JP2012149561A - Internal combustion engine controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine controller which accurately determines a gas leakage, uninfluenced by an aging deterioration of a sensor used to determine the gas leakage from a combustion chamber.SOLUTION: The internal combustion engine controller includes: a fuel injection valve 30 injecting fuel into the cylinder of the internal combustion engine 10; and an air-fuel ratio sensor 38 detecting an air-fuel ratio of an exhaust gas discharged from inside the cylinder. It is determined whether the gas leakage (compression release) from the combustion chamber 14 is generated, based on a comparison result of a first air-fuel ratio A/F1 detected by use of the air-fuel ratio sensor 38 when an intake stroke injection by use of the fuel injection valve 30 is executed, and of a second air-fuel ratio A/F2 detected by use of the air-fuel ratio sensor 38 when a compression stroke injection by use of the fuel injection valve 30 under the same operating condition as when the intake stroke injection is executed.

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 is suitable as a device that determines gas leakage from a combustion chamber.

  Conventionally, for example, Patent Document 1 discloses an internal combustion engine that can identify the cause of gas leakage from a combustion chamber. Specifically, in this conventional internal combustion engine, when the pressure in the crankcase exceeds a predetermined value, it is determined that a gas leak has occurred due to a malfunction of the piston ring. Also, depending on whether the volumetric efficiency measurement value measured or estimated during light load operation is lower than the predetermined value, the cause of the gas leakage is the intake valve closing failure or the head gasket omission. Judgment is made if there is.

JP 2005-264852 A JP-A-9-256879 JP 2007-120392 A JP 2008-208751 A

  However, as in the technique described in Patent Document 1 described above, in the method of determining the presence or absence of gas leakage from the combustion chamber by comparing the detection value of the sensor or a calculated (estimated) value based on the detected value with a predetermined value, When the sensor has deteriorated over time, there is a concern that it will be difficult to accurately determine the presence or absence of gas leakage.

  The present invention has been made to solve the above-described problems, and has made it possible to accurately determine the gas leak without being affected by the aging of the sensor used for determining the gas leak from the combustion chamber. An object of the present invention is to provide a control device for an internal combustion engine.

A first invention is a control device for an internal combustion engine,
A fuel injection valve for injecting fuel into a cylinder of the internal combustion engine;
An air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas discharged from the cylinder;
The first air-fuel ratio detected using the air-fuel ratio sensor when the intake stroke injection using the fuel injection valve is executed, and the compression using the fuel injection valve under the same operating conditions as when the intake stroke injection is executed A gas leakage determining means for determining the presence or absence of gas leakage from the combustion chamber based on a comparison result with the second air / fuel ratio detected using the air / fuel ratio sensor when performing stroke injection;
It is characterized by providing.

The second invention is the first invention, wherein
The gas leak determining means determines that the gas leak has occurred when a difference between the first air-fuel ratio and the second air-fuel ratio is greater than a predetermined value.

The third invention is a control device for an internal combustion engine,
A fuel injection valve for injecting fuel into a cylinder of the internal combustion engine;
An in-cylinder pressure sensor for detecting the in-cylinder pressure;
An intake stroke using a combustion index value calculating means for calculating a combustion index value that changes in accordance with a change in the air-fuel ratio of the in-cylinder gas based on the in-cylinder pressure detected by the in-cylinder pressure sensor, and the fuel injection valve The first combustion index value calculated using the combustion index value calculating means when executing the injection and the compression stroke injection using the fuel injection valve under the same operating conditions as when the intake stroke injection is performed A gas leakage determination means for determining the presence or absence of gas leakage from the combustion chamber based on a comparison result with the second combustion index value calculated using the combustion index value calculation means;
It is characterized by providing.

Moreover, 4th invention is set in 3rd invention,
The combustion index value is a calorific value,
The gas leak determination means generates the gas leak when a difference between a second heat generation amount as the second combustion index value and a first heat generation amount as the first combustion index value is larger than a predetermined value. It is characterized in that it is determined.

According to a fifth invention, in any one of the first to fourth inventions,
The gas leak determination means is based on a comparison result between the first air-fuel ratio and the second air-fuel ratio in two adjacent cycles or a comparison result between the first combustion index value and the second combustion index value. The gas leakage is determined.

According to a sixth invention, in any one of the first to fifth inventions,
When the gas leak determining means determines that the gas leak has occurred, the gas leak determining means further comprises a gas leak injection mode setting means for selecting the compression stroke injection.

  Under conditions where gas leaks from the combustion chamber, the air-fuel mixture leaks out of the cylinder when the intake stroke injection is performed, while the cylinder interior leaks when the compression stroke injection is performed. Air will leak out of the air. Therefore, the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor differs between the execution of the intake stroke injection and the execution of the compression stroke injection under the situation where the gas leakage occurs. According to the first invention, since the gas leakage is determined according to the relative comparison result between the first air-fuel ratio and the second air-fuel ratio at the time of execution of fuel injection in two different modes, The gas leakage can be accurately determined without being affected by the aging deterioration of the air-fuel ratio sensor used for the determination.

  The gas leak occurrence location includes an intake valve, an exhaust valve, a piston ring, and the like, but the first air-fuel ratio is greater even if gas leak from any of these locations occurs. It becomes larger than the second air-fuel ratio. Therefore, according to the second aspect of the present invention, it is determined that the gas leak has occurred when the difference between the first air fuel ratio and the second air fuel ratio is greater than a predetermined value. Can be determined with high accuracy.

  Under conditions where gas leaks from the combustion chamber, the air-fuel mixture leaks out of the cylinder when the intake stroke injection is performed, while the cylinder interior leaks when the compression stroke injection is performed. Air will leak out of the air. Therefore, the air-fuel ratio of the in-cylinder gas differs between the execution of the intake stroke injection and the execution of the compression stroke injection under the situation where the gas leakage occurs. Accordingly, the combustion index value that changes in accordance with the change in the air-fuel ratio of the in-cylinder gas is also different. According to the third aspect of the present invention, the value is calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor at the time of executing the fuel injection in two different modes, and according to the change in the air-fuel ratio of the in-cylinder gas. The gas leak is determined in accordance with the relative comparison result between the first combustion index value and the second combustion index value that change in response to the above, and this is influenced by the aging deterioration of the in-cylinder pressure sensor used for the determination of the gas leak. Therefore, it is possible to accurately determine the gas leakage.

  The gas leak occurrence location includes an intake valve, an exhaust valve, a piston ring, and the like. However, even if gas leak from any of these locations occurs, the second calorific value is greater. It becomes larger than the first calorific value. Therefore, according to the fourth aspect of the present invention, it is determined that the gas leakage has occurred when the difference between the second heat generation amount and the first heat generation amount is greater than a predetermined value. Can be determined with high accuracy.

  According to the fifth aspect, it is possible to compare the first and second air-fuel ratios or the first and second combustion index values acquired at a timing at which the operating conditions can be regarded as the same. Thereby, it is possible to accurately determine the gas leakage.

  According to the sixth aspect of the present invention, the compression stroke injection is selected when it is determined that the gas leakage has occurred, so that the unburned mixture flows into the catalyst disposed in the exhaust passage. Thus, the retreat travel can be performed while avoiding melting damage of the catalyst.

It is a figure for demonstrating the system configuration | structure of the internal combustion engine in Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure for demonstrating the system configuration | structure of the internal combustion engine in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration of an internal combustion engine 10 according to Embodiment 1 of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. A piston 12 is provided in the cylinder of the internal combustion engine 10. A combustion chamber 14 is formed on the top side of the piston 12 in the cylinder. An intake passage 16 and an exhaust passage 18 communicate with the combustion chamber 14. The intake passage 16 and the exhaust passage 18 are respectively provided with an intake valve 20 and an exhaust valve 22 for bringing the combustion chamber 14 and the intake passage 16 or the combustion chamber 14 and the exhaust passage 18 into a conduction state or a cutoff state. .

  An air flow meter 24 that outputs a signal corresponding to the flow rate of air sucked into the intake passage 16 is provided in the vicinity of the inlet of the intake passage 16. An electronically controlled throttle valve 26 is provided downstream of the air flow meter 24. An intake pressure sensor 28 for detecting intake pressure is attached downstream of the throttle valve 26.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injection valve 30 for directly injecting fuel into the combustion chamber 14 (inside the cylinder) and an ignition plug 32 for igniting the air-fuel mixture. Further, an upstream catalyst (S / C) 34 and a downstream catalyst 36 for purifying exhaust gas are disposed in the exhaust passage 18. An air-fuel ratio sensor 38 for detecting the air-fuel ratio of the exhaust gas at that position is attached to the exhaust passage 18 (more specifically, the collection portion of the exhaust manifold) upstream of the upstream catalyst 34. Here, it is assumed that the air-fuel ratio sensor 38 is a sensor that emits a substantially linear output with respect to the air-fuel ratio of the exhaust gas over a wide range.

  The system of the present embodiment includes an ECU (Electronic Control Unit) 40 as an arithmetic processing device. In addition to the air flow meter 24, the intake pressure sensor 28, and the air-fuel ratio sensor 38, an input unit of the ECU 40 is used for detecting an operating state of the internal combustion engine 10 such as a crank angle sensor 42 for detecting the engine speed. Various sensors are connected. Various actuators such as the throttle valve 26, the fuel injection valve 30, and the spark plug 32 described above are connected to the output portion of the ECU 40. The ECU 40 controls the operating state of the internal combustion engine 10 by driving the various actuators according to a predetermined program based on the sensor outputs.

[Method for Determining Gas Leakage from Combustion Chamber in Embodiment 1]
According to the system of this embodiment including the fuel injection valve 30 capable of directly injecting fuel into the cylinder, by switching the fuel injection timing, intake stroke injection for injecting fuel into the cylinder during the intake stroke, and compression It is possible to perform compression stroke injection in which fuel is injected into the cylinder during the stroke.

  Therefore, in the present embodiment, the air-fuel ratio of the exhaust gas (hereinafter referred to as “first air-fuel ratio A / F1”) detected by using the air-fuel ratio sensor 38 at the time of executing the intake stroke injection, and the intake stroke injection. Based on the comparison result with the air-fuel ratio of the exhaust gas (hereinafter referred to as “second air-fuel ratio A / F2”) detected by using the air-fuel ratio sensor 38 when the compression stroke injection is performed under the same operating conditions as at the time of execution. Thus, the presence or absence of gas leakage from the combustion chamber 14 (hereinafter referred to as “compression loss”) is determined. More specifically, in the present embodiment, after acquiring the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 in two adjacent cycles, the first air-fuel ratio A / F1 and the second air-fuel ratio A When the difference between the two air-fuel ratios A / F2 is larger than a predetermined value, it is determined that the compression loss has occurred.

  Here, specific differences that occur between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 when compression loss occurs will be individually described for each occurrence of compression loss. . As a premise, the fuel injection amount at the time of determining the compression loss is adjusted so that the air-fuel ratio of the in-cylinder gas becomes the stoichiometric air-fuel ratio (stoichiometric) in both the intake stroke injection and the compression stroke injection. It is assumed that

(Case where compression loss occurs through the exhaust valve)
In this case, if the intake stroke injection is performed, the air-fuel mixture escapes from the cylinder to the exhaust passage 18 via the exhaust valve 22. When the air-fuel mixture that has flowed out to the exhaust passage 18 reaches the air-fuel ratio sensor 38, the air and the air contained in the air-fuel ratio have higher detection sensitivity of the air-fuel ratio sensor 38. The output is slightly leaner than stoichiometric. Thereafter, when the combustion gas in the cycle in which compression loss occurs in this case reaches the air-fuel ratio sensor 38, the output of the air-fuel ratio sensor 38 becomes a value indicating stoichiometry. As a result, the first air-fuel ratio A / F1 in this case becomes a lean value close to the stoichiometric ratio as a whole when the compressed gas and the combustion gas are combined.

  On the other hand, if compression stroke injection is being performed, only air will escape from the cylinder to the exhaust passage 18 via the exhaust valve 22. As a result, the output of the air-fuel ratio sensor 38 has a lean value for the air that has flowed out to the exhaust passage 18 side, and the combustion ratio of the air-fuel ratio sensor 38 for the combustion gas in the cycle in which the compression loss has occurred in this case. The output is rich. As a result, the second air-fuel ratio A / F2 in this case is a value indicating stoichiometry as a whole of the compressed gas and the combustion gas, and the first air-fuel ratio A / F1 at the time of performing the intake stroke injection Compared to a relatively rich value.

(Case where compression loss occurs via the piston ring)
In this case, if the intake stroke injection is performed, the air-fuel mixture escapes from the cylinder to the crank chamber via the piston ring 12a (see FIG. 1). Since the air-fuel mixture that has escaped from the cylinder does not reach the air-fuel ratio sensor 38, only the combustion gas component in the cycle in which compression loss has occurred in this case contributes to the output of the air-fuel ratio sensor 38. In this case, since the air-fuel mixture escapes through the piston ring 12a, the air-fuel ratio of the combustion gas remains stoichiometric. Accordingly, the first air-fuel ratio A / F1 in this case is a value indicating stoichiometry.

  On the other hand, if compression stroke injection is being performed, only air will escape from the cylinder into the crank chamber via the piston ring 12a. Also in this case, since air that has escaped from the cylinder does not reach the air-fuel ratio sensor 38, only the combustion gas component in the cycle in which compression loss has occurred in this case contributes to the output of the air-fuel ratio sensor 38. . In this case, the air-fuel ratio of the combustion gas becomes richer than stoichiometric due to the influence of air being released through the piston ring 12a. Accordingly, the second air-fuel ratio A / F2 in this case is a richer value than the stoichiometric value, and is a relatively rich value compared to the first air-fuel ratio A / F1 when the intake stroke injection is executed.

(Case where compression loss occurs via the intake valve)
In this case, if the intake stroke injection is performed, the air-fuel mixture escapes from the cylinder to the intake passage 16 via the intake valve 20. Since the air-fuel mixture that has escaped from the cylinder does not reach the air-fuel ratio sensor 38, only the combustion gas component in the cycle in which compression loss has occurred in this case contributes to the output of the air-fuel ratio sensor 38. In this case, since the air-fuel mixture escapes through the intake valve 20, the air-fuel ratio of the combustion gas remains stoichiometric. Accordingly, the first air-fuel ratio A / F1 in this case is a value indicating stoichiometry.

  On the other hand, if the compression stroke injection is being performed, only air passes through the intake valve 20 from the cylinder to the intake passage 16. Also in this case, since air that has escaped from the cylinder does not reach the air-fuel ratio sensor 38, only the combustion gas component in the cycle in which compression loss has occurred in this case contributes to the output of the air-fuel ratio sensor 38. . In this case, the air-fuel ratio of the combustion gas becomes richer than the stoichiometry due to the influence of air being released through the intake valve 20. Further, as in the present embodiment, when the fuel injection of these two modes is executed in the two adjacent cycles in the order of the intake stroke injection and then the compression stroke injection, the fuel is sucked in the cycle in which the compression stroke injection is performed. The gas becomes air (gas richer than usual) containing the air-fuel mixture that has escaped to the intake passage 16 side during the compression stroke of the previous cycle in which the intake stroke injection has been performed. Therefore, for these reasons, the second air-fuel ratio A / F2 in this case is a richer value than the stoichiometric value, and is a relatively rich value compared to the first air-fuel ratio A / F1 when the intake stroke injection is performed. It becomes.

  If no compression loss occurs, the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 are essentially the same value. On the other hand, when the compression loss has occurred, as described above, in any of the above three cases, the second air-fuel ratio A / F2 at the time of executing the compression stroke injection is equal to that at the time of executing the intake stroke injection. It becomes a relatively rich value as compared with the first air-fuel ratio A / F1. That is, as the magnitude of the value of the air-fuel ratio A / F, the first air-fuel ratio A / F1 is larger than the second air-fuel ratio A / F2. For this reason, when the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 is larger than a predetermined value, it can be determined that compression loss has occurred.

(Specific processing in Embodiment 1)
FIG. 2 is a flowchart showing a routine executed by the ECU 40 in order to realize the compression loss determination method according to the first embodiment of the present invention. Note that at the start of this routine, it is assumed that the intake stroke injection is performed with the fuel injection amount adjusted so that the air-fuel ratio of the in-cylinder gas becomes stoichiometric. In addition, the compression loss determination process in this routine shown below is executed in order for each cylinder.

  In the routine shown in FIG. 2, first, the first air-fuel ratio A / F1 of the exhaust gas at the present time (that is, when the intake stroke injection is performed) is calculated (detected) based on the output of the air-fuel ratio (A / F) sensor 38. (Step 100). Next, the fuel injection timing (direct injection timing) by the fuel injection valve 30 is changed (step 102). Specifically, the current intake stroke injection is switched to the compression stroke injection.

  Next, the second air-fuel ratio A / F2 of the exhaust gas in the first cycle after switching to the compression stroke injection in step 102 is calculated (detected) based on the output of the air-fuel ratio (A / F) sensor 38. (Step 104). Next, it is determined whether or not the difference between the first air-fuel ratio A / F1 acquired in step 100 and the second air-fuel ratio A / F2 acquired in step 104 is greater than a predetermined value (step 106). ). The predetermined value relating to the difference between the air-fuel ratios A / F1 and A / F2 in this step 106 is a value set in advance as a value that can determine whether or not compression loss has occurred regardless of variations in the air-fuel ratio.

  If it is determined in step 106 that the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 is greater than the predetermined value, it is determined that compression loss has occurred ( Step 108). In this case, the retreat travel is performed by selecting the compression stroke injection, and the warning lamp (MIL) is turned on (step 110).

  According to the routine shown in FIG. 2 described above, when it is determined that the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 in two adjacent cycles is larger than the predetermined value, the compression is performed. It is determined that a dropout (gas leak from the combustion chamber 14) has occurred. According to such a method, the presence or absence of compression loss is determined based on the relative difference between the air-fuel ratios A / F1 and A / F2 when fuel injection is performed in two different modes. For this reason, even if the air-fuel ratio sensor 38 has deteriorated over time, it is possible to accurately determine the compression loss without being affected by the deterioration.

  In this embodiment, the mode of fuel injection is made different between intake stroke injection and compression stroke injection between two adjacent cycles. For this reason, the two air-fuel ratios A / F1 and A / F2 can be compared under the condition that the intake air amount becomes the same by assuming that the operating conditions are the same, and the gas amount due to the compression loss is the same. . Thereby, it is possible to determine compression loss with high accuracy.

  Further, according to the above routine, when the retreat travel is performed when it is determined that the compression loss has occurred, the compression stroke injection is selected. When the compression loss occurs through the exhaust valve 22, if the intake stroke injection is performed, the unburned air-fuel mixture escapes to the exhaust passage 18 side. As a result, the upstream catalyst 34 and the like may be melted. Therefore, by selecting the compression stroke injection when it is determined that the compression loss has occurred, the retreat travel can be performed while avoiding the melting damage of the upstream catalyst 34 and the like.

  By the way, in the first embodiment described above, the compression loss determination process is sequentially performed for each cylinder. However, the compression loss determination process based on the relative difference between the air-fuel ratios A / F1 and A / F2 at the time of executing fuel injection in two different modes is not limited to a mode in which each cylinder is sequentially performed. That is, the gas from each cylinder regularly arrives at the air-fuel ratio sensor 38 disposed in the (exhaust manifold) collection portion of the exhaust passage 18 in a predetermined order (explosion order). Therefore, after determining which cylinder the current output of the air-fuel ratio sensor 38 is based on the timing at which the gas arrives at the air-fuel ratio sensor 38 from each cylinder, the compression loss determination processing is performed. May be performed simultaneously for all cylinders (or a plurality of partial cylinders). Further, in the case where the above determination process is performed simultaneously for all cylinders (or a plurality of partial cylinders), in order to detect the air-fuel ratios A / F1 and A / F2 while making it less susceptible to the gas flowing out from the other cylinders. In addition, an air-fuel ratio sensor may be provided in the branch pipe portion of each cylinder (of the exhaust manifold) in the exhaust passage 18.

In the first embodiment described above, the “gas leak determination means” according to the first aspect of the present invention is realized by the ECU 40 executing the series of processes of steps 100 to 108 described above.
In the first embodiment described above, the “gas leak injection mode setting means” according to the sixth aspect of the present invention is implemented by the ECU 40 executing the processing of step 110 described above.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 3 and FIG.
[System Configuration of Embodiment 2]
FIG. 3 is a diagram for explaining a system configuration of the internal combustion engine 50 according to the second embodiment of the present invention. In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The system of the internal combustion engine 50 shown in FIG. 3 is configured similarly to the system of the internal combustion engine 10 shown in FIG. 1 except that each cylinder is provided with an in-cylinder pressure sensor 52 for detecting the in-cylinder pressure. Has been. The in-cylinder pressure sensor 52 is connected to the input unit of the ECU 40.

[Method for Determining Gas Leakage from Combustion Chamber in Embodiment 2]
The air-fuel ratio sensor 38 is less responsive than the in-cylinder pressure sensor. For this reason, in the determination method of the compression loss in the first embodiment described above, the determination of the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 is satisfied unless the compression stroke injection is continued for a certain time. There are cases where it cannot be done. In addition, the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 when the compression loss occurs through the exhaust valve 22 is greater than when the compression loss occurs due to other locations. small. Therefore, depending on the amount of gas that has escaped from the cylinder due to compression loss, the first air-fuel ratio A / F1 when compression loss occurs via the exhaust valve 22 becomes a value near the stoichiometric value. As a result, the difference between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 in this case becomes small, and it may be difficult to determine the compression loss.

  Therefore, in the present embodiment, the in-cylinder pressure sensor 52 is used in place of the air-fuel ratio sensor 38 in order to determine compression loss. A calorific value Q (hereinafter referred to as “first calorific value Q1”) calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 52 when the intake stroke injection is executed, and the intake stroke injection. A calorific value Q (hereinafter referred to as “second calorific value Q2”) calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 52 when the compression stroke injection is performed under the same operating conditions as at the time of execution. Based on these comparison results, the presence or absence of compression loss (gas leakage from the combustion chamber 14) was determined. More specifically, in the present embodiment, after acquiring the first heat generation amount Q1 and the second heat generation amount Q2 in two adjacent cycles, the first heat generation amount Q1 and the second heat generation amount Q2 are obtained. When the difference is larger than a predetermined value, it is determined that a compression loss has occurred.

  Here, specific differences that occur between the first calorific value Q1 and the second calorific value Q2 when compression loss occurs will be described individually for each occurrence of compression loss. As a premise, the fuel injection amount at the time of determining the compression loss is adjusted so that the air-fuel ratio of the in-cylinder gas becomes the stoichiometric air-fuel ratio (stoichiometric) in both the intake stroke injection and the compression stroke injection. It is assumed that

(Case where compression loss occurs through the exhaust valve)
In this case, if the intake stroke injection is performed, the air-fuel mixture escapes from the cylinder to the exhaust passage 18 via the exhaust valve 22. As a result, there is no change in the air-fuel ratio of the in-cylinder gas due to compression loss, and combustion in the cylinder where compression loss has occurred becomes combustion under stoichiometric air-fuel ratio (stoichiometric combustion). On the other hand, if compression stroke injection is being performed, only air will escape from the cylinder to the exhaust passage 18 via the exhaust valve 22. As a result, the air-fuel ratio of the in-cylinder gas at the time of combustion becomes richer than stoichiometric due to the loss of compression, so that the combustion in the cylinder where the loss of compression has occurred becomes rich combustion. The calorific value Q is maximized on the richer side than the stoichiometric air-fuel ratio due to the influence of thermal dissociation of the working gas in the cylinder. Therefore, the second calorific value Q2 when rich combustion is performed is larger than the first calorific value Q1 when stoichiometric combustion is performed.

(Case where compression loss occurs via the piston ring)
In this case, for the same reason as the case where compression loss occurs through the exhaust valve 22, the second heat value Q2 when rich combustion is performed rather than the first heat value Q1 when stoichiometric combustion is performed. Is bigger.

(Case where compression loss occurs via the intake valve)
In this case, if the intake stroke injection is performed, the air-fuel mixture escapes from the cylinder to the intake passage 16 via the intake valve 20. As a result, there is no change in the air-fuel ratio of the in-cylinder gas due to compression loss, and combustion in the cylinder where compression loss has occurred becomes combustion under stoichiometric air-fuel ratio (stoichiometric combustion). On the other hand, if the compression stroke injection is being performed, only air passes through the intake valve 20 from the cylinder to the intake passage 16. As a result, the air-fuel ratio of the in-cylinder gas at the time of combustion becomes richer than stoichiometric due to compression loss. Further, in the present embodiment, when the fuel injection of these two modes is executed in the two adjacent cycles in the order of the intake stroke injection and then the compression stroke injection, the gas sucked in the cycle in which the compression stroke injection is performed is In the previous cycle in which the intake stroke injection has been performed, air (air richer than usual) containing the air-fuel mixture that has flowed out to the intake passage 16 side during the compression stroke is obtained. Therefore, for these reasons, when the compression stroke injection is performed, the combustion in the cylinder in which the compression loss has occurred becomes rich combustion. Thus, also in this case, the second calorific value Q2 when rich combustion is performed is larger than the first calorific value Q1 when stoichiometric combustion is performed.

  If there is no compression loss, the first heat value Q1 and the second heat value Q2 are essentially the same value. On the other hand, when the compression loss has occurred, as described above, in any of the above three cases, the second calorific value Q2 when the compression stroke injection is executed is equal to the second heat generation amount Q2 when the intake stroke injection is executed. It becomes a relatively large value as compared with 1 calorific value Q1. For this reason, when the difference between the first calorific value Q1 and the calorific value Q is larger than a predetermined value, it can be determined that a compression loss has occurred.

(Specific processing in Embodiment 2)
FIG. 4 is a flowchart showing a routine executed by the ECU 40 in order to realize the compression loss determination method according to Embodiment 2 of the present invention. Note that at the start of this routine, it is assumed that the intake stroke injection is performed with the fuel injection amount adjusted so that the air-fuel ratio of the in-cylinder gas becomes stoichiometric.

In the routine shown in FIG. 4, first, the first calorific value Q1 is calculated based on the in-cylinder pressure detected using the in-cylinder pressure sensor (CPS) 52 under the situation where the intake stroke injection is being performed ( Step 200). Specifically, after the in-cylinder pressure is sequentially detected in each cylinder, the first calorific value Q1 of each cylinder is calculated in order. There is a correlation between the in-cylinder pressure during combustion of the internal combustion engine 50 and the heat generation amount (heat generation amount). Therefore, in this step 200, the in-cylinder pressure P is detected using the in-cylinder pressure sensor 52 for each predetermined crank angle in the predetermined crank angle period (combustion period) using the in-cylinder pressure sensor 52 and the crank angle sensor 42. Is done. Then, based on the in-cylinder pressure P, the in-cylinder volume V calculated based on the crank angle at the time of detecting the in-cylinder pressure P, and the specific heat ratio κ of the gas in the cylinder, for each predetermined crank angle. The calorific value ^PVκ is calculated. Then, the first heat generation amount Q1 is calculated as an integrated value of the heat generation amount ^PVκ during the predetermined crank angle period.

  Next, the fuel injection timing (direct injection timing) by the fuel injection valve 30 is changed (step 202). Specifically, the current intake stroke injection is switched to the compression stroke injection. Next, the second heat generation amount Q2 in the first cycle after switching to the compression stroke injection in the step 202 is based on the in-cylinder pressure detected by the in-cylinder pressure sensor 52 in the first cycle. The calculation is sequentially performed for each cylinder in accordance with a method similar to the method for calculating the amount Q1 (step 204).

  Next, it is determined for each cylinder whether or not the difference between the second heat generation amount Q2 calculated in step 204 and the first heat generation amount Q1 calculated in step 200 is larger than a predetermined value (step 206). ). The predetermined value relating to the difference between the heat generation amounts Q1 and Q2 in step 206 is a value set in advance as a value that can determine whether or not compression loss has occurred regardless of variations in the heat generation amount.

  If it is determined in step 206 that the difference between the second heat generation amount Q2 and the first heat generation amount Q1 is larger than the predetermined value, compression loss has occurred in the cylinder subjected to this determination. Is determined (step 208). In this case, the retreat travel is performed by selecting the compression stroke injection, and the warning lamp (MIL) is turned on (step 210), similarly to the process of step 110.

  According to the routine shown in FIG. 4 described above, when it is determined that the difference between the second heat generation amount Q2 and the first heat generation amount Q1 in two adjacent cycles is larger than the predetermined value, the compression loss (combustion chamber) 14), it is determined that a gas leak from 14) has occurred. Also with such a method, the presence or absence of compression loss is determined based on the relative difference between the calorific values Q1 and Q2 when executing fuel injection in two different modes. For this reason, even if aging deterioration occurs in the in-cylinder pressure sensor 52, it is possible to accurately determine the compression loss without being affected by the deterioration.

  Further, since the responsiveness of the in-cylinder pressure sensor 52 can be compared with that of the air-fuel ratio sensor 38, the calorific values Q1 and Q2 can be quickly calculated, and the difference between the calorific values Q1 and Q2 between the two cycles can be determined in a short time. It becomes. As a result, after the determination of the compression loss, if the compression loss does not occur, the intake stroke injection can be promptly restored. Furthermore, only the gas combusted in the cylinder contributes to the calorific values Q1 and Q2 calculated based on the in-cylinder pressure. Therefore, as in the determination method of the first embodiment using the air-fuel ratio sensor 38, it is difficult to determine the compression loss due to the small amount of gas that has escaped from the cylinder due to the compression loss. You can eliminate concerns. That is, regardless of the amount of gas due to compression loss, it is possible to compare the difference between the second heat value Q2 when the compression stroke injection is performed and the first heat value Q1 when the intake stroke injection is performed. Thereby, it is possible to determine the compression loss with high accuracy. In addition, the same effects as those of the first embodiment can be obtained.

  By the way, in the second embodiment described above, an example in which the calorific values Q1 and Q2 are used as the combustion index value based on the in-cylinder pressure detected by the in-cylinder pressure sensor 52 has been described. However, in the present invention, the combustion index value that changes according to the change in the air-fuel ratio of the in-cylinder gas is limited to the calorific value Q as long as it is a value that can be calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor. For example, it may be the torque of an internal combustion engine.

In the second embodiment described above, the first heating value Q1 is the “first combustion index value” in the third invention, and the second heating value Q2 is the “second combustion index value” in the third invention. Respectively. Further, when the ECU 40 executes the processes of the steps 200 and 204, the “combustion index value calculating means” in the third aspect of the invention executes the series of processes of the steps 200 to 208. The “gas leak determination means” in the present invention is realized.
In the second embodiment described above, the “gas leak injection mode setting means” according to the sixth aspect of the present invention is realized by the ECU 40 executing the process of step 210.

  By the way, in the first and second embodiments described above, the comparison result between the first air-fuel ratio A / F1 and the second air-fuel ratio A / F2 in the two adjacent cycles, or the first heating value Q1 and the second heating value. The compression loss is determined based on the comparison result with the amount Q2. However, in the present invention, the timing at which the first air-fuel ratio and the second air-fuel ratio or the first combustion index value and the second combustion index value are acquired is not necessarily adjacent as long as the same operating condition of the internal combustion engine is maintained. It is not limited to two cycles.

  In the first and second embodiments described above, the air-fuel ratio A / F1, A / F2, or the calorific value under the operating conditions in which the fuel injection amount is adjusted so that the air-fuel ratio of the in-cylinder gas becomes stoichiometric. Q1 and Q2 are acquired. However, the present invention determines the presence or absence of gas leakage from the combustion chamber based on a relative comparison result of two air-fuel ratios or combustion index values when performing fuel injection in two different modes. Therefore, the air-fuel ratio condition of the in-cylinder gas as a precondition of the present invention is not necessarily limited to stoichiometric as long as it is the same value at the time of each of the intake stroke injection and the compression stroke injection.

10, 50 Internal combustion engine 12 Piston 12a Piston ring 14 Combustion chamber 16 Intake passage 18 Exhaust passage 20 Intake valve 22 Exhaust valve 26 Throttle valve 30 Fuel injection valve 32 Spark plug 34 Upstream catalyst 36 Downstream catalyst 38 Air-fuel ratio sensor 40 ECU (Electronic Control) Unit)
42 Crank angle sensor 52 In-cylinder pressure sensor

Claims (6)

A fuel injection valve for injecting fuel into a cylinder of the internal combustion engine;
An air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas discharged from the cylinder;
The first air-fuel ratio detected using the air-fuel ratio sensor when the intake stroke injection using the fuel injection valve is executed, and the compression using the fuel injection valve under the same operating conditions as when the intake stroke injection is executed A gas leakage determining means for determining the presence or absence of gas leakage from the combustion chamber based on a comparison result with the second air / fuel ratio detected using the air / fuel ratio sensor when performing stroke injection;
A control device for an internal combustion engine, comprising:   2. The gas leak determination means determines that the gas leak has occurred when a difference between the first air-fuel ratio and the second air-fuel ratio is larger than a predetermined value. Control device for internal combustion engine. A fuel injection valve for injecting fuel into a cylinder of the internal combustion engine;
An in-cylinder pressure sensor for detecting the in-cylinder pressure;
An intake stroke using a combustion index value calculating means for calculating a combustion index value that changes according to a change in the air-fuel ratio of the in-cylinder gas based on the in-cylinder pressure detected by the in-cylinder pressure sensor, and the fuel injection valve The first combustion index value calculated using the combustion index value calculating means when executing the injection and the compression stroke injection using the fuel injection valve under the same operating conditions as when the intake stroke injection is performed A gas leakage determination means for determining the presence or absence of gas leakage from the combustion chamber based on a comparison result with the second combustion index value calculated using the combustion index value calculation means;
A control device for an internal combustion engine, comprising: The combustion index value is a calorific value,
The gas leak determination means generates the gas leak when a difference between a second heat generation amount as the second combustion index value and a first heat generation amount as the first combustion index value is larger than a predetermined value. 4. The control apparatus for an internal combustion engine according to claim 3, wherein it is determined that the engine is in operation.   The gas leak determination means is based on a comparison result between the first air-fuel ratio and the second air-fuel ratio in two adjacent cycles or a comparison result between the first combustion index value and the second combustion index value. 5. The control apparatus for an internal combustion engine according to claim 1, wherein the gas leakage is determined.   6. The gas leak injection mode setting means for selecting the compression stroke injection when the gas leak determination means determines that the gas leak has occurred. A control device for an internal combustion engine according to claim 1.

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