JP2014214676A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of air-fuel ratio imbalance determination between cylinders in a multi-cylinder internal combustion engine.SOLUTION: Leakage from an intake valve is determined when a rotational variation value of an engine (internal combustion engine) is equal to or more than a primary determination threshold A and an output variation value of an air-fuel ratio sensor on a catalyst upstream side is smaller than a prescribed value. When the leakage from the intake valve is determined, a threshold for imbalance determination is changed to a secondary determination threshold B (determination threshold at the time of valve leakage), and abnormality of air-fuel ratio imbalance is determined when the rotational variation value of the engine is equal to or more than the secondary determination threshold B after changed. This determination processing allows air-fuel ratio imbalance determination in consideration of valve leakage, and therefore, erroneous determination can be restrained, and accuracy of air-fuel ratio imbalance determination can be improved.

Description

  The present invention relates to a control device for a multi-cylinder internal combustion engine, and more particularly to a control device for an internal combustion engine capable of executing an air-fuel ratio imbalance determination between cylinders.

  In a multi-cylinder internal combustion engine having a plurality of cylinders, the actual air-fuel ratio may vary between cylinders due to, for example, a failure of a fuel injection system of some cylinders (failure caused by an injector). If so, emissions may deteriorate. From this point of view, in the field of automobiles, in order to prevent the traveling of a vehicle whose emission has deteriorated, an abnormality in air-fuel ratio variation between cylinders (air-fuel ratio imbalance abnormality) is determined (detected) in an on-vehicle state (air-fuel ratio). Imbalance determination OBD (On Board Diagnosis)).

  As an example of a method for determining an air-fuel ratio imbalance between cylinders, there is a method using rotational fluctuation of an internal combustion engine (for example, see Patent Document 1). In this method, when an air-fuel ratio imbalance abnormality between cylinders (hereinafter also referred to as “air-fuel ratio imbalance”) occurs, a difference occurs in torque generated between the cylinders, resulting in rotational fluctuations of the internal combustion engine (hereinafter simply referred to as “rotational fluctuations”). Is also used to determine the air-fuel ratio imbalance between the cylinders using the fluctuation in rotation as an imbalance parameter.

JP 2013-002394 A

  One of the causes of the air-fuel ratio imbalance between the cylinders may be leakage from the intake valve section (hereinafter also referred to as “valve leak”). In the above-described inter-cylinder air-fuel ratio imbalance determination method, if the air-fuel ratio imbalance determination is performed without considering such valve leak, it is determined that the air-fuel ratio imbalance is abnormal even if the emission level is not abnormal ( There is a risk of misjudgment).

  The present invention has been made in view of such a situation, and is capable of improving the accuracy of air-fuel ratio imbalance determination in a control device for an internal combustion engine capable of performing air-fuel ratio imbalance determination between cylinders. The purpose is to do.

  The present invention relates to an internal combustion engine in which an air-fuel ratio sensor (A / F sensor) is provided on the upstream side (upstream side of the exhaust flow) of a catalyst disposed in an exhaust passage. A control device for an internal combustion engine capable of executing imbalance determination for determining air-fuel ratio imbalance is assumed. In such a control device for an internal combustion engine, if the rotational fluctuation of the internal combustion engine is greater than or equal to a first determination threshold and the output fluctuation value of the air-fuel ratio sensor is smaller than a predetermined value, there is leakage from the intake valve unit. When the determination is made and it is determined that there is a leak from the intake valve portion, if the rotational fluctuation of the internal combustion engine is equal to or greater than a second determination threshold, it is determined as an air-fuel ratio imbalance.

  In the present invention, when the rotational fluctuation of the internal combustion engine is equal to or greater than a first determination threshold value and the output fluctuation value of the air-fuel ratio sensor is equal to or greater than a predetermined value (when it is determined that there is no leakage from the intake valve portion), it is empty. It is determined that the fuel ratio is imbalance.

  According to the present invention, the accuracy of air-fuel ratio imbalance determination between cylinders can be improved. This will be described below.

  First, when a valve leak occurs, the rotational fluctuation is worsened by reducing the amount of air in the combustion chamber. That is, when the valve leak occurs, the sensitivity to the air amount is large and the rotation fluctuation is large. On the other hand, the output value of the air-fuel ratio sensor does not show a large fluctuation because the sensitivity to the air amount is small. For this reason, when the rotational fluctuation is equal to or greater than the first threshold (primary determination threshold A) and the output fluctuation value of the air-fuel ratio sensor provided upstream of the catalyst is smaller than a predetermined value, the leakage from the intake valve section Therefore, it is determined that there is a valve leak. When it is determined that there is a valve leak (when a valve leak occurs), the threshold for imbalance determination is changed (changed from the primary determination threshold A to the secondary determination threshold B (valve leak determination threshold)). Thus, it becomes possible to perform air-fuel ratio imbalance determination in consideration of valve leak.

  Thus, by performing air-fuel ratio imbalance determination in consideration of valve leak, erroneous determination can be suppressed and the accuracy of air-fuel ratio imbalance determination can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the precision of the air fuel ratio imbalance determination between cylinders in a multicylinder internal combustion engine can be improved.

It is a schematic structure figure showing an example of an engine to which the present invention is applied. It is a schematic block diagram which shows only 1 cylinder of the engine of FIG. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart which shows an example of an air fuel ratio imbalance determination process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

-Engine-
1 and 2 are diagrams showing a schematic configuration of a multi-cylinder engine to which the present invention is applied. FIG. 2 shows only the configuration of one cylinder of the engine.

  The engine 1 in this example is a port injection type four-cylinder engine (spark ignition type internal combustion engine) mounted on a vehicle, and in a cylinder block 1a that constitutes each cylinder # 1, # 2, # 3, # 4. Is provided with a piston 1c that reciprocates in the vertical direction. The piston 1c is connected to the crankshaft 15 via the connecting rod 16, and the reciprocating motion of the piston 1c is converted into rotation of the crankshaft 15 by the connecting rod 16.

  A signal rotor 17 is attached to the crankshaft 15. A plurality of teeth (projections) 17a are provided on the outer periphery of the signal rotor 17 at equal angles (in this example, for example, 10 ° CA (crank angle)). Further, the signal rotor 17 has a missing tooth portion 17b in which two teeth 17a are missing.

  A crank position sensor 31 that detects a rotation angle (crank angle) [° CA] of the crankshaft 15 is disposed in the vicinity of the side of the signal rotor 17. The crank position sensor 31 is an electromagnetic pickup, for example, and generates a pulsed signal (voltage pulse) corresponding to the teeth 17a of the signal rotor 17 when the crankshaft 15 rotates. The engine speed NE can be calculated from the output signal of the crank position sensor 31.

  A water temperature sensor 32 for detecting the coolant temperature of the engine cooling water is disposed in the cylinder block 1a of the engine 1. A cylinder head 1b is provided at the upper end of the cylinder block 1a, and a combustion chamber 1d is formed between the cylinder head 1b and the piston 1c. A spark plug 3 is disposed in the combustion chamber 1 d of the engine 1. The ignition timing of the spark plug 3 is adjusted by the igniter 4. The igniter 4 is controlled by an ECU (Electronic Control Unit) 200.

  An intake passage 11 and an exhaust passage 12 are connected to the combustion chamber 1 d of the engine 1. A part of the intake passage 11 is formed by an intake port 11a and an intake manifold 11b. A surge tank 11 c is provided in the intake passage 11. A part of the exhaust passage 12 is formed by an exhaust port 12a and an exhaust manifold 12b.

  In the intake passage 11 of the engine 1, an air cleaner 7 that filters the intake air, a hot-wire air flow meter 33, an intake air temperature sensor 34 (built in the air flow meter 33), a throttle valve 5 for adjusting the intake air amount of the engine 1, etc. Is arranged. The throttle valve 5 is provided on the upstream side (upstream side of the intake flow) of the surge tank 11 c and is driven by the throttle motor 6. The opening of the throttle valve 5 is detected by a throttle opening sensor 35. The throttle opening degree of the throttle valve 5 is controlled by the ECU 200.

  An intake valve 13 is provided between the intake passage 11 and the combustion chamber 1d. By opening and closing the intake valve 13, the intake passage 11 and the combustion chamber 1d are communicated or blocked. Further, an exhaust valve 14 is provided between the exhaust passage 12 and the combustion chamber 1d, and the exhaust passage 12 and the combustion chamber 1d are communicated or blocked by opening and closing the exhaust valve 14. The opening / closing drive of the intake valve 13 and the exhaust valve 14 is performed by each rotation of the intake camshaft 21 and the exhaust camshaft 22 to which the rotation of the crankshaft 15 is transmitted via a timing chain or the like.

  Near the intake camshaft 21 is a cam position sensor 39 that generates a pulse signal when the piston 1c of a specific cylinder (for example, the first cylinder # 1) reaches the compression top dead center (compression TDC). Is provided. The cam position sensor 39 is, for example, an electromagnetic pickup, and is disposed so as to face one tooth (not shown) on the outer periphery of the rotor provided integrally with the intake camshaft 21, and the intake camshaft thereof. When 21 rotates, a pulse-like signal (voltage pulse) is output. Since the intake camshaft 21 (and the exhaust camshaft 22) rotates at a half speed of the crankshaft 15, the cam position sensor 39 becomes 1 each time the crankshaft 15 rotates twice (720 ° rotation). Two pulse signals are generated.

  An injector (fuel injection valve) 2 capable of injecting fuel is disposed in the intake port 11 a of the intake passage 11. The injector 2 is provided for each cylinder # 1 to # 4. These injectors 2... 2 are connected to a common delivery pipe 101. The delivery pipe 101 is supplied with fuel stored in a fuel tank 104 of a fuel supply system 100 (to be described later), whereby fuel is injected from the injector 2 into the intake port 11a. This injected fuel is mixed with intake air to form an air-fuel mixture and introduced into the combustion chamber 1 d of the engine 1. The air-fuel mixture (fuel + air) introduced into the combustion chamber 1d is ignited by the spark plug 3 and combusted / exploded. The piston 1c is reciprocated by the high-temperature and high-pressure combustion gas generated at this time, the crankshaft 15 is rotated, and the driving force (output torque) of the engine 1 is obtained. The combustion gas is discharged into the exhaust passage 12 when the exhaust valve 14 is opened. The engine 1 burns and explodes in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2. The operation state of the engine 1 is controlled by the ECU 200.

  The fuel supply system 100 includes a delivery pipe 101 commonly connected to the injectors 2... 2 of the cylinders # 1 to # 4, a fuel supply pipe 102 connected to the delivery pipe 101, and a fuel pump (for example, an electric pump). 103, a fuel tank 104, and the like. By driving the fuel pump 103, the fuel stored in the fuel tank 104 can be supplied to the delivery pipe 101 via the fuel supply pipe 102. Then, fuel is supplied to the injectors 2 of the cylinders # 1 to # 4 by the fuel supply system 100 having such a configuration.

  In the fuel supply system 100 configured as described above, the driving of the fuel pump 103 is controlled by the ECU 200.

On the other hand, a three-way catalyst 8 is disposed in the exhaust passage 12 of the engine 1. The three-way catalyst 8 has an O ₂ storage function (oxygen storage function) for storing (storing) oxygen. Even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio to a certain extent by this oxygen storage function, the HC , CO and NOx can be purified. That is, when the air-fuel ratio of the engine 1 becomes lean and oxygen and NOx in the exhaust gas flowing into the three-way catalyst 8 increase, the three-way catalyst 8 occludes part of the oxygen, thereby reducing and purifying NOx. Promote. On the other hand, when the air-fuel ratio of the engine 1 becomes rich and the exhaust gas flowing into the three-way catalyst 8 contains a large amount of HC and CO, the three-way catalyst 8 releases oxygen molecules stored therein, Oxygen molecules are given to these HC and CO to promote oxidation and purification.

An air-fuel ratio sensor (A / F sensor) 37 is disposed in the exhaust passage 12 upstream of the three-way catalyst 8 (upstream of the exhaust flow), and downstream of the three-way catalyst 8 (downstream of the exhaust flow). An O ₂ sensor (oxygen sensor) 38 is disposed in the exhaust passage 12. For example, a limit current type oxygen concentration sensor is applied to the air-fuel ratio sensor 37, and the air-fuel ratio can be continuously detected over a wide air-fuel ratio region. The O ₂ sensor 38 is a sensor that exhibits a characteristic (Z characteristic) in which the output value changes stepwise in the vicinity of the theoretical air-fuel ratio (stoichiometric). In this example, for example, an electromotive force type (concentration cell type) oxygen concentration Sensor is applied. Output signals of the air-fuel ratio sensor 37 and the O ₂ sensor 38 are input to the ECU 200.

The ECU 200 executes air-fuel ratio feedback control (stoichiometric control) based on the outputs of the air-fuel ratio sensor 37 and the O ₂ sensor 38. In the air-fuel ratio feedback control, main feedback control for matching the exhaust air-fuel ratio detected by the air-fuel ratio sensor 37 upstream of the three-way catalyst 8 with a stoichiometric value that is a predetermined target air-fuel ratio, and the three-way catalyst 8 Sub-feedback control is performed so that the exhaust air-fuel ratio detected by the downstream O ₂ sensor 38 matches the stoichiometric ratio (for example, as described in JP 2010-007561 A and JP 2012-167646 A). See technology).

-ECU-
As shown in FIG. 3, the ECU 200 includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, a backup RAM 204, and the like.

  The ROM 202 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 201 executes various arithmetic processes based on various control programs and maps stored in the ROM 202. The RAM 203 is a memory that temporarily stores calculation results of the CPU 201, data input from each sensor, and the backup RAM 204 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The CPU 201, the ROM 202, the RAM 203, and the backup RAM 204 are connected to each other via the bus 207, and are connected to the input interface 205 and the output interface 206.

The input interface 205 includes a crank position sensor 31, a water temperature sensor 32, an air flow meter 33, an intake air temperature sensor 34, a throttle opening sensor 35, an accelerator opening sensor 36 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, Various sensors such as a fuel ratio sensor 37, an O ₂ sensor 38, and a cam position sensor 39 are connected. Further, an ignition switch (start switch) 40 is connected to the input interface 205.

  The output interface 206 is connected to the injector 2, the igniter 4 of the spark plug 3, the throttle motor 6 of the throttle valve 5, the fuel pump 103 of the fuel supply system 100, and the like.

  The ECU 200 controls the drive of the injector 2 (fuel injection amount adjustment control), the ignition timing control of the spark plug 3, and the drive control of the throttle motor 6 of the throttle valve 5 (intake air) based on the detection signals of the various sensors described above. Amount control) and various controls of the engine 1 including the air-fuel ratio feedback control described above. Further, the ECU 200 executes the following “TDC determination for each cylinder”, “calculation of rotation fluctuation”, and “air-fuel ratio imbalance determination OBD between cylinders”.

  The control program for the internal combustion engine of the present invention is realized by the program executed by the ECU 200 described above.

-TDC determination for each cylinder-
The ECU 200 determines the compression top dead center (compression TDC) of each of the cylinders # 1 to # 4 based on the output signals of the crank position sensor 31 and the cam position sensor 39. The determination method will be described below.

  First, as described above, the crank position sensor 31 outputs the missing tooth signal once (two times in one cycle of the engine cycle) while the crankshaft 15 makes one rotation (360 ° CA). In this example, the crank position sensor 31 outputs a missing tooth signal at a predetermined crank angle before top dead center (before TDC) of the first cylinder # 1 and the fourth cylinder # 4.

  Further, as described above, the cam position sensor 39 outputs a voltage pulse once during the rotation of the crankshaft 15 (once in one cycle of the engine cycle). In this example, the cam position sensor 39 outputs a voltage pulse when the first cylinder # 1 is located at the compression top dead center (compression TDC) and the fourth cylinder # 4 is located at the exhaust top dead center (exhaust TDC). It is the composition to do.

  With this configuration, when the cam position sensor 39 generates a voltage pulse when the crank position sensor 31 outputs a missing tooth signal, it is determined that the first cylinder # 1 is a compression TDC, and the first It is determined that the compression TDC of the third cylinder # 3 is 180 ° CA after the compression TDC of the cylinder # 1. If the cam position sensor 39 does not generate a voltage pulse when the crank position sensor 31 outputs a missing tooth signal, it is determined that the fourth cylinder # 4 is a compression TDC, and the fourth cylinder # 4 After 180 ° CA from the compression TDC, it is determined that the compression TDC of the second cylinder # 2.

-Calculation of rotation fluctuation value-
In this embodiment, a predetermined rotation angle during the combustion stroke of the engine 1, for example, the time T ₃₀ required for the crankshaft 15 to rotate 30 ° CA from the compression TDC (inversely proportional to the rotation speed: rotation speed = 30 ° CA / T ₃₀ ) is calculated for each cylinder # 1 to # 4, and the difference (time difference ΔT ₃₀ ) between the cylinders at the calculated time T ₃₀ is calculated. The time difference ΔT ₃₀ calculated in this way is a value representing the rotational fluctuation of the engine 1, and hereinafter this time difference ΔT ₃₀ will be referred to as a rotational fluctuation value ΔT ₃₀ .

A specific example of the calculation process of the rotation fluctuation value ΔT ₃₀ will be described. Based on the output signals of the crank position sensor 31 and the cam position sensor 39, the ECU 200 determines the time T ₃₀ [# required for the crankshaft 15 to rotate 30 ° CA from the compression TDC during the combustion stroke of the first cylinder # 1. 1] and the crankshaft 15 rotates 30 ° CA from the compression TDC during the calculated time T ₃₀ [# 1] and during the combustion stroke of the second cylinder # 2 that has reached the previous combustion stroke. By calculating the difference from the time T ₃₀ [# 2] required for the rotation, the rotational fluctuation value ΔT ₃₀ [# 1] of the first cylinder # 1 (= T ₃₀ [# 1] −T ₃₀ [# 2]) Is calculated.

Similarly, time T ₃₀ [# 3] and time T ₃₀ required for the crankshaft 15 to rotate 30 ° CA from the compression TDC in each combustion stroke of the cylinders # 3, # 4, and # 2 of the engine 1 [# 4], time T ₃₀ [# 2] is sequentially calculated, and the third cylinder rotational fluctuation value ΔT ₃₀ [# 3] (= T ₃₀ [# 3] −T ₃₀ [# 1]), fourth Cylinder rotation fluctuation value ΔT ₃₀ [# 4] (= T ₃₀ [# 4] −T ₃₀ [# 3]) and second cylinder rotation fluctuation value ΔT ₃₀ [# 2] (= T ₃₀ [# 2] ] -T ₃₀ [# 4]).

The rotational fluctuation values ΔT ₃₀ [# 1], ΔT ₃₀ [# 2], ΔT ₃₀ [# 3], and ΔT ₃₀ [# 4] calculated as described above are air-fuel ratio imbalance determination (OBD) described later. Used as an imbalance parameter.

  The predetermined rotation angle during the combustion stroke of the engine 1 may be a value other than 30 ° CA (for example, 10 ° CA). Further, the rotation fluctuation value of the engine 1 may be calculated by another method.

-Air-fuel ratio imbalance determination between cylinders OBD-
First, as described above, one of the causes of the air-fuel ratio imbalance between cylinders is leakage from the intake valve 13 (valve leak).

  When the valve leak occurs, the internal EGR increases (when the exhaust gas recirculates to the intake system, the amount of air decreases by the amount of the exhaust gas), and the generated torque decreases, so the rotational fluctuation of the internal combustion engine increases. . However, when a valve leak occurs, there is a tendency that the behavior of the rotational fluctuation with respect to the deterioration of the emission becomes larger than in the case of a failure caused by the injector or the like. Therefore, if air-fuel ratio imbalance determination is performed without considering valve leak (the cause of air-fuel ratio imbalance is determined by the same determination threshold without distinguishing between valve leak and other causes (failure caused by injectors, etc.) If this is done, there is a risk of imbalance abnormality (judgment) even if the emission level is not abnormal.

  In order to eliminate such a point, in the present embodiment, the determination accuracy is improved by performing the air-fuel ratio imbalance determination between the cylinders in consideration of the valve leak (leakage from the intake valve 13). It is characterized by that.

  One example (air-fuel ratio imbalance determination OBD) will be described with reference to the flowchart of FIG. The processing routine of FIG. 4 is repeatedly executed at predetermined time intervals in the ECU 200.

First, in step S101, it is determined whether a determination condition for determining the air-fuel ratio imbalance is satisfied. This determination condition is satisfied when, for example, the following conditions (a) to (e) are satisfied.
(A) The engine has been warmed up. The ECU 200 determines that the warm-up is finished when the engine water temperature obtained from the output signal of the water temperature sensor 32 is equal to or higher than a predetermined value.
(B) The air-fuel ratio sensor 37 and the O ₂ sensor 38 are activated. The ECU 200 determines that the _two sensors 37 and 38 are activated when the impedances of the air-fuel ratio sensor 37 and the O ₂ sensor 38 are values corresponding to predetermined activation temperatures.
(C) The three-way catalyst 8 is activated. The ECU 200 determines that the three-way catalyst 8 is activated when the temperature of the three-way catalyst 8 estimated based on the engine operating state is a value corresponding to a predetermined activation temperature.
(D) The engine 1 is in idle operation or steady operation. The ECU 200 determines that the engine 1 is in steady operation when the fluctuation range of the engine speed NE and the load factor KL within a predetermined time is within a predetermined value. The load factor KL is the ratio (filling rate) of the intake air amount in the current operating state with respect to the maximum intake air amount to the engine 1, for example, the intake air amount obtained from the output signal of the air flow meter 33 and the crank It is calculated based on the engine speed NE obtained from the output signal of the position sensor 31.
(E) During air-fuel ratio feedback control (during stoichiometric control).

  The determination conditions for imbalance determination are not limited to these conditions.

  If the determination result in step ST101 is negative (NO), the process returns. When the determination result of step ST101 is affirmative (YES) (when the determination condition is satisfied), the process proceeds to step ST102.

In step ST102, based on the output signals of the crank position sensor 31 and the cam position sensor 39, the rotational fluctuation value ΔT ₃₀ [# 1] for each of the cylinders # 1, # 2, # 3, and # 4 is performed by the process described above. , ΔT ₃₀ [# 2], ΔT ₃₀ [# 3], ΔT ₃₀ [# 4] are calculated, and among these four rotational fluctuation values, the largest rotational fluctuation value ΔT ₃₀ (maximum value) is imbalanced. It is a parameter.

Further, in step ST 102, it calculates a primary determination threshold value A and the secondary determination threshold value with respect to the rotation fluctuation value T ₃₀ (valve leakage during determination threshold value) B. Specifically, for example, the primary determination threshold A and the secondary determination threshold B (the current engine speed NE) are referred to a map based on the engine speed NE and the load factor KL output from the crank position sensor 31. And determination thresholds A and B) corresponding to the load factor KL are calculated.

  Here, the calculation map for the primary determination threshold A is a determination that can determine an abnormality in the air-fuel ratio imbalance that occurs due to an injector-induced failure or the like (causes other than valve leak) using the engine speed NE and the load factor KL as parameters. This is a map obtained by adapting a threshold value (a value (rotation fluctuation value) for distinguishing between an imbalance abnormality and normal due to a failure caused by an injector, etc.) by experiment / simulation. The calculation map of the primary determination threshold A is stored in the ROM 202 of the ECU 200.

  Further, regarding the calculation map of the secondary determination threshold B, the determination threshold (the imbalance abnormality at the time of valve leak and the imbalance abnormality at the time of valve leak) can be determined by using the engine speed NE and the load factor KL as parameters. A map that matches the values (rotational fluctuation values) that distinguish normal from experimental values and simulations is mapped. A calculation map of the secondary determination threshold value B is also stored in the ROM 202 of the ECU 200.

  As described above, when the valve leak occurs, the behavior of the rotational fluctuation becomes larger than that at the time of the failure caused by the injector, etc., so that the engine operating state is the same (the engine speed NE and the load factor KL are the same). Case) The secondary determination threshold B is larger than the primary determination threshold A (primary determination threshold A <secondary determination threshold B).

Next, in step ST103, it is determined whether or not the rotation fluctuation value ΔT ₃₀ (maximum value) calculated in step ST102 is equal to or greater than the primary determination threshold A calculated in step ST102 (primary determination). When the determination result is negative (NO) (when [rotational fluctuation value ΔT ₃₀ <A]), it is determined to be normal (step ST110).

When the determination result of step ST103 is affirmative (YES) (when [rotational fluctuation value ΔT ₃₀ ≧ A]), the process proceeds to step ST104.

  In step ST104, it is determined whether or not the fluctuation (output fluctuation value) of the output value of the air-fuel ratio sensor 37 is smaller than a predetermined value. In step ST104, as described above, when the valve leak occurs, the rotational fluctuation deteriorates due to the decrease in the air amount (the sensitivity of the air amount is large), but the output value of the air-fuel ratio sensor 37 varies greatly. In consideration of the fact that it is not shown (the sensitivity of the air amount is small), it is a step of determining whether or not a valve leak has occurred, and the determination result of this step ST104 is a negative determination (NO) ( If the output fluctuation value of the air-fuel ratio sensor 37 is greater than or equal to a predetermined value), it is determined that there is no valve leak (no leak from the intake valve 13) and the process proceeds to step ST111, where it is determined that the air-fuel ratio imbalance between cylinders is abnormal. To do.

  As for the predetermined value (stored in the ROM 202) used for the determination in step ST104, the output fluctuation value of the air-fuel ratio sensor 37 when the valve leak occurs and the causes other than the valve leak (injector) by experiments and simulations, etc. The output fluctuation value of the air-fuel ratio sensor 37 when the air-fuel ratio imbalance has occurred due to a failure due to the cause, etc.) is acquired, and a value that can be separated between the two (a value that can determine the presence or absence of valve leak) Set according to.

  On the other hand, when the determination result of step ST104 is affirmative (YES) (when the output fluctuation value of the air-fuel ratio sensor 37 is smaller than a predetermined value), it is determined that there is a valve leak and the process proceeds to step ST105.

In step ST105, it is determined whether or not the rotational fluctuation value ΔT ₃₀ (maximum value) calculated in step ST102 is equal to or greater than the secondary determination threshold B (valve leak determination threshold) calculated in step ST102 (2 Next judgment). When the determination result is negative (NO) (when [rotational fluctuation value ΔT ₃₀ <B]), it is determined to be normal (step ST110). On the other hand, when the determination result in step ST105 is affirmative (YES) (when [rotational fluctuation value ΔT ₃₀ ≧ B]), it is determined that the air-fuel ratio imbalance between cylinders is abnormal (step ST111).
<Effect>
As described above, according to the present embodiment, when the rotational fluctuation value of the engine 1 is equal to or greater than the primary determination threshold A and the output fluctuation value of the air-fuel ratio sensor 37 on the upstream side of the catalyst is smaller than a predetermined value. Is determined to have valve leak. When it is determined that the valve leak is present, the imbalance determination threshold is changed to the secondary determination threshold B (valve leak determination threshold B), and the rotational fluctuation value of the engine 1 is equal to or greater than the changed secondary determination threshold B. When it is, it is determined that the air-fuel ratio imbalance abnormality. Thus, in the present embodiment, since the air-fuel ratio imbalance determination is performed in consideration of valve leak, erroneous determination can be suppressed and the accuracy of the air-fuel ratio imbalance determination can be improved.

-Other embodiments-
In addition, embodiment disclosed this time is an illustration in all the points, Comprising: It does not become a basis of limited interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the scope of claims. Further, the technical scope of the present invention includes all modifications within the scope and meaning equivalent to the scope of the claims.

  For example, in the above example, the present invention is applied to a four-cylinder gasoline engine. However, the present invention is not limited to this, and for example, a multi-cylinder having any other number of cylinders such as six cylinders and eight cylinders. It can also be applied to an internal combustion engine.

  In the above example, the example in which the present invention is applied to the port injection type multi-cylinder gasoline engine has been described. However, the present invention is not limited to this, and the present invention is also applicable to an in-cylinder direct injection type multi-cylinder gasoline engine. In addition to the in-line multi-cylinder gasoline engine, the present invention can be applied to a V-type multi-cylinder gasoline engine. The present invention can also be applied to a dual injection multi-cylinder gasoline engine provided with an in-cylinder injector and an intake port injector. Furthermore, the present invention can also be applied to a gas engine or an engine using biomass-derived fuel.

  In the above example, an example in which the present invention is applied to a conventional vehicle on which only an engine (internal combustion engine) is mounted has been shown. However, the present invention is not limited to this, and an engine and an electric motor (such as a motor generator or a motor) are included. It can also be applied to an engine mounted on a mounted hybrid vehicle.

  The present invention can be used for a control device for a multi-cylinder internal combustion engine, and more specifically, can be used for a control device for an internal combustion engine that performs air-fuel ratio imbalance determination between cylinders.

DESCRIPTION OF SYMBOLS 1 Engine 2 Injector 11 Intake passage 12 Exhaust passage 31 Crank position sensor 32 Water temperature sensor 33 Air flow meter 37 Air-fuel ratio sensor 39 Cam position sensor 200 ECU

Claims (2)

In an internal combustion engine having an air-fuel ratio sensor provided upstream of a catalyst disposed in an exhaust passage, an internal combustion engine capable of performing an imbalance determination for determining an air-fuel ratio imbalance between cylinders based on a rotational fluctuation of the internal combustion engine. A control device,
When the rotational fluctuation of the internal combustion engine is equal to or greater than a first determination threshold value and the output fluctuation value of the air-fuel ratio sensor is smaller than a predetermined value, it is determined that there is leakage from the intake valve unit,
When it is determined that there is a leak from the intake valve portion, and the rotational fluctuation of the internal combustion engine is greater than or equal to a second determination threshold value, an air-fuel ratio imbalance is determined. The internal combustion engine of claim 1,
An internal combustion engine control apparatus according to claim 1, wherein when the rotational fluctuation of the internal combustion engine is equal to or greater than a first determination threshold value and the output fluctuation value of the air-fuel ratio sensor is equal to or greater than a predetermined value, an air-fuel ratio imbalance is determined.

Images