Bimetallic Servovalve Flapper for Null Position Stability

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Solution Overview

Problem

Servovalves face challenges in maintaining accurate position control due to temperature-induced changes in the null position, requiring compensation through adjustments in the control signal, which complicates the system and increases costs.

Innovation Solution

A bimetallic flapper with segments made from materials having different coefficients of thermal expansion is used, allowing the flapper to automatically compensate for temperature changes by bending, thus maintaining the null position without needing signal adjustments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional single-material flapper is used, then the structure is simple and manufacturing is easy, but the null position shifts with temperature changes requiring complex compensation systems

Engineering Contradiction:

Improvenull position stabilityVSAvoidtemperature compensation system

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The flapper is constructed from two different materials with different coefficients of thermal expansion bonded together to form a bimetallic structure. This composite construction enables the flapper to automatically compensate for temperature-induced null position shifts through differential thermal expansion, eliminating the need for external temperature compensation systems while maintaining null position stability.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention exploits the principle of thermal expansion by selecting two materials with different coefficients of thermal expansion. When temperature changes occur, the two materials expand or contract at different rates, causing the bimetallic flapper to bend in a controlled manner that compensates for null position drift, thereby maintaining accurate positioning without additional compensation mechanisms.

Inventive Principle:

Principle #37Thermal expansion

2Measurement precision

If temperature compensation through control signal adjustment is implemented, then null position accuracy is maintained, but the system complexity and cost increase

Engineering Contradiction:

Improveposition control accuracyVSAvoidfeedback control system

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The bimetallic flapper structure is designed to automatically compensate for temperature-induced null position shifts through its inherent physical properties. The differential thermal expansion of the two materials causes the flapper to bend in a manner that self-corrects the null position, eliminating the need for external temperature sensors, feedback loops, or control signal adjustments, thereby maintaining position control accuracy while reducing system complexity.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The invention converts the harmful effect of temperature changes into a beneficial self-compensation mechanism. By utilizing the differential thermal expansion of the bimetallic structure, the temperature-induced dimensional changes are transformed into a corrective bending action that automatically maintains null position accuracy, turning a source of error into a compensation mechanism.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If a bimetallic flapper structure is used, then temperature compensation is achieved, but the manufacturing complexity increases

Engineering Contradiction:

Improvetemperature stabilityVSAvoidflapper fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The flapper is manufactured as a bimetallic composite structure by bonding two different materials with different coefficients of thermal expansion. This composite construction enables temperature compensation through controlled differential expansion, achieving reliable null position stability under varying temperature conditions.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention achieves temperature compensation by carefully selecting and controlling the physical parameters of the two materials, specifically their coefficients of thermal expansion. By optimizing these material parameters and their geometric configuration, the bimetallic flapper is designed to bend by a specific amount in response to temperature changes, enabling precise null position compensation.

Inventive Principle:

Principle #35Parameter changes

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 solution stabilizes the servovalve operation by mechanically compensating for temperature-induced shifts, reducing the need for complex feedback loops and temperature sensors, and enhancing reliability under varying conditions.

Implementation Method 1

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10954972B2Flapper and armature/flapper assembly for use in a servovalve

Publication Date: 2021.03.23 HAMILTON SUNDSTRAND CORP

AI summary

A flapper for use in a servovalve is described, the flapper comprising a first material and a second material, the first material having a first coefficient of thermal expansion and the second material having a second coefficient of thermal expansion and wherein the first and second coefficients of thermal expansion are different to each other. An armature/flapper assembly is also described, which comprises this flapper as well as a plate and a torsion bridge. A method of compensating for alteration of the null of a servovalve due to temperature changes in a servovalve is also described.