JP5760924B2 - In-cylinder pressure estimation device for internal combustion engine - Google Patents

Description

  The present invention relates to an in-cylinder pressure estimating device for an internal combustion engine.

  Conventionally, as disclosed in, for example, Patent Literature 1, an internal combustion engine including an in-cylinder pressure sensor is known. Further, this publication discloses determination processing for determining that pre-ignition has occurred when the in-cylinder pressure at a predetermined crank angle before ignition or the rate of increase of the in-cylinder pressure is greater than or equal to a predetermined value.

JP 2011-117325 A JP 2008-069713 A

  The maximum in-cylinder pressure obtained by the in-cylinder pressure sensor and its crank angle are important parameters because they are easy to measure and provide useful information for engine control. For example, it is used for engine output (torque) estimation and MBT ignition timing control (control at the ignition timing at which the maximum torque is generated).

  However, in recent years, in supercharged engines, because the maximum in-cylinder pressure reaches several tens of MPa due to sudden pre-ignition, it is necessary to greatly increase the maximum range (measurement upper limit value) that was several MPa in the past. . However, if the maximum range is significantly increased, the detection accuracy (minimum resolution) deteriorates, and the accuracy of other controls using the in-cylinder pressure sensor is adversely affected. Further, it is difficult to quantify the excessive in-cylinder pressure generated by pre-ignition, and even if the maximum range is set, there is a possibility that an in-cylinder pressure exceeding that will occur.

  Therefore, the maximum range is not increased more than necessary, and a method is required that can estimate the maximum in-cylinder pressure when the output of the in-cylinder pressure sensor exceeds the range due to pre-ignition or the like.

  The present invention has been made in order to solve the above-described problem, and even if the output of the in-cylinder pressure sensor exceeds the range, the in-cylinder pressure of the internal combustion engine that can accurately estimate the maximum in-cylinder pressure. An object is to provide an estimation device.

In order to achieve the above object, a first invention is an in-cylinder pressure estimating device for an internal combustion engine,
An in-cylinder pressure sensor capable of detecting an in-cylinder pressure below the set maximum range;
Crank angle and PV ^κ value when the cylinder pressure detected by the cylinder pressure sensor at a predetermined crank angle interval is P, the cylinder volume at the time of detection is V, and the specific heat ratio of gas in the cylinder is κ. PV ^κ waveform calculating means for calculating the relationship of
A range over determination means for determining whether or not a range over which the in-cylinder pressure exceeds the maximum range has occurred;
A crank angle obtaining means for obtaining a first crank angle immediately before the in-cylinder pressure exceeds the maximum range and a second crank angle immediately after the in-cylinder pressure falls below the maximum range when the range over occurs;
Means for obtaining the first crank angle and the PV ^κ value immediately before the first crank angle from the relationship, and calculating a rate of change of the PV ^κ value immediately before exceeding the maximum range (hereinafter referred to as a first rate of change);
Means for obtaining the second crank angle and the PV ^κ value immediately after the second crank angle from the relationship, and calculating a rate of change of the PV ^κ value immediately after falling below the maximum range (hereinafter referred to as a second rate of change);
Among the relationships, a PV that linearly interpolates a crank angle section from the first crank angle to the second crank angle where the range over has occurred based on the first change rate and the second change rate. ^κ waveform interpolation means;
In-cylinder pressure calculating means for calculating the in-cylinder pressure in the crank angle section by dividing the linearly interpolated PV ^κ value by V ^κ .

According to the first invention, even when pre-ignition or the like occurs, the shape of the PV ^κ waveform representing the relationship between the crank angle and the PV ^κ value is a shape close to that during normal combustion (the PV ^κ value itself is different) Paying attention to the above, linear interpolation is performed for the crank angle section in which the range is over. Since this PV interpolation can correct the PV ^κ waveform with high accuracy, the maximum in-cylinder pressure can be estimated with high accuracy even in the crank angle section where the range is over.

It is a figure for demonstrating the system configuration | structure which concerns on Embodiment 1 of this invention. It is a figure showing the cylinder pressure waveform (ignition TDC standard) at the time of normal combustion. It is a figure showing the in-cylinder pressure waveform (ignition TDC reference | standard) when the in-cylinder pressure exceeding a maximum range generate | occur | produces by preignition etc. FIG. It is a figure which shows the in-cylinder pressure waveform and PV ^kappa waveform at the time of normal combustion. It is a figure for demonstrating the in-cylinder pressure estimation process in case a range over (upper limit sticking) arises by pre-ignition etc. FIG. In Embodiment 1 of this invention, it is a flowchart of the control routine which ECU50 performs.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. The internal combustion engine 10 is a four-cycle engine mounted on a vehicle or the like and used as a power source. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  Each cylinder of the internal combustion engine 10 is provided with an injector 12 that injects fuel directly into the cylinder. The present invention is not limited to such an in-cylinder injection type internal combustion engine, but a port injection type internal combustion engine having a port injector for port-injecting fuel into an intake port, or a combination of an injector 12 and a port injector. The present invention can be similarly applied to an internal combustion engine. Each cylinder of the internal combustion engine 10 is provided with an in-cylinder pressure sensor 14 and a spark plug 15 for detecting the in-cylinder pressure.

  An intake passage 16 and an exhaust passage 18 are connected to each cylinder of the internal combustion engine 10. An intake valve 20 that opens and closes between the cylinder and the intake passage 16 is provided at the downstream end of the intake passage 16. Similarly, an exhaust valve 22 that opens and closes between the cylinder and the exhaust passage 18 is provided at the upstream end of the exhaust passage 18.

  Exhaust gas discharged from each cylinder of the internal combustion engine 10 flows into the exhaust passage 18. The internal combustion engine 10 includes a turbocharger 24 that performs supercharging with the energy of exhaust gas. The turbocharger 24 includes a turbine 24a that is rotated by the energy of the exhaust gas, and a compressor 24b that is rotated by being driven by the turbine 24a. The turbine 24 a is arranged in the middle of the exhaust passage 18, and the compressor 24 b is arranged in the middle of the intake passage 16.

  A catalyst 26 that purifies harmful components in the exhaust gas is provided in the exhaust passage 18 downstream of the turbine 24a. As the catalyst 26, for example, a three-way catalyst can be used.

  An air cleaner 28 is provided near the inlet of the intake passage 16. An air flow meter 30 for detecting the intake air amount is provided in the vicinity of the downstream side of the air cleaner 28. A compressor 24 b is provided downstream of the air flow meter 40. An intercooler 32 is provided downstream of the compressor 24b.

  The fresh air sucked through the air cleaner 28 is compressed by the compressor 24 b of the turbocharger 24 and then cooled by the intercooler 32. An electronically controlled throttle valve 34 is provided downstream of the intercooler 32. The fresh air that has passed through the throttle valve 34 flows into a surge tank 36 formed in the downstream portion of the intake passage 16. The fresh air flowing into the surge tank 36 is distributed and flows into each cylinder.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50. In addition to the in-cylinder pressure sensor 14 and the air flow meter 30 described above, various sensors for detecting the operating state of the internal combustion engine 10 such as a crank angle sensor 52 for detecting the crank angle are connected to the input portion of the ECU 50. Yes. The ECU 50 samples the output of the in-cylinder pressure sensor 14 of each cylinder at predetermined intervals and calculates parameters. The ECU 50 calculates the in-cylinder volume V determined by the engine speed and the piston position from the crank angle.

  Further, various actuators for controlling the operating state of the internal combustion engine 10 such as the injector 12, the spark plug 15, and the throttle valve 34 are connected to the output portion of the ECU 50. The ECU 50 controls the operating state of the internal combustion engine 10 by operating various actuators according to a predetermined program based on the outputs of the various sensors described above.

  FIG. 2 is a diagram illustrating an in-cylinder pressure waveform (ignition TDC reference) during normal combustion. The in-cylinder pressure is calculated according to the sensor output value of the in-cylinder pressure sensor 14. Since the maximum in-cylinder pressure at the time of normal combustion is several MPa, the maximum range of the in-cylinder pressure sensor 14 is set to be higher than that, so the maximum in-cylinder pressure at normal combustion and its crank angle can be measured. Note that the maximum range is not set high enough to detect an excessive in-cylinder pressure generated during abnormal combustion from the viewpoint of preventing deterioration in detection accuracy (minimum resolution).

  FIG. 3 is a diagram showing an in-cylinder pressure waveform (ignition TDC reference) when an in-cylinder pressure exceeding the maximum range is generated by pre-ignition or the like. The vertical axis in FIG. 3 is tens of MPa unlike FIG. In the supercharged engine as described above, the maximum in-cylinder pressure may reach several tens of MPa due to sudden occurrence of pre-ignition or the like. When an in-cylinder pressure exceeding the maximum range is generated, the sensor output value sticks to the maximum range, and therefore the in-cylinder pressure in the crank angle section where the range over has occurred cannot be directly measured. Therefore, the maximum in-cylinder pressure generated in the crank angle section cannot be directly measured. Therefore, in the system of the present embodiment, the maximum in-cylinder pressure is estimated with high accuracy even when the sensor output value exceeds the range.

[Characteristic Configuration in Embodiment 1]
In-cylinder pressure estimation processing according to the present embodiment will be described with reference to FIGS. FIG. 4 is a diagram showing an in-cylinder pressure waveform and a PV ^κ waveform during normal combustion. FIG. 4A shows an in-cylinder pressure waveform showing the relationship between the crank angle and the in-cylinder pressure in the vicinity of the ignition TDC during normal combustion. FIG. 4B shows a PV ^κ waveform showing the relationship between the crank angle and the PV ^κ value when the cylinder pressure is P, the cylinder volume at the detected crank angle is V, and the specific heat ratio κ of the gas in the cylinder. Represents. The PV ^κ waveform shown in FIG. 4B is calculated by multiplying the in-cylinder pressure waveform of FIG. 4A by V ^κ . The PV ^κ value is used as an index of the heat generation amount, and has a relationship of heat generation amount (heat generation amount) ≈PV ^κ .

FIG. 5 is a diagram for explaining in-cylinder pressure estimation processing in the case where a range over (upper limit sticking) occurs due to pre-ignition or the like. FIG. 5A shows an in-cylinder pressure waveform near the ignition TDC. FIG. 5B shows a PV ^κ waveform obtained by multiplying the in-cylinder pressure waveform of FIG. 5A by V ^κ . As shown in FIG. 5A, when an upper limit sticking occurs in which the sensor output value sticks to the maximum range (measurement upper limit value), the in-cylinder pressure in the crank angle section bc cannot be directly measured.

However, it was found that even when pre-ignition occurs, the shape of the PV ^κ waveform is close to that during normal combustion (FIG. 4B, but the PV ^κ value itself is different). Therefore, in the system of the present embodiment, the crank angle section ^bc of the PV ^κ waveform is linearly interpolated using the rate of change of the PV ^κ value before and after that section (FIG. 5B).

This linear interpolation will be specifically described. First, the crank angle b at which the in-cylinder pressure is detected immediately before the in-cylinder pressure exceeds the maximum range, and the crank angle c at which the in-cylinder pressure is detected immediately after falling below the maximum range are acquired (FIG. 5A). Then, the PV ^κ values at the crank angle b and the crank angle a at which the in-cylinder pressure is detected immediately before are obtained. From the crank angle and the PV ^κ value at these two points, a straight line 60 passing through the two points with the change rate of the PV ^κ value immediately before exceeding the maximum range as an inclination is calculated (FIG. 5B).

Similarly, PV ^kappa values at the crank angle c and the crank angle d at which the in-cylinder pressure is detected immediately after that are obtained. From the crank angle and the PV ^κ value at these two points, a straight line 62 passing through the two points with the change rate of the PV ^κ value immediately below the maximum range as an inclination is calculated (FIG. 5B). Then, as shown in FIG. 5B, the crank angle section ^bc of the PV ^κ waveform is linearly interpolated with the straight line 60 and the straight line 62.

Then, the in-cylinder pressure waveform in the crank angle section bc as shown in FIG. 5C can be obtained by dividing the PV ^κ value of the crank angle section bc subjected to linear interpolation by V ^κ . According to such a method, it is possible to estimate the maximum in-cylinder pressure generated in the crank angle section bc where the range over has occurred.

  FIG. 6 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described in-cylinder pressure estimation process. In the routine shown in FIG. 6, first, in step S100, the sensor output value of the in-cylinder pressure sensor 14 is detected every predetermined crank angle (for example, every several degrees), and the in-cylinder pressure corresponding to the sensor output value is calculated. At least the sensor output value near the ignition TDC is included.

  In step S110, it is determined whether or not a range over has occurred. For example, when there is a crank angle section in which the sensor output value reaches the maximum range, it is determined that a range over has occurred. If it is determined that no range over has occurred, the processing of this routine is terminated.

  On the other hand, if it is determined that a range over has occurred, crank angles before and after the range over are acquired in step S120. Specifically, the first crank angle immediately before the sensor output value exceeds the maximum range and the second crank angle immediately after the sensor output value falls below the maximum range are acquired. Specifically, the first crank angle is the crank angle b in FIG. 5A, and the second crank angle is the crank angle c in FIG.

In step S130, the PV ^κ value for each detected crank angle is calculated from the in-cylinder pressure detected for each predetermined crank angle in step S100. The crank angle and the PV ^κ value have a relationship represented by the PV ^κ waveform in FIG. Here, the PV ^κ value in the crank angle section bc in FIG. 5B is not accurate because the upper limit of the sensor output value has occurred (line 58 in FIG. 5B). On the other hand, the PV ^κ value in the section other than the crank angle section ^bc is accurate.

In step S140, the change rate (slope) of the PV ^κ value immediately before exceeding the maximum range is calculated. Specifically, first, the PV ^κ value at the first crank angle (crank angle b in FIG. 5B) and the crank angle (crank angle a in FIG. 5B) at which the in-cylinder pressure was detected just before that is calculated. Get each. Based on the crank angle and the PV ^κ value at these two points, the change rate of the PV ^κ value is set as an inclination, and a straight line passing through these two points (straight line 60 in FIG. 5B) is calculated.

In step S150, the rate of change (slope) of the PV ^κ value immediately after falling below the maximum range is calculated. Specifically, first, PV ^κ values at the second crank angle (crank angle c in FIG. 5B) and the crank angle (crank angle d in FIG. 5B) at which the in-cylinder pressure is detected immediately thereafter are calculated. Get each. Based on the crank angle and the PV ^κ value at these two points, the change rate of the PV ^κ value is assumed to be a slope, and a straight line passing through these two points (straight line 62 in FIG. 5B) is calculated.

In step S160, the PV ^κ waveform in the crank angle section in which the upper limit of the sensor output is stuck is linearly interpolated by two straight lines having slopes before and after the range over. Specifically, as shown in FIG. 5B, the crank angle section where the upper limit sticking occurs is linearly interpolated by the straight lines 60 and 62.

In step S170, the PV ^κ value corrected by linear interpolation is divided by V ^κ to calculate the in-cylinder pressure in the crank angle section where the upper limit sticking occurs. In step S180, the maximum in-cylinder pressure and the crank angle in the crank angle section are calculated. Thereafter, the processing of this routine is terminated.

As described above, according to the routine shown in FIG. 6, it is possible to linearly interpolate the PV ^κ waveform in the crank angle section where the upper limit sticking occurs. Since the PV ^κ waveform can be accurately interpolated by this linear interpolation, the maximum in-cylinder pressure can be calculated with high accuracy even when a range over occurs. For this reason, according to the system of the present embodiment, the maximum in-cylinder pressure and its crank angle are accurately estimated even when pre-ignition occurs while maintaining the detection accuracy without increasing the maximum range more than necessary. can do. Therefore, various controls using the in-cylinder pressure sensor output can be suitably realized, and durability of the internal combustion engine and sensor can be ensured, and fuel consumption and emission can be improved.

In the first embodiment described above, the in-cylinder pressure sensor 14 corresponds to the “in-cylinder pressure sensor” according to the first aspect of the present invention. Here, the ECU 50 executes the process of step S110, so that the “range over determination means” in the first aspect of the invention executes the process of step S120, and the “crank” in the first aspect of the invention. When the “angle obtaining means” executes the process of step S130, the “PV ^κ waveform calculating means” in the first invention executes the process of step S140, thereby “first” in the first invention. The “means for calculating the rate of change” executes the process of step S150, so that the “means of calculating the second rate of change” in the first invention executes the process of step S160. of "PV ^kappa waveform calculation means" in the invention, the first by executing the processing of step S170 A "cylinder pressure calculating means" in the invention, are realized respectively.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Injector 14 In-cylinder pressure sensor 15 Spark plug 16 Intake passage 18 Exhaust passage 20 Intake valve 22 Exhaust valve 24 Turbocharger 24a Turbine 24b Compressor 26 Catalyst 30 Air flow meter 34 Throttle valve 36 Surge tank 40 Air flow meter 52 Crank angle sensor a , B, c, d Crank angle P In-cylinder pressure V In-cylinder volume κ Specific heat ratio

Claims (1)

An in-cylinder pressure sensor capable of detecting an in-cylinder pressure below the set maximum range;
Crank angle and PV ^κ value when the cylinder pressure detected by the cylinder pressure sensor at a predetermined crank angle interval is P, the cylinder volume at the time of detection is V, and the specific heat ratio of gas in the cylinder is κ. PV ^κ waveform calculating means for calculating the relationship of
A range over determination means for determining whether or not a range over which the in-cylinder pressure exceeds the maximum range has occurred;
A crank angle obtaining means for obtaining a first crank angle immediately before the in-cylinder pressure exceeds the maximum range and a second crank angle immediately after the in-cylinder pressure falls below the maximum range when the range over occurs;
Means for obtaining the first crank angle and the PV ^κ value immediately before the first crank angle from the relationship, and calculating a rate of change of the PV ^κ value immediately before exceeding the maximum range (hereinafter referred to as a first rate of change);
Means for obtaining the second crank angle and the PV ^κ value immediately after the second crank angle from the relationship, and calculating a rate of change of the PV ^κ value immediately after falling below the maximum range (hereinafter referred to as a second rate of change);
Among the relationships, a PV that linearly interpolates a crank angle section from the first crank angle to the second crank angle where the range over has occurred based on the first change rate and the second change rate. ^κ waveform interpolation means;
In-cylinder pressure calculating means for calculating the in-cylinder pressure in the crank angle section by dividing the linearly interpolated PV ^κ value by V ^κ ;
An in-cylinder pressure estimating device for an internal combustion engine, comprising:

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