JPH05340778A - Air flowmeter - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of the output of an air flowmeter by straightening a drift current in the direction perpendicular to a straight line along which measurement cannot be performed due to heating resistors arranged on the straight line so as to stabilize the flow velocity in the measurable area of the heating resistors. CONSTITUTION:Projecting sections 1a and 1b are formed from the internal wall surface of the main flow passage 1f of the body 1 of the flowmeter so as to constituted a throttle section 1c in the main flow passage 1f. The throttle section 1c is constituted so that the direction of the segment connecting the section 1c and resistors 2c1 and 2c2 can become parallel with the direction of the maximum width of the section 1c.

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 using a heating resistor, and more particularly to an air flow rate for an internal combustion engine which constitutes an intake system of an automobile engine and is suitable for detecting the intake air amount thereof. Regarding the total.

[0002]

2. Description of the Related Art Maintaining an air-fuel ratio of a mixture supplied to an internal combustion engine at a stoichiometric air-fuel ratio is important for cleaning exhaust gas and improving fuel efficiency. In order to realize these, it is necessary to control the fuel supply to the internal combustion engine. For this purpose, an air flow meter that can accurately measure the intake air amount to the engine is required.

The conditions required for an air flow meter for an internal combustion engine that can withstand practical use are 1 to 50 to 1 to 10 pulsating flow including deviation and turbulence caused by reciprocating motion of an engine piston.
It can be used in a wide flow rate range of 0, has durability against contamination by engine backfire, etc., is lightweight and compact, and can be manufactured at low cost.

A flow meter using a heating resistor is relatively easy to match with an internal combustion engine, and output signal processing, that is, a procedure for converting to an air flow rate is simple. It has the advantages of small size, high measurement accuracy and durability, and is suitable for the above applications. Such a flow meter uses a heating resistor as a heating wire and measures using the principle of a heating wire anemometer, and operates as follows.

First, an electrically heated resistor is placed in the air flow, the resistor is used as a resistance element forming a bridge circuit, and a circuit configuration is provided to keep its temperature constant.
At this time, the flow rate is detected from the change in the voltage across the resistor when the amount of heat generated changes due to the flow velocity fluctuation near the heat generating resistor.

The bridge circuit is constructed so as to keep the resistance value of the heating resistor constant, and the heat wire element is made by processing platinum, nickel or the like, which has a large temperature dependence of resistance, into a linear or thin film shape, which is used alone. Alternatively, a bobbin of ceramics, glass, polyimide resin or the like, or one wound or connected to a substrate is used. In an air flow meter for an internal combustion engine, an unheated resistor for temperature compensation is installed independently of the heat ray resistor, and this also constitutes one resistance element of the bridge circuit.

Next, let us consider the measurement conditions in the intake pipe in which such a flow meter is installed. Focusing on the state of the flow in the intake pipe, it can be seen that there is a problem that the flow deviation occurring on the upstream side of the flow meter causes fluctuations in the measured value of the flow meter. Since the upstream intake pipe system of the flow meter is arranged in a narrow engine room, it is inevitable that many bends,
Has a right angle corner. Therefore, the air flow in the intake pipe is also deflected and disturbed by the centrifugal force at the bends and corners.
Vortices are generated, and the flow velocity distribution in the cross section of the pipe also becomes nonuniform and uneven flow. The shape of the uneven flow differs depending on the layout of the upstream piping system and the rotational mounting position of the flowmeter. If the shape of the uneven flow is different, the flow velocity near the heating resistor of the flow meter also fluctuates, and the output value of the flow meter fluctuates even though the average air flow rate passing through the pipe is constant, causing an error.
For an air flow meter that can be used practically, this output error must be smaller than the specified allowable value, and the output value must be stable in proportion to the average flow rate passing through the pipe. Hereinafter, for the sake of simplicity, the term output error will be used to mean the deviation of the output value caused by the above drift.

As an air flow meter capable of reducing the output error,
As described in Japanese Utility Model Laid-Open No. 1-102724 and Japanese Utility Model Laid-Open No. 61-195418, a plurality of heat-generating resistors are formed in a main flow path forming a part of the intake pipe or in a main flow path. Some are installed in the street. These are intended to reduce the above output error by providing a plurality of heating resistors in the cross section of the intake pipe line and averaging the detected values, that is, the flow velocity information. By the way, in the case of an air flow meter having a plurality of heating resistors, while having the advantages as described above, there are drawbacks that the manufacturing cost is high and the reliability such as durability is low. This is a particular problem when considering mass production of meters.

This increases the number of assembling steps due to the increase in the number of heating resistors, and also increases the failure rate of each heating resistor. Further, since it is necessary to supply the heating current to the plurality of heating resistors, there is a problem that the electrical durability of the current supply circuit must be improved. Therefore, considering mass production, it is not a good idea to increase the number of heating resistors more than necessary. Therefore, the flowmeter suitable for mass production has two heating resistors 11 as shown in FIGS.
The one with c1 and 11c2 is realistic. A known example of an air flow meter having two heating resistors like this example is:
It is described in FIGS. 7 and 8 of Japanese Utility Model Publication No. 62-140324.

By the way, in the case of a flowmeter using two heating resistors, there is a problem that does not exist in a flowmeter using three heating resistors as disclosed in Japanese Utility Model Laid-Open Nos. 1-102724 and 61-195418. There is. This is a problem that the amount of fluctuation of the measured value becomes large at a specific rotational mounting position on the section of the pipe where uneven flow occurs. If there is a place where the amount of fluctuation of the measured value is large at a specific rotary mounting position, the output value may be easily affected by the shape change of the upstream drift and may fluctuate. As described above, the shape of the non-uniform flow greatly depends on the layout of the upstream side intake piping system, so this is a problem that usually occurs, and is due to the following causes.

In the case of a flow meter using two heating resistors as shown in FIGS. 4 and 5 or FIGS. 7 and 8 of Japanese Utility Model Laid-Open No. 62-140324, or in Japanese Utility Model Laid-Open No. 2-71226. In the case of a flow meter in which multiple heating resistors are arranged on a straight line,
Unlike the flowmeter in which three heating resistors are arranged on a plane as in Japanese Utility Model Laid-Open No. 1-102724 and Japanese Utility Model Publication No. 61-195418, the heating resistors 11c1 and 11c2 inevitably have the heating resistors 11c1 and 11c2 as shown in FIG. They are arranged on a straight line such as the line segment EE 'that connects them. As a result, F perpendicular to the line segment EE '
The flow velocity in the F'direction cannot be measured. At this time, if there is a flow velocity region in the FF 'direction whose flow velocity is significantly different from the average flow velocity in the cross section of the pipe, the flow meter cannot pick up the flow velocity information in this region, so compared to other rotary mounting positions. ,
The output value fluctuates greatly. This means that the flowmeter has a specific position with a large output error. And
The rotational mounting position with the largest output error, the magnitude of the output error, etc. differ depending on the distribution of the drift, which depends on the layout of the piping system.

As a structure for reducing the output error, the heating resistors 50c1 and 50c are provided as shown in FIGS.
It is conceivable that the throttle portion 50 is provided in the vicinity of the wall surface of the flow path in which No. 2 is installed to rectify the drift near the cross section. For example, although the two heating resistors are not used, the installation cross section of the three heating resistors is the narrowest portion in the Japanese Utility Model Laid-Open No. 1-102724, which is substantially a diaphragm structure.

However, such a circular diaphragm is not optimal in the case of a flowmeter in which a plurality of heating resistors are arranged in a straight line, such as a flowmeter having two heating resistors.
That is, in the circular throttle portion 50 of FIGS. 6 and 7, since the air is uniformly throttled in all diametrical directions, the heating resistor 50
Even if rectification is sufficiently performed in the direction of the line segment GG 'connecting c1 and 50c2, rectification in the HH' direction perpendicular to this is insufficient, and if the deviation of the upstream flow velocity distribution is large, the output of the flow meter It happens that the error is not reduced enough. Of course, if the throttle ratio (ratio of the inlet cross-sectional area of the throttle to the outlet cross-sectional area) is made sufficiently large, rectification can be performed, but if the throttle ratio is increased, the pressure loss also increases, which causes a reduction in engine output and is not practical.

Therefore, the pressure loss is equal to or less than the circular diaphragm,
Moreover, a throttle structure suitable for a flow meter in which a plurality of heating resistors are arranged in a straight line is required.

[0015]

As described above, in the conventional flowmeter having a plurality of heating resistors, the case where the heating resistors are arranged in a straight line has not been taken into consideration. Therefore, the shape of the passage in the vicinity of the heating resistor has not been a shape suitable for rectifying the flow. As a result, there is a problem that the rectification effect is not sufficient and the output error of the flowmeter is large.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an air comprising a main flow path forming an intake passage and a plurality of heating resistors arranged in a straight line for measuring intake air. In the flowmeter, a throttle is provided in a section including a plurality of heating resistor installation sections, and line segments connecting the plurality of heating resistors are arranged in parallel in the direction of the maximum width of the throttle.

[0017]

With the provision of a diaphragm in a section including a plurality of heating resistors arranged on a straight line, and the line segments connecting the plurality of heating resistors are arranged in parallel in the direction of the maximum width, a plurality of heat generating elements are generated. A contraction flow in a direction perpendicular to the line segment connecting the resistors can be selectively performed.

That is, the region perpendicular to the line segment where the heating resistor is not installed can be contracted with a high contraction ratio. As a result, it is possible to effectively rectify the low flow velocity region and the high flow velocity region in the portion where the heating resistor is not installed. As a result,
An air flow meter with a small output error can be realized regardless of the upstream flow velocity distribution.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view taken along the mainstream axis including the throttle of the air flow meter, FIG.
FIG. 3 is a sectional view taken along the mainstream axis including the heating resistor of the air flow meter. As shown in FIGS. 1 and 3, in each of the following drawings, a white arrow represents an air flow.

Air flows in from the flow meter inlet 1d, passes through the rectifying grid 3, the throttle portion 1c, the inside and outside of the resistor holder 2a,
It flows out to the flow meter outlet 1e. The rectifying grid 3 fitted in the flow meter inlet 1d is for reducing the swirling flow generated on the upstream side.

A circuit module 2 is inserted into a flowmeter body 1 formed by die-cast integral molding via an O-ring 4 for preventing air leakage, and is fixed by screwing. The circuit module 2 includes a circuit case 2f accommodating a measuring circuit, and a heating resistor 2c1, which constitutes a measuring unit.
2c2, temperature compensating resistor 2d1 to the main flow path 1f of the flow meter
Although the resistor holder 2a is provided so as to project inside, the resistor holder 2a is integrated. By thus integrating 2f and 2a, the entire flow meter can be easily assembled. The resistor holder 2a not only supports the resistor in the main flow path, but also when the circuit module 2 is transported or when the circuit module 2 is inserted into the flowmeter body 1, the resistor holders 2c1 and 2c2 and the temperature compensator are used for temperature compensation. It also has a function of protecting the resistor 2d1 from being damaged by an impact.

The slit-shaped inlet 2 is provided in the resistor holder 2a.
e is formed, and the heating resistor 2c1,
Pins 2b1 and 2b2 having different electric polarities for supplying a heating current to 2c2 are bridged. Furthermore, the heating resistors 2c1 and 2c2 are connected and fixed to the pins 2b1 and 2b2 by spot welding in the shape of a ladder of the ladder.
b1 and b2 also serve as supports for the resistors. Further, pins 2b3 and 2b4 are projected in the resistor holder 2a, and the temperature compensating resistor 2d1 is fixed thereto by spot welding.

In this embodiment, the heating resistors 2c1 and 2c2 are provided.
The installation position of is only one half of the maximum width from the center of the maximum width of the throttle so that the influence of the other heating resistor can be avoided and each can obtain independent flow velocity information. Separated.

The main flow path 1f of the flowmeter body 1 is formed with protrusions 1a and 1b from the inner wall surface of the body, and these form a throttle portion 1c in the main flow path. The throttle is generally used as a fluid element for rectifying the non-uniform flow, but in the case of the present embodiment, in consideration of the fact that the two heating resistors are arranged on a straight line, FIG. As shown, the direction of the line segment AA 'connecting the narrowed portion 1c and the two heating resistors 2c1 and 2c2 is such that the maximum width B of the laterally long cross section of the narrowed portion 1c.
It is constructed so as to be parallel to the direction of B '.

Consider the rectification effect of the diaphragm in this embodiment. In the cross section shown in FIG. 1, the width of the main flow passage decreases, so as the air passes through the constriction, the air receives the drag force from the wall and is mainly perpendicular to the AA 'direction in this cross section. The CC ′ direction is moved toward the center of the main flow path. As a result, the flow velocity in the mainstream axis direction increases, and the flow velocity deviation mainly in the direction parallel to CC 'can be rectified. Line segment A in this diaphragm structure
Although it is not possible to effectively rectify the drift distribution in the A'direction, two heating resistors are installed in the AA 'direction, and the measured values can be averaged. The error can be reduced.

In the case of the present embodiment, it is only necessary to selectively perform the contraction in one direction, and it is not necessary to perform the contraction in all the diametrical directions as in the case of the circular throttle. Therefore, the minimum sectional area of the diaphragm can be made larger than that of the circular diaphragm, but the larger the minimum sectional area of the diaphragm, the smaller the pressure loss. As a result, the pressure loss required for suppressing the output error of the flowmeter to a required level can be reduced as compared with the case where the circular throttle is used.

The second embodiment of the present invention is shown in FIGS.
Shown in. In the case of the present embodiment, unlike the first embodiment, the flowmeter body is assembled by screwing the three flow path elements of the inflow pipe 5, the circuit module 6, and the outflow pipe 7. Inflow pipe 5
A rectifying grid 3 for removing the swirling flow is incorporated between the circuit module 6 and the circuit module 6, and the inflow pipe 5 also serves to sandwich and fix the rectifying grid 3 with the circuit module 6. The circuit module 6 is formed with projecting portions 6a1 and 6a2 projecting into the main flow path, and by combining this with the inflow pipe 5 and the outflow pipe 7, the throttle portion 6a is configured as a whole. The throttle portion 6a has the same rectifying effect as in the first embodiment. As in the present embodiment, the narrowed portion 6a
By making the main flow path separate from the main flow path and making it replaceable, it is possible to select an optimum throttle shape that rectifies the flow path depending on the flow velocity distribution state of the upstream side uneven flow.

In the case of this embodiment, the heating resistor 6c1 is connected to the pins 6b1 and 6b2, and the heating resistor 6c2 is connected to the pins 6b3 and 6b.
4, the temperature compensating resistor 6d1 is spot-welded to the pins 6b5, 6b6. The fixing of the heating resistor is the same as in the first embodiment, but the heating resistors 6c1 and 6c are used.
2. The installation direction of the temperature compensating resistor 6d1 is different from that of the first embodiment. That is, in this embodiment, the heating resistor 6c
1, 6c2 and the temperature compensating resistor 6d1 are arranged in the DD 'direction parallel to the maximum width of the diaphragm. If the heating resistor is installed in such a direction, DD ′ of the resistor is
Since the projection length in the direction becomes large and the flow velocity distribution in the DD ′ direction can be averaged over a wider range than in the first embodiment, as a result, the output error becomes smaller.

A third embodiment of the present invention is shown in FIGS.
3 shows. In this embodiment, the flowmeter body 8 and the protruding portion 8
The structure of a, 8b, the narrowed portion 8c, the circuit module 9, the outer shape of the resistor holder 9a, the method of installing the temperature compensating resistor 9d1 and the like are the same as those in the first embodiment, but the heating resistors are different.

In the case of the present embodiment, the heating resistors are formed by connecting the plate-shaped heating resistors 9c1 and 9c2 on the resistor substrate 9c, and further by bridging and holding the resistor substrate 9c in the resistor holder 9a. There is. As the material of the resistor substrate 9c, ceramics, glass, polyimide resin or the like having good heat resistance is used. The resistor holder 9a has a function of protecting the heating resistors 9c1 and 9c2 and the temperature compensating resistor 9d1 as in the case of the first embodiment.

Also in the case of this embodiment, the plate-shaped heating resistors are connected so that the longitudinal directions of 9c1 and 9c2 are parallel to the direction of the maximum width of the diaphragm, as in the second embodiment. is there. Therefore, the output error of the flowmeter can be reduced by enhancing the effect of averaging the flow velocity as in the second embodiment.

The fourth embodiment of the present invention is shown in FIGS.
6 shows. In this embodiment, the structure of the throttle portion 8c of the flow meter body, the rectification effect, and the like are the same as those in the first and third embodiments, but in the case of this embodiment, the structure of the measuring unit, that is, the resistor holder 90a. And the composition is different.

Although a rectangular heating resistor 90c1 and a temperature compensating resistor 90d1 are projected in the resistor holder 90a, the resistor holder 90a has a heating resistor 90c.
1. In addition to supporting and protecting the temperature compensating resistor 90d1, it also functions as a rectifying conduit for the air flowing near the heating resistor 90c1. Slit-shaped entrance 90e of resistor holder 90a
Is formed in an arc shape and is a bell mouth 14a as a whole, so that the flow passing through the holder internal passage 14 can be contracted and rectified.

In this embodiment, a single heating resistor 90c1 is used instead of a plurality of heating resistors.
Since 1 has a rectangular shape, it has the same drawback as when a plurality of heating resistors are installed on a straight line. Also in this embodiment, in order to prevent this, the heating resistor 90c1 is installed so that its longitudinal direction is parallel to the direction of the maximum width of the narrowed portion 8c.

The fifth embodiment of the present invention is shown in FIGS.
9 shows. The present embodiment is intended to achieve a rectifying effect with a simpler structure without forming a throttle structure on the inner wall of the passage. In the case of this embodiment, in order to perform rectification, instead of using a diaphragm, an orifice plate 13 made by making an elliptical hole in a circular plate is used.
Is a rectifying grid 3 between the inlet pipe 10 and the circuit module 11.
It is installed on the upstream side of.

In this way, the rectifying grid 3 is attached to the orifice plate 13
The reason why it is installed in close contact with is to prevent the generation of vortices in the vicinity of V ₁ and V ₂ to reduce the pressure loss.

In the case of the present embodiment as well, as in the first to third embodiments, in order to effectively utilize the rectification effect of the diaphragm, to enhance the averaging effect of the two heating resistors 11c1 and 11c2. The line segment connecting the heating resistors 11c1 and 11c2 is installed so as to be parallel to the major axis direction of the elliptical orifice hole 13a, that is, the direction of the maximum width.

In the case of this embodiment, since the orifice structure is used, there is a drawback that the pressure loss becomes large as compared with the first to third embodiments, but the orifice plate 13 can be manufactured relatively easily. Since the replacement is easy, there is an advantage that an orifice plate having a hole shape or hole size with an optimum rectifying effect can be used according to the distribution of the non-uniform flow on the upstream side.

FIG. 20 is a system configuration diagram of an intake control system to which the air flow meter for an internal combustion engine of the present invention is applied. The air indicated by the white arrow passes through the air filter 103a in the air cleaner 103, and then is sucked into the engine piston through the intake bend pipe 104, the air flow meter body 1, the throttle body 112, and the intake manifold 101. The circuit module 2 produces an output corresponding to the intake flow rate.

The throttle valve 113 installed on the downstream side of the air flow meter body 1 is interlocked with the accelerator pedal,
Controls the intake air amount. Idle speed control (ISC) attached to the throttle valve 113
The valve 114 controls the air flow rate when the throttle valve 113 is fully closed. Black arrows show the flow of fuel. The fuel sucked from the fuel injection pump 106 from the fuel tank 105 is injected into the intake manifold 101 by the injector 107, mixed with the air passing through the air flow meter 1, and sucked into the engine 100.

The control unit 110 outputs the output of the circuit module 2, the signal output indicating the rotation angle of the throttle valve 113, the output of the oxygen concentration sensor 108 installed in the exhaust manifold 111, and the engine speed sensor 109.
Is a device for calculating the fuel injection amount and the ISC valve opening degree based on the signal output of 1. The injector 107 and the ISC valve 114 are controlled based on these results.

[0042]

As described above, since the heating resistors are arranged on a straight line, it is possible to rectify a drift in a direction perpendicular to the straight line, which cannot be measured. As a result, the flow velocity in the region that can be measured by the heating resistor is also stabilized, and fluctuations in the flowmeter output are reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an air flow meter according to a first embodiment of the present invention taken along the mainstream axis including a throttle.

FIG. 2 is an I-I arrow view of the air flow meter according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of the air flow meter according to the first embodiment of the present invention, taken along the mainstream axis including the heating resistor.

FIG. 4 is a cross-sectional view of a conventional example of an air flow meter using two heating resistors, taken along the mainstream axis including the heating resistors.

5 is a view taken along the line II-II in FIG.

FIG. 6 is a cross-sectional view of a conventional example of an air flow meter having two heating resistors and a circular diaphragm, taken along the mainstream axis including the heating resistors.

7 is a view taken along the line III-III in FIG.

FIG. 8 is a sectional view taken along the mainstream axis including a throttle of an air flow meter according to a second embodiment of the present invention.

FIG. 9 is an IV-IV arrow view of the air flow meter according to the second embodiment of the present invention.

FIG. 10 is a cross-sectional view taken along a mainstream axis line in a direction perpendicular to FIG.

FIG. 11 is a cross-sectional view of the air flow meter of the third embodiment of the present invention taken along the mainstream axis including the throttle.

FIG. 12 is a view showing the VV of the air flow meter according to the third embodiment of the present invention.
View from the arrow.

FIG. 13 is a cross-sectional view of the air flow meter according to the third embodiment of the present invention taken along the mainstream axis including the heating resistor.

FIG. 14 is a sectional view of the air flow meter according to the fourth embodiment of the present invention, taken along the mainstream axis including the throttle.

FIG. 15 is a VI-VI of the air flow meter according to the fourth embodiment of the present invention.
View from the arrow.

FIG. 16 is a cross-sectional view of the air flow meter according to the fourth embodiment of the present invention taken along the mainstream axis including the heating resistor.

FIG. 17 is a sectional view taken along the mainstream axis including a throttle of an air flow meter according to a fifth embodiment of the present invention.

FIG. 18 is a VII-V of the air flow meter of the fifth embodiment of the present invention.
II arrow view.

FIG. 19 is a cross-sectional view of the air flow meter of the fifth embodiment of the present invention taken along the mainstream axis including the heating resistor.

FIG. 20 is a system diagram of an intake system of an internal combustion engine equipped with the flow rate measuring device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flowmeter body, 1a, 1b ... Projection part, 1d ... Flowmeter inlet, 1c ... Throttling part, 1e ... Flowmeter outlet, 1f ... Main channel, 2 ... Circuit module, 2a ... Resistor holder, 2e ...
Slit-shaped inlets, 2b1, 2b2, 2b3, 2b4 ... Pins ... Pins, 2c1, 2c2 ... Heating resistors, 2d1 ... Temperature compensation resistors, 2f ... Circuit case, 3 ... Rectifying grid.

Claims (1)

[Claims] 1. A main axis forming a flow path for intake air, a plurality of heat generating resistors for measuring the intake air, and a long axis and a short axis on an inner wall of the main flow path in a section including an installation position of the heat generating resistors. An air flow meter provided with a throttle having an axis, wherein the heating resistor is arranged on a straight line in the direction of the long axis.