Knut Schmidt

Vibration reduction on automotive shafts using piezoceramics

This paper reports an experimental study on active vibration reduction for automotive shafts with the use of piezoelectric material. The work focuses on an axle of an Audi A2. The demand in the automobile sector for higher comfort in the vehicle is of a great importance alongside the requirements of lighter weight and low fuel consumption. These requirements are typically in conflict with each other. One solution is the use of intelligent materials instead of viscoelastic materials and proof mass absorbers. These solutions are quite heavy especially at low frequencies. Active vibration control and piezoelectric devices are advantageous in this application due to their low mass to performance ratio. Our research study explores the use of such piezoelectric devices for an axle. In conjunction with electronics it will reduce vibrations in the first natural bending mode of the axle. Laboratory tests simulated the condition present in the road. At first a stationary set up was used, then a simulated disturbance was input at the attachment points of the shaft. Finally, a test with rotating shaft was performed. Piezoelectric devices (custom QuickPacks from ACX, a Division of Cymer) were used as sensors and as actuators to properly control the axle during the different operating conditions. The power consumption of each actuator pair was less than 20W. The work described here details the test setup, the control strategy, the hardware implementation as well as the test results obtained.

Narrow and broadband sound reduction in automotive panels

The possibility of using active control to reduce the sound radiated from a thin automotive panel between 30 and 250 Hz was explored. A steel panel representing a typical automotive application was selected, and QuickPack piezoceramic actuators were bonded on one side of the panel as a disturbance source, with inputs ranging from single-frequency sine wave to broadband band-limited white noise. A finite element model was created to determine the best sound radiating modes within the frequency band of interest, calculate mode shapes and determine the optimal location and size of the control actuators and sensors. Custom QuickPack devices were selected and bonded based on the results of the FEM. Optimal control laws were determined, using system models based on control and disturbance transfer functions. For narrowband control an inductive shunt was designed, where the kinetic energy generated when the plate moves is dissipated in a resonant RLC electric circuit. Also, both narrowband and broadband multiple input - multiple output (MIMO) control algorithms with two sensor and two actuator channels were designed and implemented on a digital signal processor (DSP). The overall sound radiated from the plate was reduced by 3dB RMS between 30-250Hz, while the peak sound reduction obtained at the target mode was 24dB.