JPH051930A - Failure detecting device for air flow meter - Google Patents

Abstract

PURPOSE:To quickly detect output reduction and emission deterioration caused by the impossibility of measuring a normal intake quantity at the time of breaking a base plate by determining the deviation between the maximum output value of an air flow meter provided in the intake passage of an engine and the minimum output value thereof, and judging that the base plate of the air flow meter is broken when this deviation is a determined value or less. CONSTITUTION:A hot wire 20 fixed to a base plate 18 is provided on the inside of a venturi tube 15 fitted in a housing provided in an intake passage to form an air flow meter 10. The current value for regularly holding the hot wire 20 at a fixed temperature is outputted to a control circuit 22. The control circuit 22 judges the failure of the air flow meter 10 when the deviation between the maximum output value of the current value and the minimum output value is a determined failure judging level or less.

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 failure detection device using a hot wire.

[0002]

2. Description of the Related Art An air flow meter of this type is disclosed, for example, in Japanese Unexamined Patent Publication No. 2-205722. Such an air flow meter is called a heat register type and uses a detection element for detecting the intake air amount of the engine. This detection element is composed of a substrate arranged in the intake passage at a right angle to the inflow direction of air, and a hot wire fixed to the substrate. While a current is applied to the hot wire to generate heat, the amount of heat generated changes according to the amount of intake air, but the amount of intake air is detected by the current value used to keep the amount of heat generated at this time constant. ing.

[0003]

However, in such a conventional air flow meter, the hot wire is fixed to and supported by the substrate as described above, and the thickness of the substrate is increased at this time. Although the strength can be increased by this, when the thickness of the substrate is increased, the heat capacity of the substrate itself increases, so that it becomes impossible to accurately detect the change in the amount of heat of the hot wire.

Therefore, in general, the thickness of the substrate is reduced to improve the accuracy of the change in the amount of heat. However, when the thickness of the substrate is reduced in this way, the substrate may be broken due to input vibration or deterioration of durability. . However, when the substrate is broken in this way, the hot wire is tilted together with the substrate with respect to the inflow direction of air, so that the amount of change in the amount of heat is reduced.
However, even if the board is broken, the hot wire itself is in the energized state, so the intake air amount is detected as if it is not defective and is output to the control circuit.

If an incorrect intake air amount signal is output as described above, proper engine control cannot be performed, and there is a problem that output is reduced or emission is deteriorated. Therefore, in view of the conventional problems, an object of the present invention is to provide a failure detection device for an air flow meter for easily detecting a failure when a substrate is broken and warning the driver of this. .

[0006]

In order to achieve such an object, the present invention is directed to an intake passage a of an engine as shown in FIG.
And a substrate b that is disposed at a position substantially orthogonal to the flow direction of the intake air
And an output deviation detecting means d for obtaining a deviation between the maximum output value and the minimum output value of the air flow meter in an air flow meter including a hot wire c fixed to the substrate b and outputting a change in heat quantity with respect to the intake air flow rate, And a failure determining means (e) for determining that the aerometer is in failure when the deviation is equal to or lower than a predetermined failure determination level.

Further, it is desirable to lower the failure determination level, which is the reference for determination by the failure determination means e, in the low intake region.

Further, it is desirable to prohibit the failure determination by the failure determination means e in the low intake region where the intake air amount is significantly reduced.

[0009]

In the air flow meter failure detection device of the present invention having the above-described structure, the amount of change in heat generated by the hot wire c is reduced when the substrate b is broken. By means d, it can be detected as a decrease in the deviation between the maximum output value and the minimum output value of the air flow meter. Then, when this deviation is equal to or lower than a predetermined failure determination level, the failure determination means e can detect the failure of the air flow meter, that is, the board b is broken and the engine is not operating normally.

Further, by lowering the failure determination level, which is the determination reference in the failure determination means e, toward the low intake region, the engine is mistakenly diagnosed as a failure when the intake amount is reduced in the low engine speed region. Can be prevented.

Further, by prohibiting the failure determination by the failure determination means e in the low intake region where the intake air amount is significantly reduced, even in this case, it is possible to prevent erroneous diagnosis of a significant intake air amount reduction as a failure. be able to.

[0012]

Embodiments of the present invention will be described in detail below with reference to the drawings. 2 to 7 show an embodiment of a failure detecting device for an air flow meter according to the present invention, FIG. 2 is a sectional view of an essential part of an air flow meter used in this device, and FIG. 3 is an enlarged perspective view of an essential part of the air flow meter. FIG. 4 is a perspective view showing a failure state of the air flow meter, FIG. 5 is an output characteristic diagram of the air flow meter, FIG. 6 is a flow chart showing an example of a process executed by the present apparatus when a failure is detected, and FIG. 7 is used for the control. It is a data map figure.

As shown in FIG. 2, the air flow meter 10 has a cylindrical housing 12 arranged in an intake passage between an air cleaner (not shown) and a throttle chamber (not shown).
Provide inside. That is, the air flow meter 10 includes a venturi pipe 16 which is concentrically attached to the inside of the housing 12 via a support member 14, and a substrate which is vertically provided above the inside of the venturi pipe 16 at a right angle to the flow direction of intake air. 1
8 and a hot wire 20 that is fixed to the substrate 18 and outputs a change in the amount of heat with respect to the intake air flow rate.

The venturi tube 16 has the support member 14
Together with this, it is integrally molded of synthetic resin, and has a throttle shape that rectifies and equalizes the intake air flowing in the direction indicated by arrow X in the figure. Further, the substrate 18 is formed of a heat-resistant thin plate as shown in FIG. 3, and its heat capacity is set as small as possible. Further, the hot wire 20 fixed to the substrate 18 is formed by arranging an extremely thin platinum wire having a diameter of about 70 μm in a meandering manner.

The hot wire 20 is heated by passing an electric current through it, and at the same time, the heat radiation amount of the hot wire 20 due to the intake air passing through the venturi pipe 16 is input to the control circuit 22. The value of the current flowing through the hot wire 20 is controlled so that the temperature of the hot wire 20 is always constant. Then, the amount of intake air that passes through the intake passage, that is, the amount of air supplied to the combustion chamber of the engine is detected based on the current value that is controlled so as to maintain the constant temperature.

By the way, the intake air amount pulsates with the opening and closing of an intake valve (not shown), and appears as the intake air amount characteristic of the air flow meter 10 shown by the solid line in FIG. That is, the solid line in the figure is the characteristic when the air flow meter 10 is normal, and the deviation between the maximum output value (Qmax) and the minimum output value (Qmin) is large.

On the other hand, when the substrate 18 is broken as shown in FIG. 4, the hot wire 20 is tilted together with the substrate 18 with respect to the intake direction, and the intake amount detected by the air flow meter 10 is a broken line in FIG. The characteristics are shown in. That is,
When the substrate 18 is broken, the deviation between the maximum output value (Qmax) and the minimum output value (Qmin) becomes smaller than that in the normal state. Therefore, in the failure detection device of the present embodiment, the maximum output value (Qmax) and the minimum output value (Q
min), the failure determination of the air flow meter 10 is performed.

Net-shaped screens 24 and 26 are attached to the inlet side end and the outlet side end of the housing 12, and dust is removed by the inlet side screen 24.
The screen 26 on the outlet side attenuates the intake pulsation propagating from the wake side.

FIG. 6 is a flow chart of the failure judgment performed by the control circuit 22. This flow is executed every predetermined short time. First, in step 100, it is determined whether the air flow meter 10 is in the energized state, and in step 101 it is determined whether the throttle sensor is operating normally. That is, step 100
Then, it is determined that the hot wire 20 is not broken, and not only when the board 18 is normally attached as shown in FIG. 3, but also when the board 18 is broken as shown in FIG. Also, it is determined that the power is on. Also,
The throttle sensor determined in step 101 detects the opening degree of the throttle valve provided in the throttle chamber, and changes the failure determination level according to the opening range detected by the throttle sensor, that is, the intake air amount. There is.

Next step 102 and step 103
Then, it is determined based on the data map of FIG. 7 which region the current throttle opening (tvo) falls within the boundary between x and y (x <y). That is, in step 102, it is determined whether or not the throttle opening is greater than or equal to x, and if it is less than x (NO), that is, if the intake air amount is extremely low, failure determination is not performed. If it is greater than or equal to x (YES), the routine proceeds to step 103, where it is determined whether the throttle opening is less than or equal to y. If y or less (YES), the process proceeds to steps 104 and 105 to make a failure determination based on the low failure determination level a. On the other hand, if y is exceeded, the process proceeds to step 106 and step 107 to make a failure determination based on a high failure determination level b (a <b).

In step 104, the air flow meter 10
Maximum output value (Qmax) and minimum output value (Qmin)
The deviation A from () is less than or equal to the failure determination level a in the previous detection value. If it is equal to or less than a (NO), the failure determination is not performed, and if it exceeds a (Y
ES) proceeds to step 105. In step 105, it is determined whether the deviation A detected this time is equal to or lower than the failure determination level a. If it is equal to or lower than a (NO), the failure determination is not performed. If it exceeds a, a warning lamp (MIL) is output in step 108. Is turned on.

Further, step 106 and step 10
7 performs the same processing as steps 104 and 105 above, and when the deviation A previously detected in step 106 exceeds the failure determination level b (YES), and when the deviation A detected this time in step 107 is the failure determination level b. If it exceeds (YES), the warning lamp is turned on in step 108. On the other hand, step 106 and step 10
If it is determined in step 7 that each is at or below the failure determination level b, no failure determination is made.

In step 100, the hot wire 2
If it is determined that 0 is disconnected, and step 10
When it is determined in 1 that the throttle valve is out of order, the process directly proceeds to step 108 and the warning lamp is turned on.

As described above, in this embodiment, when the deviation A between the maximum output value (Qmax) and the minimum output value (Qmin) of the air flow meter 10 decreases, it is detected that the substrate 18 is broken. Then, the warning lamp is turned on to notify the driver of the failure. Therefore, when the substrate 18 is broken in this way, it can be repaired promptly, and a decrease in engine output or deterioration of emission can be quickly repaired.

Further, since the intake air amount is judged by the opening of the throttle valve and the failure judgment level is set to a low value a in the low intake region (between x and y), the engine is in the low rotation region of the engine. It is possible to prevent erroneous diagnosis of a failure when the intake air amount is reduced. Further, since the failure determination is prohibited in the low intake region (x or less) where the intake amount is significantly reduced, even in this case, it is possible to prevent erroneous diagnosis of a significant intake amount reduction as a failure.

By the way, although the flow chart of FIG. 6 shows the case where the throttle opening (tvo) is used for the intake amount determination, other than this, the intake amount determination can be performed by the intake negative pressure or the engine speed, for example. it can.

[0027]

As described above, in the failure detecting device for an air flow meter according to claim 1 of the present invention, is the substrate broken due to the deviation between the maximum output value and the minimum output value of the air flow meter? You can easily determine whether. Therefore, when the board is broken in this way, it causes a decrease in output and deterioration of the emission. Therefore, when the board is broken, it can be repaired promptly and the normal operation of the engine can be maintained.

Further, according to the second aspect of the present invention, the failure judgment level due to the above deviation is lowered in the low intake region, so that when the intake air amount is reduced in the low engine speed region, it is misdiagnosed as a failure. It is possible to prevent it.

Further, according to the third aspect of the present invention, since the failure determination is prohibited in the low intake region where the intake amount is remarkably reduced, it is possible to prevent erroneous diagnosis of a significant intake amount reduction as a failure. It has various excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the concept of a failure detection device for an air flow meter according to the present invention.

FIG. 2 is a cross-sectional view of essential parts showing an embodiment of an air flow meter used in the failure detection device according to the present invention.

FIG. 3 is an enlarged perspective view of an essential part showing an embodiment of an air flow meter used in the present invention.

FIG. 4 is a perspective view showing a failure state of an embodiment of the air flow meter used in the present invention.

FIG. 5 is an output characteristic diagram of the air flow meter used in the present invention.

FIG. 6 is a flowchart showing a processing example of control executed when a failure is detected by the failure detection device according to the present invention.

FIG. 7 is a data map diagram used when a failure is detected by the failure detection device according to the present invention.

[Explanation of symbols]

10 Air Flow Meter 16 Venturi Tube 18 Substrate 20 Hot Wire 22 Control Circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Sasaki             3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda             Within the corporation

Claims (3)

[Claims] 1. An air flow meter, comprising: a substrate arranged in an intake passage of an engine, substantially orthogonal to a flow direction of intake air; and a hot wire fixed to the substrate and outputting a change in heat quantity with respect to an intake air flow rate. An output deviation detecting means for determining a deviation between the maximum output value and the minimum output value of the air flow meter, and a failure determining means for determining the failure of the air meter when the deviation is below a predetermined failure determination level are provided. Air flow meter failure detection device. 2. The failure detection device for an air flow meter according to claim 1, wherein the failure determination level is lowered in a low intake region. 3. In a low intake region where the intake amount is significantly reduced,
The failure detection device for an air flow meter according to claim 1, wherein failure judgment by the failure judgment means is prohibited.