JPS63120832A - Fuel injection quantity control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an overlean state of air-fuel ratio in the time of deceleration, by estimating an amount of air, left existing in an intake pipe, and increasing the larger a limit value the larger an estimated value of the amount of air increases, when a movable vane type air amount sensor is detected to generate overshooting. CONSTITUTION:When an engine is in operation, a control circuit, deciding whether or not an intake air amount per one revolution of the engine Q/N increases to a decision value or more, decides a movable vane type air amount sensor 2 to generate overshooting. When the overshooting is generated, a time integration value OS is calculated by subtracting the decision value L from the Q/N to successively integrate a difference. And in the time of decision of a deceleration operative condition that a throttle valve 3 is closed, a limit value corresponding to the present time integration value OS is calculated from a map of the limit value. And the engine, in which said limit value is compared with the fuel injection time obtained in accordance with the operative condition, limits the fuel injection time so that it is prevented from decreasing to the limit value or less.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection amount control method for an internal combustion engine, and in particular, the fuel injection amount is controlled based on the detected value of a movable vane type air amount sensor that detects the intake air amount. The present invention relates to a fuel injection amount control method for an internal combustion engine, in which the fuel injection amount is controlled so that the fuel injection amount does not fall below a predetermined limit value when a throttle valve is closed.

[Conventional technology]

Conventionally, a movable vane type air amount sensor detects the amount of intake air drawn into the engine, and an engine rotation speed sensor detects the engine rotation speed, and the fuel injection amount is determined from the detected intake air amount and engine rotation speed. BACKGROUND ART Internal combustion engines are known in which the amount of fuel injection is determined and controlled. In such an internal combustion engine, the intake air amount is detected using a movable vane air amount sensor equipped with a measuring plate.
During deceleration, the measuring plate undershoots and the detected value of the intake air amount becomes small, resulting in the fuel injection amount becoming too small compared to the engine required value, and the air-fuel ratio may become over-lean. In other words, the fuel injection amount is proportional to the intake air amount, so if the intake air amount sensor undershoots and the detected intake air amount becomes smaller than the intake air amount actually supplied to the engine, the fuel injection amount will decrease. , which causes the air-fuel ratio to become over-lean.

For this reason, conventionally, in order to prevent the air-fuel ratio from being overlean due to undershoot of the air amount sensor, a limit value for the fuel injection amount is provided, and the fuel injection amount is prevented from falling below this limit value during deceleration. Techniques for limiting the amount of fuel injection during deceleration using limit values include a technique described in Japanese Patent Application Laid-Open No. 138245/1983 that sets a limit value that changes depending on the engine rotation speed, and a technique that sets a limit value that changes depending on the vehicle speed. There is a technique described in Japanese Unexamined Patent Publication No. 58-74837 which sets the following.

[Problem that the invention seeks to solve]

However, the undershoot of the intake air amount sensor is also affected by the amount of depression of the accelerator pedal before deceleration. For example, when decelerating from a state where the accelerator pedal is deeply depressed, the undershoot may be caused by deceleration from a high measuring opening state. At the same time, a large amount of air remaining in the intake pipe is sucked in, increasing the pressure difference between the upstream and downstream sides of the measuring plate, resulting in a large undershoot of the measuring plate due to inertia and pressure difference. Therefore, for a short time (
For example, when performing a tip-in by opening and closing the accelerator at a cycle of 1 sec, there are two ways to do the tip-in: one without stepping on the accelerator, and the other with stepping on the accelerator to 2 or 3 degrees. Therefore, even if the vehicle speed and engine rotational speed are constant, the size of the undershoot will vary. For this reason, when setting limit values according to engine rotation speed or vehicle speed as in the past, the problem is that the limit value is constant when the engine rotation speed or vehicle speed is constant, and it is not possible to set the optimum limit value. there were.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel injection amount control method for an internal combustion engine that can set an optimal limit value during deceleration including tip-in.

[Means for solving problems]

In order to achieve the above object, the present invention determines the fuel injection amount based on the detected value of a movable vane type air amount sensor that detects the intake air amount, and when the throttle valve is closed, the fuel injection amount is determined in advance. In a fuel injection amount control method for an internal combustion engine, which controls the fuel injection amount by limiting it so that it does not fall below a set limit value, an overshoot of the movable vane air amount sensor is detected, and when overshoot is detected, a The present invention is characterized in that the remaining air amount is predicted, and the larger the predicted value of the air amount is, the larger the limit value is.

[Effect]

According to the present invention, the fuel injection amount is determined based on the detected value of the movable vane type air amount sensor that detects the intake air amount,
When the throttle valve is closed, the fuel injection valve is limited so that it does not fall below a limit value. This limit value detects overshoot of the movable vane air amount sensor, predicts the amount of air remaining in the intake pipe when overshoot is detected, and changes as this predicted value increases. be done. Here, since the air remaining in the intake pipe is supplied to the combustion chamber when the throttle valve is closed, the larger the predicted value, the greater the amount of air supplied to the combustion chamber. Therefore, by increasing the limit value as the predicted value increases, the fuel injection amount is limited to a value corresponding to the amount of air remaining in the intake pipe and supplied to the combustion chamber. Therefore, fuel corresponding to the amount of air supplied to the combustion chamber during deceleration is injected, thereby preventing the air-fuel ratio from becoming overlean.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of air remaining in the intake pipe is predicted immediately before deceleration, and the larger the amount of air remaining in the intake pipe is, the thicker the limit value is. It is possible to inject fuel corresponding to the amount of air supplied to the combustion chamber, thereby achieving the effect that over-lean air-fuel ratio during deceleration such as tip-in can be prevented.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an example of an internal combustion engine equipped with a fuel injection amount control device to which this embodiment is applicable. This engine is controlled by an electronic control circuit such as a microcomputer, and is provided downstream of the air cleaner 1 with an air flow meter 2 which is a movable vane type air amount sensor that detects the amount of intake air. The air flow meter 2 includes a convention plate rotatably installed in the damping chamber, a measuring plate connected to the compensation plate, and a potentiometer that detects the opening degree of the measuring plate. Therefore, the intake air amount is determined from the intake air amount signal output from the potentiometer as a voltage value.

A throttle valve 3 is arranged downstream of the air flow meter 2, a throttle position sensor 4 is attached to the throttle valve 3, and a surge tank 17 is arranged downstream of the throttle valve 3. The surge tank 17 is communicated with the combustion chamber of the engine via the intake manifold 5 and the suction port. Then, a fuel injection valve (fuel injector) is installed for each cylinder or for each cylinder group so as to protrude into the intake manifold 5.
8 is installed. This fuel injection valve 8 is communicated with the fuel tank 6 via the fuel pump 7.
It is configured such that fuel at a predetermined pressure is supplied to. Therefore, by opening the fuel injection valve 8 for a predetermined time,
An amount of fuel is injected according to this time.

The combustion chamber of the engine is communicated with a catalyst device (not shown) filled with a three-way catalyst through an exhaust port and an exhaust manifold. A signal that is inverted from the stoichiometric air-fuel ratio is output to this exhaust manifold. 2 sensors 15A are attached. Further, a cooling water temperature sensor 15 is attached to the engine block so as to penetrate the engine block and protrude into the water jacket. This cooling water temperature sensor 15 detects the engine cooling water temperature and outputs a water temperature signal.

A spark plug 14 is attached to each cylinder so as to penetrate the cylinder head of the engine and protrude into the combustion chamber. The spark plug 14 is connected via the distributor 11, the ignition coil 10, and the igniter 9 to a control circuit 16 composed of a microcomputer or the like.

Inside the distributor 11, a cylinder discrimination sensor 13 and a rotation angle sensor 12 are installed, each of which includes a signal rotor fixed to a distributor shaft and a pickup fixed to a distributor housing. Cylinder discrimination sensor 13 is 720'CA
The rotation angle sensor 12 outputs a cylinder discrimination signal every time the rotation angle sensor 12
Outputs an engine rotation speed signal for each CA.

As shown in FIG. 3, the throttle position sensor 4 includes a movable contact 18 for detecting throttle opening and a movable contact 19 for detecting throttle fully closed, which are attached to a plate that rotates in conjunction with the throttle valve 3. ing. The movable contact 18 for throttle opening detection is arranged so as to slide on the arc-shaped resistor 20A and the resistor 21A printed in parallel on the base, and the movable contact 19 for throttle fully closed detection is disposed on the base. It is arranged so as to slide on the printed conductors 22A and 23A. Resistor 2
One end of 0A is electrically connected to a terminal Vc connected to a power supply (5v), and the other end of the resistor 20A is connected to a grounded terminal E.
electrically connected to l. Further, one end of the resistor 21A is connected to the terminal V, and one end of the R electric body 23A is connected to the terminal I.
Connected to DL. The conductor 22A is connected to the terminal E.
It is electrically connected to I.

Throttle position sensor 4 configured as above
The equivalent circuit of is shown in FIG. The throttle opening detection movable contact 18 and the resistor 20A.

21A acts as a throttle opening sensor SN, and is connected to the movable contact 19 for detecting fully closed throttle and the conductive ffi body 2.
2A and 23A act as throttle fully closed switches SW. In addition, the terminal ■A output and the terminal IDL output are shown in FIG. A proportional throttle opening signal is output.

Further, as shown in FIG. 6, the system 711 circuit 16 includes a central processing unit (CPU) 20 and a read-only memory.
(ROM) 21, random access memory (RAM) with backup memory 22, input port 23
, an output port 24, and a bus 25 such as a data bus or a control bus that connects these ports. 'CPU 20 includes analog-digital (A
/D) Terminal 7 of air flow meter 2 and throttle position sensor 4 via converter 26 and multiplexer 27
A cooling water temperature sensor 15 (not shown) is also connected. CPU 20 is multiplexer 2
7 to sequentially input the air flow meter 2 output and the terminal 7 output (throttle opening sensor output) of the throttle position sensor 4, etc., and start the A/D converter 26 to convert the input signal into a digital signal. and import it. A rotation angle sensor 12 and a cylinder discrimination sensor 13 are connected to the input port 23 via a waveform shaping circuit 29.
A terminal IDL (throttle fully closed switch) of the throttle position sensor 4 is connected via a buffer 32. Further, the rotation angle sensor 12 and the cylinder discrimination sensor 13 are connected to the CPU 20 via a timing generation circuit 28. The timing generation circuit 28 includes the rotation angle sensor 12
Based on the output and the output of the cylinder discrimination sensor 13, an interrupt signal is generated for each predetermined crank angle and input to the CPU.

In response to this interrupt signal, the CPU stops processing the main routine and executes the interrupt routine even if the main routine is being executed. The output port 24 is connected to the fuel injection valve 8 via a drive circuit 30 including a down counter. Note that 31 is a clock generation circuit. The ROM stores in advance a control routine program, etc., which will be explained below.

Figure 1 shows a routine that predicts the amount of air remaining in the intake pipe by calculating the time integral value interrupted every short time (for example, 4m5ec). The intake air amount Q and the engine rotational speed N detected by the engine rotational speed sensor are taken in, and in step 102, the engine 1
It is determined whether the intake air ff1Q/N per rotation has exceeded a determination value for determining overshoot.

When the amount of intake air Q/N per revolution of the engine exceeds the determination value, it is determined that overshoot of the air flow meter has occurred, and a time integral value OS is calculated in step 104. This time integral value OS is obtained by sequentially integrating the difference obtained by subtracting the determination value from the intake air 51 Q/N per engine revolution.

On the other hand, when it is determined in step 102 that the intake air amount Q/N per engine revolution is less than the determination value, it is determined that no overshoot of the air flow meter has occurred, and in step 106, the throttle fully closed switch SW is output. Based on this, it is determined whether the throttle valve has been opened from the closed state. When the throttle valve is opened from the closed state, the time integral value O3 is set to 0 in step 110 and the process returns to the main routine, and when the judgment in step 106 is negative, the throttle valve remains open for a predetermined period of time ( For example, it is determined whether or not the process continues for more than 0.5 seconds. When the judgment in step 108 is affirmative, in step 110 the time integral value O8 is set to 0.
If the determination at step 108 is negative, the process directly returns to the main routine.

Here, in step 108, it is determined whether or not the throttle valve remains open for a predetermined period of time or more, in order to predict the amount of air remaining in the intake pipe based on the time integral value O8. The amount of air remaining in the intake pipe immediately before deceleration is estimated on the assumption that the intake pipe will be filled with air within a predetermined time from the time the throttle valve is opened.

As a result of the control as described above, the time integral value O3 is calculated as shown in FIG.
The integrated value of the amount of intake air per rotation is calculated.

FIG. 8 shows a calculation routine for calculating the fuel injection time TAU as the main routine of this embodiment, in which the intake air iQ and the engine rotational speed N detected in step 120 are taken in, and the basic fuel injection time is calculated in step 122. Calculate TP (=-Q/N, where K is a constant). Then, in step 124, the basic fuel injection time is multiplied by a correction coefficient C such as the intake air temperature, engine cooling water temperature, air-fuel ratio feedback correction coefficient, etc., so that the fuel injection time T
Calculate AU.

In the next step 126, it is determined whether or not the throttle valve is closed. If the throttle valve is open, step 13
0 and the throttle valve is closed, it is determined that the deceleration is in progress, and in step 128 the limit value g (O
A limit value corresponding to the current integral value O8 is calculated from the map of 3), and this limit value is set as TAUMIN.

In the next step 130, the fuel injection time TAU and the limit value T
AUMIN, and if TAU≦TAUMIN, in step 132, the value of the limit value TAUMIN is set as the value of the fuel injection time TAU, and the fuel injection time TAU is limited so as not to become less than the limit value TAUMIN.

In addition, above, an example was explained in which the amount of air remaining in the intake pipe immediately before deceleration is predicted by calculating the integral value of the amount of intake air per engine revolution, but when the throttle opening degree just before deceleration is large, If there is a large amount of air remaining in the intake pipe just before deceleration and the amount of change in throttle opening is large, it is considered that the air flow meter overshoot is large. Alternatively, it may be determined that a chute has occurred, and the output of the throttle opening sensor may be integrated to predict the amount of air remaining in the intake pipe.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a routine for calculating a time integral value according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing an internal combustion engine equipped with a fuel injection amount control device to which the present invention can be applied, and FIG. A cross-sectional view showing the throttle position sensor, Figure 4 is the third
Figure 5 is a diagram showing the signals of each part output from the throttle position sensor in Figure 3. Figure 6 is a block diagram showing details of the control circuit in Figure 2. , FIG. 7 is a diagram showing changes in airflow make output, etc., FIG. 8 is a flowchart of the fuel injection time calculation routine of the above embodiment, and FIG. 9 is a diagram showing a map of limit values. 2... Air flow meter 4... Throttle position sensor, 8... Fuel injection valve.

Claims (2)

[Claims] (1) The fuel injection amount is determined based on the detected value of the movable vane air amount sensor that detects the intake air amount, so that the fuel injection amount does not fall below a predetermined limit value when the throttle valve is closed. In a fuel injection amount control method for an internal combustion engine that controls the fuel injection amount by limiting the amount, an overshoot of the movable vane air amount sensor is detected, and when the overshoot is detected, the amount of air remaining in the intake pipe is determined. A fuel injection amount control method for an internal combustion engine, comprising predicting the amount of air, and increasing the limit value as the predicted value of the air amount increases. (2) The fuel injection amount control method for an internal combustion engine according to claim (1), wherein the predicted value of the air amount is predicted based on a time integral value of the detected value.