Apparatus for determining abnormal combustion in internal combustion engine

An object is to provide an abnormal combustion determining apparatus for an internal combustion engine that can identify a major factor causing an oil to flow into a cylinder. The abnormal combustion determining apparatus for the internal combustion engine that includes a plurality of cylinders detects, for each cylinder, a cylinder in which abnormal combustion has occurred. The cylinder in which the abnormal combustion has occurred, and a history of load applied during an operation are stored in memory. It is determined whether or not the cylinder in which the abnormal combustion has occurred and which is stored in memory, is a specific cylinder. It is determined whether or not load present in the history stored in memory and used prior to the occurrence of the abnormal combustion is higher than a threshold value. Based on a combination of a decision made by the cylinder determining means and a decision made by the load determining means, a major factor causing the oil to flow into the cylinder is identified from among relations established for factors of oil flowing into the cylinder according to the combination of these decisions made.

This is a 371 national phase application of PCT/JP2010/059129 filed 28 May 2010, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an apparatus for determining abnormal combustion in an internal combustion engine.

BACKGROUND ART

An internal combustion engine having a knocking sensor is known, as disclosed, for example, in Patent Document 1. When the knocking sensor detects knocking, control is performed to retard ignition timing in order to bring the knocking to an end. This publication also discloses an abnormal combustion determining apparatus for an internal combustion engine that determines that pre-ignition has occurred if the control of retarding the ignition timing fails to end the knocking and it is found that, on comparison, an air-fuel ratio after retarding is smaller than that before the retarding.

PRIOR ART LITERATURE

Patent Document

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

Abnormal combustion may occur when an engine oil (hereinafter referred to simply as an “oil”) flows into a cylinder. There are a number of factors that cause the oil to flow into the cylinder. To take appropriate action against the abnormal combustion, therefore, it is desirable that the factors be identified. The apparatus of the Patent Document 1 can, however, only determine that the abnormal combustion has occurred and is not able to identify the factor causing the oil to flow into the cylinder.

The present invention has been made to solve the foregoing problem and it is an object of the present invention to provide an abnormal combustion determining apparatus for an internal combustion engine that can identify a major factor causing an oil to flow into a cylinder.

Means for Solving the Problem

First aspect of the present invention is an apparatus for determining abnormal combustion in an internal combustion engine having a plurality of cylinders, comprising:

abnormal combustion detecting means for detecting, for each cylinder, a cylinder in which abnormal combustion has occurred;

abnormality occurring cylinder storage means for storing the cylinder in which abnormal combustion has occurred;

load history storage means for storing a history of load applied during an operation; and

based on the cylinder stored in the abnormality occurring cylinder storage means and the history, major factor identifying means for identifying a major factor causing an oil to flow into the cylinder from among relations established for factors of oil flowing into the cylinder according to the abnormal combustion occurring cylinder and the load.

Second aspect of the present invention is an apparatus for determining abnormal combustion in the internal combustion engine according to the first aspect, comprising:

cylinder determining means for determining whether or not the cylinder stored in the abnormality occurring cylinder storage means is a specific cylinder; and

load determining means for determining whether or not load present in the history and used prior to occurrence of the abnormal combustion is higher than a threshold value,

wherein: based on a combination of a decision made by the cylinder determining means and a decision made by the load determining means, the major factor identifying means identifies a major factor causing an oil to flow into the cylinder from among relations established for factors of oil flowing into the cylinder according to the combination of the decision made by the cylinder determining means and the decision made by the load determining means.

Third aspect of the present invention is an apparatus for determining abnormal combustion in the internal combustion engine according to the second aspect,

wherein: the major factor identifying means includes oil dropping identifying means which identifies a major factor causing an oil to flow into the cylinder as oil dropping when the cylinder stored in the abnormality occurring cylinder storage means is the specific cylinder and load present in the history and used prior to occurrence of the abnormal combustion is higher than the threshold value.

Fourth aspect of the present invention is an apparatus for determining abnormal combustion in the internal combustion engine according to the second or the third aspect,

wherein: the major factor identifying means includes oil rising identifying means which identifies a major factor causing an oil to flow into the cylinder as oil rising when the cylinder stored in the abnormality occurring cylinder storage means is the specific cylinder and load present in the history and used prior to occurrence of the abnormal combustion is equal to or less than the threshold value.

Fifth aspect of the present invention is an apparatus for determining abnormal combustion in the internal combustion engine according to the second to the forth aspects,

wherein: the major factor identifying means includes negative pressure-side blow-by identifying means which identifies a major factor causing an oil to flow into the cylinder as an oil contained in a negative pressure-side blow-by gas when the cylinder stored in the abnormality occurring cylinder storage means is unspecific cylinders and load present in the history and used prior to occurrence of the abnormal combustion is equal to or less than the threshold value.

Sixth aspect of the present invention is an apparatus for determining abnormal combustion in the internal combustion engine according to the second to the fifth aspects,

wherein: the major factor identifying means includes atmosphere-side blow-by identifying means which identifies a major factor causing an oil to flow into the cylinder as an oil contained in an atmosphere-side blow-by gas when the cylinder stored in the abnormality occurring cylinder storage means is unspecific cylinders and load present in the history and used prior to occurrence of the abnormal combustion is higher than the threshold value.

Effects of the Invention

In the first aspect of the present invention, based on the cylinder stored in the abnormality occurring cylinder storage means and the history, the major factor causing the oil to flow into the cylinder can be identified from among the relations established for the factors of oil flowing into the cylinder according to the abnormal combustion occurring cylinder and the load.

In the second aspect of the present invention, based on the combination of the decision made by the cylinder determining means and the decision made by the load determining means, the major factor causing the oil to flow into the cylinder is identified from among the relations established for the factors of oil flowing into the cylinder according to the combination of the decision made by the cylinder determining means and the decision made by the load determining means. The aspect of the present invention therefore allows a maximum of four major factors to be identified by combining the two determining means.

In the third aspect of the present invention, the major factor causing the oil to flow into the cylinder can be identified as the oil dropping when the cylinder stored in the abnormality occurring cylinder storage means is the specific cylinder and the load present in the history and used prior to the occurrence of the abnormal combustion is higher than the threshold value. The aspect of the present invention therefore allows appropriate action to be taken against the oil dropping that causes the abnormal combustion to occur.

In the fourth aspect of the present invention, the major factor causing the oil to flow into the cylinder can be identified as the oil rising when the cylinder stored in the abnormality occurring cylinder storage means is the specific cylinder and the load present in the history and used prior to the occurrence of the abnormal combustion is equal to or less than the threshold value. The aspect of the present invention therefore allows appropriate action to be taken against the oil rising that causes the abnormal combustion to occur.

In the fifth aspect of the present invention, the major factor causing the oil to flow into the cylinder can be identified as the oil contained in the negative pressure-side blow-by gas when the cylinder stored in the abnormality occurring cylinder storage means is the unspecific cylinders and the load present in the history and used prior to the occurrence of the abnormal combustion is equal to or less than the threshold value. The aspect of the present invention therefore allows appropriate action to be taken against the negative pressure-side blow-by that causes the abnormal combustion to occur.

In the sixth aspect of the present invention, the major factor causing the oil to flow into the cylinder can be identified as the oil contained in the atmosphere-side blow-by gas when the cylinder stored in the abnormality occurring cylinder storage means is the unspecific cylinders and the load present in the history and used prior to the occurrence of the abnormal combustion is higher than the threshold value. The aspect of the present invention therefore allows appropriate action to be taken against the atmosphere-side blow-by that causes the abnormal combustion to occur.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Like or corresponding parts are identified by the same reference numerals in all drawings and will not be redundantly described.

FIRST EMBODIMENT

System Configuration of the First Embodiment

FIG. 1is a schematic diagram for illustrating a system configuration of a first embodiment of the present invention. The system shown inFIG. 1includes an internal combustion engine (hereinafter referred to simply as an engine)10. The engine10includes a plurality of cylinders12. The present invention is not concerned with the number and layout of cylinders. An intake passage14and an exhaust passage16are connected to each of the cylinders12.

An air cleaner18is disposed near an inlet of the intake passage14. An air flow meter20is disposed downstream of the air cleaner18. The air flow meter20outputs an intake air amount GA that corresponds to a flow rate of fresh air drawn into the intake passage14.

A turbocharger22is disposed downstream of the air flow meter20. The turbocharger22includes a compressor22aand a turbine22b. The compressor22aand the turbine22bare integrally connected with each other by a connecting shaft. The compressor22ais rotatably driven by exhaust energy of an exhaust gas inputted to the turbine22b.

An intercooler24is disposed downstream of the compressor22a. The intercooler24cools fresh air compressed by the compressor22a. A throttle valve26is disposed downstream of the intercooler24.

An intake manifold28is disposed on the intake passage14disposed downstream of the throttle valve26. A surge tank30is disposed upstream of the intake manifold28. The intake manifold28has a downstream portion branching to be connected to each of the cylinders12.

FIG. 2is an illustration showing schematically arrangements of parts around the cylinder12shown inFIG. 1. The cylinder12includes an intake valve34, an exhaust valve36, an injector38, an ignition plug40, and a piston42. The intake valve34opens and closes between the intake passage14and a combustion chamber32. The exhaust valve36opens and closes between the exhaust passage16and the combustion chamber32. Note that the injector38shown inFIG. 2is structured to inject fuel directly into the cylinder; however, this is not the only possible arrangement and the injector38may be structured to inject fuel into an intake port.

The intake valve34has a valve stem44slidably supported by a valve stem guide48disposed in a cylinder head46. A valve stem oil seal50is disposed between the valve stem44and the valve stem guide48. The foregoing arrangements apply also to the side of the exhaust valve36. The turbine22bof the turbocharger22is disposed on the exhaust passage16on a downstream side of the exhaust valve36.

The system of this embodiment further includes a blow-by gas reduction device (PCV: positive crankcase ventilation). A negative pressure-side blow-by gas flow-back passage54has a first end connected to a crankcase52shown inFIG. 1. An oil separator chamber55and a PCV valve56are disposed midway in the negative pressure-side blow-by gas flow-back passage54. The negative pressure-side blow-by gas flow-back passage54has a second end connected to the surge tank30.

An atmosphere-side blow-by gas flow-back passage58has a first end connected to a cylinder head cover57. The atmosphere-side blow-by gas flow-back passage58has a second end connected to the intake passage14on an upstream side of the compressor22a.

The system of this embodiment includes an ECU (electronic control unit)60. Various types of sensors, which include the air flow meter20mentioned earlier, a crank angle sensor62that outputs a signal CA corresponding to a rotating angle of a crankshaft, and a cylinder pressure sensor64for detecting a cylinder pressure, are connected to an input section of the ECU60. Various types of actuators, including the throttle valve26, the injector38, and the ignition plug40described earlier, are connected to an output section of the ECU60. Based on an output from each of the sensors, the ECU60actuates a corresponding actuator in accordance with a predetermined program to thereby control an operating state of the engine10. The ECU60can calculate an engine speed NE from the signal CA from the crank angle sensor62.

Ideal fuel economy or drivability is normally achieved when the engine10is used in accordance with an optimum operation line. For reasons such as, for example, changes with time, however, abnormal combustion can occur if an engine oil (hereinafter referred to simply as an “oil”) in amount equal to or more than a design value flows into the cylinder. Such abnormal combustion tends to occur at a high rpm range under light load.

If the high rpm range under light load is used for the optimum operation line, avoiding the use of the high rpm range under light load to thereby prevent the abnormal combustion from occurring degrades acceleration performance, thus aggravating drivability. Avoiding the use of the optimum operation line aggravates fuel economy.

To enable the use of the optimum operation line after occurrence of the abnormal combustion, it becomes necessary to take appropriate action to reduce the oil flowing into the cylinder. However, in order to take the appropriate action, a major factor causing the oil to flow into the cylinder must first be correctly identified. If the factor is wrongly identified, wrong action is to be taken, leading to aggravated drivability or fuel economy.

Characteristic Processes in the First Embodiment

In the system of this embodiment, therefore, a factor relating to the oil in the abnormal combustion is to be identified. Each of first through fourth processes which the system of this embodiment performs in order to identify the major factor causing the oil to flow into the cylinder will be described below.

A first process will first be described. The first process is to identify the abnormal combustion due mainly to oil dropping. Under heavy load, a boost pressure becomes higher than an internal pressure of the cylinder head cover57. Consequently, a gas blows from the cylinder toward the side of the cylinder head46. If the valve stem oil seal50has a reduced sealing force due, for example, to changes with time, an oil flows from the side of the cylinder head46into the cylinder, which is the oil dropping (an arrow B inFIG. 2). Note that the valve stem oil seal50is disposed independently for each cylinder, so that the abnormal combustion due to the oil dropping occurs in a specific cylinder, in which the valve stem oil seal50has a reduced sealing force.

In the first process, therefore, if heavy load is heavily used before abnormal combustion occurs and the abnormal combustion occurs in a specific cylinder, the major factor relating to the oil in the abnormal combustion is to be identified as oil dropping.

A second process is to identify the abnormal combustion due mainly to oil rising.FIG. 3is an enlarged view showing a sliding portion between the piston42and the cylinder12shown inFIG. 2. Normally, an excess oil is scraped off by piston rings66. When a tension of the piston rings66becomes small due to, for example, wear, an oil tends to flow into the cylinder. Specifically, the cylinder pressure during air intake is close to an internal pressure of the surge tank30. The cylinder pressure is therefore negative under light load. In contrast, the internal pressure of the crankcase52is close to the atmospheric pressure. Consequently, if the tension of the piston rings66becomes small, an oil flows from the side of the crankcase52into the cylinder, which is the oil rising (an arrow C inFIG. 3). Note that the piston42is disposed independently for each cylinder, so that the abnormal combustion due to the oil rising occurs in a specific cylinder, in which the tension of the piston rings66becomes small.

In the second process, therefore, if light load is heavily used before abnormal combustion occurs and the abnormal combustion occurs in a specific cylinder, the major factor relating to the oil in the abnormal combustion is to be identified as oil rising.

A third process is to identify the abnormal combustion due mainly to a negative pressure-side blow-by, in which a blow-by gas flows back through the negative pressure-side blow-by gas flow-back passage54. Under light load, the internal pressure of the surge tank30is negative. By contrast, the internal pressure of the crankcase52is close to the atmospheric pressure. Consequently, a flow-back condition through the negative pressure-side blow-by gas flow-back passage54(crankcase internal pressure−surge tank pressure>0) holds true. The blow-by gas therefore flows from the side of the crankcase52back to the side of the surge tank30as shown by an arrow D ofFIG. 1. Oil contained in the flowing-back negative pressure-side blow-by gas accumulates in an intake system. The oil that has accumulated in the intake system thereafter flows into the cylinder, causing abnormal combustion. Note that the surge tank30is shared among the cylinders, so that the abnormal combustion due to the negative pressure-side blow-by occurs in unspecific cylinders.

In the third process, therefore, if light load is heavily used before abnormal combustion occurs and the abnormal combustion occurs in unspecific cylinders, the major factor relating to the oil in the abnormal combustion is to be identified as an oil contained in the negative pressure-side blow-by gas.

A fourth process is to identify the abnormal combustion due mainly to an atmosphere-side blow-by, in which a blow-by gas flows back through the atmosphere-side blow-by gas flow-back passage58. The system of this embodiment having the turbocharger22has a wide load range, in which the crankcase52internal pressure−the surge tank30internal pressure<0, when the engine is turbocharged. Under heavy load, therefore, the blow-by gas does not flow back through the negative pressure-side blow-by gas flow-back passage54. In this case, a flow-back condition through the atmosphere-side blow-by gas flow-back passage58(crankcase52internal pressure−atmospheric pressure>0) holds true. The blow-by gas therefore flows from the side of the crankcase52back to the side of the intake passage14on the upstream side of the compressor22aas shown by an arrow E ofFIG. 1. Oil contained in the flowing-back atmosphere-side blow-by gas accumulates in the intake system. The oil that has accumulated in the intake system thereafter flows into the cylinder, causing abnormal combustion. Note that the intake passage14is shared among the cylinders, so that the abnormal combustion due to the atmosphere-side blow-by occurs in unspecific cylinders.

In the fourth process, therefore, if heavy load is heavily used before abnormal combustion occurs and the abnormal combustion occurs in unspecific cylinders, the major factor relating to the oil in the abnormal combustion is to be identified as an oil contained in the atmosphere-side blow-by gas.

Specific examples for identifying the major factor relating to the oil in the abnormal combustion through the first to fourth processes described above will be described below.FIG. 4is a map for storing in memory the cylinders in which the abnormal combustion has occurred, and the number of occurrence thereof. The map shown inFIG. 4stores the cylinders in which the abnormal combustion has occurred, associated with frequency of occurrence thereof.FIG. 5is a map for storing in memory speed, load, and time during operation. A history of, for example, load is plotted onFIG. 5in sequence. The first through fourth processes identify, from these types of stored data, the major factors causing the oil to flow into the cylinder.

If, for example, the abnormal combustion frequently occurs in a particular cylinder (e.g. a single cylinder) as shown in trips1and7ofFIG. 4, it is known that the factor is either the oil dropping or the oil rising. Further, from the history ofFIG. 5, the major factor can be identified as the oil dropping (the first process) if heavy load is frequently used before the abnormal combustion occurs. On the other hand, if light load is frequently used before the abnormal combustion occurs, the major factor can be identified as the oil rising (the second process).

If the abnormal combustion occurs in unspecific cylinders (e.g. multiple cylinders) as shown in trips4and5ofFIG. 4, it is known that the factor is either the negative pressure-side blow-by or the atmosphere-side blow-by. Further, from the history ofFIG. 5, the major factor can be identified as the negative pressure-side blow-by (the third process) if light load is frequently used before the abnormal combustion occurs. On the other hand, if heavy load is frequently used before the abnormal combustion occurs, the major factor can be identified as the atmosphere-side blow-by (the fourth process).

(Abnormal Combustion Major Factor Determining Routine)

FIG. 6is a flow chart showing a routine which the ECU60performs for determining the major factor in the abnormal combustion in order to achieve the above-described operations. In the routine shown inFIG. 6, the ECU60stores in memory a trip history in step100. For example, the ECU60stores in a map corresponding to that ofFIG. 4the cylinders in which the abnormal combustion has occurred, associated with the number of occurrence thereof (or probability). Also stored in a map corresponding to that ofFIG. 5is a history of the load and the engine speed NE during the operation. The load can be estimated from, for example, the engine speed NE and the intake air amount GA. The ECU60determines that, if a combustion pressure detected by the cylinder pressure sensor64exceeds a predetermined value, the abnormal combustion has occurred in that particular cylinder. The operation of step100is repeatedly performed until a predetermined number of samples are reached.

After that, in step110, the ECU60determines whether or not the abnormal combustion has occurred. Specifically, the ECU60first acquires, from the trip history stored in step100, the number of occurrence of the abnormal combustion (or probability) for each cylinder. If the number of occurrence of the abnormal combustion (or probability) is greater than a reference value for at least one cylinder, it is determined that the abnormal combustion has occurred. If it is determined that the abnormal combustion has not occurred, the operation of this routine is terminated.

If it is determined in step110that the abnormal combustion has occurred, the ECU60next calculates the speed and load before entry in an abnormal combustion occurrence range (step120). Specifically, the ECU60calculates, from the trip history stored in step100, which specific speed and load are heavily used within a predetermined period of time before the abnormal combustion occurs. For example, the ECU60calculates an average speed and an average load in the predetermined period of time before the abnormal combustion occurs.

Then in step130, the ECU60determines, from the trip history stored in step100, whether or not the abnormal combustion occurs in a specific cylinder (e.g. a single cylinder). If it is determined that the abnormal combustion occurs in a specific cylinder, the ECU60subsequently determines, in step140, whether or not heavy load is heavily used prior to the occurrence of the abnormal combustion. Specifically, the ECU60determines that heavy load is heavily used, if the load calculated in step120is higher than a threshold value α (FIG. 5) and that light load is heavily used, if the load calculated in step120is equal to or less than the threshold value α (FIG. 5).

If it is determined in step140that heavy load is heavily used, the ECU60then determines that the major factor causing the oil to flow into the cylinder is the oil dropping (step150). The ECU60turns ON a flag indicating that the major factor relating to the oil in the abnormal combustion is the oil dropping. The operation of this routine is thereafter terminated.

If it is determined in step140, on the other hand, that light load is heavily used, the ECU60then determines that the major factor causing the oil to flow into the cylinder is the oil rising (step160). The ECU60turns ON a flag indicating that the major factor relating to the oil in the abnormal combustion is the oil rising. The operation of this routine is thereafter terminated.

If it is determined in step130that the abnormal combustion occurs in unspecific cylinders (e.g. multiple cylinders), the ECU60subsequently determines, in step170, whether or not heavy load is heavily used prior to the occurrence of the abnormal combustion. Specifically, the ECU60determines that heavy load is heavily used, if the load calculated in step120is higher than the threshold value α (FIG. 5) and that light load is heavily used, if the load calculated in step120is equal to or less than the threshold value α (FIG. 5).

If it is determined in step170that heavy load is heavily used, the ECU60then determines that the major factor causing the oil to flow into the cylinder is the oil contained in the atmosphere-side blow-by gas (step180). The ECU60turns ON a flag indicating that the major factor relating to the oil in the abnormal combustion is the oil contained in the atmosphere-side blow-by gas. The operation of this routine is thereafter terminated.

If it is determined in step170, on the other hand, that light load is heavily used, the ECU60then determines that the major factor causing the oil to flow into the cylinder is the oil contained in the negative pressure-side blow-by gas (step190). The ECU60turns ON a flag indicating that the major factor relating to the oil in the abnormal combustion is the oil contained in the negative pressure-side blow-by gas. The operation of this routine is thereafter terminated.

As described heretofore, in accordance with the routine shown inFIG. 6, the above-described four major factors relating to the oil in the abnormal combustion can be identified by combining the process of determining whether the abnormal combustion occurs in a specific cylinder or unspecific cylinders and the process of determining whether the load heavily used prior to the occurrence of the abnormal combustion is higher or lower than the threshold value α. In addition, appropriate action can be taken, in other routines, for the major factors identified in this routine.

The system of the first embodiment described above determines the major factors causing the oil to flow into the cylinder by combining all of the four processes of from the first through fourth processes described above. The first through fourth processes may, nonetheless, be performed singly or in groups of two or more.

Additionally, in the system of the first embodiment described above, the specific cylinder is a single cylinder. This is, however, not the only possible requirement. The specific cylinder may be a plurality of cylinders as long as the frequency of occurrence of the abnormal combustion can be differentiated from that of any other cylinders than the plurality of cylinders.

In addition, the system of the first embodiment described above determines the occurrence of the abnormal combustion based on the combustion pressure detected by the cylinder pressure sensor64. This is, however, not the only possible arrangement. For example, a knocking sensor may be employed instead of the cylinder pressure sensor and the occurrence of the abnormal combustion may be determined based on a knocking level detected by the knocking sensor.

In the first embodiment described above, the ECU60performs different operations of steps to achieve respective means in the first to sixth aspects of the present invention as follows. Specifically, the ECU60performs: the operation of step100to achieve the “abnormal combustion detecting means”, the “abnormality occurring cylinder storage means”, and the “load history storage means” in the first aspect of the present invention; the operations of the steps110to190to achieve the “major factor identifying means” in the first aspect of the present invention; the operation of step130to achieve the “cylinder determining means” in the second aspect of the present invention; the operation of step140or step170to achieve the “load determining means” in the second aspect of the present invention; the operation of step150to achieve the “oil dropping identifying means” in the third aspect of the present invention; the operation of step160to achieve the “oil rising identifying means” in the fourth aspect of the present invention; the operation of step190to achieve the “negative pressure-side blow-by identifying means” in the fifth aspect of the present invention; the operation of step180to achieve the “atmosphere-side blow-by identifying means” in the sixth aspect of the present invention, respectively.

Furthermore, in the first embodiment, the factors causing the oil to flow into the cylinder (steps150,160,180, and190) determined according to the combination of a cylinder decision made by the operation of step130and a load decision made by the operations of steps140and170correspond to the “relation” in the first and second aspects of the present invention, respectively.