scope:

Gear whine is controlled by managing transmission error (TE). Transmission error forces in the mesh are reacted by the bearings supporting the shafts. These forces dynamically excite the housing and cause its walls to vibrate. The walls couple with the air, making pressure waves that travel to our ears which we hear as sound. Reducing the dynamic forces on the housing reduces noise. In idler gear sets, we have an opportunity to affect gear whine by phasing the meshes. Phase is determined by the number of teeth and tooth thickness of the idler. The TE forces acting on the idler from its two meshes add vectorially and sweep out an ellipse as the gears are advanced one tooth. The size of the ellipse (magnitude of force) is related to the noise generated by the gearbox. By cleverly selecting the number of teeth on the idlers, their tooth thicknesses and the idler location, the forces from transmission error force vectors that must be reacted by the idler bearings can be substantially reduced, thereby reducing the excitation on the gearbox that causes noise.