ACTIVE CONTROL OF GEARBOX VIBRATION Brian Rebbechi Carl Howard Colin Hansen Airframes and Engines Division Aeronautical and Maritime Research Laboratory Melbourne, Victoria Australia Department of Mechanical Engineering University of Adelaide Adelaide, South Australia Australia Department of Mechanical Engineering University of Adelaide Adelaide, South Australia Australia ABSTRACT Active vibration control was successfully applied to the meshing of gear teeth inside a gearbox to reduce the vibration at the mounting points of a gearbox and the radiated sound pressure level. Magnetostrictive actuators inside the gearbox were used to move the shaft on which the input pinion was mounted, which in turn modifies the kinematic meshing behaviour of the gear teeth. An adaptive feedforward controller was used to determine the correct amplitude and phase of the force the actuators applied to the shaft to minimize the vibration at the feet of the gearbox housing. The vibration was attenuated by 20-28dB at the 1x, 5-10dB at 2x and 0-2dB at 3x gear mesh frequencies, by simultaneously minimizing the first 3 harmonics of the gear mesh frequency. INTRODUCTION In the field of transmission design, it may be advantageous to reduce the vibration transmission into the support structure. Designers often use helical or herringbone shaped gear teeth in gearboxes because they result in lower vibration levels compared to spur shaped gear teeth. Once the gear tooth shape and the manufacturing process and precision has been chosen, the resulting vibration that the gearbox exhibits is accepted as inherent and it is then left to a vibration engineer to select suitable isolators to reduce the vibration transmitted into the support structure. However even with well designed isolators there will always be some residual vibration that is transmitted into the support structure. If the source of the vibration in the gearbox can be reduced, then there will be less residual vibration in the support structure. There are essentially three mechanisms responsible for the generation of noise and vibration by gear teeth. If the transmitted force between the teeth varies in amplitude, direction or position, then the gears will vibrate and will generate noise. These mechanism occur when there is friction between the teeth, poor surface finish on the mating parts, an imperfection in the tooth profile or a transmission error, which is the relative displacement between the gear teeth [1]. This paper describes an experimental gearbox that can reduce the transmission error and the