JP4605244B2 - Variable cylinder system for internal combustion engine - Google Patents

Description

  The present invention relates to a variable cylinder system for an internal combustion engine that shuts off fuel supply to a part of the plurality of cylinders and operates the remaining cylinders according to operating conditions of the internal combustion engine having the plurality of cylinders. It is about.

  In recent years, in an internal combustion engine mounted on an automobile or the like, a technique is known in which the number of operating cylinders is changed according to the engine operating state for the purpose of reducing fuel consumption and stabilizing the combustion state of the air-fuel mixture.

  In general, when the engine has a surplus output, such as when idling, the load on each cylinder is small, so intake / exhaust loss in the intake stroke increases and combustion efficiency deteriorates. Therefore, in the above technique, in the case of a multi-cylinder engine having a plurality of cylinders, the fuel supply to specific cylinders is shut off and stopped, and the load on the operating cylinder to which the fuel is supplied is increased to increase the efficiency. As a result, fuel consumption is improved. (See Patent Document 1).

  In the above technique, in order to further reduce intake and exhaust losses in the entire internal combustion engine, control is performed so that the intake and exhaust valves are fully opened in the idle cylinder where the fuel supply is stopped, and the intake and exhaust valves are set in the idle cylinder. Techniques for keeping them fully closed have been proposed (see, for example, Patent Document 2 and Patent Document 3).

  On the other hand, an air-fuel ratio sensor has been conventionally provided in the exhaust system of an internal combustion engine, and the air-fuel ratio is feedback controlled to the stoichiometric air-fuel ratio by this sensor output, thereby effectively utilizing the purification capacity of the exhaust purification catalyst provided in the exhaust system. Techniques for improving emission characteristics are well known.

  Here, considering the air-fuel ratio feedback control during the reduced-cylinder operation described above, for example, when the intake valve and exhaust valve of the deactivated cylinder are fully opened during the reduced-cylinder operation, only intake air is discharged from the deactivated cylinder. Then, the oxygen concentration in the exhaust gas increases, and this oxygen concentration is detected by the air-fuel ratio sensor to perform air-fuel ratio feedback control, so that the air-fuel ratio of the fuel supply cylinder is shifted to the rich side.

  In the above case, there is a conventional technique in which the air-fuel ratio feedback control is stopped and the fuel supply amount is switched to open-loop control at the time of reduced-cylinder operation (see, for example, Patent Document 4). Since air-fuel ratio feedback control is sometimes not performed, control that accurately corresponds to the driving situation cannot be performed.

  In addition, even when air-fuel ratio feedback control is performed even during reduced-cylinder operation, as described above, the oxygen concentration in the exhaust gas increases, and as a result, the air-fuel ratio of the fuel supply cylinder shifts to the rich side. In addition, because the exhaust gas transport speed and the gas hit to the air-fuel ratio sensor differ between all-cylinder operation and reduced-cylinder operation, air-fuel ratio feedback under the same conditions as during all-cylinder operation during reduced-cylinder operation If the control is performed, the optimal control cannot be performed, and as a result, the emission is deteriorated.

Furthermore, during reduced-cylinder operation, for the purpose of balancing the use of the entire engine, a plurality of idle cylinder patterns with different idle cylinders are provided, and control to change the cylinders to be operated by pattern switching is performed. ing. In such a case, the exhaust gas transport speed and the amount of gas per air-fuel ratio sensor vary depending on the number and combination of operating cylinders. For this reason, it is necessary to perform optimum air-fuel ratio feedback control for each cylinder for each number and combination of operating cylinders.

Next, similarly, a description will be given of the related art regarding the exhaust gas purification apparatus for an internal combustion engine during the reduced cylinder operation. As one of means for reducing nitrogen oxide (NOx) contained in the exhaust gas of an internal combustion engine, it is known as an effective technique to install, for example, a three-way catalyst in the exhaust passage. The purification performance may deteriorate over time or due to environmental influences.

  As the three-way catalyst deteriorates, the purification ability of components such as HC, CO, and NOx in the exhaust gas decreases, so it is necessary to detect the deterioration of the three-way catalyst, and various catalyst deterioration detection methods and devices have been proposed. ing. For example, two air-fuel ratio sensors are provided upstream and downstream of the three-way catalyst, and the deterioration of the three-way catalyst is based on the locus length ratio and area ratio of the upstream air-fuel ratio sensor output and the downstream air-fuel ratio sensor output. There is a catalyst deterioration determination device and the like.

  This device has a ratio LVOS / LVOM between a downstream air-fuel ratio sensor output trajectory length LVOS and an upstream air-fuel ratio sensor output trajectory length LVOM per predetermined time, and a downstream air-fuel ratio sensor output per predetermined time and a reference value. The deterioration of the three-way catalyst is determined using the relationship of the ratio AVOS / AVOM of the enclosed area AVOS, the upstream air-fuel ratio sensor output, and the area AVOM enclosed by the reference value (see, for example, Patent Document 5). ).

Even in the above-described determination of catalyst deterioration, the exhaust transportation speed and the gas hit to the air-fuel ratio sensor differ between the all-cylinder operation and the reduced-cylinder operation. If the catalyst deterioration determination is performed under the same conditions, it may cause an erroneous determination. Further, even in the reduced-cylinder operation, the exhaust transport speed and the gas hit to the air-fuel ratio sensor differ depending on the number and combination of the operating cylinders, which may cause an erroneous determination in the catalyst deterioration determination under the same conditions.
JP-A-52-61636 JP 2002-206437 A JP 54-57009 A Japanese Patent Laid-Open No. 07-133730 Japanese Patent Application Laid-Open No. 07-34860 Japanese Patent Laid-Open No. 03-111633 Japanese Patent Laid-Open No. 04-60135 Japanese Patent Laid-Open No. 08-284727 JP 2001-115865 A

  The present invention has been made in view of the above-mentioned drawbacks of the prior art, and the object of the present invention is to make it possible to achieve the best emission characteristics for both full-cylinder operation and reduced-cylinder operation. Is to provide.

In order to achieve the above object, the present invention provides a variable cylinder system for an internal combustion engine in which control is performed so as to change the feedback gain of air-fuel ratio feedback control during so-called reduced cylinder operation and during all cylinder operation. Control is performed to change the air-fuel ratio feedback gain in accordance with the number of operating cylinders in operation and the combination of the operating cylinders.

In the present invention, the internal combustion engine having a plurality of cylinders and the fuel supply to some cylinders among the plurality of cylinders are shut off according to the operating conditions of the internal combustion engine to deactivate the some cylinders. Cylinder deactivation control means for operating the remaining cylinders, and air-fuel ratio feedback control for detecting the air-fuel ratio of the engine and performing feedback control so that the air-fuel ratio of the engine becomes the target air-fuel ratio according to the detected air-fuel ratio of the engine And the feedback control, the cylinder deactivation control unit changes the feedback gain between the reduced cylinder operation in which some cylinders are deactivated and the remaining cylinders are activated, and in the all cylinder operation in which all cylinders are activated. Air-fuel ratio feedback gain changing means for controlling as described above.

  That is, since the exhaust gas transport speed and the gas hit to the air-fuel ratio sensor are different between the reduced cylinder operation and the all cylinder operation, the control gain for optimizing the emission is also different. Therefore, the feedback gain of the air-fuel ratio feedback control is changed between the reduced-cylinder operation and the all-cylinder operation, and the feedback gain that can optimize the emission for each state is adopted.

  As a result, the best emission characteristics can be realized in both the reduced-cylinder operation and the all-cylinder operation.

  Further, the air-fuel ratio feedback gain changing means controls to change the feedback gain according to the number of operating cylinders during the reduced cylinder operation.

  In reduced-cylinder operation, the number of operating cylinders may be varied in order to prevent rotation balance as a whole engine and balance over time, but in such a case, the number of operating cylinders is reduced. Accordingly, since the exhaust gas transport speed and the gas per hit to the air-fuel ratio sensor differ, the feedback gain of the air-fuel ratio feedback control is changed according to the number of operating cylinders.

  This makes it possible to perform good air-fuel ratio feedback control in any number of operating cylinder reduction operations, and as a result, good emission characteristics can be obtained.

  The air-fuel ratio feedback gain changing means controls to change the feedback gain according to the combination of operating cylinders during the reduced cylinder operation.

  As a result, in any combination pattern of operating cylinders, the optimum feedback gain is used for each pattern, so that more accurate air-fuel ratio feedback control can be performed, and good emission characteristics can be obtained.

  In the air-fuel ratio learning control of the variable cylinder system of the internal combustion engine, the present invention employs different air-fuel ratio learning values during so-called reduced cylinder operation and during all cylinder operation, and further, the number of operating cylinders during reduced cylinder operation, Different air-fuel ratio learning values are employed depending on the combination of operating cylinders.

  In the present invention, the internal combustion engine having a plurality of cylinders, and the fuel supply to some cylinders among the plurality of cylinders are shut off according to the operating conditions of the internal combustion engines, and the some cylinders are deactivated. A cylinder deactivation control means for operating the remaining cylinders, and a feedback correction amount generating means for detecting the air-fuel ratio of the engine and generating a feedback correction amount for feedback-controlling the detected air-fuel ratio of the engine to the target air-fuel ratio And the engine air-fuel ratio of the engine subjected to feedback control in accordance with the operating state of the engine including whether or not the engine is in a reduced-cylinder operation in which at least the cylinder deactivation control unit deactivates some cylinders and activates the remaining cylinders. And an air-fuel ratio learning value setting means for setting an air-fuel ratio learning value for correcting a deviation between the target air-fuel ratio and at least the feedback correction amount and the air-fuel ratio learning value. Fuel injection amount determination means for determining an injection amount; and air-fuel ratio learning value update means for updating the air-fuel ratio learning value so as to reduce a deviation between the air-fuel ratio feedback correction amount and its reference value. It is characterized by.

  That is, when air-fuel ratio feedback control is performed, for example, variations in fuel system components such as the air flow meter 44 and the fuel injection valve 32, changes over time, non-linearity of the fuel injection valve 32, changes in operating conditions and environment, etc. Air-fuel ratio learning control is executed to sequentially update the air-fuel ratio learning value for correcting the air-fuel ratio feedback correction amount so as to reduce the deviation of the air-fuel ratio in order to correct the influence of the fluctuation of the air-fuel ratio determining factor. Even in such a case, the air-fuel ratio learning value that can optimally correct the air-fuel ratio feedback correction amount is different between the reduced-cylinder operation and the all-cylinder operation.

  Therefore, different values are used as the air-fuel ratio learning value in the air-fuel ratio learning control during the reduced-cylinder operation and during the all-cylinder operation, and the air-fuel ratio learning value that can optimize the emission for each state is adopted. It is.

  As a result, the best emission characteristics can be realized in both the reduced-cylinder operation and the all-cylinder operation.

  The air-fuel ratio learning value setting means sets an air-fuel ratio learning value according to the number of operating cylinders during the reduced-cylinder operation.

  This makes it possible to perform favorable air-fuel ratio learning control in any number of operating cylinder reduction operations, and as a result, good emission characteristics can be obtained.

  Further, the air-fuel ratio learning value setting means sets an air-fuel ratio learning value corresponding to the combination of operating cylinders during the reduced cylinder operation.

  As a result, the optimum air-fuel ratio learning value is used for each combination in any combination of operating cylinders, so that more accurate air-fuel ratio feedback control can be performed, and even better emission characteristics can be obtained.

  In the variable cylinder system of the internal combustion engine, the present invention changes the purification performance judgment value in the purification performance judgment of the exhaust purification catalyst during the so-called reduced cylinder operation and during the all cylinder operation, and further, the operating cylinder during the reduced cylinder operation The purification performance determination value is changed according to all the reduced cylinder patterns for the number of cylinders and combinations of operating cylinders.

  In the present invention, the internal combustion engine having a plurality of cylinders and the fuel supply to some cylinders among the plurality of cylinders are shut off according to the operating conditions of the internal combustion engine to deactivate the some cylinders. Cylinder deactivation control means for operating the remaining cylinders, exhaust purification means provided in the exhaust passage of the internal combustion engine, for purifying exhaust gas of the internal combustion engine, and purification performance determination for determining deterioration of the purification performance of the exhaust purification means And a cylinder deactivation control unit that cuts off fuel supply to some cylinders of the plurality of cylinders, deactivates some of the cylinders, and activates the remaining cylinders and all cylinders. And a determination value changing means for changing a purification performance determination value used when the purification performance determination means determines deterioration of the purification performance of the exhaust purification means during all cylinder operation. To do.

  In an internal combustion engine, air-fuel ratio sensors are arranged upstream and downstream of an exhaust purification catalyst, and the deterioration of the characteristics of the exhaust purification catalyst is judged by comparing the output signals of both sensors. Since the explosion interval of the internal combustion engine is different between the operation and the all-cylinder operation, the transport speed and frequency of the exhaust gas flowing into the catalyst, and the gas hit to the air-fuel ratio sensor are also different. Also changes.

Therefore, the purification performance determination value used for the purification performance determination is changed between the reduced cylinder operation and the all cylinder operation.

  This makes it possible to determine the optimal purification performance regardless of whether the cylinder reduction operation or all cylinder operation, and it is determined that the catalyst has deteriorated even though the catalyst has not deteriorated due to an erroneous determination. It is possible to eliminate problems such as determining that there is no deterioration despite deterioration, and as a result, good emission characteristics can be obtained.

  Further, the determination value changing means changes the purification performance determination value according to the number of operating cylinders during the reduced cylinder operation.

  As a result, the above-described accurate purification performance determination can be performed in any cylinder reduction operation with any number of operating cylinders.

  Further, the determination value changing means changes the purification performance determination value according to a combination of operating cylinders during a reduced cylinder operation.

  As a result, in any combination of operating cylinders, the purification performance determination value corresponding to each reduced cylinder pattern is used, so that more accurate purification performance determination is possible.

  According to the present invention, in the variable cylinder system of the internal combustion engine, the so-called reduced cylinder operation and the all cylinder operation are controlled so as to change the feedback gain of the air-fuel ratio feedback control. Although the exhaust gas transport speed and the amount of gas hitting the air-fuel ratio sensor differ from those during the cylinder operation, a feedback gain that optimizes the emission can be adopted for each state, and the best emission characteristics can be realized.

  Further, according to the present invention, in the variable cylinder system of the internal combustion engine, different air-fuel ratio learning values of the air-fuel ratio learning control are adopted during so-called reduced-cylinder operation and during all-cylinder operation. Although the exhaust gas transport speed and the gas per hit to the air-fuel ratio sensor are different between all cylinder operation, the air-fuel ratio learning value that optimizes the emission for each state can be adopted, and the best emission characteristics are realized be able to.

  Further, according to the present invention, in the variable cylinder system of the internal combustion engine, the purification performance determination value used for the purification performance determination is changed between the so-called reduced cylinder operation and the all cylinder operation. The exhaust gas transport speed and the amount of gas hitting the air-fuel ratio sensor differ from those in the all-cylinder operation, but the optimal purification performance can be judged for each state, and the purification performance of the exhaust purification catalyst deteriorates due to misjudgment. It is possible to eliminate problems such as being judged as being deteriorated despite being not, or conversely being judged as being without deterioration even though the purification performance of the exhaust purification catalyst is being deteriorated. Emission characteristics can be realized.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

(First embodiment)
1 and 2 are diagrams showing a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to the present embodiment. The internal combustion engine 1 shown in FIGS. 1 and 2 is a four-stroke cycle water-cooled gasoline engine having four cylinders 21.

  The internal combustion engine 1 includes a cylinder block 1b in which four cylinders 21 are formed, and a cylinder head 1a fixed to the upper part of the cylinder block 1b. A crankshaft 23 as an engine output shaft is rotatably supported by the cylinder block 1b. The crankshaft 23 is connected to each cylinder 21 through a connecting rod 19 and a piston 22 slidably loaded. ing.

  A timing rotor 51a having a plurality of teeth formed on the periphery is attached to the end of the crankshaft 23, and an electromagnetic pickup 51b is attached in the vicinity of the timing rotor 51a. These constitute the crank position sensor 51.

  A water temperature sensor 52 that outputs an electrical signal corresponding to the temperature of the cooling water flowing through the cooling water passage 1c is attached to the cylinder block 1b. An ignition plug 25 is attached to the cylinder head 1a, and an igniter 25a for applying a drive current to the ignition plug 25 is connected to the ignition plug 25.

  The cylinder head 1a has two open ends of the intake port 26 and two open ends of the exhaust port 27. An intake valve 28 that opens and closes each open end of the intake port 26 and an exhaust valve 29 that opens and closes each open end of the exhaust port 27 are provided so as to freely advance and retract.

  Further, an intake branch pipe 33 composed of four branch pipes is connected to the cylinder head 1 a, and each branch pipe of the intake branch pipe 33 communicates with an intake port 26 of each cylinder 21. In the cylinder head 1a, a fuel injection valve 32 is attached in the vicinity of the connection portion with the intake branch pipe 33. The intake branch pipe 33 is connected to an intake pipe 35 via a surge tank 34 for suppressing pulsation of intake air.

  The intake pipe 35 has an air flow meter 44 that outputs an electric signal corresponding to the mass of air flowing through the intake pipe 35 (intake air mass), and an intake air temperature sensor that outputs an electric signal corresponding to the temperature of the intake air. 50 is attached. A throttle valve 39 for adjusting the flow rate of the intake air flowing through the intake pipe 35 is provided in a portion of the intake pipe 35 downstream of the air flow meter 44.

  On the other hand, to the cylinder head 1a of the internal combustion engine 1, an exhaust branch pipe 45 formed so that four branch pipes merge with one collecting pipe immediately downstream of the internal combustion engine 1 is connected. This exhaust branch pipe 45 is connected to an exhaust pipe 47 via an exhaust purification catalyst 46 which is an exhaust purification means in the present embodiment. The exhaust branch pipe 45 is attached with an air-fuel ratio sensor 48 that outputs an electric signal linearly corresponding to the exhaust gas flowing through the exhaust branch pipe 45, in other words, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 46. ing.

  Here, as the above-described exhaust purification catalyst 46, when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 48 is a predetermined air-fuel ratio in the vicinity of the theoretical air-fuel ratio, hydrocarbons (HC) contained in the exhaust, one A three-way catalyst for purifying carbon oxide (CO) and nitrogen oxide (NOx) is used.

  Instead of this three-way catalyst, an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, or a catalyst formed by appropriately combining the above-mentioned various catalysts may be used. The detailed explanation is omitted.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 for controlling the operating state of the internal combustion engine 1. Various sensors such as an air flow meter 44, an air-fuel ratio sensor 48, an intake air temperature sensor 50, a crank position sensor 51, and a water temperature sensor 52 are connected to the ECU 20 via electric wiring, and output signals of the sensors are input to the ECU 20. It has become so.

  The ECU 20 is connected to an igniter 25a, a fuel injection valve 32, and the like via electrical wiring, and the ECU 20 can control the igniter 25a, the fuel injection valve 32, and the like using output signal values of various sensors as parameters. Yes.

  Here, as shown in FIG. 3, the ECU 20 includes a CPU 401, a ROM 402, a RAM 403, a backup RAM 404, an input port 405, and an output port 406 that are connected to each other via a bidirectional bus 400. A connected A / D converter (A / D) 407 is provided.

  The A / D 407 is connected to sensors such as an air flow meter 44, an air-fuel ratio sensor 48, an intake air temperature sensor 50, a water temperature sensor 52, and the like that output signals in an analog signal format through electric wiring. The A / D 407 converts the output signal of each sensor described above from an analog signal format to a digital signal format, and transmits the converted signal to the input port 405.

  The input port 405 is connected via the A / D 407 to a sensor that outputs an analog signal format signal such as the air flow meter 44, the air-fuel ratio sensor 48, the intake air temperature sensor 50, the water temperature sensor 52, and the like. At the same time, it is connected to a sensor that outputs a digital signal format signal, such as a crank position sensor 51.

  The input port 405 inputs output signals of various sensors directly or via the A / D 407 and transmits these output signals to the CPU 401 and the RAM 403 via the bidirectional bus 400.

  The output port 406 is connected to the igniter 25a, the fuel injection valve 32, and the like through electrical wiring. The output port 406 receives a control signal output from the CPU 401 via the bidirectional bus 400, and transmits the control signal to the igniter 25a, the fuel injection valve 32, and the like.

  The ROM 402 is a fuel injection amount control routine for determining the fuel injection amount, an ignition timing control routine for determining the ignition timing of the spark plug 25 of each cylinder 21, and a variable for changing the operating cylinder of the internal combustion engine 1. In addition to the application program such as the cylinder control routine, the cylinder air amount estimation and target fuel amount calculation routine, the main air-fuel ratio feedback control routine, the fuel injection control routine, the gain determination routine, and the like according to the present embodiment are stored. .

  The ROM 402 stores various control maps in addition to the application programs described above. The above-described control map is, for example, a fuel injection amount control map that indicates the relationship between the operating state of the internal combustion engine 1 and the fuel injection amount, and an ignition timing that indicates the relationship between the operating state of the internal combustion engine 1 and the ignition timing of each spark plug 25. In addition to a control map, an active cylinder number control map showing the relationship between the operating state of the internal combustion engine 1 and the active cylinders, etc., an air-fuel ratio sensor output conversion map, a gain basic value setting map, a gain determination map, etc. according to the present embodiment It is.

  The RAM 403 stores output signals of the sensors, calculation results of the CPU 401, and the like. The calculation result is, for example, the engine speed calculated based on the output signal of the crank position sensor 51. Various data stored in the RAM 403 is rewritten to the latest data every time the crank position sensor 51 outputs a signal.

  The backup RAM 404 is a non-volatile memory that retains data even after the operation of the internal combustion engine 1 is stopped. The backup RAM 404 stores learning values related to various controls, information for specifying a location where an abnormality has occurred, and the like.

  The CPU 401 operates in accordance with an application program stored in the ROM 402, and executes air-fuel ratio feedback control, which is a gist of the present invention, in addition to well-known controls such as fuel injection control and variable cylinder control.

  In the variable cylinder control, the CPU 401 changes the number of operating cylinders according to the operating state of the internal combustion engine 1. For example, when the operation state of the internal combustion engine 1 is in the low load operation region, the CPU 401 reduces the number of operating cylinders to reduce the internal combustion engine 1 and the internal combustion engine operation state is in the medium and high load operation region. Operates all cylinders 21 and operates the internal combustion engine 1 in all cylinders.

  Specifically, when each engine operation information is read, for example, if it is determined that the engine speed falls below a predetermined speed and is in the middle / low load operating range and is running at a low speed, the reduced-cylinder operation starts. Then, the reduced cylinder operation flag is set to 1.

  In the ECU 20, the CPU 401 reads the above-described variable cylinder control routine from the ROM 402 and executes it. At this time, the ECU 20 stops fuel injection to the cylinder 21 to be deactivated, and further sends a control signal to an electromagnetic valve of a valve stop mechanism (not shown) to close the intake valve 28 and the exhaust valve 29. When the condition of the reduced cylinder operation is not satisfied, the reduced cylinder operation is canceled, the reduced cylinder operation flag is reset to 0, and the entire cylinder operation is resumed.

  Therefore, in the present embodiment, the cylinder deactivation control means includes the ECU 20 including the ROM 402 storing the variable cylinder control routine and the operating cylinder number control map.

  In the following, in order to describe the air-fuel ratio feedback control according to the first embodiment in detail, the procedure of the related processing routine is sequentially shown.

FIG. 4 is a flowchart showing the processing procedure of the cylinder air amount estimation and target fuel amount calculation routine according to the present embodiment. This routine is executed for each predetermined crank angle. First, in S401, the in-cylinder air amount MC _i and the target in-cylinder fuel amount FCR _i obtained by the previous travel of this routine are updated.

That is, MC _i and FCR _i before i (i = 0, 1,..., N−1) times are MC _{i + 1} and FCR _{i + 1} before “i + 1” times. This is because the data of the cylinder air amount MC _i and the target cylinder fuel amount FCR _i for the past n times are stored in the RAM 403, and MC ₀ and FCR ₀ are newly calculated this time.

Next, in S402, the current intake air flow rate GA and engine rotational speed NE are obtained from a predetermined area of the RAM 403. Then, at S403, these GA, from the data of the NE, estimates the cylinder air amount MC ₀ supplied to the cylinder. Here, the values of GE and NE are obtained based on the output signals of the air flow meter 44 and the crank position sensor 51.

Next, in S404, based on the in-cylinder air amount MC ₀ and the stoichiometric air-fuel ratio AFT, the calculation FCR ₀ ← MC ₀ / AFT is executed, and the target to be supplied into the cylinder in order to make the air-fuel mixture stoichiometric. A fuel amount FCR ₀ is calculated. The in-cylinder air amount MC ₀ and the target fuel amount FCR ₀ calculated in this way are stored in the RAM 403 as the latest data obtained this time.

  FIG. 5 is a flowchart showing the processing procedure of the main air-fuel ratio feedback control routine. This routine is executed for each predetermined crank angle. First, in S501, it is determined whether a condition for executing feedback is satisfied.

  For example, when the coolant temperature detected by the water temperature sensor 52 is lower than a predetermined value, when the engine is started, when there is no change in the output signal of the air-fuel ratio sensor 48, when the fuel is cut, etc., the feedback condition is not satisfied. In this case, the condition is satisfied. When the condition is not satisfied, the fuel correction amount DF by feedback control is set to 0 in S507, and this routine is terminated.

When satisfied feedback condition, in S502, (the deviation between the actual cylinder fuel amount and the target cylinder fuel amount) fuel deviation is obtained by the running up to the previous routine to update the FD _i. That is, the FD _i before the i-th (i = 0, 1,..., M−1) times is set as the FD _{i + 1} before the “i + 1” -th time. This is because the fuel amount difference FD _i for the past m times is stored in the RAM 403 and the fuel deviation FD ₀ is newly calculated this time.

  Next, in S503, the output voltage value VAF of the air-fuel ratio sensor 48 is detected. In step S504, the current air-fuel ratio ABF is determined based on the output voltage value VAF and the air-fuel ratio sensor output conversion map for obtaining the actual air-fuel ratio from the VAF stored in the ROM 402.

Next, in S505, already on the basis of the cylinder air amount MC _n and target cylinder fuel amount FCR _n is calculated by the cylinder air amount estimation and target cylinder fuel amount calculation routine, FD ₀ ← MC _n / ABF- the FCR _n becomes operational, actually obtains the deviation between the amount of fuel has been burned in the cylinder i.e. actual in-cylinder fuel amount and the target cylinder fuel amount.

The reason why the in-cylinder air amount MC _n and the target in-cylinder fuel amount FCR _n are used n times in this way is that the time difference between the air-fuel ratio currently detected by the air-fuel ratio sensor 48 and the actual combustion is considered. This is because. In other words, it is necessary to store the in-cylinder air amount MC _i and the target in-cylinder fuel amount FCR _i for the past n times because of such a time difference.

Then, in S506, the _{DF ← K FP * FD 0 +} K FI * ΣFD i + K FD * (FD 0 -FD 1) becomes operational, the fuel correction amount DF by the proportional-integral-derivative control (PID control) is determined The The first term on the right side is a proportional term for PID control, and _KFP is a proportional term gain. The second term on the right side is an integral term of PID control, and _KFI is an integral term gain. The third term on the right side is the differential term of PID control, and K _FD is the differential term gain.

FIG. 6 is a flowchart showing the processing procedure of the fuel injection control routine according to the present embodiment. This routine is executed for each predetermined crank angle. First, in step S601, based on the target fuel amount FCR ₀ calculated in the above-described cylinder air amount estimation and target fuel amount calculation routine and the fuel correction amount DF calculated in the main air-fuel ratio feedback control routine, FI ← FCR _The calculation of ₀ * α + DF + β is executed to determine the fuel injection amount FI.

  Α and β are a multiplication correction coefficient and an addition correction amount determined by other operating state parameters. For example, α includes a basic correction based on signals from the respective sensors such as the intake air temperature sensor 50 and the water temperature sensor 52, and β includes a correction term obtained by other calculation or experimentally. It is out. Finally, in S602, the obtained fuel injection amount FI is set in the igniter 25a of the spark plug 25.

  Next, a gain determination routine for changing the air-fuel ratio feedback gain during the reduced-cylinder operation in the present embodiment will be described. FIG. 7 is a flowchart showing a processing procedure of a gain determination routine for specifically performing the above-described gain setting. This routine is executed at predetermined time intervals.

First, in S701, the current engine speed NE and the intake air flow rate GA are detected. Next, in S702, by dividing the GA in NE, to calculate a cylinder air amount MC ₀ as the engine load. In step S703, the proportional term gain basic value K _FPB , the integral term gain basic value K _FIB, and the derivative term gain basic value K _FDB are determined based on GN and NE and the gain basic value setting map.

Next, in S704, it is determined whether or not the engine operating state is a reduced-cylinder operation. This determination is performed by confirming the state of the reduced cylinder operation flag. If it is determined in S704 that the cylinder reduction operation is being performed, the process proceeds to S705, where the correction basic coefficient K _G for the gain basic values K _FPB , K _FIB and K _FDB is set to a predetermined value that provides the best emission characteristics during the cylinder reduction operation. Set to the value _KGA . On the other hand, when it is determined in S704 that all cylinders are in operation, the process proceeds to S706, where a predetermined value K _GB is obtained that provides the best emission characteristics during all cylinders operation.

Here, in order to determine the final feedback gain, the values of the correction coefficients K _GA and K _GB for multiplying the gain basic values K _FPB , K _FIB, and K _FDB are gain determination maps on the ROM 402. And is created on the basis of a feedback gain value required for the best emission, which is measured in advance by experiments or test running during all-cylinder operation and reduced-cylinder operation.

In the last step S707 executed after S705 or S706, the final feedback gain K is obtained by the calculation of K _FP ← K _FPB * K _G , K _FI ← K _FIB * K _G , K _FD ← K _FDB * K _G. Determine _FP , _KFI and _KFD . The feedback gains K _FP , K _FI and K _FD set in this way are used in the main air-fuel ratio feedback control routine described above.

  As described above, in the present embodiment, the air-fuel ratio feedback control means includes the ROM 402 and the CPU 401 that store the in-cylinder air amount estimation and target fuel amount calculation routine, the main air-fuel ratio feedback control routine, and the fuel injection amount control routine. The ECU 20 is configured.

  The air-fuel ratio feedback gain changing means includes an ECU 20 including a gain determination routine, a ROM 402 storing a gain determination map, and a CPU 401. Of course, the flow in the air-fuel ratio feedback control means and the air-fuel ratio feedback gain changing means is not limited to that shown above.

According to the present embodiment, in the air-fuel ratio feedback control of the internal combustion engine 1, when determining the fuel correction amount DF for calculating the fuel injection amount, K _FP , K _FI, and K that serve as control gains for PID control _FD is controlled so as to be changed between when the internal combustion engine 1 is operating with reduced cylinders and when it is operating with all cylinders.

  Therefore, even when the exhaust gas transport speed and the gas hit to the air-fuel ratio sensor 48 are different during the reduced-cylinder operation and the all-cylinder operation, the optimum air-fuel ratio feedback control can be performed in each case. The best emission characteristics can be obtained for each operating state.

(Second embodiment)
A second embodiment of the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted. Since other configurations and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.

  In reduced-cylinder operation, the number of operating cylinders may be changed in order to prevent the balance of rotation as a whole engine and the balance over time, but in this way the number of operating cylinders is changed. In this embodiment, since the exhaust gas transport speed and the amount of gas per air to the air-fuel ratio sensor 48 also change depending on the number of operating cylinders, in this embodiment, the feedback gain of the air-fuel ratio feedback control depends on the number of operating cylinders. Is changed.

  Here, the cylinder number of the cylinder to be operated is written in the operating cylinder number control map and stored in the ROM 402 together with the ignition timing and the control amount of the fuel injection amount during the reduced cylinder operation. Therefore, a data map corresponding to different numbers of operating cylinders is created in advance and stored in the ROM 402. The number of operating cylinders is switched for each predetermined event.

  That is, the number of operating cylinders is changed every time a predetermined event occurs, and the reduced cylinder operation is performed using another operating cylinder data map. For example, interrupt when 1 cylinder # 3 is an active cylinder, when 2 cylinders # 1 and # 3 are idle cylinders, and when 3 cylinders # 1, # 3 and # 4 are active cylinders It is switched by a routine.

  The above events are specifically as follows. For example, when a predetermined time has elapsed. For example, when a certain time such as one hour has elapsed since the start of the reduced-cylinder operation, the reduced-cylinder pattern is switched.

  Alternatively, it is when the internal combustion engine 1 is rotated by a predetermined rotational speed. This is to change the number of operating cylinders every time the internal combustion engine 1 rotates by a predetermined number based on information that counts a predetermined crank position signal, that is, counts up every time the crankshaft 23 makes one rotation. In addition, various examples of the above events can be given, but detailed description thereof is omitted here.

FIG. 8 is a flowchart showing the processing procedure of the gain determination routine according to the present embodiment. In S801 and S802, as in S701 and S702 of the first embodiment, the current engine speed NE and the intake air flow rate GA are detected, and by dividing GA by NE, the in-cylinder air amount as the engine load MC ₀ is calculated.

Next, in S803, as in S703 of the first embodiment, based on GN and NE and the gain basic value setting map, the proportional term gain basic value K _FPB , the integral term gain basic value K _FIB and the differential term gain basic Determine the value K _FDB . Then after it is determined whether during the reduced-cylinder operation in S804, when it is determined that the all cylinders in operation, as in the first embodiment, in S807, the correction coefficient K _G during the all-cylinder operation It is set to a predetermined value K _GB that provides the best emission characteristics.

On the other hand, when it is determined in S804 that the reduced cylinder operation is being performed, the process proceeds to S805, where the number of operating cylinders is determined. The determination of the number of operating cylinders is performed by reading out the operating cylinder number data stored in the RAM 402 described above. Then, in S806, reads the predetermined value K _GA the best emission characteristics can be obtained at each number of operating cylinders in the ROM 403, the gain determination map is set as the correction coefficient K _G.

In this case, the gain determination map storing the _KGA data for each number of operating cylinders is based on the feedback gain value required for the best emission, which is measured in advance for each number of operating cylinders through experiments or test driving. To be created.

After that, in S808, final feedback gains K _FP , K _FI, and K _FD are determined by the same calculation as in S707 shown in the first embodiment. The gains K _FP , K _FI and K _FD set in this way are used in the aforementioned main air-fuel ratio feedback control routine.

According to the present embodiment, in the air-fuel ratio feedback control of the internal combustion engine 1, when determining the fuel correction amount DF for calculating the fuel injection amount FI, K _FP , K _{FI that} serve as a feedback gain of PID control, and K _FD is changed depending on whether the internal combustion engine 1 is in the reduced cylinder operation or in the case of the all cylinder operation. When the internal combustion engine 1 is in the reduced cylinder operation, each of them is further changed according to the number of operating cylinders. In this case, the best emission characteristic is determined as a value.

  For this reason, during reduced-cylinder operation, even if the exhaust gas transport speed and the gas hit to the air-fuel ratio sensor 48 differ depending on the number of operating cylinders, optimal air-fuel ratio feedback control is possible in each case. As a result, the best emission characteristics can be obtained for each operating state.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. Here, configurations different from those of the first and second embodiments described above will be described, and description of similar configurations will be omitted. Since other configurations and operations are the same as those in the first and second embodiments, the same components are denoted by the same reference numerals and description thereof is omitted.

  FIG. 9 is a flowchart showing a processing procedure of a gain determination routine according to the third embodiment. The processing from S901 to S903 is the same as the processing from S701 to S703 and the processing from S801 to S803 described in the first and second embodiments, respectively, and thus description thereof is omitted here.

In this embodiment, the difference between the first and second embodiment, in S904, after it is determined that the cylinder cut-in operation, instead of changing the gain correction coefficient K _G the number of operating cylinders,
It is to use a gain correction coefficient K _G corresponding to a combination of operating cylinders.

  The present embodiment can also cope with a method for determining an operating cylinder in which cylinder control is performed in a well-balanced manner by changing the operating cylinder without changing the number of operating cylinders when performing the reduced cylinder operation. The cylinder number of the cylinder to be operated is written in the operating cylinder number control map and stored in the ROM 402 together with the ignition timing during the reduced cylinder operation and the control amount of the fuel injection amount.

In the present embodiment, a reduced cylinder pattern is configured for each combination of different operating cylinders,
Even if the number of operating cylinders is the same, a data map is created in advance according to each pattern and stored in the ROM 402. These reduced cylinder patterns are switched every predetermined event.

  That is, for example, a first depressurization pattern A in which two cylinders # 1 and # 3 are operating cylinders, a second depressurization pattern B in which two cylinders # 2 and # 4 are active cylinders, and # 1, # A cylinder deactivation control is performed using a map of a different cylinder reduction pattern by switching the cylinder reduction pattern every time a predetermined event occurs.

Such pattern switching discrimination is performed in an interrupt routine. In the example of the pattern shown above, all the two cylinders are active cylinders. However, the number of active cylinders includes one cylinder and three cylinders. Of course, this includes cases where the numbers are different. Note that the reduced cylinder pattern is switched to another pattern when an event similar to that described in the second embodiment occurs.

In the gain determination map in the present embodiment, in addition to the gain correction coefficient K _GB corresponding to the all cylinder operation, the gain correction coefficients K _GA1 , K _GA2, and K _GA3 corresponding to each of the above reduction cylinder patterns are used for the reduced cylinder operation. Storing.

In S904 of this embodiment, when it is determined that the all cylinders in operation, employing a predetermined value K _GB obtain the best emission characteristics as gain correction coefficient K _G in S909 includes the above embodiments Similarly, if it is determined in S904 that the reduced-cylinder operation is in progress, it is determined in S905 which reduced-cylinder pattern is being used. This determination is made, for example, by switching the pattern when the event occurs, setting a flag for the pattern, and reading the flag.

Each of the cylinders pattern A in the processing from S905 S908, selects the gain correction coefficient data K _GA1, K _GA2 or K _GA3 corresponding to B and C, is employed as the correction factor K _G. And in S909, by using the correction coefficient K _G employing above, and terminates this routine to determine the feedback gain.

In this case, the gain determination map storing the _KGA data for each cylinder pattern shows the feedback gain value required for the best emission, measured in advance by experiment or test driving for each cylinder rest pattern. Created based on.

  In the present embodiment, by adopting the flow as described above, even when the combination of operating cylinders changes during reduced-cylinder operation, the mutual influence between the cylinders, the exhaust gas transport speed, Problems such as deterioration of controllability of the air-fuel ratio control due to the difference in per-gas ratio to the fuel ratio sensor 48 can be prevented, and the best emission characteristics can always be obtained.

(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted. Since other configurations and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.

In the air-fuel ratio feedback control of the internal combustion engine according to the present embodiment, the actual engine air-fuel ratio is feedback-controlled to the theoretical air-fuel ratio AFT based on the target fuel amount FCR ₀ determined from the operation state parameter of the internal combustion engine 1. The control is performed by correcting with the feedback correction coefficient FAF and determining the fuel injection amount FI so as to obtain the optimum efficiency and exhaust conditions according to the engine operating state.

  In the present embodiment, unlike the first, second, and third embodiments, the air-fuel ratio sensor 48 in front of the exhaust purification device does not output a linear signal with respect to the oxygen concentration, but exhaust air is exhausted. A sensor having a so-called Z characteristic for detecting whether the fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio is used. Further, the difference is that control is performed using a variable called a feedback correction coefficient FAF in place of the fuel correction amount DF.

  In addition, the greatest difference between the air-fuel ratio feedback control in the present embodiment and the first, second and third embodiments is as follows.

  With regard to air-fuel ratio feedback control, in an actual engine, for example, due to various factors such as manufacturing variations and aging of the air flow meter 44, spark plug 25, etc., non-linearity of the spark plug 25, operating conditions, and environmental changes. As a result, the control air-fuel ratio deviates from the stoichiometric air-fuel ratio, so that the controllability of the air-fuel ratio control is lowered and the engine efficiency and the exhaust conditions are deteriorated.

  Therefore, the correction coefficient for correcting the deviation between the control air-fuel ratio and the theoretical air-fuel ratio during the air-fuel ratio feedback control is stored as the air-fuel ratio learning correction amount KGX together with the operation state at that time, and the same operation state is obtained. The air-fuel ratio learning correction amount KGX stored at the time may be used to perform air-fuel ratio learning control that improves the responsiveness of the air-fuel ratio control.

  FIG. 10 is a graph showing an example of the value of the air-fuel ratio learning correction amount KGX in the present embodiment. Here, the engine operating state is divided into regions based on the intake air flow rate GA, and the air-fuel ratio learning correction amount KGXj is set and stored for each region KGj.

Furthermore, in the present embodiment, there are two types of graphs of the air-fuel ratio learning correction amount KGXj, one used during reduced cylinder operation and one used during all cylinder operation. The air-fuel ratio learning correction amount KGX in each of these regions is updated by obtaining an average value of deviations from the reference value of the operation region in the actual engine operating state and the feedback correction coefficient FAF at that time in a predetermined time or cycle. The

FIG. 11 is a flowchart of an FI calculation routine that is a main routine of fuel injection control executed by the ECU 20, and is executed at regular time intervals or at predetermined crank angle timings.
First, in S1101, various increase factors FW such as the target fuel amount FCR ₀ and the increase during warm-up are calculated.

  Next, in S1102, whether or not the feedback control condition is satisfied is determined based on, for example, whether a certain period of time has elapsed after startup, whether the engine has been warmed up, or whether fuel is being cut. If the feedback control condition is satisfied, the process proceeds to S1103, and it is determined whether or not the air-fuel ratio is rich. When rich (Y), the FAF is decreased by a certain amount (KFAF) in S1105, and when lean (N), the FAF is increased by a certain amount in S1106. Subsequently, update control of an air-fuel ratio learning correction amount KGX, which will be described later, is executed in the air-fuel ratio learning subroutine of S1107.

  After that, or when it is determined in S1102 that the feedback control condition is not satisfied, the above procedure is skipped, and after FAF = 1 is set in S1104, the intake air flow rate GA currently used by the engine is set in S1108. Is determined in which air-fuel ratio learning region KGj (j is a region number shown in FIG. 10), and in S1109, the reduced-cylinder operation flag is checked to determine whether the internal combustion engine 1 is in reduced-cylinder operation. Determine if the cylinder is in operation.

  In the processes from S1110 to S1111, when the reduced-cylinder operation is in progress, it corresponds to the air-fuel ratio learning region obtained in S1108 from the air-fuel ratio learning correction amount graph (A) for reduced-cylinder operation shown in FIG. If the air-fuel ratio learning correction amount KGXA is in the all-cylinder operation, the air-fuel ratio learning correction amount KGXB corresponding to the air-fuel ratio learning region is adopted as the value of KGX from the air-fuel ratio learning correction amount graph (B).

Next, in S1112, the fuel injection amount FI is calculated by reflecting the target fuel amount FCR ₀ , the increase coefficient FW, the feedback correction coefficient FAF, and the air-fuel ratio learning correction amount KGX. Finally, in S1113, the determined fuel injection amount FI is used as the igniter 25a of the spark plug 25.
Set to.

  Next, the air-fuel ratio learning subroutine performed in S1107 will be described. FIG. 12 is a flowchart showing an air-fuel ratio learning routine for updating the air-fuel ratio learning correction amount KGX in the present embodiment, which is executed according to a command from the FI calculation routine of FIG. First, in S1201, the region number tj of the currently used air-fuel ratio learning region KGj is calculated. Next, in S1202, the value of the reduced-cylinder operation flag is confirmed. Get information.

  In S1203, has the number of operating cylinders changed since the previous execution? That is, it is determined whether the operating state has changed from reduced-cylinder operation to all-cylinder operation or from all-cylinder operation to reduced-cylinder operation. If the number of operating cylinders has changed, the process proceeds to S1206, and if not, the process proceeds to S1204. In step S1204, it is determined whether the air-fuel ratio learning region has changed since the previous execution, that is, whether j ≠ tj.

  If it has changed here, the process proceeds to S1205, the learning area number tj is updated, the skip count CSKIP is cleared in S1206, and the process ends. On the other hand, if the air-fuel ratio learning region is the same in S1204, the process proceeds to S1207, and it is determined whether it is the skip timing of the air-fuel ratio feedback control. If NO (N), the process ends. If YES (Y), the process proceeds to S1208.

In S1208, an average value FAFAV between the FAF value immediately before the previous skip (FAF ₀ ) and the FAF value immediately before the current skip is calculated. Next, in S1209, the skip count CSKIP is incremented, that is, incremented, and in S1210, for example, it is determined whether CSKIP ≧ 3, that is, whether the engine operating state remains in the learning region for a predetermined time or more.

  If it is determined that it has not stayed for a predetermined time or more, the process is terminated. In S1211, if the reduced cylinder operation flag at S1202 is 1, that is, if it is determined that the reduced cylinder operation is being performed at S1202, the process proceeds to S1212, and if it is determined that all the cylinders are being operated, the process proceeds to S1216. .

  In each case, in S1212 and S1213 or S1216 and S1217, it is determined whether the FAFAV is shifted more than 2% vertically (FAFAV> 1.02? Or FAFAV <0.98?). If it is less than -2%, in S1214 or S1218, the air-fuel ratio learning value KGXA is set for a reduced cylinder operation, and KGXB is set for a small amount of a constant value, for example 0.2%, for all cylinder operation. Update minus.

  Similarly, if the FAFAV deviation is larger than + 2%, in S1215 or S1219, the air-fuel ratio learning value KGXA is set for a reduced cylinder operation, and KGXB is set to a small fixed value, for example 0.2, for all cylinder operation. Update with a percentage plus and finish. In the present embodiment, the feedback correction amount generating means is configured to include the ECU 20 including the ROM 402 that stores the processing of S1103 to S1106 of the FI calculation routine for determining the feedback correction coefficient FAF.

  The air-fuel ratio learning value setting means includes an ECU 20 having a ROM 402 that stores the processing of S1109 to S1111 of the FI calculation routine for setting the air-fuel ratio learning correction amount KGX that is the air-fuel ratio learning value. The fuel injection amount determination means includes an ECU 20 that includes a ROM 402 that stores an FI calculation routine.

  The air-fuel ratio learning value update means includes an ECU 20 that includes a ROM 402 that stores an air-fuel ratio learning routine. Of course, the flow in the feedback correction amount generation means, the air-fuel ratio learning value setting means, the fuel injection amount determination means, the air-fuel ratio learning value update means, etc. is not limited to the above.

  According to the present embodiment, in the air-fuel ratio learning control, different air-fuel ratio learning correction amounts are adopted from the graph of FIG. 10 during the reduced-cylinder operation and during the all-cylinder operation. The data stored in the air-fuel ratio learning correction amount map is read as separate data for the cylinder operation and the all cylinder operation, and is set as the value of KGX.

  Accordingly, in the calculation of the fuel injection amount FI in the FI calculation routine, the optimum fuel injection amount FI can be calculated in each case by using the value of KGX properly depending on whether the cylinder reduction operation or the all cylinder operation is in progress. it can. Further, when the air-fuel ratio learning correction amount is updated in the air-fuel ratio learning routine, it is distinguished whether the reduced-cylinder operation or all-cylinder operation, and the air-fuel ratio learning correction amount is updated in each case. In the case of operation, the optimum value can always be set for both the case of all-cylinder operation.

  As a result, even if the exhaust gas transport speed and the gas hit to the air-fuel ratio sensor 48 are different during the reduced-cylinder operation and the all-cylinder operation, optimum air-fuel ratio feedback control can be performed in each case. The best emission characteristics can be obtained for the operating conditions.

  In the present embodiment, the case is divided depending on whether the cylinder reduction operation is being performed or the operation of all cylinders, and different air-fuel ratio learning correction amounts are used. In some cases, different air-fuel ratio learning correction amounts may be used for each number of operating cylinders. Furthermore, another air-fuel ratio learning correction amount may be used for each cylinder reduction pattern in the cylinder reduction operation.

  As a result, the air-fuel ratio learning control is accurately performed even when the exhaust gas transport speed and the gas hitting to the air-fuel ratio sensor 48 slightly differ depending on the number of operating cylinders during the reduced cylinder operation and the combination of the operating cylinders. It is possible to perform air-fuel ratio feedback control that is optimal for each case. As a result, the best emission characteristics can be obtained for each state.

(Fifth embodiment)
A fifth embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted. Since other configurations and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.

  In the present embodiment, a case will be described in which the purification performance determination of the exhaust purification catalyst 46 is performed using different purification performance determination values for the reduced-cylinder operation and for the all-cylinder operation. In the present embodiment, as shown in FIG. 13, in addition to the air-fuel ratio sensor 48 disposed on the upstream side of the exhaust purification catalyst 46, which is an exhaust purification means, an air-fuel ratio sensor 49 is provided on the downstream side of the exhaust purification catalyst 46. And the deterioration of the characteristics of the exhaust purification catalyst 46 is determined by comparing the output signals of both sensors.

However, since the explosion interval of the internal combustion engine differs between the reduced-cylinder operation and the all-cylinder operation, the transport speed, timing, and frequency of the exhaust gas flowing into the exhaust purification catalyst 46, and the gas per hit to the air-fuel ratio sensors 48 and 49 In contrast, the output values of the air-fuel ratio sensors 48 and 49 are also changed. Therefore, the purification performance determination value used for the purification performance determination is changed between the reduced cylinder operation and the all cylinder operation.

  In the present embodiment, the ratio LVOS / LVOM between the output trajectory length LVOS of the downstream air-fuel ratio sensor 49 per predetermined time and the output trajectory length LVOM of the upstream air-fuel ratio sensor 48 and the downstream air-fuel ratio per predetermined time. Three as the exhaust purification catalyst 46 using the relationship between the ratio AVOS / AVOM of the area AVOS surrounded by the output of the sensor 49 and the reference value and the area AVOM surrounded by the output of the upstream air-fuel ratio sensor 48 and the reference value. Determine the purification performance deterioration of the original catalyst.

  That is, when the exhaust purification catalyst 46 is normal, the air-fuel ratio obtained by the upstream air-fuel ratio sensor 48 of the exhaust purification catalyst 46 is made rich and lean by feedback control because of the air-fuel ratio storage effect of the exhaust purification catalyst 46. The air-fuel ratio obtained from the exhaust gas that has passed through the exhaust purification catalyst 46 is maintained in the vicinity of the theoretical air-fuel ratio, so that the downstream-side air-fuel ratio sensor 49 is compared with the output of the upstream-side air-fuel ratio sensor 48. There is little change in output.

  Further, when the purification performance of the exhaust purification catalyst 46 is deteriorated, the air-fuel ratio storage effect of the exhaust purification catalyst 46 is reduced, so that the air-fuel ratio obtained downstream of the exhaust purification catalyst 46 is obtained upstream of the exhaust purification catalyst 46. The output of the downstream air-fuel ratio sensor 49 changes in the same manner as the output of the upstream air-fuel ratio sensor 48. Based on these principles, the exhaust purification catalyst 46 has a relation LVOS / LVOM between the output trajectory length LVOS of the downstream air-fuel ratio sensor 49 and the output trajectory length LVOM of the upstream air-fuel ratio sensor 48 per predetermined time. The deterioration of the purification performance is determined.

  Further, in this embodiment, in order to prevent erroneous determination due to deterioration of the air-fuel ratio sensor 48 or 49, in addition to the locus length ratio, the area AVOS surrounded by the output of the downstream air-fuel ratio sensor 49 and the reference value and the upstream side The deterioration of the exhaust purification catalyst 46 is determined using the ratio AVOS / AVOM of the area AVOM surrounded by the output of the air-fuel ratio sensor 48 and the reference value. Since this determination method is already a known technique, a detailed description thereof will be omitted.

  FIG. 14 shows a calculation routine of the locus lengths LVOS and LVOM and the areas AVOS and AVOM. It is executed for each predetermined signal of the crank position sensor 51, that is, for each predetermined crank angle. When the routine starts in FIG. 14, it is determined in S1401 whether or not the conditions for executing the calculation of the locus length and the area are satisfied. This calculation execution condition is determined whether air-fuel ratio feedback control is being performed, whether the engine load is equal to or greater than a predetermined value, and the like.

Here, the calculation execution condition that the engine load is equal to or greater than a predetermined value is that when the engine load is low, the temperature of the exhaust purification catalyst 46 is lowered and the activity of the exhaust purification catalyst 46 is lowered. However, it is because there is a possibility that it is determined to be deteriorated. Whether or not the engine load is greater than or equal to a predetermined value is determined, for example, based on whether or not the intake air amount MC ₀ per engine revolution is greater than or equal to a predetermined value, whether or not the accelerator opening is greater than or equal to a predetermined value.

  If it is determined in S1401 that the calculation execution condition is not satisfied, the routine is terminated without calculating the trajectory length and area. If it is determined in S1401 that the conditions for calculating the locus length and the area are satisfied, the locus length LVOM and the area AVOM of the output of the upstream air-fuel ratio sensor 48 are calculated in S1402.

  In the present embodiment, both the upstream air-fuel ratio sensor 48 and the downstream air-fuel ratio sensor 49 are configured to output a linear signal with respect to the oxygen concentration.

Here, LVOM and AVOM are defined by the following equations.
LVOM = LVOM + | VOM−VOM _i−1 |, AVOM = AVOM + | VOM−V _R1
|, Where the subscript i-1 indicates the value when the previous routine was executed. V _R1 is a reference voltage for the output VOM of the upstream air-fuel ratio sensor 48, and may be, for example, V _R1 = 0 (GND level).

Next, in S1403, similarly, the locus length LVOS and the area AVOS of the output VOS of the downstream side air-fuel ratio sensor 49 are calculated by the following equations.
LVOS = LVOS + | VOS−VOS _i−1 |, AVOS = AVOS + | VOS−V _R2 |, where the subscript i−1 indicates a value when the previous routine is executed. V _R2 is a reference voltage for the output VOS of the downstream side air-fuel ratio sensor 49, and may be, for example, V _R2 = 0 (GND level). Next, in S1404, the values of VOM _i-1 and VOS _i-1 are updated in preparation for the next execution.

  By this routine, the variable LVOM, LVOS, AVOM, AVOS stores the integrated values of the locus length and area of the outputs of the upstream air-fuel ratio sensor 48 and the downstream air-fuel ratio sensor 49 each time the calculation execution condition is satisfied. .

  Next, FIG. 15 shows a purification performance determination routine using the locus length and area calculated above. It is executed for each predetermined signal of the crank position sensor 51, that is, for each predetermined crank angle, but is executed at a longer time interval than the routine shown in FIG.

  When the purification performance determination routine starts in FIG. 15, it is determined in S1501 whether or not the purification performance determination execution condition is satisfied. The purification performance determination execution conditions are the same as the calculation execution conditions shown in FIG. 14, such as whether air-fuel ratio feedback control is being performed, whether the engine load is equal to or greater than a predetermined value, and the like.

  If the execution condition of S1501 is not satisfied, the counter C20 is reset (= “0”) in S1506, and the routine is terminated without detecting deterioration. If the condition of S1501 is satisfied, the process proceeds to S1502, the counter C20 is incremented by 1, and it is determined in S1503 whether the value of the counter C20 is equal to or greater than a predetermined value CN.

  Here, the counter C20 is a count value of the number of routine executions after the purification performance determination execution condition (S1501) is established, and the predetermined value CN is the number of routine executions corresponding to 20 seconds. If it is determined in S1503 that C20 <CN, the routine is terminated without performing the purification performance determination. That is, in the present embodiment, the purification performance determination is executed when the integration of the time when the purification performance determination execution condition is satisfied reaches 20 seconds.

  If it is determined in S1503 that the condition for executing the purification performance determination execution condition is 20 seconds or longer, the purification performance determination is performed after C20 is reset in S1504. That is, in S1505, the trajectory length ratio LVOS / LVOM is calculated using LVOS and LVOM obtained in the trajectory length and area calculation routine of FIG. 14, and stored as LRATIO.

  Next, proceeding to FIG. 16, in S1606, the area ratio AVOS / AVOM is calculated using AVOS and AVOM obtained in the locus length and area calculation routine of FIG. 14, and stored as ARATIO.

In the processing from S1607 to S1613, an operation for determining whether or not the purification performance of the exhaust purification catalyst has deteriorated is shown. In the present embodiment, deterioration of the purification performance of the exhaust purification catalyst is determined based on FIG. 17 from the relationship between the locus length ratio LRATIO and the area ratio ARATIO. The hatched area in FIG. 17 is an area where it is determined that the purification performance of the exhaust purification catalyst has deteriorated. That is, when the trajectory length ratio LRATIO is equal to or smaller than the predetermined value L1, it is determined that the purification performance of the exhaust purification catalyst is sound regardless of the value of the area ratio ARATIO.

  This is because, when the purification performance of the exhaust purification catalyst is not deteriorated, the trajectory length ratio LRATIO is small regardless of whether the air-fuel ratio sensor 48 or 49 is deteriorated. Therefore, when the LRATIO is less than a predetermined value, the area ratio This is to prevent the new exhaust purification catalyst 46 from being deteriorated during steady operation.

  Here, the predetermined value L1 varies depending on the type of the exhaust purification catalyst. For example, a value of about L1 = 0.7 is set as L1. If LRATIO ≧ L1, it is determined whether or not the relationship between the area ratio ARATIO and the trajectory length ratio LRATIO is below the inclined portion of the determination line in FIG. Here, the determination line inclined portion in FIG. 17 is a straight line represented by LRATIO = (ARATIO) × A1. A1 is a predetermined constant, and is conventionally set to a value such as 0.8 because the determination line is determined based on the state during transient operation.

  In the present embodiment, the ROM 402 stores various types of values corresponding to whether the reduced-cylinder operation or the all-cylinder operation as L1 and A1 that are the purification performance determination values of the exhaust purification catalyst 46. Here, L1A and A1A are numerical values stored as values used for the purification performance determination during the reduced-cylinder operation, and L1B and A1B are numerical values stored as values used for the purification performance determination during the all-cylinder operation.

  Note that the values of L1A, A1A, L1B, and A1B are created based on the purification performance deterioration data of the exhaust purification unit 46 measured in advance by experiments in each of the reduced-cylinder operation and the all-cylinder operation.

  In the purification performance determination routine, in S1607, it is determined whether or not the reduced cylinder operation is being performed. If it is determined that the reduced-cylinder operation is in progress, the process proceeds to S1608, where L1A and A1A are read from the ROM 402 and stored as the values of L1 and A1, respectively. If it is determined in S1607 that all cylinders are in operation, the process proceeds to S1609, where L1B and A1B are read from the ROM 402 and stored as the values of L1 and A1, respectively.

Next, in S1610, the value of LRATIO is compared with the value of L1. If it is determined that L1 is larger, it is determined that the purification performance of the exhaust purification catalyst 46 has not deteriorated, the process proceeds to S1613, and ALM is reset to zero.

  If it is determined in S1610 that LRATIO is larger, the process proceeds to S1611 and the value of LRATIO is compared with the value obtained by multiplying A1 and ARATIO. Here, if it is determined that the value obtained by multiplying A1 and ARATIO is larger, as described above, it is determined that the purification performance of the exhaust purification catalyst 46 has not deteriorated, so in S1613, ALM is reset to zero.

  In this embodiment, the purification performance is determined by S1610 and 1611. However, a map of LRATIO and ARATIO corresponding to the shaded portion in FIG. The purification performance may be determined by determining whether or not the value corresponds to the shaded portion in FIG.

  If it is determined in S1610 and 1611 that the purification performance of the exhaust purification catalyst 46 has deteriorated, the alarm flag ALM is set (= “1”) in S1612. At this time, an alarm lamp (not shown) may be turned on at the same time to notify the driver of catalyst deterioration.

Next, after the above processing is completed, the value of the alarm flag ALM is stored in the backup RAM 404 as repair inspection data in S1614, and all parameters such as VOM _, VOS _, etc. are prepared in preparation for the next purification performance determination in S1615. Clear and exit the routine.

  As described above, in the present embodiment, the purification performance determination means includes the ECU 20 including the ROM 402 storing the locus length, the area calculation routine, and the purification performance determination routine, and the CPU 401. Further, the determination value changing means includes the ECU 20 including the ROM 402 and the CPU 401 that store the processes of the purification performance determination routine, particularly S1607 to S1609.

  Needless to say, the flow in the purification performance determination means and the determination value change means is not limited to the above.

  According to the present embodiment, in S1607 of the purification performance determination routine, it is determined whether the reduced-cylinder operation or all-cylinder operation is in progress, and the values corresponding to the respective operation states are adopted as L1 and A1, and then the purification performance. Since the determination is performed, there is a problem that an erroneous determination is made due to a difference in the exhaust gas transport speed, timing and frequency at the time of reduced-cylinder operation and all-cylinder operation, and a difference in gas per shot to the air-fuel ratio sensors 48 and 49. As a result, the best emission characteristics can be obtained regardless of the reduced cylinder operation or all cylinder operation.

  In this embodiment, depending on whether the reduced cylinder operation or the all cylinder operation is performed, different purification performance determination values L1 and A1 are used. However, the purification performance determination value L1A during the reduced cylinder operation, A1A may be classified in more detail, and another purification performance determination value may be used for each number of operating cylinders.

  FIG. 18 shows processing that should be substituted for the processing from S1607 to S1609 in the flow in FIG. 16 when another purification performance determination value is used for each number of operating cylinders. In FIG. 18, if it is determined in S1801 that all cylinders are in operation, the process proceeds to S1802 and the same processing as in FIG. 16 is performed. On the other hand, if it is determined in S1801 that the reduced cylinder operation is being performed, the number of operating cylinders is determined in S1803. In S1804, the purification performance determination values L1A and A1A corresponding to the determined number of operating cylinders are read from the map stored in the ROM 402 and adopted.

  The flow shown in FIG. 18 makes it possible to accurately determine the purification performance for any number of operating cylinders with reduced cylinder operation, and as a result, for any number of operating cylinders with reduced cylinder operation. The best emission characteristics can be obtained.

  Furthermore, a purification performance determination value corresponding to a combination of operating cylinders in the reduced cylinder operation may be used. FIG. 19 shows processing that should be substituted for the processing from S1607 to S1609 in the flow in FIG. 16 in this case. If it is determined in S1901 that all cylinders are in operation, the process proceeds to S1902 and the same processing as in FIG. 16 is performed.

  On the other hand, if it is determined in S1901 that the reduced cylinder operation is being performed, a reduced cylinder pattern is further determined in S1903. Then, in the processing from S1904 to S1906, the purification performance determination value corresponding to each reduced cylinder pattern, in other words, the combination of the operating cylinders is adopted.

  This makes it possible to accurately detect the exhaust gas transport speed, timing, and frequency that differ slightly depending on the combination of operating cylinders during reduced-cylinder operation, as well as the amount of gas hitting the air-fuel ratio sensors 48 and 49, without making an erroneous determination. In addition, the purification performance can be determined. As a result, the best emission characteristics can be obtained for each state.

  The types of combinations of the operating cylinders here can be the same as those considered in the third embodiment.

FIG. 1 is a plan view showing a schematic configuration of a variable cylinder system for an internal combustion engine according to a first embodiment of the present invention. FIG. 2 is a sectional view showing a schematic configuration of the variable cylinder system of the internal combustion engine according to the first embodiment of the present invention. FIG. 3 is a block diagram showing an internal configuration of the ECU according to the first embodiment of the present invention. FIG. 4 is a flowchart for the in-cylinder air amount estimation and target in-cylinder fuel amount calculation routine according to the first embodiment of the present invention. FIG. 5 is a flowchart of the main air-fuel ratio feedback control routine according to the first embodiment of the present invention. FIG. 6 is a flowchart of the fuel injection control routine according to the first embodiment of the present invention. FIG. 7 is a flowchart of the gain determination routine according to the first embodiment of the present invention. FIG. 8 is a flowchart for a gain determination routine according to the second embodiment of the present invention. FIG. 9 is a flowchart of a gain determination routine according to the third embodiment of the present invention. FIG. 10 is a graph showing the air-fuel ratio learning correction amount according to the fourth embodiment of the present invention. FIG. 11 is a flowchart of the FI calculation routine according to the fourth embodiment of the present invention. FIG. 12 is a flowchart for the air-fuel ratio learning routine according to the fourth embodiment of the present invention. FIG. 13 is a schematic view of the vicinity of the exhaust purification catalyst according to the fifth embodiment of the present invention. FIG. 14 is a flowchart of a calculation routine for locus lengths LVOS and LVOM and areas AVOS and AVOM according to the fifth embodiment of the present invention. FIG. 15 is a flowchart of a purification performance determination routine according to the fifth embodiment of the present invention. FIG. 16 is a flowchart for the latter half of the purification performance determination routine according to the fifth embodiment of the present invention. FIG. 17 is a graph showing a region where it is determined that the catalyst has deteriorated in the relationship between the locus length ratio LRATIO and the area ratio ARATIO according to the fifth embodiment of the present invention. FIG. 18 is a diagram illustrating a flowchart of an example in which the purification performance determination value according to the number of operating cylinders is adopted in the purification performance determination routine according to the fifth embodiment of the present invention. FIG. 19 is a diagram illustrating a flowchart of an example in which a purification performance determination value according to a combination of operating cylinders is adopted in a purification performance determination routine according to the fifth embodiment of the present invention.

Explanation of symbols

1 ... Internal combustion engine 20 ECU
21 ... Cylinder 25 ... Spark plug 25a ... Igniter 26 ... Intake port 27 ... Exhaust port 28 ... Intake valve 29 ... Exhaust valve 32 ... Fuel injection valve 46 ... Exhaust gas purification catalyst 47 ... exhaust pipe 48 ... air fuel ratio sensor 49 ... air fuel ratio sensor 51 ... crank position sensor

Claims (3)

  An internal combustion engine having a plurality of cylinders;
  Cylinder deactivation control means for shutting off fuel supply to some cylinders among the plurality of cylinders according to operating conditions of the internal combustion engine and deactivating some cylinders and operating the remaining cylinders;
  An exhaust gas purification means provided in an exhaust passage of the internal combustion engine for purifying exhaust gas of the internal combustion engine;
  Purification performance determination means for determining deterioration of the purification performance of the exhaust purification means;
  The cylinder deactivation control means shuts off the fuel supply to some of the plurality of cylinders, deactivates some of the cylinders and operates the remaining cylinders, and activates all the cylinders. A determination value changing means for changing a purification performance determination value used when the purification performance determination means determines deterioration of the purification performance of the exhaust purification means during all-cylinder operation.
A variable cylinder system for an internal combustion engine, comprising: The variable cylinder system for an internal combustion engine according to claim 1, wherein the determination value changing means changes the purification performance determination value according to the number of operating cylinders during the reduced-cylinder operation. The variable cylinder system for an internal combustion engine according to claim 1, wherein the determination value changing means changes the purification performance determination value in accordance with a combination of operating cylinders during reduced-cylinder operation.

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