Internal Damping Mass for Seat Belt Buckle Noise

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Solution Overview

Problem

Seat belt buckles in motor vehicles often produce rattling noises due to interactions with vehicle installations, and existing solutions like external damping layers are not fully effective in reducing these noises within the buckle casing.

Innovation Solution

The damping mass is applied internally to the case shells of the buckle casing, reducing the unoccupied interior volume and using ABS plastic and thermoplastic polyurethane materials for noise attenuation through a single operation two-component injection molding process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a damping layer is applied to the outside of the casing, then rattling noise is attenuated, but the noise propagation inside the buckle casing is not effectively prevented

Engineering Contradiction:

Improverattling noiseVSAvoidnoise propagation inside casing

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

Instead of applying the damping layer externally to the casing as in prior art, the invention inverts the approach by applying the damping mass internally to the case shells. This internal application directly addresses the noise propagation issue within the buckle casing, preventing functional noises from spreading while maintaining the rattling noise attenuation benefit.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The damping mass is nested within the buckle casing structure, specifically applied to the case shells on the inside. This nesting approach allows the damping material to be integrated into the existing casing structure, effectively filling the free interior volume and preventing noise propagation without adding external bulk.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Ease of manufacture

If foam material is used as damping material with insert-molding, then production is simplified, but the damping effectiveness inside the casing is insufficient

Engineering Contradiction:

Improveproduction processVSAvoidnoise attenuation effectiveness

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The invention uses a composite material approach by combining ABS plastic for the case shells with thermoplastic polyurethane for the damping mass. This composite material system provides superior damping effectiveness compared to foam material, while the two-component injection molding process maintains ease of manufacture by integrating both materials in a single operation.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention changes the material parameters from foam material to thermoplastic polyurethane, which provides better damping characteristics. The parameter change extends to the manufacturing process as well, transitioning from insert-molding to a two-component injection molding process that achieves both effectiveness and manufacturing efficiency.

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If the damping mass is applied internally to reduce unoccupied volume, then noise propagation is prevented, but the interior volume for functional components is reduced

Engineering Contradiction:

Improvenoise propagationVSAvoidfree interior volume

Core Design Contradiction:

Object-generated harmful factorsVSVolume of stationary object

Solution Approach 1:

The damping mass is applied locally to the case shells on the inside of the buckle casing, specifically targeting areas where noise propagation occurs. This local application approach prevents noise propagation while minimizing the impact on the overall free interior volume, as the damping mass is concentrated where it is most needed for acoustic damping.

Inventive Principle:

Principle #3Local quality

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 approach effectively reduces sound pressure levels within the buckle casing, particularly at 1,600 Hz, making the noise more pleasant for passengers and minimizing audible noise outside.

Implementation Method 1

a damping mass for noise attenuation... the damping mass is applied to the case shells on the inside of the buckle casing to reduce the interior volume of the casing that is not occupied by the locking and unlocking device

Methodology Applied

Scientific EffectDamping: Damping

Data Source

PatentUS8955204B2Buckle with housing comprising elastomeric damping mass

Publication Date: 2015.02.17 AUTOLIV DEV AB

AI summary

A buckle for a safety harness in motor vehicles includes a buckle housing and a locking and unlocking mechanism housed therein, and a buckle tongue interacting with the locking and unlocking mechanism. The plastic buckle housing is provided with a silencing damping mass. The damping mass (12) is applied to the housing shells (10, 13) on the inside of the buckle housing to reduce the interior volume of the housing not occupied by the locking and unlocking mechanism.