Worm Wheel Chamfers Prevent Tooth Tip Interference
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Solution Overview
Problem
Electric power steering system reduction gears with worm and tangent wheel types face premature tooth failure due to tooth tip interference, leading to reduced gear life, especially under high torque and low rotation speed conditions.
Innovation Solution
A reduction gear design featuring a worm screw and worm wheel with chamfers on each tooth side, greater than 50% of the geometric module, to prevent contact between larger diameter tooth parts and maintain meshing quality, achieved through double cutting machining operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional worm wheel teeth without chamfers are used, then the gear structure is simple and manufacturing is easier, but tooth tip interference occurs leading to premature tooth failure and reduced gear life
Solution Approach 1:
The patent applies chamfers locally at the tooth tips of the worm wheel, specifically designing the chamfer geometry (height h and angle α) to be greater than 50% of the geometric module. This localized modification prevents tooth tip interference while maintaining the standard worm wheel structure elsewhere, thus improving reliability without excessive complexity
Solution Approach 2:
The chamfered tooth geometry is designed in advance to prevent interference before it occurs. By pre-shaping the tooth tips with chamfers, the design eliminates the potential for tooth tip contact interference that would otherwise occur during operation, thereby extending gear life proactively
2Duration of action of stationary object
If chamfers with height greater than 50% of geometric module are added to worm wheel teeth, then tooth tip interference is prevented and gear life is extended, but manufacturing complexity increases due to double cutting operations
Solution Approach 1:
The tooth manufacturing process is segmented into two distinct cutting operations: a through-cutting operation to create the basic tooth form and chamfer, and a non-through cutting operation to complete the tooth profile. This segmentation allows each operation to be optimized independently, making the complex geometry achievable through standardized machining steps
3Ease of manufacture
If standard worm wheel teeth geometry is used, then manufacturing is simpler, but contact occurs between larger diameter parts of teeth leading to vacuum interference and deformation interference
Solution Approach 1:
The patent modifies the tooth geometry parameters by introducing chamfers with specific dimensions (height h > 50% of module m and angle α between 15°-45°). This parameter change alters the contact pattern between worm and worm wheel, preventing both vacuum interference (initial contact) and deformation interference (under load) while maintaining manufacturability
Data Source
Figure 1~5
Figure 6
AI summary
The gear has a worm wheel mounted rotatively around an axis that is non-orthogonal to another axis, and a set of teeth (4) that are provided at periphery of the worm wheel. The teeth are engaged with threads of an endless screw that is mounted rotatively around the former axis. Height (H) of chamfers (7, 8) is greater than 50 percent of geometric module of the set of teeth of the worm wheel.