Automotive Wire Harness Grommet Bellows Deformation
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Solution Overview
Problem
Conventional grommets for wire harnesses in automotive vehicles face challenges in reducing insertion force and maintaining retention force while allowing easy bending and wiring of the wire harness, as reinforcing ribs increase restoring force but hinder deformability and flexibility.
Innovation Solution
A grommet design featuring a small-diameter cylindrical portion with a radial projecting portion in the form of bellows, connected to a conical tubular outer peripheral portion with a vehicle-body locking recess, allowing easy bending and wiring by deforming during insertion and maintaining retention force through a thick portion on the small-diameter side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If reinforcing ribs are provided in the elastic portion to increase restoring force, then the grommet can maintain its shape after deformation, but the wire harness becomes hard to bend and the deformability of the grommet is reduced
Solution Approach 1:
The grommet is divided into three distinct functional portions: a small-diameter cylindrical portion for wire harness insertion, a bellows-shaped radial projecting portion for deformation during installation, and a large-diameter cylindrical portion for mounting in the through hole. This segmentation allows each portion to perform its specific function without interfering with the bendability of the wire harness while maintaining the necessary restoring force.
Solution Approach 2:
Different portions of the grommet are designed with different structural properties: the radial projecting portion is made thin-walled to allow easy deformation during installation, while the small-diameter cylindrical portion maintains sufficient thickness to provide restoring force. This local differentiation of structural properties resolves the contradiction between maintaining shape and allowing wire harness bendability.
2Strength
If the grommet is designed to maintain retention force in the through hole, then the grommet remains securely mounted, but the insertion force required to mount the grommet increases
Solution Approach 1:
The radial projecting portion is designed with a bellows shape that allows dynamic deformation during the installation process. When insertion force is applied, the bellows compresses to reduce the effective diameter, allowing easy insertion. Once installed, the bellows returns to its original shape, providing retention force to keep the grommet securely mounted in the through hole.
Solution Approach 2:
The grommet utilizes changes in dimensional parameters: the radial projecting portion changes its effective diameter through deformation, allowing it to transition from a compressed state during insertion to an expanded state for retention. This parameter change enables low insertion force while maintaining high retention force.
3Force
If the radial projecting portion is made thin to allow easy deformation, then insertion force is reduced, but the retention force may be compromised
Solution Approach 1:
The grommet is made of elastomer material that combines the properties of flexibility and elastic recovery. This material allows the radial projecting portion to be thin-walled for easy deformation during insertion while still providing sufficient retention force through elastic recovery. The composite nature of the elastomer material resolves the contradiction between thin-walled deformability and retention strength.
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 grommet reduces insertion force and enhances retention force by allowing easy deformation during mounting and preventing detachment from the through hole, while enabling flexible bending and wiring of the wire harness.
Implementation Method 1
a radial projecting portion which is in the form of bellows projecting radially outwardly from an outer peripheral position of an intermediate part of the small-diameter cylindrical portion in a longitudinal direction
Data Source
AI summary
A grommet is fit externally to a wire harness to be wired in a vehicle and mounted in a through hole of a vehicle-body panel. The grommet has a small-diameter cylindrical portion molded of elastomer and through which the wire harness is tightly inserted. A radial projection in the form of bellows projects radially out from an outer peripheral position of an intermediate longitudinal part of the small-diameter portion. An outer peripheral portion is connected to the outer peripheral end of the radial projection. The outer peripheral portion has a conical tubular shape and is connected at an intermediate longitudinal position to the radial projection. An annular vehicle-body locking recess is provided on the outer peripheral surface of a large-diameter side of the outer peripheral portion. A small-diameter side is thicker than the radial projection portion.