Electromagnetic Switch Plunger Sealing for Starter Reliability

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Solution Overview

Problem

Existing starter electromagnetic switches face issues with moisture intrusion from the plunger compartment into the contact compartment, leading to conduction defects due to ice formation and increased slidable resistance, which requires higher attractive forces and results in larger and heavier switches.

Innovation Solution

The design incorporates a cylindrical slidable member that encompasses the outer circumference of the plunger rod, providing hermeticity when the solenoid is inactive and fluid communication via vent grooves when active, minimizing moisture intrusion and negative pressure, and allowing radial movement to prevent prying and sliding resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the inner diameter of the cylindrical bore is set greater than the outer diameter of the contact pressure spring to install the spring, then the contact pressure spring can be installed inside the bore, but a spatial gap between the bore and plunger rod allows moisture to intrude from the plunger compartment into the contact compartment

Engineering Contradiction:

Improvecontact pressure spring installationVSAvoidmoisture intrusion

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

A sealing member (O-ring) is introduced as an intermediary component between the plunger rod and the cylindrical bore. This sealing member fills the spatial gap that would otherwise allow moisture intrusion, while still allowing the contact pressure spring to be installed within the bore structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bore is divided into two separate compartments: a plunger compartment and a contact compartment. The sealing member creates a barrier between these compartments, preventing moisture from the plunger compartment from entering the contact compartment while maintaining structural integrity.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the solenoid attractive force is increased to break ice on contact surfaces, then contact conduction reliability is improved, but the solenoid size and weight increase

Engineering Contradiction:

Improvecontact conductionVSAvoidsolenoid weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The sealing member is installed in advance to prevent moisture from entering the contact compartment. By eliminating the moisture source, ice formation on contact surfaces is prevented, so the solenoid does not need to generate excessive attractive force to break ice, thereby reducing solenoid size and weight requirements.

Inventive Principle:

Principle #10Preliminary action

3Weight of stationary object

If the plunger rod outer diameter is reduced to decrease solenoid weight, then solenoid weight is reduced, but the structural strength and sealing capability of the plunger rod are compromised

Engineering Contradiction:

Improvesolenoid weightVSAvoidplunger rod strength

Core Design Contradiction:

Weight of stationary objectVSStrength

Solution Approach 1:

The sealing member acts as an intermediary that compensates for the reduced structural capacity of a thinner plunger rod. It provides the necessary sealing function without requiring the plunger rod to have excessive diameter, allowing weight reduction while maintaining sealing capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces the attractive force of the solenoid, minimizing the switch's size and weight while preventing ice formation and maintaining reliable contact, even in low temperatures.

Implementation Method 1

a solenoid SL configured to form an electromagnet through energization of a coil 100 to drive a plunger 110 by means of an attractive force of the electromagnet

Methodology Applied

Scientific EffectElectromagnet: Electromagnet

Implementation Method 2

a sliding surface that is a portion of an outer circumferential periphery of the slidable member such that, when the solenoid is in its inactive state, the sliding surface is entirely circumferentially in sliding contact with the inner circumferential periphery of the cylindrical bore

Methodology Applied

Scientific EffectSliding friction: Friction

Data Source

PatentUS9070525B2Electromagnetic switch for starter

Publication Date: 2015.06.30 DENSO CORP

AI summary

An electromagnetic switch for a starter. The electromagnetic switch includes a cylindrical slidable member that is separate from a plunger, loosely encompasses an outer circumferential periphery of a plunger rod, and is axially movable integrally with the plunger. The slidable member is at least partially axially inserted into an inner circumferential periphery of a cylindrical bore. The slidable member has a sliding surface such that, when the solenoid is in its inactive state, the sliding surface is entirely circumferentially in sliding contact with the inner circumferential periphery of the cylindrical bore, and has a vent groove axially extending on the outer circumferential periphery of the slidable member such that, when the solenoid is in its active state, a plunger compartment and the contact compartment are in fluid communication with each other via the vent groove.