Plastic Gear Wheel Reinforcement for Worm Reducers
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Solution Overview
Problem
Existing gear wheels for worm gear reducers, particularly in electric power steering, face issues with breakage at the root of the tooth and shearing in the meshing zone due to significant meshing forces, leading to performance limitations of plastic materials.
Innovation Solution
The gear wheel incorporates first and second reinforcement means within the external toothing to enhance mechanical strength and fatigue resistance, with the first means transferring meshing forces to the hub and the second means decoupling reinforcement from the external toothing, using internal toothing and reinforcing blades with specific geometries, and a plastic material with fillers like glass or carbon fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the external toothing is made of plastic material, then meshing noise is reduced, but mechanical strength is insufficient under significant meshing forces
Solution Approach 1:
The external toothing is made of a composite plastic material comprising a thermoplastic matrix reinforced with glass fibers or carbon fibers. This composite structure maintains the noise reduction benefits of plastic while significantly enhancing mechanical strength to withstand meshing forces in electric power steering applications.
Solution Approach 2:
The external toothing is segmented into individual teeth that are injection-molded separately and then assembled onto the hub. This segmentation allows each tooth to be optimized for strength while maintaining the overall plastic construction benefits, and enables the use of reinforced plastic materials in each tooth component.
2Strength
If reinforcement means are arranged inside the external toothing, then mechanical strength is improved, but complexity of the gear wheel increases
Solution Approach 1:
The reinforcement means (metal inserts or fibers) are merged with the plastic toothing during the injection molding process. The metal inserts are positioned in cavities within the toothing structure, and molten plastic is injected around them, creating an integrated composite structure that strengthens the toothing without requiring separate assembly steps.
Solution Approach 2:
The hub structure serves multiple functions: it provides the mounting interface for the toothing, acts as a reservoir for the reinforcement materials, and serves as the structural core that transmits forces. The internal cavities of the hub are utilized to house the reinforcement means, eliminating the need for separate reinforcement components.
3Strength
If the plastic material is reinforced with fillers, then mechanical strength is improved, but flexibility is reduced
Solution Approach 1:
The plastic material composition is optimized with specific filler contents and distributions to achieve local quality enhancement. Glass fibers or carbon fibers are incorporated at controlled concentrations (typically 10-30% by weight) to provide localized strength enhancement at critical stress points while maintaining overall material flexibility and toughness in non-critical areas.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The wheel (1) has an outer toothing (3) made of plastic material and arranged in periphery of a hub (2). A first reinforcement unit is arranged inside the outer toothing to transfer meshing forces of the toothing toward the hub. A second reinforcement unit i.e. reinforcement strip (5), is arranged inside the outer toothing and remote from the first unit. The first unit includes an inner toothing (4) that is arranged in the periphery of the hub so as to be radially aligned with the outer toothing, where the inner toothing and the hub are made of carbon/glass fiber loaded plastic material. An independent claim is also included for a method for securing a reinforcement strip inside an outer toothing of a gear wheel.