JPH05231222A - Fuel injection timing controller - Google Patents

Abstract

PURPOSE:To provide a fuel injection timing controller for stabilizing combustion of an engine in a high load. CONSTITUTION:A value of an intake air amount Q divided by the rotational frequency N of an engine to represent an engine load is compared with a predetermined value alpha of load judging value in step 202. In the low load of the engine lower than the predetermined value alpha, asynchronous intake injection to perform fuel injection before the intake stroke is carried out in step 208. Also, in the high load, advance is made to step 212 through steps 204, 206 to perform synchronous intake injection performing fuel injection in the intake stroke. A large amount of injected fuel can be prevented from attaching to the wall surface of an intake manifold and the surface of an intake valve to make combustion unstable in the conventional way by synchronous intake injection in the high load and further the gasification of fuel is prevented from degradation due to a high temperature and a large amount of intake air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection timing control device, and more particularly to a fuel injection timing control device configured to always achieve optimum combustion regardless of the load of an internal combustion engine (engine).

[0002]

2. Description of the Related Art In an engine having a piston, as shown in FIG. 9, so-called intake asynchronous injection, in which fuel is injected into an intake manifold before an intake stroke, has been generally performed. In the case of this asynchronous intake injection, the fuel injected in the intake manifold receives the heat of the manifold wall surface and the intake valve to promote the vaporization of the fuel, and at the same time, the fuel due to the high-speed intake flow at the start of the intake valve opening. The effect of atomization can be expected, and the vaporization of the fuel in the cylinder is improved, and the combustibility is improved.
In addition, in the above-described intake asynchronous injection engine, in order to further improve the vaporization of the fuel in the intake manifold, the fuel injection timing control is usually performed by finely dividing the fuel injection performed once into a plurality of fuel injections. Is also generally known (JP-A-63-223345).

[0003]

As described above, in the engine which performs the asynchronous intake injection, when the engine has a high load, the fuel injection amount becomes large, so that vaporization occurs from the fuel injection to the start of the intake stroke. Fuel that cannot be generated,
This fuel that cannot be vaporized adheres to the wall surface of the intake manifold in a liquid state. The fuel adhering to the wall surface of the manifold is not quantitatively supplied into the cylinder, so that the air-fuel ratio of the intake air sucked into the cylinder is not stable, but if the amount of fuel adhering to the wall surface is small, it does not cause much problem. However, when the load becomes high, the intake air amount increases, so that the fuel amount also increases and the fuel wall adhesion amount also increases. Further, since the intake pipe pressure also increases as the intake air amount increases, the ratio of the fuel remaining as a liquid also increases. As a result, the higher the load becomes, the more unstable the air-fuel ratio of intake air becomes, and the more difficult it becomes to perform stable combustion.

Therefore, the present invention has been made in view of the above-mentioned problems, and the intake synchronous injection is performed at the time of high load to supply the fuel into the cylinder without adhering to the wall surface. An object of the present invention is to provide a fuel injection timing control device capable of stabilizing combustion and always performing stable combustion at all loads of the engine.

[0005]

FIG. 1 is a block diagram showing the principle of the present invention. In order to achieve the above object, the invention shown in FIG. 1 calculates a fuel injection amount corresponding to an operating state of an internal combustion engine 1, and supplies the calculated fuel injection amount of fuel before an intake stroke. In the fuel injection timing control device for injecting in the intake asynchronous injection mode 1A, the load detecting means 2 for detecting the load of the internal combustion engine 1 and the load detecting means 2
When the load detected by
Intake synchronous injection mode 1 in which fuel injection is performed during the intake stroke
The injection timing switching means 3 configured to inject the fuel at B is provided.

[0006]

In the present invention, when the load detecting means 2 detects a high load of a predetermined value or more, the injection timing switching means 3 starts the fuel injection from the intake asynchronous injection mode 1A during the intake stroke as shown in FIG. By switching to the intake-synchronized injection mode 1B, the fuel injected in a large amount in the high load state is supplied into the cylinder together with the intake air, and the fuel is prevented from adhering to the intake manifold wall surface or the intake valve surface. At this time, since the intake air supplied to the cylinder has a large amount and a high temperature due to the high load, the atomization of the fuel is promoted by the intake negative pressure wave due to the large amount of the intake air, and the fuel is further heated by the high temperature intake air. Even if the vaporization progresses in the cylinder and the intake synchronous injection mode 1B is switched, the deterioration of the fuel vaporization is prevented.

Further, liquid fuel is sucked into the cylinder,
Since the intake air in the cylinder is cooled by the amount of heat required when this liquid fuel is vaporized, that is, the latent heat of vaporization, the volumetric efficiency (density) of the intake air is improved and the occurrence of knocking is suppressed, and the ignition advance angle is increased. It is possible to improve the engine output.

In the low load state where the load is equal to or lower than a predetermined value, the intake asynchronous injection mode 1A is used as in the conventional case, so that the vaporization of the fuel is continued in a good state as described above, and stable combustion is performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a system configuration diagram of an embodiment of an internal combustion engine (engine) and its peripheral devices to which the present invention is applied. The engine of the first embodiment is a V-type 4-cylinder 4-stroke engine and an independent injection type engine that injects fuel into each cylinder independently.

In FIG. 2, 11 is an engine body, 12 is a piston, 13 is a cylinder, 14 is a spark plug, 15 is an intake valve, 16 is an exhaust valve, 18 is an exhaust pipe, and 19 is a catalytic converter for purifying exhaust gas. is there.

In the intake system, 21 is an air cleaner, 22 is an air flow meter (AFM) for measuring the amount of intake air, 24 is a throttle valve installed in the intake pipe 23, and 25 is an idle speed control valve (ISCV). ), 26 is a surge tank for preventing pulsation of intake air, and 27 is an injector for injecting fuel into the intake manifold 28. Further, 31 is a knock sensor for detecting a knocking state by measuring vibration of the engine body 11, 32 is interlocked with a crankshaft (not shown), and a high voltage generated by an igniter (not shown) is sequentially applied to the ignition plugs 14 of the four cylinders. The distributor 33 for distribution and supply is a rotation angle sensor that outputs a pulse signal 24 times per revolution of the distributor 32 (two revolutions of the crankshaft). The signal from the rotation angle sensor 33 is a signal used to supply the engine speed in this embodiment. An engine 30 includes a microcomputer, which inputs signals from various sensors and performs predetermined calculation and control based on these input signals to output predetermined signals to various actuators such as the injector 27. It is a control computer (ECU).

Here, the intake synchronous injection and the intake asynchronous injection of this embodiment will be described in more detail with reference to FIG. The intake synchronous injection is set so that the injection is completed when the intake valve reaches the maximum lift amount, so that the liquid fuel flowing into the cylinder is maximized. Further, the closer the injector is to the cylinder, the more liquid fuel will flow into the cylinder.

On the other hand, in the intake asynchronous injection, the injection is set to end immediately before the intake valve opens.

FIG. 3 is a block diagram showing concrete constituent elements of the ECU 30.

In the figure, a central processing unit (CPU) 40
Inputs and calculates data output from each sensor according to a control program, and injects 27 _-1 , 27 _-2 , 27 _-3 , 27 _{-4 of} each cylinder # 1 to # ₄ (the injector 27 is used for each cylinder). (Which is a symbol representing the injector of each of the above), and a process for controlling various actuators such as an ISCV 25 and an igniter (not shown) that determines the ignition timing. A read-only memory (ROM) 41 is a storage device that stores data such as the control program and ignition timing calculation map, and a random access memory (RAM) 42 is necessary for data output from each sensor and calculation control. It is a storage device that temporarily reads and writes data. Further, the backup random access memory (backup RAM) 43 is a storage device in which data or the like necessary for driving the engine is backed up by a battery power source even when an ignition switch (not shown) is turned off.

The input section 44 is the AFM 22, the knock sensor 3
The output signal of each sensor such as 1 is shaped by a waveform shaping circuit (not shown), and this signal is selectively output to the CPU 40 by a multiplexer (not shown).
In the input unit 44, if the output signal from each sensor is an analog signal, it is converted into a digital signal by an A / D converter. The input / output unit 45 waveform-shapes the output signal of the rotation angle sensor 33 or the like by the waveform-shaping circuit and writes this signal in the RAM 42 or the like via the input port. Input / output unit 4
The reference numeral 5 designates injectors 27 _-1 , 27 of each cylinder by a drive circuit driven via an output port in response to a command from the CPU 40.
_-2 , 27 _-3 , 27 _-4 , ISCV25, igniter, etc. are driven at a predetermined timing. The bus line 46 is the C
The various elements such as the PU 40 and the ROM 41, the input unit 44, and the input / output unit 45 are connected to each other to send various data.

FIG. 4 is a diagram showing the fuel injection timing of the injector 27 controlled by the ECU 30 for each cylinder # 1 to # 4. In the figure, the hatched portion in the upper right direction indicates the intake stroke in each cylinder, and the shaded portion indicates the fuel injection timing by the above-mentioned asynchronous intake injection in which fuel injection is performed before the start of the intake stroke. There is. Further, a portion shown by hatching to the upper left shows the fuel injection timing by the above-described intake synchronous injection in which fuel injection is performed in accordance with the intake stroke.

The engine of the first embodiment has four cylinders and four strokes. As shown in FIG.
The intake stroke is performed in the order of # 1 → # 3 → # 4 → # 2 every 80 degrees, and after the intake stroke ends in each cylinder, ignition is reached through a compression stroke of CA of about 180 degrees. In the engine of the first embodiment, by the control in the ECU 30 described later, the injection timing by the intake asynchronous injection shown in black in the figure and the injection timing by the intake synchronous injection shown by the upward-sloping hatching in the figure. It can be switched according to the engine load and other conditions.

Therefore, the ECU 30 switches the above two types of fuel injection timings in accordance with the operating conditions based on the detection data input from each sensor according to the control program stored in the ROM 41, and the load forming the present invention. The detecting means 2 and the injection timing switching means 3 are realized. Figure 5 shows EC
7 shows a flowchart of a control routine which is processed in U30 and which realizes the load detecting means 2. The routine shown in the figure is activated by interruption every predetermined time.

In the figure, first, at step 102, the AFM
The value of the intake air amount Q is input by the signal from 22. Next, at step 104, the signal from the rotation angle sensor 33 is processed to input the value of the engine speed N. In the following step 106, a process of dividing the intake air amount Q by the engine speed N is performed to obtain a value of Q / N (air amount per engine revolution) representing the load level of the engine. Then, this routine ends. Thus, the load of the engine can be detected by the routine shown in FIG. 5, and the load detecting means 2 is realized.

FIG. 6 shows a flow chart of a control routine which is also processed in the ECU 30 and realizes the injection timing switching means 3. The routine shown in the figure is activated by interruption every predetermined time.

In the figure, first, at step 202, it is judged whether or not the value of Q / N obtained by the routine shown in FIG. 5 is not less than a predetermined value α which is a load judgment criterion. If it is equal to or more than the predetermined value, that is, if the engine is in a high load state, the routine proceeds to step 204, where the intake-synchronized injection mode flag XIS is determined to determine whether the intake-synchronized injection was performed in the previous routine. It is determined whether asynchronous injection has been performed.

At step 202, the value of Q / N is a predetermined value α.
If less, that is, if the engine is in a low load state, the routine proceeds to step 208, where intake asynchronous injection is performed as in the conventional case. Then, in step 210, the flag XIS is cleared (XIS = 0), and this routine is ended. As described above, when the engine is in the low load state, the intake asynchronous injection is performed unconditionally, so that the above-described vaporization of the fuel in the intake manifold 28 and the atomization effect by the high-speed intake flow can be expected, Stable combustion can be performed in a low load state.

When XIS = 0 in step 204, that is, when the intake asynchronous injection is performed in the previous routine, the routine proceeds to step 206, where it is judged whether or not knocking has occurred. Knock sensor 31 is used to determine whether knocking has occurred.
It is performed by comparing the signal from the signal with a predetermined threshold value.
When it is detected that knocking has occurred in step 206, it means that the driver steps on the accelerator to request higher output, and the engine is in the process of increasing output,
In order to obtain the effect of increasing the output by the intake-synchronized injection described later, the routine proceeds to step 212, where the intake-synchronized injection is performed. That is,
Switching from the intake asynchronous injection to the intake synchronous injection is performed according to the above processing contents. Then, in the subsequent step 214, the flag XIS is set (XIS = 1), and this routine ends. If knocking does not occur in step 206, it is determined that the combustion is stable to some extent even under high load, and there is no problem in continuing the intake asynchronous injection as it is, and the routine proceeds to step 208. Continue jetting. Therefore, in the present routine, when the asynchronous injection is the intake in the previous routine, if the load is higher than the predetermined value α and the two conditions that knocking occurs do not meet, the asynchronous intake injection is switched to the synchronous intake injection. Is not to be done.

If XIS = 1 in step 204, that is, if the intake-synchronized injection has been continued since the last routine, the routine proceeds to step 212 without performing knocking presence / absence determination in the next step 206, and intake-synchronized injection is performed. Let it continue. If the engine has a high load, no problem will occur even if the intake synchronous injection is continued regardless of knocking. Therefore, in this routine, once the intake-synchronized injection is performed, switching to the intake asynchronous injection is not performed until the load decreases to a predetermined value by the action of step 204 regardless of knocking.

As described above, in this control routine, the degree of engine load is determined in step 202, and basically, the intake synchronous injection is performed in the high load state, and the intake asynchronous injection is performed in the low load state. Although the injection timing switching means 3 is realized, the opportunity of switching between the intake synchronous injection and the intake asynchronous injection is suppressed in steps 204 and 206 within a range that does not hinder the operation. This prevents frequent engine output fluctuations that people feel.

By performing the intake-synchronous injection at the time of a high load of a predetermined value or more of the engine, a large amount of fuel injected from the injector 27 is injected into the cylinder during the intake stroke, together with a high temperature and a large amount of intake air. Is supplied to. Next, the effects obtained by the intake-synchronized injection under the high load will be summarized and described below.

Since a large amount of fuel injected under a high load condition is included in the intake air flow in the manifold and supplied to the cylinder, the fuel hardly adheres to the intake manifold wall surface or the intake valve surface, and the conventional ,
It is possible to solve the problem of unstable combustion that has occurred due to asynchronous injection of intake air at high load.

Since the intake air supplied to the cylinder is large in amount and high in temperature due to the high load, the injection negative pressure wave by the large amount of intake air improves the fuel ejection speed and promotes atomization of the fuel. Also, the vaporization of the fuel in the cylinder is promoted by the hot intake air. Therefore, even when the fuel with large particles is directly supplied into the cylinder by the intake synchronous injection, the reduction of the engine output due to the deterioration of the fuel vaporization is prevented.

As described above, since vaporization from particulate fuel is promoted in the cylinder, the intake air in the cylinder is cooled by the latent heat of vaporization at this time. as a result,
By increasing the volumetric efficiency η _V (gas density) of the intake air, it is possible to expect an increase in the torque (engine output) of the width indicated by A in FIG. 7. Moreover, the occurrence of knocking is suppressed by cooling the intake air as described above. Normal,
Since there is a retard side of the ignition timing is timing at which the maximum torque is obtained, in FIG. 7, T ₁ knock improving component, the spark advance
By advancing from T to T _2, it is possible to expect an increase in torque (engine output) due to knock improvement in the width indicated by B. As described above, at the time of high load, a torque difference of A and B occurs between the intake synchronous injection and the intake asynchronous injection, so that the driver feels the output fluctuation of the engine when switching the injection timing. Therefore, the opportunity of switching the injection timing is suppressed as much as possible by the control routine described above.

As described above, the improved knocking eliminates the need for retarding the ignition advance angle, thereby reducing exhaust temperature and improving fuel efficiency. Further, as the knocking is improved, it becomes possible to increase the compression ratio at the engine design stage, which also improves the fuel consumption and the output.

Further, even when the load is high, when knocking does not occur, that is, when combustion is not so unstable, the conventional exhaust gas asynchronous injection improves exhaust emission.

In the low load state where the engine load is equal to or lower than a predetermined value, the intake asynchronous injection is performed as in the conventional case, so that the vaporization of the fuel can be favorably continued by the above-mentioned action and the stable combustion can be maintained.

Next, a second embodiment in which the present invention is applied to a group injection type engine which is a four cylinder four stroke engine and in which two cylinders are set as one group and fuel is injected into two groups respectively will be described. ..

FIG. 8 is a diagram showing the fuel injection timing in each of the cylinders # 1 to # 4 in the second embodiment of the present invention. In the same figure, the part shown by hatching to the right shows the intake stroke in each cylinder, and the part shown in black shows the fuel injection timing by the above-mentioned intake asynchronous injection that performs fuel injection at the stage before the start of the intake stroke, Further, a portion shown by hatching to the upper left shows the fuel injection timing by the above-described intake synchronous injection in which fuel injection is performed in accordance with the intake stroke. Also in the second embodiment, # 1 → # 3 → # 4 → # for every 180 degrees of CA.
As in the first embodiment, the intake stroke is performed in the order of two cylinders, and after each intake stroke, ignition is performed through a compression stroke of about 180 degrees CA in each cylinder.

In the second embodiment, the # 1, # 4 cylinders, and the # 2, # 3 cylinders are set as one group, and fuel injection is performed for each group at CA360 degrees. Therefore, the injection amount in one fuel injection at this time is half the amount in every 720 degrees as shown in FIG. 4, that is, when the fuel injection is performed once in one stroke. That is, in the second embodiment, the fuel injection amount required for one ignition and combustion is divided into two injections every CA 360 degrees and injection is performed before ignition.

First, referring to the case of the intake asynchronous injection shown in black in FIG. 8, for example, in the case of the # 2 cylinder, CA
Fuel injection is performed twice between 0 to 180 degrees and CA 360 to 540 degrees, then an intake stroke of CA 540 to 720 degrees is performed, and further ignition is performed through a compression stroke of CA 180 degrees. Even for the # 3 cylinder of the same group as the # 2 cylinder, although the piston strokes such as the intake stroke are all shifted by 360 degrees with respect to the # 2 cylinder, fuel injection is performed at the same timing as the # 2 cylinder, After two fuel injections, the intake stroke, compression stroke, and ignition are subsequently performed. Also in the # 1 and # 4 cylinders, although the strokes of the pistons are deviated, the intake stroke is performed after the fuel is injected twice as in the case of the # 2 and # 3 cylinders. Therefore, in the case of asynchronous intake injection, fuel injection and intake stroke are not performed simultaneously in all cylinders,
The intake asynchronous injection described above is completely achieved. Here, the first fuel injection is performed during the compression stroke of the cylinder, for example, as seen in the fuel injection of CA0 to 180 degrees in the # 2 cylinder, but in the intake asynchronous injection, the intake valve is closed. Since fuel is injected into the intake manifold, fuel injection can be performed without being affected by the compression stroke.

Next, referring to FIG. 8, in the case of intake-synchronized injection indicated by hatching to the left, for example, # 2
In the cylinder, CA 180-360 degrees and CA 540-72
Fuel injection is performed twice between 0 degrees. The second fuel injection is performed during the intake stroke of the # 2 cylinder, and the intake synchronous injection is achieved at this time. The first fuel injection is performed in the intake manifold with the intake valve closed during the combustion stroke of the # 2 cylinder, and at this time, the intake asynchronous injection is performed. Similarly, for the # 3 cylinder, although all strokes are shifted by CA360 degrees, the second fuel injection is intake synchronous injection that is performed simultaneously with the intake stroke. The same applies to the # 1 and # 4 cylinders as the # 2 and # 3 cylinders.

As described above, in the group injection type engine, the fuel injection is performed at every 360 degrees, thereby
One of the fuel injections of one time is the intake synchronous injection, and the remaining one fuel injection is the intake asynchronous injection.
Therefore, in the group injection type engine of the second embodiment, the intake synchronous injection indicated by the upward-sloping hatching causes the amount of fuel to be half of the fuel injection amount required for one combustion. In the intake stroke, the intake air is sucked into the cylinder together with the intake air, and the above-described effects of the intake synchronous injection are brought about. However, in the case of the second embodiment, since only half the amount of fuel is injected by the intake synchronous injection as compared with the first embodiment, the effect of the intake synchronous injection is that the intake synchronous injection is completely achieved. Compared with the case of the first embodiment, the effect is about half.

Next, as a third embodiment, an apparatus using the above-described fuel injection timing control in combination with ignition timing control and fuel injection amount correction control will be described. FIG. 10 shows a flow chart of a control routine which is processed in the ECU 30 in the third embodiment and realizes the injection timing switching means 3. Note that the routine shown in FIG.
Similar to the routine shown in (1), interrupt activation is performed at predetermined time intervals.

When this routine is activated, first step 3
At 00, it is determined whether the temperature THW of the cooling water of the internal combustion engine is equal to or higher than a predetermined temperature β. If THW <β, that is, if the engine has not been warmed up to the predetermined temperature, the routine proceeds to step 308, where intake asynchronous injection is performed as in the conventional case. This is because, if the engine is not sufficiently warmed up, the intake air temperature is low, and acceleration of fuel vaporization cannot be expected in intake air synchronous injection. Then, in this case, similarly to the routine shown in FIG. 6, the flag XIS of the intake synchronous injection mode is cleared (XIS = 0), and this processing is ended.

If THW ≧ β, that is, if it is determined in step 300 that the engine is sufficiently warmed up, the process proceeds to step 302. Step 302 corresponds to step 202 in FIG. 6, and determines the load state of the engine by comparing the value of Q / N with a predetermined value α.

If Q / N is less than α, "NO"
Is determined, the above steps 308 and 310 are executed, and the processing of this time is ended. This is because when the engine is operating in a low load state, fuel can be more effectively vaporized by the intake asynchronous injection as in the conventional case.

When the engine load is high and Q / N is α or more, the routine proceeds to step 304, where the injection mode in the previous routine is determined by the intake synchronous injection mode flag XIS. Then, when XIS = 0, that is, when the intake asynchronous injection is performed in the previous routine, the routine proceeds to step 306, and when XIS = 1, the routine proceeds to step 312.

Step 306 is step 2 in FIG.
Corresponding to 06, it is determined whether knocking has occurred. Here, if knocking has not occurred, it is determined that the engine maintains a stable operating state and the intake synchronous injection is continued as it is (steps 308, 31).
0) If it is detected that knocking has occurred, processing for suppressing knocking is performed as in the routine shown in FIG.

As described above, when fuel is supplied by the intake asynchronous injection to the engine operating under a load as high as Q / N ≧ α, a large amount of fuel is stored in the intake manifold 28. May not be vaporized, and some of the fuel to be supplied as a mixture may not be vaporized.
In this case, the amount of fuel supplied to the internal combustion engine becomes unstable, which in turn causes knocking.

Therefore, when knocking is detected in step 306, the routine proceeds to step 312, where the fuel injection timing is switched as in the routine of FIG. That is, the fuel injection mode is switched to the intake synchronous injection mode suitable for vaporizing a large amount of fuel by synchronizing the fuel injection timing with the generation timing of the maximum intake negative pressure wave.

When the fuel injection mode is switched to the intake synchronous injection in this way, the XIS flag is set (XIS = 1) in the following step 314. Therefore, after this
If this routine is started with W ≧ β and Q / N ≧ α, step 306 is skipped, and intake-synchronized injection is performed regardless of knocking.

When the intake asynchronous injection is switched to the intake synchronous injection to suppress the occurrence of knocking, as described in FIG. 7, the ignition timing is advanced by an angle corresponding to the improvement. It becomes possible to take out a larger torque.

Therefore, in this embodiment, when the fuel injection mode is switched to the intake-synchronized injection in the above process, the routine proceeds to step 316, where the ignition timing advance amount is corrected to such an extent that knocking does not occur. In this process, for example, the ignition timing at the time of switching the fuel injection mode is stored in the RAM 42 as a reference advance amount, and the reference advance amount is stored in the ROM 41 in advance, and the engine speed and the engine load are changed. It is realized by performing correction using a map that defines the correction advance amount.

As described above, in this embodiment, the fuel injection mode is switched to the intake synchronous injection and the ignition timing is corrected to an appropriate timing. Therefore, the energy that can be taken out as torque from the internal combustion engine is increased as compared with the conventional device, and the fuel efficiency is improved by improving the combustion efficiency.

By the way, in an internal combustion engine mounted on a vehicle, when the internal combustion engine is under a high load condition, it has been known that the exhaust system, particularly the exhaust gas purifying catalyst, is damaged by the high temperature exhaust gas discharged in that condition. To prevent this, fuel increase correction is widely performed. This fuel increase correction focuses on the fact that the temperature of the exhaust gas changes depending on the air-fuel ratio of the burning air-fuel mixture, and the temperature becomes the highest when the air-fuel mixture is near the stoichiometric air-fuel ratio.

That is, if the air-fuel mixture is kept near the stoichiometric air-fuel ratio in order to ensure good exhaust emission, the temperature of the exhaust gas discharged when the internal combustion engine is in a high load state is In order to deteriorate the catalyst early beyond the above range, the exhaust gas temperature is reduced by controlling the air-fuel mixture to be fuel rich only when the internal combustion engine is in a high load state.

On the other hand, in this embodiment, when the engine is in a constant high load state, the fuel injection mode is the intake synchronous injection. Further, when the intake synchronous injection is performed, the particulate fuel is supplied into the cylinder, and the air-fuel mixture in the cylinder is cooled by the latent heat of vaporization of the fuel as described above. As described above, when the temperature of the air-fuel mixture to be burned is lowered, the temperature of the exhaust gas discharged accordingly is lowered.

Further, in the present embodiment, as described above, when the fuel injection mode is switched to the intake synchronous injection, the ignition timing is corrected to the advanced side accordingly. When the ignition timing shifts to the advance side, the start timing of the combustion process is advanced, the combustion process is lengthened, and the compression ratio of the air-fuel mixture at the time of ignition is increased to improve its combustibility.

Therefore, in general, as soon as the ignition timing is ignitable, the air-fuel mixture is more likely to be completely combusted, and the exhaust gas temperature is lower. When the ignition timing is later, the incomplete combustion gas of higher temperature is discharged and exhausted. The temperature tends to rise. Therefore, in the configuration in which the ignition timing is corrected to the advance side when the engine is in the high load state as in the present embodiment, the exhaust gas temperature under the high load can be kept lower than in the conventional configuration.

FIG. 11 is a diagram for explaining the effect of the above-mentioned decrease in exhaust gas temperature. The curve shown by the broken line in the figure represents the relationship between the ignition timing and the exhaust temperature in the air-fuel mixture whose fuel amount has been corrected to a predetermined air-fuel ratio (fuel rich) in order to reduce the exhaust temperature in the internal combustion engine of the conventional configuration. ing.

Since the intake asynchronous injection is always used in the internal combustion engine having the conventional structure, the ignition timing is limited to the vicinity of time T _{1 in} FIG. 11 from the viewpoint of preventing knocking. Therefore,
It is not possible to advance the ignition timing to lower the exhaust gas temperature, and it is necessary to correct the amount of the air-fuel mixture to be rich in fuel so that the exhaust gas temperature becomes equal to or lower than the target exhaust gas temperature, assuming that the ignition temperature is around time T _1. was there.

On the other hand, in the present embodiment, in the high load state where the exhaust gas temperature exceeds the target exhaust gas temperature, the fuel injection mode is switched to the intake synchronous injection, and the ignition timing is advanced to the vicinity of time T _{2 in} FIG. Be horned. Therefore, the exhaust temperature at high load is significantly lower than that of the conventional engine, and the target exhaust temperature can be achieved even with a fuel-lean mixture (curve shown by the solid line in FIG. 11). Becomes

Therefore, in this embodiment, after the ignition timing advance correction is performed in step 316, the process proceeds to step 318, which is the so-called fuel increase amount calculated by another routine for lowering the exhaust gas temperature. OT increase (Over
Temperature increase) is further corrected to make the air-fuel mixture leaner than before when correcting the fuel increase.

The correction amount of the OT increase at this time is obtained by, for example, storing a one-dimensional map for the advance angle correction amount in the ROM 41 and referring to this with the advance angle correction amount calculated in step 316. be able to.

Therefore, according to this embodiment, the OT increase during the fuel increase correction is suppressed to the minimum, and the conventional problem in the fuel increase correction that the fuel consumption and the exhaust emission are deteriorated is improved.

The processing in this embodiment is completed as described above, and thereafter, the above steps 300 to 318 are repeatedly executed every time when this routine is started every predetermined time.

In the above routine, if the fluctuations in the transient state are strictly determined in steps 300 and 302, the fuel injection mode may switch rapidly. Therefore, the judgment value β at each step
There are two discrete values set for α and α. If the judgment is inverted from “NO” to “YES”, the value is discretely low, and if the judgment is inverted from “YES” to “NO”. It is discretely changed to a higher value.

Therefore, for example, in the warm-up process of the engine, if the cooling water temperature THW once becomes β or more and the intake synchronous injection is started, the fuel injection mode will not return to the asynchronous intake injection with a slight decrease in THW. Absent. Similarly, with respect to engine load fluctuations, once the judgment is reversed, the judgment value α is discretely changed, and the fuel injection mode is not switched by a slight load fluctuation thereafter.

[0067]

As described above, according to the present invention, a large amount of fuel injected when the load of the internal combustion engine is a predetermined value or more is changed from the intake asynchronous injection mode to the intake asynchronous injection mode by the injection timing switching means. Since the fuel is supplied into the cylinder together with the intake air in the synchronous injection mode, the fuel is prevented from adhering to the intake manifold wall surface or the intake valve surface, and the combustion can be stabilized even when the internal combustion engine has a high load. As a result, in addition to the low load state in which combustion is stable in the intake asynchronous injection mode, it is possible to realize control of the fuel injection timing that can always perform stable combustion in the full load state of the internal combustion engine.

Further, in the intake synchronous injection mode at the time of high load, the fuel vaporized in the cylinder increases and the cooling of the intake air in the cylinder by the latent heat of vaporization at this time is promoted, so that the volumetric efficiency of the intake air is increased. The η _V (density) is improved, the occurrence of knocking is suppressed, and the ignition advance can be performed, so that the output of the engine and the fuel consumption can be improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration diagram showing an embodiment of an internal combustion engine and its peripheral devices to which the present invention is applied.

3 is a block diagram showing specific constituent elements of the ECU in FIG. 2. FIG.

FIG. 4 is a diagram showing the fuel injection timing for each of the cylinders # 1 to # 4 in the independent injection type engine that is the first embodiment of the present invention.

FIG. 5 is a flowchart of a control routine that realizes load detection means.

FIG. 6 is a flowchart of a control routine that realizes injection timing switching means.

FIG. 7 is a diagram illustrating an effect of intake-synchronized injection.

FIG. 8 is a diagram showing a fuel injection timing in each of the cylinders # 1 to # 4 in the group injection type engine which is the second embodiment of the present invention.

FIG. 9 is a diagram illustrating intake asynchronous injection and intake synchronous injection.

FIG. 10 is a flowchart of a control routine executed in the third embodiment of the present invention.

FIG. 11 is a diagram for explaining the principle of fuel amount increase correction in the third embodiment of the present invention.

[Explanation of symbols]

 1 internal combustion engine 1A intake asynchronous injection 1B intake synchronous injection 2 load detection means 3 injection timing switching means 11 engine body 12 piston 13 cylinder 14 ignition flag 15 intake valve 16 exhaust valve 22 air flow meter (AFM) 23 intake pipe 24 throttle valve 27 injector 30 Engine Control Computer (ECU) 31 Knock Sensor 32 Distributor 33 Rotation Sensors 40 Central Processing Unit (CPU)

Claims (1)

[Claims] 1. A fuel injection that calculates a fuel injection amount corresponding to an operating state of an internal combustion engine and injects the calculated fuel injection amount of fuel in an intake asynchronous injection mode in which fuel injection is performed before an intake stroke. In the timing control device, load detection means for detecting the load of the internal combustion engine, and when the load detected by the load detection means is a high load equal to or higher than a predetermined value, in the intake synchronous injection mode in which fuel injection is performed during the intake stroke. A fuel injection timing control device comprising: an injection timing switching means configured to inject the fuel.