Abstract
The vibration and in-car noise level of a car body strongly depends on the excitations coming from the combustion engine. Its moving parts and the combustion processes cause a permanent broadband vibration input into the passive structure. The engine’s suspension points can be considered as discrete transfer paths for these forces. Today commonly used passive or semi-active mounting systems are barely able to meet the optimal engine suspension’s demands on stiffness and damping. To improve the reduction of transmitted disturbances, the concept of an active engine mount which uses piezoelectric actuators was developed. Passive elastomers and active piezoelectric elements are arranged in a parallel setup that has geometrically caused nonlinearities.
This paper introduces an adaptive design for broadband feed-forward control of the mount’s actuators in the frequency range up to several hundreds of Hz. Based on experimental data gathered from an 2.0 litre four cylinder common rail diesel engine test bench, the analysis of occurring mounting forces and motions results in an operating point dependent system behaviour for the motor dynamics. Due to this load condition dependencies and the mount’s nonlinearity, the controller scheme has to adapt its parameters according to the engine’s revolution speed and load torque. To provide the required tuning parameters for the controller, available signals from the engine management system are used, whereas the torque is calculated from online cylinder pressure measurements.
In constant driving conditions, the presented controller design can attenuate the transmitted excitations from a source of disturbances in the lower acoustically relevant frequency band and thus reduce the vibration and noise level of an attached structure. Using the Matlab/Simulink simulation environment, simulations of the designed controller over a large revolution speed range at various load torques have been made. The results are compared and evaluated with experimental tests on a downscaled model of the active mount. The developing process was based on the concept of rapid control prototyping. A final conclusion and outlook in further research is given.
Keywords: active mount, vibration control, H-infinity controller, structure-borne noise, nonlinear system