JPH0794807B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio control method for an internal combustion engine.

BACKGROUND ART For the purpose of purifying exhaust gas from an internal combustion engine and improving fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the air-fuel mixture supplied to the engine is determined according to the output signal of this oxygen concentration sensor. There is an air-fuel ratio control device that performs feedback control to a target air-fuel ratio.

As an oxygen concentration sensor used in such an air-fuel ratio control device, there is one that produces an output proportional to the oxygen concentration in the gas to be measured. For example, an electrode pair is provided on both main surfaces of a flat plate-shaped oxygen ion conductive solid electrolyte member, one electrode surface of the solid electrolyte member forms a part of a gas retention chamber, and the gas retention chamber is introduced with the gas to be measured. A limiting current type oxygen concentration sensor which communicates through a hole is disclosed in Japanese Patent Laid-Open No. 52-72286. In this oxygen concentration sensor, when the oxygen ion conductive solid electrolyte member and the electrode pair act as an oxygen pump element to supply a current between the electrodes so that the electrode on the gap chamber side becomes the negative electrode, gas is generated on the negative electrode surface side. Oxygen gas in the gas in the retention chamber is ionized, moves inside the solid electrolyte member toward the positive electrode surface, and is released as oxygen gas from the positive electrode surface. The limiting current value that can flow between the electrodes at this time is almost constant regardless of the applied voltage and is proportional to the oxygen concentration in the gas to be measured. Therefore, if the limiting current value is detected, the oxygen concentration in the gas to be measured is measured. be able to. However, when controlling the air-fuel ratio using such an oxygen concentration sensor, an output proportional to the oxygen concentration can only be obtained from the oxygen concentration in the exhaust gas when the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. Air-fuel ratio control with the target air-fuel ratio set in the rich region was impossible. Further, as an oxygen concentration sensor capable of obtaining an output proportional to the oxygen concentration in the exhaust gas in the lean and rich regions of the air-fuel ratio, two flat plate-like oxygen ion conductive solid electrolyte members are provided with electrode pairs, and two solid electrodes are provided. One of the electrode surfaces of the electrolyte member forms a part of the gas retention chamber, and the gas retention chamber communicates with the gas to be measured through the introduction hole, and the other electrode surface of the one solid electrolyte member faces the atmosphere chamber. Such a sensor is disclosed in JP-A-59-192955. In this oxygen concentration sensor, one of the oxygen ion conductive solid electrolyte member and the electrode pair acts as an oxygen concentration ratio detection battery element, and the other oxygen ion conductive solid electrolyte member and the electrode pair acts as an oxygen pump element. It has become.
When the voltage generated between the electrodes of the oxygen concentration ratio detection battery element is equal to or higher than the reference voltage, a current is supplied so that oxygen ions move in the oxygen pump element toward the gas retention chamber side electrode, and the oxygen concentration ratio detection battery element When the generated voltage between the electrodes is less than the reference voltage, by supplying current so that oxygen ions move in the oxygen pump element toward the electrode on the side opposite to the gas retention chamber side, the air-fuel ratio in the lean and rich regions is increased. The current value is proportional to the oxygen concentration.

When performing air-fuel ratio control using such an oxygen concentration proportional type oxygen concentration sensor, similar to the case of conventional air-fuel ratio control using an oxygen concentration sensor that is not proportional to oxygen concentration, the intake pipe pressure, etc. A reference value for air-fuel ratio control is set according to the engine operating parameter related to the engine load, the reference value for the target air-fuel ratio is corrected according to the output of the oxygen concentration sensor, and the output value is obtained. It is designed to control the air-fuel ratio of. However, the oxygen concentration level in the exhaust gas can be obtained from the output of the oxygen concentration sensor of the oxygen concentration proportional type, and therefore the air-fuel ratio of the supplied mixture can be detected, which is proportional to the conventional oxygen concentration. There is a demand for an air-fuel ratio control method that can obtain good drivability and exhaust gas purification performance by highly accurate air-fuel ratio control even by air-fuel ratio control using a non-type oxygen concentration sensor. In particular, during transient operation such as acceleration or deceleration operation, the change of the air-fuel ratio becomes large due to the response delay of the air-fuel ratio control, so that it is very difficult to control the air-fuel ratio with high accuracy.

A method for controlling the air-fuel ratio during acceleration / deceleration is disclosed in JP-A-60-
The method disclosed in Japanese Patent No. 224945 is known, but in the method of learning the transient increase coefficient according to only the load during acceleration / deceleration, the transient increase coefficient is not learned according to the change amount of the operating parameter during the transient. Therefore, the learning correction was delayed during acceleration / deceleration, and the optimum transient air-fuel ratio was not obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to improve the drivability during acceleration and deceleration operation and the exhaust purification performance by highly accurate air-fuel ratio control using an oxygen concentration proportional oxygen concentration sensor. It is to provide a control method.

The air-fuel ratio control method of the present invention is a reference value for air-fuel ratio control according to a plurality of engine operating parameters relating to the load of an internal combustion engine equipped with an oxygen concentration sensor that produces an output proportional to the oxygen concentration in exhaust gas. And an air-fuel ratio control value determined according to the deviation between the air-fuel ratio detected from the output of the oxygen concentration sensor and the target air-fuel ratio, and a transient correction value during acceleration or deceleration according to the amount of change in engine operating parameters. It is an air-fuel ratio control method at the time of acceleration and deceleration of an internal combustion engine that determines an output value at the time of acceleration or deceleration using, and controls the air-fuel ratio of a supply air-fuel mixture according to the determined output value. Has a data map for storing the transient correction correction value, and sets the transient correction basic value according to the detected value of the change amount during acceleration or deceleration, and the transient correction correction value corresponding to the detected value of the change amount is stored in the data map. The above-mentioned transient correction value is obtained by modifying the transient correction basic value read and set from the transient correction correction value, and the deviation between the air-fuel ratio detected from the output of the oxygen concentration sensor and the target air-fuel ratio and the read transient correction The present invention is characterized in that a new transient correction correction value is calculated according to the correction value, and the transient correction correction value is updated by writing it in the storage position of the data map corresponding to the detected value of the change amount.

EXAMPLES Examples of the present invention will be described below with reference to the drawings.

1 to 3 show an electronically controlled fuel injection device to which the air-fuel ratio control method of the present invention is applied. In this device, the oxygen concentration sensor detection unit 1 is arranged upstream of the three-way catalytic converter 5 in the exhaust pipe 3 of the engine 2, and the input / output of the oxygen concentration sensor detection unit 1 is an ECU (Electronic Control Uni
t) 4 is connected.

As shown in FIG. 2, a substantially rectangular parallelepiped oxygen ion conductive solid electrolyte member 12 is provided in the protective case 11 of the oxygen concentration sensor detection unit 1. A gas retention chamber 13 is formed in the oxygen ion conductive solid electrolyte member 12. The gas retention chamber 13 communicates with the introduction hole 14 for introducing the exhaust gas of the gas to be measured from the outside of the solid electrolyte 12, and the introduction hole 14 is located in the exhaust pipe 3 so that the gas retention chamber 13 can easily flow into the exhaust gas retention chamber 13. It Further, the oxygen ion conductive solid electrolyte member 12 is formed with an atmosphere reference chamber 15 for introducing the atmosphere so as to separate the wall from the gas retention chamber 13. An electrode pair 17 is provided on the wall between the gas retention chamber 13 and the atmospheric reference chamber 15 and on the wall opposite to the atmospheric reference chamber 15.
a, 17b, 16a and 16b are formed respectively. Solid electrolyte member 1
2 and the electrode pair 16a, 16b act as the oxygen pump element 18,
The solid electrolyte member 12 and the electrode pairs 17a and 17b act as the battery element 19. In addition, a heater element is provided on the outer wall surface of the atmospheric standard chamber 15.
20 are provided.

ZrO ₂ (zirconium dioxide) is used as the oxygen ion conductive solid electrolyte member 12, and Pt (platinum) is used as the electrodes 16a to 17b.

As shown in FIG. 3, the ECU 4 is provided with an oxygen concentration sensor control unit including a differential amplifier circuit 21, a reference voltage source 22, and a resistor 23. The electrode 16b of the oxygen pump element 18 and the electrode 17b of the battery element 19 are grounded. A differential amplifier circuit 21 is connected to the electrode 17a of the battery element 19, and the differential amplifier circuit 21 is a battery element.
It outputs a voltage according to the difference voltage between the voltage between the electrodes 17a and 17b of 19 and the output voltage of the reference voltage source 22. The output voltage of the reference voltage source 22 is a voltage (0.4 [V]) corresponding to the stoichiometric air-fuel ratio. The output terminal of the differential amplifier circuit 21 is connected to the electrode 16a of the oxygen pump element 18 via the current detection resistor 23. Both ends of the current detection resistor 23 are output ends of the oxygen concentration sensor and are connected to a control circuit 25 including a microcomputer.

The control circuit 25 includes, for example, a potentiometer, a throttle valve opening sensor 31 that generates an output voltage at a level corresponding to the opening of the throttle valve 26, and an intake pipe 27 provided in the intake pipe 27 downstream of the throttle valve 26. Absolute pressure sensor 32 that generates an output voltage at a level according to the absolute pressure inside, a water temperature sensor 33 that generates an output voltage at a level according to the cooling water temperature of the engine, and an air intake port
An intake air temperature sensor 34 that is provided in the vicinity of 28 and generates an output at a level according to the intake air temperature is connected to a crank angle sensor 35 that generates a pulse signal in synchronization with the rotation of a crankshaft (not shown) of the engine 2. Has been done. Engine 2
An injector 36 provided in the intake pipe 27 near the intake valve (not shown) is connected.

The control circuit 25 includes a differential input A / D converter 40 that converts the voltage across the current detection resistor 23 into a digital signal, a throttle valve opening sensor 31, an absolute pressure sensor 32, a water temperature sensor 33, and an intake air temperature sensor 34. A level conversion circuit 41 that converts each output level, a multiplexer 42 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 41, and an A / A that converts the signal output from this multiplexer 42 into a digital signal. D converter 4
3 and the output signal of the crank angle sensor 35
Waveform shaping circuit 44 that outputs as a signal, and waveform shaping circuit 44
A counter 45 that measures the generation interval of the TDC signal from the clock pulse generation circuit (not shown) by the number of clock pulses output from it, a drive circuit 46 that drives the injector 36, and a digital operation according to a program.
It is provided with a CPU (central processing unit) 47, a ROM 48 in which various processing programs and data are written in advance, and a RAM 49. A / D converters 40, 43, multiplexer 42, counter 4
5, drive circuit 46, CPU47, ROM48 and RAM49 are input / output bus 50
Are connected to each other by. The TDC signal is supplied from the waveform shaping circuit 44 to the CPU 47. Further, a heater current supply circuit 51 is provided in the control circuit 25. The heater current supply circuit 51 is composed of, for example, a switching element, and the CPU 47
A switching element is turned on in response to a heater current supply command from the heater element, and a heater current is supplied by applying a voltage between the terminals of the heater element 20 to heat the heater element 20. The RAM 49 is backed up so that the stored contents will not be lost even when the ignition switch (not shown) is turned off.

In such a configuration, the pump current value I _P flowing from the A / D converter 40 through the oxygen pump element 18, the throttle valve opening θth from the A / D converter 43, the intake pipe absolute pressure P _BA , the cooling water temperature T _W and Information on the intake air temperature T _A is supplied as an alternative, and information indicating the count value within the rotation pulse generation period is supplied from the counter 45 to the CPU 47 via the input / output bus 50. The CPU 47 reads the above-mentioned information in accordance with the arithmetic program stored in the ROM 48, and in synchronization with the TDC signal based on the information, the injector corresponding to the fuel supply amount to the engine 2 from the predetermined calculation formula in the fuel supply routine. 36 fuel injection times T _OUT
Is calculated. The drive circuit 46 drives the injector 36 for the fuel injection time T _OUT to supply the fuel to the engine 2.

The fuel injection time T _OUT is calculated from the following equation, for example.

T _OUT = Ti x K _O2 x K _REF x K _WOT x K _TW + T _ACC + T _DEC ......
(1) Here, Ti is a reference injection time which is a reference value for air-fuel ratio control determined by a data map search from ROM 48 according to the engine speed Ne and the intake pipe absolute pressure P _BA, and K _O2 is an oxygen concentration. Feedback correction coefficient of the air-fuel ratio set according to the output level of the sensor, T _REF is the air-fuel ratio feedback control automatic correction that is determined by the data map search from RAM49 according to the engine speed Ne and the intake pipe absolute pressure P _BA Coefficient, K _WOT is the fuel increase correction coefficient at high load, and K _TW is the cooling water temperature coefficient. Further, T _ACC is an acceleration increase value as a transient correction value during acceleration, and T _DEC is a deceleration decrease value as a transient correction value during deceleration. Ti, K _O2 , K _REF , K _WOT , K _TW , T _ACC ,
T _DEC is set in a subroutine of the fuel supply routine.

On the other hand, when the supply of the pump current to the oxygen pump element 18 is started, if the air-fuel ratio of the air-fuel mixture supplied to the engine 2 at that time is in the lean region, it is generated between the electrodes 17a and 17b of the battery element 19. Since the voltage becomes lower than the output voltage of the reference voltage source 22, the output level of the differential amplifier circuit 21 becomes a positive level, and this positive level voltage is supplied to the series circuit of the resistor 23 and the oxygen pump element 18. A pump current flows from the electrode 16a to the electrode 16b in the oxygen pump element 18, so that oxygen in the gas retention chamber 13 is ionized at the electrode 16b and moves in the oxygen pump element 18 to be released as oxygen gas from the electrode 16a. Then, oxygen in the gas retention chamber 13 is pumped out.

By pumping out oxygen in the gas retention chamber 13, an oxygen concentration difference occurs between the exhaust gas in the gas retention chamber 13 and the atmosphere in the atmosphere reference chamber 15. A voltage Vs corresponding to this oxygen concentration difference is generated between the electrodes 17a and 17b of the battery element 19, and this voltage Vs is generated by the differential amplifier circuit 21.
Is supplied to the inverting input terminal of. Since the output voltage of the differential amplifier circuit 21 is a voltage proportional to the difference voltage between the voltage Vs and the output voltage of the reference voltage source 22, the pump current value is proportional to the oxygen concentration in the exhaust gas, and the pump current value is the resistance 23. It is output as the voltage across both ends.

When the air-fuel ratio is in the rich region, the voltage Vs exceeds the output voltage of the reference voltage source 22. Therefore, the output level of the differential amplifier circuit 21 is inverted from the positive level to the negative level. Due to this negative level, the pump current flowing between the electrodes 16a and 16b of the oxygen pump element 18 decreases and the current direction is reversed. That is, since the pump current flows from the electrode 16b in the direction of the electrode 16a, external oxygen is ionized at the electrode 16a and moves in the oxygen pump element 18, and is discharged from the electrode 16b as oxygen gas into the gas retention chamber 13 to generate oxygen. Are pumped into the gas retention chamber 13. Therefore,
Oxygen is pumped in and out by supplying a pump current so that the oxygen concentration in the gas retention chamber 13 is always constant, so the pump current value I _P is the oxygen concentration in the exhaust gas in the lean and rich regions. Is proportional to each.
The feedback correction coefficient K _O2 described above is set in the K _O2 calculation subroutine according to the pump current value I _P.

Next, the procedure of the K _O2 calculation subroutine is shown in FIG.
It will be described according to the operation flow chart of 47.

In this procedure, the CPU 47 determines whether the activation of the oxygen concentration sensor is completed as shown in FIG. 4 (step 61). This determination is determined by, for example, the elapsed time from the start of supplying the heater current to the heater element 20 or the cooling water temperature Tw. If the activation of the oxygen concentration sensor is completed, the temperature T corresponding to the intake air temperature T _A reads the intake air temperature T _{A Wo2}
Is set (step 62). The temperature T _Wo2 corresponding to the intake air temperature T _A is stored in the _{ROM 48 in} advance as a T _Wo2 data map with the characteristics shown in FIG. 6, and the temperature T _Wo2 corresponding to the read intake air temperature T _A is _stored in the T _Wo2 data. Search from the map. After setting the temperature T _Wo2 , set the target air-fuel ratio AF _TAR according to each information (step 63), read the pump current value I _P (step 64), and detect the detected air-fuel ratio AF indicated by the pump current value I _{P. The ACT} is obtained from the AF data map stored beforehand in the ROM 48 (step 65). The target air-fuel ratio AF _TAR is, for example, ROM
A data map different from the AF data map stored in advance in 48 is searched and set according to the engine speed Ne and the intake pipe absolute pressure P _BA . Set target air-fuel ratio AF _TAR
Is determined to be a value in the range of 14.2 to 15.2 (step 66). In the case of AF _TAR <14.2 or AF _TAR > 15.2., The cooling water temperature Tw is read for feedback control to the target air-fuel ratio AF _TAR other than near the theoretical air-fuel ratio, and if the cooling water temperature Tw is _higher than the temperature T _Wo2 . It is determined whether there is any (step 67). If Tw ≦ T _Wo2 , it is determined whether or not the value obtained by subtracting the allowable value DAF ₁ from the detected air-fuel ratio AF _ACT is larger than the target air-fuel ratio AF _TAR (step 68). AF _ACT −DAF ₁
> When AF _TAR , the detected air-fuel ratio AF _ACT is the target air-fuel ratio AF _TAR
More a lean _{AF ACT - (AF TAR + DAF} 1) RAM49 to be stored as a present deviation Delta] AF _n (step 69), AF _ACT -D
When AF ₁ ≤ AF _TAR , it is determined whether the value obtained by adding the allowable value DAF ₁ to the detected air-fuel ratio AF _ACT is smaller than the target air-fuel ratio AF _TAR (step 70). When AF _ACT + DAF ₁ <AF _TAR , the detected air-fuel ratio AF _ACT is richer than the target air-fuel ratio AF _TAR and AF
_{ACT - (AF TAR -DAF 1)} RAM49 is stored in the as a current deviation Delta] AF _n (step _{71), AF ACT + DAF 1} ≧ AF tolerance detected air-fuel ratio AF _ACT with respect to the target air-fuel ratio AF _TAR when the _TAR DA
It is in F ₁ and this deviation ΔAF _n is stored as 0 in the RAM 49 (step 72).

If Tw> T _Wo2 , the learning control subroutine described later is executed (step 73), and then step 68 is executed to make the deviation Δ
Calculate AF _n .

Deviation Δ in step 69, step 71 or step 72
When AF _n is calculated, the proportional control coefficient K _OP is calculated from the K _OP data map stored in advance in the ROM 48 as the engine speed Ne and the deviation AF.
(= AF _ACT- AF _TAR ) according to (step 74),
The current proportional amount K _O2Pn is calculated by multiplying the proportional control coefficient K _OP by the deviation ΔAF _n (step 75). Also, R
The integral control coefficient K _OI is searched according to the engine speed Ne from the K _OI data map stored in advance in the OM48 (step 7
6), the previous integral K _{O2I n-1} is read from the RAM 49 (step 77), the integral control coefficient K _OI is multiplied by the deviation ΔAF _n , and the previous integral K _{O2I n-1} is added. Integral
Calculate K _O2In (step 78). Furthermore, the previous deviation ΔAF
_n-1 is read from RAM49 (step 79) and the previous deviation Δ
The current differential component K _O2Dn is calculated by subtracting the current deviation ΔAF _n from AF _n-1 and multiplying by the differential control coefficient K _OD of a predetermined value (step 80). And the calculated proportional
The air-fuel ratio feedback correction coefficient K _O2 is calculated by adding the K _O2Pn , the integral _{O 2 In} and the derivative K _O2Dn (step 81).

For example, if AF _ACT = 11, AF _TAR = 9, and DAF ₁ = 1, the air-fuel ratio is judged to be lean, and ΔAF _n = 1 is used to calculate the proportional component.
K _O2Pn , integral _{O 2 In} and derivative K _O2Dn are calculated. AF
_{When ACT} = 7, AF _TAR = 9, and DAF ₁ = 1, it is determined that the air-fuel ratio is rich, and ΔAF _n = -1 is used to calculate the proportional component K _O2Pn and the integral component.
_O2In and the derivative K _O2Dn are calculated. AF _ACT = 11, AF
_{When TAR} = 10 and DAF ₁ = 1, the detected air-fuel ratio AF _ACT is within the allowable value DAF _{1 with} respect to the target air-fuel ratio AF _TAR , and ΔAF _n = 0,
If this state continues, K _O2Pn = K _O2Dn = 0 and feedback control is _performed only by the integral K _O2In . In addition,
Empty since the proportional control coefficient K _OP becomes a value proportional control coefficient K _OP is considering deviations and intake mixture rate of the detected air-fuel ratio and the target air-fuel ratio by setting in accordance with the engine speed Ne and deviation ΔAF It is possible to improve the responsiveness to changes in the fuel ratio.

On the other hand, if it is determined in step 66 that 14.2 ≤ AF _TAR ≤ 15.2, a λ = 1 PID control subroutine is executed for feedback control of the theoretical air-fuel ratio target air-fuel ratio AF _TAR (step 82).

Next, in the λ = 1 PID control subroutine, as shown in FIG. 5, the cooling water temperature Tw is read and the cooling water temperature Tw is the temperature.
It is determined whether it is _larger than T _Wo2 (step 101). T
If w ≦ T _Wo2 , it is determined whether or not the value obtained by subtracting the allowable value DAF ₂ from the detected air-fuel ratio AF _ACT is larger than the target air-fuel ratio AF _TAR (step 102). When AF _ACT- DAF ₂ > AF _TAR , the detected air-fuel ratio AF _ACT is leaner than the target air-fuel ratio AF _TAR , and AF
_{ACT - (AF TAR + DAF 2} ) RAM49 is stored in the as a current deviation Delta] AF _n (step 103), the target value obtained by adding the tolerance DAF ₂ to the detected air-fuel ratio AF _ACT when the AF _ACT -DAF ₂ ≦ AF _TAR It is determined whether the air-fuel ratio is smaller than AF _TAR (step 1
04). AF _ACT + DAF ₂ <AF _TAR detected air-fuel ratio AF _ACT
Is richer than the target air-fuel ratio AF _TAR , and AF _ACT − (AF _TAR −D
AF ₂ ) is stored in RAM49 as the current deviation ΔAF _n (step 105), and when AF _ACT + DAF ₂ ≧ AF _TAR , the detected air-fuel ratio A
F _ACT is within the allowable value DAF _{2 with} respect to the target air-fuel ratio AF _TAR , and the current deviation ΔAF _{n is set} to 0 and stored in the RAM 49 (step
106).

If Tw> T _Wo2 , the learning control subroutine is executed (step 107), and then step 102 is executed to make the deviation ΔAF _n
To calculate.

When the deviation ΔAF _n is calculated in step 103, step 105 or step 106, the proportional control coefficient K _OP is converted into the engine speed Ne and the deviation ΔAF (= AF _ACT −AF _TAR ) from the K _OP data map stored in advance in the ROM 48. Search accordingly (step
108), the proportional control coefficient K _OP is multiplied by the deviation ΔAF _n to calculate the proportional portion K _O2Pn at this time (step 10).
9). Further, the integral control coefficient K _OI is searched according to the engine speed Ne from the K _OI data map stored in advance in the ROM 48 (step 110), and the previous integral K _{O2I n-1} is read from the RAM 49 (step 111). , The deviation ΔAF _n to the integral control coefficient K _OI
Is multiplied and the previous integral K _{O2I n-1} is added to calculate the current integral K _O2In (step 112). Furthermore, the previous deviation ΔAF _n-1 is read from RAM 49 (step 11
3), calculates a present differential component K _O2Dn by multiplying the differential control coefficient K _OD of subtracting the current deviation Delta] AF _n from the previous deviation Delta] AF _n-1 and a predetermined value (step 114). And
The air-fuel ratio feedback correction coefficient K _O2 is calculated by adding the calculated proportional component K _O2Pn , integral component K _O2In and derivative component K _O2Dn.
Is calculated (step 115).

After calculating the air-fuel ratio feedback correction coefficient K _O2 , the absolute value of the value obtained by subtracting the target air-fuel ratio AF _TAR from the detected air-fuel ratio AF _ACT is 0.
It is determined whether it is 5 or less (step 116). | AF _ACT
−AF _TAR | ≦ 0.5, the correction coefficient K _O2 is made equal to the predetermined value K ₁ (step 117), and it is determined whether (−1) ⁿ is greater than 0 (step 118), (−) 1) ^n> a value obtained by adding a predetermined value P ₁ in the correction coefficient K _O2 is at ⁰ and the correction coefficient K _O2 (step 119), (- 1) predetermined value P ₁ from the correction coefficient K _O2 is when ⁿ ≦ 0 A correction coefficient K _{O2 is applied} to the subtracted value (step 120). | AF _ACT −AF _TAR |> 0.5, step 11
The correction coefficient K _O2 calculated in 5 is held. The predetermined value K ₁ is, for example, the value of the correction coefficient K _O2 when controlling the air-fuel ratio to 14.7.

Therefore, when the target air-fuel ratio AF _TAR is a value near the theoretical air-fuel ratio, |
If the state of AF _ACT −AF _TAR | ≦ 0.5 continues, every time the TDC signal is generated, K _O2 + P ₁ and K _O2 −P ₁ are alternately set as the air-fuel ratio feedback correction coefficient K _O2 . The fuel injection time T _OUT is calculated by the equation (1) using this coefficient K _O2, and the fuel is injected into the engine 2 by the injector 36 for the fuel injection time T _OUT, so that the air-fuel ratio of the air-fuel mixture supplied to the engine is In response to the TDC signal, small and rich vibrations center around 14.7, and perturbation occurs in order to improve the exhaust purification efficiency by the three-way catalyst.

In step 62, the temperature T _Wo2 for determining the cooling water temperature Tw corresponding to the intake air temperature T _A is set so that the fuel adhesion amount on the inner wall of the intake pipe increases as the intake air temperature decreases, and the fuel increase correction is performed by the correction coefficient K _TW . However, the correction coefficient K _O2 is used to calculate the air-fuel ratio feedback control automatic correction coefficient K _REF in the learning control subroutine, so the amount of fuel adhering varies depending on the operating state and the air-fuel ratio detection of the supply air-fuel mixture by the oxygen concentration sensor This is because the accuracy decreases and the accuracy of the correction coefficient K _O2 also decreases. Therefore, the correction coefficient K _O2 calculated when Tw> T _Wo2 is used to calculate and update the air-fuel ratio feedback control automatic correction coefficient K _REF .

Next, the learning control subroutine according to the present invention will be described. As shown in FIG. 7, the CPU 47 first determines whether or not the transient operation flag F _TRS is 1 (step 12
1). If F _TRS = 0, it means that the normal operation was performed when the previous learning control subroutine was executed.
It is determined whether or not it is the acceleration operation (step 122), and when it is not the acceleration operation, it is further determined whether or not it is the deceleration operation (step 123). For acceleration operation, for example, throttle valve opening θt
Each time this routine is executed, h is read as a detection value, and the previous detection value θth _{n-1 of the} throttle valve opening θth is detected to the current detection value θth _n.
Is detected by detecting that the change amount Δθth (= θth _n −θth _n-1 ) is greater than a predetermined value G ⁺ , and deceleration operation is performed, for example, when the change amount Δθth is smaller than the predetermined value G ⁻ . It is determined by detecting that there is. When it is determined this time that the operation is neither acceleration operation nor deceleration operation, the air-fuel ratio feedback control automatic correction coefficient in the current operation region determined by the engine speed Ne and the intake pipe absolute pressure P _BA.
Run the K _REF calculation subroutine for updating by calculating the K _REF (step 124), the flag F _STP equal to 0 (step 125).

During acceleration or deceleration operation, the air-fuel ratio feedback correction coefficient K _O2 is set equal to 1 to stop the air-fuel ratio feedback control according to the oxygen concentration in the exhaust gas (step 126), and the transient operation flag F _{TRS is set} to 1 Is set (step 127), and the acceleration / deceleration A / F delay time ts and the acceleration / deceleration duration time tc are set (step 128). Acceleration / deceleration A
The / F delay time ts is the time required from the fuel supply in the intake system to the output of the fuel supply result to the exhaust system during acceleration or deceleration operation. In the ROM 48, the acceleration / deceleration A / F delay time ts corresponding to the engine speed Ne is stored in advance as a ts data map with the characteristics shown in FIG.
The acceleration / deceleration A / F delay time ts corresponding to the engine speed Ne at that time is searched from the ts data map. Further, the acceleration / deceleration duration time tc is a fuel increase or fuel decrease time due to one acceleration / deceleration. Similar to the acceleration / deceleration A / F delay time ts, the ROM 48 stores the acceleration / deceleration duration time tc corresponding to the engine speed Ne in advance as a tc data map in the characteristic shown in FIG. The acceleration / deceleration duration time tc corresponding to the number Ne is searched from the tc data map. After setting acceleration / deceleration A / F delay time ts and acceleration / deceleration duration time tc, timer T _A
Reset the measured value of to 0 and start the operation of timer T _A ,
The measured value of the timer T _B to initiate the operation of the reset timer T _B to 0 (step 129), and the transient learning interruption flag F _STP it is determined whether or not 1 (step 13
0). If F _STP = 0, the amount of change in throttle valve opening θth Δθth
And the engine speed Ne, the current operating range, that is, the air-fuel ratio air-fuel ratio feedback control automatic correction coefficient K _TREF (transient correction correction value) at the memory location (g, h) of the K _TREF data map formed in RAM49. Readout (step 131), resetting by making the total deviation value T equal to 0 (step 132), and determining whether or not the time ts has elapsed from the acceleration or deceleration operation detection, by the measured value of the timer T _A ( Step 133). If the time ts has elapsed, the deviation ΔAF between the target air-fuel ratio AF _TAR and the detected air-fuel ratio AF _ACT
Is calculated (step 134), the deviation total value T is added to the deviation ΔAF, and the calculated value is stored as a new deviation total value T (step 135). Then, the integrated value S is calculated by dividing the total deviation value T by the time from the time point ts to the time point tc and multiplying it by the convergence coefficient C _AD (step 136). The convergence coefficient C _AD is set to different values during acceleration operation and deceleration operation as shown in FIG. Then, whether tc has elapsed since the acceleration or deceleration operation detection is determined by the measured value of the timer T _B (Step 13
7). If the time tc has not elapsed, it is assumed that the process returns to the K _O2 calculation subroutine and the current K _O2 calculation process is completed. Time t
If c has elapsed, in step 136, the integral value S calculated from the deviation total value T from the time point ts to the time point tc has elapsed is obtained. Therefore, the integral value S is multiplied by a constant A and step Correction coefficient K read in 131
_A correction coefficient K _TREF is newly calculated by adding _TREF, and is written in the memory location (g, h) of the K _TREF data map (step 138), and the transient operation flag F _TRS and the transient learning interruption flag F _STP are reset. To set F _TRS = 0 and F _STP = 0 (step 139). If F _STP = 1 in step 130, learning is interrupted during the transition, so the integral value S is made equal to 0 (step 140), and step 137 is immediately executed. The timers T _A and T _B are formed by using a register or the like in the CPU 47 and measure the time by the coefficient of the clock pulse.
Further, g at the storage position (g, h) is classified into 1,2 ... v corresponding to the magnitude of the engine speed Ne, and h is the variation Δθt.
According to the size of h, it is classified into 1,2 ... w.

On the other hand, if F _TRS = 1 at step 121, it means that the transient learning operation was performed at the previous execution of the learning control subroutine, and therefore it is determined whether or not the transient learning interruption flag F _STP is equal to 1 (step 141). If F _STP = 0, it is determined that acceleration learning is not currently being performed because the learning during transition is not suspended (step 142). If acceleration is not performed, it is further determined whether deceleration operation is performed (step 143). .
When the acceleration operation is not detected again during the transient learning control after the acceleration operation is detected in step 122, or in step 12
In step 3, when the deceleration operation is not detected again during the transient learning control after the deceleration operation is detected, step 133 is immediately executed. Further, when the acceleration operation is detected again during the transient learning control after the acceleration operation detection in step 122, or when the deceleration operation is detected again during the transient learning control after the deceleration operation detection in step 123, the air-fuel ratio is Exact correction coefficient K from deviation ΔAF up to time tc
_{Since TREF} cannot be obtained, the learning learning interruption flag F _STP is set to 1 in order to interrupt the learning control during transient (step 144), and the elapsed time tx from the acceleration or deceleration operation detection is measured from the measured value of the timer T _B. Read (step 145), time t
It is determined whether x is greater than time ts (step 14).
6). If tx ≦ ts, the integrated value S is made equal to 0 (step 147), and if tx> ts, the target air-fuel ratio AF _TAR and the detected air-fuel ratio
The deviation ΔAF from AF _ACT is calculated (step 148), the deviation total value T is added to the deviation ΔAF, and the calculated value is stored as a new deviation total value T (step 149). Then, the total deviation value T is divided by the time from the time t s to the time t x and the integral value S is calculated by multiplying by the convergence coefficient C _AD (step 150), and the constant A is added to the integral value S. A new correction coefficient K _TREF is calculated by multiplying and adding the correction coefficient K _TREF read in step 131 _.
Write to the memory location (g, h) in the data map (step 1
51). After the correction coefficient K _TREF calculation update, perform the following steps: Step 128 sets a new deceleration duration tc is measured using the timer T _B. Therefore, if the acceleration operation or deceleration operation is detected again before the acceleration / deceleration A / F delay time ts elapses, the correction coefficient K _TREF is updated until the newly set acceleration / deceleration duration time tc elapses. That is, learning control is interrupted. In addition, acceleration / deceleration operation starts after acceleration / deceleration A / F delay time ts elapses
If it is detected again by the time elapsed, the correction coefficient K _TREF is calculated and updated using the deviation ΔAF obtained by the time of detection again,
Then, the learning control is interrupted until the newly set acceleration / deceleration duration time tc elapses.

In step 141 in the case of F _STP = 1 is whether or not the elapsed time tc from the acceleration or deceleration operation detection is determined by the measured value of the timer T _B (step 152). If the time tc has not elapsed, it is determined whether or not the acceleration operation is currently performed (step 153), and if it is not the acceleration operation, it is further determined whether or not the deceleration operation is performed (step 154). When acceleration operation is not detected during transient learning interruption, or when deceleration operation is not detected during transient learning interruption, the integral value S is made equal to 0 (step 155), and step 137 is executed. When acceleration operation is detected during transient learning interruption, or when deceleration operation is detected during transient learning interruption, steps 128 and below are executed to set a new acceleration / deceleration duration tc and timer T Measure with _B. Therefore, the learning control is interrupted until the newly set acceleration / deceleration duration time tc elapses thereafter. If the time tc has elapsed since the acceleration or deceleration operation was re-detected, the transient operation flag F _TRS and the transient learning interruption flag F _STP to enable the transient learning control during the processing of the next routine.
_Are reset to F _TRS = 0 and F _STP = 0 (step 15
6) Return to the original routine.

Next, in the T _ACC and T _DEC calculation subroutine, CPU47
First, as shown in FIG. 11, it is determined whether or not it is in the acceleration operation (step 161), and in the acceleration operation, the acceleration increase value T _ACC corresponding to the change amount Δθth of the throttle valve opening θth is set in the ROM 48.
It is searched from the T _ACC data map stored in advance (step 162), and when it is not the acceleration operation, it is determined whether it is the deceleration operation (step 163). During the deceleration operation, the deceleration reduction value T _DEC is calculated by multiplying the change amount Δθth of the throttle valve opening θth by a constant C _DEC (step 164). The acceleration increase value T _ACC retrieved in step 162 and the deceleration decrease value T _DEC calculated in step 164 are the transient correction basic values. In this way, the acceleration increase value T _ACC or the deceleration decrease value T _DEC
Is set, the current operating range determined by the change amount Δθth of the throttle valve opening θth and the engine speed Ne, that is, RAM4
Automatic correction coefficient K for transient air-fuel ratio feedback control at storage position (g, h) of K _TREF data map formed in 9
_{Read TREF} (step 165). The read correction coefficient K _TREF is a value updated by the execution of the learning control subroutine described above. Then, it is determined again whether or not it is the acceleration operation (step 166), and during the acceleration operation, the acceleration increase value T _ACC is multiplied by the correction coefficient K _TREF and the calculated value is set as a new acceleration increase value T _ACC (step 167). , Deceleration reduction value T _DEC is set to 0 (step 168). When not in acceleration operation, that is, in deceleration operation, the deceleration reduction value T _DEC is multiplied by the correction coefficient K _TREF and the calculated value is _added to the new deceleration reduction value T
_DEC is set (step 169), and the acceleration increase value T _ACC is set to 0 (step 170). When neither acceleration nor deceleration operation is performed, the acceleration increase value T _ACC and the deceleration decrease value T _DEC are set to 0 (steps 171, 172).

Next, in the K _REF calculation subroutine, as shown in FIG. 12, first, the engine speed Ne and the intake pipe absolute pressure P
_The current operating area determined according to _BA , that is, the correction coefficient K _REF stored in the storage position (i, j) of the K _REF data map is read and the correction coefficient K _REF is set as the previous value K _{REF n-1} (step 181). I at the memory location (i, j) is the engine speed Ne
X is classified according to the magnitude of 1, and j is classified into 1,2 ... y according to the magnitude of the intake pipe absolute pressure P _BA . Then, from the detected air-fuel ratio AF _ACT to the target air-fuel ratio AF _TAR
It is determined whether the absolute value of the value obtained by subtracting is less than or equal to a predetermined value DAF ₄ (for example, 1) (step 182). | AF _ACT −AF _TAR |
> DAF ₄ , the execution of the K _REF calculation subroutine is stopped and the original routine is executed again. | AF _ACT −AF _TAR | ≦ DAF ₄ , the absolute value | AF _ACT −AF _TAR | is the specified value DAF ₅ (DAF ₄ > DAF ₅ ,
For example, it is determined whether it is 0.5) or less (step 183).
When | AF _ACT −AF _TAR | ≦ DAF ₅ , the correction coefficient K _REF is calculated by the following equation and stored in the storage position (i, j) of the K _REF data map (step 184).

K _REF = C _REFN · (K _O2 −1.0) + K _{REF n-1} (2) where C _REFN is the convergence coefficient.

On the other hand, when | AF _ACT −AF _TAR |> DAF ₅ , the correction coefficient K _REF
Is calculated by the following equation and stored in the storage position (i, j) of the K _REF data map (step 185).

K _REF = C _REFW · (AF _ACT · K _O2 −AF _TAR ) ＋ K _{REF n-1} ……
(3) Here, C _REFW is a convergence coefficient, and C _REFW > C _REFN .

In this way, when the correction coefficient K _REF of the storage position (i, j) of the K _REF data map is calculated and updated, the correction coefficient K _REF is calculated.
Calculating a reciprocal IK _REF of _REF (step 186), it reads the previous integral component K _{O2I n-1} from the RAM 49 (step 187), the previous integration component K _{O2I n-1,} the previous value K _{REF n-1,} the inverse IK _REF is multiplied and the calculated value is stored in the RAM 49 as the previous integrated amount K _{O2I n-1} (step 188). The previous integral K _{O2I n-1} calculated in step 188 is used to calculate the current integral K _O2In in step 78 or step 112, thereby improving the response to the air-fuel ratio fluctuation. .

In this K _REF calculation subroutine, | AF _ACT −AF
Only when _TAR | ≤ DAF _4, the correction coefficient K _REF is 1.0 and the correction coefficient K _O2 is 1.0.
The correction coefficient K _REF of the operating region at that time is updated and learning control is performed. If | AF _ACT −AF _TAR |> DAF ₅ when calculating the correction coefficient K _REF , | A
The correction speed is increased by making the correction coefficient K _REF larger than when F _ACT −AF _TAR | ≦ DAF ₅ .

As described above, in the air-fuel ratio control method of the present invention, when the acceleration or deceleration operation is detected, the transient correction value according to the magnitude of the acceleration or deceleration is set, and the reference value is corrected by the transient correction value. Determine the output value, and when acceleration or deceleration operation is detected, the transient correction value is updated by learning control according to the deviation between the air-fuel ratio detected from the output of the oxygen concentration sensor and the target air-fuel ratio, and the transient correction value is updated. Since it can be set to an appropriate value immediately, the response delay of the air-fuel ratio control is reduced, and the air-fuel ratio during acceleration and deceleration operation can be controlled with high accuracy, improving operability and improving exhaust gas purification performance. Of.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an electronically controlled fuel injection device to which an air-fuel ratio control method of the present invention is applied, FIG. 2 is a diagram showing the inside of an oxygen concentration sensor detection part, and FIG. 3 is a diagram showing the inside of an ECU. Circuit diagram showing the circuit, fourth
FIG, FIG. 5, FIG. 7, FIG. 11 and FIG. 12 is a flow diagram illustrating the operation of the CPU, FIG. 6 is an intake air temperature T _A - shows the temperature T _Wo2 characteristics, FIG. 8 is an engine rotational speed FIG. 9 is a diagram showing Ne-acceleration / deceleration A / F delay time ts characteristics, FIG. 9 is a diagram showing engine speed Ne-acceleration / deceleration duration tc characteristics, and FIG. 10 is a convergence coefficient C with respect to a change amount Δθth of the throttle valve opening. It is a figure which shows _AD , C _REFW , and C _REFN . Explanation of symbols of main parts 1 …… Oxygen concentration sensor detection part 3 …… Exhaust pipe 4 …… ECU 12 …… Oxygen ion conductive solid electrolyte member 13 …… Gas retention chamber 14 …… Introduction hole 15 …… Atmosphere reference chamber 18 …… Oxygen pump element 19 …… Battery element 25 …… Control circuit 27 …… Intake pipe 36 …… Injector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Ohno 1-4-1 Chuo, Wako-shi, Saitama, Ltd. Inside Honda R & D Co., Ltd. (56) Reference JP-A-60-224945 (JP, A) JP JP-A-57-18440 (JP, A) JP-A-60-43137 (JP, A) JP-A-57-143136 (JP, A) JP-A-59-34447 (JP, A) JP-A-60-159347 (JP , A)

Claims (1)

[Claims] 1. A reference value for air-fuel ratio control according to a plurality of engine operating parameters relating to a load of an internal combustion engine having an oxygen concentration sensor for generating an output proportional to an oxygen concentration in exhaust gas in an exhaust system, and the oxygen. Acceleration or using the air-fuel ratio control value determined according to the deviation between the air-fuel ratio detected from the output of the concentration sensor and the target air-fuel ratio, and the transient correction value during acceleration or deceleration according to the amount of change in engine operating parameters A method for controlling an air-fuel ratio during acceleration / deceleration of an internal combustion engine, wherein an output value during deceleration is determined, and an air-fuel ratio of a supply air-fuel mixture is controlled according to the determined output value. Having a data map to store the correction value, the transient correction basic value is set according to the detected value of the change amount during acceleration or deceleration,
The transient correction value corresponding to the detected value of the change amount is read from the data map and the set transient correction basic value is corrected by the read transient correction value to obtain the transient correction value, and the oxygen concentration is obtained. A new transient correction correction value is calculated according to the deviation between the air-fuel ratio detected from the output of the sensor and the target air-fuel ratio and the read transient correction correction value, and the storage position of the data map corresponding to the detected value of the change amount. The method for controlling air-fuel ratio during acceleration / deceleration of an internal combustion engine, characterized in that: