Belted Strain Wave Gear Layout for Low-NVH Vehicle Lifts
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Solution Overview
Problem
Traditional harmonic drive gearing systems face challenges with high noise, vibration, and harshness (NVH) due to increased forces on the flexspline, which reduces fatigue life and positional accuracy, and are not adaptable to different vehicle architectures.
Innovation Solution
A wave gear apparatus with a spline, wave generator, and belt assembly, featuring an eccentric core and a ring-shaped substrate with fewer belt teeth than spline teeth, along with a bearing assembly and output member, to reduce rotational speed and generate shear force, thereby minimizing NVH and allowing for compact, lightweight, and adaptable designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If traditional harmonic drive gearing uses an elliptical wave generator to mesh teeth in two zones, then torque capacity increases, but noise, vibration, and harshness increase greatly
Solution Approach 1:
The patent uses a circular wave generator instead of an elliptical one, creating a different meshing pattern where teeth engage in a single zone rather than two diametrically opposed zones. This asymmetric change in the wave generator geometry fundamentally alters the force distribution and contact mechanics, reducing the harmful vibrations and noises while maintaining adequate torque capacity through the belt assembly's shear force mechanism
Solution Approach 2:
The patent introduces a belt assembly as an intermediary element between the wave generator and the flexspline. This belt assembly with fewer teeth than the spline creates a controlled tooth difference that generates shear force, acting as a mediator that transmits torque while reducing the direct impact forces and vibrations that occur in traditional harmonic drives
2Weight of moving object
If the flexspline is made thin-walled to achieve compact design, then weight and size are reduced, but fatigue life is greatly reduced
Solution Approach 1:
The patent employs a thin-walled flexspline with external teeth that engages with a circular spline through a belt assembly. The thin-walled construction achieves compact weight and size while the external tooth configuration and belt-mediated engagement reduce stress concentrations, thereby improving fatigue life compared to traditional internal tooth flexsplines
Solution Approach 2:
The patent replaces the traditional direct meshing mechanical system with a belt-mediated engagement system. The belt assembly substitutes for direct tooth-to-tooth contact, reducing the mechanical stresses and impact loads on the thin-walled flexspline, thus enhancing its fatigue life while maintaining the compact thin-walled design
3Volume of moving object
If a one-tooth difference between circular spline and flexspline is used, then compact design is achieved, but positional accuracy is greatly reduced
Solution Approach 1:
The patent changes the fundamental parameter relationship by using a belt assembly with fewer teeth than the circular spline, creating a controlled tooth difference. This parameter change in the belt tooth count versus spline tooth count ratio enables compact sizing while the belt's flexibility and shear force mechanism maintain positional accuracy by reducing cumulative errors and backlash
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 wave gear apparatus achieves reduced noise, vibration, and harshness, enhancing positional accuracy and adaptability to various vehicle architectures while maintaining a compact and lightweight design.
Implementation Method 1
a wave generator rotatably disposed in the spline and including an eccentric core
Implementation Method 2
generate shear force, thereby minimizing NVH
Data Source
AI summary
A wave gear apparatus comprises a spline having top, bottom, exterior, and interior surfaces. A plurality of spline teeth extend from the interior surface toward a center axis. A wave generator is rotatably disposed in the spline. A belt assembly extends about the wave generator and includes a plurality of belt teeth extending radially outwardly, whereby a total number of the belt teeth is less than a total number of the spline teeth. An output member defines a recess receiving the wave generator and the belt whereby, in response to a rotational movement from the wave generator, the output member rotates in a direction same or opposite of the wave generator. A bearing assembly is disposed between the wave generator and the belt assembly and includes a plurality of needles each extending parallel to the center axis. A vehicle lifting system including the wave gear apparatus is also disclosed herein.