Small Tooth-Difference Gear Arrangement With Low Interference
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Solution Overview
Problem
Existing internal-external gear pairs with small tooth differences often suffer from tooth interference, which can lead to inefficiencies and mechanical issues, particularly when standard gear profiles and moduli are used.
Innovation Solution
The design incorporates an internal-external gear pair with a small tooth number difference, where the internal and external gear teeth have an involute shape with no profile shift or with a profile shift that maintains pressure angles within 20% of the nominal pressure angle, and an addendum coefficient of less than 0.8.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard gear profiles and moduli are used in internal-external gear pairs with small tooth differences, then the gear design is simple and manufacturing is easier, but tooth interference occurs between gear tips
Solution Approach 1:
The patent applies profile shifting by modifying the addendum coefficient (reducing it to less than 0.8) and adjusting the dedendum coefficient accordingly. This parameter change prevents tooth interference by ensuring the gear tips do not overlap, while maintaining standard gear profiles for ease of manufacture. The modified coefficients are applied to both internal and external gears in the small tooth-difference pair.
2Reliability
If profile shift is applied to prevent tooth interference, then tooth interference is avoided, but gear efficiency decreases
Solution Approach 1:
The patent optimizes the profile shift parameters by setting the addendum coefficient to a specific range (less than 0.8) rather than applying excessive profile shifting. This controlled parameter change prevents tooth interference while minimizing the negative impact on gear efficiency. The dedendum coefficient is adjusted complementarily to maintain proper tooth clearance and engagement.
3Reliability
If the addendum coefficient is reduced to prevent tooth interference, then tooth interference is avoided, but the contact ratio decreases below 1
Solution Approach 1:
The patent compensates for the reduced theoretical contact ratio by designing the gear teeth with optimized pressure angles and profile curvature. This beforehand preparation ensures that even though the theoretical contact ratio is below 1, the actual tooth engagement remains smooth and continuous. The pressure angle optimization ensures adequate force transmission despite fewer teeth in contact.
Data Source
AI summary
A gearbox comprising an internal-external gear pair having a small tooth-difference, the internal-external gear pair comprising: an internal gear arranged about an internal gear axis and having a first number of internal gear teeth; and an external gear having an external gear axis arranged to orbit the internal gear axis and having a second number of external gear teeth, the external gear being arranged to engage with the internal gear teeth; wherein the small tooth-difference is less than a fifth of the number of internal gear teeth; and wherein the internal gear teeth and the external gear teeth have an involute shape with no profile shift, or with a profile shift below a value at which the working pressure angles of the internal-external gear pair would exceed, by more than 20%, a nominal pressure angle of the internal-external gear pair if no profile shift were applied.