JP2590522B2 - Fuel injection amount control device 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 amount control device for an internal combustion engine, and more particularly to a fuel injection amount control device for an internal combustion engine that prevents engine stall after a high-temperature restart.

[Conventional technology]

Conventionally, a basic fuel injection time is calculated based on an intake pipe pressure (absolute value) and an engine rotation speed, and the basic fuel injection time is corrected by an intake air temperature, an engine cooling water temperature, and the like to obtain a fuel injection time. There is known an internal combustion engine that controls a fuel injection amount by opening a fuel injection valve and injecting fuel for a time corresponding to a fuel injection time. In such an internal combustion engine, the rise of the engine rotational speed NE after the start, that is, after the complete explosion differs depending on the individual difference of the engine and the engine temperature at the start, but especially at high temperatures, the viscous resistance of the oil is small. Therefore, as shown in FIG. Since the pumping action of the engine sharply increases with the rapid increase of the engine speed NE, the intake pipe pressure PM sharply decreases as shown by the solid line in FIG. 2 (2). On the other hand, the fuel injection time TAU is proportional to the intake pipe pressure PM.
As shown by the solid line in FIG. When the fuel injection time TAU decreases rapidly as described above, at a high engine temperature, a smaller amount of fuel is supplied than the fuel injection amount calculated due to the influence of the vapor or the like. Suddenly drops, causing engine stall. In order to solve this problem, the basic fuel injection time TP determined by the intake pipe pressure and the engine speed is multiplied by a predetermined value to increase the fuel injection amount after starting. Basic fuel injection time when intake pipe pressure PM is small because it is increased according to the size
The TP is also small, so that when the intake pipe pressure is small, the amount of fuel increase is insufficient (the dashed line in FIG. 2 (1)). Therefore, in this method, the drop point of the intake pipe pressure PM caused by the rapid rise of the engine rotation speed, that is, the fuel injection time is sharply reduced, a lean spike occurs, a misfire occurs, and a stall occurs, resulting in a stall. However, there is a problem that the effective increase cannot be performed at the time when the stall needs the most increase after the complete explosion. In order to solve this problem, it is conceivable to increase the amount of fuel during a high-temperature restart and gradually decrease the fuel regardless of the intake pipe pressure after the start.However, the degree of increase in the engine speed after the start, the intake pipe pressure Since the fuel injection amount is determined uniformly irrespective of the degree of PM reduction, a fuel injection amount corresponding to the operating state of the engine cannot be obtained, and the emission deteriorates and the startability deteriorates.

On the other hand, Japanese Patent Application Laid-Open No. 61-135948 discloses that the intake air amount, the ratio of the intake air amount to the engine rotation speed, or the basic fuel injection time is determined for a predetermined time after the engine is started. It is disclosed that the value is maintained at or above a lower limit value determined based on a response error. By keeping the basic fuel injection time or the like at or above the lower limit value, the air-fuel ratio is prevented from becoming lean.

As a technique related to the present invention, Japanese Patent Application Laid-Open No.
There are techniques described in JP-A-633 and JP-A-61-101635.

[Problems to be solved by the invention]

However, when the throttle valve is slightly opened or the idle speed is increased after the engine starts, the intake pipe pressure itself increases.In this case, too, the intake pipe pressure PM decreases as the engine speed increases. In the method of limiting by the lower limit value of the above, there arises a problem that the basic fuel injection time or the like drops sharply before reaching the lower limit value due to the drop of the intake pipe pressure, and the engine stalls due to inertia.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to avoid an engine stall caused by a sudden decrease in a basic fuel injection amount due to a decrease in an intake pipe pressure accompanying an increase in an engine rotation speed at a high temperature restart. It is an object of the present invention to provide a fuel injection amount control device for an internal combustion engine that can perform the above.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a pressure detecting means A for detecting an intake pipe pressure as shown in FIG. 3, and a relaxation for obtaining a relaxation value in which a change in a signal output from the pressure detecting means A is reduced. Means B, determining means C for determining whether or not the engine has been restarted at a high temperature, correcting means D for increasing the degree of relaxation in the relaxing means B within a predetermined time after restarting at a high temperature, and detecting the engine rotational speed. Rotational speed detecting means, rotational speed detecting means E, and control means F for calculating a basic fuel injection time based on the relaxation value and the engine rotational speed and controlling a fuel injection amount based on the calculated basic fuel injection time. And is included.

[Action]

The pressure detecting means A of the present invention detects the intake pipe pressure, the rotational speed detecting means E detects the engine rotational speed, and the judging means C judges whether or not a high temperature restart has been performed. Mitigation measures B
Calculates a relaxation value in which a change in the signal output from the pressure detection means A is reduced. As the relaxation value, the following (1)
The weighted average value PMN shown in the equation can be used. In addition,
This weighted average value can be obtained by digital filtering processing.

Here, PMN is the current weighted average value, PMNO is the past weighted average value, and PMAD is the intake pipe pressure PM detected by the pressure detection means.
, And K is a coefficient relating to weighting.

When the determining means C determines that the high-temperature restart has been performed, the correcting means D corrects the degree of relaxation in the relaxing means B within a predetermined time after the high-temperature restart. When the weighted average value of the above equation (1) is used, the degree of relaxation can be increased by increasing the coefficient K. As a result, the change in the signal output from the pressure detecting means is significantly reduced within a predetermined time after the high temperature restart than in other cases. Therefore, even when the engine rotational speed is rapidly increased and the intake pipe pressure is rapidly decreased, the relaxation value gradually changes, and the control means determines that the relaxation value is equal to the relaxation value obtained as described above. The basic fuel injection time is calculated based on the engine speed and the fuel injection amount is controlled based on the calculated basic fuel injection time. As described above, within a predetermined time after the high-temperature restart, the change in the signal output from the pressure detecting means is greatly reduced, so that even if the actual intake pipe pressure suddenly decreases, the relaxation value gradually decreases, The basic fuel injection time calculated based on the relaxation value also gradually decreases, and a sudden decrease in the basic fuel injection time caused by a decrease in the intake pipe pressure accompanying an increase in the engine rotation speed after a high-temperature restart is prevented. Institutional stalls can be avoided.

〔The invention's effect〕

As described above, according to the present invention, the fuel injection amount is controlled using the relaxation value that gradually changes with respect to the actual intake pipe pressure change within a predetermined time after the high temperature restart. In addition, even when the actual intake pipe pressure rises sharply, the fuel injection amount does not become insufficient, whereby the effect of preventing engine stall after restarting at a high temperature can be obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 4 schematically shows an internal combustion engine provided with a fuel injection amount control device to which the present invention can be applied.

This engine is controlled by an electronic control circuit such as a microcomputer. A throttle valve 8 is disposed downstream of an air cleaner (not shown), and a voltage corresponding to the throttle opening is applied to the throttle valve 8. A linear throttle sensor 10 for outputting the pressure is provided, and a surge tank 12 is provided downstream of the throttle valve 8. A semiconductor type pressure sensor 6 is attached to the surge tank 12. The pressure sensor 6 has a small time constant (for example, 3 to 5 mse) for removing a pulsating component of the intake pipe pressure.
c) It is connected to a filter (FIG. 5) composed of a CR filter or the like having good responsiveness. This filter may be built in the pressure sensor. Further, a bypass path 14 is provided so as to bypass the throttle valve 8 and connect the upstream side of the throttle valve and the surge tank 12 downstream of the throttle valve. The bypass passage 14 has an ISC (idle speed control) valve 16B whose opening is adjusted by a pulse motor 16A having a 4-pole stator.
Is installed. The surge tank 12 is connected to a combustion chamber of the engine 20 via an intake manifold 18 and an intake port 22. A fuel injection valve 24 is attached to each cylinder so as to protrude into the intake manifold 18.

The combustion chamber of the engine 20 is connected to a catalyst device (not shown) filled with a three-way catalyst via an exhaust port 26 and an exhaust manifold 28. The exhaust manifold 28 is provided with an O ₂ sensor 30 that outputs a signal inverted at the stoichiometric air-fuel ratio. Engine block
The cooling water temperature sensor 34 is attached to the engine 32 so as to penetrate the engine block 32 and protrude into the water jacket. The coolant temperature sensor 34 detects the engine coolant temperature and outputs a coolant temperature signal, and the coolant temperature signal represents the engine temperature. The engine oil temperature may be detected to represent the engine temperature.

An ignition plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and protrude into the combustion chamber. The ignition plug 38 is connected via a distributor 40 and an igniter 42 to an electronic control circuit 44 composed of a micro computer or the like. In the distributor 40, a cylinder discriminating sensor 46 and a rotation angle sensor 48 each composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing are mounted. The cylinder discriminating sensor 46 outputs a cylinder discriminating signal, for example, every 720 ° CA, and the rotation angle sensor 48 outputs an engine speed signal, for example, every 30 ° CA.

As shown in FIG. 5, the electronic control circuit 44 includes a microprocessing unit (MPU) 60, a read-only memory (ROM) 62, a random access memory (RAM) 64, and a back-up RAM (BU-RAM). 66, an input / output port 68, an input port 70, output ports 72, 74 and 76, and a bus 75 such as a data bus and a control bus connecting them. An analog-digital (A / D) converter 78 and a multiplexer 80 are sequentially connected to the input / output port 68. The multiplexer 80 includes a resistor R and a capacitor C
The pressure sensor 6 is connected via a CR filter 7 and a buffer 82, and the cooling water temperature sensor 34 is connected via a buffer 84. Also a multiplexer
The linear throttle sensor 10 is connected to 80. MP
U60 controls the multiplexer 80 and the A / D converter 78,
The output of the pressure sensor 6, the output of the linear throttle sensor 10, and the output of the cooling water temperature sensor 34 input via the CR filter 7 are sequentially converted into digital signals and stored in the RAM 64. Therefore, the multiplexer 80, the A / D converter 78, the MPU 60, etc.
It functions as sampling means for sampling the output of the pressure sensor every predetermined time. The input port 70 is connected to the O ₂ sensor 30 via a comparator 88 and a buffer 86, and also connected to a cylinder discriminating sensor 46 and a rotation angle sensor 48 via a waveform shaping circuit 90. The output port 72 is connected to the igniter 42 via the drive circuit 92, and the output port 74
Is connected to the fuel injector 24 via a drive circuit 94 having a down counter, and the output port 76 is connected to the pulse motor 16A of the ISC valve via a drive circuit 96. In addition, 98 is a clock and 99 is a timer. In the ROM 62, a control routine program and the like described below are stored in advance.

Next, a control routine of an embodiment in which the present invention is applied to the engine will be described. In the following, description will be made using numerical values that do not hinder the present invention, but the present invention is not limited to these numerical values.

FIG. 1 is input from the A / D converter 78 at the end of A / D conversion.
This shows an interrupt routine interrupted by an A / D conversion end signal. In step 100, it is determined whether or not the A / D conversion of the intake pipe pressure PM has been completed. If the determination is affirmative, the A / D conversion of the intake pipe pressure is performed. After storing the converted PMAD in the RAM, it is determined in step 102 whether or not it is within a predetermined time (for example, 3 seconds) after starting. Whether the engine has been started or not can be determined based on the starter switch or the engine speed. When the starter switch is turned off, the starter is turned on and the engine speed becomes equal to or higher than a predetermined speed (for example, 500 rpm). Can be defined as If the determination in step 102 is affirmative, in step 104 the intake air temperature THA is set to a predetermined value α (for example, 65
° C) or not, in step 106, the engine cooling hot water THW
Is determined to be equal to or higher than a predetermined temperature β (for example, 95 ° C.) to determine whether the temperature is within a predetermined time after the high temperature restart.
If it is determined that it is within the predetermined time after the high-temperature restart, the weighting coefficient K is set to a predetermined value (for example, 64) in step 108, and if it is not within the predetermined time after the high-temperature restart, the weighting coefficient is set to a normal value in step 110. Value (for example, 4)
Set to. Then, in step 112, the weighted average value PMN of the intake pipe pressure is calculated according to the equation (1) described above, and in step 114, the weighted average value PMN is stored in a predetermined area of the RAM.

FIG. 6 shows a part of the main routine of the present embodiment. In step 120, the weighted average value PMN of the intake pipe pressure and the engine speed NE calculated as described above are fetched, and in step 122, the weighted average value is calculated. The basic fuel injection time TP is calculated based on the PMN and the engine speed NE in the same manner as in the related art.
The fuel injection time is obtained by correcting the basic fuel injection time TP with the intake air temperature, the engine cooling water temperature, and the like, and the fuel injection is performed by opening the fuel injection valve when the fuel injection timing comes.

As a result of the above control, the weighted average value PMN and the fuel injection time after the high temperature restart change as shown by the broken lines in FIGS. 2 (1) and (2).

In the above description, an example in which the coefficient in the digital filtering process is changed to change the degree of mitigation of the intake pipe pressure signal detected from the pressure sensor has been described. However, by switching using two filters having different time constants, switching is performed. The degree of relaxing the pressure sensor output may be changed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an A / D conversion end interrupt routine according to an embodiment of the present invention, and FIGS. 2 (1), (2) and (3) show fuel injection time after high temperature restart, intake pipe pressure, and engine. FIG. 3 is a block diagram corresponding to the claims of the present invention, FIG. 4 is a schematic diagram showing an internal combustion engine to which the present invention can be applied, and FIG. FIG. 6 is a block diagram showing details of the control circuit shown in FIG. 6, and FIG. 6 is a flowchart showing a part of the main routine of the above embodiment. 6 ... Pressure sensor, 10 ... Slot sensor, 24 ... Fuel injection valve, 44 ... Control circuit, 48 ... Rotation angle sensor.

Claims (1)

(57) [Claims] 1. A pressure detecting means for detecting an intake pipe pressure, a mitigation means for obtaining a relaxation value in which a change in a signal output from the pressure detecting means is reduced, and a judging means for judging whether or not a high temperature restart has been performed. Correction means for increasing the degree of relaxation in the relaxation means within a predetermined time after a high-temperature restart, rotation speed detection means for detecting an engine rotation speed, and a basic value based on the relaxation value and the engine rotation speed. Control means for calculating the fuel injection time and controlling the fuel injection amount based on the calculated basic fuel injection time, a fuel injection amount control device for an internal combustion engine.