JP2012026412A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device which can reduce soot, can avoid an abrupt rise of pressure in combustion, and can reduce combustion noise.SOLUTION: The fuel injection control device 1 of an engine 3 including a fuel injection valve 5 capable of variably controlling injection pressure includes: a pilot injection part performing pilot injection and generating burned gas in a combustion chamber 37; a swirl part generating a swirl flow in the combustion chamber 37; a main injection part performing main injection in the combustion chamber 37 in which the burned gas is generated; and a fuel injection control part controlling the pilot injection, the injection timing of the main injection, and injection pressure in an ECU 10. The fuel injection control part controls injection timing so that the burned gas which is pilot-injected from an adjacent nozzle hole and generated, and made to flow by the swirl flow and main-injected fuel are superposed, and controls injection pressure so that the pilot injection pressure becomes pressure within a predetermined range lower than main injection pressure.

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

  In recent years, automobile fuel efficiency regulations have been strengthened from the viewpoint of energy saving and prevention of global warming. A compression ignition type internal combustion engine such as a diesel engine is advantageous for achieving both low fuel consumption and high output. Therefore, it is expected to be widely spread if the high cost associated with compliance with exhaust gas regulations can be eliminated.

  For example, the development of a low-temperature combustion technique has been promoted as a technique that eliminates the need for a NOx catalyst that purifies NOx contained in the exhaust gas of a compression self-ignition internal combustion engine and reduces the post-treatment cost of exhaust gas. In this low temperature combustion technique, NOx is reduced by lowering the combustion temperature, and at the same time, soot is reduced by premixed combustion.

  In the fuel injection control apparatus for a compression ignition type internal combustion engine that performs sub-injection (equivalent to pilot injection described later) prior to main injection (equivalent to main injection described later) as the low-temperature combustion technique, main injection and sub-injection A technique for optimizing the injection timing is proposed (for example, see Patent Document 1).

Japanese Patent No. 4404154

  However, in the technique of Patent Document 1, instead of proceeding with premixing of fuel and reducing NOx and soot until the injected fuel is ignited and combusted, a rapid pressure increase is caused at the time of combustion. There was a problem of combustion noise due to.

  The present invention has been made in view of the above, and an object thereof is a fuel capable of reducing soot in low temperature combustion capable of reducing NOx and at the same time avoiding a sudden pressure increase during combustion and reducing combustion noise. To provide an injection control device.

  In order to achieve the above object, the present invention injects fuel into a combustion chamber (for example, a combustion chamber 37 described later) from a nozzle hole (for example, a nozzle hole 513 described later) provided at the tip, and varies the injection pressure. Provided is a fuel injection control device (for example, a fuel injection control device 1 described later) of an internal combustion engine (for example, a later-described engine 3) provided with a controllable fuel injection valve (for example, a fuel injection valve 5 described later). The fuel injection control device performs pilot injection by the fuel injection valve to generate burned gas in the combustion chamber (for example, a pilot injection unit described later), and generates a swirl flow in the combustion chamber. The swirl means for flowing the burned gas by the swirl flow (for example, a swirl control valve 73 and a swirl unit, which will be described later), and the main injection by the fuel injection valve into the combustion chamber generated by the burned gas. Main injection means for performing (for example, a main injection section described later), and fuel injection control means (for example, a fuel injection control section described later) for controlling the injection timing and injection pressure of the pilot injection and the main injection, The fuel injection control means includes the burned gas generated by the pilot injection from the adjacent nozzle holes and flowing by the swirl flow, The injection timing is controlled so that the fuel injected by the main injection overlaps, and the injection pressure is controlled so that the injection pressure of the pilot injection is within a predetermined range lower than the injection pressure of the main injection It is characterized by doing.

In the present invention, the injection timing is controlled so that the burned gas generated by pilot injection from the adjacent nozzle holes and flowing by the swirl flow and the fuel injected at high pressure by the main injection overlap.
As a result, the ignition temperature of the main injected fuel is promoted by increasing the ambient temperature by the burned gas generated by burning the fuel injected by the pilot (hereinafter referred to as “pilot combustion”). The combustion form is exhibited. For this reason, it can be avoided that the unburnt fuel in the cylinder is ignited at a time when there is unburned fuel, the pressure suddenly increases, and the combustion noise increases.
Further, in order to superimpose the burned gas and the fuel injected at high pressure, the mixture is changed from rich to lean during the period in which the fuel injected at high pressure burns (hereinafter referred to as “main combustion”). The air-fuel mixture can be homogenized as the combustion progresses. For this reason, combustion noise due to pressure rise can be reduced, and at the same time, the amount of soot generated can be reduced.

By the way, the injection pressure of the pilot injection is highly correlated with the pressure increase and the amount of soot generated during the main combustion. Specifically, when the pilot injection pressure is too high, the pilot injected fuel collides with the wall of the combustion chamber to promote dispersion, and the burned gas generated by pilot injection and the main injected fuel The degree of overlap is reduced. For this reason, the effect of suppressing the pressure increase during the main combustion is not sufficiently exhibited. As a result, the pressure increase increases and the combustion noise increases. On the other hand, when the pilot injection pressure is too low, the burned gas generated by the pilot injection and the main injected fuel are in the vicinity of the fuel injection valve where the main injected fuel exists as relatively large droplets. As a result of overlapping and burning, the amount of soot generated increases.
On the other hand, in the present invention, each injection pressure is controlled so that the injection pressure of the pilot injection is within a predetermined range lower than the injection pressure of the main injection set to collide with the wall surface. Thereby, it is possible to suppress the pilot-injected fuel from colliding with the wall surface of the combustion chamber, and to control the fuel so as to drift to a certain distance from the fuel injection valve. Therefore, the above problems can be avoided, and the amount of combustion noise and soot generated due to pressure increase during main combustion can be further reduced.

  Preferably, the fuel injection control means controls the injection pressure such that a ratio of the injection pressure of the pilot injection to the injection pressure of the main injection decreases with an increase in the load of the internal combustion engine.

  In the present invention, each injection pressure is controlled so that the ratio of the injection pressure of the pilot injection to the injection pressure of the main injection (hereinafter referred to as “pilot injection pressure ratio”) decreases as the load of the internal combustion engine increases. Here, the load of the internal combustion engine at the time of pilot injection is in a low load state in which the oxygen partial pressure is low under, for example, a low supercharging condition or a high EGR condition. In such a case, combustion of the fuel injected by the pilot is not performed. It does not progress sufficiently, and the effect of suppressing pressure rise during main combustion cannot be expected. Therefore, in the present invention, the pilot injection pressure ratio is increased to increase the pilot combustion as the load is lower, and the injection pressure is controlled so that the ratio of the pilot injection pressure decreases as the load on the internal combustion engine increases. In a wide operating range, the pressure rise during main combustion can be suppressed and combustion noise can be reduced.

  The fuel injection control device further includes high load operation state determination means (for example, a high load operation state determination unit described later) for determining whether or not the internal combustion engine is in a predetermined high load operation state. When it is determined that the internal combustion engine is not in the predetermined high load operation state, the means executes single pilot injection for performing the pilot injection once, and the fuel injection control means is configured to perform injection with respect to the injection pressure of the main injection. It is preferable to control the injection pressure so that the ratio of the injection pressure of the single pilot injection is within a range of approximately 20% to approximately 30%.

In the present invention, when the internal combustion engine is not in a high load operation state, single pilot injection is performed as pilot injection, and the ratio of the injection pressure of the single pilot injection to the injection pressure of the main injection is approximately 20% to approximately 30%. Each injection pressure was controlled so as to be within the range.
As a result, the reach of the single pilot-injected fuel is controlled to an appropriate range, so that the fuel can be further prevented from colliding with the wall of the combustion chamber and drift to a certain distance from the fuel injection valve. Can be controlled. Therefore, the amount of combustion noise and soot generated due to the pressure increase during main combustion can be more reliably reduced.

  The fuel injection control device further includes high load operation state determination means (for example, a high load operation state determination unit described later) for determining whether or not the internal combustion engine is in a predetermined high load operation state. When it is determined that the internal combustion engine is in the predetermined high-load operation state, the means executes double pilot injection that sequentially performs first pilot injection and second pilot injection, and the fuel injection control means The burned gas generated by the first pilot injection overlaps the fuel injected by the second pilot injection, and the burned gas generated by the second pilot injection and the fuel injected by the main injection are It is preferable to control the injection timing so as to overlap.

In the present invention, when the internal combustion engine is in a high-load operation state, double pilot injection is performed in which the first pilot injection and the second pilot injection are sequentially performed. Thus, by performing the pilot injection in two times in a high-load operation state with a high pressure increase rate, it is possible to reduce the pressure increase during pilot combustion without reducing the total amount of pilot injection. Further, since the total amount of pilot injection can be maintained, the pressure increase during main combustion can be reduced, and combustion noise can be reduced.
In addition, the burned gas generated by the first pilot injection and the fuel injected by the second pilot injection overlap, and the burned gas generated by the second pilot injection and the fuel injected by the main injection overlap. Thus, each injection timing was controlled. That is, by setting the respective injection intervals so that the burned gas and the injected fuel of the pre-injection overlap each other, the first pilot injection and the second pilot injection are combined in a region somewhat away from the fuel injection valve. The burned gas generated by the above is configured to interfere with the main injected fuel. As a result, the second pilot combustion is promoted by the first pilot combustion, and the main combustion is promoted by the second pilot combustion. Therefore, the unburnt fuel in the cylinder is ignited at once and the pressure suddenly increases. Thus, increase in combustion noise can be avoided.

  It is preferable that an aspect ratio (for example, an aspect ratio D1 / H described later) of the combustion chamber is 3.3 or more.

  In the present invention, the combustion chamber of the internal combustion engine is configured with a large aspect ratio of 3.3 or more. Thereby, the distance from the front-end | tip of a fuel injection valve to the wall surface of a combustion chamber becomes long, and can reduce the interference with the fuel by which pilot injection was carried out, and the wall surface of a combustion chamber. For this reason, the dispersion of the fuel injected by the pilot injection is suppressed, and the degree of overlap between the burned gas generated by the pilot injection and the fuel injected by the main injection is increased. Noise can be suppressed. That is, an effect equivalent to that of reducing the injection pressure of pilot injection can be obtained.

  It is preferable that a piston lip portion (for example, a piston lip portion 335 described later) forming the combustion chamber has a stepped structure (for example, a step 337 described later).

  In this invention, the piston lip portion forming the combustion chamber has a stepped structure. As a result, in a conventional combustion chamber that does not have a stepped structure, a high-concentration oxygen region is locally formed in the squish area, resulting in slow mixing of soot and residual oxygen, resulting in insufficient oxidation and reduction of soot. The situation can be avoided. That is, in the combustion chamber of the present invention, when the fuel / air mixture injected at high pressure collides with the wall surface of the combustion chamber and then flows out into the squish area where the step is provided, Collide with the wall. At this time, the dispersion of the air-fuel mixture in the circumferential direction of the piston is promoted, while the penetration force of the air-fuel mixture in the radial direction is weakened. As a result, the high-concentration oxygen region is formed in layers along the cylinder liner wall surface. Soot is sandwiched between this high-concentration oxygen region and the residual oxygen flowing in from the combustion chamber by a so-called reverse squish flow, and soot oxidation and reduction are promoted.

  According to the present invention, it is possible to provide a fuel injection control device capable of reducing soot in low temperature combustion capable of reducing NOx, and at the same time avoiding a sudden pressure increase during combustion and reducing combustion noise.

1 is a diagram showing a schematic configuration of a fuel injection control device according to an embodiment of the present invention and an internal combustion engine to which the fuel injection control device is applied. It is a schematic diagram which shows schematic structure of the fuel injection valve which concerns on the said embodiment. It is a top perspective view of the piston concerning the above-mentioned embodiment. FIG. 4 is a sectional view taken along line AA in FIG. 3. It is a figure which shows the verification result in a low load driving | running state, (A) is a swirl ratio-pilot injection pressure map figure of the maximum pressure increase rate (dp / d (theta)) max at the time of pilot combustion, (B) is at the time of main combustion FIG. 3 is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max at (C), and (C) is a swirl ratio-pilot injection pressure map of the degree of soot generation. It is a figure which shows the verification result in a medium load driving | running state, (A) is a swirl ratio-pilot injection pressure map figure of the maximum pressure increase rate (dp / d (theta)) max at the time of pilot combustion, (B) is at the time of main combustion FIG. 3 is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max at (C), and (C) is a swirl ratio-pilot injection pressure map of the degree of soot generation. It is a figure which shows the verification result in a high load driving | running state, (A) is a swirl ratio-pilot injection pressure map figure of the maximum pressure increase rate (dp / d (theta)) max at the time of pilot combustion, (B) is at the time of main combustion FIG. 3 is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max at (C), and (C) is a swirl ratio-pilot injection pressure map of the degree of soot generation. It is a figure which shows the relationship between ratio of the pilot injection pressure with respect to main injection pressure, and main injection amount. It is a figure which shows the relationship between ratio of the pilot injection quantity with respect to main injection quantity, and main injection quantity. It is a figure which shows the maximum pressure increase rate (dp / d (theta)) max at the time of main combustion when changing the aspect ratio of a combustion chamber, (A) is an aspect ratio of 3.3, (B) is an aspect. The ratio is 2.9.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a fuel injection control device 1 according to an embodiment of the present invention and an internal combustion engine (hereinafter referred to as “engine”) 3 to which the fuel injection control device 1 is applied. The engine 3 is a diesel engine that directly injects fuel into a cylinder.

The engine 3 includes an intake pipe 7, an exhaust pipe 9 and a supercharger 2. The supercharger 2 includes a turbine 21 that is driven by exhaust kinetic energy, and a compressor 23 that is rotationally driven by the turbine 21 and compresses intake air.
The turbine 21 includes a plurality of variable vanes (not shown), and is configured to change the turbine rotational speed by changing the opening of the variable vanes. The vane opening degree of the turbine 21 is electromagnetically controlled by an electronic control unit (hereinafter referred to as “ECU”) 10.

  The intake pipe 7 is configured to be branched into intake pipes 7A and 7B on the way. In the intake pipe 7A, a swirl control valve 73 is provided that generates a swirl flow in the combustion chamber 37 of the engine 3 by limiting the amount of air sucked through the intake pipe 7A. The swirl control valve 73 is controlled to be opened and closed by the ECU 10 via an actuator (not shown).

  An exhaust gas recirculation passage 6 that recirculates exhaust gas to the intake pipe 7B is provided between the upstream side of the turbine 21 of the exhaust pipe 9 and the intake pipe 7B. The exhaust gas recirculation passage 6 is provided with an exhaust gas recirculation control valve 61 for controlling the exhaust gas recirculation amount. The exhaust gas recirculation control valve 61 is subjected to open / close control and opening degree control by the ECU 10 via an actuator (not shown).

  The engine 3 includes four cylinders 31 (only one part is shown). A combustion chamber 37 is formed between the piston 33 and the cylinder head 35 of each cylinder 31.

  The cylinder head 35 is provided with an intake port 71 constituted by the intake pipes 7A and 7B and an exhaust port 91 communicating with the exhaust pipe 9 so as to communicate with the combustion chamber 37. The intake port 71 is provided with two intake valves 72 (only one is shown) that controls communication between the intake port 71 and the combustion chamber 37. The exhaust port 91 is provided with two exhaust valves 92 (only one is shown) that controls communication between the exhaust port 91 and the combustion chamber 37.

  Further, the cylinder head 35 is provided with the fuel injection valve 5 so as to face the combustion chamber 37. The fuel injection valve 5 is electrically connected to the ECU 10, and the fuel injection valve 5 is controlled to open and close by the ECU 10. The fuel injected from the fuel injection valve 5 is mixed with the air drawn into the combustion chamber 37 from the intake port 71. The air-fuel mixture generated by mixing is burned in the combustion chamber 37.

As fuel injection by the fuel injection valve 5, main injection and pilot injection are executed. The main injection is an injection operation for generating torque of the engine 3, and the pilot injection is injected by the main injection by increasing the temperature in the combustion chamber 37 by injecting a small amount of fuel in advance prior to the main injection. This is an injection operation that promotes ignition of the fuel.
Moreover, in this embodiment, according to the driving | running state of the engine 3, as said pilot injection, the single pilot injection which performs pilot injection once before main injection, and 1st pilot injection and 2nd before main injection. Double pilot injection is performed in which pilot injection is sequentially performed.

FIG. 2 is a schematic diagram showing a schematic configuration of the fuel injection valve 5. The fuel injection valve 5 is a pressure increase type fuel injection valve capable of variably controlling the fuel injection pressure.
The fuel injection valve 5 includes a needle valve 51 provided in the valve body 510 so as to be able to advance and retreat, a fuel supply passage 511 formed in a gap between the valve body 510 and the needle valve 51, and a tip of the valve body 510, for example. Six nozzle holes 513 that are provided at intervals of 60 ° in the circumferential direction and inject fuel supplied through the fuel supply passage 511, a needle piston 52 that is movable in the axial direction of the valve body 510, A needle control valve NCV53 for driving the needle piston 52.

  The fuel injection valve 5 includes, as a pressure increasing mechanism, a pressure increasing piston 54 and a pressure increasing plunger 55 that are movable in the axial direction, and a pressure increasing control valve ICV 56 that drives the pressure increasing piston 54 and the pressure increasing plunger 55. .

  The needle control valve NCV 53 and the pressure increase control valve ICV 56 are connected to the common rail 4 for accumulating fuel via the fuel supply pipe 41. The fuel supply pipe 41 branches in the middle and is connected to the fuel supply passage 511 via the fuel check valve 57.

  In the fuel injection valve 5, the injection pressure can be increased by the above-described pressure increase mechanism, and the injection pressure can be variably controlled. The pressure increase ratio is determined by the cross-sectional area ratio between the pressure increase piston 54 and the pressure increase plunger 55. For example, the injection pressure of the pilot injection can be controlled to be lower than the injection pressure of the main injection by driving the pressure increasing mechanism only during the main injection.

FIG. 3 is a top perspective view of the piston 33 according to the present embodiment, and FIG. 4 is a cross-sectional view taken along line AA of FIG.
The cylindrical piston 33 has a cavity 333 that is centered on the central axis X of the piston 33 on the top surface 331 thereof. The top surface of the piston 33 is formed in a so-called pent roof shape that inclines downward from the central axis X toward the outside in the radial direction. An annular step 337 is provided on the top surface 331 of the piston 33.

  As shown in FIG. 4, the combustion chamber 37 formed by the lower surface of the cylinder head 35 and the cavity 333 is a shallow dish-shaped combustion chamber. The annular step 337 is provided in the piston lip 335 at the inner end of the squish area 339 formed by the lower surface of the cylinder head 35 and the top surface 331 of the piston 33.

  As shown in FIG. 4, the aspect ratio of the combustion chamber 37 formed by the cavity 333 and the lower surface of the cylinder head 35 is represented by D1 / H. The combustion chamber 37 of the present embodiment is set to a large aspect ratio of 3.3 or higher.

  Returning to FIG. 1, the ECU 10 forms an input signal waveform from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like. And an arithmetic processing unit (hereinafter referred to as “CPU”). In addition, the ECU 10 includes a storage circuit that stores various calculation programs and calculation results executed by the CPU, and an output circuit that outputs a control signal to the fuel injection valve 5 and the like. With the hardware configuration described above, the ECU 10 is configured with modules including a pilot injection unit, a swirl unit, a main injection unit, a fuel injection control unit, and a high-load operation state determination unit as modules for executing fuel injection processing. The

The pilot injection unit executes pilot injection by the fuel injection valve 5. Thereby, burnt gas is generated in the combustion chamber 37, and the temperature in the combustion chamber 37 before main injection is raised.
Further, the pilot injection unit performs single pilot injection and is determined to be in the high load operation state when the engine 3 is determined not to be in the high load operation state by a high load operation state determination unit described later. In that case, double pilot injection is performed.

  The swirl unit controls the swirl of the swirl flow by generating the swirl flow in the combustion chamber 37 by controlling the opening / closing and opening of the swirl control valve 73. As a result, mixing of the fuel injected from the fuel injection valve 5 and the intake air is promoted.

  The main injection unit performs main injection by the fuel injection valve 5. Thereby, the torque of the engine 3 is generated.

The fuel injection control unit controls the injection timing, injection pressure, and injection amount of each of the pilot injection and the main injection.
The injection timing is controlled so that the burned gas generated by pilot injection from the adjacent nozzle holes and flowing by the swirl flow overlaps the fuel injected by the main injection. In particular, when performing the double pilot injection, the burned gas generated by the first pilot injection from the nozzle adjacent to the upstream side of the swirl flow and the fuel injected by the second pilot are superimposed, In addition, the burned gas generated by the second pilot injection from the nozzle adjacent to the upstream side of the swirl flow is controlled so as to overlap the main injected fuel.

The injection pressure is controlled so that the injection pressure of the pilot injection is in a predetermined range lower than the injection pressure of the main injection. Further, the pilot injection pressure ratio is controlled so as to decrease as the load of the engine 3 increases.
In particular, when performing single pilot injection, control is performed such that the ratio of the injection pressure of the single pilot injection to the injection pressure of the main injection is within a range of approximately 20% to approximately 30%. Here, “approximately 20%” and “approximately 30%” mean that ± 0.2% (that is, 1.8% to 3.2%) is included.

  The injection amount is controlled according to the required torque, and the ratio of the pilot injection amount to the main injection amount (hereinafter referred to as “pilot injection amount ratio”) in order to promote pilot combustion as the load on the engine 3 decreases. ) Is preferably controlled to be high. Further, it is preferable to increase the pilot injection pressure ratio as the pilot injection amount ratio increases.

The high load operation state determination unit determines whether or not the engine 3 is in a predetermined high load operation state. For example, when the injection amount injected last time is equal to or greater than a predetermined injection amount, it is determined that the vehicle is in a high load operation state.
The injection amount is calculated by the ECU 10 based on a detection signal from an accelerator sensor (not shown) that detects the depression amount (accelerator opening) of the accelerator pedal of the vehicle driven by the engine 3. In addition, the predetermined injection amount is set to an injection amount when the maximum pressure increase rate (dp / dθ) max cannot be reduced both in the pilot combustion and the main combustion depending on the single pilot injection.

Further, the high load operation state determination unit determines that the engine 3 is in a predetermined high load operation state, for example, when the engine 3 is in a high supercharging region that is equal to or higher than a predetermined supercharging pressure.
The above supercharging pressure is detected by a supercharging pressure sensor (not shown) provided in the intake pipe 7B. The predetermined supercharging pressure is set to a supercharging pressure at which the maximum pressure increase rate (dp / dθ) max in both pilot combustion and main combustion cannot be reduced depending on the single pilot injection. .

According to the fuel injection control device 1 of the present embodiment having the above-described configuration, the following effects are exhibited.
In the present embodiment, each injection timing is controlled so that the burned gas generated by pilot injection from the adjacent nozzle holes 513 and flowed by the swirl flow and the fuel high-pressure injected by the main injection overlap. .
As a result, the ambient temperature rises by the burned gas generated by the pilot combustion, whereby the ignition of the main injected fuel is promoted, and a combustion mode mainly composed of diffusion combustion is exhibited. For this reason, it can be avoided that the unburnt fuel in the cylinder is ignited at a time when there is unburned fuel, the pressure suddenly increases, and the combustion noise increases.
Also, in order to superimpose burned gas and fuel injected at high pressure, the mixture is changed from rich to lean during the main combustion period, and the mixture is homogenized as the combustion progresses. Can do. For this reason, combustion noise due to pressure rise can be reduced, and at the same time, the amount of soot generated can be reduced.

By the way, the injection pressure of the pilot injection is highly correlated with the pressure increase and the amount of soot generated during the main combustion. Specifically, when the pilot injection pressure is too high, the pilot-injected fuel collides with the wall surface of the combustion chamber 37 to promote dispersion, and the burned gas generated by the pilot injection and the main-injected fuel The overlapping degree of becomes smaller. For this reason, the effect of suppressing the pressure increase during the main combustion is not sufficiently exhibited. As a result, the pressure increase increases and the combustion noise increases. On the other hand, when the pilot injection pressure is too low, the burned gas generated by the pilot injection and the main injected fuel in the vicinity of the fuel injection valve 5 in which the main injected fuel exists as relatively large droplets. The amount of soot increases as a result of overlapping and burning.
On the other hand, in the present embodiment, each injection pressure is controlled so that the injection pressure of the pilot injection falls within a predetermined range lower than the injection pressure of the main injection set to collide with the wall surface. . Thereby, it is possible to suppress the pilot-injected fuel from colliding with the wall surface of the combustion chamber 37 and to control the fuel so that it drifts to a certain distance from the fuel injection valve 5. Therefore, the above problems can be avoided, and the amount of combustion noise and soot generated due to pressure increase during main combustion can be further reduced.

  In the present embodiment, each injection pressure is controlled so that the pilot injection pressure ratio decreases as the load of the engine 3 increases. Here, the load of the engine 3 at the time of pilot injection is in a low load state in which the oxygen partial pressure is low under, for example, a low supercharging condition or a high EGR condition. In such a case, combustion of the fuel injected by the pilot is not performed. It does not progress sufficiently, and the effect of suppressing pressure rise during main combustion cannot be expected. Thus, in the present embodiment, the pilot injection pressure ratio is increased to promote pilot combustion as the load is lower, and the injection pressure is controlled so that the pilot injection pressure ratio decreases as the load on the engine 3 increases. Therefore, it is possible to suppress the increase in pressure during main combustion in a wide operation region and reduce combustion noise.

In the present embodiment, when the engine 3 is not in a high load operation state, single pilot injection is performed as pilot injection, and the ratio of the injection pressure of the single pilot injection to the injection pressure of the main injection is approximately 20% to Each injection pressure was controlled so as to be within a range of approximately 30%.
Thereby, the reach of the single pilot-injected fuel is controlled to an appropriate range, so that it is possible to further suppress the fuel from colliding with the wall surface of the combustion chamber 37 and to a region away from the fuel injection valve 5 to some extent. It can be controlled to drift. Therefore, the amount of combustion noise and soot generated due to the pressure increase during main combustion can be more reliably reduced.

Further, in the present embodiment, when the engine 3 is in a high load operation state, the double pilot injection that sequentially performs the first pilot injection and the second pilot injection is executed. Thus, by performing the pilot injection in two times in a high-load operation state with a high pressure increase rate, it is possible to reduce the pressure increase during pilot combustion without reducing the total amount of pilot injection. Further, since the total amount of pilot injection can be maintained, the pressure increase during main combustion can be reduced, and combustion noise can be reduced.
In addition, the burned gas generated by the first pilot injection and the fuel injected by the second pilot injection overlap, and the burned gas generated by the second pilot injection and the fuel injected by the main injection overlap. Thus, each injection timing was controlled. That is, by setting the respective injection intervals so that the burned gas and the injected fuel of the pre-injection overlap each other, the first pilot injection and the second pilot injection are performed at a certain distance from the fuel injection valve 5. The burned gas generated by the combination is configured to interfere with the main injected fuel. As a result, the second pilot combustion is promoted by the first pilot combustion, and the main combustion is promoted by the second pilot combustion. Therefore, the unburnt fuel in the cylinder is ignited at once and the pressure suddenly increases. Thus, increase in combustion noise can be avoided.

  In the present embodiment, the combustion chamber 37 of the engine 3 is configured with a large aspect ratio of 3.3 or more. Thereby, the distance from the front-end | tip of the fuel injection valve 5 to the wall surface of the combustion chamber 37 becomes long, and interference with the fuel injected by pilot and the wall surface of the combustion chamber 37 can be relieved. For this reason, the dispersion of the fuel injected by the pilot injection is suppressed, and the degree of overlap between the burned gas generated by the pilot injection and the fuel injected by the main injection is increased. Noise can be suppressed. That is, an effect equivalent to that of reducing the injection pressure of pilot injection can be obtained.

  Further, in the present embodiment, a step 337 is provided in the piston lip portion 335 forming the combustion chamber 37 to form a stepped structure. As a result, in a conventional combustion chamber that does not have a stepped structure, a high-concentration oxygen region is locally formed in the squish area 339, resulting in slow mixing of soot and residual oxygen, resulting in insufficient oxidation and reduction of soot. Can be avoided. That is, in the combustion chamber 37 of the present embodiment, when the fuel / air mixture mainly injected at high pressure collides with the wall surface of the combustion chamber 37 and then flows out into the squish area 339 provided with the step 337, The wall collides again at the step 337. At this time, while the dispersion of the air-fuel mixture in the circumferential direction of the piston 33 is promoted, the penetration force of the air-fuel mixture in the radial direction is weakened. As a result, the high-concentration oxygen region is formed in layers along the cylinder liner wall surface. . Soot is sandwiched between this high-concentration oxygen region and the residual oxygen flowing from the combustion chamber 37 by a so-called reverse squish flow, and soot oxidation and reduction are promoted.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

[Verification]
By superimposing the burned gas generated by pilot injection and the fuel injected by main injection, and optimizing the main injection pressure and pilot injection pressure, the amount of combustion noise and soot generated due to pressure increase during combustion can be reduced. We verified the points that can be reduced.
Specifically, using a single-cylinder engine having main specifications as shown in Table 1, pilot injection is performed in three operating states, such as a low load operation state, a medium load operation state, and a high load operation state as shown in Table 2. The maximum pressure increase rate during combustion (dp / dθ) when the swirl ratio and the pilot injection pressure are changed after setting the injection timing so that the burned gas generated in step 1 and the main injected fuel overlap each other Max and wrinkle generation amount were examined. The results are shown in FIGS.

  FIG. 5 is a diagram showing a verification result in a low-load operation state, where (A) is a swirl ratio-pilot injection pressure map of a maximum pressure increase rate (dp / dθ) max during pilot combustion, and (B). Is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max during main combustion, and (C) is a swirl ratio-pilot injection pressure map of soot generation degree. FIG. 5C is a map diagram created based on the degree of soot occurrence obtained by normalizing with the maximum amount of soot produced in the cylinder. In the following verification, the maximum pressure increase rate that can achieve the target combustion noise is 0.5 MPa / ° CA, the maximum pressure increase rate is 0.5 MPa / ° CA or less, and the amount of soot generation can be reduced. (For example, the degree of wrinkle generation is 0.9 or less) was set as a preferable region.

As shown in FIG. 5A, in the low load operation state, the value of the maximum pressure increase rate (dp / dθ) max during pilot combustion is lower than 0.5 MPa / ° CA in all regions, and combustion noise The problem did not occur. Further, as shown in FIG. 5B, the value of the maximum pressure increase rate (dp / dθ) max at the time of main combustion is 0 except for a very small region where the swirl ratio is large and the pilot injection pressure is high. It was below 5 MPa / ° CA. Further, as shown in FIG. 5C, a region where the swirl ratio is less than 2.1 and the pilot injection pressure is relatively low, and a part of the region where the swirl ratio is greater than 2.5 and the pilot injection pressure is low. It was found that the amount of soot generated can be reduced.
From the above results, the maximum pressure increase rate during combustion is 0.5 MPa / ° CA, and the region where the amount of soot can be reduced is within the broken line region shown in FIGS. I found out. In particular, it was found that if the swirl ratio is in the range of 2.1 to 2.5, the amount of combustion noise and soot generation can be reduced.

Next, FIG. 6 is a diagram showing a verification result in a medium load operation state, where (A) is a swirl ratio-pilot injection pressure map of a maximum pressure increase rate (dp / dθ) max during pilot combustion, (B) is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max during main combustion, and (C) is a swirl ratio-pilot injection pressure map of soot generation degree.
As shown in FIG. 6A, in the medium load operation state, the maximum pressure increase rate (dp / dθ) max at the time of pilot injection is 0.5 MPa except for a part of the region where the pilot injection pressure is high. / ° CA. As shown in FIG. 6B, the maximum pressure increase rate (dp / dθ) max during main combustion was less than 0.5 MPa / ° CA because the swirl ratio was 2.1 to 2.5 and the pilot injection pressure was 75 MPa or less. Further, as shown in FIG. 6C, except for a region where the swirl ratio is less than about 2 and a region where the pilot injection pressure is less than 45 MPa (except for a region where the swirl ratio is 3.1 or more), It was found that the amount of soot generated can be reduced.
From the above results, the maximum pressure increase rate during combustion is 0.5 MPa / ° CA, and the region where the amount of soot can be reduced is within the broken line region shown in FIGS. 6B and 6C. I found out. Specifically, it was found that the swirl ratio was about 2.1 to 2.5 and the pilot injection pressure was in the range of 45 MPa to 75 MPa (the pilot injection pressure ratio was about 20% to about 30%).

Next, FIG. 7 is a diagram showing a verification result in a high-load operation state, in which (A) is a swirl ratio-pilot injection pressure map of a maximum pressure increase rate (dp / dθ) max during pilot combustion, (B) is a swirl ratio-pilot injection pressure map of maximum pressure increase rate (dp / dθ) max during main combustion, and (C) is a swirl ratio-pilot injection pressure map of soot generation degree.
As shown in FIG. 7A, in the high load operation state, the maximum pressure increase rate (dp / dθ) max during pilot combustion in the entire region as compared with the low load operation state and the medium load operation state described above. Was larger than 0.5 MPa / ° CA in almost all regions. From this result, it was found that when single pilot injection is executed in a high load operation state, a problem of combustion noise occurs during pilot combustion. Therefore, it was suggested that it is effective to perform the double pilot injection in the high load operation state.
Further, the maximum pressure increase rate during main combustion is 0.5 MPa / ° CA or less, and the region where the amount of soot can be reduced is within the broken line region shown in FIGS. 7B and 7C. Was suggested.

To summarize the above verification results, the swirl ratio is about 2.1 to 2.5 in the low load operation state and the medium load operation state except for the high load operation state in which the problem of combustion noise occurs in the single pilot injection. And the pilot injection pressure ratio is in the range of approximately 20% to approximately 30%, it was verified that the maximum pressure increase rate during main combustion is 0.5 MPa / ° CA or less and the amount of soot generated can be reduced. .
In addition, said swirl ratio 2.1-2.5 is a swirl ratio normally employ | adopted as a preferable swirl ratio of the shallow dish type combustion chamber used for the said embodiment and the said verification. For this reason, in low-temperature combustion near the top dead center where NOx can be reduced, by controlling the single pilot injection pressure ratio from approximately 20% to approximately 30% without actively controlling the swirl ratio, combustion noise and soot are reduced. It can be said that the generation amount of can be reduced.

Next, the relationship between the injection pressure and the injection amount was verified in the region where the combustion noise and the soot generation amount verified above can be simultaneously reduced.
Table 3 shows an example of the injection pressure and the injection amount of the pilot injection and the injection pressure and the injection amount of the main injection in the region where the combustion noise and the soot generation amount verified as described above can be simultaneously reduced. . As for the high-load operation state, an example in which double pilot injection in which the first pilot injection and the second pilot injection are sequentially performed is shown. The burned gas generated by the first pilot injection and the second pilot injection are shown. This shows an example in which the injection timing is set so that the fuel injected in step S3 overlaps with the burned gas generated by the second pilot injection and the fuel injected in the main injection.

FIG. 8 is a diagram showing the relationship between the ratio of the pilot injection pressure to the main injection pressure and the main injection amount based on the data shown in Table 3. As shown in FIG. 8, the pilot injection pressure is set lower than the main injection pressure, and the ratio of the pilot injection pressure to the main injection pressure is set lower as the main injection amount increases. It can be seen that the amount of soot generated can be reduced simultaneously. Here, in FIG. 8, the larger the main injection amount, the more the engine is in a high load operation state, and the smaller the main injection amount, the lower the load operation state. Therefore, it can be seen that the combustion noise and the soot generation amount can be simultaneously reduced by setting the ratio of the pilot injection pressure to the main injection pressure low as the engine load increases.
In the high-load operation state in which the double pilot injection is performed, the ratio of the first pilot injection pressure to the main injection pressure is set low as the main injection amount increases, and the second pilot injection pressure to the main injection pressure is set. It can be seen that by setting the ratio low, combustion noise and soot generation can be simultaneously reduced.

  FIG. 9 is a diagram showing the relationship between the pilot injection amount ratio and the main injection amount based on the data shown in Table 3. As shown in FIG. 9, it can be seen that combustion noise and soot generation can be simultaneously reduced by setting the pilot injection amount ratio higher as the main injection amount decreases. That is, it can be seen that the combustion noise and the soot generation amount can be simultaneously reduced by setting the pilot injection amount ratio high as the engine load decreases. This is because in low-load operation conditions where the oxygen partial pressure is low, such as low supercharging operation or high EGR operation, if the pilot injection amount is small, the pilot combustion does not occur and combustion occurs simultaneously with the main combustion, and the pressure rise cannot be suppressed. This is because pilot combustion is generated by increasing the pilot injection amount ratio. 8 and 9, it can be seen that it is preferable to increase the pilot injection pressure ratio as the pilot injection amount ratio increases.

Next, it verified about the point which can reduce a combustion noise more by setting the aspect-ratio of a combustion chamber to 3.3 or more.
Specifically, in the above-described single cylinder engine, the maximum pressure increase rate (dp / dθ) max during main combustion when the aspect ratio of the combustion chamber was changed was examined. The injection conditions of the pilot injection and the main injection were the same as those in the medium load operation state in Table 3.

  FIG. 10 is a diagram showing the maximum pressure increase rate (dp / dθ) max during main combustion when the aspect ratio of the combustion chamber is changed, and (A) is the one when the aspect ratio is 3.3. Yes, when (B) has an aspect ratio of 2.9. From these figures, when the aspect ratio of the combustion chamber is 3.3, the maximum pressure increase rate (dp / dθ) max may be lower than the upper limit of 0.5 MPa / ° CA at which the target combustion noise can be achieved. When the aspect ratio is less than 3.3, it can be seen that the maximum pressure increase rate (dp / dθ) max exceeds 0.5 MPa / ° CA. From this result, it was verified that the combustion noise can be further reduced by setting the aspect ratio of the combustion chamber to 3.3 or more.

DESCRIPTION OF SYMBOLS 1 ... Fuel-injection control apparatus 3 ... Engine (internal combustion engine)
5 ... Fuel injection valve 10 ... ECU (Pilot injection means, swirl means, main injection means, fuel injection control means, high load operation state determination means)
33 ... Piston 37 ... Combustion chamber 73 ... Swirl control valve (swirl means)
335 ... Piston lip 337 ... Step (stepped structure)
513 ... nozzle hole

Claims (6)

A fuel injection control device for an internal combustion engine that includes a fuel injection valve that injects fuel into a combustion chamber from a nozzle hole provided at a tip and is capable of variably controlling an injection pressure,
Pilot injection means for performing pilot injection by the fuel injection valve and generating burned gas in the combustion chamber;
Swirl means for generating a swirl flow in the combustion chamber and causing the burned gas to flow by the swirl flow;
Main injection means for performing main injection by the fuel injection valve in the combustion chamber generated by the burned gas;
Fuel injection control means for controlling the injection timing and injection pressure of the pilot injection and the main injection,
The fuel injection control means includes
The injection timing is controlled so that the burned gas generated by the pilot injection from the adjacent nozzle holes and flowing by the swirl flow and the fuel injected by the main injection overlap, and the pilot injection A fuel injection control device for an internal combustion engine, wherein the injection pressure is controlled so that an injection pressure falls within a predetermined range lower than an injection pressure of the main injection.   The fuel injection control means controls the injection pressure so that a ratio of an injection pressure of the pilot injection to an injection pressure of the main injection decreases as the load of the internal combustion engine increases. The fuel injection control device according to 1. The fuel injection control device further includes a high load operation state determination unit that determines whether or not the internal combustion engine is in a predetermined high load operation state,
When it is determined that the internal combustion engine is not in the predetermined high load operation state, the pilot injection means performs single pilot injection that performs the pilot injection once,
The fuel injection control means controls the injection pressure so that a ratio of an injection pressure of the single pilot injection to an injection pressure of the main injection is in a range of approximately 20% to approximately 30%. The fuel injection control device for an internal combustion engine according to claim 1 or 2. The fuel injection control device further includes a high load operation state determination unit that determines whether or not the internal combustion engine is in a predetermined high load operation state,
The pilot injection means, when it is determined that the internal combustion engine is in the predetermined high-load operation state, performs a double pilot injection that sequentially performs a first pilot injection and a second pilot injection;
The fuel injection control means includes the burned gas generated by the first pilot injection and the fuel injected by the second pilot injection, and the burned gas generated by the second pilot injection, 3. The fuel injection control apparatus according to claim 1, wherein the injection timing is controlled so that the fuel injected in the main injection overlaps.   The fuel injection control device according to any one of claims 1 to 4, wherein an aspect ratio of the combustion chamber is 3.3 or more.   6. The fuel injection control device according to claim 1, wherein the piston lip portion forming the combustion chamber has a stepped structure.