JP2005083323A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of making uniform and excellent mixture gas and reducing smoke and harmful emission. <P>SOLUTION: The control device for the internal combustion engine has a combustion chamber 30 formed between a cylinder head 16 and a piston 14 fitted and inserted in a cylinder, an injector 40 for directly injecting fuel into the combustion chamber 30, and an intake valve 32 and an exhaust valve 34 for respectively opening/closing an intake port 18 and an exhaust port 20 connected to the combustion chamber 30. When the piston 14 descends from an exhaust top dead point, the fuel is injected from the injector 40 while the intake valve 32 and the exhaust valve 34 are closed. The exhaust valve 34 is opened for a subsequent specified period, and thereafter, the intake valve 32 is opened. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for a direct injection internal combustion engine mounted on a vehicle.

  In general, in diesel combustion, in order to reduce harmful exhaust emissions such as smoke and NOx, it is important to promote the mixing of air and fuel, to make the in-cylinder distribution of the combustible air-fuel mixture uniform, and the like. For this reason, various measures are currently taken. One of them is a so-called premixed combustion system in which a fuel and air mixing time is secured by injecting fuel at an early stage.

  By the way, in this premixed combustion system, since fuel is injected at an early stage, problems such as deterioration in fuel consumption, increase in HC, and oil dilution due to fuel adhesion to the cylinder wall surface occur.

  Thus, in order to solve such a problem, for example, it is conceivable to employ the technique described in Patent Document 1. In this cylinder injection gasoline engine, when the piston descends during the intake stroke, the intake valve is closed for a predetermined period, thereby temporarily setting the combustion chamber to a negative pressure state. Then, when the combustion chamber is in such a negative pressure state, fuel is injected from the fuel injection valve, whereby the injected fuel is boiled under reduced pressure to promote the vaporization and diffusion of gasoline fuel.

JP-A-11-229920

  However, in the case of gasoline fuel, evaporability is high, so it can be expected to evaporate the fuel to some extent by boiling under reduced pressure, but in the case of diesel oil as fuel in diesel combustion, it is not sufficient and there is room for further improvement. It was.

  Accordingly, an object of the present invention is to provide a control device for an internal combustion engine that can create a uniform and good air-fuel mixture by further promoting fuel evaporation, and can reduce smoke and harmful emissions.

A control device for an internal combustion engine according to an aspect of the present invention that achieves the above object includes a combustion chamber formed between a cylinder head and a piston fitted in the cylinder, and fuel is directly injected into the combustion chamber. An injector, and an intake valve and an exhaust valve,
Injecting fuel from the injector with the intake valve and exhaust valve closed while the piston starts to descend from the exhaust top dead center until reaching the intake bottom dead center, and a predetermined amount after fuel injection The exhaust valve is opened during a period, and the intake valve is controlled to open after the exhaust valve is opened.
Here, it is preferable that the predetermined period is set corresponding to the required EGR amount.
Furthermore, it is preferable that the predetermined period is changed according to the temperature of the internal combustion engine.

  According to the control apparatus for an internal combustion engine according to one aspect of the present invention, when the piston descends from the exhaust top dead center, the fuel is injected from the injector while the intake port and the exhaust port are closed, so that the fuel boils under reduced pressure. Thus, atomization or vaporization is promoted. Then, the exhaust valve is opened during a predetermined period thereafter, whereby high-temperature exhaust gas (EGR) is introduced, and further evaporation and diffusion of fuel are promoted. Therefore, a uniform and good air-fuel mixture can be created, and smoke and harmful emissions can be reduced. If fresh air is introduced after boiling under reduced pressure, the atomized or vaporized fuel may be cooled and liquefied by the fresh air, and may adhere to the combustion chamber wall such as the piston head. Since fresh air is introduced after the gas is introduced into the cylinder, liquefaction of atomized or vaporized fuel is suppressed. In other words, by introducing fresh air after the exhaust gas is introduced into the cylinder, a high-temperature exhaust gas layer is formed in the vicinity of the combustion chamber wall surface of the piston head and the like, thereby suppressing adhesion due to fuel liquefaction. It is done.

  Further, if the predetermined period for opening the exhaust valve is set corresponding to the required EGR amount, it can also be used as the internal EGR, so that the EGR passage and the EGR control valve are not required, and the overall configuration is simplified.

  Furthermore, if the predetermined period during which the exhaust valve is opened is changed in accordance with the temperature of the internal combustion engine, the boiling under reduced pressure may not be sufficiently performed at a low temperature of the engine, but at this time, the amount of exhaust gas introduced increases. Therefore, the fuel can be sufficiently evaporated or diffused.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Referring to FIG. 1, a schematic configuration diagram of a cylinder injection type internal combustion engine according to the present invention is shown, and a cylinder block and a cylinder head are shown in a longitudinal sectional view. The configuration of a direct injection internal combustion engine according to the present invention will be described below with reference to FIG.

  A diesel engine (hereinafter abbreviated as an engine) 10 which is a cylinder injection type internal combustion engine is a four-valve engine comprising two intake valves and two exhaust valves, for example, a four-cylinder engine and all four cylinders. The fuel injection is possible not only in the intake stroke but also in the compression stroke. Hereinafter, one of the four cylinders will be described as a representative.

  An intake passage 2 and an exhaust passage 4 are communicated with the engine 10, and the intake passage 2 and the exhaust passage 4 are communicated with an EGR passage 6 in which an EGR control valve 7 is interposed. A compressor 5 </ b> A of a turbocharger 5 is disposed in the intake passage 2, and an intake throttle 3 is provided downstream thereof, and the compressor 5 </ b> A is configured to be driven by a turbine 5 </ b> B disposed in the exhaust passage 4. The turbocharger 5 in the present embodiment is a variable capacity turbocharger having a variable flow rate mechanism in the turbine nozzle portion, and the supercharging pressure can be controlled by changing the capacity.

  Further, as shown in the figure, a piston 14 is fitted into the cylindrical cylinder of the cylinder block 12. The cylinder head 16 has a pair of intake ports 18 that communicate with one side of the intake passage 2 via an intake manifold, and a pair of exhaust ports 20 that communicate with the exhaust passage 4 of the other side via an exhaust manifold. Is formed. The intake port 18 opens at a pair of intake ports 22 facing a combustion chamber 30 formed by the lower surface of the cylinder head 16 and the top surface of the piston 14, and the exhaust port 20 is opened at the pair of exhaust ports 24. Open to the front.

  The intake port 22 is provided with a pair of intake valves 32 for communicating and blocking between the intake port 18 and the combustion chamber 30, while the exhaust port 24 has an exhaust port 20, a combustion chamber 30, and an exhaust port 24. A pair of exhaust valves 34 are provided to communicate and shut off. The intake valve 32 and the exhaust valve 34 are linked to an intake valve drive mechanism 36 and an exhaust valve drive mechanism 38, respectively. The intake valve drive mechanism 36 and the exhaust valve drive mechanism 38 are configured by electromagnetic drive mechanisms that drive the intake valve 32 and the exhaust valve 34 forward and backward, respectively, using electromagnetic force generated when an excitation current is applied. The opening / closing timing and the lift amount can be arbitrarily controlled based on a signal from an electronic control unit (ECU) 60 described later. Therefore, for example, when the intake valve drive mechanism 36 and / or the exhaust valve drive mechanism 38 are operated based on a signal from the ECU 60, the opening / closing timing of the intake valve 32 and / or the exhaust valve 34, and thus the open period becomes longer. The variable control is short.

  In addition, the cylinder head 16 is provided with an injector 40 disposed so as to be able to directly inject fuel toward the combustion chamber 30. More specifically, the injector 40 is attached to the cylinder head 16 substantially on the cylinder axis as shown in FIG. The injector 40 is electrically connected to the ECU 60. The injector 40 is in communication with a common rail (not shown), and the fuel injection pressure is changed and controlled according to the engine load.

  Here, the intake throttle 3, the EGR control valve 7, the intake valve drive mechanism 36, the exhaust valve drive mechanism 38, and the injector 40 are connected to the output side of the ECU 60. On the other hand, on the input side of the ECU 60, a crank angle sensor 51, a cylinder discrimination sensor 52, an accelerator opening sensor 53, an intake pressure sensor 54 and an intake air temperature sensor 55 provided in the intake manifold, and an exhaust gas provided in the exhaust manifold. An atmospheric pressure sensor 56, an exhaust temperature sensor 57, and an in-cylinder pressure sensor 58 for detecting the pressure of the combustion chamber 30 in the cylinder are connected.

  The crank angle sensor 51 detects the crank angle ΘNe from the pickup signal generated at every predetermined crank angle, and obtains the engine speed Ne from the detected number within a predetermined time. The cylinder discrimination sensor 52 This is to determine the cylinder to be controlled by detecting the predetermined angle. On the other hand, the accelerator opening sensor 53 is for detecting an engine load (hereinafter referred to as accelerator opening θac), and outputs a signal corresponding to depression of the accelerator pedal 59. Here, in a predetermined operating state, the required fuel injection amount Qv, the required fresh air amount GairNew, and the required EGR amount Gegr required for good operation including the reduction of harmful emissions of the engine 10 are determined by the accelerator opening θac. It is set based on the engine speed Ne. Actually, each value is mapped in advance and stored in a predetermined memory of the ECU 60 in accordance with the operation state represented by the accelerator opening degree θac and the engine speed Ne.

  Hereinafter, one form of control of the control device of the engine 10 configured as described above will be described. Referring to FIG. 2 showing the flowchart of the control routine and FIG. 3 conceptually showing the operating state, a signal from the cylinder discrimination sensor 52 that the specific cylinder has entered the intake stroke from the exhaust top dead center. In step S10, the engine speed Ne, the accelerator opening θac, the exhaust manifold internal pressure Pex, and the intake valve 32 and the exhaust valve 34 of the cylinder are closed (see FIG. 3A). And the temperature Tex in the exhaust manifold is read. Then, the required fuel injection amount Qv, the required fresh air amount GairNew, and the required EGR amount Gegr are obtained based on the engine speed Ne and the accelerator opening degree θac. At the same time, the fuel injection timing Θinj is obtained based on the exhaust manifold internal pressure Pex and the exhaust manifold internal temperature Tex.

  In this state, the piston 14 is lowered while the intake valve 32 and the exhaust valve 34 are closed, so that the combustion chamber 30 is depressurized. In the next step S11, when the crank angle ΘNe coincides with the above-described fuel injection timing Θinj as the piston 14 is lowered, the injection is started from the injector 40 (see FIG. 3B). Then, the injection from the injector 40 is stopped when the injection period that satisfies the above-described required fuel injection amount Qv has elapsed. When fuel is injected from the injector 40, the decompressed state in the combustion chamber 30 is advanced, and the fuel injected under this low pressure (absolute value) boils under reduced pressure, and as a result, atomization or vaporization is promoted. The

  Further, in step S12, the exhaust valve 34 is opened almost simultaneously with the stop of the fuel injection (see FIG. 3C). When the exhaust valve 34 is opened, high-temperature exhaust gas is introduced into the combustion chamber 30 under a low pressure, and further evaporation of fuel atomized or vaporized by the above-described reduced-pressure boiling is promoted.

  In step S13, the in-cylinder pressure Ps detected by the in-cylinder pressure sensor 58 is read together with the crank angle ΘNe, the exhaust manifold internal pressure Pex, and the exhaust manifold internal temperature Tex. Based on these, the EGR amount introduced into the combustion chamber 30 is calculated, and the closing timing Θexclose of the exhaust valve 34 is determined based on the comparison with the required EGR amount Gegr determined in step S10. That is, since the position of the piston 14 is known from the crank angle ΘNe, the volume of the combustion chamber 30 at that time is known, and from the differential pressure between the exhaust manifold internal pressure Pex and the in-cylinder pressure Ps, for example, to what extent per unit crank angle It can be seen whether the EGR amount is introduced into the cylinder. Therefore, if this is integrated for each unit crank angle, it is possible to know how much EGR amount enters into the cylinder in total at a predetermined crank angle ΘNe, so that this expected EGR amount is less than the required EGR amount Gegr. The crank angle ΘNe that is satisfied is set as the closing timing Θexclose that determines the end of the opening period of the exhaust valve 34.

  Accordingly, the process proceeds to step S14, and when the crank angle ΘNe coincides with the closing timing Θexclose of the exhaust valve 34, the exhaust valve 34 is closed. The closing timing Θexclose of the exhaust valve 34 may be changed while being adjusted according to the temperature of the engine, using the value set in step S13 as a reference value. The engine temperature can be represented by, for example, an engine cooling water temperature by a water temperature sensor (not shown), an exhaust manifold internal temperature Tex by an exhaust temperature sensor 57, or the like. The higher the engine temperature, the more fuel evaporation and diffusion is promoted. Therefore, the higher the engine temperature, the shorter the period during which the exhaust valve 34 is opened when the piston is lowered from the exhaust top dead center.

  In step S15, after the exhaust valve 34 is closed, the intake valve 32 is opened (see FIG. 3 (D)), fresh air is introduced into the combustion chamber 30, and the above-described fuel in which evaporation is promoted. By mixing, an appropriate and uniform air-fuel mixture corresponding to the operating state is formed.

  Here, referring again to FIG. 3, the state of the intake stroke when the fuel injection timing, the opening / closing timing or opening period of the exhaust valve 34, and the opening timing of the intake valve 32 are controlled by the control device of the present invention. explain. In FIG. 3, the initial stage of the intake stroke (A), the fuel injection timing (B), the middle stage of the intake stroke (C), and the late stage of the intake stroke (D) are shown in this order. When the intake stroke is started, at the initial stage (A), the piston 14 is lowered while the intake valve 32 and the exhaust valve 34 are not opened, and the inside of the combustion chamber 30 is depressurized to be negative pressure. It becomes a state. When fuel is injected from the injector 40 in this negative pressure state (B), the fuel boils under pressure so that it is atomized or vaporized and diffused. Thus, when the exhaust valve 34 is opened and high-temperature exhaust gas (EGR) is introduced in the middle of the intake stroke (C), evaporation (vaporization) is further promoted. Then, when the intake valve 32 is opened in the late stage (D) of the intake stroke and fresh air is introduced, the vaporized fuel is well mixed with the fresh air, and a substantially uniform mixture is formed in the cylinder. is there. That is, by performing the control as described above, the fuel does not float in the combustion chamber 30 as droplets, and the top surface of the piston 14 or the combustion chamber on the cylinder wall remains as fuel droplets. The adhesion to the wall surface is eliminated, and the generation of unburned hydrocarbons (HC) and smoke is suitably prevented without slowing the combustion.

  Further, since the fuel does not adhere to the cylinder wall surface, the oil film of the lubricating oil applied every time the piston 14 moves up and down on the cylinder wall surface is not diluted with the fuel, and the lubrication between the cylinder and the piston 14 is prevented. Is maintained well, and wear of the piston ring and the cylinder wall surface is suitably prevented.

  By the way, in one form of the control described above, a so-called internal EGR by opening the exhaust valve 34 in a part of the intake stroke ensures a necessary EGR amount without performing an external EGR, and the exhaust valve 34. The control is based on the premise that the necessary amount of fresh air can be secured by opening the intake valve 32 after closing the valve. However, since the intake stroke is limited to a rotation section of 180 ° at the crank angle, there is a possibility that the required EGR amount and fresh air amount may be insufficient depending on the operating state such as at high speed of the engine.

  Therefore, for example, in the case where the open period of the exhaust valve 34 is made long in order to ensure the EGR amount, the fuel injection possible period must be shortened, but within this fuel injection possible period, When the required injection amount Qv required from the operating state cannot be injected, the injection amount in the intake stroke may be constant, and the shortage may be injected into the combustion chamber 30 near the compression top dead center.

  Further, when the EGR amount is insufficient with respect to the required EGR amount Gegr only in the above-described opening period of the exhaust valve 34, for example, the opening period of the exhaust valve 34 is kept constant, and the new intake valve 32 is opened. The shortage may be supplied as an external EGR during the air introduction period. In this case, by appropriately controlling the opening degree of the intake throttle 3, the variable nozzle of the turbocharger 5, and the EGR control valve 7, in other words, the pressure difference between the intake passage 2 and the exhaust passage 4 is communicated. By controlling the opening area of the EGR passage 6, the amount of external EGR added to fresh air is controlled.

  Further, in the above-described control mode, when it is predicted that a sufficient amount of fresh air cannot be obtained within the opening period of the intake valve 32, the opening period of the intake valve 32 is set to a certain short period. In addition, control is performed to increase the supercharging pressure by controlling the variable nozzle of the turbocharger 5 described above, so that a shortage of fresh air does not occur. The opening timing of the intake valve 32 is not limited to after the exhaust valve 34 is closed. As long as the exhaust gas is introduced first, the intake valve 32 and the exhaust valve 34 have some overlap. May be opened.

  The above-described control according to the present invention can be performed over the entire operating range of the engine, but may be performed only in a part of the operating range. That is, it may be performed only in the operation region where it is effective to perform the premixed combustion, and in other regions, the compression stroke injection by the normal intake / exhaust valve opening / closing control may be performed.

  In this embodiment, the in-cylinder pressure sensor 58 is used to detect the in-cylinder pressure Ps. However, the in-cylinder pressure Ps can also be obtained by calculation from a predetermined parameter value.

It is a schematic diagram which shows the outline | summary of one Embodiment of this invention. It is a flowchart which shows an example of the control procedure of one Embodiment of this invention. It is a diagram explaining the mode of the intake stroke of one embodiment of the present invention, (A) is the initial stage of the intake stroke, (B) is the fuel injection timing, (C) is the middle stage of the intake stroke, and (D) is the intake stroke. Shown later.

Explanation of symbols

2 Intake passage 3 Intake throttle 4 Exhaust passage 5 Turbocharger 6 EGR passage 7 EGR control valve 10 Engine 14 Piston 30 Combustion chamber 32 Intake valve 34 Exhaust valve 36 Intake valve drive mechanism 38 Exhaust valve drive mechanism 40 Injector 51 Crank angle sensor 52 Cylinder Discriminating sensor 53 Accelerator opening sensor 54 Intake pressure sensor 55 Intake temperature sensor 56 Exhaust pressure sensor 57 Exhaust temperature sensor 58 In-cylinder pressure sensor 60 ECU
ΘNe Crank angle
Ne Engine speed Θac Accelerator opening
Qv Required fuel injection amount
GairNew required fresh air volume
Gegr Required EGR amount
Pex Exhaust manifold pressure
Tex Exhaust manifold internal temperature Θinj Fuel injection timing
Ps In-cylinder pressure Θexclose Exhaust valve closing timing

Claims (3)

A combustion chamber formed between a cylinder head and a piston fitted in the cylinder;
An injector for injecting fuel directly into the combustion chamber;
An intake valve and an exhaust valve,
Injecting fuel from the injector with the intake valve and exhaust valve closed while the piston starts to descend from the exhaust top dead center until reaching the intake bottom dead center, and a predetermined amount after fuel injection A control apparatus for an internal combustion engine, wherein the exhaust valve is opened during a period, and the intake valve is opened after the exhaust valve is opened.   2. The control device for an internal combustion engine according to claim 1, wherein the predetermined period is set in accordance with a required EGR amount. The control apparatus for an internal combustion engine according to claim 1, wherein the predetermined period is changed according to a temperature of the internal combustion engine.

Images