SMA Wire Latch Release for Vehicle Headrest Actuation

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Solution Overview

Problem

Existing automotive head restraint systems obstruct driver visibility when rear seats are unoccupied, as they require manual effort to retract and re-deploy, adding weight and mechanical complexity with components like electromagnets and solenoids.

Innovation Solution

A shape memory alloy (SMA) actuator-powered latch release mechanism that allows for instant electronic control of headrests, using a spring-loaded system with a SMA wire loop, pulley, and release lever to lower and raise headrests, reducing manual effort and weight.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If an electromagnetic latch release with coil and iron core is used, then the headrest can be lowered electronically, but the device adds substantial mass and weight to the vehicle cabin

Engineering Contradiction:

Improveelectronic headrest controlVSAvoidactuator mass

Core Design Contradiction:

Extent of automationVSWeight of moving object

Solution Approach 1:

The patent replaces the traditional electromagnetic actuator (coil and iron core) with a shape memory alloy wire-based actuation system. The SMA wire converts electrical energy directly to mechanical motion through thermal expansion and phase change, eliminating the need for heavy electromagnetic components while achieving the same electronic control function for headrest deployment and retraction.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention utilizes the temperature-dependent phase change properties of shape memory alloy materials. By applying electrical current to heat the SMA wire, it transitions from austenite to martensite phase, causing controlled expansion and contraction that drives the headrest mechanism. This parameter-based actuation method achieves electronic control with minimal mass.

Inventive Principle:

Principle #35Parameter changes

2Extent of automation

If a solenoid actuator with bicycle cable is used, then the headrest can be lowered electronically, but the device adds substantial mass and extensive mechanical layout subject to failure

Engineering Contradiction:

Improveelectronic headrest controlVSAvoidmechanical layout complexity

Core Design Contradiction:

Extent of automationVSDevice complexity

Solution Approach 1:

The patent replaces the solenoid-actuated bicycle cable system with a direct-acting shape memory alloy wire mechanism. The SMA wire is integrated directly into the latch release mechanism, eliminating intermediate cable transmissions, pulleys, and connecting linkages. This reduces mechanical complexity and potential failure points while maintaining electronic actuation capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If manual effort is required to retract and re-deploy headrests, then the mechanism remains simple, but driver visibility is obstructed when rear seats are unoccupied

Engineering Contradiction:

Improvemechanism simplicityVSAvoiddriver visibility

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent introduces electronic actuation through shape memory alloy wires that can be controlled via electrical signals from the vehicle's control system. This allows automated headrest retraction when rear seats are unoccupied, improving driver visibility without requiring manual intervention, while the overall mechanism remains relatively simple compared to traditional electromagnetic or solenoid systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

Enhances driver visibility by allowing easy retraction and redeployment of headrests with minimal effort, reducing weight and mechanical complexity, while maintaining safety and support functions.

Implementation Method 1

A shape memory alloy (SMA) wire loop has opposed ends secured to adjacent electrical terminals

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

A shape memory alloy (SMA) wire loop has opposed ends secured to adjacent electrical terminals, and the loop is passed about a drive pulley

Methodology Applied

Scientific EffectShape memory alloy phase change: Shape Memory Alloy

Implementation Method 3

At least one coil spring is secured about the lateral support tube to impinge on the housing and resiliently bias it to rotate to the retracted position

Methodology Applied

Scientific EffectSpring elastic energy: Spring

Data Source

PatentUS11338715B2Shape memory alloy latch release mechanism for vehicle head restraint

Publication Date: 2022.05.24 GUMMIN MARK A

AI summary

An automotive head restraint apparatus includes a housing having a padded and upholstered exterior, the housing being rotatable about a lateral support tube that supports a lock plate having a lobe extending radially with a detent slot extending therein. A latch finger extends from a pivotable lock lever plate to releasably engage in the detent slot to latch the housing in the deployed position. A pull rod is secured to the lock lever plate, and is connected to a release lever arm at its other end. A shape memory alloy (SMA) wire loop is passed about a drive pulley that is supported by a reciprocally translatable slide. A drive arm extends from the slide to impinge on the release lever and raise the pull rod when the SMA wire loop is energized and contracted, thereby releasing the latch finger to rotate the housing to the retracted position.