Temperature detecting apparatus and thermal type flow meter using the same

A temperature detecting apparatus includes a support member made of resin and disposed in an air passage, a temperature sensor supported within the support member, and a pair of conductive members made of metal and embedded in the support member. The support member includes a surface in parallel with the intake air flow. The pair of conductive members are electrically connected to the temperature sensor. An extrusion portion is formed on the support member so as to extend along the intake air flow, and accommodates the temperature sensor at an upstream side thereof and the pair of conductive members. The conductive member includes a first extending portion extending within the extrusion portion along the air flow and a second extending portion extending from the first extending portion into the support member.

CROSS REFERENCE TO RELATED APPLICATION 
This application is based on and claims priority from Japanese Patent 
Application No. 7-153488 filed on Jun. 20, 1995, the contents of which are 
incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a temperature detecting apparatus and a 
thermal type flow meter using the same, and specifically to an 
installation structure of a temperature sensor in the thermal type flow 
meter. 
2. Description of the Related Art 
Conventionally, a thermal type flow meter mounted on a vehicle for 
measuring an amount of intake air into an engine, is known in a thermal 
type flow meter having a function portion, into which an electronic 
circuit portion and a sensor portion are integrally incorporated, within a 
flow passage of the thermal flow meter, the influence of eccentricity and 
turbulence of the air flow at an upstream side is reduced by improving the 
installation efficiency in the engine, accompanied by the downsized body. 
For decreasing the weight, the functional portion is disposed in a 
resin-formed case member. Further an intake air temperature sensor for 
sensing the temperature of the intake air passing through the fluid 
passage is integrally formed with the case member, thereby improving 
assembling performance of the intake air temperature sensor. 
However, according to such thermal type flow meter, since the intake air 
temperature sensor for sensing the temperature of the suction air passing 
through the fluid passage is provided at a position close to an electronic 
circuit accommodated in the case member, the intake air temperature sensor 
is heated by the heat generated by the electronic circuit, causing an 
error in an indicated value of the intake air temperature sensor. For this 
reason, a method of providing the intake air temperature sensor at a 
position away from an electronic circuit has been proposed. 
However, according to the method of providing the intake air temperature 
sensor away from the electronic circuit, since the casing member 
accommodating the functional parts is integrally formed with the intake 
air temperature sensor accommodating the temperature sensor element, it 
may be difficult to release the casing member with the intake air 
temperature sensor from the die unit depending on the position of the 
intake air temperature sensor when the casing member is molded. As a 
result, the die unit for forming the case member is complicated, the 
number of separate dies is increased, and the cost of manufacturing the 
thermal flow meter is increased. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a 
temperature detecting apparatus capable of reducing an error in an 
indicated value and also reducing the manufacturing cost by improving the 
installation efficiency and a thermal type flow meter using the same. 
According to the present invention, a temperature detecting apparatus 
includes a support member made of resin and disposed in an air passage, a 
temperature sensor supported within the support member, and a pair of 
conductive members made of metal and embedded in the support member. The 
support member includes a surface in parallel with the intake air flow. 
The pair of conductive members are electrically connected to the 
temperature sensor. An extrusion portion is formed on the support member 
so as to extend along the intake air flow, and accommodates the 
temperature sensor at an upstream side thereof and the pair of conductive 
members. The conductive member includes a first extending portion 
extending within the extrusion portion along the air flow and a second 
extending portion extending from the first extending portion into the 
support member. 
According to this structure, since the temperature sensor is disposed in 
the extrusion portion at the upstream side and the intake air is 
introduced from the side of the temperature sensor, the heat conducted 
through the support member is suppressed from being transmitted to the 
temperature sensor, thereby reducing the error in the indicated value of 
the temperature sensor caused by the heat conducted through the support 
body., 
When the temperature sensor is exposed in the air passage and disposed at 
the upstream side of a heating source such as an electronic circuit, the 
heat capacity of the temperature sensor element can be reduced and the 
heat conducted from the heating source to the temperature sensor can be 
transmitted to the air, thereby reducing the error in the indicated value 
of the temperature sensor due to the heat conducted from the heating body 
to the temperature sensor. In addition, since a simple structure in which 
the temperature sensor element is disposed at the upstream side of the 
heating source is employed, the structure of the die units can be 
simplified, even if the temperature sensor is integrally molded with the 
support member, for example. Accordingly, an increase in the number of the 
separate dies and the difficulty in releasing the support member can be 
prevented, and the manufacturing cost can be reduced. 
When an air clearance is formed between the temperature sensor and the 
heating source, the heat conducted from the heating source is prevented 
from being transmitted to the temperature sensor element. That is, since 
the heat conducted from the heating source is not easily transmitted to 
the temperature sensor element of the temperature sensor, the air 
clearance has the effect of reducing the error in the indicated value of 
the temperature sensor due to the heat conducted from the heating source 
to the temperature sensor element. Further, since the heat insulation 
structure which fixes the temperature sensor to the support member 
includes an air clearance between the temperature sensor and the heating 
source, the simple structure can be obtained even if the heat insulation 
structure is integrally formed with the support member, for example. For 
this reason, an increase in the number of separate dies and the difficulty 
in releasing the support member with the temperature sensor can be 
prevented, and the manufacturing cost can be reduced. 
When the air clearance is formed between the support member and the 
temperature sensor, heat conduction between the heating body and the 
temperature sensor is prevented. This clearance can reduce the contact 
area between the heating source and the support member. In this way, the 
heat is prevented from being conducted from the heating source to the 
temperature sensor fixed to the support member, because the clearance 
interrupts the conducting of the heat generated by the heating source to 
the support member. Consequently, the error in the indicated value of the 
temperature sensor due to the heat conducted by the heating body is 
reduced. In addition, since the heat insulation structure is formed by the 
air clearance between the support member for supporting the heating source 
and the heating body, the clearance can be easily formed by forming a 
plurality of protrusions between the support member and the heating 
source, for example. Accordingly, since the die units can be simplified in 
structure, even if plural protrusions are integrally formed with the 
support member, an increase in the number of the separate dies for forming 
the clearance and the difficulty in releasing the support member can be 
prevented, and the manufacturing cost can be reduced. 
Further, when the above temperature detecting apparatus is applied to a 
thermal type flow meter, the intake air temperature sensor fixed in the 
thermal type flow meter reduces the error in the indicated value due to 
the heat generated by the heating source. For this reason, the intake air 
temperature sensor can accurately sense the temperature of the fluid 
passing through the main passage, and an electric control unit or the 
like, for example, can accurately control the ignition timing control of 
an engine or the like based on the detected data obtained from the output 
of the intake air temperature sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the accompanying drawings, various embodiments of the present 
invention are described below. 
A first embodiment of the present invention is described. 
In the first embodiment, a thermal type flow meter measures an amount of 
intake air into an engine and is provided in a duct having an intake air 
passage formed at the downstream side of an air cleaner element. As shown 
in FIGS. 1 and 2, a sensor unit 10, which constitutes a main part of the 
thermal type flow meter, is installed on a duct 1. 
Duct 1 includes a first cylindrical body 3 having a main passage 2 as a 
fluid passage and a second cylindrical body 5 having a hole 4 for 
inserting sensor unit 1. These first cylindrical body 3 and second 
cylindrical body 5 are integrally molded with resin. 
Sensor unit 10 is fixedly assembled in second cylindrical body 5. Sensor 
unit 10 constitutes a major part of the thermal type flow meter and 
includes a central member 11 located at the center of main passage 2 in an 
assembled state, a flow detecting portion 8 to measure air flow rate, a 
rib 12 supporting central member 11 in main passage 2, a circuit casing 25 
made of metal fixed to rib 12 and accommodating an electronic circuit 13 
(which is later described), an electronic circuit 13 fixed to rib 12 and 
controlling and processing signals from the flow detecting portion 8, an 
installation portion 14 to secure sensor unit 10 on duct 1, an intake air 
temperature sensor 30 fixed to rib 12 and sensing the temperature of the 
intake air passing through main passage 2, and a mechanical connector 
portion 15 to electrically connect electronic circuit 13 with intake air 
temperature sensor 30. 
Central member 11 is formed in a shell shape, in which its outside diameter 
gradually increases toward the downstream direction. Central member 11 is 
provided at the central part in first cylindrical body 3 in such a manner 
that the cross-section of main passage 2 formed around the periphery of 
central member 11 is reduced. A bypass passage 16 formed in central member 
11 includes a large diameter passage 16a at an upstream side, a small 
diameter passage 16b at a downstream side, and a step portion 17 between 
large diameter passage 16a and small diameter passage 16b. Area of the 
downstream bypass passage formed by small diameter passage 16b is smaller 
than that of the upstream bypass passage formed by large diameter passage 
16a at the upstream side of step portion 17. Bypass passage 16 turns 
around at the downstream side of flow detecting section 8, and a bypass 
passage 16c having a C-shaped cross section, which turns around and 
returns to the upstream side, forms a bypass outlet portion 18 around the 
outer periphery of central member 11 at the upstream side of flow 
detecting portion 8. Bypass passage 16 is connected to main passage 1 at 
bypass outlet portion 18. Bypass outlet portion 18 opens, as shown in FIG. 
2, over nearly the entire periphery of bypass passage 16c excluding the 
portion where rib 12 is formed. 
Flow detecting portion 8 includes a flow measuring resistor 21 and a 
temperature compensating resistor 22, and these resistors 21 and 22 are 
disposed in small passage 16b and supported by support members 35 and 36 
perpendicularly with respect to the flow direction of small diameter 
passage 16b. 
Rib 12 as a supporting member supports central member 11 such that central 
member 11 is disposed approximately at the center of main passage 2. Rib 
12 is inserted in hole 4 of second cylindrical body 5 in an opening 
direction thereof. 
Installation portion 14 secures central member 11, rib 12, electronic 
circuit casing 25 and connecter portion 15 to duct 1, and is secured to a 
flange 26 of second cylindrical body 5 of duct 1. It means that, by simply 
securing installation portion 14 of sensor unit 10 to second cylindrical 
body 5, central member 11 supported on installation portion 14 by rib 12 
can be disposed approximately at the center of main passage 2. That is, by 
inserting and assembling sensor unit 10 in the opening of second 
cylindrical body 5 formed on duct 1, flow detecting portion 8 of the 
thermal type flow meter can be assembled and disposed. 
Electronic circuit 13 as a heating body includes a control electronic 
circuit (not shown) electrically connected to flow measuring resistor 21 
and temperature compensating resistor 22, and the control electronic 
circuit is accommodated in electronic circuit case 25. In addition, as 
shown in FIGS. 2 and 3, electronic circuit case 25 is secured to a concave 
portion 12b formed in rib 12 by adhesive or the like, and its periphery is 
covered with a cover 27. Accordingly, an installation surface 25a of 
electronic circuit case 25 closely contacts with concave portion 12b. 
The control circuit includes a plurality of active electronic parts such as 
semiconductor (not shown) and a plurality of passive electronic parts of 
resistance, capacitor, or the like (not shown), which are driven by the 
power source voltage supplied from a connector (which will be described 
later). Therefore, when the control circuit is operated, electronic 
circuit 13 generates heat according to the structure of the control 
circuit by the conversion from electrical energy generated from each of 
the electronic parts to thermal energy. A considerable amount of the heat 
is released from electronic circuit case 25 toward the outside. 
Accordingly, the heat released from electronic circuit casing 25 is 
conducted to rib 12, cover 27 or the like and transmitted to the intake 
air passing through main passage 2. 
On the side surface at the back side of electronic circuit case 25 of rib 
12 is provided an intake air temperature sensor 30 integrally formed with 
rib 12. Intake air temperature sensor 30 is placed so as to be exposed to 
the air in main passage 2 when installed. Intake air temperature sensor 30 
includes a temperature sensor element 31 therein, and further, as shown in 
FIG. 3, lead wires 31a and 31b of temperature sensor element 31 are 
electrically connected to band terminals 28a and 28b formed inserting to 
rib 12. 
Connector portion 15 secures terminals (not shown), which are electrically 
connected to electronic circuit 13, and terminals 28a and 28b, which are 
electrically connected to a temperature sensor element 31. Connector 
portion 15 is integrally molded with installation portion 14 with resin. 
Next, an installation structure of intake air temperature sensor 30 is 
described in detail with reference to FIGS. 2 and 3. 
As shown in FIG. 2, intake air temperature sensor 30 as a temperature 
sensing portion is disposed in main passage 2 so that intake air 
temperature sensor 30 is exposed to the air passing through main passage 
2. Intake air temperature sensor 30 senses the temperature of the air flow 
in main passage 2 accurately and transmits the heat released from 
electronic circuit case 25 located at the back side of intake air 
temperature sensor 30 to the intake air. For those purposes, as shown in 
FIG. 3, temperature sensor element 31 of intake air temperature sensor 30 
is exposed in main passage 2 so as to face toward the upstream side of the 
intake air without its periphery being covered with sensor housing 30a 
integrally formed with rib 12. Accordingly, by exposing temperature sensor 
element 31 in main passage 2 in this way, temperature sensor element 31 
can be easily cooled by the intake air flowing in main passage 2. 
As can be understood from FIG. 3, since temperature sensor element 31 is 
located at the intake air upstream side of electronic circuit casing 25 of 
electronic circuit 13, the intake air heated by the heat generated from 
electronic circuit 13 is hardly transmitted to temperature sensor element 
31. Therefore, although the heat generated from electronic circuit 13 is 
conducted to temperature sensor element 31 from lead wires 31a and 31b of 
temperature sensor 30 via electronic circuit casing 25, rib 12 and sensor 
housing 30a, since the intake air is introduced from the tip end portion 
of the temperature sensor element, the temperature sensor can be radiated 
more by means of the intake air. That is, as the heat conducted from one 
side of lead wires 31a and 31b of temperature sensor element 31 is 
transmitted to the intake air which flows towards the other side of lead 
wires 31a and 31b of temperature sensor element 31, the heat conducted 
from lead wires 31a and 31b of temperature sensor element 31 can be 
released in the intake air. According to such a heat radiation structure, 
by installing intake air temperature sensor 30 to rib 12, the increase in 
the temperature of temperature sensor element 31 due to the heat generated 
by the control circuit can be suppressed, the error in the indicated value 
of the temperature sensor element is reduced, and the intake air 
temperature can be measured with high accuracy. 
Further, since intake air temperature sensor 30 is formed in a convex shape 
toward the outside from sidewall 12a at a back side of concave portion 12b 
of rib 12, even when rib 12 and intake air temperature sensor 30 are 
integrally molded, a complicated die unit for forming is not needed. 
Accordingly, it is easy to release the rib 12 when forming the rib 12, and 
the manufacturing cost can be reduced since the number of separate dies is 
reduced. 
Next, an operation of the first embodiment according to the present 
invention is now be described. 
In FIG. 1, the air introduced through an air cleaner (not shown), which is 
assembled at the upstream side of duct 1, is introduced into main passage 
2 and flows from left to right in main passage 2 in FIG. 1. In this case, 
since the area of the main passage is throttled by central member 11, flow 
rate of the air flowing in main passage 2 increases, a negative pressure 
is generated at bypass outlet portion 18, and according to the 
differential pressure between the negative pressure and the pressure at 
bypass inlet portion 32 of bypass passage 16, the air flow is generated in 
bypass passage 16. Flow measuring resistor 21 disposed in bypass passage 
16 is heated by electronic circuit 13 to certain differential temperature 
relative to intake air temperature and measures the air flow in bypass 
passage 16. In this way, the flow rate of the intake air can be detected. 
Further, the intake air introduced into main passage 2 reaches temperature 
sensor element 31 in the direction of the tip end portion of temperature 
sensor element 31 before the intake air is heated by the heat generated 
from electronic circuit case 25 of electronic circuit 13. Therefore, the 
heat generated from electronic circuit 13 is radiated, and the intake air 
temperature in main passage 2 can be sensed and measured with high 
accuracy. 
Since bypass inlet portion 32 for forming bypass passage 16 is positioned 
approximately at the center of main passage 2, turbulence of air flowing 
through bypass passage 16 is smaller than with turbulence of the air flow 
from the upstream side. Since step portion 17 is formed at the upstream 
side of flow detecting portion 8 in bypass passage 16, air flow from the 
upstream side is smoothed by being throttled at step portion 17. In 
addition, since bypass outlet portion 18 opens approximately in a C-shape 
over nearly the entire periphery of bypass passage 16 except for rib 12 
against an eccentric air flow from the upstream side, and further, the 
outer diameter of central member 11 gradually spreads out toward the 
downstream side so as to have a function for recovering the eccentric air 
flow, the flow rate in bypass passage 16 is leveled off and is hardly 
influenced by the eccentric air flow from the upstream side. 
A second embodiment according to the present invention will now be 
described with reference to FIG. 4. In FIG. 4, parts or components 
substantially identical to those as in the first embodiment are shown with 
the same reference numerals. 
According to the second embodiment as shown in FIG. 4, temperature sensor 
element 31 includes an intake air temperature sensor 40 covered with a 
sensor housing 40a, and a slit 43 is formed between a sensor housing head 
40b for covering the periphery of temperature sensor element 31 and rib 
12. 
Intake air temperature sensor 40 is provided at a downstream side of the 
intake air as compared with the intake air temperature sensor 30 of the 
first embodiment. As shown in FIG. 4, intake air temperature sensor 40 is 
positioned approximately at the center of the back side of electronic 
circuit 13. In addition, since a periphery of temperature sensor element 
31 of intake air temperature sensor 40 is covered with sensor housing head 
40b, temperature sensor element 31 is not exposed in main passage 2 unlike 
temperature sensor element 31 of the first embodiment. 
However, since slit 43 is formed between a side wall 12a of rib 12, which 
is integrally molded with sensor housing 40a, and sensor housing head 40b, 
the heat generated from electronic circuit 13 is hardly conducted directly 
to sensor housing head 40b via rib 12. In this way, the heat generated 
from the control circuit of electronic circuit 13 (not shown) is conducted 
to temperature sensor element through electronic circuit casing 25, rib 
12, sensor housing 40a, sensor housing head 40b and lead wire 31a. 
Further, since slit 43 is formed between sidewall 12a of rib 12 and sensor 
housing head 40b, the surface area of sensor housing head 40b for covering 
the periphery of temperature sensor element 31 can be increased. According 
to such a head insulating structure, by installing intake air temperature 
sensor 40 in rib 12, the surface area of sensor housing head 40b imposed 
in main passage 2 is increased, and therefore, the increase in temperature 
of temperature sensor element due to the generation of heat is suppressed, 
thereby obtaining an effect of measuring the temperature of the intake air 
precisely in the same manner as the first embodiment. 
Further, since intake air temperature sensor 40 is formed in a convex shape 
toward the outer direction from sidewall 12a at a back side of concave 
portion 12b of rib 12, even when rib 12 and intake air temperature sensor 
30 are integrally molded, a complicated die unit for forming is not 
needed. Accordingly, it is easy to release the rib 12 when forming the rib 
12, and the manufacturing cost can be reduced since the number of separate 
dies is reduced. 
Still further, since the periphery of temperature sensor element 31 is 
covered with sensor housing head 40b, temperature sensor element 31 is 
hardly exposed to the intake air flowing into main passage 2. Accordingly, 
although any extraneous materials or the like are mixed into the intake 
air, temperature sensor element 31 is hardly damaged by such extraneous 
materials, thereby protecting temperature sensor element 31 from the 
extraneous material or the like. 
A third embodiment according to the present invention is described with 
reference to FIG. 5. In FIG. 4, parts or components substantially 
identical to those as in the first embodiment are shown with the same 
reference numerals. 
According to the third embodiment as shown in FIG. 5, a clearance 53 is 
formed between rib 12 and electronic circuit casing 25 by providing a 
protrusion portion between rib 12 and electronic circuit casing 25 of 
electronic circuit 13. 
Concave portion 12b is formed in rib 12 for receiving electronic circuit 
casing 25 of electronic circuit 13. In the first and second embodiments, 
installation surface 25a of electronic circuit casing 25 closely contacts 
with the bottom portion of the concave portion 12b by adhesives or the 
like, however, in the third embodiment, installation surface 25a of 
electronic circuit casing 25 is prevented from being adhered to the bottom 
portion of concave portion 12b by providing protrusion portions 51 on 
concave portion 12b so that clearance 53 is formed between electronic 
circuit casing 25 and the bottom of rib 12. 
Plural protrusion portions 51 are formed on the bottom of concave portion 
12b in such a manner that each protrusion portion is placed at an interval 
slightly narrower than the width of installation surface 25a of electronic 
circuit casing 25, for example. By placing the plural protrusion portions 
51 at the interval narrower than the width of installation surface 25a of 
electronic circuit casing 25, installation surface 25a of electronic 
circuit casing 25 is prevented from being adhered to the bottom portion of 
concave portion 12b, and the contacting area of electronic circuit casing 
25 and rib 12 is reduced when fixing electronic circuit casing 25 in 
reversed concave portion 12b via the plural protrusion portions 51. 
Further, as clearance 53 is formed between electronic circuit casing 25 
and rib 12, the heat generated from the control circuit in electronic 
circuit casing 25 is prevented by clearance 53 from being conducted 
directly to rib 12. The heat is allowed to be conducted to rib 12 via 
plural protrusion portions 51. Accordingly, the heat transmission to rib 
12 by the generation of heat at the control circuit is reduced, thereby 
suppressing the heat conduction to an intake air sensor 50 located at the 
back side of electronic circuit casing 25 via rib 12. 
In intake air sensor 50, a sensor housing 50a is integrally formed with rib 
12 so as to cover temperature sensor element 31 and lead wires 31a and 
31b. While rib 12 is adhered to temperature sensor element 31 via resin 
material, the heat generated by the control circuit is suppressed from 
being conducted to intake air temperature sensor 50 since clearance 53 is 
formed between electronic circuit casing 25 of the heating electronic 
circuit 13 and rib 12. By employing such a structure, the increase in 
temperature of temperature sensor element 31 due to the heat generated by 
the control circuit is suppressed, thereby allowing the intake air 
temperature to be measured accurately. 
Further, since intake air temperature sensor 50 is formed in a convex shape 
toward the outer direction from sidewall 12a at a back side of concave 
portion 12b of rib 12, even when rib 12 and intake air temperature sensor 
30 are integrally molded, a complicated die unit for forming is not 
needed, and the plural protrusion portions 51 on rib 12 can be formed in a 
convex shape without using a complicated die unit. Accordingly, in the 
same manner as the first embodiment, it is easy to release the rib 12 when 
forming the rib 12, and the manufacturing cost can be reduced since the 
number of separate dies is reduced. 
According to the third embodiment, in which protrusion portions 51 are 
provided at rib 12 and clearance 53 is formed, a plate-like heat 
insulating material or the like, for example, may be inserted between 
electronic circuit case 25 and rib 12 instead of protrusion portions 51. 
In this way, the same effect as clearance 53 can be obtained by the heat 
insulating material. 
It should be noted that the thermal type flow meter according to the 
present invention is not limited to flow meters for measuring the intake 
air flow in an engine, but also can be applied to other fluid measuring 
devices. 
Although the present invention has been fully described in connection with 
the preferred embodiments thereof with reference to the accompanying 
drawings, it is to be noted that various changes and modifications will 
become apparent to those skilled in the art. Such changes and 
modifications are to be understood as being included within the scope of 
the present invention as defined in the appended claims.