JP2001065397A - Fuel injection control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a fluctuation of torque and deterioration of a combustion condition of an engine caused by a pressure vibration of fuel in a fuel supply system in the case of injecting fuel divided in at least two times by an injector in the vicinity of the top dead center of compression in each cylinder, in a direct injection Diesel engine having a common rail type fuel supply system. SOLUTION: First/second injection timing IT1, IT2 by an injector is set so as to satisfy fuel consumption performance and emission performance by a divided injection control means when an engine is in ordinary operation. A pressure vibration of fuel according to valve opening in the first time of the injector is considered, the second injection timing IT2 is corrected so that a valve opening start interval ΔIT to a start of valve opening in the second time is in the vicinity of almost half period τ/2 the change period τof fuel pressure or any one of integer times thereof. A valve opening period from the start of valve opening in the second time to valve closing of the injector may be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine provided with a fuel injection valve facing a combustion chamber in a cylinder of an engine, wherein fuel is split at least twice by the fuel injection valve in a predetermined operation state of the engine. A fuel injection control device.

[0002]

2. Description of the Related Art Conventionally, as this type of fuel injection control device, for example, as disclosed in Japanese Patent Application Laid-Open No. 9-158810, an injector (fuel injection valve) and a high-pressure supply pump for each cylinder of a diesel engine are disclosed. There is known a fuel cell in which a common rail, which is a common pressure accumulating chamber, is interposed therebetween, and fuel stored in a predetermined high pressure state in the common rail is injected by an injector at an appropriate injection timing for each cylinder. In this system, a part of the fuel is pre-injected by the injector during the intake stroke of each cylinder, and this fuel is sufficiently mixed with the intake air in the combustion chamber to form a lean premixed gas, and the fuel remains near the compression top dead center. By injecting the fuel (main injection) to self-ignite and satisfactorily combust with the lean premix, it is possible to reduce the emission of smoke while suppressing the generation of NOx.

Further, in the above-mentioned conventional example, it has been proposed that the main fuel injection performed near the compression top dead center of each cylinder is further divided into two times. According to the report, the combustion state of the fuel injected separately will be more complete, and the burnability of the lean premixture will be improved, making it possible to realize high efficiency and low emission operation of the diesel engine. .

[0004]

With the recent rise in environmental consciousness, there has been a social demand for significantly stricter emission regulations for automobile engines than in the past, especially for diesel engines. NOx
And reduction of smoke are important issues. In this regard, in the case of a diesel engine equipped with a common rail type fuel supply system as in the above-described conventional example, the fuel is not injected in large quantities near the compression top dead center of the cylinder at once, but is divided into multiple injections. Therefore, it is possible to suppress the generation of NOx by suppressing the initial combustion from becoming excessively intense. Further, by increasing the injection pressure of the fuel, the atomization of the injected fuel and the mixing with the air are promoted, and the smoke can be reduced by improving the combustion state.

[0005] However, when the fuel injection pressure increases, the fuel pressure fluctuation in the fuel supply system such as the common rail increases substantially in proportion thereto, and this pressure fluctuation fluctuates the fuel pressure near the injector.
When the main injection is divided into a plurality of injections as described above, the time interval between the start of the first valve opening of the injector and the start of the second valve opening is extremely short, so that the second opening of the injector is performed. At the start of the valve, the pressure of the fuel supplied to the injector fluctuates greatly, and as a result, the valve opening speed of the injector varies every time, and normal fuel injection may not be performed.

Further, when the fuel pressure supplied to the injector decreases, the fuel injection amount decreases correspondingly and the output torque of the engine becomes insufficient, so that there is a possibility that torque fluctuation may occur. In addition, when the fuel pressure is low, the injection speed of the fuel from the injector is low, so that the atomization is hindered, and the spread of the fuel spray becomes insufficient, so that the desired appropriate combustion cannot be realized. There is also a problem that emission is increased.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a direct injection type in which fuel is divided into at least two injections in one combustion cycle of a cylinder. In the case of diesel engines, we devised a procedure for controlling the opening of fuel injectors, especially after the second time.
An object of the present invention is to reduce engine torque fluctuation and deterioration of a combustion state caused by fuel pressure fluctuation in a fuel supply system such as a common rail.

[0008]

In order to attain the above object, according to a first solution of the present invention, when fuel is divided into at least two injections in one combustion cycle of a cylinder, fuel is injected. In consideration of the pressure oscillation of the fuel accompanying the first opening of the injection valve, the valve opening start interval from the start of the first valve opening to the start of the second valve opening is determined by the fuel supplied to the fuel injection valve. A predetermined time interval is set so that the pressure becomes equal to or higher than a predetermined value.

More specifically, according to the first aspect of the present invention, as shown in FIG. 1, a fuel injection valve 5 for directly injecting fuel into a cylinder combustion chamber 4 of an engine 1 and a fuel injection valve 5 A pressure accumulating means 6 for storing fuel in a high pressure state equal to or higher than an injection pressure; and a split injection control means 40a for splitting and injecting fuel by the fuel injection valve 5 at least twice in one combustion cycle of a cylinder. It is assumed that the engine fuel injection control device A includes Further, there is provided a valve opening start interval setting means 40b for setting a valve opening start interval from the first valve opening start to the second valve opening start of the fuel injection valve 5 by the split injection control means 40a to a predetermined time interval. Configuration.

With the above configuration, during the operation of the engine 1, the fuel injection by the fuel injection valve 5 is performed by the divided injection control means 40a at least two times during one combustion cycle of the cylinder.
It is divided into times. At this time, even if the fuel pressure fluctuates with the first opening of the fuel injection valve 5, the second opening of the fuel injection valve 5 is started after the opening start interval has elapsed. If the valve opening start interval is set to a predetermined time interval such that the fuel pressure becomes sufficiently high, the fuel injection pressure can be prevented from drastically decreasing at the time of starting the second valve opening. Engine torque fluctuations and deterioration of the combustion state can be reduced.

According to the second aspect of the present invention, the valve opening start interval setting means reduces the valve opening start interval when the fuel pressure supplied to the fuel injection valve from the pressure accumulating means starts the first valve opening of the fuel injection valve. After that, the length is set to be equal to or longer than the time required to rise again to reach the predetermined value. Thus, even when the first and second valve opening operations of the fuel injection valve are performed at extremely short time intervals, it is possible to prevent the fuel injection pressure from dropping significantly at the time of the second valve opening. The operation and effect of the invention of claim 1 can be sufficiently obtained.

According to a third aspect of the present invention, in the second aspect of the present invention, the fuel pressure supplied to the fuel injection valve varies periodically with the elapse of time after the start of the opening of the fuel injection valve. The valve start interval setting means sets the valve opening start interval of the fuel injection valve to substantially one half cycle of the fluctuation cycle of the fuel pressure or any one of integer times thereof.

That is, in general, the pressure wave generated by the first opening of the fuel injection valve vibrates the fuel supply system for supplying fuel to the fuel injection valve, and is thereby supplied to the fuel injection valve. The fuel pressure changes periodically.
Therefore, in the present invention, the valve opening start interval setting means
By setting the valve opening start interval of the fuel injection valve to approximately one half cycle of the fluctuation cycle of the fuel pressure or any one of integral multiples thereof, the fuel injection pressure at the time of starting the second valve opening of the fuel injection valve is increased. Can be made substantially the same as the fuel injection pressure at the time of the start of the first injection, so that the amount of fuel injection and the spread of the spray can be reduced as desired to reduce engine torque fluctuation and deterioration of the combustion state. Can be prevented.

According to a fourth aspect of the present invention, in the third aspect of the present invention, there is provided a fuel pressure detecting means for detecting a pressure state of the fuel stored in the pressure accumulating means. The higher the pressure state of the fuel, the more the starting interval
It shall be set to be shorter. That is, in general, the higher the pressure state of the fuel in the fuel supply system, the higher the propagation speed of the pressure wave, and the shorter the oscillation period of the fuel pressure. Therefore, according to the present invention, the higher the pressure state of the fuel detected by the fuel pressure detecting means, the shorter the fuel pressure oscillation period, and accordingly the shorter the valve opening start interval of the fuel injection valve can be.

According to a fifth aspect of the present invention, in the second aspect of the present invention, a time measuring means for measuring an elapsed time after the first opening of the fuel injection valve by the divided injection control means is provided. . With this, the elapsed time after the start of the first opening of the fuel injection valve is measured by the time measuring means,
When the time equivalent to the valve opening start interval has elapsed,
A second opening of the fuel injection valve can be started.

According to a sixth aspect of the present invention, the engine is a direct-injection diesel engine, and the split injection control means injects fuel by the fuel injection valve twice in the vicinity of the compression top dead center of the cylinder. Because of this, the fuel injection pressure of the direct injection diesel engine is relatively high, and when fuel is divided into multiple injections by the fuel injection valve, the fuel pressure associated with the first opening of the fuel injection valve is increased. The amplitude of the vibration becomes extremely large, and the pressure fluctuation at the start of the second valve opening tends to increase. Therefore, it is very effective to perform the split injection of fuel in such a direct injection diesel engine while avoiding the adverse effect of the fuel pressure fluctuation as in the first aspect of the present invention.

Next, according to a second solution of the present invention, when fuel is divided and injected at least twice in one combustion cycle of the cylinder, the fuel associated with the first opening of the fuel injection valve is provided. When it is detected that the fuel pressure at the start of the second valve opening becomes low due to the pressure vibration of the second embodiment, the second valve opening start timing of the fuel injection valve is advanced or the valve opening period is extended. I did it.

Specifically, in the invention of claim 7, as shown in FIG. 1, fuel is directly supplied to the in-cylinder combustion chamber 4 of the engine 1.
A fuel injection valve 5 for injecting and supplying, and a pressure accumulating means 6 connected to the fuel injection valve 5 for storing fuel in a high pressure state higher than an injection pressure.
It is assumed that the fuel injection control device A of the engine includes a fuel injection valve 5 and split injection control means 40a for splitting and injecting fuel at least twice during one combustion cycle of the cylinder. Then, a pressure drop state detecting means 4 for detecting that the fuel pressure supplied from the pressure accumulating means 6 to the fuel injection valve 5 is lower than a set value.
0c, and when the pressure drop state detecting means 40c detects the pressure drop state at the time of starting the second opening of the fuel injection valve 5, the second valve opening start timing of the fuel injection valve 5 is advanced. Or a correction control unit 40d that performs at least one of correction of whether the period from the start of valve opening to the closing of the valve is extended.

With the above configuration, during the operation of the engine 1, at least two fuel injections by the fuel injection valve 5 during one combustion cycle of the cylinder are performed by the divided injection control means 40a.
It is divided into times. At this time, it is detected that the fuel pressure decreases with the first opening of the fuel injection valve 5, and that the fuel pressure supplied to the fuel injection valve 5 is lower than the set value at the start of the second valve opening. Then, the correction control unit 40d corrects at least one of whether the second valve opening start timing of the fuel injection valve 5 is advanced or the period from the valve opening start to the valve closing is extended. Done.

As a result, even when the fuel pressure becomes lower than the set value at the start of the second valve opening of the fuel injection valve 5 and the fuel injection amount is reduced, the fuel injection valve 5 is operated as described above.
The second valve opening start timing is advanced to reduce the decrease in engine output. Further, if the valve-opening period of the fuel injection valve 5 is extended, even if the fuel injection pressure decreases, the decrease in the fuel injection amount due to the decrease is alleviated, and the decrease in the engine output is reduced.

According to an eighth aspect of the present invention, in the seventh aspect of the present invention, there is provided a fuel pressure detecting means for detecting a pressure state of the fuel stored in the pressure accumulating means, and the low pressure state detecting means is supplied to the fuel injection valve. The fuel pressure is estimated based on the value detected by the fuel pressure detecting means, and when the estimated value is lower than a set value, the pressure drop state is detected. With this configuration, it is possible to accurately detect the low pressure state by the low pressure state detecting means based on the pressure state of the fuel in the pressure accumulating means, and thus to sufficiently obtain the operation and effect of the seventh aspect of the present invention. be able to.

[0022]

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

(Embodiment 1) FIG. 1 shows Embodiment 1 of the present invention.
1 shows an in-line four-cylinder diesel engine mounted on a vehicle. This engine 1 has four cylinders 2, 2, 2, 2
And a piston (not shown) is fitted in each of the cylinders 2 so as to be able to reciprocate, and a combustion chamber 4 is defined in each of the cylinders 2 by the piston. An injector (fuel injection valve) 5 is disposed at a substantially central portion of the upper surface of each combustion chamber 4 so as to extend along the axis of the cylinder 2, which is exaggerated in the figure. These injectors 5,
Are connected to a common common rail 6 (pressure accumulating means) for storing fuel in a high pressure state higher than the injection pressure.
a, 6a,... are opened and closed at a predetermined injection timing for each cylinder so that high-pressure fuel is directly injected and supplied to the combustion chamber 4 from a plurality of injection holes at the tip end. Has become.

As shown in FIG. 2, the injector 5 has an injection nozzle similar to the conventional one at the tip thereof, and the core valve 5a of the injection nozzle controls the fuel pressure supplied from the common rail 6. Receiving and opening and closing operation. That is, high-pressure fuel is supplied to the front side (lower side in the figure) of the core valve 5a of the injection nozzle by the fuel supply passage 5b, and the high-pressure fuel is supplied to the hydraulic pressure via the branch passage 5c and the three-way solenoid valve 5d. It is also supplied behind the piston 5e (upper side in the figure), so that substantially the same fuel pressure acts on both front and rear of the core valve 5a. Normally, the core valve 5a is pressed forward by the urging force of the coil spring 5f to close the injection hole 5g.

On the other hand, a three-way solenoid valve 5
When an operation signal is input to d, the operation of the three-way solenoid valve 5d causes the rear of the hydraulic piston 5e to communicate with the fuel discharge passage 5h, and the fuel pressure on the rear side of the core valve 5a decreases.
The core valve 5a is retracted by the fuel pressure applied to the front end side, and fuel is injected from the injection hole 5g. Thereafter, when the input of the operation signal is stopped, the fuel pressure is applied again behind the hydraulic piston 5e by the operation of the three-way solenoid valve 5d,
The core valve 5a advances and the injection hole 5g is closed. Reference numeral 5i shown in the figure indicates an orifice for adjusting the operation speed of the core valve 5a.

The common rail 6 shown in FIG. 1 is provided with a fuel pressure sensor 6b as fuel pressure detecting means for detecting the internal fuel pressure (common rail pressure). The common rail 6 is connected to a fuel supply pump 8 via a high-pressure fuel supply pipe 7, and the fuel supply pump 8 is connected to a fuel tank 10 via a fuel supply pipe 9. The fuel supply pump 8 operates by receiving a rotation input from the crankshaft of the engine 1 through the input shaft 8a, and sucks up the fuel in the fuel tank 10 through the fuel supply pipe 9 while filtering the fuel with the fuel filter 11. This fuel is pumped to the common rail 6 by a jerk type pumping system.

Although not shown, the fuel supply pump 8 is provided with an electromagnetic valve for adjusting a discharge amount of the pump by releasing a part of the fuel delivered by the pumping system to a fuel return pipe 12. The opening of the solenoid valve is controlled according to the value detected by the fuel pressure sensor 6b,
The common rail pressure is feedback-controlled to a predetermined value. Reference numeral 13 in the figure denotes a pressure limiter for discharging fuel from the common rail 6 when the common rail pressure becomes equal to or higher than a predetermined value, and the fuel discharged from the pressure limiter flows through a fuel return pipe 14. Is returned to the fuel tank 10. Further, the code 1
Reference numeral 5 denotes a fuel return pipe for returning a part of the fuel from the injector 5 to the fuel tank 10.

Although not shown in detail, the engine 1 has a crank angle sensor 16 for detecting a rotation angle of a crankshaft, a cam angle sensor 17 for detecting a rotation angle of an intake / exhaust system camshaft, and a cooling water temperature (not shown). An engine water temperature sensor 18 for detecting an engine water temperature is provided. The crank angle sensor 16 includes a plate to be detected provided at the end of the crankshaft, and an electromagnetic pickup arranged so as to face the outer periphery thereof. A pulse signal is output in response to the passage of the projections formed at equal intervals. The cam angle sensor 17 also includes a plurality of protrusions similarly provided at predetermined positions on the peripheral surface of the cam shaft, and an electromagnetic pickup that outputs a pulse signal when each of the protrusions passes. Reference numeral 19 denotes a vacuum pump driven by a camshaft.

An intake passage 20 for supplying air filtered by an air cleaner (not shown) is provided on one side (upper side in the figure) of the engine 1.
The downstream end of the intake passage 20 is branched for each cylinder via a surge tank 21 and communicates with the combustion chamber 4 of each cylinder 2 through an intake port. Further, the surge tank 21 is provided with a supercharging pressure sensor 22 for detecting a pressure of intake air supercharged by a turbocharger 31 described later. A hot film type air flow sensor 23 for detecting a flow rate of intake air taken into the engine 1 is arranged in the intake passage 20 in order from the upstream side to the downstream side.
And a blower 24 driven by a turbine 29 to compress the intake air, an intercooler 25 for cooling the intake air compressed by the blower 24, and an intake throttle valve 26 for restricting the middle of the intake passage 20. . The intake throttle valve 26 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state, and is opened and closed by an actuator (not shown).

On the other hand, an exhaust manifold 27 for discharging combustion gas from the combustion chamber 4 of each cylinder 2 is connected to the other side (lower side in the figure) of the engine 1. An exhaust passage 28 is connected, and a turbine 29 that is rotated by the exhaust flow and a catalyst 30 that purifies harmful components in the exhaust are arranged in this exhaust passage 28 in order from the upstream side to the downstream side. . Although not shown in detail, the turbocharger 31 including the turbine 29 and the blower 24 has a plurality of flaps disposed so as to surround the entire circumference of the turbine 29, and the nozzles are cut off by the rotation of each flap. This is a VGT (Variable Geometry Turbo) in which the area is changed to adjust the exhaust flow velocity to the turbine 29.

Further, although not shown in detail, the catalyst 30 has a cordierite carrier having a honeycomb structure having a large number of through holes extending in parallel with each other in the exhaust gas flow direction. The catalyst layer is formed on the wall surface in two layers. Specifically, the inner catalyst layer contains platinum Pt.
And a noble metal such as barium Ba as a NOx absorbent are supported on a porous material such as alumina or ceria as a support material. On the other hand, platinum Pt and rhodium Rh and Ba are formed on the outer catalyst layer as a porous material. Is supported as a support material.

When the oxygen concentration in the exhaust gas is high, that is, when the air-fuel ratio of the combustion chamber 4 is lean, the catalyst 30
While absorbing Ox, when the air-fuel ratio of the combustion chamber 4 becomes substantially near or higher than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases, the absorbed NOx is released to reduce and purify it. Type. Here, the action of absorbing and releasing NOx by barium Ba depends on the temperature state. For example, as shown in FIG. 3A, the purification rate of the catalyst 30 by absorbing NOx in the exhaust gas is about 250 ° C.
Although the temperature becomes extremely high in a temperature range of about 400 ° C., in an unwarmed state in which the temperature is lower, the temperature rapidly decreases as the temperature decreases.
When the above is reached, the NOx purification rate decreases as the temperature rises. Further, since the catalytic activity of a noble metal such as platinum Pt also decreases when the temperature is low, the purification rate when reducing and purifying NOx released from barium Ba is also less than 250 ° C. as shown in FIG. Then it drops rapidly.

In the catalyst 30, barium Ba was used.
Instead of other alkaline earth metals and sodium Na
And the like, or at least one of rare earth metals. Further, zeolite may be used as a support material of the inner catalyst layer, and in that case, alumina or ceria may be used as a support material of the outer catalyst layer. Further, as the catalyst 30, a catalyst layer in which alumina or ceria is supported as a support material is formed on the wall surface of the carrier, and a noble metal such as platinum Pt, rhodium Rh, or palladium Pd and potassium K or the like are formed on the support material. A one-layer coat type supporting an alkali metal or an alkaline earth metal such as barium Ba may be used.

The exhaust passage 28 is located at a position upstream of the turbine 29 on the exhaust side, and is branched and connected to an upstream end of an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 33 for recirculating a part of the exhaust gas to the intake side. The downstream end of the EGR passage 33 is connected to the intake passage 20 on the downstream side of the intake throttle valve 26 with respect to the intake air. An exhaust gas recirculation amount control valve (hereinafter, referred to as an EGR valve) 34 is provided. This EGR
The valve 34 is configured to be opened and closed by a negative-pressure-driven actuator 35 driven by a negative pressure from the vacuum pump 19, and linearly changes the cross-sectional area of the EGR passage 33 to the intake passage 20. The flow rate of the recirculated exhaust gas is adjusted.

Each of the injectors 5, the fuel supply pump 8, the intake throttle valve 26, the EGR valve 34 and the like are operated by a control signal from a control unit (Electronic Control Unit: hereinafter referred to as ECU) 40. On the other hand, an output signal from the fuel pressure sensor 6b, an output signal from the crank angle sensor 16 and the output signal from the cam angle sensor 17, and the engine water temperature sensor 1
8, an output signal from the air flow sensor 23, and an output signal from an accelerator opening sensor 36 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle. ing.

Then, the fuel injection amount and the injection timing (the valve opening start timing of the injector 5) by the operation of the injector 5
Is controlled according to the operating state of the engine 1 and
The operation of the high-pressure supply pump 8 controls the common rail pressure, that is, the fuel injection pressure. Further, the amount of intake air is controlled by the operation of the intake throttle valve 26, the recirculation state of the exhaust gas is controlled by the operation of the EGR valve 34, and the turbocharger 31
The operation control of the flap is performed.

(Fuel Injection Control) Specifically, the ECU 4
0, a map of a basic fuel injection amount Q experimentally determined according to changes in the target torque and the rotation speed of the engine 1 is electronically stored, and the output from the accelerator opening sensor 36 is output. Based on the target torque obtained based on the signal and the engine speed obtained based on the output signal from the crank angle sensor 16, a basic fuel injection amount Qbase corresponding to the required output of the engine 1 is obtained from the fuel injection amount map. Is read. Then, an amount of fuel corresponding to the required output is basically injected near the compression top dead center (TDC) of each cylinder 2 (hereinafter referred to as main injection), and the air-fuel ratio of the combustion chamber 4 of the engine 1 is considerably large. Driven in a lean state.

In the memory of the ECU 40, an injection mode map in which the fuel injection mode in the vicinity of the compression top dead center of the cylinder 2 is set in accordance with the target torque and the engine speed similarly to the fuel injection amount map. Is electronically stored, and an optimal injection mode is selected from the injection mode map based on the target torque of the engine 1 and the engine speed. That is, basically, as shown in FIG. 4A, the fuel is divided into two injections in the vicinity of the compression top dead center, and the fuel is divided into two injections (hereinafter, referred to as two-split injection), or as shown in FIG. Or three-split injection (hereinafter referred to as three-split injection) is selected. Also, do so twice or three times
Injection is divided into injections, and the injection stop interval Δt during the injection is changed to change the combustion state so that the fuel efficiency and the exhaust characteristics of the engine 1 are optimized.

On the other hand, N in the catalyst 30 of the exhaust passage 28
When the Ox absorption amount becomes larger than a predetermined value and the NOx absorption performance is expected to decrease (excessive absorption state), the air-fuel ratio of the combustion chamber 4 is temporarily changed mainly by increasing the fuel injection amount, as will be described in detail later. As shown in FIG. 4 (c), the fuel is controlled to a state near or substantially equal to the stoichiometric air-fuel ratio and, in addition to the main injection, a part of the fuel is injected from the initial stage of the intake stroke to the middle stage of the compression stroke. By injecting (hereinafter,
NOx release control), the concentration of oxygen in the exhaust gas is reduced, and the concentration of the reducing agent component is increased to sufficiently release and reduce NOx from the catalyst 30 to recover the purification performance of the catalyst 30 ( So-called catalyst refresh).

Here, the combustion state when the main injection is divided as described above will be described in detail. When fuel is injected by the injector 5 near the compression top dead center of the cylinder 2, the injection hole of the injector 5 The fuel injected from
Spreading into the combustion chamber 4 while forming a spray having a conical shape as a whole, the fuel is divided into small oil droplets by the friction with the air (fuel atomization), and the fuel evaporates from the surface of the oil droplets. Fuel vapor is generated (vaporization and atomization of fuel).
At this time, the air in the combustion chamber 4 is in an extremely high pressure and high viscosity state. Therefore, when the fuel is injected in a lump as in a general diesel engine, if the injection amount is large, the air The subsequent fuel oil droplets catch up with the fuel oil droplets ejected to the nozzle and are recombined, which may hinder atomization of the fuel and eventually vaporization and atomization.

On the other hand, as shown in FIGS. 4A and 4B, if the fuel is divided and injected a plurality of times, the fuel oil droplets ejected by the valve opening of the injector 5 are opened. In addition, fuel oil droplets ejected by the next valve opening are less likely to catch up, and it is possible to substantially avoid hindering atomization of fuel due to recombination of oil droplets. In addition, by further increasing the fuel injection pressure, the atomization of the fuel is further improved,
It is also possible to promote the acceleration, and in this way, the distribution of the fuel spray in the combustion chamber 4 can be made uniform and the degree of improvement in the air utilization rate can be further increased. The change in the mixing state of the fuel spray and the air due to such split injection is caused by various parameters such as the fuel injection amount, the injection timing, the injection rate, the fuel injection pressure, the number of split injections, the injection pause interval, and the like. It is considered that the fuel efficiency varies and the concentration of harmful components in the exhaust gas changes due to the change in the combustion state.

More specifically, a four-cylinder diesel engine similar to that of this embodiment (displacement is about 2000 c.
c) is operated under a relatively low load and low rotation state, and the injection pause interval Δt of the injector 5 is appropriately changed in the range of 350 to 900 microseconds (μsec) for each of the batch injection, the two-split injection, and the three-split injection. However, the crank angle at the end of injection, which changes with this, and the fuel efficiency and CO
FIGS. 5 to 8 show examples of experimental results obtained by measuring the relationship with the concentration.
Shown in

First, as shown in FIG. 5 for the CO concentration, Δt = 350, 400, 550,
The values at 700 and 900 μsec are plotted, respectively, and for the three-split injection, Δt = 400, 550, 7
Values at 00 and 900 μsec were plotted, respectively. According to the figure, the CO concentration in the exhaust gas decreases when the injection pause interval Δt of the injector 5 is short in both the two-split and three-split injections, and increases as the injection pause interval Δt becomes longer. Tend to increase. Also, as shown in FIG. 6, it can be seen that the NOx concentration in the exhaust can be reduced as the injection pause interval Δt is longer, as opposed to the CO concentration. Although not shown, the HC concentration in the exhaust gas has the same tendency as the CO concentration.

On the other hand, the change in the fuel consumption rate of the engine at this time is as shown in FIG. 7. The fuel consumption rate is improved in the two-split injection as compared with the one-shot injection. The fuel efficiency is slightly improved when
The fuel efficiency tends to deteriorate as the injection stop interval Δt becomes longer. In other words, if the number of injections and the injection pause interval Δt are increased without changing the total fuel injection amount, the output torque of the engine will decrease. The change in the exhaust gas temperature at this time is as shown in FIG.
It can be seen that the exhaust temperature is higher in the split injection, and the exhaust temperature is higher in the three-split injection than in the two-split injection. For this reason, for example, if the number of divisions of the main injection is increased before performing the NOx release control, the catalyst 30
It can be considered that the temperature state of is increased to promote the refresh.

Therefore, in the fuel injection control of this embodiment, when the catalyst 30 becomes excessively NOx-absorbed during the operation of the engine 1 and needs to be refreshed, the catalyst 30 may be in an unwarmed state. For example, first, the number of divisions of the main injection is increased to three times, the temperature state of the catalyst 30 is quickly increased, and the concentrations of CO and HC in the exhaust gas are gradually increased. Then, the oxygen concentration in the exhaust gas is reduced by correcting the fuel injection amount by increasing the fuel injection amount and the like.
The concentration of O and HC is sufficiently increased to promote the refresh of the catalyst 30 to the maximum.

Hereinafter, a specific fuel injection control processing procedure will be described with reference to flowcharts shown in FIGS. This control is executed for each cylinder in synchronization with the crank angle signal.

First, in step SA1 after the start of the flow shown in FIG. 9, data such as a crank angle signal, an air flow sensor output, an accelerator opening, and an engine water temperature are input. In the following step SA2, data is obtained from the accelerator opening. The base fuel injection amount Qbase is read from the fuel injection amount map based on the target torque obtained and the engine speed Ne obtained from the crank angle signal, and the injection timing ITbase
Is read from a preset map. In this injection timing map, the optimal injection timing corresponding to the engine water temperature Tw and the engine speed Ne is experimentally determined and recorded.For example, if the engine water temperature Tw and the engine speed Ne are different, the fuel spray Since the ignition delay time is different, the basic injection timing ITbase is set corresponding to this.

Subsequently, at step SA3, it is determined whether or not the engine coolant temperature Tw is lower than the set coolant temperature Tw0. The set water temperature Tw0 is determined by the catalyst 3 during the cold start of the engine 1.
The engine water temperature Tw is the water temperature corresponding to the unwarmed-up state of 0.
If yes is lower than the set water temperature Tw0, step S
The program proceeds to A4, in which a flag Fp indicating that the main injection is performed in three parts to promote warm-up of the catalyst 30 is turned on (Fp = 1), and the program proceeds to step SB1 in FIG. That is, if the catalyst 30 is not warmed up at the time of the cold start of the engine 1, the exhaust gas temperature is increased by dividing the main injection into three to increase the temperature of the catalyst 30. On the other hand, if the engine coolant temperature Tw is equal to or higher than the set coolant temperature Tw0 (No in step SA3), it is determined that the catalyst 30 is in a warm-up state, and the process proceeds to step SA5.

In step SA5, the amount of NOx absorbed in the catalyst 30 is estimated. This estimation may be performed, for example, by integrating the mileage of the vehicle and the total fuel injection amount during the distance, and based on the integrated value. Alternatively, the operating time of the engine 1 and the total fuel injection amount during that period are integrated, the integrated value is corrected based on the operating state of the engine 1, and the NOx absorption amount is calculated based on the corrected integrated value. It may be estimated. Then, in step SA6, it is determined whether or not the estimated value of the NOx absorption amount is equal to or more than the set value. If the estimated value is smaller than the set value, the process proceeds to step SA16. Proceeds to NO in step SA7.
The flag F1 indicating that it is the period for performing the x release control is turned on (F1 = 1), and the process proceeds to Step SA8.

In step SA8, the temperature state of the catalyst 30 (catalyst temperature Tc) is estimated. This estimation may be performed based on, for example, the history of the engine water temperature Tw for a predetermined period up to the present and the engine speed and the vehicle speed during that time, or a temperature sensor is provided in the exhaust passage 28 near the catalyst 30. Thus, the estimation may be made directly based on the output from this sensor. Then, step SA
9, the estimated catalyst temperature Tc is reduced to the first set temperature Tc1 (for example, 250 °
It is determined whether it is lower than C). If this determination is yes, the catalyst 30 has not been warmed up and the NOx absorption or release action has been considerably reduced.
Proceeding to A10, the flag Fp is turned on (Fp =
1), proceed to step SA20.

That is, the NOx absorption amount increases and the catalyst 30
Even if it is considered that the purification performance of the catalyst 30 is reduced, if the catalyst 30 is not warmed up, the refreshing of the catalyst 30 due to the release of NOx cannot be sufficiently promoted. In this case, since the reduction and purification cannot be performed sufficiently, the temperature of the catalyst 30 is increased by dividing the main injection into three times as described later.

The result of the determination in step SA9 is n
If it is o, the flow proceeds to step SA11 to clear the flag Fp, and in the next step SA12, the first timer value T1 (the initial value is zero) for measuring the elapsed time of the NOx release control is incremented. Subsequently, at Step SA13
, It is determined whether or not the first timer value T1 has become equal to or greater than a preset threshold value T10. This threshold T
Since 10 is a value corresponding to the preset NOx release control period, if the determination result is no, the process proceeds to Step SA14, and the basic fuel injection amount Qbase is set so that the air-fuel ratio of the combustion chamber 4 becomes substantially near the stoichiometric air-fuel ratio. The fuel increase correction amount Qc (Qc = R1) for increasing the fuel amount is determined, and the routine proceeds to step SA20.

That is, for example, based on the intake air amount obtained from the output of the air flow sensor 23, the fuel injection amount is calculated such that the air-fuel ratio becomes substantially near the stoichiometric air-fuel ratio with respect to this intake air amount, and the fuel increase The correction amount Qc is determined.
On the other hand, if the decision result in the step SA13 is yes, the period in which the NOx release control is performed has ended, so in step SA15 the fuel increase correction amount Qc is set to zero (Qc = 0),
In step SA16, the flag F1 is cleared (Fp =
0), and proceed to step SA20.

That is, the NOx absorption amount increases and the catalyst 30
If it is considered that the purification performance of the catalyst 30 is reduced and the catalyst 30 is in a warm-up state, the catalyst 30 is refreshed by performing NOx release control to release NOx from the catalyst 30 and purifying by reduction. I try to plan.

In step SA6, NO
In step SA17, in which it is determined that the estimated value of the x absorption amount is smaller than the set value, the state of the flag F1 is determined. If yes in the ON state (F1 = 1), the NOx emission control is in progress. On the other hand, if the flow proceeds to step SA8, and if no in the off state (F1 = 0), it is not the period for performing the NOx release control.
Clears the flag Fp (Fp = 0) and returns to step SA2
Go to 0.

Steps SA10, SA14, SA1
In step SA20 following SA6 and SA18, it is determined whether the engine 1 is in an accelerating operation state. Then, if the acceleration operation state of the engine 1 is determined based on the accelerator opening, the change state of the engine speed, and the like, the flag Fp is turned on in the subsequent step SA21 (Fp = 1), while the engine 1 accelerates. If you are not driving
Step SB in FIG.
Proceed to 1. As described above, in the acceleration operation state of the engine 1, the exhaust pressure is increased by increasing the number of times of the main injection regardless of the state of the catalyst 30, thereby increasing the turbocharger 25.
To increase the supercharging effect.

Subsequent to steps SA20 and SA21, in step SB1 of the flow shown in FIG.
It is determined whether the flag Fp is on. If this determination is no, the process proceeds to step SB6, while the determination is yes.
If s, the process proceeds to step SB2, where the basic fuel injection amount Qbase
Is added to the fuel increase correction amount Qc to calculate the total fuel injection amount Qt. Here, if the flag F1 is not in the ON state, that is, if the catalyst 30 is not in the state of excessively absorbing NOx,
Since the fuel increase correction amount Qc = 0, the total fuel injection amount Qt becomes equal to the basic fuel injection amount Qbase. Then, step SB
In the step 3, the total fuel injection amount Qt is divided into three equal parts, and the final first, second and third fuel injection amounts Q1, Q2, Q3 are respectively obtained.
And

Subsequently, in Step SB4, the first to
The third fuel injection timings IT1 to IT3 are set respectively. Here, as shown in FIG. 4C, the first injection timing IT1 is the same as the basic injection timing ITbase, and the subsequent second injection timing IT
The second and third injection timings IT3 are set with a set interval Δt (injection pause interval: for example, Δt = 900 microseconds) after the previous injection ends and the injector 5 closes. As the set interval Δt, an optimum value experimentally determined according to the operating state of the engine 1 within a range of approximately 500 microseconds to approximately 1 millisecond is recorded as a map, and is read from the map. Is set.

Subsequently, at step SB5, a control procedure of an injection end determination subroutine is executed. Although the detailed description is omitted here, when the main injection is divided into three times,
It is determined whether the end timing of the third injection is later than ATDC 35 ° CA, and when it is determined that it is later, the injection stop interval Δt between each injection is shortened, or extra fuel is supplied to the cylinder 2. The control procedure is corrected so that pre-injection is performed after the middle stage of the compression stroke. After performing the injection end determination subroutine, the process proceeds to steps SC1 to SC11 in FIG.
Execute it divided into times.

That is, in this flow, when the flag Fp is on (Fp = 1), in other words,
When the catalyst 30 is in the unwarmed state at the time of the cold start of the engine 1, when the NOx release control is performed during the operation of the engine 1, and before the fuel injection amount is increased and corrected, the unwarmed state is set. When the catalyst 30 is warmed, the main injection is set to the three-split injection at any one of the three times when the engine 1 is in the acceleration operation state.

Further, the step SB1 proceeded after it was determined in step SB1 that the flag Fp was in the off state.
At 6, it is determined whether or not the flag F1 is on. If the determination result is no (F1 = 0), the process proceeds to step SB11, while the determination result is yes (F1
= 1), the process proceeds to step B7, and the process proceeds to step SB7.
The fuel increase correction amount Qc is added to the basic fuel injection amount
To calculate the total fuel injection amount Qt. That is, the total fuel injection amount Qt is calculated so that the average air-fuel ratio of the combustion chamber 4 of the engine 1 becomes substantially equal to the stoichiometric air-fuel ratio. Then, step S
In B8, the fuel injection amount Qp and the injection timing I of the pre-injection
Set Tp respectively. That is, as the injection amount of the pre-injection, an optimum value corresponding to the operating state of the engine 1 is recorded as a map, and is read from the map. The injection ratio is, for example, 8 to 23% of the main injection.
Is set within the range.

Incidentally, the fuel injection amount Qp of the pre-injection may be used as the fuel increase correction amount Qc, so that the control calculation can be simplified. Further, as shown in FIG. 4 (c), it is preferable that the pre-injection be performed between the early stage of the intake stroke of the cylinder 2 and the first half of the compression stroke. In this embodiment, the injection timing ITp of the pre-injection is changed by the intake stroke of the cylinder 2. Set in the first half of the journey.

Subsequently, in step SB9, after subtracting the pre-injection amount Qp from the total fuel injection amount Qt, the pre-injection amount Qp is divided into three equal parts to obtain the final first, second and third fuel injection amounts Q1, Q2, and Q1, respectively. Q3. In the following step SB10, the first to third fuel injection timings are set in the same manner as in step SB4.
Set IT1 to IT3 respectively. In this case as well, the first injection timing IT1 is the same as the basic injection timing ITbase, and the subsequent second injection timing IT2 and third injection timing IT3 are obtained after the previous injection is completed and the injector 5 is closed. Set interval Δ
It is set with an interval of t. The set interval Δt is also set to a value within a range of approximately 500 microseconds to approximately 1 millisecond.
It is read from the map according to the operating state of the engine 1. Then, the process proceeds to steps SC1 to SC11 in FIG. 11, and the main injection is divided into three and executed as described later.

That is, when the flag F1 is on (F1 = 1), in other words, when the catalyst 30 is in a warm-up state and in a state of excessive NOx absorption, the combustion chamber 4 of the engine 1 becomes empty. The fuel injection amount is increased and corrected so that the fuel ratio is substantially in the vicinity of the stoichiometric air-fuel ratio or richer, and a part of the increased fuel is pre-injected in the first half of the intake stroke of the cylinder 2 while the remaining fuel is injected. Is divided into three and injected near the compression top dead center of the cylinder.

Further, at step SB6, the flag F1 is set.
Step S that is determined to be off
In B11, the basic fuel injection amount Qbase is divided into two equal parts to obtain the final first and second fuel injection quantities Q1 and Q2, respectively, and the third fuel injection quantity Q3 = 0. Subsequently, in step SB12, the first and second fuel injection timings IT1 and IT2 are set in the same manner as in steps SB4 and SB10. That is, the first injection timing IT1 is the same as the basic injection timing ITbase, and the subsequent second injection timing IT2 is
The interval is set at a set interval Δt after the first injection is completed and the injector 5 is closed. This set interval Δt is also approximately 5
A value in the range of 00 microseconds to approximately 1 millisecond,
It is read from the map according to the operating state of the engine 1. Subsequently, in step SB13, as will be described later, a control procedure of a correction routine for correcting the second fuel injection amount Q2 and the second injection timing IT2 is executed, and steps SC1 to SC in FIG.
Proceeding to C11, the main injection is divided into two and executed.

That is, when the engine 1 is cold started or when NOx
If the emission control is not performed and the engine 1 is not in the accelerating operation state, the main injection is performed in two divided times. At this time, the injection suspension period Δt may be set relatively short within the range of 100 microseconds to 1 millisecond, and in this case, as illustrated in FIG. Improvement can be achieved.

Steps SB5, SB10,
Subsequent to SB13, in step SC1 of FIG. 11, it is determined whether or not the value of the pre-injection amount Qp is zero.
If S, the process proceeds to step SC5, while if Qp ≠ 0 and NO, the process proceeds to step SC2 to determine whether or not the pre-injection timing ITp has been reached based on the crank angle signal. Then, it waits until the injection timing comes (NO in step SC2), and when the injection timing comes (YES in step SC2), the process proceeds to step SC3 to perform pre-injection, and the fuel of the injection amount Qp is injected into the combustion chamber 4 by the injector 5. Spray. Subsequently, in step SC4, the pre-injection amount is set to zero (Qp ←
0), and proceed to step SC5.

Subsequently, in step SC5, it is determined whether or not the first injection timing IT1 has been reached based on the crank angle signal.
Wait until the injection timing comes (NO in step SC5),
When the injection timing comes (YES in step SC5), the process proceeds to step SC6 to perform the first fuel injection, and the fuel of the injection amount Q1 is injected into the combustion chamber 4 by the injector 5. In the subsequent step SC7, it is similarly determined whether or not the second injection timing IT2 has been reached based on the crank angle signal, and it is waited until the injection timing has come (NO in step SC7), and if the injection timing has come (YES in step SC7). ), And proceeds to Step SC8 to execute the second fuel injection.

Subsequently, in step SC9, it is determined whether or not the value of the third fuel injection amount Q3 is zero.
If S, the process returns. If Q3 ≠ 0, NO, the process proceeds to Step SC10. Then, it is determined whether or not the third injection timing IT3 has been reached based on the crank angle signal, and it is waited until the injection timing has come (NO in step SC10). If the injection timing has come (YES in step SC10), step S is executed.
The program proceeds to C11, in which the third fuel injection is executed, and thereafter, the process returns.

With the above-described fuel injection control, in the normal operation state of the engine 1, as shown in FIG. 4A, the fuel of the basic fuel injection amount Qbase is injected from the injector 5 near the compression top dead center of each cylinder 2. The engine 1 is operated in a state where the average air-fuel ratio of the combustion chamber 4 is lean. When NOx generated by combustion is absorbed by the catalyst 30 and the amount of absorption becomes excessive, the catalyst 3
NOx release control for releasing and reducing NOx from 0 is performed.

At this time, for example, if the engine 1 is in a predetermined low-speed operation state for a long time and the catalyst 30 is in a low temperature state corresponding to the unwarmed state, first, the injector 5
Performs three-split injection of fuel, thereby increasing the exhaust gas temperature as illustrated in FIG. 8 and quickly increasing the temperature state of the catalyst 30 in the exhaust passage 28. Then, after the catalyst 30 has been warmed up, NOx release control is performed,
The fuel injection amount from the injector 5 is increased and corrected so that the average air-fuel ratio of the combustion chamber 4 becomes substantially equal to the stoichiometric air-fuel ratio, so that the oxygen concentration in the exhaust gas decreases and the reducing agent components such as CO and HC are reduced. Is sufficiently increased, NOx is promptly released from the catalyst 30 whose temperature has been raised as described above, and the catalyst is sufficiently reduced and purified. Moreover, at this time, since a part of the fuel is pre-injected in the first half of the intake stroke of the cylinder 2, even if the fuel injection amount is increased, the fuel spray does not become excessively rich, and the smoke increases rapidly. Also does not invite.

That is, in the NOx release control for refreshing the catalyst 30, the temperature state of the catalyst 30 is raised in advance before the correction of the increase in the fuel injection amount, so that the oxygen concentration in the exhaust gas is reduced by the increase in the fuel. When this is done, NOx is released very efficiently from the catalyst 30 and its N
Ox can be sufficiently reduced and purified. As a result, the time for performing the NOx release control during the operation of the engine 1 can be relatively shortened, and the deterioration of fuel efficiency due to an increase in the fuel injection amount can be suppressed.

Step SB1 of the flow shown in FIG.
According to the control procedures of SB1 and SB12, split injection control means 40a is configured to split and inject fuel at least twice in one combustion cycle of each cylinder 2 by the injector 5, and the split injection control means 40a The fuel is injected twice in the vicinity of the compression top dead center of the cylinder.

(Correction Control) By the way, in the direct injection diesel engine 1 having the common rail type fuel supply system as in this embodiment, the main injection is divided into a plurality of times as described above. The time interval from the start of the first valve opening to the start of the second valve opening is, for example, 2
３3 milliseconds or less, the effect of the fuel pressure oscillation accompanying the start of the first valve opening at the start of the second valve opening of the injector 5 is large, and the fuel due to the second valve opening is Injection may not be performed normally.

For example, a description will be given of a case of two-split injection. As shown in FIG. 12A, the fuel pressure (injector inlet pressure) supplied from the common rail 6 to the injector 5 is changed when the injector 5 is opened for the first time. It decreases greatly at the same time as the start of the valve, attenuates while fluctuating periodically with the lapse of time thereafter, and converges to the initial value P0. On the other hand, when the second valve opening of the injector 5 is started,
That is, since the second injection timing IT2 is determined so as to correspond to a request for fuel consumption or emission, as shown in FIG. 7B, the fuel pressure supplied to the injector 5 at the start of the second valve opening is shown. May be considerably reduced, and in such a case, the fuel injection amount and the injection rate fluctuate.

That is, if the fuel injection pressure at the start of the valve opening of the injector 5 is low, atomization and vaporization and atomization of the injected fuel are hindered, and the core valve 5a of the injector 5 is prevented.
(C), the amount of fuel injection in the initial stage of valve opening becomes smaller than the normal injection state indicated by the phantom line in FIG. The degree of spread becomes insufficient. As a result, the combustion state is deteriorated due to a decrease in the air utilization rate and the like, and adverse effects on the environment such as a rapid increase in emissions are concerned. In FIG. 3C, the area of the hatched portion corresponds to the fuel injection amount, but the fuel injection amount by the second valve opening of the injector 5 is considerably smaller than that of the first valve opening. Therefore, occurrence of torque fluctuation is expected.

Therefore, in this embodiment, step SB of the flow shown in FIG. 10 is a feature of the present invention.
In the thirteenth correction routine, the fuel pressure fluctuation accompanying the first valve opening of the injector 5 is taken into consideration, and the fuel pressure supplied to the injector 5 at the start of the second valve opening is adjusted to a predetermined value or more. The second valve opening start timing, that is, the second injection timing IT2 of the injector 5 is corrected. Therefore, the correction routine of step SB13 is executed by the split injection control means 40a.
This corresponds to the valve opening start interval setting means 40b that sets the valve opening start interval ΔIT from the start of the second valve opening to the start of the second valve opening so as to be a predetermined time interval.

More specifically, the fluctuation period τ of the fuel pressure supplied to the injector 5 depends on the common rail 6 and the branch pipe 6a.
Etc. and the fuel pressure in the inside. Then, as schematically shown in FIG.
Ideally, if the valve opening start interval ΔIT of the injector 5 is set to approximately one half period τ / 2 of the fluctuation period τ of the fuel pressure or any integral multiple thereof, then 2
Since the fuel pressure at the start of the second valve opening becomes substantially the same as that of the first valve opening, the influence of the pressure fluctuation can be avoided. Therefore, first, based on the signal from the fuel pressure sensor 6b,
The fluctuation period τ is estimated and calculated. That is, in general, the higher the pressure state of the fuel in the fuel supply system, the higher the propagation speed of the pressure wave and the shorter the oscillation cycle of the fuel pressure. Therefore, the fuel pressure detected by the fuel pressure sensor 6b tends to be shorter. The higher the state, the shorter the value of the fluctuation period τ is calculated.

Next, a valve opening start interval ΔIT before correction is obtained from the first and second injection timings IT 1 and IT 2 of the injector 5, and this value is calculated as the half cycle τ / of the fluctuation cycle estimated and calculated as described above.
2 or a value within a predetermined range close to an integral multiple thereof, in other words, whether or not the second injection timing IT2 is included in the range shown by hatching in FIG. Determine. Then, the second injection timing IT of the injector 5
2 is included in the range of the diagonal line, the second injection timing I
While T2 is not corrected, as shown in FIG.
The injection timing IT2 is slightly delayed from the range of the oblique line,
If the range of the immediately preceding diagonal line is closer to the range of the diagonal line existing thereafter, as shown in FIG.
Correct 2 to the advance side. That is, the valve opening start interval ΔIT of the injector 5 is set to be shorter as the common rail pressure is higher, corresponding to the shorter the fuel pressure oscillation period τ.

As shown in FIG. 8D, the second injection timing IT2 of the injector 5 before the correction is slightly ahead of the range of the diagonal line, and is closer to the range of the diagonal line immediately after the second injection timing IT2. If the second injection timing IT2 is closer to the range of the previously existing oblique line, the second injection timing IT2 may be corrected to the retard side as shown in FIG. it can. In addition, the second injection timing IT2 is cancelled, and the elapsed time after the first valve opening by the injector 5 is started is measured by a timer (time measuring means) of the ECU 40, and the valve opening is started accurately. When the time corresponding to the interval ΔIT has elapsed, the second valve opening may be started.

Therefore, according to the first embodiment, when fuel is divided into two injections by the injector 5 near the compression top dead center of the cylinder 2 during normal operation of the engine 1, the injector 5 Even if the fuel pressure fluctuates with the first valve opening, the second injection timing IT2 is corrected, so that the second valve opening of the injector 5 is started again, and the fuel pressure rises again and is close to the initial value P0. Is performed after the predetermined value of the fuel supply system has become equal to or more than the predetermined value. Therefore, even if fuel pressure oscillation occurs in the fuel supply system such as the common rail 6 and the branch pipe 6a,
Fluctuations in the fuel injection amount and the injection rate due to this can be reduced, and torque fluctuations in the engine 1 and deterioration of the combustion state can be reduced.

In particular, in this embodiment, the injector 5
Is corrected so that the first and second valve opening start intervals ΔIT of the injector 5 are substantially half cycle τ / 2 of the fuel pressure fluctuation cycle τ or any one of its integral multiples. The fuel injection pressure at the start of the second valve opening of the injector 5 becomes substantially the same value as the first time, so that the fuel injection amount, the spread of the fuel spray, and the like are aimed at. Thus, it is possible to almost eliminate torque fluctuation and deterioration of the combustion state of the engine 1.

In this embodiment, the common rail 6
A fuel pressure sensor 6b for detecting the pressure state of the fuel stored in the fuel cell is provided. The higher the pressure detected by the fuel pressure sensor 6b, the shorter the valve opening start interval ΔIT. Even if the oscillation period τ changes, the valve opening start interval Δ
IT can be set appropriately.

In this embodiment, the valve opening start interval ΔIT of the injector 5 is set so as to be close to any one of a half cycle τ / 2 of the fuel pressure fluctuation cycle τ or an integral multiple thereof. Instead, the correction may be made so as to be the time interval itself such as the substantially half cycle τ / 2.

Further, in this embodiment, the second injection timing IT2 is corrected in order to reduce the adverse effect due to the change in the fuel pressure. In addition, for example, FIG.
As shown in FIG. 7, when the fuel pressure becomes low at the start of the second valve opening of the injector 5, the second fuel injection amount Q2 is increased and corrected to compensate for the decrease in fuel injection amount due to this. When the valve opening period from the start of valve opening to valve closing is extended as shown in (c), or when the fuel pressure becomes high at the start of the second valve opening as shown in FIG. The valve opening period from the start of valve opening to valve closing may be shortened as shown in FIG. In this way, it is possible to suppress a change in the fuel injection amount due to a change in the fuel pressure and prevent a change in the torque of the engine 1.

(Embodiment 2) FIGS. 15 to 17 show a fuel injection control device A for an engine according to Embodiment 2 of the present invention. The overall configuration of the control device A shown in FIG.
Therefore, the same reference numerals are given to the same components as those in the first embodiment, and the description thereof will be omitted. And
In the control device A according to the second embodiment, when the injector 5 injects the fuel in two parts near the compression top dead center of the cylinder, the change in the fuel pressure supplied from the common rail 6 to the injector 5 is determined by the fuel pressure. The fuel pressure is estimated based on the value detected by the sensor 6a, and the fuel pressure at the second valve opening start time (second injection timing IT2) is lower than the set value due to the fuel pressure vibration accompanying the first valve opening of the injector 5. The pressure drop state detecting means 4 detects the pressure drop state.
When it is detected by 0c, the correction control means 40d corrects the second fuel injection amount Q2 and the second injection timing IT2 by the injector 5.

More specifically, as schematically shown in FIG. 16A, the fuel pressure supplied to the injector 5 attenuates while periodically fluctuating after the first valve opening of the injector 5. , Converges to the initial value P0. If the fuel pressure is equal to or more than the first set value P1 and equal to or less than the second set value P2, an appropriate fuel injection pressure is obtained,
As in the first embodiment, fuel can be injected while avoiding the influence of pressure fluctuation. Therefore, first, based on the signal from the fuel pressure sensor 6b, the fuel pressure (injector inlet pressure) actually supplied to the injector 5 is estimated and calculated. That is, the average fuel pressure in the common rail 6 is detected by the input signal from the fuel pressure sensor 6b, and the fuel pressure per unit time by the high pressure supply pump 8 and the fuel per unit time by the injector 5 of each cylinder 2 are detected. The injection amount is estimated, and the fuel pressure supplied to the injector 5 is estimated based on the detection result and the estimation result.

If the fuel pressure at the second injection timing IT2 is lower than the first set value P1, as shown in FIG. 9B, it is detected that the pressure is in a reduced state, and the fuel injection due to this is detected. In order to compensate for the decrease in the amount, a correction is made to extend the valve opening period from the start of valve opening to the valve closing as shown in FIG. On the other hand, if the fuel pressure at the second injection timing IT2 is higher than the second set value P2, as shown in FIG. As shown, a correction is made to shorten the valve opening period.
That is, by correcting the second fuel injection amount Q2 so as to cancel the change in the fuel injection pressure, the change in the actual fuel injection amount can be suppressed.

Alternatively, as shown in FIGS. 17B and 17C, the fuel pressure at the second injection timing IT2 is reduced to the first set value P1.
When the pressure is lower than the second injection timing,
IT2 may be advanced, so that even if the fuel injection pressure drops at the start of the second valve opening of the injector 5 and the fuel injection amount decreases, the injection By increasing the heat generation rate by the advance angle correction, it is possible to alleviate a decrease in engine output due to a decrease in the fuel injection amount. Conversely, when the fuel pressure at the second injection timing IT2 is higher than the second set value P2, the engine is corrected by retarding the second injection timing IT2, as shown in FIGS. An increase in output can be reduced.

Therefore, according to the second embodiment, when fuel is divided into two injections by the injector 5 near the compression top dead center of the cylinder 2 during the normal operation of the engine 1, the injector 5 The fuel pressure fluctuates with the first valve opening, and the fuel injection pressure becomes the initial value P at the time of the second valve opening.
Even if there is a large deviation from 0, the change in the engine output can be reduced by increasing or decreasing the second fuel injection amount Q2 by the correction control means 40d so as to reduce the change in the fuel injection amount due to this. Alternatively, 2 of the injectors 5
Even if the fuel injection pressure greatly deviates from the initial value P0 at the time of the second valve opening and the fuel injection amount fluctuates due to this, the second injection timing IT2 is advanced or retarded by the correction control means 40d. Thus, fluctuations in the engine output can be reduced.

(Other Embodiments) The present invention relates to the first embodiment.
Alternatively, the present invention is not limited to the embodiment 2 and includes other various embodiments. That is, in each of the above embodiments, the main injection performed near the compression top dead center of each cylinder 2 of the engine 1 is divided into two or three times. However, the present invention is not limited to this, and the main injection is performed twice or three times. It may be divided into any of seven times. Further, when performing so-called pilot injection or post-injection before and after the main injection, the valve opening start interval between the pilot injection and the main injection or the valve opening start interval between the main injection and the post-injection is determined by the main injection. The determination may be made in the same manner as the first and second valve opening start intervals of the injection.

In the second embodiment, the fuel pressure decreases with the first valve opening of the injector 5, and the fuel injection pressure becomes lower than the first set value P1 at the time of the second valve opening. Sometimes, the advance angle of the second injection timing IT2 of the injector 5 is corrected so as to suppress a decrease in engine output due to this, but the invention is not limited to this, and for example, FIGS. 18B to 18E. As schematically shown in FIG. 5, the second injection timing IT2 may be advanced or retarded so that the fuel injection pressure at the start of the valve opening becomes equal to or higher than the first set value P1.

Further, in each of the above embodiments, as shown in FIG. 2, the injector 5 in which the heart valve 5a is operated by the fuel pressure supplied from the common rail 6 is used. An injector that is opened and closed by an element or the like may be used. Even when such an injector is used, if the fuel injection pressure at the start of valve opening of the injector is low, the force due to the fuel pressure acting on the front side of the core valve becomes small, and the opening operation is slow. Therefore, a phenomenon similar to that of the above-described embodiment is observed. Therefore, it is an important operation and effect to be able to avoid the fluctuation of the fuel injection pressure at the start of the valve opening.

In each of the above embodiments, the engine 1
A catalyst 30 having a NOx absorbent is disposed in the exhaust passage 28 of the first embodiment, and the concentration of oxygen in the exhaust gas is forcibly reduced during operation of the engine 1 to release NOx from the catalyst 30. It is needless to say that the present invention is not limited to such a fuel injection control device, but can be applied to an engine without the catalyst 30 made of a NOx absorbent. Further, the engine is not limited to the diesel engine 1, but may be applied to a fuel injection control device of a gasoline engine as long as the pressure storage means for storing fuel supplied to the fuel injection valve in a high pressure state higher than the injection pressure is provided. It is.

[0095]

As described above, according to the fuel injection control apparatus for an engine according to the first aspect of the present invention, the fuel injection valve is operated during one combustion cycle of the cylinder by the split injection control means during operation of the engine. Opening interval setting means for setting a valve opening start interval from the start of the first valve opening to the start of the second valve opening at a predetermined time interval when fuel injection by the fuel injection is performed at least twice. If the valve opening start interval setting means sets the valve opening start interval to a predetermined time interval at which the fuel pressure becomes sufficiently high again, the fuel pressure fluctuates with the first valve opening. Even when this is the case, it is possible to prevent the fuel injection pressure from significantly increasing or decreasing at the start of the second valve opening, thereby reducing engine torque fluctuation and deterioration of the combustion state.

According to the second aspect of the present invention, the valve opening start interval is set to be equal to or longer than the time when the fuel pressure supplied to the fuel injection valve drops once and then rises again to a predetermined value. Even when the first and second valve opening operations of the injection valve are performed at extremely short time intervals, the fuel injection pressure is prevented from drastically decreasing at the time of the second valve opening. Can be sufficiently obtained.

According to the third aspect of the present invention, the second valve opening of the fuel injection valve is set by setting the valve opening start interval to approximately one half of the fluctuation period of the fuel pressure or an integral multiple thereof. The fuel injection pressure at the start can be made substantially the same as that at the first time, thereby preventing the engine torque fluctuation and the deterioration of the combustion state.

According to the fourth aspect of the invention, the pressure state of the fuel stored in the pressure accumulating means is detected by the fuel pressure detecting means, and the valve opening start interval is set based on the detection result.
Even if the pressure oscillation cycle changes due to a change in the pressure state of the fuel, the valve opening start interval can be appropriately set to correspond to the change.

According to the fifth aspect of the invention, one of the fuel injection valves is provided.
By measuring the elapsed time after the start of the second valve opening by the time measuring means, it is possible to start the second valve opening of the fuel injection valve when a time corresponding to the valve opening start interval has elapsed accurately. .

According to the sixth aspect of the present invention, in a direct injection type diesel engine having a relatively high fuel injection pressure, the fuel split injection can be performed while avoiding the adverse effect of the fuel pressure fluctuation as in the first aspect of the present invention. Becomes extremely effective.

According to the fuel injection control device for an engine according to the seventh aspect of the present invention, the fuel injection by the fuel injection valve is performed at least twice during one combustion cycle of the cylinder by the divided injection control means during the operation of the engine. When the fuel injection valve is divided into two, the fuel pressure becomes lower than the set value at the time of the second opening of the fuel injection valve with the first opening of the fuel injection valve. If detected, the correction control means corrects the second valve-opening start timing or valve-opening period. Therefore, even if the fuel injection amount is reduced due to a decrease in fuel pressure, the decrease in engine output due to the decrease is caused. Can be reduced.

According to the eighth aspect of the present invention, the pressure state of the fuel stored in the pressure accumulating means is detected by the fuel pressure detecting means, and the fact that the pressure is low is detected based on the detection result. The effect of the invention of Item 7 can be sufficiently obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of a diesel engine fuel injection control device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a schematic configuration of an injector.

FIG. 3 shows the NOx absorption and purification performance by the NOx absorbent (a).
FIG. 4 is a diagram showing an example of a graph showing temperature dependency of NOx reduction purification performance (b) by a catalyst metal.

FIG. 4 shows the respective injection modes when the main injection is performed collectively (a), divided into two parts (b), or divided into three parts (c), and when pre-injection is performed (d) and (e). FIG.

FIG. 5 is a graph showing a change characteristic of the CO concentration in exhaust gas when the number of divisions of fuel injection and the injection pause interval are respectively changed.

FIG. 6 is a diagram corresponding to FIG. 4 showing a change characteristic of NOx concentration in exhaust gas.

FIG. 7 is a diagram corresponding to FIG. 4, showing a change characteristic of a fuel efficiency of an engine.

FIG. 8 is a diagram corresponding to FIG. 4 showing a change characteristic of the exhaust gas temperature.

FIG. 9 is a flowchart illustrating a setting procedure of a basic fuel injection amount and a processing procedure of NOx release control in fuel injection control.

FIG. 10 is a flowchart showing a procedure for setting an injection mode in fuel injection control.

FIG. 11 is a flowchart illustrating a processing procedure of injector operation control in fuel injection control.

FIG. 12 is an explanatory diagram showing a change in fuel pressure supplied to an injector and a change in an injection rate due to the change.

FIG. 13 is an explanatory diagram showing a procedure for correcting a second valve opening start timing of the injector based on a fuel pressure fluctuation cycle.

FIG. 14 is an explanatory diagram showing a procedure for correcting the valve opening period of the injector so as to correspond to the fuel pressure.

FIG. 15 is a diagram corresponding to FIG. 1 according to the second embodiment of the present invention.

FIG. 16 is an explanatory diagram showing a procedure for estimating the fuel pressure based on the common rail pressure and correcting the valve opening period of the injector based on the estimation result so as to suppress the fluctuation of the engine output.

FIG. 17 is an explanatory diagram showing a procedure for correcting the second valve opening start timing of the injector based on the estimation result of the fuel pressure so as to suppress the fluctuation of the engine output.

FIG. 18 is an explanatory diagram showing a procedure for estimating the fuel pressure based on the common rail pressure and correcting the second valve opening start timing of the injector based on the estimation result so as to suppress the fluctuation of the engine output.

[Explanation of symbols]

 A fuel injection control device for engine 1 diesel engine 2 cylinder 4 combustion chamber 5 injector (fuel injection valve) 6 common rail (accumulation means) 6b fuel pressure sensor (fuel pressure detection means) 40a split injection control means 40b valve opening start interval setting means 40c Pressure drop detection means 40d Correction control means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G066 AA01 AA07 AA11 AA13 AC09 BA12 BA17 BA24 CB12 CC05U CD26 CE22 CE29 DA04 DB12 DB16 DC04 DC05 DC11 DC13 DC14 DC18 3G301 HA01 HA02 HA11 HA13 JA02 JA04 JA24 KA05 KA12 KA24 LA03 LB11 MA11 MA19 MA23 MA26 MA27 MA28 NA01 NA08 NB02 NE01 NE06 NE11 NE12 NE13 NE15 NE23 PA04Z PB03Z PB08Z PD12Z PE03Z PE06Z PE08Z PF03Z

Claims (8)

[Claims] A fuel is directly injected into a combustion chamber in a cylinder of an engine.
A fuel injection valve for injecting and supplying, pressure accumulating means connected to the fuel injection valve for storing fuel in a high pressure state equal to or higher than an injection pressure, and at least two times during one combustion cycle of a cylinder by the fuel injection valve. A fuel injection control device for an engine, comprising split injection control means for performing split injection and a split injection control means, wherein the split injection control means controls a valve opening start interval from the first opening of the fuel injection valve to the second opening of the fuel injection valve. A fuel injection control device for an engine, comprising: valve opening start interval setting means for setting a predetermined time interval. 2. The fuel injection valve according to claim 1, wherein the valve opening start interval setting means sets the valve opening start interval as the fuel pressure supplied from the pressure accumulating means to the fuel injection valve.
A fuel injection control device for an engine, characterized in that the fuel injection control device is configured to set a length of time equal to or longer than a time required for the pressure to decrease and increase again to reach a predetermined value with the opening of the valve. 3. The fuel supply system according to claim 2, wherein the fuel pressure supplied to the fuel injector fluctuates periodically with the elapse of time after the start of valve opening of the fuel injector. A fuel injection control device for an engine, wherein the valve opening start interval of the fuel injection valve is set to substantially one half cycle of the fluctuation cycle of the fuel pressure or any one of integral multiples thereof. . 4. The fuel supply system according to claim 3, further comprising a fuel pressure detecting means for detecting a pressure state of the fuel stored in the pressure accumulating means, wherein the valve opening start interval setting means sets the valve opening start interval of the fuel injection valve to the fuel pressure. A fuel injection control device for an engine, wherein the setting is made so as to be shorter as the state is higher. 5. The engine according to claim 2, further comprising a time measuring means for measuring an elapsed time after the first opening of the fuel injection valve is started by the split injection control means. Fuel injection control device. 6. The engine according to claim 1, wherein the engine is a direct-injection diesel engine, and the split injection control means injects the fuel by the fuel injection valve twice in the vicinity of the compression top dead center of the cylinder. A fuel injection control device for an engine, comprising: 7. Fuel is directly supplied to a combustion chamber in a cylinder of an engine.
A fuel injection valve for injecting and supplying, pressure accumulating means connected to the fuel injection valve for storing fuel in a high pressure state equal to or higher than an injection pressure, and at least two times during one combustion cycle of a cylinder by the fuel injection valve. A fuel injection control device for an engine, comprising: split injection control means for splitting and injecting fuel; and a pressure for detecting that a fuel pressure supplied from the pressure accumulating means to a fuel injection valve is a pressure drop state lower than a set value. When the pressure drop state at the time of the start of the second valve opening of the fuel injection valve is detected by the low state detection means and the pressure low state detection means, the second valve opening start timing of the fuel injection valve is advanced. And a correction control unit that performs at least one of correction for increasing the period from the start of valve opening to the closing of the valve. 8. The fuel pressure detecting means according to claim 7, further comprising fuel pressure detecting means for detecting a pressure state of the fuel stored in the pressure accumulating means, wherein the pressure drop detecting means detects the fuel pressure supplied to the fuel injection valve. The fuel injection control device for an engine is configured to estimate based on the detected value of the engine, and to detect the pressure drop state when the estimated value is lower than a set value.