JPS6116243A - Air-fuel ratio learning value controlling method of internal-combustion engine - Google Patents

Abstract

PURPOSE:To keep off a worthening of stability in an engine speed, by stopping the increase or decrease in a learning value when such a state that the engine speed is below the specified value still continues for the specified period long, while also stopping feedback control over an air-fuel ratio when this state further continues for the specified period. CONSTITUTION:During engine operation, fundamental fuel injection time is calculated on the basis of each output out of a suction pipe pressure sensor 10 and an engine speed sensor 28 at a control circuit 30. And, the fundamental fuel injection time is compensated on the basis of an air-fuel ratio feedback compensation factor to be determined according to the output of an oxygen sensor 34 and a learning value to be varied in time of idling so as to cause a mean value of this compensation factor to become a value within the specified range. At this time, when such a state that an engine speed is below the specified value still continues for the specified period, the increase and decrease of the learning value are stopped. And, when this state furthermore continues for the specified period long, compensation control (air-fuel ratio control) is made so as to be stopped as well.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an air-fuel ratio learning control method for an internal combustion engine, and in particular,
During idling, the basic fuel injection time determined by the engine load and engine speed, the air-fuel ratio feedback correction coefficient obtained based on the output signal of the engine, and the average value of the air-fuel ratio feedback correction coefficient are within a predetermined range. The present invention relates to an air-fuel ratio learning control method for an internal combustion engine during idling, which performs feedback control of the air-fuel ratio based on a learning value that is increased or decreased.

[Conventional technology]

Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas. Feedback control is performed to detect the residual oxygen concentration in the exhaust gas, estimate the air-fuel ratio, and control the air-fuel ratio to near the stoichiometric air-fuel ratio. In performing this feedback control, 0. Based on the air-fuel ratio signal output from the sensor and subjected to signal processing, the fuel injection time T and AU are determined by multiplying by the air-fuel ratio feedback correction coefficient FAF shown in FIG. The air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by opening the fuel injection valve for a time corresponding to the fuel injection time TAU. However, due to environmental changes and changes over time, changes occur in the pulp timing due to changes in the tappet flance, changes in the characteristics of the pressure sensor and air flow meter, and changes in the characteristics of the fuel injection valve. The air-fuel ratio may not be able to be controlled close to the stoichiometric air-fuel ratio. For this reason, air-fuel ratio learning control is performed so that the air-fuel ratio is always near the stoichiometric air-fuel ratio. This learning control uses learning values TAUG and KG learned under predetermined conditions as shown in a quartic equation to control the average value FAFAV of the air-fuel ratio feedback correction coefficient to a predetermined value.

TAU=(TP+TAUG)-KG,FAF
@F(t)-=-・(1) However, TAUG is the learned value when the intake throttle valve (throttle valve) is in the idle position, KG
is the learned value when the intake throttle valve is not in the idle position, F
(1) is a correction coefficient such as the warm-up increase i number and the start-up increase coefficient.

In addition, the learning value KG is determined by the engine load,
For example, when the intake pipe pressure is 200-300+nHJ+, KG, when the intake pipe pressure is 300-400tmHI, KG, 400
KGs is adopted when ~500 Hjl.

These learning values TAUG, KG (KG, , KG, , KG
, ) is the correction coefficient F when the engine cooling water temperature exceeds a predetermined value (for example, 80°C) during air-fuel ratio feedback control.
Each time AF skips a predetermined number of times, learning is performed by the following method. First, every time the air-fuel ratio feedback correction coefficient FAF skips a predetermined number of times, the arithmetic average value FAFAV of the maximum and minimum values of the correction coefficient FA and F is calculated, that is, FAFAv=A0B.
Once 2 FC, C + D,, -0 (212ゝ 2
2X is determined, and when the value of the average value FAFAV becomes a value outside a predetermined range (for example, a range of ±2% with respect to the value of the stoichiometric air-fuel ratio), the learned values TAUG and KG are increased or decreased by a predetermined value by learning. That is, when the average value FAFAV exceeds 1.02, the learned values TAUG and KG are increased by a predetermined value, and the average value FAAV is increased by a predetermined value.
Learning value TAUGX when FAV becomes less than 0.98
Decrease KG by a predetermined value.

Then, the learned values TAUG, KG learned as above
is determined by the above (1
) is applied to determine the fuel injection time TAU. As a result, when the average value FAFAV exceeds 1.02, the learned value is increased and the air-fuel ratio is controlled to the rich side, and when the average value FAFAV is less than 0.98, the learned value is decreased and the air-fuel ratio is controlled to the rich side. Controlled to lean side, average value F
Learning control is performed so that AFAV approaches 1, that is, the stoichiometric air-fuel ratio.

[Problem that the invention seeks to solve]

However, in such conventional air-fuel ratio control methods, 0. When the sensor is exposed to a low temperature atmosphere, it becomes inactive and 0. The internal resistance of the sensor increases and O! Since the voltage output from the sensor gradually decreases, 0. The inversion timing of the air-fuel ratio signal obtained from the sensor output gradually deviates from the timing corresponding to the stoichiometric air-fuel ratio. This amount of deviation is 0.
The longer the sensor is exposed to the low-temperature atmosphere, the larger it becomes. In conventional air-fuel ratio control methods, learning is performed even in such conditions, so if the learned value deviates, the air-fuel ratio cannot be controlled to the stoichiometric air-fuel ratio.
There were problems with the stability of idle rotation and worsening of emissions during idle.

In addition, if the above condition continues for a long time, the air-fuel ratio feed correction coefficient will deviate from the value corresponding to the stoichiometric air-fuel ratio, and the air-fuel ratio will no longer be able to be controlled to the stoichiometric air-fuel ratio even with feedback control, resulting in poor idle rotation stability. , there was a problem in that the emissions at idle worsened.

[Means for solving problems]

The present invention has been made to solve the above problems,
The basic fuel injection time determined by the engine load and engine speed, the air-fuel ratio feedback correction coefficient obtained based on the output signal of the zero sensor that detects the residual oxygen concentration in the exhaust gas, and the average of the air-fuel ratio feedback correction coefficients. In an air-fuel ratio learning control method for an internal combustion engine in which the air-fuel ratio is feedback-controlled based on a learned value that is increased or decreased during idling so that the value is within a predetermined range, a state in which the engine speed is below a predetermined value is detected. The invention is characterized in that the increase/decrease of the learned value is stopped when the learned value continues for a predetermined period of time, and the feedback control of the air-fuel ratio is stopped when the engine speed remains below the predetermined value for a further predetermined period.

[Effect]

According to the present invention, when the engine speed remains below a predetermined value for a predetermined period of time, that is, when the engine speed remains below a predetermined value, zero. When the sensor is exposed for a predetermined period of time, the increase or decrease of the learning value is stopped, and the air-fuel ratio is feedback-controlled based on the constant learning value when the increase or decrease is stopped, the basic fuel injection time, and the air-fuel ratio feedback correction coefficient. be done. In addition, when the engine speed remains below a predetermined value for a further predetermined period, 0. When it is determined that the sensor has been exposed for a long period of time, feedback control is stopped, and a predetermined amount of fuel is injected using feedforward control.

〔Effect of the invention〕

Therefore, according to the present invention, learning is stopped in the initial state where the sensor is exposed to low temperature exhaust gas, feedback control is stopped in the state where the sensor is exposed to low temperature exhaust gas for a long period of time, and 0. This provides the effect of preventing deterioration of the stability of the engine speed during idling and deterioration of emissions during idling due to the influence of the sensor's environmental characteristics.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a schematic diagram of an internal combustion engine equipped with an air-fuel ratio control device to which an embodiment of the present invention is applied.

An intake temperature sensor 2 is installed downstream of an air cleaner (not shown) to detect the temperature of intake air and output an intake temperature signal. A throttle valve 4 is arranged downstream of the intake air temperature sensor, and an idle switch 6 is attached which is connected to the throttle valve 4 and turns on when the throttle valve is fully closed and turns off when the throttle valve opens. A surge tank 8 is provided downstream of the throttle valve 4, and a pressure sensor 10 is attached to the surge tank 8 to detect the intake pipe pressure downstream of the throttle valve and output an intake pipe pressure signal. The surge tank 8 is communicated with a combustion chamber 14 of the engine via an intake manifold 12. This intake manifold 12 has
A fuel injection valve 16 is attached to each cylinder. The combustion chamber 14 of the engine is communicated via an exhaust manifold with a catalytic converter (not shown) filled with a three-way catalyst. Further, a water temperature sensor 20 is attached to the engine block to detect the engine cooling water temperature and output a water temperature signal. A tip of a spark plug 22 projects into the combustion chamber 14 of the engine, and a distributor 24 is connected to the spark plug 22. The distributor 24 is provided with a cylinder discrimination sensor 26 and an engine rotation speed sensor 28, each of which includes a pickup fixed to the distributor housing and a signal rotor fixed to the distributor shaft. The cylinder discrimination sensor 26 outputs a cylinder discrimination signal to a control circuit 30 constituted by a microcomputer or the like every 720° CA, for example, and outputs an engine speed signal to the control circuit 30. And the distributor 24 is an igniter 32
It is connected to the. Note that 34 is an O sensor that detects the residual acidity in the exhaust gas and outputs an air-fuel ratio signal shown in FIG.

As shown in FIG. 4, the control circuit 30 includes a central processing unit (C
PU) 36, read only memory (ROM) 38, random access memory (RAM) 40, backup RAM (BU RAM) 42, input/output port (■10) 44
, an analog/digital converter (ADC) 46, and buses such as a data bus and a control bus that connect these. A cylinder discrimination signal, a crank angle signal, an air-fuel ratio signal, and a throttle signal output from the idle switch 6 are input to the engine 1044, and a fuel injection controller 1044 controls the opening/closing time of the fuel injection valve 16 via a drive circuit. A signal and an ignition signal that controls the on/off time of the igniter 32 are output. Further, an intake pipe pressure signal, an intake air temperature signal, and a water temperature signal are input to the ADC 46 and converted into digital signals. In the above ROM33,
Control programs and the like, which will be explained in the following processing routine, are stored in advance.

In this embodiment, the fuel injection time TAυ is calculated according to the following equation (3).

TAU=(TP+TAUG), (1+KGn) @
? WL @, FAF・FTHA・(1-1-FT(1)
+τ7...°...(3) However, TP is the basic fuel injection time determined by the intake pipe pressure and engine speed;
TAUG is the o learning value, KGn (n=
1+ 2+ "") is the off-idle learning value determined according to the intake pipe pressure region divided into multiple regions as shown in Table 1, FWL is the warm-up correction coefficient, FAF
is the air-fuel ratio feedback correction coefficient shown in Fig. 2, FTH
A is an intake air temperature correction coefficient, FTC is a transient correction coefficient, and τV is an invalid injection time for voltage compensation.

Table 1 Intake pipe pressure P M -K G n100mH #≦
PM (200mHI KGI200 order H1≦PM
(300km HJI KG.

300 HJI≦PM (400 Hp K().

400 mad'≦PM (500 Dragon Hjl KG.

500mHI≦PM (600mHj KG.

The above-mentioned transient correction coefficient FTC is set to a positive predetermined value during acceleration, a negative predetermined value during deceleration, and 0 in a steady state.

The above learning values TAUG and KGn are the fifth values explained below.
Learned by the learning routine shown in the figure, the learned value TAUG is applied to the above equation (3) in all operating regions, and KGn is applied to the above equation (3) in the learned region. However, KG is also applied to the above equation (3) in the region of PM (100 Tan HJI), and is also applied to the equation (3) in the region of KGllFiPM≧600HJI.

Next, the main routine of this embodiment will be explained with reference to FIG. First, in step 80, it is determined whether the idle switch is on based on the throttle signal,
When it is determined that the idle switch is off, the count value 5KIP of the number of skips of the air-fuel ratio feedback correction coefficient FAF is set to 0 in step 90, and a learning process is executed in step 91.

On the other hand, when it is determined that the idle switch is on, step 81 determines whether the engine is rotating? NB is 0. It is determined whether the engine rotation speed Ng is below a predetermined rotation speed (for example, 1ooorpm) corresponding to the exhaust gas temperature at which the sensor becomes inactive, and if the engine rotation speed Ng exceeds the predetermined rotation speed, steps 90 and 91 are executed, and the engine If the rotational speed NEi is below the predetermined rotational speed, it is determined in step 82 whether or not the air-fuel ratio feedback correction coefficient FAT has been skipped. When it is determined that the correction coefficient FAF has been skipped, the count value 5KIP is incremented by one in step 83. In the next step 84, the count value 5K
It is determined whether the IP exceeds a predetermined value A (0, a value to which the environmental characteristics of the sensor affect the learned value), and if the count value 5KIP is less than the predetermined value A, the learning process is executed in step 91. However, if the count value 5KIP exceeds the predetermined value A, the process proceeds to step 85 without executing the learning process.

In step 85, it is determined whether or not the count value 5KIP is less than or equal to a predetermined value B that is larger than the predetermined value A (a value to which the environmental characteristics of the sensor affect feedback control). For example, in step 86, the air-fuel ratio feedback correction coefficient FAF is calculated based on the air-fuel ratio signal obtained from the Otsen output, and if the count value 5KIP exceeds the predetermined value B, the air-fuel ratio feedback correction coefficient FAF is kept constant in step 89. value(
For example, a constant value within the range of 0.98 to 1.02) is set so that the seed pack control is not performed, and the process proceeds to step 87. Then, in step 87, the basic fuel injection time T P (T P == k , g71F'
, where k is a constant), and in step 88 the above (
3) The fuel injection time TAU is calculated based on the formula, and the fuel injection valve is controlled in a step not shown so that fuel corresponding to the fuel injection time TAU is injected.

As a result of the above, when the idle switch is on, when the engine speed exceeds the predetermined speed with the idle switch on, when the engine speed is below the predetermined speed with the idle switch on and the air-fuel ratio is The learning value is learned and the air-fuel ratio foot check control is performed until the air-fuel ratio feed is skipped A number of times. Learning is prohibited and only air-fuel ratio feedback control is performed, and after the air-fuel ratio feedback correction coefficient has skipped B and -A times, learning is prohibited and air-fuel ratio feedback control is also prohibited. FIG. 7 shows the learning prohibited area and air-fuel ratio feedback prohibited area when controlled as follows.

Next, details of step 91 in FIG. 1 are shown in FIGS. 5 and 6. First, in step 100, it is determined whether the idle switch is off. When the idle switch is off, the intake pipe pressure PM is set to 10 in step 101.
It is determined whether the intake pipe pressure PM is within the range from On+H# to 600 Fuji Hg, that is, whether the intake pipe pressure PM is within the learning range. This intake pipe pressure range indicates the intake pipe pressure under steady running conditions. When the intake pipe pressure PM is within the learning range, the learning conditions from step 103 onwards are judged and the learning value is learned; when the intake pipe pressure PM is not within the learning range, the learning value is learned without learning. Proceed to the first Luachin. On the other hand, when the idle switch is on, it is determined in step 102 whether the engine speed Nε is less than a predetermined value (for example, 101,000 rpm) and the intake pipe pressure PM exceeds a predetermined value (for example, 1oomHII).

If the judgment in step 102 is affirmative, that is, in the case of normal idling, the learning conditions from step 103 onwards are judged and the learning value is learned, and if the judgment in step 102 is negative, that is, in the case of cranking or idle up. etc., proceed to the next routine without learning.

Step】03 is 0. Based on the output signal of the sensor, it is determined whether feedback control is being performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. If feedback control is not being performed, for example if lean control is being performed, abnormal learning may occur, so the process immediately proceeds to the next routine. If feedback control is being performed, the engine coolant temperature TRY is set to a predetermined value in step 104. value (e.g. 8
0°C). Cooling water temperature THW
When is below a predetermined value, learning is not performed because the engine is warming up, and when the coolant temperature THW exceeds a predetermined value, step 105 determines that the intake air temperature THA detected by the intake air temperature sensor is within a predetermined range (for example, 40°C< THA (90℃)
Determine whether the temperature is at or below. Learning is not performed when the intake air temperature THA is outside the predetermined range, that is, at extremely low temperatures or high temperatures, and when the intake air temperature THA is within the predetermined range, the air-fuel ratio feedback correction coefficient FAF is determined in step 106.
It is determined whether or not it has been skipped, and only when it has been skipped, the learning value is learned in step 107.

An example of the learning value calculation in step 107 will be explained based on FIG. 6. Note that FIG. 6 mainly shows learning of the learning value TAUG that is performed when the idle switch is turned on. First, in step 110, it is determined whether or not the air-fuel ratio feedback correction coefficient FAT has skipped a predetermined value (a value smaller than A). If the air-fuel ratio feedback correction coefficient FAT has skipped a predetermined number of times, in step 111, the air-fuel ratio is feedback based on the above equation (2). Calculate the average value FAFAV of the correction coefficients.

In the next step 112, it is determined whether the idle switch is on or not, and if the idle switch is off, step 11
In step 5, learning of the learning value KGn is executed. On the other hand, if the idle switch is on, in step 113 and step 1'1'4, the average value FATAV of the air-fuel ratio feedback correction coefficient FAF is within a predetermined range (for example, 1
．． 02≦FAFAV≧0.98), and if the average value FAFAV exceeds the upper limit, step 1
16, the learning value T A V,G is set to a predetermined value K (for example, δ
If the average value F'AFAV is less than the lower limit value, the learned value TAUG is decreased to a predetermined value in step 117.

As described above, the learning value TAUGO value is increased or decreased so that the air-fuel ratio feedback correction coefficient becomes a value within a predetermined range.

FIG. 8 shows the average value FAFAV of the learning value TAUG1 correction coefficient according to this embodiment, each change in air-fuel ratio, and a comparative example of learning in the case where learning is continued with B skipping grooves and feedback control is discontinued after B skipping. The value 'r AU G , the average value PAFAV of the correction coefficient, and each emptying of the air-fuel ratio are compared and shown. Note that the solid line indicates changes in the comparative example, and the broken line indicates changes in the present example.

In addition, although the example in which learning and feedback control are prohibited based on the number of skips has been described above, the area in which learning and feedback control are prohibited may be determined based on time. Furthermore, although the example in which the basic fuel injection time is determined based on the engine speed and the intake pipe pressure has been described above, the present invention also applies to an engine in which the basic fuel injection time is determined based on the engine speed and the amount of intake air per engine revolution. It is possible to apply

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the main routine of an embodiment of the present invention, FIG. 2 is a diagram showing changes in the air-fuel ratio feedback correction coefficient, etc., and FIG. 3 is a schematic diagram showing an engine to which the present invention is applied. 4 is a block diagram showing details of the control circuit of FIG. 3, FIG. 5 is a flowchart showing the learning routine of the above embodiment, FIG. 6 is a flowchart showing details of the learning value calculation of FIG. 5, and FIG. The figure is a diagram illustrating the learning prohibited area and the feedback control prohibited area of this embodiment, and FIG. 8 is a diagram showing changes in learning values between this embodiment and a comparative example. lO...Pressure sensor, 16...Fuel injection valve, 3
0...control circuit, 34...0. sensor.

Claims (1)

[Claims] (1) O_2 detects the basic fuel injection time determined by the engine load and engine speed and the residual oxygen concentration in the exhaust gas
The air-fuel ratio is adjusted based on the air-fuel ratio feedback correction coefficient obtained based on the output signal of the sensor and a learned value whose value is increased or decreased during idling so that the average value of the air-fuel ratio feedback correction coefficient falls within a predetermined range. In an air-fuel ratio learning control method for an internal combustion engine that performs feedback control of
When the engine speed continues to be below a predetermined value for a predetermined period, the learning value stops increasing or decreasing, and when the engine speed continues to be below the predetermined value for a further predetermined period, the air-fuel ratio feedback control is stopped. An air-fuel ratio learning control method for an internal combustion engine, characterized in that: