JP2005120908A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, reducing torque shock during transition from rich control to stoichimetric control when resetting fuel cut operation. <P>SOLUTION: The control device comprises a throttle valve 9 for adjusting the amount of air to be sucked into an engine 1 and an ECU 18 for controlling an ignition timing for the engine 1. The throttle valve 9 reduces the amount of air to be sucked into the engine depending on the degree of richness in an air-fuel ratio during rich control when resetting the fuel cut operation. The ECU 18 controls the ignition timing to be delayed corresponding to a response delay after the amount of air is reduced during rich control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine.

A fuel injection control device that sets the target air-fuel ratio to the rich side until the amount of oxygen stored in the three-way catalyst reaches a predetermined appropriate value at the time of transition from fuel cut operation to air-fuel ratio feedback control is disclosed in the following patent document 1.
JP-A-8-193537 (page 4-9, FIG. 1)

  During rich control execution at the time of fuel cut operation return, engine torque increases compared to during stoichiometric control. Thereafter, when the amount of oxygen stored in the catalyst is reduced to a predetermined appropriate value and the shift is made from rich control to stoichiometric control, there is a possibility that a torque shock due to a decrease in engine torque may occur.

  The present invention has been made to solve the above problems, and provides a control device for an internal combustion engine that can reduce torque shock when shifting from rich control to stoichiometric control at the time of return from fuel cut operation. For the purpose.

  The internal combustion engine control apparatus according to the present invention stops the fuel supply to the internal combustion engine when a predetermined fuel supply stop condition is satisfied, and controls the air-fuel ratio to be rich when returning from the fuel stop operation. The engine control device is characterized by comprising torque control means for reducing the output torque of the internal combustion engine during rich control.

  According to the control device for an internal combustion engine according to the present invention, the output torque of the internal combustion engine is reduced by the torque reduction means during the rich control at the time of return from the fuel stop operation, and the increase of the output torque due to the enrichment of the air-fuel ratio is prevented. It is suppressed. Therefore, it is possible to reduce the torque step at the time of shifting to stoichiometric control.

  The control apparatus for an internal combustion engine according to the present invention preferably includes an ignition timing control means for controlling the ignition timing of the internal combustion engine to the retard side according to the richness of the air-fuel ratio during the rich control.

  In this case, the output torque of the internal combustion engine is reduced by retarding the ignition timing during the rich control when returning from the fuel stop operation.

  The control apparatus for an internal combustion engine according to the present invention preferably includes an intake air amount adjusting means for reducing the amount of air taken into the internal combustion engine in accordance with the richness of the air-fuel ratio when the torque control means is in rich control.

  In this case, the output torque of the internal combustion engine is reduced by reducing the amount of air sucked into the internal combustion engine during the rich control when returning from the fuel stop operation.

  In the control device for an internal combustion engine according to the present invention, the torque control means includes an intake air amount adjusting means for reducing the amount of air sucked into the internal combustion engine in accordance with the richness of the air-fuel ratio during the rich control, and the air amount during the rich control. It is preferable to have ignition timing control means for controlling the ignition timing to the retard side in response to the response delay when it is decreased.

  When the amount of air sucked into the internal combustion engine is reduced by the intake air amount adjusting means, the intake air amount changes with a response delay. Therefore, the output torque of the internal combustion engine is also reduced with a response delay. According to the control apparatus for an internal combustion engine according to the present invention, the ignition timing is controlled to the retard side in response to the response delay of the air amount. Therefore, the response delay of the intake air amount, that is, the output by the ignition control having excellent responsiveness. Torque response delay can be compensated. Therefore, it is possible to suppress an increase in output torque due to enrichment of the air-fuel ratio with good responsiveness.

  According to the present invention, the output torque of the internal combustion engine is reduced during the rich control at the time of return from the fuel stop operation, and the increase in the output torque due to the rich air-fuel ratio is suppressed. Therefore, torque shock when shifting from rich control to stoichiometric control can be reduced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the figure, the same reference numerals are used for the same or corresponding parts.

  First, the configuration of the control device according to the present embodiment will be described with reference to FIG. FIG. 1 is a configuration diagram of an internal combustion engine including a control device according to the present embodiment.

  The control apparatus of this embodiment controls the engine 1 which is an internal combustion engine. Although the engine 1 is a multi-cylinder engine, only one cylinder is shown here as a cross-sectional view. As shown in FIG. 1, the engine 1 generates a driving force by igniting an air-fuel mixture in each cylinder 3 with a spark plug 2. During combustion of the engine 1, air sucked from outside passes through the intake pipe 4, is mixed with fuel injected from the injector 5, and is sucked into the cylinder 3 as an air-fuel mixture. The inside of the cylinder 3 and the intake pipe 4 are opened and closed by an intake valve 6. The air-fuel mixture combusted inside the cylinder 3 is exhausted to the exhaust pipe 7 as exhaust gas. An exhaust valve 8 opens and closes the inside of the cylinder 3 and the exhaust pipe 7.

  A throttle valve 9 that adjusts the amount of intake air taken into the cylinder 3 is disposed on the intake pipe 4. A throttle position sensor 10 for detecting the opening degree is connected to the throttle valve 9. The throttle valve 9 is connected to a throttle motor 11 and is opened and closed by the driving force of the throttle motor 11. An accelerator position sensor 12 that detects an operation amount (accelerator opening) of the accelerator pedal 16 is also provided in the vicinity of the throttle valve 9. Thus, in this embodiment, an electronically controlled throttle valve in which the opening degree of the throttle valve 9 is electronically controlled is employed. The throttle valve 9 functions as intake air amount adjusting means. Furthermore, an air flow meter 13 for detecting the amount of intake air is also mounted on the intake pipe 4.

  A crank position sensor 14 for detecting the position of the crankshaft is attached in the vicinity of the crankshaft of the engine 1. From the output of the crank position sensor 14, the position of the piston 15 in the cylinder 3 and the engine speed can be obtained.

  An exhaust purification catalyst 19 is disposed on the exhaust pipe 7. A plurality of exhaust purification catalysts may be provided on the exhaust pipe. For example, in a four-cylinder engine, one exhaust purification catalyst is arranged at a place where two cylinder exhaust pipes are gathered together, and another one is placed at a place where the remaining two cylinder exhaust pipes are gathered together. An exhaust purification catalyst can also be arranged. In the present embodiment, one exhaust purification catalyst 19 is disposed downstream of the location where the exhaust pipes for each cylinder 3 are gathered together.

  The spark plug 2, injector 5, throttle position sensor 10, throttle motor 11, accelerator position sensor 12, air flow meter 13, crank position sensor 14, and other sensors are electronic control devices (hereinafter ““ The ECU 18 is connected to the ECU 18 and is controlled based on a signal from the ECU 18 or sends a detection result to the ECU 18. A catalyst temperature sensor 21 that measures the temperature of the exhaust purification catalyst 19 disposed on the exhaust pipe 7 is also connected to the ECU 18.

Further, an air-fuel ratio sensor 25 attached to the upstream side of the exhaust purification catalyst 19 is also connected to the ECU 18. The air-fuel ratio sensor 25 detects the exhaust air-fuel ratio from the oxygen concentration in the exhaust gas at the mounting position. As the air-fuel ratio sensor 25, an O ₂ sensor that detects the exhaust air-fuel ratio on and off is used. As the air-fuel ratio sensor 25, a linear air-fuel ratio sensor that can linearly detect the exhaust air-fuel ratio may be used. Further, since the air-fuel ratio sensor 25 cannot accurately detect the air-fuel ratio unless the temperature exceeds a predetermined temperature (activation temperature), the air-fuel ratio sensor 25 is supplied via the ECU 18 so that the temperature is raised to the activation temperature early. The temperature is raised by the generated electric power.

  Further, the ECU 18 includes an injector driver that drives the injector 5, a motor driver that drives the throttle motor 11, an output circuit that outputs an ignition signal, and the like.

  The ECU 18 has its stored contents held by a microprocessor that performs calculations therein, a ROM that stores programs for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, and a battery. It has a backup RAM and the like.

  The ECU 18 includes a fuel cut portion 18a that stops (cuts) fuel supply to the engine 1 when a predetermined fuel cut condition is satisfied, and an amount of oxygen stored in the exhaust purification catalyst 19 upon return from the fuel cut operation. Accordingly, an air-fuel ratio control unit 18b that controls the air-fuel ratio of the air-fuel mixture richly, an ignition timing control unit 18c that controls the ignition timing for the air-fuel mixture, and the like are constructed. That is, the ECU 18 functions as an ignition timing control unit. The ECU 18 and the throttle valve 9 function as torque control means.

  Further, the ECU 18 also calculates the target throttle opening, calculates the oxygen storage amount stored in the exhaust purification catalyst 19, and the like.

  Here, the oxygen storage function of the exhaust purification catalyst 19 will be described. The exhaust purification catalyst 19 is a three-way catalyst having a honeycomb structure mainly composed of cordierite. A carrier layer made of a coating material such as alumina (Al2O3) or zirconia (ZrO2) is formed on the surface of the honeycomb structure, and a platinum-rhodium (Pt-Rh) noble metal catalyst material is supported on the carrier layer. ing.

  The exhaust purification catalyst 19 has a function of oxidizing unburned components (HC, CO) and simultaneously reducing nitrogen oxides (NOx) when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio. Further, the exhaust purification catalyst 19 has a property (oxygen storage function) to occlude (adsorb and store) and release oxygen molecules in the inflowing exhaust gas by supporting components such as ceria. With the oxygen storage function, HC, CO and NOx can be purified even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio to some extent. That is, the exhaust purification catalyst 19 occludes excess oxygen and removes oxygen from the nitrogen oxide NOx when the exhaust gas flowing in with the lean exhaust air-fuel ratio contains a large amount of excess oxygen and nitrogen oxide NOx. (Reducing NOx) and occluding oxygen, thereby purifying NOx. Further, the exhaust purification catalyst 19 can absorb oxygen molecules stored in the exhaust gas when the exhaust gas flowing in in a rich exhaust air-fuel ratio contains a large amount of unburned components such as hydrocarbon HC and carbon monoxide CO. These unburned components are fed to oxidize the unburned components, thereby purifying CO and HC.

  Therefore, if the exhaust purification catalyst 19 stores oxygen to the limit at which oxygen can be stored, oxygen cannot be stored when the exhaust air-fuel ratio becomes lean. Therefore, NOx purification using the oxygen storage function can be performed. Can no longer contribute. On the other hand, unless the exhaust purification catalyst 19 has released oxygen and occluded oxygen at all, oxygen cannot be released when the exhaust air-fuel ratio becomes rich. Therefore, HC and CO purification utilizing the oxygen storage function Can no longer contribute. Therefore, even if the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 19 becomes transiently lean or rich, the oxygen storage amount is accurately adjusted so that the components to be purified can be sufficiently purified. It is desirable to perform air-fuel ratio control so that the oxygen storage amount is maintained at a predetermined value while being well estimated.

  Next, the operation of the control device according to the present embodiment will be described with reference to FIGS. First, torque reduction processing using ignition retard control by the control device according to the present embodiment will be described with reference to FIG. Here, FIG. 2 is a flowchart showing a processing procedure of torque reduction processing using ignition retardation control. This torque reduction process is started and executed in synchronization with the rotation of the engine 1.

  In step S100, it is determined whether or not the rich control after the fuel cut operation return is being executed. Here, when the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value when the fuel cut operation is restored, the air-fuel ratio is controlled to be rich until the stored oxygen amount becomes less than the predetermined value.

  When step S100 is affirmed, that is, when the rich control after returning from the fuel cut operation is being executed, the process proceeds to step S102. On the other hand, if step S100 is negative, that is, if rich control is not performed, the process proceeds to step S104.

  In step S102, the ignition timing retard amount ARTDFC for reducing the engine torque that increases due to the rich air-fuel ratio to the engine torque equivalent to the stoichiometric control is calculated. The ignition timing retardation amount ARTDFC is calculated by adding the ignition timing retardation correction coefficient KARTD to the rich degree. Here, the richness is obtained according to the air-fuel ratio difference between the stoichiometric air-fuel ratio (stoichiometric) and the actual air-fuel ratio. Note that the reciprocal of the excess air ratio λ, which is the ratio of the actual supply air amount to the theoretical air amount necessary for completely burning the fuel, may be used as the rich degree. The ignition timing retardation correction coefficient KARTD is a predetermined constant. The ignition timing retardation correction coefficient KARTD may be set according to the engine speed, the engine load, and the like.

  On the other hand, the basic ignition timing is calculated based on engine operating conditions such as engine speed, intake air amount, air-fuel ratio, and the like. The target ignition timing is obtained by adding the ignition timing retard amount ARTDFC to the basic ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing corresponding to the determined target ignition timing. Thereafter, the process is temporarily exited.

  If step S100 is negative, that is, if rich control is not being performed, the ignition timing retard amount ARTDFC is set to 0 (reset) in step S104. Therefore, the basic ignition timing calculated based on the engine operating state is set as the target ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing according to the target ignition timing equal to the basic ignition timing without delaying the ignition timing. Thereafter, the process is temporarily exited.

  FIG. 3 shows changes in (a) air-fuel ratio, (b) ignition timing, and (c) engine torque in torque reduction processing using ignition retard control.

  As shown in FIG. 3A, the air-fuel ratio during the fuel cut operation is extremely lean. During the fuel cut operation, since the exhaust purification catalyst 19 is exposed to an extremely lean atmosphere, the amount of oxygen stored in the exhaust purification catalyst 19 increases. Further, during the fuel cut operation, the amount of oxygen stored in the exhaust purification catalyst 19 is calculated. The stored oxygen amount is calculated based on the exhaust air amount and the oxygen concentration. However, since the exhaust gas becomes air during the fuel cut operation, the oxygen concentration matches the oxygen ratio (about 20%) in the air.

  When the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value after the fuel cut operation is restored, the air-fuel ratio is controlled to be rich until the stored oxygen amount becomes less than the predetermined value. At this time, as shown in FIG. 3B, the ignition timing is retarded according to the richness of the air-fuel ratio.

  A dashed line in FIG. 3C shows a change in engine torque when the ignition timing is not retarded during the rich control of the air-fuel ratio. As indicated by the alternate long and short dash line in FIG. 3C, when the ignition timing retarding control is not performed, the engine torque increases due to the rich air-fuel ratio.

  On the other hand, the solid line in FIG. 3C shows the change in engine torque when the ignition timing is retarded. As shown by the solid line in FIG. 3C, the output torque of the engine 1 corresponds to the output torque at the time of stoichiometric control even when the air-fuel ratio is controlled to be rich by controlling the ignition timing to be retarded. Reduced to.

  Thus, according to the present control device, the ignition timing is retarded during the rich control after the fuel cut operation is resumed, so that the output torque of the engine 1 is reduced and the output torque due to the rich air-fuel ratio. Increase is suppressed. Therefore, the torque step at the time of the stoichiometric control transition is reduced, and the torque shock is reduced.

  Further, since the ignition timing control is excellent in responsiveness, an increase in output torque due to the rich air-fuel ratio can be suppressed with good responsiveness.

  Next, torque reduction processing using intake air amount control by the control device according to the present embodiment will be described with reference to FIGS. 4 and 5. Here, FIG. 4 is a flowchart showing a processing procedure of torque reduction processing using intake air amount control. This torque reduction process is started and executed in synchronization with the rotation of the engine 1.

  In step S200, it is determined whether or not the rich control after the fuel cut operation return is being executed. Here, when the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value when the fuel cut operation is restored, the air-fuel ratio is controlled to the rich side until the stored oxygen amount becomes less than the predetermined value.

  When step S200 is affirmed, that is, when the rich control after the fuel cut operation return is being executed, the process proceeds to step S202. On the other hand, if step S200 is negative, that is, if rich control is not performed, the process proceeds to step S204.

  In step S202, a valve closing amount TARTDFC of the throttle valve 9 for reducing the engine torque that increases due to the rich air-fuel ratio to the engine torque at the time of stoichiometric control is calculated. The throttle valve closing amount TARTDFC is calculated by adding the throttle valve closing correction coefficient KTARTD to the rich degree. Here, the richness is obtained according to the air-fuel ratio difference between the stoichiometric air-fuel ratio (stoichiometric) and the actual air-fuel ratio. Note that the reciprocal of the excess air ratio λ, which is the ratio of the actual supply air amount to the theoretical air amount necessary for completely burning the fuel, may be used as the rich degree. The throttle valve closing correction coefficient KTARTD is a predetermined constant. The throttle valve closing correction coefficient KTARTD may be set according to the engine speed, the engine load, and the like.

  On the other hand, the basic throttle valve opening is calculated based on the operating state such as the accelerator opening. The throttle valve closing amount TARTDFC is subtracted from the basic throttle valve opening to obtain the target throttle valve opening. Then, the throttle motor 11 is driven so that the obtained target throttle valve opening matches the actual throttle valve opening. Thus, the amount of air taken into the engine 1 is reduced by closing the throttle valve 9 according to the throttle valve closing amount TARTDFC. Thereafter, the process is temporarily exited.

  If step S200 is negative, that is, if rich control is not being performed, the throttle valve closing amount TARTDFC is set to 0 (reset) in step S204. Therefore, the basic throttle valve opening calculated based on the operating state such as the accelerator opening is set as the target throttle valve opening. The throttle valve 9 is opened in accordance with the target throttle valve opening equal to the basic throttle valve opening without performing the valve closing control of the throttle valve 9. Thereafter, the process is temporarily exited.

  FIG. 5 shows changes in (a) air-fuel ratio, (b) intake air amount, and (c) engine torque in torque reduction processing using intake air amount control.

  As shown in FIG. 5A, the air-fuel ratio during the fuel cut operation is extremely lean. During the fuel cut operation, since the exhaust purification catalyst 19 is exposed to an extremely lean atmosphere, the amount of oxygen stored in the exhaust purification catalyst 19 increases. Further, during the fuel cut operation, the amount of oxygen stored in the exhaust purification catalyst 19 is calculated.

  When the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value after the fuel cut operation is restored, the air-fuel ratio is controlled to be rich until the stored oxygen amount becomes less than the predetermined value. At this time, as shown in FIG. 5B, the throttle valve 9 is closed according to the richness of the air-fuel ratio, and the amount of air taken into the engine 1 is reduced.

  An alternate long and short dash line in FIG. 5C shows a change in engine torque when the valve closing control of the throttle valve 9 is not performed during the rich control of the air-fuel ratio. As indicated by the alternate long and short dash line in FIG. 5C, when the valve closing control of the throttle valve 9 is not performed, the engine torque increases due to the rich air-fuel ratio.

  On the other hand, the solid line in FIG. 5C shows the change in engine torque when the closing control of the throttle valve 9 is performed. As indicated by the solid line in FIG. 5C, even when the air-fuel ratio is controlled to be rich by controlling the throttle valve 9 to close, the output torque of the engine 1 is the output torque at the time of stoichiometric control. To a considerable extent.

  Thus, according to the present control device, the throttle valve 9 is controlled to close during the rich control after returning from the fuel cut operation, whereby the output torque of the engine 1 is reduced and the output due to the rich air-fuel ratio. An increase in torque is suppressed. Therefore, the torque step at the time of the stoichiometric control transition is reduced, and the torque shock is reduced.

  In addition, when the engine torque is reduced by closing the throttle valve opening to reduce the intake air amount, the increase in output torque due to enrichment is suppressed without causing deterioration in fuel consumption or combustion state. be able to.

  Note that the intake air amount may be adjusted using an ISC (Idle Speed Control) instead of the throttle valve 9. In this case, control is performed so as to close the opening of the valve constituting the ISC, and the intake air amount is reduced.

  Next, torque reduction processing using ignition retard control and intake air amount control by the control device according to the present embodiment will be described with reference to FIGS. Here, FIG. 6 is a flowchart showing a processing procedure of torque reduction processing using ignition retard control and intake air amount control. This torque reduction process is started and executed in synchronization with the rotation of the engine 1.

  In step S300, it is determined whether or not the rich control after the fuel cut operation return is being executed. Here, when the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value when the fuel cut operation is restored, the air-fuel ratio is controlled to the rich side until the stored oxygen amount becomes less than the predetermined value.

  When step S300 is affirmed, that is, when the rich control after the return to the fuel cut operation is being executed, the process proceeds to step S302. On the other hand, if step S300 is negative, that is, if rich control is not performed, the process proceeds to step S326.

  In step S302, a determination is made as to whether a predetermined time has elapsed after the start of rich control. If the predetermined time has not elapsed since the start of rich control, the process proceeds to step S304. On the other hand, if the predetermined time has elapsed, the process proceeds to step S306.

  If step S302 is negative, that is, if a predetermined time has not elapsed since the start of the rich control, in step S304, the engine torque that increases due to the rich air-fuel ratio is reduced to the engine torque equivalent to the stoichiometric control. A valve closing amount TARTDFC of the throttle valve 9 is calculated. Since the calculation method of the throttle valve closing amount TARTDFC is the same as or equivalent to that in step S202, the description thereof is omitted here.

  On the other hand, the basic throttle valve opening is calculated based on the operating state such as the accelerator opening. The throttle valve closing amount TARTDFC is subtracted from the basic throttle valve opening to obtain the target throttle valve opening. Then, the throttle motor 11 is driven so that the obtained target throttle valve opening matches the actual throttle valve opening. Thus, the amount of air taken into the engine 1 is reduced by closing the throttle valve 9 according to the throttle valve closing amount TARTDFC. Thereafter, the process proceeds to step S312.

  If step S302 is affirmed, that is, if a predetermined time has elapsed after the start of rich control, the valve closing amount TARTDFC of the throttle valve 9 is calculated in step S306. Here, the throttle valve closing amount TARTDFC is calculated by adding the throttle valve closing correction coefficient KTARTD to a value obtained by subtracting a predetermined value from the rich degree. Others are the same as or equivalent to step S202 described above, and a description thereof is omitted here.

  Subsequently, a limit check of the valve closing amount TARTDFC is performed in steps S308 and S310. In step S308, a determination is made as to whether or not the throttle valve closing amount TARTDFC calculated in step S306 is smaller than zero. If the throttle valve closing amount TARTDFC is smaller than 0, the throttle valve closing amount TARTDFC is set to 0 in step S310. On the other hand, when the throttle valve closing amount TARTDFC is 0 or more, the throttle valve closing amount TARTDFC calculated in step S306 is maintained.

  Then, the target throttle valve opening is obtained by subtracting the throttle valve closing amount TARTDFC from the basic throttle valve opening, and the throttle motor 11 is driven so that the target throttle valve opening and the actual throttle valve opening coincide. The Thereafter, the process proceeds to step S312.

  In step S312, whether the previous execution of this step is in the fuel cut operation and whether the current execution is after the return of the fuel cut operation, that is, whether or not to pass this step for the first time after the return of the fuel cut operation. Judgment is made. If step S312 is affirmed, the process proceeds to step S314. On the other hand, if step S312 is negative, the process proceeds to step S316.

  In step S314, the initial value of the ignition timing retardation amount ARTDFC is calculated according to the richness of the air-fuel ratio. Since the method for calculating the ignition timing retard amount ARTDFC is the same as or equivalent to that in step S102, the description thereof is omitted here. This ignition timing retardation amount ARTDFC is added to the basic ignition timing calculated based on the engine operating state to obtain the target ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing corresponding to the determined target ignition timing. Thereafter, the process is temporarily exited.

  If step S312 is negative, a determination is made in step S316 as to whether or not a predetermined time has elapsed after returning from the fuel cut operation. Here, the predetermined time is a predetermined constant determined in accordance with the response delay of the intake air amount. Since the response delay of the intake air amount varies depending on the operating state of the engine 1, the predetermined time may be set according to the engine speed, the engine load, and the like. If step S316 is negative, that is, if the predetermined time has not elapsed after returning from the fuel cut operation, the process proceeds to step S318. On the other hand, when step S316 is affirmed, that is, when a predetermined time has elapsed after returning from the fuel cut operation, the process proceeds to step S320.

In step S318, the initial value of the ignition timing retardation amount ARTDFC set in step S314 is set as the current value ARTDFC _i of the ignition timing retardation amount. This ignition timing retard amount ARTDFFC _i is added to the basic ignition timing calculated based on the engine operating state to obtain the target ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing corresponding to the determined target ignition timing. Thereafter, the process is temporarily exited.

In step S320, a value obtained by subtracting the predetermined value ARTDFCDEC from the previous value ARTDFC _i-1 of the ignition timing retardation amount is set as the current value ARTDFC _i of the ignition timing retardation amount. Here, the predetermined value ARTDFCDEC is a predetermined constant (for example, 1 deg / 1 rotation). The predetermined value ARTDFCDEC may be set according to the engine speed, engine load, and the like. By subtracting the predetermined value ARTDFCDEC every time this process is executed, the retard amount is gradually reduced, and the ignition timing is gradually brought closer to the basic ignition timing.

Subsequently, in steps S322 and S324, a limit check of the ignition timing retard amount ARTDFFC _i is performed. In step S322, a determination is made as to whether or not the ignition timing retard amount ARTDFFC _i calculated in step S320 is smaller than zero. Here, if the ignition timing retard amount ARTDFC _i is smaller than 0, the ignition timing retard amount ARTDFFC _i is set to 0 in step S324. On the other hand, the calculated ignition timing retard quantity ARTDFC _i is maintained in step S320 if the ignition timing retard quantity ARTDFC _i is zero or more. That is, when the current value ARTDFFC _i of the ignition timing retardation amount becomes 0, the subtraction of the predetermined value ARTDFCDEC is completed.

The ignition timing retard amount ARTDFFC _i set in this way is added to the basic ignition timing calculated based on the engine operating state to obtain the target ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing corresponding to the determined target ignition timing. Thereafter, the process is temporarily exited.

  If step S300 is negative, that is, if rich control is not being performed, the throttle valve closing amount TARTDFC is set to 0 (reset) in step S326. Therefore, the basic throttle valve opening calculated based on the operating state such as the accelerator opening is set as the target throttle valve opening. The throttle valve 9 is opened in accordance with the target throttle valve opening equal to the basic throttle valve opening without performing the valve closing control of the throttle valve 9.

  Subsequently, in step S328, the ignition timing retardation amount ARTDFC is set to 0 (reset). Therefore, the basic ignition timing calculated based on the engine operating state is set as the target ignition timing. Then, the air-fuel mixture in the cylinder 3 is ignited at a timing according to the target ignition timing equal to the basic ignition timing without delaying the ignition timing. Thereafter, the process is temporarily exited.

  FIG. 7 shows changes in (a) air-fuel ratio, (b) intake air amount, (c) ignition timing, and (c) engine torque in torque down control using ignition retard control and intake air amount control.

  As shown in FIG. 7A, the air-fuel ratio during the fuel cut operation is extremely lean. During the fuel cut operation, since the exhaust purification catalyst 19 is exposed to an extremely lean atmosphere, the amount of oxygen stored in the exhaust purification catalyst 19 increases. Further, during the fuel cut operation, the amount of oxygen stored in the exhaust purification catalyst 19 is calculated.

  When the stored oxygen amount of the exhaust purification catalyst 19 is equal to or greater than a predetermined value after the fuel cut operation is restored, the air-fuel ratio is controlled to be rich until the stored oxygen amount becomes less than the predetermined value. At this time, as shown in FIG. 7B, the throttle valve 9 is closed according to the richness of the air-fuel ratio, and the amount of air taken into the engine 1 is reduced. Here, the solid line indicates the change in the throttle valve opening. The alternate long and short dash line indicates a change in the intake air amount. When the throttle valve opening is driven to the valve closing side, the intake air amount decreases with a delay, as shown by the one-dot chain line in FIG. Therefore, the output torque of the engine 1 is also reduced with a response delay.

  When returning the throttle valve 9 driven to the valve closing side, the valve opening operation is performed in consideration of the response delay of the intake air amount.

  The ignition timing is retarded so as to compensate for the response delay of the intake air amount, that is, the response delay of the output torque. FIG. 7C shows how the ignition timing changes.

  The dashed line in FIG. 7 (d) shows the change in engine torque when the valve closing control and the ignition retardation control of the throttle valve 9 are not performed during the rich control of the air-fuel ratio. As indicated by the alternate long and short dash line in FIG. 7D, when the valve closing control and the ignition delay control of the throttle valve 9 are not performed, the engine torque increases due to the rich air-fuel ratio.

  On the other hand, the solid line in FIG. 7D shows changes in engine torque when the valve closing control and the ignition retardation control of the throttle valve 9 are performed. As shown by the solid line in FIG. 7D, the output torque of the engine 1 is controlled even when the throttle valve 9 is controlled to be closed and the ignition timing is retarded so that the air-fuel ratio is controlled to be rich. Is reduced to an output torque equivalent during stoichiometric control.

  Thus, according to the present control device, the output torque of the engine 1 is reduced by controlling the closing of the throttle valve 9 and retarding the ignition timing during the rich control after returning from the fuel cut operation. Thus, an increase in output torque due to the rich air-fuel ratio is suppressed. Therefore, the torque step at the time of the stoichiometric control transition is reduced, and the torque shock is reduced.

  In addition, by using both intake air amount adjustment by throttle valve closing control and ignition retard control, the increase in output torque due to enrichment is suppressed with good responsiveness without causing deterioration in fuel consumption or combustion state. can do.

  In the above embodiment, the throttle valve 9 is closed in accordance with the richness of the air-fuel ratio, the intake air amount is reduced, and the ignition timing is delayed so as to compensate for the response delay of the intake air amount, that is, the response delay of the output torque. Angle controlled. The present invention is not limited to the above embodiment, and various modifications can be made. For example, the air amount control and the ignition retard control may be executed independently. That is, the throttle valve 9 may be closed according to the richness of the air-fuel ratio to reduce the intake air amount, and the ignition timing may be retarded according to the richness of the air-fuel ratio.

  Also in this case, the output torque of the engine 1 is reduced during the rich control after returning from the fuel cut operation, and an increase in the output torque due to the rich air-fuel ratio is suppressed. Therefore, the torque step at the time of the stoichiometric control transition is reduced, and the torque shock is reduced.

It is sectional drawing of an internal combustion engine provided with the control apparatus which concerns on embodiment. It is a flowchart which shows the process sequence of the torque reduction process by ignition retard control. 4 is a timing chart showing changes in (a) air-fuel ratio, (b) ignition timing, and (c) engine torque. It is a flowchart which shows the process sequence of the torque reduction process by intake air amount control. 4 is a timing chart showing changes in (a) air-fuel ratio, (b) intake air amount, and (c) engine torque. It is a flowchart which shows the process sequence of the torque reduction process by ignition retard control and intake air amount control. 4 is a timing chart showing changes in (a) air-fuel ratio, (b) intake air amount, (c) ignition timing, and (d) engine torque.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Spark plug, 3 ... Cylinder, 4 ... Intake pipe, 5 ... Injector, 7 ... Exhaust pipe, 9 ... Throttle valve, 18 ... ECU, 18a ... Fuel cut part, 18b ... Air-fuel ratio control part, 18c ... Ignition timing controller, 19 ... Exhaust gas purification catalyst, 25 ... Air-fuel ratio sensor.

Claims (4)

In a control device for an internal combustion engine that stops fuel supply to the internal combustion engine when a predetermined fuel supply stop condition is satisfied, and controls the air-fuel ratio richly at the time of return from the fuel stop operation,
A control apparatus for an internal combustion engine, comprising torque control means for reducing an output torque of the internal combustion engine during the rich control.   2. The internal combustion engine according to claim 1, wherein the torque control unit includes an ignition timing control unit configured to control an ignition timing of the internal combustion engine to a retard side according to a rich degree of an air-fuel ratio during the rich control. Engine control device.   2. The internal combustion engine according to claim 1, wherein the torque control unit includes an intake air amount adjusting unit that reduces an air amount taken into the internal combustion engine according to a rich degree of an air-fuel ratio during the rich control. Control device. The torque control means includes an intake air amount adjusting means for reducing the amount of air taken into the internal combustion engine according to the richness of the air-fuel ratio during the rich control, and a response when the air amount is reduced during the rich control. 2. The control apparatus for an internal combustion engine according to claim 1, further comprising ignition timing control means for controlling the ignition timing to the retard side in response to the delay.

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