Harmonic Drive Disc Recliner for Automotive Seats
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Solution Overview
Problem
Existing automotive vehicle seat recliner assemblies are not compact, lightweight, or low-cost, and they suffer from gear backlash or 'chuck' issues, which lead to unintended seat back movement, and they often require larger drive motors due to limited gear ratios.
Innovation Solution
A harmonic drive disc recliner system that couples a seat back to a seat cushion using a fixed plate, a rotatable plate, and a flex spline with a wave generator, allowing for pivotal movement by meshing teeth engagement, reducing the need for large drive motors and minimizing gear backlash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional reduction gears are used in the recliner assembly, then the gear ratio can be achieved, but the assembly becomes larger, heavier, and more complex
Solution Approach 1:
The patent extracts the wave generator mechanism from traditional reduction gear systems. The wave generator, consisting of a cam and follower, directly produces the desired motion without requiring multiple stages of gear reduction, thereby simplifying the overall assembly while achieving the necessary mechanical advantage
Solution Approach 2:
Instead of using traditional gear reduction where the output shaft rotates slower than the input, the wave generator inverts the approach by using an oscillating cam mechanism that directly converts rotational input into the required oscillating output motion, eliminating the need for complex gear trains
2Power
If traditional reduction gears are used in the recliner assembly, then the gear ratio can be achieved, but the drive motor becomes larger
Solution Approach 1:
The wave generator mechanism extracts the motion conversion function from traditional gear reduction systems, allowing the use of a smaller, lighter drive motor that directly drives the cam without requiring the high torque multiplication that would necessitate large motors in conventional gear-based designs
Solution Approach 2:
The wave generator employs dynamic motion conversion where the cam profile is designed to provide the required mechanical advantage at different points in the oscillation cycle, allowing the motor to operate more efficiently with reduced size and weight while still achieving the necessary force multiplication
3Power
If traditional gear mechanisms are used, then power transmission is achieved, but gear backlash or 'chuck' occurs causing unintended movement
Solution Approach 1:
The patent replaces the traditional mechanical gear tooth engagement system with a wave generator mechanism where a cam and follower provide continuous contact and motion control. This substitution eliminates the inherent backlash of meshing gears while maintaining effective power transmission through the oscillating cam profile
Solution Approach 2:
Instead of relying on gear tooth engagement that inherently creates backlash, the wave generator inverts the approach by using a continuously contacting cam mechanism where the follower is pressed against the cam surface, eliminating play and ensuring precise position control without unintended movement
4Device complexity
If compact and lightweight design is pursued, then the recliner assembly size is reduced, but manufacturing cost may increase
Solution Approach 1:
The wave generator mechanism is segmented into modular components including the cam, follower, and supporting structure. This segmentation allows for simplified manufacturing of individual parts that can be produced using standard machining processes, reducing overall manufacturing cost while maintaining the compact design
Solution Approach 2:
The cam profile parameters are optimized to achieve the desired motion characteristics while using standard materials and manufacturing tolerances. By carefully selecting cam geometry parameters, the design achieves compact dimensions without requiring expensive custom tooling or specialized manufacturing 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 harmonic drive disc recliner system provides a compact, lightweight, and cost-effective solution with reduced gear backlash, enabling precise control and smaller motor requirements, enhancing passenger comfort and reducing unintended seat back movement.
Implementation Method 1
A wave generator is disposed within the flex spline and has an outer profile with lobes that cause the teeth on the flex spline to meshingly engage with the teeth on the fixed and rotatable plates in distinct regions corresponding with the lobes. As the wave generator rotates, the regions where the teeth on the flex spline meshingly engage with the teeth on the fixed and rotatable plates change and simultaneously the teeth on the flex spline urge the teeth on the rotatable plate to align with the teeth on the fixed plate
Data Source
AI summary
A disc recliner 18 for a seat assembly includes a fixed plate 22 secured to a seat cushion 12 and a rotatable plate 30 secured to a seat back 14. Each of the fixed and rotatable plates 22,30 has a plurality of teeth 40,48, the number of teeth not being equal. A flex spline 26 has a plurality of teeth 52, the number of teeth being equal to the number of teeth on the fixed plate 22. A wave generator 28 causes a portion of the teeth 52 on the flex spline 26 to meshingly engage with the teeth 40,48 on the fixed and rotatable plates 22,30. Rotation of the wave generator 28 causes the teeth 52 on the flex spline 26 which meshingly engage with the teeth 40,48 on the fixed and rotatable plates 22,30 to change, thereby causing the rotatable plate 30 to rotate relative to the fixed plate 22, which in turn causes the seat back 14 to pivot relative to the seat cushion 12.