JPH0526021B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to an air-fuel ratio control device that detects an unstable state of an internal combustion engine and controls the amount of fuel supplied to the internal combustion engine in accordance with the unstable state. It is.

(Prior Art to the Present Invention) Several methods have already been proposed for detecting an unstable state of an internal combustion engine and operating the internal combustion engine at the misfire limit. For example, in JP-A-58-27837, combustion fluctuations are detected by an engine sensor and the air-fuel ratio is feedback-controlled to the misfire limit air-fuel ratio.
However, due to disturbances such as differences between cylinders of internal combustion engines, differences in internal combustion engines, and torque fluctuations transmitted from the road surface,
It is extremely difficult to accurately identify the misfire limit from the unstable state of an internal combustion engine due to a lean air-fuel ratio.
Furthermore, when the air-fuel ratio exceeds the misfire limit, drivability and exhaust emissions deteriorate rapidly. Considering these points, it is extremely dangerous to operate an internal combustion engine at the misfire limit.

(Object of the present invention) In view of the above-mentioned problems, the present invention provides an air-fuel ratio control device for an internal combustion engine that detects the misfire limit in a short time and constantly operates the internal combustion engine at an air-fuel ratio that is over-concentrated by a predetermined amount above the misfire limit. It is intended for the purpose of providing.

(Characteristics of _the present invention) The present invention provides an electronically controlled internal combustion engine that has a roughness sensor that detects an unstable state of the internal combustion engine. The air-fuel ratio is step-changed to the lean side (misfire limit detection signal) with a change amount (ΔA/F ₃ ) that is within the range of 100%, and the roughness sensor output after the misfire limit detection signal is generated, that is, the unstable state of the internal combustion engine is detected. If the instability is less than the set value, the control air-fuel ratio is shifted to the lean side by a predetermined amount ΔA/F ₁ , and when it is above the set value, the control air-fuel ratio is shifted to the rich side by a predetermined amount ΔA/F ₂ . By shifting, the control air-fuel ratio, which is the basis of the operation of the internal combustion engine, is always kept on the rich side by a predetermined amount ΔA/F ₃ (+ΔA/F ₂ −ΔA/F ₁ ) from the misfire limit.

(One Embodiment of the Present Invention) FIG. 1 is a block diagram showing one embodiment of the apparatus of the present invention. The engine 1 is a known spark ignition engine mounted on an automobile, and takes in combustion air through an air cleaner 2, an intake pipe 3, and a throttle valve 4. Further, the output of the computer 3 causes the electromagnetic fuel injection valve 5 to open and supply fuel to each cylinder. The exhaust gas after combustion is released into the atmosphere through the exhaust manifold 6, exhaust pipe 7, etc. The intake pipe 3 detects the amount of intake air taken into the engine 1,
A potentiometer type intake air amount sensor 8 that outputs an analog signal according to the amount of intake air is installed. Also installed is a thermistor-type intake air temperature sensor 9 that detects the intake air temperature and outputs an analog signal according to the intake air temperature. Further, a thermistor-type water temperature sensor 10 that detects the coolant temperature and outputs an analog signal according to the coolant temperature is installed in the engine 1, and a rotation speed (number) sensor 11 is installed in the engine 1.
detects the rotational speed of the crankshaft and outputs a pulse signal with a frequency corresponding to the rotational speed. This rotational speed sensor 11 generates a pulse when each cylinder has a set crank angle. The throttle valve is also provided with a throttle sensor 12 that detects that the throttle opening is below a set value. Further, the engine 1 is provided with a roughness sensor 14 that detects an unstable state of the engine and outputs an analog signal corresponding to the unstable state. computer 13
The circuit calculates the fuel injection amount based on the detection signals of the sensors 8-12 and 14, and adjusts the fuel injection amount by controlling the opening time of the electromagnetic fuel injection valve 5.

FIG. 2 shows the configuration of the computer 13.
100 is a microprocessor (MPU) that calculates the fuel injection amount. Reference numeral 101 denotes a rotational speed counter, which inputs the signal from the rotational speed sensor 11 and counts the number of detected pulses to create rotational speed data, and also outputs an interrupt command signal to the interrupt control 102 in synchronization with the engine rotation. send. When the interrupt control section 102 receives the interrupt command signal, it operates to output an interrupt signal to the microprocessor 100 through the common bus CB. 103 is a digital input port, which inputs digital signals of a starter signal from a starter switch (not shown) and a throttle opening signal from the throttle sensor 12 to the microprocessor 1.
00. 104 is an analog input port consisting of an analog multiplexer and an A-D converter, which converts each detection signal from the intake air amount sensor 8, intake air temperature sensor 9, cooling water temperature sensor 10, and roughness sensor 14 from A to D, and sequentially outputs the data. MPU1
It has a function to import into 00. The power from the battery 15 is supplied to the power supply circuit 1 via the key switch 16.
06, and this power supply circuit 106 supplies power to other circuits and devices within the computer 13.
The RAM 107 is a temporary storage unit used during program operation, and a correction amount K for fuel injection, which will be described later, is stored in this RAM 107. 10
Reference numeral 8 denotes a read-only memory (ROM) that stores programs, various quantitative determinations, and the like. 109 is a fuel injection control counter including a register, which is composed of a down counter and converts the digital signal representing the opening time of the electromagnetic fuel injection valve 5 calculated by the MPU 100, that is, the fuel injection amount into the actual opening time of the injection valve. Convert to a pulse signal with a pulse time width (duty ratio) that gives . Reference numeral 110 represents a power amplification unit that receives a pulse signal for opening the valve and drives the electromagnetic fuel injection valve 5, and reference numeral 111 represents a timer that measures elapsed time and transmits it to the MPU 100.

That is, the rotational speed counter 101 measures the engine rotational speed at each compression top dead center of each cylinder, for example, based on the detection signal of the rotational speed sensor 11, and performs interrupt control every time the measurement ends or every one engine rotation. An interrupt command signal is supplied to section 102. The interrupt control unit generates an interrupt signal in response to the interrupt command, and causes the MPU 100 to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 3 shows a schematic flowchart of a control program of the MPU 100 for air-fuel ratio control, and the overall operation of the computer 13 will be explained using this flowchart.

First, when the key switch 16 and the starter switch are turned on and the engine is started, a start command is issued from a first step 120, and the main routine arithmetic processing is started. And step 121
Initialization is executed in step 122, and then, in step 122, the intake temperature data detected by the intake temperature sensor 9, the cooling water temperature data detected by the cooling water temperature sensor 10, and the roughness sensor 14 are Data indicating the detected unstable state of the engine is input to the MPU 100 via the analog input port 104, and throttle opening data detected by the throttle sensor 12 is input to the MPU 100 via the digital input port 103. is RAM
107. Then, the process proceeds to step 123, and from the data of the engine intake air temperature, cooling water temperature, and throttle opening obtained in step 122, a first correction amount K for controlling the increase/decrease of fuel during cold and transient conditions is determined. ₁ is calculated and RAM1
07. Next, the process proceeds to step 124, where a second test is performed based on the output data of the roughness sensor 14 that indicates the unstable state of the engine, which was acquired in step 122.
A correction amount K ₂ is calculated and stored in the RAM 107. A detailed flowchart of step 124 is shown in FIG. In step 124, it is first determined in step 200 whether or not the current period is for monitoring the roughness sensor signal. This roughness sensor signal monitoring period refers to a predetermined period of time after a misfire limit detection signal, which will be described later, is generated. If the current time is the period during which the roughness sensor signal should be motorized, the process advances to step 201 and to step 122.
The output data of the roughness sensor 14 taken in is compared with the set value, and if it is smaller than the set value, the process of step 124 is directly terminated, and if it is larger than the set value, the process proceeds to step 202 and the roughness judgment flag is set to "1". , and stores it in the RAM 107, and the process of step 124 ends. Also, step
If the current time is not the period during which the roughness sensor signal should be monitored in step 200, the process proceeds to step 203, where it is determined whether the current time is immediately after the end of the monitoring period. If the current time is not immediately after the end of the monitor period, proceed to step 204 and set the roughness judgment flag to "0".
is set and stored in the RAM 107, and the process of step 124 is completed. That is, in the process of steps 200 to 204, if the engine exhibits an unstable state immediately after the end of the monitoring period, during the monitoring period, that is, during a predetermined period after the occurrence of the misfire limit detection signal, the roughness determination flag is set to " It will be set to 1, and if it is in a stable state, it will be set to 0. Therefore, if it is determined in step 203 that the current time is immediately after the end of the monitoring period, the process proceeds to step 205, where it is determined whether the roughness flag is "1" or "0". If the flag is determined to be "0" here,
That is, if the engine is in a stable state for a predetermined period after the misfire limit detection signal is generated, the second correction amount _K2 is decreased by _ΔK1 in step 206. If the roughness determination flag is determined to be "1" in step 205, that is, if the engine is in an unstable state for a predetermined period after the misfire limit detection signal is generated, the process proceeds to step 207, where _K2 is reduced by _ΔK2 . Then, in step 208, it is determined whether the K ₂ is greater than "1.0". If it is less than "1.0", K ₂ is left unchanged, and if it is greater than "1.0", the step
Set K ₂ to "1.0" in 209. As mentioned above, the second correction amount K ₂ is a value of "1.0" or less, and the correction amount for the hourly air-fuel ratio of "1.0" is "0", and the smaller the value is less than "1.0", the leaner the air-fuel ratio is. Correct to the side. As described above, in step 124 of Fig. 3, the second correction amount is
K ₂ is calculated and stored in RAM 107.

As mentioned above, while steps 122 to 124 of the main routine are repeatedly executed,
When an interrupt signal is input from the interrupt control section 102 to the MPU 100, an interrupt routine starting from step 130 is immediately executed, as shown in FIG. Here, first, in step 131, the engine rotational speed N is input from the rotational speed counter 101.
Then, the process proceeds to step 132, where a signal representing the intake air amount Q sent from the intake air amount sensor 8 via the analog input port is taken in and stored in the RAM 107. Next, in step 133, it is determined whether or not it is the fuel injection time, and if it is not the injection time, the process branches to step 138 and returns to the main routine. If it is the injection time, then in step 134, the basic fuel injection amount (that is, the injection time width t of the electromagnetic fuel injection valve 5) determined from the engine speed N and the intake air amount Q is calculated. The calculation formula is as follows.

t=F×Q/N (F: constant) Next, in step 135, a third fuel injection amount correction amount _K3 for detecting the misfire limit is calculated.
It is stored in RAM107. A detailed flowchart of step 135 is shown in FIG. step 135
First, in step 300, it is determined whether or not it is now time to generate a misfire limit detection signal. The misfire limit detection signal refers to an operation that instantaneously changes the fuel injection amount to the lean side using a third correction amount _K3 , which will be described later, and this operation occurs at a predetermined cycle that does not impair engine drivability. I am made to do so. If it is determined in step 300 that it is not the time to generate the misfire limit detection signal, the third correction amount _K3 is set to "1.0" and stored in the RAM 107 in step 301. Note that the relationship between the correction amount _K3 and the air-fuel ratio is the same as that of the correction amount _K2 . If it is determined in step 300 that the current time is the time to generate the misfire limit detection signal, then in step 302 the correction amount _K3 is set to a predetermined value less than "1.0", that is, in this embodiment, "0.9",
Furthermore, in step 303, a roughness sensor signal monitoring period is set.

As described above, the monitoring period is a predetermined period after the misfire limit detection signal is generated, and includes a period in which the influence of the air-fuel ratio being changed to the lean side by the correction amount _K3 appears on the combustion state of the engine. Note that the period for generating the misfire limit detection signal and the value of the correction amount _K3 at that time are set in advance within a range that does not impair the drivability of the vehicle. After the third correction amount K ₃ is determined in step 135 in FIG. 3 as described above, in step 136, the fuel injection correction amounts K ₁ and K ₂ determined in the main routine and determined in the interrupt handling routine are calculated. The correction amount _K3 is stored in RAM1
Correction calculation of the injection amount (injection time width) which determines the air-fuel ratio is read from 07. Injection time width T
The calculation formula is as follows.

T=t×K ₁ ×K ₂ ×K ₃ Next, the process proceeds to step 137, where the corrected and calculated fuel injection amount data is set in the counter 109. The program then proceeds to step 138 to return to the main routine.
When returning to the main routine, the process returns to the processing step at which it was interrupted due to interrupt processing.

FIG. 6 shows the behavior of the air-fuel ratio and engine instability (ie, roughness sensor signal) due to the above operation. In FIG. 6, _TR is the misfire limit detection signal generation period, and the change in the air-fuel ratio due to the correction amount _K3 at this time is ΔA/ _F3 . Further, T _M after T _R is the roughness sensor signal monitoring period, and the amount of change in the air-fuel ratio due to the increase/decrease ΔK ₁ and ΔK ₂ of the second correction amount K ₂ according to the roughness sensor signal state during this period is ΔA/ Of F ₁ and ΔA/F ₂ , the change in air-fuel ratio ΔA/F ₃ due to the correction amount K ₃ corresponds to the first predetermined amount of the present invention, and the change in air-fuel ratio due to increase/decrease ΔK ₁ ΔA/F ₁ corresponds to the second predetermined amount of the present invention, and the air-fuel ratio change ΔA/F ₂ due to the increase/decrease ΔK ₂
corresponds to the third predetermined amount of the present invention, and as is clear from FIG. 6, ΔA/F ₃ >ΔA/F ₁ , ΔA/F ₃ >
The relationship is ΔA/F ₂ .

The roughness sensor 14 corresponds to the first means of the present invention, steps 300 and 302 in FIG. 5 correspond to the second means of the present invention, and steps 200 and 302 in FIG.
201 corresponds to the third means of the present invention, steps 205 and 206 in FIG. 4 correspond to the fourth means of the present invention,
Steps 205 and 207 in FIG. 4 correspond to the fifth means of the present invention.

As described above, according to the present invention, the control air-fuel ratio, which is the basis of engine operation, is always adjusted by a predetermined amount ΔA/F ₃ from the misfire limit.
It becomes possible to maintain the concentration on the over-concentrated side by +ΔA/F ₂ −ΔA/F ₁ .

In the embodiment described in FIG. 4, the roughness sensor output is valid only during the roughness sensor signal monitoring period, but in other embodiments, the roughness sensor output is monitored even during periods other than the monitoring period, and the roughness sensor output is The air-fuel ratio is controlled only to the rich side depending on the situation. Fourth example of the above embodiment
A detailed flowchart of another embodiment corresponding to the figure is shown in FIG. That is, in step 203, it is determined that the roughness sensor signal monitoring period has not just ended, and in step 204, the roughness determination flag is set to "0".
After setting, proceed to step 210 and step
Compare the roughness sensor output data captured in 122 with the set value, and if it is smaller than the set value, the correction amount
The calculation process for the correction amount K ₂ is completed with the value K ₂ unchanged, and if it is greater than the set value, the process branches to step 207 and the correction amount K ₂ is increased by ΔK ₂ .

(Effects of the Invention) The present invention has a configuration in which a control signal indicating a control value that increases or decreases the control air-fuel ratio by a predetermined value is applied to the fuel injection valve in response to a detection signal etc. from a roughness sensor that detects an unstable state of the engine. Therefore, the control air-fuel ratio, which is the basis of engine operation, is always determined by subtracting a second predetermined amount smaller than the first predetermined amount or adding a third predetermined amount smaller than the first predetermined amount from the first predetermined amount. This makes it possible to keep the internal combustion engine on the rich side from the misfire limit by a certain amount, thereby avoiding operation of the internal combustion engine at the misfire limit due to a lean air-fuel ratio.
This has the effect of preventing a sudden deterioration in driving performance and exhaust emissions that occurs when the air-fuel ratio exceeds the misfire limit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is a diagram showing the configuration of the microcomputer in Fig. 1, Fig. 3 is a flowchart of the control program of the microcomputer regarding air-fuel ratio control, and Fig. 4 is a diagram showing the calculation process of the correction amount K ₂ in Fig. 3. FIG. 5 is a flowchart showing the calculation process of the correction amount _K3 in FIG. FIG. 7 is a flowchart showing the calculation process for the correction amount _K2 in FIG. 11...Speed sensor, 12...Throttle opening sensor, 13...Computer, 14...Roughness sensor.

Claims (1)

[Claims] 1 In an engine air-fuel ratio control device, there is a first means for detecting the degree of instability of the combustion state of the engine, and a first means for detecting the degree of instability of the combustion state of the engine, and a first means for detecting the degree of instability of the combustion state of the engine. a second means for changing the air-fuel ratio toward the lean side by a first predetermined amount that does not impair the air-fuel ratio; and a third means for detecting the degree of instability of the engine caused by the short-term air-fuel ratio change. means for shifting the controlled air-fuel ratio to the lean side by a second predetermined amount smaller than the first predetermined amount when the detected degree of instability is below a set value; and a fifth means for shifting the controlled air-fuel ratio to the enriched side by a third predetermined amount smaller than the first predetermined amount when the degree of instability exceeds a set value, which is the basis of engine operation. The control air-fuel ratio is always kept on the rich side from the misfire limit by an amount obtained by subtracting the second predetermined amount from the first predetermined amount or adding the third predetermined amount from the first predetermined amount. An engine air-fuel ratio control device.