JP5282636B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine provided with an in-cylinder fuel injection valve and a fuel injection valve for an intake passage.

  As conventional techniques, for example, as disclosed in Japanese Patent Application Laid-Open No. 2006-194098, an in-cylinder injection valve that directly injects fuel into a cylinder of an internal combustion engine, and an intake air that injects fuel into an intake passage A control device for an internal combustion engine including a passage injection valve is known. In this prior art, when the deterioration of the combustion state is detected, fuel injection by the in-cylinder injection valve (in-cylinder injection) is performed in a plurality of times, and part of the in-cylinder injection is performed in the second half of the intake stroke or compression It is configured to be implemented during the process. As a result, in the prior art, when the combustion state deteriorates, the fuel injection amount in the cylinder is increased after the latter half of the intake stroke, and a relatively rich air-fuel mixture is formed around the spark plug. I try to stabilize the state.

JP 2006-194098 A

  By the way, in the prior art mentioned above, when a combustion state deteriorates, it is set as the structure which implements a part of in-cylinder injection after the latter half of an intake stroke. However, when the injection control according to the prior art is executed in a state where the accumulation of the intake deposit has progressed due to, for example, long-term use of the internal combustion engine, the tumble ratio of the intake port becomes large, and the intake turbulence in the compression stroke increases. Tend. As a result, in the prior art, there is a problem that combustion fluctuations increase and the combustion state deteriorates.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress intake air turbulence without reducing the stratification degree of the air-fuel mixture and improve the combustion state. An object of the present invention is to provide a control device for an internal combustion engine that can perform the above-described operation.

A first invention is an intake passage injection valve that injects fuel into an intake passage of an internal combustion engine;
An in-cylinder injection valve for injecting fuel into the cylinder of the internal combustion engine;
When performing catalyst warm-up during idle operation , fuel injection is performed during the intake stroke by the intake passage injection valve , and fuel injection is performed during the intake stroke and compression stroke by the in- cylinder injection valve. Means for performing weak stratified combustion control,
In the state where the weak stratified combustion control is executed at the time of catalyst warm-up during the idling operation, and when the condition that the combustion state is worse than the allowable level is satisfied , the fuel is injected from the in-cylinder injection valve during the compression stroke. Means for maintaining the in-cylinder injection amount of the fuel at the same injection amount as before the deterioration of the combustion state;
An injection amount control means for reducing the fuel injection amount of the intake passage injection valve and increasing the fuel injection amount during the intake stroke by the in-cylinder injection valve when the condition is satisfied ;
It is characterized by providing.

  According to the first invention, the injection amount control means reduces the fuel injection amount to the intake passage and increases the in-cylinder injection amount in the intake stroke when the combustion state deteriorates from the allowable level. Can do. As a result, the intake air turbulence can be suppressed as compared with the case where the in-cylinder injection amount in the intake stroke is not increased. Also, by reducing the amount of fuel injected into the intake passage by an amount corresponding to the increased amount of in-cylinder injection, for example, the overall fuel injection amount can be made constant without reducing the amount of in-cylinder injection in the compression stroke. Can do. As a result, it is possible to avoid deterioration of the combustion state due to a decrease in the injection amount in the compression stroke. Therefore, it is possible to reduce the combustion fluctuation caused by the intake air turbulence without lowering the stratification degree of the air-fuel mixture and realize a good combustion state.

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is explanatory drawing which shows the relationship between the tumble ratio of an intake port, and the travel distance of a vehicle. It is explanatory drawing which shows the relationship between the intake turbulence in a compression stroke, and the combustion fluctuation | variation in weak stratified combustion. It is explanatory drawing which shows an example of the combustion fluctuation suppression control by this Embodiment. It is a characteristic diagram which shows the relationship between the presence or absence of in-cylinder injection in the intake stroke and the magnitude of intake turbulence. FIG. 6 is a characteristic diagram showing a relationship between a ratio of in-cylinder injection amount in an intake stroke with respect to a port injection amount, combustion fluctuation, and exhaust HC amount. In Embodiment 1 of this invention, it is a flowchart which shows the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes a dual injection type internal combustion engine 10 on which, for example, two fuel injection valves are mounted. The cylinder 12 of the internal combustion engine 10 is provided with a combustion chamber 16 that expands and contracts by the reciprocating motion of the piston 14. The piston 14 is connected to a crankshaft 18 that is an output shaft of the internal combustion engine 10.

  The internal combustion engine 10 also includes an intake passage 20 that sucks intake air into the cylinder 12 and an exhaust passage 22 that discharges exhaust gas from the cylinder 12. The intake passage 20 is provided with an air flow meter 24 for detecting the amount of intake air and an electronically controlled throttle valve 26. The throttle valve 26 is driven by a throttle motor 28 based on the accelerator opening and the like to increase or decrease the intake air amount.

  Further, the cylinder 12 of the internal combustion engine is provided with an intake passage injection valve 30 that injects fuel into the intake passage 20 (intake port) and an in-cylinder injection valve 32 that directly injects fuel into the combustion chamber 16. . Further, the cylinder 12 includes an ignition plug 34 that ignites the air-fuel mixture in the combustion chamber 16, an intake valve 36 that opens and closes the intake passage 20 relative to the combustion chamber 16, and an exhaust passage 22 that extends from the combustion chamber 16. An exhaust valve 38 that opens and closes is provided.

  On the other hand, the system of the present embodiment includes a sensor system including a crank angle sensor 40, an in-cylinder pressure sensor 42, and the like, and an ECU (Electronic Control Unit) 50 for controlling the operating state of the internal combustion engine 10. The crank angle sensor 40 outputs a signal synchronized with the rotation of the crankshaft 18, and the ECU 50 detects the engine speed based on this output. The in-cylinder pressure sensor 42 detects the pressure in the combustion chamber 16 (in-cylinder pressure). In addition to the air flow meter 24 and the sensors 40 and 42 described above, the sensor system includes various sensors necessary for controlling the vehicle and the internal combustion engine (for example, a water temperature sensor for detecting the cooling water temperature of the internal combustion engine, the air-fuel ratio of the exhaust gas). Air-fuel ratio sensors to be detected and the like are included, and these are connected to the input side of the ECU 50. Various actuators including a throttle motor 28, injection valves 30, 32, a spark plug 34, and the like are connected to the output side of the ECU 50.

  Then, the ECU 50 drives each actuator while detecting the operation state of the internal combustion engine by the sensor system. Specifically, the fuel injection amount, injection timing, ignition timing, and the like are set based on the output of the sensor system, and the actuator is driven according to these settings. Further, when performing fuel injection control, the ECU 50 changes the ratio (injection ratio) of the fuel injection amount by the two injection valves 30 and 32 according to the operating state of the internal combustion engine, and performs homogeneous combustion control and stratification described below. Combustion control and weak stratified combustion control are implemented. These combustion controls are generally known as described in, for example, Japanese Patent Application Laid-Open No. 2006-194098.

(Homogeneous combustion control)
Homogeneous combustion control is mainly performed during normal operation of the internal combustion engine, and aims to form a homogeneous air-fuel mixture. In the homogeneous combustion control, the injection ratios of the injection valves 30 and 32 are controlled based on the engine speed, load factor, cooling water temperature, and the like obtained by the sensor system. Basically, fuel injection by the intake passage injection valve 30 (hereinafter referred to as port injection) contributes to homogenization of the air-fuel mixture, and fuel injection by the cylinder injection valve 32 (referred to as cylinder injection) has an output performance. Since it contributes to improvement, the injection ratio is determined in consideration of these characteristics.

  As a specific example, for example, during cold operation in which the injected fuel is difficult to be eliminated, the injection ratio of the port injection is increased so that the air-fuel mixture is as good as possible even in a low temperature state. Further, in the high-power operation region, it is easy to form a homogeneous air-fuel mixture only by in-cylinder injection, so the injection ratio of in-cylinder injection that is advantageous in terms of anti-knock performance and output performance is increased. In homogeneous combustion control, both port injection and in-cylinder injection are executed in the intake stroke.

(Stratified combustion control)
In the stratified combustion control, by performing in-cylinder injection mainly in the compression stroke, the rich air-fuel mixture is unevenly distributed around the spark plug 34 while the air-fuel mixture in the combustion chamber 16 is made lean overall. In this case, the port injection is performed as necessary, but may not be performed. According to the stratified combustion control, the rich air-fuel mixture concentrated in the vicinity of the spark plug can be ignited, and the ignitability of the air-fuel mixture can be ensured while realizing lean combustion. Note that if ignitability is ensured even if in-cylinder injection is performed in the intake stroke, the timing of in-cylinder injection may be set in the intake stroke.

(Weak stratified combustion control)
The weak stratified combustion control is positioned between the homogeneous combustion control and the stratified combustion control, and is performed, for example, when warming up the exhaust catalyst is promoted during idle operation. In the weak stratified combustion control, in-cylinder injection is executed at least in the compression stroke while performing port injection. In this case, in-cylinder injection is performed not only in the compression stroke, but also in both the intake stroke and the compression stroke as necessary. According to the weak stratified combustion control, a large amount of fuel can be injected from the two injection valves 30 and 32 as compared with the stratified combustion control, and the ignition timing can be greatly retarded compared with the homogeneous combustion control. Therefore, the exhaust catalyst can be warmed up efficiently.

[Features of this embodiment]
By the way, in the weak stratified combustion control described above, the combustion stability is ensured by forming a rich air-fuel mixture around the spark plug 34. In such a control, when the deposit of the intake gas advances as the vehicle travels longer, there is a problem that the intake air turbulence in the compression stroke increases and the combustion fluctuation increases. Here, FIG. 2 is an explanatory view showing the relationship between the tumble ratio of the intake port and the travel distance of the vehicle, and FIG. 3 shows the relationship between intake turbulence in the compression stroke and combustion fluctuation in weak stratified combustion. It is explanatory drawing.

  As shown in FIG. 2, in the internal combustion engine, when the travel distance of the vehicle becomes long, the accumulation of the intake deposit proceeds, and the tumble ratio of the intake port tends to increase. As is generally known, when the tumble ratio of the intake port increases, intake turbulence in the compression stroke increases accordingly. As shown in FIG. 3, the combustion fluctuation in the weak stratified combustion increases as the intake turbulence in the compression stroke increases. For this reason, in a general vehicle, the combustion fluctuation in the weak stratified combustion exceeds the allowable level with the passage of time, and the combustion state is deteriorated. Therefore, in this embodiment, the combustion fluctuation suppression control is performed when the combustion state deteriorates during the weak stratified combustion control.

(Combustion fluctuation suppression control)
FIG. 4 is an explanatory diagram showing an example of combustion fluctuation suppression control according to the present embodiment. In this figure, “PFI” indicates port injection, and “DI” indicates in-cylinder injection. Further, as is generally known, the widths of the injection pulses of PFI and DI are parameters corresponding to the fuel injection amount, and the fuel injection amount increases as the injection pulse width increases.

  As shown in FIG. 4, in the combustion fluctuation suppression control, when the combustion fluctuation exceeds a predetermined allowable level (determination value), the fuel injection amount (port injection amount) of the intake passage injection valve 30 is reduced, and the cylinder The fuel injection amount (in-cylinder injection amount) in the intake stroke by the internal injection valve 32 is increased. Here, the combustion fluctuation is an index of the variation in the combustion state, and is detected by a generally known method based on, for example, a change in the engine speed or the in-cylinder pressure, an ion current in the exhaust gas, or the like. According to the combustion fluctuation suppression control, the following effects can be obtained.

  First, FIG. 5 is a characteristic diagram showing the relationship between the presence or absence of in-cylinder injection and the magnitude of intake turbulence in the intake stroke. The in-cylinder average turbulence in the figure corresponds to the magnitude of the intake turbulence. As shown in FIG. 5, during weak stratified combustion, in-cylinder injection in the intake stroke is performed, so that intake air turbulence can be suppressed as compared with the case where the injection is not performed. However, in the control region in which only the in-cylinder injection is performed, if the in-cylinder injection amount in the intake stroke is increased, the in-cylinder injection amount in the compression stroke needs to be reduced in order to keep the entire fuel injection amount constant. . In this case, a rich air-fuel mixture cannot be sufficiently formed around the spark plug, and the combustion state may be deteriorated.

Therefore, in the combustion fluctuation suppression control, the port injection is performed when the combustion fluctuation exceeds a predetermined allowable level (determination value) during the control region in which both in-cylinder injection and port injection are performed, that is, during weak stratified combustion control. And the ratio of in- cylinder injection in the intake stroke is increased by that amount. Thereby, since the intake air turbulence can be suppressed without reducing the stratification degree of the air-fuel mixture, the combustion fluctuation can be reduced and a good combustion state can be realized as shown in FIG. Here, FIG. 6 is a characteristic diagram showing the relationship between the ratio of the in-cylinder injection amount in the intake stroke to the port injection amount, the combustion fluctuation, and the exhaust HC amount. In the present invention, the execution timing of the above-described combustion fluctuation suppression control is not necessarily limited to only during weak stratified combustion control. That is, as long as it is a control region in which both port injection and in-cylinder injection are executed, for example, a configuration in which combustion fluctuation suppression control is executed during homogeneous combustion control may be adopted.

[Specific Processing for Realizing Embodiment 1]
FIG. 7 is a flowchart showing the control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the internal combustion engine. In the routine shown in FIG. 7, it is first determined whether port injection (PFI) and in-cylinder injection (DI compression) in the compression stroke are being executed (step 100). This determination process is also established when in-cylinder injection (DI intake) in the intake stroke is executed in addition to in-cylinder injection in the port injection and compression stroke.

  When the determination in step 100 is satisfied, as described above, the combustion fluctuation is measured based on, for example, changes in the engine speed and in-cylinder pressure, the magnitude of ion current flowing in the exhaust gas, and the like (step 102). Then, it is determined whether or not the measured value of combustion fluctuation exceeds a predetermined allowable level (step 104). When this determination is established, the above-described combustion fluctuation suppression control is executed (step 106). Therefore, when the combustion state deteriorates during operation of the internal combustion engine, this can be detected and the combustion fluctuation suppression control can be executed. In the first embodiment, step 106 in FIG. 7 shows a specific example of the injection amount control means.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder 14 Piston 16 Combustion chamber 18 Crankshaft 20 Intake passage 22 Exhaust passage 24 Air flow meter 26 Throttle valve 28 Throttle motor 30 Intake passage injection valve 32 In-cylinder injection valve 34 Spark plug 36 Intake valve 38 Exhaust valve 40 Crank angle Sensor 42 In-cylinder pressure sensor 50 ECU

Claims (1)

An intake passage injection valve for injecting fuel into the intake passage of the internal combustion engine;
An in-cylinder injection valve for injecting fuel into the cylinder of the internal combustion engine;
When performing catalyst warm-up during idle operation , fuel injection is performed during the intake stroke by the intake passage injection valve , and fuel injection is performed during the intake stroke and compression stroke by the in- cylinder injection valve. Means for performing weak stratified combustion control,
In the state where the weak stratified combustion control is executed at the time of catalyst warm-up during the idling operation, and when the condition that the combustion state is worse than the allowable level is satisfied , the fuel is injected from the in-cylinder injection valve during the compression stroke. Means for maintaining the in-cylinder injection amount of the fuel at the same injection amount as before the deterioration of the combustion state;
An injection amount control means for reducing the fuel injection amount of the intake passage injection valve and increasing the fuel injection amount during the intake stroke by the in-cylinder injection valve when the condition is satisfied ;
A control device for an internal combustion engine, comprising:

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