Helical Plastic Gear With Stiff Support Body for Low-Noise Strength
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Solution Overview
Problem
Existing plastic gears with spur toothing face challenges in achieving smooth running and low noise, while also requiring high strength and being space and cost-efficient, especially in applications like motor vehicle auxiliary drives.
Innovation Solution
A gear design featuring a gear body made of a first plastic material with helical toothing and a support body made of a second plastic material with higher stiffness and lower elasticity, where the support body is integrally formed with reinforcing portions that match the helix angle of the toothing, and the gear body and support body form a substantially flat end face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If spur toothing is used in plastic gears, then the gear structure is simple and easy to manufacture, but the noise and smooth running are problematic
Solution Approach 1:
The patent changes the tooth geometry parameter from spur toothing (zero helix angle) to helical toothing with a specific helix angle (15-25 degrees). This parameter change transforms the engagement pattern from simultaneous line contact to progressive point contact, significantly reducing noise and improving smooth running while maintaining manufacturability through standard helical gear manufacturing processes.
2Object-generated harmful factors
If helical toothing is used to reduce noise, then smooth running and noise are improved, but the required strength for small gears becomes difficult to achieve
Solution Approach 1:
The patent employs composite material construction with a stiffening ring made of a different material than the gear body. The stiffening ring material is selected to have higher modulus of elasticity and higher yield strength than the gear body material, creating a composite structure that provides the necessary strength for helical toothing in small gears while maintaining noise reduction benefits.
Solution Approach 2:
The patent applies local quality enhancement by adding a stiffening ring specifically at the gear hub area where strength is most critical. The stiffening ring provides localized reinforcement without requiring the entire gear to be made from high-strength material, optimizing the strength-to-weight ratio and enabling helical toothing in small gear sizes.
3Strength
If a stiffening ring is added to provide strength, then the required strength is achieved, but the gear takes up more space
Solution Approach 1:
The stiffening ring is designed with selective thickness distribution, being thicker at critical stress locations and thinner elsewhere. This localized quality approach provides necessary strength reinforcement only where required, minimizing the overall volume increase while achieving the required strength for helical toothing in small gears.
Solution Approach 2:
The stiffening ring provides more strength than the minimum required, creating a strength reserve that allows the gear body to be made from lighter, less dense material. This partial over-engineering of the stiffening ring enables overall volume reduction by compensating with lower-density gear body material.
4Strength
If different materials are used for gear body and stiffening ring, then strength requirements are met, but manufacturing cost increases
Solution Approach 1:
The patent merges the gear body and stiffening ring into a single integrated component manufactured in one injection molding process. The stiffening ring is formed as an integral part of the gear body during the same manufacturing cycle, eliminating separate manufacturing and assembly steps. This combining approach maintains the strength benefits of different materials while reducing manufacturing cost through process integration.
Solution Approach 2:
The injection molding process is designed to perform multiple functions simultaneously: forming the gear body, creating the helical toothing, and producing the stiffening ring structure in a single operation. This multi-functionality approach consolidates what would traditionally require multiple manufacturing processes into one, reducing overall manufacturing cost despite using a complex multi-material structure.
Data Source
AI summary
A gear has a gear body made of a first plastic material. The gear body has an axis of rotation, external toothing arranged around an axis of rotation, a centrally located receiving opening, and an intermediate portion located between the external toothing and the wall of the receiving opening. The gear body is fixedly integrally formed on a support body, which is arranged at least partially in the intermediate portion and is made of a second plastic material having a higher stiffness and lower elasticity than the first plastic material, such that surface portions of the external toothing, of the wall of the receiving opening, of the intermediate portion, and of the support body form a substantially flat end face of the gear. The external toothing is helical toothing with teeth which, at least in portions, extend at a helix angle to the axis of rotation.