JPH1061466A - Fuel injection control device for internal combustion engine of inner-cylinder direct infection type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To deep a lean NOX control rate of a lean NOX catalyst high. SOLUTION: In a fuel injection control device for a inner-cylinder direct injection internal combustion engine in which an exhaust system includes a lean NOX catalyst 10, a main infection A is performed at an intake stroke or an exhaust stroke, and a subsidiary injection is performed other than the main injection, when a temperature of the lean NOX catalyst 10 is lower than a predetermined temperature, a first subsidiary infection B is performed at an expansion stroke as the subsidiary injection, HC(hydrocarbon) supplied by the first injection is burned within a cylinder, a second minor injection C is performed at the expansion stroke or the exhaust stroke after the first subsidiary injection, and only the second subsidiary injection as the subsidiary injection is performed when a temperature of the catalyst 10 is equal to or greater than the predetermined temperature, whereby a HC(hydrocarbon) amount in an exhaust gas is increased.

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. For example, JP
Japanese Patent No. 231645 discloses a lean burn type cylinder.
In order to obtain the engine driving force in a direct injection internal combustion engine,
A separate injection is performed after injection into the cylinder (hereinafter referred to as main injection).
By performing injection (hereinafter, sub-injection) into the cylinder, unburned H
NO for C_XSupplying to the selective reduction catalyst.

[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, when the fuel is again injected into the fuel chamber by the sub-injection immediately after the combustion explosion, the fuel burns, is discharged as a sufficiently high temperature exhaust gas, and flows into the catalyst. Therefore, the temperature of the catalyst or the vicinity thereof is instantaneously increased within the above-mentioned appropriate temperature range by the high-temperature exhaust gas. However, if HC is supplied by sub-injection of another cylinder after it is detected that the temperature has entered the appropriate temperature range, a period in which the catalyst does not add HC despite the above-mentioned appropriate temperature range occurs due to a time lag. There is a problem. An object of the present invention is to maintain a high purification rate of the NO _X selective reducing catalyst.

[0004]

According to the present invention, a lean NO _X catalyst is provided in an exhaust system, and a main injection is performed into a cylinder during an intake stroke or a compression stroke, and the main injection is performed separately from the main injection into the cylinder. In the fuel injection control device for an in-cylinder injection internal combustion engine configured to perform the sub-injection, the first sub-injection is performed in the expansion stroke as the sub-injection when the temperature of the lean NO _X catalyst is lower than a predetermined temperature. The HC supplied by the first injection is burned in a cylinder, and a second sub-injection is performed in an expansion stroke or an exhaust stroke after the first sub-injection to increase the amount of HC in the exhaust gas. , The lean NO _X
When the temperature of the catalyst is equal to or higher than a predetermined temperature, only the second sub-injection is performed as the sub-injection, and HC in the exhaust gas is used.
Increase volume. Thus, when the catalyst temperature is lower than the predetermined temperature, the HC supplied by the first sub-injection
Are burned, and the HC supplied by the second sub-injection flows into the lean NO _X catalyst without being burned, and when the catalyst temperature is equal to or higher than a predetermined temperature, the HC supplied by the second sub-injection is burned. Instead, it flows into the lean NO _X catalyst.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes an engine body of a direct injection type diesel internal combustion engine, 2 denotes a piston, 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. The exhaust port 5 is provided with a lean NO through an exhaust manifold 7 and an exhaust pipe 8.
It is connected to a NO _X selective reduction catalyst 10 as an _X catalyst.

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 the in-cylinder temperature in the middle stage of the expansion stroke is high, H supplied to the cylinder by the first sub-injection B
C is burned and burned off. At this time the exhaust gas temperature rises and increased exhaust gas temperature is _the NO _X selective reducing catalyst 10
Flows into Thus the catalyst temperature of the NO _X selective reducing catalyst 10 is raised, the optimum temperature T ₀ or more. HC quantity supplied by the first auxiliary injection is controlled to an amount required to bring the catalyst temperature T in optimum temperature T _0. 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. In this case _the NO _X selective reducing catalyst 1
Since the temperature of 0 is already higher than the optimum temperature T ₀ , the purifying action is performed at a high purifying rate by an appropriate amount of high boiling point HC which has flowed into the NO _X selective reduction catalyst 10 thereafter. In the above description, the injection timing of the first sub-injection is set to the middle stage of the expansion stroke. The top dead center (T
The crank angle after DC) is 0 ° to 120 °. However,
At a crank angle of 0 ° to 90 ° after the top dead center, there is a possibility that HC supplied by the main injection A is still burning, and if HC supplied by the sub-injection is burned, a torque fluctuation occurs. The first sub-injection B preferably has a crank angle of 90 ° to 120 ° after the top dead center. In addition, the injection timing of the second sub-injection C is in the latter half 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 combusted, and generally has a crank angle of 150 ° to 180 ° after the top dead center. Also, the first sub-injection B
Then, an amount of HC sufficient to raise the catalyst temperature of the NO _X selective reduction catalyst 10 is supplied into the cylinder, and the second sub-injection C adjusts the catalyst temperature and the NO _X amount in the exhaust gas at that time. Accordingly, the NO _X 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 exhausted 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.

[0011]

According to the present invention, when the catalyst temperature is lower than the predetermined temperature, most of the HC by the first sub-injection is burned, so that the exhaust gas whose temperature has risen due to the combustion becomes lean NO _X. flows into the catalyst can be maintained in close or a predetermined temperature in a predetermined temperature the temperature of the lean NO _X catalyst. Further, most of the HC supplied by the second sub-injection flows into the lean NO _X catalyst without being affected by the heat in the cylinder, so that an appropriate amount of HC for the purification action is supplied to the lean NO _X catalyst, Lean NO _X
A high purification rate of the catalyst can be secured.

[Brief description of the drawings]

FIG. 1 is a view showing an in-cylinder direct injection internal combustion engine equipped 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 illustrating a relationship between a crank angle and a fuel injection valve opening / closing signal in fuel injection control performed when it is determined that a catalyst temperature is equal to or higher than a predetermined temperature.

FIG. 4 is a diagram illustrating 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. 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.

[Explanation of symbols]

10: NO _X selective reduction catalyst A: Main injection B: First sub-injection C: Second sub-injection

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display F01N 3/28 ZAB F02D 41/02 330A 3/36 ZAB 9523-3G 41/34 ZABF F02D 41/02 330 45/00 ZAB 41/34 ZAB 310R 45/00 ZAB B01D 53/36 ZAB 310 102H (72) Inventor Tetsu Iguchi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Toshiaki Tanaka Aichi 1 Toyota Town, Toyota City, Japan

Claims (1)

[Claims] 1. An in-cylinder injection in which a lean NO _X catalyst is provided in an exhaust system, and a main injection is performed into a cylinder during an intake stroke or a compression stroke, and a sub-injection is performed separately from the main injection into the cylinder. In the fuel injection control device for an internal combustion engine, when the temperature of the lean NO _X catalyst is lower than a predetermined temperature, a first sub-injection is performed in the expansion stroke as the sub-injection, and the HC supplied by the first injection is supplied. burning in the cylinder, further subjected to a second auxiliary injection in the first expansion stroke or exhaust stroke after the auxiliary injection, to increase the HC amount in the exhaust gas, the temperature of the lean NO _X catalyst in advance A fuel injection control apparatus for a direct injection type internal combustion engine, characterized in that when the temperature is equal to or higher than a predetermined temperature, only the second sub-injection is performed as the sub-injection to increase the amount of HC in the exhaust gas.