JP5120333B2 - Air flow meter failure diagnosis device - Google Patents

Description

  The present invention relates to a failure diagnosis device for an air flow meter of an internal combustion engine.

  In a control system for a gasoline engine or a diesel engine, an air flow meter is provided in an intake passage through which air sucked into the engine flows, and the intake air amount is detected by the air flow meter (see, for example, Patent Document 1).

  Further, Patent Document 2 discloses a failure diagnosis device that performs failure diagnosis of such an air flow meter. In the failure diagnosis device of Patent Document 2, the control system of an internal combustion engine in which an intake passage is composed of a plurality of passages and an air flow meter is provided in each passage, the measurement results of the air flow meters are compared with each other. Diagnose a failure.

JP 2007-231840 A JP 2007-309222 A

  Incidentally, in recent years, the importance of airflow meter failure diagnosis is increasing in order to comply with strict OBD (vehicle-mounted failure diagnosis device) laws and regulations.

  Further, in the diesel engine, in order to reduce NOx in the exhaust gas, a part of the exhaust gas is recirculated to the intake passage, and the amount of the recirculated exhaust gas is calculated by adding the recirculated exhaust gas and the intake air amount, Since it is estimated from the intake air amount, it is important to detect the intake air amount with high accuracy. In a gasoline engine, since the fuel injection amount is controlled so that the mixing ratio of fuel and air supplied to the engine is optimal, it is important to detect the intake air amount with high accuracy.

  For this reason, it is necessary to be able to detect that the air flow meter is faulty when the amount of intake air cannot be detected with high accuracy due to a disconnection or short circuit of the air flow meter or a characteristic abnormality due to deterioration over time.

  On the other hand, although the failure diagnosis apparatus described in Patent Document 2 described above can detect a failure of the air flow meter, an air flow meter different from the failure diagnosis target air flow meter is required. If a plurality of devices are not provided, it is necessary to separately attach a special device such as an air flow meter to the control system of the internal combustion engine for failure diagnosis. It is not preferable to attach a special device for diagnosing the trouble of the air flow meter because it leads to an increase in the cost of the entire control system of the internal combustion engine.

  In view of the above, an object of the present invention is to provide an air flow meter failure diagnosis apparatus capable of performing failure diagnosis without mounting a special device different from the components of the control system of the internal combustion engine.

In order to achieve the above object, according to the first aspect of the present invention, when the rotational speed of the internal combustion engine detected by the rotational speed sensor (33) is lower than a predetermined speed, the throttle detected by the throttle opening sensor (26). First estimation means (S4) for estimating the intake air amount using the opening of the valve (25) and the rotational speed detected by the rotational speed sensor (33);
By comparing the intake air amount obtained by the first estimating means (S4) with the intake air amount measured by the air flow meter (21), it is determined whether or not the air flow meter (21) is abnormal. First determination means (S5);
When the rotational speed of the internal combustion engine detected by the rotational speed sensor (33) is higher than a predetermined speed, the pressure of the intake air detected by the intake pressure sensor (27) and the rotational speed detected by the rotational speed sensor (33) Second estimating means (S9) for estimating the intake air amount using
By comparing the intake air amount obtained by the second estimating means (S9) with the intake air amount measured by the air flow meter (21), it is determined whether or not the air flow meter (21) is abnormal. Second determination means (S10);
It comprises a failure determination means (S8) for determining a failure of the air flow meter (21) when at least one of the first determination means (S5) and the second determination means (S10) is determined to be abnormal. .

  As described above, the present invention utilizes the characteristic of indirectly measuring the intake air amount of the throttle opening sensor (26) and the intake pressure sensor (27), which are general components of a control system for an internal combustion engine. The failure of the air flow meter is diagnosed by comparing the intake air amount measured indirectly and the intake air amount directly measured by the air flow meter. Therefore, according to the present invention, failure diagnosis is possible without mounting a special device separate from the components of the control system of the internal combustion engine.

  In the first aspect of the invention, for example, as described in the second aspect, when both the first determination means (S5) and the second determination means (S10) determine that there is an abnormality, the failure confirmation means ( If S8) determines the failure of the air flow meter (21), a highly reliable failure diagnosis result can be obtained.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a mimetic diagram showing the whole diesel engine control system composition in a 1st embodiment of the present invention. (A) is a diagram showing the relationship between the intake air amount and the output voltage of the AFM, (b) is a diagram showing the relationship between the intake air amount and the throttle valve opening, and (c) is a graph showing the relationship between the intake air amount and the intake air amount. It is a figure which shows the relationship with the pressure of intake air. 2 is a flowchart of AFM failure diagnosis processing executed by an ECU in FIG. 1. It is a map for estimating the amount of intake air from the opening of the throttle valve or the pressure of intake air and the engine speed.

(First embodiment)
In FIG. 1, the control system of the diesel engine in this embodiment is shown. In this embodiment, the failure diagnosis device for an air flow meter of the present invention is applied to a control system for a diesel engine as an internal combustion engine mounted on a vehicle.

  The diesel engine control system shown in FIG. 1 includes an engine 11, an intake passage 12 through which the air taken into the engine 11, that is, intake air flows, an exhaust passage 13 through which exhaust gas from the engine 11 flows, and an exhaust passage 13. An EGR passage 14 that recirculates part of the flowing exhaust gas to the intake passage 12 and an ECU 40 as an engine control device are provided. Note that the intake passage 12, the exhaust passage 13, and the EGR passage 14 are each configured by piping or the like.

  On the upstream side of the intake air flow in the intake passage 12, the flow rate of the intake air flowing through the intake passage 12, that is, the air flow meter (hereinafter referred to as AFM) 21 for measuring the intake air amount and the temperature of the intake air passing through the AFM 21. A first intake air temperature sensor 22 is provided for measuring. The AFM 21 is a mass flow method for detecting the amount of intake air, and directly measures the amount of intake air. For example, a hot-wire type is adopted.

  A compressor 23 a of a turbocharger 23 that supercharges intake air is provided on the downstream side of the AFM 21 in the intake passage 12. On the downstream side of the compressor 23a of the turbocharger 23 in the intake passage 12, a second intake air temperature sensor 24 for measuring the temperature of the intake air after passing through the compressor 23a, a throttle valve 25 for adjusting the intake air amount, and a throttle A throttle opening sensor 26 that detects the opening of the valve 25 is provided.

  The throttle valve 25 has, for example, a butterfly door, and the intake air amount is adjusted by adjusting the passage area of the intake passage 12 with the butterfly door. For example, the throttle valve 25 is configured to recirculate exhaust gas from the EGR passage 14 to the intake passage 12 by making the opening smaller than fully open and generating a negative pressure downstream of the throttle valve 25. It is used.

  An intake pressure sensor 27 that detects the pressure of intake air is provided on the downstream side of the throttle valve 25 in the intake passage 12. As the intake pressure sensor 27, for example, a semiconductor pressure sensor is employed. The intake pressure sensor 27 detects, for example, the total pressure of the mixed gas of the recirculated exhaust gas and the intake air from the EGR passage 14, calculates the total amount of the mixed gas, and the calculation result and the intake air measured by the AFM 21. It is used to estimate the recirculated exhaust gas quantity from the quantity.

  The EGR passage 14 is provided with an EGR valve 28 that adjusts the amount of recirculated exhaust gas, and the exhaust passage 13 is provided with a turbine 23b of the turbocharger 23.

  The engine 11 is provided with an injector 31 that directly injects fuel into the cylinder. Further, the engine 11 is provided with a coolant temperature sensor 32 for detecting the engine coolant temperature and a crank angle sensor 33 as an engine rotation speed sensor for detecting the engine rotation speed.

  Various sensors such as the AFM 21, the throttle opening sensor 26, the intake pressure sensor 27, and the crank angle sensor 33 described above output detection results to the ECU 40. The ECU 40 includes a microcomputer including a CPU, ROM, EEPROM, RAM, etc. (not shown), and performs arithmetic processing according to a program stored in the microcomputer. The ECU 40 controls the fuel injection by the injector 31 based on input signals from various sensors, the fuel injection control for controlling the injection amount, the injection timing, and the like, and the exhaust gas is recirculated to the engine 11 for NOx in the exhaust gas. EGR control for reducing the AFM 21 and failure diagnosis processing of the AFM 21 are performed. In the EGR control of the ECU 40, for example, the opening degrees of the throttle valve 25 and the EGR valve 28 are adjusted based on input signals from the throttle opening degree sensor 26 and the intake pressure sensor 27 so that a desired recirculated exhaust gas amount is obtained. The

  The failure diagnosis process of the AFM 21 executed by the ECU 40 uses a characteristic that can indirectly measure the intake air amount of a general component used for engine control in the engine control system. This is a process for diagnosing a failure of the AFM 21 by comparing the intake air amount measured in step 1 and the intake air amount directly measured by the AFM 21.

  Here, as general components of the engine control system that can indirectly measure the intake air amount, an intake pressure sensor 27 and a throttle opening sensor 26 that detects the opening of the throttle valve 25 are provided. Is mentioned.

  2A shows the relationship between the intake air amount and the output voltage of the AFM 21, FIG. 2B shows the relationship between the intake air amount and the throttle valve opening, and FIG. 2C shows the intake air amount and the pressure of the intake air. Shows the relationship.

  As shown in FIG. 2A, the AFM 21 can output a voltage corresponding to the amount of air taken into the engine, and can detect the amount of intake air regardless of the engine speed and the engine load.

  On the other hand, as shown in FIG. 2B, there is a predetermined functional relationship between the intake air amount and the throttle opening of the throttle valve 25 according to the engine speed. Therefore, the intake air amount can be estimated from the throttle opening and the engine speed. In this estimation of the intake air amount, the intake air temperature is also referred to. Further, since this intake air amount estimation method is the same method as a conventional intake air amount detection device that detects the intake air amount by the throttle speed method, a detailed description of this intake air amount estimation method is omitted. To do.

  However, as shown in FIG. 2B, when the engine speed is low or medium, the throttle opening and the air amount are linear when the throttle opening is higher than a predetermined opening TA1, for example, 50%. Therefore, the intake air amount cannot be accurately detected from the throttle opening.

  On the contrary, if the throttle opening is a low opening lower than the predetermined opening TA1, the throttle opening and the air amount have a linear relationship regardless of the engine speed. The amount of air can be detected with high accuracy. By the way, the vehicle situation where the throttle opening is low is generally when the vehicle speed is low and when the engine load is small. Therefore, when the engine speed is low, for example, less than 2000 rpm In addition, it can be said that the intake air amount can be detected with high accuracy from the throttle opening.

  Further, as shown in FIG. 2C, there is a predetermined functional relationship between the intake air amount and the intake air pressure according to the engine speed. Therefore, the intake air amount can be estimated from the intake air pressure and the engine speed. Since this intake air amount estimation method is the same method as a conventional intake air amount detection device that detects the intake air amount by the speed density method, a detailed description of this intake air amount estimation method is omitted. . In order to accurately detect the intake air amount, it is preferable to refer to the intake air temperature measured by the second intake temperature sensor 24.

  However, when the engine speed is low, the flow of intake air is low, and the pressure changes abruptly when the amount of air increases slightly. As can be seen from FIG. Since the pressure of the intake air does not have a linear relationship, the amount of intake air cannot be accurately detected from the pressure of the intake air.

  On the contrary, when the engine speed is medium and high, for example, when the speed is higher than 2000 rpm, the linear relationship between the intake air amount and the intake air pressure is understood from FIG. Therefore, the intake air amount can be detected with high accuracy from the pressure of the intake air.

  Next, the failure diagnosis process of the AFM 21 executed by the ECU 40 will be specifically described. FIG. 3 shows a flowchart of the failure diagnosis process of the AFM 21. This failure diagnosis process is executed at a predetermined cycle after the engine 11 is started. Each step shown in FIG. 3 corresponds to a function as one means of the ECU 40.

  First, in step S1, it is determined whether or not the engine speed is in a low speed range. That is, the engine speed is calculated from the detection signal input from the crank angle sensor 33, and it is determined whether or not the calculated engine speed is lower than a predetermined speed. The predetermined speed is stored in the ECU 40. As described above, the intake air amount can be detected with high accuracy from the throttle opening when the speed is lower than the predetermined speed, and when the speed is higher than the predetermined speed. It is set so that the amount of intake air can be detected with high accuracy from the pressure of the intake air, for example, 2000 rpm. In addition, this predetermined speed can be changed in the range of 1500-2500 rpm, for example.

  If the engine speed is in the low speed range, the process proceeds to step S2, and if it is in the high speed range, the process proceeds to step S3.

  In step S2, it is determined whether the abnormality of the AFM 21 has been confirmed in the low speed region of engine rotation. That is, it is determined whether or not the abnormality of the AFM 21 is confirmed and the fact is stored in the ECU 30 in steps S5 and S6 described later. If the abnormality of the AFM 21 is confirmed, the series of flows shown in FIG. 3 is completed, and the process returns to the start again. The abnormality determination of the AFM 21 is executed.

  In step S4, the intake air amount is calculated from the throttle opening and the engine speed. For example, the throttle opening is calculated from the detection signal of the throttle opening sensor 26, and based on the throttle opening, the engine speed calculated in step S1, and the map shown in FIG. Then, the intake air amount is calculated. The map shown in FIG. 4 is obtained by examining the relationship among the throttle opening or intake air pressure, the engine speed, and the intake air amount in advance. The vertical axis represents the throttle opening or intake air pressure, and the horizontal axis Is the engine rotational speed Ne, and the intake air amount can be estimated from the combination of the value on the vertical axis and the value on the horizontal axis. This intake air amount is, for example, the mass of air per unit time. In this way, the intake air amount is indirectly measured from the throttle opening and the engine speed. Step S4 corresponds to first estimation means or estimation means for estimating the intake air amount using the throttle valve opening and the rotational speed detected by the rotational speed sensor in the present invention.

  Further, the intake air amount is directly measured by the AFM 21. That is, the intake air amount is calculated from the output voltage of the AFM 21. This intake air amount is also the air mass per unit time, for example. Note that the measurement timing is set so that the intake air amount directly measured by the AFM 21 and the intake air amount indirectly measured from the throttle opening and the engine rotational speed are the same intake air flow rate. deep.

  Subsequently, in step S5, it is determined whether or not the AFM 21 is abnormal in the low speed region. That is, the intake air amount directly measured by the AFM 21 is compared with the intake air amount indirectly measured from the throttle opening, and it is determined whether or not the difference between the two is larger than a predetermined amount. This step S5 corresponds to first determination means or determination means for determining whether or not the air flow meter in the present invention is abnormal. In step S5, the determination is made using the intake air amount measured by the AFM 21 in step S4. Instead, the intake air amount measured for engine control may be used.

If the difference between the two is smaller than the predetermined amount, it is determined that the AFM 21 is normal, the series of flows shown in FIG. 3 ends, and the process returns to the start again. On the other hand, if the difference therebetween is Kere size than the predetermined amount, determines that AFM21 is abnormal, the process proceeds to step S6. Here, it is determined whether or not the AFM 21 is abnormal depending on whether or not the difference between the two is larger than a predetermined amount. It may be determined whether or not.

  In step S6, the abnormality of the AFM 21 is determined in the low speed region of the engine rotation, and that effect is stored in the ECU 40.

  Subsequently, in step S7, it is determined whether or not the abnormality of the AFM 21 has been confirmed in the high speed region of engine rotation. That is, it is determined whether or not the abnormality of the AFM 21 is confirmed and the fact is stored in the ECU 30 in step S11 described later. If the abnormality of the AFM 21 is confirmed in the high speed range, the process proceeds to step S8, and the failure of the AFM 21 is confirmed. On the other hand, if the abnormality of the AFM 21 is not fixed in the high speed range, the series of flows shown in FIG.

  If it is determined in step S1 that the engine rotation speed is not the low speed region but the high speed region, the process proceeds to step S3, and it is determined whether or not the abnormality of the AFM 21 has been confirmed in the high speed region. That is, similarly to step S7, it is determined whether or not the abnormality of the AFM 21 is confirmed in step S11 to be described later and that fact is stored in the ECU 30. If the abnormality of the AFM 21 is confirmed, the series of flows shown in FIG. 3 ends, and the process returns to the start again. On the other hand, if the abnormality of the AFM 21 is not confirmed, the process proceeds to steps S9 and S10, and the abnormality determination of the AFM 21 in the high speed range is executed.

  In step S9, the amount of intake air is calculated from the pressure of the intake air and the engine speed. For example, the pressure of the intake air is calculated from the detection signal of the intake pressure sensor 27, the pressure of the intake air, the engine speed calculated in step S1, and the vertical axis stored in advance in the ECU 40 is the pressure of the intake air. The intake air amount is calculated based on a map shown in FIG. At this time, the EGR valve 28 is fully closed so that the intake pressure sensor 27 detects the pressure of the intake air not including the recirculated exhaust gas. In this way, the intake air amount is indirectly measured from the pressure of the intake air and the engine speed. This step S9 corresponds to second estimation means or estimation means for estimating the intake air amount using the pressure of the intake air and the rotational speed detected by the rotational speed sensor.

  In step S9, the intake air amount is directly measured by the AFM 21, as in step S4.

  Subsequently, in step S10, it is determined whether or not the AFM 21 is abnormal in the high speed range. That is, the intake air amount measured by the AFM 21 is compared with the intake air amount indirectly measured from the pressure of the intake air, and it is determined whether or not the difference between the two is larger than a predetermined amount. This step S10 corresponds to second determination means or determination means for determining whether or not the air flow meter in the present invention is abnormal. In step S10, the determination is made using the intake air amount measured by the AFM 21 in step S9. Instead, the intake air amount measured for engine control may be used.

  If the difference between the two is smaller than the predetermined amount, it is determined that the AFM 21 is normal, the series of flows shown in FIG. On the other hand, if the difference between the two is smaller than the predetermined amount, it is determined that the AFM 21 is abnormal, and the process proceeds to step S11. Here, it is determined whether or not the AFM 21 is abnormal depending on whether or not the difference between the two is greater than a predetermined amount. However, whether or not the AFM 21 is abnormal depending on whether or not the ratio between the two is out of a predetermined range such as around 1.0. It may be determined whether or not.

  In step S11, the abnormality of the AFM 21 in the high speed range is confirmed, and that effect is stored in the ECU 40.

  Subsequently, in step S12, it is determined whether or not the abnormality of the AFM 21 has been confirmed in the low speed region of engine rotation. That is, in step S6, it is determined whether or not the abnormality of the AFM 21 is confirmed and that is stored in the ECU 30. If it is determined in step S6 that the abnormality of the AFM 21 has not been confirmed, the series of flows shown in FIG. 3 ends, and the process returns to the start again. On the other hand, if the abnormality of the AFM 21 is confirmed, the process proceeds to step S8.

  In step S8, since the abnormality of the AFM 21 is determined in both the low speed region and the high speed region of the engine rotation, the failure of the AFM 21 is determined. Thereafter, a failure of the AFM 21 is notified to the vehicle occupant by a notification means such as a lamp or a buzzer indicating the failure, or the failure of the AFM 21 is stored as diagnosis information. This step S8 corresponds to failure determination means for determining a failure of the air flow meter in the present invention.

  As described above, the ECU 40 executes the failure diagnosis process for the AFM 21 and ends the failure diagnosis process when the failure of the AFM 21 is confirmed or when the engine 11 is stopped.

  As described above, in the present embodiment, when the engine rotation speed is in the low speed range, the intake air amount indirectly measured from the throttle opening and the engine rotation speed is compared with the intake air amount directly measured by the AFM 21. Yes. If the engine rotational speed is in the low speed range, the intake air amount can be detected with high accuracy from the throttle opening and the engine rotational speed, so that the presence or absence of abnormality of the AFM 21 can be diagnosed with high accuracy.

  Similarly, in the present embodiment, when the engine rotation speed is in a high speed range, the intake air amount indirectly measured from the pressure of the intake air and the engine rotation speed is compared with the intake air amount directly measured by the AFM 21. Yes. If the engine rotation speed is in a high speed range, the intake air amount can be detected with high accuracy from the pressure of the intake air and the engine rotation speed, so that the presence or absence of abnormality of the AFM 21 can be diagnosed with high accuracy.

  Furthermore, in the present embodiment, when the abnormality of the AFM 21 is determined when the engine rotation speed is both the low speed range and the high speed range, the failure of the AFM 21 is determined, so that a highly reliable failure diagnosis result can be obtained.

(Other embodiments)
(1) In the above-described embodiment, when both of the abnormality confirmation in the low speed region in step S6 and the abnormality confirmation in the high speed region in step S11 are completed in the failure diagnosis process of the AFM 21 executed by the ECU 40, the step Although the failure of the AFM 21 is determined in S8, even if both are not complete, the failure of the AFM 21 may be determined in step S8 when an abnormality is determined in either step S6 or step S11.

  (2) In the above-described embodiment, the intake air amount indirectly measured from the throttle opening and the intake air amount indirectly measured from the pressure of the intake air are respectively the intake air amount directly measured by the AFM 21 and Although the comparison has been made, a failure of the AFM 21 may be diagnosed by comparing only one of them with the intake air amount directly measured by the AFM 21.

  Also in this case, as in the above-described embodiment, the intake air amount indirectly measured from the throttle opening is compared with the intake air amount directly measured by the AFM 21 only when the engine speed is in the low speed range. By determining whether or not the AFM 21 has failed, it is possible to diagnose the presence or absence of the failure of the AFM 21 with high accuracy. Further, only when the engine speed is in the high speed range, the intake air amount indirectly measured from the pressure of the intake air is compared with the intake air amount directly measured by the AFM 21 to determine whether or not the AFM 21 has failed. Therefore, it is possible to diagnose the presence or absence of a failure of the AFM 21 with high accuracy.

  (3) In the embodiment described above, the intake air amount per unit time is compared in the comparison between the intake air amount measured indirectly and the intake air amount directly measured by the AFM 21. The amount of intake air may be compared.

  (4) In the above-described embodiment, the air flow meter failure diagnosis device of the present invention is applied to a control system for a diesel engine as an internal combustion engine. However, even if it is applied to a control system for a gasoline engine as an internal combustion engine. good. For example, even in a gasoline engine control system, if an air flow meter and an intake pressure sensor are used to estimate the EGR amount, the air flow meter failure diagnosis apparatus of the present invention is applicable.

  (5) The above-described embodiments may be arbitrarily combined within a feasible range.

DESCRIPTION OF SYMBOLS 11 Internal combustion engine 12 Intake passage 21 Air flow meter 25 Throttle valve 26 Throttle opening sensor 27 Intake pressure sensor 33 Crank angle sensor (rotational speed sensor of internal combustion engine)
40 ECU

Claims (2)

An intake passage (12) through which intake air taken into the internal combustion engine (11) flows;
An air flow meter (21) provided in the intake passage (12) for directly measuring an intake air amount;
A throttle valve (25) that is provided in the intake passage (12) separately from the air flow meter (21) and adjusts the intake air amount;
A throttle opening sensor (26) for detecting the opening of the throttle valve (25);
An intake pressure sensor (27) that is provided in the intake passage (12) separately from the air flow meter (21) and detects the pressure of intake air;
A rotational speed sensor (33) provided in the internal combustion engine (11) for detecting the rotational speed of the internal combustion engine;
When the rotational speed detected by the rotational speed sensor (33) is lower than a predetermined speed, the opening of the throttle valve (25) detected by the throttle opening sensor (26) and the rotational speed First estimation means (S4) for estimating the amount of intake air using the rotational speed detected by the sensor (33);
Whether or not the air flow meter (21) is abnormal by comparing the intake air amount obtained by the first estimating means (S4) with the intake air amount directly measured by the air flow meter (21). First determination means (S5) for determining
When the rotational speed detected by the rotational speed sensor (33) is higher than the predetermined speed, the intake air pressure detected by the intake pressure sensor (27) and the rotational speed detected by the rotational speed sensor (33). Second estimation means (S9) for estimating the intake air amount using
Whether the air flow meter (21) is abnormal by comparing the intake air amount obtained by the second estimation means (S9) and the intake air amount directly measured by the air flow meter (21). Second determination means (S10) for determining
A failure determination means (S8) for determining a failure of the air flow meter (21) when at least one of the first determination means (S5) and the second determination means (S10) is determined to be abnormal. Airflow meter failure diagnosis device.   The failure determination means (S8) determines a failure of the air flow meter (21) when both the first determination means (S5) and the second determination means (S10) are determined to be abnormal. The failure diagnosis apparatus for an air flow meter according to claim 1.

Images