Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1998-12-18
2001-11-20
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C073S001340, C702S183000
Reexamination Certificate
active
06321165
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an air flow meter comprising a heating resistor provided in an air passage. The flow of air is measured, and a constant temperature control circuit keeps the temperature of the heating resistor at a predetermined value by controlling a current supplied to the heating resistor. The invention particularly relates to a heating resistor type air flow measurement apparatus suitable for the measurement of the intake air flow in an automobile engine.
In recent years, a method of controlling the amount of fuel supplied as a function of intake air flow has generally been used in engines (internal combustion engines) for automobiles. In such a control method, an air flow meter is widely used. A heating resistor type air flow measurement apparatus is one such air flow meter, and today, is in mainstream use.
An output signal of the heating resistor type air flow measurement apparatus is supplied, for example, to an ECU (engine control unit) of an automobile. The output signal is supplied, for example, to control the amount of fuel supplied to the engine. While the output signal is supplied, it is necessary to perform predetermined adjustment of an air flow signal or calibration.
By calibration is meant scale matching of instruments and adjustment so that the zero point and the spun (sensitivity) fall within predetermined specification ranges.
In the prior art, the flow-detection characteristics of each heating resistor type air flow measurement apparatus is checked and adjusted so as to fall within a range of specifications before product-shipment.
A resistance trimming method of adjusting a value of the resistance of a resistor is widely used today as such an adjusting method. By using the resistance trimming method, the zero point and the spun are adjusted so that the measurement output may fall within the range of specifications.
An alternative to the resistance trimming method is described in U.S. Pat. No. 4,669,052. This alternative is described as “an electronic trimming” or a multi-points correction method which uses digital data.
In the multi-points correction method, correction is made by using the digital data instead of the resistance value of a resistor. A map in which the predetermined data are stored is retrieved, an air flow is corrected by obtaining an air flow value and a flow error, and a signal indicative of the correct flow is output.
The characteristics of the flow correction data QaMap (q,a,b) used are checked for every apparatus, after product completion, and the data required to correct the error are calculated and maintained. The correction processing by the flow correction data QaMap (q,a,b) corresponds to the adjustment processing in resistance trimming. The trimmed and calibrated flow value is obtained as an after-correction flow value QaRef.
In the prior art, the flow correction data QaMap (q,a,b) for trimming are stored in the primary memory means, for example, before product shipment. The flow correction data QaMap (q,a,b) are read from the primary memory means when the operation of the apparatus is started up; for example, these data are read when turning the power switch on. The flow correction data QaMaP (q,a,b) read are stored in the predetermined memory set on a program area or the secondary memory means to be used as a Q map.
As the primary memory means, for example, EEPROM (Electrically Erasable/Programmable Read Only Memory) is used. This is a kind of nonvolatile memory which makes it possible to read/write data at any time.
In the above-mentioned prior art, the reliability of the flow correction data stored in the secondary memory means is not taken into consideration. There is, therefore, a problem in that an abnormal measurement flow value is output, as it is, even when the flow correction data become abnormal.
If the secondary memory is set on the program area, then the probability that the table data (Q map) stored in the secondary memory means to correct the flow will become abnormal is low. However, there is a possibility that the data set before product shipment will change, because the original flow correction data stored in a memory, such as the EEPROM or the primary memory means, can possibly be read/written after product installation.
Therefore, a write-protect for the data is provided, except for the adjusting step for the product. In the above-mentioned prior art, however, the data are read from the EEPROM, for example, when turning the power on. Consequently, there is fear that the data are written erroneously. As a result, the flow correction data actually used in the correction process may become abnormal.
When the data are read erroneously, the data for use in the correction of the flow error become abnormal, and thus suitable correction can not be made. As a result, the output value of a sensor (data after correction) does not fall within the range determined by the specifications, and the control of an engine becomes abnormal.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a heating resistor type air flow measurement apparatus using an electronically trimming method in which the occurrence of a flow error caused by an abnormality in the flow correction data can be prevented in advance, and in which a suitable flow value, with error-correction, is output at any time.
According to one aspect of the present invention, in a heating resistor type air flow measurement apparatus, flow correction data are read out from a predetermined primary memory means and stored in a secondary memory means. An air flow signal is then calibrated, by the flow correction data stored in the secondary memory means, when starting the apparatus up. The apparatus comprises a diagnosis means for determining whether or not the flow correction data stored in the primary memory means are correct. The determination processing of the flow correction data by the diagnosis means is performed at least at the starting-up point of the apparatus.
According to the diagnosing method of the present invention, it is possible to determine whether or not the flow correction data actually used for the correction are abnormal. As a result, there is no fear that an engine control based on the abnormal flow correction data will continue.
REFERENCES:
patent: 4375667 (1983-03-01), Buchan
patent: 4404846 (1983-09-01), Yamauchi et al.
patent: 4669052 (1987-05-01), Bianco
patent: 4719794 (1988-01-01), Ruiz
patent: 5050562 (1991-09-01), Ishii et al.
patent: 5107812 (1992-04-01), Takamoto et al.
patent: 5469750 (1995-11-01), Lloyd et al.
patent: 5638788 (1997-06-01), Sanvido et al.
patent: 6151547 (2000-11-01), Kumar et al.
Kanke Atsushi
Ohta Kenji
Crowell & Moring LLP
Hitachi , Ltd.
Hoff Marc S.
Raymond Edward
LandOfFree
Air flow measurement apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Air flow measurement apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Air flow measurement apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2598753