JPS636421A - Hot wire type flow meter - Google Patents

Abstract

PURPOSE:To prevent dust particles from sticking on a hot wire by arranging electrothermic nets which catch dirt particles in sucked air on the upstream side of a heat wire part arranged in an air passage and supplying a heating current for burning out the dirt particles to the electrothermic nets. CONSTITUTION:The plural electrothermic nets 6a and 6b are arranged opposite each other at the upstream side of the installation part of the hot wire 4 in the air passage of a main body 1; and the electrothermic net 6a is used as a discharging electrode and the electrothermic net 6b is used as a dust collecting electrode. When an air flow is measured, a high voltage, e.g. 1kV is applied between the electrothermic nets 6a and 6b to charge dust electrostatically and forcibly on the side of the electrothermic net 6a and collect the dust electrostatically on the side of the electrothermic electrode 6b. Then, a burning current is supplied to the electrothermic net 6b after the air flow rate is measured to burn out the dust sticking on the electrothermic net 6b. Consequently, dust particles are securely prevented from sticking on the hot wire 4 for flow rate measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot-wire flowmeter, and particularly to a hot-wire flowmeter suitable for measuring the intake air flow rate of an automobile engine.

[Conventional technology]

BACKGROUND ART In recent years, in order to improve fuel efficiency and purify exhaust gas in automobile engines, systems that measure the intake air flow rate and control the air-fuel ratio 1 ignition timing using a fuel injection control means (microcomputer) have become popular. A flow meter for measuring the intake air flow rate is disclosed in Japanese Patent Application Laid-Open No. 58-26221, for example.

Japanese Patent Publication No. 59-190624, Publication No. 59-50939
As disclosed in Japanese Patent Publication No. 2003-120026, there is a method that measures the air flow rate using the resistance temperature characteristics of a hot wire. This type of air flow meter has advantages such as high-speed response and does not require much installation space, so it is suitable for measuring the amount of intake air in automobile engines. This had the problem of particles adhering to it and measurement accuracy decreasing over time. Therefore.

In the air flow meter disclosed in JP-A No. 58-26221, the shape of the air passage is bent to prevent dust from entering the hot wire section, and in the air flow meter disclosed in JP-A No. 59-190624, the shape of the air passage is bent to prevent dust from entering the hot wire section. A dirt adhesion prevention member is provided to inertially separate dust.
In the air flow meter No. 39, consideration is given to heating the dust and the like attached to the hot wire to a high temperature to burn it off.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional hot wire flowmeter.

Various measures have been taken to prevent dirt particles from adhering to the hot wire section, but among the above-mentioned methods, there are methods that prevent dirt particles from going around the hot wire section and methods that inertially separate dirt particles. It is difficult to completely avoid dirt particles, and in the case of a method in which a heating current is passed through the heating wire part itself, the heating wire part is heated to a high temperature to burn off the dirt particles.
There was a risk that the hot wire life and detection accuracy would deteriorate over time.

The present invention has been made in view of the above points, and its purpose is to prevent dirt particles from adhering to the hot wire, maintain stable measurement accuracy over a long period of time, and provide a PA with excellent durability. , to provide a wire flow meter.

[Means for solving problems]

In order to achieve the above object, the present invention arranges an electric heating net for catching dirt particles in the intake air on the upstream side of a hot wire section provided in an air passage, and also has a heating net for burning off dirt particles in this electric heating net. The heating current is applied at appropriate times.

[Effect]

According to the present invention having such a configuration, dirt particles such as dust in the intake air passing through the air passage are caught and burned off by the electric heating net before reaching the hot wire for measuring flow rate. It is possible to sufficiently prevent adhesion from entering the hot wire portion. Further, since the burning off of dirt particles is carried out by the electric heating net, there is no need to flow a burning current through the hot wire portion for measuring air flow rate as in the conventional method, and the measurement accuracy and life of the hot wire can be improved.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 to 6.

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, FIG. 3 is a plan view of the electric heating network used in the above embodiment, and FIG. 4 5 is a partial sectional view of the electric heating network, FIG. 5 is an electric circuit diagram of the above embodiment, and FIG. 6 is an electrical operation waveform diagram of the above embodiment. In Figure 1,
Reference numeral 1 denotes a main body of the hot wire flow rate measuring device, which is composed of a main body 1a and a subbody 1b. A main air passage 2 and a bypass air passage 3 are arranged inside the main body 1 . The bypass air passage 3 bypasses the main air passage 2, and a heat wire (temperature-sensitive resistor) 4 and a temperature compensation wire 5 are disposed in a part of the passage. The hot wire 4 is a platinum wire wound around a ceramic bobbin, and forms a bridge together with the compensation wire 5 and resistors R□ and R2, which will be described later. The outlet side of the bypass air flow path 3 forms an annular flow path 3a as shown in FIG. 2, and its outlet 3b communicates with the main air path 2. As described above, the heat wire 4 and the temperature compensation wire 5
are arranged in the bypass air passage 3, but by adopting such an arrangement structure, the hot wire 4. The compensation wire 5 can be made small, and the annular flow path 3a allows the heating wire 4. The influence of airflow turbulence on the compensation line 5 is reduced.

6 is an electric heating network, electric heating, 11216 is the figure 3 and 4
As shown in the figure, a large number of metal fittings 62 are arranged inside an insulating ring 61 made of an insulator (for example, ceramic).
The electric heating wire (for example, nichrome wire) 63 is stretched in a net shape, and the electric heating wire 4146 thus formed is placed in the air passage 1a located upstream of the main air passage 2 and the bypass air passage 3 of the main body 1. has been done.

7 is a circuit section that has the function of a hot wire flowmeter and a function of passing a heating current through the electric heating network 6.6 The circuit section 7, as shown in FIG. 5, has a heating wire 4, a temperature compensation wire 5, Resistor R1,
It has a bridge made up of R2, and a power supply voltage is applied between point a and point b of the bridge via switch SW and transistor P1. Further, the 0 point and the d point of the bridge are connected to the input side of the differential amplifier 8, and the output side of the differential amplifier 8 is connected to the base side of the transistor P. By forming such a bridge configuration, a current is set to flow through the hot wire 4 to maintain a constant temperature, and for example, when the temperature (resistance) of the hot wire 4 is cooled according to the degree of air flow, the difference Due to the current control action of the dynamic amplifier 8 and the transistor P□, an increasing current flows through the hot wire 4 to maintain a predetermined temperature. Further, a signal line 9 is drawn out from point C of the bridge, and a change in the heating current of the thermal RIA 4 is detected by a resistor R to obtain an air flow rate measurement signal V. In addition, switch SW
For example, when an air flow meter is applied to an automobile,
Equivalent to an engine key switch.

B is a child terminal of the power supply, and G is one terminal of the power supply.

1o is a circuit for passing a heating current for burnout to the electric heater w46 described above, and the circuit 10 includes a transistor T1 that performs an on-off operation by an on-off operation of a switch SW;
Transistor T2 is turned on for a predetermined time by discharging the energization control capacitor C when the transistor T□ is turned off.
and voltage dividing resistor R□.

It is composed of R4, R5, etc., and is set so that when the transistor T2 is turned on, a heating current Ih for burning out flows from the source to the electric heater 4Iy16.

Next, the operation of this embodiment will be explained.

For example, when applied as an air flow meter for a car engine, the key switch SW is closed when the car is in operation, so the bridge of one circuit section 7 is in the air flow measurement state with the power supply voltage applied. In this state, the air Q that has flowed into the main body 1 is separated into a main flow rate Q1 and a bypass flow rate Q2 in the A1 section as shown in FIG. It passes through the installation part of the line 5, passes through the annular passage 3a of the main body 1, and merges with the main flow rate Q1 again. When the bypass air flow rate Q2 passes through the hot wire 4 and the temperature compensation line 5, the bypass air flow rate is measured as follows.

The resistance value of the heating wire 4 is Rh, and the resistance value of the temperature compensation wire 42 is Re.
Then, the stable state of the bridge circuit is as follows. That is, by detecting the temperature of the air flowing through the bypass air passage 3 based on the change in the resistance value Rc of the temperature compensation line 5, the heating temperature of the hot wire 4 can be determined. - On the other hand, the amount of heat taken away by Qz due to the heating power of the hot wire 4 and heat transfer is approximately expressed by equation (2).

r ”Rh= (A + B herT)A T
----(2) Work; Heating current A, B of the hot wire; Constant Qz; Bypass flow rate ΔT; Temperature difference between the hot wire and air, that is, the temperature difference between the hot wire and air determined by equation (1); From equation (2), the air flow signal V can be obtained by detecting the heating current of the hot wire using the resistor R1. Since the relationship between the bypass flow fix Q 2 and the intake air flow rate Q is constant, the intake air flow rate Q can be determined based on the air flow rate signal V.

When measuring the air flow rate, dust in the intake air passing through the main body 1 attaches to the heating net 6 and is captured before reaching the installation part of the heating wire 4. The dust attached to the heating wire is burned off when the switch SW is opened, that is, after the air flow rate is measured. This burn-off operation is shown in FIG. In other words, during the period from 1 to t2 when measuring the air flow rate (when the switch SW is on), the transistor T1 is on and the transistor T2 is off, so the burnout current 7 flows through the electric heater 4@6. do not have. Further, capacitor C is in a charged state.

Next, when the switch SW is turned off (after time tz), the transistor T1 is turned off, so the voltage Vc charged in the capacitor C is discharged, the partial voltage VF is applied to the base of the transistor Tz, and the transistor T2 is turned on for a predetermined time. ,
A large current flows for a short period of time in the Denketsu Zenmachi 6 to incinerate the dust. At time t3 when the capacitor C has finished discharging, the transistor T2 is turned off and the burnout is automatically stopped. Therefore, according to this embodiment, since the electric heating pad 6 can collect and burn off the dust, it is possible to reliably prevent the hot wire from being contaminated by dirt particles such as dust, and the hot wire flow rate is excellent in reliability and durability. Needles can be provided. In addition, dust collection, electric heating lI4 of the burning pot
6 has a rectifying effect on the fluid flow, improves the accuracy of the flowmeter, and can also serve as a protective net for hot wires during handling.

FIG. 7 shows a schematic diagram of the structure in which the hot wire flowmeter of the above embodiment is applied to an automobile. In FIG. 7, part 8 is a hot wire type flowmeter, and the above-mentioned electric heating net 6 is arranged on the upstream side of the air passage of the main body 1. , 11 is the engine intake manifold.

12 is an air cleaner housing an air filter 13; 14;
is the engine control control unit.

15 is an injector for injecting fuel.

This system is installed on the engine intake manifold 1
1, and other signals (not shown) such as engine speed, cooling water temperature, etc.
The control unit 14 performs arithmetic processing together with data such as the throttle opening degree, and outputs the optimum fuel amount in that state to the injector 15. However, in such an application example, although the air in the air flow rate measuring section S is purified in the air cleaner 13,
Dust with a diameter of 0 to 40 μm flows in mixed with air.

This dust adheres to the electric heating net 6 due to friction and inertia caused by friction with the air filter 13, and is burned off when the electric heating net 6 is energized. Therefore, heat ray 4. It is possible to sufficiently prevent dirt particles from adhering to the temperature compensation wire 5, maintain the flow rate measurement accuracy of the hot wire 4, and improve durability.

FIG. 8 shows a second embodiment of the present invention, and in the figure, the same reference numerals as in the above-described embodiment indicate the same or common elements. One feature of this embodiment is that a plurality of electric heating nets 6a are provided on the upstream side of the heating wire 4 installation part in the air passage of the main body 1.

6b are arranged facing each other, the electric heating net 6a side is used as a discharge electrode, and 6b
A high voltage of IKV, for example, is applied between the heating nets 6a and 6b using the collecting electrode on the side of the heating net Ga, and the dust is forcibly electrified on the heating net Ga side, and the dust is electrostatically collected on the 6b side. After measuring the air flow rate, a burning current is applied to the heating net 6b to burn off the dust attached to the heating net 6b. 9th
The figure shows the circuit section 7' of this embodiment. In the circuit section 7', reference numeral 10' has the same configuration as the burnout current on-off control circuit 10 of the first embodiment (FIG. 5) described above, and an air Ryuti1!
It has a fixed bridge. 20 is an oscillation circuit used for high voltage generation, and 21 is a transformer. When the switch SW is closed (when measuring air flow rate), the 1 oscillation circuit 20 and transformer 21 are activated to generate the electric heating network 6a.

A high voltage for electrostatic precipitation is applied to 6b, and switch S
It is set so that when W is opened, a heating current flows through the burnout current on-off control circuit 10 to the heating grid 6b on the collector M electrode side. Therefore, in this embodiment, dirt particles such as dust in the intake air are collected electrically and burned off, thereby improving the dust collection efficiency and further preventing dirt particles from adhering to the flow rate measuring hot wire 4. can be increased.

FIG. 10 shows a control circuit 7' for the electric heating nets 6a, 6b and the air flow measuring bridge provided in a control unit 14 of the engine control device. In this case, the control unit 14 can perform the burnout operation. This is advantageous when performing complex burn-off operations.

11 and 12 show a third embodiment of the present invention. In this embodiment, a flow rate measuring passage 3' is provided in the main air passage 2' of the main body 1, The air flow rate is measured by installing a hot wire 4 made of, for example, a platinum wire and a temperature compensation wire 5, which is a film resistor, inside the air flow passage 3' in the main air passage 2'. By installing the heating nets 6a and 6b on the upstream side, the same effects as in each of the embodiments described above can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reliably prevent dirt particles from adhering to the hot wire for flow rate measurement, maintain stable flow rate measurement accuracy over a long period of time, and provide a hot wire flow rate method with excellent durability. We can provide a meter.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention. 2 is a sectional view taken along the line A-A in FIG. 1, FIG. 3 is a plan view of the electric heating net used in the above embodiment, FIG. The figure is a circuit diagram of the above embodiment, No. 6
The figure is an operating waveform diagram explaining the operating state of the circuit in FIG.
FIG. 7 is a system diagram showing the state in which the above embodiment is applied to an air-fuel ratio control system for an automobile engine, and FIG.
FIG. 9 is a partial circuit diagram of the second embodiment, FIG. 10 is a circuit diagram showing another example of a heating network, and FIG. FIG. 12, a longitudinal sectional view showing the third embodiment of the invention, is a view taken in the direction of the X direction in FIG. 11. 1... Flow meter body, 2... Main air passage, 3... Bypass air passage, 4... Heat wire, 5... Temperature compensation line,
6... Electric heating net, 6a, 6b... Electric heating net, 7... Air flow rate measurement and burnout current control circuit. Kaori, 3 Kuni Tachibana 4-'s $6 figure #r'T mouth μ No. S concave dormitory 10 mouths

Claims (1)

[Claims] 1. In a hot-wire flowmeter in which a hot wire for measuring the flow rate of intake air is provided in a part of the air passage, dirt particles in the intake air are captured on the upstream side of the hot wire installation part in the air passage. 1. A hot-wire flowmeter characterized in that an electric heating net is disposed, and the electric heating net is set so that a heating current for burning off dirt particles is applied at a suitable time. 2. In claim 1, the electric heating net is composed of a plurality of heating wires, and between the heating wires, a high voltage is always applied during measurement of air flow rate to perform electrostatic precipitation. type flow meter. 3. A hot wire flowmeter according to claim 1 or 2, in which the heating current to the electric heating network is applied after measuring the air flow rate.