Ball Joint Housing Converts Plastic Shrinkage to Preload

Solution Overview

Problem

Existing ball joints for motor vehicle chassis parts face challenges in achieving high extraction forces, precise friction moments, and low wear, while also being cost-effective and avoiding issues with plastic shrinkage during over-molding.

Innovation Solution

A ball joint design featuring a plastic one-piece housing enclosing two bearing shells with a gap between them, allowing for axial displacement and conversion of plastic shrinkage into contact pressure, along with engagement sections for centering and locking, and lubricant grooves for post-molding greasing, which reduces material thickness and enhances resilience and stiffness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If plastic material is injected around bearing shells for housing, then housing strength and stability are improved, but plastic shrinkage during curing makes reliable connection more difficult

Engineering Contradiction:

Improvehousing strengthVSAvoidconnection precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent converts the harmful plastic shrinkage during curing into a beneficial contact pressure that urges the bearing shells against the spherical portion. The housing is designed with a slightly larger inner diameter than the outer diameter of the bearing shells, allowing shrinkage to create the necessary preload force rather than causing connection failures

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the dimensional parameters of the housing and bearing shells to accommodate plastic shrinkage. The housing's inner diameter is intentionally made larger than the bearing shell's outer diameter by a specific amount (0.05-0.2 mm) to compensate for shrinkage and maintain reliable connection

Inventive Principle:

Principle #35Parameter changes

2Force

If bearing shells are heavily deformed to press against spherical portion with preload force, then extraction forces are improved, but device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improveextraction forceVSAvoidassembly complexity

Core Design Contradiction:

ForceVSDevice complexity

Solution Approach 1:

The patent divides the bearing support structure into two separate bearing shells with a gap between them, rather than using a single deformed bearing. This segmentation allows the shells to be pre-assembled on the ball stud and then enclosed by the housing, which provides the preload force through shrinkage rather than requiring heavy deformation of the shells themselves

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces the plastic housing as an intermediary that applies preload force to the bearing shells through shrinkage, rather than directly deforming the bearing shells to achieve the required preload. The housing acts as a mediator that converts shrinkage into the necessary contact pressure

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If bearing shells are supported against each other, then structural stability is improved, but contact pressure and preload force are reduced

Engineering Contradiction:

Improvestructural stabilityVSAvoidcontact pressure

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The patent introduces the plastic housing as an intermediary that applies preload force to the bearing shells through shrinkage, rather than directly deforming the bearing shells to achieve the required preload. The housing acts as a mediator that converts shrinkage into the necessary contact pressure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the dimensional parameters of the housing and bearing shells to accommodate plastic shrinkage. The housing's inner diameter is intentionally made larger than the bearing shell's outer diameter by a specific amount (0.05-0.2 mm) to compensate for shrinkage and maintain reliable connection

Inventive Principle:

Principle #35Parameter changes

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 design achieves improved performance with reduced production costs, enhanced stability, and effective preload adjustment, avoiding the limitations of plastic shrinkage and ensuring reliable connection without an outer housing, while maintaining low wear and precise friction.

Implementation Method 1

the plastic that is injected around the bearing shells will shrink during curing, which makes a reliable connection with the actual housing more difficult

Methodology Applied

Scientific EffectPlastic shrinkage: Thermal Contraction

Data Source

PatentUS11339824B2Ball-and-socket joint for chassis parts of a motor vehicle

Publication Date: 2022.05.24 THK RHYTHM AUTOMOTIVE GMBH

AI summary

A ball joint including a ball stud which has a spherical portion, two bearing shells that are arranged on the spherical portion such that there is a small gap between the two bearing shells, and a housing that is made from plastic in one piece and encloses the two bearing shells such that the two bearing shells are urged against the spherical portion by the housing.