JP2017218969A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve combustion stability by properly controlling an airflow for an induction operation when performing control for activating an exhaust purification catalyst, in an engine constitution in which an injector has a fuel spray progressing toward a direction of an ignition plug, a contour face of the fuel spray passes a lower part of an electrode part of the ignition plug, and a tumble flow is generated even if the ignition plug is arranged in the vicinity of a center of a ceiling part of a combustion chamber, and the injector is arranged in a position at an external peripheral side of a cylinder bore in a crank axial direction rather than a position of the ignition plug.SOLUTION: There are performed intake stroke injection, ignition in an ignition period during an expansion stroke, and expansion stroke injection in a form in which the finish timing of the injection period becomes an advance side rather than the finish timing of the ignition period by using the injection period which is at least partially overlapped on the ignition timing. A lift amount of an intake valve 26 at a remote side from the injector 36 is set larger than a lift amount of another intake valve 26 so that an airflow progressing toward the injector 36 from the ignition plug 32 is generated.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a control device for an internal combustion engine, and in particular, controls an internal combustion engine that includes an injector and a spark plug in a ceiling portion of a combustion chamber and a catalyst that purifies exhaust from the combustion chamber (an exhaust purification catalyst). The present invention relates to a control device.

  For example, Patent Document 1 discloses an internal combustion engine that includes two intake valves and two exhaust valves disposed on the ceiling portion of the combustion chamber, and in which an ignition plug and an injector are disposed near the center of the ceiling portion. Has been. More specifically, Patent Document 1 discloses an engine configuration in which an injector is provided in the vicinity of the center of the ceiling portion at a position on the outer peripheral side of the cylinder bore in the crankshaft direction with respect to a position where a spark plug is provided. ing.

JP-A-2005-180202 JP 2012-112263 A

  By the way, in the internal combustion engine having the engine configuration described in Patent Document 1, in order to activate the exhaust purification catalyst at an early stage, the following additional combustion control is added and the following combustion control is performed. It is conceivable to execute. That is, the additional configuration related to the injector is that the injector has a fuel spray directed toward the spark plug, and the direction of the injection hole is such that the outer surface of the fuel spray passes below the electrode portion of the spark plug. It is set. In addition, the combustion control here means that the first fuel injection is performed on the advance side of the compression top dead center, ignition is performed in the ignition period located in the expansion stroke, and at least a part of the ignition period. The second fuel injection is executed during the expansion stroke in such a manner that the end timing of the injection period is on the more advanced side than the end timing of the ignition period using the overlapping injection periods. When such combustion control is performed while adding an additional configuration related to the injector, the fuel injected in a high pressure state from the injector as the second fuel injection forms a low pressure portion by removing the surrounding air (entry). Inment). Therefore, when the second fuel injection is performed in such a manner that the injection period ends during the discharge period, the initial flame generated by the ignition in the expansion stroke to the fuel spray by the first fuel injection is directed in the direction of the spark plug. It is attracted to the low pressure part formed around the fuel spray of the second fuel injection heading. As a result, the initial flame attracted to the low pressure portion comes into contact with the fuel spray by the second fuel injection and grows by involving it. As a result, the combustion speed of the air-fuel mixture is improved, combustion is stabilized, and combustion fluctuations can be suppressed.

  On the other hand, an internal combustion engine in which a tumble flow is generated in a combustion chamber for the purpose of improving combustion is known. The tumble flow referred to here is one that swirls in the combustion chamber so as to go from the intake valve side to the exhaust valve side at the ceiling. For this reason, when a tumble flow is generated in an internal combustion engine in which an additional configuration related to an injector is added to the engine configuration described in Patent Document 1, the injection direction of fuel spray toward the direction of the spark plug and the ceiling portion The direction of tumble flow does not match. As a result, when the second fuel injection is performed during the execution of the above-described combustion control, the initial flame generated by the ignition in the expansion stroke to the fuel spray by the first fuel injection is an air flow (here, a tumble flow). Therefore, it is impossible to approach the fuel spray by the second fuel injection. If this initial flame can be brought close to the fuel spray by the second fuel injection by the air flow, it is considered that the effect of improving the combustion stability using the attracting action can be further extracted.

  The present invention has been made in order to solve the above-described problems. An ignition plug is arranged near the center of the ceiling of the combustion chamber, and the outer periphery of the cylinder bore in the crankshaft direction rather than the position where the ignition plug is provided. Even in the case of adopting an engine configuration in which an injector is provided near the center of the ceiling at the side position, this injector has fuel spray directed toward the spark plug, and the outer surface of the fuel spray is the spark plug The airflow generated in the combustion chamber when the direction of the nozzle hole is set so as to pass below the electrode portion of the engine and control for activation of the exhaust purification catalyst is performed in an engine configuration in which a tumble flow is generated It is an object of the present invention to provide a control device for an internal combustion engine that can improve combustion stability by appropriately controlling the engine for the attraction action.

  An internal combustion engine control apparatus according to the present invention includes two intake valves and two exhaust valves disposed on a ceiling portion of a combustion chamber, an ignition device having an ignition plug disposed near the center of the ceiling portion, The fuel spray is disposed near the center of the ceiling at a position on the outer peripheral side of the cylinder bore in the crankshaft direction from the position where the spark plug is provided, and has fuel spray toward the direction of the spark plug, and has an outer shell of the fuel spray An injector in which the direction of the injection hole is set so that the surface passes below the electrode portion of the spark plug, and a variable valve mechanism that can control the two intake valves so that the lift amounts of the two intake valves are different And an exhaust gas purification catalyst for purifying exhaust gas from the combustion chamber, and controls an internal combustion engine in which a tumble flow is generated in the combustion chamber. The control device includes a combustion control unit and a valve control unit. The combustion control unit controls the injector so that the first fuel injection on the advance side from the compression top dead center is executed as the control for activating the exhaust purification catalyst, and is positioned during the expansion stroke. The ignition device is controlled so that ignition is performed in the ignition period, and the end timing of the injection period is advanced from the end timing of the ignition period by using an injection period at least partially overlapping with the ignition period. The injector is controlled such that the second fuel injection is performed during the expansion stroke in a manner that is on the corner side. The valve control unit is one of the two intake valves that is farther from the injector so that when the control by the combustion control unit is executed, an air flow from the spark plug toward the injector is generated. The variable valve mechanism is controlled so that the lift amount of the intake valve is larger than the lift amount of the intake valve closer to the injector.

  According to the present invention, when the control for activating the exhaust purification catalyst is executed, the lift amount of the intake valve far from the injector is closer to the injector so that the airflow from the spark plug to the injector is generated. The variable valve mechanism is controlled to be larger than the lift amount of the intake valve. As a result, the airflow generated in the combustion chamber can be appropriately controlled for the attraction action, and the combustion stability can be improved using the airflow.

It is a figure for demonstrating the system configuration | structure which concerns on Embodiment 1 of this invention. It is the figure which looked down at the combustion chamber from the axial direction of the cylinder. It is a figure showing an example of each injection period by the injector in catalyst warm-up control, and an ignition period (discharge period in an electrode part) by an ignition plug. It is a figure for demonstrating the attracting action of the initial flame by expansion stroke injection. It is a figure for demonstrating control of the lift amount of the intake valve performed during the catalyst warm-up control using an attraction action. It is a figure showing the relationship between each of the fluctuation rate of combustion, the flow velocity between injectors and plugs, and the inclination. It is a figure showing the relationship between inclination and the maximum lift amount difference of an intake valve. It is a flowchart which shows an example of the process which ECU performs in Embodiment 1 of this invention.

[Description of system configuration]
FIG. 1 is a diagram (a diagram viewed from the crankshaft direction) for explaining a system configuration according to Embodiment 1 of the present invention. FIG. 2 is a view of the combustion chamber 20 as viewed from the axial direction of the cylinder.

  As shown in FIG. 1, the system according to the present embodiment includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 is a four-stroke one-cycle engine and has a plurality of cylinders. However, only one of the cylinders 12 is shown in FIG. The internal combustion engine 10 includes a cylinder block 14 in which a cylinder 12 is formed, and a cylinder head 16 disposed on the cylinder block 14. A piston 18 that reciprocates in the axial direction (vertical direction in the present embodiment) is disposed in the cylinder 12. The combustion chamber 20 of the internal combustion engine 10 is defined by at least the wall surface of the cylinder block 14, the lower surface of the cylinder head 16, and the upper surface of the piston 18.

  Two intake ports 22 and two exhaust ports 24 communicating with the combustion chamber 20 are formed in the cylinder head 16. An intake valve 26 is provided at an opening portion of the intake port 22 that communicates with the combustion chamber 20, and an exhaust valve 28 is provided at an opening portion of the exhaust port 24 that communicates with the combustion chamber 20. In the exhaust passage of the internal combustion engine 10 (not shown in the drawings other than the passage in the exhaust port 24 in FIG. 1), an exhaust purification catalyst (not shown) is disposed at a site downstream of the exhaust port 24. As an example, the exhaust purification catalyst is a ternary that purifies nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) in the exhaust when the atmosphere of the activated catalyst is in the vicinity of stoichiometry. A catalyst is mentioned.

  The valve opening characteristics of the intake valve 26 can be changed by the intake variable valve mechanism 30. More specifically, the intake variable valve mechanism 30 is configured to be able to control these intake valves 26 so that the lift amounts of the two intake valves 26 arranged in the same cylinder are different using a known configuration. Has been.

  A spark plug 32 is provided in the cylinder head 16 at a position slightly closer to the exhaust valve 28 than the center of the ceiling of the combustion chamber 20. The spark plug 32 includes an electrode portion 34 including a center electrode and a ground electrode at the tip. As shown in FIG. 2, the tip protrudes into the combustion chamber 20 at a position near the center of the combustion chamber 20 and on the outer peripheral side of the cylinder bore in the crankshaft direction from the position where the ignition plug 32 is provided. Thus, an injector 36 is provided.

  The injector 36 is connected to a fuel supply system (not shown) including a fuel tank, a delivery pipe, a supply pump, and the like. A plurality of injection holes (not shown) are formed radially at the tip of the injector 36, and when the injector 36 is opened, fuel is injected from these injection holes in a high pressure state. In the injector 36, the outer surface (hereinafter also referred to as “spray outer surface”) of the fuel spray (see FIG. 4 described later) closest to the spark plug 32 among the fuel sprays injected radially from the nozzle holes is an ignition plug. The direction of the nozzle hole is set in advance so as to pass below the 32 electrode portions 34. The outline drawn in FIG. 4 represents the outline of the fuel spray closest to the spark plug 32 in the fuel spray from the injector 36.

  In addition, the internal combustion engine 10 of the present embodiment is configured to generate a tumble flow in the intake air introduced from the intake port 22 into the combustion chamber 20 by devising the shape of the intake port 22 as an example. More specifically, the tumble flow generated in the internal combustion engine 10 swirls in the combustion chamber 20 so as to go from the intake port 22 side to the exhaust port 24 side at the ceiling of the combustion chamber 20.

  As shown in FIG. 1, the system according to the present embodiment includes an electronic control unit (ECU) 40. The ECU 40 includes a RAM (Random Access Memory), a ROM (Read Only Memory), a CPU (Central Processing Unit), and the like. The ECU 40 captures and processes signals from various sensors mounted on the vehicle. The various sensors include a crank angle sensor 42 that detects the rotation angle of the crankshaft connected to the piston 18, an accelerator opening sensor 44 that detects the amount of depression of the accelerator pedal by the driver of the vehicle, and cooling of the internal combustion engine 10. And a temperature sensor 46 for detecting a water temperature (hereinafter also referred to as “engine cooling water temperature”). The ECU 40 processes the signals of the acquired sensors and operates various actuators according to a predetermined control program. The actuator operated by the ECU 40 includes at least the above-described injector 36 and an ignition device (components other than the ignition plug 32 are not shown).

[Control at engine start]
In the present embodiment, the control immediately after the cold start of the internal combustion engine 10 by the ECU 40 shown in FIG. 1 is a control (hereinafter also referred to as “catalyst warm-up control”) that promotes activation of the exhaust purification catalyst. (FI) Performed during operation. The catalyst warm-up control executed by the ECU 40 will be described with reference to FIGS. 3 and 4.

  FIG. 3 is a diagram illustrating an example of each injection period by the injector 36 during catalyst warm-up control and an ignition period by the spark plug 32 (discharge period at the electrode unit 34). As shown in FIG. 3, during the catalyst warm-up control, the first fuel injection (first fuel injection) by the injector 36 is performed in the intake stroke, and in the expansion stroke after the compression top dead center, A small amount of second fuel injection (second fuel injection) is performed as compared with fuel injection. In the following description, the first fuel injection (first fuel injection) is also referred to as “intake stroke injection”, and the second fuel injection (second fuel injection) is also referred to as “expansion stroke injection”. In the present embodiment, as an example, the fuel injection amount in each stroke is determined so that the air-fuel ratio of all fuels including intake stroke injection and expansion stroke injection becomes the stoichiometric air-fuel ratio. For this reason, the air-fuel ratio of the air-fuel mixture generated by the intake stroke injection is slightly leaner than the stoichiometric air-fuel ratio. The first fuel injection may be a fuel injection that is performed in the compression stroke instead of or in addition to the intake stroke injection. Further, the first fuel injection may be performed by being divided into a plurality of times.

  Further, as shown in FIG. 3, during the catalyst warm-up control, the ignition period start timing (discharge start timing) by the spark plug 32 is set to the retard side from the compression top dead center. In FIG. 3, the expansion stroke injection is performed on the retard side with respect to the start timing of the ignition period, but the expansion stroke injection may be started on the advance side with respect to the start timing of the ignition period. More specifically, in order to obtain the attracting action described later, at least a part of the injection period of the expansion stroke injection overlaps with the ignition period, and the end timing of the expansion stroke injection advances from the end timing of the ignition period. Must be located on the corner side. If this condition is satisfied, the expansion stroke injection (second fuel injection) may be performed in a plurality of times.

(Attraction by expansion stroke injection)
FIG. 4 is a diagram for explaining the attracting action of the initial flame by the expansion stroke injection. 4 corresponds to a diagram schematically showing the configuration around the combustion chamber 20 cut along the line AA shown in FIG. FIG. 4 depicts a discharge spark generated at the electrode portion 34 during the ignition period of the spark plug 32 and an initial flame (flame core) generated by the contact of the fuel spray with the intake stroke injection and the discharge spark. It is. FIG. 4 shows only the fuel spray closest to the spark plug 32 among the fuel sprays by the expansion stroke injection.

  When the expansion stroke injection is performed as shown in FIG. 4, a low pressure portion is formed around the fuel spray. For this reason, the initial flame produced from the discharge spark of the electrode part 34 formed during the expansion stroke is attracted by the fuel spray passing below the electrode part 34 as shown in FIG. Due to the fuel spray of the expansion stroke injection, a region in the combustion chamber 20 where the air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio and is turbulent is formed. When the initial flame attracted by the fuel spray reaches this region, the flame grows at once and the combustion proceeds rapidly. Thereby, compared with the example which does not involve such expansion stroke injection, the combustion speed of the air-fuel mixture is improved, the combustion is stabilized, and the combustion fluctuation between cycles that adversely affects drivability is suppressed.

(Promotion of attracting action using in-cylinder airflow)
As described above, the in-cylinder airflow generated as a premise in the internal combustion engine 10 is a tumble flow that swirls in the combustion chamber 20 from the intake port 22 side toward the exhaust port 24 side in the ceiling portion of the combustion chamber 20. . On the other hand, the injector 36 is provided at a position on the outer peripheral side of the cylinder bore in the crankshaft direction from the position where the ignition plug 32 is provided. Therefore, according to the combination of the tumble flow having this shape and the arrangement of the injector 36, the injection direction of the fuel spray directed toward the ignition plug 32 by the expansion stroke injection does not coincide with the traveling direction of the tumble flow on the ceiling. . As a result, the initial flame generated by the ignition in the expansion stroke to the fuel spray by the intake stroke injection during the catalyst warm-up control cannot be brought close to the fuel spray by the expansion stroke injection by the tumble flow. However, if this initial flame can be brought close to the fuel spray by the expansion stroke injection by some in-cylinder airflow, it is considered that the effect of improving the combustion stability using the attracting action can be further extracted.

  FIG. 5 is a diagram for explaining the control of the lift amount of the intake valve 26 that is executed during the catalyst warm-up control using the attracting action. FIG. 5B schematically shows a configuration around the combustion chamber 20 cut along the line BB in FIG. 5A (the same as the line AA in FIG. 2).

  In the present embodiment, the tumble flow generated as a premise as described above is used as a base flow, and the air flow from the spark plug 32 to the injector 36 at the ceiling of the combustion chamber 20 during the catalyst warm-up control. The intake variable valve mechanism 30 is controlled so as to be generated. Specifically, the lift amount of the intake valve 26 farther from the injector 36 (right side in FIG. 5A) is larger than the lift amount of the intake valve 26 closer to the injector 36 (left side in FIG. 5A). I decided to make it bigger. More specifically, the lift amount referred to here is the maximum lift amount obtained during one opening / closing period of the intake valve 26.

  By providing a lift amount difference (maximum lift amount difference) for the two intake valves 26 in the same cylinder in the above-described manner, the swirl component in the counterclockwise direction in FIG. Can be added. As a result, the tumble flow turning axis is inclined, so that the tumble flow can be inclined. Hereinafter, the tumble flow in which the turning axis is inclined in this manner is also referred to as “oblique tumble flow”. Further, when the swirl flow component is added to the tumble flow in this way, the swirl center of the swirl flow component is offset from the cylinder center to the intake side (IN side) or the exhaust side (EX side) when viewed from the axial direction of the cylinder. . For this reason, it becomes possible to appropriately generate an air flow from the spark plug 32 toward the injector 36 by appropriately setting an inclination described later.

  Here, the ratio (tumble ratio / swirl ratio) of the tumble ratio (angular speed of the tumble flow / engine rotational speed) to the swirl ratio (angular speed of the swirl flow / engine rotational speed) is referred to as “gradient”. According to this definition, the inclination becomes zero when only the swirl flow is generated without generating the tumble flow, and becomes higher as the tumble ratio becomes relatively larger than the swirl ratio. By appropriately setting this inclination using the method described below with reference to FIGS. 6 and 7, as shown in FIG. 5A, an oblique tumble flow from the spark plug 32 toward the injector 36 is generated. Can be generated. As a result, as shown in FIG. 5B, the discharge spark and the initial flame can be brought close to the fuel spray by the expansion stroke injection by the oblique tumble flow. For this reason, since the attracting action can be promoted using the in-cylinder airflow (oblique tumble flow), the combustion stability can be further improved.

  FIG. 6 shows the relationship between the combustion fluctuation rate and the injector-plug flow velocity and the inclination. FIG. 7 shows the relationship between the inclination and the maximum lift amount difference of the intake valve 26. By changing the inclination, the direction of the airflow flowing in the vicinity of the spark plug 32 and the injector 36 can be changed. The change in the inclination is the difference in the maximum lift amount of the intake valve 26 (the difference obtained by subtracting the maximum lift amount of the intake valve 26 closer to the injector 36 from the maximum lift amount of the intake valve 26 farther from the injector 36). It can be done by changing. More specifically, as shown in FIG. 7, the degree of inclination increases as the maximum lift amount difference increases.

  As shown in FIG. 6, as the inclination increases, the gas flow rate between the injector 36 and the spark plug 32 increases. On the other hand, the combustion fluctuation rate becomes a downwardly convex curve with respect to the inclination, and shows a minimum value at a certain inclination A. When the configuration in which ignition and fuel injection in the expansion stroke are performed while using the attraction action is employed, the combustion stability improves (that is, the combustion fluctuation rate decreases) when the attraction action is obtained more effectively. The attraction action should be most effectively obtained when the airflow from the spark plug 32 toward the injector 36 is properly obtained. Therefore, it can be determined that the airflow (oblique tumble flow) from the spark plug 32 toward the injector 36 is appropriately obtained in the vicinity of the slope A where the combustion fluctuation rate has the minimum value. For this reason, by acquiring the relationship shown in FIG. 6 through experiments, simulations, and the like, it is possible to grasp the inclination A at which the airflow from the spark plug 32 toward the injector 36 is obtained. Then, by acquiring the relationship shown in FIG. 7 through experiments, simulations, or the like, the maximum lift amount difference B of the intake valve 26 necessary for realizing the inclination A can be grasped. Then, by controlling the intake variable valve mechanism 30 so that the maximum lift amount difference B is realized during the catalyst warm-up control, an airflow from the spark plug 32 toward the injector 36 can be obtained.

[Specific Processing in Embodiment 1]
FIG. 8 is a flowchart showing an example of processing executed by the ECU 40 in the first embodiment of the present invention. The routine shown in FIG. 8 is started immediately after the internal combustion engine 10 is started.

  In the routine shown in FIG. 8, the ECU 40 first determines whether or not a fast idling (FI) operation with a catalyst warm-up mode should be performed based on the engine coolant temperature or the like (step 100). As a result, when the determination in step 100 is established, the ECU 40 controls the intake variable valve mechanism 30 so that the maximum lift amount difference B of the intake valve 26 shown in FIG. 102).

  Next, the ECU 40 executes the intake stroke injection and the ignition and fuel injection during the expansion stroke in the mode shown in FIG. 2 as FI combustion control (catalyst warm-up control) (step 104). Next, the ECU 40 determines whether or not a condition for ending the catalyst warm-up mode is satisfied (step 106). The establishment of this end condition can be determined based on, for example, whether or not the integrated intake air amount has reached a predetermined value after the start of the catalyst warm-up mode.

  According to the processing of the routine shown in FIG. 8 described above, the maximum lift amount of the intake valve 26 far from the injector 36 is closer to the intake valve 36 while the catalyst warm-up control using the attracting action is being executed. The tumble flow is changed so that the air flow from the spark plug 32 to the injector 36 is provided by providing a difference in the maximum lift amount of the two intake valves 26 in the same cylinder in such a manner that it is larger than the maximum lift amount of 26. Is done. Thereby, since the attracting action can be promoted using the in-cylinder airflow (oblique tumble flow), the combustion stability can be further improved.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder 14 Cylinder block 16 Cylinder head 18 Piston 20 Combustion chamber 22 Intake port 24 Exhaust port 26 Intake valve 28 Exhaust valve 30 Intake variable valve mechanism 32 Spark plug 34 Electrode part 36 Injector 40 Electronic control unit (ECU)
42 Crank angle sensor 44 Accelerator opening sensor 46 Temperature sensor

Claims (1)

Two intake valves and two exhaust valves located on the ceiling of the combustion chamber;
An ignition device having an ignition plug disposed near the center of the ceiling portion;
The fuel spray is disposed near the center of the ceiling portion at a position on the outer peripheral side of the cylinder bore in the crankshaft direction from the position where the spark plug is provided, and has a fuel spray toward the spark plug, and the fuel spray An injector in which the direction of the injection hole is set so that the outer surface passes below the electrode portion of the spark plug;
A variable valve mechanism capable of controlling the two intake valves so that the lift amounts of the two intake valves are different;
An exhaust purification catalyst for purifying exhaust from the combustion chamber;
A control device for controlling an internal combustion engine in which a tumble flow is generated in the combustion chamber,
As the control for activating the exhaust purification catalyst, the injector is controlled so that the first fuel injection at the advance side from the compression top dead center is executed, and the ignition is executed in the ignition period located in the expansion stroke. The ignition device is controlled as described above, and the end timing of the injection period is advanced from the end timing of the ignition period by using an injection period at least partially overlapping with the ignition period. A combustion controller for controlling the injector so that a second fuel injection is performed during the expansion stroke;
When the control by the combustion control unit is executed, the lift amount of the intake valve farther from the injector of the two intake valves is such that an air flow from the spark plug toward the injector is generated. A valve control unit that controls the variable valve mechanism so as to be larger than the lift amount of the intake valve closer to the injector;
A control device for an internal combustion engine, comprising:

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