JPH0774751B2 - Thermal air flow meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type air flow meter,
Particularly, the present invention relates to a thermal air flow meter suitable for detecting the intake air amount of an internal combustion engine.

[0002]

2. Description of the Related Art As a conventional thermal air flow meter, for example, there is a thermal air flow meter described in JP-A-53-81159.

[0003]

Since the thermal type air flow meter used for the internal combustion engine is installed in the engine room,
Exposed to high temperatures. Therefore, the internal pressure in the case in which the drive circuit unit is sealed increases due to the temperature rise.

However, the above-mentioned prior art has not sufficiently considered the point of preventing the temperature rise in the case where the drive circuit section is hermetically sealed.

An object of the present invention is to provide a thermal type air flow meter having excellent heat resistance.

The above object is to provide a heating resistor for detecting the air flow rate, a drive circuit section for controlling heat generation of the heating resistor and outputting a signal corresponding to the air flow rate, and a case where the drive circuit section is sealed. And a connector section for electrically connecting the drive circuit section and the outside, in a thermal air flow meter, one end of which is opened in the case and the other end of which is the connector.
This is achieved by providing a ventilation means that is open to the inside of the part and that vents the inside of the case and the inside of the connector part.

Since the inside of the case where the drive circuit is hermetically sealed and the inside of the connector section for electrically connecting the drive circuit section and the outside are connected by the ventilation means, even if the temperature around the air flow meter rises. It is possible to prevent the pressure inside the case from rising. Also, open the other end of the ventilation means inside the connector.
As a result, water drops can be prevented from entering the case.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to illustrated embodiments.

FIG. 1 is a schematic view of a heating resistor, which is a hot wire 1 of the heating resistor for sensing the amount of intake air.
And cold wire 2 of a resistor for sensing intake air temperature
In each case, a platinum wire 102 is wound on an alumina bobbin 101 having a diameter of 0.5φ and a length of about 2 mm, both ends of which are welded to lead wires 103, and the surface is coated with a glass material 104. It is a small one.
As shown in FIG. 2, the hot wire 1 and the cold wire 2 having such a structure have a main passage 105 through which most of the intake air passes and a bypass passage 1 through which a part of the intake air is divided.
06 is installed in the bypass passage 106 of the body 107.

By the way, the body 107 shown in FIG. 2 has a main passage 105 for air, a bypass passage 106, and a mounting portion 108 for the module 47 constituting the drive circuit portion, and is made of aluminum die casting.

FIG. 3 is an exploded perspective view showing the entire structure of the present invention, FIG. 4 is a cross-sectional view of a main portion of the module 47, FIG. 5 is a bottom portion thereof, and FIGS. 6 and 7 are I-I and II of FIG. It is a figure which shows a II cross section.

In these figures, the case 48 of the module 47 is formed of a thermoplastic resin having excellent heat resistance such as glass fiber reinforced unsaturated polyester resin.

A preferred embodiment of the present invention will be described below.

The metal pins 49 to 52 and the respective pins 4
The metal terminals 53 to 56 welded to 9 to 52, the power supply terminal 44, the output terminal 45, the ground terminal 46, the pipe 57, and the metal collar 58 are the case 4 described above.
8 is integrally molded. Case 48 is 0.8-1 mm
It has a box-like shape with a thin bottom surface 95, and has a circumferential groove 96 on the outer peripheral wall thereof, and a connector 97 is also integrally formed. Pins 49-52 and terminals 53-5
6 is a hot wire 1 arranged in the bypass passage 106
In addition to holding the cold wire 2, the hot wire 1 and the cold wire 2 are electrically connected to the hybrid IC forming the drive circuit portion of the module 47. In addition, the pipe 57 is a closed case 48.
The inside and the inside of the connector are vented to prevent the case internal pressure from increasing due to the temperature increase in the case 48.
After molding the case 48, the lead wires 103 of the hot wire 1 and the cold wire 2 are welded to the pins 49 to 52, respectively. Pins 49 to 5 on the bottom surface of the case 48
2 is located at the apex of the rectangle. Further, the base 89 made of a metal plate has a hole 92 for receiving the terminals 53 to 56 integrally formed with the case 48.
Here, the terminals 53 to 56 are the terminals 53 to 56.
Drive circuit 6 of the connection portion with the drive circuit 63 and the connection portion of the pins 49 to 52 with the hot wire 1 and the cold wire 2.
3 has a bent portion such that the projected position on the circuit formation surface is displaced.

By adopting such a structure, the following effects can be achieved. Since the terminals 53 to 56 are plate-shaped, they can be easily electrically connected to the drive circuit. In addition, the terminal is connected to the drive circuit of the terminal and the hot wire 1 and cold wire 2 of the pin.
The drive circuit 63 has a bent portion such that the position of the connection portion of the drive circuit 63 projected onto the circuit formation surface of the drive circuit 63 is displaced and the hole 92 for inserting the terminals 53 to 56 is provided in the metal base 89. The entire thermal type flow meter can be made compact without restriction of the circuit configuration and installation position of the hot wire 1 and the cold wire 2.

Further, the pins 49 to 52 for electrically connecting the hot wire 1 and the drive circuit 63 and the terminal 53.
Since ~ 56 is molded with a synthetic resin and the terminal is plate-shaped, even if the vibration of the vehicle is transmitted, contact failure does not occur between the pin and the terminal, and high vibration resistance can be secured. Further, the bent portions 59 provided in the terminals 53 to 56 and the holes 60 provided in the case 48.
.About.62, the insert fittings such as the terminal 53 are accurately held in the mold when the case 48 is molded.

The hybrid IC 63 includes a resistor such as a resistor 11 and a conductor pattern 64 to 68 which form a drive circuit.
A semiconductor element such as an operational amplifier chip 70 and chip capacitors 42 and 43 are formed on a ceramic substrate 69 on which the like is printed.
Pads for connecting capacitors such as the ceramic substrate 69 and external elements and external circuits.
Is soldered.

The insulating plate 88 is thinner than the ceramic substrate 69, and is made by depositing dungsten on a portion 87 of the ceramic substrate 86 having a thickness of about 0.3 to 0.4 mm and then nickel-plating the insulating plate 88. The power transistor chip 7 and the pad 84 are soldered to 88.

A base 89 made of a metal plate has a wall 90 on its outer periphery, a projection 91 on a part of the wall 90, and a case 48 on the bottom.
Has a hole 92 for receiving the terminals 53 to 56 integrally formed with the ceramic substrate 69, a projection 93 for positioning the insulating plate 88, and a stepped portion 94 at one end. The pad 85 is soldered. The base 89 has a ceramic substrate 69 and an insulating plate 88.
Is bonded and fixed in place with a soft adhesive such as silicone rubber.

The above-mentioned base 89 is adhesively fixed to the bottom surface 95 of the case at a predetermined position in the case 48.

Between terminals, that is, the hybrid IC 6
The pads 70, 71 of No. 3 are connected to the terminals 53, 54 formed by connecting the hot wire 1, and the pads 72, 7
Reference numeral 3 denotes terminals 55 and 56 to which cold wires 2 arranged on both sides of the terminals 53 and 54 are connected (terminals 55 and 56 of the cold wire 2 contrary to the embodiment).
May be placed inside) and the pad 74
Is a pad 84 to which the connector of the power transistor 7 is connected, a pad 75 is a base, a pad 76 is an emitter, a pad 77 is a power supply terminal 44, a pad 78 is an output terminal 45, and a pad 79 is a ground terminal 46. Pad 79
The pad 80 connected by a conductor pattern is electrically connected to the pad 85 on the base 89, and the pad 82 is electrically connected to the pads 81 and 83 by a metal wire such as an aluminum wire.

By connecting the pad 80 and the pad 85, the base 89 becomes the ground potential.

Here, the power supply terminal 44, the output terminal 45, the ground terminal 46 and the hybrid I connected to these terminals.
The pads 77, 78, 79 on C63 are arranged such that the ground terminal 46 and the pad 79 connected to it are between the other terminals.

Further, the chip capacitors 42 and 43 for removing the external surge and noise are the pads 77 and 7.
It is arranged in the immediate vicinity of 8, 79 via a short conductor pattern.

The above-mentioned module subassembly is mounted on the module mounting portion 108 of the body 107 with the screw 97 sandwiching the sealing O-ring 96, and the resistors 13, 15, 27 and 30 shown in FIG. Trimming is performed to adjust the output voltage with respect to the air flow rate.

After adjusting the output voltage, a cover 98 made of a metal plate is covered so as to contact the wall 90 of the base 89 so as to cover the hybrid IC 63, the power transistor 7, and the terminals 53 to 56, and the protrusion 91 of the base 89 is used. It is welded.

In order to protect the hybrid IC 63 from moisture and the like through a small hole 99 provided in the cover 98, a soft resin 100 (generally gel-like) such as silicon rubber is placed in the case 48 to a height where the end face of the ventilation pipe 57 is not blocked. filling,
Hardened.

Thereafter, a cap 109 made of the same material as the case 47 is bonded to the case 47 with its rib 110 fitted in the groove 96 of the case 47.

A ground terminal 46 which is the ground of the drive circuit section
Alternatively, the electrical connection between the base 89 and the body 107 of the metal body can be arbitrarily made as needed.

In the thermal type flow meter constructed as above, the hot wire 1 and the cold wire 2 (the cold wire 2 is for detecting the air temperature, which constitutes a part of the drive circuit. (It can be installed in the module if the temperature is almost the same or if high accuracy is not required.) It is necessary to place it in the air passage outside the module, and the structure of this part is very important. Although complicated, it holds a hot wire and a cold wire, and an electric conductor support that electrically connects the hot wire and cold wire to the drive circuit part is integrated into a synthetic resin case that houses the drive circuit. Since it is formed in a simple structure, it has a simple structure, is small and lightweight, and has outstanding productivity.

Further, since the case 48 has a box-shaped structure with a bottom surface 95, the resin 100 filled for keeping the drive circuit unit water-resistant is not leaked and the water resistance is excellent.

Further, the pins 49 to 52, which are the features of the present invention,
Since the terminals 53 and 56 can be relatively freely arranged in the mold of the case 48, the hot wire 4,
There is an effect that the connection terminals 53 to 56 for connecting to the drive circuit unit can be arranged in a form less restricted by the arrangement of the cold wire 2.

[0033]

According to the present invention, since it is possible to prevent the case internal pressure from increasing due to the temperature increase, the air flow meter can be installed in a high temperature environment.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a heating resistor used in the present invention.

FIG. 2 is a view showing a vertical cross section of a main part of a thermal air flow meter according to the present invention.

FIG. 3 is an exploded perspective view of a module.

FIG. 4 is a cross-sectional view of the main part of the module.

5 is a bottom view of the module shown in FIG.

6 is a cross-sectional view taken along the line I-I of FIG.

7 is a sectional view taken along line II-II of FIG.

[Explanation of symbols]

1, 2 ... Heating resistor, 48 ... Case, 63 ... Hybrid IC (driving circuit), 89 ... Metal base.

Claims (1)

[Claims] 1. A heating resistor for detecting an air flow rate, a drive circuit section for controlling heat generation of the heating resistor and outputting a signal corresponding to the air flow rate, and a case in which the drive circuit section is sealed. In a thermal type air flowmeter having the drive circuit section and a connector section for electrically connecting the outside, one end is
Open inside the case and open the other end inside the connector
The thermal air flow meter is provided with a ventilation means for ventilating the inside of the case and the inside of the connector portion.