JPS61194317A - Direct-heating type flow-rate sensor - Google Patents

Abstract

PURPOSE:To improve response property of a flow-rate sensor, by constructing a substrate with a material of poor thermal conductivity and a supporting member with that of excellent thermal conductivity and installing a heat- throttling member between a duct and the supporting member. CONSTITUTION:Both ends of a film-type resistance 7 are supported by a supporting member 13 of excellent thermal conductivity, heat transferred from the resistance 7 to the member 13 is radiated quickly to a liquid. Further, on the ends on both sides of the member 13 are provided with notches 13a, as namely, heat-throttling members and by this arrangements, thermal insulating effect of the members 13 is strengthened. The supporting member 13 is fixed to a duct through a member 12 of poor thermal conductivity and thus, thermal insulating effect of the member 13 is improved. Consequently, film-type resistance 7 and supporting member 13 become in a floating condition in the liquid and its heat mass is minimized and the responsivity of the flow-rate sensor is improved.

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 airflow meters) for detecting the amount of intake air have been mainstream, but recently temperature-dependent resistance sensors, which have advantages such as small size and good response, have been introduced. A thermal type using

Further, air flow rate sensors having temperature-dependent resistance include indirect heating type and direct heating type. Indirectly heated air flow sensors include a heating resistor, a temperature-dependent resistor downstream of the heating resistor for detecting the temperature of the heated airflow, and a temperature-dependent resistor upstream of the heating resistor for detecting the temperature of the airflow before heating. A temperature-dependent resistor is provided, the current value of the heating resistor is feedback-controlled so that the temperature difference between the two temperature-dependent resistors is constant, and the air flow rate is detected by the voltage applied to the heating resistor. On the other hand, in a directly heated type air flow sensor, which has a faster response speed than an indirectly heated type, a film resistor is provided as a heat generating resistor and a resistor for detecting the temperature of the heated air flow. The current value of the membrane resistor is feedback-controlled so that the temperature difference with the temperature-dependent resistor for detecting the temperature of the air flow before heating is a constant value, and the air flow rate is detected by the voltage applied to the membrane resistor. It is something to do.

Normally, the responsiveness and dynamic range of an air flow sensor that keeps the difference between the heat generation temperature of the membrane resistor and the intake air temperature before heating to a constant value is determined by the heat capacity (heat mass) of the heat generating part including the membrane resistor and the degree of insulation effect. determined by In other words, in order to have the best response and the largest dynamic range, the mass of the heat generating part including the membrane resistor should be as small as possible, and ideally that part should be completely floating in the airflow. It is to bring the situation to a certain state.

Substrates for the above-mentioned film resistors include flexible types such as resin films, and solid types such as silicon, glass, and ceramic. Flexible type circuit boards are subject to large changes over time, and countermeasures against this change are also difficult. In addition, solid type substrates require a certain degree of thickness compared to flexible types for strength.
In addition, since it has better thermal conductivity than the flexible type, it has less insulation effect.For this reason, when using a solid type board, in order to increase the insulation effect, the holding member must have a high thermal conductivity. For example, ceramic is used.

[Problem that the invention seeks to solve]

Among solid type substrates, the thermal conductivity of glass and ceramic is usually 0.01ca#/ca+ -sec
-deg or less, which is lower than the thermal conductivity of silicon, and therefore, it can be expected to have a good heat insulating effect, so there is a desire to use it as a substrate for a flow rate sensor.

However, materials with poor thermal conductivity such as glass and ceramics have a large heat loss ((total calorific value of the membrane resistor) - (amount of heat dissipated from the membrane resistor to the fluid)), and as a result, the responsiveness of the flow sensor The problem is that it gets worse.

[Means for solving problems]

An object of the present invention is to provide a flow sensor with good responsiveness using a solid type substrate, and its means include:
In a directly heated flow sensor in which a substrate on which a membrane resistor is formed is housed in a duct by being supported by a holding member, the substrate is made of a material with poor thermal conductivity, and the holding member is made of a material with good thermal conductivity. The directly heated flow rate sensor is characterized in that a thermal throttle is provided between the holding member and the duct.

[For production]

According to the above-mentioned means, the heat that is not radiated from the substrate itself of the membrane resistor to the fluid is actively radiated from the holding member having good thermal conductivity to the fluid. At this time, since the space between the holding member and the duct is thermally throttled using a resin or the like having poor thermal conductivity, the sensor main body including the membrane resistor and the holding member floats in the fluid. As a result, the heat mass becomes smaller and the responsiveness of the flow sensor improves compared to when a substrate with good thermal conductivity, such as a silicon substrate, is used and a holding member with poor thermal conductivity is used.

〔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 a membrane resistor according to the present invention is applied, and FIGS. 4 and 5 are enlarged vertical cross-sectional views of the sensor portion of FIG. 3. and a cross-sectional view. 3 to 5, air is taken into an intake passage 2 of an internal combustion engine 1 via an air cleaner 3 and a rectifying grid 4. In FIGS. A measuring tube (duct) 5 is fixed in the intake passage 2 via a stay 6, and a membrane resistor 7 as an electric heater for measuring the air flow rate is provided inside the measuring tube 5. Further, a temperature dependent resistor 8 is provided outside the stay 6 to compensate for the outside temperature. The membrane resistor 7, together with a temperature-dependent resistor 8, is connected to a sensor circuit 9 formed on the hybrid substrate.

The sensor circuit 9 feedback-controls the amount of heat generated by the membrane resistor 7 so that the difference between the temperature of the membrane resistor 7 and the temperature of the temperature-dependent resistor 8 is constant, and the sensor output v0 is sent to the control circuit 10.
supply to. 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. 6, the sensor circuit 9 includes a membrane resistor 7, a temperature-dependent resistor 8, and resistors 91 and 9 forming a bridge circuit.
2, a comparator 93, a transistor 94 controlled by the output of the comparator 93, and a voltage buffer 95. In other words, the air flow rate increases and the temperature of the membrane resistor 7 (thermistor in this case) decreases, and as a result, the resistance value of the membrane resistor 7 decreases to vI - v, I, and the output of the comparator 93 The conductivity of transistor 94 increases. Therefore, the amount of heat generated by the film resistor 7 increases, and at the same time, the collector potential of the transistor 94, that is, the output voltage V of the voltage buffer 95 increases. Conversely, when the air flow rate decreases and the temperature of the membrane resistor 7 increases, the resistance value of the membrane resistor 7 increases to V,>V, and the conductivity of the transistor 94 decreases due to the output of the comparator 93. do. Therefore, the membrane resistor 7
The amount of heat generated by the transistor 94 decreases, and at the same time, the collector potential of the transistor 94, that is, the output voltage v0 of the voltage buffer 95 decreases. In this way, the temperature of the membrane resistor 7 is feedback-controlled to a value determined by the outside air temperature, and the output voltage v0 indicates the air flow rate.

Note that 12 in FIG. 5 is a backfire resistant protector.

FIG. 1 is a plan view showing the holding portion of the membrane resistor according to the present invention, and is a view seen from the direction of the arrow (■) in FIG.

In FIG. 1, the membrane resistor 7 has a substrate made of a material with relatively poor thermal conductivity, such as glass or ceramic, as will be described later. Both ends of the membrane resistor 7 are supported by a holding member 13 made of aluminum, copper, etc. with good thermal conductivity, so that the heat transferred from the membrane resistor 7 to the holding member 13 is quickly transferred from the holding member 13 to the fluid. Heat is radiated to Further, each side end of the holding member 13 is formed with a notch 13a, that is, thermally drawn, thereby increasing the heat insulating effect of the holding member 13. moreover,
The holding member 13 is fixed to the duct 5 via a member 1 having poor thermal conductivity, such as polyimide resin, thereby increasing the heat insulating effect of the holding member 13. Note that the member 12 also constitutes a backfire resistant protector as described above.

Therefore, the membrane resistor 7 and the holding member 13 are in a state of floating in the fluid, and most of the heat generated by the membrane resistor 7 is radiated into the fluid by the membrane resistor 7 or the retaining member 13.

Note that the thermal aperture can be achieved by reducing the thermal passage at the side end of the holding member 13, and may be achieved by means other than notches.

FIG. 2 is an enlarged view of the membrane resistor 7 shown in FIG.

As shown in FIG. 2, for example, platinum (Pt) is deposited on a glass substrate 71 with a thickness of 100 μm by vapor deposition and etching.
A film resistance pattern 72 made of Ni/Kel (Ni), Nichrome (Ni-Cr), etc. is formed, and a portion 72a shown within the dotted line frame acts as a heat generating portion.

In this case, since metal is used as the holding member 13, the signal extraction portion of the membrane resistor 7? 2b is directly connected to the holding member 13. Further, a film resistance pattern 72 can also be formed on the screen of the glass substrate 71.

Note that as the substrate 71, ceramics such as alumina (AttO) and mullite (3Alz03@2SiOt) can also be used. Furthermore, the present invention can be applied to flow sensors other than air flow sensors, such as liquid flow sensors.

〔Effect of the invention〕

As explained above, according to the present invention, a flow rate sensor with good responsiveness can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the holding part of the membrane resistor according to the present invention, FIG. 2 is an enlarged view of the membrane resistor in FIG. 1, and FIG. 3 is a direct heating type having the membrane resistor according to the present invention. An overall schematic diagram showing an internal combustion engine to which an air flow rate sensor is applied, Figures 4 and 5 are shown in Figure 3.
FIG. 6 is an enlarged plan view and cross-sectional view of the membrane resistor 6 shown in the figure, and FIG. 6 is a circuit diagram of the sensor circuit shown in FIG. 3. 1... Internal combustion engine, 2... Intake passage, 5...
...Measurement tube (duct), 7...Membrane resistor, 8...
Temperature-dependent resistance, 9...Sensor circuit, 10-...
Control circuit, 13... Holding member. 7: Film resistance 12: Member with poor thermal conductivity 13: Holding member 13q: Notch Fig. 2 7: Film resistance 7]: Substrate 72: Film resistance pattern 720: Heat generating part 13: Holding member 1: Internal combustion Engine 2: Intake passage 6: Duct 7: Membrane resistance 8: Temperature dependent resistance 9: Sensor circuit Figure 4 8: Temperature dependent resistance 8: Temperature dependent resistance

Claims (1)

[Scope of Claims] 1. A directly heated flow sensor in which a substrate on which a membrane resistor is formed is housed in a duct by being supported by a holding member, wherein the substrate is made of a material with poor thermal conductivity; A directly heated flow rate sensor, characterized in that the member is made of a material with good thermal conductivity, and a thermal throttle is provided between the holding member and the duct. 2. The direct heating type flow sensor according to claim 1, wherein the substrate is made of glass. 3. Claim 1 in which the substrate is made of ceramic
The direct heating type flow sensor described in section. 4. The direct heating type flow sensor according to claim 1, wherein the holding member is made of metal such as aluminum or copper. 5. The direct heating type flow sensor according to claim 1, wherein the thermal throttling is performed by a resin with poor thermal conductivity provided between the holding member and the duct. 6. The direct heating type flow sensor according to claim 1, wherein the thermal throttling is performed by reducing a thermal passage at a side end of the holding member. 7. The direct heating type flow sensor according to claim 1, wherein the film resistor is formed on the screen of the substrate.