JPS5931412A - hot wire air flow meter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot wire air flow meter, and more particularly to a hot wire air flow meter for detecting the intake air amount of an internal combustion engine.

This Yuzu hot wire air flow meter is installed in the engine room, so it must satisfy the following performance requirements.

(1) Due to the small installation space in the engine room, it is small and bulky.

(2) The ambient temperature range for single-layer use is about -40-120t:', and the air flow rate must be measured with high accuracy as well as having sufficient reliability in this temperature range.

(3) Vibrations are large, and even when installed on the vehicle body, 10
It must have vibration resistance of approximately 0G, and approximately 30G when installed on the engine body.

(4) Spark ignition engines should not malfunction due to noise such as sparks generated by the ignition system. Also, other institutions must not malfunction due to high frequency noise caused by external radio waves.

(5) It must have sufficient water resistance since it will be exposed to water during operation.

An object of the present invention is to provide a hot wire type air flow meter for an internal combustion engine that satisfies the above-mentioned performance.

The present invention holds a heating resistor (hereinafter referred to as a hot wire) that is installed in an air passage and senses the amount of intake air, and also integrally forms a terminal that electrically connects this to a drive circuit section. A drive circuit consisting of a hybrid IC is housed in a plastic case made of plastic, placed on a metal plate for shielding external radio waves and dissipating heat. The present invention is characterized by providing a hot-wire air flow meter with excellent performance and productivity.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 1 is a diagram schematically showing a heating resistor, and the hot wire 1 of the heating resistor for sensing the amount of intake air and the cold wire 2 of the resistor for sensing the intake air temperature both have a diameter of 0.5φ. , an alumina bobbin 101 with a length of about 2 tubes.
It has a very small structure in which a platinum wire 102 is wound around the wire, both ends of which are welded to a lead wire 103, and the surface is coated with a glass material 104. The hot wire 1 and cold wire 2 having such a structure are connected to a main passage 105 through which most of the intake air passes, as shown in FIG.
and is installed in a bypass passage 106 of a body 107 having a bypass passage 106 through which part of the intake air is divided.

FIG. 3 is a drive circuit diagram of a hot edge type flowmeter, and this drive circuit is a hot wire 1. cold wire 2
．． Operational amplifiers 3 to 6. Power transistor 7, Zener diode 8-10. Resistors 11-38, capacitor 39
~43.

1 to 4.7.11 to 25, 40.41 constitute a hot wire drive section, 6, 10.26 to 33 constitute an output stage amplification section, and 5.8.34 to 37.39 constitute a constant voltage circuit. It makes up the department.

The portion consisting of 9.38 and 42.43 is a circuit for protection against external surges and noise. In addition, the power terminal 44
is the (G) terminal of the battery, the output terminal 45 is the input terminal of a microcomputer that controls the engine based on the output signal of this airflow meter, and the ground terminal 46 is the (G) terminal of the battery and The ground end of the microcomputer mentioned above is connected.

In such a configuration, a current is supplied to the hot wire 1 by the power transistor 7 to heat the hot wire 1 and keep the temperature of the hot wire 1 higher than the intake air temperature by a certain temperature. At this time, only a minute current is allowed to flow through the cold wire 2 so that heat generation can be ignored. Therefore, the cold wire 2 is at the same temperature as the intake air temperature, and the intake air temperature is corrected. When the airflow hits the hot wire 1, the temperature difference between the temperature of the hot wire 1 and the intake air temperature is controlled to be constant by the operation of the hot wire drive unit described above. This control reduces the potential difference between both ends of the hot wire 10 to resistors 12 and 13.
This is realized by applying feedback so that the voltage divided by , and the voltage obtained by amplifying the voltage drop across the resistor 11 caused by the current flowing through the hot wire 1 by the operational amplifier 3 are always equal.

Here, the relationship between the air flow rate Q and the current ■ flowing through the hot wire 1 is expressed by equation (1).

I”RHo(1+CITH) = (c++cav/i
')) @ (T)I 'rc)--(1) However,
R, Ho: Resistance value a of hot wire 1 of OC: Temperature coefficient of resistance To of hot wire 1: Temperature (heating state) of hot wire 1 9゛c:
Temperature of cold wire 2 (i.e. air temperature) c,',c,: constant Therefore, if (T■Tc) is proportional to (1+ffT■), the current ■ flowing through hot wire l depends only on the air flow rate Q do. The circuit shown in Figure 3 is based on this principle,
By measuring the current ■ of the hot wire l (resistance 1
It measures the air flow rate without being affected by the air temperature (as a voltage drop of 1).

By the way, the body 107 shown in FIG. 2 has a main air passage 105. Bypass passage 106. It has a mounting part 108 for a module 47 that constitutes a drive circuit part, and is made of aluminum die-casting.

FIG. 4 is an exploded perspective view showing the overall configuration of the present invention.

5 is a cross-sectional view of the main part of the module 47, FIG. 6 is a bottom view thereof, and FIGS. 7 and 8 are 1-I and I[ of FIG.
It is a figure showing a -II cross section.

In these figures, a case 48 of a module 47 is molded from a thermoplastic resin with excellent heat resistance, such as glass fiber-reinforced unsaturated polyester resin. metal bottle 4
9 to 52, metallic terminals 53 to 56 and power terminals 44 welded to each of the bins 49 to 52. Output terminal 45. Earth terminal 46 and pipe 57. The metallic collar 58 is integrally molded with the case 48 described above.

The case 48 has a box shape with a thin bottom surface 95 of about 0.8 to 1 m+n, has a groove 96 all around its outer circumferential wall, and a connector portion 97 is also integrally formed.

The bins 49 to 52 and the terminals 53 to 56 hold the hot wire 1 and the cold wire 2 disposed in the bypass passage 106, and also hold the hot wire 1 and the cold wire 2 together with a hybrid IC that constitutes the drive circuit section of the module 47. It is an electrical connection.

The pipe 57 ventilates the inside of the sealed case 48 and the connector part, and prevents the inside of the case from rising due to a temperature rise inside the case 48. case 48
After forming, hot wire 1 and cold wire 2
The leads 103 are welded to the bottles 49-52, respectively. The bins 49 to 52 on the bottom surface of the case 48 are arranged at the vertices of a rectangle.

The bent portions 59 provided on the terminals 53 to 56 and the holes 60 to 62 provided in the case 48 are used to accurately hold insert fittings such as the terminal 53 in the mold during molding of the case 48.

The hybrid 1-ICs 6 and 3 have semiconductor elements such as an operational amplifier chip 70 and chip capacitors 42 and 43 mounted on a ceramic substrate 69 on which resistors such as the resistor 11 and conductor patterns 64 to 68, etc., constituting the 1 drive circuit are printed. Pads 70-83 for connecting the capacitor and ceramic substrate 69 to internal and external elements and circuits are soldered.

The insulating plate 88 is thinner than the ceramic substrate 69 and has a thickness of 0.3~
It is made by depositing tungsten on a part 87 of a ceramic substrate 86 with a thickness of 0.4 brightness and then plating it with nickel.
and pad 84 are soldered.

The pace 89 made of a metal plate has a wall 90.1 person 9 on its outer periphery.
0, a hole 92 on the bottom for receiving the terminals 53 to 56 formed integrally with the case 48, a protrusion 93 for positioning the ceramic substrate 69 and the insulating plate 88, and one end thereof. It has a stepped portion 94, and a pad 85 is soldered to the stepped portion 94.

The above-mentioned ceramic substrate 69° insulating plate 88 is adhesively fixed in a predetermined position to this paste 89 with a soft adhesive such as a silicone rubber adhesive.

The polished pace 89 is adhesively fixed to the bottom surface 95 of the case 48 at a predetermined position within the case 48 .

Between each terminal, that is, pad 7 of the hybrid IC 63
0.71 is terminal 5 formed by connecting hot wire 1
3.54, and the pads 72.73 are connected to terminals 55.56 to which the cold wires 2 placed on both sides of the terminals 53.54 are connected (contrary to the embodiment, the pads 72.73 are connected to the terminals 55.56 of the cold wires 2). 56 within 1111
1), and the pad 74 is connected to a pad 84 to which the collector of the power transistor 7 is connected.
, pad 75 is the pace, pad 76 is the emitter,
Pad 77 is the power terminal 44, and pad 78 is the output terminal 4.
5, the pad 79 is connected to the ground 14, the pad 80 is connected to the pad 85 on the paste 89, and the pad 82 is connected to the pad 81 and 83 by wire bonding with a metal wire such as an aluminum wire. and electrically connected.

By connecting pad 80 and pad 85, pace 8
9 becomes about 1L of earth.

Here, the power terminal 44. Output terminal 45. Earth terminal 46
The pads 77, 78, 79 on the hybrid IC 63 connected thereto are located between the ground terminal 46 and the pad 79 connected thereto between the other terminals. It is arranged in E direction.

Chip capacitors 42 and 43 for removing energy and noise are placed in the immediate vicinity of pads 77 and 7879 via a 1-wire conductor pattern.

The two sets of module sub-assemblies are inserted into the body 10 with the sealing 01J ring 96 and screws 97.
The resistors 13, 15, 27, and 30 shown in FIG. 3 are mounted on the module mounting portion 108 of No. 7 and are functionally trimmed to adjust the output voltage for an air flow of -1°.

After adjusting the output voltage, the metal plate cover 98 is connected to 7, hybrid IC 63 and power transistor 71 terminal 53.
The base 89 is covered with the wall 90 of the base 89 so as to be in contact with the wall 90 of the base 89, and is in contact with the protrusion 91 of the base 89.

The hybrid IC 6 is inserted through the small hole 99 provided in the cover 98.
3 from moisture etc., a soft resin 100 (generally gel-like) such as silicone rubber is filled into the case 48 and hardened to a height that does not block the end surface of the ventilation pipe 57.

Thereafter, a cap 109 made of the same material as the case 47 is placed on the case 47 by fitting its lip 110 into the groove 96 of the case 47.

The electrical connection between the ground terminal 46 or the base 89, which is the ground for the drive circuit section, and the metal body 107 can be made as desired.

In the hot wire flow rate configured in this way, the hot wire 1 and the cold wire 2 (the two cold wires that constitute part of the drive circuit detect the air temperature, and the temperature inside the module and the air temperature are almost the same). (It is also possible to install it inside the module under certain conditions or when high precision is not required.) It is necessary to place it in the air passage outside the module, and the structure of this part is very complicated. However, according to the present invention, as explained below, the support for the electric conductor that holds the hot wire and the cold wire and electrically connects the hot wire, the cold wire, and the drive circuit section is attached to the drive circuit. Because it is integrally molded into a synthetic resin case that houses the material, it has a simple structure, small size, and light stitching, resulting in extremely high productivity.

In addition, since the case 48 has a box-shaped structure with a bottom surface 95, the resin 1 filled to maintain the water resistance of the drive circuit section
No leakage and excellent water resistance.

Furthermore, pins 49 to 52. The terminals 53, 56 can be placed relatively freely within the mold of the case 48, and the hot wire 1. There is an advantage that the connection terminals 53 to 56 with the shape drive circuit section can be arranged without being restricted by the arrangement of the cold wires 2.

Further, the current for heating the hot wire 1 varies depending on the air flow rate, but is approximately 100 to 200 mA, and at this time, the power transistor 7 generates about 1.5 parts of heat. If this heat is not efficiently dissipated to the outside of the module 47, problems will occur, such as damage to the power transistor 7 and changes in output characteristics due to the temperature characteristics of the circuit elements constituting the hybrid IC 63 due to an increase in the temperature of the hybrid IC 63.

However, in the present invention, since the power transistor 7 is mounted on the spacer plate 89 of the seven metal plates via the thin insulating plate 88, heat can be radiated to the base 89 having a large area. Furthermore, since the bottom surface 95 of the case 48 is made thin, the heat transmitted to the base 89 can be effectively dissipated to the metal body 107 through a large area, thereby improving heat resistance and temperature characteristics. .

The above-described broken base 89 has the effect of absorbing high frequency noise caused by external radio waves. This high frequency noise absorption effect has two effects; one is the noise that enters through the wire noise (not shown) to which the module 47 is connected; Connect the circuit ground terminal 46 (pad 80) to the base 89 (pad 85) with a short metal wire, i.e., low impedance.
), the noise entering the drive circuit 7 is released to the base 89 having a large area. The second effect is to shield high frequency noise from directly entering the hybrid 1C63. For this, a metal cover 98 and a base 89 are used to create a hybrid I C63.
Although it is effective to surround the
The cover 98 can also be omitted.

On the other hand, in an internal combustion engine, there are cases where the body 107 is attached to the IH internal combustion engine main body and grounded, and cases where the body 107 is attached to an air cleaner and is attached with a floating potential. In the former case, if the ground terminal of the drive circuit is electrically connected to the body 107, there will be two points of grounding, one through the wire harness and the other through the body i07, which will cause problems in terms of noise resistance, etc. Therefore, the ground terminal 46 of the drive circuit and the body 107 must not be electrically connected. In the latter case, ground terminal 4 of the drive circuit
If the ground terminal 46 and the body 107 are not electrically connected, external noise will be applied to the drive circuit via the body 107 which has a floating potential. Therefore, it is necessary to electrically connect the ground terminal 46 and the body 107.

In the present invention, 1. Ground terminal 46, which is the ground for the drive circuit. Pace 89 and body 107 are combined into a thin case 48
The front surface 95 of the module 47 is insulated so as not to interfere with heat dissipation. When the body 107 is attached to the body 107, the ground of the drive circuit and the body 107 can be electrically connected by a simple method such as attaching the body 107 together with the body 107.

As described above, according to the present invention, it is small, lightweight, vibration resistant,
This has the effect of realizing a hot-wire air flow meter with excellent resistance to electromagnetic interference, heat resistance, and productivity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an outline of a heating resistor, FIG. 2 is a diagram showing a longitudinal section of the main part of the hot wire air flowmeter according to the present invention, FIG. 3 is a diagram showing an embodiment of the drive circuit, and FIG. is an exploded perspective view of the module, Figure 5 is a cross-sectional view of the main part of the module, and Figure 6 is a cross-sectional view of the main part of the module.
The figure is a bottom view, Figure 7 is a sectional view taken along line II in Figure 5, and Figure 8
The figure is a sectional view taken along line II-II in FIG. 1.2... Heating resistor, 48... Case, 63...
Hybrid IC (drive circuit), 89...metallic base Figure 6 (/6', l/θ

Claims (1)

[Claims] 1. A heating resistor installed in the air passage to sense the air flow rate, and controlling the current of the heating resistor and outputting the output current of the heating resistor as a signal corresponding to the air flow needle. In a hot-wire air flowmeter having a drive circuit section to be taken out, the drive circuit composed of a no-brid IC is placed on a metal plate electrically connected to the ground of the drive circuit. A hot wire air flowmeter characterized by being housed in a box-shaped case with a bottom made of synthetic resin. 2. A patent characterized in that an electrical conductor support that supports the heating resistor and electrically connects the heating resistor and the drive circuit is integrally molded with a synthetic resin case that houses the drive circuit. A hot wire air flowmeter according to claim 1.