Plastic Gear Wheel With Internal Toothing For Worm Reducer
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Solution Overview
Problem
The existing gear wheels in worm gear reducers, particularly in electric power steering systems, face issues with noise reduction and mechanical strength due to significant meshing forces, leading to common breakage at the root of the tooth, and plastic materials are nearing their performance limits.
Innovation Solution
A gear wheel design featuring a plastic external toothing with an internal toothing that transfers meshing forces to the hub, incorporating a constriction zone and a radial alignment to enhance mechanical strength, flexibility, and fatigue resistance, while maintaining reduced noise levels and using a hub material with a higher modulus of elasticity than the external toothing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the external toothing is made of plastic material to reduce meshing noise, then noise is reduced, but mechanical strength decreases leading to tooth root breakage
Solution Approach 1:
The gear wheel combines plastic material for the external toothing with a metal hub featuring internal toothing. This composite structure allows the plastic external toothing to maintain noise-reducing properties while the metal internal toothing provides the necessary mechanical strength to handle significant meshing forces in electric power steering applications.
Solution Approach 2:
The gear wheel is divided into two functional segments: the external toothing made of plastic material that contacts the endless screw and reduces noise, and the internal toothing integrated into the metal hub that provides structural strength. This segmentation allows each part to optimize its specific function without compromising the other.
2Strength
If the external toothing is made stiffer to increase mechanical strength, then strength improves, but flexibility decreases causing excessive stress concentration
Solution Approach 1:
The external toothing features a localized thin section or constriction zone at the root circle area. This local modification reduces stiffness in the critical stress region while maintaining overall structural integrity. The thinner section at the root allows the external toothing to flex under load, preventing stress concentration and improving fatigue resistance.
3Strength
If the plastic material is made thicker to increase strength, then mechanical strength improves, but manufacturing complexity and cost increase
Solution Approach 1:
The design changes the geometric parameters of the external toothing by introducing a thin section or constriction zone at the root circle. This parameter modification optimizes the strength-to-weight ratio and allows for simpler manufacturing processes. The constrained geometry can be efficiently produced using injection molding techniques without requiring excessive material or complex multi-step manufacturing.
Data Source
Figure 1~3
Figure 4~5
AI summary
The wheel (1) has a hub including a peripheral zone (20). External gear teeth (3) are adapted to be engaged with a worm gear. The peripheral zone comprises internal gear teeth (4) having a radial alignment with the external teeth so as to transfer engaging efforts of the external teeth toward the hub. The internal teeth present a radial section including a throttling zone (6) that is arranged to radial height of a dedendum circle of the external teeth. The hub is made of plastic material having filler selected from a group comprising glass fibers and carbon fibers.