JPH0131020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects the air-fuel ratio based on the exhaust components of an engine such as an automobile, and uses this detection signal to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine to a predetermined air-fuel ratio. The present invention relates to an air-fuel ratio control method.

A conventional air-fuel ratio control method involves integrating the output of an air-fuel ratio sensor and performing simple integral control using this integrated signal. Therefore, during transient engine operation, if the basic air-fuel ratio changes faster than the correction speed of the integral control, the correction cannot catch up. Further, when the air-fuel ratio sensor is inactive, feedback control of the air-fuel ratio cannot be performed, and sufficient air-fuel ratio control cannot be performed, resulting in deterioration of exhaust gas. In other words, such a control method is good when the engine is operating in a relatively stable operating state, but it is difficult to learn in other acceleration ranges where a large amount of harmful exhaust gas components are emitted, so the correction speed of integral control is It cannot keep up with fluctuations in the basic air-fuel ratio, resulting in deterioration of exhaust gas. This problem is particularly noticeable in a fuel injection device in which the amount of fuel supplied is programmed based on intake pipe pressure and rotational speed, or in a fuel injection device in which the amount of fuel supplied is programmed based on throttle valve opening and rotational speed.

Also, to elaborate more on the fuel injector when programmed with intake pipe pressure and rotational speed:
The main factors that cause an error between the basic air-fuel ratio and the target air-fuel ratio are (1) changes over time or production variations in the tappet clearance of the engine's intake and exhaust valves, (2) production variations and changes over time in the injector, (3) ) Changes in atmospheric pressure (for example, when driving at high altitudes).

Through investigation, the inventors have found that the errors caused by these three factors vary depending on the operating conditions.

The error due to factor (1) is largest at idle;
The larger the intake pipe pressure is in terms of absolute value, and the higher the rotation, the smaller it is.

The error due to factor (2) becomes larger as the load becomes smaller (lower intake pipe pressure), and becomes smaller as the load becomes larger.

The error due to factor (3) remains the same regardless of the operating conditions.

Therefore, when errors due to three factors occur simultaneously, the error due to factor (1) is dominant in the idle state, and the difference due to factor (2) is dominant in the light load operating state. It was also found that the error due to factor (3) becomes dominant under high-load operating conditions.

The purpose of the present invention is to improve the conventional integral control method of the air-fuel ratio using the output signal of the air-fuel ratio sensor, and to quickly and without delay in response even during engine transients.
The air-fuel ratio can be controlled to a predetermined air-fuel ratio, and even when the air-fuel ratio sensor is inactive when the engine is at low temperature and feedback control cannot be performed, the air-fuel ratio can be accurately controlled based on the engine condition correction amount stored in the storage device. An object of the present invention is to provide a fuel ratio control method.

In the present invention, the predetermined basic fuel injection amount is directly determined by the integral correction value that is obtained by integrating the output signal of the air-fuel sensor and that varies upward and downward around a predetermined value that represents a state that does not require air-fuel ratio correction. Without correction, first, the integral correction value is larger or smaller than the above-mentioned predetermined value for a predetermined operating state of the engine operating range, that is, an idle state, a steady running normal load state, and a steady running high load state. The engine condition correction amount to be decreased or increased is calculated according to the above determination, and the engine condition correction injection amount is calculated by adding these engine condition correction amounts to the basic fuel injection amount. Next, the engine condition correction injection amount is multiplied by the integral correction value to calculate the fuel injection amount, and the injection valve is controlled by a signal representing this fuel injection amount. In this case, each engine condition correction amount is calculated by multiplying the basic fuel injection amount by a coefficient _k2 that decreases or increases around a predetermined reference value depending on whether the integral correction value is larger or smaller than a predetermined value. , is further calculated by multiplying the intake pipe negative pressure by a coefficient C which is inversely proportional to the engine speed, and for steady running normal load conditions, it decreases around a predetermined reference value depending on whether the integral correction value is larger or smaller than a predetermined value. Or, it is calculated by multiplying the basic fuel injection amount by the increasing coefficient _k1 , and for steady running high load conditions, the coefficient decreases or increases around a predetermined reference value depending on whether the integral correction value is larger or smaller than the predetermined value.
The value of k ₃ directly becomes the correction amount.

In addition, the predetermined engine operating state for calculating these correction coefficients k ₂ , k ₁ and k ₃ is that when these coefficients are stored in a storage device, the above-mentioned basic air-fuel ratio has an error with respect to the target air-fuel ratio. Learning control is performed for each factor in the state where its contribution rate is the largest, and a certain amount of sample time is required for this learning. Particularly in the case of automobile engines, idling or constant operating conditions are the most learnable operating conditions. Relatively stable conditions such as when driving through traffic are selected, but for actual correction, the latest correction coefficients k ₂ , k ₁ and k are used in all driving ranges, including transient periods other than these driving conditions. Correction based on ₃ is performed. Therefore, for example, in an idle state, the correction amount is calculated by the most recent coefficients k ₁ and k ₃ stored in addition to the coefficient k ₂ , which is calculated in that state and directly reflects that state, and also in a steady running normal load. In the state, in addition to the coefficient k ₁ calculated in that state, engine state correction is performed using k ₂ and k ₃ calculated and stored in the recent idle state and steady running high load state before transitioning to that state. The amount is calculated. Therefore, even if the operating state of the engine changes from one state to another, the overall correction amount will not change suddenly, maintaining smooth engine operation, and also during transient engine operation. Correction control can also be performed without delay in response.

In addition, since the engine condition correction coefficients k ₂ , k ₁ and k ₃ are stored in the storage device, even if the air-fuel ratio sensor is inactive when the engine is at low temperature, feedback control of the air-fuel ratio can be performed using the stored coefficients. can.

In addition, among the engine condition correction amounts, the idle state correction amount uses coefficient C, which is inversely proportional to intake pipe pressure and rotational speed, at the same time as coefficient _k2 , so the correction amount becomes small in areas of high rotation and load, so the tappet clearance can be reduced. Appropriate corrections can be made in response to changes.

The present invention will be explained below with reference to the drawings.

In FIG. 1, an engine 1 is a known four-stroke spark ignition engine mounted on an automobile, and intakes combustion air through an air cleaner 2, an intake pipe 3, and a throttle valve 4.

Further, fuel is supplied from a fuel system (not shown) through electromagnetic fuel injection valves 5 provided corresponding to each cylinder. The exhaust gas after combustion is discharged into the atmosphere through an exhaust manifold 6, an exhaust pipe 7, and a three-way catalytic converter 8. The pressure downstream of the throttle valve in the intake pipe 3 is measured by a known semiconductor pressure sensor 11 (intake pipe pressure sensor).
Detected by The pressure sensor outputs an analog voltage signal. Furthermore, the intake pipe 3 has an intake air temperature sensor 1 that detects the temperature of the air taken into the engine.
2. A water temperature sensor 13 is installed in the engine 1 to detect the cooling water temperature. Furthermore, the exhaust manifold 6 detects the air-fuel ratio from the oxygen concentration in the exhaust gas, and when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich), it is about 1 volt (high level), and when it is larger than the stoichiometric air-fuel ratio (lean), it is about 0.1 volt. An air-fuel ratio sensor 14 that outputs a low level voltage is installed. The rotational speed sensor 15 detects the rotational speed of the crankshaft of the engine 1 and outputs a pulse signal with a frequency corresponding to the rotational speed. The control unit 20 is a circuit that calculates the fuel injection amount based on the detection signals of the sensors 11 to 15, and controls the opening time of the electromagnetic fuel injection valve 5 to adjust the fuel injection amount.

The control unit 20 will be explained with reference to FIG.

100 is a microprocessor (CPU) that calculates the fuel injection amount. A rotation speed counter 101 counts the engine rotation speed based on a signal from the rotation speed sensor 15. Further, this rotation number counter 101 is synchronized with the engine rotation and the interrupt control unit 10
Send an interrupt command signal to 2. When interrupt control section 102 receives this signal, it outputs an interrupt signal to microprocessor 100 via common bus 150. 103 is a digital input port that inputs digital signals such as an output signal from a comparator that compares the output of the air-fuel ratio sensor 14 with a predetermined ratio level and a starter signal from a starter switch 16 that turns on and off the operation of a starter (not shown) to the microprocessor 100. to communicate.

104 is an analog input port consisting of an analog multiplexer and an A-D converter; an intake pipe pressure sensor 11, an intake air temperature sensor 12, and a cooling water temperature sensor 1.
The microprocessor 100 has a function of converting each signal from the microprocessor 100 into digital data and sequentially reading the signals into the microprocessor 100. Output information from each of these units 101, 102, 103, and 104 is transmitted to the microprocessor 100 through a common bus 150. A power supply circuit 105 supplies power to a RAM 107, which will be described later. 17
18 is a battery, and 18 is a key switch, but the power supply circuit 105 is directly connected to the battery 17 without passing through the key switch 18. I will explain later
Power is constantly applied to the RAM 107 regardless of the key switch 18.

106 is also a power supply circuit, which is connected to the battery 17 through the key switch 18. The power supply circuit 106 supplies power to parts other than the RAM 107, which will be described later. 107 is a temporary storage unit (RAM) that is used temporarily during program operation.
As mentioned above, power is always applied regardless of the key switch 18, and the memory contents are not lost even if the key switch 18 is turned off and the engine operation is stopped, thus forming a non-volatile memory. The engine condition correction coefficients k ₁ , k ₂ , k ₃ described later are also stored in this RAM 10.
7 is memorized.

A read-only memory (ROM) 108 stores programs, various constants, and the like. 10
Reference numeral 9 is a fuel injection time control counter including a register, which is configured to count down, and is operated by a microprocessor (CPU) 100.
A digital signal representing the opening time of the electromagnetic fuel injection valve 5, that is, the amount of fuel to be injected, is converted into a pulse signal having a pulse duration giving the actual opening time of the electromagnetic fuel injection valve 5.

Reference numeral 110 denotes a power amplification unit that drives the electromagnetic fuel injection valve 5. 111 measures the elapsed time with a timer.
The information is transmitted to the CPU 100. Rotation number counter 101
measures the engine rotation speed once per engine rotation based on the output of the rotation speed sensor 15, and supplies an interrupt command signal to the interrupt control section 102 at the end of the measurement. The interrupt control section 102 generates an interrupt signal from the signal, and causes the microprocessor 100 to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 3 shows a schematic flowchart of the microcomputer 100, and the functions of the microcomputer 100 will be explained based on this flowchart. When the key switch 18 and starter switch 16 are turned on to start the engine, the main routine arithmetic processing starts at the start of the first step 1000, initialization processing is executed at step 1001, and analog input port is opened at step 1002. Digital values corresponding to the cooling water temperature and intake air temperature are read from 104. In step 1003, a correction value _k1 is calculated using a known formula based on the result, and the result is
Store in RAM107. In step 1004, the signal of the air-fuel ratio sensor 14 is inputted from the digital input port, and an integral correction value _k2 , which will be described later, is increased or decreased as a function of the elapsed time by the timer 111, and this correction value _k2 is
Store in RAM107. FIG. 4 shows a processing step 1004 for increasing or decreasing this integral correction value _k2 , that is, integrating it.
This is a detailed flowchart. First step
In step 400, it is determined whether the air-fuel ratio detector is activated or whether return control of the air-fuel ratio is possible based on the cooling water temperature, etc., and if return control is not possible, that is, in the case of an open loop, the process proceeds to step 406. The correction value k ₂ is set to k ₂ =1, and the process proceeds to step 405. If return control is possible, proceed to step 401. Step 401
Then, it is determined whether the elapsed time has passed the unit time _Δt1 , and if it has not passed, this process step 1004 is ended without performing the integral process of _k2 . If the time Δt ₁ has elapsed, the process proceeds to step 402, and if the air-fuel ratio is rich and the output of the air-fuel ratio sensor 14 is a rich high level signal, the process proceeds to step 403, where the air-fuel ratio is calculated in the previous cycle. The corrected value k ₂ is decreased by △k ₂ , and the process proceeds to step 405, where the new correction value k ₂ is stored in the RAM 107.
Store in. In step 402, if the air-fuel ratio is lean and the output of the air-fuel ratio sensor 14 is a low level signal indicating lean, the process proceeds to step 404, where _k2 is added by _Δk2 , and the process proceeds to step 405. In this way, the correction value _k2 is increased or decreased. In this way, the integral correction value k ₂ changes above and below a predetermined value representing a state in which air-fuel ratio correction is not required.

In step 1005 of FIG. 3, the coefficients k ₁ , k ₂ , and k ₃ for calculating the engine condition correction amount are increased or decreased.
The result is stored in RAM 107.

In FIG. 5, coefficients k ₁ , k ₂ and k ₃ are processed and stored. That is, this is a detailed flowchart of step 1005 for memory processing.

In step 501, it is determined whether the elapsed time has passed the unit time _Δt2 , and if _Δt2 has not passed, the memory processing step 1005 is ended. If the engine speed has elapsed, the process advances to step 502, where the rotational speed N and intake pipe pressure P stored in the RAM 107 are set to the operating conditions (600<N<900rpm, 200<P<400mm) representing the idle state.
Hg). When the described operating conditions are met, the process proceeds to step 503, where the value of the integral correction value _k2 is determined. If k ₂ =1, nothing is done and this processing step 1005 ends. If k ₂ > 1 in step 503, proceed to step 504; if k ₂ < 1, proceed to step 504.
Proceed to 505. In steps 504 and 505, the coefficient _k2 is
k ₂ is added or subtracted, the newly obtained k ₂ is stored in the RAM 107 in step 506, and the process proceeds to step 1005.
end.

If the stated conditions are not met in step 502, the process proceeds to step 507, where it is determined whether the rotational speed N is within the range of 1400 to 3000 rpm, which represents a steady running condition.If it is not within this range, no processing is performed at step 1005, and the process ends. do. When it is within the range of 1400 to 3000 rpm, the process proceeds to step 508, where it is determined whether the intake pipe pressure P is within the range of 250 to 400 mmHg, which represents the normal load, and when it is within the above range, the process proceeds to step 509. Intake pipe pressure P
is not in the range of 250 to 400 mmHg, the process proceeds to step 513, and the intake pipe pressure P is set to 400, which indicates a high load.
Determine if it is within the range of ~650mmHg. If it is not in the above area, no processing is performed and this step 1005 is ended.

In step 509, the value of the integral correction value _k2 is determined.
If k ₂ =1, nothing is done and this processing step 1005 ends.

If k ₂ >1, proceed to step 510; if k ₂ <1, proceed to step 511. In steps 510 and 511, △ _k3 is added or subtracted from the coefficient _k3 , and the step
In step 512, the newly obtained coefficient _k3 is stored in the RAM 107, and step 1005 is ended.

When the intake pipe pressure P is between 400 and 650 mmHg, the process proceeds to step 514, where the value of the integral correction value _k2 is determined.

If k ₂ =1, nothing is done and this process step 1005
end.

If k ₂ >1, proceed to step 515; if k ₂ <1, proceed to step 516. In steps 515 and 516, △k ₁ is added or subtracted from the coefficient k ₁ , and the step
In step 517, the newly obtained coefficient _k1 is stored in the RAM 107, and step 1005 is ended.

Normally, the main routine processes 1002 to 1005 are repeatedly executed according to the control program. When an interrupt signal for fuel injection amount calculation is input from the interrupt control unit 102, the microcomputer 1
00 immediately interrupts the main routine processing even if it is in progress and moves to the interrupt processing routine at step 1010. In step 1011, revolution counter 1
In step 1012, a signal representing the intake pipe pressure P is taken in from the analog input port 104, and in step 1013, the engine speed N and intake pipe pressure P are input as main signals. For use in routine calculations
Store in RAM107. Next, in step 1014, the basic fuel injection amount T _P (that is, the injection time width of the electromagnetic fuel injection valve 5), which is preprogrammed in the ROM 108 as a two-dimensional map of the engine speed N and the intake pipe pressure P, is interpolated. Calculate and find. Next, in step 1015, various correction values and correction coefficients for fuel injection obtained in the main routine are
It reads out from the RAM 107 and performs correction calculation of the injection amount (injection time width) that determines the air-fuel ratio. The calculation formula for the injection time width T is T={(1+k ₁ +k ₂ *C)*T _P +k ₃ }*k ₁ *k ₂ .

As can be seen from this formula, (1+k ₁ +k ₂ *C) *T _P +k ₃ is an engine that adds the engine condition correction amount calculated based on the three correction coefficients k ₁ , k ₂ , and k ₃ to the basic injection amount. It represents the state correction injection amount, of which k ₁ *T _P is the steady running high load state correction amount, k ₂ *C * T _P is the idle state correction amount, and k ₃ is the steady running normal load state correction amount. . Further, C is given as a function of intake pipe pressure P and rotational speed N by the following calculation formula: C=C ₀ /P*N (C ₀ is a constant).

Next, in step 1016, data on the corrected fuel injection amount T is set in the counter 109. Next, the process advances to step 1017 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. The general functions of the microprocessor 100 are as described above.

As described above, since the engine condition correction amount is corrected using the three coefficients k ₁ , k ₂ , and k ₃ , it is possible to finely correct deviations in the basic air-fuel ratio in each driving mode caused by various factors. .

Further, k ₁ , k ₂ , and k ₃ are all learned only under idle or stable operating conditions, and correction is performed over the entire range, so that acceleration/deceleration ranges that cannot be learned can be appropriately corrected.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an apparatus for explaining an embodiment of the present invention, FIG. 2 is a block diagram of the control circuit shown in FIG. 1, and FIG. 3 is a schematic diagram of the microprocessor shown in FIG. Flowchart: FIG. 4 shows a detailed flowchart of step 1004 shown in FIG. 3, and FIG. 5 shows a detailed flowchart of step 1005 shown in FIG. 1...Engine, 5...Fuel injection valve, 11...
Intake pressure sensor, 14... Air-fuel ratio sensor, 15...
Rotational speed sensor, 20... control unit.

Claims (1)

[Claims] 1. A method comprising an air-fuel ratio sensor that detects an air-fuel ratio based on engine exhaust gas components, and controlling the air-fuel ratio of a mixture supplied to the engine to a predetermined air-fuel ratio based on a signal from the air-fuel ratio sensor. A first correction value is obtained by integrating the signal from the air-fuel ratio sensor, and a first correction value is calculated based on the first correction value for each of three engine operating states: an idle state, a normal load operating state, and a high load operating state. calculate each engine condition correction value and update and store it in a storage device, and calculate the basic fuel amount to the engine according to the engine condition correction value updated and stored in the idle state and the engine state updated and stored in the normal load state. The air-fuel ratio is characterized in that the air-fuel ratio is multiplicatively corrected with a correction value, and further corrected additively with an engine state correction value updated and stored in the high load state, and the corrected fuel amount is supplied to the engine. Control method.