JPH0470519A - Semiconductor flowmeter - Google Patents

Abstract

PURPOSE:To simultaneously incorporate signal processing circuits such as ICs or the like onto a supporting body thereby reducing noises and manufacturing costs and improving the reliability by using such one that has sufficient mechanical strength for the supporting body of a semiconductor device. CONSTITUTION:A heat generating transistor 30 is used as a semiconductor element of this flowmeter, which is fixedly mounted to a main body 40 comprised of a plate- like first supporting part 42 and a rod-like second supporting part 44. At least one pair of temperature sensors 32a, 32b are provided for the supporting part 44 to detect the flow of heat. Moreover, there are provided a first operation controlling means 50 for controlling the generation of heat of the semiconductor element so that the temperature of the supporting body has a constant temperature difference from the temperature of the fluid, a second operation controlling means 60 for driving the semiconductor element and outputting a detecting signal corresponding to the consumed power, and a third operation controlling means 70 for outputting a detecting signal proportional to the detected flow of heat in the second supporting part 44. In a fourth operation controlling means 80, the amount of heat radiated through the supporting body 40 is subtracted from the heat generated by the semiconductor element based on the outputs of the second and third controlling means 60, 70. Accordingly, the flow rate of the fluid is operated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor flowmeter, particularly a semiconductor flowmeter that measures a fluid flow rate based on the amount of heat transferred from a heat source installed in a flow path to a fluid. Regarding.

[Prior Art] Currently, combustion control is performed in many automobile engines using electronics in order to purify exhaust gas and improve fuel efficiency. This system uses multiple physical quantities related to combustion (intake air volume,

The system detects the oxygen concentration in exhaust gas, intake air concentration, engine temperature, etc. using a sensor, processes these measured values using a microcomputer, and determines the fuel injection timing and amount based on the processing results. It's in control.

Among the sensors used for this type of purpose, various types of sensors are currently used as sensors for detecting the amount of intake air. For example, movable vane flowmeters, Karman vortex flowmeters, hot wire flowmeters, and flowmeters that use a negative pressure sensor to determine air flow rate based on pressure loss are currently in use.

Each of these flowmeters is sufficient for current requirements. However, in order to perform more advanced combustion control,
Further improvements in accuracy, responsiveness, etc. are required. Each of the above-mentioned types of flowmeters has advantages and disadvantages, but hot wire flowmeters are the most promising in terms of accuracy and responsiveness.

FIG. 13 shows a principle diagram of a thermal flowmeter that measures fluid flow rate using a heat source like the hot wire flowmeter. When the heating element 20 heated to a temperature Th higher than the fluid temperature is installed in the flow path of the fluid 10 at the temperature Tf, the heating element 2
The amount of heat QL removed from 0 to the fluid 10 is generally
It is expressed by the following equation as a function of the mass flow rate (ρ·V) and each temperature Th and Tf.

QIDCfL f (ρ・v), Th, Tf) In such a heat transfer system, if the temperatures Tf and Th are selected within a range where the change in the physical property values of the fluid 10 is small (in many cases, under this condition measurement), the amount of heat Q1 is the temperature difference (T
h-Tf), it is expressed by the following equation.

Q1χf2 +ρ ・v l X (T h
-T f )... (2) Therefore, when the temperature difference (Th - Tf) is kept constant, the amount of heat Q1 is simply the mass flow rate (ρ・V) of the fluid 10.
becomes a function of

Further, when only the temperature Th of the heating element 20 is kept constant, the relationship between the amount of heat Q1 and the fluid flow rate (ρ·V) can be determined by measuring and correcting the fluid temperature Tf.

Therefore, if the amount of heat Q1 taken from the heating element 20 to the fluid 10 can be accurately measured, the fluid flow rate can be detected based on this amount of heat Q1.

FIG. 14 shows an example of a conventional hot wire flowmeter created based on such a measurement principle. In this hot wire type flowmeter, thin metal wires 22 are attached to both ends of a heater 20H that functions as a heating element, and both thin metal wires 22 are fixed to mounting portions 24.24 provided on the side walls of the flow path. Then, the heater 20a is energized and heated through the thin metal wire 22, and the fluid flow rate is measured based on the amount of heat generated Q.

However, strictly speaking, the heat generation IQ of the heater 20a is expressed by the following equation.

Q=Ql +Q2 +Q3 (3) In this, Ql is the amount of heat taken directly from the heater 20a to the fluid 10, and Q2 is the amount of heat taken from the fluid 10 through the thin metal wire 22.
Q3 is the amount of heat transferred from the heater 20a to the attachment portion 24 via the thin metal wire 22. Therefore, if Q2゜Q3 is large, the calorific value Q and fluid 1
The amount of heat Ql removed to zero does not match, and the measurement accuracy of the fluid flow rate decreases. For the purpose of Q2, this hot wire flowmeter uses a sufficiently thin thin metal wire 22 as the member supporting the heater 20a to reduce its heat capacity. Q3 is reduced to improve measurement accuracy.

[Problems to be Solved by the Invention] As described above, the conventional hot wire flowmeter is excellent in terms of accuracy and responsiveness, but the thin metal wire 22 is used to support the heater 20a.
Because it uses That is, a flow meter for measuring the intake air amount of the engine is provided within the intake pipe. For this reason, engine vibrations are directly transmitted to the flowmeter, and there is also the impact of backfires, so if the flowmeter is not strong enough,
There was a problem in that the thin wire 22 was damaged during use. Therefore, when using the current hot wire flowmeter for engine control, measures such as installing a bypass in the intake pipe and installing the flowmeter in the bypass, or installing a protector etc. behind the flowmeter are taken. However, there was a problem in that the inherent high precision and high-speed response characteristics of the hot wire flowmeter itself were significantly impaired.

Moreover, in order to solve such a problem, the heater 20a
It is also conceivable to provide this on a support made of, for example, ceramics, but if this is done, the heat capacity of the support will increase, and this will result in the above-mentioned Q2. There was a problem in that the value of Q3 also increased, resulting in a significant decrease in accuracy and responsiveness.

[Object of the Invention] The present invention has been made in view of such conventional problems, and its purpose is to provide a flowmeter with good accuracy and responsiveness, as well as sufficient mechanical strength, like hot wire flowmeters. Our objective is to provide a semiconductor flowmeter.

[Means and Effects for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor flowmeter that is installed in a fluid flow path and measures the flow rate of the fluid, including: a semiconductor formed as a heat generation source; a support body having an element, a first support part to which the semiconductor element is attached and fixed, and a second support part that supports the first support part so that the semiconductor element is located in the flow path; at least one pair of temperature sensors for detecting heat flow attached to the second support part to detect heat flow; a second arithmetic control means that drives the semiconductor element and outputs a detection signal corresponding to its power consumption; and a second arithmetic control means that drives the semiconductor element and outputs a detection signal corresponding to its power consumption; subtracting the amount of heat radiated through the support from the amount of heat generated by the semiconductor element based on the outputs of the second and third calculation and control means; a fourth calculation control means for correcting and calculating the flow rate of the fluid; If H is the average heat transfer coefficient per unit length at the maximum flow rate from the support part 2 to the fluid, the temperature sensor pair is within a distance of (K-5/H)l/2 from the semiconductor element. The second
It is characterized by being arranged on the support part of.

In this, the semiconductor flow meter includes a fluid temperature sensor that detects fluid temperature, and the first calculation control means controls the semiconductor flowmeter so that the support body temperature has a constant temperature difference with respect to the detected fluid temperature. It is preferable to control the amount of heat generated by the element.

Furthermore, it is preferable that the temperature sensor pair is provided with a temperature shielding member for preventing heat conduction to the fluid.

Next, the semiconductor flowmeter of the present invention will be explained in more detail.

FIG. 1 shows the structure of the element section of the semiconductor flowmeter of the present invention.

This semiconductor flowmeter uses a heat generating transistor 3o as a semiconductor element, and this heat generating transistor 30
is mounted and fixed on the support 4o. This support 4o
is configured as a rod shape, a plate shape, or a combination thereof, and in the figure, the heat generating transistor 3
It is composed of a plate-shaped first support part 42 that supports the o, and a rod-shaped second support part 44 that extends from the first support part 42 and is fixed on the mounting part 46 .

Further, the second support portion 44 includes a heat generating transistor 30.
At least one pair of temperature sensors 32 is provided to detect the heat flow toward the mounting portion 46. In the figure, this temperature sensor pair 32 includes a temperature sensor 32a provided on the side of the heat generating transistor 30, and a temperature sensor 32a provided on the side of the heat generating transistor 30, and and a temperature sensor 32b provided on the 46 side.

When the element section 100 configured as described above is placed on the flow path of the fluid 10 and the heat generating transistor 30 is heated by electricity, in addition to the amount of heat Q1 taken directly from the heat generating transistor 30 to the fluid 10, the heat generating transistor 30 is transferred to the heat generating transistor 30. Support 4
The amount of heat Q2 is taken away from the support body 40 to the fluid 10 by heat conduction to the fluid 10, and the amount of heat Q3 is taken away by heat transfer to the attachment part 46 via the support body 40. If the heat capacity of the support body 40 is large, Q2. The value of Q3 also increases.

Of the amount of heat Q2 taken from the support body 40 to the fluid 10, the amount of heat taken from the first support portion 42 to the fluid 10 can be made sufficiently small by matching this portion to the shape of the heat generating transistor 30; It is difficult to reduce the amount of heat Q2 taken from the support portion 44 to the fluid 10 because this portion requires sufficient mechanical strength.

Therefore, when the amount of heat generated by the heat generating transistor 30 is Q, the relationship expressed by the following equation holds between Ql, Ql, and Q3, and the values of Ql and Q3 are values that cannot be ignored with respect to Ql.

Q-Ql +Q2 +Q3, = (3) As mentioned above, the flow rate of the fluid 10 is
0 directly transferred to the fluid 10, therefore, in order to detect the fluid flow rate, from the heat generation amount Q of the heat generating transistor 30, Q2.
It is necessary to subtract the value of Q3.

Ql = Q-02-Q3 (4) Here, the above (Ql + Q3) is the second support part 44
When the thermal conductivity of is K and the cross-sectional area is 81 and the temperature gradient near the heat generating transistor of the second support portion 44 is d T/d L, it is expressed by the following equation.

Consideration of (Ql +Q3)−−3−dT/dLQ3 Now, let us first examine the above-mentioned Q3.

For example, a first support portion 4 is provided in a tube 12 through which fluid 10 flows.
If the element part 100 is mounted so that only 2 is exposed, the amount of heat Q2 taken from the support body 40 to the fluid 10 is almost ignored and can be considered as Ql-0.

Under this condition, the temperature distribution of the second support part 44 is the same as that of the first support part 44.
The temperature gradient dT becomes as shown by the characteristic curve A in Figure 2.
/dL has a constant value within the second support portion 44.

Therefore, the amount of heat Q3 taken away by heat conduction to the attachment part 46 via the support body 40 is the amount of heat Q3 taken away by the pair of temperature sensors 32a.

32b is arranged on the second support part 44, the distance between the pair of temperature sensors 32a32b is dL, the temperature difference is dT, and the second support in the area 44a where the pair of temperature sensors 32 is provided. Assuming that the thermal conductivity of the portion 44 is K and the cross-sectional area is S, it is determined by the following equation.

-5-dT/dL for Q3-- (6) In this, since the cross-sectional area S of the thermal conductivity is a constant and the distance dL between the temperature sensor pair 32 is also constant, the temperature sensor Q3 can be easily determined from the temperature difference dT between pair 32.

Therefore, by substituting Q3 obtained in this way into the above equation (4), it is possible to accurately calculate Ql from the heat generation amount Q of the heat generating transistor 30, and thereby the overall structure of the element section 100, It becomes possible to accurately and easily measure the fluid flow rate over a wide flow rate range without being affected by the temperature of the attachment part 46, etc.

Consideration of Ql and Q3 However, as mentioned above, flow rate measurement under the condition that there is no heat conduction Q2 is only possible in some cases, such as when measuring liquid flow rate. In many cases, the second support portion 44 is exposed to the fluid to be measured and Ql cannot be ignored.

FIG. 3 shows a support 40 in the conduit 12 through which the fluid 10 flows.
This is an example in which the element section 100 is arranged so that the entire element section 100 is exposed.

As described above, the relationship expressed by the following equation holds between the heat generation amount Q of the heat generating transistor 30 and the above-mentioned Ql and Q3.

Q-Ql +Q2 +03 Therefore, as described above, the amount of heat Q1 taken from the heat generating transistor 30 to the fluid 10 is expressed as Ql -Q-(Q2 +03).

Here, the value of (Q2 +03) is expressed by the following equation using the thermal conductivity K and cross-sectional area S of the second support portion 44, and the temperature gradient dT/dL in the vicinity of the heat generating transistor.

(Q2 +Q3)−−5・(d T/d L)
(5) Here, in the case of the usage example shown in FIG. 2 where Q2 does not exist, the temperature gradient is constant and Q3 can be easily determined as described above.

On the other hand, when there is heat transfer Q2 from the second support part 44 to the fluid 10, the temperature gradient on the second support part 40 is not constant but complex, as shown in characteristic curve B in FIG. Changes to

Therefore, in equation (5), the temperature gradient dT/dL of the second support portion 44 in the vicinity of the heat generating transistor, which is necessary to obtain (Q2 +03), cannot generally be obtained.

Here, the case where the shape of the support body 40 in the region 44b between the temperature sensor 32b and the heat generating transmitter 30 can be considered to be uniform in its length direction, and the temperature distribution in the lateral direction is smaller than the temperature distribution in the length direction. Suppose.

In this case, from the heat generating transistor 30 to the second support portion 4
4, the temperature distribution T (X) is the heating temperature Th of the heat generating transistor 30, and the detection temperature T of the temperature sensor 32b.
t (however, T (X2) ), the temperature Tf of the fluid 10
It is known that it can be expressed by the following equation using . Here, X represents the distance from the heat generating transistor 30.

(Left below) T(X) −A −e”” +B −e−””+T
f However, A, B, and α shall be expressed by the following formula.

α-fH/(K-S)l''Here, H represents the average heat transfer coefficient per unit length of the temperature difference from the second support portion 44 to the fluid 10 of 1°C, and K is represents the thermal conductivity of the second support portion 44, and S represents the thermal conductivity of the second support portion 44;
4, and XI and X2 represent the positions of temperature sensors 32a and 32b from the heat generating transistor.

Temperature difference between temperature sensors 32a and 32b [T(XI)
T (X2 ) is expressed by the following equation by carrying out Tiller expansion of the exponential term of the seventh equation.

T (XI) - T (X2) - (XI
-x2 ) ・T' (0) + (rh
−T ()((α ・XI)2 (α ・X
2)2)+(α2・Xl3
2 ・Xl 3 ) - α ... (8) Here, if the positions X, , The higher-order terms that occur have negligible values.

Therefore, from the heat generating transistor 30 to the second support portion 40
The heat flow (Q2 +Q3) to -5-T-(0) is approximately expressed by the following equation.

(Q2 +Q3) − H + (Th−”rf) (X, 10X2
)... (9) In the open equation, the second term is T(XI).

Even in this case, it is not possible to determine (Q2 +03) from the temperature difference between two points because it is a quantity that cannot be determined from T(X2). However, instead of Ql, which I originally tried to find, X2. Since all Xl are constants, the value of this second term is
Detected temperature difference between temperature sensors 32a and 32b (T (X2
) T (XI) can be easily obtained from l. In this way, the value of Ql' shown in Equation 10 is determined based on the shape of the support between the temperature sensor pair 32 and the mounting part 46 and the shape of the support between the temperature sensor pair 32 and the mounting part 46.
can be determined without being affected by the temperature.

Furthermore, by substituting the third equation and the ninth equation into the tenth equation, the tenth equation can be rewritten as the following equation.

... (10) This problem can be solved by using the value .

That is, the first term of this equation 10 is the amount of heat generated by the heat generating transistor 30, and can be easily determined from the power consumption of the heat generating transistor 30. Furthermore, in the second term of Equation 10, K, S.

Here, Q1 is the average heat transfer coefficient per unit length and 1° C. from the heating section (heat generating transistor 30) to the fluid 10, and
If the length of is Lh, then Ql - (Th - Tf) x Lh
xH” (12) Therefore, Ql” shown in the above equation (11) can be expressed by the following equation.

Ql　”= xLhxH" -C-Ql ... (13) However, C shall be expressed by the following formula.

In this formula, X, , X2 are temperature sensors 32a, 3
2b, HlH'' is the value for the position of the fluid 10 and the support 42 of the transistor 30, the temperature sensor pair 32.
This is a value related to the shape of the installation part support 44a, and Lh is the length of the transistor 30. Therefore, C shown in the 14th formula becomes a constant.

Therefore, by determining the value of C in advance by measurement, etc., and substituting the value of Ql' determined by the above-mentioned formula 10 into the following formula, it is possible to determine the structure of the support between the temperature sensor 32b and the mounting portion 46, It becomes possible to obtain the value of Ql without being affected by the temperature of the portion 46, etc.

Ql-Ql'/C... (I5) Thus, according to the invention, the temperature sensor 32a.

Even when the temperature sensors 32a and 32b located between the heat generating transistor 30 and the mounting portion 46 are exposed to the fluid 10, the temperature fWX+, By arranging the sensor so that it is within the range of , it is possible to obtain the value of <Ql with sufficient accuracy, so it is not affected by the structure of the support between the temperature sensor 32b and the mounting part 46, the temperature of the mounting part 46, etc. In other words, it becomes possible to accurately measure the flow rate over a wide flow rate range using a support with sufficient strength.

Arithmetic Control Circuit FIG. 4 shows an arithmetic control circuit used in the flowmeter of the present invention.

The first arithmetic control circuit 50 controls the amount of heat generated by the heat generating transistor 30 so that the temperature of the first support part 42 of the support body 40 is constant or has a constant temperature difference with respect to the temperature Tf of the fluid 10. .

Therefore, when using the flowmeter of the present invention as shown in FIG. 3, it is preferable to provide a fluid temperature sensor close to the support 40 for measuring the temperature of the fluid.

The second arithmetic control circuit 60 drives the heat generating transistor 30 at a constant voltage or constant current to send a detection signal S1 proportional to the power W consumed by the heat generating transistor 30 to the fourth arithmetic control circuit 80. Control the direction. This signal Sl has a value corresponding to Q in the tenth equation.

In this case, in the present invention, as a heat generation source, a semiconductor element,
In particular, since the heat generating transistor 30 is used and is driven at a constant current or constant voltage, the signal S1 proportional to the amount of heat generated
can be easily output. On the other hand, when a resistance heating element such as resistive platinum is conventionally used as a heat source, the amount of heat generated is proportional to the square of the voltage applied to the resistor, so an electrical output proportional to the amount of heat generated is obtained. This was extremely difficult.

Further, the third calculation control circuit 7o calculates a detection signal S2 proportional to the heat flow in the second support #44 detected using the temperature sensor pair 32, and outputs a signal S2 to the fourth calculation control circuit 80. Output. This detection signal S2 is fT (X2)
The value is proportional to T (XI) l.

Then, the fourth arithmetic control circuit 8o calculates Ql'' by using the signals Sl and S2 inputted from the second and third arithmetic control circuits 60, and calculates Ql''.
This Ql'' is substituted into the above-mentioned formula 15, and Ql is calculated and output.

That is, first, based on the signal St input from the second arithmetic control circuit 6o, the amount of heat generated Q of the heat generating transistor 30 is calculated.
and calculate the second term of the 10th equation based on the signal s2 output from the third calculation control circuit 70,
Substitute this into the above equation 10 to find Ql''.

Then, the obtained Ql'' is substituted into the above equation 15 to calculate and output Ql.The constant C in the above equation 15 may depend on the type of fluid and the structure of the element, or whether it is the fluid to be measured or air. If it is determined, the value may be set in advance by measurement or the like, since it simply depends on the structure of the element and is a constant that is not affected by the air flow rate.

In this manner, according to the present invention, the fourth arithmetic control circuit 8
0, the heat generation amount Q of the heat generation transistor 30 is calculated from Q
2. Subtract Q3 and fluid 1 from heat generating transistor 30
It is possible to determine the amount of heat Q1 that is directly taken away by the fluid, and output a signal S3 representing the fluid flow rate based on the amount of heat Q1 thus determined.

Although the temperature sensor pair 32 and the support body 36 between the temperature sensor pair 32 and the heat generating transistor 30 are not uniform in the length direction, the temperature distribution in the lateral direction is smaller than the temperature distribution in the length direction. In this case, as the average heat transfer coefficient H per unit length from the support 40 to the fluid 10 on a 1°C side, the temperature sensor pair 32 and the support 36 between the temperature sensor pair 32 and the heat generating transistor 30 Using the average value H8, as the product (K-5) of the thermal conductivity of the support and its cross-sectional area S, calculate 32 questions about the temperature sensor pair and the support 36 between the temperature sensor pair 32 and the heat generating transformer/star 3o. The average value of (K
-8)". In this case, based on a similar argument, the position WX+, [(K −S) '/H”
] By arranging it so that it is within the range, the thermal conduction term can be corrected with sufficient accuracy, and it can be used over a wide flow rate range without being affected by the overall structure of the element or the temperature of the mounting part. It becomes possible to measure the fluid flow rate with high accuracy.

Further, in cases where there is a temperature distribution in the flow direction in the support area where the temperature sensor pair 32 is provided, or as shown in FIG.
44-2..., the plurality of temperature sensor pairs 312-1, 32-2...
The same method as above can be achieved by attaching . It is possible to deal with this using

On the other hand, if the temperature sensor pair 32 is directly exposed to the fluid and the above conditions are no longer satisfied, an enclosure or a All you have to do is coat it with a thermal insulator. In this case, the cross-sectional area of the support 40 on which the temperature sensor pair 32 is provided is S, the thermal conductivity is K, and at the maximum flow rate, the fluid 10 from the support 40 on which the temperature sensor pair 32 is provided is
Assuming that the average heat transfer coefficient per unit length is H, the temperature sensor pair 32 may be positioned within a distance (K - S /H) ''2 from the heat generating transistor 30.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a semiconductor flowmeter that can detect fluid flow rate with high accuracy and responsiveness, and has sufficient mechanical strength. There is an effect.

In particular, according to the present invention, a structure having sufficient mechanical strength can be used as a support for a semiconductor element used as a heat source. This makes it possible to simultaneously incorporate a signal processing circuit such as an IC on the support, thereby reducing noise, production costs, and improving reliability.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail based on the drawings.

A preferred example of the present invention is shown in FIGS. 5 to 8, and the semiconductor flow meter of the embodiment is formed for the purpose of measuring the intake air flow rate of an automobile engine. The range of inspiratory flow rate to be measured for this purpose is usually about 0.
04tz/5-cd to about 8.0 glS-c-.

First, the element section 100 of the semiconductor flowmeter according to this embodiment
The configuration will be explained based on FIGS. 5 and 6.

In the flowmeter of the embodiment, the support 40 has a width of 1 city.

A rectangular silicon substrate with a length of 5mm and a thickness of 01mm is used, and a bipolar transistor 30 of 0.4 mm x O, 9 mil is installed in a region 0.5+n++ from the tip (first support part). It was arranged as a semiconductor element for heat generation, and semiconductor p/n jangkunyong was used as a temperature sensor pair 32 at a position of 0.5 chin and a position of 1.5 yen from the tip (second support part). Diode D2. It has a configuration in which D3 is arranged.

In the element section 100 configured in this way, the second support section 44 of the support body 40 is attached to the attachment section 46 in FIGS.
As shown in B), it is configured to be attached via a joint 26. Therefore, not only the heat generating transistor 30 but also the temperature sensor pair 32 are exposed to the air flow 10.

The product (K-3) of the thermal conductivity and cross-sectional area of the support body 40 formed using a silicon substrate is (K-5)-0,015V.
/sw ・k Te, maximum flow rate (8, Og/5-cd
), the value of the average heat transfer coefficient to the air flow 10 per jaw length is 52. Therefore, the diode D for the temperature sensor shown in FIGS.
2 D3 is connected from the heat generating transistor 30 (K-3/
H)", that is, within 5.2m+e.

FIG. 7 shows a state in which the element portion 100 formed as described above is placed in a tube 12 having an inner diameter of 60 mm through which an air flow 10 flows. In the embodiment, the element section 100 includes:
The element surface 100a is installed parallel to the air flow 10, and the length direction of the element section 100 is orthogonal to the air flow 10.

A diode DI having a configuration similar to that of the temperature sensor pair 32 is installed upstream of this element section 100 as a temperature sensor for detecting air temperature.

FIG. 8 shows a circuit configuration for measuring the intake air flow rate using the element section 100.

In the embodiment, the first operational control circuit 50 is configured using an operational amplifier At and a resistor R1, and includes a temperature sensor pair 3.
A diode D2.2 provided as D2. Of Da, the temperature of the support body where Da is arranged is detected using the diode D3 on the heat generating transistor 30 side. Since the temperature of the support body detected using this diode D3 is approximately equal to the temperature of the first support portion where the heat generating transistor 30 is disposed, the temperature detected using this Da is The amount of heat generated by the transistor 30 is controlled so that there is a constant temperature difference (in this case, 100° C.) with respect to the air flow temperature Tf detected.

In this embodiment, the temperature control of the heat generating transistor 30 is performed as follows.
Although this is done using the diode D3 on the heat generating transistor side of the temperature sensor pair 32, the same problem will not occur even if a temperature sensor other than the temperature sensor pair 32 is used to control the temperature of the heat generating transistor 30. do not have.

In the description of this embodiment, the temperature uniformity of the heat generating transistor 30 was not particularly mentioned, or since temperature non-uniformity of the heat generating transistor generally causes a measurement error.
It is necessary to ensure uniformity as necessary. In the case of this embodiment, the amount of heat generated is controlled simply by using the temperature of the diode D3, but the design is such that measurement errors due to non-uniformity of temperature within the heat generating transistor 30 are sufficiently small. There is no problem with this point.

Further, the second arithmetic control circuit 60 includes a constant voltage diode D
4 (Zener voltage Vt), an operational amplifier A2, and resistors R2 and R3.
0 is driven at a constant voltage, and a voltage (V t +QxR2
/Vt) as the detection signal S1 and the fourth arithmetic control circuit 8.
Output towards 0.

Further, the third arithmetic control circuit 70 includes an operational amplifier A3. A
4. A5, resistors R4, R5, R6, etc., and a diode D3 that constitutes the temperature sensor pair 32.
and a voltage proportional to the detected temperature difference ΔT of D2 [2X10
zuXΔTX (1+2xR5/R4)] is detected as the signal S2
The signal is outputted to the fourth arithmetic control circuit 80 as a signal. Here, the temperature coefficient of the diode D2 Da, that is, the p/n junction temperature sensor, was set to -2X 10-3 V/'C.

The fourth operational control circuit 80 includes an operational amplifier A6 and a resistor R.
Based on the signals SL and S2 output from both arithmetic and control circuits 60 and 70, the 10th and 14th equations are
By calculating the formula, the air flow 1 from the heat generating transistor 30 is
0 outputs a voltage S3 proportional to the amount of heat Q1 taken away.

This makes it possible to accurately measure the amount of intake air without being influenced by Q2°Q3.

Note that the variable resistor R4 used in the third arithmetic control circuit 70 is a resistor for adjusting the output to be 0 under no wind conditions, and adjusts the heat conduction term and the amount of heat generated. It is for.

(Experimental Results) The results of measuring the air flow rate at an air temperature of 15° C. using the flowmeter of this example will be described below.

The temperature of the intake wall of an automobile engine rises to about 100℃ during operation, so the temperature of the mounting part may be 15℃, 50℃,
The air flow rate was measured at 100°C.

FIG. 9 shows the value of the power consumed by the heat generating transistor 30 converted from the measured voltage when the heat generating transistor 30 is energized and heated so that the detected temperature of the diode D3 is maintained at 115°C. As shown in FIG. 9, the amount of heat required to heat the air to 115° C. varies greatly depending on the temperature of the intake pipe wall. For this reason, the conventional method of determining the intake air amount from the calorific value cannot be applied when a silicon substrate with high thermal conductivity is used as the support 40 as in this embodiment.

FIG. 10 shows a heat generating transistor 30 using the present invention.
From the calorific value Q, the thermal conduction term Q2. The relationship between the output S3 and the air flow rate when Q3 is corrected and subtracted is shown (10th
The vertical axis in the figure is the output voltage converted to heat amount).

As is clear from FIG. 10, the output S3 obtained using the present invention is almost unaffected by the temperature fluctuation of the intake pipe wall, and is largely dependent on the amount of air. It is clear that the amount of air can be easily determined, and the superiority of the present invention will be understood.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the gist of the present invention.

For example, in this embodiment, the electric circuit section is configured separately from the element section 100, but since a silicon substrate is used as the support 40 in this embodiment, an IC or the like including the electric circuit section can be installed in the support 40 at the same time. By incorporating it, it is possible to further reduce costs, improve reliability, and make it more compact.

Further, in the embodiments described above, the present invention has been explained by taking as an example the case where the present invention is used to measure the flow rate of an air flow, but the present invention is not limited to this, and can be widely used for measuring the flow rate of other gases and liquids.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of the element section of a semiconductor flowmeter according to the present invention, FIGS. 2 and 3 are explanatory diagrams of the element section shown in FIG. 1 attached to a flow path, and FIG. 1 is a block diagram of an arithmetic and control circuit that measures fluid flow rate using the element section shown in FIG. 1, and FIGS. 5 and 6 are explanatory diagrams of the specific configuration of the element section of the semiconductor flowmeter of the present invention. , FIG. 7 is an explanatory diagram showing an example of a state in which the element section is arranged in an air supply pipe of an engine, FIG. 8 is a circuit diagram showing a specific configuration of the arithmetic and control circuit shown in FIG. 4, and FIG. Figure 9 is a characteristic diagram showing the relationship between the power consumption of the transistor provided in the element section and the measured air flow rate, and Figure 10 is the measured air flow rate measured using the 'semiconductor type flowmeter of the present invention. FIG. 11 is an explanatory diagram showing the other two sides of the element part of the semiconductor flowmeter of the present invention, FIG. 12 is an explanatory diagram of the temperature distribution of the support, and FIG. 13 is a diagram of the thermal flowmeter of the present invention. Figure 14 is an explanatory diagram of a conventional hot wire flowmeter. DESCRIPTION OF SYMBOLS 10... Fluid, 30... Heat generating transistor, 32... Temperature sensor pair, 40... Support body, 42...
- First support part, 44... Second support part, 50...
1st arithmetic control circuit, 60...2nd arithmetic control circuit, 70...3rd arithmetic control circuit, 80...4th arithmetic control circuit, Dl...fluid temperature sensor, D2. D3...Diode as a temperature sensor. Figure 1 Agent: Patent attorney Yukio Fuse (and 1 other person) Figure 12 Pipe diagram Figure tn (Air volume (g/s)) Power required for 1 heating Figure Ln (Air flow rate (g/s) s)) Output diagram diagram diagram diagram diagram diagram diagram heating element 20 obtained using the present invention

Claims (2)

[Claims] (1) A semiconductor flow meter that is installed in a fluid flow path and measures the flow rate of the fluid, which includes a semiconductor element formed as a heat generation source, a first support part to which the semiconductor element is attached and fixed, and a semiconductor element formed as a heat generation source. a support body having a second support part that supports the first support part so that the semiconductor element is positioned in the flow path; and at least a pair of heat flow detectors attached to the second support part to detect heat flow. a first arithmetic control means for controlling the amount of heat generated by the semiconductor element so that the temperature of the support body with respect to the temperature of the fluid is a constant temperature difference; a second arithmetic control means that outputs a detection signal that is detected using the temperature sensor pair; a third arithmetic control means that outputs a detection signal that is proportional to the heat flow within the second support portion detected using the temperature sensor pair; and a fourth arithmetic control means that calculates the flow rate of the fluid by subtracting and correcting the amount of heat radiated through the support from the amount of heat generated by the semiconductor element based on the output of the third arithmetic control means. S, the thermal conductivity of the support material is K, the average per unit length at the time of maximum flow rate from the second support to the fluid. When the heat transfer coefficient is H, the temperature sensor pair is placed within a distance of (K S/H) 1/2 from the semiconductor element.
A semiconductor type flowmeter characterized in that it is arranged on a supporting part. (2) In claim (1), the first calculation control means includes a fluid temperature sensor that detects the fluid temperature, and the first calculation control means is configured to adjust the temperature of the support body to a constant temperature difference with respect to the detected fluid temperature. A semiconductor flowmeter characterized by controlling the amount of heat generated by a semiconductor element.