Gearboxes are typically sources of vibration, either because they are in the transmission path from the engine to the structure so they transmit vibration coming from the engine or they transmit their own vibration at the gear mesh frequency and its corresponding side-bands. The latter can be heard as a whining noise coming from the gears. The level of whining noise can be exacerbated if the gear mesh frequency matches one of the natural frequencies of any of the components or subsystems in the transmission path. In vehicular applications, rear axle gear whine noise is caused mainly by the gear mesh vibration in the powertrain. This vibration is in turn transmitted thru the rear axle gear housing, the corresponding sub-frame, as well as other support structures to the vehicle cabin as an unpleasant tonal noise dubbed gear whine.
Active vibration control, using proof mass actuation of the rear sub-frame was used to mitigate gear mesh vibration in an all-wheel drive test vehicle exhibiting whine noise at around 450 Hz. Proof mass actuators (PMAs) generate force by pushing against a suspended mass and thus do not need an anchor point.
The effectiveness of active control in absorbing the shaker induced vibration of rear sub-frame of a test car was successfully demonstrated by examining the extent of reduction in the vibration of the rear sub-frame as well as the sound pressure inside the vehicle. Two electromagnetic proof mass actuators, mounted on the rear sub-frame of the vehicle, were used as the active elements. An accelerometer placed next to each actuator was used as the feedback sensor. Moreover, rolling dynamometer tests showed the effectiveness of active control in substantial reduction in vibration of the rear sub-frame and pressure inside the cabin caused by the rear differential gear mesh.