JP2000205020A - Fuel injection control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress deterioration of combustibility by injecting fuel dividedly into plural times in one cycle when an operating region is shifted from a first operating region to a second operating region in which an EGR rate target value lower than that set in the first operating region is set. SOLUTION: In an ECU 40 for inputting output signals of an aero flow sensor 26, a throttle sensor 28, an engine rotating speed sensor 37, and the like, it is judged by operating condition judging means 42 which of a region A for carrying out a stratified burning operation at the time of a low and intermediate rotation and low load operation having few a fuel injection rate, a region B of a load higher than the region A in a low rotation region, and an intermediate and high rotation and a high load region and a low load and high rotation region C is a present operating condition. In the case where the region C is judged, homogenous combustion operation is carried out, and the operation is carried out by means of partial injection without batch injection. Namely, after only a part of fuel is injected in an early stage (first half of an intake stroke), the rest of fuel is injected in a latter period (latter half of the intake stroke).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an engine having an exhaust gas recirculation function.

[0002]

2. Description of the Related Art Some conventional engines are designed to perform stable operation while performing so-called lean combustion in a low-speed operation region where a required fuel injection amount is small. For example, Japanese Patent Application Laid-Open No. 8-189405 discloses that in a so-called direct injection engine in which fuel is directly injected into a combustion chamber, in a low-speed low-load region, fuel is injected into a region near an ignition plug in the latter half of a compression stroke. Is disclosed in which a region surrounding a region is made lean to perform stratified combustion.

On the other hand, as means for reducing nitrogen oxides (NOx) contained in exhaust gas of an engine, for example, as shown in Japanese Patent Application Laid-Open No. 6-229322, a part of the exhaust gas is supplied to an intake system. Devices that perform EGR for recirculation have become widely known.

When such EGR is performed, the EGR
If the rate is set too high, the flammability is significantly reduced, and there is a limit to increasing the EGR rate. However, in the region where the above-described stratified charge combustion operation is performed, fuel is unevenly distributed around the ignition plug in the combustion chamber, and the outside thereof is a very fuel-lean region. However, it is in a state where the flammability is not adversely affected. Therefore, in recent years, a device for performing EGR control such as increasing the exhaust gas recirculation amount in the stratified combustion operation region more than in other regions (uniform combustion region) has been developed.

[0005]

As described above, in an engine in which the EGR amount is changed between the stratified combustion operation region and the uniform combustion operation region, when the engine shifts from the stratified combustion operation region to the uniform combustion operation region, for example, during acceleration. , Along with the transition
It is necessary to throttle the R valve to quickly reduce the EGR amount. However, since there is a considerable response delay between the time the EGR valve opening is reduced and the time the EGR gas in the cylinder is actually sufficiently reduced, even if the uniform combustion operation has already started during the delay time. Regardless, a large amount of EGR remains in the cylinder, and there is a disadvantage that the combustibility is significantly reduced during this period. Such an inconvenience is not limited to the transition from the stratified combustion operation region to the uniform combustion operation region, but may occur at the transition from the operation region with a relatively large allowable EGR amount to a small operation region.

In recent years, as a means for reducing NOx in exhaust gas even when a lean operation such as the above-described stratified charge combustion operation is performed, NOx in the exhaust gas is reduced in a lean state where the excess air ratio of the exhaust gas is large. It is known that a lean NOx catalyst that adsorbs and releases the adsorbed NOx in a rich state with a small excess air ratio is arranged in an exhaust passage. If the temperature deviates from the limited temperature range, the temperature significantly decreases. Therefore, when the lean NOx catalyst is used, it is necessary to maintain the exhaust gas temperature in a suitable range.

[0007] In view of such circumstances, the present invention provides an EGR
It is an object of the present invention to provide an engine fuel injection control device capable of effectively suppressing a decrease in flammability when shifting from an operation region with a high target value to a low operation region, and further absorbs NOx in a lean state in an exhaust passage. An object of the present invention is to provide a fuel injection control device for an engine capable of achieving the suppression of the decrease in combustibility while maintaining the exhaust temperature within a range where the NOx absorption performance can be maintained high when the NOx absorbent is provided.

[0008]

According to the present invention, as a means for solving the above-mentioned problems, a first operation region and a region adjacent to the first operation region and set in the first operation region are set. E
A fuel injection control device for an engine having a second operation region in which an EGR amount target value lower than the GR amount target value is set, wherein the first operation region is shifted from the first operation region to the second operation region. The fuel injection control device is provided with fuel injection control means for performing split injection in which fuel is injected in a plurality of times during a cycle.

According to this configuration, split injection is performed at the time of transition from the first operation region to the second operation region. In this split injection, only part of the fuel is injected early and diffuses sufficiently before the remaining fuel is injected in the latter period. A uniform air-fuel mixture is formed, and high flammability is ensured.
Therefore, such split injection is performed from the first operation region (that is, the region where the EGR target value is high) to the second region (EG
By performing the shift at the time of shifting to the region where the R target value is low), the deterioration of the combustibility due to the response delay of the actual decrease in the EGR amount at the time of the shift is effectively suppressed.

The first operating region and the second operating region may be regions where the EGR amount target values are relatively different. For example, when the stratified combustion operation is performed in the low load region and the uniform combustion operation is performed in the high load region, the EGR of the low load region (stratified combustion operation region) is higher than that of the high load region (uniform combustion operation region). Since the tolerance is high and a higher EGR amount target value can be set, the low load region may be set as the first operation region and the high load region may be set as the second operation region.

The apparatus according to the present invention can be applied to a port injection type engine in which fuel is injected into an intake port in front of an intake valve, but is applicable to a direct injection type engine in which fuel is directly injected into a combustion chamber. It is more effective if applied.

In this case, the divided injection may be performed a plurality of times during the intake stroke.
The fuel injection may be performed separately for the intake stroke and the compression stroke.

Further, the present invention provides a stratified charge combustion operation region in which the stratified charge combustion operation is performed in a low load region, and a load region higher than the stratified charge combustion operation region, in which a uniform combustion operation is performed. A uniform combustion operation region in which an exhaust gas recirculation amount target value lower than the exhaust gas recirculation amount target value set in the stratified combustion operation region is set, and the excess air ratio in the exhaust gas in the exhaust passage is large. A fuel injection control device for an engine provided with a NOx absorbent that absorbs NOx at times, wherein the fuel is divided into a plurality of times during one cycle in a high rotation region where the engine speed is equal to or higher than a predetermined value in the uniform combustion operation region. In the low rotation region where the engine speed is lower than the predetermined value, the first split injection is performed only when shifting from the stratified combustion operation region to the uniform combustion operation region.
The fuel injection control device is provided with a fuel injection control means for performing a second split injection in which fuel is injected a plurality of times during a cycle.

According to this configuration, even in the region where the same uniform combustion operation is performed, in the high rotation region where the exhaust gas temperature is relatively high, the first injection of the fuel divided into a plurality of times during one cycle is performed. By performing the split injection, the combustion speed and the combustion efficiency are increased as compared with the case of the batch injection, and the exhaust gas temperature is reduced accordingly. Therefore, this exhaust temperature is NO
It is prevented from being higher than the temperature range favorable for the x-absorber.

Conversely, in the low rotation region where the exhaust gas temperature is relatively low, split injection is not performed in principle, but collective injection is performed. Therefore, the execution of the split injection lowers the exhaust gas temperature from a temperature range favorable for the NOx absorbent. Is also prevented from lowering. In addition, from the stratified combustion operation region where the EGR amount target value is high, the EG
At the time of shifting to the uniform combustion operation region where the R amount target value is low, the second split injection is performed, so that E
Deterioration of flammability due to a response delay of the GR amount decrease is effectively suppressed. Since the second split injection is a temporary one that is performed only at the time of shifting from the stratified combustion operation region to the uniform combustion operation region, the exhaust gas temperature is excessively lowered due to the split injection (that is, the NOx absorbing material is not used). Lower than the convenient temperature range) is avoided.

The means for "performing the second split injection only at the time of transition from the stratified combustion operation region to the uniform combustion operation region" includes, for example, switching from the stratified combustion operation region to the uniform combustion operation region. The second split injection may be performed until a predetermined time elapses from the time when the injection is performed.

The device according to the present invention is also applicable to a port injection type engine in which fuel is injected into an intake port before an intake valve, but is applied to a direct injection type engine in which fuel is directly injected into a combustion chamber. It will be more effective.

Also in this case, the second split injection may be such that fuel injection is performed a plurality of times during the intake stroke, or the fuel injection is performed separately in the intake stroke and the compression stroke. You may.

When the NOx absorbent and the three-way catalyst are used together, the exhaust temperature suitable for the three-way catalyst is higher than the exhaust temperature favorable for the NOx absorbent.
It is preferable to provide a three-way catalyst upstream of the absorbent.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

A main body 10 of the engine shown in FIG. 1 has a plurality of cylinders 12, each of which has a piston 14 mounted therein, and a combustion chamber 16 formed above each piston 14. In this embodiment, two intake ports and an exhaust port are opened to the combustion chamber 16, and each intake port and the exhaust port are connected to the intake valve 17 and the exhaust valve 1 respectively.
8 for opening and closing.

A spark plug 20 is provided at the top of each combustion chamber 16, and the tip of the plug faces the combustion chamber 16. In addition, the injectors 2 are disposed in the respective combustion chambers 16 from the side.
The fuel injector 2 is configured such that a front end portion (ie, a fuel injection portion) faces and fuel is directly injected from the injector 22 into the combustion chamber 16. That is, this engine is a direct injection engine. Each injector 22 has a built-in needle valve and solenoid (not shown), and when a pulse signal described later is input to the solenoid, fuel is injected at a timing corresponding to the pulse input timing by an amount corresponding to the pulse width. It is configured as follows.

An intake passage 24 is connected to the intake port. The intake passage 24 is provided with an air cleaner 25, an air flow sensor 26, an electric throttle 28 having a throttle sensor and a throttle valve, and a surge tank 30 in this order from the upstream side. The downstream passage of the surge tank 30 is an independent intake passage that branches corresponding to each intake port.

In the illustrated example, the downstream portion of each independent intake passage branches into two passages 24a, 24b, and each passage 24a, 24b
4b is connected into the combustion chamber 16 and the passage 24b
Is provided with an on-off valve 31 for swirl generation.
The on-off valve 31 is driven by an actuator (not shown) to open and close. When the on-off valve 31 closes the second passage 24b, swirl is generated in the combustion chamber 15 by intake air passing only through the first passage 24a. The swirl is generated and weakened as the on-off valve 31 is opened.

On the other hand, an exhaust passage 34 is connected to the exhaust port. In the middle of the exhaust passage 34, a three-way catalyst 35 and a lean NOx catalyst (N
Ox absorber 36). In these catalysts, a catalyst layer is formed on the wall of each through-hole of a cordierite carrier having a honeycomb structure having a large number of through-holes extending in parallel with each other along the axial direction.

The three-way catalyst 35 purifies NOx, CO and HC when the exhaust gas is near the stoichiometric air-fuel efficiency. On the other hand, the lean NOx catalyst 36 adsorbs NOx in a lean state where the excess air ratio of the exhaust gas is large, and releases the adsorbed NOx in a rich state where the excess air ratio of the exhaust gas is small. The lean NOx catalyst 36 exhibits an effective purification performance when the exhaust temperature is in a specific temperature range lower than the exhaust temperature suitable for the three-way catalyst 35, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 10-151353. As described above, the carrier was coated with an inner catalyst layer on which alumina carrying a noble metal such as Pt and an alkaline earth metal such as barium, and an outer catalyst layer on which zeolite carrying platinum and rhodium were carried. Those are suitable.

An EG for recirculating exhaust gas toward the intake passage 24 is provided between the intake passage 24 and the exhaust passage 34.
An R passage 32 is provided. The inlet end of the EGR passage 32 is connected to a portion of the exhaust passage 34 further upstream of the three-way catalyst 35. The outlet end is the intake passage 24
Is connected to an intake collecting portion (a portion upstream of the surge tank 30) on the downstream side of the electric throttle 28 in FIG. An EGR valve 33 is provided at this outlet end.
By driving the EGR valve 33, the EGR flow rate can be adjusted.

The engine is equipped with various sensors such as an engine speed sensor 37 and an accelerator opening sensor 38 in addition to the throttle sensor and the air flow sensor 26. The output signals (detection signals) of these sensors are provided by the ECU.
(Control unit) 40. The ECU 40 includes an operation state determination unit 42, a throttle control unit 44, a fuel control unit 46, and an EGR control unit 48 as functions related to the fuel control and the EGR control.

The operating state determining means 42 fetches the output signals of the sensors and determines which of the operating regions shown in FIG. 2 the current operating state of the engine belongs to. Each operating region is defined based on the engine speed Ne and the engine load Pe.

In the figure, a region A is a stratified charge combustion operation during a low-medium-speed low-load operation with a small fuel injection amount, that is, collective injection of fuel only in the latter half of the compression stroke.
The entire area is an area for performing a combustion operation in which only the vicinity of the ignition plug 20 is ignited relatively and locally as compared with other areas while the fuel is in a lean state.

The region B is a low rotation region where the engine speed is lower than a predetermined value and a region where the load is higher than that of the region A, and a region where uniform combustion is performed by collectively injecting fuel in the intake stroke. .

The region C is a region where the engine speed is higher than a predetermined value, that is, a region of medium to high rotation and high load, and a region of low load and high rotation. In the same manner as in region B, uniform combustion operation is performed. This is an area where the operation by the first split injection is performed. That is, in this region C, first, only a part of the fuel is injected early (in the first embodiment, the injection is performed in the first half of the intake stroke), the fuel is made uniform in the cylinder, and the remaining fuel is injected late (the present embodiment). In this case, the combustion operation is performed in which the fuel is injected in the latter half of the intake stroke and ignition is performed.

In the example shown in FIG. 2, the batch injection operation region B is set in a region where the engine load is extremely high even in the high rotation region.

The throttle control means 44 performs feedback control of the throttle opening of the electric throttle 28 based on the detection signal of the throttle sensor in each operation region in order to realize an intake air amount suitable for the combustion.

The fuel control means 46 includes the operating state determination means 4
The fuel injection amount and the fuel injection timing corresponding to the combustion in the operation region determined by the step 2 are determined, and a command signal is output to an unillustrated injector driver, so that the fuel injection timing has a width corresponding to the fuel injection amount. Pulse signal from injector 22
Output to In this embodiment, the fuel injection amount is set such that the lean combustion is performed in the region A and the combustion is performed at an excess air ratio of approximately 1 in the regions B and C.

The EGR control means 48 controls the opening of the EGR valve 33 so that the actual EGR amount matches a target value set according to each operation region. In this embodiment, the intake air amount expected to be detected when the EGR valve 33 is assumed to be closed (that is, when EGR is not performed), and actually detected by the air flow sensor 26. The present EGR amount is obtained from the difference from the intake air amount, and the opening degree of the EGR valve 33 is feedback-controlled so that the EGR amount approaches the target EGR amount corresponding to the current operation state.

As for the EGR amount target value, a target value in a region A which is a stratified combustion operation region is set to be larger than a target value in another region which is a uniform combustion operation region. This takes into account that the influence of the EGR gas introduction on the combustibility is smaller in the stratified combustion operation than in the uniform combustion operation because the fuel is unevenly distributed around the spark plug.

Next, a specific fuel injection control operation performed by the ECU 40 will be described with reference to a time chart of FIG. 3 and a flowchart of FIG.

First, the engine speed Ne and the accelerator opening Acc are fetched (step S1 in FIG. 4). And
After storing the previously determined operating area DA as the immediately preceding operating area DAO, the current operating area DA is determined again based on the detection signal captured in step S1 (step S1).
3). When the newly determined area DA is the area A (YES in step S4), the stratified charge combustion operation by the batch injection in the lean state is performed (step S5), and when the determined area DA is the area C ( NO in steps S4 and S6), split injection with the excess air ratio substantially equal to 1 (first injection)
Perform uniform combustion operation by split injection (step S)
7).

On the other hand, if the newly determined area DA is the area B (NO in step S4, Y in step S6)
ES), confirm the immediately preceding operation area DAO. If the immediately preceding operation area DAO is not in the area A (N in step S8)
O) In principle, uniform combustion operation is performed by batch injection at an excess air ratio of approximately 1 (step S9), but when the immediately preceding operation area DAO is the area A (YE in step S8).
S), that is, when shifting from the region A, which is a stratified combustion operation region having a high target EGR amount, to a region B, which is a uniform combustion operation region having a low EGR amount target value, the split injection is performed only for a predetermined time (the second split injection). ) Is performed.

Specifically, first, a built-in timer is set (step S10), and until the remaining time of the timer becomes zero, the uniform combustion operation by the divided injection with the excess air ratio being 1 is performed (step S10). S11, S12), when the timer remaining time becomes 0 (YE in step S12)
S), that is, after a certain period of time has elapsed from the time of switching to the region B, a uniform combustion operation by batch injection is performed in principle (step S9).

According to this device, the following excellent effects can be obtained.

A) Suppression of Combustibility Degradation at the Time of Shifting to Region Change in In-Cylinder EGR Amount and Throttle Opening TVO and Change of Early Injection Pulse Signal and Late Injection Pulse Signal when Second Split Injection is Performed Is shown in FIG. Since the target value of the EGR amount sharply decreases from the time point of the area switching shown in FIG.
Control for reducing the opening degree of the EGR valve 33 is performed. However, there is a considerable delay time from when the EGR valve 33 is reduced to when the actual in-cylinder EGR amount is sufficiently reduced. Therefore, during this delay time (transition period), a large amount of EGR gas remains in the cylinder even though the uniform combustion operation has already started, and if no measures are taken, the combustibility may be significantly reduced. There is.

On the other hand, in the apparatus according to the present embodiment, the split injection (second split injection) is temporarily performed during the transition period to promote uniformization of the injected fuel in the cylinder. It is possible to effectively suppress a decrease in flammability caused by a response delay in the reduction of the EGR amount.

B) Maintaining the Performance of the Lean NOx Catalyst 36 In the high-load region of the high-load region where the exhaust gas temperature tends to be high (region C), the split injection (first split injection) is executed to perform the combustion speed. And increasing the combustion efficiency, the exhaust gas temperature becomes too high (that is, the lean NOx catalyst 3
(Exceeding the temperature range suitable for 6).

Conversely, in the low rotation region (region B) where the exhaust gas temperature tends to be low even in the high load region, only the batch injection is performed in principle, so that the exhaust gas temperature is lowered by performing the split injection as described above. Too much (ie lean N
(Below a temperature range suitable for the Ox catalyst 36). Further, even in the case where the split injection (second split injection) is performed at the time of transition from the area A to the area B, the split injection is only a temporary operation for covering a decrease in flammability caused by a response delay in reducing the EGR amount. Therefore, it is possible to sufficiently prevent the exhaust gas temperature from excessively decreasing.

That is, in this device, it is possible to achieve both suppression of the deterioration of the combustibility and maintenance of the performance of the lean NOx catalyst 36.

The present invention is not limited to such an embodiment, but can take the following embodiments.

In the above-described embodiment, as a means for performing the divided injection only at the transition from the area A to the area B, the elapsed time from the time of the area switching is measured. However, the present invention is not limited to this. For example, control may be performed such that the actual EGR amount is measured and the divided injection is performed only until the measured EGR amount reaches the target EGR amount in the region B.

In the above embodiment, the fuel injection is performed twice in the intake stroke as the first divided injection and the second divided injection. However, the fuel may be divided into three or more times. The fuel may be injected separately into the stroke and the compression stroke.

When the lean NOx catalyst 36 is not used, it is possible to freely set the region where the split injection is performed. In addition, whether or not the three-way catalyst 35 is used may be appropriately determined.

In the above embodiment, the invention is applied to a direct injection type engine. However, the present invention is not limited to this, and is widely applied to engines in which operation regions having different target EGR values are set adjacent to each other. Applicable. For example,
Even in a port injection engine that injects fuel into the intake port just before the intake valve, the engine shifts from a stratified combustion operation region in which a high EGR amount target value is set to a uniform combustion operation region in which a low EGR amount target value is set. At times, split injection may be performed.

Also, in an engine in which uniform combustion operation is performed in the entire operation range, when the engine shifts from another operation range to a low-load low-speed range in which a low EGR amount target value is set due to low flammability, for example. By performing the split injection as described above, it is possible to effectively suppress the deterioration of the combustibility due to the response delay of the reduction of the EGR amount, as in the above-described embodiment.

[0054]

As described above, according to the present invention, the split injection is performed when shifting from the first operation region to the second operation region having a lower EGR amount target value. In addition, there is an effect that deterioration of flammability caused by a response delay of the EGR amount reduction at the time of the transition can be effectively suppressed.

Further, the stratified charge combustion operation is performed at a low load, and the stratified charge combustion operation region in which the target value of the exhaust gas recirculation amount is high is:
It has a uniform combustion operation region in which uniform combustion operation is performed under high load and has a low exhaust gas recirculation target value, and a NOx absorbing material that absorbs NOx when the excess air ratio in the exhaust gas is large is provided in the exhaust passage. The first split injection is performed in a high rotation region where the engine speed is equal to or more than a predetermined value in the uniform combustion operation region, and the stratified combustion operation is performed in a low rotation region where the engine rotation speed is less than the predetermined value. In the case where the second split injection is performed only at the time of transition from the region to the uniform combustion operation region, the exhaust gas temperature is set to the NO.
While maintaining the temperature suitable for the x-absorbing material, there is an effect that deterioration of combustibility at the time of shifting from the stratified combustion operation region to the uniform combustion operation region can be effectively suppressed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a graph showing each operating region set in the engine.

FIG. 3 is a diagram showing an example of a transition E from a region A to a region B shown in FIG.
It is a time chart which shows a time change of GR amount etc.

FIG. 4 is a flowchart showing the details of fuel injection control executed in the engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Engine main body 16 Combustion chamber 22 Injector 24 Intake passage 32 EGR passage 33 EGR valve 34 Exhaust passage 35 Three-way catalyst 36 Lean NOx catalyst 40 ECU 42 Operating state determination means 46 Fuel control means 48 EGR control means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masayuki Tetsuno 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture F-term (reference) 3G301 HA01 HA04 HA13 HA16 JA00 KA08 KA09 LA00 LA03 MA19 MA26 ND01 PA01Z PA11Z PD15A PD15Z PE01Z PF03Z

Claims (11)

[Claims] A first operating region and an exhaust gas recirculation amount target value adjacent to the first operation region and lower than an exhaust gas recirculation amount target value set in the first operation region are set. A fuel injection control device for an engine having a second operating region, wherein a split injection for injecting fuel in one cycle in a plurality of times during a transition from the first operating region to the second operating region is provided. A fuel injection control device for an engine, comprising a fuel injection control means for performing the control. 2. The fuel injection control device for an engine according to claim 1, wherein the first operation region is a low load region where a stratified combustion operation is performed, and the second operation region is a uniform combustion operation. A fuel injection control device for an engine, which is in a high load region. 3. The fuel injection control device for an engine according to claim 1, wherein the engine is a direct injection type engine in which fuel is directly injected into a combustion chamber of the engine. Control device. 4. The engine fuel injection control device according to claim 3, wherein the fuel injection control means causes the fuel injection to be performed a plurality of times during an intake stroke as the divided injection. Fuel injection control device. 5. The fuel injection control device for an engine according to claim 3, wherein the fuel injection control means causes the fuel injection to be performed in the intake stroke and the compression stroke as the divided injection. Engine fuel injection control device. 6. A stratified combustion operation region in which a stratified combustion operation is performed in a low load region and a region on a higher load side than the stratified combustion operation region, in which a uniform combustion operation is performed and the stratified combustion operation is performed. NOx that absorbs NOx when the excess air ratio in the exhaust gas is high, with a uniform combustion operation region in which a target exhaust gas recirculation amount is set lower than the target exhaust gas recirculation amount set in the combustion operation region. An engine fuel injection control device in which an absorbent is provided in an exhaust passage, wherein fuel is divided into a plurality of injections in one cycle in a high rotation region where the engine speed is equal to or more than a predetermined value in the uniform combustion operation region. In the low rotation region where the engine speed is less than the predetermined value, the fuel is divided into a plurality of injections during one cycle only in the transition from the stratified combustion operation region to the uniform combustion operation region. The fuel injection control device for an engine characterized by comprising a fuel injection control means for causing the second split injection to. 7. The fuel injection control device for an engine according to claim 6, wherein the fuel injection control means switches from the stratified combustion operation region to the uniform combustion operation region in a low rotation region where the engine speed is less than the predetermined value. The fuel injection control device for an engine, wherein the second split injection is performed until a predetermined time elapses from a time when the fuel injection control is performed. 8. The fuel injection control device for an engine according to claim 6, wherein the engine is a direct injection type engine in which fuel is directly injected into a combustion chamber of the engine. Control device. 9. The fuel injection control device for an engine according to claim 8, wherein the fuel injection control means causes the fuel injection to be performed a plurality of times during an intake stroke as the second split injection. Engine fuel injection control device. 10. The fuel injection control device for an engine according to claim 8, wherein the fuel injection control means performs the fuel injection in the intake stroke and the compression stroke as the second divided injection. A fuel injection control device for an engine, comprising: 11. The fuel injection control device for an engine according to claim 6, wherein a three-way catalyst is provided upstream of the NOx absorbent in an exhaust passage of the engine. Engine fuel injection control device.