Variable Reluctance Plunger Solenoid for Soft Start
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Designers of vehicle starters with soft start motor engagement systems face challenges in balancing the pull-in coil's resistance to avoid thermal failure and excessive electromagnetic force, which can lead to gear abutment issues and premature wear, while also ensuring the hold-in coil provides sufficient magnetic force for engine cranking.
Innovation Solution
A solenoid design featuring a pull-in coil with increased flux leakage and a hold-in coil with minimal flux leakage, arranged adjacent to each other on a spool, allowing for low resistance in the pull-in coil to reduce abutment force and high hold-in force without thermal interference, using a plunger with a circumferential notch to vary magnetic reluctance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the pull-in coil resistance is decreased to reduce abutment force, then the electromagnetic force during engagement is reduced, but thermal failure risk increases due to excessive current
Solution Approach 1:
The plunger is designed with a circumferential notch that creates a localized region of different magnetic properties. This notch concentrates the magnetic flux in specific areas while reducing it in others, allowing the pull-in coil to generate sufficient electromagnetic force for engagement without requiring excessive current that would cause thermal failure. The local modification of magnetic circuit geometry resolves the contradiction between force generation and thermal management.
Solution Approach 2:
The invention changes the magnetic circuit parameters by introducing the circumferential notch on the plunger. This geometric parameter change modifies the magnetic reluctance distribution, enabling the pull-in coil to achieve the required electromagnetic force with optimized current levels. The notch creates variable magnetic paths that reduce the overall current requirement, thereby reducing thermal stress while maintaining adequate engagement force.
2Volume of moving object
If the hold-in coil is positioned adjacent to the pull-in coil on the spool, then space is optimized, but thermal interference from the pull-in coil affects the hold-in coil performance
Solution Approach 1:
The spool structure serves as an intermediary thermal barrier between the pull-in coil and hold-in coil. The spool material and geometry are designed to provide thermal isolation, allowing the two coils to be positioned adjacent to each other for space optimization while preventing excessive thermal transfer. This intermediary structure enables close positioning without direct thermal interference.
Solution Approach 2:
The spool is designed with specific local geometric features and material properties that create thermal zones. The structure provides localized thermal management, allowing the pull-in coil area to handle high thermal loads during engagement while the hold-in coil area maintains stable temperatures for continuous operation. This local differentiation of thermal characteristics resolves the contradiction between space optimization and thermal interference prevention.
3Force
If the pull-in coil is designed with increased flux leakage to reduce abutment force, then the electromagnetic efficiency decreases, but the impact force during gear engagement is reduced
Solution Approach 1:
The circumferential notch on the plunger changes the magnetic circuit parameters to create controlled flux leakage paths. This geometric parameter modification allows the magnetic flux to distribute more evenly, reducing concentration at the abutment point while maintaining overall electromagnetic efficiency. The notch creates alternative magnetic paths that reduce impact force without proportionally increasing energy consumption.
Solution Approach 2:
The notch creates local variations in magnetic flux distribution, concentrating flux in certain areas while allowing leakage in others. This local quality differentiation enables the system to reduce impact force at the gear engagement point while maintaining sufficient overall electromagnetic efficiency for plunger actuation. The selective flux management resolves the contradiction between impact force reduction and efficiency maintenance.
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 impact force during gear engagement, increases torque during soft start, and minimizes thermal stress on the hold-in coil, enhancing the solenoid's performance and longevity.
Implementation Method 1
Energization of the pull-in coil and hold-in coil moves a solenoid shaft (also referred to herein as the 'plunger') in an axial direction
Implementation Method 2
the hold-in coil provides sufficient electromagnetic force to hold the plunger in place and maintain the electrical contacts in a closed position
Implementation Method 3
The circumferential notch includes a portion with a second diameter that is less than the first diameter
Data Source
AI summary
A solenoid for a vehicle starter includes at least one coil with a passage extending through the coil in an axial direction. The solenoid further includes a plunger configured to move in the axial direction within the passage. The plunger includes a cylindrical outer surface with a substantially uniform diameter and a circumferential notch. The cylindrical outer surface includes a first portion with a first diameter on one side of the circumferential notch, and a second portion with the first diameter on an opposite side of the circumferential notch. The circumferential notch includes a portion with a second diameter that is less than the first diameter.