JP2001090592A - Fuel injection control device for in-cylinder injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improving the precision of fuel injection control by preventing the dispersion of a fuel injection amount in separate injection of fuel. SOLUTION: In an in-cylinder injection engine which has an injector 18 for injecting fuel directly into a combustion chamber and a fuel injection control means 83 for controlling a required amount of fuel to be injected separate times in a preset operation range by the injector 18, a time interval from ending fuel injection at the first stage to starting fuel injection at the second stage is set to be a reference time or longer, required for preventing the dispersion of fuel injection to injection pulses, in separate injection of fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a direct injection engine having an injector for directly injecting fuel into a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, in a direct injection engine in which fuel is directly injected into a combustion chamber, an injector is required to inject a required amount of fuel in a plurality of injections in order to improve the combustibility in a specific operating state. Various devices are known. For example, in an apparatus disclosed in Japanese Patent Application Laid-Open No. 8-189405, a split injection region is set in a transition period from a stratified combustion region to a uniform combustion region in a direct injection engine, and in this region, the pre-injection and compression of an intake stroke are performed. The fuel is injected separately from the latter injection of the stroke.

[0003] In the above-described in-cylinder injection engine, a target fuel injection amount is calculated by adding various correction values to a basic fuel injection amount obtained from a preset map or the like according to the operating state. By outputting an electric signal having a pulse width corresponding to the target fuel injection amount to the solenoid coil of the injector, fuel injection control is performed such that the injector is opened and fuel is injected for a time corresponding to the pulse width. It has become. And
At the time of split injection of fuel, by dividing an injection pulse having a pulse width converted based on the target fuel injection amount into a plurality of parts and reading out an optimum injection timing corresponding to an operation state from a preset map or the like. Is configured to be performed.

[0004]

When the fuel is divided into a plurality of injections at the injection timing set according to the operating state of the engine as described above, the fuel injection at the end of the preceding stage is terminated. From the end of the first-stage injection to the start of the second-stage injection, the time interval from the end of the first-stage injection to the start of the second-stage injection is reduced. There is a problem that the injection amount tends to vary.

That is, in the above-described in-cylinder injection engine,
Due to the high injection pressure of the fuel, when the fuel injection is performed at a high pressure, the needle valve of the injector is closed and the fuel injection is stopped, the fuel is injected into the fuel supply pipe from the delivery pipe to the injector. Fuel pulsation occurs due to the sudden change in pressure. Therefore, if the fuel injection in the subsequent stage is started before the fuel pulsation is not sufficiently contained after the fuel injection in the preceding stage is completed, the injection amount of the fuel injected in the subsequent stage is affected by the fuel pulsation, and this causes a variation. There was a problem that could not be avoided.

[0006] When the fuel is divided and injected into the former stage and the latter stage as described above, the valve body of the injector, that is, the needle valve, is deprived of heat by the first injected fuel and undergoes thermal contraction. Accordingly, the fuel injection amount tends to increase during the second fuel injection, and the accuracy of the fuel injection control is likely to decrease due to the change in the fuel density due to the influence of heat.

[0007] The present invention has been made in view of such circumstances, and it is possible to prevent variations in the amount of fuel injection during divided fuel injection, thereby improving the accuracy of fuel injection control. It is an object of the present invention to provide a fuel control device for an injection engine.

[0008]

The invention according to claim 1 is
An in-cylinder injection engine including an injector that directly injects fuel into the combustion chamber and a fuel injection control unit that controls a required amount of fuel to be injected in a plurality of times from the injector in a predetermined operation region. At the time of split injection of the fuel, the time interval from the end of the previous stage fuel injection to the start of the subsequent stage fuel injection is set to be equal to or longer than the reference time required to prevent variation in fuel injection with respect to the injection pulse. is there.

According to the above configuration, when the fuel is injected a plurality of times in the predetermined operation range, the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is set to a certain value or more. Will be. As a result, at the time of split injection of the fuel, it is possible to prevent variations in the fuel injection at the subsequent stage with respect to the injection pulse, thereby improving the accuracy of the fuel injection control.

According to a second aspect of the present invention, in the fuel injection control apparatus for a direct injection type engine according to the first aspect, the reference time is set at a fuel pulsation generated in a fuel supply pipe due to a needle valve lift of an injector. Is set in accordance with the time in which is settled.

According to the above configuration, when the fuel is divided and injected in a plurality of times in the predetermined operation region, the fuel pulsation caused by the needle valve lift is settled after the end of the fuel injection in the preceding stage, and the fuel in the subsequent stage is stopped. Injection will be started. As a result, it is possible to prevent variations in the fuel injection at the subsequent stage with respect to the injection pulse, thereby improving the accuracy of the fuel injection control.

According to a third aspect of the present invention, in the fuel injection control device for a direct injection type engine according to the first or second aspect, a divided injection region for performing divided injection of fuel in an intake stroke in a high engine speed region. And the time interval between the end of the preceding fuel injection and the start of the subsequent fuel injection in the divided injection region is set to be equal to or longer than the reference time.

[0013] According to the above configuration, in performing the split injection of fuel in the intake stroke in the high engine speed range, the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is not less than a certain value. By being set, the time interval at the time of the divided injection is prevented from becoming extremely short due to the high engine speed, and the variation in fuel injection with respect to the injection pulse is effectively prevented from becoming large. You.

[0014] The invention according to claim 4 is the above-mentioned claims 1-3.
In the fuel injection control device for a direct injection type engine according to any one of the above, the split injection region of the fuel is an operation region where the air-fuel ratio is substantially the stoichiometric air-fuel ratio, and the air-fuel ratio sensor provided in the exhaust passage detects This is set in a feedback control region for executing feedback control of the fuel injection amount based on the value.

According to the above configuration, in the feedback control for executing the feedback control of the fuel injection amount based on the detection value of the air-fuel ratio sensor provided in the exhaust passage in the operation region where the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio, The fuel is injected a plurality of times, and the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is set to a certain value or more. In this way, it is possible to prevent a variation in fuel injection with respect to the injection pulse from occurring at the time of the subsequent fuel injection, and to appropriately execute the feedback control for matching the total fuel injection amount to the target fuel injection amount.

According to a fifth aspect of the present invention, there is provided an injector for directly injecting fuel into a combustion chamber, and fuel injection such that an air-fuel ratio becomes substantially a stoichiometric air-fuel ratio based on a detection value of an air-fuel ratio sensor provided in an exhaust passage. In a direct-injection engine having feedback control means for feedback-controlling the amount, in the specific operation in which the feedback control is performed,
Fuel injection control means for controlling the injector to inject fuel in a plurality of injections, and injection characteristic learning for learning the correspondence between the injection pulse width corresponding to one injection of the divided injection fuel and the fuel injection amount. Means for performing the learning control, the time interval from the end of the fuel injection at the preceding stage to the start of the fuel injection at the subsequent stage is set to a reference time required to prevent the variation of the fuel injection with respect to the injection pulse. This is the setting made above.

According to the above configuration, when the feedback control is executed so that the air-fuel ratio becomes substantially equal to the stoichiometric air-fuel ratio, learning for correcting variations in the injection characteristics of the injector is performed. Since the thermal efficiency is lower than during the lean operation by the stratified combustion, the fuel injection amount becomes larger than that during the lean operation.However, the fuel injection is performed in the intake stroke in a divided manner, so that the divided one time operation is performed. The injection amount corresponding to the injection pulse becomes a small injection region. When the learning control is performed, the time interval from the end of the previous stage fuel injection to the start of the subsequent stage fuel injection is set to a certain value or more. Therefore, the learning of the injection characteristics in the minute injection region of the fuel is accurately performed.

According to a sixth aspect of the present invention, in the fuel injection control device for a direct injection type engine according to the fifth aspect, the learning by the injection characteristic learning means is performed in an idle operation region of the engine or an operation region near the idle. At this time, the suction that secures the intake air amount corresponding to the fuel injection amount set so that the injection pulse width corresponding to one time of the divided injection fuel becomes substantially equal to the minimum injection pulse width in the stratified lean operation. It is provided with air amount adjusting means and ignition timing retard means for retarding ignition timing.

According to the above configuration, learning for correcting variations in the injection characteristics of the injectors is performed in the idling operation region of the engine or in the operation region near idling, and the air-fuel ratio is adjusted during execution of the learning control. While maintaining the stoichiometric air-fuel ratio, the fuel injection amount and the corresponding intake air amount are adjusted so that the injection pulse width for one split injection is substantially equal to the minimum pulse width during stratified lean operation, and ignition is performed. When the timing is retarded, the learning is performed with high accuracy in a state where the increase in the engine speed is suppressed.

According to a seventh aspect of the present invention, there is provided an injector for directly injecting fuel into a combustion chamber, and a fuel injection control means for controlling the injector to inject a required amount of fuel in a plurality of times in a predetermined operation range. In the in-cylinder injection type engine provided with the above, the time interval from the end of the fuel injection at the preceding stage to the start of the fuel injection at the subsequent stage is set to 3 msec or more at the time of the split injection of the fuel.

According to the above configuration, when the fuel is divided into a plurality of injections in the predetermined operation range, the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is 3 ms.
By setting the value to ec or more, it is possible to prevent variations in the fuel injection at the subsequent stage with respect to the injection pulse, thereby improving the accuracy of the fuel injection control.

[0022]

1 to 5 show a first embodiment of a control device for a direct injection engine according to the present invention.
As shown in FIGS. 1 and 2, the engine body 1 has a plurality of cylinders 2a to 2d, and each of the cylinders 2a to 2d has:
The fuel chamber 5 is located above the piston 4 inserted in the cylinder bore.
Are formed. An intake port 7 and an exhaust port 8 are opened in the combustion chamber 5. The intake port 7 and the exhaust port 8 are opened and closed by an intake valve 9 and an exhaust valve 10, respectively. Reference numeral 10 is configured to be opened and closed by a valve operating mechanism including camshafts 11 and 12 and the like.

At the center of the combustion chamber 5, a spark plug 15
Is disposed, and the tip of the plug faces the combustion chamber 5.
The ignition plug 15 is connected to an ignition coil 16. The front end of the injector 18 faces the combustion chamber 5 from the side, and fuel is directly injected from the injector 18 into the combustion chamber 5. The injector 18 of each of the cylinders 2a to 2d
0 delivery pipe 21.

The fuel circuit 20 includes a delivery pipe 21
Supply passage 22 and return passage 23 connected to
Between the fuel tank 24 and the fuel supply passage 22,
In-tank fuel pump 25, filters 26 and 27, high-pressure fuel pump 28, and high-pressure side pressure regulator 29
And a low pressure side pressure regulator 30 are provided,
A passage (not shown) that bypasses the high-pressure side pressure regulator 29 is provided, and a bypass valve 31 that opens and closes this passage is provided.

The operation of the bypass valve 31 makes it possible to change the fuel pressure. That is, when the bypass valve 31 is closed while the high-pressure fuel pump 28 is operating, the fuel pressure is adjusted to a predetermined high pressure by the pressure adjusting operation of the high-pressure side pressure regulator 29, and the bypass valve 31 is opened. In such a case, the high-pressure side pressure regulator 29 does not substantially function, and the fuel pressure is adjusted to a predetermined low pressure by the pressure adjusting operation of the low-pressure side pressure regulator 30.

The engine body 1 has an intake passage 40.
And the exhaust passage 41 are connected. The above intake passage 4
0, an air cleaner 43, an air flow sensor 44, a throttle valve 45 driven by a motor 46, and a surge tank 47 are provided in this order from the upstream side.
Further, an ISC passage 50 that bypasses the throttle valve 45 is provided. The ISC passage 50 is provided with an ISC valve 51 that controls an air flow rate in this passage.

Downstream of the surge tank 47, there is provided an independent intake passage 53 for each cylinder communicating with the intake port 7 of each of the cylinders 2a to 2d. In each independent intake passage 53,
A swirl control valve 54 is provided. The swirl control valve 54 is driven by an actuator 55 such as a step motor or the like to open and close, and the opening and closing action controls the intake swirl.

On the other hand, the O ₂ for detecting the air-fuel ratio by detecting the oxygen concentration in the exhaust gas is provided in the exhaust passage 41.
An air-fuel ratio sensor including the sensor 57 is provided. In those embodiments, provided as the O ₂ sensor 57 has been used so-called .lamda.o ₂ sensor output at the stoichiometric air-fuel ratio (lambda = 1) is inverted, the O ₂ sensor 57 to the collecting portion near the exhaust manifold Have been. Further, the above O ₂ sensor 5
Downstream of 7, a catalyst 58 for purifying exhaust gas is provided.

In FIG. 1, reference numeral 60 denotes a control unit (ECU) for controlling the engine.
The detection signals a, b, and b from the air flow sensor 44, the throttle opening sensor 48, and the O ₂ sensor 57
c, a crank angle signal d for detecting the engine speed and a cylinder discrimination signal e are input from a distributor 61 linked to the camshaft 12, and an accelerator for detecting an accelerator opening (accelerator pedal depression amount). Detection signals f, g, and h from an opening sensor 62, an intake air temperature sensor 63 that detects the temperature of intake air, a water temperature sensor 64 that detects the temperature of engine cooling water, and the like are also input.

The ECU 60 outputs a signal j for controlling fuel injection to the injector 18 via the injector drive unit 66,
A signal k for controlling the ignition timing is output to the motor 6 and a signal l for controlling the throttle opening via a throttle drive unit 67 to the motor 46 for driving the throttle valve.
And further outputs a signal m for controlling the ISC valve 51,
It is configured to output a signal n or the like for controlling the bypass valve 31 of the fuel circuit 20.

FIG. 3 shows an example of a specific structure of the injector 18. The injector 18 includes a housing 70 having an injection port 70a and a valve seat 70b at a distal end thereof, a needle valve 71 disposed therein to open and close the injection port 70a, and a plunger 72 for causing the needle valve 71 to stroke. , A spring 73 for holding the valve closed, and a coil 74, so that fuel is introduced into a hollow portion provided at the center of the injector 18.

The injector drive unit 66 is controlled by the injection pulse signal output from the ECU 60.
And the plunger 72 is driven so as to lift the needle valve 71 in response thereto, and fuel is injected from the injection port 70a accordingly.

As shown in FIG. 4, the ECU 60 includes:
Injection amount / injection timing calculating means 80 for calculating the fuel injection amount and injection timing, and injection pulse output means 81 for outputting an injection pulse signal having a pulse width corresponding to the fuel injection amount
And a feedback control means 82 for performing feedback control of the fuel injection amount, and a fuel injection control means 83 for executing split injection described later.

The above-mentioned injection amount / injection timing calculating means 80 determines, based on a detection signal output from each sensor such as the air flow sensor 44, which operating region of the graph shown in FIG. The determination is made, and the fuel injection amount and the injection timing corresponding to the operation region are calculated.

In the above map, in the low-rotation low-load operation region where the fuel injection amount is small, the fuel is injected only in the compression stroke, so that the entire inside of the combustion chamber 5 is kept in a fuel-lean state while only the vicinity of the ignition plug 15 is present. Is a stratified combustion region in which the fuel is ignited relatively and locally in a rich state relative to other regions. In this region, the injection pulse is applied so as to perform the batch injection in the compression stroke as shown in FIG. Set Td.

The region on the higher rotation side or higher load side than the stratified combustion region is a uniform combustion region in which fuel is injected during the intake stroke and sufficiently diffused in the cylinder before ignition. Among the uniform combustion regions, in the high rotation region where the diffusion speed is relatively high, the injection pulse Ta is set so as to perform the batch injection during the intake stroke as shown in FIG. 6B, while the diffusion speed is relatively low. In the middle / low rotation speed range α, in order to avoid generation of smoke due to poor fuel diffusion, split injection of the intake stroke is performed in which the required fuel is injected twice during the intake stroke as shown in FIG. The injection pulses Tb and Tc are set as described above. .

The injection pulse output means 81 outputs the injection amount
The fuel injection amount calculated by the injection timing calculation means 80 is converted into a pulse width, and an injection pulse having this pulse width is output to the injector 18 via the drive unit 51 at a timing corresponding to the fuel injection timing. This injector 18 is configured to be driven.

The feedback control means 82
Performs feedback control of the fuel injection amount so that the air-fuel ratio becomes the stoichiometric air-fuel ratio in accordance with the detected value of the air-fuel ratio by the O ₂ sensor 57 provided in the exhaust passage 41 when a predetermined feedback condition is satisfied. It is configured as follows.
That is, a feedback correction term for the fuel injection amount is obtained by the feedback control means 82 based on the output of the O ₂ sensor 57 by PI control or the like, and the basic fuel obtained based on the feedback correction term and the intake air amount and the like. The feedback control is executed by calculating the final fuel injection amount based on the injection amount.

This feedback control is executed in the operation region (the uniform combustion region excluding the enrich region near the full load) where the stoichiometric air-fuel ratio is set in the uniform combustion region. Even during the warm-up period,
This is executed at the stoichiometric air-fuel ratio to promote warm-up. Therefore, the air-fuel ratio is leaner than the stoichiometric air-fuel ratio by stratification of the air-fuel mixture from the warm-up time point of the engine when the engine temperature has risen to the predetermined temperature when the engine is under a low load, and is lower than the predetermined temperature. When the engine has been warmed up to the set temperature, the fuel injection amount from the injector 18 is feedback controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.

The fuel injection control means 83 performs a learning control, which will be described later, during a specific operation in which the feedback control is performed, for example, when the engine is in the uniform combustion region α at a relatively high load and high speed, and when the engine is half warmed up. Is performed, the fuel injection is performed a plurality of times in the intake stroke. This split injection of fuel is performed by dividing the injection pulse obtained by converting the fuel injection amount in the injection pulse output means 81 into a plurality of injection pulses. In this embodiment, FIG. As shown in the figure, the injection pulse is divided into two injection pulses Tb and Tc at a division ratio of 1/2 of the target fuel injection amount.

Further, the fuel injection control means 83 divides the fuel into two times, the first and second periods, during the divided injection of fuel, from the end of the previous stage to the start of the second stage. In the case of injecting fuel, the time interval from the end point of the first-stage injection to the start point of the second-stage injection is set to a reference time required to prevent the fuel injection from varying with respect to the injection pulse, for example, 3 msec or more. Is configured.

The control operation performed by the ECU 60 will be described with reference to the flowchart shown in FIG.
When the control operation is started, first, it is determined whether or not the operation region of the engine is the divided injection region α in FIG. 5 (step S1). If the determination is YES, the injection amount / injection timing calculating means is determined. A time interval T from the end of fuel injection in the first half to the start of fuel injection in the second half is calculated based on the fuel injection amount of the first half, the fuel injection timing of the previous half, and the engine speed determined in step 80 (step). S2).

Next, it is determined whether or not the time interval T calculated in step S2 is 3 msec or more (step S3). If the determination is YES, the injection amount / injection timing calculating means 80 determines A timer for injecting fuel is set in accordance with the obtained fuel injection amount and injection timing (step S4).

On the other hand, if it is determined NO in step S3 and it is confirmed that the time interval T is less than 3 msec, the time interval from the end of the fuel injection in the first half to the start of the fuel injection in the second half is determined. After recalculating the injection timing in the previous and subsequent periods so that T becomes 3 msec (step S
5) The process proceeds to step S4.

As described above, the injector 18 for directly injecting fuel into the combustion chamber and the fuel injection control means 83 for controlling the injector 18 to inject a required amount of fuel in a plurality of times in a predetermined operation range. In the in-cylinder injection engine provided, the time interval from the end of the previous (first half) fuel injection to the start of the second (late) fuel injection during the split injection of the fuel is prevented from varying the fuel injection with respect to the injection pulse. Is set to be equal to or longer than the reference time required to prevent the occurrence of a situation in which the fuel injection amount in the subsequent stage becomes inaccurate due to this variation in fuel injection, and the total fuel injection amount is set to the target fuel injection amount. Control for matching the amount can be appropriately performed.

That is, when the fuel split injection is executed, the pulse width of the injection pulse is set to 0.3 to 0.75 msec.
c, various values are set within the range, and the engine speed is set to 3000 rpm or 1500 rpm.
Under the condition that the cooling water temperature of the engine is set to various values within the range of 50 to 90 #, and the ignition retard amount with respect to the basic ignition timing is set to various values within the range of 0 to 25 degrees, When the time interval from the end of fuel injection to the start of fuel injection at the subsequent stage is variously changed, as shown in FIG.
In an area shorter than sec, the fuel injection amount at the subsequent stage tends to fluctuate significantly.

This is because, in a cylinder injection type engine having a high fuel injection pressure, the fuel pulsation caused by a sudden change in the fuel pressure in the fuel supply pipe from the delivery pipe 21 to the injector 18 after the end of the previous fuel injection. It is considered that if the fuel pulsation is started and the fuel injection at the subsequent stage is started before the fuel pulsation is not sufficiently contained, the fuel injection amount to be injected at the subsequent stage is affected by the pulsation.

Accordingly, the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is 3 ms.
When the time is shorter than the reference time set to about ec, control of the fuel injection amount is difficult because the fuel injection amount at the subsequent stage with respect to the injection pulse varies.
When the time interval between the divided injections is set to be equal to or longer than the reference time of about 3 msec as described above, it is possible to prevent the occurrence of the control failure due to the above-described variation in the fuel injection and to reduce the total fuel injection amount to the target fuel injection amount. Control for matching the amount can be appropriately performed.

In FIG. 7, a line β is obtained under the above conditions.
The graph shows the average fuel injection amount when the time interval from the end of the first stage fuel injection to the start of the second stage fuel injection is variously changed. The average fuel injection amount indicated by the line β tends to increase as the time interval becomes shorter. This is because the shorter the time interval is, the more the fuel injected per unit time is increased due to the fact that the needle valve 71 is deprived of heat by the fuel injected in the preceding stage and thermally contracts. Conceivable.

In a region where the time interval from the end of the first stage fuel injection to the start of the second stage fuel injection is less than 3 msec, the fuel injection amount increases due to the thermal contraction of the needle valve 71 as described above. Due to the influence of the fuel pulsation, the fuel injection amount to be injected in the subsequent stage varies, so that the difference between the target fuel injection amount calculated according to the operating state of the engine and the actual fuel injection amount is reduced. It is inevitable that the size will increase significantly. On the other hand, in the region where the time interval at the time of the divided injection is 3 msec or more, the variation of the actual fuel injection amount with respect to the average fuel injection amount indicated by the line β is small, so that the target fuel injection calculated by the calculation is calculated. By correcting the amount based on the average fuel injection amount, it is possible to accurately control the total fuel injection amount and the target fuel injection amount.

In the above embodiment, as shown in FIG. 7, the dispersion of the fuel injection with respect to the fuel injection pulse is experimentally obtained in various operating states, and it is necessary to prevent the dispersion based on the experimental data. 3
msec, and at the time of split fuel injection, the time interval from the end of the previous fuel injection to the start of the subsequent fuel injection is uniformly set to 3 msec or more.
With the control device having a simple configuration, it is possible to prevent a variation in fuel injection at a later stage with respect to the injection pulse from occurring, and to quickly and appropriately execute control for matching the total fuel injection amount to the target fuel injection amount. .

It should be noted that instead of the above configuration, the reference time for preventing the variation of the fuel injection with respect to the injection pulse is set as follows:
The fuel injection amount is individually obtained in accordance with the individual difference of the injector 18 or each operating state, etc., and the time interval from the end point of the preceding fuel injection to the start point of the subsequent fuel injection is individually set according to the reference time, and the fuel May be configured to control the injection timing.

Further, the time during which the fuel pulsation generated in the fuel supply pipe due to the needle valve lift of the injector 18 is settled may be determined experimentally or by calculation, and the reference time may be set based on this value. In the case of such a configuration, at the time of split injection of fuel, after the fuel pulsation caused by the needle valve lift is settled from the end of the previous fuel injection, the subsequent fuel injection is started, It is possible to prevent a control error due to the fuel pulsation from occurring, and effectively prevent a fuel injection amount at the subsequent stage from being varied.

In the above-described embodiment, the divided injection region α for performing the divided injection of the fuel in the intake stroke is provided in the uniform combustion region provided on the higher rotation side than the stratified combustion region. The time interval from the end of the preceding fuel injection to the beginning of the subsequent fuel injection in α is
Since the time is set to be equal to or longer than the reference time, it is possible to prevent the time interval during the split injection from becoming extremely short due to a high engine speed. Therefore, it is possible to reliably prevent the occurrence of a control error due to the fuel pulsation or the like in the high rotation region of the engine, and to prevent a variation in the fuel injection amount in the subsequent stage.

Further, the divided fuel injection region is defined as an operating region where the air-fuel ratio becomes the stoichiometric air-fuel ratio, and the fuel injection amount is determined based on the detection value of the air-fuel ratio sensor including the O ₂ sensor 57 provided in the exhaust passage 41. When the feedback control region is set to execute the feedback control, the fuel is injected in a plurality of times at the time of the feedback control, and the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is set. By setting the reference time to be equal to or longer than the reference time, it is possible to prevent variations in the amount of fuel injection at the subsequent stage, and thus there is an advantage that the feedback control can be appropriately performed.

Note that, as shown in FIG.
Next, an injection characteristic learning means 84 for learning the correspondence between the fuel injection pulse width and the fuel injection amount to obtain a learning correction value, and controlling the ISC valve 51 to adjust the intake air amount when the learning is performed. Ignition timing retarding means for controlling the ignition timing calculated by the ISC control means 85, the intake air amount adjusting means 86, and the basic ignition timing calculating means 91 in accordance with the operating condition of the engine to be retarded when the learning control is performed. 92 may be provided.

During the specific operation in which the feedback control of the fuel injection amount is performed by the feedback control means 82, the injection characteristic learning means 84 performs the feedback correction term ( Based on the feedback control amount), the learning correction value is obtained by learning the correspondence between the injection pulse width corresponding to one divided fuel injection and the fuel injection amount.

The ISC control means 85 controls the ISC valve 51 during the idling operation of the engine to adjust the intake flow rate so as to make the idle speed equal to the target value. Further, in the intake air amount adjusting means 86, the split injection of the fuel by the fuel injection control means 83 and the learning by the injection characteristic learning means 84 are performed in the idle operation area of the engine or the operation area near the idle in the intake stroke. During this time, the control of the intake air flow rate by the ISC control means 85 is regulated.

Specifically, in the no-load low-rotation region such as the idling operation region, the injection pulse width corresponding to one split injection is set so as to be substantially equal to the minimum injection pulse width in the stratified lean operation. The intake air amount is adjusted in accordance with the fuel injection amount that has been set. That is, when performing the divided injection in the intake stroke for the learning, when the basic fuel injection amount is set to be larger than that in the normal idle operation, a predetermined amount larger than the normal time is set correspondingly. The control amount of the ISC valve 51 is set by the intake air amount adjusting means 86 so as to secure the intake air amount. As a result, while the air-fuel ratio is set to the stoichiometric air-fuel ratio, the fuel injection amount and the intake air corresponding to the fuel injection amount are set so that the pulse width corresponding to one injection of the split injection is substantially equal to the minimum pulse width during the stratified lean operation. A volume adjustment will be made.

The ignition timing retarding means 92 includes:
In order to suppress an increase in the engine speed due to the adjustment of the intake air amount and the fuel injection amount as described above in the idle operation region of the engine or an operation region near the idle, the ignition timing is retarded and the torque is reduced. Thus, when the injection characteristic learning means 84 executes learning, control is performed to set the engine speed to a target value such as during idling.

The control operation executed by the ECU 60 will be described with reference to the flowchart shown in FIG. When the control operation is started, first, it is determined whether or not the operation region of the engine is the divided injection region α in FIG. 5 (step S11). If the determination is NO, the learning by the injection characteristic learning means 84 is performed. It is determined whether or not the operation is in the operation region in which is performed (step S12).

That is, if the split injection is performed during the feedback control by the feedback control means 82 in a semi-warmed state before the engine is warmed up, a low load such that the fuel injection amount falls within the peculiar region B in FIG. If it is within the range, it is determined that the range is the operation range in which the learning of the injection characteristics is performed. FIG. 11 shows the characteristics of the injector 18. In most of the general area A in the variable fuel injection range, the injection pulse width and the fuel injection amount have a proportional proportional correspondence. On the other hand, the characteristic region B has a different characteristic from the general region A due to an increase in the ratio of the valve lift intermediate period to the valve closing period, etc.

In the case where it is determined to be YES in the above step S12 and it is confirmed that the region is for learning, or in the case where it is determined to be YES and it is confirmed that it is the divided injection region α in the above step S11, From the fuel injection amount of the first half obtained by the injection amount / injection timing calculating means 80, the fuel injection timing of the preceding and following periods, and the engine speed, from the end of the first period fuel injection to the start of the second period fuel injection. Is calculated (step S13).

Next, it is determined whether or not the time interval T is equal to or longer than a reference time set to about 3 msec (step S14). If the determination is YES, the injection amount / injection timing calculating means 80 is determined. A timer for injecting fuel is set in accordance with the fuel injection amount and the injection timing obtained in (step S15).

On the other hand, if NO is determined in step S14, the time interval T from the end of the first-stage fuel injection to the start of the second-stage fuel injection is set to a reference time set to about 3 msec. Next, after recalculating the injection timings of the preceding and following periods (step S16), the above-described step S1 is performed.
Go to 5.

According to the above-described embodiment, among the injection characteristics of the injector 18 shown in FIG. 11, the correspondence between the injection pulse width in the singular region B where the above-mentioned minute injection amount is obtained and the fuel injection amount is properly adjusted. Thus, the learning correction value at the time of the feedback control can be accurately obtained.
That is, if an error occurs in the conversion of the injection pulse width due to a difference in the correspondence between the injection pulse width and the fuel injection amount due to individual differences of the injectors 18 or the like, the error appears in the feedback correction term in the air-fuel ratio feedback control. From this feedback correction term, a learning correction value corresponding to the deviation of the correspondence can be obtained.

After the learning correction at the time of the split injection is performed, this is reflected in the fuel injection control in the case where stratified combustion is performed by the compression stroke injection in the low-speed low-speed region after the warm-up. That is, when the stratified charge combustion is performed by the compression stroke injection in the low-speed low-speed region and the air-fuel ratio is made lean, the injection amount is reduced due to the enhancement of the thermal efficiency, and the injection amount point b in the singular region B is reduced. However, in this case, the fuel injection amount is obtained based on the accelerator opening, the engine speed, and the like.When converting the fuel injection amount into the injection pulse width, the learning correction value is read, and By executing the added control, the accuracy of the fuel injection control can be improved.

In the above embodiment, the ISC control means 85 and the intake air amount adjusting means 86 for controlling the ISC valve 51 to adjust the intake air amount at the time of learning the fuel injection characteristics, and the basic ignition timing calculating means 91 Since the ignition timing retarding means 92 for retarding the calculated ignition timing is provided, the learning accuracy of the fuel injection characteristic in the air-fuel ratio feedback control during the semi-warm-up operation is reduced particularly in the idling operation region or the operation region in the vicinity thereof. Can be prevented.

That is, when the learning correction value of the singular region B is obtained by performing the divided injection of the intake stroke during the feedback control based on the detection value of the O ₂ sensor 57, in the normal control state such as the idling operation region, Although the fuel injection amount increases due to poor thermal efficiency compared to the case of lean operation, it does not become twice. Therefore, if the injection pulse width according to the fuel injection amount is divided, the injection pulse width after division becomes stratified. It becomes smaller than the minimum pulse width in the lean operation region and the like.

Therefore, in the present embodiment, when performing the split injection of the intake stroke in an idling operation region or the like during the air-fuel ratio feedback control, the split air amount and the basic fuel injection amount are made larger than those at the normal time, thereby making the split. The subsequent injection pulse width is set to be equal to the minimum pulse width during stratified lean operation, thereby improving the learning accuracy near the minimum pulse width.

If the intake air amount and the fuel injection amount are merely controlled to be larger than those in the normal state as described above, the idle speed increases more than necessary.
In a vehicle with an automatic transmission, there is a problem that unnecessary creep running occurs during idling operation in the D range in a vehicle with an automatic transmission. For this reason, in the present embodiment, in such a case, the ignition timing is retarded to suppress an increase in the engine speed due to an increase in the intake air amount and the fuel injection amount, thereby avoiding the above-described inconvenience and reducing the engine speed. Control to set a target value during idling operation or the like can be appropriately performed.

In each of the above embodiments, an example has been described in which the fuel is injected twice in the intake stroke by the fuel injection control means 83. However, the fuel is injected three times in the first, middle and late stages. The fuel may be separately injected. In this case, the time interval from the end of the first-stage injection to the start of the middle-stage injection and the time interval from the end of the middle-stage injection to the start of the second-stage injection are respectively set to be equal to or longer than the reference time. Become.

Further, the λO ₂ sensor is used as the air-fuel ratio sensor, and the fuel injection characteristic is learned when the fuel injection amount is feedback-controlled so as to obtain the stoichiometric air-fuel ratio in accordance with the output of the λO ₂ sensor. Instead of a mode, a linear O ₂ sensor whose output changes substantially linearly in accordance with the air-fuel ratio may be used. In this case, the feedback control can be performed even in an operation range other than the stoichiometric air-fuel ratio. However, even when the above linear O ₂ sensor is used, the detection accuracy near the stoichiometric air-fuel ratio is the highest, and the detection accuracy tends to decrease as the distance from the stoichiometric air-fuel ratio increases. It is preferable to learn the fuel injection characteristics during the feedback control.

If the fuel injection amount at the subsequent stage varies during execution of such learning control, the accuracy of the learning control itself deteriorates, and if this is reflected in the control of the fuel injection amount, the subsequent control accuracy is rather reduced. Getting worse. Further, since the learning control is executed, the injection time interval of the front and rear stages may be shorter than that of the normal idling time and may be easily affected by the fuel pulsation. The effect of setting the interval to be longer than the reference time is remarkable.

[0075]

As described above, the present invention provides an injector for directly injecting fuel into a combustion chamber and a fuel injection for controlling a required amount of fuel to be injected in a plurality of times from the injector in a predetermined operation range. In the direct injection type engine provided with the control means, at the time of the split injection of the fuel, the time interval from the end of the fuel injection at the preceding stage to the start of the fuel injection at the subsequent stage is set to prevent the variation of the fuel injection with respect to the injection pulse. Is set to be equal to or longer than the reference time required to prevent the occurrence of a situation in which the fuel injection amount in the subsequent stage becomes inaccurate due to this fuel injection variation, and the total fuel injection amount is set to the target fuel injection amount. There is an advantage that the matching control can be executed properly.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of an engine body and its vicinity.

FIG. 3 is a sectional view of an injector provided in the engine.

FIG. 4 is a block diagram showing a functional configuration of an ECU.

FIG. 5 is a graph showing each operation region set in the engine.

FIG. 6 is a graph showing a fuel injection timing in each of the operation ranges.

FIG. 7 is a graph showing a relationship between a time interval of split injection and a fluctuation state of a fuel injection amount.

FIG. 8 is a flowchart showing a control operation executed in the ECU.

FIG. 9 is a block diagram showing another specific example of the ECU.

FIG. 10 is a flowchart showing a control operation executed in the ECU.

FIG. 11 is a graph showing characteristics of a correspondence relationship between a fuel injection amount of an injector and an injection pulse width.

[Explanation of symbols]

1 engine body 5 combustion chamber 18 injector 57 O ₂ sensor (air-fuel ratio sensor) 60 ECU 71 needle valve 82 feedback control means 83 fuel injection control means 84 injection characteristic learning means 86 the intake air amount adjusting means 92 an ignition timing retard means

Continued on the front page F term (reference) 3G022 AA07 AA08 BA01 CA03 CA06 CA09 DA02 EA07 GA05 GA06 GA08 GA09 GA11 3G084 AA04 BA13 BA15 BA17 CA03 CA04 CA09 DA04 DA23 EA07 EB11 EB17 EC02 EC03 FA02 FA07 FA10 FA13 FA17 FA20 FA301 FA33 FA39 FA39 HA17 JA00 JA05 KA07 KA08 KA09 KA24 LA00 LA04 LA05 LB01 LB04 LC04 MA01 MA12 MA19 MA20 MA26 MA27 ND01 ND33 NE14 NE15 NE23 PA01Z PA10Z PA11Z PA15A PB03A PB03Z PB05Z PD03A PD04A PE01A PE01Z PE05Z PE08Z

Claims (7)

[Claims] An in-cylinder having an injector for directly injecting fuel into a combustion chamber, and fuel injection control means for controlling a required amount of fuel to be injected in a plurality of times from the injector in a predetermined operation region. In an injection engine,
At the time of split injection of the fuel, the time interval from the end of the previous fuel injection to the start of the subsequent fuel injection is set to be equal to or longer than the reference time required to prevent variation in fuel injection with respect to the injection pulse. A fuel injection control device for a direct injection engine. 2. The fuel injection control device for a direct injection type engine according to claim 1, wherein the reference time corresponds to a time in which a fuel pulsation generated in a fuel supply pipe due to a needle valve lift of the injector falls. A fuel injection control device for a direct injection type engine, wherein the fuel injection control device is set. 3. The fuel injection control device for a direct injection type engine according to claim 1, wherein a split injection region for performing split injection of fuel in an intake stroke is provided in a high speed region of the engine. A fuel injection control device for an in-cylinder injection engine, wherein a time interval from a time point at which fuel injection ends at a preceding stage to a time point at which fuel injection starts at a later stage is set to be equal to or longer than the reference time. 4. The fuel injection control device for a direct injection type engine according to claim 1, wherein the split injection region of the fuel is an operating region where the air-fuel ratio is substantially equal to the stoichiometric air-fuel ratio. A fuel injection control device for a direct injection engine, wherein the feedback control region is set in a feedback control region for executing a feedback control of a fuel injection amount based on a detection value of an air-fuel ratio sensor provided in a passage. 5. An injector for directly injecting fuel into a combustion chamber, and a feedback for feedback-controlling a fuel injection amount based on a detection value of an air-fuel ratio sensor provided in an exhaust passage so that an air-fuel ratio becomes substantially a stoichiometric air-fuel ratio. A fuel injection control means for controlling the injector to inject fuel in a plurality of times during a specific operation in which the feedback control is performed, and the divided injected fuel. And a fuel injection amount learning means for learning a correspondence relationship between the injection pulse width and the fuel injection amount corresponding to one injection of the fuel injection amount. The time interval is set to be equal to or longer than a reference time required to prevent variation in fuel injection with respect to the injection pulse. A fuel injection control device for a direct injection engine. 6. The fuel injection control device for a direct injection type engine according to claim 5, wherein when the learning by the injection characteristic learning means is performed in an idle operation region of the engine or in an operation region near idle, the divided injection is performed. Intake air amount adjusting means for securing an intake air amount corresponding to a fuel injection amount set such that an injection pulse width corresponding to one fuel injection is substantially equal to a minimum injection pulse width during stratified lean operation; A fuel injection control device for a direct injection type engine, comprising: ignition timing retard means for retarding the timing. 7. An in-cylinder having an injector for directly injecting fuel into a combustion chamber and fuel injection control means for controlling a required amount of fuel to be injected in a plurality of times from the injector in a predetermined operation region. In an injection engine,
At the time of the fuel split injection, the time interval from the end of the preceding fuel injection to the start of the subsequent fuel injection is 3 msec.
A fuel injection control device for a direct injection engine, which is set as described above.