JPH09112251A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control at all times NOx. SOLUTION: An exhaust emission control device has a fuel supply device 20, 32, 40 for injecting fuel into a plurality of cylinders of an engine 1, a NOx catalyst 12 mounted in an exhaust passage 10 of the engine, and a sub-injection means 70 for secondarily injecting fuel into the fuel supply device as a reducing agent of the NOx catalyst after fuel is mainly injected and the sub-injection means 70 secondarily injects the fuel into one cylinder of the engine 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device, and more particularly, to NO by supplying a reducing agent by in-cylinder injection.
The present invention relates to an exhaust emission control device for a diesel engine that regenerates a catalyst.

[0002]

Related Background Art Exhaust gas emitted from an engine may contain substances such as carbon monoxide (CO) and nitrogen oxides (NOx), which may adversely affect the environment. Therefore, usually, a catalyst device such as a three-way catalyst is provided in the exhaust passage, and these substances are purified by the catalyst device.
The exhaust gas is emitted into the atmosphere as harmless. In particular, in a diesel engine, since NOx is contained in a large amount in exhaust gas, an NOx catalyst of a system that purifies NOx by repeatedly adsorbing and reducing NOx is often used.

NOx for such a diesel engine
In the catalyst, a reducing agent is appropriately added to the NOx catalyst in order to reduce the adsorbed NOx. As a method of adding this reducing agent, an appropriate amount of fuel (light oil) is intermittently sub-injected into each cylinder by an injector separately from the main injection of combustion fuel, whereby hydrocarbon (HC) is contained in the exhaust gas. There is known a method of in-cylinder injection in which a NOx catalyst is contained in a reducing atmosphere.

FIG. 7 shows the timing of sub-injection when in-cylinder injection is performed in a diesel engine consisting of four in-line cylinders. In this case, as shown in FIG. It is performed in the latter half of the compression stroke, whereas it is performed in the expansion stroke. Further, in FIG. 8, the sub-injection amount at this time is shown together with the sub-injection amount to each cylinder by the length of the bar line, but the sub-injection to each cylinder is carried out each time in this manner and The sub injection amount is the same in all cylinders.

[0005]

By the way, the amount of fuel required to reduce the NOx adsorbed on the NOx catalyst in one auxiliary injection is only about 2% of the amount of fuel injected in one main injection. It is a very small amount. Therefore, it is extremely difficult to always accurately inject a small amount of fuel in this way, and the injection amount tends to vary. As a result, the NOx purification rate may not be maintained stably.

Further, the combustion gas expanded by the combustion of the main injected fuel in the compression stroke has an extremely high temperature together with the pressure. Therefore, if the sub-injection is carried out too early, the oxidation reaction of the fuel may proceed excessively.
Therefore, it is desirable to carry out the sub-injection as late as possible after the expansion stroke. The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide an exhaust emission control device for a diesel engine that can constantly purify NOx in a stable manner.

[0007]

In order to achieve the above object, the invention of claim 1 is provided in a fuel supply device for injecting fuel into a plurality of cylinders of an engine, and an exhaust passage of the engine. In an exhaust emission control device for a diesel engine, comprising a NOx catalyst, and having a sub-injection unit that performs a sub-injection of the fuel by the fuel supply device as a reducing agent of the NOx catalyst after the main injection of the fuel, the sub-injection unit is the The feature is that the sub injection is performed only in one cylinder of the engine.

Therefore, the sub-injection by the fuel supply device is always carried out for only one cylinder, and the amount of fuel sub-injected at one time is relatively large. As a result, the fuel is injected more reliably than in the case where a small amount of fuel is injected into each cylinder, so that the dispersion of the injection amount is reduced and the purification rate of NOx adsorbed on the NOx catalyst is improved. According to the invention of claim 2, a fuel supply device for injecting fuel into a plurality of cylinders of the engine, and an NO provided in an exhaust passage of the engine.
In an exhaust emission control device for a diesel engine, which includes an x catalyst and has a sub injection unit that performs a sub injection of the fuel by the fuel supply device as a reducing agent of the NOx catalyst after the main injection of the fuel, the sub injection unit is the It is characterized in that the sub-injection is intermittently performed with respect to the main injection for all cylinders of the engine.

Therefore, the sub-injection by the fuel supply device is intermittently carried out in all the cylinders, and the amount of fuel to be sub-injected at one time is made relatively large. As a result, the fuel is more surely injected than in the case where the fuel is injected into each cylinder in small amounts each time, so that the variation in the injection amount is reduced and the purification rate of NOx adsorbed on the NOx catalyst is improved. Claim 3
In the invention, the sub-injection means performs the sub-injection with respect to the main injection every predetermined cycle. Therefore, the sub-injection by the fuel supply device is periodically performed at intervals of a predetermined cycle with respect to the main injection in all cylinders, and the amount of fuel to be sub-injected at one time depends on the execution interval of the sub-injection. Much done As a result, the fuel is more surely injected than in the case where the fuel is injected into each cylinder in small amounts each time, so that the variation in the injection amount is reduced and the purification rate of NOx adsorbed on the NOx catalyst is improved.

Further, in the invention of claim 4, the sub-injection means performs the sub-injection in the exhaust stroke of each of the cylinders. Therefore, the fuel from the secondary injection is
It is supplied into the combustion gas having a relatively low temperature immediately before being exhausted, and has a sufficient function as a reducing agent for NOx without excessive oxidation reaction. In the invention of claim 5,
The sub-injection means performs the sub-injection in the expansion stroke of each of the cylinders. Therefore, the fuel injected by the secondary injection is surely activated in the expanding combustion gas and has a good function as a NOx reducing agent.

Further, in the invention of claim 6, the fuel supply device includes a fuel supply pump, a fuel pressure accumulating chamber for accumulating the fuel supplied by the fuel supply pump at a predetermined pressure, and a fuel in the fuel accumulating chamber. It is characterized by comprising injectors for injecting into the combustion chamber of each cylinder at the predetermined pressure, and fuel supply control means for controlling the fuel injection amount and the fuel injection timing of the fuel injected from these injectors.
Therefore, at the time of sub-injection, fuel whose pressure is accumulated in the fuel pressure accumulator and whose fuel injection amount and fuel injection timing are appropriately controlled is injected from the injector of each cylinder, and more stable sub-injection is realized.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, the first embodiment will be described. FIG.
1 is a schematic configuration diagram of an internal combustion engine including an in-line 4-cylinder diesel engine (hereinafter, simply referred to as engine) 1 to which the first embodiment of the present invention is applied. It should be noted that the engine 1 in the figure shows only the first cylinder out of the four cylinders for the sake of convenience. Hereinafter, description will be given based on this first cylinder, and the same applies to the other cylinders. Is omitted.

As shown in the figure, an exhaust pipe 10 which is an exhaust passage for exhaust gas extends from the engine 1 so as to communicate with an exhaust port 3 provided in a cylinder 2.
An exhaust valve 4 that opens and closes according to the rotation of the crankshaft 6 is provided. A NOx catalyst 12 is connected to the tip of the exhaust pipe line 10, and a muffler 14 is connected to the NOx catalyst 12. The NOx catalyst 12 once adsorbs NOx (nitrogen oxide) in the exhaust gas, and in the reducing environment where a large amount of hydrocarbons (HC) is present, the adsorbed Nx.
It has the function of reducing Ox. The NOx catalyst 12 is a known one, and detailed description thereof is omitted here.

An injector 20, which is a fuel injection device, is attached to each cylinder of the engine 1 so as to face the inside of the cylinder 2, whereby fuel (light oil in this case) is provided.
Is injected (main injection) into the cylinder 2 in the compression stroke and burned to drive the engine 1. Although not shown, the injector 20 is provided for each cylinder. The injector 20 is connected to one end of a conduit 30 for supplying fuel to the injector 20, and the other end of the conduit 30 is connected to the pressure accumulating chamber 3
2 are connected. Although not shown, injectors 20 of other cylinders are similarly connected to the pressure accumulating chamber 32. A pipeline 38 extends from the pressure accumulating chamber 32, and the pipeline 38 connects the high pressure feed pump 4 of the pump unit 40.
2 is connected to the pump unit 40, and
It is connected to the fuel tank 62 via. As a result, the fuel in the fuel tank 62 is fed into the high pressure feed pump 4
After being pressurized by 2, the fuel is supplied to the injector 20 through the pressure accumulating chamber 32 and injected. At this time, the fuel pressurized by the high-pressure feed pump 42 is once adjusted to a high pressure of a predetermined pressure and held in the pressure accumulating chamber 32, and is injected at this high predetermined pressure.

Reference numeral 70 in the figure denotes an electronic control unit (ECU) which functions as fuel supply control means to control the fuel injection amount, fuel injection timing and the like, and which executes sub injection as sub injection means. On the input side, a pressure sensor 80 attached to the accumulator chamber 32 for detecting the pressure in the accumulator chamber 32 and a temperature sensor 8 attached to the exhaust gas inflow portion of the NOx catalyst 12 for detecting the temperature of the NOx catalyst 12 are provided.
2, an engine rotation sensor 84 that monitors the rotation of the rotating plate 6a of the crankshaft 6 to detect the crank angle and the engine rotation speed, and a rotation of the rotating plate 6b to detect the cylinder to which fuel injection should be performed. A cylinder discrimination sensor 86 and a load sensor 88 or the like provided on the accelerator pedal 90 for detecting an engine load are electrically connected. On the other hand, on the output side, solenoid valves (reference numeral 2 in FIG. 2) provided in the injector 20 and the high-pressure feed pump 42 described above, respectively.
2 and 54) are electrically connected.

FIG. 2 shows the fuel injection system shown in FIG. 1, that is, the injector 20, which is a pressure accumulating unit injector (fuel supply device), the pressure accumulating chamber 32, the pump units 40 and E.
A more detailed structure of the CU 70 is shown, and the pressure accumulating unit injector will be described in more detail below with reference to FIG. Pipe line 30 connected to the injector 20
Is the port 21 of the three-way solenoid valve 21 inside the injector 20.
a. Solenoid valve 21 in injector 20
From the upstream side of the pipe line 30 with respect to the injector 20,
A pipe line 22 is branched and extends toward the tip of the nozzle. The pipe line 22 communicates with a nozzle hole 23 formed in the tip portion 20a of the injector 20. That is, the accumulator 3 is always
The high-pressure fuel in 2 reaches the nozzle hole 23 via the conduit 22.

A leak passage 31 extends from the port 21b of the solenoid valve 21 to the outside of the injector 20, and the tip of the leak passage 31 reaches the drain tank 63. Further, from the port 21c of the electromagnetic valve 21, a pipe line 24 is formed which extends inside the injector 20 toward the tip of the injector 20, and the pipe line 24 is the pipe line 24.
a and the conduit 24b are branched and merged again. Pipeline 24
A check valve 24c is provided in a, while the conduit 24
An orifice 24d is provided at b.

Further, the pipe line 24 communicates with a cylinder hole 25 formed in the center of the injector 20, and a piston 26 is provided in the cylinder hole 25.
5 is slidably inserted. On the other hand, the cylinder hole 2
A needle 27 is inserted closer to the tip portion 20a than the piston 26 in the piston 5. A coil spring 28 is provided between the piston 26 and the head 27a of the needle 27.
Is interposed.

As shown in the figure, the tip portion 27b of the needle 27 is inserted into the above-mentioned nozzle hole 23,
The tip 27c reaches the ejection port 23 formed at the tip of the nozzle hole 23. A small gap is formed between the needle 27 and the nozzle hole 23 so that fuel can flow therethrough. Further, the tip 27c has a steeple shape, and the tapered surface on the outer periphery thereof and the upper end opening edge of the injection port 23 cooperate with each other to form an injection valve.

By the way, in the injector 20, the port 2 of the solenoid valve 21 is normally in a non-energized state.
1a communicates with the port 21c. As a result, the fuel reaches the nozzle hole 23 through the pipe line 22, and
It also reaches the inside of the cylinder hole 25 via the pipe line 24. Therefore, at this time, the piston 26 moves the coil spring 28 at a pressure equal to the fuel pressure in the pressure accumulating chamber 32, that is, a predetermined pressure.
It has been pushed down against the
The tip 27c of 7 contacts the upper opening edge of the injection port 23, and the injection valve is closed.

On the other hand, when the solenoid valve 21 receives a drive signal from the ECU 70, the port 21b and the port 21c are in communication with each other this time. When the port 21b and the port 21c communicate with each other, the fuel in the cylinder hole 25 is urged by the coil spring 28 so that the orifice 24d and the port 2
It is discharged to the leak conduit 31 via 1b. As a result, the fuel pressure in the cylinder hole 25 decreases,
Needle 27 that was in contact with the upper opening edge of injection port 23
However, due to the fuel pressure in the pipe line 22, the injection valve is opened by being urged against the coil spring 28, and as a result, the fuel in the pipe line 22 passes through the gap between the needle 27 and the nozzle hole 23 and the injection port. It will be injected from 23.

Reference numeral 20b in the figure denotes a tip portion 20a.
Is a cap for fixing to the main body of the injector 20.
The flow limit valve 3 is provided between the pressure accumulating chamber 32 and the conduit 30.
4 are interposed. This flow limit valve 34
Limits the flow of fuel from the pressure accumulating chamber 32 to the pipe line 30. When the fuel pressure in the pressure accumulating chamber 32 becomes much higher than the fuel pressure in the pipe line 30, the fuel flow is restricted. It will be closed to stop it.

A leak pipe 36 extends from the pressure accumulating chamber 32 toward the drain tank 64, and a pressure valve 37 is interposed in the leak pipe 36. The pressure valve 37 serves to release the fuel in the pressure accumulating chamber 32 when the fuel pressure in the pressure accumulating chamber 32 exceeds a predetermined pressure and rises excessively. The pipe line 38 extends into the high-pressure feed pump 42 of the pump unit 40 and communicates with the cylinder hole 44. Inside the cylinder hole 44, the piston 48
Is slidably inserted, and the seat portion 48a at the lower end of the piston 48 has a chamber 4 formed continuously with the cylinder hole 44.
Inside of 9, the cam 50 is in contact with the cam 50 which rotates integrally with the crankshaft 6. A coil spring 52 is contracted between a shoulder portion 42a and a seat portion 48a, which are formed in a stepwise manner in a continuous portion of the cylinder hole 44 and the chamber 49. This causes the piston 48 to move to the coil spring 5
While resisting the urging force of 2, the crankshaft 6 rotates, that is, the cam 50 slides up and down along the Linda hole 44 in accordance with the rotation of the cam 50.

The above-mentioned pipeline 60 is connected to a portion of the pipeline 38 in the high-pressure feed pump 42 near the cylinder hole 44. An electromagnetic valve 54 for adjusting the flow passage area of the pipe 60, that is, the opening degree is interposed in the pipe 60, and a pump 56 driven by the crankshaft 6 is provided near the fuel tank 62 of the pipe 60. Is installed. Therefore, after the fuel in the fuel tank 62 is sucked up by the pump 56, the flow rate of the fuel is adjusted by the electromagnetic valve 54 and reaches the inside of the cylinder hole 44.

Further, the conduit 3 in the high pressure feed pump 42
A pressure valve 46 is provided in a portion closer to the pressure accumulating chamber 32 than the connecting portion between the conduit 38 and the conduit 60 of No. 8. The pressure valve 46 shuts off the flow of fuel in the pipe 38 to maintain the pressure in the pressure accumulating chamber 32, but when the fuel pressure in the cylinder hole 44 becomes higher than the fuel pressure in the pressure accumulating chamber 32. It is configured to open. That is, when the piston 48 slides in the vertical direction as described above, the fuel in the cylinder hole 44 is pressurized and the fuel pressure in the cylinder hole 44 becomes higher than the fuel pressure in the pressure accumulating chamber 32. At that time, the pressure valve 46 is opened, so that the fuel is filled from the inside of the cylinder hole 44 into the pressure accumulating chamber 32 through the pipe line 38.

At this time, a part of the fuel in the cylinder hole 44, which is pressurized by the piston 48, is returned to the side of the conduit 60 according to the opening degree of the solenoid valve 54. The discharge pressure discharged from the cylinder hole 44 toward the pressure accumulating chamber 32 is adjusted according to the amount of fuel, and the fuel pressure is set as the pressure in the pressure accumulating chamber 32. That is, when the pressure sensor 80 provided in the pressure accumulating chamber 32 detects a change in the fuel pressure in the pressure accumulating chamber 32, a drive signal is supplied from the ECU 70 to the solenoid valve 54 to change the opening degree of the solenoid valve 54. The fuel pressure in the pressure accumulating chamber 32 is controlled so that the fuel pressure in the accumulating chamber 32 is always maintained at an appropriate predetermined pressure.

The structure of the exhaust purification system has been described above, but the sub-injection for reducing and removing the NOx adsorbed on the NOx catalyst 12 will be described below. An input signal from the temperature sensor 82 causes the NOx catalyst 12 to reach a predetermined temperature (for example, 30
0 ° C.), or when it is determined that the engine rotation speed has reached a predetermined value based on the input signal from the engine rotation sensor 84, or the load sensor 88.
The load is determined by the input signal from the
When it is determined that the temperature has reached 0%), the ECU 70 starts the sub injection. While this sub-injection is being performed, EC
The U70 constantly monitors the input signal from the cylinder discrimination sensor 86, instantaneously discriminates the cylinder in which the secondary injection should be performed according to this input signal, and outputs a drive signal to the solenoid valve 21 of the injector 20 of the corresponding cylinder. Will be output.

FIG. 3 shows the timing of performing the sub-injection together with the timing of the main injection. Here, the sub-injection is performed in the exhaust stroke, not in the expansion stroke, in all the first to fourth cylinders. . Specifically, based on the crank angle information from the engine rotation sensor 84, the ECU 70
Supplies a drive signal to the solenoid valve 21 at a timing about 5 ° before the timing at which the exhaust stroke ends. As a result, the fuel in the cylinder hole 25 gradually escapes to the leak conduit 31 via the orifice 24d, and thus the needle 27
Is lifted by the fuel pressure in the pipe line 22, the injection valve is opened, and the fuel is injected. This injection is for a predetermined period (for example,
It is carried out until the exhaust stroke is completed).

Incidentally, when the engine speed of the engine 1 increases or decreases, the opening time of the injection valve normally changes accordingly, and the amount of fuel injected at a predetermined pressure also changes. Then, the fuel injection amount is the leak amount to the leak conduit 31, that is, the biasing force of the coil spring 28, because the magnitude of the drive signal supplied to the solenoid valve 21 is suitably changed by the ECU 70 according to the engine rotation speed. Is adjusted, whereby the maximum opening of the injection valve under a predetermined pressure is adjusted, and the increase / decrease is satisfactorily controlled. Therefore, the fuel injection amount by the sub injection is always kept constant regardless of the engine speed.

Further, in FIG. 4, the sub-injection pattern at this time and the sub-injection amount to each cylinder are shown by the length of each bar line. Here, as shown in FIG. Secondary injection is performed only in the first cylinder of the cylinders. The fuel injection amount at this time is approximately four times the injection amount of one time when the fuel is uniformly injected into each cylinder (see FIG. 8) as in the conventional case, that is, the amount for four cylinders.

As described above, by performing the sub-injection in the exhaust stroke and further by executing only one first cylinder, the NOx adsorbed on the NOx catalyst 12 can be satisfactorily promoted without excessively promoting the oxidation reaction of the fuel. By reducing and purifying, and by increasing the amount of fuel injected at one time,
It is possible to suppress the variation in the injection amount for each injection by increasing the injection amount at an intermediate time point where relatively stable injection is realized other than the injection start and end times, and to inject the fuel reliably and stably. As a result, the NOx adsorbed on the NOx catalyst 12 can be sufficiently reduced to increase the NOx purification rate.

Next, a second embodiment will be described. In the second embodiment, the exhaust purification device having the same configuration as that of the first embodiment is applied (see FIGS. 1 and 2), and therefore the description of the configuration of the device will be omitted. Different sub-injection contents will be described. FIG. 5 shows the timing of performing the sub-injection together with the main injection, but here as well, as in the case of FIG. 3 described above, the sub-injection is performed in the exhaust stroke, not in the expansion stroke.

In FIG. 6, the sub-injection pattern at this time and the sub-injection amount to each cylinder are shown by the length of the bar line. Here, as shown in the same figure, the sub-injection is the first. It is performed every other cycle for the main injection cycle in each of the cylinders to the fourth cylinder. The fuel injection amount at this time is
When the fuel is uniformly injected into each cylinder as in the conventional case (see FIG. 8)
The injection amount for one injection is approximately twice, that is, the injection amount for each injection is two times.

As described above, the secondary injection is performed in the exhaust stroke and is performed every other cycle in the main injection cycle, so that the fuel oxidation reaction does not proceed excessively as in the case of the first embodiment. The NOx adsorbed on the NOx catalyst 12 can be reduced and purified satisfactorily, and the fuel injection amount injected at one time is increased to increase the injection amount at an intermediate point other than the injection start and end points. As a result, it is possible to suppress variations in the injection amount for each injection to a small extent, and to reliably and stably inject the fuel to sufficiently reduce the NOx adsorbed on the NOx catalyst 12 and increase the NOx purification rate.

Further, in the case of the second embodiment, since all the injectors 20 of each cylinder are used evenly, there is no need to overuse one injector 20 as in the first embodiment, and the injector 20 is biased. It is also possible to avoid deterioration. In the first and second embodiments, the timing of performing the secondary injection is the exhaust stroke, but it may be the expansion stroke as in the conventional case (see FIG. 7), and even in this case,
N adsorbed on the NOx catalyst 12 by sufficiently stabilizing the secondary injection
It is possible to increase the purification rate of Ox. However, in this case, it is preferable to carry out the sub-injection at a timing as late as possible in the expansion stroke, and it is preferable to set the fuel injection amount to a slightly large amount in consideration of the amount of the oxidation reaction.

Further, in the first and second embodiments, the solenoid valve 2
The magnitude of the drive signal supplied to 1 is changed according to the engine rotation speed, so that the maximum opening under a predetermined pressure of the injection valve constituted by the outer peripheral tapered surface of the tip 27c of the needle 27 and the injection port 23 is changed. By adjusting it, the fuel injection amount was controlled to increase or decrease so as to be constant regardless of the engine rotation speed.
Not limited to this, the output timing of the drive signal supplied to the solenoid valve 21, that is, the fuel injection timing is changed according to the engine rotation speed, thereby changing the length of the fuel injection period and increasing or decreasing the fuel injection amount. You may

In the second embodiment, the sub-injection is performed every other cycle of the main injection. However, the present invention is not limited to this, and the sub-injection is performed every predetermined cycle of the main injection (two or more cycles). You may make it implement.

[0038]

As described above, according to the exhaust emission control system of the diesel engine of the first aspect, the fuel supply system for injecting fuel into the plurality of cylinders of the engine and the NOx provided in the exhaust passage of the engine. In a diesel engine exhaust gas purification device having a catalyst and having a sub-injection unit that performs a sub-injection of fuel by a fuel supply device as a reducing agent of a NOx catalyst after main injection of fuel, the sub-injection unit is
Since the sub-injection is performed only in the cylinder, the amount of fuel to be sub-injected at one time can be made relatively large by always performing the sub-injection by the fuel supply device in only one cylinder. It is possible to inject fuel more reliably than in the case of injecting a small amount of each in small portions, and it is possible to reduce the dispersion of the injection amount and improve the purification rate of NOx adsorbed on the NOx catalyst.

Further, according to the exhaust purification system of the diesel engine of the second aspect, the fuel supply system for injecting fuel into the plurality of cylinders of the engine and the NOx catalyst provided in the exhaust passage of the engine are provided. In an exhaust emission control device for a diesel engine having a sub-injection means for sub-injecting fuel by a fuel supply device as a reducing agent of the NOx catalyst after the main injection, the sub-injection means targets all cylinders of the engine with respect to the main injection. Since the sub-injection is intermittently performed, it is possible to relatively increase the amount of fuel to be sub-injected at one time by intermittently performing the sub-injection by the fuel supply device to all the cylinders. The fuel can be injected more surely than in the case of injecting a small amount each time, and the variation of the injection amount can be reduced and the purification rate of NOx adsorbed on the NOx catalyst can be improved. .

Further, according to the exhaust gas purifying apparatus for a diesel engine of the third aspect, the sub-injection means performs the sub-injection with respect to the main injection every predetermined cycle, so that the sub-injection by the fuel supply device is performed for all cylinders. It is possible to increase the amount of fuel to be sub-injected at one time in accordance with the execution interval of the sub-injection by periodically performing the fuel injection at intervals of every predetermined cycle of, and thereby to divide the fuel into each cylinder by a minute amount each time. The fuel can be injected more reliably than in the case of direct injection, and the variation of the injection amount can be reduced and the purification rate of NOx adsorbed on the NOx catalyst can be improved.

Further, according to the exhaust purification system of the diesel engine of the fourth aspect, since the sub-injection means performs the sub-injection in the exhaust stroke of each cylinder, NOx reduction without excessively oxidizing the fuel due to the sub-injection. It can function sufficiently as an agent. Further, according to the exhaust emission control system of the diesel engine of claim 5, since the sub-injection means performs the sub-injection in the expansion stroke of each cylinder, it reliably activates the fuel by the sub-injection and functions well as a NOx reducing agent. Can be made.

Further, according to the exhaust purification system of the diesel engine of the sixth aspect, the fuel supply device includes the fuel supply pump, the fuel pressure accumulating chamber for accumulating the fuel supplied by the fuel supply pump at a predetermined pressure, and the fuel pressure accumulating chamber. Since it is composed of injectors for injecting the fuel in the fuel pressure accumulating chamber into the combustion chambers of the respective cylinders at a predetermined pressure, and fuel supply control means for controlling the fuel injection amount and the fuel injection timing of the fuel injected from these injectors, the auxiliary injection At times, fuel whose pressure is accumulated in the fuel accumulator and whose fuel injection amount and fuel injection timing are appropriately controlled can be injected from the injector of each cylinder, and more stable sub-injection can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including an exhaust emission control device.

FIG. 2 is a detailed view showing the pressure accumulating unit injector shown in FIG.

FIG. 3 is a diagram showing a sub injection timing of the exhaust emission control device of the first embodiment.

FIG. 4 is a diagram showing a sub-injection pattern and a sub-injection amount of the exhaust emission control device of the first embodiment.

FIG. 5 is a diagram showing a sub injection timing of the exhaust emission control device of the second embodiment.

FIG. 6 is a diagram showing a sub-injection pattern and a sub-injection amount of the exhaust emission control device of the second embodiment.

FIG. 7 is a diagram showing a sub injection timing of a conventional exhaust emission control device.

FIG. 8 is a diagram showing a sub-injection pattern and a sub-injection amount of a conventional exhaust emission control device.

[Explanation of Codes] 1 Diesel engine 2 Cylinder 10 Exhaust pipe (exhaust passage) 12 NOx catalyst 20 Injector 32 Accumulation chamber (fuel accumulation chamber) 40 Pump unit 42 High pressure feed pump (fuel supply pump) 62 Fuel tank 70 Electronic control unit (ECU)

Claims (6)

[Claims] 1. A fuel supply device for injecting fuel into a plurality of cylinders of an engine, and a NOx catalyst provided in an exhaust passage of the engine, wherein the fuel is used as a reducing agent for the NOx catalyst after main injection of fuel. In a diesel engine exhaust gas purification device having a sub-injection means for performing a sub-injection of fuel by a supply device, the sub-injection means carries out the sub-injection to only one cylinder of the engine. Purification device. 2. A fuel supply device for injecting fuel into a plurality of cylinders of an engine, and a NOx catalyst provided in an exhaust passage of the engine, wherein the fuel is used as a reducing agent for the NOx catalyst after main injection of fuel. In an exhaust emission control device for a diesel engine having a sub-injection unit that performs a sub-injection of fuel by a supply device, the sub-injection unit intermittently applies the sub-injection to the main injection for all cylinders of the engine. An exhaust emission control device for a diesel engine, which is characterized by being performed. 3. The sub-injection means performs the sub-injection on the main injection every predetermined cycle.
An exhaust emission control device for a diesel engine according to claim 2. 4. The sub-injection means performs the sub-injection in an exhaust stroke of the cylinder.
4. An exhaust emission control device for a diesel engine according to any one of 3 to 3. 5. The sub-injection means performs the sub-injection in an expansion stroke of the cylinder.
4. An exhaust emission control device for a diesel engine according to any one of 3 to 3. 6. The fuel supply device comprises a fuel supply pump, a fuel pressure accumulating chamber for accumulating the fuel supplied by the fuel supply pump at a predetermined pressure, and fuel in the fuel accumulating chamber to a combustion chamber of each cylinder. 6. The injector according to claim 1, comprising injectors for injecting at a predetermined pressure, and fuel supply control means for controlling a fuel injection amount and a fuel injection timing of fuel injected from the injectors. Exhaust purification device for diesel engine.