Abstract
Today a passenger car’s engine represents one of the main sources for the occurring in-car vibrations and noises. Forces resolving from the oscillating parts and the combustion processes lead to a revolution speed dependent spectrum of excitations. The engine’s mounting points can be considered as discrete paths for the transmission of this unwanted structure-borne noise, which is inducted into the car body and spreads all over the passive structure. Although the ratio of electrical powering systems in new powertrain concepts will increase in future trends - which will reduce the emitted noise levels - the number of full electrical driven cars on road will grow slowly. Due to their high energy density, fossil or synthetic fuels will still be used in combustion machines for probably several decades. Combinations of the powering concepts as in hybrid cars will bring up new challenges to fulfil the demands on comfort.
The authors propose an approach to a dynamic mounting interface based on piezoelectric elements which gives the opportunity to attenuate the transmitted vibrations and thus reduce the level of excitation for the passive car structure. It consists of passive rubber elements to support the static loads of the engine’s mass on the one hand, and piezoelectric actuators to attenuate the dynamic loads from the combustion processes and from the oscillating motor parts on the other. The chosen setup has nonlinear system behaviour for various engine load scenarios which is linearised for certain operating points, defined by the deflection of the mount. One of the key factors for the performance of the active mount is the design of the implemented controller. This paper focuses on the developed control strategies for the nonlinear interface. First a feedback control algorithm, that uses a self-sensing piezo approach to determine the mount device’s state of force, is introduced. The applied current on the actuators is used as a force related quantity to be feed back to the controller. This configuration reduces the number of additionally required sensor systems and thus the costs of the device. Another opportunity of sensing the dynamic forces is proposed, which uses strain gauges applied directly onto the piezoelectric elements. Both methods are tested experimentally on a model of the proposed active mount. The results are presented and discussed. Finally an outlook in further research regarding alternative controller designs is given.
KEYWORDS: active mount, vibration control, self-sensing actuator, structure-borne noise, nonlinear system