Measuring and testing – Simulating operating condition – Marine
Patent
1996-02-13
1998-05-12
Dombroske, George M.
Measuring and testing
Simulating operating condition
Marine
732025, 7320411, 36443103, 36443104, F02D 4118, F02D 4500, G01F 168, G01F 172
Patent
active
057508895
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an air flow rate measuring apparatus with a thermal air flow meter which is used in, for example, an electronic fuel injection system for a vehicle engine, and more particularly to an air flow rate measuring apparatus and measuring method to which a signal processing method for accurately measuring a pulsating flow rate is applied.
BACKGROUND ART
A thermal air flow meter is arranged, for example, on the upper stream side of the intake duct of an engine above a throttle and is used for the purpose of measuring an intake air flow rate of vehicle engine having an electronic fuel injection system. In this kind of thermal air flow meter, a situation can occur where an air flow sensor for a vehicle having a slow response exhibits an abnormally lowered value of the detected flow rate due to an influence caused by a pulsation flow which is generated in the intake duct in a state in which the throttle opening angle is large or in a state in which a load is large. This is disclosed by JP-B-59-17371. It is explained that the lowering is mainly caused from the slow response of the sensor and the non-linear output characteristic thereof it is further explained that the problem of lowering can be avoided by using a fine hot wire which has a high-speed response or a linearizer by which the output is linearized at a high speed. In the thermal air flow meter disclosed by the JP-B-59-17371, a compensation is made for the lowering of the detected flow rate by detecting the full amplitude of the pulsating sensor output, multiplying the detected amplitude value by a correction factor and adding the result of multiplication to the value of a mean output.
The compensation for a signal in the thermal air flow meter is roughly classified into two ways. An example disclosed by SAE Paper No. 880561 or SAE Paper No. 940377 uses a model of the thermal air flow meter in which a response delay is added to a variation in flow rate and a non-linear output characteristic is further added so that the value of addition is taken as the output of the thermal air flow meter. Also, an example disclosed by JP-B-6-13859 or JP-A-4-358743 uses a method in which signal processing for compensating for a response is performed for the signal of a thermal air flow meter having a slow response to determine a true flow rate. In this method, the signal is transformed to a flow rate by use of a linearizer prior to an inverse transformation for response compensation and the inverse transformation is thereafter performed to compensate for the response. In substance, both the methods disclosed by JP-B-6-13859 and JP-A-4-35873 perform the inverse transformation in a model of the thermal air flow meter. The inverse transformation is a signal processing operation for correcting the response delay of the input/output characteristic of the system. By the inverse transformation, the output is transformed so that it becomes the same in amplitude and phase as the original input signal.
The outline of the model of a thermal air flow meter shown in FIG. 1 of the SAE Paper No. 880561 is shown in FIG. 15. In this model, a pulsating flow rate is first added with a delay 501 caused by the heat capacity of a thermal element and the transfer of heat to a base material and is further added with a non-linear output characteristic 502. Also, in a mathematical model shown by equation 8 and equation 8b of the SAE Paper No. 940377 and dealing with a model similar to that in the SAE Paper No. 880561, the ultimate output signal waveform is a waveform which is smoothed by the addition of the first-order response delay to the flow rate waveform and is further added with a non-linear output characteristic.
In the models disclosed by the JP-B-6-13859 and the JP-A-4-358743, a true variation in flow rate is determined by processing the output signal in a sequence reverse order to that in the above-mentioned example. The outline of the inverse transformation signal processing is shown in FIG. 16. In this model, the output of a thermal air
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Arai Nobukatsu
Kobayashi Chihiro
Kowatari Takehiko
Dombroske George M.
Hitachi , Ltd.
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