JP2000227036A - Controller for spark ignition type direct injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out learning control in a good state, and improve fuel injection accuracy by controlling so as to hold a combustion temperature nearly constantly, on learning control of injection characteristic in a fine pulse width region of an injector, in a device wherein a direct injection stratified burning operation is operated in a prescribed operating region of low load and low rotation. SOLUTION: In the case of injection characteristic learning control of an injector 6 by an ECU 50, a fuel injection rate is feed back controlled 61 on the basis of an output signal of an O2 sensor 22 so as to set an air-fuel ratio to a stoichiometric air-fuel ratio, and a target injection rate is calculated 62 from various kinds of correcting rate including a feed back correcting rate to be obtain in this time, and a reference injection rate according to an operating condition. Fuel injection is separated by separation injection means 64 in a specified operating region in a region where feed back control is carried out, that is a half-warming-up time of an engine, a corresponding relation between a pulse width per injection and a fuel injection rate is learnt 69. At the time of learning, an ignition timing is corrected 67 so as to nearly constantly hold a combustion temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a spark ignition type direct injection engine, and more particularly to a learning correction control in a minute pulse width region of an injector, and relates to a field of engine fuel injection technology.

[0002]

2. Description of the Related Art In recent years, in a spark ignition type engine for a vehicle or the like, a direct injection stratified combustion system for improving fuel efficiency may be adopted as a combustion system. In this method, fuel is injected directly into a combustion chamber from an injector during a compression stroke in a predetermined operating region on a low-load, low-speed side to form a mixture having a required concentration near an ignition plug, thereby forming an overall mixture. This is to make the air-fuel ratio significantly leaner than the stoichiometric air-fuel ratio.

[0003] On the other hand, the injector is configured to be opened by an injection pulse of a drive signal output at an injection timing set in accordance with an operation state to inject fuel, and the injection amount is controlled by the injector amount. , That is, the pulse width of the injection pulse. In this case, each injector has a predetermined injection characteristic with respect to the pulse width of the injection pulse, and converts the target injection amount set according to the operating state into the pulse width of the injection pulse according to this characteristic. The characteristics vary depending on the individual injectors. Therefore, conventionally, the relationship between the pulse width and the injection amount is learned for each injector, and the injection characteristics are corrected based on the learning result.

This learning control determines whether the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is leaner (oxygen excess state) or richer (oxygen insufficient state) than the stoichiometric air-fuel ratio based on the residual oxygen concentration in the exhaust gas. This is performed by feedback control of the air-fuel ratio using the O ₂ sensor to be detected. In other words, this feedback control is to control the air-fuel ratio to the stoichiometric air-fuel ratio (A / F = 14.7) by increasing or decreasing the fuel injection amount from the injector according to the signal from the O ₂ sensor. If the air-fuel ratio is kept at the stoichiometric air-fuel ratio by this control, the amount of fuel supplied can be calculated from the value and the separately measured intake air amount, and therefore, the output to the injector at that time is obtained. The relationship between the pulse width and the injection amount can be determined by reading the pulse width of the injection pulse.

[0005] By performing this for a plurality of operating states, the characteristics of the injection amount with respect to the pulse width of the injector are grasped. By calculating the pulse width of the injection pulse in accordance with the characteristics, the fuel injection amount is set to the target value. It will be controlled correctly.

Incidentally, the injection characteristics of the injector as described above, for example, as shown in FIG.
A linear tendency is exhibited in most of the regions P1 equal to or greater than 0, which is the basic characteristic X of the injector. It shows the characteristic Y. Then, in the operation region where the above-described stratified combustion is performed, in particular, during the stratified combustion operation in a low load region such as at the time of idling, the injection amount belongs to the region P2 showing the unique characteristic Y.

Therefore, when the injection amount is to be controlled with high accuracy in this stratified combustion region, the small pulse width region P2
It is necessary to correctly learn the injection characteristic (singular characteristic Y) of the injector in the above. However, since the above learning control is performed under feedback control for controlling the air-fuel ratio to the stoichiometric air-fuel ratio, Even in the idle state where the fuel injection amount is small, there is a problem that data can be obtained only in the area P1 of the basic characteristic X and the injection characteristic Y in the small pulse width area P2 cannot be learned.

[0008] To address this problem,
According to Japanese Patent Application Laid-Open No. 6-214995, in the surge operation region corresponding to the minute pulse width region P2, the injection amount is converted into the pulse width by using a coefficient different from the region exhibiting the basic characteristics. Is corrected so that the generated torque of each cylinder becomes equal.

[0009]

However, in the invention disclosed in the above publication, the injection characteristics of each injector are corrected so that the relative torque variation between the cylinders is eliminated. Does not require an absolute correspondence between injection quantity and pulse width.
This correction is performed in the small pulse width region P2 shown in FIG.
However, in this area P2, a very small deviation of the injection timing or the pulse width greatly affects the variation of the injection amount, so that accurate correction cannot be expected.

On the other hand, as shown in FIG. 12, this type of injector A has a valve body B having an injection port B 'at the tip.
The needle valve C is housed so that it can be stroked in the axial direction,
This is urged toward the distal end by a spring D, and the distal end portion C ′ is seated on a seating surface B ″ around the above-mentioned nozzle hole B ′, thereby closing the nozzle hole B ′ and energizing the solenoid E, The needle valve C is lifted against the urging force of the spring D, and the tip C 'is separated from the seating surface B "to open the injection port B'. Is injected from the injection port B '.
However, even if the lift time of the needle valve C, that is, the pulse width of the injection pulse for energizing the solenoid E is the same, there is a problem that the injection amount changes depending on the temperature of the tip.

That is, the valve body B and the needle valve C have different coefficients of thermal expansion, and the valve body B directly attached to the cylinder head is more susceptible to the combustion temperature than the needle valve C. The area of the fuel passage generated between the front end portion C 'and the bearing surface B "during the lift of the vehicle differs depending on the combustion temperature.
As a result, even if the pulse width of the injection pulse is the same, the injection amount will be different.

Therefore, the present invention relates to a spark-ignition engine that performs a direct injection stratified charge combustion operation in a predetermined low-load, low-speed operation region, and changes the combustion temperature during learning control of the injection characteristics in the minute pulse width region of the injector. It is an object of the present invention to perform the learning control satisfactorily by controlling the fuel injection amount during the stratified combustion operation with high accuracy.

[0013]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized in that it is configured as follows.

First, the invention of claim 1 of the present application (hereinafter referred to as the first invention)
The invention relates to a control device for a spark ignition engine.
An injector for directly injecting fuel into the combustion chamber, and injector driving means for converting the fuel injection amount from the injector into a pulse width of a drive signal and outputting the pulse width to the injector are provided, and the stoichiometric air-fuel ratio in a low load region. the spark-ignition direct injection engine lean operation region is provided to operate is set to leaner than fuel ratio, the fuel injection amount by the injector on the basis of a signal from the O ₂ sensor for detecting the residual oxygen concentration in the exhaust gas Feedback control means for performing feedback control to control the air-fuel ratio to a stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio, and a specific operation area within a low load area where the feedback control is performed by the means
The fuel injection by the injector is divided into a plurality of times during the period from the intake stroke to the compression stroke, and the fuel injection by the injector is divided into plural times. Learning means for learning the correspondence between the pulse width and the fuel injection amount for each injection, and while learning is performed by the means,
Ignition timing correction means for correcting the ignition timing such that the combustion temperature is maintained substantially constant.

According to a second aspect of the present invention (hereinafter referred to as a second aspect), in the first aspect, the ignition timing correction means corrects the ignition timing to the retard side when the intake air amount increases. I do.

According to a third aspect of the invention (hereinafter referred to as a third aspect), in the first aspect or the second aspect, the split injection means performs the fuel injection by the injector in the first half of the intake stroke and in the first half of the compression stroke. It is characterized in that it is divided and performed.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the specific operating region is a condition where the engine temperature is higher than a predetermined temperature in a low load and low speed region. It is characterized in that it is an operation area.

According to a fifth aspect of the present invention (hereinafter referred to as a fifth aspect), the low-load low-rotation region is a no-load low-rotation region.

According to a sixth aspect of the invention (hereinafter referred to as a sixth aspect), in the fifth aspect, an external load increase detecting means for detecting an increase in an external load acting on the engine in a no-load, low-speed region is provided. The ignition timing correction means corrects the ignition timing so that the combustion temperature is maintained substantially constant when the increase in the external load is detected by the means.

Further, the invention of claim 7 (hereinafter referred to as the seventh invention) is the same as the fifth invention, wherein the correction of the ignition timing by the ignition timing correction means in the no-load, low-rotation region is performed based on the maximum torque generation timing. MBT (minimum spar) on the retard side
It is characterized in that it is performed within a certain range centered on the reference ignition timing set further on the retard side than kadvance for best torque).

On the other hand, the invention of claim 8 (hereinafter referred to as an eighth invention) is characterized in that, in the first invention or the second invention, the correction of the ignition timing by the ignition timing correction means is performed within a certain range including the maximum torque generation timing. Is performed.

In a ninth aspect of the present invention, the correction of the ignition timing by the ignition timing correction means is performed based on the reference ignition timing set on the retard side of the maximum torque generation timing. Is performed mainly.

Further, the invention of claim 10 (hereinafter referred to as a tenth invention)
The invention is characterized in that, in the first invention or the second invention, the split injection means performs the fuel injection by the injector in a plurality of times during the intake stroke.

The invention of claim 11 (hereinafter referred to as an eleventh embodiment)
Similarly, in the first invention or the second invention, the lean operation region in which the air-fuel ratio is controlled to the lean operation in the first invention or the second invention is a stratified combustion operation region in which fuel is supplied to the vicinity of the ignition plug and burned in the compression stroke. It is characterized by the following.

With the above arrangement, the following effects can be obtained according to the present invention.

First, according to the first aspect of the present invention, the fuel injection amount is fed back so that the air-fuel ratio becomes the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio based on the signal from the O ₂ sensor in the specific operation region within the low load region. When the fuel injection is controlled, the fuel injection is divided into a plurality of times during the period from the intake stroke to the compression stroke, so that the total injection amount becomes the stoichiometric air-fuel ratio or the air-fuel ratio close to the stoichiometric air-fuel ratio as described above. Even if the injection amount is relatively large, the injection amount of each divided injection is a relatively small amount obtained by dividing the total injection amount by the number of divisions, if the pulse width of each injection pulse is the same, and the injection amount of the injector Injection can be performed in a minute pulse width region in which the injection characteristics show unique characteristics.

Therefore, the pulse width in the minute pulse width region is obtained from the value obtained by dividing the total injection amount obtained from the air-fuel ratio and the intake air amount by the number of divisions and the pulse width of each divided injection pulse output at that time. And the injection amount is learned, and by collecting a plurality of the learning data in the feedback region, it becomes possible to grasp the unique characteristic of the injector in the minute pulse width region. is there. Then, by controlling the injection amount of the injector based on this characteristic, the fuel control in the case where the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio during the stratified charge combustion operation or the like is performed with high accuracy.

In particular, in the present invention, while the learning data is being collected as described above, the combustion temperature is maintained substantially constant by the ignition timing correction control. When there is a fluctuation or the like, a situation in which the injection amount for the same pulse width changes due to a change in the combustion temperature accompanying the fluctuation is avoided,
Learning data is always collected under the same conditions,
The injection characteristics of the injector in the minute pulse width region can be grasped more accurately.

In this case, according to the second aspect of the present invention, the ignition timing correction control is performed when the intake air amount is increased for the purpose of, for example, maintaining the rotation speed against an increase in the external load. The time will be retarded. Therefore, the increase in the combustion temperature due to the increase in the intake air amount is offset by the retard of the ignition timing, and the combustion temperature is kept substantially constant during the learning control.

According to the third aspect of the present invention, as the divided fuel injection for learning, the first half injection is executed in the first half of the intake stroke and the second half injection is executed in the first half of the compression stroke. And the temperature at the injector tip is substantially equal.

That is, if the first-stage injection and the second-stage injection are executed at times when the in-cylinder pressure is different, the injection amount for the same pulse width differs, and accurate learning data cannot be collected. Also, if the time interval between the first injection and the second injection is short, the second injection is performed immediately after the needle valve is cooled by the first injection, and both injections are performed in a state where the temperature of the needle valve is different. However, since the temperature of the needle valve affects the area of the fuel passage between the needle valve tip and the seat surface when the injector is opened, the first injection and the second injection are continuously performed. In this case, the injection amounts of both injections for the same pulse width will differ in the direction in which the injection amount of the latter injection is greater than the injection amount of the previous injection, and accurate learning data will be obtained as in the above case. Will not be able to do it.

Therefore, as described above, in the third invention, the first-stage injection and the second-stage injection are executed in the first half of the intake stroke and the first half of the compression stroke, respectively, in which the in-cylinder pressure is substantially equal and the time interval is relatively wide. Thus, accurate learning data can be obtained.

According to the fourth aspect of the present invention, the specific operation range during the air-fuel ratio feedback control for performing the learning control is performed when the engine temperature is equal to or higher than a predetermined temperature, that is, when the engine is at a low load and a low speed in a warm-up state or a half-warm-up state. In the steady operation region, in other words, a region in which the fuel injection amount is small and stable, and the time interval between each injection is long, the learning control makes it possible to obtain accurate data on the injection characteristics of the injector. Will be collected.

According to the fifth invention, the low-load low-rotation region in the fourth invention is a no-load, low-rotation operation region, that is, an idle region, so that more accurate learning data is collected. Will be done.

Further, according to the sixth aspect of the invention, when an increase in the external load acting on the engine is detected in the no-load, low-speed range, that is, the idle range, the ignition timing is retarded. As a result, an increase in the combustion temperature due to the effect of the external load is offset, and even when the external load increases, learning data can be collected under a constant temperature condition.

According to the seventh aspect of the invention, in the no-load, low-speed region, that is, in the idle region, the ignition timing is corrected by the MB on the retard side of the maximum torque generation timing.
This is performed within a certain range centered on the reference ignition timing set further on the retard side than T, but this range is the range in which the rotation fluctuation during idling is the smallest,
Therefore, by performing the ignition timing correction control in this range, stable control of the combustion temperature becomes possible, and as a result, highly accurate learning data can be obtained.

On the other hand, according to the eighth invention, the correction of the ignition timing by the ignition timing correction means is performed within a certain range including the maximum torque generation timing. This is a range in which the change appears relatively sensitively. Therefore, the combustion temperature can be appropriately and accurately controlled by controlling the ignition timing, so that accurate learning data is collected.

According to the ninth aspect, the correction of the ignition timing in the eighth aspect is performed within a certain range including the maximum torque generation timing, centering on the reference ignition timing set on the retard side of the timing. Therefore, the combustion temperature can be more appropriately and accurately controlled by correcting the ignition timing.

Further, according to the tenth aspect of the present invention, all the divided injections of the fuel during the learning control are performed during the intake stroke. In this case, the learning control is performed in the region where the fuel injection amount is relatively large. Thus, the fuel is sufficiently vaporized and atomized, and the learning data is collected under a favorable combustion state.

According to the eleventh invention, the first and the second
Since the effect of the invention is obtained by the engine having the stratified combustion operation region, the fuel control can be accurately performed in the stratified combustion operation region in which the air-fuel ratio is set to lean.

[0041]

Embodiments of the present invention will be described below.

FIG. 1 shows a control system of a spark ignition type direct injection engine 1 according to the present embodiment. In this figure, an engine body 2 has a plurality of cylinders, for example, four cylinders as shown in FIG. And a combustion chamber 4 defined by the piston 3 is formed in each cylinder. An ignition plug 5 is provided at the upper center of the combustion chamber 4 and an injector 6 is provided so as to face the inside of the combustion chamber 4 from the side.
Is provided. Further, an intake port 7 and an exhaust port 8 are provided, and these ports 7 and 8 are driven by camshafts 9 and 10, respectively.
2, it can be opened and closed respectively.

An intake passage 13 and an exhaust passage 14 communicating with the combustion chamber 4 through the intake port 7 and the exhaust port 8 are provided. Of these, the intake passage 13 has an air cleaner 15, an air flow A sensor 16, a throttle valve 17, and a surge tank 18 are provided, and a bypass passage 19 that bypasses the throttle valve 17 is provided. In the bypass passage 19, when the throttle valve 17 is fully closed and idling, the combustion chamber 4 is closed. An idle speed control valve (hereinafter, referred to as an ISC valve) 20 for adjusting an amount of intake air to be supplied to control an idle speed is provided.

The downstream side of the surge tank 18 is an independent intake passage 13a for each cylinder, and is connected to the intake port 7 for each cylinder. Each independent intake passage 13a is provided with a swirl generation valve 21 that generates swirl in the combustion chamber 4 by intake air.

On the other hand, the air-fuel ratio in the exhaust passage 14 is based on the stoichiometric air-fuel ratio (A / F) based on the residual oxygen concentration in the exhaust gas.
= 14.7), an O2 sensor 22 for detecting rich or lean is provided, and a catalyst device 23 for purifying exhaust gas is provided downstream thereof.

Further, the engine 1 is provided with a fuel system 30 for supplying fuel to the injector 6. The fuel system 30 includes a fuel tank 31 and a delivery pipe 3 for distributing and supplying fuel to the injector 6 of each cylinder.
2 and a fuel supply passage 33 provided between the fuel tank 31 and the delivery pipe 32. The fuel supply passage 33 is provided in the fuel tank 31, and a filter is provided on the suction side. A low-pressure fuel pump 34, a filter 35, a high-pressure fuel pump 36, and a high-pressure side pressure regulator 37 are provided, and a fuel supply passage 33 between the low-pressure fuel pump 34 and the high-pressure fuel pump 36 has a low-pressure side. A pressure regulator 38 is connected to regulate the fuel to a low pressure. Also,
The high pressure side pressure regulator 37 and the fuel tank 3
A return passage 39 is provided between the fuel tank 31 and the fuel tank 31 via the return passage 39.

The engine 1 is provided with a control unit (hereinafter, referred to as an ECU) 50 that operates the above-described devices to comprehensively control the operation state. A signal from an intake air temperature sensor 51 for detecting the temperature of intake air, a signal indicating the amount of intake air from the air flow sensor 16, a signal from a throttle opening sensor 52 for detecting the opening of the throttle valve 17, and a camshaft. 10, a crank angle signal from a crank angle sensor 53 linked to 10, a signal from a water temperature sensor 54 for detecting the temperature of engine cooling water, a signal from the O ₂ sensor 22 indicating whether the air-fuel ratio is rich or lean, depression of an accelerator pedal A signal from the accelerator opening sensor 55 for detecting the amount is input.

The ECU 50 operates the throttle valve 17 according to the various engine states indicated by these signals.
56 for opening and closing the actuator, ISC valve 2
0, a control signal is output to an actuator 57 for opening and closing the swirl generation valve 21, an injector 6, an ignition circuit 58 for igniting the ignition plug 5, and the like, and the intake air amount, fuel injection amount and injection timing, swirl generation, and ignition The timing is controlled.

Here, among the control functions of the ECU 50, the configuration of a portion related to the air-fuel ratio control or the injection characteristic learning control of the injector 6 will be described with reference to FIG. 3. As a basic component of this portion, the ECU 50 O ₂ sensor 2
Feedback control means 61 for inputting a signal from
An injection amount / injection timing calculating means 62 for calculating a fuel injection amount and an injection timing by the injector 6; converting the injection amount calculated by the calculating means 62 into a pulse width of the injection pulse; Calculation means 62
Injection pulse output means 63 for outputting to the injector 6 at the time calculated in the above, divided injection means 64 for dividing and executing the fuel injection in a predetermined operation region, and injection characteristic learning for performing learning control of the injection characteristic of the injector 6 Means 65.

Among these means, first, the feedback control means 61 determines the fuel injection amount based on the signal from the O ₂ sensor 22 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio when a predetermined feedback condition is satisfied. Perform feedback control. That is, when the signal from the O ₂ sensor 22 indicates that the air-fuel ratio is rich, the fuel injection amount is reduced, and the signal from the sensor 22 indicates that the air-fuel ratio is lean. If so, a feedback correction amount is calculated according to a predetermined arithmetic expression so as to increase the fuel injection amount, and this is output to the injection amount / injection timing calculating means 62.

The injection amount / injection timing calculating means 62
The basic injection amount corresponding to the operating state at that time is read from a preset map, and the target injection amount is calculated from the basic injection amount, the feedback correction amount sent from the feedback control means 61, and other various correction amounts. Is calculated, and the injection timing corresponding to the operating state at that time is calculated from a map set in advance. in this case,
The injection amount / injection timing calculating means 62 sets the injection timing in the latter half of the compression stroke so as to execute stratified combustion, for example, in the low-load low-rotation side region, and sets the target injection so that the air-fuel ratio becomes lean. In the high-load and high-speed regions, the injection timing is set to the intake stroke so that uniform combustion is performed, and the target injection amount is set so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. I do.

The injection pulse output means 63 converts the target injection amount calculated as described above by the injection amount / injection timing calculating means 62 into a pulse width, and uses the injection pulse of the pulse width as a drive signal. , And outputs it to the injector 6 at a timing corresponding to the injection timing calculated by the injection amount / injection timing calculation means 62. In this case, the injection pulse output unit 63 converts the target injection amount into a pulse width based on the injection characteristics for each injector 6 learned and stored by the injection characteristic learning unit 65.

On the other hand, the split injection means 64 splits the fuel injection into a plurality of times in a specific operation region in the region where the feedback control is performed, for example, when the engine is half warmed up. . This division of the fuel injection is performed by dividing an injection pulse having a pulse width corresponding to the target injection amount into a plurality of pulses and outputting the divided pulses to the injector 6 at different times. In this embodiment, FIG. As shown in the figure, the injection pulse having a pulse width corresponding to the target injection amount is divided into １ ／, and the first injection pulse PL is divided into the second injection pulse PT at a predetermined timing in the first half of the intake stroke.
At the predetermined time in the first half of the compression stroke.

Further, at a predetermined time during the feedback control for setting the air-fuel ratio to the stoichiometric air-fuel ratio as described above, the injection characteristic learning means 65 and the target injection amount including the feedback correction amount and the like, and the output injection pulse The pulse width is sampled, and the injection characteristics as shown in FIG. 11 described above are learned for each injector 6 based on these values. In particular, the divided injection means 64 performs the divided injection. At this time, data on the injection amount for the divided pulse width is collected from the pulse width of each divided injection pulse and the fuel injection amount at that time.

Further, the ECU 50 includes an ISC control means 66 for controlling the ISC valve 20 in connection with learning control of the injection characteristics of the injector 6, and an ignition timing of the ignition plug 5 for performing the learning control with high accuracy. And an ignition timing correcting means 67 for correcting and controlling the ignition timing.

Among them, the ISC control means 66 controls the opening of the ISC valve 20 while detecting the engine speed calculated based on the crank angle signal from the crank angle sensor 53 when the throttle valve 17 is fully closed and idling. The idle rotation speed is maintained at the target rotation speed by adjusting the degree and controlling the amount of intake air from the bypass passage 19.

The ignition timing correcting means 67 improves the accuracy of the learning control by always performing the learning control under the same combustion temperature.
The ignition timing is corrected based on the amount of intake air indicated by the signal from the engine, the coolant temperature indicated by the signal from the water temperature sensor 54, and the like. In this case, in this embodiment, as shown in FIG. 5, the control is performed within a certain range centered on the reference ignition timing set further on the retard side than the retard MBT on the maximum torque generation timing.

Next, the specific operation of the injection characteristic learning control of the injector 6, particularly the learning control of the injection characteristic in the minute pulse width region including the ignition timing correction control, will be described with reference to the flowchart shown in FIG.

In this control, first, at step S1, the engine speed calculated based on the crank angle signal from the crank angle sensor 53, the throttle opening detected by the throttle opening sensor 52, and the water temperature sensor 54 detect the engine speed. The cooling water temperature, the air-fuel ratio detected by the O ₂ sensor 22, and the like are read.

Next, in step S2, it is determined whether or not the engine is in a warm-up state (including a semi-warm-up state) based on the cooling water temperature.
In S3, it is determined whether the air-fuel ratio is in a region where the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.
It is determined whether or not feedback control for controlling the air-fuel ratio to the stoichiometric air-fuel ratio is being performed.

If feedback control is being performed,
In step S5, it is determined whether or not the vehicle is in an idle state with no load and low rotation. If the vehicle is in the idle state, it is further determined in step 6 whether or not the learning control can be performed. This determination is made based on, for example, whether or not the vehicle is in a steady operation state in which the intake air amount is stable. That is, it is difficult to perform accurate learning control during a transition in which the amount of intake air is changing, so that learning control is performed only during steady operation. Other conditions are added as needed.

If it is determined that the learning control can be executed as a result of each of the above determinations, then, as step S7, the divided injection is performed at a division ratio of 50%: 50%. That is, during the normal feedback control, the feedback correction amount is calculated according to the output of the O ₂ sensor 22, the target injection amount is obtained from the feedback correction amount and the basic injection amount, etc., and the target injection amount and the injector The pulse width of the injection pulse is obtained from the injection characteristic of the above or the conversion coefficient based on this characteristic. During the learning control in the idle state, this pulse width is divided into two by the above division ratio, and the divided pulse width is divided into two. The injection pulse is output as the first-stage injection pulse PL and the second-stage injection pulse PT at a predetermined timing in the first half of the intake stroke and a predetermined timing in the first half of the compression stroke shown in FIG.

In step S8, the ISC valve 2
The idle speed control by 0 is executed. As described above, this control is performed to maintain the idle speed at the target speed in response to an external load acting on the engine. Assuming that an external load such as a compressor for an air conditioner is applied to the engine, the ISC valve 20 is opened to maintain the idle speed at the target speed in response to the external load. Alternatively, control is performed to increase the degree of opening, whereby the amount of intake air from the bypass passage 19 to the combustion chamber 4 is increased, as indicated by reference character A in FIG. At this time, the fuel injection amount is also increased by the operation of the feedback control for maintaining the air-fuel ratio at the stoichiometric air-fuel ratio, as shown by reference numeral A in FIG.

Further, in step S9, ignition timing correction control for keeping the combustion temperature constant during the learning control is performed. In this control, for example, as described above, when an external load acts on the engine and the intake air amount and the fuel injection amount are increased accordingly, the combustion temperature rises, but this rise in combustion temperature is offset. Then, in order to keep the combustion temperature substantially constant, the ignition timing is corrected to the retard side.

That is, as shown in FIG. 8, the engine tends to decrease the maximum combustion temperature when the ignition timing is retarded. Therefore, when the external load acts or increases, the ignition timing is retarded according to the increase in the intake air amount accompanying the control of the ISC valve 20, for example, as shown in FIG.
As shown in FIG. 9, the ignition timing is read from a map set in advance, and the retard amount according to the water temperature is read from the map shown in FIG. 9, and the ignition timing retarded according to the intake air amount and the water temperature at that time. Is calculated, and the ignition plug 5 is ignited at the retard-corrected ignition timing, as shown by reference numeral c in FIG.

As a result, the increase in the combustion temperature due to the increase in the external load is offset by the retard correction of the ignition timing, and as shown by reference numeral d in FIG. 7, the combustion temperature is substantially the same as that before the action of the external load. It is to be maintained. When the external load is released, the ignition timing is returned to the reference ignition timing.

Then, in step S10, data on the feedback control and the split injection as described above, specifically, the pulses of the split injection pulses PL and PT corrected to control the air-fuel ratio to the stoichiometric air-fuel ratio. The width and the actually injected fuel amount calculated based on the intake air amount indicated by the signal from the air flow sensor 15 are sampled. Further, in step S11, the average value of a plurality of sampling data of the injection amount is sampled. By dividing by 2,
The fuel injection amount corresponding to the pulse width of the divided injection pulses PL and PT is calculated.

As a result, even though the total injection amount is relatively large, the injection amount of each divided injection becomes small, and the correspondence between the pulse width and the injection amount in the small pulse width region P2 shown in FIG. 11 is obtained. Become.

In particular, when learning the injection characteristics in the minute pulse width region P2 by the split injection, as described above, the control for maintaining the combustion temperature constant irrespective of the effect of the external load by the ignition timing correction control is performed. Since this is performed, erroneous learning due to a change in combustion temperature is avoided. That is, when the combustion temperature changes, as described above,
As the temperature of the injector tip also changes and the fuel passage area at the time of valve opening changes, the injection amount for the same pulse width is not constant. Is kept constant, the same injection amount is obtained for the same pulse width, and accurate learning data is collected.

The injection characteristics of each injector 6 in the minute pulse width region obtained as described above are obtained by setting the air-fuel ratio to lean and stratifying in the low-load low-speed region where fuel is injected during the compression stroke. This is reflected during the combustion operation, and the fuel control during the stratified combustion operation is performed accurately.

When the injection pulse division ratio is 50%: 50% as in this embodiment, the divided 2
Since the two injection pulses have the same injection amount range, the injection characteristics in the small pulse width region can be accurately obtained.

Further, since the first injection pulse PL and the second injection pulse PT of the divided injection are output respectively in the first half of the intake stroke and the first half of the compression stroke, as shown in FIG. And the time interval is relatively long, and therefore, as described above, both injections are performed under the same conditions with respect to the in-cylinder pressure and the needle valve temperature, so that accuracy is improved. Good learning data will be obtained.

In this embodiment, since the learning control is performed at the time of idling in the warm-up state or the half-warm-up state, the fuel injection amount is small and stable, and the time between each injection is small. The learning data is collected in a state where the interval is long, and accurate data is collected.

Note that any of the divided injections may be performed during the intake stroke. In this case, the fuel is sufficiently vaporized and atomized during the learning control in a region where the fuel injection amount is relatively large. The learning data is collected under a good combustion state.

Further, in this embodiment, the ignition timing is corrected within a certain range around a reference ignition timing set further on the retard side than the retard MBT of the maximum torque generation timing, that is, the fluctuation of the idle speed. Is performed in the region with the least number, so that accurate learning data can be obtained.

The range of correction of the ignition timing is as follows.
If it is performed within a certain range including the maximum torque generation timing and centering on the reference ignition timing set on the retard side of that timing, this range is a range where the change of the combustion temperature appears relatively sensitive to the change of the ignition timing. Therefore, the combustion temperature can be appropriately and accurately controlled by controlling the ignition timing, and as a result, highly accurate learning data is collected.

[0077]

As described above, according to the present invention, a lean operation region in which the air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio is provided in the low load region, and O ₂ is provided in the predetermined operation region.
In an engine in which feedback control for controlling the air-fuel ratio to a stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio based on a signal from a sensor is performed, divided injection is performed by dividing fuel injection into a plurality of times during execution of the feedback control. By learning the correspondence between the pulse width and the injection amount in the minute pulse width region of the injector by doing, and during the learning control, the combustion temperature is kept almost constant by the ignition timing correction control, In the meantime, even if the intake air amount or the fuel injection amount changes due to an external load or the like, the combustion temperature is kept constant, and the same injection amount can be obtained for the same pulse width. As a result, the injection characteristics of the injector in the minute pulse width region are accurately grasped, and the injector is operated with the air-fuel ratio set leaner than the stoichiometric air-fuel ratio by controlling the injection amount of the injector based on this characteristic. Fuel control is performed with high accuracy during stratified charge combustion operation or the like.

In this case, if divided injection of fuel for learning is performed in the first half of the intake stroke and the latter injection in the first half of the compression stroke, the in-cylinder pressure is substantially equal and the divided fuel is divided. The time interval of each injection performed can be widened, so that accurate learning data can be obtained.

Further, if this learning control is performed in a steady operation region at a low load and a low rotation speed in a warm-up state or a half-warm-up state, particularly at idle in a no-load state, more accurate learning control is performed. Data will be collected.

Further, if the ignition timing is corrected within a certain range centered on the reference ignition timing set further on the retard side than the MBT on the retard side of the maximum torque generation timing, the rotation fluctuation during idling is minimized. The ignition timing correction control is performed in the region, the learning control is performed under a more stable combustion temperature, and the retard is set to the retard side within a certain range including the maximum torque generation timing. If the ignition timing is performed centering on the reference ignition timing, the combustion temperature can be more appropriately and accurately controlled by the correction of the ignition timing, and similarly accurate learning data can be obtained.

If all of the divided injections are performed during the intake stroke, the fuel is sufficiently vaporized and atomized during the learning control in the region where the fuel injection amount is relatively large, and good combustion is achieved. Learning data will be collected under the state.

As described above, the injection characteristics in the minute pulse width region of the injector are accurately grasped, so that the fuel control during the stratified combustion operation with a lean air-fuel ratio is performed accurately. As a result, the fuel efficiency is further improved.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of the engine.

FIG. 3 is a block diagram illustrating a configuration of a main part of a control unit.

FIG. 4 is a diagram showing the timing of split injection.

FIG. 5 is a diagram showing a range of ignition timing correction control.

FIG. 6 is a flowchart showing an operation of learning control of injection characteristics.

FIG. 7 is a time chart showing changes in data when an external load is applied during learning control.

FIG. 8 is a diagram showing a change in combustion temperature due to retard control of the ignition timing.

FIG. 9 is a map of an ignition timing retard amount with respect to an intake air amount.

FIG. 10 is a map of a water temperature correction coefficient of the ignition timing retard amount.

FIG. 11 is a view showing injection characteristics of an injector.

FIG. 12 is a sectional view of a main part showing a configuration of an injector.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 5 Spark plug 6 Injector 22 O ₂ sensor 50 Control unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeo Yamauchi 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Masayuki Tetsuno 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Stock F-term in the company (reference) PA11Z PD03A PD03Z PE01Z PE03Z PE08Z PF03Z PF11Z

Claims (11)

[Claims] 1. An injector for directly injecting fuel into a combustion chamber, and injector driving means for converting a fuel injection amount from the injector into a pulse width of a drive signal and outputting the pulse width to an injector, and in a low load region. A control device for a spark ignition type direct injection engine provided with a lean operation region in which an air-fuel ratio is set to be leaner than a stoichiometric air-fuel ratio, and a signal from an O ₂ sensor for detecting a residual oxygen concentration in exhaust gas Feedback control means for controlling the air-fuel ratio to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio by controlling the fuel injection amount by the injector based on In the region, the fuel injection by the injector is performed in a plurality of times during a period from the intake stroke to the compression stroke. Split injection means, learning means for learning the correspondence between the pulse width and the fuel injection amount for one injection based on the control amount by the feedback control means when performing the split injection by the means, An ignition timing correction means for correcting the ignition timing so that the combustion temperature is kept substantially constant while learning is performed by the means. 2. The control apparatus according to claim 1, wherein the ignition timing correction means corrects the ignition timing to the retard side when the intake air amount increases. 3. The spark ignition type direct injection system according to claim 1, wherein the split injection means splits the fuel injection by the injector into a first half of an intake stroke and a first half of a compression stroke. Control unit for injection engine. 4. The spark-ignition direct-injection engine according to claim 1, wherein the specific operation region is a steady operation region in a low-load low-rotation region in which the engine temperature is equal to or higher than a predetermined temperature. Control device. 5. The control device according to claim 4, wherein the low-load low-rotation range is a no-load low-rotation range. 6. An external load increase detecting means for detecting an increase in an external load acting on the engine in a no-load, low-speed region, wherein the ignition timing correction means performs combustion when the increase in the external load is detected by the means. 6. The control apparatus for a spark ignition type direct injection engine according to claim 5, wherein the ignition timing is corrected so as to keep the temperature substantially constant. 7. The correction of the ignition timing by the ignition timing correction means in the no-load, low-rotation region is performed within a certain range around a reference ignition timing set further on the retard side than the retard side MBT of the maximum torque generation timing. The control device for a spark ignition type direct injection engine according to claim 5, wherein the control is performed by: 8. The control of a spark ignition type direct injection engine according to claim 1, wherein the correction of the ignition timing by the ignition timing correction means is performed within a certain range including the maximum torque generation timing. apparatus. 9. The spark-ignition direct-injection engine according to claim 8, wherein the correction of the ignition timing by the ignition timing correction means is performed centering on the reference ignition timing set on the retard side of the maximum torque generation timing. Control device. 10. The spark-ignition direct-injection engine control according to claim 1, wherein the split injection means performs fuel injection by the injector in a plurality of times during the intake stroke. apparatus. 11. The stratified combustion operation region in which the lean operation region in which the air-fuel ratio is controlled to a lean operation is a stratified combustion operation region in which fuel is supplied to the vicinity of the ignition plug and burned in the compression stroke. Item 3. A control device for a spark ignition type direct injection engine according to Item 2.