JPH0477856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a heat generating resistance type air flow meter, and more particularly to a heat generating resistance type air flow meter for measuring the intake air flow rate of an internal combustion engine.

[Background of the invention]

A heating resistor type air flow meter has been proposed that measures the air flow rate flowing through the bypass passage by installing a heating resistor and an air temperature measuring resistor in a bypass passage provided in parallel with the main passage ( For example, Japanese Patent Application Laid-open No. 135916/1983).

This type of heating resistance type air flow meter is equipped with a heating resistor that measures the flow rate, and if the temperature of the body that forms part of the intake air passage is different from the intake air temperature, the intake air amount can be detected and measured. It is known from experience that errors occur. As a method to reduce this measurement error, as shown in Japanese Patent Application Laid-open No. 56-108908 and Japanese Patent Application Laid-open No. 56-18721, the heating resistor and the air temperature measuring resistor are supported in the same shape and length. It is known to be supported by pins and placed at symmetrical positions on the same plane perpendicular to the air flow.

However, if the heating resistor and the air temperature measuring resistor are placed close to each other, the air temperature measuring resistor may be heated by the radiant heat of the heating resistor, causing measurement errors, or conversely, the air temperature measuring resistor may cause measurement errors. The disturbed airflow hits the heating resistor, causing a pulsating flow without a stable output. This causes a problem that so-called signal output noise increases.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heating resistance type air flow meter that can accurately measure mass air flow rate even when the temperature of a body constituting an intake air passage and the intake air temperature are different. It is in.

The gist of the present invention is as follows.

That is, the present invention provides a heat generating resistor for measuring air flow rate and an air temperature measuring resistor in a sub passage which has a passage cross-sectional area smaller than that of the main passage and into which a portion of the air flowing into the main passage flows. In addition, in the heating resistance type air flowmeter, the air temperature measuring resistor is arranged to be shifted to the outside in the radial direction of the sub passage with respect to the heating resistor, in which the air temperature measuring resistor is mounted in the sub passage. By making the diameter of the portion where the heating resistor is attached larger than the diameter of the portion where the heating resistor is attached, and controlling the thermal conductivity between the body, the air temperature measuring resistor, and the heating resistor, the intake air temperature can be adjusted. The aim is to accurately measure the mass air flow rate even when the temperatures of the air intake air passage and the body that make up the intake air passage differ.

As described above, the heating resistor type air flow meter according to the present invention maintains a constant temperature difference between the heating resistor and the air, and measures the mass air flow rate from the amount of heat released, without being affected by the temperature of the body. In order to accurately measure the mass air flow rate, it is necessary to ensure that the amount of heat radiation described above is not affected by the temperature of the body. Therefore, by configuring as described above, the thermal conductivity between the body and the air temperature measuring resistor and the heating resistor can be controlled, and the influence of the body temperature when the intake air temperature and the body temperature are different. is given equally to the heating resistor and the air temperature measuring resistor, so that the amount of heat released from the heating resistor is not affected by the body temperature, and the mass air flow rate can be measured with high accuracy.

Further, since the sub-passage is formed to have a large diameter at the portion where the air temperature measuring resistor is attached, fluid resistance within the sub-passage is reduced, and a large amount of air can be flowed into the sub-passage. Then, when the air flowing into the sub-passage flows through the small-diameter portion where the heating resistor is attached, the flow velocity increases and the flow velocity distribution becomes stable. If the flow rate is measured using a heating resistor for a large amount of air whose flow velocity is stabilized in this way, it becomes possible to measure the air flow rate with even higher accuracy.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 1 shows an embodiment of the present invention, and FIG. 2 is a plan view of FIG. 1.

In the figure, the body 50 includes a main passage 51
and a bypass passage 52 are provided. This bypass passage 52 includes a straight pipe portion 53 and a tapered portion 58.
The air that has passed through the straight pipe section 54 having a larger diameter than the straight pipe section 53 and the bypass passage 52 is transferred to the main passage 5.
It is comprised of a bending part 55 for returning to 1, a ring part 56, and an outlet part 57. The heating resistor 1 is supported within the straight tube section 53 by support pins 5, and the air temperature measuring resistor 2 is supported within the straight tube section 54 by support pins 6. The heating resistor 1 that measures the air flow rate and the air temperature measuring resistor 2 use the same element, and as shown in Figure 3, a platinum wire 102 is attached to an alumina bobbin 101 with a diameter of 0.5 mm and a length of 2 mm. After winding the wire and welding both ends to the lead wire 103, a thin glass coating 104 is applied to the surface.These are a main passage 51 through which most of the intake air passes, and a bypass passage through which a part of the intake air is diverted. The bypass passage 52 of the body 50 has a bypass passage 52 .

Here, the temperature of the heating resistor 1 is maintained by a constant value higher than the temperature of the air temperature measuring resistor 2 by a drive circuit 3 shown in FIG.

In addition, a heating resistor 1 and an air temperature measuring resistor 2
As shown in FIG. 1, leads 103 are welded to the tips of support pins 5 and 6 that are integrally insert-molded into the case 4 of the drive circuit 3 molded from synthetic resin, and are installed in the bypass passage 52. ing. In this way, the heating resistor 1 and the air temperature measuring resistor 2 are electrically connected to the drive circuit 3 by the support pins 5 and 6.

Intake air flows into the body 50 from the direction of arrow P1 through an air cleaner (not shown), and is divided into a main passage 51 and a bypass passage 52. The air branched into the bypass passage 52 passes through the straight pipe section 53 where the heating resistor 1 is installed, the straight pipe section 54 where the air temperature measuring resistor 2 is installed, and reaches the bent section 55.
The main passage 5 passes through the ring portion 56 as shown in the figure.
The outlet section 57 opened at the narrowest part of the main passage 5
It merges with the air of 1.

Straight pipe portions 53 and 54 forming the bypass passage 52
The cross-sectional area of each of the bent portion 55, the ring portion 56, and the outlet portion 57 is the smallest in the straight pipe portion 53 where the heating resistor 1 is disposed.

Further, a taper 58 is provided at the connecting portion between the straight pipe portion 53 and the straight pipe portion 54 so as not to cause disturbance in the air flow, and the shape of the portion forming the passage wall of the case 4 is also the same.

Here, the heating resistor 1 is installed upstream of the air temperature measuring resistor 2 in order to apply an undisturbed air flow.

Further, as shown in FIG. 6, since the air flow heated by the heat generating resistor 1 passes through the downstream part 59 of the heat generating resistor 1, the air temperature measuring resistor 2 is connected to the downstream part 59 of the heat generating resistor 1 from the part through which this heated air flow passes. It is staggered and installed.

FIG. 8 shows a conventionally known technique that satisfies the condition of avoiding the influence of the heated air flow of the heating resistor 1 described above. That is,
Since the length L _H from the heating resistor 1 to the case 4 that forms part of the wall surface of the bypass passage 52 is different from the length L C from the air temperature measuring resistor 2 to the case 4, the length L _C from the heating resistor 1 to the case 4 is different. 4 or case 4
The heat conduction coefficient λ _H between the case 4 and the body 50 to which it is attached differs, and the heat conduction coefficient λ _C between the air temperature measuring resistor and the case 4 differs, and the influence of the temperature of the body 50 differs. Therefore, if the temperature of the intake air differs from the temperature of the body 50, the difference in heat conduction directly causes a measurement error.

In contrast, in the embodiment of the present invention, the cross-sectional area of the passage 54 in the part where the air temperature measuring resistor 2 is installed is made larger than the cross-section of the passage 53 in the part where the heating resistor 1 is installed. Heat generating resistor 1
With the air temperature measuring resistor 2 installed in a position where the heated air does not pass through, the length L _H between the heating resistor 1 and the case 4, and the length L from the air temperature measuring resistor 2 to the case 4. _C is made equal.

Therefore, the thermal conductivity coefficient λ _H between the heating resistor 1 and the case 4 and the thermal conductive coefficient λ _C between the air temperature measuring resistor 2 and the case 4 are made almost the same.

The influence on the measurement accuracy of the temperature of the body 50 is as follows.
_The dimensions L _{H and}
Making L _C the same does not necessarily minimize the error, and the details are determined by experiments including air flow _.
It is necessary to determine the relationship between L _C and L C and the relationship between passages 53 and 54.

Another cause of measurement errors when the body temperature and air temperature are different is that the body temperature heats or cools the air passing through the bypass passage, causing it to differ from the air temperature in the main passage.

This will be explained below using an example in which the temperature of the body is higher than the intake air.

The relationship between the air flow velocities in the main passage 51 and the bypass passage 52 is as follows.

Main passage ΔP/ρ _M = C _M U _M ² /2g ...(1) Bypass passage ΔP/ρ _B = C _B U _B ² /2g ...(2) From (1) and (2) Here, ΔP: Pressure difference between the inlet 60 and outlet 57 of the bypass passage 52 U _M , U _B : Flow velocity of the main passage 51 and the bypass passage 52 C _M , C _B : Flow coefficient of the main passage 51 and the bypass passage 52 ρ _M , ρ _B : Main passage 51, bypass passage 5
Air density of 2 When the temperature of the body 50 is higher than the intake air temperature, the temperature of the bypass air flow becomes higher than the temperature of the main air flow because the ratio of the body wall area facing the bypass passage to the cross-sectional area of the passage is large. easy. In this case, in equation (3), ρ _B becomes small and C _B becomes large. As a result, the mass flow rate (ρ _B ·U _B /ρ _M · _UM ) in the main passage 51 and the bypass passage 52 becomes small, resulting in a measurement error on the negative side.

Here, in order to reduce this amount of change, it is necessary to reduce the body wall area facing the bypass passage with respect to the cross-sectional area of the bypass passage 52, that is, to increase the area of the bypass passage to make it difficult for the air in the bypass to be heated by the body. Bye. Further, it is sufficient to reduce the change in the flow rate coefficient C _B due to the temperature of the bypass passage. On the other hand, increasing the cross-sectional area of the entire bypass passage 52 has an effect on the above two points, but the flow velocity at the heating resistor 1 portion at the same flow rate decreases as the cross-sectional area increases, resulting in a decrease in detection sensitivity. do. There are problems such as the smaller the flow velocity, the greater the influence of the body wall temperature on the heating resistor.

On the other hand, in the embodiment according to the present invention,
Part where heating resistor 1 is installed (straight pipe part 53)
With respect to the cross-sectional area of
6. Since the cross-sectional area of the outlet portion 57 is increased,
It is possible to reduce the decrease in ρ _B and the increase in C _B without reducing the flow velocity of the air flow passing through the heating resistor 1, and it is possible to improve measurement accuracy when the intake air temperature and the body temperature are different. .

Note that C _B is the flow coefficient of the entire bypass passage,
If only the cross-sectional area of the heating resistor 1 placement part (straight pipe part 53) is made smaller and the other parts made larger, there will be almost no difference compared to when the whole is made larger, and the flow velocity will be improved compared to before enlarging 54 to 57.

FIG. 9 shows the results of an experiment in which the embodiment of the present invention was applied and the intake air temperature and body temperature were considered. In the figure, A indicates the body temperature, and B indicates the intake air temperature.

As shown in Figure 9C, conventional heating resistance type air flowmeters cause significant measurement errors when the intake air flow rate is low, that is, when starting at low speed or idling, making it impossible to obtain stable engine rotation. . In contrast, according to the embodiment of the present invention, the measurement error could be significantly reduced as shown in FIG. 9D. Therefore, it is possible to obtain an appropriate engine speed without causing unevenness in the engine speed.

Another embodiment of the invention is shown in FIG. This embodiment differs from the embodiment illustrated in FIG.
The heating resistor 1 is provided on the downstream side, the air temperature measuring resistor 2 is provided on the upstream side, and the air temperature measuring resistor 2 is installed from the straight pipe section 154 of the bypass passage 52 to which the heating resistor 1 is installed. This is because the diameter of the straight pipe portion 53 of the bypass passage 52 is increased.

That is, the bypass passage 52 is connected to the straight pipe section 153.
, a taper 158 , a straight pipe section 154 , a bent section 155 for returning air that has passed through the bypass passage 52 to the main passage 51 , a ring section 156 , and an outlet section 157 . This straight pipe portion 153 is formed to have a larger diameter than the straight pipe portion 154. Further, the heating resistor 1 is supported within the straight pipe portion 154 by the support pin 6, and the straight pipe portion 153
An air temperature measuring resistor 2 is supported therein by a support pin 5.

Intake air flows into the body 50 from the direction of arrow P1 through an air cleaner (not shown), and is divided into a main passage 51 and a bypass passage 52. The air branched into the bypass passage 52 passes through the straight pipe section 153 where the air temperature measuring resistor 2 is installed, and the heating resistor 1.
The bent portion 155 passes through the straight pipe portion 154 where the
The main passage 51 passes through the ring portion 156.
The outlet section 157 opens at the narrowest part of the main passage 5.
It merges with the air of 1. The cross-sectional area of each of the straight pipe portions 153, 154, bent portion 155, ring portion 156, and outlet portion 157 constituting the bypass passage 52 is the smallest in the straight pipe portion 154 where the heating resistor 1 is disposed.

Further, a taper 158 is provided at the connecting portion between the straight pipe portion 153 and the straight pipe portion 154 so as not to cause disturbance in the air flow, and the shape of the portion constituting the passage wall of the case 4 is also the same. Although the air temperature measuring resistor 2 is provided upstream of the heating resistor 1, the straight pipe section 153 to which the air temperature measuring resistor 2 is mounted is
Since it is formed to have a larger diameter than the straight pipe section 154 to which the heating resistor 1 is attached, there is no possibility that the air temperature measuring resistor 2 will cause turbulence in the air flow and the heating resistor 1 will be affected. An air temperature measuring resistor 2 is provided at a position where the air temperature is not present. By doing so, the same effect as the embodiment shown in FIG. 1 can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to accurately measure the mass air flow rate even when the temperature of the body constituting the intake air passage and the intake air temperature are different.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, FIG. 3 is an overall configuration diagram of a resistor, FIG. 4 is a control circuit diagram, and FIG. Figure-
6 is a partially enlarged view of the resistor mounting portion in FIG. 1, FIG. 7 is a plan view of FIG. 6, and FIG. 8 is a partially enlarged view of the conventional resistor mounting portion. FIG. 9 is a measurement diagram of flow rate errors between the conventional example and this embodiment, and FIG. 10 is a sectional view showing another embodiment of the present invention. 1... Heat generating resistor, 2... Air temperature measuring resistor, 5
1...Main passage, 52...Bypass passage, 53,5
4,153,154...straight pipe section, 55,155...bent section, 56,156...ring section, 57,157...
Exit part.

Claims (1)

[Claims] 1. A heat generating resistor for measuring air flow rate and an air temperature measuring resistor are installed in a sub passage which has a passage cross-sectional area smaller than that of the main passage and into which a part of the air flowing into the main passage flows. and the air temperature measuring resistor is arranged to be shifted to the outside in the radial direction of the sub passage with respect to the heating resistor, 1. A heat generating resistor type air flow meter, characterized in that a diameter of a portion to which the heat generating resistor is attached is larger than a diameter of a portion to which the heat generating resistor is attached.