Composite Spur Gear Structure for Low-Noise Load-Stable Meshing
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Solution Overview
Problem
Spur gears used in high mechanical load and temperature fluctuation applications face issues with noise generation, wear, and deformation due to the limitations of using plastic materials, which are exacerbated by thermal expansion and axial forces in helical gearing, making them unsuitable for large-scale production.
Innovation Solution
A spur gear design comprising an outer part made of a high-performance plastic, an insert part made of metal, and a connecting part made of a different plastic, with injection-molded sections and undercuts to ensure a positive connection and prevent slipping, allowing for low-noise operation and reduced wear under high mechanical loads and temperature fluctuations while being cost-effective.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If plastic spur gears are used to reduce noise and weight, then noise level is reduced and weight is decreased, but under high mechanical loads and high temperatures, deformations occur leading to meshing problems and increased stress
Solution Approach 1:
The gear is constructed as a composite structure with a metal insert providing structural strength and stiffness to resist deformations under load, while the plastic outer part provides noise reduction and weight savings. This composite approach allows the gear to maintain dimensional stability under high mechanical loads and temperatures while preserving the noise-reducing benefits of plastic.
Solution Approach 2:
The gear is divided into distinct functional segments: a metal insert for structural support and an outer plastic part for noise reduction and tooth engagement. This segmentation allows each material to perform its optimal function - the metal core prevents deformation while the plastic exterior reduces noise.
2Strength
If fiber-reinforced materials are used to increase stiffness, then stiffness is improved, but wear and fiber abrasion on the teeth increase
Solution Approach 1:
Instead of using fiber-reinforced plastic throughout, the invention uses a metal insert combined with unreinforced or lightly reinforced plastic for the outer part. This provides the necessary stiffness through the metal core without introducing fiber abrasion into the gear teeth contact surfaces.
Solution Approach 2:
The metal insert is strategically positioned in the gear hub and root areas where high stiffness is needed to prevent deformation, while the tooth surfaces use smooth plastic material that minimizes wear and abrasion during meshing.
3Strength
If a large metal insert is used in plastic gear ring, then structural strength is improved, but manufacturing complexity increases and material loss occurs
Solution Approach 1:
The injection molding process is designed so that the outer plastic part automatically forms during molding, with the metal insert already in position. The plastic flows around the insert and solidifies, creating the gear structure with the insert embedded. This self-assembly during molding eliminates complex post-assembly operations and reduces manufacturing steps.
Solution Approach 2:
The invention combines the metal insert placement and plastic gear formation into a single integrated injection molding operation. The metal insert serves as both a structural component and a molding core, eliminating the need for separate assembly steps and reducing overall manufacturing complexity.
4Ease of manufacture
If spot-gating process is used for injection molding around insert, then manufacturing is simplified, but weld lines are created representing weak points
Solution Approach 1:
The invention changes the gating parameters by using a screen-gating process with specific flow control that allows the molten plastic to wrap around the metal insert without creating weld lines. By controlling the flow rate, temperature, and gating geometry, the plastic solidifies before meeting from opposite sides, eliminating weld line formation while maintaining manufacturing simplicity.
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 design achieves low-noise operation and reduced wear by optimizing the mechanical properties of the plastics used and minimizing axial deformations, enabling efficient torque transmission and cost-effective production.
Implementation Method 1
connecting part made of a second plastic arranged between the insert and the outer part for positively interlocking connection
Implementation Method 2
under high mechanical loads and high temperatures, correspondingly high deformations occur in the spur gears
Implementation Method 3
Compared to metal spur gears, plastic spur gears exhibit increased thermal expansion. Therefore, at high temperatures, the diameter of the spur gears in the gear pair increases
Implementation Method 4
Either the molten plastic is injected around the insert using a spot-gating process
Data Source
Figure 1~2
Figure 3~4e
Figure 5a~6c
AI summary
The present application relates to a gear pair (10) for a spur gear transmission (46), comprising a first spur gear (12) and a second spur gear (14) which can be meshed together, wherein the first spur gear (12) is made entirely or partially of metal or plastic, and the second spur gear (14) comprises an outer part (16) with a toothed ring (18) made of a first plastic and with a number of injection-molded sections (21), an insert (20) made of metal, and a connecting part (22) made of a second plastic arranged between the insert (20) and the outer part (16) for a positive-locking and/or material-locking connection of the insert (20) and the outer part. The invention further relates to the second spur gear (14) as such, wherein the injection-molded sections (21) are covered by the connecting part (22).and/or wherein the connecting part (22) has undercuts (39) at least along an axis of rotation (T) of the spur gear (14), a spur gear transmission with such a gear pair and a method for manufacturing a second spur gear (14) which is used for such a spur gear transmission.