JP2010265771A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an insufficient torque caused by the sudden acceleration of a vehicle, in an exhaust emission control device for an internal combustion engine performing rich combustion in order to reduce NOx occluded in a NOx catalyst. <P>SOLUTION: An acceleration rate a of the vehicle is obtained (S21). Whether or not a sudden acceleration of the vehicle should be performed is determined (S22) by determining whether or not the acceleration rate a is higher than a predetermined threshold acceleration rate b. When it is determined that the sudden acceleration of the vehicle should be performed (S22:YES), a permission determination flag F for permitting the performance of the rich combustion is set to OFF (F=0) (S23), and normal combustion is performed instead of performing the rich combustion. Since torque is controlled by controlling the amount of fuel injected with respect to fresh air volume in the normal combustion, the torque can be controlled to target torque by adjusting the amount of fuel injected even if the fresh air volume can not follow target air volume in some degree. Therefore, cases of insufficient torque can be reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with a NOx catalyst.

  In a diesel engine or the like, a storage reduction type NOx catalyst (NOx catalyst, Lean NOx Trap, LNT) may be disposed in the middle of an exhaust pipe for the purpose of purifying nitrogen oxide (NOx) in exhaust gas. In the LNT, NOx is occluded in a basic lean atmosphere in a diesel engine, and the occluded NOx is reduced to harmless nitrogen and released by switching to a rich atmosphere at intervals.

  Here, when switching to the rich atmosphere and performing NOx reduction when the intake air amount is large, it is necessary to increase the combustion injection amount in order to obtain a rich air-fuel ratio. Therefore, fuel consumption is worse than when the intake air amount is small. Therefore, in the invention of Patent Document 1, when the intake air amount is in a low flow rate state, the rich atmosphere is switched to perform NOx reduction.

JP 2005-113775 A

  By the way, as a method for forming a rich atmosphere, rich combustion, which is combustion for generating rich gas in an engine cylinder, is known. In this rich combustion, the throttle for controlling the amount of fresh air is set to a smaller opening than that for normal combustion, which is combustion in an engine cylinder with a lean atmosphere, and the amount of fresh air is reduced. The air-fuel ratio is made richer (for example, 14.5 or less) than that at the time of combustion.

  Here, FIG. 12 shows (a) the time change of the acceleration rate of the vehicle, (b) the time change of the fresh air amount, and (c) the time change of the torque during the conventional rich combustion. In FIG. 5B, the broken line indicates the change over time of the target fresh air amount, and the solid line indicates the change over time of the actual fresh air amount. Further, in FIG. 5C, the broken line indicates the change over time of the target torque, and the solid line indicates the change over time of the actual torque. As shown in FIG. 12 (a), when the acceleration rate of the vehicle rapidly increases, the target fresh air amount also increases as shown in FIG. 12 (b). When the target fresh air amount increases, the target torque also increases as shown in FIG. That is, when the acceleration rate of the vehicle suddenly rises, the vehicle is able to accelerate rapidly and rapidly by increasing the amount of fresh air and increasing the torque.

  However, in reality, when the acceleration rate of the vehicle suddenly increases during the rich combustion, the actual fresh air amount cannot follow the target fresh air amount as shown in FIG. In the rich combustion in which the torque is controlled by controlling the fresh air amount with respect to the fuel injection amount, if the fresh air amount cannot follow the target fresh air amount, as shown in FIG. It becomes smaller than the torque, resulting in insufficient torque. Thus, when the torque becomes insufficient, rapid acceleration cannot be performed quickly, and drivability deteriorates. In the invention of Patent Document 1, as described above, the atmosphere is switched to the rich atmosphere when the intake air amount is in a low flow rate state. However, the above problem occurs when the acceleration rate of the vehicle rapidly increases in the rich atmosphere state.

  The present invention has been made in view of the above problems, and in an exhaust gas purification apparatus for an internal combustion engine that performs rich combustion to reduce NOx stored in a NOx catalyst, torque shortage due to rapid acceleration of the vehicle It is an object to reduce the occurrence of the problem.

In order to solve the above-described problems, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of an internal combustion engine mounted on a vehicle and stores NOx in a lean atmosphere and reduces NOx stored in a rich atmosphere. NOx catalyst,
In an exhaust gas purification apparatus for an internal combustion engine, comprising: combustion control means for performing rich combustion, which is combustion in the internal combustion engine in a rich atmosphere, in order to reduce NOx occluded by the NOx catalyst,
An acceleration rate acquisition means for acquiring an acceleration rate of the vehicle;
Rapid acceleration determination means for determining whether or not the vehicle accelerates rapidly by determining whether or not the acceleration rate acquired by the acceleration rate acquisition means is greater than a predetermined threshold acceleration rate;
The combustion control means does not execute the rich combustion when the sudden acceleration judgment means judges that the vehicle is suddenly accelerated.

  According to this, when it is determined by the rapid acceleration determination means that the vehicle is accelerated rapidly, the combustion control means does not execute rich combustion. That is, when the vehicle suddenly accelerates while rich combustion is being performed, the rich combustion is stopped. If the vehicle suddenly accelerates during normal combustion, it is not switched to rich combustion. As a result, normal combustion is performed when the vehicle accelerates rapidly. In normal combustion, the throttle opening is larger and the amount of fresh air is larger than in rich combustion, so the fresh air follows the target fresh air even during sudden acceleration of the vehicle. What can not be reduced. In addition, during normal combustion, the torque is controlled by controlling the fuel injection amount with respect to the new air amount, so the fuel injection amount is adjusted even if the new air amount cannot follow the target fresh air amount. Thus, the torque can be controlled to the target torque. Therefore, the torque shortage can be reduced.

Further, the exhaust gas purification apparatus for an internal combustion engine of the present invention includes an oxygen concentration acquisition means for acquiring the oxygen concentration in the cylinder,
EGR rate acquisition means for acquiring an EGR rate indicating how much exhaust gas has been guided to the intake side by the EGR device that guides a part of the exhaust to the intake side;
The combustion control means sets the throttle for controlling the amount of fresh air to a lean atmosphere when the sudden acceleration determination means determines that the vehicle accelerates rapidly when the rich combustion is being performed. The normal combustion opening degree determined as the opening degree during normal combustion that is combustion in the internal combustion engine is controlled, and the fuel injection amount is set to the normal combustion injection amount determined as the fuel injection amount during the normal combustion. Control and execute by switching to the normal combustion,
Further, immediately after it is determined that the vehicle accelerates rapidly, the combustion control means makes the fuel injection amount smaller than the normal combustion injection amount in accordance with the oxygen concentration in the cylinder and the EGR rate, so that the EGR The torque is prevented from fluctuating due to the influence of unburned fuel contained in the exhaust gas in the rich combustion immediately before being led to the intake side by the device.

  As described above, when it is determined that the vehicle accelerates rapidly during the rich combustion, the throttle is controlled to the normal combustion opening, and the fuel injection amount is controlled to the normal combustion injection amount. Can switch to normal combustion. Here, when a part of the exhaust is led to the intake side by the EGR device, a part of the unburned fuel contained in the exhaust in the previous rich combustion is led to the intake side, and the unburned fuel Fuel is sucked into the cylinder. Therefore, when the throttle is controlled to the normal combustion opening and the fuel injection amount is controlled to the normal combustion injection amount to switch to the normal combustion, immediately after that, the amount of fuel in the cylinder is larger than that in the normal normal combustion. turn into. That is, an unintended air-fuel ratio is generated, and an unintended torque is generated, so that drivability is deteriorated.

  Therefore, immediately after it is determined that the vehicle is accelerated rapidly, the combustion control means makes the fuel injection amount smaller than the normal combustion injection amount according to the oxygen concentration in the cylinder and the EGR rate. According to this, the EGR rate can be used as an index of how much unburned fuel contained in the exhaust gas in the previous rich combustion has been led to the intake side, so the EGR rate and the oxygen concentration in the cylinder Based on this, the fuel injection amount that achieves the intended air-fuel ratio is determined. Therefore, even immediately after switching from the rich combustion to the normal combustion, it is possible to prevent the torque from fluctuating due to the influence of unburned fuel in the immediately preceding rich combustion, and thus it is possible to prevent drivability from deteriorating.

Further, the exhaust gas purification apparatus for an internal combustion engine of the present invention, a duration measuring means for measuring a duration during which the acceleration rate is larger than the threshold acceleration rate,
A duration determination unit that determines whether the duration measured by the duration measurement unit is less than or greater than a predetermined first threshold time;
Even if it is determined that the vehicle suddenly accelerates when the combustion control means is performing the rich combustion, the rich combustion is performed while the duration is determined to be less than the first threshold time. May be continuously executed, and when it is determined that the duration is greater than the first threshold time, the normal combustion may be switched.

  According to this, even when it is determined that the vehicle accelerates rapidly when rich combustion is being performed, the rich combustion is not performed while the duration is determined to be smaller than the first threshold time. Since it is continuously executed, it is possible to prevent frequent switching between rich combustion and normal combustion, for example, when the vehicle is rapidly accelerated. As a result, it is possible to suppress frequent occurrence of torque fluctuation when switching between rich combustion and normal combustion, and it is possible to prevent deterioration of fuel consumption due to execution of rich combustion with a short execution time and little effect.

  However, if the rich combustion is maintained for too long while the vehicle is accelerating rapidly, as described above, drivability deteriorates due to insufficient torque. Therefore, when the duration of rapid acceleration of the vehicle is greater than the first threshold time, the combustion is switched from rich combustion to normal combustion. Switching to normal combustion makes it easier for the fresh air amount to follow the target fresh air amount, and even during rapid acceleration, the torque can be controlled to the target torque by adjusting the fuel injection amount.

Further, the exhaust gas purification apparatus for an internal combustion engine of the present invention, a duration measuring means for measuring a duration during which the acceleration rate is larger than the threshold acceleration rate,
A duration determination unit that determines whether the duration measured by the duration measurement unit is less than or greater than a predetermined second threshold time;
Even if it is determined that the vehicle accelerates rapidly when the combustion control means is executing the rich combustion, while the duration time is determined to be smaller than the second threshold time, the throttle control unit Is controlled to a larger opening than the opening during rich combustion determined as the opening during rich combustion, and after-burning, which is sub-injection subsequent to main fuel injection, is performed. In the meantime, when the acceleration rate becomes smaller than the threshold acceleration rate, the normal rich combustion is restored, and when it is determined that the duration is longer than the second threshold time, the normal combustion is performed. You may make it switch.

  According to this, even when it is determined that the vehicle accelerates rapidly when rich combustion is being performed, it is determined that the duration is shorter than the second threshold time without immediately switching to normal combustion. During this time, after-burning rich combustion is performed. In the rich combustion with the after, the opening of the throttle is larger than the opening at the time of rich combustion. Accordingly, since the amount of fresh air is larger than that during normal rich combustion, the amount of fresh air can more easily follow the target fresh air amount than during normal rich combustion. As a result, a shortage of torque can be reduced as compared to when normal rich combustion is maintained. On the other hand, in the rich combustion with after, the amount of fresh air is larger than in the case of normal rich combustion, so surplus oxygen in the cylinder increases. Thus, in rich combustion with after, after injection, which is sub-injection subsequent to main fuel injection, is performed to consume surplus oxygen and maintain a rich atmosphere. Thereby, NOx occluded in the NOx catalyst can be reduced.

  In addition, even when it is determined that the vehicle accelerates rapidly when rich combustion is being performed, it is immediately switched to normal combustion while the duration is determined to be less than the second threshold time. Since after-burning rich combustion is executed without frequent switching, for example, when the vehicle is accelerated rapidly, it is possible to prevent frequent switching between normal rich combustion and normal combustion. As a result, it is possible to suppress frequent torque fluctuations at the time of switching between normal rich combustion and normal combustion, and it is possible to prevent deterioration in fuel consumption due to execution of rich combustion with a short execution time and little effect.

  However, after-burn rich combustion has a smaller amount of fresh air than that of normal combustion, so the ability of the fresh air amount to follow the target fresh air amount is inferior to that of normal combustion. Therefore, when it is determined that the duration of the rapid acceleration of the vehicle is greater than the second threshold time, switching to normal combustion is performed. As a result, for example, when the vehicle is accelerating rapidly for a long time, the combustion is switched to normal combustion, so that it is possible to prevent deterioration of drivability due to insufficient torque.

  On the other hand, after-rich rich combustion is inferior in ability to reduce NOx compared to normal rich combustion. Therefore, when after-burning rich combustion is being performed, if the acceleration rate of the vehicle becomes smaller than the threshold acceleration rate, normal rich combustion is restored. Thus, when the vehicle stops accelerating suddenly, normal rich combustion is restored, so that NOx can be reduced efficiently. In this case, since the vehicle is not accelerated rapidly, drivability due to insufficient torque does not deteriorate.

  By the way, when the vehicle suddenly accelerates, the torque is instantaneously increased to try to realize the rapid acceleration. That is, when the vehicle suddenly accelerates, the driver depresses the accelerator pedal greatly, and the differential value of the displacement amount of the accelerator pedal increases. Therefore, the acceleration rate acquisition means can acquire the differential value of the displacement amount of the accelerator pedal as the acceleration rate. Further, when the vehicle accelerates rapidly, the rotational speed of the internal combustion engine increases instantaneously, and the differential value of the rotational speed of the internal combustion engine increases. Therefore, the acceleration rate acquisition means may acquire the differential value of the rotational speed of the internal combustion engine as the vehicle acceleration rate.

It is the figure which showed the schematic diagram of the diesel engine of 1st, 2nd embodiment. 3 is a flowchart showing a main routine of combustion control processing executed by an ECU 50. It is the flowchart which showed the detail of the process of step S13 of FIG. 2 in 1st embodiment. It is the flowchart which showed the detail of the process of step S16 of FIG. It is the flowchart which showed the detail of the process of step S18 of FIG. It is a figure for demonstrating the fluctuation | variation of the opening degree of the intake throttle valve 12, the fuel injection amount, and the torque at the time of switching from rich combustion to normal combustion. It is the figure which showed the time change of various signals. It is a figure for demonstrating that it does not become insufficient torque even at the time of the rapid acceleration of a vehicle. It is the flowchart which showed the detail of the process of step S13 in 2nd embodiment. In a 2nd embodiment, it is a figure for explaining what kind of fuel injection is performed by each combustion, an opening of intake throttle valve 12, etc. It is a figure for demonstrating whether rich combustion may be performed based on the instruction | command Q and the engine speed NE. It is a figure for demonstrating that it will become torque short when the vehicle accelerates rapidly when rich combustion is performed conventionally.

(First embodiment)
Hereinafter, a first embodiment of an exhaust emission control device for an internal combustion engine of the present invention will be described with reference to the drawings. First, FIG. 1 shows a schematic diagram of a diesel engine as a first embodiment of the present invention. FIG. 1 shows a diesel engine 1 and an intake system, an exhaust system, an exhaust gas recirculation system, and an electronic control unit (ECU) 50 for controlling them.

  First, in the intake system, air is sent to the cylinder 20 through the intake passage 10. An air flow meter 11 and an intake throttle valve 12 are arranged in the intake passage 10. The amount of fresh air (air amount) taken in by the air flow meter 11 is measured, and the information is sent to the ECU 50. Further, the amount of fresh air drawn into the cylinder increases or decreases depending on the opening degree of the intake throttle valve 12 disposed on the downstream side of the air flow meter 11.

  The cylinder 20 of the diesel engine 1 (internal combustion engine) is provided with an injector 21 at the cylinder head. In accordance with a command from the ECU 50, fuel supplied from a common rail (not shown) is injected from the injector 21 into the cylinder 20. The injection timing and the injection amount are determined by the ECU 50 based on the required torque, the engine speed, and the like.

  In the exhaust system, an NOx storage reduction catalyst 41 (NOx catalyst) is provided on the exhaust passage 40. The fuel in the cylinder 20 is lean (usually the A / F value is 17 or more in diesel), and NOx in the exhaust is stored in the NOx storage reduction catalyst 41 during normal combustion, and the fuel is excessive (usually A / F). (F value is 14.5 or less) NOx occluded during rich combustion is reduced to harmless nitrogen and discharged. An A / F sensor 42 (air-fuel ratio sensor) is disposed on the exhaust passage 40, and the numerical value of the A / F value measured by the sensor is sent to the ECU 50.

  Further, an EGR passage 30 for returning exhaust gas from the exhaust passage 40 to the intake passage 10 is provided as an exhaust gas recirculation system. An EGR valve 31 is disposed on the EGR passage 30, and its opening / closing is controlled by a command from the ECU 50, thereby adjusting the recirculation amount of the exhaust gas. The EGR passage 30 and the EGR valve 31 correspond to the “EGR device” of the present invention.

  In addition, an accelerator sensor 61 that outputs an electric signal corresponding to the state (displacement amount) of an accelerator pedal corresponding to a driving operation unit for notifying the vehicle side of the driver's required torque as a command Q is connected to the ECU 50.

  An engine speed sensor 62 that measures the speed NE (per unit time) of the engine 1 is connected to the ECU 50. The engine speed sensor 62 may be, for example, a crank angle sensor that measures the rotation angle of a crank (not shown) connected to the engine 1. Then, the detected value of the crank angle sensor is sent to the ECU 50, and the ECU 50 calculates the rotational speed NE of the engine 1.

  The ECU 50 has a normal computer structure, and includes a CPU (not shown) for performing various calculations and a memory 53 for storing various information. The ECU 50 detects the operating state based on the detection signals from the various sensors, calculates the optimal fuel injection amount, injection timing, injection pressure, etc. according to the operating state, and controls the fuel injection to the engine 1. To do. Further, the amount of fresh air is controlled by adjusting the opening of the intake throttle valve 12 (throttle), and the amount of EGR is controlled by adjusting the opening of the EGR valve 31.

  The ECU 50 further includes a low-pass filter (LPF) 51 that removes noise from detection signals from the various sensors, and a differentiator 52 that outputs a signal corresponding to a differential value of the input signal.

  Further, the ECU 50 functions as the “combustion control means” of the present invention, and performs normal combustion, which is combustion in a lean atmosphere, while reducing the NOx stored in the NOx catalyst 41 at intervals. A combustion control process for executing rich combustion, which is combustion in a rich atmosphere, is executed. In normal combustion, the opening of the intake throttle valve 12 is controlled to the normal combustion opening determined as the opening during normal combustion, and the normal combustion in which the fuel injection amount is determined as the fuel injection amount during normal combustion. It is controlled by the hourly injection amount and burned in a lean atmosphere where the A / F value is 17 or more. On the other hand, in rich combustion, the opening degree of the intake throttle valve 12 is controlled to a rich combustion opening degree that is determined as the opening degree in the rich combustion and is larger than the normal combustion opening degree. In the rich combustion, the fuel injection amount is controlled to a rich combustion injection amount that is smaller than the normal combustion injection amount, which is determined as the fuel injection amount in the rich combustion. In rich combustion, combustion is performed in a rich atmosphere where the A / F value is 14.5 or less.

  FIG. 2 is a flowchart showing a main routine of the combustion control process. Hereinafter, the combustion control process will be described with reference to the flowchart of FIG. Note that the combustion control process of FIG. 2 is repeatedly executed at regular intervals when normal combustion is being executed.

  First, in step S11, the amount of NOx stored in the NOx catalyst 41 is estimated. Specifically, for example, a plane indicating an operation state with the engine speed NE and the load as coordinate axes is partitioned into a plurality of areas, and the NOx occlusion amount per unit time from the engine 1 in each area is stored in the memory 53. Store in advance. Then, in step S11, processing for accumulating the NOx occlusion amount in the corresponding region is performed according to the transition of the operation state. Here, the engine speed NE may be measured by the engine speed sensor 62. The load may be a measured value of the accelerator sensor 61. The fuel injection amount in the engine 1 may be used instead of the load. In that case, a command value from the ECU 50 may be used as the value of the fuel injection amount.

  In subsequent step S12, it is determined whether or not the NOx occluded in the NOx catalyst 41 needs to be reduced by determining whether or not the NOx occlusion amount estimated in step S11 is greater than or equal to a predetermined value. Here, until the NOx occlusion amount becomes equal to or greater than the predetermined value (S12: NO), the processes of steps S11 and S12 are repeated. During this period, the normal combustion is continuously performed, so the NOx occlusion amount gradually increases. And when NOx occlusion amount becomes more than predetermined value (S12: YES), processing is advanced to Step S13.

  In step S13, a process of determining whether or not to perform rich combustion based on the acceleration rate of the vehicle is executed. FIG. 3 is a flowchart showing details of the process in step S13. Hereinafter, the details of the process of step S13 will be described with reference to the flowchart of FIG.

  First, in step S21, the vehicle acceleration rate a is acquired to determine whether or not the vehicle accelerates rapidly. Specifically, first, the command Q indicating the accelerator pedal displacement amount is acquired from the accelerator sensor 61 by removing noise with the LPF 51. The ECU 50 that executes step S21 corresponds to the “acceleration rate acquisition means” of the present invention. Here, FIG. 7A is a diagram illustrating the time change of the acquired command Q. In FIG. 7A, a plurality of periods P1 to P9 are shown for easy explanation of the characteristics of the signal of the command Q. As shown in FIG. 7A, the command Q varies greatly in the periods P2, P4, and P6. In addition, during the periods P1, P3, and P5, it changes with a gentle gradient. In the period P7, the command Q increases with a substantially constant gradient. In the periods P8 and P9, the command Q increases with a larger gradient than the period P7.

  Furthermore, in step S21, the acquired command Q is input to the differentiator 52, and the differential value of the command Q is acquired as the vehicle acceleration rate a. Thus, the reason why the differential value of the command Q is the acceleration rate a of the vehicle is that when the driver suddenly accelerates the vehicle, the driver greatly depresses the accelerator pedal to increase the torque rapidly. Here, FIG.7 (b) is the figure which showed the time change of the differential value of the instruction | command Q of Fig.7 (a) as an illustration of the acceleration rate a of a vehicle. As shown in FIG. 7 (b), it can be seen that the acceleration rate a of the vehicle increases during the periods P2, P4, P6, P8, and P9 where the fluctuation of the command Q is large.

  In subsequent step S22, it is determined whether or not the vehicle accelerates rapidly by determining whether or not the acceleration rate a of the vehicle is greater than a predetermined threshold acceleration rate b. Note that the rapid acceleration referred to here is acceleration in which the fresh air amount cannot follow the target fresh air amount at the time of rich combustion and the torque becomes insufficient. Specifically, for example, acceleration that can output only less than 80% of the target torque. In this case, the threshold acceleration rate b is an acceleration rate at which 80% of the target torque is output. In FIG. 7B, the threshold acceleration rate b is shown. As shown in FIG. 7B, the acceleration rate a of the vehicle is greater than the threshold acceleration rate b in the periods P2, P4, P6, P8, and P9, and the acceleration is performed in the other periods P1, P3, P5, and P7. The rate a is equal to or less than the threshold acceleration rate b. The ECU 50 that executes step S22 corresponds to the “rapid acceleration determination means” of the present invention.

  In step S22, when it is determined that the acceleration rate a of the vehicle is greater than the predetermined threshold acceleration rate b and the vehicle suddenly accelerates (S22: YES), the process proceeds to step S23, and the permission determination flag F that permits rich combustion. Is turned off (F = 0) and stored in the memory 53. Thereafter, the process of the flowchart of FIG. On the other hand, when it is determined that the vehicle acceleration rate a is equal to or less than the predetermined threshold acceleration rate b and the vehicle does not accelerate rapidly (S22: NO), the process proceeds to step S24, where the permission determination flag F is set to ON (F = 1), stored in the memory 53. Thereafter, the process of the flowchart of FIG.

  Returning to the processing of the flowchart of FIG. 2, in step S <b> 14, it is determined whether or not rich combustion can be performed based on the value of the permission determination flag F stored in the memory 53. Specifically, when the permission determination flag F is ON (F = 1), it is determined that rich combustion can be performed, while when the permission determination flag F is OFF (F = 0), rich combustion is performed. Is determined to be infeasible. Here, while the permission determination flag F is OFF (F = 0) (S14: NO), whether or not the rich combustion can be executed based on the acceleration rate a of the vehicle without executing the rich combustion. The process of step S13 for determining is repeated. That is, while the vehicle is rapidly accelerating, rich combustion is not executed and normal combustion is continuously executed. Therefore, it is possible to prevent the torque from becoming insufficient during sudden acceleration of the vehicle.

  On the other hand, if the permission determination flag F is ON (F = 1) (S14: YES), the process proceeds to step S15, and the opening of the intake throttle valve 12 is switched from the normal combustion opening to the rich combustion opening. The fuel injection amount is switched from the normal combustion injection amount to the rich combustion injection amount to switch from the normal combustion to the rich combustion. Accordingly, since the lean atmosphere is switched to the rich atmosphere, the NOx stored in the NOx catalyst 41 is reduced.

  By the way, the vehicle may accelerate suddenly even during the rich combustion. In this case, the torque may be insufficient. Therefore, in subsequent step S16, it is determined whether or not rich combustion can be continued based on the acceleration rate a of the vehicle. FIG. 4 is a flowchart showing details of the process for determining whether or not the rich combustion in step S16 can be continued. Hereinafter, the details of the process of step S16 will be described with reference to the flowchart of FIG.

  First, in step S32, the acceleration rate a of the vehicle is acquired as in step S21 described above. The ECU 50 that executes step S32 corresponds to the “acceleration rate acquisition means” of the present invention.

  In subsequent step S33, it is determined whether or not the acceleration rate a of the vehicle acquired in step S32 is larger than the threshold acceleration rate b. The ECU 50 that executes step S33 corresponds to the “rapid acceleration determination means” of the present invention. When the acceleration rate a of the vehicle is equal to or less than the threshold acceleration rate b (S33: NO), the process proceeds to step S34, and rich combustion is continued and executed as it is. In step S35, the permission determination flag F for permitting rich combustion is turned ON (F = 1) and stored in the memory 53. Next, in step S39, the OFF counter C (duration) for measuring the time during which the vehicle acceleration rate a is greater than the threshold acceleration rate b is reset (C = 0) and stored in the memory 53. To do. Thereafter, the process of the flowchart of FIG. 4 is exited.

  On the other hand, when the acceleration rate a of the vehicle is larger than the threshold acceleration rate b in step S33 (S33: YES), the process proceeds to step S36, and the value of the OFF counter C stored in the memory 53 is incremented by 1 (C = C + 1). In step S37, it is determined whether or not the value of the OFF counter C is greater than a predetermined first threshold C1 (first threshold time). When the value of the OFF counter C is smaller than the predetermined first threshold value C1 (S37: NO), the process proceeds to step S40, and the permission determination flag F is turned ON (F = 1) and stored in the memory 53. Thereafter, the process of the flowchart of FIG. 4 is exited.

  In this case, the process of the flowchart of FIG. 4 is executed again. That is, the acceleration rate a of the vehicle is acquired again (S32), and it is determined whether or not the acceleration rate a of the vehicle is still larger than the threshold acceleration rate b (S33). If the vehicle acceleration rate a is still greater than the threshold acceleration rate b (S33: YES), the value of the OFF counter C is incremented by 1 (S36), and the value of the OFF counter C is greater than the predetermined first threshold value C1. It is determined whether or not it is larger (S37). Therefore, as long as the acceleration rate a of the vehicle is larger than the threshold acceleration rate b, the OFF counter C increases with time. That is, the OFF counter C indicates the duration time during which the vehicle acceleration rate a is greater than the threshold acceleration rate b. Further, the rich combustion is continuously executed until the value of the OFF counter C becomes larger than the predetermined first threshold value C1. The ECU 50 that executes step S36 and step S39 corresponds to the “continuation time measuring means” of the present invention. Further, the ECU 50 that executes step S37 corresponds to the “continuation time determination means” of the present invention.

  If the acceleration rate a of the vehicle becomes smaller than the threshold acceleration rate b (S33: NO) before the value of the OFF counter C becomes larger than the predetermined first threshold value C1 (S37: NO), rich combustion is performed. Is continuously executed (S34), and the permission determination flag F is turned ON (F = 1) (S35). That is, even if the vehicle acceleration rate a is greater than the threshold acceleration rate b, the vehicle acceleration rate a is greater than the threshold acceleration rate b during a certain period of time when the value of the OFF counter C becomes the predetermined first threshold C1. When it becomes smaller, rich combustion is continuously performed. The first threshold C1 is determined based on how long the rich combustion can be allowed in a state where the vehicle is rapidly accelerating. As described above, when the vehicle suddenly accelerates during rich combustion, the torque becomes insufficient, but the shortage becomes larger as the time during which the vehicle is rapidly accelerated becomes longer. Therefore, the first threshold C1 is determined based on the allowable degree of torque shortage. Thereby, for example, when the state in which the vehicle is rapidly accelerated is short, frequent switching between rich combustion and normal combustion can be prevented. As a result, it is possible to suppress frequent occurrence of torque fluctuation when switching between rich combustion and normal combustion, and it is possible to prevent deterioration of fuel consumption due to execution of rich combustion with a short execution time and little effect.

  On the other hand, when the value of the OFF counter C becomes larger than the predetermined first threshold C1 in step S37 (S37: YES), the process proceeds to step S38, and the permission determination flag F is set to OFF (F = 0) and the memory is set. 53. In this case, as described later, the rich combustion is switched to the normal combustion. Thereafter, the process of the flowchart of FIG. 4 is exited.

  Here, FIG. 7C is a diagram showing a time change of the OFF counter C with respect to the command Q in FIG. 7A and the acceleration rate a in FIG. 7B. FIG. 7C also shows the first threshold value C1. FIG. 7D is a diagram showing the change over time of the permission determination flag F with respect to the command Q in FIG. 7A and the acceleration rate a in FIG. As shown in FIGS. 7C and 7D, in the periods P1, P3, P5, and P7, since the acceleration rate a is equal to or less than the threshold acceleration rate b (see FIG. 7B), the OFF counter C Is zero, and the permission determination flag F is ON. In the periods P2, P4, P6, P8, and P9, the acceleration rate a is larger than the threshold acceleration rate b (see FIG. 7B), so the OFF counter C is increasing. However, in the periods P2, P4, P6, and P8, since the value of the OFF counter C is equal to or less than the first threshold C1, the permission determination flag F remains ON. That is, rich combustion is continuously performed. On the other hand, in the period P9, the value of the OFF counter C is larger than the first threshold C1, and the permission determination flag F is OFF. That is, in the period P9, the rich combustion is switched to the normal combustion. Eventually, in the periods P1 to P8, the permission determination flag F is turned ON and rich combustion is continued, and it can be seen that the rich combustion and the normal combustion are not frequently switched.

  Returning to the processing of the flowchart of FIG. 2, in step S <b> 17, it is determined based on the value of the permission determination flag F stored in the memory 53 whether or not rich combustion can be continued. Specifically, when the permission determination flag F is ON (F = 1), it is determined that the rich combustion can be continued, while the permission determination flag F is OFF (F = 0). In this case, it is determined that rich combustion cannot be continued. Here, when the permission determination flag F is ON (F = 1) (S17: YES), the rich combustion is continuously executed, and the process returns to step S16, as described above. Then, it is determined whether or not rich combustion can be continued again. On the other hand, when the permission determination flag F is OFF (F = 0) (S17: NO), the process proceeds to step S18, and a process of switching from rich combustion to normal combustion is executed.

  FIG. 5 is a flowchart showing details of the process of switching from rich combustion to normal combustion in step S18. Hereinafter, the details of the process of step S18 will be described with reference to the flowchart of FIG.

  First, in step S51, the in-cylinder oxygen concentration that is the oxygen concentration in the cylinder 20 is calculated and acquired. Specifically, the in-cylinder oxygen concentration is calculated as the sum of the intake oxygen concentration sucked from the intake passage 10 and the reflux oxygen concentration recirculated through the EGR passage 30. The inhaled oxygen concentration may be a value obtained by multiplying, for example, the weight of fresh air measured by the air flow meter 11 and the proportion of oxygen weight in the atmosphere (about 21%). At this time, if the air flow meter 11 is located before the intake throttle valve 12, a differential pressure sensor for measuring the differential pressure across the intake throttle valve 12 is provided, and the air flow meter 11 is operated according to the measured value of the differential pressure sensor. The measurement value of the meter 11 may be corrected. On the other hand, the reflux oxygen concentration can be calculated based on the measured value of the A / F sensor 42 and the opening degree of the EGR valve 31. The ECU 50 that executes step S51 corresponds to the “oxygen concentration acquisition unit” of the present invention.

  In subsequent step S52, an EGR rate indicating how much exhaust gas has been guided to the intake side by the EGR device including the EGR passage 30 and the EGR valve 31 is calculated and acquired. This may be calculated based on the opening degree of the EGR valve 31. The ECU 50 that executes step S52 corresponds to the “EGR rate acquisition means” of the present invention.

  In the subsequent step S53, when the opening of the intake throttle valve 12 is controlled to the opening at the time of normal combustion determined as the opening at the time of normal combustion, fuel injection that provides a lean atmosphere with a predetermined A / F value is performed. The amount is determined based on the in-cylinder oxygen concentration and the EGR rate. Specifically, for example, a map of the fuel injection amount using the in-cylinder oxygen concentration and the EGR rate as parameters may be stored in the memory 53 in advance. Here, the predetermined A / F value is such that the opening degree of the intake throttle valve 12 is controlled to the normal combustion opening degree after a certain amount of time has elapsed after switching from rich combustion to normal combustion. The fuel injection amount is determined as an A / F value during normal normal combustion in which the fuel injection amount is controlled to the normal combustion injection amount determined as the fuel injection amount during normal combustion.

  As described above, the fuel injection amount is determined based on the in-cylinder oxygen concentration and the EGR rate when one of the unburned fuels contained in the exhaust gas in the immediately preceding rich combustion is determined when switching from rich combustion to normal combustion. The part is guided to the intake side by the EGR device, and the unburned fuel is sucked into the cylinder. In other words, when the intake throttle valve 12 is controlled to the normal combustion opening and the fuel injection amount is controlled to the normal combustion injection amount to switch to the normal combustion, immediately after that, the in-cylinder is more in-cylinder than in the normal normal combustion. This is because there will be more fuel. As a result, an unintended A / F value is generated, and an unintended torque is generated, so that drivability is deteriorated.

  Therefore, since the EGR rate can be used as an index of how much unburned fuel contained in the exhaust gas in the previous rich combustion is led to the intake side, based on the EGR rate and the oxygen concentration in the cylinder, The fuel injection amount that achieves the predetermined A / F value is determined.

  In the following step S54, the opening degree of the intake throttle valve 12 is controlled to the above-described normal combustion opening degree, and the fuel injection amount determined in step S53 is controlled to execute normal combustion immediately after switching for a certain period of time. . Accordingly, even immediately after switching from rich combustion to normal combustion, it becomes the same as the A / F value during normal normal combustion, so that it is possible to prevent unintended torque from being generated.

  Here, FIG. 6 is a diagram for explaining fluctuations in the opening degree, fuel injection amount, and torque of the intake throttle valve 12 at the time of switching from rich combustion to normal combustion, and FIG. 12 shows the transition of the opening degree, FIG. 5B shows the transition of the fuel injection amount, and FIG. 4C shows the transition of the torque. As shown in FIG. 6 (a), the opening of the intake throttle valve 12 is an opening at the time of normal combustion during normal combustion, and an opening at the time of rich combustion during rich combustion. Even immediately after switching from rich combustion to normal combustion, the opening of the intake throttle valve 12 is the normal combustion opening.

  Further, as shown in FIG. 6B, the fuel injection amount is the normal combustion injection amount during normal combustion, and the rich combustion injection amount during rich combustion. However, immediately after switching from rich combustion to normal combustion, the fuel injection amount is a fuel injection amount 81 that is smaller than the normal combustion injection amount 82. This is because, as described above, immediately after switching from rich combustion to normal combustion, a part of the unburned fuel contained in the exhaust gas in the previous rich combustion is guided to the intake side by the EGR device. That is, the fuel injection amount 81 is smaller than the normal combustion injection amount 82 in consideration of the amount of unburned fuel. The fuel injection amount 81 is the smallest immediately after switching from rich combustion to normal combustion, and gradually approaches the normal combustion injection amount 82 as time elapses. This is because the influence of unburned fuel in the rich combustion immediately before the switching remains most.

  Thereby, as shown in FIG.6 (c), it turns out that the torque 85 does not fluctuate even immediately after switching from rich combustion to normal combustion. FIG. 6C also shows the torque 84 when the fuel injection amount is the normal combustion injection amount 82 immediately after switching from rich combustion to normal combustion. Thus, it can be seen that the torque 84 fluctuates if the fuel injection amount is the normal combustion injection amount 82 immediately after switching. This is because the amount of fuel in the cylinder becomes larger than that in normal normal combustion due to the influence of unburned fuel in the previous rich combustion.

  Further, instead of the normal combustion injection amount 82, the period T for performing the normal combustion immediately after switching using the fuel injection amount 81 determined based on the EGR rate and the in-cylinder oxygen concentration is, for example, the fuel injection A period during which the amount 81 is substantially the same as the normal combustion injection amount 82 is determined in advance. Alternatively, the period T is changed each time so that the normal combustion immediately after switching is executed until the determined fuel injection amount 81 becomes substantially the same as the normal combustion injection amount 82 without setting the period T in advance. Then, during the period T, the processing of steps S51 to S54 described above is executed, and normal combustion immediately after switching is executed.

  In actuality, even in the same normal combustion, the normal combustion opening degree and the normal combustion injection amount are varied depending on the environment or the like. However, for convenience of explanation in FIG. The injection quantity during combustion is assumed to be constant. Similarly, the rich combustion opening and the rich combustion injection amount are also constant.

  Returning to the processing of the flowchart of FIG. 5, after performing normal combustion immediately after switching for the period T immediately after switching (S54), the process proceeds to step S55, and the opening of the intake throttle valve 12 is opened during normal combustion. The normal injection is performed by controlling the fuel injection amount to the normal combustion injection amount. Thereafter, the process of the flowchart of FIG. 5 is exited, and the process of the flowchart of FIG. 2 is terminated.

  In this way, when the vehicle accelerates rapidly, rich combustion is not executed. That is, when the vehicle suddenly accelerates while rich combustion is being performed, the rich combustion is stopped. If the vehicle suddenly accelerates during normal combustion, it does not switch to rich combustion. As a result, normal combustion is performed when the vehicle accelerates rapidly. Here, FIG. 8 is a diagram for explaining that the torque does not become insufficient even when the vehicle is suddenly accelerated. (A) Time variation of acceleration rate a of vehicle, (b) Time variation of fresh air amount and ( c) The time change of the torque is shown. In FIG. 5B, the broken line indicates the change over time of the target fresh air amount, and the solid line indicates the change over time of the actual fresh air amount. Further, in FIG. 5C, the broken line indicates the change over time of the target torque, and the solid line indicates the change over time of the actual torque. As shown in FIG. 8A, when the acceleration rate a of the vehicle rapidly increases, the target fresh air amount also increases as shown in FIG. 8B. When the target fresh air amount increases, the target torque also increases as shown in FIG. That is, when the acceleration rate a of the vehicle rapidly increases, the vehicle is rapidly accelerated rapidly by increasing the amount of fresh air and increasing the torque. However, in practice, when the acceleration rate a of the vehicle rapidly increases, the actual fresh air amount cannot follow the target fresh air amount, as shown in FIG. 8B. Therefore, in the present invention, when the acceleration rate a of the vehicle rapidly rises during the rich combustion, the rich combustion is switched to the normal combustion. As a result, during normal combustion, the torque is controlled by controlling the fuel injection amount with respect to the fresh air amount. Therefore, even if the fresh air amount cannot slightly follow the target fresh air amount, FIG. As shown in c), the torque can be controlled to the target torque.

(Second embodiment)
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described focusing on the differences from the first embodiment. In the first embodiment, even when it is determined that the vehicle accelerates rapidly when rich combustion is being performed, the rich combustion is continued for a certain time without immediately switching to normal combustion. . In the second embodiment, as in the first embodiment, when rich combustion is being executed, even if it is determined that the vehicle accelerates suddenly, the vehicle is not immediately switched to normal combustion for a certain period of time. Continues rich combustion. Further, in the second embodiment, after the fixed time has elapsed, the rich combustion with after, which is a modification of the rich combustion, is performed without switching to the normal combustion for the fixed time.

  Here, the rich combustion with after is combustion in which the opening degree of the intake throttle valve is larger than the opening degree during rich combustion. Further, after-rich rich combustion is combustion in which after injection, which is sub-injection subsequent to main fuel injection, is executed. The main fuel injection amount is the rich fuel injection amount at the time of rich combustion.

  The configuration of the exhaust gas purification apparatus for an internal combustion engine in the second embodiment is the same as that in the first embodiment shown in FIG. In the second embodiment, the processes in the flowcharts of FIGS. 2 and 5 are executed as in the first embodiment. However, the details of the processing in step S13 in FIG. 2 are different from those in the first embodiment (FIG. 4). Details of the process in step S13 will be described below. FIG. 9 is a flowchart showing details of the process in step S13. In FIG. 9, the same processes as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 9, steps S <b> 41 to S <b> 44 are added as compared with the processing of the first embodiment (FIG. 4). That is, in step S37, when the value of the OFF counter C is larger than the predetermined first threshold C1 (first threshold time) (S37: YES), the process proceeds to step S41, and the value of the OFF counter C is set to the first threshold. It is determined whether or not it is smaller than a predetermined second threshold C2 (second threshold time) that is larger than C1. When the value of the OFF counter C is smaller than the second threshold C2 (S41: YES), the process proceeds to step S42, and after-burning rich combustion is executed. In the rich combustion with after, as described above, the intake throttle valve 12 is controlled to an opening larger than the opening during rich combustion, and after injection, which is sub-injection subsequent to main fuel injection, is executed. The ECU 50 that executes step S41 corresponds to the “continuation time determination means” of the present invention.

  Thus, in the rich combustion with after, the intake throttle valve 12 has an opening larger than the opening at the time of rich combustion, so the amount of fresh air becomes larger than that at the time of normal rich combustion. Therefore, it becomes easier for the fresh air amount to follow the target fresh air amount than in the case of normal rich combustion, and a shortage of torque can be reduced compared to the case of maintaining normal rich combustion.

  On the other hand, in the rich combustion with after, the amount of fresh air is larger than in the case of normal rich combustion, so surplus oxygen in the cylinder increases. Thus, in rich combustion with after, after injection, which is sub-injection subsequent to main fuel injection, is performed to consume surplus oxygen and maintain a rich atmosphere. Thereby, NOx occluded in the NOx catalyst can be reduced.

  In other words, after-burn rich combustion is a combustion that combines the properties of rich combustion and normal combustion, and reduces NOx stored in the NOx catalyst, resulting in insufficient torque even during rapid acceleration of the vehicle. Is reduced combustion.

  However, after-burn rich combustion has a smaller amount of fresh air than that of normal combustion, so the ability of the fresh air amount to follow the target fresh air amount is inferior to that of normal combustion. Further, after-rich rich combustion has a lower ability to reduce NOx than normal rich combustion.

  After rich combustion with after is executed in step S42, the process proceeds to step S43, where the permission determination flag F is turned on (F = 1) and stored in the memory 53. Thereafter, the processing of the flowchart of FIG. 9 ends. As described above, when after-burning rich combustion is executed, the permission determination flag F is turned ON. Therefore, it is determined in step S17 of FIG. 2 that rich combustion can be continued, and the processing of the flowchart of FIG. 9 is performed again. Will be executed. As a result, the acceleration rate a of the vehicle is acquired again (S32), and when the acceleration rate a is larger than the threshold acceleration rate b (S33: YES), the OFF counter C is incremented by 1 (S36). Then, as long as the OFF counter C is smaller than the second threshold C2 (S41: YES), after-added rich combustion continues to be executed. On the other hand, when the vehicle acceleration rate a becomes equal to or less than the threshold acceleration rate b (S33: NO), the rich combustion with after-switching is switched to the normal rich combustion (S34). Then, the OFF counter C is reset (S39), and the process of the flowchart of FIG. 9 is executed again.

  Thus, after rich combustion has a lower ability to reduce NOx than normal rich combustion, the acceleration rate a of the vehicle becomes smaller than the threshold acceleration rate b when the rich combustion with after is executed. If it is, the normal rich combustion is restored. Thus, when the vehicle stops accelerating suddenly, normal rich combustion is restored, so that NOx can be reduced efficiently.

  On the other hand, when after-burning rich combustion is executed and the OFF counter C becomes equal to or larger than the second threshold C2 (S41: NO), the process proceeds to step S44, and the permission determination flag F is set to OFF (F = 0). Store in the memory 53. Thereafter, the processing of the flowchart of FIG. 9 ends. In this case, it is determined in step S17 of FIG. 2 that the rich combustion cannot be continued (S17: NO), and the normal combustion is switched (S18).

  As described above, after-burn rich combustion is inferior to normal combustion in the ability of the fresh air amount to follow the target fresh air amount. Therefore, when it is determined that the OFF counter C is greater than the second threshold C2, normal combustion is performed. It has been switched to. As a result, for example, when the vehicle is accelerating rapidly for a long time, the combustion is switched to normal combustion, so that it is possible to prevent deterioration of drivability due to insufficient torque.

  Thus, even when the vehicle suddenly accelerates while rich combustion is being performed, rich combustion is continued if the OFF counter C is smaller than the first threshold C1. Further, even when the vehicle suddenly accelerates while rich combustion is being performed, after-off rich combustion is continued if the OFF counter C is smaller than the second threshold value C2. Then, when the OFF counter C becomes equal to or greater than the second threshold value C2, it switches to normal combustion. Therefore, after-burn rich combustion is executed for a time corresponding to the difference between the second threshold C2 and the first threshold C1 at the maximum. That is, the longer the first threshold C1 is, the longer the time during which rich combustion is continued. In addition, as the difference between the second threshold value C2 and the first threshold value C1 is larger, the time during which after-burning rich combustion is performed becomes longer. Accordingly, the first threshold C1 is determined based on how much rich combustion can be performed in a state where the vehicle is rapidly accelerating, as in the first embodiment. It is also determined based on whether the execution of after-burning rich combustion can be allowed to a certain extent. Further, the second threshold value C2 is determined based on how long the execution of after-addition rich combustion can be permitted. Note that the first threshold C1 in the second embodiment and the first threshold C1 in the first embodiment may be set to different values.

  Here, again, referring to FIG. 10, what kind of fuel injection is performed in each combustion, the opening degree of the intake throttle valve 12, and the like will be described. In FIG. 10, (a) normal rich combustion, (b) after-burn rich combustion, and (c) normal combustion are shown. In the figure, each mountain represents fuel injection, and the largest mountain represents main injection. The peaks in parentheses indicate pilot injection that is injected before the main injection, and in each combustion, pilot injection may be executed in addition to the main injection.

  As shown in FIG. 10 (a), in the normal rich combustion, the main injection is executed, but the fuel injection amount (rich fuel injection amount) is larger than that in the rich combustion with after-charge and the normal combustion. Yes. Further, in normal rich combustion, the opening of the intake throttle valve 12 (the opening at the time of rich combustion) is smaller than that in rich combustion with after-charge and normal combustion. Thus, a rich atmosphere can be created, and NOx stored in the NOx catalyst 41 can be reduced.

  Further, as shown in FIG. 10B, in rich combustion with after, after injection is executed subsequent to main injection. The fuel injection amount in the main injection is the same as that in normal rich combustion (the rich combustion injection amount). In the rich combustion with after, the opening of the intake throttle valve 12 is larger than that in the normal rich combustion (the opening at the time of rich combustion), but that in the normal combustion (the opening at the time of normal combustion). It is smaller than As a result, it is possible to combine the properties of normal rich combustion and normal combustion, reducing NOx stored in the NOx catalyst, and reducing the lack of torque even during sudden acceleration of the vehicle. .

  Further, as shown in FIG. 10 (c), in the normal combustion, the main injection is executed, but the fuel injection amount (normal fuel injection amount) is smaller than that in the normal rich combustion and after rich combustion. ing. Further, in the normal combustion, the opening degree of the intake throttle valve 12 (the opening degree during normal combustion) is larger than that in normal rich combustion and rich combustion with after. As a result, a lean atmosphere can be created, the NOx catalyst 41 can be made to store NOx, and it is possible to reduce the occurrence of insufficient torque even during sudden acceleration of the vehicle.

  As described above, the normal rich combustion in FIG. 10A and the after rich combustion in FIG. 10B are switched, and the after rich combustion in FIG. It switches between normal combustion of Drawing 10 (c).

  The present invention is not limited to the first and second embodiments described above, and various modifications can be made without departing from the scope of the claims. For example, in the second embodiment, after rich combustion is continued for a certain period of time, switching to after-burning rich combustion is performed, but switching to after-burning rich combustion may be performed immediately. In this case, the process (S37, S40) related to the first threshold C1 may be omitted in the flowchart of FIG.

  In the first and second embodiments, the differential value of the command Q indicating the accelerator pedal displacement amount is acquired from the accelerator sensor 61 as the vehicle acceleration rate a. Thus, the reason why the differential value of the command Q is the acceleration rate a of the vehicle is that when the driver suddenly accelerates the vehicle, the driver greatly depresses the accelerator pedal to increase the torque rapidly. However, the present invention is not limited to this, and in addition to the differential value of the command Q, the differential value of the engine speed NE may be used as the vehicle acceleration rate a. This is because when the vehicle accelerates rapidly, the engine speed NE increases rapidly. In this case, as shown in FIG. 11, whether or not the rich combustion may be executed is determined based on the command Q and the engine speed NE. That is, when the permission determination flag F is turned on based on the command Q and the permission determination flag F is turned on based on the engine speed NE, it is determined that rich combustion may be executed. Thus, by using the differential value of the engine speed NE in addition to the differential value of the command Q, it can be determined more accurately whether or not the vehicle accelerates rapidly.

1 Diesel engine (internal combustion engine)
12 Intake throttle valve (throttle)
20 cylinder 21 injector 30 EGR passage 31 EGR valve 40 exhaust passage 41 NOx catalyst 42 A / F sensor 50 ECU (combustion control means)
51 Low-pass filter (LPF)
52 Differentiator 53 Memory 61 Accelerator sensor 62 Engine speed sensor (rotation speed sensor)
S21, S32 Acceleration rate acquisition means S22, S33 Rapid acceleration determination means S51 Oxygen concentration acquisition means S52 EGR rate acquisition means S36, S39 Duration measurement means S37, S41 Duration determination means a Vehicle acceleration rate b Threshold acceleration rate C OFF counter (Duration)
C1 first threshold (first threshold time)
C2 Second threshold (second threshold time)

Claims (5)

A NOx catalyst which is provided in an exhaust passage of an internal combustion engine mounted on a vehicle and which stores NOx in a lean atmosphere and reduces NOx stored in a rich atmosphere;
In an exhaust gas purification apparatus for an internal combustion engine, comprising: combustion control means for performing rich combustion, which is combustion in the internal combustion engine in a rich atmosphere, in order to reduce NOx occluded by the NOx catalyst,
An acceleration rate acquisition means for acquiring an acceleration rate of the vehicle;
Rapid acceleration determination means for determining whether or not the vehicle accelerates rapidly by determining whether or not the acceleration rate acquired by the acceleration rate acquisition means is greater than a predetermined threshold acceleration rate;
The exhaust emission control device for an internal combustion engine, wherein the combustion control means does not execute the rich combustion when the sudden acceleration judgment means judges that the vehicle is suddenly accelerated. Oxygen concentration acquisition means for acquiring the oxygen concentration in the cylinder;
EGR rate acquisition means for acquiring an EGR rate indicating how much exhaust gas has been guided to the intake side by the EGR device that guides a part of the exhaust to the intake side;
The combustion control means sets the throttle for controlling the amount of fresh air to a lean atmosphere when the sudden acceleration determination means determines that the vehicle accelerates rapidly when the rich combustion is being performed. The normal combustion opening degree determined as the opening degree during normal combustion that is combustion in the internal combustion engine is controlled, and the fuel injection amount is set to the normal combustion injection amount determined as the fuel injection amount during the normal combustion. Control and execute by switching to the normal combustion,
Further, immediately after it is determined that the vehicle accelerates rapidly, the combustion control means makes the fuel injection amount smaller than the normal combustion injection amount in accordance with the oxygen concentration in the cylinder and the EGR rate, so that the EGR 2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein torque fluctuation is suppressed by the influence of unburned fuel contained in the exhaust gas in the rich combustion immediately before being led to the intake side by the device. apparatus. A duration measuring means for measuring a duration during which the acceleration rate is greater than the threshold acceleration rate; and
A duration determination unit that determines whether the duration measured by the duration measurement unit is less than or greater than a predetermined first threshold time;
Even if it is determined that the vehicle suddenly accelerates when the combustion control means is performing the rich combustion, the rich combustion is performed while the duration is determined to be less than the first threshold time. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein when the duration is determined to be longer than the first threshold time, the normal combustion is switched. A duration measuring means for measuring a duration during which the acceleration rate is greater than the threshold acceleration rate; and
A duration determination unit that determines whether the duration measured by the duration measurement unit is less than or greater than a predetermined second threshold time;
Even if it is determined that the vehicle accelerates rapidly when the combustion control means is executing the rich combustion, while the duration time is determined to be smaller than the second threshold time, the throttle control unit Is controlled to a larger opening than the opening during rich combustion determined as the opening during rich combustion, and after-burning, which is sub-injection subsequent to main fuel injection, is performed. In the meantime, when the acceleration rate becomes smaller than the threshold acceleration rate, the normal rich combustion is restored, and when it is determined that the duration is longer than the second threshold time, the normal combustion is performed. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is switched.   The acceleration rate acquisition means includes a differential value of the displacement amount detected by an accelerator sensor that detects a displacement amount of an accelerator pedal, and a rotation speed of the internal combustion engine detected by a rotation speed senna that detects a rotation speed of the internal combustion engine. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein at least one of a plurality of differential values is acquired as the acceleration rate.

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