JPH03257328A - Hot wire type air flowmeter - Google Patents

Abstract

PURPOSE:To prevent the detachment of a member or the lowering of anti-radio- fault characteristics due to vibration or heat stress by mounting an axial flow bypass passage constituting member on the upstream side of an air passage and using a conductive material as the material quality of the cover of a hot wire element holding bypass passage. CONSTITUTION:The cover 6 of a bypass passage is inserted in a main passage 1 on the upstream side of a body 5 and the holder 10 of a control module 8 is further inserted in the tubular part 16 of the cover 6 through the insertion hole 5a of the body 5 and the cover 6 is clamped to a bypass bridge 14 on the upstream side of the body 5 by two screws 7. Since the cover 6 and the screws 7 are pressed to the bridge by the air flowing through the passage 1 from the upstream part to the downstream part, the falling thereof is prevented. A cover 6A is formed from a conductive material and electrically connected to the metal base 11 of the module 8 through a holder sleeve 12 made of the conductive material in the same way. By this constitution, earth potential is held and a hot wire element 3 and an electricity-sensitive resistance element 4 are shielded from a radio wave.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a hot wire air flow meter for measuring the intake air flow rate of an internal combustion engine such as a gasoline engine, and particularly to a hot wire air flow meter for use in automobiles whose main body is made of synthetic resin. The present invention relates to a hot wire air flow meter suitable for measuring the intake air flow rate of a gasoline engine.

[Conventional technology]

In recent years, hot wire air flowmeters have been widely adopted for measuring the intake flow rate of automobile gasoline engines.
As described in the specification of No. 0846, there is an axial flow bypass passage type hot wire air flow meter.

In the hot wire air flow meter described in this specification, the bypass passage portion is configured as a bypass bridge portion having a bypass passage inlet, and this bypass bridge portion is formed integrally with the main body of the air flow meter. , the passage cover is installed by screwing it in from the downstream side of the airflow.

Note that related devices of this type include, for example, Japanese Patent Application Publication No. 63-55419 Japanese Unexamined Patent Publication No. 1991-91018 Japanese Unexamined Patent Publication No. 1-126513 Examples include those based on the following.

[Problem to be solved by the invention]

The above-mentioned conventional technology has a problem in that the member forming the bypass passage separates from the main body due to vibration, thermal expansion, etc. when it is attached to the engine and used. If the components were not taken into account and separated from the main body, there was a problem in that there was a risk of damage to the engine.

4- Furthermore, in the above-mentioned conventional technology, sufficient consideration was not given to the use of synthetic resin for the main body material, and there was a problem in that the use of synthetic resin reduced the radio wave interference resistance characteristics.

An object of the present invention is to provide a hot wire air flow meter in which the members constituting the bypass passage do not separate from the main body even due to vibration or thermal expansion, and there is no risk of engine damage. be.

Another object of the present invention is to provide a hot wire type air flow meter that can always accurately measure air flow rate without the risk of deterioration in electromagnetic interference resistance even when the main body is made of synthetic resin.

[Means for Solving the Problems] In order to achieve the above object, the present invention is such that the member constituting the axial flow bypass passage is installed from the upstream side of the air passage, and Even when synthetic resin is used, the bypass passage cover that holds the hot wire element is made of a conductive material.

[Effect]

Since the bypass passage cover constituting the axial flow bypass passage is installed from the upstream side of the air passage, the air flow in the air passage causes a force to be applied to the bypass passage cover in a direction that presses it against the mounting surface. There is no possibility that the bypass passage cover will fall off from the main body.

In addition, even if the main body is made of synthetic resin, the material of the bypass passage cover that holds the hot wire element is conductive, so by grounding it, a radio wave shielding function can be obtained and the decline in radio interference resistance can be suppressed. .

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hot wire air flow meter according to the present invention will be explained in detail below using illustrated embodiments.

1 to 3 show an embodiment of the present invention, in which FIG. 1 is an exploded perspective view, FIG. 2 is a vertical sectional view, and FIG. 3 is a plan view. As shown in these figures, The hot-wire air flow meter according to this embodiment is broadly divided into a body 5 having a main passage 1 and a control module 8 that generates a flow rate detection signal.

The main passage 1 constitutes a part of the intake passage of the engine, through which the air taken in by the engine flows in the direction of the arrow in FIG. Therefore, in FIGS. 1 and 2, the upper side of the figure is the upstream side of the air passage, and FIG. 3 is a view seen from the upstream side.

Reference numeral 2 denotes a bypass passage, which is formed by a bypass passage cover 6, whose population 2a opens toward the upstream side at approximately the center of the main passage 1, and air flowing in from here is passed through a bypass bridge 14 integrated into the body 5. The formed passage divides into both sides at the center of the downstream side, and the main passage 1 is opened from the outlets 14a and 14b that open near the periphery of the main passage 1.
It is configured to rejoin the

3 is a hot wire element, and 4 is a temperature sensitive resistance element, which extend from the control module 8 in such a way that they are positioned in the bypass passage 2, as is particularly clear from FIGS. 2 and 3. It is attached to the tip of the holder 10.

The amount of air that is 1 to 3% of the amount of air flowing through the main passage 1 flows through the bypass passage 2, and this air flow rate is detected to determine the total air flow rate passing through the main passage 1, that is, the intake flow rate of the engine. It is designed to be measured.

16 is a tubular portion formed in the bypass passage cover 6;
In particular, as is clear from FIG. 1, the holder 10 of the control module 8 is inserted through an insertion hole 5a formed in the body 5.

Therefore, in this embodiment, as shown in FIG.
The bypass passage cover 6 is inserted into the main passage 1 from the upstream side of the body 5, and the holder 10 of the control module 8 is further inserted into the tubular portion 16 of the bypass passage cover 6 through the insertion hole 5a of the body 5. However, by tightening the bypass passage cover 6 to the bypass bridge 14 using the two screws 7, also from the upstream side, the bypass passage 2 is assembled, and as a result, the bypass passage cover 6 and the screws are tightened. 7 are all subjected to a force that presses them against the bypass bridge 14 by the air flowing from upstream to downstream in the main passage 1, and in the unlikely event that they fall into the main passage 1. Furthermore, the holder 10 is inserted into the insertion hole 5a inside the tubular portion 16.
Since the bypass passage cover 6 is inserted through the can be prevented from falling.

Here, the control module 8 is mounted with screws after its metal base 11 is positioned by the mounting seat 5b of the body 5, but at this time, the insertion hole 5a has a
□As shown in FIG. 2, a ○ ring 9 is provided, which provides a predetermined air sealing property.

Next, FIG. 4 shows another embodiment of the present invention, in which:
6A is a bypass passage cover made of a conductive material, for example a metal material such as aluminum, 12 is a holder sleeve also made of a conductive material, and the others are the embodiments shown in FIGS. 1 to 3. However, Miboday 5 is made of suitable synthetic resin materials such as PBT (polybutylene terephthanol), PET (polyethylene
It is made from plastic materials such as terephthanol.

Making hot-wire air flowmeters made of synthetic resin is an extremely effective means of reducing weight and cost, but on the other hand, it has the problem of significantly reducing the radio interference resistance of the flowmeter. be. In other words, if the body 5 etc. are made of synthetic resin, the shielding function against radio waves will disappear,
The hot wire elements and heat-sensitive resistance elements present in the bypass passage function as antennas, picking up radio waves and causing malfunctions.

Characteristic 7a in Figure 7 shows the results of measuring the radio interference resistance of a hot-wire air flowmeter made of synthetic resin using the TEM CELL method.
It can be seen that it has decreased to below.

In general, it is known that engine control-related electronic devices installed in automobiles malfunction due to the influence of radio waves when the voltage drops below approximately 20 V/m, causing problems such as engine stoppage and runaway.

According to the embodiment of the lever according to FIG. 4, however, the bypass channel cover 6A is made of an electrically conductive material, which is connected to the control module 8 via a holder sleeve 12 also made of an electrically conductive material. Since they are electrically connected to the metal base 11 and are kept at ground potential as a result, the hot wire element 3 and the heat sensitive resistance element 4 are connected to the bypass passage cover 6.
Since radio waves are sufficiently shielded by A, even if all other parts such as the body 5 are made of synthetic resin, as shown in characteristic 7b in FIG.
An electric field strength of V/m or more can be obtained, and sufficient electromagnetic interference resistance can be reliably provided.

Next, FIG. 5 shows yet another embodiment of the present invention, in which a portion of the tubular portion 16 of the bypass passage cover 6 (the portion indicated by 16a in FIG. 1) is removed to control the The holder 10 of the module 8 is directly exposed to the air flow in the main passage 1. In this case, a ring 13 is provided at the tip of the holder 10, and a portion of the tubular portion 16 described above is removed. This is to reliably prevent air leakage that could otherwise occur.

According to the embodiment shown in FIG. 5, since the holder 10 is sufficiently cooled by the air flow, the heat-sensitive resistance element 4 is not affected by the heat transmitted from the holder 10, and the air is reliably cooled. It is possible to perform compensation according to the temperature of the flow rate, and it is possible to easily obtain accurate flow rate measurement.

To explain this below, first, FIG. 8 shows the temperature characteristics of the inner wall of the main passage of the hot-wire air flow meter, but if a portion of the tubular portion 16 described above had not been removed, then The temperature of the inner wall of the main passage is conducted to the heat-sensitive resistance element 4 through the holder 10, and as a result,
In this case, as shown in characteristic 8a in Fig. 8, when the air flow rate is Q, the measurement error ΔQ/Q becomes a fairly large value of about +8% in the measurement region around Q = 10 to zoKg/h. , when this is installed in a car, driving stability will be significantly reduced, especially when starting the engine.

According to the embodiment of FIG. 5, the holder 10
Since the temperature of is maintained at the temperature of the air in the main passage 1, its thermal influence on the heat-sensitive resistance element 4 is completely eliminated, and as shown in characteristic 8b of FIG. 8, the measurement error ΔQ /
Q- It can be suppressed to about 12%, and as mentioned above,
Accurate flow rate measurement can be easily obtained, and the engine can always be accurately and stably controlled.

Further, FIG. 6 also shows an embodiment of the present invention, and in this embodiment, a circle ring 15 is interposed at the joint of the bypass passage cover 6 to the bypass bridge 14, so that sealing performance between these members can be easily obtained. The other configurations are the same as the embodiment described in FIGS. 1 to 5.

According to this embodiment, even if the finishing accuracy of the joint between the bypass passage cover 6 and the bypass bridge 14 is lowered, reliable sealing performance can be easily obtained, which is advantageous for use with synthetic resin. .

Furthermore, instead of the O-ring 15 in the embodiment of FIG. 6, a suitable adhesive may be used to provide a seal between the bypass passage cover 6 and the bypass bridge 14. At this time, if the adhesive used can be expected to have a certain level of reliability, the mounting screws 7 shown in Figures 1 and 3 can be omitted and the assembly can be performed using only the adhesive. (This allows further cost reduction.

In addition, at this time, in the example made of synthetic resin,
The above-mentioned bypass passage cover 6 and bypass bridge 14
Needless to say, a thermo-pressure welding method or an ultrasonic welding method may be used for assembly.

〔Effect of the invention〕

According to the present invention, the members constituting the axial flow bypass passage are
Since it is installed from the upstream side of the air passage, there is no chance of parts falling off due to vibration or thermal stress, and damage to the engine can be reliably avoided, and the electromagnetic interference resistance characteristics can easily be reduced due to the use of synthetic resin. Because it can be suppressed to
A highly accurate hot wire air flow meter can be provided at low cost.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view showing an embodiment of a hot wire air flowmeter according to the present invention, Fig. 2 is a longitudinal sectional view, Fig. 3 is a plan view, and Figs. 4, 5, and 6 are respectively A partial sectional view showing another embodiment of the present invention, FIG. 7 is a characteristic diagram showing radio wave interference resistance,
FIG. 8 is a characteristic diagram showing a flow rate measurement error due to temperature. 1... Main passage, 2... Bypass passage, 3... Heat wire element, 4... Heat sensitive resistance element, 5... Body, 6...Bypass passage cover 7...Mounting screws, 8...
... Control module, 9.13.15 ... O-ring, 10 ... Holder 11 ... Metal base, 12 ... Holder sleeve, 14.
... Bypass bridge, 16 ... Tubular part.

Claims (1)

[Claims] 1. In an axial bypass type hot wire air flow meter in which a hot wire detection element is installed in a bypass passage arranged in the main air passage, a A bypass bridge member having a mounting surface facing upstream is provided, and a bypass passage cover member constituting the bypass passage is inserted into the mounting surface of the bypass bridge member from the upstream side of the main air passage in the air flow direction. A hot wire air flowmeter characterized in that it is installed in a mounted manner. 2. In the invention of claim 1, the bypass passage cover member includes a bypass passage inlet opening opening on the upstream side in the air flow direction, and a bypass passage inlet opening of the main air passage for inserting the holder member of the control module. A hot wire air flowmeter characterized by having a tubular portion opening toward an inner wall surface. 3. The hot wire according to claim 1, wherein the bypass passage cover member is attached to the bypass bridge member by a mounting screw screwed into the bypass bridge member from an upstream side in the air flow direction. type air flow meter. 4. In the invention of claim 2, the holder member is configured to be inserted into the tubular part of the bypass passage cover member from outside the wall part of the air passage through a hole formed in the wall part. A hot wire air flowmeter characterized by: 5. The hot wire air flow meter according to claim 1, wherein at least the bypass passage cover member is made of a conductive material, and the cover member is maintained at a ground potential. 6. The hot wire air flow meter according to claim 5, wherein the bypass passage cover member is electrically connected to the conductive base of the control module. 7. In the invention as set forth in claim 6, the electrical connection between the bypass passage cover member and the conductive base of the control module is provided by a metallic conductor fitted into a hole formed in the wall surface of the air passage. A hot wire air flowmeter characterized in that it is configured to be provided by a holder sleeve. 8. In the invention according to claim 4, at least a portion of the tubular portion of the bypass passage cover member is removed, and at least a portion of the holder member is directly exposed to the air flow in the main air passage. A hot wire air flowmeter featuring the following. 9. The hot wire air flow meter according to claim 1, wherein the sealing function at the attachment portion of the bypass passage cover member to the bypass bridge member is provided by an O-ring. 10. The hot-wire air flowmeter according to claim 1, wherein the sealing function at the attachment portion of the bypass passage cover member to the bypass bridge member is provided by applying an adhesive. 11. In the invention of claim 1, the bypass passage cover member and the bypass bridge member are formed of a predetermined synthetic resin material, and the attachment of the bypass passage cover member to the bypass bridge member is performed by thermo-pressure welding and ultrasonic bonding. A hot wire air flowmeter characterized in that at least one of the following is provided.