JPS6360217B2 - - Google Patents

Description

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

A conventional air-fuel ratio control method has been simple integral control based on the output of an air-fuel ratio sensor, that is, control that calculates the amount of correction of the air-fuel mixture air-fuel ratio by determining the air-fuel ratio of the exhaust system. Therefore, during transient engine operation,
If the fluctuation in the basic air-fuel ratio is faster than the correction speed of the integral control, the air-fuel ratio correction cannot keep 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 and drivability.

The present invention has been made in view of the above points, and in addition to integral processing control based on the output of an air-fuel ratio sensor, a value corresponding to the integral correction amount is stored in a memory as an engine state correction amount for each engine state. snow,
By performing feedback control of the air-fuel ratio using the correction amount corresponding to the engine state at that time and the integral correction amount at that time among the stored correction amounts, the predetermined air-fuel ratio is quickly achieved without response delay even during engine transients. The aim is to be able to control the air-fuel ratio accurately based on the engine condition correction amount stored in memory even when feedback control is not possible, such as when the air-fuel ratio sensor is inactive when the engine is at low temperature. .

Additionally, the present inventors have discovered that in engines equipped with a canister-based evaporative system, when the evaporative system is in operation, the amount of engine condition correction may differ from that under normal conditions due to the influence of evaporated fuel in the fuel tank. If the engine is stopped in that state, the engine condition correction amount just before that time will be stored in the memory, and when the engine is started again after the engine has cooled down, the previously stored engine condition correction amount will be used. It was discovered that this did not match well with the engine condition at that time, leading to poor drivability and poor exhaust gas purification. In order to further solve this problem, the present invention focuses on idle operation that is not affected by evaporated fuel (the current evaporative system operates during off-idle operation other than idle operation), and uses an integral correction amount only during idle operation. Calculate the engine condition correction amount based on The engine condition correction amount is calculated from the following combinations.

The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 shows a first embodiment, in which an engine 1 is a known four-stroke spark ignition engine installed in an automobile, and combustion air is supplied to an air cleaner 2,
It is inhaled through 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 released into the atmosphere through an exhaust manifold 6, an exhaust pipe 7, a three-way catalytic converter 8, and the like. The intake pipe 3 includes a potentiometer-type intake air amount sensor 11 that detects the amount of intake air taken into the engine 1 and outputs an analog voltage according to the amount of intake air.
A thermistor-type intake temperature sensor 12 is installed, which detects the temperature of air taken into the engine 1 and outputs an analog voltage (or analog detection signal) according to the intake temperature. Also, in engine 1,
A thermistor-type water temperature sensor 13 that detects the cooling water temperature and outputs an analog voltage (analog detection signal) according to the cooling water temperature is installed in the exhaust manifold 6, and further, the exhaust manifold 6 is equipped with a sensor that detects the air-fuel ratio from the oxygen concentration in the exhaust gas. When the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (i.e., rich), the air-fuel ratio outputs a voltage of about 1 volt (high level in this case), and when it is larger than the stoichiometric air-fuel ratio (i.e., lean), it outputs a voltage of about 0.1 volt (low level in this case). A fuel ratio sensor 14 is installed. The rotational speed (or rotational speed) sensor 15 is the engine 1
detects the rotational speed of the crankshaft and outputs a pulse signal with a frequency corresponding to the rotational speed. For example, an ignition coil of an ignition device may be used as the rotation speed (rotation speed) sensor 15, and an ignition pulse signal from the primary terminal of the ignition coil may be used as the rotation speed signal. Idle switch (IDLE SW) 16
detects the throttle fully closed position. Control circuit 2
0 is a circuit that calculates the fuel injection amount based on the detection signals of each sensor 11 to 16, and the electromagnetic fuel injection valve 5
The fuel injection amount is adjusted by controlling the valve opening time.

The control circuit 20 will be explained with reference to FIG.
100 is a microprocessor (ie, CPU) that calculates the fuel injection amount. A rotation speed counter 101 counts the engine rotation speed based on the signal from the rotation speed (rotation speed) sensor 15 in FIG.

Further, this rotation number counter 101 sends an interrupt command signal to the interrupt control section 102 in synchronization with the engine rotation. When the interrupt control section 102 receives this signal, it outputs an interrupt signal to the microprocessor 100 through the common path 150, and causes the microprocessor 100 to execute an interrupt processing routine for calculating the fuel injection amount. A digital input port 103 transmits to the microprocessor 100 digital signals such as a signal from the air-fuel ratio sensor 14 and a starter signal from a starter switch that turns on and off the operation of a starter (not shown). 104
is an analog input port intake air amount sensor 11 (first
), the intake air temperature sensor 12 (see Fig. 1), and the cooling water temperature sensor 13 (see Fig. 1), each signal is converted from analog to digital and sequentially read into the microprocessor 100. Each of these units 101, 102, 1
The output information of 03 and 104 is transmitted to the microprocessor 100 through the common path 150. 1
A power supply circuit 05 supplies power to a RAM 107, which will be described later. 17 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. Therefore, power is always applied to the RAM 107, which will be described later, 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. Reference numeral 107 is a temporary storage unit (i.e. RAM) which is used temporarily during program operation, but as mentioned above, power is always applied regardless of the key switch 18, so even if the key switch 18 is turned off and the engine operation is stopped, the memory contents are not retained. It is structured so that it does not disappear and forms a non-volatile memory. Second correction amount described later
_K3 is also stored in this RAM 107. 108
is a read-only memory (ie, ROM) that stores programs and various constants. Reference numeral 109 is a fuel injection time control counter including a register, which is composed of a down counter, and is operated by a microprocessor (CPU) 100.
The digital signal representing the valve opening time (Fig. 1), that is, the fuel injection amount, is applied to the actual electromagnetic fuel injection valve 5 (first
It is converted into a pulse signal with a pulse time width that gives the valve opening time shown in Figure). 110 is a power amplification section that drives the electromagnetic fuel injection valve 5 (FIG. 1). 111 measures the timer elapsed time and transmits it to the CPU 100.

Figure 3 shows a microprocessor (CPU) 100
(Figure 2) shows a schematic flowchart.Based on this flowchart, the microprocessor 1
The functions of the 00 will be explained as well as the operation of the entire configuration. When the key switch 18 (Fig. 2) and the starter switch are turned on to start the engine, the main routine calculation process starts at the start of the first step 1000, and then the main routine starts at step 1001.
Initialization processing is executed. step 100
4 at analog input port 104 (Fig. 2)
Read digital values corresponding to the cooling water temperature and intake air temperature. In step 1005, a correction amount _K1 , which will be described later, is calculated from the result and the result is stored in the RAM 107 (FIG. 2). In step 1006, the signal of the air-fuel ratio sensor 14 is inputted from the digital input port 103 (Fig. 2), and the signal of the air-fuel ratio sensor 14 is inputted to the timer 111 (Fig. 2).
The correction amount K ₂ will be described later as a function of elapsed time by
Increase or decrease this correction amount K ₂ , that is, the integral processing information
Store in RAM107. FIG. 4 is a detailed flowchart of a processing step 1006 in which the correction amount _K2 as the integral processing information is increased or decreased, that is, integrated. First, in step 400, the air-fuel ratio sensor 1 is
4 (Figure 1) is in an active state.
Alternatively, it is determined whether feedback control of the air-fuel ratio is possible based on the cooling water temperature, etc., and if feedback control is not possible, that is, in the case of an open loop, the process proceeds to step 406, sets the correction amount K ₂ to K ₂ =1, and proceeds to step 405. move on. If feedback control is possible, proceed to step 401. In step 401, the elapsed time is the unit time △t ₁
It is determined whether or not it has passed, and if it has not passed, this processing step 1006 is ended without making any correction for _K2 . If time △t ₁ has elapsed, step 40
If the air-fuel ratio is rich, proceed to step 2 and check the air-fuel ratio sensor 1.
If the output of 4 (FIGS. 1 and 2) is a rich high-level signal, the process proceeds to step 403, where the K ₂ obtained in the previous cycle is decreased by △K ₂ , and the process proceeds to step 405, where this new correction is applied. amount K ₂ to RAM1
07 (Figure 2). In step 402, the air-fuel ratio is lean and the air-fuel ratio sensor 14
If the output of (Figures 1 and 2) is a low level signal indicating lean, proceed to step 404 and change K ₂ to △K ₂
Then, the process proceeds to step 405. In this way, the correction amount _K2 is increased or decreased. Step 1 in Figure 3
In 007, the correction amount _K3 is increased or decreased, and the result is stored in the RAM.
107 (FIG. 2). FIG. 5 is a detailed flowchart of step 1007 in which the correction amount _K3 is processed and stored in the RAM 107 (FIG. 2), that is, it is stored. In step 501, it is determined whether the engine is in idle operation based on the signal from the idle switch 16 (FIGS. 1 and 2), and if it is off-idle (when the throttle is at a position other than the idle position), a memory processing step 1007 is performed. If the throttle is idle (when the throttle is in the idle position, that is, the fully closed position), the process proceeds to step 502. In step 502, it is measured whether the elapsed time has passed the unit time Δt ₂ or not. If Δt ₂ has not passed, the memory processing step 1007 is ended, and if it has, the process proceeds to step 503 and the process of K ₂ is performed. Determine the value.
If K ₂ =1 (that is, when the air-fuel ratio sensor 14 is inactive or air-fuel ratio feedback control cannot be performed), this processing step 1007 is ended without doing anything.

Note that the correction amount _K3 forms a map as shown in FIG. 6 depending on the intake air amount Q. In this case, the throttle fully closed position detection switch (i.e. IDLE SW)
16 (Fig. 1, Fig. 2) is distinguished by ON and OFF,
Each is divided into 32 parts according to the amount of intake air, starting from the smallest amount of air. For example, when the IDLE SW is ON, the n-th correction amount K ₃ is expressed as K ¹ _o , and when the IDLE SW is OFF, the n-th correction amount K ₃ is expressed as K ² _o . The intake air amount at the n-th point is the same whether the IDLE SW is ON or OFF. Considering the operating conditions, the correction amount K ₃ during idling or deceleration is displayed as K ¹ _o , and during steady state or acceleration it is displayed as K ² _o . As a general representation, in FIG. 5, the correction amount K ₃ is expressed as K ^m _o .

In FIG. 5, if K ₂ >1 in step 503, the process proceeds to step 504, increments K ¹ _o obtained in the previous cycle by △K ₃ , and stores the result in the RAM 107 (FIG. 2) in step 506. . If K ₂ <1 in step 503, the process proceeds to step 505, where K ¹ _o obtained in the previous cycle is decreased by ΔK ₃ , and in step 506, the result is stored in RAM 107 (FIG. 2). In step 507, the total correction amount ^Km _o is determined by _calculation based on the correction amount ^1o obtained in step 506, and the RAM 107
(FIG. 2), and this processing step 1007
end. Note that the method for determining K ₃ (=K ^m _o ) will be described later. In FIG. 3, when step 1007 in the main routine is completed, the process returns to step 1004.

Normally, the main routine processes 1004 to 1007 are repeatedly executed according to the control program. However, the interrupt control unit 102 (FIG. 2)
When the interrupt signal for the fuel injection calculation is input from the microprocessor 100, even if the microprocessor 100 is processing the main routine, it immediately interrupts the processing and moves to the interrupt processing routine at step 1010. In step 1011, the rotation number counter 101 (second
In step 1012, a signal representing the intake air amount (i.e., intake air amount) Q is taken in from the analog input port 104 (Fig. 2), and then in step 1.
In 013, the RAM 10 is used to use the rotational speed N and the intake air amount Q as parameters for storing the correction amount _K3 in the calculation processing of the main routine.
7 (Figure 2). Next step 1014
The basic fuel injection amount determined from the engine speed N and intake air amount Q (that is, the electromagnetic fuel injection valve 5
Calculate the injection time width t) (Figures 1 and 2).
The calculation formula is t=F× ^Q _N (F: constant). Next, in step 1015, various correction amounts for fuel injection determined in the main routine are stored in the RAM 107 (Fig. 2).
A correction calculation is made for the injection amount (i.e., injection time width) that determines the air-fuel ratio. The formula for calculating the injection time width T is T=t×K ₁ ×K ₂ ×K ₃ . Next, in step 1016, the corrected and calculated fuel injection amount data is set in the counter 109 (FIG. 2). Next, the process advances to step 1017 and returns 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, a large number of second correction amounts K ₃ (=K ^m _o ) are prepared according to the intake air amount, so that an appropriate correction amount corresponding to the engine operating condition can be used immediately. . Control with quick response is possible for all operating conditions, including transient conditions. Furthermore, since the second correction amount _K3 is modified in accordance with the operating condition, it can be automatically corrected for changes over time and deterioration of the engine and sensors.

Figure 7 shows the evaporative system. fuel tank 3
The evaporated fuel from 0 is led to the canister 40 through the pipe 31. The evaporated fuel collected in the canister 40 passes through the pipe 41 and the fixed fastener 42 during off-idling, especially when the engine is under medium or light load, and is guided into the intake pipe 3 via the throttle valve 4.

FIG. 8 shows the influence of evaporated fuel on the engine condition correction amount _K3 . Correction amount when there is no evaporated fuel
K ₃ is shown by a broken line (characteristic A in the figure), and the correction amount K ₃ when there is evaporated fuel is shown by a solid line (characteristic B in the figure). The shaded area is the overrich amount (overrich area) due to evaporated fuel. IDLE SW ON
At the time, there was no overrichness, and IDLE SW
The smaller the OFF intake air amount (the smaller the Q division number), the larger the overrich amount.

FIG. 9 shows a method for determining the correction amount _K3 . The correction amount _K3 stored in the RAM 107 at step 506 in FIG.
This is only the solid line part on the SW ON side. step 50
When determining the overall correction amount K ^m _o in step 506, first, the solid line portion on the IDLE SW OFF side indicated by B is the same intake air amount as on the IDLE SW ON side, and the correction amount K obtained in step 506 is the same as that on the IDLE SW ON side. Use ₃ as is. Second, the dashed line portions of both A and B are calculated from engine parameters, such as engine intake air amount Q, engine rotational speed N, or intake pipe internal pressure, singly or in combination. FIG. 9 shows an example of a method of correcting K ₃ by inverse proportion to the engine intake air amount Q. A in the diagram,
B and C show typical patterns.
For example, characteristic A is the correction amount _K3 when the idle air-fuel ratio becomes leaner than the set air-fuel ratio, which tends to occur when air leaks occur in the engine intake pipe, crank chamber, etc. Characteristic B is a case where the idle air-fuel ratio is the same as the set air-fuel ratio and there is no need to correct it.

Characteristic C tends to occur due to changes in the intake air amount sensor over time (such as dirt), and the idle air-fuel ratio becomes richer than the set value. In this case, the concentration is highest during idling operation (excluding deceleration) when the engine intake air amount Q is small, and the effect becomes smaller as the air amount Q increases. The correction method based on the inverse proportion of the air amount Q works very well and allows correct correction.

As described above, the present invention is a method that includes an air-fuel ratio sensor that detects an air-fuel ratio based on exhaust gas components of an engine, and controls the air-fuel ratio based on a signal from the air-fuel ratio sensor. Integrating the signal, calculating an engine condition correction amount corresponding to the engine operating condition based on the integral correction amount obtained by this integral processing and storing it in a storage means, and calculating the engine condition correction amount obtained by this calculation. The air-fuel ratio is controlled by the above-mentioned integral correction amount, and the air-fuel ratio can be controlled to the target air-fuel ratio with good response even during engine transients, and even when feedback control cannot be performed, such as when the air-fuel ratio sensor is inactive, the air-fuel ratio can be controlled. It becomes possible to accurately control the air-fuel ratio using the corrected engine state correction amount. Furthermore, the amount of engine condition correction may differ from that under normal conditions due to the influence of evaporated fuel, etc., and if the engine is stopped in that condition, the immediately preceding engine condition correction amount is stored in memory, so it is necessary to wait until the engine has cooled down. When the engine is restarted, this engine condition correction amount becomes an inappropriate value, which may lead to poor drivability and poor exhaust gas purification. However, in the present invention, the focus is on idling operation that is not affected by evaporated fuel, and the amount of correction is made only during idling. A countermeasure can be taken by determining the engine state correction amount based on the integral correction amount, and calculating the engine state correction amount from the engine state correction amount during idling operation and engine parameters during off-idling operation, which is susceptible to the influence of evaporated fuel.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention;
2 is a block diagram of the control circuit shown in FIG. 1, FIG. 3 is a schematic flowchart of the microprocessor shown in FIG. 2, and FIG. 4 is a detailed flowchart of step 1006 shown in FIG. 3. Figure 5 is the third
6 is a map of the engine condition correction amount _K3 used to explain the operation of the embodiment shown in FIG. 1, FIG. 7 is a schematic diagram of the evaporative system, and FIG. The figure is a characteristic diagram showing the influence of evaporated fuel on the engine condition correction amount _K3 , and FIG. 9 is a diagram showing the method for determining the engine condition correction amount _K3 . DESCRIPTION OF SYMBOLS 1...Engine, 11...Air amount sensor, 14...Air-fuel ratio sensor, 15...Rotational speed sensor, 16...Idle switch, 20...Control circuit, 100...Microprocessor (CPU), 107...Temporary memory forming non-volatile memory Unit (RAM).

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 feedback controlling the air-fuel ratio of an intake air-fuel mixture based on a signal from the air-fuel ratio sensor, the method comprising: a step of performing integral processing, a step of detecting various engine operating conditions including at least the throttle position of the engine, and a step of detecting various engine operating conditions including at least the throttle position of the engine; A step of calculating the engine condition correction amount and storing it in the storage means as an engine condition correction amount at idle, and calculating the engine condition correction amount at idle obtained in this way and the engine condition when the throttle is at a position other than idle. a step of calculating an engine condition correction amount using engine parameters such as intake air amount, engine rotational speed, or intake pipe internal pressure alone or in combination, and storing this in a storage means as an engine condition correction amount during off-idling; An air-fuel ratio control method comprising the step of controlling an air-fuel ratio of an intake air-fuel mixture according to a current engine operating state using a correction amount and the stored engine state correction amount.