JPH0241688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air flow rate measuring device for an internal combustion engine.
In particular, the present invention relates to an air flow measuring device that measures the amount of intake air passing through an air passage of an internal combustion engine using a hot wire air flow meter.

Conventionally, various methods have been used to measure the amount of intake air in internal combustion engines, but among these methods, methods using hot wire air flowmeters generally have good response and can measure the mass flow rate of air. Therefore, it is widely used because it does not require atmospheric pressure correction.
Regarding this, JP-A-49-48893, JP-A-47-
No. 19227 and Japanese Patent Application Laid-Open No. 51-64134 and is well known.

However, a flow measuring device using a hot wire air flowmeter has the disadvantage that its heat capacity must be reduced in order to improve responsiveness, and the sensing portion has a fine structure, resulting in poor durability. In particular, they have the disadvantage of being susceptible to fundamental damage from backup fire that occurs when the internal combustion engine is malfunctioning. In addition, not only during backfire, but also when there is intense pulsation due to engine rotation, supply air may flow backwards.On the other hand, due to the nature of hot wire air flowmeters, even if there is a backward flow, it will output the same as if it were rectified. When a backflow occurs, a value larger than the actual amount of intake air is detected and a signal based on this is output, which has the disadvantage that the measured value becomes inaccurate.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air flow rate measuring device for an internal combustion engine that can eliminate the drawbacks of the prior art as described above and perform stable and highly accurate measurements regardless of the operating state of the internal combustion engine. In particular, the main objective is to provide an air flow rate measuring device with improved measurement accuracy when accompanied by an intake air flow of an internal combustion engine.

That is, according to the present invention, in an air flow rate measuring device that measures the amount of intake air passing through an air supply passage of an internal combustion engine, air is placed on the upstream side of a flow rate measuring tube that is attached to protrude in a direction across the air supply passage. An air intake port is provided and an air outlet is provided on the downstream side surface, an air passageway leading from the air intake port to the air outlet is formed by a partition wall extending in the length direction within the flow velocity measuring tube, and an air passageway is formed in the air passageway. An air flow rate measuring device for an internal combustion engine is provided, which is characterized in that it includes a hot wire flow meter having a flow rate measuring resistor installed therein.

The operating principle and various preferred embodiments of the present invention will be explained below with reference to the drawings.

FIG. 1 is an explanatory diagram of the operating principle of the present invention.

In Figure 1, air supply passage 1 which is the main air passage
In an air flow measuring device of the type in which a bypass passage (bypass air passage) 20 is formed in the bypass passage and a flow rate measuring resistor 6 of a hot wire flowmeter is installed in the bypass passage, when the intake air flow of the internal combustion engine flows backward. The air flow in the bypass passage 20 is as follows. Note that the arrow X in FIG. 1 indicates the flow direction of air during backflow.

In FIG. 1, assuming that the air flow in the air supply passage 1 is an incompressible one-dimensional flow and ignoring its friction loss, the following relational expression is obtained.

∂u/∂t+u∂u/∂x=-1/p∂p/∂x...(1) ∂/∂x(u _A )=0...(2) Here, A is the passage cross-sectional area and u is the air In the flow velocity, p is the pressure, ρ is the air density, x is the distance along the flow direction from the reference point, and t is the time, Equation (1) shows the equation of motion, and Equation (2) shows the equation of continuity.

When formula (1 ₎ is integrated from the air inlet _A to the air outlet B of the bypass air _passage 20 in FIG. Become. Here l ₁ is the distance from point A to point B.

According to equation (3), the pressure at point B becomes higher than the pressure at point A during backflow, so the air flow in the bypass air passage 20 is as shown by arrow Y. In this case, since the hot wire air flow meter outputs the same signal as during rectification even during reverse flow, ideally the bypass air passage 20 where the resistor (hot wire) 6 for measuring flow velocity during reverse flow is installed. It is necessary to reduce the air flow velocity inside to zero.
For this purpose, the pressure difference between point A and point B needs to be almost zero. According to equation (3), this means that the distance l ₁ from point A to point B is made small and as close to zero as possible.

However, it is difficult to completely reduce the pressure difference between points A and B during backflow to zero. For this reason, a method can be considered to prevent the air in the bypass air passage 20 from moving due to the pressure difference. To achieve this, it is sufficient to increase the inertia of the air within the bypass air passage 20. That is, by ensuring a certain length of the bypass air passage 20 or by providing a surge tank within the bypass air passage 20, the inertia of the air can be increased.

The present invention has been made in consideration of the above operating principle, and the feature of the present invention is that a constant resistor (hot wire) on the flow velocity side of a hot wire type anemometer is installed in the bypass air passage or an air passage equivalent to this. In the installation, the linear distance l ₁ in the air supply passage 1 between the inlet and outlet of the bypass air passage is made small, and
The objective is to maintain the inertia of the air within the bypass air passage above a predetermined value.

In this case, if a surge tank chamber is provided in the middle of the air passage, the inertia of the air within the air passage can be greatly increased.

Various embodiments of the present invention will be described below with reference to FIGS. 2 to 10.

FIGS. 2 and 3 are diagrams showing an embodiment of the air flow measuring device for an internal combustion engine according to the present invention.

In FIG. 2, air flows into the air supply passage 1 from above in the direction of arrow Z and flows into the internal combustion engine located below. Note that air is supplied to the internal combustion engine through a throttle valve (not shown) of a carburetor installed downstream of the air supply passage 1 shown.

A bench lily 2 is provided on the side wall of the air supply passage 1 to reduce the cross-sectional area of the passage and make the air flow velocity distribution uniform. A flow rate measuring tube 3 is installed on the wall of the air supply passage 1 in the area of the bench lily 2 so as to protrude in a direction across the air supply passage. An air intake port 4 is formed on the upstream side surface of the flow rate measuring tube, and an air outlet 10 is formed on the downstream end surface 2. The inside of the flow rate measuring tube 3 is partitioned into an upstream portion and a downstream portion by a partition wall 22 extending in the length direction, and the partition wall 22 allows a relatively long pipe to connect from the air intake port 4 to the air outlet 10. An air passage 5 is formed.

Inside the air passage 5, that is, in the case of illustration, at the right end folded portion of the air passage 5, a flow rate measuring resistor 6 and a temperature compensating resistor 7 of a hot wire air flow meter are installed. Further, a rectifying grid 23 is provided on the upstream side of the flow rate measuring resistor 6 in the air passage 5. Reference numeral 8 indicates an electronic circuit of the hot-wire air flowmeter, which is electrically connected to the flow rate measuring resistor 6 and temperature compensation resistor 7, and receives signals from these to determine the air flow rate. Calculate. Further, reference numeral 9 indicates an electronic circuit cover that covers the electronic circuit 8.

In FIG. 2, the air intake port 4 is configured to receive total pressure (dynamic pressure + static pressure), and the air outlet 10 has an opening surface parallel to the flow so that only static pressure is applied. It's summery. By doing so, only the dynamic pressure of the air flow acts between the air intake port 4 and the air outlet 10 of the flow rate measuring tube 3. Furthermore, by providing the rectifying grid 23, the air flow within the air passage 5 is rectified.
This has the effect of improving the precision of the measurement signal in the hot wire flowmeter and preventing damage to the flow velocity measuring resistor 6 and the temperature compensating resistor 7.

According to the embodiment shown in FIGS. 2 and 3 described above, the distance l ₁ shown in FIG. 1 and the distance between the air intake port 4 and the air outlet in FIG. 2 can be minimized. Moreover, since the air intake port 4 is provided toward the upstream side of the flow rate measurement tube 3, only the dynamic pressure of the intake air can be taken in, and only the forward flow component can be measured with high accuracy. Furthermore, since the distance between the flow velocity measuring resistor 6 and the air intake port 4 can be increased, the inertia is increased, and the transmission of pulse-like pressure fluctuations can be absorbed or slowed down, and the flow velocity can be measured. Since the resistor 6 portion does not cause backflow, stable and highly accurate flow rate measurement can be performed regardless of the operating state of the internal combustion engine. In particular, even if the intake air flow to the internal combustion engine is accompanied by a backflow, the air outlet 10 does not face the backflow, so the backflow component is discarded, and the accuracy of measuring the amount of intake air can be significantly improved.

FIGS. 4 and 5 are views showing a second embodiment in which a surge tank chamber 11 is provided in the air passage 5 of FIGS. 2 and 3. FIG. This embodiment differs from the embodiments shown in FIGS. 2 and 3 only in that a surge tank chamber 11 is provided, and all other structures are substantially the same.

By providing the surge tank chamber 11, it is possible to further increase the inertia of the air in the air passage 5, and by flattening the pulsating flow of the intake air flow, the accuracy of flow rate measurement is further improved. be able to.

6 and 7 are diagrams showing a third embodiment of the air flow measuring device for an internal combustion engine according to the present invention. In this embodiment, the flow rate measuring tube 3 is extended across the air supply passage 1 into the opposite wall (the wall of the bench lily 2) in the embodiments shown in FIGS. 4 and 5, and is fixed at both ends. Efforts are being made to improve mechanical strength. In this case, the air intake port 4 is formed on the upstream side wall surface of the flow rate measuring tube, and the air outlet 10 is formed on the side surface substantially parallel to the air flow in the air supply passage 1. As shown in the figure, the air intake port and air outlet are formed approximately in the center of the air supply passage. In this case as well, total pressure (dynamic pressure + static pressure) acts on the air intake port 4,
Only static pressure acts on the air outlet 10.

In addition, the air intake port 4 and the air outlet 1 of the measuring tube 3
The left side of 0, that is, the space opposite the resistors 6 and 7, can also serve as a surge tank.

The rest of the structure of the embodiment of FIGS. 6 and 7 is substantially the same as the embodiment shown in FIGS. 4 and 5, and corresponding parts are designated by the same reference numerals.

FIGS. 8 and 9 are diagrams showing a fourth embodiment of the air flow measuring device for an internal combustion engine according to the present invention. This embodiment differs from the embodiments shown in FIGS. 6 and 7 in that the air outlet 10 is located on the downstream side (the
The difference is that it is formed on the side (lower side in the figure).
The other configurations are substantially the same. According to this embodiment, dynamic pressure is applied when the air flows backward through the air outlet 10, so that an output obtained by subtracting the backward flow of the air flow can be obtained. That is, when a backflow occurs, the influence of this backflow can be taken into account to ideally bring the flow rate (forward flow direction) measured value by the flow rate measuring resistor 6 closer to the actual flow rate value.

In contrast to the embodiments of FIGS. 8 and 9, in the embodiments shown in FIGS. 2 to 7, the air outlet 10
Since only static pressure was applied to the sensor, it had the effect of blocking the influence of backflow when it occurs (setting all backflow values to zero) and preventing measurement errors due to backflow.
In the fourth embodiment shown in FIGS. 8 and 9, the influence of backflow is actively taken into account and the backflow is subtracted from the normal flow to ideally measure the true flow rate.

Let's explain the meaning of "subtracting the reverse flow from the forward flow" above. In Fig. 8, the air passage 5 provided along the partition wall 22 has a sufficient length, and the surge tank chamber 11 is also attached, so that the inertia of the air within the passage is sufficiently large. . Therefore, even if a pulsed backflow enters the air outlet 10, a transmission delay occurs due to the viscous resistance in the passage and the pressure wave absorption effect by the surge tank chamber 11.
In the flow velocity measuring resistor 6 portion, the forward flow cannot be reduced to zero. In other words, a component obtained by subtracting the reverse flow from the forward flow remains.

Therefore, since the distance between the air intake port 4 and the air outlet 10 is extremely short, the difference in the static pressure of the backflow becomes very small, and the air passage 5 due to the difference in the static pressure of the backflow becomes small.
Internal backflow is almost eliminated.

The flow rate measuring resistor 6 is a detection end that cannot distinguish between forward flow and reverse flow, so when reverse flow enters, it detects as if the forward flow has increased. In other words, reverse flow = error. Therefore, the present invention is configured such that the backflow, which is the cause of the error, does not reach the detection end.

Together with the fact that the backflow is reduced by the absorption effect and the inertia of the air in the air passage 5 is increased, an accurate air flow measuring device for an internal combustion engine has been created.

FIG. 10 is a diagram illustrating the cross-sectional shape of the flow rate measuring tube 3 of the various embodiments described above. Figure 10A
10B shows a case in which a vertically long measuring tube with a rectangular cross section is used and air passages 5 with a substantially square cross section are formed above and below it, and FIG. This is an example in which the air passage 5 is partitioned, and FIG. 10C shows an example in which a measuring tube 3 having a streamlined cross section is used to prevent the flow inside the air supply passage 1 from becoming sloppy.

As is clear from the above description, it is possible to obtain an air flow measuring device for an internal combustion engine that can prevent measurement errors due to backflow and can perform highly accurate flow measurement.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the operating principle of the air flow measuring device for an internal combustion engine according to the present invention, FIG. 2 is a longitudinal sectional view showing a first embodiment of the air flow measuring device for an internal combustion engine according to the present invention, and FIG. 2 is an end view taken from the middle line - in FIG. 2, FIG. 4 is a longitudinal cross-sectional view showing the main part of the second embodiment of the air flow measuring device for an internal combustion engine of the present invention, and FIG. 6 is a longitudinal cross-sectional view showing the main part of the third embodiment of the air flow measuring device for an internal combustion engine of the present invention, and FIG. 7 is an end view taken along the line - in FIG. 6. 8 is a longitudinal cross-sectional view showing the main part of the fourth embodiment of the air flow measuring device for an internal combustion engine of the present invention, and FIG. 9 is an end view taken along the line - in FIG. 8. FIG. 10 is a sectional view showing three examples of the cross-sectional shape of the flow rate measuring tube constituting the bypass passage, 1...Air supply passage, 2...Venture, 3...Flow rate measuring tube, 4...Air intake port, 5... Air passage, 6... Resistor for flow rate measurement, 7... Resistor for temperature compensation, 10... Air outlet, 11... Surge tank chamber, 22... Partition wall,
23... Rectifier grid.

Claims (1)

[Scope of Claims] 1. In an air flow measuring device for measuring the amount of intake air passing through an air supply passage of an internal combustion engine, a flow rate measuring tube is provided so as to protrude in a direction across the air supply passage, and a flow rate measuring tube is provided on the upstream side of this tube. An air intake port is provided on the downstream side, an air outlet is provided on the downstream side, an air passage is formed from the air intake port to the air outlet by a partition wall extending in the length direction within the flow rate measuring tube, and the air passage is installed within the air passage. 1. An air flow rate measuring device for an internal combustion engine, comprising a hot wire flowmeter having a resistor for measuring flow rate. 2. The air flow rate measuring device for an internal combustion engine according to claim 1, wherein a rectifying grid is provided upstream of the flow rate measuring resistor in the air passage. 3. The air flow rate measuring device according to claim 1 or 2, wherein an internal combustion engine is characterized in that a surge tank chamber is provided in the middle of the air passage to increase the inertia of the air in the air passage. air flow measuring device.