JP3341592B2 - Fuel injection control device for in-cylinder direct injection internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection control device for a direct injection type internal combustion engine.

[0002]

2. Description of the Related Art In order to ensure high fuel efficiency, an air-fuel ratio is extremely low.
The lean mixture to most engine operating areas.
There is a known lean-burn internal combustion engine
ing. Large amounts of NO in lean burn internal combustion engines_XDischarge
This NO_XExhaust purification catalyst to purify
Must be placed in the system. Well known three-way catalyst
This is because the air-fuel ratio of the exhaust gas is
Oxygen concentration in exhaust gas to show good purification characteristics
Use three-way catalysts in lean burn internal combustion engines
NO using_XCannot be satisfactorily purified. Therefore
In a lean burn internal combustion engine, the air-fuel ratio of the exhaust
Sometimes NO in the presence of appropriate amounts of HC, CO, etc. _XTo HC, C
Lean NO that selectively reacts with O_XNO as catalyst_X
A selective reduction catalyst is used. NO as described above_XReturn
NO with original catalyst_XIn order to purify the catalyst, an appropriate amount of HC
Components and the like are required. However, direct injection type internal combustion
The amount of HC components and the like in the exhaust gas during normal operation of the engine is extremely small.
Disappears. For this reason, in the normal operation state, the catalyst NO_XPurification
Conversion ability is reduced. To prevent this,
NO periodically during air-fuel ratio operation_XH for selective reduction catalyst
It is necessary to supply the C component and the like.

[0003]

The way _the NO _X selective reducing catalyst [0008] There are proper temperature range for purification action. That is, when the catalyst temperature is below the appropriate temperature range, an appropriate amount of HC
However, even if NO flows into the catalyst, HC and NO _X do not react, and a sufficient purifying action is not performed. Therefore, HC and NO _X react even at relatively low temperatures if the HC component in the highly active HC.
In order to generate such highly active HC from the sub-injection, it is necessary to bring the sub-injection timing close to the explosion timing. That is, the fuel is reformed into highly active HC by the heat of the explosion. However, in order to generate this highly active HC, it is necessary to supply the fuel in consideration of the loss of the fuel due to the heat at the time of the explosion. Therefore, there is a problem that a large amount of HC is required. An object of the present invention is to maintain a high purification rate of the NO _X selective reducing catalyst.

[0004]

According to a first aspect of the present invention, in order to solve the problems], comprising a lean NO _X catalyst in the exhaust system performs a main injection into the cylinder in the intake stroke or compression stroke, separately from the main injection In the fuel injection control device for a direct injection type internal combustion engine, which performs a sub-injection into a cylinder, performs a first sub-injection in an expansion stroke as the sub-injection to generate HC pyrolysis products, The second sub-injection is performed in the expansion stroke or the exhaust stroke after the first sub-injection, and the HC in the exhaust gas
Increase volume. As a result, the thermally decomposed HC and the undecomposed HC are supplied to the lean NO _X catalyst. According to a second aspect of the present invention, in the fuel injection control apparatus for a direct injection type internal combustion engine according to the first aspect, an oxidation catalyst is provided in an exhaust system on an upstream side of the lean NO _X catalyst, and HC for adding HC to the lean NO _X catalyst
When the temperature of the lean NO _X catalyst is lower than a predetermined temperature, the first sub-injection and the second sub-injection are performed, and the temperature of the lean NO _X catalyst is predetermined. When the temperature is equal to or higher than the temperature, HC is added by the HC adding means. Thus, when the catalyst temperature is lower than a predetermined temperature, H
C is supplied to the lean NO _X catalyst via the oxidation catalyst. When the catalyst temperature is equal to or higher than a predetermined temperature, HC is directly supplied to the lean NO _X catalyst by the HC adding means without passing through the oxidation catalyst.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an engine body of a direct injection type diesel internal combustion engine;
Reference numeral 3 denotes a combustion chamber, 4 denotes an exhaust valve, and 5 denotes an exhaust port.
A fuel injection valve 6 for injecting fuel into the combustion chamber 3 is attached to each cylinder. Exhaust port 5 is connected to _the NO _X selective reducing catalyst 10 as the lean NO _X catalyst through the exhaust manifold 7 and an exhaust pipe 8.

The electronic control unit 40 is composed of a digital computer and is connected to each other via a bidirectional bus 41. A CPU (microprocessor) 42, a RAM (random access memory) 43, and a ROM (read-on memory).
44, an input port 45 and an output port 46. A temperature sensor 12 for generating an output voltage proportional to the catalyst temperature is attached to the NO _X selective reduction catalyst 10, and the output voltage of the temperature sensor 12 is input to an input port 45 via an AD converter 47. The input port 45 is provided with the crank angle sensor 14 that generates an output pulse every time the crankshaft of the engine body 1 rotates, for example, 30 degrees.
It is connected via a converter 48. Further, the input port 45
The accelerator depression amount sensor 16 that generates an output voltage proportional to the accelerator depression amount D is attached to the input port. The output voltage of the accelerator depression amount sensor 16 is input to the input port 45 via the AD converter 49. The CPU 42 calculates the engine speed of the engine body 1 based on the output pulse. On the other hand, the output ports 46 are connected to the fuel injection valves 6 via the corresponding drive circuits 50, respectively.

Next, the operation of the fuel injection control device according to the present invention will be described. During engine operation, the temperature of the NO _X selective reducing catalyst 10 is detected by the temperature sensor 12, the temperature at which the temperature of the NO _X selective reducing catalyst 10 is predetermined at least the optimum temperature T ₀ in the present embodiment (see FIG. 2) It is determined whether or not there is. When it is determined that the temperature of the NO _X selective reduction catalyst 10 is equal to or higher than the optimum temperature T ₀ , the fuel injection control of FIG. 3 is performed. That is, the main injection A is performed from the fuel injection valve 6 into the cylinder immediately after the top dead center (TDC) at which the compression stroke is completed, and the sub-injection is performed from the fuel injection valve 6 into the cylinder at a later stage of the expansion stroke after the main injection A. (Hereinafter, the second sub-injection) C is performed. Since the in-cylinder temperature in the second half of the expansion stroke is not high enough to burn or reform HC, the HC injected into the cylinder by the second sub-injection C is not burned or reformed. It flows into the high-boiling HC to remain laden _the NO _X selective reducing catalyst 10. The NO _X selective reduction catalyst 10 is supplied with an appropriate amount of high boiling point HC, and performs a purification operation at a high purification rate. When it is determined that the temperature of the NO _X selective reduction catalyst 10 is lower than the optimum temperature T ₀ , the fuel injection control of FIG. 4 is performed. That is, the main injection A is performed from the fuel injection valve 6 into the cylinder immediately after the top dead center (TDC) at which the compression stroke is completed, and the sub-injection is performed from the fuel injection valve 6 into the cylinder during the middle stage of the expansion stroke after the main injection A. (Hereinafter, a first sub-injection) B is performed, and a second sub-injection C is performed from the fuel injection valve 6 into the cylinder at a later stage of the expansion stroke after the first sub-injection B. Since cylinder temperature of the expansion stroke mid relatively high, the HC fed into the cylinder is reformed thermal decomposition product by the first auxiliary injection B, that low-boiling HC, and the supply to _the NO _X selective reducing catalyst 10 Is done. In the latter half of the expansion stroke, since the in-cylinder temperature is low as described above, the HC supplied into the cylinder by the second sub-injection C is not burned or reformed and contains a large amount of high-boiling-point HC. _It flows into the _X selective reduction catalyst 10. In the NO _X selective reduction catalyst 10, the purifying action of the NO _X selective reducing catalyst 10 is started by the low boiling point HC having high activity first, and thereafter, the purifying action is performed by the high boiling point HC. As described above, the purifying action is performed quickly and favorably, and the control is performed so that an appropriate amount of low boiling point and high boiling point HC is supplied to the NO _X selective reduction catalyst 10. Therefore, the purifying action is performed at a high purification rate. In the above description, the injection timing of the first sub-injection is set to the middle stage of the expansion stroke. However, the first sub-injection B is capable of reforming the HC supplied by the first sub-injection B to the low boiling point HC. It is sufficient to select a timing at a temperature, and the crank angle is approximately 90 ° to 150 ° after the top dead center (TDC) when the compression stroke is completed. However, the crank angle after top dead center is 90 ° to 120 °
In this case, the inside of the cylinder is at a high temperature due to the combustion of HC supplied by the main injection A, and there is a possibility that the sub-injection of HC at this injection timing may burn out. Preferably, the crank angle is between 120 ° and 150 °. Although the injection timing of the second sub-injection C is set in the latter stage of the expansion stroke, the second sub-injection C may be performed by selecting a timing at which the inside of the cylinder is at a temperature at which HC is not reformed or burned. The crank angle is approximately 150 ° to 360 ° after the top dead center including the stroke. Further, in the first auxiliary injection B, and supplies the amount of HC low boiling HC is generated in an amount sufficient to initiate the cleaning action even at low _the NO _X selective reducing catalyst 10 comparatively temperature into the cylinder, the NO _X according to the catalyst temperature and the amount of NO _X in the exhaust gas at that time the second auxiliary injection C
The selective reduction catalyst 10 supplies an amount of HC showing the highest purification rate into the cylinder.

By the way to determine the amount of NO _X in the exhaust gas it is difficult to directly. Therefore, in the present invention, the NO _X amount in the exhaust gas is estimated from the operating state of the engine. That is, as the engine speed N increases, the amount of exhaust gas discharged from the engine per unit time increases. Therefore, as the engine speed N increases, N is discharged from the engine per unit time.
The O _X amount increases. Further, as the engine load increases, that is, as the accelerator depression amount D increases, the amount of exhaust gas discharged from each combustion chamber 3 increases, and the combustion temperature increases. Therefore, as the engine load increases, that is, the accelerator depression amount D decreases. NO _X emitted per unit time from the engine as it becomes higher
The amount increases. FIG. 5 shows the relationship between the NO _X amount discharged from the engine per unit time, the accelerator depression amount D, and the engine speed N obtained by the experiment. In FIG. 5, each curve shows the same NO _X amount. Is shown. As shown in FIG. 5, the NO _X amount discharged from the engine per unit time increases as the accelerator depression amount D increases, and increases as the engine speed N increases. The NO _X amount shown in FIG. 5 is stored in advance in the ROM 42 in the form of a map as shown in FIG.

FIG. 7 shows a flowchart of the injection control according to the present invention. Detecting the catalyst temperature T of the NO _X selective reducing catalyst 10 in step S12 after the main injection A is performed in step S10. Then whether the catalyst temperature T is the optimum temperature T ₀ or more is determined proceeds to step S14. In step S14, the catalyst temperature T
Is determined to be equal to or higher than the optimum temperature T ₀ , the process proceeds to step S16, the second sub-injection C is performed, and the processing cycle ends. Step S when the catalyst temperature T is determined to not optimum temperature T ₀ or more in step S14
18, the first sub-injection B is performed, and then step S
Proceeding to 16, the second sub-injection C is performed, and the processing cycle ends. In the present invention, the above-described injection control is always performed in all engine cycles, but may be performed in every predetermined engine cycle or every predetermined time in some cases.

In the above description, the optimum temperature T at which the purification rate becomes the highest is obtained.
_The sub-injection is controlled by determining whether or not the catalyst temperature T is equal to or greater than _0, but a predetermined temperature is set as desired, and the sub-injection is controlled according to the predetermined temperature. It is determined whether the catalyst temperature is within an appropriate temperature range where the purification rate is relatively high (for example, the temperature range T _{1 to} T ₂ in FIG. 2), below the appropriate temperature range, or above the appropriate temperature range. The sub-injection may be controlled as needed at that time. Further, in the present application, the fuel injection control device applied to the diesel internal combustion engine has been described. However, the present invention can be applied to a direct injection spark ignition type internal combustion engine of a lean burn type.
Further, when the air-fuel ratio of the exhaust gas is lean, NO _X is absorbed, and when the oxygen concentration in the exhaust gas decreases, the absorbed NO _X is absorbed.
It is also possible to apply the present invention to a NO _X catalyst that releases NO.

FIG. 8 shows a second embodiment of the present invention.
You. In the second embodiment, the engine body 1 and the NO_XSelective touch
Acid for purifying CO in exhaust gas between the medium 10
The oxidation catalyst 18 is disposed, and the oxidation catalyst 18 and NO_XChoice
HC addition means 20 is provided between the catalyst and the reduction catalyst 10.
I have. On the other hand, when the output port 46
It is connected to the C adding means 20. Other configurations are first implementation
Same as the form. As shown in FIG._XChoice
The reduction catalyst 10 has an optimum temperature T at which the purification rate is highest.₀But
is there. Therefore, in order to maintain a high purification rate, the catalyst temperature must be increased.
Optimal temperature T ₀It is important to maintain. So the real
In the embodiment, NO is determined by the temperature sensor 12._XSelective reduction catalyst 1
0 catalyst temperature is detected, NO_XTemperature of selective reduction catalyst 10
Is the optimal temperature T₀When lower, as in the first embodiment
The first and second sub-injections B and C are performed, and the low boiling point HC and the high
Exhaust gas flows out of the cylinder with the boiling point HC mixed
I do. At this time, the catalyst temperature T is set to the optimum temperature T.₀In order to
HC in which required amounts of low-boiling HC and high-boiling HC are generated
The amount is controlled so as to be supplied by the sub-injection. NO_XSelection
When the catalyst temperature of the selective reduction catalyst 10 is low, the oxidation catalyst 18
Of the oxidation catalyst 18 is often relatively low.
And it is difficult to burn HC. However the book
In the embodiment, exhaust gas in which low-boiling HC and high-boiling HC are mixed is described.
Since the gas flows into the oxidation catalyst 18,
Even from a low boiling point HC with high activity even when the medium temperature is relatively low
Combustion starts and then high-boiling HC is burned and generates heat.
You. Exhaust gas whose temperature has been increased in the oxidation catalyst 18
NO_XThe temperature of the selective reduction catalyst 10 is increased and NO
_XThe temperature of the selective reduction catalyst 10 is the optimum temperature T₀Becomes NO
_XThe temperature of the selective reduction catalyst 10 is the optimum temperature T₀If it is over
At this time, only the HC adding means 20 is operated, and the oxidation catalyst 18 is activated.
High boiling point HC is directly NO_XProvided to the selective reduction catalyst 10
Pay. At this time, the H supplied by the HC adding means 20
C amount is NO_XCatalyst temperature and exhaust gas of the selective reduction catalyst 10
NO in gas_XThe optimum temperature T calculated from the quantity₀Above
And NO_XThe amount at which the selective reduction catalyst 10 shows the highest purification rate
Is controlled.

FIG. 9 is a flowchart of the fuel injection control in the second embodiment. NO _X in step S22 after the main injection A is performed in step S20
The catalyst temperature T of the selective reduction catalyst 10 is detected. Then whether the catalyst temperature T is the optimum temperature T ₀ or more is determined the program proceeds to step S24. When it is determined in step S24 that the catalyst temperature T is equal to or higher than the optimum temperature T ₀ , the process proceeds to step S25, in which the HC adding means 20 is operated and the HC
Is added and the processing cycle is terminated. When it is determined in step S24 that the catalyst temperature T is lower than the minimum temperature T ₀ , the process proceeds to step S28 to perform the first sub-injection B, and then proceeds to step S30 to perform the second sub-injection C. finish.

[0013]

According to the first aspect of the present invention, the highly active HC is supplied to the catalyst by the first sub-injection, and the highly active HC and NOx react in the catalyst even when the catalyst temperature is relatively low. . The low-activity HC generated by the second sub-injection by the reaction heat also reacts with NOx in a chain to perform a purification action. As a result, even if the catalyst has a relatively low temperature, the purification rate can be improved, and the amount of sub-injected fuel burned in the combustion chamber can be minimized, so that deterioration in fuel efficiency can be prevented. According to claim 2 of the present invention, high boiling point temperature is supplied by the thermal decomposition product and a second sub-injection that has been modified by a predetermined when lower than the temperature in the cylinder of the lean NOx catalyst Since HC is burned in the oxidation catalyst and the exhaust gas temperature rises, the temperature of the lean NOx catalyst located downstream of the oxidation catalyst rises to a predetermined temperature or higher, and on the other hand, a temperature equal to or higher than the predetermined temperature When it becomes lean NOx by HC addition means
Since high boiling point HC is supplied to the catalyst, NO in the exhaust gas
x can be satisfactorily purified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a diesel internal combustion engine provided with a NO _X selective reduction catalyst.

FIG. 2 is a diagram showing a relationship between a catalyst temperature of a NO _X selective reduction catalyst and a NO _X purification rate.

FIG. 3 is a diagram showing a relationship between a crank angle and a fuel injection valve opening / closing signal in fuel injection control performed when it is not determined that the catalyst temperature is equal to or higher than a predetermined temperature.

FIG. 4 is a diagram showing a relationship between a crank angle and a fuel injection valve opening / closing signal in fuel injection control performed when it is determined that the catalyst temperature is equal to or higher than a predetermined temperature.

FIG. 5 is a diagram showing the amount of NO _X discharged from the engine body.

FIG. 6 is a diagram showing a map for estimating the NO _X amount discharged from the engine body.

FIG. 7 is a flowchart showing fuel injection control according to the present invention.

FIG. 8 is a diagram showing a diesel internal combustion engine provided with a NO _X selective reduction catalyst and an oxidation catalyst.

FIG. 9 is a flowchart illustrating fuel injection control according to a second embodiment of the present invention.

[Explanation of symbols]

10 NOx selective reduction catalyst 18 Oxidation catalyst 20 HC adding means A Main injection B Sub-injection C Second sub-injection

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/28 301 F01N 3/28 ZAB 3/36 ZABB ZAB F02D 41/04 385A 3/36 ZAB 45/00 310R F02D 41/04 385 B01D 53/36 ZAB 45/00 310 102H (56) Reference JP-A-8-74561 (JP, A) JP-A-4-231645 (JP, A) JP-A-5-214926 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 395

Claims (2)

(57) [Claims] 1. An in-cylinder direct injection system in which a lean NO _X catalyst is provided in an exhaust system to perform a main injection into a cylinder during an intake stroke or a compression stroke, and to perform a sub-injection into the cylinder separately from the main injection. In the fuel injection control device for an injection-type internal combustion engine, a first sub-injection is performed in the expansion stroke as the sub-injection,
Direct injection type internal combustion engine characterized by generating a thermal decomposition product and further performing a second sub-injection in an expansion stroke or an exhaust stroke after the first sub-injection to increase the amount of HC in exhaust gas. Engine fuel injection control device. 2. An exhaust system upstream of the lean NO _X catalyst is provided with an oxidation catalyst, and the oxidation catalyst and the lean N
O comprising the HC addition means for adding HC between the _X catalyst, when the temperature of the lean NO _X catalyst is lower than a predetermined temperature is carried out and the first sub-injection and the second sub-injection, 2. A fuel injection system according to claim 1, wherein said HC adding means adds HC when the temperature of said lean NO _X catalyst is equal to or higher than a predetermined temperature. Control device.