JPH11182318A - Failure diagnosis device for intake air amount detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform failure diagnosis of an intake air amount detecting device having a reverse flow detecting function. SOLUTION: A valiation amplitude ΔUs is calculated when an operation condition causing generation of intake pulsative motion is detected (S1, S2). When the amplitude ΔUs is determined to be a threshold value or more, an air flow meter is determined to be normal (S3, S4). When the amplitude is less than the threshold value, failure of the air flow meter is determined. An MIL is lit, and fail safe controlling is performed (S3, S5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for diagnosing a failure of an intake air amount detecting device including a backflow detecting function of an internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine equipped with an electronically controlled fuel injection device, a method of detecting an intake air flow rate and controlling a fuel injection amount in proportion to a cylinder intake air amount to control an air-fuel ratio to a target value is known. General. In this control, if the air flow meter that detects the intake air amount such as the intake air flow rate or the intake pressure fails, the fuel injection amount and, consequently, the air-fuel ratio cannot be controlled normally. Therefore, the failure is diagnosed.

[0003]

In a normal air flow meter, when the intake air flow rate is 0, the output voltage becomes a minimum voltage (0 V) or a maximum voltage (for example, 5 V). The output voltage changes in a range from the minimum voltage to the maximum voltage according to the level of the intake air flow rate. A fault diagnosis is performed to determine that a short circuit or disconnection has occurred when the above-mentioned sticking occurs.

When a reverse flow occurs in the intake air flow rate, the air flow meter detects the reverse flow without distinguishing it from the forward flow. Therefore, if control of the fuel injection amount or the like is performed based on the detection result, erroneous control may occur. Doing so results in an undesirable state. For this reason, an air flow meter that outputs an intermediate voltage (for example, 1 V) when the intake air flow rate is 0, and outputs the forward flow and the reverse flow of the intake air on the larger side and the smaller side is output. Have been.

When performing a failure diagnosis of an air flow meter having this type of backflow detection function, a failure in which the intake air flow rate sticks to the intermediate voltage or other intermediate voltage when the intake air flow rate is zero sticks to the aforementioned minimum voltage and maximum voltage. Diagnosis cannot be made by state failure diagnosis. The present invention has been made in view of such a conventional problem, and is capable of diagnosing a failure such as sticking to an intermediate voltage of an intake air flow detecting device having the above-mentioned reverse flow detecting function. An object of the present invention is to provide a failure diagnosis device for a device.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, the amount of intake air of the internal combustion engine is detected, and the detected voltage when the amount of intake air is zero is reduced. Diagnosing the performance of the intake air amount detection device that outputs the detection voltage of the intake air amount in the forward flow on one side of the side larger than the detection voltage and the side smaller than the detection voltage, and outputs the detection voltage of the intake air amount in the reverse flow on the other side Operating state determining means for determining a predetermined operating state in which intake pulsation exceeding a predetermined level occurs, and an output of the intake air amount detecting device when the predetermined operating state is determined. Output change width detection means for detecting a change width of the voltage; and a failure for diagnosing that the intake air amount detection device has failed when the change width of the output voltage detected by the output change width detection means is equal to or less than a predetermined level. Diagnostic means. The features.

According to the first aspect of the present invention, when it is determined that the vehicle is in a predetermined operating state in which intake pulsation exceeding a predetermined level is generated, the variation range of the output voltage of the intake air amount detecting device is less than a predetermined level. At times, the output voltage does not change in accordance with the intake pulsation, so that it can be diagnosed that the intake air amount detecting device has failed. Note that the diagnosis can be performed only by software processing without requiring a special circuit for the failure diagnosis and without increasing the cost.

The invention according to claim 2 detects the intake air amount of the internal combustion engine as shown in FIG. 2, and detects a difference between the detection voltage when the intake air amount is zero and the detection voltage larger than the detection voltage. A device for diagnosing the performance of an intake air amount detection device that outputs a detection voltage of a forward flow intake air amount on one side with a smaller side and outputs a detection voltage of a reverse flow intake air amount on the other side, An operation detecting means for detecting a state in which the engine is operating, and when the output voltage of the intake air amount detecting device is a value corresponding to 0 when the operation of the engine is detected. And a failure diagnosing means for diagnosing that the intake air amount detecting device has failed.

According to the second aspect of the invention, when it is detected that the engine is operating, the output voltage of the intake air amount detecting device is equivalent to the intake air amount of zero, though the intake air should flow. When the value becomes the value, it can be diagnosed that the intake air amount detecting device has failed. Also in this case, the diagnosis can be performed only by software processing without requiring a special circuit for failure diagnosis and without increasing the cost.

According to a third aspect of the present invention, as shown in FIG. 3, the amount of intake air of the internal combustion engine is detected, and the detected voltage when the amount of intake air is 0 is larger than the detected voltage. A device for diagnosing the performance of an intake air amount detection device that outputs a detection voltage of a forward flow intake air amount on one side with a smaller side and outputs a detection voltage of a reverse flow intake air amount on the other side, Operating state determining means for determining a predetermined operating state that generates a predetermined amount of intake pulsation, and detecting a change width of an output voltage of the intake air amount detecting device when the predetermined operating state is determined. Output change width detecting means, an operation detecting means for detecting a state of operation of the engine, and a change width of the output voltage detected by the output change width detecting means is equal to or less than a predetermined level, and the engine is operated. Has been detected Failure diagnosis means for diagnosing that the intake air amount detection device has failed when the output voltage of the intake air amount detection device is a value corresponding to the intake air amount of 0. Features.

According to the third aspect of the present invention, when it is determined that the vehicle is in a predetermined operating state in which intake pulsation exceeding a predetermined level is generated, the variation of the output voltage of the intake air amount detecting device is less than a predetermined level. Only when the operation of the engine is detected and the output voltage is equal to the intake air amount 0, it is diagnosed that the intake air amount detecting device is out of order. By making the failure diagnosis conditions stricter in this way, the erroneous diagnosis rate is reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 4 showing an internal combustion engine provided with an intake air amount detecting device according to one embodiment and a control system thereof, air is supplied to the internal combustion engine 1 via an air cleaner 2, an intake duct 3, a throttle chamber 4, and an intake manifold 5. Inhaled.

The intake duct 3 is provided with an air flow meter 6 as an intake air flow rate detecting device having a backflow detecting function, and detects the intake air flow rate Q as a mass flow rate. The air flow meter 6 has a circuit configuration as shown in FIG. In FIG. 5, a first detection resistor 63 and a second detection resistor 63 are provided on a substrate 61 disposed in the intake duct 3 with a heater 62 interposed therebetween in the flow direction of the intake air.
64 and are arranged. The heater 62 is controlled to be energized by a heater control circuit 65. The first detection resistor 63 and the second detection resistor 64 have a characteristic that the resistance value changes depending on the temperature. Connected to form a bridge circuit. First detection resistor 63 and second detection resistor 64
Are connected to the positive and negative terminals of an amplifier 68, the output voltage of the amplifier 68 is output to the A / D converter as a detected value of the intake air flow rate, and Converted to a value.

When the intake air flow rate is zero, the amplifier
The output voltage from 68 is set to be, for example, 1 V,
When the intake air flows forward, the first detection resistor 63
Since the second detection resistor 64 is located on the downstream side of the intake air heated by the heater 62, it is heated via the intake air because the second detection resistor 64 is located on the downstream side of the intake air heated by the heater 62. , A temperature difference occurs between the first detection resistor 63 and the second detection resistor 64. Further, as the intake air flow rate increases, the amount of heat received by the second detection resistor 64 via the intake air increases, so that the temperature difference between the second detection resistor 64 and the first detection resistor 63 increases.
According to the temperature difference, the first detection resistor 63 and the second detection resistor 64
, The potential difference input to the amplifier 68 increases, and the output voltage of the amplifier 68 increases.

On the other hand, when the intake air flows backward, only the first detection resistor 63 is heated via the intake air heated by the heater 62. A temperature difference and a resistance value difference are generated in opposite directions, whereby the potential difference input to the amplifier 68 is reduced, and the output voltage is reduced from the output voltage (1 V) in the state of the zero intake air flow rate. Therefore, the characteristic of the output voltage Us (V) of the air flow meter 6 is as follows.
As shown in the figure.

Returning to FIG. 4, the throttle chamber 4 is provided with a throttle valve 7 which is linked to an accelerator pedal (not shown) or driven by an actuator.
The intake air flow rate Q is controlled. The intake manifold 5 includes a collector portion 5a downstream of the throttle valve 7 and a branch portion 5b branched for each further downstream cylinder. Each branch portion 5b has an electromagnetic fuel injection valve 8 as a fuel injection means.
For injecting and supplying fuel which is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator.

A crank angle sensor 9 outputs a reference signal for each predetermined crank angle position corresponding to a specific stroke of each cylinder and outputs a unit crank angle signal for each unit crank angle (for example, 1 ° or 2 °). A water temperature sensor 10 for detecting the temperature of the cooling water of the engine, a throttle sensor 11 for detecting the opening of the throttle valve 7 and the like are provided, and detection signals from these are input to a control unit 12 with a built-in microcomputer.

The control unit 12 detects the engine speed N by measuring the cycle of each reference signal output from the crank angle sensor 9 or the number of unit crank angle signal inputs within a certain period of time. The fuel injection control and the ignition control are performed in accordance with the engine operating state obtained based on the above, while the failure diagnosis of the air flow meter 6 which is the intake air amount detection device is performed as follows.

FIG. 6 shows a flowchart of a failure diagnosis routine of the air flow meter according to the first embodiment. In step 1, it is determined whether or not the operating condition is such that the engine 1 generates an intake pulsation of a predetermined level or more. In particular,
It is determined whether or not the engine rotation speed Ne is equal to or higher than a predetermined value (for example, 1200 rpm) (other engine load conditions such as a throttle opening degree and a predetermined time after the start switch is turned off may be added). .

If the operation condition of step 1 is satisfied, the process proceeds to step 2 and the output voltage Us of the air flow meter 6 is used.
Is calculated. For example, the maximum value and the minimum value are sampled at a plurality of points, and the difference between them is averaged to calculate the change width ΔUs. In step 3, it is determined whether or not the change width ΔUs is equal to or greater than a predetermined threshold.
This threshold value is set to a value slightly smaller than the change width of the output voltage generated when the air flow meter 6 is normal according to the intake pulsation generated when the above-mentioned operating condition is satisfied.

If the variation width .DELTA.Us calculated in step 3 is equal to or larger than the threshold value, the output voltage has changed according to the intake pulsation, so that the air flow meter 6 is determined to be normal (step 4). If it is less than the threshold value, it is determined that the air flow meter 6 is out of order because the output voltage has not changed in response to the intake pulsation, and a warning light (MIL) is turned on to issue a warning and an appropriate failure The safe control is executed (step 5).

Next, a second embodiment will be described with reference to a flow chart of an air flow meter failure diagnosis routine shown in FIG. In step 11, it is determined whether or not the engine 1 is operating, that is, whether or not the output voltage of the air flow meter 6 is in a state where the intake air amount should be a value sufficiently separated from a value equivalent to zero. The operating conditions may be set such that the intake air amount is sufficiently large by adding engine load conditions such as the engine speed and the throttle opening.

If it is determined in step 11 that the engine 1 is operating, the routine proceeds to step 12, where the air flow meter 6
Is determined to be a value (for example, 1 V) corresponding to the intake air amount 0. If the value is not equivalent to the intake air amount 0 in step 12, the air flow meter 6 is determined to be normal (step 13). If the value is equivalent to the intake air amount 0, the air flow meter 6 is out of order. Then, the warning lamp (MIL) is turned on to issue a warning, and appropriate fail-safe control is executed (step 14).

FIG. 8 shows a flowchart of a failure diagnosis routine of the air flow meter according to the third embodiment. In the third embodiment, the second embodiment is different from the first embodiment in the second embodiment.
The airflow meter is diagnosed as having a failure when both failure diagnosis conditions with the embodiment of the present invention are satisfied.
In step 21, it is determined whether or not the engine 1 is operating. If it is determined that the engine 1 is operating, the process proceeds to step 22, in which whether or not the output voltage of the air flow meter 6 is a value corresponding to the intake air amount 0 is determined. Is determined.

If the output voltage of the air flow meter 6 has not reached the value corresponding to the intake air amount 0, it is determined that the air flow meter 6 is normal (step 23). Proceeding to 24, it is determined whether or not the operating condition is such that the engine 1 generates intake pulsation of a predetermined level or more. And, when the above operating conditions are satisfied,
After calculating the change width ΔUs of the output voltage Us of the air flow meter 6 (step 25), it is determined whether the calculated change width ΔUs is equal to or larger than a predetermined threshold value (step 26).
If it is equal to or greater than the threshold value, the air flow meter 6 is determined to be normal (step 22). If it is less than the threshold value, it is determined that the air flow meter 6 has failed, and a warning light (MIL) is turned on. The lamp is lit to give a warning, and appropriate fail-safe control is executed (step 27).

By making the failure diagnosis conditions stricter, the erroneous diagnosis rate is reduced. In the third embodiment, the determination condition of step 21 is determined as to whether or not the engine 1 is under the operating condition for generating the intake pulsation of a predetermined level or more (the engine 1 is operated, of course). A configuration in which the determination in step 23 is omitted may be adopted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the invention according to claim 1;

FIG. 2 is a block diagram showing the configuration and functions of the invention according to claim 2;

FIG. 3 is a block diagram showing the configuration and functions of the invention according to claim 3;

FIG. 4 is a system configuration diagram according to an embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of an air flow meter according to the embodiment.

FIG. 6 is a flowchart illustrating a diagnosis routine of the air flow meter according to the first embodiment.

FIG. 7 is a flowchart illustrating a diagnosis routine of the air flow meter according to the second embodiment.

FIG. 8 is a flowchart illustrating a diagnosis routine of the air flow meter according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 6 Air flow meter 7 Throttle valve 9 Crank angle sensor 10 Water temperature sensor 11 Throttle sensor 12 Control unit 62 Heater 63 First detection resistor 64 Second detection resistor 65 Heater control circuit 66, 67 Fixed resistor 68 Amplifier

Claims (3)

[Claims] An intake air amount of an internal combustion engine is detected, and a detection of a forward voltage intake air amount is detected on one of a side larger than the detected voltage and a side smaller than the detected voltage when the intake air amount is zero. A device for diagnosing the performance of an intake air amount detection device that outputs a voltage and outputs a detection voltage of a reverse flow intake air amount on the other side, and determines a predetermined operation state that generates intake pulsation of a predetermined level or more. Operating state discriminating means, an output change width detecting means for detecting a change width of an output voltage of the intake air amount detecting device when it is determined that the predetermined operating state is obtained, and the output change width detecting means Failure diagnosis means for diagnosing that the intake air amount detection device has failed when the variation width of the output voltage detected by the detection device is equal to or less than a predetermined level. Failure diagnosis device. 2. A method for detecting an intake air amount of an internal combustion engine and detecting a forward flow intake air amount on one of a side larger than the detected voltage and a side smaller than the detected voltage when the intake air amount is zero. Operation detection means for outputting a voltage and diagnosing the performance of an intake air amount detection device that outputs a detection voltage of a reverse flow intake air amount on the other side, the operation detection means detecting an operation state of the engine; A failure that diagnoses that the intake air amount detection device has failed when the output voltage of the intake air amount detection device is a value corresponding to 0 when the engine is detected to be operating. A failure diagnosis device for an intake air amount detection device, comprising: diagnosis means. 3. An intake air amount of an internal combustion engine is detected, and a detection is made of a forward flow intake air amount on one of a side larger than the detected voltage and a side smaller than the detected voltage when the intake air amount is zero. A device for diagnosing the performance of an intake air amount detection device that outputs a voltage and outputs a detection voltage of a reverse flow intake air amount on the other side, and determines a predetermined operation state that generates a predetermined amount of intake pulsation. Operating state determining means; output change width detecting means for detecting a change width of an output voltage of the intake air amount detecting device when the predetermined operating state is determined; and a state in which the engine is operated. Operation detection means for detecting the amount of intake air when the change width of the output voltage detected by the output change width detection means is equal to or less than a predetermined level, and when it is detected that the engine is operating. The output voltage of the device is empty A failure diagnosis means for diagnosing that the intake air amount detecting device has failed when the air volume has a value corresponding to 0; and a failure diagnostic device for the intake air amount detecting device.