How do you reduce gear noise? Breaking the symmetry

giugno 04, 2025

Have you ever wondered how to reduce gear noise in hybrid drive systems? The answer might surprise you: break the symmetry.

In the automotive sector, especially in hybrid traction systems with electric kinematics, quietness isn’t just a value-added feature — it's a design necessity. In a recent technical test, we were asked to investigate how to reduce gear noise in a real-world application. Our approach? Simple in theory: produce several variants of the same component, each with slight modifications to the flank profiles, and test them on a test bench.

Goal: reduce gear noise

The goal was clear: lower the perceived noise level while maintaining full system functionality. To achieve this, we adopted an experimental method — controlled geometry modifications acting on a parameter known as fHβ, which measures the helix angle error. Non-optimized fHβ values can increase friction, noise, and vibrations, especially in high dynamic load applications.

Method: optimizing the fHβ parameter

The fHβ parameter measures the deviation of the helix direction from the theoretical path. In practical terms, it indicates how much the gear profile deviates along the axis compared to the ideal helical trajectory. A poorly optimized fHβ can lead to vibrations, friction, and significant noise increases — particularly in high acoustic performance requirements.

Result: controlled asymmetry reduces noise

Contrary to intuitive expectations, the best result didn’t come from a symmetric geometry or simply loosening tolerances. Instead, by precisely adjusting fHβ, we achieved a concrete benefit with differentiated modifications between the active and passive flanks:

Active flank: –20 μm ±11 μm
Passive flank: –15 μm ±11 μm

This seemingly small difference had a significant effect on reducing perceived noise. It confirms once again that, when working with such fine tolerances, controlled asymmetry can become a powerful ally in improving acoustic comfort.

The acoustic performance of a gear depends not only on machining quality or heat treatment but also on smart, sometimes counterintuitive design choices. In this case, the best solution was precisely the one that broke the symmetry.

Have you ever faced similar challenges? GSI gears is a partner on your side to create new projects.

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How do you reduce gear noise? Breaking the symmetry

Goal: reduce gear noise

Method: optimizing the fHβ parameter

Result: controlled asymmetry reduces noise

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