JP3335278B2 - 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
It is necessary that components and the like are adsorbed. However
Air-fuel ratio of exhaust gas during normal operation of lean burn internal combustion engine
Is very lean, so the amount of HC component etc. in the exhaust
Extremely low. For this reason, the normal lean air-fuel ratio
If the state continues, the adsorbed HC components etc. will cause NO in the exhaust_XReturn of
NO originally consumed_XHC adsorption in the selective reduction catalyst is reduced
The catalyst NO_XPurification ability has decreased
U. To prevent this, perform lean air-fuel ratio operation.
NO on a regular basis_XSupplying HC components etc. to the selective reduction catalyst
And always NO_XAppropriate amount of HC component in selective reduction catalyst
Must be adsorbed. For example, JP-A-4-23
Japanese Patent No. 1645 discloses a lean burn type direct injection in a cylinder.
In-cylinder internal combustion engine
Injection (hereinafter referred to as “main injection”) followed by separate injection
(Hereinafter, sub-injection) into the cylinder to reduce unburned HC
NO_XSupplying to the selective reduction catalyst.

[0003]

Supplying a suitable amount of HC amount for purification action of however _the NO _X selective reducing catalyst [0006] to the sub-injection by the cylinder, a part of HC cylinder temperature was fed as a high temperature It burns away and the desired amount of unburned HC
Can not be supplied to the O _X selective reducing catalyst, it is impossible to secure a high purification rate. An object of the present invention is to secure 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, the main injection At a predetermined injection timing during the expansion stroke or the exhaust stroke separately to perform sub-injection into the cylinder ,
Among the sequentially arriving injection timings, the sub-injection at some injection timings is stopped, and the stop ratio at which the sub-injection is stopped while the injection timing reaches a certain number of times is controlled. As the stop ratio increases, In- cylinder direct injection type internal combustion engine fuel injection control device with increased sub injection quantity
Here, the higher the exhaust gas temperature, the higher the stop ratio .
As a result, one sub-injection was applied as the exhaust temperature increased
The amount of HC is increased .

[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. A temperature sensor 14 that generates an output voltage proportional to the exhaust gas temperature is attached to the exhaust pipe 8, and the output voltage of the temperature sensor 14 is input to an input port 45 via an AD converter 48. The input port 45 has a crank angle sensor 1 that generates an output pulse every time the crankshaft of the engine body 1 rotates, for example, 30 degrees.
6 is connected via an AD converter 49. Further, the input port 45 is provided with an accelerator pedal depression amount sensor 18 for generating an output voltage proportional to the accelerator pedal depression amount D, and the output voltage of the accelerator pedal depression amount sensor 18 is converted to an AD converter 50.
Through the input port 45. The CPU 42 calculates the engine speed of the engine body 1 based on the output pulse. On the other hand, the output port 46 is connected to the corresponding drive circuit 5.
0 is connected to the fuel injection valve 6.

Next, the operation of the fuel injection control device according to the first embodiment of the present invention will be described. In the present embodiment, the main injection is performed from the fuel injection valve 6 into the cylinder immediately after the compression top dead center, and the sub-injection is performed from the fuel injection valve 6 into the cylinder during the expansion stroke or the exhaust stroke after the main injection. Regarding the sub-injection, the timing and frequency of the sub-injection and the amount of HC injected per sub-injection are controlled according to the catalyst temperature of the NO _X selective reduction catalyst 10, the exhaust temperature, and the NO _X amount in the exhaust gas. However, the catalyst temperature may be estimated from the exhaust gas temperature. First, the timing of the sub-injection will be described. Although the NO _X selective reduction catalyst 10 has an appropriate temperature range in which the purifying action is performed, in the present application, when the temperature of the NO _X selective reduction catalyst 10 is relatively low within the appropriate temperature range, N
O _X selects the low-boiling HC elicit purification action of the reduction catalyst N
O _X has been found that may be supplied to the selective reduction catalyst. The higher the in-cylinder temperature, the greater the amount of low boiling point H
Since there is a tendency to be modified to C, subjected to sub injection at a timing of the expansion stroke from the mid high expansion stroke initial of cylinder temperature, and supplies a large amount of low-boiling HC to _the NO _X selective reducing catalyst 10. Furthermore, as the temperature of the NO _X selective reducing catalyst 10 becomes high, delaying the injection timing of the sub injection is gradually, to increase the high-boiling HC that remains without modified than the low-boiling HC. Once even a catalyst temperature is relatively low temperature, after the cleaning effect by the low-boiling HC began in reducing the amount of HC better to perform purification action by the high-boiling HC is consumed in _the NO _X selective reducing catalyst convenient. this is,
Low boiling HC high boiling HC is pyrolyzed has higher activity than the high-boiling HC, there is a advantage that the temperature of _the NO _X selective reducing catalyst is relatively low draw the NO _X purification action, while in often resulting in burned before performing the purification effect and flows into _the NO _X selective reducing catalyst, to cover the amount of HC necessary for purification effect of low-boiling HC is because that requires a large amount of fuel. Therefore, NO _X selective reducing catalyst 1
Delaying the timing of the sub injection as the temperature of 0 becomes higher, it is to increase the proportion of high-boiling HC in the HC supplied to _the NO _X selective reducing catalyst 10.

Next, the frequency of sub-injections and the number of injections per sub-injection
Control of the amount of HC to be emitted will be described. Shown in FIG.
As described above, when the exhaust gas temperature T falls within the first temperature range T₁When in
Indicates that the sub-injection should be
Do. The exhaust temperature T is in the second temperature range T_TwoIn order
Ratio of injection timing of sub-injection that arrives next twice
Performs sub injection. Hereinafter, the third temperature range T_ThreeThen one in three
Times, fourth temperature range T_FourThen, the sub-injection is performed once every four times. This
At the same time, the frequency of sub-injection
Therefore, the amount of HC injected per sub-injection is increased.
You. Also, at a predetermined number of injection timings,
The number of times the sub-injection is stopped may be controlled. For example, in FIG.
As shown, the exhaust gas temperature T falls within the first temperature range T.₁In
5 sub-injections per 5 engine cycles
Two temperature range T_TwoFive times per engine cycle
Four sub injections are performed. That is, the second temperature range T _TwoAt
Stops the sub-injection once. In the following, the third temperature range T_Three
, The sub-injection is stopped twice and the fourth temperature range T_Four
, The sub-injection is stopped three times. Furthermore, like this
Rate of sub-injection as exhaust temperature T rises
That is injected simultaneously with each sub-injection
Increase C content. HC amount injected per sub-injection
The amount of HC that is not exposed to the in-cylinder atmosphere increases
Therefore, over a predetermined number of injection timings
Of the HC supplied by the sub-injection, it is burned in the cylinder
The amount of HC is reduced as compared with the conventional case (see FIG. 4), and NO_XChoice
The amount of HC supplied to the reduction catalyst 10 can be controlled to a desired amount.
You. Further reduce the amount of HC actually injected by the sub-injection
However, since the amount of HC that is burned is small,
There is also an advantage that an appropriate amount of HC can be secured.
You.

[0009] using the amount of NO _X in the exhaust gas to determine the amount of HC to be injected per sub injection once, it is difficult to determine the amount of NO _X in the exhaust gas 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, the NO _X amount discharged from the engine per unit time 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.
That is, as the accelerator depression amount D increases, the NO _X amount discharged from the engine per unit time increases. FIG. 5 shows the NO discharged from the engine per unit time determined by the experiment.
_The relationship between the _X amount, the accelerator depression amount D, and the engine speed N is shown. In FIG. 5, each curve shows the same NO _X amount. 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. In addition,
The NO _X amount shown in FIG. 5 is stored in the ROM 44 in advance in the form of a map as shown in FIG.

In the present application, a fuel injection control device applied to a diesel internal combustion engine has been described. However, a lean-burn type direct injection spark ignition type internal combustion engine can also be applied. Moreover the air-fuel ratio of the exhaust gas is absorbed NO _X when the lean, the oxygen concentration in the exhaust gas absorbed and reduced N
It is also possible to apply the present invention to a NO _X catalyst that releases O _X.

FIG. 7 shows a second embodiment of the present invention. In the second embodiment, the second cylinder # 2, the third cylinder # 3, and the fourth cylinder # 4 (hereinafter, cylinder group) have fuel injection valves 6b, 6 respectively.
c and 6d are attached. The cylinder group is connected to the first NO _X via an exhaust manifold 7 and an exhaust pipe 8b.
It is connected to the selective reduction catalyst 10a. In this embodiment, in order to improve the overall NO _X purification rate, the second NO _X selective reduction catalyst 10b is provided downstream of the first NO _X selective reduction catalyst 10a.
Place. On the other hand, a fuel injection valve 6a is attached to the first cylinder # 1. The first cylinder # 1 is connected to an exhaust pipe 8c between the first NO _X selective reduction catalyst 10a and the second NO _X selective reduction catalyst 10b via an exhaust pipe 8a. Furthermore, the first NO
_A first temperature sensor 12a for generating an output voltage proportional to the catalyst temperature is attached to the _X selective reduction catalyst 10a, and a second temperature sensor 1
2b is attached. These first and second temperature sensors 12a and 12b are input to an input port 45 via AD converters 47 and 48. On the other hand, the output port 46 is connected to each of the fuel injection valves 6a to 6a through the corresponding drive circuit 50.
6d. Here, the cylinders are divided into the first cylinder # 1, the second cylinder # 2, the third cylinder # 3, and the fourth cylinder # 4, but this does not limit the present invention, and the third cylinder # 3 When the second downstream and a fourth cylinder ♯4 via the first _the NO _X selective reducing catalyst 10a on the upstream side _the NO _X selective reducing catalyst 1
The first cylinder group connected to 0b, the first cylinder ♯1 a second cylinder ♯2 the first upstream _the NO _X selective reducing catalyst 10a
The a and bypass downstream two _the NO _X selective reducing catalyst 1
It is also possible to use a second group of cylinders connected to 0b.

In the second embodiment, the injection control of the sub-injection is performed as follows. In the first cylinder ♯1 second _the NO _X selective reducing catalyst 10b performs sub injection when in the appropriate temperature range. On the other hand, performs the sub injection when the first _the NO _X selective reducing catalyst 10a is within the proper temperature range is cylinder group. By selecting in this manner the cylinder or cylinder group to perform a sub injection according to the catalyst temperature, to precisely control each _the NO _X selective reducing catalyst 10a, the amount of HC supplied to 10b each _the NO _X selective reducing catalyst be able to. As in the prior art, for example, to connect all the cylinders first to the first _the NO _X selective reducing catalyst, in the form of arranging the second _the NO _X selective reducing catalyst on the downstream side of the first _the NO _X selective reducing catalyst, selected first NO _X When the temperature of the reduction catalyst is equal to or higher than the appropriate temperature range, the HC supplied by the sub-injection becomes the first NO _X
It burns off with the selective reduction catalyst. Therefore, even if the downstream side of the second _the NO _X selective reducing catalyst had the appropriate temperature range, it is impossible to purify the exhaust gas. However, in this embodiment, the supplied HC amount is set to NO.
_{Since the} control can be performed for each _X selective reduction catalyst, the above conventional problem is solved.

[0013]

According to the first invention , HC is burned off.
H per sub-injection depending on the exhaust gas temperature
Control the amount of C. Therefore, a certain number of times
It desired HC to be supplied to the NO _X selective reducing catalyst over grayed
Can be more accurately control the amount, NO _X selective reducing catalyst
A high purification rate of the medium 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 illustrating a relationship between a catalyst temperature of a NO _X selective reduction catalyst and a sub-injection interval.

FIG. 3 is a diagram showing a relationship between a catalyst temperature and the number of injections.

FIG. 4 is a diagram showing a relationship between exhaust gas temperature and HC concentration.

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 view illustrating a direct injection type internal combustion engine according to a second embodiment of the present invention.

[Explanation of symbols]

6: fuel injection valve 10: NO _X selective reduction catalyst 10a: first NO _X selective reduction catalyst 10b: second NO _X selective reduction catalyst

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoichi Iwata 1st Toyota Town, Toyota City, Aichi Prefecture Examiner at Toyota Motor Corporation Inspector Yoichi Tokomura (56) References JP-A-6-117225 (JP, A) JP-A-9-112251 (JP, A) JP-A-8-261052 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41 / 34 ZAB F01N 3/20 ZAB F01N 3/24 ZAB F02D 41/02 301 F02D 41/04 330

Claims (1)

(57) [Claims] 1. An exhaust system comprising a lean NO _X catalyst for performing a main injection into a cylinder during an intake stroke or a compression stroke, and a predetermined injection timing during an expansion stroke or an exhaust stroke separately from the main injection. In the cylinder, the sub-injection is performed, the sub-injection is stopped at a part of the injection timings sequentially arrived , and the sub-injection is stopped while the injection timing reaches a certain number of times. Fuel injection control for an in- cylinder direct injection internal combustion engine in which a sub injection amount is increased as the stop ratio is increased.
In the device, the higher the exhaust temperature, the higher the stop ratio
The fuel injection control apparatus for a cylinder direct injection internal combustion engine, characterized in that the.