JP2615680B2 - Air-fuel ratio learning control method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention [relates] relates to an air-fuel ratio learning control method for an internal combustion engine, particularly the engine load and the engine rotational speed and the basic fuel injection time determined by the output signal of the O ₂ sensor Air-fuel ratio feedback control coefficient for an internal combustion engine that feedback-controls the air-fuel ratio based on a learning value that is increased or decreased so that the average value of the air-fuel ratio feedback correction coefficient obtained based on the air-fuel ratio feedback coefficient is within a predetermined range. About.

[Conventional technology]

Conventionally, carbon monoxide in the exhaust gas, and the three-way catalyst is used to purify hydrocarbons and nitrogen oxides simultaneously in the exhaust gas by the O ₂ sensor for better purification rate of the three-way catalyst Feedback control is performed to detect the residual oxygen concentration, estimate the combustion air-fuel ratio, and control the combustion air-fuel ratio near the stoichiometric air-fuel ratio. In performing the feedback control, a basic fuel injection time TP in a predetermined operation region determined by an engine load (intake pipe pressure PM or intake air amount Q) and an engine speed NE is stored in a table. Is multiplied by the air-fuel ratio feedback correction factor FAF shown in FIG. 7 for proportionally integrating the fuel injection valve based on the air-fuel ratio signal output from the O ₂ sensor and subjected to signal processing. Thus, the fuel injection time TAU is obtained, and the fuel injection valve is opened for a time corresponding to the fuel injection time TAU, thereby controlling the air-fuel ratio to near the stoichiometric air-fuel ratio. In the above table, only the basic fuel injection time within the predetermined operation range is stored. Therefore, when the engine load or the engine speed becomes a value outside the predetermined operation range, the current engine load and the engine speed are changed to the current values. The closest basic fuel injection time is determined from the above table. However, changes in valve timing due to changes in tapet clearance due to environmental changes and changes over time,
Changes in the characteristics of the pressure sensor and the air flow meter, and changes in the characteristics of the fuel injection valve may occur, making it impossible to control the fuel injection amount to the required fuel injection amount of the engine, so that the air-fuel ratio cannot be controlled near the stoichiometric air-fuel ratio. For this reason, air-fuel ratio learning control is performed to control the air-fuel ratio so that it is always near the stoichiometric air-fuel ratio (Japanese Patent Application Laid-Open Nos. 61-16243 and 60-233).
No. 328). In this learning control, the average value FAFAV of the air-fuel ratio feedback correction coefficient is controlled to a predetermined value using a learning value KGi learned under predetermined conditions as shown in the following equation.

TAU = TP ・ KGi ・ FAF ・ F (t) (1) where F (t) is a correction coefficient such as a warm-up increase coefficient or a start-time increase coefficient. The learning value KGi is determined according to the engine load.

The learning value KGi is learned by the following method every time the correction coefficient FAF is skipped a predetermined number of times during the air-fuel ratio feedback control and when the engine cooling water temperature exceeds a predetermined value (for example, 80 ° C.). First, each time the air-fuel ratio feedback correction coefficient FAF is skipped a predetermined number of times, the air-fuel ratio feedback correction coefficient
From the arithmetic mean value FAFAV of the maximum and minimum values of FAF, that is, A, B, C... Shown in FIG. When the average FAFAV falls outside a predetermined range (for example, a range of ± 2% of the stoichiometric air-fuel ratio), the learning value KGi is increased or decreased by learning. That is, the learning value KGi is increased by a predetermined amount when the average value FAFAV exceeds 1.02, and the learning value KGi is increased when the average value FAFAV becomes less than 0.98.
Is decreased by a predetermined value.

The learning value KGi learned as described above is applied to the above equation (1) according to the open / close state of the throttle valve and the magnitude of the intake pipe pressure (or the amount of intake air per one revolution of the engine). The injection time TAU is determined. As a result,
When the average value FAFAV exceeds 1.02, the learning value is increased, the air-fuel ratio is controlled to the rich side, and the average value FAFAV becomes 0.98.
When the value is less than the learning value, the learning value is reduced and the air-fuel ratio is controlled to the lean side.

[Problems to be solved by the invention]

However, in the above technique, when the operating state is out of the predetermined operating area, the basic fuel injection time in the state closest to the operating state is used by using a table in which the basic fuel time in the predetermined operating area is determined. Therefore, the fuel injection amount controlled by the basic fuel injection time deviates from the engine required value and is erroneously learned. For example, considering the vicinity of the idling condition, if the engine speed is reduced at the equal intake pipe pressure, the suction efficiency is reduced and the required injection amount is reduced.
If the engine speed falls below the minimum engine speed that defines the basic fuel injection time in the table, the basic fuel injection time will be fixed at a value corresponding to this minimum engine speed, and Excessive fuel is injected (eg, 10% rich). At this time, since the air-fuel ratio is fed back controlled on the basis of the O ₂ sensor output, the air-fuel ratio is made to be fed back controlled to the stoichiometric air-fuel ratio, since the excessive fuel by the basic fuel injection time is injected The air-fuel ratio feedback correction coefficient decreases and the learning value KGi decreases. (Eg, 0.9). Therefore, for example, when idling, the rotation falls to outside the table area due to an electric load or the like, and learning is performed in that state. When the electric load disappears and rotation returns to the inside of the table area, the learning value is deviated. Until the value becomes a normal value, the control air-fuel ratio becomes lean, causing rough idle or engine stall.

The present invention has been made in order to solve the above-described problem. The learning value learned outside the operating region in which the table of the basic fuel injection time is determined is used to determine the air-fuel ratio when the vehicle returns to the operating region and operates. It is an object of the present invention to provide an air-fuel ratio learning control method for an internal combustion engine in which the deviation is prevented.

[Means for solving the problem]

In order to achieve the above object, the present invention stores a basic fuel injection time in a predetermined operation region determined by an engine load and an engine rotation speed in a table, and when the current operation state exists in the predetermined operation region, The basic fuel injection time corresponding to the current operating state is calculated from the table, and the basic fuel injection time corresponding to the operating state closest to the current operating state from the table when the current operating state is outside the predetermined operating range. O ₂ for detecting the calculated basic fuel injection time and the residual oxygen concentration in the exhaust gas
The air-fuel ratio feedback correction coefficient obtained based on the output signal of the sensor, and a learning value that is increased or decreased so that the average value of the air-fuel ratio feedback correction coefficient becomes a value within a predetermined range. And an air-fuel ratio learning control method for an internal combustion engine that performs feedback control of an air-fuel ratio outside the predetermined operation range, wherein the increase / decrease of the learning value is stopped when the current operation state is outside the predetermined operation range. .

[Action]

According to the present invention, the basic fuel injection time in the predetermined operating region determined by the engine load and the engine rotation speed is stored in the table, and the current operating state is determined by the predetermined operating region in the table storing the basic fuel injection time. When it is outside, the increase / decrease of the learning value is stopped, and the air-fuel ratio is controlled based on the constant learning value at which the increase / decrease is stopped, the basic fuel injection time obtained from the table, and the air-fuel ratio feedback correction coefficient. Is done. Therefore, even when the air-fuel ratio is controlled using the basic fuel injection time that does not correspond to the current operation state, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio by the air-fuel ratio feedback correction coefficient. At this time, since the learning value is not updated, the air-fuel ratio does not shift due to the learning value even when the operation returns from the outside of the operation region where the table is defined to the inside of the operation region where the table is defined.

〔The invention's effect〕

As described above, according to the present invention, the basic fuel injection time in the predetermined operation area is stored in the table, and when the current operation state is outside the predetermined operation area, the operation closest to the current operation state from the table is performed. The basic fuel injection time corresponding to the state is calculated and the learning value is not increased or decreased, and the air-fuel ratio is calculated based on the calculated basic fuel injection time, the air-fuel ratio feedback correction coefficient and the learning value inside and outside the predetermined operation region. Since the feedback control is performed, the air-fuel ratio can be controlled to the stoichiometric air-fuel ratio even when the current operation state exists in the region where the basic fuel injection time is not determined, and the table can be controlled from outside the table region. Immediately after returning to the range, the learning value becomes the optimal value, and engine stall, idling instability, and exhaust Emitsushiyon and worsening driver kink Tei, it is possible to prevent the catalyst exhaust odor, effect is obtained that.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a four-cylinder four-cycle spark ignition internal combustion engine (engine) equipped with a fuel injection amount control device to which the present invention can be applied.
1 shows an outline.

This engine is controlled by a microcomputer 44. A throttle valve 8 is disposed downstream of an air cleaner (not shown), and a surge tank 12 is provided downstream of the throttle valve 8. An idle switch 10 which is turned on when the throttle valve 8 is fully closed is attached to the throttle valve 8. A semiconductor type pressure sensor 6 is attached to the surge tank 12. The output terminal of the pressure sensor 6 has a small time constant (for example, 1 to 10 msec) for removing a pulsating component of the intake pipe pressure and has a responsive CR filter (third filter).
(Fig.) This filter may be built in the pressure sensor. A bypass circuit bypasses the throttle valve 8 and communicates with the surge tank 12 on the upstream side of the throttle valve and the surge tank 12 on the downstream side of the throttle valve.
14 are provided. The degree of opening of the bypass passage 14 is adjusted by a pulse motor 16A having a four-pole stator.
SC (idle speed control) valve 16B is attached. The surge tank 12 is connected to a combustion chamber of the engine 20 via an intake manifold 18 and an intake port 22. And this intake manifold 18
A fuel injection valve 24 is attached to each cylinder so as to protrude inside.

The combustion chamber of the engine 20 is connected to a catalyst device (not shown) filled with a three-way catalyst via an exhaust port 26 and an exhaust manifold 28. The exhaust manifold 28 is provided with an O ₂ sensor 30 that outputs a signal inverted at the stoichiometric air-fuel ratio. Engine block
The cooling water temperature sensor 34 is attached to the engine 32 so as to penetrate the engine block 32 and protrude into the water jacket. The coolant temperature sensor 34 detects the engine coolant temperature and outputs a coolant temperature signal, and the coolant temperature signal represents the engine temperature. The engine oil temperature may be detected to represent the engine temperature.

An ignition plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and protrude into the combustion chamber. The spark plug 38 is connected to a micro computer 44 via a distributor 40 and an igniter 42. In the distributor 40, a cylinder discriminating sensor 46 and a rotation angle sensor each composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing are provided.
48 are installed. The cylinder discrimination sensor 46 is, for example, 720
A cylinder discriminating signal consisting of a pulse train generated every CA is output, and the rotation angle sensor 48 outputs an engine rotation speed signal consisting of a pulse train generated every 30 CA, for example.

As shown in FIG. 3, the micro computer 44 includes a micro processing unit (MPU) 60, a read only memory (ROM) 62, a random access memory (RA).
M) 64, back-up plum (BU-RAM) 66, I / O ports
68, an input port 70, output ports 72, 74, and 76, and a bus 75 such as a data bus or a control bus for connecting them. Analog input / output port 68
A digital (A / D) converter 78 and a multiplexer 80 are sequentially connected. The pressure sensor 6 is connected to the multiplexer 80 via a filter 7 composed of a resistor R and a capacitor C and a buffer 82, and the cooling water temperature sensor 34 is connected via a buffer 84. The MPU 60 controls the multiplexer 80 and the A / D converter 78 to sequentially convert the output of the pressure sensor 6 and the output of the cooling water temperature sensor 34 input via the filter 7 into digital signals and store them in the RAM 64. Therefore, multiplexer 80, A / D converter 78 and M
The PU 60 and the like function as sampling means for sampling the output of the pressure sensor every predetermined time. The input port 70, O ₂ sensor 30 via the comparator 88 and buffer 86
And a cylinder discriminating sensor 46 and a rotation angle sensor 48 are connected via a waveform shaping circuit 90. The input switch 70 is connected to the idle switch 10.
The output port 72 is connected to the igniter 42 via a drive circuit 92, and the output port 74 is a drive circuit having a down counter.
Connected to fuel injector 24 via 94, and output port
Reference numeral 76 is connected to a pulse motor 16A of the ICS valve via a drive circuit 96. In addition, 98 is a clock and 99 is a counter. In the ROM 62, a control routine program and the like described below are stored in advance. Further, as shown in FIG. 4, the ROM stores the intake pipe pressure in a region where the engine speed NE is N ₁ ≦ NE ≦ N ₂ and the intake pipe pressure PM is P ₁ ≦ PM ≦ P _2.
Basic fuel injection time TP determined by PM and engine speed NE
Is stored in advance. N ₁ is, for example, 600 rpm,
P ₁ is a 170mmHg for example. In the RAM, the learning values KGi shown in Table 1 below (= KG0, KG1, KG2, KG3, KG4, KG
5, KG6, KG7), KG1 to KG7 are stored corresponding to the intake pipe pressure PM when the throttle valve is open, and the learning value KG0 when the throttle valve is closed is stored. I have. Note that the initial value of the learning value KGi is 1.0.

Next, the above control routine will be described. FIG. 1 shows a learning routine. In steps 100 and 102, the current operating state is N ₁ ≦ NE ≦ N ₂ and P
₁ ≦ PM ≦ P ₂ in the region, that is, determines whether or not present in the area of the table that defines the basic fuel injection time TP. When both the determinations in steps 100 and 102 are affirmative, it is determined in step 104 whether other learning conditions are satisfied. Other learning conditions include the air-fuel ratio feedback control during the air-fuel ratio feedback control, the instantaneous fuel increase and the start-up fuel increase being zero, and the air-fuel ratio feedback control from the time when the air-fuel ratio open loop control is switched to the air-fuel ratio feedback control. FAF is performed a predetermined number of times
6 times) or more (proportional operation), the absolute value of the change amount of the intake pipe pressure between designated crank angles is equal to or less than a predetermined value (for example, 3 mmHg / 360 CA), or the idle switch is off. Battery voltage is a predetermined value (for example, 12V)
When all of these conditions are satisfied at the same time, it is determined that the learning condition has been satisfied. Step 10
When it is determined that the learning conditions are satisfied in 4,
At step 106, a learning process is executed.

FIG. 5 shows the details of the step 106. In step 110, the average value FAFAV of the air-fuel ratio feedback correction coefficient FAF (calculated in step 122 in FIG. 6) as shown in the equation (2) described above. Is calculated. Step 112
Then, it is determined which of the learning values KG0 to KG7 is to be learned (a learning range). This learning range is the class value KG
It is divided into predetermined ranges as shown in Table 2 according to 0 to KG7.

In the next steps 114 and 116, it is determined whether or not the average value FAFAV of the air-fuel ratio feedback correction coefficient FAF is within a predetermined range (for example, 0.98 <FAFAV <1.02). If so, the learning value is not updated. On the other hand, if the average value FAFAV exceeds the upper limit value, the learning value determined in step 112 is increased by a predetermined value (for example, 0.02) in step 118, and if the average value FAFAV is less than the lower limit value, the process proceeds to step 120. Step 112
The learning value determined in (1) is reduced by a predetermined value (for example, 0.02).

Figure 6 is a predetermined time (for example, 4 msec) shows a routine that is executed every calculates the fuel injection time TAU, and calculates an air-fuel ratio fed back correction coefficient FAF based on the O ₂ sensor output in step 122. The air-fuel ratio fed back correction coefficient FAF changes in accordance with the O ₂ sensor output as shown in Figure 7. In the next step 124, the current intake pipe pressure PM and engine speed are obtained from the table shown in FIG.
Calculate the basic fuel injection time TP corresponding to NE. When the current intake pipe pressure or the engine speed is out of the range of the table, the value of the table closest to the current intake pipe pressure or the engine speed is adopted. In the next step 126, the fuel injection time TAU is calculated according to the above equation (1).

Here, when calculating the fuel injection time TAU, the learning value KG0 is adopted when the idle switch is on, and the learning value KGi is adopted when the idle switch is off and the intake pipe pressure is less than 210 mmHg. When it is off and the intake pipe pressure is 690 mmHg or more, the learning value KG7 is adopted. Otherwise, the learning value corresponding to the current intake pipe pressure determined by interpolation from Table 1 is adopted. In addition, all conditions such as not being in the starting state, the engine cooling water temperature being equal to or higher than a predetermined value (for example, 40 ° C.), the OTP increase performed to reduce the exhaust gas temperature at high load or high rotation being zero, and not being in the fuel cut condition are satisfied. When the condition is satisfied, it is determined that the air-fuel ratio feedback condition has been satisfied, and step 122
The air-fuel ratio feedback correction coefficient FAF calculated in the above is used as it is in the calculation of the fuel injection time. However, if at least one of the above conditions is negatively determined and it is determined that the air-fuel ratio feedback condition is not satisfied, the air-fuel ratio The value of the feedback correction coefficient FAF is set to 1.0 and used for calculating the fuel injection time.

As a result of the above control, when the average value of the air-fuel ratio feedback correction coefficient is large, that is, when the air-fuel ratio lean tendency is indicated, the learned value is increased and the fuel injection is executed. In the case where the average value decreases when the average value decreases, that is, when the average value decreases, that is, when the air-fuel ratio shows a tendency to decrease, the average value increases because the learning value is reduced and the fuel injection is performed. To a value within a predetermined range. In addition, since the learning value is not updated when the current operation state is outside the area of the table, erroneous learning due to a difference in the basic fuel injection time is prevented.

In the internal combustion engine described above, the OTP is increased at the time of high load or high rotation, and the air-fuel ratio feedback control is stopped at this time, and learning is not performed at high load or high rotation. it may be omitted decisions of NE ≦ N ₂ and step 102 of determining PM ≦ P _2. In the above description, an example in which the basic fuel injection time is determined by the intake pipe pressure and the engine speed is described. However, the present invention is also applicable to an internal combustion engine in which the basic fuel injection time is determined by the intake air amount and the engine speed. is there.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a learning routine according to an embodiment of the present invention;
2 is a schematic diagram of an internal combustion engine to which the present invention can be applied, FIG. 3 is a block diagram showing details of the control circuit of FIG. 2, FIG. 4 is a diagram showing a table of basic fuel injection time, and FIG. FIG. 6 is a flowchart showing details of step 106, FIG. 6 is a flowchart showing a fuel injection time calculation routine, and FIG. 7 is a diagram showing changes in the O ₂ sensor output and the air-fuel ratio feedback correction coefficient. 6 ... Pressure sensor, 10 ... Idle switch, 24 ... Fuel injection valve.

Claims (1)

(57) [Claims] 1. A basic fuel injection time in a predetermined operation range determined by an engine load and an engine rotation speed is stored in a table, and when a current operation state exists in the predetermined operation range, a current operation state is determined from the table. And calculating the basic fuel injection time corresponding to the operating state closest to the current operating state from the table when the current operating state is outside the predetermined operating range. a basic fuel injection time, the air-fuel ratio feedback correction coefficient obtained on the basis of the output signal of the O ₂ sensor for detecting the residual oxygen concentration in the exhaust gas, the mean value of the air-fuel ratio feedback correction coefficient is a value within a predetermined range The feedback value of the air-fuel ratio in the predetermined operation region and the air-fuel ratio in the outside of the predetermined operation region based on the learning value that is increased or decreased In the air-fuel ratio learning control method of the engine, the air-fuel ratio learning control method for an internal combustion engine, characterized in that stops the increase or decrease of the learning value when the current operating condition is present outside the predetermined operating region.