JP2012145041A - Control system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control system of an internal combustion engine, capable of identifying where an abnormality occurs from among an intake valve, an exhaust valve, and a piston ring.SOLUTION: If there is an abnormality in an intake valve 34, unburned fuel in a combustion chamber 26 flows back toward an intake passage 30 (Fig.3(i)). Thus, the flown back unburned fuel flows into the combustion chamber 26 together with injected fuel in or after the next timing. An actual air-fuel ratio therefore shifts toward a fuel rich side than a target air-fuel ratio. If there is an abnormality in an exhaust valve 36, fresh air in the combustion chamber 26 flows out to an exhaust passage 32 before combustion (Fig.3(ii)). The actual air-fuel ratio therefore shifts toward a fuel lean side than the target air-fuel ratio. If there is an abnormality in a piston ring (Fig.3(iii)), a shift of the actual air-fuel ratio as described above is kept within a prescribed range.

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine that performs various abnormality diagnosis based on in-cylinder pressure.

  Conventionally, for example, in Patent Document 1, the time change rate of the compression pressure is calculated from the detected value of the in-cylinder pressure, the time change rate of the exhaust temperature is calculated from the detected value of the exhaust temperature sensor, and these two time change rates are calculated. A control apparatus for an internal combustion engine that uses an intake valve (IN valve), an exhaust valve (EX valve), and a piston ring to identify occurrence of abnormality is disclosed. In this control device, specifically, the time change rate of the compression pressure is compared with a threshold value, and if the time change rate of the compression pressure is larger than the threshold value, there is an abnormality in any of the intake valve, the exhaust valve, and the piston ring. Judge that there is. In addition, if it is determined that there is an abnormality in any of the intake valve, exhaust valve, or piston ring, the time change rate of the exhaust temperature is compared with a threshold value, and the time change rate of the exhaust temperature is greater than the threshold value. In this case, it is determined that an abnormality has occurred in the intake valve or the exhaust valve. If the rate of change in the exhaust temperature with time is smaller than the threshold value, it is determined that an abnormality has occurred in the piston ring.

JP 2008-208751 A JP 2009-144613 A JP 2007-224862 A Japanese Patent Laid-Open No. 04-148030 Japanese Patent Laid-Open No. 08-121242

  However, the above control device can not only determine whether an abnormality has occurred in the intake valve or the exhaust valve, but cannot determine which of the intake valve or the exhaust valve has occurred. Therefore, there is a high possibility that it is determined that an abnormality has occurred in a normal intake valve or exhaust valve.

  The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide a control device for an internal combustion engine that can specify which one of an intake valve, an exhaust valve, and a piston ring is abnormal.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of the internal combustion engine;
When the detected value of the in-cylinder pressure is smaller than a predetermined abnormality occurrence determination value, any abnormality among the intake valve, the exhaust valve, and the piston ring of the internal combustion engine is determined using a deviation between the target air-fuel ratio and the actual air-fuel ratio. An abnormality identifying means for identifying whether or not
It is characterized by providing.

According to a second invention, in the first invention,
The deviation is an air-fuel ratio difference obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio,
The abnormality specifying means determines that the intake valve is abnormal when the air-fuel ratio difference is equal to or greater than a first threshold value greater than zero, and when the air-fuel ratio difference is equal to or less than a second threshold value smaller than zero, the exhaust valve abnormality is determined. And when it is smaller than the first threshold value and larger than the second threshold value, it is determined that the piston ring is abnormal.

According to a third invention, in the first or second invention,
Oil dilution rate calculating means for calculating an oil dilution rate using the rate of decrease of the in-cylinder pressure;
An oil dilution abnormality determining means for determining an oil dilution abnormality when the abnormality specifying means is specified as an abnormality of the piston ring and the oil dilution rate is larger than a predetermined oil abnormality determination value;
It is characterized by providing.

A fourth invention is any one of the first to third inventions,
A supercharger capable of supercharging intake air supplied to the internal combustion engine and changing a supercharging pressure;
Oil dilution rate calculating means for calculating an oil dilution rate using the rate of decrease of the in-cylinder pressure;
An occurrence probability calculating means for calculating an occurrence probability of pre-ignition at the oil dilution rate;
A supercharging pressure control means for controlling the supercharging pressure so that the occurrence probability does not exceed a predetermined limit value when the abnormality specifying means specifies the abnormality of the piston ring;
It is characterized by providing.

  According to the first invention, it is possible to specify which of the intake valve, the exhaust valve, and the piston ring is abnormal by using the deviation between the target air-fuel ratio and the actual air-fuel ratio. If the intake valve is abnormal, the fuel in the cylinder flows backward to the intake passage side, and flows again into the cylinder together with the fuel injected at the next and subsequent timings, so the air-fuel ratio shifts to the fuel rich side. On the other hand, if the exhaust valve is abnormal, fresh air in the cylinder flows into the exhaust passage before combustion, so the air-fuel ratio shifts to the fuel lean side. If these deviations do not occur, it is understood that there is no abnormality in the intake valve or the exhaust valve. Therefore, if the deviation between the target air-fuel ratio and the actual air-fuel ratio is used, it can be specified which of the intake valve, the exhaust valve, and the piston ring is abnormal.

  According to the second invention, when the air-fuel ratio difference obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio is equal to or larger than the first threshold value greater than zero, it is determined that the intake valve is abnormal, and the second threshold value smaller than zero is determined. In the following cases, it is determined that the exhaust valve is abnormal, and when it is smaller than the first threshold and larger than the second threshold, it can be determined that the piston ring is abnormal. As described above, when the intake valve is abnormal, the air-fuel ratio becomes lean, and when the exhaust valve is abnormal, the air-fuel ratio becomes rich. Therefore, when the intake valve is abnormal, the air-fuel ratio difference is calculated as a positive value, and when the exhaust valve is abnormal, the air-fuel ratio difference is calculated as a negative value. Therefore, when the air-fuel ratio difference is equal to or greater than the first threshold, it can be determined that the intake valve is abnormal, and when it is equal to or less than the second threshold, it can be determined that the exhaust valve is abnormal. If the air-fuel ratio difference is a value between the first threshold value and the second threshold value, it can be determined that there is no abnormality in the intake valve or the exhaust valve, so it can be determined that there is an abnormality in the piston ring.

  According to the third aspect of the present invention, it is possible to determine that the oil dilution is abnormal when the abnormality specifying means specifies that the piston ring is abnormal and the oil dilution rate is larger than a predetermined oil abnormality determination value. Accordingly, it is possible to prompt the driver to take necessary measures such as instructing the driver to change oil.

  According to the fourth invention, in an internal combustion engine equipped with a supercharger, when the abnormality identifying means identifies the abnormality of the piston ring, the supercharging is performed so that the occurrence probability of pre-ignition does not exceed a predetermined limit value. The pressure can be controlled. Therefore, a good supercharging effect can be obtained while suppressing deterioration of drivability.

2 is a diagram for describing a system configuration according to Embodiment 1. FIG. It is a figure which shows the relationship between crank angle (theta) and compression pressure Pc. It is a figure for demonstrating the specific method of the piston ring abnormality generation location. 5 is a flowchart showing abnormality occurrence location specifying control executed by an ECU 50 in the first embodiment. 6 is a flowchart showing oil dilution rate abnormality determination control executed by an ECU 50 in the second embodiment. It is a figure for demonstrating the fall rate of compression pressure Pc. It is a characteristic diagram which shows the relationship between the fall rate of compression pressure Pc, and the increase rate of blow-by gas. FIG. 10 is a diagram for describing a system configuration of a third embodiment. In Embodiment 3, it is a flowchart which shows the supercharging pressure control performed by ECU50. It is a characteristic diagram which showed the relationship between the oil dilution rate and the occurrence frequency of preignition. FIG. 6 is a characteristic diagram showing the relationship between the limit value of supercharging pressure and the occurrence frequency of pre-ignition.

Embodiment 1 FIG.
[Description of system configuration]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system according to the present embodiment includes an engine 10 as an internal combustion engine. The number of cylinders and the cylinder arrangement of the engine 10 are not particularly limited.

  The engine 10 includes a cylinder block 14 having a piston 12 therein. The piston 12 is connected to the crankshaft 16 via a crank mechanism. The crankshaft 16 is provided inside a crankcase 18 that forms part of the cylinder block 14. An oil pan 22 that stores oil 20 is provided at the bottom of the crankcase 18.

  A cylinder head 24 is assembled to the upper part of the cylinder block 14. A space from the upper surface of the piston 12 to the cylinder head 24 forms a combustion chamber 26. The cylinder head 24 is provided with an in-cylinder pressure sensor 28 for detecting the pressure (in-cylinder pressure) in the combustion chamber 26.

  The cylinder head 24 includes an intake passage 30 and an exhaust passage 32 that communicate with the combustion chamber 26. An intake valve 34 is provided at a connection portion between the intake passage 30 and the combustion chamber 26. Similarly, an exhaust valve 36 is provided at a connection portion between the exhaust passage 32 and the combustion chamber 26. A catalyst 38 for purifying the exhaust gas is provided in the middle of the exhaust passage 32. An air-fuel ratio sensor 40 that detects the exhaust air-fuel ratio is provided upstream of the catalyst 38.

  Further, the system of the present embodiment includes an ECU (Electronic Control Unit) 50. On the input side of the ECU 50, the above-described in-cylinder pressure sensor 28, air-fuel ratio sensor 40, and other various sensors necessary for controlling the vehicle and the engine 10 are connected. On the other hand, various actuators including an intake valve 34 and an exhaust valve 36 are connected to the output side of the ECU 50. The ECU 50 controls the operation of the engine 10 by detecting the operation information of the engine 10 by the various sensors described above and driving each actuator based on the detection result.

[Features of Embodiment 1]
One of the operation controls of the engine 10 by the ECU 50 is air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 40. In the air-fuel ratio feedback control, the ECU 50 determines the amount of fuel supplied to the combustion chamber 26 so that the air-fuel ratio acquired from the air-fuel ratio sensor 40 (hereinafter also referred to as “actual air-fuel ratio”) becomes the target air-fuel ratio. Control. Note that the air-fuel ratio feedback control itself is well known and is not a main part of the present invention, so that further explanation is omitted here.

  By the way, in the engine 10, damage to the piston ring and a decrease in tension not only decrease the output performance of the engine but also increase the blow-by gas and increase the oil 20 that enters the combustion chamber 26 from the crankcase 18 side. Here, the blow-by gas refers to an unburned fuel-containing gas that flows into the crankcase 18 through the gap between the piston 12 and the cylinder wall surface, that is, through the back surface of the piston ring. If the blow-by gas increases, not only the oil 20 is diluted, but also the unburned fuel evaporated from the oil 20 flows into the combustion chamber 26 again, leading to problems such as air-fuel ratio deviation and drivability deterioration. Further, when the oil 20 enters the combustion chamber 26 from the crankcase 18 side (so-called oil rise), the oil self-ignites to induce pre-ignition, leading to problems such as drivability deterioration and engine damage. Therefore, it is desirable that the occurrence of abnormality in the piston ring can be detected with high accuracy.

  One technique for detecting the occurrence of an abnormality in the piston ring is a technique for detecting the amount of blow-by gas. Specifically, a method of measuring the pressure inside the crankcase 18, a method of estimating from the intake pipe pressure, a method of detecting from the air-fuel ratio sensor 40, and the like can be given. However, since none of these methods specify a cylinder, it is not possible to specify which cylinder has an abnormality in the piston ring. In this respect, since the in-cylinder pressure sensor 28 can be installed for each combustion chamber 26, the amount of blow-by gas can be estimated by using the detection value of the in-cylinder pressure sensor 28 (hereinafter also referred to as “compression pressure Pc”).

  With reference to FIG. 2, the estimation method of the amount of blow-by gas using the compression pressure Pc is demonstrated. FIG. 2 is a diagram showing the relationship between the crank angle θ and the compression pressure Pc. When an abnormality occurs in the piston ring, a large amount of blow-by gas flows into the crankcase 18. Therefore, as shown in FIG. 2, when the piston ring abnormality occurs (broken line), the compression pressure Pc is lower than when the piston ring is normal (solid line). Accordingly, the blow-by gas amount can be estimated based on the degree of decrease in the compression pressure Pc.

  However, the decrease in the compression pressure Pc is not limited to when an abnormality occurs in the piston ring. That is, even when an abnormality occurs in the intake valve 34 and the exhaust valve 36, the compression pressure Pc decreases. Therefore, it is difficult to distinguish which of the intake valve 34, the exhaust valve 36, and the piston ring is abnormal only by the compression pressure Pc. Therefore, in the present embodiment, when the occurrence of an abnormality is detected by the compression pressure Pc, the location where the abnormality has occurred is specified using the actual air-fuel ratio.

  FIG. 3 is a view for explaining a method for identifying a piston ring abnormality occurrence location in the present embodiment. As shown in FIG. 3I, if the intake valve 34 is abnormal, unburned fuel in the combustion chamber 26 flows backward to the intake passage 30 side. Therefore, the unburned fuel that has flowed back flows into the combustion chamber 26 together with the injected fuel at the next and subsequent timings. Therefore, the actual air-fuel ratio is shifted to the fuel rich side from the target air-fuel ratio.

  Further, as shown in FIG. 3 (ii), if the exhaust valve 36 is abnormal, fresh air in the combustion chamber 26 flows into the exhaust passage 32 before combustion. For this reason, the actual air-fuel ratio is shifted to the fuel lean side from the target air-fuel ratio. On the other hand, as shown in FIG. 3 (iii), if the piston ring is abnormal, the actual air-fuel ratio does not change (change is small). Therefore, if the actual air-fuel ratio is used, it is possible to specify which of the intake valve 34, the exhaust valve 36, and the piston ring is abnormal. Therefore, when the compression pressure Pc decreases, the occurrence of an abnormality in the piston ring can be accurately detected.

[Specific Processing in Embodiment 1]
Next, specific processing for realizing the above-described specific method will be described with reference to FIG. FIG. 4 is a flowchart showing abnormality occurrence location specifying control executed by the ECU 50 in the present embodiment.

  In the routine shown in FIG. 4, first, the ECU 50 acquires the compression pressure Pc (step 100). The compression pressure Pc is measured during the compression stroke of the engine 10, for example, at the timing when the crank angle θ shown in FIG. Subsequently, the ECU 50 determines whether or not the compression pressure Pc acquired in step 100 is smaller than the threshold value α (step 110). In this step, as the threshold value α, a value stored in the ECU 50 in advance as a normal value under the same operating conditions as when this routine is executed is used. However, as the threshold value α, it is also possible to use the average value of the compression pressure Pc in the other cylinders when this routine is executed.

  If it is determined in step 110 that the compression pressure Pc <threshold α is not satisfied, it can be determined that no abnormality has occurred in any of the intake valve 34, the exhaust valve 36, and the piston ring, and the ECU 50 executes this routine. finish. On the other hand, if it is determined in step 110 that the compression pressure Pc <the threshold value α, the ECU 50 determines that the air-fuel ratio change amount (refers to a value obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio; the same applies hereinafter). It is determined whether or not the threshold value is equal to or greater than the threshold β (step 120). In this step, the air-fuel ratio change amount is calculated in correspondence with the detection timing of the compression pressure Pc. The threshold value β is an abnormality determination value of the intake valve 34, and is set according to the exhaust emission and drivability limit values, and uses a value stored in the ECU 50 in advance. If the intake valve 34 is abnormal, the actual air-fuel ratio shifts to the fuel rich side with respect to the target air-fuel ratio, and therefore the air-fuel ratio change amount takes a positive value. For this reason, the threshold value β is set as a value larger than zero.

  When it is determined in step 120 that the air-fuel ratio change amount ≧ the threshold value β, the ECU 50 determines that an abnormality has occurred in the intake valve 34 (step 130). On the other hand, when it is determined that the air-fuel ratio change amount <the threshold value β, the ECU 50 determines whether the air-fuel ratio change amount is equal to or less than the threshold value γ (step 140). In this step, the value calculated in step 120 is used as the air-fuel ratio change amount. Further, the threshold value γ is an abnormality determination value of the exhaust valve 36, and is set according to a limit value of exhaust emission or drivability, and uses a value stored in the ECU 50 in advance. If the exhaust valve 36 is abnormal, the actual air-fuel ratio shifts to the fuel lean side with respect to the target air-fuel ratio, so the air-fuel ratio change amount takes a negative value. Therefore, the threshold value γ is set as a value smaller than zero.

  When it is determined in step 140 that the air-fuel ratio change amount ≦ the threshold value γ, the ECU 50 determines that an abnormality has occurred in the exhaust valve 36 (step 150). On the other hand, if it is determined that the air-fuel ratio change amount> threshold value γ, it can be determined that no abnormality has occurred in the intake valve 34 or the exhaust valve 36, so the ECU 50 has an abnormality in the piston ring. Is determined (step 160). As described above, according to the routine shown in FIG. 4, when the compression pressure Pc is smaller than the threshold value α, it is determined whether the cause is caused by any abnormality of the intake valve 34, the exhaust valve 36, or the piston ring. It can be identified with high accuracy.

  By the way, in the first embodiment, the value obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio is used as the air-fuel ratio change amount, and then the threshold values β and γ are respectively larger than zero and smaller than zero. However, other values may be used as the air-fuel ratio change amount, and the signs of the threshold values β and γ are not necessarily the same as in the present embodiment. For example, if the value obtained by subtracting the target air-fuel ratio from the actual air-fuel ratio is used as the air-fuel ratio change amount, the threshold values β and γ can be set as a value smaller than zero and a value larger than zero, respectively. As described above, the signs of the threshold values β and γ change depending on how the air-fuel ratio change amount is set. Can be substituted.

  In the above embodiment, the in-cylinder pressure sensor 28 corresponds to the “in-cylinder pressure detecting means” in the first invention. Further, in the first embodiment, the “abnormality specifying means” in the first aspect of the present invention is realized by the ECU 50 executing a series of processes of steps 110 to 160 in FIG. 4.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that the system shown in FIG. 1 is used and the oil dilution rate abnormality determination control shown in FIG. 5 is executed when an abnormality occurs in the piston ring. Therefore, in this embodiment, the difference from the first embodiment will be mainly described, and the description of the same matters will be simplified or omitted.

[Specific Processing in Second Embodiment]
FIG. 5 is a flowchart showing oil dilution rate abnormality determination control executed by the ECU 50 in the present embodiment. In the routine shown in FIG. 5, first, the ECU 50 determines whether or not an abnormality has occurred in the piston ring (step 200). Specifically, ECU 50 determines whether or not the process of step 160 in FIG. 4 has been executed. If it is determined in step 200 that there is no abnormality in the piston ring, the ECU 50 ends this routine.

On the other hand, if it is determined in step 200 that an abnormality has occurred in the piston ring, the ECU 50 calculates the rate of decrease in the compression pressure Pc (step 210). FIG. 6 is a diagram for explaining the reduction rate of the compression pressure Pc. As indicated by an arrow in FIG. 6, the rate of decrease in the compression pressure Pc is calculated as the value of the compression pressure Pc with respect to the compression pressure Pc ₀ at normal time. In this step, the compression pressure Pc acquired in step 100 in FIG. 3 is used.

  Subsequently, the ECU 50 calculates the increase rate of blow-by gas from the decrease rate of the compression pressure Pc calculated in step 210 (step 220). FIG. 7 is a characteristic diagram showing the relationship between the decrease rate of the compression pressure Pc and the increase rate of blow-by gas. In this step 220, the increase rate of blow-by gas is calculated with reference to the map of the characteristic diagram shown in FIG.

Subsequently, the ECU 50 calculates the oil dilution rate based on the blow-by gas increase rate calculated in step 220 (step 230). Specifically, the oil dilution rate is obtained by the following formula (1).
Oil dilution rate = cumulative oil diluted fuel amount / (oil amount + cumulative oil diluted fuel amount) × 100 (1)
In the above equation (1), the oil amount is an initial value of the oil 20, and the cumulative oil dilution amount is a value obtained by sequentially integrating the oil dilution amount per cycle represented by the following equation (2).
Oil dilution amount per cycle = oil dilution coefficient × cylinder air amount × blow-by gas increase rate / actual air / fuel ratio (2)
In the above equation (2), the oil dilution coefficient is a value determined by the engine 10. The in-cylinder air amount can be calculated from the intake air amount and the engine speed NE.

  Subsequently, the ECU 50 determines whether or not the oil dilution rate calculated in step 230 is larger than the threshold value δ (step 240). Here, a value stored in the ECU 50 in advance as the upper limit value of the oil dilution rate is used as the threshold value δ. If it is determined that the oil dilution ratio> the threshold δ, the ECU 50 determines that the oil dilution is abnormal (step 250), and turns on a warning lamp on the instrument panel of the vehicle, for example. On the other hand, if it is determined that the oil dilution ratio ≦ the threshold δ, it can be determined that there is some margin in the oil dilution ratio although an abnormality has occurred in the piston ring, the ECU 50 ends this routine.

  As described above, according to the routine shown in FIG. 5, the warning lamp can be turned on when it is determined that the piston ring is abnormal and the oil dilution rate is larger than the threshold value δ. Accordingly, it is possible to prompt the driver to take necessary measures such as instructing the driver to change oil.

  In the second embodiment, the ECU 50 executes the process of step 230 in FIG. 5 so that the “oil dilution rate calculating means” in the third aspect of the invention executes the process of step 240 in FIG. Thus, the “oil dilution abnormality determining means” in the third aspect of the present invention is realized.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIGS. The present embodiment is characterized in that, in a system in which a supercharger is added to the system of FIG. 1, the supercharging pressure control shown in FIG. 9 is executed when calculating the oil dilution rate. Therefore, in this embodiment, the difference from the first embodiment will be mainly described, and the description of the same matters will be simplified or omitted.

[Description of system configuration]
FIG. 8 is a diagram for explaining the system configuration of the present embodiment. The system of this embodiment includes a turbocharger 42. The turbocharger 42 includes a compressor 42a and a turbine 42b. The compressor 42 a is arranged in the middle of the intake passage 30, and the turbine 42 b is arranged in the middle of the exhaust passage 32.

  The turbine 42b includes a plurality of rotatable nozzle vanes (not shown), and is configured so that the opening degree of the turbine nozzle formed between the nozzle vanes can be changed. The turbine nozzle can increase the boost pressure as the opening is increased, and can decrease the boost pressure as the opening is decreased. Further, the system of the present embodiment includes a bypass passage 44 that bypasses the turbine 42 b and a waste gate valve 46 that adjusts the exhaust gas flow rate to the bypass passage 44 in the middle of the exhaust passage 32.

[Features of Embodiment 3]
As described above, the system of this embodiment includes the turbocharger 42. Therefore, the probability of occurrence of pre-ignition due to oil self-ignition increases particularly during high-load operation. Therefore, in this embodiment, the pre-ignition occurrence probability is obtained from the oil dilution rate, and the supercharging pressure control is executed so that the turbocharger 42 is operated within the allowable range of the occurrence probability. Thereby, the favorable supercharging effect can be acquired, suppressing generation | occurrence | production of preignition.

[Specific Processing in Embodiment 3]
FIG. 9 is a flowchart showing the supercharging pressure control executed by the ECU 50 in the present embodiment. In the routine shown in FIG. 9, first, the ECU 50 calculates the oil dilution rate (step 300). The process of step 300 is the same as the series of processes of steps 200 to 230 in FIG. Subsequently, the ECU 50 estimates the pre-ignition occurrence frequency (step 310). FIG. 10 is a characteristic diagram showing the relationship between the oil dilution rate and the occurrence frequency of pre-ignition. As shown in FIG. 10, in the region where the oil dilution rate is low, the occurrence frequency of the pre-ignition is low, but as the oil dilution rate increases, the occurrence frequency of the pre-ignition increases rapidly. In step 310, the occurrence frequency of pre-ignition is calculated with reference to the map of the characteristic diagram shown in FIG.

  Subsequently, the ECU 50 estimates the limit value of the supercharging pressure based on the pre-ignition occurrence frequency calculated in step 310 (step 320). FIG. 11 is a characteristic diagram showing the relationship between the limit value of the supercharging pressure and the occurrence frequency of pre-ignition. In step 320, the limit value of the supercharging pressure is estimated with reference to the map of the characteristic diagram shown in FIG.

  Subsequently, the ECU 50 determines whether or not the actual supercharging pressure is higher than the limit value of the supercharging pressure estimated in step 320 (step 330). In this step, the actual supercharging pressure can be obtained, for example, by detecting the pressure in the intake passage 30 on the downstream side of the compressor 42a with a pressure sensor. When the actual supercharging pressure is larger than the limit value, the opening of the turbine nozzle is increased so as to lower the supercharging pressure (step 340), and when the actual supercharging pressure is smaller than the limit value. Decreases the opening of the turbine nozzle so as to increase the supercharging pressure (step 350).

  As described above, according to the routine shown in FIG. 9, the limit value of the supercharging pressure is estimated from the pre-ignition occurrence frequency, and the actual supercharging pressure can be controlled so that the supercharging pressure falls below this limit value. Therefore, it is possible to obtain a good supercharging effect while suppressing the occurrence of preignition.

  In the present embodiment, the supercharging pressure is increased or decreased by controlling the opening of the turbine nozzle. However, the supercharging pressure may be increased or decreased by opening or closing the waste gate valve 46. That is, as long as various actuators in the system are controlled so that the actual supercharging pressure falls below the limit value, the present embodiment can be applied as a modification of the present embodiment.

  In the third embodiment, when the ECU 50 executes the process of step 300 in FIG. 9, the “oil dilution rate calculating means” in the fourth aspect of the invention executes the process of step 310 in FIG. As a result, the “occurrence probability calculating means” in the fourth invention realizes the “supercharging pressure control means” in the fourth invention by executing the series of processing of steps 330 to 350 in FIG. ing.

DESCRIPTION OF SYMBOLS 10 Engine 12 Piston 28 Cylinder pressure sensor 34 Intake valve 36 Exhaust valve 40 Air-fuel ratio sensor 50 ECU

Claims (4)

In-cylinder pressure detecting means for detecting the in-cylinder pressure of the internal combustion engine;
When the detected value of the in-cylinder pressure is smaller than a predetermined abnormality occurrence determination value, any abnormality among the intake valve, the exhaust valve, and the piston ring of the internal combustion engine is determined using a deviation between the target air-fuel ratio and the actual air-fuel ratio. An abnormality identifying means for identifying whether or not
A control device for an internal combustion engine, comprising: The deviation is an air-fuel ratio difference obtained by subtracting the actual air-fuel ratio from the target air-fuel ratio,
The abnormality specifying means determines that the intake valve is abnormal when the air-fuel ratio difference is equal to or greater than a first threshold value greater than zero, and when the air-fuel ratio difference is equal to or less than a second threshold value smaller than zero, the exhaust valve abnormality is determined. 2. The control device for an internal combustion engine according to claim 1, wherein when the pressure is smaller than the first threshold and larger than the second threshold, it is determined that the piston ring is abnormal. Oil dilution rate calculating means for calculating an oil dilution rate using the rate of decrease of the in-cylinder pressure;
An oil dilution abnormality determining means for determining an oil dilution abnormality when the abnormality specifying means is specified as an abnormality of the piston ring and the oil dilution rate is larger than a predetermined oil abnormality determination value;
The control apparatus for an internal combustion engine according to claim 1, further comprising: A supercharger capable of supercharging intake air supplied to the internal combustion engine and changing a supercharging pressure;
Oil dilution rate calculating means for calculating an oil dilution rate using the rate of decrease of the in-cylinder pressure;
An occurrence probability calculating means for calculating an occurrence probability of pre-ignition at the oil dilution rate;
A supercharging pressure control means for controlling the supercharging pressure so that the occurrence probability does not exceed a predetermined limit value when the abnormality specifying means specifies the abnormality of the piston ring;
The control device for an internal combustion engine according to any one of claims 1 to 3, further comprising:

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