JPH0641133Y2 - Heat wire type flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a hot wire type flow meter suitably used for detecting an intake air flow rate of, for example, an automobile engine.

[Conventional technology]

Generally, in an automobile engine or the like, a heat ray resistance including a heat-sensitive element is disposed in the middle of the intake passage, and the intake air flow rate is detected by cooling the heat ray resistance with intake air flowing in the intake passage. A hot wire type flow meter is used.

Therefore, FIG. 3 shows a conventional hot wire type flow meter of this type.

In the figure, reference numeral 1 denotes a heat sensitive element as a heat ray resistance whose resistance value R _H changes in response to a temperature change, and the heat sensitive element 1 is disposed in an intake passage (not shown) of an engine together with a temperature compensating resistor 2. The intake air flowing through the intake passage is cooled. Here, the thermosensitive element 1 is formed by using a material such as platinum whose resistance value changes sensitively to a temperature change, and for example, a platinum wire is wound around an insulating cylindrical body such as ceramic or a platinum thin film is formed. It is composed of a small resistance element or the like formed by vapor deposition. The temperature compensating resistor 2 is formed by depositing platinum on a substrate such as alumina by a method such as sputtering, and its resistance value is R _K.

Reference numerals 3 and 4 denote a flow rate adjusting resistance and a reference resistance arranged outside the intake passage, and the flow rate adjusting resistance 3 and the reference resistance 4 have resistance values R ₂ and R ₃ , respectively. Is connected in series with the temperature compensation resistor 2 and the heat sensitive element 1. A series circuit including the heat sensitive element 1 and the reference resistor 4 and a series circuit including the temperature compensating resistor 2 and the flow rate adjusting resistor 3 are connected in parallel at a connection point 7 and 8 between a battery 11 and a ground, which will be described later. The bridge circuit is configured as shown in.

Reference numeral 9 denotes a differential amplifier whose input side is connected to the connection points 5 and 6 and whose output side is connected to the base side of the power transistor 10. The differential amplifier 9 is a direct current based on the potential difference between the connection points 5 and 6. The supply current supplied from the battery 11 as a power source to the thermosensitive element 1 and the like is controlled via the power transistor 10. That is, when the potential of the connection point 6 becomes higher, the output of the differential amplifier 9 decreases and the collector current of the power transistor 10 increases, which increases the supply current supplied to the thermosensitive element 1 and the like. To do. Further, when the potential at the connection point 6 decreases, the supply current decreases in the opposite manner to the above case. The differential amplifier 9, the power transistor 10, and the like are mounted together with the flow rate adjusting resistor 3 and the reference resistor 4 on an insulating substrate (not shown) outside the intake passage.

In the hot-wire type flow meter configured as described above, first, a current is supplied from the battery 11 to the heat-sensitive element 1 or the like via the power transistor 10 or the like to heat the heat-sensitive element 1 to, for example, about 240 ° C. When the flow velocity of the intake air flowing in the intake passage increases and the intake air flow rate increases, the thermosensitive element 1 is cooled more greatly. Therefore, the resistance value of the thermosensitive element 1
R _H tends to decrease, the potential of the connection point 6 rises, and the connection point
The differential amplifier 9 controls the power transistor 10 so as to increase the current supplied from the battery 11 by the potential difference between 5 and 6. As a result, the temperature of the heat sensitive element 1 is set to about 240 ° C., and the heat sensitive element 1 can be heated so as to keep its resistance value R _H constant. For example, a voltage signal corresponding to the intake air flow rate is extracted from the voltage across the reference resistor 4. be able to.

That is, the differential amplifier 9 and the power transistor 10 and the like perform constant resistance control for keeping the resistance value R _H of the heat sensitive element 1 constant, and during this constant resistance control, the resistance value R _H of the heat sensitive element 1 is changed to the temperature compensation resistance 2 , Resistance value of flow rate adjustment resistor 3 and reference resistor 4
For R _K , R ₂ and R ₃ , The control value satisfies the relation
It is heated to a predetermined temperature of about 0 ° C. The resistance values R _K , R
₂ is a much larger value than the resistances R _H and R ₃ .

[Problems to be solved by the device]

By the way, in the above-mentioned prior art, when the thermosensitive element 1 is cooled as the intake air flow rate is increased, the current supplied to the thermosensitive element 1 is kept in order to keep the resistance value R _H of the thermosensitive element 1 constant. Therefore, for example, when the supply current I _H flows in the series circuit of the heat sensitive element 1 and the reference resistor 4, H = 0.24 × I _H ² × R ₃ (cal / cal sec) (2) Joule heat H is generated and the reference resistor 4 self-heats. The resistance value R ₃ of the reference resistor 4 is R ₃ ′ = R ₃ (1 + α ₃ × ΔT) according to changes in Joule heat H and ambient temperature (3) where α ₃ : temperature coefficient ΔT: Increase in resistance value R ₃ ′, which is the amount of temperature change.

Therefore, in the prior art, as the resistance value R ₃ of the reference resistor 4 changes to R ₃ ′, not only the value of the supply current I _H changes, but also the heat-sensitive element defined by the equation (1). There is a problem in that the resistance value R _{H of} 1 deviates from a predetermined control value, and the accuracy of flow rate detection by the hot-wire flowmeter decreases. Further, in order to prevent the resistance value R ₃ of the reference resistor 4 from changing to R ₃ ′, the temperature coefficient α ₃ is very small, for example, by using a special material such as manganin as a winding resistor, It is also known that the reference resistor 4 is formed. However, in this case, since the winding resistance must be formed by using a special material such as manganin, there is a problem that the cost is increased and the winding cannot be formed compactly, and the mounting work is troublesome.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can prevent the control value of the heat wire resistance from shifting.
The present invention provides a hot wire type flow meter capable of improving detection accuracy.

[Means for Solving the Problems]

The feature of the configuration adopted by the present invention to solve the above-mentioned problem is that the reference resistor and the flow rate adjusting resistor are arranged on an insulating substrate so as to face each other with a thin insulating layer interposed therebetween, and the reference resistor The temperature of the flow control resistor and that of the flow control resistor are made uniform.

Further, it is preferable that the reference resistor and the flow rate adjusting resistor are formed by using the same resistor material, and are laminated and arranged on the substrate.

[Action]

With the above configuration, the temperatures of the reference resistance and the flow rate adjustment resistance can be made uniform, and the control value of the heat ray resistance (heat-sensitive element) based on the equation (1) can be prevented from shifting due to temperature change. Further, if the reference resistance and the flow rate adjusting resistance are made of the same resistor material, it is possible to more effectively suppress the deviation of the control value of the heat ray resistance.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the embodiment, the same components as those of the prior art shown in FIG. 3 described above are designated by the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 21 denotes a substrate located outside the intake passage and provided inside a casing (not shown) of the heat ray flow meter,
The substrate 21 is formed of an insulating material such as ceramics, and a predetermined printed wiring (not shown) is provided on the substrate 21 by means of printing or the like. A differential amplifier 9, a power transistor 10 and the like are arranged on the substrate 21 in the middle of the printed wiring.

Reference numeral 22 denotes a reference resistance disposed on the substrate 21 in the middle of the printed wiring, and the reference resistance 22 is, for example, a predetermined thick film resistor material having a temperature coefficient of α ₃ printed on the substrate 21. By firing, it is formed into a rectangular plate shape, and has a resistance value R ₃ like the reference resistance 4 described in the prior art. The reference resistor 22 has a temperature change amount of ΔT
When adapted to vary a resistance value R ₃ to R ₃ 'by the equation (3). Reference numeral 23 denotes an insulating layer provided on the substrate 21 so as to cover the reference resistor 22, the insulating layer 23 is formed in a thin film by an insulating material such as glass, and the thin film portion 23A covers the reference resistor 22. It is like this.

Reference numeral 24 denotes a flow rate adjusting resistor stacked on the substrate 21 so as to face the reference resistor 22 with a large contact area across the thin film portion 23A, and the flow rate adjusting resistor 24 has, for example, a temperature coefficient α ₂ on the thin film 23. It is formed into a wide rectangle by printing and firing a predetermined thick film resistor material, and has a resistance value R ₂ like the flow rate adjusting resistor 3 described in the prior art. Further, the flow rate adjusting resistor 24 is connected to a printed wiring (not shown) arranged on the thin film 23, and is connected to the reference resistor 22 (resistance value R ₃ ) on the substrate 21 via this printed wiring as shown in FIG. They are connected at the connection point 8 shown.

Here, the flow rate adjusting resistor 24 is a thin film portion 23A on the reference resistor 22.
Since it is laminated through the, the resistance value R ₂ has a uniform temperature change amount ΔT like the reference resistance 22, and the resistance value R ₂ is the same as in (3) above.
Much like the equation, it changes to _{R 2 '= R 2 (1} + α 2 ΔT) ...... (4) composed of resistance R _2'. And the flow rate adjustment resistor
If 24 is formed using the same thick film resistor material as the reference resistor 22, the temperature coefficient α ₂ is α ₂ = α ₃ , and the resistance value R ₂ ′ is R ₂ ′ = R ₂ ′ = R ₂ (1 + α ₃ ΔT) (5)

Further, 25 denotes a protective layer adapted to cover the flow rate adjusting resistor 24 and the like, and the protective layer 25 is made of an insulating material such as glass, and mounted on the substrate 21 for the differential amplifier 9 and the power transistor 10. The reference resistor 22, the flow rate adjusting resistor 24 and the like are insulated from the outside together with the insulating layer 23.
When the protective layer 25 is formed so as to cover the upper surface side of the substrate 21 over almost the entire surface, the insulating layer 23 can insulate at least the reference resistor 22 and the flow rate adjusting resistor 24 by the thin film portion 23A. It may be provided on the substrate 21.

The hot wire type flow meter according to the present embodiment has the above-mentioned configuration, and its basic operation is not particularly different from that according to the prior art.

Therefore, in this embodiment, since the reference resistor 22 and the flow rate adjusting resistor 24 are laminated on the substrate 21 via the thin film portion 23A, the reference resistor 22 and the flow rate adjusting resistor 24 have a substantially large contact area. The two can be made to face each other, and the temperatures of both can be made uniform at all times, and the temperature change amount ΔT can be made the same value. If the reference resistor 22 and the flow rate adjusting resistor 24 are made of the same thick film resistor material, the temperature coefficients α ₃ and α ₂ are the same (α ₃ = α ₂ ), so that the respective resistance values R _3, wherein the R ₂ (3) type, can be changed as (5) the resistance R ₃ as shown in the expression ', R _2'.

Therefore, when the resistance value R _H of the thermosensitive element 1 is set to a control value that satisfies the above formula (1), the resistance values R ₃ , R ₂ of the reference resistor 22 and the flow rate adjusting resistor 24 change to R ₃ ′, R ₂ ′. Even if it changes as follows, the resistance R _H of the heat sensitive element 1 can be calculated by the equations (1), (3), and (5). And the resistance value R ₃ of the reference resistor 22 changes to the resistance value R ₃ ′ due to a temperature change, the relationship of the above equation (1) can always be satisfied, and the resistance as the control value of the thermosensitive element 1 can be set. value
It is possible to prevent the deviation of R _H and improve the detection accuracy of the hot wire flow meter.

Even if the reference resistor 22 and the flow rate adjusting resistor 24 are not formed of the same resistor material, the temperature coefficient α ₃ ,
If α ₂ is a substantially equal value (α ₃ ≈α ₂ ), the resistance values R ₃ and R ₂ of the _{two become} resistance values R ₃ ′ and R ₂ ′ depending on the temperature change amount ΔT.
In this case as well, the relationship of the equation (1) can be substantially satisfied, and the resistance value R _H as the control value of the heat-sensitive element 1 can be effectively suppressed from shifting. it can.

If the reference resistor 22 and the flow rate adjusting resistor 24 are made of the same resistor material or a material having substantially the same temperature coefficients α ₃ and α ₂ , the reference resistor 22 is made of a special material such as manganin as described in the prior art. Since it is not necessary to form 22, the reference resistance 22 and the like can be formed compactly with an inexpensive resistor material, and the temperature characteristics of the hot wire type flow meter can be improved at low cost, and various effects are exhibited.

In the above embodiment, the reference resistor 22 is provided on the substrate 21,
Although it has been described that the flow rate adjusting resistor 24 is laminated on the reference resistor 22 via the insulating layer 23, in place of this, the flow rate adjusting resistor 24 is provided on the substrate 21, and the thin film is formed on the flow rate adjusting resistor 24.
The reference resistor 22 may be laminated via 23.
Further, the reference resistor 22 and the flow rate adjusting resistor do not necessarily have to be laminated, and any arrangement structure can be used as long as they can face each other with a thin insulating layer interposed therebetween and can equalize the temperature of both. It's okay.

[Effect of device]

As described above in detail, according to the present invention, the reference resistance and the flow rate adjusting resistance are arranged so as to face each other with the thin insulating layer sandwiched therebetween, and the temperature of both is made uniform. Further, it is possible to effectively prevent the resistance value as the control value of the heat wire resistance from being shifted due to the change of the resistance value of the reference resistance, and it is possible to improve the detection accuracy. Further, if the reference resistance and the flow rate adjusting resistance are made of the same material, the reference resistance can be made of an inexpensive material in a compact manner, and the temperature characteristics can be improved at low cost.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention, FIG. 1 is a plan view showing resistors and the like laminated on a substrate, and FIG.
FIG. 3 is an enlarged sectional view taken along the line II-II in the figure, and FIG. 3 is a circuit diagram of a hot wire type flow meter showing a conventional technique. 1 ... Heat sensitive element (heat wire resistance), 2 ... Temperature compensation resistance, 9
...... Differential amplifier, 10 …… Power transistor, 11 …… Battery (power supply), 21 …… Board, 22 …… Reference resistance, 23 ……
Insulating layer, 24 …… Flow rate adjusting resistor, 25 …… Protective layer.

Claims (2)

[Scope of utility model registration request] 1. A heat wire resistance and a temperature compensation resistance, which are cooled by intake air flowing in the intake passage, are arranged in the intake passage of the engine, and a reference resistance and a flow rate adjustment resistance are provided outside the intake passage. A bridge circuit is formed by connecting a series circuit composed of the heat wire resistance and the reference resistance and a series circuit composed of the temperature compensation resistance and the flow rate adjustment resistance in parallel between the power source and the ground. In the hot-wire type flow meter, the reference resistance and the flow rate adjusting resistance are arranged on an insulating substrate so as to face each other with a thin insulating layer interposed therebetween, and the temperature of the reference resistance and the flow rate adjusting resistance are made uniform. A hot-wire type flow meter characterized by having the above structure. 2. The heat wire according to claim 1, wherein the reference resistance and the flow rate adjusting resistance are formed by using the same resistor material, and are laminated and arranged on the substrate. Flow meter.