comprising first and second jaw arms (122, 123) being displaceable relative to each other along the axis of the spool. The jaw arms have opposing clamping surfaces, wherein the clamping surfaces are arranged to be drawn towards each other as the jaw arms are drawn away from each other, such that a feedback member can be clamped between the opposed clamping surfaces of the jaw arms and thereby secured relative to the spool. The first jaw arm may extend from a first spool end (116) to the central region and the second jaw arm may extend from a second spool end (118) to the central region, each jaw arm providing a tensioning portion (124, 125) in the spool end and a head portion (126, 127; 401, 402) in the central region. The head portions of the first and second jaw arms may each provide a head (126a, 127a; 401 a, 402a); the head of one jaw arm may be positioned beyond the head of the other jaw arm in a direction along the axis of the spool, the head having the clamping surface. The heads may be arranged to be drawn towards each other when under tension from the tensioning portion.