JPH04313027A - Thermal type flow sensor - Google Patents

Abstract

PURPOSE:To improve the output sensitivity of a thermal type flow sensor by increasing the convective heat transferring amount from a heat sensitive element for heat generation to a fluid. CONSTITUTION:A meandering recessing and projecting section is formed on the surface of a substrate 1 and another recessing and projecting section which is parallel to the flowing direction of a fluid is formed on the rear of the substrate 1. In addition, the convective heat transferring amount from a temperature sensitive resistance pattern 2 to a fluid is increased by forming heat sensitive resistance patterns 2 in the projecting sections of the recessing and projecting section on the surface and increasing the heat transferring area by means of both recessing and projecting sections on the surface and rear of the substrate 1. Therefore, the responsiveness of this sensor is improved, since the convective heat transferring amount to the fluid is increased and the output sensitivity of this sensor is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal flow rate sensor having an improved temperature-sensitive resistance element for detecting the flow rate of air taken into an engine.

0002

2. Description of the Related Art Generally, when installing an electronically controlled fuel injection system in an automobile engine, it is important to accurately measure the amount of air intake into the engine in order to control the air-fuel ratio. Conventionally, vane type air flow sensors have been the mainstream, but recently, thermal type flow sensors that are small, can obtain a mass flow rate, and have good responsiveness are becoming popular.

This thermal flow rate sensor supplies current to a temperature-sensitive resistor disposed in the intake air to generate heat, and utilizes the phenomenon of heat transfer from this heating element to the intake air, and is used as a detection circuit. A constant temperature measurement method with excellent responsiveness is commonly used.

This constant temperature measurement method is a method in which a bridge circuit and a differential amplifier are configured so that the temperature of the heating element is always a certain temperature higher than the intake air temperature, and the amount of heat transferred from the heating element to the air is measured. .

FIG. 11 shows a plan view of a heat-generating temperature sensing element of a conventional thermal flow sensor, and FIG. 12 shows a sectional view taken along line FF in FIG.
Shown below. The heat-generating temperature sensing element shown in FIGS. 11 and 12 is disclosed in Japanese Patent Application Laid-Open No. 60-235020. In FIGS. 11 and 12, 101 is 20 to 50
A corrosion-resistant metal plate of about μm, 102 is an insulating layer 10
6 is a temperature-dependent resistance pattern formed by processing it into a meandering shape. This insulating layer 106 is an extremely thin insulating layer formed on the metal plate 1.

[0006] The heat-generating temperature-sensitive element constructed as described above is small, and many elements can be manufactured from a single substrate, so it is excellent in mass production.

A bridge circuit shown in FIG. 13 is constructed by the temperature-sensitive resistor and fixed resistor having the above-described structure. This figure 1
3, 107 is a temperature-sensitive resistor for generating heat; 108 is a temperature-sensitive resistor for detecting intake temperature, which has a similar structure to the temperature-sensitive resistor for generating heat 107 and has a resistance value more than 50 times larger than that of the temperature-sensitive resistor for generating heat 107; 109; 110 and 111 are fixed resistances.

A bridge circuit is constituted by the temperature-sensitive resistor 7 for heat generation, the temperature-sensitive resistor 108 for detecting intake temperature, and the fixed resistors 109 to 110, and is connected to the bridge. Further, the emitter of the power transistor 113 is connected to a battery power source.

Next, the operation will be explained. When the bridge circuit is in a balanced state, each bridge resistor satisfies the following equation. RH・R2 = (RK +R1)・R3 However, RH
is the resistance value of the heat-generating temperature-sensitive resistor 7, RK is the resistance value of the intake temperature detection temperature-sensitive resistor 108, and R1, R2, and R3 are the resistance values of the fixed resistors 109, 110, and 111, respectively.

That is, by supplying the heating current I from the power transistor 113 to the heat-generating temperature-sensitive resistor 107 so that the unbalanced voltage of the bridge becomes almost zero, the resistance value of the heat-generating temperature-sensitive resistor 107, that is, the temperature is kept constant.

In this state of thermal equilibrium, the heating current I is a function only of the mass flow rate Qm of the fluid. Therefore, by measuring the heating current I as a voltage drop across the bridge resistor R3 at the output terminal 114, the mass flow rate can be detected.

0012

[Problems to be Solved by the Invention] Since the principle of conventional thermal flow rate sensors utilizes convection heat transfer between a heating element and a fluid, other heat transfer (such as heat conduction to a holding member or heat radiation) ) is as small as possible, the sensor sensitivity improves. Conversely, the output sensitivity of the sensor improves as the ratio of the amount of convective heat transfer to the total amount of heat transferred from the heating element increases.

However, the conventional thermal flow sensor
Since both surfaces of the heat-generating temperature sensing element are flat, the heat transfer area cannot be increased, and the amount of convective heat transfer, which is proportional to the heat transfer area, cannot be increased. Therefore, there was a problem that the output sensitivity of the sensor was relatively low.

[0014] Furthermore, since the heat conduction loss to the holding member also affects the responsiveness, reducing the proportion of the heat conduction loss to the holding member to the total amount of heat transfer is one of the challenges for improving the responsiveness. There is also.

The present invention has been made to solve the above-mentioned problems, and aims to provide a thermal flow sensor with improved output sensitivity and response.

[0016]

[Means for Solving the Problems] A thermal flow sensor according to the present invention has a heat-generating temperature-sensing element in which a part or all of the portions on both sides of the element that come into contact with fluid have an uneven structure.

[0017]

[Operation] In the thermal flow sensor of the present invention, part or all of the parts on both sides of the heat-generating temperature sensing element that come into contact with the fluid have an uneven structure, so the heat transfer area is increased and the heat transfer area from the heating element to the fluid is increased. The amount of heat transferred by convection increases.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the thermal flow rate sensor of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a heat-generating temperature-sensitive element showing one embodiment thereof, and FIG. 2 is a sectional view taken along the line AA in FIG. In both FIGS. 1 and 2, 1 is a silicon single crystal substrate (
(hereinafter referred to as a substrate), 1a is a surface unevenness formed on the front surface of the substrate 1, 1b is a back surface unevenness formed on the back surface of the substrate 1, and 2 is a temperature-dependent resistor formed on the substrate 1 by vapor deposition etc. A temperature-sensitive resistor pattern is formed by etching a temperature-sensitive resistive film as a body into a meandering shape. 3 is an electrode extraction portion provided at an end of the temperature-sensitive resistor pattern.

Next, the operation will be explained. In this embodiment, as shown in FIGS. 1 and 2, both surfaces of the substrate 1 are provided with a concavo-convex structure, so that the transmission area from the heat-generating temperature-sensitive element to the fluid becomes large. Surface unevenness portion 1 on the front side of the substrate 1
The convex portion a has the same meandering shape as the temperature-sensitive resistor pattern 2, and the concave and convex portions 1b on the back side of the substrate 1 are formed parallel to the fluid flow, making the substrate 1 anisotropic. Obtained by etching.

In this embodiment, the temperature-sensitive resistor pattern 2 is formed on a convex portion of the surface unevenness 1a of the substrate 1.

Further, although FIG. 1 shows an uneven portion having a wall surface perpendicular to the substrate 1, the uneven portion may have a curved surface obtained by isotropic etching of the substrate 1 on the wall surface. do not have. In this way, by increasing the heat transfer area, the amount of convective heat transfer from the heat-generating temperature sensing element to the fluid increases, and the output sensitivity and responsiveness of the sensor are improved.

Next, a second embodiment of the thermal flow sensor of the present invention will be described. FIG. 3 is a plan view of the heat-generating temperature sensing element in this second embodiment, and FIG.
It is a sectional view taken along the B line. In the first embodiment, the temperature-sensitive pattern 2 is formed in the convex portion of the surface unevenness 1a on the front side of the substrate 1, but in this second embodiment, on the contrary, the temperature-sensitive resistor pattern 2 is formed in the concave portion. The same effect can be expected in this case as well. In this case, the concave portion on the front surface side of the substrate 1 has the same meandering shape as the temperature-sensitive resistor pattern 2.

Next, a third embodiment of the present invention will be described. FIG. 5 is a plan view of the heat-generating temperature sensing element in the thermal flow sensor of the present invention, and FIG. 6 is a cross-sectional view taken along line CC in FIG. In both FIGS. 5 and 6, the substrate 1 and temperature-sensitive resistor pattern 2 are exactly the same as those in the first embodiment shown in FIGS. 1 and 2, but in this third embodiment, , forming the back surface unevenness portion 1b on the back surface of the substrate 1 is the same as in the first and second embodiments described above, but the surface side of the substrate 1 is not directly formed with unevenness, but is formed on a flat surface. A temperature-sensitive resistance film is formed on the remaining surface, and a temperature-sensitive resistance pattern 2 is formed by etching. Then, a good heat conductive film 4 that can be etched is covered over the temperature sensitive resistor pattern 2, and the good heat conductive film 4 is etched to form the uneven portions 4a.
form.

[0024] By increasing the heat transfer area in this manner, the amount of convective heat transfer from the heat-generating temperature sensing element to the fluid increases, and the output sensitivity and responsiveness of the sensor are improved.

In the third embodiment, the temperature-sensitive resistor pattern 2 was formed by etching the temperature-sensitive resistor film formed on the substrate 1, but as a fourth embodiment of the present invention, As shown in the plan view of FIG. 7 and the cross-sectional view of FIG. 8 taken along line D-D in FIG.
The resistor pattern 2 may be processed into a meandering shape using the pattern groove 5 formed using laser trimming.

Next, a fifth embodiment of the present invention will be described. A plan view of the heat-generating temperature sensing element in this fifth embodiment is shown in FIG. 9, and a cross-sectional view taken along line E--E in FIG. 9 is shown in FIG.

Reference numerals 1 to 3 in FIGS. 9 and 10 indicate the same or equivalent parts as in the first embodiment shown in FIGS. 1 and 2 above. In this fifth embodiment, a temperature-sensitive resistive film is formed on the flat surface of the substrate 1 by vapor deposition or the like, and this temperature-sensitive resistive film 4 is processed by etching or laser trimming to form a meandering shape. After forming temperature resistance pattern 2,
Both sides of the substrate 1 are coated with a good heat conductive film 4 that can be etched, and uneven parts 4a and 4b are formed on the good heat conductive film 4.

In this manner, by increasing the heat transfer area, the amount of convective heat transfer from the heat-generating temperature sensing element to the fluid increases, and the output sensitivity and responsiveness of the sensor are improved. In this embodiment, the substrate 1 need not be a silicon single crystal substrate, but may be an insulating substrate made of alumina, polyimide, etc., or an insulating substrate that cannot be etched.

[0029]

As described above, according to the present invention, a part or all of the parts on both sides of the heat-generating temperature-sensitive element that come in contact with the fluid have an uneven structure, so that the heat transfer area becomes large and the heat-generating element The amount of convective heat transfer from to the fluid increases. As a result, the output sensitivity of the sensor is improved and the responsiveness is also improved.

[Brief explanation of drawings]

FIG. 1 is a plan view of a heat-generating temperature sensing element in a thermal flow sensor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line AA in FIG. 1;

FIG. 3 is a plan view of a heat-generating temperature sensing element in a thermal flow sensor according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view taken along line BB in FIG. 3;

FIG. 5 is a plan view of a heat-generating heat-sensitive resistance element in a thermal flow sensor according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view taken along line CC in FIG. 5;

FIG. 7 is a plan view of a heat-generating heat-sensitive resistance element in a thermal flow sensor according to a fourth embodiment of the present invention.

8 is a cross-sectional view taken along line DD in FIG. 7. FIG.

FIG. 9 is a plan view of a heat-generating heat-sensitive resistance element in a thermal flow sensor according to a fifth embodiment of the present invention.

10 is a cross-sectional view taken along line E-E in FIG. 9; FIG.

FIG. 11 is a plan view of a heat-generating heat-sensitive resistance element in a conventional thermal flow sensor.

12 is a cross-sectional view taken along line FF in FIG. 11. FIG.

FIG. 13 is a circuit diagram showing a bridge circuit used in a constant temperature measurement method in a conventional thermal flow sensor.

[Explanation of symbols]

1 Board 1a Uneven structure on the surface side of substrate 1 1b Uneven structure on the back side of substrate 1 2 Temperature-sensitive resistance pattern 3 Electrode extraction part 4. Good thermal conductive film 4a, 4b Uneven parts of good thermal conductive film 5 Pattern groove 6 Insulating layer

Claims (1)

[Claims] 1. A temperature-dependent resistor formed in a meandering shape on a substrate so as to be in contact with a flowing fluid, and an uneven portion formed on at least a portion of a portion of the temperature-dependent resistor that is in contact with the fluid. A thermal flow sensor equipped with