Multi-Action Plunger Switch for Extended Stroke Reliability
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Solution Overview
Problem
Conventional plunger switches have limited stroke length, which poses problems when the travel of an object exceeds the allowable distance, leading to potential misactivation and increased adjustment time in applications like lawn mowers and garden tractors.
Innovation Solution
A multi-action plunger arrangement with first and second plungers in axial alignment, supported by biasing members with differing spring constants, allowing for a change of state when the second plunger compresses from a normal to a first actuated position, and maintaining the state as the first plunger translates further, providing additional travel without changing the electrical state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional plunger switch is used, then the switch can be actuated reliably, but the stroke length is limited which causes misactivation when object travel exceeds the allowable distance
Solution Approach 1:
The plunger switch is divided into multiple independent plungers (first plunger and second plunger) that can move independently within the same actuation space. This segmentation allows each plunger to have its own stroke length and activation characteristics, enabling the switch to accommodate longer object travel distances while maintaining reliable activation at the appropriate stroke position.
2Length of moving object
If the plunger stroke length is increased to accommodate longer object travel, then the travel limitation is removed, but the switch may become misactivated or require increased adjustment time
Solution Approach 1:
Different plungers are assigned different local qualities through varying biasing member characteristics (spring constants). The first plunger has a biasing member with a first spring constant optimized for its activation threshold, while the second plunger has a biasing member with a second spring constant optimized for its activation threshold. This allows each plunger to activate at different stroke positions without requiring extensive adjustment, reducing adjustment time while accommodating the needed stroke length.
3Length of moving object
If a single plunger is used, then the switch structure is simple, but additional travel beyond the activation point cannot be accommodated without changing the electrical state
Solution Approach 1:
The first plunger is positioned within the same actuation space as the second plunger, with both plungers nested within the housing. The wiper contact is positioned to engage with the second plunger's actuation surface. This nested arrangement allows the switch to accommodate extended travel distances by having the first plunger move further than the second plunger, while maintaining a compact overall structure and avoiding the need for complex external linkage mechanisms.
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 multi-action plunger arrangement enables additional travel without altering the electrical state, acting as a safety mechanism and reducing wear, while eliminating the need for indirect contact devices like cams or linkages, resulting in efficient and cost-effective mounting.
Implementation Method 1
first and second biasing members having differing load constants, such that the first and second plungers are actuated at different loads during use
Data Source
AI summary
A plunger switch and method comprises a multi-action plunger arrangement having first and second plungers in axial alignment such that the first plunger is centrally located about the second plunger. The second plunger has an annular wall for supporting at least one conductive wiper contact. The plunger switch further comprises first and second biasing members having differing load constants, such that the first and second plungers are actuated at different loads during use and a plurality of terminals for communicating an electrical path. The switch also comprises a housing having a central opening for supporting the plunger arrangement. The second plunger and second second biasing member cooperate with the conductive wiper contact such that compressing of the second biasing member from a normal position to a first actuated position results in a change of state of the switch assembly.