JP2000136744A - Control device for internal combustion engine - Google Patents

Abstract

(57) Abstract: A control device for an internal combustion engine that can prevent a combustion state from deteriorating based on intake air temperature is provided. When an intake air temperature of an engine is low, a combustion chamber is reduced.
The temperature of the air-fuel mixture to be charged also decreases, and in this state of exhaust gas recirculation, the combustion state deteriorates due to an excessive amount of EGR. The electronic control unit of the engine 11 calculates an EGR intake temperature correction coefficient for reducing the EGR amount based on the intake air temperature or a fuel intake temperature correction coefficient for increasing and correcting the fuel injection amount. Based on these correction factors, E
By correcting the GR amount and the fuel injection amount, the combustion state can be stabilized when the intake air temperature is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine having a mechanism for recirculating exhaust gas to an intake system.

[0002]

2. Description of the Related Art In recent years, an internal combustion engine of the type that directly injects fuel into a combustion chamber, such as the internal combustion engine described in Japanese Patent Application Laid-Open No. 8-189405, has been proposed and put into practical use. In such an internal combustion engine, in order to improve fuel efficiency and obtain sufficient engine output, a combustion method is switched according to an engine operating state.

[0003] That is, as the engine operating state becomes high rotation and high load, the combustion method becomes “stratified combustion”, “weak stratified combustion”,
The mode is sequentially switched to “homogeneous lean combustion” and “homogeneous stoichiometric combustion”. By changing the combustion method in this manner, the higher the rotation speed and the higher the load that requires a high output, the higher the air-fuel ratio becomes on the rich side and a higher output is obtained. As the air-fuel ratio becomes leaner, the air-fuel ratio becomes leaner, and the fuel efficiency is improved.

In the above-mentioned "homogeneous stoichiometric combustion", a homogeneous air-fuel mixture having a stoichiometric air-fuel ratio is formed in the combustion chamber by injecting and supplying fuel into the combustion chamber during an intake stroke of the internal combustion engine, and the air-fuel mixture is burned. By doing so, a sufficient engine output is obtained.

In the "homogeneous lean combustion", a smaller amount of fuel is injected into the combustion chamber during the intake stroke of the internal combustion engine than in the "homogeneous stoichiometric combustion", whereby a homogeneous air-fuel ratio leaner than the stoichiometric air-fuel ratio is obtained. Forming an air-fuel mixture in the combustion chamber,
The air-fuel mixture is stably burned by the swirl in the combustion chamber.

On the other hand, in "weak stratified combustion", fuel is injected and supplied into the combustion chamber during the intake stroke and the compression stroke of the internal combustion engine, and the average air-fuel ratio becomes a leaner value than in "homogeneous lean combustion". Air is formed in the combustion chamber. In such "weak stratified combustion", the fuel injected and supplied during the intake stroke is evenly dispersed by the swirl into the air in the combustion chamber,
The fuel injected and supplied during the compression stroke is collected around the spark plug by a swirl and a recess provided in the head of the piston. As described above, the fuel injection is performed in two stages, the intake stroke and the compression stroke, so that the fuel is mixed by the intermediate combustion method (“weak stratified combustion”) between “homogeneous lean combustion” and “stratified combustion” described later. Qi combustion takes place.

In the "stratified combustion", fuel is injected and supplied into the combustion chamber during the compression stroke of the internal combustion engine, and the air-fuel mixture having an average air-fuel ratio leaner than that in the "weak stratified combustion" is supplied to the combustion chamber. Formed. The fuel injected and supplied during the compression stroke in this way is collected around the spark plug by the swirl and the depression in the piston head. Therefore, even if the average air-fuel ratio of the air-fuel mixture is greater than that during "stratified stratified combustion", the fuel concentration of the air-fuel mixture around the plug is increased, and good air-fuel mixture is ignited, and the air-fuel mixture becomes stable Will start burning.

As described above, the combustion system of the internal combustion engine is switched among “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion” in accordance with the engine operating state, as described above. Fuel efficiency can be improved and sufficient engine output can be obtained.

[0009]

By the way, in an internal combustion engine of a type that switches the combustion system, such as the internal combustion engine described in the publication, exhaust gas in which part of exhaust gas is recirculated to an intake system in order to reduce emissions. A recirculation (EGR) mechanism is employed. When the exhaust gas is recirculated to the intake system by the EGR mechanism, the temperature in the combustion chamber is reduced, the generation of nitrogen oxides (NOx) is suppressed, and the emission is reduced.

[0010] However, the intake air temperature of the internal combustion engine fluctuates depending on the ambient temperature. However, when the ambient temperature is low and the intake air temperature is lower than normal, the temperature of the air-fuel mixture charged into the combustion chamber is low. If the exhaust gas is recirculated as described above, the combustion state of the mixture will deteriorate. Then, due to such deterioration of the combustion state of the air-fuel mixture, misfire or the like may occur and drivability and fuel efficiency may be deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for an internal combustion engine which can prevent a combustion state from being deteriorated based on an intake air temperature. It is in.

[0012]

According to the first aspect of the present invention, there is provided an exhaust gas recirculation mechanism for recirculating exhaust gas to an intake system, and a predetermined control for controlling the operation of the internal combustion engine. A control unit for controlling a system in accordance with a control amount required based on an engine operating state, wherein the control unit controls an intake air temperature of the internal combustion engine; And a correction means for correcting the control amount to a value on the side where the combustion state of the internal combustion engine is stabilized, as the intake air temperature is lower than a predetermined reference value.

With this configuration, as the intake air temperature of the internal combustion engine is lower than the predetermined reference value, the control amount for controlling the operation of the internal combustion engine is largely corrected to stabilize the combustion state. When the air temperature is lower than usual and the exhaust gas recirculation amount becomes excessive, the deterioration of the combustion state is prevented.

According to a second aspect of the present invention, in the first aspect of the present invention, the combustion system of the internal combustion engine is switched in accordance with an engine operating state, and the correction means is configured to adjust the intake air in accordance with the combustion system. The correction amount of the control amount based on the temperature is made variable.

According to the above configuration, the correction amount of the control amount for controlling the operation of the internal combustion engine is made variable in accordance with the combustion system of the internal combustion engine. By correcting the control amount by the amount, it is possible to prevent the combustion state from deteriorating when the intake air temperature is low.

According to a third aspect of the present invention, in the second aspect of the invention, the correction means is configured to determine the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the intake air temperature as the air-fuel ratio becomes leaner. The correction amount of the control amount is set to be large toward the stable combustion state.

The leaner the air-fuel ratio of the air-fuel mixture to be burned, the more easily the combustion deteriorates due to the exhaust gas recirculation when the intake air temperature is low. According to this configuration, the correction amount is set such that the more the air-fuel ratio of the air-fuel mixture becomes leaner, the greater the correction toward the stable combustion state in the control amount for controlling the operation of the internal combustion engine becomes. . Therefore, even in an internal combustion engine in which the combustion method is switched, the combustion state deteriorates when the intake air temperature is low by correcting the control amount for controlling the operating state of the internal combustion engine based on the correction amount. Can be prevented.

According to a fourth aspect of the present invention, in the third aspect of the invention, the combustion system of the internal combustion engine is a stratified combustion,
Switching between weak stratified combustion, homogeneous lean combustion, and homogeneous stoichiometric combustion, wherein the correction means adjusts the intake air temperature in the order of homogeneous stoichiometric combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion. Based on this, the correction amount of the control amount is set to a large value on the stable combustion state side.

When the combustion system of the internal combustion engine is homogeneous stoichiometric combustion,
As the state changes to homogeneous lean combustion, weak stratified combustion, and stratified combustion, the air-fuel ratio of the air-fuel mixture to be burned becomes lean, and the deterioration of combustion tends to occur based on exhaust gas recirculation when the intake air temperature is low. According to this configuration, as the combustion system of the internal combustion engine becomes homogeneous stoichiometric combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion, the combustion state in the control amount for controlling the operation of the internal combustion engine is shifted to a stable side. The correction amount is set so that the correction becomes large. Therefore, even in an internal combustion engine whose combustion method is switched between homogeneous stoichiometric combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion, the control amount for controlling the operating state of the internal combustion engine based on the correction amount is set. By making the correction, it is possible to prevent the combustion state from deteriorating when the intake air temperature is low.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the correction means corrects the control amount by taking into account at least one of an engine speed and an engine load. Is set.

Since the amount of exhaust gas recirculation changes depending on the engine speed and the engine load, the same configuration is used to set the correction amount of the control amount for controlling the operation of the internal combustion engine in consideration of the engine speed and the engine load. Thus, the correction amount of the control amount can be set to a more appropriate value.

According to a sixth aspect of the present invention, in the invention of the fifth aspect, the correction means shifts the control amount to a stable combustion state as the engine speed and the engine load increase the exhaust gas recirculation amount. Is set to be large.

According to this configuration, the correction of the control amount for controlling the operation of the internal combustion engine to the side where the combustion state is stabilized becomes larger as the engine revolving speed and the engine load increase the exhaust gas recirculation amount. Is set, the correction amount can be set to a more appropriate value.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the control amount is an exhaust gas recirculation amount by the exhaust gas recirculation mechanism, and the correction means is an intake air temperature. The lower the is, the more the exhaust gas recirculation amount is reduced.

According to this configuration, the lower the intake air temperature, the larger the exhaust recirculation amount is corrected to the reduction side, so that even when the intake air temperature is low, the exhaust recirculation amount is set to an appropriate value, and The deterioration of the state can be prevented.

According to an eighth aspect of the present invention, in the invention according to any one of the first to sixth aspects, the control amount is a fuel injection amount of the internal combustion engine set according to an engine operating state, and The means is to increase and correct the fuel injection amount as the intake air temperature is lower.

According to this structure, the lower the intake air temperature is, the more the fuel injection amount is corrected and the combustion state is stabilized, so that the exhaust recirculation amount is excessive when the intake air temperature is low. Even after that, the deterioration of the combustion state can be prevented.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a first embodiment in which the present invention is applied to an in-line four-cylinder automobile gasoline engine will be described.
An embodiment will be described with reference to FIGS.

As shown in FIG. 1, the engine 11 has a total of four pistons 12 (only one is shown in FIG. 1) provided so as to be able to reciprocate in a cylinder block 11a. The heads of these pistons 12 are formed with depressions 12a necessary for performing stratified combustion. These pistons 12 are connected via a connecting rod 13 to a crankshaft 14 which is an output shaft. The reciprocating movement of the piston 12 is controlled by the connecting rod 13.
Thus, the rotation is converted into the rotation of the crankshaft 14.

A signal rotor 14a is attached to the crankshaft 14. This signal rotor 14
A plurality of protrusions 14b are provided at equal angles around the axis of the crankshaft 14 on the outer peripheral portion of a. A crank position sensor 14c is provided on the side of the signal rotor 14a. Then, as the crankshaft 14 rotates and the projections 14b of the signal rotor 14a sequentially pass by the side of the crank position sensor 14c, pulse-like detection corresponding to the passage of the projections 14b is obtained from the sensor 14c. A signal is output.

The cylinder block 11a is provided with a water temperature sensor 11b for detecting the cooling water temperature THW of the engine 11 as the engine temperature of the engine 11. Further, a cylinder head 15 is provided at an upper end of the cylinder block 11a, and a combustion chamber 16 is provided between the cylinder head 15 and the piston 12. This combustion chamber 16
Has an intake port 17 provided in the cylinder head 15.
And the exhaust port 18 communicate with each other. Each of the intake port 17 and the exhaust port 18 has an intake valve 1
9 and an exhaust valve 20 are provided.

On the other hand, as shown in FIG. 1, an intake camshaft 21 and an exhaust camshaft 22 for opening and closing the intake valve 19 and the exhaust valve 20 are rotatably supported on the cylinder head 15. The intake and exhaust camshafts 21 and 22 are connected to the crankshaft 1 via a timing belt and gears (both not shown).
4 and the rotation of the crankshaft 14 is transmitted by the belt and gears. Then, when the intake camshaft 21 rotates, the intake valve 19 is driven to open and close, and the intake port 17 and the combustion chamber 16 are communicated and shut off. When the exhaust camshaft 22 rotates,
The exhaust valve 20 is driven to open and close, and the exhaust port 18 and the combustion chamber 16 are communicated and shut off.

In the cylinder head 15, a cam position sensor 21b for detecting a protrusion 21a provided on the outer peripheral surface of the intake camshaft 21 and outputting a detection signal is provided on a side of the intake camshaft 21. When the intake camshaft 21 rotates, the protrusion 21a of the shaft 21 passes by the side of the cam position sensor 21b. In this state, the cam position sensor 21b
Thus, the detection signal is output at predetermined intervals corresponding to the passage of the protrusion 21a.

The intake port 17 and the exhaust port 18
An intake pipe 30 and an exhaust pipe 31 are connected to each other.
The interior of the intake pipe 30 and the interior of the intake port 17 include an intake passage 32.
The exhaust pipe 31 and the exhaust port 18 form an exhaust passage 33. A throttle valve 23 is provided in an upstream portion of the intake passage 32. The throttle valve 23 is rotated by driving a throttle motor 24 composed of a direct current (DC) motor to adjust the opening. The opening of the throttle valve 23 is detected by a throttle position sensor 44.

The driving of the throttle motor 24 is controlled based on the amount of depression of an accelerator pedal 25 provided in the interior of the vehicle (accelerator depression amount). That is, when the driver of the vehicle depresses the accelerator pedal 25, the accelerator depression amount becomes equal to the accelerator position sensor 26.
And the drive of the throttle motor 24 is controlled based on the detection signal of the sensor 26. The throttle valve 2 based on the drive control of the throttle motor 24
By adjusting the opening degree of 3, the air flow area of the intake passage 32 changes, and the amount of air drawn into the combustion chamber 16 is adjusted.

In the intake passage 32, the throttle valve 2
A vacuum sensor 36 for detecting a pressure in the passage 32 is provided in a portion located downstream of the passage 3. Then, the vacuum sensor 36 outputs a detection signal corresponding to the detected pressure in the intake passage 32. Furthermore, the intake passage 3
An intake air temperature sensor 37 for detecting the temperature of the air (intake air) passing through the passage 32 is provided at a portion of the engine 2 located upstream of the throttle valve 23. The intake air temperature sensor 37 detects the detected intake air temperature (intake air temperature) TH
A detection signal corresponding to A is output.

As shown in FIG. 1, the cylinder head 15 has a fuel injection valve 40 for injecting fuel into the combustion chamber 16 and a mixture of fuel and air charged in the combustion chamber 16. And an ignition plug 41 for performing ignition. The ignition timing of the air-fuel mixture by the ignition plug 41 is adjusted by an igniter 41a provided above the ignition plug 41.

When fuel is injected from the fuel injection valve 40 into the combustion chamber 16, the fuel is mixed with air drawn into the combustion chamber 16 through the intake passage 32, and
A mixture of air and fuel is formed in 6. Further, the air-fuel mixture in the combustion chamber 16 is ignited by the ignition plug 41 and burns, and the air-fuel mixture after the combustion is sent to the exhaust passage 33 as exhaust gas.

On the other hand, the throttle valve 2 in the intake passage 32
The downstream side of the third passage 3 communicates with the exhaust passage 33 via an exhaust gas recirculation (EGR) passage 42. This EGR passage 42
Is provided with an EGR valve 43 having a step motor 43a. Then, the EGR valve 43
The opening is adjusted by controlling the drive of the stepping motor 43a. By adjusting the opening degree of the EGR valve 43, the amount of exhaust gas (EGR amount) recirculated to the intake passage 32 via the exhaust passage 33 is adjusted. When the exhaust gas of the engine 11 is recirculated to the intake passage 32, the temperature in the combustion chamber 16 decreases, and the nitrogen oxide (N
Ox) is suppressed and emission is reduced.

Next, the electrical configuration of the control device for the engine 11 in this embodiment will be described with reference to FIG. This control device includes fuel injection amount control, fuel injection timing control, ignition timing control, throttle opening control, EGR control, etc.
An electronic control unit (hereinafter referred to as “ECU”) 92 for controlling the operation state of the engine 11 is provided. The ECU 92 is configured as a logical operation circuit including a ROM 93, a CPU 94, a RAM 95, a backup RAM 96, and the like.

The ROM 93 is a memory that stores various control programs and maps and the like that are referred to when executing the various control programs.
The arithmetic processing is executed based on various control programs and maps stored in the OM 93. The RAM 95 is a CPU
94 is a memory for temporarily storing the calculation result at 94, data input from each sensor, and the like.
Reference numeral 6 denotes a nonvolatile memory for storing data to be stored when the engine 11 is stopped. And ROM93, CP
The U 94, the RAM 95, and the backup RAM 96 are connected to each other via a bus 97, and are also connected to an external input circuit 98 and an external output circuit 99.

The external input circuit 98 includes a water temperature sensor 11
b, a crank position sensor 14c, a cam position sensor 21b, an accelerator position sensor 26, a vacuum sensor 36, an intake air temperature sensor 37, a throttle position sensor 44, and the like. On the other hand, the throttle output motor 24, the fuel injection valve 40, the igniter 41a, the EGR valve 43, and the like are connected to the external output circuit 99.

The ECU 92 configured as described above determines the engine speed NE based on the detection signal from the crank position sensor 14c. Further, based on the detection signal from the accelerator position sensor 26 or the vacuum sensor 36 and the engine speed NE, a basic fuel injection amount Qbse representing the load on the engine 11 is obtained. ECU 92
Referring to a map including a homogeneous stoichiometric combustion region A, a homogeneous lean combustion region B, a weak stratified combustion region C, and a stratified combustion region D, as shown in FIG. 3, the engine speed NE and the basic fuel injection amount Qbse Determine the combustion method for the internal combustion engine. That is, the ECU 92 sets the combustion method of the internal combustion engine to “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, or “the homogeneous lean combustion” depending on which of the regions A to D the engine speed NE and the basic fuel injection amount Qbse are located in. "Weak stratified combustion" and "stratified combustion" are determined.

As is apparent from the map shown in FIG. 3, as the operation state of the engine 11 shifts to high rotation and high load, the combustion method of the engine 11 is “stratified combustion”, “weak stratified combustion”, and “homogeneous lean combustion”. Combustion "and" homogeneous stoichiometric combustion "sequentially. The reason for changing the combustion method is to use “homogeneous combustion” during high-speed and high-load operation where high power is required, to increase the engine output by reducing the air-fuel ratio of the air-fuel mixture, and to reduce the engine speed at low speeds that do not require very high output. At low load, the stratified charge combustion is performed to increase the air-fuel ratio to improve fuel efficiency.

Here, when each combustion mode is executed, E
Regarding the combustion control mode executed through the CU 92,
A description will be given for each of the "homogeneous stoichiometric combustion", "homogeneous lean combustion", "weak stratified combustion", and "stratified combustion".

"Homogeneous stoichiometric combustion" When the combustion method of the engine 11 is determined to be "homogeneous stoichiometric combustion", the ECU 92 determines the intake pressure PM and the engine speed NE obtained based on the detection signal from the vacuum sensor 36. Based on the map, the basic fuel injection amount Qbse is calculated. The basic fuel injection amount Qbse thus calculated increases as the engine speed NE increases and the intake pressure PM increases. The ECU 92 controls the fuel injection valve 4
0 to control the basic fuel injection amount Qbs.
e during the intake stroke of the engine 11 during the intake stroke of the engine 11.
Spray from. Further, the ECU 92 performs air-fuel ratio feedback correction of the fuel injection amount to control the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio. Further, the ECU 92 controls the throttle motor 2 so that the throttle opening, the ignition timing, the EGR amount and the like are suitable for “homogeneous stoichiometric combustion”.
4. Drive control of the igniter 41a and the EGR valve 43.

"Homogeneous Lean Combustion" When the combustion system of the engine 11 is determined to be "homogeneous lean combustion", the ECU 92 refers to a well-known map and calculates the basic fuel injection based on the accelerator pedal depression amount and the engine speed NE. Map the quantity Qbse. The basic fuel injection amount Qbse calculated in this manner becomes a larger value as the engine speed NE increases and the accelerator depression amount increases. The ECU 92 controls the driving of the fuel injection valve 40 to supply an amount of fuel corresponding to the final fuel injection amount Qfin obtained based on the basic fuel injection amount Qbse to the engine 1.
The fuel is injected from the fuel injection valve 40 during the first intake stroke. The air-fuel ratio of the mixture formed in the combustion chamber 16 by such fuel injection is set to a value (for example, 15 to 23) larger than the stoichiometric air-fuel ratio. The ECU 92 also controls the throttle motor 2 so that the throttle opening, ignition timing, EGR amount, and the like are suitable for “homogeneous lean combustion”.
4. Drive control of the igniter 41a, the EGR valve 43, and the like.

"Weak stratified combustion" When the combustion mode of the engine 11 is determined to be "weak stratified combustion", the ECU 92 calculates the basic fuel injection amount Qbse from the accelerator pedal depression amount and the engine speed NE in the same manner as described above. I do. The ECU 92 controls the driving of the fuel injection valve 40 to supply an amount of fuel corresponding to the final fuel injection amount Qfin obtained based on the basic fuel injection amount Qbse to the engine 1.
The fuel is injected into the intake stroke and the compression stroke. The air-fuel ratio of the air-fuel mixture formed in the combustion chamber 16 by such fuel injection is set to a value leaner than the air-fuel ratio at the time of “homogeneous lean combustion” (for example, 20 to 23). Also, E
The CU 92 controls the drive of the throttle motor 24, the igniter 41a, the EGR valve 43, and the like such that the throttle opening, the ignition timing, the EGR amount, and the like are suitable for “weak stratified combustion”.

In the "weak stratified combustion", the fuel injected and supplied during the intake stroke is evenly dispersed in the air, and the fuel injected and supplied during the compression stroke is provided at the head of the piston 12. Collected around the spark plug 41 by the recess 12a thus formed. As described above, the fuel injection is performed in two stages, the intake stroke and the compression stroke, so that the air-fuel mixture is mixed in a combustion mode (weak stratified combustion) intermediate between the above-described "homogeneous lean combustion" and "stratified combustion" described later. Is performed, and the "weak stratified combustion" suppresses torque shock when switching between "homogeneous lean combustion" and "stratified combustion".

"Stratified Combustion" When the combustion mode of the engine 11 is determined to be "stratified combustion", the ECU 92 calculates the basic fuel injection amount Qbse from the accelerator pedal depression amount and the engine speed NE in the same manner as described above. The ECU 92 injects an amount of fuel corresponding to the final fuel injection amount Qfin obtained based on the basic fuel injection amount Qbse during the compression stroke of the engine 11. In the air-fuel mixture formed in the combustion chamber 16 by such fuel injection,
The air-fuel ratio is set to a value leaner than the air-fuel ratio at the time of “weak stratified combustion” (for example, 25 to 50). The ECU 92
Controls the drive of the throttle motor 24, the igniter 41a, the EGR valve 43, and the like such that the throttle opening, the ignition timing, the EGR amount, and the like are suitable for “stratified combustion”.

At the time of such “stratified combustion”, the fuel injected from the fuel injection valve 40 during the compression stroke of the engine 11 enters into the depression 12 a provided in the head of the piston 12, and moves by the piston 12. The fuel is collected around the spark plug 41. By collecting fuel around the ignition plug 41 in this manner, the combustion chamber 16
Even if the average air-fuel ratio of the entire air-fuel mixture inside is larger than that during “weak stratified combustion”, the air-fuel ratio of the air-fuel mixture around the plug 41 is determined to be suitable for ignition, and good air-fuel mixture is ignited. Will be

Next, an outline of the exhaust gas recirculation control in this embodiment will be described. The ECU 92 determines the target EGR amount Etr according to each combustion method based on the operating state of the engine 11.
g is calculated, and the opening degree of the EGR valve 43 is controlled so that the actual EGR amount in the engine 11 becomes the calculated target EGR amount Etrg. Here, FIG. 6 shows a transition tendency of the EGR amount controlled as described above with respect to changes in the engine speed NE and the basic fuel injection amount Qbse. As is clear from the figure, the EGR amount changes so as to become largest in the high-speed high-load region in the stratified combustion region D, and gradually increase toward the high-speed high-load region.

The NOx generated during the combustion of the air-fuel mixture increases as the air-fuel ratio of the air-fuel mixture becomes leaner.
By changing the EGR amount as described above, the generation of NOx is suitably suppressed. Further, the reason that the EGR amount is reduced in the low-speed low-load region in the stratified combustion region D is that if the EGR amount is excessively large in the low-speed low-load region, the combustion state may be deteriorated and a misfire or the like may occur. It is.

By the way, for example, when the ambient temperature is low, the intake air temperature THA of the engine 11 becomes lower than usual, and when the intake air temperature THA is low, the temperature of the air-fuel mixture charged into the combustion chamber 16 also becomes lower. In this state, when exhaust gas recirculation (EGR) is performed by the same amount as when the ambient temperature is high, E
The GR amount becomes excessive and the combustion state of the air-fuel mixture deteriorates, causing misfiring or reducing drivability.

Therefore, the ECU 92 detects the EGR intake temperature correction coefficient C1tha for correcting the EGR amount by the intake temperature sensor 37 so that the EGR amount decreases as the intake temperature THA becomes lower than a predetermined reference value. The map is calculated based on the intake air temperature THA. E calculated in this way
The maximum value of the GR intake temperature correction coefficient C1tha is “1.0”.
Therefore, the value becomes smaller as the intake air temperature THA becomes lower than the reference value. By correcting the EGR amount to the decreasing side using the EGR intake temperature correction coefficient C1tha, the correction of the EGR amount to the decreasing side increases as the intake air temperature THA becomes lower than the reference value.

Further, a map for calculating the EGR intake temperature correction coefficient C1tha is set for each combustion method, and the EGR intake temperature correction coefficient C1tha according to the combustion method based on the intake temperature THA with reference to these maps. Is calculated. FIG. 4 shows a transition of the thus calculated EGR intake temperature correction coefficient C1tha with respect to a change in the intake air temperature THA for each combustion method. In FIG. 4, solid lines L1 to L4 indicate changes in the EGR intake air temperature correction coefficient C1tha during "stratified combustion", "weak stratified combustion", "homogeneous lean stratified combustion", and "homogeneous stoichiometric combustion", respectively. It is. As is apparent from the figure, the leaner the air-fuel ratio becomes, the smaller the EGR intake temperature correction coefficient C1tha with respect to the intake temperature THA and the smaller the EGR intake temperature correction coefficient C1tha with respect to the decrease in the intake temperature THA. The amount of decrease becomes large.

By making the EGR intake temperature correction coefficient C1tha obtained based on the intake air temperature THA variable for each combustion method, even in the engine 11 whose combustion method is switched, the EGR intake temperature correction coefficient C1tha
The EGR amount corrected to the decrease side on the basis of the above becomes an appropriate value regardless of the intake air temperature THA. Therefore, the EGR amount becomes a value on the increase side from the appropriate value, and the combustion state deteriorates.
The R amount becomes a value on the decrease side from the appropriate value and the EGR valve 4
3 is prevented from increasing and the pumping loss of the engine 11 is increased.

Further, when the EGR amount is corrected to the decreasing side as described above, the combustion state is improved by the reduced amount of the EGR amount, and the combustion speed of the air-fuel mixture is increased. In the present embodiment, the retard amount of the ignition timing by the ignition plug 41 is increased in accordance with the increase in the combustion speed of the air-fuel mixture based on the decrease correction of the EGR amount, and even when the combustion speed is increased due to the decrease correction of the EGR amount. A good combustion state can be maintained.

That is, the ECU 92 determines the target ignition timing SAtrg according to each combustion method based on the operating state of the engine 11.
And the drive of the igniter 41a is controlled such that the actual ignition timing of the engine 11 becomes the calculated target ignition timing SAtrg. Further, the ECU 92 maps the ignition intake temperature correction coefficient C2tha for correcting the ignition timing based on the intake air temperature THA so that the ignition timing is retarded as the intake temperature THA becomes lower and the EGR amount reduction correction becomes larger. Calculate. The ignition temperature correction coefficient C2 for ignition
A map for calculating tha is also set for each combustion system, and an ignition air temperature correction coefficient C2tha for ignition is calculated according to the combustion system based on the intake air temperature THA with reference to these maps.

FIG. 5 shows the transition of the calculated intake air temperature correction coefficient C2tha with respect to the change of the intake air temperature THA for each combustion method. In FIG. 5, solid lines L5 to L8
Shows the transition of the ignition intake air temperature correction coefficient C2tha during "stratified combustion", "weak stratified combustion", "homogeneous lean stratified combustion", and "homogeneous stoichiometric combustion", respectively.
As is clear from the figure, as the air-fuel ratio to be burned becomes leaner, the ignition temperature correction coefficient C2tha for the intake air temperature THA becomes smaller and the intake air temperature THA becomes smaller.
The decrease amount of the ignition intake air temperature correction coefficient C2tha with respect to the decrease is large. The maximum value of the ignition intake air temperature correction coefficient C2tha is also "1.0".

By correcting the ignition timing to the retard side by using the ignition intake air temperature correction coefficient C2tha, the intake air temperature T
The correction of the ignition timing to the retard side increases as the HA decreases and the correction for decreasing the EGR amount increases. Therefore, when the combustion speed of the air-fuel mixture increases based on the correction for decreasing the EGR amount, the ignition timing retard amount increases and the ignition timing is retarded, and the combustion speed of the air-fuel mixture increases as described above. Even if it rises, the combustion state of the air-fuel mixture is favorably maintained.

Further, like the EGR intake temperature correction coefficient C1tha that is variable for each combustion method, the ignition intake temperature correction coefficient C2tha is also variable for each combustion method. Therefore, even if the EGR amount is corrected to the decreasing side based on the EGR intake air temperature correction coefficient C1tha and the combustion speed of the air-fuel mixture increases, the ignition timing retard correction amount can be accurately adjusted in accordance with the increase in the combustion speed. The combustion state of the air-fuel mixture can be favorably maintained.

Next, a procedure for calculating the target EGR amount Etrg and the target ignition timing SAtrg will be described with reference to FIGS. 7 and 8 show the target EGR amount Etr
9 is a flowchart showing a control amount calculation routine for calculating control amounts for controlling the operation of the engine 11, such as g and a target ignition timing SAtrg. The control amount calculation routine is executed by the ECU 92 at, for example, a time interruption every predetermined time.

In the same routine, steps S101 to S101
S104 (FIG. 7) is for determining the combustion mode of the engine 11. Then, step S10 shown in FIG.
5, S106, steps S107 and S108, steps S109 and S110, and steps S111 and S112.
The processing of "stratified combustion", "weak stratified combustion",
This is for calculating the target EGR amount Etrg and the target ignition timing SAtrg during “homogeneous lean combustion” and “homogeneous stoichiometric combustion”.

The ECU 92 determines whether the cooling water temperature THW is equal to or higher than a predetermined value a (for example, 40 ° C.) as the process of step S101. If the cooling water temperature is not equal to or higher than the predetermined value a, the process proceeds to step S111 (FIG. 8), and the cooling water temperature TH
If W is equal to or larger than the predetermined value a, the process proceeds to step S102. E
The CU 92 determines whether or not the basic fuel injection amount Qbse is equal to or smaller than the determination value QDJ, as the process in step S102. This determination value QDJ is equal to the homogeneous stoichiometric combustion area A shown in FIG.
And a value located on the boundary between the homogeneous lean burn region B and the homogeneous lean burn region B. Then, in the process of step S102, when it is determined that the operating state of the engine 11 is in the homogeneous stoichiometric combustion region A and that “Qbse ≦ QDJ” is not satisfied, the process proceeds to step S111 (FIG. 8).

The ECU 92 calculates the target EGR amount Etrg at the time of "homogeneous stoichiometric combustion" as the process of step S111. That is, the engine speed NE is obtained based on the detection signal from the crank position sensor 14c, and the throttle opening is obtained based on the detection signal from the throttle position sensor 44. Based on the engine speed NE and the throttle opening, a basic EGR amount Ebse is calculated with reference to a known map, and the calculated basic EGR amount Ebse is added to the EGR intake temperature correction coefficient Cb.
The value obtained by multiplying 1 tha is set as the target EGR amount Etrg.

When the target EGR amount Ettrg is calculated in this manner, the ECU 92 determines that the actual EGR amount is equal to the target EGR amount Etrg.
The drive of the EGR valve 43 is controlled based on the target EGR amount Etrg by another routine so that the value becomes trg. The EGR intake temperature correction coefficient C1tha for calculating the target EGR amount Etrg changes as shown by a solid line L4 in FIG. 4 with respect to a change in the intake air temperature THA. Therefore, the intake air temperature T
As the HA is lower than the reference value, the correction of the actual EGR amount to the decreasing side is increased, and during the “homogeneous stoichiometric combustion”, the combustion is performed based on the fact that the EGR amount becomes larger than the appropriate value when the intake air temperature THA is low. Deterioration of the condition is prevented. Further, the EGR amount becomes smaller than the appropriate value, and E
An increase in pumping loss due to an increase in the throttle amount of the GR valve 43 is also prevented.

The ECU 92 then proceeds to step S112 in which the target ignition timing S for "homogeneous stoichiometric combustion" is set.
Calculate Atrg. That is, the basic ignition timing S is determined by referring to a known map based on the engine speed NE and the intake pressure PM.
Abse is calculated by a map, and the calculated basic ignition timing S
A value obtained by multiplying Abse by the intake air temperature correction coefficient for ignition C2tha is set as a target ignition timing SAtrg. The basic ignition timing SAbse is calculated as a value on the advance side as the engine speed NE increases and the intake pressure PM decreases.

After the target ignition timing SAtrg is calculated as described above, the ECU 92 drives and controls the igniter 41a based on the target ignition timing SAtrg by another routine so that the actual ignition timing becomes the same target ignition timing SAtrg. I do. The ignition intake temperature correction coefficient C2tha for calculating the target ignition timing SAtrg changes as shown by a solid line L8 in FIG. 5 with respect to a change in the intake air temperature THA. Therefore, as the intake air temperature THA decreases and the correction for decreasing the EGR amount increases, the correction of the ignition timing to the retard side increases. Therefore, at the time of "homogeneous stoichiometric combustion", even if the combustion speed of the air-fuel mixture increases based on the EGR amount reduction correction by the EGR intake temperature correction coefficient C1tha, the ignition timing is delayed by the ignition intake temperature correction coefficient C2tha. The combustion state of the air-fuel mixture is favorably maintained by the angle correction.

On the other hand, in the process of S102 (FIG. 7), the operating state of the engine 11 is changed to the homogeneous stoichiometric combustion region A
(Qbse ≦ QDJ)
If it is determined that is, the process proceeds to step S103. ECU
The step 92 judges whether or not the basic fuel injection amount Qbse is equal to or smaller than the judgment value QA as the process of step S103. This determination value QA is a value located on the boundary between the stratified combustion region D and the weakly stratified combustion region C shown in FIG. Then, in the process of step S103, the operating state of the engine 11 is not in the stratified combustion region D, but is "Qbse ≦ Q
If it is not "A", the process proceeds to step S104.

The ECU 92 determines whether or not the basic fuel injection amount Qbse is equal to or smaller than the determination value QB as the process of step S104. This determination value QB is a value located on the boundary between the weak stratified combustion region C and the homogeneous lean combustion region B shown in FIG. Then, in the process of step S104,
If it is determined that the operating state of the engine 11 is located within the homogeneous lean combustion region B and that “Qbse ≦ QB” is not satisfied, the process proceeds to step S109 (FIG. 8).

The ECU 92 calculates the target EGR amount Etrg at the time of “homogeneous lean combustion” as the process of step S109. That is, the basic EGR amount E is referred to based on the engine speed NE and the basic fuel injection amount Qbse by referring to a known map.
bse is calculated by a map, and the calculated basic EGR amount Ebs is calculated.
The value obtained by multiplying e by the EGR intake temperature correction coefficient C1tha is set as the target EGR amount Etrg. The EGR intake temperature correction coefficient C1tha changes as shown by the solid line L3 in FIG. 4 with respect to the change in the intake air temperature THA, and has a smaller value than at the time of “homogeneous stoichiometric combustion” (solid line L4).

Therefore, even during the “homogeneous lean combustion”, the actual EGR becomes smaller as the intake air temperature THA becomes lower than the reference value.
The correction to the reduction side of the amount is increased, but the correction to the reduction side of the EGR amount is set to be larger than that in the “homogeneous stoichiometric combustion”. This is because the deterioration of the combustion state based on the excessive EGR amount is more likely to occur during “homogeneous lean combustion” than during “homogeneous stoichiometric combustion”. That is, by correcting the EGR amount on the decreasing side with the EGR intake temperature correction coefficient C1tha during “homogeneous lean combustion”, which is smaller than the EGR intake temperature correction coefficient C1tha during “homogeneous stoichiometric combustion”, ”, The intake air temperature THA
When the EGR amount is low, the deterioration of the combustion state based on the EGR amount becoming larger than the appropriate value is prevented. EG
An increase in the pumping loss due to an increase in the throttle amount of the EGR valve 43 when the R amount becomes smaller than the appropriate value is also prevented.

Next, the ECU 92 performs the process of step S110, in which the target ignition timing SA at the time of “homogeneous lean combustion” is set.
Calculate trg. That is, the basic ignition timing SAbse is map-calculated with reference to a known map based on the engine speed NE and the throttle opening, and the calculated basic ignition timing SAbse is multiplied by the ignition intake temperature correction coefficient C2tha. The ignition timing is set to SAtrg. The intake air temperature correction coefficient C2tha for ignition changes as shown by a solid line L7 in FIG. 5 with respect to a change in the intake air temperature THA, and is smaller than that during “homogeneous stoichiometric combustion” (solid line L8).

Therefore, even in the case of "homogeneous lean combustion", the correction of the ignition timing to the retard side is increased as the intake air temperature THA decreases and the correction for decreasing the EGR amount increases. The correction to the corner side is set to be larger than that at the time of “homogeneous stoichiometric combustion”. This is because E is higher during homogeneous lean combustion than during homogeneous stoichiometric combustion.
This is because the correction of the EGR amount to the decreasing side by the GR intake temperature correction coefficient C1tha is large, and the increase in the combustion speed of the air-fuel mixture based on the EGR amount decreasing correction becomes large. That is,
Intake air temperature correction coefficient C2th for ignition during "homogeneous stoichiometric combustion"
By correcting the ignition timing on the retard side with the intake air temperature correction coefficient C2tha for "homogeneous lean combustion" which is smaller than "a", the "homogeneous lean combustion" is larger than the "homogeneous stoichiometric combustion". Even if the combustion speed of the air-fuel mixture increases based on the EGR amount reduction correction, the combustion state of the air-fuel mixture is favorably maintained.

On the other hand, in the process of step S104 (FIG. 7), when it is determined that the operating state of the engine 11 is located within the weak stratified combustion region C and that “Qbse ≦ QB” is satisfied, step S107 is performed. Proceed to (FIG. 8).

The ECU 92 calculates a target EGR amount Etrg at the time of "weak stratified combustion" as the process of step S107. That is, a basic EGR amount Ebse is map-calculated with reference to a known map based on the engine speed NE and the throttle opening, and the calculated basic EGR amount Ebse is added to the EGR amount.
Multiplied by the intake air temperature correction coefficient C1tha for the target EGR
Let the amount be Etrg. The EGR intake temperature correction coefficient C1tha
Changes as indicated by the solid line L2 in FIG. 4 with respect to the change in the intake air temperature THA, and has a smaller value than at the time of “homogeneous lean combustion” (solid line L3).

Therefore, even in the case of "weak stratified combustion", the correction of the actual EGR amount to the decreasing side is increased as the intake air temperature THA becomes lower than the reference value. It is assumed to be larger than that during “homogeneous lean combustion”. This is because the deterioration of the combustion state due to the excessive EGR amount is more likely to occur during “weak stratified combustion” than during “homogeneous lean combustion”. That is, the EGR intake temperature correction coefficient C1tha during “weak stratified combustion” becomes smaller than the EGR intake temperature correction coefficient C1tha during “homogeneous lean combustion”.
By correcting the R amount on the decreasing side, it is possible to prevent the deterioration of the combustion state based on the fact that the EGR amount becomes larger than the appropriate value when the intake air temperature THA is low during "weak stratified combustion". Further, it is possible to prevent the pumping loss from increasing due to the EGR amount becoming smaller than the appropriate value and the throttle amount of the EGR valve 43 increasing.

Subsequently, the ECU 92 performs a process of step S108, in which the target ignition timing SAtrg at the time of “weak stratified combustion” is set.
Is calculated. That is, the basic ignition timing SAbse is map-calculated with reference to a known map based on the engine speed NE and the basic fuel injection amount Qbse, and the calculated basic ignition timing SAbse is multiplied by an ignition intake air temperature correction coefficient C2tha. Is the target ignition timing SAtrg. The ignition intake temperature correction coefficient C2tha for the ignition is shown in FIG.
The solid line L6 changes as shown by a solid line L6, and is smaller than that at the time of "homogeneous lean combustion" (solid line L7).

Therefore, even in the case of "weak stratified combustion", as the intake air temperature THA decreases and the correction for decreasing the EGR amount increases, the correction of the ignition timing to the retard side increases.
The correction of the ignition timing to the retard side is set to be larger than that at the time of “homogeneous lean combustion”. This is because the correction of the EGR amount to the decreasing side by the EGR intake air temperature correction coefficient C1tha is larger in the "weak stratified combustion" than in the "homogeneous lean combustion", and the combustion speed of the air-fuel mixture increases based on the EGR amount decreasing correction. Is to be large. That is, the ignition timing is corrected on the retard side with the ignition intake air temperature correction coefficient C2tha for "weak stratified combustion", which is smaller than the ignition air temperature correction coefficient C2tha for "homogeneous lean combustion", whereby "weak stratification" is obtained. At the time of "combustion", the combustion state of the air-fuel mixture is favorably maintained even if the combustion speed of the air-fuel mixture is increased based on the above-described correction for decreasing the EGR amount which is larger than that at the time of "homogeneous lean combustion".

On the other hand, in the process of step S103 (FIG. 7), the operating state of the engine 11 is changed to the stratified combustion region D.
If it is determined that “Q ≦ QA”, the process proceeds to step S105 (FIG. 8).

The ECU 92 calculates the target EGR amount Etrg at the time of "stratified combustion" as the process of step S105. That is, a basic EGR amount Ebse is map-calculated with reference to a known map based on the engine speed NE and the throttle opening, and the calculated basic EGR amount Ebse is added to the EGR amount.
Multiplied by the intake air temperature correction coefficient C1tha for the target EGR
Let the amount be Etrg. The EGR intake temperature correction coefficient C1tha
Changes as indicated by the solid line L1 in FIG. 4 with respect to the change in the intake air temperature THA, and has a smaller value than at the time of “weak stratified combustion” (solid line L2).

Accordingly, even in the case of "stratified combustion", the correction of the actual EGR amount to the decreasing side is increased as the intake air temperature THA becomes lower than the reference value. It is assumed to be larger than that in the case of "weak stratified combustion". This is because the deterioration of the combustion state due to the excessive EGR amount is more likely to occur during “stratified combustion” than during “weakly stratified combustion”. That is, the EG during “stratified combustion” becomes smaller than the EGR intake air temperature correction coefficient C1tha during “weak stratified combustion”.
By correcting the EGR amount on the decreasing side with the intake air temperature correction coefficient C1tha for R, the combustion state deteriorates at the time of "stratified combustion" because the EGR amount becomes larger than an appropriate value when the intake air temperature THA is low. That is prevented. Further, it is possible to prevent the pumping loss from increasing due to the EGR amount becoming smaller than the appropriate value and the throttle amount of the EGR valve 43 increasing.

Subsequently, the ECU 92 calculates a target ignition timing SAtrg at the time of “stratified combustion” as a process of step S106. That is, the basic ignition timing SAbse is map-calculated with reference to a known map based on the engine speed NE and the basic fuel injection amount Qbse, and the calculated basic ignition timing SAbse is multiplied by an ignition intake air temperature correction coefficient C2tha. Is the target ignition timing SAtrg. The ignition air temperature correction coefficient C2tha for ignition is shown in FIG.
At the time of "weak stratified combustion" (solid line L6).

Therefore, even in the case of "stratified combustion", the correction of the ignition timing to the retard side increases as the intake air temperature THA decreases and the correction for decreasing the EGR amount increases, but the ignition timing is retarded. The correction to the side is set to be larger than that at the time of “weak stratified combustion”. This is because the EGR intake air temperature correction coefficient C1th is lower during “stratified combustion” than during “weakly stratified combustion”.
a, the correction of the EGR amount to the decreasing side is large.
This is because the increase in the combustion speed of the air-fuel mixture based on the correction for decreasing the amount of R increases. That is, the ignition timing is corrected on the retard side by the ignition intake temperature correction coefficient C2tha for "stratified combustion", which is smaller than the ignition intake temperature correction coefficient C2tha for "weak stratified combustion", to thereby achieve "stratified combustion". At times,
Even if the combustion speed of the air-fuel mixture increases based on the above-described reduction correction of the EGR amount that is larger than that during "weak stratified combustion," the combustion state of the air-fuel mixture is maintained in a good state.

According to this embodiment in which the processing described in detail above is performed, the following effects can be obtained. (1) When the EGR amount becomes excessive when the intake air temperature THA is lower than usual, an EGR intake air temperature correction coefficient C1tha is calculated based on the intake air temperature THA, and the correction coefficient C1tha is calculated.
In order to stabilize the combustion state based on the EGR amount, the EGR amount is corrected to be reduced, so that the deterioration of the combustion state is prevented.
Therefore, when the intake air temperature THA is low, it is possible to prevent the combustion state from deteriorating due to the excessive EGR amount, thereby preventing a misfire or a decrease in drivability.

(2) In the combustion system of the engine 11, the air-fuel ratio of the air-fuel mixture to be burned is changed in the order of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”. Become lean. Therefore, the EGR when the intake air temperature THA is low in the order of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”.
The combustion state is likely to be deteriorated due to the excessive amount. However, in the present embodiment, E for reducing the EGR amount is corrected.
The GR intake temperature correction coefficient C1tha is reduced as shown in FIG. 4 in the order of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”. Therefore, the engine 1 whose combustion mode is switched as described above
1, the EGR amount is corrected to the decreasing side based on the EGR intake temperature correction coefficient C1tha, thereby obtaining the intake air temperature TH.
Regardless of A, the EGR amount can be set to an appropriate value.
Since the EGR amount becomes an appropriate value in this manner, even in the engine 11 in which the combustion method is switched, the combustion state is deteriorated based on the excessive EGR amount when the intake air temperature THA is low, and misfire and drivability are reduced. Can be prevented.

(3) The above E with respect to the change of the intake air temperature THA
Just as the transition tendency of the GR intake temperature correction coefficient C1tha differs for each combustion method, the transition tendency of the ignition intake temperature correction coefficient C2tha for the change in the intake temperature THA differs for each combustion method. Therefore, by correcting the ignition timing to the retard side based on the ignition intake air temperature correction coefficient C2tha, the correction to the retard side is "homogeneous stoichiometric combustion".
"Homogeneous lean combustion", "weak stratified combustion", and "stratified combustion" increase in this order. Therefore, the correction of the EGR amount to the decreasing side based on the EGR intake temperature correction coefficient C1tha differs for each combustion system, and even if the combustion speed of the mixture changes based on the EGR amount decreasing correction differs for each combustion system, By correcting the ignition timing to the retard side based on the ignition intake air temperature correction coefficient C2tha, the combustion state of the air-fuel mixture can be appropriately maintained.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment in that when the intake air temperature THA is low, the combustion state is stabilized by increasing the fuel injection amount instead of decreasing the EGR amount to stabilize the combustion state. Therefore, in the present embodiment, only different portions from the first embodiment will be described, and detailed description of the same portions as the first embodiment will be omitted.

First, the outline of the fuel injection amount control in this embodiment will be described. For example, when the ambient temperature is low and the intake air temperature THA is lower than normal, the temperature of the air-fuel mixture charged into the combustion chamber 16 also decreases. If exhaust gas recirculation (EGR) is performed as usual in this state, the EGR amount becomes excessive. As a result, the combustion state of the air-fuel mixture deteriorates, causing misfiring and reduced drivability.

Therefore, the ECU 92 sets the fuel intake temperature correction coefficient CFtha for correcting the fuel injection amount based on the intake temperature THA so that the fuel injection amount increases as the intake temperature THA becomes lower than a predetermined reference value. Perform a map operation. The fuel intake temperature correction coefficient CFtha thus calculated has a maximum value of “1.0”, and increases as the intake temperature THA decreases.

By correcting the fuel injection amount to the increase side using the fuel intake temperature correction coefficient CFtha, the correction amount of the fuel injection amount to the increase side becomes larger as the intake air temperature THA becomes lower than the reference value. Therefore, even if the combustion state deteriorates due to the excessive EGR amount when the intake air temperature THA is low, the combustion state is stabilized by the correction of the increase in the fuel injection amount. It is possible to prevent the deterioration of the ability.

Further, a map for calculating the fuel intake temperature correction coefficient CFtha is set for each combustion system, and the fuel intake temperature correction coefficient CFtha for the combustion system based on the intake air temperature THA with reference to these maps. Is calculated. The intake air temperature T of the fuel intake air temperature correction coefficient CFtha calculated in this way.
The transition tendency with respect to the change of the HA differs for each combustion method. Each map is set in advance so that the transition tendency of the fuel intake temperature correction coefficient CFtha becomes an optimum state according to each combustion method.

As described above, the fuel intake temperature correction coefficient CFtha
Is variable for each combustion method, even in the engine 11 in which the combustion method is switched, when the combustion state deteriorates due to the excessive EGR amount when the intake air temperature THA is low, the fuel injection amount is reduced. The combustion state can be accurately stabilized by the increase correction. Therefore, it is possible to prevent a misfire or a decrease in drivability based on the deterioration of the combustion state.

Next, a procedure for calculating the final fuel injection amount Qfin used for the fuel injection amount control will be described with reference to FIG. FIG. 9 is an injection amount calculation routine for calculating the final fuel injection amount Qfin. The injection amount calculation routine is executed by the ECU 92 at, for example, a time interruption every predetermined time.

In the same routine, steps S201 to S201
The process of S204 is for determining the combustion method of the engine 11. Steps S205 to S208
Is for calculating the final fuel injection amount Qfin at the time of "stratified combustion", "weak stratified combustion", "homogeneous lean combustion", and "homogeneous stoichiometric combustion".

In the same routine, the ECU 92 sets the cooling water temperature THW to a predetermined value a as a process of step S201.
(For example, 40 ° C.) or more. If the cooling water temperature THW is not equal to or higher than the predetermined value a, the process proceeds to step S208. If the cooling water temperature THW is equal to or higher than the predetermined value a, the process proceeds to step S202. The ECU 92 determines whether or not the basic fuel injection amount Qbse is equal to or smaller than the determination value QDJ as the process of step S202. Then, the operating state of the engine 11 is a state located in the homogeneous stoichiometric combustion area A,
If it is determined that “Qbse ≦ QDJ” is not satisfied, step S2 is performed.
Proceed to 08.

The ECU 92 determines the final fuel injection amount Qfin during “homogeneous stoichiometric combustion” as the process of step S208.
Is calculated. That is, the final fuel injection amount Qfin is obtained by multiplying the basic fuel injection amount Qbse calculated by referring to a known map based on the intake pressure PM and the engine speed NE by a fuel intake temperature correction coefficient CFtha. After the final fuel injection amount Qfin is calculated by the processing in step S208, EC
U92 temporarily ends the injection amount calculation routine.

When the final fuel injection amount Qfin is calculated in this manner, the ECU 92 controls the driving of the fuel injection valve 40 by another routine, and outputs an amount of fuel corresponding to the final fuel injection amount Qfin from the fuel injection valve 40. Inject. The fuel intake temperature correction coefficient CFtha for calculating the final fuel injection amount Qfin increases as the intake temperature THA becomes lower than a predetermined reference value. Therefore, at the time of "homogeneous stoichiometric combustion", even if the combustion state deteriorates due to the excessive EGR amount when the intake air temperature THA is low, the correction of the actual fuel injection amount to the increasing side is increased as the intake air temperature THA is lower. This stabilizes the combustion state.

On the other hand, in the process of S202, the operating state of the engine 11 is changed to the homogeneous stoichiometric combustion area A (FIG. 3).
If it is determined that “Qbse ≦ QDJ” is not satisfied, the process proceeds to step S203. The ECU 92
As the process of step S103, the basic fuel injection amount Qbse
Is determined to be equal to or less than the determination value QA. Then, in the process of step S103, the operation state of the engine 11 is not in the stratified combustion region D, but is set to "Qbse ≦
If it is not “QA”, the process proceeds to step S204.

The ECU 92 determines whether or not the basic fuel injection amount Qbse is equal to or smaller than the determination value QB as the process of step S204. Then, in the process of step S204, when it is determined that the operation state of the engine 11 is located within the homogeneous lean combustion region B and that “Qbse ≦ QB” is not satisfied, the process proceeds to step S207.

The ECU 92 calculates the final fuel injection amount Qfin at the time of "homogeneous lean combustion" as the process of step S207. That is, the accelerator pedal depression amount and the engine speed NE
A final fuel injection amount Qfin is obtained by multiplying a basic fuel injection amount Qbse calculated with reference to a known map based on the above by a fuel intake temperature correction coefficient CFtha. Step S207
After the final fuel injection amount Qfin is calculated by the processing of
The CU 92 temporarily ends the injection amount calculation routine.

When the final fuel injection amount Qfin is calculated in this way, the ECU 92 controls the drive of the fuel injection valve 40 by another routine, and outputs the amount of fuel corresponding to the final fuel injection amount Qfin from the fuel injection valve 40. Inject. The fuel intake temperature correction coefficient CFtha for calculating the final fuel injection amount Qfin increases as the intake temperature THA becomes lower than a predetermined reference value. Therefore, at the time of "homogeneous lean combustion", even if the combustion state deteriorates due to the excessive EGR amount when the intake air temperature THA is low, the correction of the actual fuel injection amount to the increasing side is increased as the intake air temperature THA is lower. This stabilizes the combustion state.

On the other hand, in the process of step S204, when it is determined that the operation state of the engine 11 is located in the weak stratified combustion region C and that “Qbse ≦ QB”, the process proceeds to step S206.

The ECU 92 calculates the final fuel injection amount Qfin at the time of "weak stratified combustion" as the process of step S206. That is, the final fuel injection amount Qfin is obtained by multiplying the basic fuel injection amount Qbse calculated by referring to a known map based on the accelerator pedal depression amount and the engine speed NE by a fuel intake temperature correction coefficient CFtha. After the final fuel injection amount Qfin is calculated by the processing of step S206, the ECU
A step 92 temporarily ends the injection amount calculation routine.

When the final fuel injection amount Qfin is calculated in this manner, the ECU 92 controls the drive of the fuel injection valve 40 by another routine, and supplies the fuel of the amount corresponding to the final fuel injection amount Qfin from the fuel injection valve 40. Inject. The fuel intake temperature correction coefficient CFtha for calculating the final fuel injection amount Qfin increases as the intake temperature THA becomes lower than a predetermined reference value. Therefore, at the time of "weak stratified combustion",
Even if the combustion state deteriorates due to an excessive amount of EGR when the intake air temperature THA is low, the combustion state is stabilized by increasing the correction of the actual fuel injection amount to the increasing side as the intake air temperature THA is lower. Can be

On the other hand, if it is determined in step S203 that the operation state of the engine 11 is in the stratified combustion region D and that "Q≤QA", the process proceeds to step S205.

The ECU 92 calculates the final fuel injection amount Qfin at the time of "stratified combustion" as the process of step S205. That is, the basic fuel injection amount Q calculated by referring to a known map based on the accelerator pedal depression amount and the engine speed NE.
The value obtained by multiplying bse by the fuel intake temperature correction coefficient CFtha is defined as the final fuel injection amount Qfin. After the final fuel injection amount Qfin is calculated by the processing in step S205, the ECU 9
2 temporarily ends the injection amount calculation routine.

When the final fuel injection amount Qfin is calculated in this manner, the ECU 92 controls the drive of the fuel injection valve 40 by another routine, and outputs an amount of fuel corresponding to the final fuel injection amount Qfin from the fuel injection valve 40. Inject. The fuel intake temperature correction coefficient CFtha for calculating the final fuel injection amount Qfin increases as the intake temperature THA becomes lower than a predetermined reference value. Therefore, in the "stratified combustion", even if the combustion state deteriorates due to the excessive EGR amount when the intake air temperature THA is low, the correction of the actual fuel injection amount to the increasing side is increased as the intake air temperature THA is lower. This stabilizes the combustion state.

According to the present embodiment in which the processing described in detail above is performed, the following effects can be obtained. (4) Even if the EGR amount becomes excessive when the intake air temperature THA is low and the combustion state deteriorates, the fuel injection amount is increased and corrected by the fuel intake air temperature correction coefficient CFtha calculated based on the intake air temperature THA. As a result, the combustion state is stabilized, and misfire and drivability due to the deterioration of the combustion state are prevented.

(5) In the combustion system of the engine 11, the air-fuel ratio of the air-fuel mixture to be burned is changed in the order of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”. Become lean. Therefore, the EGR when the intake air temperature THA is low in the order of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”.
The combustion state is likely to be deteriorated due to the excessive amount. However, in the present embodiment, each map for calculating the fuel intake temperature correction coefficient CFtha is set so that the transition tendency of the fuel intake temperature correction coefficient CFtha with respect to the change of the intake temperature THA becomes an optimum state for each combustion method. The settings are made. Therefore,
In the engine 11 whose combustion mode is switched as described above, even if the combustion state deteriorates due to an excessive amount of EGR when the intake air temperature THA is low, the fuel intake air temperature correction coefficient C
By correcting the fuel injection amount to the increasing side based on Ftha, the combustion state can be accurately stabilized.

The above embodiments can be modified, for example, as follows. In the first embodiment, the EGR intake temperature correction coefficient C1tha
Was calculated based only on the intake air temperature THA, but its EGR
When calculating the intake air temperature correction coefficient C1tha, the engine speed NE and the basic fuel injection amount Qbse (load) may be considered. For example, the EGR intake temperature correction coefficient C1tha may be multiplied by a correction coefficient Cegr whose reference value is "1.0" obtained from the engine speed NE and the basic fuel injection amount Qbse. Here, FIG. 10 shows transition trends of the correction coefficient Cegr with respect to changes in the engine speed NE and the basic fuel injection amount Qbse. As is clear from the figure, the correction coefficient Cegr becomes smallest in the high-speed high-load region in the stratified combustion region D, and gradually decreases toward the high-speed high-load region. That is, the correction coefficient Cegr is equal to EG
The EGR intake temperature correction coefficient C1tha is determined to be smaller as the engine speed NE and the basic fuel injection amount Qbse increase in the R amount. In this case, the correction coefficient C
The EGR intake temperature correction coefficient C1 is obtained by the correction by egr.
tha will be more appropriate.

Instead of obtaining the correction coefficient Cegr for correcting the EGR intake temperature correction coefficient C1tha based on both the engine speed NE and the basic fuel injection amount Qbse, the engine speed NE and the basic fuel injection amount are calculated. Qbse
The correction coefficient Cegr may be obtained based on either of the above.

The correction coefficient Cegr for correcting the EGR intake temperature correction coefficient C1tha may be reflected in the correction of the ignition timing. That is, the ignition temperature correction coefficient C2tha may be multiplied by the correction coefficient Cegr. In this case, EG
Even if the R intake temperature correction coefficient C1tha is multiplied by the correction coefficient Cegr, the ignition timing is adjusted in accordance therewith, so that the combustion state of the engine 11 can be maintained in a good condition.

In the second embodiment, when calculating the fuel intake temperature correction coefficient CFtha, the engine speed NE basic fuel injection amount Qbse (load) may be added. For example, the EGR intake temperature correction coefficient C1tha may be multiplied by a correction coefficient Cfuel obtained from the engine speed NE and the basic fuel injection amount Qbse and having a reference value of “1.0”.
Here, the engine speed NE and the basic fuel injection amount Qbse
Fig. 11 shows the transition trend of the correction coefficient Cfuel with respect to the change of
Shown in As is apparent from FIG.
Is largest in the high-speed high-load region in the stratified combustion region D, and gradually increases toward the high-speed high-load region. That is, the correction coefficient Cfuel is determined such that the fuel intake temperature correction coefficient CFtha increases as the engine speed NE and the basic fuel injection amount Qbse increase with an increase in the EGR amount. In this case, the correction by the correction coefficient Cfuel makes the fuel intake temperature correction coefficient CFtha more appropriate.

In each of the above embodiments, the EGR intake temperature correction for the change in the intake air temperature THA is performed for each of the combustion modes “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”. Although the transition trends of the coefficient C1tha and the fuel intake temperature correction coefficient CFtha are different, the present invention is not limited to this. That is, for example, during execution of so-called lean combustion, such as "homogeneous lean combustion", "weak stratified combustion", and "stratified combustion", an EGR intake temperature correction coefficient C1tha and a fuel intake temperature correction coefficient for a change in intake air temperature THA. The transition tendency of CFtha may be the same. Also, only in "weak stratified combustion" and "stratified combustion"
EGR intake temperature correction coefficient C for change in intake temperature THA
The transition tendency of 1tha and the fuel intake temperature correction coefficient CFtha may be the same. Further, in each combustion mode, the EGR intake temperature correction coefficient C1th with respect to the change in the intake temperature THA.
a and the transition tendency of the fuel correction coefficient CFtha may be the same.

In the first embodiment, the ignition intake air temperature correction for the change in the intake air temperature THA is performed for each of the combustion systems of “homogeneous stoichiometric combustion”, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”. Although the transition tendency of the coefficient C2tha is made different, the present invention is not limited to this. That is, for example, during the execution of so-called lean combustion, ie, “homogeneous lean combustion”, “weak stratified combustion”, and “stratified combustion”, even if the transition tendency of the ignition intake air temperature correction coefficient C2tha with respect to the change of the intake air temperature THA is the same. Good. In addition, "weak stratified combustion",
Only in "stratified combustion", the transition tendency of the ignition intake air temperature correction coefficient C2tha with respect to the change of the intake air temperature THA may be the same. Further, in any of the combustion systems, the ignition intake air temperature correction coefficient C2th for the change in the intake air temperature THA.
The transition tendency of a may be the same.

In the first embodiment, it is not always necessary to correct the ignition timing to the retard side. Next, technical ideas other than the claims that can be understood from the above embodiments are described below together with their effects.

(1) In the control device for an internal combustion engine according to the seventh aspect, as the correction amount is set such that the correction means increases the correction of the exhaust gas recirculation amount to the decreasing side, the internal combustion engine is controlled by the correction means. A control device for an internal combustion engine, further comprising an ignition timing correction means for correcting the ignition timing to a retard side.

In general, the combustion rate of the air-fuel mixture increases as the amount of exhaust gas recirculation decreases. According to this configuration, the ignition timing of the internal combustion engine is corrected to the retard side as the correction amount is set such that the correction of the exhaust gas recirculation amount to the reduction side is increased. Even if the circulation amount is corrected, the combustion state is properly maintained.

[0121]

According to the first aspect of the present invention, as the intake air temperature of the internal combustion engine is lower than the predetermined reference value, the control amount for controlling the operation of the internal combustion engine increases toward the side for stabilizing the combustion state. Since the correction is made, it is possible to prevent the combustion state from deteriorating when the intake air temperature is lower than usual and the exhaust gas recirculation amount becomes excessive.

According to the second aspect of the present invention, the correction amount of the control amount for controlling the operation of the internal combustion engine is made variable in accordance with the combustion system of the internal combustion engine. Even when the control amount is corrected by the correction amount, the deterioration of the combustion state when the intake air temperature is low can be prevented.

According to the third aspect of the present invention, the correction amount for correcting the control amount for controlling the operation of the internal combustion engine to the stable combustion state side is increased as the air-fuel ratio of the air-fuel mixture becomes leaner. Therefore, even in an internal combustion engine in which the combustion method is switched, the combustion state deteriorates when the intake air temperature is low by correcting the control amount for controlling the operation state of the internal combustion engine based on the correction amount. Can be prevented.

According to the fourth aspect of the present invention, as the combustion system of the internal combustion engine becomes homogeneous stoichiometric combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion, the combustion at a control amount for controlling the operation of the internal combustion engine is performed. The correction amount is set so that the correction toward the state where the state is stabilized becomes large. for that reason,
Even in an internal combustion engine whose combustion method is switched between homogeneous stoichiometric combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion, the control amount for controlling the operating state of the internal combustion engine is corrected based on the correction amount. This can prevent the combustion state from deteriorating when the intake air temperature is low.

According to the fifth aspect of the present invention, since the exhaust gas recirculation amount changes depending on the engine speed and the engine load, the control amount for controlling the operation of the internal combustion engine in consideration of the engine speed and the engine load. By setting the correction amount of
The correction amount of the control amount can be set to a more appropriate value.

According to the sixth aspect of the present invention, the control amount for controlling the operation of the internal combustion engine is corrected so that the combustion state becomes more stable as the engine speed and the engine load increase the exhaust gas recirculation amount. Since the correction amount is set so as to increase, the correction amount can be set to a more appropriate value.

According to the seventh aspect of the present invention, the lower the intake air temperature is, the larger the exhaust recirculation amount is corrected to the decreasing side, so that even when the intake air temperature is low, the exhaust recirculation amount can be properly adjusted. Value, it is possible to prevent the deterioration of the combustion state.

According to the eighth aspect of the present invention, the lower the intake air temperature is, the more the fuel injection amount is increased and the combustion state is stabilized, so that the exhaust recirculation is performed when the intake air temperature is low. Even if the amount is excessive, the deterioration of the combustion state can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an entire engine to which a control device according to a first embodiment is applied.

FIG. 2 is a block diagram showing an electrical configuration of the control device.

FIG. 3 is a map referred to when determining the combustion mode of the engine.

FIG. 4 is a graph showing a transition tendency of an EGR intake air temperature correction coefficient with respect to a change in intake air temperature for each combustion method.

FIG. 5 is a graph showing a transition tendency of an ignition intake air temperature correction coefficient with respect to a change in intake air temperature for each combustion method.

FIG. 6 is a diagram showing a transition trend of an EGR amount with respect to changes in an engine speed and a fuel injection amount.

FIG. 7 is a flowchart showing a procedure for calculating a control amount such as a target EGR amount and a target ignition timing.

FIG. 8 is a flowchart showing a procedure for calculating a control amount such as a target EGR amount and a target ignition timing.

FIG. 9 is a flowchart showing a procedure for calculating a final fuel injection amount in the second embodiment.

FIG. 10 is a diagram showing a transition tendency with respect to changes in engine speed and fuel injection amount in a correction coefficient for correcting an intake temperature correction coefficient for EGR.

FIG. 11 is a diagram showing a transition tendency with respect to changes in engine speed and fuel injection amount in a correction coefficient for correcting a fuel intake temperature correction coefficient.

[Explanation of symbols]

11 ... engine, 14 c ... crank position sensor,
26 ... Accelerator position sensor, 36 ... Vacuum sensor, 37 ... Intake air temperature sensor, 40 ... Fuel injection valve, 42 ...
EGR passage, 43 ... EGR valve, 43a ... Step motor. 44: throttle position sensor; 92: electronic control unit (ECU).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301E F-term (Reference) 3G084 AA04 BA05 BA09 BA13 BA20 DA02 DA05 DA28 EB08 FA02 FA10 FA11 FA33 FA38 3G092 AA01 AA06 AA09 AA17 BA01 BA04 BA09 BB01 BB06 DC03 DC09 DE03S EA02 EA11 FA03 FA15 HA04Z HA06Z HB01X HB01Z HD07X HD07Z HE01Z HE03Z HE08Z 3G301 HA01 HA04 HA13 PE03 PA03 MA03 PE01 MA03 JA03 PE03 MA01

Claims (8)

[Claims] An exhaust gas recirculation mechanism for recirculating exhaust gas to an intake system, and control means for controlling a predetermined control system for controlling the operation of the internal combustion engine in accordance with a control amount required based on an engine operating state. In the control device for an internal combustion engine, an intake air temperature detecting means for detecting an intake air temperature of the internal combustion engine, and the control amount is increased as the intake air temperature detected by the intake air temperature detecting means is lower than a predetermined reference value. A control device for an internal combustion engine comprising: correction means for largely correcting the combustion state of the engine to be stabilized. 2. The combustion system of the internal combustion engine is switched in accordance with an operating state of the engine, and the correction means varies a correction amount of the control amount based on an intake air temperature in accordance with the combustion system. Item 2. The control device for an internal combustion engine according to Item 1. 3. The correction means sets the correction amount of the control amount based on the intake air temperature to be larger on the stable combustion state side as the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine becomes leaner. The control device for an internal combustion engine according to claim 2. 4. The combustion system of the internal combustion engine is switched between stratified combustion, weak stratified combustion, homogeneous lean combustion, and homogeneous stoichiometric combustion, and the correction means includes a homogeneous stoichiometric combustion, a homogeneous lean combustion. 4. The control device for an internal combustion engine according to claim 3, wherein the correction amount of the control amount based on the intake air temperature is set to be larger on the stable combustion state side in the order of weak stratified combustion and stratified combustion. 5. The control device for an internal combustion engine according to claim 1, wherein said correction means sets the correction amount of said control amount in consideration of at least one of an engine speed and an engine load. 6. The internal combustion engine according to claim 5, wherein the correction means sets the correction amount of the control amount to a stable combustion state larger as the exhaust gas recirculation amount increases at an engine speed and an engine load. Control device. 7. The exhaust gas recirculation mechanism according to claim 1, wherein the control amount is an exhaust gas recirculation amount by the exhaust gas recirculation mechanism, and the correction means reduces and corrects the exhaust gas recirculation amount as the intake air temperature decreases. 3. The control device for an internal combustion engine according to claim 1. 8. The control amount is a fuel injection amount of the internal combustion engine set according to an engine operating state, and the correction means corrects the fuel injection amount by increasing the lower the intake air temperature. 7. The control device for an internal combustion engine according to any one of 6.