JPS6236521A - Direct-heating type flow-rate sensor - 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 [Field of Industrial Application] The present invention relates to a directly heated flow rate sensor having a membrane resistor, for example, an air flow rate sensor for detecting the intake air amount of an internal combustion engine.

[Conventional technology]

Generally, in an electronically controlled internal combustion engine, the intake air amount of the engine is one of the important operating state parameters for controlling basic fuel injection amount, basic ignition timing, etc. Conventionally, vane-type air flow sensors (also called air flow meters) for detecting the amount of intake air have been mainstream, but recently temperature-dependent resistance sensors, which have the advantages of small size and good response, have been introduced. A thermal type using

Furthermore, there are two types of air flow rate sensors having temperature-dependent resistance: indirect heating type and direct heating type. For example, an indirectly heated air flow sensor includes a heat generating resistor provided in an intake passage of an engine, and two temperature dependent resistors provided upstream and downstream thereof. In this case, the temperature-dependent resistance on the upstream side detects the temperature of the air flow before being heated by the heating resistor, that is, it is for outdoor temperature compensation, and the temperature-dependent resistance on the downstream side is used to detect the temperature of the air flow before being heated by the heating resistor. Detects the temperature of the airflow. As a result, the current value of the heating resistor is feedback-controlled so that the temperature difference between the temperature-dependent resistance on the downstream side and the temperature-dependent resistance on the upstream side is constant, and the air flow rate (mass) is controlled by the voltage applied to the heating resistor. It is something to detect.

In addition, the temperature-dependent resistance for outdoor temperature compensation on the upstream side was deleted,
- If the heating resistor in the downstream example is controlled so that the temperature of the temperature-dependent resistor is constant, the air flow rate as a volumetric capacity can be detected (Reference: Japanese Patent Publication No. 54-9662 Hiro! 8). On the other hand,
A directly heated air flow sensor, which has a faster response speed than an indirectly heated type, includes a heat generating resistor that is provided in the intake passage of the engine and also serves as temperature detection, and a temperature dependent resistor that is provided upstream of the heat generating resistor. In this case, similarly to the indirect heating type, the upstream temperature-dependent resistance detects the temperature of the air flow before being heated by the heating resistor, that is, it is used to compensate for the outside air temperature. With this, the current value of the heating resistor is feedback-controlled so that the temperature difference between the heating resistor and the temperature-dependent resistance upstream thereof is constant, and the air flow rate (mass) is detected by the voltage applied to the heating resistor. It is. In this case as well, if the temperature-dependent resistance for compensating the outside air temperature is deleted and the heating resistor is controlled so that the temperature of the heating resistor is constant, the air flow rate as a volumetric capacity can be detected.

Normally, the responsiveness and dynamic range of an air flow sensor that keeps the difference between the heat generation temperature of the heat generation resistor (belly type resistor) and the intake air temperature constant, or the temperature of the heat generation temperature of the belly type resistor, includes the membrane resistance. It is determined by the heat capacity (heat mass) of the total heat section and temperature detection section and the degree of insulation effect. In other words, in order to achieve the best response and the largest dynamic range, the mass of the entire heat section and temperature detection section, including the abdominal resistor, should be made as small as possible, and ideally that part should be completely removed. The idea is to make it float in the airflow. For this reason, the board on which the abdominal resistor is formed is usually supported on a holding member with excellent heat dissipation properties via a heat insulating member, and at this time, between the board and the heat insulating member and between the heat insulating member and the holding member. They are also bonded using a bonding agent that has a heat insulating effect. For example, a resin adhesive, flint glass with low thermal conductivity, or the like is used as a bonding agent that has a heat insulating effect.

This further enhances the heat insulation effect of the board.

[Problem that the invention seeks to solve]

However, in the conventional type described above, since the bonding agent has a heat insulating effect, the heat insulating effect varies due to manufacturing variations in its thickness, condition, etc., and this effect changes characteristics such as sensor response and dynamic range. There is a problem.

[Means for solving problems]

An object of the present invention is to provide a direct heating type flow sensor in which the output characteristics of the sensor do not change due to manufacturing variations in the joining members. be.

[For production]

According to the above-mentioned means, since the bonding member does not have a heat insulating effect, the heat insulating effect is determined only by the heat insulating member, and therefore, the heat insulating effect on the substrate becomes uniform.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is an overall schematic diagram showing an internal combustion engine to which a directly heated air flow sensor having an abdominal resistance according to the present invention is applied.

In FIG. 2, air is taken into an intake passage 2 of an internal combustion engine 1 via an air cleaner 3 and a rectifying grid 4. As shown in FIG. A holding member (for example, aluminum) 5 is provided in this air passage 2.
A temperature dependent resistor (abdominal resistor) 6 which also serves as a heat generating heater is provided therein for measuring the air flow rate.

The abdominal type resistor 6 is connected by a flexible wiring 7 to a sensor circuit 9 formed on a hybrid board, together with a temperature-dependent resistor 8 that compensates for the outside temperature.

The sensor circuit 9 feedback-controls the amount of heat generated by the resistor 6 so that the temperature of the abdominal resistor 6 is constant with respect to the outside air temperature, and supplies the sensor output V0 to the control circuit 10. The control circuit 10 is composed of, for example, a microcomputer, and controls the fuel injection valve 11 and the like.

As shown in FIG. 3, the sensor circuit 9 includes an abdominal resistor 6, a temperature-dependent resistor 8, and resistors 91 and 9 forming a bridge circuit.
2, composed of a comparator 93, a transistor 94 controlled by the output of the comparator 93, and a voltage buffer 95, that is, the air flow rate increases and the membrane resistor 6 (in this case,
When the temperature of the thermistor (thermistor) decreases, and as a result, the resistance value of the film resistor 6 decreases to 1≦V, l, the conductivity of the transistor 94 increases due to the output of the comparator 93. Therefore, the amount of heat generated by the film resistor 6 increases, and at the same time, the collector potential of the transistor 94, that is, the output voltage of the voltage buffer 95 increases. will rise. Conversely, when the air flow rate decreases and the temperature of the membrane resistor 6 increases, the resistance value of the membrane resistor 6 increases to V,>VR, and the conductivity of the transistor 94 decreases due to the output of the comparator 93. Therefore, the amount of heat generated by the film resistor 6 decreases, and at the same time, the output voltage of the voltage buffer 95 decreases.

decreases. In this way, the temperature of the membrane resistor 6 is feedback-controlled to a value determined by the outside air temperature, and the output voltage . represents the air flow rate.

4 is an enlarged view of the vicinity of the membrane resistor 6 shown in FIG. 2, and FIG. 5 is a sectional view taken along the line V--V in FIG. 4. As shown in FIGS. 4 and 5, only one end of the membrane resistor 6 is supported by the holding member 5 via the heat insulating member 12. As shown in FIGS. If the membrane resistor 6 is fixed to the holding member 6 by holding the membrane resistor 6 at both ends, the membrane resistor 6 acts as a strain gauge, and therefore, the distortion of the membrane resistor 6 causes a change in its output. The above-mentioned cantilever holding of the membrane resistor 6 prevents such a strain gauge effect.

Further, the flexible wiring 7 is sandwiched between flexible insulating resin films, and includes a patterned conductor (for example, C
u), and has a structure that is more resistant to corrosion, disconnection, etc. than bonding wires.

FIG. 1 is a sectional view showing the structure near the heat insulating member 12 of FIG. 5. FIG. As shown in FIG.
There is an Au baked layer 13-1 as the joining member 13 between the
and an Au-3i common layer 13-2. In other words, an Au baked layer 13-1 is formed in advance on one surface of the heat insulating member 12, and when this is pressed against the substrate 6 with moderate pressure and heated at about 400°C, Au-5 is formed at these interfaces.
The i-eutectic layer 13-2 is generated, and the substrate 6 and the heat insulating member 12 are joined.

On the other hand, the heat insulating member 12 and the holding member 5 (for example, A3.
(luminium or copper), an electroless plating layer 14-1 as a bonding member 14 and a Pb-3
An n-solder layer 14-2 is formed. That is, the electroless plating layer 14-1 is previously formed on the other surface of the heat insulating member 13, and this is joined to the holding member 5 by the Pb-5o solder layer 14-2.

With this configuration, the bonding members 13 and 14 both have excellent thermal conductivity, while the heat insulating member 12 has poor thermal conductivity, so that the heat insulating effect on the substrate 6 depends on the heat insulating member 12. Therefore, even if the joining members 13, 1
Even if the thickness and condition of the substrate 4 change, the heat insulation effect on the substrate 6 is not affected at all.

In addition to mullite, ceramic materials, glass materials, and resin materials such as polyimide can also be used as the heat insulating member.

〔Effect of the invention〕

As explained above, according to the present invention, since the joining member does not have a heat insulating effect, the heat insulating effect on the substrate depends only on the heat insulating member. It can prevent changes in characteristics such as range.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the vicinity of a heat insulating member of a directly heated flow rate sensor according to the present invention, and FIG. 2 shows an internal combustion engine to which a directly heated air flow sensor having a membrane resistor according to the present invention is applied. Overall schematic diagram, Figure 3 is a circuit diagram of the sensor circuit in Figure 2, Figure 4 is an enlarged view of the vicinity of the membrane resistor in Figure 2, and Figure 5 is a sectional view taken along the line V-V in Figure 4. be. 5: Holding member, 6: Film resistor, 7: Flexible wiring, 12: Heat insulation member, 13 Two-joining member, 13-1:
Au paste baked layer, 13-1: Au-Si eutectic layer, 14: Joining member, 14-1: Electroless Ni plating layer, 14-2: Pb-Sn solder layer.

Claims (1)

[Claims] 1. In a direct heating type flow sensor in which a substrate on which a membrane resistor is formed is supported by a holding member with excellent heat dissipation properties via a heat insulating member, the space between the substrate and the heat insulating member, and the heat insulating member and the holding member are joined together by a joining member having excellent thermal conductivity.