JPH10274086A - Fuel injection control device for diesel engine - Google Patents

Abstract

(57) [Problem] To improve the startability of an engine by performing pilot injection and main injection at the time of engine start, and further improving the ignitability by the pilot injection. SOLUTION: In a diesel engine, a period from cranking at the time of engine start to an increase in engine speed due to a complete explosion is determined by a start determination means 31, and an injection control means 33 controls the starting fuel during the period. As the injection, a plurality of pilot injections are performed, and then the main injection is performed. Of these pilot injections, the injection start timing of the final pilot injection closest to the main injection is 30 ° before the top dead center in crank angle. Control is performed so as to be performed thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control apparatus for a diesel engine in which a main injection is performed by a fuel injection means and a pilot injection for injecting a small amount of fuel prior to the main injection at the time of engine start. It is.

[0002]

2. Description of the Related Art Conventionally, various types of diesel engine fuel injection devices in which pilot injection is performed prior to main injection at the time of engine startup are known.

For example, in the apparatus disclosed in Japanese Patent Application Laid-Open No. 62-75047, first, pilot injection is performed, and whether or not ignition has been performed by the pilot injection is determined based on a signal from an ignition sensor. If the ignition is not performed, the main injection is performed, but if the ignition is not performed, the main injection is stopped to prevent a large amount of unburned gas from being discharged and to suppress the generation of white smoke and smoke. .

[0004]

In the apparatus disclosed in the above publication, the main injection is stopped when the ignition is not performed by the pilot injection in order to prevent deterioration of the emission when a misfire occurs at the start. However, it is not intended to enhance the ignitability, and does not exert a sufficient effect in accelerating the starting. This publication also discloses that the pilot injection is performed a plurality of times, but does not particularly consider a setting effective for promoting the start.

In view of such circumstances, the present invention can improve the startability of the engine by further improving the ignitability by the pilot injection while performing the pilot injection and the main injection at the time of engine start. A fuel injection control device for a diesel engine is provided.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a fuel injection control apparatus for a diesel engine in which a main injection is performed by a fuel injection means and a pilot injection for injecting a small amount of fuel prior to the main injection at the time of engine start. And
During the period from the start of cranking at the time of starting the engine to the rise of the engine speed due to the complete explosion, as the starting fuel injection, a plurality of pilot injections are performed, and then the main injection is performed. Injection control means is provided for controlling the injection start timing of the final pilot injection closest to the main injection among the injections to be 30 ° or more before the top dead center in crank angle.

[0007] According to this configuration, in the fuel injection for starting performed during the period from the start of cranking at the time of starting the engine to the rise of the engine speed due to the complete explosion, of the multiple pilot injections, the fuel injection in the combustion chamber is included. The fuel from the pilot injection performed relatively early before the pressure rises to an ignitable level is mixed with the air in the combustion chamber to form a premixed gas, after which the pressure in the combustion chamber can ignite After that, the final pilot injection is performed. At this time, the pre-mixed air by the previously injected fuel burns relatively rapidly in a short time, so-called pre-mixed combustion is performed, and the ignitability is enhanced by the pre-mixed combustion, and the fuel by the later injection is used. By performing so-called diffusion combustion by gradually burning and diffusing from an unmixed state, the combustion period is extended, the combustion is continued until the main injection timing, and the combustion of the main injection fuel is achieved. Thus, the startability is enhanced.

[0008] In the present invention, it is preferable that the injection amount is set so as to increase as the side closer to the main injection in a plurality of pilot injections in the starting fuel injection. In this manner, in the pilot injection performed earlier, the fuel is reduced in a range necessary for forming the air-fuel mixture for the premixed combustion, while in the pilot injection close to the main injection, the combustion is reliably performed by the main injection. Fuel that can be sustained until the time is provided.

If the final pilot injection of the plurality of pilot injections in the fuel injection for starting is performed before the top dead center, and the main injection is started after the top dead center, the main injection can be performed. The combustion by the injection surely acts on the engine as positive work, and the start is efficiently promoted.

Further, it is effective to set the first pilot injection of the plurality of pilot injections in the fuel injection for starting to be performed at a timing before the crank angle of 30 ° before the top dead center. , A premixed gas is formed.

[0011]

FIG. 1 shows an embodiment of a fuel injection control device for a diesel engine according to the present invention. In this figure, reference numeral 1 denotes an engine body of a diesel engine, which includes a plurality of cylinders 2. A fuel injection device for injecting fuel into the combustion chamber of each cylinder 2 is provided for the engine body 1, and in this embodiment, a so-called common rail type fuel injection device is provided. That is, each cylinder 2 is provided with an injection nozzle (fuel injection means) 3 for performing fuel injection by operating a needle valve by a solenoid in accordance with a control signal, and a high-pressure cylinder. Each of the injection nozzles 3 is connected to a common rail 4 that stores the fuel.

The common rail 4 is connected to a fuel pump 6 via a fuel passage 5, and the pump 6 is connected to a fuel tank (not shown). The high-pressure fuel pumped from the fuel pump 6 is supplied to each injection nozzle 3 via the common rail 4. The fuel passage 5 is provided with a pressure regulating valve 7 as a pressure regulating means for regulating the pressure of the fuel sent to the common rail 4 to regulate the injection pressure of the injection nozzle 3, and the pressure regulating valve according to a control signal. The above operation allows the injection pressure to be changed. Further, a pressure sensor 8 is provided on the common rail 4, and the pressure sensor 8 detects the injection pressure.

An intake manifold 11 downstream of the intake passage 10 and an exhaust manifold 13 upstream of the exhaust passage 12 are connected to the engine body 1. A compressor of the turbocharger 15 is provided in the middle of the intake passage 10, and a turbine of the turbocharger 15 is provided in the middle of the exhaust passage 12.

In the turbocharger 15, the turbine is driven by the energy of the exhaust gas, and the turbocharger 15 supercharges the intake air by rotating the compressor in conjunction with the turbine. In this embodiment, in particular, the turbine blades can be expanded and contracted. A variable supercharging pressure turbo is used which has a structure capable of increasing the supercharging performance from a low-speed region to a high-speed region by expanding and contracting the turbine blade according to a state. The turbocharger 15 is provided with a supercharging pressure controller 16 that adjusts a supercharging pressure according to a control signal.

The turbocharger 1 in the intake passage 10
An intercooler 17 for cooling the supercharged air is provided downstream of the compressor No. 5, and an air flow meter 18 for detecting an intake air amount is provided upstream of the compressor. On the other hand, a catalyst 19 for purifying exhaust gas is provided downstream of the turbine of the turbocharger 15 in the exhaust passage 12.

Further, the exhaust passage 12 and the intake passage 10
Between the EGR passage 2 for recirculating exhaust gas to the intake system
0 is provided, and an EGR valve 23 for controlling an EGR amount is provided in the EGR passage 20. The EGR valve 23 is operated by an EGR valve controller 24. In this embodiment, the above E
The first EGR passage 21 and the second EGR passage 21 are disposed on the exhaust passage side of the GR passage 20.
An EGR passage 22 is formed, and one of the passages 21 and 22 is opened to the intake passage side or both passages are closed via the EGR valve 23.

The first EGR passage 21 is connected to the exhaust manifold 13 or an upstream portion of the exhaust passage near the exhaust manifold 13 so as to recirculate exhaust gas having a small temperature drop in the exhaust passage. It is opened at times. The second EGR passage 22 is provided in the exhaust passage 12 so that relatively low-temperature exhaust gas can be recirculated.
Is connected to the downstream side.

The injection nozzle 3, pressure regulating valve 7, supercharging pressure controller 16 and EGR valve controller 24
Are controlled by a control unit (ECU) 30. The control unit 30 receives detection signals from the pressure sensor 8 and the air flow meter 18, a rotation speed sensor 25 for detecting an engine rotation speed, an accelerator opening sensor 26 for detecting an amount of depression of an accelerator pedal, Detection signals from a water temperature sensor 27 for detecting the engine water temperature, a catalyst temperature sensor 28 for detecting the catalyst temperature, an ignition switch 29a, a starter switch 29b and the like are also input.

FIG. 2 is a functional block diagram showing a control system. In this figure, the control unit 30
Includes a start determination unit 31, a temperature state determination unit 32, an injection control unit 33, and an EGR control unit.

The start judging means 31 judges a start state based on signals from the ignition switch 29a, starter switch 29b, rotation speed sensor 25 and the like. That is, when starting the engine, as shown in FIG. 3, the ignition switch 29a from being the ON (t ₀ time) First, the starter switch 29b is ON (t
Engine by being a _one time) is cranking is rotated at very low rotation is started by the starter, from the rose engine speed slightly by the engine of the initial explosion (t ₂ time) during the cranking, further when reaches the complete combustion (t ₃ time points) in the engine speed rapidly increases, rises to the fast idle rotation speed if the engine is cold. The start determination means 31 examines such behavior of the engine, and determines a state before cranking and a state during a period (t _{1 to} t ₃ ) from the start of cranking to the time when the engine speed increases due to complete explosion. And the state after the complete explosion.

The temperature state discriminating means 32 discriminates, based on signals from the water temperature sensor 27 and the catalyst temperature sensor 28, whether the engine is in a cold start or a warm start, and determines whether the catalyst 19 is in a cold state. It is determined whether the engine is in a warm-up state.

The injection control means 33, based on the determination by the start determination means 31 and the temperature state determination means 32,
During the period from the start of cranking to the point when the engine speed increases due to the complete explosion, the main injection is performed after a plurality of pilot injections are performed as the starting fuel injection. A specific example of the control of the starting fuel injection will be described with reference to FIG.

In the example shown in FIG. 4, two pilot injections A and B are performed prior to the main injection C. In the following description, the first pilot injection A and B will be described in order to distinguish these pilot injections A and B. The injection is referred to as split injection A, and the second pilot injection is simply referred to as pilot injection B.

The split injection A is performed before the pressure in the combustion chamber rises to a ignitable pressure in the compression stroke.
For example, BTDC 30 ° CA (30 degrees before top dead center at crank angle)
°). Pilot injection B above
Is TDC (top dead center) after BTDC 30 ° CA
Done earlier. Main injection C is started after TDC.

Further, the injection amount of the split injection A and the pilot injection B is made smaller than the injection amount of the main injection C, and the injection amount of the pilot injection B is made larger than that of the split injection A. In other words, the injection amount of the split injection A is reduced within a range necessary for forming an air-fuel mixture for premixed combustion as described later in detail, while the pilot injection B
In order to ensure that fuel that can be maintained until the main injection timing is obtained, the injection amount is increased compared to the split injection A.

As shown in the flow chart of FIG. 5 described later, in this embodiment, in addition to the above-described control of the fuel injection for starting, when the catalyst is in a cold state after the complete combustion of the engine, the main injection C A post-stroke injection D indicated by a broken line in FIG. 4 is performed from the subsequent expansion stroke to the compression stroke.

The EGR control means 34, based on the discrimination by the start discriminating means 31 and the temperature state discriminating means 32, starts from the start of cranking during the cold start to the time when the engine speed increases due to complete explosion. During the period, the EGR valve controller 24 is controlled so that the first EGR passage 21 is opened to the intake passage 10.

Therefore, in this embodiment, as shown in FIG. 3, from the start of cranking to the complete explosion at the time of cold start, the multi-stage injection (split, pilot and main injection) and the first EGR passage 21 are performed. EGR is performed, and multi-stage injection and post-stroke injection are performed until a warm-up state occurs after a complete explosion.

Next, an example of control of fuel injection at the time of starting by the apparatus of this embodiment will be described with reference to the flowchart of FIG.

The process shown in this flowchart is started by turning on the ignition switch 29a (step S1). First, an engine water temperature and a catalyst temperature are input (step S2). It is determined whether the start is a warm start or a warm start (step S3).

If it is determined that the engine is a cold start, then if it is determined in step S4 that the starter has been turned on, the main injection timing T, the required injection amount Q and the injection pressure at the time of startup are determined in step S5. P is determined according to the water temperature and the like, and in step S6, the injection pattern is determined so that the split injection A, the pilot injection B, and the main injection C are performed. That is, each injection A,
The timings of B and C and the injection amounts are determined, and the injections A, B and C are executed. In addition, such fuel injection control is performed, and in step S7, the first EGR
The solenoid of the EGR valve 23 is controlled so that the passage 21 is opened.

Subsequently, in step S8, the engine speed and its angular velocity fluctuation are examined, and based on this, the process proceeds to step S9.
It is determined whether or not a complete explosion has occurred, and the processes of steps S5 to S8 are repeated until the complete explosion is reached.

When it is determined in step S9 that the complete explosion has been reached, the solenoid of the EGR valve 23 is controlled so that the EGR passage is closed in step S10. The injection timing is determined, and the post-stroke injection D is executed in step S11. Further, the catalyst temperature is detected in step S13, and it is determined whether or not the catalyst temperature has risen to a predetermined warm-up temperature in step S14. If the catalyst temperature is lower than the warm-up temperature, the processing in steps S11 to S13 is performed. Repeated. When it is determined in step S14 that the catalyst temperature has reached the warm-up temperature, the process proceeds to step S15, in which an idle map operation, which is a control state during normal idle operation, is performed.

On the other hand, if it is determined in step S3 that the engine is a warm start, then in step S16 the starter O is started.
When it is determined that N has been reached, the main injection timing T at the start, the required injection amount Q, and the injection pressure P are determined according to the water temperature and the like in step S17, and in step S18,
The injection pattern is determined so that the split injection A, the pilot injection B, and the main injection C are performed. Then, the fuel injection is controlled based on this injection pattern, and in step S19, the solenoid of the EGR valve 23 is controlled so that the EGR passage is closed.

Subsequently, in step S20, the engine speed and its angular velocity fluctuation are checked, and based on this, the step S20 is executed.
At 21 it is determined whether or not a complete explosion has occurred, and the processes of steps S17 to S20 are repeated until the complete explosion. When it is determined in step S21 that a complete explosion has occurred,
Moving to step S15, an idle map operation, which is a control state during normal idle operation, is performed.

According to the apparatus of the present embodiment as described above,
During the period from the start of cranking at the time of engine start until complete explosion (period t ₁ ~t ₃ in FIG. 3), as starting fuel injection, so that the split injection A, pilot injection B and the main injection C are sequentially performed Injection pattern.

In this injection pattern, first, split injection A is performed at a time substantially before the top dead center of the compression stroke. At this time, the in-cylinder pressure is relatively low, and ignition does not occur. Piston 4 as shown by the two-dot chain line
1 is relatively far from the top dead center, the injected fuel is injected into the main combustion chamber 4 formed on the piston upper surface 41.
The fuel gas spreads outward from the cylinder 1 and adheres to the piston top surface and the cylinder wall surface outside the main combustion chamber 41. Thereafter, the fuel gradually evaporates to form a premixed gas (flammable mixture) in the combustion chamber.

Next, after BTDC 30 ° CA, TDC
During this time, the pilot injection B is performed, and at this time, the piston 40 has risen to a position close to the top dead center as shown by the solid line in FIG. 6, so that fuel is injected into the main combustion chamber 41. At the same time, since the pressure inside the cylinder has increased to the level at which ignition is possible, the premixed air that already exists burns relatively quickly in a short period of time, so-called premixed combustion enhances ignitability. Can be Along with the ignition by the premixed combustion, so-called diffusion combustion is performed in which the fuel injected into the main combustion chamber 41 gradually diffuses while burning from an unmixed state.

In this case, the premixed combustion is completed in a short time, but the diffusion combustion using this as the ignition is performed relatively slowly, so that the combustion period is extended and the combustion is continued until after the top dead center. I do. Then, by performing the main injection while the combustion by the pilot injection B is sustained, the combustion of the fuel of the main injection is achieved.

In this way, ignition and combustibility at the time of starting are enhanced, and starting is promoted. Further, the injection amount of the pilot injection B is smaller than that of the main injection C, and the injection amount of the split injection A is even smaller than that of the pilot injection B, as long as a premixed gas for ignition is formed. By igniting and burning satisfactorily with relatively little fuel, and by starting the main injection after the top dead center,
Combustion from the main injection acts on the engine as positive work. By these actions, compared with the conventional device,
The starting torque is earned with a small amount of fuel, and the starting is promoted efficiently.

Further, by promoting the starting in this manner, deterioration of the emission due to misfiring at the time of starting is suppressed.

Further, in the apparatus of the present embodiment, the first E
Since the GR passage 21 is opened, it is more advantageous to improve startability. That is, when a misfire occurs, the unburned gas is discharged to the exhaust passage 12, but the unburned gas is returned from the first EGR passage 21 to the combustion chamber through the intake passage 10, so that the unburned gas is discharged in the next compression stroke. Like the split injection A, it forms a premixed gas, which contributes to the improvement of ignitability. Further, when combustion is performed, the exhaust gas having a relatively high temperature is recirculated, and the recirculated gas increases the in-cylinder temperature, so that the effect of promoting the start can be obtained.

When shifting to the first idling operation after the complete explosion, the EGR is stopped, so that the deterioration of the combustibility (generation of smoke) due to the EGR during the first idling operation in which the fuel is increased to increase the engine speed. Invitation is avoided.

After the complete explosion during cold start, the catalyst 1
When the engine 9 is in a cold state, a small amount of fuel is injected during the period from the expansion stroke to the exhaust stroke after the main injection, so that a small amount of fuel due to the subsequent stroke injection raises the temperature of the catalyst. , The catalyst 19 is warmed up early.

In the above embodiment, two pilot injections (split injections A) prior to the main injection C during the period from the start of cranking when the engine is started to the complete explosion.
And pilot injection B), but three or more pilot injections may be performed. In this case as well, at least the final pilot injection is BTDC 30 °.
It may be performed after CA and before TDC.

The control of the EGR and the like is not limited to the above embodiment. For example, the first EGR passage 21 may be opened from a cranking to a complete explosion even during a warm start.

[0047]

As described above, the fuel injection control apparatus for a diesel engine according to the present invention performs a plurality of pilot injections during the period from cranking to complete explosion at the time of engine start, and then performs the main injection. In addition, since the injection start timing of the final pilot injection is controlled so as to be at least 30 ° before the top dead center in crank angle, the ignitability is increased while the ignitability is increased by the premixed combustion of the fuel injected earlier. The fuel of the pilot injection is diffused and combustion is maintained until the main injection timing, so that the combustion of the fuel of the main injection can be achieved. This increases the starting torque,
Startability can be greatly improved.

In the present invention, in particular, of the plurality of pilot injections in the starting fuel injection, the injection amount is set so as to be larger toward the side closer to the main injection. By setting the final pilot injection of the pilot injection before the top dead center and setting the main injection to start after the top dead center, the start can be efficiently promoted.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram showing the overall configuration of a diesel engine fuel injection control device according to the present invention.

FIG. 2 is a functional block diagram showing a configuration inside a control unit.

FIG. 3 is an explanatory diagram showing a change in the rotational speed and a change in a control state after the engine is started.

FIG. 4 is a diagram showing a fuel injection pattern and an injection timing when the engine is started.

FIG. 5 is a flowchart showing a fuel injection control operation at the time of starting the engine.

FIG. 6 is an explanatory diagram showing a state during a split injection and a pilot injection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 3 Injection nozzle 25 Engine speed sensor 27 Water temperature sensor 29a Ignition switch 29b Starter switch 30 Control unit 31 Start-up determination means 33 Injection control means

Claims (4)

[Claims] 1. A fuel injection control device for a diesel engine in which a main injection is performed from fuel injection means and a pilot injection for injecting a small amount of fuel prior to the main injection at the time of engine start. During the period from the start of cranking until the engine speed rises due to a complete explosion, as the starting fuel injection, a plurality of pilot injections are performed, and then the main injection is performed. A fuel injection control device for a diesel engine, comprising injection control means for controlling the injection start timing of the final pilot injection closest to the main injection so as to be 30 ° or more before top dead center in crank angle. 2. The fuel injection control device for a diesel engine according to claim 1, wherein, out of a plurality of pilot injections in the fuel injection for starting, the injection amount is set closer to the side closer to the main injection. 3. The method according to claim 1, wherein a final pilot injection of a plurality of pilot injections in the fuel injection for starting is performed before a top dead center, and a main injection is started after a top dead center. The fuel injection control device for a diesel engine according to claim 1 or 2. 4. The method according to claim 1, wherein the first pilot injection of the plurality of pilot injections in the starting fuel injection is performed at a timing before the crank angle of 30 ° before the top dead center. Item 3. A fuel injection control device for a diesel engine according to item 1 or 2.