JP2002038995A - Fuel injection device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform split injection of a fuel in a diesel engine without impairing combustion stability. SOLUTION: In the injection of a fuel near the top dead center of a cylinder in compression strokes it is split into plurality of times by a fuel injection valve 5 for keeping on combustion with fuel injection but if an engine is estimated to be low in-cylinder temperature condition, the split injection form of the fuel is changed or is injected in a lump, instead of split injection, so that an injection finishing time is made earlier than in the case that it is estimated to be in a high temperature condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for a diesel engine having a fuel injection valve for directly injecting fuel into a combustion chamber in a cylinder.

[0002]

2. Description of the Related Art In a diesel engine of this kind, a fuel required for one combustion cycle is collectively injected near a top dead center of a compression stroke (hereinafter, referred to as a collective injection). Accordingly, pilot injection for injecting a small amount of fuel is performed prior to the batch injection. On the other hand, there is also known a divided injection in which the fuel is not injected in a lump but is injected a plurality of times near the top dead center of the compression stroke.

[0003] For example, Japanese Patent Application Laid-Open No. 9-209866 describes that split injection is started from the top dead center of the compression stroke, and the injection amount of each injection is increased in later injections. The purpose is to control the heat release rate in the combustion chamber in a wide and appropriate manner. JP-A-10-122084
The publication discloses that a pre-injection of a small amount of fuel is performed to cause ignition in a combustion chamber, and a subsequent main injection is divided into a plurality of injections to generate soot and NOx (nitrogen oxide). It is stated that the amount is reduced.

Japanese Patent Application Laid-Open No. 10-141124 discloses a preliminary injection for injecting fuel at an early stage of an intake stroke, a main injection for injecting fuel near a top dead center of a compression stroke, and a pilot injection before main injection. By doing so, partial lean premixed compression ignition combustion is performed, reducing the emission of black smoke and improving fuel efficiency while suppressing the generation of NOx, and only the main injection when starting the engine in cold weather. It is described that ensuring startability and suppressing excessive generation of white smoke.

[0005]

Proper split injection in a diesel engine as described above is advantageous for controlling the rate of heat generation in the combustion chamber and reducing flue gas and NOx. However, if split injection is performed when the in-cylinder temperature is low, for example, when the engine is started, combustion becomes unstable, leading to deterioration of startability and emission characteristics. This is because, when the fuel is divided and injected, a predetermined injection suspension time (a period from the time when the fuel injection valve is closed to the time when it is next opened) must be provided, so that the end of the fuel injection is delayed. This is because the temperature in the cylinder becomes considerably low.

[0006] In addition, during low rotation and low load operation such as during idling operation, pilot injection for the purpose of reducing combustion noise and pre-injection for injecting fuel from the intake stroke to the first half of the compression stroke as premixed compression ignition combustion are performed. May be At this time, the injection start timing may be retarded to increase the exhaust gas temperature in order to improve the exhaust gas purification efficiency by the catalyst, but even in this case, if the fuel split injection is executed, the end of the fuel injection is considerable. And its flammability deteriorates.

[0007] The present invention is to solve such a problem.

[0008]

For this purpose, the present invention provides
Split injection of fuel is appropriately suppressed or prohibited.

That is, the present invention provides a fuel injection valve disposed so as to face an in-cylinder combustion chamber of an engine, required output detecting means for detecting required output of the engine, and detection by the required output detecting means. Injection amount determining means for determining a fuel injection amount in accordance with the result, wherein the fuel having the injection amount determined by the injection amount determining means is supplied to the fuel injection valve near the top dead center of the compression stroke of the cylinder, and In a fuel injection device for a diesel engine that injects the fuel in a plurality of times so that the combustion by the injection continues, a temperature state estimating means for estimating a state related to the level of the in-cylinder temperature of the engine, and the temperature state estimating means When it is estimated that the engine is in a predetermined low temperature state with respect to the in-cylinder temperature, the fuel injection end timing is earlier than when it is estimated that the engine is in a high temperature state. As, characterized in that it comprises a injection mode changing means for the injection mode for injecting collectively without dividing the split in the form of injection change or fuel of the fuel.

Accordingly, when the in-cylinder temperature of the engine is high and flammability is good, split injection is executed to improve emission performance, improve fuel efficiency, increase exhaust pressure (improve supercharging), and reduce exhaust gas. When the in-cylinder temperature of the engine is low while obtaining the desired effect such as a rise in temperature, the end of the fuel injection is advanced by changing the split injection mode or prohibiting the split injection, which is advantageous for ensuring combustion stability. In other words, it is possible to avoid deterioration of emission properties such as generation of soot. The injection end timing may be set so as not to exceed, for example, 35 ° CA after the top dead center of the compression stroke during the low engine load operation, and to not exceed 45 ° CA after the top dead center of the compression stroke during the high engine load operation.

The level of the in-cylinder temperature can be estimated based on, for example, whether a predetermined time has elapsed since the start of the engine or based on the temperature of the engine cooling water.

Further, the present invention provides a fuel injection valve disposed so as to face an in-cylinder combustion chamber of an engine, required output detecting means for detecting required output of the engine, and detection by the required output detecting means. An injection amount determining means for determining a fuel injection amount according to the result, wherein the fuel having the injection amount determined by the injection amount determining means is injected by the fuel injection valve near the top dead center of the compression stroke of the cylinder. And a fuel injection mode in which a small amount of fuel is injected by the fuel injection valve before the main injection, and the fuel of the injection amount is burned as the main injection. Split injection that is split into multiple injections to continue,
In the fuel injection device for a diesel engine having the simultaneous injection of the fuel of the injection amount, the injection period from the start to the end of the main injection does not perform the early injection when the early injection is performed. It is characterized by comprising an injection mode changing means for changing the mode of the split injection so as to shorten the time, or adopting the mode of the batch injection instead of the split injection.

That is, the present invention changes the injection mode depending on whether pilot injection or pre-injection for premixed compression ignition combustion is performed instead of estimating the in-cylinder temperature. Specifically, when such early injection is performed, the form of split injection is changed such that the injection period from the start to the end of main injection is shortened, or the form of collective injection is adopted instead of split injection. Things. Thus, during idling operation in which early injection is performed or during low engine speed operation, the end timing of fuel injection can be advanced to ensure combustion stability.

When the start timing of the main injection is delayed in conjunction with the early injection, the change of the injection form is particularly useful. That is, it is possible to prevent the end timing of the fuel injection from being delayed even when the start timing of the main injection is delayed.

The change of the form of the split injection can be executed by reducing the number of splits or by shortening the injection pause time from when the fuel injection valve is closed to when it is opened again.

[0016]

As described above, according to the present invention, when the in-cylinder temperature of the engine is low, when the early injection is performed, and when the main injection start timing is delayed together with the early injection, By changing the fuel split injection mode or prohibiting the split injection, the end timing of the fuel injection is prevented from being delayed.In normal times, the split injection is executed to improve emission performance, improve fuel efficiency, and reduce exhaust pressure. When priority should be given to ensuring combustion stability while obtaining the desired effects of split injection, such as an increase (improvement of supercharging) and an increase in exhaust gas temperature, the end timing of fuel injection should be advanced to degrade flammability. Can be avoided, which is advantageous for improving emission characteristics such as reduction of soot generation.

[0017]

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

FIG. 1 shows the overall configuration of a fuel injection device A for a water-cooled diesel engine according to an embodiment of the present invention.
Is an engine body of a multi-cylinder diesel engine mounted on a vehicle. The engine body 1 has a plurality of cylinders 2 (1
Only one piston is shown in each cylinder 2.
Are inserted so as to be able to reciprocate, and a combustion chamber 4 is formed in each cylinder 2 by the cylinder 2 and the piston 3. An injector (fuel injection valve) 5 is disposed substantially at the center of the upper surface of the combustion chamber 4 with the injection hole at the tip end facing the combustion chamber 4, and the injection hole is provided at a predetermined injection timing for each cylinder. Are opened and closed to inject fuel directly into the combustion chamber 4.

Each of the injectors 5 is connected to a common common rail (accumulator) 6 for storing high-pressure fuel.
A high-pressure supply pump 8 driven by a crankshaft 7 is connected to the common rail 6. The high-pressure supply pump 8 operates so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at a predetermined value or more. A crank angle sensor 9 for detecting a rotation angle of the crank shaft 7 is provided.
Is composed of a plate to be detected (not shown) provided at the end of the crankshaft 7 and an electromagnetic pickup arranged opposite to the outer periphery thereof, and the electromagnetic pickup is provided around the entire outer periphery of the plate to be detected. A pulse signal is output in response to the passage of the projections formed at predetermined angles.

Reference numeral 10 denotes an intake passage for supplying intake air (air) filtered by an air cleaner (not shown) to the combustion chamber 4 of the engine body 1. At a downstream end of the intake passage 10, a surge tank (not shown) is provided. Each passage branched from the surge tank is connected to each cylinder 2 by an intake port.
Are connected to the combustion chamber 4. The surge tank is provided with an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2. The intake passage 10 includes, in order from the upstream side to the downstream side, a hot film type air flow sensor 11 for detecting a flow rate of intake air sucked into the engine body 1, and a blower 12 driven by a turbine 21 to compress the intake air. And an intercooler 13 for cooling the intake air compressed by the blower 12 and an intake throttle valve (intake air amount adjusting means) 14 for reducing the sectional area of the intake passage 10. The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described below, the magnitude of the negative pressure acting on the diaphragm 15 is negative pressure. The opening degree of the valve is controlled by being adjusted by the control electromagnetic valve 16. Further, the intake throttle valve 1
4 is provided with a sensor (not shown) for detecting the opening degree.

Reference numeral 20 denotes an exhaust passage for discharging exhaust gas from the combustion chamber 4 of each cylinder 2 and is connected to the combustion chamber 4 of each cylinder 2 via an exhaust manifold. The exhaust passage 20 includes, in order from the upstream side to the downstream side, a linear O2 sensor 17 for detecting the oxygen concentration in the exhaust gas, a turbine 21 rotated by the exhaust flow, and HC and CO in the exhaust gas.
And a catalytic converter 22 capable of purifying NOx.

An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake side is branched from a portion of the exhaust passage 20 upstream of the turbine 21, and a portion downstream of the EGR passage 23. The end is connected to the intake passage 10 downstream of the intake throttle valve 14. Near the downstream end in the middle of the EGR passage 23, an exhaust gas recirculation amount adjusting valve (intake air amount adjusting means: hereinafter referred to as an EGR valve) whose opening degree can be adjusted.
A part of the exhaust gas is recirculated to the intake passage 10 while adjusting a flow rate of the exhaust gas in the exhaust passage 20 by the EGR valve 24.

The EGR valve 24 is of a negative pressure responsive type, and a negative pressure passage 27 is connected to a negative pressure chamber of the valve box. The negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. The negative pressure passage 27 is controlled by a control signal (current) from an ECU 35 described later. By opening and closing 27, the negative pressure for driving the EGR valve in the negative pressure chamber is adjusted, whereby the opening of the EGR passage 23 is linearly adjusted.

The turbocharger 25 is a VGT (Variable Geometry Turbo), to which a diaphragm 30 is attached, and a solenoid valve 3 for negative pressure control.
By adjusting the negative pressure acting on the diaphragm 30 by 1, the sectional area of the exhaust gas passage is adjusted.

Each of the injectors 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25
Are operated by a control signal from a control unit (Engine Control Unit: hereinafter referred to as ECU) 35. On the other hand, the ECU 35 receives the output signal from the pressure sensor 6a, the output signal from the crank angle sensor 9, the output signal from the pressure sensor 10a, the output signal from the air flow sensor 11, and the output signal from the O2 sensor 17. An output signal, an output signal from the temperature sensor 18, an output signal from the lift sensor 26 of the EGR valve 24, and an accelerator opening sensor for detecting an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle. 3
2 and at least an output signal from a sensor (not shown) for detecting the engine coolant temperature.

The fuel injection amount (fuel supply amount) and the fuel injection timing (ignition timing) of the injector 5 are controlled in accordance with the operation state of the engine body 1, and the common rail pressure by the operation of the high-pressure supply pump 8, ie, the common rail pressure, The fuel injection pressure is controlled, and in addition, the EGR valve 24 is controlled.
And the operation control of the turbocharger 25 (VGT control).

(Fuel Injection Control) The ECU 35 stores a target torque map in which the optimum value of the target torque is experimentally determined and recorded with respect to changes in the accelerator opening (engine load) and the engine speed, and the target torque map. A fuel injection amount map in which an optimum fuel injection amount Q experimentally determined according to changes in the torque and the rotation speed is recorded and provided electronically in a memory. Normally, the accelerator opening based on the output signal from the accelerator opening sensor 32 and the crank angle sensor 9
A target torque is obtained based on the engine speed based on the output signal from the ECU, a fuel injection amount Q is obtained based on the target torque and the engine speed, and the common rail pressure detected by the fuel injection amount Q and the pressure sensor 6a is calculated. On the basis of the,
The excitation time (valve opening time) of each injector 5 is determined. After correcting the fuel injection amount obtained as described above according to the engine water temperature, the atmospheric pressure, and the like,
The fuel injection amount after this correction may be used as the fuel injection amount Q.

By the basic fuel injection control as described above, a quantity of fuel corresponding to the target torque of the engine 1 (the required output to the engine 1) is supplied, and the average air-fuel ratio in the combustion chamber 4 of the engine 1 is reduced. Pretty lean (A / F ≧
18) It is operated in the state. The accelerator opening sensor 3
2 and the crank angle sensor 9 correspond to required output detecting means for detecting required output to the engine 1.

A feature of the present invention is that the fuel injection amount Q determined on the basis of the result of detection by the required output detecting means is controlled by the injector 5 near the top dead center of the compression stroke of the cylinder and the combustion by fuel injection is performed. Combustion stability is achieved by splitting the fuel into multiple injections so as to continue, and by changing the split injection mode or prohibiting the split injection according to the engine operating condition so that the end timing of the main injection is not delayed. In order to improve the emission performance.

-Regarding Split Injection- That is, as shown in FIG. 2A, depending on the operating state of the engine, whether the main injection fuel is injected collectively near the compression top dead center (hereinafter referred to as collective injection) Alternatively, as shown in FIG. 3B, the fuel is divided into two injections (called two-split injection), or as shown in FIG. 3C, the fuel is split into three injections (called three-split injection). ) Is selected. When the fuel is divided into two or three injections in such a manner, the injection suspension time Δt during the injection is changed so that the fuel consumption performance and the exhaust characteristics of the engine 1 are optimized. The combustion state is changed. In addition, during the idling operation or low-speed operation of the engine, pilot injection (early injection) is performed, and the main injection start timing is retarded (retarded).

In the fuel injection modes shown in FIGS. 2A to 2C, the actual excitation time (valve opening time) of the injector 5 is detected not only by the fuel injection amount but also by the pressure sensor 6a. Determined by taking into account the common rail pressure that has been applied.

Here, the combustion state when the main injection is divided will be described. When fuel is injected by the injector 5 near the compression top dead center of the cylinder 2, the injector 5
The fuel injected from the orifice of No. spreads into the combustion chamber 4 while forming a spray having a conical shape as a whole, and is divided by the friction with air into fine oil droplets (atomization of the fuel). Fuel evaporates from the surface of the oil droplets to generate fuel vapor (vaporization and atomization of fuel). At this time, the combustion chamber 4
Since the air inside is in a state of extremely high pressure and high viscosity, as shown in FIG. 2 (a), when the fuel is injected in a lump, if the injection amount is large, it is jetted out first. Subsequent fuel oil droplets catch up with the fuel oil droplets and recombine, which may hinder atomization of the fuel and, consequently, vaporization and atomization.

On the other hand, as shown in FIGS. 2 (b) and 2 (c), when the fuel is divided and injected a plurality of times, the fuel oil droplets ejected by the valve opening of the injector 5 can be reduced. In addition, the fuel oil droplets ejected by the next valve opening are less likely to catch up, and it is possible to substantially prevent the atomization of the fuel from being hindered due to the recombination of the oil droplets. Further, it is possible to further increase the fuel injection pressure to further promote the atomization of the fuel, so that the uniformity of the fuel spray distribution in the combustion chamber and the improvement of the air utilization rate can be further improved. Can be enhanced. And the change of the mixing state of the fuel spray and the air by such split injection is the fuel injection amount,
Various parameters such as injection timing, injection rate, fuel pressure, number of divided injections, injection pause time, etc. and their mutual relations also change, and the combustion state changes accordingly, so that the fuel consumption performance and exhaust temperature of the engine 1 are changed. Or C in the exhaust gas
It is considered that the concentration of gas components such as O, HC, and NOx changes.

A four-cylinder diesel engine equipped with a turbocharger similar to that of this embodiment (displacement is about 20
00cc) in a relatively low load and low rotation state (about 1500
rpm), and for each of the batch injection, the two-split injection, and the three-split injection, the injection pause time Δt of the injector 5 is appropriately changed in the range of 350 to 900 microseconds (μs), and the injection changes accordingly. FIG. 3 shows an example of an experimental result obtained by measuring the relationship between the crank angle at the end of the test, the exhaust gas temperature, the exhaust pressure, the fuel efficiency, the amount of smoke (soot), and the like.
10 to FIG.

FIG. 3 shows the test results for the exhaust gas temperature. According to the figure, the exhaust gas temperature is higher in the two-split injection than in the one-shot injection, and the exhaust gas temperature is higher in the three-split injection than in the two-split injection. In the same figure, in the two-split injection and the three-split injection, the exhaust gas temperature is measured while appropriately changing the injection stop time Δt of the injector 5 in the range of 350 to 900 microseconds (μs). If there is, it is understood that the exhaust gas temperature becomes higher when the injection suspension time Δt is extended. In two-split injection, Δt = 350, 400, 700, 900 μs
Are plotted, and for the three-split injection, Δt = 400, 550, 700,
The exhaust gas temperature at 900 μs is plotted.

FIG. 4 shows the test results of the exhaust pressure. It can be seen from FIG. 4 that when the number of divisions of the fuel injection and the injection pause time Δt are increased, the exhaust pressure is increased similarly to the exhaust gas temperature. In other words, if the fuel is divided and injected, the end time of the combustion is delayed by that much, so the exhaust energy naturally increases, and the improvement in the flammability improves the combustion energy itself even with the same amount of fuel. Therefore, both the exhaust gas temperature and the exhaust pressure increase as shown in the test results. If the exhaust energy is increased in this manner, the supercharging capacity of the turbocharger 25 is also improved, so that the supercharging pressure (boost pressure) can be increased as shown in FIG.

FIG. 6 shows a test result of the measurement of the change of the fuel consumption rate in the same manner. As shown in FIG. 6, the fuel consumption rate of the two-split injection is more improved than that of the one-shot injection. It can be seen from the graph that the fuel efficiency is slightly improved when the injection stop time Δt of the injector 5 is short, but deteriorates as the injection stop time Δt increases. this is,
This is because the combustion efficiency is improved and the mechanical efficiency is improved by the split injection, while at the same time the thermal efficiency is lowered. Therefore, it can be said that it is preferable not to delay the end timing of the injection too much.

Further, similarly, the measurement results of the emission amounts of smoke, NOx, CO and HC, which are harmful components in the exhaust gas, are shown in FIGS. 7 to 10, respectively. That is, FIG.
According to the above, in both of the two-split and three-split injections, the smoke amount can be reduced when the injection pause time Δt of the injector 5 is short, while the smoke amount increases as the injection pause time Δt increases. I understand. Also, in the case of NOx shown in FIG. 8, it can be seen that in both the two-split and three-split injections, the longer the injection pause time Δt of the injector 5 can reduce the generation of NOx. Furthermore, as shown in FIG. 9 and FIG. 10, the same tendency as that of smoke is observed in the amounts of CO and HC emissions.

As for the number of divisions, if the number of divisions is set to three as shown in the above figures, the exhaust gas temperature,
The exhaust pressure and the supercharging pressure increase, and the NOx amount decreases. On the other hand, regarding the amount of smoke and CO emission, if the injection stop time Δt of the injector 5 is shortened, it does not increase significantly even if the number of divisions is increased, but may decrease it. In addition, the HC emission is reduced by performing two-split or three-split injection as compared with the one-shot injection.

Hereinafter, a specific fuel injection control procedure will be described.

Control Example 1 FIG. 11 is a flowchart relating to control example 1. This control is executed for each cylinder in synchronization with the crank angle signal.

In step A1 after the start, data such as a crank angle signal, an air flow sensor output, and an accelerator opening are read. In the following step A2, a target torque is set by referring to the map based on the accelerator opening and the engine speed, and the fuel injection amount Q is determined by referring to the map based on the engine speed, the target torque and the intake air amount. To determine. This step A2 constitutes the injection amount determining means.

In the following step A3, a basic injection timing It is set with reference to a map based on the engine speed and the target torque. The basic injection timing It corresponds to the start timing of the main injection (first fuel injection in the case of split injection), and is set before the top dead center of the compression stroke. In addition, since the ignition delay time of the fuel spray is different when the engine water temperature and the engine speed are different, to respond to this, the basic injection timing It becomes smaller as the engine water temperature becomes lower.
Also, the setting is made such that the higher the engine speed, the faster the speed.

In the following step A4, it is determined whether or not the engine has been started, that is, whether or not the combustion has been completed, based on the crank angle signal.
Proceeding to 5, the batch injection of fuel is executed at the fuel injection amount Q determined in step A2 and the injection timing It set in step A3. That is, split injection is prohibited because the temperature in the cylinder of the engine is low, and the engine is reliably started with improved combustion stability.

When the explosion is completed, the routine proceeds to step A6, where it is determined whether or not the engine is in idling operation based on the accelerator opening. That is, when the increasing change speed of the accelerator opening is equal to or more than the predetermined value, it is determined that the engine is in the acceleration operation. If it is during the acceleration operation, the process proceeds to step A7, where three-split injection is set and executed (step A5). That is, the fuel injection amount Q is equally divided and the first injection amount Q
The first injection amount Q2 and the third injection amount Q3 are given, and the injection pause time Δt is relatively long 500 to 1
An optimum value is given from the range of 000 μs. Injection pause time Δ
The reason why t is lengthened is that this increases the exhaust pressure (see FIG. 4), which is advantageous for acceleration.

When the engine is not in the accelerating operation, the process proceeds to step A8, and it is determined whether or not a predetermined time has elapsed since the complete explosion of the engine. That is, the engine determines whether or not the operating state is such that the in-cylinder temperature is high. When the predetermined time has elapsed, it is determined that the in-cylinder temperature is high.

When it is determined in step A8 that the predetermined time has not elapsed (the in-cylinder temperature is low), the flow proceeds to step A5, in which the fuel injection amount Q determined in step A2 is set in step A3. Batch injection of fuel is performed at the injected injection timing It. That is, when the split injection is performed, the fuel injection end timing is delayed and the combustibility deteriorates, so that the split injection is prohibited.

When it is determined in step A8 that the predetermined time has elapsed, the process proceeds to step A9, in which the in-cylinder temperature is low based on the engine coolant temperature (the coolant temperature is 70 ° C. or less or
(When the temperature is 0 ° C. or less). If the cooling water temperature is low, the process proceeds to step A10 to determine whether or not the engine is idling, and if it is the idling operation, the process proceeds to step A11 to set the injection amount and the injection timing to perform pilot injection. I do. The program further proceeds to step A12 to retard the main injection start timing It by the crank angle Ic1, and then proceeds to step A5 to execute pilot injection and main injection (batch injection). Even when the engine is not idling, even when it is determined in step A13 that the engine is running at a low engine speed, the same pilot injection and batch injection are executed.

During idle operation or low-speed operation, pilot injection is performed to reduce engine combustion noise. Further, when pilot injection is performed, the combustion start timing is retarded because combustion properties can be obtained even if the injection start timing is slightly delayed, thereby delaying the injection end timing and raising the exhaust gas temperature to increase the catalyst temperature. The activity of is intended. However, when the cooling water temperature is low and cold, if the split injection is performed, the injection end timing becomes too late, the combustion property deteriorates, and the amount of soot and HC generated increases. Injection is assumed.

If it is determined in step A13 that the engine is not in the low-speed operation, that is, the engine is in the medium-speed or high-speed operation state, the process proceeds to step A14, in which the three-split injection is set and the injection is executed (step A13). A5). That is, the fuel injection amount Q is equally divided and given as the first, second, and third injection amounts Q1, Q2, and Q3, and an optimal value is given as the injection suspension time Δt from the range of 50 to 700 μs. In this case, since the retard of the injection start timing is not performed, the split injection is adopted.

If it is determined in step A9 that the cooling water temperature is high, the process proceeds to step A15, where it is determined whether the engine is idling. If it is idle, the process proceeds to step A16 and the pilot is operated. The injection amount and the injection timing are set to perform the injection. Step A17
, The main injection start timing It is retarded by the crank angle Ic2, and the routine proceeds to step A18, where the injection amounts Q1, Q2 and the injection pause time Δt (5
An appropriate Δt) is set from the range of 0 to 500 μs, and the process proceeds to step A5 to execute the pilot injection and the two-split injection. In addition, even when the engine is not idling, step A
Even when it is determined in step 19 that the operating state is such that the engine speed is low, the same pilot injection and two-split injection are executed.

The reason why the injection is divided into two in step A18 while the injection is divided into three in step A14 is that the main injection start timing It is retarded. That is, 3
In the case of split injection, the end timing of injection becomes too late, so that the two-split injection with a small number of splits is adopted from the viewpoint of securing combustion stability and improving emission characteristics. Step A18 may be a three-split injection that shortens the injection stop time Δt.

The setting of the pilot injection in step A16 is for reducing engine combustion noise.
The retard amount Ic2 of No. 7 is made smaller than the retard amount Ic1 in step A12 in the cold state. This is because the catalyst temperature is low during the idling operation or the low-speed operation, and therefore, the increase in the exhaust gas temperature due to the split injection in step A18 (see FIG. 3) is prioritized for improving the activity of the catalyst. In other words, when the retard amount Ic2 is increased, the injection end timing is further delayed by the split injection, which leads to deterioration of combustibility and generation of soot. Therefore, the retard amount Ic2 here is suppressed to a small range.

If it is determined in step A19 that the engine is not in the low-speed operation, that is, the engine is in the medium-speed or high-speed operation state, the process proceeds to step A14, in which three-split injection is set and the injection is executed (step A19). A5).

In the above control example, the pilot injection is performed only during the idling operation and the low rotation operation. However, the pilot injection is also performed when it is determined in step A13 or A19 that the rotation is the middle rotation or the high rotation operation. By continuing, the sound of the engine may not be suddenly changed.

FIG. 12 is a flowchart of the control example 2. In the control example 1, when the in-cylinder temperature is low, the split injection is prohibited. In the control example 2, the split injection is executed. However, in order to prevent the injection end timing from being delayed, in other words, to adopt a split injection mode in which the time from the start to the end of the main injection does not become long.

Steps B1 to B8 after the start are the same as those in the control example 1. If it is determined in step B8 that the predetermined time has not elapsed since the complete explosion, the process proceeds to step B9, where two-split injection is set and the injection is executed (step B8).
5). That is, the fuel injection amount Q is equally divided and given as the first injection amount Q1 and the second injection amount Q2, and the optimal value is given as the injection pause time Δt from the range of 700 to 1000 μs. Although the split injection is performed, the injection end timing is prevented from being delayed as the two-split injection due to the low in-cylinder temperature. However, the injection suspension time Δt is made as long as possible in order to increase the temperature of the catalyst early (see FIG. 3).

If it is determined in step B8 that the predetermined time has elapsed, the process proceeds to step B10 to determine whether the in-cylinder temperature is low based on the cooling water temperature of the engine (when the cooling water temperature is 70 ° C. or less or 80 ° C. or less). Determine whether or not. If the cooling water temperature is low, the flow proceeds to step B11 to determine whether or not the idling operation is performed. If the cooling water temperature is the idling operation, the flow proceeds to step B12 to set the injection amount and the injection timing to perform the pilot injection. I do. Further, the process proceeds to step B13, in which the start timing It of the main injection is retarded by the crank angle Ic, and the process proceeds to step B14, where the injection amounts Q1, Q2 and the injection pause time Δt are set to execute the two-split injection, and the process proceeds to step B5. Then, the pilot injection and the two-split injection are executed. Even when the engine is not idling, the same pilot injection and two-split injection are executed when it is determined in step B15 that the engine is running at a low engine speed.

The setting of the pilot injection in step B12 is for reducing engine combustion noise.
Is set for raising the temperature of the exhaust gas, and the two-split injection in step B14 is also for raising the temperature of the exhaust gas (see FIG. 3). It is advantageous to set the injection pause time Δt to be short in order to suppress the generation of smoke, CO and HC (see FIGS. 7, 9 and 10).

If it is determined in step B15 that the engine is not in the low-speed operation, that is, that the engine is in the medium-speed or high-speed operation state, the process proceeds to step B16, in which the three-split injection is set and the injection is executed (step B16). B5). That is, the fuel injection amount Q is equally divided and given as the first, second, and third injection amounts Q1, Q2, and Q3, and an optimal value is given as the injection suspension time Δt from the range of 200 to 1000 μs. The injection suspension time Δt is set longer as the cooling water temperature is lower to increase the temperature of the exhaust gas (see FIG. 3).

The reason why the step B16 is the three-split injection but the step B14 is the two-split injection is because the main injection start timing It is retarded. That is, if the injection is divided into three, the injection end timing becomes too late.
From the viewpoints of ensuring combustion stability and improving emission characteristics, two-split injection with a small number of splits is employed. Step B14 is the injection suspension time Δ
t may be shortened.

If it is determined in step B10 that the cooling water temperature is high, the process proceeds to step B17 to determine whether or not the engine is idling.
Proceeding to steps B12 to B14, the pilot injection, the retard of the main injection start timing, and the two-split injection are performed. Even if it is not the idling operation, when it is determined in the step B18 that it is the low rotation operation, the process similarly proceeds to the steps B12 to B14.

If it is determined in step B18 that the engine is not in the low-speed operation, that is, the engine is in the middle-speed or high-speed operation state, the flow proceeds to step B19, in which the two-split injection is set and the injection is executed (step B18). B5). During middle rotation or high rotation operation of the engine, the catalyst temperature is considerably high. Therefore, the exhaust gas temperature is not increased by the three-split injection, and the two-split injection is performed to give priority to the improvement of fuel efficiency.

In the above control example, the pilot injection is performed only during the idling operation and the low rotation operation. However, the pilot injection is also performed when it is determined in the step B15 or B18 that the rotation is the middle rotation or the high rotation operation. By continuing, the sound of the engine may not be suddenly changed.

The number of divided injections can be arbitrarily set within the range of about 2 to 7 in accordance with the gist of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a fuel injection device for a diesel engine according to the present invention.

FIG. 2 is an explanatory diagram of batch injection, split injection, and pilot injection according to the present invention.

FIG. 3 is a graph showing a change characteristic of an exhaust gas temperature of an engine when an injection mode of a main injection is changed.

FIG. 4 is a graph showing a change characteristic of an exhaust pressure of an engine when an injection mode of a main injection is changed.

FIG. 5 is a graph showing a change characteristic of a boost pressure of an engine when an injection mode of a main injection is changed.

FIG. 6 is a graph showing a change characteristic of a fuel efficiency of an engine when an injection mode of a main injection is changed.

FIG. 7 is a graph showing a change characteristic of a smoke emission amount from an engine when an injection mode of a main injection is changed.

FIG. 8 is a graph showing a change characteristic of an NOx emission amount from an engine when an injection mode of a main injection is changed.

FIG. 9 is a graph showing a change characteristic of a CO emission amount from an engine when an injection mode of a main injection is changed.

FIG. 10 is a graph showing a change characteristic of an HC discharge amount from an engine when an injection mode of main injection is changed.

FIG. 11 is a flowchart of a fuel injection control example 1 according to the present invention.

FIG. 12 is a flowchart of a fuel injection control example 2 according to the present invention.

[Explanation of symbols]

 B Fuel Injection Device 1 Diesel Engine 2 Cylinder 4 Combustion Chamber 5 Injector (Fuel Injection Valve) 9 Crank Angle Sensor (Requested Output Detecting Means) 22 Catalyst 23 Exhaust Recirculation Path 24 Exhaust Recirculation Control Valve 25 Turbocharger 32 Accelerator Opening Sensor (required output detection means) 35 ECU (control unit)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G066 AA07 AB02 AC09 BA17 BA22 BA24 BA25 BA26 CD26 DA04 DA09 DB01 DB07 DB12 DC04 DC09 DC14 DC18 3G301 HA02 JA00 JA02 JA24 JA25 JA26 JA37 KA01 KA07 KA08 KA23 LB11 MA11 MA18 MA23 NC01 NC02 NE11 NE12 PA01A PA07A PA15A PB08A PD04A PE03A PE08A PF03A

Claims (4)

[Claims] A fuel injection valve disposed so as to face a combustion chamber in a cylinder of the engine; a required output detecting means for detecting a required output of the engine; An injection amount determining means for determining a fuel injection amount, wherein the fuel having the injection amount determined by the injection amount determining means is near the top dead center of the compression stroke of the cylinder by the fuel injection valve, and is burned by fuel injection. In a fuel injection device for a diesel engine that injects the fuel in a plurality of times so as to continue, temperature state estimating means for estimating a state related to the level of the in-cylinder temperature of the engine; When it is estimated that the internal temperature is in a predetermined low temperature state, the fuel injection is terminated earlier than when it is estimated that the internal temperature is high. The fuel injection system of a diesel engine, characterized in that it comprises a injection mode changing means for the injection mode for injecting collectively without splitting the split in the form of injection change or fuel. 2. A fuel injection valve disposed to face a combustion chamber in a cylinder of an engine, a required output detecting means for detecting a required output of the engine, and a request output detecting means for detecting a required output of the engine. An injection amount determining means for determining a fuel injection amount, wherein only the main injection is performed in which the fuel of the injection amount determined by the injection amount determining means is injected by the fuel injection valve near the top dead center of the compression stroke of the cylinder. And an injection mode for performing an early injection in which a small amount of fuel is injected by the fuel injection valve before the main injection. Further, as the main injection mode, a plurality of fuels are injected so that combustion of the fuel of the injection amount continues. When the above-mentioned early injection is performed in a fuel injection device for a diesel engine having a divided injection in which injection is performed in divided injections and a collective injection in which the fuel of the injection amount is collectively injected, Injection mode changing means for changing the mode of split injection so as to shorten the injection period from the start to the end of injection even when the early injection is not performed or adopting the mode of batch injection instead of split injection A fuel injection device for a diesel engine. 3. The fuel injection device for a diesel engine according to claim 2, wherein the start timing of the main injection is retarded when the early injection is performed. apparatus. 4. The fuel injection device for a diesel engine according to claim 2, wherein the mode of the split injection is changed by reducing the number of splits or by injection from when the fuel injection valve is closed to when it is opened next time. A fuel injection device for a diesel engine, which is executed by shortening a downtime.