Active vibration control of a mounting bracket for automotive gearboxes

The aim of this paper is to investigate the use of active vibration control in automotive gearboxes mounting brackets to reduce tonal disturbances. A combination of piezoelectric accelerometers and an internally preloaded piezo stack actuator is used to counteract their unbalanced caused vibrations. Initially, a numerical modal analysis was carried out to identify the normal modes in the frequency range of interest. The piezo stack was simulated by a ROD element and its effect numerically characterized. The upper and lower faces of the stack were mechanically coupled with the bracket structure, whereas the active control strategy involved the relative displacement of two opposite points of the bracket. To this aim, dedicated interfaces were designed to integrate the stack into the mounting bracket. In order to control the vibrations in correspondence of the second bending mode (1599.4Hz), the primary disturbance, simulated by a shaker, was modelled in the frequency domain using a white noise signal. A narrow window of 20Hz was initially selected as the control system domain. Then, this frequency range has been made gradually wider around the resonance peak, in order to optimize the control effect, and then extended up to 80 Hz when undesired effects occurred. Primary and secondary control plants were firstly numerically fitted from the measured responses and excitations using system identification techniques, and then used for the active controller design and simulations.