Design of an active exhaust attenuating valve for internal combustion engines

An active silencer to attenuate internal combustion engine exhaust noise is developed. The silencer consists of an electrically controlled valve connected to a buffer volume. The pulsating flow from the engine is buffered in the volume and the valve resistance is continuously controlled such that only the mean flow passes to the atmosphere. This flow is free of fluctuations and consequently free of sound. The design of the active silencer is carried out using electrical analog circuits. First, the interaction between the active silencer and the engine will be studied using an analog circuit including the combustion engine and a linearized active silencer. Then, a detailed valve model is built in a separate electrical analog circuit. It includes the electrical, the mechanical and the flow-dynamic properties of the actuator valve. The actuator valve concept is then simulated, from which a prototype can be constructed. The active silencer has been tested on a cold engine simulator. This device generates realistic exhaust noise with the associated gas flow using compressed air. The silencer can attenuate pulsations from engines at very low revolution speed, without passive elements preconnected between the engine and the active silencer. This is not possible using loudspeaker based active silencers.