JP5459236B2 - In-cylinder pressure sensor abnormality detection device - Google Patents

Description

  The present invention relates to an in-cylinder pressure sensor abnormality detection device. More specifically, the present invention relates to an abnormality detection device for an in-cylinder pressure sensor installed for each cylinder of an internal combustion engine.

  In Patent Document 1, the air-fuel ratio for each cylinder is detected based on the output of an in-cylinder pressure sensor installed for each of a plurality of cylinders of the internal combustion engine, and the fuel injection amount is set so that the air-fuel ratio does not vary among the cylinders. Control is disclosed.

JP 2007-2111707 A JP 2006-336581 A JP 2009-203880 A JP 2009-203381 A JP 2007-315193 A

  In the configuration of the technique disclosed in Patent Document 1, control is performed so as to eliminate variations in the air-fuel ratio based on the output of the in-cylinder pressure sensor installed in each cylinder of the internal combustion engine. However, since the in-cylinder pressure sensor is placed in a harsh environment such as a combustion chamber of each cylinder, the characteristics of the in-cylinder pressure sensor are likely to change due to the influence of temperature and changes over time. When the characteristics of the in-cylinder pressure sensor of a certain cylinder have changed greatly, even if control is performed to suppress variation in the air-fuel ratio between the cylinders based on the output of the in-cylinder pressure sensor, the variation cannot be suppressed as a result. It will be.

  Therefore, in the control using the in-cylinder pressure sensor, it is desired to determine whether the in-cylinder pressure sensor is abnormal. The presence or absence of abnormality of the in-cylinder pressure sensor can be easily determined by comparing the outputs of the in-cylinder pressure sensor if it is ensured that the air-fuel ratio between the cylinders is constant. However, in an environment where there is variation in the air-fuel ratio between cylinders, it is determined whether the variation in the output of the in-cylinder pressure sensor is due to abnormalities in the in-cylinder pressure sensor or due to other factors such as variations between cylinders. Therefore, it is difficult to detect abnormality of the in-cylinder pressure sensor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an abnormality detection device capable of detecting an abnormality of an in-cylinder pressure sensor regardless of the presence or absence of variation in air-fuel ratio between cylinders.

In order to achieve the above object, a first invention is an in-cylinder pressure sensor abnormality detection device comprising:
First determining whether or not the air-fuel ratio varies among the plurality of cylinders based on a first air-fuel ratio detected according to the output of an in-cylinder pressure sensor installed in each of the plurality of cylinders of the internal combustion engine. Discrimination means;
Second discrimination for discriminating whether or not the air-fuel ratio varies among the plurality of cylinders based on a second air-fuel ratio detected according to an output of an air-fuel ratio sensor disposed in an exhaust path of the internal combustion engine Means,
An air-fuel ratio control means for performing air-fuel ratio control based on the output of the in-cylinder pressure sensor when the determination result by the first determination means and the determination result by the second determination means do not match;
Third discriminating means for discriminating whether or not there is variation among the plurality of cylinders according to the second air-fuel ratio after the air-fuel ratio control by the air-fuel ratio control means;
An abnormality determining unit that determines that the in-cylinder pressure sensor is abnormal when the third determining unit determines that there is variation among the plurality of cylinders;
Is provided.

According to a second aspect, in the first aspect, when it is determined that there is a variation by the first determination unit, and it is determined that there is no variation by the second determination unit, the air-fuel ratio, the heat generation amount And cylinder specifying means for specifying a specific cylinder in which the value of any parameter of the maximum in-cylinder pressure is different from other cylinders,
The air-fuel ratio control means controls based on the output of the in-cylinder pressure sensor so that the difference between the parameter value of the specific cylinder and the parameter value of the other cylinder is within a predetermined range,
The abnormality determining means determines that the in-cylinder pressure sensor is abnormal when the third determining means determines that there is a variation.

According to a third invention, in the first or second invention,
The air-fuel ratio control means determines that there is no variation by the first determination means, and when it is determined by the second determination means that variation has occurred, the first air-fuel ratio of each of the plurality of cylinders The air-fuel ratio of each of the plurality of cylinders is controlled so that the change amount of
The three determining means determines whether or not there is a variation among the plurality of cylinders in the amount of change in the second air-fuel ratio that has occurred as a result of the air-fuel ratio control by the air-fuel ratio control means,
The abnormality determining means determines that the in-cylinder pressure sensor is abnormal when the third determining means determines that the change amount varies.

  According to a fourth invention, in any one of the first to third inventions, the discrimination result of the first discrimination means and the discrimination result of the second discrimination means, or the discrimination result of the first discrimination means and the second Imbalance determining means for determining whether or not the air-fuel ratio actually varies among the plurality of cylinders according to the determination result of the determining means and the determination result of the third determining means is further provided. .

A fifth invention is an abnormality detection device for an in-cylinder pressure sensor,
The air-fuel ratio is adjusted based on the output of the in-cylinder pressure sensor so that the amount of change for each cylinder of the air-fuel ratio detected according to the output of the in-cylinder pressure sensor disposed in each of the plurality of cylinders of the internal combustion engine is constant. Air-fuel ratio control means to control;
An air-fuel ratio for detecting, for each cylinder, an amount of change in the air-fuel ratio detected in accordance with the output of an air-fuel ratio sensor disposed in the exhaust path of the internal combustion engine before and after the air-fuel ratio control by the air-fuel ratio control means. Change amount detection means;
A discriminating means for discriminating whether or not the amount of change in the air-fuel ratio varies among the cylinders;
An abnormality determining means for determining that the in-cylinder pressure sensor is abnormal when it is recognized that the amount of change varies.
Is provided.

  According to the first aspect of the invention, there is a difference between the determination results of the air-fuel ratio variation determination between the cylinders according to the output of the in-cylinder pressure sensor and the air-fuel ratio variation determination between the cylinders according to the output of the air-fuel ratio sensor. In this case, after performing the air-fuel ratio control in accordance with the in-cylinder pressure sensor output, the presence or absence of variation in the air-fuel ratio generated in the air-fuel ratio sensor output is detected, thereby determining whether the in-cylinder pressure sensor is abnormal. Therefore, it is possible to detect the abnormality of the in-cylinder pressure sensor with high accuracy regardless of whether or not the air-fuel ratio between the cylinders actually varies.

  According to the second invention, when it is assumed that the air-fuel ratio varies according to the output of the in-cylinder pressure sensor, the predetermined parameter values between the cylinders are compared, and the parameter values are matched between the cylinders. Be controlled. By this control, it is possible to eliminate a factor that may cause variation in the air-fuel ratio between the cylinders, and it is possible to detect abnormality of the in-cylinder pressure sensor with high accuracy.

  According to the third invention, when it is determined that the air-fuel ratio according to the output of the air-fuel ratio sensor has a variation, the change amount of the air-fuel ratio according to the output of the in-cylinder pressure sensor is made constant, Air-fuel ratio control based on the output of the in-cylinder pressure sensor is performed. As a result, it is possible to detect the abnormality of the in-cylinder pressure sensor with high accuracy by eliminating factors that may cause variation in the air-fuel ratio between the cylinders.

  According to the fourth invention, it is possible to determine whether or not there is actually a variation between the cylinders regardless of whether or not the in-cylinder pressure sensor is abnormal.

  According to the fifth aspect of the invention, the air-fuel ratio control based on the output of the in-cylinder pressure sensor is performed so that the change amount of the air-fuel ratio according to the output of the in-cylinder pressure sensor becomes constant. As a result, even when factors that may cause variation in the air-fuel ratio between cylinders overlap, it is possible to eliminate other factors and detect an abnormality of the in-cylinder pressure sensor with high accuracy.

It is a schematic diagram for demonstrating the whole structure of the system in Embodiment 1 of this invention. It is a flowchart for demonstrating the control routine which a control apparatus performs in Embodiment 1 of this invention. It is a flowchart for demonstrating the control routine which a control apparatus performs in Embodiment 2 of this invention.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.
Embodiment 1 FIG.
[System Configuration of Embodiment 1]

  FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system of this embodiment includes an internal combustion engine 2 used as a power source for a vehicle.

  The internal combustion engine 2 has a plurality of cylinders 4, and FIG. 1 shows a cross section of one of the cylinders. Each cylinder 4 is provided with a piston 6. The piston 6 is connected to the crankshaft via a crank mechanism. A crank angle sensor 8 is provided in the vicinity of the crankshaft. The crank angle sensor 8 is a sensor that generates an output corresponding to the rotation angle of the crankshaft. The internal combustion engine 2 is provided with a water temperature sensor 10. The water temperature sensor 10 is a sensor that emits an output corresponding to the temperature of the cooling water circulating in the internal combustion engine 2.

  Each cylinder 4 is provided with an injector 12 for injecting fuel into the combustion chamber of the cylinder 4, an ignition plug 14 for igniting an air-fuel mixture in the combustion chamber, and an in-cylinder pressure sensor 16. The in-cylinder pressure sensor 16 is a sensor that generates an output corresponding to the pressure in the combustion chamber (in-cylinder pressure), and here, a CPS (Combustion Pressure Sensor) is used.

  Each cylinder 4 is provided with an intake valve 18 that opens and closes between the intake port and the combustion chamber, and an exhaust valve 20 that opens and closes between the exhaust port and the combustion chamber. An intake passage 22 communicates with the intake port of each cylinder 4. An air flow meter 24 for detecting the intake air amount is disposed in the intake passage 22. A throttle valve 26 is disposed upstream of the air flow meter 24. The throttle valve 26 is an electronically controlled throttle valve that is opened and closed by a throttle motor.

  An exhaust path 30 communicates with the exhaust port of each cylinder. An air-fuel ratio sensor 32 that detects the air-fuel ratio of the exhaust gas is attached downstream of the joining portion of the exhaust path 30. In the exhaust passage 30 downstream of the air-fuel ratio sensor 32, an S / C catalyst 34 and a U / F catalyst 36 for purifying exhaust gas are installed.

  The system according to the first embodiment includes a control device 40. In addition to the in-cylinder pressure sensor 16, the crank angle sensor 8, the water temperature sensor 10, the air flow meter 24, the throttle position sensor, the air-fuel ratio sensor 32, and the like, various sensors are connected to the input side of the control device 40. Various actuators are connected to the output side of the control device 40 in addition to the above-described injector 12, spark plug 14, throttle motor, and the like. The control device 40 executes a predetermined program based on input information from various sensors and operates various actuators to control the operating state of the internal combustion engine 2.

[Characteristic control of the first embodiment]
In the control executed by the ECU 40 as the control device in the first embodiment, detection of the first air-fuel ratio (hereinafter also referred to as “CPS_A / F”) based on the output of the in-cylinder pressure sensor 16, Control for detecting an abnormality of the in-cylinder pressure sensor 16 including detection of a second air-fuel ratio (hereinafter also referred to as “AFS_A / F”) based on the output is included.

  Specifically, the in-cylinder pressure sensor 16 installed in each cylinder generates an output corresponding to the in-cylinder pressure of the cylinder. The control device 40 obtains the current in-cylinder pressure according to the output of the in-cylinder pressure sensor 16, and the in-cylinder pressure, the ignition timing, the intake air amount obtained according to the outputs from the various sensors, the current volume of the combustion chamber, The first air-fuel ratio CPS_A / F is calculated for each cylinder from the intake air temperature and the like.

  On the other hand, the air-fuel ratio sensor 32 installed in the exhaust path 30 emits an output corresponding to the air-fuel ratio in the exhaust path 30. The control device 40 calculates the second air-fuel ratio AFS_A / F for each cylinder using an exhaust gas model or the like based on the output of the crank angle sensor 8 or the output of the air-fuel ratio sensor 32.

  Here, the intake air amount and the fuel injection amount may deviate from the target amounts between the cylinders due to aging of the intake system / valve system of the cylinders, deterioration of the injector 12 over time, and the like. In this case, even when all the cylinders are controlled to have the same air-fuel ratio, variations in the air-fuel ratio among the cylinders (hereinafter also referred to as “air-fuel ratio imbalance”) may occur.

  In particular, since the in-cylinder pressure sensor 16 is placed in a harsh environment such as a combustion chamber of a cylinder, its characteristics may change due to the influence of temperature, aging, etc., and for example, a gain abnormality may occur. Since the in-cylinder pressure sensor 16 is arranged for each cylinder, when an abnormality occurs in a certain in-cylinder pressure sensor 16, the CPS_A / F of that cylinder is different from the CPS_A / F of other cylinders. As a result, even if the air-fuel ratio imbalance does not actually occur between the cylinders, a situation where it is detected that there is an air-fuel ratio imbalance may occur.

  Therefore, in the first embodiment, the control device 40 determines whether the detected air-fuel ratio imbalance is due to the actually occurring variation in the air-fuel ratio between the cylinders or the characteristics of the in-cylinder pressure sensor 16 and the like. The presence or absence of air-fuel ratio imbalance and the presence or absence of abnormality of the in-cylinder pressure sensor 16 are detected by distinguishing whether the change is due to a change.

  Specifically, first, based on the output of the in-cylinder pressure sensor 16 for each cylinder, the first air-fuel ratio CPS_A / F for each cylinder is detected and compared. As a result, if there is a predetermined difference or more in the CPS_A / F of each cylinder, the air-fuel ratio imbalance is present, and if no difference is recognized, the air-fuel ratio imbalance is absent. For the sake of simplicity, hereinafter, this imbalance determination method based on the output of the in-cylinder pressure sensor 16 will also be referred to as a “CPS method”.

  Further, the second air-fuel ratio AFS_A / F for each cylinder is detected based on the output of the air-fuel ratio sensor 32 installed in the exhaust passage 30 and compared. If there is a predetermined difference or more in the AFS_A / F of each cylinder, the air-fuel ratio imbalance is present, and if no difference is recognized, the air-fuel ratio imbalance is absent. Hereinafter, this imbalance determination method based on the output of the air-fuel ratio sensor 32 is also referred to as an “AFS method”.

  The control device 40 compares the determination results of both the CPS method and the AFS method, and if the two results are different, further executes control for confirming whether the in-cylinder pressure sensor 16 is abnormal. .

  More specifically, as described in (1) to (4) below, control is performed for determining whether or not there is an air-fuel ratio imbalance and whether or not the in-cylinder pressure sensor 16 is abnormal.

(1) When the CPS method is imbalanced and the AFS method is imbalanced In this case, the air-fuel ratio imbalance that actually occurs between the cylinders is correctly detected by both the CPS method and the AFS method. It is considered a thing. Therefore, it is determined that there is an air-fuel ratio imbalance. The determination based on the output of the in-cylinder pressure sensor 16 is normal, and the in-cylinder pressure sensor 16 is determined to be normal.

(2) In the case of imbalance in the CPS method and no imbalance in the AFS method The following two cases can be considered as the causes of different judgments by the CPS method and the AFS method.
(A) There is no air-fuel ratio imbalance, and the cylinder pressure sensor 16 is abnormal. That is, the variation in CPS_A / F for each cylinder is due to the abnormality of the in-cylinder pressure sensor 16, and the determination by the AFS method is correct.
(B) There is an air-fuel ratio imbalance, and the cylinder pressure sensor 16 is normal. The in-cylinder imbalance actually generated by the in-cylinder pressure sensor 16 is correctly detected. The determination of no imbalance in the AFS method is based on a single error of the air-fuel ratio sensor 32 or the like.

  The control device 40 determines whether the difference between the CFS method and the AFS method in the case (2) is the case (A) or (B) above, and the in-cylinder pressure sensor 16 is abnormal. In order to confirm the presence or absence of the following, the following control is performed.

  First, air-fuel ratio feedback control based on the output of the in-cylinder pressure sensor 16 is performed so that CPS_A / F does not vary among cylinders. In a state where the variation in CPS_A / F is not detected, AFS_A / F is detected for each cylinder and compared.

  As a result, if there is no variation in AFS_A / F, it is considered that the variation among the cylinders has been eliminated by the air-fuel ratio control based on the output of the in-cylinder pressure sensor 16. Therefore, the case (b), that is, the in-cylinder pressure sensor 16 is normal, and the determination of no imbalance by the first AFS_A / F is considered as a single error such as noise of the air-fuel ratio sensor 32. In this case, it is determined that there is an air-fuel ratio imbalance, and it is determined that there is no abnormality in the in-cylinder pressure sensor 16.

  On the other hand, even if air-fuel ratio imbalance is removed by performing air-fuel ratio control based on CPS_A / F, if variation is still recognized in AFS_A / F for each cylinder, air-fuel ratio is not controlled in control based on the output of in-cylinder pressure sensor 16. It seems that the imbalance has not been removed. Therefore, it is determined that the variation in CPS_A / F between the cylinders (i), that is, the abnormality of the in-cylinder pressure sensor 16 is not caused by the actual air-fuel ratio imbalance. Accordingly, in this case, it is determined that there is no air-fuel ratio imbalance, and the in-cylinder pressure sensor 16 is determined to be abnormal.

(3) When there is no imbalance by the CPS method and when there is an imbalance by the AFS method The following two cases can be considered as the causes of different judgments by the CPS method and the AFS method.
(C) There is an air-fuel ratio imbalance, and the cylinder pressure sensor 16 is abnormal.
(D) There is no air-fuel ratio imbalance, and the cylinder pressure sensor 16 is normal. The determination by the AFS method is based on a single error of the air-fuel ratio sensor 32 or the like.
The control device 40 determines whether the case is (C) or (D), and performs the following control in order to confirm whether the in-cylinder pressure sensor 16 is abnormal.

  First, in order for each cylinder, the fuel injection amount is changed by a predetermined value of CPS_A / F to give an air-fuel ratio imbalance between the cylinders. Thereafter, the change amount of AFS_A / F before and after changing the fuel injection amount is detected and compared for each cylinder.

  As a result, when a cylinder whose detected AFS_A / F change amount is different from the change amount of the other cylinders can be identified, the above-mentioned case (c), that is, there is an air-fuel ratio imbalance, and the in-cylinder pressure sensor 16 is abnormal. It is determined.

  On the other hand, when a cylinder whose AFS_A / F change amount is different from the change amount of the other cylinders cannot be specified by the above control, there is no air-fuel ratio imbalance in case (d), that is, the in-cylinder pressure sensor 16 is also normal. It is determined.

(4) When there is no imbalance determination by the CPS method and no imbalance determination by the AFS method In this case, it is considered that the current state of no air-fuel ratio imbalance has been correctly confirmed by the CPS method and the AFS method. Therefore, it is determined that there is no air-fuel ratio imbalance and the in-cylinder pressure sensor 16 is normal.

  By the above control, in the first embodiment, even in an environment where the air-fuel ratio imbalance actually occurs, the factor of the overlapping variation is eliminated, the presence or absence of the air-fuel ratio imbalance, and the in-cylinder pressure sensor The presence or absence of 16 abnormalities can be distinguished and detected.

[Specific control routine]
FIG. 2 is a diagram for illustrating a control routine executed by control device 40 in the first embodiment of the present invention. The routine of FIG. 2 is repeatedly executed at regular intervals. In the routine of FIG. 2, first, it is determined whether or not a condition for executing abnormality detection is satisfied (S102). Specifically, whether the in-cylinder pressure sensor 16 and the air-fuel ratio sensor 32 are warmed up, whether the engine speed, the load factor, the vehicle speed, and the change rate thereof are within a predetermined range are determined in advance in the control device 40. The determination is made based on whether or not the stored execution condition is satisfied. If the establishment of the abnormality detection execution condition is not recognized in step S102, the current process ends.

  On the other hand, if the execution condition is confirmed to be satisfied in step S102, then CPS_A / F in the same cycle of each cylinder is detected (S104). CPS_A / F is obtained according to the output of the in-cylinder pressure sensor 16 installed in each cylinder.

  Next, AFS_A / F within the same cycle is detected for each cylinder (S106). AFS_A / F is obtained according to the output of the air-fuel ratio sensor 32 installed in the exhaust path 30.

  Next, it is determined by the CPS method whether or not the air-fuel ratio imbalance is recognized (S108). This determination is made based on whether or not there is a difference of a predetermined value or more in CPS_A / F of each cylinder detected in step S104.

  Whether it is determined in step S108 that there is an air-fuel ratio imbalance or if it is determined that there is no air-fuel ratio imbalance, then in step S110 or S112, there is an air-fuel ratio imbalance according to the AFS method. It is determined whether or not it is recognized. This determination is made based on whether or not a difference of a predetermined value or more has occurred in the AFS_A / F of each cylinder detected in step S106.

  If it is determined in step S108 that there is an air-fuel ratio imbalance, and if it is determined in step S110 that there is an air-fuel ratio imbalance (case (1) above), it is determined that there is an air-fuel ratio imbalance (S114). It is determined that there is no abnormality in the sensor 16 (S116). Thereafter, the current process ends.

  If it is determined in step S108 that there is an air-fuel ratio imbalance, and if it is determined in step S110 that there is no air-fuel ratio imbalance (case (2) above), then it is determined whether or not an execution condition is satisfied. (S118). The execution condition here is a condition for determining whether or not a stable state equivalent to a steady state is recognized, and is stored in the control device 40 in advance. If the conditions are not satisfied, the current process ends.

  On the other hand, if it is determined in step S118 that the execution condition is satisfied, a cylinder (specific cylinder) in which the air-fuel ratio CPS_A / F varies is specified (S120). That is, by comparing CPS_A / F of each cylinder, a cylinder having a CPS_A / F greatly different from other cylinders is specified.

  Next, air-fuel ratio feedback control is executed so that the CPS_A / F of this specific cylinder becomes the same as the air-fuel ratio of the other cylinders (S122). Here, the CPS_A / F of the specific cylinder is controlled to match the CPS_A / F of the other cylinders by adjusting the fuel injection amount of the specific cylinder.

  After the variation in CPS_A / F between the cylinders is eliminated, AFS_A / F is then obtained (S124). AFS_A / F is obtained based on the output of the air-fuel ratio sensor 32 installed in the exhaust path 30.

  Next, it is determined whether or not the air-fuel ratio imbalance is recognized by the AFS method (S126). Here, it is determined whether or not there is a difference of a predetermined value or more between the air-fuel ratios AFS_A / F of the respective cylinders obtained in step S124.

  In step S126, when it is not recognized that there is an air-fuel ratio imbalance (the above case (b)), it has been confirmed that the air-fuel ratio imbalance has been eliminated by the air-fuel ratio feedback control based on the output of the in-cylinder pressure sensor 16. That is, the in-cylinder pressure sensor 16 is normal, and the reason why the determination by the CFS method in step S108 differs from the determination by the AFS method in step S110 is considered to be due to the noise of the single air-fuel ratio sensor 32 or the like. Therefore, in this case, it is determined that there is an air-fuel ratio imbalance (S114), it is determined that there is no abnormality in the in-cylinder pressure sensor 16 (S116), and the current process ends.

  On the other hand, if it is determined in step S126 that there is an air-fuel ratio imbalance (case (I) above), it is considered that the air-fuel ratio imbalance has not been eliminated by feedback control based on the output of the in-cylinder pressure sensor 16. It is done. In this case, the determination difference between the CPS method and the AFS method is determined to be due to a failure of the in-cylinder pressure sensor 16. In this case, it is determined that there is no air-fuel ratio imbalance (S128), and it is determined that the in-cylinder pressure sensor 16 is abnormal (S130).

  If it is determined in step S108 that there is no air-fuel ratio imbalance, and if it is further determined in step S112 that there is an air-fuel ratio imbalance (case (3) above), then whether or not the execution condition is satisfied. Is determined (S132). The execution condition here is a condition for determining whether or not a stable state equivalent to a steady state is recognized, and is stored in the control device 40 in advance. If the conditions are not satisfied, the current process ends.

  On the other hand, if it is determined in step S132 that the execution condition is satisfied, then the fuel injection amount is increased in order for each cylinder (S134). As a result, an air-fuel ratio imbalance is temporarily generated between the cylinders.

  Next, AFS_A / F is detected (S136). Next, a change amount of AFS_A / F is obtained for each cylinder (S138). The change amount of AFS_A / F is obtained as a difference between AFS_A / F detected before the fuel increase in step S134 and AFS_A / F detected in step S136 after the increase.

  Next, it is determined whether or not the air-fuel ratio variation varies among the cylinders (S140). This determination is performed based on whether or not the difference between the cylinders in the air-fuel ratio change obtained in step S138 is larger than a predetermined value that is a criterion for determination.

  If it is determined in step S140 that the variation in the air-fuel ratio has changed (case (c) above), it is determined that there is an air-fuel ratio imbalance (S138). Next, it is determined that the in-cylinder pressure sensor 16 is abnormal (S140). This is because it is determined that there is no air-fuel ratio imbalance in the determination based on the in-cylinder pressure sensor 16 in step S108 even though the air-fuel ratio imbalance has occurred.

  If there is no variation in the amount of change in step S140 (case (d) above), there is no air-fuel ratio imbalance (S146), it is determined that the in-cylinder pressure sensor 16 is normal (S148), and the current process ends. To do.

  Further, when it is not recognized that there is an imbalance by the CPS method in step S108 and it is not recognized that there is an air-fuel ratio imbalance by the AFS method in step S112 (case (4) above), the determination by the CPS method is also performed. The determination by the AFS method also agrees without imbalance. Accordingly, in this case, it is determined that there is no air-fuel ratio imbalance (S146), and it is determined that there is no abnormality in the in-cylinder pressure sensor (S148).

  As described above, according to the system of the first embodiment, the failure of the in-cylinder pressure sensor 16 can be determined by comparing the expected value at the time of failure of the in-cylinder pressure sensor and the expected value at the time of normal operation. As a result, even in an environment where air-fuel ratio imbalance occurs, it is possible to reliably detect with high accuracy by distinguishing the presence or absence of air-fuel ratio imbalance and the presence or absence of failure of the in-cylinder pressure sensor 16.

  In the first embodiment, when there is an imbalance in the CPS method (2) and there is no imbalance in the AFS method, air-fuel ratio control is performed to adjust the fuel amount of a specific cylinder based on CPS_A / F ( (S122) After controlling so that CPS_A / F becomes constant, the presence or absence of imbalance is confirmed again by the AFS method (S126), and the presence or absence of air-fuel ratio imbalance and the presence or absence of failure of in-cylinder pressure sensor 16 are determined. Explained when to do. However, the present invention is not limited to this. When there is imbalance in the CPS method and no imbalance in the AFS method, instead of the control based on the CPS_A / F (S120 to S122), the parameter values such as the calorific value and the maximum in-cylinder pressure Pmax are used as a reference. A cylinder having a parameter value different from that of the other cylinder may be specified, and control may be performed so that the parameter value of the specified cylinder matches that of the other cylinder. Also in this case, it is possible to determine the presence / absence of imbalance by the AFS method after control, and to determine the presence / absence of imbalance between cylinders and the presence / absence of failure of the in-cylinder pressure sensor 16 based on the result.

  For example, in the first embodiment, the “first determination unit” of the present invention is realized by executing the process of step S108, and the “first determination unit” is executed by executing the process of step S110 or step S112. "2 discriminating means" is realized, "air-fuel ratio control means" is realized by executing the processing of step S122 or step S134, and "third discriminating means" is realized by executing the processing of step S126 or S140. By implementing the processing in step S130 or S144, an “abnormality determination unit” is realized.

Embodiment 2. FIG.
The system according to the second embodiment of the present invention has the same configuration as that shown in FIG. When detecting an abnormality of the in-cylinder pressure sensor 16, the system of the second embodiment first changes the fuel amount so that the air-fuel ratio CPS_A / F changes by a predetermined value for each cylinder. Then, the amount of change in AFS_A / F is detected before and after the change in fuel amount for each cylinder. If a cylinder having a different AFS_A / F change amount from the other cylinders can be identified, it is determined that the in-cylinder pressure sensor 16 has failed.

  FIG. 3 is a flowchart for illustrating a control routine executed by control device 40 in the second embodiment of the present invention. The routine of FIG. 3 is a routine that is repeatedly executed at regular intervals. In FIG. 3, it is first determined whether or not an execution condition is satisfied (S202). The execution condition here is a condition for determining whether or not a stable state equivalent to a steady state is recognized, and is stored in the control device 40 in advance. If the conditions are not satisfied, the current process ends.

  If it is determined in step S202 that the execution condition is satisfied, then AFS_A / F of each cylinder is detected (S204).

  Next, the fuel injection amount is changed in order for each cylinder (S206). Here, the fuel injection amount to each cylinder is adjusted according to the output of the in-cylinder pressure sensor 16 so that the change amount of CPS_A / F of each cylinder becomes constant.

  Next, AFS_A / F is detected (S208). Next, a change amount of AFS_A / F is obtained for each cylinder (S210). The change amount of AFS_A / F is obtained as a difference between AFS_A / F in step S204 detected before the fuel amount change and AFS_A / F detected in step S208 after the change.

  Next, it is determined whether or not there is variation in the amount of change between the cylinders (S212). This determination is performed based on whether or not the difference between the cylinders in the amount of change obtained in step S210 is greater than a predetermined value serving as a determination criterion.

  If it is determined in step S212 that there is a difference in the amount of change, it is determined that the in-cylinder pressure sensor 16 is abnormal (S214). On the other hand, if there is no variation in the amount of change in step S212, it is determined that the in-cylinder pressure sensor 16 is normal (S216), and the current process ends.

  The routine of FIG. 3 is the process (S132 to S148) performed after step S108 of the routine of FIG. 2 is determined to have no imbalance in the CPS method, and is determined to have imbalance in the AFS method in step S112. It is almost the same thing. However, in the system of the second embodiment, the abnormality determination of the in-cylinder pressure sensor 16 can be performed without performing the process of comparing the coincidence / mismatch between the determination by the CPS method and the determination result by the AFS method. Thereby, abnormality detection of the in-cylinder pressure sensor can be performed more easily. However, in this process, it is not determined whether the air-fuel ratio imbalance actually occurs.

  Note that, for example, the “air-fuel ratio control means” of the present invention is realized by executing the process of step S206 of the second embodiment, and the “air-fuel ratio change amount detection” is performed by executing the process of step S210. "Means" is realized, and "determination means" is realized by executing the process of step S212, and "abnormality determination means" is realized by executing the process of step S214.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., the reference is made unless otherwise specified or the number is clearly specified in principle. The invention is not limited to the numbers. The structures, steps, and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

2 Internal combustion engine 16 In-cylinder pressure sensor 32 Air-fuel ratio sensor 40 Control device

Claims (5)

First determining whether or not the air-fuel ratio varies among the plurality of cylinders based on a first air-fuel ratio detected according to the output of an in-cylinder pressure sensor installed in each of the plurality of cylinders of the internal combustion engine. Discrimination means;
Second discrimination for discriminating whether or not the air-fuel ratio varies among the plurality of cylinders based on a second air-fuel ratio detected according to an output of an air-fuel ratio sensor disposed in an exhaust path of the internal combustion engine Means,
An air-fuel ratio control means for performing air-fuel ratio control based on the output of the in-cylinder pressure sensor when the determination result by the first determination means and the determination result by the second determination means do not match;
Third discriminating means for discriminating whether or not there is variation among the plurality of cylinders according to the second air-fuel ratio after the air-fuel ratio control by the air-fuel ratio control means;
An abnormality determining unit that determines that the in-cylinder pressure sensor is abnormal when the third determining unit determines that there is variation among the plurality of cylinders;
An abnormality detection device for an in-cylinder pressure sensor, comprising: When it is determined that there is a variation by the first determination unit and it is determined that there is no variation by the second determination unit, one of the parameters of the air-fuel ratio, the heat generation amount, and the maximum in-cylinder pressure is set. A cylinder specifying means for specifying a specific cylinder having a value different from other cylinders;
The air-fuel ratio control means controls based on the output of the in-cylinder pressure sensor so that the difference between the parameter value of the specific cylinder and the parameter value of the other cylinder is within a predetermined range,
2. The in-cylinder pressure sensor abnormality detection device according to claim 1, wherein the abnormality determination unit determines that the in-cylinder pressure sensor is abnormal when the third determination unit determines that there is variation. 3. The air-fuel ratio control means determines that there is no variation by the first determination means, and when it is determined by the second determination means that variation has occurred, the first air-fuel ratio of each of the plurality of cylinders The air-fuel ratio of each of the plurality of cylinders is controlled so that the change amount of
The three determining means determines whether or not there is a variation among the plurality of cylinders in the amount of change in the second air-fuel ratio that has occurred as a result of the air-fuel ratio control by the air-fuel ratio control means,
3. The in-cylinder pressure according to claim 1, wherein the abnormality determining unit determines that the in-cylinder pressure sensor is abnormal when the third determining unit determines that the variation is varied. Sensor abnormality detection device.   Depending on the discrimination result of the first discrimination means and the discrimination result of the second discrimination means, or the discrimination result of the first discrimination means, the discrimination result of the second discrimination means, and the discrimination result of the third discrimination means 4. The imbalance determining means for determining whether or not the air-fuel ratio actually varies among the plurality of cylinders is further provided. 5. In-cylinder pressure sensor abnormality detection device. The air-fuel ratio is adjusted based on the output of the in-cylinder pressure sensor so that the amount of change for each cylinder of the air-fuel ratio detected according to the output of the in-cylinder pressure sensor disposed in each of the plurality of cylinders of the internal combustion engine is constant. Air-fuel ratio control means to control;
An air-fuel ratio for detecting, for each cylinder, an amount of change in the air-fuel ratio detected in accordance with the output of an air-fuel ratio sensor disposed in the exhaust path of the internal combustion engine before and after the air-fuel ratio control by the air-fuel ratio control means. Change amount detection means;
A discriminating means for discriminating whether or not the amount of change in the air-fuel ratio varies among the cylinders;
An abnormality determining means for determining that the in-cylinder pressure sensor is abnormal when it is recognized that the amount of change varies.
A failure determination device for an in-cylinder pressure sensor.

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