JP2000145522A - Control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress a generating rate of a harmful material without deteriorating durability of an engine by controlling an operation of fuel injection means, and carrying out first and second injection operations at places where a crank rotating angle is a specified angle position before a compression top dead point and near a compression top dead point. SOLUTION: When an engine 17 is operated, in an ECU 21, a target load is found out on the basis of an acceleration opening and engine rotating speed, it is judged whether an operating condition of the engine is in an execution region of two step injection or not on the basis of engine rotating speed and the target load. In the case where the operating condition is in the execution region of two step injection, an auxiliary injection rate Q1 and a main injection rate Q2 are calculated, and two step injection is executed. Namely, fuel is injected from an injector 18 by the auxiliary injection rate Q1 at a place where a rotating angle of a crankshaft is 100 deg. to 40 deg. before a compression top dead point, and fuel is injected near the compression top dead point by the main injection rate Q2. It is thus possible to suppress that fuel is stuck on an inner wall of a cylinder so as to reduce the generation of black smoke and NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a diesel engine which performs two fuel injections in one cycle of combustion.

[0002]

2. Description of the Related Art A diesel engine is widely known as an internal combustion engine in which fuel is directly injected into a cylinder. This diesel engine does not spark-ignite like a gasoline engine, but injects fuel directly into air heated to a high temperature by high compression to spontaneously ignite. However, in this diesel engine, at high load, a large amount of fuel is injected into the combustion chamber in order to increase the engine output. Oxygen and nitrogen combine in the atmosphere to form nitrogen oxides (NOx), and these harmful substances are contained in the exhaust gas.

[0003] In order to prevent the generation of black smoke and nitrogen oxides in the combustion chamber, Japanese Patent Application Laid-Open No.
There is one disclosed in Japanese Patent No. 36945. "Combustion method in diesel engine" disclosed in this publication
Performs a first combustion injection by combustion injection means into combustion air sucked in during an intake stroke to generate an air-fuel mixture, compresses the air-fuel mixture in a compression stroke, and then burns the air-fuel mixture at an appropriate time near a compression top dead center. The fuel is burned by performing a second combustion injection by the injection means to obtain an explosion, and the explosion stroke and the exhaust stroke are performed.

Therefore, by injecting the fuel in the intake stroke in advance, the fuel is completely vaporized in the compression stroke to be in a mixed gas state suitable for combustion, and complete combustion can be obtained.
Further, since a small amount of combustion is injected near the compression top dead center, it is possible to ideally and integrally perform complete combustion. Therefore, generation of black smoke and generation of nitrogen oxides can be suppressed.

[0005]

However, in the above-mentioned conventional "combustion method in a diesel engine", the first fuel injection is performed in a low-temperature intake stroke.
In this intake stroke injection, since the temperature in the cylinder is much lower than the boiling point of the fuel, the fuel adheres to the wall surface without being vaporized during flying. The fuel deposited on the wall is then vaporized by the in-cylinder temperature that rises with the compression, forming an air-fuel mixture. However, a rich air-fuel mixture is generated at the wall-deposited portion, causing premature ignition and knocking. Problem.
There is also a problem that part of the first injected fuel adheres to the cylinder liner to dilute the engine oil and reduce engine durability. For this reason, at present, the effect of suppressing generation of black smoke and nitrogen oxide has not been sufficiently obtained.

SUMMARY OF THE INVENTION The present invention solves such a problem, and controls a diesel engine in which generation of harmful substances is suppressed without deteriorating engine durability by performing two fuel injections at appropriate times. It is intended to provide a device.

[0007]

According to the present invention, there is provided a diesel engine control apparatus for achieving the above-mentioned object by controlling fuel injection means for directly injecting fuel into a combustion chamber and controlling the operation of the fuel injection means. Fuel injection control means for performing the first injection and the second injection at a crankshaft rotation angle of 100 ° to 40 ° before the compression top dead center and in the vicinity of the compression top dead center is provided.

Therefore, the first injection is performed when the crankshaft rotation angle is 100 ° to 40 ° before the compression top dead center, and then the second injection is performed near the compression top dead center, so that the fuel injected to the cylinder liner or the like can be obtained. It is possible to stabilize combustion while suppressing the generation of harmful substances while suppressing the adhesion of harmful substances.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration of a control system for a diesel engine according to an embodiment of the present invention, FIG. 2 is a graph showing sub injection timing, FIG. 3 is a graph showing main injection and sub injection ranges, and FIG. 3 shows a flowchart of control by the control device for the diesel engine of the embodiment.

In the control apparatus for a diesel engine according to the present embodiment, as shown in FIG. 1, reference numeral 11 denotes a fuel tank, which has a fuel filter 12 and a low-pressure fuel pump 13. A high-pressure fuel pump 15 is connected to a feed path 14a of a fuel passage 14 connected to the low-pressure fuel pump 13, and a common rail 16 as an accumulator is connected downstream of the high-pressure fuel pump 15; 16 is provided with four injectors 18 as fuel injection means for injecting fuel into four combustion chambers of an engine 17. Each injector 18 is connected to the fuel tank 11 by a return path 14 b of the fuel path 14. Return paths 14c and 14d are connected to the upstream side of the high-pressure fuel pump 15 and the common rail 16 in the supply path 14a of the fuel passage 14, respectively. Control valves 19 and 20 are connected to the return paths 14c and 14d, respectively. It is installed.

Accordingly, the low-pressure fuel pump 13 pressurizes the fuel in the fuel tank 11 to some extent, and
4a, and the low-pressure fuel is further pressurized by the high-pressure fuel pump 15 to increase the fuel pressure to a predetermined pressure. At this time, the discharge pressure from the low-pressure fuel pump 13 is stabilized to a predetermined range by the low-pressure control valve 19, and the discharge pressure from the high-pressure fuel pump 15 is further stabilized to a predetermined range by the high-pressure control valve 20. And the common rail 16
The fuel of a predetermined pressure is supplied from each injector 18 of the engine 1
A predetermined amount is injected into each combustion chamber 7.

An electronic control unit (ECU) 21 having a function of a fuel injection control means has an accelerator opening APS.
, The engine speed Ne and the engine coolant temperature WT are input.
A target load Pe is determined based on the engine speed Ne and the engine speed Ne, an air-fuel ratio, a fuel injection amount, and the like are determined based on the engine speed Ne and the target load Pe, and fuel injection is performed at a predetermined injection timing. It has become. Further, a pressure sensor 22 is mounted on the common rail 16, and the detected value is determined by the ECU.
21 is input.

By the way, as shown in FIG.
21 is a crankshaft rotation angle of 100 ° before compression top dead center
In the vicinity of the compression top dead center of ２40 °, two-stage injection for performing the first injection and the second injection from the injector 18 is executed. That is, the ECU 21 determines that the crankshaft rotation angle is between 100 ° and 40 ° before the compression top dead center (in the present embodiment, 6 degrees).
0 °), an early sub-injection (first injection) is performed, and then a main injection (second injection) is performed near the compression top dead center. Engine 1
The in-cylinder (combustion chamber) temperature of the cylinder 7 rises from the intake stroke to the compression stroke, reaches the highest temperature at the compression top dead center, and the self-ignition temperature in the cylinder increases because the in-cylinder pressure increases in the compression stroke. It is descending toward.

[0015] Therefore, while the in-cylinder temperature is somewhat high and the fuel is easily vaporized, the sub-injection is performed at a time when the self-ignition temperature is lower than the self-ignition temperature and the self-ignition is difficult, so that the injected fuel is vaporized immediately to the cylinder inner wall. At the same time, since it is a flying fuel, mixing with air is promoted, a lean mixture can be formed quickly, and premature ignition can be avoided. Also, after that, while the temperature in the cylinder is high and the fuel is easily vaporized, the main injection fuel is vaporized immediately by performing the main injection at a time when self-ignition is likely to occur, and the vaporized fuel at the time of the main injection ignited. Burning the sub-injection fuel,
Combustion can be stabilized. Accordingly, premature ignition of the sub-injected fuel can be prevented, adhesion of the injected fuel to the inner wall of the cylinder can be suppressed, and generation of black smoke and generation of nitrogen oxides can be suppressed.

In the graph of FIG. 2, the in-cylinder temperature indicates the operating state (for example, the presence or absence of an intercooler, the supercharging pressure, the EG
R, compression ratio, etc.) in the range indicated by the two-dot chain line, and the self-ignition temperature of the injected fuel in the cylinder also varies in the boiling point range. What is necessary is just to set suitably in the range of 100 degrees-40 degrees before compression top dead center according to temperature time.

The injection amount of the sub-injection executed between 100 ° and 40 ° before the compression top dead center is determined by the sub-injection amount map shown in FIG. 3 based on the engine speed Ne and the target load Pe. When the boost pressure is high, the high-pressure compressed air is likely to self-ignite due to the output of a boost sensor (not shown). Therefore, the ECU 21 prohibits the two-stage injection. Is also good.

Here, a specific control by the control apparatus for a diesel engine of the present embodiment described above will be described with reference to FIG.
A description will be given based on the flowchart of FIG.

In step S1, the accelerator pedal opening AP
S and the engine speed Ne are read, and in step S2, it is determined whether or not the current operating state of the engine is in the execution region of the two-stage injection. That is, the ECU 21 determines the target load P based on the accelerator opening APS and the engine speed Ne.
e is determined, and is determined based on the sub-injection amount map shown in FIG. 3 based on the engine speed Ne and the target load Pe. Note that, as described above, the determination may be made based on the engine coolant temperature WT.

Then, if it is determined in step S2 that it is not in the execution region of the two-stage injection, the process proceeds to step S3,
ECU21 computes the main injection amount Q _2, at step S4, by performing a single-stage injection for injecting a main injection amount Q ₂ from the injector 18 to a predetermined injection axis.

On the other hand, if it is determined in step S2 that the engine is in the execution region of the two-stage injection, the process proceeds to step S5, and E
CU21 calculates a sub injection amount Q ₁ and the main injection amount Q _2, at step S6, the execution of the two-stage injection. That is, the compression top dead center 100 ° sub injection amount Q ₁ from the injector 18 to 40
° In injected and injected at the compression top dead center near the main injection amount Q _2.

As described above, in the control apparatus for a diesel engine according to the present embodiment, the temperature in the cylinder is high and the fuel is liable to vaporize, but is difficult to spontaneously ignite.
The sub-injection is performed at a timing of ° to 40 °, and thereafter the main injection is performed at a time when the temperature in the cylinder is high and the fuel is likely to vaporize and self-ignite. Therefore, the injected fuel at the time of the sub-injection evaporates immediately to suppress the adhesion to the inner wall of the cylinder, and it is possible to prevent a decrease in the amount of fuel actually contributing to the combustion. By igniting by mixing with the vaporized fuel, combustion can be stabilized, knock can be prevented, and generation of black smoke and generation of nitrogen oxides can be suppressed.

[0023]

As described in detail in the above embodiment, according to the control apparatus for a diesel engine of the present invention, the rotation angle of the crankshaft is from 100 ° before compression top dead center.
By performing the first injection and the second injection in the vicinity of the compression top dead center at 40 °, the fuel is immediately vaporized due to the high in-cylinder temperature during the first injection, and the premature ignition occurs simultaneously with the suppression of the adhesion to the inner wall of the cylinder. In addition to preventing the occurrence of knocking due to the fuel, the fuel vaporized immediately at the time of the second injection mixes with the fuel vaporized at the time of the sub-injection and ignites, thereby stabilizing the combustion to generate black smoke and generate nitrogen oxides. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a control device for a diesel engine according to an embodiment of the present invention.

FIG. 2 is a graph showing main injection and sub injection timings.

FIG. 3 is a graph showing a sub-injection region.

FIG. 4 is a flowchart of control performed by the diesel engine control device according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Fuel tank 13 Low pressure fuel pump 14 Fuel passage 14a Supply path 14b, 14c, 14d Return path 15 High pressure fuel pump 16 Common rail 17 Engine 18 Injector (fuel injection means) 20 Electronic control unit, ECU (Fuel injection control means)

Claims (1)

[Claims] 1. A fuel injection means for directly injecting fuel into a combustion chamber, and an operation of the fuel injection means is controlled so that a crankshaft rotation angle becomes 100 ° to 40 ° before a compression top dead center and near a compression top dead center. And a fuel injection control means for performing a first injection and a second injection.