JPH0623550B2 - Fuel injection control method for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control method for an internal combustion engine, and more particularly to a fuel injection control based on a pressure in an intake pipe during deceleration in an internal combustion engine of an automobile. .

[Prior Art] Conventionally, in an automobile in which the internal combustion engine is a fuel injection type and the fuel injection amount is controlled based on the pressure in the intake pipe (hereinafter referred to as intake pressure), when the vehicle decelerates, the load of the internal combustion engine is reduced According to the value of the first-order differential of the intake pressure, the process of reducing the fuel injection amount has been performed.

However, the process of reducing the fuel injection amount according to the value of the first-order differential of the intake pressure as described above has a poor responsiveness as compared with the actual reduction of the load of the internal combustion engine. In other words, due to the delayed timing, the weight reduction process was not performed at the required timing. Therefore, especially in a sudden deceleration, the vehicle becomes overrich due to insufficient weight reduction in the initial stage, and becomes too lean from the middle to become over lean, which causes deterioration of drivability during deceleration and increase of pollutants in exhaust gas.

[Object of the Invention] As a result of earnest studies, the present inventor has made earnest studies for the purpose of solving the above problems and performing fuel injection amount reduction control during deceleration with good responsiveness. The present invention has been completed, focusing on the coupling with the second derivative.

[Effects of the Invention] FIG. 1 is a flowchart showing a processing procedure that is a basic configuration of the present invention.

Here, step P1 represents a process of reading the intake pressure (PM). Step P2 represents a process of obtaining the first-order differential value (ΔPM) of PM. Step P3
Represents a process of obtaining a second-order differential value (Δ ² PM) of PM. Step P4 represents a process of determining whether or not ΔPM is less than or equal to a negative predetermined value. Step P5 is Δ ² P
This represents a process of determining whether M is equal to or less than a negative predetermined value. The predetermined value of step P4 and the predetermined value of P5 are different. Step P6 represents a process for reducing the fuel injection amount.

The flow of processing in this flowchart is as follows. First, PM is read in step P1, and then ΔP
After calculating M, and then calculating Δ ² PM in step P3, if ΔPM is less than or equal to a negative predetermined value in step P4 and Δ ² PM is less than or equal to a negative predetermined value in next step P5, The process of step P6 is executed to perform the fuel injection amount reduction process.

If it is determined in either step P4 or step P5 that the predetermined value is exceeded, step P6 is not executed.

In this way, fuel injection is controlled.

[Operation] In the fuel injection control method of the present invention, the first-order differential value with time is equal to or smaller than the first predetermined value, and the second-order differential value with time is the second.
When the value is equal to or less than the predetermined value, the process is performed to reduce the fuel injection amount, so that in addition to the reduction of the intake amount, the period in which the fuel adhering to the intake pipe is additionally sucked into the combustion chamber becomes rich. It is possible to detect the initial stage of deceleration, and as a result, the fuel is further reduced only during the early stage of deceleration, which becomes rich.

[Examples] Hereinafter, the present invention will be described with reference to the drawings with reference to Examples.

2 and 3 show a schematic configuration example of an internal combustion engine to which the method of the present invention is applied, FIG. 2 is a schematic system diagram of the engine, and FIG. 3 is a block diagram showing a fuel injection control circuit and its related parts. Is. In FIG. 2, 1 represents an engine,
The engine 1 has an air cleaner 2, a throttle valve 4,
Air is supplied through the surge tank 5, the intake manifold 6, and the intake valve 7. The surge tank 5 and the intake manifold 6 form an intake pipe. Fuel injected from a fuel injection valve 8 provided in the intake manifold 6 is sent into a cylinder 9 together with air, ignited by a spark plug, and exhaust gas is discharged.
Exhaust valve 10, exhaust manifold 1
1 and the exhaust purification device 12 to the atmosphere.

Further, a crank angle sensor 14 provided in the distributor 13, a water temperature sensor 15 provided on the outer wall of the cylinder 9 for detecting the engine cooling water temperature, an oxygen (O ₂ ) sensor 16 provided in the exhaust manifold 11 for detecting an air-fuel ratio, As a detection signal of each sensor such as a throttle opening sensor 17 for detecting the opening of the throttle valve 4, an intake air temperature sensor 18 for detecting the temperature of intake air, and an intake pressure sensor 19 attached to the surge tank 5 for detecting intake pressure. Based on
A fuel injection control circuit (hereinafter simply referred to as a control circuit) 20 calculates a fuel injection amount, and the valve opening time of the fuel injection valve 8 is controlled based on the calculation result to inject a required amount of fuel.

In the figure, 21 is a battery power source and 22 is a key switch.

In FIG. 3, the control circuit 20 includes a central processing unit (hereinafter referred to as CPU) 30 and an output interface 3.
1. A read-only memory (hereinafter referred to as ROM) 32 for storing control programs and control data, a readable / writable memory (hereinafter referred to as RAM) 33, and a multiplexer are built-in, and an analog signal of each sensor is digitally selected. An A / D converter 34 that converts the signal into a signal and sends the signal to the CPU 30, a waveform shaping circuit 35 that shapes the signal of the crank angle sensor 14,
It is composed of an interrupt processing timer 37 and the like. A main control program (not shown) appropriately corrects the basic injection amount water temperature based on signals from the sensor 15, the O ₂ sensor 16 and the like to obtain an actual injection amount, and then injects it in synchronization with the rotation of the crankshaft. .

Further, in the ROM 32, a control program is stored in the form of a subroutine shown in the flowchart of FIG.

FIG. 4 is a flowchart showing the flow of processing of a subroutine which is an embodiment of the present invention.

Here, step P50 represents a process for reading the intake pressure (PM). This step is P
If M is required, its value may be used without any special processing. Step P51 represents a process for obtaining the difference between the current intake pressure (PM) and the intake pressure (PMO) at the time of the execution of this subroutine the previous time, that is, the change amount ΔPM of the intake pressure. Since this subroutine is executed in a constant cycle, ΔPM can be treated as the value of the first-order derivative of the intake pressure with time.

Step P52 represents a process of setting the current intake pressure (PM) to the previous intake pressure (PMO) for the next use.

Step P53 is the difference between the change amount of the current intake pressure (.DELTA.PM) and the change amount of the intake pressure determined in the same manner at the previous present subroutine executed (ΔPMO), i.e. the intake pressure acceleration (delta ² P
M) is obtained. Since ΔPM is the value of the first-order derivative of the intake pressure with respect to time, Δ ² PM can be treated as the value of the second-order derivative of the intake pressure with respect to time.

Step P54 represents a process of setting the first differential value (ΔPM) of the current intake pressure to the previous first differential value (ΔPMO) of the intake pressure for use in the next subroutine.

Step P55 represents a process of determining whether or not ΔPM is less than or equal to a negative predetermined value α. The negative predetermined value α is -20 to -6
A value in the range of 0 mmHg / 20 msec is preferable for effective control.

Step P56 represents a process of determining whether or not Δ ² PM is equal to or less than the negative predetermined value β. The negative predetermined value β is -5-20
A value within the range of mmHg / (20 msec) ² is preferable for effective control.

Step P57 represents a process of setting a lower limit value for the fuel injection time τ. Since the fuel injection pressure is constant, the length of τ determines the fuel injection amount proportional to it. The lower limit value mentioned above is that in the region where τ is present, fuel injection is not actually performed due to the nature of the injection valve. Since it is meaningless to set τ in this region, it is necessary to set τ before that region even if the reduction processing is performed. The value immediately before that corresponds to the lower limit.

Next, each of the above steps will be described according to the flow of processing.

After the ignition switch is turned on and the engine is started,
The processing of this subroutine is started.

First, when the processing comes into this subroutine, step P
PM is read at 50, and ΔPM is obtained at step P51.
Is calculated, PM is set in PMO in step P52, Δ ² PM is calculated in step P53, and ΔPM is set in ΔPMO in step P54.

Next, at step P55, it is judged if ΔPM is not more than α. Here, if ΔPM exceeds α, “NO”
It is determined that this subroutine is exited from B. In this case, the fuel injection time τ remains set by the processing other than this subroutine and does not change.

If ΔPM is less than or equal to α in step P55, "YE
S ”, and then Δ ² PM is β in step P56.
It is determined whether or not the following.

If the value exceeds Δ ² PM by β, it is determined to be “NO”, and this subroutine is exited from B. In this case, the fuel injection time τ remains set by the processing other than this subroutine and does not change.

If Δ ² PM is less than or equal to β in step P56, "Y
It is determined to be "ES", then the lower limit value is set to τ in step P57, and this subroutine is exited from B. That is, by setting τ to the shortest time, the controllable minimum amount of fuel is set.

In short, the above-described series of processing shows that the fuel injection amount is reduced to the lower limit value when ΔPM is α or less and Δ ² PM is β or less.

Next, the above processing will be described with reference to the graph of FIG. Here, a is a graph showing the change over time of the intake pressure (PM), b
Is a graph showing the temporal change of the first-order derivative (ΔPM) of the intake pressure with time, and c is the second-order derivative (Δ ² ) of the intake pressure with time.
PM is a graph showing the time change of PM, and d is a graph showing the time change of the fuel injection time (τ).

First, assuming that the vehicle is running steadily before time T1, there is no change in engine load, and all graphs draw straight lines parallel to the time axis.

Next, when the accelerator pedal is depressed after the time point T1, the opening degree of the throttle valve 4 becomes large, so that the inflow amount of air into the intake pipe increases and the intake pressure (PM) rises until the time point T5. Subsequently, after time T5, the steady state becomes faster.

From T1 to T5, ΔPM starts from 0 and ends at time T2.
Changes to form one peak with a peak at 0
Return to.

On the other hand, Δ ² PM starts from a value of 0 and once forms one peak by time T2 and then forms one valley after time T2.
Return to 0 again. During this period, Δ ² PM is at time T3 in the valley.
Is less than the negative predetermined value β from T4 to T4, but ΔP
Since M has not fallen below the negative predetermined value α during this period, τ only shows a change corresponding to a change in PM, as shown in the graph d. This is determined as "YES" in step P55 of subroutine A, but "NO" in step P56.
Represents the case of being determined.

Next, consider a case where the accelerator is returned at time T6 to start deceleration operation after steady running at high speed from time T5.

PM is once rapidly reduced from time T6, slightly returned from time T12, and then settles to a constant value at time T15 due to low-speed steady running.

During this time, ΔPM forms a trough between times T6 and T12. Among them, the value between the time points T8 and T11 is equal to or less than α.

On the other hand, Δ ² PM forms a large valley in the first half of the period from T6 to T15. Further within this time points T7 and T9
The value between and is less than or equal to β.

Therefore, the time period in which ΔPM is less than α and Δ ² PM is less than β is between time points T8 and T9, and during this time, it is determined as “YES” in both steps P55 and P56 of subroutine A. Will be done.

As a result, between the time points T8 and T9, τ is reduced to its lower limit value. This is subroutine A
This corresponds to the process of step P57. During this period, the fuel injection amount is reduced by an amount corresponding to the area S1 of the graph d as compared with the case where the control is simply performed according to the PM indicated by the dotted line.

Τ between time points T10 and T14 in the graph d is set to the lower limit value. This is as shown by the dotted line when τ is set to a value according to PM, but even if τ is set to the lower limit value or less, the injection amount is actually uncertain, and in that case, the lower limit value is set. This is because the setting process is performed separately.

Since the present embodiment is configured in this manner, the fuel injection time, that is, the injection amount can be reduced to the minimum amount only in the first half of deceleration, and as a result, it is extremely effective against the engine load change of the fuel injection control during deceleration. With simple processing, it is possible to perform appropriate fuel injection control with good responsiveness, which further reduces fuel in the initial stage of deceleration, improves drivability at the time of deceleration, and causes an increase in pollutants in exhaust gas. There is no.

That is, when the reduction correction is performed at the time of deceleration, the fuel that has adhered to the intake pipe among the fuel that has been injected in the past remains, and these fuels are sucked into the combustion chamber at once. In the conventional control, the fuel injection amount reduction correction is simply performed by the first-order differential value of the intake pressure, so that the control delay is caused by the fuel adhering to the intake pipe, which makes the overrich even worse. Furthermore, in the conventional control, since the reduction correction is continued only during the deceleration state by only the first derivative of the intake pressure, even after the fuel adhering to the pipe wall is lost, the reduction is performed unnecessarily and becomes over lean. It was In the present embodiment, the fuel consumption amount is corrected only in the first half portion during deceleration.Therefore, the fuel amount adhered to the intake pipe is reduced in the first half portion so that overrich does not occur, and the fuel amount attached to the intake pipe is reduced in the latter half portion. There is no effect of and the amount of fuel corresponding to the load (intake pressure) does not cause over lean.

In the above-described embodiment, the reduction process of τ to the lower limit value is performed, but the fuel injection process may be stopped during the fuel cut process in addition to the reduction process to the lower limit value. In this case, for example, as the process of step P57, the fuel cut flag may be set to 1 and the fuel cut process may be executed.

As another method, in step P57, the weight reduction coefficient of τ may be set to a value less than 1, and τ may be corrected by the product of the weight reduction coefficients. In this case, the weight reduction coefficient is preferably set to 0.5 to 0.95.

[Effects of the Invention] As described in detail above, according to the fuel injection method for an internal combustion engine of the present invention, a fuel injection control method for an internal combustion engine that calculates a fuel injection amount based on the pressure in the intake pipe and controls a fuel injection valve is provided. When the first-order differential value of the pressure with time is equal to or less than a first predetermined value and the second-order differential value of the pressure with time is equal to or less than a second predetermined value, the fuel injection amount is decreased. With extremely simple processing, it becomes possible to perform appropriate responsive fuel injection control that further reduces fuel in the initial stage of deceleration, improving drivability, reducing pollutants in exhaust gas, and reducing fuel consumption. Is possible.

[Brief description of drawings]

FIG. 1 is a flowchart showing the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram of an internal combustion engine to which the present invention is applied, and FIG.
FIG. 4 is a block diagram of the fuel injection control circuit and its related parts. FIG. 4 is a flow chart showing an embodiment of the present invention.
FIG. 5 shows a graph showing the operation of the processing. 1 ... Internal combustion engine 8 ... Fuel injection valve 19 ... Intake pressure sensor 20 ... Fuel injection control circuit

Claims (1)

[Claims] 1. A fuel injection control method for an internal combustion engine, which calculates a fuel injection amount based on a pressure in an intake pipe to control a fuel injection valve, wherein a first-order differential value of the pressure with time is equal to or smaller than a first predetermined value. A fuel injection control method for an internal combustion engine, wherein the fuel injection amount is reduced when a second-order differential value of the pressure with time is equal to or less than a second predetermined value.