JP2007309261A - Temperature estimating device and control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the temperature in the vicinity of a combustion chamber without depending on engine water temperature. <P>SOLUTION: This temperature estimating device is provided with a cylinder internal pressure detecting means for detecting the pressure inside the combustion chamber of an engine and an estimating means for estimating motoring pressure of the engine. The temperature estimating device is further provided with an identifying means for identifying a correction parameter to correct the detected pressure such that a deviation between the pressure detected by the cylinder internal pressure detecting means and the motoring pressure is minimized in a compression stroke of the engine and a temperature estimating means for estimating the temperature of the cylinder internal pressure detecting means based on the correction parameter. The temperature of the cylinder internal pressure detecting means in the vicinity of the combustion chamber of the engine can be estimated based on the correction parameter for correcting detected output by the cylinder internal pressure detecting means without depending on the engine water temperature. After start of the engine, also in a period until the engine water temperature increases, the temperature in the vicinity of the combustion chamber can be estimated without depending on the engine water temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine temperature estimation device and a control device using the same.

One of the parameters used for various controls of an internal combustion engine (hereinafter referred to as an engine) is the cooling water temperature of the engine. In Patent Document 1, when the engine water temperature detected by the temperature sensor installed in the engine block is lower than a predetermined value (for example, 33 ° C.), it is estimated that the fuel atomization rate is low and the intake air temperature is low. It describes that the fuel injection control is performed by changing the estimated value of the intake air temperature as the water temperature increases.
Japanese Patent Publication No. 8-30442

  However, since there is a large time delay in the change in the temperature of the cooling water in relation to the temperature near the combustion chamber of the engine, when the engine is started from a cold state, the temperature of the cooling water will change to the temperature near the combustion chamber. There will be a large time delay before reflection.

  Therefore, there is a need for a technique for estimating the temperature near the combustion chamber without depending on the engine water temperature. In particular, there is a need for a technique for estimating the temperature in the vicinity of the combustion chamber without depending on the engine water temperature during the period from when the engine is started until the engine water temperature rises.

  The temperature estimation device according to the present invention includes in-cylinder pressure detection means for detecting the pressure in the combustion chamber of the engine and estimation means for estimating the motoring pressure of the engine. This temperature estimation device is used for identifying a correction parameter for correcting a detected pressure so that a deviation between the pressure detected by the cylinder pressure detecting means and the motoring pressure is minimized in the compression stroke of the engine. And temperature estimation means for estimating the temperature of the in-cylinder pressure detection means based on the correction parameter.

  According to this invention, the temperature of the in-cylinder pressure detecting means in the vicinity of the combustion chamber of the engine can be estimated based on the correction parameter for correcting the detection output by the in-cylinder pressure detecting means without depending on the engine water temperature. .

  In one aspect of the present invention (claim 2), the motoring pressure estimating means includes a crank angle detecting means for detecting a crank angle of the engine, and a combustion chamber of the engine based on the crank angle detected by the crank angle detecting means. Means for calculating the volume of the motor, and the motoring pressure is estimated by an arithmetic expression including the calculated volume.

  The control device of the present invention (Claim 3) is configured to control the engine using the temperature estimated by the temperature estimation means instead of the engine water temperature when the engine is started.

  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 air-fuel ratio control 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 = 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 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 PD (θ) according to the above-described correction formula PS = PD (θ) k ₁ + C ₁ . The sensor output correction unit 17 passes the corrected sensor output value PS 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.

この式を逆行列を使って変形すると、次のようになる。

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) is passed to the combustion pressure detector 41.

  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).

  The PC (θ) thus obtained is used for air-fuel ratio control for each cylinder as described in, for example, Japanese Patent Application No. 2005-097518 by the applicant of the present application, and also used for various engine controls.

  Incidentally, the in-cylinder pressure sensor is a piezoelectric ceramic element, and converts a movement amount of electric charges generated by a distortion of the piezoelectric element due to combustion pressure in the cylinder into a voltage by a charge amplifier. The piezoelectric constant of this piezoelectric element, that is, the charge generated per force applied to the piezoelectric element, increases as the temperature rises.

FIG. 4 shows the relationship between such temperature characteristics and the correction of the output of the in-cylinder pressure sensor. As described above, the output of the in-cylinder pressure sensor is corrected according to the correction formula PS = PD (θ) k ₁ + C ₁ . k ₁ is a proportional coefficient for correcting the sensor output so as to match the motoring pressure as a model, and is called a model fitting coefficient. FIG. 4A shows the behavior when the temperature of the in-cylinder pressure sensor is sufficiently high. The solid line waveform in the left figure represents the motoring pressure, and the dotted line waveform represents the sensor output PD (θ). The waveform of the dotted line in the diagram on the right side of FIG. 4A represents the in-cylinder pressure PS corrected by the above correction equation.

FIG. 4B shows the behavior when the temperature of the in-cylinder pressure sensor is low after the engine is started. The solid waveform in the left figure represents the motoring pressure, and the dotted waveform represents the sensor output PD (θ). The dotted waveform in the right diagram of FIG. 4B represents the in-cylinder pressure PS corrected by the above correction equation. As can be seen from this, the coefficient k ₁ increases as the temperature decreases.

FIG. 5 is a diagram showing the relationship between the temperature of the in-cylinder pressure sensor and the rate of decrease in sensor output. Based on the engine water temperature of 85 ° C. when the engine is completely warmed up, the rate at which the sensor output decreases when the sensor temperature decreases is shown. Based on this relationship, the sensor temperature can be obtained from the rate of change of the output of the in-cylinder pressure sensor. In the present invention, a parameter corresponding to the rate of change of the output of the in-cylinder pressure sensor, using the correction coefficient k ₁ of the foregoing. In a state where the engine is not sufficiently warmed up, the correction coefficient k ₁ changes in inverse proportion to the temperature, so that the sensor temperature can be obtained from the rate of change of the coefficient k ₁ .

The average K1dave rate of change of the coefficients k _1, obtained in the following manner. First, when the engine is sufficiently warm (e.g., when the engine coolant temperature is above 85 ° C.), and calculates the learning value K1refh (each cylinder) values of k ₁ of each cylinder parameter identification unit 23 is calculated. Then, the rate of change of k ₁ for each cylinder, i.e. determine the ratio between K1refh of k ₁ and its cylinders of each cylinder, calculates the sum of the rate of change of all the cylinders, by dividing this sum by the number of cylinders, the coefficient The average value K1dave of the rate of change of k ₁ is obtained.

Figure 6 shows the relationship between the temperature of the average value K1dave rate of change of the coefficients k ₁ and cylinder pressure sensor. Returning to FIG. 1, the temperature estimation unit 61 calculates the average value K1dave of the rate of change from the coefficient k ₁ passed from the parameter identification unit 23, and stores the table corresponding to FIG. 6 stored in the ROM of the electronic control unit. To obtain the temperature of the in-cylinder pressure sensor.

  Since the temperature of the in-cylinder pressure sensor thus obtained represents the temperature in the vicinity of the combustion chamber of the engine, it can be used for various controls of the engine. For example, in the technique described in Patent Document 1 shown in the background art, the engine water temperature can be used instead of the engine water temperature in a state where the engine water temperature after starting the engine has not sufficiently increased. This temperature can also be used for air-fuel ratio control.

  While the present invention has been described with respect to specific embodiments, the present invention is not limited to such embodiments. 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. The figure which shows the relationship between a motoring pressure and the correction process of a cylinder pressure sensor output. The figure which shows the relationship between the temperature of a cylinder pressure sensor, and the fall rate of a sensor output. The graph which shows the relationship between the average value of the change rate of the correction coefficient which correct | amends a cylinder pressure sensor output, and the temperature of a combustion chamber vicinity.

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 Air-fuel ratio correction unit 49 Fuel injection amount calculation unit

Claims (3)

In-cylinder pressure detecting means for detecting the pressure in the combustion chamber of the internal combustion engine;
Estimating means for estimating the motoring pressure of the internal combustion engine;
Identifying means for identifying a correction parameter for correcting the detected pressure so that a deviation between the pressure detected by the in-cylinder pressure detecting means and the motoring pressure is minimized in the compression stroke of the internal combustion engine;
Temperature estimating means for estimating the temperature of the in-cylinder pressure detecting means based on the correction parameter;
A temperature estimation device for an internal combustion engine comprising: The motoring pressure estimation means is
Crank angle detecting means for detecting a crank angle of the internal combustion engine;
Means for calculating the volume of the combustion chamber of the internal combustion engine based on the crank angle detected by the crank angle detection means,
Estimating the motoring pressure by an arithmetic expression including the calculated volume;
The temperature estimation apparatus according to claim 1. 2. The temperature estimation device according to claim 1, wherein when the internal combustion engine is started, the internal combustion engine is controlled using a temperature estimated by the temperature estimation means instead of the water temperature of the internal combustion engine. Control device for internal combustion engine.

Images