JP4646819B2 - Abnormality determination device for internal combustion engine - Google Patents

Description

  The present invention relates to an apparatus for determining an abnormality in a fuel supply system of an internal combustion engine.

In Patent Document 1, an air-fuel ratio for each cylinder is estimated using an exhaust system model based on an output of an air-fuel ratio sensor provided in the exhaust system and an observer, and the air-fuel ratio deviation between the cylinders is eliminated. In addition, in the technology for performing feedback control of the air-fuel ratio of each cylinder, a technology is disclosed in which abnormality of the cylinder is determined when the correction term of the air-fuel ratio feedback is not within a predetermined range.
Patent No. 2684011

  However, in the conventional technique such as Patent Document 1, abnormality detection is executed based on the exhaust system model. Therefore, unless it is executed in a state where the operation state is stable (for example, during steady running), the influence of the estimation accuracy of the air-fuel ratio is affected. May cause a misjudgment.

  An object of the present invention is to provide an abnormality determination device for an internal combustion engine that can accurately detect an abnormality in a fuel supply system regardless of an operating state.

  The present invention provides an abnormality determination device for an internal combustion engine that calculates an ignition delay from in-cylinder pressure detection means provided in each cylinder and determines an abnormality in a fuel supply system based on an air-fuel ratio correction coefficient calculated from the ignition delay. provide. This device is provided for each cylinder of the internal combustion engine, and includes a pressure detection means for detecting the pressure in the cylinder, an estimation means for estimating the motoring pressure of the internal combustion engine, and a period from the compression stroke to the combustion stroke of the internal combustion engine. An ignition delay calculating means for detecting a time when a difference between the cylinder pressure and the motoring pressure exceeds a predetermined value as a combustion start time, and calculating an ignition delay from the ignition time to the combustion start time for each cylinder; An average value of the ignition delay of each cylinder is calculated, and a deviation between the average value of the air-fuel ratio of each cylinder and the air-fuel ratio of each cylinder is calculated based on a deviation between the average value and the ignition delay of each cylinder. Means for calculating a correction coefficient for correcting the air-fuel ratio of each cylinder so as to eliminate the fuel ratio deviation, and an abnormality detection means for detecting that an abnormality has occurred in the fuel supply system when the correction coefficient is outside a predetermined range And having.

  According to the present invention, since the air-fuel ratio correction coefficient serving as a criterion for abnormality determination is calculated from the output of the in-cylinder pressure sensor, it is possible to detect abnormality with high accuracy regardless of the operating state.

  According to one embodiment of the present invention, the estimating means estimates the motoring pressure for each crank angle using a predetermined arithmetic expression. The ignition delay calculating means further includes correction means for correcting the cylinder pressure so as to minimize the deviation between the cylinder pressure and the motoring pressure in the compression stroke of the internal combustion engine, and the cylinder corrected by the correction means. A time point at which the difference between the internal pressure and the motoring pressure exceeds a predetermined value is detected as a combustion start time point.

  According to an embodiment of the present invention, the abnormality detection means stops the EGR system of the internal combustion engine when the correction coefficient is outside the predetermined range, and when the correction coefficient is shifted within the predetermined range, Judge that there is an abnormality in the EGR system.

  According to one embodiment of the present invention, the abnormality detecting means stops the purge system of the internal combustion engine when the correction coefficient is outside the predetermined range, and when the correction coefficient is within the predetermined range, Determine that the system is abnormal.

  According to one embodiment of the present invention, the abnormality detection means performs the abnormality determination of the EGR system and the purge system when the correction coefficient is outside the predetermined range, and when it is not determined that there is an abnormality in any of the systems. Determines that there is an abnormality in the fuel injection system.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of an abnormality determination device for an internal combustion engine according to an embodiment of the present invention. The electronic control unit 10 is a computer provided with a central processing unit (CPU). The electronic control unit includes a read only memory (ROM) that stores computer programs and a random access memory (RAM) that provides a work area for the processor and temporarily stores data and programs. The input / output interface 11 receives detection signals from various parts of the engine, performs A / D (analog / digital) conversion, and passes them to the next stage. Further, the input / output interface 11 sends a control signal based on the calculation result of the CPU to each part of the engine. In FIG. 1, the electronic control unit is shown by functional blocks showing functions related to the present invention.

  First, the principle of the sensor output correction method according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 shows the pressure in the combustion chamber of the cylinder in the range of the crank angle from -180 degrees to 180 degrees. The range of the crank angle from -180 degrees to 0 degrees is the compression stroke, and from 0 degrees to 180 degrees. Expansion (combustion) stroke. Curve 1 shows the transition of the motoring pressure (pressure at the time of misfire) of one cylinder of the engine, and curve 3 shows the transition of the in-cylinder pressure when normal combustion is performed in the same cylinder. The crank angle of 0 degrees is the top dead center, the motoring pressure peaks at the top dead center, and the in-cylinder pressure during combustion (curve 3) peaks near the ignition time after the top dead center.

  In this embodiment, a correction formula for correcting the detection output of the pressure detection means (in-cylinder pressure sensor 12 in FIG. 1) in a period before reaching top dead center in the compression stroke, for example, a period indicated by “a” in FIG. Identify the parameters. A black dot 5 indicates a detection output by the in-cylinder pressure sensor 12. The in-cylinder pressure sensor 12 is placed in a harsh environment such as an engine combustion chamber, and its characteristics change due to the influence of temperature, aging, and the like. In this embodiment, the detection output is corrected so that the detection output of the in-cylinder pressure sensor 12 is substantially on the curve 1 of the motoring pressure. The detection output corrected in this way is indicated by white dots 7.

The detection output is corrected by applying the correction expression PS = PD (θ) k ₁ + C ₁ to the detection output PD (θ) of the in-cylinder pressure sensor. k ₁ is a correction coefficient, and C ₁ is a constant. θ is a crank angle. The two parameters k ₁ and C ₁ of this correction formula are the above-described correction of the estimated value PM of the motoring pressure and the detection output of the in-cylinder pressure sensor during the compression stroke, for example, the period indicated by “a” in FIG. Calculation is performed by the least square method so that the square of the difference (PM−PS) from the value PS corrected by the equation is minimized.

  The combustion state of the cylinder can be determined using the sensor output corrected in this way. After the start of combustion of the air-fuel mixture in the combustion (expansion) stroke, for example, during the period indicated by “b” in FIG. 2, the detection output 7 (white dot) obtained by correcting the output of the in-cylinder pressure sensor 12 and the state equation Is determined based on the relationship with the motoring pressure PM (curve 1) calculated in (5). For example, when PS / PM is smaller than a predetermined threshold value, it can be determined that a misfire has occurred.

  Referring to FIG. 1 again, the in-cylinder pressure sensor 12 is a piezoelectric element and is provided in the vicinity of a spark plug of each cylinder (cylinder) of the engine. The pressure sensor 12 outputs a charge signal corresponding to the pressure in the cylinder. This signal is converted into a voltage signal by the charge amplifier 31 and outputted, and then outputted to the input / output interface 11 through the low-pass filter 33. The input / output interface 11 sends a signal from the pressure sensor 12 to the sampling unit 13. The sampling unit 13 samples this signal at a predetermined period, for example, a period of 1/10 kHz, and passes the sample value to the sensor output detection unit 15.

The sensor output correction unit 17 corrects the sensor output PD (θ) according to the above-described correction formula PS = PD (θ) k ₁ + C ₁ . The sensor output correction unit 17 passes the sensor output value PS corrected for each crank angle of 15 degrees to the combustion pressure detection unit 41.

On the other hand, the combustion chamber volume calculation unit 19 calculates the cylinder combustion chamber volume V _c according to the crank angle θ using the following equation.

In the above equation, m represents the displacement from the top dead center of the piston 8 calculated from the relationship of FIG. λ = l / r where r is the crank radius and l is the connecting rod length. V _dead is the volume of the combustion chamber when the piston is at top dead center, and _Apstn is the cross-sectional area of the piston.

In general, it is known that the state equation of the combustion chamber is expressed by the following equation (3).

  In Equation (3), G is an air flow meter or intake air amount obtained based on the engine speed and intake pressure, R is a gas constant, T is an operating state such as an intake air temperature sensor or engine water temperature, for example. This is the intake air temperature obtained based on this. k is a correction coefficient, and C is a constant.

In this embodiment, the pressure in the combustion chamber is measured in advance using a quartz piezoelectric pressure sensor that is not affected by the temperature change of the sensor mounting portion in advance, and this measured value is made to correspond to the equation (3) to The value k ₀ and the value C ₀ of C are obtained. The motoring pressure is estimated using the following equation (4) obtained by substituting this into equation (3).

The motoring pressure estimation unit 20 includes a basic motoring pressure calculation unit 21 and a motoring pressure correction unit 22. The basic motoring pressure calculator 21 calculates a basic motoring pressure GRT / V, which is a basic item in the equation (3). The motoring pressure correction unit 22 corrects the basic motoring pressure using the parameters k ₀ and C ₀ obtained in advance as described above. The parameters k ₀ and C ₀ are prepared as a table that can be referred to according to a parameter representing the engine load state such as the intake pipe pressure or the engine speed.

  The motoring pressure estimation unit 20 may alternatively be configured by only the basic motoring pressure calculation unit 21. In this case, the motoring pressure PM is the basic motoring pressure GRT / V calculated by the basic motoring pressure calculator 21.

The parameter identification unit 23 calculates an error (PM−) between the estimated motoring pressure value PM calculated by the motoring pressure estimation unit 20 in the compression stroke and the in-cylinder pressure PS based on the in-cylinder pressure sensor 12 output from the sensor output correction unit 17. The parameters k ₁ and C ₁ of the correction formula for correcting the sensor output by the least square method are identified so that (PS) is minimized. The sensor output detection unit 15 samples the output of the pressure sensor at a period of, for example, 1/10 kHz, and sets the average value of the sample values as the sensor output value PD (θ) at the timing synchronized with the crank angle. hand over. The parameter identification unit 23 executes a calculation for identifying parameters of the correction formula in the compression stroke of the cylinder. The correction formula PS = PD (θ) k ₁ + C ₁ is applied to the estimated motoring pressure value PM (θ) corresponding to the crank angle obtained from the motoring pressure correction unit and the sensor output value PD (θ) at the same crank angle. The square of the difference from the applied value PS, that is, k ₁ and C _{1 at} which (PM (θ) −PD (θ) k ₁ −C ₁ ) ² is minimized is obtained by a known least square method.

When the discrete value of PM is represented by y (i) and the sample value (discrete value) of the in-cylinder pressure PD obtained from the in-cylinder pressure sensor is represented by x (i), X (i) ^T = [x (0) , x (1),..., x (n)], Y (i) ^T = [y (0), y (1),..., y (n)]. The sum of the squares of the discrete values of errors is expressed by the following equation (5). The sample value is taken at a period of 1/10 kHz, and the value of i is up to 100, for example.

In order to obtain k and C that minimize the value of F, it is only necessary to obtain k and C at which the partial differentiation of F (k, C) with respect to k and C is zero. This can be expressed as follows:

The right side of Equations (6) and (7) is organized as follows.

This can be expressed as a matrix as follows.

When this equation is transformed using an inverse matrix, it becomes as follows.

Here, the inverse matrix on the right side is expressed by the following equation.

  The sensor output correction unit 17 corrects the sensor output in the combustion stroke using the parameters thus identified.

  The correction unit 17 corrects the sensor output PD (θ) using the parameters thus identified. The corrected sensor output PS (θ) for each predetermined crank angle (for example, 15 degrees) is passed to the combustion pressure detector 41. The correction unit 17 may be omitted, and the output PD (θ) for each predetermined crank angle output by the sensor output detection unit 15 may be used as it is as the sensor output PS (θ).

  The combustion pressure detection unit 41 calculates a pressure PC (θ) generated by pure combustion when the air-fuel mixture burns in the cylinder of the engine. Referring to FIG. 2, the pressure PS (θ) (curve 3) detected based on the output of the in-cylinder pressure sensor 12 is changed to the motoring pressure PM (θ), which is the cylinder pressure when there is no combustion, by combustion. The resulting pressure PC (θ) is added. Therefore, it is possible to calculate PC (θ) by an arithmetic expression of PC (θ) = PS (θ) −PM (θ).

  Referring to FIG. 4, the combustion start time detection unit 43 searches the determination value DP_C for determining the combustion start point from a table using the intake air pressure PB as a parameter (S101), and is calculated as described above. When the combustion pressure PC (θ) (S103) exceeds this judgment value (S105), the ignition flag is set to 1 (S105). Since the calculated combustion pressure PC (θ) oscillates near the combustion start time of the air-fuel mixture, the crank angle when PC (θ) exceeds the judgment value first is used as the ignition time, and this angle is This is represented by θ_DLY_bs (S111).

  The ignition delay calculation unit 45 in FIG. 1 calculates the ignition delay D_θ_DLY (n) by subtracting the ignition time θ_DLY_bs from the crank angle IG (θ) ignited on the spark plug (FIG. 4, S113). When the ignition delay is larger than a predetermined maximum value (S115), the maximum value is set as a parameter D_θ_DLY_IG (n) for calculating an average value (S123). When the ignition delay D_θ_DLY (n) is smaller than a predetermined minimum value (S117), the minimum value is set in the parameter D_θ_DLY_IG (n) (S121). When the ignition delay D_θ_DLY_ (n) is between the maximum value and the minimum value, this is set in the parameter D_θ_DLY_IG (n) (S119). The 16 moving averages of the parameter D_θ_DLY_IG (n) are set as the average ignition delay θ_DLY_av (S125).

  Referring to FIG. 1 again, the air-fuel ratio correction unit 47 and the fuel injection amount calculation unit 49 make the air-fuel ratio of each cylinder uniform in each bank of the engine based on the ignition delay of each cylinder included in the bank. The fuel injection amount of each cylinder is adjusted by correcting the air-fuel ratio for each cylinder. As shown in FIG. 6, there is a correlation between the air-fuel ratio and the ignition delay. For example, when the air-fuel ratio is the stoichiometric air-fuel ratio of 14.7, the ignition delay of the cylinder is 0 [deg] and is ignited simultaneously with the ignition. The ignition delay of the cylinder increases as the air-fuel ratio advances toward a lean state that is greater than the stoichiometric air-fuel ratio. On the other hand, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, ignition is performed at a timing earlier than ignition. Therefore, the air-fuel ratio is estimated from the ignition delay of each cylinder, and the air-fuel ratio feedback control is performed by adjusting the fuel injection amount by correcting the air-fuel ratio of each cylinder so that the estimated air-fuel ratio becomes uniform. .

  Referring to FIG. 5, the air-fuel ratio correction unit 47 first determines the average ignition delay D_θDLYAVB for each bank from the ignition delay θ_DLY_av # (# is the cylinder number) of each cylinder calculated by the average ignition delay calculation unit 45. (S201), and the deviation DD_θDLYAV # between the ignition delay θ_DLY_av # and the average value D_θDLYAVB of each cylinder is calculated from the equation (11) (S203).

DD_θDLYAV # = θ_DLY_av # − D_θDLYAVB (11)
However, # is a cylinder number, and a deviation is calculated for each cylinder.

  Subsequently, the ignition delay deviation DD_θDLYAV # of each cylinder is converted into an air-fuel ratio deviation KCPERRX # (S205). This conversion is performed, for example, using a conversion map based on the correlation between the air-fuel ratio and the ignition delay as shown in FIG. Here, the air-fuel ratio deviation KCPERRX # is a deviation between the air-fuel ratio of each cylinder and the average value of the air-fuel ratios of all cylinders in the bank.

  In steps S201 to S205, instead, the air-fuel ratio of each cylinder is estimated using the conversion map from the ignition delay θ_DLY_av # of each cylinder calculated by the average ignition delay calculating unit 45, and the air-fuel ratio of these air-fuel ratios is calculated. An average value may be calculated, and a deviation KCPERRX # between the estimated air-fuel ratio of each cylinder and the average value may be calculated.

Based on the air-fuel ratio deviation KCPERRX # of each cylinder, the air-fuel ratio correction coefficient kcpcyl # of each cylinder is calculated as shown in Expression (12) (S207).

Here, Kp and Ki are feedback gains. The second term on the right side of Equation (12) is a proportional term, and the third term is an integral term. That is, Equation (12) calculates the feedback amount of PI control with the input being the air-fuel ratio deviation KCPERRX #, and calculates the correction coefficient centered on 1.

  Here, PID control to which a differential term is added may be applied to the second and subsequent terms on the right side of Expression (12). Other feedback control methods can also be applied.

  Subsequently, the average value KCPCYLAVB of the air-fuel ratio correction coefficient kcpcyl # is obtained for each bank (S209), and the air-fuel ratio correction coefficient of each cylinder is normalized with the average value as shown in equation (13) (S211).

KCPCYL # = kcpcyl # / KCPCYLAVB (13)
By such normalization, the average value of the air-fuel ratio correction coefficient becomes 1, so that the air-fuel ratio of each cylinder can be corrected without changing the air-fuel ratio of the entire bank.

  Further, the air-fuel ratio correction coefficient KCPCYL # is subjected to limit processing (S213), and the correction coefficient KCPCYL # is sent to the fuel injection amount calculation unit 49.

  The fuel injection amount calculation unit 49 calculates the valve opening time TOUT of the injector 51 that determines the fuel injection amount in the cylinder from the equation (14) (S215 in FIG. 5).

TOUT = KCPCYL # × Required valve opening time + Power supply voltage correction value (14)
The command value of the calculated valve opening time TOUT is sent to the injector 51.

  In this way, the air-fuel ratio of each cylinder in the bank is made uniform by adjusting the fuel injection amount of each cylinder and correcting the air-fuel ratio.

  Referring to FIG. 1 again, the abnormality determination unit 53 detects an abnormality of each cylinder based on the air-fuel ratio correction coefficient KCPCYL #. The abnormality determination unit 53 determines that there is some abnormality in the fuel supply system for the cylinder whose air-fuel ratio correction coefficient KCPCYL # is out of the predetermined range. Then, any one of the exhaust gas recirculation (EGR) device 55, the purge system 57, and the injector 51 is determined as a failure part. The EGR device 55 is a device that introduces part of the exhaust gas into the intake pipe and mixes it with the intake air. The purge system 57 is a system that introduces the fuel vaporized in the fuel tank into the intake pipe of the engine and burns it together with the fuel injected by the injector 51.

  Hereinafter, the process performed by the abnormality determination unit 51 will be described with reference to FIG.

  The abnormality determination unit 51 smoothes the air-fuel ratio correction coefficient KCPCYL # of each cylinder calculated by the air-fuel ratio correction unit 47, and calculates a smoothed correction coefficient KAVCYL # (S301). The annealing calculation is performed according to, for example, the equation (15).

KAVCYL # = C × KCPCYL # + (1−C) × KAVCYL # (previous value) (15)

Here, C is the amount of annealing, for example 0.008.

  At the beginning of the abnormality detection process, the failure part is not determined (S303), the flag for stopping the EGR device 55 is not set (F_EGRCUT = 0) (S305), and the flag for stopping the purge system 57 is also set. Since there is not (F_PGEGRCUT = 0) (S307), it is first checked whether or not the smoothed correction coefficient KAVCYL # is out of the predetermined range (S309). If KAVCYL # is outside the predetermined range, it is determined that some abnormality has occurred in the cylinder # (# is the cylinder number) (S311). When an abnormality is detected (S313), a flag for stopping the EGR device 55 is set (F_EGRCUT = 1) (S315).

  After the EGR device 55 is stopped, this flow branches in step S305 and proceeds to step S317 and subsequent steps. It is confirmed whether or not the correction coefficient KAVCYL # has shifted to a predetermined range by stopping the EGR device 55 (S317). If it is within the predetermined range, it is determined that the failed part causing the current abnormality detection is the EGR device 55, and the process is terminated (S319). If the correction coefficient KAVCYL # is still outside the predetermined range, it is determined that the EGR device 55 is operating normally, the operation of the EGR device is resumed (F_EGRCUT = 0), and the purge system is stopped. A flag is set (F_PGEGRCUT = 1) (S321).

  After the purge system 57 is stopped, this flow branches in step S307 and proceeds to step S323 and subsequent steps. It is confirmed whether or not the correction coefficient KAVCYL # has shifted to a predetermined range by stopping the purge system 57 (S323). If it is within the predetermined range, it is determined that the faulty part causing the current abnormality detection is the purge system 57, and the process is terminated (S325). If the correction coefficient KAVCYL # is still outside the predetermined range, it is determined that the purge system 57 is operating normally, and it is determined that the failed part causing the current abnormality is the injector 51 and processed. Is finished (S327).

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment. Moreover, it can be used for both gasoline engines and diesel engines.

1 is a block diagram illustrating an overall configuration of an air-fuel ratio control apparatus according to an embodiment of the present invention. It is a figure which shows the motoring pressure curve and the curve of the correction value of the sensor output at the time of combustion. It is a conceptual diagram for calculating a piston position. It is a flowchart which shows the main flow of ignition delay calculation. It is a flowchart which shows the process which calculates the fuel injection amount of each cylinder. It is a graph which shows the relationship between an ignition delay and an air fuel ratio. It is a flowchart of an abnormality detection process.

Explanation of symbols

10 Electronic control unit (ECU)
12 In-cylinder pressure sensor 15 Sensor output detection unit 20 Motoring pressure estimation unit 45 Average ignition delay calculation unit 47 Inter-cylinder air-fuel ratio correction unit 49 Fuel injection amount calculation unit 53 Abnormality determination unit 51 Injector 55 EGR device 57 Purge system

Claims (5)

An apparatus for determining abnormality of an internal combustion engine,
Pressure detecting means provided for each cylinder of the internal combustion engine for detecting the pressure in the cylinder;
Estimating means for estimating the motoring pressure of the internal combustion engine;
In the period from the compression stroke to the combustion stroke of the internal combustion engine, a time point at which the difference between the pressure in the cylinder and the motoring pressure exceeds a predetermined value is detected as a combustion start time point, and the combustion start time point from the ignition time point for each cylinder. An ignition delay calculating means for calculating an ignition delay until
An average value of the ignition delay of each cylinder is calculated, and a deviation between the average value of the air-fuel ratio of each cylinder and the air-fuel ratio of each cylinder is calculated based on a deviation between the average value and the ignition delay of each cylinder. Means for calculating a correction coefficient for correcting the air-fuel ratio of each cylinder so as to eliminate the air-fuel ratio deviation;
An abnormality detecting means for detecting that an abnormality has occurred in the fuel supply system when the correction coefficient is outside the predetermined range;
An abnormality determination device for an internal combustion engine having The estimating means estimates the motoring pressure for each crank angle by a predetermined arithmetic expression;
The ignition delay calculating means further includes a correcting means for correcting the cylinder pressure so as to minimize a deviation between the cylinder pressure and the motoring pressure in a compression stroke of the internal combustion engine, and the correction means Detecting a time when a difference between the corrected in-cylinder pressure and the motoring pressure exceeds a predetermined value as a combustion start time;
The abnormality determination device according to claim 1.   The abnormality detecting means stops the EGR system of the internal combustion engine when the correction coefficient is out of a predetermined range, and when the correction coefficient changes within the predetermined range, there is an abnormality in the EGR system. The abnormality determination device according to claim 1, wherein the abnormality determination device determines that there is one.   The abnormality detecting means stops the purge system of the internal combustion engine when the correction coefficient is outside the predetermined range, and when the correction coefficient is shifted within the predetermined range, there is an abnormality in the purge system. The abnormality determination device according to claim 1, wherein the abnormality determination device determines that there is one. When the abnormality detection means performs an abnormality determination of the EGR system and the purge system when the correction coefficient is outside a predetermined range, and when it is not determined that there is an abnormality in either system, the fuel injection system The abnormality determination device according to claim 1, wherein it is determined that there is an abnormality.

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