JPH08313318A - Heat sensitive type flow rate detector - Google Patents

Abstract

PURPOSE: To shorten a time for attaining the thermal equilibrium condition of respective portions, and to improve responsiveness and measuring accuracy by setting the resistance of a heating portion to be several times or more as high as the resistance of a lead portion, and embedding one end of a heater in the interior of a heat insulating hold member. CONSTITUTION: The resistance Rh of a meander-like heating portion 3a with approximately uniform width, which is formed by providing a resistance film 3 in a range of 40 to 80% from one end of an insulating board 2 in a lengthwise direction, is five time or more as high as the resistance Rs of a lead portion 3b, which is provided continuing with the heating portion 3a as far as the other end of the board 2. Since the ratio Rs/Rh of both resistances Rh, Rh becomes small, a heating quantity flowing to fluid via a hold member 5 becomes small so that a starting time is reduced. Since an area occupied by the film 3 is large in the area of the board 2, in detecting the temperature change of the board 2 by the film 3 no response delay is allowed. Since the one end of a heater 1, one part of the lead portion 3b, an electrode portion 3c, and the like are sealed inside the member 5, the heating quantity flowing to liquid is reduced. Thereby, a time for attaining the thermal equilibrium condition is shortened so that responsiveness and measuring accuracy are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate detecting device for measuring the intake air flow rate of an engine, and more particularly to optimization of the structure and size distribution of a heat-sensitive flow rate detecting element (hereinafter, simply referred to as a detecting element). is there.

[0002]

2. Description of the Related Art Generally, in an electronically controlled fuel injection system for an automobile engine, it is necessary to accurately measure the intake air flow rate to the engine for air-fuel ratio control. Recently, as an air flow rate detecting device, a heat-sensitive type flow rate detecting device (hereinafter, simply referred to as a flow rate detecting device) having a small size and a high mass flow signal and excellent responsiveness is used. The flow rate detecting device is provided with a heating element for electrically heating inside the passage of the fluid,
Utilizing that the resistance of the heating element changes with temperature,
The flow velocity or flow rate inside the fluid passage is detected by the cooling effect of the heating element that accompanies the fluid flow. As a heating element, a temperature-dependent resistance film (hereinafter simply referred to as a resistance film) such as platinum is generally formed on a flat plate-shaped insulating substrate (hereinafter simply referred to as a substrate) such as glass or ceramic. One end or both ends of this heating element is supported by heat insulation and used as a detection element.

FIG. 16 shows the structure of a conventional detecting element described in Japanese Patent Laid-Open No. 62-98219. As shown in the figure, the heating element 1 has a resistive film 3 formed on the surface of a substrate 2 and patterns of a heating portion 3a, lead portions 3b, and electrode portions 3c. Holding member 5 ₁ obtained by applying an insulating film on a metal surface, arranged parallel to the air flow, the longitudinal end of the heating element 1 are bonded and fixed via a heat insulating member. A conductive film 7 ₁ is formed on the insulating film in the vicinity where the heating element 1 is fixed by bonding, and the electrode portion 3 of the heating element 1 is formed by the bonding wire 6.
It is connected to c. In the detection element, the amount of heat flowing from the heat generating portion 3a to the holding member 5 ₁ is suppressed in this way.
Since the resistance of the resistance film 3 changes with temperature, the resistance film 3
The average temperature of the resistance film 3 is kept constant by controlling the heating current flowing through the resistance film 3 so that the resistance of the resistance film 3 becomes constant.
However, the contact area between the support member 5 ₁ and the heat insulating member must be increased to some extent in view of the vibration resistance and shock resistance of the detection element. Since the holding member 5 ₁ is made of metal as described above and has a high thermal conductivity, when the heating element 1 is heated with an electric current, the amount of heat flowing from the heating element 1 to the holding member 5 ₁ becomes a level that cannot be ignored. The resistance of the lead portion 3b is relatively larger than the total resistance of the resistance film 3, and the Joule heat generated in this portion during heating is large. Therefore, the temperature of the lead portion 3b is high and the amount of heat flowing from the lead portion 3b to the holding member 5 ₁ is large, which deteriorates the flow rate detection accuracy and responsiveness of the fluid to be measured (hereinafter, simply referred to as fluid). . Also,
Since the bonding wire 6 is exposed to the fluid, there is a high possibility that the bonding wire 6 will be damaged due to collision with foreign matter or vibration.
There is a problem of lack of reliability.

FIG. 17 shows a structure of a conventional detecting element different from the above. Similar to the detection element described above, the resistance film 3 is formed on the surface of the substrate 2, and the pattern of the heating portion 3a and the electrode portion 3c is formed. The heating element 1 is inserted and fixed in a holding member 5 made of a heat resistant resin having a small thermal conductivity. The terminal pin 7 and the electrode portion 3c are connected to each other by the bonding wire 6 and the resistance film 3. The resistance of the bonding wire 6 and the terminal pin 7 is much smaller than that of the resistance film 3. Since the heating element 1 is fixed by the holding member 5 made of a heat resistant resin having a small thermal conductivity, the amount of heat flowing from the heating element 1 to the fluid through the holding member 5 is smaller than that described above. Further, since there is no film-shaped lead portion having a relatively large resistance, the above-mentioned problem due to heat generation in the lead portion does not occur. However, since the terminal pin 7 and the bonding wire 6 are exposed to the fluid, there is a high possibility of foreign matter collision or damage due to vibration, and the reliability is low. Further, there is a problem in that the flow of the fluid is disturbed in the vicinity of the fixed portion of the heating element 1 and the stability of flow rate detection and the variation of characteristics occur. Furthermore, due to careless handling, the heating element 1 may break near the fixed portion, but even in such a case, the electrical connection may be maintained through the bonding wire, and the flow rate detection may be performed. There have also been problems such as difficulty in diagnosing device failures.

[0005]

In order to improve the reliability of the electrical connection by the bonding wire and prevent the flow of the fluid from being disturbed, it is necessary to prevent the bonding wire from being exposed to the fluid. . But,
If the lead part that connects the resistance film and the external electronic circuit is on the same substrate as the heat generating part, the resistance of the lead part becomes large in the conventional pattern of the heat generating part, the lead part, and the electrode part, and the heating current causes A response delay occurs due to heat generation in the lead section. In other words, there is a quantity of heat that flows from the lead portion to the holding member, and this is transferred to the fluid, so that a large time delay occurs until a thermal equilibrium state is reached, and the responsiveness deteriorates when the flow rate changes.

Further, as shown in FIG. 16, when the ratio of the area of the resistive film to the area of the substrate in the heat generating portion is small, a delay occurs until the temperature change of the substrate 2 is detected by the resistive film, and the flow rate changes. If you do, a response delay occurs. The reason for this is that the thickness of the substrate is larger than that of the resistive film with high thermal conductivity, and the temperature of the resistive film is affected by the temperature of the substrate in the portion in contact with the resistive film. If the temperature is large, it is considered that there is a delay in the temperature of the substrate following the temperature of the nearby resistive film.

Further, if the response time is small when the flow rate changes, the start-up time, which is the time from the supply of the heating current until the steady state is reached, becomes long, and conversely, if the start-up time is short, the flow rate changes. There was a problem that the responsiveness when doing was poor. It is considered that this is because the ratio of the area of the heating element to the area exposed to the fluid is not appropriate. That is, the start-up time largely depends on the time from the start of supplying the heating current to the time when the heating element and the holding member reach the thermal equilibrium state. Therefore, in order for the temperature of the heating element support portion to quickly react with the temperature of the fluid, the area of the heating portion should be small. On the other hand, the response when the flow rate changes is faster as the amount of heat flowing to the fluid from the lead portion or the holding member is smaller and the rate at which this amount of heat changes with the change in flow rate is smaller, so it is better to increase the heat generation area. It is considered that the responsiveness is improved.

[0008]

According to a first aspect of the present invention, there is provided a flow rate detecting device in which a heating element having a resistance of a heating portion which is 5 times or more the resistance of the lead portion is used as a detecting element, and one end of the heating element is connected to the lead portion. A part of the electrode portion and the terminal pin are both embedded and supported inside a heat insulating holding member so that the support portion is not exposed to a fluid.

According to a second aspect of the invention, there is provided the flow rate detecting device according to the first aspect of the invention, in which the area of the heat generating portion of the detecting element is 40% to 80% of the area of the portion of the detecting element exposed to the fluid.

According to a third aspect of the present invention, there is provided the flow rate detecting device according to the first aspect of the invention, in which the surface area of the resistive film in the heat generating portion of the detecting element is 50% or more of the substrate area in the heat generating portion.

[0011]

In the invention according to claim 1, the fluid is not disturbed in the holding member portion of the detection element, and the amount of heat generated in the lead portion of the detection element is reduced, so that the temperature of the lead portion is lowered and the lead portion is reduced. After that, the amount of heat flowing to the side of the fixing member decreases, and the temperature change of the holding member due to the cooling effect of the fluid decreases.

According to the second aspect of the present invention, the fluid is not disturbed in the holding member portion of the detecting element, and the amount of heat generated in the lead portion of the detecting element is reduced, so that the temperature of the lead portion is lowered and the lead portion is reduced. The amount of heat flowing to the side of the fixing member via the flow rate is further reduced, and the temperature change of the holding member due to the cooling effect of the fluid is reduced.

According to the third aspect of the invention, the fluid is not disturbed in the holding member portion of the detection element, the temperature uniformity in the heat generating portion is improved, and the heat generation amount in the lead portion of the detection element is reduced. As a result, the temperature of the lead portion decreases, the amount of heat flowing to the fixing member side via the lead portion further decreases, and the temperature change of the holding member due to the cooling effect of the fluid decreases.

[0014]

【Example】

Example 1. Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a detecting element according to a first embodiment of the present invention, FIG. 1 is a plan view and a sectional view in the middle of attaching a heating element to a holding member, and FIG. 2 is a sectional view of a completed detecting element. Is. Note that the same reference numerals are used for the same or corresponding portions as those of the conventional detection element, and duplicate description will be omitted. In the figure, reference numeral 1 is a heating element composed of a substrate 2 and a resistance film 3 formed on the surface thereof. The substrate 2 has a thickness of 0.15 to 0.2 mm, a width of 1.5 to 2 mm, and a length of 12 to
A 15 mm strip of alumina ceramic or glass flat plate, on one surface of which metal such as platinum or nickel whose resistance changes with temperature is formed into a uniform thickness by a method such as vapor deposition, sputtering or printing. Resistive film 3 with part of the film removed by methods such as laser trimming
Is formed. The resistance film 3 is provided in a range of 40 to 80% from one end in the longitudinal direction of the resistance film formation surface of the substrate 2, and the meander-shaped heat generating portion 3a having a substantially uniform width is formed. The surface area of the resistance film 3 in the heat generating portion 3a is 50 with respect to the area of the substrate 1 at the portion having the heat generating portion 3a.
% (Hereinafter, the ratio of the area of the substrate 2 where the heating portion 3a is present to the area of one surface of the substrate 2 is the heating portion ratio, and the surface area of the resistance film 3 in the heating portion 3a is the heating portion 3).
The ratio of the portion having a to the area of the substrate 2 is referred to as a heat generating film ratio). The width of the resistance film in the heat generating portion 3a is about 1/3 or less of the width of the resistance film in the lead portion 3b. Reference numeral 4 denotes a protective film formed by forming the resistive film 3 and then applying overcoat glass on the resistive film forming surface. An opening is provided near the end portion on the lead portion 3b side to form the electrode portion 3c. There is.
Reference numeral 5 is a holding member made of resin that is molded integrally with the terminal pin 7, and the tip of the heating element 1 on the lead portion 3b side is bonded. 6 is a bonding wire for connecting the electrode portion 3c and the terminal pin 7, 8 is a cover, and 9 is a holding member 5.
This is a sealing material in which an epoxy resin or the like is sealed from a gap so that air bubbles do not enter a space formed between the cover 8 and the cover 8. An electric current is supplied from the terminal pin 7 to heat the heating element 1 with Joule heat.

FIG. 3 is a structural diagram of a sensor portion in a flow rate detecting device in which the detecting element described with reference to FIGS. 1 and 2 is installed in a fluid flow path. An inner duct 21 for mounting a sensor is provided at the center of the fluid flow path 20, and a rectifying device 22 such as a honeycomb or a mold lattice is provided on the upstream side of the inner duct 21. The heating element portion of the detection element 10 is mounted inside the inner duct 21 in parallel with the fluid flow direction or at an elevation angle of 20 to 30 °. The holding member portion of the detection element 10 is embedded in the stay portion 21 ₁ of the inner duct 21 so as not to disturb the flow of fluid. Further, on the upstream side of the detecting element 10, there is provided a compensating temperature detecting element 11 composed of the same temperature-dependent resistance as the detecting element.

Next, the structure of the flow rate detector and its operation will be described. FIG. 4 is a schematic diagram showing a circuit configuration inside the detection element, in which the resistance of the heating portion 3a of the heating element 1 is represented by R
The resistance of h and the lead portion is represented by Rs. Also, FIG.
FIG. 4 is a control circuit diagram showing the principle of flow rate detection. In the figure,
10 is a detecting element, 11 is a temperature detecting element for compensation, 12, 1
Fixed resistance elements 3 and 14 form a bridge circuit together with the detection element 10 and the compensation temperature detection element 11, and the output thereof is supplied to the differential amplifier 15. In addition,
Reference numeral 16 is a heating current supply transistor. Differential amplifier 1
Since the differential gain of 5 is large, the heating current flows in the bridge circuit so that the output voltage of the bridge circuit becomes almost 0,
The resistance of the detection element 10 is balanced so as to be constant.
The sum of the resistances of the detection element 10 and the fixed resistance element 14 is 1/50 or less of the sum of the resistances of the compensation temperature detection element 11 and the resistance elements 12 and 13, and most of the heating current flows through the detection element 10. A flow rate signal is obtained as the voltage between the terminals of the fixed resistance element 14.

FIG. 6 shows the temperature distribution of the detecting element in the operating state of the flow rate detecting device. The horizontal axis represents the distance from the free end of the heating element 1, 3a is a heat generating portion, and 3b is a lead portion.
Curve A shows resistance ratio Rs / Rh = 0.3, curve B shows resistance ratio R
It is a temperature distribution when s / Rh = 0.1. In either case, the detection elements 10 operate so that the resistances are the same. During the operation of the flow rate detection device, the resistance of the detection element 10 becomes substantially equal to the resistance determined by the average temperature of the heat generating portion near the free end when the resistance ratio Rs / Rh is small. On the other hand, the resistance ratio Rs
When / Rh is large, the resistance is determined by the average temperature of the heating portion 3a and the lead portion 3b near the holding member 5. Therefore, in the latter case, the temperature of the lead portion becomes relatively higher, and in the latter case, the amount of heat generated for maintaining the resistance of the detection element constant becomes larger.

FIG. 7 shows a state of the output signal after the heating current supply is started. The horizontal axis represents time, the vertical axis represents the flow rate signal obtained as the output voltage, and t ₀ represents the heating current supply start point.
The output voltage rises to the saturation point of the bridge voltage immediately after the heating current starts to be supplied, but the resistance increases as the temperature of the detection element increases, so that the heating current decreases and the magnitude of the output signal also decreases, eventually reaching a balanced state. Hereinafter, the time from the start of heating current supply to the equilibrium state is called the startup time T _ON .

FIG. 8 shows the relationship between the ratio of the resistance Rs of the lead portion to the resistance Rh of the heating portion and the starting time T _ON . Resistance ratio R
As s / Rh is smaller, the amount of heat generated in the lead portion is smaller, so the amount of heat flowing to the holding portion is smaller and the startup time T _ON is reduced. As shown in the figure, the starting time T _ON rapidly increases in the range where the resistance ratio Rs / Rh is 0.2 or more.

FIG. 9 shows the response when the flow rate is changed stepwise. Hereinafter, the time from the rise of the flow rate to the steady state is called the response time _Tr . FIG. 10 shows the relationship between the heat generating portion ratio, the start time T _ON, and the response time T _r . When the heat generating portion ratio decreases, the temperature in the lead portion decreases, so that the start-up time T _ON decreases. On the other hand, in the range of the heat generating portion ratio from 0.1 to 0.8, the response time T _r decreases as the heat generating portion ratio increases. It can be considered that this is because the amount of heat flowing from the heat generating portion to the fluid relatively increases as the heat generating portion ratio increases. It should be noted that when the heating portion ratio is 0.8 or more, both the response times T _ON and T _r tend to increase. It can be considered that this is because when the heat generating portion ratio is 0.8 or more, the influence of the amount of heat flowing from the heat generating portion to the holding member having a large thermal time constant becomes large. From the above, it can be said that it is preferable to set the heating portion ratio in the range of 0.4 to 0.8.

FIG. 11 shows the relationship between the heating film ratio and the response time T _r . When the heating film ratio is about 0.5 or less, there is a delay before the temperature change of the substrate 2 appears as the resistance change of the resistance film 3, and the response time T _r tends to increase. From this, it can be said that the heating film ratio is preferably about 0.5 or more.

In the above description, the thickness of the resistance film is determined by the heating portion 3
Although a and the lead portion 3b are the same, the film thickness of the resistance film from the lead portion to the electrode portion may be larger than the film thickness of the heat generating portion as shown in the sectional view of the detection element of FIG. In this case, the resistance film cross-sectional area of the lead portion may be made equal to or larger than those in FIGS. As a result, the ratio of the resistance Rs of the lead portion to the resistance Rh of the heat generating portion can be set smaller, and the temperature of the lead portion can be lowered to reduce the amount of heat flowing from the lead portion to the holding member. It becomes possible to further shorten the time.

Further, as shown in FIG. 13, the lead portion and the electrode portion may be formed of a metal film 3d made of, for example, copper, aluminum or the like having a volume resistivity smaller than that of the resistance film. The same effect as in the case of FIG. 12 is obtained.

Further, as shown in FIG. 14, a metal film 3d made of a conductive material such as copper or aluminum may be formed on the lead portion and the electrode portion. The same effect as in FIGS. 12 and 13 can be obtained.

Example 2. A second embodiment of the present invention will be described below with reference to the drawings. FIG. 15 is a sectional view of the detecting element according to this embodiment. The difference from the first embodiment is the substrate 2
The heat generating part 3a is arranged at the central part of the above, and the lead parts 3b are arranged at both ends one by one so as to be fixed at both ends. Since the heating element is fixed at both ends, the pattern width of the resistance film of the lead portion can be set to be relatively large and the resistance ratio Rs / Rh
Can be made smaller. Also, the strength against external force can be increased. Of course, the lead portion can be configured as shown in FIGS.

[0026]

According to the first aspect of the present invention, the fluid is not disturbed in the holding member portion of the detection element, and the amount of heat generated in the lead portion of the detection element is reduced, so that the temperature of the lead portion is reduced. The amount of heat that flows through the lead to the fixing member decreases, and the temperature change of the holding member due to the cooling effect of the fluid decreases, so the time from the application of the heating current to the thermal equilibrium of each part is shortened. , The response is improved and the measurement accuracy is improved. Furthermore, since the bonding wire does not come into contact with the fluid, damage due to collision with foreign matter, vibration, etc. is eliminated and reliability is improved.

According to the second aspect of the present invention, the distribution of the heat generation amount between the heat generating portion and the lead portion is more preferable than that of the first aspect of the invention, so that the responsiveness and the measurement accuracy are further improved and improved.

According to the third aspect of the invention, the temperature uniformity in the heat generating portion is increased, the responsiveness to the flow rate change is improved, and the measurement accuracy is further improved, as compared with the first aspect of the invention.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view of a detection element according to a first embodiment of the present invention.

FIG. 2 is an assembled sectional view of the detection element according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a flow rate detecting device according to a first embodiment of the present invention.

FIG. 4 is a circuit diagram of a detection element according to the first embodiment of the present invention.

FIG. 5 is a control circuit diagram showing the principle of flow rate detection according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a temperature distribution in the detection element according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a start-up response of the flow rate detection device according to the first embodiment of the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the resistance ratio of the heating portion and the lead portion of the detection element according to the first embodiment of the present invention and the startup time.

FIG. 9 is an explanatory diagram showing the responsiveness of the flow rate detection device according to the first embodiment of the present invention to changes in step flow rate.

FIG. 10 is a characteristic diagram showing the relationship between the start-up time and step response time of the detection element and the heating section ratio according to the first example of the present invention.

FIG. 11 is a characteristic diagram showing the relationship between the step response time and the heating film ratio of the detection element according to the first example of the present invention.

FIG. 12 is a cross-sectional view of the detection element in which the lead portion structure is changed in the first embodiment of the present invention.

FIG. 13 is a sectional view of still another modification of the detection element according to the first embodiment of the present invention.

FIG. 14 is a sectional view of still another modification of the detection element according to the first embodiment of the present invention.

FIG. 15 is a sectional view of a detection element according to a second embodiment of the present invention.

FIG. 16 is a plan view of a conventional detection element.

FIG. 17 is a plan view of a conventional detection element different from that of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heating element 2 Insulating substrate 3 Resistive film 3a Heating part 3b Lead part 3c Electrode part
3d Conductive film 4 Protective film 5 Holding member 6 Bonding wire 7 Terminal pin 8 Cover 9 Encapsulating material 10 Detecting element 11 Compensating temperature detecting element 20 Flow path 21 Inner duct 22
Rectifier

Claims (3)

[Claims] 1. A temperature-dependent resistance film is formed on an insulating substrate, a meandering heat generating portion is provided at a position apart from a supporting portion of the insulating substrate, and an electrode portion for connection to the outside is provided. A heating element having a film-shaped lead portion connecting between the heating portion and the electrode portion, and a conductive portion supporting the heating element and electrically connected to the outside through the electrode portion. In a heat-sensitive detection device having a flow rate detection element including a holding member, the resistance of the heating portion is 5 times or more the resistance of the lead portion, and the end portion of the heating element is part of the lead portion, the electrode. And a conductive part electrically connected to the outside via the electrode part and the electrode part are embedded in the heat insulating holding member for isolating the fluid to be measured, and the holding member embedded part of the heating element is used. Except in the flow path of the fluid to be measured Thermosensitive flow rate detecting device being characterized in that disposed. 2. The heat-sensitive flow rate according to claim 1, wherein an area of the heat generating portion is 40% to 80% of an area of a portion of the flow rate detecting element exposed to the fluid to be measured. Detection device. 3. The pattern width of the heat generating portion is substantially uniform, and the surface area of the temperature dependent resistance film of the heat generating portion is 50% or more of the area of the insulating substrate in the heat generating portion. The heat-sensitive flow rate detecting device according to claim 1.