Gear Mechanism with Variable Thread Play for Headrest Drive
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Solution Overview
Problem
Existing gear transmissions with thread-based drives, such as those in headrests, face issues with axial play and misalignment, leading to inefficiencies and jamming, especially when using different material pairings like plastic and metal, which are exacerbated by temperature fluctuations.
Innovation Solution
A gear transmission design featuring a primary and secondary thread with varying axial play in different areas to minimize axial movement and accommodate thermal expansion, where one thread is elastic to ensure contact across the entire thread length under load, reducing unwanted axial movements and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thread pairing is designed to be play-free to meet thermal expansion requirements, then reliability improves, but manufacturing precision becomes more difficult due to different material expansion coefficients
Solution Approach 1:
The thread pairing is divided into multiple axial areas (first area, second area, third area) with different thread play characteristics. The first area has reduced thread play to meet thermal expansion requirements, while the second area maintains larger thread play for material pairing accommodation, effectively segmenting the functional requirements along the axial direction.
Solution Approach 2:
Different axial areas of the thread pairing are given different local qualities regarding thread play. The first area is designed with minimal play for reliability, while other areas have larger play to accommodate manufacturing variations and material properties, allowing each region to optimize for its specific functional requirement.
2Ease of manufacture
If different material pairings (plastic/metal) are used in thread pairing, then ease of manufacture improves, but axial play increases due to different expansion coefficients
Solution Approach 1:
The thread pairing is segmented axially into regions with different play characteristics. The first area compensates for the large axial play inherent in plastic/metal material pairings by providing a zone with reduced play that accommodates thermal expansion, while allowing other areas to maintain the manufacturing advantages of different materials.
Solution Approach 2:
The thread play parameter is changed axially along the thread pairing. By varying the thread play from larger values in some areas to reduced values in the first area, the design adapts to the different expansion coefficients of plastic and metal materials while maintaining overall functionality and reliability.
3Reliability
If thread length is increased to reduce axial play, then reliability improves, but device complexity increases
Solution Approach 1:
Rather than uniformly increasing thread length throughout, the invention segments the thread pairing axially into areas with different play characteristics. This allows the first area to provide stable engagement with reduced play over a specific axial portion, while avoiding the need to increase the total thread length excessively, thus maintaining simpler device structure.
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 solution effectively minimizes axial play and prevents jamming by allowing flexible deformation of threads under load, maintaining reliable operation across a wide temperature range and reducing noise from unwanted movements.
Implementation Method 1
At least one of the threads, i.e. the primary thread and/or the secondary thread, is designed to be elastic or plastically deformable
Implementation Method 2
The thread pairing is designed, for example, in at least one area in such a way that it meets the requirements for the material pairing between the threads or gear parts involved in the thread pairing with the corresponding thermal expansion
Data Source
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AI summary
The invention relates, inter alia, to a gear mechanism having a first gear mechanism part with a primary thread (35) and having a second gear mechanism part with a secondary thread (22), a thread pairing (35/22) being configured with a thread play between the primary thread and the secondary thread. The special feature consists in that a first thread play is configured in at least one region (A) of the thread pairing (35/22), and a second thread play which is different from the first thread play is configured in at least one second region (B) of the thread pairing (35/22).