JP2007139793A - Gas flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means suitable for high integration of an electronic circuit in a gas flowmeter and high precision of output characteristic regulation. <P>SOLUTION: This gas flowmeter is constituted of a noise reduction circuit for reducing an overvoltage impressed to an electric power source, a surge and a high-frequency noise, a gas flow rate detecting circuit, and a digital regulation circuit. Nonlinear regulation is also allowed therein by selecting a regulation operation expression by a linear expression prepared preliminarily, based on an input value, in the regulation computation. The number of terminals is reduced by using a sensor output route and a data input/output route in common in an integrated circuit, and by providing a means for changing over the both routes by a switch. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas flow meter for controlling an automobile, and particularly suitable for achieving high integration of an electronic circuit, a noise reduction circuit, an adjustment method, a reduction of adjustment terminals and output terminals, and a gas flow rate having an output circuit. Regarding the total.

  There is a gas flow meter that detects the air flow rate of an internal combustion engine. As an example of the gas flow meter, there is a constant temperature control hot-wire gas flow meter described in Non-Patent Document 1. FIG. 25 shows a schematic configuration of a gas flow rate detection circuit DECT1 to which this configuration is applied. The gas flow rate detection circuit mainly includes an operational amplifier OP1, a power transistor Tr1, a heating resistor Rh also called a hot wire or a hot wire, a gas temperature measuring resistor Rc and resistors R1 and R2 also called a cold wire or a cold wire. In this configuration, the temperature of the heating resistor Rh is always constant, that is, the resistance value is constant by maintaining the bridge balance with the operational amplifier OP1.

  In this flow rate detection circuit DECT1, since the heat radiation from the heating resistor Rh increases as the gas flow rate increases, the heating current increases. Since this heating current is proportional to the voltage across the resistor R1, the gas flow rate can be detected by measuring this voltage. The voltage output converted by the current detection resistor R1 is processed by an adjustment circuit having predetermined input / output characteristics so as to obtain the required output signal characteristics of the gas flowmeter.

  In addition, as shown in FIG. 26, there is a feeling that the gas flow temperature is measured so as to be affected by the heat from the heating resistor Rh upstream and downstream of the heating resistor of the constant temperature control hot-wire gas flow meter. There is also a flow rate detection circuit DECT2 having a configuration in which the temperature resistors Ru and Rd are arranged and connected in series. Depending on the gas flow rate, the upstream temperature sensitive resistor Ru is cooled to lower the resistance value, and the downstream temperature sensitive resistor Rd receives the gas flow warmed by the heating resistor Rh, and the temperature rises to increase the resistance value. Will rise. Accordingly, since the potential at the connection point between the temperature sensitive resistors Ru and Rd changes, the gas flow rate can be detected by measuring this voltage.

  Further, as shown in FIG. 27, the gas flow temperature is measured so as to be influenced by the heat from the heating resistor Rh upstream and downstream of the heating resistor Rh of the above-mentioned constant temperature control hot wire gas flowmeter. Two temperature sensitive resistors are arranged in pairs, and a pair of resistors Ru1 and Rd1 are connected in series in the upstream and downstream order, and a pair of resistors Rd2 and Ru2 are connected in series in the order of downstream and upstream. As a configuration, there is also a flow rate detection circuit DECT3 configured to measure a potential difference between connection points. In accordance with the gas flow rate, the upstream side resistors Ru1 and Ru2 are cooled to lower the resistance value, and the downstream side resistors Rd1 and Rd2 receive the gas flow warmed by the heating resistor Rh, and the temperature rises to increase the resistance value. Will rise. Therefore, since the potential difference of the bridge changes, the gas flow rate can be detected by measuring this voltage difference.

  By the way, various surges and overvoltages are applied to an electronic circuit that adjusts the output characteristics of a gas flow meter mounted on an automobile as defined in the standards of Non-Patent Documents 2 and 3. These standards are designed to prevent electronic circuits from malfunctioning or failing due to surge voltage generated by engine ignition, overvoltage due to battery stacking when the engine is started in cold weather, and high-frequency noise generated from various electronic devices. It is established for the purpose of making. On the other hand, electronic circuits have been integrated in order to reduce manufacturing costs, and more recently, in order to comply with exhaust gas regulations, it has become necessary to improve the accuracy of gas flowmeters corresponding to higher functionality of engine control. It is coming. Since automobiles have a wide operating temperature range of −40 ° C. to 130 ° C., it is necessary to prevent changes in output with respect to temperature changes.

  Conventionally, various overvoltage protection circuits have been used for surges and overvoltages. As an example, there is a circuit using a Zener diode ZD and a current limiting resistor R shown in FIG. The circuit of FIG. 28 is a kind of a general constant voltage circuit, and a current applied to the Zener diode ZD via the current limiting resistor R is caused by the voltage applied to the connection terminal VBB to the battery. Even when is applied, the voltage at the power supply terminal Vcc to each part of the circuit is clamped by the Zener voltage of the Zener diode ZD, thereby providing overvoltage protection.

  For example, according to Patent Document 1, an overvoltage detection circuit using a resistor and a Zener diode and an overvoltage protection circuit using a switching circuit formed of a bipolar transistor have been proposed as conventional techniques. The overvoltage protection circuit described here is for the protection of microwave FETs (field effect transistors), and an overvoltage higher than the sum of the zener voltage of the zener diode and the base-emitter voltage of the switching transistor is applied to the power supply receiving terminal. When this occurs, the switching circuit is operated to disconnect the load from the power supply line so that overvoltage is not applied to the load.

  Next, it is necessary to adjust the zero point and span (output range) so that the voltage output of the flow rate detection circuits DECT1 to DECT3 in FIGS. Currently, analog circuits are mainly used for this adjustment circuit, but it is considered that adjustment can be made with high accuracy by digitization.

  Table 1 shows a comparison between an analog circuit and a digital circuit (see Non-Patent Document 4).

アナログ回路は、デジタル回路と比較して、回路が小型であり、低消費電力であるが、抵抗などの素子を用いているため、製造ばらつきが生じ、また、経年変化による変化が生じるため、デジタル回路に比べ精度、安定性の点で劣る。一方、デジタル回路は、アナログ回路と比較して、精度、安定性に優れるが、回路が大きく、消費電力も大きくなる。しかし、近年の集積回路製造技術の急速な進歩により、微細加工が可能となったため、回路が小型化され、消費電力も小さくなり、様々な産業分野に応用されている。気体流量計にデジタル調整回路を適用した例としては、特許文献２、特許文献３、特許文献４などがあげられる。

Analog circuits are smaller and have lower power consumption than digital circuits, but they use resistors and other elements, resulting in manufacturing variations and changes due to aging. It is inferior in accuracy and stability compared to the circuit. On the other hand, the digital circuit is more accurate and stable than the analog circuit, but the circuit is large and the power consumption is large. However, recent advances in integrated circuit manufacturing technology have enabled microfabrication, resulting in smaller circuits and lower power consumption, and are being applied in various industrial fields. Examples of applying the digital adjustment circuit to the gas flow meter include Patent Document 2, Patent Document 3, and Patent Document 4.

  Table 2 shows a comparison between analog adjustment and digital adjustment as an adjustment circuit for the gas flowmeter.

アナログ調整の概略回路構成は、演算増幅器ＯＰ２、トリミング抵抗Ｒｓ１、Ｒｚ１、抵抗Ｒｓ２、Ｒｚ２からなり、流量検出回路ＤＥＣＴからの電圧出力を、トリミング抵抗Ｒｚ１、Ｒｓ１をトリミングすることによりゼロ点、スパンを調整し、所望の気体流量に対する出力を得る回路である。トリミング抵抗Ｒｓ、Ｒｚとして、ハイブリッドＩＣ上に印刷された厚膜抵抗やＩＣ上の薄膜抵抗がある。

The schematic circuit configuration of the analog adjustment includes an operational amplifier OP2, trimming resistors Rs1, Rz1, resistors Rs2, Rz2, and the voltage output from the flow rate detection circuit DECT is trimmed by trimming resistors Rz1, Rs1 to obtain a zero point and a span. It is a circuit that adjusts to obtain an output for a desired gas flow rate. The trimming resistors Rs and Rz include a thick film resistor printed on the hybrid IC and a thin film resistor on the IC.

  For trimming the resistor, a laser trimmer device or the like is used. However, when trimming is performed with high accuracy, there is a problem that it takes a long time to perform the trimming operation and the trimming cannot be performed again. Further, since only two points are adjusted, it is difficult to perform complicated adjustment such as nonlinear adjustment of output characteristics. Furthermore, in the analog circuit, if the output specification for the gas flow rate changes, the resistance value needs to be redesigned. In some cases, it is necessary to redesign the pattern of the hybrid IC substrate, which increases the design man-hours.

  On the other hand, in the case of a digital adjustment circuit, the output specification can be changed by changing the adjustment coefficient without changing the circuit pattern, so that the design man-hours can be reduced. As this digital adjustment circuit, for example, the method described in Patent Document 2 has been proposed. The general configuration of the digital adjustment is that the voltage output from the flow rate detection circuit DECT is converted to a digital value by the analog / digital converter AD, and then the zero point and span adjustment are performed by calculation by the digital arithmetic unit CALC. It is a circuit that obtains an analog output with respect to a desired gas flow rate by converting it into an analog signal by the DA. The adjustment coefficient in this calculation is stored in a storage device MEM such as a PROM. Further, since the digital arithmetic unit CALC can easily perform non-linear calculations, not only zero point and span adjustment but also non-linear adjustment can be easily performed in the output adjustment. By this non-linear adjustment, the adjustment accuracy becomes ± 2% or less.

  As another example of the digital adjustment, there is a configuration shown in Patent Document 4 above. This configuration is the same as the digital adjustment circuit shown in Table 2, but the oversampling analog-to-digital converter including the delta-sigma modulator is used as the analog-to-digital converter AD to reduce the circuit scale. is doing.

  Furthermore, as another example of the digital adjustment, there is a configuration disclosed in Patent Document 5. The adjustment coefficient for executing the adjustment operation by the arithmetic unit is written in a storage element such as a PROM via a terminal of a digital input / output circuit that communicates with the outside of the sensor. In addition, the publication describes that a cubic polynomial is used as the adjustment calculation.

  As yet another example of the digital adjustment, there is a configuration shown in Patent Document 6. In this configuration, the flow rate signal from the gas flow rate detection circuit is converted into a rectangular wave signal, and the counter is counted up at a certain rate only during the period when the rectangular wave is “1”. An adjustment coefficient is added to this count value and output.

  Further, since the heating current flowing through the heating resistor Rh is not affected by the voltage fluctuation of the supply power source (for example, battery), the voltage output of the gas flow rate detection circuit DECT1 has a non-ratiometric characteristic, but the output of the gas flow meter There are specifications for ratiometric analog output and digital output in addition to non-ratiometric analog output.

  As a circuit configuration for realizing a ratiometric analog output circuit, there is a method described in Patent Document 7. In this circuit, an external ratiometric output reference voltage is divided by two resistors, and the divided voltage is input to an operational amplifier to realize a ratiometric output. By setting the sum of the two resistors to about 10 k ohms, the current to be supplied from the reference voltage is relatively small at about 0.5 mA.

  The digital output circuit has a configuration described in Patent Document 8. This circuit configuration is an integrated circuit in which at least a constant temperature control circuit, a zero point / span adjustment circuit, and a voltage control oscillator are integrated into one chip.

  Furthermore, there is a method described in Patent Document 9 as a configuration in which an analog output and a digital output are associated with each other by a single circuit board. This is because both the analog output terminal and the digital output terminal are provided on one circuit board, both the analog and digital outputs are output to the output connector, and only one of the output signals is selected or used. In this configuration, only one of the output connectors is selectively connected with a wire.

JP-A-9-307361 Japanese Patent No. 3073089 JP-A-8-62010 Japanese Patent Laid-Open No. 11-118552 JP 2000-338193 A Japanese Patent Laid-Open No. 11-94620 Japanese Patent Laid-Open No. 2-85724 JP-A-8-247815 JP-A-5-203475 Journal of Frid Mechanics, 47 (1971), pages 577 to 599 (J. Fluid Mech., Vol 47 (1971), PP577-599). International Standard Organization (ISO) 7637 standard Automotive Standard (JASO) D001-94 Standard Supervised by Satoshi Iwata, CMOS analog circuit design technology, Trikes (1998)

  The above prior art is not optimized when integrating and digitizing circuits to promote cost reduction, downsizing, and high precision adjustment of gas flowmeters. There is such a problem.

  In particular, a C-MOS is used for high integration and digitization of a circuit, but this is weak against surge and overvoltage as compared with a bipolar transistor used in an analog circuit, and it is necessary to take sufficient measures.

  First, in the overvoltage protection circuit, in the circuit of FIG. 28, when the current of the circuit to be connected is large, it is necessary to reduce the resistance value in order to prevent the voltage drop due to the current limiting resistor. In order to increase the electrical resistance of ZD so as to sufficiently withstand overcurrent, the size and cost of parts are increased, which is not preferable.

  Next, in Patent Document 5, nonlinear adjustment is performed by a cubic equation. However, if the nonlinear adjustment is required to be a quartic equation or more, calculation time is increased, and each output characteristic is compared with an ideal characteristic. When there is a steep characteristic change, there is a case where such a polynomial cannot be completely adjusted.

  Next, in the integration of the electronic circuit in the gas flow meter by the digital circuit, at the time of adjustment, it is necessary to write the adjustment coefficient to a writable storage device, so that an additional terminal is required. In addition, there are specifications for ratiometric analog output, non-ratiometric analog output, and digital output as sensor outputs. When integrating circuits, all of these specifications can be supported to reduce manufacturing costs. It is necessary to do so. However, simply adding a terminal as in the method disclosed in Patent Document 6 for these measures causes an increase in chip area, which is not preferable.

  Next, when the adjustment calculation is digitized, a digital / analog converter may be required at the output stage. Since this digital-analog converter includes an amplifier circuit for output to the outside, current consumption is about several mA. When trying to drive a digital-to-analog converter using an external reference voltage for ratiometric output, the digital-to-analog converter cannot be driven if the maximum current supplied from this power supply is small, so the reference voltage must be directly There is a problem that it cannot be connected to the power supply terminal of the digital / analog converter.

  SUMMARY OF THE INVENTION An object of the present invention is to provide means for solving the problems of cost reduction, high integration of electronic circuits, high precision adjustment, digital circuit formation, and miniaturization in the gas flow meter.

  The gas flow meter of the present invention stores a gas flow rate detection circuit that outputs a gas flow rate flowing in a gas passage as a voltage signal, an adjustment circuit that adjusts a voltage output from the flow rate detection circuit, and data for adjustment. The storage device includes a data input / output circuit having two external data communication terminals for writing adjustment data from the outside and for reading data to the outside. The external data communication terminal of the data input / output circuit is also used as an output terminal for the detected flow rate. With such a configuration, the gas flow meter can be reduced in size.

  Preferably, data in which the adjustment circuit reads / writes data between the storage device and the outside after a predetermined number of pulses of 2 pulses or more is input to any of the external data communication terminals of the data input / output circuit It is characterized by having means for shifting to the communication mode. With such a configuration, it is possible to prevent erroneous transition to the communication mode even when pulse noise is applied during normal use.

  The gas flowmeter of the present invention includes a gas flow rate detection circuit that outputs a gas flow rate flowing through the gas passage as a voltage signal, an adjustment circuit that adjusts a voltage output from the flow rate detection circuit, and data for adjustment. When the storage device has a storage device, the storage device includes a data input / output circuit having two external data communication terminals for writing adjustment data from the outside and reading data from the outside. The external data communication terminal of the data input / output circuit also serves as an output terminal for the detected flow rate, and the adjustment circuit is provided with output selection means for switching an output signal, and a ratiometric analog output as the output signal for the detected gas flow rate, It is characterized by taking out non-ratiometric analog output and digital output. With such a configuration, a single gas flow meter can cope with various output specifications and can be standardized, and the manufacturing cost can be reduced.

  Preferably, the output selection means provided in the adjustment circuit is characterized in that the ratiometric analog output, the non-ratiometric analog output, and the digital output circuit are formed on the same integrated circuit. With such a configuration, the circuit can be reduced in size.

According to the present invention, in a digitally adjusted gas flow meter, even if a C-MOS that is weak against surge and overvoltage is used for high integration and digitization, an effect of preventing failure and malfunction can be obtained.
Further, in the overvoltage protection circuit included in the noise reduction circuit of the electronic circuit in the gas flow meter, an effect of suppressing a decrease in the supply voltage from the voltage supply terminal due to a voltage drop due to a current limiting resistor necessary for the overvoltage protection circuit, and a voltage limiter The effect that the circuit can be reduced can be obtained.

  In addition, in the calculation of the characteristic adjustment of the output of the gas flow meter, the calculation is performed by selecting the adjustment calculation formula based on the primary expression prepared in advance according to the input value, so that the calculation time is short and the nonlinear adjustment can be achieved. . Furthermore, the substrate temperature can be adjusted simultaneously.

  In addition, by serving as a flow rate signal output / data input / output route, there is no need for an increase in the number of terminals. It is possible to obtain an effect that can correspond to all specifications of analog output and digital output. Further, the digital / analog converter can be driven even if the maximum current supplied from the external reference voltage is small with respect to the digital / analog converter in the output stage.

  As described above, an optimized integrated circuit and configuration can be provided in the case where the circuit is integrated and digitized in order to promote cost reduction and high-precision output of the gas flow meter.

  Hereinafter, the configuration of a gas flow meter, an integrated circuit, and an adjustment circuit according to the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 shows the configuration of a gas flow meter according to a first embodiment of the present invention. This configuration includes a gas flow rate detection circuit, a digital adjustment circuit, a regulator, and a noise reduction circuit. The gas flow rate detection circuit outputs the gas flow rate flowing through the gas passage as a voltage signal. The gas flow rate detection circuit outputs the gas flow rate flowing through the gas passage as a voltage signal by detecting the current flowing through the resistor arranged in the gas passage and the voltage appearing, for example, as a voltage signal. A flow rate detection circuit DECT1 can be used.

  The voltage output is input to a digital adjustment circuit. As one of the configurations of the digital adjustment circuit, as shown in Table 2 (b), after the voltage output from the flow rate detection circuit is converted into a digital value by the analog / digital converter AD1, the zero point is obtained by the digital arithmetic unit CALC. This is a circuit configuration in which adjustment of the span and the like is performed by calculation and converted into an analog signal by a digital / analog converter DA to obtain an analog output for a desired gas flow rate. Furthermore, the analog / digital converter AD, the digital arithmetic unit CALC, and the digital / analog converter DA are driven, and the regulator is a reference voltage for the analog / digital converter AD and the digital / analog converter DA.

  The noise reduction circuit is a circuit that reduces surge, overvoltage, and high frequency noise and supplies a stable power supply voltage. A part of the digital adjustment circuit uses a C-MOS that can break down due to surge or overvoltage, and it may malfunction due to high-frequency electromagnetic noise generated from various electronic devices. The noise reduction circuit is connected to the power supply terminal via a regulator. Note that a bipolar transistor may be used for part or all of the digital adjustment circuit, and this noise reduction circuit may be connected to the power supply units of various circuits included in the air flow meter.

  As shown in FIG. 2, the noise reduction circuit 100 includes a surge applied to the power supply terminal VBB, an overvoltage protection circuit 101 that protects the gas flow rate detection circuit and the adjustment circuit from an overvoltage, and a high frequency noise reduction circuit 102 that reduces high frequency noise. Consists of. The noise reduction circuit 100 supplies a supply voltage with reduced overvoltage, surge, and high-frequency noise from two or more terminals to circuits Ld1 and Ld2 such as a gas flow rate detection circuit and an adjustment circuit. When the minimum voltages required for the circuits Ld1 and Ld2 are different, the voltages supplied from the voltage supply terminals may be made different.

  Next, an overvoltage protection circuit which is a part of the noise reduction circuit will be described with reference to FIG. The overvoltage protection circuit 103 is composed of a voltage limiter circuit 110, two current limiting resistors Ra and Rb, and diodes D2 and D3, and an automobile battery (storage battery) (not shown) is connected via a power supply terminal VBB and a ground terminal GND. ) Or the like, and DC power that is overvoltage protected is supplied to the circuits Ld1 and Ld2 connected to the two voltage supply terminals Vcc1 and Vcc2.

  The voltage limiter circuit 110 is a circuit in which a current flows when a voltage exceeds a certain voltage, and an overvoltage such as a surge voltage applied between the power supply terminal VBB and the ground terminal GND by connecting a current limiting resistor in series. Clips and absorbs overvoltage energy.

  For example, as shown in FIG. 4, the voltage limiter circuit 110 uses a circuit in which several zener diodes ZD1 to ZD1 to n are connected in series and Nch D-MOS M is added. This is a configuration in which when a voltage higher than that in the Zener diode groups ZD1 to ZDn is applied, the Nch D-MOS M is turned on and a surge current flows. This makes it possible to reduce the Zener diode through which almost no current flows, and to reduce the size. Note that a bipolar transistor may be used in place of the Nch D-MOS of the voltage limiter circuit, or the voltage limiter circuit may be formed of only a Zener diode.

  Returning to FIG. 3, the diode D3 prevents the current from the resistor Rb from flowing into the circuit Ld1 or the current from the resistor Ra into the circuit Ld2, and supplies different supply voltages from the voltage supply terminals Vcc1 and Vcc2. Have a job. For example, as shown in FIG. 5, the diode D3 has a configuration in which a base and an emitter are connected using a bipolar transistor. As a result, the diode can be manufactured in the process of manufacturing the bipolar transistor, so that the manufacturing process can be reduced.

  Here, it is assumed that the resistance Ra is larger than the resistance Rb. If a positive surge voltage that should protect the circuits Ld1 and Ld2 is applied between the power supply terminal VBB and the ground terminal GND, the surge current mainly flows through the current limiting resistor Rb and the voltage limiter circuit 110. The circuit Ld2 is protected from surge. Further, the voltage at the voltage supply terminal Vcc1 becomes almost the same as the voltage at the voltage supply terminal Vcc2 by the diode D3, and the circuit Ld1 is also protected from the surge. On the other hand, when a negative surge voltage is applied, the surge current flows through the diode D2 and the current limiting resistor Rb, and the circuits Ld1 and Ld2 are protected from the surge.

Another configuration is the overvoltage protection circuit 104 of FIG. This is a configuration in which the diode D2 is reconnected to the position of the diode D1 with respect to FIG.
If a positive surge voltage that should protect the circuits Ld1 and Ld2 is applied between the power supply terminal VBB and the ground terminal GND, the surge current mainly flows through the current limiting resistor Rb and the voltage limiter circuit 110. The circuit Ld2 is protected from surge. Further, the voltage at the voltage supply terminal Vcc1 becomes almost the same as the voltage at the voltage supply terminal Vcc2 by the diode D3, and the circuit Ld1 is also protected from the surge. Further, for a negative surge, the surge current flows through the diodes D1, D3 and the current limiting resistor Rb, and the circuits Ld1, Ld2 are protected from the surge.

Another configuration is the overvoltage protection circuit 105 in FIG. This is a configuration in which a voltage limit circuit 111 and a diode D1 are connected in series to a current limiting resistor Ra, and a Zener diode ZD is connected between the voltage supply terminals Vcc1 and Vcc2 with respect to FIG.
If a positive surge voltage that should protect the circuits Ld1 and Ld2 is applied between the power supply terminal VBB and the ground terminal GND, the surge current mainly passes through the current limiting resistor Rb, the Zener diode ZD, and the voltage limiter circuit 111. By flowing, the circuits Ld1 and Ld2 are protected from surge. For negative surges, the surge current flows through the diode D1, the Zener diode ZD, and the current limiting resistor Rb, and the circuits Ld1 and Ld2 are protected from the surge.

  Furthermore, there is an overvoltage protection circuit 106 of FIG. 8 as another configuration. The overvoltage protection circuit 106 includes voltage limiter circuits 110 and 111, two current limiting resistors Ra and Rb, and diodes D1 and D2, and is connected to a battery of an automobile (not shown) via a power supply terminal VBB and a ground terminal GND. DC power is supplied from (storage battery) or the like, and overvoltage-protected DC power is supplied to the circuits Ld1 and Ld2 connected to the voltage supply terminals Vcc1 and Vcc2.

  Here, it is assumed that the minimum voltage and the minimum current required for the circuits Ld1 and Ld2 are different. The current limiting resistors Ra and Rb normally cause a voltage drop due to the current flowing through the circuits Ld1 and Ld2, but the resistance values of the current limiting resistors Ra and Rb are within the minimum supply voltage range required for the circuits 1 and 2. Is increased, the voltage limiter circuit can be reduced and the circuit can be miniaturized.

  By the way, the present invention is particularly suitable when applied to a gas flow meter circuit having a digital adjustment circuit, and a specific example is shown in FIG. Here, the case where the overvoltage protection circuit 103 of FIG. 3 is used will be described. As the circuit Ld1 in FIG. 3, an operational amplifier OP1 which is a part of the flow rate detection circuit DECT1 shown in FIG. 25 is connected. Further, as the circuit Ld2, a regulator REG for supplying a necessary reference voltage to each part of the gas flow meter circuit is connected.

  Since the operational amplifier OP1 controls the power transistor Tr1, the supply current required for the operational amplifier OP1 may be small (assuming about 1.5 mA), but a relatively high supply voltage is required to drive the power transistor Tr1. is there. For example, it is necessary to be able to produce an output of about 5.5V even when the battery voltage is lowered when the engine of an automobile is started and the voltage of the power supply terminal VBB becomes 6V. On the other hand, the regulator REG supplies voltage to the analog / digital converter AD1, the digital arithmetic unit CALC, the digital / analog converter DA, etc. of the digital adjustment circuit shown in Table 2 (b), and the supply current required for the regulator REG. Is relatively large (assuming about 15 mA), but even if the voltage of the power supply terminal VBB drops to 6V, it is only necessary to always output 5V.

  If the overvoltage protection circuit is configured as shown in FIG. 28 and an attempt is made to supply overvoltage protected voltage from one voltage supply terminal to both the operational amplifier OP1 and the regulator REG, the voltage at the power supply terminal VBB is 6V. From the condition that the supply voltage is 5.5 V and the supply current is 16.5 mA, the resistance value of the current limiting resistor R needs to be 30 ohms, for example.

  On the other hand, in the overvoltage protection circuit 103 of FIG. 9, the resistance value can be increased as compared with the general overvoltage protection circuit of FIG. That is, the current limiting resistor Ra has a voltage drop of 0.5 V or less when the current flows 1.5 mA, and the current limiting resistor Rb has a voltage drop of 1 V or less when the current flows 15 mA. 250 ohms and resistance Rb may be 50 ohms. Therefore, since the current flowing through the voltage limiter circuit 110, that is, the energy is reduced, the required electric resistance is reduced, and the voltage limiter circuit 110 can be reduced.

  In addition, some or all of the elements included in the overvoltage protection circuit, the flow rate detection circuit DECT, and the digital adjustment circuit are formed on the same integrated circuit using a BCD (bipolar, C-MOS, D-MOS) process or the like. It is possible to achieve downsizing and reduction in manufacturing cost by integrating in the system. The configuration of the overvoltage protection circuit according to the present invention can be applied in the same way even if the voltage supply terminal Vcc is increased to three or more terminals.

Next, regarding the improvement in accuracy of the adjustment of the sensor output characteristics, with reference to FIGS. 10 to 13, (1) an example of the adjustment calculation in the present invention is compared with (2) the conventional example in which only the zero point and the span are adjusted. I will explain.
FIG. 10 shows an output voltage characteristic with respect to the flow rate in the flow rate detection circuit DECT, and this output voltage is adjusted by the adjustment circuit so as to be (A) ideal output indicated by a thin line in FIG. To do.

  First, (2) in the case of the conventional example in which only the zero point and the span are adjusted, the adjustment calculation formula in the adjustment circuit in FIG. 11 is a linear relationship regardless of the input voltage value. When the output voltage characteristic with respect to the flow rate in the flow rate detection circuit of FIG. (A) The error from the ideal output is shown in (2) of FIG. On the other hand, (1) In the example of the adjustment calculation according to the present invention, as shown in FIG. 11, the input / output characteristics of the adjustment circuit are obtained by dividing the input range of the input voltage signal into two, Different adjustment calculation formulas (in this example, the simplest primary formula) are defined. When the output voltage characteristic with respect to the flow rate in the flow rate detection circuit of FIG. (A) When the error from the ideal output is shown in FIG. 13 in an overlapped manner with the conventional example of (2), it becomes as shown in (1), and it can be seen that the adjustment error becomes small.

  In this example, the input range of the input voltage signal is divided into the simplest two. However, in order to further reduce the adjustment error, the number of divisions may be increased and an adjustment arithmetic expression may be given to each. . For example, when it is divided into four, it is as shown in (3) of FIG. Further, the adjustment calculation formula may be a quadratic or higher-order relational formula to reduce the adjustment error. However, in this case, there is a problem that the circuit scale increases or the calculation time becomes long in digital calculation.

In this example, the error is considered as a quadratic function characteristic, but even if the error is a cubic (or higher) function characteristic or a steep characteristic, the number of divisions can be increased. Adjustment error can be reduced.
Such an adjustment circuit can be easily realized by digitizing the adjustment circuit. An example of this digital adjustment circuit is shown in the digital adjustment of Table 2 (b).

  This digital adjustment circuit converts the voltage output of the flow rate detection circuits DECT1 and DECT2 shown in FIGS. 25 and 26 into a digital value by the analog / digital converter AD1, adjusts and calculates the output characteristics by the digital calculator CALC, The digital / analog converter DA obtains an analog output. The digital arithmetic unit CALC is controlled, and the program for adjustment calculation, the adjustment coefficient necessary for the adjustment calculation formula, and the data temporarily stored for calculation can be written in the read-only memory such as ROM, PROM etc. Stored in a storage device MEM such as a rewritable memory such as a random access memory or an EEPROM, and a readable / writable memory such as a RAM.

  By the way, for an arbitrary differentiable function y = f (x), when a is a constant, and | x−a | is extremely small, f (x) = f (a) + f ′ ( a) It is expressed by (x−a), that is, in the slight change range of x, the arbitrary function can be replaced with a linear expression.

So about Din and Dout,
Dout = F (Din) (Formula 1)
Then, the linear expression Dout = A · Din + B (Expression 2)
Can be replaced. However, since it is not practical to give a linear expression to all Din, and almost the same primary adjustment calculation expression can be used within a certain Din range, the axis of Din is divided into the division points Din ( 1), Din (2),. . . , Din (n) is divided into n, and a first-order adjustment calculation formula for each divided section

を与えることにした。

Decided to give.

  A flowchart of the calculation based on this is shown in FIG. First, k that satisfies Din (k) ≦ Din <Din (k + 1) is searched from Din input to the digital computing unit CALC. Next, the output is adjusted by calling the coefficients A (k) and B (k) from the storage device MEM and performing the calculation according to the adjustment arithmetic expression (Expression 3) by the digital arithmetic unit CALC.

Here, the number n of division points is 2 to the i power. The digital value Din is represented by a binary number and is expressed by m (= n + 1 or more) bits. As for the dividing points, the upper i bits are arbitrary values, and the remaining lower mi bits are all 0. That is, Din (k) is
i bit m−i bit Din (1) = 0 0 0 0 0 0 .... 0 0
Din (2) = 0 0 1 0 0 .... 0 0
:
:
Din (n) = 1 1 1 0 0 .... 0 0 (Formula 4)
And That is, the divided sections are equal. To adjust the sensor output, if the upper i bits of Din are k (binary representation), Din is always Din (k) ≦ Din <Din (k + 1)
It becomes. Accordingly, the coefficients of the adjustment calculation formula are A (k) and B (k). That is, A (k) and B (k) having the higher-order i bits of Din as labels may be read from the storage device and adjusted by the digital arithmetic unit CALC.

Such a search method is effective when the number of divisions increases, because the time required for the search does not change even if the number of divisions increases.
In addition, it is not necessary to uniformly measure n measurement points at the time of adjustment of the gas flowmeter before the adjustment value is written, and measurement is performed at an arbitrary point, and the n adjustment coefficients A (k) and B (k) are Find and write by interpolation.

Further, the straight line approximated by the equal division has a graph relationship shown in FIG. That is, using the remaining lower-order m-i bits of the upper-order i bits used for searching for a section with Din,
Dout = A · (the lower order mi bits of Din) + B (Formula 5)
If this adjustment calculation formula is used, the possibility of overflow in the calculation is reduced.

  By the way, the voltage output V converted by the current detection resistor Rh of the gas flow rate detection circuit DECT and the flow rate Q have a relationship expressed by a quaternary equation as shown in FIG. Here, if it is necessary to output linear output characteristics such as V∝Q with respect to Q, a method of expressing a quaternary expression by linear approximation by increasing the number of divisions can be used. In the case of this gas flow meter, the error due to the quadratic equation and linear approximation is about 3% in 16 divisions, about 0.8% in 32 divisions, about 0.2% in 64 divisions, and about 0.05% in 128 divisions It becomes. If the number of divisions is increased, the error due to the linear approximation of the quaternary equation is naturally reduced and approaches a linear output characteristic with respect to the flow rate Q, but considering the error allowed for the output characteristic of the gas flow meter, the division is 32. It is good to do it above.

Next, adjustment of temperature characteristics will be described.
The temperature characteristics of the gas flowmeter, that is, the change in the output characteristics due to temperature, can be broadly divided into the intake circuit temperature characteristics when the circuit board temperature is constant and the gas temperature changes, and the circuit board temperature when the gas temperature is constant. There are two substrate temperature characteristics (also referred to as module temperature characteristics) when changed. Here, adjustment of the substrate temperature characteristics will be described. As for the intake air temperature characteristic, by appropriately setting the resistance value of the heating resistor Rh, the gas temperature measuring resistor Rc, the resistance temperature coefficient (TCR), and the resistance values of the resistors R1, R2 of the flow rate detection circuit DECT1, Can be small. In addition, since the intake air temperature characteristic is flow-dependent and difficult to completely eliminate, it is difficult to make it completely zero. Can be set to zero.

  On the other hand, the substrate temperature characteristic is mainly caused by the temperature characteristic of the output voltage of the regulator that supplies the reference voltage to the analog / digital converter AD and the digital / analog converter DA. A schematic configuration of a circuit for adjusting the temperature characteristic is shown in FIG. To adjust the temperature characteristics of the digital adjustment circuit shown in Table 2 (b), a temperature sensor TS and an analog / digital converter AD2 that converts the output into a digital value are added and input to the digital arithmetic unit CALC. Yes.

  First, the temperature sensor TS necessary for adjusting the temperature characteristics is arranged in the vicinity of the regulator having the temperature characteristics. As a configuration of this temperature sensor, for example, as shown in FIG. 17, there is a configuration using a constant current source IS and one to several diodes D. For example, when three diodes are connected in series, the output with respect to the temperature change changes at a rate of about −6 to −5 mV / ° C., and the linearity is good.

  Further, if the supply voltage of the regulator changes linearly with respect to the temperature, the temperature adjustment can be performed by a linear expression. Such a regulator is realized by using a band gap reference power supply circuit (band gap voltage source circuit). The schematic configuration of this circuit is shown in FIG. 18, and is composed of two diode-connected transistors Q1 and Q2, an operational amplifier OP3, and resistors R7, R8, and R9.

The current flowing through the transistors Q1 and Q2 becomes a constant ratio determined by the resistance values of the resistors R8 and R9 by using the operational amplifier OP3. At this time, the output voltage of the operational amplifier OP3 is stabilized so that the sum of the base-emitter voltage of the transistor Q2 and the voltage drop of the resistor R7 is equal to the base-emitter voltage of the transistor Q1. The voltage drop across the resistor R7 is equal to the difference between the base-emitter voltages of the transistors Q2 and Q1, which is proportional to the thermal voltage V _T = kT / q, so that the resistors R8, R9 and the transistors Q2, Q1 The flowing current has a first-order positive temperature characteristic.

In general, since the base-emitter voltage has a negative temperature characteristic, the band gap reference power source is the sum of the base-emitter voltage of the transistors Q2, Q1 and the voltage drop of the resistor R7 proportional to the thermal voltage V _T. The reference voltage, which is the output of the circuit, can set a first-order temperature coefficient by changing the resistance values of the resistors R7, R8, and R9. Actually, since each element included in the bandgap reference power supply circuit has a slightly non-linear temperature coefficient, the output voltage of the reference power supply circuit has a slightly non-linear characteristic on the high temperature side with respect to a temperature change.

Since the output of the temperature sensor TS and the supply voltage of the regulator that supplies the reference voltage have a first-order temperature characteristic with respect to the temperature change, the adjustment of the temperature characteristic is performed by the adjustment arithmetic expression (Formula 2) for Din of A and B It is only necessary to add a first-order adjustment term for temperature in the adjustment term, that is, a, b, c, d as coefficients.
Dout = (a · Dtemp + b) · Din + (c · Dtemp + d) (Formula 6)
Is given by

  Therefore, the adjustment calculation expression is a combination of (Expression 3) and (Expression 4), and a (k), b (k), c (k), and d (k) are coefficients.

で与えられる。

Given in.

  In order to adjust the output of the sensor, similarly to the flowchart of FIG. 14, k that satisfies Din (k) ≦ Din <Din (k + 1) is searched, and coefficients a (k), b (k), The output is adjusted by calling c (k) and d (k) from the storage device and performing calculation according to the adjustment calculation formula (Formula 7) by the digital calculator CALC.

In order to further simplify the adjustment for temperature, Dout = (C · Dtemp + D) · (A · Din + B) (Equation 8) using C and D as coefficients instead of the calculation adjustment equation (Equation 6).
It is also good. This formula is an arithmetic formula that first performs an adjustment calculation related to the flow rate and then performs an adjustment calculation related to the temperature.

  Further, since the regulator has a slightly non-linear temperature characteristic, adjustment may be made by changing the arithmetic expression according to the output value of the temperature sensor in the same manner as the flow rate adjustment in order to improve the adjustment accuracy with respect to the temperature characteristic. FIG. 19 shows an example in which (a) an adjustment is made by changing the arithmetic expression depending on the output value of the temperature sensor (here, divided into two), compared with an example of (b) uniform adjustment. Here, it is assumed that the input value to the adjustment circuit is constant, that is, the intake air temperature characteristic is zero and the flow rate is constant. If the example of the adjustment calculation formula for the temperature characteristic of the regulator shown in FIG. 18 is shown in FIG. 19 (1), the output characteristic after adjustment for the temperature characteristic is as shown in FIG.

  Further, the arithmetic expression for adjusting the temperature characteristic may be a quadratic expression or more. Furthermore, in order to adjust the intake air temperature characteristic, it is possible to add a gas temperature sensor and an analog / digital converter and perform the same adjustment calculation as described above.

By the way, if a storage device such as a rewritable EEPROM is used as a storage device for the adjustment coefficient, another vehicle can be obtained by taking out a gas flow meter that can still be used from a vehicle that has become unnecessary and changing the output specifications. Can be used.
In addition, in the manufacturing process, at present, in the adjustment, first, a gas is flowed before the adjustment, the adjustment amount of the output characteristic is determined, and the adjustment is performed. When an EEPROM is used, an adjustment coefficient is written in advance, and the gas flow meter that has become NG in the characteristic confirmation test may be readjusted. That is, by using the EEPROM, there is an advantage that the recyclability is improved and the manufacturing cost is reduced.

  Further, there is a configuration as shown in FIG. 20 as a digital adjustment circuit. This is substantially the same configuration as that of FIG. 16, but is a configuration in which the differential output type flow rate detection circuit DECT3 shown in FIG. 27 is connected to the analog / digital converter AD1. Further, a switch group SWS is added so that the flow rate detection circuits DECT1 and DECT2 shown in FIGS. 25 and 26 can be connected, so that the single-phase input and the differential input can be switched. Further, a frequency output circuit FC is added as an output circuit. The adjustment calculation can be performed in the same way.

  Next, FIG. 21 shows the ratio of input / output terminals for communication necessary for data communication between the flow rate signal output terminal of the gas flow meter and the storage device in which the adjustment data is written, and the flow rate signal output of the gas flow meter. It is possible to output either metric analog output, non-ratio metric analog output, or digital output, and the number of terminals can be reduced by combining the data communication input / output path and flow rate signal output path. It is an example explaining the Example of this invention. The sensor output circuit unit 201 mainly includes a digital / analog converter DA, a frequency output circuit FC, and switches SW1 and SW2.

  A digital value obtained by adjusting and calculating by the digital arithmetic unit CALC is input to the digital / analog converter DA and the frequency output circuit FC. The digital / analog converter DA converts an input digital value into an analog voltage output. The reference of the analog voltage output is a voltage supplied to the digital / analog converter DA, and this voltage is supplied to the voltage generated by the electronic circuit inside the gas flow meter and the ratiometric reference voltage terminal 232 from the outside. It is possible to switch between a non-ratiometric voltage output and a ratiometric output by switching a voltage (for example, a reference voltage of an analog / digital converter of an automobile engine control unit) with a switch SW2. The frequency output circuit FC outputs the input digital value as a desired digital output. The analog voltage output and digital output are switched by the switch SW2. These switches SW1 and SW2 are switched by data stored in the storage device MEM during sensor adjustment.

  In addition, the data input / output circuit unit 202 that transfers data between the storage device MEM that writes the adjustment coefficient and switch switching setting at the time of sensor adjustment and the outside of the gas flow meter mainly includes the number of data bits (8 bits, 16 bits) and a data conversion circuit I / O for converting 1-bit data at the time of data transfer to the outside, and a direction to output a DIRECTION signal indicating whether the data conversion circuit I / O inputs or outputs data Signal output circuit DIR, clock detection circuit CECT for detecting the clock signal input to the CLOCK terminal, switch for switching whether the data signal is input to or output from the data conversion circuit I / O according to the signal from the direction signal output circuit DIR It is composed of SW4.

  A detection signal from the clock detection circuit CECT is input to the data conversion circuit I / O, and the data conversion circuit operates. If the switch SW3 is added and the switch SW3 is switched by this detection signal, the flow signal output path and the data input / output path can be combined into one path in the integrated circuit. In addition, a detection signal is output after a predetermined number of pulses are input to the clock detection circuit CDECT so that the switch SW3 is not erroneously switched due to pulse noise entering the CLOCK terminal.

  FIG. 22 shows an example of a data timing chart during data input / output. When the CLOCK signal 251 is input to the CLOCK terminal, the clock detection circuit CDECT operates to generate the START signal 252. The switch SW3 is switched by this START signal 252. Further, the DIRECTION signal 253 is switched by a predetermined number of clock pulses. The switch SW4 is switched by the DIRETION signal 253 to switch the data flow direction, that is, the DATA IN signal 254 and the DATA OUT signal 255.

  FIG. 23 showing another embodiment of the present invention shows the ratio of the input / output terminals for communication necessary for communication between the flow rate signal output terminal of the gas flow meter and the storage element for writing the adjustment information, and the ratio of the output as the sensor output. Any one of the metric analog output, the non-ratio metric analog output, and the pulse output can be output, and the communication input / output terminal and the sensor output terminal can be combined to reduce the number of terminals.

  A difference from FIG. 21 is that a VF conversion circuit VF that converts an analog voltage into a digital output is inserted after the digital / analog converter DA, and the analog voltage output or the digital output is switched by a switch SW1. Since the operation of this configuration is the same as that of FIG. With this configuration, the connection terminal with the outside of the gas flow meter can be realized with at least four terminals of a power supply terminal, a ground terminal, a flow rate signal output / data input / output terminal, and a data input / output terminal.

  By the way, when the maximum current supplied from the external reference voltage from the engine control unit is small and this external reference voltage is directly connected to the digital / analog converter DA, the current consumption is large because the amplifier circuit of the output stage is included. The digital / analog converter DA may not be driven. Therefore, as shown in FIG. 24, a buffer circuit in which the power supply of the operational amplifier OP4 is connected to a battery voltage (not shown) is inserted, the input of the buffer circuit is used as a resistor, and the output is connected to the power supply terminal of the digital / analog converter DA. Since the current is supplied from the operational amplifier OP4, the digital / analog converter DA can be driven. Note that the load resistance Ri of the buffer circuit is about 10 k ohms.

It is a schematic circuit block diagram of the gas flowmeter in this invention. It is a schematic circuit block diagram of the noise reduction circuit applied to the gas flowmeter in this invention. It is a schematic circuit block diagram of the overvoltage protection circuit used for the gas flowmeter in this invention. It is a figure which shows an example of the voltage limit circuit used for the overvoltage protection circuit in this invention. It is a schematic circuit block diagram of the overvoltage protection circuit used for the gas flowmeter in this invention. It is a schematic circuit block diagram of the overvoltage protection circuit used for the gas flowmeter in this invention. It is a figure which shows an example of the diode used for the overvoltage protection circuit in this invention. It is a schematic circuit block diagram of the overvoltage protection circuit used for the gas flowmeter in this invention. It is a schematic circuit block diagram of the overvoltage protection circuit used for the gas flowmeter in this invention. It is the figure which showed an example of the output characteristic of the flow volume detection circuit of a gas flowmeter. It is the figure which showed an example of the input-output characteristic in the adjustment circuit of the gas flowmeter in this invention. It is the figure which showed an example of the output characteristic after adjustment of the gas flowmeter in this invention. It is the figure which showed the error of the output characteristic after adjustment of the gas flowmeter in this invention. It is the figure which showed the flowchart of the adjustment calculation used for the gas flowmeter in this invention. It is the figure which showed the principle of the adjustment calculation used for the gas flowmeter in this invention. It is a schematic circuit block diagram of the adjustment circuit used for the gas flowmeter in this invention. It is the figure which showed an example of the temperature sensor circuit. It is the figure which showed an example of the regulator circuit. It is the figure which showed an example of the output characteristic after the temperature characteristic adjustment of the gas flowmeter in this invention. It is a schematic circuit block diagram of the adjustment circuit used for the gas flowmeter in this invention. It is a schematic circuit block diagram of the data communication input / output circuit and sensor output circuit used in the gas flowmeter according to the present invention. It is the figure which showed the outline of the timing chart of each terminal of the input / output circuit for data communication in FIG. It is a schematic circuit block diagram of the data communication input / output circuit and sensor output circuit used in the gas flowmeter according to the present invention. It is a schematic circuit block diagram of the power supply circuit part of the digital-analog converter circuit used for the gas flowmeter in this invention. It is the schematic which showed an example of the flow volume detection circuit. It is the schematic which showed an example of the flow volume detection circuit. It is the schematic which showed an example of the flow volume detection circuit. It is the figure which showed an example of the schematic circuit structure of the overvoltage protection circuit used conventionally.

Explanation of symbols

  DECT ... flow rate detection circuit, OP ... operational amplifier, Tr ... power transistor, Rh ... hot wire (heat wire), Rc ... cold wire (cold wire), R ... resistance, Ru ... upstream temperature sensitive resistor, Rd ... downstream side Temperature sensitive resistor, 100 ... Noise reduction circuit, 101 ... Overvoltage protection circuit, 102 ... High frequency noise reduction circuit, 110, 111 ... Voltage limiter circuit, ZD ... Zener diode, D ... Diode, VBB ... Power supply terminal, GND ... Ground Terminal, REG ... Regulator, 201 ... Sensor output circuit section, 202 ... Data input / output circuit section, SW ... Switch, AD ... Analog to digital converter, CALC ... Digital arithmetic unit, DA ... Digital / analog converter, FC ... Frequency Output circuit, VF ... VF conversion circuit, TS ... temperature sensor, MEM ... memory device, I / O ... data conversion circuit.

Claims (4)

  A gas flow meter having a gas flow rate detection circuit that outputs a gas flow rate flowing in the gas passage as a voltage signal, an adjustment circuit that adjusts a voltage output from the flow rate detection circuit, and a storage device that stores data for adjustment The storage device includes a data input / output circuit having two external data communication terminals for writing adjustment data from the outside and reading data to the outside, and external data of the data input / output circuit. A gas flowmeter characterized in that the communication terminal also serves as an output terminal for the detected flow rate.   2. The data read / write operation according to claim 1, wherein the adjustment circuit reads / writes data between the storage device and the outside after a predetermined number of pulses of two or more pulses is input to any of the external data communication terminals of the data input / output circuit. A gas flowmeter characterized by having means for shifting to a data communication mode.   A gas flow meter having a gas flow rate detection circuit that outputs a gas flow rate flowing in the gas passage as a voltage signal, an adjustment circuit that adjusts a voltage output from the flow rate detection circuit, and a storage device that stores data for adjustment The storage device includes a data input / output circuit having two external data communication terminals for writing adjustment data from the outside and reading data to the outside, and external data of the data input / output circuit. The communication terminal also serves as an output terminal for the detected flow rate, and the adjustment circuit is provided with output selection means for switching the output signal, and ratiometric analog output, non-ratiometric analog output, and digital output as the detected gas flow rate output signal A gas flow meter characterized by taking out   4. The output selection means provided in the adjustment circuit according to claim 3, wherein the ratiometric analog output, the non-ratiometric analog output, and the digital output circuit are formed on the same integrated circuit. Gas flow meter.

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