Planetary Gear Train Tooth Profile Design for Friction Reduction
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Solution Overview
Problem
The existing planetary gear trains of the internal engagement type lack a definitive design standard for the size of the run-out portion, leading to decreased torque transmission efficiency and durability due to potential contact between the external and internal gear teeth in non-engagement areas.
Innovation Solution
The planetary gear train design incorporates specific cross-sectional shapes for the external and internal gear teeth, with the external tooth-front surface positioned radially inward from a reference epicycloid curved line and the internal tooth-front surface positioned radially outward from a hypocycloid curved line, forming a run-out portion to prevent contact in non-engagement areas and ensuring a contact surface length of at least 20% of the total surface length in engagement areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a run-out portion is formed at the tooth-front portion of gear teeth to avoid contact in non-engagement areas, then friction loss is reduced and torque transmission efficiency is improved, but the contact surface length of the gear tooth is decreased and durability is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the depth and position of the run-out portion through specific geometric parameters. The run-out portion depth is set to satisfy the inequality 0 < h ≤ (R2 - R1) × 0.3, where R1 is the pitch radius of the external gear and R2 is the pitch radius of the internal gear. This parameter optimization allows the run-out portion to prevent tooth-front contact in non-engagement areas while maintaining sufficient contact surface length in engagement areas, thereby reducing friction loss without compromising durability
Solution Approach 2:
The patent applies local quality by creating a run-out portion only at specific locations - the tooth-front portion of either the external gear or internal gear, but not both. This localized modification is made at the precise position where teeth may incorrectly contact in non-engagement areas, while leaving the main engagement surfaces intact. The run-out portion is formed only in the non-engagement area, preserving the quality and contact surface of the engagement area, thus preventing friction loss without affecting durability
2Productivity
If the run-out portion depth is increased to prevent tooth contact in non-engagement areas, then torque transmission efficiency is improved, but the contact surface length is further decreased and durability is reduced
Solution Approach 1:
The patent establishes a precise parameter range for the run-out portion depth h, defined by the inequality 0 < h ≤ (R2 - R1) × 0.3. This parameter optimization ensures that the run-out portion is deep enough to prevent tooth-front contact in non-engagement areas, thereby improving torque transmission efficiency, while simultaneously being shallow enough to preserve sufficient contact surface length in engagement areas, maintaining durability. The parameter (R2 - R1) represents the difference between pitch radii, providing a scalable design criterion
Solution Approach 2:
The patent applies partial action by forming a run-out portion that is just sufficient to prevent harmful tooth-front contact, rather than removing excessive material. The depth is controlled to be greater than zero to ensure contact prevention, but limited to 30% of the pitch radius difference to avoid over-removal of material. This partial modification achieves the necessary friction reduction without excessively compromising the contact surface length and durability
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
This design effectively prevents friction loss and durability issues by minimizing contact between gears in non-engagement areas and maintaining high torque transmission efficiency, while ensuring adequate contact surface length for durability in engagement areas.
Implementation Method 1
A transverse cross-sectional shape of the external tooth-bottom surface as well as a transverse cross-sectional shape of the external bottom-side contact surface is formed by a hypocycloid curved line
Implementation Method 2
a transverse cross-sectional shape of the external front-side contact surface is formed by an epicycloid curved line
Data Source
AI summary
Each of an external tooth-bottom surface and an external bottom-side contact surface has a cross-sectional shape formed by a hypocycloid curved line. An external front-side contact surface has a cross-sectional shape formed by an epicycloid curved line. An external tooth-front surface is formed at a radial-inside position of a reference epicycloid curved line, that is, a position closer to a first pitch circle of an external gear. A possible contact between a tooth-front portion of the external gear and a tooth-front portion of an internal gear can be avoided. A connecting point between the external tooth-front surface and the external front-side contact surface is located at such a position that a contact surface length of an external tooth-contact surface is larger than twenty percent of a total tooth surface of the external gear.