Compact Belted Strain Wave Gear for Low-NVH Torque Transfer
Find Innovative SolutionsGenerate Solutions
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 while maintaining a compact and lightweight design.
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 easier assembly and adaptability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional harmonic drive gearing uses an elliptical wave generator with two fewer teeth on the flexspline than the circular spline, then torque capacity is increased through ratcheting torque, but noise, vibration, and harshness (NVH) greatly increase and positional accuracy is reduced
Solution Approach 1:
A belt assembly with fewer teeth than the circular spline acts as an intermediary between the circular spline and the output member. The belt assembly includes a flexible belt that engages with the circular spline teeth and transfers motion to the output member, mediating the interaction to reduce direct tooth-to-tooth contact forces and resulting NVH while maintaining torque capacity
Solution Approach 2:
The invention changes the tooth count parameter relationship from the traditional (N-2) configuration to a new configuration where the belt assembly has fewer teeth than the circular spline by a different amount. This parameter change allows the system to operate without ratcheting torque conditions, reducing NVH while maintaining adequate torque capacity through the belt's flexible engagement
2Strength
If traditional harmonic drive gearing uses an elliptical wave generator, then torque capacity is increased, but fatigue life of the flexspline is greatly reduced
Solution Approach 1:
The belt assembly serves as a mediator that distributes contact forces more evenly across multiple belt teeth during each rotation cycle, preventing the concentrated stress cycles that cause flexspline fatigue while still transmitting the necessary torque to the output member
Solution Approach 2:
By changing the tooth count relationship and using a belt assembly with fewer teeth than the circular spline, the system avoids the ratcheting torque condition that creates extreme stress cycles on the flexspline, thereby extending fatigue life while maintaining torque capacity
3Volume of moving object
If the wave generator is made compact with a short minor axis, then the flexspline can completely unmesh in zones along the minor axis, but the system becomes unbalanced and positional accuracy is reduced
Solution Approach 1:
The belt assembly acts as an intermediary that decouples the wave generator's unbalanced motion from the output member, allowing the compact wave generator to function while the belt smooths out the motion transmission to maintain positional accuracy
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 (NVH) levels, enhances positional accuracy, and is adaptable to various vehicle architectures while maintaining a compact and lightweight design, improving the overall performance and reliability of the harmonic drive system.
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
Implementation Method 3
a belt assembly extending about the wave generator. The belt assembly includes a ring-shaped substrate defining a plurality of belt teeth extending radially outwardly and configured to engage the spline teeth, whereby a total number of the belt teeth is less than a total number of the spline teeth
Implementation Method 4
a bearing assembly disposed between the wave generator and the belt assembly and including a plurality of needles each extending parallel to the center axis
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A wave gear apparatus (20) comprises a spline (22) having top, bottom, exterior, and interior surfaces. A plurality of spline teeth (42) extends from the interior surface toward a center axis. A wave generator (24) is rotatably disposed in the spline (22). A belt assembly (26) extends about the wave generator (24) and includes a plurality of belt teeth (52) extending radially outwardly, whereby a total number of the belt teeth (52) is less than a total number of the spline teeth (42). An output member (28) defines a recess receiving the wave generator (24) and the belt assembly (26), whereby, in response to a rotational movement from the wave generator (24), the output member (28) rotates in a direction same or opposite of the wave generator (24). A bearing assembly (450) is disposed between the wave generator (24) and the belt assembly (26) and includes a plurality of needles (454) each extending parallel to the center axis. A vehicle lifting system including the wave gear apparatus is also disclosed herein.