JP2005120983A - Fuel injection control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the accumulation of deposits on the distal end of a fuel injection valve in a cylinder direct injection spark ignition type engine right after continuous high load operation. <P>SOLUTION: In the condition of low load operation right after continuous high load operation, an increase in target idling speed, twice injection in one stroke, change-over to a homogeneous combustion mode, the prohibition of speed reduction fuel-cut are performed only for a preset period. Thus, the distal-end temperature of the fuel injection valve is quickly reduced by cooling with fuel to suppress the accumulation of deposits on the distal end of the injection valve. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel injection control device for an engine, and more particularly to a technique for suppressing deposit accumulation on the tip of a fuel injection valve.

Conventionally, in an engine equipped with a fuel injection valve that directly injects fuel into a combustion chamber, when the fuel adheres to the nozzle hole, the volatile component in the fuel evaporates due to the heat of the fuel injection valve, and the volatility in the fuel is low It is known that carbonized components are deposited as deposits on the nozzle hole.
Conventionally, there have been techniques disclosed in Patent Documents 1 to 3 as techniques for suppressing the above deposit deposition.

In Patent Document 1, the tip temperature of the fuel injection valve is calculated based on the fuel injection amount, the engine speed, the coolant temperature, and the engine combustion mode, and the calculated tip temperature is set based on the injection interval. If the temperature is higher than that, the temperature of the fuel injection valve is lowered by lowering the cooling water temperature.
Further, in Patent Document 2, as the injection interval becomes longer, the ignition timing is retarded so that the combustion becomes slower, and since the injection interval is shorter, the adhesion of the carbonized component to the injection hole portion does not proceed. When it is washed away by the injection, rapid combustion is performed.

Moreover, in the thing of patent document 3, in the low load high rotation area | region, fuel injection time is extended by reducing fuel pressure and injecting required fuel, and this suppresses the raise of the tip temperature of a fuel injection valve. I am doing so.
JP 2002-098022 A Japanese Patent Laid-Open No. 2002-130022 JP 09-195820 A

By the way, in the thing of patent document 1, the state in which the injection valve front-end | tip temperature was high appeared by the delay of the follow-up of the injection valve temperature with respect to the change of cooling water temperature, and the deposit might accumulate gradually on the injection- valve front-end | tip.
Moreover, in the thing of patent document 2, in low load driving | running (it includes idling driving | running | working) from which the injection interval becomes long, combustion becomes unstable by extending fuel injection time, and there exists a possibility that combustion with good fuel efficiency cannot be realized. there were.

Furthermore, in the thing of patent document 3, when the fuel pressure is lowered, the spray shape changes, and there is a possibility that stable combustion with good fuel efficiency cannot be realized.
The present invention has been made in view of the above problems, and an object thereof is to provide an engine fuel injection control device capable of suppressing deposit accumulation without deteriorating combustibility.

  For this reason, in the present invention, the fuel injection condition by the fuel injection valve is set to a condition different from that during the normal low load operation only for a predetermined period when the engine becomes a low load operation after the high load continuous operation.

  According to such a configuration, the tip temperature of the fuel injection valve increases when the engine continues to operate at a high load, but the tip temperature of the fuel injection valve decreases with a delay even when the engine is removed from the high load operation. However, at this time, the fuel injection condition is different from the normal condition, i.e., the fuel injection valve tip is actively cooled, or the fuel injection can remove the deposit. By setting the conditions, deposit accumulation at the tip of the fuel injection valve can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an in-cylinder direct injection spark ignition engine that is an engine in the embodiment.
In FIG. 1, an internal combustion engine 1 has a combustion chamber 5 constituted by a cylinder head 2, a cylinder block 3 and a piston 4.
Fresh air is introduced into the combustion chamber 5 from an intake port 7 via an intake valve 6, and exhaust gas is discharged from an exhaust port 9 via an exhaust valve 8.

The intake valve 6 is driven to open and close by an intake side camshaft 10, and the exhaust valve 8 is driven to open and close by an exhaust side camshaft 11.
A fuel injection valve 12 is installed in the approximate center of the upper surface of the combustion chamber 5.
The fuel injection valve 12 is a hole nozzle type fuel injection valve having a plurality of injection holes.
A circular cavity 4a is formed in a portion of the crown of the piston 4 facing the fuel injection valve 14 on the substantially same central axis as the central axis of the fuel injection valve 14. Under the stratified operation conditions, the fuel injection valve 14 The fuel injected from the fuel is received by the cavity 4a, and forms an air-fuel mixture stratified mainly in the cavity 4a and in the upper part thereof.

  Here, the spray central axis of the fuel injection valve 12 and the bottom wall of the cavity 4a where the spray collides form an obtuse angle, and the peripheral wall of the cavity 4a that becomes the spray traveling direction after the spray collision is on the fuel injection valve 12 side The angle between adjacent sprays of the sprays injected from the plurality of nozzle holes of the fuel injection valve 12 is set to be equal to or less than a single spray angle.

An ignition plug 13 is disposed on the upper surface of the combustion chamber 5 on the exhaust valve 8 side adjacent to the fuel injection valve 12, and the air-fuel mixture is ignited and burned by the ignition plug 13.
The in-cylinder direct injection spark ignition engine 1 is integrally controlled by an engine control unit (ECU) 14 incorporating a microcomputer.
Detection signals from the crank angle sensor 21, the coolant temperature sensor 22, and the accelerator opening sensor 23 are input to the ECU 14, and each control is performed based on these signals.

  Further, as a combustion mode of the engine 1, fuel injection is performed during the compression stroke (particularly in the latter half of the compression stroke), thereby realizing a stratified combustion mode for realizing lean operation and improving fuel efficiency, and during the intake stroke (particularly in the first half of the intake stroke). ) And a homogeneous combustion mode that realizes stoichiometric operation (theoretical air-fuel ratio operation), and either the stratified combustion mode or the homogeneous combustion mode is selected according to the operating state. It has become.

The ECU 14 selects either the homogeneous combustion mode or the stratified combustion mode based on the engine load, the engine speed, the coolant temperature, and the like, and supplies the fuel injection valve 12 with an amount of fuel corresponding to the required air-fuel ratio. Let spray from.
Further, the ECU 14 evaporates the volatile component in the fuel adhering to the tip of the fuel injection valve 12 by the heat of the fuel injection valve 12, and deposits the low volatile carbonized component in the fuel in the nozzle hole portion as a deposit. Control to prevent this.

FIG. 2 shows the temperature change at the tip of the fuel injection valve when the internal combustion engine 1 is decelerated and then enters idle operation after continuing high load operation.
When the internal combustion engine 1 continues high load operation, the temperature at the tip of the injection valve shows a high state. However, even if the operation state leaves the high load operation, the temperature at the tip of the fuel injection valve has a time delay and is temporarily Shows a high state.

For this reason, at the time of low load operation immediately after continuous high load operation, the fuel remaining at the tip of the injection valve is solidified and deposited as a deposit.
Therefore, the ECU 14 controls the fuel injection condition of the fuel injection valve 12 to a condition different from that during normal low-load operation during low-load operation immediately after continuous high-load operation, thereby suppressing deposit adhesion and accumulation. To do.

The flowchart of FIG. 3 shows a first embodiment of the control for suppressing the adhesion / deposition of the deposit.
In the flowchart of FIG. 3, in step S <b> 1, it is determined whether or not the engine 1 is in a high load operation state based on, for example, whether or not the throttle opening is equal to or greater than a predetermined opening.
And if it determines with it being a high load driving | running state, it will progress to step S2 and will count up the timer TM1 for measuring the continuous driving | running time in high load.

In the next step S3, it is determined whether or not the value of the timer TM1 is equal to or greater than a predetermined value t1, and if the value of the timer TM1 is less than the predetermined value t1, the present routine is terminated and the timer TM1 is terminated. When the value becomes equal to or greater than the predetermined value t1, the process proceeds to step S4.
In step S4, 1 is set to the control flag.
On the other hand, if it is determined in step S1 that the engine 1 is not in the high load operation state, the process proceeds to step S5, and the timer TM1 is reset to zero.

In the next step S6, it is determined whether or not 1 is set in the control flag.
If the control flag = 1, the process proceeds to step S7.
In step S7, the timer TM2 for measuring the elapsed time after the continuous high load operation is changed to the low load operation is counted up.
In step S8, by comparing the value of the timer TM2 with a predetermined value t2, it is estimated whether the tip temperature of the fuel injection valve 12 is still high immediately after the continuous high load operation.

In step S8, when the value of the timer TM2 is equal to or less than the predetermined value t2, it is estimated that the tip temperature of the fuel injection valve 12 is still high, and the process proceeds to step S11.
In step S11, it is determined whether or not the low load operation state is idle operation.
When it is during idling, the process proceeds to step S12, and the target idling speed during idling is set to a higher value than usual (see FIG. 4).

During idling, the intake air amount is feedback controlled so that the actual rotational speed matches the target idle rotational speed.
If the rotational speed during idling is increased, the fuel injection interval can be shortened and the tip temperature of the fuel injector 12 can be lowered, so that solidification of fuel at the tip of the fuel injector 12 can be prevented. .

When it is determined in step S8 that the value of the timer TM2 has exceeded the predetermined value t2, the influence of the continuous high load operation is eliminated, and the tip temperature of the fuel injection valve 12 becomes a relatively low temperature commensurate with the low load operation. It is estimated that the control flag has decreased to step S9, and the control flag is reset to zero.
When the control flag is reset to 0, if it is in the low load operation state next time, the process proceeds from step S6 to step S10, the timer TM2 is reset to 0, and then this routine is terminated.

The flowchart of FIG. 5 shows a second embodiment of the control for suppressing the adhesion / deposition of the deposit.
In the flowchart of FIG. 5, the processes of steps S21 to S30 are the same as steps S1 to S10 of the flowchart of FIG. 3, and only the process when it is determined that the value of the timer TM2 is equal to or less than the predetermined value t2. Since they are different, description of step S21 to step S30 is omitted.

If it is determined in step S28 that the value of the timer TM2 is equal to or less than the predetermined value t2 in the flowchart of FIG. 5, the process proceeds to step S31.
In step S31, fuel injection that is normally performed once in one stroke is performed in two steps in one stroke (see FIG. 6).
As described above, when the fuel injection valve 12 immediately after the continuous high load operation has a high temperature as a dependency, if the required fuel amount is injected in two times, a short period of time is generated at the tip of the fuel injection valve 12. The fuel evaporates twice inside, and cooling is promoted.

Therefore, solidification of the fuel at the tip of the fuel injection valve 12 can be prevented.
The flowchart of FIG. 7 shows a third embodiment of the control for suppressing the adhesion / deposition of the deposit.
In the flowchart of FIG. 7, the processes of steps S41 to S50 are the same as steps S1 to S10 of the flowchart of FIG. 3, and only the process when it is determined that the value of the timer TM2 is equal to or less than the predetermined value t2. Since they are different, description of step S41 to step S50 is omitted.

If it is determined in step S48 that the value of the timer TM2 is equal to or less than the predetermined value t2 in the flowchart of FIG. 7, the process proceeds to step S51.
In step S51, it is determined whether or not the combustion mode that is normally set is the stratified combustion mode from the operating conditions (load / rotation) at that time.
When the stratified combustion mode condition is satisfied, the process proceeds to step S52 to forcibly switch the normal stratified combustion mode to the homogeneous combustion mode (see FIG. 8).

In the homogeneous combustion mode, the target air-fuel ratio is richer than that in the stratified combustion mode, and the fuel injection amount is larger than that in the stratified combustion mode. Therefore, the cooling of the fuel injection valve 12 by the fuel is promoted. Thus, the tip temperature of the tip 12 quickly decreases, and solidification of fuel at the tip can be prevented.
The flowchart of FIG. 9 shows a fourth embodiment of the control for suppressing the adhesion / deposition of the deposit.

In the flowchart of FIG. 9, the processes of steps S61 to S70 are the same as steps S1 to S10 of the flowchart of FIG. 3, and only the process when it is determined that the value of the timer TM2 is equal to or less than the predetermined value t2. Since they are different, the description of step S61 to step S70 is omitted.
If it is determined in step S68 in the flowchart of FIG. 9 that the value of the timer TM2 is equal to or smaller than the predetermined value t2, the process proceeds to step S71.

In step S71, deceleration fuel cut is prohibited (see FIG. 10).
The deceleration fuel cut means that the fuel cut is started when the throttle is fully closed and the engine rotational speed is higher than the start rotational speed, and the throttle is opened, or the engine rotational speed is the recovery rotational speed (with the throttle fully closed. This is a control for reducing the HC emission amount at the time of deceleration and improving the fuel consumption by resuming the fuel injection when it falls below the (starting rotational speed).

If the deceleration fuel cut is executed in a state where the tip temperature of the fuel injection valve 12 is high, the fuel at the tip of the injection valve is solidified and remains as a deposit.
Therefore, by prohibiting the fuel cut and injecting the fuel, the fuel injection valve 12 is cooled by the fuel and the injection hole is washed away by the fuel to prevent the fuel from solidifying.

In order to prevent the fuel cut from being excessively prohibited, the deceleration fuel cut may be started when the fuel cut prohibition time exceeds a predetermined time.
The flowchart of FIG. 11 shows a fifth embodiment of the control for suppressing the adhesion / deposition of the deposit.
In the flowchart of FIG. 11, the processes of steps S81 to S90 are the same as steps S1 to S10 of the flowchart of FIG. 3, and only the process when it is determined that the value of the timer TM2 is equal to or less than the predetermined value t2. Since they are different, the description of step S81 to step S90 is omitted.

If it is determined in step S88 that the value of the timer TM2 is equal to or less than the predetermined value t2 in the flowchart of FIG. 11, the process proceeds to step S91.
In step S91, a process for reducing the tip temperature of the fuel injection valve 12 is executed.
Specifically, the processing of step S91 is the prohibition of the increase in the target idle rotation speed, the two-stroke injection, the switching to the homogeneous combustion mode, and the deceleration fuel cut shown in the first to fourth embodiments. is there.

In the next step S92, the fuel injection pressure of the fuel injection valve 12 is set higher than usual (see FIG. 12).
The fuel injection pressure is increased by switching the target adjustment pressure by a pressure regulator that adjusts the pressure of the fuel supplied to the fuel injection valve 12.
The process of promoting the cooling of the fuel injection valve 12 in step S91 prevents the solidification of the fuel at the tip of the fuel injection valve 12, but if the solidification of the fuel at the tip has occurred, the high pressure It is removed by injection of the converted fuel.

Accordingly, deposits can be prevented from being deposited even when the solidification of the fuel cannot be completely prevented by the process of promoting the cooling of the fuel injection valve 12.
If the fuel injection valve 12 having a plurality of injection holes is used and the cavity 4a receives the fuel spray as in the present embodiment, the formation of the air-fuel mixture particularly during stratified combustion is performed at the injection hole portion. In this way, it is difficult to be affected by deposit accumulation, and by controlling the deposit accumulation as described above, combustion stability can be effectively maintained.

  That is, since the angle formed by the sprays from the adjacent nozzle holes of the fuel injection valve 12 is set to be equal to or less than a single spray angle, even if the spray shape from a certain nozzle hole changes due to deposit accumulation, The peripheral shape of the cavity 4a, which does not greatly affect the spray shape of the adjacent nozzle hole, forms an obtuse angle with the bottom wall of the cavity 4a where the fuel spray collides, and becomes the spray traveling direction after the spray collision Since it is curved toward the injection valve 12 side, the fuel spray can be collected near the center of the combustion chamber 5 even if there is a slight change in the spray shape.

Accordingly, if control is performed in the engine 1 that includes the hole nozzle type fuel injection valve 12 and the cavity 4a formed on the crown surface of the piston 4 receives the fuel spray, to suppress adhesion and accumulation of the deposit, the deposit It is possible to effectively prevent the deterioration of combustibility due to the accumulation of slag.
Further, in the above embodiment, as the processing for reducing the tip temperature of the fuel injection valve 12, the increase in the target idle rotation speed, the two-stroke injection, the switching to the homogeneous combustion mode, and the prohibition of the deceleration fuel cut are shown. If executed by combining a plurality of these, the tip temperature of the fuel injection valve can be reduced more effectively.

The system block diagram of the fuel-injection control apparatus in embodiment. The time chart which shows the change of the front-end | tip temperature of a fuel injection valve immediately after a continuous high load driving | operation. The flowchart which shows 1st Embodiment of control for suppressing adhesion and accumulation of the deposit to the injection valve front-end | tip. The time chart which shows the control characteristic in the said 1st Embodiment. The flowchart which shows 2nd Embodiment of control for suppressing adhesion and accumulation of the deposit to the injection valve front-end | tip. The time chart which shows the control characteristic in the said 2nd Embodiment. The flowchart which shows 3rd Embodiment of control for suppressing adhesion and accumulation of the deposit to the injection valve front-end | tip. The time chart which shows the control characteristic in the said 3rd Embodiment. The flowchart which shows 4th Embodiment of control for suppressing adhesion and accumulation of the deposit to an injection valve front-end | tip. The time chart which shows the control characteristic in the said 4th Embodiment. The flowchart which shows 5th Embodiment of control for suppressing adhesion and accumulation of the deposit to the injection valve front-end | tip. The time chart which shows the control characteristic in the said 5th Embodiment.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder head, 3 ... Cylinder block, 4 ... Piston, 4a ... Cavity, 5 ... Combustion chamber, 6 ... Intake valve, 7 ... Intake port, 8 ... Exhaust valve, 9 ... Exhaust port, 10 ... Intake side camshaft, 11 ... Exhaust side camshaft 11, 12 ... Fuel injection valve, 13 ... Spark plug, 14 ... Engine control unit (ECU), 21 ... Crank angle sensor, 22 ... Cooling water temperature sensor, 23 ... Accelerator opening Sensor

Claims (8)

A fuel injection control device for an engine having a fuel injection valve for directly injecting fuel into a combustion chamber,
The engine fuel is characterized in that the fuel injection condition by the fuel injection valve is set to a condition different from that during normal low-load operation only during a predetermined period when the engine becomes low-load operation after continuous high-load operation of the engine. Injection control device.   The engine fuel injection according to claim 1, wherein when the low load operation after the high load continuous operation is an idle operation, the target rotational speed during the idle operation is set higher than normal during the predetermined period. Control device.   In the low-load operation after the high-load continuous operation, the required fuel injection amount per cycle that is injected once during normal low-load operation is injected in a plurality of times for the predetermined period. The engine fuel injection control device according to claim 1.   The engine fuel injection control device according to claim 1, wherein when the low load operation after the high load continuous operation is a stratified combustion operation condition, the homogeneous combustion operation is forcibly performed only for the predetermined period.   2. The engine fuel injection control device according to claim 1, wherein in the deceleration operation in which the high load continuous operation is switched to the low load operation, the deceleration fuel cut is prohibited for the predetermined period.   2. The fuel injection control device for an engine according to claim 1, wherein in the low load operation after the high load continuous operation, the fuel injection pressure of the fuel injection valve is set higher than normal for the predetermined period.   7. The fuel injection valve according to claim 1, wherein the fuel injection valve is a hole nozzle type fuel injection valve having a plurality of injection holes, and includes a cavity for receiving fuel spray from the fuel injection valve on a piston. The fuel injection control device for an engine according to claim 1.   The spray central axis of the fuel injection valve and the cavity bottom wall where the spray collides form an obtuse angle, and the cavity peripheral wall that becomes the spray traveling direction after the spray collision is curved toward the fuel injection valve side The fuel injection control for an engine according to claim 7, wherein an angle formed by adjacent sprays among the sprays sprayed from the plurality of nozzle holes is set to be equal to or less than a single spray angle. apparatus.

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