JPS6217657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for feedback controlling the air-fuel ratio state of an internal combustion engine using signals from an air-fuel ratio sensor.

An air-fuel ratio sensor (hereinafter referred to as A/F sensor) that detects the air-fuel ratio state of the engine in the exhaust system of the internal combustion engine;
For example, an air-fuel ratio feedback control system that controls the air-fuel ratio state of the engine by installing an oxygen concentration detector that detects the oxygen concentration in exhaust gas and controlling the fuel supply amount or air supply amount according to the detection result is well known. Are known. This type of system is provided with a function to stop air-fuel ratio feedback control when the A/F sensor fails or is inactive. That is, in addition to the normal comparison function that has an A/F comparison level for comparing the output voltage of the A/F sensor and performing feedback control of the air-fuel ratio based on the result, there is also a function for knowing the activation state of the A/F sensor. A monitor comparison function is provided having a monitor comparison level. This monitor comparison level is set to a value smaller than the A/F comparison level. If the output voltage of the A/F sensor continues to be higher than this monitor comparison level for a predetermined period of time, the A/F sensor is considered inactive, and the air-fuel ratio feedback control is forcibly stopped. In other words, it becomes open loop control. If the A/F sensor's temperature is low and its activity is poor, the response delay will be large, especially when the air-fuel ratio state of the atmosphere changes from the rich side to the lean side with respect to the stoichiometric air-fuel ratio (hereinafter referred to as rich → lean change). Become. Therefore, in such a case, by using open-loop control as described above, the air-fuel ratio is significantly controlled in a lean direction, thereby eliminating the possibility of deterioration of driving characteristics or even stalling of the engine.

However, this type of feedback control system has the following problems. in general,
There is a difference between the air-fuel ratio state where the output voltage of the A/F sensor is reversed and the air-fuel ratio state where the purification efficiency of the catalytic converter is optimal. An operation is often performed to increase the delay time or skip width of the output voltage to shift the center of the air-fuel ratio after feedback control toward the rich side. In such a case, when the engine is at high rotational speed or under high load, the flow rate of the gas used for combustion becomes faster, or the temperature of the A/F sensor becomes higher, which shortens the reaction delay time. The frequency of the output becomes significantly higher,
As a result, the output voltage of the A/F sensor does not fall below the monitor comparison level, and the aforementioned feedback control stop function is activated. That is, in this case,
Even though feedback control is desired, it is stopped and becomes open loop control.

Therefore, the present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to solve the above-mentioned problems of the prior art. An object of the present invention is to provide an air-fuel ratio control method that can prevent switching to open-loop control.

A feature of the present invention that achieves the above-mentioned object is to compare the output signal value of an air-fuel ratio sensor that detects the air-fuel ratio state of the internal combustion engine with a first reference value, and to determine the air-fuel ratio state of the engine according to the comparison result. and the output signal maintains a value representing an air-fuel ratio state on the leaner side than the first reference value and a value representing an air-fuel ratio state on the richer side than the second reference value for a predetermined period of time or longer. In this case, in the air-fuel ratio control method in which the feedback control is stopped, the second reference value is changed when the engine is in a high rotation speed operating state or a high load operating state.

The present invention will be explained in detail below using the drawings.

FIG. 1 shows a block diagram of a fuel injection control system for an internal combustion engine as an embodiment of the present invention. In the figure, 10 is an air flow sensor that generates an intake air amount signal having an analog voltage level corresponding to the intake air amount of the engine, and 11 is a water temperature sensor that generates a water temperature signal having an analog voltage level corresponding to the cooling water temperature. 12 is a crank angle sensor that generates a pulse at each predetermined crank angle position of the engine, for example, every 30° or 180° from a crank angle position of 0°, and 13 is installed in the exhaust system of the engine to detect exhaust gas. This is an A/F sensor that outputs a signal depending on the concentration of a specific component, for example, an oxygen component.

This A/F sensor 13 detects when the engine air-fuel ratio is on the rich side (rich side) than the stoichiometric air-fuel ratio.
It outputs a rich signal of about 1V, and a lean signal of about 0.1 to 0.2V when it is on the lean side. In FIG. 1, 14 is a fuel injection solenoid valve provided for each cylinder or a plurality of cylinders in the intake system of the engine.

Signals from each of the above-mentioned sensors 10 to 13 as well as sensors (not shown) are sent to an electronic control unit 15 including a microcomputer, which calculates the optimal fuel supply amount according to the operating condition of the engine, and finally controls the fuel injection valve. The air-fuel ratio control is performed by controlling the injection time of 14.

Next, the configuration of this electronic control unit 15 will be described. 16 is an analog multiplexer that selects a signal from one of the sensors 10 and 11, as well as a sensor (not shown); 17 is an analog signal selected by the multiplexer 16; A/D converter that converts signals into digital signals,
18 is a gate circuit which is controlled to open and close by a pulse sent from the crank angle sensor 12, for example every 30 degrees of crank angle, and which controls the passage of a clock applied via a line 19; A count and latch circuit 21 counts and stores data corresponding to the result and therefore the reciprocal of the engine rotational speed; 21 is the A/F sensor 13;
After comparing the output signal level and the first reference level (A/F comparison level) to form rich and lean signals of "1" and "0", an A/F inversion point pulse is generated at their inversion point. and sends each inversion point pulse to the interrupt latch circuit 24, and compares a second reference level (monitor comparison level) smaller than the first reference level with the output signal level of the A/F sensor 13, Comparing and discriminating circuits are shown which form falling and rising monitor inversion point pulses and send them to the timer circuit 23 when the output signal level crosses the monitor comparison level from top to bottom or from bottom to top.

The above-mentioned monitor comparison level of the comparison/discrimination circuit 21 is selectively changed according to the signal applied from the input/output port 22.

The timer circuit 23 is reset by the falling monitor inversion point pulse applied from the comparison/discrimination circuit 21, and is reset to the line 19 by the rising monitor inversion point pulse.
This is a counter circuit that starts counting the clocks applied through the A/F sensor 13, and creates data corresponding to the duration T when the output signal level of the A/F sensor 13 continuously exceeds the monitor comparison level. The signal is configured to be sent to the input port 25.
Furthermore, in FIG. 1, 26 is an output port where output data corresponding to one injection time τ of the fuel injection valve 14 is stored, and 27 is an output port that forms an injection signal having a pulse width according to the output data. Reference numeral 28 indicates an output control circuit that outputs an injection signal in synchronization with the crank angle pulse sent through the crank angle pulse, and 29 indicates a power amplification circuit for the injection signal.

multiplexer 16, A/D converter 17,
Count and latch circuit 20, input/output port 2
2. The input port 25, the interrupt latch circuit 24, and the output port 25 are connected via a common bus 30 to an I/O port that includes a memory 31 such as RAM and ROM, a central processing unit (CPU) 32, and a clock generation circuit that constitute the microcomputer. 0 and the memory control device 33.

A calculation program related to fuel injection time and the like is stored in the ROM of the memory 31, and when an initialization signal is applied to the CPU 32, calculation processing based on this calculation program is started. In this case, the signals from sensors 10 and 11 are
Multiplexer 16 and A/D converter 1 in response to a time-synchronized interrupt signal generated at predetermined intervals.
7 is controlled, they are converted into intake air amount data Q and water temperature data, respectively, and are stored in the RAM of the memory 31.
stored within. Further, data 1/N regarding the rotational speed stored in the count and latch circuit 20
is stored in the RAM of the memory 31 at every predetermined crank angle.

FIG. 2 is a circuit diagram showing an example of the configuration of the comparison/discrimination circuit 21 shown in FIG. 1. In the same figure, 13 is A/
F sensor, 40 a comparator with an A/F comparison level, 41 a comparator with a monitor comparison level, 4
2 and 43 are pulse generators that generate A/F inversion point pulses at the rising and falling points of the output of the comparator 40, that is, the inversion points of the rich and lean signals, respectively; 4;
Reference numerals 4 and 45 indicate pulse generators that generate monitor inversion point pulses at the rising and falling points of the output of the comparator 41, that is, at the inversion points, respectively. Pulses output from pulse generators 42 and 43 are sent to the interrupt latch circuit 24 mentioned above, and pulses output from pulse generators 44 and 45 are sent to timer circuit 23, respectively.

When the signal applied from the input/output port 22 via the line 46 is at a low level, the monitor comparison level of the comparator 41 is kept at a constant value smaller than the A/F comparison level of the comparator 40, but the input/output port When the signal from 22 becomes high level, transistor 47 is turned on and voltage dividing resistor 48 is shorted, so that the monitor comparison level increases by a predetermined value. The increased monitor comparison level is not limited to this, but may match the A/F comparison level, for example.

Next, the operation of this embodiment will be explained.

When a crankshaft synchronization interrupt signal is sent from the interrupt latch circuit 24 at each predetermined crank angle position, the CPU 32 performs arithmetic processing regarding the fuel injection time τ. That is, the following calculation process is performed: τ=Q/N・K・(A/F)・R+τ〓. However, in the above equation, (A/F) is an air-fuel ratio feedback coefficient, R is another correction coefficient such as warm-up correction, and τ is an invalid injection time correction coefficient of the fuel injection valve. The output data regarding the calculated fuel injection time τ is sent to the output control circuit 27 via the output port 26 as described above, and becomes a fuel injection signal to control the opening time of the fuel injection valve 14. As a result, the engine air-fuel ratio feedback control is performed.

The air-fuel ratio feedback coefficient (A/F) is calculated based on the signal sent from the comparison/discrimination circuit 21, and this calculation process will be described in the flowcharts of FIGS. 3 and 4 and 5 below.
This will be explained using the waveform diagram shown in the figure.

When the A/F inversion point pulse is applied from the comparison/discrimination circuit 21 via the interrupt latch circuit 24,
The CPU 32 performs the interrupt processing shown in FIG. First, in step 50, the interrupt is set to lean→
It is determined whether the interrupt is an interrupt at the time of a rich change or an interrupt at the time of a change from rich to lean. If the interrupt is from lean to rich, the process proceeds to step 51, and if it is the rich to lean interrupt, the process proceeds to step 52. Step 5
1, the feedback coefficient (A/F)
is decreased by a constant A, and as a result, skip control of the air-fuel ratio at the time of change from lean to rich (fifth
Part a of Figure A) is performed. On the other hand, step 5
In 2, the feedback coefficient (A/F)
is increased by a constant B, and as a result, skip control of the air-fuel ratio at the time of rich → lean change (fifth
Part b in Figure A) is performed. When the processing in step 51 or 52 is completed, the program returns to the main routine.

After the interrupt processing shown in FIG. 3 is executed, a time interrupt signal is sent to the interrupt latch circuit 24 at predetermined intervals.
This causes the CPU 32 to execute the time interrupt process shown in FIG. That is, first, in step 60, it is determined whether data N representing the actual rotational speed of the engine has exceeded a predetermined value, that is, whether the engine has reached a high rotational speed. If the rotation speed is not high, the process advances to step 61, and the data of the duration T given by the timer circuit 23, that is, the data of the time T during which the output signal level of the A/F sensor 13 is equal to or higher than the monitor comparison level, is It is determined whether or not it is larger than a predetermined value D. T/D
In this case, the A/F sensor 13 is assumed to be in an active state, and normal air-fuel ratio feedback control is performed.

That is, in step 62, it is determined whether a rich signal or a lean signal is currently being output. If the lean→rich interrupt process is performed and the rich signal is output, the process advances to step 63, where the feedback coefficient (A/F) is decreased by a predetermined value E, and the process returns to the main routine. After the next time interrupt processing, if this step 63 is repeated, (A/F) becomes the fifth
The fuel injection amount gradually decreases as shown in c in Figure A, and as a result, the fuel injection amount gradually decreases and the air-fuel ratio is controlled in a lean direction. In the case of rich→lean interrupt processing, the feedback coefficient (A/F) is increased by a predetermined value E in step 64, and when the processing in step 64 is repeated,
(A/F) gradually increases as shown in d of FIG. 5A, and as a result, the air-fuel ratio is controlled in the rich direction. In addition, FIG. 5A shows the output signal e of the A/F sensor 13 and the air-fuel ratio feedback coefficient (A/F) when the engine is at a light load and low rotational speed and the A/F sensor 13 is active. It represents. In the same figure, the A/F comparison level and g represent the monitor comparison level.

When the engine is in a light load, low rotational speed operating state and the A/F sensor 13 is inactive, the level of the output signal e of the A/F sensor 13 is at the monitor comparison level g, as shown in FIG. 5B. Always bigger. As a result, when the aforementioned duration time T counted by the timer circuit 23 becomes equal to or greater than the predetermined value D, this is determined in step 61 and the program branches to step 65. In step 65, (A/F) is made equal to 1, thereby stopping air-fuel ratio feedback control. In other words, it becomes open loop control.

Next, a case where the engine is in a high rotational speed operating state will be explained. As shown in FIG. 5C, when the skip control amount of the feedback coefficient (A/F) is symmetrical, that is, steps 51 and 5 shown in FIG.
If the constants A and B in 2 are equal to each other, then
Even if the engine reaches high rotational speed and the A/F sensor 1
Even if the frequency of the output signal of 3 becomes high, this A/
Since there is a period in which the value of the output signal e of the F sensor 13 is lower than the monitor comparison level g, open loop control will not occur erroneously.

As shown in FIG. 5D, when asymmetric skip control is performed, according to the prior art, the A/F sensor 13
There is a possibility that the output signal e of the motor always becomes larger than the monitor comparison level g in a high rotational speed operating state. However, in this embodiment, step 60
If it is determined that the engine rotational speed has reached a high rotational speed exceeding the predetermined value c, the process proceeds to step 66, where control is performed to increase the monitor comparison level.
Specifically, in step 66, the signal sent from the input/output port 22 to the comparison/discrimination circuit 21 via the line 46 is inverted to a high level. This turns on the transistor 47 in FIG. 2, and the resistor 4
8 is shorted, and the monitor comparison level of comparator 41 rises. For example, as shown in FIG. 5D, the monitor comparison level is increased from g to g'. Therefore, according to this embodiment, in a high rotational speed operating state in which the A/F sensor 13 is considered to be fully activated, open loop control is performed even though feedback control of the air-fuel ratio is desired. This can prevent such inconvenient situations from occurring.

Although the method of the present invention has been described above using a swiped program digital fuel injection control system, the present invention can also be achieved using an analog fuel injection control system. below,
An embodiment of the latter system will be described using the block diagram of FIG.

In FIG. 6, air flow sensor 10, A/
The F sensor 13, fuel injection valve 14, comparators 40 and 41, voltage dividing resistor 48, and transistor 48 are exactly the same as those shown in FIGS. 1 and 2. Further, in FIG. 6, 70 is a rotational speed sensor that generates an analog voltage according to the rotational speed of the engine. By sending the rotational speed signal obtained from the sensor 70 and the intake air amount signal obtained from the air flow sensor 10 to the calculation circuit 71, part of the calculation processing τ ₀ =Q/N·K regarding the fuel injection time τ is performed. be exposed. The output of the arithmetic circuit 71 is sent to the increase correction circuit 72, and in this circuit 72, the value (A/F) of the air-fuel ratio feedback signal sent from the integrator 73 is further multiplied by a constant R, and further, the invalid injection time τ is corrected. Finally, an injection signal having a pulse width corresponding to the fuel injection time τ is formed. This injection signal is transmitted to the power amplifier circuit 7.
4, the injection valve 14 is energized and the amount of fuel corresponding to the calculated fuel injection time τ is supplied to the engine. The detailed configuration and operation of the arithmetic circuit 71, increase correction circuit 72, etc. described above are described in, for example, Japanese Patent Application Laid-Open No. 49/1989.
The description is omitted because it is publicly known from Publication No.-67016 and the like.

The output signal level of the A/F sensor 13 is
0 is compared with the A/F comparison level, and the integration direction of the integrator 73 is controlled according to the comparison result, thereby forming an air-fuel ratio feedback signal. However, in this embodiment, the skip control circuit is omitted.

The output signal level of the A/F sensor 13 is
When the monitor comparison level of 1 is exceeded, the output of the comparator 41 becomes high level, and the capacitor 75 connects to the resistor 76.
is gradually charged by the current flowing through it. When the output signal level of the A/F sensor 13 exceeds the monitor comparison level for a predetermined time or more, the terminal voltage of the capacitor 75 becomes higher than the comparison reference voltage of the comparator 77, and as a result, the transistor 78 turns on. Become. As a result, the integrating capacitor 73a of the integrator 73 is short-circuited, and the output of the integrator 73, that is, the air-fuel ratio feedback signal, becomes a constant value, resulting in open loop control.

When the engine is in a high rotational speed operating state, the output voltage of the speed sensor 70 becomes higher than the comparison reference voltage of the comparator 79, and as a result, the transistor 47 is turned on and the voltage dividing resistor 48 is short-circuited. As a result, the monitor comparison level of the comparator 41 increases.
The effects of this embodiment are the same as those of the previous embodiment, and therefore their explanation will be omitted.

In the embodiment described above, the monitor comparison level is raised when the engine speed increases, but this is to change it to the stoichiometric air-fuel ratio level, and it depends on the characteristics of the A/F sensor etc. may be lowered. Furthermore, the monitor comparison level may be raised or lowered even when the load on the engine becomes high. Furthermore, the monitor comparison level may be raised or lowered when either the rotational speed or the load becomes higher. In addition, as a method of detecting that the engine has become under high load, it is also possible to detect that the negative pressure in the intake passage downstream of the throttle valve has fallen below a predetermined value, or to detect that the opening degree of the throttle valve has exceeded a predetermined value. It may also be possible to detect that this has occurred. Furthermore, it may be detected that the intake air amount or speed of the engine exceeds a predetermined value.

As explained in detail above, the method of the present invention changes the monitor comparison level when the engine is operating at high rotational speed or under high load, so that the A/F sensor is not fully activated. There is no fear that the feedback control will be inadvertently set to open-loop control during the above-mentioned operating state, which is considered to be in a state of operation.

The method of the invention also has the advantage that it can be achieved with a very simple construction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
1 is a detailed circuit diagram of a part of FIG. 1, FIGS. 3 and 4 are flowcharts of a part of arithmetic processing in the above embodiment, and FIG. 5 is a waveform diagram explaining the operation of the above embodiment. FIG. 6 is a block diagram of another embodiment of the invention. 10... Air flow sensor, 12... Crank angle sensor, 13... A/F sensor, 14... Fuel injection valve, 15... Electronic control unit, 21... Comparison/discrimination circuit, 23... Timer circuit, 31... ...Memory, 32...CPU, 40, 41, 77, 79...
...Comparator, 47, 78...Transistor, 48...
...Voltage resistance, 70... Rotation speed sensor, 71...
Arithmetic circuit, 72... Increase correction circuit, 73... Integrator, 75... Capacitor, 76... Resistor.

Claims (1)

[Claims] 1 Compare the output signal value of an air-fuel ratio sensor that detects the air-fuel ratio state of the internal combustion engine with a first reference value, and perform feedback control of the air-fuel ratio state of the engine according to the comparison result, and also control the air-fuel ratio state of the engine so that the output signal The feedback control is stopped when a value representing an air-fuel ratio state that is richer than the second reference value, which represents an air-fuel ratio state that is leaner than the first reference value, is maintained for a predetermined period of time or longer. An air-fuel ratio control method for an internal combustion engine, characterized in that the second reference value is changed when the engine is in a high rotation speed operating state or a high load operating state.