JP3878198B2 - Thermal flow meter - Google Patents

Description

  The present invention relates to a device for detecting a flow rate, and more particularly to a flow rate sensor for an internal combustion engine, a flow rate sensor used in a fuel cell system, or the like.

  2. Description of the Related Art Conventionally, a thermal type air flow sensor that is provided in an intake air passage of an internal combustion engine such as an automobile and measures an intake air amount has become mainstream because it can directly detect the mass air amount. Recently, attention has been paid to the fact that an air flow sensor manufactured by a semiconductor micromachining technology has a high-speed response and can detect a reverse flow by utilizing the speed of the response.

  A technique of such a thermal air flow sensor using a conventional semiconductor substrate is disclosed in, for example, Japanese Patent Publication No. 6-63801. In the conventional embodiment, a current is passed through a heater resistor disposed between the upstream temperature sensor and the downstream temperature sensor to generate heat, and a flow rate signal is obtained by the difference in output signals between the upstream temperature sensor and the downstream temperature sensor. It is a thing of composition.

  The prior art has a problem that the resistance value of the heating resistor itself changes due to the heating of the heating resistor formed in the thin portion.

  For this reason, as described in Japanese Patent Publication No. 6-63801 described above, there has been proposed one in which a correction means is provided in the control circuit so that the flow rate characteristic does not change even if the resistance value changes.

  However, there are problems that the circuit structure is complicated and the sensor structure is complicated. Further, no consideration is given to changes with time of components mounted on the circuit board.

  Further, the temperature of the heating resistor needs to adjust the resistance of one side of the constant temperature difference bridge on the circuit board, which is one of the causes of increasing the manufacturing cost.

  Furthermore, the fixed resistor used for the constant temperature difference bridge formed on the circuit board actually has a slight resistance temperature coefficient, and when the ambient temperature changes due to the variation, the heating temperature of the heating resistor varies, This is a cause of variations in temperature characteristics.

  Further, since the fixed resistance itself changes with time, this is a factor of characteristic change.

  Recently, the demand for radio interference has become stricter, and it is necessary to improve resistance to radio interference.

  An object of the present invention is to provide a thermal flow rate measuring apparatus that is inexpensive and excellent in reliability.

  The above object can be solved by the invention described in the appended claims.

  For example, if the resistor forming the constant temperature difference control circuit is formed of a temperature sensitive resistor, the tendency of the resistance change when it changes over time can be made the same.

  When the constant temperature difference control resistors change with time at the same ratio, the output error becomes very small, so that the reliability can be improved. As a constant temperature difference control circuit, a bridge circuit is simple in configuration and excellent.

  In addition, if the constant temperature difference control circuit can be formed with the same temperature sensitive resistor, it can be formed in the same process at the same time, which is advantageous in terms of cost. In particular, the resistance temperature coefficient variation can be reduced, so that the temperature characteristic variation can be reduced. .

  Since a heating resistor is formed in the constant temperature difference control circuit, the circuit configuration is simplified, which is advantageous for downsizing.

  Since the constant temperature difference control resistor mounted on the circuit board is formed in one substrate, the resistance wiring can be minimized. For this reason, the wiring portion becomes difficult to become an antenna and becomes extremely strong against radio wave interference.

  In addition, the thermal flow rate measuring device is mounted in an engine room for automobiles, but in that case, the vicinity of the sensor unit exposed to intake air that is difficult to receive engine radiation is advantageous as a temperature environment condition. Therefore, the present invention, in which a constant temperature difference control resistor and a heating resistor are formed on one substrate and exposed to a fluid, is advantageous with respect to a change with time.

  If the constant temperature difference control resistor is formed by the same process, the resistance ratio can always be controlled to be constant even if the absolute value variation of the resistance is large. If the resistance ratio of the constant temperature difference control circuit is the same, the heating temperature of the heating resistor can be manufactured with almost no variation even without adjustment.

  This eliminates the need for adjustment work such as laser trimming for adjusting the heating temperature of the heating resistor, which has been conventionally required, and simplifies the process.

  According to the present embodiment, it is possible to detect a flow rate with high accuracy even in a thermally severe environment such as an engine room, and to provide a highly reliable thermal flow measurement device at a low cost. it can.

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

  FIG. 1 shows the structure of a thermal flow sensor element 26 for detecting the flow rate used in the thermal flow rate measuring apparatus 1 according to the first embodiment of the present invention and its wiring pattern diagram. FIG. 2 is a circuit diagram including the thermal flow sensor element 26 shown in FIG. 1, and FIG. 3 is a cross-sectional view showing a state in which the thermal flow measuring device 1 is actually mounted in the intake pipe of the internal combustion engine. The first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the thermal flow sensor element 26 has a thin portion 7 formed in a substrate 2 such as a semiconductor, and a heating resistor 10, an upstream temperature sensor 30, and a downstream temperature sensor 31 are disposed therein. The structure is thermally insulated from 2. The temperature sensitive resistors 11, 12, and 13 are formed of the same material as the heating resistor 10. Each resistor has an electrode 51 made of aluminum or the like for electrical connection with the outside. The substrate 2 made of a semiconductor or the like is formed of, for example, silicon, and the thin portion 7 forms a cavity by anisotropic etching using an etchant such as potassium hydroxide from the back surface of the substrate 2. In the flow sensor element 26 having such a configuration, the size of the substrate 2 is about 2.5 mm × 6 mm × 0.3 mm, the thin portion 7 is about 0.5 mm × 1 mm, and the thickness of the thin portion 7 is about 0.0015 mm. belongs to. The temperature sensitive resistor material is generally a resistor in which polysilicon or single crystal silicon is doped with impurities, or platinum, gold, copper, aluminum, chromium, nickel, tungsten, permalloy (FeNi), titanium. Etc. are used.

  As shown in FIG. 2, the heating resistor 10 forms a bridge circuit with the temperature sensitive resistors 11, 12, 13, and the heating temperature of the heating resistor 10 is the resistance value of the temperature sensitive resistors 11, 12, 13. And is controlled to be heated at a substantially constant temperature difference ΔT with respect to the ambient temperature by feedback control using the differential amplifier 41, the transistor 45, etc. ing. Specifically, for example, in the case of the heating resistor 10 where ΔT is controlled at 150 ° C., the heating temperature is about 170 ° C. when the ambient temperature is 20 ° C., and about 250 ° C. when the ambient temperature is 100 ° C. Become.

  The heating temperature is controlled to be substantially the same even if the flow rate is changed. Hereinafter, a control method similar to this is simply referred to as a constant temperature difference control method, and the circuit is referred to as a constant temperature difference bridge or a constant temperature difference control circuit.

  The output 44 of the thermal flow measuring device 1 can be obtained by a temperature sensor bridge formed by the temperature sensors 30 and 31 formed at the upstream and downstream of the heating resistor 10 and the fixed resistors 61 and 62. That is, since the temperatures of the upstream temperature sensor 30 and the downstream temperature sensor 31 are equal in the absence of wind, the output is zero when the resistance values of the upstream and downstream temperature sensors 30, 31 are equal and the resistance values of the fixed resistors 61, 62 are equal. It becomes.

  When a flow is generated here and, for example, a fluid flow 6 is generated from upstream to downstream as shown in FIG. 1, the upstream temperature sensor 30 is cooled, and conversely, the downstream temperature sensor 31 is heated by the heating resistor 10. In response to this, the temperature rises and a difference occurs between the resistance values of the upstream and downstream temperature sensors 30, 31, which becomes the flow rate output 44. Similarly, when a fluid flow occurs from the downstream side to the upstream side, the output 44 changes in the opposite direction to that described above, so that it is possible to detect the flow rate including the reverse flow.

The thermal flow rate measuring device 1 of the present invention is used, for example, for detecting the intake air flow rate of an internal combustion engine and supplying fuel corresponding to the amount of air to the engine. Therefore, the thermal flow measuring device 1 is installed between the air cleaner 102 and the throttle body 109 in the engine room, and includes a circuit board 4, a housing 3 and the like as shown in FIG. The sub-passage 52 is formed, and the thermal flow sensor element 26 is disposed in the sub-passage 52.

  The inside of the engine room is the same as the temperature of the outside air when the engine is started, and the temperature of the intake air to be sucked is in the range of about -30 ° C to 40 ° C. On the other hand, after warm-up, due to the heat effect from the engine, the surface of the main passage 5 rises up to about 125 ° C. and the intake air temperature rises to about 100 ° C. For this reason, the thermal flow measuring device 1 is required not to generate an output error in a wide temperature range of about −30 ° C. to 100 ° C. or 125 ° C. In the conventional thermal flow measuring device 1, a part of the constant temperature difference bridge resistance for controlling the heating resistor 10 at a constant temperature difference is formed on the circuit board 4 with a fixed resistance. However, even if it is a fixed resistance, the resistance temperature coefficient is not completely zero, and generally has a resistance temperature coefficient of about 0 ± 50ppm. If the ambient temperature changes due to this resistance temperature coefficient variation, the bridge balance Is one of the causes of variations in temperature characteristics.

  Further, in cold districts, it is assumed that the engine is warmed up in the garage and travels after warming up. However, immediately after traveling, the surface of the main passage 5 is heated by the heat of the engine, whereas the intake air is cooled. In such a transient state, the thermal flow sensor element 26 exposed to the intake air is cold and the circuit board 4 is in a high temperature state. In the case of the conventional example, there is no problem if the temperature coefficient of resistance of the constant temperature difference bridge fixed resistor mounted on the circuit board 4 is completely zero, but if there is a variation of about 0 ± 50 ppm as described above, This upsets the bridge balance and causes the output 44 to fluctuate.

  Furthermore, since the resistance values of the heating resistor 10 and the constant temperature difference bridge resistor have manufacturing variations, if the adjustment is not performed, the heating temperature variation of the heating resistor 10 becomes very large. Therefore, in the conventional thermal flow measuring device 1, it is necessary to individually adjust the fixed resistor for the constant temperature difference bridge by trimming with a laser or the like on the circuit board 4, which causes an increase in cost.

  Further, the heating temperature of the heating resistor 10 is, for example, about 100 ° C. to 200 ° C. with respect to the ambient temperature. Therefore, when the intake air temperature is 100 ° C., the heating resistor 10 has a maximum temperature of about 200 ° C. to 300 ° C. Become.

  Therefore, when used for a long time, the heating resistor 10 gradually deteriorates and the resistance value changes. The temperature of the circuit board 4 is also affected by the same heat as described above, and at the same time, the temperature rises to about 125 ° C. which is the same as the surface temperature of the main passage 5 due to the heat effect of heat-generating components such as transistors mounted on the surface of the circuit board 4. To do. In the case where the fixed resistor for the constant temperature difference bridge is formed by printing or the like as in the conventional example, the fixed resistor gradually deteriorates and the resistance value changes. There is a problem that the flow rate characteristic changes due to this resistance change.

  Conventionally, a metal material such as aluminum has been used for the main passage 5, but recently a resin material is becoming mainstream for weight reduction. On the other hand, the demand for radio interference is becoming stricter, and it is necessary to improve resistance to radio interference.

  An excellent point obtained by forming all constant temperature difference bridge resistors as temperature sensitive resistors in the same substrate as in the present invention will be described below.

  First, even if all the constant temperature difference bridges are temperature sensitive resistors as in the present invention, it will be clarified that they operate correctly compared with the conventional example.

  In the circuit diagram of FIG. 2, the constant temperature difference bridge is a portion including the heating resistor 10 and including three temperature sensitive resistors 11, 12, and 13. Although not shown, among the constant temperature difference bridges, one in which the temperature sensitive resistors 12 and 13 are formed by fixed resistors is a conventional constant temperature difference bridge example.

First, in the constant temperature difference bridge shown in FIG. 2, the resistance value of the heating resistor 10 at 0 ° C. is Rh 0, the resistance value of the temperature sensitive resistor 11 is Ra 0, and the resistance value of the temperature sensitive resistor 12 is 0 ° C. Assuming that the resistance value of Rb0 and the temperature sensitive resistor 13 at 0 ° C. is Rc 0 and the temperature coefficient of resistance [° C. ⁻¹ ] is all the same value α, the relationship between the resistance values at an arbitrary temperature T ° C. is (1), (2), (3), and (4).

Rh = Rh0 × (1 + α × T) (1)
Ra = Ra0 × (1 + α × T) (2)
Rb = Rb0 × (1 + α × T) (3)
Rc = Rc0 × (1 + α × T) (4)
Here, Rh, Ra, Rb, and Rc are resistance values at an arbitrary temperature T ° C.

  Further, since Rh is controlled to be higher than Ra, Rb, and Rc by a constant temperature ΔT ° C., equation (1) can be expressed by the following equation (5).

Rht = Rh0 × (1 + α × (T + ΔT)) (5)
Here, Rht is a resistance value at the time of actual constant temperature difference bridge operation.

  On the other hand, the equilibrium condition of the constant temperature difference bridge can be expressed by the following equation (6).

Rht × Rc = Ra × Rb (6)
Substituting the equations (2), (3), (4), (5) into the equation (6), the following equation (7) is obtained.

Rh0 × (1 + α × (T + ΔT)) × Rc0 × (1 + α × T)
= Ra0 × (1 + α × T) × Rb0 × (1 + α × T) (7)
Here, when the condition that Rb and Rc are the same temperature is added, the equation (7) can be expressed by the following equation (8).

Rh0 × (1 + α × (T + ΔT))
= Ra0 × (1 + α × T) × Rb0 / Rc0 (8)
This equation (8) is exactly the same as the equilibrium condition when Rb and Rc are formed of fixed resistors, and represents that the constant temperature difference can be controlled.

  That is, the authors noted that all constant temperature difference bridge resistances can be formed of temperature sensitive resistors by devising the structure so that Rb and Rc have the same temperature.

Therefore, Rb and Rc are formed on the substrate 2 using silicon or the like having good thermal conductivity so that Rb and Rc have the same temperature, or the temperature sensitive resistors 12 and 13 are formed as shown in FIG.
(Rb, Rc) are arranged close to each other.

  As can be seen from equation (6), the same holds true even if the ambient temperature is detected by Rb instead of detecting the ambient temperature by Ra, and Ra and Rc have the same temperature.

  When the constant temperature difference bridge is formed by the same material and the same process as in the present invention, there are the following advantages.

  Although the absolute value variation of the resistance value depends on the process conditions, it is about ± 30%, but the resistance ratio Rh / Rb of Rh and Rb and the resistance ratio Ra / Rc of Ra and Rc are patterned in the same process. , Hardly fluctuate. Further, since all resistors are formed in the same substrate, the temperature coefficient of resistance hardly varies.

  When a resistor is actually patterned using a semiconductor process and the resistance ratio is actually measured, Rh / Rb and Ra / Rc are ± 0.07% or less. The absolute value variation of the resistance temperature coefficient is about ± 1% between lots, but it has been found that the resistance temperature coefficient can be almost zero within the same lot and within the same substrate 2.

Then, as shown in Table 1, by applying the present invention, the heating temperature variation of the heating resistor 10 can be set to about ± 1 ° C. even without adjustment. This is a significant improvement over the conventional heating temperature variation of ± 14 ° C., and is a level where adjustment can be eliminated.

  Therefore, by applying the present invention, the adjustment process of the heating temperature of the heating resistor 10 can be omitted, thereby reducing the cost. Further, since the fixed resistor for the constant temperature difference bridge is not formed on the circuit board 4, the circuit board 4 can be downsized.

  Further, when the present invention having a structure in which all the temperature sensitive resistors are formed on the substrate 2 and exposed to the intake air is applied, the surface of the main passage 5 and the circuit board 4 rise to about 125 ° C. as described above. Since the intake air rises only to about 100 ° C., it is thermally advantageous. Therefore, the change with time of Rb and Rc can be reduced.

Moreover, even if the resistances of Rb and Rc change with time, both Rb and Rc show the same change because they receive the thermal history under the same environmental conditions. Then, since the bridge balance of the constant temperature difference bridge does not change, the heating temperature difference ΔT of the heating resistor 10 can be prevented from changing. Thereby, the change of the output 44 can be prevented and the reliability can be improved.

Further, Table 1 and Table 2 in FIG. 23 and FIG. 24 show that if the present invention is applied, the temperature characteristic variation is also improved. The variation of the temperature coefficient of resistance of the temperature sensitive resistor is, for example, 2000 ± 20 ppm / ° C. as shown in FIG. Also, the resistance temperature coefficient variation within the same substrate 2 is almost zero, and is about ± 2 ppm / ° C. When the present invention is applied, when the ambient temperature is 20 ° C., the heating temperature of the heating resistor 10 is about 170 ° C. ± 2 ° C. Further, the heating temperature when the ambient temperature changes to 80 ° C. is about 247 ° C. ± 2 ° C., and it can be seen that the variation in the heating temperature is very small even if the ambient temperature changes.

  On the other hand, in the case of the conventional example, the resistance temperature coefficient of the fixed resistors Rb and Rc formed on the circuit board 4 by printing or the like is basically 0 ppm / ° C., but the variation is large and about ± 50 ppm / ° C. In the conventional example, when the ambient temperature is 20 ° C., the heating temperature of the heating resistor 10 can be relatively small as about 170 ° C. ± 3 ° C. However, when the ambient temperature reaches 80 ° C., the heating temperature is about 247 ° C. ± 8 ° C. Thus, the variation becomes large. Due to this variation, the temperature characteristic variation becomes large.

  FIG. 4 shows a comparison of variations in temperature characteristics when the ambient temperature of the conventional invention is changed from 20 ° C. to 80 ° C. FIG. 4A shows the temperature characteristic variation according to the present invention, and FIG. 4B shows the variation of the conventional invention. In this way, if the present invention is applied, it is possible to greatly reduce variation.

  Further, in the case where the constant temperature difference bridges are all formed on the same substrate 2 as in the present invention, the resistance temperature coefficient variation of Rb and Rc can be made very small, and both resistances can be achieved by arranging Rb and Rc close to each other. Since the temperature difference can be made difficult to occur, fluctuations in the output 44 can be prevented even under environmental conditions that cause a temperature difference between the intake air and the circuit board.

  Furthermore, since all the constant temperature difference bridges are formed on the same substrate 2, the wiring between the temperature sensitive resistors can be made very small, which is advantageous for radio wave interference. This is because, in the structure in which the constant temperature difference bridge resistance is formed on both the substrate 2 and the circuit board 4 as in the conventional example, the wiring portion becomes long and the wiring portion becomes an antenna for receiving radio waves. This is because it is not present in the present invention.

  As a means for obtaining the same effect as described above, for example, it may be possible to form Rh and Ra on one substrate 2 and Rb and Rc on another substrate 2 and combine them. In that case, the number of steps increases, but the effect of omitting the step of adjusting the heating temperature or improving the variation in temperature characteristics is almost the same, and in order to separate Rb and Rc from the heating resistor 10, It is advantageous.

  If the main purpose is to improve reliability, it is effective to simply form all the resistors used for the constant temperature difference bridge with temperature sensitive resistors made of the same material. This is because, with the same material, the tendency of change with time is relatively consistent, and the balance of the constant temperature difference bridge does not change.

  Various materials can be considered for the upstream temperature sensor 30 and the downstream temperature sensor 31, but they can be made of the same material as the heating resistor 10 and the temperature sensitive resistors 11, 12, and 13. If the same material is used, since all the resistors can be formed by a single resistance forming process, the manufacturing process can be simplified.

  Next, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 6 shows the structure of the thermal flow sensor element 26 and its wiring pattern diagram. FIG. 7 shows a circuit diagram including the thermal flow sensor element 26 shown in FIG. The manufacturing method of the thermal flow sensor element 26 is similar to that described with reference to FIG.

  As shown in FIG. 6, a thin-walled portion 7 is formed near the center of the substrate 2, and the temperature-sensitive resistor 24 and the heating resistor 10 are disposed close to each other. Further, upstream temperature sensors 30 and 33 and downstream temperature sensors 31 and 32 are formed upstream and downstream of the heating resistor 10. Here, the heating resistor 10 and the four temperature sensitive resistors 22, 23, 24, and 25 are formed of the same process and the same material. Of course, it is more preferable that the upstream / downstream temperature sensors 30, 33, 31, and 32 are manufactured by the same process because the process is not complicated.

  As shown in FIG. 7, the temperature sensitive resistor 24 is connected to other temperature sensitive resistors 22, 23, 25 formed in the same substrate 2 to form a bridge. When the heating resistor 10 is cooled by the flow of the fluid, the temperature-sensitive resistor 24 arranged in proximity is also cooled, and the bridge balance changes. The heating resistor 10 is controlled at a constant temperature difference by feedback control of the change by the differential amplifier 41 and the transistor 45.

  The present invention can also be applied to a constant temperature difference control system composed of such a heating resistor 10 and four temperature sensitive resistors 22, 23, 24, 25. A similar constant temperature difference control system is also applicable to the constant temperature difference control system of the present invention. The concept of the present invention can be applied to other constant temperature difference control circuits that are included in the concept of the temperature difference control circuit and are not described in detail but are conventionally known. In any case, at least four or more temperature sensitive resistors are required for the constant temperature difference control.

  The effects of the present invention are the same as described above, and will not be described.

  Next, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 8 shows the structure of the thermal flow sensor element 26 and its wiring pattern diagram. FIG. 9 shows a circuit diagram including the thermal flow sensor element 26 shown in FIG. The manufacturing method of the thermal flow sensor element 26 is similar to that described with reference to FIG.

As shown in FIG. 8, a thin portion 7 is formed on the substrate 2, and there are two heating resistors 14,
18 is arranged close to the upstream and downstream of the fluid flow. Then, three temperature sensitive resistors 15, 16, and 17 are connected to the upstream heating resistor 14, and three temperature sensitive resistors 19, 20, and 21 are connected to the downstream heating resistor 18. All resistors are made of the same process and temperature sensitive resistors of the same material. The heating resistors 14 and 18 are operated by independent constant temperature difference bridges as shown in FIG. When the fluid flow 6 occurs, the heat of the upstream side heating resistor 14 is received by the downstream side heating resistor 18, so the amount of heat released from the downstream side heating resistor 18 decreases, and when the flow in the opposite direction occurs, the upstream side heating resistor The amount of heat released from the body 14 is reduced. By utilizing this, a fluid flow direction output 47 and a flow rate output 44 can be obtained.

  The application of the present invention is particularly effective in the case of the thermal flow measuring device 1 of such a system.

  That is, the difference in heating temperature ΔT between the two heating resistors 14 and 18 becomes an error factor if they do not operate substantially the same when the ambient temperature changes or the flow rate changes. If the total resistance of the two constant temperature difference bridges is formed of the same temperature sensitive resistor as in the present invention, the resistance ratio and resistance temperature coefficient of the two constant temperature difference bridges can be made substantially the same, so that they always operate in the same manner. be able to. Further, as shown in FIG. 8, the temperature sensitive resistors 15 and 19 of the two constant temperature difference bridges are arranged close to each other so that the same temperature is obtained as much as possible, and similarly the temperature sensitive resistors 16, 17, 20, and 21 are arranged close to each other. If it is arranged and made to have the same temperature as much as possible, the heating temperature difference ΔT of both the heating resistors 14 and 18 operates in the same manner, so that higher accuracy can be achieved. . Other effects are the same as described above, and will be omitted.

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

  FIG. 10 shows the structure of the thermal flow sensor element 26 and its wiring pattern. An alumina ceramic substrate having a thickness of about 0.1 mm was used as the substrate 2, and a heating resistor 10 and temperature sensitive resistors 11, 12, 13 were formed by patterning after sputtering a thin film such as platinum on one surface of the substrate 2. Is.

  The heating resistor 10 and the temperature sensitive resistors 11, 12, 13 are connected to form a constant temperature difference bridge. If the slit 54 is formed between the heating resistor 10 and the temperature sensitive resistors 11, 12, and 13 to prevent heat conduction from the heating resistor 10 as shown in FIG. 10, the present invention can be applied. . The effect is the same as described above, and will be omitted.

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

As shown in FIG. 11, a thin portion 7 is formed on the substrate 2, and the thin portion 7 is thermally insulated from the substrate 2. A heat generating resistor 10 is formed in the thin portion 7, and the heat generating resistor 10 is provided with temperature sensitive resistors 11, 12, 13, 13 a, 13 b that are electrically connected. The resistance values of the temperature sensitive resistors 13 a and 13 b are 10% or less of the temperature sensitive resistor 13. Here, the resistance during the operation of the heating resistor 10 is Rht, the resistance value during the operation of the temperature sensing resistor 11 is Ra, the resistance value during the operation of the temperature sensing resistor 12 is Rb, and the operation of the temperature sensing resistor 13 is performed. The resistance value at the time is Rc, the resistance value when the temperature sensitive resistor 13a is operated is Rca, the resistance value when the temperature sensitive resistor 13b is operated is Rcb, and the resistance temperature coefficients are all the same value and α. For example, it is assumed that a bridge represented by the following formula (9) is formed.

Rht × Rc = Ra × Rb (9)
As shown in FIGS. 23 and 24, the heating temperature has a variation of about ± 1 ° C. or ± 2 ° C., and the variation cannot be completely eliminated. Therefore, in order to further increase the accuracy, it is more preferable to change the bridge balance as shown in the following equations (10), (11), and (12) using Rca and Rcb connected to Rc. is there.

Rht × (Rc + Rca) = Ra × Rb (10)
Rht × (Rc + Rcb) = Ra × Rb (11)
Rht × (Rc + Rca + Rcb) = Ra × Rb (12)
The combination of resistances shown in the equations (9), (10), (11), and (12) may be cheap because the wiring of the electrode 51 may be changed and adjustment such as trimming by a laser or the like is unnecessary in the process. . In particular, it is effective in absorbing the variation in heating temperature caused by the variation in resistance temperature coefficient.

  Since the resistance temperature coefficient does not vary greatly within the same lot, it is only necessary to change the connection of the electrodes 51 depending on the lot. Therefore, there is basically no adjustment. The temperature sensitive resistors for fine adjustment of the heating temperature such as Rca and Rcb shown in the figure may be formed of series resistance or parallel resistance, and if the substrate 2 has a margin, the number is increased. High accuracy can be achieved.

  It should be noted that the fine-adjustment temperature-sensitive resistor described here is similarly established when combined with any bridge resistor constituting a constant temperature difference bridge as can be seen from Equation (9).

  Next, other embodiments of the present invention will be described below.

  As shown in FIG. 4, the temperature characteristic has a flow rate dependency such that a minus error is caused at a low flow rate and a plus error is caused at a high flow rate. If all the constant temperature difference bridges are formed of temperature sensitive resistors, variations in temperature characteristics can be reduced, but such flow rate dependency improvement is difficult.

  In order to reduce the error based on the flow rate dependency, the temperature sensor 8 is formed on the substrate 2 as shown in FIG. 11, and the temperature detected by the temperature sensor 8 and the flow rate output of the thermal flow sensor element 26 can be obtained. And Then, as shown in FIG. 12, the flow rate output of the thermal flow sensor element 26 and the temperature sensor output are input to the correction circuit 46, where the dependency on the flow rate is corrected and output, thereby further reducing the temperature characteristic error. It is.

  The temperature sensor 8 is particularly preferably formed of a material used for the constant temperature difference bridge. If the same material is used for the simultaneous process, the same temperature coefficient of resistance can be obtained, so that correction of flow rate dependency is relatively easy.

  Although the heating resistor 10 is formed in the thin portion 7 and is thermally insulated from the substrate 2, the heating resistor 10 transmits heat to the substrate 2 to a small extent, and the temperature sensitive resistors 11, 12, 13, etc. However, the temperature rises if the substrate 2 is small or if the heat dissipation of the substrate 2 is poor. In this case, the temperature of the temperature sensor 8 also rises, so that an error may occur in correction of the flow rate dependency. Therefore, as shown in FIG. 11, it is more effective to dispose the temperature sensor 8 in the second thin portion 7 a and thermally insulate from the substrate 2.

  Further, although the error slightly increases, the temperature sensor may be built in the correction circuit 46. In this case, wiring for connecting the temperature sensor 8 and the correction circuit 46 is not necessary.

  Note that the temperature sensor 8 described here can also be used as it is for detecting the intake air temperature used for engine control. In particular, a structure in which the temperature sensor 8 is disposed in the second thin portion 7a is more suitable because of its quick response.

  Next, an application example of the present invention will be described with reference to FIG.

  If all the constant temperature difference bridges are formed of temperature sensitive resistors as shown in FIG. 13, the thermal flow sensor element 26, the differential amplifier 41, the transistor 45, the correction circuit 46, etc. are formed in one substrate 2 made of the same semiconductor. It can also be formed.

  In the conventional example, even if they are integrated, there is a fixed resistance for the constant temperature difference bridge and there is adjustment of the heating temperature, so that a circuit board 4 other than the board is required. If the constant temperature difference bridge resistors are all formed of the same temperature sensitive resistor as in the present invention, the circuit board 4 becomes unnecessary, and further miniaturization and cost reduction are possible.

  The most advantageous point of integration is that when the thermal flow sensor element 26 is cooled by intake air, the differential amplifier 41, the transistor 45, the correction circuit 46, etc. formed in the same substrate 2 are also cooled at the same time. Therefore, the temperature is always the same as that of the thermal flow sensor element 26.

  As a result, in the conventional example, if there is a temperature difference between the intake air temperature and the circuit board 4 or temperature irregularities are generated in the circuit board 4, the temperature characteristics of the electronic components mounted on the circuit board 4 vary in a complicated manner. Although an error of the output 44 has occurred, if the present invention is applied, the error can be greatly reduced. The sub passage 52 may have a bend. If a curved sub-passage is used, the thermal flow sensor element 26 in which many resistors and circuits are formed can be further protected from dust, droplets, and backfire contained in the flow.

  Next, another embodiment of the present invention will be described with reference to FIG. 14, FIG. 15, FIG. 16, and FIG.

  FIG. 14 is a partially enlarged view of the thermal type flow sensor element 26, and FIGS. 15 and 16 are examples of temperature distribution in the section AA of FIG. FIG. 5 shows an example of resistance change when the heating resistor 10 is energized and heated at about 250.degree.

  As shown in FIG. 14, the thermal flow sensor element 26 is provided with a heating resistor 10 and temperature sensitive resistors 11, 12, and 13. Here, the resistance when the heating resistor 10 is operated is Rht, the resistance value when the temperature-sensitive resistor 11 is operated is Ra, the resistance value when the temperature-sensitive resistor 12 is operated is Rb, and the temperature-sensitive resistor 13 is operated. If the resistance value at the time is Rc and the temperature coefficient of resistance is all the same value and α, for example, a constant temperature difference bridge represented by the following equation (13) can be formed.

Rht × Rc = Ra × Rb (13)
The heating resistor that is always heated and used gradually changes its resistance as shown in FIG. (X) in FIG. 5 shows a time-dependent change of the polysilicon thin film resistor and (Y) shows a change in the platinum thin film resistor over time. Thus, the tendency of the change varies depending on the material used for the heating resistor 10. ing.

  First, a change in temperature distribution when the resistance value gradually increases like a polysilicon thin film resistor will be described with reference to FIG. Even if the resistance value of the heating resistor 10, that is, Rht increases due to deterioration with time, the bridge balance of the equation (13) does not change, so the heating temperature decreases by the amount of increase in Rht resistance.

  FIG. 15 shows an example of the actual measurement. FIG. 15A shows the temperature distribution before the resistance change, and FIG. 15B shows the temperature distribution after the resistance change. Comparing (a) and (b), it can be seen that the temperature distribution does not change uniformly, but the amount of change is smaller at higher temperatures.

  The reason for this is that the higher the temperature portion, the more the change with time is more remarkable and the resistance increase is larger, and the Joule heat is increased by the resistance increase than the other portions.

  If this temperature distribution change is positively used, it is possible to prevent the heating temperature from decreasing due to the resistance aging of the heating resistor 10. That is, as shown in FIG. 14, Rb is formed in the vicinity of the region where the temperature of the heating resistor 10 is the highest, and Rc is formed in the vicinity of the low region.

  The heating resistor 10 is formed in the thin wall portion 7 and is thermally insulated, but a little heat is conducted to the substrate 2, so that a slight temperature difference between Rb and Rc is caused by the difference in the pattern arrangement. Will occur.

  When the temperature distribution shown in FIG. 15A changes from the temperature distribution shown in FIG. 15A to the temperature distribution shown in FIG. 15B due to changes over time, there is almost no temperature change in the Rb portion, but the temperature in the Rc portion slightly decreases. For this reason, the resistance value of Rc is lowered to change the bridge balance, and as a result, it is possible to prevent the heating temperature from being lowered. It is also conceivable that a part of the Rc and Rb patterns is arranged in the thin portion 7 and this temperature distribution change is used more actively.

  If the heating temperature change of the heating resistor 10 can be prevented in this way, the characteristic change of the output 44 can be prevented.

  It should be noted that the concept of the present invention can be applied to the thermal type flow sensor of FIGS. 1, 6, 6 and 8 and the effect is the same.

  Next, the temperature distribution change when the resistance value gradually decreases like a platinum thin film resistor will be described with reference to FIG. When the heating resistor 10 changes with time and the resistance decreases, the heating temperature rises contrary to the case of the polysilicon thin film resistor described above. FIG. 16 shows an actual measurement example, where (a) shows the temperature distribution before the resistance change, and (c) shows the temperature distribution after the resistance change. As can be seen by comparing (a) and (c), the temperature distribution does not change uniformly, but the amount of change is smaller as the temperature is higher. The reason for this is that the higher the temperature portion, the more the change with time and the greater the decrease in resistance, and the lower the Joule heat by the amount of resistance decrease compared to the other portions.

  The pattern arrangement is exactly the same as described above. As shown in FIG. 14, Rb is formed in the vicinity of the region where the temperature of the heating resistor is highest, and Rc is formed in the vicinity of the low region. Then, when the temperature distribution changes due to a change over time, there is almost no temperature change in Rb, but Rc slightly rises in temperature, so that the resistance value of Rc increases, and as a result, the heating temperature can be prevented from rising.

  Next, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 17 shows the structure of the thermal flow sensor element 26 and its wiring pattern diagram. FIG. 18 is a circuit diagram including the thermal flow sensor element 26 shown in FIG.

  As shown in FIG. 17, if the temperature-sensitive resistor 22 is connected from the middle of the wiring of the heating resistor 10, useless resistance between the heating resistor 10 and the electrode 51 can be reduced. If the wiring resistance is reduced, the voltage of the power source 42 required for heating the heating resistor can be reduced accordingly. In particular, a 12V battery is used for automobiles, and particularly when the engine is started, the voltage may drop to about 6V. Therefore, the lower the drive voltage, the more advantageous as the thermal flow rate measuring device 1.

  On the other hand, with this configuration, the lead-out temperature sensitive resistor 22 is formed in the wiring portion for inputting to the differential amplifier 41. When this resistance changes with temperature, the input voltage of the differential amplifier 41 changes and appears as a heating temperature change of the heating resistor 10.

  Therefore, in the present invention, the drawer temperature sensitive resistor 23 having substantially the same resistance value as that of the above-described drawer temperature sensitive resistor 22 is formed in the other wiring portion input to the differential amplifier 41 by a simultaneous process.

  The circuit diagram is shown in FIG. The lead-out temperature sensitive resistors 22 and 23 are formed in the wiring portion that is input from the constant temperature difference bridge to the differential amplifier 41 as in this configuration, but these resistance values have the same value and the same resistance temperature coefficient. The heating temperature will not change. Therefore, when the present invention is applied, there is an effect of reducing the power supply voltage without causing temperature characteristic variation.

  Next, other embodiments of the present invention will be described below.

  First, the heating temperature of the heating resistor 10 described above with reference to FIGS. 23 and 24 will be supplemented. The heating temperature of the heating resistor 10 in Table 2 is 170 ° C. when the ambient temperature is 20 ° C., and 150 ° C. when expressed as a temperature difference ΔT with respect to the ambient temperature. Similarly, when the ambient temperature is 80 ° C., ΔT 167 ° C. (247 ° C.-80 ° C.).

  That is, in the above-described constant temperature difference bridge, ΔT tends to slightly increase as the ambient temperature increases. The fact that the temperature of the heating resistor 10 is high at a high temperature has no room for a change with time.

  Some conventional examples have been devised so that ΔT of the heating resistor 10 can be arbitrarily changed when the ambient temperature changes. As an example, as shown in the circuit diagram of FIG. 22, a configuration in which a fixed resistor 67 is connected in series to the temperature-sensitive resistor 11 of a constant temperature difference bridge is known.

  Therefore, the present invention has devised means for obtaining the same effect using a temperature sensitive resistor.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 19 shows the structure of the thermal flow sensor element 26, in which the heating resistor 10 and the temperature sensitive resistors 11, 12, 13 are formed by the same material and process. When a polysilicon thin film resistor is used as the material, the temperature coefficient of resistance is approximately 2000 ppm / ° C. Then, the second temperature sensitive resistors 24 and 25 having another resistance temperature coefficient, for example, platinum thin film resistors are formed and electrically connected to the temperature sensitive resistor 13. The temperature coefficient of resistance of the platinum thin film resistor is about 3000 ppm / ° C.

  The circuit diagram is shown in FIG. When such a combination is performed, the resistance change with respect to the ambient temperature change is larger in the portion where the temperature sensitive resistor 13 and the second temperature sensitive resistors 24 and 25 are combined than in the other temperature sensitive resistors 12.

  Therefore, by appropriately setting the resistance values of the second temperature sensitive resistors 24 and 25, ΔT of the heating resistor 10 when the ambient temperature rises can be arbitrarily reduced.

  It is also possible to form the electrode material 51 and the second temperature sensitive resistors 24, 25 from the same material. In this case, a new process is performed to form the second temperature sensitive resistors 24, 25. It is possible to implement without adding. As these materials, a platinum thin film or an aluminum thin film having a relatively high temperature coefficient of resistance is suitable.

Note that the heating temperature resistor 10 and the temperature sensitive resistors 11, 12, 13 may have higher resistance temperature coefficients than the second temperature sensitive resistors 24, 25. In that case, the same effect can be obtained by combining the temperature sensitive resistor 11 or the temperature sensitive resistor 12 with the second temperature sensitive resistors 24 and 25.

  In addition, as described with reference to FIG. 5, the tendency of resistance change with time is opposite in a semiconductor material such as a polysilicon thin film and a metal material such as a platinum thin film. Therefore, when the present invention is applied, for example, even if the resistance of the heating resistor increases with time, the resistance of the second temperature-sensitive resistor decreases, so that the heating temperature of the heating resistor can be reduced. Therefore, there is also an effect that it is possible to provide a highly reliable thermal flow rate measuring device 1.

FIG. 24 shows an embodiment used for an internal combustion engine, particularly a gasoline engine. The intake air 101 to the engine is in the air cleaner 102, the body 105, the duct 106, the throttle angle sensor 107, the idle air control valve 108, the passage in the middle of the intake passage where the throttle body 109 is integrated with the intake manifold 110, or the bypass passage Thus, the flow rate is detected by the thermal flow measuring device 1 according to the present invention, and the signal is taken into the control unit 111 in the form of a signal such as voltage and frequency, and the injector 112, the tachometer 113, the engine cylinder 114, An embodiment used for controlling a combustion section structure and subsystem comprising an exhaust manifold 115, a gas 116, and an oximeter 117.

  In the case of a diesel engine, the basic configuration is substantially the same, and the present invention can be applied. That is, the flow rate is detected by the thermal flow rate measuring device 1 of the present invention disposed in the middle of the air cleaner 102 and the intake manifold 115 of the diesel engine, and the signal is taken into the control unit 111.

  Recently, due to social demands such as stricter exhaust gas regulations for automobiles and prevention of air pollution, electric power is generated using propane gas vehicles, natural gas vehicles, or fuel cells using hydrogen and oxygen as fuel. There is a lot of research into moving it.

  It is also possible to apply the thermal flow rate measuring device of the present invention to a system that detects these flow rates and appropriately controls the fuel supply amount.

It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a circuit diagram containing the thermal type flow sensor element shown in FIG. It is sectional drawing which shows the thermal type flow measuring apparatus which has the thermal type flow sensor element shown in FIG. It is a figure for demonstrating the temperature characteristic dispersion | variation of the thermal type flow measuring apparatus by this invention. It is a figure for demonstrating an example of the resistance time-dependent change of a heating resistor. It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a circuit diagram containing the thermal type flow sensor element shown in FIG. It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a circuit diagram containing the thermal type flow sensor element shown in FIG. It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a wiring pattern figure of the thermal type flow sensor element by this invention. 1 is a circuit diagram including a thermal flow sensor element according to the present invention. It is sectional drawing which shows the thermal type flow measuring apparatus which has the thermal type flow sensor element by this invention. It is the elements on larger scale of the thermal type flow sensor element by this invention. FIG. 15 is a temperature distribution diagram of a heating resistor for explaining the effect of the present invention shown in FIG. 14. FIG. 15 is a temperature distribution diagram of a heating resistor for explaining the effect of the present invention shown in FIG. 14. It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a circuit diagram containing the thermal type flow sensor element shown in FIG. It is a wiring pattern figure of the thermal type flow sensor element by this invention. It is a circuit diagram containing a thermal type flow sensor element. 1 is a system diagram of an internal combustion engine according to the present invention. It is a circuit diagram containing the thermal type flow sensor element by conventional invention. It is a table | surface for demonstrating the effect of the thermal type flow measuring device by this invention. It is a table | surface for demonstrating the effect of the thermal type flow measuring device by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thermal flow measuring device, 2 ... Board | substrate, 3 ... Housing, 4 ... Circuit board, 5 ... Main passage, 6 ... Fluid flow, 7, 7a ... Thin part, 8 ... Temperature sensor, 9 ... Resin sealing, 10, 14, 18 ... exothermic resistor, 11, 12, 13, 13a, 13b, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25 ... temperature sensitive resistor, 26 ... thermal flow rate Sensor element, 46... Correction circuit,
47 ... flow direction output, 51 ... electrode.

Claims (18)

A heating resistor provided in the passage through which the fluid flows;
A first resistor;
A second resistor;
A third resistor;
A bridge circuit composed of the heating resistor, the first resistor, the second resistor, and the third resistor;
A thermal flow measuring device that radiates heat to the fluid from the heating resistor and measures the flow rate of the fluid,
The heating resistor, the first resistor, the second resistor, and the third resistor have substantially the same resistance temperature coefficient;
A thermal flow rate measuring apparatus, wherein at least two of the first resistor, the second resistor, and the third resistor are disposed close to each other. In claim 1,
The product of the resistance value of the heating resistor and the resistance value of the third resistor is balanced with the product of the resistance value of the first resistor and the resistance value of the second resistor. A thermal flow measuring device in which the current and / or voltage of a bridge circuit is controlled. In claim 1,
Thermal flow measurement, wherein the two resistors are placed on a common metal and / or silicon substrate via an insulating layer so that the two resistors are exposed to substantially the same temperature. apparatus. In claim 1,
Temperature detection means is provided on both sides of the heating resistor,
A thermal flow rate measuring device that measures the flow rate of the passage based on the output of the temperature detecting means. In claim 4,
It has a silicon substrate on which a thin part is formed,
The thermal flow rate measuring apparatus, wherein the temperature detecting means and the heating resistor are supported on the thin portion through an insulating layer and installed in the passage. In claim 1,
The said flow path has a bending part, The thermal type flow measuring device characterized by the above-mentioned. A heating resistor provided in the passage through which the fluid flows;
A first resistor;
A second resistor;
A third resistor;
A bridge circuit composed of the heating resistor, the first resistor, the second resistor, and the third resistor;
A thermal flow measuring device that radiates heat to the fluid from the heating resistor and measures the flow rate of the fluid,
The heating resistor, the first resistor, the second resistor, and the third resistor have substantially the same resistance temperature coefficient;
A thermal flow rate measuring apparatus, wherein at least two of the first resistor, the second resistor, and the third resistor are exposed to substantially the same temperature. In claim 7,
The product of the resistance value of the heating resistor and the resistance value of the third resistor is balanced with the product of the resistance value of the first resistor and the resistance value of the second resistor. A thermal flow measuring device in which the current and / or voltage of a bridge circuit is controlled. In claim 7,
The thermal flow rate measuring apparatus according to claim 1, wherein the two resistors are exposed to substantially the same temperature by being installed close to each other. In claim 7,
Thermal flow measurement, wherein the two resistors are placed on a common metal and / or silicon substrate via an insulating layer so that the two resistors are exposed to substantially the same temperature. apparatus. In claim 7,
Temperature detection means is provided on both sides of the heating resistor,
A thermal flow rate measuring device that measures the flow rate of the passage based on the output of the temperature detecting means. In claim 11,
It has a silicon substrate on which a thin part is formed,
The thermal flow rate measuring apparatus, wherein the temperature detecting means and the heating resistor are supported on the thin portion through an insulating layer and installed in the passage. In claim 7,
The said flow path has a bending part, The thermal type flow measuring device characterized by the above-mentioned. A heating resistor provided in the passage through which the fluid flows;
A first resistor;
A second resistor;
A third resistor;
A bridge circuit composed of the heating resistor, the first resistor, the second resistor, and the third resistor;
A thermal flow measuring device that radiates heat to the fluid from the heating resistor and measures the flow rate of the fluid,
The heating resistor, the first resistor, the second resistor, and the third resistor are made of substantially the same material,
The first resistor, the second resistor, and at least two of the third resistors are disposed on a common metal and / or silicon substrate via an insulating layer. Characteristic thermal flow measurement device. In claim 14,
The product of the resistance value of the heating resistor and the resistance value of the third resistor is balanced with the product of the resistance value of the first resistor and the resistance value of the second resistor. A thermal flow measuring device in which the current and / or voltage of a bridge circuit is controlled. In claim 14,
The thermal flow rate measuring device, wherein the two resistors are installed close to each other. In claim 14,
A thin portion formed on the substrate;
Temperature detecting means provided on both sides of the heating resistor,
The temperature detecting means and the heating resistor are supported on the thin wall portion via an insulating layer, installed in the passage,
A thermal flow rate measuring device that measures the flow rate of the passage based on the output of the temperature detecting means. Engine,
The thermal air flow meter according to any one of claims 1 to 17, attached to an intake pipe of the engine,
Fuel supply means for supplying fuel to the engine;
Control means for controlling the fuel supply means based on the output of the thermal air flow meter;
Engine system equipped with.

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