Control device for an internal combustion engine and method for controlling the same

Abstract

The present invention provides a control device for internal combustion engine and a control method for the same which are capable of suppressing a worsening of emissions during fuel cutoff recovery.　The control device for an internal combustion engine performs feedback control of the air-fuel ratio of an internal combustion engine. When combustion is restarted after fuel cutoff in the internal combustion engine, an increased amount of fuel is supplied in a state where air-fuel ratio feedback is stopped, and an air-fuel ratio criterion is set in accordance with the rich-side peak value of the air-fuel ratio after commencement of fuel increase. The present invention is characterized in that when the set air-fuel ratio criterion is met after fuel increase, the air-fuel ratio feedback is commenced.

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine and a control method thereof, and more particularly to an improvement in air-fuel ratio control during fuel cut recovery.

Background Art

[0002] Patent Document 1 describes an air-fuel ratio control method and an air-fuel ratio control device for an internal combustion engine that perform fuel cut during deceleration of a vehicle and stop air-fuel ratio feedback control. In this Patent Document 1, when the air-fuel ratio reaches within a predetermined range near the target air-fuel ratio after the resumption of fuel supply until the end of fuel increment, or when the duration of open-loop control reaches a predetermined upper limit time, the air-fuel ratio feedback control is resumed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the resumption of air-fuel ratio feedback control is determined by the target air-fuel ratio, when a temporary deviation in the air-fuel ratio occurs due to manufacturing variations of parts or injector failures, etc., the resumption of feedback control is delayed. During this delay period, emissions may deteriorate. Also, if it is determined by the duration of open-loop control, emissions may still deteriorate until the predetermined upper limit time is reached.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an internal combustion engine and a control method thereof that can suppress deterioration of emissions during fuel cut recovery.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a control device for an internal combustion engine that provides feedback control of the air-fuel ratio of the internal combustion engine, wherein the control device provides feedback control of the air-fuel ratio when combustion is restarted after fuel cut-off of the internal combustion engine. control With the system stopped, the amount of fuel supplied is increased, and the rich-side peak value of the air-fuel ratio after the start of the fuel increase is detected. The detected rich-side peak value of the air-fuel ratio is Ideal air-fuel ratio Air-fuel ratio set to sandwich the center Criteria for restarting feedback control and the rich-side peak value of the air-fuel ratio under normal conditions against 、 Shifted towards the rich side doing In some cases The aforementioned restart criteria Shift to the rich side , Shifted towards the side doing In some cases The aforementioned restart criteria Shift to the lean side ,before After increasing the amount of fuel, The air-fuel ratio shift done Reopening When the criteria are met, the air-fuel ratio feedback control of Reopening A control device for an internal combustion engine is provided, configured to do so.

[0007] Furthermore, according to another aspect of the present invention, a control method for an internal combustion engine that provides feedback control of the air-fuel ratio of the internal combustion engine, wherein the control method involves cutting off the supply of fuel to the internal combustion engine and, when the combustion of the internal combustion engine is restarted after the supply of fuel has been cut off, providing air-fuel ratio feedback control. control This involves increasing the amount of fuel supplied to the internal combustion engine while the engine is stopped, The rich-side peak value of the air-fuel ratio after the start of increasing the fuel amount is detected, and the detected rich-side peak value of the air-fuel ratio is Ideal air-fuel ratio Air-fuel ratio set to sandwich the center Criteria for restarting feedback control and the rich-side peak value of the air-fuel ratio under normal conditions against 、 Shifted towards the rich side doing In some cases The aforementioned restart criteria Shift to the rich side , Shifted towards the side doing In some cases The aforementioned restart criteria Lean to the shift Toss And, after increasing the amount of fuel, The air-fuel ratio shift When the air-fuel ratio criteria are met, the air-fuel ratio feedback control Control of the internal combustion engine by Reopening There is provided a control method for an internal combustion engine including performing

Advantages of the Invention

[0008] In the present invention, at the time of fuel cut recovery, by setting an air-fuel ratio criterion according to the rich-side peak value of the air-fuel ratio after the start of fuel increase, the air-fuel ratio feedback control after fuel cut recovery can be restarted at an appropriate early timing without waiting for the elapse of a predetermined timeout time. Therefore, according to the present invention, it is possible to provide a control device for an internal combustion engine and a control method thereof that can suppress deterioration of emissions at the time of fuel cut recovery.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic configuration diagram for explaining a control device for an internal combustion engine according to an embodiment of the present invention. [Figure 2] It is a functional block diagram showing an extraction of a main part of the control device shown in FIG. 1. [Figure 3] It is for explaining a control method for an internal combustion engine according to an embodiment of the present invention, and is a flowchart showing a control determination operation. [Figure 4] It is a control method following FIG. 3, and is a flowchart showing a criterion calculation operation. [Figure 5A] It is a diagram for explaining the calculation of the first air-fuel ratio correction start criterion in FIG. 4. [Figure 5B] It is a diagram for explaining the calculation of the second air-fuel ratio correction start criterion in FIG. 4. [Figure 6] It shows a method for discriminating a deviation between a rich and a lean air-fuel ratio, and is a waveform diagram when the air-fuel ratio deviates and there is no response delay of the air-fuel ratio. [Figure 7] It shows a method for discriminating a deviation between a rich and a lean air-fuel ratio, and is a waveform diagram when the air-fuel ratio deviates and there is a response delay of the air-fuel ratio. [Figure 8]The criteria for restarting the air-fuel ratio feedback according to the state of the air-fuel ratio deviation are shown, and it is a waveform diagram when the air-fuel ratio deviates and there is no response delay in the air-fuel ratio. [Figure 9] The criteria for restarting the air-fuel ratio feedback according to the state of the air-fuel ratio deviation are shown, and it is a waveform diagram when the air-fuel ratio deviates and there is a response delay in the air-fuel ratio. [Figure 10] It is a control method following FIG. 4 and is a flowchart showing the operation of calculating the feedback correction amount. [Figure 11] It is a diagram for explaining the calculation of the air-fuel ratio correction start criteria in FIG. 10. [Figure 12] It is a timing chart for explaining the calculation of the A / F deviation. [Figure 13] It is a timing chart showing the air-fuel ratio, air-fuel ratio correction, and NOx generation status in the control method of a conventional internal combustion engine. [Figure 14] It is a timing chart showing the air-fuel ratio, air-fuel ratio correction, and NOx generation status in the control method of an internal combustion engine according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is for explaining a control device for an internal combustion engine according to an embodiment of the present invention, and shows a schematic configuration of the internal combustion engine 11 and its control device 51. In the internal combustion engine 11, the intake air passes through the air flow meter 12, the electronically controlled throttle valve 13, and the collector 14 in this order, and then is sucked into the combustion chamber 17 through the intake pipe 15 and the intake valve 16 provided in each cylinder.

[0011] The fuel injection valves 21 are respectively installed in the intake pipes 15 of each cylinder, and fuel is injected into the intake pipes 15. Note that the internal combustion engine 11 may be a direct injection type internal combustion engine in which the fuel injection valve 21 directly injects fuel into the combustion chamber 17.

[0012] Furthermore, the internal combustion engine 11 is equipped with an ignition system 24 having an ignition coil 22 and a spark plug 23 for each cylinder. The fuel-air mixture in the combustion chamber 17 is ignited and combusted by a spark generated by the spark plug 23, and the exhaust gas produced in the combustion chamber 17 is discharged through the exhaust valve 25 to the exhaust pipe 26 provided in each cylinder.

[0013] The exhaust system of the internal combustion engine 11 includes a first exhaust gas purification catalyst 31 and a second exhaust gas purification catalyst 33. The first exhaust gas purification catalyst 31 and the second exhaust gas purification catalyst 33 are exhaust gas purification devices that purify the exhaust gas from the internal combustion engine 11 through the action of a catalyst (for example, a three-way catalyst) that has oxygen storage capacity. The first exhaust gas purification catalyst 31 is positioned directly below the manifold of the exhaust pipe 26, and the second exhaust gas purification catalyst 33 is positioned in the exhaust duct 32 downstream of the first exhaust gas purification catalyst 31.

[0014] Furthermore, the internal combustion engine 11 is equipped with an air-fuel ratio sensor 34 and an oxygen sensor 35 as exhaust sensors for detecting the air-fuel ratio of the exhaust gas of the internal combustion engine 11. The air-fuel ratio sensor 34 is a full-range air-fuel ratio sensor that obtains a linear output signal RABF corresponding to the air-fuel ratio of the exhaust gas, and is installed upstream of the first exhaust gas purification catalyst 31.

[0015] On the other hand, the oxygen sensor 35 is a rich / lean sensor that detects whether the exhaust air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio (in other words, the excess air ratio λ=1), and is installed downstream of the first exhaust purification catalyst 31, more specifically, downstream of the first exhaust purification catalyst 31 and upstream of the second exhaust purification catalyst 33. The oxygen sensor 35 generates an electromotive force corresponding to the oxygen concentration in the exhaust gas, and the output signal VO2R (output voltage) changes abruptly at the stoichiometric air-fuel ratio. For example, the oxygen sensor 35 outputs a voltage of about 1V when the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio, and outputs a voltage close to 0V when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio.

[0016] Furthermore, the internal combustion engine 11 is equipped with an exhaust gas recirculation device 43. The exhaust gas recirculation device 43 includes an exhaust gas recirculation pipe 41 that connects the exhaust pipe 26 and the collector 14, and an exhaust gas recirculation control valve 42 that controls the exhaust gas recirculation flow rate by adjusting the opening area of ​​the exhaust gas recirculation pipe 41.

[0017] The control device 51 is an electronic control device for controlling the operation of the internal combustion engine 11, and includes a microcomputer 51A. The microcomputer 51A includes a microprocessor 51A1, non-volatile memory 51A2, and volatile memory (not shown in the figure).

[0018] The control device 51 then acquires detection signals from various sensors and, through calculation processing based on these detection signals, determines and outputs operation signals to control fuel injection by the fuel injector 21, the opening degree of the electronically controlled throttle valve 13, ignition by the spark plug 23, the opening degree of the exhaust recirculation control valve 42, and so on, thereby controlling the operation of the internal combustion engine 11.

[0019] The control device 51 acquires the output signal RABF from the air-fuel ratio sensor 34 and the output signal VO2R from the oxygen sensor 35, as well as the intake air flow signal QA related to the intake air flow rate of the internal combustion engine 11 output by the air flow meter 12, the rotation signal POS related to the rotational angle position of the crankshaft 53 output by the crank angle sensor 52, the water temperature signal TW related to the coolant temperature of the internal combustion engine 11 output by the water temperature sensor 54, and the accelerator opening signal ACC related to the opening degree of the accelerator pedal 56 output by the accelerator opening sensor 55.

[0020] The control device 51 calculates the target ignition timing and target exhaust gas recirculation flow rate according to the engine operating conditions detected based on the various signals acquired (specifically, engine rotational speed, engine load, engine temperature, etc.), outputs an ignition control signal to the ignition coil 22 according to the target ignition timing, and outputs an opening control signal to the exhaust gas recirculation control valve 42 according to the target exhaust gas recirculation flow rate. Furthermore, the control device 51 calculates a target opening degree TA of the electronically controlled throttle valve 13 from the accelerator opening signal ACC, and controls the throttle motor of the electronically controlled throttle valve 13 according to the target opening degree TA.

[0021] Furthermore, the control device 51 calculates a fuel injection pulse width TI [ms], which is proportional to the amount of fuel injected from the fuel injection valve 21 in one combustion cycle, based on the engine operating conditions. The control device 51 then controls the air-fuel ratio of the internal combustion engine 11 by outputting an injection pulse signal with a fuel injection pulse width TI to the fuel injection valve 21 at a predetermined injection timing for each cylinder, thereby controlling the amount of fuel supplied to the internal combustion engine 11.

[0022] Here, in the operating region where the air-fuel ratio feedback control conditions are met, the control device 51 corrects the fuel injection pulse width TI based on the output signal RABF of the air-fuel ratio sensor 34 and the output signal VO2R of the oxygen sensor 35, that is, the air-fuel ratio of the exhaust upstream of the first exhaust gas purification catalyst 31 and the air-fuel ratio of the exhaust downstream of the first exhaust gas purification catalyst 31, and automatically adjusts the air-fuel ratio of the internal combustion engine 11. Furthermore, the control device 51 has a function to set air-fuel ratio criteria according to the rich-side peak value of the air-fuel ratio after the fuel enrichment has started, and to change the preset reference value of the air-fuel ratio criteria according to the rich-side peak value of the air-fuel ratio when air-fuel ratio feedback is restarted.

[0023] Figure 2 is a functional block diagram showing the essential parts of the control device 51 shown in Figure 1. The control device 51 includes the functions of an air-fuel ratio control unit 511, a measurement unit 512, a control determination unit 513, a criteria calculation unit 514, and a feedback correction amount calculation unit 515, all as software.

[0024] The air-fuel ratio control unit 511 performs active air-fuel ratio control, which is a control that adjusts the fuel injection amount so that the air-fuel ratio of the exhaust downstream of the first exhaust purification catalyst 31 alternately switches between rich and lean. The air-fuel ratio control unit 511, for example, controls the fuel injection valve 21 to reverse the air-fuel ratio of the exhaust downstream of the first exhaust purification catalyst 31 from rich to lean. In this case, it gradually reduces the fuel injection amount using PI control to make the air-fuel ratio lean. Once the air-fuel ratio of the exhaust downstream of the first exhaust purification catalyst 31 has reversed to lean, it gradually increases the fuel injection amount using PI control to make the air-fuel ratio rich.

[0025] The measurement unit 512 acquires detection signals from the air flow meter 12, air-fuel ratio sensor 34, oxygen sensor 35, crank angle sensor 52, water temperature sensor 54, and accelerator opening sensor 55. The control determination unit 513 performs calculation processing based on these detection signals and executes a control determination operation. Specifically, it detects the peak value of the air-fuel ratio after the start of fuel cut recovery and detects the amount of deviation of the air-fuel ratio from this rich-side peak value. Here, the peak value is the value at which the amount of change in the air-fuel ratio (the point of change from rich to lean) is maximum. The detection determination of the peak value is performed by detecting the point at which the sign of the parameter change amount of the actual air-fuel ratio reverses (for example, from positive to negative) after the start of fuel enrichment following the fuel cut. The calculation of this peak value of the air-fuel ratio is performed by calculating the value of the first rich-side peak detected after the start of fuel enrichment following the fuel cut.

[0026] As described above, the amount of deviation in the air-fuel ratio is calculated by detecting the rich-side peak of the air-fuel ratio and using this peak value as the basis. The criteria calculation unit 514 calculates appropriate criteria (criteria different from normal control) corresponding to the amount of deviation in the air-fuel ratio based on the calculation processing results of the control determination unit 513. The criteria calculated by this criteria calculation unit 514 are the criteria for restarting air-fuel ratio feedback. Then, the feedback correction amount calculation unit 515 calculates the feedback correction amount from the calculated criteria, and air-fuel ratio correction is performed based on this feedback correction amount.

[0027] In other words, the control determination unit 513 performs control determination operations as shown in the flowchart of Figure 3. First, it determines whether or not the vehicle equipped with the internal combustion engine 11 is in motion based on information such as the vehicle speed signal input from a vehicle speed sensor (not shown), the accelerator opening signal ACC input from the accelerator opening sensor 55, the water temperature signal TW input from the water temperature sensor 54, and the rotation signal POS input from the crank angle sensor 52 (step ST1). If it is determined that the vehicle is in motion, it determines whether or not the accelerator is off (step ST2).

[0028] Then, when it is determined that the accelerator has been released, the fuel injector 21 is controlled to cut off the fuel supply (step ST3), and the air-fuel ratio correction is stopped (step ST4). If it is determined in step ST1 that the vehicle is not moving, and if it is determined in step ST2 that the accelerator is not released, the control determination is terminated and the system returns to other control operations.

[0029] In the next step, ST5, it is determined whether or not a recovery from fuel cut has occurred. Recovery from fuel cut (fuel cut recovery) is performed, for example, by the driver pressing the accelerator pedal 56. If a fuel cut recovery is determined, the amount of fuel injected is increased (step ST6), and the air-fuel ratio is monitored by the air-fuel ratio sensor 34 and the oxygen sensor 35 (step ST7). Subsequently, the change in the air-fuel ratio (Δair-fuel ratio) is calculated (step ST8). Here, Δair-fuel ratio is "air-fuel ratio - previous air-fuel ratio value (50 msec ago)".

[0030] Next, the previous change in the air-fuel ratio (ΔAir-Fuel Ratio Previous Value) is compared with the current change in the air-fuel ratio (ΔAir-Fuel Ratio) (Step ST9). If the ΔAir-Fuel Ratio Previous Value is smaller than the ΔAir-Fuel Ratio, the air-fuel ratio peak value is saved (for example, stored in memory 51A2) (Step ST10). Subsequently, the extracted air-fuel ratio peak value is compared with the reference value to determine whether "Reference Value > Extracted Peak Value" (Step ST11). If the reference value is determined to be smaller than or equal to the extracted peak value, it is determined whether "Reference Value < Extracted Peak Value" (Step ST12). If the reference value is determined to be larger than or equal to the extracted peak value, normal control is performed and the process ends (Step ST13).

[0031] On the other hand, if the reference value is determined to be greater than the extracted peak value in step ST11, and if the reference value is determined to be less than the extracted peak value in step ST12, the criteria calculation unit 514 calculates the criteria, respectively. Step ST11 detects the amount of air-fuel ratio rich deviation, and step ST12 detects the amount of air-fuel ratio lean deviation. If the extracted air-fuel ratio peak value differs from the reference value, the criteria for restarting air-fuel ratio feedback are calculated and the air-fuel ratio criteria are changed according to the amount of air-fuel ratio rich or lean deviation.

[0032] The criteria calculation unit 514 performs the criteria calculation operation as shown in the flowchart of Figure 4. In step ST14, the calculation of "air-fuel ratio peak reference value - air-fuel ratio peak value" is performed to obtain the air-fuel ratio peak deviation value (step ST15). Next, the first air-fuel ratio correction start criterion is calculated (step ST16). The first air-fuel ratio correction start criterion is the correction amount on the rich side. Subsequently, the second air-fuel ratio correction start criterion is calculated (step ST17). The second air-fuel ratio correction start criterion is the correction amount on the lean side.

[0033] Figure 5A shows the relationship between input and output when the criteria calculation unit 514 calculates the first air-fuel ratio correction start criteria in step ST16. When the input (rich side) changes to "-2.0", "-1.5", "-1.0", "-0.5", "0.5", "1.0", "1.5", and "2.0", the output becomes "12.4", "12.9", "13.4", "13.9", "14.9", "15.4", "15.9", and "16.4", respectively.

[0034] Figure 5B shows the relationship between input and output when the criteria calculation unit 514 calculates the second air-fuel ratio correction start criterion in step ST17. When the input (lean deviation side) changes to "-2.0", "-1.5", "-1.0", "-0.5", "0.5", "1.0", "1.5", and "2.0", the output becomes "13.0", "13.5", "14.0", "14.5", "15.5", "16.0", "16.5", and "17.0", respectively.

[0035] Next, it is determined whether the fuel enrichment is complete (step ST18), and if it is determined to be complete, the timer starts counting (step ST19). In the next step, ST20, the timer count value is compared with the criteria. If "timer count value < criteria", it is determined whether "air-fuel ratio ≥ first criterion" (step ST21). If the air-fuel ratio is greater than or equal to the first criterion, it is determined whether "air-fuel ratio ≤ second criterion" (step ST22).

[0036] Then, if the air-fuel ratio is less than or equal to the second criterion, and if the timer count value in step ST20 is greater than or equal to the criterion, the feedback correction amount is calculated. Furthermore, if fuel enrichment is not completed in step ST18, if the air-fuel ratio is less than the first criterion in step ST21, or if the air-fuel ratio is greater than the second criterion in step ST22, the process returns to step ST14 and repeats the operations up to step ST22.

[0037] Figures 6 and 7 show methods for determining whether the air-fuel ratio is rich or lean, respectively. Figure 6 shows the waveform when the air-fuel ratio is off but there is no response delay, and Figure 7 shows the waveform when the air-fuel ratio is off but there is a response delay. Figures 8 and 9 show the criteria for restarting air-fuel ratio feedback depending on the state of the air-fuel ratio off, respectively. Figure 8 shows the waveform when the air-fuel ratio is off but there is no response delay, and Figure 9 shows the waveform when the air-fuel ratio is off but there is a response delay.

[0038] As shown in Figure 6, the rich-side peak value under normal conditions temporarily deviates from a predetermined range ΔP centered on the ideal air-fuel ratio (14.7), but converges quickly. The rich or lean deviation of the air-fuel ratio is determined by the size of the gap with the rich-side peak of the air-fuel ratio. This rich-side peak is the value when the direction of change in the air-fuel ratio reverses from the rich direction to the lean direction. Figure 7 shows an ATF response delay period between times T1 and T2 compared to Figure 6, but from time T2 onward it is the same as in Figure 6. Therefore, even with the delay in the air-fuel ratio response, the deterioration of emissions is essentially only between times T1 and T2, and the impact on exhaust is minimal.

[0039] Furthermore, as shown in Figure 8, the air-fuel ratio may deviate from the normal value towards either the rich side or the lean side. Therefore, the restart criteria for the feedback control, which are set to be fluctuating around the ideal air-fuel ratio (14.7), are changed (shifted) as shown by arrow AA when the air-fuel ratio deviates from the normal value towards the rich side. Also, when the air-fuel ratio deviates from the normal value towards the lean side, the criteria are changed (shifted) as shown by arrow AB. Note that while Figure 9 shows an ATF response delay period between times T1 and T2 compared to Figure 8, the situation after time T2 is the same as in Figure 8. Therefore, even with the delay in the air-fuel ratio response, the deterioration of emissions is essentially only between times T1 and T2, and the impact on exhaust is minimal.

[0040] Figure 10 shows the calculation operation of the feedback correction amount performed by the feedback correction amount calculation unit 515. After the fuel enrichment is complete, if the timer count value is greater than or equal to the criteria, and the air-fuel ratio is greater than or equal to the first criterion and less than or equal to the second criterion, the air-fuel ratio peak deviation value is calculated (step ST23), and the feedback correction amount is calculated based on this air-fuel ratio peak deviation value (step ST24). Subsequently, air-fuel ratio correction is started based on this feedback correction amount (step ST25). In this way, the amount of change in the feedback gain of the air-fuel ratio control is changed according to the set air-fuel ratio criteria. Then, when the air-fuel ratio after the fuel cut recovery is complete exceeds the criteria determined above, the air-fuel ratio feedback is restarted.

[0041] Figure 11 is a diagram illustrating the calculation of the air-fuel ratio correction start criteria in Figure 10. It shows the relationship between the input and output when calculating the feedback correction amount in step ST24. When the input (air-fuel ratio deviation value) changes to "-2.0", "-1.5", "-1.0", "-0.5", "0.5", "1.0", "1.5", and "2.0", the output becomes "0.05", "0.03", "0.02", "0.01", "0.01", "0.02", "0.03", and "0.05", respectively. Thus, when the deviation of the rich-side peak value of the air-fuel ratio is large, it is good to reduce the amount of change in the feedback gain.

[0042] Figure 12 is a timing chart illustrating the calculation of the A / F deviation. At time t0, fuel cut is performed on the internal combustion engine 11, air-fuel ratio correction is prohibited, and air-fuel ratio correction is stopped. At the next time t1, when the accelerator is detected by the accelerator opening signal ACC, fuel cut recovery is performed and combustion of the internal combustion engine 11 is restarted. Between times t1 and t2, fuel is supplied with increased amount (rich spike) while air-fuel ratio feedback is stopped.

[0043] In this case, the air-fuel ratio will deviate from the target air-fuel ratio (shown by the dashed line) to the measured value (shown by the solid line) from the rich spike until the restart of air-fuel ratio feedback control. The difference between the air-fuel ratio peak reference value and the measured value is the air-fuel ratio peak deviation value. Subsequently, when correction of the air-fuel ratio is permitted at time t3, after a predetermined period of time has elapsed, the air-fuel ratio feedback control is restarted, and the deviation in the air-fuel ratio gradually decreases, approaching the target air-fuel ratio.

[0044] Figures 13 and 14 show a comparison of the air-fuel ratio, air-fuel ratio correction, and NOx generation in a conventional control method for an internal combustion engine and an embodiment of the present invention, respectively. As shown in Figure 13, conventionally, between times t2 and t3, the air-fuel ratio deviates from the target air-fuel ratio from the rich spike until the restart of air-fuel ratio feedback control, resulting in worsening NOx emissions and adverse effects even after time t3 when air-fuel ratio feedback control is started.

[0045] In contrast, the present invention sets air-fuel ratio criteria according to the rich-side peak value of the air-fuel ratio after the fuel increase begins during fuel cut recovery, thereby enabling the air-fuel ratio feedback control after fuel cut recovery to be restarted at an appropriate early timing without waiting for a predetermined timeout period to elapse. This makes it possible to provide a control device and control method for an internal combustion engine that can suppress the deterioration of emissions during fuel cut-off recovery.

[0046] As explained above, the present invention improves the accuracy of air-fuel ratio control and mitigates emission deterioration caused by air-fuel ratio deviations. As a result, it has been confirmed that the regulatory values ​​for ULEV (ultralow emission vehicle) 50 can be satisfied. Moreover, since there is no need to add new equipment or parts, the cost of exhaust gas countermeasures can also be reduced. Therefore, a control device for an internal combustion engine and a control method thereof can be obtained that can suppress the deterioration of emissions during fuel cut-off recovery.

[0047] The configurations and control methods described in the embodiments described above are merely schematic representations to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the embodiments described, and can be modified in various forms as long as it does not deviate from the scope of the technical idea set forth in the claims. [Explanation of Symbols]

[0048] 11...Internal combustion engine, 12...Air flow meter, 31...First exhaust gas purification catalyst, 34...Air-fuel ratio sensor, 35...Oxygen sensor (exhaust sensor), 51...Control device, 51A...Microcomputer, 51A1...Microprocessor, 51A2...Non-volatile memory, 511...Air-fuel ratio control unit, 512...Measurement unit, 513...Control determination unit, 514...Criteria calculation unit, 515...Feedback correction amount calculation unit

Claims

1. A control device for an internal combustion engine that provides feedback control of the air-fuel ratio of the internal combustion engine, wherein the control device is When combustion restarts after the fuel cut-off of the internal combustion engine, the air-fuel ratio feedback control is stopped, and the amount of fuel supplied is increased. The rich-side peak value of the air-fuel ratio after the fuel enrichment begins is detected, and if the detected rich-side peak value of the air-fuel ratio is shifted to the rich side relative to the restart criteria of the air-fuel ratio feedback control, which are set to sandwich the ideal air-fuel ratio, and the rich-side peak value of the normal air-fuel ratio, the restart criteria are shifted to the rich side; if it is shifted to the lean side, the restart criteria are shifted to the lean side. After the fuel increase, when the air-fuel ratio reaches the shifted restart criteria, the air-fuel ratio feedback control is restarted. A control device for an internal combustion engine, characterized by being configured in such a way.

2. The control device for an internal combustion engine according to claim 1, wherein the control device is configured to restart the air-fuel ratio feedback control after a predetermined timeout period if the air-fuel ratio does not reach the shifted restart criteria.

3. The control device for an internal combustion engine according to claim 1, wherein the rich-side peak value of the air-fuel ratio is the value obtained when the air-fuel ratio reverses from the rich side to the lean side.

4. The control device for an internal combustion engine according to claim 1, wherein if a rich-side peak of the air-fuel ratio occurs during a fuel enrichment period, when the enrichment is completed, the control device is configured to determine an air-fuel ratio peak deviation value according to the rich-side peak value of the air-fuel ratio, calculate a feedback correction amount based on this air-fuel ratio peak deviation value, and restart air-fuel ratio feedback control.

5. The control device for an internal combustion engine according to claim 1, wherein the control device sets a reference value for the rich-side peak value of the air-fuel ratio in advance, compares the reference value with the actual rich-side peak value of the air-fuel ratio, and shifts the restart criterion to the rich side if it is determined that the reference value is greater than the actual rich-side peak value of the air-fuel ratio, and shifts the restart criterion to the lean side if it is determined that the reference value is less than the actual rich-side peak value of the air-fuel ratio.

6. The control device for an internal combustion engine according to claim 1, wherein the shifted restart criteria are leaner than the rich-side peak value of the air-fuel ratio.

7. A control method for an internal combustion engine that provides feedback control of the air-fuel ratio of the internal combustion engine, wherein the control method is: Cutting off the fuel supply to the internal combustion engine, When restarting combustion of the internal combustion engine after the aforementioned fuel supply has been cut off, the fuel is increased and supplied to the internal combustion engine with the air-fuel ratio feedback control stopped. The rich-side peak value of the air-fuel ratio after the fuel enrichment begins is detected, and if the detected rich-side peak value of the air-fuel ratio is shifted to the rich side relative to the restart criteria of the air-fuel ratio feedback control, which are set to sandwich the ideal air-fuel ratio, and the rich-side peak value of the normal air-fuel ratio, the restart criteria are shifted to the rich side; if it is shifted to the lean side, the restart criteria are shifted to the lean side. After the fuel increase, when the air-fuel ratio reaches the shifted restart criteria, the control of the internal combustion engine by the air-fuel ratio feedback control is restarted. A control method for an internal combustion engine, characterized by comprising the following:

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