Appliance Airflow Detection Using Differential Thermistor Heating

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Solution Overview

Problem

Existing airflow detection methods in appliances, such as thermal switches and sail switches, face limitations including slow reaction times, calibration challenges, and issues with false indications due to dust and mechanical fragility, particularly when the fan discharge is directed towards the floor.

Innovation Solution

An airflow detecting device comprising a first thermistor or similar device that self-heats and a second device that measures ambient temperature, generating a voltage differential inversely proportional to airflow rate, allowing for accurate airflow measurement and detection within the appliance's cooling pathway.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thermal switch is used to detect airflow, then the device is disposed away from fan intake/discharge ends avoiding negative airflow impact, but the reaction time becomes relatively slow

Engineering Contradiction:

Improveairflow detection accuracyVSAvoidreaction time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces the mechanical thermal switch system with an electronic system using a thermistor and microcontroller. The thermistor provides rapid electrical signal response to temperature changes caused by airflow, eliminating the mechanical delays inherent in thermal switches while maintaining reliable detection through electronic measurement and processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Speed

If a sail switch is used to detect airflow, then the reaction time becomes very fast, but the device becomes mechanically fragile and prone to damage during repair and shipping

Engineering Contradiction:

Improvereaction timeVSAvoidmechanical durability

Core Design Contradiction:

SpeedVSStrength

Solution Approach 1:

The patent replaces the fragile mechanical sail switch with a solid-state electronic system. The thermistor and microcontroller provide fast response to airflow changes through electrical measurements, completely eliminating the mechanical components that are susceptible to damage during repair operations and shipping disturbances.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If a sail switch is used with fan discharge directed toward the floor, then the configuration is compact, but the sail collects dust and grease causing false indications of fan working condition

Engineering Contradiction:

Improveinstallation configurationVSAvoiddetection accuracy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the sail switch mechanism with an electronic thermistor-based system that detects airflow through temperature changes. This electronic approach eliminates the physical sail that collects dust and grease, providing reliable airflow detection even in compact configurations where the fan discharge is directed toward the floor, without suffering from contamination-related false indications.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Ease of manufacture

If a thermal switch is used to detect airflow, then the device requires minimal calibration, but significant calibration and testing are needed to prove it works in all oven working conditions

Engineering Contradiction:

Improvecalibration effortVSAvoidperformance across working conditions

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent replaces the thermal switch with an electronic system using a thermistor and microcontroller that can be precisely calibrated through software. This electronic measurement system allows for accurate characterization of airflow across all oven working conditions through programmable thresholds and compensation algorithms, providing both ease of manufacture and reliable performance throughout the full operating range.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 provides a reliable and efficient means to determine airflow presence and rate, enabling safety-related tasks like de-energizing heating elements when airflow is insufficient, while minimizing false indications and mechanical issues.

Implementation Method 1

a first device (e.g., a first thermistor or like device) that generates a self-heating effect

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

measures the local ambient temperature around both devices. The first device and the second device provide a voltage differential that corresponds to a difference in temperature between the first device and the second device that is inversely proportional to the rate of airflow

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS9194588B2Appliance airflow detection using differential heating of electronic devices

Publication Date: 2015.11.24 HAIER US APPLIANCE SOLUTIONS INC

AI summary

Apparatus and methods are disclosed to measure airflow within a chassis-cooling pathway of an appliance. The rate of airflow is determined based on the differential heating among a pair of sensor devices, such as thermistors, transistors, diodes or resistive thermal devices operating at distinctly different power levels. The appliance utilizes the calculated airflow rate to perform safety-related tasks, such as de-energizing heating elements when low or no airflow is detected.