JP2004197704A - Engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the worsening of combustion during restoring fuel cut due to inactive gas residing in a combustion chamber during sudden deceleration. <P>SOLUTION: This engine control device for performing fuel cut when authorized conditions are established and then for resuming fuel supply when the conditions of restoring the fuel cut are established, comprises combustion improving means 31, 13, 14 for improving the conditions of combustion in the combustion chamber during restoring the fuel cut when the rate or amount of remaining gas in the combustion chamber at or right before starting the fuel cut is a specified value or more and the fuel cut is performed during sudden deceleration. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an engine (internal combustion engine), and more particularly to control during deceleration.
[0002]
[Prior art]
When the engine is decelerated, for example, when the intake throttle valve is fully closed and the rotational speed of the engine is higher than a first predetermined value, the fuel supply is stopped (hereinafter referred to as "fuel cut") to improve fuel efficiency. After that, when the engine rotation speed decreases and becomes equal to or less than the second predetermined value, the fuel supply is restarted assuming that the condition for returning from the fuel cut is satisfied. There is one in which an EGR (exhaust gas recirculation) valve is opened at the time of fuel cut and the EGR valve is closed before resuming fuel supply (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-11-101144
[0004]
[Problems to be solved by the invention]
By the way, for the purpose of further improving the fuel efficiency and purifying the exhaust gas, it is necessary to perform a larger amount of EGR in the partial load range for the engine having the EGR valve in the EGR passage that connects the exhaust passage and the intake passage, and it is also necessary to maintain a constant operating angle. In an engine provided with an intake valve timing control mechanism (hereinafter, referred to as a "VTC mechanism") capable of continuously controlling the phase of an intake valve cam as it is, the amount of overlap of the intake and exhaust valves is increased to increase the amount of overlap in the combustion chamber. It is required to increase the amount of inert gas remaining in the steel.
[0005]
Therefore, when an experiment was conducted, a large amount of EGR was performed by the EGR valve during steady or moderate acceleration, and a large amount of inert gas was introduced into the combustion chamber by increasing the amount of overlap between the intake and exhaust valves by the VTC mechanism. Fuel cut is also performed during rapid deceleration from a state in which gas remains. At this time, if the vehicle suddenly decelerates to the idle state, when returning from the fuel cut near the idle state, the effect of a large amount of inert gas remains largely, and the combustion state in the combustion chamber remains unstable, so the engine stall It turns out that it can cause.
[0006]
This will be described with reference to FIG. 2. FIG. 2 is a model diagram showing an operation when an engine equipped with both an EGR valve and a VTC mechanism is decelerated to an idle state.
[0007]
Consider a case where the vehicle is traveling at a constant speed with the accelerator pedal depressed to some extent. At this time, since the load is a partial load, the EGR valve is opened to a predetermined opening degree so as to obtain a target EGR rate corresponding to the load and the engine speed at that time, and the load and the engine speed at that time are obtained. The cam shaft is rotated by the VTC mechanism on the advance side with respect to the cam sprocket by the amount of the target cam phase so that a target cam phase corresponding to the target cam phase is obtained.
[0008]
When the accelerator pedal is slowly returned to decelerate from this state and the foot is released from the accelerator pedal, the intake throttle valve closes responsively to the idle position and the intake air amount decreases. After temporarily increasing, it gradually decreases to the idling rotation speed (see the second dashed line in FIG. 2).
[0009]
If a predetermined permission condition is satisfied at the time of this deceleration, fuel cut is performed. Fuel cut is intended to reduce fuel consumption by prohibiting fuel injection from a fuel injection valve up to predetermined operating conditions of the engine during vehicle deceleration that does not require engine output. The predetermined operating condition is, for example, the engine speed or the vehicle speed, and the fuel cut is continued until the engine speed falls below the set engine speed or the vehicle speed.
[0010]
Further, as the load (specifically, the accelerator opening, which is the amount of depression of the accelerator pedal) accompanying the deceleration operation decreases, the target EGR rate and the target VTC phase gradually decrease to values at the time of idling (FIG. 2). 3rd stage and 5th stage). Since the combustion state in the combustion chamber is originally unstable during idling, the target EGR rate is 0% and the target VTC phase is returned to the most retarded position.
[0011]
In this case, since the EGR valve actuator and the VTC mechanism actuator have a response delay, the actual EGR valve opening and the actual VTC phase decrease with a predetermined inclination. This is because the EGR valve actuator and the VTC mechanism actuator have an upper limit speed, and cannot move at a speed exceeding the upper limit speed. That is, the predetermined inclination from the illustrated t1 represents the upper limit speed of the EGR valve actuator and the VTC mechanism actuator. Thus, when the EGR valve actuator and the VTC mechanism actuator move, the total residual gas ratio (= total inert gas amount / total gas amount), which is the ratio of the total inert gas amount in the combustion chamber to the total gas amount in the combustion chamber, is obtained. Looking at what happens after t1 when fuel cut is started, the total residual gas ratio has increased rather than before the start of fuel cut. The reason why the total residual gas rate increases rather immediately after t1 than before t1 is due to a difference in response delay between the intake throttle valve and the EGR valve. That is, since the intake throttle valve closes responsively, the responsiveness of the EGR valve is poorer, so that the amount of inert gas is relatively increased compared to the amount of fresh air.
[0012]
If there is such an increase in the total residual gas rate immediately after the start of the fuel cut, naturally, the decrease in the total residual gas rate is delayed, and the combustion state continues to be bad during that time.
[0013]
Then, when the deceleration proceeds and the engine rotation speed reaches a predetermined fuel cut return rotation speed higher than the idle rotation speed at the timing of t2, the fuel injection is restarted. When the engine is completely detonated by the restart of the fuel supply, the engine rotation speed sharply increases and thereafter settles to the idle rotation speed (see the second dashed line in FIG. 2).
[0014]
In the case of deceleration in which the accelerator pedal is returned relatively slowly (normal deceleration), the time required for the engine rotational speed to reach the fuel cut return rotational speed, that is, the time from t1 to t2, Since the response times of the EGR valve actuator and the VTC mechanism actuator (the actual EGR valve opening and the time Δte, Δtv until the actual VTC phase reaches the value at the time of idling from t1) are shorter, the fuel cut return rotation speed is reached. At the timing of t2, the total residual gas ratio has sufficiently decreased, and thus idling can be maintained after returning from the fuel cut.
[0015]
However, when the vehicle suddenly decelerates, the timing at which the engine rotational speed reaches the fuel cut return rotational speed is advanced from t2 to t2 '(see the solid line in the second stage in FIG. 2), whereas the EGR valve actuator, VTC The response times Δte and Δtv of the actuator do not change. Due to this difference, at the time of sudden deceleration, the total residual gas rate at t2 ', at which the fuel cut return rotation speed is reached, is higher than that at the time of normal deceleration, and the combustion state after fuel cut return is poor by the higher the total residual gas rate. Therefore, it is conceivable that idling cannot be maintained and engine stall may occur (see the solid line at the second stage in FIG. 2).
[0016]
When it is desired to set a high target EGR rate or a high target VTC phase in a partial load range in order to improve the fuel efficiency and enhance the exhaust purification effect, the response times Δte and Δtv of the EGR valve actuator and the VTC mechanism actuator tend to be long. Thus, this problem can be even more pronounced.
[0017]
In view of the above, an object of the present invention is to improve deterioration of combustion at the time of fuel cut recovery due to inert gas remaining in a combustion chamber at the time of rapid deceleration in an engine equipped with an EGR valve, a VTC mechanism, and the like from the viewpoints of fuel efficiency improvement and exhaust gas purification. And
[0018]
On the other hand, in the above-described conventional apparatus, the EGR valve is closed before the fuel supply is restarted because exhaust gas (inert gas) is prevented from being supplied to the engine when the fuel supply is restarted, and the inert gas is introduced into the combustion chamber. This is to prevent residual fuel from remaining and prevent deterioration of combustion when restarting fuel supply by allowing only fresh air containing a large amount of oxygen to exist in the combustion chamber when fuel supply is restarted. As described above, the conventional device merely prevents the inert gas from remaining in order to prevent the deterioration of combustion when the fuel supply is restarted. And the fuel cut is performed at the time of rapid deceleration from the state where a large amount of inert gas remains in the combustion chamber by increasing the amount of overlap of the intake and exhaust valves by the VTC mechanism, As a result, it is recognized that a large amount of inert gas remains in the combustion chamber when the fuel supply is restarted, and the technical idea is different from that of the present invention which attempts to improve the unstable combustion state. Due to this difference in technical idea, the conventional device opens the EGR valve at the time of fuel cut and closes the EGR valve prior to restarting fuel supply, whereas the present invention closes the EGR valve at the time of fuel cut. The configuration is very different.
[0019]
[Means for Solving the Problems]
The present invention relates to an engine control device that performs fuel cut when a permission condition is satisfied and then restarts fuel supply when a condition for returning from fuel cut is satisfied. When the residual gas rate or the residual gas amount in the chamber is equal to or more than a specified value and the fuel cut is performed at the time of rapid deceleration, a combustion improving means for improving a combustion state in the combustion chamber when returning from the fuel cut is provided.
[0020]
【The invention's effect】
At steady or moderate acceleration with the aim of further improving fuel efficiency and reducing NOx, a large amount of EGR is attempted by the EGR valve, or the amount of overlap between the intake and exhaust valves is increased by using a variable valve mechanism to increase the combustion chamber. If a large amount of inert gas is left in the fuel cell, fuel cut is performed even when sudden deceleration is performed from those states. At this time, the fresh air decreases responsively in response to the rapid movement of the intake throttle valve, whereas the reduction of the inert gas tends to be delayed particularly due to the response delay of the EGR valve actuator. The rate and the residual gas amount become larger immediately after the start of the fuel cut than before the start of the fuel cut, and the combustion state becomes unstable at once. Then, it takes a certain period of time for the residual gas rate and the residual gas amount in the combustion chamber, which has risen once, to decrease.
[0021]
On the other hand, since the rotation decreases rapidly during rapid deceleration, when returning from fuel cut, the total residual gas ratio and residual gas amount in the combustion chamber have not yet decreased, and the combustion state in the combustion chamber is unstable. It remains.
[0022]
Therefore, if left unattended, an engine stall may be caused.However, according to the present invention, the increase in the residual gas rate in the combustion chamber immediately after the fuel cut is caused by the increase in the combustion at the start of the fuel cut or immediately before the start of the fuel cut. Responding to the residual gas rate and the residual gas amount in the chamber, when the fuel gas starts and immediately before the start, when the residual gas rate and the residual gas amount in the combustion chamber are more than the specified values, when returning from the fuel cut during sudden deceleration It is estimated that the combustion state is deteriorating, and when returning from the fuel cut at the time of sudden deceleration, the combustion state in the deteriorating combustion chamber is positively improved.
[0023]
For example, when returning from fuel cut, multiple ignitions are performed multiple times per one cycle of engine operation, so that even in a state where the residual gas rate and the residual gas amount in the combustion chamber are large, the ignition probability of the mixture in the combustion chamber is improved, Also, the return rotation speed from the fuel cut is set high, and the return from the fuel cut is performed with the intake air amount increased compared to the normal deceleration, so that the generated torque is improved. Stable combustion can be ensured even in a state where the rate and the residual gas amount are large.
[0024]
In this way, when the deterioration of combustion at the time of returning from the fuel cut is improved, it is possible to avoid a situation leading to engine stall. Accordingly, during steady or moderate acceleration, a large amount of EGR is performed by the EGR valve, or a large amount of inert gas remains in the combustion chamber by using a variable valve mechanism to increase the amount of overlap between the intake and exhaust valves. It is possible to further improve fuel efficiency and reduce NOx.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0026]
FIG. 1 is a schematic diagram for explaining the system of the present invention.
[0027]
After the air is stored in the intake collector 2, it is introduced into the combustion chamber 5 of each cylinder via the intake manifold 3. The fuel is injected and supplied from a fuel injector 21 arranged in the intake port 4 of each cylinder. The fuel injected into the air evaporates and mixes with the air to form a gas (air mixture) and flows into the combustion chamber 5. This air-fuel mixture is confined in the combustion chamber 5 by closing the intake valve 15, and is compressed by the rise of the piston 6.
[0028]
In order to ignite the compressed air-fuel mixture with a high-pressure spark, an ignition device 11 of an electronic power distribution system having an ignition coil with a built-in power transistor in each cylinder is provided. That is, the ignition device 11 includes an ignition coil 13 for storing electric energy from a battery, a power transistor for energizing and interrupting the primary side of the ignition coil 13, and a primary current for the ignition coil 13 provided on the ceiling of the combustion chamber 5. And a spark plug 14 that receives a high voltage generated on the secondary side of the ignition coil 13 by the interruption of the spark plug 13 and performs a spark discharge.
[0029]
The ignition timing at which the fuel efficiency is the best is determined as the basic ignition timing. The engine controller 31 calculates the basic ignition timing according to the operating conditions (engine load and rotation speed), and the actual crank angle is set to this ignition timing. When they match, the ignition timing is controlled by cutting off the primary current of the ignition plug 14 via the power transistor 13.
[0030]
This ignition timing is slightly before the compression top dead center. When a spark is blown by the ignition plug 14 and ignites the compressed air-fuel mixture in the combustion chamber 5, the flame spreads and burns explosively, and the gas generated by this combustion is exploded. The pressure performs the task of pushing down the piston 6. This work is taken out as the rotational force of the crankshaft 7. The burned gas (exhaust gas) is discharged to the exhaust passage 8 when the exhaust valve 16 is opened.
[0031]
The exhaust passage 8 includes a three-way catalyst 9. When the air-fuel ratio of the exhaust gas is in a narrow range (window) centered on the stoichiometric air-fuel ratio, the three-way catalyst 9 can simultaneously efficiently remove harmful three components such as HC, CO, and NOx contained in the exhaust gas. Since the air-fuel ratio is the ratio of the amount of intake air to the amount of fuel, the amount of intake air introduced into the combustion chamber 5 per one cycle of the engine (in a 4-cycle engine, 720 ° section in crank angle) and the amount of The engine controller 31 controls the fuel from the fuel injector 21 based on the intake air flow rate signal from the air flow meter 32 and the signal from the crank angle sensors (33, 34) so that the ratio with the fuel injection amount becomes the stoichiometric air-fuel ratio. The injection amount is determined, and the O is provided upstream of the three-way catalyst 9. _Two The air-fuel ratio is feedback-controlled based on a signal from a sensor (not shown).
[0032]
An upstream of the intake collector 2 is provided with a so-called electronic control throttle 22 in which an intake 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 sets a target air for realizing the target torque. The amount is determined, and the opening degree of the intake throttle valve 23 is controlled via the throttle motor 24 so that the target air amount is obtained.
[0033]
An EGR device is provided to improve fuel efficiency and reduce NOx. The EGR device includes an EGR passage 25 communicating the exhaust passage 8 with the intake manifold 3, and an EGR valve capable of adjusting the amount (or rate) of exhaust gas (inert gas) flowing to the intake manifold 3 via the EGR passage 25. And an actuator 27 (for example, a step motor) for driving the EGR valve 26. The engine controller 31 controls the EGR valve opening so as to obtain a target EGR rate (see FIG. 8) according to the operating conditions. . When the inert gas is introduced into the intake manifold 3, the pumping loss is reduced and the fuel consumption is accordingly improved, and the combustion temperature is reduced, so that the generation of NOx is suppressed.
[0034]
A cam sprocket and a crank sprocket are respectively attached to the front portions of the intake valve camshaft 28 and the crankshaft 7, and a timing chain (not shown) is wrapped around these sprockets so that the intake valve camshaft 28 is mounted on the engine. Although driven by the crankshaft 7, a VTC mechanism 29 (variable valve gear) is provided between the cam sprocket and the intake valve camshaft 28. In this VTC mechanism 29, when no signal is given to the VTC mechanism actuator, the intake valve camshaft 28 is at the most retarded position, and the more the control amount given to the VTC mechanism actuator, the more the camshaft for the intake valve 28 rotates to the advance side. The rotation angle of the intake valve camshaft 28 is hereinafter referred to as “cam phase”.
[0035]
When the cam phase, that is, the opening / closing timing of the intake valve 15 is changed, the amount of the inert gas remaining in the combustion chamber 5 changes. As the amount of inert gas in the combustion chamber 5 increases, the pumping loss decreases and the fuel efficiency improves, so how much inert gas should remain in the combustion chamber 5 depending on the operating conditions is determined in advance as the target cam phase. The engine controller 31 calculates the target cam phase (see FIG. 19) from the operating conditions (engine load and rotation speed) at that time, and the actual cam phase detected by the actual cam phase sensor 34 matches this target cam phase. To control the cam phase via the VTC mechanism actuator.
[0036]
Here, since the EGR valve 27 and the VTC mechanism 29 have an equivalent function in terms of introducing an inert gas into the combustion chamber 5, the EGR valve 27 uses the EGR valve 27 to distinguish between the two inert gases. The inert gas introduced into the combustion chamber 5 by the VTC mechanism 29 is referred to as “internal inert gas”, and the inert gas introduced into the combustion chamber 5 by the VTC mechanism 29 is referred to as “internal inert gas”. In addition, the inert gas remaining in the combustion chamber 5 combining the two is referred to as “total residual gas”. When no distinction is made between the external inert gas and the internal inert gas remaining in the combustion chamber 5, it is referred to as "residual gas".
[0037]
The operation of the engine equipped with the EGR valve 27 and the VTC mechanism 29 when the vehicle is decelerated to the idle state will be described with reference to the model of FIG.
[0038]
It is assumed that the vehicle is running at a constant speed with the accelerator pedal 41 depressed to some extent. At this time, since the load is a partial load, the EGR valve 26 is opened to a predetermined opening degree so that a target EGR rate corresponding to the load and the engine rotation speed at that time is obtained. The VTC mechanism 29 rotates the camshaft 28 on the advance side with respect to the cam sprocket by the amount of the target cam phase so as to obtain the target cam phase corresponding to the speed.
[0039]
When the accelerator pedal 41 is slowly returned to decelerate from this state and the leg is released from the accelerator pedal 41, the intake throttle valve 23 closes to the idling position and the intake air amount decreases. After a more temporary increase, it gradually decreases to the idling rotational speed (see the second dashed line in FIG. 2).
[0040]
If a predetermined permission condition is satisfied at the time of this deceleration, fuel cut is performed. Fuel cut is intended to reduce fuel consumption by prohibiting fuel injection from the fuel injector 21 until a predetermined operating condition of the engine is satisfied during vehicle deceleration that does not require output of the engine. The predetermined operating condition is, for example, that the engine speed or the vehicle speed falls below a predetermined value, and the fuel cut is continued until immediately before this condition is satisfied.
[0041]
Further, as the load (specifically, the accelerator opening, which is the amount of depression of the accelerator pedal 41) accompanying the deceleration operation decreases, the target EGR rate and the target VTC phase gradually decrease to values at the time of idling (FIG. 2, 3rd stage and 5th stage). This is because the target EGR rate is 0 and the target VTC phase returns to the most retarded position because the combustion state is originally unstable during idling.
[0042]
In this case, since the actuators of the EGR valve 26 and the VTC mechanism 28 have a response delay, the actual EGR valve opening and the actual VTC phase decrease with a predetermined slope. This is because the EGR valve actuator 27 and the VTC mechanism actuator have an upper limit speed, and cannot move at a speed exceeding the upper limit speed. That is, the predetermined inclination represents the upper limit speed of the EGR valve actuator 27 and the VTC mechanism actuator. As described above, when the EGR valve actuator 27 and the VTC mechanism actuator move, the total residual gas ratio, which is the ratio of the total inert gas amount in the combustion chamber 5 to the total gas amount in the combustion chamber 5, changes. The total residual gas rate has increased rather than before the start of fuel cut. The reason why the total residual gas rate increases rather immediately after t1 than before t1 is due to a difference in response delay between the intake throttle valve 23 and the EGR valve 26. That is, the intake throttle valve 23 closes responsively, whereas the EGR valve 26 has poorer responsiveness, so that the amount of inert gas is relatively larger than the amount of fresh air.
[0043]
If there is such an increase in the total residual gas rate immediately after the start of the fuel cut, naturally, the decrease in the total residual gas rate is delayed, and the combustion state continues to be bad during that time.
[0044]
Then, when the deceleration proceeds and the engine rotation speed reaches a predetermined fuel cut return rotation speed higher than the idle rotation speed at the timing of t2, the fuel injection is restarted. When the engine is completely detonated by the restart of the fuel supply, the engine rotation speed sharply increases and thereafter settles to the idle rotation speed (see the second dashed line in FIG. 2).
[0045]
As described above, when the accelerator pedal 41 is decelerated relatively slowly (during normal deceleration), the time until the engine rotation speed reaches the fuel cut return rotation speed, that is, the time from t1 to t2, , The response time of the EGR valve actuator 27 and the VTC mechanism actuator (the time Δte, Δtv until the actual EGR valve opening and the actual VTC phase reach the idling value from t1) are shorter, so that the fuel cut return rotational speed is reduced. The total residual gas ratio is sufficiently reduced at the time t2 when the fuel cut is reached, so that the idling can be maintained after returning from the fuel cut.
[0046]
However, at the time of rapid deceleration of the vehicle, the timing at which the engine rotation speed reaches the fuel cut return rotation speed is advanced from t2 to t2 '(see the solid line in the second stage in FIG. 2), whereas the EGR valve actuator 27, The response times Δte and Δtv of the VTC actuator do not change. Due to this difference, at the time of rapid deceleration, the total residual gas ratio at t2 ', at which the fuel cut return rotation speed is reached, is higher than that at the time of normal deceleration, and the combustion state after fuel cut return is poor by the higher the total residual gas ratio. Therefore, it is conceivable that idling cannot be maintained and engine stall may occur (see the solid line at the second stage in FIG. 2).
[0047]
When it is desired to set a high target EGR rate or a high target VTC phase in a partial load range in order to improve the fuel economy and enhance the exhaust purification effect, the response times Δte and Δtv of the EGR valve actuator 27 and the VTC mechanism actuator tend to be long. Therefore, this problem becomes more remarkable.
[0048]
According to the present invention, when the total residual gas ratio in the combustion chamber 5 immediately before (or at the time of) the start of the fuel cut is equal to or more than a specified value and the fuel cut is at the time of rapid deceleration, the present invention is applied to such an engine. When returning, the combustion state in the combustion chamber 5 is improved. Instead of the total residual gas rate in the combustion chamber 5 immediately before (or at the start) of the fuel cut, the total residual gas amount in the combustion chamber 5 immediately before (or at the start) of the fuel cut may be used. . Specifically, the combustion improvement at the time of fuel cut return is improved by multiple ignitions per cycle using one spark plug 14, or the fuel cut return rotation speed is set to a higher rotation speed than usual. It is done by doing. Instead of multiple ignitions per cycle at one location, multiple ignitions at multiple locations per cycle may be performed.
[0049]
This will be described with reference to FIGS. 3 and 4. FIGS. 3 and 4 are waveform diagrams showing the same conditions as those indicated by the broken lines in FIG. 2, that is, the actions of the first and second embodiments when sudden deceleration is performed. is there.
[0050]
First, FIG. 3 is different from the case shown by the broken line in FIG. 2 only in the lowermost stage. That is, in the first embodiment shown in FIG. 3, when the fuel cut during the rapid deceleration and the total residual gas ratio immediately before the start of the fuel cut is equal to or more than the specified value, the engine speed is returned to the fuel cut at t2 ′. When the rotation speed is reached, the combustion state is improved by performing multiple ignitions per cycle by the spark plug 14 in the combustion chamber 5 where the total residual gas rate is high.
[0051]
Next, in the second embodiment shown in FIG. 4, when the fuel cut during the rapid deceleration and the total residual gas ratio immediately before the start of the fuel cut is equal to or more than the specified value, the fuel cut return rotation speed is reduced during the normal deceleration. The timing for returning from the fuel cut is advanced from t2 'to t4.
[0052]
This control executed by the engine controller 31 will be described in detail with reference to a flowchart shown below. Here, FIGS. 5, 6, 7, 12, 13, and 14 are flowcharts for realizing FIG. 3, and FIGS. 15 to 18 are flowcharts for realizing FIG.
[0053]
To explain from the first embodiment, FIG. 5 is for setting a fuel cut execution flag, which is executed at regular intervals (for example, every 10 msec).
[0054]
In step 1, the fuel cut execution flag (initial setting to zero) is checked. Here, a description will be given assuming that the fuel cut execution flag is 0. At this time, the process proceeds to steps 2 and 3 to determine whether the fuel cut permission condition is satisfied this time and whether the fuel cut permission condition was not satisfied last time. See if it is.
[0055]
The fuel cut permission condition is defined by the driving state of the vehicle. For example, the fuel cut permission condition is satisfied when all of the following conditions are satisfied.
[0056]
(1) The signal from the idle switch 43 is ON. Here, the idle switch 43 is a switch that is turned on when the accelerator opening is zero, and is turned off when the accelerator pedal 41 is depressed.
[0057]
(2) The engine speed exceeds a predetermined value.
[0058]
(3) The vehicle speed detected by the vehicle speed sensor 44 exceeds a predetermined value.
[0059]
When the fuel cut permission condition is satisfied this time and the fuel cut permission condition is not satisfied last time, that is, when the fuel cut permission condition is satisfied for the first time this time, the process proceeds to step 4 and the fuel cut execution flag is set to 1. Otherwise, step 4 is skipped and the current process ends.
[0060]
FIG. 6 is for setting the multiple ignition permission flag, and is executed at regular intervals (for example, every 10 msec).
[0061]
In step 11, the multiple ignition permission flag (initial setting to zero) is checked. In the following, it is assumed that the multiple ignition permission flag is 0. At this time, the process proceeds to steps 12, 13 and 14 to check whether all the following conditions are satisfied.
[0062]
(4) The fuel cut execution flag must be 1.
[0063]
(5) During rapid deceleration.
[0064]
(6) The total residual gas ratio is equal to or higher than a specified value.
[0065]
Here, the rapid deceleration of (5) is, for example, when all of the following conditions are satisfied.
[0066]
<1> The return speed of the accelerator pedal 41 before the start of the fuel cut is higher than a predetermined value.
[0067]
<2> The brake pedal 45 is depressed. That is, the signal from the brake switch 46 is ON.
[0068]
<3> The reduction in vehicle speed per hour is larger than a predetermined value.
[0069]
Further, the calculation of the total residual gas ratio in the above (6) will be described with reference to the flowchart of FIG. The total residual gas ratio calculated here becomes a value immediately before the start of the fuel cut.
[0070]
In FIG. 7, in step 21, a target EGR rate Megr is calculated by searching a map containing the contents of FIG. 8 from the engine load (for example, a basic injection pulse width Tp to be described later) and the rotation speed. Enter the active gas rate.
[0071]
In step 23, a basic internal inert gas ratio is calculated by searching a map having the contents shown in FIG. 9 from the load and the rotation speed of the engine. The basic internal inert gas rate is an internal inert gas rate corresponding to the operating conditions (load, rotation speed) when the VTC mechanism 29 is at the most retarded position.
[0072]
In step 24, a correction coefficient is calculated from the actual cam phase (or target cam phase) detected by the cam phase sensor 34 by retrieving a table containing the contents shown in FIG. Is calculated as the internal inert gas ratio.
[0073]
The correction coefficient is a value that becomes larger than 1.0 as the cam phase becomes larger as shown in FIG. The reason why the correction coefficient is increased as the cam phase increases is that the overlap amount of the intake and exhaust valves increases as the cam phase increases as shown in FIG. 11, and the internal inert gas ratio increases accordingly. It is because it becomes.
[0074]
In step 26, the sum of the internal inert gas rate and the external inert gas rate is calculated as the total residual gas rate in the combustion chamber 5.
[0075]
The specified value of (6) is a constant value. Here, how to determine the specified value will be described with reference to FIG. That is, FIG. 20 shows the characteristics in which the horizontal axis represents the total residual gas ratio, and the vertical axis represents the combustion stability and fuel efficiency. It can be seen that when the total residual gas rate is A, the fuel efficiency is the best, and as the total residual gas rate becomes higher than A, the combustion stability becomes worse. The fact that the total residual gas ratio is larger than t1 in FIGS. 2 and 3 means that the total residual gas ratio is larger than A and the combustion stability is degrading in FIG. Therefore, when the combustion stability limit is written, a region exceeding the total residual gas ratio B corresponding to the combustion stability limit is a combustion unstable region. Since it is necessary to improve combustion in this unstable combustion region, a specified value may be determined based on B. Finally, the specified value is determined by matching. Since the combustion stability limit shown in FIG. 20 can be changed depending on the operating conditions, the specified value can be set according to the operating conditions.
[0076]
When all of the above (4) to (6) are satisfied, that is, when the total residual gas ratio is equal to or more than the specified value immediately before the start of the fuel cut at the time of rapid deceleration, it is determined from the total residual gas ratio immediately before the start of the fuel cut. Therefore, when the rapid deceleration to the idling rotation speed is continued, it is estimated that the combustion chamber 5 is in an unstable combustion state at the time of the fuel cut recovery, and the occurrence of engine stall may be considered. At this time, the routine proceeds to step 15, where the multiple ignition permission flag (initial setting to zero) = 1 is set. When the multiple ignition permission flag is 1, multiple ignition by the spark plug 14 is permitted.
[0077]
On the other hand, if any of the above (4) to (6) is not satisfied, step 15 is skipped and the current process is terminated.
[0078]
FIG. 12 is for setting the fuel cut return flag, and is executed at regular intervals (for example, every 10 msec).
[0079]
In step 31, the fuel cut return flag (initial setting to zero) is checked. In the following, it is assumed that the fuel-cut return flag is 0. At this time, the process proceeds to steps 32 and 33 to check whether all of the following conditions are satisfied.
[0080]
(7) The fuel cut execution flag must be 1.
[0081]
(8) Fuel cut return condition is satisfied.
[0082]
Here, the fuel cut return condition (8) is satisfied, for example, when one of the following conditions is satisfied.
[0083]
<4> The engine rotation speed is equal to or lower than the fuel cut return rotation speed Nrcv1.
[0084]
<5> The vehicle speed is equal to or lower than a predetermined value.
[0085]
If all of the above conditions (7) and (8) are satisfied, the routine proceeds to step 34, where the fuel cut return flag is set to "1". In step 35, the fuel cut execution flag is set to 0 in preparation for the next fuel cut processing.
[0086]
FIG. 13 is for calculating the number of ignitions and the fuel injection pulse width, and is executed at regular intervals (for example, every 10 msec).
[0087]
In step 41, the fuel cut execution flag is checked. When the fuel cut execution flag is 0, that is, during normal operation, the routine proceeds to steps 42 and 43, in which the number of ignitions n is set to one per cycle. In the case of sequential injection, the fuel injection pulse width Ti is calculated by the following equation. .
[0088]
Ti = Tp × Tfbya × (α + αm−1) × 2 + Ts (1)
Here, Tp: basic injection pulse width,
Tfbya: target equivalent ratio,
α: air-fuel ratio feedback correction coefficient,
αm: Air-fuel ratio learning value,
Ts: invalid pulse width,
On the other hand, when the fuel cut execution flag is 1, the process proceeds from step 41 to steps 44 and 45 to check the fuel cut return flag and the multiple ignition permission flag. When the fuel-cut return flag is "0", the routine proceeds to steps 46 and 47 in order to perform the fuel-cut, the number of ignitions n is set to zero, and the fuel injection pulse width Ti is set to Ti = Ts. At this time, no fuel is injected.
[0089]
When the fuel cut return flag is 1 and the multiple ignition permission flag is 0, the operations of steps 42 and 43 are executed to restart the fuel supply.
[0090]
On the other hand, when the fuel cut return flag = 1 and the multiple ignition permission flag = 1, the process proceeds to step 48 to improve the combustion state while restarting the fuel supply, and the number of ignitions n is set to two, and Perform the operation of. Here, the number of times of ignition per cycle may be constant irrespective of the total residual gas ratio in the combustion chamber 5, or the number may be set variably according to the total residual gas ratio.
[0091]
The ignition number n and the fuel injection pulse width Ti calculated in this manner are used for ignition control and fuel injection control, respectively, to control the ignition timing and the fuel injection amount.
[0092]
As a result, when the multiple ignition permission flag is set to 1, the multiple ignition is performed twice per engine operation cycle by the spark plug 14 when returning from the fuel cut.
[0093]
FIG. 14 is for performing feedback control of the idle rotation speed, and is executed at regular intervals (for example, every 10 msec).
[0094]
In step 51, it is determined whether or not the engine is idling based on a signal from the idle switch 43. If the engine is idling, the routine proceeds to step 52, where a deviation ΔN (= NSET−Ne) between the target idle rotation speed NSET and the actual rotation speed Ne is calculated, and the absolute value of the deviation ΔN is compared with a predetermined value in step 53. The predetermined value is a value that defines an allowable range around the target idle rotation speed NSET, and is, for example, about 50 RPM.
[0095]
If the absolute value of the deviation ΔN from the target idle rotation speed NSET exceeds a predetermined value, feedback control of the idle rotation speed is performed in step 54 so that the actual rotation speed Ne falls within an allowable range centered on the target idle rotation speed. Do. That is, when the actual rotation speed Ne is lower than NSET-predetermined value, the intake throttle valve 23 is opened to increase the amount of intake air. Conversely, when the actual rotation speed Ne is higher than NSET + predetermined value, the intake throttle valve 23 is closed. To reduce the amount of intake air.
[0096]
As a result, when the actual rotation speed Ne falls within the allowable range centered on the target idle rotation speed, no more multiple ignitions are required, so the process proceeds from step 53 to step 55 where the multiple ignition permission flag is set to 0. In step 56, the fuel cut return flag is set to 0 to prepare for the next fuel cut processing. Here, the period in which the multiple ignition permission flag is 1, that is, the period in which multiple ignition is performed is a period from when the fuel cut is restored to when idling is maintained.
[0097]
Next, a second embodiment will be described. FIGS. 15, 16, 17, and 18 are replaced with FIGS. 6, 12, 13, and 14, respectively, of the first embodiment. In FIGS. 15, 16, 17, and 18, the same steps as those in FIGS. 15, 16, 17, and 18 are denoted by the same step numbers.
[0098]
To explain mainly the differences from the first embodiment, FIG. 15 is for setting the fuel cut return rotation speed up flag, and when all of the above (4) to (6) are satisfied, the routine proceeds to step 62, Instead of the multiple ignition permission flag, the fuel cut return rotation speed up flag = 1 is set.
FIG. 16 is for setting a fuel cut return flag, and the fuel cut return condition in step 33 is different from that of the first embodiment. That is, in the first embodiment, the fuel cut return rotation speed is Nrcv1 in the above <4>, but a value higher than this value is set as the fuel cut return rotation speed Nrcv2 in the second embodiment.
[0099]
Here, the fuel cut return rotation speed Nrcv2 may be a fixed value added to the fuel cut return rotation speed Nrcv1 of the first embodiment, or may be determined according to the total residual gas rate in the combustion chamber 5 immediately before the start of the fuel cut. May be set.
[0100]
As described above, when the fuel cut return rotation speed is set to be high, the return from the fuel cut is performed in a state where the intake air amount is increased as compared with the normal deceleration.
[0101]
When the engine speed decreases during fuel cut and becomes lower than the fuel cut return rotation speed Nrcv2, the fuel cut return flag becomes 1 in step 34. In this case, the fuel cut return rotation speed up flag is set in step 71. = 0. This is to prepare for the next fuel cut processing.
[0102]
Since the multiple ignition is not performed in the second embodiment, FIGS. 17 and 18 can be obtained by removing the portion related to the multiple ignition from FIGS. 13 and 14 of the first embodiment.
[0103]
Here, the operation of the present embodiment will be described.
[0104]
At steady or moderate acceleration for the purpose of further improving fuel efficiency and reducing NOx, the EGR valve 26 attempts to perform a large amount of EGR, or the VTC mechanism 29 is used to increase the amount of overlap between the intake and exhaust valves 15 and 16. If a large amount of inert gas is to be left in the combustion chamber 5 by such a method, fuel cut is performed even when sudden deceleration is performed from those states. At this time, the fresh air decreases responsively in response to the quick movement of the intake throttle valve 23, whereas the reduction of the inert gas tends to be delayed due to the response delay of the EGR valve actuator 27. Immediately after the start of fuel cut, rather than before the start of fuel cut, and the combustion state becomes unstable at once. Then, it takes a certain time for the total residual gas ratio in the combustion chamber 5 that has once risen to decrease.
[0105]
On the other hand, since the rotation decreases rapidly during rapid deceleration, when returning from the fuel cut, the total residual gas ratio in the combustion chamber 5 has not yet decreased, and the combustion state in the combustion chamber 5 is unstable. It remains.
[0106]
Therefore, if left unattended, the engine may stall. According to the present embodiment (the invention described in claim 1), the residual gas rate in the combustion chamber 5 immediately after the fuel cut is performed. Increase corresponds to the residual gas rate in the combustion chamber 5 immediately before the start of the fuel cut. When the residual gas rate in the combustion chamber 5 immediately before the start of the fuel cut is equal to or more than a specified value, the fuel cut during the rapid deceleration starts. It is assumed that the combustion state is degraded at the time of return of the combustion chamber, and when returning from the fuel cut at the time of sudden deceleration, the combustion state within the combustion chamber 5 thus degraded is positively improved. did.
[0107]
For example, in the first embodiment (the invention according to claim 2), when returning from fuel cut, the ignition plug 14 performs multiple ignitions twice per engine operation cycle, so that the total residual gas in the combustion chamber 5 Even in a state where the rate is high, the probability of ignition of the air-fuel mixture in the combustion chamber 5 is improved, and in the second embodiment (the invention according to claim 3), the return rotation speed from the fuel cut is set to be high, Since the return from fuel cut is performed with the intake air amount increased compared to deceleration, the generated torque is improved, which ensures stable combustion even when the total residual gas ratio is high when returning from fuel cut. it can.
[0108]
In this way, when the deterioration of combustion at the time of returning from the fuel cut is improved, it is possible to avoid a situation leading to engine stall. Thus, during steady or moderate acceleration, a large amount of EGR is performed by the EGR valve 26, or the VTC mechanism 29 is used to increase the amount of overlap between the intake and exhaust valves to allow a large amount of inert gas to enter the combustion chamber 5. As a result, it is possible to further improve fuel efficiency and reduce NOx.
[0109]
In the embodiment, the case where both the EGR device and the VTC mechanism are provided has been described. However, the present invention is not limited to this, and the present invention can be applied to a device having at least one. Further, the VTC mechanism is an example of a variable valve mechanism, and the variable valve mechanism is not limited to the embodiment.
[0110]
In the embodiment, in order to improve the combustion state, the case where multiple ignition is performed and the case where the fuel cut return lower limit rotation speed is set to a higher rotation side than that during normal deceleration are separately shown, but both are simultaneously adopted. You can also.
[Brief description of the drawings]
FIG. 1 is a system schematic diagram of a first embodiment.
FIG. 2 is a waveform chart for explaining a difference between normal deceleration and rapid deceleration.
FIG. 3 is a waveform chart for explaining the operation of the first embodiment.
FIG. 4 is a waveform chart for explaining the operation of the second embodiment.
FIG. 5 is a flowchart for explaining setting of a fuel cut execution flag.
FIG. 6 is a flowchart for explaining setting of a multiple ignition permission flag.
FIG. 7 is a flowchart for explaining calculation of a total residual gas rate.
FIG. 8 is a characteristic diagram of a target EGR rate.
FIG. 9 is a characteristic diagram of a basic internal inert gas ratio.
FIG. 10 is a characteristic diagram of a correction coefficient.
FIG. 11 is a characteristic diagram of an overlap amount.
FIG. 12 is a flowchart for explaining setting of a fuel cut return flag.
FIG. 13 is a flowchart for explaining the calculation of the number of ignitions and the fuel injection pulse width.
FIG. 14 is a flowchart illustrating idle rotation speed control.
FIG. 15 is a flowchart for explaining setting of a return lower limit rotation speed up flag according to the second embodiment.
FIG. 16 is a flowchart illustrating setting of a fuel-cut return flag according to the second embodiment.
FIG. 17 is a flowchart for explaining calculation of a fuel injection pulse width according to the second embodiment.
FIG. 18 is a flowchart illustrating idle speed control according to a second embodiment.
FIG. 19 is a characteristic diagram of a target cam phase.
FIG. 20 is a characteristic diagram of combustion stability and fuel efficiency with respect to the total residual gas rate.
[Explanation of symbols]
14 Ignition coil
15 Spark plug
22 Fuel injector
25 EGR passage
26 EGR valve
29 VTC mechanism (variable valve mechanism)
31 Engine Controller
43 Idle switch

Claims (11)

In the engine control device, the fuel cut is performed when the permission condition is satisfied, and the fuel supply is restarted when the return condition from the fuel cut is satisfied.
When the residual gas ratio or residual gas amount in the combustion chamber immediately before or immediately after the start of fuel cut is equal to or more than the specified value and the fuel cut is performed during rapid deceleration, the combustion state in the combustion chamber is improved when returning from the fuel cut. An engine control device comprising combustion improvement means. 2. The engine control device according to claim 1, wherein the combustion improvement at the time of returning to the fuel cut is performed by multiple ignitions per cycle or multi-point ignition at a plurality of points per cycle. When the engine cut-off speed is equal to or lower than the fuel cut-return speed after the fuel supply is stopped, the fuel cut-return condition is satisfied. The engine control device according to claim 1, wherein the control is performed by setting the rotation speed to a higher rotation side than the time. An EGR passage and an EGR valve capable of controlling an EGR rate are provided, and the residual gas rate or the residual gas amount in the combustion chamber at or immediately before the start of the fuel cut is determined by the EGR rate or the EGR valve at or immediately before the start of the fuel cut. The engine control device according to any one of claims 1 to 3, wherein the calculation is performed in accordance with an opening degree. The engine according to any one of claims 1 to 3, further comprising an EGR passage and an EGR valve capable of controlling an EGR rate, wherein the EGR valve is closed when the stop of the fuel supply is started. Control device. A variable valve device capable of changing at least a valve operation mode of an intake valve according to an operation condition is provided, and the residual gas rate or the residual gas amount in the combustion chamber at or immediately before the start of the fuel cut is determined at the start or the start of the fuel cut. The engine control device according to any one of claims 1 to 3, wherein the calculation is performed in accordance with the immediately preceding valve operation mode. An EGR passage, an EGR valve capable of controlling an EGR rate, and a variable valve operating device capable of changing at least a valve operating mode of an intake valve in accordance with operating conditions; and a residual valve in the combustion chamber at or immediately before the start of the fuel cut. The gas rate or the residual gas amount is obtained by calculating the external inert gas rate or the external inert gas amount obtained from the EGR rate or the EGR valve opening immediately before or immediately after the start of the fuel cut, and the internal inert gas rate or the internal gas obtained from the valve operation mode. The engine control device according to any one of claims 1 to 3, wherein the calculation is performed based on the inert gas amount. 4. The engine control device according to claim 1, wherein the prescribed value is a constant value. 3. The engine according to claim 2, wherein the number of times of the multiple ignitions or the number of the points of the multipoint ignition is determined according to a residual gas rate or a residual gas amount in a combustion chamber at or immediately after the start of fuel cut. Control device. 3. The engine control device according to claim 2, wherein the multiple ignition or the multi-point ignition is performed for a period until the idle is maintained. 4. The engine control device according to claim 3, wherein the fuel cut return rotation speed is set according to a residual gas rate or a residual gas amount in the combustion chamber at or immediately before the start of the fuel cut. 5.

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