JP3757998B2 - In-cylinder injection type internal combustion engine control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct injection internal combustion engine mounted on a vehicle.
[0002]
[Related background]
In a spark ignition internal combustion engine mounted on a vehicle, an in-cylinder injection type gasoline engine that directly injects fuel into a combustion chamber is used instead of an intake pipe injection type in order to reduce harmful exhaust gas components and improve fuel efficiency. Various proposals have been made.
In a cylinder injection type gasoline engine, for example, during low load operation, fuel is injected mainly during the compression stroke, and an air-fuel mixture close to the stoichiometric air-fuel ratio is locally formed around the spark plug and in the cavity. Thus, good combustion can be realized even with a lean air-fuel ratio as a whole (this is referred to as “stratified combustion”). On the other hand, during medium and high load operation, fuel is injected during the intake stroke, a uniform air-fuel ratio mixture is formed in the combustion chamber, and a large amount of fuel is burned in the same manner as an intake pipe injection type gasoline engine (this (Referred to as “premixed combustion”), it is possible to ensure the output required during acceleration or high-speed traveling.
[0003]
[Problems to be solved by the invention]
In such an engine, it is conceivable to set so as to improve idle fuel efficiency by performing stratified combustion (super-lean operation) during idling. However, when supercharging or the like is not performed in stratified combustion at idling, the amount of air supplied into the cylinder is only supplied by the amount of air corresponding to the full load (throttle fully open). The output that can be obtained is determined. That is, in the stratified combustion, if the fuel ratio with respect to the amount of air increases more than a certain amount, the air-fuel mixture around the spark plug becomes too thick and misfires or smoke is generated. For this reason, the maximum output at the time of stratified combustion is determined by the maximum fuel amount suitable for the air amount corresponding to the full load. The air-fuel ratio in the combustion chamber when the maximum output of stratified combustion occurs is still leaner than the stoichiometric air-fuel ratio, so the maximum amount of fuel that can be supplied during stratified combustion is smaller than that during premixing. The maximum output is also low. For this reason, when an external load such as an air conditioner or power steering is applied during idling, there is a limit to increasing the fuel amount in response to this, so the output obtained during stratified combustion should be supported. The engine speed may drop and engine stall may occur in some cases.
[0004]
Further, in a conventional port injection type lean combustion internal combustion engine different from the above-described cylinder injection type internal combustion engine, when an external load is applied during idling, the rotation speed is likely to fluctuate. Discloses a technique for prohibiting lean operation and shifting to stoichiometric (theoretical air-fuel ratio) operation (Japanese Patent Laid-Open No. 60-17234).
[0005]
However, in the above known example, since the operation state is switched to the stoichiometric operation based on the operation signal of the auxiliary machinery (air conditioner etc.), the operation state is actually in spite of the state where the lean operation can be continued. Will be switched, resulting in a problem that idle fuel consumption deteriorates. In addition, since the operation state is switched by the output of the operation signal, the environmental condition (e.g., high altitude where the intake air density is low) or the transmission (T / M) in the lean operation state even though the operation signal is not output. In the known example, the lean operation is continued in the known example, and the output during the lean operation cannot cope with the load increase as described above, and the engine speed drops or the engine There is a risk of stalling.
[0006]
The present invention has been made in view of the above-mentioned points, and even when the load increases due to operations other than the operation of auxiliary equipment such as a change in environmental conditions or a failure of the transmission, it is possible to reliably reduce the rotational speed at the time of idling. An object of the present invention is to provide a control device for a direct injection internal combustion engine that can be prevented.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, according to the first aspect of the present invention, fuel is directly injected into the combustion chamber, premixed combustion and stratified combustion are switched according to the operating state, and stratified combustion is performed during idling. In addition, in the control apparatus for a direct injection type internal combustion engine provided with output control means for increasing the fuel amount with respect to the increase in the external load at the time of idling and changing the engine output to the increase side, the fuel amount or the Switch to the premixed combustion when the parameter related to the fuel amount exceeds a predetermined valueThe predetermined value is a value corresponding to the air-fuel ratio at which the stratified combustion is allowed with respect to the fully open air amount or the air amount in the vicinity thereof.It is a composition.
[0008]
  That is, the fuel is increased within an air-fuel ratio range in which the output can be increased by stratified combustion in response to an increase in the external load on the engine during idling. Here, in the case of an engine that is operating in an air-fuel ratio range with good fuel efficiency by reducing the intake flow rate to some extent during normal idling when the external load is not so large, the air-fuel ratio range with good fuel efficiency is increased as the external load increases. It is conceivable to increase the amount of air (that is, the amount of fuel) while maintaining the amount of fuel so that when the amount of air reaches the upper limit, the air-fuel ratio is increased beyond the low fuel consumption range to the rich side. . In addition, in the case of basically the fully open air amount at the time of idling, only the fuel increase amount is performed as the external load increases. In any case, the upper limit air fuel that allows the stratified combustion with respect to the fully open air amount or the air amount in the vicinity of the supplied fuel amount.Specific phaseIf this value is reached, that is, the amount of fuel or the parameter that correlates to the amount of fuelA value corresponding to the air-fuel ratio at which the stratified combustion is allowed with respect to the fully open air amount or the air amount in the vicinity thereofIs exceeded, the stratified combustion mode is switched to the premixed combustion mode to enable further response to an external load, thereby preventing the occurrence of a stall due to a drop in the engine speed.
[0009]
  Claims2According to the present invention described in the above, fuel is directly injected into the combustion chamber, switching between premixed combustion and stratified combustion according to the operating state, stratified combustion is performed during idling, and external load is increased during idling. In a control apparatus for a direct injection type internal combustion engine having an output control means for increasing an air amount, increasing a fuel in response to the increased air amount, and changing an engine output to an increase side, When the air amount or a parameter correlated with the air amount exceeds a predetermined value, the premixed combustion is switched.
  Claim3According to the present invention described in the above, the predetermined value is set to a value lower than the maximum air amount allowed for the stratified combustion.
  Claim4According to the present invention described in (1), the predetermined value is set to about 70% of the maximum air amount.
[0010]
That is, the air amount and the fuel amount are increased while the air-fuel ratio is substantially constant in the vicinity of a specific air-fuel ratio advantageous in terms of combustion in response to an increase in the external load on the engine during idling. At this time, the fuel amount and the air amount may be increased at the same time while keeping the air-fuel ratio constant, but the relationship between the fuel amount and the air amount is slightly changed within the range between the lower limit air-fuel ratio and the upper limit air-fuel ratio. You may do it. That is, when an increase in the external load is detected by each load switch or a drop in the idle speed, first, the fuel amount is increased and the air-fuel ratio is reduced, and even when the air-fuel ratio reaches the lower limit air-fuel ratio, the external load is still If the response to the load is insufficient, the air amount is increased to change the air-fuel ratio to the upper limit air-fuel ratio, and the fuel amount is further increased to lower the air-fuel ratio toward the lower limit value. It is also possible to cope with the increased external load by repeating this alternately increasing amount of fuel and air.
[0011]
As described above, as a result of coping with the increase in external load by increasing the amount of fuel and air simultaneously or alternately, if the value correlated with the air amount at this time exceeds a certain value (threshold), super lean operation (stratified) Further increase in output due to combustion) is determined to be impossible or less effective and switched to premixed combustion, and the operation shifts to stoichiometric operation where large torque can be generated. Thereby, a drop in engine speed is prevented, and engine stall is prevented.
[0012]
  Claim3And claims4As described above, it is preferable that the predetermined value is set lower than the maximum amount of air allowed for stratified combustion. The reason for this is that when the predetermined value is set to the maximum air amount, a delay occurs when the engine operation is switched due to an increase in the external load.Therefore, when switching from stratified combustion to premixed combustion, a large external load is caused. If there is a risk of misfire, etc., and from the viewpoint of idle fuel consumption, even if the range of stratified combustion is expanded with the predetermined value as the maximum air amount, the fuel consumption is large in the vicinity of the maximum air amount and in the case of premixed combustion. This is because there is no difference, and premixed combustion has merit in terms of combustion stability.
[0013]
  Claims2As described above, when the control is performed to switch the combustion state to the premixed combustion by checking the air amount or its correlation value during idling, the air amount or its correlation value is preferably controlled using a volume flow rate. The reason for this is that if the control of switching the combustion state by the fuel amount or the like is performed at a high altitude where the intake air density is lowered, a change in the fuel amount corresponding to the change in the intake air density cannot be obtained, and thus there is a problem such as a drop in the rotational speed. This is because control must be performed by adding the correction of the intake air density to the fuel amount, and the control becomes complicated.
[0014]
In the control for switching the combustion state to the premixed combustion by looking at the fuel amount or its correlation value at the time of idling as in claim 1, the intake density correction is added to the fuel amount at high altitude where the intake density changes. It is preferable to perform control. Thereby, it is possible to reliably prevent the rotation speed from dropping even at high altitudes.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a control device for a direct injection gasoline engine according to the present invention mounted on a vehicle. The cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 4 together with an ignition plug 3 for each cylinder, so that fuel is directly injected into the combustion chamber 5. A hemispherical cavity 8 is formed on the top surface of the piston 7 that reciprocates while sliding in the cylinder 6 at a position where fuel spray from the fuel injection valve 4 reaches near the top dead center. . Further, the theoretical compression ratio of the engine 1 is set higher (about 12 in this embodiment) than that of the intake pipe injection type. As the valve operating mechanism, a DOHC four-valve type is adopted, and an intake side camshaft 11 and an exhaust side camshaft 12 are rotatable at the upper part of the cylinder head 2 so as to drive the intake and exhaust valves 9 and 10, respectively. Is retained.
[0016]
An intake port 13 is formed in the cylinder head 2 so as to pass between the camshafts 11 and 12 in a substantially upright direction, and an intake air flow passing through the intake port 13 will be described later in the combustion chamber 5. A reverse tumble flow is generated. On the other hand, the exhaust port 14 is formed in a substantially horizontal direction as in a normal engine, but a large-diameter EGR port 15 is branched obliquely. In the figure, 16 is a water temperature sensor for detecting the cooling water temperature TW, and 17 is a crank angle sensor for outputting a crank angle signal SGT at a predetermined crank position (5 ° BTDC and 75 ° BTDC in this embodiment) of each cylinder. Reference numeral 19 denotes an ignition coil that outputs a high voltage to the spark plug 3. A cylinder discriminating sensor (not shown) that outputs a cylinder discriminating signal SGC is attached to a camshaft or the like that rotates at half the number of revolutions of the crankshaft to discriminate which cylinder the crank angle signal SGT belongs to. .
[0017]
An intake pipe 25 having an air cleaner 22, a throttle body 23, and a stepper motor type idle speed control valve (hereinafter referred to as an idle adjustment valve) 24 is connected to the intake port 13 via an intake manifold 21 having a surge tank 20. is doing. Further, the intake pipe 25 is provided with a large-diameter air bypass pipe 26 that bypasses the throttle body 23 and introduces intake air into the intake manifold 21. A bypass valve (referred to as an ABV valve) 27 is provided. Note that the air bypass pipe 26 has a flow passage area similar to that of the intake pipe 25, and when the ABV valve 27 is fully opened, the intake air in an amount required in the low and medium speed range of the engine 1 can flow. . On the other hand, the idle adjustment valve 24 has a smaller flow path area than the ABV valve 27, and the idle adjustment valve 24 is used when adjusting the intake air amount with high accuracy.
[0018]
The throttle body 23 includes a butterfly throttle valve 28 that opens and closes a flow path, a throttle sensor 29 that detects accelerator opening information by detecting the opening θth of the throttle valve 28, and an idle that detects a fully closed state. A switch 30 is provided. An air pressure sensor 31 and an intake air temperature sensor 32 for obtaining the intake air density are disposed inside the air cleaner 22 and output signals corresponding to the atmospheric pressure Pa and the intake air temperature Ta. Further, a Karman vortex type airflow sensor 33 is disposed in the vicinity of the inlet of the intake pipe 25 and outputs a vortex generation signal proportional to the volumetric air flow rate Qa per intake stroke.
[0019]
On the other hand, the exhaust port 14 has an O₂ An exhaust pipe 43 having a three-way catalyst 42 and a muffler (not shown) is connected through an exhaust manifold 41 to which the sensor 40 is attached. The EGR port 15 is connected to the downstream of the throttle valve 28 and the upstream of the intake manifold 21 via a large-diameter EGR pipe 44, and a stepper motor type EGR valve 45 is provided in the pipeline. It has been.
[0020]
The fuel tank 50 is installed at the rear of the vehicle body (not shown). Then, the fuel stored in the fuel tank 50 is sucked up by the electric low-pressure fuel pump 51 and fed to the engine 1 side through the low-pressure feed pipe 52. The fuel pressure in the low-pressure feed pipe 52 is regulated to a relatively low pressure (hereinafter referred to as a low fuel pressure) by a first fuel pressure regulator 54 interposed in the pipe line of the return pipe 53. The fuel supplied to the engine 1 side is supplied to each fuel injection valve 4 through a high-pressure feed pipe 56 and a delivery pipe 57 by a high-pressure fuel pump 55 attached to the cylinder head 2. In this embodiment, the high-pressure fuel pump 55 is a swash plate axial piston type, is driven by the exhaust camshaft 12, and generates a high discharge pressure even when the engine 1 is idling. The fuel pressure in the delivery pipe 57 is regulated to a relatively high pressure (hereinafter referred to as a high fuel pressure) by a second fuel pressure regulator 59 interposed in the pipe line of the return pipe 58. In the figure, reference numeral 60 denotes an electromagnetic fuel pressure switching valve attached to the second fuel pressure regulator 59, which relieves the fuel in the ON state and lowers the fuel pressure in the delivery pipe 57 to a predetermined value. Reference numeral 61 denotes a return pipe that returns the fuel that has been lubricated or cooled to the high-pressure fuel pump 55 to the fuel tank 50.
[0021]
An ECU (Electronic Control Unit) 70 is installed in the vehicle interior. The ECU 70 is a storage device (ROM, RAM, non-volatile RAM) for storing input / output devices (not shown), control programs, control maps, and the like. Etc.), a central processing unit (CPU), a timer counter, and the like are provided to perform overall control of the engine 1.
On the input side of the ECU 70, switches for detecting the operation status of an air conditioner device, a power steering device, an automatic transmission, etc., which become a load on the engine 1 during operation, that is, an air conditioner switch (A / C / SW) 34, power steering A switch (P / S · SW) 35, an inhibitor switch (INH · SW) 36, and the like are connected to each other, and each detection signal is supplied to the ECU 70. In addition to the various sensors and switches described above, the ECU 70 is connected to a number of switches and sensors (not shown) on the input side, and various warning lights and devices are also connected to the output side. ing.
[0022]
The ECU 70 determines the fuel injection end time, the ignition timing, the introduction amount of EGR gas, and the like based on the input signals from the various sensors and switches described above, and the fuel injection valve. 4. Drive control of the ignition coil 19, the EGR valve 45, etc.
Next, the basic flow of engine control will be briefly described.
[0023]
When the engine is cold, when the driver starts the ignition key or when the engine 1 reaches a predetermined number of revolutions, the ECU 70 turns on the low-pressure fuel pump 51 and the fuel pressure switching valve 60 so that the fuel injection valve 4 has a low fuel pressure fuel. Supply. This is because when the engine 1 is stopped or cranked, the high-pressure fuel pump 55 operates only completely or incompletely, so that the fuel is based on the discharge pressure of the low-pressure fuel pump 51 and the opening time of the fuel injection valve 4. This is because the injection amount must be determined. At the same time, the engine 1 is cranked by a cell motor (not shown), and at the same time, fuel injection control by the ECU 70 is started. At this time, the ECU 70 selects the intake stroke injection mode and injects fuel so that the air-fuel ratio becomes relatively rich. This is because the fuel vaporization rate is low when the engine is cold, and therefore misfire and discharge of unburned fuel (HC) are inevitable when injection is performed in the compression stroke injection mode. Further, since the ECU 70 closes the ABV valve 27 at the time of starting, the intake air to the combustion chamber 5 is supplied from the gap of the throttle valve 28 or the idle adjustment valve 24. Note that the idle adjustment valve 24 and the ABV valve 27 are centrally managed by the ECU 70, and the respective valve opening amounts are determined according to the necessary introduction amount of intake air (bypass air) that bypasses the throttle valve 28.
[0024]
When the start is completed and the engine 1 starts idling operation, the high pressure fuel pump 55 starts the rated discharge operation. Therefore, the ECU 70 turns off the fuel pressure switching valve 60 and supplies high fuel pressure fuel to the fuel injection valve 4. . At this time, as a matter of course, the fuel injection amount is determined based on the high fuel pressure and the valve opening time of the fuel injection valve 4. Until the cooling water temperature TW rises to a predetermined value, the ECU 70 selects the intake stroke injection mode and injects fuel in the same manner as at the start, and the ABV valve 27 is also closed continuously. Control of the idle speed according to the increase or decrease of the load of auxiliary equipment such as an air conditioner is performed by the idle adjustment valve 24 (the ABV valve 27 is also opened as necessary) in the same manner as the intake pipe injection type. . Further, after a predetermined cycle has elapsed, O₂ When the sensor 40 reaches the activation temperature, the ECU 70₂ Air-fuel ratio feedback control is started according to the output voltage of the sensor 40, and harmful exhaust gas components are purified by the three-way catalyst 42. As described above, when the engine is cold, fuel injection control substantially the same as that of the intake pipe injection type is performed. However, since there is no adhesion of fuel droplets to the wall surface of the intake pipe 13, the response and accuracy of the control are increased. .
[0025]
When the warm-up of the engine 1 is completed, the ECU 70 determines from the fuel injection control map based on the target in-cylinder effective pressure (target load) Pe obtained from the throttle opening θth and the like and the engine speed (rotation speed) Ne. The fuel injection control area is searched, the fuel injection mode and the fuel injection amount are determined and the fuel injection valve 4 is driven, and the valve opening control of the ABV valve 27 and the EGR valve 45 is also performed.
[0026]
For example, since the compression stroke injection lean region indicated by the oblique lines in FIG. 2 is in a low load / low rotation operation such as an idle operation, the ECU 70 selects the compression stroke injection mode and operates the ABV valve 27 and the EGR valve 40 in an operating state. And the fuel is injected so that the air-fuel ratio becomes lean (in this embodiment, about 20 to 40). At this time, the vaporization rate of the fuel rises and the intake flow flowing in from the intake port 13 forms a reverse tumble flow, so that the fuel spray injected into the cavity 8 of the piston 7 is surrounded by the spark plug 3 at the time of ignition. Therefore, combustion (stratified combustion) is possible even when the air-fuel ratio is extremely lean as a whole (for example, the total air-fuel ratio is about 50). As a result, the amount of CO and HC emitted becomes extremely small, and the amount of NOx emitted can be kept low by the recirculation of the exhaust gas. In addition, the fuel consumption is greatly improved in combination with the reduction of the pumping loss by opening the ABV valve 27 and the EGR valve 40. And control of the idle speed according to increase / decrease in load is performed by increasing / decreasing air amount and fuel injection amount.
[0027]
More specifically, in response to an increase in the external load on the engine during idling, the idle adjustment valve 24 (ABV valve if necessary) is set by a signal from the ECU 70 to increase the air amount and the fuel amount while keeping the air-fuel ratio substantially constant. And the fuel injection valve 4 are controlled. That is, the ECU 70 stores in advance fuel injection amount (fuel increase amount) corresponding to each load switch ON signal (corresponding to an increase in external load) and opening degree data, and the load switch outputs an ON signal. The data stored in the ECU 70 is read by the load switch signal, and the fuel injection valve 4 and the idle adjustment valve 24 are controlled based on the data. When an ON signal is output from each load switch, the external load increases by the number of ON signals of the load switch, so the data from the ECU 70 is added and output to the fuel injection valve 4 and the idle adjustment valve 24. The As a result, the air amount and the fuel amount are controlled while maintaining a preset air-fuel ratio so as to be able to cope with a range of load increase even if the external load increases due to the operation of the load switch. Further, when the external load increases except for the load switch, the idling engine speed drops. Therefore, the degree of the engine speed drop is detected, and the fuel injection valve 4 and the idle adjustment valve 24 are connected to the lower limit air-fuel ratio and the upper limit air-fuel ratio. It is controlled within the range of the fuel ratio. That is, desired rotation speed feedback control is performed. In this case, first, when the fuel amount of the fuel injection valve 4 is increased to reduce the air-fuel ratio, even when the air-fuel ratio reaches the lower limit air-fuel ratio, the response to the external load is still insufficient (that is, the idle speed is When the value is below the predetermined value), the idle adjustment valve 24 is driven in the opening direction by a signal from the ECU 70 to increase the air amount to change the air-fuel ratio to the upper limit air-fuel ratio, and further increase the fuel amount. Reduce the air-fuel ratio toward the lower limit. The increased external load is dealt with by repeating this alternately increasing amount of fuel and air.
[0028]
In the compression stroke injection mode, the fuel spray injected from the injection valve 4 must ride on the reverse tumble flow and reach the spark plug 3, and the fuel evaporates until reaching the ignition point. Therefore, an air-fuel mixture that can be easily ignited must be formed. When the average air-fuel ratio is 20 or less, an overrich mixture is locally generated in the vicinity of the spark plug 3 and so-called rich misfire occurs. On the other hand, when the average air-fuel ratio exceeds 40, misfire (so-called lean misfire) occurs exceeding the lean limit. It becomes easy. For this reason, as described later, fuel injection start and end timings and ignition timings are accurately controlled, and the average air-fuel ratio is set to be in the range of 20-40.
[0029]
Further, when the vehicle is traveling at low and medium speeds, the ECU 70 becomes a lean region or stoichiometric feedback region (stoichiometric air-fuel ratio feedback control region) according to the intake stroke injection mode in FIG. 2 according to the load state and the engine speed Ne. Selects the intake stroke injection mode and injects fuel so as to achieve a predetermined air-fuel ratio.
That is, in the lean region of the intake stroke injection mode, the valve opening amount and the fuel injection amount of the ABV valve 27 are controlled so that the air-fuel ratio becomes relatively lean (for example, about 20 to 23), and in the stoichiometric feedback region. The ABV valve 27 and the EGR valve 45 are controlled to open and close (however, the EGR valve 45 is controlled to open and close only in a specific region of the stoichiometric feedback region), and O₂ Air-fuel ratio feedback control is performed according to the output voltage of the sensor 40. Since the intake air flow that flows in from the intake port 13 forms a reverse tumble flow, the lean air-fuel ratio due to the effect of turbulence due to the reverse tumble is adjusted even in the lean region of the intake stroke injection mode by adjusting the fuel injection start timing or end timing. But it can be ignited. In the stoichiometric feedback region, a large output is obtained with a relatively high compression ratio, and harmful exhaust gas components are purified by the three-way catalyst 42.
[0030]
The ECU 70 selects the intake stroke injection mode and closes the ABV valve 27 at the time of sudden acceleration or high-speed driving, and closes the ABV valve 27, depending on the throttle opening θth, the engine rotational speed Ne, etc. Then, the fuel is injected so that the air-fuel ratio becomes relatively rich. In this case, since the intake port 13 is substantially upright with respect to the combustion chamber 5 in addition to the high compression ratio and the intake flow forming a reverse tumble flow, a high output can be obtained also by the inertia effect. .
[0031]
Further, during coasting operation during medium-high speed traveling, the fuel cut region in FIG. 2 is reached, so the ECU 70 stops fuel injection completely. Thereby, the fuel consumption is improved and the emission amount of harmful exhaust gas components is also reduced. Note that the fuel cut is immediately stopped when the engine rotational speed Ne is lower than the return rotational speed or when the driver depresses the accelerator pedal.
[0032]
Next, a description will be given of a control procedure related to the present invention, which prevents a decrease in the number of revolutions during idling when the load increases due to an operation other than auxiliary operations such as a change in environmental conditions or a transmission failure.
The flowchart shown in FIG. 3 is executed by the ECU 70 every time a crank angle signal is output from the crank angle sensor 17. The ECU 70 detects the engine speed Ne detected from the crank angle signal generation time interval from the crank angle sensor 17 in step S10 in FIG. 3, the throttle valve opening θth detected by the throttle sensor 29, and the one intake air detected by the airflow sensor 33. Read the intake air volume (volumetric air flow rate) Qa per stroke. Next, the ECU 70 calculates the optimum target average effective pressure Pe according to the throttle valve opening θth and the engine speed Ne by, for example, a four-point interpolation method from the target average effective pressure map stored in advance in the storage device. (Step S11). The target average effective pressure Pe is a target in-cylinder effective pressure (load value) that correlates with the engine output desired by the driver, and the ECU 70 determines the fuel supply amount (target empty) based on the target average effective pressure (target load) Pe. Fuel ratio) and ignition timing are set. Next, the ECU 70 calculates the volume efficiency Ev by dividing the intake air amount (volume flow rate) Qa by the volume of the combustion chamber 5 (step S12). This volumetric efficiency Ev is an index related to the amount of oxygen that is supplied to each combustion chamber 5 and can be involved in combustion per unit intake stroke (per cylinder), and is an indication of the valve opening time (Ting) of the fuel injection valve 4. Used for calculation.
[0033]
Next, the ECU 70 determines whether or not the engine is in an idle operation state (step S13). When the ECU 70 is not in an idle operation state, the ECU 70 sets the operation mode according to the target average effective pressure Pe and the engine speed Ne (step S17). . For example, during low and medium speed traveling, the intake stroke injection mode is selected so as to be in the lean region or stoichiometric feedback region (theoretical air / fuel ratio feedback control region) according to the intake stroke injection mode in FIG. The fuel is injected so that
[0034]
When the ECU 70 determines that it is in the idling operation state in step S13, the ECU 70 determines whether or not the transmission is in the D range (step S14). When the ECU 70 is not in the D range, the volume efficiency Ev is greater than a predetermined value Ev0. (Step S15), if not large, it is determined that the volumetric efficiency Ev is small, that is, it is determined that the idle adjustment valve 24 is not largely controlled in the opening direction due to an increase in external load. (Step S18), and when the volumetric efficiency Ev is larger than the predetermined value Ev0, the idle adjustment valve 24 is largely controlled in the opening direction for some reason, and it is difficult to increase the output by the super lean operation (or small effect). It shifts to stoichiometric operation (premixed combustion) which can determine that it is and can generate a big torque. (Step S19).
[0035]
The predetermined value Ev0 is set to about 70%. The reason is that the predetermined value Ev0 can be set to the maximum amount of air allowed for super lean operation (stratified combustion), that is, the volumetric efficiency is close to 100%, but the predetermined value Ev0 is set to be close to 100%. In some cases, there are the following problems.
In order to increase the output to cope with the increase in the external load, it is necessary to switch the operation mode. However, when the volumetric efficiency Ev is operating near 100%, the operation mode is switched if a larger external load is applied for some reason. In this case, there is a problem that the response to the drop in the rotational speed is delayed because of a delay. Further, from the viewpoint of idle fuel efficiency, when the volumetric efficiency Ev is near 100%, there is no change in fuel efficiency between stratified combustion and premixed combustion, and premixed combustion has advantages in terms of combustion stability. The value Ev0 is set to a low value to some extent. If the above point is not a concern, the predetermined value Ev0 may be set closer to 100%. In the present embodiment, the predetermined value Ev0 is a fixed value of about 70%, but it may be changed according to the number of rotations.
[0036]
When the ECU 70 determines that it is in the D range in step S14, it determines whether or not a load, for example, an air conditioner switch is turned on (step S16). When the air conditioner switch is turned off, the ECU 70 proceeds to step S15 and the air conditioner switch is turned on. Sometimes, in addition to the increase in load due to the D range, the load further increases. In the super lean operation, it is determined that it is difficult to increase the output with respect to the increase in the external load, and the routine proceeds to step S19, where the stoichiometric operation (premixed combustion) ).
[0037]
Since the engine 1 is not supercharged, the amount of air equivalent to the throttle fully open is not supplied. Therefore, the torque that can be generated during idling during super lean operation (stratified combustion) is limited. For this reason, if the air conditioner operates when the vehicle is stopped in the D range and the engine is in an idle state, even if the air amount at the time of full load (throttle fully open) is supplied, the torque is insufficient and the engine rotation There is a risk of engine stalling as the number drops. Since the air-fuel ratio is controlled at the same air-fuel ratio (A / F) during idling, the air amount is proportional to the load, and increasing the air amount (volumetric efficiency Ev) increases the load for some reason. That is. Therefore, when the volume efficiency Ev correlated with the air amount at this time exceeds the threshold value (Ev0), the ECU 70 determines that the super lean operation (stratified combustion) is impossible and can generate a larger torque. Switch to stoichio operation and keep idle. As a result, it is possible to reliably prevent a decrease in the rotational speed during idling even when the load increases due to other than the operation of auxiliary equipment such as a change in environmental conditions or a failure of the transmission.
[0038]
When the volumetric efficiency Ev is kept constant at the air-fuel ratio A / F, the torque information has a proportional relationship with the air amount. Therefore, there is a method of making the air-fuel ratio rich when the volumetric efficiency increases. Also, there is a limit to making the air-fuel ratio rich in the compression lean. For this reason, the excess air ratio approaches 1 in the early injection mode or stoichiometric operation (premixed combustion) on the safe side so that sufficient torque is generated.
[0039]
  In this way, since an increase in torque cannot be expected in super lean operation (stratified combustion), switching to stoichiometric operation (premixed combustion) allows the air-fuel ratio (A / F) to be higher than that in super lean operation. It can occur and the load condition (environmental change) continues for a long timeanyEven if the load increases due to such a malfunction, it is possible to perform idle operation.
[0040]
In the above embodiment, the stratified combustion is switched directly to the premixed combustion (stoichiometric operation) according to the change in the volumetric efficiency Ev. However, the stratified combustion is switched to the premixed lean combustion (first lean mode), and then It may be set to switch to premixed combustion (stoichio).
In the above embodiment, the intake air amount is detected by the air flow sensor, and the load state is determined based on the volumetric efficiency Ev calculated from the air amount, and the operation state is switched. However, the idle adjustment valve, ABV (air bypass valve) ), A load state may be determined according to an opening signal such as an electronic throttle, and the operation state may be switched.
[0041]
Furthermore, instead of the volumetric efficiency Ev, the intake pipe negative pressure may be detected to switch the operation state. In the case where the air-fuel ratio at the time of idling is controlled to be within a substantially constant range, the operation state is switched by detecting that the fuel amount as a parameter correlated with the air amount has reached the upper limit value. Anyway.
Further, in the present embodiment, the control combined with the switching of the operation state by the load signal of an air conditioner or the like as in the above-described known example has been described. However, in order to simplify the control, the operation state is performed only with the volumetric efficiency Ev0. May be switched.
[0042]
Furthermore, in the above-described embodiment, when the volumetric efficiency Ev exceeds the predetermined value Ev0, the stoichiometric operation is performed. However, the predetermined value Ev0 is set to be lower, and a change in the rotational speed after the predetermined value Ev0 is exceeded is detected. When the change in the number is large and it is predicted that it is difficult to increase the output due to the stratified combustion, it may be set to switch to the premixed combustion (stoichiometric operation, first lean mode).
[0043]
【The invention's effect】
As described above, according to the present invention, it is determined that the fuel efficiency is improved by performing the stratified combustion at the time of idling, the engine load is increased by operating the air conditioner or the like at the time of idling, and the increase of the torque is not expected in the stratified combustion. By switching to stoichiometric operation at this time, it is possible to increase the torque and prevent the engine speed from dropping during idling. In addition, it is possible to reliably prevent a decrease in the number of revolutions during idling even when the load increases due to other than the operation of auxiliary equipment such as a change in environmental conditions or a transmission failure.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a control device for a direct injection internal combustion engine according to the present invention.
FIG. 2 is a diagram showing a determination map for a fuel injection mode.
FIG. 3 is a flowchart showing an engine control procedure according to the present invention.
[Explanation of symbols]
1 engine
4 Fuel injection valve
5 Combustion chamber
17 Crank angle sensor
25 Intake pipe
26 Air bypass pipe
27 ABV valve
28 Throttle valve
29 Throttle sensor
31 Atmospheric pressure sensor
32 Intake air temperature sensor
70 ECU

Claims (4)

Fuel is injected directly into the combustion chamber, switching between premixed combustion and stratified combustion according to the operating state, stratified combustion is performed during idling, the fuel amount is increased against the increase in external load during idling, and engine output is increased. In a control apparatus for a direct injection internal combustion engine provided with an output control means for changing to an increase side, when the fuel amount or a parameter correlated with the fuel amount exceeds a predetermined value at the time of idling, switching to the premixed combustion is performed. The predetermined value is a value corresponding to an air-fuel ratio at which the stratified combustion is allowed with respect to a fully open air amount or an air amount in the vicinity thereof, and a control apparatus for a direct injection internal combustion engine.   Fuel is injected directly into the combustion chamber, switching between premixed combustion and stratified combustion according to the operating condition, and stratified combustion is performed during idling, and the amount of air is increased in response to an increase in external load during idling. In a control apparatus for a direct injection type internal combustion engine having an output control means for changing the engine output to the increase side by increasing the fuel in response to the increase in the amount of fuel, the parameter relating to the air amount or the air amount at the time of idling The control device for a direct injection internal combustion engine, wherein when the engine exceeds a predetermined value, the premixed combustion is switched to. The control apparatus for a direct injection internal combustion engine according to claim 2 , wherein the predetermined value is set to a value lower than a maximum air amount in which the stratified combustion is allowed. The control device for a direct injection internal combustion engine according to claim 3 , wherein the predetermined value is set to about 70% of the maximum air amount.

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