JP2002048614A - Heating resistor type air flow-rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal resistance type air flow-rate measuring device where a pressure loss caused by a straightening lattice is less and a high flow- rate detection precision is easily provided. SOLUTION: A resin straightening lattice 12 is attached to an inlet of a main air path so that a thick front end part 13a by draft of a lattice part 13 faces the upper stream side of an air flow F while a gently expanding shape is provided by draft toward a rear end part 13b on the lower stream side, in the air path, resulting in no separation vortex behind the rear end part 13b. Since reducing of an effective cross-section area of the air path under the separation vortex is suppressed, higher precision is provided by the rectifying lattice 12 while a pressure loss is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a flow rate of air by providing a heating resistor in a flow path, and more particularly to a heating resistor type air flow measurement apparatus suitable for measuring an intake air flow rate of an internal combustion engine. About.

[0002]

2. Description of the Related Art In recent years, in an internal combustion engine, in particular, an automobile engine, it has become common to measure the intake air flow rate and control the fuel supply amount according to the measurement result. An air flow measuring device is used, and one of them is a heating resistor type air flow measuring device.

A general example of this heating resistor type air flow measuring device will be described with reference to FIG. As shown in the figure, in this heating resistor type air flow measurement device, a heating resistor 5 and a temperature sensing resistor 6 are arranged in a passage 3 of the air whose flow rate is to be measured, and are used as detection elements. The heating resistor 5 and the temperature-sensitive resistor 6 are connected to an electronic circuit 7 for detecting an air flow signal.

The electronic circuit 7 includes a resistor R1 connected to the heating resistor 5 and the temperature-sensitive resistor 6 for forming a bridge circuit.
0, R11 and a transistor 9 for controlling the current I supplied to this bridge circuit from the power supply Vbatt.
It is composed of an operational amplifier OP1, and although not shown, the whole is modularized.

The input of the operational amplifier OP1 is connected to resistors 5, 6
And the resistor R10, R11, and the output is connected to the base of the transistor 9. Accordingly, when the transistor 9 is turned on, a current I having a value corresponding to the degree of the conduction is supplied to the bridge circuit, and is shunted to the heating resistor 5 and the temperature-sensitive resistor 6. Ih is supplied.

At this time, the current flowing through the temperature-sensitive resistor 6 is
The resistance of each resistor and the resistor is set to a predetermined value so that the heating current Ih of the heating resistor 5 can be suppressed to a value sufficiently smaller than the heating current Ih. It can be neglected, so that temperature compensation is provided.

The heating resistor 5 generates heat by the current Ih and its temperature rises. The temperature is determined by the balance between the amount of heat generated by the current Ih and the amount of heat dissipated by air in the passage 3 at this time. The resistance value of the heating resistor 5 is determined by its own temperature. Also, at this time, the amount of heat dissipated from the heating resistor 5 increases as the flow rate of the air in the passage 3 increases because the degree of cooling increases as the flow F of the air increases.

Accordingly, when air flows in the passage 3 and a large amount of heat is dissipated from the heating resistor 5, the temperature of the heating resistor 5 decreases and the resistance value decreases, so that the balance of the bridge circuit changes and the operational amplifier OP1 Increases, the transistor 9 is further biased in the conduction direction, and the heating current Ih
To prevent the temperature of the heating resistor 5 from lowering, and to maintain the equilibrium state of the bridge circuit.

As a result, the magnitude of the heating current Ih flowing through the heating resistor 5 becomes a value corresponding to the flow velocity of the air flow indicated by the arrow F, and the air flow rate is measured. Heating current I at this time
The magnitude of h appears as a voltage drop across resistor R10, from which an output signal Vout representative of the air flow can be obtained. The output signal Vout is further converted into a signal such as a voltage value, a frequency value, and a current value, and is output from the air flow measuring device to the control unit as a flow signal representing the intake air.

As described above, the heating resistor 5 serves as a detecting element for detecting the flow velocity of the air and outputting it as an air flow rate. Must be sufficiently uniform, or if the air is turbulent, the detection accuracy of the flow rate will be affected.

On the other hand, an engine for an automobile or the like is configured so that outside air is sucked in through an air cleaner or the like, and therefore, a large turbulence occurs in the flow of air in front of the heating resistor 5. Therefore, it is necessary to rectify the flow of air upstream of the heating resistor 5, and therefore, it is customary to provide a rectifying grid, for example, as disclosed in JP-A-8-201136.

Here, as the rectifying grid, a resin rectifying grid formed by molding a mold, which is advantageous in terms of cost, has conventionally been the mainstream. Disclosed is a technique in which the wall thickness of the portion is increased by the die-cutting gradient, and the end face of the portion is attached to the downstream side in the air flow direction, and the flow rectifying effect is enhanced by the flow contraction effect. are doing.

FIG. 4 shows a rectifying grid 10 formed by stamping and resin molding according to the prior art described above. Here, the grid portion 11 of the rectifying grid 10 is shown by a cross section taken along a plane perpendicular to the longitudinal direction. Have been. In this figure, the main air passage constituting member 2 is illustrated, and a state in which the rectifying grid 10 is attached thereto is shown.

As shown in the drawing, the rectifying grid 10 has a front end 11a on the side opposite to the mold dividing surface S for resin molding, the end of the grid 11 facing the air flow direction F. It is attached to the inlet side opening of the cylindrical main air passage component 2 so that the mold dividing surface S side is the rear end 11b.

As a result, in the rectifying grid 10, as shown in the drawing, the rear end portion 11b, which is made thicker than the front end portion 11a, due to the die-cutting gradient for resin molding, flows in the air flow direction. It is arranged on the downstream side of F so that the rectification effect of the air is enhanced by the contraction effect by this.

[0016]

In the above prior art, no consideration is given to the occurrence of separation vortices of the air flow behind the flow straightening grid, and the effective air flow passage area is reduced, and the pressure loss is reduced. There was a problem that it would increase.

That is, in the prior art, as shown in FIG. 4, after the air flow is reduced by the grid portion 11 in the rectifying grid 10, the air flow rapidly expands after the rear end portion 11b. As a result, a separation vortex T is generated. As a result, as shown by A, the effective sectional area of the air passage is further reduced, and the pressure loss increases.

It is an object of the present invention to provide a thermal resistance type air flow measuring device which has a small pressure loss due to a rectifying grid and can easily obtain a high flow rate detection accuracy.

[0019]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heating resistor type air flow measuring device provided with a rectifying grid formed by die-cut resin molding. By providing a thick portion provided by a die-cutting gradient, and having the one end located on the upstream side of the air flow, the cross-sectional area of the air passage is gradually increased toward the downstream side in the straightening grid. Is achieved as it is. At this time, the one end may be formed in a semicircular shape.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a heating resistor type air flow measuring device according to the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 shows an embodiment in which the present invention is applied to a sub-air passage type heating resistor type air flow measuring device. In the drawing, 1 is a main air passage, 2 is a main air passage constituent member, and 3 is a main air passage constituent member. A sub air passage 4; a sub air passage component;
5 is a heating resistor, 6 is a temperature-sensitive resistor, 8 is a module, 1
Reference numeral 2 denotes a resin rectifying grid.

Here, in the embodiment of FIG. 1, the auxiliary air passage 3 corresponds to the air passage in FIG. 3, the heating resistor 5 and the temperature sensing resistor 6 are the same, and the module 8 is the same as that of FIG. The electronic circuit 7 is modularized. The sub air passage 3 is formed in the module 8 by the sub passage member 4 so as to surround the heating resistor 5. The module 8 is attached to the main air passage component 2 such that the passage 3 is located at a predetermined position in the main air passage 1.

Therefore, also in this embodiment, the operation as the heating resistor type air flow measuring device is the same as that of the general device described with reference to FIG. However, the embodiment of the present invention is not limited to the heating resistor type air flow measuring device of the auxiliary air passage type, but can be applied to any heating resistor type air flow measuring device provided with a resin rectifying grid. Needless to say.

Next, the resin rectifying grating 12 in this embodiment corresponds to the rectifying grating 10 in the prior art shown in FIG. 4, and the lattice portion of the resin rectifying grating 12 has the shape shown in FIG. Made in. Here, 13 is a lattice portion, 13a is a front end portion of the lattice portion 13, 13b is a rear end portion 13, and S is a mold dividing surface.

Therefore, the rectifying grid 12 is different from the rectifying grid 10 according to the prior art shown in FIG. So that the main air passage component 2
At the entrance opening of the vehicle.

As a result, in this embodiment, of the front end and the rear end of the lattice portion 13, the one whose thickness is larger due to the draft for resin molding is larger at the front end 1.
3a, the thinner end is the rear end 13
4 also differs from the prior art of FIG. At this time, the shape of the front end portion 13a is also different from that of the related art in that it is formed in a semicircular shape as shown in the figure.

Next, the rectifying grid 12 in this embodiment is described.
Will be described. In the case of the rectifying grid 12, the shape of the grid portion 13 is such that the thickness decreases from the front to the rear in the flow of air indicated by the arrow F,
For this reason, in this portion, the air passage is formed by the front end 13a.
And then gradually spreads downstream.

As a result, in the path of the air flow up to the rear end portion 13b, as shown in the drawing, air flow separation H occurs on the side surface of the lattice portion 13, but after the rear end portion 13b,
Since there is no rapid expansion of the air flow, the generation of separation vortices is small, and the reduction of the effective cross-sectional area of the air flow due to the separation vortices can be sufficiently suppressed.

Therefore, according to this embodiment, since there is no possibility that the effective cross-sectional area A of the air passage is reduced after the rectification grid 12, the air flow rectification function of the air flow rectification grid 12 is impaired. Pressure loss can be reduced
As a result, a high flow rate detection accuracy can be obtained with a small pressure loss, and a high-performance heating resistance type air flow measuring device can be easily provided.

Here, the rectifying grid 12 according to this embodiment
At the front end 13a to the rear end 1
Considering the degree of reduction in thickness up to 3b, from the viewpoint of reducing pressure loss, a divergence angle of around 6 ° is considered to be optimal. Therefore, it is desirable to approach this angle.

However, the divergence angle is often limited by the structure required for the lattice portion, and thus cannot be so large. However, the required 2
Even with a divergence angle of about 3 °, according to the rectifying grid 12, a considerable reduction in pressure loss can be obtained.
There is no danger of a problem in implementation.

In this embodiment, as shown in FIG. 2, since the front end 13a of the grid portion 13 is formed in a semicircular shape, the dynamic pressure received by the air flow on the front end 13a of the grid portion 13 is reduced. As a result, the pressure loss can be further reduced.

[0032]

According to the present invention, since the pressure loss due to the rectifying grid can be reduced, it is possible to provide a heating resistor type air flow measuring device which is less likely to affect the output characteristics of the engine.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of a heating resistance type air flow measuring device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a resin flow regulating grid according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of an example of a heating resistance type air flow measuring device.

FIG. 4 is an enlarged cross-sectional view showing an example of a conventional resin rectifying grating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main air passage 2 Main air passage constituent member 3 Sub air passage 4 Sub air passage constituent member 5 Heating resistor 6 Temperature sensitive resistor 7 Electronic circuit 8 Module 9 Transistor 12 Resin rectifying grating 13 Grid portion 13a Front end portion 13b Rear end Part A Effective cross-sectional area of air passage F Flow direction of air flow H Separation of air flow S-type split surface T Separation vortex

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Chihiro Kobayashi 2520 Takaba, Hitachinaka-shi, Ibaraki F-term within the Automotive Equipment Group, Hitachi, Ltd. (Reference) 2F035 AA02 EA03 EA05 GA01

Claims (2)

[Claims] 1. A heating resistor type air flow measuring device provided with a rectifying grid formed by die-cut resin molding, wherein a thick-walled portion is provided at one end of the rectifying grid along a flow direction of the grid. Characterized in that the cross-sectional area of the air passage is gradually increased toward the downstream side in the rectification grid by locating the end of the heat flow upstream of the air flow. Resistor type air flow measurement device. 2. The heating resistor type air flow measuring device according to claim 1, wherein said one end is formed in a semicircular shape.