JPH1151729A - Fluid detecting sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid detecting sensor capable of constituting a highly accurate and highly responsive airflow sensor. SOLUTION: A linking member 16 is provided to link a heater 10 and downstream-side and upstream-side temperature measuring resistors 8 and 9 arranged at equal intervals with respect to the heater 10 so as to enable thermal conduction between them. The linking member 16 is normally formed of the same material as that of the temperature measuring resistors 8 and 9 or that of the heater 10. In addition, the linking member 16 is formed of a member in the shape of a narrow line similarly to the temperature measuring resistors 8 and 9 or the heater 10. In this case, the linking member 16 is connected so that a boundary layer formed on the surface of the linking member 16 by air flowing in a perpendicular direction with respect to the temperature measuring resistors 8 and 9 may become thin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid detection sensor suitable for a vehicle air flow sensor or the like.

[0002]

BACKGROUND OF THE INVENTION Conventionally, as an air flow sensor for a vehicle, there have been known air flow sensors of a hot wire type and a hot film type. These types of air flow sensors are designed to calculate the flow rate of a fluid from a temperature change of a heating temperature measuring element arranged in a flowing fluid. The principle of these airflow sensors is as follows. That is, a temperature measuring element having a predetermined correspondence between the temperature and the electric resistance is arranged in a heated state in the flowing fluid, and the temperature change is measured. Since the temperature change of the temperature measuring element depends on the amount of fluid flowing while taking heat by contacting the temperature measuring element, the flow rate of the fluid flowing across the temperature measuring element by measuring the temperature change is measured. That is, the flow rate can be known. Here, since the temperature change of the temperature measuring element corresponds to the electric resistance value, the temperature change of the temperature measuring element can be known by measuring the change of the electric resistance value of the temperature measuring element, and based on this, That is, the flow rate of the fluid can be known.

As a known technique using such a heating type measuring element, for example, those disclosed in JP-A-61-138126 and JP-A-4-72523 are known. Japanese Patent Application Laid-Open No. 61-138126 discloses a device in which a hot film element member 17 is used as a heating member so that the flow of air in any direction can be measured. JP-A-4-72523 describes that
A flow sensor of a type using each heater element for one temperature measuring resistor is disclosed.

[0004]

The conventional type of fluid detection sensor disclosed in the above publication tends to be relatively large for this kind of application, and therefore has a high measurement accuracy or responsiveness. It was not satisfactory in terms of aspects. In particular, recently, in EGR control of a vehicle, EGR control is performed.
There is a growing demand for engine operation with the maximum amount of fuel being introduced, and high responsiveness and accuracy of airflow sensors are required to perform engine control under such severe conditions. .

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a fluid detection sensor capable of forming an airflow sensor with high accuracy and high responsiveness. And In order to achieve this object, the present inventors have discovered that it is important to promote the miniaturization of the fluid detection sensor, and have found conditions for achieving the miniaturization of the fluid detection sensor. In order to achieve the above object, a fluid detection sensor of the present invention is provided with a linear temperature measuring means arranged so as to cross a fluid flow and an upstream position so as to have a predetermined distance from the temperature measuring means. And a connecting means for connecting both of the heat generating means and the temperature measuring means and the heat generating means for permitting heat transfer.

The temperature measuring means arranged upstream and / or downstream of the heat generating means in order to achieve the miniaturization as described above is preferably constituted by a thin wire, and has a space between the heat generating means and the heat measuring means. It is necessary to make it as narrow as possible, as long as it is only affected by the heat transfer due to the flow of the fluid. In this case, the temperature of the heating means is several hundred degrees Celsius
Since the temperature of the flowing fluid is about the ambient temperature, the temperature difference from the temperature measuring means is extremely large, but the temperature difference from the ambient temperature of the fluid to be measured for the flow rate is small. The present inventors have focused on the fact that the greater the difference between the temperature measuring means and the fluid temperature, the more susceptible to changes in the fluid flow state, and actively heat transfer between the heating means and the temperature measuring means. By doing so, a large temperature difference between the temperature measuring means and the fluid was secured, and the sensitivity of the temperature measuring means was successfully improved.

In a preferred embodiment, the temperature measuring means includes:
It has a temperature measuring element for measuring the temperature by utilizing the fact that the electric resistance changes in response to the temperature change, and a support for supporting the temperature measuring element, and the connecting means is integrally formed with the support. As a result, heat from the heat generating means is transmitted to the temperature measuring element. Preferably,
The width of the support in the fluid flow direction is about 10 to 50 μm. A typical form of the temperature measuring means is a thin wire structure. In particular, a single crystal thin wire using the same material as the silicon substrate is preferable. In a preferred embodiment, the fluid boundary layer on the surface of the connecting portion is configured to be restricted as much as possible.

[0008] When the boundary layer of the fluid becomes thicker, the flow of the fluid in the boundary layer becomes slower, so that the responsiveness of the sensor to changes in the state of the flow is reduced. It is desirable. For this purpose, for example, the temperature measuring means is connected so as to cross the connecting portion obliquely to the flow direction so that the length in the flow direction of the fluid is as short as possible. As described above, when the connecting portion is arranged so as to cross the fluid flow, formation of a boundary layer of the fluid formed on the surface of the connecting portion is hindered. As a result, the state around the connecting portion represents the state of the fluid at that moment, and good sensor responsiveness can be secured.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
In this embodiment, the present invention is applied to an airflow sensor of a vehicle. Referring to FIG. 1, there is shown an air flow sensor 2 disposed in an intake passage 1, and the air flow sensor 2 is arranged so as to be orthogonal to an intake air flow flowing through the intake passage 1 as indicated by an arrow 3. It comprises a fluid detecting element 4 having a fluid detecting element, that is, a temperature measuring resistor, and a signal processing circuit section 5 for processing a signal from the fluid sensor. As shown in FIGS. 2 and 3, the fluid detection sensor 4 having the fluid detection element disposed in the intake passage 1 includes a substrate 7 having a groove 6 extending along the air flow direction. The fluid detection elements 8, 9 are arranged so as to extend perpendicular to the air flow.

The fluid detecting elements 8 and 9 of the present embodiment are each formed of a thin wire-shaped resistance thermometer whose electric resistance changes according to the temperature. The resistance temperature detector of the present example is arranged at right angles to the air flow as described above,
Book is provided. A thin wire heater 10 is provided between the upstream and downstream resistance temperature detectors as a heat supply source through an air flow to the resistance temperature detector. In this case, the heater is connected to the upstream and downstream resistance temperature detectors 8 and 9.
Extend equidistantly from either of them. Both ends of the resistance temperature detectors 8 and 9 are connected to terminals 12 and 1 formed of a silicon chip provided on a step 11 of the substrate on both sides of the groove 6.
3 is connected. The heater 10 is connected to a power supply terminal 14 and a temperature detection terminal 15.

The output of the resistance temperature detector is transmitted to the processing circuit via the terminals 12, 13, 14, and 15, and the temperature of the heater 10 is detected. Is supplied via the Internet. The electric power is controlled so that the temperature of the heater 10 becomes higher than the air temperature by a predetermined temperature. It is not necessary to make the temperature difference between the heater 10 and the air temperature constant, but if the temperature difference is made constant, the amount of heat taken off by the air from the heater 10 becomes a function of the air flow rate, so that the subsequent processing becomes easier. There is.
In this example, the heater 10 and the heater 10
A connecting member 16 is provided for connecting the upstream and downstream temperature measuring resistors 8 and 9 arranged at equal intervals to the heat-transfer resistors 8 and 9 so as to conduct heat.

The connecting member 16 is usually made of the same material as the resistance temperature detectors 8, 9 or the heater 10. Further, similarly to the temperature measuring resistors 8 and 9 or the heater 10, the temperature measuring resistors 8 and 9 and the heater 10 are formed of thin line-shaped members. In this case, the connecting member 1
6 is a resistance temperature detector 8, 9 as shown in FIG. 4 or FIG.
It is preferable that the air flowing in the direction perpendicular to the connection member 16 be connected so that a boundary layer formed on the surface of the connecting member 16 becomes thin. For this purpose, the connecting member connects the heater and the resistance temperature detector so that the portion extending in the direction along the air flow is reduced. In the above structure,
The operation of the fluid detection sensor 4 will be described. As described above, in this example, the heater 10 is set to be higher by a predetermined temperature than the measured temperature of the air.

The heater 10 is connected to the connecting member 16.
The resistance temperature detectors 8 and 9 which receive heat supply by the heat conduction of
The temperature rises to near the temperature of the heater 10. When the air in the intake passage 1 is stationary, that is, when the flow rate is zero, the temperatures of the two resistance temperature detectors 8 and 9 are equal. However, when the air flows, the temperature of the temperature measuring resistors 8 and 9 in the air flow decreases because the heat is taken away by the air. In this case, the resistance temperature detector 8 on the upstream side of the air flow
Is constantly in contact with fresh air, so that the temperature tends to decrease. On the other hand, the resistance temperature detector 9 on the downstream side of the air flow is
By contacting the upstream temperature measuring resistor 8 and the heater 10, heat is taken from these and the temperature is slightly increased as compared with fresh air. For this reason, the temperature decreasing tendency of the downstream temperature measuring resistor is smaller than that of the upstream temperature measuring resistor.

In the fluid detection sensor 4 of this embodiment, the temperature change of the resistance temperature detector is detected as a change in electric resistance, and the change in resistance can be detected by a detecting means such as a Wheatstone bridge. . Then, by knowing the resistance value of the resistance temperature detector, the temperature of the resistance temperature element can be known from the relationship between the resistance value of the material and the temperature determined in advance. Since the relationship between the temperature change and the flow rate is also known, the flow rate of air crossing the resistance temperature detector can be determined by knowing the temperature of the resistance temperature detector. The structure of this example is
The reason why the detection accuracy can be improved will be described. With reference to FIGS. 6 and 7, a description will be given of the temperature change of the heater 10 and the resistance temperature detectors arranged on both sides thereof at the same distance from the heater.

FIG. 6 shows a heater 10 and resistance temperature detectors 8 and 9.
FIG. 7 is an explanatory diagram of a temperature state when the and are not connected. In FIG. 6, the temperature of the heater 10 is set at about 200 ° C., and the air temperature at this time is set to 20 ° C. That is, the temperature difference is 180 ° C. And the resistance temperature detectors 8 and 9 on both sides
When the air is stationary, the temperature is the same as the ambient air temperature (solid line in the figure), and a temperature change occurs when the air starts to flow. In this case, the temperature of the upstream resistance temperature detector is the same as the air temperature, and the downstream resistance temperature sensor exchanges heat with the heater 10 and comes into contact with the heated air, thereby increasing the temperature (see FIG. Broken line). However, considering that the fluid detection sensor according to the present invention is small, the amount of heat supplied from the heater 10 is relatively small as compared with the amount of air in contact with the fluid detection sensor.
Very slight. Therefore, the temperature rise of the resistance temperature detectors 8 and 9 also becomes small, and it is difficult to improve the detection accuracy.

On the other hand, when the heater 10 and the resistance temperature detector are connected so as to conduct heat as in the present invention, as shown in FIG. Therefore, the temperature difference from the ambient air temperature becomes extremely large, and heat exchange with the air when the air flows is promoted. Further, since the heat capacity of the air flowing across the fluid detection sensor 4 is larger than the heat capacity of the resistance temperature detector, the cooling effect of the resistance temperature detectors 8 and 9 becomes remarkable. That is, the temperature change of the resistance temperature detector increases, and the sensitivity to the flow rate change is improved.
In this case, the degree of temperature change differs between the upstream side and the downstream side for the above-described reason, and the upstream side is large and the downstream side is small. Therefore, the flow direction and the flow rate of the air can be detected with high responsiveness and high accuracy by the fluid detection sensor of this embodiment.

Next, an example of a manufacturing procedure of the fluid detection sensor of this embodiment will be described. The fluid detection sensor of this example can be manufactured using etching. As shown in FIG. 8A, first, an oxide film is formed on a silicon substrate. Then, as shown in FIG. 8B, a chromium film is formed to a thickness of about 500 angstroms by a sputtering method or the like, and a platinum film of about 2000 angstroms is formed thereon.
Chromium forms a layer that improves the adhesion between platinum and the substrate. In this state, a predetermined resistance pattern is patterned by photolithography. Next, as shown in FIG. 8C, the oxide film other than the portions constituting the heater, the resistance temperature detector, and the connecting member is removed (oxide film patterning). Next, as shown in FIG. 8D, the base silicon substrate is deeply etched (reactive etching with SF6 + O2 gas). Then, as shown in FIG. 8E, the substrate is immersed in an etching solution such as KOH to penetrate the lower portion of the portion that becomes a thin line (lateral crystal anisotropic etching).

In this way, it is possible to form a fluid detection sensor comprising heaters arranged in parallel on the silicon substrate, temperature measuring resistors on both sides thereof, and a connecting member for connecting the heater and the temperature measuring resistors. In the above example, a description has been given of an example in which the resistance temperature detectors are arranged on both sides of the heater to constitute the fluid detection sensor.However, it is not always necessary to arrange them on both sides. Good.

[0019]

As described above, according to the present invention, the detection accuracy can be improved by connecting the heater and the fluid detecting element disposed in at least one of the fluid flow directions to the heater in a heat conductive state. It is possible to provide a fluid detection sensor that is smaller in size than the conventional fluid detection sensor and has good responsiveness.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an air flow sensor to which the present invention can be suitably applied;

FIG. 2 is an enlarged view of a part of a fluid detection sensor A of the air flow sensor of FIG. 1,

FIG. 3 is a perspective view of the fluid detection sensor of FIG. 2;

FIG. 4 is an explanatory diagram showing an example of a connection state between a connection member and a fluid detection element of a fluid detection sensor.

FIG. 5 is a view similar to FIG. 4, showing another example of a connection state between a connection member and a fluid detection element of a fluid detection sensor.

FIG. 6 is an explanatory diagram showing a temperature state of a fluid detection sensor using a conventional thin line;

FIG. 7 is a view similar to FIG. 6, showing a fluid detection sensor according to the present invention;

FIG. 8 is an explanatory view showing one example of a manufacturing procedure of the fluid detection sensor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intake path 2 Air flow sensor 4 Fluid detection sensor 8, 9 Resistance temperature detector 10 Heater 16 Connecting member.

Claims (4)

[Claims] 1. A linear temperature measuring means arranged so as to cross a flow of a fluid, a heat generating means arranged at a position on an upstream side with a predetermined interval from the temperature measuring means, and the temperature measuring means. A fluid detection sensor, further comprising a connecting means for connecting both of which allows heat transfer between the fluid detecting means and the heat generating means. 2. The method according to claim 1, wherein said temperature measuring means comprises:
It has a temperature measuring element for measuring the temperature by utilizing the fact that the electric resistance changes in response to the temperature change, and a support for supporting the temperature measuring element, and the connecting means is integrally formed with the support. The fluid detection sensor is adapted to transmit heat from the heat generating means to a temperature measuring element. 3. The fluid detection sensor according to claim 2, wherein the width of the support in the fluid flow direction is about 10 to 50 μm. 4. The fluid detection sensor according to claim 1, wherein the fluid detection layer is configured to limit the formation of a fluid boundary layer on the surface of the connecting portion.