Logarithmic Spiral Gear Fitting for Vehicle Seat Stability
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Solution Overview
Problem
Conventional gear fittings for vehicle seat backrest adjustment face instability and play issues due to single contact points and unsuitable force ratios, leading to undesirable wobbling movements and reduced stability.
Innovation Solution
A gear fitting with a logarithmic spiral tooth design and an eccentric planetary gear system, which allows for stepless adjustment and stable contact force distribution, avoiding single contact points and enhancing stability by using a crescent-shaped or wedge segment eccentric mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional gear fittings use single contact points between gear wheel and ring gear, then the structure is simple, but stability deteriorates and wobbling movements occur
Solution Approach 1:
The patent divides the single contact point into multiple contact points by designing specific tooth profiles with logarithmic spiral sections. This segmentation allows force distribution across multiple points simultaneously, enhancing stability while maintaining the basic gear structure.
Solution Approach 2:
The invention transitions from a single-point contact (0D) to multi-point contact (1D/2D) by utilizing the three-dimensional logarithmic spiral tooth profile. This dimensional change enables simultaneous contact at multiple locations, reducing wobbling and improving stability.
2Ease of manufacture
If conventional gear fittings use single contact points, then manufacturing is easier, but play and instability increase
Solution Approach 1:
The patent employs logarithmic spiral curves with specific curvature characteristics to define the tooth profiles. This curved geometry naturally guides contact forces through multiple points, eliminating play while remaining manufacturable using conventional gear cutting methods adapted for spiral profiles.
3Device complexity
If the contact force acts along the eccentricity extension, then the transmission is simple, but stability deteriorates due to unstable force distribution
Solution Approach 1:
The logarithmic spiral tooth profiles create an asymmetric force distribution pattern that deliberately shifts contact points away from the eccentricity extension line. This asymmetric arrangement establishes a stable three-point support system with forces distributed at defined angles, preventing the instability associated with linear force alignment.
4Ease of manufacture
If conventional flank shapes are used, then manufacturing is straightforward, but force ratios are not physically correct leading to instability
Solution Approach 1:
The patent changes the fundamental geometric parameters of the tooth profile from conventional shapes (involute, cycloid) to logarithmic spiral profiles with specifically calculated growth rates and angles. These parameter changes ensure that force ratios match physical requirements for stable operation, while the profiles remain manufacturable using modified gear cutting processes.
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 provides stable and continuous adjustment of the vehicle seat backrest with reduced wobbling, ensuring self-locking and play-free operation by distributing contact forces evenly and creating a stable three-point support system.
Implementation Method 1
the rolling movement, to determine from this the surface contour of the teeth required in the respective situation
Implementation Method 2
The eccentric, which consists for example of two wedge segments stretched apart by means of a spring
Implementation Method 3
The use of an eccentric planetary gear in a fitting allows a stepless adjustment of the inclination of the backrest
Implementation Method 4
two wedge segments stretched apart by means of a spring
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
The invention relates to a fitting (10), in particular for a motor vehicle seat, having a first fitting part (11), on which a gear rim (17) is formed, a second fitting part (12) on which a gearwheel (16) is formed, wherein the gearwheel meshes with the gear rim (17), whereby the two fitting parts (11, 12) are in geared connection with each other. The fitting also has a rotatably mounted, revolving eccentric driven by a driving element for driving a relative rolling motion of gearwheel (16) and gear rim (17), wherein during this rolling motion a tooth flank (16d) of a tooth (16a) of the gearwheel (16) rests against a tooth flank (17d) of a tooth (17a) of the gear rim (17) at a contact point (K). The tooth flanks (16d, 17d) of the teeth (16a, 17a) of the gearwheel (16) and gear rim (17) resting against each other at the contact point (K) each follow the course of a portion of a respective logarithmic spiral.