JP5321844B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine that performs fuel injection using both a port injection valve and an in-cylinder injection valve.

  An engine (internal combustion engine) mounted on an automobile includes an engine that directly injects fuel from a high-pressure injector (in-cylinder injection valve) into a combustion chamber in the cylinder. Recently, in order to supplement the resolution of the injection amount of the high pressure injector, such a direct injection engine is also used in combination with a low pressure injector (port injection valve) that injects fuel into the intake port (upstream of the intake valve), for example. Is a low pressure injector, low and medium load areas are divided into low pressure injectors and high pressure injectors, and high load areas are injected with high pressure injectors, depending on engine operating conditions. Engines that supply fuel to the market have appeared on the market (see Patent Document 1, Non-Patent Documents 1 and 2).

By the way, in order to purify exhaust, automobile engines are required to purify exhaust gas with a catalyst immediately after the engine is started.
However, at the time of cold start, since the catalyst is not warmed up, the exhaust gas is not easily purified by the catalyst. For this reason, in a direct injection engine, the temperature of the catalyst is quickly raised to the activation temperature, so that the air-fuel ratio becomes lean in the vicinity of the stoichiometric air-fuel ratio (stoichio) by the injection in the compression stroke of the high-pressure injector immediately after the cold start. Combustion is performed with an air-fuel mixture, and fuel is stably combusted in a combustion chamber. This operation is referred to as “compressed light lean operation”.

  In an engine equipped with a recent high-pressure injector and low-pressure injector, fuel is not injected only from the high-pressure injector, but is injected separately into the high-pressure injector and the low-pressure injector (divided injection mode), so that an easily combusted air-fuel mixture is produced. Secured and operated in a compressed light lean operation. Specifically, in the compression-slight lean operation, fuel is injected (port injection) from the low pressure injector at the normal mode injection timing (expansion to suction stroke), and fuel is injected from the high pressure injector in the second half of the compression stroke, for example. (In-cylinder injection) (see Non-Patent Documents 1 and 2).

  In the compression light lean operation performed by this divided injection, a homogeneous air-fuel mixture is supplied into the combustion chamber by port injection, and the air-fuel mixture around the spark plug is stratified by in-cylinder injection. For this reason, ignition is promoted and combustion in the combustion chamber is considerably stabilized. In this compression slight lean operation, the combustion in the combustion chamber is extremely stable, so that the ignition timing can be considerably retarded (retarded), and the exhaust gas temperature can be considerably increased. Therefore, there is a feature that the temperature of the catalyst can be increased quickly.

JP-A-11-336645

Automotive Engineering March, 2010 issue “Engine” in the left column of P56 2010 MotorFan illustrated Ver.38 P35

By the way, in such an engine, it has been a problem to reduce unburned fuel (unburned HC) discharged from the cold start until the catalyst reaches the activation temperature.
In other words, in the compression / slight lean operation, the vaporization of the fuel injected into the intake port is surely promoted by the combined use of the port injection in the expansion / intake stroke, and the time until the catalyst is activated can be shortened. However, since the engine is in a cold state, the fuel injected into the intake port may be supplied to the combustion chamber without being sufficiently vaporized. For this reason, even if the time is shortened until the catalyst is activated by the compression-slight lean operation, unburned HC may be discharged before the catalyst is activated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel injection control device for an internal combustion engine that can reduce the amount of HC discharged during the compression / slight lean operation without disturbing the compression / slight lean operation.

In order to achieve the above object, a first aspect of the present invention provides an in-cylinder injection valve that supplies fuel to a combustion chamber of an internal combustion engine, a port injection valve that supplies fuel into an intake port of the internal combustion engine, and a combustion At least a port injection mode for supplying fuel to the chamber only with the port injection valve, and a divided injection mode for supplying fuel to the combustion chamber divided into the in-cylinder injection valve and the port injection valve, depending on the operating state of the internal combustion engine A fuel injection control device for an internal combustion engine comprising a fuel injection control means for selecting a fuel injection mode, wherein the fuel injection control means injects fuel with a cylinder injection valve during a compression stroke of the internal combustion engine and ratio select split injection mode when the compression slight lean operation to lean around the stoichiometric air-fuel ratio and the fuel injection timing of in-port injection valve split injection mode in the compression slight lean operation, Than the fuel injection timing of the port injection valve in the injection mode according to the operating condition was assumed to be advanced.
According to the same configuration, the fuel injected into the intake port in the compression / slight lean operation is injected from the advanced timing as compared with the fuel injection timing of the other injection modes, and the period of staying in the intake port is long. Therefore, it takes time to vaporize the fuel, and the vaporization of the fuel is promoted. As a result, immediately after the engine cold start when the compression-slight lean operation starts, a sufficiently vaporized air-fuel mixture is supplied to the combustion chamber and unburned fuel (unburned fuel) discharged from the engine start until the catalyst activation temperature is reached. HC) emissions are reduced. In addition, since the in-cylinder injection in the compression / slight lean operation is not changed, the compression / slight lean operation in which the temperature of the catalyst is raised quickly is not hindered.

According to the second aspect of the present invention, the fuel injection timing of the port injection valve in the split injection mode in the compression-slight lean operation is as follows so that the time to vaporize the fuel can be obtained as much as possible by using the timing when the intake valve is closed. The compression stroke of the internal combustion engine was assumed.
According to the third aspect of the present invention, when the pressure of the fuel supplied to the in-cylinder injection valve is lower than a predetermined value so that the HC emission can be suppressed even at a slight time until the start of the compression-slight lean operation, the port injection is performed. The mode was selected, and the injection timing of the port injection valve in the port injection mode was the period from the expansion stroke to the exhaust stroke.

  According to the first aspect of the present invention, the fuel injected by the port during the compression lean lean operation can be vaporized by the advance of the injection timing. It can be supplied from the intake port to the combustion chamber. Thereby, the discharge | emission of the unburned fuel (unburned HC) discharged | emitted after an engine start until a catalyst reaches activation temperature is reduced. In addition, since the in-cylinder injection timing that is the main component of the compression / slight lean operation has not been changed, the operation of quickly raising the temperature of the catalyst can be maintained satisfactorily.

Therefore, it is possible to reduce the amount of HC exhausted from the engine during the compression / slight lean operation without disturbing the compression / slight lean operation.
According to the second aspect of the present invention, it is possible to obtain as much fuel vaporization time as possible by using the time when the intake valve is closed, and the effect of reducing the HC emission amount is exhibited.
According to the third aspect of the invention, when the pressure of the fuel supplied to the in-cylinder injection valve is not ensured, the mode is switched to the port injection mode in which the injection timing is from the expansion stroke to the exhaust stroke, and the fuel enters the intake port. Since it is sufficiently vaporized, it is possible to suppress HC emission even when the fuel pressure for performing the compressed sleek lean operation is small.

The figure which shows schematic structure of the fuel-injection control apparatus of the internal combustion engine which concerns on one Embodiment of this invention. The flowchart which shows the control flow of the fuel injection control apparatus. The diagram which shows the behavior of each part of the internal combustion engine in the same control flow. The figure which shows the fuel-injection time at the time of the compression light lean operation of the control flow.

Hereinafter, the present invention will be described based on an embodiment shown in FIGS.
FIG. 1 shows a schematic configuration of a main part of an automobile multi-cylinder engine 1 (internal combustion engine) mounted on an automobile (vehicle) and a fuel injection control device 2 of the engine 1.
The basic structure of the engine 1 will be described. In FIG. 1, 5 is a cylinder block having a cylinder 6, and 7 is a cylinder head mounted on the head of the cylinder block 5. A combustion chamber 8 is formed on the lower surface of the cylinder head 7 facing the cylinder 6. An intake port 12 that is opened and closed by an intake valve 10 and an exhaust port 14 that is opened and closed by an exhaust valve 13 are formed on both sides of the combustion chamber 8. The intake port 12 is connected to the air cleaner 18 via the electronic throttle 6 and the air flow sensor 17, and combustion air can be taken into the combustion chamber 8 from the air cleaner 18. The exhaust port 14 is connected to a catalytic converter 20 constituting the exhaust gas purifying device 19, and the exhaust gas can be purified by a catalyst 21 built in the catalytic converter 20. The cylinder head 7 includes a high-pressure injector 22 (equivalent to the in-cylinder injection valve of the present application) that injects fuel directly into the combustion chamber 8 and a low-pressure injector 23 (injection of the port injection valve of the present application) that injects fuel into the intake port 12. Equivalent). Among these, the low pressure injector 23 is connected to the fuel tank 26 via the feed pump 25. The high-pressure injector 22 is connected to a high-pressure pump 26 that is branched from the discharge side of the feed pump 25. That is, as for the fuel in the fuel tank 26, the fuel pumped by the feed pump 25 is injected as it is from the low-pressure injector 23 as low-pressure fuel, or further pressurized by the high-pressure pump 27 and injected from the high-pressure injector 22 as high-pressure fuel. . A piston 29 is housed in the cylinder 6 so as to be able to reciprocate. The piston 29 is connected to a crankshaft (not shown) via a connecting rod 28. Further, the cylinder head 7 is provided with a spark plug 30. The engine 1 operates from a predetermined combustion cycle, that is, an intake stroke, a compression stroke, an expansion (combustion) stroke, from operations such as ignition of the ignition plug 30, reciprocation of the piston 29, injector injection, and opening / closing of the intake / exhaust valves 12 and 13. Four cycles that repeat the exhaust stroke are formed, and the power obtained by the piston 25 is output from a crankshaft (not shown).

The fuel injection control device 2 is a device that mainly controls the high-pressure injector 22 and the low-pressure injector 23. The apparatus 2 is configured using a control unit 35 (corresponding to the fuel injection control means of the present application) configured to control each unit of the engine 1, which includes, for example, a CPU, peripheral electronic circuits, and a memory.
That is, the control unit 35 is set with a normal mode in which the high pressure injector 22 and the low pressure injector 23 are sprayed according to the operating state of the engine 1. The normal mode is, for example, an injection mode in which low-pressure fuel is injected from the low-pressure injector 23 only at a low load during an extremely low load, and a high-pressure injector 22 at a low / medium load. An injection mode in which low pressure fuel is injected in an expansion stroke to an intake stroke and high pressure fuel is injected in an exhaust stroke to an intake stroke while changing a split ratio in accordance with a load in a divided injection mode divided into a low pressure injector 23, and at high load It has a setting for selecting an injection mode in which high-pressure fuel is injected only from the high-pressure injector 22 in the exhaust stroke to the intake stroke, and a setting for controlling the fuel injection amount in the selected mode in accordance with the operating state of the engine 1. In any of the injection modes, for example, control is performed so as to obtain a stoichiometric air-fuel ratio in the compression stroke, and fuel is burned in the combustion chamber 8 utilizing the characteristics of in-cylinder injection and port injection (stoichiometric direct injection engine). In order to execute these modes, the control unit 35 inputs various information necessary for determining the operating region and operating state of the engine, such as accelerator opening information, engine speed information, and air amount information (airflow sensor 17). I am letting.

  In addition to this, the control unit 35 is set with a function of performing a compression sleek lean operation immediately after the cold start of the engine 1. The compression sleek lean operation is an operation in which the temperature of the cold catalyst 21 is raised to the activation temperature at an early stage. In this compression slight lean operation, a split injection mode in which fuel is injected into the high pressure injector 22 and the low pressure injector 23 immediately after the cold start of the engine 1 is selected, and the combustion air-fuel ratio is the theoretical air in the compression stroke by this split injection. This is done by making the lean in the vicinity of the fuel ratio (stoichio). For example, the air-fuel ratio A / F in the compression stroke is set to an air-fuel ratio (for example, around 15.5) that is slightly leaner than the theoretical mixture ratio. In this air-fuel ratio operation, combustion is extremely stable. For this reason, during the compression / slight lean operation, the ignition timing is delayed more than usual and retarded (retarded) to the limit. Thus, the time until the catalyst 21 reaches the activation temperature can be shortened. In order to execute the compression slur lean operation, the control unit 35 inputs various information necessary for the compression slur lean operation such as ignition switch start information, cooling water temperature information (engine cold state), and the like.

During the compression lean operation, since the engine 1 is in a cold state, the fuel injected through the port is not sufficiently vaporized, and unburned fuel (unburned HC) is discharged before the catalyst 21 reaches the activation temperature. May be. Therefore, a function for improving this is set in the control unit 35.
This setting is to advance only the fuel injection timing of the low-pressure injector 23 in the split injection mode performed in the compression / slight lean operation so as to obtain the fuel vaporization period as much as possible. Specifically, the fuel injection timing of the low-pressure injector 23 is advanced from the fuel injection timing (port injection) performed by the low-pressure injector 23 in other operating states (including the normal mode). In particular, as shown in FIG. 4, the compression stroke of the engine 1, specifically, the first half of the compression stroke (the time when the intake valve 10 is closed) is advanced so that the fuel vaporization time can be obtained as much as possible. .

  Further, when the pressure (fuel pressure) of the fuel supplied to the high pressure injector 22 is lower than the required pressure value, which is a predetermined value, the control unit 35 discharges HC in order to avoid inducing an unstable combustion state. A setting to switch to a port injection mode in which the period from the expansion stroke to the exhaust stroke is set as the fuel injection timing, for example, the port injection mode in which fuel is injected only from the low pressure injector 22 in which the exhaust stroke is set as the injection timing. Has been. Therefore, fuel pressure information is input to the control unit 35 from the fuel pressure sensor 36 that detects the fuel pressure supplied to the high pressure injector 22. Further, even when the engine speed after starting is not stable, it is assumed that an unstable combustion state is caused.If the engine speed does not become stable after engine starting, it is necessary for the engine speed to stabilize here. If the predetermined time A is not exceeded, the operation is not switched to the compression sleek lean operation.

FIG. 2 shows a control flow relating to such a compression / slight lean operation, FIG. 3 shows the behavior of each part of the engine at this time, and FIG. 4 shows the fuel injection timing of each injector 22, 23. . 2 to 4, PI represents port injection, and DI represents in-cylinder injection.
The fuel injection of the engine 1 will be described with reference to the control flow shown in FIG. The routine of the same flow is repeated every predetermined time.

That is, for example, in order to drive an automobile, it is assumed that an ignition switch is operated and a starter (not shown) is operated at a low outside air temperature (for example, 10 ° C. or less) (fast start).
The engine 1 at this time has a low cooling water temperature. It is also cranking. Therefore, the control part 35 determines with it being cold start in step S1, progresses to step S2, and also determines with cranking being in step S2.

  Then, it progresses to step S3 and the control part 35 selects the port injection mode which injects only from the low pressure injector 23, for example, and injects the starting fuel into the intake port 12 from the low pressure injector 23. This port injection is performed, for example, during the exhaust stroke of the engine 1. This fuel is supplied to the combustion chamber 8 through the intake port 12. During this time, the fuel is vaporized. The start may be performed in a mode in which fuel is injected into the cylinder by the high-pressure injector 23 (intake stroke injection).

  By the subsequent ignition operation of the spark plug 30, the air-fuel mixture supplied into the combustion chamber 8 is ignited. Then, the engine 1 starts to start, and the rotational speed of the engine 1 starts to increase rapidly as shown in FIG. The control unit 35 performs control to reduce the injection amount and control to advance the ignition timing of the spark plug 30 according to the increase in the engine speed, and proceeds to idling while stabilizing the combustion. During this time, the high-pressure pump 27 is driven by the crank output, and the fuel pressure supplied to the high-pressure injector 22 gradually increases.

  As the engine 1 starts, the process proceeds from step S2 to step S4. Step S4 determines whether or not the engine speed immediately after starting is stable. Here, for example, the engine speed is set with a threshold value determined based on the start history of the engine 1, for example, a predetermined time A (elapsed time: FIG. 3) indicating that the engine speed has been stabilized since the engine start. It is determined whether the number is in a stable state. It may be determined whether the engine speed is stable by another determination method.

  If it is determined that the elapsed time has exceeded the predetermined time A, the control unit 35 determines that the rotational speed of the engine 1 is in a stable state, and proceeds to step S5. This step S5 is to determine the end of the compression sleek lean operation. In step S5, the elapsed time from the start of the engine is set to, for example, a predetermined time B (> predetermined time A) to determine the end of the compression / slight lean operation. Since the predetermined time B has not yet been reached at the time immediately after the start, the process proceeds to the subsequent step S6.

  In step S6, it is determined whether or not the fuel pressure of the high pressure injector 22 is ensured to a predetermined value (by detection of the fuel pressure sensor 36). At this time, if it is determined that the fuel pressure (high pressure) required for the compression / slight lean operation has been secured, the process proceeds to step S7 where it is determined whether or not the catalyst 21 is in a fast idle state where early warm-up of the catalyst 21 is required. If it is determined in step S6 that the fuel pressure required for the compression-slight lean operation has not yet been secured, the process returns to step S3 and the exhaust stroke injection (port injection) from only the low-pressure injector 23 is continued.

  Step S7 is to determine whether the accelerator opening is fully closed, for example. Here, if it is determined that the accelerator is fully closed, it is determined that early warm-up of the catalyst 21 is necessary, and the process proceeds to step S8, where the compression is performed by fuel injection (split injection mode) divided into the high pressure injector 22 and the low pressure injector 22. Run the operation. Then, in order to obtain an air-fuel ratio slightly leaner than the theoretical mixture ratio (for example, around 15.5) in the compression stroke, the most low period of time during which the intake valve 10 is closed from the low pressure injector 23 as shown in FIG. A variable amount of idling fuel is injected in the first half of the early compression stroke (port injection: PI), and the remaining fuel is injected from the high pressure injector 22 in the compression stroke, for example, in the second half of the compression stroke (in-cylinder injection: DI) (split injection). .

  The port-injected fuel travels toward the fuel chamber 8 while being vaporized in the intake port 12. By this port injection, a homogeneous air-fuel mixture is supplied into the combustion chamber 8, and by the in-cylinder injection, the air-fuel mixture around the spark plug 30 is stratified to promote ignitability. Combustion in the combustion chamber 8 is extremely stable. For this reason, the control unit 35 retards the ignition timing of the spark plug 30 as shown in FIG. 3, and retards it to the limit, for example. This significantly increases the exhaust gas temperature. With this exhaust gas, the temperature of the catalyst 21 is quickly raised to the activation temperature.

  When a predetermined time B has elapsed from the start of the engine, the control unit 35 determines that the temperature of the catalyst 21 has risen to the catalyst activation temperature, ends the compression-slight lean operation, and injects fuel according to the normal engine operating state. That is, the mode is switched to the normal mode (injection only by the low pressure injector 23, injection divided into the high pressure injector 22 and the low pressure injector 23, and injection only by the high pressure injector 22). In addition, when the accelerator pedal is depressed during the compression / slight lean operation and the accelerator opening increases, the compression / slight lean operation is terminated and the mode is switched to the normal mode (because the increased fuel increases the exhaust gas temperature).

At this time, the compression light lean operation performed immediately after the cold start is such that the engine 1 is in the cold state, so that the fuel injected from the low pressure injector 23 is easily supplied to the combustion chamber 8 without being sufficiently vaporized. Due to this, there is a concern that a large amount of unburned fuel (unburned HC) is discharged before the catalyst 21 is activated.
Here, since the port injection responsible for the compression light lean operation of the present embodiment injects fuel at a timing advanced from the other injection modes as described above, the period in which the fuel is in the intake port 12 of the fuel is considerable. become longer. For this reason, the fuel that has been port-injected can be considerably vaporized by using the intake valve 10 while it is closed. This is because the fuel vaporization is accelerated by the advancement of the injection timing of the port injection, and a sufficiently vaporized mixture can be supplied into the combustion chamber 8 immediately after the cold start, and good combustion is achieved in the combustion chamber 8. Done within.

Thereby, when the engine is cold, unburned fuel (unburned HC) discharged from the start of the engine until the catalyst activation temperature is reached is suppressed. In addition, since the in-cylinder injection timing that is the main subject of the compression / slight lean operation is not changed at all, the operation for raising the temperature of the catalyst 21 at an early stage is maintained well as it is at the beginning.
Therefore, the amount of HC exhausted during the compression / slight lean operation can be reduced without disturbing the compression / slight lean operation in which the temperature of the catalyst 21 is increased quickly by the advance of the injection timing of the port injection.

Moreover, if the injection timing of the port injection in the compression / slight lean operation is set to the compression stroke of the engine 1, particularly the first half of the compression stroke, the fuel vaporization time can be obtained as much as possible by using the closing timing of the intake valve 10. It is effective for reducing emissions.
In addition, when the fuel pressure of in-cylinder injection is not ensured, the fuel is switched to the injection mode in which the fuel is port-injected in the exhaust stroke (expansion stroke), and the fuel is sufficiently vaporized in the intake port 12 where the intake valve 10 is closed. The discharge of HC can be suppressed for a short time (until the fuel pressure is secured) from the start of the compression to the lean lean operation.

  In addition, since the engine speed after the start of the engine becomes stable after the engine is started, the switching to the compression / slight lean operation can be performed in consideration of the temperature increase of the catalyst 8 and HC reduction. The catalyst temperature raising performance and the maximum HC reduction performance can be exhibited. In particular, the compression / slight lean operation is effective in the case of stable idling (accelerator fully closed) immediately after the cold start.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit of the present invention. For example, in one embodiment, the present invention is applied to a stoichiometric direct injection engine. However, the present invention is not limited thereto, and the present invention may be applied to a lean burn direct injection engine. In one embodiment, the present invention is applied to an engine that selects three injection modes such as port injection, split injection by in-cylinder injection and port injection, and in-cylinder injection. However, the present invention is not limited to this. May be any engine that has at least port injection and split injection. Further, in the embodiment, an example in which the in-cylinder injection that is a main subject of the compression sleek lean operation is not changed is shown, but the embodiment is not limited thereto. In addition, since the time from fuel injection to combustion becomes longer due to the advance timing of port injection, the response to changes in engine operating conditions that occur during this period, for example, sudden changes in engine speed, becomes a problem. The amount of fuel for in-cylinder injection may be increased or decreased as appropriate according to changes in the situation.

1 engine (internal combustion engine)
2 Fuel Injection Control Device 6 Cylinder 8 Combustion Chamber 10 Intake Valve 12 Intake Port 21 Catalyst 22 High Pressure Injector (In-Cylinder Injection Valve)
23 Low pressure injector (port injection valve)
35 Control unit (fuel injection control unit)

Claims (3)

An in-cylinder injection valve for supplying fuel to the combustion chamber of the internal combustion engine;
A port injection valve for supplying fuel into the intake port of the internal combustion engine;
An internal combustion engine having at least a port injection mode in which fuel is supplied only to the port injection valve to the combustion chamber, and a split injection mode in which fuel is supplied separately to the in-cylinder injection port and the port injection valve to the combustion chamber; A fuel injection control means for selecting a fuel injection mode according to the operating state of the internal combustion engine, comprising:
The fuel injection control means selects the split injection mode at the time of compression slur lean operation in which fuel is injected by the in-cylinder injection valve in the compression stroke of the internal combustion engine and the combustion air-fuel ratio is lean near the stoichiometric air-fuel ratio. The fuel injection timing from the port injection valve in the split injection mode in the compression / slight lean operation is advanced with respect to the fuel injection timing of the port injection valve in the injection mode according to another operation state. 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 fuel injection timing of the port injection valve in the split injection mode in the compression-slight lean operation is a compression stroke of the internal combustion engine.   The fuel injection control means selects the port injection mode when the pressure of the fuel supplied to the in-cylinder injection valve is lower than a predetermined value, and sets the injection timing of the port injection valve in the port injection mode to an expansion stroke. The fuel injection control device for an internal combustion engine according to claim 1 or 2, wherein a period from an exhaust stroke to an exhaust stroke is set.

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