JP2000205012A - Fuel injection timing control device for internal combustion engine - Google Patents

Abstract

(57) Abstract: The present invention relates to a control device for an internal combustion engine, and aims to prevent an air-fuel ratio from becoming lean or rich when switching from intake synchronous injection to intake asynchronous injection. SOLUTION: An increase flag _Ff is set to "1" at a timing of switching from intake synchronous injection to intake asynchronous injection. If step 200 increase flag F _f is set to "1", the initial value C ₀ is substituted for the increasing coefficient C _f in step 202. On the other hand, if the increase flag F _f is not set to "1", in step 206-210, the increase coefficient C _f is gradually reduced as the lower limit of "1". In the fuel injection amount calculating routine, the target injection amount is determined by the basic fuel injection amount increase coefficient C _f is multiplied.

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 system for an internal combustion engine, and more particularly to a fuel injection timing control system for an internal combustion engine having a function of selectively performing intake synchronous injection and intake asynchronous injection. .

[0002]

2. Description of the Related Art Conventionally, after a warm-up of an internal combustion engine, intake asynchronous injection, in which fuel injection is performed before opening of an intake valve, is executed,
In a cold state, intake synchronous injection is performed in which fuel injection is performed during opening of an intake valve. When the asynchronous intake injection is performed, the injected fuel adheres to a wall surface or the like in the intake port, and a part of the attached fuel is vaporized and then sucked into the combustion chamber. Therefore, according to the intake asynchronous injection, the emission in the exhaust gas is reduced by improving the mixing property between the fuel and the air. On the other hand, when the intake synchronous injection is executed, the adhesion of the fuel to the port is suppressed, and the injected fuel is sucked into the combustion chamber without being vaporized. Therefore,
According to the intake synchronous injection, the startability of the internal combustion engine in a cold state is improved by ensuring a sufficient amount of fuel sucked into the combustion chamber.

As described above, the intake synchronous injection is performed in a state where almost no fuel is attached to the intake port, whereas the asynchronous intake injection has a considerable amount of fuel attached to the intake port. It is executed on the assumption that For this reason,
When the switching from the intake synchronous injection to the intake asynchronous injection is performed, the amount of the injected fuel remaining in the intake port while being attached to the intake port increases. In this case, the amount of fuel sucked into the combustion chamber decreases, and the air-fuel ratio temporarily becomes lean, so that the combustion stability decreases.

In order to avoid such a disadvantage, for example, in a combustion injection timing control apparatus for an internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 7-197833, when switching from intake synchronous injection to intake asynchronous injection, prior to the actual fuel injection, Pre-injection is performed. According to such a method, the total amount of the fuel injection amount is increased by the amount of the preliminary injection, thereby preventing the air-fuel ratio from becoming lean due to switching from the intake synchronous injection to the intake asynchronous injection.

[0005]

By the way, when switching from the intake synchronous injection to the intake asynchronous injection, the fuel adhering to the intake port increases every time fuel injection is performed, and eventually becomes saturated. Accordingly, the amount of fuel that adheres to the intake port of the injected fuel gradually decreases, and accordingly, the amount of fuel that is sucked into the combustion chamber gradually increases. However, in the above-described conventional control device, the preliminary injection amount is determined based on the engine operating state at the time of switching from the intake synchronous injection to the intake asynchronous injection. Therefore, if the amount of fuel sucked into the combustion chamber gradually increases after the switching of the injection timing, the air-fuel ratio becomes richer. In this regard, the conventional control device is not always optimal for maintaining an appropriate air-fuel ratio when switching from intake synchronous injection to intake asynchronous injection.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a fuel injection timing control device for an internal combustion engine capable of maintaining an appropriate air-fuel ratio when switching from intake synchronous injection to intake asynchronous injection. The purpose is to provide.

[0007]

The above object is achieved by the present invention.
Injection timing control means for selectively executing intake synchronous injection in which fuel injection is performed during opening of an intake valve and asynchronous intake injection in which fuel injection is performed before opening of an intake valve, as described in A fuel injection timing control device for an internal combustion engine, comprising: a switching time increasing means for increasing a fuel injection amount as compared with a normal time at the time of switching from synchronous injection to the intake asynchronous injection, wherein the switching time increasing means comprises: This is achieved by a fuel injection timing control device for an internal combustion engine that gradually reduces the increase amount of the fuel injection amount with time after switching from the intake synchronous injection to the intake asynchronous injection.

In the present invention, during execution of the intake synchronous injection, the amount of fuel adhering to the intake port is small.
On the other hand, during the execution of the asynchronous intake injection, a relatively large amount of fuel is attached to the intake port. For this reason, when the switching from the intake synchronous injection to the intake asynchronous injection is performed, the amount of the injected fuel that adheres to the intake port and is not sucked into the combustion chamber increases. On the other hand, the switching time increasing means increases the fuel injection amount at the time of switching from the intake synchronous injection to the intake asynchronous injection, thereby preventing the air-fuel ratio from becoming lean at the time of switching. After switching from the intake synchronous injection to the intake asynchronous injection, the amount of fuel attached to the intake port gradually increases. Accordingly, of the injected fuel, the amount of fuel adhering to the intake port gradually decreases, and the amount of fuel sucked into the combustion chamber gradually increases. Therefore, according to the present invention, the switching-time increasing means gradually reduces the increase amount of the fuel injection amount, thereby preventing the air-fuel ratio from becoming rich after switching to the intake asynchronous injection. As described above, according to the present invention, it is possible to prevent the air-fuel ratio from becoming rich or lean when switching from the intake synchronous injection to the intake asynchronous injection, and to maintain an appropriate air-fuel ratio.

[0009]

FIG. 1 is a block diagram of a system to which a fuel injection timing control device for an internal combustion engine according to a first embodiment of the present invention is applied. The system of this embodiment is an internal combustion engine 10
It has. The internal combustion engine 10 is controlled by the ECU 12. The internal combustion engine 10 includes a cylinder block 14. Inside the cylinder block 14, the cylinder 16
And a water jacket 18. The water jacket 18 is provided with a water temperature sensor 19. The water temperature sensor 19 outputs a signal to the ECU 12 according to the temperature of the cooling water flowing inside the water jacket 18 (hereinafter, referred to as water temperature THW). The ECU 12 detects the water temperature THW based on the output signal of the water temperature sensor 19.

A piston 20 is provided inside the cylinder 16. The piston 20 can slide vertically inside the cylinder 16 in FIG. A cylinder head 22 is fixed to an upper portion of the cylinder block 14. An intake port 24 and an exhaust port 26 are formed in the cylinder head 22. The bottom surface of the cylinder head 22, the upper surface of the piston 20, and the side wall of the cylinder 16 define a combustion chamber. The above-described intake port 24 and exhaust port 26 are both
8 is open. The tip of the ignition plug 30 is exposed in the combustion chamber 28. The ignition plug 30 ignites fuel in the combustion chamber 28 by receiving an ignition signal from the ECU 12.

The internal combustion engine 10 also includes an intake valve 34 and an exhaust valve 36. Openings of the intake port 24 and the exhaust port 26 to the combustion chamber 28 are respectively provided with intake valves 3
4 and a valve seat corresponding to the exhaust valve 36 are provided. The intake valve 34 and the exhaust valve 36 open and close the intake port 24 and the exhaust port 26, respectively, by separating from and seating on each valve seat.

The intake port 24 has an intake manifold 3
8 are in communication. A fuel injection valve 40 is provided in the intake manifold 38. The fuel injection valve 40 is ECU1
The fuel is injected into the intake manifold 38 in accordance with the command signal given from Step 2. A surge tank 42 communicates with the upstream side of the intake manifold 38. An intake pipe 44 communicates further upstream of the surge tank 42. The intake pipe 44 is provided with a throttle valve 46.

An air flow meter 50 communicates upstream of the intake pipe 44. The air flow meter 50 outputs a signal corresponding to the flow rate of the air passing therethrough to the ECU 12. The ECU 12 detects the intake air amount GA of the internal combustion engine 10 based on the output signal of the air flow meter 50. An air cleaner 52 communicates further upstream of the air flow meter 50. The outside air filtered by the air cleaner 52 flows into the intake pipe 44.

On the other hand, an exhaust passage 54 communicates with the exhaust port 26 of the internal combustion engine. An O ₂ sensor 56 is provided in the exhaust passage 54. The O ₂ sensor 56 outputs a signal corresponding to the concentration of oxygen contained in the exhaust gas to the ECU 12. A catalytic converter 58 is provided downstream of the O ₂ sensor 56 in the exhaust passage 54. The catalytic converter 58 includes a hydrocarbon (HC) contained in the exhaust gas,
Carbon monoxide (CO), and for purifying the exhaust gas by adsorbing the nitrogen oxides (NO _X).

The internal combustion engine 10 also includes a crank angle sensor 62. The crank angle sensor 62 outputs a pulse signal to the ECU 12 every time the internal combustion engine 10 rotates by a predetermined crank angle. The ECU 12 detects the rotation speed of the internal combustion engine 10 (hereinafter, referred to as engine speed NE) based on the output signal of the crank angle sensor 62. In the system of the present embodiment, during the normal operation of the internal combustion engine 10, the intake asynchronous injection, in which the fuel injection is performed before the intake valve 34 is opened, is executed. According to the intake asynchronous injection, the fuel injected from the fuel injection valve 40 is supplied into the intake port 24 (for example,
After adhering to the back surface of the umbrella portion of the intake valve 34, the wall surface around the opening to the combustion chamber 28, etc., the mixture with air is improved by vaporization. And such an air-fuel mixture forms the combustion chamber 28.
By the combustion in the exhaust gas, the emission contained in the exhaust gas is reduced.

The fuel properties of the internal combustion engine 10 are as follows:
May change depending on season. That is, a light fuel that evaporates easily in winter, when the temperature is low, and a heavy fuel that hardly evaporates in summer, when the temperature is high, may be used. When heavy fuel is used, if the above-described asynchronous intake injection is performed during the cold start of the internal combustion engine 10, the fuel attached to the intake port 24 does not sufficiently vaporize, and the fuel supplied to the combustion chamber 28 is not provided. The combustion state becomes unstable due to the shortage of the amount.

Therefore, in this embodiment, when it is determined that heavy fuel is being used, fuel injection is performed during opening of the intake valve 34 in order to ensure combustion stability during cold start. The intake synchronous injection is executed, and at the time when the combustion stability of the internal combustion engine 10 is secured, the intake synchronous injection is returned to the intake asynchronous injection. FIG. 2 is a flowchart of a routine executed by the ECU 12 to realize the above functions. The routine shown in FIG. 2 is a periodic interruption routine started at predetermined time intervals. In addition, EC
When the control switching flag F is set to "0", U12 executes the intake asynchronous injection and sets the control switching flag F
Is set to "1", intake synchronous injection is executed. Further, the control switching flag F is initialized to “0”.

When the routine shown in FIG. 2 is started, first, the processing of step 108 is executed. In step 108, it is determined whether or not the intake air amount GA of the internal combustion engine 10 is less than a predetermined value c. In general, the combustion tends to be unstable as the intake air amount GA is smaller. Therefore, step 1
If GA <c is satisfied in step 08, it is determined that there is a possibility that combustion may become unstable, and then step 110
Is performed. On the other hand, in step 108, G
If A <c is not satisfied, the control switching flag F is set to "0" in step 111, and then the current routine is terminated.

In step 110, it is determined whether or not the elapsed time T after the start of the internal combustion engine 10 is less than a predetermined value d. The predetermined value d is set to a value larger than the predetermined value a. If T <d is satisfied in step 110, the process of step 112 is executed next. on the other hand,
If T <d is not satisfied in step 110, the control switching flag F is set to “0” in step 111, and then the current routine is terminated.

In step 112, it is determined whether or not the water temperature THW is lower than a predetermined value e. The predetermined value e is set to a value larger than the predetermined value b. Step 112
If THW <e holds, it is determined that the internal combustion engine 10 has not yet been warmed up.
4 is executed. On the other hand, if THW <e is not satisfied in step 112, the control switching flag F is set to “0” in step 111, and then the current routine is terminated.

In step 114, it is determined whether or not the engine speed NE is less than a predetermined value f. As a result, NE
If <f is satisfied, it is determined that the combustion state is unstable and heavy fuel is being used, and then step 11
In step 6, the control switching flag F is set to "1", so that the intake synchronous injection is executed, and then the current routine is terminated.

On the other hand, if NE <f is not satisfied in step 114, the current routine is terminated without changing the value of the control switching flag F. As described above, according to the routine shown in FIG. 2, when the intake air amount GA is less than c, the elapsed time T after the start is less than d, and the water temperature THW is less than e, the engine speed is reduced. It is determined that heavy fuel is being used when NE has dropped below the predetermined value f. In this case, the control switching flag F is set to "1" in step 116, and the intake synchronous injection is executed, thereby stabilizing the combustion state.

Also, when the intake synchronous injection control is executed, if a negative determination is made in step 108, 110, or 112, it is determined that the combustion state has been stabilized, and then in step 111, the control switching flag is set. By setting F to “0”, switching from intake synchronous injection to intake asynchronous injection is performed. By the way, when the intake synchronous injection is executed, most of the injected fuel is sucked into the combustion chamber 28 without adhering to the intake port 24. For this reason, during the execution of the intake synchronous injection, the amount of fuel adhering in the intake port 24 (hereinafter, referred to as the actual port adhesion amount) is small. On the other hand, as described above, the intake asynchronous injection is based on the premise that a considerable amount of fuel adheres to the intake port 24, and the adhered fuel is vaporized and taken into the combustion chamber 28. Therefore, immediately after switching from the intake synchronous injection to the intake asynchronous injection, the fuel injected from the fuel injection valve 40 remains at the intake port 24 without adhering to the combustion chamber 28 while being attached to the intake port 24. The amount of fuel (i.e., the difference between the amount of fuel injected from fuel injector 40 and the amount of fuel drawn into combustion chamber 28);
Hereinafter, this will be referred to as port consumption). in this case,
As the amount of fuel sucked into the combustion chamber 28 decreases, the air-fuel ratio becomes lean, causing deterioration of combustion stability.

FIG. 3 shows, by a solid line and a broken line, an example of a change in the actual port attachment amount and the port consumption amount with respect to the number of fuel injections after switching from the intake synchronous injection to the intake asynchronous injection. . As shown by the solid line in FIG. 3, after switching from the intake synchronous injection to the intake asynchronous injection, the actual port adhesion amount increases each time fuel injection is performed, and eventually saturates. On the other hand, as indicated by the broken line in FIG. 3, the port consumption gradually decreases from the value Q ₀ immediately after the switching as the actual port adhesion amount increases, and becomes almost zero when the actual port adhesion amount reaches the saturation amount. Becomes

As described above, immediately after switching from the intake synchronous injection to the intake asynchronous injection, the port consumption is large (the amount of fuel sucked into the combustion chamber 28 is small) because the actual port adhesion amount is small. As the amount of deposit increases, the port consumption gradually decreases (the amount of fuel sucked into the combustion chamber 28 gradually increases). Therefore, in order to prevent leaning at the time of switching from the intake synchronous injection to the intake asynchronous injection, for example, the port consumption Q ₀ immediately after the switching is used.
If the fuel injection amount is increased by an amount corresponding to the above, the air-fuel ratio becomes rich due to the subsequent decrease in the port consumption. On the other hand, if the increase in the fuel injection amount is reduced in anticipation of a decrease in the port consumption, the air-fuel ratio becomes lean immediately after switching.

On the other hand, in the system of this embodiment,
In consideration of the decrease in the port consumption as described above, after switching from the intake synchronous injection to the intake asynchronous injection, the increase width of the fuel injection amount is gradually reduced to prevent the air-fuel ratio from becoming lean and rich. It is characterized in that an appropriate air-fuel ratio can be maintained by using this method. The function of this embodiment is the same as the ECU 1
2 is realized by executing the routine shown in FIGS.

FIGS. 4 and 5 are flowcharts of a routine executed by the ECU 12 to increase the fuel injection amount when switching from the intake synchronous injection to the intake asynchronous injection. The routine shown in FIGS. 4 and 5 is a periodic interruption routine that is started at a predetermined time interval for each cylinder. First, the contents of the routine shown in FIG. 4 will be described. When the routine shown in FIG. 4 is started, first, the processing of step 150 is executed.

In step 150, it is determined whether or not the control switching flag F has been set to "1". As a result, F
= 1, the intake synchronous injection is being executed,
It is determined that the fuel injection amount need not be increased. In this case, in step 152, the increase flag _Ff is set to "0". In step 154, the current value of the control switching flag F is stored as F _prev , and then the current routine is terminated. On the other hand, if F = 1 is not satisfied in step 150, the process of step 156 is executed next.

In step 156, the previous routine is executed.
Whether the control switching flag F has been set to "1"
Or F_prevIt is determined whether or not = 1 holds.
You. As a result, F_prev= 1 if the previous rule
Between the routine and the current routine.
Changed from "1" to "0", that is, intake synchronous injection
Is switched to asynchronous intake injection
You. In this case, it is determined that the fuel injection amount should be increased.
Then, at step 158, the increase flag F _fBut
Set to “1”. The processing of step 158 ends.
Then, in step 154, the control switching flag F
Value is F_prevThis routine ends after being stored as
Is done. On the other hand, in step 156, F_prev= 1 is incorrect
If it is established, the intake non-synchronization continues from the previous routine.
It is determined that the initial injection is being performed. In this case,
After the processing of steps 152 and 154 is performed,
The routine ends.

Next, the contents of the routine shown in FIG. 5 will be described. When the routine shown in FIG. 5 is started, first, the process of step 200 is executed. In step 200, it is determined whether or not the increase flag _Ff is set to "1". As a result, if F _f = 1 holds, the process of step 202 is executed next.

In step 202, the initial value C ₀ is substituted for the increase coefficient C _f . The ECU 12 multiplies the basic fuel injection amount determined based on the operating state of the internal combustion engine 10 by the increase coefficient C _f in a fuel injection amount calculation routine executed separately from the present routine, thereby obtaining the target value of the fuel injection amount. To determine. That is, the increase coefficient C _f is a value corresponding to an increase rate with respect to the basic fuel injection amount when increasing the fuel injection amount. The initial value C ₀ is a value set according to the port consumption Q ₀ immediately after switching from the intake synchronous injection to the intake asynchronous injection, and satisfies C ₀ > 1. When the processing of step 202 is completed, next step 204
In, after the value of the increase coefficient C _f is stored in the cprev,
This routine is ended.

On the other hand, in step 200, F _f
If = 1 holds, the process of step 206 is executed next. In step 206, the increase coefficient C _f is set to a value smaller by a predetermined value D than the previous value of the increase coefficient C _f (that is, C prev). The predetermined value D is determined according to the decreasing gradient of the port consumption as shown by the broken line in FIG.

In step 208 following step 206, it is determined whether or not the increase coefficient _Cf is less than "1". As a result, if C _f <1 holds, step 2
10 "1" is substituted into C _f in, then the value of the increase coefficient C _f in step 204 after being stored in cprev, the present routine is ended. Step 2
If C _f <1 is not satisfied in 06, the routine of this time is ended after the processing of step 204 is executed.

According to the routines shown in FIGS. 4 and 5, the increase coefficient C _f is set to the initial value C ₀ immediately after the switching from the intake synchronous injection to the intake asynchronous injection is performed. Is increased, and thereafter, an increase coefficient C _f
Is reduced by a predetermined value D until the value reaches “1”,
The increase amount of the fuel injection amount gradually decreases. As described above, in the present embodiment, the amount of increase in the fuel injection amount also decreases in accordance with the decrease in the port adhesion amount after switching from the intake synchronous injection to the intake asynchronous injection. Therefore, according to the system of the present embodiment, the change in the amount of fuel sucked into the combustion chamber 28 after switching from the intake synchronous injection to the intake asynchronous injection is suppressed, whereby the air-fuel ratio is appropriately maintained. Becomes possible.

[0035] In the above embodiment, it was decided to reduce the increasing coefficient C _f with a constant gradient by the predetermined value D, is not limited to this, the reduction characteristics of the port consumption after switching to the intake asynchronous injection Accordingly, the decreasing gradient of the increase coefficient C _f may be changed. In addition, "1" is set for the increase coefficient Cf.
The increase coefficient Cf may be reduced at a fixed rate by multiplying by a smaller value.

In the above embodiment, the fuel injection amount is increased by multiplying the basic fuel injection amount by the increase coefficient Cf in the fuel injection amount calculation routine. However, the present invention is not limited to this. It is also possible to obtain a temporary increase and add this increase to the basic fuel injection amount.
Further, in the above-described embodiment, the amount of fuel to be injected at the regular fuel injection timing is increased. However, the present invention is not limited to this. The injection may be performed at a timing different from the regular timing.

In the above embodiment, the ECU 12
Executes the routine shown in FIG. 2 and executes the intake synchronous injection or the asynchronous intake injection in accordance with the value of the control switching flag F, whereby the ECU 12 executes the injection timing control means described in FIG. By executing the routine shown in FIG. 5, the switching time increasing means described in the claims is realized.

[0038]

As described above, according to the present invention, when switching from the intake synchronous injection to the intake asynchronous injection, the air-fuel ratio can be prevented from becoming rich or lean and an appropriate air-fuel ratio can be maintained. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system to which a fuel injection timing control device for an internal combustion engine according to the present invention is applied.

FIG. 2 is a flowchart of a routine executed by an ECU to determine an injection timing in one embodiment of the present invention.

FIG. 3 shows the amount (solid line) of fuel adhering in an intake port after switching from intake synchronous injection to intake asynchronous injection, and fuel of the injected fuel remaining adhering in the intake port. FIG. 7 is a diagram illustrating a change in the amount (broken line) of the fuel injection amount with respect to the number of fuel injections.

FIG. 4 is a flowchart of a routine executed by an ECU to determine a timing of switching from intake synchronous injection to intake asynchronous injection in the present embodiment.

FIG. 5 is a diagram showing an example in which the fuel injection amount is increased at the time of switching from intake synchronous injection to intake asynchronous injection in this embodiment.
It is a flowchart of the routine which CU performs.

[Explanation of symbols]

 10 Internal combustion engine 12 ECU

Claims (1)

[Claims] An injection timing control means for selectively executing intake synchronous injection in which fuel injection is performed during opening of an intake valve and asynchronous intake injection in which fuel injection is performed before opening of the intake valve; At the time of switching from synchronous injection to the intake asynchronous injection,
A fuel injection timing control device for an internal combustion engine, comprising: a switching time increasing means for increasing a fuel injection amount as compared with a normal time, wherein the switching time increasing means is configured to switch the intake synchronous injection to the intake asynchronous injection. A fuel injection timing control device for an internal combustion engine, characterized in that the amount of increase in the fuel injection amount is gradually reduced over time.