JPH0571390A - Fuel injection amount control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To ensure a theoretical air-fuel ratio even during the re-start of fuel injection, so as to attempt prevention of contamination of exhaust gas and improve engine response by setting a first fuel injection amount after the re-start of fuel injection to a valve at least one time or more as large as a fundamental injection amount to satisfy the theoretical air-fuel ratio. CONSTITUTION:An ECU 4A controls the opening time, of a fuel injection valve 3a i.e., a fuel injection amount, based on detection signals from the pressure sensor 7a of a surge tank 2A, the crank angle sensor 18 of a crank shaft, the water temperature sensor 15 of cooling water 14. Fuel is intermittently injected in synchronism with rotation of an internal combustion engine and fuel required for one combustion is injected in a state to be divided into at least two lots. In this case, the ECU 4A re-starts injection of fuel when a throttle 5a is opened after injection of fuel is stopped when there is no need for the feed of fuel in a deceleration state wherein the throttle 5a is fully closed. A first fuel injection amount after the re-start of injection of fuel is set to a valve at least one time or more as large as a fundamental injection amount to satisfy a theoretical air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine (engine).
When inhaling a mixture of air and fuel into the cylinder of
The present invention relates to a control method for injecting an optimum amount of fuel according to the operating state of an internal combustion engine.

Exhaust gas from a gasoline engine contains substances harmful to the human body, such as carbon monoxide CO, hydrocarbons HC, and nitrogen oxides NO _x . Further, in order to protect human health and protect the global environment, it is strongly desired to reduce these harmful substances.

On the other hand, there is a three-way catalyst as a device for purifying exhaust gas by oxidizing and reducing the harmful substances. However, the effective range of the purification capacity is limited to a narrow range (window) where the air-fuel ratio of the air-fuel mixture supplied to the engine is near the theoretical air-fuel ratio (A / F = 14.7).

Therefore, air-fuel ratio control, that is, fuel injection amount control, is performed to keep the combustion state of gasoline in a good state and to effectively utilize the capacity of the three-way catalyst.

On the other hand, reducing the fuel consumption of the engine and improving the fuel consumption makes it possible to effectively use energy resources, and at the same time suppresses the total amount of harmful substances in the exhaust gas.

As one method of improving fuel efficiency, when the throttle is fully closed and the engine speed is in a decelerating state, gasoline or fuel is supplied until the engine speed drops to a certain value. There is a method of stopping (fuel injection). Note that there is also a method of stopping fuel injection when the engine is in a high rotation state that causes damage.

However, when the fuel injection is restarted, the air-fuel ratio may temporarily become lean, and during that time, not only a good combustion state cannot be obtained, but also the toxic substance is discharged from the window of the three-way catalyst. The amount increases. In particular, it is remarkable when the fuel is simultaneously injected in a multi-cylinder engine.

Therefore, there is a demand for a method of optimally controlling the air-fuel ratio, that is, a method of controlling the fuel injection amount even when the injection is restarted after the fuel injection is stopped.

[0009]

[Prior Art]

(1) Air-fuel ratio control system The air-fuel ratio is controlled by detecting the amount of air taken in by the engine and injecting the optimum amount of fuel with respect to the amount of air. The air-fuel ratio control system can be roughly classified into three types according to the method of detecting the intake air amount.

FIG. 5 is a block diagram for explaining the air-fuel ratio control system, (a) is a diagram for explaining the mass flow system, and (b) is a diagram.
FIG. 6 is a diagram illustrating a speed density system, and (c) is a diagram illustrating a throttle speed system.

FIG. 5 exemplifies intake pipe injection in which fuel (gasoline) is injected from the fuel injection valve 3 into the intake pipe 2 when the mixture is sucked into the engine 1. The fuel injection amount q is EC.
Control is performed based on the calculation results of U (Electronic Control Unit) 4a, 4b, 4c.

1) Mass Flow Method The mass flow method is a method in which an intake air amount is directly measured by an air flow meter, that is, an air flow meter 6.

That is, the intake air amount Q per unit time
Is divided by the number of combustion cycles obtained from the rotation speed N _E of the engine 1, the intake air amount per one combustion cycle can be obtained.

2) Speed Density Method In the speed density method, the intake pressure in the intake pipe 2 is detected by the pressure sensor 7, and the intake air amount is estimated from the intake pipe pressure P and the rotation speed N _{E of the} engine 1. Is.

That is, the memory of the ECU 4b has equal intake air amount data in which the intake pipe pressure P and the rotation speed N _{E of the} engine 1 are mapped as variables, and the intake air amount is estimated from the data. It is a method of seeking.

3) Throttle speed system The throttle speed system detects the opening of the throttle 5 by the throttle opening sensor 8 and estimates the intake air amount from the throttle opening α and the rotation speed N _{E of the} engine 1. Is.

That is, the memory of the ECU 4c has equal intake air amount data in which the throttle opening α and the rotational speed N _{E of the} engine 1 are mapped as variables, and the intake air amount is estimated from the data. It is a method of seeking.

(2) Fuel injection method and injection timing FIG. 6 is a diagram for explaining the fuel injection method. (A) shows MPI.
(MultiPoint Injection) is a block diagram for explaining the intake pipe injection, and (b) is a timing chart for explaining the timing of the four-cylinder simultaneous injection.

The method of performing the same-time-interrupted injection in multiple cylinders by the MPI type intake pipe injection is as shown in FIG. 6 (a).
Fuel injection valves 3 _-1 to each manifold, 3 _-2, 3 _-3, 3 _-4 provided, fuel injection valves 3 _-1, 3 _-2, 3 _-3, 3 _-4 ECU 4a (4b, 4c)
It is a method of simultaneously driving with.

Therefore, it has the advantages that the fuel injection valve drive circuit is common and the fuel is evenly distributed to each cylinder, and it is the current mainstream as a method with high cost performance.

On the other hand, FIG. 6 (b) is a timing chart in the case of simultaneous injection of four cylinders at every 360 ° CA (Crank Angle) in a four cylinder engine.
Fuel is injected at T _J1 , T _J2 , T _J3 , T _J4 , .... Therefore, the fuel amount required for one combustion is divided into two injections and supplied.

By the way, in the first cylinder, the fuel injection timing T _J2 between the compression cycle T _S2 and the explosion cycle T _S3 and the fuel injection timing T _J3 between the exhaust cycle T _S4 and the intake cycle T _S5 are set. In the intake cycle T _S5 , the fuel injected in the above is sucked into the cylinder as a mixture.

(3) Stopping fuel injection and asynchronous fuel injection In vehicles such as automobiles, in order to reduce fuel consumption and suppress the total amount of harmful substances in exhaust gas, the engine is braked with the throttle fully closed. If you are in
A method of stopping fuel supply to the engine, that is, fuel injection is used. Incidentally, stopping the fuel injection is generally called fuel cut (F / C: Fuel Cut).

FIG. 7 is a diagram for explaining the fuel cut and the asynchronous injection. (A) is a characteristic diagram for explaining the relationship between the fuel cut rotation speed and the restart rotation speed with respect to the engine coolant temperature.
(b) is a diagram showing the change over time of the throttle opening, and (c) is a timing chart for explaining the fuel injection timing. The time axes of (b) and (c) are shown on the same time axis.

1) Fuel Cut Characteristics As shown in FIG. 7 (a), when the throttle is fully closed and the engine rotation speed N _E is N _CUT or more, the fuel supply is not required and the fuel supply is not necessary. Judge and cut the fuel. However, the engine rotation speed N _E is the restart rotation speed N _{E
When the} temperature falls below _RET , fuel supply is started to prevent the engine from stopping. The fuel cut control is also performed by the ECUs 4a, 4b, 4c shown in FIG.

By the way, the lower the cooling water temperature t _{W, the} N _CUT
The reason why the N _RET and N _RET are set high is to prevent fuel cut in the idling state. Further, if the throttle is opened during the fuel cut, the fuel injection will be restarted immediately.

2) Resumption of fuel injection and asynchronous injection FIG. 7 (b) shows that the throttle opening is fully closed until time T ₁ .
It shows that the throttle opens from the time T ₁ to the time T ₂ . Therefore, the timing chart of FIG. 7C shows that fuel is not injected at the fuel injection timing T _J1 and fuel is intermittently injected every 360 ° CA after the fuel injection timing T _J2 . ..

However, when fuel injection is restarted from the fuel injection timing T _J2, only air is still sucked in the intake cycle T _S2 of the third cylinder, and the engine response temporarily deteriorates.

Therefore, as soon as the throttle starts to open at time T ₁ , a predetermined fixed amount of fuel is injected at the asynchronous timing T _JX to prevent deterioration of response.

[0030]

[Problems to be Solved by the Invention] However, if a fixed amount of fuel is injected at the asynchronous timing T _JX ,
There are the following problems.

The air-fuel mixture sucked into the suction cycle T _S2 of the third cylinder is likely to be in a lean state without having a stoichiometric air-fuel ratio.

The fuel quantity of the air-fuel mixture drawn in the intake cycle T _S3 of the fourth cylinder and the intake cycle T _S4 of the second cylinder is
It is the sum of the fuel injection amount at the asynchronous timing T _{JX and} the fuel injection amount at the synchronous fuel injection timing T _J2 , but not the stoichiometric air-fuel ratio.

Immediately after the fuel injection is restarted, all the fuel adhering to the intake pipe is sucked and dried. Therefore, an error occurs in the air-fuel ratio control until the fuel adheres to the intake pipe and the amount of adherence becomes stable.

A technical object of the present invention is to prevent pollution of exhaust gas and to prevent engine response by establishing a fuel injection amount control method for realizing a stoichiometric air-fuel ratio even when fuel injection is restarted after fuel cut. Is to raise.

[0035]

FIG. 1 is a diagram for explaining the principle of the present invention. (A) is a timing chart showing fuel injection restart timing, and (b) is a timing chart showing each cycle of a 4-cycle engine. , (C) is a timing chart for explaining the fuel injection timing, (d) is a timing chart for explaining the fuel injection timing including asynchronous fuel injection, and (e) is a model diagram for explaining the fuel adhering to the intake pipe. .. The time axes of (a) to (d) are the same time axis.

The present invention is characterized in that the fuel injection amount immediately after restarting fuel injection is controlled so as to satisfy the stoichiometric air-fuel ratio.

(1) Basic control method (see FIGS. 1 (a) (b) (c)) Fuel is intermittently injected into the intake pipe in synchronization with the rotation of the internal combustion engine, and the fuel required for one combustion is also provided. In the fuel injection method in which the fuel injection is performed at least twice, the fuel injection is stopped when the fuel supply is unnecessary in the deceleration state where the throttle is fully closed, and then the fuel injection is restarted when the throttle is opened. The fuel injection amount is controlled as follows.

That is, the first fuel injection amount after restarting the fuel injection is a value that is at least one time the basic injection amount TP ₁ satisfying the theoretical air-fuel ratio, which is obtained from the amount of air taken in by the internal combustion engine. This is a fuel injection amount control method for an internal combustion engine in which k ₁ · TP ₁ (k ₁ > 1).

(2) Fuel injection amount control method for performing asynchronous injection (see FIGS. 1 (a) (b) (d)) That is, in the fuel injection amount control method for an internal combustion engine of (1) above, after fuel injection is restarted. First fuel injection k ₁ · TP
This is a fuel injection amount control method in which ₁ (k ₁ > 1) is performed immediately after the throttle is opened and is asynchronous with the rotation of the internal combustion engine.

(3) Fuel injection amount control method considering the intake pipe adhesion amount (see FIG. 1 (e)) That is, when fuel injection is restarted in the fuel injection amount control methods of (1) and (2) above. Is a fuel injection amount control method for controlling the fuel injection amount by adding Δq to the amount of fuel adhering to and remaining in the intake pipe.

(4) Fuel injection amount control method preventing air-fuel ratio rich (A / F ratio too small) (see FIG. 1 (d)) That is, in the fuel injection amount control method of (3) above,
The upper limit value TAU _MAX provided in the fuel injection amount required to one combustion, of the basic injection amount to satisfy the stoichiometric air-fuel ratio of the upper limit value TAU _MAX.
This is a method of controlling the fuel injection amount within 2 times.

[0042]

[Action]

(1) Basic control method (Refer to Fig. 1 (a) (b) (c)) 1 When the fuel required for combustion is injected at least twice or more, immediately after restarting the fuel injection, There are cylinders that cannot receive fuel injection.

Therefore, the first fuel injection amount immediately after the fuel injection is restarted is the basic injection amount TP ₁ which satisfies the theoretical air-fuel ratio.
It is possible to prevent the air-fuel ratio from becoming lean by setting the amount k ₁ · TP ₁ (k ₁ > 1) that is at least 1 time or more.

(2) Fuel injection amount control method for performing asynchronous injection (see FIGS. 1 (a) (b) (d)) First time of synchronized fuel injection timing after the throttle is opened and fuel injection is restarted. Even if the fuel of k ₁ · TP ₁ is injected into the cylinder, only the air is sucked into the cylinder in the suction cycle before the timing, and the engine response is not improved.

That is, immediately after the throttle is opened, by injecting an amount k ₂ · TP ₁₁ (k ₂ > 1) that is at least one time the basic injection amount TP ₁₁ that satisfies the theoretical air-fuel ratio, It is possible to prevent the air-fuel ratio from becoming lean.

(3) Fuel injection amount control method in consideration of adhering amount of intake pipe (see FIG. 1 (e)) When fuel injection is stopped, the intake pipe that has been wet with fuel until then is completely sucked by air intake. To dry.

Therefore, immediately after the fuel injection is restarted, the air-fuel ratio can be controlled without error by adding the fuel amount Δq adhering to the intake pipe to control the fuel injection amount.

(4) Fuel injection amount control method that prevents air-fuel ratio rich (A / F ratio too small) (see FIG. 1 (d)) In the fuel injection immediately after restarting the fuel injection, the basic injection amount TP
_By injecting more than 1 time (k ₁ · TP ₁ ),
It is possible to avoid lean conditions and improve engine response.

However, the air-fuel mixture becomes rich in the cylinder that sucks the fuel injection portion immediately after the fuel injection is restarted and the next fuel injection portion.

When the opening change immediately after the opening of the throttle is differentiated with respect to time and the fuel injection amount is determined by predicting the throttle opening and the intake air amount at the fuel injection timing, the differentiation timing is determined. An error may occur between the throttle opening predicted value and the actual throttle opening, and the air-fuel mixture may become rich.

Therefore, the fuel injection amount required for one combustion has an upper limit.
Value TAU_MAXIs installed, the air-fuel ratio becomes excessively high.
It is possible to prevent the switch from being in a chi state. Also, the upper limit
 TAU _MAXIs the basic injection amount of 1.
Optimum within 2 times, and above that, air-fuel ratio rich
(A / F ratio is too small).

[0052]

EXAMPLES Next, a fuel injection amount control method according to the present invention will be described.
Examples will be used to explain how it can be realized in practice.

(1) Structure FIG. 2 is a model diagram for explaining the embodiment, in which only the fuel injection system is extracted and shown. Moreover, the engine shows only one cylinder as a model.

1) Intake / Exhaust System Intake air is purified by the air cleaner 9 and the intake air amount is controlled by the throttle 5a. And surge tank 2A
And it is sucked into the combustion chamber 13 through the intake pipe (manifold) 2a and the intake valve 10.

On the other hand, the burned exhaust gas is discharged into the atmosphere through the exhaust valve 11, the exhaust pipe 16 and the three-way catalyst 17.

2) Fuel Injection Amount Control System The air-fuel ratio control system of this embodiment is a speed density system which estimates the intake air amount from the intake pipe pressure and the engine rotation speed.

That is, a pressure sensor 7a for measuring the intake pressure is provided in the surge tank 2A, and a crank angle sensor 18 is provided on the crankshaft of the engine. Further, a water temperature sensor 15 that measures the temperature of the engine cooling water 14 is provided to enable correction of the fuel injection amount according to the engine temperature.

Then, the detection signals of these sensors 7a, 18 and 15 are sent to the ECU 4 constituted by a microcomputer system.
Input to A and control the valve opening time of the fuel injection valve 3a from its output port to control the fuel injection amount.

(2) Operation In this embodiment, the control of the fuel injection amount can be realized on the software of the ECU 4A.

FIG. 3 is a flow chart for explaining the operation of the embodiment. (A) is a diagram showing a control procedure when fuel injection is restarted after fuel injection is stopped, and (b) is control while fuel injection is stopped. It is a figure which shows a procedure. Further, FIG. 4 is also a flow chart for explaining the operation of the embodiment, and is a diagram showing a normal fuel injection amount control procedure.

3 and 4, symbol TP is a basic injection amount that satisfies the theoretical air-fuel ratio, TAU is the fuel injection amount, and ΣTAU is the amount of fuel injected per combustion cycle, that is, the injection amount. The integrated value. The symbol k is a constant.

1) Fuel injection stop control (see FIG. 3 (b)) When the throttle 5a is fully closed and the engine speed is, for example, a value of N _CUT or more in FIG. 7 (a), fuel injection is stopped. Stop. Therefore, in this case, the injection amount 0 (zero) is added to ΣTAU at each injection timing. That is, step S201 is that.

2) Fuel injection restart control (see FIG. 3 (a)) Whether the throttle 5a started to open during the fuel injection stop control, or the engine speed was N as illustrated in FIG. 7 (a).
_When it reaches below _RET , fuel injection is restarted.

In restarting fuel injection, the intake air amount is estimated from the intake pipe pressure and the engine speed,
That is, the intake air amount is obtained from the map data stored and possessed by the ECU 4A, and the basic injection amount TP that satisfies the theoretical air-fuel ratio is calculated in step S101.

Subsequently, in step S102, the fuel injection amount TAU in consideration of the amount of fuel adhering to the intake pipe 2a is obtained. That is, the value obtained by multiplying the basic injection amount TP by the constant k is obtained. Then, only the basic injection amount TP is added to ΣTAU.

The value of the constant k differs depending on the engine, but about 1.1 can be given as an example. However, if the value exceeds 1.2, the air-fuel ratio may become excessively rich.

Then, in step S103, the fuel injection amount TAU previously calculated is injected. That is, in actuality, k · TP is injected and only the basic injection amount TP is considered as the integrated value ΣTAU.

3) Normal fuel injection amount control (see FIG. 4) In step S301, it is determined whether or not it is time to clear the injection amount integrated value ΣTAU. That is, ΣTAU is cleared when the intake of the cylinder is completed, and the accumulation of the fuel injection amount required for one combustion is started.

Therefore, 0 is substituted into ΣTAU only in step S302 only when the clear timing is obtained in step S301.

Then, in step S303, the fuel injection amount TAU _-1 at the next injection timing is obtained from the intake air amount obtained from the map data. Note that TAU _-1 is the injection amount per injection when the fuel amount (basic injection amount TP) required for one combustion is injected in multiple times.

Then, in step S304, the injection amount integrated value Σ
Fuel injection amount calculation result before TAU TAU _-1And add
The result is a predetermined maximum TAU_MAXIs less than
Or not. The maximum value TAU_MAXIs the basic injection amount
Set to a value about 1.2 times TP. By the way, more
At the value, the air-fuel ratio is rich (A / F ratio is too small)
Become.

That is, in step S304, it is determined whether or not the fuel injection amount required for one combustion does not become excessive.

Then, in step S304, the maximum value TAU _MAX
If it is determined that the value exceeds the maximum value TAU _{MAX, the} value obtained by subtracting the fuel injection amount integrated value ΣTAU up to that point is substituted into TAU _-2 in step S306. Note that TAU _-2 is the injection amount that is actually injected thereafter. Then, the maximum value TAU _MAX is substituted for the integrated value ΣTAU.

On the other hand, if it is determined in step S304 that the maximum value TAU _MAX is not exceeded, then in step S305 T
Substitute AU _-2 with the fuel injection amount TAU _-1 calculated in step S303. Then, the previous TAU _-2 is added and integrated to the integrated value ΣTAU.

As a result of the above processing, finally step S30
At 7, the fuel injection amount TAU _-2 is injected. Therefore, even if the fuel is injected k times the basic injection amount TP after restarting the fuel injection, the total amount of the injected fuel does not reach the excessive rich state.

[0076]

As described above, according to the fuel injection amount control method of the present invention, fuel injection that satisfies the theoretical air-fuel ratio can be performed even when fuel injection is restarted. As a result, the exhaust gas can be prevented from being contaminated and the engine response can be improved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention, where (a) is a timing chart showing fuel injection restart timing, (b) is a timing chart showing each cycle of a 4-cycle engine, and (c) is fuel injection timing. FIG. 6 is a timing chart to be described, (d) is a timing chart to explain fuel injection timing including asynchronous fuel injection, and (e) is a model diagram to explain fuel adhering to the intake pipe.

FIG. 2 is a model diagram for explaining the embodiment, in which only the fuel injection system is extracted and shown.

FIG. 3 is a flow chart explaining the operation of the embodiment,
(a) is a diagram showing a control procedure when fuel injection is restarted after stopping fuel injection, and (b) is a diagram showing a control procedure when fuel injection is stopped.

FIG. 4 is a flow chart for explaining the operation of the embodiment and is a diagram showing a normal fuel injection amount control procedure.

FIG. 5 is a block diagram illustrating an air-fuel ratio control system,
(a) is a diagram illustrating a mass flow system, (b) is a diagram illustrating a speed density system, and (c) is a diagram illustrating a throttle speed system.

FIG. 6 is a diagram illustrating a fuel injection method, in which (a) is MPI.
(MultiPoint Injection) is a block diagram for explaining the intake pipe injection, and (b) is a timing chart for explaining the timing of the four-cylinder simultaneous injection.

FIG. 7 is a diagram illustrating fuel cut and asynchronous injection, (a)
Is a characteristic diagram illustrating the relationship between the fuel cut rotation speed and the restart rotation speed with respect to the engine cooling water temperature, (b) is a diagram showing the time change of the throttle opening, and (c) is a timing explaining the fuel injection timing. Chart.

[Explanation of symbols]

1 engine 2,2a intake pipes 2A surge tank _{3,3 -1, 3 -1, 3 -1} , 3 -1, 3a fuel injectors 4a, 4b, 4c, 4A ECU (Electronic Control
Unit) 5,5a Throttle 6 Air flow meter 7,7a Pressure sensor 8 Throttle opening sensor 9 Air cleaner 10 Intake valve 11 Exhaust valve 12 Spark plug 13 Combustion chamber 14 Cooling water 15 Water temperature sensor 16 Exhaust pipe 17 Three way catalyst 18 Crank angle sensor Q Intake air amount q Fuel injection amount N _E Engine rotation speed P Intake pipe pressure α Throttle opening t _W Cooling water temperature N _CUT Fuel injection stop rotation speed N _RET Fuel injection restart rotation speed

Claims (4)

[Claims] 1. A fuel injection method in which fuel is intermittently injected into an intake pipe in synchronization with rotation of an internal combustion engine, and fuel required for one combustion is injected at least twice or more, and a throttle is fully closed. When the fuel injection is stopped in the decelerated state where the fuel supply is unnecessary and then the fuel injection is restarted when the throttle is opened, the internal combustion engine determines the first fuel injection amount after restarting the fuel injection. At least 1 time more than the basic injection amount (TP ₁ ) that satisfies the theoretical air-fuel ratio, which is obtained from the intake air amount (k ₁
・ TP ₁ ), and a method for controlling the fuel injection amount of an internal combustion engine. 2. The fuel injection amount control method for an internal combustion engine according to claim 1, wherein the first fuel injection (k ₁ · TP ₁ ) after restarting fuel injection is performed immediately after the throttle is opened, The method of controlling the fuel injection amount of an internal combustion engine is characterized in that it is performed asynchronously with the rotation of the engine. 3. The fuel injection amount control method for an internal combustion engine according to claim 1, wherein the fuel injection is performed by taking into account the amount of fuel (Δq) adhering to and remaining in the intake pipe when the fuel injection is restarted. A fuel injection amount control method for an internal combustion engine, comprising: controlling the fuel injection amount. 4. The fuel injection amount control method for an internal combustion engine according to claim 3, wherein an upper limit value (TAU _MAX ) is provided for the fuel injection amount required for one combustion,
The fuel injection amount control method for an internal combustion engine, wherein the upper limit value (TAU _MAX ) is set within 1.2 times the basic injection amount that satisfies the theoretical air-fuel ratio.