JP2000054884A - Fuel injection control method for cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain superior cold start-up performance and to improve fuel consumption and exhaust emission. SOLUTION: This spark ignition type cylinder injection type engine, which has a cylinder injecting injector 5 capable of directly injecting a required fuel into its combustion chamber 4, takes air into the combustion chamber 4, compresses the intake air with its piston 3, injects the fuel into a cylinder directly, and ignites and burns the fuel. In this engine, when a pressure detected by an injection pressure detecting means 15 is not less than an injectable set value at the time of a start, injection timing is controlled by the fuel injector 5 capable of changing the injection timing, such that a combustion mode becomes a stratified charge combustion mode until an engine speed detected by an engine speed detecting means 13 reaches to an ignition deciding set value. Until a temperature of cooling water reaches to a warming-up finishing set value after ignition, the injection timing is set in an intake stroke and is controlled by the fuel injector 5 such that the combustion mode becomes a homogeneous mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to switching between stratified combustion and homogeneous combustion by controlling in-cylinder injection timing to achieve not only good cold start performance but also improvement in fuel consumption and exhaust emission. The present invention relates to a fuel injection control method for an in-cylinder injection type internal combustion engine which can be performed.

[0002]

2. Description of the Related Art A conventional fuel injection control device for a direct injection type internal combustion engine (Japanese Patent Laid-Open No. 10-30468) adjusts the injection timing when the cooling water temperature at start-up is lower than a set cold determination temperature, for example, 60 ° C. Even after a complete explosion in which the rotation speed is equal to or higher than the set complete explosion determination rotation speed so as to achieve homogeneous combustion, homogeneous (uniform) combustion is performed until the set cooling water temperature reaches, for example, 80 ° C. as shown in FIG. To maintain. Then, when the cooling water temperature is equal to or higher than the set cold determination temperature during warm-up, and the load shifts from a high load to a low load range, stratified combustion is set.

On the other hand, when the engine is restarted after being temporarily stopped, the cooling water temperature is equal to or higher than the cold determination temperature, and the fuel injection pressure is a pressure that can sufficiently atomize the spray particle diameter. If it is a set value, the injection timing is set to the compression stroke so that stratified combustion is performed from the start.

As another method, in a conventional in-cylinder injection engine (Japanese Patent Application Laid-Open No. 61-250354), an intake port injector SI is provided separately from the in-cylinder injector DI as shown in FIG. When the engine temperature is low, such as at the time of starting, the proportion of fuel injected from the intake port injector SI is increased to supply a sufficiently premixed mixture into the cylinder, and at the same time, the in-cylinder injector The DI was also injected into the cylinder so that the fuel was stratified, and the rich mixture near the spark plug was ignited by sparks, thereby improving the startability.

[0005] Further, by decreasing the proportion of fuel injected into the intake port as the engine temperature rises and increasing the proportion of fuel injected in the cylinder relatively, the combustion mode is gradually changed from a uniform combustion field to a stratified combustion field. Was to be migrated.

[0006]

SUMMARY OF THE INVENTION A fuel injection control apparatus for a conventional direct injection type internal combustion engine (Japanese Patent Laid-Open No. 10-30468).
In the case of No.), fuel is injected during the intake stroke in order to achieve warm-up homogeneous combustion at cold start. However, during cold start, the in-cylinder ambient temperature and piston temperature are low. Of fuel cannot be mixed by evaporation. Injected fuel evaporates slowly, and to compensate for this, a method of introducing more fuel than necessary into the cylinder and making the average in-cylinder A / F richer than the stoichiometric ratio to secure the mixture concentration is actually used. Is often used. However, in this case, there is a problem that the fuel vaporized late is discharged as a large amount of unburned THC.

FIG. 7 shows the THC discharged from the cold start to the end of warm-up in the conventional homogeneous combustion of the engine. In this method, for the reason described above, a sharp TH
C rise is seen.

The above-described conventional in-cylinder injection engine (Japanese Unexamined Patent Publication No.
-250354), an intake port injector is provided in addition to the in-cylinder injector, and although the ignitability is improved, the required fuel pressure is increased between the in-cylinder injector and the intake port injector. Are extremely different from each other, so that at least two fuel supply lines are required, the structure is complicated, and there is a problem that the cost is increased due to an increase in the number of parts. Further, since a large amount of fuel adheres to the intake port, more fuel injection than necessary is necessary for starting.

Therefore, the present inventor has paid attention to the technical knowledge of the present invention that switches between stratified combustion and homogeneous combustion by controlling the in-cylinder injection timing. That is, in a direct injection internal combustion engine equipped with a fuel injection valve that injects fuel into the combustion chamber, if the fuel injection pressure exceeds a set value at which fuel can be injected at the time of starting, the rotation speed of the internal combustion engine is set to an ignition determination set value. Until the fuel injection timing is controlled so that the combustion mode in the combustion chamber is stratified combustion. Control so that As a result, the present invention has been achieved which achieves not only good cold start performance, but also the object of improving fuel efficiency and exhaust emission.

[0010]

According to a first aspect of the present invention, there is provided a fuel injection control method for a direct injection internal combustion engine, comprising a cylinder having a fuel injection valve for injecting fuel into a combustion chamber. In the case of the internal injection type internal combustion engine, if the fuel injection pressure exceeds the settable value at the time of start-up, the combustion mode in the combustion chamber becomes stratified combustion until the rotation speed of the internal combustion engine reaches the set value for ignition determination. In addition to controlling the fuel injection timing, the fuel injection timing is controlled so that the combustion mode is homogeneous until the coolant temperature reaches the warm-up completion set value of the internal combustion engine after ignition.

[0011]

According to the fuel injection control method for a direct injection type internal combustion engine of the present invention having the above-described structure, when the fuel injection pressure exceeds a set value at which fuel can be injected at the time of starting, the rotation speed of the internal combustion engine is ignited. Until the set value for determination is reached, the fuel injection timing is set to the compression stroke so that the combustion mode in the combustion chamber becomes stratified combustion. In this compression stroke, the air temperature is high due to the compression by the piston, the fuel is easily vaporized, and a rich air-fuel mixture is easily formed around the ignition plug, so that stable ignition can be performed with the minimum necessary fuel. Furthermore, since the injection timing is set to the intake stroke so that the combustion mode is homogeneous, the average gas temperature and the exhaust gas temperature in the cylinder rise until the cooling water temperature reaches the warm-up completion set value of the internal combustion engine after ignition. And institutions,
The catalyst warm-up is accelerated, and not only good cold start performance is obtained, but also fuel efficiency and exhaust emission are improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings.

(First Embodiment) A fuel injection control method for a direct injection internal combustion engine according to a first embodiment includes an in-cylinder injector capable of directly injecting a required fuel into a combustion chamber, and air is injected into the combustion chamber. At the start of a spark-ignition type direct injection engine in which the intake air is compressed by the piston, the fuel is directly injected into the cylinder, and the fuel is ignited and burned.
When the pressure detected by the injection pressure detection means is equal to or higher than the set value at which injection is possible, the combustion mode becomes stratified combustion until the rotation number detected by the engine rotation number detection means reaches the ignition determination set value. The injection timing is set to a compression stroke by a variable fuel injection device, and after ignition, the injection timing is set so that the combustion mode is homogeneous by the fuel injection device until the coolant temperature reaches a warm-up completion set value. The setting control is performed for the intake stroke.

The fuel injection control method for a direct injection internal combustion engine according to the first embodiment, which has the above-described operation, can be accurately modified to control from stratified combustion to homogeneous combustion, and is suitable for ignition at start. It is possible to obtain an excellent starting performance by forming an air-fuel mixture and significantly improve fuel efficiency and exhaust emission.

(Second Embodiment) A fuel injection control method for a direct injection internal combustion engine according to a second embodiment of the present invention is directed to a spark ignition type cylinder having a direct injection injector capable of directly injecting a required fuel into a combustion chamber. In the injection engine, when the pressure detected by the injection pressure detecting means at the start is equal to or less than the settable value for injection, fuel is not injected until the pressure is increased to the settable value for injection by the high-pressure fuel supply means. Is to do so.

In the fuel injection control method for a direct injection type internal combustion engine according to the second embodiment, when the pressure detected by the injection pressure detecting means at the time of starting is equal to or lower than the injection set value, the high pressure fuel supply means. The fuel is not injected until the pressure is increased to a value equal to or higher than the settable value. Here, the injectable set value indicates a fuel injection pressure necessary for stratified combustion. Since the stratified combustion injects fuel into the cylinder at the end of the compression stroke, the back pressure of the injection field is high, and the interval from injection to ignition is short. Since it is necessary to form an ignitable air-fuel mixture around the fuel cell, high injection pressure has the effect of promoting atomization of the injected fuel.

(Third Embodiment) In a fuel injection control method for a direct injection internal combustion engine according to a third embodiment, the injection start timing of stratified combustion is set at least one or more times during a compression stroke after a complete intake stroke. By setting the injection timing to the compression stroke at the start, the fuel can transfer heat from the high temperature air during the compression stroke, and the evaporation of the fuel is promoted and it can be evaporated quickly,
There is an effect that the air-fuel mixture can be surely formed by the ignition timing.

(Fourth Embodiment) The fuel injection control method for a direct injection internal combustion engine according to the fourth embodiment is applied to a direct injection internal combustion engine as shown in the schematic diagram of FIG. The combustion chamber 4 is constituted by the cylinder head 1, the cylinder block 2 on which the cylinder head 1 is mounted, and the piston 3, and the fuel of the in-cylinder injector 5 is arranged so as to face the combustion chamber 4. The injection port and the electrode of the ignition plug 6 are arranged.

The cylinder head 1 has the combustion chamber 4
An intake port 7 and an exhaust port 8 are formed and arranged so as to communicate with each other. The intake port 7 is provided with a throttle valve 9 driven by a throttle actuator.

The in-cylinder injector 5 is connected to a high-pressure fuel supply means 10. The high-pressure fuel supply means 10 serves to pump the fuel to supply the fuel pressure to be applied to the in-cylinder injector 5.

The injection timing of the fuel injected from the in-cylinder injector 5, the ignition timing of the ignition plug 6, and the opening of the throttle valve 9 are determined by an electronic control unit (EC).
U) 11.

The ECU 11 receives a crank angle output signal of a crank angle sensor 13 detected from a crank rotor 12 mounted on a crankshaft and the like, a stroke determination output signal of a stroke determination sensor 14, and a fuel pressure sensor 15. The fuel pressure applied to the in-cylinder injector and the coolant temperature detected by the coolant temperature sensor 16 are:
Each is input as control information.

The fuel injection control method for a direct injection internal combustion engine according to the fourth embodiment will be described with reference to the flowchart shown in FIG. First, at the start, the driver turns on the ignition switch to turn on the power to the ECU 11, and the control system is initialized.

In step S1, the fuel pressure applied to the in-cylinder injector 5 is detected, and it is determined whether the fuel pressure is equal to or higher than a preset injection enable value. This injection set value indicates the fuel injection pressure required for stratified combustion.

In the stratified combustion, fuel is injected into the cylinder at the end of the compression stroke, so that the back pressure of the injection field is high.
In addition, since the interval from injection to ignition is short,
Since it is necessary to form an ignitable air-fuel mixture around the ignition plug 6 in a short time, a high injection pressure
It is necessary to promote atomization of the injected fuel.

If it is determined in step S1 that the fuel pressure allows stratified charge combustion, the process proceeds to step S2. When the driver sets the ignition switch to the starter motor start position, in step S3, stratified charge combustion is selected as the combustion mode, and the fuel injection timing is set to the compression stroke so as to achieve stratified charge combustion.

Then, the engine is rotated by a starter motor to start the engine. Here, during the compression stroke, the pressure in the combustion chamber 4 is increased by the compression operation of the piston as shown in FIG.
° C). On the other hand, when the fuel is injected in the intake stroke as in the conventional start, the temperature in the combustion chamber 4 is almost the same as the outside air temperature and is low.

In the fourth embodiment, by setting the injection timing to the compression stroke at the time of starting, the fuel can transfer heat from the high-temperature air during the compression stroke, and the evaporation of the fuel is promoted and the fuel can be evaporated quickly. The mixture can be surely formed by the ignition timing. In addition, since the formation of a liquid film formed by the collision of fuel with the piston is suppressed, the generation of deposits is reduced. At this time, the first injection is performed at least once during a compression stroke after a complete intake stroke in order to make the temperature rise by compression of air by the piston effective.

If the fuel line pressure is low at the time of starting and the fuel pressure is equal to or lower than the settable value for injection, at step S4
Even if the driver drives the engine with the ignition switch, as long as the fuel pressure is determined to be equal to or less than the settable value at step S5, cranking is continued without injecting fuel, and the engine-driven high-pressure fuel supply means 10 is not driven. Wait for the fuel pressure to rise due to

When the fuel pressure becomes equal to or higher than the set value for enabling injection,
Injection starts and stratified combustion. This fuel pressure rise time is
There is no problem because the time is as short as 0.5 second or less.

In order to secure the required fuel pressure in stratified combustion at the time of start, the high-pressure fuel supply means 10 is driven by, for example, an electric or other power other than the engine rotational power before cranking, regardless of the above method. The fuel pressure required at the start of stratified combustion may be secured in advance by pumping the fuel to the pressure accumulating chamber upstream of the in-cylinder injector.

The determination of ignition is made in step S6.
If the engine speed is equal to or greater than a preset ignition determination set value (for example, 600 rpm), it is determined that ignition has occurred. If it is less than that, the operation according to the stratified combustion setting is continued.

After the ignition, if the cooling water temperature 16 is equal to or lower than the warm-up completion set value, in step S7, the setting of the injection timing is immediately changed from the compression stroke to the intake stroke, and a transition is made to homogeneous combustion. This is because the homogeneous combustion has better warm-up performance of the engine and the catalyst, and can reduce the time until the cooling water temperature reaches the warm-up completion set value in the stratified combustion.

The throttle valve opening and the fuel injection amount at the time of homogeneous combustion are changed at each cooling water temperature according to the values written in the ROM in the ECU 11 so that the predetermined air-fuel ratio A falls within the catalyst activation temperature range. / F.
Note that the injection timing is fixed to a predetermined timing of the intake stroke.

On the other hand, if the cooling water temperature has reached the warm-up completion set value after ignition, it is determined that warm-up is complete, and R
The operation shifts to the MAP control written in the OM.

The fuel injection control method for a direct injection type internal combustion engine according to the fourth embodiment having the above-described operation is different from the conventional control from homogeneous combustion to stratified combustion by temperature, and is different from stratified combustion to homogeneous combustion. It is. As a result, it is possible to obtain good starting performance, and to greatly improve fuel efficiency and exhaust emission.

In the fuel injection control method for a direct injection internal combustion engine according to the fourth embodiment, the following effects can be obtained by performing stratified combustion until ignition until the engine is started. (1) Compared to the conventional start by homogeneous combustion, there is no increase in the start of fuel, the fuel injection can be greatly reduced, and the fuel efficiency can be improved. (2) Since the throttle loss of the throttle valve 9 can be reduced, fuel efficiency can be improved. (3) Inject fuel in the compression stroke as shown in FIG.
Because the evaporation of fuel is promoted and the mixture can be reliably formed,
There is no misfire and steep TH immediately after start-up seen in the conventional method
Emission of C can be eliminated.

Further, according to the fuel injection control method for a direct injection type internal combustion engine of the fourth embodiment, as shown in FIG. 4, T is discharged from a cold start to a warm-up end in stratified charge combustion.
The effect of preventing a large amount of unburned fuel from being discharged due to a steep rise of THC discharged from the cold start to the end of warm-up in the conventional homogeneous combustion of HC. Play.

The above-described embodiments have been described by way of example only, and the present invention is not limited to these embodiments. Those skilled in the art will recognize from the claims, the detailed description of the invention, and the drawings. Modifications and additions are possible without departing from the technical idea of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic diagram schematically showing a direct injection internal combustion engine to which a fuel injection control method according to a fourth embodiment of the present invention is applied.

FIG. 2 is a chart showing a control flow of a fuel injection control method according to a fourth embodiment.

FIG. 3 is a diagram showing a relationship between pressure and temperature in a stroke of a direct injection internal combustion engine to which a fuel injection control method according to a fourth embodiment is applied.

FIG. 4 is a diagram showing a change in THC discharged from the start of startup to the end of warm-up in the fourth embodiment.

FIG. 5 is a time chart illustrating control for switching from uniform combustion to stratified combustion in a conventional fuel injection control device.

FIG. 6 is a cross-sectional view showing a direct injection internal combustion engine to which a conventional fuel injection control method is applied.

FIG. 7 is a diagram showing a change in THC discharged from the start of a conventional apparatus to the end of warm-up in a conventional apparatus.

[Description of Signs] 1 Cylinder head 2 Cylinder block 3 Piston 4 Combustion chamber 5 Injector 6 Spark plug 7 Intake port 8 Exhaust port 9 Throttle valve 10 High-pressure fuel supply means 11 Electronic control unit (ECU) 12 Crank rotor 13 Crank angle sensor 14 Stroke determination sensor 15 fuel pressure sensor 16 cooling water temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00 312 F02D 45/00 312Q (72) Inventor Makoto Koike Okamachi, Nagakute-cho, Aichi-gun, Aichi Prefecture 41 No. 1 Inside Toyota Central Research Laboratories Co., Ltd. (72) Inventor Tatsuo Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G023 AA02 AA04 AA08 AB01 AC04 AD02 AG01 3G084 BA15 CA01 CA02 DA02 DA09 DA10 FA00 FA20 FA33 FA38 FA39 3G301 HA01 HA04 HA16 JA02 JA23 JA26 KA01 KA05 LB04 LB11 MA18 PB08Z PE01Z PE03Z PE05Z PE08Z

Claims (1)

[Claims] In a cylinder injection type internal combustion engine having a fuel injection valve for injecting fuel into a combustion chamber, if the fuel injection pressure exceeds a set value at which fuel can be injected at the time of starting, the rotation speed of the internal combustion engine is determined to be ignition. Up to the set value for
The fuel injection timing is controlled so that the combustion mode in the combustion chamber is stratified combustion, and the fuel is controlled so that the combustion mode becomes homogeneous combustion after ignition until the cooling water temperature reaches a set value of warm-up completion of the internal combustion engine. A fuel injection control method for a direct injection internal combustion engine, comprising controlling an injection timing.