JP2002227697A - Fuel injection device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To peel injection device of internal combustion engine in this invention enables control of a knock certainly about the fuel injection equipment of an internal combustion engine, without causing the fall of an output. SOLUTION: If a knock is detected by the knock detection means 7, fuel will be injected from the fuel injection valve of both of the 2nd fuel injection 6 valves which inject direct fuel in the 1st fuel injection valve 5 prepared in the inhalation of air passage 2, and a combustion chamber. Thereby, when a knock actually arises, it is switched to certainly suitable fuel injection mode, a knock is controlled without causing an output fall.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for an internal combustion engine suitable for use in an internal combustion engine that injects fuel into an intake passage.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 6 (B), as the temperature of a combustion chamber becomes higher and the pressure of the combustion chamber becomes higher, fuel is more likely to self-ignite and the engine is more likely to knock. Further, as shown in FIG. 6A, the self-ignition region also depends on the air-fuel ratio. If the air-fuel ratio is too large, the air-fuel mixture is too lean to self-ignite, and the air-fuel ratio is small. If it is too long, the mixture will be too rich this time and will not self-ignite. On the other hand, the air-fuel ratio of 12 to 18
Knocking is likely to occur in a small area.

In addition, when the engine is running at a low speed, the time during which the mixture is exposed to the high temperature combustion chamber wall is prolonged, and the temperature of the mixture rises. Knock is likely to occur. Conventionally, when such knocking occurs, knocking is generally suppressed by retarding the ignition timing, but if the ignition timing is retarded, a decrease in output cannot be avoided.

[0004] Japanese Patent No. 2668680 discloses a technique for suppressing knocking without lowering the output. In a spark ignition type in-cylinder direct injection engine, a fuel injection mode in which only in-cylinder injection is performed, an in-cylinder injection mode is disclosed. There is disclosed a technique in which a fuel injection mode in which intake injection is combined and a fuel injection mode in which only intake air is injected are appropriately switched in accordance with an operation state.

[0005]

However, in such a technique, the fuel injection mode is switched for each preset operation region, and thus does not accurately correspond to an actual operation condition. Further, there is a case where an operation region set in advance due to manufacturing variations of individual engines is incompatible with an actual engine. For this reason, there is a possibility that an appropriate fuel injection mode is not set even though knocking actually occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and when knocking occurs, knocking can be reliably suppressed without lowering the output.
An object of the present invention is to provide a fuel injection device for an internal combustion engine.

[0007]

According to the first aspect of the present invention, when knocking is detected by the knock detecting means, the first fuel injection valve provided in the intake passage and the combustion chamber are provided. Fuel is injected from both fuel injection valves of the second fuel injection valve that directly injects fuel into the fuel injection valve.

[0008] Thus, when knocking actually occurs, the fuel injection mode is reliably switched to the appropriate fuel injection mode, and knocking can be suppressed without lowering the output.
In the fuel injection device for an internal combustion engine according to the second aspect of the present invention, when knocking is detected by knock detection means,
During the intake stroke, fuel is injected from the first fuel injection valve in such an amount that the air-fuel ratio becomes about 30 to 60, and then during the compression stroke, the amount of fuel from which the total air-fuel ratio becomes stoichiometric or rich from the second fuel injection valve is obtained. It is injected.

Thus, the fuel injection from the second fuel injection valve enters the combustion chamber in which the lean air-fuel mixture (air-fuel ratio 30 to 60) formed in advance by the fuel injection from the first fuel injection valve in the cylinder spreads. , An air-fuel mixture having a partially high fuel concentration flows. At this time, the air-fuel mixture formed by the fuel injection from the first fuel injection valve is sufficiently lean to prevent self-ignition, and the rich mixture formed by the fuel injection from the second fuel injection valve. The air-fuel mixture does not self-ignite because there is no time for the reaction before knocking to proceed until ignition by the spark plug thereafter. As a result, knocking is suppressed without causing self-ignition of the fuel. Further, since the overall air-fuel ratio is stoichiometric or rich, a decrease in output is also suppressed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel injection device for an internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings. FIG. In the present embodiment, a general intake injection engine 1 that injects fuel into an intake passage and mixes intake air and fuel is used as a base, as an internal combustion engine (engine). A multipoint injection type engine in which an injector (referred to as a first fuel injection valve or a main injector) 5 is provided in each intake passage is applied.

In FIG. 1, 1A is a cylinder (cylinder), 1B is a piston, and 2 is an intake passage. On the upstream side of the intake passage 2, a surge tank 8 and an intake manifold 9 are provided.
The intake passage 2 is configured to include the surge tank 8 and the intake manifold 9. As shown in FIG. 1, the engine 1 has a spark plug 3 at the top of the combustion chamber, and is configured as a spark ignition type engine in which fuel is ignited by sparks of the spark plug. The engine 1 further includes an injector (referred to as a second fuel injection valve or sub-injector) 6 whose injection hole is arranged in the combustion chamber so as to inject fuel directly into the combustion chamber.

The sub-injector 6 is an injector capable of injecting fuel at a high pressure during a compression stroke, and is supplied with fuel pressurized by a high-pressure pump (not shown). On the other hand, the engine 1 is provided with a knock sensor (knock detecting means) 7 for detecting knocking when it occurs. As the knock sensor 7, a knock sensor of a type that detects abnormal vibration of a cylinder block of the engine 1 is applied in the present embodiment. In addition, a knock sensor that detects knocking based on fluctuations in the engine speed is used. A sensor may be used.

Information detected by the knock sensor 7 is input to an electronic control unit (ECU) 10.
In the ECU 10, based on information from the knock sensor 7,
An operation control signal for each of the injectors 5 and 6 is set. In the present embodiment, when it is determined by the ECU 10 that knocking has occurred based on the detection information from the knock sensor 7, fuel injection is performed from the two injectors 5 and 6 to suppress the knocking. It has become. The fuel injection mode in which fuel is injected from the two injectors 5 and 6 is hereinafter referred to as a split injection mode, and the operating state in which knocking has occurred is referred to as a specific operating state.

In a normal operation state in which knocking does not occur, the operation of the sub-injector 6 is prohibited by the ECU 10, and the intake passage 2 by the main injector 5 is controlled.
Fuel injection mode (hereinafter referred to as intake pipe injection mode)
It can be switched to. As described above, the engine 1 operates by injecting fuel from the main injector 5 during normal operation, and in the specific operation state where knocking is detected, the fuel is supplied from the two injectors 5 and 6 to suppress knocking. It is configured so that injection is performed.

Here, when knocking is detected, a small amount of fuel that cannot self-ignite is injected from the main injector 5 into the intake passage 2 and the remaining fuel is injected from the sub-injector 6 into the cylinder (during the compression stroke). The fuel is injected directly into the combustion chamber. Specifically, in this split injection mode, the stoichiometric or rich mixture (that is, the total air-fuel ratio is equal to the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio) is determined by the total injection amount (total injection amount) of the intake pipe injection and the direct injection in the cylinder. The fuel injection amount is set such that an air-fuel mixture smaller than the fuel ratio is formed.

In this case, as the fuel injection timing, the intake pipe injection by the main injector 5 is performed in the exhaust stroke or the intake stroke (preferably, the exhaust stroke in which the fuel atomization time in the intake pipe can be long), and the sub-injector 6 In-cylinder direct injection is performed in the compression stroke. After performing intake pipe injection by the main injector 5, the sub-injector 6
However, since the fuel supplied into the cylinder by the intake pipe injection ignites itself and promotes knocking, the injection fuel should not be ignited by the intake pipe injection. The fuel is injected in such an amount that the fuel concentration becomes lean.

That is, as shown in FIG. 6 (A), for example, when the air-fuel ratio A / F is about 18 to 12 near the stoichiometric air-fuel ratio, the fuel easily self-ignites, but the fuel concentration of the air-fuel mixture is reduced. The more it deviates from the vicinity of the stoichiometric air-fuel ratio, the more difficult it is for the fuel to self-ignite. In order to apply fumigation, it is necessary to mix fuel into the intake air to the extent that the mixture does not self-ignite while atomizing or evaporating the fuel during the intake stroke. A lean mixture (an air-fuel ratio A / F that is significantly higher than near the stoichiometric air-fuel ratio) may be created. Note that fumigation is an intake stroke in a diesel engine, in which fuel is atomized or evaporated and mixed into the intake to such an extent that the air-fuel mixture does not self-ignite, and the ignition delay is caused by a pre-flame reaction during the compression stroke. By shortening it, knocking is prevented. In the past, fumigation could only be applied to diesel engines, but this time, a similar approach has become feasible for spark ignition engines.

Here, during the intake pipe injection, the fuel injection is performed by setting the injection amount so that the air-fuel ratio becomes about 30 to 60. On the other hand, the fuel is directly injected into the cylinder (in the cylinder) from the sub-injector 6 so that the fuel becomes a stoichiometric or rich mixture with the total injection amount of the in-cylinder direct injection and the intake pipe injection. In the present embodiment, the fuel injection is performed by setting an injection amount corresponding to an air-fuel ratio of about 15 to 20 during direct in-cylinder injection so as to form a mixture having a total air-fuel ratio (total air-fuel ratio) of about 12. Is to be performed.

That is, if the air-fuel ratio at the time of the intake pipe injection is about 60, and if the fuel injection is performed at the injection amount corresponding to the air-fuel ratio of about 15 at the time of direct in-cylinder injection, the total air-fuel ratio corresponding to the total injection amount becomes 12 Degree (ie, 1/12 = 1/60 + 1 /
15) and the air-fuel ratio at the time of intake pipe injection is 30
If the fuel injection is performed with the injection amount corresponding to the air-fuel ratio of about 20 during the direct injection in the cylinder, the total air-fuel ratio corresponding to the total injection amount becomes about 12 (that is, 1/12 = 1/30 +
1/20).

As described above, in the split injection mode, the ECU 10 determines that the engine 1 is in the specific operation state (ie, knocking has occurred) based on the detection information from the knock sensor 7. The engine 1 is operated by general premixed combustion by fuel injection from the main injector 5 during normal operation in which knocking does not occur.

Here, the operation of knock suppression by such split injection will be described. At the time of in-cylinder direct injection, as shown in FIG. 2 (A), fuel-lean mixture previously formed by intake pipe injection is used. Air (air-fuel ratio A / F = 30-6)
0), the mixture having a partially high fuel concentration by the in-cylinder direct injection (total air-fuel ratio A / F = 15 to 2)
Since the fuel corresponding to 0 is injected, the mixture having a high fuel concentration flows into the vicinity of the ignition plug 3 in a laminar flow.

At this time, the air-fuel mixture formed by the injection of the intake pipe from the main injector 5 is sufficiently lean to prevent self-ignition, and forms a laminar flow by direct injection into the cylinder from the sub-injector 6. The rich mixture thus formed does not self-ignite because there is no time for the reaction before knocking to proceed until ignition by the ignition plug 3 thereafter. This is considered to be the function of suppressing knocking by split injection, and as a result, ignition by the ignition plug 3 is performed without causing self-ignition of fuel.

As a result, first, the rich mixture in the vicinity of the ignition plug 3 is ignited, and the rich mixture that forms a laminar flow starts burning. This rich mixture lacks air at the time of combustion, so that a large amount of soot is generated by the combustion. However, as shown in FIG. 2B, the lean mixture formed by the intake pipe injection is used. It is presumed that the ki is burning using the generated soot as an ignition source.

That is, the lean air-fuel mixture formed by the intake pipe injection allows the excess air around the layered rich air-fuel mixture formed by the direct injection in the cylinder to be effectively used, and the combustion energy is reduced. And a large output can be obtained, and the generation of soot in the combustion chamber, which poses a problem when burning a relatively rich air-fuel mixture by stratified combustion by in-cylinder direct injection, is significantly increased. It can be suppressed to a.

Note that a prohibition region may be provided for this split injection mode. Here, the prohibition region is set to a predetermined temperature (for example, −10 °, which is not limited to the cooling water temperature but may be any detectable parameter corresponding to the engine temperature.
C) The following areas are set. This is because if the engine temperature is low, the atomization of the fuel becomes worse, and if the fuel of the intake pipe injection is difficult to atomize, the fumigation condition may not be satisfied and the knock prevention effect may not be obtained.

Next, how to set the injection amount ratio and the injection timing of the in-cylinder direct injection in the split injection mode will be described with reference to FIGS. 3 and 4 are diagrams showing examples of characteristics of a spark ignition type direct injection internal combustion engine having different specifications. In each of these figures, (A) shows the engine speed Ne, ignition timing and intake pipe injection. It explains the setting of the injection amount ratio (in-cylinder direct injection pulse / total injection pulse) and the injection timing of in-cylinder direct injection when the timing is fixed to a predetermined value and the total air-fuel ratio is set to 12, (B) shows the knock limit output characteristic obtained by the setting shown in (A).

First, referring to FIG. 3, FIG.
As shown in (A), when the timing of in-cylinder direct injection is advanced,
Since the pre-knock reaction proceeds, there is a knock region. If the ratio of the direct injection amount in the cylinder to the total injection amount is increased, the total H
C (THC), that is, the total amount of hydrocarbons becomes excessively large, and the generation of smoke becomes excessive as the timing of in-cylinder direct injection is delayed and the ratio of in-cylinder direct injection amount is increased, and the in-cylinder direct injection timing And in the area as shown in the figure according to the in-cylinder direct injection amount ratio, there is an area where rotation fluctuation is large and causes misfire,
Further, there is a minimum required torque equal output line in a curve as shown in the figure according to the in-cylinder direct injection timing and the in-cylinder direct injection amount ratio.

From these various conditions, on the premise that knock does not occur (that is, it is not a knock region) and that misfire does not occur (that it is not a misfire region),
THC does not become excessive, and the generation of smoke does not become excessive,
And, as an area where the minimum required torque can be obtained,
In FIG. 3A, there is a divided injection area A1 indicated by hatching.

Here, this area A1 is mainly defined by the minimum required torque equal output line.
The requirements for defining the area A1 are different even for the same engine depending on the setting of the smoke generation limit value and the minimum required torque value. If the operating conditions are different even for the same engine, the requirements for defining the area A1 also differ.

Further, if the specifications of the engine are different, the operating conditions are the same and the specified conditions are the same (no knock or misfire occurs, but the THC or smoke generation limit value and the minimum required torque value are also equal). However, as in the area A2 shown by hatching in FIG.
This is different from the area A1 shown in FIG. And, among such divided injection areas A1 and A2, points P1 and P2 that satisfy the specified conditions in the best balance are shown in FIG.
4 (A) and FIG. 4 (A), each is indicated by a circle.

As shown in the areas A1 and A2 in FIGS. 3A and 4A, the area suitable for performing the divided injection is such that the direct injection timing in the cylinder is about 30 to 100 ° BTDC. , The ratio of the direct injection amount in the cylinder is about 60 to 90%. Taking these two engines as an example, such a numerical range can be set as a divided injection region, and this numerical range is almost the same for most engines, but changes in engine characteristics, operating conditions, and region defining conditions In some cases, a shift may occur in the divided injection region, and such in-cylinder direct injection timing may be about 30 to 100 ° BTDC,
The numerical value that the direct injection amount ratio in the cylinder is about 60 to 90% is
It is a guide for setting numerical values, and it is desirable to set according to the characteristics of each engine, operating conditions, and region defining conditions.

When direct injection in the cylinder is performed under the conditions of the points P1 and P2 in the divided injection areas A1 and A2, compared with the case of fuel injection only by the intake pipe injection at the same air-fuel ratio (= 12), As shown in FIGS. 3B and 4B, the knock limit output is greatly improved. The knock limit output is obtained by advancing the ignition timing within a range in which knock does not occur. For this reason, the effect is particularly great in the low to medium engine speed and high load regions where knocking is likely to occur.

Further, in the fuel injection using only the intake pipe injection, knocking occurs unless the ignition timing is significantly retarded in a low engine speed range, whereas in the split injection, the engine speed is reduced by idling. The ignition timing is equivalent to the intake pipe injection in a very low range, such as during cranking below the rotation, but can be advanced in the higher rotation speed range, and such advance of the ignition timing is also helped. The knock limit power is greatly improved.

Since the fuel injection device for an internal combustion engine according to one embodiment of the present invention is configured as described above, for example, as shown in FIG. 5, a split injection mode (split injection control)
Is performed. That is, first, the temperature of the cooling water of the engine 1 is read (step S10), and the information from the knock sensor 7 is read (step S20).

Then, it is determined based on the cooling water temperature whether or not the divided injection is prohibited (step S30). That is, if the cooling water temperature is equal to or lower than the predetermined temperature, it is determined that the divided injection is prohibited. If it is the divided injection prohibition region, the process proceeds to step S80, and the flag A is determined. This flag A is set to 1 at the time of split injection control, and is set to 0 if split injection control is not being performed. Here, if the flag A is 1 (ie, during the split injection control), the process proceeds to step S90, where the split injection control is canceled (the split injection control ends), and the flag A is returned to 0. If the flag A is not 1 (that is, during the divided injection control), the process returns.

On the other hand, if it is not the divided injection prohibition region, the process proceeds from step S30 to step S40, and it is determined whether knocking actually occurs. If it is determined in step S40 that knocking has not occurred, the process proceeds to step S80 and performs the above-described processing. If it is determined in step S40 that knocking has occurred,
Proceeding to step S50, the flag A is determined. here,
If the flag A is 1 (i.e., during split injection control), the routine returns.

On the other hand, if it is determined in step S50 that the flag A is not 1, the flow advances to step S60 to execute split injection control (split injection mode). Then, after the end of the split injection control, the process proceeds to step S70, sets the flag A to 1, and returns. As described above, according to the fuel injection device for an internal combustion engine of the present embodiment, when knocking actually occurs, fuel injection is performed from both the main injector 5 and the sub-injector 6, thereby accurately reflecting the operating state of the engine. There is an advantage that the knock suppression processing can be executed. Further, when knocking occurs, by performing fuel injection from both the main injector 5 and the sub-injector 6, there is an advantage that knocking can be reliably suppressed. Further, conventionally, when knocking occurs, the ignition timing has to be retarded to reduce the output. On the other hand, there is an advantage that the ignition timing can be advanced and the output can be improved.

Further, since the engine can be made advantageous for knocking, the original compression ratio can be set higher. Thereby, the output can be further improved, and the fuel efficiency can be improved. Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above-described embodiment, a case has been described in which the present invention is applied to a multipoint injection engine.
Fuel injection (intake pipe injection) for all cylinders with one injector
The present invention may be applied to a single point injection type engine that performs the following. In this case, the main injector 5 may be provided in the surge tank 8 or the intake manifold 9. Of course, when the main injector 5 is provided in the intake manifold 9, the injector 5 is provided at a position upstream of a position where the manifold branches for each cylinder.

Further, in the case of performing the split injection, the amount of fuel injected from each of the injectors 5 and 6 may be specified instead of the air-fuel ratio. For example, the main injector 5 may inject one-fourth of the total fuel amount during the intake pipe injection, and the sub-injector 6 may inject the remaining three-fourth of the fuel amount during direct in-cylinder injection.

[0040]

As described above in detail, according to the fuel injection system for an internal combustion engine of the present invention, when the knocking actually occurs, the first fuel injection valve and the second fuel injection valve are connected. By performing fuel injection from both, there is an advantage that knock suppression processing that accurately reflects the operating state of the internal combustion engine can be executed. In addition, when knocking occurs, by performing fuel injection from both the first and second fuel injection valves, there is an advantage that output can be improved while suppressing knocking.

According to the fuel injection device for an internal combustion engine of the present invention, when knocking is detected by the knock detection means, the air-fuel ratio from the first fuel injection valve to about 30 to 60 during the intake stroke. By injecting an amount of fuel that becomes the total air-fuel ratio from the second fuel injection valve during the compression stroke, and then stoichiometric or rich,
There is an advantage that knocking can be reliably suppressed and output can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main configuration of a fuel injection device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a view for explaining the principle of knocking suppression by a fuel injection device for an internal combustion engine according to one embodiment of the present invention, where (A) shows a state at the time of in-cylinder direct injection, and (B)
Indicates the state of the latter stage of combustion after ignition.

3A and 3B are diagrams illustrating a setting example of in-cylinder direct injection and its effect in a fuel injection device for an internal combustion engine according to an embodiment of the present invention, and FIG. 3A illustrates a ratio of in-cylinder direct injection and an injection timing; (B) shows the characteristic of improving the knock limit output by split injection.

FIG. 4 is a diagram showing another setting example of in-cylinder direct injection and its effect in the fuel injection device for an internal combustion engine according to one embodiment of the present invention, and FIG. (B) shows the characteristic of improving knock limit output by split injection.

FIG. 5 is a flowchart illustrating the operation of the fuel injection device for an internal combustion engine according to one embodiment of the present invention.

FIG. 6 is a diagram showing a general knock generation characteristic (self-ignition limit), wherein FIG.
(B) relates to temperature and pressure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine (engine) 5 1st fuel injection valve (main injector) 6 2nd fuel injection valve (sub-injector) 7 Knock detection means (knock sensor) 10 Control means (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00 345 F02D 45/00 345B 368 368B F02M 61/14 310 F02M 61/14 310A 63/00 63 / 00 PF term (reference) 3G023 AA02 AA06 AB01 AC02 AC04 AD01 AG01 3G066 AA02 AA05 AB02 AD10 AD12 BA00 BA16 CC34 CD28 DA01 DA04 DC00 DC09 DC14 3G084 BA11 BA15 DA38 EB08 EB11 EB22 EC01 FA20 FA25 FA33 FA38 FA39 HA01 HA01 JA01 LB02 LB03 LB04 MA03 MA11 MA18 PC08A PE02A PE08A

Claims (2)

[Claims] A first fuel injection valve provided in an intake passage; a second fuel injection valve for injecting fuel directly into a combustion chamber; and knock detection means for detecting knocking. A fuel injection device for an internal combustion engine, wherein when knocking is detected, fuel is injected from both of the first fuel injection valve and the second fuel injection valve. 2. When knocking is detected by the knock detection means, an amount of fuel having an air-fuel ratio of about 30 to 60 is injected from the first fuel injection valve during an intake stroke, and the second fuel is injected during the compression stroke. Characterized in that the fuel is injected from the fuel injection valve in an amount such that the total air-fuel ratio becomes stoichiometric or rich,
The fuel injection device for an internal combustion engine according to claim 1.