JPH1122541A - Direct-injection-type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely diagnose adhesion situation of deposit in a combustion chamber, by providing a diagnosis injection time setting means which forcibly sets fuel injection time on advance side than a usual angle, and comparing combustion speed at diagnosis injection time with standard combustion speed to diagnose adhesion situation of deposit. SOLUTION: During operating of an engine 1, a control module 10 judges whether it takes a given time after starting of the engine 1 or not. When it is YES and water temperature of the engine 1 is higher than a given temperature, and in warming condition, whether combustion state is uniform combustion operation or not is judged from an output signal of a water sensor 8. When it is uniform combustion operation, subsequently whether operation state is normal operation or not is judged, and when it is normal operation, in order to diagnose deposit adhesion fuel injection timing is advanced to a first half of intake process. Then, combustion speed when fuel injection time is forcibly advanced is detected, this combustion speed is compared with standard combustion speed when deposit is not adhered, and adhesion amount is diagnosed from the difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasoline internal combustion engine which injects fuel directly into a combustion chamber, and more particularly to a direct injection type internal combustion engine capable of diagnosing a deposit state of a combustion chamber such as a piston crown.

[0002]

2. Description of the Related Art As a conventional direct injection type internal combustion engine, for example, one described in Japanese Patent Application Laid-Open No. 6-207542 is known. This is because the fuel injection timing is the intake stroke injection at medium to high loads and medium to high rotations (so-called homogeneous combustion), while the injection timing is the compression stroke injection at low to medium loads and low to medium rotations ( So-called stratified combustion)
It improves fuel efficiency and exhaust performance at low to medium loads and low to medium speeds.

In the stratified combustion operation, a recess is formed on the piston crown surface, and fuel is injected from the fuel injection valve toward the piston crown recess at the end of the compression stroke at low to medium load and low to medium rotation. Only a very limited space near the ignition plug is burned with a combustible mixture ratio. A region other than the above-mentioned limited space, which occupies most of the space in the combustion chamber, becomes a very thin mixture, and the entire combustion chamber becomes a super-lean mixture, so that it has a feature of excellent fuel economy and exhaust performance.

[0004] On the other hand, the homogeneous combustion operation means that fuel is injected from the fuel injection valve toward the entire combustion chamber during the intake stroke at medium to high loads and medium to high revolutions, and combustion is performed in a combustible premixed state. It is to let.

[0005] Switching between stratified combustion and homogeneous combustion is performed when the operating conditions change from low to medium to high load / rotation.
Change from stratified combustion (ultra lean) to homogeneous lean combustion → homogeneous combustion (stoichiometric or rich). This is because the gas flow in the combustion chamber becomes stronger as the speed becomes low → medium / high load / revolution, and the fuel injected near the spark plug so as to have a combustible mixture ratio diffuses into a space other than the limited space, causing ignition. Since the mixing ratio in the vicinity of the plug becomes lean and stable combustion cannot be obtained, the combustion is switched to homogeneous combustion.

[0006]

By the way, when such combustion is repeated, so-called deposits may accumulate in the concave portions formed on the piston crown surface. Since the deposit adsorbs the injected fuel, the degree of mixing of the fuel with the air in the combustion chamber (mixing efficiency) is reduced and a uniform mixture is not obtained, which adversely affects the operability and emission. There was such a problem.

However, in the conventional direct injection type internal combustion engine, there is no means for judging the adhesion state of the deposit, and the driver or a car maintenance engineer diagnoses the adhesion state of the deposit without disassembling the internal combustion engine. Could not.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and has as its object to provide a direct injection type internal combustion engine capable of diagnosing the state of deposit adhesion in a combustion chamber.

[0009]

In a gasoline internal combustion engine in which fuel is directly injected into a combustion chamber, generally, homogeneous combustion and stratified combustion are selectively used in terms of fuel efficiency, output, emission, and the like. In this type of direct injection type internal combustion engine,
A recess is formed in the piston crown surface so that stratified combustion can be performed.

As shown in FIG. 3, the relationship between the combustion injection timing and the combustion speed during homogeneous combustion is such that the combustion speed decreases when the injection timing is advanced, and the combustion speed increases when the injection timing is retarded. Become. From the viewpoints of fuel efficiency, output, emission, etc., it is considered that a higher combustion speed is preferable. Therefore, the normal combustion timing is set to the point A shown in the figure, but if deposits adhere to the piston crown surface in this state, As shown by the broken line in the figure, there is a tendency that the combustion speed further decreases on the advance side of the injection timing.

This mechanism will be described with reference to FIGS. 4 and 5. As shown in FIG. 4, when the fuel is advanced at an early stage of the intake stroke and the fuel is injected, the fuel enters the concave portion of the piston crown surface. Thereafter, the fuel moves together with the piston and is difficult to mix and diffuse. Even in the vicinity of the compression top dead center, the inside of the recess is rich, and the area around the spark plug becomes lean, so that a homogeneous air-fuel mixture cannot be obtained. Therefore, when the fuel injection timing is advanced, the combustion speed becomes slow. In such a case, if the deposit on the piston crown surface is remarkable, the injected fuel is adsorbed on the deposit, and this tendency is further promoted.
For this reason, the combustion speed is further reduced.

On the other hand, as shown in FIG. 5, when fuel is injected in the latter half of the intake stroke, the fuel mixes and diffuses with the air in the entire combustion chamber without reaching the recess in the piston crown surface. Even near the dead center, a homogeneous mixture is obtained in the entire combustion chamber, and as a result, the combustion speed is increased. When fuel is injected late in the intake stroke, the fuel does not reach the piston crown surface, so this tendency is not affected by the deposit state.

Utilizing such characteristics during the homogeneous combustion operation,
In the present invention, the deposit state is determined by forcibly advancing the fuel injection timing from the standard set point during the homogeneous combustion operation and measuring the combustion speed at this time.
That is, the difference between the solid line (without deposit attached) and the dotted line (with deposited deposit) on the advance side in FIG. 3 is used to identify the amount of deposit attached.

Further, in the present invention, since the combustion speed is intentionally reduced, it is desirable that the diagnosis be performed in a state where the fuel consumption and the emission are not affected much.
For this reason, the timing of diagnosis is also taken into consideration.

That is, in order to achieve the above object, the direct injection type internal combustion engine according to the first aspect of the present invention is a direct injection type internal combustion engine which directly injects fuel into a combustion chamber, in an operating state in which fuel is injected during an intake stroke. At one time, diagnostic injection timing setting means for forcibly setting the fuel injection timing to a more advanced angle than normal, and combustion detecting the combustion speed when the fuel injection timing is set to a more advanced angle than normal Speed detection means, standard combustion speed storage means for previously storing a standard combustion speed in a state where no deposit is attached to the combustion chamber, and a combustion speed detected by the combustion speed detection means and the standard combustion speed storage means. An adhesion state diagnosing means for diagnosing the adhesion state of the deposit by comparing with the stored standard combustion speed is provided.

In the direct injection type internal combustion engine according to the first aspect of the invention, the fuel injection timing is forcibly advanced in an operation state in which fuel is injected in the intake stroke, that is, in a homogeneous combustion operation state, and the combustion at that time is performed. Detect speed. The burning rate is compared with a standard burning rate when there is no deposit, and the amount of deposit is diagnosed based on a difference in the burning rate correlated with the deposit.

According to a second aspect of the present invention, in the direct injection type internal combustion engine, the diagnostic injection timing setting means advances the fuel injection timing more than usual in a low load and a low rotation range of a fuel injection region in an intake stroke. It is forcibly set on the side.

According to a third aspect of the present invention, in the direct injection type internal combustion engine, the diagnostic injection timing setting means forcibly sets the fuel injection timing to be more advanced than usual in a region close to a region where fuel is injected in a compression stroke. It is characteristically set.

As for the emission, if the emission concentration is the same, the emission amount decreases as the intake air amount decreases, and the emission amount increases as the intake air amount increases. This is because discharge amount = concentration × intake air amount × specific gravity of exhaust gas. The same can be said for fuel economy. Therefore, in the homogeneous combustion, the least effect on the fuel consumption and the emission is in the low-load, low-rotation region, and the low-load and the low-injection region in the intake stroke (homogeneous combustion operation region) according to claim 2. This is a region close to a low rotation region, in other words, a region in which fuel is injected in the compression stroke (stratified combustion operation region). This minimizes the impact on fuel economy and emissions.

According to a fourth aspect of the present invention, there is provided a direct injection type internal combustion engine further comprising: idle determination means for determining an idle state; and combustion mode changing means for setting a fuel injection timing to an intake stroke when the engine is in an idle state. Is established, the fuel injection timing is forcibly set to a more advanced side than the fuel injection timing in the normal intake stroke.

When the operation at a very low speed is repeated for a long time, the combustion temperature is low and the deposits become remarkable, so that the frequency of diagnosis needs to be increased. In a direct injection internal combustion engine, the idle state is usually set to a stratified combustion operation. For this reason, in the direct injection type internal combustion engine according to the fourth aspect, even when the fuel injection is performed in the compression stroke, that is, in the stratified combustion operation state, the fuel injection is forcibly switched to the homogeneous combustion operation, and the diagnosis condition is changed. When the condition is satisfied, the fuel injection timing is forcibly advanced to execute a diagnosis of deposit adhesion. This makes it possible to increase the frequency of diagnosis when deposits become significant.

According to a fourth aspect of the present invention, in the direct injection type internal combustion engine, the diagnosis condition is that the idle state continues for a predetermined time or more, or the idle state continues for a predetermined time or more,
It is preferable that the temperature is low. This is because the influence on fuel consumption and emission is small, and the combustion state is stable, and an accurate diagnosis result can be obtained.

[0023]

According to the direct injection type internal combustion engine of the present invention, the amount of deposits deposited on the combustion chamber can be identified only by advancing the fuel injection timing and measuring the combustion speed at that time, and the fuel consumption and Measures can be taken to reduce output and emissions.

According to the direct injection type internal combustion engine of the second and third aspects, even when the fuel injection timing is forcibly advanced to diagnose the deposit adhesion, the influence on the fuel consumption and the emission is minimized. can do.

According to the direct injection type internal combustion engine of the fourth aspect, the frequency of diagnosis can be increased in an idling state in which deposits are significantly attached.

According to the direct injection type internal combustion engine according to the fifth and sixth aspects, an accurate diagnosis result can be obtained with little influence on fuel consumption and emission, stable combustion state.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram showing a first embodiment of a direct injection type internal combustion engine of the present invention, and FIG. 6 is a block diagram showing a specific example thereof. As shown in FIG. 6, upstream of the engine 1,
An air cleaner 2 for purifying intake air, an air flow meter 3 for measuring the amount of intake air, and a throttle chamber 4 for controlling the amount of intake air are provided. The output of the air flow meter 3 is sent to a control module 10 as a signal. Is sent as

Further, downstream of the throttle chamber 4,
An intake pipe 5 is provided, and an injector 6 is attached to face a combustion chamber of the engine 1 directly.

The engine 1 has an ignition plug 7 for igniting the air-fuel mixture, a water temperature sensor 8 for detecting a warm-up state of the engine 1, and a crank angle sensor 9 for detecting the number of revolutions of the engine 1. The outputs of the water temperature sensor 8 and the crank angle sensor 9 are sent to the control module 10 as signals.

The control module 10 uses the amount of intake air sent from the air flow meter 3, the water temperature data sent from the water temperature sensor 8, and the engine speed sent from the crank angle sensor 9 to perform homogeneous combustion. Alternatively, an operation state and a region in which stratified combustion is performed are determined, a fuel injection amount, a fuel injection timing, and an ignition timing according to each combustion mode are calculated, and fuel is injected into the combustion chamber by the injector 7.

Here, the homogeneous combustion produces a homogeneous mixture in the combustion chamber, the mixture ratio is stoichiometric to rich or lean, and the fuel injection timing is the intake stroke. On the other hand, in the stratified combustion, the air-fuel mixture is collected near the ignition plug to generate a lean mixture ratio in the entire combustion chamber, and the fuel injection timing is set in the compression stroke.

On the other hand, in the mounting portion of the ignition plug 7 in the combustion chamber,
A washer sensor (combustion speed detecting means) 11 for detecting the combustion state of the engine is attached, and the combustion speed is detected by an output signal sent from the washer sensor 11 to the control module 10.

The diagnostic injection timing setting means, the adhesion state diagnosing means and the standard combustion speed storage means of the present invention shown in FIG. 1 are all constituted by a microcomputer built in the control module 10.

Next, the operation will be described. As shown in FIG.
A predetermined time Tst (for example, 1
Minute) has elapsed (S1). When the engine 1 is started, combustion may not be stable due to an increase in fuel at the time of start or a wall flow state when the engine was stopped last time. During this time, the combustion is not suitable for the deposit adhesion diagnosis of the present embodiment. To avoid.

When one minute has passed since the start of the engine 1, the routine proceeds to step 2, where it is determined from the output signal of the water temperature sensor 8 whether or not the water temperature Tw of the engine 1 is equal to or higher than a predetermined temperature (for example, 80 ° C.) ( S2). The temperature of the engine cooling water indicates the warm-up state of the engine 1. The combustion may not be stable below a predetermined temperature, and during this time, it is not suitable for the deposit adhesion diagnosis of the present embodiment. That's why.

If the temperature of the engine cooling water is 80 ° C. or higher, the routine proceeds to step 3, where it is determined whether the combustion mode is a homogeneous combustion operation (S3). This determination is performed based on the engine load and the engine speed obtained from the output signals of the air flow meter 3 and the crank angle sensor 9 with reference to FIG. FIG. 3 shows the region where the homogeneous combustion operation is executed and the region where the stratified combustion operation is executed in relation to the engine load and the engine speed. If it is an area, go to the next step 4.

In step 4, it is determined whether the operating state of the engine 1 is a steady operation. Since the charging efficiency and the like change depending on the operation region of the engine, the combustion speed also changes, and a stable combustion speed cannot be detected in a transient operation state over a plurality of operation regions. During this time, it is not suitable for the deposit adhesion diagnosis of the present embodiment, so that it is avoided.

Here, normally, the fuel injection timing is set to the latter half of the intake stroke. After detecting the operating conditions, that is, the engine load and the engine speed in step 5, the deposit adhesion diagnosis is executed. In step 6, the fuel injection timing is advanced to the first half of the intake stroke. The amount of advance at this time is an amount corresponding to the operating condition detected in step 5.

Next, at step 7, the combustion period (θ10
After detecting (−90), a comparison is made in step 8 with a standard combustion period when there is no deposit adhesion in the advanced state under the operating conditions determined in step 5, and the difference (Δθ10−90) Is calculated.

The combustion period θ10-90 is defined as 10 to 90% when the amount of heat generated by one combustion is 100%.
And also referred to as the main combustion period. This main combustion period θ10−
If 90 is short, combustion is fast, and if 90 is long, combustion is slow. By detecting this, the state of combustion can be determined. By the way, 0 to 100% of one combustion
10% is referred to as the initial combustion period θig-10.

The main combustion period θ10-90 can be specifically detected by, for example, a washer-shaped sensor 11 inserted between the ignition plug and the cylinder head. In other words, utilizing the fact that the stress in the fastening portion of the ignition plug decreases when the pressure in the combustion chamber increases, the washer sensor 11 detects the pressure during combustion, and the control unit 10
By calculating the pressure generated from the difference between the combustion pressure and the non-combustion pressure, and further obtaining the heat generation amount, that is, the heat generation amount from the specific heat between the generated pressure and the stroke volume for each crank angle, θ10
-90 can be calculated.

In step 9, the actual combustion period determined in step 8 is determined using a map (see FIG. 8) showing the relationship between the difference Δθ10-90 in the combustion period and the amount of deposits which have been determined in advance. Is applied to estimate a deposit adhesion state.

Incidentally, since the combustion speed changes depending on the operating conditions, and the difference Δθ10-90 also changes, a map showing the relationship between the difference Δθ10-90 in the combustion period and the amount of deposit attached is prepared for each operating condition. . Alternatively, the value obtained in step 8 may be the ratio Δθ10−90 / θ10−90 of the difference between the combustion period and the combustion period. In this case, the relationship between the change rate of the combustion period and the deposit amount is shown. You will have a map.

Next, at step 10, it is determined whether or not the estimated deposit amount is equal to or larger than a predetermined value. Deposits are present, but if the degree is small, fuel economy and emissions are not adversely affected, so this is determined. Here, if the deposit amount exceeds the predetermined value, the process proceeds to step 11, where the deposit state and the degree thereof are displayed to the driver or maintenance technician. If the deposit amount does not reach the predetermined value, the process returns without any problem.

Second Embodiment FIG. 9 is a part of a flowchart of a second embodiment of the present invention, in which step 12 is added between steps 5 and 6 of the flowchart shown in FIG. Other configurations and processes are the same as those of the above-described first embodiment.

In the present embodiment, after detecting the operating conditions (engine load and engine speed) in step 5, and performing the deposit adhesion diagnosis under the operating conditions in step 12, the influence on the fuel consumption and emission is considered. Is determined whether there is little.

As shown in FIG. 10, the homogeneous combustion operation is generally a combustion mode in a medium to high load and a medium to high rotation amount range. Among them, a hatched region shown in FIG. An area close to the area is an area that can be said to have the least effect on fuel efficiency and emission.

As for the emission, if the emission concentration is the same, the emission amount is smaller as the intake air amount is smaller, and the emission amount is larger as the intake air amount is larger. This is because discharge amount = concentration × intake air amount × specific gravity of exhaust gas. The same can be said for fuel economy. Therefore, in the homogeneous combustion, the least effect on the fuel consumption and the emission is in the low load and low rotation region. In the homogeneous combustion operation region, the shaded portion shown in FIG.

Such a region is detected based on the engine load and the engine speed. If the region is a hatched region as shown in the figure, the process proceeds to step 6, but otherwise returns.

As described above, when the deposit adhesion diagnosis is performed, the influence on the fuel consumption and the emission can be minimized by adopting the region where the engine load and the engine speed are small.

Third Embodiment FIG. 2 is a block diagram showing a third embodiment of the present invention.
A combustion mode changing unit and an idle determining unit are added to the first embodiment of FIG. FIG. 12 is a flowchart of the embodiment, in which processes S13 to S21 when it is determined in step 3 that the operation is not the homogeneous combustion operation are added.

If the operation at a very low speed is repeated for a long time, the combustion temperature is low and the adhesion of deposits becomes remarkable, so that it is necessary to increase the frequency of diagnosis. In the present embodiment, when it is determined that the combustion operation is not the homogeneous combustion operation in step 3, first, in step 13, it is determined whether or not a predetermined time (for example, 10 minutes) has elapsed in the low-temperature operation state.

As shown in FIG. 11, when the operation is not the homogeneous combustion operation, that is, in the case of the stratified combustion operation, a low load and a low rotation region are included. If the operation in such a low-temperature mode continues to some extent, it is considered that the deposition of the deposit also progresses. Therefore, the possibility of the progress of the deposition of the deposit is determined. Here, if the operation state in the low-temperature region has been continued for 10 minutes or more, it is determined that the deposit is progressing, and the process proceeds to step S14.

At step 14, it is determined whether or not a predetermined time (for example, 10 minutes) has elapsed since the idle state. In this case, it is desirable to perform the deposit adhesion diagnosis in an idle state having the least effect on fuel consumption and emission, and to determine the possibility of such an idle state being maintained. If the idle state lasts for a predetermined period of time, it is highly likely that it has stopped, for example, waiting for a traffic light, and since the idle state has passed to some extent, the combustion state is stable, making it easy to diagnose deposit adhesion This is because it can be performed accurately.

In the next step 15, the fuel injection timing and the ignition timing are switched to those for the homogeneous combustion operation so as to forcibly perform homogeneous combustion. Originally, the idling state is performed in the stratified combustion operation. However, in order to minimize the influence on the fuel consumption and the emission caused by the deposit adhesion diagnosis, the operation is intentionally set to the homogeneous combustion operation.

In step 16, the fuel injection timing is advanced by an amount corresponding to the idling state, and in step 17, the combustion period θ10-90, which is a parameter related to the combustion speed in the advanced state, is detected.

In the next step 18, this combustion period θ1
0-90 and the standard combustion period in which the engine is advanced in the idle state and there is no deposit, and the difference Δθ1
Find 0-90. In step 19, the difference Δθ10-90 between the actual combustion periods calculated in step 18 is applied using a map indicating the relationship between the difference Δθ10-90 between the combustion periods and the amount of deposits, which is obtained in advance. Estimate the deposit status.

In the next step 20, it is determined whether or not the estimated deposit amount is equal to or more than a predetermined value. Deposits are present, but if the degree is small, fuel economy and emissions are not adversely affected, so this is determined. If the deposit amount exceeds the predetermined value, the process proceeds to step 21 to display the deposit state and the degree thereof to a driver or a maintenance technician. If the deposit amount does not reach the predetermined value, the process returns without any problem.

The embodiments described above are described for facilitating the understanding of the present invention, but are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a direct injection internal combustion engine of the present invention.

FIG. 2 is a block diagram showing a third embodiment of the direct injection internal combustion engine of the present invention.

FIG. 3 is a graph showing a relationship between a fuel injection timing and a combustion speed during a homogeneous combustion operation.

FIG. 4 is a diagram for explaining a combustion state during a homogeneous combustion operation (first-stage intake stroke injection).

FIG. 5 is a diagram illustrating a combustion state during a homogeneous combustion operation (late injection in an intake stroke).

FIG. 6 is a block diagram showing an embodiment in which the direct injection internal combustion engine of the present invention is embodied more.

FIG. 7 is a flowchart showing the operation of the first embodiment of the present invention.

FIG. 8 is a graph showing a relationship between a combustion period θ10-90 and a deposit amount.

FIG. 9 is a flowchart showing a main part of the operation of the second embodiment of the present invention.

FIG. 10 is a graph showing operating ranges of a homogeneous combustion operation and a stratified combustion operation, and shows a deposit adhesion diagnosis region in the first and second embodiments.

FIG. 11 is a graph showing operation regions of a homogeneous combustion operation and a stratified combustion operation, and shows a low temperature mode region in the third embodiment.

FIG. 12 is a flowchart showing the operation of the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Air cleaner 3 ... Air flow meter 4 ... Throttle chamber 5 ... Intake pipe 6 ... Injector 7 ... Spark plug 8 ... Water temperature sensor 9 ... Crank angle sensor 10 ... Control module

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 330 F02D 41/04 330P 335 335Z G01M 15/00 G01M 15/00 Z

Claims (7)

[Claims] In a direct injection type internal combustion engine in which fuel is directly injected into a combustion chamber, when in an operation state in which fuel is injected in an intake stroke,
Diagnostic injection timing setting means for forcibly setting the fuel injection timing to an advanced angle than normal, and combustion speed detecting means for detecting the combustion speed when the fuel injection timing is set to an advanced angle than normal Standard combustion speed storage means for storing in advance a standard combustion speed in a state where no deposit is attached to the combustion chamber; and a combustion speed detected by the combustion speed detection means and stored in the standard combustion speed storage means. A direct-injection internal combustion engine, comprising: an adhesion status diagnosis unit that diagnoses an adhesion status of a deposit by comparing the standard combustion speed with a standard combustion speed. 2. The diagnostic injection timing setting means forcibly sets the fuel injection timing to a more advanced angle than usual in a low load and low rotation range of a fuel injection range in an intake stroke. The direct injection type internal combustion engine according to claim 1, wherein 3. The diagnostic injection timing setting means according to claim 1, wherein said diagnostic injection timing setting means includes:
2. The direct injection internal combustion engine according to claim 1, wherein the fuel injection timing is forcibly set to a more advanced side than usual. 4. An engine according to claim 1, further comprising: an idle determining means for determining an idle state; and a combustion mode change for setting the fuel injection timing to an intake stroke when the engine is in the idle state. The direct injection type internal combustion engine according to any one of claims 1 to 3, wherein the fuel injection timing is forcibly set to a more advanced side than the fuel injection timing in the intake stroke. 5. The direct injection internal combustion engine according to claim 4, wherein the diagnosis condition is that the idle state continues for a predetermined time or more. 6. The direct injection internal combustion engine according to claim 4, wherein the diagnosis condition is that the idle state continues for a predetermined time or more and the temperature is low. 7. The direct injection internal combustion engine according to claim 4, wherein fuel is injected during a compression stroke in an idle state other than at the time of said diagnosis.