JPS6394040A - Method of controlling fuel injection amount for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the mixture from being excessively lean during deceleration, by previously determining the relationship between the rotational speed and the intake- air pipe pressure of an engine, and by determining the amount of fuel injection in accordance with a previously determined pressure when the intake-air pipe pressure is lower than a pressure corresponding to a certain rotational speed. CONSTITUTION:A control device 20 receives a detection signal from an intake-air pressure sensor 4 which is disposed in a surge tank 3a in an intake manifold 3, together with detection signals from an opening degree sensor 10 for a throttle valve 8 and the like, and controls the amount of fuel injection from a fuel injection valve 2. The control device 20 stores the relationship between the rotational speed and the intake-air pressure obtained during full closing of the throttle valve 8, previously in memory. Further, during deceleration during which the throttle valve 8 is fully closed, when the intake-air pressure is lower than a pressure valve corresponding to the rotational speed stored in the memory, the fuel injection amount is computed by use of this stored value. with this arrangement, it is possible to prevent the mixture from being excessively lean due to a delay in detection of the intake-air pressure.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the fuel injection amount of an internal combustion engine,
In particular, the present invention relates to a method of determining fuel injection amount based on intake pipe pressure.

[Prior art] In order to determine the amount of fuel injected into the internal combustion engine, it is necessary to know the shape of the air introduced into the combustion chamber.There are currently two types of methods for detecting this air intake. has been done. One method is to directly measure the amount of air passing through the intake pipe with an airflow meter, etc., and the other method is to take advantage of the fact that the pressure inside the intake pipe has a relatively good correspondence with the amount of air sucked into the combustion chamber. This is a method of determining the amount of intake air based on intake pipe pressure. Note that this method does not actually calculate the intake air amount, but directly determines the fuel injection amount from the intake pipe pressure.

Based on the intake air amount determined in this way, the final fuel injection amount is determined by making corrections that take into account other state quantities of the internal combustion engine, such as the temperature of the cooling water. Depending on the state of the engine, conditions or changes that cannot be predicted in advance may occur, and rotation may become irregular. For example, if you run the internal combustion engine idly (so-called racing) when there is almost no load, the internal combustion engine's rotational speed will rise and fall very quickly, making it difficult to control the amount of fuel injected normally. Methods may not be able to keep up with the phenomenon.

Various proposals have been made to cope with such sudden changes in the state of the internal combustion engine, one of which is a method disclosed in Japanese Patent Laid-Open No. 61-25930 by the applicant of the present application. The method for calculating the average value of engine rotational speed is to increase the weighting of the average value calculated last time, reduce the weighting of the rotational speed detected this time, and calculate a new average value from both. The amount of fuel injection is increased or decreased in proportion to the difference between this value and the currently detected rotational speed. This makes it possible to reduce the drop in rotational speed after racing, so-called undershoot.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, since the fuel injection amount is corrected based on the change in the rotational speed of the internal combustion engine,
There is a possibility that the amount of fuel injected is too much or too little, and it cannot be said to be sufficient. Furthermore, since the fuel injection amount is increased only after the rotational speed has decreased, control responsiveness cannot be said to be sufficient. In particular, after the aforementioned racing, when the throttle valve is fully open and the rotational speed is decreasing, when the range of an automatic car is changed from the neutral range to the drive range, the rotational speed suddenly decreases. This is a problem specific to systems that determine fuel injection amount based on intake pipe pressure. In other words, the detection of pressure changes by the intake pipe pressure sensor is delayed by the capacity of the intake pipe, surge tank, etc., and the fuel injection amount based on such detected pressure is corrected by changes in rotational speed. However, it is difficult to supply just the right amount of fuel.

[Means for solving the problems] The present invention, which was made to solve the above problems,
As shown in the figure, in the fuel injection amount control method for an internal combustion engine in which the fuel injection amount is determined based on the intake pipe pressure P of the internal combustion engine, the rotational speed of the internal combustion engine when the throttle valve is fully open is Relationship between N and intake pipe pressure P = f
(N) is determined in advance (31), and the intake pipe pressure f (N
Fuel injection amount control for an internal combustion engine characterized in that (S4), when the intake pipe pressure f (NX) is smaller than X), (S5) the fuel injection amount is determined (S6) based on the determined intake pipe pressure The gist is the method.

Here, the relationship P=f (N>) between the predetermined rotational speed N and the intake pipe pressure P is determined in advance for each internal combustion engine over a wide range of rotational speed N, or is temporarily determined. A method may also be used in which the relationship for such a wide range of rotational speeds N is successively corrected using the actual rotational speed N and intake pipe pressure P when the internal combustion engine is in steady idle mode.

[Operation] First, the rotational speed NX and intake pipe pressure PX at each point in time are detected (Sl). Then, it is determined whether the throttle valve is currently fully open (S2). This can be detected by a throttle valve opening sensor or a switch called an idle switch. When the throttle valve is fully open, it is not subject to this control, so the following method is not performed.

It is detected that the throttle valve is fully open (S2
), the detected intake pipe pressure PX, the detected rotational speed NX at the same time, the rotational speed N and intake pipe pressure P when the throttle valve is idle, which is determined for a predetermined wide range of rotational speeds N. It is determined whether or not the intake pipe pressure f(NX> is determined by the relationship P=f(N)) (S3). As mentioned above, this may be determined in advance through experiments for each internal combustion engine, or such a relationship may be determined for a standard internal combustion engine, and the actual rotational speed N and intake air when the internal combustion engine is in a steady idle state are determined. A method may also be used in which the relationship is successively corrected based on the value of the pipe pressure P. If PX<f (NX>) in step S3, it means that the detected intake pipe pressure PX is the same as the rotation speed N detected at the same time.
This indicates a low value that deviates from the normal relationship with X.

If fuel injection 1 is calculated based on this low intake pipe pressure PX, the mixture will become too lean and may cause irregular rotation or stall, so if PX < f (NX), then f (
NX) is used as the basis for determining the fuel injection amount (S4
, 35). Note that when PX≧f(NX), the value of the detected intake pipe pressure PX is used as it is as the basis for determining the fuel injection amount (S3.35).

[Example] An example in which the present invention is applied to fuel injection amount control of an electronically controlled gasoline engine will be described below. FIG. 2 shows a schematic configuration of an engine, an electronic control device, and related devices to which this embodiment is applied. The engine 1 includes a fuel injection valve 2 provided for each cylinder and injecting fuel, an intake manifold 3, an intake pressure sensor 4 provided in a surge tank 3a and detecting the pressure of intake air sent to the engine 1, and the engine 1. a throttle valve 8 linked to the accelerator pedal 7, and a throttle position sensor 10 that is linked to the throttle valve 8 and outputs a signal according to the opening degree of the throttle valve 8. Bypass path 12 which is an air path that bypasses throttle valve 8
, an idle adjust screw 14 for adjusting the opening area of the bypass passage 12, and an idle switch 15 for detecting that the throttle valve 8 is fully open.

The engine 1 and its peripheral equipment also include a distributor 1 that rotates in conjunction with a crankshaft (not shown).
6, a rotational speed sensor 18 detects the rotational speed of the engine 1, and an electronic control device 20 that controls the fuel injection amount of the fuel injection valve 2 based on data from the various sensors described above.
Also included.

Next, the electrical system of this embodiment will be explained using the block diagram shown in FIG.

As shown in FIG. 3, the electronic control device 20 inputs and calculates data output from each sensor according to a control program, and is a central control device that performs processing to control the operation of various devices such as the fuel injection valve 2. Processing unit (CPtJ) 30, a read-only memory (ROM>31) in which data such as the control program and a map for calculating the ignition advance angle are stored; data input to the electronic control unit 20 and necessary for calculation control. A random access memory (RAM>32) in which data is temporarily stored; a backup random access memory (RAM>32) backed up by a battery to retain data necessary for subsequent engine operation even if a key switch (not shown) is turned off; Backup RAM) 33, intake pressure sensor 4. Water temperature sensor 6
, throttle position sensor 10. It is provided with an input section 34 that A/D converts the signal from the idle switch 15 and inputs the signal as required. Moreover, this electronic control system @20 includes a fuel 1 injector 2 and a rotational speed sensor 18. an input/output section 35 that inputs and outputs pulse signals to and from the vehicle speed sensor 19;
CPU30. Each element such as ROM 31 and input section 34. A path line 36 that connects the input/output section 35 and sends each data
It also has

The electronic control unit 20 takes in the detection data input from each sensor, calculates the optimal fuel injection m and ignition timing according to the operating conditions, and also controls whether the idle switch 15 is turned on or not.
That is, when the throttle valve 8 is fully open, the detection data from the intake pressure sensor 4 is also checked by the process described later.

Next, a method of controlling the fuel injection amount when the throttle valve 8 is fully closed, which is executed by the CPU 30, will be explained using the flowchart shown in FIG.

FIG. 4 shows a flowchart of a routine for calculating correction values for sequentially correcting the relationship between rotational speed and intake pipe pressure determined for a predetermined standard engine, which will be described later, during steady idle operation. This routine is 32
It is processed by the CPU 30 by interrupt every msec. When this routine starts,
First, in step 110, the value of the counter CPM is 32.
Check whether the above conditions are met. CPM<32
If so, the CPM value is increased by 1 in step 120, and this routine ends. The purpose of checking the counter CPM is to wait for a time of 32 msec x 32 times = 1 sec since the execution interval of this routine is 32 msec. CP at step 110
If it is determined that M≧32, the counter CP is set in step 130.
After resetting to M@O, it is checked in step 140 whether the idle switch 15 is turned on.

If the idle switch 15 is OFF and the throttle valve is not fully closed, this routine ends as is. Only when the idle switch 15 is ON, in step 150, the intake pipe pressure PM and rotational speed NE of the engine 1 at that time are input. This may be input directly from the intake pressure sensor 4 and the rotational speed sensor 18 in this routine, or a value detected in a fuel injection amount determination routine executed separately may be used.

Next, in step 160, this rotational speed NE is set to 70Orp.
Check if it is less than m, NE>70Orp
If it is m, this routine ends as is. This is a check to select only the steady idling state. If NE≦70Orpm, proceed to step 170;
The average intake pipe pressure PMAV is calculated using the following formula.

PMAV= (31xPMAV+PM)/32...(
1) This is calculated by weighting the previously calculated average intake pipe pressure PMAV (PMAV> on the right side with 31 and weighting the currently detected intake pipe pressure PM with 1), taking the average, and calculating the new PMAV.
That is. Similarly, in step 180, the average rotational speed NEAV is calculated using the following equation.

N EAV = (31xN EAV + N E > /3
2...(2) Next, in step 190, the above-mentioned relationship p=fn, +> between the standard engine speed N and the intake pipe pressure P, which is predetermined and stored in the ROM 31, is determined. The average rotation speed NEAV is substituted and stored in the variable LPMG. An example of this relationship P=f (N) is shown in FIG. In addition, R.O.
The method of storing the information in M31 may be in the form of a function or in the form of a table of discrete values. If stored in table form, step 190 requires interpolation calculations. Then, in step 200, the value of the variable LPMG, that is, f (NE
AV> is subtracted and stored in the variable DLPMID. The value of this variable DLPMID is later used in the fuel injection inclination calculation routine to correct the function P=f(N) over the entire rotational speed range. With this, the present correction value calculation routine is temporarily ended.

FIG. 6 is a flowchart of a routine for determining the fuel injection amount when the throttle valve 8 is fully open. This routine synchronizes with the rotation of engine 1 and performs one rotation per revolution.
times, thus twice per cycle. When this routine starts, first in step 210 it is checked whether the idle switch 15 is turned on. If the idle switch 15 is OFF here, this routine ends as is. Alternatively, the process may jump from here to a routine for determining the fuel injection port when the throttle valve 8 is not fully open. When it is detected in step 210 that the idle switch 15 is ON, that is, that the throttle valve 8 is fully closed, the current intake pipe pressure PM and rotational speed NE are input in step 220. Next, in step 230, the value of the rotation speed NE detected in step 220 is substituted into the relationship P=f(N> shown in FIG. 5) to obtain LPMG. If it is stored in the form of a table, interpolation calculation is performed.Next, step 24
0, the correction value DLPMID calculated in the correction value calculation routine is added to the obtained PMG to obtain the corrected estimated intake pipe pressure LMTPM. The process in step 240 is performed by correcting the standard relationship P=f (N) (solid line) in FIG.
N) (dotted line) to obtain the intake pipe pressure LMTPM. Next, in step 250, it is determined whether the measured intake pipe pressure PM is smaller than the estimated intake pipe pressure LMTPM. Here, the condition PM<LMTPM means that when the engine rotational speed NE suddenly changes, for example when the automatic transmission range is changed from N to D when the rotational speed is decreasing after racing, the cylinder This may occur because the pressure change at is not yet transmitted to the intake pressure sensor 4 located in the surge tank 3a. FIG. 7 shows the intake pipe pressure PM detected by the intake pressure sensor 4 (solid line) and the pressure in the cylinder (dotted line) when the rotational speed of the engine 1 suddenly decreases.
shows the time course of The detected value of the intake pressure sensor 4 shows a time delay of Δt with respect to a change in the cylinder pressure. If it is determined in step 250 that PM<LMTPM,
At step 260, the value of LMTPM is substituted into PM.

If PM≧LMTPM, the value of PM is not changed.

In these processes, if the intake pipe pressure PM detected by the intake pressure sensor 4 does not accurately reflect the cylinder pressure due to the pressure transmission delay and is lower than that, the fuel injection amount is reduced accordingly. In order to prevent the mixture in the cylinder from becoming too lean, the value of LMTPM, that is, the intake pipe pressure fc (N
E) (Steps 230 and 240>) is set as the minimum limit (guard).

Thereafter, in step 270, the fuel injection amount gA TALJ is calculated using a predetermined relational expression g(PM) based on the intake pipe pressure PM, and this routine is temporarily terminated.

As described above, this embodiment detects excessive and low pressures that occur when the rotational speed of the engine 1 suddenly changes and can lead to irregular engine rotation or stoppage due to a delay in the transmission of the cylinder internal pressure to the intake pressure sensor 4. Can be properly guarded.

In the above embodiment, the relationship P=f (N> stored in advance in the ROM 31 is corrected every second during steady idle linking to better reflect the state of the engine 1 at each point in time. This can be omitted, and the fourth
The illustrated routine and step 240 in FIG. 6 can be omitted. Even in this case, step 250 in FIG.
This is because guarding is performed by H.260.

[Effects of the Invention] By guarding the minimum value of the detected intake pipe pressure according to the present invention,
Even when the rotational speed of the internal combustion engine suddenly drops, the amount of fuel injected is relatively reduced due to a delay in the detection of intake pipe pressure (the air-fuel mixture becomes too lean), even though a large amount of fuel is required. This has the effect of maintaining normal rotation of the internal combustion engine.

[Brief explanation of the drawing]

Fig. 1 is a flowchart illustrating the general flow of the present invention, Fig. 2 is a schematic configuration diagram of a gasoline engine and its peripheral equipment to which an embodiment of the present invention is applied, and Fig. 3 shows the configuration of an electronic control device. Block diagram, Figure 4 is a flowchart of the correction fL calculation routine performed by the CPU, Figure 5 is the RO
Graph showing the relationship between standard engine speed and intake pipe pressure stored in M and the relationship after correction, No. 6
The figure is a flowchart of the fuel injection port calculation routine performed by the CPU when the throttle valve is fully open, and Figure 7 is a graph showing the temporal changes in the intake pressure sensor detection value and cylinder pressure when the engine speed suddenly drops. . 1... Engine 2... Fuel injection valve 4... Intake pressure sensor 8... Throttle valve 12... Bypass path 15... Idle switch 18... Rotational speed sensor 20... Electronic control Device

Claims (1)

[Claims] 1. In a fuel injection amount control method for an internal combustion engine that determines the fuel injection amount based on the intake pipe pressure of the internal combustion engine, the relationship between the rotational speed of the internal combustion engine and the intake pipe pressure when the throttle valve is fully closed is determined in advance. and when the intake pipe pressure of the internal combustion engine is smaller than the intake pipe pressure determined by the rotational speed of the internal combustion engine at that time and the relationship, the fuel injection amount is determined based on the determined intake pipe pressure. A fuel injection amount control method for an internal combustion engine, characterized in that: