Ribbed Planet Gear Structure for Fatigue-Resistant Assembly
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Solution Overview
Problem
Existing planetary gears face challenges in achieving high fatigue strength and easy assembly while being cost-effective, particularly in mass production and high-load applications, where injection molding processes often compromise strength and assembly efficiency.
Innovation Solution
The design incorporates a planet wheel with ribs and stop projections that distribute load, reduce stress, and allow for continuous contact with mating surfaces, along with a planet carrier featuring bearing sections and latching projections for easy assembly and torque transmission, optimized for plastic manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If planetary gears are manufactured from plastic using injection molding, then mass production at low cost is achieved, but fatigue strength and maximum transmissible abuse torque are reduced
Solution Approach 1:
The planet gear is segmented into multiple load-bearing elements: the wheel body, multiple ribs extending from the planet gear axis to the gear ring, and leading projections on each rib. This segmentation distributes mechanical loads across multiple stress paths, preventing stress concentration at single points and improving overall fatigue strength of the plastic component
Solution Approach 2:
The design implements local quality by concentrating material and structural complexity at high-stress zones: the ribs are positioned to align with load paths from the planet gear axis to the gear ring, and leading projections are placed at the front contact points. This ensures enhanced local strength where fatigue loads are highest, while maintaining cost-effective plastic manufacturing
2Strength
If classic planet carrier designs are used, then structural strength is maintained, but manufacturing complexity and cost increase
Solution Approach 1:
The planet carrier design merges multiple functions into unified structural elements: the bearing sections are integrated directly into the carrier body, locking projections are formed as part of the carrier structure, and torque transmission features are combined with the overall carrier geometry. This reduces the number of separate components and assembly steps while maintaining structural integrity
Solution Approach 2:
The planet carrier is designed as a multi-functional component that simultaneously provides: bearing support for planet gears, positioning features for alignment, locking mechanisms for secure mounting, and torque transmission paths. This universal design consolidates multiple functions into a single manufactured part, reducing overall system complexity
3Strength
If ribs are added to distribute load, then fatigue strength is improved, but manufacturing precision requirements increase
Solution Approach 1:
The rib structures are designed with predetermined geometric relationships to the planet gear axis and gear ring, establishing load distribution paths before the component is subjected to operational loads. The ribs are positioned and dimensioned in advance during the injection molding process to create inherent load-bearing pathways that guide stress flow
Solution Approach 2:
The design optimizes rib parameters (cross-sectional area, spacing, curvature radius) to achieve adequate load distribution with relaxed tolerance requirements. By adjusting these geometric parameters, the structure achieves sufficient fatigue strength while maintaining compatibility with standard injection molding capabilities and reasonable precision levels
Data Source
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AI summary
The present invention relates to a planet gear (10) for a planetary gear set (14), comprising a gear body (16) and a planet gear shaft (22) which defines a planet gear rotation axis (APR) of the planet gear (10), wherein the gear body (16) comprises a toothed ring (30) with a first number (n1) of teeth (31) and a second number (n2) of ribs (32), wherein the ribs (32) extend between the planet gear shaft (22) and the toothed ring (30), and planet gear leading projections (40) are arranged on the ribs (32) which project along the planet gear rotation axis (APR) beyond the toothed ring (30).Furthermore, the invention relates to a planet carrier (44) for such a planet gear (10), comprising an insert (68) for dissipating a torque from the carrier body (46), which is connected to the first disk-shaped body (48), wherein the first disk-shaped body (48) forms a first free planet carrier end face (70) on which a number of stiffening ribs (72) are arranged.