Dryer Centrifugal Switch Bypass Circuit for Reverse Tumble Heating

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Solution Overview

Problem

Centrifugal switches in dryers cause long restart times for gas heating elements and unnecessary activation/deactivation in reversible dryers, leading to increased cycle time and reduced switch reliability, while removing them poses safety risks by allowing stationary heating.

Innovation Solution

A centrifugal switch bypass circuit using a bypass relay and relay hold circuit, operated by an optocoupler, NPN transistor, and field effect transistor, allows the heating element to remain energized during drum rotation reversals without energizing it when the drum is stationary, using a controlled time constant and monitoring the drum's rotation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the centrifugal switch is used to control heating element operation, then safety is improved by preventing heating when drum is stationary, but drying cycle time increases due to long restart delays and frequent activation/deactivation

Engineering Contradiction:

ImprovesafetyVSAvoiddrying cycle time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The bypass relay is activated in advance before the drum comes to a complete stop, allowing the heating element to remain energized during the reversal transition. This preliminary action prevents the heating element from being deactivated and restarted, eliminating the long restart delay and reducing overall drying cycle time while maintaining safety through the relay's timed control

Inventive Principle:

Principle #10Preliminary action

2Loss of time

If the centrifugal switch is completely bypassed to eliminate restart delays, then drying cycle time is reduced, but safety is compromised by allowing heating element to operate when drum is stationary

Engineering Contradiction:

Improvedrying cycle timeVSAvoidsafety

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The relay hold circuit provides feedback control by monitoring the bypass relay state and maintaining it during drum reversal. This feedback mechanism ensures the heating element remains energized only during the appropriate time window (drum reversal) and not when the drum is stationary for extended periods, balancing safety with cycle time reduction

Inventive Principle:

Principle #23Feedback

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 reduces drying cycle time and extends the life of the centrifugal switch by maintaining heating element energization during drum direction changes while preventing runaway heating conditions, eliminating the need for software-dependent safety measures.

Implementation Method 1

a bypass relay operatively connected to the heating element and configured to bypass the centrifugal switch

Methodology Applied

Scientific EffectElectrical current flow: Conduction (electrical)

Implementation Method 2

a relay hold circuit operatively connected to the bypass relay and configured to cause the bypass relay to continue bypassing the centrifugal switch during rotational direction reversal

Methodology Applied

Scientific EffectElectromagnetic holding: Electromagnet

Data Source

PatentUS8872074B2Centrifugal switch bypass for reverse tumble dryers

Publication Date: 2014.10.28 HAIER US APPLIANCE SOLUTIONS INC

AI summary

Systems and methods for bypassing a centrifugal switch are disclosed. The systems may include a bypass relay operatively connected to the heating element and configured to bypass the centrifugal switch prior to the drum reversing rotational direction, and allow the heating element to remain energized during the drum reversing rotational direction. The centrifugal switch bypass circuit further includes a relay hold circuit operatively connected to the bypass relay and configured to cause the bypass relay to continue bypassing the centrifugal switch during the drum reversing rotational direction. The method may include, once the drum begins reversing the rotational direction, utilizing a bypass relay to bypassing the centrifugal switch. Finally, the method may include utilizing a relay hold circuit to cause the bypass relay to continue bypassing the centrifugal switch during reversal of the rotational direction.