Ultrasonic gas flowmeter as well as device to measure exhaust flows of internal combustion engines and method to determine flow of gases

Abstract

An ultrasonic gas flowmeter includes a measuring pipe with flowing gas, transmitting and receiving sound transducers, transmission and reception electronics, and evaluation electronics. The sound transducers () are designed as capacitive electro-acoustic ultrasonic transducers to construct a flowmeter with improved capacity, especially in view of temperature stability and the reduction and consideration of a temperature profile. Devices () are provided to level the gas temperature profile and to minimize the influence of the temperature profile on the flow measurement. A more accurate and dependable detection of the volume flow or the mass flow of gases is to be achieved, especially in highly dynamic flows, for the method of determining the flow of gases whereby the mean flow velocity is determined and the flowing gas quantity is determined with highly synchronized resolution from the two transit times of two acoustic signals. In addition, an assessed value is computed () for the flow after the determination of the transit times and the assessed value is corrected at least by means of a characteristic temperature of the gas and the temperature of the wall of the measuring pipe ().