JP2002174541A - Thermal flow meter - Google Patents

Abstract

(57) [Problem] To improve the sensor sensitivity without adding a special circuit in a thermal air flow meter. SOLUTION: Temperature measuring resistors 211d and 211e are formed at an upstream portion and a downstream portion of heat generating resistors 211a and 211b,
The flow rate of the fluid is measured from the temperature difference of the resistance temperature detector. The heat generating resistor is divided into a plurality of parts like 211a and 211b. The plurality of divided heating resistors 211a, 21
1b are arranged in an upstream and downstream positional relationship and connected in series. The sensitivity of the flow rate signal output based on the temperature difference signal of the temperature measuring resistors 211d and 211e is improved by the output characteristic of the midpoint potential of the heating resistor divided into a plurality of portions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring apparatus suitable for detecting, for example, an intake air amount of an internal combustion engine and other various gas flow rates, and more particularly, to using a temperature-sensitive resistor such as a heating resistor. The present invention relates to a thermal type flow measuring device for measuring the flow rate of a fluid.

[0002]

2. Description of the Related Art As an intake air flow rate measuring device used in an electronically controlled fuel injection device of an internal combustion engine of an automobile or the like, a large number of thermal air flow measuring devices are used because they can directly detect a mass air amount.

There are various types of heating resistors used in this type of thermal type flow measuring device. For example, a platinum wire wound around a bobbin and coated with glass,
There is a method in which a thin film resistor is formed on a ceramic substrate or a silicon substrate.

As a method of detecting the flow rate, the heating resistor is controlled so as to maintain a constant temperature difference with respect to the intake air temperature.
A method of directly detecting the air flow rate from the current flowing through the heating resistor arranged in the intake passage, and a method of arranging a temperature measuring resistor (temperature detecting resistor) on both sides of the heating resistor and detecting the temperature with the temperature measuring resistor A method of detecting the air flow rate based on the difference may be used.

The former method tends to have higher sensitivity on the high flow rate side than on the low flow rate side, and performs air flow measurement in only one direction.

[0006] The latter method enables the measurement of air flow in both forward and backward flows, and is considered to be relatively sensitive.

In the case of an engine having four cylinders or less in an automobile, the pulsation amplitude of the intake air amount is large at low rotation and high load, and a partial backflow (pulsation flow) occurs. , Output is required according to the flow direction. The latter method, that is, a method of measuring the air flow rate based on the temperature difference between the temperature measuring resistors arranged on both sides of the heating resistor, meets the above-mentioned requirements because an output is obtained according to the direction of the forward flow or the backward flow. be able to.

However, since each of these methods has advantages and disadvantages depending on the application, a method used in combination with an analog circuit is disclosed in JP-A-9-318412 and JP-A-11-5195.
No. 4, for example. This is because the latter method has relatively high sensitivity, but the temperature difference output of the RTD saturates the sensitivity at the high flow rate side and lowers the detection accuracy. A good former method is used together, and their outputs are added by a differential amplifier and output.

As a method of compensating for the temperature difference output of such a relatively sensitive temperature measuring resistor (temperature detecting resistor), in addition to the above-described method of compensating for the sensitivity, it is possible to divide the temperature difference by the temperature rise of the heater. Output compensation method (Tokuhei 6-
No. 63801) and a method of temperature compensation (Japanese Patent Publication No.
No. 64080).

In addition, Japanese Patent Application Laid-Open No. Hei 6-160142 discloses a method of compensating a temperature difference output of a resistance temperature detector by detecting a medium temperature in an automobile.

On the other hand, as a digital method using AD conversion, a method of correcting a zero point by the output of a resistance temperature detector is described in Japanese Patent Application Laid-Open No. Hei 6-230021. A method of digitally correcting a temperature is described in Japanese Patent Application Laid-Open No. H11-94620.

[0012]

As described above, in the thermal type air flow measuring device, especially in the latter case (temperature difference method using a resistance temperature detector), a method for compensating the accuracy of the temperature difference output of the resistance temperature detector. Various methods have been proposed.

However, in a system in which an analog circuit is added later to compensate for the sensitivity of the temperature difference output, the circuit scale becomes large and it is not suitable for miniaturization. Also, in the method of digitally compensating for the zero point or the method of compensating for the temperature, adjustment of the sensitivity of the entire sensor has not been considered much.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal type flow rate measuring apparatus using a temperature difference output method of a resistance temperature detector, without adding a special circuit, to sensor sensitivity, particularly in a high flow rate range which has been considered as a conventional problem. It is an object of the present invention to provide a measuring device capable of improving the measurement.

[0015]

In order to achieve the above object, according to the present invention, a temperature measuring resistor is formed at an upstream portion and a downstream portion of a heating resistor, and a temperature difference of the temperature measuring resistor is used to detect a fluid. In a thermal type flow rate measuring device for measuring a flow rate, the heating resistor is divided into a plurality, and the divided heating resistors are arranged in an upstream, downstream positional relationship and connected in series, and divided into a plurality. The sensitivity of the flow rate signal output based on the temperature difference signal of the temperature measuring resistor is improved by the output characteristic of the midpoint potential of the heating resistor.

As one embodiment, a flow rate measuring device using a midpoint potential between the heating resistors as a power source of the temperature measuring resistor is proposed.

In another aspect, a temperature difference signal between the heating resistors and a temperature difference signal between the temperature measuring resistors are input to a digital circuit, and a flow rate output signal is formed based on these signals. The proposed flow measuring device is proposed.

The output sensitivity can be easily adjusted by directly applying one signal used for applications having different measurement ranges (one for heat generation and the other for temperature measurement) according to the flow direction and flow rate of the other. Accuracy can be improved.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a thermal type flow measuring device (for example, an air flow measuring device of an internal combustion engine) according to a first embodiment of the present invention. FIG. 2 is a top view of an air flow measuring device used in the above embodiment. FIG. 3 is a cross-sectional view taken along the line AB, FIG. 4 is an explanatory diagram showing an example of a temperature distribution when the air flow measuring element is used,
FIG. 5 is a diagram showing the relationship between the sensor sensitivity and the flow rate.

In FIG. 1, the air flow measuring device is roughly divided into a gauge circuit 1 and a digital correction circuit 2 for signal processing.
Consists of twenty.

Gauge circuit 1 driven by power supply 101
Are the heating resistors 211a and 211b and the temperature compensation resistor 211
c, a Wheatstone bridge circuit 2 including resistors 13, 14, and 17;

The heating resistors 211a and 211 are divided into two parts.
11b are connected in series, and these heating resistors and resistors 1
3 is taken as one midpoint of the bridge, and the temperature compensating resistor 2
11c, a point between the resistor 17 and the adjusting resistor 14 is set as the other middle point of the bridge.

The heating resistors 211a and 211b and the temperature compensating resistor 211c are composed of temperature-sensitive resistors having temperature-dependent characteristics. A heating resistor 211a connected in series,
For example, a thin film or thick film of platinum or tungsten as a heating element is formed on a plate-shaped glass or ceramic substrate, or a thin film or thick film of platinum or tungsten as a heating resistor is formed on a semiconductor substrate such as silicon. , A polysilicon resistor, or a single-crystal silicon resistor.

The Wheatstone bridge circuit 2 uses the differential amplifier 15 and the transistor 16 to generate heating resistors 211a and 211 so that the potential difference at the bridge midpoint becomes zero.
It is configured to adjust the current flowing through b.

Heating resistors 211a, 2b of bridge circuit 2
The midpoint potential of the differential amplifier 15b is input to the positive input terminal of the differential amplifier 15, the midpoint potential of the temperature compensation resistor 211c is input to the negative input terminal of the differential amplifier 15, and the output terminal of the differential amplifier 15 is output. Is the heating current control transistor 1
6 is connected to the base.

The bridge circuit 2 includes a heating resistor 211
The heating current flowing through the heating resistors 211a and 211b is controlled so that the difference between the heating temperature of the heating resistors 211a and 211b and the air temperature sensed by the temperature compensation resistor 211c becomes a predetermined temperature difference.

That is, these heating resistors 211a, 211a,
When 211b is arranged in the air flow path, the amount of heat taken from the heating resistor changes according to the air flow rate. As the air flow rate (air flow rate) increases and the heating temperature of the heating resistors 211a and 211b decreases, the output of the differential amplifier 15 increases and the heating resistors 211a and 211b are further heated (heating temperature and air The current is controlled so that the temperature difference from the temperature becomes a predetermined temperature difference.

The conventional heating resistor is composed of one piece, and the method of detecting the air flow rate from the midpoint potential (Vr1 in FIG. 1) between the heating resistor and the potential detecting resistor is a conventional heating resistor directly. This is a flow detection method. In this embodiment, instead of this, as described above, the heating resistor of the Wheatstone bridge circuit 2 for controlling the heating current is constituted by two (plural) heating resistors 211a and 211b connected in series.
The heating resistor 211a is arranged on the upstream side with reference to the forward flow, and the heating resistor 211b is arranged on the downstream side.

Further, a circuit (hereinafter, referred to as a semi-bridge circuit) 3 similar to a bridge circuit described below is connected to the bridge circuit 2.

The semi-bridge circuit 3 includes a heating resistor 211
a, RTD 2 for detecting temperatures upstream and downstream of 211b
11d, 211e, temperature compensation resistor 21 for air temperature
1f, an adjusting resistor 18 and a resistor 19. The temperature compensating resistor 211f, the resistor 18, and the upstream temperature measuring resistor (temperature detecting resistor) 211d are connected in series, and the resistor 19 and the downstream temperature measuring resistor 211e are connected in series.

The resistance temperature detectors 211d and 211e are shown in FIG.
And the heating resistors 211a and 211b as shown in FIG.
Are disposed on the same substrate 211.

The temperature measuring resistor 211d detects the temperature of the substrate upstream of the heat generating resistors 211a and 211b which are transferred to the substrate 211, and the temperature measuring resistor 211e detects the temperature of the heat generating resistor transferred to the substrate 211. The substrate temperature on the downstream side of 211a and 211b is detected. Here, the terms “upstream side” and “downstream side” refer to the forward direction of the airflow to be measured as a reference.

The resistance temperature detectors 211d and 211e are connected to a common ground side. On the other hand, a resistance temperature detector 211d
Is connected to the resistor 18 and the temperature compensation resistor 2
The transistor (NPN transistor) 16 is connected to the emitter voltage V2 side (the high voltage side of the heating resistor 211a) via 11f. Also, the other grounding side of the other temperature measuring resistor 211e is connected to the midpoint of the heating resistors 211a and 211b via the resistor 19, and the intermediate voltage Vm of the heating resistors 211a and 211b connects the resistor 19 with the resistor 19. It is configured to be applied via

FIG. 2 shows the heating resistors 211a and 211a.
b, temperature measuring resistors 211d, 211e, temperature compensating resistor 21
An example of a pattern when 1c and 211f are formed as a thin film on a silicon semiconductor substrate 211 is shown.

The heating resistors 211a and 211b are formed in a series by a strip-shaped thin film resistor, are formed by a pattern folded at an intermediate point, and are arranged in parallel with each other in an upstream and downstream positional relationship. One end 211a 'of the heat generating resistor 211a and one end 211b' of the heat generating resistor 211b serve as connection terminals, and a terminal 211g drawn out from an intermediate point via a conductor serves as a terminal for drawing out the intermediate potential Vm of the heat generating resistor.

The temperature measuring resistors 211d and 211e are arranged in parallel so as to sandwich the heating resistors 211a and 211b, and their terminals 211d ', 211d ", and 21d".
1e 'and 211e "are provided via conductors.

Heating resistor 2 on silicon substrate 211
11a, 211b and temperature measuring resistors 211d, 2 for temperature detection
As shown in FIG. 3, the substrate 211 is etched from the back surface (at the position indicated by the symbol S) at a position where 11e is present, and the diaphragm 4 having a small heat capacity is formed. The heating resistors 211 a and 211 b and the temperature measuring resistor 2 are placed on the diaphragm 4.
11d and 211e, the resistance thermometer 2
11d and 211e improve the thermal sensitivity to the heating resistors 211a and 211b.

On the other hand, the temperature compensation resistors 211c and 211f are:
The heating resistors 211a and 211b are arranged at a location away from the location of the heating resistors 211a and 211b (a location that is not easily affected by temperature due to heating). Of the substrate 211, the temperature compensation resistor 211c,
The portion where the 211f resistance pattern is located has the thickest structure.

The resistance patterns of the temperature compensating resistors 211c and 211f are also folded back in a belt shape. By this return, these terminals 211c ', 211c ", 211
f ', 211f ", a terminal 21 of a heating resistor or a temperature measuring resistor
1a ', 211b', 211d ', 211d ", 211
e ′, 211e ″ and 211g are arranged in a line on one side of the substrate 211.

In this embodiment, basically, the resistance temperature detector 2
This adopts a method of measuring the air flow rate from the difference between the temperature detected at 11d and the temperature detected at the resistance temperature detector 211e.

In this system, another bridge circuit for the temperature measuring resistor is conventionally formed independently of a Wheatstone bridge circuit for heat generation, and a constant voltage power supply Vdd is provided.
However, such a temperature difference detection method has good sensitivity on the low flow rate side due to differential detection, and is suitable for detecting bidirectional flow including backflow. Sensitivity on the high flow side drops (saturates) because it is driven by voltage
Had properties.

In this embodiment, in order to improve the sensitivity on the high flow rate side, particularly on the forward flow direction, the two heating resistors 211a and 211b are connected in series as described above, and The heating resistors 211a and 211b are arranged in an upstream and downstream positional relationship. Further, the semi-bridge circuit 3 for temperature measurement described above is used.

Prior to the description of the sensitivity improvement on the high flow rate side, the operation of the gauge circuit 1 for the temperature difference type flow rate measurement of this embodiment and the signal processing operation of the digital correction circuit 220 connected to the subsequent stage will be described.

First, details of the operation of the gauge circuit will be described with reference to FIG.

FIG. 4 shows the temperature distribution for the heating resistors 211a and 211b and the temperature measuring resistors 211d and 211e. The flow is upstream on the heating resistor 211a side and downstream on the heating resistor 211b side.

When there is no flow of the intake air, each of the heating resistors 211a and 211b has the same temperature, and
It is considered that 1d and 211e also have the same temperature.

Here, for example, when a flow occurs from the upstream to the downstream, the temperature of the upstream temperature measuring resistor 211d decreases and the temperature of the downstream temperature measuring resistor 211e increases.
This is because the upstream temperature measuring resistor 211d exchanges heat with unheated air, whereas the downstream temperature measuring resistor 211d
e is because it is thermally affected by the heated air.

In particular, since the temperature measuring resistors 211d and 211e are arranged at the places where the temperature change is most likely to occur, the temperature difference dTm according to the flow can be detected with high sensitivity.

On the other hand, also in the heating resistors 211a and 211b, when air flows, for the same reason as described above, the upstream heating resistor 211a and the downstream heating resistor 211b.
And a temperature difference dThLR occurs. However, the bridge circuit operates so that the heating resistors 211a and 211b are collectively controlled at a constant temperature difference, and is arranged at the top of the temperature distribution where temperature change is unlikely to occur.

The intermediate voltage Vm of the heating resistors 211a and 211b is applied to the temperature measuring resistor 211e, while an emitter potential (higher voltage side potential) V2 of a higher voltage is applied to the temperature measuring resistor 211d. Thus, the sensitivity of the temperature difference dTm can be naturally improved according to the flow direction and the flow rate as described later.

In this embodiment, the resistance temperature detector 211d
The potentials Vb1 and Vb2 at the bridge midpoint between the resistance 18 and the resistance bulb 211e and the resistance 19 are calculated by the digital correction circuit 2.
Enter 20.

The digital correction circuit 220 has two analog / digital converters 221a and 221b. The analog / digital converter 221a converts the voltage values Vb1 and Vb2 corresponding to the flow rate into digital values and reads them. The analog / digital converter 221b is a digital correction circuit 22.
The temperature of 0 is detected by the temperature detection circuit 241.

The voltage values Vb1 and Vb2 and the temperature detection signal are adjusted by calculation as digital quantities, and the output voltage difference between the voltage values Vb1 and Vb2 is calculated by the arithmetic circuit 222 (the output voltage difference is dTm = dTmR + dTmL in FIG. 4). )
And sends a signal as an output voltage (flow signal) Vout of the digital / analog converter 224 to an engine control unit or the like.

Here, the digital correction circuit 220 has a CPU
An arithmetic circuit 222 including 222a, RAM 222b, and ROM 222c, an oscillator 226, a PROM 223, and the like.

The PROM 223 only needs to be able to record the variation or the like of the output sensitivity of the individual sensor as an adjustment value one or more times.
The invention is not limited to a ROM or a flash ROM.

The voltage Vcc supplied from the outside is input to the internal power supply / protection circuit 228 as a power supply, and is connected to the digital / analog converter 224 via the switch 225a as the power supply voltage Vref1 depending on the external voltage Vcc. Used as a reference.

The switch 225a is connected to the digital correction circuit 2
The voltage Vre generated by the reference voltage circuit 229 inside
f2 and the power supply voltage Vre depending on the external voltage Vcc.
f1 is switched.

The analog-to-digital converter 221a requires precision because the outputs Vb1, Vb2, etc. of the bridge circuit are directly input. However, in order to secure the precision and reduce the circuit scale, for example, a ΔΣ type An analog-to-digital converter may be used.

The digital / analog converter 224 can change the reference voltage by a switch 225a. This is for freely selecting a reference when interfacing with an analog value. The reference voltage of the connected analog / digital converter on the control unit side and the externally supplied voltage Vcc are the same or synchronized. If the power supply voltage Vref1 is varied, the power supply voltage Vref1 is used as a reference. If the reference voltage Vref2 is not relevant to the control unit, an independent reference voltage Vref2 is selected. It is configured.

In the present embodiment, the midpoint voltage of the heating resistors 211a and 211b connected in series is
By separately applying the voltage to 11d and 211e, the sensitivity of the temperature difference according to the flow direction and the flow rate can be optimized in advance.

Here, the reason why the output (sensor sensitivity) of the flow sensor of the air flow measuring device in this embodiment is improved will be described with reference to FIG.

In FIG. 5, the abscissa represents the air flow rate, and the right side shows a forward flow area and the left side shows a reverse flow area with reference to the center coordinates (zero flow rate). The vertical axis is the sensor output voltage (sensor sensitivity).

In FIG. 5, Vq2 is a sensor output characteristic of a conventional heating resistor direct flow detection method (a method of measuring an air flow rate from a current flowing through a heating resistor of a bridge circuit), and there is only one heating resistor. Yes, and the directionality of the air flow is not observed unlike the temperature difference method. Therefore, in this case, the sensor output characteristics of the forward flow and the backward flow are symmetrical.

Vq2 'is divided into two heating resistors of the above-described heating resistor direct flow detection type and connected in series.
As shown in FIG. 2 of the present embodiment, when the two heating resistors (corresponding to the heating resistors 211a and 211b in FIG. 2) are arranged in a positional relationship of upstream and downstream. Output characteristics.

In the case of the output characteristic Vq2 ', the output characteristic V
As shown by the arrow, the sensitivity of the output voltage of the forward current increases and the sensitivity of the output voltage of the reverse current decreases as compared with q2. The sensitivity characteristic Vq4 is obtained by extracting the change (output component) of the sensitivity. Vq4 is the heating resistors 211a, 21a in FIG.
This corresponds to a sensor output fluctuation dThLR based on the temperature difference between the heating resistors when 1b is disposed upstream and downstream. Vq
In the case of No. 4, since the heating resistors are arranged upstream and downstream, the directivity of the output changes due to the forward flow and reverse flow of air.

The output characteristic Vq2 'can be expressed by the following equation.

[0068]

(Equation 1)

The output characteristic Vq1 is the output characteristic of the conventional temperature difference type thermal air flow sensor. In this case, there is one heating resistor, and the upstream of the heating resistor,
A temperature measuring resistor is arranged downstream, and the temperature measuring resistor is a sensor output characteristic of a system in which a constant voltage power supply is applied by being incorporated in a bridge circuit independent of a bridge circuit of a heating resistor.
Vq1 corresponds to an output difference (temperature difference) between the two resistance temperature detectors (corresponding to dTm in FIG. 4). In this case, the directionality of the output changes due to the forward flow and reverse flow of air.

The output characteristic Vq3 'is the sensor output characteristic according to the present embodiment. In this case, the emitter voltage V2 is applied to the temperature measuring resistor 211d of the semi-bridge circuit 3 for temperature measurement.
(Potential on the high voltage side of the heating resistor 211a) is applied, and the midpoint potential Vm between the heating resistors 211a and 211b is applied to the temperature measuring resistor 211f.
The temperature difference output sensitivity Vq4 = dThLR of the heating resistor based on the upstream and downstream positional relations of 1a and 211b affects the power supply circuit of the semi-bridge circuit 3 for temperature measurement to the output characteristic Vq2 'of FIG. Equivalent to.

Therefore, the output characteristic Vq3 'is Vq3
And the sensor sensitivity of the output characteristic Vq2 'is taken into account, and can be expressed as in the following equation.

[0072]

(Equation 2)

As a result, the sensor output characteristic Vq3 'of the air flow measuring device according to the present embodiment can be greatly improved on the downstream side, especially in the high flow region, as compared with the output characteristic Vq1 of the conventional temperature difference method. In the present embodiment, the sensor output characteristics on the reverse flow side cannot be expected to improve significantly (sensitivity improvement) on the high flow region side, but there is no problem. That is, in an air flow meter used in a normal automobile or the like, the operation detection area is generally wider on the forward flow side than on the reverse flow side as a sensor in many cases. This is because the backflow is generated only under the specific condition that the engine blows back. Usually, only the downstream side needs to be detected, and it is not necessary to widen the operation area on the backflow side.

The output characteristic Vq3 is the output characteristic of another comparative example with respect to the present embodiment. In this comparative example, a Wheatstone bridge circuit incorporating the temperature measuring resistors 211d and 211e is formed, and this is used as a constant voltage power supply. This is an example in which the emitter potential V2 is applied instead (the heating resistor is not divided into two and the midpoint voltage is not used).

The output characteristic in the case of this comparative example is expressed by the following equation.

[0076]

(Equation 3)

In the case of this comparative example, the output characteristics of the sensor are improved, but the output characteristics (sensitivity characteristics) on the high flow rate side in the forward flow region are better than the output characteristics Vq3 'of this embodiment. .

According to this embodiment, in a thermal air flow meter of a temperature difference type using a resistance temperature detector, a sensitivity characteristic in a high flow rate region in a forward flow direction, which has been desired to be improved, has been simplified. In addition, by using the midpoint potential of the bridge circuit 2 on the heat generation side as the power supply of the temperature measurement circuit (semi-bridge) 3, the sensor output sensitivity can be improved at low cost.

Since the sensitivity of the conventional sensor is the same for both the forward flow and the backward flow, if the sensor signal is directly input to the analog / digital converter, the effective resolution on the forward flow side is partially lost. Regarding this point, for example, the resistance thermometer 2
This can also be achieved by inputting the signals Vb1 and Vb2 of 11d and 211e with a differential amplifier or the like while changing the sensitivity on the forward flow side and the sensitivity on the reverse flow side, but the size is reduced by the addition of the differential amplifier and peripheral circuits. It is not suitable for the above and also causes a cost increase.
In the present invention, such an increase in cost can be avoided.

As described above, according to the present embodiment, it is possible to optimize the sensor sensitivity according to the flow direction by devising the power supply of the resistance temperature detectors 211d and 211e.

That is, a plurality of divided heating resistors are arranged in an upstream / downstream positional relationship and connected in series.
The sensitivity of the flow rate signal output based on the temperature difference signal of the temperature measuring resistor can be improved by the output characteristic of the midpoint potential of the plurality of divided heating resistors.

As an example, the downstream side requiring sensitivity is increased,
By making the backflow side smaller, it becomes possible to obtain good performance as an air flow meter for a vehicle that supports backflow.
According to this embodiment, particularly, there is an effect that the sensitivity can be optimized only by the sensor without adding a special circuit or the like.
In addition, there is an effect that the sensitivity of the analog / digital converter can be optimized at low cost.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the gauge circuit 1 for flow measurement also comprises a Wheatstone circuit 2 incorporating a heating resistor and a semi-bridge circuit 3 incorporating a temperature measuring resistor.

In the present embodiment, while the above-described embodiment of FIG. 1 uses two heating resistors, the heating resistor 213 incorporated in the aforementioned Wheatstone bridge 2 is replaced by 213.
a, 213b, 213c, and 213d, and are arranged in a bridge type 2 '. 7, the heating resistors 213a and 213b are arranged on the upstream side of the substrate 212 on the basis of the forward flow, and the heating resistors 213c and 213d are arranged on the downstream side, as shown in FIG.

The temperature measuring resistors 214 (the temperature measuring resistors 211d and 211 shown in FIG. 1) disposed upstream and downstream of the heat generating resistor 213, respectively.
e) 214a, 214b, 21
4c and 214d, and the temperature measuring resistors 214a and 214b are arranged on the upstream side with respect to the forward flow as shown in FIG.
Are arranged, and the temperature measuring resistors 214c and 214d are arranged on the downstream side. This is arranged in a semi-bridge shape as follows.

The temperature measuring resistors 214a and 214d are connected in series, while the temperature measuring resistors 214c and 214b are connected in series. The heating resistors 213c and 21 connected in series are connected to the high potential side (anti-ground side) of the temperature measuring resistor 214a.
The midpoint voltage between 3d is applied and the other resistance temperature detector 2
The midpoint potential between the heating resistors 213a and 213b connected in series is applied to the high potential side (anti-ground side) of 14c.

The resistance temperature detectors 214d and 214b are commonly grounded.

In this embodiment, the differential amplifier 15 is provided with an output amplifying function equivalent to a power transistor, and the output is applied to the Wheatstone bridge 2.

The temperature measuring resistors 214a, 214b, 214
c, output dV of the semi-bridge 2 composed of 214d
(The midpoint potential Vb1 between the temperature measuring resistors 214a and 214d and the midpoint potential Vb1 and Vb between the temperature measuring resistors 214c and 214b.
2) is input to the analog / digital converter 221a of the digital correction circuit 240.

The Wheatstone bridge 2 includes heating resistors 213a, 213b, 213c, and 213d, a temperature compensating resistor 211c, and resistors 13, 14, and 17. The digital correction circuit 240 is a signal processing circuit corresponding to the digital correction circuit 220 in FIG.

The digital correction circuit 240 of the present embodiment incorporates a differential amplifier 15 for driving the Wheatstone bridge 2 and an adjustment circuit 242 for adjusting the value of the resistor 14 to set the heating temperature of the heating resistor.

Power is supplied from the battery 101 to the power / protection circuit 228. The resistors and the digital correction circuit 240 are all integrated on the same substrate.

In this method, separately formed patterns may be finally bonded on the substrate, or the patterns may be formed on the same substrate from the beginning or simultaneously. Further, the heating resistors 213a, 213b, 213c, 213
d and resistance temperature detectors 214a, 214b, 214c, 214
Although d is formed on a diaphragm having a substrate as thin as several μm, it may be formed from the back surface by etching or the like, or may be formed from the front surface using a sacrificial layer.

In the digital correction circuit 240, an analog
Means for detecting the substrate temperature by the digital converter 221b and correcting the temperature of the detection signal of the sensor, and a digital / frequency converter 24 for converting a normal voltage output to a frequency and outputting the frequency.
2 etc. are also provided.

FIG. 7 shows a layout when integrated on the same substrate. For example, using a silicon substrate as the substrate,
The heating resistors 213a, 213b, 213c, 213d and the temperature measuring resistors 214a, 214b, 214c, 214d,
The temperature compensation resistor 211c and the digital correction circuit 240 have different device structures in the thickness direction but are patterned in the same plane.

The heating resistor 213 is divided into four and connected in a bridge shape, and has a structure in which a terminal is drawn out from each connection point. As a result, the heating resistor 213a,
213b, 213c, and 213d have a pattern that is folded twice.

For example, a connection point between the heating resistors 213a and 213c is connected to an output terminal of the differential amplifier circuit 15 via a terminal 213 '. Heating resistors 213a, 213b
(Intermediate point) is externally connected to the terminal 214c 'of the resistance bulb 214c via the terminal 213-1.

The connection point (intermediate point) between the heating resistors 213c and 213d is externally connected to one end of the temperature measuring resistor 214a via terminals 213-2 and 214a '.

The other end of the temperature measuring resistor 214a is connected to the temperature measuring resistor 214 via a terminal 214a ″ and a terminal 214d ′.
d is externally connected to one end.

The temperature measuring resistor 214c is connected to the temperature measuring resistor 214b via a terminal 214c ″.

In this embodiment, the output dV (flow rate signal) extracted from the middle point of the semi-bridge 3 of the resistance temperature detector is input to the digital correction circuit 240 for signal processing.

The improvement of the sensor sensitivity of this embodiment will be described with reference to the sensor output operation characteristic diagram of FIG.

Heating resistors 213a, 213b, 213
c, 213d, the potential difference dVm between the midpoint voltages Vm1, Vm2 of the bridge circuit
a, 213b, 213c, and 213d show differences in temperature distribution.

Heating resistors 213a to 213 divided into four
13d is controlled so as to maintain a predetermined temperature with respect to the air temperature, so that a temperature distribution hardly occurs. However, by using a plurality of heating resistors and arranging them in a positional relationship upstream and downstream as in this embodiment, a slight temperature difference occurs.

As a result, the potential difference dVm becomes an output larger than the reference voltage Vq0 in accordance with the direction of the flow.

Temperature measuring resistors 214a, 214b, 214
c, the output of 214d of the semi-bridge circuit 3 is the voltage Vm
1. Assuming that Vm2 is constant, the temperature difference output characteristic dV 'when the bridge is driven at a normal constant voltage is obtained. This is a characteristic in which a temperature difference hardly occurs on the high flow rate side and is saturated as described above.

On the other hand, in the present embodiment, the heating resistor 2
By applying midpoint voltages Vm1 and Vm2 of the bridge circuit composed of 13a, 213b, 213c and 213d to the semi-bridge circuit 3 for temperature measurement, dVm affects the temperature difference output characteristics of the semi-bridge circuit 3. That is, the sensitivity of the temperature difference output characteristic can be improved over the entire flow rate region by the same mechanism as in the first embodiment, as indicated by the reference symbol dV. At the same time, the sensitivity to the flow direction can be improved.

The temperature difference output characteristic dV can be considered as an output substantially equivalent to the following equation.

[0110]

(Equation 4)

According to this embodiment, for example, even when the size of the heating resistor is small and it is difficult to obtain the sensitivity only with the temperature measuring resistor, the sensitivity according to the flow direction and the flow rate can be improved. There is.

Further, by reducing the heat capacity of the heat-generating portion, the resistor portion and the circuit portion can be integrated, and the size can be easily reduced.

Next, a third embodiment of the present invention will be described with reference to FIG.

In this embodiment, the Wheatstone bridge circuit 2 for driving the heating resistor in the gauge circuit 1
Four heating resistors 213 as in the embodiment of FIG.
a, 213b, 213c, 213d, a bridge circuit 2 ', a temperature compensation resistor 213c, resistors 13, 14, 1
7. In addition, the temperature measuring circuit also has a temperature measuring resistor 214a, 214b, 214c, 2 as in the embodiment of FIG.
It is composed of a 14d semi-bridge circuit 3.

The difference from the embodiment of FIG. 6 is that the power supply protection circuit 228 applies a constant voltage to the semi-bridge circuit 3 for voltage application. However, as described below, the midpoint potential difference dVm (= Vm
1-Vm2) is added to the digital correction circuit 240 as described below to the temperature difference output dV of the semi-bridge circuit 3 for temperature measurement.
Is reflected by using.

That is, the midpoint voltages Vm1 and Vm2 of the bridge circuit for heat generation are not directly connected to the resistance temperature detector, and the analog / digital converter 221 of the digital correction circuit 240
Enter c. Similarly, resistance temperature detectors 214a, 214
The outputs Vb1 and Vb2 of b, 214c and 214d are also input to the analog / digital converter 221a. The same operation as that described in the second embodiment is performed in the digital correction circuit 240 to obtain the same effect.

According to the present embodiment, an extra analog-to-digital converter is required and the operation becomes complicated in comparison with the digital correction circuit 240 described in the previous embodiment, but sensitivity using parameters is used. There are also specific effects such as easy correction. Here, the correction for the output Vout can be realized by the following equation as an example.

[0118]

(Equation 5)

[0119]

(Equation 6)

Analog / digital converters 221a, 22
This operation is unnecessary if 1c can be differentially input. The output correction is as follows.

[0121]

(Equation 7)

As a result, with respect to the basic sensitivity tendency of the output characteristic dV, good characteristics can be obtained even on the high flow rate side by sensitivity correction. Alternatively, the following equation can be used instead of Equations 5 and 6.

[0123]

(Equation 8)

This equation is not limited to the temperature difference between the heating resistors,
By calculating the flow rate sensitivity, the same effect as in the second embodiment can be obtained. In addition, the above equation (8) is modified according to the condition according to the direction of the flow as follows, so that finer grain correction can be performed.

[0125]

(Equation 9)

In this case, the output corresponding to the flow rate has a high sensitivity on the forward flow side and a low sensitivity on the reverse flow side. At the time of output from the sensor, when the interface with the engine control unit etc. is taken with voltage,
This can be easily realized without using any special conversion means such as signal compression.

In the present embodiment, since the sensitivity can be corrected even if the heat capacity of the heating resistor is reduced, for example, the digital correction circuit 240 including the differential amplifier 15 for driving the heating resistor 213 includes, for example, an engine control unit. And the like, and can operate only with the voltage signal Vcc from the same, and has the effect of eliminating the need for wiring from the battery. As in the previous embodiment, when the resistor and the digital correction circuit 240 are integrated on the same substrate, the power supply from the battery is not directly used, so that the withstand voltage of the entire semiconductor circuit can be reduced.
Another effect is that the cost can be reduced.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

The configuration of this embodiment is basically the same as the embodiment of FIG.

The difference is that a switch circuit 250 is provided between the heat-generating Wheatstone bridge circuit 2 and the transistor 16 for driving the same.
0 is the interface (I /
O) The structure can be controlled by 251.
Further, in order to detect a current flowing through the heating resistors 211a and 211b, the voltage Vr1 above the resistor 13 is converted into an analog signal.
It is input to the digital converter 221b.

This is because, for example, the voltage applied to the bridge when the sensor is activated is set to the reference voltage Vref1 from the digital correction circuit 220 by switching the switch 250, so that the heating resistor 211a when the reference voltage Vref1 is applied, The heating temperature of 211b, the temperature detecting resistors 211d and 211e, the resistors 18 and 19, and the temperature compensating resistor 21
1f is a simulated bridge, and the middle point potential Vb1,
Find the difference between Vb2. When the flow rate is zero, the voltage is adjusted so that a potential difference is not originally generated. However, an offset voltage may be generated due to a temporal change in resistance or the like. This is considered that the higher the temperature of the resistor, the more likely it is to deteriorate. Therefore, if an unbalance occurs due to the resistance change of the heating resistors 211a, 211b, the temperature measuring resistors 211d, 211e.
The potentials Vb1 and Vb2 also fluctuate.

Therefore, the reference voltage Vr is previously set at the time of adjustment.
Using ef1, the temperature change of the heating resistors 211a and 211b due to the switching of the switch circuit 250 for a short time and the potential difference (temperature difference) of the temperature detecting resistors 211d and 211e are recorded. The calculation is performed again and compared with the previously recorded value. As a result, for example, if deterioration of the heating resistors 211a and 211b is recognized, the deterioration of the resistors is compensated by using the deterioration correction data prepared in advance. By the above-described diagnostic operation, it is possible to provide a sensor system with less characteristic deterioration even in the long term. According to this embodiment, there is an effect that a sensor excellent in change with time can be provided by a simple circuit.

By optimizing the sensitivity with the above-mentioned elements such as the heating resistor and the temperature measuring resistor, an air flow meter having good sensitivity and high accuracy can be obtained, and optimization in the engine control of the automobile can be achieved. There is an effect that the exhaust gas from the fuel can be reduced.

The flow rate measuring apparatus using the above embodiments can be used for detecting a gas flow of hydrogen gas in a fuel cell or the like. The features are that the sensitivity can be easily optimized and the flow rate range can be widened in the embodiments described above, and that a resistor resistant to corrosion by hydrogen can be used as the resistor. In particular, using a resistor such as a polysilicon resistor for the resistor and lowering the heating temperature, it is possible to prevent corrosion when using platinum or the like for the resistor and obtain good characteristics including reliability. There is an excellent effect that it can be done.

[0135]

According to the present invention, in the thermal type flow rate measuring device of the temperature difference type, there is an effect that the sensor sensitivity can be optimized according to the flow amount and direction.
Particularly, there is an effect that the sensitivity can be optimized only by the sensor without adding a special circuit or the like as a flow meter. The sensitivity of the analog / digital converter can be optimized at low cost.

Depending on the digital adjustment means, sensitivity correction and temperature correction can be easily performed in accordance with the flow direction of the flow rate, and the performance is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a top view of an air flow measuring element used in the embodiment.

FIG. 3 is a sectional view taken along line AB in FIG. 2;

FIG. 4 is an explanatory diagram showing an example of a temperature distribution when the air flow measuring element is used.

FIG. 5 is a diagram showing a relationship between a sensor sensitivity and a flow rate in the embodiment.

FIG. 6 is a circuit diagram according to a second embodiment of the present invention.

FIG. 7 is a top view of an air flow measuring element used in the embodiment.

FIG. 8 is a diagram showing a relationship between sensor sensitivity and flow rate used in the embodiment.

FIG. 9 is a circuit diagram according to a third embodiment of the present invention.

FIG. 10 is a circuit diagram according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hot-wire drive circuit, 101 ... Power supply, 211 ... Silicon substrate, 211a, 211b, 213a, 213b, 213
c, 213d: heating resistor, 211c, 211f: temperature compensation resistor, 211d, 211e, 214a, 214b,
214c, 214d: resistance temperature detectors, 13, 14, 17,
18, 19: resistor, 15: differential amplifier, 16: transistor, 229: reference voltage, 220, 240: digital correction circuit, 221a, 221b, 221c: analog / digital converter, 222: arithmetic circuit, 222a: CPU,
222b: RAM, 222c: ROM, 223: PRO
M, 224, 224b ... digital / analog converter, 2
25a, 225b switch, 226 oscillator, 227
... Serial communication interface, 22
8 power supply / protection circuit, 311a, 311b analog-digital conversion processing, 242 adjustment circuit, 251 I / O,
250 ... Switch circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masamichi Yamada 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor Keiichi Nakata 2520 Takada, Hitachinaka-shi, Ibaraki Prefecture Address Hitachi, Ltd. Automotive Equipment Group (72) Inventor Hiroshi Yoneda 2477 Takaba, Hitachinaka-shi, Ibaraki F-term in Hitachi Car Engineering Co., Ltd. 2F035 AA02 EA05 EA05 EA08 EA09

Claims (10)

[Claims] 1. A thermal type flow measuring device which forms a temperature measuring resistor at an upstream portion and a downstream portion of a heating resistor and measures a flow rate of a fluid from a temperature difference between the temperature measuring resistors, wherein the heating resistor is The plurality of divided heating resistors are arranged in an upstream and downstream positional relationship and connected in series, and the temperature measurement is performed based on the output characteristic of the midpoint potential of the divided heating resistors. A thermal type flow measuring device characterized by improving the sensitivity of a flow signal output based on a temperature difference signal of a resistor. 2. A thermal type flow rate measuring device in which a temperature measuring resistor is formed at an upstream portion and a downstream portion of a heating resistor and a flow rate of a fluid is measured from a temperature difference between the temperature measuring resistors. The heating resistors divided into a plurality are arranged in an upstream and downstream positional relationship and connected in series, and a midpoint potential between these heating resistors is used as a power source of the temperature measuring resistor. A thermal type flow measuring device, characterized in that: 3. The heating resistor divided into a plurality of parts is incorporated in a bridge circuit together with a temperature compensating resistor.
The plurality of resistance temperature detectors forming a downstream positional relationship are commonly connected on the ground side, one anti-ground side of the resistance temperature detector is connected to the high voltage side of the heating resistor, and the other resistance temperature detector is connected to the other side. The thermal type flow measurement device according to claim 1, wherein an anti-ground side of the thermal resistor is connected to a midpoint between the heating resistors. 4. The plurality of divided heating resistors are incorporated in a bridge circuit, and a heating resistor is arranged on each side of the bridge, and the plurality of temperature measuring resistors having an upstream and downstream positional relationship. Are connected in common to the grounding side, and the anti-grounding side of one resistance thermometer is connected to one midpoint of the bridge, and the anti-grounding side of the other resistance thermometer is connected to the other end of the bridge. 3. The device according to claim 1, which is connected to one of the middle points.
The thermal type flow measuring device as described in the above. 5. A bridge circuit incorporating the heating resistor, and a bridge circuit incorporating the temperature measuring resistor, wherein the power supplies of these bridge circuits are independent of each other and have an upstream and downstream positional relationship. A temperature difference signal between the heating resistors, and a temperature difference signal between the temperature measuring resistors forming an upstream and downstream positional relationship are input to a digital circuit,
2. The thermal flow measuring device according to claim 1, wherein a flow output signal is formed based on these signals. 6. The thermal flow rate according to claim 1, wherein the deterioration of the resistance due to the aging of the heating resistor is compensated by adjusting the heating temperature of the heating resistor. measuring device. 7. The deterioration of the resistance of the heating resistor due to a change with time can be determined by determining a temperature difference between an upstream and a downstream according to a flow direction obtained from the heating resistor or a current value according to a flow rate and the temperature measuring resistor. 7. The thermal flow measurement device according to claim 6, wherein the detection is performed using a temperature difference between upstream and downstream according to the direction of the flow obtained from the body. 8. The heat generation device according to claim 6, wherein the deterioration of the resistance due to the aging of the heating resistor is detected by switching from a power supply for current control applied to a drive circuit of the heating resistor to a reference voltage power supply. Type flow rate measuring device. 9. A thermal air flow measuring device for an internal combustion engine, comprising the thermal flow measuring device according to claim 1. Description: 10. A gas flow meter comprising the thermal flow measuring device according to claim 1. Description: