JP2016061262A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine that can suppress occurrence of misfire and reduction of torque during premixing compression self-ignition combustion.SOLUTION: A control device for an internal combustion engine includes: an exhaust valve 22 opened/closed to communicate/block an exhaust passage 24a and a combustion chamber 7 with/from each other; an exhaust side variable valve train 23 that can optionally change opening/closing timing of the exhaust valve 22; a cylinder internal pressure sensor 30 for detecting internal pressure of a cylinder 5; and an ECU 3 that determines that excessive combustion has occurred in main combustion in the case where timing of the main combustion when the cylinder internal pressure detected by the cylinder internal pressure sensor 30 exceeds a preset pressure threshold value is advanced from a preset excessive combustion threshold value, so as to increase fuel injection amount of closed time injection by preset closed time injection increase amount and delay the opening/closing timing of the exhaust valve 22 immediately before a closed period in accordance with the fuel injection amount of the closed time injection.SELECTED DRAWING: Figure 1

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 having a premixed compression auto-ignition combustion function.

  Conventionally, as a combustion mode of an internal combustion engine such as a gasoline engine, SI (Spark Ignition) combustion in which an air-fuel mixture is forcibly ignited by spark discharge from a spark plug has been widely used. Development of a gasoline engine that uses premixed compression self-ignition combustion, which introduces the burned gas and self-ignites the air-fuel mixture, as a combustion mode is underway. Here, the premixed compression self-ignition combustion is referred to as HCCI (Homogeneous Charge Compression Ignition) combustion.

  In this HCCI combustion, the air-fuel mixture in the cylinder is compressed, and the air-fuel mixture is self-ignited regardless of spark ignition by increasing the temperature and pressure. HCCI combustion is combustion in which self-ignition occurs at various locations in the cylinder at the same time, and has an advantage that the combustion period is shorter than that of SI combustion and higher thermal efficiency can be obtained.

  In an internal combustion engine having such an HCCI combustion function, a negative valve overlap that closes both the intake valve and the exhaust valve from the exhaust stroke to the intake stroke and seals the exhaust gas as an internal EGR (Exhaust Gas Recirculation) gas in the combustion chamber. Some (NVO: Negative Valve Overlap) periods are provided, and the internal cylinder temperature, which is the temperature in the combustion chamber, is increased by internal EGR gas. There is also an NVO injection that injects fuel during the NVO period. The fuel produced by NVO injection is exposed to a high-pressure and high-temperature environment, and thus immediately causes combustion (hereinafter referred to as “NVO combustion”). For this reason, the in-cylinder temperature can be raised prior to the main combustion in the compression stroke, and misfire of the main combustion can be suppressed.

  In an internal combustion engine that performs such NVO combustion, the exhaust gas when the main combustion becomes excessive combustion contains almost no unburned fuel. Therefore, in the NVO combustion immediately after the main combustion that has become excessive combustion, since there is little unburned fuel in the internal EGR gas, the temperature rise in the cylinder is suppressed, and the combustion in the main combustion in the next cycle is deteriorated.

  In order to solve such a problem, in Patent Document 1, in the NVO period immediately after the main combustion that has become excessive combustion, the fuel injection amount of NVO injection is increased to make NVO combustion active and raise the in-cylinder temperature. Control devices for internal combustion engines have been proposed. Thereby, it can prevent that the combustion of the main combustion of the next cycle of the main combustion which became excess combustion deteriorates.

JP 2013-19345 A

  However, in such a control device for an internal combustion engine described in Patent Document 1, the amount of in-cylinder gas during the NVO period increases because the fuel injection amount of NVO injection is increased to activate NVO combustion. The ratio of the residual gas amount G to the fuel amount F in the cylinder before main combustion in the next cycle (hereinafter simply referred to as “G / F”) becomes large. As a result, G / F at the time of main combustion in the next cycle is below the misfire limit, and there is a problem that misfire occurs or torque decreases.

  Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can suppress the occurrence of misfire and torque reduction during premixed compression self-ignition combustion.

  An aspect of the invention of a control device for an internal combustion engine that solves the above problems is configured to be able to switch between spark ignition combustion and premixed compression auto-ignition combustion, and includes both an intake valve and an exhaust valve from the exhaust stroke to the intake stroke. A closed period is provided to close and seal off the exhaust gas in the combustion chamber. During the closed period, fuel is injected into the combustion chamber, and injection is performed when the fuel is injected. A control device for an internal combustion engine that performs compression self-ignition combustion, a main combustion detection unit that detects the occurrence of premixed compression self-ignition combustion, and an exhaust-side variable valve mechanism that can arbitrarily change the opening / closing timing of the exhaust valve, When the occurrence of premixed compression auto-ignition combustion advances beyond a preset threshold value, the fuel injection amount of the injection at the time of blockage is increased, and the exhaust immediately before the blockage period according to the fuel injection amount of the injection at the time of blockage Valve In which and a control unit to delay the closing timing.

  Thus, according to one aspect of the present invention, it is possible to suppress the occurrence of misfire and torque reduction during premixed compression self-ignition combustion.

FIG. 1 is a diagram showing a control device for an internal combustion engine according to an embodiment of the present invention, and is a conceptual block diagram thereof. FIG. 2 is a diagram illustrating a control apparatus for an internal combustion engine according to an embodiment of the present invention, and is a flowchart for explaining the combustion stabilization process. FIG. 3 is a diagram showing a control apparatus for an internal combustion engine according to an embodiment of the present invention, and is a time chart showing a change in the ratio of the residual gas amount to the fuel amount in the cylinder by the combustion stabilization process. FIG. 4 is a diagram showing a control device for an internal combustion engine according to an embodiment of the present invention, and is a graph showing an engine load change rate according to an injection amount at the time of blockage and an exhaust valve retardation amount. FIG. 5 is a diagram showing a control device for an internal combustion engine according to an embodiment of the present invention, and is a graph showing the ratio of the residual gas amount to the fuel amount in the cylinder according to the injection amount at the time of blockage and the exhaust valve retard amount. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, a vehicle 1 equipped with an internal combustion engine control apparatus according to an embodiment of the present invention includes an internal combustion engine type engine 2 and an ECU (Electronic Control Unit) 3 as a control unit. .

  The engine 2 is formed with a cylinder 5 as a cylinder. The cylinder 5 houses a piston 6 that can reciprocate up and down in the cylinder 5. A combustion chamber 7 is provided in the upper part of the cylinder 5. The combustion chamber 7 is provided with an in-cylinder pressure sensor 30 for grasping the in-cylinder pressure that is the pressure inside the cylinder 5.

  The engine 2 is a so-called four-cycle gasoline engine that performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston 6 reciprocates in the cylinder 5.

  The piston 6 is connected to the crankshaft via a connecting rod (not shown). The connecting rod converts the reciprocating motion of the piston 6 into the rotational motion of the crankshaft.

  The combustion chamber 7 is provided with a spark plug 8 and an injector 9. The spark plug 8 is disposed in a state in which an electrode protrudes into the combustion chamber 7, and its ignition timing is adjusted by an igniter (not shown). The injector 9 is a so-called in-cylinder fuel injection valve that injects fuel supplied from a fuel tank (not shown) by a fuel pump into the combustion chamber 7.

  The engine 2 is provided with an intake port 11 and an exhaust port 21. The intake port 11 communicates the combustion chamber 7 with an intake passage 14a described later. The intake port 11 is provided with an intake valve 12.

  The intake valve 12 is opened and closed so as to communicate or block the intake passage 14a and the combustion chamber 7. The intake valve 12 is opened and closed by an intake side variable valve mechanism 13.

  As the intake side variable valve mechanism 13, for example, an electromagnetic variable valve mechanism that opens and closes the intake valve 12 by an electromagnetic actuator composed of an electromagnet and a spring can be used. Specifically, the intake side variable valve mechanism 13 opens the intake valve 12 that is normally urged in the valve closing direction by a spring by attracting a movable portion fixed to the intake valve 12 by excitation of an electromagnet. It is designed to move in the valve direction.

  The intake side variable valve mechanism 13 is electrically connected to the ECU 3 so that the excitation and de-excitation of the electromagnet is controlled by the ECU 3. Therefore, the ECU 3 can arbitrarily change the opening / closing timing of the intake valve 12, thereby easily adjusting the valve opening period of the intake valve 12.

  The intake side variable valve mechanism 13 may be a hydraulic variable valve mechanism using a hydraulic actuator instead of the electromagnetic actuator. Further, as the intake side variable valve mechanism 13, a mechanical variable valve mechanism that can change the opening / closing timing of the intake valve 12 using cam members such as a main cam and a sub cam may be used.

  Further, the intake side variable valve mechanism 13 is configured such that, for example, the exciting current for the electromagnet is adjusted by the ECU 3 so that the lift amount of the intake valve 12 can be continuously changed with the opening / closing timing of the intake valve 12. It may be.

  An intake pipe 14 is connected to the intake port 11. An intake passage 14 a communicating with the intake port 11 is formed in the intake pipe 14. An electronically controlled throttle valve 15 is provided in the intake passage 14a. The throttle valve 15 is electrically connected to the ECU 3.

  The throttle valve 15 adjusts the intake air amount of the engine 2 by controlling the throttle opening degree according to a command signal from the ECU 3.

  On the other hand, the exhaust port 21 is provided with an exhaust valve 22. The exhaust valve 22 is opened and closed so as to communicate or block an exhaust passage 24a described later and the combustion chamber 7. The exhaust valve 22 is opened and closed by an exhaust side variable valve mechanism 23.

  Since the exhaust side variable valve mechanism 23 has the same configuration as the intake side variable valve mechanism 13 described above, detailed description thereof is omitted, but the excitation and deexcitation of the electromagnet is controlled by the ECU 3 so that the exhaust The opening / closing timing of the valve 22 is arbitrarily changed. The exhaust side variable valve mechanism 23 may be a hydraulic variable valve mechanism using a hydraulic actuator instead of the electromagnetic actuator. Further, as the exhaust-side variable valve mechanism 23, a mechanical variable valve mechanism that can change the opening / closing timing of the exhaust valve 22 using cam members such as a main cam and a sub cam may be used. Therefore, the ECU 3 can easily adjust the valve opening period of the exhaust valve 22.

  An exhaust pipe 24 is connected to the exhaust port 21. An exhaust passage 24 a communicating with the exhaust port 21 is formed in the exhaust pipe 24.

  The engine 2 configured as described above is an ignition type engine in which an air-fuel mixture of intake air and injected fuel whose flow rate is adjusted by a throttle valve 15 is ignited by an ignition plug 8 to be ignited. Further, by adjusting the opening / closing timing of the intake valve 12 and the exhaust valve 22 by the intake side variable valve mechanism 13 and the exhaust side variable valve mechanism 23, the injected fuel and intake air are mixed in the combustion chamber 7 in advance. Premixed compression self-ignition combustion (HCCI combustion) in which the air-fuel mixture is compressed and self-ignited is possible. That is, the SI mode by spark ignition combustion and the HCCI mode by HCCI combustion can be switched.

  In the present embodiment, the operating state of the engine 2 configured as described above is controlled by the ECU 3. The ECU 3 includes a computer unit that includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a flash memory, an input port, and an output port.

  A program for causing the computer unit to function as the ECU 3 is stored in the ROM of the ECU 3 together with various control constants and various maps. That is, in the ECU 3, the computer unit functions as the ECU 3 when the CPU executes a program stored in the ROM.

  In addition to the in-cylinder pressure sensor 30 described above, various sensors such as an accelerator opening sensor 31 and a crank angle sensor 32 are connected to the input side of the ECU 3. Here, the accelerator opening sensor 31 detects an accelerator opening that is an opening of an accelerator pedal (not shown) operated by the driver when, for example, an acceleration is requested. The crank angle sensor 32 detects the rotation angle of the crankshaft. The ECU 3 calculates the engine speed based on the detection result input from the crank angle sensor 32.

  On the other hand, various control objects such as the above-described ignition plug 8, injector 9, throttle valve 15, intake side variable valve mechanism 13 and exhaust side variable valve mechanism 23 are connected to the output side of the ECU 3.

  The ECU 3 switches between SI combustion and HCCI combustion according to the operating state of the engine 2. Specifically, the ECU 3 determines whether the operation region of the engine 2 is in the SI combustion region or the HCCI combustion region by referring to a combustion region map using the engine speed and the engine load as parameters. Based on the determination, whether to perform SI combustion or HCCI combustion is selected.

  The ECU 3 calculates an engine load as an engine load based on the accelerator opening input from the accelerator opening sensor 31 and the engine speed calculated from the detection result input from the crank angle sensor 32.

  In the HCCI mode in which the HCCI combustion is performed, the ECU 3 performs the valve timing of the intake valve 12 and the exhaust valve 22 for outputting the engine load requested by the driver based on the engine speed and the engine load, and the fuel injection by the injector 9. Determine the amount.

  Further, in the HCCI mode, the ECU 3 sets a blockage period (NVO period) during which both the intake valve 12 and the exhaust valve 22 are closed from the exhaust stroke to the intake stroke. In addition, the ECU 3 is configured to perform injection at the time of blockage in which fuel is injected from the injector 9 during the blockage period. Then, after the injection at the time of closing, the ECU 3 performs main injection for injecting a larger amount of fuel than the injection at the time of closing in a predetermined period from the intake stroke to the compression stroke.

  In addition, it is not necessary to perform all the injection at the time of blockage during the blockade period, and at least half of the injection at the time of blockage may be performed during the blockage period. Moreover, you may make it perform all the injections at the time of blockade during a blockade period. The timing of injection at the time of blockage is set from the operating state of the engine 2.

  The ECU 3 monitors the in-cylinder pressure input from the in-cylinder pressure sensor 30, and the main combustion timing at which the in-cylinder pressure detected by the in-cylinder pressure sensor 30 is higher than a preset pressure threshold is set to a preset excess combustion threshold. If the angle of advance is more advanced, it is determined that the main combustion is excessively burned, and the fuel injection amount of the injection at the time of blockage is increased by a preset increase in injection at the time of blockade. Further, the ECU 3 decreases the fuel injection amount of the main injection immediately after the increased injection at the time of blockade by the increase in injection at the time of blockade. In short, control is performed so that the total fuel injection amount of the injection at the time of closing and the main injection does not change. That is, the in-cylinder pressure sensor 30 constitutes a main combustion detection unit according to the present invention.

  Here, the pressure threshold is an in-cylinder pressure that can identify main combustion, and is obtained in advance by experiments or the like and stored in the ROM of the ECU 3. Further, the excess combustion threshold is a rotation angle of the crankshaft that can identify excess combustion, and is obtained in advance by experiments or the like and stored in the ROM of the ECU 3. Further, the increase in injection at the time of blockade is an increment of the fuel injection amount that can compensate for the fuel shortage when the main combustion is excessively burned, and is obtained in advance by experiments or the like and stored in the ROM of the ECU 3.

  Further, when the ECU 3 determines that the main combustion has excessively burned, the ECU 3 delays the opening / closing timing of the exhaust valve 22 immediately before entering the blockage period by a preset exhaust valve retardation amount. Here, the exhaust valve retard amount is the amount of the crankshaft rotation angle that delays the opening and closing timing of the exhaust valve 22, and is obtained, for example, from a map described later in which the exhaust valve retard amount is determined from the injection amount at the time of blockade. This map is obtained in advance by experiments or the like and stored in the ROM of the ECU 3.

  Thus, by delaying the opening and closing timing of the exhaust valve 22, the amount of residual gas in the cylinder before injection at the time of blockage is reduced, and G / F in the next cycle is suppressed. As a result, the G / F in the main combustion of the next cycle can be suppressed below the misfire limit, and the occurrence of misfire and torque reduction can be suppressed.

  A combustion stabilization process performed by the control apparatus for an internal combustion engine according to the present embodiment configured as described above will be described with reference to FIG. The combustion stabilization process described below is started when the mode is shifted to the HCCI mode in which HCCI combustion is performed, is executed at a preset time interval, and is stopped when the mode is shifted to the SI mode in which SI combustion is performed.

  First, the ECU 3 calculates the engine load based on the accelerator opening and the engine speed (step S11). Next, the ECU 3 determines the valve timing and the fuel injection amount based on the engine speed and the engine load, and controls various control objects (step S12).

  Next, the ECU 3 determines whether or not the timing of main combustion has advanced from the above-described excessive combustion threshold (step S13). When it is determined that the main combustion timing is not advanced from the excessive combustion threshold, the ECU 3 ends the process.

  On the other hand, when it is determined that the timing of the main combustion is advanced from the excessive combustion threshold, the ECU 3 increases the injection amount at the time of blockage by the amount of increase in the injection at the time of blockage and increases the injection amount at the time of blockade. The main injection amount is set so as to decrease by the amount (step S14). Next, the ECU 3 retards the opening / closing timing of the exhaust valve 22 by the exhaust valve retardation amount based on the increased injection amount at the time of closing (step S15).

The effect | action by such a combustion stabilization process is demonstrated with reference to FIG.
As shown in the upper part of FIG. 3, in the control device for a conventional internal combustion engine, when the main combustion is advanced by excessive combustion (indicated by EC in the figure), the injection amount at the time of blockage is increased. Since the injection amount is increased to activate the combustion at the time of blockage, which is the combustion during the blockage period, the amount of residual gas in the cylinder during the blockage period increases. As a result, the G / F before the main combustion in the next cycle becomes equal to or greater than the misfire limit, which may cause misfire or torque reduction.

  In the present embodiment, as shown in the lower part of FIG. 3, when the main combustion is advanced by excessive combustion (indicated by EC in the figure), the injection amount at the time of blockage is increased. Further, the opening / closing timing of the exhaust valve 22 is delayed by an exhaust valve retardation amount corresponding to the increased injection amount at the time of closing. When the opening / closing timing of the exhaust valve 22 is delayed, as shown in “Piston speed” in FIG. 3, the exhaust valve 22 is opened at the timing when the piston speed is increased (portion surrounded by a one-dot chain line in the figure). A lot of gas is discharged.

  Further, when the opening / closing timing of the exhaust valve 22 is delayed, the exhaust valve 22 is opened at a timing (a portion surrounded by a one-dot chain line in the figure) at which the in-cylinder volume decreases as shown in “in-cylinder volume” of FIG. A lot of burned gas is discharged. For this reason, the residual gas amount in the cylinder during the sealing period is reduced. As a result, the G / F before main combustion in the next cycle becomes smaller than the misfire limit, and the occurrence of misfire and torque reduction can be suppressed.

  A map in which the exhaust valve retardation amount is determined from the injection amount at the time of closing of the control device for the internal combustion engine will be described.

  FIG. 4 is a graph showing the rate of change [%] of the engine load depending on the injection amount at the time of closing and the exhaust valve retard amount. In order to prevent the engine load from changing due to the adjustment of the opening / closing timing of the exhaust valve 22 due to the increase in the injection amount at the time of blockage, a range in which the change amount of the engine load is within ± 1% or less (for example, surrounded by a bold line in the figure) The opening / closing timing of the exhaust valve 22 is adjusted within this range.

  FIG. 5 is a graph showing the value of G / F depending on the injection amount at the time of closing and the exhaust valve retard amount. A range surrounded by a dotted line in the figure indicates the adjustable range of FIG. The opening / closing timing of the exhaust valve 22 is adjusted so that the G / F does not change even if the injection amount at the time of blockage is increased within the adjustable range of FIG. For example, the exhaust valve retard amount is determined so as to enter the adjustment target region surrounded by the bold line in the figure.

  Thus, in the above-described embodiment, when the timing of main combustion at which the in-cylinder pressure detected by the in-cylinder pressure sensor 30 is higher than a preset pressure threshold is advanced from a preset excess combustion threshold, It is determined that the main combustion is excessively burned, and the fuel injection amount of the injection at the time of blockage is increased by a preset increase in injection amount at the time of the blockade, and the exhaust valve 22 immediately before the blockage period is set according to the fuel injection amount of the injection at the time of blockage. ECU3 which delays opening and closing time is provided.

  Accordingly, the opening / closing timing of the exhaust valve is delayed according to the fuel injection amount of the injection at the time of blockage, and the exhaust valve 22 is opened at a timing at which a large amount of burned gas can be discharged. For this reason, it is possible to reduce the amount of residual gas in the cylinder before injection at the time of blockage by discharging a large amount of burned gas, reducing the amount of residual gas before main combustion in the next cycle, and at the time of premixed compression auto-ignition combustion The occurrence of misfire and torque reduction can be suppressed.

  Further, the ECU 3 increases the amount by which the opening / closing timing of the exhaust valve 22 immediately before the blockage period is delayed as the fuel injection amount of the block-time injection increases.

  Thereby, the opening / closing timing of the exhaust valve 22 immediately before the closing period is delayed as the fuel injection amount of the injection at the closing time is larger. For this reason, as the fuel injection amount at the time of blockage increases, the amount of burned gas can be discharged to reduce the amount of residual gas in the cylinder before injection at the time of blockage, and the amount of residual gas before main combustion in the next cycle can be reduced. This can reduce the occurrence of misfire and torque reduction during premixed compression self-ignition combustion.

  While embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that changes may be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

1 Vehicle 2 Engine (Internal combustion engine)
3 ECU (control unit)
7 Combustion chamber 9 Injector 21 Exhaust port 22 Exhaust valve 23 Exhaust side variable valve mechanism 30 In-cylinder pressure sensor (main combustion detector)

Claims (2)

The spark ignition combustion and the premixed compression auto-ignition combustion are configured to be switchable,
From the exhaust stroke to the intake stroke, both the intake valve and the exhaust valve are closed to provide a blockage period in which the exhaust gas is sealed in the combustion chamber, and during the blockage period, fuel is injected into the combustion chamber during blockade injection. A control apparatus for an internal combustion engine that performs the premixed compression auto-ignition combustion after raising the combustion chamber temperature by combustion of the remaining fuel,
A main combustion detector for detecting the occurrence of the premixed compression auto-ignition combustion;
An exhaust side variable valve mechanism capable of arbitrarily changing the opening and closing timing of the exhaust valve;
When the occurrence of the premixed compression self-ignition combustion is advanced by a predetermined threshold value or more, the fuel injection amount of the injection at the time of closing is increased, and the sealing period according to the fuel injection amount of the injection at the time of sealing A control unit for delaying the opening / closing timing of the exhaust valve immediately before.   2. The control device for an internal combustion engine according to claim 1, wherein the control unit increases the amount of delaying the opening / closing timing of the exhaust valve immediately before the blocking period as the fuel injection amount of the injection at the time of blocking increases.

Images