JP2007126989A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

An air-fuel ratio control apparatus for an internal combustion engine that can suppress the occurrence of torque fluctuation and improve fuel efficiency when controlling the air-fuel ratio by switching from the lean side to the rich side.
An air-fuel ratio control apparatus for an internal combustion engine includes an ECU. When the air-fuel ratio switching condition for switching the air-fuel ratio AF of the air-fuel mixture from the lean side to the rich side from the stoichiometric air-fuel ratio is satisfied (when step 20 is YES), the ECU 2 sets the new air amount QAIR for the rich spike. Control to decrease to the target fresh air amount QAIR_RICH (steps 26 to 29) and increase the fuel injection amount QINJ when QAIR ≤ QAIR_REF is satisfied during the new air amount control (when step 64 is YES) (Step 69). Then, after AF ≦ AF_RICHH is established (after step 65 becomes YES), feedback control to the target air-fuel ratio AF_RICH for rich spike of the air-fuel ratio AF is executed (step 72).
[Selection] Figure 8

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that controls the air-fuel ratio of an air-fuel mixture supplied into a cylinder by switching between a lean side and a rich side rather than a stoichiometric air-fuel ratio.

  Conventionally, what was described in patent document 1 is known as a control apparatus which controls the excess air ratio of an internal combustion engine. Here, since the excess air ratio is substantially equal to the “air-fuel ratio”, the excess air ratio is referred to as “the air-fuel ratio” in the following description. This internal combustion engine is of a diesel engine type and includes a NOx purification catalyst that purifies NOx in exhaust gas.

  In this control device, the air-fuel ratio is normally controlled to the lean side by a fuel-advanced control method as described below. Specifically, first, the target engine torque is calculated according to the accelerator opening and the engine speed, the basic value of the target air-fuel ratio is calculated according to the target engine torque and the engine speed, and this is set as the target. Set as air-fuel ratio. Next, the fuel injection amount is calculated by searching a map according to the target engine torque and the engine speed. On the other hand, the target fresh air amount is calculated based on the fuel injection amount and the rich target air-fuel ratio. As a result, control is performed so that the air-fuel ratio becomes the lean target air-fuel ratio.

  On the other hand, at the time of reduction control of the NOx purification catalyst (hereinafter referred to as “rich spike control”), the air-fuel ratio of the air-fuel mixture is controlled to the rich side by an air-preceding control method. Specifically, first, the basic value of the target fresh air amount is calculated by searching a map according to the target engine torque and the engine speed, and the air-fuel ratio correction coefficient is calculated based on the target air-fuel ratio on the rich side and the engine. The target fresh air amount is calculated by searching the map according to the rotational speed and multiplying the basic value of the target fresh air amount by an air-fuel ratio correction coefficient or the like. Next, the fuel injection amount is calculated based on the target air-fuel ratio and the fresh air amount. As a result, control is performed so that the air-fuel ratio becomes the rich target air-fuel ratio.

  Further, when the air-fuel ratio control is switched from the normal time control to the rich spike control, the target air-fuel ratio is calculated by performing a delay process, that is, a weighted average process, on the basic value of the target air-fuel ratio. This is to suppress torque fluctuations that occur when the air-fuel ratio changes stepwise from the lean side to the rich side. Further, in this delay processing, the time constant is set to a relatively small value in order to avoid an excessive decrease in the change rate of the air-fuel ratio.

JP 2003-90250 A

  According to the above conventional control device, when the air-fuel ratio control is switched from the normal time control to the rich spike control, the control method is switched from the fuel leading type to the air leading type. It takes time for the amount to actually drop. As described above, at the time of this control switching, the target air-fuel ratio delay process is executed, but the time constant is set to a relatively small value until the fresh air amount actually decreases. During this time, the fuel injection amount temporarily increases due to the target air-fuel ratio being set to a rich value. As a result, torque fluctuations occur, and fuel consumption is wasted, which may lead to deterioration in fuel consumption.

  The present invention has been made in order to solve the above-described problem, and when controlling the air-fuel ratio by switching from the lean side to the rich side, it is possible to suppress the occurrence of torque fluctuations and improve the fuel consumption. An object is to provide an air-fuel ratio control device.

  In order to achieve the above object, according to the first aspect of the present invention, by controlling the fresh air amount QAIR and the fuel amount (fuel injection amount QINJ) supplied into the cylinder 3a, the air-fuel mixture in the cylinder is emptied. An air-fuel ratio control device 1 for an internal combustion engine 3 that controls the fuel ratio AF by switching from the stoichiometric air-fuel ratio to a lean side and a rich side, and a new air amount detecting means (ECU 2, air flow sensor 21) for detecting a new air amount QAIR When the air-fuel ratio switching condition for switching the air-fuel ratio AF of the air-fuel mixture from the lean side to the rich side from the stoichiometric air-fuel ratio is satisfied (when the determination result in step 20 is YES), the new air amount QAIR is set to a predetermined value. New air amount control means (ECU2, steps 26 to 29) for controlling to decrease to the target value (target fresh air amount QAIR_RICH for rich spike), and fresh air by the new air amount control means When the detected fresh air amount QAIR reaches a predetermined target value or a predetermined threshold value QAIR_REF that is larger than the predetermined target value during the decrease control to the predetermined target value (the determination result of step 64 is YES) And a fuel amount control means (ECU2, step 69) for controlling the fuel amount (fuel injection amount QINJ) to the increase side.

  According to this air-fuel ratio control apparatus for an internal combustion engine, when the air-fuel ratio switching condition for switching the air-fuel ratio of the air-fuel mixture from the lean side to the rich side with respect to the stoichiometric air-fuel ratio is satisfied, When the amount of fresh air detected reaches a predetermined target value or a predetermined threshold value larger than the predetermined target value during the control, the amount is controlled to decrease to a predetermined target value. The fuel amount is controlled to be increased by the fuel amount control means. As described above, when the amount of fresh air supplied into the cylinder is surely reduced to a predetermined target value or a predetermined threshold value, the fuel amount is controlled to increase. Unlike the conventional case where the fuel injection amount temporarily increases until it decreases, the occurrence of torque fluctuation can be reliably suppressed and fuel consumption can be avoided by avoiding unnecessary fuel consumption. (Note that “detection of fresh air amount” in the present specification is not limited to detecting the fresh air amount directly by a sensor, but includes calculating or estimating the fresh air amount).

  The invention according to claim 2 is the control apparatus 1 for the internal combustion engine 3 according to claim 1, wherein the air-fuel ratio detection means (ECU2, LAF sensor 22) for detecting the air-fuel ratio AF of the air-fuel mixture and the fuel amount control means are used. After the air-fuel ratio AF of the air-fuel mixture detected during the control to increase the fuel amount becomes equal to or lower than the predetermined air-fuel ratio (predetermined upper limit threshold AF_RICHH) (after the determination result in step 65 becomes YES) ), Air-fuel ratio control means (ECU2, step 72) for performing feedback control so that the air-fuel ratio AF of the air-fuel mixture becomes a predetermined rich target air-fuel ratio (target air-fuel ratio for rich spike AF_RICH). Features.

  According to this air-fuel ratio control apparatus for an internal combustion engine, the air-fuel ratio control is performed when the air-fuel ratio of the air-fuel mixture detected during the control to increase the fuel amount by the fuel amount control means becomes equal to or lower than the predetermined air-fuel ratio. By means, air-fuel ratio feedback control is started so that the air-fuel ratio of the air-fuel mixture becomes a predetermined rich target air-fuel ratio. Therefore, when the predetermined air-fuel ratio is set to a value near the predetermined rich-side target air-fuel ratio and leaner than the predetermined air-fuel ratio, the air-fuel ratio approaches the predetermined rich-side target air-fuel ratio. The feedback control of the fuel ratio can be started. As a result, the convergence of the air-fuel ratio with respect to a predetermined rich target air-fuel ratio can be improved, and the control accuracy can be improved (in the present specification, “air-fuel ratio detection” (Including not only directly detecting the air-fuel ratio but also calculating or estimating the air-fuel ratio).

  Hereinafter, an air-fuel ratio control apparatus for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an internal combustion engine (hereinafter referred to as “engine”) 3 to which the air-fuel ratio control device 1 of the present embodiment is applied, and FIG. 2 shows a schematic configuration of the air-fuel ratio control device 1. . As shown in FIG. 2, the air-fuel ratio control device 1 includes an ECU 2. The ECU 2 executes various control processes such as air-fuel ratio control according to the operating state of the engine 3, as will be described later. To do.

  The engine 3 is an in-line four-cylinder diesel engine mounted on a vehicle (not shown), and includes four sets of cylinders 3a and pistons 3b (only one set is shown), a crankshaft 3c, and the like. The engine 3 is provided with a crank angle sensor 20. The crank angle sensor 20 includes a magnet rotor and an MRE pickup, and outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft 3c rotates.

  The CRK signal is output at one pulse every predetermined crank angle (for example, 30 °), and the ECU 2 calculates the engine speed NE (hereinafter referred to as “engine speed”) NE based on the CRK signal. The TDC signal is a signal indicating that the piston 3b of each cylinder 3a is at a predetermined crank angle position slightly ahead of the TDC position of the intake stroke, and one pulse is output for each predetermined crank angle.

  The engine 3 is provided with a fuel injection valve 4 for each cylinder 3a (only one is shown), and each fuel injection valve 4 is electrically connected to the ECU 2. As described later, the ECU 2 controls the valve opening time and the valve opening / closing timing of the fuel injection valve 4, thereby controlling the fuel injection amount and the fuel injection timing.

  On the other hand, an air flow sensor 21, a turbocharger 7, a throttle valve mechanism 8, and a swirl valve mechanism 9 are provided in the intake passage 6 of the engine 3 in order from the upstream side. The air flow sensor 21 (fresh air amount detection means) is constituted by a hot-wire air flow meter, detects the flow rate of fresh air passing through a throttle valve 8a described later, and outputs a detection signal representing the flow to the ECU 2. The ECU 2 calculates a fresh air amount QAIR sucked into the cylinder 3a based on the detection signal of the air flow sensor 21.

  The turbocharger 7 includes a compressor blade 7a provided on the downstream side of the air flow sensor 21 in the intake passage 6, a turbine blade 7b provided in the middle of the exhaust passage 11, and rotating integrally with the compressor blade 7a. Variable vanes 7c (only two are shown), a vane actuator 7d for driving the variable vanes 7c, and the like.

  In the turbocharger 7, when the turbine blade 7 b is rotationally driven by the exhaust gas in the exhaust passage 11, the compressor blade 7 a integrated therewith is also rotated at the same time, so that fresh air in the intake passage 6 is pressurized. That is, the supercharging operation is executed.

  The variable vane 7c is for changing the supercharging pressure generated by the turbocharger 7, and is rotatably attached to the wall of the portion of the housing that houses the turbine blade 7b. The variable vane 7c is mechanically coupled to an actuator (not shown) connected to the ECU 2. The ECU 2 changes the rotational speed of the turbine blade 7b, that is, the rotational speed of the compressor blade 7a by changing the opening of the variable vane 7c via the actuator and changing the amount of exhaust gas blown to the turbine blade 7b. , Control the supercharging pressure.

  On the other hand, the throttle valve mechanism 8 includes a throttle valve 8a and a TH actuator 8b for driving the throttle valve 8a. The throttle valve 8a is rotatably provided in the middle of the intake passage 6, and changes the flow rate of fresh air passing through the throttle valve 8a by the change in the opening degree accompanying the rotation. The TH actuator 8b is a combination of a motor and a reduction gear mechanism (both not shown), and is electrically connected to the ECU 2. The ECU 2 controls the opening degree of the throttle valve 8a via the TH actuator 8b.

  Further, the portion of the intake passage 6 on the downstream side of the throttle valve mechanism 8 is an intake manifold 6a including one collecting portion and four branch portions branched therefrom. The passage in the intake manifold 6a is divided into a swirl passage 6b and a bypass passage 6c from the collecting portion to each branch portion, and these passages 6b and 6c communicate with the cylinder 3a through two intake ports, respectively. ing.

  The above-described swirl valve mechanism 9 stirs the air-fuel mixture in the cylinder 3a by generating a swirl in the cylinder 3a. The swirl valve 9a provided in the swirl passage 6b and a swirl actuator that drives the swirl valve 9a. 9b and the like. The swirl actuator 9b is a combination of a motor and a reduction gear mechanism (both not shown), and is electrically connected to the ECU 2. The ECU 2 changes the opening degree of the swirl valve 9a via the swirl actuator 9b, thereby controlling the state of occurrence of the swirl.

  Further, the engine 3 is provided with an exhaust gas recirculation device 10. The exhaust gas recirculation device 10 recirculates a part of the exhaust gas in the exhaust passage 11 to the intake passage 6 side, an EGR passage 10a connected between the intake passage 6 and the exhaust passage 11, and the EGR passage 10a. And an EGR control valve 10b for opening and closing the valve. One end of the EGR passage 10 a opens to a portion upstream of the turbine blade 7 b of the exhaust passage 11, and the other end opens to a bypass passage 6 c of the intake passage 6.

  The EGR control valve 10b is a linear electromagnetic valve whose lift changes linearly between a maximum value and a minimum value, and is electrically connected to the ECU 2. The ECU 2 changes the opening degree of the EGR passage 10a via the EGR control valve 10b, thereby controlling the recirculation amount of the exhaust gas. That is, EGR control is executed.

  On the other hand, on the downstream side of the turbine blade 7b in the exhaust passage 11, a LAF sensor 22 and an exhaust purification catalyst 12 are provided in order from the upstream side. The LAF sensor 22 (air-fuel ratio detecting means) is composed of zirconia, a platinum electrode, and the like, and flows in the exhaust passage 11 in a wide range of air-fuel ratios from a rich region richer than the theoretical air-fuel ratio to an extremely lean region. The oxygen concentration in the exhaust gas is detected linearly, and a detection signal representing it is output to the ECU 2. The ECU 2 calculates the air-fuel ratio of the exhaust gas, that is, the air-fuel ratio AF of the air-fuel mixture, based on the detection signal of the LAF sensor 22.

  Further, when the temperature of the exhaust purification catalyst 12 is equal to or higher than a predetermined activation temperature, the exhaust purification catalyst 12 is maintained in an activated state, thereby purifying NOx, HC and CO in the exhaust gas flowing through the exhaust passage 11.

  Further, an accelerator opening sensor 23 is connected to the ECU 2. The accelerator opening sensor 23 detects a depression amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) of the vehicle, and outputs a detection signal indicating it to the ECU 2.

  The ECU 2 includes a microcomputer including a CPU, a RAM, a ROM, an I / O interface (all not shown), and the engine 2 according to the detection signals of the various sensors 20 to 23 described above. 3 is determined, and air-fuel ratio control processing or the like is executed as described below according to the operating state. As a result, in the engine 3, the air-fuel ratio AF of the air-fuel mixture is controlled to a lean value during normal operation, and during rich spike control, the rich side value is used to reduce NOx trapped by the exhaust purification catalyst 12. To be controlled. In the present embodiment, the ECU 2 corresponds to a new air amount detection means, a new air amount control means, a fuel amount control means, an air-fuel ratio detection means, and an air-fuel ratio control means.

  Next, a rich spike control execution condition determination process executed by the ECU 2 will be described with reference to FIG. This process determines whether or not the execution condition of the rich spike control for reducing the NOx trapped by the exhaust purification catalyst 12 is satisfied, and is executed at a predetermined control cycle (for example, 10 msec). .

  In this process, first, in step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), it is determined whether or not the time count value TM_RICH of the rich timer is 0. As will be described later, the rich timer measures the execution time of the rich spike control, and the measured value TM_RICH is set to 0 when the engine is started.

  When the determination result of step 1 is YES and the rich spike control is not executed, the process proceeds to step 2 to calculate the NOx emission amount QNOx. Specifically, first, the required torque PMCMD is calculated by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP, and then according to the required torque PMCMD and the engine speed NE, The NOx emission amount QNOx is calculated by searching a map (not shown).

  Next, the process proceeds to step 3 to calculate the NOx trapping amount S_QNOx. This NOx trap amount S_QNOx corresponds to an estimated value of the NOx amount trapped by the exhaust purification catalyst 12, and is specifically calculated as an integrated value of the NOx exhaust amount QNOx. That is, the NOx trapping amount S_QNOx is calculated by adding the NOx discharge amount QNOx calculated in step 2 to the previous value of the NOx trapping amount.

  In step 4 following step 3, it is determined whether or not the accelerator opening AP is smaller than a predetermined value APREF. The predetermined value APREF is for determining that the accelerator pedal is not depressed, and is set to a value (for example, 1 °) that can determine that the accelerator pedal is not depressed.

  If the determination result is YES and the accelerator pedal is not depressed, it is determined that the condition for executing the rich spike control is not satisfied, and the routine proceeds to step 11 to set the rich condition flag F_RICH to “0”. After setting to, this process ends.

  On the other hand, if the determination result in step 4 is NO and the accelerator pedal is depressed, the process proceeds to step 5 to determine whether or not the NOx trapping amount S_QNOx is equal to or greater than a predetermined value SQREF. When the determination result is NO, as described above, after executing step 11, the present process is terminated.

  On the other hand, when the determination result in step 5 is YES, it is determined that the execution condition of the rich spike control is satisfied, and in step 6, the NOx trapping amount S_QNOx is set to 0, and then in step 7, the rich timer The time value TM_RICH is set to a predetermined value TMREF (for example, a value corresponding to 5 sec).

  Next, the routine proceeds to step 8 where the rich condition flag F_RICH is set to “1” to indicate that the execution condition of the rich spike control is satisfied. Next, at step 9, the time count value TM_RICH of the rich timer is decremented. Then, this process is terminated.

  On the other hand, if the determination result in step 1 is NO and rich spike control is being executed, the process proceeds to step 10 to determine whether or not the accelerator pedal opening AP is smaller than the predetermined value APREF as in step 4 described above. . When the determination result is NO, it is determined that the rich spike control should be continuously executed, and as described above, after executing Steps 8 and 9, this process is terminated.

  On the other hand, when the determination result of step 10 is YES and the accelerator pedal is not depressed, as described above, after executing step 11, this process is terminated.

  Next, the air-fuel ratio control process executed by the ECU 2 will be described with reference to FIG. This process controls the air-fuel ratio of the air-fuel mixture supplied into the cylinder 3a by executing a new air amount control process and a fuel injection control process, as described below. For example, it is executed at a TDC signal generation timing).

  In this process, first, in step 20, it is determined whether or not the rich condition flag F_RICH described above is “1”. When the determination result is NO and the execution condition of the rich spike control is not satisfied, the air-fuel ratio control process for lean operation is executed as described below. Specifically, a fresh air amount control process for lean operation is executed in steps 21 to 24, and a fuel injection control process for lean operation is executed in step 25.

  First, at step 21, an EGR control process for lean operation is executed. Specifically, the required torque PMCMD is calculated by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP, and then not shown according to the required torque PMCMD and the engine speed NE. By searching the map, the target fresh air amount QAIR_LEAN for lean operation is calculated. Then, the EGR control valve 10b is controlled by a predetermined feedback control algorithm so that the fresh air amount QAIR converges to the target fresh air amount QAIR_LEAN for lean operation.

  Next, the routine proceeds to step 22 where a throttle valve control process for lean operation is executed. Specifically, the target throttle valve opening TH_CMD is set to a predetermined fully open value TH_WOT. Thereby, a control input corresponding to the target throttle valve opening TH_CMD is input to the TH actuator 8b, and as a result, the throttle valve 8a is controlled to be fully opened.

  Next, at step 23, a supercharging pressure control process for lean operation is executed. Specifically, a target opening for lean operation of the variable vane 7c is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE. Thereby, the supercharging pressure is controlled by inputting a control input corresponding to the target opening for lean operation to the vane actuator 7d.

  In step 24 following step 23, a swirl control process for lean operation is executed. Specifically, a target swirl opening degree for lean operation of the swirl valve 9a is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE. Thereby, the swirl is controlled by inputting the control input corresponding to the target swirl opening degree for the lean operation to the swirl actuator 9b.

  Next, the routine proceeds to step 25 where a fuel injection control process for lean operation is executed. Specifically, a basic fuel injection amount is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE, and this is corrected according to various operating state parameters (for example, engine water temperature). As a result, the fuel injection amount QINJ_LEAN for lean operation is calculated. The lean operation fuel injection amount QINJ_LEAN is calculated as the valve opening time of the fuel injection valve 4. Next, a fuel injection start timing φINJ_LEAN for lean operation is calculated by searching a map (not shown) according to the fuel injection amount QINJ_LEAN for lean operation and the engine speed NE. Based on the fuel injection amount QINJ_LEAN for lean operation calculated as described above and the fuel injection start timing φINJ_LEAN for lean operation, the valve opening time, the valve opening timing, and the valve closing timing of the fuel injection valve 4 are controlled. .

  By the air-fuel ratio control process for lean operation in the above steps 21 to 25, the air-fuel ratio AF is controlled so as to converge to the target air-fuel ratio AF_LEAN for lean operation.

  On the other hand, when the determination result of step 20 is YES and the execution condition of the rich spike control is satisfied, the rich spike control process is executed as described below. That is, a fresh air amount control process for rich spike is executed in steps 26 to 29, and a fuel injection control process for rich spike is executed in step 30.

  First, at step 26, an EGR control process for rich spike is executed. Specifically, this process is executed as shown in FIG. As shown in the figure, first, at step 40, it is determined whether or not the fresh air amount QAIR is less than or equal to a threshold value QAIR_REF. This threshold value QAIR_REF is a value for determining whether or not the fresh air amount QAIR has decreased to near the target fresh air amount QAIR_RICH (predetermined target value) for the rich spike, and is calculated by the method described below. The

  That is, first, the required torque PMCMD is calculated by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP, and then the map (not shown) according to the required torque PMCMD and the engine speed NE. By searching for the target fresh air amount QAIR_RICH for the rich spike. Then, a threshold value QAIR_REF is calculated by adding a predetermined value to the target fresh air amount QAIR_RICH for the rich spike. In other words, the threshold value QAIR_REF is calculated as a value slightly larger than the target fresh air amount QAIR_RICH for rich spike.

  If the determination result in step 40 is NO and the degree of divergence of the fresh air amount QAIR with respect to the rich spike target fresh air amount QAIR_RICH is large, the routine proceeds to step 41, where a plurality of feedback rich values for transient rich are set. . Specifically, each of the plurality of transient rich feedback gains calculates a required torque PMCMD by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP. It is calculated by searching a plurality of maps for transient rich time (not shown) according to PMCMD and engine speed NE.

  On the other hand, when the determination result in step 40 is YES and the fresh air amount QAIR has decreased to the vicinity of the target fresh air amount QAIR_RICH for rich spike, the routine proceeds to step 42 where a plurality of feedback gain values for normal rich are set. To do. Specifically, each of the plurality of normal rich feedback gains calculates a required torque PMCMD by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP. It is calculated by searching a plurality of normal rich time maps (not shown) according to PMCMD and the engine speed NE.

  In this step 42, each of the plurality of normal rich feedback gains is set to a value smaller than the plurality of transient rich feedback gains described above. When the degree of divergence of the fresh air amount QAIR with respect to the target fresh air amount QAIR_RICH for the rich spike is large, the convergence rate of the new air amount QAIR with respect to the target fresh air amount QAIR_RICH for the rich spike is increased and the fresh air amount QAIR is This is for avoiding undershoot or the like when the convergence to the vicinity of the target fresh air amount QAIR_RICH for the rich spike and improving the convergence.

  In step 43 following step 41 or 42, an EGR control process is executed. Specifically, using the feedback gain for transient rich or normal rich set in step 41 or 42 above, the new air volume QAIR is for rich spikes by a predetermined feedback control algorithm (for example, PID control algorithm). The EGR control valve 10b is controlled so as to converge to the target fresh air amount QAIR_RICH. Thereafter, this process is terminated.

  Returning to FIG. 4, after the rich spike EGR control process is executed in step 26 as described above, the routine proceeds to step 27, where the rich spike throttle valve control process is executed. Specifically, this process is executed as shown in FIG. That is, as shown in the figure, first, at step 50, it is determined whether or not the fresh air amount QAIR is less than or equal to the above-described threshold value QAIR_REF.

  When the determination result is NO and the degree of divergence of the fresh air amount QAIR with respect to the target air amount QAIR_RICH for the rich spike is large, the process proceeds to step 51 to calculate the first opening TH_MAP1. Specifically, the first opening TH_MAP1 is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE.

  Next, the routine proceeds to step 52, where the target throttle valve opening TH_CMD is set to the first opening TH_MAP1 and then this process is terminated.

  On the other hand, when the determination result in step 50 is YES and the fresh air amount QAIR decreases to the vicinity of the target fresh air amount QAIR_RICH for rich spike, the routine proceeds to step 53, where the second opening TH_MAP2 is calculated. The second opening TH_MAP2 is calculated as a value that satisfies TH_MAP2> THMAP1. Specifically, the second opening TH_MAP2 is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE.

Next, the routine proceeds to step 54, where the target throttle valve opening TH_CMD is calculated by the following equation (1), and then this processing is terminated. That is, the target throttle valve opening TH_CMD is calculated as a value obtained by subjecting the second opening TH_MAP2 to a temporary delay process (weighted average process). In the following equation (1), α is a predetermined value set so that 0 <α <1 is satisfied, and TH_CMDZ is a previous value of the target throttle valve opening.

  As described above, in the process of FIG. 6, when the degree of deviation of the fresh air amount QAIR from the rich fresh spike target fresh air amount QAIR_RICH is large, the target throttle valve opening TH_CMD is set to the first opening TH_MAP1. This is to increase the convergence speed of the fresh air amount QAIR with respect to the target new air amount QAIR_RICH for the rich spike when the fresh air amount QAIR is deviated to the lean side with respect to the target fresh air amount QAIR_RICH for the rich spike. It is.

  On the other hand, when the fresh air amount QAIR decreases to the vicinity of the target fresh air amount QAIR_RICH for the rich spike, the target throttle valve opening TH_CMD is subjected to a temporary delay process on the second opening TH_MAP2 that is larger than the first opening TH_MAP1. Calculated as a value. This is to improve the convergence of the new air amount QAIR with respect to the target air amount QAIR_RICH for the rich spike in the new air amount control. That is, the second opening TH_MAP2 is set to a value that can optimally ensure the convergence of the fresh air amount QAIR with respect to the rich fresh spike target fresh air amount QAIR_RICH, but the target throttle valve opening TH_CMD is set to the first opening. When changing from TH_MAP1 to the second opening TH_MAP2 in a stepped manner, the convergence of the fresh air amount QAIR with respect to the target fresh air amount QAIR_RICH for the rich spike may be lowered. Therefore, a temporary delay process is performed on the second opening TH_MAP2. This is to avoid it.

  When the target throttle valve opening TH_CMD is calculated as described above, the corresponding control input is input to the TH actuator 8b, and as a result, the throttle valve opening TH becomes the target throttle valve opening TH_CMD. Be controlled.

  Returning to FIG. 4, after the rich spike throttle valve control process is executed in step 27 as described above, the routine proceeds to step 28 where the rich spike supercharging pressure control process is executed. Specifically, the target opening for the rich spike of the variable vane 7c is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE. Accordingly, the supercharging pressure is controlled by inputting a control input corresponding to the target opening for the rich spike to the vane actuator 7d.

  In step 29 following step 28, a swirl control process for rich spike is executed. Specifically, the target swirl opening for the rich spike of the swirl valve 9a is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE. Thereby, the control input corresponding to the target swirl opening for the rich spike is input to the swirl actuator 9b, so that the swirl occurrence state is controlled.

  Next, the routine proceeds to step 30, where fuel injection control processing for rich spike is executed, and the fuel injection amount QINJ (fuel amount) and the fuel injection start timing φINJ are calculated as described below. Thereafter, this process is terminated.

  Specifically, the rich spike fuel injection control process is executed as shown in FIG. That is, first, in step 60, it is determined whether or not the previous value F_RICHZ of the rich condition flag is “1”.

  If the determination result is NO and the current loop is the first time that the rich spike control execution condition is satisfied, the process proceeds to step 61 where both the transient control flag F_TRANS and the rich FB control execution flag F_RICHFB are set to “0”. At the same time, after setting the time value TM_RICHFB of the feedback execution timer to the predetermined value TMSET, the routine proceeds to step 62 described later. On the other hand, if the decision result in the step 60 is YES and the execution condition of the rich spike control is satisfied even in the previous loop, the process proceeds to the step 62 as it is.

  In step 62 following step 60 or 61, it is determined whether or not the rich FB control execution flag F_RICHFB is “1”. When the determination result is NO and the rich FB control described later is not executed, the process proceeds to step 63 to determine whether or not the transient control flag F_TRANS is “1”. When the determination result is NO and the transient control described later is not executed, the routine proceeds to step 64, where it is determined whether or not the fresh air amount QAIR is less than or equal to the threshold value QAIR_REF described above.

  If the determination result is NO and the degree of divergence of the fresh air amount QAIR with respect to the target air amount QAIR_RICH for rich spike is large, the routine proceeds to step 73 and rich preparation control processing is executed. In this rich preparation control process, the fuel injection amount QINJ and the fuel injection start timing φINJ are calculated by the same technique as the fuel injection control process for lean operation in step 25 described above. That is, the fuel injection amount QINJ and the fuel injection start timing φINJ are respectively calculated as the same value as the fuel injection amount QINJ_LEAN fuel injection start timing φINJ_LEAN for lean operation, and thereby the valve opening time and valve opening timing of the fuel injection valve 4 are calculated. The valve closing timing is also controlled in the same manner as the fuel injection control process for lean operation. After executing step 73 as described above, the present process is terminated.

  On the other hand, when the determination result in step 64 is YES and the fresh air amount QAIR has decreased to the vicinity of the target fresh air amount QAIR_RICH for rich spike, the routine proceeds to step 65, where the air-fuel ratio AF is below the predetermined upper threshold AF_RICHH. It is determined whether or not. The predetermined upper limit threshold AF_RICHH is set to a value slightly leaner than the target air-fuel ratio AF_RICH for rich spike (for example, value 15). In the present embodiment, the predetermined upper limit threshold AF_RICHH corresponds to a predetermined air-fuel ratio, and the rich spike target air-fuel ratio AF_RICH corresponds to a predetermined rich-side air-fuel ratio.

  When the determination result of step 65 is NO, the process proceeds to step 66 and the time count value TM_RICHFB of the feedback execution timer is decremented. Next, at step 67, it is determined whether or not the measured value TM_RICHFB of the feedback execution timer is 0.

  When the determination result is NO, it is determined that the execution condition of the transient control process is satisfied, the process proceeds to step 68, and the transient control flag F_TRANS is set to “1” to represent it. As a result, in the subsequent loop, the determination result in step 63 is YES, and in this case, the process proceeds to step 65 described above.

  In step 69 following step 68, a transient control process is executed. In this transient control process, the fuel injection amount QINJ and the fuel injection start timing φINJ are calculated as described below.

First, the feedforward correction term QINJ_FF of the fuel injection amount QINJ is calculated by the following equation (2).

  QINJ_FFMAP in the above equation (2) is a basic value of the feedforward correction term, and is calculated by searching a map (not shown) according to the rich spike target fresh air amount QAIR_RICH and the engine speed NE. In addition, as the target fresh air amount QAIR_LEAN for lean operation in Expression (2), a value calculated during lean operation immediately before the rich condition flag F_RICH is switched from “0” to “1” is used. As is apparent from the above equation (2), in this transient control process, the feedforward correction term QINJ_FF gradually increases to the basic value QINJ_FFMAP as the fresh air amount QAIR approaches the rich spike target fresh air amount QAIR_RICH. It is calculated so as to increase.

Next, the fuel injection amount QINJ is calculated by the following equation (3). Here, QINJ_MAP in the following equation (3) is a basic fuel injection amount, and is calculated by searching a map (not shown) according to the required torque PMCMD and the engine speed NE.

  As shown in the above equation (3), the fuel injection amount QINJ is calculated as the sum of the basic fuel injection amount QINJ_MAP and the feedforward correction term QINJ_FF, and as described above, the feedforward correction term QINJ_FF is the basic value. Since the fuel injection amount QINJ is calculated so as to gradually increase to QINJ_FFMAP, the value (QINJ_MAP + QINJ_FFMAP) from the basic fuel injection amount QINJ_MAP is also obtained as the fresh air amount QAIR approaches the target new air amount QAIR_RICH for rich spike. It is calculated so as to increase gradually.

Next, the fuel injection start timing φINJ is calculated by the following equation (4).

  ΦINJ_RICH in the above equation (4) is the fuel injection start timing for the rich spike, and is calculated by searching a map (not shown) according to the fuel injection amount QINJ and the engine speed NE calculated in the above equation (2). Is done. In addition, φINJ_LEAN in Equation (4) is the fuel injection start timing for lean operation, and uses a value calculated during lean operation immediately before the rich condition flag F_RICH switches from “0” to “1”.

  As described above, after executing the transient control process of step 69, the present process is terminated.

  On the other hand, if the determination result in step 65 is YES and AF ≦ AF_RICHH is satisfied, it is determined that the rich FB control process described later should be executed, and the routine proceeds to step 70 where the time value TM_RICHFB of the feedback execution timer is set to the value. Set to 0. Next, the routine proceeds to step 71 where the rich FB control execution flag F_RICHFB is set to “1” to indicate that the rich FB control processing should be executed. Thereby, in the loop after the next time, the determination result of step 62 becomes YES, and in this case, the process proceeds to step 72 described below.

  In step 72 following step 62 or 70, a rich FB control process is executed. Specifically, as described below, the fuel injection amount QINJ and the fuel injection start timing φINJ are calculated.

First, the feedforward correction term QINJ_FF of the fuel injection amount QINJ is calculated by the following equation (5).

  Here, as shown in the above equation (5), the feedforward correction term QINJ_FF is a ratio (QAIR / QAIR_RICH) of the fresh air amount and the target fresh air amount for the rich spike to the basic value QINJ_FFMAP of the feedforward correction term. It is calculated by multiplying. This is because when the accelerator opening AP changes suddenly and becomes a sudden acceleration state or a sudden deceleration state, the convergence of the new air amount QAIR with respect to the target fresh air amount QAIR_RICH for the rich spike only by correction by a feedback correction term QINJ_FB described later. This is to compensate for the decrease in operability, which may lead to a decrease in operability and exhaust gas characteristics.

Next, the fuel injection amount QINJ is calculated by the following equation (6).

  Here, QINJ_FB in the above equation (6) is a feedback correction term of the fuel injection amount QINJ, and is calculated by a predetermined feedback control algorithm so that the air-fuel ratio AF converges to the target air-fuel ratio AF_RICH for rich spike. . That is, in this rich FB control process, the fuel injection amount QINJ is feedback-controlled so that the air-fuel ratio AF converges to the target air-fuel ratio AF_RICH for rich spike. In this case, limit processing is performed so that the air-fuel ratio AF falls within a range defined by a predetermined upper limit threshold value AF_RICHH and a lower limit threshold value AF_RICHL (for example, value 13). Further, the rich spike target air-fuel ratio AF_RICH is set to a predetermined value (for example, a value of 14).

  Next, the fuel injection start timing φINJ_RICH for the rich spike is calculated by searching a map (not shown) according to the fuel injection amount QINJ and the engine speed NE calculated by the above equation (6), and this is started. Set as timing φINJ. As described above, after executing step 72, the present process is terminated.

  On the other hand, when the determination result in step 67 is YES, that is, when AF> AF_RICHH is maintained and a time corresponding to the predetermined value TMSET has elapsed, it is determined that the rich FB control process should be executed, and As described above, after executing Steps 71 and 72, the present process is terminated.

  Next, an example of the air-fuel ratio control result by the air-fuel ratio control apparatus 1 of the present embodiment will be described with reference to FIGS. FIGS. 8 and 9 show examples of control results when the normal lean operation air-fuel ratio control process is shifted to the rich spike air-fuel ratio control process and then returned to the lean operation air-fuel ratio control process. ing.

  First, in the control result example shown in FIG. 8, after the rich spike control execution condition is satisfied and the rich condition flag F_RICH is set to “1” (time t1), the rich spike use in steps 26 to 30 described above is performed. The fresh air amount control process and the fuel injection control process are executed. In particular, in the fuel injection control process, the rich preparation control process in step 73 described above is executed. As a result, the fresh air amount QAIR decreases toward the rich spike target fresh air amount QAIR_RICH, and the fuel injection amount QINJ is held at the lean operation fuel injection amount QINJ_LEAN. As a result, the air-fuel ratio AF is controlled so as to change from the target air-fuel ratio AF_LEAN for lean operation toward the target air-fuel ratio AF_RICH for rich spike.

  Then, when the fresh air amount QAIR reaches the threshold value QAIR_REF (time t2), in the fuel injection control process, the transient control process of step 69 described above is executed. Accordingly, the feedforward correction term QINJ_FF of the fuel injection amount QINJ is calculated by the above-described equation (2), so that the fuel injection is performed as the fresh air amount QAIR approaches the rich fresh spike target fresh air amount QAIR_RICH. The amount QINJ is controlled to gradually increase, and the fuel injection start timing φINJ is also calculated by the above-described equation (4) so that the fuel injection start timing φINJ_LEAN for lean operation is gradually advanced. Be controlled. That is, the fuel injection start timing φINJ is gradually controlled to the advance side.

  Thereafter, when the air-fuel ratio AF reaches a predetermined upper limit threshold value AF_RICHH (time t3), in the fuel injection control process, the rich FB control process in step 72 described above is started, so that the air-fuel ratio AF becomes rich. Control is performed so as to converge to the target air-fuel ratio AF_RICH for spike. Then, when the time corresponding to the predetermined value TMREF described above has elapsed (time t4), F_RICH = 0, and thereafter the air-fuel ratio control process for lean operation in steps 21 to 25 described above is executed. Thereby, the air-fuel ratio AF is controlled to become the target air-fuel ratio AF_LEAN for lean operation.

  On the other hand, in the control result example shown in FIG. 9, after F_RICH = 1 is established (time t11), the fresh air amount control process for rich spike and the rich preparation control process in the fuel injection control process are executed, and QAIR ≦ QAIR_REF Although the transient control process in the fuel injection control process is executed after the time (time t12) is established, TM_RICHFB = 0 is established (time t13) before the air-fuel ratio AF reaches the predetermined upper limit threshold AF_RICHH. ), The rich FB control process in the fuel injection control process is started, and the air-fuel ratio AF is controlled to converge to the target air-fuel ratio AF_RICH for rich spike. Then, after the time corresponding to the predetermined value TMREF has elapsed (time t14), the air-fuel ratio AF is controlled to become the target air-fuel ratio AF_LEAN for lean operation.

  As described above, in the air-fuel ratio control apparatus 1 of the present embodiment, even when it takes time for the air-fuel ratio AF to reach the predetermined upper limit threshold AF_RICHH, when the time measurement of the feedback execution timer ends, Since the rich FB control process in the fuel injection control process is started, the air-fuel ratio AF can be reliably controlled by the rich spike target air-fuel ratio AF_RICH.

  FIG. 10 also shows the feedforward correction term QINJ_FF of the fuel injection amount QINJ in the transient control process in order to clearly show the torque fluctuation suppression state by the transient control process of the fuel injection control process of the present embodiment. FIG. 11 shows an example of the control result when calculated in 2). For comparison, FIG. 11 calculates the feedforward correction term QINJ_FF of the fuel injection amount QINJ as the basic value QINJ_FFMAP without executing the transient control process. An example of the control result is shown. In both figures, TRQ represents the torque generated by the engine 3, and QINJ1 is a fuel injection amount value corresponding to QINJ_MAP + QINJ_MAPFF.

  First, in the control result of FIG. 11, when QAIR ≦ QAIR_REF is satisfied (time t32), the fuel injection amount QINJ is increased from the fuel injection amount QINJ_LEAN for lean operation to the value QINJ1 in a stepped manner. It can be seen that a large torque fluctuation occurs. On the other hand, in the control result of the present embodiment in FIG. 10, after the time point (time t22) when QAIR ≦ QAIR_REF is satisfied, as described above, in the transient control process, the feedforward correction is performed by the above-described equation (2). The term QINJ_FF is calculated so as to gradually increase to the basic value QINJ_FFMAP as the fresh air amount QAIR approaches the rich spike target fresh air amount QAIR_RICH, so that the fuel injection amount QINJ is the control result of FIG. It can be seen that the value is increased to the value QINJ1 more slowly than in the example, whereby the torque fluctuation is clearly reduced. That is, it can be seen that the torque fluctuation at the time of shifting from lean control to rich spike control can be suppressed by the transient control process.

  Further, FIG. 12 shows an example of the control result of the air-fuel ratio AF when the rich FB control process of the present embodiment is executed during the rich spike control, and FIG. 13 shows the rich FB control process for comparison. 5 shows an example of the control result when the feedforward correction term QINJ_FF is calculated by QINJ_FF = QINJ_FFMAP instead of Equation (5), that is, when QAIR / QAIR_RICH = 1 in Equation (5). Note that AF1 in both figures indicates a predetermined value (for example, value 20) of the lean side air-fuel ratio, and in the curve showing the air-fuel ratio AF in both figures, the region of AF> AF1 is omitted. Furthermore, VP in both figures represents the vehicle speed.

  First, it can be seen from the control result of FIG. 13 that the air-fuel ratio AF significantly undershoots the rich spike target air-fuel ratio AF_RICH during rapid acceleration or the like, and does not readily converge. On the other hand, in the control result by the rich FB control process of the present embodiment in FIG. 12, the air-fuel ratio AF hardly undershoots the target air-fuel ratio AF_RICH for rich spike even during sudden acceleration. It turns out that it is controlled so that it may converge quickly.

  That is, as in this embodiment, the feedforward correction term QINJ_FF is calculated by calculating the feedforward correction term QINJ_FF using the ratio (QAIR / QAIR_RICH) between the fresh air amount and the target fresh air amount for rich spike as a multiplication term. It can be calculated as a value reflecting the degree of divergence of the fresh air amount QAIR with respect to the target fresh air amount QAIR_RICH for spikes. As a result, the fuel injection amount QINJ can be calculated while quickly reflecting the degree of divergence of the new air amount QAIR with respect to the target air amount QAIR_RICH for the rich spike, so that the convergence of the air / fuel ratio AF with respect to the target air / fuel ratio AF_RICH for the rich spike is achieved. Can be improved.

  As described above, according to the air-fuel ratio control apparatus 1 of the present embodiment, the fresh air amount QAIR is executed by executing the new air amount control process for rich spike when the execution condition of the rich spike control is satisfied. Is controlled to decrease to the target air quantity QAIR_RICH for the rich spike, and the rich preparation control process in the fuel injection control process for the rich spike is executed, so that the fuel injection quantity QINJ is kept constant. . As a result, the air-fuel ratio AF is controlled so as to change from the target air-fuel ratio AF_LEAN for lean operation toward the target air-fuel ratio AF_RICH for rich spike.

  Then, when QAIR ≦ QAIR_REF is satisfied and the fresh air amount QAIR is reduced to the vicinity of the target air amount QAIR_RICH for the rich spike, the transient control processing in the fuel injection control processing is executed, so that the new air amount QAIR is The fuel injection amount QINJ is controlled to gradually increase as the target fresh air amount QAIR_RICH for the rich spike is approached, and the fuel injection start timing φINJ is gradually controlled to the advance side. As a result, unlike the conventional case where the fuel injection amount temporarily increases until the fresh air amount actually decreases, it is possible to reliably suppress the occurrence of torque fluctuations and avoid unnecessary fuel consumption. By doing so, fuel consumption can be improved.

  Furthermore, during the execution of the transient control process, the rich FB control process in the fuel injection control process is started at the timing when AF ≦ AF_RICHH is satisfied. That is, since the air-fuel ratio AF is controlled to converge to the rich spike target air-fuel ratio AF_RICH at the timing when the air-fuel ratio AF approaches the vicinity of the target air-fuel ratio AF_RICH for rich spike, the target air-fuel ratio for rich spike is controlled. The convergence of the air-fuel ratio AF with respect to AF_RICH can be improved, and the control accuracy can be improved.

  In addition, as described above, in the rich FB control process, the feedforward correction term QINJ_FF is calculated as a value reflecting the deviation degree of the fresh air amount QAIR with respect to the target fresh air amount QAIR_RICH for rich spike. The fuel injection amount QINJ can be calculated while quickly reflecting the degree of divergence of the new air amount QAIR with respect to the target air amount QAIR_RICH for the rich spike. As a result, the convergence of the air-fuel ratio AF with respect to the target air-fuel ratio AF_RICH for rich spike can be further improved.

  The embodiment is an example in which the predetermined threshold value QAIR_REF is calculated as a value slightly larger than the rich spike target fresh air amount QAIR_RICH. However, the predetermined threshold value QAIR_REF is set to a target value for rich spike. It may be calculated as a value equal to the volume QAIR_RICH. In this way, the same operational effects as the control method of the embodiment can be obtained, but when both are compared, the control method of the embodiment controls the air-fuel ratio AF more quickly by the rich side value. be able to.

Further, in the above-described transient control process, the feedforward correction term QINJ_FF of the fuel injection amount QINJ may be calculated by the following equation (7) instead of the equation (2) of the embodiment. Even if it does in this way, the effect similar to the transient control process of embodiment can be acquired.

In the rich FB control process described above, the feedforward correction term QINJ_FF for the fuel injection amount QINJ may be calculated by the following equation (8) instead of the equation (5) of the embodiment. Even if it does in this way, the effect similar to the rich FB control process of embodiment can be acquired.

  The embodiment is an example in which the air-fuel ratio control apparatus 1 is applied to a diesel engine type internal combustion engine 3. However, the air-fuel ratio control apparatus of the present invention is not limited to this and can be applied to various internal combustion engines. For example, the air-fuel ratio control device may be applied to a gasoline engine.

  The embodiment is an example in which the airflow sensor 21 and the ECU 2 are used as the fresh air amount detecting means. However, the fresh air amount detecting means of the present invention is not limited to this, and may be any device that can detect the fresh air amount. . For example, as a fresh air amount detection means, a sensor for detecting another operating state parameter representing the fresh air amount and the ECU 2 may be used, and the ECU 2 may calculate the fresh air amount based on the detection signal of the sensor.

  Further, the embodiment is an example in which the LAF sensor 22 and the ECU 2 are used as the air-fuel ratio detection means. However, the air-fuel ratio detection means of the present invention is not limited to this and may be any one that can detect the air-fuel ratio of the air-fuel mixture. . For example, as the air-fuel ratio detection means, a sensor that detects other operating state parameters representing the air-fuel ratio and the ECU 2 may be used, and the air-fuel ratio may be calculated by the ECU 2 based on the detection signal of this sensor.

1 is a diagram schematically showing a schematic configuration of an internal combustion engine to which an air-fuel ratio control apparatus according to an embodiment of the present invention is applied. It is a block diagram which shows schematic structure of an air fuel ratio control apparatus. It is a flowchart which shows the execution condition determination process of rich spike control. It is a flowchart which shows an air fuel ratio control process. It is a flowchart which shows the EGR control process for rich spikes. It is a flowchart which shows the throttle valve control process for rich spikes. It is a flowchart which shows the fuel injection control process for rich spikes. It is a timing chart which shows the example of a control result at the time of performing rich spike control processing. It is a timing chart which shows the other example of a control result at the time of performing a rich spike control process. It is a timing chart which shows the example of a control result at the time of performing the transient control process in a fuel-injection control process. It is a timing chart which shows the control result of a comparative example. It is a timing chart which shows the example of a control result at the time of performing rich FB control processing in fuel injection control processing. It is a timing chart which shows the control result of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air fuel ratio control apparatus 2 ECU (New air quantity detection means, fresh air quantity control means, fuel quantity control means, air fuel ratio detection means, air fuel ratio control means)
3 Internal combustion engine 3a Cylinder 21 Air flow sensor (new air quantity detection means)
22 LAF sensor (air-fuel ratio detection means)
QAIR Fresh air volume QAIR_RICH Target fresh air volume for rich spikes (predetermined target value)
QAIR_REF Predetermined threshold
QINJ Fuel injection amount (fuel amount)
AF Air-fuel ratio of air-fuel mixture AF_RICHH Predetermined upper threshold (predetermined air-fuel ratio)
AF_RICH Target air-fuel ratio for rich spike (predetermined rich-side target air-fuel ratio)

Claims (2)

Air-fuel ratio control of an internal combustion engine that controls the air-fuel ratio of the air-fuel mixture in the cylinder by switching the lean-air side and the rich-side from the stoichiometric air-fuel ratio by controlling the amount of fresh air and fuel supplied to the cylinder, respectively. A device,
A new air amount detecting means for detecting the new air amount;
A new air amount control that controls the fresh air amount to decrease to a predetermined target value when an air-fuel ratio switching condition for switching the air-fuel ratio of the air-fuel mixture from the lean side to the rich side from the stoichiometric air-fuel ratio is satisfied. Means,
During the reduction control of the fresh air amount to the predetermined target value by the fresh air amount control means, the detected fresh air amount becomes the predetermined target value or a predetermined threshold value larger than the predetermined target value. Fuel amount control means for controlling the fuel amount to the increase side when the fuel amount is reached;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: Air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture;
After the air-fuel ratio of the air-fuel mixture detected during the control of the fuel amount to the increase side by the fuel amount control means becomes equal to or lower than the predetermined air-fuel ratio, the air-fuel ratio of the air-fuel mixture is changed to the predetermined rich-side target air-fuel ratio. Air-fuel ratio control means for performing feedback control so that
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, further comprising:

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