Variable Reluctance Sensor Vibration Isolation

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Solution Overview

Problem

Variable reluctance sensors in gas turbine engines and gearboxes suffer from noise and microphony in their output signals due to environmental vibrations, which alter the magnetic permeability of the pole piece and induce unwanted electrical currents, especially at high frequencies and temperatures.

Innovation Solution

The magnetic pole piece is rigidly fixed to the side wall of the sensor housing, with the front face being more flexible and less massive, reducing strain transfer and noise; this can be achieved through welding, brazing, or mechanical fixings, and optionally using a rigid intermediate structure or additional support like a ring or cup to minimize stress on the pole piece.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the pole piece is rigidly fixed to the housing front face, then the sensor is protected from shock loads, but environmental vibrations induce strain in the pole piece causing noise and microphony in the output signal

Engineering Contradiction:

Improveprotection from shock loadsVSAvoidnoise and microphony in output signal

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The housing is divided into two distinct parts: a rigid back portion that provides shock load protection, and a flexible front face that isolates the pole piece from vibrational strain. This segmentation allows each part to perform its specific function without interfering with the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A damping material is introduced as an intermediary layer between the rigid housing back and the flexible housing front. This material absorbs and dissipates vibrational energy, preventing it from being transmitted to the pole piece while maintaining structural integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If the housing front face is made rigid to protect the pole piece, then shock loads are resisted, but the pole piece experiences strain from vibrations altering magnetic permeability

Engineering Contradiction:

Improveresistance to shock loadsVSAvoidaccuracy of speed and torque measurement

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

Different parts of the housing have different mechanical properties: the back portion is rigid for shock protection, while the front face is flexible to isolate vibrations. This local differentiation of mechanical properties allows simultaneous achievement of shock resistance and vibration isolation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The housing is constructed as a composite structure combining rigid and flexible materials in specific configurations. This composite approach enables the housing to exhibit both shock-resistant and vibration-isolating characteristics in different regions.

Inventive Principle:

Principle #40Composite materials

3Stability of the object's composition

If the pole piece is securely mounted to the housing, then structural stability is improved, but environmental vibrations transfer strain to the pole piece inducing unwanted electrical currents

Engineering Contradiction:

Improvestructural stability of sensorVSAvoidunwanted electrical currents from strain

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The flexible housing front face acts as a pre-configured cushion that absorbs vibrational strain before it can be transmitted to the pole piece. This beforehand cushioning prevents strain-induced electrical currents while maintaining structural stability.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 significantly reduces noise and microphony in the sensor output, allowing reliable measurement of speed and torque in harsh, vibrating environments at various frequency levels and high temperatures, while maintaining protection from shock loads.

Implementation Method 1

Variable reluctance sensors are used to monitor both the speed of rotating shafts and the torque loading on shafts

Methodology Applied

Scientific EffectVariable reluctance: Magnetic Reluctance

Implementation Method 2

As each tooth of the phonic wheels passes close to the front face of the pole piece there is a change in the magnetic flux experienced by the conductive wire 31

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 3

environmental vibrations, which alter the magnetic permeability of the pole piece and induce unwanted electrical currents

Methodology Applied

Scientific EffectVibration isolation: Vibration

Data Source

PatentEP3267207B1Speed or torque probe for gas turbine engines

Publication Date: 2020.01.01 WESTON AEROSPACE

Figure 1a~1b
Figure 2a~3
Figure 4~5

AI summary

The invention comprises a variable reluctance sensor for sensing the speed or torque of a shaft in a gear box or gas turbine engine, comprising a magnetic pole piece; a conductive wire wrapped around the pole piece; a housing surrounding the pole piece, the housing having a front face and at least one side wall, wherein, in use, the front face is positioned proximate to an object to be sensed, wherein the pole piece extends through the front face of the housing and the front face of the housing is substantially less rigid than the side wall of the housing by forming the front face substantially thinner and less massive than the sidewalls of the housing. By having a front face that is able to flex, less stress is exerted on the pole piece under external vibration, when the pole piece is firmly connected to the front face.