Practical Analysis of Quiet Gear Design
Core Principles
Adhere to the principles of low impact, low friction, and low vibration, focusing on practical parameters, processes, and taboos. It is directly applicable to on-site engineering design, manufacturing, and installation, balancing quietness and strength without complex theories.

1. Core Practical Design Parameters
1.1 Basic Parameters (Mandatory)

Module and Number of TeethUse the smallest module that meets strength requirements.Pinion teeth number (z_1 = 25sim35) (avoid <17 to prevent undercutting and high noise).
Tooth Profile and Helix AnglePrefer helical gears (5–10 dB quieter than spur gears).Helix angle (beta = 8^circsim15^circ) (exceeding 15° causes overheating and bearing damage).Herringbone gears for high-end quiet applications.
Pressure Angle17.5°–19° for quietness; standard 20° for general use (select by application).
Contact Ratio and Face WidthTotal contact ratio (varepsilon geq1.4) (≥1.5 for precision scenarios).Face width coefficient (psi_d = 0.4sim0.8) (excessive width leads to uneven load).

1.2 Tooth Profile Modification

Tip Relief: 5–20 μm (thinning the entry side to avoid impact; mandatory for high-speed and heavy-load).
Lead Modification:Crowning: 5–15 μm (slight convex center to compensate for shaft deformation).End relief (prevents edge loading).

1.3 Manufacturing Accuracy and Surface Quality (Strict Control)

Accuracy Grade: ISO 6 for general quietness; ISO 5 for precision/high speed (control profile and pitch error strictly).
Surface Roughness: (Raleq0.8 mutext{m}) (general); (Raleq0.4 mutext{m}) (precision).
Process Route: Hobbing → Shaving → Grinding → Honing (all steps required).

1.4 Material and Heat Treatment

Materials:Heavy-load & high-speed: 20CrMnTi, 20CrNiMoA.Quietness priority: Nodular cast iron.Light-load & low-speed: POM/PEEK (plastic).
Heat Treatment: Carburizing and quenching + low-temperature tempering; surface HRC 58–65.Prefer vacuum heat treatment (small deformation).
Matching Hardness: Pinion 20–30 HB harder than gear (easier running-in, lower noise).

1.5 Structure and Lubrication

Backlash: 0.005–0.012 mm (micro-clearance to prevent impact; controlled by center distance).
Damping and Vibration Isolation: Rubber-filled holes in web; rubber isolation pads on housing.
Shafting and Housing: High-rigidity short-span shafts; P4/P5 class bearings (low clearance); thick-wall housing with ribs.
Lubrication: Low-viscosity synthetic gear oil with friction reducers; regular inspection (insufficient oil causes loud noise).

2. Simplified Design and Verification Process

Select parameters based on load and speed.
Calculate modification values via software (no complex simulation needed).
Define process route per accuracy and roughness requirements.
Prototype and test noise: mass production if qualified; adjust modification/clearance if not.

3. Practical Taboos

Do not blindly increase the module (wastes material and increases noise).
Helix angle shall not exceed 15° (shaft deformation and bearing failure).
Do not set modification values randomly (insufficient/excessive causes noise; software calculation is accurate).
Do not skip vacuum heat treatment (large deformation leads to noisy meshing).
Do not adjust backlash arbitrarily (excessive causes impact; insufficient causes jamming).
Do not ignore lubrication (insufficient/aged oil doubles noise).
Must calibrate coaxiality and center distance during installation (deviation causes uneven load and noise).
Plastic gears are not for heavy-load and high-speed (failure and noise surge in later stage).