Gear Noise

Gear whine – Generated by meshing gears due to the vibration caused by failure of the rolling action between the mating teeth due to:

Minute imperfections in manufacture of

  • Tooth pitch circle (radius and centre) – see Gear Design
  • Tooth involute form – gear profile error results in the generation of gear noise at sub-harmonics of the fundamental gear meshing frequency.
  • Gear shaft
  • Gear shaft bearing position
  • Gear tooth finish
  • Tooth helix angles (relative)
  • Radii at tooth tip and root

Small design errors leading to

  • Excessive tooth deflection under load
  • Shaft deflection under load
  • Housing deflection (movement between gear centres)
  • Inappropriate lubrication
  • Hydraulic lock (oil trapped between gear teeth in mesh)

The resulting meshing frequency is the product of the number of teeth on a gear and its rotational speed in rev per second. It follows, therefore, that any pair of gears in mesh have the same meshing frequency. The vibration produced by meshing gears can possibly excite a number of ‘sympathetic’ components, these may be the shaft on which the gear runs (torsional or bending mode), panel resonance in the gearbox casing, crossmembers, body panels etc. The transmission path into the vehicle may be either ‘structure borne’ or ‘airborne’.

Gear rattle – In a geared timing drive, impacts occur between the teeth on meshing gears as backlash is taken up in either direction. At some speeds, the rattle finds a resonance in which shaft and gear inertias combine with non-linear tooth deflection to form a resonant torsional spring – inertia mass system. One solution to the rattle problem is to keep the load constant.

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