JP2011252472A - Control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an engine that can prevent exhaust emission characteristics from significantly degrading within all operating ranges including a range with a high air amount and a high exhaust temperature even if a low noble metal catalyst is used and the catalyst degrades to some degree.SOLUTION: The control device includes a means for setting a target air-fuel ratio for an air-fuel ratio before the catalyst, an air-fuel ratio control means for performing a feedback control of a fuel injection amount based on outputs from an upstream air-fuel ratio sensor 51 and a downstream Osensor 52 so as to converge the air-fuel ratio before the catalyst to the target air-fuel ratio, a degradation level learning means for detecting a degradation level of the catalyst by using the output from the downstream Osensor 52 and a degradation degree detection threshold S3 that is set to be within or near a stoichiometric range, and for storing and updating the detected degradation level as a learning value for every operating range, and a learning value reflecting means for correcting the target air-fuel ratio by using the learning value stored in the learning means.

Description

The present invention relates to a control device that controls an air / fuel ratio of an engine, and more particularly to a target air / fuel ratio by using a catalyst downstream O ₂ sensor (oxygen concentration sensor) in addition to a catalyst upstream air / fuel ratio sensor. The present invention relates to an engine control apparatus that performs feedback control so as to converge on the engine.

In conventional air-fuel ratio control, considering the air-fuel ratio controllability at the time of transition such as acceleration / deceleration, an air-fuel ratio sensor is provided upstream of the catalyst in the exhaust passage, and main feedback with high convergence to the target air-fuel ratio is achieved. The control was performed, and an O ₂ sensor was provided on the downstream side of the catalyst to perform sub feedback control. The main feedback control using the catalyst upstream air-fuel ratio sensor output increases the fuel injection amount when the air-fuel ratio of exhaust gas flowing into the catalyst (referred to as the pre-catalyst air-fuel ratio) becomes leaner than the target air-fuel ratio. When the pre-catalyst air-fuel ratio becomes richer than the target air-fuel ratio, the fuel injection amount is reduced. Sub feedback control using the catalyst downstream O ₂ sensor output, when the air-fuel ratio of the exhaust gas flowing out from the catalyst (referred to as air-fuel ratio after the catalyst) became leaner than the stoichiometric air-fuel ratio (stoichiometric), a fuel injection amount When the post-catalyst air-fuel ratio becomes richer than the stoichiometric air-fuel ratio (stoichiometric), the fuel injection amount is decreased (see Patent Document 1).

JP 2005-48711 A

  In recent years, exhaust gas regulations have become stricter, but in order to reduce the cost of automobiles, a case where a low noble metal catalyst with a reduced amount of noble metal contained therein is used as a catalyst compared to conventional ordinary catalysts. Tend to increase.

  However, when the catalyst, particularly a low precious metal catalyst, is deteriorated, the reduction capability is greatly reduced depending on the operation region. In the conventional air-fuel ratio control (PID feedback control for the fuel injection amount), the exhaust emission is dependent on the operation region. Properties can be significantly degraded. In other words, when the catalyst deteriorates, the exhaust emission characteristics vary between operating regions.

This is presumed to be because the O ₂ storage amount further decreases in the operation region (high air amount region) where the exhaust temperature is high, in addition to the reduction of the noble metal of the catalyst and the decrease in the O ₂ storage capability due to deterioration. Here, the deterioration of the catalyst referred to here is a deterioration with a moderate degree of deterioration that is not judged as “failure” by the self-diagnosis function.

This will be described with reference to FIGS. FIG. 4 shows a case where a normal catalyst is used, and FIG. 5 shows a case where a low precious metal catalyst is used, (A) intake air amount, (B) air-fuel ratio correction value, and (C) catalyst downstream side. O ₂ is a time chart showing an example of a change of the sensor output (voltage).

When a normal catalyst is used (FIG. 4), the required O ₂ storage capacity is maintained even if the operating range changes from a low air volume to a high air volume (high exhaust temperature). In addition, the fluctuation of the downstream O ₂ sensor output is small, and it can be controlled almost in the stoichiometric region.

On the other hand, when a low precious metal catalyst is used (FIG. 5), the O ₂ storage capacity is higher than that of a normal catalyst when the operating region changes from a low air amount to a high air amount region and the exhaust gas temperature becomes high. In the normal air-fuel ratio control, the sensitivity on the lean side increases, the downstream O ₂ sensor output fluctuates greatly, and the post-catalyst air-fuel ratio cannot be maintained near the stoichiometric range (enclosed by the broken line E). Exhaust emissions characteristics deteriorate.

  As described above, the low noble metal catalyst is more likely to deteriorate the exhaust emission characteristics at the time of deterioration than the conventional normal catalyst, and this tendency is strong particularly in a high air amount region where the exhaust temperature is high. In the conventional air-fuel ratio control, the target air-fuel ratio and control gain are set for each operating region, but there is no means to change it according to the degree of catalyst deterioration, and the exhaust emission characteristics deteriorate significantly in a specific operating region. There is a risk that.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to perform all operations including a high air amount and a high exhaust temperature region even if a low noble metal catalyst is used and the catalyst is somewhat deteriorated. An object of the present invention is to provide an engine control device capable of preventing deterioration of exhaust emission characteristics in a region.

In order to achieve the above object, an engine control apparatus according to the present invention basically includes an exhaust purification catalyst provided in an exhaust passage, and a linear for detecting a pre-catalyst air-fuel ratio upstream of the catalyst. An upstream air-fuel ratio sensor having an output characteristic of _{2 is provided, and} a downstream O ₂ that outputs a switching signal for identifying whether the post-catalyst air-fuel ratio is richer or leaner than stoichiometric is downstream of the catalyst. A sensor is provided, and the pre-catalyst air-fuel ratio is set to the target air-fuel ratio based on means for setting a target air-fuel ratio for the pre-catalyst air-fuel ratio and outputs of the upstream air-fuel ratio sensor and the downstream O ₂ sensor. in order to converge, the air-fuel ratio control means for performing feedback control of the fuel injection amount, the downstream O ₂ sensor output and the stoichiometric region or deterioration degree detection threshold set in the vicinity thereof And a deterioration degree learning means for storing and updating the detected deterioration degree as a learning value for each operation region, and a learning value stored in the learning means. Learning value reflecting means for reflecting in the feedback control performed by the air-fuel ratio control means.

  In the engine control apparatus according to the present invention, the target air-fuel ratio and control gain are corrected for each operation region in accordance with the degree of deterioration of the catalyst, so the post-catalyst air-fuel ratio is changed from the stoichiometric region to the lean side or the rich side. In the entire operation region including a high air amount and a high exhaust temperature region, even if a low noble metal catalyst is used and the catalyst is somewhat deteriorated, Exhaust emission characteristics can be prevented from deteriorating so much.

  In addition, since the catalyst deterioration degree is stored and updated as a learning value for each operation region divided according to the engine speed and the engine load, the learning and storage that is stored and updated for each operation region during the next operation is performed. Since the target air-fuel ratio and control gain are corrected using the values, the post-catalyst air-fuel ratio converges quickly in the stoichiometric region, and as a result, deterioration of exhaust emission characteristics can be further suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows one Embodiment of the control apparatus which concerns on this invention with an example of the vehicle-mounted engine to which it is applied. Schematic which shows ECU shown by FIG. 1, and the structure around it. The functional block diagram which shows the outline | summary of the various control which ECU performs. When conventional catalysts are used, a time chart showing an example of a change in such downstream O ₂ sensor output. When low precious metal catalyst is used, a time chart showing an example of a change in such downstream O ₂ sensor output. FIG. 2 is a block diagram for explaining an example of air-fuel ratio control by the engine control device shown in FIG. 1. The figure which shows the relationship between the count value of the deterioration degree counter in the example of the air fuel ratio control shown in FIG. 6, and a target air fuel ratio correction value. The figure which shows the example of a setting of the threshold value for deterioration degree detection in an example of the air fuel ratio control shown by FIG. The figure which shows the example of a setting of the threshold value for deterioration degree detection in an example of the air fuel ratio control shown by FIG. FIG. 7 is a diagram for explaining a technique for detecting the degree of catalyst deterioration using the output of the downstream O ₂ sensor and the threshold value for detecting the degree of catalyst deterioration in an example of the air-fuel ratio control shown in FIG. 6. FIG. 7 is a diagram for explaining a technique for detecting the degree of catalyst deterioration using the output of the downstream O ₂ sensor and the threshold value for detecting the degree of catalyst deterioration in an example of the air-fuel ratio control shown in FIG. 6. In the example of the air-fuel ratio control shown in FIG. 6, when the ratio ε is equal to or smaller than the first set ratio, (A) intake air amount, (B) catalyst deterioration degree counter (count value), (C) target air-fuel ratio, (D) Time chart showing changes in downstream O ₂ sensor output. In the example of the air-fuel ratio control shown in FIG. 6, when the ratio ε is equal to or greater than the second set ratio, (A) intake air amount, (B) catalyst deterioration degree counter (count value), (C) target air-fuel ratio, (D) Time chart showing changes in downstream O ₂ sensor output. FIG. 3 is a block diagram for explaining another example of air-fuel ratio control by the engine control device shown in FIG. 1. The block diagram which shows the detailed structural example of P component calculation means in the case of calculating a control gain according to the deterioration degree of a catalyst in the block 620 (control gain calculation) of FIG. FIG. 15 is a block diagram illustrating a detailed configuration example of a D component calculation unit when a control gain is calculated according to the degree of catalyst deterioration in block 620 (control gain calculation) of FIG. 14. FIG. 15 is a block diagram showing a detailed configuration example of an I component calculating unit when calculating a control gain according to the degree of catalyst deterioration in block 620 (control gain calculation) of FIG. 14. In another example of the air-fuel ratio control shown in FIG. 14, when the ratio ε is equal to or less than the first set ratio, (A) intake air amount, (B) catalyst deterioration degree counter (count value), (C) P minutes , (D) downstream O ₂ sensor output time chart showing an example of a change in. In another example of the air-fuel ratio control shown in FIG. 14, when the ratio ε is equal to or larger than the second set ratio, (A) intake air amount, (B) catalyst deterioration degree counter (count value), (C) P minutes , (D) downstream O ₂ sensor output time chart showing an example of a change in.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an engine control device according to the present invention together with an example of an in-vehicle engine to which the engine control device is applied.

  In FIG. 1, an engine 10 to which the engine control device 1 of the present embodiment is applied includes, for example, four cylinders # 1, # 2, # 3, and # 4 (in the figure, the # 1 cylinder is shown as a representative). A spark ignition type multi-cylinder engine having a cylinder head 11a and a cylinder block 11b, and slidably fitted in each cylinder # 1, # 2, # 3, # 4 of the cylinder 11. The piston 15 is connected to the crankshaft 13 via a connecting rod. Above the piston 15, a combustion working chamber 17 having a combustion chamber (ceiling or roof) having a predetermined shape is defined, and the combustion working chamber 17 of each cylinder # 1, # 2, # 3, # 4 is ignited. A spark plug 35 to which a high-voltage ignition signal is supplied from the coil 34 is provided.

  The air used for the combustion of fuel is from an air cleaner (not shown), a tubular passage portion (throttle body 26, etc.) in which the throttle valve 25 is disposed, a collector 27, an intake manifold (manifold) 28, and an intake port 29. Through the intake passage 20 composed of the like and the like, and is sucked into the combustion working chambers 17 of the cylinders # 1, # 2, # 3, and # 4 via the intake valve 21 arranged at the downstream end (end portion of the intake port 29). Is done. A fuel injection valve 30 for injecting fuel toward the intake port 29 is provided for each cylinder (# 1, # 2, # 3, # 4) in the downstream portion of the intake passage 20 (intake manifold 28). Further, the collector 27 is provided with an intake pressure sensor 59 for detecting an intake pipe internal pressure (an internal pressure downstream of the throttle valve 25 in the intake passage 20).

  In addition, the engine 10 of this example is provided with an ISC (idle speed control) passage 46 that bypasses the throttle valve 25 in order to converge the engine speed to the target idle speed during idling operation. An ISC valve 45 for adjusting the passage cross-sectional area is provided.

The air-fuel mixture of the air sucked into the combustion working chamber 17 and the fuel injected from the fuel injection valve 30 is burned by spark ignition by the spark plug 35, and the combustion waste gas (exhaust gas) is burned into the combustion working chamber 17. Is discharged to the outside (in the atmosphere) through an exhaust passage 40 including an exhaust port, an exhaust manifold, an exhaust pipe and the like through an exhaust valve 22. An exhaust purification catalyst (three-way catalyst) 50 is disposed in the exhaust passage 40, and a linear air-fuel ratio sensor 51 (hereinafter referred to as “linear air-fuel ratio sensor 51”) having an output characteristic linear with respect to the pre-catalyst air-fuel ratio is disposed upstream of the catalyst 50. The upstream air-fuel ratio sensor 51 is disposed, and a switching signal for identifying whether the post-catalyst air-fuel ratio is richer or leaner than stoichiometric (theoretical air-fuel ratio) is output downstream of the catalyst 50. An O ₂ sensor 52 (hereinafter referred to as a downstream O ₂ sensor 52) is disposed. As the catalyst 50, a low noble metal catalyst is used in which the amount of noble metal contained therein is reduced as compared with a conventional normal catalyst.

  Further, in the fuel injection valve 30 provided for each cylinder (# 1, # 2, # 3, # 4), the fuel (gasoline etc.) in the fuel tank 71 is provided with a fuel pump 72, a fuel pressure regulator 73, and the like. The fuel injection mechanism 30 is supplied after being adjusted to a predetermined fuel pressure by the fuel supply mechanism 70, and the fuel injection valve 30 is supplied from an ECU (engine control unit) 100, which will be described later. A duty (= pulse width = The valve is driven to open by a drive pulse signal corresponding to the valve opening time, and an amount of fuel corresponding to the valve opening time is injected toward the intake port 29.

  On the other hand, in order to perform various controls of the engine 10, that is, fuel injection control (air-fuel ratio control) by the fuel injection valve 30, ignition timing control by the spark plug 35, ISC control, etc. Engine control unit) 100 is provided.

  As shown in FIG. 2, the ECU 100 is basically well known in hardware and includes an MPU 151, an EP-ROM 152, a RAM 153, an A / D & D / A converter, a drive circuit, and the like. It is composed of an I / O driver 155 and the like. Note that the RAM 153 (volatile memory) may be connected to a backup power supply for the purpose of storing memory contents even when the ignition key switch 49 is OFF and no power is supplied to the ECU 100. In this example, the MPU 151, the EP-ROM 152, the RAM 153, and the I / O driver 155 are separately provided. However, in recent years, some of them are combined into one, and these may be used. Needless to say.

  In the control unit 100, signals from various sensors as described later are input as inputs, predetermined calculation processing is executed, various control signals calculated as the calculation results are generated, and fuel injection as an actuator is performed. A predetermined control signal is supplied to the valve 30, the ignition coil 34, the ISC valve 45, the failure alarm device 48, etc. at a predetermined timing to execute fuel injection control (air-fuel ratio control), ignition timing control, ISC control, and the like.

  The ECU 100 receives, as an input signal, a signal corresponding to the opening of the throttle valve 25 detected by the throttle opening sensor 54, a crankshaft obtained from a crank angle sensor (rotational speed sensor) 55 attached to the crankshaft 13. 13 (a toothed disk provided in) is a signal representing the rotation / phase (crank angle) (a pulse signal is output from the crank angle sensor 55, for example, every rotation angle), A signal representing the rotation and phase of the camshaft 23 (a toothed disk provided on the camshaft 23) obtained from the cam angle sensor 56 provided (a pulse signal is output from the cam angle sensor 56, for example, every 180 ° C.). Based on this pulse signal and the pulse signal from the crank angle sensor 55, cylinder determination or the like is performed), from the three-way catalyst 50 in the exhaust passage 40 A signal corresponding to the exhaust air-fuel ratio from the upstream air-fuel ratio sensor 51 disposed on the flow side, a signal corresponding to the engine cooling water temperature detected by the water temperature sensor 58 disposed in the cylinder block 12, and the intake passage 20 A signal corresponding to the intake pipe internal pressure detected by the provided intake pressure sensor 59, a signal from an ignition key switch 49 which is a main switch for operating and stopping the engine 10, and the like are supplied. Furthermore, information such as the shift position of the transmission and the vehicle speed is provided from the vehicle (integrated) control unit through inter-unit communication.

  The ECU 100 recognizes the operating state of the engine 10 based on the various input signals, and based on the operating state, the ECU 100 performs main fuel injection control (air-fuel ratio control), ignition timing control, idle speed control, and the like. Calculate the amount of operation.

  The ECU 100 that performs the control as described above includes an engine speed calculation means 101, a basic injection amount calculation means 102, a basic injection amount correction coefficient calculation means 103, a basic ignition timing calculation, as shown in functional blocks in FIG. Means 104, F / B control coefficient calculation means 105, catalyst deterioration degree detection means 106, post-catalyst air-fuel ratio detection means 107, target air-fuel ratio correction value calculation means 108, acceleration / deceleration determination means 109, basic injection amount correction means 110, basic Ignition timing correction means 111 and ISC control means 112 are provided.

  The engine speed calculation means 101 counts the number of times the pulse signal from the crank angle sensor 55 changes per unit time (for example, the rise or fall of the pulse) (the number of arrivals) and performs a predetermined arithmetic process to perform the unit. Calculate the engine speed per hour.

  The basic injection amount calculation means 102 uses the engine speed calculated by the engine speed calculation means 101 and the intake pipe internal pressure detected by the intake pressure sensor 59 as the engine load, and the basic injection according to the engine operating state (operating region). Calculate the quantity. As the engine load, an intake air amount detected by an air flow sensor or the like may be used instead of the intake pipe internal pressure.

  The basic injection amount correction coefficient calculation unit 103 sets a correction coefficient in each operation region for the basic injection amount calculated by the basic injection amount calculation unit 102 by map search or the like.

  The basic ignition timing calculation means 104 sets an optimal ignition timing in each operating region of the engine based on the aforementioned engine speed and intake pipe internal pressure (engine load) by map search or the like.

  The F / B control coefficient calculation means 105 is based on the engine speed, the intake pipe internal pressure (engine load), the output of the upstream air-fuel ratio sensor 51, etc., the target air-fuel ratio, the difference between the target air-fuel ratio and the actual air-fuel ratio, PID A control gain (F / B control coefficient) of feedback control is calculated. The target air-fuel ratio is set by reading out the optimum target air-fuel ratio in each engine operation region by map search or the like based on the engine speed and the engine load.

The catalyst deterioration degree detection means 106 detects the deterioration degree of the catalyst 50 based on the outputs of the upstream air-fuel ratio sensor 51 and the downstream O ₂ sensor 52.

The post-catalyst air-fuel ratio detection means 107 detects the air-fuel ratio (post-catalyst air-fuel ratio) of the exhaust gas that has passed through the catalyst 50 based on the output of the downstream O ₂ sensor 52.

  The target air-fuel ratio correction value calculation means 108 calculates a correction value for correcting the target air-fuel ratio set by the F / B control coefficient calculation means 105 based on the degree of catalyst deterioration and the post-catalyst air-fuel ratio.

  The acceleration / deceleration determination means 109 obtains the amount of change (rate of change) of the throttle opening per unit time based on the signal from the throttle opening sensor 54, and whether the engine is in an acceleration state based on the amount of change, etc. Determine whether the vehicle is in a deceleration state. This determination result is provided to the ignition timing correction means 111 for calculating the ignition timing correction amount during acceleration / deceleration.

  The basic injection amount correction means 110 performs the above-described basic injection amount correction using a basic injection amount correction coefficient, correction using an engine coolant temperature, correction using an F / B control coefficient, and the like.

  The basic ignition timing correction means 111 performs correction based on engine coolant temperature, acceleration / deceleration correction, etc. on the ignition timing set by the basic ignition timing calculation means 104 described above.

  The ISC control means 112 supplies a drive control signal to the ISC valve 45 so that the amount of intake air flowing through the ISC passage 46 becomes the target flow rate so that the engine speed during idle operation converges to the target idle speed and is maintained. . The drive control signal is also supplied to the basic ignition timing correction means 111 and used for correcting the ignition timing during idle operation.

  Next, an example of air-fuel ratio control in the present embodiment will be described with reference to the block diagram of FIG.

In FIG. 6, in a block 601, the output (voltage) of the upstream air-fuel ratio sensor 51 is converted into an air-fuel ratio. In block 602, a target ternary point (target air-fuel ratio) of the pre-catalyst air-fuel ratio is obtained from the engine speed and intake pipe internal pressure (or engine load such as intake air amount) by map search or the like. In block 603, the post-catalyst air-fuel ratio is detected from the output of the downstream O ₂ sensor 52, and the target air-fuel ratio is finely adjusted by the adder / subtractor 609 so that the post-catalyst air-fuel ratio falls within the stoichiometric region (window) (fuel). PID feedback control for the injection amount is performed).

Blocks 604 to 608 show the characteristic portion of the present invention. In block 604, based on the output of the downstream O ₂ sensor 52, a catalyst deterioration degree detection threshold (described later) whose post-catalyst air-fuel ratio is the third threshold is used. A ratio ε (= TRL / TRR) of the time TRR determined to be rich with respect to the time TRL determined to be lean is calculated. In block 605, the deterioration degree counter is counted up (Count = n + 1) based on the ratio ε (details will be described later with reference to FIGS. 10 and 11).

  Further, the count value of the deterioration degree counter is determined in block 606 according to the time ratio ε (separately when the sensitivity on the lean side is high and the sensitivity on the rich side is high). In the first storage unit M1 and the second storage unit M2, for each operation region divided by the engine speed and the intake pipe internal pressure, the learning value is stored (stored), and the engine is operated to enter the corresponding operation region. Each time it enters, the learning value stored in the operation area is updated.

  In block 607, a correction value of the target air-fuel ratio is calculated according to the count value of the deterioration degree counter, and the target air-fuel ratio is further corrected by an adder / subtractor 608. The adder / subtractor 610 obtains a PID feedback control coefficient (control gain) for the fuel injection amount based on the output of the upstream air / fuel ratio sensor 51 so that the pre-catalyst air / fuel ratio converges to the target air / fuel ratio calculated by the adder / subtractor 608. . The block 611 is a correction limiter for preventing the correction value according to the degree of deterioration of the catalyst 50 calculated in the block 607 from becoming excessive.

  As shown in FIG. 7, the correction value of the target air-fuel ratio obtained in block 607 in FIG. 6 is set to a value that increases stepwise as the count value of the deterioration degree counter increases by table search.

On the other hand, for the output of the downstream O ₂ sensor 52, as shown in FIGS. 8 and 9, a first threshold value S1, a second threshold value S2, and a third threshold value S3 are set. The first threshold value S1 is a threshold value for determining that the post-catalyst air-fuel ratio is richer than the stoichiometric region, and the second threshold value S2 is for determining that the post-catalyst air-fuel ratio is leaner than the stoichiometric region. It is a threshold value (a region between the first threshold value and the second threshold value is a stoichiometric region). Further, the third threshold value S3 is a catalyst deterioration degree detection threshold value used in the block 604 of FIG. 6, and in this example, as shown in FIG. 8, in the vicinity of the first threshold value S1 (slightly more than S1). (Lean side) threshold value S3A (used when the sensitivity on the lean side is high) and threshold value S3B (rich side) near the second threshold value S2 (slightly richer than S2) as shown in FIG. Two types) are available.

Next, a method for detecting the degree of deterioration of the catalyst 50 using the output of the downstream O ₂ sensor 52 and the third threshold value S3 (catalyst deterioration degree detection threshold value) will be described with reference to FIGS. explain.

As shown in FIG. 10, when the sensitivity on the lean side is high, a threshold value S3A in the vicinity of the first threshold value S1 is used as the third threshold value S3. In this case, the output from the downstream O ₂ sensor 52 crosses the threshold value S3A from the lean side to the rich side until the threshold value S3A is crossed from the lean side to the rich side again as one cycle, and in each cycle, the downstream O ₂ sensor The rich side time TRR when the output of 52 is equal to or greater than the threshold value S3A and the lean side time TRL where the output of the downstream O ₂ sensor 52 is equal to or less than the threshold value S3A are measured, and the ratio ε = TRLn / TRRn (n is the cycle number). calculate. When the ratio ε is equal to or less than the first set ratio (for example, 1/3), the count value of the catalyst deterioration degree counter is increased by 1.

As shown in FIG. 11, when the sensitivity on the rich side is high, a threshold value S3B in the vicinity of the second threshold value S2 is used as the third threshold value S3. In this case, the output threshold S3B of the downstream O ₂ sensor 52 again threshold S3B from across from the rich side to the lean side from the rich side to cross the lean side as one cycle, in each cycle, the downstream O ₂ sensor The rich side time TRR when the output of 52 is equal to or higher than the threshold value S3B and the lean side time TRL when the output of the downstream O ₂ sensor 52 is equal to or lower than the threshold value S3B are measured, and the ratio ε = TRLn / TRRn (n is the cycle number) calculate. When the ratio ε is equal to or greater than the second set ratio (for example, 3/1), the count value of the catalyst deterioration degree counter is increased by 1.

12 shows a case where the ratio ε is less than or equal to the first set ratio (FIG. 10), and FIG. 13 shows a case where the ratio ε is greater than or equal to the second set ratio (FIG. 11). It is a time chart showing a change in deterioration degree counter (count value), (C) target air-fuel ratio (solid line is control of this embodiment, broken line is conventional control), (D) downstream O ₂ sensor output (voltage). .

  As a representative of FIG. 12, correction of the target air-fuel ratio in the air-fuel ratio control of the present embodiment will be described. Since FIG. 13 is the reverse correction of FIG. 12, the description is omitted.

When the engine operating region starts to shift from a low air amount to a high air amount region (high exhaust temperature region), the output of the downstream O ₂ sensor 52 crosses the third threshold value S3, and the ratio ε (= TRL / TRR) becomes equal to or less than the first set ratio, and the catalyst deterioration degree counter is counted up. At this time, the target air-fuel ratio is gradually lowered to the lean side in accordance with a correction value set according to the catalyst deterioration degree counter (count value). As a result, the post-catalyst air-fuel ratio falls within the stoichiometric region.

  The correction value of the target air-fuel ratio is not held in the table as shown in FIG. 7, but when a preset count value is reached, such as points A and B in FIG. You may make it correct | amend by predetermined value.

  In this way, by correcting the target air-fuel ratio for each operation region in accordance with the degree of deterioration of the catalyst 50, the post-catalyst air-fuel ratio is suppressed from greatly deviating from the stoichiometric region to the lean side or the rich side, and near the stoichiometric range. Therefore, even if a low precious metal catalyst is used and the catalyst is somewhat deteriorated, the exhaust emission characteristics can be prevented from deteriorating so much in all operating regions including a high air amount and a high exhaust temperature region.

  Further, the count value of the deterioration degree counter is stored and updated as a learning value for each operation region divided according to the engine speed and the intake pipe internal pressure (engine load) as described above. Sometimes, the target air-fuel ratio is corrected using the learned value stored and updated for each operation region. By learning the degree of catalyst deterioration for each operation region in this manner, the post-catalyst air-fuel ratio converges quickly in the stoichiometric region, and as a result, deterioration of exhaust emission characteristics can be further suppressed.

  In the block diagram showing the air-fuel ratio control example shown in FIG. 6 described above, the target air-fuel ratio is corrected according to the degree of deterioration of the catalyst 50. However, instead of the target air-fuel ratio, the control gain (PID feedback control) P minutes, I minutes, and D minutes) may be corrected.

  Hereinafter, a case where the control gain (P, I, and D) is corrected according to the degree of deterioration of the catalyst 50 will be described.

  FIG. 14 is an air-fuel ratio control block diagram corresponding to FIG. 6, and portions corresponding to the respective portions shown in FIG.

  Here, the count value (learned value) of the deterioration degree counter stored and updated in block 606 is used for the calculation (correction) of the control gain (P minutes, I minutes, and D minutes) in block 620.

  FIG. 15 shows a detailed configuration example of the P component calculation means when the control gain is calculated according to the count value of the catalyst deterioration degree counter, in other words, according to the deterioration degree of the catalyst 50 in the block 620 of FIG. It is a block diagram.

  In block 1501, the base P is set by table search according to the difference between the pre-catalyst air-fuel ratio obtained from the output of the upstream air-fuel ratio sensor 51 and the target air-fuel ratio obtained in blocks 602 and 603 and the adder / subtractor 609. . A plurality of types (for example, three types in this case) of tables for the base P are prepared in accordance with the degree of deterioration of the catalyst 50, and the tables for the three types of base P (X1, X2, X3) are prepared as the catalyst. It is designed to be used by switching according to the degree of deterioration. That is, the pace P is changed (corrected) according to the degree of deterioration of the catalyst 50. In this example, for the base P, a value having no interpolation value is searched for the difference from the target air-fuel ratio.

  In block 1502, a map search is performed for the P-component gain KP based on the engine speed and the intake pipe internal pressure. A multiplier 1503 multiplies the P component gain KP by the base P component and outputs the P component.

  FIG. 16 is a block diagram showing a detailed configuration example of the D component calculation means when the control gain is calculated according to the degree of deterioration of the catalyst 50 in the block 620 of FIG.

  Here, the delay unit 1601 and the adder 1602 calculate the amount of change per unit time (difference change rate) of the difference between the pre-catalyst air-fuel ratio and the target air-fuel ratio obtained from the output of the upstream air-fuel ratio sensor 51. In block 1603, the base D is set without interpolation by table search according to the difference change rate. A plurality of types (for example, three types) of tables for the base D are prepared according to the degree of deterioration of the catalyst 50, and the tables for the three types of base D (Y1, Y2, Y3) are prepared as catalyst bases. It is designed to be used by switching according to the degree of deterioration. That is, the pace D is changed (corrected) according to the degree of deterioration of the catalyst 50. In block 1604, a map search is performed for the D gain KD based on the engine speed and the intake pipe internal pressure. A multiplier 1605 multiplies the D component gain KD by the base D component and outputs the D component.

  FIG. 17 is a block diagram showing a detailed configuration example of the I component calculating means when calculating the control gain according to the degree of deterioration of the catalyst 50 in the block 620 of FIG.

  In block 1701, the base I component is not interpolated by table search according to the difference between the pre-catalyst air-fuel ratio obtained from the output of the upstream air-fuel ratio sensor 51 and the target air-fuel ratio obtained in blocks 602 and 603 and the adder / subtractor 609. Set with. A plurality of types (for example, three types in this case) of the base I table are prepared in accordance with the degree of deterioration of the catalyst 50. The three base I tables (Z1, Z2, Z3) It is designed to be used by switching according to the degree of deterioration. That is, the pace I is changed (corrected) according to the degree of deterioration of the catalyst 50. The base I is integrated by a delay unit 1702 and an adder 1703. In block 1704, a map search is performed for the I-component gain KI based on the engine speed and the intake pipe internal pressure. The multiplier 1705 multiplies the I component gain KI by the base I component and outputs the I component.

18 shows a case where the ratio ε is equal to or lower than the first set ratio (FIG. 10), and FIG. 19 shows a case where the ratio ε is equal to or higher than the second set ratio (FIG. 11). deterioration degree counter (count value) is a time chart showing changes in (C) P content (solid line control of this embodiment, and the broken line of the conventional control), (D) downstream O ₂ sensor output (voltage).

  As a representative of FIG. 18, correction of the control gain (P component) in the air-fuel ratio control of this example will be described. Since FIG. 19 is the reverse correction of FIG. 18, the description is omitted.

When the engine operating region starts to shift from a low air amount to a high air amount region (high exhaust temperature region), the output of the downstream O ₂ sensor 52 crosses the third threshold value S3 (catalyst deterioration degree detection threshold value). Thus, the ratio ε (= TRL / TRR) becomes equal to or less than the first set ratio, and the catalyst deterioration degree counter is counted up. At this time, the P component (base P component) is selected from the tables X1, X2, and X3 according to the degree of deterioration of the catalyst. Here, for example, the rich side gain is the same as the current state, and only the lean side gain is set to be smaller than normal, and when the count value of the deterioration degree counter is further increased, only the lean side gain is set to be smaller.

  In this way, by correcting the control gain for each operation region according to the degree of deterioration of the catalyst 50, the post-catalyst air-fuel ratio is suppressed from greatly deviating from the stoichiometric region to the lean side or the rich side, and is maintained near the stoichiometric range. Therefore, even if a low precious metal catalyst is used and the catalyst is somewhat deteriorated, the exhaust emission characteristics can be prevented from deteriorating so much in all operation regions including a high air amount and a high exhaust temperature region.

  Further, the count value of the deterioration degree counter is stored and updated as a learning value for each operation region divided according to the engine speed and the intake pipe internal pressure (engine load) as described above. Sometimes, the target air-fuel ratio is corrected using the learned value stored and updated for each operation region. By learning the degree of catalyst deterioration for each operation region in this manner, the post-catalyst air-fuel ratio converges quickly in the stoichiometric region, and as a result, deterioration of exhaust emission characteristics can be further suppressed.

1 engine control unit 10 engine 20 intake manifold 25 throttle valve 30 fuel injection valve 34 an ignition coil 35 an ignition plug 40 exhaust passage 50 three-way catalyst 51 upstream air-fuel ratio sensor 52 downstream _{O 2} sensor 55 crank angle sensor 59 intake pressure sensor 100 ECU
101 engine speed calculation means 102 basic injection amount calculation means 103 basic injection amount correction coefficient calculation means 105 F / B control coefficient calculation means 106 catalyst deterioration degree detection means 108 target air-fuel ratio correction value calculation means 110 basic injection amount correction means

Claims (7)

An exhaust purification catalyst is provided in the exhaust passage, and an upstream air-fuel ratio sensor having a linear output characteristic for detecting the pre-catalyst air-fuel ratio is provided upstream from the catalyst, and downstream from the catalyst. An engine control device provided with a downstream O ₂ sensor that outputs a switching signal for identifying whether the post-catalyst air-fuel ratio is richer or leaner than stoichiometric,
Based on the means for setting the target air-fuel ratio for the pre-catalyst air-fuel ratio and the outputs of the upstream air-fuel ratio sensor and the downstream O ₂ sensor, a fuel is used to converge the pre-catalyst air-fuel ratio to the target air-fuel ratio. The degree of deterioration of the catalyst is detected by using air-fuel ratio control means for performing feedback control on the injection amount, the output of the downstream O ₂ sensor, and a deterioration degree detection threshold value set in or near the stoichiometric region. A deterioration degree learning means for storing and updating the detected deterioration degree as a learning value for each operation region, and a learning value stored in the learning means is reflected in the feedback control performed by the air-fuel ratio control means. And a learning value reflecting means. An engine control device comprising: The deterioration degree learning means determines whether the output of the downstream O ₂ sensor crosses the deterioration degree detection threshold value from the lean side to the rich side and then crosses the deterioration degree detection threshold value from the lean side to the rich side again. As a cycle, in each cycle, the rich side time when the output of the downstream O ₂ sensor is not less than the deterioration degree detection threshold and the lean side time that is not more than the deterioration degree detection threshold are measured, and the lean side time is measured. When the ratio of the rich side time to the first set ratio is equal to or less than the first set ratio, the catalyst deterioration degree count value is counted up, and the count value is used as the learning value of the catalyst deterioration degree for each operation region. The engine control device according to claim 1, wherein the engine control device stores and updates the storage unit. The deterioration degree learning means determines whether the downstream O ₂ sensor output crosses the deterioration degree detection threshold value from the rich side to the lean side and then crosses the deterioration degree detection threshold value again from the rich side to the lean side. As a cycle, in each cycle, the rich side time when the output of the downstream O ₂ sensor is not less than the deterioration degree detection threshold and the lean side time that is not more than the deterioration degree detection threshold are measured, and the lean side time is measured. When the ratio of the rich side time to the second ratio is equal to or greater than the second set ratio, the catalyst deterioration degree count value is counted up, and the count value is used as the learning value of the catalyst deterioration degree for each operation region. The engine control device according to claim 1, wherein the engine control device is stored and updated in a storage unit.   The threshold value for detecting the degree of deterioration is set to a level different from a threshold value for determining whether the post-catalyst air-fuel ratio is richer or leaner than the stoichiometric region. The control apparatus of the engine as described in any one of 1-3.   The engine control device according to any one of claims 1 to 4, wherein the learning value reflecting means is configured to correct the target air-fuel ratio using the learning value.   5. The learning value reflecting means is adapted to correct a control gain of the feedback control performed by the air-fuel ratio control means using the learning value. The engine control device described.   The engine control device according to any one of claims 1 to 6, wherein the operation region is divided according to an engine speed and an engine load.

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