JP3460431B2 - Exhaust gas recirculation control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device suitable for use mainly in an engine that burns at a lean air-fuel ratio, and in particular, it requires recirculation amount control by switching combustion modes or the like. The present invention relates to an exhaust gas recirculation control device suitable for use in an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, as a vehicle engine, a lean burn engine has been proposed in which a combustion air-fuel ratio is set higher than a theoretical air-fuel ratio from the viewpoint of improving fuel efficiency. By the way, the lean burn engine generally improves fuel efficiency as the combustion air-fuel ratio increases, but
There is a limit due to deterioration of combustion. As a method to raise this limit as much as possible, while minimizing the air-fuel ratio in the vicinity of the ignition point in the combustion chamber, while maintaining a large overall air-fuel ratio in the combustion chamber,
Techniques for performing stratified combustion have been proposed.

In addition, in-cylinder injection engines in which fuel is directly injected into cylinders have been developed so that the engine can be operated with a leaner mixture of fuel. In particular, in such an in-cylinder injection type engine, for example, fuel injection can be performed in the latter half of the compression stroke, so that a laminar vertical vortex flow such as a tumble flow is generated in the cylinder, and the ignition plug is ignited to the laminar vertical vortex flow. By injecting fuel immediately before (for example, in the latter stage of the compression stroke), it is possible to realize fuel-efficient operation with an extremely lean mixture as a whole while ensuring combustibility by making only the vicinity of the spark plug a rich mixture. .

[0004]

By the way, when performing lean combustion, it is known that the NOx production amount decreases as the combustion air-fuel ratio increases, but when lean stratified combustion is performed. Since the air-fuel ratio in the vicinity of the ignition point is relatively small, there is a certain limit in reducing the amount of NOx produced.

In addition to the steady operation in which the pursuit of low fuel consumption is permitted, a relatively high output may be required in an automobile engine, such as during acceleration including slow acceleration. During operation, it is necessary to reduce the combustion air-fuel ratio to some extent below the limit air-fuel ratio during steady operation. That is, in the lean burn engine,
A first lean operation in which the air-fuel ratio is maximized (for example, an air-fuel ratio of 24 to 30 or higher) and a second lean operation in which the air-fuel ratio is made smaller than that in the first lean operation to secure the output (for example, an air-fuel ratio of 15- 23) or stoichiometric operation.

By the way, in the second lean operation and stoichiometric operation, combustion is possible without intentionally performing stratified combustion, and when stratified combustion is carried out similarly to the first lean operation, a local empty space near the ignition point is generated. If the fuel ratio becomes smaller and the amount of HC produced increases, or if the local air-fuel ratio becomes extremely small, the smoke limit rather deteriorates combustion. Therefore, in the second lean operation and stoichiometric operation, it is desirable to make the air-fuel ratio in the combustion chamber uniform throughout.

That is, it is conceivable to selectively perform homogeneous mixed combustion (premixed combustion) and stratified combustion at a lean air-fuel ratio in an automobile engine. Fuel is mixed (premixed) by injecting fuel earlier than in the case of stratified combustion, in addition to lean combustion operation (stratified lean combustion operation) by stratified combustion that uses later-stage injection and uses stratified longitudinal vortex flow. However, it is conceivable that the premixed combustion operation, in which the combustion operation is performed in a state where the fuel concentration is richer than that in the case of stratified combustion, may be selectively used based on the load state and the rotational speed state of the engine.
Note that, hereinafter, the stratified lean combustion operation is also referred to as the late lean combustion operation because the fuel injection is in the latter half.If the air-fuel ratio is leaner than stoichio in the premixed combustion operation, the fuel injection is compared to this and the lean lean combustion operation is in the first half. Also called driving.

In an engine that performs such stratified combustion and premixed combustion, it is particularly required to reduce NOx during stratified combustion operation. As means for reducing this NOx, exhaust gas recirculation (EGR) is used. ) Can be used. By the way, if a large amount of EGR is injected during the lean combustion operation or stoichio operation in the previous term,
There is a problem that combustion deteriorates. That is, as shown in FIG. 11, the air-fuel ratio is changed to the stoichiometric air-fuel ratio (stoichio).
When increasing EGR to lean (that is, when changing from stoichiometric air-fuel ratio combustion operation to early lean combustion operation and late lean combustion operation), when EGR is input, NOx
Although it is effective in reducing the fuel consumption, the fuel consumption characteristics are almost the same as in the case where EGR is not supplied as shown by the solid line in FIG. 11 (B), but the combustion stability is as shown in FIG. 11 (A). When EGR is injected, it deteriorates significantly in the lean combustion operation in the first period, and slightly worse in the stoichio operation than in the lean combustion operation in the latter period. Even in the stoichio operation, the combustion stability deteriorates significantly when a large amount of EGR is introduced.

Therefore, it is necessary to secure the combustion stability in such a case, and it is conceivable to introduce or stop the EGR control. For example, between the early lean combustion operation and the late lean combustion operation, When the operation mode is switched, when the intake air amount control that cancels the output change at the time of switching is performed, the intake air amount adjustment and the EG
Since R is introduced (or stopped) at the same time, the following problems can be considered.

That is, for example, when the lean combustion operation in the first period or the stoichiometric operation in the first period is switched to the lean combustion operation in the second period, it is desired to change the EGR from the stopped state to the introduced state and increase the intake air amount to increase the air-fuel ratio. At this time, since the negative pressure downstream of the throttle valve is reduced by the introduction of EGR, the amount of fresh air introduced is reduced, which causes a sudden output fluctuation (torque shock), and the engine mounted on the vehicle does not drive the driver. It is easy to lose the ability.

Note that, for example, Japanese Patent Laid-Open No. 6-200834 discloses an air-fuel ratio control device for an internal combustion engine equipped with a bypass passage and EGR. It is intended to reduce NOx and suppress torque fluctuations when switching to fuel ratio control, but between the above-described premix operation (that is, the first lean combustion operation or the first stoichio operation) and the second lean combustion operation. There is no suggestion of a technology capable of solving each problem at the time of switching the operating state such as.

Also, a large amount of EG depending on the air-fuel ratio, such as between the late lean and the early lean or the early stoichio.
Considering the case where the R flow rate is changed stepwise, EG
When the R flow rate is decreased, rapid combustion does not cause deterioration of combustion, but when increasing the EGR flow rate, a rapid increase may cause transient deterioration of combustion.

The present invention was devised in view of the above-mentioned problems, and provides a lean combustion engine with reduced NOx production while ensuring combustion stability in lean or stoichio air-fuel ratio combustion operation by premixing. Furthermore, when switching the operating state related to the air-fuel ratio control, the intake amount is switched and the control state of the exhaust gas recirculation control is appropriately switched to achieve both efficient operation and exhaust gas purification. The exhaust gas recirculation control is made possible so as to avoid the output shortage and the torque shock caused by the above, and further to suppress the transient combustion deterioration when the EGR introduction amount (exhaust gas recirculation amount) is changed. The purpose is to provide a device.

[0014]

Therefore, in the exhaust gas recirculation control device of the present invention according to claim 1, the premixed combustion and the total air-fuel ratio in the combustion chamber are larger than the total air-fuel ratio of the premixed combustion. discharged with performing either combustion of stratified combustion
In an internal combustion engine in which a part of gas is recirculated into the intake passage, the exhaust gas recirculation amount at the time of stratified combustion is determined by the premixed combustion.
Set a value higher than the exhaust gas recirculation amount, and
The combustion state of the combustion engine is switched from the premixed combustion to the stratified combustion.
When changing, change the intake air amount accompanying the change of the total air-fuel ratio
After that, change the exhaust gas recirculation amount
It is characterized by controlling .

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

As a result, for example, the combustion operation in a state where the air-fuel ratio is extremely large by the stratified combustion (that is, the state where the fuel concentration is extremely lean) and the state where the air-fuel ratio is smaller than that in the stratified combustion by the premix combustion (that is, Switching to combustion operation when the fuel concentration is lean to some extent is also smoothly performed. In addition, during stratified combustion, the engine can be operated with relatively less fuel than during premixed combustion.

According to a second aspect of the present invention, there is provided the exhaust gas recirculation control device according to the first aspect, wherein the premixed combustion is performed.
Is the air-fuel ratio is larger than the theoretical air-fuel ratio and the exhaust gas recirculation
Including a premix lean mode without introducing
When the combustion mode is switched to stratified combustion,
After changing the intake air amount accompanying the switching of the ratio, the exhaust gas
It is characterized by controlling so as to change the amount of recirculation .

Thus, for example, the theory of premixed combustion
From a slightly leaner combustion operation than the air-fuel ratio to stratified combustion
When switching to a leaner combustion operation, change the intake air amount and the exhaust gas recirculation amount (whether the exhaust gas recirculation is blocked or not).
The change of the exhaust gas recirculation amount is likely to cause a drastic output fluctuation (torque shock) and impair the drivability of the engine installed in the vehicle. By delaying, the reduction of the fresh air introduction amount is suppressed, and the combustion state can be switched while suppressing the output fluctuation.

[0029]

[0030]

[0031]

[0032] The exhaust gas recirculation control device of the present invention described in claim 3, in the configuration of claim 1, wherein the air-fuel ratio is larger when the stratified combustion, the outlet gas recirculation amount or discharge of returning to the intake passage It is characterized in that it is configured to be greater the opening degree of the gas recirculation control valve.

With this structure, stratified combustion is performed when the total air-fuel ratio in the combustion chamber is in the lean air-fuel ratio region. Although controlling the reflux to the parallel to emissions within an intake passage of the gas from this, this time, the larger the air-fuel ratio when the laminar burning, the outlet gas recirculation amount to be recirculated to the intake passage also
Is control <br/> control so as to increase the opening degree of the exhaust gas recirculation control valve.

According to the exhaust gas recirculation control device of the present invention described in claim 4, in the structure described in claim 3, the comprehensive air-fuel ratio at the time of stratified combustion is set to about 23 or more. It has a feature. Therefore, the operation is performed with a very lean fuel concentration and a small amount of fuel. The exhaust gas recirculation control device of the present invention according to claim 5 has the structure according to claim 1.
As a device for returning a part of the exhaust gas to the intake passage.
Te, instead exhaust gas is refluxed to the intake passage from the exhaust passage
A valve for controlling the flow rate, and a actuator for driving the valve in accordance with the combustion state of the internal combustion engine, the driving speed of the closing direction relative to the driving speed in the opening direction of the Bal <br/> Bed is characterized by controlling the actuator so that a high speed towards the.

With such a configuration, when the exhaust gas amount is increased, the increasing speed becomes relatively slow, and a rapid increase in the exhaust gas amount, that is, a rapid decrease in fresh air is avoided, and the exhaust gas amount is increased. In the case of decreasing, the decrease speed becomes faster, the amount of exhaust gas can be decreased rapidly, and the fresh air can be increased rapidly.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 10 show an exhaust gas recirculation control device and an internal combustion engine having the device as one embodiment of the present invention. It is a thing. The internal combustion engine (hereinafter referred to as engine) according to the present embodiment is a gasoline engine.

First, the structure of the engine according to this embodiment will be described. In FIG. 1, 1 is an engine body, 2 is an intake passage, 3 is a throttle valve installation portion, 4 is an air cleaner, 5 is a bypass passage (first bypass passage). aisle),
6 is a bypass valve. The intake passage 2 is configured such that an intake pipe 7, a surge tank 8, and an intake manifold 9 are connected in this order from the upstream side, and the bypass passage 5 is provided on the upstream side of the surge tank 8.

Further, the bypass valve provided in the bypass passage 5 (which is called an air bypass valve (ABV)) is the same as the first air bypass valve (first valve) 10 provided in parallel with each other in this embodiment. It comprises a second air bypass valve (second valve) 11. That is, the bypass valve installation location of the bypass passage 5 branches into two passage portions 5a and 5b, and the passage portions 5a and 5b are configured to have the same flow passage area.

The first air bypass valve 10 and the second air bypass valve 10
The air bypass valve 11 is also a solenoid valve of the same standard and having the same size, but the first air bypass valve 10 is an on / off valve, and the second air bypass valve 1
1 is a duty control valve. Therefore, the first air bypass valve 10 is switched between the fully closed state and the fully open state, and the second air bypass valve 11 repeats the on / off operation in accordance with the set duty ratio and the time average valve opening degree is changed. Adjusted.

Reference numeral 12 is an idle speed controller (ISC), which is a bypass passage (second bypass passage) 13 and an ISC valve (third bypass valve) as a bypass valve.
Valve 14 and the ISC valve 14 is driven by a stepper motor (not shown). 15
Is a throttle valve, and the bypass passage 13 and the bypass passage 5 are connected to the intake passage 2 at their upstream and downstream ends so as to bypass the portion of the intake passage 2 where the throttle valve 15 is attached.

The first air bypass valve 10 and the second air bypass valve
The opening control of the air bypass valve 11 and the ISC valve 14 is controlled so that the total flow rate depending on the opening degree of each of these valves becomes a required air bypass flow rate. Therefore, at the time of switching between the lean combustion operation and the rich combustion operation, the air bypass flow rate can be promptly changed by the on / off control of the first air bypass valve 10, and the fine adjustment of the air bypass flow rate can be performed by the second air bypass valve 11 and the second air bypass valve 11. It can be performed by the ISC valve 14.

The opening / closing control of the first air bypass valve 10, the second air bypass valve 11 and the ISC valve 14 is performed through an electronic control unit (ECU) 16. Further, 17 is an exhaust passage, and 18 is a combustion chamber. An intake valve 19 and an exhaust valve 20 are provided at openings of the intake passage 2 and the exhaust passage 17 to the combustion chamber 18, that is, the intake port 2A and the exhaust port 17A. Has been done. Further, 21 is a fuel injection valve (injector), and in this embodiment, the injector 21 is arranged so as to directly inject fuel into the combustion chamber 18.

22 is a fuel tank, and 23A-23
E is a fuel supply path, 24 is a low pressure fuel pump, 25 is a high pressure fuel pump, 26 is a low pressure regulator, 27 is a high pressure regulator, 28 is a delivery pipe, and the fuel tank 22
The fuel inside is driven by the low-pressure fuel pump 24, and is further pressurized by the high-pressure fuel pump 25 so that the fuel supply path 23 is kept in a predetermined high pressure state.
A, 23B and the delivery pipe 28 are supplied to the injector 21. At this time, the fuel pressure discharged from the low pressure fuel pump 24 is equal to the low pressure regulator 2
The fuel pressure regulated by 6 and pressurized by the high-pressure fuel pump 25 and guided to the delivery pipe 28 is the high-pressure regulator 2.
The pressure is adjusted at 7.

Reference numeral 29 is an exhaust gas recirculation passage (EGR passage), 30 is a valve (EGR valve) for adjusting the amount of exhaust gas recirculation through the EGR 29, 31 is a flow passage for returning blow-by gas, and 32 Is a passage for active ventilation of the crank chamber, 33 is a valve for active ventilation of the crank chamber, 34 is a canister, and 35 is an exhaust gas purifying catalyst (here, a three-way catalyst).

Here, the EGR valve 30 will be explained. As shown in FIG. 2, the EGR valve 30 has a flow passage consisting of an inflow passage 30B and an outflow passage 30C in a valve case 30A, and this inflow passage 30B is provided. And outflow channel 30C
Between the valve seat 30D and this valve seat 3
A valve body (spool valve) 30E that can come into close contact with 0D is provided.

The valve body 30E is accurately driven by a stepper motor 30F to a required opening degree, and is equipped with a return spring 30G for urging the valve body 30E toward the closing side in case of failure of the stepper motor 30F. There is. As a result, when the stepper motor 30F fails, the valve body 30E is closed and the EGR is stopped. Also,
Reference numeral 30H denotes a carbon removal filter that removes carbon from the sliding portion of the valve body 30E to prevent sticking (stick) of the valve body 30E.

As shown in FIG. 1, the ECU 16 controls the opening / closing or opening of the first air bypass valve 10, the second air bypass valve 11 and the ISC valve 14, as well as the injector 21 and an ignition plug (not shown). The control of the ignition coil and the EGR valve and the fuel pressure control by the high pressure regulator 27 are also performed. For these controls, as shown in FIG. 1, an air flow sensor (not shown), an intake air temperature sensor 36, and a throttle position sensor (TP
S) 37, idle switch 38, boost sensor 3
9, air conditioner switch (not shown), shift position sensor (not shown), vehicle speed sensor (not shown), power steering switch (not shown) for detecting the operating state of the power steering, starter switch (not shown), first cylinder detection A sensor 40, a crank angle sensor 41, a water temperature sensor 42 for detecting the engine cooling water temperature, an O ₂ sensor 43 for detecting the oxygen concentration in the exhaust gas, and the like are provided and connected to the ECU 16. Here, a heater is attached to the O ₂ sensor 43, and the temperature is adjusted by controlling the heater through the ECU 16. The control through the ECU 16 will be further described later.

Next, the control contents of the engine through the ECU 16 will be described based on the control block diagram of FIG. In this engine, there are the late lean combustion operation mode, the early lean combustion operation mode, the stoichio feedback operation combustion operation mode, and the open loop combustion operation mode as the operation modes of the engine, and the EGR is operated in each mode. The case where EGR is stopped is set, and one of these modes is selected according to the operating state of the engine, the traveling state of the vehicle, and the like.

Of these, the late lean combustion operation mode is
In this embodiment, the total air-fuel ratio is set to a region of about 24 or more, and the leanest combustion can be realized. However, in this mode, fuel injection is performed at a stage extremely close to the ignition timing, such as in the latter stage of the compression stroke, and Fuel is collected in the vicinity of the spark plug to be partially rich and lean overall, while ensuring ignitability and combustion stability while performing economical operation. The region of the late lean combustion operation mode (lean combustion operation mode of stratified combustion) may be set to a range lower than that of this embodiment and a total air-fuel ratio of about 23 or more, or higher than that of this embodiment. You may set it.

Also, lean combustion can be realized in the early lean operation mode, but in this mode, the fuel injection is performed before the late lean operation mode, and the fuel is premixed so that the overall air-fuel ratio is higher than the theoretical air-fuel ratio. The lean operation is performed while ensuring ignition performance and combustion stability while obtaining a certain output. Here, the region of the previous lean combustion operation mode is set to a region where the total air-fuel ratio is about 24 or less and the stoichiometric air-fuel ratio or more.

In the stoichio feedback combustion operation mode, a sufficient engine output can be efficiently obtained while maintaining the air-fuel ratio in the stoichiometric state based on the output of the O ₂ sensor. Further, in the open loop combustion operation mode, combustion is performed with stoichio or a rich air-fuel ratio by open loop control so that sufficient output can be obtained during acceleration or starting. In these modes, premixed combustion based on fuel injection in the intake stroke is performed.

First, the opening control of the valves 10, 11 and 14 will be described. As shown in FIG. 3, the engine rotation based on the throttle opening θth detected by the throttle sensor and the detection information from the crank angle sensor. A target engine load (target Pe) is set based on the map from the speed Ne (block B1). On the other hand, if the air conditioner is turned on based on the information from the air conditioner switch, the correction amount ΔPeac corresponding to the air conditioner is set from the engine speed Ne based on the map (block B2), and the power steering is performed based on the information from the power steering switch. If is on, the power steering corresponding correction amount ΔPeps is set from the engine speed Ne based on the map (block B
3) At the time of starting based on the information from the inhibitor switch, the inhibitor-corresponding correction amount ΔPeinh is set based on the map from the engine rotation speed Ne (block B).
4).

Then, the corresponding correction amount ΔPea
The target Pe is corrected by c, ΔPeps, and ΔPeinh. Then, the corrected target Pe is appropriately filtered through the switch S1 (block B5), and from the target Pe and the engine rotation speed Ne thus obtained,
Required air volume (or target intake air volume) based on the map
A control amount Pos related to the valve opening degree according to Q is set.

In setting the control amount Pos, one selected from a plurality of maps according to the operating state of the engine is used as shown in a block B7, and the switch S is used.
Through 2 and S3, a signal is output according to the operating state of the engine. Here, maps are provided for the three operating modes of the engine, namely, the late lean mode in which the leanest combustion occurs, the first lean mode in which the leanest combustion occurs next, and the EGR operation in the stoichio operating mode. The required air amount is set only in these modes.

Further, when the idle operation state is established by the switch S4, the control amount ISCQ of the required air amount (or target intake air amount) ISCQ based on the feedback of the engine speed is shown as shown in block B8.
s (in this case, the target opening is mainly the ISC valve) is set. The control amount P thus obtained
Whether the first air bypass valve 10 is turned on or off according to os or ISCPos (block B
9), the duty ratio of the second air bypass valve 11 is set (block B10), the opening position of the ISC valve 14 is set (block B11), and the first air bypass valve 10, the second air bypass valve 11, The ISC valve 14 is controlled to the required state. The setting of the duty ratio of the second air bypass valve 11 (block B1
0), setting the opening position of the ISC valve 14 (block B
Regarding 11), hysteresis is provided, and different maps are used when the required air amount increases and when it decreases.

The opening control of the first air bypass valve 10, the second air bypass valve 11 and the ISC valve 14 is mutually performed. Further, each control of the injector, the ignition coil, and the EGR will be described based on FIGS. In order to drive the injector, it is necessary to set the injection start timing and the injection end timing of the injector, but here, the injector drive time Tinj and the injection end timing of the injector are set, and based on this, The timing of driving the injector is determined while back-calculating the injection start timing of the injector.

To set the injector drive time Tinj,
First, the air-fuel ratio A / F is set based on the map from the corrected target Pe and the engine speed Ne that have been filtered (block B6) (block B12). The setting map in this case is also provided for the four modes of the EGR operation in the late lean mode, the EGR stopped in the late lean mode, the lean mode in the early period, and the open loop mode, depending on the operating state of the engine. It is used by selecting one.

The injector drive time Tinj is calculated from the air-fuel ratio A / F thus obtained, the boost pressure pb detected by the boost sensor, and the intake air amount Qpb obtained from the volumetric efficiency correction value (block B13). The volumetric efficiency correction value is set from the engine rotation speed Ne based on a map corresponding to the operating state (block B19).
The map in this case (block B19) shows that the EGR is operating in the late lean mode, the EGR is stopped in the late lean mode, the early lean mode, the EGR is operating in open loop operation or stoichio feedback operation, and the open loop operation is performed. Or EG with stoichio feedback operation
It is provided for 5 modes of R stop.

Then, the injector drive time Tinj
Injector non-uniformity correction for each cylinder (block B14)
And cylinder dead time correction (block B15). On the other hand, the deceleration fuel injection time TDEC is calculated from the target Pe and the engine speed Ne (block B
16) At the time of deceleration and during the lean lean combustion operation, the injector drive time Tinj obtained at block B13 and the fuel injection time TDEC for this deceleration are obtained through the switch S5.
Select the smaller one of and (block B17),
This is the injector drive time.

The injection end timing of the injector is also set by the filtering target P after the filtering process (block B6).
From e and the engine rotation speed Ne, the air-fuel ratio A / F is set based on the map (block B18). The setting map in this case is also provided for four modes, that is, the EGR is operating in the late lean mode, the EGR is stopped in the late lean mode, the lean mode in the early period, and the open loop operation or the stoichio feedback operation mode. The one selected according to the operating state of the engine is used.

In the latter lean mode, the water temperature is corrected to the injection end timing thus obtained to obtain the injection end timing. The injector is driven based on the injector drive time Tinj and the injection end timing thus obtained. Also, regarding the ignition timing of the spark plug by the ignition coil, the corrected target Pe and the engine speed N that have been filtered (block B6) are also processed.
Based on e, the ignition timing is set based on the map (block B20). The setting maps in this case are as follows: EGR is operating in late lean mode, EGR is stopped in late lean mode, EGR is in early lean mode, EGR is operating in stoichio feedback operation, and EGR is in open loop operation or stoichio feedback operation. It is provided for 5 modes that are stopped. Various retard corrections (including advance corrections) are applied to the ignition timing thus obtained (block B
21) Based on this, the ignition coil is controlled.

Particularly, for the retard correction and the advance angle correction, the required amount is retarded in the early lean mode by the premixed combustion, and the required amount is advanced in the late lean mode by the stratified combustion. In premixed combustion, where the exhaust gas is introduced or little introduced so that the combustion speed is faster, retarding the ignition timing to ignite later is a knocking prevention effect, and the exhaust gas is introduced, which slows the combustion speed. In the stratified combustion, it is advantageous to save fuel consumption by advancing the ignition timing to ignite the ignition earlier.

As for the EGR flow rate control, as shown in FIGS. 3 and 4, the EGR flow rate is calculated based on the map from the corrected target Pe and the engine speed Ne which have been filtered (block B6). Set (block B22). The setting map in this case is for the 4 modes of the late lean mode in the D range, the late lean mode in the N range, the stoichio feedback operation mode in the D range, and the stoichio feedback operation mode in the N range. It is provided.

The EGR flow rate thus obtained is subjected to water temperature correction (block B23), a control amount (duty ratio) is set according to the opening (block B24), and the EGR flow rate is controlled. Water temperature correction (block B23)
As for the engine operating condition (here, the latter lean mode and stoichio feedback operating mode
The map according to the mode) is used.

For example, the target opening degree Etp of the EGR valve
Can be calculated by the following equation from the basic opening degree Ebtp corresponding to the EGR flow rate obtained in block B22 and the water temperature correction coefficient Kwt obtained in block B23. Etp = Ebtp × several Kwt Further, for such a target opening degree Etp of the EGR valve, a target step as a control amount (adjustment amount) of the EGR valve can be set from a map as shown in FIG. .

Further, here, the operating state of the engine is
The EGR introduction is performed only in the stoichio combustion operation mode or the late lean combustion operation mode, and in other cases, that is, in the early lean combustion operation mode and the open loop mode, the EGR introduction is not performed. This is because, in the case of lean in the previous period, when EGR is injected, combustion deteriorates, and the effect of reducing NOx and improving fuel efficiency is very small. Especially, increasing the EGR flow rate may lead to misfire. This is because a large amount of EGR cannot be introduced in the mode. Further, in the open loop mode, the priority is given to securing the engine output.

In principle, the amount of EGR introduced in the stoichiometric operation mode is set smaller than that in the latter lean. This is to introduce EGR mainly for the purpose of improving fuel economy during stoichiometric operation.
This is because the combustion deteriorates if a large amount of EGR is introduced.
The EGR introduction rate during the stoichiometric operation is about 20 to 25% at the maximum, and it may be 0 if it is the minimum.

Further, during stratified combustion (in the late lean combustion operation mode), the larger the air-fuel ratio, the larger the exhaust gas recirculated into the intake passage is set. The introduction rate of EGR at this time is about 30 to 60%. Depending on the engine, the EGR introduction rate during stratified combustion may be exceptionally set lower than during stoichiometric operation from the viewpoint of suppressing deterioration of combustion.

Next, setting of the EGR introduction rate and the air-fuel ratio during the late lean combustion operation will be described with reference to FIG. FIG. 7 shows an example in a general operation state as the late lean combustion operation, for example, when the engine rotation state is 15
The conditions are 00 rpm and a net average effective pressure of 0.3 MPa.

In FIG. 7, the horizontal axis is the air-fuel ratio (A / F) and the vertical axis is the NOx emission rate. This NOx emission rate is the NOx emission amount during the late lean combustion operation relative to the NOx emission amount during the stoichiometric operation. It is the ratio of quantity. Further, in the figure, a curve L1 indicates a stable combustion limit, and stable combustion cannot be performed by the late lean combustion operation outside the curve (that is, on the left side or the lower side). Curve L2 is intake air (= fresh air + EG
WO under the condition that R) is 0.1 MPa (that is, about 1 atm)
It is T (throttle fully open), and driving outside of this curve (that is, to the right or below) cannot be performed.

Curves a1 to a3 show the fuel consumption improvement rate, that is, the fuel consumption improvement rate in the late lean combustion operation with respect to the fuel consumption in stoichio operation. The curve a1 shows the fuel consumption improvement rate of 10%, and the curve a2 shows the fuel consumption. The improvement rate is 20%, and the curve a3 shows the fuel consumption improvement rate of 30%. The curves b1 to b3 are EGR.
The introduction rate, that is, the ratio of the EGR introduction amount in the intake air amount is shown. The curve b1 is the EGR introduction rate 0%, and the curve b2 is the EGR.
The introduction rate is 20%, and the curve b3 shows the EGR introduction rate of 40%.

The late lean combustion operation is performed by the curve L in FIG.
It is possible to operate in a region above 1, 2, and within this region, the air-fuel ratio (A / F) is set so that the fuel consumption improvement rate is high and the NOx reduction rate is high (that is, the NOx emission rate is low).
By setting the EGR introduction rate and the EGR introduction rate, both improvement of fuel consumption and reduction of NOx are achieved. For example, as in the hatched region in FIG. 7, the late lean combustion operation is performed in the region where the fuel consumption improvement rate is 30% or more and the NOx reduction rate is 90% or more (that is, the NOx emission rate is 10% or more). So that the air-fuel ratio and E
It is conceivable to set the GR introduction rate. Note that FIG.
Among them, L3 shows a NOx reduction rate of 90%.

In the example shown in FIG. 7, the air-fuel ratio is about 28-.
33 or more, and the EGR introduction rate is set to any of 30 to 60%, the fuel efficiency improvement rate is 30% or more and the NOx reduction rate is 90% or more. However, the late lean combustion operation by stable combustion can be performed. Of course, FIG. 7 shows a typical example in the late lean combustion operation, and such characteristics change depending on the load condition of the engine and the engine speed, and the fuel consumption improvement rate is high depending on each operation condition. NOx
It suffices to set the air-fuel ratio and the EGR introduction rate such that the reduction rate becomes high, and perform the control based on these settings.

In this case, the fuel consumption improvement rate as described above is 30.
%, The target value of NOx reduction rate of 90% or more cannot always be achieved, but depending on the operating state, the air-fuel ratio and the EGR introduction rate are set with emphasis on the fuel efficiency improvement rate, and the NOx reduction rate is also reduced. Air-fuel ratio and E
It is conceivable to set the GR introduction rate. In addition,
The operation of the engine is not always the steady operation, and the operating state often changes from time to time. In this way, the operating mode can be switched appropriately according to the changing operating state.
Even in the late lean combustion operation mode, the target air-fuel ratio and the target EGR introduction rate are changed according to the changing operating state. In this case, in addition to the method of simultaneously changing the target air-fuel ratio and the target EGR introduction rate, a method of emphasizing the target air-fuel ratio control, for example, changing the target air-fuel ratio and then changing the target EGR introduction rate is also considered. To be

By the way, when the engine is in operation, the combustion mode is switched according to changes in the load condition and the number of revolutions. Normally, when the load increases from the low load condition, the latter lean combustion operation mode is changed to the previous period. After the lean combustion operation mode, the stoichio combustion operation mode is switched to, and if the load further increases, the open loop mode (enriched combustion operation mode) is switched to. vice versa,
When the load decreases from the high load state, for example, the stoichio combustion operation mode is switched to the latter lean combustion operation mode and then to the latter lean combustion operation mode. However, if there is an acceleration or start command from the driver, the latter lean mode is directly switched to the stoichio mode.

Generally, with respect to the engine speed and the engine load, the enriched combustion operation mode, the stoichio combustion operation mode, the early lean combustion operation mode, and the late lean combustion operation mode are set in a region tendency as shown in FIG. It

At this time, the EGR introduction is performed in the late lean combustion operation mode and the stoichiometric combustion operation mode, but the EGR introduction is not performed in the other modes. Therefore, EGR switching (switching between introduction and stop) is performed together with mode switching. However, when the operation mode is switched from the early-stage lean combustion operation or pre-stochio operation with premixed combustion to the late-stage lean combustion operation with stratified combustion, and the operation mode from the early-stage lean combustion operation to pre-stoichio operation during premixed combustion. When the amount of EGR introduced increases as in switching, the amount of fresh air introduced decreases, causing a sudden output fluctuation (torque shock),
A vehicle-mounted engine is likely to impair drivability.

Therefore, in the present apparatus, particularly, when the operation mode is switched from the early lean combustion operation by the premixed combustion or the early stoichio combustion operation to the late lean combustion operation by the stratified combustion, and the early lean combustion operation in the premixed combustion. From the previous term to the stoichio combustion operation, the intake air amount adjustment and the EGR switching are made to shift,
After adjusting the intake air amount according to the switching of the air-fuel ratio, EG
The introduction or stop of R is switched.

That is, as shown in FIG. 5 (A), when the operation mode is switched from the early stoichio combustion operation to the late lean combustion operation, the EGR is switched as shown in FIG. 5 (B). I'm trying to delay. Since switching of the operation mode as described above shifts to an operation requiring acceleration, it is desirable to secure the amount of fresh air introduced and obtain the target output. EG
If the amount of R is adjusted at the same time, the amount of fresh air introduced cannot be secured sufficiently by the introduction of EGR, and the target engine output cannot be obtained, resulting in deterioration of drivability. For this reason, the EGR introduction is delayed so that a sufficient amount of fresh air is introduced and an adequate engine output is obtained.

Further, as shown in FIG. 5 (A), when the operation mode is switched from the early stoichio combustion operation to the late lean combustion operation, the EGR is switched as shown in FIG. 5 (B). I'm trying to delay. In the case of such switching of the operation mode, there is a lean combustion operation state in the previous period (that is, operation in which the combustion state deteriorates) in the process of switching change, and if EGR is introduced in this process, output change occurs. This leads to deterioration of drivability. Therefore, E
The GR introduction is delayed to prevent the EGR introduction during the lean combustion operation state in the first half of the period.

Further, as shown in FIG. 5 (A), when the operation mode is switched from the early lean combustion operation to the late lean combustion operation, the EGR is switched as shown in FIG. 5 (B). I'm trying to delay. Even in the case of such operation mode switching, the switching from the early lean combustion operation to the late lean combustion operation does not occur instantaneously, and during the transition transition, the lean combustion operation does not completely shift to the late lean combustion operation and EG with the remaining
In some cases, R may be introduced, and in such a situation, the output changes similarly to the above and causes deterioration of drivability. Therefore, the EGR introduction is delayed to prevent the EGR introduction during the lean combustion operation in the first half period.

When switching from the early lean combustion operation to the late lean combustion operation, the EGR switching may not be delayed. This is because when the change from the early lean combustion operation to the late lean combustion operation is small and the change in the set air-fuel ratio is small and the required air amount is small, EGR adjustment (here, EGR introduction) is performed to adjust the intake air amount. This is because the EGR does not hinder the increase change in the intake air amount even if performed at the same time.

Further, the above-mentioned EGR switching delay time can be set according to the characteristics of each engine as the time until the combustion becomes stable after the mode switching.

Further, here, at the time of switching from the stoichiometric combustion operation and the late lean combustion operation to the early lean combustion operation,
Also, when switching from the late lean combustion operation to the stoichiometric combustion operation, the EGR switching is not delayed. This is because the stoichio combustion operation, the switching from the late lean combustion operation to the early lean combustion operation, and the switching from the late lean combustion operation to the stoichio combustion operation
By stopping or reducing GR, the negative pressure downstream of the throttle valve increases and the amount of fresh air introduced increases,
Since it is rather convenient to increase the air-fuel ratio, the EGR switching is performed at the same time when the flow rate of the air bypass for switching (increase) the air-fuel ratio is increased.

Further, here, the EGR is performed even in the stoichio combustion operation mode or the late lean combustion operation mode.
When the prohibition conditions are met, that is, at engine stall, at start,
When the engine operating condition detecting means is abnormal (for example, when the atmospheric pressure sensor fails) or when decelerating in a mode other than the lean combustion operating mode, the EGR valve is controlled to be fully closed. Further, when such an EGR prohibition condition is released, the EGR valve is controlled to be switched from fully closed to a required opening degree.

Here, a specific control method for opening / closing drive of the EGR valve using the stepper motor will be described with reference to FIGS.
This will be described with reference to the flowchart in FIG. Although the target EGR valve opening degree P _S is set in this description, the target EGR valve opening degree P _S corresponds to the above-mentioned target opening degree Etp of the EGR valve. First, a method for setting the EGR valve opening will be described with reference to FIG. An EGR valve opening degree setting routine as shown in FIG. 9 is conceivable. First, it is determined whether the engine is in the starting mode (step A10). Here, if the engine is not in the starting mode, it is determined whether the engine is in the cold state (step A10). A2
0) Here, if the engine is not in the cold state, it is determined whether the initialization flag of the stepper motor is set (step A30). Here, if the initialization flag is not set, the process proceeds to step A50, but either the engine is in the start mode, the engine is in the cold state, or the initialization flag of the stepper motor is set. For example, since it is not the EGR introduction condition, the routine proceeds to step A40, where the target EGR valve opening degree P _{S is set} to be fully closed (that is, P _S = 0).

On the other hand, if it proceeds to step A50, it is judged whether or not the current fuel injection mode is the late injection mode (specifically, the late lean combustion operation mode). If it is not the latter injection mode, the operation goes to step A60. Then, it is determined whether or not the lean mode (specifically, the lean combustion operation mode in the first half period) is entered. Here, if it is not the lean mode (the previous period lean combustion operation mode), proceed to step A70,
It is determined whether or not the enrichment mode (enriched combustion operation mode).

If the enrichment mode is not set, the stoichio mode (stoichio combustion operation mode) is set,
First, in step A72, it is determined whether or not the mode timer 2 has reached the set value. Here, if the mode timer 2 has reached the set value, the process proceeds to step A74, the mode timer 3 is set to the initial value 0, and the process proceeds to step A80.

By the way, the mode timer 2 and the mode timer 3, together with the mode timer 1 which will be described later, are used to delay the switching timing of the EGR control from the intake air amount adjustment at the time of mode switching. That is, the mode timer 1 is provided to delay the introduction start timing of the EGR control from the intake amount adjustment when the mode is switched from the early lean combustion operation mode to the late lean combustion operation mode. Is always reset to 0 in step A110, which will be described later, in the early lean combustion operation mode, so the introduction of EGR is started until the time corresponding to the set value elapses after switching from the early lean combustion operation mode to the late lean combustion operation mode. Will be delayed. As described above, when switching from the early lean combustion operation to the late lean combustion operation, the EGR switching may not be delayed. Therefore, when the EGR switching is not delayed, The set value for the timer 1 is 0.

The mode timer 2 is provided for delaying the introduction start timing of the EGR control from the intake air amount adjustment when the mode is switched from the previous lean combustion operation mode to the previous stoichio combustion operation mode. 2 is also always reset to 0 in the previous period lean combustion operation mode in step A110, so until the time corresponding to the set value elapses after switching from the previous period lean combustion operation mode to the previous period stoichio combustion operation mode, EG
The start of introduction of R will be delayed.

Further, the mode timer 3 is provided so as to delay the introduction amount increase timing of the EGR control from the intake amount adjustment when the mode is switched from the early stoichio combustion operation mode to the late lean combustion operation mode. Since the mode timer 3 is always reset to 0 in the above-described stoichio combustion operation mode in step A74,
The start of increasing the amount of EGR introduced will be delayed until the time corresponding to the set value elapses after switching from the first-stage stoichio combustion operation mode to the second-stage lean combustion operation mode.

Therefore, after a lapse of time corresponding to the set value after switching from the previous lean combustion operation mode to the previous stoichio combustion operation mode, it is determined in step A72 that the mode timer 2 has reached the set value, and step A7
After step 4, the process proceeds to step A80, where EGR is introduced according to the previous period stoichio combustion operation mode.
That is, in step A80, the operating state of the engine, that is,
The target EGR valve opening degree P _SSTO is set according to the setting characteristics in the stoichiometric mode according to the engine speed and the engine load. Target EGR valve opening P _SSTO during this stoichiometric operation
As described above, the maximum EGR introduction rate is 20 to 25%.
The opening is set to a degree, and E
The GR introduction rate may be set to 0, that is, the fully closed state may be set.

Then, the target EGR set in this way
The valve opening P _SSTO is set to the target EGR for the EGR valve opening control command.
The valve opening degree is set to P _S (step A90). On the other hand, if it is determined in step A72 that the mode timer 2 has not reached the set value, or if it is determined in step A70 that the mode is the enrichment mode, the process proceeds to step A120 and the target E
Set the GR valve opening P _S to fully closed (that is, P _S = 0),
Meet the output demand by increasing the introduction rate of fresh air.

When it is determined in step A60 that the engine is in the lean mode (previous period lean combustion operation mode), the process proceeds to step A110, and the mode timers 1 and 2 are set to their initial values, that is, 0. After the processing of step A110,
In step A120, the target EGR valve opening degree P _S is set to be fully closed (that is, P _S = 0), the introduction rate of fresh air is increased, and the previous period lean combustion operation mode, that is, intake stroke lean combustion is performed. Ensure combustion stability during operation.

If it is determined in step A50 that the current fuel injection mode is the late injection mode, step A13 is executed.
In step 0, it is determined whether the mode timer 1 has reached the set value. As described above, the mode timer 1 is always reset to 0 in the lean combustion operation mode in the first term (step A110). Therefore, until the time corresponding to the set value elapses from the first lean mode to the second lean mode, Similar to the lean mode, the target EGR valve opening degree P _S
Are fully closed (ie, P _S = 0).

When the mode timer 1 has passed the time corresponding to the set value, the routine proceeds to step A140, where it is determined whether or not the mode timer 3 has reached the set value. As described above, the mode timer 3 is always reset to 0 in the previous period stoichio combustion operation mode (step A74), and therefore, until the time period corresponding to the set value elapses after switching from the previous period stoichio mode to the late lean mode. Target EG
The R valve opening degree P _S is set to the value (that is, P _S = P _SSTO ) set in step A90 of the immediately preceding stoichiometric mode.

After the time corresponding to the set value elapses after switching from the first stoichio mode to the second lean mode, the mode timer 3 reaches the set value.
Then, the target EGR valve opening degree P _SLEAN is set according to the operating condition of the engine, that is, the engine speed and the engine load, with the set characteristic in the latter lean period. As described above, the target EGR valve opening degree P _SLEAN during the latter lean operation is actually the EGR introduction rate of 30 depending on the air-fuel ratio (A / F).
The opening is about 60%.

Then, the target EGR set in this way
The valve opening P _SLEAN is set to the target EG for the EGR valve opening control command.
The R valve opening is set to P _S (step A160). In this way, the target opening P _S of the EGR valve can be set, and further, the drive control of the EGR valve can be performed by the method shown in FIG. 10. Note that, here, it is set so that when the stepper motor for driving the EGR valve is normally rotated, it is driven in the opening direction, and when the stepper motor is rotated in the reverse direction, it is driven in the closing direction.

Further, here, three drive cycles of the reverse drive (open drive cycle) T1, the forward drive cycle (close drive cycle) T2, and the initialization drive cycle T3 are set as the drive cycle of the stepper motor. And T3>
The relationship of T1> T2, that is, the forward drive cycle (close drive cycle) T2 is set to the shortest, the reverse drive cycle (open drive cycle) T1 is set to the shortest, and the initialization drive cycle T3 is set to the longest. ing.

The drive cycle for initialization T3 is set to be the longest. When the stepper motor is driven to a mechanical limit position such as a fully closed position or a fully opened position of the valve, the driven body, that is, the valve body is mechanically collided. There is a risk of bouncing. Therefore, if the bounce is performed at the fully closed position or the fully opened position at the time of initialization, the valve body cannot be reliably driven to the fully closed position or the fully opened position.

Therefore, in order to avoid such a bounce, the drive cycle T3 for initialization is set to be long so that the substantial drive speed of the stepper motor is moderated. Further, the reverse rotation drive cycle (open drive cycle) T1 is set to the forward rotation drive cycle (closed drive cycle) T2.
The longer the EGR valve is opened, the slower the EGR valve opening speed should be by slowing down the substantial drive speed of the stepper motor in a relatively long cycle T1 to avoid a sudden EGR introduction. It is what on the other hand,
In the EGR valve closing drive, the stepper motor driving speed is increased in a relatively short cycle T2, the EGR valve opening speed is increased, and the EGR introduction is stopped quickly. This is because the engine output can be increased and the engine output can be promptly increased.

As shown in FIG. 10, first, it is judged whether or not the initialization flag of the stepper motor is set (step B10). Here, if the initialization flag is not set, step B20
Then, it is determined whether or not there is an initialization command for the stepper motor (STM). This initialization command is issued immediately after the engine is stopped or the key switch is turned on.

If there is an initialization command for the stepper motor (STM), the flow advances to step B30 to set an initialization flag, and in step B40, a predetermined value β is set as the initialization drive pulse number PP, and step B
Go to 50. It should be noted that this predetermined value β is the number of steps to be driven when the stepper motor is initialized, and for example, by setting it to be equal to or more than the total number of steps to drive the stepper motor (that is, the number of steps to drive the valve from fully open to fully closed), You can make sure initialization.

When it is determined in step B10 that the initialization flag is set, the process also goes to step B50. In step B50, it is determined whether the initialization drive pulse number PP is 0 or not. If the initialization drive pulse number PP is 0, the initialization flag is reset (step B60) and the process proceeds to step B80. If the initialization drive pulse number PP is not 0, the initialization drive pulse number PP is reduced by one step (step B70), and the process proceeds to step B110.

At step B110, the drive cycle T3 for initialization is set as the target drive pulse cycle data T0 of the stepper motor. On the other hand, if it is determined in step B20 that there is no initialization command, step B80
To the difference ΔP (= P _S −P between the target opening (target position) P _S and the actual opening (actual position) Pr of the EGR valve.
r) is calculated, and it is further determined in step B90 whether the difference ΔP is smaller than a predetermined value −α.

The predetermined value α corresponds to the allowable error range of the opening degree of the EGR valve, and if the magnitude of the difference ΔP (= │ΔP│) is smaller than the predetermined value α (that is, -α≤ΔP≤ α), E
It is assumed that the GR valve has reached the target opening. Step B
If it is determined at 90 that the difference ΔP is smaller than the predetermined value −α, that is, if the target opening P _S is smaller than the actual opening Pr and this difference is smaller than the predetermined value α, the stepper motor is operated. It is necessary to rotate normally, and first, the process proceeds to step B100, where it is determined whether the actual opening (actual position) Pr is equal to or less than a predetermined value γ. The actual opening (actual position) Pr is a predetermined value γ
If the following is true, the process advances to step B110 to set the initialization drive cycle T3 as the target drive pulse cycle data T0.

This is because when the actual position Pr becomes equal to or less than the predetermined value γ, if the valve body is driven to the fully closed position in the normal rotation drive cycle, the valve body may mechanically collide and bounce. There is to avoid this. Such a valve body collision may occur even if the valve body is not at the actual fully closed position if the stepper motor is out of step at the initial setting stage. However, if the valve body is driven to the fully closed position while the driving speed is fast in consideration of the responsiveness of the valve body, the valve body may mechanically collide and bounce. Especially when driving to the fully closed position, there is a high risk of bouncing. Therefore, in order to avoid such bounce, the substantial drive speed of the stepper motor is attempted to be moderated by using the initialization drive cycle T3.

After the processing of step B110 is completed, the forward rotation flag is set (this flag is set when the stepper motor is driven in the forward rotation) at step B120, and the routine proceeds to step B130. On the other hand, if the actual position Pr is not less than or equal to the predetermined value γ, the process proceeds to step B210,
A relatively short drive pulse cycle T2 is set as the target drive pulse cycle data T0. Then, the process proceeds to step B120, the forward rotation flag is set, and the process proceeds to step B130.

If it is determined in step B90 that the difference ΔP is not smaller than the predetermined value −α, the process proceeds to step B220, where it is determined whether the difference ΔP is larger than the predetermined value α. Here, if the difference ΔP is not larger than the predetermined value α, it is determined that the EGR valve has reached the target opening degree, and the current drive control is not performed. Step B220
When it is determined that the difference ΔP is larger than the predetermined value α, that is, when the target opening P _S is larger than the actual opening Pr and this difference is larger than the predetermined value α, the stepper motor is reversed. It is necessary to proceed. First, the process proceeds to step B230, and the drive pulse cycle T1 which is relatively longer than that during normal rotation (close drive) is set as the target drive pulse cycle data T0. Then, the process proceeds to step B240, the forward rotation flag is reset, and the process proceeds to step B130.

Then, the routine proceeds to step B130, where it is judged if the period measuring timer value T is equal to or longer than the target drive pulse period T0. If the period measurement timer value T is not equal to or greater than the target drive pulse period T0, the process returns. If the period measurement timer value T is equal to or greater than the target drive pulse period T0, the process proceeds to step B140, and the drive timer value T is first set. After resetting to 0, it is determined in step B150 whether the forward rotation flag is set.

When the forward rotation flag is set,
In step B160, it is determined whether the reverse rotation timer is equal to or greater than the predetermined value TS. This reverse rotation timer is reset to 0 during reverse rotation drive (step B260). Therefore, when switching from the reverse rotation drive state to the normal rotation drive state, the forward rotation drive cannot be started until the predetermined value TS or more has elapsed after the reverse rotation drive was stopped. It is like this. This predetermined value TS waits for the movement due to the inertial force of the valve body to subside when switching between forward rotation and reverse rotation,
It is a standby time for forward / reverse rotation switching to be reversed, and the predetermined value TS is set longer than any of the above-mentioned cycles T1, T2, T3 (that is, TS>T3>T1>).
T2).

Therefore, at least when the reverse rotation drive is completed and the forward rotation / reverse rotation switching standby time TS has elapsed, the forward rotation timer is reset to 0 in step B170, and then the closing side drive pulse is applied to the stepper motor (STM). Only one pulse (normal drive pulse) is output (step B180).
Then, it is determined whether or not the actual potentiometer data is in the fully closed position (Pr = 0) (step B190), and if the actual potentiometer data is not in the fully closed position, the actual potentio data P is obtained.
The drive pulse 1 is subtracted from r (step B200).

On the other hand, when the reverse rotation flag is set, it is determined in step B250 whether the forward rotation timer is equal to or larger than the predetermined value TS. This forward rotation timer is reset to 0 at the time of forward rotation drive as described above (step B17).
Therefore, when switching from the normal rotation driving state to the reverse rotation driving state, the normal rotation driving cannot be started until the predetermined value TS or more elapses after the normal rotation driving is stopped. This predetermined value TS is also a normal rotation / reverse rotation switching standby time in which the rotation due to the inertial force of the valve body is settled when the normal rotation / reverse rotation is switched as described above, and then the reverse rotation is tried. TS is set longer than any of the above-mentioned periods T1, T2, T3 (that is, TS>T3>T1> T2).

Therefore, at least when the forward rotation drive is completed and the forward rotation / reverse rotation switching standby time TS has elapsed, the reverse rotation timer is reset to 0 in step B260, and then the open side drive pulse is applied to the stepper motor (STM). Only one pulse (reverse rotation drive pulse) is output (step B270).
Then, the process proceeds to step B280, where the actual potentiometer data Pr is increased by the drive pulse 1.

Since the exhaust gas recirculation control device as one embodiment of the present invention is constructed as described above, the operating mode of the engine can be set in accordance with the operating state of the engine.
The late lean combustion operation mode, the early lean combustion operation mode, the stoichio feedback operation combustion operation mode, and the open loop combustion operation mode are selected, and the air-fuel ratio, the fuel amount, the ignition timing, and the EGR are controlled according to each mode.

The fuel amount is controlled as a fuel injection amount according to the output state required for the engine, and the air-fuel ratio corresponding to this fuel injection amount is controlled by the air bypass valves 10, 11 in addition to the throttle valve 15. , ISC valve 14
It is controlled through opening / closing control, opening control, and the like. Also, E
The GR can also be switched on / off according to the operation mode, but in this device, as shown in FIG. 5, when the operation mode is switched between the early lean combustion operation and the late lean combustion operation, the intake air amount adjustment is performed. After adjusting the intake air amount according to the air-fuel ratio switching,
The EGR is introduced or stopped.

As a result, as shown in FIG. 6A, in the early lean combustion operation, NOx decreases with the air-fuel ratio, and in the late lean combustion operation, NOx increases with the air-fuel ratio without EGR. Due to NO
x can be positively reduced. Also,
During stoichio operation, EGR while ensuring combustion stability
NOx can be reduced while appropriately introducing.

Also, when the late lean combustion operation is switched to the early lean operation or stoichiometric operation, the air-fuel ratio can be promptly reduced, the shortage of the engine output can be avoided, and the desired output increase can be promptly achieved. Can be realized. In addition, when the lean burn operation in the previous period or stoichiometric operation is switched to the lean burn operation in the latter period, it is possible to secure the amount of fresh air introduced, avoid sudden output fluctuations (torque shock), and drive the engine in the vehicle. It is possible to avoid deterioration of the ability.

As shown in FIG. 6B, NOx is changed according to the EGR rate (ratio of the amount of EGR to fresh air).
A reduction effect can be obtained, but during late lean combustion operation, E
A sufficient NOx reduction effect can be obtained by increasing the GR rate. In particular, at the time of stratified combustion (in the late lean combustion operation mode), as the air-fuel ratio becomes larger, the exhaust gas recirculated into the intake passage becomes larger, whereby a sufficient NOx reduction effect can be obtained. it can.

Further, since the ignition timing is retarded by the required amount in the early lean mode by the premixed combustion, and the ignition timing is advanced by the required amount in the late lean mode by the stratified combustion, the exhaust gas is not introduced or little is introduced. In premixed combustion, which accelerates the combustion speed, retarding the ignition timing to ignite the ignition later has the knocking-preventing effect, and because exhaust gas is introduced, the ignition timing is advanced in stratified combustion where the combustion speed slows down. It is advantageous to save fuel consumption by igniting early.

Further, in this embodiment, since the first air bypass valve 10 and the second air bypass valve 11 are of the same standard so that parts can be shared, there is also a cost reduction effect. In the present embodiment, the first air bypass valve 10, the second air bypass valve 11 and the IS
Although three valves including the C valve 14 are provided, it is also possible to omit one of the second air bypass valve 11 and the ISC valve 14 and control the air bypass flow rate with only two valves, for example. Be done. For example, the flow rate of the air bypass may be controlled only from the first air bypass valve 10 and the second air bypass valve 11,
It is also possible to configure only the first air bypass valve 10 and the ISC valve 14.

Also in this case, when the EGR stop is switched to the EGR closed, the air bypass flow rate can be instantly increased mainly by switching from the off state to the on state by the first air bypass valve 10, and the second air bypass valve can be used. Valve 11
Or by adding flow control by the ISC valve 14,
The required fresh air intake amount can be secured with good responsiveness.

Further, in this exhaust gas recirculation control device, the EG
The driving stepper motor for the R valve has a short drive cycle when it is closed, and is quickly closed, and a long drive cycle when it is opened and is gently opened, which has the following advantages. In the case of a combustion change that switches from stratified combustion that emphasizes fuel economy (late lean operation) to premixed combustion that emphasizes ensuring output (stoichio operation or lean operation in the previous term), it is considered that the engine output demand is increasing. At this time, the EGR valve is driven to be closed promptly to cut or decrease the flow rate of the exhaust gas, so that the amount of fresh air introduced can be increased rapidly and the output of the engine can be output without deteriorating the combustion. Can respond to requests quickly.

Further, in the case of a combustion change that switches from premixed combustion (stoichio operation or early lean operation) to stratified combustion (late lean operation), the EGR valve is gently opened and the exhaust gas amount is gradually increased. It is possible to switch to stratified combustion while purifying exhaust gas (reducing NOx) by the amount of introduced exhaust gas without causing deterioration of combustion at the time of transition, without causing deterioration of combustion at the time of transition.

It is needless to say that the driving speed control of the EGR valve is not limited to the stepper motor, but a negative pressure valve, a DC motor, a linear solenoid, or the like can be applied. When the EGR valve is initialized or when the EGR valve is fully closed, the stepper motor is driven at a slow speed with a long drive cycle, preventing valve bounce and preventing stepper motor out-of-step operation. Is performed reliably and can be initialized accurately.

Furthermore, since the time lag (TS) is given when the EGR valve is driven in the reverse direction, there is an advantage that the inertial force of the EGR valve does not affect the operation of the EGR valve and the EGR valve operates reliably. .

Further, the exhaust gas recirculation control device of the present invention is
As in the present embodiment, the use of a direct injection internal combustion engine has a great effect, but the present exhaust gas recirculation control device is not limited to such an internal combustion engine, but an intake system of another internal combustion engine. It is also widely applicable to.

[0128]

As described in detail above, according to the exhaust gas recirculation control device of the present invention as set forth in claim 1, the premixed combustion,
The total air-fuel ratio in the combustion chamber is larger than the total air-fuel ratio of the premixed combustion, and either of the stratified combustion and the exhaust gas is discharged.
In an internal combustion engine that recirculates a part of the output gas into the intake passage, the exhaust gas recirculation amount at the time of stratified combustion
Set a value higher than the exhaust gas recirculation amount, and
The combustion state of the combustion engine is switched from the premixed combustion to the stratified combustion.
When changing, change the intake air amount accompanying the change of the total air-fuel ratio
After that, change the exhaust gas recirculation amount
Due to the configuration of control , extremely efficient combustion can be realized during stratified combustion, and a remarkable fuel efficiency improvement effect can be obtained, and output accompanying switching of combustion states while achieving both such efficient operation and exhaust gas purification. It becomes possible to avoid the shortage and the occurrence of torque shock.

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

According to the exhaust gas recirculation control device of the present invention described in claim 2, in the structure described in claim 1, the premixing is performed.
Combustion has an air-fuel ratio greater than the theoretical air-fuel ratio and exhaust gas
A premix lean mode that does not introduce reflux,
When switching from lean mode to stratified combustion,
The exhaust gas recirculation amount is changed after switching the air-fuel ratio.
The pre-mixing recirculation is achieved while achieving both efficient operation and exhaust gas purification by being configured so as to control
The lean combustion mode is better than the premix lean mode.
It becomes possible to surely avoid the occurrence of output shortage and torque shock due to the switching of the lean stratified combustion to the combustion state, and it is possible to improve drivability.

[0137]

[0138]

[0139] According to the exhaust gas recirculation control device of the present invention described in claim 3, in the configuration of claim 1, wherein the air-fuel ratio is larger when the stratified combustion, the outlet gas recirculation amount to be recirculated to the intake passage Or open the exhaust gas recirculation control valve
By being configured to set a large degree ,
In the case of lean burn operation by stratified burn combustion, exhaust gas can be sufficiently purified (NOx reduction) while ensuring combustion stability.

According to the exhaust gas recirculation control device of the present invention described in claim 4, in the structure described in claim 3, the stratified fuel is used.
By setting the total air-fuel ratio at the time of burning to about 23 or more, it is possible to significantly improve fuel efficiency. Claim 5
According to the exhaust gas recirculation control device of the present invention as claimed, claim
In the configuration of 1, the part of the exhaust gas is introduced into the intake passage.
As an apparatus for recirculating a valve for controlling the exhaust gas quantity is recirculated to the intake passage from the exhaust passage, of the internal combustion engine
An actuator for driving the valve according to a combustion state , and a closing direction with respect to a driving speed in the opening direction of the valve.
The actuator so that at high speed towards the driving speed of the
By controlling the order in which a sudden increase in exhaust emissions recirculation amount is avoided, it is possible to ensure the combustion stability of the engine, when reducing the exhaust gas recirculation amount, to quickly decrease the exhaust gas recirculation amount Therefore, by promptly introducing fresh air, the output of the engine can be increased quickly and the drivability can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of an internal combustion engine having an exhaust gas recirculation control device as an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of an exhaust gas recirculation control valve according to the exhaust gas recirculation control device as one embodiment of the present invention.

FIG. 3 is a control block diagram of an exhaust gas recirculation control device as an embodiment of the present invention.

FIG. 4 is a control block diagram of an internal combustion engine having an exhaust gas recirculation control device as one embodiment of the present invention.

FIG. 5 is a diagram showing a control example of an exhaust gas recirculation control device as one embodiment of the present invention, (A) relating to an operation mode, and (B) relating to an EGR state.

FIG. 6 is a diagram showing an effect by control of an exhaust gas recirculation control device as one embodiment of the present invention, (A) shows an effect of reducing NOx in exhaust gas with respect to air-fuel ratio control,
(B) shows the NOx reduction effect in the exhaust gas with respect to the exhaust gas introduction rate (EGR rate).

FIG. 7 is a diagram illustrating setting of the EGR introduction rate and the air-fuel ratio during the late lean combustion operation in the exhaust gas recirculation control device as one embodiment of the present invention.

FIG. 8 is a diagram illustrating an operation mode of an internal combustion engine having an exhaust gas recirculation control device according to an embodiment of the present invention.

FIG. 9 is a flowchart showing an example of setting the opening degree of the EGR valve in the exhaust gas recirculation control device as one embodiment of the present invention.

FIG. 10 is a flowchart showing an example of an EGR valve driving method in the exhaust gas recirculation control device as one embodiment of the present invention.

11A and 11B are views for explaining the problems of the present invention, in which FIG. 11A shows a characteristic relating to combustion stability, and FIG. 11B shows a characteristic relating to fuel efficiency (fuel consumption).

[Explanation of symbols]

1 engine body 2 intake passage 2A intake port 3 throttle valve installation portion 4 air cleaner 5 bypass passage (first bypass passage) 5a, 5b passage portion 6 bypass valve 7 intake pipe 8 surge tank 9 intake manifold 10 first air bypass valve (first 1 valve) 11 2nd air bypass valve (2nd valve) 12 idle speed controller (ISC) 13 bypass passage (2nd bypass passage) 14 ISC valve (3rd valve) as a bypass valve 15 throttle valve 16 electronic control unit ( ECU) 17 exhaust passage 17A exhaust port 18 combustion chamber 19 intake valve 20 exhaust valve 21 fuel injection valve (injector) 22 Fuel tanks 23A-23E Fuel supply passage 24 Low-pressure fuel pump 25 High-pressure fuel pump 26 Low-pressure regulator 27 High-pressure regulator 28 Delivery pipe 29 Exhaust gas recirculation passage (EGR passage) 30 EGR valve 30A Valve case 30B Inflow passage 30C Outflow passage 30D Valve seat 30E Valve body (spool valve) ) 30F Stepper motor 30G Return spring 30H Carbon removal filter 31 Blow-by gas reduction flow path 32 Crank chamber active ventilation passage 33 Crank chamber active ventilation valve 34 Canister 35 Exhaust gas purification catalyst 36 Intake temperature sensor 37 Throttle position sensor (TPS) 38 Idle switch 39 Boost sensor 40 First cylinder detection sensor 41 Crank angle sensor 42 Water temperature sensor 43 O ₂ sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 335 F02D 41/04 335B 43/00 301 43/00 301B 301J 301L 301N F02P 5/15 F02P 5/15 B (72 ) Inventor Katsuhiko Miyamoto, 33-5, Shiba, Minato-ku, Tokyo, Mitsubishi Motors Corporation (72) Inventor, Jun Takemura, 5-33, Shiba, Minato-ku, Tokyo, Tokyo (56) ) Reference JP-A-6-200836 (JP, A) JP-A-6-200835 (JP, A) JP-A-6-200834 (JP, A) JP-A-62-41941 (JP, A) JP-A 5-231212 (JP, A) JP 61-268845 (JP, A) JP 5-302548 (JP, A) JP 7-293353 (JP, A) JP 62-253918 (JP, A) JP-A-4-234552 (JP , A) JP 4-203454 (JP, A) JP 63-124849 (JP, A) JP 7-103049 (JP, A) JP 7-269416 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F02M 25/07 570 F02M 25/07 550 F02B 17/00 F02D 41/02 301 F02D 41/04 315 F02D 41/04 335 F02D 43/00 301 F02P 5 / 15

Claims (5)

(57) [Claims] 1. What is premixed combustion and stratified combustion in which the total air-fuel ratio in the combustion chamber is greater than the total air-fuel ratio in the premixed combustion ?
Some of the exhaust gas will be burned while the other is burned
In an internal combustion engine that recirculates inside the exhaust gas, the exhaust gas recirculation amount at the time of stratified combustion is discharged at the premixed combustion time.
The internal combustion engine is set to a value larger than the gas recirculation amount.
The combustion state of Seki was switched from the premixed combustion to the stratified combustion.
Change the intake air amount when the total air-fuel ratio is changed.
Control to change the exhaust gas recirculation amount after
An exhaust gas recirculation control device characterized by: 2. In the premixed combustion, the air-fuel ratio is the theoretical air-fuel ratio.
Larger premixed lean without introducing exhaust gas recirculation
Mode, including switching from the premixed lean mode to stratified combustion
In addition, the intake air amount is changed according to the switching of the total air-fuel ratio.
The exhaust gas recirculation control device according to claim 1, wherein the exhaust gas recirculation control device is controlled to change the exhaust gas recirculation amount. Wherein the larger the air-fuel ratio during the stratified combustion, the outlet gas recirculation amount or an exhaust recirculating into intake passage
Configured to be greater the opening degree of the gas recirculation control valve out
Characterized in that it is made, the exhaust gas recirculation control device according to claim 1. 4. The total air-fuel ratio during the stratified combustion is about 23.
The exhaust gas recirculation control device according to claim 3, wherein the exhaust gas recirculation control device is set as described above. 5. A part of the exhaust gas is returned to the intake passage.
As that device, a valve for controlling the exhaust gas recirculation amount to be recirculated to the intake passage from the exhaust passage, the combustion of the internal combustion engine
Including an actuator for driving the valve depending on the state
See, controls the actuator so that at high speed towards the driving speed of the closing direction relative to the driving speed in the opening direction of the valve
Characterized in that that the exhaust gas recirculation control device according to claim 1.