JP2006138205A - Combustion condition-detection device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve reliability of motoring pressure detection of an internal combustion engine and determine combustion condition. <P>SOLUTION: A combustion condition detection device comprises a cylinder pressure detection means for a combustion chamber of the internal combustion engine, a crank angle detection means for detecting a crank angle of the internal combustion engine, a calculation means for calculating a volume of the combustion chamber based on the crank angle detected by the crank angle detection means, and an estimation means for estimating the motoring pressure of the internal combustion engine with an operation equation including the calculated volume. The combustion condition detection device further comprises a correction means for correcting the pressure detected by the cylinder pressure detection means according to a correction equation, an identification means for identifying parameters of the correction equation for minimizing an error between the detected pressure corrected by the correction means and the pressure estimated by the estimation means, and the pressure detected by the cylinder pressure detection means in a combustion stroke of the internal combustion engine. The combustion condition is judged based on a relation between the detected pressure corrected by the correction means and the pressure estimated by the estimation means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a misfire detection technique for an internal combustion engine.

In Patent Document 1, the in-cylinder pressure of a combustion chamber of an internal combustion engine is detected for each predetermined crank angle, and the bias amount of the in-cylinder pressure detection signal is determined based on the in-cylinder pressure detection signal sampled during the sampling period and the combustion chamber volume. And the sampled cylinder pressure signal is corrected based on the set bias amount, and the transition of the motoring pressure (pressure at the time of misfire) is estimated based on the corrected cylinder pressure and the combustion chamber volume. It is described. In the combustion cycle, this estimated pressure is compared with the pressure detected by the sensor to determine the presence or absence of misfire.
JP-A-3-246373

  According to the prior art, the motoring pressure is estimated based on the in-cylinder pressure and the combustion chamber volume by correcting the pressure detection signal with the bias amount to obtain the in-cylinder pressure. However, in this method, when the in-cylinder pressure suddenly changes during the transient operation of the internal combustion engine, the detected pressure is corrected by the bias amount at a certain point. Due to changes in sensor output characteristics due to temperature changes in parts, changes in characteristics due to deterioration over time, etc., there is a difficulty in correcting the pressure detection value due to the bias amount, and thus it is estimated from the corrected pressure value. There was a problem with the reliability of motoring pressure, and there was a problem with the reliability of misfire determination.

  In one form (Claim 1), the present invention detects in-cylinder pressure detection means for a combustion chamber of an internal combustion engine (engine), crank angle detection means for detecting a crank angle of the internal combustion engine, and crank angle detection means. Calculation means for calculating the volume of the combustion chamber based on the crank angle, and estimation means for estimating the motoring pressure of the internal combustion engine by an arithmetic expression including the calculated volume. Further, the combustion state detection device includes a correction unit that corrects a pressure detected by the in-cylinder pressure detection unit according to a correction formula in a compression stroke of the internal combustion engine, a detection pressure that is corrected by the correction unit, and an estimation unit. An identification means for identifying a parameter of the correction formula so as to minimize an error from an estimated pressure, and a pressure detected by an in-cylinder pressure detection means in a combustion stroke of the internal combustion engine. The combustion state is determined based on the relationship between the detected pressure corrected by the correcting means and the pressure estimated by the estimating means.

  According to the present invention, the parameters of the correction equation for correcting this detection output are identified so that the error between the detection output of the in-cylinder pressure detection means and the motoring pressure estimated according to the arithmetic expression including the combustion chamber volume is minimized. Is done. Since this parameter is used for correcting the detection output in the combustion stroke that is identified in the compression stroke and immediately after that, the reliability of the detection output can be improved.

  In one embodiment of the present invention (Claim 2), the estimation means includes motoring pressure calculation means for calculating a basic motoring pressure based on the volume of the combustion chamber. In another embodiment of the present invention (Claim 3), the estimation means includes correction means for correcting the basic motoring pressure using a predetermined parameter.

  Furthermore, in one aspect of the present invention, the identification means calculates a standard deviation between the estimated pressure and the corrected pressure, and when the standard deviation is equal to or less than a predetermined value, the estimated pressure is corrected. The identified parameters are adopted as the deviation of the measured pressure converges.

  In one embodiment of the present invention, the determination means determines misfire of the internal combustion engine. This misfire determination is performed by comparing the ratio between the estimated pressure and the corrected pressure with a predetermined value.

  Furthermore, in one aspect of the present invention, a determination stage setting means for setting a misfire determination section in the combustion stroke of the internal combustion engine is provided, and the determination stage is changed according to the operating state of the internal combustion engine.

  The combustion stroke of an internal combustion engine is after ignition in a gasoline engine and after fuel injection in a diesel engine.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the combustion state detection apparatus 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 misfire determination performed in 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 the present invention, the correction for correcting the detection output of the in-cylinder pressure detecting means (in-cylinder pressure sensor 12 in FIG. 1) in the period before reaching the top dead center in the compression stroke, for example, the period indicated by “a” in FIG. Identify the parameters of the formula. 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 the present invention, 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 = PS (θ) k ₁ + C ₁ to the detection output PS (θ) of the in-cylinder pressure sensor. k ₁ is a correction coefficient, and C ₁ is a constant. 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.

  Next, after the start of combustion of the air-fuel mixture in the combustion (expansion) stroke, for example, in a period indicated by “b” in FIG. 2, a detection output 7 (white dot) obtained by correcting the output of the in-cylinder pressure sensor 12, Based on the relationship with the motoring pressure PM (curve 1) calculated by the state equation, it is determined whether or not a combustion state, for example, misfire has occurred. In one embodiment, it is determined that a misfire has occurred when PS / PM is less than a predetermined threshold.

  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 PS (θ) according to the above-described correction formula PS = PS (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 misfire determination unit 27.

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 7 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, for example, an air flow meter or intake air amount obtained based on the engine speed and intake pressure, R is a gas constant, and 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 the first embodiment of the present invention, as a motoring pressure estimation value based on the gas state equation of the combustion chamber, for example, a quartz piezoelectric pressure sensor that is not affected by a temperature change or the like of the sensor mounting portion is used. The pressure is measured, and the k value k ₀ and the C value C ₀ calculated by associating the measured value with the equation (3) are obtained, and these are substituted into the equation (3) to obtain the following ( 4) Estimate the motoring pressure using the equation.

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 an engine load state such as intake pipe pressure or engine rotation.

In the second embodiment of the present invention shown in FIG. 8, the motoring pressure correction unit 22 is not provided, and the basic motoring pressure GRT / V _C calculated by the basic motoring pressure calculation unit 21 is the combustion chamber. It is used as an estimated value of motoring pressure based on the gas state equation.

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 PM 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 PS (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 = PS (θ) k ₁ + C ₁ is applied to the motoring pressure estimation value PM (θ) corresponding to the crank angle obtained from the motoring pressure correction unit and the sensor output value PS (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) −PS (θ) k ₁ −C ₁ ) ² is minimized is determined by a known least square method.

When the discrete value of PM is expressed by y (i) and the sample value (discrete value) of the in-cylinder pressure PS obtained from the in-cylinder pressure sensor is expressed by x (i), P ′ ^T = [p ′ (0), p '(1),…, p' (n)], P ^T = [p (0), p (1),…, p (n)], X (i) ^T = [x (0), x (1), ..., x (n)]. The sum of the squares of the discrete values of the error (P′−P) 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) can be summarized 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 misfire determination unit 27 estimates the in-cylinder pressure PS detected by the in-cylinder pressure sensor 12 and corrected by the sensor output correction unit 17 in the period b (FIG. 2) after the ignition time, and the motoring pressure estimation at the same time. The presence or absence of misfire is determined based on the estimated motoring pressure value PM calculated by the unit 20. In this embodiment, the misfire determination unit 27 determines that a misfire has occurred when PS / PM is smaller than a predetermined threshold value α.

FIG. 4 is a flowchart showing a flow of processing executed every 15 crank angles. It is determined whether it is before top dead center in the compression stroke (S101). If it is before top dead center, the process of identifying the parameter of the sensor output correction formula is entered, and parameters k ₁ and C ₁ are updated (S115). ).

  If it is not before compression top dead center in step S101, it is checked whether or not the misfire MIL on flag is 1 (S103). If this flag is 1, it means that misfire has already been determined several times and a misfire warning has been issued. If this flag is not 1, the process proceeds to misfire determination processing (S105). As a result, when misfire is determined and the misfire flag is set to 1 (S107), the count of the number of misfires is advanced (S109). When the misfire determination process (S105) runs, the determination cycle count, that is, the number of cycles is counted up (S111). The number of cycles is counted so that a misfire MIL (misfire warning) can be generated based on how many misfires have occurred in a given number of cycles. When the misfire MIL ON flag is 1, the cycle number count and misfire count are reset, and the process ends (S113).

Next, details of the misfire determination process (S105) of FIG. 4 will be described with reference to FIG. First, the displacement (distance) m from the position of the top dead center of the piston to the current position is calculated by the equation (1) shown above (S131). Next, using this displacement m, the current volume V _c of the cylinder is calculated by equation (2) (S133). The intake air temperature is read from a temperature sensor provided in the intake pipe of the engine (S135), and the estimated value PM of the motoring pressure is calculated by the equation (3) shown above (S137).

  The actual in-cylinder pressure based on the output of the in-cylinder pressure sensor is read (S139), and is corrected by the correction equation described above (S141). Based on the engine speed NE and the absolute pressure PB of the intake pipe, a threshold map for misfire determination is searched (S143). Since the motoring pressure varies depending on the load state of the engine, a determination threshold value corresponding to the load state is prepared in advance as a map, and this map is searched.

  Next, a determination stage is selected (S145). This is because the misfire determination is performed at the most appropriate timing according to the state of the engine. For example, if the engine intake / exhaust valve has a variable valve mechanism that can change the timing, the timing is set for high rotation. The determination stage is selected depending on whether it is controlled, in an idle state, or in a fire mode (a mode in which high-temperature exhaust is sent to the exhaust system to activate the exhaust system catalyst immediately after engine startup). . Each stage map is set with a period during which misfire determination may be performed (a specific period within period b in FIG. 2). In step S147 of FIG. 5, this specific period is called a determination gate.

  If it is in the determination gate, it is determined whether or not the ratio PS / PM between the corrected actual measured value PS of the cylinder pressure and the estimated motoring pressure PM is larger than the determination threshold value searched in step S143 (S149). If the ratio PS / PM is larger than the threshold value, it is determined that the ignition is normally performed, and the process ends. When the ratio PS / PM is less than or equal to the threshold value, it is determined that misfire has occurred, and the misfire flag is set to 1 (S151). If misfire occurs more than the determination value in a predetermined period, it is determined that misfire has been established, and a misfire alarm (misfire MIL) is turned on.

The flow of parameter identification processing will be described with reference to FIG. The parameter identification process is performed near the end of the compression stroke, that is, near the top dead center. The state where the piston is near the end of the compression stroke is called the identification stage. When in the identification stage, the piston position is calculated according to the above-described equation (1) using the data acquired at the measurement stage described later, and the cylinder capacity is calculated according to the equation (2) (S163). The intake air amount and the intake air temperature are read (S165), and the partial differential of equation (4) is solved to identify the parameters k ₁ and C ₁ (S167). Next, error variance and standard deviation are calculated (S169). This is a calculation for determining whether or not the state equation shown in the equation (3) converges according to the identified parameters, which will be described later with reference to FIG.

  In step S161, when it is not in the identification stage, it is determined whether or not it is in the measurement stage for collecting data used for the parameter identification calculation (S171). If it is in this stage, the data is fetched into the buffer (S173), The calculation result is reset (S175), and the process ends. Even when not in the measurement stage, the previous calculation result is reset and the process is terminated.

Turning to FIG. 7, the in-cylinder pressure PS calculated by the in-cylinder pressure sensor calculated using the identified parameter k ₁ and C ₁ and PS = PS (θ) k ₁ + C ₁ and the gas state in the combustion chamber The variance of the difference from the estimated motoring pressure value PM calculated from the equation, and the standard deviation or their approximate values are calculated. The basic idea is that when the standard deviation is less than or equal to a predetermined value, it is determined that the error between the estimated motoring pressure value PM and the actual measurement value PS converges, and the identified parameters k ₁ and C ₁ are determined as appropriate parameters. Is to be adopted. When the error does not converge, there may be a failure such as noise occurring due to an abnormality in the in-cylinder pressure sensor or an overflow of calculation.

  The estimated value PM of the motoring pressure is calculated from the equation (3) (S181), and the error E (i) = PM-PS is calculated (S183). Based on the error E (i), the variance or its approximate value σ is calculated by a known calculation method (S189).

  The standard deviation STDV is calculated as the square root of the variance thus calculated (S191). When the standard deviation is equal to or larger than a predetermined threshold (S193), it is determined that the error does not converge, and the convergence failure flag (F_ Convergence_NG) is set to 1 (S195). The number of times the convergence failure flag becomes 1 is counted up (S199), and when the count becomes 100 or more (S201), a flag indicating abnormality of the in-cylinder pressure sensor is set to 1. 7 is calculated in the identification process (once per cycle). The count up in step S199 is a count up every 15 degrees of crank angle.

  If the standard deviation does not reach the threshold value in step S193, it is assumed that the error converges, the convergence failure flag is set to 0 (S197), and the process is terminated.

  Specifically, the misfire warning lights a warning light on the driver's seat panel, informs the driver of the abnormality by voice when the engine starts, prompts the repair, forcibly switches the vehicle to abnormal mode operation, and repairs it. It is emitted by methods such as forcing.

  FIG. 8 is a functional block diagram of the second embodiment of the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, the motoring pressure correction unit 22 is omitted from the functional block diagram of FIG. 1, and the basic motoring pressure calculated by the basic motoring pressure calculation unit 21 is based on the gas state equation of the combustion chamber. Used as ring pressure estimate.

  Although the present invention has been described with respect to specific embodiments, the present invention is not limited to such embodiments, and can be used for both gasoline engines and diesel engines.

The functional block diagram of 1st Embodiment of this invention. The figure showing a motoring pressure curve and a pressure curve when ignition was produced. The conceptual diagram for calculating a piston position. The flowchart which shows the main flow of a misfire detection process. The flowchart which shows the flow of a misfire determination process. The flowchart which shows the flow of a parameter identification process. The flowchart which shows the flow of a process of convergence determination. The functional block diagram of 2nd Embodiment of this invention.

Explanation of symbols

10 Electronic control unit (ECU)
12 In-cylinder pressure sensor 15 Sensor output detection unit 17 Sensor output correction unit 19 Combustion chamber (cylinder) volume calculation unit 20 Motoring pressure estimation unit 21 Basic motoring pressure calculation unit 22 Motoring pressure correction unit 23 Parameter identification unit

Claims (7)

In-cylinder pressure detection means for the combustion chamber of the internal combustion engine;
Crank angle detecting means for detecting a crank angle of the internal combustion engine;
A combustion state detection device for an internal combustion engine comprising:
Calculating means for calculating the volume of the combustion chamber based on the crank angle detected by the crank angle detecting means;
Estimating means for estimating a motoring pressure of the internal combustion engine by an arithmetic expression including the calculated volume;
Correction means for correcting the pressure detected by the in-cylinder pressure detection means in accordance with a correction formula in the compression stroke of the internal combustion engine;
Identifying means for identifying a parameter of the correction equation so as to minimize an error between the pressure corrected by the correcting means and the pressure estimated by the estimating means;
A determination unit that determines a combustion state based on a relationship between a pressure corrected by the correction unit and a pressure estimated by the estimation unit in a combustion stroke of the internal combustion engine;
A combustion state detection device comprising: The estimation means includes
The apparatus according to claim 1, further comprising a motoring pressure calculating unit that calculates a basic motoring pressure based on the volume of the combustion chamber calculated by the calculating unit.   The apparatus according to claim 2, wherein the estimation unit includes a correction unit that corrects the basic motoring pressure using a predetermined parameter.   The identification means calculates a standard deviation between the estimated pressure and the corrected pressure, and when the standard deviation is equal to or smaller than a predetermined value, the deviation between the estimated pressure and the corrected pressure converges. An apparatus according to any of claims 1 to 3, wherein the apparatus employs the identified parameters.   The apparatus according to any one of claims 1 to 4, wherein the determination means determines misfire of the internal combustion engine.   6. The apparatus of claim 5, wherein the misfire determination is performed by comparing a ratio of the estimated pressure to the corrected pressure with a predetermined value.   6. The apparatus according to claim 5, further comprising determination stage setting means for setting a misfire determination section in a combustion stroke of the internal combustion engine, wherein the determination stage is changed according to an operating state of the internal combustion engine.

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