JP2013204581A - Intake air quantity measurement device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem caused in the event of disconnection or short circuit in a pulse output type air flow sensor, wherein a signal shows an extremely abnormal value in the succeeding sampling period, and, even if a determination time is shortened as much as possible, an engine failure occurs and shifting to a fail safe operation is not possible.SOLUTION: An intake air quantity measurement device of an engine includes a second air quantity calculation means for calculating an air quantity in the event of an abnormality based on a cycle, a frequency or an intake air quantity immediately before it is determined that a temporary abnormality has occurred during a period from the time when the temporary abnormality has occurred in an air flow sensor to the time when it is determined that a failure has occurred in the air flow sensor, and a third air quantity calculation means for calculating an air quantity in the event of a failure as a substitute using an engine load parameter other than the intake air quantity, such as a throttle position, and an engine speed after it is determined that a failure has occurred in the air flow sensor.

Description

  The present invention relates to an intake air amount measuring device for an engine including an air flow sensor that outputs a pulse signal at time intervals (cycles) according to the intake air amount.

  In recent years, especially in the field of in-vehicle engines, it has become an important issue to improve fuel economy, exhaust emission characteristics, etc. Therefore, signals from analog sensors are A / D received by control units with built-in microcomputers. It is common to control the fuel injection amount (air-fuel ratio), the ignition timing, and the like, which are the main engine operation amounts, through conversion and digital arithmetic processing. In particular, since the accuracy required by the method of indirectly detecting the volume of intake air as a volumetric flow rate using an intake pipe pressure sensor is difficult to obtain, use an airflow sensor that can detect the mass flow rate, and further measure it by digital processing. It is desirable to increase accuracy.

  As the air flow sensor, a voltage output type that outputs a voltage at a level corresponding to the amount of intake air is generally used, but recently, high measurement accuracy is required as described above. As can be seen from 2 and 2 etc., an air flow sensor called a pulse output type or a frequency output type that outputs a pulse signal as a detection signal at a time interval (period) according to the amount of intake air is becoming widespread.

  When measuring the amount of intake air using an airflow sensor called this pulse (frequency) output type, usually the rising edge (or falling edge) of pulses coming from the airflow sensor one after another is detected, and the time of each pulse Time interval from the time when the leading edge (or falling edge) of the preceding pulse is detected to the time when the rising edge (or falling edge) of the succeeding pulse is detected (hereinafter referred to as pulse edge interval). Or simply referred to as an edge interval) is measured as a cycle by a built-in timer function, and the intake air amount used for engine control such as fuel injection control is calculated using the measured cycle.

  Further, when calculating the intake air amount using the cycle, the calculation timing of the intake air amount is set at every predetermined sampling cycle (period) or every predetermined rotation angle of the crankshaft, and immediately before this calculation timing. A case where the value of the cycle obtained in step S is converted into an intake air amount, a case where a plurality of the cycles are obtained in the sampling period, an average cycle thereof is calculated, and an average cycle is converted into an intake air amount; There is.

  In addition, if a failure occurs in the air flow sensor and its wiring system (hereinafter sometimes simply referred to as an air flow sensor), it may interfere with engine control. If it is determined that the alarm is given to the driver by lighting or blinking the lamp on the driver's seat panel and issuing a warning to the driver, for example, as described in Patent Document 3, It is known to compare a detection signal from an air flow sensor with a preset abnormality determination threshold value to determine whether or not a failure has occurred.

Japanese Patent No. 3808038 Japanese Patent Laid-Open No. 2-129522 Japanese Patent No. 3483968

  By the way, when the airflow sensor is of a voltage output type, a method is used in which the voltage value that has passed through the time constant of the input circuit is AD converted to an air amount. Because of the calculation processing by the microcomputer, the air amount is calculated as digital detection processing synchronized with a predetermined period or crank angle, but the output signal of the airflow sensor is analog in continuity.

  When disconnection, short circuit to the battery voltage VB, etc. occur in the airflow sensor wiring system, the output of the voltage output type airflow sensor changes as a first-order lag output due to the time constant of the input circuit as described above. Whether or not a failure has occurred in the air flow sensor is generally determined that a failure has occurred when a state in which the voltage value exceeds the upper and lower thresholds continues for a predetermined time.

  There are two types of air flow sensor failures: temporary ones (called temporary abnormalities) that occur due to momentary disconnection of connectors and harnesses that make up the wiring system, external noise, etc. Although there is a failure, the predetermined time for failure determination (time exceeding the threshold) required for airflow sensor failure determination is incorrect when the airflow sensor failure is the temporary abnormality. In order to avoid this, it is preferable to set the time as long as possible.

  On the other hand, if the airflow sensor failure is a true failure, it may impair the drivability and safety at the time of traveling, especially in the idle state when traveling or when the vehicle is stopped, Since it is required to immediately shift to the fail-safe operation when it is determined that there is a failure, it is preferable to set the time as short as possible.

  In this way, the required time for failure determination differs between the case where the failure of the air flow sensor is a temporary abnormality and the case where it is a true failure. Finding a fault as soon as possible should be given top priority, and it is desirable to set the fault judgment time as short as possible.

  Here, when the airflow sensor is a voltage output type, when a disconnection or short circuit occurs, the signal at the time of determination is abnormal due to a first-order lag output due to the time constant of the input circuit as described above. Although the value can be calculated as the intake air amount, the failure determination time can be set to a time during which the transition to the fail-safe operation can be performed without reaching the stall.

  On the other hand, when the airflow sensor is of the pulse (frequency) output type, it is necessary to measure the number of pulses in a predetermined sampling period or the edge interval (cycle, frequency) of the pulse signal and convert it to the intake air amount.

  If a break or short occurs in this pulse output type airflow sensor, the signal will change immediately to L (= 0V) and H (= 5V) because of the pulse signal even if there is a time constant of the input circuit. Therefore, there is almost no first-order lag output as in the voltage output method, and the signal shows an extreme abnormal value in the next sampling period. Therefore, there is a problem that the operation cannot be shifted to the fail-safe operation.

  The present invention has been made in view of the above circumstances, and the object of the present invention is when a temporary abnormality occurs in an air flow sensor that outputs a pulse signal at a time interval corresponding to the amount of intake air, as well as a true failure. It is an object of the present invention to provide an intake air amount measuring device for an engine that can detect the occurrence of occurrence of an intake air with certainty and obtain an alternative intake air amount as accurately as possible.

  In order to achieve the above object, an intake air amount measuring apparatus for an engine according to the present invention measures the edge intervals of pulse signals from an air flow sensor as sequential periods, and based on a frequency that is a measured period or a reciprocal thereof. Based on the first air amount calculating means for calculating the intake air amount used for engine control and the frequency or the intake air amount converted from the first air amount, and / or the frequency Or a temporary abnormality determination means for determining that a temporary abnormality has occurred in the air flow sensor when the intake air amount converted therefrom falls below or exceeds a predetermined abnormality determination threshold; It is determined whether or not a failure has occurred in the airflow sensor based on the frequency and a threshold value for failure determination that has been determined in advance. From the time when it is determined by the failure determination means and the temporary abnormality determination means that a temporary abnormality has occurred in the airflow sensor, until the time when the failure determination means determines that a failure has occurred in the airflow sensor. A second air amount calculating means for calculating an abnormality air amount based on the period, frequency or intake air amount before it is determined that the temporary abnormality has occurred, and the failure determining means. After determining that a failure has occurred in the air flow sensor, a third method of calculating an alternative failure air amount using an engine load parameter other than the intake air amount such as the throttle opening and the engine speed. And an air amount calculation means.

  According to the present invention, when a failure such as a disconnection in the air flow sensor or a short circuit to the battery voltage (VB) occurs, this failure can be reliably detected and other than the intake air amount such as the throttle opening degree. Since the alternative intake air amount is calculated using the engine load parameter, it is possible to shift to the fail-safe operation without reaching the engine stall.

Furthermore, even when a temporary abnormality occurs due to a momentary disconnection of the vehicle connector or harness, the air amount close to the actual intake air amount can be calculated by the second air amount calculating means. , Stability can be prevented.
Problems, configurations, and effects other than those described above will be clarified by the following embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows one Example of the intake air amount measuring apparatus based on this invention with the vehicle-mounted engine to which it is applied. FIG. 2 is a diagram for explaining an engine control system including the control unit shown in FIG. The functional block diagram with which an example of an intake air amount calculation method in case an airflow sensor is a pulse (frequency) output type is used. The figure used for description of an example of the intake air amount calculation method when the airflow sensor is a voltage output type. The characteristic view which shows the relationship between the output frequency and period of an airflow sensor, and the amount of intake air. The functional block diagram with which it uses for description of an example of the intake air amount calculation method with which the airflow sensor abnormal failure countermeasure of the Example of this invention was taken. The time chart used for description of an example of the calculation method of the intake air amount when the airflow sensor is normal. The time chart used for description of an example of the intake air amount calculation method at the time of an airflow sensor failure. FIG. 6 is a time chart used for comparison when (A) the airflow sensor is a voltage output type and (B) the airflow sensor is a pulse (frequency) output type when the airflow sensor fails. The time chart which is provided for description of the example of calculation of the intake air amount in which the countermeasures against the abnormal failure of the air flow sensor of the embodiment of the present invention are taken. The flowchart which shows an example of the process sequence at the time of calculating | requiring a pulse edge space | interval (period) in the present invention Example. The flowchart which shows an example of the process sequence at the time of calculating | requiring an intake air amount in this invention Example. The flowchart which shows an example of the process sequence performed when determining whether the failure generate | occur | produced in the Example of this invention. The flowchart which shows an example of the process sequence performed at the time of determination whether the temporary abnormality in this invention Example has generate | occur | produced. The flowchart with which it uses for description of the process sequence which calculates | requires the failure era change air quantity in this invention Example.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an intake air amount measurement device according to the present invention together with an example of an in-vehicle engine to which the intake air amount measurement device is applied.

  In FIG. 1, an engine 10 to which the intake air amount measuring device of the present embodiment is applied is, for example, a port injection type multi-cylinder engine (MPI type) having four cylinders (# 1, # 2, # 3, # 4). Engine) having a cylinder 11 composed of a cylinder head 11a and a cylinder block 11b, and a piston 15 slidably inserted into each cylinder of the cylinder 11. The piston 15 is connected via a connecting rod 14. Are connected to the crankshaft 13. A combustion chamber 17 having a ceiling with a predetermined shape is defined above the piston 15, and an ignition plug 35 to which a high-voltage ignition signal is supplied from the ignition coil 34 is erected in the combustion chamber 17 of each cylinder. Has been.

  The air used for fuel combustion passes from the air cleaner 22 through the intake passage 20 including the throttle body 26, the collector 27, the intake manifold 28, the intake port 29, etc. where the electric throttle 25 is disposed, and at the downstream end. The air is sucked into the combustion chamber 17 of each cylinder via an intake valve 21 that is disposed at the end of an intake port 29 and is driven to open and close by an intake camshaft 23. A fuel injection valve 30 that injects fuel toward the intake port 29 is provided for each cylinder in the intake manifold 28 that is the downstream portion of the intake passage 20.

The mixture of the air sucked into the combustion chamber 17 and the fuel injected from the fuel injection valve 30 is combusted by spark ignition by the spark plug 35 connected to the ignition coil 34, and the exhaust gas is burned into the combustion chamber 17. Then, the exhaust gas is discharged into the outside atmosphere through an exhaust passage 22 including an exhaust port, an exhaust manifold, an exhaust pipe, and the like through an exhaust valve 22 that is opened and closed by an exhaust camshaft 24. A three-way catalyst 60 for purifying exhaust gas is disposed in the exhaust passage 40, and on the upstream side of the catalyst 60, a linear air-fuel ratio sensor 51 having an output characteristic linear with respect to the air-fuel ratio before catalyst is disposed, An O ₂ sensor 52 that outputs a switching signal for identifying whether the post-catalyst air-fuel ratio is richer or leaner than the stoichiometric (stoichiometric air-fuel ratio) is disposed downstream of the catalyst 60.

  The fuel injection valve 30 provided for each cylinder is supplied with fuel in the fuel tank 71 adjusted to a predetermined fuel pressure by a fuel supply mechanism having a fuel pump 72, a fuel pressure regulator 73, etc. The valve 30 is driven to open by a fuel injection pulse signal having a duty (= pulse width = corresponding to the valve opening time) supplied from the control unit 100 described later and corresponding to the operation state at that time. An amount of fuel corresponding to the time is injected toward the intake port 29.

  On the other hand, a control unit 100 with a built-in microcomputer is provided to perform various controls of the engine 10, that is, fuel injection control (air-fuel ratio control) by the fuel injection valve 30, ignition timing control by the spark plug 35, and the like. It has been.

  As shown in FIG. 2, the control unit 100 is basically well-known hardware, and includes an I / O including a CPU 101, an EP-ROM 102, a RAM 103, an A / D & D / A converter, and the like. / OLSI105 etc. In this example, the CPU 101, the EP-ROM 102, the RAM 103, and the I / O LSI 105 are provided separately, but in recent years, some of them are combined into one, and it may be used. Needless to say.

  The I / OLSI 105 of the control unit 100 has an input signal as an input signal that is a hot wire type (hot wire type, thermal type, thermal resistance type, which will be described in detail later) on the upstream side of the electric throttle 25 in the intake passage 20. A signal corresponding to the intake air amount detected by the air flow sensor 50, a signal corresponding to the opening degree of the electric throttle 25 detected by the throttle sensor 54, a crank angle sensor (attached to the crankshaft 13) Crank angle signal representing the rotation / phase (crank angle) of the crankshaft 13 obtained from the rotation speed sensor 55, and the rotation / phase of the camshaft 23 obtained from the cam angle sensor 56 attached to the exhaust camshaft 24. A cam angle signal, a signal corresponding to the exhaust air / fuel ratio from the air / fuel ratio sensors 51 and 52 disposed in the exhaust passage 40, a signal corresponding to the accelerator pedal depression amount from the accelerator sensor 53, and the cylinder block 11b. A signal corresponding to the engine cooling water temperature detected by the water temperature sensor 58, a signal corresponding to the intake air temperature detected by the intake air temperature sensor 59 disposed at the most upstream part in the intake passage 20, and an annex to the control unit 100 A signal corresponding to the atmospheric pressure from the atmospheric pressure sensor 57 is supplied, and a signal from the ignition key 49 which is a main switch for operating and stopping the engine 10 is also supplied. Information such as the machine shift position and vehicle speed is also provided from the vehicle control unit through inter-unit communication.

  In accordance with the program stored in the EP-ROM 102, the control unit 100 takes in the signals from the sensors as inputs, executes predetermined arithmetic processing, grasps the operating state of the engine 10, and based on this operating state. The main operation amount of the engine 10 such as the fuel injection amount, ignition timing, throttle opening, etc. is calculated to generate necessary control signals, and the fuel injection valve 30, ignition coil 34, electric Fuel injection control (air-fuel ratio control), ignition timing control, throttle opening control, and the like are performed by supplying the control throttle 25 with predetermined timing.

Next, the hot wire airflow sensor 50 will be described.
The air flow sensor 50 increases the amount of current flowing through the heat wire (heating resistor) placed in the air flow to be measured as the intake air amount (mass flow rate) increases, and conversely decreases as the intake air amount decreases. A bridge circuit is formed, and is extracted as a voltage signal from the flowing heating resistance current. The voltage signal corresponding to the intake air amount is converted into a frequency by voltage frequency (VF conversion circuit) conversion, and the signal of the output signal voltage changes from the air flow sensor 50 according to the air amount, in other words, the detection signal. As shown, pulse signals are output at time intervals (cycles) according to the amount of intake air.

FIGS. 5A and 5B show the relationship between the output frequency and period of the air flow sensor and the intake air amount.
As shown in the figure, when the amount of intake air is small, the frequency of the output signal is low, and when the amount of intake air is large, the frequency of the output signal is high and its characteristics are nonlinear. Since the frequency and the cycle are in a reciprocal relationship, the relationship between the cycle and the intake air amount is a reverse characteristic of the relationship between the frequency and the intake air amount. In addition, since the sensor output is set according to the required air amount of the engine, the relationship between the frequency and the intake air amount or the relationship between the cycle and the intake air amount may be reversed, and the characteristic may be linear. However, only the conversion table changes for arithmetic processing.

  Here, in the case of the non-linear characteristics as shown in the figure, since the amount of change in the air amount per unit period (frequency) is not uniform, for example, when trying to control based on the failure state or the amount of change, the air amount It is necessary to consider whether to use the value converted to, or to use the period (frequency).

  The control unit 100 calculates the intake air amount using the pulse signal from the air flow sensor 50, and uses the obtained intake air amount for the fuel injection control, ignition timing control, throttle opening control, and the like. Here, taking fuel injection control as an example, the control unit 100 performs pulse edge intervals (period Pt) of the pulse signal from the airflow sensor 50 in blocks 151 and 152 as shown by functional blocks in FIG. Is calculated by the built-in timer, and the frequency Fu which is the reciprocal (1 / Pt) is calculated, and the calculated frequency Fu is calculated in the block 153 of the frequency-air amount conversion block 150, for example, FIG. Is converted into an intake air amount by collating with a frequency-intake air amount conversion table expressed by the relationship shown in FIG. 6 and subjected to digital filter processing so that the converted intake air amount can be used for various controls in block 154. An intake air amount Q is obtained, based on the intake air amount Q in block 155 and the engine speed obtained using the crank angle signal from the crank angle sensor 55 in block 156. The basic fuel injection amount is calculated, and the exhaust amount calculated based on the correction amount corresponding to the engine coolant temperature detected by the water temperature sensor 58 and the signals from the air-fuel ratio sensors 51 and 52 is calculated. The fuel injection amount is calculated by adding a correction coefficient according to the fuel ratio, etc., and a drive pulse signal Tout having a fuel injection pulse width (duty) corresponding to the fuel injection amount is generated to give a predetermined value to the fuel injection valve 30. Supply at the timing.

  Similarly, the intake air amount Q is also used for ignition timing control, throttle opening control, and the like, and the calculation results thereof are stored in the RAM 103 or EP-ROM 102.

  The intake air amount Q is an intake air amount used for engine control such as fuel injection control, and this intake air amount Q is called a use intake air amount or simply an air amount Q (Qa, Qb, Qc...). There is.

  Next, before explaining the abnormality / failure related processing of the pulse (frequency) output type hot-wire airflow sensor 50 of the embodiment of the present invention, a method for calculating the intake air amount when using a conventional voltage output type airflow sensor Will be described with reference to FIG.

  In the conventional example shown in FIG. 4, the intake air amount calculation is performed after high-frequency noise is cut by a predetermined first-order lag filter effect via a CR filter circuit indicated by C1 and R1 as an input processing circuit inside the control unit. A / D conversion block 211 of block 210 performs AD conversion, and the converted voltage equivalent value is taken in as Vu, and this voltage value Vu is converted into intake air amount by digital filter block 212. The block 212 and subsequent blocks are the same as the block 155 and subsequent blocks in FIG.

  FIG. 7 is a diagram for explaining the relationship between the output signal of the pulse (frequency) output type airflow sensor 50 and the cycle calculation timing.

  Hereinafter, the calculation method of the calculated air amounts Qa to Qd from the time point Ta to the time point Td, which is the flow rate calculation timing in FIG. 7, will be specifically described. The flow rate calculation timing is executed at a predetermined sampling interval (Tsm), for example, every 2 ms.

  First, the timer counter detects the rising edge of the pulse signal that is the output of the airflow sensor 50, and stores the timer value at that time.

  At the sampling timing (time point) Ta, the timer count value (cycle Pt_an) calculated immediately before is once converted into the frequency Fu (= 1 / Pt_an), and then the frequency-air amount as shown in FIG. The air quantity Qa is obtained by converting into a flow rate unit using a conversion table.

  Here, an example is shown in which Q is calculated based on the previous pulse period, but multiple pulse periods are detected during the sampling interval (period Tsm), so these are averaged to calculate Q. The technique to be taken.

  Similarly, at the next sampling timing Tb, the air amount Qb is obtained using the timer count value Pt_b4 stored immediately before, and thereafter Qc, Qd,... [Q (n)] are obtained in the same manner.

  In the above example, the frequency Fu is converted to the air amount QFo having the flow rate unit by the conversion table, but the cycle Pt_an is directly converted to the air amount by the cycle-air amount conversion table as shown in FIG. You may make it convert.

  On the other hand, FIG. 8 shows an example in which the output signal from the airflow sensor 50 does not come after time point I due to disconnection under the same conditions as in the case shown in FIG.

  In the above state, since no pulse is detected after time point I, the timer counter (Pt_c3) at the next sampling timing Tc becomes an air amount Qc that is extremely smaller than the air amount Qb at the previous sampling timing Tb. The air amount Qd at the sampling timing Td is substantially equal to zero. That is, when a disconnection occurs, the minimum value of the air amount is detected when the sampling period Tsm is 2 degrees (4 ms) at the maximum.

  Fig. 9 (A) shows a case where a disconnection occurs in a conventional voltage output type air flow sensor, and Fig. 9 (B) shows a case where a disconnection occurs in a pulse output type air flow sensor (no abnormality / failure countermeasures). The occurrence time of each disconnection is indicated by I ′ and I.

  First, when a disconnection occurs at the time point I ′ in the voltage output type airflow sensor of FIG. 9 (A), the AD conversion capture value from the sensor is V1 ( From V), the attenuation as indicated by Vu is followed to reach the V2 (V) value. The calculated air amount at this time follows the attenuation shown in Q1 to Qv.

  Whether or not a failure has occurred is determined by comparing the sensor output with the failure determination threshold VL (V) [greater than 0 (V)]. When the failure judgment time starts to be measured at time J 'when the value falls below, the failure occurs at time K' when the time that falls below the failure judgment threshold VL (V) reaches the judgment time tDg. Determination (confirmation) is made, and a failure confirmation flag fVD is set. The transition to fail-safe control is executed with the setting of this flag as a trigger, and until the failure is confirmed, it is controlled by the detected air amount Q, so the air amount Qv is the minimal amount of Q2. (However, it is slightly larger than 0), and the engine speed decreases from N1 to Nv to N2. When transitioning to fail-safe control at time K ', if Q2 is large to some extent, the speed can be restored as indicated by N2 to N3 (broken line), and the engine does not reach the engine stall state. can do.

  On the other hand, in the pulse output type airflow sensor shown in FIG. 9 (B), the edge interval of the pulse signal from the airflow sensor of (a) was measured as a period, and the measurement was performed as shown in (a ′). The frequency is obtained from the period. In this pulse output type air flow sensor 50 in Fig. 9 (B), if no abnormality or failure countermeasures are taken, assuming that a disconnection occurs at the time point I, the frequency is as indicated by Fu from F1 (Hz). Follows the proper attenuation and reaches the F2 (Hz) value. The air amount calculation value at this time attenuates from Q1 to QFo.

  The determination of whether or not a failure has occurred is performed based on the failure determination threshold value FLs (Hz) for the frequency, measurement of the failure determination time is started at time point J, and the failure determination threshold value FLs ( It is determined (determined) that a failure has occurred at the time point K when the time below (Hz) has reached the predetermined determination time tDg, and a failure determination flag (fFDs) is set. The transition to fail-safe control is executed with this flag set as a trigger, and until the failure is confirmed, it is controlled by the detected air volume (QFo). The engine reaches the minimum value, and the engine speed follows N1 to Nf, and Nf2 reaches the engine stall state. When fail-safe control is entered at time K, it is not possible to return from a state such as an engine stall, so an operation such as restart is required.

Next, an embodiment of the present invention (when an abnormality / failure countermeasure is taken for the airflow sensor 50) will be described with reference to FIGS.
As shown in the functional block in FIG. 6, when the air flow sensor 50 is normal, the pulse edge interval (period Pt) of the pulse signal from the air flow sensor 50 is set as described above with reference to FIG. While measuring with the built-in timer (block 151 in FIG. 3), the block 152 calculates the frequency Fu which is the reciprocal (1 / Pt), and the calculated frequency Fu is calculated in the frequency-air amount conversion block 150, for example, Digital filter processing so that the intake air amount can be converted into the intake air amount by referring to the frequency-intake air amount conversion table expressed in the relationship shown in 5 (A), and the converted intake air amount can be used for various controls. To obtain the intake air amount Q (QFo), and in block 155, use this intake air amount Q (QFo) and the engine speed to calculate the fuel injection amount according to the operating state of the engine and respond to this fuel injection amount Fuel injection pulse width (du Supplied at a predetermined timing to generate the drive pulse signal Tout having a tee) to the fuel injection valve 30.

In addition to the above, in the present embodiment, measures are taken as follows when an abnormality or failure occurs in the airflow sensor 50.
That is, a temporary failure determination means 320 for determining whether or not a temporary failure has occurred (hereinafter referred to as a temporary failure in order to distinguish it from a true failure), and whether or not a true failure has occurred A failure determination means 370 for determining the above-described period-frequency calculation block 152 for calculating a normal intake air amount (sometimes referred to as a normal air amount) QFo in which no abnormal failure has occurred in the airflow sensor 50; A first air amount calculating means 140 comprising a frequency-air amount conversion block 150 and the like; a second air amount calculating means 330 for calculating an abnormal air amount QFw when a temporary abnormality occurs; If it is determined that an abnormality has occurred in the air flow sensor 50 and the third air amount calculating means 350 for calculating the intake air amount (air amount for failure) QFs as an alternative when a failure occurs, Normal air volume QFo calculated by the air volume calculation means 140 When the air flow sensor 50 is determined (determined) that the air flow sensor 50 and the air flow sensor 50 are switched to the air flow amount QFw for the time of abnormality calculated by the second air amount calculating means 330. Failure that switches from the air amount QFu (normal air amount QFo or abnormal air amount QFw) from the abnormal time switching means 335 to the failure air amount QFs calculated by the third air amount calculating means 350 Hour switching means 345.

  The temporary abnormality determination means 320 determines whether an abnormality has occurred in the air flow sensor 50 based on the frequency Fu calculated in the period-frequency calculation block 152 and the air amount QFo calculated in the frequency-air amount conversion block 150. (Details will be described later).

  The failure determination means 370 determines (determines) whether or not a failure has occurred in the airflow sensor 50 based on the frequency Fu calculated by the period-frequency calculation block 152.

  The second air amount calculation means 330 is based on the frequency Fu calculated in the period-frequency calculation block 152 and the air amount QFo immediately before calculated in the frequency-air amount conversion block 150. Is calculated.

  Temporary abnormality determination means 320 includes sudden change determination means 321 for determining whether or not the frequency Fu or air amount QFo has changed suddenly, and the frequency Fu or air amount QFo and a preset abnormality determination threshold value. When there is an abnormality threshold value comparison means 322 to compare, and it is determined that an abnormality has occurred in the air flow sensor 50 by at least one of them, the abnormality time switching means 335 causes the first air amount calculation means 140 to Switching from the calculated normal air amount QFo to the abnormal-time air amount QFw calculated by the second air amount calculating means 330 is performed.

  As described above, the period from when it is determined that a temporary abnormality has occurred by the temporary abnormality determination unit 320 to when it is determined (determined) that the air flow sensor 50 has failed by the failure determination unit 370 is abnormal. In the hour switching means 335, the abnormal time air amount QFw is used as the air amount Q.

  In addition, when the failure determination means 370 determines that the airflow sensor 50 has failed and is confirmed, the failure switching means 345 causes the air amount QFu (normal air amount QFo or abnormal time use) Switching from the air amount QFw) to the failure air amount QFs calculated by the third air amount calculating means 350 is performed.

  FIG. 10 shows, in the case of using the pulse output type airflow sensor 50, a solid line in the case where the countermeasure against the abnormal failure as described with reference to FIG. 6 is taken. A broken line indicates a case where a failure such as a disconnection or a VB short-circuit occurs when no failure countermeasure is taken.

  In the pulse (frequency) output type airflow sensor 50, the pulse signal disappears even when the signal line is shorted to VB, so the determination method is the same as in the case of disconnection.

  In the embodiment of the present invention, the absolute value of the difference from the previous value is taken every predetermined time from the time point I until the threshold value FLs (Hz), QLs reaches the determination threshold value FLs (Hz) from the time point I, and | dF / dt | = (Fu-Fu [old]) or | dQ / dt | = (QFo-QFo [old]) is calculated as “for sudden change determination” ([old]: previous value).

  On the other hand, as the air amount QFw at the time of abnormality, a value obtained by applying a first-order lag digital filter shown in the equation (1) is calculated every predetermined time. Here, the gain G is preferably set to a small value, that is, a value that lengthens the decay time.

Further, as other means, the average value as shown in the equation (2) for each sampling period, or the latest value or the above equation (1) in a time (for example, 20 ms) longer than the sampling period (for example, 2 ms) A method of updating and saving the filter calculation result and the average value of equation (2) is used.
These calculations are always performed, and once it is determined that the abnormality is temporary, new updating is stopped and the previous value is held until the normal range is reached.

  Next, at time point I, the low-side failure determination threshold value FLs for determining whether or not “failure has been confirmed” is set for the frequency at a predetermined calculation cycle from a fixed value or a table setting value. In addition, the air amount Q includes a low-side abnormality determination threshold value QLs for determining whether or not a “temporary abnormality” has occurred, and a threshold value dQLs for “sudden change determination”. These are set in advance, and are set by searching from a map value or a table value set in advance according to the parameters representing the engine load other than the intake air amount such as the engine speed and the throttle opening and the charging efficiency. Yes.

  Here, the abnormality determination threshold value QLs for determining whether or not “temporary abnormality” has occurred is different from the failure determination threshold value for “Failure determination” with respect to the frequency, not the air amount Q. (In this case, the abnormality determination threshold FLs' is higher than the threshold for “Failure determination”). In some cases, it is possible to detect the occurrence of a “temporary abnormality” earlier depending on the frequency. Further, the threshold value dQLs for “sudden change determination” is set to an air amount change amount per unit time which is impossible in a normal operation state.

  As described above, when a disconnection occurs at time point I, the frequency follows the attenuation shown by Fu from F1 (Hz) and reaches the F2 (Hz) value. The calculated air amount at this time follows the attenuation from Q1 to QFo indicated by the broken line.

At this time, | dQ / dt | for sudden change judgment takes the peak value shown in dQf_a, and when the judgment threshold value dQLs is exceeded, [1] “Recognizes sudden change” and [2] “Temporary abnormality” judgment When it falls below the threshold value QLs, it is recognized as a temporary abnormality.
Whether or not a “temporary abnormality” has occurred is determined by whether or not one of the following (i) and (ii) is satisfied.
(i): When [1] or [2] above is established
(ii): When [1] and [2] above are true

  The former (i) is a value that is not normally possible as a value that is larger than the fastest possible change amount due to | dQ / dt | in a region with a relatively large air amount such as full throttle when the air amount characteristic is nonlinear. Can be set in advance, which is advantageous when fast detection is desired.

  The latter (ii) means that the certainty of temporary abnormality judgment is increased, and it has the effect of avoiding erroneous judgment of sudden change establishment, but because there is a possibility that detection can be sent accordingly, actual driving The selection should be made in consideration of the effect on sex.

  As described above, it is possible to determine whether or not a `` temporary abnormality '' has occurred earlier than when the frequency falls below the failure determination threshold value FLs (Hz)). It is possible to shift to the abnormal air amount QFw calculation by the second air amount calculation means 330.

  As shown in FIG. 10 (d), the abnormal air amount QFw calculated by the second air amount calculating means 330 is QFw [1] in the digital filter of Equation (1) and QFw in Equation (2). It becomes a value like [2], and even if a temporary abnormality occurs, it is calculated as an air amount that has not been reduced so much, based on the previous value.

  If the disconnection or VB short-circuit condition continues even during control using the above-mentioned abnormal air volume QFw, the failure determination time is measured at the point J when the low-side threshold FLs for "Failure determination" is reached. Is determined (confirmed) at the time K when the time below the failure determination threshold value FLs (Hz) reaches the predetermined determination time tDg, and the failure determination flag (fFDs) is set. The At this time point K, the operation proceeds to the failure time air amount calculation by the third air amount calculation means 350, and control using the failure time air amount QFs is performed from Qf2_a1 or Qf2_a2 at the time point K.

  As described above, in the conventional control, the Qf2 air amount has already reached the minimum value, the engine speed has traced from N1 to Nf, and Nf2 has reached the stalled state, but at time point K, it shifts to fail-safe control. Therefore, it is possible to avoid a situation where the engine speed drops to N2f_a close to 0, and since the speed can be restored and maintained after the time point K, it is surely prevented that the engine stalls. be able to.

  Next, an example of a program (processing procedure) executed when the control unit 100 calculates the intake air amount (when normal and when abnormality / failure occurs) will be described with reference to the flowcharts of FIGS.

  FIG. 11 shows the processing that is started at every rising or falling pulse edge of the frequency signal detected from the airflow sensor 50. Generally, it is started as an interrupt calculation processing, and the same processing as the microcomputer function Some have

  First, when an edge is detected in step 510, the count value Pt (n) measured by the timer function is latched in step 520. Next, at step 530, the difference from Pt (n-1) stored at the previous edge detection is taken, and Pt is calculated. This is the latest frequency information.

  FIG. 12 shows each calculation means repeatedly executed at a sampling cycle, for example, 2 ms of the program calculation job cycle. In step 1000, the cycle Pt is calculated by the processing procedure shown in FIG. Then, in the next step 1010, an operation equivalent to 1 / Pt division is performed to calculate the frequency Fu for each pulse.

  In step 1020, QFo is calculated from the calculated frequency Fu using a frequency-air amount conversion table as shown in block 150 of FIG.

  In the next step 1030, the calculated QFo or Fu and the difference amounts dQ / dt and dF / dt from the previous value are calculated.In step 1040, the above-mentioned equation (1) or equation (2) etc. Calculate air volume QFw.

  In step 1050, a failure determination process is performed, and in step 1060, a temporary abnormality (shown in FIGS. 13 and 14) determination process is performed. The process proceeds to step 1100 to determine whether or not a failure is determined (determined). If it is determined (determined) that there is a failure, the process proceeds to step 1110, the failure air amount QFs is set as the air amount Q, and this routine is terminated.

  If it is determined in step 1100 that the failure has not been confirmed, the process proceeds to step 1200 to determine whether or not there is a temporary abnormality. If it is determined that there is a temporary abnormality, in step 1210, the abnormality air amount QFw is set as the air amount Q, and this routine ends.

  If it is determined in step 1200 that there is no temporary abnormality, that is, it is determined to be normal, the process proceeds to step 1300, the normal air amount QFo is set to the air amount Q as it is, and this routine is ended.

  Here, the failure determination process (M) in step 1050 of FIG. 12 will be described in detail with reference to FIG. 13, and the temporary abnormality determination process (R) in step 1060 will be described in detail with reference to FIG.

  The failure determination process (M) shown in FIG. 13 compares the frequency Fu with the low-side failure determination threshold value FLs in step 2000. If Fu is greater than FLs, proceed to step 2100, check the OK timer count value, and if the OK count timer is greater than the predetermined time tDok, that is, if the elapsed time from time point I is longer than the predetermined time tDok, proceed to step 2220, The failure confirmation flag fFDg and the NG timer tDg are cleared, RETURNed, and the process proceeds to Step 1060 in FIG.

  If the elapsed time from the time point I has not reached the predetermined time tDok in step 2100, the OK count timer is counted up in step 2220 and RETURNed.

  If “YES” in step 2000, that is, if the frequency Fu is smaller than the failure determination FLs, the process proceeds to step 2110, the NG timer count value is checked, and the NG timer is larger than tDg, that is, the elapsed time from time point J is predetermined for failure determination. If it is longer than the time tDok, the process proceeds to step 2130, the failure confirmation flag fFDg is set, the OK timer (tDok) is cleared in step 2140, RETURN is performed, and the process proceeds to step 1060 in FIG. If the elapsed time does not reach the predetermined time tDg in step 2110, the NG count timer is incremented in step 2120 and RETURNed.

  The temporary abnormality determination process (R) shown in FIG. 14 has two methods (a) and (b) .In the method (a), in step 3000, the determination of `` sudden change establishment '' is made. Compare with threshold (dFLs, or dQLs). If No, that is, smaller than the threshold value, the process proceeds to step 3100, and further compared with the low-side threshold value QLs for sudden change determination. If No, that is, normal state, the process proceeds to step 3200.

  If larger than the threshold value in step 3000, the process proceeds to step 3300, a temporary abnormality flag (fdgck) is set, RETURN is performed, and the process proceeds to step 1100 in FIG.

  In step 3100, the absolute level of QFn is compared. If it is small, that is, outside the normal range, the process proceeds to step 3300, a temporary abnormality flag (fdgck) is set, RETURN is performed, and the process proceeds to step 1100 in FIG.

  In Step 3200, it is determined whether or not the absolute level of the frequency Fu is within the normal range. If it is within the normal range, the temporary abnormality flag fdgck is cleared and RETURN is performed in Step 3400.

  If it is not in the normal range in step 3200, RETURN is performed. That is, once a temporary abnormality is set in step 3300, the determination is held unless the frequency (Fu) returns to the normal range. For example, even if a temporary momentary interruption occurs, it is determined that the abnormality is a temporary abnormality, and once it has shifted to the abnormal air amount QFw and returned to the normal range, it returns to the normal air amount QFo. By doing so, deterioration of drivability can be prevented.

FIG. 14 (b) shows that a temporary abnormality determination is established at step 3300 ′ when the sudden change determination at step 3000 is established and the absolute level of QFn is outside the normal range at step 3100 ′. It is a thing. This process means that the certainty of temporary abnormality determination is increased, and there is an effect of avoiding erroneous determination of sudden change determination, but there is a possibility that detection can be sent accordingly. If the threshold value QLs on the low side is not reached, it is not determined as a temporary abnormality, and calculation is performed using the detected air amount QFo. There is also an effect that the possibility of erroneous determination of sudden change determination can be prevented, for example, when the amount suddenly decreases.
Whether to take FIG. 14 (a) or (b) above may be determined in consideration of the influence on the actual drivability of the vehicle.

  On the other hand, as shown in FIG. 15, apart from the above calculation timing, for example, at a timing repeatedly executed at the calculation job cycle of the program, such as 10 ms, the failure-time air amount QFs is changed to the engine speed and the throttle opening (etc. The engine load parameters other than the intake air amount, the charging efficiency, etc.) are calculated.

  As described above, the calculation of the intake air amount Q can be realized so as not to impair the drivability of the engine and the vehicle in the transition to the fail-safe operation when a temporary abnormality occurs or a failure occurs.

10 engine
11 cylinders
20 Air intake passage
25 Electric throttle
30 Fuel injection valve
34 Ignition coil
35 Spark plug
50 Hot wire air flow sensor
55 Crank angle sensor
100 control unit

Claims (6)

An intake air amount measuring device for an engine comprising an air flow sensor that outputs a pulse signal at a time interval corresponding to an intake air amount,
First air amount calculation means for calculating an intake air amount to be used for engine control based on a frequency which is a cycle which is a cycle which is the measured cycle or its reciprocal, while measuring the edge interval of the pulse signal from the air flow sensor sequentially. ,
Based on the frequency or the intake air amount converted from the frequency, it is recognized that they have suddenly changed, and / or the frequency or the intake air amount converted from the predetermined threshold for abnormality determination is set. A temporary abnormality determining means for determining that a temporary abnormality has occurred in the air flow sensor when the air flow sensor is turned down or up;
Failure determination means for determining whether or not a failure has occurred in the airflow sensor based on the frequency and a threshold value for failure determination determined in advance;
After the temporary abnormality determining means determines that a temporary abnormality has occurred in the air flow sensor, the temporary abnormality determination means determines that the failure has occurred in the air flow sensor. A second air amount calculating means for calculating an abnormality air amount based on the period, frequency or intake air amount before it is determined that an abnormality has occurred;
Third air amount calculating means for calculating a substitute air amount for failure based on an engine load parameter other than the intake air amount after it is determined by the failure determining means that the air flow sensor has failed. And an intake air amount measuring device for an engine, comprising:   The temporary abnormality determining means obtains a change amount per predetermined time or predetermined crank angle of the frequency or intake air amount, and when the change amount exceeds a predetermined threshold value, the frequency or intake air amount 2. The intake air amount measuring device for an engine according to claim 1, wherein the amount of the intake air is recognized as having suddenly changed.   3. The abnormality determination threshold value is set based on engine load parameters other than the intake air amount, such as engine speed and throttle opening, and charging efficiency. Engine intake air volume measuring device.   The second air amount calculation means is the period, frequency or intake air amount immediately before it is determined that the temporary abnormality has occurred, or the period, frequency or intake air amount within a predetermined period including immediately before. The engine intake air amount measuring device according to any one of claims 1 to 3, wherein the abnormality air amount is calculated on the basis of the air pressure.   5. The abnormal air amount according to claim 1, wherein the second air amount calculating means obtains the abnormal air amount by performing a filtering process by a first-order lag calculation or a weighted average calculation on the frequency or the intake air amount. The intake air amount measuring device for an engine according to any one of the above.   After the air flow sensor is determined to have failed, the third air amount calculation means is the substitute, using the engine speed, the throttle opening as the engine load parameter other than the intake air amount, and the charging efficiency. The engine intake air amount measuring device according to any one of claims 1 to 5, wherein a failure air amount is calculated.

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