Measuring and testing – Simulating operating condition – Marine
Patent
1992-04-01
1993-09-07
Myracle, Jerry W.
Measuring and testing
Simulating operating condition
Marine
G01M 1500
Patent
active
052418570
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for correcting a measuring error of a hot-film air-mass meter occurring as the result of backflow.
BACKGROUND INFORMATION
Hot-film air-mass meters can be used to detect the air mass drawn in by internal-combustion engines. These meters have a heated element, which is situated in the air flow to be measured and is cooled in this manner. In particular, it is possible to use the heated element as part of an electric bridge circuit and to keep it at a constant overtemperature relative to the intake air temperature by means of a current flowing through this element. With this principle, the required heating current is a measure for the air mass drawn in by the engine. The pulsations of the intake air, which possibly occur in certain operating ranges of an internal-combustion engine, can cause the measuring result to be corrupted. This is particularly the case when a so-called backflow occurs, since the hot-film air-mass meter cannot distinguish the direction of flow.
It is generally known to provide a hot-film air-mass meter with an evaluation circuit, so that a backflow can be recognized using programming technology. A high computing power is required for this. The backflow is recognized from the evaluation of the signal waveshape.
Furthermore, when backflows occur, it is known to adjust the output signal from a hot-film air-mass meter with a correction value. In certain operating ranges, however, only a very inaccurate result is able to be attained.
SUMMARY OF THE INVENTION
In contrast, the method according to the present invention has the advantage that even when backflows occur, there is a high degree of accuracy in detecting the air mass and thus the load value of the internal-combustion engine. It is not necessary to evaluate the signal waveshape, which is relatively costly and requires an appropriate computing capacity. Rather, the air mass measured with the hot-film air-mass meter is defined as a first value and compared to a second value, which is determined using another independently working method for determining air volume. Dependent upon the operating range existing at the time, either one or the other value is drawn upon as a valid variable that determines the air mass. Preferably, the air mass is determined per stroke of the internal-combustion engine, which, in the case of the internal-combustion engine provided with an injection system and stoichiometric combustion, is proportional to the injection time of the injection valves bringing in the fuel. In order to always be able to adapt individually to the conditions existing at the time, in accordance with the present invention, a correction signal is extracted in at least one backflowfree operating range from a comparison of the first and the second value and used to correct the second value in operating ranges that have backflow. Thus, the present invention involves applying the value acquired by the hot-film air-mass meter in certain operating ranges and, in other operating ranges in which the value acquired by the hot-film air-mass meter is inaccurate, working with another value that had been determined on the basis of a different method for determining air volume, whereby errors occurring with the mentioned method for determining air volume are corrected using an adaptation method. The correction signal which enables the adaptation is extracted thereby by comparing the first and the second value in an operating range which is free of backflow. The invention therefore makes use of the realization that no backflow occurs in certain operating ranges, so that the hot-film air-mass meter supplies correct data. These data constitute the basis, namely a calibration value, for the result determined according to the second method for determining air volume. In this respect, in ranges in which the hot-film air-mass meter supplies results which are inaccurate due to backflow, a very high accuracy is achieved by means of the adaptation according to the present invention with a meth
REFERENCES:
patent: 4571990 (1986-02-01), Honig
Hirschmann Klaus
Junginger Erich
Schnaibel Eberhard
Myracle Jerry W.
Robert & Bosch GmbH
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