JP6387934B2 - Engine control device - Google Patents

Description

  The present invention relates to an apparatus for controlling an engine including a plurality of cylinders, an exhaust passage through which exhaust gas discharged from each cylinder flows, and a purification device including a catalyst provided in the exhaust passage and capable of storing oxygen. About.

  Conventionally, in order to purify exhaust gas, a purification device including a catalyst capable of storing oxygen (for example, a three-way catalyst) is provided in an exhaust passage of an engine. In addition, it is known that in such a catalyst, the catalyst can be activated by repeatedly storing and releasing oxygen. On the other hand, for example, Patent Document 1 discloses an apparatus that performs so-called perturbation control that forcibly oscillates the air-fuel ratio of an air-fuel mixture in an engine cylinder in order to activate the catalyst and increase its purification capability. ing.

  Further, as disclosed in Patent Document 2, an oxygen concentration detection means is provided for detecting the oxygen concentration in the exhaust passage and the air-fuel ratio of the air-fuel mixture in the cylinder provided in the exhaust passage of the engine. In order to measure the output characteristics of the means, there is known an apparatus that performs control for varying the air-fuel ratio of the air-fuel mixture in the cylinder.

JP 2007-239698 A JP 2011-247148 A

  Here, if the control for varying the air-fuel ratio of the air-fuel mixture in the cylinder and the perturbation control are performed in order to measure the output characteristics of the detection means as described above, the air-fuel ratio fluctuates excessively and misfires occur. May occur.

  The present invention has been made in view of the above circumstances, and provides an engine control apparatus that can ensure combustion stability by avoiding misfire and the like while activating a catalyst by performing perturbation control. The purpose is to provide.

In order to solve the above problems, the present invention provides a plurality of cylinders, an exhaust passage through which exhaust gas discharged from each cylinder flows, and a purification device including a catalyst provided in the exhaust passage and capable of storing oxygen. And an air-fuel ratio changing means capable of changing the air-fuel ratio of the air-fuel mixture in each cylinder, and a portion of the exhaust passage that is provided upstream of the purifier. Oxygen concentration detecting means capable of detecting the oxygen concentration of the gas passing through the engine, and control means for controlling each part of the engine including the air / fuel ratio changing means, the control means comprising oxygen and fuel supplied to the catalyst The perturbation control for causing the air-fuel ratio of each cylinder to vary with the predetermined amplitude while varying the air-fuel ratio of the cylinders by the air-fuel ratio changing means so that the amount varies, and the air-fuel ratio changing means It is possible to perform an abnormality determination control that varies the air-fuel ratio of the air-fuel mixture and determines whether or not the output characteristics of the oxygen concentration detection means are abnormal based on the output result of the oxygen concentration detection means that accompanies the fluctuation. While the abnormality determination control is being performed, the perturbation control is prohibited, and in the operation region where the engine speed is less than a preset reference speed, the lower the engine speed, the more empty the perturbation control. An engine control device is provided, wherein the amplitude of the fuel ratio is reduced and the amplitude of the air-fuel ratio in the perturbation control is reduced as the engine speed is higher in the region above the reference speed. 1).

  According to the present invention, the abnormality determination control and the perturbation control can be performed, but the perturbation control is limited when the abnormality determination control is performed. Therefore, the determination of the output characteristics of the oxygen concentration detection means and the activation of the catalyst are performed. In addition, it is possible to ensure the combustion stability by avoiding misfires and the like accompanying the simultaneous execution of these controls. That is, if the perturbation control is performed as usual when the abnormality determination control is performed, the air-fuel ratio of the air-fuel mixture in the cylinder may change excessively and become excessively lean or rich, and misfires may occur. On the other hand, in the present invention, since perturbation control is restricted when the abnormality determination control is performed, this misfire or the like can be suppressed.

In the present invention, the air-fuel ratio amplitude in the perturbation control is made smaller as the engine speed is lower in the operating range where the engine speed is less than the preset reference speed. That is, the lower the engine speed is, the more easily the engine vibration and noise are sensed, the smaller the variation of the air-fuel ratio, and the smaller the engine torque variation and thus the engine vibration and noise. Therefore, it is possible to more reliably prevent the ride comfort from deteriorating while performing perturbation control to activate the catalyst.

  As described above, according to the engine control apparatus of the present invention, it is possible to ensure combustion stability by activating the catalyst by performing fuel perturbation control while avoiding misfire and the like.

It is a figure showing composition of an engine system concerning one embodiment of the present invention. FIG. 2 is a schematic plan view showing a part of the engine system shown in FIG. 1. It is the block diagram which showed the control system of the engine system shown in FIG. It is the figure which showed the change of the air fuel ratio at the time of perturbation control implementation. It is the figure which showed the relationship between an engine speed and the increase / decrease rate. It is the flowchart which showed the procedure of perturbation control. It is the flowchart which showed the procedure of AWS control. It is the flowchart which showed the procedure of LAFS diagnostic control. It is the figure which showed the change of the air fuel ratio at the time of LAFS control implementation, and the change of the output of a linear O2 sensor. It is the flowchart which showed the procedure of post-F / C enrichment control. It is the flowchart which showed the setting procedure of the perturbation execution flag. It is the figure which showed the implementation area | region of perturbation control.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which an engine control device according to an embodiment of the present invention is applied. The engine system of this embodiment includes a four-stroke engine main body 1, an intake passage 50 for introducing combustion air into the engine main body 1, and an exhaust passage 60 for exhausting exhaust from the engine main body 1 to the outside. It has. FIG. 2 is a schematic plan view showing a part of the engine system. As shown in FIG. 2, the engine body 1 is a four-cylinder engine having four cylinders 2a arranged in a predetermined direction.

  As shown in FIG. 1, an engine body 1 is inserted into a cylinder block 2 in which a cylinder 2a is formed, a cylinder head 3 provided on the upper surface of the cylinder block 2, and a cylinder 2a so as to be slidable back and forth. And a piston 4.

  A combustion chamber 5 is formed above the piston 4. Fuel is injected from the injector 11 into the combustion chamber 5. The injected fuel / air mixture is combusted in the combustion chamber 5, and the piston 4 is pushed down by the expansion force generated by the combustion and reciprocates up and down.

  The piston 4 is connected to the crankshaft 15 via a connecting rod, and the crankshaft 15 rotates around the central axis according to the reciprocating motion of the piston 4.

  The cylinder block 2 is provided with an engine speed sensor SW1 that detects the speed of the crankshaft 15 as the engine speed.

  The cylinder head 3 is provided with a pair of injectors 11 and spark plugs 10 for igniting a mixture of fuel and air injected from the injectors 11 by spark discharge for each cylinder 2a.

  The injector 11 has an injection port at the tip, and this injection port is provided so as to face the combustion chamber 5 of each cylinder 2a from the side of the intake side.

  The spark plug 10 has an electrode for discharging sparks at the tip, and is provided so as to face the combustion chamber 5 of each cylinder 2a from above.

  The cylinder head 3 includes an intake port 6 for introducing air supplied from the intake passage 50 into the combustion chamber 5 of each cylinder 2a, an intake valve 8 for opening and closing the intake port 6, and the combustion chamber 5 of each cylinder 2a. Are provided with an exhaust port 7 for leading the exhaust gas generated in step 1 to the exhaust passage 60 and an exhaust valve 9 for opening and closing the exhaust port 7.

An air cleaner 51, a throttle valve 54, and a surge tank 55 are provided in the intake passage 50 in order from the upstream side, and air that has been filtered by the air cleaner 51 is introduced into the engine body 1. The throttle valve 54 is a valve capable of opening and closing the intake passage 50, and the amount of intake air flowing through the intake passage 50, that is, the amount of air flowing into the cylinder 2a, is adjusted according to the opening of the throttle valve 54. . The intake passage 50 is provided with an air flow sensor SW2 for detecting the flow rate of the intake air flowing through the intake passage 50 and the filling amount of the cylinder 2a. In the present embodiment, the air flow sensor SW2 is provided in a portion of the intake passage 50 between the air cleaner 51 and the throttle valve 54 (immediately downstream of the air cleaner 51).

  As shown in FIG. 2, the exhaust passage 60 according to the present embodiment has a structure called so-called 4-2-1 exhaust, and each cylinder 2a (exhaust port 7 of each cylinder 2a) is individually provided. Four first independent passages 60a to be connected, two second independent passages 60b connected in common to the passage 60a corresponding to the cylinder 2a in which the exhaust order is not continuous among these passages 60a, and these passages 60b And one collective passage 60c connected in common.

  As shown in FIG. 1, the exhaust passage 60 is provided with a first catalytic converter (purification device) 63 and a second catalytic converter (purification device) 64 in order from the upstream side. Each catalytic converter 63, 64 contains a catalyst capable of storing oxygen, that is, a catalyst 63a, 64a having oxygen storage capability. In the present embodiment, three-way catalysts 63a and 64a are built in the catalytic converters 63 and 64, respectively.

  The catalytic converters 63 and 64 are provided in the collecting passage 60c of the exhaust passage 60, and are provided on the downstream side of the portion where the exhaust discharged from the exhaust port 7 of each cylinder 2a gathers. Accordingly, in the present embodiment, the distance between the engine body 1 and each of the catalytic converters 63 and 64 is relatively long.

  Here, the second catalytic converter 64 is an auxiliary device for purifying exhaust gas that could not be purified by the first catalytic converter 63, and may be omitted. Further, perturbation control for activating the catalyst described below is mainly performed on the first catalytic converter 63.

  A linear O2 sensor (oxygen concentration detection means) SW3 for detecting the oxygen concentration of the exhaust gas passing through this portion is provided in a portion of the exhaust passage 60 upstream of the first catalytic converter 63. In the present embodiment, the linear O2 sensor SW3 is provided near the upstream end of the first catalytic converter 63. The linear O2 sensor SW3 exhibits linear output characteristics with respect to the oxygen concentration in the exhaust gas.

  A lambda sensor for detecting whether the air-fuel ratio of the exhaust gas passing through this portion of the exhaust passage 60 is between the first catalytic converter 63 and the second catalytic converter 64 is equal to or lower than the stoichiometric air-fuel ratio. SW4 is provided. The lambda sensor SW4 has a predetermined first voltage V1 (for example, 1 V) when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio (that is, stoichiometric) or smaller than the stoichiometric air-fuel ratio (that is, rich). When the air-fuel ratio is greater (ie, lean), the second voltage (eg, 0 V) is lower than the first voltage V1.

  Here, the air-fuel ratio of the air-fuel mixture in the cylinder 2a is determined by changing the filling amount by changing the opening of the throttle valve 54, and / or the amount of fuel injected from the injector 11 into the cylinder 2a (fuel injection). It can be changed by changing the amount. That is, the throttle valve 54 and the injector 11 function as air-fuel ratio changing means capable of changing the air-fuel ratio of the air-fuel mixture in each cylinder 2a. However, in the present embodiment, the air-fuel ratio in the cylinder 2a is changed by changing the fuel injection amount in perturbation control, LAFS control, and post-F / C enrichment control described later.

(2) Control System Next, the control system of the engine system will be described with reference to FIG. The engine system of the present embodiment is mounted on a vehicle such as an automobile and is controlled by an ECU (engine control unit, control means) 100 provided in the vehicle. As is well known, the ECU 100 is a microprocessor including a CPU, ROM, RAM, I / F, and the like.

  Information from various sensors is input to the ECU 100. For example, the ECU 100 is electrically connected to an engine speed sensor SW1, an airflow sensor SW2, a linear O2 sensor SW3, and a lambda sensor SW4, and input signals (engine speed, charging amount, first catalyst) from these sensors. The oxygen concentration of the exhaust gas immediately before the converter 63 and the air-fuel ratio after passing through the first catalytic converter 63). The engine body 1 is provided with an engine water temperature sensor SW5 for detecting the engine water temperature. The vehicle is also provided with an accelerator opening sensor SW6 for detecting the opening of an accelerator pedal (not shown) operated by the driver, a vehicle speed sensor SW7 for detecting the vehicle speed, and an ignition switch (IG switch) SW8. The signals (engine water temperature, accelerator opening, vehicle speed) detected by these sensors SW5 to 8 and the signal of the IG switch SW8 are also input to the ECU 100.

  The ECU 100 controls each part of the engine system while executing various calculations based on input signals from the sensors (SW1 to SW7, etc.) and the switches (SW8, etc.). That is, the ECU 100 is electrically connected to the spark plug 10, the injector 11, the throttle valve 54, and the like, and outputs a drive control signal to each of these devices based on the calculation result and the like.

  The ECU 100 functionally includes a catalyst temperature estimation unit 101 and a main control unit 110. The main control unit 110 is a part that controls the spark plug 10, the injector 11, and the throttle valve 54, and functionally includes a base control execution unit 111, a perturbation control execution unit 112, an AWS control execution unit 113, and LAFS diagnostic control execution. Unit 114 and post-F / C enrichment control execution unit 115.

  The catalyst temperature estimation unit 101 estimates a catalyst temperature Tcat, which is the temperature of the catalyst 63a in the first catalytic converter 63.

  The catalyst temperature estimation unit 101 estimates the temperature of the catalyst 63a by adding the temperature increase amount of the exhaust gas in the first catalytic converter 63 to the temperature of the exhaust gas flowing into the first catalytic converter 63.

  The temperature of the exhaust gas flowing into the first catalytic converter 63 is the temperature of the exhaust gas in the exhaust port 7, the amount of temperature increase of the exhaust gas due to combustion (so-called post-combustion) generated in the exhaust passage 60, and the exhaust gas due to heat dissipation in the exhaust passage 60. The temperature drop amount of each is calculated, and after adding the delay of exhaust gas, these are added together and calculated.

  Here, the temperature of the exhaust gas in the exhaust port 7 is estimated from the engine speed, the filling amount, the air-fuel ratio in the cylinder 2a, and the closing timing of the exhaust valve 9. The amount of exhaust gas temperature rise due to combustion generated in the exhaust passage 60 is the amount of air that has flowed into the exhaust passage 60, that is, the amount of fresh air blown (estimated from the filling amount and the air-fuel ratio) and the air in the cylinder 2a. Estimated from the fuel ratio. The amount of temperature reduction of the exhaust gas due to heat radiation in the exhaust passage 60 is estimated from the vehicle speed, the filling amount, and the outside air temperature.

  Further, the temperature increase amount of the exhaust gas in the first catalytic converter 63 is calculated as the temperature increase amount of the exhaust gas due to the catalytic reaction and the temperature increase amount of the exhaust gas due to the afterburning in the first catalytic converter 63, and these are calculated. Calculate by adding up.

  Here, the temperature rise amount of the exhaust gas due to the catalytic reaction is estimated from the engine speed, the filling amount, and the air-fuel ratio in the cylinder 2a. The amount of temperature increase of the exhaust gas due to afterburning in the first catalytic converter 63 is estimated from the amount of fresh air blown and the air-fuel ratio in the cylinder 2a.

  The base control execution unit 111 performs control during normal operation (when control by each of the control execution units 112 to 115 is not performed).

  The base control execution unit 111 determines the target value of the filling amount, the air-fuel ratio in the cylinder 2a (mixing in the cylinder 2a) according to the engine speed and the engine load (the required engine load value calculated from the accelerator opening). The target value of the air / fuel ratio) is set, and each actuator is controlled so that these are realized.

  Specifically, the base control execution unit 111 sets the opening degree of the throttle valve 54 based on the target value of the filling amount, and issues a control signal to the throttle valve 54 so as to reach this opening degree. For example, the target value of the filling amount is extracted from a map set in advance for the engine speed and the engine load, and the opening degree of the throttle valve 54 is extracted from a map set in advance for the filling amount and the throttle valve 54. Is done.

  The base control execution unit 111 calculates a required fuel injection amount based on the target value and the charging amount of the air-fuel ratio in the cylinder 2a, and linear O2 so that the air-fuel ratio in the cylinder 2a becomes the target value. The fuel injection amount is feedback controlled using the output value of the sensor SW3, and a control signal is output to the injector 11. In the present embodiment, the target value of the air-fuel ratio in the cylinder 2a is the stoichiometric air-fuel ratio in the entire operation region. Further, the base control execution unit 111 sets an ignition timing according to the engine speed, the engine load, and the like, and outputs a control signal to the spark plug 10. For example, the ignition timing is extracted from a map set in advance for the engine speed, the engine load, and the like.

  Hereinafter, the target values of the opening degree of the throttle valve 54, the fuel injection amount, and the air-fuel ratio in the cylinder 2a set by the base control execution unit 111 are referred to as a basic throttle valve opening degree, a basic injection amount, and a basic air-fuel ratio, respectively.

  Next, the control contents of the other control execution units 112 to 115 will be described.

(I) Perturbation control execution unit The perturbation control execution unit 112 activates the catalyst (in this embodiment, mainly activates the catalyst 63a of the first catalytic converter 63), more specifically, the catalyst 63a. In order to activate the precious metal contained therein, so-called perturbation control is performed to forcibly oscillate the air-fuel ratio of the cylinder 2a in order to increase or decrease the amount of oxygen and fuel supplied to the catalyst 63a. That is, in the catalyst having the oxygen storage ability, the purification ability can be increased by activating the catalyst by repeating the storage and release of oxygen, and in this embodiment, the purification ability is secured by using this. To do.

  The perturbation control execution unit 112 oscillates the air-fuel ratio of the cylinder 2a when a perturbation execution flag Fp, which will be described later, becomes 1, and execution of the perturbation control is permitted.

In the present embodiment, the air / fuel ratio (hereinafter sometimes referred to as the base air / fuel ratio) in a state where the perturbation control is not performed is used as a reference, and a value obtained by multiplying the base air / fuel ratio by a predetermined increase / decrease rate C is used as the amplitude. Oscillate the air-fuel ratio. For example, when control during normal operation is performed by the base control execution unit 111, the value obtained by multiplying the theoretical air-fuel ratio by a predetermined increase / decrease rate C with the theoretical air-fuel ratio being the basic air-fuel ratio as a reference, The air / fuel ratio is vibrated. Further, as shown in FIG. 4, the air-fuel ratio is increased or decreased for each cylinder along the ignition order. That is, the air-fuel ratio is vibrated by increasing the air-fuel ratio in the first cylinder, decreasing the air-fuel ratio in the third cylinder, increasing the air-fuel ratio again in the fourth cylinder, and decreasing the air-fuel ratio in the second cylinder.

  Note that the air-fuel ratio oscillation method is not limited to this. For example, the air-fuel ratio may be changed for each of a plurality of cylinders. In addition to the example shown in FIG. 4, the air-fuel ratio may be first decreased at the start of perturbation control. However, as shown in FIG. 4, if the air-fuel ratio is changed alternately in the order of ignition, the air-fuel ratio vibration becomes high-frequency vibration, so that the passenger is less likely to experience the engine vibration accompanying the air-fuel ratio vibration. Comfort can be improved. Further, the amount of oxygen and fuel supplied to the catalyst can be frequently changed, and the catalyst can be activated earlier.

In the present embodiment, when the perturbation control is performed, the increase / decrease rate C is changed according to the engine speed as shown in FIG. Specifically, an area where the engine speed is equal to or higher than the first speed N1 (lower limit speed) and equal to or lower than the third speed (reference speed) N3 (the area including the area indicated by A2_1 and the area indicated by A2_2) ), The increase / decrease rate C is increased as the engine speed increases. Specifically, in the low speed region A2_1 where the engine speed is not less than the first speed N1 and not more than the second speed N2, the increase / decrease rate C is increased as the engine speed increases. In the example shown in FIG. 5, the increase / decrease rate C is increased from the minimum increase / decrease rate C_min toward the maximum increase / decrease rate C_max in proportion to the engine speed. On the other hand, the increase / decrease rate C is constant at the maximum increase / decrease rate C_max in the medium rotation region A2_2 where the engine speed is greater than or equal to the second revolution number N2 and less than or equal to the third revolution number. In the high speed region A2_3 where the engine speed is equal to or higher than the third speed N3, the increase / decrease rate C is decreased as the engine speed increases. In the example shown in FIG. 5, the increase / decrease rate C is decreased from the maximum increase / decrease rate C_max toward the minimum increase / decrease rate C_min as the engine speed increases. Further, the increase / decrease rate C is reduced in proportion to the engine speed. In this embodiment, the area A0 (see FIG. 12) where the engine speed is less than the first speed N1 and the area A4 where the engine speed is equal to or greater than the fourth speed N4 (upper limit speed) (see FIG. 12). ) Does not perform perturbation control.

  The control procedure of the perturbation control execution unit 112 is shown in the flowchart of FIG.

  As shown in FIG. 6, the perturbation control execution unit 112 first reads a perturbation execution flag Fp in step S1. Next, in step S2, it is determined whether the perturbation execution flag Fp is 1. If this determination is NO, the process returns to step S1. On the other hand, if the determination in step S2 is YES and the perturbation execution flag Fp is 1, the process proceeds to step S3.

  In step S3, the engine speed is read.

  Next, in step S4, as described above, the increase / decrease rate C is set according to the engine speed as shown in FIG.

  Next, in step S5, perturbation control is performed. That is, the air-fuel ratio is increased or decreased from the base air-fuel ratio by the change rate C for each cylinder 2a. Specifically, when the base air-fuel ratio is the basic air-fuel ratio, the fuel amount increase / decrease amount corresponding to the air-fuel ratio obtained by multiplying the basic air-fuel ratio by the increase / decrease rate C, that is, the fuel obtained by multiplying the basic injection amount by the increase / decrease rate C. The amount of increase / decrease in the amount is calculated, and the fuel injection amount is increased or decreased from the basic injection amount.

These steps S3 to S5 are repeated until the perturbation execution flag Fp becomes 0 in step S6. That is, the fuel injection amount is increased and decreased to vibrate until the perturbation execution flag Fp becomes 0, and thereby the air-fuel ratio is increased and decreased to be vibrated.

(Ii) AWS control execution unit 113
The AWS control execution unit 113 executes so-called AWS (Accelerated Warm-up System) control for warming up and activating these early when the temperature of the catalyst is low. In this embodiment, this control is executed with reference to the catalyst 63a of the first catalytic converter 63. However, by executing this control, the catalyst 64a of the second catalytic converter 64 is also combined with the catalyst 63a of the first catalytic converter 63. Warm up early.

  The contents of control by the AWS control execution unit 113 will be described with reference to the flowchart of FIG.

  First, in step S11, the estimated catalyst temperature Tcat and the vehicle speed estimated by the catalyst temperature estimation unit 101 are read.

  Next, in step S12, it is determined whether or not the estimated catalyst temperature Tcat is lower than a preset AWS execution temperature Tcat_AWS. The AWS execution temperature Tcat_AWS is the temperature of the catalyst 63a when the catalyst 63a is lighted off (when the purification rate of the catalyst 63a is 50%), and is set in advance by experiments or the like. If this determination is NO, the estimated catalyst temperature Tcat is equal to or higher than the AWS execution temperature Tcat_AWS, and the catalyst 63a is light-off, the process is terminated without executing the AWS control. On the other hand, if the determination in step S12 is YES and the estimated catalyst temperature Tcat is less than the AWS execution temperature Tcat_AWS and the catalyst 63a is not lighted off, the process proceeds to step S13.

  In step S13, it is determined whether or not the vehicle speed is equal to or lower than a preset AWS permission speed. In this embodiment, the AWS permission speed is set to a value near zero. If this determination is NO, that is, if the vehicle speed is higher than the AWS permitted speed, the processing is terminated as it is.

  On the other hand, if the determination in step S13 is YES and the vehicle speed is less than or equal to the AWS permitted speed, the process proceeds to step S14 to perform the AWS control. Specifically, in step S14, the filling amount of each cylinder 2a is increased and the ignition timing is retarded. In the present embodiment, the fuel is divided and injected in accordance with this.

  Specifically, the filling amount of each cylinder 2a is increased more than the filling amount at the time of executing the basic control. In the present embodiment, the filling amount of each cylinder 2a is increased by making the opening degree of the throttle valve 54 more open than the basic throttle valve opening degree. Further, the ignition timing is retarded from the basic ignition timing. In this embodiment, the ignition timing is set to a time that greatly exceeds the compression top dead center. Further, the fuel is divided and injected into a first injection that is performed in the latter half of the intake stroke and a second injection that is performed in the middle of the compression stroke.

  When the ignition timing is retarded as described above, the temperature of the exhaust gas rises and high-temperature exhaust gas is introduced into the catalyst 63a, so that the catalyst 63a can be heated to be activated. Moreover, the torque and engine speed can be maintained by increasing the filling amount of each cylinder 2a. Further, since the fuel is divided and injected as described above, the air-fuel mixture in the cylinder 2a is weakly stratified. That is, a lean air-fuel mixture layer is formed in the entire cylinder 2a by the first injection, and a rich air-fuel mixture layer is formed around the spark plug 10 by the second injection. Therefore, combustion stability can be ensured while retarding the ignition timing.

Thus, in the present embodiment, when the estimated catalyst temperature Tcat is lower than the AWS execution temperature Tcat_AWS and the vehicle speed is equal to or lower than the AWS permission speed, the ignition timing is retarded by increasing the filling amount of each cylinder 2a. The AWS control for dividing and injecting the catalyst 63
Realization of early activation of a and 64a.

(Iii) LAFS diagnosis control execution unit 114
The LAFS diagnosis control execution unit 114 performs LAFS diagnosis control (abnormality determination control) for determining whether or not the output characteristic of the linear O2 sensor SW3 is normal.

  The control content of the LAFS diagnostic control execution unit 114 will be described using the flowchart of FIG.

  First, in step S21, it is determined whether the LAFS diagnosis execution condition is satisfied. In the present embodiment, it is assumed that the LAFS diagnosis execution condition is satisfied when the engine is in steady operation. Specifically, the LAFS diagnosis is performed when the engine water temperature is equal to or higher than a predetermined temperature, the engine has been warmed up, and the fluctuation amount of the engine speed and the fluctuation amount of the filling amount are sufficiently small. It is determined that the execution condition is satisfied.

  If the determination in step S21 is NO and the LAFS diagnosis execution condition is not satisfied, the process is terminated without performing the subsequent diagnosis.

  On the other hand, if the determination in step S21 is YES and it is determined that the LAFS diagnosis execution condition is satisfied, the process proceeds to step S22. In step S22, the air-fuel ratio is uniformly changed for all cylinders 2a. Specifically, as shown by the solid line in FIG. 9, the air-fuel ratios of all the four cylinders 2a are set to a value higher than the basic air-fuel ratio (for example, the theoretical air-fuel ratio) by a predetermined amount (for example, lean higher than the theoretical air-fuel ratio), and thereafter Return to basic air-fuel ratio.

  Returning to FIG. 8, after step S22, the process proceeds to step S23. In step S23, the time constant of the output change of the linear O2 sensor SW3 is measured. Specifically, the output of the linear O2 sensor SW3 becomes as indicated by a chain line in FIG. 9 along with the change in the air-fuel ratio. Therefore, the time constant of this output change (the time from when the output change starts until it reaches 63% of the total change amount) is measured. Specifically, the time constant related to the output change when the air-fuel ratio is raised and the time constant related to the output change when the air-fuel ratio is returned to the basic air-fuel ratio are measured.

  Next, in step S24, it is determined whether or not the number of times the time constant has been measured is greater than or equal to a preset reference number. If this determination is NO, the process returns to step S21, and steps S21 to S23 are performed. That is, while it is determined that the LAFS diagnosis execution condition is satisfied and the number of times the time constant is measured is less than the reference number, the air-fuel ratio of the cylinder 2a is basically set for each alternate combustion cycle as shown by the solid line in FIG. Increase the air-fuel ratio and measure the time constant.

  On the other hand, if the determination in step S24 is YES and the number of times the time constant is measured exceeds the reference number, the process proceeds to step S25.

  In step S25, it is determined whether or not the time constant measured in step S24 is within a preset normal range.

  If the determination in step S25 is YES, the process proceeds to step S26 and it is determined that the linear O2 sensor SW3 is normal. On the other hand, if determination of step S25 is NO, it will progress to step S27 and will determine with linear O2 sensor SW3 being abnormal (failure etc.). When it is determined that the linear O2 sensor SW3 is abnormal, MIL lighting or the like is performed.

As described above, in this embodiment, the air-fuel ratio of the cylinder is increased for every separate combustion cycle. That is, the air-fuel ratio is increased or decreased with two combustion cycles as one cycle. And linear O2 sensor SW
3 is determined as to whether or not the output characteristic is normal.

(Iv) Post-F / C enrichment control execution unit 115
The post-F / C enrichment control execution unit 115 sets the oxygen storage amount of the catalyst 63a of the first catalytic converter 63 after the end of the fuel cut (F / C) at the time of deceleration or the like in order to ensure the purification capability of the catalyst 63a. Perform post-F / C enrichment control to be reduced. Note that the oxygen storage amount of the catalyst 63a of the second catalytic converter 63 is also reduced by performing this control. That is, when the fuel is cut, a large amount of air, that is, oxygen is supplied to the catalyst 63a, and the oxygen storage amount of the catalyst 63a increases. For this reason, after the fuel cut is completed, the reducing ability of the catalyst 63a is not sufficiently exhibited, and the exhaust gas performance may be deteriorated. Therefore, in this embodiment, the post-F / C post-enrichment control execution unit 115 performs control to reduce the oxygen storage amount of the catalyst 63a after the end of the fuel cut, and recovers the reducing ability of the catalyst 63a. In this embodiment, the post-F / C enrichment control execution unit 115 determines whether the state of the catalyst 63a is normal.

  The control content of the post-F / C enrichment control execution unit 115 will be described using the flowchart of FIG.

  First, in step S31, it is determined whether or not the fuel cut has ended, that is, whether or not the fuel cut state has shifted to a normal operation, that is, an operation in which fuel is supplied into the cylinder 2a. If this determination is NO, the process is terminated as it is. On the other hand, if this determination is YES, the process proceeds to step S32.

  In step S32, a rich operation is performed in which the air-fuel ratio of the cylinder 2a is made smaller by making it smaller than the stoichiometric air-fuel ratio. Specifically, the fuel injection amount is made larger than the amount corresponding to the theoretical air-fuel ratio.

  Next, in step S33, an excess fuel integrated value is calculated. The excess fuel integrated value is obtained by subtracting the amount of fuel supplied to the catalyst 63a by performing the rich operation of step S32, that is, the amount of fuel injected into the cylinder 2a from the amount corresponding to the stoichiometric air-fuel ratio. The integrated value is an integrated value, and the post-F / C enrichment control execution unit 115 integrates this amount every time step S32 is performed.

  After step S33, the process proceeds to step S34. In step S34, it is determined whether or not the output value of the lambda sensor SW4 is equal to or greater than the determination output value V0. The determination output value V0 is set to a value slightly larger than the second voltage V2 that is an output value when the air-fuel ratio of the exhaust gas is lean and the exhaust gas contains a large amount of oxygen.

  In step S34, based on the output value of the lambda sensor SW4, it is determined whether or not the oxygen storage amount of the catalyst 63a has been reduced to near zero with the execution of step S32.

  Specifically, as described above, the oxygen storage amount of the catalyst 63a is increased by the fuel cut and becomes the saturated oxygen amount or an amount close thereto, but when the air-fuel ratio of the cylinder 2a is made rich in step S33, the fuel is supplied to the catalyst 63a. Is supplied, the fuel reacts with the oxygen stored in the catalyst 63a in the catalyst 63a, and the amount of oxygen stored in the catalyst 63a is reduced accordingly. Therefore, when step S32 is repeated, the oxygen storage amount of the catalyst 63a is reduced to zero. When the oxygen storage amount of the catalyst 63a becomes close to 0 in this way, as a result of the fuel that has failed to react with the catalyst 63a on the downstream side of the catalyst 63a and where the lambda sensor SW4 is installed, the output of the lambda sensor SW4 Increases from the second voltage V2 to the first voltage V1 over the determination output value V0. Therefore, if the output of the lambda sensor SW4 becomes equal to or higher than the determination output value V0, it can be determined that the oxygen storage amount of the catalyst 63a has been reduced to near zero.

  If the determination in step S34 is NO and the output value of the lambda sensor SW4 is not greater than or equal to the determination output value V0, the process returns to step S32 and repeats steps S32 and S33. That is, in the present embodiment, the air-fuel ratio of the cylinder 2a is made rich and the amount corresponding to the stoichiometry is subtracted from the injected fuel until the determination in step S34 becomes YES and the oxygen storage amount of the catalyst 63a becomes zero. The excess fuel integrated value is calculated by integrating the measured amount.

  On the other hand, if the determination in step S34 is YES and it is determined that the output value of the lambda sensor SW4 is equal to or greater than the determination output value V0 and the oxygen storage amount of the catalyst 63a is close to 0, the process proceeds to step S35.

  In step S35, normal operation is performed. That is, the rich operation is terminated and the control shifts to the normal operation.

  Next, in step S36, it is determined whether or not the final excess fuel integrated value when the determination in step S34 is YES is smaller than a preset reference integrated value. If this determination is YES, the process proceeds to step S37 to determine that the catalyst 63a is abnormal. On the other hand, if this determination is NO, the process proceeds to step S38, and it is determined that the catalyst 63a is normal.

  That is, the final excess fuel integrated value is determined to be YES in step S31 (after the fuel cut is completed) and determined to be YES in step S34 (the output value of the lambda sensor SW4 is determined and output). The total amount of fuel supplied to the catalyst 63a and reacted at the catalyst 63a until the oxygen storage amount of the catalyst 63a reaches the saturated oxygen amount and close to zero. And a value corresponding to the saturated oxygen amount of the catalyst 63a. The reference integrated value is a fuel amount corresponding to the normal saturated oxygen amount of the catalyst 63a. Therefore, if the final excess fuel integrated value is smaller than the reference integrated value, it can be determined that the maximum amount of oxygen that can be occluded is lower than the normal amount due to deterioration of the catalyst 63a or the like. On the other hand, if the final excess fuel integrated value is greater than or equal to the reference integrated value, it can be determined that the maximum amount of oxygen that can be stored is greater than or equal to the normal amount and that the catalyst is normal.

  As described above, in this embodiment, after the fuel cut is completed, the air-fuel ratio in the cylinder 2a is made rich to release the oxygen stored in the catalyst 63a, and at this time, it is determined whether the catalyst 63a is normal. To do.

(3) Perturbation Control Permit Determination Next, the perturbation control permission determination procedure, that is, the perturbation execution flag Fp setting procedure will be described with reference to the flowchart of FIG.

  First, in step S41, the operating state is read. For example, the estimated catalyst temperature Tcat, the vehicle speed, the filling amount of each cylinder 2a, and the like are read.

Next, in step S42, it is determined whether or not the estimated catalyst temperature Tcat is lower than a preset perturbation execution temperature Tcat_p1. The perturbation execution temperature Tcat_p1 is the temperature of the catalyst 63a in a state where the catalyst 63a is activated to some extent (a state in which the purification rate is a predetermined value greater than 0). For example, the perturbation execution temperature Tcat_p1 is set to substantially the same value as the AWS execution temperature Tcat_AWS. If this determination is YES and the estimated catalyst temperature Tcat is less than the perturbation execution temperature Tcat_p1, the process proceeds to step S50, where it is determined that perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. Thus, in this embodiment, the estimated catalyst temperature Tcat
Is less than the perturbation execution temperature Tcat_p1 and the activity of the catalyst 63a is not sufficient, the execution of the perturbation control is prohibited. That is, when the activity of the catalyst 63a is low, the catalyst 63a cannot sufficiently store / release oxygen, and the activation effect of the catalyst 63a is small even if perturbation control is performed. Therefore, in this case, execution of perturbation control is prohibited. On the other hand, if the determination in step S42 is no, the process proceeds to step S43.

  Next, in step S43, it is determined whether or not the vehicle is stopped. Specifically, it is determined whether the vehicle speed is 0 or less. If this determination is YES and the vehicle is stopped, the process proceeds to step S50, where it is determined that the perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. Thus, in this embodiment, when the vehicle is stopped, the execution of perturbation control is prohibited. On the other hand, if the determination in step S43 is no, the process proceeds to step S44.

  In step S44, it is determined whether AWS control is being performed. This determination can be made according to the value of this flag, for example, by setting a flag whose value changes depending on whether or not the AWS control is being executed. If this determination is YES and the AWS control is being performed, the process proceeds to step S50, where it is determined that the perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. As described above, in the present embodiment, when the AWS control is performed, the execution of the perturbation control is prohibited. On the other hand, if the determination in step S44 is no, the process proceeds to step S45.

  In step S45, it is determined whether post-F / C enrichment control is being performed. This determination can be made according to the value of this flag, for example, by setting a flag whose value changes depending on whether or not the post-F / C enrichment control is being performed. If this determination is YES and post-F / C enrichment control is being performed, the process proceeds to step S50, where perturbation control is determined to be prohibited, and the perturbation execution flag Fp is set to zero. Thus, in the present embodiment, when the post-F / C enrichment control is being performed, the perturbation control is prohibited. On the other hand, if the determination in step S45 is no, the process proceeds to step S46.

  In step S46, it is determined whether LAFS diagnostic control is being performed. This determination can be made according to the value of this flag, for example, by setting a flag whose value changes depending on whether LAFS diagnostic control is being executed. If this determination is YES and LAFS diagnostic control is being performed, the process proceeds to step S50, where it is determined that perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. As described above, in the present embodiment, when LAFS diagnosis control is being performed, execution of perturbation control is prohibited. On the other hand, if the determination in step S46 is no, the process proceeds to step S47.

  In step S47, it is determined whether or not the filling amount of each cylinder 2a is less than the lower limit filling amount. If this determination is YES and the filling amount is less than the lower limit filling amount, the process proceeds to step S50, where it is determined that the perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. That is, in the present embodiment, as shown in FIG. 12, the perturbation control is performed in the first region A1 in which the filling amount of the cylinder 2a is less than the lower limit filling amount L1 and the filling amount is small and the engine load is low. Prohibit implementation.

  As shown in FIG. 12, the lower limit filling amount L1 is set to a smaller value as the engine speed is higher. In the example shown in FIG. 12, the lower limit filling amount L1 is set so as to decrease as the engine speed increases, and in particular, to decrease in proportion to the engine speed.

  If the determination in step S47 is no, the process proceeds to step S48.

  In step S48, it is determined whether or not the filling amount of each cylinder 2a is greater than or equal to the upper limit filling amount. If this determination is YES and the filling amount is equal to or greater than the upper limit filling amount, the process proceeds to step S50, where it is determined that perturbation control is prohibited, and the perturbation execution flag Fp is set to zero. That is, in the present embodiment, as shown in FIG. 12, perturbation control is performed in the third region A3 where the filling amount of the cylinder 2a is equal to or greater than the upper limit filling amount L2 and the filling amount is large and the engine load is high. Ban.

  As shown in FIG. 12, the upper limit filling amount L2 is set to a larger value as the engine speed is higher. In the example shown in FIG. 12, the upper limit charging amount L2 is set so as to increase as the engine speed increases, and in particular, increase in proportion to the engine speed.

  Thus, in this embodiment, perturbation control is performed only in the second region A2 where the filling amount is between the lower limit filling amount L1 and the upper limit filling amount L2.

  Here, as described above, the lower limit filling amount L1 is set to a smaller value as the engine speed increases, and the upper limit filling amount L2 is set to a larger value as the engine speed increases, and the second region A2 is: The higher the engine speed, the wider the filling range.

  Note that A2_1, A2_2, and A2_3 illustrated in FIG. 11 respectively represent the low rotation region A2_1, the middle rotation region A2_2, and the high rotation region A2_3 described above. As described above, in the present embodiment, In the case where the perturbation control is performed in the two areas A2, the increase / decrease rate C is individually set according to the engine speed.

  If the determination in step S48 is no, the process proceeds to step S49.

  In step S49, it is determined that perturbation control is permitted, that is, perturbation control is executed, and the perturbation execution flag Fp is set to 1.

(4) Operation As described above, in the present embodiment, LAFS diagnostic control (diagnostic control of the linear O2 sensor SW3) is performed while the vehicle is stopped, the AWS control is being performed, the post-F / C enrichment control is being performed. In the case of the inside, and when the filling amount of the cylinder 2a is less than the lower limit filling amount L1 and the filling amount of the cylinder 2a is equal to or larger than the upper limit filling amount L2, the implementation of the perturbation control is prohibited. Therefore, perturbation control is appropriately performed to activate the catalyst 63a, thereby improving purification performance and suppressing deterioration in riding comfort and exhaust gas performance associated with performing perturbation control. .

  This will be specifically described below.

  In the perturbation control, the air-fuel ratio of the cylinder 2a is changed rich and lean with respect to the base air-fuel ratio. Therefore, when the perturbation control is performed, the engine torque varies, and the engine vibration and noise increase. On the other hand, it is easy for passengers to feel engine vibration and noise while the vehicle is stopped. Therefore, if perturbation control is performed while the vehicle is stopped, it is easy for the occupant to feel that engine vibration and noise have increased. On the other hand, in this embodiment, execution of perturbation control is prohibited while the vehicle is stopped. Accordingly, it is possible to avoid an increase in engine vibration and noise that are detected by the occupant when the vehicle is stopped, and to improve the riding comfort.

  Also, the AWS control is control for activating the catalyst 63a, and the AWS control is performed when the temperature of the catalyst 63a is low and not sufficiently activated. In such a state where the temperature of the catalyst 63a is low and not sufficiently active, the catalyst 63a cannot sufficiently store / release oxygen. For this reason, even if the perturbation control is performed during the execution of the AWS control, the activation effect of the catalyst 63a by the execution of the perturbation control is small. Further, if perturbation control is performed in a state where the catalyst 63a is not activated to make the air-fuel ratio rich, unburned HC or the like is discharged without being purified by the catalyst 63a, and exhaust gas performance deteriorates. On the other hand, in this embodiment, execution of perturbation control is prohibited during execution of AWS control. Therefore, it is possible to avoid deterioration of exhaust gas performance due to the implementation of perturbation control.

  In the LAFS diagnostic control, as described above, the air-fuel ratio in the cylinder 2a is changed from the basic air-fuel ratio to lean. Therefore, if the air-fuel ratio of the cylinder 2a is changed at this time, the combustion stability is remarkably deteriorated. That is, if the air-fuel ratio in the cylinder 2a becomes lean due to the execution of LAFS diagnostic control, and if the air-fuel ratio is further leaned by perturbation control using this as a reference, there is a risk that significant engine torque reduction or misfire will occur. is there. On the other hand, in this embodiment, execution of perturbation control is prohibited during execution of LAFS diagnostic control. Therefore, by performing the perturbation control, it is possible to prevent the engine torque from being lowered or misfire, and to ensure the combustion stability.

  Further, as described above, in the LAFS diagnostic control, the air-fuel ratio is maintained at the same value during one combustion cycle, and the air-fuel ratio is changed every time one combustion cycle ends, and the time constant of the linear O2 sensor SW3 accompanying this change. Based on this, it is determined whether or not the output characteristics of the linear O2 sensor SW3 are normal. Therefore, when perturbation control is performed when LAFS diagnostic control is performed and the air-fuel ratio fluctuates during one combustion cycle, the output of the linear O2 sensor SW3 is not stable and the time constant of the output characteristics of the linear O2 sensor SW3 There is a risk that the detection accuracy of. On the other hand, in the present embodiment, since the execution of perturbation control is prohibited during the execution of LAFS diagnostic control, the time constant of the linear O2 sensor SW3 is detected more accurately, and abnormality determination of this sensor SW3 is performed. It can be done more appropriately.

  Further, when the post-F / C enrichment control is performed, the air-fuel ratio of the cylinder 2a is made rich as described above. Therefore, if the perturbation control is performed at this time to make the air-fuel ratio of the cylinder 2a richer, the fluctuation of the engine torque becomes remarkably large. In addition, when perturbation control is performed to make the air-fuel ratio of the cylinder 2a and thus the air-fuel ratio of the gas flowing into the catalyst 63a lean, it is possible to accurately determine whether or not the catalyst 63a is normal when the post-F / C enrichment control is performed. Can't do well. That is, as described above, in the present embodiment, when the post-F / C enrichment control is performed (after the fuel cut ends and until the output of the lambda sensor SW4 becomes equal to or higher than the reference output value), the rich gas is added to the catalyst 63a. The catalyst 63a is determined by associating the integrated value of the amount of fuel contained in this gas with the saturated oxygen amount of the catalyst 63a. Therefore, if a lean gas is supplied to the catalyst 63a after the fuel cut is completed, the saturated oxygen amount of the catalyst 63a cannot be calculated appropriately, and the determination accuracy of whether the catalyst 63a is normal deteriorates. On the other hand, in the present embodiment, perturbation control is prohibited during the post-F / C enrichment control. Therefore, it is possible to avoid the fluctuation of the engine torque from being increased by performing the perturbation control, and to accurately determine whether or not the catalyst 63a is normal.

Further, the combustion stability is not high in the operation region where the filling amount of the cylinder 2a is small and the engine load is low. For this reason, if perturbation control is performed in such an operating range to make the air-fuel ratio of the cylinder 2a lean, combustion stability may deteriorate and misfire may occur. Further, in the operation region where the filling amount of the cylinder 2a is small and the fuel injection amount is small, the fluctuation amount of oxygen and fuel supplied to the catalyst 63a can be kept small even if the perturbation control is performed. The effect of catalyst activation obtained by is not great.

  On the other hand, in the present embodiment, the perturbation control is prohibited in the first region A1 where the filling amount of the cylinder 2a is less than the lower limit filling amount L1. Therefore, it is possible to avoid the deterioration of combustion stability and the increase of engine torque fluctuation, the increase of vibration and noise, and the deterioration of running performance and riding comfort by performing perturbation control.

  In addition, it is possible to effectively suppress the deterioration of fuel consumption performance associated with the implementation of perturbation control without significantly impairing the catalyst activation effect. That is, in the perturbation control, the fuel efficiency is deteriorated because the air-fuel ratio is made rich. For this reason, when there are few opportunities for performing perturbation control, the catalyst activation effect is reduced, while deterioration in fuel efficiency can be suppressed.

  In particular, when the engine speed is low, the gas flow in the cylinder 2a is small, so the flame propagation performance is low and the combustion stability tends to be low. On the other hand, in this embodiment, the lower limit filling amount L1 is increased as the engine speed is lower. Therefore, combustion stability can be ensured more reliably.

  Further, in the operation region where the filling amount of the cylinder 2a is large and the engine load is high, the amount of fuel supplied to the cylinder 2a is large. For this reason, when perturbation control is performed in such an operating range to vary the air-fuel ratio of the cylinder 2a, the amount of variation in the amount of fuel supplied to the cylinder 2a increases and the variation in engine torque increases. On the other hand, in the present embodiment, the perturbation control is prohibited in the third region A3 where the filling amount of the cylinder 2a is equal to or greater than the upper limit filling amount L2. Accordingly, it is possible to avoid an increase in vibration and noise due to large fluctuations in engine torque by performing perturbation control.

  In particular, when the engine speed is low, it is easy for the occupant to sense changes in engine torque. On the other hand, in this embodiment, the upper limit filling amount L2 is lowered as the engine speed is lower. Therefore, the vibration and noise felt by the occupant can be kept small, and the riding comfort can be improved.

  Further, in the present embodiment, the increase / decrease rate C is increased as the engine speed is higher in the low speed area A2_1 where the engine speed is low in the second operation area A2 where the perturbation control is permitted to be performed. That is, it is configured such that the lower the engine speed and the easier the engine torque fluctuation is felt, the smaller the increase / decrease rate C and the smaller the air / fuel ratio fluctuation and the smaller the engine torque fluctuation. Therefore, it is possible to improve the riding comfort more reliably while activating the catalyst 63a by performing the perturbation control.

  In the present embodiment, the increase / decrease rate C is made smaller as the engine speed is higher in the high speed area A2_3 where the engine speed is high in the second operation area A2 where the perturbation control is permitted to be performed. That is, as described above, in this embodiment, the perturbation control is not performed when the engine speed is equal to or higher than the fourth speed N4, but the engine is shifted from the third speed N3 toward the fourth speed N4. The increase / decrease rate C is reduced as the rotational speed increases. Therefore, in the operating range of the third rotation speed N3 or higher, the change rate C when the engine speed changes, that is, the change in the air-fuel ratio can be kept small, and the air-fuel ratio can be changed smoothly during acceleration / deceleration.

(5) Modification In the above embodiment, the case where the AWS control and the post-F / C enrichment control are performed has been described, but these controls may be omitted.

  Further, although the case where the perturbation control is performed only when the vehicle is traveling has been described, the perturbation control may be performed when the vehicle is stopped.

  Further, the case where the perturbation control is performed only when the estimated catalyst temperature Tcat is equal to or higher than the perturbation execution temperature Tcat_p1 has been described. However, the perturbation control may be performed regardless of the estimated catalyst temperature Tcat.

  Further, the first region A1 in which the filling amount of the cylinder 2a is less than the lower limit filling amount L1, the third region A3 in which the filling amount of the cylinder 2a is equal to or more than the upper limit filling amount L2, the operation region A0 having a low engine speed, and the high engine speed. In the operation region A4, perturbation control may be performed.

  Further, the lower limit filling amount L1 and the upper limit filling amount L2 may be constant values regardless of the engine speed.

  In the above embodiment, the case where the perturbation control is prohibited when the LAFS diagnostic control is performed has been described. However, while the perturbation control is performed when the LAFS diagnostic control is performed, the amplitude of the air-fuel ratio, that is, the increase / decrease rate C The perturbation control may be limited by making it smaller than when LAFS diagnostic control is not performed. For example, the perturbation control may be performed with the increase / decrease rate C when the LAFS diagnostic control is performed as a predetermined ratio (a value smaller than 100%) of the increase / decrease rate when the LAFS diagnostic control is not performed. In this case, when the air-fuel ratio is leaner than the basic air-fuel ratio by performing LAFS diagnostic control, the air-fuel ratio is increased or decreased with respect to the lean air-fuel ratio. When the air-fuel ratio is returned to the basic air-fuel ratio, the air-fuel ratio is increased or decreased with respect to the basic air-fuel ratio.

  Even in this case (when performing perturbation control while reducing the amplitude of the air-fuel ratio at the time of LAF diagnostic control), the amount of fluctuation in the air-fuel ratio can be suppressed to a small value, thereby avoiding misfiring and the like to stabilize combustion. Sex can be secured. In this case, since many opportunities for performing perturbation control are secured, the catalyst can be activated more reliably.

1 Engine Body 2a Cylinder 63 First Catalytic Converter (Purification Device)
63a Catalyst 100 ECU (control means)
SW3 linear O2 sensor (oxygen concentration detection means)

Claims (1)

In an apparatus for controlling an engine comprising a plurality of cylinders, an exhaust passage through which exhaust gas discharged from each cylinder flows, and a purification device including a catalyst provided in the exhaust passage and capable of storing oxygen,
  Air-fuel ratio changing means capable of changing the air-fuel ratio of the air-fuel mixture in each cylinder,
  An oxygen concentration detection means provided in a portion of the exhaust passage upstream of the purification device and capable of detecting the oxygen concentration of the gas passing through the portion;
  Control means for controlling each part of the engine including the air-fuel ratio changing means,
  The control means includes
  Perturbation control in which the air-fuel ratio of each cylinder is made to vibrate with a predetermined amplitude while varying the air-fuel ratio of each cylinder by the air-fuel ratio changing means so that the amount of oxygen and fuel supplied to the catalyst varies, and An abnormality determination control for varying the air-fuel ratio of the air-fuel mixture by the air-fuel ratio changing means and determining whether or not the oxygen concentration detecting means is abnormal based on the output characteristics of the oxygen concentration detecting means accompanying the fluctuation. Can be implemented and
  While the abnormality determination control is being performed, the perturbation control is prohibited, and the air-fuel ratio amplitude in the perturbation control is reduced as the engine speed is lower in the operating range where the engine speed is less than the preset reference speed. An engine control apparatus, characterized in that the amplitude of the air-fuel ratio in the perturbation control is reduced as the engine speed is higher in a region that is smaller than the reference speed.