JP2959748B2 - Combustion control method for in-cylinder injection engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control method for an in-cylinder injection engine in which fuel is directly injected into a cylinder and burned by spark ignition, and more particularly to a cylinder for improving combustion controllability at a lean air-fuel ratio. The present invention relates to a combustion control method for an internal injection engine.

[0002]

2. Description of the Related Art Generally, in a direct injection engine in which fuel is directly injected into a cylinder and burned by spark ignition,
Many employ a stratified combustion method. In this stratified combustion system, fuel is injected late in the compression stroke to stratify the air-fuel mixture of fuel and air to ignite a relatively rich air-fuel mixture near the spark plug. Driving at a fuel ratio becomes possible, and low fuel consumption can be realized.

[0003] However, the formation of the air-fuel mixture in the stratified combustion system is greatly affected by the spray characteristics such as the injection rate of the injector and the spray angle, and as shown in FIG. May be unburned because it is too lean, leading to an increase in unburned hydrocarbon (HC) emissions. Also, as shown in FIG. 19, when the fuel injection amount is large, the initial combustion becomes active and the first half of the heat generation pattern tends to be large, and the burned gas burned in the first half is compressed in the second half, and the nitrogen oxide ( NOX) tends to occur.

Further, in the stratified combustion system, the exhaust gas temperature is significantly higher than that of the conventional engine due to the high thermal efficiency, the reduction of heat loss to exhaust gas, and the large amount of heated air per unit fuel. In particular, in a low load region including idling, the temperature falls below the lower limit temperature of the catalyst which is matched based on the exhaust gas temperature of the conventional engine, and as a result, the exhaust gas purification performance deteriorates. There is a risk.

To solve the problem of the decrease in exhaust gas temperature in the direct injection engine, Japanese Patent Laid-Open No. 4-183922 discloses that a second fuel injection is performed in an expansion stroke or an exhaust stroke in addition to a normal fuel injection. A technique has been disclosed in which exhaust gas temperature is increased by re-ignition to activate a catalyst.

[0006]

However, in the above-mentioned prior art, since it is necessary to perform ignition twice in one cycle, not only the consumption of ignition energy is increased, but also the first fuel injection and the normal fuel injection are performed. After the main combustion by ignition is completed, the second fuel is re-injected in the expansion stroke or the exhaust stroke, and then re-ignition is performed in the exhaust stroke, so that there is an interval between the first main combustion and the second re-combustion. In addition, it is difficult to form an ignitable air-fuel mixture in the vicinity of the ignition plug due to a decrease in the temperature of the in-cylinder gas, so that the possibility of occurrence of ignition failure in the second ignition increases, and the combustion controllability deteriorates.

[0007] In this case, if an abnormal situation occurs in which the fuel is not burned by the second injection, raw gas is released and the durability of the catalyst is remarkably reduced.
Exhaust emissions can be significantly worse.

The present invention has been made in view of the above circumstances, and improves the combustion controllability at a lean air-fuel ratio, eliminates the unburned region at the end of the air-fuel mixture, improves combustion efficiency, improves exhaust emissions, and improves exhaust gas temperature. It is an object of the present invention to provide a method for controlling combustion in a direct injection engine, which can activate and maintain the catalyst at an early stage due to a rise in the temperature.

[0009]

According to the first aspect of the present invention,
Main combustion is performed based on engine speed and engine load.
When setting the main injection amount that determines the injection amount of the main fuel for
In both cases, the flame spread from the burned part by the main fuel
Setting the amount of auxiliary fuel injection that can be burned by
The main fuel according to the main injection amount is supplied to the intake stroke or the compression stroke.
It was injected into the cylinder in this the procedure Ru main fuel is burned by spark ignition, then, the engine speed of the auxiliary fuel by the injection amount during the expansion stroke due to combustion of the main fuel
And injecting at least one or more the cylinder according to the engine load, characterized in that a procedure for burning the unburned gas by the flame propagation from the burned portion.

According to a second aspect of the present invention, the engine speed and
Primary fuel for performing main combustion based on engine load
In addition to setting the first injection amount that determines the injection amount of fuel,
An amount of the second fuel that can be burned by the flame propagation from the burning part
Setting a second injection amount that determines the injection amount of
Injection stroke or compression stroke of the first fuel by one injection amount
Was injected into the cylinder in, ignitable and procedures for burning the first fuel by the spark ignition, then a burning late in the expansion stroke due to combustion of the first fuel by flame propagation from the burned portion Time, the second injection amount
The second fuel injected into the cylinder that is characterized that you and a procedure for burning unburned gas.

According to a third aspect of the present invention, the engine speed and
Primary fuel for performing main combustion based on engine load
In addition to setting the first injection amount that determines the injection amount of fuel,
Second and third quantities that can be burned by flame propagation from the firing part
Set the second and third injection amounts to determine the fuel injection amount
And injecting the first fuel based on the first injection amount into the cylinder during the suction stroke or the compression stroke .
Of the procedure Ru is burned by spark ignition of the fuel, then the time can be ignited by flame propagation from a combustion late combusted portion of the expansion stroke due to combustion of the first fuel,
The second fuel by the second injection amount is injected into the cylinder, the procedure Ru is afterburning, the combustion late reburning according to the second fuel in the expansion stroke, the flame propagation from the burned portion the ignitable period, the third fuel by the third injection amount is injected into the cylinder, and a procedure for burning unburned gas
Characterized by comprising. The invention according to claim 4 is characterized in that
The activity of the catalyst when the engine operating condition is in the low engine load and low engine speed range
Procedures for determining whether an area is difficult to
When the operating condition is in the region where catalyst activation is possible
Selects one fuel injection per cylinder per cycle,
Operating state based on engine speed and engine load
1 combustion per cycle per normal cylinder
The amount of fuel injection is set, and the amount of fuel
Inject into the cylinder during the intake or compression stroke,
When it is possible to ignite the mixture by the above fuel injected into the cylinder
Of ignition during the period and the engine operating condition
When it is in the region where the shift is difficult,
Select multiple fuel injections and reduce the amount
And the main injection amount for performing main combustion, and the main injection amount
Fire from the burned part due to the main injection fuel
The second or second time the amount that can be burned by flame propagation
Subsequent injection amounts are referred to as engine speed and engine speed, respectively.
It is difficult to set based on the load and activate the catalyst
The main injection amount when
During the stroke or compression stroke, fuel is injected into the cylinder,
Ignition is performed when it is possible to ignite the air-fuel mixture
Then, in the later stage of combustion in the expansion stroke,
At the time when ignition is possible by flame propagation, the second injection
Inject fuel by the amount of injection, or the amount of injection after the second time
And characterized in that a procedure for sequentially injecting fuel by
I do. The invention described in claim 5 is the same as the invention described in claim 4.
And the plurality of times is three or more times, and one cycle per cylinder
When multiple fuel injections are selected per
The main fuel injection amount is smaller than the normal fuel injection amount.
The injection quantity and the main injection fuel which is smaller than the main injection quantity and which
Of the amount that can be burned by flame propagation from the burned part
The injection amounts for the second and third injections are
Set based on gin speed and engine load.
In the later stage of the expansion stroke due to the combustion of the injected fuel,
When ignition is possible due to flame propagation from the combustion section, the above
Inject the fuel according to the second injection amount, and further expand the same
When ignition is possible within the stroke due to flame propagation from the burned part
Fuel in the third and subsequent injection quantities during the
And features. The invention according to claim 6 is an engine rotation
One cylinder according to operating condition based on number and engine load
Set the amount of main injection appropriate for one combustion per cycle.
The main injection amount of fuel in the intake stroke or
During the compression stroke, fuel is injected into the cylinder,
The ignition at a time when the mixture can be ignited.
The activity of the catalyst when the engine operating condition is in the low engine load and low engine speed range
Procedures for determining whether an area is difficult to
When the operating condition is in the area where catalyst activation is difficult
Selects two fuel injections per cylinder per cycle,
Furthermore, the flame propagation from the burned part by the main injection fuel
Therefore, the second injection amount of the combustible amount is set, and
In the later stage of the expansion stroke due to the combustion of the main injection fuel,
At the time when ignition is possible by flame propagation from the burned part,
A procedure for injecting fuel according to the second injection amount.
It is characterized by. The invention according to claim 7 is an engine
Operating conditions based on engine speed and engine load.
Amount of main injection appropriate for one combustion cycle per cylinder
The procedure for setting the amount and the fuel for the main injection amount
Alternatively, the main injection is performed by injecting into the cylinder during the compression stroke.
Procedure to ignite when it is possible to ignite the fuel-air mixture
When the engine operating condition is
Procedure to determine whether the medium is in an area where activation is difficult
Engine operating conditions are in areas where catalyst activation is difficult.
The exhaust temperature rise based on the engine operating conditions.
The target exhaust temperature as target value to set, the target exhaust temperature
A procedure for comparing with the predetermined temperature,
Over two degrees, two fuels per cylinder per cycle
Injection is selected, and the burned part by the main injection fuel
Second injection of an amount that can be burned by flame propagation
Volume during the expansion stroke due to the combustion of the main injection fuel.
Ignition due to flame propagation from the burned part at the later stage of combustion
Inject fuel at the second injection amount when possible
And when the target exhaust temperature falls below a predetermined temperature.
Select the ignition timing retard correction and select the main injection fuel
To retard ignition timing and correct ignition timing
And a sequence. Claim 8
Corresponds to one cycle per cylinder in the invention of claim 7.
Or when two fuel injections are being performed or ignition
Exhaust gas temperature may be
Detect and compare the exhaust gas temperature with the target exhaust temperature
Procedure and execution of fuel injection twice per cylinder 1 cycle
If the exhaust gas temperature has not reached the target exhaust temperature
If not, the second injection amount is increased, while
Exhaust gas temperature can be monitored during ignition timing retard correction.
When the target exhaust temperature has not been reached,
Procedures for further retarding the injection timing and ignition timing
It is characterized by being prepared for. The invention according to claim 9 is
Adapts to operating conditions based on engine speed and engine load.
The amount of main fuel appropriate for one combustion per cylinder per cycle
Procedure for setting the injection amount, and injecting the fuel of the main injection amount
During the stroke or compression stroke, fuel is injected into the cylinder,
Hand that ignites when it is possible to ignite the fuel-air mixture
And the target value of the exhaust gas temperature rise based on the engine operating condition.
Procedure for setting the target exhaust gas temperature and starting the engine
Procedure to determine whether the engine is running
Compares the target exhaust temperature with a first predetermined temperature and
Jin cold start determination procedure and engine cold start
When starting the engine except for the
Hand for comparing with a second predetermined temperature lower than the first predetermined temperature
Normally, during normal operation, the fuel
Are the conditions for performing three injections in order to suppress the cost rate?
The procedure for determining whether or not the engine
When three injections are performed during normal operation, one cylinder, one cylinder
Select three fuel injections per cycle and
Combustion by flame propagation from burned part by main injection fuel
Set the possible second and third injection quantities,
In the later stage of the expansion stroke due to the combustion of the main injection fuel,
At the time when ignition is possible by flame propagation from the burned part,
Inject the fuel according to the second injection amount, and then
Can be ignited by flame propagation from the burned part within the same expansion stroke
Procedure for injecting fuel with the third injection amount at a time when it is practicable
And the target at the start of the engine except for the cold start of the engine
When the exhaust gas temperature is equal to or higher than the second predetermined temperature or during normal operation
When the three-time injection condition is not satisfied, one cylinder and one cycle
2 fuel injections per fuel,
Of the amount combustible by flame propagation from the burned part
Set the second injection amount, and expand
In the late stage of combustion in the stretching process, flame propagation from the burned part
Therefore, when ignition is possible, the second injection amount
Fuel injection procedure and engine except cold engine start
At startup and the target exhaust gas temperature falls below the second predetermined temperature
Sometimes, the ignition timing retard correction is selected and the main injection
Retard fuel injection timing and retard ignition timing
And a procedure for performing the above steps.

[0012]

According to the first aspect of the present invention, the engine speed and
Injection of main fuel for main combustion based on engine load
In addition to setting the main injection amount that determines the injection amount, this main fuel
Of the amount that can be burned by flame propagation from the burned part
Set the injection amount of auxiliary fuel. And the main injection amount
The fuel injection into the cylinder in the intake stroke or compression stroke
The main fuel is burned by spark ignition to perform main combustion.
Let Then, above by the combustion of the main fuel during the expansion stroke
Engine auxiliary fuel by serial injection amount speed and the engine
Inject into the cylinder at least once according to the load, and
The unburned gas is burned by the flame propagation from the burning part .

According to the second aspect of the present invention, the engine speed
And a first for performing main combustion based on engine load.
Set the first injection quantity that determines the fuel injection quantity, and
By the propagation of flame from the burned part by the first fuel
The second injection amount that determines the amount of the second fuel that can be burned is
Set. Then, the first fuel based on the first injection amount
And injected into the cylinder in the intake stroke or compression stroke,
The first fuel is burned Ri by the spark ignition takes place the main combustion
Let Then, in the expansion stroke due to the combustion of the first fuel ,
In the later stage of combustion of the
At the time when a fire is possible, the second fuel based on the second injection amount is injected into the cylinder to burn unburned gas.

According to the third aspect of the present invention, the engine speed
And a first for performing main combustion based on engine load.
Set the first injection amount that determines the fuel injection amount, and
The second and third quantities that can be burned by flame propagation from the combustion section
The second injection amount and the third injection amount that determine the fuel injection amount of No. 3 are set.
Set. Then, the first fuel based on the first injection amount is
It was injected into the cylinder in the intake stroke or compression stroke, the <br/> first fuel to perform the main combustion is combusted Ri by the spark ignition
You. Then, in the expansion stroke due to the combustion of the first fuel ,
Ignition due to flame propagation from the burned part at the later stage of combustion
At a possible time, the second fuel based on the second injection amount is injected into the cylinder and re-burned. In addition, during this expansion stroke
Combustion late reburning by serial second fuel, the burnt portion
The third injection quantity at a time when ignition is possible by the flame propagation
The third fuel by then injected into the cylinder, combusting the unburned gases. According to the invention described in claim 4, the engine operating state
Has difficulty in activating the catalyst in the low engine speed and low speed range.
The engine operating condition is determined to be within the
When the engine is in the region where
Or select one fuel injection. And the engine rotation
Normal according to operating conditions based on the number and engine load
Fuel injection amount appropriate for one combustion per cylinder per cycle
Set the injection amount, and then inject the fuel of this injection amount into the suction stroke or pressure.
Injection into the cylinder during the contraction stroke
The ignition is performed when the mixture can be ignited. On the other hand,
When the engine operation is in the area where catalyst activation is difficult
Select multiple fuel injections per cycle per cylinder
I do. At this time, the fuel injection amount is smaller than the above-described fuel injection amount.
And the main injection amount for performing main combustion, and the main injection amount
Fire from the burned part due to the main injection fuel
The second or second time the amount that can be burned by flame propagation
Subsequent injection amounts are based on the engine operating conditions.
To set. Then, the fuel based on the main injection amount is sucked in.
Injection into the cylinder during the compression stroke or the compression stroke.
Ignition is performed when it is possible to ignite the mixture
After the later stage of combustion in the expansion stroke,
At the time when ignition is possible by flame propagation, the second injection
Inject the fuel by the amount, or to the injection amount for the second and subsequent injections
And then sequentially inject fuel. At this time, the invention described in claim 5
In the light, the above-mentioned plural times are three or more times,
State is in the area where catalyst activation is difficult and one cylinder, one cycle
When multiple fuel injections are selected per fuel,
Smaller than the fuel injection amount for one injection per cylinder cycle
And the main injection amount for performing main combustion, and the main injection amount
Fire from the burned part due to the main injection fuel
2nd and 3rd and subsequent times of the amount that can be burned by flame propagation
Set the descending injection amount based on the engine state
I do. In the expansion stroke due to the combustion of the main injection fuel,
In the later stage of combustion of the
When the fire is possible, inject fuel with the second injection amount
Fire, and flame propagation from the burned part within the same expansion stroke
Depending on the amount of injection from the third time on when ignition is possible
Inject fuel sequentially. According to the sixth aspect of the present invention,
Depending on operating conditions based on gin speed and engine load
The amount of main injection corresponding to one combustion per cylinder
By setting the injection amount, the fuel of this main injection amount is
Is injected into the cylinder during the compression stroke.
The ignition is performed at a time when the air-fuel mixture can be ignited. Ma
In addition, when the engine operating condition is
It is determined whether the medium is in an area where activation of the medium is difficult. Soshi
The engine operating condition is in an area where catalyst activation is difficult.
Fuel injection twice per cylinder per cycle
Selected and further fired from the burned part by the main injected fuel
Set the second injection amount that can be burned by flame propagation
In the later stage of combustion in the expansion stroke due to the combustion of the main injection fuel
When can be ignited by flame propagation from the burned part
Then, the fuel is injected by the second injection amount. Contract
According to the invention as set forth in claim 7, the engine speed and the engine load are reduced.
Per cylinder per cycle depending on operating conditions based on load
The main injection amount is set to an amount appropriate for one combustion, and
Injection of fuel into the cylinder during the intake or compression strokes.
To ignite the mixture by the main injection fuel
At the time, the ignition is performed. Also, if the engine
In areas where engine activation is difficult in low-load low-rotation range engines
It is determined whether or not there is. Then, the engine operation status
When the engine is in an area where activation of the medium is difficult,
Target exhaust temperature as target value of exhaust temperature rise based on state
Is set, and the target exhaust temperature is compared with a predetermined temperature. Soshi
When the target exhaust temperature is equal to or higher than a predetermined temperature,
Choose two fuel injections per cycle and
Combustion by flame propagation from burned part by main injection fuel
Set the possible second injection quantity and set the main injection fuel
Late combustion in the expansion stroke due to combustion
During the time when ignition is possible due to the flame propagation,
The fuel is injected according to the injection amount. On the other hand, the target exhaust temperature
If the temperature falls below the predetermined temperature, select the ignition timing retard correction.
To delay the injection timing of the main injection fuel and
The ignition timing is corrected for retard. At that time, the invention described in claim 8
Means that two fuel injections are performed per cylinder per cycle
Or the ignition timing is being retarded
When detecting the exhaust gas temperature, the exhaust gas temperature
Compare with target exhaust temperature. And one cylinder per cycle
The exhaust gas temperature rises during the execution of two fuel injections
If the target exhaust temperature has not been reached, the second injection
Increase the firing rate. On the other hand, under the execution of the ignition timing retard correction,
The exhaust gas temperature has not reached the target exhaust temperature
In this case, the injection timing and ignition timing of the main injection fuel are further delayed.
Correct the angle. According to the ninth aspect, the engine speed
And one cylinder 1 according to the operating state based on the engine load
Set the amount of main injection appropriate for one combustion per cycle
Then, the fuel of this main injection amount is supplied to the intake stroke or the compression stroke.
The fuel is injected into the cylinder at
Ignition is performed when it is possible to ignite. Also, engine
Target exhaust temperature as a target value
Set the air temperature and start the engine or normal operation
Judge. When starting the engine,
Engine cold start by comparing exhaust temperature with first predetermined temperature
Engine start except cold start
In some cases, the target exhaust temperature is further reduced to the first predetermined temperature.
Compare with a lower second predetermined temperature. On the other hand, normal operation
In some cases, the fuel consumption rate must be kept below the target exhaust temperature.
To judge whether it is in the condition to perform three injections
You. As a result of these judgments, when the engine is cold started, or
When three injections are performed during normal operation, one cylinder
Select three fuel injections per cycle and
Combustion by flame propagation from the burned part by main injection fuel
Set the second and third injection amount of bakeable amount,
In the latter stage of combustion in the expansion stroke due to the combustion of the main injection fuel.
Time that can be ignited by flame propagation from the burned part I
, The fuel is injected by the second injection amount,
Later, in the same expansion stroke, by flame propagation from the burned part
When the fuel can be ignited, the fuel is injected by the third injection amount.
Let Also, when starting the engine except for cold engine start
And when the target exhaust temperature is equal to or higher than the second predetermined temperature,
In normal operation, when the condition for performing three injections is not satisfied, one cylinder 1
Select two fuel injections per cycle and select the main injection
Combustible by flame propagation from burned part by fuel
The second injection amount is set, and the combustion of the main injection fuel is performed.
In the later stage of combustion in the expansion stroke due to
At the time when ignition is possible by flame propagation, the second injection
Inject fuel by volume. On the other hand,
Excluding when the engine is started and the target exhaust temperature is the second predetermined temperature
When the temperature falls below the degree, select the ignition timing retard correction,
The ignition timing is retarded while the injection timing of the main injection fuel is retarded.
Correct the retard angle.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 relate to a first embodiment of the present invention, FIG. 1 is a flowchart of a fuel injection setting routine, FIG. 2 is a schematic configuration diagram of an engine control system, FIG. 3 is a functional block diagram of an electronic control unit, and FIG. FIG. 5 is an explanatory view schematically showing a combustion process by two injections, FIG. 5 is an explanatory view schematically showing the relationship between heat generation pattern generation and NOX generation by two injections, and FIG.
FIG. 7 is an explanatory view of the conditions for performing the round injection, FIG. 7 is a timing chart of the fuel injection and ignition, and FIG.

In FIG. 2, reference numeral 1 denotes an in-cylinder injection engine for directly injecting fuel into a cylinder and burning an air-fuel mixture by spark ignition, and a throttle valve having a throttle valve provided in an intake system of the engine 1. Body 2 is interposed,
An air flow meter 3 is provided upstream of the throttle body 2.
The air cleaner 4 is attached via the air cleaner. On the other hand, the exhaust system of the engine 1 has a catalyst 5 for purifying exhaust gas.
The muffler 6 is attached downstream of the catalyst 5.

An injector 7 for directly injecting high-pressure fuel and a spark plug 8 face the combustion chamber of the engine 1. The injector 7 and the spark plug 8 are arranged in a positional relationship such that a relatively rich mixture is formed around the spark discharge portion of the spark plug 8 by the fuel injected from the injector 7 so as to be suitable for stratified combustion. Has been established.

The ignition plug 8 is connected to the ignition coil 1.
0 is connected to the secondary winding of the ignition coil 10 and an electronic control unit (EC
U) An igniter 11 driven and controlled by 20 is connected.

The ECU 20 includes a main processing unit CP
U21, a ROM 22 storing fixed data such as control programs and various maps, a RAM 23 storing data obtained by processing signals from the sensors and data processed by the CPU 21, and detecting an engine state. An input interface 24 for inputting signals from various sensors and an output interface 25 for outputting a control signal from the CPU 21 to various actuators are configured with a microcomputer connected to each other via a bus line 26 as a core. I have.

The input interface 24 includes the air flow meter 3, the throttle opening sensor 12 for detecting the opening of a throttle valve provided on the throttle body 2, and the crank angle sensor 13 for detecting the crank angle of the engine 1. A cylinder discriminating sensor 14 for discriminating a fuel injection and ignition target cylinder, a water temperature sensor 15 for detecting a cooling water temperature of the engine 1, an exhaust temperature sensor 16 for detecting an exhaust gas temperature immediately before the catalyst 5, and the like are connected. I have.

On the other hand, the igniter 11 is connected to the output interface 25, and the intake throttle actuator 17 and the injector 7 provided on the throttle body 2 are connected via drive circuits 29 and 30. .

The CPU 21 calculates various control amounts such as a fuel injection amount and an ignition timing based on various data stored in the RAM 23 in accordance with a control program stored in the ROM 22, and outputs corresponding signals to the injector 7. To the igniter 11 and the like to maintain the combustion state of the engine 1 in an optimum state.

In the combustion control of the engine 1, 1
Normal combustion control in which fuel injection and ignition are performed once per cycle, that is, fuel is injected once from an injector 7 into a cylinder in an intake stroke or a compression stroke, and a mixture of the fuel is discharged from a spark plug 8 from a spark plug 8. Under normal operating conditions, the first main fuel injected into a cylinder in a suction stroke or a compression stroke is ignited by spark discharge and burned under a predetermined operating condition. The auxiliary fuel is injected into the cylinder at least once during the expansion stroke due to the combustion of, and the unburned gas is burned by the flame propagation from the burned portion.

For example, when performing two fuel injections per cycle, the first fuel as the main fuel is burned by spark ignition, and in the later stage of the expansion stroke due to the combustion of the first fuel, The second fuel as the auxiliary fuel is injected into the cylinder at a timing at which it can be ignited by flame propagation from the burned portion without re-ignition. In the case of performing three fuel injections per cycle, the third fuel as the auxiliary fuel is similarly discharged from the already burned portion without re-ignition in the later stage of the reburning with the second fuel. The fuel is injected into the cylinder at the timing when it can be ignited by the flame transmission.

That is, as described above, in the case of a normal one-shot injection, the injection amount is relatively large from the viewpoint of the spray diffusion, and the spray diffusion becomes excessive and the terminal gas is too lean. (See FIG. 18), and when the first fuel injection amount is large, the heat generation pattern of the initial combustion is large, and nitrogen oxide (NOX) tends to be generated (see FIG. 19).

For this reason, in the normal combustion control, if the diffusion of the fuel spray is excessive and the end gas is expected to be too lean and many unburned parts are expected to be generated, the first main fuel to be burned by spark discharge is generated. The injection amount is slightly reduced, and then the second injection is performed in the later stage of the expansion stroke using the first main fuel.
Is injected into the cylinder to re-burn, and further, the third, fourth,... Fuel is injected within the expansion stroke according to the conditions.

[0027] Thus, as shown in FIG. 4, first by to the main combustion at rather low unburned area of the air-fuel mixture ends of the combustion non lean air-fuel ratio the fuel, further second fuel (or first (3rd, 4th,... Fuel) reburns the unburned gas remaining in the quench layer on the combustion chamber wall surface and the clevis formed between the piston and the piston ring and the cylinder wall surface. As shown in FIG. 5, NOx generation can be suppressed by suppressing heat generation in the first half,
Combustibility can be improved. That is, the combustion efficiency is improved, and the gas temperature at the latter stage of the combustion in the expansion stroke can be increased to maintain the activation of the catalyst 5.

The above EC for realizing the above combustion control
The functional configuration of U20 is shown in FIG. 3 and includes an engine speed calculating unit 51, a crank position detecting unit 52, and an operating condition detecting unit 5.
3, a combustion control function by an injection condition determining unit 54, a fuel injection amount setting unit 55, a fuel injection timing setting unit 56, an ignition timing setting unit 57, a fuel injection timing setting unit 58, an ignition timing setting unit 59, and driving units 60 and 61. Is realized.

An engine speed calculating section 51 calculates an engine speed N based on a signal from the crank angle sensor 13, and a crank position detecting section 52 outputs a signal from the crank angle sensor 13 and a signal from the cylinder discriminating sensor 14. The crank angle of each cylinder is detected based on the signals.

The operating condition detecting section 53 detects the engine load, terminates the fuel injection immediately before the ignition in the latter stage of the compression stroke, and ignites the air-fuel mixture around the spark discharge section of the spark plug 8 according to the engine load. Either stratified combustion in which a lean mixture in the combustion chamber is propagated by the ignited fire, or fuel is injected early in the intake stroke, uniformly mixed in the cylinder, and then ignited and burned Is determined. As the engine load, for example, a basic fuel injection amount Tp (Tp = K × Q) calculated from the intake air amount Q obtained from a signal from the air flow meter 3 and the engine speed N from the engine speed calculation unit 51. / N; K
Adopts a correction coefficient by the injector 7).

The injection condition determination unit 54 determines whether the current operating state requires a plurality of fuel injections, and sends the fuel injection amount setting unit 55 and the fuel injection timing setting unit 56 according to the determination result. Is output.

More specifically, as shown in FIG. 6, in an operation range determined by the engine speed N and the basic fuel injection amount Tp as the engine load, the exhaust gas temperature is determined only by the main combustion by the first fuel injection. A region where the activation of the catalyst 5 is low (for example, a low-speed and low-load region of stratified combustion) is experimentally specified in advance and stored in a map of the ROM 22, and by referring to this map, It is determined whether or not the current operation region satisfies the condition within the double injection execution region. After performing the second injection, the activation state of the catalyst 5 is determined from the exhaust gas temperature detected by the exhaust gas temperature sensor 16. It is determined whether or not the third, fourth,... Injections are necessary to maintain.

The fuel injection amount setting unit 55 sets a fuel injection amount according to the number of fuel injections per cycle instructed by the injection condition determination unit 54. In other words, when the fuel injection condition determination unit 54 instructs one fuel injection per cycle, the fuel injection amount Ti is set to an amount corresponding to the normal single combustion according to the operating state. The injection amount Ti is obtained, for example, by calculating the basic fuel injection amount Tp calculated by the operating condition detecting unit 53 by the throttle opening sensor 12,
Various increase correction amounts COEF based on various parameters indicating the operating state obtained by a signal from the water temperature sensor 15 and the like.
And the injector 7 that changes according to the battery voltage VB
Is set by correcting with the voltage correction amount TS for correcting the response delay time of the above.

When the injection condition determination unit 54 instructs two or more fuel injections per cycle,
A fuel injection amount slightly smaller than the fuel injection amount Ti is set as a first injection amount Ti1 for the first time of burning by spark discharge, and the second and subsequent fuel injection amounts Ti2, Ti2,
Ti3,... Are set to an amount that can be ignited by the flame propagation from the burned part.

The first injection amount Ti1 is determined, for example, by an experiment or the like in advance with respect to an operation region determined by the basic fuel injection amount Tp and the engine speed N so that the diffusion of the fuel spray and the heat generation rate become optimum. Find it and store it in the map,
It is set by referring to this map. The second and subsequent injection amounts Ti2, Ti3,... Are amounts that can be burned by the flame propagation from the burned portion, for example, the first injection amount Ti1.
Is set to a predetermined ratio with respect to the third injection amount T
After i3, the second injection amount Ti2 is set to be equal to or slightly larger than the second injection amount Ti2.

In the fuel injection timing setting section 56, the operating condition based on the engine speed N and the basic fuel injection amount Tp is determined based on the combustion method determined by the operating condition detecting section 53 and the instruction from the injection condition determining section 54. In the case of normal fuel injection once per cycle, the injection timing T INJ according to the combustion method is used. In the case of n fuel injections per cycle, the first injection timing T INJ1 and the second injection timing T INJ are used. The subsequent second injection timing TINJ2, third injection timing TINJ3,.
Output to the fuel injection timing setting unit 58.

In this case, the first injection timing (TINJ, TI
NJ1) is determined as the injection start timing in the case of the uniform combustion system, and as the injection end timing in the case of stratified combustion, and the second and subsequent injection timings TINJ2, TINJ3,.
For the operating condition based on the basic fuel injection amount Tp and the basic fuel injection amount Tp, the injection timing at which the n-th injected fuel is reliably ignited by the flame propagation of the burned portion is set, for example, by referring to a map.

For example, in the case of performing two fuel injections per cycle, in order to burn the fuel from the second injection without re-ignition in the latter half of the original first combustion, as shown in FIG. The injection start timing of the second fuel injection may be in a range of approximately 10 ° to 80 ° after the top dead center. However, if the second injection timing is too close to the main combustion timing, smoke is generated due to insufficient fuel diffusion. On the other hand, if the second injection timing is too far from the timing of the main combustion, excessive diffusion of fuel not only causes insufficient exhaust gas temperature rise but also increases HC, NOX, etc., and deteriorates exhaust emission.

Therefore, the optimum injection timing within a range in which these are not deteriorated is specified in advance by an experiment using the engine speed N and the basic fuel injection amount Tp as parameters and stored in a map, so that the injection timing can be adjusted according to the operating conditions. Set the optimal injection timing. Although the optimum value of the injection timing is different in absolute value due to the difference between the engine specifications, the second cycle, the fourth cycle, etc., it can be qualitatively applied to all the in-cylinder injection engines. There is no need to relight the injected fuel.

In this embodiment, the optimum injection timing, the optimum injection timing of which has been confirmed by experiments, is shown in FIG. 7 for the second fuel injection from the initial stage to the middle stage of the expansion stroke of the main combustion. Thus, it is in the range of 30 ° to 60 ° after the top dead center. In the case of performing the third injection, the injection timing is set at a timing at which the fuel of the third injection is injected into the cylinder immediately before the end of the combustion by the second injection so that the fuel can be ignited. The injection timing for the third and subsequent injections is set at around 90 to 120 ° after the dead center, at a timing when the next fuel is injected into the cylinder immediately before the end of the combustion by the previous injection in the expansion stroke and ignition is possible. Is set.

In the ignition timing setting unit 57, the engine speed N and the basic fuel injection amount Tp from the operating condition detecting unit 53 are determined.
Is determined by referring to a map, for example, and a final ignition timing θIG is set by adding a water temperature correction advance value based on the cooling water temperature to the basic ignition timing θBASE.

The fuel injection timing setting section 58 converts the injection timing from the fuel injection timing setting section 56 into the injection timing detected by the crank position detection section 52 with respect to the reference crank angle position of the cylinder to be injected. A signal corresponding to the fuel injection amount from the fuel injection amount setting unit 55 is output to the injector 7 via the driving unit 60.

The ignition timing setting section 59 converts the ignition timing θIG from the ignition timing setting section 57 into an ignition timing with respect to the crank angle reference position of the cylinder to be ignited detected by the crank position detection section 52, and a corresponding signal Is output to the igniter 11 via the drive unit 61.

Next, the fuel injection setting process of the ECU 20 will be described.
This will be described with reference to the flowchart of FIG.

The fuel injection setting routine shown in FIG. 1 is executed, for example, at predetermined intervals. First, in step S51, the engine speed N and the basic fuel injection amount Tp as the engine load are read, and at the same time, The operation conditions are detected by reading the number of times of injection of. Then step
Proceeding to S52, it is determined whether or not the current operating condition satisfies the n-time injection execution condition.

In this case, if the previous injection is one normal injection per cycle, the current operation region is set within the two-injection execution region using the engine speed N and the basic fuel injection amount Tp as parameters. Is checked by referring to the map. If the injection has already been performed twice before, it is determined whether or not the third or later injection is necessary based on the exhaust gas temperature from the exhaust gas temperature sensor 16. Find out.

As a result, for example, in the case of high-load operation of uniform combustion, or in the case of stratified combustion, when two or more injections are not required as in high-speed, low-load operation, etc. In order to execute one fuel injection per cycle, the process proceeds from step S52 to step S53. On the other hand, when stratified combustion requires two or more injections, such as during low-speed / low-load operation, 1 The process proceeds from step S52 to step S55 to execute n fuel injections per cycle.

When fuel injection is performed once per cycle, in step S53, various increment corrections COEF based on engine operating state parameters based on signals from the throttle opening sensor 12, the water temperature sensor 15, and the like, and the battery voltage VB
The basic fuel injection amount Tp is corrected by the voltage correction amount TS based on the above, and the fuel injection amount Ti is set (Ti = Tp × COEF +
TS). Then, in step S54, the fuel injection timing TINJ is set according to the combustion method, and the routine exits.

In the case where fuel injection is performed twice or more per cycle, the first injection amount Ti1 at which the diffusion of fuel spray and the heat generation rate become optimum is set with reference to a map in step S55. The first injection amount Ti1 is multiplied by a predetermined ratio to set a second injection amount Ti2, a third injection amount Ti3,... That are combustible by the flame propagation from the burned portion.

In step S56, the first injection timing TINJ1 is set in the same manner as the normal stratified combustion injection timing TINJ, and the second and subsequent injected fuels are reliably ignited by the flame propagation from the burned portion. The second injection timing TINJ2,
.. Are set with reference to a map based on the engine speed N and the basic fuel injection amount Tp, and the routine exits.

When the above routine is completed, the first fuel injection amount and the injection timing set in step S53 or step S55 are set in the injection timer, and the timer is started based on the predetermined crank angle of the cylinder to be injected. Then, the first fuel is injected. Similarly, ignition is performed by an ignition timer that starts on the basis of a predetermined crank angle, and the mixture in the combustion chamber is ignited to start main combustion.

In this case, if two or more injections are performed under stratified combustion having good fuel economy and exhaust gas characteristics, the first
The injection amount Ti1 is injected in the latter stage of the compression stroke, and the second injection amount Ti2 is supplied into the cylinder at an optimum timing immediately before the end of the main combustion by the first injection, so that flame propagation from the main combustion can be performed without re-ignition. the second combustion is initiated me by the.
The second combustion is work to piston spent increase mainly the exhaust gas temperature without made little, if insufficient increase in the exhaust gas temperature in this second combustion, the same expansion The third injection amount Ti3 or later that is possible within the stroke is injected,
Reburning is continued by the propagation of the flame from the burned portion.

That is, in order to maintain the activity of the catalyst 5, a certain degree of exhaust gas temperature is required. Conventionally, when the exhaust gas temperature is low in a normal single injection, the fuel injection is delayed or the ignition timing is reduced. However, as shown by the broken line in FIG. 8, there have been problems such as that the exhaust gas temperature does not rise sufficiently and that the fuel efficiency deteriorates remarkably. .

However, in this embodiment, in addition to the main combustion by the normal fuel injection and ignition once per cycle, two or more fuel injections are further performed within the expansion stroke by the main combustion to perform the combustion already. Since the fuel is reburned by the flame transmission from the part, the controllability of the combustion can be improved. As a result, the exhaust gas temperature can be effectively raised and the catalyst 5 can be activated as shown by the solid line in FIG. 8, without increasing the generation of smoke and the increase of HC and NOx. You can get it.

In this case, the fuel after the second injection is not ignited by the ignition but is ignited by the flame propagation from the burned portion, so that it is not necessary to perform ignition twice or more in one cycle, and the ignition energy Can be surely reburned while suppressing the consumption of the fuel.

9 to 11 relate to a second embodiment of the present invention. FIG. 9 is a functional block diagram of an electronic control unit.
Is a flowchart of a main injection setting routine, and FIG.
It is a flowchart of an injection setting routine.

This embodiment is different from the above-described first embodiment by 1
After the normal fuel injection is performed once per cycle, when the exhaust gas temperature is low and activation of the catalyst 5 cannot be expected, the amount that can effectively increase the exhaust gas temperature while minimizing fuel consumption deterioration is minimized. The second fuel injection is added.

That is, in the present embodiment, the function of the ECU 20 is such that a function for controlling the second fuel injection is added to the function for controlling the normal fuel injection and ignition timing. As shown in FIG.
A main injection amount setting unit 55a and a main injection timing setting unit 56a as functions for setting the normal fuel injection times;
As a function for setting the second fuel injection, a second injection condition determination unit 54a, a second injection amount setting unit 55b, and a second injection timing setting unit 56b are added. Other configurations are the same as those in the first embodiment.

The main injection amount setting section 55a sets a normal fuel injection amount Ti per cycle as a main injection amount, and a normal injection timing TINJ corresponding to the main injection amount Ti as a main injection timing. It is set by the main injection timing setting section 56a.

The two-time injection condition determination unit 54a determines whether or not to perform the two-time injection in addition to the normal main injection. The two-time injection condition determination unit 54 in the first embodiment described above. It has the same function as the injection determination.

The second injection amount setting section 55b is a second injection amount setting portion that is capable of igniting by the main combustion flame propagation by the first main injection.
Although the injection amount Ti2 is set, the basic fuel injection amount Tp which is the base of the main injection amount Ti is different from that of the first embodiment.
Is set based on the second injection amount Ti2. The second injection timing TINJ2 corresponding to the second injection amount Ti2 is the second injection timing TINJ2.
The second injection timing T is determined by the injection timing setting unit 56b.
INJ2 is the same as the injection timing determined by the fuel injection timing setting unit 56 of the first embodiment.

The second injection amount Ti2 may be adjusted in an increasing direction with the minimum ignitable amount set in advance by, for example, experiments as a lower limit.

Hereinafter, the operation related to the double injection by the ECU 20 will be described with reference to the main injection setting routine of FIG.
A description will be given according to each flowchart of the first second injection setting routine.

First, in the main injection setting routine of FIG.
In step S101, the basic fuel injection amount Tp is read from a predetermined address in the RAM 23, and in step S102, the engine operation state parameters based on signals from the throttle opening sensor 12, the water temperature sensor 15, and the like are read.

Next, the process proceeds to step S103, and from the engine operating state parameters read in step S102,
After setting the various increase correction amounts COEF, in step S104, a voltage correction amount TS based on the battery voltage VB is set, and the process proceeds to step S105.

In step S105, the basic fuel injection amount Tp read in step S101 is multiplied by the various increase correction amounts COEF set in step S103, and the voltage correction amount TS set in step S104 is added. To set the main injection amount Ti (Ti = Tp × COEF + TS). Then, in step S106, the main injection timing TINJ is set according to the combustion method, and the routine exits.

In the second injection setting routine shown in FIG. 11, when the engine speed N and the basic fuel injection amount Tp as the engine load are read in step S151 to detect operating conditions, in step S152 the operating conditions are detected. It is checked whether or not satisfies the condition for performing the double injection. As previously mentioned,
Whether or not the condition for performing the two-time injection is satisfied is determined by using the engine speed N and the basic fuel injection amount Tp as parameters.
It is checked by referring to the map whether or not it is within the round injection execution area.

As a result, for example, in the case of high load operation of uniform combustion, or in the case where stratified combustion does not satisfy the conditions for performing the double injection as in the case of high rotation and low load operation, the routine exits the routine. When the injection is not performed twice and the conditions for performing the double injection are satisfied, such as during low-speed / low-load operation in stratified combustion, the above-described steps S152 to S153 are performed.
Then, the second injection amount Ti2 is set. Then, the process proceeds to a step S154, wherein the engine speed N and the basic fuel injection amount Tp
Based on the above, the optimum second injection timing TINJ2 is set by referring to the map, and the routine exits.

When the above routines are completed, the main injection amount Ti and the main injection timing TINJ are set in the injection timer, the timer is started based on the predetermined crank angle of the cylinder to be injected, and the first fuel injection is performed. . Similarly, ignition is performed by an ignition timer that starts on the basis of a predetermined crank angle, and the mixture in the combustion chamber is ignited to start main combustion.

Also in the present embodiment, when the condition for performing the two-time injection is satisfied under the stratified combustion having good fuel consumption and exhaust gas characteristics, the main injection amount Ti is injected in the latter half of the compression stroke, and the main injection amount Ti is injected by the main injection. At the optimal timing immediately before the end of the combustion, the second injection amount Ti2 is supplied into the combustion chamber, effectively raising the exhaust gas temperature to maintain the activation of the catalyst 5, and
Fuel economy degradation can be minimized.

FIGS. 12 and 13 relate to a third embodiment of the present invention. FIG. 12 is a functional block diagram of the electronic control unit, and FIG. 13 is a flowchart of an exhaust gas temperature raising routine.

In this embodiment, the combustion control is performed by selecting either the double injection or the ignition timing retard according to the operating conditions, and the exhaust gas temperature is raised. As shown in FIG.
In addition to the functional configuration of the ECU 20 in the second embodiment, a target exhaust gas temperature setting unit 71 is provided instead of the two-time injection condition determination unit 54a, and a temperature rise method selection unit 72 and an ignition timing retard unit 73 are added. Things.

The target exhaust gas temperature setting section 71 determines whether or not the current operating state is an operating region where activation of the catalyst 5 is not expected and a region where the exhaust gas temperature should be increased. If it is determined that it is the area to be exhausted, a target temperature for raising the exhaust gas temperature is set. For the target temperature (target exhaust temperature), a target value set in advance in consideration of the specifications of the catalyst 5 and the like is stored in, for example, a map or the like. The map is used to determine the engine speed N and the basic fuel injection amount Tp as parameters. And is output to the temperature rise method selection unit 72.

In the temperature rise method selection unit 72, the target exhaust temperature set by the target exhaust temperature setting unit 71 is set to 2
One of exhaust gas temperature rise due to multiple injections and exhaust gas temperature rise due to ignition timing retard is selected. For example, during idle operation, it has been experimentally confirmed that the exhaust gas temperature increasing effect is larger in the case of double injection than in the ignition timing retard, but the fuel consumption is worse in the case of double injection than in the ignition timing retard. Therefore, in order to achieve the maximum heating effect with the minimum fuel consumption, it is necessary to change the exhaust gas heating method according to the target exhaust temperature.

Therefore, the target exhaust temperature is compared with a predetermined temperature.
If the target temperature is relatively low, the ignition timing retard that can reduce the fuel consumption deterioration more than the two-time injection is selected, and if the target temperature is high, the two-time injection with a larger temperature increasing effect is selected. In the present embodiment, when the target exhaust gas temperature at the time of idling is about 300 ° C. or more, the exhaust gas temperature is selected by the ignition timing retard and the instruction output of the ignition timing retard is performed, and the target exhaust temperature exceeds 300 ° C. or more. In case 2
The exhaust gas temperature increase by the second injection is selected and the instruction output of the second injection is performed.

When the temperature rise method selection section 72 selects the exhaust gas temperature rise by two injections, as described in the second embodiment, the second injection amount setting section 55b
The second injection amount Ti2 and the second injection timing TINJ2 are set by the second injection timing setting unit 56b.

If the temperature rise method selection section 72 selects exhaust gas temperature rise by ignition timing retard,
The ignition timing retard unit 73 sets the ignition timing retard amount θRD with reference to an ignition timing retard correction map based on the engine speed N and the basic fuel injection amount Tp.
7 is output. It goes without saying that the main injection timing is also delayed at this time.

In this embodiment, after the main injection setting routine described in the second embodiment is executed, the exhaust gas temperature increasing routine shown in FIG. 13 is executed, and after the first main injection, two injections or ignition timing retards are performed. The exhaust gas temperature is increased.

In this exhaust gas temperature raising routine, when the operating conditions based on the engine speed N and the basic fuel injection amount Tp are detected in step S201, it is determined in step S202 whether or not the operating conditions are the exhaust temperature raising execution conditions. If NO, the routine is exited, and if YES, the process proceeds to step S203, where a map is referred to based on the engine speed N and the basic fuel injection amount Tp, and a target exhaust temperature is set according to the operating conditions.

Next, the process proceeds to step S204, where
It is determined whether or not the target exhaust gas temperature set in S203 is equal to or higher than 300 ° C.
Select multiple injections and if less than 300 ° C, step
Select ignition retard in S208.

If the double injection is selected in step S205, the second injection amount Ti2 and the second injection timing TINJ2 are set in steps S206 and S207, respectively, and the routine exits. In step S208, the ignition retard is set. If you select
In step S209, the ignition timing retard amount θRD is set, and the routine exits. When the ignition timing retard amount θRD is set, the main injection timing is naturally delayed.

In the present embodiment, since the optimum treatment for activating the catalyst is selected according to the operating conditions, the maximum exhaust gas temperature increasing effect can be obtained with the minimum fuel consumption, and the deterioration of the fuel efficiency can be minimized. Can be kept to a minimum.

In this embodiment, an example during idling operation has been described. However, even in operating conditions other than idling operation, the target exhaust temperature is set based on the engine speed N and the basic fuel injection amount Tp. The same processing is performed.

FIGS. 14 and 15 relate to a fourth embodiment of the present invention. FIG. 14 is a functional block diagram of the electronic control unit, and FIG. 15 is a flowchart of an exhaust gas temperature feedback routine.

This embodiment is different from the third embodiment in that the signal from the exhaust gas temperature sensor 16 is fed back and the second injection amount Ti2 and the ignition timing retard amount θRD are adjusted so that the exhaust gas temperature reaches the target exhaust gas temperature. Is to be corrected.

Therefore, in the present embodiment, as shown in FIG. 14, the actual exhaust gas temperature detected by the exhaust gas temperature sensor 16 and the target exhaust gas temperature set by the target exhaust gas temperature setting section 71 are different from those of the third embodiment. And outputs a deviation of the actual exhaust gas temperature from the target exhaust gas temperature. Based on the output from the comparison unit 74, the second injection amount Ti2 or the ignition amount in the second injection amount setting unit 55b is determined. The ignition timing correction amount θRD in the timing retard section 73 is adjusted.

In this embodiment, after the exhaust gas temperature raising routine (FIG. 13) described in the third embodiment is executed, the exhaust gas temperature feedback routine shown in FIG. 15 is executed. Give feedback to approach the target value.

That is, first, in step S301, it is checked whether or not the exhaust gas temperature is being raised. If the exhaust gas temperature is not being increased, the routine is exited. If the exhaust gas temperature is being increased, the process proceeds to step S302. Proceed to exhaust temperature sensor 16
The actual exhaust gas temperature is measured based on the signal from

Next, the routine proceeds to step S303, where it is determined whether or not the exhaust gas temperature measured in step S302 has reached the target exhaust temperature. If it has not reached, it is checked in step S304 whether or not what is selected as the exhaust gas temperature rise is injection twice.

If the two-time injection is selected, the second injection amount Ti2 is increased in step S305 to exit the routine. If the ignition timing retard is selected, the ignition timing is determined in step S306. The retard amount θRD is further retarded and the routine exits. Also at this time, the main injection timing is delayed according to the ignition timing retard amount.

As a result, the exhaust gas temperature can be quickly converged to the target value, and the exhaust gas temperature can be efficiently raised to activate the catalyst 5.

FIGS. 16 and 17 relate to a fifth embodiment of the present invention. FIG. 16 is a functional block diagram of an electronic control unit, and FIG. 17 is a flowchart of an exhaust gas temperature raising routine.

In this embodiment, after the second injection is performed, the third injection is further performed according to the activation state of the catalyst. The functional configuration of the third embodiment is different from that of the third embodiment described above. 75, third injection amount setting unit 76, third injection timing setting unit 77
In addition, the functions of the target exhaust gas temperature setting unit 71 and the temperature rise method selection unit 72 are slightly changed.

The catalyst activation determination section 75 determines whether or not the catalyst has reached the activation temperature based on a signal from the exhaust gas temperature sensor 16 and outputs the result to the temperature increase method selection section 72.

The target exhaust gas temperature setting section 71 sets the target exhaust gas temperature in accordance with the state at the time of starting and the state of normal operation. This target exhaust gas temperature is generally 400 ° C. or higher during cold start for early activation of the catalyst. On the other hand, in a normal case not during start, as described in the third embodiment, In consideration of the specifications of the catalyst 5, the engine speed N and the basic fuel injection amount Tp are stored in advance in a map or the like as parameters.

The temperature rise method selection unit 72 sets the target exhaust temperature set by the target exhaust temperature setting unit 71 to a first predetermined temperature,
Compared to the second predetermined temperature , 3
Times injection, double injection, selects what Re of the exhaust gas Atsushi Nobori by an ignition timing retard. In this embodiment, the target exhaust
Cold start at a temperature of 400 ° C. or more as the first predetermined temperature
When moving , select exhaust temperature rise by three injections, 400 °
Is less than C, as the second predetermined temperature, the fourth embodiment in the same <br/> like, 300 ° C what to the exhaust gas Atsushi Nobori by double injection and by an ignition timing retard exhaust gas Atsushi Nobori in the boundary Choose one.

That is, since the three-time injection is employed at the time of the cold start, the maximum exhaust gas temperature increasing effect can be obtained. In other cases, the fuel consumption can be improved by appropriately selecting the two-time injection and the ignition timing retard. The rate can be suppressed. In addition, even at normal time, even if the target exhaust temperature is the same, 2
In the case where fuel consumption is better when three injections are performed than three injections, three injections are selected. As a result, the fuel consumption rate can be reduced.

When the exhaust gas temperature increase by three injections is selected by the temperature increase method selection unit 72, the second injection amount setting unit 55b and the second injection timing setting unit 56b set the second injection amount setting unit 55b. In addition to the injection amount Ti2 and the second injection timing TINJ2, a third injection amount setting unit 76 and a third injection timing setting unit 77
Thus, the third injection amount Ti3 and the third injection timing TINJ3 are set, respectively.

In this case, the third injection amount Ti3 is equal to the above-described first injection amount Ti3.
As described in the embodiment, the second injection amount Ti2 is set to be equal to or slightly larger than the second injection amount Ti2.
Is that the fuel of the third injection is injected into the cylinder immediately before the end of the combustion by the second injection to ignite 90 to 12 after the top dead center.
It is set near 0 °.

In this embodiment, after the main injection setting routine described in the second embodiment is executed, the exhaust gas temperature increasing routine shown in FIG. 17 is executed, and the exhaust gas is discharged by one of three injections, two injections, and ignition timing retard. Perform gas heating.

That is, at step S401 in FIG. 17, when the engine speed N and the basic fuel injection amount Tp are read and the operating conditions are detected, at step S402 the water temperature is detected based on the signal from the water temperature sensor 15, and In S403, it is determined whether a start condition is satisfied.

If the starting condition is satisfied, the target exhaust temperature is set in step S404, and it is checked in step S405 whether the target exhaust temperature is 400 ° C. or higher. In this case, the process proceeds from step S403 to step S414 to set a target exhaust gas temperature.

If the target exhaust gas temperature is lower than 400 ° C. at the start in step S405 (normal start), it is checked in step S406 whether the target exhaust gas temperature is 300 ° C. or higher. As a result, when the temperature is 300 ° C. or more,
In step S407, two injections are selected, and steps S408, S409
Then, the second injection amount Ti2 and the second injection timing TINJ2 are set, respectively, and the process exits from the routine.
After selecting ignition retard in step S410, step S4
At 11, the ignition timing retard amount θRD is set, and the routine exits.

On the other hand, if the target exhaust gas temperature is 400 ° C. or higher (at the time of a cold start) in step S405, the process proceeds from step S405 to step S412, where the second injection amount Ti
2. After setting the third injection amount Ti3, in step S413, the second injection timing TINJ2 and the third injection timing TINJ3 are set and the routine exits.

As a result, the temperature of the exhaust gas can be rapidly and significantly increased at the time of a cold start, and the early activation of the catalyst 5 is promoted to greatly reduce the exhaust gas discharged without being purified before the activation of the catalyst. Can be reduced.

In the case of normal operation, the above steps
After setting the target exhaust temperature in S414, further in step S415,
Judgment is made as to whether or not the conditions for performing three injections to suppress the fuel consumption rate with respect to the set target exhaust temperature are satisfied.
If it is determined that the conditions for performing the second injection are satisfied, the process proceeds to step S412, and the second injection amount Ti2 and the third injection amount Ti3 are set. In step S413, the second injection timing TINJ2 and the third injection timing TINJ3 are set. Set and exit the routine.

On the other hand, if it is determined in step S415 that only the two injections are performed, that is, the condition for performing the three injections is not satisfied, the second injection amount Ti2 and the second injection amount Ti2 are determined in steps S408 and S409, respectively.
The injection timing TINJ2 is set and the routine exits. Thus, the fuel consumption rate can be suppressed while maintaining the activity of the catalyst.

[0108]

As described above, according to the present invention, it is possible to surely generate post-combustion without re-ignition following combustion by normal spark ignition, and to maintain the end of the air-fuel mixture at the lean air-fuel ratio. Excellent effects are obtained, such as elimination of the combustion region, improvement in combustion efficiency, improvement in exhaust emission, and early activation and maintenance of catalyst due to increase in exhaust gas temperature.

[Brief description of the drawings]

FIG. 1 is a flowchart of a fuel injection setting routine according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an engine control system according to the first embodiment;

FIG. 3 is a functional block diagram of the electronic control unit according to the first embodiment;

FIG. 4 is an explanatory view schematically showing a combustion process by two injections according to the first embodiment;

FIG. 5: As above, generation of heat generation pattern by two injections and N
Explanatory diagram schematically showing the relationship with OX generation

FIG. 6 is an explanatory diagram of a double injection execution condition according to the first embodiment;

FIG. 7 is a timing chart of fuel injection and ignition according to the first embodiment;

FIG. 8 is an explanatory diagram showing a relationship between exhaust gas temperature and fuel efficiency.

FIG. 9 is a functional block diagram of an electronic control unit according to a second embodiment of the present invention.

FIG. 10 is a flowchart of a main injection setting routine according to the second embodiment;

FIG. 11 is a flowchart of a second injection setting routine.

FIG. 12 is a functional block diagram of an electronic control unit according to a third embodiment of the present invention.

FIG. 13 is a flowchart of an exhaust gas temperature raising routine according to the first embodiment;

FIG. 14 is a functional block diagram of an electronic control unit according to a fourth embodiment of the present invention.

FIG. 15 is a flowchart of an exhaust gas temperature feedback routine according to the second embodiment;

FIG. 16 is a functional block diagram of an electronic control unit according to a fifth embodiment of the present invention.

FIG. 17 is a flowchart of an exhaust gas temperature raising routine according to the third embodiment;

FIG. 18 is an explanatory view schematically showing a combustion process by a conventional single injection.

FIG. 19 is an explanatory view schematically showing the relationship between the heat generation pattern generation and the NOx generation by the conventional single injection.

[Explanation of symbols]

 1 In-cylinder injection engine Ti Main injection amount TINJ Main injection timing Ti1 First injection amount TINJ1 First injection timing Ti2 Second injection amount TIIN2 Second injection timing Ti3 Third injection amount TIIN3 Third injection timing

Claims (9)

(57) [Claims] 1. An engine based on an engine speed and an engine load.
Main injection to determine the main fuel injection amount for performing main combustion
In addition to setting the amount, the main fuel
Set the amount of auxiliary fuel that can be burned by flame propagation.
The main fuel according to the main injection amount and the intake stroke or the compression stroke.
Was injected into the cylinder in a procedure Ru by burning the main fuel by the spark ignition, then, the injection during the expansion stroke due to combustion of the main fuel
Amount of supplementary fuel for engine speed and engine load
Depending was injected at least once within the cylinder, and a procedure for burning the unburned gas by the flame propagation from the burned portion
A method for controlling combustion of a direct injection engine, comprising: 2. An engine based on an engine speed and an engine load.
To determine the injection amount of the first fuel for performing the main combustion.
1 In addition to setting the injection amount, the flame propagation from the burned part
Therefore, the second amount that determines the amount of the second fuel that can be burned is determined.
And procedures for setting the injection amount, the first fuel by the first injection amount, and injected into the cylinder in the intake stroke or pressure <br/> compression stroke, Ru the first fuel is burned by spark ignition procedure If, then, the time that can be ignited by flame propagation from the a combustion late combusted portion of the expansion stroke due to combustion of the first fuel injection and the second fuel by the second injection amount into the cylinder and, combustion control method for a cylinder injection engine, characterized in that a procedure for burning unburned gas. 3. An engine based on an engine speed and an engine load.
To determine the injection amount of the first fuel for performing the main combustion.
1 In addition to setting the injection amount, the flame propagation from the burned part
Therefore, the amounts of the second and third fuels that can be burned are determined.
Setting the second injection amount and the third injection amount, and injecting the first fuel based on the first injection amount into the cylinder during the intake stroke or the compression stroke . a step of Ru is burned by spark ignition, after which the time can be ignited by flame propagation from the burned part a combustion late in the expansion stroke due to combustion of the first fuel, the second by the second injection amount the second fuel injected into the cylinder, the procedure for re-combustion, the combustion late reburning according to the second fuel in the expansion stroke, time that can be ignited by flame propagation from the burned portion
In, the third fuel by the third injection amount is injected into the cylinder, a combustion control method for a cylinder injection engine, characterized in that a procedure for burning unburned gas. 4. The engine operating state is low engine low load
Judgment whether the catalyst is located in the area where it is difficult to activate the catalyst
Steps to If the engine operating state is in the area where the catalyst can be activated
One fuel injection per cylinder per cycle
Operating conditions based on engine speed and engine load.
One combustion cycle per cylinder, depending on the condition
Set an appropriate amount of fuel injection and set the fuel injection amount
Is injected into the cylinder during the intake stroke or the compression stroke.
To ignite the fuel-air mixture injected into the cylinder.
The procedure for igniting when If the engine is operating in an area where catalyst activation is difficult
Multiple fuel injections per cylinder
To perform the main combustion with a smaller amount than the above fuel injection amount.
The main injection amount is smaller than the main injection amount and the main injection amount is smaller than the main injection amount.
Can be burned by flame propagation from the burned part by propellant
The second or subsequent injection amount
Set based on engine speed and engine load, respectively.
Steps When the catalyst is in an area where activation of the catalyst is difficult, the main injection
Fuel in the cylinder during the intake or compression stroke
To ignite the mixture by the main injection fuel
Ignition, and then later in the combustion phase of the expansion stroke.
Ignited by flame propagation from the burned part
Inject the fuel according to the second injection amount, or
A procedure of sequentially injecting fuel according to the second and subsequent injection amounts;
Control of in-cylinder injection engine characterized by comprising:
Method. 5. The method according to claim 1, wherein the plurality of times is three or more times, Multiple fuel injections per cylinder per cycle selected
Sometimes, the fuel injection amount is smaller than the normal fuel injection amount and the main fuel
A main injection amount for performing baking, and a smaller amount than the main injection amount and
The main injection fuel causes flame propagation from the burned part.
Amount that can be burned And the injection amount after the second and third
Based on the engine speed and engine load, respectively.
Set In the latter stage of combustion in the expansion stroke due to the combustion of the main injection fuel.
Ignited by flame propagation from the burned part
Then, the fuel of the second injection amount is injected,
Ignition by flame propagation from burned part in the same expansion stroke
Inject fuel with the third and subsequent injection quantities sequentially when possible
5. The in-cylinder injection engine according to claim 4, wherein:
Combustion control method. 6. Based on an engine speed and an engine load.
One fuel cycle per cylinder according to the operating conditions
A procedure for setting a main injection amount that is commensurate with baking; The main injection amount of fuel is supplied during the intake stroke or the compression stroke.
And injected into the cylinder to reach the air-fuel mixture
A procedure for igniting when it can be fired, When the operating condition of the catalyst in the low
A procedure for determining whether or not an area is difficult to activate; If the engine is operating in an area where catalyst activation is difficult
Two fuel injections per cylinder per cycle
Further, the flame transfer from the burned portion by the main injection fuel is performed.
Set the second injection amount that can be burned by sowing
The latter half of the combustion in the expansion stroke due to the combustion of the main injection fuel
And it can be ignited by flame propagation from the burned part
For injecting fuel with the second injection amount during the period
Combustion control for a direct injection engine, characterized by comprising:
Your way. 7. An engine based on an engine speed and an engine load.
One fuel cycle per cylinder according to the operating conditions
A procedure for setting a main injection amount that is commensurate with baking; The main injection amount of fuel is supplied during the intake stroke or the compression stroke.
And injected into the cylinder to reach the air-fuel mixture
A procedure for igniting when it can be fired, When the operating condition of the catalyst in the low
A procedure for determining whether or not an area is difficult to activate; If the engine is operating in an area where catalyst activation is difficult
The target value of the exhaust gas temperature rise based on the engine operating condition.
Set the target exhaust temperature as
A procedure for comparing with temperature; When the target exhaust temperature is equal to or higher than a predetermined temperature, one cylinder 1
2 times per cycle Select fuel injection and
Combustion by flame propagation from burned part by main injection fuel
Set the possible second injection quantity and set the main injection fuel
Late combustion in the expansion stroke due to combustion
During the time when ignition is possible due to the flame propagation,
A procedure for injecting fuel with an injection amount of When the target exhaust temperature is lower than the predetermined temperature,
Select the phase retard correction, and adjust the injection timing of the main injection fuel.
Procedure for retarding the ignition timing and retarding the ignition timing.
A combustion control method for a direct injection engine. 8. Two fuel injections per cylinder per cycle
Is being executed or the ignition timing is retarded.
When the exhaust gas temperature is detected,
Comparing the temperature with the target exhaust temperature, Under the execution of two fuel injections per cycle per cylinder
The exhaust gas temperature has not reached the target exhaust temperature
In the meantime, the second injection amount is increased, while the ignition timing
The exhaust gas temperature reaches the target exhaust temperature
If not reached, the injection timing of the main injection fuel
And a procedure to further retard the ignition timing.
The fuel for a direct injection engine according to claim 7, characterized in that:
Baking control method. 9. Based on an engine speed and an engine load,
One fuel cycle per cylinder according to the operating conditions
A procedure for setting a main injection amount that is commensurate with baking; The main injection amount of fuel is supplied during the intake stroke or the compression stroke.
And injected into the cylinder to reach the air-fuel mixture
A procedure for igniting when it can be fired, The target value of the exhaust gas temperature rise based on the engine operating state
A procedure for setting a target exhaust temperature; A procedure for determining whether to start the engine or normal operation, When the engine is started, the target exhaust temperature is set to a first predetermined temperature.
To judge whether or not the engine is cold starting by comparing the temperature
When, When starting the engine, except for starting the engine cold,
A second predetermined temperature lower than the first predetermined temperature;
Steps to compare with degrees, During normal operation, the fuel consumption rate is
Whether it is in the condition to perform three injections in order to suppress
The steps to determine Injected three times during cold start of engine or during normal operation
Under these conditions, three fuel cycles per cylinder
Fuel injection, and further burned by the main injection fuel
The second time the amount that can be burned by the flame propagation from the part and
The third injection amount is set, and the amount of combustion of the main injection fuel is set.
In the later stage of combustion in the expansion stroke
At the time when ignition is possible by sowing,
And then in the same expansion stroke,
3rd injection at a time when ignition is possible due to flame propagation from
A procedure for injecting fuel by the amount of radiation; Exhaust and target exhaust at engine start except cold start
When the temperature is equal to or higher than the second predetermined temperature or during normal operation, 3
When the injection condition is not satisfied, one cylinder and one cycle
2 fuel injections and select the fuel injection
The second time the amount that can be burned by the flame propagation from the combustion part
The injection amount is set, and the expansion
At the later stage of combustion, and due to the propagation of flame from the burned part.
When the fuel can be ignited by the second injection amount
A procedure for injecting Exhaust and target exhaust at engine start except cold start
When the temperature falls below the second predetermined temperature, the ignition timing is retarded.
Select angle correction to delay the injection timing of the main injection fuel.
And a procedure for retarding the ignition timing.
A method for controlling combustion of a direct injection engine.