JP2009114889A - Fuel injection control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology capable of inhibiting dilution of lubricating oil while inhibiting increase of combustion noise in a fuel injection control system for an internal combustion engine provided with a fuel injection valve capable of injecting fuel directly into a cylinder. <P>SOLUTION: In a fuel injection control system for an internal combustion engine provided with a fuel injection valve injecting fuel directly into the cylinder, a pressure increasing process for increasing injection pressure of post injection as compared to injection pressure of main injection is executed when the fuel injection valve need to do post injection after doing main injection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection control technique for an internal combustion engine provided with a fuel injection valve capable of injecting fuel into a cylinder.

In an internal combustion engine in which a fuel injection valve directly injects fuel into a cylinder, a technique has been proposed for increasing the fuel injection pressure when the dilution of lubricating oil (engine oil) by the injected fuel becomes high (for example, Patent Documents). 1).
JP-A-10-317936 JP 2001-241370 A JP 2003-269291 A

  By the way, when the fuel injection pressure is increased, vaporization and atomization of fuel injected from the fuel injection valve (hereinafter referred to as “injected fuel”) is promoted, so that dilution of the lubricating oil can be reduced. Although it is possible, there is a problem that the injected fuel burns sharply and generates a large combustion noise.

  The present invention has been made in view of various circumstances as described above, and an object thereof is to provide combustion noise in a fuel injection control system for an internal combustion engine having a fuel injection valve capable of directly injecting fuel into a cylinder. The present invention provides a technology capable of suppressing the dilution of the lubricating oil while suppressing the increase in the amount of oil.

  In the present invention, in order to solve the above-described problem, when post injection is performed after the fuel injection valve performs main injection, only the injection pressure of post injection is increased.

  More specifically, the present invention relates to a fuel injection control system for an internal combustion engine having a fuel injection valve that directly injects fuel into a cylinder, and when the fuel injection valve performs post injection after performing main injection, Control means for performing a pressure increasing process for increasing the injection pressure of the post injection with respect to the injection pressure of the injection is provided.

  The dilution of the lubricating oil becomes significant when the fuel (injected fuel) injected from the fuel injection valve adheres to the cylinder bore wall surface. The injected fuel adhering to the cylinder bore wall surface (hereinafter referred to as “wall surface adhering fuel”) increases when fuel injection is performed at a timing when the piston is separated from the top dead center. As fuel injection performed at such timing, post injection can be exemplified.

  Therefore, if the wall-attached fuel during post injection can be reduced, dilution of the lubricating oil can be effectively suppressed. As a method for reducing the fuel adhering to the wall surface, a method for promoting vaporization / atomization of the injected fuel is effective. As a method for promoting vaporization / atomization of the injected fuel, a method for increasing the fuel injection pressure can be exemplified.

  However, when the injection pressure of the main injection (hereinafter referred to as “main injection pressure”) is increased together with the injection pressure of the post injection (hereinafter referred to as “post injection pressure”), the fuel injected by the main injection burns sharply. Therefore, the contradiction that the combustion noise becomes large occurs.

  In contrast, the fuel injection control system for an internal combustion engine according to the present invention increases the post injection pressure with respect to the main injection pressure (preferably, only the post injection pressure is increased without changing the main injection pressure). The fuel adhering to the wall surface can be reduced while avoiding an increase in noise. As a result, it is possible to suppress dilution of the lubricating oil while suppressing an increase in combustion noise.

  When the temperature of the cylinder bore wall surface or the atmospheric temperature in the cylinder is high, the fuel adhering to the wall surface decreases and most of the wall surface adhering fuel desorbs (evaporates) from the cylinder bore wall surface. Therefore, when the temperature of the cylinder bore wall surface or the atmospheric temperature in the cylinder is high, the pressure increasing process may not be performed. Further, the post-injection pressure at the time of executing the pressure increasing process may be lowered as the temperature of the cylinder bore wall surface or the atmospheric temperature in the cylinder increases.

  The fuel injection control system for an internal combustion engine according to the present invention may include an acquisition unit that acquires the dilution degree of the lubricating oil by the injected fuel. In this case, the control means may not perform the pressure increasing process if the dilution degree of the lubricating oil is less than the allowable limit.

  By the way, the number of post injections per cycle is not limited to one and may be multiple times. In the case where a plurality of post injections are performed per cycle, it is preferable that the control means perform a pressure increasing process such that the injection pressure becomes higher as the post injection whose injection timing is delayed.

  The later the timing of post injection, the lower the pressure in the cylinder. The lower the pressure in the cylinder, the easier it is for the injected fuel to reach the cylinder bore wall surface. On the other hand, the fuel adhering to the wall surface can be surely reduced when the injection pressure is increased in the post-injection with later injection timing.

  In the fuel injection control system for an internal combustion engine according to the present invention, the control means may increase the post injection pressure as the ratio of the post injection amount to the main injection amount increases.

  The main injection pressure tends to be set lower as the amount of main injected fuel (main injection amount) decreases. Therefore, if the amount of increase in the post injection pressure relative to the main injection pressure (the difference between the main injection pressure and the post injection pressure) is made constant regardless of the main injection amount (main injection pressure), the post injection pressure is reduced when the main injection amount is small. There is a possibility that the injection pressure becomes excessively low.

  On the other hand, when the post injection pressure is increased as the ratio of the post injection amount to the main injection amount increases, the post injection pressure when the main injection amount is small can be sufficiently increased. As a result, even when the main injection amount is small, the wall surface attached fuel can be reduced.

  In the present invention, as a specific execution method of the pressure increasing process, a method in which the lift amount of the needle valve at the time of post injection is larger than the lift amount of the needle valve at the time of main injection can be exemplified.

  According to the present invention, in a fuel injection control system for an internal combustion engine provided with a fuel injection valve capable of directly injecting fuel into a cylinder, dilution of lubricating oil can be suppressed while suppressing an increase in combustion noise.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a fuel injection control system for an internal combustion engine according to the present invention.

  An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders.

  A piston 3 is slidably inserted into the cylinder 2 of the internal combustion engine 1. A combustion chamber 4 is formed above the piston 3 in the cylinder 2. The internal combustion engine 1 includes an intake port 5 and an exhaust port 6 that communicate with the combustion chamber 4.

  The intake port 5 communicates with the intake passage 50. The exhaust port 6 communicates with the exhaust passage 60. The internal combustion engine 1 includes an intake valve 7 that opens and closes an open end of an intake port 5 that faces the combustion chamber 4, and an exhaust valve 8 that opens and closes an open end of the exhaust port 6 that faces the combustion chamber 4.

  The internal combustion engine 1 includes a fuel injection valve 9 that directly injects fuel into the cylinder 2. The fuel injection valve 9 communicates with the common rail 11 via the delivery pipe 10.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 12. The ECU 12 electrically controls the fuel injection valve 9 and the like according to output signals from various sensors such as the water temperature sensor 13 and the rail pressure sensor 14. The water temperature sensor 13 is a sensor that measures the temperature of the cooling water circulating in the internal combustion engine 1, and the rail pressure sensor 14 is a sensor that measures the fuel pressure (rail pressure) stored in the common rail 11.

  For example, the ECU 12 determines the injection amount and injection timing of pilot injection and main injection according to the operating conditions determined from the output signals of various sensors, and controls the fuel injection valve 9 according to the determined injection amount and injection timing.

  Further, the ECU 12 needs to raise the temperature of the exhaust gas or supply fuel as a reducing agent to an exhaust gas purification device (not shown) (for example, a particulate filter or a NOx catalyst) disposed in the exhaust passage 60. When there is, for example, the fuel injection valve 9 is controlled so that post injection is performed in addition to pilot injection and main injection.

  Incidentally, the post injection is performed when the piston 3 is separated from the top dead center in the expansion stroke or the exhaust stroke. Therefore, post-injected fuel (hereinafter referred to as “post-injected fuel”) tends to adhere to the inner wall surface (cylinder bore wall surface) of the cylinder 2. The fuel adhering to the cylinder bore wall surface (the wall surface adhering fuel) may dilute the lubricating oil without desorbing (evaporating) from the cylinder bore wall surface. When the dilution of the lubricating oil proceeds, the lubricating oil may not be able to exhibit a desired lubricating performance.

  In order to solve such a problem, it is conceivable to increase the fuel injection pressure to promote the vaporization / atomization of the injected fuel, thereby reducing the wall-attached fuel. As a specific method for increasing the fuel injection pressure, a method for increasing the rail pressure of the common rail 11 is generally used.

  However, when the rail pressure is increased, not only the post injection pressure but also the main injection pressure is increased. If the main injection pressure is increased carelessly, the main injected fuel (hereinafter referred to as “main injected fuel”) burns sharply, which may increase combustion noise.

  Therefore, in this embodiment, when the fuel injection valve 9 needs to perform post injection, the ECU 12 performs a pressure increasing process for increasing only the post injection pressure without increasing the main injection pressure or the pilot injection pressure. I made it.

  Here, a specific execution method of the boosting process will be described. FIG. 2 is a diagram showing a schematic configuration of the fuel injection valve 9.

  The fuel injection valve 9 includes a nozzle body 100 in which a cylinder 101 is formed, and a needle valve 200 that can reciprocate in the cylinder 101 in the axial direction.

  A sack 103 protrudes from the tip of the cylinder 101 (lower end in FIG. 2) via a conical valve seat 102. A plurality of nozzle holes 104 are formed in the sac 103.

  The needle valve 200 includes a valve shaft 201 having an outer diameter smaller than that of the cylinder 101. A valve body 202 having a conical shape is formed at the tip of the valve shaft 201 (the lower end in FIG. 1), like the valve seat 102.

  A large-diameter shaft portion 203 having an outer diameter larger than the outer diameter of the valve shaft 201 and slightly smaller than the inner diameter of the cylinder 101 is formed in the middle of the valve shaft 201. The base end (the upper end in FIG. 1) of the valve shaft 201 is in contact with the spring 300. The spring 300 biases the needle valve 200 in the valve closing direction (downward in FIG. 1).

  A fuel reservoir 400 is formed between the valve shaft 201 on the distal end side of the large-diameter shaft portion 203 and the cylinder 101. A control chamber 500 is formed between the valve shaft 201 on the base end side of the large-diameter shaft portion 203 and the cylinder 101.

  The nozzle body 100 is formed with a fuel supply path 600 for supplying high-pressure fuel to the fuel reservoir 400 and the control chamber 500. The fuel supply path 600 communicates with the common rail 11 via the delivery pipe 10 described above.

  Further, the nozzle body 100 is provided with a pressure reducing mechanism 700 that adjusts the pressure in the control chamber 500. The decompression mechanism 700 includes, for example, a passage for releasing the fuel in the control chamber 500 to the outside of the control chamber 500 (for example, a fuel tank) and a valve mechanism that opens and closes the passage. The opening and closing of the valve mechanism is electrically controlled by the ECU 12.

  In the fuel injection valve 9 configured as described above, the high-pressure fuel stored in the common rail 11 is supplied to the fuel reservoir 400 and the control chamber 500 via the delivery pipe 10 and the fuel supply path 600. The fuel pressure and the fuel pressure in the control chamber 500 are equalized.

  Therefore, when the pressure reducing mechanism 700 does not release the fuel in the control chamber 500, the needle valve 200 is pressed in the valve closing direction by the biasing force of the spring 300, and the valve body 202 is seated on the valve seat 102 (that is, closed). Valve state).

  On the other hand, when the decompression mechanism 700 releases the fuel in the control chamber 500, the fuel pressure in the control chamber 500 decreases. When the fuel pressure in the fuel reservoir 400 becomes higher than the sum of the fuel pressure in the control chamber 500 and the biasing force of the spring 300, the fuel pressure in the fuel reservoir 400 displaces the needle valve 200 in the valve opening direction. As a result, the valve body 202 is separated from the valve seat 102 (that is, the valve is opened).

  Thereafter, when the decompression mechanism 700 stops releasing the fuel, the fuel pressure in the control chamber 500 returns to a pressure equivalent to the fuel pressure in the fuel pool 400 by the high-pressure fuel supplied from the fuel supply path 600 to the control chamber 500. As a result, the needle valve 200 receives the biasing force of the spring 300 and returns to the valve closing position.

  Here, when the fuel injection valve 9 is opened, the fuel passes through a narrow gap formed between the valve body 202 and the valve seat 102, and the pressure loss at that time is caused by the valve body 202 and the valve seat 102. The smaller the gap, the smaller. This means that the injection pressure increases as the lift amount of the needle valve 200 increases.

  The lift amount of the needle valve 200 varies depending on the magnitude of the difference between the fuel pressure in the control chamber 500 and the fuel pressure in the fuel reservoir 400 (hereinafter referred to as “control differential pressure”). For example, the lift amount of the needle valve 200 decreases as the control differential pressure decreases.

  Therefore, the ECU 12 unnecessarily increases the pilot injection pressure and the main injection pressure by controlling the pressure reducing mechanism 700 so that the control differential pressure during post injection becomes larger than the control differential pressure during main injection. The post injection pressure can be increased.

  When the pressure increasing process is performed by such a method, it becomes possible to reduce the fuel adhering to the wall surface without increasing the combustion noise. Therefore, according to the fuel injection control system of the internal combustion engine of the present embodiment, it is possible to suppress the dilution of the lubricating oil without increasing the combustion noise.

  Next, the execution procedure of the boosting process in the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing the boosting processing routine. The boosting process routine is a routine stored in advance in the ROM of the ECU 12 and is periodically executed by the ECU 12.

  In the pressure increasing process routine, the ECU 12 first obtains the control differential pressure ΔPfm of the main injection timing based on the operating conditions (engine speed and engine load) of the internal combustion engine 1 in S101. The relationship between the control differential pressure ΔPfm and the operating conditions may be mapped in advance.

  In S102, the ECU 12 determines whether or not post injection is being performed. If an affirmative determination is made in S101, the ECU 12 proceeds to S103, and if a negative determination is made in S101, the ECU 12 temporarily ends the execution of this routine.

  In S103, the ECU 12 calculates a control differential pressure ΔPfp (= ΔPfm + α) during post injection by adding a predetermined value α to the control differential pressure ΔPfm during main injection. The predetermined value α may be a fixed value obtained experimentally in advance.

  In this case, the ECU 12 controls the pressure reducing mechanism 700 according to the control differential pressure ΔPfm acquired in S101 at the time of main injection, and the pressure reducing mechanism 700 according to the control differential pressure ΔPfp calculated at S103 at the time of post injection. Will be controlled.

  Thus, the control means concerning this invention is implement | achieved when ECU12 performs a pressure | voltage rise process routine. As a result, it is possible to suppress dilution of the lubricating oil without increasing the combustion noise.

The wall surface adhering fuel decreases as the temperature of the cylinder bore wall surface and the atmospheric temperature in the cylinder 2 increase, and easily desorbs (evaporates) from the cylinder bore wall surface. Therefore, the pressure increasing process as described above may be performed only when the temperature of the cylinder bore wall surface or the atmospheric temperature in the cylinder 2 is low. At this time, the temperature of the cylinder bore wall surface and the atmospheric temperature in the cylinder 2 correlate with the temperature of the cooling water temperature (measured value of the water temperature sensor 13), so the ECU 12 has a measured value of the water temperature sensor 13 lower than a predetermined reference temperature. Only in some cases, the boosting process may be performed.

  Further, the amount of the fuel adhering to the wall surface that can dilute the lubricating oil decreases as the temperature of the cylinder bore wall surface or the atmospheric temperature in the cylinder 2 increases. Therefore, the predetermined value α is set to a larger value as the cooling water temperature decreases. May be.

  Further, when the dilution degree of the lubricating oil can be acquired, the pressure increasing process may be performed only when the dilution degree reaches the allowable limit.

<Example 2>
Next, a second embodiment of the present invention will be described. Here, a configuration different from the first embodiment described above will be described, and the description of the same configuration will be omitted.

  In the present embodiment, a method for executing the boosting process when post injection is performed a plurality of times per cycle will be described.

  When a plurality of post injections are performed per cycle, the later the injection timing, the more easily the injected fuel reaches the cylinder bore wall surface. This is because the pressure in the cylinder 2 decreases as the injection timing is delayed.

  Therefore, in the pressure increasing process of the present embodiment, the ECU 12 does not uniformly increase the injection pressure of a plurality of post injections, but controls the pressure reducing mechanism 700 so that the post injection with a later injection timing becomes higher in injection pressure. I made it. Specifically, the value of the predetermined value α described above may be increased as the post-injection is delayed.

  When the pressure increasing process is performed by such a method, it is possible to reduce the fuel adhering to the wall surface even when post injection is performed a plurality of times per cycle. Therefore, even when a plurality of post injections are performed per cycle, it is possible to suppress the dilution of the lubricating oil while avoiding an increase in combustion noise.

<Example 3>
Next, a third embodiment of the present invention will be described. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the present embodiment, an example will be described in which the magnitude of the control differential pressure is changed in accordance with the amount of main injected fuel (main injection amount).

  The fuel pressure (rail pressure) stored in the common rail 11 may be lowered as the main injection amount decreases. Therefore, when the difference between the main injection pressure and the post injection pressure (in other words, the magnitude of the control differential pressure) is made constant regardless of the main injection amount (in other words, the rail pressure), the main injection amount is small. In addition, the post injection pressure may be excessively lowered.

  Therefore, in the pressure increasing process of the present embodiment, the ECU 12 sets the pressure reducing mechanism 700 so that the control differential pressure increases as the ratio of the post injection amount to the main injection amount increases (in other words, the main injection amount decreases). I tried to control it. Specifically, the value of the predetermined value α described above may be increased as the ratio of the post injection amount to the main injection amount increases.

In this case, even if the rail pressure is low, the post injection pressure can be sufficiently increased. As a result, even when the main injection amount is small, the wall surface attached fuel can be reduced.

  Therefore, according to the fuel injection control system of the internal combustion engine of the present embodiment, it is possible to more reliably suppress the dilution of the lubricating oil caused by the post injection.

  In this embodiment, the fuel injection valve 9 capable of changing the lift amount of the needle valve 200 by adjusting the differential pressure (control differential pressure) between the fuel reservoir 400 and the control chamber 500 is illustrated. Of course, it is not limited to an injection valve. The point is that the fuel injection valve may have any configuration as long as the lift amount of the needle valve can be changed.

It is a figure which shows schematic structure of the fuel-injection control system of an internal combustion engine. It is a figure which shows schematic structure of a fuel injection valve. It is a flowchart which shows a pressure | voltage rise process routine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Piston 4 ... Combustion chamber 5 ... Intake port 6 ... Exhaust port 9 ... .... Fuel injection valve 10 ... Delivery pipe 11 ... Common rail 12 ... ECU
DESCRIPTION OF SYMBOLS 100 ... Nozzle body 101 ... Cylinder 102 ... Valve seat 103 ... Sack 104 ... Injection hole 200 ... Needle valve 201 ... Valve shaft 202 ... Valve body 203 ... Large-diameter shaft portion 300 ... Spring 400 ... Fuel pool 500 ... Control chamber 600 ... Fuel supply path 700 ... Pressure reduction mechanism

Claims (5)

In a fuel injection control system for an internal combustion engine provided with a fuel injection valve for directly injecting fuel into a cylinder,
An internal combustion engine comprising control means for performing a boosting process for increasing the injection pressure of the post injection with respect to the injection pressure of the main injection when the fuel injection valve performs the post injection after performing the main injection Fuel injection control system. The acquisition unit according to claim 1, further comprising an acquisition unit configured to acquire a degree of dilution of the lubricating oil by the fuel injected from the fuel injection valve,
The fuel injection control system for an internal combustion engine, wherein when the degree of dilution acquired by the acquisition unit is less than an allowable limit, the control unit does not perform the boosting process.   3. The fuel injection control for an internal combustion engine according to claim 1, wherein when the post-injection is performed a plurality of times per cycle, the control means increases the injection pressure as the post-injection has a later injection timing. system.   4. The fuel injection control system for an internal combustion engine according to claim 1, wherein the control means increases the injection pressure of the post injection as the ratio of the post injection amount to the main injection amount increases. In any one of Claims 1-4, the said fuel injection valve is a valve which opens and closes an injection hole by the lift operation | movement of a needle valve,
2. The fuel injection control system for an internal combustion engine according to claim 1, wherein the boosting process is a process of making the lift amount of the needle valve at the time of post injection larger than the lift amount of the needle valve at the time of main injection.

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