JP4798647B2 - In-cylinder pressure sensor abnormality detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detecting technique capable of absorbing fluctuation in output characteristics of a sensor, and capable of enhancing precision of abnormality detection. <P>SOLUTION: This abnormality detector for a pressure detecting means of the present invention includes 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 a motoring pressure of the internal combustion engine by an operation expression including the calculated volume, an identification means for identifying a correction parameter for minimizing a deviation, in a compression stroke of the internal combustion engine, based on a deviation between the pressure detected by the pressure detecting means and the motoring pressure detected by the estimation means, and an abnormality detecting means for detecting the abnormality of the pressure detecting means, by comparing the motoring pressure with the detected pressure corrected with the correction parameter, when cutting fuel. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

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 using an arithmetic expression including the calculated volume, and detecting the pressure in the compression stroke of the internal combustion engine. Based on the deviation between the pressure and the motoring pressure estimated by the estimating means, identification means for identifying a correction parameter for minimizing the deviation, and correction by the motoring pressure and the correction parameter at the time of fuel cut Provided is an abnormality detection device for pressure detection means, comprising an abnormality detection means for detecting an abnormality of the pressure detection means by comparing with the detected pressure.

  According to the present invention, the sensor abnormality is determined based on the degree of matching between the detected pressure and the motoring pressure at which the deviation is minimized by the correction parameter. Therefore, it is possible to absorb fluctuations in the detected value due to temperature change, aging deterioration, etc., and improve the accuracy of abnormality detection.

  In one embodiment of the present invention, the abnormality detection means obtains an integrated value of the deviation between the motoring pressure and the corrected detected pressure in a predetermined range in one cycle of the internal combustion engine, and the integrated value is less than the predetermined value. If it is larger, it is determined as abnormal.

  In one embodiment of the present invention, the abnormality detection means stores a crank angle at which the detected pressure is maximum, and determines that an abnormality occurs when the crank angle is outside a predetermined range.

  Further, in one embodiment of the present invention, the abnormality detection device of the pressure detection means detects the combustion state based on the detected pressure corrected by the correction parameter and the motoring pressure in the combustion stroke of the internal combustion engine. A determination means for determining is further provided.

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

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:

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 value PS detected by the in-cylinder pressure sensor 12 and corrected by the sensor output correction unit 17 and the motoring pressure estimation at the same time in the period b (FIG. 2) after the ignition time point. 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.

  With reference to FIG. 4, the sensor abnormality detection method of this embodiment is demonstrated. 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, and the correction parameters may be identified particularly in the compression stroke, so that both waveforms are almost the same. It has been corrected. That is, if the pressure sensor is operating normally, the behavior of the sensor output at the time of fuel cut and the behavior of the motoring pressure are almost the same.

  As described above, the motoring pressure and the sensor detection pressure at the time of fuel cut corrected by the above-described correction method are characterized by having a high degree of fitness. Therefore, in this embodiment, the sensor abnormality is detected by comparing the behavior of the sensor output and the motoring pressure when the fuel is cut.

Referring to FIG. 1 again, the sensor abnormality detection unit 29 receives the sensor output PS corrected from the sensor output correction unit 17 and the motoring pressure PM from the motoring pressure calculation unit 20. 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 a 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 calculates an error integrated value S_DP of the sensor output PS and the motoring pressure PM by the following equation.

  Here, θ is the crank angle, and PS (θ) and PM (θ) are the sensor output and the motoring pressure at the crank angle θ. Dθ is a sample angle and varies depending on the number of crank rotations. For example, sampling is performed every 0.5 degrees up to 4000 rpm, and sampling is performed every 1 degree above 4000 rpm. The integration range may be an arbitrary range in one cycle of the engine. In the present embodiment, for example, the integration range is set from the compression stroke to the combustion stroke. Here, the compression stroke is a stroke in which the intake / exhaust valve is closed and the piston rises. The combustion stroke is a stroke after ignition by a plug in a gasoline engine, and a stroke after fuel injection in a diesel engine. In the present embodiment, for example, the integration is performed when the crank angle θ is in the range of −70 degrees to 90 degrees.

  Subsequently, the sensor abnormality detection unit 29 performs sensor abnormality determination using the calculated error integral value S_DP. A large error integration value S_DP indicates that there are many errors in the waveforms of the sensor output PS and the motoring pressure PM. Therefore, a predetermined threshold is set, and if S_DP is equal to or greater than the threshold, it is determined that the sensor is abnormal.

  Further, the sensor abnormality detection unit 29 detects the crank angle θ_PSmax that maximizes the sensor output PS. Since the motoring pressure PM has a maximum value when the volume in the cylinder is minimum, the maximum pressure is obtained when the crank angle is 0 degrees. It is considered that the sensor output PS at the time of fuel cut also takes the maximum value around the crank angle of 0 degree. Therefore, an allowable range is set across the crank angle of 0 degree, and if θ_PSmax is out of this range, it is determined that the sensor is abnormal.

  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. Since no explosion occurs in the cylinder when the fuel is cut, the detected pressure waveform of the normally operating sensor should match the motoring pressure waveform. The sensor abnormality detection method according to the present invention utilizes this feature and can be applied when fuel is 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, the deviation integrated value S_DP between the sensor output PS corrected by the correction equation PS = PS (θ) k ₁ + C ₁ and the motoring pressure PM is calculated by the equation (11). The integration interval is, for example, a crank angle range of −70 degrees to 90 degrees. The integration interval can be changed according to the crank rotation speed. For example, the integration interval up to 4000 rpm is every 0.5 degrees, and the integration interval above 4000 rpm is every 1 degree.

  In step S109, it is checked whether the deviation integral value S_DP is larger than a predetermined value. If the deviation integrated value S_DP is larger than the predetermined value, it is determined that there is an error exceeding the allowable range between the waveform of the sensor output PS and the waveform of the motoring pressure PM, and it is determined that there is some abnormality in the sensor, and the process proceeds to step S117. . If the deviation integral value S_DP is less than or equal to the predetermined value, the process proceeds to step S111.

  In steps S111 and S113, the crank angle θ_PSmax at which the waveform of the sensor output PS shows the maximum value is obtained, and it is checked whether it is outside the predetermined range. In the case of a normally operating sensor, the maximum pressure when the fuel is cut is at a position where the crank angle is about 0 degrees. The crank angle of 0 degrees is the timing when the compression stroke changes to the expansion stroke. Accordingly, the predetermined upper limit value in step S111 and the predetermined lower limit value in step S113 are set with a crank angle of 0 degrees. If the crank angle θ_PSmax at which the waveform of the sensor output PS shows the maximum value is outside the predetermined range, it is determined that there is some abnormality in the sensor, and the process proceeds to the abnormality detection process after step S117. If the crank angle θ_PSmax at which the waveform of the sensor output PS shows the maximum value is within the predetermined range, it is determined that there is no sensor abnormality, and the process proceeds to step S115.

  Hereinafter, the abnormality detection process after step S117 will be described.

  In step S117, 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 S119, 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 S121. If the abnormality detection counter is not 0, the process is terminated as it is.

  In step S121, 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, as a result of the processing in steps S109, S111, and S113, if the sensor measurement signal PS matches the motoring signal PM and it is determined that there is no abnormality in the pressure sensor, the process proceeds to step S115. In step S115, 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 (2)

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 means for detecting an abnormality of the detection means by comparing the motoring pressure and the detected pressure corrected by the correction parameter at the time of fuel cut ;
The abnormality detecting means obtains an integrated value of a deviation between the motoring pressure and the corrected detected pressure in a predetermined range in one cycle of the internal combustion engine, and if the integrated value is larger than a predetermined value, the abnormality is detected. An abnormality detection device for pressure detection means for determining . 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 means for detecting an abnormality of the detection means by comparing the motoring pressure and the detected pressure corrected by the correction parameter at the time of fuel cut;
The abnormality detection device of the pressure detection means, wherein the abnormality detection means stores a crank angle at which the corrected detected pressure is maximum, and determines that an abnormality occurs when the crank angle is outside a predetermined range .

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