JPH05223609A - Air flowmeter - Google Patents

Abstract

PURPOSE:To achieve higher intake air measuring accuracy, a protection of a hot wire and a cold wire and higher radio wave resistance disturbing characteristic with a rectifier grid concerning an air flowmeter for an internal combustion engine. CONSTITUTION:A cylinder which has a cylindrical or polygonal sectional area covering a hot wire 1 and a cold wire 2 is so arranged to be molded integral with a body 4 or to contact an earth of an electronic circuit electrically. This enables the elimination of a rectifier grid provided separately at an outlet or inlet of introducing intake air and achieves an effect of reducing the unit cost with a reduction in the number of parts and a reduction in the manhour. Besides, an air flowmeter with excellent quality can be supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow meter equipped with an electronic circuit for detecting the intake air flow rate of an internal combustion engine,
Particularly, it relates to rectification of intake air and resistance to radio interference.

[0002]

2. Description of the Related Art In a conventional hot-wire type air flow meter, as described in Japanese Utility Model Application Laid-Open No. 57-84418, a rectifying grid is installed in an intake air introducing portion of a body forming a passage.

[0003]

However, in the above-mentioned prior art, it is necessary to mount the rectifying grid, which is installed upstream of the temperature-sensitive heating resistor, on the body forming the intake air passage. There is a problem that the cost increases due to the increase. An object of the present invention is to provide an air flow meter with high measurement accuracy and to supply an inexpensive air flow meter by improving the rectification effect of unstable intake air and supplying a uniform air flow to the temperature-sensitive heating resistor. To do.

Another object of the present invention is to prevent radio noise or radio waves transmitted from a radio from entering the temperature-sensitive heating resistor and causing an electronic circuit to malfunction.

[0005]

In order to achieve the above object, the temperature-sensitive heating resistor and its support are formed of a mesh tube formed of a conductive material having a cylindrical or polygonal cross-sectional area. Achieved by covering.

In particular, when the temperature-sensitive heating element is covered with a cylindrical or polygonal tube, it is electrically connected to the conductive portion of the body or the conductive portion of the module and, if necessary, further connected to the ground of the electronic circuit. This is achieved by making an electrical connection.

[0007]

When measuring the intake air flow rate of the internal combustion engine, it is important to supply a uniform air flow to the temperature-sensitive heating resistor in order to improve the measurement accuracy. However, when the intake air passes through a meandering duct, the air flow is eccentric or eccentric to produce a biased air flow, that is, an uneven air flow in the intake air passage of the body comes into contact with the heating temperature-sensitive resistor. In order to worsen the measurement accuracy of the intake air flow rate, the intake air flow is equalized and the measurement accuracy is improved by covering the intake air introduction part of the air flow meter and the area around the temperature-sensitive heating resistor with a rectifying grid such as a mesh. You can

Further, a rectifying grid such as a mesh formed of a conductive material that covers the temperature-sensitive heating resistor and its support is electrically connected to the conductive portion of the body or the conductive portion of the module. Thus, the resistance to radio interference can be improved. Further, grounding can improve the resistance to electromagnetic interference. This is because the inside of a cylinder having a cylindrical or polygonal cross-sectional area that covers the temperature-sensitive heat-generating resistor serves as a shield space for protecting the temperature-sensitive heat-generating resistor, and radio waves and radio waves transmitted by radio waves are rectified by the rectifying grid. This is because the shield space formed by can escape to the ground and prevent the propagating radio waves and stray radio waves from entering the electronic circuit from the temperature-sensitive heating resistor and malfunctioning.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a cross-sectional structural view of an air flow meter for measuring the air flow rate of an internal combustion engine. FIG. 2 is a view seen from the front direction of FIG. Reference numeral 1 is a hot wire formed by forming a platinum thin film on an alumina bobbin, laser-trimming it into a spiral shape, and coating the surface with a glass material. Reference numeral 2 is a temperature compensating resistor, which is a cold wire having the same resistance value as the hot wire 1. The hot wire 1 and the cold wire 2 are electrically connected to the electronic circuit 3.
The hot wire 1 and the cold wire 2 of this air flow meter are installed in the air passage of the body 4 formed by the air passage through which the intake air passes and the portion that houses the electronic circuit. Further, the electronic circuit 3 supplies an applied current for heating the hot wire 1 to a constant temperature. As for this heating temperature, the difference between the hot wire 1 and the intake air temperature is kept constant regardless of the amount of intake air, and the air temperature is corrected by the cold wire 2. Therefore, when the high flow rate flows in the intake air passage, a high current is passed, and when the low flow rate is passed, a low current is passed to keep the temperature difference between the hot wire 1 and the cold wire 2 constant. There is a monotonically increasing function relationship between the current flowing through the hot wire 1 and the intake air flow rate, and the intake air flow rate is measured by the above relationship.

FIG. 3 shows the structure of the rectifying grid 5 which covers the hot wire 1 and the cold wire 2. The rectifying grid 5 is a cylinder (a) or a cylinder (b) having a polygonal cross-sectional area,
(C) is formed of a conductive metal mesh. As shown in FIG. 5, the rectifying grid 5 is formed integrally with the body 4 at the time of injection molding using metal or plastic, or is formed by inserting the rectifying grid 5 into the molded body 4. According to this embodiment, the accuracy of measuring the intake air of the air flow meter is improved, and the hot wire 1 and the cold wire 2 are protected from blowback such as backfire.

FIG. 4 shows an embodiment for improving the resistance to radio interference. The structure is such that the ground of the electronic circuit 3 of the air flow meter shown in FIGS. 1 and 2 and the rectifying grid 5 are brought into electrical contact. For this electrical contact, the conductive lead 6 is fixed to the ground terminal of the electronic circuit 3 by welding or soldering. One of the rectifying grids 5 and the conductive leads 6 is connected by welding or a structure in which holes are formed in the rectifying grids 5 and the conductive leads 6 for screwing. In the above structure, even if the conductive lead 6 is not used, it is sufficiently effective to connect the rectifying grid 5 and the shield case 7 electrically by screwing or welding. Further, it is not necessary to use the metal lead 6 by integrally molding the body 4 and the rectifying grid 5 with conductive metal or conductive plastic. According to the present embodiment, there is an effect of preventing radio waves and propagating radio waves such as radio from entering the electronic circuit 3 through the hot wire 1 and the cold wire 2 and malfunctioning.

[0013]

According to the present invention, since the measurement accuracy of the intake air flow rate can be improved and the hot wire 1 and the cold wire 2 can be protected from the blowback such as backfire, the intake air passage can be provided above and downstream. The rectifying grids installed in each can be eliminated, and the cost can be reduced by reducing the number of parts and man-hours.

Further, since the resistance to electromagnetic interference can be improved, there is an effect that it is possible to provide a stable air flow meter of a quality which is not easily affected by propagating radio waves or stray radio waves.

[Brief description of drawings]

FIG. 1 is a side sectional view of an air flow meter of the present invention.

FIG. 2 is a front sectional view of the air flow meter of the present invention.

FIG. 3 is a structural diagram of a rectifying grid of the air flow meter of the present invention.

FIG. 4 is a diagram showing a method of electrically connecting a rectifying grid and a ground.

FIG. 5 is an enlarged view of a portion A of a rectifying grid mounting structure.

[Explanation of symbols]

1 ... Hot wire, 2 ... Cold wire, 3 ... Electronic circuit, 4 ... Body, 5 ... Rectifier grid, 6 ... Conductive lead, 7
... shield case, 8 ... support.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Igarashi 2477 Kashima Yatsu Kashima, Katsuta City, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd.

Claims (3)

[Claims] 1. A body and a module, which are installed in the air to form a temperature-sensitive heating resistor and an intake air passage, and the temperature-sensitive heating resistor are heated to a predetermined temperature, and the heating voltage is applied to the air flow rate. In an air flow meter having a drive circuit for converting into an output signal corresponding to the above, installed in an intake air passage of a module comprising the temperature-sensitive heating resistor and a drive circuit for converting the heating voltage thereof into an output signal. An air flow meter characterized in that only the temperature-sensitive heat generating resistor and its support are covered with a rectifying grid such as a mesh made of a conductive metal. 2. When the temperature-sensitive heating resistor and its support are covered with a rectifying grid such as a mesh formed of a conductive material in claim 1, the mesh formed of a conductive material is used for the conductive portion of the module. Or an air flow meter characterized by being electrically connected to a conductive portion of the body or electrically connected to the ground of an electronic circuit. 3. An air flow meter according to claim 1, wherein the temperature-sensitive heat generating resistor and its support are covered with a cylindrical or polygonal conductive tube.