JP2006284533A - Abnormality detector for cylinder pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detecting technique capable of absorbing fluctuation of an output characteristic in a sensor and capable of enhancing precision of abnormality detection. <P>SOLUTION: This abnormality detector of the present invention for a pressure detecting means is provided with the pressure detecting means (sensor) for detecting a cylinder pressure of a combustion chamber in an internal combustion engine, a crank angle detecting 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 detecting means, an estimation means for estimating motoring pressure of the internal combustion engine by a computation expression including the calculated volume, an identification means for identifying a correction parameter for minimizing a deviation, based on the deviation between the pressure detected by the pressure detecting means, and the motoring pressure estimated by the estimation means, in a compression stroke of the internal combustion engine, and an abnormality detecting means for detecting abnormality of the pressure detecting means, based on the correction parameter, when fuel is cut off. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an abnormality detection method for an in-cylinder pressure sensor installed in a combustion chamber of an internal combustion engine.

As a conventional method for discriminating an abnormality of a cylinder pressure sensor installed in a combustion chamber of an internal combustion engine, for example, Patent Document 1 discloses a sensor abnormality based on a sensor output during fuel cut (non-combustion) and a sensor output during combustion. A method for discriminating the above is disclosed. This technique compares the average pressure during one combustion cycle at the time of fuel cut with the average pressure during one combustion cycle at the time of combustion, and determines sensor abnormality according to the difference between the two.
Patent No. 3544228

  However, the output characteristics of the sensor may fluctuate due to a temperature change or aging of the mounting portion of the in-cylinder pressure sensor. The average value of the sensor output measured in such a situation is low in reliability, and there is a problem that false detection of sensor abnormality increases.

  Therefore, there is a need for a technique that can absorb fluctuations in the output characteristics of the sensor and improve the accuracy of abnormality detection.

  The present invention is based on pressure detection means (sensor) for detecting the in-cylinder pressure of a combustion chamber of an internal combustion engine, crank angle detection means for detecting a crank angle of the internal combustion engine, and a crank angle detected by the crank angle detection means. And calculating means for calculating the volume of the combustion chamber, estimating means for estimating the motoring pressure of the internal combustion engine by an arithmetic expression including the calculated volume, and detecting the pressure in the compression stroke of the internal combustion engine. Based on a deviation between the pressure and the motoring pressure estimated by the estimation means, an identification means for identifying a correction parameter for minimizing the deviation, and an abnormality of the pressure detection means based on the correction parameter at the time of fuel cut An abnormality detection device for pressure detection means is provided.

  According to the present invention, the sensor abnormality is determined based on the magnitude and fluctuation of the correction parameter. The correction parameter reflects the compatibility between the sensor output before correction and the motoring pressure. Further, the motoring pressure is obtained without being affected by fluctuations in sensor output. Therefore, the present invention can improve the accuracy of abnormality detection as compared with the prior art.

  In one embodiment of the present invention, the abnormality detection means determines that an abnormality has occurred when the correction parameter is outside a predetermined range.

  In one embodiment of the present invention, the abnormality detection means obtains a difference between an average value of the correction parameter for a predetermined number of times and the correction parameter, and determines that the abnormality is abnormal when the difference is larger than the predetermined value.

  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 a combustion state detection apparatus 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 = 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. 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 Based on the relationship with the motoring pressure PM (curve 1) calculated in step 1, it is determined whether a combustion state, for example, misfire has occurred. 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 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 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 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 represented by y (i) and the sample value (discrete value) of the in-cylinder pressure PS 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 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.

  Next, a sensor abnormality detection method according to the present embodiment will be described with reference to FIG. FIG. 4 is a graph showing the motoring pressure PM (dotted line 1) and the in-cylinder pressure PS at the time of fuel cut (solid line 9). The horizontal axis of the graph is the crank angle, and the vertical axis is the pressure with the maximum pressure in one combustion cycle being 100 [%]. Since the fuel injection into the cylinder is stopped when the fuel is cut, no explosion occurs in the expansion stroke. Therefore, the in-cylinder pressure should be equal to the motoring pressure. That is, the pressure at the top dead center (crank angle 0 degree) with the smallest volume becomes maximum, and the pressure decreases as the crank angle increases and the volume also increases. In addition, the sensor output correction method described above corrects the sensor output even when there is a drift or sensitivity deterioration. In particular, the correction parameters are identified during the compression stroke, and the waveforms of both are almost the same. It has been corrected to become.

  As described above, at the time of fuel cut, the motoring pressure and the sensor detection pressure corrected by the above-described correction method have a feature of having high adaptability. In addition, the sensor output initially matches the motoring pressure without correction (the parameters at this time are K1 = 1 and C1 = 0), and the correction parameters are the current sensor output and the motoring pressure. It is a value reflecting the degree of fitness of. In other words, the correction parameter tends to increase as the sensor detection performance deteriorates or drifts, and an excessively large value indicates that some kind of malfunction has occurred in the sensor and accurate detection has not been performed. .

  Therefore, in this embodiment, the sensor abnormality is detected by verifying the value of the correction parameter of the sensor output at the time of fuel cut.

Referring to FIG. 1 again, the sensor abnormality detection unit 29 receives the correction parameters k ₁ and C ₁ from the parameter identification unit 23. The sensor abnormality detection unit 29 also receives a fuel cut flag indicating whether or not the target cylinder is in a fuel cut state. In general, fuel cut is a process of stopping fuel injection mainly for the purpose of improving fuel consumption. Specifically, it is performed when the engine is running at high speed, when the throttle valve is fully closed, when the pressure in the intake pipe is reduced, or when traction control is executed.

When it is determined by the fuel cut flag that the fuel is cut, the sensor abnormality detection unit 29 performs sensor abnormality determination using the correction parameters K ₁ and C ₁ . As described above, if the sensor is operating normally, the correction parameter will not deviate significantly from the parameter (K1 = 1, C1 = 0) when the motoring pressure and the sensor output completely match. it is conceivable that. Therefore, an appropriate correction parameter range is set in advance, and when the correction parameter is out of the predetermined range, it is determined that the sensor is abnormal. The predetermined ranges are, for example, 0.5 <K1 <2.0 and −0.3 <C1 <0.3.

  When the correction parameters K1 and C1 are within a predetermined range, the sensor abnormality detection unit 29 subsequently calculates correction parameter deviations DK1 and DC1 by the following equations.

DK1 = | K1 − K1_ave | (11)
DC1 = | C1 − C1_ave | (12)
Here, K1_ave and C1_ave are average values of correction parameters for a plurality of cycles including the current values of K1 and C1. The number of cycles for calculating the average value may be any number, for example, 16 times.

  The large deviations DK1 and DC1 indicate that the value of the current correction parameter has changed extremely compared to the correction parameters so far. A sudden change in the correction parameter indicates that some abnormality has suddenly occurred in the sensor. Therefore, a predetermined threshold value is set, and if DK1 and DC1 are equal to or greater than the threshold value, it is determined that the sensor is abnormal. The threshold values are, for example, DK1> 1.0 and DC1> 0.2.

  FIG. 5 is a flowchart showing the flow of processing in the sensor abnormality detection unit 29.

  In step S101, it is checked whether or not the sensor abnormality flag is 1. A sensor abnormality flag of 1 indicates that a sensor abnormality has already been detected. If the flag is not 1, the process proceeds to step S103. If the sensor abnormality flag is already 1, the process is terminated.

  In step S103, it is checked whether the crank rotation speed is equal to or greater than a predetermined value. If the crank rotational speed is equal to or greater than the predetermined value, the process proceeds to step S105. If the crank rotational speed is less than or equal to a predetermined value, the process is terminated.

  In step S105, it is checked whether or not the target cylinder is under fuel cut. If the fuel is being cut, the process proceeds to step S107. If the fuel is not being cut, the process is terminated.

  In step S107, it is checked whether or not the correction parameter K1 is within a predetermined range. If the correction parameter K1 is outside the predetermined range, it is determined that the sensor has an abnormality such as sensitivity deterioration, and the process proceeds to an abnormality detection process after step S119. If the correction parameter K1 is within the predetermined range, it is determined that there is no sensor abnormality, and the process proceeds to step S109.

  In step S109, it is checked whether or not the correction parameter C1 is within a predetermined range. If the correction parameter C1 is outside the predetermined range, it is determined that there is an abnormality such as excessive drift in the sensor, and the process proceeds to the abnormality detection process after step S119. If the correction parameter C1 is within the predetermined range, it is determined that there is no sensor abnormality, and the process proceeds to step S109.

  Subsequently, in step S111, the deviations DK1 and DC1 of the correction parameters K1 and C1 are calculated using the equations (11) and (12). The deviation is obtained with respect to the average value of the parameters for a plurality of cycles. The number of cycles for calculating the average value may be any number, for example, 16 times.

  In step S113, it is checked whether or not the deviation DK1 is larger than a predetermined value. If the deviation DK1 is greater than the predetermined value, it is determined that an abnormality such as sensitivity deterioration has suddenly occurred in the sensor, and the process proceeds to step S119. If the deviation DK1 is less than or equal to the predetermined value, the process proceeds to step S115.

  In step S115, it is checked whether or not the deviation DC1 is larger than a predetermined value. If the deviation DC1 is greater than the predetermined value, it is determined that an abnormality such as excessive drift has suddenly occurred in the sensor, and the process proceeds to step S119. If the deviation DK1 is less than or equal to the predetermined value, the process proceeds to step S117.

  Hereinafter, the abnormality detection process after step S119 will be described.

  In step S119, one abnormality detection counter is decremented. The initial value of the abnormality detection counter is set to an integer larger than 1 in order to avoid erroneous abnormality detection due to a sudden sensor malfunction. For this reason, sensor abnormality is not detected unless abnormality is detected a plurality of times.

  In step S121, it is checked whether or not the abnormality detection counter is zero. The fact that the abnormality detection counter is 0 indicates that the sensor abnormality determination has been performed a predetermined number of times set by the initial value of the counter. If the abnormality detection counter is 0, the process proceeds to step S123. If the abnormality detection counter is not 0, the process is terminated as it is.

  In step S123, since it is determined that there is some abnormality in the pressure sensor, the sensor abnormality flag is set to 1, and the process is terminated.

  On the other hand, if it is determined that there is no abnormality in the pressure sensor as a result of the processes in steps S107, S109, S113, and S115, the process proceeds to step S117. In step S117, the abnormality detection counter is reset to the initial value, and the process ends.

  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.

It is a block diagram which shows the whole structure of the combustion state detection apparatus which is one Embodiment of this 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 figure which shows a motoring pressure and the cylinder pressure at the time of fuel cut. It is a flowchart showing the flow of the process in a sensor abnormality detection part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic control unit 12 In-cylinder pressure sensor 15 Sensor output detection part 17 Sensor output correction part 19 Combustion chamber (cylinder) volume calculation part 20 Motoring pressure estimation part 21 Basic motoring pressure calculation part 22 Motoring pressure correction part 23 Parameter identification 29 Sensor abnormality detection unit

Claims (3)

Pressure detecting means for detecting the in-cylinder pressure of the combustion chamber of the internal combustion engine;
Crank angle detecting means for detecting a crank angle of the internal combustion engine;
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;
In the compression stroke of the internal combustion engine, a correction parameter for minimizing the deviation is identified based on the deviation between the pressure detected by the pressure detecting means and the motoring pressure estimated by the estimating means. An identification means;
An abnormality detection device for pressure detection means, comprising: an abnormality detection means for detecting an abnormality of the pressure detection means based on the correction parameter at the time of fuel cut.   The abnormality detection device for pressure detection means according to claim 1, wherein the abnormality detection means determines that an abnormality occurs when the correction parameter is outside a predetermined range. 3. The abnormality detection unit according to claim 1, wherein the abnormality detection unit obtains a difference between an average value of the correction parameter for a predetermined number of times and the correction parameter, and determines that the abnormality is abnormal when the difference is larger than a predetermined value. Abnormality detection device for pressure detection means.

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