JP2003222042A - Direct injection spark ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stratified combustion through compression stroke injection for early activation of catalyst in cooling a machine, to improve stability of the combustion, and also to reduce HC emission. <P>SOLUTION: A direct injection spark ignition type internal combustion engine is provided with a fuel injection valve 9 which is permitted to direct so that the velocity of fuel injection in the direction of traversing the inside of a cylinder becomes larger than the velocity toward a piston. On the other hand, fuel injection is carried out in compression stroke at the time of cooling the machine, while controlling injection quantity so that the air/fuel ratio within the cylinder is rendered to be a stoichiometric or a slightly lean value, thereby performing stratified combustion. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection spark ignition type internal combustion engine, and more particularly to a technique for improving combustion when cold.

[0002]

2. Description of the Related Art In recent years, a direct injection spark ignition type internal combustion engine having a structure for directly injecting and supplying fuel into a combustion chamber of an engine has been attracting attention. In this type, combustion mode switching control is performed according to engine operating conditions. In other words, by injecting fuel in the intake stroke to diffuse the fuel into the combustion chamber and form a homogeneous mixture, homogeneous combustion is performed, and by injecting fuel in the compression stroke, local combustion is performed around the spark plug. In general, switching control is performed to stratified combustion in which a stratified mixture is formed.

By the way, when the engine is cold, the fuel injected into the cylinder has a low temperature on the wall surface of the combustion chamber, so that the vaporization of the fuel is poor in performing the same combustion state as compared with the normal complete warm state. Therefore, excess fuel is injected to make the mixture ratio concentration near the spark plug substantially constant. Conventionally, in order to accelerate the early activation of the exhaust purification catalyst provided in the exhaust passage, in order to reduce the emission of unburned HC and harmful exhaust components by increasing the amount of these fuels in the process from the engine cold start to the complete warm-up, The following exhaust gas temperature raising device has been proposed.

In Japanese Unexamined Patent Publication No. 10-169488, when the exhaust gas temperature rise is required, compression stroke injection is performed to make the local air-fuel ratio around the spark plug rich, and the injection timing is greatly retarded. Therefore, incomplete combustion of overrich is caused around the spark plug. Therefore,
The exhaust temperature rises because the unburned components react with the excess oxygen in the cylinder as the cylinder flows thereafter.

Further, in Japanese Unexamined Patent Publication No. 2000-240485, when the catalyst temperature increase is required similarly to the above, the compression stroke injection is performed so that the air-fuel ratio of the engine becomes close to stoichiometric (theoretical air-fuel ratio). In particular, in the case of a cold start, it is proposed that after the start, intake stroke injection is performed until a predetermined number of revolutions is reached, and then two steps of intake stroke injection (or compression stroke injection) and expansion stroke injection are performed. Injection is performed, and the compression stroke injection in the vicinity of stoichiometry is performed through the two-stage injection.

[0006]

However, the above-mentioned conventional techniques have the following problems. That is, stratified charge combustion is performed by performing compression stroke injection in the cold state after starting, and at this time, since the surroundings of the spark plug are in an overrich state, incomplete combustion occurs and unburned residue remains. There is a problem that fuel HC and harmful exhaust components may be discharged.

Further, after the start, when the temperature rise of the catalyst is required, the compression stroke injection in the vicinity of stoichiometry is performed. Therefore, the fuel amount increase by the intake stroke injection between the start and the temperature rise request is made. There was a problem that a large amount of unburned HC was discharged in the region. Further, after the start, when carrying out the compression stroke injection in the vicinity of the stoichiometric state, due to the vaporization and the mixture formation of the fuel injected into the cylinder due to the temperature inside the cylinder,
In order to ensure the stability of combustion and raise the temperature of the catalyst with the minimum deterioration in fuel consumption, the temperature rise control by the expansion stroke injection (additional fuel) was performed before the compression stroke injection Before the reduction of unburned HC by the stroke injection, there is a problem that the expansion stroke injection causes a remarkable deterioration of fuel efficiency.

In view of the above situation, the present invention improves the stability of stratified charge combustion by compression stroke injection when the engine is cold, reduces the amount of HC emission, and thus improves the combustion stability. An object of the present invention is to provide a direct injection spark ignition type internal combustion engine that can improve the fuel efficiency by enabling transition to stratified combustion by compression stroke injection at an early stage.

[0009]

For this reason, according to the first aspect of the present invention, the direct injection spark ignition is provided with the fuel injection valve for directly injecting the fuel into the cylinder and the spark plug for spark ignition of the air-fuel mixture in the cylinder. In the internal combustion engine, the fuel injection valve is configured such that the flow velocity of the fuel spray in the direction traversing the inside of the cylinder is higher than the flow velocity toward the piston side, while fuel injection is performed in the compression stroke when the engine is cold. A control means is provided for controlling the fuel injection amount so that the air-fuel ratio in the cylinder becomes stoichiometric or slightly lean while performing the stratified combustion.

The invention of claim 2 is characterized in that, in the invention of claim 1, an exhaust purification catalyst is provided in the exhaust passage. According to a third aspect of the present invention, in the first or second aspect of the invention, the fuel injection valve is provided so as to be directed from the intake side of the cylinder head to the exhaust side and is inclined downward, and its injection port is with respect to the injection valve axis. And is deflected to the cylinder head side.

According to a fourth aspect of the invention, in the first to third aspects of the invention, the control means causes the homogeneous combustion by the intake stroke injection to be performed immediately after the engine is started, and then directly shifts to the stratified combustion by the compression stroke injection. It is characterized by In the invention of claim 5, in the invention of claim 4, the control means sets the air-fuel ratio at the time of intake stroke injection immediately after the engine is started to be richer than stoichiometric, and the air-fuel ratio at the time of subsequent compression stroke injection is slightly less than stoichiometric. It is characterized by being lean.

In the invention of claim 6, in the invention of claim 4 or 5, it is determined that the condition for shifting to the stratified charge combustion by the compression stroke injection is equal to or higher than a predetermined temperature at which the piston crown surface temperature indicates a high temperature state. It is characterized in that it sometimes holds. In the invention of claim 7, in the invention of claim 6, it is determined that the piston crown surface temperature is equal to or higher than the predetermined temperature because the pseudo water temperature as a parameter correlating with the piston crown surface temperature is equal to or higher than a predetermined temperature. The pseudo water temperature is calculated with a delay with respect to the change of the cooling water temperature, based on the initial value according to the starting cooling water temperature and the delay correction coefficient according to the intake air amount in each predetermined cycle. It is characterized by

According to an eighth aspect of the present invention, in the first to seventh aspects of the present invention, a fuel property estimating means for estimating the fuel property is provided, and the control means makes the air-fuel ratio in the cylinder stoichiometric or slightly lean. It is characterized in that the required fuel amount is corrected and calculated according to the fuel property. In the invention of claim 9, in the invention of claim 8, the control means is
It is characterized in that the required fuel amount is greatly reduced and corrected as the fuel is lighter in accordance with the fuel property.

The invention of claim 10 is characterized in that, in the invention of claim 8 or 9, the correction amount according to the fuel property is determined based on the engine speed. Further, the invention of claim 11 is characterized in that the fuel injection amount is increased according to the correction amount as the engine speed is lower. In the invention of claim 12, in the invention of claim 8 or 9,
The correction amount according to the fuel property is determined based on the engine temperature. Further, in the invention of claim 13,
According to the correction amount, the fuel injection amount is increased as the engine temperature is lower.

According to a fourteenth aspect of the present invention, in the eighth to thirteenth aspects, the control means performs the correction according to the fuel property during the open control of the required fuel amount. A fifteenth aspect of the present invention is characterized in that, in the eighth to thirteenth aspects, the control means performs the correction according to the fuel property during the feedback control of the required fuel amount.

[0016]

According to the invention of claim 1, the following effects can be obtained. In the cold state immediately after starting, the fuel vaporization was not good, so unnecessary fuel was added to ensure stable combustion.However, the flow velocity of the fuel spray in the direction that traverses the inside of the cylinder is greater than the flow velocity toward the piston side. The compression stroke injection is performed so as to be large, and the air-fuel ratio of the entire cylinder is controlled to be stoichiometric or slightly lean, so that a mixture richer than stoichiometric is formed in the vicinity of the spark plug and outside the vicinity of the spark plug ( A lean air-fuel mixture is also formed in the vicinity of the opposite cylinder wall) than stoichiometry, and a flammable air-fuel mixture is present in the entire cylinder, ensuring the same level of stability as homogeneous combustion during conventional cooling while maintaining combustion. It is possible to improve efficiency and reduce the emission of unburned HC.

In particular, since the fuel spray toward the piston crown surface and rebounding to the spark plug can be reduced, rich misfire of the spark plug can be prevented and combustion stability can be improved. Further, by burning the rich air-fuel mixture around the spark plug and the lean air-fuel mixture in the vicinity of the cylinder wall, it is possible to raise the combustion temperature by improving the efficiency of the oxidation reaction, thereby reducing unburned HC and warming up the engine. Can be shortened.

Further, since the combustion stability in the stratified charge combustion can be improved, the stratified charge combustion can be started early after the start,
The fuel efficiency is improved accordingly. According to the invention of claim 2, the exhaust purification catalyst can be activated early by being applied to the internal combustion engine having the exhaust purification catalyst in the exhaust passage. Claim 3
According to the invention, the desired spray form can be obtained by deflecting the injection port of the fuel injection valve.

According to the fourth aspect of the present invention, the homogeneous combustion by the intake stroke injection immediately after the start is directly switched to the stratified combustion by the compression stroke injection, so that the engine (catalyst when the exhaust purification catalyst is provided) is lowered. It can be warmed up with fuel efficiency, and the amount of HC exhausted by the completion of warming up can be further reduced. According to the invention of claim 5, the air-fuel ratio at the time of intake stroke injection immediately after the engine is started is richer than stoichiometric, and the air-fuel ratio at the time of subsequent compression stroke injection is made slightly leaner than stoichiometric, so that the engine (exhaust gas purification When a catalyst is provided, the catalyst can be warmed up with low fuel consumption, and the amount of HC discharged by the completion of warming up can be reduced more than ever.

According to the sixth aspect of the present invention, stratification combustion by compression stroke injection is performed after the crown surface temperature becomes high, so that the air-fuel mixture is well formed around the spark plug by utilizing the piston crown surface. it can. According to the invention of claim 7, it can be easily and relatively accurately determined by the pseudo water temperature that the crown surface temperature has become high.

According to the eighth aspect of the present invention, when the stratified charge combustion is performed by the compression stroke injection, the fuel injection amount is corrected according to the fuel property, so that the air-fuel mixture around the spark plug is changed to the fuel property. Therefore, the air-fuel ratio can always be controlled to an appropriate value, and thus the incomplete combustion products generated around the spark plug can be post-reacted with oxygen remaining in the cylinder and burned out.

According to the ninth aspect of the present invention, the lighter the fuel is, the larger the fuel injection amount is corrected so that the air-fuel ratio around the spark plug deviates from the proper range due to the high volatility. It is possible to prevent the misfire caused by the decrease. According to the invention of claim 10, by determining the correction amount based on the engine speed, the fuel injection amount can be corrected corresponding to the gas flow speed. In particular, as in the invention of claim 11, the fuel injection amount is increased as the rotational speed is lower, that is, when the gas flow is undeveloped, thereby supplementing the fuel components adhering to the wall surface that are not vaporized and mixing around the plug. The air-fuel ratio of air can be controlled more accurately.

According to the twelfth aspect of the present invention, by determining the correction amount based on the engine temperature, the fuel injection amount can be corrected corresponding to the warm-up state. In particular, as in the invention of claim 13, as the engine temperature is lower, that is, when the warm-up is not advanced and the fuel components adhering to the wall surface are less likely to be vaporized, the fuel injection amount is increased to mix around the plugs. The air-fuel ratio of air can be controlled more accurately.

According to the fourteenth aspect of the present invention, by performing the correction according to the fuel property during the open control of the fuel injection amount, it is possible to compensate the variation of the air-fuel ratio with respect to the stored value due to the difference of the fuel property. According to the invention of claim 15, the target air-fuel ratio can be accurately achieved by performing the correction according to the fuel property during the feedback control of the fuel injection amount, so that the amount of fuel required to raise the exhaust temperature can be increased. It is possible to accurately supply the oxygen or to ensure the oxygen necessary for the post-reaction of incomplete combustion products.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration of an embodiment of the present invention, which will be described first. An intake passage 2 of the engine 1 is provided with an air flow meter 3 for detecting an intake air amount Qa and a throttle valve 4 for controlling the intake air amount Qa. Further, a swirl control valve is provided downstream of a branch portion to each cylinder. 5 are provided. A fuel injection valve 9 is provided so as to face the combustion chamber 8 of each cylinder defined by the cylinder head 6 and the piston 7.

The fuel injection valve 9 is driven to open by a drive pulse signal set in a control unit 50, which will be described later. The fuel injection valve 9 is pressure-fed from a fuel pump (not shown) and burns fuel controlled to a predetermined pressure by a pressure regulator (not shown). It can be directly injected and supplied into the chamber 8. An ignition plug 10 is provided so as to face the combustion chamber 8 of each cylinder, and the ignition plug 10 performs spark ignition on the air-fuel mixture based on an ignition signal from the control unit 50.

On the other hand, in the exhaust passage 11, an air-fuel ratio sensor 12 for detecting the concentration of a specific component (for example, oxygen) in the exhaust to detect the air-fuel ratio of the exhaust gas and thus the intake air-fuel mixture.
(A rich / lean output oxygen sensor may be used, or a wide-range air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide range may be provided.) An exhaust purification catalyst 13 for purification is provided. As the exhaust purification catalyst 13, a stoichiometric [theoretical air-fuel ratio; A / F (air weight / fuel weight) = 14.
7] A three-way catalyst capable of purifying the exhaust gas by oxidizing CO and HC in the exhaust gas and reducing NOx in the vicinity thereof,
Alternatively, an oxidation catalyst or the like that oxidizes CO and HC in the exhaust gas can be used.

Further, on the downstream side of the exhaust purification catalyst 13, the concentration of a specific component (eg oxygen) in the exhaust gas is detected,
A downstream oxygen sensor 14 for lean output is provided. Here, according to the detection value of the downstream oxygen sensor 14,
By correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 12 to suppress a control error due to deterioration of the air-fuel ratio sensor 12 (for adopting a so-called dual air-fuel ratio sensor system), Downstream oxygen sensor 1
4 is provided, the downstream oxygen sensor 14 can be omitted if only the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 12 needs to be performed. When the air-fuel ratio feedback control is not performed, both the air-fuel ratio sensor 12 and the downstream oxygen sensor 14 can be omitted.

In this embodiment, the crank angle sensor 15 is provided and the control unit 50 is provided.
Then, the crank unit angle signal output from the crank angle sensor 15 in synchronization with the engine rotation is counted for a certain time,
Alternatively, the engine speed Ne can be detected by measuring the cycle of the crank reference angle signal. Further, a water temperature sensor 16 for detecting the cooling water temperature (water temperature) Tw in the cooling jacket is provided facing the cooling jacket of the engine 1. Further, a throttle sensor 17 (which can also function as an idle switch) for detecting the opening of the throttle valve 4 is provided.

By the way, in the present embodiment, the throttle valve control device 18 capable of controlling the opening degree of the throttle valve 4 by an actuator such as a DC motor.
Is provided. The throttle valve control device 18 is
Electronically controlling the opening of the throttle valve 4 based on a drive signal from the control unit 50 so that a required torque calculated based on the accelerator pedal operation amount of the driver detected by the accelerator pedal sensor 19 can be achieved. Can be configured as.

The detection signals from the various sensors are CP
U, ROM, RAM, A / D converter, input / output interface, and the like are input to a control unit 50 composed of a microcomputer, and the control unit 50 detects based on signals from the sensors. Depending on the operating state, the opening of the throttle valve 4 is controlled via the throttle valve control device 18, the fuel injection valve 9 is driven to control the fuel injection amount (fuel supply amount), and the ignition timing is adjusted. Is set to control ignition of the spark plug 10 at the ignition timing.

Note that, for example, fuel is injected into the combustion chamber 8 in a compression stroke in a predetermined operating state (low / medium load region, etc.) to form a layered combustible mixture around the spark plug 10 in the combustion chamber 8. While the stratified charge combustion can be performed by the fuel injection, the fuel is injected into the combustion chamber 8 in the intake stroke in other operating states (such as the high load region) to form the air-fuel mixture having a substantially homogeneous mixture ratio in the entire combustion chamber 8. The fuel injection timing (injection timing) is also configured to be changeable according to the operating state so that homogeneous combustion can be performed.

By the way, in the control unit 50 according to this embodiment, the exhaust purification catalyst 13 is activated early while suppressing the emission of HC into the atmosphere from the start of the engine until the exhaust purification catalyst 13 is activated. In order to achieve this, input signals from various sensors such as the key switch 20 are received and, for example, the following control is performed.

Specifically, for example, the flowchart shown in FIG. 2 is executed. Step 1
(Indicated as S1 in the figure. The same applies hereinafter), the key switch 2
It is determined whether or not the ignition signal of 0 is turned on (whether the key position is set to the ignition ON position).
If YES, the process proceeds to step 2, and if NO, this flow ends.

In step 2, it is determined whether or not the start signal of the key switch 20 is turned on (whether the key position is the start position). That is, it is determined whether or not there is a cranking request by a starter motor (not shown). If YES, it is determined that there is a cranking request for starting, and the process proceeds to step 3. If NO, it is determined that there is no cranking request and the process returns to step 1.

In step 3, the drive of the starter motor is started and the engine 1 is cranked as in the conventional case. In the next step 4, as in the conventional case, the intake stroke injection is performed as the fuel injection for starting, so that the homogeneous combustion by the intake stroke injection is performed. In the next step 5, it is determined whether or not the exhaust purification catalyst 13 has been activated. The determination is, for example, whether or not the downstream oxygen sensor 14 provided facing the exhaust passage 11 is activated (determined in step 12), as shown as an example in the flowchart of FIG. 3 described later. It can be replaced by That is, whether or not the exhaust purification catalyst 13 is activated can be determined based on the state of change in the detection signal of the downstream oxygen sensor 14 as shown in FIG.

Further, it is possible to detect the engine water temperature Tw or the oil temperature, estimate the temperature of the exhaust purification catalyst 13 (or the outlet temperature), and judge the activation of the exhaust purification catalyst 13 based on the result, or The determination can also be made by directly detecting the temperature (or the outlet temperature) of the exhaust purification catalyst 13. If the catalyst is not activated (YE
If S), go to step 6. On the other hand, if the catalyst is activated (if NO), it is determined that the control for accelerating the catalyst activation is not necessary, and the process proceeds to step 10, and in order to improve the fuel consumption, the normal combustion control similar to the conventional one is performed. The combustion is performed in a combustion mode (homogeneous stoichiometric combustion, homogeneous lean combustion, stratified lean combustion) according to the operating state, and the present flow ends.

In step 6, the crown surface temperature of the piston 7,
In particular, it is determined whether or not the surface temperature of the bowl portion 7a recessed in the crown surface of the piston is equal to or higher than a predetermined temperature (permission temperature for transition to compression stroke injection). Such a determination can be made by directly detecting it with a thermocouple or the like embedded in the piston 7 (particularly its crown surface), or by estimating the engine water temperature Tw or the oil temperature, the crown surface temperature of the piston 7 can be estimated. , It can also be performed based on the result.

Specifically, for example, as shown in the flow chart of FIG. 5 described later as an example, it can be performed based on the pseudo water temperature TWF that correlates with the piston crown surface temperature. 6, the pseudo water temperature TWF correlated with the piston crown surface temperature is estimated and calculated,
It is possible to determine whether or not the result has reached a predetermined value TWF1 (temperature for permitting transition to compression stroke injection).

If YES, go to step 7. On the other hand, in the case of NO, when stratified charge combustion is performed by compression stroke injection for accelerating catalyst activation, which will be described later, since the piston crown surface temperature is lower than a predetermined value, stratification mixing using the piston crown surface is performed. It is said that atomization and promotion of vaporization will not be performed well, which may reduce ignitability, combustion stability, and engine stability (engine drivability).
In order to prohibit the transition to the stratified charge combustion by the compression stroke injection and continue the homogeneous combustion by the intake stroke injection, the process returns to step 4.

In step 7, it is judged whether or not the conditions for performing the stratified charge combustion by the compression stroke injection are satisfied. For example, as shown in the flowchart of FIG. 7, which will be described later, the determination impairs the engine drivability when performing the compression stroke injection, regardless of whether the stratified charge combustion by the compression stroke injection is idle or running. It is to judge whether or not stable operation can be performed.

Specifically, in step 31, signals (eg, Tw, Ne, Q) from various sensors associated with the engine are set.
(a, etc.) is input to the control unit 50 and read. In step 32, for the read value,
RAM built in the control unit 50 in advance
By comparing the value with the value, it is determined whether or not the combustion stability can be implemented when the fuel is injected in the compression stroke injection.

The values after A / D conversion of all signal input values are R
If it is within the set range of the AM value, YES is determined and the process proceeds to step 33, the compression stroke injection permission flag FLG is set to 1, and this flow is ended. On the other hand, if any of the A / D converted values of the signal input value is outside the setting range of the RAM value, it is determined that the transition to the compression stroke injection is impossible, and step 3
4, the compression stroke injection permission flag FLG is set to 0,
This flow ends.

Therefore, in step 7, the process proceeds to step 8 only when the compression stroke injection permission flag FLG becomes 1, and when the compression stroke injection permission flag FLG is 0, the compression stroke injection is not permitted and the step immediately follows. Go to 10,
The process shifts to normal combustion control according to the operating state, and the present flow ends. In step 8, since the catalyst is not activated and it is necessary to promote the catalyst activation, and when the piston crown surface temperature is equal to or higher than the predetermined value, the stratified mixture can be satisfactorily generated. The transition to the stratified charge combustion by the compression stroke injection is permitted to perform the cold stratified charge combustion (stoichiometric stratified charge combustion).

Specifically, for example, a total fuel amount (fuel weight necessary to achieve a slight lean from stoichiometric) capable of being substantially completely burned with an intake air amount per combustion cycle is burned in a compression stroke. The mixture is injected and supplied into the chamber 8, and an air-fuel mixture which is relatively richer (higher in fuel concentration) than stoichiometric is formed around the ignition plug 10 in a substantially layered form and burned.

According to the cold stratified combustion as described above,
Compared with conventional homogeneous combustion or combustion by expansion stroke injection after main combustion, the exhaust gas temperature can be raised without significantly deteriorating fuel efficiency, and it is discharged from the combustion chamber to the exhaust passage. Unburned HC can be reduced. That is, according to cold stratified combustion,
Compared to the case of warming up in the conventional combustion mode (combustion in which additional fuel is injected after the latter stage of combustion (after the expansion stroke or during the exhaust stroke) in addition to homogeneous combustion, homogeneous lean, stratified lean) From the start to the activation of the exhaust purification catalyst 13, it is possible to accelerate the early activation of the exhaust purification catalyst 13 while suppressing the fuel consumption and suppressing the emission of HC into the atmosphere.

Next, at step 9, the exhaust purification catalyst 13 is prepared by the same method as at step 5 (flowchart in FIG. 3).
Is activated (warm-up completed). Yes
If so, go to step 10. If NO, the process returns to step 8 to continue the cold stratified combustion until the exhaust purification catalyst 13 is activated. In step 10,
Depending on the operating condition, shift to a combustion mode (homogeneous stoichiometric combustion, homogeneous lean combustion, stratified lean combustion, etc.) that can achieve desired exhaust performance, fuel efficiency performance, driving performance (output performance, stability, etc.). After this, this flow ends.

In the present embodiment, in an operating state where the combustibility of the compression stroke injection may be adversely affected (for example, when the piston crown surface temperature is lower than a predetermined temperature),
Although it is configured such that the transition to the cold stratified charge combustion is prohibited, such a configuration may not be adopted when the early activation of the exhaust purification catalyst 13 is to be given the highest priority (that is, Step 6 in the flowchart of FIG. 2 can be omitted).

Here, the determination of the activity of the exhaust purification catalyst will be described with reference to the time chart of FIG. 4 according to the flowchart of FIG. In step 11, it is determined whether the downstream oxygen sensor 14 is not heated by the heater. If NO (if done), the influence of heating by the heater is great, and an error occurs in the activation determination of the downstream oxygen sensor 14 and thus the exhaust purification catalyst 13, and this flow is ended. On the other hand, if YES (if not performed), it is determined that the activation of the downstream oxygen sensor 14 and thus the exhaust purification catalyst 13 can be accurately performed, and the process proceeds to step 12.

In step 12, the downstream oxygen sensor 14
Is activated. For example, as shown in FIG. 4, when the output voltage of the downstream oxygen sensor 14 is maintained at the initial voltage V0, a predetermined level (V0 + dV) is reached.
It is possible to make a judgment based on whether or not R) has occurred. On the contrary, it is also possible to make a determination based on whether or not a predetermined level (V0 + dVL) is reached from the state where the initial voltage V0 is maintained. Further, it may be configured to determine whether or not the downstream oxygen sensor 14 is activated based on the output of the downstream oxygen sensor 14 being rich / lean inverted a predetermined number of times. If NO, repeat step 12 until activation is determined, and if YES, proceed to step 13.

In step 13, it is judged that the exhaust purification catalyst 13 has been activated. That is, the downstream oxygen sensor 14 provided on the downstream side of the exhaust purification catalyst 13 is activated as follows.
Exhaust gas temperature rise on the outlet side of the exhaust purification catalyst 13 (oxidation reaction)
Therefore, it is determined (estimated) that the upstream side exhaust purification catalyst 13 has been activated. Step 1
In 4, the energization control of the heater of the downstream oxygen sensor 14 (control for maintaining the temperature of the downstream oxygen sensor 14 at a predetermined temperature, etc.) is started, and then this flow is ended.

Next, the piston crown surface temperature determination will be described with reference to the time chart of FIG. 6 according to the flowchart of FIG. In step 21, the pseudo water temperature TWF [t] (t is the elapsed time after the ignition signal is turned on) correlated with the piston crown surface temperature is estimated and calculated by the method as shown in FIG. 6, and the estimated and calculated pseudo water temperature is calculated. TWF
It is determined whether [t] is equal to or higher than the predetermined temperature TWF1.

The pseudo water temperature TWF is the starting water temperature TWe.
Depending on 0, the delay correction coefficient K starts from the pseudo water temperature initial value TWF0 and is determined by the intake air amount Qa per unit time.
It converges toward the engine water temperature Twe with a first-order delay by twf. TWF [t] = TWe [t]-(TWe [t] -TWF [t-1]
) × (1−Ktwf) where TWF [0] = TWe [0], t is IGN / SW
-Elapsed time after ON. In addition, pseudo water temperature initial value TWF
0 can be obtained by referring to the table or the like shown in FIG. 6 based on the starting water temperature TWe0, and the delay correction coefficient K
twf can be obtained based on the intake air amount Qa by referring to the table shown in FIG.

When the judgment in step 21 is YES (TWF
If [t] ≥ TWF1), the process proceeds to step 22 and NO.
If so, the process returns to step 21. Step 22
Then, it is determined that the piston crown surface temperature is equal to or higher than the predetermined value, and the present flow ends. Next, the cold stratified combustion will be described in more detail. In the conventional compression stroke injection, the temperature of the piston crown surface and the cylinder wall is low in the engine cold state, and the vaporization of the fuel directly injected into the cylinder is poor,
It was difficult to form a good combustible mixture around the spark plug.

In Japanese Unexamined Patent Publication No. 10-169488, in the compression stroke injection in the complete warming process, the fuel is controlled and the fuel injection timing is retarded so that the air-fuel mixture around the spark plug is overriched while the spark plug is sparked. There is a region where residual oxygen exists in places other than the vicinity, and a control means for performing the in-cylinder oxidation reaction in the latter half of the main combustion is presented. Also,
Japanese Patent Laid-Open No. 2000-240485 discloses that, in an engine state immediately after the start of a cold machine, the temperature raising means by compression stroke injection has a slow oxidation reaction of CO and HC in the exhaust purification catalyst and does not promote the temperature raising property. Before the compression stroke injection control,
There are cases where two-stage injection such as compression stroke injection + expansion stroke injection is performed.

From the above, in order to improve the combustion stability by the compression stroke injection in the engine cold state and to raise the temperature of the exhaust purification catalyst by promoting the in-cylinder oxidation reaction due to residual oxygen, good combustion and fuel consumption are not necessarily deteriorated as much as possible. It seems that the method has not been established. Against this background, the present invention focuses on stratified combustion, which is so-called stratified combustion, which is realized at the time of complete warming, and vaporizes the fuel injected into the cylinder sufficiently even in the engine cold state. It proposes injection valve characteristics and combustion control that can achieve combustion stability even if not done. Also, even if the intake stroke injection immediately after the start of the conventional cold machine is shifted to the compression stroke injection, the combustion stability equal to or higher than that is ensured, and the air-fuel ratio of the engine is set to the stoichiometric or slightly lean side. The exhaust gas temperature raising property was also improved.

The fuel injection valve 9 used in the present invention will be described with reference to FIG. 8 (or FIG. 9) and FIG. 10 together with the combustion chamber structure. A bowl portion (recess, cavity) 7a having a center at a position offset from the center to the intake valve side is formed on the crown surface of the piston 7, and is located above the peripheral edge portion of the bowl portion 7a on the piston center side. An ignition plug 10 is arranged at a substantially central portion of the cylinder head 6.

On the other hand, the fuel injection valve 9 is connected to the cylinder head 6
On the intake valve side of the fuel injection valve 9 from the intake valve side to the exhaust valve side at an obliquely downward attachment angle, while deflecting the injection port (orifice) 9a (the injection center line OC) of the fuel injection valve 9 with respect to the injection valve axis BC. By performing such processing (deflection angle β), the spray (the injection center line OC) from the injection port 9a is deflected toward the cylinder head 6 side with respect to the injection valve axis BC, and the spray flow velocity (L1) in the deflected direction is obtained. Is higher than the spray flow velocity (L2) on the anti-deflection side.

Here, the spray characteristic of the fuel injection valve 9 is most influenced by the orifice deflection angle β at the tip of the injection valve, and the contact length of fuel can be changed by the orifice deflection angle β. As a result, at the time of fuel injection, the velocity of the fuel spray passing through the long contact point inside the orifice is attenuated, and the fuel spray passing through the short contact point is suppressed from being attenuated. Becomes stronger, the injection amount also increases at the same time.

Finally, the air-fuel mixture distribution formed in the combustion chamber differs depending on the combination of the engine body temperature, the total fuel injection amount, the intake air amount depending on the operating conditions, and the injection and ignition timing control. The characteristics are largely left to the structure of the injection valve. Next, before describing the mixture formation in the engine cold state in the present invention, first, the mixture formation by the compression stroke injection at the time of complete warming will be described with reference to FIG.

FIG. 8 shows a state of the fuel spray injected from the fuel injection valve and the vaporized mixture during so-called stratified combustion when the engine is completely warmed. The fuel injection timing is set to a timing at which a combustible air-fuel mixture can be formed around the ignition plug 9 in the compression process (a time at which the fuel injected at the cylinder gas temperature during compression can be sufficiently vaporized) and a gas flow (swirl flow). It is determined by the time, etc., at which the vehicle is ridden and stored in the bowl portion 7a of the crown surface of the piston 7 without spilling. Actually, since it depends on the operating state of the engine and the torque required by the driver, the ignition timing and
A predetermined constant is set by referring to a storage device built in the control unit 50.

FIG. 8 shows the next state. (1) Since the amount of intake air is large at the tip of the spray due to the requirement of stratified combustion and the pressure at the compression end in the cylinder is high, the reach distance of the spray is shorter than that of the intake stroke injection. (2) At the tip of the spray, the penetration temperature of the spray is reduced due to the increased vaporization due to the high temperature at the compression end. (3) Further, the spray penetration force is weakened by the generation of gas flow at the time of suction by the swirl control valve and the retention of the swirl flow in the compression stroke, and the spray spreading outside the piston bowl portion is suppressed. (4) The gas mixture vaporized on and near the top surface of the piston is held in the bowl by the swirl flow, and a combustible gas mixture is formed near the spark plug.

Further, in the formation of the air-fuel mixture at the time of complete warming, the fuel injection direction of the injection valve is deflected not to the piston side but to the cylinder head side by the improvement of the injection valve tip structure, and the piston rises due to the spray shape. In the middle compression stroke,
By preventing the injected fuel spray in the piston direction from directly hitting the crown surface of the piston, an even combustible mixture is formed around the spark plug on the piston bowl.

The injection amount is set so that the in-cylinder average theoretical air-fuel ratio is 25 to 40, and even if the entire injection amount is vaporized, it does not spread to the entire region in the cylinder. Further, immediately after the injection, heat is received from the high temperature gas in the cylinder and vaporization occurs from the spray tip portion, so the penetration force of the spray is suppressed. Further, the spread of the air-fuel mixture at the time of ignition is concentrated around the spark plug due to the gas flow.

On the other hand, the formation of the air-fuel mixture by the compression stroke injection when the engine is cold according to the present invention will be described with reference to FIG.
FIG. 9 shows the next state. (1) Since the total fuel injection amount is increased by 20 to 30% with respect to the complete warm stratified charge combustion due to the combustion requirement during cold engine, the injection period becomes longer and the spray reach distance becomes longer. (2) Also, due to the difference from the stratified charge combustion requirement at the time of complete warming, the compression end pressure in the cylinder decreases due to the decrease in the intake air amount, and at the same time the compression end temperature also decreases, so the penetration force of the injected fuel The hindrance is small, and the vaporization of the spray tip is poorly promoted.
The spray is widely dispersed outside the bowl. (3) Furthermore, due to the decrease in the intake air amount, the gas flow is weakened against the completely warmed layer, and the spray is dispersed.

The injection timing is examined based on the injection timing at the time of complete warming, but it is determined by the following requirements. At an injection timing earlier than that at the time of complete warming, the total fuel injection amount is large in the first place, and the gas temperature at the compression end in the compression process is lower than that at the time of complete warming Since the temperature inside the cylinder is low because the air compression is delayed, the fuel is not sufficiently vaporized, and the fuel is concentrated on the cylinder wall side in the direction opposite to the injection valve, making it difficult to form a combustible mixture near the spark plug. There is.

On the contrary, if the injection timing is too late from the injection timing at the time of complete warming, the injection is performed in the compression stroke period in the first place,
The time for vaporizing the fuel is shortened and it becomes impossible to generate a combustible mixture. In addition, because the injection timing is delayed and the piston position approaches top dead center, the injected spray directly hits the crown surface of the piston, causing problems such as smoke and misfire due to a decrease in insulation resistance of the spark plug. And the like are more likely to occur.

From the above, the injection timing of the compression stroke injection during cold engine is uniquely determined. Actually, it is determined by the engine condition for setting the average air-fuel ratio in the cylinder.
Note that FIG. 11 shows the state of mixture formation by the intake stroke injection, and the injection timing is 40 to 9 with respect to the intake TDC.
It was set to 0 ° ATDC. Further, FIG. 12 shows a state of mixture formation at the time of completely warmed stratified charge combustion.
280 to 300 ° ATDC with respect to DC. Further, FIG. 13 shows a state of mixture formation by the compression stroke injection at the time of cold engine, and the injection timing is relative to the intake air TDC.
It was set to 280 to 300 ° ATDC.

By the way, although the air-fuel mixture is formed by the compression stroke injection when the engine is cold, there are the following differences from the above-described compression stroke injection control during the complete warming. The setting range of the in-cylinder average air-fuel ratio at the time of cooling is different from the stratified charge combustion requirement at the time of complete warming, and from various performances of the engine (relationship between air-fuel ratio A / F and combustion stability and HC concentration) shown in FIG. , From the stoichiometric to the lean side. This is presumably because the air-fuel ratio around the spark plug reaches the misfire limit on the rich side of stoichiometry. On the contrary, the exhaust temperature of the lean side decreases and the exhaust of HC increases. This is because the air-fuel mixture outside the vicinity of the spark plug becomes too lean, flame propagation does not reach and unburned fuel remains, and the oxidation reaction is attenuated due to the decrease in combustion temperature and the in-cylinder temperature. It is considered to be a thing.

Next, due to operating conditions such as fast idle immediately after starting, the engine rotation and the required required torque are low, and the intake air intake amount is reduced as compared with the case of complete warming. As a result, the compression end gas temperature during the compression stroke during cooling is
It decreases unlike the case of a completely warm stratification request. Further, since the intake air amount decreases, the swirl flow at the end of the intake stroke and the compression stroke becomes weaker than the completely warm stratified layer, and the sprayed mixture injected into the cylinder is less likely to be contained in the piston bowl portion.

Further, as the temperature at the compression end decreases and the total injection amount increases, the fuel injected during the compression stroke during cooling is different from that during complete warm stratification, as shown in FIG. The air-fuel mixture also spreads in the opposite direction to the mounting of the injection valve outside the bowl. As described above, the air-fuel mixture formed by the cold compression stroke injection exists not only near the spark plug but also on the crown surface of the piston and near the cylinder wall. That is, the morphology of the air-fuel mixture is different from that of the air-fuel mixture formed due to the combustion during the complete warm stratification.

Specifically, since the spray is dispersed over the entire combustion chamber, the air-fuel ratio around the spark plug can be kept away from the misfire limit rich air-fuel ratio. Since an air-fuel ratio that is leaner than approximately stoichiometric can be formed on the cylinder wall surface (Fig. 13 shows the formation of air-fuel mixture), unlike the air layer at the time of complete warm stratification, the combustion flame reaches the end and the combustion quench occurs. The unburned HC due to the amount is reduced. Further, since the air-fuel ratio difference formed around the spark plug and near the cylinder wall is small, the flame propagation speed is fast (see FIG. 17), the combustion efficiency is good, and the residual oxygen in the cylinder is effectively oxidized, so that the exhaust gas is exhausted. A rise in temperature has been obtained.

The advantage of the compression stroke injection in the cold state according to the present invention is that the misfire limit rich air-fuel mixture is not formed in the vicinity of the spark plug due to the improvement of the spray characteristics of the injection valve even under the condition that the fuel vaporization in the engine cold is bad. It is possible to switch combustion immediately after starting. In addition, since the combustion efficiency is improved by allowing the air-fuel mixture to be dispersed throughout the combustion chamber, it is possible to raise the temperature of the exhaust gas, reduce the harmful components emitted during engine cooling, and increase the temperature of the catalyst purification device immediately after startup. It can be made extremely fast, and the deterioration of fuel consumption can be suppressed more than the case of forming other air-fuel mixture.

FIG. 15 shows the heat generation rate due to completely warm stratified combustion and combustion by compression stroke injection during cold engine. It can be seen that the complete warm stratified combustion has a short ignition delay period and rapid combustion occurs around the spark plug. Further, when estimated from the end time of heat generation, it can be seen that the complete warm stratified charge combustion is earlier than the combustion by the cold compression stroke injection because the air layer exists on the cylinder wall surface side. On the contrary, it can be inferred that in the combustion by the compression stroke injection during cold engine, a lean air-fuel mixture layer is formed instead of the air layer.

Regarding the ignition delay period, as shown in FIG. 16, it is understood that the combustion in the conventional intake stroke injection has a long ignition delay period. The short ignition delay period of the combustion due to the cold compression stroke injection confirms that the air-fuel mixture richer than stoichiometry is formed in the vicinity of the spark plug.
It should be noted that FIG. 17 verifies the combustion period in which 90% of the injected fuel burns, and in the case of the cold compression stroke injection, the combustion period is short because the flame propagation speed is high.

Next, how the fuel injection amount is calculated according to the combustion mode will be described. In the case of a combustion mode other than the cold stratified charge combustion, the fuel injection amount is roughly calculated as follows. The control unit 50 calculates the basic fuel injection pulse width (basic injection amount) Tpt corresponding to the target air-fuel ratio based on the intake air amount Qa and the engine speed Ne. C is a constant.

Tpt = C × Qa / Ne Then, the calculated Tpt is used as the water temperature correction coefficient Kw, the post-starting amount increase correction coefficient Kas, and the air-fuel ratio feedback correction coefficient L.
The effective fuel injection pulse width CTI is calculated by making a correction using AMD and the target air-fuel ratio correction coefficient Z. In addition, Ts is an invalid injection time. CTI = Tpt × (1 + Kw + Kas + ...) × LA
MD × Z + Ts In the formula, LAMD is increased / decreased by proportional-plus-integral control or the like according to the air-fuel ratio detection result based on the input signal from the air-fuel ratio sensor 12, and by correcting Tpt by this, The air-fuel ratio is feedback-controlled to the target air-fuel ratio. When the air-fuel ratio feedback correction is not performed at the time of cold stratified combustion, LAMD is fixed to a predetermined value (for example, 1).

In the case of cold stratified combustion,
The fuel injection amount is calculated as follows. The effective fuel injection pulse width CTI in this case is the correction term related to Tpt in the above injection amount calculation formula (for example, the post-starting amount increase correction coefficient Ka).
It is calculated by changing s). Therefore, FIG.
The procedure for calculating the correction coefficient Kas during cold stratified charge combustion will be described with reference to the flowchart shown in FIG.
It should be noted that this routine is executed every predetermined time (for example, 10 ms).

In S41, it is determined whether or not the cold stratified charge combustion control is permitted. If it is determined that it is permitted, the increase correction coefficient Kas after startup is set to NAKA.
The processing proceeds to S42 in order to replace it with S and use this as a correction coefficient in cold stratified combustion. On the other hand, when it is determined that the permission has not been granted, the normal post-starting amount increase correction coefficient Kas corresponding to the cooling water temperature Tw is obtained. At this time, Kas is Tw
Becomes smaller, the target equivalent ratio changes as shown in t2 to 5 of FIG.

In S42, the cooling water temperature Tw and the engine speed Ne are detected based on the input signals from the water temperature sensor and the crank angle sensor. In S43, based on the cooling water temperature Tw, the water temperature correction amount NTKAS of the post-starting increase correction coefficient is read with reference to the map having the tendency shown in FIG. NTKAS is generally set to a larger value as Tw is lower. When the water temperature is low, it can be judged that the wall surface of the combustion chamber is cold and it is difficult to vaporize the fuel components adhering to the wall surface.Therefore, there is a large amount of fuel to be injected to form a mixture with the same air-fuel ratio around the spark plug. Because it will be.

Further, the water temperature correction amount NTKAS is set to a different value depending on the fuel property even with a constant water temperature, and the lighter the fuel, the smaller the value. Light fuel has higher volatility than heavy fuel, and even if the same amount is injected, the amount of fuel components adhering to the wall surface will decrease.Therefore, the injection amount itself should be reduced by that amount, regardless of the fuel properties. This is because the air-fuel mixture has the same air-fuel ratio.

The fuel property is preferably estimated by the method disclosed in the prior publication of the present applicant (Japanese Patent Laid-Open No. 2000-297689). This method is based on so-called learning control, and is roughly as follows. The learning act is carried out when the specified fuel property estimation and execution permission conditions are satisfied at the time of starting. Then, under these conditions, the response waveform of the exhaust air-fuel ratio with respect to the change in the fuel injection amount is sampled, and the input / output data is analyzed to estimate the fuel property. Specifically, the parameters of the plant model are adjusted based on the input / output data so that the prediction error with the reference model that is the plant model for the reference fuel (generally, heavy fuel) is minimized, Identify the plant model for the fuel used. Then, the cutoff frequency fc _Real of the identified plant model is calculated,
The calculated fc _Real is the cutoff frequency fc of the reference model
Compare with _Ref . As a result, if fc _{Re al>} fc _Ref, estimates that use fuel is lighter than the reference fuel.
Of course, for the fuel property estimation, various methods such as direct detection by a sensor can be adopted other than the above method.

At S44, based on the engine speed Ne,
The rotational speed correction amount NTNKAS of the post-starting increase correction coefficient is read with reference to the map having the tendency as shown in FIG. NTNKAS is generally set to a larger value when Ne is lower. At low rotation speed, the gas flow in the cylinder is weak and the fuel components adhering to the wall surface are difficult to vaporize, so the amount of fuel to be injected to form a mixture with the same air-fuel ratio around the spark plug increases. Because.

Further, the rotational speed correction amount NTNKAS is set to a different value depending on the fuel property even at a constant rotational speed, and is set to a smaller value as the fuel is lighter. Considering the high volatility of the light fuel, reduce the injection amount itself,
This is because the air-fuel mixture around the spark plug has the same air-fuel ratio. It should be noted that the maps shown in FIGS. 19 and 20 are used only during traveling (for example, in a low load region other than the idle region), and NTKAS and NT are set as fixed values during idle.
NKAS may be used.

At S45, the product NAKAS = NTKAS of the water temperature correction amount NTKAS and the rotation speed correction speed NTNKAS.
* Calculate NTNKAS. In S46, the latest NAK
Save AS. The stored NAKAS is reflected in the calculation of the effective fuel injection pulse width CTI as the correction coefficient Kas during cold stratified combustion (Kas = NAK).
AS = NTKAS × NTNKAS).

Next, the operation of the combustion control according to this embodiment will be described with reference to the time chart shown in FIG. The chart shows changes with time of the ignition timing, the opening degree of the swirl control valve, the target equivalence ratio, and the engine speed, in contrast to the transition of the combustion form from the start to the warm-up. According to this embodiment, when the start signal is turned on at time t0, the engine is cranked, and the ignition timing is gradually advanced according to the rotation at that time. Then, time t1
When the complete explosion is completed and the start signal is turned off, the ignition timing is fixed at a predetermined timing set in correspondence with the cooling water temperature Tw and the engine speed Ne.

From the start, the target equivalence ratio is corrected and set to a rich side from the stoichiometric equivalent in accordance with the cooling water temperature Tw for stability. Then, when the warm-up operation is started, the increased fuel amount is gradually reduced as Tw increases. When it is determined that the fuel property estimation is completed at time t2, and further that the crown surface temperature of the piston has risen to a predetermined temperature or more at time t3, switching to cold stratified combustion for exhaust gas temperature rise is performed. Is allowed. In response to this, the swirl control valve is driven to the fully closed position (the ignition timing is retarded correspondingly), and when it is determined that the swirl control valve is fully closed at time t4, the time t
In 5, the combustion mode is switched from homogeneous combustion by intake stroke injection to stratified combustion by compression stroke injection. At this time, the fuel injection timing is the compression stroke (50 to 80
The ignition timing is retarded corresponding to the change to ().

In cold stratified combustion for increasing the temperature of exhaust gas from time t5, the target equivalence ratio is set to stoichiometric or slightly lean side in the entire combustion chamber. However, as a result of the post-starting amount increase correction coefficient Kas (= NAKAS) being set as described above, the target equivalence ratio is set to a different value according to the fuel property, and the lighter the value, the lower the fuel injection amount. Is reduced. Here, according to the present embodiment, the cooling water temperature Tw also contributes to the setting of the target equivalence ratio, but for simplicity, the movement caused by the change of Tw is not shown here.

By setting the equivalence ratio as described above, an air-fuel mixture having a stoichiometric or slightly lean air-fuel ratio is formed near the spark plug at the ignition timing. Therefore, in the vicinity of the spark plug, the fuel is not completely burned and incomplete combustion products such as unburned HC and CO are produced. However, the production amount of these products is an appropriate amount, and the oxygen remaining in the cylinder is small. It reacts with and burns off. Then, the combustion gas is heated by the heat generated at this time, and the exhaust gas temperature is raised.

When it is determined that the catalyst is rapidly heated and activated at time t6 while the exhaust temperature is maintained at a high temperature by cold stratified combustion, normal combustion control (here, at t7) is performed. Homogeneous stoichiometric combustion). Then, the ignition timing is advanced correspondingly. However, even before the catalyst is activated, when the accelerator is depressed greatly, in order to secure the operation performance, the normal combustion control is performed at that time.

When the swirl control valve is driven toward the fully open position in response to the transition of the combustion mode, the ignition timing is advanced correspondingly. In the above description, the air-fuel ratio feedback correction coefficient LAMD of the injection amount calculation formula is fixed to 1 and the combustion injection amount is open-controlled during cold stratified combustion, but LAMD is made to function and feedback to the target air-fuel ratio is performed. While controlling, the fuel property may be reflected in the injection amount calculation formula at this time.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

[Fig. 2] Flow chart of combustion control

FIG. 3 is a flowchart for determining catalyst activity.

FIG. 4 is a time chart for explaining catalyst activity determination.

FIG. 5 is a flowchart for determining the piston crown surface temperature.

FIG. 6 is a time chart for explaining the determination of the piston crown surface temperature.

FIG. 7 is a flowchart for determining a compression stroke injection condition.

FIG. 8 is a schematic diagram for explaining a spray form at the time of completely warmed stratified charge combustion.

FIG. 9 is a schematic diagram for explaining a spray form at the time of cold-stage compression stroke injection.

FIG. 10 is a structural diagram of a fuel injection valve

FIG. 11 is a schematic diagram for explaining air-fuel mixture formation during intake stroke injection.

FIG. 12 is a schematic diagram for explaining mixture formation during completely warmed stratified charge combustion.

FIG. 13 is a schematic diagram for explaining air-fuel mixture formation during cold-stroke compression stroke injection.

FIG. 14 is a diagram for explaining combustion performance by compression stroke injection.

FIG. 15 is a diagram showing a heat release rate.

FIG. 16 is a diagram showing an ignition delay period.

FIG. 17 is a diagram showing a combustion period

FIG. 18 is a flowchart for calculating the increase correction coefficient after starting.

FIG. 19 is a diagram showing a setting map for water temperature correction.

FIG. 20 is a diagram showing a setting map for rotation speed correction.

FIG. 21 is a time chart showing the operation of combustion control.

[Explanation of symbols]

1 Internal combustion engine 2 Intake passage 3 Air flow meter 4 Throttle valve 5 swirl control valve 6 cylinder head 7 pistons 7a Bowl part 8 Combustion chamber 9 Fuel injection valve 9a nozzle 10 Spark plug 11 exhaust passage 12 Air-fuel ratio sensor 13 Exhaust purification catalyst 14 Downstream oxygen sensor 15 Crank angle sensor 16 Water temperature sensor 17 Throttle sensor 18 Throttle control device 19 Accelerator pedal sensor 20 key switch 50 control unit

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02B 23/10 F02B 23/10 M F02D 41/14 310 F02D 41/14 310L 41/34 41/34 E 45/00 312 45/00 312B 312N 312Q Q360 360B 364 364K F02M 61/14 310 F02M 61/14 310A F term (reference) 3G023 AA02 AA04 AB03 AC05 AD02 AD06 AD09 AD29 DC08 DC04 CC22G4U06CC22U4C09 AD22 BA43 BA06 AD12 BA43 BA14 BA05 BA09 BA13 BA15 BA17 BA21 CA02 CA03 DA02 DA10 DA25 EA11 EB08 EB11 EB17 EC01 EC03 EC04 FA07 FA10 FA14 FA20 FA27 FA30 FA33 FA36 3G301 HA04 HA16 HA17 JA02 JA23 JA26 JA28 KA02 KA07 LA03 LA05 LB04 MA01 MA11 MA13 MA01 MA02 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA29 MA02 MA02 MA02 MA02 MA02 MA02 MA02 ND21 ND45 NE01 NE06 NE13 NE15 NE16 NE22 PA01Z PA11Z PB02Z PD03Z PD04Z PD05Z PD09Z PD12 PE01Z PE08 PF03Z PF16Z

Claims (15)

[Claims] 1. A direct injection spark ignition internal combustion engine comprising a fuel injection valve for directly injecting fuel into a cylinder and a spark plug for spark ignition of a mixture gas in the cylinder, wherein the fuel injection valve is a fuel spray for the same. Is configured so that the flow velocity in the direction traversing the inside of the cylinder is higher than the flow velocity toward the piston side, while fuel is injected in the compression stroke when the engine is cold, and the air-fuel ratio in the cylinder is stoichiometric or slightly lean. A direct injection spark ignition type internal combustion engine, characterized in that a control means for controlling the fuel injection amount to perform stratified charge combustion is provided. 2. A direct injection spark ignition type internal combustion engine according to claim 1, wherein an exhaust purification catalyst is provided in the exhaust passage. 3. The fuel injection valve is provided so as to be directed from the intake side to the exhaust side of the cylinder head and inclined downward, and its injection port is deflected toward the cylinder head side with respect to the injection valve axis. The direct injection spark ignition type internal combustion engine according to claim 1 or 2. 4. The control means causes the homogeneous combustion by the intake stroke injection to be performed immediately after the engine is started, and then directly shifts to the stratified combustion by the compression stroke injection. A direct injection spark ignition type internal combustion engine according to any one of the claims. 5. The control means sets the air-fuel ratio at the time of intake stroke injection immediately after the engine is started to be richer than stoichiometric, and makes the air-fuel ratio at the subsequent compression stroke injection slightly leaner than stoichiometric. Item 4. A direct injection spark ignition type internal combustion engine according to item 4. 6. The condition for transitioning to the stratified charge combustion by the compression stroke injection is satisfied when it is determined that the piston crown surface temperature is equal to or higher than a predetermined temperature indicating a high temperature state. Item 5. A direct injection spark ignition internal combustion engine according to Item 5. 7. The piston crown surface temperature is determined to be equal to or higher than the predetermined temperature when the pseudo water temperature as a parameter correlating with the piston crown surface temperature is equal to or higher than a predetermined temperature, and the pseudo water temperature is the cooling water at startup. 7. The calculation is performed with a delay with respect to the change of the cooling water temperature, based on an initial value according to the temperature and a delay correction coefficient according to the intake air amount for each predetermined cycle. A direct injection spark ignition type internal combustion engine as described. 8. A fuel property estimating means for estimating a fuel property, wherein the control means calculates and corrects a required fuel amount for making the air-fuel ratio in the cylinder stoichiometric or slightly lean according to the fuel property. The direct injection spark ignition type internal combustion engine according to any one of claims 1 to 7, characterized in that. 9. The direct injection spark ignition type internal combustion engine according to claim 8, wherein said control means performs a large amount reduction correction of the required fuel amount as the fuel is lighter, depending on the fuel property. 10. The direct injection spark ignition type internal combustion engine according to claim 8 or 9, wherein the correction amount according to the fuel property is determined based on the engine speed. 11. The direct injection spark ignition internal combustion engine according to claim 10, wherein the fuel injection amount is increased according to the correction amount as the engine speed is lower. 12. The direct injection spark ignition type internal combustion engine according to claim 8 or 9, wherein the correction amount according to the fuel property is determined based on the engine temperature. 13. The fuel injection amount is increased according to the correction amount as the engine temperature is lower.
2. A direct injection spark ignition type internal combustion engine according to 2. 14. The direct injection spark ignition according to any one of claims 8 to 13, wherein the control means performs the correction according to the fuel property during the open control of the required fuel amount. Internal combustion engine. 15. The direct injection spark ignition according to any one of claims 8 to 13, wherein the control means performs the correction according to the fuel property during the feedback control of the required fuel amount. Internal combustion engine.