1. Field of the Invention
The invention relates to a measuring device for recording a gas mass flow of an internal combustion engine. The measuring device includes a sensor element which is used to record the gas mass flow and an evaluation circuit which is connected downstream of the sensor element.
2. Description of the Related Art
Such a measuring device is disclosed in U.S. Pat. No. 4,986,243. The known measuring device comprises a sensor element which is composed of a heating element and a temperature sensor. The current through the heating element is set in such a manner that the temperature difference between the heating element and the temperature sensor remains the same. In this case, the current flowing through the heating element is a measure of the air mass flow. Such measuring devices are generally arranged in the intake section of internal combustion engines in which an air/fuel mixture is caused to explode under compression. In this case, the power output from the internal combustion engine depends on the ratio of fuel mass to air mass. In order to control the engine, it is therefore very important to accurately determine the air mass which is drawn in.
Different aging effects which may result in signal distortion occur during operation of the known sensor elements. These aging effects may be caused by deposits of dirt or material drifts. Since the demands imposed on the level of pollution of the exhaust gas are becoming increasingly strict, the signal distortion due to the different aging effects cannot be accepted.
U.S. Pat. No. 4,754,650 also discloses a measuring device which can be used to determine the gas mass flow with the aid of ultrasound. Two ultrasound transducers which are opposite one another and emit an ultrasound signal that is transverse to the direction of flow of the gas mass flow are provided in the known measuring device. The propagation time of the ultrasound signal in the direction of flow and counter to the direction of flow can be used to infer the gas mass flow. This type of known measuring device is also subject to aging phenomena. So that the aging phenomena can be compensated for, the aging phenomena must be able to be quantitatively recorded.