JP2009079517A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily inhibit deterioration of catalyst caused by execution of fuel cut by effectively reducing the temperature of a catalyst before execution of fuel cut in a control device for an internal combustion engine. <P>SOLUTION: This device is provided with a variable exhaust valve train 34 capable of varying open timing and close timing of an exhaust valve 32. Valve timing (open and close timing) of the exhaust valve 32 is controlled toward the most retarded position from a present control position (Figure 3(B)) at timing t1 when fuel cut execution conditions are satisfied. After that, fuel cut is executed at timing t2 when the valve timing of the exhaust valve 32 is controlled to the most retarded position (Figure 3 (C)). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that performs fuel cut.

  Conventionally, for example, Patent Document 1 discloses a fuel cut control device for an internal combustion engine that performs fuel cut in a predetermined operating state. In this conventional control device, the temperature of the catalyst is lowered by increasing the amount of air flowing through the catalyst arranged in the exhaust passage when the fuel cut is performed. The conventional control device described above suppresses the deterioration of the catalyst by suppressing the supply of a high-temperature and lean gas to the catalyst during the fuel cut.

JP 2004-132185 A JP 2006-144665 A JP 2005-163743 A

  The catalyst inflow gas immediately after the start of the fuel cut is high temperature. In the above-described conventional technique, no consideration is given in that the high-temperature exhaust gas is prevented from being supplied to the catalyst immediately after the start of the fuel cut. For this reason, there is a concern that the effect of lowering the temperature of the catalyst cannot be sufficiently exhibited.

  The present invention has been made to solve the above-described problems, and can effectively reduce the temperature of the catalyst prior to the execution of the fuel cut. An object of the present invention is to provide a control device for an internal combustion engine that can satisfactorily suppress deterioration of the engine.

A first invention is a catalyst disposed in an exhaust passage of an internal combustion engine;
Fuel cut execution means for performing fuel cut;
Fuel cut condition determining means for determining success or failure of the fuel cut execution condition;
A variable valve mechanism capable of changing at least one of the opening timing and closing timing of the exhaust valve;
Valve timing control means for retarding at least one of the opening timing and closing timing of the exhaust valve to the retard side when the fuel cut execution condition is satisfied;
It is characterized by providing.

  In a second aspect based on the first aspect, the fuel cut execution means executes a fuel cut after the retard control is performed.

  According to a third aspect of the present invention, in the second aspect, the valve timing control means performs the fuel cut under a situation where at least the opening timing of the exhaust valve is controlled to be retarded when the fuel cut execution condition is satisfied. When the degree of decrease in the temperature of the gas flowing into the catalyst becomes low after the start of the operation, the opening timing of the exhaust valve is controlled to be quickly opened to the advance side.

  In a fourth aspect based on the third aspect, the valve timing control means may cause the catalyst to be in a supercooled state under the situation where the quick opening control is performed during execution of fuel cut. When predicted, the opening timing of the exhaust valve is controlled to be delayed to the retarded angle side.

Further, a fifth invention provides a catalyst disposed in an exhaust passage of an internal combustion engine,
Fuel cut execution means for performing fuel cut;
Fuel cut condition determining means for determining success or failure of the fuel cut execution condition;
A variable valve mechanism capable of changing at least one of the opening timing and closing timing of the exhaust valve;
Valve timing control means for controlling the advance of at least one of the opening timing and closing timing of the exhaust valve to the advance side when the fuel cut execution condition is satisfied;
It is characterized by providing.

  According to a sixth aspect, in the fifth aspect, the fuel cut execution means executes a fuel cut after the advance angle control is performed.

  According to a seventh aspect of the present invention based on the sixth aspect, the valve timing control unit is configured to perform the fuel cut execution after the start of fuel cut in a situation where the advance angle control is performed when the fuel cut execution condition is satisfied. When the degree of decrease in the temperature of the gas flowing into the catalyst becomes low, at least one of the opening timing and closing timing of the exhaust valve is controlled to be retarded.

  Further, in an eighth aspect based on the seventh aspect, the valve timing control unit may cause the catalyst to be in a supercooled state under a situation where the retardation control is performed during execution of fuel cut. When predicted, at least one of the opening timing and closing timing of the exhaust valve is controlled to the advance side.

According to the first invention, when the fuel cut execution condition is satisfied, at least one of the opening timing and closing timing of the exhaust valve is retarded to the retard side. When the opening timing of the exhaust valve is controlled to the retard side, the gas subjected to the combustion is sufficiently expanded in the combustion chamber to be introduced into the catalyst after the temperature is lowered. Further, when the closing timing of the exhaust valve is controlled to the retard side, the amount of gas remaining in the combustion chamber can be increased, so that the amount of high-temperature exhaust gas introduced into the catalyst can be reduced.
For this reason, according to the present invention, the exhaust gas temperature (catalyst-containing gas temperature) can be effectively reduced prior to the fuel cut. As a result, immediately after the start of the fuel cut, it is possible to suppress the high temperature burned gas and lean gas (fresh air) containing a large amount of oxygen from being supplied to the catalyst at the same time, and to suppress the deterioration of the catalyst well. It becomes possible to do.

  According to the second invention, the fuel cut is performed while effectively suppressing the deterioration of the catalyst after effectively reducing the exhaust gas temperature (gas temperature containing the catalyst) by the retard control in the first invention. Will be able to.

  According to the third aspect of the present invention, the fresh air introduced into the combustion chamber during the fuel cut is discharged by quickly discharging the normal temperature fresh air taken into the cylinder by the quick opening control of the exhaust valve. An increase in temperature due to heat exchange with a wall surface or the like can be effectively suppressed. As a result, the exhaust gas temperature (catalyst containing gas temperature) can be reliably lowered even during the fuel cut. For this reason, it becomes possible to more reliably suppress the deterioration of the catalyst during the fuel cut.

  According to the fourth aspect of the present invention, by taking a long time for the normal temperature fresh air taken into the cylinder to take away the heat around the combustion chamber by the slow opening control of the exhaust valve, the catalyst purification performance is improved from the viewpoint of exhaust emission It is possible to suppress the exhaust gas temperature (catalyst-containing gas temperature) from decreasing to an extent that it falls below the allowable lower limit. For this reason, it is possible to prevent the catalyst from being overcooled before returning from the fuel cut, and to avoid deterioration of exhaust emission due to a decrease in the purification ability of the catalyst after returning from the fuel cut. be able to.

According to the fifth aspect of the invention, when the fuel cut execution condition is satisfied, at least one of the opening timing and closing timing of the exhaust valve is advanced to the advance side. When the opening timing of the exhaust valve is controlled to the advance side, the flow velocity of the gas passing through the exhaust valve when the exhaust valve is opened increases, so the gas and the surroundings (the combustion chamber wall surface, the exhaust port, The heat transfer coefficient between the exhaust valve and the like increases. For this reason, the burnt gas is introduced into the catalyst after the temperature has dropped due to the transfer of heat from the burnt gas that has been heated to a temperature higher than that of the combustion chamber wall, etc. Will come to be. Further, when the closing timing of the exhaust valve is controlled to the advance side, the amount of gas remaining in the combustion chamber can be increased, so that the amount of high-temperature exhaust gas introduced into the catalyst can be decreased.
For this reason, according to the present invention, the exhaust gas temperature (catalyst-containing gas temperature) can be effectively reduced prior to the fuel cut. As a result, immediately after the start of the fuel cut, it is possible to suppress the high temperature burned gas and lean gas (fresh air) containing a large amount of oxygen from being supplied to the catalyst at the same time, and to suppress the deterioration of the catalyst well. It becomes possible to do.

  According to the sixth aspect of the present invention, the exhaust gas temperature (gas temperature with catalyst) is effectively reduced by the advance angle control in the fifth aspect of the invention, and then fuel cut is performed while satisfactorily suppressing deterioration of the catalyst. Will be able to.

According to the seventh invention, when the slow opening control of the exhaust valve is performed, the flow rate of the gas when the exhaust valve is opened can be lowered. As a result, when the fuel cut is started and the fresh air at normal temperature has circulated in the combustion chamber, the heat around the combustion chamber can be made less likely to be taken away by the fresh air discharged into the exhaust passage. . Also, when exhaust valve slow closing control is performed, it is avoided that normal temperature fresh air is trapped in the combustion chamber as in the case of exhaust valve early closing control, The heat around the combustion chamber can be made less likely to be taken away by fresh air.
Thus, according to the present invention, the heat around the combustion chamber can be made less likely to be taken away by fresh air, so that the exhaust gas temperature (catalyst-containing gas temperature) can be reliably lowered during the fuel cut. It becomes like this. For this reason, it becomes possible to more reliably suppress the deterioration of the catalyst during the fuel cut.

According to the eighth aspect of the invention, when the quick opening control of the exhaust valve is performed, the gas flow rate when the exhaust valve is opened can be increased. As a result, when the fuel cut is started and the fresh air at normal temperature has circulated in the combustion chamber, the heat around the combustion chamber can be easily taken away by the fresh air discharged into the exhaust passage. . In addition, when the exhaust valve early closing control is performed, fresh air at room temperature is temporarily confined in the combustion chamber during the exhaust stroke. Also by this, the heat around the combustion chamber can be easily taken away by fresh air.
As described above, according to the present invention, the heat around the combustion chamber can be easily taken away by fresh air, so that the catalyst purification performance is lowered to a level lower than the lower limit allowed from the viewpoint of exhaust emission. Thus, it is possible to suppress the exhaust gas temperature (catalyst-containing gas temperature) from decreasing. For this reason, it is possible to prevent the catalyst from being overcooled before returning from the fuel cut, and to avoid deterioration of exhaust emission due to a decrease in the purification ability of the catalyst after returning from the fuel cut. be able to.

Embodiment 1 FIG.
[System configuration]
FIG. 1 is a diagram for explaining a configuration of an internal combustion engine 10 according to a first embodiment of the present invention. The system of this embodiment includes an internal combustion engine 10. A piston 12 is provided in the cylinder of the internal combustion engine 10. A combustion chamber 14 is formed in the cylinder of the internal combustion engine 10 on the top side of the piston 12. An intake passage 16 and an exhaust passage 18 communicate with the combustion chamber 14.

  An air flow meter 20 that outputs a signal corresponding to the flow rate of air sucked into the intake passage 16 is provided in the vicinity of the inlet of the intake passage 16. A throttle valve 22 is provided downstream of the air flow meter 20. The throttle valve 22 is an electronically controlled throttle valve that can control the throttle opening independently of the accelerator opening. In the vicinity of the throttle valve 22, a throttle sensor 24 for detecting the throttle opening is disposed.

  A fuel injection valve 26 for injecting fuel into the intake port of the internal combustion engine 10 is disposed downstream of the throttle valve 22. A spark plug 28 is attached to the cylinder head of the internal combustion engine 10 so as to protrude from the top of the combustion chamber 14 into the combustion chamber 14. The intake port and the exhaust port are respectively provided with an intake valve 30 and an exhaust valve 32 for bringing the combustion chamber 14 and the intake passage 16 or the combustion chamber 14 and the exhaust passage 18 into a conductive state or a cut-off state.

  The system shown in FIG. 1 includes an exhaust variable valve mechanism 34 for opening and closing the exhaust valve 32. The specific configuration of the exhaust variable valve mechanism 34 is not particularly limited, but here it is assumed to be a VVT mechanism that continuously varies the phase of a cam (not shown) that drives the exhaust valve 32.

  FIG. 2 is a view for explaining a variable range of the opening / closing timing of the exhaust valve 32 by the exhaust variable valve mechanism 34 shown in FIG. According to the exhaust variable valve mechanism 34 having the VVT mechanism, the opening / closing timing of the exhaust valve 32 is adjusted in FIG. 2 while the working angle is fixed by adjusting the advance amount of the exhaust cam shaft with respect to the crankshaft. Adjustment can be made within the variable range shown.

  More specifically, in the example of the exhaust valve timing shown in FIG. 2, when the opening / closing timing of the exhaust valve 32 is most advanced, the exhaust valve 32 is opened at about 100 ° CA after compression top dead center. After that, it closes at a predetermined time before exhaust top dead center. Further, when the opening / closing timing of the exhaust valve 32 is most retarded, the exhaust valve 32 is opened at a predetermined time before the expansion bottom dead center, and then a predetermined time after the exhaust top dead center. It will be closed with. The opening / closing timing of the intake valve 30 is opened at a predetermined timing before the exhaust top dead center, and then closed at a predetermined timing after the intake bottom dead center, as indicated by the dashed arrow in FIG. Is set.

  The internal combustion engine 10 includes a crank angle sensor 36 in the vicinity of the crankshaft. The crank angle sensor 36 is a sensor that reverses the Hi output and the Lo output each time the crankshaft rotates by a predetermined rotation angle. According to the output of the crank angle sensor 36, it is possible to detect the rotational position and rotational speed of the crankshaft, and further the engine rotational speed and the like. The internal combustion engine 10 includes a cam angle sensor 38 in the vicinity of an exhaust camshaft (not shown). The cam angle sensor 38 is a sensor having the same configuration as the crank angle sensor 36. According to the output of the cam angle sensor 38, the rotational position (advance amount) of the exhaust cam shaft can be detected.

  An upstream catalyst (SC) 40 and a downstream catalyst (UF) 42 for purifying exhaust gas are arranged in series in the exhaust passage 18 of the internal combustion engine 10. Further, an air-fuel ratio sensor 44 for detecting the exhaust air-fuel ratio at that position is disposed upstream of the upstream catalyst 40. Further, an oxygen sensor 46 that generates a signal corresponding to whether the air-fuel ratio at that position is rich or lean is disposed between the upstream catalyst 40 and the downstream catalyst 42.

  The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 48. In addition to the various sensors described above, the ECU 480 is connected to an accelerator position sensor 50 for detecting the accelerator opening, the various actuators described above, and the like. The ECU 48 can control the operating state of the internal combustion engine 10 based on those sensor outputs.

[Catalyst degradation suppression control of Embodiment 1]
In the system of the present embodiment configured as described above, when the throttle opening is set to the idle opening during the operation of the internal combustion engine 10, a process for stopping fuel injection, that is, a fuel cut (fuel cut: F / C) is executed. Since fuel injection is not performed during the fuel cut, the gas flowing into the catalyst 40 or the like is extremely lean. When a lean gas flows into the high temperature catalyst 40 or the like, the deterioration of the catalyst 40 or the like easily proceeds.

  Immediately after the start of the fuel cut is immediately after the combustion is stopped, high-temperature burned gas exists as residual gas in the cylinder. As a result, immediately after the start of the fuel cut, such high-temperature burned gas is discharged into the exhaust passage 18 together with fresh air not subjected to combustion. For this reason, particularly immediately after the start of the fuel cut, the temperature of the gas flowing into the catalyst 40 or the like (hereinafter also referred to as “catalyst-containing gas temperature”) becomes high. Therefore, in the present embodiment, in order to suppress the deterioration of the catalyst 40 and the like by reducing the temperature of the gas containing the catalyst during the fuel cut, control as described below with reference to FIG. 3 is performed. Yes.

  FIG. 3 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 1 of the present invention. More specifically, FIG. 3A shows a waveform indicating the success or failure of the fuel cut (fuel cut) execution condition, and FIG. 3B shows a change in the advance amount of the opening / closing timing (valve timing) of the exhaust valve 32. 3 (C) shows a waveform indicating whether or not a fuel cut is performed, and FIG. 3 (D) shows a change in exhaust gas temperature.

  As shown in FIG. 3, in the present embodiment, the fuel cut is not performed immediately at the time t1 when the predetermined fuel cut execution condition is satisfied, but is shown in FIGS. 3 (B) and 3 (C). As described above, the fuel cut is performed at the time point t2 when the valve timing (opening / closing timing) of the exhaust valve 32 is controlled to the most retarded position.

  When the valve timing of the exhaust valve 32 is controlled to the most retarded position so that the opening timing of the exhaust valve 32 is sufficiently delayed to the vicinity of the expansion bottom dead center, it is subjected to combustion. The gas is expanded into the combustion chamber 14 and is introduced into the catalyst 40 after the temperature is lowered.

  Further, if the valve timing of the exhaust valve 32 is controlled to the most retarded position so that the closing timing of the exhaust valve 32 is delayed beyond the exhaust top dead center, the exhaust passage in the exhaust stroke is controlled. The gas once discharged to 18 is re-inhaled into the cylinder. As a result, the amount of gas remaining in the combustion chamber 14 can be increased, so that the amount of high-temperature exhaust gas introduced into the catalyst 40 or the like can be reduced. In addition, the temperature of the residual gas to be discharged after the next cycle can be lowered by mixing the residual gas with the fresh air taken into the cylinder in the next cycle.

  For this reason, according to the control of the present embodiment, at the time t1 when the fuel cut execution condition is satisfied, the exhaust valve 32 is opened late and closed later than the opening / closing timing at the time t1 is satisfied, whereby FIG. As shown in (D), the exhaust gas temperature (catalyst-containing gas temperature) can be effectively reduced prior to the fuel cut. As a result, immediately after the start of the fuel cut, it is possible to suppress a high-temperature burned gas and a lean gas (fresh air) containing a large amount of oxygen from being supplied to the catalyst 40 etc. at the same time, and the catalyst 40 etc. deteriorates. Can be suppressed satisfactorily.

FIG. 4 is a flowchart of a routine executed by the ECU 48 in the first embodiment in order to realize the above function.
In the routine shown in FIG. 4, first, it is determined based on the throttle opening, the engine speed, and the like whether or not the execution condition of fuel cut (fuel cut) control is satisfied (step 100).

  As a result, when it is determined that the execution condition of the fuel cut control is not satisfied, the fuel cut is not executed (step 102). On the other hand, if it is determined that the fuel cut control execution condition is satisfied, the exhaust variable valve mechanism is configured so that the exhaust valve timing reaches the most retarded position from the current control position based on the operating state of the internal combustion engine 10. 34 is controlled (step 104).

  Next, it is determined based on the output of the exhaust cam angle sensor 38 whether or not the exhaust valve timing is controlled to the most retarded position (step 106). As a result, while the determination is not satisfied, the fuel cut is not performed (step 102), and when the determination is satisfied, the fuel cut is performed (step 108).

  Incidentally, in the first embodiment described above, the variable exhaust valve mechanism 34 that can adjust the opening / closing timing of the exhaust valve 32 with the working angle fixed is provided. The mechanism is not limited to a mechanism having such a VVT mechanism, but may be, for example, an electromagnetically driven valve that opens and closes the exhaust valve 32 with electromagnetic force. According to such an electromagnetically driven valve, the opening timing and closing timing of the exhaust valve 32 can be individually adjusted to arbitrary timings.

  In Embodiment 1 described above, the opening / closing timing of the exhaust valve 32 is controlled to the most retarded position at the time t1 when the fuel cut execution condition is satisfied. It is not limited to. That is, for example, when a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve to an arbitrary timing is provided, at the time t1 when the fuel cut execution condition is satisfied, At least one of the opening timing and closing timing of the exhaust valve 32 may be sufficiently delayed.

  In the first embodiment described above, the ECU 48 executes the processing of steps 106 and 108, so that the “fuel cut execution means” in the first invention executes the processing of step 100. The “valve timing control means” in the first aspect of the present invention is realized by executing the processing of step 104 in the “fuel cut condition determination means” in the first aspect of the invention.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 5 and FIG.
The system of this embodiment is realized by causing the ECU 48 to execute the routine of FIG. 6 instead of the routine of FIG. 4 using the hardware configuration shown in FIG.

  In the first embodiment described above, when the fuel cut execution condition is satisfied, the fuel cut is performed after the valve timing (opening / closing timing) of the exhaust valve 32 is controlled to the most retarded position. . By the way, the gas exchanged in the combustion chamber 14 during the fuel cut is air at normal temperature (fresh air), unlike before the fuel cut. For this reason, if the opening / closing timing of the exhaust valve 32 is maintained at the most retarded position even during the fuel cut, the heat around the combustion chamber 14 (such as the wall surface of the combustion chamber) is taken into the combustion chamber 14. There is a possibility that the temperature of the gas discharged from the cylinder rises. Such an increase in the gas temperature prevents the temperature of the gas containing the catalyst from being lowered during the fuel cut.

FIG. 5 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 2 of the present invention.
Therefore, in the present embodiment, when the fuel cut is performed after the valve timing of the exhaust valve 32 is controlled to the most retarded position, as shown in FIG. The valve timing of the exhaust valve 32 is controlled to the most advanced position in order to quickly open the exhaust valve 32 at the time t3 when it is determined that the degree of decrease in the catalyst-containing gas temperature has become low due to the movement of.

  According to such control, it is possible to prevent the heat around the combustion chamber 14 from being taken away by the fresh air by discharging the gas (fresh air) taken into the combustion chamber 14 at an early stage. As a result, as shown in FIG. 5D, the exhaust gas temperature (catalyst containing gas temperature) can be reliably reduced even during the fuel cut. For this reason, it becomes possible to suppress deterioration of the catalyst 40 and the like more reliably during the fuel cut.

FIG. 6 is a flowchart of a routine executed by the ECU 48 in the second embodiment in order to realize the above function. In FIG. 6, the same steps as those shown in FIG. 4 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 6, after confirming that the valve timing of the exhaust valve 32 has been controlled to the most retarded position (step 106), if the fuel cut is being performed (step 108), then, It is determined whether or not a gas having an excessive oxygen content (normal temperature air) flows into the catalyst 40 or the like (step 200). In this step 200, by making such a determination, it is determined whether or not the degree of decrease in the catalyst-containing gas temperature has decreased due to the transfer of heat to the fresh air. More specifically, in this step 200, when the air-fuel ratio becomes 18 or more, for example, based on the output of the air-fuel ratio sensor 44, a gas with an excessive oxygen content flowing into the catalyst 40 or the like. It is judged.

  When the determination in step 200 is established, that is, when it can be determined that the degree of decrease in the temperature of the gas with catalyst is low, the valve timing of the exhaust valve 32 reaches the most advanced angle position from the current most retarded position. Thus, the exhaust variable valve mechanism 34 is controlled (step 202).

  By the way, in Embodiment 2 described above, when it can be determined that the degree of decrease in the catalyst-containing gas temperature has become low during the fuel cut, the exhaust gas that adjusts the opening / closing timing of the exhaust valve 32 with the operating angle fixed. Although the variable valve mechanism 34 controls the valve timing of the exhaust valve 32 to the most advanced position, the present invention is not limited to such control. That is, for example, in the case where a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve to an arbitrary timing is provided, the temperature of the gas containing the catalyst is reduced during the fuel cut. When it can be determined that the degree of decrease is low, only the opening timing of the exhaust valve 32 may be advanced sufficiently.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. 7 and FIG.
The system of the present embodiment is realized by causing the ECU 48 to execute the routine of FIG. 8 instead of the routine of FIG. 6 using the hardware configuration shown in FIG.

  In the second embodiment described above, when the fuel cut is performed after the valve timing of the exhaust valve 32 is controlled to the most retarded position, it is determined that the degree of decrease in the catalyst-containing gas temperature has decreased. The valve timing of the exhaust valve 32 is controlled to the most advanced position. However, the temperature of the air (fresh air) sucked into the combustion chamber 14 is lower than the catalyst bed temperature. For this reason, when the fuel cut is performed for a long time, the control of the second embodiment described above continues to be executed for a long time, the catalyst temperature gradually decreases, and the catalyst 40 and the like are overcooled. There is a possibility of becoming.

  In addition, if the catalyst 40 or the like becomes too cold, there is a concern that the purification ability of the catalyst 40 or the like may be reduced. And when recovery from a fuel cut is performed after the catalyst 40 etc. have become too cold, there exists a concern about the deterioration of exhaust emission because the purification ability of the catalyst 40 etc. has fallen.

  FIG. 7 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 3 of the present invention. More specifically, FIG. 7E, which is newly added to FIG. 3 and FIG. 5 in FIG. 7, shows a change in the integrated intake air amount during the period in which the fuel cut is being executed. ing.

  In the present embodiment, in order to solve the above-described problem, when the fuel cut is performed in a state where the valve timing of the exhaust valve 32 is controlled to the most advanced position, as shown in FIG. Thus, at the time t4 when the integrated intake air amount during the fuel cut exceeds a predetermined determination line for determining whether or not the catalyst purification capacity has decreased, the valve of the exhaust valve 32 is to be opened slowly. The timing is again controlled to the most retarded position.

  According to the control as described above, the valve timing of the exhaust valve 32 is controlled again to the most retarded position only when it is determined that the catalyst 40 or the like is too cold during the fuel cut. It takes a long time for the fresh air at normal temperature taken in to take away the heat around the combustion chamber 14. As a result, as shown in FIG. 7D, the exhaust gas temperature (catalyst-containing gas temperature) is lowered to such an extent that the catalyst purification performance falls below the lower limit value that is acceptable from the viewpoint of exhaust emission. Can be suppressed. For this reason, it is possible to prevent the catalyst 40 and the like from being overcooled before returning from the fuel cut, and exhaust emission deteriorates due to a decrease in the purifying ability of the catalyst 40 and the like after the return from the fuel cut. Can be avoided. As described above, according to the control of the present embodiment, it is possible to suitably achieve both prevention of purification ability reduction of the catalyst 40 and the like and suppression of fuel consumption due to execution of fuel cut.

FIG. 8 is a flowchart of a routine executed by the ECU 48 in the third embodiment in order to realize the above function. In FIG. 8, the same steps as those shown in FIG. 6 in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 8, when the fuel cut is executed with the valve timing of the exhaust valve 32 being controlled to the most advanced position (step 202), the condition for determining the catalyst purification capacity reduction is then satisfied. It is determined whether or not (step 300). In this step 300, by making such a determination, it is determined whether or not the catalyst purification capacity is close to a lower limit value that is acceptable from the viewpoint of exhaust emission. More specifically, in step 300, as described above with reference to FIG. 7, when the integrated air amount during the fuel cut is larger than a predetermined value, the condition for determining the decrease in the catalyst purification performance is satisfied. It is judged that

  As a result, when the determination in step 300 is established, that is, when it is predicted that the catalyst 40 and the like will be in a supercooled state before returning from the fuel cut, the valve timing of the exhaust valve 32 is the current maximum timing. The exhaust variable valve mechanism 34 is controlled so as to reach the most retarded position from the advanced position (step 302).

  By the way, in the above-described third embodiment, when it is predicted that the catalyst 40 and the like will be in a supercooled state before returning from the fuel cut, the opening / closing timing of the exhaust valve 32 is adjusted with the operating angle fixed. The valve timing of the exhaust valve 32 is controlled to the most retarded position by the exhaust variable valve mechanism 34 that performs this, but the present invention is not limited to such control. That is, for example, in the case where a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve is provided at an arbitrary timing, the catalyst 40 or the like is set before returning from the fuel cut. When it is predicted that a supercooled state will occur, only the opening timing of the exhaust valve 32 may be sufficiently delayed.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG. 9 and FIG.
The system of the present embodiment is realized by causing the ECU 48 to execute the routine of FIG. 10 instead of the routine of FIG. 8 using the hardware configuration shown in FIG.

  In Embodiment 3 described above, when the fuel cut is performed with the valve timing of the exhaust valve 32 controlled to the most advanced position, the catalyst is based on the integrated intake air amount during the fuel cut. The presence or absence of a decrease in purification performance (decrease in catalyst temperature) is determined. On the other hand, the present embodiment is characterized in that the presence or absence of a decrease in catalyst purification performance (a decrease in catalyst temperature) is determined based on the fuel cut execution time.

  FIG. 9 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 4 of the present invention. More specifically, FIG. 9E newly added to FIG. 3 and FIG. 5 in FIG. 9 shows the counter value of the fuel cut execution time.

  In this embodiment, when the fuel cut is performed with the valve timing of the exhaust valve 32 controlled to the most advanced position, as shown in FIG. At a time point t4 when a predetermined determination line for determining whether or not there is a decrease in performance is exceeded, the valve timing of the exhaust valve 32 is again controlled to the most retarded position in order to open the exhaust valve 32 slowly. According to such control, the same effects as those of the third embodiment described above can be obtained.

FIG. 10 is a flowchart of a routine executed by the ECU 48 in the fourth embodiment in order to realize the above function. 10, the same steps as those shown in FIG. 8 in the third embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 10, when the fuel cut is performed with the valve timing of the exhaust valve 32 being controlled to the most advanced position (step 202), the condition for determining the catalyst purification capacity decrease is then satisfied. It is determined whether or not (step 400). More specifically, in step 400, as described above with reference to FIG. 9, when the fuel cut execution time is longer than a predetermined value, it is determined that the condition for determining the catalyst purification capacity decrease is satisfied. The

  As a result, when the determination in step 400 is established, that is, when it is predicted that the catalyst 40 or the like will be in a supercooled state before returning from the fuel cut, the valve timing of the exhaust valve 32 is the current maximum timing. The exhaust variable valve mechanism 34 is controlled so as to reach the most retarded position from the advanced position (step 302).

Embodiment 5 FIG.
Next, Embodiment 5 of the present invention will be described with reference to FIG. 11 and FIG.
The system of the present embodiment is realized by causing the ECU 48 to execute the routine of FIG. 12 instead of the routine of FIG. 4 using the hardware configuration shown in FIG.

FIG. 11 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 5 of the present invention.
In the first embodiment described above, when the fuel cut execution condition is satisfied in order to suppress the deterioration of the catalyst 40 and the like by reducing the temperature of the gas containing the catalyst during the fuel cut, the valve of the exhaust valve 32 is satisfied. The fuel cut is performed after the timing (opening / closing timing) is controlled to the most retarded position.

  On the other hand, as shown in FIG. 11, in this embodiment, at the time t1 when the fuel cut execution condition is satisfied, the valve timing (opening / closing timing) of the exhaust valve 32 is directed from the current control position to the most advanced position. To control. The fuel cut is performed at time t2 when the valve timing of the exhaust valve is controlled to the most advanced position.

  When the valve timing of the exhaust valve 32 is controlled to the most advanced position, the pressure in the combustion chamber 14 and the exhaust passage 18 is controlled in a state where the opening timing of the exhaust valve 32 is sufficiently advanced. The exhaust valve 32 is opened with a large difference. As a result, when the exhaust valve 32 is opened, the flow rate of the gas passing through the exhaust valve 32 increases, so that the heat transfer coefficient between the gas and the surroundings (combustion chamber wall surface, exhaust port, exhaust valve 32, etc.). Becomes higher. For this reason, the burnt gas is reduced to a temperature such as the catalyst 40 or the like after the temperature is lowered due to the transfer of heat from the burnt gas that is higher in temperature than the combustion chamber wall surface due to being subjected to combustion. Will be introduced.

  Further, if the valve timing of the exhaust valve 32 is controlled to the most advanced position, the closing timing of the exhaust valve 32 is advanced so as to be before the exhaust top dead center. In the exhaust stroke, the intake and exhaust valves 30 and 32 are temporarily confined in the combustion chamber 14 in a state where both are closed (negative valve overlap state). At this time, the gas temperature in the cylinder is lowered by the transfer of heat from the burned gas having a temperature higher than that of the combustion chamber wall surface to the combustion chamber wall surface. Further, according to such early closing control of the exhaust valve 32, the amount of gas remaining in the combustion chamber 14 is also increased, so that the amount of high-temperature exhaust gas introduced into the catalyst 40 or the like can be reduced. Furthermore, the temperature of the residual gas that will be discharged after the next cycle can be reduced by mixing the residual gas with the fresh air taken into the cylinder in the next cycle.

  Therefore, according to the control of the present embodiment, at the time t1 when the fuel cut execution condition is satisfied, the exhaust valve 32 is opened earlier and closed earlier than the opening / closing timing at the time t1. 11 (D), the exhaust gas temperature (catalyst containing gas temperature) can be more effectively lowered prior to the fuel cut. Thereby, after the start of the fuel cut, it is possible to prevent the high temperature burned gas and the lean gas (fresh air) containing a large amount of oxygen from being supplied to the catalyst 40 and the like at the same time. It becomes possible to suppress well.

FIG. 12 is a flowchart of a routine executed by the ECU 48 in the fifth embodiment in order to realize the above function. In FIG. 12, the same steps as those shown in FIG. 4 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 12, when it is determined that the fuel cut control execution condition is satisfied, the exhaust valve timing is set to reach the most advanced position from the current control position based on the operating state of the internal combustion engine 10. The exhaust variable valve mechanism 34 is controlled (step 500).

  Next, it is determined based on the output of the exhaust cam angle sensor 38 whether or not the exhaust valve timing is controlled to the most advanced position (step 502). As a result, while the determination is not satisfied, the fuel cut is not performed (step 102), and when the determination is satisfied, the fuel cut is performed (step 108).

  By the way, in Embodiment 5 described above, the opening / closing timing of the exhaust valve 32 is controlled to the most advanced angle position at the time t1 when the fuel cut execution condition is satisfied. It is not limited to. That is, for example, when a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve to an arbitrary timing is provided, at the time t1 when the fuel cut execution condition is satisfied, At least one of the opening timing and closing timing of the exhaust valve 32 may be sufficiently advanced.

  In the fifth embodiment described above, the ECU 48 executes the processes of steps 106 and 108, so that the “fuel cut execution means” in the fifth aspect of the invention executes the process of step 100. The “valve timing control means” according to the fifth aspect of the present invention is realized by executing the processing of step 500 in the “fuel cut condition determination means” according to the fifth aspect of the invention.

Embodiment 6 FIG.
Next, Embodiment 6 of the present invention will be described with reference to FIG. 13 and FIG.
The system of the present embodiment is realized by causing the ECU 48 to execute the routine of FIG. 14 instead of the routine of FIG. 12 using the hardware configuration shown in FIG.

  In the fifth embodiment described above, when the fuel cut execution condition is satisfied, the fuel cut is performed after the valve timing (opening / closing timing) of the exhaust valve 32 is controlled to the most advanced position. . As already described in the second embodiment, if the open / close timing of the exhaust valve 32 is maintained at the most advanced position even during the fuel cut, the heat around the combustion chamber 14 (such as the wall surface of the combustion chamber). May move to fresh air taken into the combustion chamber 14, and the temperature of the gas discharged from the cylinder may rise. Such an increase in the gas temperature prevents the temperature of the gas containing the catalyst from being lowered during the fuel cut.

FIG. 13 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 6 of the present invention.
Therefore, in the present embodiment, when the fuel cut is performed after the valve timing of the exhaust valve 32 is controlled to the most advanced position, as shown in FIG. The valve timing of the exhaust valve 32 is controlled to the most retarded position so that the exhaust valve 32 is slowly opened and closed at the time t3 when it is determined that the degree of decrease in the catalyst-containing gas temperature has become low due to the movement of .

  According to such control, the opening timing of the exhaust valve 32 is sufficiently delayed to the vicinity of the expansion bottom dead center, so that the gas flow rate when the exhaust valve 32 is opened can be lowered. As a result, when the fuel cut is started and the fresh air at normal temperature has circulated in the combustion chamber 14, the heat around the combustion chamber 14 is not easily taken away by the fresh air discharged to the exhaust passage 18. can do.

  Further, according to such control, the closing timing of the exhaust valve 32 is sufficiently delayed beyond the exhaust top dead center, so that the fresh air at normal temperature performs the early closing control of the exhaust valve 32. Thus, it is possible to avoid being trapped in the combustion chamber 14, and this also makes it difficult for the heat around the combustion chamber 14 to be taken away by fresh air.

  According to the control of the present embodiment, the heat around the combustion chamber 14 can be made difficult to be taken away by fresh air as described above. Therefore, as shown in FIG. The gas temperature (gas temperature with catalyst) can be reliably reduced. For this reason, it becomes possible to suppress deterioration of the catalyst 40 and the like more reliably during the fuel cut.

FIG. 14 is a flowchart of a routine executed by the ECU 48 in the sixth embodiment to realize the above function. In FIG. 14, the same steps as those shown in FIG. 12 in the fifth embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 14, after confirming that the valve timing of the exhaust valve 32 is controlled to the most advanced position (step 502), when the fuel cut is performed (step 108), then, It is determined whether or not a gas having an excessive oxygen content (normal temperature air) flows into the catalyst 40 or the like (step 200).

  As a result, when the determination in step 200 is established, that is, when it can be determined that the degree of decrease in the catalyst-containing gas temperature is low, the valve timing of the exhaust valve 32 is changed from the current most advanced position to the most retarded position. The exhaust variable valve mechanism 34 is controlled so as to reach (step 600).

  By the way, in the above-described sixth embodiment, when it can be determined that the degree of decrease in the catalyst-containing gas temperature has become low during the fuel cut, the exhaust gas that adjusts the opening / closing timing of the exhaust valve 32 with the working angle fixed. The valve timing of the exhaust valve 32 is controlled to the most retarded position by the variable valve mechanism 34, but the present invention is not limited to such control. That is, for example, in the case where a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve to an arbitrary timing is provided, the temperature of the gas containing the catalyst is reduced during the fuel cut. When it can be determined that the degree of decrease is low, only one of the opening timing and closing timing of the exhaust valve 32 may be sufficiently delayed.

Embodiment 7 FIG.
Next, Embodiment 7 of the present invention will be described with reference to FIG. 15 and FIG.
The system of this embodiment is realized by causing the ECU 48 to execute the routine of FIG. 16 instead of the routine of FIG. 14 using the hardware configuration shown in FIG.

FIG. 15 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 7 of the present invention.
In the above-described sixth embodiment, when the fuel cut is performed after the valve timing of the exhaust valve 32 is controlled to the most advanced position, it is determined that the degree of decrease in the catalyst-containing gas temperature has decreased. The valve timing of the exhaust valve 32 is controlled to the most retarded position.

  Further, in the present embodiment, the exhaust gas control is performed in order to avoid overcooling of the catalyst 40 and the like by continuing the control of the sixth embodiment described above for a long time during the fuel cut. When the fuel cut is performed with the valve timing of the valve 32 controlled to the most retarded position, as shown in FIG. 15 (E), the integrated intake air amount during the fuel cut is the catalyst purification capacity. The valve timing of the exhaust valve 32 is again controlled to the most advanced position in order to quickly open and close the exhaust valve 32 at a time t4 when a predetermined determination line for determining whether or not there is a decrease in the exhaust valve 32 is exceeded. .

  According to such control, since the opening timing of the exhaust valve 32 is sufficiently advanced, the gas flow rate when the exhaust valve 32 is opened can be increased. As a result, when the fuel cut is started and the fresh air at normal temperature circulates in the combustion chamber 14, the heat around the combustion chamber 14 is easily lost to the fresh air discharged to the exhaust passage 18. can do.

  Further, according to such control, the closing timing of the exhaust valve 32 is sufficiently advanced before exhaust top dead center, so that fresh air at room temperature temporarily enters the combustion chamber 14 in the exhaust stroke. Become trapped. Also by this, the heat around the combustion chamber 14 can be easily taken away by fresh air.

  According to the control of the present embodiment, the heat around the combustion chamber 14 can be easily taken away by the fresh air as described above, so that the catalyst purification ability is the viewpoint of exhaust emission as shown in FIG. The exhaust gas temperature (catalyst-containing gas temperature) can be suppressed from decreasing to the extent that the lower limit is lower than the allowable lower limit. In addition, the same effects as those of the third embodiment can be obtained.

FIG. 16 is a flowchart of a routine executed by the ECU 48 in the seventh embodiment in order to realize the above function. In FIG. 16, the same steps as those shown in FIG. 14 in the sixth embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 16, when the fuel cut is executed with the valve timing of the exhaust valve 32 being controlled to the most retarded position (step 600), then the condition for determining the catalyst purification capacity reduction is established. It is determined whether or not (step 300).

  As a result, when the determination in step 300 is established, that is, when it is predicted that the catalyst 40 and the like will be in a supercooled state before returning from the fuel cut, the valve timing of the exhaust valve 32 is the current maximum timing. The exhaust variable valve mechanism 34 is controlled so as to reach the most advanced position from the retarded position (step 700).

  By the way, in the seventh embodiment described above, when it is predicted that the catalyst 40 and the like will be in a supercooled state before returning from the fuel cut, the opening / closing timing of the exhaust valve 32 is adjusted with the operating angle fixed. Although the exhaust variable valve mechanism 34 that controls the valve timing of the exhaust valve 32 is set to the most advanced angle position, the present invention is not limited to such control. That is, for example, in the case where a mechanism capable of individually adjusting the opening timing and closing timing of the exhaust valve 32 such as the electromagnetically driven valve is provided at an arbitrary timing, the catalyst 40 or the like is set before returning from the fuel cut. When it is predicted that a supercooled state will occur, only one of the opening timing and closing timing of the exhaust valve 32 may be sufficiently advanced.

Embodiment 8 FIG.
Next, an eighth embodiment of the present invention will be described with reference to FIG. 17 and FIG.
The system of the present embodiment is realized by causing the ECU 48 to execute the routine of FIG. 18 instead of the routine of FIG. 16 using the hardware configuration shown in FIG.

  In the above-described seventh embodiment, when the fuel cut is performed with the valve timing of the exhaust valve 32 controlled to the most retarded position, the catalyst is based on the integrated intake air amount during the fuel cut. The presence or absence of a decrease in purification performance (decrease in catalyst temperature) is determined. On the other hand, the present embodiment is characterized in that the presence or absence of a decrease in catalyst purification performance (a decrease in catalyst temperature) is determined based on the fuel cut execution time.

FIG. 17 is a time chart for explaining characteristic control executed at the time of fuel cut in Embodiment 8 of the present invention.
In this embodiment, when the fuel cut is performed in a state where the valve timing of the exhaust valve 32 is controlled to the most retarded position, as shown in FIG. At a time point t4 when a predetermined determination line for determining whether or not the purification capacity is reduced is exceeded, the valve timing of the exhaust valve 32 is again controlled to the most advanced position in order to quickly open and close the exhaust valve 32. I have to. According to such control, an effect similar to that of the seventh embodiment described above can be obtained.

FIG. 18 is a flowchart of a routine executed by the ECU 48 in the eighth embodiment in order to realize the above function. In FIG. 18, the same steps as those shown in FIG. 16 in the seventh embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
In the routine shown in FIG. 18, when the fuel cut is performed in a state where the valve timing of the exhaust valve 32 is controlled to the most retarded position (step 600), the execution time of the fuel cut then exceeds the predetermined value. Is determined as to whether or not a condition for determining the catalyst purification capacity decrease is satisfied (step 400).

  As a result, when the determination in step 400 is established, that is, when it is predicted that the catalyst 40 or the like will be in a supercooled state before returning from the fuel cut, the valve timing of the exhaust valve 32 is the current maximum timing. The exhaust variable valve mechanism 34 is controlled so as to reach the most advanced position from the retarded position (step 700).

It is a figure for demonstrating the structure of the internal combustion engine of Embodiment 1 of this invention. It is a figure for demonstrating the variable range of the opening-and-closing timing of the exhaust valve by the exhaust variable valve mechanism shown in FIG. 4 is a time chart for explaining characteristic control executed in fuel cut in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. In Embodiment 2 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 2 of this invention. In Embodiment 3 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 3 of the present invention. In Embodiment 4 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 4 of this invention. In Embodiment 5 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 5 of this invention. In Embodiment 6 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 6 of this invention. In Embodiment 7 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 7 of this invention. In Embodiment 8 of this invention, it is a time chart for demonstrating the characteristic control performed at the time of a fuel cut. It is a flowchart of the routine performed in Embodiment 8 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Combustion chamber 16 Intake passage 18 Exhaust passage 22 Throttle valve 26 Fuel injection valve 28 Spark plug 30 Intake valve 32 Exhaust valve 34 Exhaust variable valve mechanism 36 Crank angle sensor 38 Cam angle sensor 40 Upstream catalyst 42 Downstream catalyst 48 ECU (Electronic Control Unit)

Claims (8)

A catalyst disposed in the exhaust passage of the internal combustion engine;
Fuel cut execution means for performing fuel cut;
Fuel cut condition determining means for determining success or failure of the fuel cut execution condition;
A variable valve mechanism capable of changing at least one of the opening timing and closing timing of the exhaust valve;
Valve timing control means for retarding at least one of the opening timing and closing timing of the exhaust valve to the retard side when the fuel cut execution condition is satisfied;
A control device for an internal combustion engine, comprising:   2. The control apparatus for an internal combustion engine according to claim 1, wherein the fuel cut execution means executes the fuel cut after the retard control is performed.   The valve timing control means is a degree of decrease in the temperature of gas flowing into the catalyst after the start of fuel cut under the condition that at least the opening timing of the exhaust valve is retarded when the fuel cut execution condition is satisfied 3. The control device for an internal combustion engine according to claim 2, wherein when the engine speed becomes low, the opening timing of the exhaust valve is controlled to quickly open toward the advance side.   The valve timing control means delays the opening timing of the exhaust valve when it is predicted that the catalyst will be in a supercooled state under the situation where the early opening control is being performed during the fuel cut. 4. The control apparatus for an internal combustion engine according to claim 3, wherein the control is performed so that the corner is slowly opened. A catalyst disposed in the exhaust passage of the internal combustion engine;
Fuel cut execution means for performing fuel cut;
Fuel cut condition determining means for determining success or failure of the fuel cut execution condition;
A variable valve mechanism capable of changing at least one of the opening timing and closing timing of the exhaust valve;
Valve timing control means for controlling the advance of at least one of the opening timing and closing timing of the exhaust valve to the advance side when the fuel cut execution condition is satisfied;
A control device for an internal combustion engine, comprising:   6. The control apparatus for an internal combustion engine according to claim 5, wherein the fuel cut execution means executes the fuel cut after the advance angle control is performed.   The valve timing control means, when the advance angle control is performed when the fuel cut execution condition is satisfied, when the degree of decrease in the temperature of the gas flowing into the catalyst after the start of the fuel cut is low 7. The control apparatus for an internal combustion engine according to claim 6, wherein at least one of an opening timing and a closing timing of the exhaust valve is retarded to a retard side.   The valve timing control means is configured to open and close the exhaust valve when the catalyst is predicted to be in a supercooled state under the condition in which the retard control is performed during fuel cut. 8. The control apparatus for an internal combustion engine according to claim 7, wherein at least one of the timings is controlled to the advance side.

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