JP2002047973A - Fuel injection controller of direct injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection amount controller of a direct injection engine capable of preventing the occurrence of torque fluctuation and misfire even if a demand for reducing torque is given during stratified combustion in the direct injection engine. SOLUTION: Target torque is calculated based on demand torque and a torque reduction amount to call out a speed for engine rotation Ne at step 101. A combustion mode is selected based on the target torque value at step 102. The target torque value calculated at step 101 is converted into injection time at step 105 to judge whether this value is larger than TAUmin or not at step 106. If this value is larger than TAUmin according to the results of judgement, fuel injection is controlled by stratified combustion at step 100 and is switched over to homogeneous combustion at step 111 if the value is smaller than TAUmin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection control device for a direct injection engine.

[0002]

2. Description of the Related Art Conventionally, a technique is known in which fuel is directly injected into a combustion chamber of an internal combustion engine, and a stratified combustion is performed by forming a thin air-fuel mixture only in the vicinity of an ignition plug in a compression stroke. In such prior art, when a request for fuel cut is entered,
To reduce the fuel injection amount to zero from the normal operation state, a torque shock occurs. Further, even after returning from the fuel cut, a torque shock occurs by setting the fuel injection amount to the target torque.

[0003] In the technique disclosed in Japanese Patent Application Laid-Open No. 03-070836, in the case where control is performed by homogeneous combustion, when setting a restart supply amount of fuel after returning from a fuel cut, a decrease in an injection amount, an ignition retardation, and the like. The torque shock after returning from the fuel cut, which is the above problem, is suppressed by executing the above.

In the technique disclosed in Japanese Patent Application Laid-Open No. 09-021369, if the fuel injection amount set when performing torque suppression is small, the fuel injection time is shortened, so that the fuel injection amount is accurately controlled. Focusing on the problem that the required fuel injection amount cannot be obtained, the required fuel injection time is secured by increasing the injection time by lowering the fuel pressure when the required fuel injection amount is small.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 03-070
When the technique disclosed in Japanese Patent No. 836 is applied to an internal combustion engine controlled by stratified combustion, the fuel injection amount is originally small due to stratification. Therefore, when the fuel injection amount is reduced after returning from the fuel cut, the injection time for ensuring the injector performance is secured. It is below the lower guard value. When the injection time becomes equal to or less than the lower limit guard value, the fuel injection time is set to the lower limit guard value in order to secure injector performance. In particular, since the torque during stratified combustion depends on the fuel injection amount, if the fuel injection time is set to the lower limit guard value, the required torque may not be satisfied and a torque shock may be generated.

In the technique disclosed in Japanese Patent Application Laid-Open No. 09-021369, the fuel pressure is lowered to perform the fuel injection in order to secure the fuel injection time. Since the characteristics are deteriorated, there is a possibility that a misfire or an engine stall may occur. Further time is required to further lower the fuel pressure, which is practically impossible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fuel injection amount control device for a direct injection engine that can prevent torque fluctuations and misfires even when there is a demand for torque reduction during stratified charge combustion.

[0008]

According to the first aspect of the present invention,
During stratified charge combustion, when the required torque value set by the required torque setting means falls below the lower limit, the combustion mode is switched from stratified charge combustion to homogeneous charge combustion.

Thus, when the required torque value is smaller than the lower limit guard value, control can be performed by homogeneous combustion. In stratified combustion, the control is performed with a small amount of fuel injection, so the fuel injection amount may be lower than the lower limit guard value.However, in homogeneous combustion, the injected fuel amount is larger than in stratified combustion, so fuel The required torque can be realized without the injection amount falling below the lower limit. Further, in the homogeneous combustion, the required torque is determined by the engine load such as the intake air amount without depending on the fuel injection amount. Therefore, the control can be performed with high accuracy for the above two reasons.

According to the second aspect of the invention, at the time of stratified combustion,
When there is a request for torque suppression, such as before the execution of a fuel cut or immediately after a return, the torque is suppressed by the torque suppression means. At this time, when the torque value finally set by the suppression of the torque is smaller than the lower limit, the combustion mode is switched from stratified combustion to homogeneous combustion.

Thus, when the value is smaller than the lower limit guard value, the control can be performed by homogeneous combustion. Stratified combustion is controlled in each operating state with a smaller amount of fuel injection than in homogeneous combustion, so if torque is controlled by the amount of fuel injection, it sufficiently responds to the demand for torque suppression. Can not. Therefore, the mode is switched to homogeneous combustion. In the homogeneous combustion, the torque is determined not by the fuel injection amount but by the engine load such as the intake air amount, so that accurate control can be performed without the fuel injection amount falling on the lower limit.

According to the third aspect of the invention, at the time of stratified combustion,
When the fuel injection time that satisfies the required torque is smaller than the lower limit by the required injection time setting means, the combustion mode is switched from stratified combustion to homogeneous combustion.

Accordingly, when the value is smaller than the lower limit, the control can be performed by homogeneous combustion. In stratified combustion, control is performed with a small amount of fuel injection, so the fuel injection time may be smaller than the lower limit that can ensure the performance of the fuel injection valve. In the normal operation state, the fuel injection time does not fall below the lower limit. Further, in the homogeneous combustion, since the torque is determined not by the fuel injection amount but by the engine load such as the intake air amount, the target torque can be realized, and the control can be performed with high accuracy.

According to the invention of claim 4, at the time of stratified combustion,
When a torque suppression request is received, such as before the execution of a fuel cut or immediately after a return, etc., the first fuel injection time is shortened to satisfy the target torque, and the second fuel injection time is set according to the torque suppression. . If the second fuel injection time is smaller than the lower limit, the combustion mode is switched from stratified combustion to homogeneous combustion.

Accordingly, even if the second fuel injection time is shorter than the lower limit for ensuring the injector performance, the control can be switched to the homogeneous combustion in response to the request for torque suppression. In stratified combustion, control is performed with a small amount of fuel injection, so the fuel injection time may be smaller than the lower limit that can ensure the performance of the fuel injection valve. More than
In the stratified combustion, since the torque is determined not by the fuel injection amount but by the engine load such as the intake air amount, the final torque according to the request for torque suppression can be realized, so that the torque shock can be suppressed.

According to a fifth aspect of the present invention, in the fuel injection control apparatus for a direct injection engine according to any one of the first to fourth aspects, the ignition is performed during switching from stratified combustion to homogeneous combustion. The ignition timing controlled by the timing control means and the fuel injection timing controlled by the injection timing control means are retarded.

Normally, when switching from stratified combustion to homogeneous combustion, the opening of the throttle valve is adjusted. At the time of stratified charge combustion, the throttle valve opening is set to a large value and the amount of fuel is controlled to control the throttle valve. However, when the throttle is closed, there is a delay in transporting the intake air, so that the air amount does not immediately correspond to the throttle opening and a delay occurs. Here, in order to switch to homogeneous combustion, a large fuel injection amount is required. For this reason, the torque may increase, and drivability may be deteriorated. Therefore, by controlling as in the present invention, it is possible to set a delay when switching from stratified combustion to homogeneous combustion, and to switch the ignition and retard the injection timing during stratified combustion during the delay. Torque fluctuation at the time can be suppressed.

[0018]

<First Embodiment> A first embodiment of the present invention will be described.

First, a schematic configuration of the entire engine control system will be described with reference to FIG. In-cylinder injection engine 1
An air cleaner 13 is provided at the most upstream portion of one intake pipe 12, and a throttle valve 15 whose opening is adjusted by a DC motor 14 (throttle control means) is provided downstream of the air cleaner 13. DC motor 14 is an engine electronic control circuit (hereinafter referred to as “ECU”) 1
By driving based on the output signal from 6, the opening degree of the throttle valve 15 (throttle opening degree) is controlled, and the amount of intake air to each cylinder is adjusted according to the throttle opening degree. A throttle sensor 17 for detecting a throttle opening is provided near the throttle valve 15.

A surge tank 19 is provided downstream of the throttle valve 15. An intake manifold 20 for introducing air into each cylinder of the engine 11 is connected to the surge tank 19. Intake manifold 20 for each cylinder
Inside, a first intake path 21 and a second intake path 22 are respectively connected to two ports 23 formed in each cylinder of the engine 11.

A swirl control valve 24 is disposed in the second intake passage 22 of each cylinder. The swirl control valve 24 of each cylinder is connected to a step motor 26 via a common shaft 25. When the step motor 26 is driven based on an output signal from the ECU 16, the opening of the swirl control valve 24 is controlled, and the swirl flow intensity in each cylinder is adjusted by multiplying the opening. In the direct injection engine, the swirl control valve 24 is controlled on the open side during homogeneous combustion to secure an intake air amount, and during stratified combustion, the swirl control valve 24 is closed to inject fuel near the spark plug and swirl. It is controlled to create a flow. A swirl control valve sensor 27 that detects the degree of opening of the swirl control valve 24 is attached to the step motor 26.

A fuel injection valve 28 for directly injecting fuel into the cylinder is mounted on an upper part of each cylinder of the engine 11. Fuel sent from the fuel tank 43 to the fuel delivery pipe 30 through the fuel pipe 29 is directly injected into the cylinder from the fuel injection valve 28 of each cylinder, and the fuel is supplied to the intake port 23.
A mixture is formed by mixing with intake air introduced from the air.

Further, an ignition plug (not shown) is attached to the cylinder head of the engine 11 for each cylinder, and the mixture in the cylinder is ignited by the spark discharge of each ignition plug. The cylinder discrimination sensor 32 generates an output pulse when a specific cylinder (for example, the first cylinder) reaches the intake top dead center.
An output pulse is generated each time one crank angle rotates a fixed angle (for example, 30 ° C. A). From these output pulses, the crank angle and the engine rotation speed Ne are detected, and cylinder discrimination is performed.

On the other hand, the exhaust gas discharged from each exhaust port 35 of the engine 11 joins one exhaust pipe 37 via an exhaust manifold 36. In the exhaust pipe 37, a three-way catalyst 38 for purifying exhaust gas near the theoretical air-fuel ratio and a NOx storage type lean NOx catalyst 39 are arranged in series. The lean NOx catalyst 39 stores NOx in the exhaust during lean operation in which the oxygen concentration in the exhaust is high, and when the air-fuel ratio is switched to rich and the oxygen concentration in the exhaust decreases,
The stored NOx is reduced and purified and released.

An EGR pipe 40 for recirculating a part of the exhaust gas to the intake system is connected between the upstream side of the three-way catalyst 38 of the exhaust pipe 37 and the surge tank 19.
An EGR valve 41 is provided in the middle of the R pipe 40.
The opening of the EGR valve 41 is controlled based on an output signal from the ECU 16, and the EGR amount is adjusted according to the opening. Further, the accelerator pedal 18 is provided with an accelerator sensor 42 for detecting an accelerator opening.

Further, a purge pipe 45 for purging (discharging) the adsorbed fuel evaporative gas to the intake system is connected between the canister 44 for adsorbing the evaporative gas in the fuel tank 43 and the intake pipe 12. In the middle of the purge pipe 45, a purge valve 46 for adjusting the amount of fuel evaporative gas (purge amount) purged to the intake system according to the opening degree is provided.

The output signals of the various sensors described above are supplied to the ECU
16 is input. The ECU 16 is mainly composed of a microcomputer, and according to a control program stored in a built-in ROM (storage medium), based on various sensor outputs, the DC motor 14, the step motor 26, the fuel injection valve 28, the ignition Plug, EGR valve 41,
The operation of the purge valve 46 is controlled.

During the operation of the engine 11, the ECU 16 switches the combustion mode between stratified combustion and homogeneous combustion in response to a request for switching the combustion mode. In the stratified combustion, a small amount of fuel is injected in the compression stroke and the ignition plug is switched on. A lean air-fuel mixture is burned by forming a rich air-fuel mixture partially in the periphery as compared with other parts. Further, in the homogeneous combustion, the fuel injection amount is increased so as to be near or slightly richer than the stoichiometric air-fuel ratio, and the fuel is injected in the intake stroke to burn the homogeneous mixture.

Next, control blocks performed by the ECU 16 will be described with reference to FIG. First, the required torque is set by the required torque setting unit 50 from two parameters, the accelerator opening and the engine rotation speed Ne. The method of setting the required torque may be a two-dimensional map of the accelerator opening and the engine speed Ne, or may be set by calculation. In the torque-down amount calculating section 51, a required torque-down amount according to the driving state is set based on the F / C pre / post-processing request section 52, the traction down request section 53, the shift request section 54, and the like. Then, the required torque setting unit 50
The target torque value is set from the respective torque values set by the torque mode setting unit and the combustion mode setting unit 5.
5 is input.

Next, in the combustion mode setting section 55, one of the stratified combustion and the homogeneous combustion is set based on the set target torque. As a setting method, for example, a method in which stratified combustion and homogeneous combustion are set by a map based on the engine rotation speed Ne and the target torque as shown in FIG. 2 may be used. Further, the fuel injection amount or the fuel injection time may be used instead of the torque. Thus, when the combustion mode is set and, for example, stratified charge combustion is selected, the injection amount setting unit 56 converts the set target torque value into a fuel injection amount. The injection time setting unit 56 converts the fuel injection amount set by the fuel injection amount setting unit 56 into a fuel injection time based on the fuel pressure. Further, the injection time is compared with TAUmin, and it is determined whether the injection time is greater than TAUmin.
As shown in FIG. 3, TAUmin is the minimum value of the fuel injection time during which the fuel injection valve 28 can perform stable fuel injection.

The fuel injection time TAU by the fuel injection valve 28
Is smaller than TAUmin, the combustion mode is switched again by the combustion mode setting unit 55, and the fuel injection amount for homogeneous combustion is calculated by the injection amount setting unit 56. Then, in each parameter setting section 58, the injection timing, throttle opening, EG
Control parameters such as the R valve 41 and the variable valve timing mechanism are set, and the output stage 59 outputs each parameter.

The fuel injection control shown in the control block will be described in detail with reference to the flowchart of FIG. In the flowchart of FIG. 5, first, at step 101, the engine rotation speed Ne and the required torque are called, and the routine proceeds to step 102. In step 101, FIG.
The required torque and the amount of torque reduction may be called out as in the control block (1), and the target torque value finally set may be called out from these two torque values.

In step 102, the combustion mode is set by the map shown in FIG. 2 based on the called engine speed Ne and the target torque. The combustion mode is set to a homogeneous combustion at a high load, and to a stratified combustion at a low load.

In step 103, the combustion mode set as described above is determined. Here, if it is determined that stratified charge combustion has occurred, the routine proceeds to step 104. on the other hand,
If it is determined that the combustion is homogeneous, the process proceeds to step 110.

In step 104, the fuel injection amount is calculated. The setting of the fuel injection amount may be set by a map obtained from the engine speed Ne and the target torque shown in FIG. 6, or may be obtained by calculation. When the fuel injection amount is set in this way, the routine proceeds to step 105, where the fuel injection time TAU is calculated. When calculating the fuel injection time TAU, the fuel injection amount depends on the fuel pressure, so that the correction based on the fuel pressure is performed.
As shown in FIG. 7, the fuel pressure correction coefficient is set such that the higher the fuel pressure, the shorter the fuel injection time TAU, and the lower the fuel pressure, the longer the fuel injection time TAU. The fuel injection amount TAU (= (Qstrt × injector characteristics + ineffective injection time) × fuel pressure correction coefficient) is calculated in consideration of such fuel pressure correction, injector characteristics and invalid injection time.

In step 106, it is determined whether the fuel injection time TAU calculated as described above is longer than TAUmin. Fuel injection time TAU is TAUm
If it is larger than "in", the process proceeds to step 107 to execute the control by stratified combustion. In step 107, since there is no need to switch the combustion mode, the request for switching TAUmin is turned off. In step 108, control in the stratification mode is performed, and the routine ends.

On the other hand, at step 106, the fuel injection amount TA
If U is smaller than TAUmin, the fuel injection amount TA
If U is guarded by TAUmin, the target torque will be lost and the drivability will deteriorate. Therefore, in order to set the TAUmin for homogeneous combustion in step 109 to switch to homogeneous combustion, the TA for homogeneous combustion is set.
A request to switch to Umin is turned on, and the routine proceeds to step 110.

In step 110, the homogeneous mode is selected to perform control in the conventionally known homogeneous mode. Then, in step 111, the fuel injection amount for homogeneous combustion is calculated, and this routine ends. The calculation of the fuel injection amount for homogeneous combustion is based on the intake air amount and the engine speed N.
It is calculated based on the operating state such as e. The combustion mode requires a larger amount of fuel injection to fill the cylinder of the internal combustion engine with a uniform air-fuel mixture than the stratified combustion, so that the required torque must be satisfied without affecting TAUmin. Can be. The method of calculating the fuel injection amount for homogeneous combustion is
For example, it may be performed by a conventionally known technique.

Next, an ignition retard amount SArt for torque suppression control performed in response to a TAUmin switching request.
d, a method of setting the injection retard amount AIrtd will be described with reference to the flowchart of FIG. This routine is driven by a routine different from the main routine of FIG.

First, at step 121, it is determined whether or not the TAUmin switching request is ON. Where TA
If the Umin switching request is ON, step 12
Proceed to 2. In step 122, it is determined whether or not the switching from stratified combustion to homogeneous combustion has been completed. The determination is made at the time of switching from stratified combustion to homogeneous combustion. If it is determined that the switching has not been completed, the routine proceeds to step 123, where the ignition retard amount SArtd is calculated. As a calculation method, for example, as shown in FIG. 9, the calculation may be performed based on a map in which the ignition retard amount SArtd is set to be large in accordance with an increase in TAU, or may be calculated by calculation. When the ignition retard amount SArtd is calculated in this manner, the injection retard amount A
Irtd is calculated. At this time, the injection timing is changed from the compression stroke to the intake stroke. As a method of calculating the injection retard amount, for example, as shown in FIG.
The calculation may be performed based on a map in which the injection retard amount AIrtd is set to be large as the d increases, or may be calculated by calculation.

Next, the routine for calculating the ignition timing will be described with reference to the flowchart shown in FIG. In this routine, the ignition timing is set in consideration of the ignition retard amount SArtd set in the flowchart of FIG. 8 with respect to the basic ignition timing.

First, at step 131, the engine speed Ne and the target torque are read, and the routine proceeds to step 132. In step 132, it is determined whether the current combustion mode is stratified combustion. Here, if it is determined that stratified charge combustion has occurred, the routine proceeds to step 133. In step 133, the basic ignition timing SAbase is determined by the map for stratified combustion set from the engine speed Ne and the required torque read in step 131. When the basic ignition timing SAbase is set in this way, the routine proceeds to step 134. At the time of stratified combustion, control is performed by the throttle opening and the fuel injection amount, so that 0 is input to various correction coefficients for the ignition timing, and the routine proceeds to step 137.

On the other hand, if it is determined in step 132 that the combustion mode is homogeneous combustion, the routine proceeds to step 135, where the engine speed N
The basic ignition timing SAbase is set by a map for homogeneous combustion determined by e and the required torque. Then, in step 136, various correction amounts are set according to the deviation between the target air-fuel ratio and the actual air-fuel ratio and other various operating conditions, and the routine proceeds to step 137.

In step 137, the ignition timing SA (= SAbase +
Various correction amounts + SArtd) are set. When setting,
In switching from stratified combustion to homogeneous combustion when there is a TAUmin switching request, the ignition retard amount SArtd set in step 123 in the flowchart of FIG. 8 is reflected, and this routine ends.

Next, an injection timing calculation routine is similarly set using the flowchart shown in FIG. In this routine, the injection timing is set in consideration of the injection timing retard amount AIrtd set in the flowchart of FIG. 8 with respect to the basic injection timing.

First, at step 141, the engine speed Ne and the target torque are read, and the routine proceeds to step 132. In step 132, it is determined whether or not the current combustion mode is stratified combustion. Here, if it is determined that the combustion mode is stratified combustion, the routine proceeds to step 143. In step 143, the basic injection timing AIbase is determined by a map for stratified combustion set from the engine speed Ne and the required torque read in step 141. When the basic injection timing AIbase is set in this way, the process proceeds to step 144. At the time of stratified combustion, control is performed based on the throttle opening and the fuel injection amount, so 0 is input to various correction coefficients for the injection timing, and the routine proceeds to step 147.

On the other hand, if it is determined in step 142 that the combustion mode is homogeneous combustion, the routine proceeds to step 145, where the engine rotation speed N
The basic injection timing AIbase is set by a map for homogeneous combustion determined by e and the required torque. Then, in step 146, various correction amounts are set according to the deviation between the target air-fuel ratio and the actual air-fuel ratio and other various operating conditions, and the routine proceeds to step 137.

In step 137, the ignition timing AI (= AIbase +
Various correction amounts + AIrtd) are set. When setting,
In switching from stratified combustion to homogeneous combustion when there is a TAUmin switching request, the injection delay amount AIrtd set in step 124 in the flowchart of FIG. 8 is reflected, and this routine ends.

The time chart controlled in this manner will be described with reference to FIG. 14 in comparison with the prior art shown in FIG. Here, an example is shown in which the combustion mode is controlled by stratified combustion as shown in FIG. 13 (e), and a request for fuel cut-off is entered according to the accelerator opening. The fuel cut is required when the accelerator is fully closed, the idle switch is on, and the rotation speed is equal to or lower than a predetermined rotation speed.

FIG. 13 (a) shows the accelerator opening, and the engine speed N depends on the accelerator opening.
When e becomes equal to or lower than the predetermined rotation speed as shown in FIG. 13B, an F / C flag indicating a fuel cut request is set as shown in FIG. 13D. When the F / C flag is turned on, the fuel is cut off by setting the fuel injection time TAU to 0 as shown in FIG. Then, the F / C shown in FIG.
The flag is turned off. At this time, the fuel injection amount TAU is set low in order to suppress the torque shock according to the torque suppression request. As a result, the fuel injection time TAU becomes T
It will fall below AUmin, and stable combustion will not be obtained and misfire will occur.

In this embodiment, the engine is prevented from misfiring by switching the combustion mode from stratified combustion to homogeneous combustion when the fuel injection time TAU is shorter than TAUmin. This will be described with reference to the time chart shown in FIG. (A description of a portion overlapping with FIG. 13 is omitted).

When the F / C flag is turned off as shown in FIG. 14D, first, the fuel injection time TAU is set. At this time, if the fuel injection time TAU is smaller than TAUmin, the combustion mode is switched from stratified combustion to homogeneous combustion as shown in FIG. In the homogeneous combustion as compared with the stratified combustion, the fuel is injected more, so that it does not fall below TAUmin. Thereafter, when the fuel injection amount TAU during control in stratified combustion exceeds TAUmin, the combustion mode is switched to homogeneous combustion. By performing such control, the engine rotation speed Ne is increased as shown in FIG.
Can be controlled without causing torque fluctuation.

Next, the control shown in the flowcharts of FIGS. 8, 11 and 12 will be described with reference to the time chart of FIG. As shown in FIG. 15A, when the request for switching the combustion mode is switched from stratified combustion to homogeneous combustion, the throttle opening is changed according to the switching.
It is controlled to the closing side as shown in FIG. This is because in stratified charge combustion, the throttle valve 15 is set near full open and is controlled by the fuel injection amount. Therefore, when switching to homogeneous combustion, the throttle valve 15 needs to be controlled to the closed side. However, since the intake air amount has a transport delay as compared with the throttle opening, the actual intake amount is delayed. If the combustion mode is switched in this state, a torque shock occurs because fuel injection is performed for an intake air amount larger than necessary. Therefore, as shown in FIG. 15 (c), a delay is provided in the actual switching timing, and the ignition delay and the injection delay in the stratified combustion are performed during the period when the switching to the homogeneous combustion is actually performed after the request to switch to the homogeneous combustion is input. By performing cornering, torque fluctuation is suppressed.

In this embodiment, the required torque value set by the required torque setting unit 50 and the torque reduction amount calculated by the torque reduction amount calculation unit 51 are shown in the control block of FIG. And target torque setting unit 5
5, the target torque value is finally set, and when the target torque value becomes smaller than TAUmin, the combustion mode is switched. However, the required torque value set by the required torque setting unit 50 is directly guarded. It may be configured as follows.

In the present embodiment, the required torque setting means and the target torque setting means correspond to step 101 in the flowchart of FIG. 5, the switching means corresponds to step 202 in the flowchart of FIG. The required injection time setting means and the required injection time suppressing means correspond to and function in steps 101 and 105 in FIG. 5, respectively.

<Second Embodiment> In the present embodiment, control for switching from stratified combustion to homogeneous combustion is performed depending on whether or not the torque value is equal to or lower than the lower limit as compared with the flow chart of FIG. 5 in the first embodiment. We are implementing. The same steps as those in the flowchart of FIG. 5 are denoted by the same reference numerals, and will be described with reference to FIG. (The description of the same steps is omitted).

At step 101, the engine speed Ne
And torque are called. In step 102, a combustion mode is selected. Then, in step 103, the selected combustion mode is determined. If it is determined that the selected combustion mode is homogeneous combustion, the process proceeds to step 110. If it is determined in step 103 that the combustion mode is stratified combustion, it is determined in step 200 whether the torque called in step 101 is smaller than a lower limit value. The lower limit value may have a torque value that can secure the fuel injection performance of the injector during stratified combustion as a map or may be calculated by calculation.

The torque value called in step 101 is compared with the lower limit value. If the torque value is smaller than the lower limit value, the control is switched from the stratified combustion control to the homogeneous combustion control. Then, the process proceeds to step 110. The processing after step 110 is the same as that of the first embodiment shown in FIG.
This is the same as the flowchart of FIG. On the other hand, when the torque value is larger than the lower limit value, the process proceeds to step 104. In step 104, the fuel injection amount is calculated based on the torque value called in step 101 to perform the control in stratified combustion, and the routine proceeds to step 105. In step 105, the fuel injection time is calculated based on the fuel injection amount calculated in step 104.
Proceed to 8. In step 108, the conditions necessary for the control in the stratified combustion are set, and the routine ends.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of the present embodiment.

FIG. 2 is a diagram for selecting a combustion mode based on an engine rotation speed Ne and a target torque.

FIG. 3 is a basic characteristic diagram of a fuel injection valve.

FIG. 4 is a control block diagram of the present embodiment.

FIG. 5 is a flowchart illustrating control of the present embodiment and the first embodiment.

FIG. 6 is a map diagram for setting a basic fuel injection amount based on an engine speed and a target torque in the embodiment.

FIG. 7 is a diagram showing a fuel pressure correction map for setting a correction amount for a fuel pressure applied to a fuel injection valve.

FIG. 8 is a flowchart for calculating an ignition retard amount and an injection retard amount according to the present embodiment.

FIG. 9 is a diagram for obtaining an ignition retard amount from a target injection time in the present embodiment.

FIG. 10 is a diagram for obtaining an injection retard amount from an ignition retard amount in the present embodiment.

FIG. 11 is a flowchart for calculating an ignition timing according to the present embodiment and the first embodiment.

FIG. 12 is a flowchart for calculating an injection timing in the present embodiment and the first embodiment.

FIG. 13 is a time chart according to the related art.

FIG. 14 is a time chart of the present embodiment and the first embodiment.

FIG. 15 is a time chart showing a transport delay of the intake air amount.

FIG. 16 is a flowchart illustrating switching control according to the present embodiment and the second embodiment.

[Explanation of symbols]

11: in-cylinder injection engine, 12: intake pipe, 14: DC
Motor, 15: throttle valve, 16: ECU, 17: throttle sensor, 18: accelerator pedal, 19: surge tank, 24: swirl control valve, 26: step motor, 27: swirl control valve sensor, 28: fuel injection valve,
37 ... exhaust pipe.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301J F02P 5/15 F02P 5/15 B F-term (Reference) 3G022 AA03 AA07 AA10 CA06 CA09 DA02 EA03 FA06 FB08 GA01 GA02 GA05 GA08 GA20 3G084 AA03 AA04 BA02 BA13 BA15 BA17 BA20 BA27 CA03 DA11 EB09 EB12 FA10 FA32 FA33 FA38 FA39 3G301 HA01 HA04 HA06 HA13 HA14 HA16 JA04 KA08 KA24 LA05 LC04 NE05 LC05 LC04 NE19 PA11Z PA17Z PB03Z PB05Z PB08Z PE01Z PE03Z PE05Z PE06Z PF03Z

Claims (5)

[Claims] 1. A fuel injection control device for a direct injection engine capable of directly injecting fuel into a cylinder and switching between stratified combustion and homogeneous combustion, a required torque setting means for setting a required torque, Switching means for switching from stratified combustion to homogeneous combustion when it is determined that the required torque value set by the required torque setting means is equal to or less than the lower limit value. . 2. A fuel injection amount control device for a direct injection engine capable of directly injecting fuel into a cylinder and switching between stratified combustion and homogeneous combustion, comprising: a required torque setting means for setting a required torque; Torque suppression means for suppressing torque generated by the engine in accordance with the target torque; target torque setting means for setting a target torque based on the request torque and a torque suppression request by the torque suppression means; A switching device for switching from stratified combustion to homogeneous combustion when it is determined that the target torque value set by the setting device is equal to or less than the lower limit value, the fuel injection control device for a direct injection engine. 3. A fuel injection control apparatus for a direct injection engine capable of directly injecting fuel into a cylinder and switching between stratified combustion and homogeneous combustion, wherein a first fuel injection time is set based on a required torque. Injection time setting means, when the fuel injection time is shorter than a predetermined lower limit injection time,
Lower limit guard means for guarding the fuel injection time with the lower limit injection time; and, during stratified charge combustion, when the fuel injection time set by the required injection time setting means becomes equal to or less than the lower limit injection time, the stratified charge is homogeneously switched to the lower limit injection time. A fuel injection control device for a direct injection engine, comprising: switching means for switching to combustion. 4. A fuel injection control device for a direct injection engine capable of directly injecting fuel into a cylinder and switching between stratified combustion and homogeneous combustion, wherein a first fuel injection time is set based on a required torque. A first injection time setting means for shortening the first fuel injection time set by the first injection time setting means for suppressing the generated torque when there is a torque suppression request during stratified combustion; Injection time reducing means for setting a fuel injection time; and switching means for switching from stratified combustion to homogeneous combustion when the second fuel injection time is equal to or less than a lower limit injection time during stratified combustion. Fuel injection control device for direct injection engine. 5. An ignition timing control means for controlling an ignition timing, and an injection timing control means for controlling a fuel injection timing, wherein the switching means controls the ignition timing during switching from stratified combustion to homogeneous combustion. The direct injection engine according to any one of claims 1 to 4, wherein the ignition timing controlled by the means and the fuel injection timing controlled by the injection timing control means are retarded. Fuel injection control device.