JPS6134422A - Hot wire type air flowmeter - Google Patents

Abstract

PURPOSE:To improve accuracy of an air flowmeter, by making a bypass, in which an air temperature measuring resistor is arranged, larger than a bypass, in which a heating resistor is arranged, and equalizing the effect of the temperature of a body on both resistors. CONSTITUTION:In a body 50, a main path 51 and a bypass 52 are provided. The bypass 52 is constituted of a straight tube part 53, a tapered part 58, a straight tube part 54, whose diameter is larger than that of the straight tube part 53, and a bent part 55. In the straight tube part 53, a heating resistor 1 is supported by a supporting pin 5. In the straight tube part 54, an air temperature measuring resistor 2 is supported by a supporting pin 6. The resistor 2 is deviated from a part, where the airflow heated by a resistor 1 passes. Since the straight tube part 54 is thicker than the straight tube part 53, the distance between the resistor 1 and the body is made equal to the distance between the resistor 2 and the body. Thus the effect of the body temperature is made equal.

Description

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

[Background of the invention]

If a heating resistor for measuring the flow rate is installed and the temperature of the body that forms part of the intake air passage is different from the intake air temperature, the procedure for detecting and measuring the amount of intake air, - Fushi 1 -
JJB11bL-1F11□F ν^N1 Support the heating resistor and the air temperature measuring resistor with support pins of the same shape and length, and place them on the same plane perpendicular to the air flow. It is known that the elements are placed in symmetrical positions. ' 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 be disturbed by the air temperature measuring resistor. When the airflow hits the heating resistor, it does not provide a stable output and causes pulsating current. This causes a problem that the number of so-called signal output nozzles increases.

For this reason, there is a problem in that it is necessary to increase the cross-sectional area of the passage where the heating resistor is disposed, and the flowmeter becomes large.

[Purpose of the invention]

An object of the present invention is to accurately measure the mass air flow (.) even when the temperature of the body constituting the suction air vibration passage and the temperature of the intake air are different. Our purpose is to provide flowmeters.

The gist of the present invention is as follows.

In other words, the passage cross section of the portion of the bypass passage where the air temperature measuring resistor is placed is made larger than the passage cross section where the heating resistor for measuring the flow rate is placed, so that the mounting surface of the support for the air temperature measuring resistor and the passage are made larger. By making the distance from the center larger than the distance between the mounting surface of the support of the heating resistor and the center of the passage, and controlling the thermal conductivity between the body, the air temperature measuring resistor, and the heating resistor, The aim is to accurately measure the mass air flow rate even when the temperature of the intake air and the temperature of the body forming the intake air passage are different.

In this way, the hot wire 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 heat radiation amount, and can accurately measure the mass air flow rate without being affected by the body temperature. In order to measure the mass air flow rate, it is necessary to ensure that the above-mentioned amount of heat radiation is not affected by the temperature of the body. Therefore, the passage cross section of the part of the bypass passage where the air temperature measuring resistor is placed is parallel to the part where the heating resistor for measuring the flow rate is placed, and the mounting surface of the support of the air temperature measuring resistor is Thermal conductivity between the body and the air temperature measuring resistor and the heating resistor can be controlled by increasing the distance between the center of the passage and the heating resistor: the mounting surface of the support and the center of the passage. , when the intake air temperature and the body temperature are different, the influence of the body temperature is applied 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; This makes it possible to measure the mass air flow rate with high 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 5.1.
A bypass passage 52 is provided. This IPA passage 52 has a straight pipe section 53 and a Q/<58
', a straight pipe part 54 having a larger diameter than the straight pipe part 53, a 19 part 55 for returning the air that has passed through the bypass passage 52 to the main passage 51, a ring part 56, and an outlet part 52. There is. The heating resistor 1 is supported within the straight pipe portion 53 by support pins 5, and the air temperature measuring resistor 2 is supported within the straight pipe portion 54 by support pins 6. Using the heating resistor 1 for measuring the air flow rate and the air temperature measuring resistor or the same element, a platinum wire is attached to an alumina bobbin 101 with a diameter of 0.5 m and a length of 2 m, as shown in Fig. 3. 102 is wound, both ends of which are welded to lead wires 103, and then a thin glass coating 104 is applied to the surface. It is installed in a bypass passage 52 of a body 50 having 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.

Furthermore, as shown in FIG. 1, the heating resistor 1 and the air temperature measuring resistor 2 are connected to the tips of support pins 5 and 6 that are integrally insert-molded into the drive circuit 30 case 4, which is molded from synthetic resin, respectively. A lead 103 is welded to the bypass passage 52 and installed in the bypass passage 52. 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 5.6.

The intake air passes through an air cleaner (not shown) as indicated by arrow P1.
It flows into the body 50 from this direction and is divided into a main passage 51 and a bypass passage 52. The air branched into the bypass passage 52 passes through a straight pipe section 53 in which the heat generating resistor 1 is installed and a straight pipe section 54 in which the air temperature measuring resistor 2 is installed, and then flows into 19 sections 55.
Finally, as shown in FIG. 5', the air in the main passage 51 is flushed out through the ring part 56 and at the outlet part 57 which opens at the narrowest part of the main passage 51.

Straight pipe portion 53, 54 curved υ portion 5 constituting the bypass passage 52
5. The cross-sectional area of 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.

In addition, a taper 58 is provided at the connecting part between the straight pipe part 53 and the straight pipe part 54 so as not to cause turbulence in the air flow.
The shapes of the parts constituting the 0 passage wall are also the same.

Here, the heating resistor 1 is installed upstream of the resistor 2 for measuring an air temperature of 7 degrees 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 above-mentioned condition of avoiding the influence of the heated air liquid on the heating resistor 1. That is, since the length Lss from the heating resistor 1 to the case 4 forming a part of the wall surface of the bypass passage 52 is different from the length Lc from the air temperature measuring resistor 2 to the case 4, 4, that is, the heat conduction coefficient λH between the body 5o to which the case 4 is attached and the heat conduction coefficient λC between the air temperature measuring resistor and the case 4 are different, and the influence of the temperature on the body 50 is different. 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. When the air temperature measuring resistor 2 is installed in a position where the air heated by the body L does not pass through, the length Lm between the heating resistor 1 and the case 4 and the length from the air temperature measuring resistor 2 to the case 4 are determined. Lc is made equal.

Therefore, the thermal conductivity coefficient λH between the heating resistor 1 and the case 4 and the thermal conductivity coefficient λC 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 determined not only by the thermal conductivity coefficients λ and λC, but also by the amount of heat radiated from the support bin 5°6 into the air.

Making LH and Lc the same does not necessarily minimize the error, and the details are based on experiments including air flow.
It is necessary to determine the relationship between c and the passages 53 and 54.

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

This will be explained below, taking as an example a case where the temperature of the body is higher than that of the intake air.

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

Here, ΔP: Inlet 60 and outlet 57 of the bypass passage 52
Pressure difference UM, Us: main passage 51, bypass passage 52
Flow velocity CM, C1: Flow coefficient ρM of the main passage 51 and bypass passage 52, ρ11 = Air density of the main passage 51 and bypass passage 52 If the temperature of the body 50 is higher than the intake air temperature, the temperature of the bypass air flow is Compared to the temperature of the main airflow, the temperature tends to be high because the ratio of the body wall area facing the bypass passage to the cross-sectional area of the passage is large.

In this case, in (8) 2, ρB is small and CI is large. As a result, the main passage 51 and the bypass passage 5
When the mass flow rate ratio (ρ1·Ul/ρMllUM) of 2 is small, a measurement error on the negative side occurs.

Here, in order to reduce this amount of change, the bypass passage 5
Facing the bypass passage for a cross-sectional area of 2.

What is necessary is to reduce the body wall area, that is, increase the area of the bypass passage to make it difficult for the bypass air to be heated by the body. Further, it is sufficient to reduce the change in the flow rate coefficient CJI due to the temperature of the bypass passage. On the other hand, increasing the cross-sectional area of the bypass passage 52 as a whole has an effect on the above two points, but the flow velocity of the generating resistor 1 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, the cross-sectional area of the part (straight pipe part 53) where the heating resistor 1 is installed is different from that of the other part constituting the bypass passage 52, the straight pipe part 54.
Since the cross-sectional areas of the 19 part 55, the ring part 56, and the outlet part 57 are made large, it is possible to reduce the decrease in ρ magazine and the increase in CI without reducing the flow velocity of the air flow passing through the heating resistor 1. This can improve measurement accuracy when the intake air temperature and body temperature are different.

Note that C is the flow coefficient of the entire bypass passage, and only the section where the heating resistor 1 is placed (straight pipe section 53) has a small cross-sectional area.
If you make the other parts larger, there will be almost no difference compared to making the whole part larger, and the flow velocity will improve before you enlarge 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 i indicates the intake air temperature.

As shown in Figure 9C, conventional hot-wire air flowmeters cause significant measurement errors when the intake air flow rate is low, that is, at low-speed starting 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 Figure 9. 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 shown in FIG. 1 in that the heating resistor 1 is provided on the downstream side, the air temperature measuring resistor 2 is provided on the upstream side,
Straight pipe section 5 of bypass passage 52 to which heating resistor 1 is attached
4, the relationship between the straight pipe portion 53 of the bypass passage 52 to which the air temperature measuring resistor 2 is mounted is increased.

That is, the bypass passage 52 includes the straight pipe section 153, the taper 158, the straight pipe section 154, and the bypass
19 part 155 for returning the air that has passed through the passage 52 to the main passage 51, a ring part 156, and an outlet part 15.
2. This straight pipe portion 153 is formed to have a larger diameter than the straight pipe portion 154. Also, the straight pipe part 5
The heat generating resistor 1 is supported within the straight pipe portion 153 by a support pin 6, and the air temperature measuring resistor 2 is supported within the straight pipe portion 153 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 diverted to the bypass passage 52+ passes through the straight pipe part 153 where the air temperature measuring resistor 2 is installed, the straight pipe part 154 where the heat generating resistor 1 is installed, reaches the curved υ part 155, and passes through the ring part 156. The air passes through the narrowest part of the main passage 51 and merges with the air in the main passage 51 at an open outlet section 157. Straight pipe parts 153, 154, 19 part 155, resig part 156, which constitute bypass passage 52,
The cross-sectional area of each outlet portion 157 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 turbulence in the air flow.
The shape of the portion of the case 4 that forms the passage wall is also the same.

The air temperature measuring resistor 2 is provided upstream of the heating resistor 1, and the straight pipe section 153 to which the air temperature measuring resistor 2 is mounted is the same as the straight pipe section 15 to which the heating resistor 1 is mounted.
Since 4 and υ are formed to have large diameters, the air temperature measuring resistor 2 causes turbulence in the air flow, and the air temperature measuring resistor 2 is installed at a position where the heating resistor 1 is not affected. There is. By doing so, it is possible to obtain the same effect as the embodiment shown in FIG.

〔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 I-I sectional view, Figure 6 is a partially enlarged view of the resistor mounting part in Figure 1, Figure 7 is a plan view of Figure 6, and Figure 8 is a part of the conventional resistor mounting part. An enlarged view, 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
Domain passage, 52... Bypass passage, 53, 54° 153.154... Straight pipe part, 55.155... Curved part, 56.156... Ring part, 57.157...
Exit part.

Claims (1)

[Claims] 1. In a hot-wire air flow meter in which a heating resistor for measuring air flow rate and an air temperature measuring resistor are installed in a bypass passage, a part of the bypass passage is formed to have a larger diameter than the other part, and the above-mentioned A hot wire air flowmeter characterized in that the air temperature measuring resistor is installed in a bypass passage having a diameter larger than that of the bypass passage in which the heating resistor is installed.