JPH0593639A - Flow-rate/flow-speed measuring apparatus - Google Patents

Abstract

PURPOSE:To detect the accurate speed or the flow rate of fluid by making correction to the outside air temperature with a simple circuit constitution. CONSTITUTION:An upstream-side temperature detecting part 11, a heater part 9 and a downstream-side temperature detecting part 12 are arranged on a flow- speed detecting surface 2A of a sensor main body 2 in this order along the flowing direction (v) of fluid. A temperature correcting part 10 is provided at the rear side of a substrate part 2B in parallel with the heater part 11. The temperature correcting part 10 and the heater part 9 is constituted of a thermistors, and the temperature detecting parts 11 and 12 are constituted of posistors. A specified current I is supplied into the series circuit of the upstream- side temperature detecting part 11, the heater part 9 and the downstream-side temperature detecting part 12 from a constant-current power supply 13. The temperature difference between the temperature detecting parts 11 and 12 is detected as an output voltage V from amplifier circuits 15, 16 and 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter suitable for measuring the intake air amount, exhaust gas amount, etc. of an engine.

[0002]

2. Description of the Related Art Generally, a hot wire type flow meter using a platinum wire is known as a flow meter for measuring the intake air amount of a vehicle engine.

However, this type of hot-wire type flow meter uses a platinum wire as a heating wire, so that it is expensive and a sensor ring having a platinum wire or a bobbin wound is disposed in the flow path. Since this has to be done, there is a problem that the pressure loss becomes large in the case of the small diameter flow path.

In order to solve this problem, the present inventor has previously proposed Japanese Patent Application No. 2-227615, in which a substrate disposed in the flow path along the flow direction of the fluid and a central portion of the surface of the substrate. And a heater section for heating the temperature of the substrate to a temperature distribution that decreases as it goes from the central portion to the upstream side and the downstream side, and heaters provided on the surface of the substrate located upstream and downstream of the heater portion, respectively. A temperature sensing unit that senses the upstream and downstream temperatures that change according to the flow velocity of the fluid flowing in the flow path while being heated by the conduction heat from the temperature sensing unit; and circuit means that extracts the differential output of each temperature sensing unit. We have proposed a flow meter equipped with it (hereinafter referred to as prior art).

When a fluid flows in the flow path, the temperature distribution of the substrate shifts from upstream to downstream according to the flow velocity. As a result, the temperature on the upstream side with respect to each temperature sensing unit decreases and the temperature on the downstream side increases. The differential output of the temperature sensing unit obtained by detecting each of these temperatures is taken out by a bridge circuit configured as circuit means and converted into a fluid flow velocity, that is, a flow rate. Therefore, it is possible to provide a small-sized flow meter with a small pressure loss, and it is possible to measure the flow rate of a high temperature fluid by using a thermistor having a negative temperature characteristic such as SiC fiber for each temperature sensing portion.

[0006]

By the way, in the above-mentioned prior art, the temperature correction is not taken into consideration. Therefore, the temperature of the heater section and the sensitivity of each temperature sensing section change with the change of the outside air temperature. However, there is an unsolved problem that an accurate flow rate or flow velocity cannot be measured.

Further, when the temperature correction resistor is used in the bridge circuit, the bridge circuit must be balanced each time the temperature changes, and the circuit configuration of the correction circuit becomes complicated.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention corrects the temperature with a simple circuit configuration and can accurately measure the flow rate and the flow rate regardless of the change of the outside air temperature. An object is to provide a flow velocity measuring device.

[0009]

A flow rate / velocity measuring apparatus adopted by the first invention to solve the above-mentioned problems is a substrate disposed along a flow of a fluid in a flow channel, and the substrate. A heater portion which is disposed in the central portion of the surface of the substrate and which heats the temperature distribution on the substrate so as to become lower as it goes upstream and downstream from the central portion; Upstream of the heater unit, and a temperature correction unit that is connected in parallel to the heater unit and has a resistance value larger than that of the heater unit and that has the same temperature characteristics as the heater unit. , Located on the downstream side and spaced apart from the heater portion by a predetermined distance, respectively, on the surface of the substrate, and having a resistance value extremely smaller than the resistance value of the heater portion and different from the heater portion. Upstream consisting of elements with Temperature detection unit, a downstream temperature detection unit, a constant current supply unit that supplies a predetermined current to a series circuit including the downstream temperature detection unit, the heater unit, and the upstream temperature detection unit, and the detection from each of the temperature detection units. It is composed of a flow rate / flow rate detecting means for detecting the flow rate / flow rate by a signal.

The flow rate / velocity measuring device adopted by the second invention is a substrate arranged along the flow of a fluid in the flow path and a central portion of the surface of the substrate. The temperature distribution of the heater so as to become lower from the central part toward the upstream and the downstream, and a heater part composed of elements having positive or negative temperature characteristics, and the heater part located upstream and downstream of the heater part. An upstream side temperature detection unit, which is arranged on the surface of the substrate at a predetermined interval and has an extremely small resistance value with respect to the resistance value of the heater unit and has the same temperature characteristics as the heater unit, The downstream side temperature detecting section, a constant current supplying means for supplying a predetermined current to a series circuit including the downstream side temperature detecting section, the heater section and the upstream side temperature detecting section, and a flow rate by a detection signal from each of the temperature detecting sections.
It is composed of a flow rate / flow rate detecting means for detecting the flow rate.

[0011]

In the first aspect of the present invention having the above-described structure, the rate of change in the resistance value of the heater section and that of the temperature correction section depending on the outside air temperature can be made the same, so that the current supplied to the heater section and the temperature correction section is The ratio does not change, and the temperature difference between the heater section and the temperature compensating section can always be kept constant regardless of changes in the outside air temperature. ..

Further, according to the second aspect of the present invention, the rate of change in the resistance value due to the outside air temperature can be made the same for the heater section and each temperature detecting section, and the heater section can respond to changes in the temperature distribution on the substrate. The detection sensitivity of each temperature detection unit can be made to correspond.

[0013]

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

1 to 8 show a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a detecting portion of the flow velocity measuring device according to the present embodiment, and the detecting portion 1 includes a sensor body 2 described later,
A heater section 9 provided on the sensor body 2, a temperature correction section 10 provided on the back side of the heater section 9, and a predetermined space upstream and downstream with the heater section 9 sandwiched therebetween. The upstream side temperature detecting section 11 and the downstream side temperature detecting section 12 provided in the second section are generally configured.

Reference numeral 2 denotes a sensor main body as a substrate, the sensor main body 2 is made of a ceramic material or the like, and the sensor main body 2 is flush with a flow passage forming wall 3 (only part of which is shown) for a fluid (for example, air). 2B that becomes the flow velocity detection surface 2A of
And a small-diameter square tube portion 2C formed outward from the plate portion 2B, and an axially intermediate outer peripheral surface of the square tube portion 2C, which is provided so as to project outward, respectively. It is composed of locking claw portions 2D, 2D that are locked to the forming wall 3.

Reference numeral 4 denotes a print pattern formed on the flow velocity detecting surface 2A of the sensor body 2. The print pattern 4 extends parallel to the short direction of the sensor body 2 and extends in the air flow direction v. I-shaped upstream pattern 4A and downstream pattern 4B located on the upstream and downstream sides,
The U-shaped intermediate patterns 4C and 4 formed between the patterns 4A and 4B so as to open upward in FIG.
D and one of the patterns 4A, 4B, 4C, 4D (on the lower side in FIG. 1), the patterns 4A, 4B, 4
Terminal pins 5, 6, and 7, which will be described later, are provided which are connected to C and 4D and are fitted into the board portion 2B.

Terminal pins 5 and 5 are connected to one side of each upstream pattern 4A and one side of the intermediate pattern 4C located on the left side, and are inserted into the board portion 2B, and 6 and 6 are each downstream side. The terminal pins 7, 7, ... Connected to one side of the pattern 4B and one side of the intermediate pattern 4D located on the right side and inserted into the board portion 2B are the intermediate patterns 4C, 4D.
The terminal pins connected to the vertices on one side and inserted into the board portion 2B are shown. Reference numerals 8 and 8 denote temperature correction patterns which are located between the terminal pins 7 and are formed on the back side of the substrate portion 2B so as to extend in the short direction.

Reference numeral 9 denotes a heater portion formed in a thin film shape on the other side (upper side in FIG. 1) between the intermediate patterns 4C by means such as vapor deposition. The heater portion 9 has a negative temperature characteristic (for example, It is composed of a thermistor having a resistance value RH while having a transition metal oxide).

Reference numeral 10 denotes a temperature correction portion which is located on the back side of the heater portion 9 and is formed in a thin film on the other side between the temperature correction patterns 8 by means such as vapor deposition. The thermistor is made of the same material as the heater portion 9 having a negative temperature characteristic and has a resistance value Rr (> RH).

Reference numerals 11 and 12 denote the upstream patterns 4A,
An upstream temperature detecting portion and a downstream temperature detecting portion, which are formed in a thin film by means such as vapor deposition, are shown on the other side between the downstream patterns 4B, and the detecting portions 11 and 12 have positive temperature characteristics (for example, titanic acid). It is composed of a posistor having a resistance value R0 (<< RH) while having a barium type or a silicon type).

The upstream temperature detector 11, the heater unit 9 and the downstream temperature detector 12 are arranged so as to be aligned in a straight line with respect to the air flow direction v, and the uppermost stream side terminal is provided via the pattern 4. The pin 5 and the most downstream terminal pin 6 are connected in series.

Next, the structure of the detection circuit of the flow velocity measuring device will be described with reference to FIG.

In FIG. 4, reference numeral 13 denotes the upstream temperature detecting section 1
1, a constant current power supply as a constant current supply means for supplying a predetermined current I to a series circuit composed of the heater unit 9 and the downstream temperature detection unit 12, the constant current power supply 13 is connected to the terminal pin 6 on the most downstream side At the same time, it is connected to the earth 14 via the terminal pin 5 on the most upstream side.

Reference numerals 15, 16 and 17 denote amplifying circuits as flow velocity detecting means. An upstream temperature detecting section 11 is connected to each input terminal of the amplifying circuit 15 via each terminal pin 5 or the like.
The downstream temperature detection unit 12 is connected to each input terminal of the amplifier circuit 16 via each terminal pin 6 and the like, and the output terminals of the amplifier circuits 15 and 16 are connected to each input terminal of the amplifier circuit 17. The output terminal of the amplifier circuit 17 is the output unit 18
The output voltage V0 is output between the output section 18 and the ground 14.

The flow velocity measuring device according to this embodiment has the above-mentioned structure, and its detecting operation will be described below with reference to FIGS. 5 and 8.

Now, considering the change in the outside air temperature t which affects the detection unit 1, the current I flowing through the heater unit 9 is considered.
H is

[0028]

[Equation 1] However, α is the ratio of the current set by each resistance value, and the electric power WH in the heater unit 9 is

[0029]

Becomes Equation 2] ^{WH = RH · IH 2 = RH} · (α · I) 2, the temperature T heater unit 9 corresponding to the power WH
It becomes H.

Further, the current Ir flowing through the temperature correction unit 10
Is

[0031]

[Equation 3] Therefore, the power Wr in the temperature correction unit 10 is

[0032]

Equation 4] ^{Wr = Rr · Ir 2 = Rr} · {(1-α) · I} becomes ^2, the temperature compensating section 10 becomes the ambient temperature Tf corresponding to the power Wr.

Here, when the outside air temperature t changes,
Since the heater unit 9 and the temperature correction unit 10 are composed of thermistors having the same negative temperature characteristics, the heater unit 9
And the resistance change rate of the resistance value Rr of the temperature correction unit 10 are the same, and the current ratio α is always constant regardless of the outside air temperature t. Then, as shown in FIG. 5, the difference between the heater temperature TH of the heater unit 9 and the ambient temperature Tf of the temperature correction unit 10 is always a constant temperature difference ΔT.

Next, the temperature distribution on the sensor body 2 of the heater section 9 will be described with reference to FIGS. 6 and 7.

In FIG. 6, 19 shows the temperature distribution of the heater portion 9 when the velocity v of the air is zero. The temperature distribution 19 has a maximum heater temperature TH and spreads upstream and downstream. As a result of the distribution, the temperature of the same temperature T0 is detected in each of the detectors 11 and 12.

When the air flows in the direction of arrow v, the temperature distribution of the heater section 9 moves from 19 to 20, as shown in FIG. 7, and the upstream side temperature detecting section 11 detects the temperature T1. The temperature T2 (<T1) is detected in the downstream temperature detector 12. On the other hand, the temperature distribution is moved to the downstream side according to the velocity v of the air. Then, this temperature difference ΔT (= T2 -T
1), heater temperature TH and ambient temperature Tf

[0037]

[Equation 5] The formula of is established.

Further, by modifying the above equation 5,

[0039]

[Equation 6] The air velocity v can be calculated from the temperature difference between the detection units 11 and 12.

Therefore, in the detection circuit of this embodiment,
The decrease in temperature from T0 to T1 in the upstream temperature detection unit 11 due to the velocity of air v is detected as a change in resistance value, and the increase in temperature from T0 to T2 in the downstream temperature detection unit 12 is detected as resistance. A change in the resistance value is detected, and the change in each resistance value is amplified by the amplifier circuits 15 and 16 to obtain output voltages V1 and V2. The difference between the output voltages V1 and V2 is amplified by the amplifier circuit 17, and the output unit 18 is provided. Outputs an output voltage V0.

Then, as shown in FIG. 8, the output characteristic of the output voltage V0 corresponding to the velocity v of the air can be obtained.

Thus, in this embodiment, even when the outside air temperature t changes, the change in the resistance value of the heater unit 9 and the temperature correction unit 10 can be changed at the same ratio, so that even when the outside air temperature t changes. The temperature difference ΔT between the temperature TH of the heater unit 9 and the ambient temperature Tf of the temperature correction unit 10 can be kept constant. As a result, the temperature can be corrected with a simple circuit configuration and the accurate flow velocity can be detected.

Further, by configuring the detecting portion 1 as described above, since it is not arranged so as to project into the flow path as in the prior art, the pressure loss can be reduced and the small diameter flow can be obtained. It can also be used on the road. Further, in the detection circuit, it is not necessary to configure a bridge circuit or a separate electric circuit for temperature compensation as in the prior art, so that the flow velocity measuring device can be a low cost with a simple circuit configuration.

Further, since the heater unit 9, the temperature correction unit 10, and the temperature detection units 11 and 12 are constituted by thermistors, it is possible to form a flow velocity measuring device having good responsiveness.

In the first embodiment, the heater portion 9
The temperature correction unit 10 is configured by a thermistor having a negative temperature characteristic, and the upstream temperature detection unit 11 and the downstream temperature detection unit 12 are configured by a posistor having a positive temperature characteristic, but the present invention is not limited to this. , The heater part and the temperature compensating part are composed of a posistor having a positive temperature characteristic,
The upstream temperature detecting section and the downstream temperature detecting section may be configured by thermistors having negative temperature characteristics. Further, each temperature detecting unit, heater unit, and temperature correcting unit may be made of SiC fiber.

Next, FIGS. 9 to 12 show a second embodiment of the present invention. The feature of this embodiment is that the heater section and each temperature detecting section are composed of temperature detecting elements (SiC fibers) having the same temperature characteristics. The same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 21 denotes a detector of the flow velocity measuring device according to the present embodiment. The detector 21 has substantially the same structure as the above-mentioned detector 1, and includes a sensor main body 22 described later and a sensor main body 22. The heater part 27 provided and the heater part 2
It is roughly composed of an upstream temperature detecting portion 28 and a downstream temperature detecting portion 29 provided on the sensor main body 22 with a predetermined distance therebetween on the upstream side and the downstream side with 7 in between.

Reference numeral 22 denotes a sensor body as a substrate. The sensor body 22 is made of a ceramic material or the like, and the sensor body 22 serves as a flow velocity detecting surface 22A which is flush with the air flow path forming wall 3. A small-diameter square tubular portion 22C formed outward from the plate portion 22B, and an axially intermediate portion of the outer peripheral surface of the square tubular portion 22C which is provided so as to project outward, It is composed of locking claw portions 22D and 22D that are locked to the forming wall 3.

Reference numeral 23 denotes the flow velocity detecting surface 2 of the sensor body 22.
2A shows a print pattern formed on the 2A side, and the print pattern 23 has a lower pattern 23A provided by extending to the lower side and the upper side in FIG. 9 in a stepwise manner with respect to the air flow direction v as shown in FIG. , Upper pattern 23B,
Terminal pins 24, 25, 26 described later are provided at each end of each pattern 23A, 23B.

24 and 24 are positioned at right angles to the air flow direction v, one of which is connected to the upstream end of the lower pattern 23A and is inserted into the board portion 22B.
25 and 25 are located at right angles to the air flow direction v,
One is connected to the downstream end of the upper pattern 23B, and the terminal pins 26, 26 inserted into the board portion 22B are connected to the downstream and upstream ends of the patterns 23A and 23B, respectively. , And the terminal pins inserted into the board portion 22B.

27 is connected between the terminal pins 26,
Shows a heater part attached on the flow velocity detection surface 22A,
The heater portion 27 is made of SiC fiber having a negative temperature characteristic, and has a resistance value RH by being provided so as to be folded back a plurality of times between the terminal pins 26.

Reference numerals 28 and 29 denote an upstream side temperature detecting section and a downstream side temperature detecting section which are respectively connected between the respective terminal pins 24 and 25 and are adhered onto the flow velocity detecting surface 22A. 28 and 29 are made of SiC fiber having a negative temperature characteristic, and have a resistance value R0 (<< RH) by connecting each of the terminal pins 24 and 25 in a straight line.

The upstream side temperature detecting portion 28, the heater portion 27 and the downstream side temperature detecting portion 29 are arranged in a straight line on the flow velocity detecting surface 22A in the air flow direction v, and the pattern 23 is formed. It is connected in series between the terminal pins 24 and 25 via.

The detecting unit 21 having such a configuration is shown in FIG.
As shown in FIG. 4, the detection circuit is connected to the same detection circuit as that of the first embodiment.

The upstream side temperature detecting section 28 is connected to each input terminal of the amplifier circuit 15 via each terminal pin 24 and the like, and is connected to each input terminal of the amplifier circuit 16 to the downstream side via each terminal pin 25 and the like. The side temperature detector 29 is connected to the amplifier circuit 17
The output terminals of the amplifier circuits 15 and 16 are connected to the respective input terminals of. The output terminal of the amplifier circuit 17 is connected to the output section 18, and the output voltage V0 is output between the output section 18 and the ground 14.

The flow velocity measuring device according to the present embodiment has the above-mentioned structure, and its detecting operation is almost the same as that of the above-mentioned first embodiment.

Here, considering the case where the outside air temperature changes, since the heater section 27 and the temperature detecting sections 28 and 29 are composed of thermistors having the same temperature characteristics, they are detected by the temperature detecting sections 28 and 29. The voltage to be set is set by the change of each resistance value R0. Since the resistance value R0 of the temperature detection units 28 and 29 has the same amount of change with respect to the change of the outside air temperature, even if the outside air temperature changes,
The difference between the resistance values of the temperature detecting portions 28 and 29 does not change, and the relationship of the above-mentioned expression 6 is established, and the difference between the resistance values irrelevant to the outside air temperature can always be output from the amplifier circuit 17 as the output voltage V0. .

Therefore, also in this embodiment, the temperature difference between the temperature detecting portions 28 and 29 can be detected with high accuracy regardless of the change in the outside air temperature, and the accurate air velocity v can be measured.

In the second embodiment, the heater section 2
7 and the temperature detecting portions 28 and 29 are configured as thermistors having negative temperature characteristics by using SiC fibers, but the present invention is not limited to this, and may be configured as positive transistors having positive temperature characteristics.

Further, in each of the above embodiments, the velocity v of air is
Although the flow velocity measuring device for measuring is described, the flow rate measuring device can be configured by setting the constant A or a in Expression 6 in consideration of the cross-sectional area of the flow path.

[0061]

As described above in detail, according to the first aspect of the present invention, the upstream side temperature detecting portion, the heater portion, and the downstream side temperature detecting portion are arranged on the substrate in this order from the upstream side along the fluid flow. The temperature correction unit and the heater unit have the same temperature characteristics, and each temperature detection unit has a temperature different from that of the heater unit. In the second invention, the temperature detecting element having characteristics is provided, and in the second invention, the upstream temperature detecting unit, the heater unit, and the downstream temperature detecting unit are arranged on the substrate in this order from the upstream side along the flow of the fluid.
Since each temperature detection unit and the heater unit are configured by the temperature detection element having the same temperature characteristic, it is possible to accurately detect the temperature difference of each temperature detection unit regardless of the change in the outside air temperature.
Accurate flow rate and velocity of fluid can be measured.

Furthermore, since a temperature compensation circuit for the outside air temperature is not specially provided, a low cost flow rate / flow velocity measuring device can be obtained.

[Brief description of drawings]

FIG. 1 is a front view showing a detection unit of a flow velocity measuring device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a rear view of the detection unit.

FIG. 4 is a configuration diagram of a detection circuit of the flow velocity measuring device according to the first embodiment.

FIG. 5 is a characteristic diagram showing a relationship between outside air temperature and heater temperature.

FIG. 6 is an explanatory diagram showing a temperature distribution on a detection unit when the speed is zero.

FIG. 7 is an explanatory diagram showing a temperature distribution on a detection unit at a speed v.

FIG. 8 is a characteristic diagram showing the relationship between speed and output voltage.

FIG. 9 is a front view showing a detecting portion of a flow velocity measuring device according to a second embodiment of the present invention.

10 is a cross-sectional view taken along arrow XX in FIG.

FIG. 11 is a rear view of the detection unit.

FIG. 12 is a configuration diagram of a detection circuit of a flow velocity measuring device according to a second embodiment.

[Explanation of symbols]

 1, 21 Detection part 2, 22 Sensor main body (substrate) 3 Flow path forming wall (flow path) 9, 27 Heater part 11, 28 Upstream temperature detection part 12, 29 Downstream temperature detection part 13 Constant current power supply (constant current) Supplying means) 15, 16, 17 Amplifying circuit (flow rate / flow velocity detecting means)

Claims (2)

[Claims] 1. A substrate disposed along a flow of a fluid in a flow channel, and a substrate disposed on a central portion of the surface of the substrate, the temperature distribution on the substrate being lowered from the central portion toward upstream and downstream. And a heater part consisting of an element having a positive or negative temperature characteristic for heating so that it is connected in parallel to the heater part outside the flow path, and has a resistance value larger than the resistance value of the heater part, And a temperature correction unit formed of an element having the same temperature characteristic as that of the heater unit, and disposed on the upstream side and the downstream side of the heater unit and spaced apart from the heater unit by a predetermined distance on the surface of the substrate, respectively. An upstream temperature detection unit, a downstream temperature detection unit, and an upstream temperature detection unit and a downstream temperature detection unit, which have resistance values extremely smaller than the resistance value of the heater unit and have different temperature characteristics from the heater unit. And the upstream temperature detector A flow rate / flow rate measuring device comprising constant current supply means for supplying a predetermined current to the series circuit, and flow rate / flow rate detection means for detecting the flow rate / flow rate based on the detection signal from each of the temperature detecting sections. 2. A substrate disposed along a fluid flow in a flow channel, and a substrate disposed at a central portion of the surface of the substrate, the temperature distribution on the substrate being lowered from the central portion toward the upstream side and the downstream side. And a heater portion formed of an element having a positive or negative temperature characteristic for heating so that the heater portion is positioned upstream and downstream of the heater portion and spaced apart from the heater portion by a predetermined distance. And an upstream side temperature detecting section, a downstream side temperature detecting section, and a downstream side temperature detecting section, each of which has an extremely small resistance value with respect to the resistance value of the heater section and which has the same temperature characteristic as that of the heater section. A constant current supply means for supplying a predetermined current to a series circuit composed of a heater part and an upstream temperature detection part, and a flow rate / flow rate detection means for detecting a flow rate / flow rate from a detection signal from each of the temperature detection parts. Flow rate / velocity measurement equipment Place