JP2008267294A - Control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of further surely restraining the deterioration in emission in a state of recognizing that an exhaust emission control catalyst of an internal combustion engine is deteriorated or possibly deteriorated. <P>SOLUTION: This control system of the internal combustion engine can advance the ignition timing of a spark plug forward more than MBT being the ignition timing capable of substantially maximizing torque of the internal combustion engine, and restrains an increase in HC in exhaust gas by advancing the ignition timing forward more than MBT (S104), when recognizing that the exhaust emission control catalyst of the internal combustion engine is deteriorated (S102), in cold starting (S101). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a system for controlling a spark ignition type internal combustion engine.

  As regulations on harmful components (for example, HC, CO, NOx) in exhaust discharged from an internal combustion engine of an automobile are strengthened, a technology for purifying harmful components in exhaust with an exhaust purification catalyst has been proposed. Here, a typical example of the exhaust purification catalyst is a three-way catalyst that simultaneously processes NOx reduction and HC and CO oxidation.

  This exhaust purification catalyst may have its purification capability deteriorated due to secular change or thermal degradation. When the purification capability of the exhaust purification catalyst deteriorates, the purification efficiency of HC or the like in the exhaust gas decreases, and the internal combustion engine Emissions sometimes worsened.

On the other hand, in the conventional spark ignition type internal combustion engine, the ignition timing is advanced ahead of MBT (Minimum spark advance for Best Torque), thereby promoting the temperature rise of the cooling water, and thus the warming up of the internal combustion engine. There is known a technique for improving (see, for example, Patent Document 1). Although the above-described conventional technology considers the warm-up property of the internal combustion engine, it does not consider the point of improving the emission of the internal combustion engine.
JP 2000-240547 A JP 2006-057494 A JP 2001-059444 A

  The present invention has been made in view of the above-described circumstances, and a purpose thereof is a technology that can more reliably suppress deterioration of emissions in a state where deterioration or possibility of deterioration of an exhaust purification catalyst of an internal combustion engine is recognized. Is to provide.

  In order to solve the above-described problems, the present invention provides an internal combustion engine control system capable of advancing the ignition timing before MBT, which is the ignition timing at which the torque in the internal combustion engine becomes substantially maximum. The greatest feature is to suppress the increase in HC in the exhaust gas by advancing the ignition timing before the MBT when the purification catalyst is deteriorated or the possibility of deterioration is detected.

More specifically, an over-advance means for advancing the ignition timing of the spark ignition type internal combustion engine before MBT,
An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies exhaust gas passing through the exhaust passage;
Purification capacity deterioration determination means for determining deterioration or possibility of deterioration of the purification capacity of the exhaust purification catalyst,
When the purification capacity deterioration determining means determines that the purification capacity of the exhaust purification catalyst has deteriorated or is likely to deteriorate, the ignition timing is advanced before MBT by the over-advance angle means. It is characterized by that.

Here, the fuel adhering to the wall surface in the cylinder of the internal combustion engine or the fuel before adhering (hereinafter collectively referred to as “in-cylinder adhering fuel”) is not burned without being used for combustion. In some cases, the cylinder is discharged from the cylinder. At that time, if the exhaust purification catalyst disposed in the exhaust system of the internal combustion engine is in a state in which the purification capability is lowered due to aging or thermal deterioration, the above-mentioned unburned fuel component is released to the outside without being purified in the catalyst. There was a case. As a result, emission may be deteriorated.

  In contrast, as a result of the inventor's earnest experiment and verification, when the ignition timing is advanced to the front of MBT (hereinafter referred to as “over-advanced angle”) in a spark ignition type internal combustion engine, the cylinder It has been found that unburned fuel components (eg, HC; hereinafter simply abbreviated as “HC”) discharged from within are significantly reduced.

  This is because, when the ignition timing is over-advanced, the amount of the air-fuel mixture that burns before compression top dead center increases. In addition to the temperature effect, the pressure in the cylinder (hereinafter referred to as “in-cylinder pressure”) and the peak value of the in-cylinder temperature are increased, and the fuel adhering to the cylinder and / or the fuel before adhering to the wall surface in the cylinder is vaporized. It is considered that the oxidation is promoted.

  In view of this, the control system for an internal combustion engine according to the present invention causes the ignition timing of the internal combustion engine to advance excessively when it is determined that the purification capability of the exhaust purification catalyst has deteriorated or is likely to deteriorate in the internal combustion engine. The HC discharged from the internal combustion engine is reduced by making the angle.

  According to this, when the purification capacity of the exhaust purification catalyst of the internal combustion engine is reduced, the peak value of the in-cylinder temperature is increased by over-advancing the ignition timing, and oxidation of in-cylinder attached fuel in the cylinder or Since vaporization is promoted, the amount of HC discharged from the internal combustion engine is reduced. Then, even if the purification capability of the exhaust purification catalyst is reduced, it is possible to reduce HC released to the outside without being purified by the exhaust purification catalyst. As a result, emission deterioration can be suppressed.

In the present invention, when the exhaust purification catalyst is warmed up,
When the purification capability deterioration determining means determines that the purification capability of the exhaust purification catalyst has deteriorated,
The over-advance means may advance the ignition timing to an ignition timing that is before MBT and at which the pressure in the cylinder of the internal combustion engine is highest near TDC.

  Here, when the exhaust purification catalyst is warmed up in the cold state, generally, control is often performed to retard the ignition timing in the internal combustion engine and increase the intake air amount. This is intended to reduce the total amount of released HC to the outside by warming up the exhaust purification catalyst earlier even if HC discharged from the internal combustion engine increases. However, when such control is performed, in a state where the purification capacity of the exhaust purification catalyst is lowered, since a significant improvement in purification capacity due to warm-up cannot be expected, the total amount of HC released to the outside There was a case where it increased.

  Therefore, in the present invention, when the purification capacity deterioration determining means determines that the purification capacity of the exhaust purification catalyst has deteriorated when the exhaust purification catalyst is warmed up, the ignition timing of the internal combustion engine is set to be earlier than MBT. The ignition timing is advanced to an ignition timing at which the pressure in the cylinder of the internal combustion engine becomes maximum near TDC.

  Here, when the ignition timing of the internal combustion engine is an ignition timing before MBT, and the ignition pressure is advanced to an ignition timing at which the pressure in the cylinder of the internal combustion engine becomes maximum near TDC, the combustion chamber temperature of the internal combustion engine It has been found that the peak value of can be made substantially high. Therefore, in the present invention, the amount of HC discharged from the internal combustion engine can be reduced most efficiently.

  As a result, the amount of HC released outside without being purified by the exhaust purification catalyst is more reliably reduced even under the disadvantageous condition that the exhaust purification catalyst has a reduced purification capacity and the exhaust purification catalyst is warming up. be able to.

In addition, according to the present invention, further comprising a fuel cut means for stopping fuel supply to the combustion chamber of the internal combustion engine,
When it is detected that the temperature of the exhaust purification catalyst is equal to or higher than a predetermined temperature, the purification capability deterioration determining means may deteriorate the purification capability of the exhaust purification catalyst in a predetermined lean atmosphere. If judged,
While stopping the fuel supply to the combustion chamber by the fuel cut means may be prohibited, the ignition timing of the internal combustion engine may be advanced ahead of MBT by the over advance means.

  Here, a case is considered in which the fuel is cut and the atmosphere of the exhaust purification catalyst becomes lean, for example, when the accelerator is turned off while the exhaust purification catalyst is at a high temperature that is equal to or higher than a predetermined temperature. If such a state continues for a long time, the exhaust purification catalyst becomes a high temperature and peroxygen concentration state, sintering may occur in the noble metal in the catalyst, and the exhaust purification catalyst may deteriorate.

  In order to suppress this, when the exhaust purification catalyst is at a temperature higher than the predetermined temperature, even if the accelerator is turned off, the fuel cut is prohibited and the intake air and fuel are not allowed to misfire. In many cases, the catalyst deterioration suppression control for continuing the combustion is performed.

  In this case, the fuel cut is executed when the temperature of the exhaust purification catalyst is lowered to a temperature at which deterioration is not promoted even if a large amount of oxygen flows into the exhaust purification catalyst. In addition, when performing catalyst deterioration suppression control, in conjunction with this, the ignition timing in the internal combustion engine is often controlled to be retarded from the MBT to reduce the generated torque so that the feeling of deceleration is not impaired. It was.

  However, in the combination of the catalyst deterioration suppression control and the control for setting the ignition timing to the retard side from the MBT as described above, the time during which the temperature of the exhaust purification catalyst is maintained at a high temperature becomes longer, and the process shifts to fuel cut. Since it takes time to lower the temperature of the exhaust purification catalyst to the extent possible, it may be disadvantageous in terms of fuel consumption. Further, since the time during which the temperature of the exhaust purification catalyst is maintained at a high temperature becomes longer, it may be disadvantageous in terms of suppressing the deterioration of the catalyst.

  In contrast, in the present invention, the purification performance of the exhaust purification catalyst deteriorates when the temperature of the exhaust purification catalyst is equal to or higher than the predetermined temperature and the purification capability deterioration determination means is in a lean atmosphere such as the accelerator is turned off. When it is determined that there is a possibility, the stop of fuel supply to the combustion chamber of the internal combustion engine is prohibited, and the ignition timing of the internal combustion engine is advanced ahead of MBT by the over-advance means.

  Then, by prohibiting the fuel cut, a large amount of oxygen can be prevented from flowing into the exhaust purification device. Further, by advancing the ignition timing of the internal combustion engine ahead of MBT, it is possible to reduce HC flowing into the exhaust purification catalyst, reduce the generated torque in the internal combustion engine, and reduce the exhaust gas temperature. Therefore, the feeling of deceleration given to the driver can be maintained, and the temperature of the exhaust purification catalyst can be quickly reduced.

If it does so, since time until it transfers to a fuel cut can be shortened, a fuel consumption can be improved and deterioration of an exhaust gas purification catalyst can be suppressed more reliably. Note that, in the above, the predetermined temperature is a catalyst as a threshold value that is determined that there is a possibility that the purification ability of the exhaust purification catalyst is deteriorated when a large amount of oxygen flows when the exhaust purification catalyst is at or above this temperature. The temperature, which is obtained in advance by experiments or the like. In addition, the predetermined lean atmosphere means a state in which the oxygen concentration of exhaust gas has increased due to fuel cut.

Further, in the present invention, over-advance means for advancing the ignition timing of the spark ignition type internal combustion engine before MBT,
An exhaust purification catalyst for purifying exhaust gas that is provided in the exhaust passage of the internal combustion engine and passes through the exhaust passage;
A fuel cut means for stopping fuel supply to a combustion chamber of the internal combustion engine in a predetermined deceleration state related to the internal combustion engine;
In the predetermined deceleration state, when the exhaust purification catalyst is in a high temperature state equal to or higher than a predetermined temperature, fuel supply to the combustion chamber by the fuel cut means is performed in order to suppress deterioration of the purification capability of the exhaust purification catalyst. May be prohibited, and the ignition timing of the internal combustion engine may be advanced before MBT by the over advance angle means.

  This also prohibits the fuel cut when the exhaust purification catalyst is in a predetermined deceleration state at a high temperature that is equal to or higher than the predetermined temperature, thereby suppressing a large amount of oxygen from flowing into the exhaust purification catalyst. Further, by advancing the ignition timing of the internal combustion engine ahead of MBT, HC flowing into the exhaust purification catalyst can be reduced, the generated torque can be reduced, and the exhaust gas temperature can be reduced. Therefore, the feeling of deceleration given to the driver can be maintained, and the temperature of the exhaust purification catalyst can be quickly reduced.

  Here, the predetermined deceleration state is, for example, an accelerator-off state or a vehicle maximum speed limiter, which means a deceleration state with a fuel cut. The predetermined temperature is a catalyst temperature as a threshold at which it is judged that there is a possibility that the purification ability of the exhaust purification catalyst will deteriorate when a large amount of oxygen flows when the exhaust purification catalyst is above this temperature. Yes, it is obtained in advance through experiments.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  According to the present invention, it is possible to more reliably suppress the deterioration of emissions in a state where the deterioration or possibility of deterioration of the exhaust purification catalyst of the internal combustion engine is recognized.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine control system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a four-stroke cycle spark ignition type internal combustion engine (gasoline engine) having a plurality of cylinders 2. The cylinder 2 of the internal combustion engine 1 is connected to the intake passage 30 through the intake port 3 and is connected to the exhaust passage 40 through the exhaust port 4.

  The intake port 3 is provided with a fuel injection valve 5 that injects fuel into the cylinder 2. The intake passage 30 is provided with a throttle valve 6 that controls the amount of air flowing through the intake passage 30. An intake pressure sensor 7 that measures the pressure (intake pressure) in the intake passage 30 is provided in the intake passage 30 downstream of the throttle valve 6. An air flow meter 8 that measures the amount of air flowing through the intake passage 30 is provided in the intake passage 30 upstream of the throttle valve 6.

On the other hand, an exhaust purification device 9 is disposed in the exhaust passage 40. The exhaust purification device 9 includes a catalyst such as a three-way catalyst as an exhaust purification catalyst, and purifies exhaust when it is in a predetermined activation temperature range. An air-fuel ratio sensor 21 that measures the air-fuel ratio of the exhaust gas flowing into the exhaust purification device 9 is provided on the upstream side of the exhaust purification device 9 in the exhaust passage 40. Further, on the downstream side of the exhaust purification device 9 in the exhaust passage 40, an O ₂ sensor 22 that measures the oxygen concentration of the exhaust discharged from the exhaust purification device 9 and the temperature of the exhaust discharged from the exhaust purification device 9 are measured. Thus, a catalyst temperature sensor 23 for detecting the temperature of the catalyst in the exhaust purification device 9 is provided.

  Further, the internal combustion engine 1 is provided with an intake valve 10 that opens and closes an open end of the intake port 3 facing the cylinder 2 and an exhaust valve 11 that opens and closes an open end of the exhaust port 4 facing the cylinder 2. The intake valve 10 and the exhaust valve 11 are driven to open and close by an intake camshaft 12 and an exhaust camshaft 13, respectively.

  A spark plug 14 for igniting the air-fuel mixture in the cylinder 2 is disposed at the upper part of the cylinder 2. A piston 15 is slidably inserted into the cylinder 2. The piston 15 is connected to the crankshaft 17 via a connecting rod 16.

  A crank position sensor 18 that detects a rotation angle of the crankshaft 17 is disposed in the vicinity of the crankshaft 17. Furthermore, a water temperature sensor 19 for measuring the temperature of the cooling water circulating through the internal combustion engine 1 is attached to the internal combustion engine 1.

The internal combustion engine 1 configured as described above is provided with an ECU 20. The ECU 20 is an electronic control unit that includes a CPU, a ROM, a RAM, and the like. The ECU 20 is electrically connected to various sensors such as the crank position sensor 18, the water temperature sensor 19, the air-fuel ratio sensor 21, the O ₂ sensor 22, and the catalyst temperature sensor 23, and can input measurement values of the various sensors. It has become.

  The ECU 20 electrically controls the fuel injection valve 5, the throttle valve 6, and the spark plug 14 based on the measured values of the various sensors described above.

Here, the warm-up control of the exhaust emission control device 9 when the internal combustion engine 1 is cold started will be considered. That is, when the internal combustion engine 1 is cold-started, the temperature of the exhaust purification device 9 is also lowered, so that the catalyst in the exhaust purification device 9 is not activated, and in this state HC and NOx are exchanged with the internal combustion engine 1.
Even if it is discharged from the water, it is difficult to sufficiently purify them.

  Therefore, when the internal combustion engine 1 is cold-started, it is necessary to warm up the exhaust purification device 9 as early as possible. In order to warm up the exhaust purification device 9, conventionally, in the idling operation at the time of cold start of the internal combustion engine 1, control for delaying the ignition timing of the spark plug 14 and increasing the intake air amount has been performed. It was. In other words, the ignition timing of the spark plug 14 is retarded to raise the exhaust gas temperature and to increase the amount of exhaust gas so that the heat energy supplied to the exhaust gas purification device 9 is increased.

  Next, consider the case where the purification capability of the exhaust emission control device 9 has deteriorated due to secular change or thermal deterioration. In the idling operation at the time of cold start of the internal combustion engine 1 with the purification ability of the exhaust purification device 9 deteriorated, as described above, the control for retarding the ignition timing of the spark plug 14 and increasing the intake air amount is performed. When this is done, the amount of HC discharged from the internal combustion engine 1 is increased, whereas the purification capacity of the exhaust purification device 9 is reduced, so that it is discharged outside without being purified by the exhaust purification device 9. There was a risk that the amount of HC would increase.

  In contrast, as a result of the inventor's earnest experiment and verification, when the ignition timing is advanced to the front of MBT (hereinafter referred to as “over-advanced angle”) in a spark ignition type internal combustion engine, the cylinder It has been found that HC discharged from within is significantly reduced.

  This is because when the ignition timing is over-advanced, the amount of the air-fuel mixture combusted before the compression top dead center increases. In addition to the temperature increase effect, the peak value of the pressure in the cylinder 2 (hereinafter referred to as “in-cylinder pressure”) and the in-cylinder temperature is increased, and before adhering to the in-cylinder attached fuel and / or the wall surface in the cylinder 2. This is thought to be due to the acceleration of fuel vaporization and oxidation.

  FIG. 2 is a graph showing how the relationship between various parameters in the cylinder 2 and the crank angle changes depending on the ignition timing in the cylinder 2. The horizontal axis represents the crank angle of the internal combustion engine 1, and the vertical axis represents each parameter in the cylinder 2. In FIG. 2, the graph when the ignition of the spark plug 14 is performed on the advance side (hereinafter referred to as “over-advance angle”) before the MBT is indicated by a solid line, and the graph when the ignition is performed by the MBT. Is indicated by a broken line, and a graph when ignition is performed at the compression top dead center (TDC) is indicated by a one-dot chain line.

  When the ignition timing is over-advanced, the air-fuel mixture burned before the compression top dead center is compared to when the ignition timing is set to MBT and when the ignition timing is set to compression top dead center (TDC). The amount of increases. For this reason, the peak of heat energy generated by the combustion of the air-fuel mixture (see the heat generation rate, generated heat amount, and combustion mass ratio in FIG. 2) shifts to before the compression top dead center.

  Therefore, in-cylinder pressure during the period from the compression stroke to the expansion stroke is obtained by a synergistic effect of the temperature increase / pressure increase effect due to the combustion of the air-fuel mixture and the compression effect due to the piston ascending operation (operation from bottom dead center to top dead center) In addition, the peak value of the in-cylinder temperature increases significantly. Note that, since the excessive advance angle of the ignition timing before the MBT is executed according to a command from the ECU 20, the excessive advance means includes the ECU 20 in this embodiment.

  In the present embodiment, by using the above-described phenomenon, the ignition timing of the internal combustion engine 1 is further advanced from the MBT at the cold start of the internal combustion engine 1 when the exhaust purification device 9 is deteriorated. The amount of HC discharged from the internal combustion engine 1 is reduced, and the amount of HC released outside without being purified by the exhaust purification device 9 is reduced.

  FIG. 3 shows a graph of the relationship between the ignition timing and torque in the cylinder 2 and the maximum in-cylinder temperature. The horizontal axis represents the ignition timing of the spark plug 14, and the vertical axis represents the torque and the maximum temperature in the cylinder. As can be seen from FIG. 3, the torque generated in the internal combustion engine 1 is greatest when the ignition timing is MBT. As the ignition timing is advanced to the front of MBT, the torque decreases while the in-cylinder maximum temperature increases and reaches the highest in ST1.

  Thus, by advancing the ignition timing to before MBT, the in-cylinder maximum temperature can be increased, and the amount of HC discharged from the internal combustion engine 1 when the internal combustion engine 1 is cold started can be reduced. It is possible to suppress the deterioration of the emission due to the deterioration of the exhaust purification device 9.

  In the present embodiment, the target ignition timing when the ignition timing is over-advanced is particularly an ignition timing at which the in-cylinder pressure becomes maximum at TDC as shown in FIG. It is known that this ignition timing corresponds to ST1 that is the ignition timing at which the maximum in-cylinder temperature becomes the highest in FIG. 3, and by setting the ignition timing in this way, it is most efficiently discharged from the internal combustion engine 1. It is possible to reduce the amount of HC.

However, the ignition timing is excessively advanced, and the misfire limit ignition timing (ST2) determined by the operating state.
), The risk of misfire increases, so it is necessary to prevent the ignition timing from being advanced from the misfire limit ignition timing (ST2). Similarly, if the ignition timing is advanced from the knock limit ignition timing (ST3) determined by the operating state, the risk of knocking increases, so the ignition timing is advanced from the knock limit ignition timing. It is necessary not to become. Accordingly, in this embodiment, as shown in the lower graph of FIG. 3, ST1, ST2, and ST3 are derived, respectively, and the ignition plug 14 of the spark plug 14 is reached up to the most retarded ignition timing among the three ignition timings. The ignition timing was advanced. FIG. 5 shows examples of graphs that serve as the basis of maps of the relationship between the operating state of the internal combustion engine 1 and ST1, ST2, and ST3, respectively.

  Next, FIG. 6 shows a flowchart of the catalyst deterioration warm-up routine in this embodiment. This routine is a program stored in the ROM of the ECU 20, and is executed by the ECU 20 every predetermined period while the internal combustion engine 1 is in operation.

  When this routine is executed, it is first determined in S101 whether or not it is a cold start. Specifically, it may be determined by reading the output signal of the coolant temperature sensor 19 into the ECU 20 and comparing it with a predetermined determination temperature. If it is determined in S101 that it is not during a cold start, this routine is immediately terminated. On the other hand, if it is determined in S101 that the engine is cold starting, the process proceeds to S102.

In S102, it is determined whether or not it is determined that the catalyst purification capacity of the exhaust purification device 9 has deteriorated. Specifically, the difference in the HC concentration before and after the exhaust purification device 9 obtained from the output signals of the air-fuel ratio sensor 21 upstream of the exhaust purification device 9 and the O ₂ sensor 22 downstream of the exhaust purification device 9. Based on the above, determination may be made based on whether or not deterioration of the purification capacity of the catalyst has been detected during the previous operation of the internal combustion engine 1. Here, when it is determined that the purification ability of the catalyst has not been deteriorated, the process proceeds to S103. On the other hand, if it is determined that the purification capacity of the catalyst has deteriorated, the process proceeds to S104.

  In S103, the ignition timing of the spark plug 14 in the internal combustion engine 1 is retarded and the intake air amount is increased. Thereby, the thermal energy supplied from the exhaust gas to the exhaust gas purification device 9 is increased. That is, even if the amount of HC emission from the internal combustion engine 1 is increased, the control for warming up the catalyst at an early stage is selected. Here, it is also possible to feedback control the idle speed of the internal combustion engine 1 by controlling the intake air amount so as to maintain an appropriate target idle speed when the catalyst is warmed up. When the process of S103 is completed, this routine is temporarily ended.

  In S104, the ignition timing of the spark plug 14 in the internal combustion engine 1 is advanced to a point before MBT, the peak value of the temperature in the cylinder 2 is increased, and the amount of HC discharged from the internal combustion engine 1 itself is reduced. . Thereby, even if the purification capacity of the catalyst of the exhaust purification device 9 is deteriorated, HC is prevented from being released to the outside without being purified by the exhaust purification device 9. In this case, too, the ignition timing is over-advanced and the intake air amount is controlled so that the idle speed of the internal combustion engine 1 is feedback-controlled so that the target idle speed is maintained at an appropriate value when the catalyst is warmed up. Also good. In this case, the idle speed may be about 1500 rpm, for example. When the process of S104 is completed, this routine is temporarily ended.

  As described above, in the present embodiment, when it is determined that the catalyst purification capacity of the exhaust purification device 9 has deteriorated, the ignition timing is advanced to before MBT at the cold start. It was. As a result, the amount of HC introduced into the catalyst whose purification capacity has deteriorated and has not been warmed up can be reduced, and the amount of HC discharged to the outside can be reduced.

  Note that the ECU 20 that executes the process of S102 in the catalyst deterioration warm-up routine of the present embodiment constitutes a purification capacity deterioration determining means in the present embodiment.

  Next, a second embodiment of the present invention will be described. In this embodiment, when it is determined that there is a possibility that the purification performance may deteriorate if a large amount of oxygen flows in when the temperature of the exhaust purification device is high, even if the accelerator is turned off, the fuel cut is performed immediately. An example in which the exhaust gas temperature is lowered by advancing the ignition timing before MBT while continuing to supply the fuel to the combustion chamber without performing the above will be described. The internal combustion engine 1 and its intake / exhaust system and control system in this embodiment are the same as those shown in FIG.

  Here, consider a case where the accelerator is turned off while the temperature of the catalyst of the exhaust purification device 9 is high. In such a case, if the fuel cut is performed as it is, a large amount of oxygen flows into the catalyst of the exhaust gas purification device 9, so that there is a possibility that the catalyst deteriorates because the noble metal in the catalyst causes sintering. Therefore, conventionally, in such a case, the fuel supply to the combustion chamber of the internal combustion engine 1 is continued to suppress excessive oxygen inflow to the catalyst, and the ignition timing of the spark plug 14 is retarded to provide a feeling of deceleration. I was getting control. The fuel is cut when the temperature of the catalyst gradually decreases.

  However, in this conventional control, the exhaust gas temperature also rises due to the retard of the ignition timing, the period during which the catalyst is exposed to a high temperature becomes longer, and there is a possibility that the period until the fuel cut can be executed becomes longer. It was. If it does so, it may become disadvantageous also from the viewpoint of the fuel consumption before changing to fuel cut, and a viewpoint of deterioration of a catalyst.

  Therefore, in the present embodiment, when a fuel cut request such as an accelerator OFF occurs when the temperature of the catalyst of the exhaust purification device 9 is high, first, the ignition timing of the spark plug 14 is advanced to an earlier time than MBT. I decided to let them. Thus, the temperature of the exhaust gas is lowered, and the fuel cut is executed after the temperature of the catalyst of the exhaust gas purification device 9 is lowered to such an extent that it does not rise excessively even when a large amount of oxygen is introduced.

  By doing so, when a fuel cut request such as accelerator OFF occurs, first, the ignition timing of the spark plug 14 is advanced to a position before MBT, so that the temperature of the exhaust can be lowered, and the exhaust purification device The temperature of the catalyst of 9 can be reduced more efficiently. Further, at that time, the torque of the internal combustion engine 1 can be sufficiently reduced, and a sufficient feeling of deceleration can be obtained.

  And since it can be made the state which can perform fuel cut earlier, it is advantageous also from a viewpoint of improvement in fuel consumption, and suppression of degradation of the catalyst of exhaust gas purification device 9.

  FIG. 7 shows a graph regarding the relationship between the ignition timing of the spark plug 14 and the torque and exhaust temperature of the internal combustion engine 1. As shown in the figure, the torque of the internal combustion engine 1 is reduced when the ignition timing of the spark plug 14 is advanced to a point before MBT, as in the case where the ignition timing of the spark plug 14 is retarded. Can do. Further, the exhaust temperature can be lowered to a lower temperature by advancing the ignition timing of the spark plug 14 from the MBT.

  Next, FIG. 8 shows a flowchart of the fuel cut routine at the time of high catalyst temperature in this embodiment. This routine is a program stored in the ROM of the ECU 20, and is executed by the ECU 20 every predetermined period while the internal combustion engine 1 is in operation.

  When this routine is executed, first in S201, it is determined whether or not the engine speed of the internal combustion engine 1 is equal to or greater than a predetermined direct fuel cut prohibition speed. Specifically, it is determined by reading an output signal from the crank position sensor 18 into the ECU 20 and comparing it with a predetermined direct fuel cut prohibiting rotation speed. Here, the direct fuel cut prohibition rotational speed refers to the catalyst of the exhaust purification apparatus 9 when the engine speed is higher than this and the temperature of the catalyst of the exhaust purification apparatus 9 is higher than the direct fuel cut prohibition temperature described later. This is the threshold engine speed at which there is a possibility that the catalyst may deteriorate due to an excessive amount of inflowing oxygen, and is obtained in advance through experiments or the like. If it is determined that the engine speed is lower than the direct fuel cut prohibition speed, the process proceeds to S204. On the other hand, if it is determined that the engine speed is equal to or greater than the direct fuel cut prohibition speed, the process proceeds to S202.

  In S202, it is determined whether or not the temperature of the catalyst of the exhaust purification device 9 is equal to or higher than the direct fuel cut prohibition temperature. Here, the direct fuel cut prohibition temperature means that when the temperature of the catalyst of the exhaust purification device 9 is higher than this, the catalyst deteriorates if the amount of oxygen flowing into the catalyst is large (in other words, the temperature of the catalyst). Is lower than this, it is the catalyst temperature as a threshold that is considered that the catalyst does not deteriorate even if the amount of inflowing oxygen is large. If it is determined that the catalyst temperature is equal to or higher than the fuel cut prohibition temperature, the process proceeds to S203. If it is determined that the catalyst temperature is lower than the direct fuel cut prohibition temperature, the process skips S203 and proceeds to S204.

  In S203, the ignition timing of the spark plug 14 is advanced to before MBT. Thereby, the torque of the internal combustion engine 1 is reduced and the exhaust temperature is lowered. When the process of S203 ends, the process proceeds to S204.

  In S204, the fuel supply from the fuel addition valve 5 to the combustion chamber is stopped and the fuel cut is performed. When the processing of S204 ends, this routine is once ended.

  As described above, in the present embodiment, when the temperature of the catalyst of the exhaust purification device 9 is equal to or higher than the direct fuel cut prohibition temperature and the engine speed is equal to or higher than the direct fuel cut prohibition speed, Since it is determined that there is a possibility that the catalyst of the exhaust emission control device 9 is deteriorated if the fuel cut is performed in this state, the ignition timing of the spark plug 14 is advanced to a position before MBT.

  Thereby, before the temperature of the catalyst of the exhaust emission control device 9 decreases and shifts to fuel cut, a sufficient feeling of deceleration can be obtained. Further, since the temperature of the catalyst of the exhaust purification device 9 can be lowered early and the fuel can be cut early, it is advantageous from the viewpoint of fuel consumption and catalyst deterioration.

  In the above-described catalyst high temperature fuel cut routine, the ECU 20 that executes the processes of S201 and S202 constitutes a purification capability deterioration determining means. Moreover, ECU20 which performs the process of S204 comprises a fuel cut means. Further, the direct fuel cut prohibition temperature in S202 corresponds to a predetermined temperature in the present embodiment.

It is a figure which shows schematic structure of the internal combustion engine, the intake / exhaust system, and the control system in the Example of this invention. It is a graph which shows the relationship between the ignition timing in the cylinder which concerns on the Example of this invention, and the state in a cylinder. It is a graph which shows the relationship between the ignition timing in the cylinder which concerns on the Example of this invention, the torque of an internal combustion engine, and the highest in-cylinder temperature. It is a graph for demonstrating the difference by the ignition timing of the relationship between the crank angle and cylinder pressure in the cylinder which concerns on the Example of this invention. FIG. 5 is a graph serving as a reference of a map showing the relationship between the operating state of the internal combustion engine according to the embodiment of the present invention and the ignition timing at which the in-cylinder pressure becomes maximum at TDC, the ignition timing at the misfire limit, and the ignition timing at the knock limit. It is an example. It is a flowchart which shows the warming-up routine at the time of catalyst deterioration which concerns on Example 1 of this invention. It is a graph which shows the relationship between the ignition timing in Example 2 of this invention, the torque of an internal combustion engine, and exhaust temperature. It is a flowchart which shows the fuel cut routine at the time of the catalyst high temperature which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Intake port 4 ... Exhaust port 5 ... Fuel injection valve 6 ... Throttle valve 7.・ ・ ・ ・ Intake pressure sensor 8 ・ Air flow meter 9 ・ Exhaust gas purification device 10 ・ ・ ・ ・ Intake valve 11 ・ ・ ・ ・ Exhaust valve 12 ・ ・ ・ ・ Intake side camshaft 13 ・ ・・ ・ Exhaust camshaft 14 ・ ・ ・ ・ Spark plug 15 ・ ・ ・ ・ Piston 16 ・ ・ ・ ・ Connecting rod 17 ・ ・ ・ ・ Crankshaft 18 ・ ・ ・ ・ Crank position sensor 19 ・ ・ ・ ・ Water temperature sensor 20 ・... ECU
21... Air-fuel ratio sensor 22... O ₂ sensor 23... Catalyst temperature sensor 30.

Claims (4)

Over-advance means for advancing the ignition timing of the spark ignition type internal combustion engine before MBT;
An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies exhaust gas passing through the exhaust passage;
Purification capacity deterioration determination means for determining deterioration or possibility of deterioration of the purification capacity of the exhaust purification catalyst,
When the purification capacity deterioration determining means determines that the purification capacity of the exhaust purification catalyst has deteriorated or is likely to deteriorate, the ignition timing is advanced before MBT by the over-advance angle means. A control system for an internal combustion engine. When the exhaust purification catalyst is warmed up,
When the purification capability deterioration determining means determines that the purification capability of the exhaust purification catalyst has deteriorated,
2. The ignition timing according to claim 1, wherein the ignition timing is advanced to an ignition timing at which the pressure in the cylinder of the internal combustion engine becomes maximum near TDC by the over-advance means. Control system for internal combustion engine. Fuel cutting means for stopping fuel supply to the combustion chamber of the internal combustion engine,
When it is detected that the temperature of the exhaust purification catalyst is equal to or higher than a predetermined temperature, the purification capability deterioration determining means may deteriorate the purification capability of the exhaust purification catalyst in a predetermined lean atmosphere. If judged,
2. The fuel cut to the combustion chamber by the fuel cut means is prohibited, and the ignition timing of the internal combustion engine is advanced to the front of MBT by the over-advance angle means. Control system for internal combustion engine. Over-advance means for advancing the ignition timing of the spark ignition type internal combustion engine before MBT;
An exhaust purification catalyst for purifying exhaust gas that is provided in the exhaust passage of the internal combustion engine and passes through the exhaust passage;
A fuel cut means for stopping fuel supply to a combustion chamber of the internal combustion engine in a predetermined deceleration state related to the internal combustion engine;
In the predetermined deceleration state, when the exhaust purification catalyst is in a high temperature state equal to or higher than a predetermined temperature, fuel supply to the combustion chamber by the fuel cut means is performed in order to suppress deterioration of the purification capability of the exhaust purification catalyst. And the ignition timing of the internal combustion engine is advanced before MBT by the over advance means.

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