JPH0251055B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an electromagnetically controlled fuel injection internal combustion engine.

In an electronically controlled fuel injection internal combustion engine, during idling operation, when the accelerator pedal is depressed and then immediately released, so-called racing, the engine may stall during the process in which the throttle valve returns to the idle position. That is, when the accelerator pedal is released from a state in which the accelerator pedal is depressed, the engine speed suddenly drops to the idle setting speed (for example, 700 RPM). When the engine speed drops to the idle setting speed, the so-called
An idle speed control device such as an ISC device controls the engine speed to a set idle speed. This control, for example, uses a control valve (so-called ISC) that controls the amount of intake air to the engine using an electric signal (pulse signal) with an ON-OFF ratio (so-called duty ratio) depending on the set engine speed.
valve). However, when the accelerator pedal is released from a state in which the accelerator pedal is depressed in racing, there is no reverse driving force from the drive wheels, so the engine speed decreases much more rapidly than in a normal case. Because the engine speed decreases too suddenly, the response of the air-fuel ratio control system, especially the intake air amount or intake pipe pressure sensor, becomes incompatible with this sudden decrease in engine speed, and the optimum air-fuel ratio cannot be adjusted. The air-fuel ratio becomes richer or leaner than the appropriate air-fuel ratio, resulting in poor combustion efficiency. For example, in a so-called L-J type air-fuel ratio control device that measures the amount of intake air using a vane-type air flow meter and controls the air-fuel ratio, if the engine speed suddenly decreases, the measuring plate Since the movement lags behind the decrease in engine speed, the air flow meter detects an amount greater than the actual intake air amount, and the fuel injection amount is greater than the actual intake air amount, resulting in a rich air-fuel ratio. . On the other hand, in the so-called DJ type air-fuel ratio control device, which measures the amount of intake air using an intake pipe pressure sensor and controls the air-fuel ratio, the responsiveness of the intake pipe pressure sensor is too good, causing the engine speed to drop suddenly. In such a transient state, the amount of intake air detected by the sensor will be less than the actual amount of intake air due to so-called undershoot, so the amount of fuel injection will be insufficient for the actual amount of intake air, and the amount of air will increase. The fuel ratio becomes lean.

Japanese Patent Application Laid-Open No. 54-67126 discloses a technique for controlling fuel cut during deceleration operation of an engine, in which the engine rotational speed at which the fuel cut returns to fuel supply when the deceleration is large is set to a large value. That is,
Normally, in a fuel-injected internal combustion engine, fuel is cut to prevent catalyst heating during deceleration operation when the engine speed is high to a certain extent, and when the engine speed drops to around the idle speed, the fuel cut is stopped and the fuel is cut. Restart supply. Even during racing, the engine speed may be higher than the speed at which fuel cut is performed, so when the accelerator pedal is released, the fuel cut condition may be entered. In this case, fuel cut is executed and the engine speed is reduced to idle. Fuel cut is stopped when the rotation speed drops to around the same level. However, in racing, when the accelerator pedal is released, the engine speed suddenly drops, resulting in a delay in recovery from fuel cut.
Even when the engine speed returns to idle, the fuel cut condition may continue and the engine may stall. Therefore, Japanese Patent Application Laid-Open No. 54-67126 detects when the engine speed in racing suddenly drops, sets the fuel cut stop rotation speed high, and stops fuel cut early to prevent stalling. .

However, simply increasing the engine speed at which fuel cut is stopped does not sufficiently compensate for the air-fuel ratio when the engine speed drops to idle. That is, the fuel supply operation cannot keep up with the rapid decrease in rotational speed, and an appropriate amount of fuel cannot be supplied.

Japanese Patent Application Laid-open No. 78138/1983 proposes detecting the rotational fluctuation range during idling and changing the air-fuel ratio, that is, the fuel amount, so as to reduce the fluctuation range. This method can eliminate rotational fluctuations during idle. However, in racing, this method does not provide a countermeasure against stalling due to an inappropriate air-fuel ratio when the rotational speed suddenly drops when the accelerator pedal is released.
That is, when the accelerator pedal is suddenly released during racing, the calculation of the fuel injection amount will not be able to catch up with the sudden change in the engine condition, and the calculated value will result in an excessive or insufficient fuel injection amount.

Therefore, an object of the present invention is to provide a device that can prevent such engine stall during racing.

To achieve this object, the electronically controlled internal combustion engine of the present invention has an air-fuel ratio control means for controlling the air-fuel ratio to an appropriate air-fuel ratio by controlling the amount of fuel supplied, as shown in FIG. A first detection means A that detects the idle position of the valve, a second detection means B that detects the engine rotation speed, and a state in which the engine rotation speed is equal to or lower than the set rotation speed corresponding to the set idle rotation speed during engine idling operation. a first determining means C for determining the rate of decrease in the engine speed; a calculating means D for calculating the rate of decrease in the engine speed; a second determining means E for determining a state in which the rate of decrease in the engine speed is greater than a predetermined rate of decrease in the engine speed. , when the throttle valve is in the idle position, the rate of decrease in engine speed is greater than the predetermined rate of decrease,
Fuel supply amount correction means F for correcting the fuel supply amount by the air-fuel ratio control device means G to a value for controlling the air-fuel ratio to the appropriate air-fuel ratio when the engine rotation speed is below the set rotation speed. do.

The first detection means A detects the idle position of the throttle valve.

The second detection means B detects the engine rotation speed.

The first determination means C determines a state in which the engine rotation speed is equal to or lower than a set rotation speed corresponding to a set idle rotation speed during engine idling operation.

Calculation unit D calculates the rate of decrease in engine speed.

The second determining means E determines a state in which the rate of decrease in engine speed is greater than a predetermined rate of decrease in engine speed.

The fuel supply amount correcting means F adjusts the fuel supply amount and the air-fuel ratio to the appropriate air-fuel ratio when the throttle valve is in the idle position, the rate of decrease in engine speed is greater than a predetermined rate of decrease, and the engine speed is at the set number of rotations. According to the present invention, the engine speed rapidly drops to the idle speed after the accelerator pedal is revved up, so that the amount of fuel supplied by the air-fuel ratio control means is corrected. If the calculated value becomes inappropriate, stall can be prevented by correcting the fuel supply amount from the original amount and making the air-fuel ratio appropriate.

To explain with reference to the drawings below, air from an air cleaner (not shown) is measured by an air flow meter 10, passes through a throttle valve 12, a surge tank 14, and fuel from a fuel injection valve 16, and passes through an intake valve 18 into a combustion chamber. Enter 20. Exhaust gas is taken out from the combustion chamber 20 through an exhaust valve 22 to an exhaust manifold 24. Distributor 26 distributes ignition current to spark plugs 27 .

Reference numeral 28 denotes a control circuit built in a microcomputer for controlling the operation of the internal combustion engine, into which signals from various sensors representing the engine operating state are input. That is, the air flow meter 10 described above generates a signal representative of the intake air amount Q. The intake air temperature sensor 32 detects the intake air temperature THA. A cooling water temperature sensor 34 is provided in the engine cooling water jacket and detects the cooling water temperature THA. The rotation angle sensor 36 generates a pulse signal corresponding to the rotation speed N of the rotation shaft of the distributor 26. Additionally, an oxygen concentration sensor 38 is provided within the exhaust pipe 24 and generates an air/fuel ratio signal. idle switch 3
9 detects when the throttle valve 12 is fully closed. The ignition switch 41 or a switch linked thereto has the role of detecting when the engine is started and ensuring that the control method of the present invention is not executed at the time of start.

FIG. 2 is a block diagram showing the configuration of the control circuit 28. Signals from the air flow meter 10, water temperature sensor 34, and intake air temperature sensor 32 are sent to buffers 42, 43, 44, AD converters 46, 48, and
50 to input port 52. The signal from the oxygen concentration sensor 38 passes through a buffer 54, is compared with the stoichiometric air-fuel ratio by a comparator 56, and enters the input port 52 as a "1" or "0" signal. Rotation angle sensor 36, idle switch 3
9. The signal from the ignition switch 41 enters the input port 52 as a digital signal via buffers 58, 59, and 60. The input port 52 is
It is connected to the ROM 61, RAM 62, MPU 64, and flag register 65 via a bus 66. Furthermore, the bus 66 is connected to an output port 68 and a down counter 70. A clock generator 72 timings the operation of the MPU 64 and is connected to a set input of a flip-flop circuit 74, whose reset input is connected to a down counter 70. The output of flip-flop circuit 74 operates fuel injector 16 via amplifier 78.

By the way, if we look at the air-fuel ratio control in the above system, the intake air amount signal from the air flow meter 10, the water temperature signal from the water temperature sensor 34, the intake air temperature signal from the intake air temperature sensor 32, and the rotation speed signal from the rotation speed sensor 36. is stored in a predetermined register of the input port 52. Clock pulse generator 7
2, the MPU 64 takes in data regarding the intake air amount Q, water temperature THW, intake air temperature THA, and rotational speed N stored in the register of the input port 52.

Next, the MPU 64 calculates the fuel injection time t from these
Calculate. The number of pulses corresponding to this fuel injection time t is corrected by the air-fuel ratio signal from the oxygen concentration sensor 38, and then set in the down counter 70 via the output port 68, and the countdown starts from a predetermined crank angle. The flip-flop 74 opens the fuel injection valve 16 via the amplifier 78 to inject fuel.

When a countdown corresponding to the fuel injection time t is performed, the flip-flop 74 is reset, the fuel injection valve 16 is closed, and the next cycle begins.

The above operations are performed by the main routine stored in the ROM 61, but since this itself is well known, detailed explanation will be omitted.

By the way, in the system described above, when the throttle valve is returned to fully closed during engine racing, when the engine speed N decreases as shown in l1 in Fig. ₃ and becomes below the idle setting speed N _O , the fuel will run out.
As m ₁ tends to increase, the air-fuel ratio becomes overbalanced as shown in n ₁ , which may lead to an engine stall as shown in l ₁ '. In order to solve this problem, the present invention detects the racing state and corrects the fuel supply and corrects the air-fuel ratio when the idle rotation speed falls below the set idle speed _N.sub.O. This method will be explained below with reference to the flowcharts of FIGS. 4 and 5.

First, step 100 indicates the start of an interrupt for the air-fuel ratio correction flag setting routine.

In step 101, the MPU 64 looks at the predetermined register of the input port 12 and turns on the idle switch 39.
Check whether is ON or not. If NO, air-fuel ratio correction is unnecessary, so the process goes to step 102, ends the interrupt, and returns to the main routine.

If 101 is YES, the MPU looks at the register of input port 12 at 103 and determines the engine speed N.
Compare the idle set rotation speed N _O stored in the ROM to see if the engine speed has fallen below the idle set speed. If NO, the interrupt ends at 102.

If 103 is YES, it is determined in 104 whether or not it is racing. This judgment is based on the engine speed N
This is done by looking at the rate of descent and determining whether it is steeper than a predetermined value. If it is not racing (NO), go to step 102.

If 104 is YES, ie racing, then 105
In step 2, it is determined whether the initiation switch is ON or not, that is, whether or not the engine is starting. Even during startup, the engine speed N is the idle speed
This is to prevent the method of the present invention from being executed at the time of start-up since the temperature may drop below N _O. YES
If so, it is the time of starting, so go to step 102.

If the answer in step 105 is NO, it is necessary to correct the air-fuel ratio, so a flag is set in step 106, the flag register 65 is set, and step 102
This ends this fuel correction flag setting subroutine.

In FIG. 5, 110 indicates the start of an interruption of the air-fuel ratio correction routine.

In step 111, the MPU 64 checks the flag register 65 and determines whether there is a flag.
If NO, air-fuel ratio correction is not necessary, so 112
ends this subroutine.

If step 111 is YES, step 1
Go to 13th. In this step, the MPU 64 determines whether there is a rotational speed at which the air-fuel ratio should be corrected. If NO, no correction is necessary and the process goes to step 112.

If YES, fuel correction is performed in step 114. As a method of making this correction, for example, as shown in FIG. 6, a correction coefficient for fuel reduction is determined in accordance with the rotational speed, and the down counter 70 is set by multiplying the above-mentioned valve opening time t by this correction coefficient. Therefore, the fuel supply amount is reduced according to the correction coefficient, and air-fuel ratio correction is performed.

The routine of FIG. 5 ends at step 112.

According to the present invention, when the racing speed drops below the idle speed N _O , the fuel amount becomes m ₂ as shown in Fig. 3.
It will be reduced as follows. As a result, the air-fuel ratio is prevented from becoming richer as shown in Figure _n2 , and a sudden drop in rotational speed is avoided as shown in Figure _l2 , and engine stall does not occur.

In addition, although the case where engine stall is prevented by reducing the amount of fuel during racing has been described above, in some types of engines, the air-fuel ratio fluctuates towards the lean side. In this case, 1 in Figure 5
Step 14 involves increasing the amount of fuel, which is also within the scope of the method of the present invention.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram of the system of the present invention, Fig. 2 is a block diagram of the control circuit, Fig. 3 is a graph explaining changes in rotation speed, fuel injection amount, and air-fuel ratio over time during racing, Fig. 4, FIG. 5 is a flowchart showing the device of the present invention, and FIG. 6 is a diagram showing an example of the fuel injection amount correction device. FIG. 7 is a functional block diagram showing the configuration of the present invention. 10... Air flow meter, 12... Throttle valve, 16... Fuel injection valve, 20... Combustion chamber,
28...Control circuit, 39...Idle switch,
41...Ignition switch.

Claims (1)

[Scope of Claims] 1. In an electronically controlled internal combustion engine having an air-fuel ratio control means for controlling the air-fuel ratio to an appropriate air-fuel ratio by controlling the amount of fuel supplied, a first detection means for detecting the idle position of the throttle valve. , a second detection means for detecting the engine rotation speed, a first determination means for determining a state in which the engine rotation speed is equal to or less than a set rotation speed corresponding to the set idle rotation speed during engine idling operation, a decrease in the engine rotation speed; a calculating means for calculating the speed; a second determining means for determining a state in which the rate of decrease in engine speed is greater than a predetermined rate of decrease in engine speed; greater than the speed;
An air-fuel ratio control device for an internal combustion engine, comprising: fuel supply amount correction means for correcting the fuel supply amount to a value for controlling the air-fuel ratio to the appropriate air-fuel ratio when the engine speed is below the set rotation speed. .