JP2008002435A - Control method and control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of an engine maintaining target rotation speed during idling by suppressing variation of residual gas quantity in a combustion chamber giving big influence on stability of combustion. <P>SOLUTION: An engine controller 31 includes a process procedure delaying ignition timing from timing for start to timing for catalyst warming up acceleration in a stepped manner at timing when target rotation speed is reached during idling, a process procedure starting opening a throttle valve before the timing by predetermined period of time to supply intake air quantity necessary for retaining the target rotation speed at the timing to the combustion chamber, a process procedure temporally increasing fuel injection quantity from a fuel injection valve during a period from realization of the target rotation speed until convergence of change of intake pressure or intake air flow speed with setting timing when the throttle valve starts opening as a start point, process procedure estimating combustion fluctuation quantity of the engine, and a process procedure correcting ignition timing for catalyst warming up acceleration based on the estimated combustion fluctuation quantity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an engine (internal combustion engine) control method and control device, and more particularly to control at a cold start.

After the complete explosion due to the cranking in the cold state, the ignition timing is set as the starting ignition timing until the engine speed increases, and after the engine speed increases, the activation of the catalyst is promoted. There is one that retards the ignition timing stepwise to a predetermined crank angle position after compression top dead center (see Patent Document 1).
Japanese Patent Laid-Open No. 8-232645

  By the way, in the technique of Patent Document 1, before the ignition timing is retarded stepwise to a predetermined crank angle position after compression top dead center, the intake air amount is increased by increasing the ISC opening, etc. It is proposed that it is preferable to further increase the intake air amount after the timing of retarding the timing stepwise, and this makes smoothing or speeding up of the engine.

  However, although it is intended to smooth or speed up the engine blow-up, it is wasteful to increase the engine rotation speed beyond the target rotation speed during idling in terms of fuel consumption. It will be consumed. Therefore, from the viewpoint of improving fuel efficiency, it is preferable that the engine speed is converged to the target speed at idling without overshooting after the complete explosion, even during cold start.

  Therefore, at the timing when the engine speed from cranking reaches the target speed at idling, the ignition timing is retarded in steps from the ignition timing for starting to the ignition timing for promoting catalyst warm-up, and fuel efficiency is improved. In view of the above, the throttle valve is set so that the intake air amount required to maintain the engine speed at the target speed at idling is supplied to the combustion chamber at the timing when the engine speed reaches the target speed at idling. Considering the response delay of the intake air amount from the position to the combustion chamber, a configuration is considered in which the throttle valve starts to open at a timing before a predetermined period before the timing at which the engine rotation speed reaches the target rotation speed during idling.

  And when I experimented with this configuration, after the engine rotation speed reached the target rotation speed during idling as expected, the engine rotation speed did not blow up beyond the target rotation speed during idling. However, it has been newly found that the actual air-fuel ratio leans beyond the combustion stability limit, resulting in a drop in rotation from the target rotation speed during idling or an increase in HC.

  Therefore, when the engine speed from cranking reaches the target speed at idling, the ignition timing is retarded stepwise from the ignition timing for starting to the ignition timing for promoting catalyst warm-up. The target engine speed when the engine is idling so that the intake air amount required to maintain the engine speed at the target engine speed during idling is supplied to the combustion chamber when the target engine speed during idling is reached. The throttle valve starts to open a predetermined time before the timing at which the intake valve reaches, and the timing at which the throttle valve starts to open is used as a starting point, and the intake pressure or intake port intake flow velocity after the engine rotational speed reaches the target rotational speed at idle Until the change converges, the fuel injection amount from the fuel injection valve is temporarily increased to cold start. The engine speed after the complete explosion is quickly converged toward the target speed during idling while promoting warm-up of the catalyst, and the actual speed is also reduced after the engine speed reaches the target speed during idling. It is conceivable to use an engine control method and control device in which the fuel ratio does not exceed the combustion stability limit and does not become lean.

  On the other hand, a variable valve timing and lift mechanism that can variably control the opening and closing timing of the intake valve is provided, and this variable valve timing is set so that the overlap between the opening period of the intake valve and the opening period of the exhaust valve becomes large when cranking starts.・ Some engines set the command value to be given to the lift mechanism. In this engine, during the cold start, the variable valve timing and lift mechanism is activated to move the intake valve open / close timing to the advance position to the initial position, thereby overlapping the intake valve open period and the exhaust valve open period. I try to make it bigger. This is mainly due to the fuel wall flow in the intake port wall during cold start using the return of hot exhaust gas from the exhaust port that overlaps the open period of the intake valve and the open period of the exhaust valve to the intake port. This is to promote atomization.

  Variations in combustion chamber residual gas due to variations in intake valve opening and closing timing, ignition timing, and air-fuel ratio variations due to the operation of the variable valve timing and lift mechanism. Variations in combustion due to variations in the residual gas in the combustion chamber Occurs, and the idle rotation speed fluctuates. Thus, if the fluctuation of the idle rotation speed occurs, it becomes difficult to maintain the engine rotation speed at the target rotation speed at the time of idling.

  In view of this, the present invention provides a combustion chamber that can be used even if the residual gas amount in the combustion chamber varies due to variations in the opening / closing timing of the intake valve accompanying the operation of the variable valve timing / lift mechanism, as well as variations in the ignition timing and air-fuel ratio. It is an object of the present invention to provide an engine control method and control device that suppresses variations in the amount of residual gas in the combustion chamber, which is thought to have a significant effect on stability, and maintains the engine speed at the target speed during idling. And

  The present invention relates to an engine provided with a catalyst in an exhaust passage and a fuel injection valve for injecting fuel in an intake passage (for example, an intake port), respectively, at the timing when the engine speed from cranking reaches the target speed at idling. The ignition timing is retarded stepwise from the ignition timing for starting to the ignition timing for promoting catalyst warm-up, and the engine speed is set to the target speed at idling when the engine speed reaches the target speed at idling. The throttle valve starts to open a predetermined period before the timing at which the engine speed reaches the target rotational speed during idling so that the amount of intake air necessary to maintain the speed is supplied to the combustion chamber. Starting from the opening timing, the intake pressure or intake air after the engine speed reaches the target speed at idle During up change in inspiratory flow rate of over preparative converges, configured to temporarily increase the fuel injection amount from the fuel injection valve. Furthermore, the present invention is configured to estimate the combustion fluctuation amount of the engine and correct the ignition timing for promoting the catalyst warm-up based on the estimated combustion fluctuation amount.

  In addition, the present invention includes a variable valve timing lift mechanism that can variably control the opening / closing timing of the intake valve, as well as a catalyst in the exhaust passage and a fuel injection valve that injects fuel in the intake passage. In the engine where the command value to be given to this variable valve timing and lift mechanism is set so that the overlap between the opening period of the intake valve and the opening period of the exhaust valve becomes large at the time, the engine speed from cranking is idle The ignition timing is retarded stepwise from the start ignition timing to the catalyst warm-up promotion ignition timing when the target engine speed reaches the target engine speed, and the engine speed reaches the target engine speed at idle. The amount of intake air necessary to maintain the engine speed at the target speed during idling is supplied to the combustion chamber. As described above, the throttle valve starts to open a predetermined period before the timing at which the engine speed reaches the target speed at idling, and the timing at which the throttle valve starts to open is the starting point. After reaching the speed, until the change in intake pressure or intake flow velocity at the intake port converges, the fuel injection amount from the fuel injection valve is temporarily increased, the engine combustion fluctuation amount is estimated, and the engine rotational speed is estimated. When the estimated combustion fluctuation amount is equal to or greater than the threshold after the start of the air-fuel ratio feedback control after the timing when the engine reaches the target rotational speed during idling, the overlap between the intake valve open period and the exhaust valve open period is reduced. Correct the command value given to the variable valve timing and lift mechanism on the side or promote the catalyst warm-up It is configured so as to correct the fire time to the advance side.

  According to the present invention, the ignition timing is retarded stepwise from the ignition timing for starting to the ignition timing for promoting catalyst warm-up at the timing when the engine rotational speed from the start reaches the target rotational speed at the time of idling, When the engine speed is at idle, the intake air amount necessary to maintain the engine speed at the target speed at idling is supplied to the combustion chamber when the engine speed reaches the target speed at idling. Since the throttle valve starts to open a predetermined time before the timing of reaching the target rotational speed of the engine, the exhaust temperature is raised early while suppressing the blow-up after the engine rotational speed reaches the target rotational speed during idling. Thus, the catalyst activation time can be shortened while suppressing wasteful fuel consumption.

  In this case, the intake pressure and / or the intake port intake flow velocity may continue to change for a while after the engine rotation speed reaches the target rotation speed during idling. As the air pressure and the intake air flow velocity of the intake port change, the fuel wall flow rate at the intake port wall decreases, and the amount of fuel supplied to the combustion chamber is reduced accordingly, and the air-fuel ratio of the air-fuel mixture in the combustion chamber reaches the combustion stability limit. However, according to the present invention, the engine rotational speed reaches the target rotational speed at the time of idling, starting from the timing at which the throttle valve starts to open. After that, the fuel injection amount from the fuel injection valve is temporarily increased until the change in the intake pressure or the intake air flow velocity at the intake port converges. Even if the intake pressure or the intake air flow velocity at the intake port continues to change after reaching the rotation speed, the air-fuel ratio of the air-fuel mixture in the combustion chamber exceeds the combustion stability limit and becomes lean. Can be prevented. As a result, it is possible to suppress an increase in HC after the engine rotation speed reaches the target rotation speed during idling and a drop in rotation from the target rotation speed during idling.

  In addition, variation in residual gas amount in the combustion chamber due to variation in ignition timing for promoting catalyst warm-up can be considered as a cause of combustion fluctuations after the timing when the engine rotation speed reaches the target rotation speed at idle. According to the present invention, the engine combustion fluctuation amount is estimated, and the ignition timing for promoting catalyst warm-up is corrected based on the estimated combustion fluctuation amount. Therefore, the engine rotation speed has reached the target rotation speed during idling. Combustion fluctuations due to variations in the amount of residual gas in the combustion chamber due to variations in the ignition timing for promoting catalyst warm-up after the timing can be suppressed.

  In addition, after the start of air-fuel ratio feedback control, it is considered that even if there is a variation in the residual gas amount in the combustion chamber due to the variation, the air-fuel ratio feedback control is started. The cause of the later combustion fluctuation is the variation in the overlap of the intake valve opening period and the exhaust valve opening period, that is, the variation in the residual gas amount in the combustion chamber due to the variation in the opening and closing timing of the intake valve by the variable valve timing and lift mechanism. Or the variation in the amount of residual gas in the combustion chamber due to the variation in the ignition timing for promoting catalyst warm-up. In this case, according to the present invention, the combustion fluctuation amount of the engine is estimated, and after the start of the air-fuel ratio feedback control after the timing when the engine rotation speed reaches the target rotation speed during idling, the estimated combustion fluctuation amount is equal to or greater than the threshold value. The command value given to the variable valve timing / lift mechanism is corrected so that the overlap between the opening period of the intake valve and the opening period of the exhaust valve becomes smaller, or the ignition timing for promoting the catalyst warm-up is set. Because it is corrected to the advance side, combustion fluctuations due to variations in the amount of residual gas in the combustion chamber due to variations in intake valve opening and closing timing by the variable valve timing and lift mechanism and variations in ignition timing for promoting catalyst warm-up are suppressed. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 7 is actually the technical content of the prior invention (see Japanese Patent Application No. 2006-101497) that is the premise of the present invention, and the present invention is positioned as an improved invention of this prior invention. The parts changed by the present invention with respect to the prior invention will be described with reference to FIG.

  FIG. 1 shows a schematic configuration of an engine control apparatus used directly for carrying out an engine control method.

  The air metered by the throttle valve 23 is stored in the intake collector 2 and then introduced into the combustion chamber 5 of each cylinder via the intake manifold 3. Fuel is intermittently injected and supplied into the intake port at a predetermined timing from a fuel injection valve 21 disposed in the intake port 4 of each cylinder. The fuel injected into the intake port 4 is mixed with air to form an air-fuel mixture. The air-fuel mixture is confined in the combustion chamber 5 by closing the intake valve 15, compressed by the rise of the piston 6, and the spark plug 14. It is ignited and burns. The gas pressure due to the combustion works to push down the piston 6, and the reciprocating motion of the piston 6 is converted into the rotational motion of the crankshaft 7. The combusted gas (exhaust gas) is discharged into the exhaust passage 8 when the exhaust valve 16 is opened.

A first catalyst 9 (start-up catalyst) is provided in the manifold passage portion of the exhaust passage 8, and a second catalyst 10 is provided at a position below the floor of the vehicle. These two catalysts 9, 10 are, for example, all three-way catalysts, and when the air-fuel ratio of the exhaust is in a narrow range centered on the stoichiometric air-fuel ratio, the three-way catalyst simultaneously converts HC, CO, and NOx contained in the exhaust. It can be removed efficiently. For this reason, the engine controller 31 to which the intake air amount signal from the air flow meter 32 and the signal from the crank angle sensor (the position sensor 33 and the phase sensor 34) are input is based on these signals and the basic from the fuel injection valve 21. The fuel injection amount is determined, and the air-fuel ratio is feedback-controlled based on a signal from an O ₂ sensor 35 provided upstream of the first catalyst 9.

On the other hand, at the time of cold start, the catalyst is activated early, and the O ₂ sensor 35 is also activated early to execute air-fuel ratio feedback control. Therefore, the O ₂ sensor 35 is immediately started by a heater (not shown). heating, looking at signals from the O ₂ sensor 35, O ₂ sensor 35 is started feedback control of the air-fuel ratio at the timing of activation.

  In addition, the structure of the catalysts 9 and 10 is not restricted to this. For example, in order to improve fuel efficiency after completion of engine warm-up, when operating at a leaner air / fuel ratio than the stoichiometric air / fuel ratio in the low-load side operation region, NOx generated frequently during lean operation is absorbed. For this reason, the second catalyst 10 is constituted by a NOx trap catalyst, and this NOx trap catalyst is provided with a three-way catalyst function, but such a constitution may also be used.

  The throttle valve 23 is driven by a throttle motor 24. Since the torque required by the driver appears in the amount of depression of the accelerator pedal 41 (accelerator opening), the engine controller 31 determines a target torque based on a signal from the accelerator sensor 42, and a target air for realizing this target torque. The throttle valve drive device (not shown) controls the opening degree of the throttle valve 23 via the throttle motor 24 so that the target air amount is obtained.

  Further, the rotational phase difference between the variable valve lift mechanism 26 composed of a multi-joint link mechanism for continuously and variably controlling the valve lift amount of the intake valve 15, and the crankshaft 7 and the intake valve camshaft 25. A variable valve timing mechanism 27 is provided for continuously varying and controlling the opening / closing timing of the intake valve 15.

  Now, the engine speed from the cranking in the cold state is blown up well, and the ignition timing is retarded in order to warm up the first catalyst 9 provided in the exhaust passage 8 at an early stage. Yes. This situation will be specifically described in the case of a four-cylinder engine with reference to FIG.

  First, the current control will be described. At present, as indicated by the one-dot chain line at the top of FIG. 2, the engine speed corresponds to the first explosion in three cylinders from the timing t0 when the starter switch is switched from OFF to ON for starting. It fluctuates, and the engine speed rapidly increases due to the explosion of the fourth cylinder, and blows up across the target speed NSET during idling at the timing of t2 (see the one-dot chain line). From the timing of t2 when the engine speed reaches the target engine speed NSET during idling, the intake air that can maintain the target engine speed NSET during idling is shown in FIG. The throttle valve opening is stepwise opened to a predetermined opening TVO1 so as to be introduced into the combustion chamber 5.

  In addition, the fuel injection amount is that not all of the injected fuel is sucked into the combustion chamber 5 at the beginning of the cold start, but a part of the injected fuel amount adheres to the intake port 4 wall or the back of the intake valve 15 umbrella, Since it is used to form a so-called fuel wall flow that flows in a liquid state on the intake port wall, a fuel supply delay to the combustion chamber 5 occurs. For this reason, as shown by the alternate long and short dash line in the fourth stage of FIG. 2, while much of the fuel wall flow on the intake port wall is deprived at the beginning of the start, extra fuel is injected and supplied, and the fuel wall flow is formed. The fuel injection amount is gradually decreased from the timing when many are not lost.

  On the other hand, the ignition timing is currently set to the first ignition timing ADV1, which is the ignition timing for starting from the timing of t0, as shown by the one-dot chain line in the second stage of FIG. 2, and from the timing of t2, The 1st catalyst 9 is gradually switched to the second ignition timing ADV2 that is greatly retarded in order to promote warm-up.

  Here, if the engine rotation speed from cranking is divided into the front and the rear at the timing t2 when the engine rotation speed reaches the target rotation speed during idling, the engine rotation speed Ne is blown after t2 from the viewpoint of improving fuel efficiency. It is desirable to quickly settle down to the target rotational speed NSET during idling without increasing. This is because fuel consumption increases as the engine speed increases beyond the target rotational speed NSET during idling.

  It is desirable that the actual air-fuel ratio settles to the stoichiometric air-fuel ratio after t2. This is because the first catalyst 9 after completion of warm-up can simultaneously purify the harmful three components (HC, CO, NOx) only when it is in a narrow range centered on the stoichiometric air-fuel ratio.

  Therefore, at the timing t2 when the engine rotational speed Ne from the cranking reaches the target rotational speed NSET during idling, the ignition timing is changed from the first ignition timing ADV1 to the first ignition timing ADV1 as shown by the solid line in the second stage of FIG. 2 From the viewpoint of improving the fuel efficiency, the ignition timing ADV2 is retarded stepwise, and the engine rotational speed Ne is set to the idling target rotational speed at the timing t2 when the engine rotational speed Ne reaches the idling target rotational speed NSET. In consideration of the response delay of the intake air amount from the throttle valve position to the combustion chamber 5 so that the intake air amount required to be held in NSET is supplied to the combustion chamber 5, a solid line in the fifth stage of FIG. As shown in Fig. 5, the throttle speed is slower than the timing t1 a predetermined period before the timing t2 when the engine speed Ne reaches the target rotational speed NSET during idling. Considering a configuration in which the tor valve 23 starts to open (the timing of t1 is determined by adaptation (based on an experimental method), or the engine rotation speed reaches a predetermined rotation speed set lower than the target rotation speed NSET during idling) Can be decided as the timing.

  As a result of experiments with this configuration, after the engine speed Ne has reached the target engine speed NSET during idling, the engine speed does not exceed the target engine speed NSET during idling. However, as indicated by the one-dot chain line in the sixth stage of FIG. 2, the actual air-fuel ratio is the stoichiometric air-fuel ratio (at the timing t2 when the engine speed Ne reaches the target engine speed NSET during idling). However, after that, the combustion stability limit line was exceeded, and the engine became lean, and this excessive leaning newly increased HC as shown by the one-dot chain line in the seventh stage of FIG. found.

  The experiment was conducted by assuming that this is mainly due to the fuel wall flow in the intake port 4 wall. As shown in the third stage of FIG. 2, the engine speed Ne is the target rotation when idling. The intake pressure continued to decrease after the timing t2 when the speed NSET was reached. That is, the fuel wall flow rate of the intake port wall depends on the pressure of the portion where the fuel wall flow flows (that is, the intake pressure) and the intake flow velocity of the portion where the fuel wall flow flows (the intake flow velocity of the intake port 4). The characteristic becomes smaller (this is because the vaporization characteristic of the fuel becomes better as the intake pressure becomes smaller), and becomes smaller as the intake flow velocity of the intake port 4 becomes larger (this means that the vaporization of the fuel becomes larger as the intake flow velocity of the intake port 4 becomes larger). Characteristics (because the characteristics are improved), the intake pressure and the intake port flow velocity at the intake port and the intake port flow velocity at the timing t2 in the middle of the change in the intake pressure and intake port flow velocity are the predetermined values. The fuel wall flow rate at the timing of t3 that becomes converged to (becomes a state of being settled almost unchanged from the normal fluctuation state that follows) becomes smaller. Since the amount of fuel flowing into the combustion chamber 5 includes this fuel wall flow rate, the reduction in the fuel wall flow rate during the period from t2 to t3 means that the amount of fuel flowing into the combustion chamber 5 also decreases this fuel wall flow rate. Therefore, even if the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio at the timing of t2, the actual air-fuel ratio goes to the lean side as the fuel wall flow rate decreases, It seems to have become leaner than the combustion stability limit.

  Therefore, the present invention performs the following three operations.

  [1] From the timing t2 when the engine rotational speed Ne reaches the target rotational speed NSET at the time of idling, the engine rotational speed Ne exceeds the target rotational speed NSET at the time of idling while promoting warm-up of the first catalyst 9 in particular. 2, as indicated by a solid line in the second stage of FIG. 2, the ignition timing is t2, and the first ignition timing (ignition timing for starting) ADV1 to the second ignition timing (catalyst warm-up). The ignition timing for acceleration) is retarded stepwise to ADV2. Such ignition timing control is executed for each cylinder. Here, idling means a state in which the driver does not depress the accelerator pedal 41. The target rotational speed NSET at the time of idling is a conforming value.

  [2] In order to maintain the engine rotational speed Ne at the idling target rotational speed NSET from the timing t2, the intake air amount necessary to maintain the idling target rotational speed NSET is supplied to the combustion chamber 5. Yes, the air supply to the combustion chamber 5 needs to be completed at the timing of t2. In this case, it is the throttle valve 23 provided in the intake passage upstream of the intake collector 2 that controls the intake air amount in the current engine, and therefore, the response of the intake air amount from the throttle valve position to the combustion chamber 5. In consideration of the delay, as indicated by the solid line in the fifth stage of FIG. 2, the throttle valve 23 starts to open toward the predetermined value TVO1 at the timing t1 before the predetermined period before t2, and is predetermined at the timing t2. Try to settle to the value TVO1.

  [3] Although the engine rotational speed Ne settles to the target rotational speed NSET during idling due to the step delay of the ignition timing at t2, the fuel wall flow rate decreases due to a change in the intake pressure immediately after that and the intake port intake air flow velocity. Since the air-fuel ratio becomes excessively lean and HC increases (or the engine speed Ne decreases from the target rotational speed NSET during idling), in order to prevent this increase in HC, As shown by the solid line in the fourth stage, the fuel wall flow rate to the combustion chamber 5 starts from the timing t1 when the throttle valve 23 starts to open until t3 when the change in the intake air pressure and the intake air flow velocity of the intake port is settled. The fuel injection amount is temporarily increased to compensate for the decrease.

  Here, on the premise of the current fuel injection control, the post-startup increase correction coefficient KAS is used to execute the operation [3]. This will be described in detail with reference to FIG. 3. The uppermost stage in FIG. 3 is the same as the uppermost stage in FIG. The second stage of FIG. 3 shows the movement of the ignition timing by the operation [1], and the fourth stage shows the movement of the throttle valve opening by the operation [2].

  First, at present, as indicated by a one-dot chain line in the third stage of FIG. 3, the initial value KAS0 (0.3 in the figure) is set as the post-startup increase correction coefficient KAS from the timing t0 when the starter switch 36 is switched from OFF to ON. After that, the engine speed Ne is decreased toward zero at a predetermined speed from the timing t5 when the engine speed Ne reaches the complete explosion speed N0. On the other hand, in the present invention, as indicated by a solid line in the third stage of FIG. 3, the initial value KAS0 is held until the timing t2, and is decreased toward zero at a predetermined speed from the timing t2. That is, the timing for decreasing the post-startup increase correction coefficient KAS from the initial value KAS0 is delayed from t5 to t2. As a result, the area indicated by hatching in the third stage of FIG. 3 is the amount of fuel increase, and excessive leaning exceeding the combustion stability limit of the air-fuel ratio can be prevented.

  As described above, the actual air-fuel ratio obtained when the timing for decreasing the post-startup increase correction coefficient KAS from the initial value KAS0 is delayed from t5 to t2 (the fuel injection amount from the fuel injection valve is temporarily increased). The theoretical air-fuel ratio has been confirmed. That is, the post-startup increase correction coefficient KAS (fuel injection from the fuel injection valve 21) so that the actual air-fuel ratio obtained when the fuel injection amount from the fuel injection valve 21 is temporarily increased becomes the stoichiometric air-fuel ratio. The amount of increase) is set.

  Here, the post-startup amount increase correction coefficient KAS is constant (initial value KAS0) between t5 and t2, and thereafter linearly decreases. However, the present invention is not limited to this. The point is that the timing of t3 starts from the timing of t5 at which the throttle valve 23 starts to open, and the timing of t3 when the change of the intake pressure and the intake flow velocity of the intake port converges after the timing when the engine rotational speed Ne reaches the target rotational speed NSET during idling. In the meantime, the post-startup increase correction coefficient KAS may be changed so that the fuel injection amount from the fuel injection valve 21 is temporarily increased.

  In addition, the fuel injection amount from the fuel injection valve is temporarily increased by delaying the timing at which the post-startup increase correction coefficient KAS is decreased from the initial value KAS0 from t5 to t2. However, the present invention is not limited to this. For example, a new increase correction coefficient is introduced separately from the post-startup increase correction coefficient KAS, and the timing of t5 at which the throttle valve 23 starts to be opened by this increase correction coefficient is the starting point. The fuel injection amount from the fuel injection valve 21 may be temporarily increased until the time t3 when the change of the intake pressure or the intake air flow velocity of the intake port converges after the timing of reaching NSET.

  In FIG. 3, the timing at t5 when the engine rotational speed Ne reaches the complete explosion rotational speed N0 is set as the timing at which the throttle valve 23 starts to be opened, but is not limited to this.

Also, as described above, the air-fuel ratio feedback control is started at the timing when the O ₂ sensor 35 is activated. The timing at which the air-fuel ratio feedback control is started is the target rotation when the engine speed Ne is idle. If the change in the intake pressure or the intake flow velocity at the intake port comes before the timing t3 after the timing when the speed NSET is reached, the operation of [3] above is canceled and the current operation is restored. Is preferred. This is because the actual air-fuel ratio is kept within a predetermined window width centered on the stoichiometric air-fuel ratio by the air-fuel ratio feedback control, thereby preventing excessive leaning.

  This control executed by the engine controller 31 will be described in detail with reference to the following flowchart.

  FIG. 4 is for setting a complete explosion flag and a target rotation arrival flag, and is executed at regular time intervals (for example, every 100 ms).

  In FIG. 4, in step 1, the engine speed Ne is read. The engine speed Ne is calculated based on signals from the crank angle sensors (33, 34).

  Step 2 looks at the complete explosion flag. This complete explosion flag is a flag that is initially set to zero when an ignition switch (not shown) is switched from OFF to ON. For this reason, since the complete explosion flag = 0 at the beginning, the process proceeds from step 2 to step 3 to compare the engine rotation speed Ne with the complete explosion rotation speed N0 (for example, 1000 rpm). The complete explosion speed N0 is a conforming value. If the engine rotational speed Ne has not reached the complete explosion rotational speed N0, the current process is terminated.

  When the engine speed Ne reaches the complete explosion speed N0 in Step 3 (Ne ≧ N0), the process proceeds to Step 4 to set the complete explosion flag = 1 to indicate that the engine speed Ne has reached the complete explosion speed N0.

  In step 5, a timer is started (timer value TIME = 0). This timer is for measuring the elapsed time from when the engine speed Ne reaches the complete explosion speed N0.

  Since the complete explosion flag = 1, the process proceeds from step 2 to step 6 from the next time. In step 6, the timer value TIME is compared with the predetermined value DT. The predetermined value DT is preliminarily adapted at a time interval from the timing when the engine rotational speed Ne reaches the complete explosion rotational speed N0 to the timing when the engine rotational speed Ne reaches the target rotational speed NSET during idling (see FIG. 3). Since the timer value TIME is initially less than the predetermined value DT when the timer is started, the process proceeds to step 7 and the timer value TIME is incremented by the control period (100 ms).

  If the increment of the timer value TIME in step 7 is repeated several times, the timer value TIME eventually becomes equal to or greater than the predetermined value DT. At this time, the process proceeds from step 6 to step 8 to set the target rotation arrival flag (initially set to zero when the ignition switch is switched from OFF to ON) = 1 to indicate that the target rotation speed NSET during idling has been reached.

  FIG. 5 is for calculating the ignition timing command value and the throttle valve target opening, and is executed at regular intervals (for example, every 100 ms) following the flow of FIG.

  In FIG. 5, in step 21, it is determined whether or not the ignition switch is switched from OFF to ON. When the ignition switch is switched from OFF to ON, the routine proceeds to step 22 where the cooling water temperature TW detected by the water temperature sensor 37 is taken in as the starting water temperature TWINT, and the first ignition timing ADV1 is set according to the starting water temperature TWINT. In step 23, the calculated first ignition timing ADV1 is transferred to the ignition timing command value ADV. The first ignition timing ADV1 is the optimal ignition timing for starting and is largely on the advance side.

  In step 24, an initial value (for example, zero) is input to the throttle valve target opening tTVO.

  After the ignition switch is switched from OFF to ON, that is, when the ignition switch is turned ON, the process proceeds from step 21 to steps 25 and 26. In steps 25 and 26, the complete explosion flag and the target rotation arrival flag (both flags are set according to FIG. 4) are observed. When the complete explosion flag = 0, the routine proceeds to step 27, where the first ignition timing ADV1 calculated when the ignition switch is switched from OFF to ON is maintained. Also at this time, the operation of step 24 is executed.

  When the complete explosion flag = 1 and the target rotation arrival flag = 0, the routine proceeds from step 26 to step 28, where the first ignition timing ADV1 calculated when the ignition switch is switched from OFF to ON is maintained.

  In step 29, the throttle valve target opening tTVO is calculated by the following equation.

tTVO = tTVO (previous) + ΔTVO (1)
Where ΔTVO: constant value,
tTVO (previous): previous value of tTVO,
Here, the predetermined value ΔTVO in the equation (1) is a value that determines an increment of the throttle valve target opening per predetermined time, and this value is a timing at which the engine rotational speed Ne reaches the target rotational speed NSET during idling. Thus, the throttle valve target opening tTVO is determined in advance so as to reach a predetermined value TVO1 described later. The initial value of “tTVO (previous)”, which is the previous value of the throttle valve target opening, is set to zero.

  In step 30, the throttle valve target opening tTVO is compared with a predetermined value TVO1. The predetermined value TVO1 is the throttle valve opening when the minimum intake air amount necessary to generate the torque for maintaining the target rotational speed NSET flows. The predetermined value TVO1 is obtained in advance by adaptation.

  After experiencing step 29 for the first time during the engine operation this time, the throttle valve target opening tTVO is less than the predetermined value TVO1, and thus the current process is terminated. Until the target rotation arrival flag = 1, the operation in step 29 is repeated, and the throttle valve target opening tTVO gradually increases. Immediately before the target rotation arrival flag = 1, the throttle valve target opening tTVO becomes equal to or greater than the predetermined value TVO1. At this time, the routine proceeds from step 30 to step 31 to maintain the throttle valve target opening tTVO at the same value as the previous time.

  When the target rotation arrival flag = 1, the routine proceeds from step 26 to step 32, where the second ignition timing ADV2 is calculated according to the cooling water temperature TW detected by the water temperature sensor 37, and this is calculated at step 33. Move to command value ADV.

  The second ignition timing ADV2 is an ignition timing for promoting warm-up of the first catalyst 9 at the time of cold start, and is set on the retard side with respect to the ignition timing after completion of warm-up of the first catalyst 9. Therefore, the ignition timing is stepwise from the first ignition timing ADV1 to the second ignition timing ADV2 at the timing t2 when the engine rotational speed Ne reaches the target rotational speed NSET as shown in the second stage of FIG. It will be switched.

  In step 34, the throttle valve target opening degree tTVO is maintained at the same value (= TVO1) as the previous time.

  The ignition timing command value ADV calculated in this way is transferred to the output register, and the primary current of the ignition coil is cut off at a timing when the actual crank angle coincides with the ignition timing command value ADV.

  Further, in the slot valve drive device that receives the throttle valve target opening tTVO, the throttle motor 24 is driven so that the actual throttle valve opening coincides with the throttle valve target opening tTVO.

  FIG. 6 is for calculating the target equivalent ratio TFBYA, and is executed at regular intervals (for example, every 100 ms).

  In FIG. 6, in step 41, it is determined whether or not the ignition switch is switched from OFF to ON. When the ignition switch is switched from OFF to ON, the routine proceeds to step 42, where the initial value KAS0 of the post-startup increase correction coefficient is calculated according to the starting water temperature TWINT detected by the water temperature sensor 37, and this is calculated at step 43. To shift to the increase correction coefficient KAS after starting. The initial value KAS0 of the post-startup increase correction coefficient is a value that increases as the starting water temperature TWINT decreases.

  After the ignition switch is switched from OFF to ON, that is, when the ignition switch is turned on, the routine proceeds from step 41 to step 44. In step 44, the target rotation arrival flag is checked (set according to FIG. 4). When the target rotation arrival flag = 0, the routine proceeds to step 45, where the post-startup increase correction coefficient KAS is maintained at the same value as before (that is, the initial value KAS0).

  When the target rotation arrival flag = 1, the routine proceeds from step 44 to step 46, where the post-startup increase correction coefficient KAS is compared with zero. Since the post-startup increase correction coefficient KAS is greater than zero at the timing when the target rotation arrival flag = 1 (because the initial value KAS0 is entered), the routine proceeds to step 47, where the post-startup increase correction coefficient KAS is calculated by the following equation. .

KAS = KAS (previous) −Δt × KAS (previous) (2)
Where Δt is a constant value,
KAS (previous): previous value of KAS,
Here, the predetermined value Δt in the equation (2) is a value that determines a decrease per predetermined time of the post-startup increase correction coefficient KAS, and this value becomes zero at the timing of t3 when the intake pressure converges to a constant value. In addition, it is determined in advance by conformity. The initial value of “KAS (previous)”, which is the previous value of the increase correction coefficient after starting, is KAS0.

  When the target rotation arrival flag = 1, when the operation in step 47 is repeated, the post-startup increase correction coefficient KAS gradually decreases. Accordingly, the post-startup increase correction coefficient KAS is compared with zero at step 48, and when the post-startup increase correction coefficient KAS becomes a negative value, the routine proceeds to step 49 where the post-startup increase correction coefficient KAS = 0.

  In this way, the post-startup increase correction coefficient KAS is a value that gradually decreases to zero from the timing when the engine rotational speed Ne coincides with the target rotational speed NSET during idling.

  At present, the post-start-up increase correction coefficient KAS is gradually smaller than the timing when the engine rotational speed Ne reaches the complete explosion rotational speed N0. However, in the present invention, the engine rotational speed Ne is equal to the target rotational speed NSET during idling. The initial value is maintained until the coincidence timing, and the engine rotation speed Ne becomes gradually smaller than the coincidence with the target rotation speed NSET during idling.

  Steps 50 and 51 are the same as the current situation. That is, in step 50, the water temperature increase correction coefficient KTW is calculated according to the cooling water temperature Tw detected by the water temperature sensor 37 at that time. The water temperature increase correction coefficient KTW is a value that increases as the cooling water temperature Tw decreases.

  In step 51, the target equivalent ratio TFBYA is calculated by the following equation using the water temperature increase correction coefficient KTW and the post-startup increase correction coefficient KAS.

TFBYA = 1 + KTW + KAS (3)
The target equivalent ratio TFBYA is a value centering on 1.0, and after the engine warm-up is completed, TFBYA = 1 (KTW = 0, KAS = 0), thereby obtaining a stoichiometric air-fuel mixture. . At the cold start, the post-startup increase correction coefficient KAS is added, so the target equivalent ratio TFBYA exceeds 1.0, because the fuel wall flow rate is taken into consideration. That is, at the time of cold start, the target equivalence ratio TFBYA exceeds 1.0, but the stoichiometric air-fuel mixture is obtained at the timing when the engine speed reaches the target speed NSET during idling. .

  FIG. 7 is for calculating the fuel injection pulse width Ti. The float of FIG. 6 is executed independently at regular time intervals (for example, every 100 ms). This flow is the same as the current situation.

  In FIG. 7, in step 61, the starting fuel injection pulse width Ti1 is calculated by the following equation.

Ti1 = TST × KNST × KTST (4)
Where TST: basic injection pulse width at start,
KNST: rotational speed correction coefficient,
KTST: Time correction coefficient,
Since the method of obtaining the basic injection pulse width TST, the rotational speed correction coefficient KNST, and the time correction coefficient KTST at the start is well known, detailed description thereof is omitted.

  In step 62, it is determined whether or not the output of the air flow meter 32 has been input. If the output of the air flow meter 32 is not input, the steps 63 and 64 are skipped and the routine proceeds to a step 65, where the starting fuel injection pulse width Ti1 is moved to the final fuel injection pulse width Ti.

  On the other hand, when the output of the air flow meter 32 is input, the process proceeds from step 62 to step 63, and the normal fuel injection pulse width Ti2 is calculated by the following equation using the target equivalent ratio TFBYA obtained from FIG.

Ti2 = (Tp × TFBYA + Kathos) × (α + αm−1) × 2 + Ts
... (5)
Where Tp: basic injection pulse width,
TFBYA: target equivalent ratio,
Kathos: Transient correction amount,
α: Air-fuel ratio feedback correction coefficient,
αm: air-fuel ratio learning value,
Ts: Invalid injection pulse width,
The basic injection pulse width Tp, transient correction amount Kathos, air-fuel ratio feedback correction coefficient α, air-fuel ratio learning value αm, and invalid injection pulse width Ts in equation (5) are well known. For example, the basic injection pulse width Tp is calculated by the following equation.

Tp = K × Qa / Ne (6)
Where Qa: the intake air amount calculated from the air flow meter 32,
The air / fuel ratio of the air-fuel mixture is set to the stoichiometric air / fuel ratio by the constant K in the equation (6). Therefore, while the post-startup increase correction coefficient KAS is a positive value exceeding zero, the fuel injection amount (fuel injection pulse width Ti) from the fuel injection valve 21 is corrected to be increased.

  The transient correction amount Kathos in the equation (5) is a value that is basically calculated based on the engine load, the rotational speed, and the temperature of the fuel adhering portion in consideration of the fuel wall flow rate of the intake port wall. It is considered that sometimes this transient correction amount Kathos works to increase the fuel injection amount by the amount deprived as the fuel wall flow of the intake port wall from the fuel injection amount. As a result, the air-fuel ratio is excessively leaned. This is because the calculation of the transient correction amount Kathos does not take into account changes in the intake pressure or the intake port flow velocity.

  In steps 64 to 66, the starting fuel injection pulse width Ti1 and the normal fuel injection pulse width Ti2 are compared, and the larger one is selected as the final fuel injection pulse width Ti.

  The post-startup increase correction coefficient KAS is used for fuel injection when the normal fuel injection pulse width Ti2 is adopted as the final fuel injection pulse width Ti. That is, in the present invention, it is assumed that the normal fuel injection pulse width Ti2 is larger than the starting fuel injection pulse width Ti1 immediately before the timing t5 in FIG.

  The fuel injection pulse width Ti calculated in this way is transferred to the output register, and when the predetermined fuel injection timing is reached, the fuel injection valves 21 of the respective cylinders are opened sequentially only during the pulse width Ti.

  The above description with reference to FIGS. 1 to 7 is actually the technical content of the prior invention (see Japanese Patent Application No. 2006-101497) that is the premise of the present invention, and the present invention is positioned as an improved invention of this prior invention. Is.

  Then, the part which changed with this invention with respect to the prior invention next is demonstrated.

  The flowchart of FIG. 9 is the first embodiment of the present invention, and replaces FIG. 5 of the prior invention.

  Although the prior invention has been described with respect to an engine that does not include both the variable valve lift mechanism 26 and the variable valve timing mechanism 27, the first embodiment of the present invention is directed to an engine that includes the variable valve timing mechanism 27. In addition, the thing provided with the variable valve lift mechanism 26 is not outside the scope of the present invention. When the variable valve timing mechanism 27 and the variable valve lift mechanism 26 are collectively referred to as “variable valve timing / lift mechanism”, both the mechanisms 27 and 26 are one aspect of the variable valve timing / lift mechanism.

  Now, in an engine equipped with a variable valve timing mechanism (hereinafter referred to as “VTC mechanism”) 27, the VTC mechanism 27 is operated during cold start, and the opening / closing timing of the intake valve 15 is set to the default position (when the VTC mechanism 27 is not operated). The position is moved to the advance side from the initial position to increase the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16. This is mainly due to the wall of the intake port 4 at the time of cold start using the blowback of high-temperature exhaust gas from the exhaust port that overlaps the open period of the intake valve 15 and the open period of the exhaust valve 16 to the intake port 4. This is to promote atomization of the fuel wall flow.

  However, when the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16 is increased to increase the amount of residual gas in the combustion chamber, fluctuations in combustion occur due to variations in the amount of residual gas in the combustion chamber, resulting in an idle rotation speed. Variations occur. When the fluctuation of the idle rotation speed occurs in this way, it becomes difficult to maintain the engine rotation speed at the target rotation speed NSET during idling.

  Therefore, in the first embodiment of the present invention, the engine combustion fluctuation amount is estimated on the premise of an engine that increases the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16 during cold start, and the estimation is performed. The combustion fluctuation amount is maintained near a predetermined threshold value. Here, as the threshold value, a limit value at which the combustion fluctuation amount should not increase is set in advance. Specifically, as shown in FIG. 8, after the timing t2 when the engine rotational speed Ne from the cranking reaches the target rotational speed at the time of idling, a variance value σPi of torque fluctuation is calculated (the amount of combustion fluctuation is calculated). And the ignition timing for promoting catalyst warm-up is retarded at a predetermined speed from the second ignition timing ADV2 until the calculated torque fluctuation variance σPi exceeds a predetermined threshold at the timing t6. In order to increase the temperature of the exhaust gas, further warm-up of the first catalyst 9 is promoted. When the combustion state becomes worse due to this retardation correction and the variance value σPi of torque fluctuation exceeds the threshold at the timing of t6, this time, the ignition timing for promoting catalyst warm-up is set to a predetermined speed based on the value immediately before t6. By correcting to the advance side, the combustion is improved and the idling rotational speed is stabilized, so that the variance value σPi of torque fluctuation falls below the threshold value. When the torque fluctuation variance σPi falls below the threshold value at the timing of t7 by this advance angle correction, the value immediately before t7 is corrected to the retard side again at a predetermined speed with reference to the value immediately before t7 to increase the temperature of the exhaust gas. The warm-up of the catalyst 9 is promoted.

  In FIG. 9, the differences from FIG. 5 of the prior invention will be mainly described. Steps 71 to 74 are newly added to FIG. 5 of the prior invention. That is, at step 71, the variance value σPi of torque fluctuation is compared with the threshold value. As the threshold value, a limit value is set in advance so that the variance value of the torque fluctuation cannot be increased any more. When the torque fluctuation variance σPi is less than the threshold value, it is determined that the combustion is stable, and the routine proceeds to step 72 where the ignition timing correction amount hAD1 is calculated by the following equation.

hAD1 = hAD1 (previous) −ΔAD1 (7)
Where ΔAD1 is a constant value,
hAD1 (previous): previous value of hAD1
Here, the predetermined value ΔAD1 in the equation (7) is a value for determining the retard amount per predetermined time of the ignition timing. The initial value of “hAD1 (previous)”, which is the previous value of the ignition timing correction amount, is set to zero. For this reason, if the torque fluctuation variance σPi continues to be less than the threshold value, that is, the ignition timing is retarded by the margin up to the threshold value to further promote catalyst warm-up, the ignition timing correction amount hAD1 is negative. It grows with the value of.

  On the other hand, when the variance value σPi of torque fluctuation is equal to or greater than the threshold value, it is determined that the combustion is unstable, the process proceeds from step 71 to step 72, and the ignition timing correction amount hAD1 is calculated by the following equation.

hAD1 = hAD1 (previous) + ΔAD2 (8)
Where ΔAD2: constant value,
hAD1 (previous): previous value of hAD1
Here, the predetermined value ΔAD2 in the equation (8) is a value that determines the advance amount per predetermined time of the ignition timing. The initial value of “hAD1 (previous)”, which is the previous value of the ignition timing correction amount, is set to zero. For this reason, if the torque fluctuation variance value σPi continues to be equal to or greater than the threshold value, that is, if the combustion value is unstable beyond the threshold value, the ignition timing is advanced to stabilize the combustion state. Increases with positive values.

  In step 73, a value obtained by adding the ignition timing correction amount hAD1 calculated in this way to the second ignition timing ADV2 is set as an ignition timing command value ADV. Since the unit of the ignition timing command value ADV is a crank angle measured from the compression top dead center, the retard correction amount is obtained if the ignition timing correction amount hAD1 is a negative value, and the ignition timing correction amount hAD1 is positive. If it is a value, it becomes an advance correction amount. That is, the ignition timing is gradually retarded if the torque fluctuation variance value σPi is less than the threshold value, and the ignition timing is gradually advanced if the torque fluctuation variance value σPi is the threshold value or more. Become.

  Since the torque fluctuation variance value σPi has a correlation (proportional relationship) with the misfire parameter MIC (average value thereof), it may be obtained in proportion to the misfire parameter MIC in another flow (not shown). Since the method for obtaining the misfire parameter MIC is detailed in Japanese Patent Laid-Open No. 9-68095, the description thereof is omitted here.

  Here, the effect of the first embodiment of the present invention will be described.

  First, the same effect as the prior invention will be described first.

  According to the first embodiment of the present invention (the invention described in claims 1 and 8), the ignition timing is set to the first ignition timing at the timing when the engine rotational speed Ne from the cranking reaches the target rotational speed NSET during idling. ADV1 (ignition timing for starting) is retarded stepwise from second ignition timing ADV2 (ignition timing for promoting catalyst warm-up) (see steps 26 and 32 in FIG. 5), and the engine speed Ne is idle. From the throttle valve position to the combustion chamber 5 so that the intake air amount necessary to maintain the engine rotation speed Ne at the target rotation speed NSET during idling is supplied to the combustion chamber 5 at the timing when the target rotation speed NSET is reached. In consideration of the response delay of the intake air amount of the engine, the timing before the predetermined period DT from the timing when the engine speed Ne reaches the target engine speed NSET during idling. Since the throttle valve 23 starts to open from the engine t1 (see steps 25, 26, 29, 30, and 31 in FIG. 5), the engine speed Ne is suppressed from being blown up after reaching the target speed NSET during idling. The exhaust temperature can be raised at an early stage (see the solid line at the bottom of FIG. 2), and the catalyst activation time can be shortened while suppressing wasteful fuel consumption.

  In this case, the intake pressure and the intake air flow velocity of the intake port 4 may continue to change for a while after the engine rotation speed Ne reaches the target rotation speed NSET during idling. The fuel wall flow rate at the intake port wall decreases with changes in the intake pressure and the intake air flow velocity of the intake port 4, and the amount of fuel supplied to the combustion chamber 5 is insufficient accordingly, and the air-fuel ratio of the air-fuel mixture in the combustion chamber Is over the combustion stability limit, resulting in an increase in HC and a drop in rotation from the target rotational speed NSET during idling. The first embodiment of the present invention (described in claims 1 and 8) According to the invention, starting from the timing at which the throttle valve 23 starts to be opened, the intake pressure or the intake flow velocity of the intake port 4 changes after the engine rotational speed Ne reaches the target rotational speed NSET during idling. The fuel injection amount from the fuel injection valve 21 is temporarily increased by using the post-startup increase correction coefficient KAS until the bundle is bundled (see steps 44, 45, and 51 in FIG. 6), so that the engine speed Ne is Even after the target rotational speed NSET at the time of idling is reached, the air-fuel ratio of the air-fuel mixture in the combustion chamber exceeds the combustion stability limit even if the intake pressure or the intake air flow velocity of the intake port 4 continues to decrease. Can be prevented. As a result, it is possible to suppress an increase in HC after the engine rotational speed Ne reaches the target rotational speed NSET during idling and a decrease in rotation from the target rotational speed NSET during idling (see the solid line in the seventh stage in FIG. 2).

  Next, the effect of the part which improved the prior invention is demonstrated.

  As a cause of the combustion fluctuation after the timing when the engine rotational speed Ne reaches the target rotational speed NSET at the time of idling, the variation in the residual gas amount in the combustion chamber due to the variation in the ignition timing for promoting the catalyst warm-up can be considered. According to the first embodiment of the present invention (the invention described in claims 1 and 8), a variance value σPi of the engine torque fluctuation is calculated (a combustion fluctuation amount is estimated), and the calculated torque fluctuation variance is calculated. Based on the value σPi, when the torque fluctuation variance value σPi is equal to or greater than the threshold value, the ignition timing for promoting catalyst warm-up is corrected to the advance side (see steps 26, 32, 71, 74, 73 in FIG. 9). Combustion fluctuations due to variations in the amount of residual gas in the combustion chamber due to variations in the ignition timing for promoting catalyst warm-up after the timing when the engine rotation speed has reached the target rotation speed during idling It can be suppressed.

  Further, when the engine torque fluctuation variance value σPi is less than the threshold after the timing when the engine rotation speed Ne reaches the idling target rotation speed NSET, the ignition timing for promoting catalyst warm-up is corrected to the retard side. (Refer to Steps 26, 32, 71, 72, and 73 in FIG. 9) The exhaust gas can be further heated, and warming up of the first catalyst 9 can be promoted.

  Next, the flowcharts of FIGS. 12A and 12B are for calculating the ignition timing command value, the throttle valve target opening, and the target VTC operating angle according to the second embodiment of the present invention. This replaces FIG. 9 of the embodiment. The same step numbers are assigned to the same parts as in FIG. 5 of the prior invention and FIG. 9 of the first embodiment.

  Now, after the start of the air-fuel ratio feedback control, it is considered that even if there is a variation in the residual gas amount in the combustion chamber due to the air-fuel ratio variation, it is considered that it has been eliminated by the air-fuel ratio feedback control. The cause of the combustion fluctuation is a variation in overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16, that is, a variation in the residual gas amount in the combustion chamber due to a variation in the opening / closing timing of the intake valve 15 by the VTC mechanism 27. It is also considered that there is variation in the amount of residual gas in the combustion chamber due to variation in ignition timing for promoting catalyst warm-up.

Therefore, in the second embodiment, the VTC mechanism 27 is operated during cold start so that the opening / closing timing of the intake valve 15 is moved from the default position to the initial position, and the intake valve 15 is opened and the exhaust valve 16 is opened. The following control is performed for an object whose period overlap is increased.
<1> After the timing at which the engine rotational speed reaches the target rotational speed during idling and after the start of air-fuel ratio feedback control, when the variance value σPi of torque fluctuation is equal to or greater than the threshold, the opening period of the intake valve 15 and the exhaust valve The VTC operating angle (command value given to the VTC mechanism 27) is corrected to the side where the overlap in the open period of 16 becomes smaller, or the ignition timing for promoting catalyst warm-up is corrected to the advanced side.
<2> By correcting the VTC operating angle so that the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16 becomes smaller, the VTC operating angle when the variance value σPi of torque fluctuation becomes less than the threshold value This is stored as a learning value 1 (first learning value), and the VTC operating angle is set to this learning value 1 at the start of the next cranking.
<3> By correcting the ignition timing for promoting catalyst warm-up to the advance side, the ignition timing for promoting catalyst warm-up when the variance value σPi of torque fluctuation becomes less than the threshold value is learned value 2 (second learning) Value)), and the ignition timing is calculated from the first ignition timing ADV1 (ignition timing for starting) at the timing when the engine rotation speed from the cranking reaches the target rotation speed during idling after the next cranking starts. Step by step to 2.
<4> Comparing the variation in the opening / closing timing of the intake valve 15 by the VTC mechanism 27 and the variation in the ignition timing for promoting catalyst warm-up, the opening / closing timing of the intake valve 15 by the VTC mechanism 27 is more likely to vary due to component variations and the like. . On the other hand, the variation in ignition timing for promoting catalyst warm-up is relatively small. Therefore, even if the VTC operating angle is corrected first and the VTC operating angle is corrected to the limit value, when the variance value σPi of the torque fluctuation is equal to or greater than the threshold value, the VTC operating angle is maintained at the limit value, and then the catalyst The ignition timing for promoting warm-up is corrected to the advance side.

  In the following, the above <1> and <3> will be described in detail with reference to FIG. 10, and the above <1> and <4> will be described in detail with reference to FIG.

  As shown in FIG. 10, if the variance value σPi of torque fluctuation exceeds the threshold at the timing t11 when the air-fuel ratio feedback control is started (see the third stage in FIG. 10), the opening period of the intake valve 15 and The side where the overlap of the open period of the exhaust valve 16 becomes smaller, that is, the VTC operating angle (command value given to the VTC mechanism 27) is gradually reduced to correct the opening / closing timing of the intake valve 15 (see FIG. 10). (Refer to the fourth stage) By reducing the amount of residual gas in the combustion chamber, the combustion can be stabilized. Then, since the variance value σPi of the torque fluctuation is less than the threshold value at the timing t12 (see the third stage in FIG. 10), the VTC operating angle (= A) at that time is maintained (see the fourth stage). The VTC operating angle at that time is stored as a learning value 1 (= A), and is used at the next engine start.

  The upper four stages of FIG. 10 show before learning of the VTC operating angle, while the lower two stages of FIG. 10 show after learning of the VTC operating angle. That is, after learning the VT operating angle, the VTC operating angle is set to the learning value 1 (= A) and cranking is started (see the bottom row in FIG. 10). As a result, assuming that the air-fuel ratio feedback control is started at the same timing t11 as before the learning of the VTC operating angle, the variance value σPi of the torque fluctuation remains below the threshold at the timing t11 after the learning of the VTC operating angle. (See the second row from the bottom of FIG. 10).

  On the other hand, FIG. 11 shows a case where the variance value σPi of the torque fluctuation does not fall below the threshold even though the VTC operating angle is reduced to the limit value (= a). Here, the limit value of the VTC operating angle is determined from a request to ensure a certain overlap for the exhaust request, and is adapted in advance. If the variance value σPi of torque fluctuation does not fall below the threshold at the timing of t14 when the VTC operating angle is reduced from the initial position (ROM setting initial value) to the limit value (see the third stage in FIG. 11), VTC operation is further performed. Since the angle cannot be reduced, information indicating that the VTC operating angle has been reduced to the limit value is stored. Then, while maintaining the VTC operating angle at the limit value from the timing of t14 (see the fourth stage in FIG. 11), this time, the ignition timing for promoting catalyst warm-up is gradually advanced from the second ignition timing ADV2. (Refer to the fifth stage in FIG. 11), the combustion is directed in a stable direction. In the figure, since the variance value σPi of torque fluctuation falls below the threshold value at the timing t15 (see the third stage in FIG. 11), the ignition timing (= B) for promoting catalyst warm-up at that time is the learning value 2 (= B) (refer to the fifth stage in FIG. 11), and will be used at the next engine start.

  The upper five stages in FIG. 11 show before learning of the ignition timing for promoting catalyst warm-up, while the lower three stages in FIG. 11 show after learning of the ignition timing for promoting catalyst warm-up. That is, after learning the ignition timing for promoting catalyst warm-up, the VTC operating angle is set to the limit value (= a) and cranking is started (see the second stage from the bottom of FIG. 11), and The ignition timing is switched from the first ignition timing ADV1 to the learning value 2 (= B), which is the ignition timing for promoting catalyst warm-up, at the timing t2 when the engine rotation speed reaches the target rotation speed NSET during idling (maximum in FIG. 11). See below). Since the combustion stability is improved by such control, if the air-fuel ratio feedback control is started at the same timing t11 as that before learning the ignition timing for promoting catalyst warm-up, after learning the ignition timing for promoting catalyst warm-up The torque variation variance σPi falls below the threshold at the timing of t11 (see the third row from the bottom of FIG. 11).

  In FIG. 12A and FIG. 12B, the part different from FIG. 5 of the prior invention will be mainly described. When the target attainment flag = 1, after the operation of step 32 is performed, FIG. Proceed to Steps 81 to 87 will be described later.

In FIG. 12B, in step 88, it is determined whether or not the feedback control of the air-fuel ratio has started. If the O ₂ sensor 35 is not activated, it is determined that the air-fuel ratio feedback control is started, and the operations of steps 33 and 34 are executed in the same manner as in the prior invention.

If the O ₂ sensor 35 is activated, it is determined that the feedback control of the air-fuel ratio has started, and the routine proceeds from step 88 to step 89 where the torque fluctuation variance value σPi is compared with the threshold value. Since the variance value σPi of the torque fluctuation has a correlation (proportional relationship) with the misfire parameter MIC (average value thereof), it may be obtained in proportion to the misfire parameter MIC in another flow as in the first embodiment. . When the variance value σPi of the torque fluctuation is equal to or greater than the threshold value, it is determined that the combustion is unstable, and the process proceeds to step 90 and subsequent steps, and the target VTC operating angle tVTC is gradually reduced within the range up to the limit value a. By reducing the overlap between the open period of the valve 15 and the open period of the exhaust valve 16, the combustion is stabilized. For this purpose, first, at step 90, it is checked whether or not the VTC limit flag (initially set to zero at the time of factory shipment) = 1, and at step 91 whether or not the target VTC operating angle tVTC has reached the limit value a. Now, assuming that the VTC limit flag = 0 and the target VTC operating angle tVTC is greater than the limit value a and has not reached the limit value a, the routine proceeds to step 92, where the VTC operating angle decrease correction amount hVTC is set to the next. In step 93, a value obtained by subtracting the VTC operating angle decrease correction amount hVTC from the initial value of the VTC operating angle is set as a target VTC operating angle tVTC. In step 94, the second ignition timing ADV2 is set as an ignition timing command. Move to the value ADV.

hVTC = hVTC (previous) + ΔVTC (9)
Where ΔVTC: constant value,
hVTC (previous): previous value of hVTC,
Here, the predetermined value ΔVTC in the equation (9) is a value that determines the amount of decrease in the VTC operating angle per predetermined time. The initial value of “hVTC (previous)”, which is the previous value of the decrease correction amount of the VTC operating angle, is set to zero. Therefore, if the torque fluctuation variance value σPi continues to be equal to or greater than the threshold value, that is, if the combustion value is unstable beyond the threshold value, the VTC operating angle is decreased to open the intake valve 15 and the exhaust valve 16. In order to reduce the overlap and stabilize the combustion state, the VTC operating angle decrease correction amount hVTC increases with a positive value, and the target VTC operating angle tVTC decreases and approaches the limit value a. go.

  The initial value of the VTC operating angle is a value set in advance in order to increase the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16 from the start of cranking.

  When the variance value σPi of the torque fluctuation becomes less than the threshold value due to the correction of the decrease in the VTC operating angle, the process proceeds from step 89 to step 95, and the VTC limit flag is checked. Here, before the target VTC operating angle tVTC reaches the limit value a, the variance value σPi of the torque fluctuation is below the threshold value, so that the VTC limit flag = 0. For this reason, the process proceeds from step 95 to step 96, where the value of the VTC operating angle decrease correction amount hVTC (the value obtained in the previous step 92) is stored in a predetermined memory as a decrease correction amount learning value. In 97, a learned flag 1 = 1 is set to indicate that the reduction correction amount of the VTC operating angle has been learned. The value of this learned flag 1 is stored in an EEPROM or the like so as not to disappear even after the engine is stopped. In step 98, a value obtained by subtracting the decrease correction amount learning value from the initial value of the VTC operating angle is set as the target VTC operating angle tVTC. In step 99, the second ignition timing ADV2 is shifted to the ignition timing command value ADV.

  On the other hand, when the target variation VTC operation angle tVTC is less than or equal to the limit value a while the variance value σPi of torque fluctuation does not fall below the threshold value, the routine proceeds from step 91 to step 100, where the target VTC operation angle tVTC is reduced to the limit value a. In order to represent that the VTC limit flag is set to 1, the target VTC operating angle tVTC is set to the limit value a in step 101.

  In step 102, the ignition timing advance correction amount hAD2 is calculated by the following equation, and the ignition timing advance amount hAD2 thus calculated in step 103 is added to the second ignition timing ADV2 to determine the ignition timing. The command value is ADV.

hAD2 = hAD2 (previous) + ΔAD2 (10)
Where ΔAD2: constant value,
hAD2 (previous): previous value of hAD2,
Here, the predetermined value ΔAD2 in the equation (10) is a value that determines the advance amount per predetermined time of the ignition timing. The initial value of “hAD2 (previous)”, which is the previous value of the ignition timing advance correction amount, is set to zero. For this reason, if the state where the variance value σPi of the torque fluctuation continues to be equal to or greater than the threshold value, that is, if the combustion value is unstable beyond the threshold value, the ignition timing is advanced to stabilize the combustion state. The amount hAD1 increases with a positive value, and the ignition timing for promoting catalyst warm-up is gradually advanced from the second ignition timing ADV2.

  When the variance value σPi of the torque fluctuation becomes less than the threshold value due to the advance correction of the ignition timing for promoting the catalyst warm-up, the process proceeds from step 89 to step 95, where the VTC limit flag is checked. Here, after the target VTC operating angle tVTC reaches the limit value a, the variation value σPi of torque fluctuation is less than the threshold value due to the advance correction of the ignition timing for promoting catalyst warm-up, so the VTC limit flag = 1. It has become. For this reason, the routine proceeds from step 95 to step 104, where the value of the advance angle correction amount hADV of the ignition timing for promoting catalyst warm-up at that time (previously obtained in step 102) is used as the advance angle correction amount learning value. In step 105, a learned flag 2 = 1 is set in step 105 to indicate that the advance correction amount hADV of the ignition timing for promoting catalyst warm-up has been learned. The value of the learned flag 2 is also stored in an EEPROM or the like so as not to disappear after the engine is stopped. In step 106, the value obtained by adding the advance correction amount learning value to the second ignition timing ADV2 is set as the ignition timing command value ADV. In step 106, the target VTC operating angle tVTC is set to the limit value a.

  When the next engine operation is started, FIG. 12A is started. In this case, when the ignition switch is switched from OFF to ON, the process proceeds to Steps 81 and 82. Therefore, each value of the learned flag 1 and the learned flag 2 stored in the EEPROM or the like is checked. When the learned flag 1 = 0 and the learned flag 2 = 0, in step 85, the initial value of the VTC operating angle is set as the target VTC operating angle tVTC. Although this operation is not shown in FIG. 9 of the first embodiment, it is the same as the first embodiment.

  On the other hand, when the learned flag 1 = 1, the routine proceeds from step 81 to step 83, where a value obtained by subtracting the decrease correction amount learning value from the initial value of the VTC operating angle is set as the target VTC operating angle tVTC. Compared with FIG. 10, a value obtained by subtracting the decrease correction amount learning value from the initial value of the VTC operating angle corresponds to the learning value 1 (= A). When the learned flag 1 = 0 and the learned flag 2 = 1, the process proceeds from step 81 or 82 to step 84, where the limit value a is set as the target VTC operating angle tVTC.

  Thereafter, when the target achievement flag = 1, the routine proceeds from step 26 to step 86, where the value of the learned flag 2 stored in the EEPROM or the like is examined. When the learned flag 2 = 0, the operation of step 32 is executed and then the process proceeds to FIG.

  On the other hand, when the learned flag 2 = 1, the routine proceeds from step 86 to step 87, where the value obtained by adding the advance correction amount learning value to the second ignition timing ADV2 is set as the ignition timing command value ADV. Compared to FIG. 11, the value obtained by adding the advance correction amount learning value to the second ignition timing ADV2 corresponds to the learning value 2 (= B).

  Here, the effect of 2nd Embodiment is demonstrated.

  After the start of air-fuel ratio feedback control, it is considered that even if there is a variation in the amount of residual gas in the combustion chamber due to the variation in air-fuel ratio, it is considered that it has been eliminated by the air-fuel ratio feedback control. Is caused by the variation in the overlap between the opening period of the intake valve 15 and the opening period of the exhaust valve 16, that is, the variation in the residual gas amount in the combustion chamber due to the variation in the opening / closing timing of the intake valve 15 by the VTC mechanism 27, or It is considered that there is variation in the amount of residual gas in the combustion chamber due to variation in the second ignition timing ADV2 (ignition timing for promoting catalyst warm-up).

  In this case, according to the second embodiment (the invention described in claims 2 and 9), the variance value σPi of the engine torque fluctuation is calculated (estimating the fluctuation quantity of combustion), and the engine speed Ne is idle. When the calculated torque fluctuation variance σPi is equal to or greater than the threshold after the start of the air-fuel ratio feedback control after the time when the target rotational speed NSET is reached, the intake valve 15 open period and the exhaust valve 16 open period are over. Since the VTC operating angle (command value given to the variable valve timing / lift mechanism) is corrected to the side where the lap becomes smaller, or the ignition timing for promoting catalyst warm-up is corrected to the advance side (step of FIG. 12B) 88 to 94, 100 to 103), due to variations in the opening / closing timing of the intake valve 15 by the VTC mechanism 27 and variations in the ignition timing for promoting catalyst warm-up. It is possible to suppress fluctuations in combustion associated with variations in the amount of residual gas in the combustion chamber.

  In addition, when the variation in the opening / closing timing of the intake valve 15 by the VTC mechanism 27 is compared with the variation in the ignition timing for promoting catalyst warm-up, the opening / closing timing of the intake valve 15 by the VTC mechanism 27 is more likely to vary due to component variations. On the other hand, the variation in ignition timing for promoting catalyst warm-up is relatively small. According to the second embodiment (the invention described in claims 5 and 12), as the first step, the VTC operating angle (the command value given to the variable valve timing / lift mechanism), which has the larger variation, is corrected first. Further, since the ignition timing for promoting catalyst warm-up, which has a smaller variation, is corrected later, it is possible to stabilize combustion more effectively.

  Next, the flowchart of FIG. 15 is a third embodiment, which replaces FIG. 7 of the prior invention, the first and second embodiments. The same step numbers are assigned to the same parts as those in FIG. 7 of the prior invention, the first and second embodiments.

  The third embodiment is based on the second embodiment. That is, according to the second embodiment, in the control after the start of the engine operation this time, by correcting the ignition timing for promoting catalyst warm-up to the advance side while maintaining the VTC operating angle at the limit value, the dispersion of torque fluctuations Since the advance angle correction amount has already been learned for the ignition timing for promoting catalyst warm-up when the value σPi is less than the threshold value, the VTC operating angle is set to the limit value at the start of the next cranking, and After the cranking is started, the ignition timing is learned from the first ignition timing ADV1 (starting ignition timing) to the second ignition timing ADV2 at the timing when the engine rotation speed from the cranking reaches the target rotation speed during idling. The value is retarded stepwise to the value obtained by adding the values (that is, the learning value 2). Then, after that, that is, the ignition timing is stepped from the first ignition timing ADV1 (starting ignition timing) to the second ignition timing ADV2 plus the advance correction amount learning value (that is, the learning value 2). If combustion fluctuation occurs again after retarding and before starting the subsequent air-fuel ratio feedback control, it can be specified that the cause of the combustion fluctuation is the variation in the air-fuel ratio.

  Therefore, in the third embodiment, the catalyst warm-up promotion is performed when the variance value σPi of the torque fluctuation becomes less than the threshold value by correcting the ignition timing for promoting the catalyst warm-up to the advance side after the start of the engine operation this time. Is stored as an advance correction amount learning value, and the VTC operating angle is set to the limit value at the start of the next cranking, and the engine speed from the cranking is idle after the start of the cranking. The ignition timing is changed from the first ignition timing ADV1 (starting ignition timing) to the second ignition timing ADV2 by adding the advance correction amount learning value (that is, the learning value 2) at the timing when the target rotational speed is reached. After the retardation in steps and before the start of the subsequent air-fuel ratio feedback control, when the variance value σPi of torque fluctuation is equal to or greater than the threshold value, the air-fuel ratio is corrected to the rich side. is there.

  Specifically, as shown in FIG. 13, when the next cranking starts, the VTC operating angle is set to the limit value (= a) at the timing of t0 and cranking is started, and the engine speed Ne from the cranking is started. Although the ignition timing for promoting catalyst warm-up is switched from the first ignition timing ADV1 to the learning value 2 (= B) at the timing t2 when the engine reaches the target rotational speed during idling, the torque fluctuation dispersion value σPi Therefore, in the period after the timing t2 and before the start of the air-fuel ratio feedback control, the air-fuel ratio is corrected to the rich side, that is, the fuel injection pulse width is increased and the combustion is stabilized. Dodge. Since the variance value σPi of torque fluctuation falls below the threshold value at the timing t17 before the start of the air-fuel ratio feedback control (see the fourth stage in FIG. 13), the fuel injection pulse width at that time (for example, C) is maintained. At the same time, the fuel injection pulse width (= C) at that time is stored as a learning value 3 (third learning value) and used at the next engine start.

  FIG. 13 shows the operation before learning of the fuel injection pulse width, while FIG. 14 shows the operation after learning of the fuel injection pulse width, that is, from the start of the next next cranking. That is, after learning the fuel injection pulse width, the fuel injection pulse width is set to the learning value 3 (= C) at the timing t2 when the engine rotational speed from cranking reaches the target rotational speed during idling (FIG. 14). See bottom row). By such control, even if there is a variation in the air-fuel ratio, deterioration of combustion fluctuation due to the variation in the residual gas amount in the combustion chamber due to the variation in the air-fuel ratio is suppressed, so t18 before starting the air-fuel ratio feedback control At this timing, the variance value σPi of torque fluctuation is below the threshold value (see the fourth row in FIG. 14).

  In FIG. 15, the part different from FIG. 7 of the prior invention and the first and second embodiments will be mainly described. If the target arrival flag = 0, the current process is terminated.

  When the target attainment flag = 1, the routine proceeds to step 112 where the learned flag 3 is viewed. The learned flag 3 is initially set to zero at the time of shipment from the factory. Here, if the learned flag 3 = 0, the process proceeds to steps 113 and 114, and the value of the learned flag 2 stored in the EEPROM or the like (set and stored in step 105 in FIG. 12B). ) And whether or not it is before the start of air-fuel ratio feedback control is determined. When the learned flag 2 = 0 or after the start of air-fuel ratio feedback control, the current process is terminated.

  When the learned flag 2 = 1 and before the start of air-fuel ratio feedback control, the routine proceeds to step 115, where the torque fluctuation dispersion value σPi is compared with the threshold value. When the variance value σPi of the torque fluctuation is equal to or greater than the threshold value, it is determined that the combustion is unstable and the cause is the variation in the air-fuel ratio, and the routine proceeds to step 116 where the fuel injection pulse width increase correction amount hTi is calculated by the following equation. In step 117, a value obtained by adding the fuel injection pulse width increase correction amount hTi to the normal fuel injection pulse width Ti2 is set as the fuel injection pulse width Ti.

hTi = hTi (previous) + ΔTi (11)
Where ΔTi is a constant value,
hTi (previous): previous value of hTi,
Here, the predetermined value ΔTi in the equation (11) is a value that determines the amount of increase in the fuel injection pulse width per predetermined time. Zero is set in the initial value of “hTi (previous)” which is the previous value of the increase correction amount of the fuel injection pulse width. For this reason, if the variance value σPi of the torque fluctuation continues to be equal to or greater than the threshold, that is, if the combustion exceeds the threshold and the combustion is unstable, the fuel injection pulse width is increased to stabilize the combustion state. The increase correction amount hTi increases with a positive value. That is, by correcting the air-fuel ratio to the rich side, the combustion is stabilized.

  When the variation value σPi of torque fluctuation becomes less than the threshold value due to the increase correction of the fuel injection pulse width after the target arrival flag = 1, the routine proceeds from step 115 to step 118, where the fuel injection pulse width increase correction amount hTi. (Previously obtained in step 116) is stored in a predetermined memory as an increase correction amount learning value, and in step 119, the learned flag 3 = in order to indicate that the increase correction amount of the fuel injection pulse width has been learned. Set to 1. The value of this learned flag 3 is stored in an EEPROM or the like so as not to disappear even after the engine is stopped. In step 120, a value obtained by adding the increase correction amount learning value to the normal fuel injection pulse width Ti2 is set as the fuel injection pulse width Ti. Compared with FIG. 13, a value obtained by adding the increase correction amount learned value to the normal fuel injection pulse width Ti <b> 2 corresponds to the learned value 3.

  With the learned flag 3 = 1, after the next cranking starts, the routine proceeds from step 112 to step 121, where the value obtained by adding the increase correction amount learning value to the normal fuel injection pulse width Ti2 is set as the fuel injection pulse width Ti.

  Here, the function and effect of the third embodiment will be described.

  According to the third embodiment (the inventions described in claims 6 and 13), the variance value σPi (estimated combustion fluctuation amount) of torque fluctuation is obtained by correcting the ignition timing for promoting catalyst warm-up to the advance side. The advance correction amount of the ignition timing for promoting catalyst warm-up when it becomes less than the threshold value is stored as an advance correction amount learning value, and the VTC operating angle is set to a limit value at the start of the next cranking, and the After the cranking starts, the ignition timing for promoting catalyst warm-up is changed from the first ignition timing ADV1 (starting ignition timing) to the second ignition timing ADV2 at the timing when the engine rotation speed from the cranking reaches the target rotation speed during idling. The torque fluctuation variance σPi is greater than or equal to the threshold value after stepwise delaying to a value obtained by adding the advance correction amount learning value to (ie, learning value 2) and before starting the subsequent air-fuel ratio feedback control. Since the fuel injection pulse width is corrected to the increase side (the air-fuel ratio is corrected to the rich side) (see steps 111 to 117 in FIG. 15), it accompanies the variation in the residual gas amount in the combustion chamber due to the variation in the air-fuel ratio. The deterioration of combustion fluctuation can also be suppressed.

  According to the third embodiment (the invention described in claims 7 and 14), the torque fluctuation is corrected by correcting the fuel injection pulse width to the increase side (correcting the air-fuel ratio to the rich side) after the start of the next cranking. Is stored as an increase correction amount learning value, and the VTC operating angle is set to a limit value at the start of the next next cranking. In addition, after the cranking starts, the ignition timing is advanced from the first ignition timing ADV1 (starting ignition timing) to the second ignition timing ADV2 at a timing when the engine rotation speed from the cranking reaches the target rotation speed at the time of idling. The fuel injection pulse width is set after stepwise retarding to a value obtained by adding the correction amount learning value (that is, the second learning value) and before starting the subsequent air-fuel ratio feedback control. Since the fuel injection pulse width Ti2 is always set to a value obtained by adding the increase correction amount learning value (that is, the air-fuel ratio is set to the learning value 3) (see steps 112 and 121 in FIG. 15), At the start of cranking, the VTC operating angle is set to a limit value, and after the cranking is started, the ignition timing is set to the first ignition timing ADV1 (starting timing) at the timing when the engine rotational speed from the cranking reaches the target rotational speed at the time of idling. Ignition timing) to the second ignition timing ADV2 to which the advance correction amount learning value is added (that is, the second learning value) is retarded in a stepwise manner and before the start of the subsequent air-fuel ratio feedback control. It is possible to suppress the deterioration of combustion fluctuation due to the variation in the amount of residual gas in the combustion chamber due to the variation in the air-fuel ratio.

  The ignition timing retardation processing procedure according to claim 1 is performed by steps 26, 32, and 33 in FIG. 5, and the intake air amount supply processing procedure is performed by steps 25, 26, 29, 30, and 31 in FIG. The increase processing procedure is performed by steps 44, 45, and 51 in FIG. 6, the combustion fluctuation amount estimation processing procedure is performed by step 71 in FIG. 9, and the ignition timing correction processing procedure is performed by steps 71, 74, and 73 in FIG. Yes.

  The ignition timing retarding processing procedure according to claim 2 is performed by steps 26, 32, and 33 in FIG. 5, and the intake air amount supply processing procedure is performed by steps 25, 26, 29, 30, and 31 in FIG. 6 is performed in steps 44, 45, and 51 in FIG. 6, the combustion variation estimation process procedure is performed in step 89 in FIG. 12B, and the command value / ignition timing correction process procedure is performed in steps 89 to 94, 100 in FIG. ˜103, respectively.

  The function of the ignition timing retarding means according to claim 8 is performed by steps 26, 32, 33 of FIG. 5, and the function of the intake air amount supplying means is performed by steps 25, 26, 29, 30, 31 of FIG. The function of the injection amount increasing means is based on steps 44, 45 and 51 in FIG. 6, the function of the combustion fluctuation amount estimating means is based on step 71 in FIG. 9, and the function of the ignition timing correcting means is based on steps 71, 74 and 73 in FIG. Each has been fulfilled.

The function of the ignition timing retarding means according to claim 9 is performed by steps 26, 32, 33 of FIG. 5, and the function of the intake air amount supplying means is performed by steps 25, 26, 29, 30, 31 of FIG. The function of the injection amount increasing means is in steps 44, 45 and 51 of FIG. 6, the function of the combustion fluctuation amount estimating means is in step 89 of FIG. 12B, and the function of the command value / ignition timing correcting means is in step of FIG. 89 to 94 and 100 to 103, respectively.

The schematic block diagram of the control apparatus of the engine of prior invention. The wave form diagram for demonstrating the effect | action of a prior invention compared with the present control. The wave form diagram for demonstrating the control method of prior invention. The flowchart for demonstrating the setting of two flags of prior invention. The flowchart for demonstrating calculation of the ignition timing command value and throttle valve target opening of a prior invention. The flowchart for demonstrating calculation of the target equivalent ratio of a prior invention. The flowchart for demonstrating calculation of the fuel-injection pulse width of a prior invention. The wave form diagram for demonstrating the effect | action of 1st Embodiment of this invention. The flowchart for demonstrating calculation of the ignition timing command value and throttle valve target opening of 1st Embodiment of this invention. The wave form diagram for demonstrating the effect | action of 2nd Embodiment. The wave form diagram for demonstrating the effect | action of 2nd Embodiment. The flowchart for demonstrating calculation of the ignition timing command value of 2nd Embodiment, the throttle valve target opening, and the target VTC operating angle. The flowchart for demonstrating calculation of the ignition timing command value of 2nd Embodiment, the throttle valve target opening, and the target VTC operating angle. The wave form diagram for demonstrating the effect | action of 3rd Embodiment. The wave form diagram for demonstrating the effect | action of 3rd Embodiment. The flowchart for demonstrating calculation of the fuel-injection pulse width of 3rd Embodiment.

Explanation of symbols

5 Combustion chamber 9 First catalyst 14 Spark plug 21 Fuel injection valve 23 Throttle valve 27 VTC mechanism (variable valve timing / lift mechanism)
31 Engine controller 33, 34 Crank angle sensor 36 Starter switch 37 Water temperature sensor

Claims (14)

In an engine provided with a catalyst in the exhaust passage and a fuel injection valve for injecting fuel in the intake passage,
Ignition timing retarding procedure that retards the ignition timing step by step from the ignition timing for starting to the ignition timing for promoting catalyst warm-up when the engine speed from cranking reaches the target rotational speed at idle When,
When the engine speed is at idle, the intake air amount necessary to maintain the engine speed at the target speed at idling is supplied to the combustion chamber when the engine speed reaches the target speed at idling. Intake air amount supply processing procedure for starting to open the throttle valve a predetermined period before the timing of reaching the target rotational speed of
The fuel injection from the fuel injection valve starts from the timing at which the throttle valve begins to open until the change in the intake pressure or the intake air flow velocity at the intake port converges after the engine rotational speed reaches the target rotational speed during idling. A fuel injection amount increase processing procedure for temporarily increasing the amount;
A combustion fluctuation amount estimation processing procedure for estimating the combustion fluctuation amount of the engine;
An ignition timing correction processing procedure that corrects the ignition timing for promoting catalyst warm-up based on the estimated amount of combustion fluctuation. In addition to the catalyst in the exhaust passage and the fuel injection valve that injects fuel in the intake passage, it also has a variable valve timing and lift mechanism that can variably control the opening and closing timing of the intake valve. In the engine that sets the command value to be given to this variable valve timing and lift mechanism so that the overlap of the open period of the exhaust valve becomes large,
Ignition timing retarding procedure that retards the ignition timing step by step from the ignition timing for starting to the ignition timing for promoting catalyst warm-up when the engine speed from cranking reaches the target rotational speed at idle When,
When the engine speed is at idle, the intake air amount necessary to maintain the engine speed at the target speed at idling is supplied to the combustion chamber when the engine speed reaches the target speed at idling. Intake air amount supply processing procedure for starting to open the throttle valve a predetermined period before the timing of reaching the target rotational speed of
The fuel injection from the fuel injection valve starts from the timing at which the throttle valve begins to open until the change in the intake pressure or the intake air flow velocity at the intake port converges after the engine rotational speed reaches the target rotational speed during idling. A fuel injection amount increase processing procedure for temporarily increasing the amount;
A combustion fluctuation amount estimation processing procedure for estimating the combustion fluctuation amount of the engine;
After the timing when the engine rotational speed reaches the target rotational speed during idling, the intake valve is set so as to increase when cranking starts when the estimated combustion fluctuation amount is greater than or equal to the threshold value after the start of air-fuel ratio feedback control. A command value for correcting the command value given to the variable valve timing / lift mechanism to the side where the overlap between the open period and the open period of the exhaust valve becomes smaller or to correct the ignition timing for promoting catalyst warm-up to the advance side An engine control method comprising: an ignition timing correction processing procedure.   By correcting the command value given to the variable valve timing / lift mechanism on the side where the overlap between the opening period of the intake valve and the opening period of the exhaust valve becomes smaller, the estimated combustion fluctuation amount becomes less than a threshold value. A command value to be given to the variable valve timing / lift mechanism is stored as a first learning value, and a command value to be given to the variable valve timing / lift mechanism at the start of the next cranking is set to the first learning value. The engine control method according to claim 2.   The ignition timing for promoting catalyst warm-up is stored as a second learning value when the estimated combustion fluctuation amount becomes less than a threshold value by correcting the ignition timing for promoting catalyst warm-up to an advance side. After the next cranking starts, the ignition timing is retarded stepwise from the starting ignition timing to the second learning value at the timing when the engine rotational speed from the cranking reaches the target rotational speed at idling. The engine control method according to claim 2, wherein:   When the command value to be given to the variable valve timing and lift mechanism is corrected first, and the command value to be given to the variable valve timing and lift mechanism is corrected to a limit value, the estimated combustion fluctuation amount is not less than a threshold value. The engine control method according to claim 2, wherein the ignition timing for promoting catalyst warm-up is corrected to an advance side.   The ignition timing for promoting catalyst warm-up is stored as a second learning value when the estimated combustion fluctuation amount becomes less than a threshold value by correcting the ignition timing for promoting catalyst warm-up to an advance side. The command value to be given to the variable valve timing / lift mechanism at the start of the next cranking is set to the limit value, and the timing at which the engine speed from the cranking reaches the target speed at the time of idling after the cranking starts. After the ignition timing is retarded stepwise from the starting ignition timing to the second learning value and before the subsequent air-fuel ratio feedback control is started, if the estimated combustion fluctuation amount is greater than or equal to the threshold value, The engine control method according to claim 5, wherein the fuel ratio is corrected to a rich side.   By correcting the air-fuel ratio to the rich side, the air-fuel ratio when the estimated combustion fluctuation amount becomes less than a threshold value is stored as a third learning value, and the variable valve is stored at the next next cranking start time. The command value to be given to the timing / lift mechanism is set to the limit value, and after the cranking starts, the ignition timing is changed from the starting ignition timing at the timing when the engine rotation speed from the cranking reaches the target rotation speed during idling. The engine according to claim 6, wherein the air-fuel ratio is set to the third learning value after stepwise retarding to the second learning value and before starting the subsequent air-fuel ratio feedback control. Control method. In an engine provided with a catalyst in the exhaust passage and a fuel injection valve for injecting fuel in the intake passage,
Ignition timing retarding means for retarding the ignition timing step by step from the ignition timing for starting to the ignition timing for promoting catalyst warm-up when the engine speed from cranking reaches the target rotational speed at idle ,
When the engine speed is at idle, the intake air amount necessary to maintain the engine speed at the target speed at idling is supplied to the combustion chamber when the engine speed reaches the target speed at idling. Intake air amount supply means for starting to open the throttle valve a predetermined period before the timing to reach the target rotational speed of
The fuel injection from the fuel injection valve starts from the timing at which the throttle valve begins to open until the change in the intake pressure or the intake air flow velocity at the intake port converges after the engine rotational speed reaches the target rotational speed during idling. Fuel injection amount increasing means for temporarily increasing the amount;
Combustion fluctuation amount estimating means for estimating the engine combustion fluctuation amount;
An engine control device comprising: ignition timing correction means for correcting the ignition timing for promoting catalyst warm-up based on the estimated combustion fluctuation amount. In addition to the catalyst in the exhaust passage and the fuel injection valve that injects fuel in the intake passage, it also has a variable valve timing and lift mechanism that can variably control the opening and closing timing of the intake valve. In the engine that sets the command value to be given to this variable valve timing and lift mechanism so that the overlap of the open period of the exhaust valve becomes large,
Ignition timing retarding means for retarding the ignition timing step by step from the ignition timing for starting to the ignition timing for promoting catalyst warm-up when the engine speed from cranking reaches the target rotational speed at idle ,
When the engine speed is at idle, the intake air amount necessary to maintain the engine speed at the target speed at idling is supplied to the combustion chamber when the engine speed reaches the target speed at idling. Intake air amount supply means for starting to open the throttle valve a predetermined period before the timing to reach the target rotational speed of
The fuel injection from the fuel injection valve starts from the timing at which the throttle valve begins to open until the change in the intake pressure or the intake air flow velocity at the intake port converges after the engine rotational speed reaches the target rotational speed during idling. Fuel injection amount increasing means for temporarily increasing the amount;
Combustion fluctuation amount estimating means for estimating the engine combustion fluctuation amount;
After the timing when the engine rotational speed reaches the target rotational speed during idling, the intake valve is set so as to increase when cranking starts when the estimated combustion fluctuation amount is greater than or equal to the threshold value after the start of air-fuel ratio feedback control. A command value for correcting the command value given to the variable valve timing / lift mechanism to the side where the overlap between the open period and the open period of the exhaust valve becomes smaller or to correct the ignition timing for promoting catalyst warm-up to the advance side An engine control device comprising ignition timing correction means.   By correcting the command value given to the variable valve timing / lift mechanism on the side where the overlap between the opening period of the intake valve and the opening period of the exhaust valve becomes smaller, the estimated combustion fluctuation amount becomes less than a threshold value. A command value to be given to the variable valve timing / lift mechanism is stored as a first learning value, and a command value to be given to the variable valve timing / lift mechanism at the start of the next cranking is set to the first learning value. The engine control device according to claim 9.   The ignition timing for promoting catalyst warm-up is stored as a second learning value when the estimated combustion fluctuation amount becomes less than a threshold value by correcting the ignition timing for promoting catalyst warm-up to an advance side. After the next cranking starts, the ignition timing is retarded stepwise from the starting ignition timing to the second learning value at the timing when the engine rotational speed from the cranking reaches the target rotational speed at idling. The engine control device according to claim 9, wherein:   When the command value to be given to the variable valve timing and lift mechanism is corrected first, and the command value to be given to the variable valve timing and lift mechanism is corrected to a limit value, the estimated combustion fluctuation amount is not less than a threshold value. The engine control device according to claim 9, wherein the ignition timing for promoting catalyst warm-up is corrected to an advance side.   The ignition timing for promoting catalyst warm-up is stored as a second learning value when the estimated combustion fluctuation amount becomes less than a threshold value by correcting the ignition timing for promoting catalyst warm-up to an advance side. The command value to be given to the variable valve timing / lift mechanism at the start of the next cranking is set to the limit value, and the timing at which the engine speed from the cranking reaches the target speed at the time of idling after the cranking starts. After the ignition timing is retarded stepwise from the starting ignition timing to the second learning value and before the subsequent air-fuel ratio feedback control is started, if the estimated combustion fluctuation amount is greater than or equal to the threshold value, The engine control device according to claim 12, wherein the fuel ratio is corrected to a rich side.   By correcting the air-fuel ratio to the rich side, the air-fuel ratio when the estimated combustion fluctuation amount becomes less than a threshold value is stored as a third learning value, and the variable valve is stored at the next next cranking start time. The command value given to the timing / lift mechanism is set to the above limit value, and the ignition timing is changed from the ignition timing for starting at the timing when the engine speed from cranking reaches the target speed at idling after the cranking starts. The engine according to claim 13, wherein the air-fuel ratio is set to the third learning value after stepwise retarding to the second learning value and before starting the subsequent air-fuel ratio feedback control. Control device.