JPS6235225A - Direct heat type flow rate sensor - Google Patents

Abstract

PURPOSE:To provide a heat insulating effect which is uniform with respect to temp. by using members having such characteristic that the changes of the heat conductivity with temp. are positive and negative to constitute the heat insulating member. CONSTITUTION:The heat insulating member 12 is constituted of the respective layers including an Au-Si eutectic (adhesive) layer 121, a mullite material 122, a heat resistant adhesive agent 123, a polyimide material 124 and solder 125. The mullite material 122 exhibits the negative characteristic in the change of the heat conductivity with temp. and the polyimide material 124 exhibits the positive characteristic. The positive and negative characteristics are offset and the change of the heat conductivity with temp. is decreased as a whole if the thickness is adequately selected. The heat conductivity is thus made uniform (constant) and the output change of the direct heat type flow rate sensor is decreased.

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 the basic fuel injection amount, basic ignition timing, and the like. 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.

Note that if you delete the ambient temperature/degree dependent resistance on the upstream side and control the heating resistor so that the temperature of the temperature dependent resistance on the downstream side is constant, the air flow rate as a volumetric capacity can be detected (see: Special Publication No. 54-9662). On the other hand, a directly heated type air flow sensor, which has a faster response speed than an indirectly heated type, is equipped with a heating resistor that also serves as temperature detection, installed in the engine's intake passage, and a temperature-dependent resistor installed upstream of the heating resistor. There is. 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. As a result, 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 controlled by the voltage applied to the heating resistor.
This is to detect. 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 generating resistor (belly type resistor) and the intake air temperature constant, or the heat generating temperature of the belly type resistor, includes the belly type resistance. It is determined by the heat capacity (heat mass) of the heat generating part and temperature sensing part and the degree of insulation effect. In other words, in order to have the best response and the largest dynamic range, the mass of the heat generating part and temperature sensing part including the abdominal resistor should be as small as possible, and ideally that part should be completely surrounded by air. It is to be in a state of floating in the flow (see:
(Japanese Patent Application No. 60-25232).

[One problem to be solved by the invention] However, normally, a heat insulating member has a positive characteristic or a negative characteristic in the change in thermal conductivity with respect to temperature, and therefore,
There is a problem in that the heat insulating effect of the heat insulating member changes depending on the temperature of the air flow, and as a result, the output characteristics of the sensor change.

[Means for solving problems]

An object of the present invention is to provide a directly heated flow rate sensor whose output characteristics do not change with respect to the temperature of the air flow. and a member having negative characteristics.

[For production]

According to the above-mentioned means, it is possible to make the thermal conductivity of the heat insulating member uniform (constant) with respect to the temperature, and thereby,
The heat insulating effect of the heat insulating member becomes uniform with respect to temperature.

〔Example〕

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

FIG. 3 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. 3, 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 V 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. 4, the sensor circuit 9 includes an abdominal resistor 6, a temperature-dependent resistor 8, and resistors 91 and 9 forming a bridge circuit.
2. It is composed of a comparator 93, a transistor 94 controlled by the output of the comparator 93, and a voltage filter 95, that is, the air flow rate increases and the abdominal resistor 6 (in this case,
When the temperature of the thermistor (thermistor) decreases, and as a result, the resistance value of the belly-type resistor 6 decreases so that 1≦vR, the conductivity of the transistor 94 increases due to the output of the comparator 93. Therefore, the amount of heat generated by the abdominal resistor 6 increases, and at the same time, the collector potential of the transistor 94, that is, the output voltage v0 of the voltage buffer 95 increases. Conversely, when the air flow rate decreases and the temperature of the abdominal resistor 6 increases, the resistance value of the abdominal resistor 6 increases to V,>VR, and the conductivity of the transistor 94 decreases due to the output of the comparator 93. Therefore, abdominal resistance 60
The amount of heat generated decreases, and at the same time, the output voltage VQ of voltage buffer 95 decreases. In this way, the temperature of the abdominal resistor 6 is subjected to feed puncture control so that it becomes a value determined by the outside air temperature, and the output voltage V0 indicates the air flow rate.

The fifth time is an enlarged view of the vicinity of the abdominal resistor 6 in FIG. 3, and FIG. 6 is a sectional view taken along the line Vl-VI in FIG. As shown in FIGS. 5 and 6, only one end of the abdominal resistor 6 is supported by the holding member 5 via the heat insulating member 12. As shown in FIGS. Note that when the abdominal resistor 6 is fixed to the holding member 6 by holding both sides, the abdominal resistor 6 acts as a strain gauge, and therefore the abdominal resistor 6 acts as a strain gauge.
The disadvantage is that the distortion causes a change in the output.

The above-mentioned cantilever holding of the abdominal resistor 6 prevents such a strain gauge effect.

FIG. 7 is an enlarged view of the flexible wiring 7 shown in FIG. 5, and FIG. 8 is a sectional view taken along the line ■--■ in FIG. As shown in FIGS. 7 and 8, the flexible wiring 7 is composed of a flexible insulating resin film 701, patterned conductors (for example, Cu) 702a, 702b, and a flexible insulating resin film 703.

The joint parts A and B are joined to the Au butt part of the abdominal resistor 6 by, for example, eutectic Au-3n. In this way, since the conductors 702a and 702b are covered with flexible insulating resin, they have a structure that is more resistant to corrosion, disconnection, etc. than bonding wires.

FIG. 1 is a sectional view showing the detailed structure of the heat insulating member 12 of FIG. 6. FIG. As shown in FIG. 1, the heat insulating member 12 includes an adhesive (for example, an Au Si eutectic layer) 121, a mullite heat insulating material 122, and an adhesive (for example, a heat-resistant resin adhesive) 123.
, polyimide insulation material 124 , and adhesive (eg, solder) 125 . Here, as shown in FIG. 2, the mullite heat insulating material 122 exhibits a negative change in thermal conductivity with respect to temperature, and the polyimide heat insulating material 124 exhibits a positive characteristic in a change in thermal conductivity with respect to temperature. Therefore, it is clear that if the thickness of the mullite insulation material 122 and the thickness of the polyimide insulation material 124 are appropriately set, the above-mentioned pressure and negative characteristics can be offset and the change in thermal conductivity with respect to temperature of the insulation member 12 as a whole can be reduced. be.

In this way, changes in the thermal conductivity of the heat insulating member 12 with respect to temperature can be reduced, and ideally, the thermal conductivity of the heat insulating member 12 with respect to temperature can be made uniform (constant).

Note that ceramic or glass-based materials can be used instead of mullite as heat insulating materials that exhibit negative characteristics in terms of thermal conductivity changes with respect to temperature; As the heat insulating material shown, a resin material can also be used instead of polyimide. moreover,
In FIG. 1, materials whose thermal conductivity changes with respect to temperature have positive and negative characteristics are combined in a layered manner, but it is also possible to mix these materials.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reduce the change in thermal conductivity with respect to temperature of the heat insulating member, or in other words, it is possible to make the thermal conductivity of the heat insulating member with respect to temperature uniform (constant). Even if a temperature change occurs, it is possible to reduce the change in the loss rate of heat escaping from the abdominal resistor through the heat insulating member to the holding member. Therefore, changes in sensor output due to temperature changes can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the heat insulating member of the direct heating type flow sensor according to the present invention, FIG. 2 is a graph showing the thermal conductivity characteristics with respect to temperature of the heat insulating material used in the heat insulating member of FIG. 1, and FIG. is an overall schematic diagram showing an internal combustion engine to which a directly heated air flow sensor having a schematic resistance according to the present invention is applied, FIG. 4 is a circuit diagram of the sensor circuit in FIG. 3, and FIG. An enlarged view of the vicinity of the formula resistor, Figure 6 is vr-v in Figure 5.
7 is an enlarged view of the flexible wiring 7 shown in FIG. 5, and FIG. 8 is a sectional view taken along the line ■-■ in FIG. 7. 5: Holding member, 6: Abdominal resistance, 7: Flexible wiring, 12: Heat insulating member, 121: Adhesive, 122: Mullite heat insulating material, 123: Adhesive, 124: Polyimide heat insulating material, 125: Adhesive. 5... Holding member 6... Abdominal resistor 12... Heat insulating member 125... Adhesive Fig. 2 1... Internal combustion engine 7... Flexible wiring 9... Sensor circuit Fig. 4 635 ．． Schematic resistance 8... Temperature dependent resistance Figure 7 701.703... Flexible resin 702a,
702b...Conductor

Claims (1)

[Scope of Claims] 1. In a directly heated flow sensor in which a substrate on which a membrane resistor is formed is supported by a holding member through a heat insulating member, the heat insulating member 1. A directly heated flow rate sensor comprising a member having a positive characteristic and a member having a negative characteristic, wherein the thermal conductivity of the heat insulating member with respect to temperature is made uniform. 2. The direct heating type flow sensor according to claim 1, wherein the member with positive characteristics and the member with negative characteristics are layered. 3. The direct heating type flow sensor according to claim 1, wherein the member having the positive characteristic and the member having the negative characteristic are mixed.