JP2008202465A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inject a fuel in a flowing direction (normal tumble flow) desirable for forming an air-fuel mixture in an engine in which the direction of the tumble flow is changed midway in an intake stroke. <P>SOLUTION: A timing at which the direction of the tumble flow is changed from a reverse direction to a normal direction is estimated from the intake air amount and the rotational speed of an engine. The time Tmax between the changing timing and an injection completion limit timing is calculated. When a requested injection time Ti is smaller than the time Tmax, the fuel injection is started at the changing timing. When the requested injection time Ti is equal to or longer than the time Tmax, the timing on the upstream side of the injection completion limit timing by the requested injection timing Ti is taken as an injection start timing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a technique for controlling injection timing during an intake stroke in a fuel injection valve that directly injects fuel into a combustion chamber.

In Patent Document 1, in an in-cylinder direct injection type spark ignition internal combustion engine that directly injects fuel into a combustion chamber, a fuel injection start timing during an intake stroke determined from a fuel injection end timing and a fuel injection pulse width is set as an advance angle. The restriction is described based on the limit value.
JP 2006-090230 A

In a direct-injection spark ignition internal combustion engine, when fuel injected from a fuel injection valve collides and adheres to the piston crown in liquid form, incomplete combustion of the fuel occurs at the piston crown, resulting in poor fuel vaporization. There is a risk that smoke will be generated.
Therefore, in the prior art, a limit of the start timing in the intake stroke injection is set, and the injection start timing is not advanced beyond this limit.

However, experimental verification by the present inventor has revealed that switching of the air flow direction occurs during the intake stroke, and that the switching timing may vary depending on engine operating conditions.
For example, in an engine set to generate a tumble flow in the combustion chamber, an air flow (reverse tumble flow) from the intake port to the piston immediately below occurs in the initial stage of the intake stroke, and then from the intake port to the exhaust port. There is a case where the air flow (forward tumble flow) is changed to the direction of the piston and then returns to the intake port.

Here, in the case where the fuel injection valve is provided in the periphery of the combustion chamber on the intake port side, if fuel injection is performed at a stage where air flow (reverse tumble flow) from the intake port toward the piston directly below is generated, The spray is pushed away by the air flow and adheres to the piston crown surface.
Therefore, as in the past, with the restriction by the fixed injection start limit value, vaporization / mixing is performed by injecting fuel at the earliest possible time while avoiding the adhesion of fuel to the piston crown in response to changes in operating conditions. Qi homogenization could not be promoted to the maximum.

  The present invention has been made in view of the above problems, and is preferable for air-fuel mixture formation even when the direction of air flow changes during the intake stroke, and the timing of the change changes depending on operating conditions. It is an object of the present invention to provide a fuel injection control device for an internal combustion engine that can perform fuel injection under air flow conditions.

Therefore, according to the first aspect of the present invention, the switching timing of the air flow direction during the intake stroke is estimated based on the operating condition of the engine, and fuel is directly injected into the combustion chamber according to the estimated switching timing. The injection timing in the intake stroke of the fuel injection valve is set.
According to the above invention, for example, when the direction of the tumble flow generated in the combustion chamber reverses in the middle of the intake stroke, the flow direction switching timing is estimated from the engine operating conditions, and the flow preferable for the mixture formation The injection timing in the intake stroke is set in accordance with the estimated switching timing so that the fuel is mainly injected in the direction.

Therefore, for example, it can be avoided that the fuel is injected in an air flow state where a large amount of fuel adheres to the piston without excessively shifting the injection timing.
The invention according to claim 2 is characterized in that the switching timing is estimated based on an engine rotational speed and / or an intake air amount of the engine.
According to the above invention, when the timing of switching the air flow direction changes based on the engine rotational speed and / or the intake air amount of the engine, the change in the switching timing is accurately estimated to be more appropriate. The fuel can be injected at a proper injection timing.

  According to a third aspect of the present invention, the fuel injection valve is provided in the periphery of the combustion chamber on the intake port side, and the switching of the air flow direction flows from the intake port toward the piston directly below, and then exhausts on the piston crown surface. This is the switching timing from the reverse tumble flow that flows to the port side to the forward tumble flow that flows from the intake port to the exhaust port side and then turns to the piston side and returns to the intake port side. It is characterized by timing.

According to the invention, in the initial stage of the intake stroke, a reverse tumble flow that flows from the intake port toward the piston directly below and then flows on the piston crown surface to the exhaust port side is generated, and then flows from the intake port to the exhaust port side. After that, the direction is changed to the forward tumble flow which turns to the piston side and returns to the intake port side.
Here, since the fuel injection valve is provided in the combustion chamber peripheral portion on the intake port side, when fuel injection is performed in the state where the reverse tumble flow is generated, the spray is pushed away by the air flow toward the piston, and the piston crown surface. Many fuels will adhere in a liquid state.

On the other hand, if the fuel injection is performed in a state where the forward tumble flow is generated, the fuel spray gets on the air flow, so that the fuel can be prevented from adhering to the piston crown and the mixture can be homogenized. .
Therefore, fuel injection is started from the timing of switching to the forward tumble flow so as not to be injected in the initial period of the intake stroke in which the reverse tumble flow is generated, and fuel adhesion to the piston crown surface is suppressed, Homogenize.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a system diagram showing an internal combustion engine to which the present invention is applied.
An internal combustion engine 1 shown in FIG. 1 is an in-cylinder direct injection spark ignition engine.
An intake passage 4 is connected to a combustion chamber 3 formed by the piston 2 of the internal combustion engine 1 via an intake valve (not shown), and an exhaust passage 5 is connected via an exhaust valve (not shown). It is connected.

The intake passage 4 is provided with an air flow meter 6 for detecting the intake air amount of the internal combustion engine 1 and an electronically controlled throttle valve 7 that is opened and closed by an actuator 8 to adjust the intake air amount. .
The exhaust passage 5 is provided with a catalytic converter 10 for exhaust purification.
The exhaust passage 5 upstream of the catalytic converter 10 is provided with an air-fuel ratio sensor 11 that detects the air-fuel ratio in the internal combustion engine 1 based on the oxygen concentration in the exhaust gas.

A spark plug 14 is disposed at the center top of the combustion chamber 3.
A fuel injection valve 15 that directly injects fuel into the combustion chamber 3 is disposed on the side of the combustion chamber 3 on the intake passage 4 side.
The fuel injection valve 15 provided for each cylinder is connected to a fuel gallery pipe 18, and fuel is distributed and supplied from the fuel gallery pipe 18 to the fuel injection valves 15. The fuel adjusted to a predetermined pressure by the high-pressure fuel pump 16 and the pressure regulator 17 is supplied.

The fuel injection valve 15 injects an amount of fuel proportional to the valve opening time.
The fuel gallery pipe 18 is provided with a fuel pressure sensor 19 for detecting the fuel pressure in the fuel gallery pipe 18, and the pressure regulator 17 is maintained so that the fuel pressure detected by the fuel pressure sensor 19 is maintained at a set pressure. Be controlled.
The high-pressure fuel pump 16 is supplied with fuel in a fuel tank (not shown) by a low-pressure fuel pump 20.

Further, the internal combustion engine 1 includes a water temperature sensor 21 that detects the temperature of the cooling water of the internal combustion engine 1, a crank angle sensor 22 that detects a crank angle, an accelerator opening sensor 23 that detects an accelerator pedal depression amount by a driver, and the like. Is provided.
The fuel injection amount, injection timing, ignition timing, etc. of the internal combustion engine 1 are controlled by a control unit 25 having a built-in microcomputer. The control unit 25 detects from the above-described various sensors. An injection control signal, an ignition control signal, etc. are output by inputting a signal and performing arithmetic processing by a program stored in advance.

Specifically, the control unit 25 determines whether to use a combustion method, that is, homogeneous combustion or stratified combustion, according to the engine operating conditions detected by detection signals from various sensors, and adjusts to this. Thus, the opening degree of the electronic control throttle valve 7, the fuel injection timing and fuel injection amount of the fuel injection valve 15, the ignition timing of the spark plug 14, and the like are controlled.
The fuel injection control by the control unit 25 is performed as follows.

In the low rotation / low load region after the completion of warm-up of the internal combustion engine 1, fuel spray is collected in the vicinity of the spark plug 14 by performing fuel injection at an appropriate time in the compression stroke as a normal stratified combustion operation. Thereby, extremely lean stratified combustion with an air-fuel ratio of about 30 to 40 is realized.
Further, in the middle / high rotation / medium / high load region after the completion of warm-up, a homogeneous air-fuel mixture is generated in the cylinder by performing fuel injection during the intake stroke as a normal homogeneous combustion operation.

In the homogeneous combustion operation, switching between homogeneous stoichiometric combustion in which the target air-fuel ratio is the stoichiometric air-fuel ratio and homogeneous lean combustion in which the target air-fuel ratio is about 20 to 30 lean is performed according to the operating conditions.
Further, in the present embodiment, the shape of the intake port 31 is set so that a tumble flow (a forward tumble flow described later) is generated in the combustion chamber 3 in the intake stroke, but as shown in FIG. The direction of tumble flow (air flow) is reversed during the intake stroke due to a change in the suction force accompanying the lowering of the piston 2.

That is, in the initial stage of the intake stroke (immediately after the intake valve is opened), after the air flows from the intake port 31 toward the piston 2 directly below, the tumble flow flowing on the crown surface of the piston 2 toward the exhaust port 32 is generated. Generated. The tumble flow flows counterclockwise in FIG. 2, and in the present application, the tumble flow flowing counterclockwise is referred to as a reverse tumble flow.
On the other hand, as the piston 2 approaches the bottom dead center, the force pulling the intake air toward the piston 2 becomes weaker, and the inertial force of the air flowing through the intake port 31 becomes relatively stronger, which is opposite to the reverse tumble flow. A tumble flow is generated. The tumble flow opposite to the reverse tumble flow flows clockwise in FIG. 2, and in the present application, the tumble flow flowing clockwise is referred to as a forward tumble flow.

The forward tumble flow is a flow that flows from the intake port 31 to the exhaust port 32 side, then turns to the piston 2 side and returns to the intake port 31 side, so that the forward tumble flow is generated. 31 shapes are set.
Note that the switching timing (crank angle position) from the reverse tumble flow to the forward tumble flow shown in FIG. 2 is a timing when the reference intake air amount and the reference engine rotation speed are satisfied, and the switching timing is It changes according to the amount of intake air and engine speed.

  Here, since the fuel injection valve 15 injects fuel slightly downward (obliquely toward the piston side) from the intake port 31 side to the exhaust port 32 side, the fuel spray directing direction and the forward tumble are The direction of the air flow flowing from the intake port 31 to the exhaust port 32 side substantially coincides, and the fuel spray injected from the fuel injection valve 15 directly flows in the combustion chamber 3 on the forward tumble flow. As a result, vaporization and homogenization of the fuel spray can be achieved.

On the other hand, when fuel is injected from the fuel injection valve 15 at the initial stage of the intake stroke in which a reverse tumble flow is generated, the fuel spray is pushed away by the airflow flowing directly from the intake port 31 toward the piston 2, and the piston crown surface. Will hit the piston crown surface in liquid form.
Therefore, in this embodiment, the fuel is injected in the intake stroke as shown in the flowchart of FIG. 3 in order to prevent the fuel from adhering to the piston crown surface by spraying the reverse tumble flow. Determine the injection timing.

In the flowchart of FIG. 3, in step S101, it is determined whether or not the current engine load / engine speed conditions are within a homogeneous combustion region in which a homogeneous mixture formed by intake stroke injection is combusted.
When it is within the homogeneous combustion region, the process proceeds to step S102 and subsequent steps to determine the injection timing during the intake stroke.

First, in step S102, the intake air amount Q and the engine rotational speed Ne at that time are detected.
In the next step S103, a map that stores in advance the timing of switching from reverse tumble flow to forward tumble flow (crank angle at which switching occurs) for each intake air amount Q and engine rotational speed Ne is referred to. The switching timing corresponding to the intake air amount Q and the engine speed Ne is searched.

That is, the timing of switching from the reverse tumble flow to the forward tumble flow is estimated from the intake air amount Q and the engine rotational speed Ne at that time.
In a simple manner, the switching timing can be estimated from only the intake air amount Q or only from the engine rotational speed Ne.
In step S104, a time Tmax from the switching timing to the limit timing of the end of injection is calculated.

The limit timing of the end of injection is the crank angle position during the intake stroke, which is preferably not delayed as the end timing of fuel injection, and is stored in advance as a fixed value, or the engine load / engine speed / cooling It can be variably set according to the water temperature (engine temperature) or the like.
The time Tmax corresponds to the maximum injection time during which fuel injection can be started from the switching timing.

In step S105, the required injection time (requested fuel injection amount) Ti at that time is compared with the maximum injection time Tmax.
Here, if the required injection time Ti is equal to or shorter than the maximum injection time Tmax, even if the injection is started from the switching timing, the injection can be completed by the limit timing of the end of the injection.

Therefore, if the required injection time Ti is less than or equal to the maximum injection time Tmax, the process proceeds to step S106, and the timing at which the reverse tumble flow is switched to the forward tumble flow is set as the injection start timing.
If fuel injection is started from the timing of switching the tumble flow, fuel injection is not performed in the generation state of the reverse tumble flow, it is possible to suppress the adhesion of fuel to the piston crown surface, and smoke caused by poor fuel vaporization Occurrence can be prevented.

Furthermore, the injection start timing will change in conjunction with the change of the switching timing due to the change of the operating condition, and the injection can be started as early as possible while avoiding the generation period of the reverse tumble flow, Vaporization and homogenization can be promoted sufficiently.
On the other hand, when the required injection time Ti exceeds the maximum injection time Tmax, the injection cannot be completed by the end timing of the injection if the injection is started from the tumble flow switching timing. Become.

Therefore, if the required injection time Ti exceeds the maximum injection time Tmax, the process proceeds to step S107, and a timing that is the required injection time Ti before the limit timing of the end of the injection is determined as the injection start timing.
In this case, the injection start timing is advanced from the tumble flow switching timing, and the initial fuel injection is performed in the reverse tumble flow generation state. However, the injection starts from the tumble flow switching timing. The period until the end limit time is the fuel injection period, and the part that cannot be injected in this period is injected before the tumble flow switching timing, so the amount of fuel injected in the reverse tumble flow generation state The amount of fuel adhering to the piston crown can be minimized.

If the effect of injecting fuel in the reverse tumble flow state is greater than the effect of delaying the actual injection timing from the limit timing of the end of injection, the actual injection timing is greater than the limit timing of the end of injection. Even when the delay is delayed, the fuel injection can be started from the switching timing of the tumble flow.
Further, the portion where the required injection time Ti exceeds the maximum injection time Tmax can be distributed to the injection after the limit timing of the end of injection and the injection before the switching timing of the tumble flow.

Furthermore, when the switching timing of the tumble flow is set as the injection start timing, the timing at which the tumble flow becomes 0 is not limited to the injection start timing, and a time point slightly before the tumble flow becomes 0 is set. It can be the injection start timing.
Further, when the required injection time Ti exceeds the maximum injection time Tmax, the fuel injection can be started based on the injection start timing separately determined from the engine load, the engine speed, and the like.

In addition, when fuel injection is performed in, for example, an intake stroke and a compression stroke, the injection start timing in the intake stroke can be set as a tumble flow switching timing.
The flowchart of FIG. 4 shows a second embodiment of injection timing control.
In step S201, it is determined whether or not the current engine load / engine speed conditions are within a homogeneous combustion region in which a homogeneous mixture formed by intake stroke injection is combusted.

When it is in the homogeneous combustion region, the process proceeds to step S202 and subsequent steps to determine the injection timing during the intake stroke.
First, in step S202, the intake air amount Q and the engine rotational speed Ne at that time are detected.
In the next step S203, a map that stores in advance the switching timing (crank angle at which switching occurs) from reverse tumble flow to forward tumble flow for each intake air amount Q and engine rotational speed Ne is referenced. The switching timing corresponding to the intake air amount Q and the engine speed Ne is searched.

That is, the timing of switching from the reverse tumble flow to the forward tumble flow is estimated from the intake air amount Q and the engine rotational speed Ne at that time.
In a simple manner, the switching timing can be estimated from only the intake air amount Q or only from the engine rotational speed Ne.
In step S204, it is determined whether or not the required injection time (required fuel injection amount) Ti at that time is equal to or less than a reference time Ts stored in advance.

If the required injection time (requested fuel injection amount) Ti is equal to or less than the reference time Ts, the process proceeds to step S205, and the timing at which the reverse tumble flow obtained in step S203 is switched to the forward tumble flow is set as the injection start timing. .
On the other hand, if the required injection time (required fuel injection amount) Ti exceeds the reference time Ts, the process proceeds to step S206, and the standard injection start timing that is earlier than the switching timing from the reverse tumble flow to the forward tumble flow. Is the final injection start timing.

The standard injection start timing may be a fixed value or may be variably set from the intake air amount Q and / or the engine rotational speed Ne.
According to the second embodiment, when the required injection time (required fuel injection amount) Ti is short (small), it is difficult to obtain sufficient homogenization using in-cylinder gas flow. Since the fuel is injected after switching to the above, homogenization using the gas flow can be sufficiently obtained.

The flowchart of FIG. 5 shows a third embodiment of injection timing control.
In step S301, it is determined whether or not the current engine load / engine speed conditions are within a homogeneous combustion region in which a homogeneous mixture formed by intake stroke injection is combusted.
When it is in the homogeneous combustion region, the process proceeds to step S302 and subsequent steps to determine the injection timing during the intake stroke.

First, in step S302, the intake air amount Q and the engine rotational speed Ne at that time are detected.
In the next step S303, a map in which the timing of switching from reverse tumble flow to forward tumble flow (crank angle at which switching occurs) is stored in advance for each intake air amount Q and engine rotational speed Ne is obtained. The switching timing corresponding to the intake air amount Q and the engine speed Ne is searched.

That is, the timing of switching from the reverse tumble flow to the forward tumble flow is estimated from the intake air amount Q and the engine rotational speed Ne at that time.
In a simple manner, the switching timing can be estimated from only the intake air amount Q or only from the engine rotational speed Ne.
In step S304, a standard injection start timing is calculated. The standard injection start timing may be a fixed value, or may be variably set from the intake air amount Q and / or the engine rotational speed Ne.

In step S305, when fuel injection is started at the standard injection start timing, it is calculated what percentage of the total required injection time (required fuel injection amount) Ti in the intake stroke is injected in the reverse tumble flow period. To do.
In step S306, the fuel ratio X injected in the reverse tumble flow period is compared with the threshold value SL. If the fuel ratio X is equal to or less than the threshold value SL, the process proceeds to step S307, and the injection calculated in step S305 is performed. The start timing is set to the final injection start timing as it is.

On the other hand, when the fuel ratio X exceeds the threshold SL, the process proceeds to step S308, and the injection start timing at which the fuel ratio X can be made equal to or less than the threshold SL is calculated.
Specifically, the injection start timing in which the amount corresponding to the threshold SL of the required injection time (required fuel injection amount) Ti in the intake stroke is injected in the reverse tumble flow period is changed from the reverse tumble flow to the forward tumble flow. And the required injection time (required fuel injection amount) Ti at that time.

According to the third embodiment, since the injection start timing is changed so that the fuel ratio X injected in the reverse tumble flow period becomes equal to or less than the threshold value SL, most of the fuel is injected in the reverse tumble flow period. By doing so, it can be avoided that a large amount of fuel adheres to the piston crown surface and a homogeneous mixture cannot be generated.
In the above embodiment, the engine that generates the tumble flow is taken as an example. However, in the engine set to generate the swirl flow in the intake stroke, for example, the original swirl flow is not generated in the initial stage of the intake stroke. The present invention can also be applied to the case where an airflow flowing directly from the intake port toward the piston is generated.

Next, inventions other than those described in the claims that can be grasped from the above-described embodiment will be described together with the effects thereof.
(A) When the switching timing is an injection start timing, the injection start timing is shifted before the switching timing when the injection end timing exceeds a predetermined limit timing. A fuel injection control device for an internal combustion engine according to claim 3.

According to the above invention, when the fuel injection is started at the switching timing from the reverse tumble flow to the forward tumble flow during the intake stroke, the end of the injection is later than the predetermined limit time. Shifts the injection start timing before the switching timing from the reverse tumble flow to the forward tumble flow, so that the fuel injection ends before the limit time.
Therefore, the fuel injection is continued beyond the end limit timing while avoiding the fuel injection in the reverse tumble flow state where the air flow direction before the switching timing of the tumble flow direction is not preferable for the mixture formation. Can be prevented.
(B) The fuel injection control device for an internal combustion engine according to claim 3, wherein when the requested fuel injection amount is equal to or less than a predetermined value, the switching timing is set as an injection start timing.

According to the above invention, when the generation of a homogeneous mixture is difficult because the required fuel injection amount is small, the forward tumble flow is advantageous for the generation of the homogeneous mixture after the switching timing of the air flow direction. Therefore, even when the fuel injection amount is small, it is possible to generate a homogeneous air-fuel mixture using air flow.
(C) The fuel injection valve is provided in the periphery of the combustion chamber on the intake port side, and the switching of the air flow direction flows from the intake port toward the piston immediately below, and then on the piston crown surface to the exhaust port side. This is the switching timing from the flowing reverse tumble flow to the forward tumble flow that flows from the intake port to the exhaust port side, then turns to the piston side and returns to the intake port side, and is injected during the reverse tumble flow period 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the injection timing is determined so that the fuel amount is equal to or less than a predetermined ratio of the total fuel amount injected in the intake stroke.

According to the above invention, the ratio of the amount of fuel injected during reverse tumble flow to the amount of fuel injected during forward tumble flow is determined, and the ratio of the amount of fuel injected during reverse tumble flow is excessive. The injection timing is determined so as not to become.
Therefore, it can be prevented that most of the fuel is injected during the reverse tumble flow and the generation of the homogeneous air-fuel mixture using the air flow cannot be achieved.

1 is a system diagram of an internal combustion engine in an embodiment of the present invention. The figure which shows the switching characteristic of the tumble flow in embodiment. The flowchart which shows 1st Embodiment of injection timing control. The flowchart which shows 2nd Embodiment of injection timing control. The flowchart which shows 3rd Embodiment of injection timing control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Piston, 3 ... Combustion chamber, 6 ... Air flow meter, 14 ... Spark plug, 15 ... Fuel injection valve, 22 ... Crank angle sensor, 25 ... Control unit, 31 ... Intake port

Claims (3)

In a fuel injection control device for an internal combustion engine provided with a fuel injection valve for directly injecting fuel into a combustion chamber,
The switching timing of the air flow direction during the intake stroke is estimated based on the operating condition of the engine, and the injection timing in the intake stroke of the fuel injection valve is set according to the estimated switching timing. A fuel injection control device for an internal combustion engine.   2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the switching timing is estimated based on an engine speed and / or an intake air amount of the engine.   The fuel injection valve is provided in the periphery of the combustion chamber on the intake port side, and the reverse tumble flows on the piston crown surface to the exhaust port side after the switching of the air flow direction flows from the intake port toward the piston immediately below It is a switching timing from a flow to a forward tumble flow that flows from the intake port to the exhaust port side and then turns to the piston side and returns to the intake port side, and the switching timing is set as an injection start timing. A fuel injection control device for an internal combustion engine according to claim 1 or 2.

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