Cylindrical Worm Gear with Longitudinal Crowning for Power Seat Adjusters
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Solution Overview
Problem
Conventional seat track assemblies experience misalignment, vibration, and noise issues due to sensitive worm gear drives, which are costly and require additional manufacturing steps, such as deburring and thrust washer usage, leading to increased assembly complexity and axial play.
Innovation Solution
A power seat length adjuster assembly utilizing a cylindrical worm with longitudinally crowned threads and a single-enveloping worm gear, manufactured using injection molding and hobbing processes, respectively, to achieve theoretical point contact and reduce sensitivity to misalignment and manufacturing errors, eliminating the need for thrust washers and deburring, while incorporating compressible support members for noise and vibration dampening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional worm gear drives are used, then the seat adjustment mechanism can be implemented, but misalignment and sensitivity to manufacturing errors occur leading to vibration and noise
Solution Approach 1:
The patent applies curvature to the worm gear tooth surfaces through longitudinal crowning, transforming the originally cylindrical straight teeth into curved surfaces. This crowning creates a parabolic profile along the tooth length, which centers the contact area and reduces edge loading. The curved tooth surfaces better accommodate misalignment and manufacturing tolerances, thereby reducing vibration and noise while maintaining reliable seat adjustment functionality.
Solution Approach 2:
The patent modifies the geometric parameters of the worm gear by implementing longitudinal crowning with specific parabolic profiles. This changes the contact characteristics from line contact at edges to distributed point contact across the tooth surface. The parameter modification includes adjusting the tooth profile curvature radius and crown height to optimize contact patterns, reducing sensitivity to misalignment and eliminating the need for thrust washers.
2Force
If conventional worm gear drives with thrust washers and deburring are used, then axial loads can be managed, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the thrust washer component from the conventional worm gear assembly. By redesigning the worm gear teeth with longitudinal crowning, the axial load-bearing function previously performed by separate thrust washers is integrated directly into the gear tooth structure itself. This simplification removes the need for additional parts, reduces assembly complexity, and eliminates deburring operations while maintaining adequate axial load capacity.
Solution Approach 2:
The patent merges the axial load management function with the primary tooth engagement structure. The longitudinally crowned tooth profile integrates both the driving function and the axial load-bearing function into a single unified component structure, eliminating the need for separate thrust washers and simplifying the overall assembly.
3Power
If conventional helical gear drives are used, then power transmission can be achieved, but misalignment sensitivity and transmission errors increase
Solution Approach 1:
The patent applies longitudinal crowning to create curved tooth surfaces that are more tolerant of misalignment. The parabolic crown profile distributes contact pressure more evenly across the tooth face, reducing the impact of manufacturing errors and assembly misalignment on power transmission accuracy. This curvature modification maintains effective power transmission while reducing sensitivity to precision variations.
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 reduces vibrations and noise, enhances manufacturing efficiency, and minimizes axial displacement, providing a cost-effective and robust seat adjustment mechanism with improved contact surface roughness and reduced transmission errors.
Implementation Method 1
a cylindrical worm with longitudinally crowned threads and a single-enveloping worm gear, manufactured using injection molding and hobbing processes, respectively, to achieve theoretical point contact
Implementation Method 2
The drive member, e.g. the worm, may be actuated through the flex drive shaft and the driven member may be integral with an inner threaded spindle nut. Each drive assembly may include the rotatable spindle nut that threadingly receives a lead screw extending longitudinally along and fixed to a lower track assembly.
Data Source
AI summary
A seat adjustment assembly includes a housing, a worm, a gear, and a rail. The worm is disposed within the housing for rotation about a first axis and including a helical thread defining an arcuate profile extending about the first axis. The gear is disposed within the housing for rotation about a second axis and is meshingly-engaged with the worm. The rail extends through the housing and the gear for rotation about a third axis. The rail is meshingly-engaged with the gear.