JP2001055950A - Fuel injection control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate discharging of NOx etc., from catalyst without causing deterioration of fuel consumption performance nor abrupt increasing of smoke in a fuel injection control device which is prepared by arranging NOx absorption and reduction type catalyst on an exhaust passage of a direct injection type diesel engine, and reducing oxygen density in exhaust gas for refreshing the catalyst by increasingly correcting a fuel injection amount when the NOx absorption amount in the catalyst is increased. SOLUTION: Injection amount and form of fuel from an injector 5 are controlled by a reference fuel injection control means 35a according to a target torque and a rotational speed of an engine 1. Main injection is carried out in a divided form near a top dead center of compression of a cylinder by an injection form correction means 35c when temperature of catalyst 22 is low at the time of discharging NOx from the catalyst 22. Afterward, the fuel injection amount is increasingly corrected by an injection amount correction means 35b. IN addition, pre-injection is carried out in an initial stage of compression stroke of the cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of disposing an NOx absorbent for absorbing NOx in exhaust gas in an oxygen-excess atmosphere in an exhaust passage of a diesel engine. The present invention relates to a fuel injection control device that controls a fuel injection amount and the like so that the oxygen concentration of the fuel injection decreases.

[0002]

2. Description of the Related Art Conventionally, as a fuel injection control device for a diesel engine of this type, for example, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent No. 61, in addition to performing normal fuel injection near the compression top dead center of a cylinder, in a predetermined operation state, a small amount of fuel (light oil) is additionally supplied from the middle stage of the expansion stroke to the exhaust stroke. Further, there is known an apparatus in which the function of a NOx absorbent provided in an exhaust passage is restored (refreshed) by increasing the concentration of a reducing agent component in exhaust gas.

That is, a diesel engine is usually operated in a state where the air-fuel ratio is considerably lean (for example, A / F ≧ 18 and the oxygen concentration in the exhaust gas is 4% or more). It is extremely difficult to reduce and purify NOx with NOx.
There is a technique using a so-called NOx absorbent that absorbs x and releases NOx when the oxygen concentration decreases.

[0004] Since the NOx absorbent has the property that its absorption performance decreases as the amount of NOx absorbed increases, the conventional fuel injection device requires that the absorption performance of the NOx absorbent be reduced before the NOx absorption material greatly decreases. Additional fuel is injected during the expansion stroke of the cylinder, and the combustion (afterburning) of this fuel consumes oxygen in the exhaust gas to reduce the oxygen concentration to, for example, 0.5% or less, and also reduces CO, HC, etc. in the exhaust gas. , The concentration of the reducing agent component is increased, the release of the NOx from the NOx absorbent is promoted by the reducing agent component, and the NOx is sufficiently reduced and purified to recover the absorption performance of the NOx absorbent. .

[0005]

In general, it is known that the above-mentioned NOx absorbents absorb and release NOx depending on the temperature condition. For example, NO in exhaust gas by NOx absorbent
Although the x purification rate is sufficiently high in a predetermined temperature range, for example, as shown in FIG. 3 (a), it has a characteristic that it rapidly decreases when the catalyst having a low temperature state is not warmed up. With respect to such characteristics of the NOx absorbent, the exhaust temperature of a diesel engine having excellent thermal efficiency tends to be lower than that of a gasoline engine.
There is a problem in that the temperature state of the x-absorbing material becomes lower than the predetermined temperature range, and the effect of absorbing and releasing NOx cannot be sufficiently exerted.

Further, when the additional fuel is injected during the expansion stroke of the cylinder when the NOx absorbent is refreshed as in the above-described conventional example, the combustion state of the fuel is significantly deteriorated, and the amount of smoke emission is reduced. There is a possibility that the fuel consumption will increase rapidly, and extra fuel that does not contribute to the engine output will be injected.

[0007] The present invention has been made in view of the above points, and an object thereof is to dispose a NOx absorbent in an exhaust passage of a diesel engine to purify NOx in exhaust gas in an oxygen-excess atmosphere. In what we did,
In particular, by devising the procedure of the fuel injection control at the time of refreshing the NOx absorbent, the temperature state of the NOx absorbent is raised to promote NOx emission and the like without causing deterioration in fuel efficiency and a sudden increase in smoke. It is in.

[0008]

In order to achieve the above-mentioned object, according to a solution of the present invention, when a NOx absorbent is disposed in an exhaust passage, when the NOx is released from the NOx absorbent, At the latest, the fuel injection amount is increased and corrected, and at the same time, the fuel injection (hereinafter also referred to as main injection) in the vicinity of the compression top dead center of the cylinder by the fuel injection valve is performed in a plurality of times.

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 combustion chamber 4 in a cylinder 2 of an engine 1 and an exhaust passage 20 of the engine 1 are provided. And a NOx absorbent 22 that absorbs NOx in exhaust gas in an oxygen-rich atmosphere having a high oxygen concentration and releases the absorbed NOx as the oxygen concentration decreases. Basic fuel injection control means 35a for controlling the state at least in accordance with the operating state of the engine 1; and fuel by the fuel injection valve 5 such that when releasing NOx from the NOx absorbent 22, the oxygen concentration in the exhaust gas is reduced. It is assumed that the fuel injection control device A of the diesel engine includes an injection amount correction unit 35b for increasing and correcting the injection amount. When the NOx is released from the NOx absorbent 22, the fuel is injected by the fuel injection valve 5 several times in the vicinity of the compression top dead center of the cylinder 2 at the same time as the increase correction of the fuel injection amount by the injection amount correction means 35b at the latest. A configuration is provided in which an injection mode correction unit 35c that performs split injection is provided.

With the above configuration, when NOx is released from the NOx absorbent 22 during operation of the engine 1, the injection by the injection form correction means 35c is performed at the latest when the fuel injection amount is corrected to be increased by the injection amount correction means 35b. Correction control of the mode is performed, and the main injection is performed by the fuel injection valve 5 in a plurality of times. As a result, the state of mixing of the fuel injected with the air near the compression top dead center of the cylinder 2 with the air is greatly improved, the rate of heat generation by combustion increases, and the end of combustion shifts to the retard side, and the exhaust gas is exhausted. As the temperature rises,
The temperature state of the NOx absorbent 22 is quickly raised.

Further, since the fuel injection amount is increased and corrected by the injection amount correcting means 35b, the concentration of oxygen in the exhaust gas decreases and the concentration of the reducing agent components such as CO and HC increases. It is possible to promote the release of NOx from the NOx absorbent 22 having a high temperature state and sufficiently reduce and purify the NOx. Moreover, since the combustion state is greatly improved by the division of the main injection, even if the fuel injection amount is increased, the smoke does not suddenly increase.

According to the second aspect of the present invention, the injection mode correcting means is configured to split and inject the fuel by the fuel injection valve before the fuel injection amount is increased by the injection amount correcting means.

[0013] By doing so, before increasing the fuel injection amount for refreshing the NOx absorbent, the NO.
Since the temperature state of the x-absorbing material can be increased, the NOx absorbing material can be refreshed extremely efficiently. In addition, by dividing the fuel injection, the H
Since the C and CO concentrations tend to increase, even if the air-fuel ratio of the combustion chamber of the engine temporarily becomes a state in which NOx is actively generated with the increase in the fuel injection amount thereafter, NO to the atmosphere is reduced.
It is possible to suppress a rapid increase in x emission.

According to the third aspect of the present invention, the injection mode correction means sets the number of divisions of the fuel injection in the vicinity of the compression top dead center of the cylinder to any one of 2 to 7 times.
It is assumed that the fuel injection valve is opened and closed so that the injection stop interval from once closing to next opening is within the range of 500 microseconds to 1 millisecond. In this case, the function and effect of the invention of claim 1 or 2 can be sufficiently obtained.

According to a fourth aspect of the present invention, the basic fuel injection control means causes the fuel injection valve to collectively inject fuel near the compression top dead center of the cylinder. By doing so, the number of opening and closing operations of the fuel injection valve can be relatively reduced, and the reliability of the fuel injection valve is improved.

According to the fifth aspect of the present invention, the basic fuel injection control means injects the fuel in two or more times near the compression top dead center of the cylinder by the fuel injection valve, and closes the fuel injection valve once. The opening / closing operation is performed so that the injection pause interval from one time to the next opening is within the range of 100 microseconds to 1 millisecond. Further, the injection mode correction means increases at least one of the number of divisions of fuel injection by the fuel injection valve and the injection suspension interval.

In this configuration, even in the normal running state of the vehicle, the division of the main injection is controlled by the basic fuel injection control means, so that the combustion is improved as a whole. Also, if the number of divisions of the fuel injection or the injection pause interval is increased, the C
Since the concentrations of O and HC tend to increase, when the NOx absorbent is refreshed, this fact can be used to promote the refresh of the NOx absorbent.

According to a sixth aspect of the present invention, the injection mode correcting means in the second aspect of the present invention is configured such that the number of divisions of the fuel injection in the vicinity of the compression top dead center of the cylinder is corrected before the fuel injection amount is increased. It should be corrected so that it becomes larger than after the start. As a result, when the number of divisions of the fuel injection is increased, the exhaust gas temperature tends to increase. Therefore, the temperature state of the NOx absorbent can be quickly increased before the increase in the fuel injection amount is corrected.

According to the seventh aspect of the present invention, when the fuel injection amount is increased by the injection amount correcting means, the injection mode correcting means is controlled by the fuel injection valve in addition to the fuel injection near the compression top dead center of the cylinder. At least one additional fuel injection shall be performed. By doing so, even if the total fuel injection amount in one combustion cycle of the engine increases, the fuel injection amount near the compression top dead center does not become excessively large. Fluctuations can be suppressed.

According to an eighth aspect of the present invention, the injection mode correction means in the seventh aspect of the invention causes the sub-injection of any one of the intake stroke or the compression stroke of the cylinder or the first half of the expansion stroke as additional fuel injection. In addition, at least one of the number of fuel injection divisions and the injection pause interval near the compression top dead center of the cylinder is corrected so that the output torque of the engine decreases. As a result, the increase in the engine output due to the correction of the increase in the fuel injection amount is moderated, and the occurrence of torque shock when the NOx absorbent is refreshed can be prevented.

According to a ninth aspect of the present invention, the injection mode correcting means according to the eighth aspect of the present invention causes the fuel injection valve to inject an amount of fuel corresponding to the required output of the engine in the vicinity of the compression top dead center of the cylinder. It is assumed that the fuel for the increase correction by the amount correction means is sub-injected. In this way, in the vicinity of the compression top dead center of the cylinder, the fuel injection valve injects the basic fuel injection amount corresponding to the required output of the engine, while the fuel for the increase correction is injected by the secondary injection. As a result, the control procedure is simplified.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Overall Configuration) FIG. 2 shows an overall configuration of a diesel engine fuel injection control device A according to an embodiment of the present invention, and 1 is a multi-cylinder diesel engine mounted on a vehicle. This engine 1 has a plurality of cylinders 2,
(Only one is shown), and a piston 3 is inserted into each cylinder 2 so as to be able to reciprocate, and a combustion chamber 4 is defined in each cylinder 2 by 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 is opened and closed at a predetermined injection timing for each cylinder. Then, the fuel is directly supplied to the combustion chamber 4 by injection.

Each of the injectors 5 is connected to a common rail 6 for storing fuel in a high pressure state. The common rail 6 is provided with a pressure sensor 6a for detecting an internal fuel pressure (common rail pressure), and is connected to a high-pressure supply pump 8 driven by a crankshaft 7. By operation, the fuel pressure in the common rail 6 is maintained at a predetermined value or more. Further, a crank angle sensor 9 including an electromagnetic pickup for detecting a rotation angle of the crank shaft 7 is provided. The crank angle sensor 9 is disposed so as to oppose the outer periphery of a plate to be detected (not shown) provided at the end of the crankshaft 7, and a protrusion formed on the outer periphery of the plate to be detected , A pulse signal is output.

An intake passage 10 for supplying intake air (air) filtered by an air cleaner (not shown) to the combustion chamber 4 of each cylinder 2 is connected to one side (left side in the figure) of the engine 1.
The downstream end of the intake passage 10 is branched into cylinders via a surge tank (not shown), and communicates with the combustion chamber 4 of each cylinder 2 through an intake port. Further, an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2 in the surge tank is provided. 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 taken into the engine 1, and a blower 12 driven by a turbine 21 to compress the intake air. An intercooler 13 for cooling intake air compressed by the blower 12, and an intake passage 1
And an intake throttle valve 14 for reducing the cross-sectional area of zero. 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 diaphragm 1
The opening degree of the valve is controlled by adjusting the magnitude of the negative pressure acting on 5 by the negative pressure control electromagnetic valve 16.

On the other hand, an exhaust passage 2 for discharging exhaust gas from the combustion chamber 4 of each cylinder 2 is provided on the other side of the engine 1 (right side in the figure).
The upstream end of the exhaust passage 20 is branched, and communicates with the combustion chamber 4 of each cylinder 2 through an exhaust port (not shown). An O2 sensor 17 for detecting the concentration is provided. Further, a water temperature sensor 18 for detecting a cooling water temperature (engine water temperature) facing the water jacket of the engine 1 is provided. Further, the exhaust passage 2
At 0, a turbine 21 rotated by an exhaust flow and an exhaust gas purifying catalyst 22 for purifying harmful components in the exhaust gas are arranged in order from the upstream side to the downstream side. Although not shown in detail, the turbocharger 25 including the turbine 21 and the blower 12 has a plurality of flaps disposed so as to surround the entire periphery of the turbine 21, 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 21.

The catalyst 22 has a cordierite carrier (carrier member) having a honeycomb structure having a large number of through holes extending parallel to each other along an axial direction (flow direction of exhaust gas).
, And two catalyst layers are formed on the walls of each through hole. Specifically, a noble metal such as platinum Pt and barium Ba as a NOx absorbent are supported on the inner catalyst layer by using a porous material such as alumina or ceria as a support material, while the outer catalyst layer is supported by the outer catalyst layer. Platinum Pt and Rhodium R
h and Ba are supported on a porous material of zeolite 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 22
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 condition. For example, as shown in FIG. 3A, the purification rate of the catalyst 22 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. The temperature condition is 400 °
When the temperature exceeds C, the NOx purification rate decreases with an increase in temperature. 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. Is rapidly falling.

In the catalyst 22, barium Ba is 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 22, 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, and 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 20 is a portion upstream of the turbine 21 and is branched and connected to an upstream end of an exhaust gas recirculation passage 23 (hereinafter, referred to as an EGR passage) for recirculating a part of exhaust gas to the intake side. The downstream end of the EGR passage 23 is connected to the intake passage 10 downstream of the intake throttle valve 14, and a negative pressure operated exhaust gas recirculation amount control valve 24 ( (Hereinafter referred to as EGR valve)
And a part of the exhaust gas in the exhaust passage 20 is
Exhaust recirculation means for recirculating air to the intake passage 10 while adjusting the flow rate by the valve 24 is provided. That is, the EGR
The opening degree of the valve 24 is linearly adjustable. A diaphragm 26 for operating the valve body is connected to a vacuum pump (negative pressure source) 29 by a negative pressure passage 27, and the diaphragm 26 is connected to the vacuum pump 27. The operation of the installed solenoid valve 28 causes E
The opening / closing operation is performed by adjusting the GR valve driving negative pressure.

A diaphragm 30 is attached to the flap of the turbocharger 25 similarly to the EGR valve 24, and the diaphragm 3 is controlled by a solenoid valve 31 for negative pressure control.
By adjusting the negative pressure acting on zero, the operation amount of the flap is adjusted.

Each of the injectors 5, high-pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25
The flaps etc. of the control unit (Engine Contoro
l Unit: hereinafter referred to as ECU). On the other hand, this ECU 3
5, an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9 (crank angle signal), an output signal from the air flow sensor 11, an O2 sensor 17
And the output signal from the water temperature sensor 18,
At least an output signal from an accelerator opening sensor 32 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle is input.

Then, the fuel injection control by the operation of the injector 5 is performed, the fuel injection amount and the fuel injection timing are controlled according to the operating state of the engine 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. Further, the recirculation amount of the exhaust gas is adjusted by the operation of the EGR valve 24, and the air-fuel ratio of each of the in-cylinder combustion chambers 4 is controlled according to the operating state of the engine 1. In addition to this, the intake air The control of the intake air amount by the operation of the throttle valve 14 and the operation control of the flap of the turbocharger 25 are performed.

(Fuel Injection Control) Specifically, the ECU 3
5 stores electronically a map of a basic fuel injection amount Q experimentally determined in accordance with changes in the target torque and the rotation speed of the engine 1. The output from the accelerator opening sensor 32 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 9, 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 35, an injection mode map in which the fuel injection mode near the compression top dead center of the cylinder 2 is set in accordance with the target torque and the engine speed in the same manner as in 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, as shown in FIG. 4 (a), the fuel is injected collectively near the compression top dead center (hereinafter referred to as collective injection), or divided into two injections as shown in FIG. 4 (b). Either injection (called two-split injection) or three-split injection as shown in FIG. 3C (called three-split injection) is selected.
When the injection is divided into injections, the injection stop interval Δt during the injection is changed to change the combustion state so that the fuel consumption performance and the exhaust characteristics of the engine 1 are optimized.

On the other hand, N in the catalyst 22 of the exhaust passage 20
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 (d), the fuel is controlled to a state near or substantially equal to the stoichiometric air-fuel ratio. By performing the injection by the pre-injection (sub-injection), the concentration of oxygen in the exhaust gas is reduced and the concentration of the reducing agent component is increased, so that the NOx absorbed from the catalyst 22 is released and sufficiently reduced and purified. , NOx release control).

In the fuel injection modes shown in FIGS. 4A to 4D, 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. It is determined in consideration of the common rail pressure. When the main injection is divided, the end timing of the third injection is 35 ° CA (ATD
(C35 ° CA), but in this case, in order to avoid the deterioration of the combustion state of the fuel injected so late, as shown in FIG.
A part of the fuel is pre-injected after the middle stage of the compression stroke of the cylinder 2.

Here, the combustion state when the main injection near the compression top dead center of the cylinder 2 is performed as described above will be described. The fuel is injected by the injector 5 near the compression top dead center of the cylinder 2. When the fuel is injected, the fuel injected from the injection hole of the injector 5 spreads into the combustion chamber 4 while forming a spray having a conical shape as a whole, and splits into small oil droplets by friction with air (fuel Of the oil droplets, and the fuel evaporates from the surface of the oil droplets to generate fuel vapor (vaporization and atomization of the fuel). At this time, since the air in the combustion chamber 4 is in a state of extremely high pressure and high viscosity, as shown in FIG. Subsequent fuel oil droplets catch up with the previously ejected fuel oil droplets and recombine, which may hinder atomization of the fuel and eventually vaporization and atomization.

On the other hand, as shown in FIGS. 4B and 4C, if the fuel is divided and injected plural times, the fuel oil droplets ejected by the valve opening of the injector 5 will 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 the injection timing, the injection rate, the fuel pressure, the number of divided injections, the injection pause interval, and the relationship between them also change, and the combustion state changes with the change. Or CO in the exhaust,
It is considered that the concentration of gas components such as HC and NOx changes.

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. 8. The exhaust gas temperature is higher in the two-split injection than in the batch injection, and the exhaust temperature is higher in the three-split injection than the two-split injection. It turns out that it becomes. From this, it is considered that, for example, by performing the split control of the main injection before performing the NOx release control, the temperature state of the catalyst 22 can be increased and the refresh thereof can be promoted.

Therefore, in the fuel injection control of this embodiment, when the catalyst 22 becomes excessively NOx-absorbed during the operation of the engine 1 and needs to be refreshed, the catalyst 22 may be in an unwarmed state. For example, first, the split control of the main injection is performed to quickly raise the temperature state of the catalyst 22 and gradually increase the CO and HC concentrations in the exhaust gas. continue,
By increasing the amount of fuel injection and the like, the concentration of oxygen in the exhaust gas is reduced, and the concentrations of CO and HC are sufficiently increased to promote the refresh of the catalyst 22 to the maximum.

Hereinafter, a specific fuel injection control 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 O2 sensor output, an accelerator opening, and an engine coolant temperature are input. Based on the target torque obtained from the opening degree and the engine speed Ne obtained from the crank angle signal, the basic fuel injection amount Qbase is read from the fuel injection amount map, 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 of the engine is different, the basic injection timing ITba
se is set.

Subsequently, at step SA3, it is determined whether or not the engine coolant temperature Tw is lower than the set coolant temperature Tw0. This set water temperature Tw0 is the value of the catalyst 2 during the cold start of the engine 1.
2 is the water temperature corresponding to the non-warmed-up state, and the engine water temperature Tw
If yes is lower than the set water temperature Tw0, step S
Proceeding to A4, the flag Fp indicating that the main injection split control is to be performed in order to promote warm-up of the catalyst 22 is turned on (Fp = 1), and the process proceeds to step SB1 in FIG. That is, if the catalyst 22 is not warmed up at the time of the cold start of the engine 1, the exhaust temperature is increased by the split control of the main injection so as to increase the temperature of the catalyst 22. 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 22 is in a warm-up state, and the process proceeds to step SA5.

In step SA5, the amount of NOx absorbed by the catalyst 22 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 22 (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 the period, or a temperature sensor is provided in the exhaust passage 20 near the catalyst 22. Thus, the estimation may be made directly based on the output from this sensor. Then, step SA
9, the estimated catalyst temperature Tc becomes equal to the first set temperature Tc1 (for example, 250 ° C.) at which the NOx removal performance of the catalyst 22 becomes low.
It is determined whether it is lower than C). If the determination is yes, the catalyst 22 is not warmed up and the NOx absorption or release action is 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 22
Even if it is considered that the purification performance of the catalyst 22 is reduced, if the catalyst 22 is not warmed up, the refreshing of the catalyst 22 due to the release of NOx cannot be sufficiently promoted. At this time, the temperature of the catalyst 22 is raised by split control of the main injection as described later, since the reduction and purification cannot be sufficiently performed.

The result of the determination at 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 11, a fuel injection amount is calculated such that the air-fuel ratio becomes substantially near the stoichiometric air-fuel ratio with respect to the intake air amount, and the fuel increase amount is calculated. 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 22
If it is considered that the purification performance of the catalyst 22 decreases, and the catalyst 22 is in a warm-up state, the catalyst 22 is refreshed by performing NOx release control to release NOx from the catalyst 22 and reducing and purifying. 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 accelerating operation state of the engine 1, by performing the split control of the main injection regardless of the state of the catalyst 22, the exhaust pressure is increased and the supercharging effect of the turbocharger 25 is enhanced. .

Following 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 22 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 first steps are performed.
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 explanation is omitted, it is determined whether the end timing of the third injection is later than ATDC 35 ° CA when the main injection is divided, and when it is determined that the end timing is later than the ATDC 35 ° CA, Of the injection stop interval Δt of FIG.
As shown in (e), the pre-injection amount Qp and the injection timing ITp are set in order to pre-inject excess fuel after the middle stage of the compression stroke of the cylinder 2. Then, after performing the injection end determination subroutine, step S in FIG.
Proceeding to C1 to SC11, the main injection is divided into three and executed as described later.

That is, in this flow, when the flag Fp is on (Fp = 1), in other words,
When the catalyst 22 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 22 is warmed up, the split control of the main injection is performed at any one of the three times when the engine 1 is in the accelerating operation state.

Further, at step SB1, it is determined that the flag Fp is in the OFF state, and the process proceeds to step SB1.
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. 4D, it is preferable that the pre-injection is performed from the beginning of the intake stroke of the cylinder 2 to the first half of the compression stroke. In this embodiment, the injection timing ITp of the pre-injection is determined by the intake timing 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 22 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 injection timing IT based on the crank angle signal
It is determined whether or not the fuel injection amount has reached base, and the flow waits until the injection timing comes (no in step SB11). If the injection timing comes (yes in step SB11), the routine proceeds to step SB12, where the main injection is performed and the basic fuel injection amount Qbase is calculated. The fuel is collectively injected into the combustion chamber 4 by the injector 5 and then returns. In other words, in the normal operating state of the engine 1, the fuel injection is performed collectively, so that the number of opening and closing operations of the injector 5 can be relatively reduced, and the reliability can be improved.

Then, steps SB5 and S5 in FIG.
Subsequent to B10, in step SC1 of FIG. 11, it is determined whether or not the value of the pre-injection amount Qp is zero.
If so, the process proceeds to step SC5, while if NO in QpＮＯ0, 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 is reached (NO in step SC2), and if the injection timing is reached (YES in step SC2), the process proceeds to step S2.
Proceeding to C3, pre-injection is performed, and fuel of the injection amount Qp is injected into the combustion chamber 4 by the injector 5. 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 come 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.

In each of the flows shown in FIGS. 9 to 11, at step SA2 shown in FIG. 9, the basic fuel injection amount and the like are determined according to the target torque of the engine 1, and at steps SC1 to SC11 shown in FIG. The basic fuel injection control means 35a for controlling the fuel injection state by the injector 5 according to at least the operating state of the engine 1 is constituted by the control procedure of injecting the fuel by the injector 5. The basic fuel injection control means 35
In the normal operation state of the engine 1, the fuel is collectively injected by the injector 5 near the compression top dead center of the cylinder.

Step SA6 of the flow shown in FIG.
According to the control procedures of steps SA16 to SA16, an injection amount correcting means 35b configured to increase and correct the fuel injection amount by the injector 5 so as to reduce the oxygen concentration in the exhaust gas when NOx is released from the catalyst 22 is configured. The injection amount correction means 35b corrects the fuel injection amount 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.

Further, step S in the flow shown in FIG.
According to the control procedure of each step of B1 to SB10, the catalyst 2
When NOx is released from the injection amount correction means 3,
Before the increase correction of the fuel injection amount is performed by the fuel injection amount 5b, an injection mode correcting means 35c is configured to inject the fuel by the injector 5 three times in the vicinity of the compression top dead center of the cylinder. When the fuel injection amount is increased by the injection amount correcting means 35b, the injection mode correcting means 35c performs pre-injection in the compression stroke by the injector 5 in addition to the main injection near the compression top dead center of the cylinder. Is performed.

Therefore, according to the diesel engine fuel injection control device A according to this embodiment, first, in the normal operation state, the basic fuel injection control means 35a causes each of the cylinders 2 as shown in FIG. The fuel of the basic fuel injection amount Qbase is collectively injected from the injector 5 near the compression top dead center, and the engine 1 is operated with the average air-fuel ratio of the combustion chamber 4 being lean. Then, when NOx generated by combustion is absorbed by the catalyst 22 and the amount of absorption becomes excessive, NOx release control for releasing NOx from the catalyst 22 to reduce and purify 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 22 is in a low temperature state corresponding to the unwarmed state, first, the main injection by the injection form correction means 35c is performed. Is performed, and the fuel is injected three times by the injector 5 near the compression top dead center of the cylinder. By this split injection, the mixing state of the fuel spray with the air is greatly improved, the air utilization rate is also improved, the heat generation rate by combustion is increased, and the end of combustion is shifted to the retard side. As shown in FIG. 2, the exhaust gas temperature rises, whereby the temperature state of the catalyst 22 in the exhaust passage 20 can be quickly raised.

After the catalyst 22 is quickly heated to a warm-up state as described above, NOx release control is performed, and the average air-fuel ratio of the combustion chamber is reduced by the injection amount correction means 35b to substantially the stoichiometric air-fuel ratio. The fuel injection amount from the injector 5 is corrected so as to increase the fuel ratio. As a result, the concentration of oxygen in the exhaust gas is reduced and the concentration of the reducing agent component such as CO or HC is sufficiently increased, so that NOx is quickly released from the catalyst 22, which has been heated as described above, and Can be reduced and purified. In addition, 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, so that the smoke Can be prevented from increasing rapidly.

That is, in this embodiment, during the NOx release control for refreshing the catalyst 22, the temperature state of the catalyst 22 is raised in advance before the correction of the increase of the fuel injection amount, so that the amount of fuel in the exhaust gas is increased. When the oxygen concentration is reduced, NOx can be released from the catalyst 22 with high efficiency, and the NOx can be sufficiently reduced and purified.

In addition, the main injection division control performed before the fuel injection amount is increased and corrected as described above allows the H
Since the C and CO concentrations increase, even if the generation of NOx temporarily becomes active due to the subsequent increase correction of the fuel injection amount,
The generated NOx will react with CO and HC,
NOx emissions to the atmosphere do not increase rapidly.

As described above, as a result that the catalyst 22 can be refreshed very efficiently, the time for performing the NOx release control during the operation of the engine 1 can be relatively shortened, so that the fuel injection amount can be increased. The accompanying deterioration in fuel efficiency can be suppressed. In addition, due to the split control of the main injection, as described above, the combustion state becomes extremely good, and the injection end timing is relatively late, but during that time, the pressure in the combustion chamber 4 is relatively long and sufficient. Maintained in a high state, the mechanical efficiency is also improved by the improvement of the so-called equal capacity, and the fuel efficiency is improved.

(Other Embodiments) The present invention is not limited to the above embodiments, but includes other various embodiments. That is, in the above-described embodiment, the fuel is divided into three injections by the split control of the main injection. However, the present invention is not limited to this.
As the O concentration increases and the temperature state of the catalyst 22 increases,
The number of divisions may be set to any one of 2 to 7 times.

In the above embodiment, the main injection is performed collectively in the normal operation state of the engine 1. However, the present invention is not limited to this, and the main injection is basically performed in two or more times. The injection suspension period Δt may be set relatively short within a range of 100 microseconds to 1 millisecond. By doing so, for example, by making the main injection a two-split injection, the fuel efficiency can be improved as shown in FIG. In this case, at least one of the number of divisions of the main injection or the injection pause interval Δt may be increased at the time of the NOx release control, whereby the same operation and effect as the above embodiment can be obtained. Can be

In the above embodiment, the temperature state of the catalyst 22 is estimated, and when the temperature state is low, the split control of the main injection for raising the temperature of the catalyst 22 is performed prior to the correction of the increase in the fuel injection amount. But it is not limited to this.
When performing the Ox release control, the temperature state of the catalyst 22 may be first increased by the split control of the main injection, and then the fuel injection amount may be increased. At that time,
The number of divisions of the main injection may be greater before the fuel injection amount is increased than after the start of the increase correction, so that the temperature of the catalyst 22 can be more effectively increased. (See FIG. 8).

Further, in the above-described embodiment, the injector 5 is used as an additional injection other than the main injection during the NOx release control.
, The pre-injection is performed in the intake stroke or the compression stroke of the cylinder. However, the present invention is not limited to this, and additional fuel injection (post-injection) may be performed in the expansion stroke or the exhaust stroke of the cylinder. . For example, by performing pre-injection in the high load operation state of the engine 1 and performing post-injection in the low and medium load operation state of the engine 1, it is possible to increase smoke in a wide operating region where the load state of the engine 1 is different. The oxygen concentration in the exhaust gas can be reduced while suppressing it.

Alternatively, the pre-injection is performed, or the post-injection is performed particularly in the first half of the cylinder expansion stroke.
At least one of the number of divisions of the main injection and the injection pause interval may be increased. In this way, even if the fuel injection amount is increased by the pre- and post-injections, the increase in engine output due to the increase is reduced. Thus, it is possible to prevent the occurrence of torque shock accompanying the NOx release control.

[0080]

As described above, according to the fuel injection control apparatus for a diesel engine according to the first aspect of the present invention,
When NOx is released from the NOx absorbent during operation of the engine, the main injection is divided into a plurality of times at the latest when the fuel injection amount is increased and corrected by the injection amount correction means.
Since the temperature of the Ox absorbent is quickly raised, the concentration of oxygen in the exhaust gas is reduced and the concentration of the reducing agent component is increased by the correction of the increase in the fuel injection amount, so that the NOx emission from the NOx absorbent is increased. Etc. can be sufficiently promoted, and the NOx absorbent can be refreshed while suppressing fuel consumption deterioration. Further, since the combustion state can be greatly improved by the split control of the main injection, it is possible to prevent a sudden increase in smoke.

According to the second aspect of the present invention, when the NOx absorbent is refreshed, the split control of the main injection is started before the fuel injection amount is increased and corrected, so that the temperature state of the NOx absorbent is raised in advance. Thus, the NOx absorbent can be refreshed very efficiently. Further, it is possible to suppress a temporary increase in the NOx emission amount when the fuel injection amount is increased.

According to the third aspect of the present invention, the number of divisions of the main injection is set to 2 to 7 times, and the injection pause interval is set to 50 times.
By setting the time in the range of 0 microsecond to 1 millisecond, the effect of the invention of claim 1 or 2 can be sufficiently obtained.

According to the fourth aspect of the present invention, in the normal operation state of the engine, the main injection is performed as a batch injection, so that the number of opening and closing operations of the fuel injection valve can be relatively reduced, and the reliability can be improved.

According to the fifth aspect of the present invention, even if the engine is in a normal operating state, the main injection is divided into injections, so that the combustion can be improved as a whole. In addition, when the NOx absorbent is refreshed, refreshing can be promoted by increasing the number of divisions and the injection suspension interval.

According to the sixth aspect of the present invention, when the NOx absorbent is refreshed, the number of divisions of the main injection is corrected so as to be larger before the increase in the fuel injection amount is corrected.
The temperature state of the x-absorbing material can be quickly raised.

According to the seventh aspect of the present invention, when a fuel injection amount is corrected to be increased, a part of the fuel is additionally injected, so that deterioration of the combustion state of the engine and torque fluctuation can be suppressed.

According to the invention of claim 8, when the NOx absorbent is refreshed, the increase in the engine output due to the increase in the fuel injection amount can be alleviated, and the torque shock can be prevented.

According to the ninth aspect of the present invention, the control procedure can be simplified by performing the main injection of the basic fuel injection amount corresponding to the required output of the engine and pre-injecting the increased amount of fuel.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing an overall configuration of a fuel injection control device for a diesel engine according to the embodiment.

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.

[Explanation of symbols]

 A fuel injection control device for diesel engine 1 diesel engine 2 cylinder 4 combustion chamber 5 injector (fuel injection valve) 20 exhaust passage 22 catalyst (NOx absorbent) 35a basic fuel injection control means 35b injection amount correction means 35c injection form correction means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsunori Kondo 3-1, Fuchi-cho, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Akihide Takami 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. F term (reference) 3G091 AA02 AA11 AA13 AA18 AB05 AB06 AB09 BA14 BA15 CA18 CA26 CB02 CB03 DA02 DB06 DB10 DC06 EA01 EA05 EA06 EA07 EA07 EA16 EA18 EA30 EA34 FA04 FB10 FB11 FB12 FC07 GA03 GB03W02 JA25 KA00 KA05 LB11 MA01 MA11 MA19 MA20 MA23 MA26 MA27 NA00 NA04 NA08 NB02 NB06 NB11 NB14 NC02 NE01 NE13 NE14 NE15 NE23 PA04Z PA07Z PB08Z PD02Z PD12Z PE01Z PE03Z PE08Z PF03Z

Claims (9)

[Claims] A fuel is directly injected into a combustion chamber in a cylinder of an engine.
A fuel injection valve for injecting and supplying, and a NOx absorber disposed in an exhaust passage of the engine for absorbing NOx in exhaust gas in an oxygen-rich atmosphere having a high oxygen concentration and releasing the absorbed NOx with a decrease in oxygen concentration. Basic fuel injection control means for controlling a fuel injection state by the fuel injection valve according to at least an operation state of an engine; and when releasing NOx from the NOx absorbent, an oxygen concentration in exhaust gas is reduced. A fuel injection control device for a diesel engine, comprising: an injection amount correction unit that increases and corrects a fuel injection amount by the fuel injection valve. When NOx is released from the NOx absorbent, the fuel injection amount by the injection amount correction unit at the latest. At the same time as the increase correction of the fuel injection amount, the fuel injection valve injects fuel in a plurality of times in the vicinity of the compression top dead center of the cylinder. A fuel injection control device for a diesel engine, comprising a corrector. 2. The fuel injection control device according to claim 1, wherein the injection mode correction unit is configured to split and inject the fuel by the fuel injection valve before the fuel injection amount is increased by the injection amount correction unit. Diesel engine fuel injection control device. 3. The injection mode correction means according to claim 1, wherein the number of divisions of fuel injection in the vicinity of the compression top dead center of the cylinder is set to any one of 2 to 7 times. A fuel injection control device for a diesel engine, wherein a fuel injection valve is operated to open and close so that an injection stop interval from once closing to next opening is within a range of 500 microseconds to 1 millisecond. . 4. A diesel engine according to claim 1, wherein the basic fuel injection control means injects the fuel collectively near the compression top dead center of the cylinder by the fuel injection valve. Engine fuel injection control device. 5. The fuel injection control device according to claim 1, wherein the basic fuel injection control means injects the fuel in two or more times near the compression top dead center of the cylinder by the fuel injection valve. The valve is operated to open and close so that the injection pause interval from once closing to the next opening is within the range of 100 microseconds to 1 millisecond. A fuel injection control device for a diesel engine, wherein at least one of the number of divisions and the injection suspension interval is increased. 6. The injection mode correction means according to claim 2, wherein the number of divisions of the fuel injection in the vicinity of the compression top dead center of the cylinder is greater before the increase correction of the fuel injection amount than after the start of the increase correction. And a fuel injection control device for a diesel engine. 7. The fuel injection control device according to claim 1, wherein when the fuel injection amount is increased by the fuel injection amount correcting means, the fuel injection amount is corrected in addition to the fuel injection near the compression top dead center of the cylinder. A fuel injection control device for a diesel engine, wherein the fuel injection valve is configured to perform at least one additional fuel injection. 8. The fuel injection control device according to claim 7, wherein the injection mode correction means performs a sub-injection in any one of an intake stroke or a compression stroke or an expansion stroke of the cylinder as an additional fuel injection, and a compression top dead center of the cylinder. A fuel injection control device for a diesel engine, wherein at least one of the number of divisions of fuel injection and the injection pause interval near a point is corrected so that the output torque of the engine decreases. 9. The fuel injection valve according to claim 8, wherein the injection mode correction means causes the fuel injection valve to inject a quantity of fuel corresponding to the required output of the engine near the compression top dead center of the cylinder. A fuel injection control device for a diesel engine, which performs sub-injection of minute fuel.